DE4334933A1 - Method and device for positive disconnection of hand-operated working equipment - Google Patents

Abstract

The invention relates to a method and the corresponding device for positive disconnection of hand-operated working equipment in working situations, such as a rotating tool tilting, being stalled or being destroyed. The working equipment removes the material abrasively from the workpiece and engages with the workpiece in a positively locking or force-fitting manner. The solution according to the invention is intended to provide disconnection reliably and at a low cost in order to reduce the danger to the operator in emergency situations. In this case, the vibration (oscillation) acceleration of the working equipment is measured and the function a(t) in a predetermined time interval (T) of constant size is determined from the individual measured values. Subsequently, a comparison is carried out to determine whether this function a(t) has no zero crossing within this time interval (T). If none of the function values within the time interval (T) correspond to the zero crossing, a disconnection signal is generated and the working equipment is disconnected.

Description

The invention relates to a method according to the Oberbe handle of claim 1 and the corresponding Device for this. For tools with rotating Tools such as angle grinders, circular saws and Drills, it comes through either operating, through Workpiece defects or destruction of the tool always again that, for example, by tilting the Suddenly forces us to the work equipment that are no longer mastered by the operator can become serious injuries can.

The prevailing shutdown protection are either slip clutches or act thermally de Bimetal cut-off safeguards in such work tel installed, their shutdown due to the high Time constant much too late or in certain emergencies  len does not take place at all because the required There is no warming or the security system is too slow ghost.

It is therefore an object of the invention, the possibility to create hand-operated tools with rotating the tools quickly, safely and with little opening switch off the wall to the danger of the operating personnel reduce in emergency situations.

According to the invention, this task is characterized by the drawing part of claim 1 for the method and of claim 6 included for the device Features resolved.

Advantageous refinements and developments of Invention arise with the in the subordinate Features mentioned claims.

Step during normal operation Vibration accelerations in all three possible spaces directions and can with suitable vibration sensors are recorded and recorded over time. Single or multi-axis measuring sensors are used as sensors Accelerometers in question, which have a nor male, d. H. about not a particularly fine feeling must have. The curves measured in this way have a stochastic character and they occur relatively large distances from tip to tip. Two The measured amplitudes occur regularly Signs of change. This leads to the fact that Device mass, i.e. the work equipment not in trans accelerated lator or rotating movement becomes. But there is a handling error and the working tool jams with the tool if  this in a form-fitting engagement with the work piece is located, or otherwise operate conditionally suddenly as a result of the workpiece intervention high forces in the workpiece becomes the work equipment due to this force attack translational or accelerated rotationally, and this acceleration not only affects the work equipment, it will detected very quickly by the vibration sensor. This can can now be used to the effect that with permanent Determination of the time course of the measured Acceleration values in a given time interval vall size is checked whether the function values of the Summation curve within this zero interval have passages or whether such passages are not available. The absence of such a zero passages can be an indication that through a external influence on the work equipment a danger to the operating personnel who caused that can. In the case where a force from the tool affects the work equipment and the work equipment is accelerated in translation or rotation, namely, the effect occurs that the function values or their mathematically further processed (e.g. Differentiation) equivalent values, in the considered Time interval are shifted in one direction and no more zero crossings occur.

This can be done in an analog or after Digi Talalization of the measured values also digitally in an elec tronic comparators should be monitored, and should no zero crossing after a specified period of time, a change of sign between measured or their processed vibration acceleration values a signal can be sent electronically generated that at least drive the factory  switches off and one with a little more effort the brake acting on the tool is activated and / or an existing one between tool and drive Clutch is disconnected.

However, during normal operation also occur Operating states in which a similar one Influence is exerted on the work equipment and it as a result, a Summation curve is determined that no zero through has gears and in such cases undesirable is also switched off.

Such states are, for example, the movement of the Work equipment outside the workpiece, the on cutting of the workpiece, oscillating work movement and pulling the tool out of the factory piece. To switch off in such a work situation to prevent them, those for such operations typical function value curves in digitized Form within a knowledge base of a store chips that are in the work equipment and also with the currently determined function course of values of vibration acceleration ver like. This comparison gives a match the function value curves compared with each other, although none within the considered interval Zero crossings were determined, the generation a shutdown signal prevented because an operation condition was recognized that does not require a shutdown makes such.

