CA2228554C - Method of measuring operation characteristic of proportional electromagnetic control valve, method of controlling operation of hydraulic cylinder, and method of modifying operation characteristic of proportional electromagnetic control valve - Google Patents
Method of measuring operation characteristic of proportional electromagnetic control valve, method of controlling operation of hydraulic cylinder, and method of modifying operation characteristic of proportional electromagnetic control valve Download PDFInfo
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- CA2228554C CA2228554C CA002228554A CA2228554A CA2228554C CA 2228554 C CA2228554 C CA 2228554C CA 002228554 A CA002228554 A CA 002228554A CA 2228554 A CA2228554 A CA 2228554A CA 2228554 C CA2228554 C CA 2228554C
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- control valve
- pressure
- proportional electromagnetic
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B19/00—Testing; Calibrating; Fault detection or monitoring; Simulation or modelling of fluid-pressure systems or apparatus not otherwise provided for
- F15B19/002—Calibrating
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
- B29C45/17—Component parts, details or accessories; Auxiliary operations
- B29C45/76—Measuring, controlling or regulating
- B29C45/77—Measuring, controlling or regulating of velocity or pressure of moulding material
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D16/00—Control of fluid pressure
- G05D16/20—Control of fluid pressure characterised by the use of electric means
- G05D16/2006—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means
- G05D16/2013—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means using throttling means as controlling means
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D16/00—Control of fluid pressure
- G05D16/20—Control of fluid pressure characterised by the use of electric means
- G05D16/2006—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means
- G05D16/2013—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means using throttling means as controlling means
- G05D16/2022—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means using throttling means as controlling means actuated by a proportional solenoid
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76003—Measured parameter
- B29C2945/76006—Pressure
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76003—Measured parameter
- B29C2945/76033—Electric current or voltage
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76003—Measured parameter
- B29C2945/76066—Time
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76003—Measured parameter
- B29C2945/76083—Position
- B29C2945/76096—Distance
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76003—Measured parameter
- B29C2945/7611—Velocity
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76177—Location of measurement
- B29C2945/76297—Fluids
- B29C2945/76307—Fluids hydraulic fluids
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76344—Phase or stage of measurement
- B29C2945/76381—Injection
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76451—Measurement means
- B29C2945/76488—Magnetic, electro-magnetic
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76494—Controlled parameter
- B29C2945/76498—Pressure
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76494—Controlled parameter
- B29C2945/76551—Time
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76655—Location of control
- B29C2945/76775—Fluids
- B29C2945/76785—Fluids hydraulic fluids
Abstract
The present invention relates to a method by which an operation characteristic of a proportional electromagnetic control valve can be automatically measured in a short period of time. For this purpose, in the operation characteristic measuring method of the present invention, when the proportional electromagnetic control valve to be measured is a proportional electromagnetic pressure control valve, at each step for measuring a pressure of a hydraulic circuit, the pressure is measured with a predetermined interval of time, the pressure is assumed to be stabilized at a point of time when a difference ~P between thus measured pressure value and the previously measured pressure value becomes a predetermined level e or less, and the measured pressure value at this point of time is employed as a pressure corresponding to a load current at this step. The present invention is used at the time when an injection molding machine is inspected at its manufacturing site upon shipping and at the time when the injection molding machine is controlled while being actually operated.
Description
CA 02228~4 1998-02-06 SPECIFICATION
TITLE OF THE INVENTION
METHOD OF MEASURING OPERATION CHARACTERISTIC OF PROPOR-5TIONAL ELECTROMAGNETIC CONTROL VALVE, METHOD OF
CONTROLLING OPERATION OF HYDRAULIC CYLINDER, AND METHOD OF
MODIFYING OPERATION CHARACTERISTIC OF PROPORTIONAL ELEC-TROMAGNETIC CONTROL VALVE
1) Field of the Invention This invention relates to a method of actually measuring a pressure-current characteristic as an operationcharacteristicofaproportionalelectromagnetic 15control valve in a hydraulic circuit or a velocity-current characteristic of a hydraulic cylinderi a method of con-trolling, based on thus measured result, an operation state of the hydraulic cylinderi and a method of modifying a prestored operation characteristic. In particular, the 20present invention relates to a method of measuring an operationcharacteristicofaproportionalelectromagnetic control valve, a method of controlling an operation of a hydraulic cylinder, and a method of modifying an operation characteristicoftheproportionalvalvewhich aresuitably 25used when an injection molding machine is inspected at its CA 02228~4 1998-02-06 manufacturing site upon shipping or when the injection molding machine is controlled while being actually oper-ated.
TITLE OF THE INVENTION
METHOD OF MEASURING OPERATION CHARACTERISTIC OF PROPOR-5TIONAL ELECTROMAGNETIC CONTROL VALVE, METHOD OF
CONTROLLING OPERATION OF HYDRAULIC CYLINDER, AND METHOD OF
MODIFYING OPERATION CHARACTERISTIC OF PROPORTIONAL ELEC-TROMAGNETIC CONTROL VALVE
1) Field of the Invention This invention relates to a method of actually measuring a pressure-current characteristic as an operationcharacteristicofaproportionalelectromagnetic 15control valve in a hydraulic circuit or a velocity-current characteristic of a hydraulic cylinderi a method of con-trolling, based on thus measured result, an operation state of the hydraulic cylinderi and a method of modifying a prestored operation characteristic. In particular, the 20present invention relates to a method of measuring an operationcharacteristicofaproportionalelectromagnetic control valve, a method of controlling an operation of a hydraulic cylinder, and a method of modifying an operation characteristicoftheproportionalvalvewhich aresuitably 25used when an injection molding machine is inspected at its CA 02228~4 1998-02-06 manufacturing site upon shipping or when the injection molding machine is controlled while being actually oper-ated.
2) Description of the Related Art In an injection molding machine, while a hydraulic pressure from a hydraulic pump or accumulator is supplied to a hydraulic cylinder (injection cylinder, closing cylinder, nozzle touch cylinder, or the like) via a proportional electromagnetic control valve (proportional electromagnetic flow control valve or proportional elec-tromagnetic pressure control valve) so as to control velocity or pressure, such a proportional electromagnetic control valve yields a large fluctuation in its characteristic in general.
Consequently, prior to shipment of an injection molding machine, its hydraulic circuit is operated in the actual machine, several points of pressure levels or flow levels of its proportional electromagnetic control valve with respecttoitsload current are measured, thusmeasured levels are compared with a reference characteristic at-tached to the proportional electromagnetic control valve, and the gain of the load current output circuit for the proportional electromagnetic control valve is manually adjustedbefore shipp.ing. In most cases, however, only the maximum and minimum levels are measured for output current CA 02228~4 1998-02-06 adjustment and, also under the influence of differences among machines and circuit configurations, thus modified characteristic may not have a high accuracy.
Japanese Patent Publication No. SHO 64-9177 dis-closes a technique in which, in order to enhance accuracy of an actually employed characteristic, the characteristic of a proportional electromagnetic control valve built in an injection molding machine is actually measured before shipping its hardware, a correction characteristic table providing a relationship between an ordered level and an output level is prepared according to thus measured result, and the proportional electromagnetic valve is controlled with reference to the contents of this correction characteristic table upon actually operating the hardware.
In the characteristic auto-modifying technique for a proportional electromagnetic control valve disclosed in the above-mentioned publication, the proportional electromagnetic control valve is operated with its input levels successively changing from the minimum input level to maximum input level so that their corresponding numeral output levels are initially measured and, according to a result of comprehended relationship between these numerous actually measured levels and their corresponding ordered levels, the correction characteristic table is prepared such that the output level is proportional to the input CA 02228~4 1998-02-06 level.
In such a technique for measuring the characteristic of a proportional electromagnetic control valve, while numerous points from the minimum input level to maximum input level are actually measured and plotted when pre-paring the correction characteristic table, there may be cases where, due to the condition under which a hydraulic cylinder is used and the like, the maximum pressure or maximum velocity cannot be attained in the state where the proportional electromagnetic control valve is built in the machine. In such a case, the characteristic of the proportional electromagnetic valve cannot be modified.
Also, the number of measuring points may be so large that an enormous amount of labor and time is necessitated.
Therefore, Japanese Patent Application Laid-Open (Kokai) No. HEI 5-57777 discloses a technique in which reference characteristic curve data of a proportional electromagnetic control valve of the same type as that of theproportionalelectromagneticcontrolvalvebuiltinthe machine are prestored in a storage circuit in a microcomputer in a control unit of the injection molding machine, the microcomputer causes the proportional elec-tromagnetic control valve to operate (in a test run) by given ordered levels at predetermined two points, output (pressure or velocity) levels corresponding thereto are CA 02228~4 1998-02-06 respectively measured, and then, according to the two points of ordered levels and output levels obtained by the test run and the above-mentioned reference characteristic curve data, output levels corresponding to individual points on the reference characteristic curve are succes-sively computed to recompose the characteristic curve.
In the technique in which the actually measured level and the reference characteristic table attached to the proportional electromagnetic control valve are compared with each other, and the maximum and minimum levels are regulated by gain adjustment of a load current output circuit amplifier of the proportional electromagnetic control valve so as to modify characteristic levels of the proportional electromagnetic control valve, as mentioned above, however, data of proportional electromagnetic control valve differ among different machines and, also under the influence of differences in circuit configura-tions, a linearity may not be obtained between the ordered and executed levels, thus deteriorating the accuracy ofthe modified characteristic.
In the technique in which a characteristic is actually measured, a correction characteristic table keeping a relationship between ordered and output levels is prepared, and a correction characteristic is added so as to control the proportional electromagnetic control CA 02228~4 1998-02-06 valve as disclosed in Japanese Patent Publication No.
64-9177, numerous points from the minimum input level to maximum input level must be actually measured to prepare the correction characteristic table as mentioned above.
Here, since the number of measured points is large, an enormous amount of labor and time is necessary.
In the method disclosed in Japanese Patent Application Laid-Open (Kokai) No. HEI 5-57777 in which characteristic data of the proportional electromagnetic control valve are obtained on the analogy of two points of data, correct data may not be obtained from the two points alone since the original data are a curve constituted by a polynomial function.
In the foregoing method in which a data table is retrieved, an accurate resolution as fine as 0.1% cannot be obtained.
Inthe conventionalpressure measurementin an actual hydraulic circuit, in the case where pressure is relatively low, the pressure is measured after a rising overshoot upon switching hydraulic pressure is suppressed. When the number of measuring points is large, however, it takes much time therefor. When measuring velocity, since time by which a predetermined position travels a predetermined distance is measured to determine the velocity. Accord-ingly, it takes much time for measurement at the minimum CA 02228~4 1998-02-06 velocity, and an enormous amount of time is required for measuring numerous points.
SUMMARY OF THE INVENTION
In view of such problems, it is a first object of the present invention to provide a method of measuring an operationcharacteristicofaproportionalelectromagnetic control valve, which allows the operation characteristic to be automatically measuredin a short period oftime, thus shortening the time required for inspection upon shipment.
