METHOD FOR CONTROLLING A PROSTHETIC FOOT

Description

[0001] The invention relates to a method for controlling a prosthetic foot having a foot part and a lower leg part connected to each other by means of a joint allowing plantar flexion and dorsal flexion, the joint having adjustable damping.

[0002] Such prosthetic feet have long been known in the art. The joint that connects the foot section to the lower leg section forms the ankle joint of the prosthetic foot. This is usually a pivot joint that allows the foot section to pivot relative to the lower leg section around a single pivot axis. However, multi-axis pivot joints or other arrangements are also possible. In prosthetic feet of the type described here, the joint allows plantar flexion and dorsiflexion. Dorsiflexion describes a pivoting of the foot section around the pivot axis of the joint, during which the forefoot area, especially the toes, are moved upward, i.e., toward the lower leg. Plantar flexion is the opposite movement.

[0003] The joint is a damped joint. Consequently, a force or torque must be exerted to overcome the damping of the joint and achieve pivoting of the foot section relative to the lower leg section. Such modifications are known in a wide variety of forms from the prior art. With hydraulic damping, for example, when the foot section pivots relative to the lower leg section, hydraulic fluid is forced from a first cylinder into a second cylinder. This occurs via a fluid connection that contains, for example, a throttle valve. This valve can be adjusted, resulting in a faster or slower flow through the fluid connection. This makes it easier or more difficult to pivot the two components connected by the joint relative to one another. This adjusts the damping.

[0004] The joints described here preferably do not have a drive that could, for example, pivot the foot section relative to the lower leg section. These joints are called passive joints. A powered, or active, joint is known from US Pat. No. 10,314,723 B2. In this joint, the drive is used to move the position of the various components of the prosthesis in order to achieve the desired force application point. This must be repeated with each step, even under constant conditions, such as the movement state of the prosthesis wearer or the surface over which the wearer walks. This makes the process very energy-intensive and only applicable to active prostheses.

[0005] DE 603 ​​09 685 T2, which discloses the preamble of claim 1, and US 2002 / 0138153 A1 describe damped joints of orthopedic devices that feature a magnetorheological damping system. DE 20 2016 107 294 U1, on the other hand, describes a hydraulic system.

[0006] In a prosthetic foot of the type described here, the lower leg section can be very short. In this case, it includes, in particular, a connecting piece, for example, a pyramid adapter, to which a lower leg tube or another form of artificial lower leg can be arranged. Alternatively, the lower leg section can also be longer and formed integrally with the lower leg tube or at least part of a lower leg tube. At the end of this lower leg facing away from the joint, there is then another connecting piece, for example, a pyramid adapter, to which another prosthetic element, for example, a lower leg tube or a prosthetic knee joint, can be arranged.

[0007] It has been shown to be advantageous to adjust the cushioning if, for example, the wearer of the prosthetic foot changes shoes. With a hard shoe, for example one with a firm leather sole, less cushioning of the joint of the prosthetic foot is necessary than with a very soft shoe, such as a running shoe, a sports shoe or a slipper. Therefore, prosthetic feet are known from the prior art that have an adjustment device through which the wearer of the prosthetic foot can independently adjust the degree of cushioning of the prosthetic foot. The disadvantage, however, is that the wearer can only adjust the degree of cushioning according to their own feeling and perception, and the set cushioning cannot be reproduced for different shoes. In particular, it is not possible to save the different cushioning levels for different shoes.

[0008] There are also known prosthetic feet that use sensors to determine whether the wearer is walking uphill or downhill. In this case, the cushioning can be automatically adjusted, with the cushioning being increased in the direction of dorsiflexion on the downhill path and in the direction of plantarflexion on the uphill path. The disadvantage, however, is that this is not possible for different shoes.

[0009] An alternative embodiment known from the prior art provides for a damping element that cushions the joint to be replaced when the user of the prosthetic foot changes shoes. This is complex and requires the user to carry the necessary damping elements with them.

