GB2440753A

GB2440753A - Force sensor and programmable spring emulator

Info

Publication number: GB2440753A
Application number: GB0615526A
Authority: GB
Inventors: William Bigge
Original assignee: University of Sussex
Current assignee: University of Sussex
Priority date: 2006-08-04
Filing date: 2006-08-04
Publication date: 2008-02-13
Also published as: GB0615526D0; WO2008015460A2; WO2008015460A3

Abstract

A force sensor 3 comprises first and second members 5,7 which are coupled such as to be movable in one axis relative to one another. Pairs of deformable elastic elements 9 are disposed between the first and second members 5,7 such that a force as applied to one of the first and second members causes deformation of the elastic element 9 and is transferred to the other of the first and second members. A sensor element 11 is provided for measuring the relative deflection of the first and second members, which deflection corresponds to the applied force. First and second members are rotatably coupled about a rotational axis. In another embodiment the members could be linearly coupled to be moveable along a linear axis.

Description

1 2440753

FORCE SENSOR AND PROGRAMMABLE SPRING EMULATOR

The present invention relates to a force sensor for sensing the degree of force, either as a rotary or linear force, as applied by an actuator, and a programmable spring emulator which utilizes such a force sensor to emulate a spring system.

In one aspect the present invention provides a force sensor, comprising: first and second members which are coupled such as to be movable in one axis relative to one another; 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; 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 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 sensor comprises: a pair of deformable 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 sensor comprises: a plurality of pairs of deformable 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 includes a cavity in which the at least one pair of elastic elements is disposed 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 elastic element comprises a material which has a non-linear response to the applied force.

Preferably, the material is a rubber material. * **

In one embodiment the sensor element comprises a potentiometer. S...

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 spring device which incorporates the above-described sensor.

In another aspect the present invention provides 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 spring 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 further aspect the present invention provides a programmable spring S..

device, comprising: an actuator for driving an output element; a force S... 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. 5 * * S * **

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. * S.. S...

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 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 spring 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 at least one force profile maps a combination of ::::: springs.

In one embodiment the actuator includes a reduction gear assembly.

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 -.

*1* the cover plate removed; *0SS Figure 4 illustrates an exploded perspective view of the force sensor of Figure 1, with the cover plate removed; Figure 5 the output of the 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; Figure 7 illustrates an exploded perspective view of the force sensor of Figure 6; Figure 8 illustrates a programmable spring emulator in accordance with one embodiment of the present invention; Figure 9 models a linear system, where a load is mounted on a rail and free to slide in either direction; Figure 10 models the linear system of Figure 9, but where further including springs at the respective ends of the rail; Figure 11 graphically represents a force profile for the linear system of Figure 10; Figure 12 illustrates the force profiles of one example system which employs hysteresis; Figure 13 represents an exemplary force profile for two springs which are configured to maintain the output element of the emulator of Figure 8 in a predetermined position; :.:::. Figure 14 represents a change in the profile bias of the force profile of Figure **. 13 which is such as to cause movement of the output element; *...

: Figure 15 represents a change in the scaling factor of the force profile of Figure 13 which is such as to change the compliancy of the emulated springs;

S

* .: Figure 16 illustrates an exemplary force profile of a highly complex spring system for emulation by the emulator of Figure 8; and Figure 17 illustrates a programmable spring emulator as one modification of the emulator of Figure 8.

Figures 1 to 4 illustrate a force sensor 3 in accordance with a first embodiment of the present invention.

The force sensor 3 comprises first and second members 5, 7 which are coupled such as to be movable in one axis relative to one another, 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 respective ones of the deformable elastic elements 9 and is transferred to the other of the first and second members 5, 7, and 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, but in another embodiment could be linearly coupled such as to be movable in a linear axis.

The first member 5 comprises a body element 15, which includes a cavity 17 which houses the deformable elastic elements 9 and in which the second body element 7 is movably disposed, in this embodiment rotatably disposed, :*:::. and a cover plate 18 for enclosing the cavity 17 of the body element 15, as will be described in moredetail hereinbelow. S...

.. : The cavity 11 comprises first and second cavity sections 19, 21, in this embodiment disposed in opposed relation, which each contain a pair of deformable elastic elements 9 which are disposed in opposed relation, between which extend respective force transfer arms 25 of the second member 7, such that rotation of the second member 7 causes the force transfer members 25 thereof to compress one of the deformable elastic elements 9 of each pair of the deformable elastic elements 9 in dependence upon the relative sense of rotation of the first and second members 5, 7.

The second body member 7 comprises a coupling element 23, in this embodiment a shaft, to which an actuator is coupled, and at least one, in this embodiment first and second force transfer arms 25, which extend radially from the coupling element 23 and between the deformable elastic elements 9 of each pair of the deformable elastic elements 9. In this embodiment the first and second force transfer arms 25 are oppositely directed.

-10 -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, from which the applied force can be calculated.

In this embodiment the elastic elements 9 provide a non-linear response to the 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, as illustrated in Figure 5.

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. S.. * S S...

In this embodiment the first member 5 includes a spur gear 31 which forms SI'S *.. : 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. S. I

S 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.

-11 -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 * ** * * S *5** ** 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 S...

: 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. *5 * * S *

* (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 -12 -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 8 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, 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.

-13 -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 9 and 10 of the accompanying drawings.

-14 -Figure 9 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 10 again represents a linear system, but where springs 125, 127 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 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 11 graphically represents such a force profile for the linear system of Figure 10, where a positive force will drive S..

* 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. ** S * * S

* 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.

-15 -Figure 12 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 (Ti, 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, Figures 13 represents a force profile where two springs hold the output element 103 in a predetermined position, and Figure 14 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 15 represents a change in the scaling * factor as compared to the profile of Figure 13. * . * * *

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 16, 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 -16 -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 17. **** * S S S. *

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 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 -17 -without departing from the scope of the invention as defined by the appended claims. * I. * * S S... *. * . a... S... * S I *S I

S S..

