WO2008015460A2 - Force transducer, force sensor and programmable emulator - Google Patents

Force transducer, force sensor and programmable emulator Download PDF

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Publication number
WO2008015460A2
WO2008015460A2 PCT/GB2007/002971 GB2007002971W WO2008015460A2 WO 2008015460 A2 WO2008015460 A2 WO 2008015460A2 GB 2007002971 W GB2007002971 W GB 2007002971W WO 2008015460 A2 WO2008015460 A2 WO 2008015460A2
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WO
WIPO (PCT)
Prior art keywords
force
actuator
output element
programmable device
operative
Prior art date
Application number
PCT/GB2007/002971
Other languages
French (fr)
Other versions
WO2008015460A3 (en
Inventor
William Bigge
Original Assignee
University Of Sussex Intellectual Property Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by University Of Sussex Intellectual Property Ltd filed Critical University Of Sussex Intellectual Property Ltd
Publication of WO2008015460A2 publication Critical patent/WO2008015460A2/en
Publication of WO2008015460A3 publication Critical patent/WO2008015460A3/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L3/00—Measuring torque, work, mechanical power, or mechanical efficiency, in general
    • G01L3/02—Rotary-transmission dynamometers
    • G01L3/04—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft
    • G01L3/10—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating
    • G01L3/107—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating involving potentiometric means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J13/00—Controls for manipulators
    • B25J13/08—Controls for manipulators by means of sensing devices, e.g. viewing or touching devices
    • B25J13/085—Force or torque sensors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00—Programme-controlled manipulators
    • B25J9/16—Programme controls
    • B25J9/1694—Programme controls characterised by use of sensors other than normal servo-feedback from position, speed or acceleration sensors, perception control, multi-sensor controlled systems, sensor fusion
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L3/00—Measuring torque, work, mechanical power, or mechanical efficiency, in general
    • G01L3/02—Rotary-transmission dynamometers
    • G01L3/14—Rotary-transmission dynamometers wherein the torque-transmitting element is other than a torsionally-flexible shaft
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L3/00—Measuring torque, work, mechanical power, or mechanical efficiency, in general
    • G01L3/02—Rotary-transmission dynamometers
    • G01L3/14—Rotary-transmission dynamometers wherein the torque-transmitting element is other than a torsionally-flexible shaft
    • G01L3/1478—Rotary-transmission dynamometers wherein the torque-transmitting element is other than a torsionally-flexible shaft involving hinged levers
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/37—Measurements
    • G05B2219/37357—Force, pressure, weight or deflection

Definitions

  • the present invention relates to a force transducer for transducing an applied force, either as a rotary or linear force, as applied by an actuator, a force sensor which incorporates such a force transducer for sensing the degree of the applied force, and a programmable emulator which utilizes such a force sensor.
  • Force transducers and force sensors are known in the art, and it is an aim of the present invention to provide an alternative or improved force transducer and force sensor, and also provide a programmable emulator which utilizes such a force sensor.
  • the present invention provides a force transducer, comprising: first and second members which are coupled such as to be movable in one axis relative to one another; and an elastic element which is disposed between the first and second members, such that a force as applied to one of the first and second members causes deformation of the elastic element and is transferred to the other of the first and second members, with the relative deflection of the first and second members corresponding to the applied force.
  • first and second members are rotationally coupled about a rotational axis.
  • first and second members are linearly coupled such as to be movable in a linear axis.
  • the transducer comprises: a pair of elastic elements which are disposed between the first and second members, such that a respective one of the elastic elements of the pair of elastic elements is deformed in dependence upon the sense of relative movement of the first and second members.
  • the transducer comprises: a plurality of pairs of elastic elements which are disposed between the first and second members, such that respective ones of the elastic elements of each of the pairs of elastic elements are deformed in dependence upon the sense of relative movement of the first and second members.
  • one of the first and second members receives the at least one pair of elastic elements and the other of the first and second members includes at least one force transfer element which is disposed between the elastic elements of the at least one pair of elastic elements, such that the at least one force transfer element engages a respective one of the elastic elements of the at least one pair of elastic elements in dependence upon the sense of movement of the first and second members.
  • the force transfer element includes a roller which is supported in offset relation to and rotatable about an axis parallel to the movement axis.
  • the one of the first and second members includes a cavity in which the at least one pair of elastic elements is disposed.
  • the cavity defines at least one pair of engagement surfaces, which engagement surfaces are located to the opposite sides of the respective ones of the elastic elements of the at least one pair of elastic elements and are configured such that a respective one of the elastic elements is brought into engagement with a respective one of the engagement surfaces in dependence upon the relative sense of movement of the first and second members.
  • the engagement surfaces are outwardly flaring relative to the movement axis of the first and second members.
  • the engagement surfaces are arcuate surfaces.
  • the engagement surfaces are configured such that, on application of an increasing force, the respective elastic element is progressively brought into engagement with the respective engagement surface, with the distal point of engagement of the respective elastic element moving along a length of the respective engagement surface, thereby shortening the effective length of the respective elastic element and providing a non-linear response to the applied force.
  • the engagement surfaces of the at least one pair of engagement surfaces are disposed in opposed, symmetrical relation relative to the movement axis.
  • the elastic elements comprise a material which has a non-linear response to the applied force.
  • the material is a rubber material.
  • the elastic elements comprise spring elements.
  • the elastic elements comprise leaf spring elements.
  • the elastic elements are provided by respective arms of a single, unitary leaf spring.
  • the present invention provides a force sensor, comprising: the above-described transducer; and a sensor element for measuring the relative deflection of the first and second members, which deflection corresponds to the applied force.
  • the sensor element comprises a potentiometer.
  • one of the first and second members includes a gear or pulley wheel, whereby the sensor is coupled to an actuator.
  • one of the first and second members includes a spur gear, whereby the sensor is operative in a gear assembly.
  • the present invention also extends to a programmable device, in particular a programmable spring device, which incorporates the above-described sensor.
  • the present invention provides a programmable device, in particular a programmable spring device, comprising: an actuator for driving an output element; the above-described force sensor, through which the output element is driven, which is operative to measure a force as applied to the output element; and a controller for controlling the actuator in response to the force as measured by the force sensor, such that a predeterminable force is maintained on the output element.
  • the programmable device further comprises: a position sensor which is operative to measure a position of the output element; and wherein the controller is operative to control the actuator in response to the force and position as measured by the force and position sensors, such that, for predeterminable positions, a predeterminable force is maintained on the output element.
  • controller is operative to control the actuator in accordance with at least one force profile which maps a force value in relation to the position of the output element.
  • the at least one force profile maps a non-linear spring. In one embodiment the at least one force profile maps a combination of springs.
  • the controller is operative to control the actuator in accordance with first and second force profiles, such that one of the force profiles is followed when the output element is moved in a first sense and the other of the force profiles is followed when the output element is moved in the other sense, whereby the first and second force profiles provide for hysteresis.
  • controller is operative to control the actuator in accordance with at least one damping profile which maps a speed value in relation to the position of the output element.
  • the actuator is an electric motor, the power of which is controlled by the controller.
  • the actuator includes a reduction gear assembly.
  • the controller includes a user interface, which is operative to receive input manually from a user or from a computer via a communications network.
  • the present invention further extends to an actuator device which incorporates the above-described sensor.
  • the actuator device is a series elastic actuator.
  • the present invention still further extends to a haptic device which incorporates the above-described sensor.
  • the present invention yet further extends to a robotic device which incorporates the above-described sensor.
  • the robotic device is an autonomous robot.