It is a second object of the present invention to provide a method of controlling an operation of a hydraulic cylinder, which allows the hydraulic cylinder to be con-trolled constantly at a high accuracy according to the automatically measured operation characteristic.
It is a third object of the present invention to provide a method of modifying an operation characteristic of a proportional electromagnetic control valve, which allows an operation characteristic kept in a memory to be automatically modified after shipping the machine, so that the operationcharacteristicmatchingthepresent statecan always be maintained.
In order to achieve the above-mentioned objects, the method of measuring an operation characteristic of a proportional electromagnetic control valve in accordance CA 02228~4 1998-02-06 with the present invention is, in a hydraulic circuit in which a hydraulic cylinder is operated as a proportional electromagnetic control valve adjusts hydraulic pressure and flow rate, when the proportional electromagnetic control valve is a proportional electromagnetic pressure control valve which controls a hydraulic pressure in re-sponse to a load current, a method of measuring a pres-sure-current characteristic as the operation characteristic of the proportional electromagnetic pres-sure control valve by successively changing the load current with respect t:o the proportional electromagnetic pressure control valve stepwise and measuring a pressure of the hydraulic circuit corresponding to the load current at each step in a closed operation state of the hydraulic circuit; wherein, at each step for measuring the pressure of the hydraulic circuit, the pressure is measured at a predetermined interva:L of time, the pressure is assumed to be stabilized at a point of time when a difference between thus measured pressure value and the previously measured pressure value becomes a predetermined level or smaller, and the measured pressure value at this point of time is employed as the pressure corresponding to the load current at this step.
In the method of measuring an operation characteristic of a proportional electromagnetic control CA 02228~4 1998-02-06 valve in accordance with the present invention mentioned above, even in the case where pressure is relatively low, a pressure obtained when the inclination of a declining curveofrisingovershootuponswitchinghydraulicpressure becomes a predetermined level or smaller is employed as the measured value, whereby the measurement time can be shortened. Accordingly, even when numerous points are measured, the period of time for measuring the operation characteristic can be reduced, thus allowing the time required for the inspection upon shipping or the like to greatly decrease.
Also, the method of measuring an operation characteristic of a proportional electromagnetic control valve in accordance with the present invention is, in a hydraulic circuit in which a hydraulic cylinder is operated as a proportional electromagnetic control valve adjusts hydraulic pressure and flow rate, when the proportional electromagnetic control valve is a proportional electro-magnetic flow control valve which controls a flow rate in response to a load current, a method of measuring a velocity-current characteristic as the operation charac-teristic of the proportional electromagnetic flow control valve by causing the :hydraulic cylinder to attain an operablestate, successivelychangingtheloadcurrentwith respect to the proportional electromagnetic flow control CA 02228~4 1998-02-06 valve stepwise so as to operate the hydraulic cylinder, and computing a velocity of a hydraulic ram of the hydraulic cylinder corresponding to the load current at each step;
wherein, at each step for computing the velocity of the hydraulic ram, a traveling distance of the hydraulic ram by a predetermined period of time is measured, and a velocity computed according to the traveling distance is employed as the velocity corresponding to the load current at this step.
In the above-mentioned method of measuring an operationcharacteristicofaproportionalelectromagnetic control valve in accordance with the present invention, the traveling distance for a predetermined time is measured so as to determine the velocity, thus allowing the measuring time to become shorter as compared with the conventional method, in particular, on the minimum velocity side.
Accordingly, even when numerous points are measured, the period of time for measuring the operation characteristic can be reduced, thus allowing the time required for the inspection upon shipping or the like to greatly decrease.
The method of controlling an operation of a hydraulic cylinder in accordance with the present invention is a method of controlling an operation state of the hydraulic cylinder by adjusting hydraulic pressure and flow rate by a hydraulic circuit having a proportional electromagnetic CA 02228~4 1998-02-06 control valve; wherein an operation characteristic of the proportional electromagnetic control valve is measured by one of the above-mentioned two methods of measuring an operationcharacteristicofaproportionalelectromagnetic control valve and is stored into a memory and, when specifying a hydraulic pressure to the hydraulic cylinder oravelocityofthehydraulic ramofthehydrauliccylinder, an operation characteristic value matching thus specified level is read out from the memory and is converted into an executive current, which is then applied to the proportionalelectromagneticcontrol valveso astocontrol the operation state of the hydraulic cylinder.
In the above-mentioned method of controlling an operation of a hydraulic cylinder in accordance with the present invention, when the hydraulic pressure of the hydraulic cylinder or the velocity of the hydraulic ram is specified at the time of actual operation, the current characteristic value matching thus specified level is read out from the memory and is converted into an executive current so as to be applied to the proportional electromagnetic control valve, whereby the operation state of the hydraulic cylinder is controlled. Therefore, ac-cording to the automatically measured operation characteristic, the hydraulic cylinder can be always controlled with a high accuracy.
CA 02228~4 1998-02-06 Also, the method of controlling an operation of a hydrauliccylinderinaccordancewiththepresentinvention is a method of controlling an operation state of the hydrauliccylinderbyadjustinghydraulicpressure andflow rate by a hydraulic circuit having a proportional electromagnetic control valve; wherein an operation characteristicoftheproportionalelectromagneticcontrol valve is measured by one of the above-mentioned two methods of measuring an operation characteristic of a proportional electromagnetic control valve and is stored in a memory, a table for relating a load current level to the measured operation characteristic value at each step is prepared, interpolation is performed between points plotted on the table so as to determine a continuous function, which is then stored into a memory as the operation characteristic of the proportional electromagnetic control valve, the function is read out from the memory upon actual operation of the hydraulic cylinder, an executive current level is computed according to the function and a target level for hydraulic pressure to the hydraulic cylinder or velocity of a hydraulic ram ofthe hydraulic cylinder, and a current corresponding to the executive current level is applied to the proportional electromagnetic control valve so as to control the operation state of the hydraulic cylinder.
In the method of controlling an operation of a CA 02228~4 1998-02-06 hydrauliccylinderinaccordance withthepresentinvention, the operation characteristic stored in the memory as a function is automatically modified and rewritten in response to a request for automatic modification.
Consequently, even when the proportional electromagnetic control valve built in the hydraulic circuit or functional parts relating to hydraulic pressure or flow rate are repaired or exchanged, the operation characteristic of the proportional electromagnetic control valve stored in the memory can be automatically modified while the machine is kept installed as it is, and the hydraulic cylinder can always be controlled with a high accuracy according to thus automatically modified operation characteristic.
Further, the method of modifying an operation characteristic of a p:roportional electromagnetic control valve in accordance with the present invention is, when, in order to control an operation state of a hydraulic cylinder by adjusting hydraulic pressure and flow rate by a hydraulic circuit having a proportional electromagnetic control valve, an operation characteristic value corre-sponding to a load current level of the proportional electromagnetic control valve is prestored into a memory as a characteristic curve, a method of modifying the characteristic curve stored in the memoryi wherein a hy-draulic pressure or f.Low rate of the hydraulic circuit is CA 02228~4 l998-02-06 specified, a load current level of the proportional electromagnetic control valve corresponding to thus specified level is read out from the characteristic curve in thememory, acurrent correspondingtothus read-outload current level is applied to the proportional electromag-netic control valve, the pressure or flow rate of the hydrauliccircuitcorrespondingtothis currentisactually measured, a load current level of the proportional electromagnetic control valve corresponding to thus actually measured valu.e is read out from the characteristic curve inthe memory, a differencebetweenthusobtainedload current level and an .initial load current level is added to or subtracted from the initial load current level, and a current level resulting from this adding or subtracting operation is written into the memory as a modified load current level corresponding to the specified level so as tomodifytheloadcurrent level ofthecharacteristiccurve in the memory.
In the above-mentioned method of modifying an operationcharacteristicofaproportionalelectromagnetic control valve in accordance with the present invention, in the case where an operation characteristic value corre-sponding to the load current level of the proportional electromagnetic control valve is prestored in the memory as a characteristic curve, the characteristic curve CA 02228~4 1998-02-06 (operation characteristic) can be automatically modified after shipping the machine. Accordingly, even when the proportional electromagnetic control valve built in the hydrauliccircuit or functionalparts relatingtohydraulic pressure or flow rate are repaired or exchanged, the operation characteristic corresponding to the current state can always be held in the memory while the machine is kept installed as it is.
FIG. 1 is a view for explaining a method of measuring an operation characteristic of a proportional electromagnetic pressure control valve in accordance with an embodiment of the present invention;
FIG. 2 is a graph showing a rising state of hydraulic pressure in a hydraulic circuit of this embodiment;
FIG. 3A is a lateral sectional view schematically showing an injection cylinder in order to explain a technique for measuring velocity of a conventional injection ram;
FIG. 3B is a lateral sectional view schematically showing an injection cylinder in order to explain a method of measuring an operation characteristic of a proportional electromagnetic flow control valve (technique for measuring velocity of an injection ram) in this embodiment;
CA 02228~4 l998-02-06 FIG. 4 is a view showing a configuration of the hydraulic circuit and control system in an injection molding machine in accordance with this embodiment;
FIG. 5 is a block diagram functionally showing a detailedconfigurationofthehydrauliccircuit andcontrol system in order to explain a method of controlling an operation of an injection cylinder (method of modifying an operationcharacteristicofaproportionalelectromagnetic pressure control valve) in this embodiment; and FIG. 6 iS a view for explaining another example of method of modifying an operation characteristic of a proportional electromagnetic pressure control valve in accordance with this embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following, an embodiment of the present invention will be explained with reference to the accom-panying drawings.
Explained in this embodiment is a case where the present invention is applied to a hydraulic operation control circuit for an injection molding machine, which comprises ahydraulicpump, aswitchingvalve, andthe like, and adjusts hydraulic pressure and flow rate so as to operate the hydraulic cylinder, as will be explained later, therebyperforming ac:losingoperation, injectionofmelted CA 02228~4 l998-02-06 resin, and the like.
First, with reference to FIG. 4, the configuration ofthehydrauliccircuitand controlsystemoftheinjection moldingmachineto which the methodofthepresentinvention is applied will be explained. Depicted in FIG. 4 are an injection cylinder (hydraulic cylinder) 1 of the injection molding machine whose operation is to be controlled in this embodiment, an injection ram (hydraulic ram) 2 within the injection cylinder 1, and an injection screw 2a connected to the injection ram 2.
Also depicted a:re a position sensor 3 for detecting an amount of movement: of the injection ram 2, a direc-tion-switching valve 4 for turning on/off an injecting operation of the injection cylinder 1, a proportional electromagnetic flow control valve (proportional electromagnetic control valve) 5 for controlling the flow rate of a hydraulic operating fluid to the injection cylinder 1 in response to a load current from a control unit 12, a proportional electromagnetic pressure control valve (proportional electromagnetic control valve) 6 for con-trolling the pressure of the hydraulic operating fluid in response to a load current from the control unit 12, a continuous flow pump 7 which is driven by a motor (M) 7a so as to rotate at a predetermined rpm, a check valve 8, and a pressure sensor 9 for detecting pressure in this CA 02228~4 l998-02-06 hydraulic circuit.
