METHOD FOR CONTROLLING A PROSTHETIC FOOT

Abstract

The invention relates to a method for controlling a prosthetic foot (10) which has an upper part (11) with a fastening element (13) for a proximal prosthetic component (20) and a foot part (12) mounted thereon so as to be pivotable about a pivot axis (15), comprising a resistance device (40) used to counteract a pivoting movement of the foot part (12) relative to the upper part (11) by way of an adjustable resistance (Am), and comprising a control device (70) which is coupled to the resistance device (40) and to at least one sensor (60) and by means of which the resistance to pivoting is set on the basis of sensor data, wherein ground contact of the foot part (12) with the ground is determined by way of at least one sensor (60), wherein the relative spatial position of the foot part (12) and/or of the upper part (11) is determined using an inertial measurement unit (30) and wherein the resistance (Am) to pivoting is altered on the basis of the presence or lack of ground contact and the determined relative spatial position and/or the determined route of the relative spatial position.

Claims

1-18. (canceled)

19. A method for controlling a prosthetic foot that comprises an upper part having a fastening element for a proximal prosthesis component and a foot part mounted thereon so as to be pivotable about a pivot axis, having a resistance device with which an adjustable resistance is presented against a pivoting movement of the foot part relative to the upper part, and having a control device which is coupled with the resistance device and with at least one sensor and by means of which the resistance against pivoting is set as a function of sensor data, the method comprising: determining ground contact of the foot part with the ground by means of at least one sensor, determining the spatial attitude of the foot part and/or of the upper part by means of an inertial measurement unit, and modifying the resistance against pivoting as a function of at least one of the presence or absence of ground contact and the spatial attitude that has been determined or the profile that has been determined of the spatial attitude.

20. The method of claim 19, wherein the presence or absence of ground contact is determined by means of a ground reaction force, the ground reaction force being determined by means of at least one force sensor on at least one of the foot part, the upper part, or the proximal prosthesis component.

21. The method of claim 19, wherein the presence or absence of ground contact is determined by means of at least one acceleration sensor on at least one of the foot part, the upper part, or on the proximal prosthesis component.

22. The method of claim 19, further comprising determining at least one of a status of the foot part relative to the upper part or a pivoting movement of the foot part with respect to the upper part, and modifying the resistance against pivoting as a function of at least one of the status or pivoting movement that has been determined.

23. The method of claim 19, wherein the ground reaction force is determined by one or more of at least one contact switch, a deformation of a resilient element, the recording of one or more of a rotational or translational relative position of two components connected flexibly to one another, a pressure measurement film or a strain gauge as the sensor.

24. The method of claim 19, wherein the magnitude of the ground reaction force is measured, and the pivoting resistance is reduced or increased, or pivoting is blocked, when a threshold value of the ground reaction force is reached or exceeded.

25. The method of claim 24, wherein the threshold value is set to between 5% and 50% of the body weight of the patient.

26. The method of claim 19, wherein the angle between the foot part and the upper part or the proximal prosthesis component is measured, and the measured angle or angle profile and the spatial attitude that has been determined of the upper part or of the proximal prosthesis component are used in order to modify the resistance.

27. The method of claim 26, wherein a dorsal movement is enabled or prevented as a function at least one of the measured angle between the upper part and the foot part or a spatial attitude angle.

28. The method of claim 27, wherein the maximum dorsal flexion angle between the upper part and the foot part is adjusted as a function of at least one of the ground surface inclination or heel height.

29. The method of claim 28, wherein the adjustment of a dorsal flexion stop is carried out through a plurality of substeps up to the maximum dorsal flexion angle.

30. The method of claim 26, wherein a further dorsal flexion is prevented when a limit value is reached for an inclination of the upper part or of the proximal prosthesis component, and a further dorsal flexion is prevented when a limit value is reached for the angle between the upper part and the foot part, the criterion occurring earlier being dominant.

31. The method of claim 19, wherein during standing, a dorsal flexion is locked when reaching a defined threshold value of the spatial orientation of the upper part or of the proximal prosthesis component.

