METHOD FOR CONTROLLING A LOWER LEG PROSTHESIS AND LOWER LEG PROSTHESIS

Description

[0001] The invention relates to a method for controlling a lower leg prosthesis comprising a foot element, a lower leg element pivotably arranged thereon, and an adjustable resistance device for applying resistance to pivoting of the foot element relative to the lower leg element. The invention further relates to a lower leg prosthesis that is controllable by means of such a method.

[0002] A method for operating a lower leg prosthesis is known, for example, from US 2022 / 304831 A1 and US 2013 / 0310949 A1. US 10 314 724 B2 and US 2018 / 0008434 A1 each describe prosthetic foot elements that, together with a lower leg element, can form a lower leg prosthesis. The prosthetic feet each have an ankle joint, which may be hydraulically damped. Document US 2022 / 304831 A1 is considered the closest prior art.

[0003] US patent 2018 / 0147074 A1 describes a shock absorber for a prosthetic joint, and JP patent 2013 / 070785 A describes an exoskeleton.

[0004] Lower leg prostheses of the type described above can generate varying levels of resistance to the rotation of the foot element relative to the lower leg element during a gait cycle via an adjustable resistance device. This has long been used in the prior art to imitate the natural gait pattern. It is generally important that the resistance is significantly increased approximately midway through the stance phase of a gait cycle. This often goes so far that further rotation of the foot element relative to the lower leg element is no longer possible from this point onward. The stance phase of a gait cycle is defined by the point at which the foot element is in contact with the ground.

[0005] From the moment the resistance is increased, further pivoting of the foot element relative to the lower leg element is either impossible or significantly more difficult. The foot then rolls off via the forefoot, which is essentially formed by the toes. This changes the lever length over which the foot rolls.

[0006] It is known from the prior art to make the point at which the resistance is increased dependent on the gradient of the surface. If the carrier, for example, goes up a ramp, the switching point at which the resistance is increased should be shifted backward within the step cycle, i.e., to a later point.

[0007] Often, a foot element and / or a lower leg element equipped with an absolute angle sensor is used to determine the inclination of the foot element during the stance phase of the gait cycle. This makes it easy to determine whether the wearer is walking up or down an inclined plane, such as a ramp. However, this method is not applicable when determining whether the wearer of the lower leg prosthesis is going up or down stairs. The inclination angle of the foot element is the same regardless of the direction of movement because the stair tread is horizontal. Furthermore, the described method reaches its limits when the terrain on which the wearer of the lower leg prosthesis is moving is not a level surface.If the surface is uneven, it is not possible, or at least not always possible, to reliably determine the slope of the ground and when the switching point should be based on the inclination of the foot element.

[0008] From DE 10 2012 125 256 A1, it is therefore known to define two switching angles. The first switching angle is defined as a predetermined ankle angle value between the lower leg element and the foot element. Thus, as soon as the ankle angle, which is detected to control the lower leg prosthesis, reaches this predetermined ankle angle value, the first switching angle is considered reached. The second switching angle is defined as a predetermined lower leg angle value of the absolute angle of the lower leg. Regardless of the value of the ankle angle between the lower leg element and the foot element, the second switching angle is considered reached when the absolute angle of the lower leg reaches the predetermined lower leg angle value. In order to control the lower leg prosthesis, it must now be determined which of the two defined switching angles should be the angle at which the resistance of the resistance device should be increased.In the prior art, it is proposed to always use the switching angle that occurs first within the respective step cycle, regardless of the detected position of the foot element in the stance phase.

[0009] This is a good choice in many situations, but it leads to problems in some. The first switching angle can, for example, be defined as a right angle, i.e., a 90° angle. This means that when the first switching angle is defined, there is a right angle between the lower leg element and the foot element, for example, the contact surface with the ground. The second switching angle can also be defined as a 90° angle. This means that the second switching angle is reached when the lower leg element is perpendicular, i.e., parallel to the acting force of gravity.

[0010] These definitions of the two switching angles mean that when walking downwards along a ramp, the second switching angle is reached first. The resistance is therefore increased when the lower leg element is vertical, which provides a secure stance but results in an unnatural gait. When walking upwards along the ramp, however, this definition of the two switching angles means that the first switching angle is reached first. This is too early when walking upwards and leads to a premature increase in the resistance applied by the resistance device.

[0011] The invention is therefore based on the objective of further developing a method for controlling a lower leg prosthesis in such a way that safe and comfortable walking can be made possible more effectively.