The above-mentioned direction-switching valve 4, control valves 5 and 6, pump 7, check valve 8, and the like constitute the hydraulic circuit for operating the injection cylinder 1 at an injecting process caused by the injection screw 2a.
On the other hand, provided are an operation panel 11 for setting and inputting various kinds of information such as specified levels (control target levels) for pressure of the hydraulic circuit, velocity of the injection ram 2 (flow rate of the hydraulic circuit), and the like to the control unit 12 explained later, and the control unit 12, which receives signals from the position sensor 3 and pressure sensor 9 and applies a load current to each of the control valves 5 and 6 so as to control the hydraulic circuit, thereby controlling the operation state of the injection cyli.nder 1. The control unit 12 is constituted by, in addition to a CPU 13 as an arithmetic processing unit, a memory 14, a D/A converter 15, an output amplifier 16, and an A/D converter 17 which are built therein.
Here, the CPU 13 actually controls an operation state of the injection cylinder 1 in addition to measur-ing/modifying operation characteristics of the control valves 5 and 6 which will be explained later; whereas the CA 02228~4 1998-02-06 memory 14 stores the operation characteristics of the control valves 5 and 6 as will be explained later.
On the otherhand, the D/A converter 15 converts, from digital to analog, control signals (load current level signals) sent from the CPU 13 for the respective control valves 5 and 6. The amplifier (output amplifier) 16 amplifies the control signals from the D/A converter 15 and outputs thus amplified signals to their corresponding control valves 5 and 6. The A/D converter 17 converts analog detection signals from the position sensor 3 and pressure sensor 9 into digital signals and outputs thus converted signals to the CPU 13.
Explained in the following with reference to FIGs.
1 to 3 is a method of automatically inspecting, in a working manner, a pressure-current characteristic (operation characteristic) of the proportional electromagnetic pressure control valve 6 or relationship between velocity of the injection cylinder 1 and the load current level to the proportional electromagnetic flow control valve 5 [a velocity-current characteristic of the injection cylinder 1, and an operation c:haracteristic (flow rate-current characteristic) of the proportional electromagnetic flow control valve 5] when the injection molding machine equipped with the hydraulic circuit and control unit 12 of thisembodimentconstructedasmentionedaboveisinspected CA 02228~4 1998-02-06 uponshipmentinthe site where the machineismanufactured.
FIG. 2 iS a graph showing a rising state of hydraulic pressure in the hydraulic circuit of this embodiment. It illustrates a result obtained when, in this embodiment, the hydraulic pump 7 is driven, the injection cylinder 1 is operated under hydraulic pressure, the injection ram 2 of the injection cylinder 1 in the actual machine is pressed into the end portion of the stroke for closing, melted resin injection, and the like such that the hydraulic circuit attains a closed state, the load current with respect to the proportional elect:romagnetic pressure control valve 6 is successively changed stepwise, and the pressure of the hydraulic circuit is measured by the pressure sensor 9.
As shown in FIG. 2, in a low pressure band (Nos. 1 to 4), an overshoot occurs in each step of measurement, and then pressure gradually converges at the set pressure.
Since it takes a certain time for pressure to stabilize, a delay timer has conventionally been provided (see Ts in FIG. 2 for its set level) to retard the pressure measuring timing. In such a measuring technique, however, the measuring timing uniformly delays even in the case where the set pressure is so high that pressure stabilizes in a short time, whereby it:takes an enormous amount of time to measure pressure (measure an operation characteristic).
For measuring pressure in order to measure an CA 02228~4 1998-02-06 operation characteristic in this embodiment, upon measuring one step of pressure, as shown in the pres-sure-declining curve after overshoot represented in FIG.
1, pressure is repeatedly measured by the pressure sensor 9 at a constant time interval t, the CPU 13 of the control unit 12 assumes pressure to be stabilized when a difference ~P between the measured value and the previously measured valuebecomesasufficientlysmall constantnumericalvalue e or less, and this pressure is taken in as an operation pressure of the proportional electromagnetic pressure control valve 6 corresponding to the load current at this step.
Consequently, without necessitating a certain wait time Ts for each measurement step before measurement as in the conventional case, measurement is effected with a timing at which pressure is assumed to be stabilized for each measurement step. Therefore, the pressure measure-ment time requires only T1, thus allowing the operation pressure in the next step to be measured after the time T1 is elapsed. Thus, the total time required for preparing a pressure-current characteristic curve in the CPU 13 of the control unit 12 can be made much shorter than that in the conventional case.
Here, as shown in FIG. 2, overshoot hardly occurs in a high pressure band (Nos. 5 to 7). Even in such a case, CA 02228~4 1998-02-06 in the measuring method of this embodiment, it is unnecessary to wait for the certain time Ts before measurement in each measurement step, as mentioned above, whereby measurement is effected with a timing T2 at which pressure is assumed t:o be stabilized.
Meanwhile, FIG. 3A is a lateral sectional view schematically showing the injection cylinder 1 for explaining a conventional technique for measuring velocity of the injection ram 2; whereas FIG . 3B is a lateral sectional view schematically showing the injection cylinderl forexplain.ing amethodofmeasuringanoperation characteristic of the proportional electromagnetic flow control valve 5 (technique for measuring velocity of the injection ram 2) in t:his embodiment.
When measuring an operation characteristic of the proportional electromagnetic flow control valve 5, while the injection cylinder 1 of the actual machine is set to an operable state, the load current to the proportional electromagnetic flow control valve 5 is successively changed stepwise, and the velocity of the injection ram 2 is measured while the injection cylinder 1 is caused to operate.
Here, in the conventional technique shown in FIG. 3A, a timetbywhich the injectionram2 travels apredetermined distance lo is measured so as to compute a velocity lo/t.
CA 02228~4 1998-02-06 In this embodiment, by contrast, as shown in FIG. 3B, a distance x by which t:he injection ram 2 travels in a predetermined time t~:is precisely measured by means of the position sensor 3 and is fed into the CPU 13 of the control unit 12, whereby the velocity of the injection ram 2 is computed asx/to. Then, the CPU 13 multiplies thusmeasured and computed velocity of the injection ram (hydraulic ram) 2 by the pressure-receiving area of the injection cylinder 1 so as to compute a fl.ow rate, and causes it to correspond to the load current at each step, thereby forming a characteristic curve concerning the flow rate-current characteristic of the proportional electromagnetic flow control valve 5.
In the conventional technique shown in FIG. 3A, concerning the time for traveling an approach distance m and the measurement distance l~, in particular when the current of the proportional electromagnetic flow control valve 5 is low (flow rate is low), not only the measurement time becomes longer, but also the time required for the hydraulic ram 2 to return becomes longer. In the technique of the embodiment shown in FIG. 3B, by contrast, when the approach time and measurement time are respectively set to 0.5 second and 1.5 seconds beforehand, for example, the measurement time is always constant whether the current of the proportional electromagnetic flow control valve 5 is CA 02228~4 l998-02-06 high or low, thus allowing the measurement to be completed in much shorter time than in the conventional technique shown in FIG. 3A.
In this embodiment, according to the data measured by such a technique as that mentioned above, characteristic curves for the proportional electromagnetic flow control valve 5 and proportional electromagnetic pressure control valve 6 are prepared, and thus prepared characteristic curves are stored in the memory 14 of the control unit 12.
In the case where such a characteristic curve has already been stored in the memory 14, the characteristic curve in the memory14isrewritten ormodifiedbythecharacteristic curve prepared by the above-mentioned technique.
When the operating hydraulic pressure of the injection cylinder 1 or velocity of the injection ram 2 in the injection molding machine is specified upon actual driving, theCPU13Ofthecontrolunitl2 readsoutacurrent characteristic level corresponding to thus specified value from the memory 14, converts thus read-out level to an executive current, and applies this current to the proportional electromagnetic flow control valve 5 and proportional electromagnetic pressure control valve 6 via the D/A converter 15 and amplifier 16. As a result, the operation state of the injection cylinder 1 is controlled so as to attain the specified value.
- CA 02228~4 1998-02-06 In the following, explanation will be provided for a method of modifying the pressure-current characteristic of the proportional electromagnetic pressure control valve 6 or flow rate-current characteristic of the proportional electromagnetic flow control valve 5 thus written in the memory 14. This embodiment encompasses two kinds of modifying method. First and second examples thereof will be respectively explained with reference to FIGs. 5 and 6.
FIG. 5 is a block diagram functionally showing a detailedconfigurationofthehydrauliccircuitandcontrol system in order to explain a method of controlling an operation of the injection cylinder 1 (method of modifying an operation characteristic of the proportional electro-magnetic pressure control valve 6) in this embodiment.
This process will be explained in detail with reference to FIG. 5, additionally in view of the modifying and rewriting function for the pressure characteristic in the proportional electromagnetic pressure control valve 6 in the hydraulic circuit shown in FIG. 4.
(1) When a request for automatically modifying the pressure characteristic is issued from the operation panel 11 to the CPU 13, a pressure-specifying level Pn stored in a memory (not depicted) built in a processing section 13a of the CPU 13 is sent to the memory 14, and a load current level In corresponding to the pressure-specifying level Pn CA 02228~4 l998-02-06 -2 6- ' is read out from a reference curve Ps of a pressure-current characteristic function table stored in the memory 14 to the processing section 13a of the CPU 13 so as to be temporarily kept there.
(2) According to a current (which corresponds to the current level In) outputted from the processing section 13a of the CPU 13 via the D/A converter 15 and amplifier 16, the proportional electromagnetic pressure control valve 6 is operated, whereby the pressure of the hydraulic circuit for driving the injection cylinder 1 is controlled. Then, an actual pressure Pn' of the hydraulic circuit is measured by the pressure sensor 9, and thus measured signal is sent to an arithmetic section 13b of the CPU 13 by way of the A/Dconverter17. Here, the actualpressurePn'ismeasured bythetechniquepreviouslyexplainedwithreferenceto FIG.
1.
Consequently, prior to shipment of an injection molding machine, its hydraulic circuit is operated in the actual machine, several points of pressure levels or flow levels of its proportional electromagnetic control valve with respecttoitsload current are measured, thusmeasured levels are compared with a reference characteristic at-tached to the proportional electromagnetic control valve, and the gain of the load current output circuit for the proportional electromagnetic control valve is manually adjustedbefore shipp.ing. In most cases, however, only the maximum and minimum levels are measured for output current CA 02228~4 1998-02-06 adjustment and, also under the influence of differences among machines and circuit configurations, thus modified characteristic may not have a high accuracy.
Japanese Patent Publication No. SHO 64-9177 dis-closes a technique in which, in order to enhance accuracy of an actually employed characteristic, the characteristic of a proportional electromagnetic control valve built in an injection molding machine is actually measured before shipping its hardware, a correction characteristic table providing a relationship between an ordered level and an output level is prepared according to thus measured result, and the proportional electromagnetic valve is controlled with reference to the contents of this correction characteristic table upon actually operating the hardware.
