Prosthetic leg, knee joint, and control method and control program for knee joint

Abstract

A prosthetic leg 10 comprises: a thigh connection part; a lower leg section that is connected to the thigh connection part and that is provided rotatably around a knee shaft; a load acquisition unit 130 that acquires a load applied to the prosthetic leg via a thigh section; a knee angle acquisition unit 110 that acquires a knee angle formed between a shaft of the lower leg section and a shaft of the thigh section; and a rotation resistance control unit 100 that controls the rotation resistance of the knee shaft. When the knee angle exceeds a prescribed bouncing angle, the rotation resistance control part 100 executes bouncing control for strengthening the rotation resistance so as to limit a further increase of the knee angle, determines, on the basis of the load acquired by the load acquisition part 130 during execution of the bouncing control, whether the position of the load is in an end position state within a prescribed end range, and ends the bouncing control when a continuation time of the end position state exceeds a prescribed time.

Description

Prosthesis, knee joint, control method of knee joint, and control program

[0001] The present invention relates to the technology of prostheses.

[0002] As a knee joint or prosthesis worn on the lower limb by a person who has lost a foot due to injury or illness, there is known one that controls the rotational resistance of the knee axis according to the walking phase of the user (see, for example, Patent Document 1). In the stance phase where the prosthesis is grounded and a load is applied, the rotational resistance of the knee axis is increased so that the knee does not bend due to the load. In the swing phase where the prosthesis leaves the ground and is swung, the rotational resistance of the knee axis is decreased so that the knee is bent and the prosthesis does not contact the ground.

[0003] International Publication No. 2019 / 221037

[0004] For example, for users with low exercise ability such as low-activity persons and the elderly, there is known a bouncing function that restricts further flexion of the knee joint when the user reaches a slightly flexed position where the user is in a semi-sitting position and the knee is slightly bent. Thereby, the user can walk with confidence without being wary of knee collapse.

[0005] On the other hand, for example, when trying to sit down from a bouncing state, since the flexion of the knee joint is restricted, the user can basically only bend the healthy foot when sitting down. Therefore, it is assumed that the user performs a predetermined operation while sitting to解除 the bouncing state, but it may become an unnatural operation that has nothing to do with the sitting operation.

[0006] Therefore, in order to further improve convenience, a technique for解除 the bouncing state with a natural posture is required.

[0007] In view of the above, an object of the present invention is to provide a technique for解除 the bouncing state with a natural posture when sitting down.

[0008] To solve the above problems, a prosthetic leg according to one aspect of the present invention comprises a thigh connection portion provided on the thigh side, a lower leg portion connected to the thigh connection portion and rotatable around a knee axis, a load acquisition portion that acquires the load applied to the prosthetic leg via the thigh portion, a knee angle acquisition portion that acquires the knee angle formed by the axis of the lower leg portion and the axis of the thigh portion, and a rotational resistance control portion that controls the rotational resistance of the knee axis, wherein the rotational resistance control portion performs bouncing control to strengthen the rotational resistance to limit further increase of the knee angle when the knee angle exceeds a predetermined bouncing angle, and the rotational resistance control portion determines whether the position of the load is in a predetermined end position state within a predetermined end range based on the load acquired by the load acquisition portion while the bouncing control is being performed, and terminates the bouncing control when the duration of the end position state exceeds a predetermined time.

[0009] A knee joint in another aspect of the present invention comprises a thigh connection portion provided on the thigh side, a lower leg portion connected to the thigh connection portion and rotatable around a knee axis, a load acquisition portion that acquires the load applied to the lower leg portion via the thigh portion, a knee angle acquisition portion that acquires the knee angle formed by the axis of the lower leg portion and the axis of the thigh portion, and a rotational resistance control portion that controls the rotational resistance of the knee axis, wherein the rotational resistance control portion performs bouncing control to increase the rotational resistance to limit further increase of the knee angle when the knee angle exceeds a predetermined bouncing angle, and the rotational resistance control portion determines whether the position of the load is in a predetermined end position state within a predetermined end range based on the load acquired by the load acquisition portion while the bouncing control is being performed, and terminates the bouncing control when the duration of the end position state exceeds a predetermined time.

[0010] A control method in yet another aspect of the present invention is a control method for a knee joint comprising: a thigh connecting portion provided on the thigh side; a lower leg portion connected to the thigh connecting portion and rotatable around a knee axis; a load acquisition unit for acquiring a load applied to the lower leg portion via the thigh portion; a knee angle acquisition unit for acquiring a knee angle formed by the axis of the lower leg portion and the axis of the thigh portion; and a rotational resistance control unit for controlling the rotational resistance of the knee axis, the method comprising: performing bouncing control to strengthen the rotational resistance to limit further increase of the knee angle when the knee angle exceeds a predetermined bouncing angle; determining whether the position of the load is in a predetermined end position state within a predetermined end range based on the load acquired by the load acquisition unit while the bouncing control is being performed; and terminating the bouncing control when the duration of the end position state exceeds a predetermined time.