  • the present invention provides a programmable device, in particular a programmable spring device, comprising: an actuator for driving an output element; a force sensor, through which the output element is driven, which is operative to measure a force as applied to the output element; and a controller for controlling the actuator in response to the force as measured by the force sensor, such that a predeterminable force is maintained on the output element.
  • the programmable device further comprises: a position sensor which is operative to measure a position of the output element; and wherein the controller is operative to control the actuator in response to the force and position as measured by the force and position sensors, such that, for predeterminable positions, a predeterminable force is maintained on the output element.
  • controller is operative to control the actuator in accordance with at least one force profile which maps a force value in relation to the position of the output element.
  • the at least one force profile maps a non-linear spring.
  • the at least one force profile maps a combination of springs.
  • the controller is operative to control the actuator in accordance with first and second force profiles, such that one of the force profiles is followed when the output element is moved in a first sense and the other of the force profiles is followed when the output element is moved in the other sense, whereby the first and second force profiles provide for hysteresis.
  • controller is operative to control the actuator in accordance with at least one damping profile which maps a speed value in relation to the position of the output element.
  • the actuator is an electric motor, the power of which is controlled by the controller.
  • the actuator includes a reduction gear assembly.
  • the controller includes a user interface, which is operative to receive input manually from a user or from a computer via a communications network.
  • the present invention provides a programmable device, in particular a programmable spring device, comprising: an actuator for driving an output element; a position sensor which is operative to measure a position of the output element; and a controller which is operative to control the actuator in response to the position as measured by the position sensor, such that the output element is maintained at a predetermined position.
  • the programmable device further comprises: a force sensor, through which the output element is driven, which is operative to measure a force as applied to the output element; and wherein the controller is operative to control the actuator in response to the force and position as measured by the force and position sensors, such that, for predeterminable positions, a predeterminable force is maintained on the output element.
  • the controller is operative to control the actuator in accordance with at least one force profile which maps a force value in relation to the position of the output element.
  • the at least one force profile maps a non-linear spring.
  • the at least one force profile maps a combination of springs.
  • the controller is operative to control the actuator in accordance with first and second force profiles, such that one of the force profiles is followed when the output element is moved in a first sense and the other of the force profiles is followed when the output element is moved in the other sense, whereby the first and second force profiles provide for hysteresis.
  • controller is operative to control the actuator in accordance with at least one damping profile which maps a speed value in relation to the position of the output element.
  • the actuator is an electric motor, the power of which is controlled by the controller.
  • the actuator includes a reduction gear assembly.
  • the controller includes a user interface, which is operative to receive input manually from a user or from a computer via a communications network.
  • Figure 1 illustrates a perspective view of a force sensor in accordance with one embodiment of the present invention, where illustrated from above;
  • Figure 2 illustrates a perspective view of the force sensor of Figure 1, where illustrated from below;
  • Figure 3 illustrates a perspective view of the force sensor of Figure 1, with the cover plate removed;
  • Figure 4 illustrates an exploded perspective view of the force sensor of Figure 1, with the cover plate removed;
  • Figure 5 represents the output of the force sensor of Figure 1 as a function of applied force
  • Figure 6 illustrates a force sensor as one modification of the force sensor of Figure 1, where mounted to a shaft;
  • Figure 7 illustrates an exploded perspective view of the force sensor of Figure 6
  • Figure 8 illustrates a perspective view of a force transducer in accordance with an alternative embodiment of the present invention for application in the force sensor of Figure 1;
  • Figure 9 illustrates an exploded perspective view of the force transducer of Figure 8.
  • Figure 10 illustrates a programmable spring emulator in accordance with one embodiment of the present invention
  • Figure 11 models a linear system, where a load is mounted on a rail and free to slide in either direction;
  • Figure 12 models the linear system of Figure 11, but where further including springs at the respective ends of the rail;
  • Figure 13 graphically represents a force profile for the linear system of Figure 12;
  • Figure 14 illustrates the force profiles of one example system which employs hysteresis
  • Figure 15 represents an exemplary force profile for two springs which are configured to maintain the output element of the emulator of Figure 10 in a predetermined position
  • Figure 16 represents a change in the profile bias of the force profile of Figure 15, which is such as to cause movement of the output element;
  • Figure 17 represents a change in the scaling factor of the force profile of Figure 15, which is such as to change the compliancy of the emulated springs;
  • Figure 18 illustrates an exemplary force profile of a highly-complex spring system for emulation by the emulator of Figure 10;
  • Figure 19 illustrates a programmable spring emulator as one modification of the emulator of Figure 10.
  • Figures 1 to 4 illustrate a force sensor 3 in accordance with a first embodiment of the present invention.
  • the force sensor 3 comprises a force transducer 4, which comprises first and second members 5, 7 which are coupled such as to be movable in one axis relative to one another in response to application of a force to one of the first and second members 5, 7, and at least one pair, in this embodiment first and second pairs of deformable elastic elements 9 which are disposed between the first and second members ' 5, 7 such that a force as applied to one of the first and second members 5, 7 causes deformation of a respective one of the elastic elements 9 of the at least one pair of elastic elements 9, and is transferred to the other of the first and second members 5, 7.
  • a force transducer 4 which comprises first and second members 5, 7 which are coupled such as to be movable in one axis relative to one another in response to application of a force to one of the first and second members 5, 7, and at least one pair, in this embodiment first and second pairs of deformable elastic elements 9 which are disposed between the first and second members ' 5, 7 such that a force as applied to one of the first and second members 5, 7 causes deformation of
  • the force sensor 3 further comprises a sensor element 11 for measuring the relative deflection of the first and second members 5, 7.
  • first and second members 5, 7 are rotatably coupled about a rotational axis, such as to measure a rotary torque, but in another embodiment could be linearly coupled, such as to be movable in a linear axis and measure a linear torque.
  • the first member 5 comprises a body element 15, which includes a cavity 17 which houses the elastic elements 9 and in which the second member 7 is movably disposed, in this embodiment rotatably disposed, and a closure element 18, in this embodiment a cover plate, for enclosing the cavity 17 of the body element 15.
  • the cavity 17 comprises first and second cavity sections 19, 21, in this embodiment disposed in opposed relation about the rotational axis of the second member 7, which each contain a pair of the elastic elements 9, which are disposed in opposed relation and between which extend respective force transfer elements 25 of the second member 7, such that rotation of the second member 7 relative to the first member 5 causes the force transfer elements 25 to compress one of the elastic elements 9 of each of the pairs of the elastic elements 9 in dependence upon the relative sense of rotation of the first and second members 5, 7.
  • the second member 7 comprises a coupling element 23, in this embodiment a shaft, to which an actuator is in use coupled, and at least one, in this embodiment first and second force transfer elements 25, in this embodiment arms, which extend radially from the coupling element 23 and between the elastic elements 9 of each of the pairs of the elastic elements 9.
  • first and second force transfer elements 25 are oppositely directed.
  • the elastic elements 9 are cylindrical in shape, but could have other shapes.
  • the elastic elements 9 are formed of a rubber material.
  • the elastic elements 9 provide a non-linear response to an applied force, such that the force sensor 3 has a high sensitivity to low forces, when under least compression, and a reduced sensitivity at higher forces, thereby providing a sensor with a wide dynamic range, and typically an approximately sigmoidal response, as represented in Figure 5.
  • the sensor element 11 comprises a potentiometer which provides for measurement of the relative deflection of the first and second members 5, 7, and hence compression of the respective ones of the elastic elements 9, from which the applied force can be calculated.
  • the sensor element 11 could comprise an alternative displacement sensor.
  • Figures 6 and 7 illustrate a force sensor 3 as one modification of the force sensor 3 of the above-described embodiment, where implemented as a torque sensing elastic spur gear for fitting to a rotating shaft as part of a gear reduction system.