In the characteristic auto-modifying technique for a proportional electromagnetic control valve disclosed in the above-mentioned publication, the proportional electromagnetic control valve is operated with its input levels successively changing from the minimum input level to maximum input level so that their corresponding numeral output levels are initially measured and, according to a result of comprehended relationship between these numerous actually measured levels and their corresponding ordered levels, the correction characteristic table is prepared such that the output level is proportional to the input CA 02228~4 1998-02-06 level.
In such a technique for measuring the characteristic of a proportional electromagnetic control valve, while numerous points from the minimum input level to maximum input level are actually measured and plotted when pre-paring the correction characteristic table, there may be cases where, due to the condition under which a hydraulic cylinder is used and the like, the maximum pressure or maximum velocity cannot be attained in the state where the proportional electromagnetic control valve is built in the machine. In such a case, the characteristic of the proportional electromagnetic valve cannot be modified.
Also, the number of measuring points may be so large that an enormous amount of labor and time is necessitated.
Therefore, Japanese Patent Application Laid-Open (Kokai) No. HEI 5-57777 discloses a technique in which reference characteristic curve data of a proportional electromagnetic control valve of the same type as that of theproportionalelectromagneticcontrolvalvebuiltinthe machine are prestored in a storage circuit in a microcomputer in a control unit of the injection molding machine, the microcomputer causes the proportional elec-tromagnetic control valve to operate (in a test run) by given ordered levels at predetermined two points, output (pressure or velocity) levels corresponding thereto are CA 02228~4 1998-02-06 respectively measured, and then, according to the two points of ordered levels and output levels obtained by the test run and the above-mentioned reference characteristic curve data, output levels corresponding to individual points on the reference characteristic curve are succes-sively computed to recompose the characteristic curve.
In the technique in which the actually measured level and the reference characteristic table attached to the proportional electromagnetic control valve are compared with each other, and the maximum and minimum levels are regulated by gain adjustment of a load current output circuit amplifier of the proportional electromagnetic control valve so as to modify characteristic levels of the proportional electromagnetic control valve, as mentioned above, however, data of proportional electromagnetic control valve differ among different machines and, also under the influence of differences in circuit configura-tions, a linearity may not be obtained between the ordered and executed levels, thus deteriorating the accuracy ofthe modified characteristic.
In the technique in which a characteristic is actually measured, a correction characteristic table keeping a relationship between ordered and output levels is prepared, and a correction characteristic is added so as to control the proportional electromagnetic control CA 02228~4 1998-02-06 valve as disclosed in Japanese Patent Publication No.
64-9177, numerous points from the minimum input level to maximum input level must be actually measured to prepare the correction characteristic table as mentioned above.
Here, since the number of measured points is large, an enormous amount of labor and time is necessary.
In the method disclosed in Japanese Patent Application Laid-Open (Kokai) No. HEI 5-57777 in which characteristic data of the proportional electromagnetic control valve are obtained on the analogy of two points of data, correct data may not be obtained from the two points alone since the original data are a curve constituted by a polynomial function.
In the foregoing method in which a data table is retrieved, an accurate resolution as fine as 0.1% cannot be obtained.
Inthe conventionalpressure measurementin an actual hydraulic circuit, in the case where pressure is relatively low, the pressure is measured after a rising overshoot upon switching hydraulic pressure is suppressed. When the number of measuring points is large, however, it takes much time therefor. When measuring velocity, since time by which a predetermined position travels a predetermined distance is measured to determine the velocity. Accord-ingly, it takes much time for measurement at the minimum CA 02228~4 1998-02-06 velocity, and an enormous amount of time is required for measuring numerous points.
SUMMARY OF THE INVENTION
In view of such problems, it is a first object of the present invention to provide a method of measuring an operationcharacteristicofaproportionalelectromagnetic control valve, which allows the operation characteristic to be automatically measuredin a short period oftime, thus shortening the time required for inspection upon shipment.
It is a second object of the present invention to provide a method of controlling an operation of a hydraulic cylinder, which allows the hydraulic cylinder to be con-trolled constantly at a high accuracy according to the automatically measured operation characteristic.
It is a third object of the present invention to provide a method of modifying an operation characteristic of a proportional electromagnetic control valve, which allows an operation characteristic kept in a memory to be automatically modified after shipping the machine, so that the operationcharacteristicmatchingthepresent statecan always be maintained.
In order to achieve the above-mentioned objects, the method of measuring an operation characteristic of a proportional electromagnetic control valve in accordance CA 02228~4 1998-02-06 with the present invention is, in a hydraulic circuit in which a hydraulic cylinder is operated as a proportional electromagnetic control valve adjusts hydraulic pressure and flow rate, when the proportional electromagnetic control valve is a proportional electromagnetic pressure control valve which controls a hydraulic pressure in re-sponse to a load current, a method of measuring a pres-sure-current characteristic as the operation characteristic of the proportional electromagnetic pres-sure control valve by successively changing the load current with respect t:o the proportional electromagnetic pressure control valve stepwise and measuring a pressure of the hydraulic circuit corresponding to the load current at each step in a closed operation state of the hydraulic circuit; wherein, at each step for measuring the pressure of the hydraulic circuit, the pressure is measured at a predetermined interva:L of time, the pressure is assumed to be stabilized at a point of time when a difference between thus measured pressure value and the previously measured pressure value becomes a predetermined level or smaller, and the measured pressure value at this point of time is employed as the pressure corresponding to the load current at this step.
In the method of measuring an operation characteristic of a proportional electromagnetic control CA 02228~4 1998-02-06 valve in accordance with the present invention mentioned above, even in the case where pressure is relatively low, a pressure obtained when the inclination of a declining curveofrisingovershootuponswitchinghydraulicpressure becomes a predetermined level or smaller is employed as the measured value, whereby the measurement time can be shortened. Accordingly, even when numerous points are measured, the period of time for measuring the operation characteristic can be reduced, thus allowing the time required for the inspection upon shipping or the like to greatly decrease.
Also, the method of measuring an operation characteristic of a proportional electromagnetic control valve in accordance with the present invention is, in a hydraulic circuit in which a hydraulic cylinder is operated as a proportional electromagnetic control valve adjusts hydraulic pressure and flow rate, when the proportional electromagnetic control valve is a proportional electro-magnetic flow control valve which controls a flow rate in response to a load current, a method of measuring a velocity-current characteristic as the operation charac-teristic of the proportional electromagnetic flow control valve by causing the :hydraulic cylinder to attain an operablestate, successivelychangingtheloadcurrentwith respect to the proportional electromagnetic flow control CA 02228~4 1998-02-06 valve stepwise so as to operate the hydraulic cylinder, and computing a velocity of a hydraulic ram of the hydraulic cylinder corresponding to the load current at each step;
wherein, at each step for computing the velocity of the hydraulic ram, a traveling distance of the hydraulic ram by a predetermined period of time is measured, and a velocity computed according to the traveling distance is employed as the velocity corresponding to the load current at this step.
In the above-mentioned method of measuring an operationcharacteristicofaproportionalelectromagnetic control valve in accordance with the present invention, the traveling distance for a predetermined time is measured so as to determine the velocity, thus allowing the measuring time to become shorter as compared with the conventional method, in particular, on the minimum velocity side.
Accordingly, even when numerous points are measured, the period of time for measuring the operation characteristic can be reduced, thus allowing the time required for the inspection upon shipping or the like to greatly decrease.
The method of controlling an operation of a hydraulic cylinder in accordance with the present invention is a method of controlling an operation state of the hydraulic cylinder by adjusting hydraulic pressure and flow rate by a hydraulic circuit having a proportional electromagnetic CA 02228~4 1998-02-06 control valve; wherein an operation characteristic of the proportional electromagnetic control valve is measured by one of the above-mentioned two methods of measuring an operationcharacteristicofaproportionalelectromagnetic control valve and is stored into a memory and, when specifying a hydraulic pressure to the hydraulic cylinder oravelocityofthehydraulic ramofthehydrauliccylinder, an operation characteristic value matching thus specified level is read out from the memory and is converted into an executive current, which is then applied to the proportionalelectromagneticcontrol valveso astocontrol the operation state of the hydraulic cylinder.
In the above-mentioned method of controlling an operation of a hydraulic cylinder in accordance with the present invention, when the hydraulic pressure of the hydraulic cylinder or the velocity of the hydraulic ram is specified at the time of actual operation, the current characteristic value matching thus specified level is read out from the memory and is converted into an executive current so as to be applied to the proportional electromagnetic control valve, whereby the operation state of the hydraulic cylinder is controlled. Therefore, ac-cording to the automatically measured operation characteristic, the hydraulic cylinder can be always controlled with a high accuracy.
CA 02228~4 1998-02-06 Also, the method of controlling an operation of a hydrauliccylinderinaccordancewiththepresentinvention is a method of controlling an operation state of the hydrauliccylinderbyadjustinghydraulicpressure andflow rate by a hydraulic circuit having a proportional electromagnetic control valve; wherein an operation characteristicoftheproportionalelectromagneticcontrol valve is measured by one of the above-mentioned two methods of measuring an operation characteristic of a proportional electromagnetic control valve and is stored in a memory, a table for relating a load current level to the measured operation characteristic value at each step is prepared, interpolation is performed between points plotted on the table so as to determine a continuous function, which is then stored into a memory as the operation characteristic of the proportional electromagnetic control valve, the function is read out from the memory upon actual operation of the hydraulic cylinder, an executive current level is computed according to the function and a target level for hydraulic pressure to the hydraulic cylinder or velocity of a hydraulic ram ofthe hydraulic cylinder, and a current corresponding to the executive current level is applied to the proportional electromagnetic control valve so as to control the operation state of the hydraulic cylinder.
In the method of controlling an operation of a CA 02228~4 1998-02-06 hydrauliccylinderinaccordance withthepresentinvention, the operation characteristic stored in the memory as a function is automatically modified and rewritten in response to a request for automatic modification.
Consequently, even when the proportional electromagnetic control valve built in the hydraulic circuit or functional parts relating to hydraulic pressure or flow rate are repaired or exchanged, the operation characteristic of the proportional electromagnetic control valve stored in the memory can be automatically modified while the machine is kept installed as it is, and the hydraulic cylinder can always be controlled with a high accuracy according to thus automatically modified operation characteristic.
Further, the method of modifying an operation characteristic of a p:roportional electromagnetic control valve in accordance with the present invention is, when, in order to control an operation state of a hydraulic cylinder by adjusting hydraulic pressure and flow rate by a hydraulic circuit having a proportional electromagnetic control valve, an operation characteristic value corre-sponding to a load current level of the proportional electromagnetic control valve is prestored into a memory as a characteristic curve, a method of modifying the characteristic curve stored in the memoryi wherein a hy-draulic pressure or f.Low rate of the hydraulic circuit is CA 02228~4 l998-02-06 specified, a load current level of the proportional electromagnetic control valve corresponding to thus specified level is read out from the characteristic curve in thememory, acurrent correspondingtothus read-outload current level is applied to the proportional electromag-netic control valve, the pressure or flow rate of the hydrauliccircuitcorrespondingtothis currentisactually measured, a load current level of the proportional electromagnetic control valve corresponding to thus actually measured valu.e is read out from the characteristic curve inthe memory, a differencebetweenthusobtainedload current level and an .initial load current level is added to or subtracted from the initial load current level, and a current level resulting from this adding or subtracting operation is written into the memory as a modified load current level corresponding to the specified level so as tomodifytheloadcurrent level ofthecharacteristiccurve in the memory.
