METHOD FOR CONTROLLING AN ARTIFICIAL KNEE JOINT

Abstract

A method for controlling an artificial knee joint comprising an upper part and a lower part pivotally connected to each other, a resistance unit arranged between the upper part and the lower part and having an adjusting device to adjust the damping resistance, a control unit, the adjustment taking place on the basis of sensor data from at least one sensor. During the swing phase at least one of the knee angle (KA), the knee angle velocity (KAV), the knee angle acceleration (KAA), the lower limb angle, the lower limb velocity, the lower limb acceleration, the ankle moment (AM) and the axial force (AF) is sensed, the curve of the parameter is determined and the damping resistance is changed when, after an extreme value of the parameter is reached, the monotonic behavior of the curve of the parameter changes within the swing phase.

Claims

1. A method for controlling an artificial knee joint, the method comprising: providing an upper part and a lower part which are pivotally connected to each other 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 vary the damping resistance, a control unit which is coupled to the adjustment device and which is connected to at least one sensor, the adjustment being carried out using sensor data from the at least one sensor; capturing during a swing phase, at least one characteristic from a knee angle, a knee angle velocity, a knee angle acceleration, a below-knee angle, a below-knee velocity, a below-knee acceleration, an ankle moment, and an axial load; determining a profile of the characteristic; varying the damping resistance if, after reaching an extremum of the characteristic, a monotonic behavior of the profile of the characteristic changes within the swing phase.

2. The method as claimed in claim 1, wherein the damping resistance is increased.

3. The method as claimed in claim 2, wherein the damping resistance is increased to a level of the stance phase damping or therebeyond.

4. The method as claimed in claim 1, wherein a maximum is used as an extremum for the below-knee angle, the below-knee velocity, the below-knee acceleration, the knee angle, the knee angle velocity or the knee angle acceleration.

5. The method as claimed in claim 1, wherein the damping resistance in the swing phase is lowered to a level below a swing phase standard resistance if an ankle moment or an axial force are zero or have dropped below a threshold and at least one of the knee angle, the knee angle velocity, and the knee angle acceleration changes in the monotonic behavior after reaching the extremum.

6. The method as claimed in claim 1, wherein a threshold that needs to be exceeded so that the damping resistance is varied is set for the characteristics.

7. The method as claimed in claim 1 wherein a time threshold that needs to be exceeded after reaching the extremum so that the damping resistance is varied is set.

8. The method as claimed in claim 1, wherein the extrema of the characteristics are ascertained in real time.

9. The method as claimed in claim 1, wherein variations of the damping resistance are registered and stored in a memory.

10. The method as claimed in claim 1, wherein changes in the monotonic behavior that occur during the course of an unimpeded swing phase are not taken into account.

11. A method for controlling an artificial knee joint, the method comprising: providing an upper part and a lower part, a damping device, and a control unit, the upper and lower parts being pivotally connected to each other, the resistance unit having an adjustment device to adjust the damping resistance, the control unit being coupled to the adjustment device and at least one sensor and operable to adjust the damping resistance using sensor data from the at least one sensor; capturing, during a swing phase, at least one characteristic from at least one of a knee angle, a knee angle velocity, a knee angle acceleration, a below-knee angle, a below-knee velocity, a below-knee acceleration, an ankle moment, and an axial load; determining a profile of the characteristic; varying the damping resistance if a monotonic behavior of the profile of the characteristic changes within the swing phase after reaching an extremum of the characteristic.

12. The method as claimed in claim 11, wherein varying the damping resistance includes increasing the damping resistance.

13. The method as claimed in claim 12, wherein increasing the damping resistance includes increasing the damping resistance to at least a level of a stance phase damping.

14. The method as claimed in claim 11, wherein a maximum is used as an extremum for the below-knee angle, the below-knee velocity, the below-knee acceleration, the knee angle, the knee angle velocity or the knee angle acceleration.

15. The method as claimed in claim 11, further comprising lowering the damping resistance in the swing phase to a level below a swing phase resistance if an ankle moment or an axial force are zero or have dropped below a threshold and at least one of the knee angle, the knee angle velocity, and the knee angle acceleration changes in the monotonic behavior after reaching the extremum.

16. The method as claimed in claim 11, further comprising setting a threshold to be exceeded so that the damping resistance is varied for the characteristics.

17. The method as claimed in claim 11, further comprising setting a time threshold to be exceeded after reaching the extremum so that the damping resistance is varied.

18. The method as claimed in claim 11, further comprising ascertaining the extrema of the characteristics in real time.

19. The method as claimed in claim 11, further comprising registering variations of the damping resistance and storing the registered variations in a memory.

20. The method as claimed in claim 11, wherein changes in the monotonic behavior that occur during the course of an unimpeded swing phase are not taken into account.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] An exemplary embodiment of the invention will be discussed in more detail below on the basis of the appended figures. In the figures:

[0026] FIG. 1—shows a schematic illustration of a prosthesis,

[0027] FIG. 2—shows a schematic profile of the characteristics;

[0028] FIG. 3—shows a schematic illustration of taking a threshold into account; and

[0029] FIG. 4—is a flow diagram illustrating an example controls steps of the present disclosure.