  • the first member 5 includes a spur gear 31 which forms part of a gear reduction system
  • the force sensor 3 further includes a bearing 33, in this embodiment a radial bearing, for supporting the coupling element 23 of the second member 7.
  • Figures 8 and 9 illustrate a force transducer 4 in accordance with an alternative embodiment of the present invention for use in the force sensor 3 of the first-described embodiment.
  • the force transducer similarly to that of the above-described first embodiment, comprises first and second members 55, 57 which are coupled such as to be movable in one axis relative to one another in response to application of a force to one of the first and second members 55, 57.
  • the force transducer 4 comprises a pair of deformable elastic elements 59 which are disposed between the first and second members 55, 57 such that a force as applied to one of the first and second members 55, 57 causes deformation of a respective one of the elastic elements 59, and is transferred to the other of the first and second members 55, 57.
  • the elastic elements 59 are spring elements, here leaf spring elements, which are formed of a sheet metal, typically steel.
  • the elastic elements 59 are provided by the respective arms of a single, unitary leaf spring 61, as will be described in more detail hereinbelow.
  • first and second members 55, 57 are rotatably coupled about a rotational axis, such as to measure a rotary torque, but in another embodiment could be linearly coupled, such as to be movable in a linear axis and measure a linear torque.
  • the first member 55 comprises a body element 65 to which an actuator, such as an electric motor and gearbox, is coupled, such as by a gear or pulley wheel which is attached or integrally formed with the body element 55.
  • the body element 65 includes a cavity 67 which houses the elastic elements 59 and in which the second member 57 is movably disposed, in this embodiment rotatably disposed, and a closure element (not illustrated), typically a cover plate, for enclosing the cavity 67 of the body element 65.
  • the cavity 67 defines first and second cavity sections 69, 71 in opposed sides of the second member 57, in this embodiment disposed in opposed relation about the rotational axis of the second member 57.
  • the body element 55 includes a support 73, which is located within the first cavity section 69 of the cavity 67 and to which the elastic elements 59 are fixed at one end thereof, such as to extend beyond the respective lateral sides of the second member 57 and into the second cavity section 71 of the cavity 67.
  • the support 73 here a cylindrical post, is disposed within the cavity 67 such as to define a recess 75, here a substantially U- shaped recess, which captively receives the leaf spring member 61, such that the elastic elements 59, as defined by the arms of the leaf spring member 61, extend beyond the respective lateral sides of the second member 57 and into the second lateral section 71 of the cavity 67.
  • the cavity 67 defines a pair of arcuate, outwardly-flaring engagement surfaces 77, each of symmetrical shape in mirror relation about the rotational axis of the second member 57, which are located to the opposite sides of the elastic elements 59 and are configured such that a respective one of the elastic elements 59 is brought into engagement with a respective one of the engagement surfaces 77 in dependence upon the relative sense of movement of the first and second members 55, 57, and such that, on application of an increasing force, the distal point of engagement of the respective elastic element 59 moves outwardly along a length of the respective engagement surface 77, thereby shortening the effective length of the respective elastic element 59.
  • This reduction in the effective length of the respective elastic element 59 provides for a non-linear response to the applied force, with the degree of displacement per unit force being greatest when the elastic element 59 is under minimum displacement and the force transducer 4 is at its centre or equilibrium position and the degree of displacement per unit force being lowest when the elastic element 59 is under maximum displacement.
  • This configuration provides a response to an applied force that is approximately sigmoidal, with maximum sensitivity when subjected to low forces and minimum sensitivity when subjected to high forces.
  • the second member 57 comprises a coupling element 83, in this embodiment a shaft, and a force transfer element 85, which is radially offset from the axis of the coupling element 83 and disposed between the elastic elements 59, such that, on movement of the second member 57, in this embodiment rotation of the second member 57, the force transfer element 85 acts to deflect a respective one of the elastic elements 59, such as to bring the elastic element 59 into progressive engagement with the respective engagement surface 77 as defined by the body element 65.
  • the force transfer element 85 includes a roller 89 which is supported in offset relation to the coupling element 83 and rotatable about an axis parallel to the coupling element 83.
  • the above-described force sensor 3 has many applications, which include the following:
  • the force sensor 3 can function as a programmable spring when coupling an actuator, such as an electric motor, to a mechanical load or end effector with a position sensor, allowing the actuator to respond to forces applied to the mechanism by maintaining a predetermined position using predetermined force.
  • an actuator such as an electric motor
  • the effector When a force is applied to an end effector, the effector will be deflected from the predetermined position, typically by a predetermined angle, generating an opposing force which is specified by the force command, and, when the applied force is removed, the effector will return to the predetermined position as if biased by a spring.
  • control parameters include the set point or angle to which the effector will return under the influence of the electronic springs, the spring constants that act on the effector in each direction, and the linearity and damping of the springs,
  • the force sensor 3 can be utilized to construct a series elastic actuator [1], where the force sensor 3 couples an actuator to a load and a closed loop feedback system is employed to drive the actuator to deliver a predetermined force.
  • This device in being simple to manufacture, is a particularly cost-effective means of implementing such an actuator.
  • the force sensor 3 can be utilized to provide for mirroring of the operation of actuators, where the sensor outputs from one device are fed to the sensor inputs of another device and the sensor inputs of the one device are fed to the sensor outputs of the other device.
  • One example of such an implementation is in a radio-controlled model, for example, a toy car, where the control joystick contains one set of actuators and the steering mechanism of the model is controlled by another actuator. Movement of the control joystick will cause the steering actuator to move and the resistance encountered by the steering actuator is fed to the actuators of the control joystick, thereby enabling the user to feel the forces experience by the model.
  • the force sensor 3 can be used to control the movements of joints in a robot, with the force-sensing facility allowing the limbs of the robot to behave in a range of ways, from completely compliant joints, to sprung joints and rigid joints. By specifying compliant behaviour, the robot is able to respond to external, environmental forces, thereby exploiting natural dynamics to produce more robust behaviour.
  • Figure 10 illustrates a programmable spring emulator in accordance with a first embodiment of the present invention.
  • the programmable spring emulator comprises an actuator 101 for driving an output element 103, in this embodiment a rotatable shaft, a force sensor 105, such as the force sensor of the above-described embodiments, through which the output element 103 is driven, which is operative to measure a force as applied to the output element 103, a position sensor 107 for measuring the position, in this embodiment the angle, of the output element 103, and a controller 109 for controlling the actuator 101 in response to one or both of the force and position of the output element 103 as measured by feedback from the force and position sensors 105, 107.
  • the actuator 101 is an electric motor, the power of which is controlled by the controller 109 in response to one or both of the force and position of the output element 103 as measured by feedback from the force and position sensors 105, 107.
  • the actuator 101 includes a reduction gear assembly 111, but in other embodiments the reduction gear assembly 111 could be omitted.
  • the output element 103 can be driven to any desired position and effect any desired force, within the mechanical limits of the overall system.
  • One particular application is in driving a robotic limb.
  • the controller 109 comprises an embedded computer system, a microcontroller, which acts to receive signals from the force and position sensors 105, 107 and deliver a control signal to the actuator 101, in this embodiment via a power amplifier.
  • the controller 109 can receive control inputs, via a user interface 115, either by manual input or from a computer via a communications network.
  • the controller 109 allows for operation of the emulator in one of a number of modes, which provides for (i) force sensing, where only the input from the force sensor 105 is utilized to maintain the output element 103 at a predetermined force, (ii) position sensing, where only the input from the position sensor 107 is utilized to maintain the output element 103 at a predetermined position, and (iii) combined force and positioning sensing, where the inputs from the force and position sensors 105, 107 are utilized to maintain the output element 103 at a predetermined force and position.