[0011] A control program in yet another aspect of the present invention is a control program for a knee joint comprising: a thigh connection portion provided on the thigh side; a lower leg portion connected to the thigh connection portion and rotatable around a knee axis; a load acquisition unit for acquiring the load applied to the lower leg portion via the thigh portion; a knee angle acquisition unit for acquiring the knee angle formed by the axis of the lower leg portion and the axis of the thigh portion; and a rotational resistance control unit for controlling the rotational resistance of the knee axis, wherein the program causes a computer to perform bouncing control to increase the rotational resistance so as to limit further increases in the knee angle when the knee angle exceeds a predetermined bouncing angle; a step of determining whether the position of the load is in a predetermined end position state within a predetermined end range based on the load acquired by the load acquisition unit while the bouncing control is being performed; and a step of terminating the bouncing control when the duration of the end position state exceeds a predetermined time.

[0012] Furthermore, any combination of the above components, as well as conversions of the expression of the present invention between methods, apparatus, systems, recording media, computer programs, etc., are also valid embodiments of the present invention.

[0013] According to the present invention, the knee joint can be controlled in a natural posture.

[0014] This shows the schematic configuration of the knee joint and prosthesis that constitute the bilateral knee joint device. This shows the schematic configuration of the knee joint and prosthesis that constitute the bilateral knee joint device. This shows a simplified representation of the transitions of the knee angle θ, thigh angle Ψ, and shin angle Φ according to the walking phase of the prosthesis user. This shows the cylinder and control mechanism. This shows the flow of oil during flexion or extension of the knee joint. This schematically shows the functional block responsible for flexion control of the knee joint. This is a flowchart of the flexion control of the knee joint in the first embodiment. This is a diagram illustrating the walking phase of the prosthesis user on a downhill slope. This is a flowchart of the flexion control of the knee joint in the second embodiment.

[0015] Figures 1 and 2 of the first embodiment show a schematic configuration of the knee joint 20 and prosthetic leg 10 according to the first embodiment of the present invention. In this specification, "forward direction" and "backward direction" mean the forward and backward directions of the prosthetic leg 10 in its normal use state, respectively. "Upward direction" and "downward direction" mean the vertically upward direction and the vertically downward direction of the prosthetic leg 10 in its normal use state, respectively. "Left and right direction" means a horizontal direction perpendicular to the front and back directions, and refers to the direction as viewed from the user's viewpoint in the normal use state of the prosthetic leg 10.

[0016] The prosthetic leg 10 comprises a plastic socket 11 as the thigh portion, a thigh joint 22 to which the socket 11 is connected, a lower leg portion 21 connected to the thigh joint 22 and rotatable around a knee axis 23, and a foot portion 12 connected to the lower end of the lower leg portion 21. The thigh joint 22 to which the socket 11 is connected and the lower leg portion 21 rotate relative to each other around a knee axis 23 which is perpendicular to the plane of the paper in Figure 1 (i.e., extends parallel to the left-right direction), thereby flexing and extending the knee joint 20, which corresponds to the knee joint. The foot portion 12 is formed of an elastic material, and its relative posture is kept constant by elasticity when the load from the ground is small, such as when not touching the ground or when standing upright. When the load from the ground is large, such as when walking, the elastic material deforms elastically to generate propulsive force to push off the ground.

[0017] The knee joint 20 comprises a lower leg portion 21 formed by a high-strength frame, a thigh connection portion 22 connected to a socket 11 as a thigh portion and rotatably connected to the lower leg portion 21 around a knee axis 23, a cylinder 30 that restricts or allows rotational movement around the knee axis 23, i.e., flexion and extension movement of the knee joint 20, and a control mechanism 40 that drives the cylinder 30. Although Figure 1 shows a knee joint 20 in which the thigh connection portion 22 and the lower leg portion 21 are connected by a single link and rotatable around a single knee axis 23 at a specific position, the present invention can also be applied to a knee joint 20 in which the thigh connection portion 22 and the lower leg portion 21 are connected by, for example, two links, front and rear, and rotatable around a knee axis 23 which is virtually and instantaneously formed inside a total of four connection points.

[0018] The amount of extension and retraction of the cylinder 30 and the knee angle, which is the rotation angle of the knee joint 20 around the knee axis 23, correspond almost one-to-one. A knee angle sensor 60, which acts as a knee angle acquisition unit to measure the amount of extension and retraction of the cylinder 30 and detect the knee angle of the knee joint 20, is provided near the cylinder 30 and the thigh connection part 22. The knee angle detected by the knee angle sensor 60 is used by the control unit 50. The knee angle sensor 60 can be made up of any sensor capable of measuring the amount of extension and retraction of the cylinder 30. For example, the knee angle sensor 60 can be made up of a Hall element capable of detecting the position of a magnet embedded in a piston rod 34 that moves with the extension and retraction of the cylinder 30. The knee angle is the angle between the axis of the thigh or the axis of the socket 11 as the thigh and the axis of the lower leg 21. For example, as shown in Figure 1, the knee angle is 0 degrees when the user of the prosthetic leg 10 is standing upright and the axis of the socket 11 and the axis of the lower leg 21 are in a straight line. Furthermore, when the user of the prosthetic leg 10 is seated, and the axis of the lower leg portion 21 remains in the vertical direction as shown in Figure 1, the axis of the socket 11 changes to a horizontal direction, the knee angle becomes 90 degrees.