[0012] The invention solves the stated problem by a method for controlling a lower leg prosthesis, which has a foot element, a lower leg element pivotably arranged thereon, and an adjustable resistance device for applying resistance against pivoting of the foot element relative to the lower leg element, wherein a first switching angle is defined as a predetermined ankle angle value between the lower leg element and the foot element, and a second switching angle is defined as a predetermined lower leg angle value of the absolute angle of the lower leg.According to the invention, the method determines, at least in part, from a height difference between the position of the foot element in a step cycle and the position of the foot element in the previous step cycle, whether the wearer of the lower leg prosthesis is moving downhill, and the resistance of the resistance device is increased to a predetermined resistance when a blocking criterion is met. According to the invention, the blocking criterion is met when it has been determined that the wearer is not moving downhill and the second switching angle has been reached, or when it has been determined that the wearer is moving downhill and the switching angle reached later in the step cycle has been reached.

[0013] Unlike the prior art, the method according to the invention does not require the inclination of the foot element during the stance phase of the stepping cycle. Instead, it determines whether the carrier is moving downhill, disregarding the local inclination of the ground, which is decisive for the inclination of the foot element during the stance phase. If the determination shows that the carrier is not moving downhill, the resistance of the resistance device is increased when the second switching angle is reached. This occurs when the absolute angle of the lower leg reaches the predetermined lower leg angle value. Consequently, the increase in resistance is completely independent of the local inclination of the ground and thus also of the inclination of the foot element during the stance phase. However, if the determination shows that the carrier is moving downhill, the blocking criterion is met when the later switching angle in the stepping cycle is reached.

[0014] This creates a gait pattern that is as natural as possible, provided it is correctly detected whether the wearer of the lower leg prosthesis is walking downhill or not. However, methods for controlling a lower leg prosthesis should preferably ensure safe operation of the prosthesis even in the event of incorrect detection or determination, as the wearer could otherwise fall and injure themselves. Therefore, if the method according to the invention incorrectly detects that the wearer is walking downhill, the switching angle reached later in the step cycle is used to increase the resistance of the resistance device. Since the wearer is not actually walking downhill in this case, but rather, for example, uphill, this is the second switching angle, which is defined as a predetermined lower leg angle value. Consequently, the correct switching angle is used even in the case of an incorrect detection of walking downhill.

[0015] If, however, the wearer is walking downhill and this is incorrectly not detected, the second switching angle is used as the blocking criterion. The resistance is therefore increased when the absolute angle of the lower leg reaches the predetermined lower leg value. This is usually the switching angle reached earlier in a step cycle when walking downhill, and thus the wrong switching angle for a wearer walking downhill. While this does not result in an optimal gait pattern, it allows for stable standing and is therefore not a significant safety issue. The effect of this miscontrol on the wearer is relatively unproblematic, especially with a foot equipped with a carbon spring, as the wearer can roll over the forefoot thanks to the carbon spring and is thus slowed down.

[0016] Preferably, the predetermined resistance value is so large that further pivoting of the foot element relative to the lower leg element is completely prevented.

[0017] Preferably, the height difference between the position of the foot element during the stance phase of the two step cycles is determined. The position of a foot element changes during the stance phase not only forwards but also perpendicular to it. After the end of the stance phase, the foot is lifted and only placed back on the ground at the beginning of the next stance phase. To determine a meaningful height difference, it is advantageous to use the same point in time within the two consecutive step cycles to determine the foot's position at that specific moment and calculate the difference. Preferably, the position is determined during the stance phase. Determining the position during the stance phase is particularly advantageous because it remains constant over a longer period, namely the duration of the stance phase, and can therefore be determined very accurately.

[0018] InIn a preferred embodiment, however, the difference in elevation is not used directly to determine whether the prosthesis wearer is walking uphill or downhill. Instead, a gradient angle is preferably calculated from the difference in elevation and a difference in length, which is also determined from the difference in the positions of the foot element at a specific point in time within two successive step cycles. This results in a gradient triangle whose gradient angle can be easily calculated. This gradient angle is preferably used as a criterion to determine whether the prosthesis wearer is walking uphill or downhill. In a preferred embodiment, the gradient angle is compared with a predetermined threshold angle. If the gradient angle is above the predetermined threshold angle, the wearer of the lower leg prosthesis is not considered to be walking downhill.However, if the angle of inclination is below the predetermined limit angle, the support is considered to be descending.

