METHOD FOR CONTROLLING A CHANGE OF DAMPING IN AN ARTIFICIAL JOINT

Abstract

A method for controlling a change of resistance in an artificial joint of an orthosis, an exoskeleton or prosthesis of a lower extremity. The artificial joint has an upper part and a lower part which are secured on each other so as to be pivotable about a pivot axis, a damper unit is secured between the upper part and the lower part in order to provide a resistance to flexion or extension of the artificial joint, and the damper unit is assigned an adjusting mechanism via which the resistance is changed when a sensor signal of a control unit assigned to the adjusting mechanism activates the adjusting mechanism. The resistance is changed as a function of the position and/or length of the measured or calculated leg tendon and/or the time derivatives thereof.

Claims

1-11. (canceled)

12. A method for controlling a change in resistance in an artificial joint of an orthosis, an exoskeleton, or prosthesis of a lower extremity, the method comprising: providing an artificial joint having an upper part and a lower part which are fastened to one another pivotably about a pivot axis, a resistance unit fastened between the upper part and the lower part in order to provide a resistance to flexion or extension of the artificial joint, the resistance unit being assigned an adjustment device operable to change the resistance if a sensor signal of a control unit assigned to the adjustment device activates the adjustment device; changing the flexion resistance or extension resistance based on at least one of a position and an orientation of at least one of the upper part and the lower part.

13. The method as claimed in claim 12, wherein a lower leg angle or a thigh angle is directly measured using an inertial angle sensor, or is determined using a position sensor on a thigh or lower leg and a knee angle sensor.

14. The method as claimed in claim 12, wherein a quotient is determined from a change in a thigh speed or a lower leg speed, the quotient being used for an assessment of the walking situation.

15. The method as claimed in claim 14, wherein a force sensor for detecting forces in the lower part detects a stance phase or standing.

16. The method as claimed in claim 12, wherein the resistance is changed additionally in a manner dependent on a change in position of at least one of the upper part and the lower part.

17. The method as claimed in claim 12, wherein the artificial joint is formed as a hip joint, a knee joint, or an ankle joint.

18. The method as claimed in claim 12, wherein during forward walking on level ground, the upper part and the lower part rotate in a forward direction.

19. The method as claimed in claim 12, wherein during walking downwardly on an inclined ground, a thigh angle remains substantially constant.

20. The method as claimed in claim 12, wherein during walking down stairs, the upper part rotates backward.

21. A method for controlling a change in resistance in an artificial joint of an orthosis, an exoskeleton, or prosthesis of a lower extremity, the method comprising: providing an artificial joint having an upper part, a lower part, a resistance unit, and an adjustment device, the upper part being pivotally connected to the lower part, the resistance unit providing a flexion resistance or an extension resistance, the adjustment device including a control unit, the adjustment device being operable to change the flexion resistance or extension resistance if a sensor signal of the control unit activates the adjustment device; changing the flexion resistance or extension resistance based on at least one of a position and an orientation of at least one of the upper part and the lower part.

22. The method as claimed in claim 21, wherein a lower leg angle or a thigh angle is directly measured using an inertial angle sensor, or is determined using a position sensor on a thigh or lower leg and a knee angle sensor.

23. The method as claimed in claim 21, wherein a quotient is determined from a change in a thigh angle or lower leg angle, the quotient being used for an assessment of the walking situation.

24. The method as claimed in claim 21, wherein a quotient is determined from a change in a thigh speed or a lower leg speed, the quotient being used for an assessment of the walking situation.

25. The method as claimed in claim 24, further comprising detecting forces in the lower part with a sensor during a stance phase or standing.

26. The method as claimed in claim 21, further comprising changing the resistance in a manner dependent on a position or change in position of at least one of the upper part and the lower part.

27. The method as claimed in claim 21, wherein the artificial joint is formed as a hip joint, a knee joint, or an ankle joint.

28. The method as claimed in claim 21, wherein during forward walking on level ground, the upper part and the lower part rotate in a forward direction.

29. The method as claimed in claim 21, wherein during walking downwardly on an inclined ground, the thigh angle remains substantially constant.