In the above-mentioned method of modifying an operationcharacteristicofaproportionalelectromagnetic control valve in accordance with the present invention, in the case where an operation characteristic value corre-sponding to the load current level of the proportional electromagnetic control valve is prestored in the memory as a characteristic curve, the characteristic curve CA 02228~4 1998-02-06 (operation characteristic) can be automatically modified after shipping the machine. Accordingly, even when the proportional electromagnetic control valve built in the hydrauliccircuit or functionalparts relatingtohydraulic pressure or flow rate are repaired or exchanged, the operation characteristic corresponding to the current state can always be held in the memory while the machine is kept installed as it is.
FIG. 1 is a view for explaining a method of measuring an operation characteristic of a proportional electromagnetic pressure control valve in accordance with an embodiment of the present invention;
FIG. 2 is a graph showing a rising state of hydraulic pressure in a hydraulic circuit of this embodiment;
FIG. 3A is a lateral sectional view schematically showing an injection cylinder in order to explain a technique for measuring velocity of a conventional injection ram;
FIG. 3B is a lateral sectional view schematically showing an injection cylinder in order to explain a method of measuring an operation characteristic of a proportional electromagnetic flow control valve (technique for measuring velocity of an injection ram) in this embodiment;
CA 02228~4 l998-02-06 FIG. 4 is a view showing a configuration of the hydraulic circuit and control system in an injection molding machine in accordance with this embodiment;
FIG. 5 is a block diagram functionally showing a detailedconfigurationofthehydrauliccircuit andcontrol system in order to explain a method of controlling an operation of an injection cylinder (method of modifying an operationcharacteristicofaproportionalelectromagnetic pressure control valve) in this embodiment; and FIG. 6 iS a view for explaining another example of method of modifying an operation characteristic of a proportional electromagnetic pressure control valve in accordance with this embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following, an embodiment of the present invention will be explained with reference to the accom-panying drawings.
Explained in this embodiment is a case where the present invention is applied to a hydraulic operation control circuit for an injection molding machine, which comprises ahydraulicpump, aswitchingvalve, andthe like, and adjusts hydraulic pressure and flow rate so as to operate the hydraulic cylinder, as will be explained later, therebyperforming ac:losingoperation, injectionofmelted CA 02228~4 l998-02-06 resin, and the like.
First, with reference to FIG. 4, the configuration ofthehydrauliccircuitand controlsystemoftheinjection moldingmachineto which the methodofthepresentinvention is applied will be explained. Depicted in FIG. 4 are an injection cylinder (hydraulic cylinder) 1 of the injection molding machine whose operation is to be controlled in this embodiment, an injection ram (hydraulic ram) 2 within the injection cylinder 1, and an injection screw 2a connected to the injection ram 2.
Also depicted a:re a position sensor 3 for detecting an amount of movement: of the injection ram 2, a direc-tion-switching valve 4 for turning on/off an injecting operation of the injection cylinder 1, a proportional electromagnetic flow control valve (proportional electromagnetic control valve) 5 for controlling the flow rate of a hydraulic operating fluid to the injection cylinder 1 in response to a load current from a control unit 12, a proportional electromagnetic pressure control valve (proportional electromagnetic control valve) 6 for con-trolling the pressure of the hydraulic operating fluid in response to a load current from the control unit 12, a continuous flow pump 7 which is driven by a motor (M) 7a so as to rotate at a predetermined rpm, a check valve 8, and a pressure sensor 9 for detecting pressure in this CA 02228~4 l998-02-06 hydraulic circuit.
The above-mentioned direction-switching valve 4, control valves 5 and 6, pump 7, check valve 8, and the like constitute the hydraulic circuit for operating the injection cylinder 1 at an injecting process caused by the injection screw 2a.
On the other hand, provided are an operation panel 11 for setting and inputting various kinds of information such as specified levels (control target levels) for pressure of the hydraulic circuit, velocity of the injection ram 2 (flow rate of the hydraulic circuit), and the like to the control unit 12 explained later, and the control unit 12, which receives signals from the position sensor 3 and pressure sensor 9 and applies a load current to each of the control valves 5 and 6 so as to control the hydraulic circuit, thereby controlling the operation state of the injection cyli.nder 1. The control unit 12 is constituted by, in addition to a CPU 13 as an arithmetic processing unit, a memory 14, a D/A converter 15, an output amplifier 16, and an A/D converter 17 which are built therein.
Here, the CPU 13 actually controls an operation state of the injection cylinder 1 in addition to measur-ing/modifying operation characteristics of the control valves 5 and 6 which will be explained later; whereas the CA 02228~4 1998-02-06 memory 14 stores the operation characteristics of the control valves 5 and 6 as will be explained later.
On the otherhand, the D/A converter 15 converts, from digital to analog, control signals (load current level signals) sent from the CPU 13 for the respective control valves 5 and 6. The amplifier (output amplifier) 16 amplifies the control signals from the D/A converter 15 and outputs thus amplified signals to their corresponding control valves 5 and 6. The A/D converter 17 converts analog detection signals from the position sensor 3 and pressure sensor 9 into digital signals and outputs thus converted signals to the CPU 13.
Explained in the following with reference to FIGs.
1 to 3 is a method of automatically inspecting, in a working manner, a pressure-current characteristic (operation characteristic) of the proportional electromagnetic pressure control valve 6 or relationship between velocity of the injection cylinder 1 and the load current level to the proportional electromagnetic flow control valve 5 [a velocity-current characteristic of the injection cylinder 1, and an operation c:haracteristic (flow rate-current characteristic) of the proportional electromagnetic flow control valve 5] when the injection molding machine equipped with the hydraulic circuit and control unit 12 of thisembodimentconstructedasmentionedaboveisinspected CA 02228~4 1998-02-06 uponshipmentinthe site where the machineismanufactured.
FIG. 2 iS a graph showing a rising state of hydraulic pressure in the hydraulic circuit of this embodiment. It illustrates a result obtained when, in this embodiment, the hydraulic pump 7 is driven, the injection cylinder 1 is operated under hydraulic pressure, the injection ram 2 of the injection cylinder 1 in the actual machine is pressed into the end portion of the stroke for closing, melted resin injection, and the like such that the hydraulic circuit attains a closed state, the load current with respect to the proportional elect:romagnetic pressure control valve 6 is successively changed stepwise, and the pressure of the hydraulic circuit is measured by the pressure sensor 9.
As shown in FIG. 2, in a low pressure band (Nos. 1 to 4), an overshoot occurs in each step of measurement, and then pressure gradually converges at the set pressure.
Since it takes a certain time for pressure to stabilize, a delay timer has conventionally been provided (see Ts in FIG. 2 for its set level) to retard the pressure measuring timing. In such a measuring technique, however, the measuring timing uniformly delays even in the case where the set pressure is so high that pressure stabilizes in a short time, whereby it:takes an enormous amount of time to measure pressure (measure an operation characteristic).
For measuring pressure in order to measure an CA 02228~4 1998-02-06 operation characteristic in this embodiment, upon measuring one step of pressure, as shown in the pres-sure-declining curve after overshoot represented in FIG.
1, pressure is repeatedly measured by the pressure sensor 9 at a constant time interval t, the CPU 13 of the control unit 12 assumes pressure to be stabilized when a difference ~P between the measured value and the previously measured valuebecomesasufficientlysmall constantnumericalvalue e or less, and this pressure is taken in as an operation pressure of the proportional electromagnetic pressure control valve 6 corresponding to the load current at this step.
Consequently, without necessitating a certain wait time Ts for each measurement step before measurement as in the conventional case, measurement is effected with a timing at which pressure is assumed to be stabilized for each measurement step. Therefore, the pressure measure-ment time requires only T1, thus allowing the operation pressure in the next step to be measured after the time T1 is elapsed. Thus, the total time required for preparing a pressure-current characteristic curve in the CPU 13 of the control unit 12 can be made much shorter than that in the conventional case.
Here, as shown in FIG. 2, overshoot hardly occurs in a high pressure band (Nos. 5 to 7). Even in such a case, CA 02228~4 1998-02-06 in the measuring method of this embodiment, it is unnecessary to wait for the certain time Ts before measurement in each measurement step, as mentioned above, whereby measurement is effected with a timing T2 at which pressure is assumed t:o be stabilized.
Meanwhile, FIG. 3A is a lateral sectional view schematically showing the injection cylinder 1 for explaining a conventional technique for measuring velocity of the injection ram 2; whereas FIG . 3B is a lateral sectional view schematically showing the injection cylinderl forexplain.ing amethodofmeasuringanoperation characteristic of the proportional electromagnetic flow control valve 5 (technique for measuring velocity of the injection ram 2) in t:his embodiment.
When measuring an operation characteristic of the proportional electromagnetic flow control valve 5, while the injection cylinder 1 of the actual machine is set to an operable state, the load current to the proportional electromagnetic flow control valve 5 is successively changed stepwise, and the velocity of the injection ram 2 is measured while the injection cylinder 1 is caused to operate.
Here, in the conventional technique shown in FIG. 3A, a timetbywhich the injectionram2 travels apredetermined distance lo is measured so as to compute a velocity lo/t.
CA 02228~4 1998-02-06 In this embodiment, by contrast, as shown in FIG. 3B, a distance x by which t:he injection ram 2 travels in a predetermined time t~:is precisely measured by means of the position sensor 3 and is fed into the CPU 13 of the control unit 12, whereby the velocity of the injection ram 2 is computed asx/to. Then, the CPU 13 multiplies thusmeasured and computed velocity of the injection ram (hydraulic ram) 2 by the pressure-receiving area of the injection cylinder 1 so as to compute a fl.ow rate, and causes it to correspond to the load current at each step, thereby forming a characteristic curve concerning the flow rate-current characteristic of the proportional electromagnetic flow control valve 5.
In the conventional technique shown in FIG. 3A, concerning the time for traveling an approach distance m and the measurement distance l~, in particular when the current of the proportional electromagnetic flow control valve 5 is low (flow rate is low), not only the measurement time becomes longer, but also the time required for the hydraulic ram 2 to return becomes longer. In the technique of the embodiment shown in FIG. 3B, by contrast, when the approach time and measurement time are respectively set to 0.5 second and 1.5 seconds beforehand, for example, the measurement time is always constant whether the current of the proportional electromagnetic flow control valve 5 is CA 02228~4 l998-02-06 high or low, thus allowing the measurement to be completed in much shorter time than in the conventional technique shown in FIG. 3A.
In this embodiment, according to the data measured by such a technique as that mentioned above, characteristic curves for the proportional electromagnetic flow control valve 5 and proportional electromagnetic pressure control valve 6 are prepared, and thus prepared characteristic curves are stored in the memory 14 of the control unit 12.
In the case where such a characteristic curve has already been stored in the memory 14, the characteristic curve in the memory14isrewritten ormodifiedbythecharacteristic curve prepared by the above-mentioned technique.