  • the emulator utilizes a feedback loop between the force sensor 105 and the actuator 101, such that a predetermined force is maintained on the output element 103. A zero force can be specified, and, in this condition, the output element 103 would be completely free to move under any external perturbations.
  • Figure 11 represents a linear system, where a load 121 is mounted on a rail 123 and free to slide in either direction. This representation is equivalent to a device operating in a force-control mode with a zero force setting.
  • Figure 12 again represents a linear system, but where springs 125, 127, as resilient, biasing elements, are mounted at the respective ends of the rail 123, such that the load 121 is free to move in the central section of the rail 123, but a force is applied to the load 121 to return the load 121 to the central section of the rail 123 when the load 121 encounters one of the springs 125, 127.
  • the behaviour of the emulator is achieved by defining a force profile, here as a numerical data set, which maps a force value for each position as measured by the position sensor 107.
  • the emulator repeatedly measures the position of the output element 103 and applies the appropriate force to the output element 103 as defined by the force profile.
  • Figure 13 graphically represents such a force profile for the linear system of Figure 12, where a positive force will drive the system to increase the position of the load 121 and a negative force will drive the system to decrease the position of the load 121.
  • the emulator is not limited by mechanics and it is possible to define non-linear springs or combinations of non-linear springs, all of which can be dynamically altered during operation.
  • the emulator need not be restricted to a single profile, but different profiles can be used at different points.
  • the emulator allows for switching between profiles at particular positions, thereby enabling the emulator to exhibit mechanical hysteresis or latching between two states.
  • Figure 14 illustrates the force profiles of one exemplary system which employs hysteresis.
  • the system utilizes two profiles (Profile 1, Profile 2), each of which models a single linear spring which is designed to drive the actuator to opposite ends of its range of movement.
  • the dashed sections in each of the profiles represent the positions (Tl, T2) when the emulator will switch between the profiles, as represented by the arrows.
  • the profiles can utilize a profile bias by means of which a force profile can be shifted up or down by a predetermined amount in order to cause movement of the output element 103.
  • Figure 15 represents a force profile where two springs hold the output element 103 in a predetermined position
  • Figure 16 represents a change in the profile bias to cause movement of the output element 103.
  • the profiles can utilize a scaling value by means of which the spring constants can be increased or decreased, in order to make the system more compliant.
  • Figure 17 represents a change in the scaling factor as compared to the profile of Figure 15.
  • the present invention also allows for emulation of damping behaviour by controlling the speed of movement of the output element 103, where the speed of movement of the output element 103 is determined from the rate of change in position, as measured by the position sensor 107.
  • damping behaviour is emulated by the use of damping profiles, which operate in an analogous manner to the above- described force profiles.
  • each force profile can be linked to a pair of damping profiles, one for each direction of movement.
  • the damping profiles allow for different control of the speed of movement of the output element 103 when moving in different directions. In this way, the system can behave as if constrained by a set of springs which exhibit different damping dependent upon the direction of movement of the output element 103.
  • the actuator 101 is disposed orthogonally to the output element 103, such that the output element 103 is dual ended, which finds particular application in robotic systems, such as in joints, and in particular leg joints.
  • the actuator 101 is coupled to the output element 103 by a bevel gear assembly 131, and the position sensor 107 is supported by a circuit board 133 of the controller 109.

Abstract

A force transducer, a force sensor and a programmable emulator, the force transducer comprising : first and second members which are coupled such as to be movable in one axis relative to one another; and a deformable elastic element which is disposed between the first and second members, such that a force as applied to one of the first and second members causes deformation of the elastic element and is transferred to the other of the first and second members, with the relative deflection of the first and second members corresponding to the applied force.

Description

FORCE TRANSDUCER, FORCE SENSOR AND PROGRAMMABLE EMULATOR
The present invention relates to a force transducer for transducing an applied force, either as a rotary or linear force, as applied by an actuator, a force sensor which incorporates such a force transducer for sensing the degree of the applied force, and a programmable emulator which utilizes such a force sensor.
Force transducers and force sensors are known in the art, and it is an aim of the present invention to provide an alternative or improved force transducer and force sensor, and also provide a programmable emulator which utilizes such a force sensor.
In one aspect the present invention provides a force transducer, comprising: first and second members which are coupled such as to be movable in one axis relative to one another; and an elastic element which is disposed between the first and second members, such that a force as applied to one of the first and second members causes deformation of the elastic element and is transferred to the other of the first and second members, with the relative deflection of the first and second members corresponding to the applied force.
In one embodiment the first and second members are rotationally coupled about a rotational axis.
In another embodiment the first and second members are linearly coupled such as to be movable in a linear axis.
In one embodiment the transducer comprises: a pair of elastic elements which are disposed between the first and second members, such that a respective one of the elastic elements of the pair of elastic elements is deformed in dependence upon the sense of relative movement of the first and second members.
In another embodiment the transducer comprises: a plurality of pairs of elastic elements which are disposed between the first and second members, such that respective ones of the elastic elements of each of the pairs of elastic elements are deformed in dependence upon the sense of relative movement of the first and second members.
In one embodiment one of the first and second members receives the at least one pair of elastic elements and the other of the first and second members includes at least one force transfer element which is disposed between the elastic elements of the at least one pair of elastic elements, such that the at least one force transfer element engages a respective one of the elastic elements of the at least one pair of elastic elements in dependence upon the sense of movement of the first and second members.
In one embodiment the force transfer element includes a roller which is supported in offset relation to and rotatable about an axis parallel to the movement axis.
In one embodiment the one of the first and second members includes a cavity in which the at least one pair of elastic elements is disposed.
In one embodiment the cavity defines at least one pair of engagement surfaces, which engagement surfaces are located to the opposite sides of the respective ones of the elastic elements of the at least one pair of elastic elements and are configured such that a respective one of the elastic elements is brought into engagement with a respective one of the engagement surfaces in dependence upon the relative sense of movement of the first and second members. In one embodiment the engagement surfaces are outwardly flaring relative to the movement axis of the first and second members.
In one embodiment the engagement surfaces are arcuate surfaces.
In one embodiment the engagement surfaces are configured such that, on application of an increasing force, the respective elastic element is progressively brought into engagement with the respective engagement surface, with the distal point of engagement of the respective elastic element moving along a length of the respective engagement surface, thereby shortening the effective length of the respective elastic element and providing a non-linear response to the applied force.
In one embodiment the engagement surfaces of the at least one pair of engagement surfaces are disposed in opposed, symmetrical relation relative to the movement axis.
In one embodiment the elastic elements comprise a material which has a non-linear response to the applied force.
In one embodiment the material is a rubber material.
In another embodiment the elastic elements comprise spring elements.
In one embodiment the elastic elements comprise leaf spring elements.
In one embodiment the elastic elements are provided by respective arms of a single, unitary leaf spring.
In another aspect the present invention provides a force sensor, comprising: the above-described transducer; and a sensor element for measuring the relative deflection of the first and second members, which deflection corresponds to the applied force. In one embodiment the sensor element comprises a potentiometer.
In one embodiment one of the first and second members includes a gear or pulley wheel, whereby the sensor is coupled to an actuator.
In one embodiment one of the first and second members includes a spur gear, whereby the sensor is operative in a gear assembly.
The present invention also extends to a programmable device, in particular a programmable spring device, which incorporates the above-described sensor.
In a further aspect the present invention provides a programmable device, in particular a programmable spring device, comprising: an actuator for driving an output element; the above-described force sensor, through which the output element is driven, which is operative to measure a force as applied to the output element; and a controller for controlling the actuator in response to the force as measured by the force sensor, such that a predeterminable force is maintained on the output element.