[0019] A load sensor 70 is provided at the lower end of the lower leg portion 21 to detect the load value (vertical load) of the knee joint 20 on the foot portion 12. The load sensor 70 is connected to the control unit 50. The load sensor 70 in this embodiment consists of two strain sensors arranged side by side at the ankle portion, on the toe side (front side) and the heel side (rear side), with reference to a predetermined reference position of the ankle portion (for example, the center of gravity of the ankle portion). Based on the load detection results from the two strain sensors (such as the magnitude and direction of the load at each position of the ankle portion), the control unit 50 can obtain information regarding the moment of the vertical load around the ankle axis that is perpendicular to the plane of Figure 1 (i.e., extends parallel to the left-right direction) passing through the reference position of the ankle portion. For example, if a counterclockwise moment around the ankle axis is considered positive, then when a load is applied to the toe side (front side), the load sensor 70 in this embodiment obtains a positive moment value. In this case, the moment value is calculated from the difference between the magnitude of strain detected by the strain sensor located on the heel side and the magnitude of strain detected by the strain sensor located on the toe side. The calculation to convert the strain detected by the strain sensors into load may also be performed by the control unit 50. In this case, the load sensor 70 provides the detected strain to the control unit 50. Furthermore, since the control unit 50 can recognize the walking phase of the prosthetic leg 10 user from the magnitude and direction of the load measured by the load sensor 70, it can calculate the stride length and walking speed.

[0020] In addition to the knee angle sensor 60, an inertial sensor 75 may be provided as a knee angle acquisition unit to measure the velocity (angular velocity) and / or acceleration (angular acceleration) in the translational and / or rotational directions of the three axes that control the movement of the lower leg portion 21. Of the posture of the lower leg portion 21 detected by the inertial sensor 75, the shin angle, which is the inclination angle that the axis of the lower leg portion 21 makes with respect to the vertical line passing through the knee axis 23, and the thigh angle, which is the inclination angle that the axis of the socket 11, which is the thigh portion, makes with respect to the vertical line passing through the knee axis 23 and can be calculated from the shin angle, can be used to control the knee joint 20 of this embodiment. The inertial sensor 75 can be installed at any location on the lower leg portion 21. For example, the inertial sensor 75 is mounted together with the control unit 50 on a control board installed on the outer circumference of the cylinder 30.

[0021] The shin angle is the inclination of the lower leg portion 21 from a vertical line passing through the knee axis 23, and the knee angle is the inclination of the axis of the socket 11 from the axis of the lower leg portion 21. By adding these two together, the thigh angle, which is the inclination of the axis of the socket 11 from the vertical line passing through the knee axis 23, can be calculated. Alternatively, the thigh angle may be directly measured by providing an inertial sensor on the socket 11 or the thigh connection portion 22. In this case, the shin angle can be calculated based on the measured knee angle and thigh angle. Similarly, even if a knee angle sensor 60 is not provided, the knee angle can be calculated by measuring the thigh angle and shin angle.

[0022] Figure 3 shows a simplified illustration of the transitions in knee angle θ, thigh angle Ψ, and shin angle Φ according to the user's walking phases (A) to (G) of the prosthetic leg 10. Walking phase (A) is the initial contact phase (IC), when the prosthetic leg 10 makes contact with the ground. Walking phase (B) is the loading response phase (LR), when the user's weight is supported by the prosthetic leg 10 that is in contact with the ground. Walking phase (C) is the mid-stance phase (MSt) to the terminal stance phase (TSt), when the user's center of gravity moves forward of the prosthetic leg 10 while the prosthetic leg 10 supports the user's weight. Walking phase (D) is the pre-swing phase (PSw), when the user pushes off the ground with the prosthetic leg 10 to transition to the subsequent swing phase. The walking phases (E), (F), and (G) are the initial swing phase (ISw: also called Initial Swing), the mid-swing phase (MSw: also called Mid Swing), and the terminal swing phase (TSw: also called Terminal Swing), respectively, during which the prosthetic leg 10, having left the ground, swings from rear to front.

[0023] The thigh angle Ψ is defined as negative (shown as -Ψ) when the socket 11 is tilted forward around the knee axis 23, and positive (shown as +Ψ) when it is tilted backward, with respect to the vertical line passing through the knee axis 23. The shin angle Φ is defined as positive (shown as +Φ) when the lower leg portion 21 is tilted forward around the knee axis 23, with respect to the vertical line passing through the knee axis 23, and negative (shown as -Φ) when it is tilted backward. The knee angle θ is defined as positive (shown as +θ) when the lower leg portion 21 is tilted backward around the knee axis, with respect to the axis of the socket 11. The knee angle θ, thigh angle Ψ, and shin angle Φ defined as described above always satisfy the relationship "θ + Φ = Ψ".