When the operating hydraulic pressure of the injection cylinder 1 or velocity of the injection ram 2 in the injection molding machine is specified upon actual driving, theCPU13Ofthecontrolunitl2 readsoutacurrent characteristic level corresponding to thus specified value from the memory 14, converts thus read-out level to an executive current, and applies this current to the proportional electromagnetic flow control valve 5 and proportional electromagnetic pressure control valve 6 via the D/A converter 15 and amplifier 16. As a result, the operation state of the injection cylinder 1 is controlled so as to attain the specified value.
- CA 02228~4 1998-02-06 In the following, explanation will be provided for a method of modifying the pressure-current characteristic of the proportional electromagnetic pressure control valve 6 or flow rate-current characteristic of the proportional electromagnetic flow control valve 5 thus written in the memory 14. This embodiment encompasses two kinds of modifying method. First and second examples thereof will be respectively explained with reference to FIGs. 5 and 6.
FIG. 5 is a block diagram functionally showing a detailedconfigurationofthehydrauliccircuitandcontrol system in order to explain a method of controlling an operation of the injection cylinder 1 (method of modifying an operation characteristic of the proportional electro-magnetic pressure control valve 6) in this embodiment.
This process will be explained in detail with reference to FIG. 5, additionally in view of the modifying and rewriting function for the pressure characteristic in the proportional electromagnetic pressure control valve 6 in the hydraulic circuit shown in FIG. 4.
(1) When a request for automatically modifying the pressure characteristic is issued from the operation panel 11 to the CPU 13, a pressure-specifying level Pn stored in a memory (not depicted) built in a processing section 13a of the CPU 13 is sent to the memory 14, and a load current level In corresponding to the pressure-specifying level Pn CA 02228~4 l998-02-06 -2 6- ' is read out from a reference curve Ps of a pressure-current characteristic function table stored in the memory 14 to the processing section 13a of the CPU 13 so as to be temporarily kept there.
(2) According to a current (which corresponds to the current level In) outputted from the processing section 13a of the CPU 13 via the D/A converter 15 and amplifier 16, the proportional electromagnetic pressure control valve 6 is operated, whereby the pressure of the hydraulic circuit for driving the injection cylinder 1 is controlled. Then, an actual pressure Pn' of the hydraulic circuit is measured by the pressure sensor 9, and thus measured signal is sent to an arithmetic section 13b of the CPU 13 by way of the A/Dconverter17. Here, the actualpressurePn'ismeasured bythetechniquepreviouslyexplainedwithreferenceto FIG.
1.
(3) In the arithmetic section 13b of the CPU 13, according to the actual pressure Pn' and the load current level In kept in the processing section 13a of the CPU 13 in the above-mentioned step (1), the actual pressure Pn' is plotted on the pressure-current characteristic function table.
(4) As explained above as represented by the pres-sure-specifying level Pn, pressure-specifying levels P1to P~ are successively fed to the memory 14, current levels CA 02228~4 1998-02-06 Il to I~ respectively corresponding to the pressure-specifying levels are read out from the characteristic curve Ps of the pressure-current characteristic function table in the memory 14 to the processing section 13a of the CPU 13 so as to be temporarily kept there, actual pressures Pl' to P~' of the hydraulic pressure are fed to the arithmetic section 13b of the CPU 13 and successively plotted on the pressure-current characteristic function table, and interpolation is made between thus plotted points, thereby yielding a continuous actual pressure characteristic curve Pr as shown in FIG. 5. Since this characteristic curve Pr has a form analogous to that of the characteristic curve Ps in the initial reference characteristic function table, the constant of function concerning the characteristic curve Ps is modified so that the new characteristic curve Pr is adopted as the function.
(5) In place of the function of the initial reference characteristic function table, the new characteristic curve Pr is written into the memory 14 as a function, so as to be ready for actual operation. When controlling actual operation, the CPU 13 uses the new function so as to determine a load current level of the proportional electromagnetic pressure control valve 6 corresponding to an arbitrary pressure-specifying level. Namely, a target pressure or target ram velocity is set from the operation CA 02228~4 l998-02-06 panel 11 so as to be transmitted to the CPU 13 of the control unit 12; whereas the CPU 13 reads out the above-mentioned function from the memory 14, computes a load current level correspondingtothetargetlevel accordingtothe function, and outputs a currentc:orresponding to thus computed result via the D/A converter 15 and amplifier 16, thus operating and controlling the proportional electromagnetic pressure control valve 6 and proportional electromagnetic flow control valve 5.
While a method of modifying an operation characteristicappliedtotheproportionalelectromagnetic pressure control valve 6 is explained as an example in the foregoing, a technique similar to that mentioned above is applied to a case where an operation characteristic (flow rate-current characteristic) of the proportional electromagnetic flow control valve 5 is to be modified.
On the other hand, FIG. 6 is a view for explaining the second example of method of modifying an operation characteristic of the proportional electromagnetic pres-sure control valve 6 in accordance with this embodiment.
Here, it is assumed that reference representative values of the characteristic curve for pressure with respect to the load current level of the proportional electromagnetic pressure control valve 6 (curve referred to as Ps in FIG.
While a method of modifying an operation characteristicappliedtotheproportionalelectromagnetic pressure control valve 6 is explained as an example in the foregoing, a technique similar to that mentioned above is applied to a case where an operation characteristic (flow rate-current characteristic) of the proportional electromagnetic flow control valve 5 is to be modified.
On the other hand, FIG. 6 is a view for explaining the second example of method of modifying an operation characteristic of the proportional electromagnetic pres-sure control valve 6 in accordance with this embodiment.
Here, it is assumed that reference representative values of the characteristic curve for pressure with respect to the load current level of the proportional electromagnetic pressure control valve 6 (curve referred to as Ps in FIG.
6), which are attached thereto by a maker of the CA 02228~4 1998-02-06 proportional electromagnetic pressure control valve, are prestored in the memory 14 of the control unit 12 as being A/D converted.
Here, when a pressure Pa of the hydraulic circuit is specified from the operation panel 11 to the CPU 13 in order to modify this characteristic curve Ps, the CPU 13 reads out a load current level Ia corresponding to this specified value Pa from the characteristic curve Ps stored in the memory 14, and this load current level Ia is D/A-converted by the D/A converter 15 and, after being constantly amplified by the amplifier 16, is outputted to the proportional electromagnetic pressure control valve 6.
Then, a pressure Pa' corresponding to this current level Ia is measured by the pressure sensor 9, and thus actually measured value is fed to the CPU 13 after being converted from analog to digital by the A/D converter 17.
Here, the actually measured pressure value Pa' is deter-mined according to the technique previously explained with reference to FI~. 1.
The CPU 13 compares the actually measured pressure value Pa' with the reference representative value Pa of the characteristic curve, replaces the actually measured pressure value Pa' with the specified value, reads out a current level Ia' corresponding to the actually measured value Pa' from the reference representative characteristic CA 02228~4 1998-02-06 curve Ps, adds (or subtracts) a difference ~I between the current level Ia' and the initial load current level Ia to (from) the initial load current level Ia, and replaces a load current level Ib obtained as a result of this arithmetic operation with the load current level of the reference representat:ive characteristic curve Ps, thus rewriting the memory 14.
In this manner, the current level of the characteristic curve Ps with respect to a certain specified value can be modifiecl.
As the foregoing technique is repeated while the magnitude of pressure is changed, the characteristic curve Ps stored in the memory 14 is rewritten into a modified characteristic curveE~rofpressure andcurrentsuch asthat shown in FIG. 6 as dotted line.
When the characteristic curve approximates a line or when the difference ~I is small, thus modified characteristic curve Pr has a practically sufficient accuracy. Accordingly, the above-mentioned method of modifying an operation characteristic can simply effect modification in the manufacturing site or molding site, thus being quite convenient.
Though the method of modifying an operation characteristicappliedtotheproportionalelectromagnetic pressure control valve 6 is explained as an example in the CA 02228~4 1998-02-06 foregoing, a technique similar thereto is applied to the case where the operation characteristic (flow rate-current characteristic) of the proportional electromagnetic flow control valve 5 is to be modified.
Thus, in accordance with this embodiment, upon the shipping inspection at the manufacturing site of the in~ection molding machine, the pressure-current characteristic of the proportional electromagnetic pres-sure control valve 6 or velocity-current characteristic of the hydraulic cylinder 1 (flow rate-current characteristic of the proportional electromagnetic flow control valve 5), which becomes a reference for instructing and operating the hydraulic circuit, is automatically inspected and modified in a working manner, whereby the executive value corre-spondingtothespecifi.edvaluecanbecorrectlyreproduced, thus making it possible to yield a correct resolution as fine as about 0.1%.
Also, even when the proportional electromagnetic control valves 5 and 6 built in the hydraulic circuit or functional parts relating to hydraulic pressure and flow rate are repaired or exchanged, characteristics of the proportional electromagnetic control valves 5 and 6 can be automatically modified while the machine is kept installed as lt lS.
Since the load current level is modified such that CA 02228~4 1998-02-06 the specified value and the executive value coincide with each other and then is stored in the memory 14 so as to be read out when necessary, the points of measurement become less when the specified values are determined beforehand, thus allowing the measurement time to become shorter.
Further, in the pressure measuring technique of this embodiment, even in the case where pressure is relatively low, the pressure obtained when the inclination of the declining curve of rising overshoot upon switching hydraulic pressure becomes a predetermined level or less is employed as a measured value, whereby the measurement time can be shortened. Also, in the velocity measuring technique of this embodiment, since the distance of travel in a predetermined time is measured so as to determine velocity, measurement time can be made shorter than that in the conventional case, in particular, on the minimum velocity side. Therefore, even when numerous points are to be measured, time required for measuring an operation characteristic can be greatly reduced.
As explained in the foregoing, in accordance with this embodiment, the actually measured value is automatically modified to the specified value, and the characteristic curves of the proportional electromagnetic control valves 5 and 6 themselves are recomposed and stored in the memory 14. When the actual machine is operated, the CA 02228~4 1998-02-06 operation characteristics can be read out from the memory 14 so as to control the proportional electromagnetic control valves 5 and 6. Also, the shipping inspection can be effected in a short time, whereas the characteristics can be automatically adjusted in a molding factory after the machine is shipped.
Though the above-mentioned embodiment is explained with an example in which the injection cylinder 1 is used;
in a proportional electromagnetic pressure control valve for controlling pressure of a closing cylinder, an operation characteristic can also be modified by the same pressure measuring method while the closingcylinder is set to a closed state. Also, in a back-pressure proportional electromagnetic pressure control valve, an operation characteristic can be modified in a method similar to that mentioned above when pressure oil is supplied thereto while the injection cylinder is set to a closed state.
Though the above-mentioned embodiment explains a case where the present invention is applied to a hydraulic circuit foroperatingvarious kinds ofcylinders (injection cylinder and the like) in the injection molding machine;
without being restrict:ed thereto, the present invention is also applicable to various kinds of apparatus where a hydraulic circuit for operating a hydraulic cylinder is equippedwithaproportionalelectromagneticcontrol valve, whereby advantageous effects similar to those mentioned above can be obtained.