32. The method of claim 31, wherein the locking of the dorsal flexion is released in the event of one or more of an increase in a ground reaction force to more than 50% of the patient's weight, a change in a rotation rate of the upper part or occurrence of an angular acceleration of the upper part.

33. The method of claim 19, wherein when walking on a downward sloping ground surface, a dorsal flexion stop is adjusted in the direction of an increased dorsal flexion angle.

34. The method of claim 33, wherein when walking on a downward sloping ground surface, the dorsal flexion stop is increased by from 100% to 500% compared with walking on the flat.

35. The method of claim 19, wherein the foot part is moved back into an initial status in a swing phase.

36. The method of claim 19, wherein the resistance of the resistance device is set to a minimum value in the event of a vertical orientation of the upper part.

Description

[0023] Exemplary embodiments of the invention will be explained in more detail below with the aid of the figures, in which:

[0024] FIG. 1—shows a side view of a prosthetic foot with proximal components;

[0025] FIGS. 2 to 4—show schematic representations of prostheses with prosthetic feet;

[0026] FIG. 5—shows a control example;

[0027] FIG. 6—shows an anklebone angle profile when walking on an incline;

[0028] FIG. 7—shows a schematic representation of a walking situation; and

[0029] FIGS. 8 and 9—show resistance profiles as a function of the lower leg angle.

[0030] FIG. 1 represents a side view of a prosthetic foot 10 having an upper part 11 and a foot part 12, which are coupled with one another so as to be pivotable about a pivot axis 15. A fastening element 13 in the form of a pyramid adapter is arranged at the proximal end of the upper part 11. By means of the fastening element 13, it is possible to fasten proximal prosthesis components 20, for example a lower leg tube or a lower leg part having a prosthetic knee joint and an integrated damper, releasably onto the prosthetic foot 10. In the exemplary embodiment represented, the prosthetic foot 10 has precisely one pivot axis 15 in order to form an ankle joint. A sensor 60, which detects ground contact of the foot part 12, is arranged on the lower side of the foot part 12. The sensor 60 may be formed as an electrical contact element, as a pressure sensor, as a strain gauge or another configuration of a force sensor. In the exemplary embodiment represented, the ground contact sensor 60 is arranged in the forefoot region of the foot part 12. Alternatively or in addition, a ground contact sensor may also be arranged in the heel region or metatarsal region. Ground contact may also be determined by means of other sensors 60, for example by means of an axial force sensor which is arranged on the upper part 11 or on the fastening element 13. Likewise, a corresponding sensor device 60 may be arranged on the proximal prosthesis component 20, for example as a strain gauge or pressure sensor at a connecting point on the lower leg tube, on the lower leg part and/or on a knee part.

[0031] Arranged inside the prosthetic foot 10, there is furthermore a resistance device 40 with which it is possible to apply an adjustable resistance to plantar flexion or dorsal flexion. The resistance device 40 may be formed as a hydraulic damper, a damper on the basis of a magnetorheological liquid, as a mechanical brake or as a motor correspondingly operated in generator operation. In order to set the resistance device 40 based on sensor data and data of an inertial measurement unit 30 (IMU), the sensors or sensing devices 30, 60 are coupled with a control device 70, for example by means of a cable connection or wirelessly by means of a radio connection, in order to adjust or set the resistance against pivoting in one or the other direction about the pivot axis 15 as a function of the sensor data.

[0032] FIG. 2 shows a schematic representation of the prosthetic device with the prosthetic foot 10, the proximal prosthesis component 20 in the form of a lower leg socket, as well as the inertial angle sensor 30 or IMU fastened on the lower leg tube. The prosthetic foot 10 is mounted on the lower leg socket 20 so as to be pivotable by means of a joint about the axis 15. The upper part 11 and the fastening element 13 are not indicated for reasons of clarity. The IMU 30 is fixed either permanently or removably on the lower leg tube. A control device 70, which is coupled with the ground contact sensor 60, with the IMU 30 and with the resistance device 40, is furthermore arranged on the lower leg socket 20. The arrangement of the inertial angle sensor 30 or IMU may be carried out in a way that is integrated into or releasably fastened on a part, which is connected to the lower leg tube and the lower leg socket 20, of the prosthetic foot 10. It is likewise possible to arrange the sensor 60 not on the heel but on a metatarsal region, on the upper part or on the joint. Alternatively, a plurality of sensors 60 are arranged on the foot part 12.