In one embodiment the programmable device further comprises: a position sensor which is operative to measure a position of the output element; and wherein the controller is operative to control the actuator in response to the force and position as measured by the force and position sensors, such that, for predeterminable positions, a predeterminable force is maintained on the output element.
In one embodiment the controller is operative to control the actuator in accordance with at least one force profile which maps a force value in relation to the position of the output element.
In one embodiment the at least one force profile maps a non-linear spring. In one embodiment the at least one force profile maps a combination of springs.
In one embodiment the controller is operative to control the actuator in accordance with first and second force profiles, such that one of the force profiles is followed when the output element is moved in a first sense and the other of the force profiles is followed when the output element is moved in the other sense, whereby the first and second force profiles provide for hysteresis.
In one embodiment the controller is operative to control the actuator in accordance with at least one damping profile which maps a speed value in relation to the position of the output element.
In one embodiment the actuator is an electric motor, the power of which is controlled by the controller.
In one embodiment the actuator includes a reduction gear assembly.
In one embodiment the controller includes a user interface, which is operative to receive input manually from a user or from a computer via a communications network.
The present invention further extends to an actuator device which incorporates the above-described sensor.
In one embodiment the actuator device is a series elastic actuator.
The present invention still further extends to a haptic device which incorporates the above-described sensor. The present invention yet further extends to a robotic device which incorporates the above-described sensor.
In one embodiment the robotic device is an autonomous robot.
In a still further aspect the present invention provides a programmable device, in particular a programmable spring device, comprising: an actuator for driving an output element; a force sensor, through which the output element is driven, which is operative to measure a force as applied to the output element; and a controller for controlling the actuator in response to the force as measured by the force sensor, such that a predeterminable force is maintained on the output element.
In one embodiment the programmable device further comprises: a position sensor which is operative to measure a position of the output element; and wherein the controller is operative to control the actuator in response to the force and position as measured by the force and position sensors, such that, for predeterminable positions, a predeterminable force is maintained on the output element.
In one embodiment the controller is operative to control the actuator in accordance with at least one force profile which maps a force value in relation to the position of the output element.
In one embodiment the at least one force profile maps a non-linear spring.
In one embodiment the at least one force profile maps a combination of springs.
In one embodiment the controller is operative to control the actuator in accordance with first and second force profiles, such that one of the force profiles is followed when the output element is moved in a first sense and the other of the force profiles is followed when the output element is moved in the other sense, whereby the first and second force profiles provide for hysteresis.
In one embodiment the controller is operative to control the actuator in accordance with at least one damping profile which maps a speed value in relation to the position of the output element.
In one embodiment the actuator is an electric motor, the power of which is controlled by the controller.
In one embodiment the actuator includes a reduction gear assembly.
In one embodiment the controller includes a user interface, which is operative to receive input manually from a user or from a computer via a communications network.
In a yet further aspect the present invention provides a programmable device, in particular a programmable spring device, comprising: an actuator for driving an output element; a position sensor which is operative to measure a position of the output element; and a controller which is operative to control the actuator in response to the position as measured by the position sensor, such that the output element is maintained at a predetermined position.
In one embodiment the programmable device further comprises: a force sensor, through which the output element is driven, which is operative to measure a force as applied to the output element; and wherein the controller is operative to control the actuator in response to the force and position as measured by the force and position sensors, such that, for predeterminable positions, a predeterminable force is maintained on the output element. In one embodiment the controller is operative to control the actuator in accordance with at least one force profile which maps a force value in relation to the position of the output element.
In one embodiment the at least one force profile maps a non-linear spring.
In one embodiment the at least one force profile maps a combination of springs.
In one embodiment the controller is operative to control the actuator in accordance with first and second force profiles, such that one of the force profiles is followed when the output element is moved in a first sense and the other of the force profiles is followed when the output element is moved in the other sense, whereby the first and second force profiles provide for hysteresis.
In one embodiment the controller is operative to control the actuator in accordance with at least one damping profile which maps a speed value in relation to the position of the output element.
In one embodiment the actuator is an electric motor, the power of which is controlled by the controller.
In one embodiment the actuator includes a reduction gear assembly.
In one embodiment the controller includes a user interface, which is operative to receive input manually from a user or from a computer via a communications network.
Preferred embodiments of the present invention will now be described hereinbelow by way of example only with reference to the accompanying drawings, in which: Figure 1 illustrates a perspective view of a force sensor in accordance with one embodiment of the present invention, where illustrated from above;
Figure 2 illustrates a perspective view of the force sensor of Figure 1, where illustrated from below;
Figure 3 illustrates a perspective view of the force sensor of Figure 1, with the cover plate removed;
Figure 4 illustrates an exploded perspective view of the force sensor of Figure 1, with the cover plate removed;
Figure 5 represents the output of the force sensor of Figure 1 as a function of applied force;
Figure 6 illustrates a force sensor as one modification of the force sensor of Figure 1, where mounted to a shaft;
Figure 7 illustrates an exploded perspective view of the force sensor of Figure 6;
Figure 8 illustrates a perspective view of a force transducer in accordance with an alternative embodiment of the present invention for application in the force sensor of Figure 1;
Figure 9 illustrates an exploded perspective view of the force transducer of Figure 8;
Figure 10 illustrates a programmable spring emulator in accordance with one embodiment of the present invention;
Figure 11 models a linear system, where a load is mounted on a rail and free to slide in either direction; Figure 12 models the linear system of Figure 11, but where further including springs at the respective ends of the rail;
Figure 13 graphically represents a force profile for the linear system of Figure 12;
Figure 14 illustrates the force profiles of one example system which employs hysteresis;
Figure 15 represents an exemplary force profile for two springs which are configured to maintain the output element of the emulator of Figure 10 in a predetermined position;
Figure 16 represents a change in the profile bias of the force profile of Figure 15, which is such as to cause movement of the output element;
Figure 17 represents a change in the scaling factor of the force profile of Figure 15, which is such as to change the compliancy of the emulated springs;
Figure 18 illustrates an exemplary force profile of a highly-complex spring system for emulation by the emulator of Figure 10; and
Figure 19 illustrates a programmable spring emulator as one modification of the emulator of Figure 10.
Figures 1 to 4 illustrate a force sensor 3 in accordance with a first embodiment of the present invention.
The force sensor 3 comprises a force transducer 4, which comprises first and second members 5, 7 which are coupled such as to be movable in one axis relative to one another in response to application of a force to one of the first and second members 5, 7, and at least one pair, in this embodiment first and second pairs of deformable elastic elements 9 which are disposed between the first and second members' 5, 7 such that a force as applied to one of the first and second members 5, 7 causes deformation of a respective one of the elastic elements 9 of the at least one pair of elastic elements 9, and is transferred to the other of the first and second members 5, 7.
The force sensor 3 further comprises a sensor element 11 for measuring the relative deflection of the first and second members 5, 7.
In this embodiment the first and second members 5, 7 are rotatably coupled about a rotational axis, such as to measure a rotary torque, but in another embodiment could be linearly coupled, such as to be movable in a linear axis and measure a linear torque.
The first member 5 comprises a body element 15, which includes a cavity 17 which houses the elastic elements 9 and in which the second member 7 is movably disposed, in this embodiment rotatably disposed, and a closure element 18, in this embodiment a cover plate, for enclosing the cavity 17 of the body element 15.
The cavity 17 comprises first and second cavity sections 19, 21, in this embodiment disposed in opposed relation about the rotational axis of the second member 7, which each contain a pair of the elastic elements 9, which are disposed in opposed relation and between which extend respective force transfer elements 25 of the second member 7, such that rotation of the second member 7 relative to the first member 5 causes the force transfer elements 25 to compress one of the elastic elements 9 of each of the pairs of the elastic elements 9 in dependence upon the relative sense of rotation of the first and second members 5, 7.