30. The method as claimed in claim 21, wherein during walking down stairs, the thigh rotates backward.

Description

[0026] Exemplary embodiments of the invention will be discussed in more detail below on the basis of the appended figures. In the figures:

[0027] FIG. 1shows a schematic illustration of a leg prosthesis,

[0028] FIG. 2shows a schematic illustration of a knee prosthesis with angles;

[0029] FIG. 3shows an illustration as per FIG. 2 with parameter assignment;

[0030] FIGS. 4a-4cshow illustrations of different situations during walking; and

[0031] FIG. 5shows various illustrations of a thigh angle versus the leg orientation.

[0032] FIG. 1 shows, in a schematic illustration, a leg prosthesis with an upper part 1 to which a thigh socket 10 for receiving a thigh stump is fastened. A lower part 2 designed as a lower leg part is arranged pivotably on the upper part 1. The lower part 2 is mounted on the upper part 1 pivotably about a pivot axis 4. The lower part 2 has a lower leg tube 5, to the distal end of which there is fastened a prosthetic foot 3 in which there may be accommodated a device for determining the axial force acting on the lower leg tube 5 and the ankle moment acting about the fastening point of the prosthetic foot 3 to the lower leg tube 5.

[0033] In or on the lower part 2 there is arranged a resistance device 6 which may be formed for example as a damper or actuator and which is supported between the upper part 1 and the lower part 2 in order to provide an adjustable extension resistance and flexion resistance. The resistance device 6 is assigned an adjustment device 7, for example a motor, a magnet or some other actuator, by means of which the respective resistance R within the resistance unit 6 can be varied. If the resistance unit 6 is formed as a hydraulic damper or pneumatic damper, it is possible by means of the adjustment device 7 for the respective flow cross section of a flow transfer channel to be increased or decreased in size. It is likewise possible for the flow resistance to be varied in some other way by means of the adjustment device 7. This may be realized for example by opening or closing valves or changing viscosities or magnetorheological characteristics. If the resistance unit is formed as an electric motor operating as a generator, it is possible for an increase or decrease in the respective resistances to flexion or extension to be set through variation of the electrical resistance. The resistance unit may also be formed as a mechanical resistance to flexion or extension, as a friction brake or as an elastomer element with variable deformation resistance or a magnetorheological damper.

[0034] To be able to activate or deactivate the adjustment device 7, a control device 8 is assigned to the lower part 2, in particular is accommodated in a lower leg trim, by means of which control device a corresponding activation or deactivation signal is output to the adjustment device 7. The adjustment device 7 is activated or deactivated on the basis of sensor data, and the sensor data are provided by one or more sensors 9 which are arranged on the artificial knee joint. These may be angle sensors, inertial angle sensors, acceleration sensors and/or force sensors. The sensors 9 are connected to the control device 8, for example by cable or by means of a wireless transmission device. In the exemplary embodiment illustrated, the sensor 9 is formed inter alia as a knee angle sensor or inertial angle sensor. The sensors may be arranged on the thigh socket 10, on the upper part 1, on the lower part 2, on the lower leg tube 5 or on the foot part 3. In the case of orthoses, the sensors are fastened to the respectively corresponding rails, joint parts or foot parts; the sensors 9 may also be fastened to the limbs themselves.

[0035] The entire step cycle from the heel strike via toe lift-off to the new, next heel strike HS, and thus also the entire swing phase with the swing phase extension and the swing phase flexion, is monitored by means of the sensors 9.

[0036] FIG. 2 shows, in a side view, a prosthetic knee joint with the thigh socket 10, the upper part 1, the lower part 2 which is mounted pivotably about a knee axis 4 and which has the resistance unit 6 arranged therein, the distal lower leg tube 5, and the prosthetic foot fastened to the latter, in a flexed position. The leg chord L.sub.C extends between a foot point F.sub.P and a hip center of rotation H.sub.R. The leg chord L.sub.C is the connection between the hip center of rotation H.sub.R and the foot point F.sub.P; by means of the orientation of the leg chord L.sub.C, conclusions can be drawn regarding the movement presently being performed, and in particular, different movements or walking situations can be distinguished from one another. The foot point F.sub.P may be situated in the center of the foot; an alternative definition of the foot point F.sub.P is the instantaneous center of rotation of the polar movement, the pivot axis of the ankle joint or the projection of the longitudinal extent of the lower part 2 to the level of the sole of the foot. Shown as a characteristic variable for the position of the leg chord L.sub.C is the leg chord angle .sub.B, which is defined as the angle between the leg chord L.sub.C and a vertical V. In the illustrated position of the prosthesis device, the upper part 1 is flexed relative to the lower part 2 by an angle; the leg chord L.sub.C is thus tilted in the rearward direction. As a result, there is also a thigh angle .sub.T relative to the vertical V. The thigh angle .sub.T increases relative to the vertical V if, for example, the lower part 2 remains vertical and the upper part 1 is pivoted counterclockwise in the illustrated exemplary embodiment about the pivot axis 4. A reference variable for the thigh angle .sub.T is the connecting line between the hip center of rotation H.sub.R and the knee axis 4; the distance between the two points along said connecting line simultaneously defines the thigh length L.sub.T.