[0024] As shown in the figure, in the initial contact phase (A), the knee angle θ is approximately zero, the thigh angle Ψ is positive, and the shin angle Φ is positive; in the load response phase (B), the knee angle θ is approximately zero, the thigh angle Ψ is positive, and the shin angle Φ is positive; in the mid-to-late stance phase (C), the knee angle θ is approximately zero, the thigh angle Ψ is negative, and the shin angle Φ is negative; in the pre-swing phase (D), the knee angle θ is positive, the thigh angle Ψ is negative, and the shin angle Φ is negative; in the early swing phase (E), the knee angle θ is positive, the thigh angle Ψ is positive, and the shin angle Φ is negative; in the mid-swing phase (F), the knee angle θ is positive, the thigh angle Ψ is positive, and the shin angle Φ is negative; and in the late swing phase (G), the knee angle θ is positive, the thigh angle Ψ is positive, and the shin angle Φ is positive.

[0025] Focusing on the knee angle θ, during the stance phase (A) to (C) when the prosthetic leg 10 is in contact with the ground and supports the user's weight, the knee angle θ is approximately zero. During the pre-swing phase (D) between the stance phase (A) to (C) and the swing phase (E) to (G), the knee angle θ ranges from approximately zero to a positive value. During the swing phase (E) to (G) when the prosthetic leg 10 leaves the ground and swings out, the knee angle θ increases or decreases monotonically, reaching a maximum value in the mid-swing phase (F).

[0026] This control of the knee angle θ, i.e., the flexion control of the knee joint 20, is performed by the control unit 50 via the control mechanism 40 and the cylinder 30. Specifically, during the stance phase (A) to (C), the knee angle θ is kept approximately zero by increasing the hydraulic resistance of the cylinder 30 to limit rotation around the knee axis 23, so that the knee joint 20 does not flex under the user's weight. During the pre-swing phase (D), the knee angle θ becomes positive by lowering the hydraulic resistance of the cylinder 30 to allow rotation around the knee axis 23, so that the knee joint 20 can begin to flex in preparation for the subsequent swing phase (E) to (G). During the swing phase (E) to (G), the hydraulic resistance of the cylinder 30 is kept low to facilitate flexion of the knee joint 20, so that the prosthetic leg 10, which swings off the ground, does not come into contact with the ground.

[0027] A vibrator 85 is provided in the thigh connection portion 22 or the lower leg portion 21. The vibrator 85 provides notifications and warnings to the user wearing the prosthetic leg 10 through vibration and is controlled by the control unit 50.

[0028] The control unit 50 controls the control mechanism 40 based on measurement information from various sensors such as the knee angle sensor 60 and the load sensor 70, thereby controlling the resistance to the extension and retraction movement of the cylinder 30, i.e., the rotational resistance of the knee axis 23 during the flexion and extension movements of the knee joint 20. A battery 55 that supplies power to various parts of the knee joint 20 is connected to the control unit 50. In Figure 2, the control mechanism 40, the control unit 50, and the battery 55 are shown outside the knee joint 20, but in reality, they are installed inside the lower leg portion 21 as components of the knee joint 20.

[0029] The cylinder 30 is a hydraulic cylinder that uses oil as a working fluid to generate resistance, thereby limiting or allowing the bending or extending motion of the knee joint 20. The cylinder 30 is supported by an upper support point 31 located near the knee axis 23, which rotatably connects the socket 11 and the lower leg portion 21, and a lower support point 32 connected to a part of the lower leg portion 21, and is extendable and retractable between the two support points. In the contraction process, when the cylinder length decreases, the knee joint 20 performs a bending motion in which it rotates counterclockwise around the knee axis 23 in the direction shown in Figure 1, and in the extension process, when the cylinder length increases, the knee joint 20 performs an extension motion in which it rotates clockwise around the knee axis 23 in the direction shown in Figure 1. Here, the cylinder length refers to the length between the upper support point 31 and the lower support point 32 of the cylinder 30.

[0030] Next, the cylinder 30 and the control mechanism 40 will be described with reference to Figure 4. The cylinder 30 includes a cylinder tube 33, a piston rod 34 inserted from one end of the cylinder tube 33 (the right end in Figure 4) and movable along the longitudinal direction of the cylinder tube 33 (the left-right direction in Figure 4), and a piston 35 fixed to the piston rod 34 inside the cylinder tube 33 and sliding longitudinally along the inner wall of the cylinder tube 33. The inside of the cylinder tube 33 is divided by the piston 35 into a first cavity 36 at one end (the right end in Figure 4) and a second cavity 37 at the other end (the left end in Figure 4). The first cavity 36 and the second cavity 37 are filled with oil, which is the working fluid.