[0010] The invention is therefore based on the object of proposing a method for controlling the prosthetic foot, in which it is possible to react to different shoes with possibly different heel heights as well as to different movement states, without the wearer of the prosthetic foot having to replace components or make adjustments independently.

[0011] The invention solves the problem by a method for controlling a prosthetic foot of the type described above, which comprises the following steps: a) Recording measured values ​​that allow statements about the rollover behavior of the prosthetic foot by means of at least one sensor, b) comparing the recorded measured values ​​and / or at least one parameter determined therefrom with stored target values ​​and c) adjusting the damping depending on the comparison, wherein the measured values ​​are recorded several times during a step cycle, wherein preferably a course of the measured values ​​over at least part of the step cycle, preferably the entire step cycle, is compared with a course of the stored target values.

[0012] The rollover behavior of a prosthetic foot describes how the parameters of the prosthetic foot, which describe its movement, behave during the rollover, i.e., during the stance phase of a gait cycle in which the prosthetic foot is in contact with the ground. These parameters can be directly measurable variables, such as torque, force, or angle. Alternatively or additionally, these parameters can also be determined from the measured variables.

[0013] The invention is based on the finding that a healthy foot adapts its own rollover behavior very quickly so that the rollover behavior of the foot-shoe system remains virtually constant. The foot compensates for the different rollover behaviors caused, for example, by shoes and soles of varying hardness and flexibility. It is therefore unnecessary to store a multitude of different target values ​​for the same measured value or parameter in order to provide suitable target values ​​for each shoe, each heel height, and each movement pattern. Rather, the target values ​​can be used almost universally for all shoes and heel heights, and at least partially for different movement patterns.Of course, it is important to ensure that the selected measured values ​​recorded by the at least one sensor and / or the at least one parameter determined from them are comparable with the stored target values. The target values ​​are therefore target values ​​for the respective measured values ​​and / or the at least one parameter determined from them.

[0014] According to the invention, such measured values ​​that allow conclusions about this rollover behavior are recorded using at least one measured value. They are then compared, for example, with target values ​​for these recorded measured values. Alternatively or additionally, one or more parameters are determined from the measured values, which are then compared with the target values ​​for this at least one parameter. The damping is adjusted depending on the comparison. Depending on the result of the comparison, a strong adjustment, a weak adjustment, or no adjustment can be made.

[0015] Preferably, the damping is only adjusted if the measured values ​​and / or the at least one parameter determined therefrom exceed a predetermined distance from the target values.

[0016] During the comparison, a distance between the measured values ​​and / or the at least one parameter and this target value is determined. This can be, for example, a difference, a ratio, a standard deviation, or another deviation. A predetermined limit value, the so-called predetermined distance, is previously determined and also stored. The determined distance, which was determined during the comparison between the measured value and / or parameter and the target value, is then compared with the predetermined distance. If the determined distance is greater, the damping can be adjusted; for example, the sign of the distance determines whether the damping needs to be increased or decreased.

[0017] According to the invention, the measured values ​​are recorded multiple times during the step cycle. Since they are intended to provide information about the rollover behavior, i.e. the behavior of parameters or measured variables of the prosthetic foot over the course of at least part of a step cycle, preferably over the stance phase, particularly preferably over the entire step cycle, it is advantageous to determine the temporal course of the measured values ​​over at least part of the step cycle, preferably the stance phase, particularly preferably the entire step cycle. If the measured values ​​themselves cannot be compared with target values, the respective at least one parameter and / or its temporal course must be determined from the measured values ​​and / or the temporal course of the measured values. It can be advantageous to first determine the temporal course of the measured values ​​and then directly determine the temporal course of the parameter from this.Alternatively, it may be advantageous to determine at least one parameter from the respective measured value at each measurement time and then to determine the temporal course of the parameter.