[0037] In FIG. 3, in addition to the variables in FIG. 2, the knee angle .sub.K is plotted, which is the angle between the thigh segment, represented by the connecting line between the knee axis 4 and the hip center of rotation H.sub.R, and the longitudinal extent of the lower part 2. The knee angle .sub.K is 0 if the prosthesis device is in a maximally extended position. This means that the longitudinal extent of the lower part 2 is aligned with the longitudinal extent of the upper part 1, that is to say the connection between the knee axis 4 and the hip center of rotation H.sub.R is aligned with the connecting line between the knee axis 4 and the foot point F.sub.P if the latter lies on the axis of the longitudinal extent of the lower leg tube 5.

[0038] The lower leg length L.sub.S is defined by the spacing between the knee axis 4 and the foot point F.sub.P. The lower leg angle .sub.S is the angle between the vertical V and the connecting line between the foot point F.sub.P and the knee axis 4. In the illustrated exemplary embodiment with the prosthetic knee joint flexed by an angle .sub.K, the lower leg angle .sub.S is tilted positively in a forward walking direction, the thigh angle .sub.T is oriented in the backward direction relative to the vertical, and the leg chord L.sub.C is tilted backward by the angle .sub.B. The length L.sub.B of the leg chord L.sub.c is defined by the spacing between the hip center of rotation H.sub.R and the foot point F.sub.P.

[0039] The length L.sub.B of the leg chord L.sub.C can be calculated from the known segment lengths L.sub.T and L.sub.S in conjunction with the knee angle. In addition to inertial angle sensors 9 which may be arranged on the lower part 2 or the upper part 1 or the thigh socket 10 or the lower leg tube 5, the orientation or the leg chord angle .sub.B may also be estimated from a combination of the lower leg angle .sub.S in conjunction with a weighted knee angle .sub.K, wherein the formula for this is

.sub.B=.sub.S+d.sub.K

, where d lies between 0.4 and 0.6, and is in particular 0.5.

[0040] With the knowledge of the length L.sub.B and orientation .sub.B of the leg chord L.sub.C and possibly the derivatives with respect to time of said variables, it is possible to follow the rolling movement in the stance phase independently of stance phase flexion or stance phase extension, and to obtain knowledge regarding the progression of the movement. By means of the change in the leg chord orientation or in the leg chord angle .sub.B, the movement progression can be followed both in the stance phase and in the swing phase, such that said variable can be taken into consideration for the control of the stance phase behavior and/or swing phase behavior through adaptation of the damper settings.

[0041] The thigh, angle .sub.T and also the lower leg angle .sub.S, which can also be referred to as segment angles, may be measured by means of inertial sensors which are situated on the respective segment. Alternatively, a calculation is performed by means of only one inertial sensor on the segment not involved in each case and the knee angle .sub.K, which is determined by means of a knee angle sensor.

[0042] FIG. 4a shows two sections of a leg position for walking on a level surface. The left-hand illustration shows the prosthesis device shortly after the heel strike; the length L.sub.B of the leg chord L.sub.C is approximately at a maximum, because the leg chord angle (not shown) .sub.B approximately corresponds to the thigh angle .sub.S. During the further course of the step, a forward progression occurs, the prosthesis device as a whole rotates forward, and the leg chord L.sub.C is pivoted forward about the foot point F.sub.P, which may also be situated in an ankle joint, such that the leg chord L.sub.C is situated in front of the vertical. It can be seen from FIG. 4a that, over the major part of the forward progression when walking on a level surface, the thigh or thigh socket 10 is jointly displaced forward together with the leg chord L.sub.C in the case of an approximately extended knee joint, and a change in the knee angle does not occur.