[0031] The control mechanism 40 is a hydraulic drive mechanism that drives the cylinder 30 to extend and retract using hydraulic pressure. The control mechanism 40 has an extension-side hydraulic circuit 41 and a flexion-side hydraulic circuit 42, respectively, connected to the cylinder 30. The extension-side hydraulic circuit 41 and the flexion-side hydraulic circuit 42 communicate with the first cavity 36 at one end and with the second cavity 37 at the other end. The extension-side hydraulic circuit 41 has an extension-side valve 43, which is a valve that can open and close the flow path of oil that generates rotational resistance of the knee axis 23, and an extension-side check valve 44. When the extension-side valve 43 is in the open state, oil can flow through the extension-side hydraulic circuit 41, but due to the action of the extension-side check valve 44, the oil flows only in the direction from the first cavity 36 to the second cavity 37 and not in the reverse direction.

[0032] The flexion-side hydraulic circuit 42 includes a flexion-side valve 45 and a flexion-side check valve 46, which are valves that can open and close the flow path of oil that generates rotational resistance of the knee axis 23. When the flexion-side valve 45 is open, oil can flow through the flexion-side hydraulic circuit 42, but due to the action of the flexion-side check valve 46, the oil flows only in the direction from the second cavity 37 to the first cavity 36 and not in the reverse direction. The extension-side valve 43 and the flexion-side valve 45 are individually controlled by the control unit 50. The opening degree of each valve can take any value between fully open (maximum opening) and fully closed (minimum opening). When each valve is fully closed, the flow of oil is blocked and the hydraulic resistance is maximized. Also, as the opening degree of each valve increases towards fully open, the cross-sectional area through which oil can flow within each valve increases, so the hydraulic resistance decreases.

[0033] Figure 5(a) shows the oil flow during the flexion movement of the knee joint 20. Flexion is a contraction process in which the cylinder length decreases, with the piston rod 34 retracting to the left in Figure 5 and the piston 35 moving to the retraction side. The oil pushed out from the second cavity 37 by the movement of the piston 35 cannot flow through the extension-side hydraulic circuit 41 which has an extension-side check valve 44, so it flows through the flexion-side hydraulic circuit 42 and into the first cavity 36. At this time, by lowering the opening of the flexion-side valve 45, the oil can be made less likely to flow through the flexion-side hydraulic circuit 42, thereby limiting the flexion movement of the knee joint 20. In this way, the control unit 50 controls the opening of the flexion-side valve 45, thereby constituting the rotational resistance control unit of the present invention that controls the rotational resistance of the knee axis 23 during the flexion movement of the knee joint 20.

[0034] Figure 5(b) shows the oil flow during the extension operation of the knee joint 20. Extension is an extension process in which the cylinder length increases, and the piston rod 34 extends to the right in Figure 5, causing the piston 35 to move to the push-out side. The oil pushed out from the first cavity 36 by the movement of the piston 35 cannot flow through the bending-side hydraulic circuit 42 which has a bending-side check valve 46, so it flows through the extension-side hydraulic circuit 41 and flows into the second cavity 37. At this time, if the opening of the extension-side valve 43 is reduced, the oil can be made less likely to flow through the extension-side hydraulic circuit 41, thereby limiting the extension operation of the knee joint 20. In this way, the control unit 50 controls the opening of the extension-side valve 43, thereby constituting the rotational resistance control unit of the present invention that controls the rotational resistance of the knee axis 23 during the extension operation of the knee joint 20.

[0035] Returning to Figure 2, we will provide additional information about the various sensors installed on the prosthetic leg 10.

[0036] The knee angle sensor 60 measures the extension and retraction position of the piston rod 34. For example, the position of a magnet attached to the piston rod 34 is measured by a magnetic sensor provided inside the cylinder tube 33. Since there is a one-to-one correspondence between the extension and retraction position of the piston rod 34 and the knee angle of the knee joint 20 or the rotation angle of the knee axis 23, the knee angle sensor 60 can convert the detected extension and retraction position of the piston rod 34 into the knee angle of the knee joint 20. Alternatively, the calculation to convert the extension and retraction position of the piston rod 34 to the knee angle of the knee joint 20 may be performed by the control unit 50. In this case, the knee angle sensor 60 measures the extension and retraction position of the piston rod 34 and provides it to the control unit 50.

[0037] The inertial sensor 75 detects the posture and movement of the lower leg 21 based on the measured velocity and / or acceleration of each axis. For example, the walking phase of the prosthetic leg 10 user can be recognized from the changes in velocity / acceleration measured by the inertial sensor 75, and the position of the lower leg 21 during walking can be tracked by integrating the measured values ​​of the inertial sensor 75, so the stride length (displacement per step) and walking speed per step can be determined. The control unit 50 performs calculations such as integrating the measured values ​​of the inertial sensor 75 to determine the position.