[0033] FIG. 3 schematically represents a further prosthetic device, in which a second proximal prosthesis component 50 is arranged on the lower leg part 20. The second proximal prosthesis component 50 is, for example, an upper leg socket having a tube connecting to a prosthetic knee joint 25. In the exemplary embodiment represented, the IMU 30 is again arranged on the lower leg tube 20, although the inertial angle sensor 30 and optionally also the control device 40 may alternatively be integrated or releasably fastened on the knee joint 25 or on the upper leg socket 50 or on a connecting part between the upper leg socket 50 and the knee joint 25. Likewise, the IMU 30 may be arranged on an upper part of a prosthetic knee joint. In conjunction with an angle sensor, which records the angle between the lower leg part 20 and the proximal component 50, the spatial attitude of the lower leg part 20 may be detected from the spatial attitude of the second proximal component 50. Load, acceleration and/or angle sensors 60, which are arranged on the foot part 12 and on the ankle joint in the region of the pivot axis 15, are furthermore provided in the exemplary embodiment of FIG. 3. The load sensors 60 are for example axial force sensors, pressure sensors, for example in the form of contact switches, pressure measurement films and/or a strain gauge and/or torque sensors, in order to measure the respective load on the prosthetic device. The sensors 30, 60 are coupled with the control device 70 (not represented).

[0034] In FIG. 4, the control device 40 is formed disconnected and spatially separated from the inertial angle sensor 30 and is coupled with the prosthetic foot 10 by means of a wireless connection. The data transmission from the sensing devices to the control device 40 may take place by means of radio, WLAN, Bluetooth®, NFC or other transmission means.

[0035] With the sensors 60 and the IMU 30 the resistance against pivoting can be controlled precisely. The one sensor 30 determines the ground contact of the foot part 12 and therefore ensures that the prosthetic foot 10 is in the standing phase. At the same time, the spatial attitude of the foot part 12 and/or of the upper part 11 is determined by means of the IMU 30. If ground contact of the foot part 12 is detected, for example by a pressure sensor 60 fastened on the sole, the simultaneously determined spatial attitude of the foot part 12 and/or of the upper part 11 is recorded and used in order to control the resistance. This leads to superimposed control based on the spatial attitude of the foot part 12 and/or of the upper part 11 in conjunction with the detection of the standing phase, so that an increased reliability can be achieved during the setting of the respective resistance. This increased reliability is obtained particularly in situation transitions, that is to say when there are variations of the ground surface, for example when the ground surface inclination changes, or when the step rhythm varies, for example when changing from walking on the flat to climbing stairs or from walking on a ramp to walking on the flat or climbing stairs. In this case, the status of the upper part 11 relative to the foot part 12 may in particular also be taken into consideration as a further influencing quantity and sensor value. For this purpose, an ankle joint angle needs to be determined, for example by means of an angle sensor 60 directly on the pivot axis 15 or by means of the IMU 30 on the foot part 12 and on the upper part 11, or on a proximal prosthesis component 20 fastened thereto.

[0036] If for example, in the absence of ground contact of the foot part 12, which is determined via the ground reaction force by means of a force sensor on the foot part 12, on the upper part 11 and/or on the proximal prosthesis component 20, a spatial attitude change is detected by means of an IMU 30, whether it is a change in the spatial attitude of the proximal prosthesis component 20 or of the upper part 11 or of the foot part 12, this means for the control that a different resistance than in the standing phase is set in the resistance device 40 in a swing phase, which the prosthetic foot evidently is in. While in the event of a spatial attitude change, for example of the foot part 12, when there is a standing phase, it may be deduced that a rolling movement of the prosthetic foot has taken place and a terminal standing phase is assumed, in which the dorsal flexion is intended to be prevented and an increased dorsal flexion resistance must therefore be provided, for the same displacement of the foot part 11 in space during the swing phase a dorsal flexion may be desired in order to permit free swinging of the prosthetic foot, so that the dorsal flexion resistance is in this case reduced and an actuator is optionally activated in order to permit dorsal flexion of the foot part 12. The actuator may, for example, be formed as a passive energy storage unit which is unlocked in the swing phase so that resetting takes place at least into a neutral attitude. Alternatively, the actuator is an active drive or motor which moves the foot part back into its initial position.