Here, when a pressure Pa of the hydraulic circuit is specified from the operation panel 11 to the CPU 13 in order to modify this characteristic curve Ps, the CPU 13 reads out a load current level Ia corresponding to this specified value Pa from the characteristic curve Ps stored in the memory 14, and this load current level Ia is D/A-converted by the D/A converter 15 and, after being constantly amplified by the amplifier 16, is outputted to the proportional electromagnetic pressure control valve 6.
Then, a pressure Pa' corresponding to this current level Ia is measured by the pressure sensor 9, and thus actually measured value is fed to the CPU 13 after being converted from analog to digital by the A/D converter 17.
Here, the actually measured pressure value Pa' is deter-mined according to the technique previously explained with reference to FI~. 1.
The CPU 13 compares the actually measured pressure value Pa' with the reference representative value Pa of the characteristic curve, replaces the actually measured pressure value Pa' with the specified value, reads out a current level Ia' corresponding to the actually measured value Pa' from the reference representative characteristic CA 02228~4 1998-02-06 curve Ps, adds (or subtracts) a difference ~I between the current level Ia' and the initial load current level Ia to (from) the initial load current level Ia, and replaces a load current level Ib obtained as a result of this arithmetic operation with the load current level of the reference representat:ive characteristic curve Ps, thus rewriting the memory 14.
In this manner, the current level of the characteristic curve Ps with respect to a certain specified value can be modifiecl.
As the foregoing technique is repeated while the magnitude of pressure is changed, the characteristic curve Ps stored in the memory 14 is rewritten into a modified characteristic curveE~rofpressure andcurrentsuch asthat shown in FIG. 6 as dotted line.
When the characteristic curve approximates a line or when the difference ~I is small, thus modified characteristic curve Pr has a practically sufficient accuracy. Accordingly, the above-mentioned method of modifying an operation characteristic can simply effect modification in the manufacturing site or molding site, thus being quite convenient.
Though the method of modifying an operation characteristicappliedtotheproportionalelectromagnetic pressure control valve 6 is explained as an example in the CA 02228~4 1998-02-06 foregoing, a technique similar thereto is applied to the case where the operation characteristic (flow rate-current characteristic) of the proportional electromagnetic flow control valve 5 is to be modified.
Thus, in accordance with this embodiment, upon the shipping inspection at the manufacturing site of the in~ection molding machine, the pressure-current characteristic of the proportional electromagnetic pres-sure control valve 6 or velocity-current characteristic of the hydraulic cylinder 1 (flow rate-current characteristic of the proportional electromagnetic flow control valve 5), which becomes a reference for instructing and operating the hydraulic circuit, is automatically inspected and modified in a working manner, whereby the executive value corre-spondingtothespecifi.edvaluecanbecorrectlyreproduced, thus making it possible to yield a correct resolution as fine as about 0.1%.
Also, even when the proportional electromagnetic control valves 5 and 6 built in the hydraulic circuit or functional parts relating to hydraulic pressure and flow rate are repaired or exchanged, characteristics of the proportional electromagnetic control valves 5 and 6 can be automatically modified while the machine is kept installed as lt lS.
Since the load current level is modified such that CA 02228~4 1998-02-06 the specified value and the executive value coincide with each other and then is stored in the memory 14 so as to be read out when necessary, the points of measurement become less when the specified values are determined beforehand, thus allowing the measurement time to become shorter.
Further, in the pressure measuring technique of this embodiment, even in the case where pressure is relatively low, the pressure obtained when the inclination of the declining curve of rising overshoot upon switching hydraulic pressure becomes a predetermined level or less is employed as a measured value, whereby the measurement time can be shortened. Also, in the velocity measuring technique of this embodiment, since the distance of travel in a predetermined time is measured so as to determine velocity, measurement time can be made shorter than that in the conventional case, in particular, on the minimum velocity side. Therefore, even when numerous points are to be measured, time required for measuring an operation characteristic can be greatly reduced.
As explained in the foregoing, in accordance with this embodiment, the actually measured value is automatically modified to the specified value, and the characteristic curves of the proportional electromagnetic control valves 5 and 6 themselves are recomposed and stored in the memory 14. When the actual machine is operated, the CA 02228~4 1998-02-06 operation characteristics can be read out from the memory 14 so as to control the proportional electromagnetic control valves 5 and 6. Also, the shipping inspection can be effected in a short time, whereas the characteristics can be automatically adjusted in a molding factory after the machine is shipped.
Though the above-mentioned embodiment is explained with an example in which the injection cylinder 1 is used;
in a proportional electromagnetic pressure control valve for controlling pressure of a closing cylinder, an operation characteristic can also be modified by the same pressure measuring method while the closingcylinder is set to a closed state. Also, in a back-pressure proportional electromagnetic pressure control valve, an operation characteristic can be modified in a method similar to that mentioned above when pressure oil is supplied thereto while the injection cylinder is set to a closed state.
Though the above-mentioned embodiment explains a case where the present invention is applied to a hydraulic circuit foroperatingvarious kinds ofcylinders (injection cylinder and the like) in the injection molding machine;
without being restrict:ed thereto, the present invention is also applicable to various kinds of apparatus where a hydraulic circuit for operating a hydraulic cylinder is equippedwithaproportionalelectromagneticcontrol valve, whereby advantageous effects similar to those mentioned above can be obtained.
Claims (7)
1. A method of measuring an operation characteristic of a proportional electromagnetic control valve, said method comprising:
in a hydraulic circuit in which a hydraulic cylinder is operated as proportional electromagnetic control valve adjusts hydraulic pressure and flow rate, when said proportional electromagnetic control valve is a proportional electromagnetic pressure control valve which controls a hydraulic pressure in response to a load current, successively changing the load current with respect to said proportional electromagnetic pressure control valve stepwise in a closed operation state of said hydraulic circuit; and at each step, measuring a pressure of said hydraulic circuit at a predetermined interval of time, assuming the pressure to be stabilized at a point of time when a difference between thus measured pressure value and the previously measured pressure value becomes a predetermined level or smaller, and employing the measured pressure value at said point of time as the pressure corresponding to the load current at said step, so as to measure a pressure-current characteristic as the operation characteristic of said proportional electromagnetic pressure control valve.
in a hydraulic circuit in which a hydraulic cylinder is operated as proportional electromagnetic control valve adjusts hydraulic pressure and flow rate, when said proportional electromagnetic control valve is a proportional electromagnetic pressure control valve which controls a hydraulic pressure in response to a load current, successively changing the load current with respect to said proportional electromagnetic pressure control valve stepwise in a closed operation state of said hydraulic circuit; and at each step, measuring a pressure of said hydraulic circuit at a predetermined interval of time, assuming the pressure to be stabilized at a point of time when a difference between thus measured pressure value and the previously measured pressure value becomes a predetermined level or smaller, and employing the measured pressure value at said point of time as the pressure corresponding to the load current at said step, so as to measure a pressure-current characteristic as the operation characteristic of said proportional electromagnetic pressure control valve.
2. A method of measuring an operation characteristic of a proportional electromagnetic control valve, said method comprising:
in a hydraulic circuit in which a hydraulic cylinder is operated as a proportional electromagnetic control valve adjusts hydraulic pressure and flow rate, when said proportional electromagnetic control valve is a proportional electromagnetic flow control valve which controls a flow rate in response to a load current, causing said hydraulic cylinder to attain an operable state;
successively changing the load current with respect to said proportional electromagnetic flow control valve stepwise so as to operate said hydraulic cylinder; and at each step, measuring a traveling distance of a hydraulic ram of said hydraulic cylinder by a predetermined period of time, and employing a velocity computed according to said traveling distance as the velocity corresponding to the load current at said step, so as to measure a velocity-current characteristic as the operation characteristic of said proportional electromagnetic flow control valve.
in a hydraulic circuit in which a hydraulic cylinder is operated as a proportional electromagnetic control valve adjusts hydraulic pressure and flow rate, when said proportional electromagnetic control valve is a proportional electromagnetic flow control valve which controls a flow rate in response to a load current, causing said hydraulic cylinder to attain an operable state;
successively changing the load current with respect to said proportional electromagnetic flow control valve stepwise so as to operate said hydraulic cylinder; and at each step, measuring a traveling distance of a hydraulic ram of said hydraulic cylinder by a predetermined period of time, and employing a velocity computed according to said traveling distance as the velocity corresponding to the load current at said step, so as to measure a velocity-current characteristic as the operation characteristic of said proportional electromagnetic flow control valve.
3. A method of controlling an operation of a hydraulic cylinder in which an operation state of a hydraulic cylinder is controlled as a hydraulic circuit having a proportional electromagnetic control valve adjusts hydraulic pressure and flow rate, said method comprising:
when said proportional electromagnetic control valve is a proportional electromagnetic pressure control valve which controls a hydraulic pressure in response to a load current, successively changing the load current with respect to said proportional electromagnetic pressure control valve stepwise in a closed operation state of said hydraulic circuit; at each step, measuring a pressure of said hydraulic circuit at a predetermined interval of time, assuming the pressure to be stabilized at a point of time when a difference between thus measured pressure value and the previously measured pressure value becomes a predetermined level or smaller, and employing the measured pressure value at said point of time as the pressure corresponding to the load current at said step, so as to measure a pressure-current characteristic as the operation characteristic of said proportional electromagnetic pressure control valve; and storing thus measured operation characteristic of said proportional electromagnetic pressure control valve into a memory; and then, when specifying a hydraulic pressure to said hydraulic cylinder, reading out an operation characteristic value matching thus specified level from said memory, converting thus read-out characteristic value into an executive current, and applying said executive current to said proportional electromagnetic pressure control valve so as to control the operation state of said hydraulic cylinder.
when said proportional electromagnetic control valve is a proportional electromagnetic pressure control valve which controls a hydraulic pressure in response to a load current, successively changing the load current with respect to said proportional electromagnetic pressure control valve stepwise in a closed operation state of said hydraulic circuit; at each step, measuring a pressure of said hydraulic circuit at a predetermined interval of time, assuming the pressure to be stabilized at a point of time when a difference between thus measured pressure value and the previously measured pressure value becomes a predetermined level or smaller, and employing the measured pressure value at said point of time as the pressure corresponding to the load current at said step, so as to measure a pressure-current characteristic as the operation characteristic of said proportional electromagnetic pressure control valve; and storing thus measured operation characteristic of said proportional electromagnetic pressure control valve into a memory; and then, when specifying a hydraulic pressure to said hydraulic cylinder, reading out an operation characteristic value matching thus specified level from said memory, converting thus read-out characteristic value into an executive current, and applying said executive current to said proportional electromagnetic pressure control valve so as to control the operation state of said hydraulic cylinder.