[0038] The load sensor 70 is composed of, for example, a strain sensor and is installed in the ankle area between the lower leg portion 21 and the foot portion 12. The load applied to the ankle area causes strain in the object constituting the strain sensor, and the load can be measured by detecting this strain. If such a load sensor is installed in the thigh connection portion 22, the load applied to the knee joint can also be measured.

[0039] The temperature sensor 80 measures the temperature of the cylinder 30 or the temperature of the oil inside the cylinder 30. For example, it detects when the cylinder 30 becomes hot due to heat generated by hydraulic resistance and switches to a high-temperature mode that restricts the operation of the knee joint 20. Also, because the hydraulic resistance changes in response to temperature changes due to the physical properties of the oil, the control unit 50 can control the control mechanism 40 according to the temperature measured by the temperature sensor 80 to achieve the desired hydraulic resistance. Specifically, a control data set for the control mechanism 40 to achieve each value of hydraulic resistance is created for each temperature and stored in the control unit 50. The control unit 50 selects the control data set corresponding to the temperature measured by the temperature sensor 80 and uses it for control.

[0040] Figure 6 schematically shows the functional block responsible for flexion control of the knee joint 20. This figure shows only the components of the prosthetic leg 10 that are involved in flexion control of the knee joint 20. In addition, the components shown are provided on the knee joint 20, except for the socket 11, and the components responsible for information processing, such as the rotational resistance control unit 100, are implemented in the control unit 50.

[0041] The knee angle acquisition unit 110 acquires the knee angle, which is the angle between the axis of the thigh or the axis of the socket 11 as the thigh and the axis of the lower leg 21. The knee angle acquisition unit 110 acquires the detection result of the knee angle sensor 60 as the knee angle.

[0042] The load acquisition unit 130 acquires the load applied to the lower leg portion 21. The load acquisition unit 130 acquires the detection result of the load sensor 70 as the load applied to the lower leg portion 21.

[0043] When the inertial sensor 75 is provided, an inclination angle acquisition unit including a thigh angle calculation unit 111 that acquires the thigh angle Ψ, which is the inclination angle formed by the socket 11 as the thigh portion with respect to the vertical line passing through the knee axis 23, may be provided at all times or at a predetermined time interval. As described above, since the knee angle θ, the thigh angle Ψ, and the calf angle Φ satisfy the relational expression "θ + Φ = Ψ", the thigh angle calculation unit 111 can calculate the thigh angle Ψ = θ + Φ based on the knee angle θ measured by the knee angle sensor 60 and the calf angle Φ measured by the inertial sensor 75. In addition, since the thigh angle Ψ can be calculated based on the knee angle θ and the calf angle Φ as described above, it is not essential for the thigh angle calculation unit 111 to acquire information regarding the thigh angle Ψ from the socket 11. Further, an angular velocity acquisition unit 120 including a thigh angular velocity acquisition unit 121 (thigh portion inclination angular velocity acquisition unit) that acquires the angular velocity of the thigh angle Ψ and a calf angular velocity acquisition unit 122 that acquires the angular velocity of the calf angle Φ may be provided. Specifically, the thigh angular velocity acquisition unit 121 obtains the thigh angular velocity by differentiating the thigh angle Ψ calculated by the thigh angle calculation unit 111 with respect to time, and the calf angular velocity acquisition unit 122 obtains the calf angular velocity by differentiating the calf angle Φ measured by the inertial sensor 75 with respect to time. When the inertial sensor 75 as the calf angle sensor can directly measure the calf angular velocity, the inertial sensor 75 itself constitutes the calf angular velocity acquisition unit 122. Further, the thigh angular velocity may be calculated based on the calf angular velocity acquired by the calf angular velocity acquisition unit 122 and the knee angular velocity obtained by differentiating the knee angle θ measured by the knee angle sensor 60 with respect to time.

[0044] The rotational resistance control unit 100 controls the rotational resistance of the knee axis 23 (hereinafter also referred to as the flexion resistance). The rotational resistance control unit 100 includes a flexion resistance control unit 101, a state determination unit 102, a counting unit 103, and a seating determination unit 104.

[0045] The flexion resistance control unit 101 controls the flexion resistance during the flexion operation of the knee joint 20 by controlling the opening degree of the flexion side valve 45.

[0046] The state determination unit 102 determines whether it is the end position state described later.

[0047] The counting unit 103 executes various counting processes. The counting unit 103 of the present embodiment counts the duration of the end position state. For example, when the bouncing control ends, the counting unit resets the counting of the end position state.

[0048] The seating determination unit 104 determines whether the user is seated. For example, the seating determination unit 104 determines that the user is seated when a state where the knee angle θ is a certain degree or more and the vertical load is a certain degree or less has elapsed for a certain period of time. Alternatively, based on the detection result of the knee angle sensor 60, it may be determined that the knee angle θ is within a predetermined range near 90°, and based on the detection result of the inertial sensor 75, it may be determined that the user has stopped, and then it may be determined that the user is seated.