[0037] The absence of ground contact may, alternatively or in addition, be determined by means of an acceleration sensor 60 on the foot part 12, on the upper part 11 and/or on the proximal prosthesis component 20. For example, if no acceleration of one of the two components takes place despite a load relaxation of the foot part 12 or of the upper part 11, a static state may be deduced, for example the existence of a standing phase. In the event of a pure vertical acceleration without a horizontal proportion, lifting of the prosthetic foot without a forward movement may be deduced, for example in order to step over an obstacle or in order to climb stairs. Based on the acceleration data of the acceleration sensor 60, it is possible to deduce either independently or in conjunction with a force sensor whether there is ground contact and which phase of the movement the respective prosthetic foot is in, if movement is identified.

[0038] Besides the absolute attitudes and the accelerations, it is likewise provided that the status of the foot part 12 relative to the upper part 11 and/or a pivoting movement of the foot part 12 relative to the upper part 11 is determined. The status may be determined by means of an angle sensor 60, and the pivoting movement is detected by means of the time derivative of the angle sensor data or by means of an acceleration sensor. The adjustment movement and the status of the foot part 12 relative to the upper part 11, and therefore also relative to the proximal prosthesis component 20 which is generally coupled rigidly on the upper part 11, also contributes to the reliability of the control.

[0039] FIG. 5 shows an example of a control based on the spatial attitude of the prosthetic foot, or of its components, and the angle between the foot part 12 and the upper part 11. Pure regulation by means of the anklebone angle, that is to say the status of the foot part 12 relative to the upper part 11, is represented in the lower curve with the broken line AA. Regulation only from the spatial attitude is represented in the broken line SP, and the total regulation is the solid line CC in the upper profile. Depending on the situation identified, a setpoint anklebone angle and a setpoint orientation of the upper part 11, or of the lower leg part 20, were respectively specified. A full match of the respective actual value with the setpoint angle gives the value 1, so that no adjustment is necessary, but depending on the degree of discrepancy the value changes and therefore so does the necessary adjustment of the resistance device. If the control were for example carried out only based on the spatial attitude curve SP, for a value of 0.4 a relatively small adjustment of the resistance value to approximately 0.8 would be necessary, while with unique control based on the anklebone angle and the curve AA an adjustment to 0.95 would be necessary. Conversely, for a value of 0.8 with unique control by means of the ankle joint angle and the curve AA, adjustment to 0.2 would be necessary, while with regulation by means of the spatial attitude based on the curve SP an adjustment to 0.35 would take place. For the respective control of the resistance device 40, the safer output value is set in each case, so that the upper curve CC which is represented by the solid line is obtained. Particularly during transitions from inclined ground surfaces to climbing stairs or in other transition situations, for example from walking on the flat to walking on a ramp, such a combination of the control of the resistance device 40 based on spatial attitude angles and relative angle values is particularly advantageous.

[0040] FIG. 6 represents the ankle joint angle, that is to say the angle between the foot part 12 and the upper part 11 over the course of a plurality of steps. Starting from an initial position, which is denoted by “0”, during normal walking on the flat a more or less uniform amplitude is executed above and below an initial status. Positive values indicate plantar flexion and negative values indicate dorsal flexion. The transition from walking on the flat to walking upward on a ramp takes place at the value of approximately 6900. The upper part needs to be displaced further in the direction of the foot part when walking uphill on a ramp, so that an increased dorsal flexion takes place. This is kept almost unchanged for walking on the ramp until, at 7500, a level place is reached once again and the resistance device can adapt again to walking on the flat.