To establish such a situation more reliably len can be parallel to the measured Vibration signal also determined another measured variable  be representative of the drive state of the Is working equipment. The current strength is available for this ke indirectly on the burden on the Tool works, can be closed. The cha characteristic and the individual amounts of the functions a (t) and I (t) or their appropriate mathematical form mung used. As transformations are ne ben also the differentiated function value curves Processing of mean value courses.

So it becomes exactly like the vibration measurement process, i.e. the measured current signal in a predetermined interval also in the Knowledge base stored representative electricity strength curves for states in which a shutdown the machine should not be compared, and that Only the drive switch-off signal is generated testifies when all comparisons give the desired result have reached and a condition has been recognized which creates a danger for the operating personnel can.

For the comparison of the measured current strength over the Represent time with those stored in the knowledge base Differential current waveforms can also be a difference decorative element can be interposed, so that the Ver not with the directly measured current values is carried out, but the measured values first be differentiated and compared with the diffe differentiated and accordingly differentiated set values is carried out.

The method can be done using only one Vibration sensor, which is preferably very firm, i. H. Free play on or in the housing of the work equipment  is carried out. For attachment of the sensor should take into account that the Attack of unwanted forces in dangerous situations drive situations on the tool and by the Vibration sensor can be picked up well. He should therefore either be near the tool or taking into account an appropriate He arranged in the handle area of the work equipment his. After passing through the measured values in an analog Digital converter is determined from the, now in di gitalized form of available measurements of radio curve for a sufficiently small period of time tervall determined. Then all Function values checked by a comparator, whether zero crossings have occurred or not. Should no zero crossings have been determined at least the willingness to generate one Shutdown signal produced, or in a simple Embodiment of the invention the signal directly to Drive directed and the drive switched off and possibly activated a braking device that acts directly on the rotating tool and quickly slows down as much as possible to reduce the risk of injury exclude as possible.

However, should a forced shutdown also in Ar beit situations avoided for Be service personnel do not pose a danger, however alone comparing whether zero crossings have occurred or not, can be determined is an additional comparison required. This is the radio development of the observed interval the parallel or serial to the first comparison in another comparator with those in knowledge based on stored function values, the  are representative of conditions that are not shutdown require comparison. If this comparison shows that there is no correspondence between the function value curves the shutdown signal is final released, and the signal delivery to a Emergency shutdown can take place.

In the event of an even greater security against unwanted shutdown, d. H. one more secure Recognizability of such conditions in which not is to be switched in another comparator with an additional current strength measurement sensor determined current strength curve with electricity also stored in the knowledge base strength curves compared. The shutdown signal will only generated if in this case too matching the measured with one in the knowledge based stored history is determined. Additional It must be checked whether the condition dI / dt <0 is fulfilled is, d. H. that the load that the drive demands will increase. This indicates that a loading drive situation is critical can and the generation of a shutdown signal via is required at all. It is avoided that in the Case in which no increase in load is determined at for example, if the tool is out of the sphere of influence the workpiece is removed, be switched off can.

The comparison can of course also be made after the corresponding measured values of a differentiation have undergone and the function value history of the differentiated values with those in the wis stored values.

FIG. 1 is shown in a stochastic course of gemes Senen vibration acceleration in a completely normal operation condition. In contrast to this, the diagram shown in FIG. 2 shows how the function values a (t) of the measured acceleration are deflected in one direction within a predetermined time interval T by an external influence and the individual function values a (t) only with a common one Signs are signed (sign (a (t)) = const.), So zero crossings between individual function values can no longer be determined.

Figs. 3 to 6 can be found in typical acceleration and current waveforms for the example of a separation grinder, the operating states are available for loading in which an emergency shutdown is not desired, but that would meet the regelungstechni rule requirements for signal delivery.

So you can see in the diagrams, which are shown in Fig. 3, for example, the typical current profile at idle, that is, in the state in which the workpiece is not in engagement with the work. The diagrams shown in FIG. 4 represent the cutting process of the workpiece, FIG. 5 represents oscillating work movements and FIG. 6 the extraction of the tool from the parting line.

These function value curves must therefore be in the Knowledge base, for example of a microcomputer, for comparison with the determined either only Acceleration measurements and / or the current measurement values are made available.  

Fig. 7, on the other hand, reflects the function value curves for tilting the cutting disc of a cutting grinder, which makes an emergency shutdown or braking of the tool necessary. So should such function value curves for vibration acceleration and / or current have been determined, a comparison with the function value curves shown in FIGS . 3 to 6, which were stored in the knowledge base, can only lead to the result that there is no agreement and therefore a shutdown is absolutely necessary.