The second member 7 comprises a coupling element 23, in this embodiment a shaft, to which an actuator is in use coupled, and at least one, in this embodiment first and second force transfer elements 25, in this embodiment arms, which extend radially from the coupling element 23 and between the elastic elements 9 of each of the pairs of the elastic elements 9. In this embodiment the first and second force transfer elements 25 are oppositely directed.
In this embodiment the elastic elements 9 are cylindrical in shape, but could have other shapes.
In this embodiment the elastic elements 9 are formed of a rubber material.
In this embodiment the elastic elements 9 provide a non-linear response to an applied force, such that the force sensor 3 has a high sensitivity to low forces, when under least compression, and a reduced sensitivity at higher forces, thereby providing a sensor with a wide dynamic range, and typically an approximately sigmoidal response, as represented in Figure 5.
In this embodiment the sensor element 11 comprises a potentiometer which provides for measurement of the relative deflection of the first and second members 5, 7, and hence compression of the respective ones of the elastic elements 9, from which the applied force can be calculated. In another embodiment the sensor element 11 could comprise an alternative displacement sensor.
Figures 6 and 7 illustrate a force sensor 3 as one modification of the force sensor 3 of the above-described embodiment, where implemented as a torque sensing elastic spur gear for fitting to a rotating shaft as part of a gear reduction system.
In this embodiment the first member 5 includes a spur gear 31 which forms part of a gear reduction system, and the force sensor 3 further includes a bearing 33, in this embodiment a radial bearing, for supporting the coupling element 23 of the second member 7. Figures 8 and 9 illustrate a force transducer 4 in accordance with an alternative embodiment of the present invention for use in the force sensor 3 of the first-described embodiment.
The force transducer 4, similarly to that of the above-described first embodiment, comprises first and second members 55, 57 which are coupled such as to be movable in one axis relative to one another in response to application of a force to one of the first and second members 55, 57.
In this embodiment, again similarly to that of the above-described first embodiment, the force transducer 4 comprises a pair of deformable elastic elements 59 which are disposed between the first and second members 55, 57 such that a force as applied to one of the first and second members 55, 57 causes deformation of a respective one of the elastic elements 59, and is transferred to the other of the first and second members 55, 57.
In this embodiment the elastic elements 59 are spring elements, here leaf spring elements, which are formed of a sheet metal, typically steel.
In this embodiment the elastic elements 59 are provided by the respective arms of a single, unitary leaf spring 61, as will be described in more detail hereinbelow.
In this embodiment the first and second members 55, 57 are rotatably coupled about a rotational axis, such as to measure a rotary torque, but in another embodiment could be linearly coupled, such as to be movable in a linear axis and measure a linear torque.
The first member 55 comprises a body element 65 to which an actuator, such as an electric motor and gearbox, is coupled, such as by a gear or pulley wheel which is attached or integrally formed with the body element 55. The body element 65 includes a cavity 67 which houses the elastic elements 59 and in which the second member 57 is movably disposed, in this embodiment rotatably disposed, and a closure element (not illustrated), typically a cover plate, for enclosing the cavity 67 of the body element 65.
In this embodiment the cavity 67 defines first and second cavity sections 69, 71 in opposed sides of the second member 57, in this embodiment disposed in opposed relation about the rotational axis of the second member 57.
In this embodiment the body element 55 includes a support 73, which is located within the first cavity section 69 of the cavity 67 and to which the elastic elements 59 are fixed at one end thereof, such as to extend beyond the respective lateral sides of the second member 57 and into the second cavity section 71 of the cavity 67.
In this embodiment the support 73, here a cylindrical post, is disposed within the cavity 67 such as to define a recess 75, here a substantially U- shaped recess, which captively receives the leaf spring member 61, such that the elastic elements 59, as defined by the arms of the leaf spring member 61, extend beyond the respective lateral sides of the second member 57 and into the second lateral section 71 of the cavity 67.
In this embodiment the cavity 67 defines a pair of arcuate, outwardly-flaring engagement surfaces 77, each of symmetrical shape in mirror relation about the rotational axis of the second member 57, which are located to the opposite sides of the elastic elements 59 and are configured such that a respective one of the elastic elements 59 is brought into engagement with a respective one of the engagement surfaces 77 in dependence upon the relative sense of movement of the first and second members 55, 57, and such that, on application of an increasing force, the distal point of engagement of the respective elastic element 59 moves outwardly along a length of the respective engagement surface 77, thereby shortening the effective length of the respective elastic element 59.
This reduction in the effective length of the respective elastic element 59 provides for a non-linear response to the applied force, with the degree of displacement per unit force being greatest when the elastic element 59 is under minimum displacement and the force transducer 4 is at its centre or equilibrium position and the degree of displacement per unit force being lowest when the elastic element 59 is under maximum displacement. This configuration provides a response to an applied force that is approximately sigmoidal, with maximum sensitivity when subjected to low forces and minimum sensitivity when subjected to high forces.
The second member 57 comprises a coupling element 83, in this embodiment a shaft, and a force transfer element 85, which is radially offset from the axis of the coupling element 83 and disposed between the elastic elements 59, such that, on movement of the second member 57, in this embodiment rotation of the second member 57, the force transfer element 85 acts to deflect a respective one of the elastic elements 59, such as to bring the elastic element 59 into progressive engagement with the respective engagement surface 77 as defined by the body element 65.
In this embodiment the force transfer element 85 includes a roller 89 which is supported in offset relation to the coupling element 83 and rotatable about an axis parallel to the coupling element 83. Through the provision of a roller 89 as the engagement surface with the respective elastic element 59, sliding friction between the force transfer element 85 and the respective elastic element 59 is reduced.
The above-described force sensor 3 has many applications, which include the following:
(i) Programmable Spring The force sensor 3 can function as a programmable spring when coupling an actuator, such as an electric motor, to a mechanical load or end effector with a position sensor, allowing the actuator to respond to forces applied to the mechanism by maintaining a predetermined position using predetermined force.
When a force is applied to an end effector, the effector will be deflected from the predetermined position, typically by a predetermined angle, generating an opposing force which is specified by the force command, and, when the applied force is removed, the effector will return to the predetermined position as if biased by a spring.
By utilizing a control system, springs can be specified through the use of control parameters to alter the dynamics of the mechanism. The control parameters include the set point or angle to which the effector will return under the influence of the electronic springs, the spring constants that act on the effector in each direction, and the linearity and damping of the springs,
(ii) Series Elastic Actuators
The force sensor 3 can be utilized to construct a series elastic actuator [1], where the force sensor 3 couples an actuator to a load and a closed loop feedback system is employed to drive the actuator to deliver a predetermined force. This device, in being simple to manufacture, is a particularly cost-effective means of implementing such an actuator.
(iii) Haptics
The force sensor 3 can be utilized to provide for mirroring of the operation of actuators, where the sensor outputs from one device are fed to the sensor inputs of another device and the sensor inputs of the one device are fed to the sensor outputs of the other device.
One example of such an implementation is in a radio-controlled model, for example, a toy car, where the control joystick contains one set of actuators and the steering mechanism of the model is controlled by another actuator. Movement of the control joystick will cause the steering actuator to move and the resistance encountered by the steering actuator is fed to the actuators of the control joystick, thereby enabling the user to feel the forces experience by the model.