[0049] The flexion resistance control unit 101 of the present embodiment executes bouncing control when the user reaches a slight flexion position where the knee is slightly bent. The bouncing control is a control that increases the flexion resistance (i.e., rotational resistance) so as to limit a further increase in the knee angle θ by reducing the opening degree of the flexion side valve 45 when the knee angle θ reaches a predetermined bouncing angle. In the bouncing control of the present embodiment, when the knee angle θ reaches a predetermined bouncing angle (for example, 10°), the flexion side valve 45 is fully closed to maximize the flexion resistance. By this bouncing control, when the user reaches a slight flexion position where the knee is slightly bent due to a posture change such as sitting halfway, a further flexion of the knee joint 20 is restricted, and the knee cannot bend further to the flexion side. As a result, the user can walk with confidence without worrying about knee folding. In the bouncing control, it is not essential to maximize the flexion resistance, and it is sufficient to set a flexion resistance that can limit a further flexion of the knee joint 20. Hereinafter, a state where a further flexion of the knee joint 20 is restricted by the bouncing control may be referred to as a bouncing state.

[0050] On the other hand, in the bouncing state, the prosthetic leg 10 does not bend, so when the user sits down, only the healthy leg can be bent, making a comfortable sitting motion difficult. Therefore, when the user attempts to sit down with the prosthetic leg 10 in the bouncing state, the flexion resistance control unit 101 releases the bouncing state and performs yielding control. Yielding control is a control that controls the flexion valve 45 to a pre-adjusted state between the fully open state and the fully closed state, allowing the knee to bend slowly with appropriate flexion resistance. As a result, the user can sit down with peace of mind without worrying about knee buckling. Hereinafter, the state in which appropriate flexion resistance is applied to the knee joint 20 by yielding control may be referred to as the yielding state.

[0051] Here, for example, when transitioning from a bouncing state to a yielding state, it is assumed that the user releases the bouncing state by moving the prosthetic leg 10 so that the shin angle Φ exceeds a predetermined angle. In this case, for example, the user would need to unnaturally extend their leg forward and support their body with their hands. However, in the bouncing state, the flexion of the knee joint 20 is restricted, so when sitting down, the user can basically only bend their healthy leg. Therefore, the user may be forced into an unnatural posture when releasing the bouncing state during the sitting motion.

[0052] Based on the above, the process for controlling the flexion of the knee joint in the first embodiment will now be explained. Figure 7 is a flowchart of the process S100 for controlling the flexion of the knee joint in the first embodiment. Here, the explanation will be given using the case where the process S100 is started from a standing position and the user sits down as an example, but the process S100 may also be applied when the user stands up from a seated position, for example.

[0053] In step S101, the knee angle sensor 60 acquires the knee angle θ. At this time, the bending resistance control unit 101 suppresses the knee from bending suddenly and sharply by yielding control.

[0054] In step S102, the bending resistance control unit 101 determines whether the knee angle θ obtained in step S101 has become a bouncing angle. If the knee angle θ has become a bouncing angle (Y in step S102), process S100 proceeds to step S103. If the knee angle θ has not become a bouncing angle (N in step S102), process S100 returns to step S101.

[0055] In step S103, the bending resistance control unit 101 performs bouncing control.

[0056] In step S104, the knee angle sensor 60 acquires the knee angle θ after the bouncing control.

[0057] In step S105, the bending resistance control unit 101 determines whether the knee angle θ obtained in step S104 is less than the bouncing angle. If the knee angle θ is less than the bouncing angle (Y in step S105), process S100 proceeds to step S106. If the knee angle θ remains at or above the bouncing angle (N in step S105), process S100 proceeds to step S107.

[0058] In step S106, the bending resistance control unit 101 terminates the bouncing control. This is because, if the knee angle θ transitions from being the bouncing angle in step S102 to being less than the bouncing angle in step S105, it is assumed that the user has transitioned from a posture in which the knee joint 20 is flexed to a posture in which it is extended. After step S106, process S100 returns to step S101.

[0059] In step S107, the load acquisition unit 130 acquires the load applied to the lower leg portion 21.

[0060] In step S108, the state determination unit 102 determines whether the bouncing state is maintained based on the load acquired by the load acquisition unit 130. For example, the state determination unit 102 determines whether the position of the load applied to the lower leg 21 is within a predetermined end range (end position state). In this embodiment, the state determination unit 102 determines that the end position state is reached when the position of the load applied to the lower leg 21 is within the predetermined end range, which is the range from the reference position of the ankle towards the toes (front). If it is determined that the end position state is reached (Y in step S108), processing S100 proceeds to step S109. If it is not the end position state (N in step S108), processing S100 returns to step S104.

[0061] In step S109, the counting unit 103 counts the duration of the end position state.

[0062] In step S110, the state determination unit 102 determines whether the duration of the end position state exceeds a predetermined time. Here, the predetermined time is, for example, 0.5 seconds. If the duration exceeds the predetermined time (Y in step S110), process S100 proceeds to step S111. If the duration does not exceed the predetermined time (N in step S110), process S100 returns to step S104.