DETAILED DESCRIPTION

[0030] 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 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.

[0031] 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 within the resistance device 6 can be varied. If the resistance device 6 is formed as a hydraulic damper, it is possible by means of the adjustment device 7 for the respective flow cross section to be increased or decreased in size. This may be realized by opening or closing valves or changing viscosities or magnetorheological properties. 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.

[0032] 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 cover, 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.

[0033] 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.

[0034] In order to control the damping by way of the resistance device 6, it is the knee angle profile and the first and second derivative thereof with respect to time that are monitored in particular. The knee angle KA is plotted in FIG. 2 over time. Likewise, the profile of the knee angle velocity KAV and the knee angle acceleration KAA are illustrated over time in FIG. 2. Moreover, the diagram illustrates the load in the form of an axial force AF and ankle moment AM, which substantially correspond in terms of their profile such that both load variables AF, AM are illustrated using a single curve.

[0035] There is a reduction in the axial load AF and in the ankle moment AM as well within the scope of the terminal stance phase TSt; the knee angle KA, the knee angle velocity KAV and the knee angle acceleration KAA increase after completion of the terminal stance phase TSt. The profile of the knee angle KA is substantially bell-shaped and increases, up to a knee angle maximum, until the end of the swing phase flexion SwF in order then to reduce in the swing phase extension phase SwE, likewise in a substantially bell-shaped manner, until the heel strike HS and to be present upon heel strike HS in the maximally extended position, in which the knee angle KA is assumed to be zero degrees.

[0036] The knee angle velocity KAY has a substantially sinusoidal profile. A comparatively quick rise in the knee angle velocity KAV can be determined at the start of the swing phase, i.e. in the so-called pre-swing phase PSw; after reaching a local maximum, the knee angle velocity drops to zero when a maximum knee angle KA is reached, becomes negative, reaches a relative minimum and then increases again up to the heel strike HS in order to be zero when a maximum extended position is reached.

[0037] The knee angle acceleration KAA reaches its relative maximum at the end of the pre-swing phase PSw before the maximum of the knee angle velocity KAV, it has a first zero crossing when the maximum knee angle velocity KAV is reached, reaches a minimum in the region of the zero crossing of the knee angle velocity KAV and reaches a second relative maximum at the end of the swing phase extension.

[0038] The knee angle profile, knee angle velocity profile and knee angle acceleration profile illustrated thus respectively occur when there is unimpeded walking. A disturbance, for example stumbling, can be assumed if the knee angle KA has reached a local maximum and dropped below it again, and subsequently increases again, as illustrated by the dashed line KA.sub.1 in FIG. 2.

[0039] Furthermore, a disturbance or stumbling can be assumed if, after reaching a local maximum of the knee angle velocity KAY and after a decrease in the knee angle velocity KAV, the latter increases again within the swing phase, as illustrated by the curve profile KAV.sub.2. Likewise, stumbling can be assumed if the knee angle acceleration KAA reduces again after reaching a local maximum and subsequently increases again, as illustrated by the curve profile KAA.sub.3.

[0040] The respective maxima of the curve profiles are determined in real time. In order to be able to tolerate the signal noise or slight movement deviations, thresholds a may be defined for the drop below the respective maxima and the increase in the curve profile or of the sensor signal.

[0041] FIG. 3 schematically illustrates a characteristic profile. The damping setting is not varied for as long as the threshold a is not exceeded, i.e. a deviation within a certain time threshold T is not sufficiently large. If the characteristic profile exceeds a pre-determined threshold a within a predetermined time interval T, the assumption is made on the part of the controller that stumbling is present, for example that the foot catches when walking or impacts on an obstacle with the heel, in order then to undertake a variation in the damping.

[0042] The damping usually is increased; the level of increase can vary but the stance phase damping level is usually set to be higher, although this is not mandatory.

[0043] In order to decide whether a reduction or an increase in the flexion resistance occurs, it is possible to take into account a load on the lower part 2, for example by way of the occurrence of an ankle moment AM. If an axial force AF occurs during a normally occurring time interval during the walking, a termination of the swing phase and, hence, a disturbance in the gait pattern can be expected, and so an increase or decrease in the flexion damping is indicated. If an axial force component occurs in the distal direction, a further swing through of the prosthetic foot may be necessary, and so reduction in the flexion resistance is advantageous and set accordingly.

[0044] In addition to the knee angle KA and the derivatives thereof with respect to time, it is also possible to use the load on the lower part during the swing phase, i.e. an axial force AF or an ankle moment AM, for control purposes. After reaching a minimum after the toe off with an axial force AF or an ankle moment AM of zero, each increase in the axial force AF or in the ankle moment AM within a normally provided time interval until the heel strike HS is identified as a disturbance which leads to a change in the damper settings.