S * S *5 * S.. * S. * S* S *S

-18 -References: [1] US-496419 For the avoidance of doubt, the content of the above-mentioned references are incorporated herein by reference. * 0* * . S S... S... * S S... * S* *. *

S *

S * * * S S S** S S* S * . . S **

Claims

CLAIMS

1. A force sensor, comprising: first and second members which are coupled such as to be movable in one axis relative to one another; 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; and a sensor element for measuring the relative deflection of the first and second members, which deflection corresponds to the applied force.

2. The sensor of claim 1, wherein the first and second members are : rotationally coupled about a rotational axis. **1S

3. The sensor of claim 1, wherein the first and second members are linearly coupled such as to be movable in a linear axis.

* 4. The sensor of any of claims 1 to 3, comprising: : * * a pair of deformable 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 sensor of any of claims 1 to 3, comprising: a plurality of pairs of deformable 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.

-20 - 6. The sensor of claim 4 or 5, wherein one of the first and second members includes a cavity in which the at least one pair of elastic elements is disposed and the other of the first and second members includes at least one force transfer arm which is disposed between the elastic elements of the at least one pair of elastic elements, such that the at least one force transfer arm 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 sensor of any of claims 1 to 6, wherein the elastic element comprises a material which has a non-linear response to the applied force.

8. The sensor of claim 7, wherein the material is a rubber material. 0*** * * ***.

9. The sensor of any of claim 1 to 8, wherein the sensor element comprises a potentiometer.

10. The sensor of any of claims 1 to 9, wherein one of the first and second members includes a spur gear, whereby the sensor is operative in a gear assembly.

11. A programmable spring device incorporating the sensor of any of claims 1 to 10.

12. A programmable spring device, comprising: an actuator for driving an output element; the force sensor of any of claims 1 to 10, through which the output element is driven, which is operative to measure a force as applied to the output element; and -21 -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.

13. The programmable spring device of claim 12, 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.

14. The programmable spring device of claim 13, 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 e output element. **1

*.. : 15. The programmable spring device of claim 13, wherein the at least one force profile maps a non-linear spring. * * a. * I.. S

16. The programmable spring device of claim 14 or 15, wherein the at least one force profile maps a combination of springs.

17. The programmable spring device of any of claims 14 to 16, 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.

18. The programmable spring device of any of claims 14 to 17, wherein the controller is operative to control the actuator in accordance with -22 -at least one damping profile which maps a speed value in relation to the position of the output element.

19. The programmable spring device of any of claims 12 to 18, wherein the actuator is an electric motor, the power of which is controlled by the controller.

20. The programmable spring device of any of claims 12 to 19, wherein the actuator includes a reduction gear assembly.

21. The programmable spring device of any of claims 12 to 20, 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.

: 22. An actuator device incorporating the sensor of any of claims 1 to 10. S... S...

23. The actuator device of claim 22, wherein the actuator device is a *:::: series elastic actuator. S..

* 24. A haptic device incorporating the sensor of any of claims 1 to 10. * . * * S

:::.: 25. A robotic de,ice incorporating the sensor of any of claims 1 to 10.

26. The robotic device of claim 25, wherein the robotic device is an autonomous robot.

27. 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 -23 -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.

28. The programmable spring device of claim 27, 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.

29. The programmable spring device of claim 28, 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. S...

30. The programmable spring device of claim 29, wherein the at least one force profile maps a non-linear spring.

31. The programmable spring device of claim 29 or 30, wherein the at :. least one force profile maps a combination of springs. * S.

* 32. The programmable spring device of any of claims 29 to 31, 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.

33. The programmable spring device of any of claims 29 to 32, wherein the controller is operative to control the actuator in accordance with -24 -at least one damping profile which maps a speed value in relation to the position of the output element.

34. The programmable spring device of any of claims 29 to 33, wherein the actuator is an electric motor, the power of which is controlled by the controller.

35. The programmable spring device of any of claims 29 to 34, wherein the actuator includes a reduction gear assembly.

36. The programmable spring device of any of claims 29 to 35, 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.

37. A programmable spring device, comprising: :.:::. an actuator for driving an output element; S...

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 S. * the position as measured by the position sensor, such that the output element is maintained at a predetermined position. S. * * . .

* 38. The programmable spring device of claim 37, 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.

39. The programmable spring device of claim 38, wherein the controller is operative to control the actuator in accordance with at least one force -25 -profile which maps a force value in relation to the position of the output element.

40. The programmable spring device of claim 39, wherein the at least one force profile maps a non-linear spring.

41. The programmable spring device of claim 39 or 40, wherein the at least one force profile maps a combination of springs.

42. The programmable spring device of any of claims 39 to 41, 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. S... S...

43. The programmable spring device of any of claims 39 to 42, 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 S..

the position of the output element. * . * . S

*:*. 44. The programmable spring device of any of claims 37 to 43, wherein the actuator is an electric motor, the power of which is controlled by the controller.

45. The programmable spring device of any of claims 37 to 44, wherein the actuator includes a reduction gear assembly.

46. The programmable spring device of any of claims 37 to 45, 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.

-26 - 47. A force sensor substantially as hereinbefore described with reference to Figures 1 to 5 or Figures 6 and 7 of the accompanying drawings.

48. A programmable spring device substantially as hereinbefore described with reference to Figures 8 to 16 or Figure 17, optionally in conjunction with Figures 1 to 5 or Figures 6 and 7, of the accompanying drawings. * ** * S S *SS* S... * I I... * .

II I

S S.. * S * I I I.. I

II I S *I S.