[0018] Preferably, plantar damping, i.e., the damping that counteracts plantar flexion, is adjusted. The course of plantar flexion is preferably adjusted via the ankle angle and / or the lower leg angle. The ankle angle is the angle between the lower leg and the foot. The lower leg angle is the absolute angle of the lower leg, for example, the angle between the lower leg and the vertical. The vertical is the direction in which the Earth's gravitational field acts. The course is preferably adjusted at the beginning of heel strike, particularly before the beginning of heel strike. Further adjustment during the stride is preferably not made.

[0019] In one embodiment of the method, the adjusted damping is present during heel strike, the so-called heel strike. Since this is the first part of the stance phase in a step cycle, the measured values ​​and / or the at least one parameter determined therefrom from the previous step are used. Preferably, the damping is not changed or adjusted again during the remainder of the stance phase or is controlled and adjusted based on the measured values ​​and / or the at least one parameter determined therefrom from the previous step. This reduces the required computing effort and allows the method to be carried out in an energy-saving manner. In some embodiments of the method, it is advantageous if further adjustments are made during a step. This can be done, for example, in real-time control.

[0020] The measured values ​​preferably include a vertical force and a torque at the joint, whereby a force introduction point, and particularly preferably a temporal progression of the force introduction point, is determined from the measured values. In the stance phase of a step cycle, the prosthetic foot is in contact with the ground. This begins with heel strike. From this moment on, the load on the foot initially increases and with it a vertical force. A vertical force acts in the same direction as the weight force. At the same time, a torque acts on the joint of the prosthetic foot, and the foot performs plantar flexion. The contact area with the ground increases until the moment the foot rests fully on the ground. This results in dorsiflexion, while the lower leg is pivoted relative to the foot. The upper body moves further forward.Even if the foot is fully in contact with the floor during this period, the point of force application continues to move forward. The vertical force remains constant because the foot is fully loaded and the other foot is in the swing phase, during which it has no contact with the ground. A torque acts on the joint, causing dorsiflexion. At the end of a stance phase, the foot pushes the body forward, increasing the vertical force and exerting a torque on the joint, causing plantar flexion again. This process is almost independent of the choice of footwear and the direction of movement, for example uphill or downhill on an incline or along a flat surface. However, the strength of the torque and the vertical force, and in particular the speed at which the point of force application moves forward, depend heavily on these parameters.In order to ensure a natural-looking movement for the wearer of the prosthetic foot, the cushioning is adjusted accordingly.

[0021] Alternatively or additionally, the force application point and / or its temporal progression is measured directly, and the measured values ​​include it. This can be achieved, for example, if the at least one sensor has a plurality of pressure sensors arranged on a sole of the foot part. Particularly preferably, this is a pressure-sensitive layer arranged on the sole of the foot part. The plurality of pressure sensors or the pressure-sensitive layer is capable of determining the acting pressure, and thus the vertical force, at different positions on the sole of the foot part. Since this occurs in a distribution across the sole of the foot part, the force application point does not need to be laboriously determined from the measured values, but can be read almost directly from the measured values.If this happens several times during a gait cycle, the temporal progression, i.e. the position of the force application point as a function of time, can be determined and stored.

[0022] Regardless of how the force application point or the temporal progression of the force application point is determined, it is advantageous to approximate the temporal progression of the force application point using a circular segment with a center point and a radius. This center point and radius are preferably compared with corresponding stored target values ​​for the center point and radius. Approximating the temporal progression of the force application point using a circular segment can be achieved using almost all known fitting methods in which measured values ​​are fitted to a curve.

[0023] Conventionally, the distance between the force application point and the ankle joint's rotation axis is approximately 0 to 7 cm in the heel area. In the forefoot area, it is between 0 and 15 cm. The shin angle, i.e., the absolute angle of the shin relative to the vertical, varies between -30° and +40°, with 0° representing the vertical. Assuming a segment of a circle for the optimal course of the force application point, the resulting radius is approximately 0.5 m.