[0019] Preferably the limiting angle is between 0° and -10°, particularly preferably -3°.

[0020] Preferably, the predetermined ankle angle is between 80° and 100°, particularly preferably 90°. Advantageously, the predetermined lower leg angle is also between 80° and 100°, preferably 90°. Preferably, the predetermined ankle angle is modified by a correction angle that results from the heel height of the shoe worn by the wearer. The higher the heel of the shoe, the greater the predetermined ankle angle. The greater the heel height, the more the neutral position of the ankle shifts, i.e., the angle between the foot element and the lower leg element in relaxed standing. This change in the neutral position is taken into account by the correction angle.

[0021] The heel height depends on the foot length. For example, a foot length of 22 cm and a heel height of 3 cm would result in an angle of approximately 8°. The measured angle, or alternatively the predetermined ankle angle value, must be corrected by this angle, which constitutes the correction angle, in the form of an offset.

[0022] The invention further solves the stated problem by means of a lower leg prosthesis with a foot element, a lower leg element pivotably arranged thereon, and an adjustable resistance device for applying resistance against pivoting of the foot element relative to the lower leg element, wherein the lower leg prosthesis has at least one sensor for determining a height difference, at least one sensor for determining the ankle angle, at least one sensor for determining the absolute angle of the lower leg, and an electrical control system configured to carry out a method according to one of the preceding embodiments.

[0023] The sensor for determining the absolute angle of the lower leg element is preferably an IMU (inertial measurement unit), for example, a combination of accelerometers and / or gyroscopes, which determine the orientation of the lower leg element in space and calculate the absolute angle of the lower leg element from this. Alternatively or additionally, the sensor is configured to determine the absolute angle of the foot element and the angle between the foot element and the lower leg element, so that the absolute angle of the lower leg element is calculated from these values.

[0024] The electrical control is preferably an electronic data processing device. Particularly preferably, the at least one sensor for determining the ankle angle comprises at least one absolute angle sensor for determining the absolute angle of the lower leg element and at least one absolute angle sensor for determining the absolute angle of the foot element.

[0025] With the aid of the accompanying illustrations, some exemplary embodiments of the present invention are explained in more detail below. They show: Figure 1 - the schematic representation of various measured quantities and Figure 2a - 2d - the achievement of the block criterion under different substrates.

[0026] Figure 1 Figure 1 schematically shows a portion of a lower leg prosthesis with a foot element 2, to which a lower leg element 4 is attached. The foot element 2 is pivotable relative to the lower leg element 4. Figure 1The figure shows the position of the lower leg prosthesis in three successive stance phases, i.e., the stance phases of three consecutive step cycles. The foot element 2 is in contact with the surface 6 in each of these phases. This surface 6 has a local inclination that corresponds to the inclination of the foot element 2 at the respective location on the surface 6. This local inclination is illustrated by the triangle shown below the foot element 2. It does not have to be used to control the lower leg prosthesis and is preferably not used.

[0027] Instead, in the illustrated embodiment, a height difference 8 and a length difference 10 are determined, whereby the respective difference between the positions of the foot element 2 between two successive steps is calculated. In the illustrated embodiment, both are as large between the first and second positions shown as they are between the second and third positions shown. The global slope of the substrate 6 is therefore constant, although the local slope can vary considerably, as it does in the illustrated example.

[0028] In Figure 1The direction of the lower leg element 4 is represented by a line 12. The first switching angle corresponds to a predetermined value of the angle between the line 12 and the local inclination of the base 12, which corresponds to the direction of the foot element 2. The second switching angle corresponds to a predetermined orientation of the line 12, i.e., a predetermined value of the absolute angle of the lower leg element 4.

[0029] In the following, the first switching angle should correspond to an ankle angle value of 90° and the second switching angle to an absolute angle of 90°, i.e. a vertical alignment of the lower leg element 4.

[0030] In Figure 2aThe lower leg prosthesis is schematically depicted on a flat surface 6. Line 12, shown as a dashed line, is perpendicular to the surface 6, thus reaching the first switching angle. Line 12 is also vertically oriented, thus reaching the second switching angle as well. The prosthesis wearer is not walking downhill. If this is correctly detected by the system, the second switching angle is used for control, and the resistance of the (not shown) resistance device is increased when the lower leg element 4 is vertically oriented. If the system incorrectly detects that the wearer is walking downhill, the second switching angle reached is used for control. Since both switching angles are reached simultaneously, no problem occurs, and the increase in resistance takes place at the correct time, as expected by the prosthesis wearer.