(iv) Autonomous Robots
The force sensor 3 can be used to control the movements of joints in a robot, with the force-sensing facility allowing the limbs of the robot to behave in a range of ways, from completely compliant joints, to sprung joints and rigid joints. By specifying compliant behaviour, the robot is able to respond to external, environmental forces, thereby exploiting natural dynamics to produce more robust behaviour.
Figure 10 illustrates a programmable spring emulator in accordance with a first embodiment of the present invention.
The programmable spring emulator comprises an actuator 101 for driving an output element 103, in this embodiment a rotatable shaft, a force sensor 105, such as the force sensor of the above-described embodiments, through which the output element 103 is driven, which is operative to measure a force as applied to the output element 103, a position sensor 107 for measuring the position, in this embodiment the angle, of the output element 103, and a controller 109 for controlling the actuator 101 in response to one or both of the force and position of the output element 103 as measured by feedback from the force and position sensors 105, 107. In this embodiment the actuator 101 is an electric motor, the power of which is controlled by the controller 109 in response to one or both of the force and position of the output element 103 as measured by feedback from the force and position sensors 105, 107.
In this embodiment the actuator 101 includes a reduction gear assembly 111, but in other embodiments the reduction gear assembly 111 could be omitted.
In utilizing feedback from the force and position sensors 105, 107, the output element 103 can be driven to any desired position and effect any desired force, within the mechanical limits of the overall system. One particular application is in driving a robotic limb.
In one embodiment the controller 109 comprises an embedded computer system, a microcontroller, which acts to receive signals from the force and position sensors 105, 107 and deliver a control signal to the actuator 101, in this embodiment via a power amplifier.
In this embodiment the controller 109 can receive control inputs, via a user interface 115, either by manual input or from a computer via a communications network.
In this embodiment the controller 109 allows for operation of the emulator in one of a number of modes, which provides for (i) force sensing, where only the input from the force sensor 105 is utilized to maintain the output element 103 at a predetermined force, (ii) position sensing, where only the input from the position sensor 107 is utilized to maintain the output element 103 at a predetermined position, and (iii) combined force and positioning sensing, where the inputs from the force and position sensors 105, 107 are utilized to maintain the output element 103 at a predetermined force and position. In operating as a programmable spring, the emulator utilizes a feedback loop between the force sensor 105 and the actuator 101, such that a predetermined force is maintained on the output element 103. A zero force can be specified, and, in this condition, the output element 103 would be completely free to move under any external perturbations.
The principles of the programmable spring of the present invention will be described in more detail with reference to Figures 11 and 12 of the accompanying drawings.
Figure 11 represents a linear system, where a load 121 is mounted on a rail 123 and free to slide in either direction. This representation is equivalent to a device operating in a force-control mode with a zero force setting.
Figure 12 again represents a linear system, but where springs 125, 127, as resilient, biasing elements, are mounted at the respective ends of the rail 123, such that the load 121 is free to move in the central section of the rail 123, but a force is applied to the load 121 to return the load 121 to the central section of the rail 123 when the load 121 encounters one of the springs 125, 127.
In this embodiment the behaviour of the emulator is achieved by defining a force profile, here as a numerical data set, which maps a force value for each position as measured by the position sensor 107. During operation of the emulator, the emulator repeatedly measures the position of the output element 103 and applies the appropriate force to the output element 103 as defined by the force profile. Figure 13 graphically represents such a force profile for the linear system of Figure 12, where a positive force will drive the system to increase the position of the load 121 and a negative force will drive the system to decrease the position of the load 121.
By so defining the required behaviour by means of a profile, the emulator is not limited by mechanics and it is possible to define non-linear springs or combinations of non-linear springs, all of which can be dynamically altered during operation.
Also, in operation, the emulator need not be restricted to a single profile, but different profiles can be used at different points. For example, the emulator allows for switching between profiles at particular positions, thereby enabling the emulator to exhibit mechanical hysteresis or latching between two states.
Figure 14 illustrates the force profiles of one exemplary system which employs hysteresis. In this embodiment the system utilizes two profiles (Profile 1, Profile 2), each of which models a single linear spring which is designed to drive the actuator to opposite ends of its range of movement. The dashed sections in each of the profiles represent the positions (Tl, T2) when the emulator will switch between the profiles, as represented by the arrows.
In one embodiment the profiles can utilize a profile bias by means of which a force profile can be shifted up or down by a predetermined amount in order to cause movement of the output element 103. By way of exemplification, Figure 15 represents a force profile where two springs hold the output element 103 in a predetermined position, and Figure 16 represents a change in the profile bias to cause movement of the output element 103.
In another embodiment the profiles can utilize a scaling value by means of which the spring constants can be increased or decreased, in order to make the system more compliant. Figure 17 represents a change in the scaling factor as compared to the profile of Figure 15.
This means of altering a force profile by changing the profile bias and the scaling factor is particularly efficient in avoiding the need for uploading large amounts of data as otherwise would be required in defining each different force profile. It will be understood that the present invention is not restricted to simple spring systems, but can be utilized to emulate highly-complex systems. One such embodiment is represented in Figure 18, where the direction of force across various positions is indicated by the illustrated arrows.
In addition to emulating spring systems, the present invention also allows for emulation of damping behaviour by controlling the speed of movement of the output element 103, where the speed of movement of the output element 103 is determined from the rate of change in position, as measured by the position sensor 107.
In this embodiment such damping behaviour is emulated by the use of damping profiles, which operate in an analogous manner to the above- described force profiles.
In one embodiment each force profile can be linked to a pair of damping profiles, one for each direction of movement. With this configuration, the damping profiles allow for different control of the speed of movement of the output element 103 when moving in different directions. In this way, the system can behave as if constrained by a set of springs which exhibit different damping dependent upon the direction of movement of the output element 103.
One modification of the above-described programmable spring emulator is illustrated in Figure 19.
In this embodiment the actuator 101 is disposed orthogonally to the output element 103, such that the output element 103 is dual ended, which finds particular application in robotic systems, such as in joints, and in particular leg joints. In this embodiment the actuator 101 is coupled to the output element 103 by a bevel gear assembly 131, and the position sensor 107 is supported by a circuit board 133 of the controller 109.
Operation of this modified emulator is the same as for the above-described emulator.
Finally, it will be understood that the present invention has been described in its preferred embodiments and can be modified in many different ways without departing from the scope of the invention as defined by the appended claims.
References:
[1] US-A-5650704
For the avoidance of doubt, the content of the above-mentioned references is incorporated herein by reference.

Claims

1. A force transducer, comprising: first and second members which are coupled such as to be movable in one axis relative to one another; and an elastic element which is disposed between the first and second members, such that a force as applied to one of the first and second members causes deformation of the elastic element and is transferred to the other of the first and second members, with the relative deflection of the first and second members corresponding to the applied force.
2. The transducer of claim 1, wherein the first and second members are rotationally coupled about a rotational axis.
3. The transducer of claim 1, wherein the first and second members are linearly coupled such as to be movable in a linear axis.
4. The transducer of any of claims 1 to 3, comprising: a pair of elastic elements which are disposed between the first and second members, such that a respective one of the elastic elements of the pair of elastic elements is deformed in dependence upon the sense of relative movement of the first and second members.
5. The transducer of any of claims 1 to 3, comprising: a plurality of pairs of elastic elements which are disposed between the first and second members, such that respective ones of the elastic elements of each of the pairs of elastic elements are deformed in dependence upon the sense of relative movement of the first and second members.
6. The transducer of claim 4 or 5, wherein one of the first and second members receives the at least one pair of elastic elements and the other of the first and second members includes at least one force transfer element which is disposed between the elastic elements of the at least one pair of elastic elements, such that the at least one force transfer element engages a respective one of the elastic elements of the at least one pair of elastic elements in dependence upon the sense of movement of the first and second members.
