METHOD FOR CONTROLLING THE STANDING-PHASE DAMPING OF AN ARTIFICIAL KNEE JOINT

Abstract

A method for controlling the standing-phase damping of an artificial knee joint comprising an upper part and a lower part which are secured together in a pivotal manner about a pivot axis, a resistance unit which is arranged between the upper part and the lower part and has an adjustment device via which the damping resistance can be modified, and a control unit which is coupled to the adjustment device and which is connected to at least one sensor. The adjustment is carried out on the basis of sensor data, and the knee angle is detected by the at least one sensor during the standing-phase inflexion up to the terminal standing phase. The flexion damping is increased to a level above an initial flexion damping in order to prevent a further inflexion upon reaching a specified maximum knee angle.

Claims

1. A method for controlling the stance phase damping of an artificial knee joint, the method comprising: providing an upper part and a lower part which are fastened to one another in a manner pivotable about a pivot axis, a resistance unit which is arranged between the upper part and the lower part and which has an adjustment device to modify the damping resistance, a control unit which is coupled to the adjustment device and which is connected to at least one sensor, wherein the adjustment is carried out using sensor data from the at least one sensor; detecting, during stance phase flexion up until the terminal stance phase, a knee angle using the at least one sensor; increasing the flexion damping to a level above an initial flexion damping to a point of prevention of further flexion when a set maximum knee angle is reached, wherein the flexion damping is held constant during an initial heel strike and the flexion damping is increased in a manner dependent on a load.

2. The method as claimed in claim 1, wherein the flexion damping is held at the point of prevention of further flexion when the maximum knee angle is reached.

3. (canceled)

4. The method as claimed in claim 1, wherein a forward rotation of the lower part about a distal center of rotation is detected and, in the case of a continued forward rotation after the maximum knee angle is reached, the flexion damping is decreased.

5. The method as claimed in claim 1, wherein the flexion damping is decreased after at least one of an overshooting of a set range of a forward rotation and a decreasing knee angle.

6. The method as claimed in claim 4, wherein the flexion damping is decreased to a value greater than or equal to the initial stance phase flexion damping.

7. The method as claimed in claim 1, wherein the flexion damping is decreased after a set maximum knee angle is reached and after a relative forward rotation of the lower part.

8. The method as claimed in claim 1, wherein the maximum knee angle is selected and set from a range between 7° and 12° or from a range between 9° and 11°.

9. The method as claimed in claim 1, wherein the maximum knee angle is defined using statistical evaluations of detected knee angles for walking on a level surface.

10. The method as claimed in claim 1, wherein the maximum knee angle individually set for a respective user of the artificial knee joint.

11. A method to control the stance phase damping of an artificial knee joint, the method comprising: providing an upper part, a lower part, a resistance unit, a control unit, and at least one sensor coupled to the control unit, the upper and lower parts being pivotally connected to each other, the resistance unit having an adjustment device and being operable to modify a damping resistance of the artificial knee joint, and the control unit is coupled to the adjustment device to control adjustments to the damping resistance based on sensor data from the at least one sensor; detecting a knee angle with the at least one sensor during a stance phase flexion up to a terminal stance phase; increasing the flexion damping when a set maximum knee angle is reached to a level above an initial flexion damping to a level that prevents further flexion; holding the flexion damping constant during an initial heel strike; and increasing the flexion damping in a manner dependent on a load.

12. The method as claimed in claim 11, further comprising holding the flexion damping at the level that prevents further flexion when the maximum knee angle is reached.

13. The method as claimed in claim 11, further comprising detecting a forward rotation of the lower part about a distal center of rotation and decreasing the flexion damping after the maximum knee angle is reached during a continued forward rotation.

14. The method as claimed in claim 11, further comprising decreasing the flexion damping after detecting at least one of an overshooting of a set range of a forward rotation and a decreasing knee angle.

15. The method as claimed in claim 14, further comprising decreasing the flexion damping to a value greater than or equal to the initial stance phase flexion damping.

16. The method as claimed in claim 11, further comprising decreasing the flexion damping after reaching a set maximum knee angle and after a relative forward rotation of the lower part.

17. The method as claimed in claim 11, wherein the maximum knee angle is selected and set from a range between 7° and 12° or from a range between 9° and 11°.

18. The method as claimed in claim 11, wherein the maximum knee angle is defined using statistical evaluations of detected knee angles for walking on a level surface.

19. The method as claimed in claim 11, wherein the maximum knee angle is individually set for a respective user of the artificial knee joint.

20. The method as claimed in claim 1, wherein the detecting occurs between heel strike and terminal stance phase at a point when the lower part is fully extended and the knee angle is zero.

21. The method as claimed in claim 11, wherein the detecting occurs between heel strike and terminal stance phase at a point when the lower part is fully extended and the knee angle is zero.