[0031] In Figure 2bThe situation is depicted in which the surface 6 is designed as an ascending ramp. Since the wearer is not walking downhill in this case either, the second switching angle is used to control the prosthesis. The resistance is therefore increased when the absolute angle of the lower leg element 4, in Figure 2b So line 12 is vertical. This is in Figure 2b shown. Had it been incorrectly detected that the carrier was going downhill, the control system would have increased the resistance when the switching angle was reached later. This is shown in the Figure 2b The situation shown is the second switching angle, so that in both cases the increase in resistance occurs at the time expected by the user or wearer of the prosthesis.

[0032] In Figure 2cThe situation is depicted in which the surface 6 is designed as a sloping ramp. In this case, the wearer is walking downhill. Therefore, the first switching angle is used to control the prosthesis. The resistance is thus increased when the ankle angle between line 12 of the lower leg element 4 and the foot element 2 is 90°. This is shown in Figure 2c As shown, if it had been incorrectly detected that the carrier was not moving downhill, the control system would have increased the resistance when the second switching angle was reached. The resistance increase then occurred when the lower leg element, and thus its line 12, was vertical. This happened earlier than the carrier expected, but it did not result in a risk of falling, as the early increase in resistance ensured continued stability.

[0033] Figure 2dThis illustrates the situation in which the wearer of the lower leg prosthesis is not walking downhill, but the surface 6 has a local unevenness. In this case, the second switching angle is used to control the prosthesis, which is shown in Figure 2d has been achieved. Reference symbol list

[0034] 2 Foot element 4 Lower leg element 6 Ground 8 Height difference 10 Length difference 12 Line

Claims

1. A method for controlling a lower leg prosthesis comprising a foot element (2), a lower leg element (4) pivotably arranged thereon and an adjustable resistance device for applying a resistance against a swivelling of the foot element (2) relative to the lower leg element (4), wherein - a first switching angle is defined as a predetermined ankle angle value between the lower leg element (4) and the foot element (2), - a second switching angle is defined as a predetermined lower leg angle value of the absolute angle of the lower leg element (4), the method comprising the steps: - determining, at least also on the basis of a height difference (8) between the position of the foot element (2) in a step cycle and the position of the foot element (2) in the previous step cycle, whether the wearer of the lower leg prosthesis is walking downhill, and - increasing the resistance of the resistance device to a predetermined resistance value when a block criterion is met, wherein the block criterion is met if it has been determined that the wearer is not walking downhill and the second switching angle is reached, or if it has been determined that the wearer is walking downhill and the switching angle reached later in the step cycle is reached.

2. The method according to claim 1, characterized in that the predetermined resistance value is big enough to prevent a further swivelling of the foot element (2) relative to the lower leg element (4).

3. The method according to claim 1 or 2, characterized in that the height difference (8) between the position of the foot element (2) in the stance phase of the two step cycles is determined.

4. The method according to one of the preceding claims, characterized in that a pitch angle, which is determined from the height difference (8) and a length difference (10) between the positions of the foot element (2), is used to determine whether the wearer of the lower leg prosthesis is walking downhill.

5. The method according to claim 4, characterized in that the wearer is deemed to be walking downhill if the pitch angle is smaller than a limit angle, which is preferably between 0° and -10° and particularly preferably is -3°.

6. The method according to one of the preceding claims, characterized in that the predetermined ankle angle value is between 80° and 100°, preferably 90°.

7. The method according to one of the preceding claims, characterized in that the predetermined lower leg angle value is between 80° and 100°, preferably 90°.

8. A lower leg prosthesis with a foot element (2), a lower leg element (4) pivotably arranged thereon and an adjustable resistance device for applying a resistance against a swivelling of the foot element (2) relative to the lower leg element (4), wherein the lower leg prosthesis comprises at least one sensor for determining a height difference (8), at least one sensor for determining an ankle angle, at least one sensor for determining the absolute angle of the lower leg element (4), and an electrical control unit that is configured to conduct a method according to one of the preceding claims.

9. The lower leg prosthesis according to claim 8, characterized in that the at least one sensor for determining the ankle angle comprises an absolute angle sensor for determining the absolute angle of the lower leg element (4) and an absolute angle sensor for determining the absolute angle of the foot element (2).