4. A method of controlling an operation of a hydraulic cylinder in which an operation state of a hydraulic cylinder is controlled as a hydraulic circuit having a proportional electromagnetic control valve adjusts hydraulic pressure and flow rate, said method comprising:
when said proportional electromagnetic control valve is a proportional electromagnetic flow control valve which controls a flow rate in response to a load current, causing said hydraulic cylinder to attain an operable state;
successively changing the load current with respect to said proportional electromagnetic flow control valve stepwise so as to operate said hydraulic cylinder; at each step, measuring a traveling distance of a hydraulic ram of said hydraulic cylinder by a predetermined period of time, and employing a velocity computed according to said traveling distance as the velocity corresponding to the load current at said step, so as to measure a velocity-current characteristic as the operation characteristic of said proportional electromagnetic flow control valve; and storing thus measured operation characteristic of said proportional electromagnetic flow control valve into a memory; and then, when specifying a velocity of said hydraulic ram of said hydraulic cylinder, reading out an operation characteristic value matching thus specified level from said memory, converting thus read-out characteristic value into an executive current, and applying said executive current to said proportional electromagnetic flow control valve so as to control the operation state of said hydraulic cylinder.
when said proportional electromagnetic control valve is a proportional electromagnetic flow control valve which controls a flow rate in response to a load current, causing said hydraulic cylinder to attain an operable state;
successively changing the load current with respect to said proportional electromagnetic flow control valve stepwise so as to operate said hydraulic cylinder; at each step, measuring a traveling distance of a hydraulic ram of said hydraulic cylinder by a predetermined period of time, and employing a velocity computed according to said traveling distance as the velocity corresponding to the load current at said step, so as to measure a velocity-current characteristic as the operation characteristic of said proportional electromagnetic flow control valve; and storing thus measured operation characteristic of said proportional electromagnetic flow control valve into a memory; and then, when specifying a velocity of said hydraulic ram of said hydraulic cylinder, reading out an operation characteristic value matching thus specified level from said memory, converting thus read-out characteristic value into an executive current, and applying said executive current to said proportional electromagnetic flow control valve so as to control the operation state of said hydraulic cylinder.
5. A method of controlling an operation of a hydraulic cylinder in which an operation state of a hydraulic cylinder is controlled as a hydraulic circuit having a proportional electromagnetic control valve adjusts hydraulic pressure and flow rate, said method comprising:
when said proportional electromagnetic control valve is a proportional electromagnetic pressure control valve which controls a hydraulic pressure in response to a load current, successively changing the load current with respect to said proportional electromagnetic pressure control valve stepwise in a closed operation state of said hydraulic circuit; at each step, measuring a pressure of said hydraulic circuit at a predetermined interval of time, assuming the pressure to be stabilized at a point of time when a difference between thus measured pressure value and the previously measured pressure value becomes a predetermined level or smaller, and employing a level of the measured pressure at said point of time as the pressure corresponding to the load current at said step, so as to measure a pressure-current characteristic as the operation characteristic of said proportional electromagnetic pressure control valve; preparing a table for relating a load current level to the measured operation characteristic value at each step; performing interpolation between points plotted on said table so as to determine a continuous function; and storing said function into a memory as an operation characteristic of said proportional electromagnetic pressure control valve; and then reading out said function from said memory upon actual operation of said hydraulic cylinder, computing an executive current level according to said function and a target level for hydraulic pressure to said hydraulic cylinder, and applying a current corresponding to said executive current level to said proportional electromagnetic pressure control valve so as to control the operation state of said hydraulic cylinder.
when said proportional electromagnetic control valve is a proportional electromagnetic pressure control valve which controls a hydraulic pressure in response to a load current, successively changing the load current with respect to said proportional electromagnetic pressure control valve stepwise in a closed operation state of said hydraulic circuit; at each step, measuring a pressure of said hydraulic circuit at a predetermined interval of time, assuming the pressure to be stabilized at a point of time when a difference between thus measured pressure value and the previously measured pressure value becomes a predetermined level or smaller, and employing a level of the measured pressure at said point of time as the pressure corresponding to the load current at said step, so as to measure a pressure-current characteristic as the operation characteristic of said proportional electromagnetic pressure control valve; preparing a table for relating a load current level to the measured operation characteristic value at each step; performing interpolation between points plotted on said table so as to determine a continuous function; and storing said function into a memory as an operation characteristic of said proportional electromagnetic pressure control valve; and then reading out said function from said memory upon actual operation of said hydraulic cylinder, computing an executive current level according to said function and a target level for hydraulic pressure to said hydraulic cylinder, and applying a current corresponding to said executive current level to said proportional electromagnetic pressure control valve so as to control the operation state of said hydraulic cylinder.
6. A method of controlling an operation of a hydraulic cylinder in which an operation state of a hydraulic cylinder is controlled as a hydraulic circuit having a proportional electromagnetic control valve adjusts hydraulic pressure and flow rate, said method comprising:
when said proportional electromagnetic control valve is a proportional electromagnetic flow control valve which controls a flow rate in response to a load current, causing said hydraulic cylinder to attain an operable state;
successively changing the load current with respect to said proportional electromagnetic flow control valve stepwise so as to operate said hydraulic cylinder; at each step, measuring a traveling distance of a hydraulic ram of said hydraulic cylinder by a predetermined period of time, and employing a velocity computed according to said traveling distance as the velocity corresponding to the load current at said step, so as to measure a velocity-current characteristic as the operation characteristic of said proportional electromagnetic flow control valve; preparing a table for relating a load current level to the measured operation characteristic value at each step; performing interpolation between points plotted on said table so as to determine a continuous function; and storing said function into a memory as an operation characteristic of said proportional electromagnetic flow control valve; and then reading out said function from said memory upon actual operation of said hydraulic cylinder, computing an executive current level according to said function and a target level for velocity of said hydraulic ram of said hydraulic cylinder, and applying a current corresponding to said executive current level to said proportional electromagnetic flow control valve so as to control the operation state of said hydraulic cylinder.
when said proportional electromagnetic control valve is a proportional electromagnetic flow control valve which controls a flow rate in response to a load current, causing said hydraulic cylinder to attain an operable state;
successively changing the load current with respect to said proportional electromagnetic flow control valve stepwise so as to operate said hydraulic cylinder; at each step, measuring a traveling distance of a hydraulic ram of said hydraulic cylinder by a predetermined period of time, and employing a velocity computed according to said traveling distance as the velocity corresponding to the load current at said step, so as to measure a velocity-current characteristic as the operation characteristic of said proportional electromagnetic flow control valve; preparing a table for relating a load current level to the measured operation characteristic value at each step; performing interpolation between points plotted on said table so as to determine a continuous function; and storing said function into a memory as an operation characteristic of said proportional electromagnetic flow control valve; and then reading out said function from said memory upon actual operation of said hydraulic cylinder, computing an executive current level according to said function and a target level for velocity of said hydraulic ram of said hydraulic cylinder, and applying a current corresponding to said executive current level to said proportional electromagnetic flow control valve so as to control the operation state of said hydraulic cylinder.
7. A method of modifying an operation characteristic of a proportional electromagnetic control valve in which when, in order to control an operation state of a hydraulic cylinder by adjusting hydraulic pressure and flow rate by a hydraulic circuit having a proportional electromagnetic control valve, an operation characteristic value corresponding to a load current level of said proportional electromagnetic control valve is prestored into a memory as a characteristic curve, said characteristic curve stored in said memory is modified, said method comprising:
specifying a hydraulic pressure or flow rate of said hydraulic circuit, reading out a load current level of said proportional electromagnetic control valve corresponding to thus specified level from said characteristic curve in said memory, applying a current corresponding to thus read-out load current level to said proportional electromagnetic control valve, actually measuring a pressure or flow rate of said hydraulic circuit corresponding to said current, reading out a load current level of said proportional electromagnetic control valve corresponding to thus actually measured value from said characteristic curve in said memory, adding or subtracting a difference between thus obtained load current level and an initial load current level to or from said initial load current level, and writing a current level resulting from said adding or subtracting operation into said memory as a modified load current level corresponding to said specified level so as to modify said load current level of said characteristic curve in said memory.
specifying a hydraulic pressure or flow rate of said hydraulic circuit, reading out a load current level of said proportional electromagnetic control valve corresponding to thus specified level from said characteristic curve in said memory, applying a current corresponding to thus read-out load current level to said proportional electromagnetic control valve, actually measuring a pressure or flow rate of said hydraulic circuit corresponding to said current, reading out a load current level of said proportional electromagnetic control valve corresponding to thus actually measured value from said characteristic curve in said memory, adding or subtracting a difference between thus obtained load current level and an initial load current level to or from said initial load current level, and writing a current level resulting from said adding or subtracting operation into said memory as a modified load current level corresponding to said specified level so as to modify said load current level of said characteristic curve in said memory.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JPHEI9-35160 | 1997-02-19 | ||
| JP9035160A JPH10230539A (en) | 1997-02-19 | 1997-02-19 | Measuring method of working characteristic of proportional solenoid control valve, working controlling method of hydraulic cylinder, and working characteristic correcting method of proportional solenoid control valve |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2228554A1 CA2228554A1 (en) | 1998-08-19 |
| CA2228554C true CA2228554C (en) | 2001-05-08 |
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ID=12434135
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002228554A Expired - Fee Related CA2228554C (en) | 1997-02-19 | 1998-02-06 | Method of measuring operation characteristic of proportional electromagnetic control valve, method of controlling operation of hydraulic cylinder, and method of modifying operation characteristic of proportional electromagnetic control valve |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US6192299B1 (en) |
| JP (1) | JPH10230539A (en) |
| CA (1) | CA2228554C (en) |
| DE (1) | DE19806544B4 (en) |
| IT (1) | IT1298263B1 (en) |
| TW (1) | TW355159B (en) |
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| JP2756077B2 (en) * | 1993-12-27 | 1998-05-25 | 東芝機械株式会社 | Automatic setting method of injection molding speed condition of injection molding machine |
| DE19525141C1 (en) * | 1995-07-11 | 1996-11-28 | Karl Hehl | Injection moulding machine control |
| US6108587A (en) * | 1996-12-11 | 2000-08-22 | Rockwell Technologies, Llc | Injection molding controller with machine modeling |
| US5918195A (en) * | 1997-05-08 | 1999-06-29 | Case Corporation | Calibration of a command device in control system |
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1997
- 1997-02-19 JP JP9035160A patent/JPH10230539A/en active Pending
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1998
- 1998-02-06 CA CA002228554A patent/CA2228554C/en not_active Expired - Fee Related
- 1998-02-10 US US09/021,414 patent/US6192299B1/en not_active Expired - Fee Related
- 1998-02-17 IT IT98MI000297A patent/IT1298263B1/en active IP Right Grant
- 1998-02-17 DE DE19806544A patent/DE19806544B4/en not_active Expired - Fee Related
- 1998-02-19 TW TW087102317A patent/TW355159B/en active
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| TW355159B (en) | 1999-04-01 |
| DE19806544A1 (en) | 1998-08-20 |
| CA2228554A1 (en) | 1998-08-19 |
| DE19806544B4 (en) | 2005-02-17 |
| US6192299B1 (en) | 2001-02-20 |
| IT1298263B1 (en) | 1999-12-20 |
| JPH10230539A (en) | 1998-09-02 |
| ITMI980297A1 (en) | 1999-08-17 |
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