In the following, a possibility for targeted Ge generation of a switch-off signal in the event of a tilt of the tool on cutters who described the.

With a sampling rate of 4 kHz the vibration acceleration on the cut-off machine in two levels measured. A suitable sensor can be used for this or a separate sensor is used for each level become. The measuring levels must have a sufficient Nei to each other to avoid any possible tilt tion and the resulting force effect to be able to recognize the work equipment quickly and safely nen. The angle of inclination of the two measuring planes to one another other should be at least 30 °.

It is essential that the time interval between the measured acceleration values is constant or after formation of the time function that Function values (acceleration / time) in temporal equal distance (equidistant) for each measuring plane in a counter can be read. The process of on Reading in the counter begins with zero  passage of a determined acceleration value and also ends with the same event.

With each read-in process, the current count value j _{i is assigned} the value of dI _eff (t) / dt measured at the same time as the acceleration, i.e. a value that provides information about the load behavior of the drive.

The resulting pair of values Z _i / d _eff (t) / dt is continuously saved in the form in which it corresponds to the inclusion in a diagram, the number Z on the ordinate and the load behavior dI _eff (t) / dt with the unit A / s is plotted on the abscissa. With continuous storage (entry in the diagram), there is an elementary curve for which the condition

sign (a (t)) = const.

is satisfied.

As a second condition for the start and end of a counting process, the condition dI _eff (t) / dt <0, which is checked with a further comparison, can alternatively or cumulatively be used. It should be noted here that the counting process is ended or started when the measured acceleration has a zero crossing in only one of the two monitored levels.

The knowledge base can also contain the diagram shown in FIG. 8 in a suitable form. In this, an empirically obtained boundary line A is drawn, which separates the practical area, as occurs under conditions in which a shutdown is undesirable, from the area in which shutdown is required. If the count value Z _{i reaches} a value that lies beyond the limit line A in the switch-off range, the trigger signal for the emergency switch-off is generated immediately.

The boundary line A with its inclination reflects that a shutdown of the energy supply in strong Load increase after a short time, i.e. at smaller counts Z, takes place.

At the selected measuring frequency, which may still be can be increased, it is ensured that the time delay between recognizing and actually switching off small enough and the risk compared to conventional security devices significantly reduced is.

Claims (10)

1. A method for the forced switching off of hand-held tools as a result of canting, blocking or destruction of a rotating tool that abrasively removes material from the workpiece and is in positive or frictional engagement in the workpiece, characterized in that the vibration acceleration of the work is measured by means and from the measured individual values, the function a (t) is determined in a predetermined time interval (T) of constant size and then it is compared whether there is no zero crossing of this function a (t) within this time interval (T), all the function values are within of the time interval (T) outside the zero crossing, a switch-off signal is generated and the working equipment is switched off. 2. The method according to claim 1, characterized in net that the shutdown signal is a tool brake facility activated. 3. The method according to claim 1, characterized in net that the shutdown signal is one between factory stuff and drive arranged clutch separates. 4. The method according to claim 1, characterized in net that in a knowledge base functional value cure vein courses a (t), the normal practice-relevant Represent operating states in which one Signal provision should not take place, abge are laid with be in the time interval (T)  also agreed the function value curve and only if they do not match a history stored in the knowledge base the shutdown signal is generated. 5. The method according to claim 1 and 4, characterized records that in addition the measured current strength course compared in the time interval (T) becomes. 6. Device for performing the method according to Claim 1, characterized in that the Ar a vibration sensor is attached, whose measured signals in a summation limb for a predetermined time interval (T) are processable and pairs of values a (t) one downstream comparator can be fed, the in connection with a counter when reached a predetermined number of consecutive a mismatch a shutdown signal generated. 7. The device according to claim 6, characterized records that the vibration sensor for the Mes solution is formed in at least two levels. 8. The device according to claim 6, characterized records that the determined summation values feedable to at least one second comparator are in a comparison with in a knowledge based on stored function value curves and the switch-off signal can only be generated if no match of all function values stands.   9. The device according to claim 6, characterized records that parallel to the vibration sensor Current sensor is present, the measured values feedable to at least one second comparator are in a comparison with in a knowledge based on stored function value curves 1 (t) and the shutdown signal can only be generated is if there is no match of all functional values exist. 10. The device according to claim 9, characterized records that the measured current measured values before comparing to determining the increase the function values to a differentiator are feasible and the comparison with the differen adorned measured values and the corresponding in the Knowledge base stored comparative values follows.