[0024] Alternatively or additionally, the measured values ​​include a lower leg angle and a foot angle, preferably their temporal progression. Particularly preferably, a ratio of the lower leg angle and the foot angle and / or its temporal progression is determined. In this embodiment, too, the invention is based on the finding that, for example, the ratio of the lower leg angle and the foot angle during the stance phase of the gait cycle is almost independent of the choice of footwear and its heel height. The foot angle and the lower leg angle can be determined, for example, using so-called inertial sensors, which are able to determine the angle relative to the vertical or the horizontal. The vertical is the direction in which gravity and the force of weight act, while the horizontal is perpendicular to the vertical.For example, if the ratio of lower leg angle to foot angle changes too quickly, the damping can be increased to slow down a change in the foot angle, which is essentially caused by pivoting the foot part relative to the lower leg part.

[0025] Preferably, the comparison and, if necessary, the adjustment of the damping is carried out multiple times, preferably equidistantly in time, during a portion of a step cycle, preferably over the entire step cycle. Consequently, the comparison between the measured data and / or the at least one parameter determined from them and the stored target values ​​is carried out at multiple points in time, particularly during the stance phase. Whenever the difference between the measured values ​​and / or the determined parameter and the stored target values ​​during this comparison is greater than a predetermined distance, the damping is adjusted. This can also be done multiple times during a step cycle, if necessary, preferably multiple times during the stance phase.

[0026] The damping is preferably hydraulic and / or magnetorheological damping. Both have the advantage that they can be adjusted very quickly, as few moving parts are required to adjust the damping, or in the case of magnetorheological damping, no moving parts at all. Hydraulic damping can be the embodiment already described, in which a hydraulic fluid is moved from one volume to another when the foot section is pivoted relative to the lower leg section. This is done via a fluid line or fluid connection that contains, for example, a throttle valve. If the damping is to be increased, the throttle valve is closed further, so that the flow resistance in the fluid connection is increased. If damping is to be decreased, the valve is opened further, so that the flow resistance is reduced.

[0027] Magnetorheological damping uses a fluid or working medium whose flowability, viscosity, and / or elasticity can be influenced by a magnetic field. If, for example, damping is to be increased, a magnetic field to which the magnetorheological fluid is exposed is intensified. This reduces the viscosity and thus increases the flow resistance to which the fluid opposes.

[0028] Preferably, the foot part has at least one spring element whose spring stiffness is adjusted when the measured values ​​exceed a predetermined distance from the target values. This is a second possibility for modifying the rollover behavior of the prosthetic foot and adapting it to the desired behavior.

[0029] The invention further achieves the stated object by a prosthetic foot with a foot part and a lower leg part, which are connected to one another by a joint that allows plantar flexion and dorsiflexion, wherein the joint features adjustable damping. The prosthetic foot is characterized in that it has an electronic data processing device configured to carry out a method described here. Preferably, the prosthetic foot has an electronic data memory in which the target values ​​are stored. Measurement values ​​are recorded by at least one sensor, which may or may not be part of the prosthetic foot, and transmitted to the electronic data processing device.This compares the measured values ​​either with target values ​​stored in the electronic data memory or determines the temporal course of the measured values ​​or at least one parameter or its temporal course from the measured values.

[0030] Some embodiments of the present invention are explained in more detail below with the aid of the accompanying figures. Figures 1 to 3 - schematic representations of process sequences according to different embodiments of the present invention and Figure 4 - the course of an exemplary measured value.

[0031] Figure 1 shows a simple procedure. First, in a definition step 2, initial damping values ​​are determined for the damping of the prosthetic foot joint. These initial damping values ​​are used to perform at least the first step taken by the prosthetic foot.

[0032] In a recording step 4, the measured values ​​are recorded using at least one sensor arranged on the prosthetic foot or an element attached thereto. These measured values ​​relate, for example, to the course of a force introduction point as a function of the lower leg angle and / or the ankle angle. To determine the course, the position of the force introduction point must be recorded several times in succession over at least a portion of the stride. Preferably, the measurement begins at heel strike, and the measurements preferably extend over the entire plantar flexion phase of the stride.