[0043] FIG. 4b shows walking on a downwardly directed ramp. The left-hand illustration shows increased flexion in the prosthetic knee joint, the thigh socket 10 has been pivoted about the knee axis 4, and the orientation of the leg chord L.sub.C corresponds approximately to that in the setting-down phase when walking on a level surface.

[0044] The further profile of the movement when walking down a ramp is shown in the right-hand illustration of FIG. 4b. A rolling movement about the foot point F.sub.P like-wise occurs, the leg chord L.sub.C rotates forward about the foot point F.sub.P, and the thigh angle .sub.S remains in a virtually constant position owing to increased flexion about the knee axis 4, that is to say the orientation of the thigh or thigh socket 10 in space does not change, or changes only insignificantly, while the leg chord L.sub.C performs a forward rotation.

[0045] A third walking situation, specifically walking down stairs, is illustrated in FIG. 4c. The position of the individual components of the prothesis device corresponds, in the initial position shown in the left-hand illustration, to walking down a ramp. The leg chord L.sub.C is inclined backward, that is to say is tilted backward counter-clockwise relative to the vertical. During the further course of alternating walking down stairs, the prosthesis device is flexed, pivoting of the upper part 1 relative to the lower part 2 occurs, the knee angle .sub.K increases, and likewise, the length L.sub.P of the leg chord L.sub.C decreases. The orientation of the leg chord L.sub.C changes less than when walking on a level surface or when walking down a ramp, that is to say a forward rotation of the leg chord L.sub.C occurs only to a relatively small extent, and the leg chord angle .sub.B relative to the vertical is thus smaller than in the case of walking on a level surface or walking down a ramp.

[0046] In the walking situations in FIGS. 4a to 4c, forward progression occurs, that is to say the leg rolls forward. A suitable parameter or an auxiliary variable for distinguishing and detecting the respective walking situation is the quotient between the change in the thigh angle .sub.T or in the lower leg angle .sub.S and the change in the leg orientation or in the leg chord angle .sub.B. Likewise, the derivatives with respect to time are suitable and provided as characteristic variables, that is to say the quotient of the change in the angular speeds of the leg chord L.sub.C and of the thigh or the lower leg.

[0047] The profiles of the respective angles are plotted in FIG. 5; curve a shows the profile of the angle for walking on a level surface, curve b shows the profile of the leg chord and thigh angles for walking down a ramp, and curve c shows the profile of the angle for walking down stairs.

[0048] It is clear that all curves a, b, c have a different profile, and in particular, the gradient k differs for the respective curve profile. The gradient k can be determined as a differential quotient; the formula for this is

k=(.sub.T1.sub.T0)/(.sub.B1.sub.B0)

[0049] The gradient k.sub.1 for walking on a level surface is much steeper than the gradient k.sub.2 for walking down a ramp. Whereas, in the case of walking on a level surface as per curve a, the change in the thigh angle .sub.T is substantially aligned with the change in the leg chord angle .sub.B, and the gradient is approximately 1, the thigh angle .sub.T when walking down a ramp is approximately constant, such that a much shallower gradient k.sub.2 is realized for walking down a ramp. In the case of walking down stairs, the leg chord angle .sub.B decreases to a much lesser extent than the thigh angle .sub.T, such that the gradient k.sub.3 when walking down stairs assumes a negative value.

[0050] In a manner dependent on the detected quotients or the respective gradient k.sub.1, k.sub.2, k.sub.3, an adaptation of the resistances can be performed; in the case of walking down a ramp being detected as per curve profile b, the standard setting for walking on a level surface may be changed such that yielding occurs, and thus reduced flexion is present at a corresponding leg chord angle .sub.B. If a negative gradient k.sub.3 as per curve c in FIG. 5 is detected, it can be assumed that walking down stairs is being performed. A slow leg-bending movement or the prevention of a complete lock-up of the prosthesis device should be avoided in order to prevent a catapult effect.

[0051] Correspondingly characteristic phase diagrams are obtained if, instead of the angles, the angular speeds or angular accelerations of leg chord and thigh or lower legs are plotted.

[0052] With the method according to the invention, no forces or force profiles need to be measured or evaluated in order to make a distinction between walking situations and the movement progression thereof. It is basically the case that only angles are measured, calculated or estimated and used as a basis for the change in the damper setting.