[0041] The adjustment of the resistance device 40 may also be used to adjust the initial value for an adjustment around an initial attitude. By the shift of the zero point, around which the control of the resistance of the prosthetic device is carried out, adaptation may for example be carried out to different inclination angles in the ground surface or to different heel heights. Both for plantar flexion and for dorsal flexion, stops at which the resistance device 40 has and occupies a maximum value may be set in order to prevent further flexion. Thus, when reaching a limit value for an inclination of the upper part 11 or of the proximal prosthesis component 20 adjacent thereto, a further dorsal flexion can be prevented. The limit value for the inclination is in this case determined by means of the IMU 30 or from a combination of the spatial attitude values of the foot part and of an anklebone angle. Corresponding locking of the dorsal flexion may also be achieved when reaching a maximum dorsal flexion angle, the criterion respectively occurring earlier, that is to say the maximum spatial attitude or the maximum dorsal flexion angle, being the deciding factor for when locking is achieved.

[0042] FIG. 7 shows a schematic representation of the prosthetic foot having the foot part 12, which is mounted in an articulated fashion on the proximal prosthesis component 20. The foot part 12 is placed on a downwardly inclined plane. If the user of the prosthetic device is not in movement but is standing, dorsal flexion locking of the dorsal flexion may take place, for example with fixed vertical positioning, despite the usual initial status of the foot part 12 relative to the upper part 11 not being reached. If a variation of the heel height or a varying ground surface inclination is ascertained, for example because of significant discrepancies of the movement patterns and the angle profiles, as explained with the aid of FIG. 6, the adaptation and displacement of the zero status, around which dorsal flexion and plantar flexion take place, may be carried out stepwise so that an adaptation to a modified ground surface inclination takes place successively and the change amplitudes are not so great. If walking on an inclined ground surface is identified, the dorsal flexion may be adjusted accordingly. When walking on a downward ground surface, as represented in FIG. 7, the dorsal flexion stop may be adjusted in the direction of a reduced dorsal flexion angle, while with an opposite movement, that is to say uphill, the dorsal flexion stop may be adjusted in the direction of an increased dorsal flexion angle in order to accommodate the movement sequence according to FIG. 6.

[0043] The foot part 12 may in each case be moved back in the swing phase into an initial status, which forms the so-called zero attitude, around which dorsal flexion and plantar flexion are carried out with the corresponding resistance profile.

[0044] FIG. 8 represents a schematic representation of a resistance profile or of an ankle moment Am as a function of the lower leg angle LLa. The lower leg angle LLa corresponds substantially to the orientation of the upper part 11 of the prosthetic foot, since a proximal component such as a lower leg tube or the lower part of a prosthetic knee joint constitutes a rectilinear extension of the upper part. For a lower leg angle of 0°, the upper part and the lower leg part are in an initial status or vertical status, negative values corresponding to a plantar flexion of the foot part and positive values corresponding to a dorsal flexion.

[0045] The resistance or the ankle moment Am, which provides a resistance against displacement of the foot part relative to the upper part or the lower leg, is plotted as a function of the lower leg angle LLa. FIG. 8 represents the ascending of a ramp. After the heel strike and a relatively large plantar flexion, the foot part moves in the direction of an initial position, or a zero status, the ankle moment initially increasing and then decreasing when approaching the initial status, until it reaches a minimum value when reaching the initial status and a vertical orientation of the upper part. A minimum value may also be reached several times during a step cycle. In the event of an increasing dorsal flexion, the ankle moment and the resistance Am are increased until a maximum resistance value is reached for a lower leg angle of about 20 to 30° with respect to the vertical. Subsequently, the ankle moment decreases with increasing dorsal flexion.

[0046] FIG. 9 represents the resistance profile Am as a function of the lower leg angle when walking up a ramp. When walking up a ramp, no plantar flexion is generally to be expected, so that planting the foot on a rising ground surface starting from a normal status leads to dorsal flexion. Starting from this, an increase in the resistance Am or in the ankle moment takes place substantially more rapidly in comparison with walking down a ramp, so that the maximum value occurs in a range of between 10° and 20° dorsal flexions of the foot part. With an increasing dorsal flexion, the resistance Am is reduced until a maximum end stop is reached.