7. The transducer of claim 6, wherein the force transfer element includes a roller which is supported in offset relation to and rotatable about an axis parallel to the movement axis.
8. The transducer of claim 6 or 7, wherein the one of the first and second members includes a cavity in which the at least one pair of elastic elements is disposed.
9. The transducer of claim 8, wherein the cavity defines at least one pair of engagement surfaces, which engagement surfaces are located to the opposite sides of the respective ones of the elastic elements of the at least one pair of elastic elements and are configured such that a respective one of the elastic elements is brought into engagement with a respective one of the engagement surfaces in dependence upon the relative sense of movement of the first and second members.
10. The transducer of claim 9, wherein the engagement surfaces are outwardly-flaring relative to the movement axis of the first and second members.
11. The transducer of claim 10, wherein the engagement surfaces are arcuate surfaces.
12. The transducer of any of claims 9 to 11, wherein the engagement surfaces are configured such that, on application of an increasing force, the respective elastic element is progressively brought into engagement with the respective engagement surface, with the distal point of engagement of the respective elastic element moving along a length of the respective engagement surface, thereby shortening the effective length of the respective elastic element and providing a nonlinear response to the applied force.
13. The transducer of claim 12, wherein the engagement surfaces of the at least one pair of engagement surfaces are disposed in opposed, symmetrical relation relative to the movement axis.
14. The transducer of any of claims 1 to 13, wherein the elastic elements comprise a material which has a non-linear response to the applied force.
15. The transducer of claim 14, wherein the material is a rubber material.
16. The transducer of any of claims 1 to 13, wherein the elastic elements comprise spring elements.
17. The transducer of claim 16, wherein the elastic elements comprise leaf spring elements.
18. The transducer of claim 17, wherein the elastic elements are provided by respective arms of a single, unitary leaf spring.
19. A force sensor, comprising: the transducer of any of claims 1 to 18; and a sensor element for measuring the relative deflection of the first and second members, which deflection corresponds to the applied force.
20. The sensor of claim 19, wherein the sensor element comprises a potentiometer.
21. The sensor of claim 19 or 20, wherein one of the first and second members includes a gear or pulley wheel, whereby the sensor is coupled to an actuator.
22. The sensor of claim 19 or 20, wherein one of the first and second members includes a spur gear, whereby the sensor is operative in a gear assembly.
23. A programmable device incorporating the sensor of any of claims 19 to 22.
24. A programmable device, comprising: an actuator for driving an output element; the force sensor of any of claims 19 to 22, through which the output element is driven, which is operative to measure a force as applied to the output element; and a controller for controlling the actuator in response to the force as measured by the force sensor, such that a predeterminable force is maintained on the output element.
25. The programmable device of claim 24, further comprising: a position sensor which is operative to measure a position of the output element; and wherein the controller is operative to control the actuator in response to the force and position as measured by the force and position sensors, such that, for predeterminable positions, a predeterminable force is maintained on the output element.
26. The programmable device of claim 25, wherein the controller is operative to control the actuator in accordance with at least one force profile which maps a force value in relation to the position of the output element.
27. The programmable device of claim 26, wherein the at least one force profile maps a non-linear spring.
28. The programmable device of claim 26 or 27, wherein the at least one force profile maps a combination of springs.
29. The programmable device of any of claims 26 to 28, wherein the controller is operative to control the actuator in accordance with first and second force profiles, such that one of the force profiles is followed when the output element is moved in a first sense and the other of the force profiles is followed when the output element is moved in the other sense, whereby the first and second force profiles provide for hysteresis.
30. The programmable device of any of claims 26 to 29, wherein the controller is operative to control the actuator in accordance with at least one damping profile which maps a speed value in relation to the position of the output element.
31. The programmable device of any of claims 24 to 30, wherein the actuator is an electric motor, the power of which is controlled by the controller.
32. The programmable device of any of claims 24 to 31, wherein the actuator includes a reduction gear assembly.
33. The programmable device of any of claims 24 to 32, wherein the controller includes a user interface, which is operative to receive input manually from a user or from a computer via a communications network.
34. An actuator device incorporating the sensor of any of claims 19 to 22.
35. The actuator device of claim 34, wherein the actuator device is a series elastic actuator.
36. A haptic device incorporating the sensor of any of claims 19 to 22.
37. A robotic device incorporating the sensor of any of claims 19 to 22.
38. The robotic device of claim 37, wherein the robotic device is an autonomous robot.
39. A programmable device, comprising : an actuator for driving an output element; a force sensor, through which the output element is driven, which is operative to measure a force as applied to the output element; and a controller for controlling the actuator in response to the force as measured by the force sensor, such that a predeterminable force is maintained on the output element.
40. The programmable device of claim 39, further comprising: a position sensor which is operative to measure a position of the output element; and wherein the controller is operative to control the actuator in response to the force and position as measured by the force and position sensors, such that, for predeterminable positions, a predeterminable force is maintained on the output element.
41. The programmable device of claim 40, wherein the controller is operative to control the actuator in accordance with at least one force profile which maps a force value in relation to the position of the output element.
42. The programmable device of claim 41, wherein the at least one force profile maps a non-linear spring.
43. The programmable device of claim 41 or 42, wherein the at least one force profile maps a combination of springs.
44. The programmable device of any of claims 41 to 43, wherein the controller is operative to control the actuator in accordance with first and second force profiles, such that one of the force profiles is followed when the output element is moved in a first sense and the other of the force profiles is followed when the output element is moved in the other sense, whereby the first and second force profiles provide for hysteresis.
45. The programmable device of any of claims 40 to 44, wherein the controller is operative to control the actuator in accordance with at least one damping profile which maps a speed value in relation to the position of the output element.
46. The programmable device of any of claims 39 to 45, wherein the actuator is an electric motor, the power of which is controlled by the controller.
47. The programmable device of any of claims 39 to 46, wherein the actuator includes a reduction gear assembly.
48. The programmable device of any of claims 39 to 47, wherein the controller includes a user interface, which is operative to receive input manually from a user or from a computer via a communications network.
49. A programmable device, comprising: an actuator for driving an output element; a position sensor which is operative to measure a position of the output element; and a controller which is operative to control the actuator in response to the position as measured by the position sensor, such that the output element is maintained at a predetermined position.
50. The programmable device of claim 49, further comprising: a force sensor, through which the output element is driven, which is operative to measure a force as applied to the output element; and wherein the controller is operative to control the actuator in response to the force and position as measured by the force and position sensors, such that, for predeterminable positions, a predeterminable force is maintained on the output element.
51. The programmable device of claim 50, wherein the controller is operative to control the actuator in accordance with at least one force profile which maps a force value in relation to the position of the output element.
52. The programmable device of claim 51, wherein the at least one force profile maps a non-linear spring.
53. The programmable device of claim 51 or 52, wherein the at least one force profile maps a combination of springs.
54. The programmable device of any of claims 51 to 53, wherein the controller is operative to control the actuator in accordance with first and second force profiles, such that one of the force profiles is followed when the output element is moved in a first sense and the other of the force profiles is followed when the output element is moved in the other sense, whereby the first and second force profiles provide for hysteresis.
55. The programmable device of any of claims 50 to 54, wherein the controller is operative to control the actuator in accordance with at least one damping profile which maps a speed value in relation to the position of the output element.
56. The programmable device of any of claims 49 to 55, wherein the actuator is an electric motor, the power of which is controlled by the controller.
57. The programmable device of any of claims 49 to 56, wherein the actuator includes a reduction gear assembly.
58. The programmable device of any of claims 49 to 57, wherein the controller includes a user interface, which is operative to receive input manually from a user or from a computer via a communications network.
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