[0033] In a comparison step 6, the measured curve of the force application point is compared with a target curve. A gap between the measured curve and the target curve is determined, and the deviation is quantified.

[0034] Based on this distance, the damping is adjusted in an adjustment step 8, preferably before the next step begins. The next acquisition step 4 is then performed in the next step, and the respective measured values—in this case, the curve of the force application point—are recorded again.

[0035] Figure 2 shows a similar procedure. Here, too, initial damping values ​​for the joint of the prosthetic foot are determined in determination step 2. Subsequently, the measured values ​​are recorded in acquisition step 4. These are compared with the corresponding target data in comparison step 6. Unlike in Figure 1In the embodiment shown, an additional test step 10 checks whether the deviation determined in comparison step 6, i.e., the distance between the measured values / or the at least one parameter determined therefrom and the stored target values, exceeds a predetermined limit. If this is not the case, no adjustment of the damping is made along the "No" path 12. The deviation is too small. Instead, a detection step 4 is performed again in the next step, which the wearer performs with the prosthetic foot.

[0036] If, however, the determined distance is greater than the predetermined limit, the system proceeds along the "Yes" path 14 to adjustment step 8, so that the damping of the joint is adjusted.

[0037] Figure 3shows a more detailed description of the process. The definition step 2 has been omitted for clarity. In acquisition step 4, measured values ​​are recorded, which are, for example, sensor data. Figure 3 Two acquisition steps 4 are shown, which do not necessarily have to be performed both times. They describe different procedures that can be performed alternatively or in addition to each other. The measured values ​​acquired from the lower acquisition step 4 are recorded in a recording step 16 over at least part of the stance phase of the step, but preferably over the entire stance phase of the step.

[0038] The measured values ​​resulting from the upper acquisition step 4 are converted in a conversion step 18 into at least one parameter based on the measured values. In the next method step, the parameter thus determined is then recorded over at least part of the stance phase of the step, but preferably over the entire stance phase of the step. This also constitutes a recording step 16.

[0039] Following this recording step 16, the determined and recorded parameter can be directly compared in comparison step 6 with target values ​​provided as reference values ​​from an electronic data storage device 20, which is shown only schematically. Subsequently, in adjustment step 8, the damping is adjusted based on this comparison. Alternatively, in a second conversion step 22, a further parameter can be created from the curve of the characteristic value or the previously calculated parameter. If this is the case, this curve of the characteristic value or parameter is then compared in comparison step 6, and the damping is adjusted based on this comparison in adjustment step 8.

[0040] In a preferred embodiment of the method, the measured values ​​acquired in the lower acquisition step 4, which were recorded in the lower recording step 16, are processed together with the parameters determined in the second conversion step 22, for example, by creating a phase diagram 24. This can then also be compared with target values ​​from the electronic data storage 20 in the comparison step 6.

[0041] Figure 4shows a schematic diagram of a measured value. The position of the force introduction point is plotted on the vertical Y-axis and the foot angle, i.e. the angle between the foot part and the ground on which the wearer of the prosthesis walks, is plotted on the horizontal X-axis. A target curve 26 shows the desired course. During a step, the course begins in the lower left quadrant. The force introduction point (COP) is in the heel area and begins at heel strike. This is represented by the first pictogram 28. If you follow the target curve as the foot angle increases, you can see that the force introduction point initially remains at the heel before moving upwards in the diagram shown, i.e. towards the forefoot.

[0042] The origin of the diagram represents the point at which the foot rests fully on the ground and the lower leg swings over the foot. This is schematically represented by the second pictogram 30. As the foot angle increases, the force application point continues to move toward the forefoot before remaining in the area of ​​the toes until they release from the ground. This situation is illustrated in the third pictogram 32.