Description

[0023] An exemplary embodiment of the invention will be discussed in more detail below on the basis of the appended figures. In the figures:

[0024] FIG. 1—shows a schematic illustration of a leg prosthesis; and

[0025] FIG. 2—shows an illustration of a control diagram.

[0026] 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.

[0027] 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 device 6 can be varied. If the resistance device 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 device 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.

[0028] 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, 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.

[0029] The entire step cycle from the heel strike 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.

[0030] In FIG. 2, the knee angle α and the flexion damping F.sub.D are plotted versus the time in a diagram. The knee angle α is depicted for two walking situations from the start of the stance phase, that is to say from the heel strike HS, up until the terminal stance phase. The lower curve profile α.sub.P shows the knee angle profile for walking on a level surface, and the upper curve profile α.sub.S shows the knee angle profile for walking down a ramp or stairs, wherein the illustration here relates to the aided leg in the case of alternating walking.

[0031] The normal knee angle profile for walking on a level surface as per curve α.sub.P begins at a fully extended position in the region of the heel strike HS, leads, after the initial ground contact, to an increase of the knee angle α up to a local maximum α.sub.max at the end of the loading response, before then decreasing again during the middle stance phase. The leg is then in an approximately extended position; during the further course of the step, the knee angle α increases again in the region of the terminal stance phase and pre-swing phase.

[0032] The knee angle profile for alternating walking down ramps, as illustrated in curve as, has no decrease at the end of the loading response, with the artificial knee joint rather remaining at a constant value α.sub.max until it is then flexed further earlier than in the case of walking on a level surface.

[0033] To provide reliable damping behavior for the stance phase flexion for both gait patterns, the damping resistance F.sub.D or flexion resistance is initially set to an initial damping level F.sub.DI which permits flexion of the artificial knee joint upon the initial ground contact but dampens and brakes the flexion in order to prevent a collapse of the artificial knee joint. Said initial flexion damping F.sub.DI is initially maintained at a constant level until the knee angle α has reached a threshold value. In the exemplary embodiment illustrated, the threshold value amounts to approximately 30% of the set maximum knee angle α.sub.max that is admissible or considered to be admissible; the increase of the flexion damping F.sub.D begins almost directly after the heel strike. Alternatively, the threshold value may also lie at a greater knee angle, for example at 50% or 70% of the set maximum knee angle α.sub.max that is admissible or considered to be admissible. When the set threshold value for the knee angle α is reached, the flexion damping F.sub.D is increased in order to brake the further flexion of the knee joint and block said flexion when the maximum knee angle α.sub.max is reached. In the illustrated exemplary embodiment, the flexion damping is increased progressively, though it may also be increased degressively or linearly. When the maximum knee angle α.sub.max is reached, the flexion damping F.sub.D is at the maximum flexion damping value F.sub.Dmax, at which further flexion is no longer possible. Said resistance value F.sub.Dmax is held over a set time period ΔT; a plateau D.sub.P of the maximum flexion resistance F.sub.Dmax forms, and no flexion of the artificial knee joint is possible during said time.

[0034] The time period ΔT for which said level F.sub.Dmax is held is detected either by means of a timing switching element or by means of the detection of a forward rotation Δφ of the lower part 2, for example of the lower leg tube 5, or a pivoting movement about the ankle joint of the prosthetic foot 3. If a further forward rotation by the angle φ occurs, which can be detected by means of acceleration sensors, angle sensors and/or inertial angle sensors, the user of the artificial knee joint moves further forward. A possible angle range for a further forward rotation φ can be assumed to be pivot angles of 5° to 10°. After the threshold value for the further forward rotation is reached or the time elapses, the flexion damping F.sub.Dmax is decreased. In the exemplary embodiment illustrated, the decrease is degressive, such that initially a rapid decrease of the flexion damping is effected, for example in order to permit a further flexion when walking down a ramp, as shown by the profile of the curve α.sub.S. Other profiles of the decrease in damping may be set, for example progressively or linearly. In the plateau region with the resistance plateau D.sub.P during the time ΔT, no further flexion movement of the artificial knee joint occurs. Only after the flexion resistance F.sub.D decreases to a level below the maximum flexion resistance F.sub.Dmax, in the illustrated exemplary embodiment above a level of the initial flexion damping F.sub.DI in the region of the decrease curve F.sub.DS, is an increasing flexion made possible.

[0035] The advantage of such control lies in the high level of safety, which is based on an initial knee flexion always limited to the maximum knee angle α.sub.max, without the extent of movement or the functionality during the further movement sequence being restricted here. If the maximum knee angle α.sub.max is reached and the leg rotates further forward without knee extension occurring, as shown in the curve as, the flexion damping F.sub.D is reduced in continuous fashion to a high level of damping, possibly to the initial flexion damping F.sub.DI. Thus, when walking down ramps or stairs, it is ensured, without any loss of safety, that an undisrupted further movement sequence is possible.