[0043] Different measured curves are represented by the thin, solid line 34 and the dashed line 36. In line 34, the force application point moves away from the heel of the foot earlier than in the target curve, meaning the foot does not plantarflex sufficiently. A heel lever, represented by the double arrow 38, is reduced. To correct this deviation from the target curve, the damping is reduced, i.e., the resistance opposing movement is reduced. This allows line 34 to be moved toward the target curve. The foot now plantarflexes more quickly.

[0044] The dashed line 36 deviates from the target curve in the other direction. Here, the cushioning is too soft, causing the foot to plantar flex too quickly. Therefore, the force application point initially doesn't move with increasing foot angle. It only moves from the heel toward the forefoot when the foot angle is larger than desired. In this case, the cushioning should be increased. List of reference symbols:

[0045] 2Determination step 4Capture step 6Comparison step 8Adjustment step 10Test step 12"No" path 14"Yes" path 16Recording step 18Conversion step 20Electronic data storage 22Second conversion step 24Phase diagram 26Target curve 28First pictogram 30Second pictogram 32Third pictogram 34Solid line 36Dashed line 38Heel lever

Claims

1. A method for controlling a prosthetic foot that has a foot part and a lower leg part which are connected to each other by means of a joint that allows a plantar flexion and a dorsal flexion, the damping behavior of the joint being adjustable, wherein the method comprises the following steps: a) detecting measured values which allow for statements to be made about the rollover behavior of the prosthetic foot by means of at least one sensor, characterized in that b) comparing the detected measured values and / or at least one parameter determined from said values with stored target values, and c) adjusting the damping behavior depending on the comparison, wherein the measured values are detected multiple times during a step cycle, wherein a course of the measured values across at least one part of the step cycle is compared with a course of the stored target values.

2. The method according to claim 1, characterized in that the damping behavior is only adjusted when the difference between measured values and / or the at least one parameter determined from said values and the target values exceed a predetermined gap.

3. The method according to claim 1 or 2, characterized in that a course of the measured values across the entire step cycle, is compared with a course of the stored target values.

4. The method according to one of the preceding claims, characterized in that a course of the plantar damping as a function of the ankle angle and / or the lower leg angle is adjusted, wherein the course is preferably adjusted at the start of the heel strike, particularly preferably before the start of the heel strike, and no further adjustment of the course occurs over the remaining course of the step.

5. The method according to one of the preceding claims, characterized in that the measured values include a vertical force and a torque on the joint, wherein preferably a force application point, particularly preferably a course of the force application point, is determined from the measured values.

6. The method according to one of the preceding claims, characterized in that the measured values contain the force application point and / or its chronological profile, and the at least one sensor comprises a plurality of pressure sensors, preferably a pressure-sensitive layer on a lower side of a sole of the foot part.

7. The method according to claim 5 or 6, characterized in that the chronological profile of the force application point is approximated by a segment of a circle with a center point and radius, which are compared with a stored center point and / or radius.

8. The method according to one of the preceding claims, characterized in that the measured values are a lower leg angle and a foot angle, preferably their chronological profiles, wherein it is especially preferable if a ratio of lower leg angle to foot angle and / or its chronological profile is determined.

9. The method according to one of the preceding claims, characterized in that the comparison and, if necessary, the adjustment of the damping behavior is performed multiple times, preferably at equidistant intervals, during part of a step cycle, preferably across the entire step cycle.

10. The method according to one of the preceding claims, characterized in that the damping is a hydraulic and / or magnetorheological damping.

11. The method according to one of the preceding claims, characterized in that the foot part has at least one spring element, the spring stiffness of which is adjusted when the measured values exceed a predetermined distance from the target values.

12. A prosthetic foot with a foot part and a lower leg part that are connected to each other via a joint which allows a plantar flexion and a dorsal flexion, the damping behavior of the joint being adjustable, characterized by an electronic data processing device that is configured to conduct a method according to one of the preceding claims.