[0063] In step S111, the bending resistance control unit 101 terminates the bouncing control. This allows the user to further flex the knee joint 20.

[0064] In step S112, the bending resistance control unit 101 performs yielding control. This allows the user to sit down slowly without worrying about their knees bending.

[0065] In step S113, the seating determination unit 104 determines whether the user has sat down. If the user has sat down (Y in step S113), process S100 proceeds to step S114. If the user has not sat down (N in step S113), process S100 returns to step S112.

[0066] In step S114, the bending resistance control unit 101 terminates the yielding control. After step S114, process S100 returns to step S101.

[0067] After the seating determination unit 104 determines that the user is seated (steps S113 to S114), if the user stands up, the knee angle θ decreases as the user stands up, and when the knee angle θ becomes the bouncing angle, bouncing control is executed (steps S101 to S103). When the user stands up further and the knee angle θ becomes less than the bouncing angle, the bouncing control ends (steps S104 to S106). After that, the user can complete standing.

[0068] The knee joint of this embodiment includes a thigh connection portion 22 provided on the thigh side, a lower leg portion 21 connected to the thigh connection portion 22 and rotatable around a knee axis 23, a load acquisition unit 130 that acquires the load applied to the lower leg portion 21 via the thigh, a knee angle acquisition unit that acquires the knee angle formed by the axis of the lower leg portion 21 and the axis of the thigh, and a rotational resistance control unit 100 that controls the rotational resistance of the knee axis 23. The rotational resistance control unit 100 performs bouncing control by increasing the rotational resistance to limit further increases in the knee angle when the knee angle exceeds a predetermined bouncing angle. While the bouncing control is being performed, the rotational resistance control unit 100 determines whether the position of the load is in a predetermined end position state based on the load acquired by the load acquisition unit 130, and terminates the bouncing control when the duration of the end position state exceeds a predetermined time. With this configuration, since the decision to release the bouncing control is made based on the position of the load applied to the lower leg portion 21, it is possible to release the bouncing control in a natural posture when sitting.

[0069] The position of the load acting on the lower leg portion 21 may be determined based on the position of the point of application of the resultant force of the ground reaction forces generated from the loads acting on each position of the lower leg portion 21, or it may be determined based on the position of the point of application of the resultant force of the loads acting on each position of the lower leg portion 21. For example, if the difference between the vertical load detected by the heel-side strain sensor and the vertical load detected by the toe-side strain sensor is greater than or equal to a positive threshold, the position of the load acting on the lower leg portion 21 is considered to be on the toe side with respect to the reference position. Alternatively, if the difference between the vertical load moment detected by the toe-side strain sensor and the vertical load moment detected by the heel-side strain sensor is greater than or equal to a threshold, the load may be considered to be located on the side (toe side or heel side) where the strain sensor that detected a larger load moment is located, with respect to the reference position.

[0070] The moment of the load detected by the strain sensor may be stored chronologically in the memory unit (not shown) of the control unit 50, and the decision of whether or not to release the bouncing control may be made by taking into account the calculated change in moment. For example, if the change in moment continues to decrease for a predetermined time before reaching the end position state, the rotational resistance control unit 100 does not have to terminate the bouncing control even if the end position state continues for a predetermined time. If the change in moment decreases before reaching the end position state, the possibility of walking is low, so it is possible to suppress the misjudgment of ending the bouncing control.

[0071] The load position considered to be the final position can be either on the toe side or the heel side, but it is preferable to set it on the toe side. Here, Figure 8 illustrates the walking phases (H) to (J) of a user of the prosthetic leg 10 on a downhill slope. Walking phase (H) is the initial contact phase, when the prosthetic leg 10 makes contact with the ground. Walking phase (I) is the load response phase, when the user's weight is supported by the contacted prosthetic leg 10. Walking phase (J) is the mid-stance phase, when the user's center of gravity moves forward of the prosthetic leg 10 while the prosthetic leg 10 is supporting the weight. As shown in Figure 8, in walking phase (I), the knee angle θ becomes the bouncing angle, so bouncing control is executed. As a result, the user can walk downhill with confidence without worrying about knee buckling. Here, on a downhill slope, it is normal for the user to shift their center of gravity backward to avoid falling forward. Therefore, if the termination range is set towards the rear, the load position tends to shift towards the rear on downhill slopes, leading to a misjudgment of the end of the bouncing control and an increased likelihood of knee buckling. In contrast, in this embodiment, the termination range is the area towards the toes of the prosthetic leg. This configuration makes it possible to suppress misjudgments of the end of the bouncing control on downhill slopes.

[0072] The second embodiment of the present invention will be described below. In the drawings and description of the second embodiment, the same or equivalent components and members as in the first embodiment will be denoted by the same reference numerals. Descriptions that overlap with the first embodiment will be omitted as appropriate, and the description will focus on the configurations that differ from the first embodiment.

[0073] Figure 9 is a flowchart showing the process S200 related to the flexion control of the knee joint in the second embodiment. Steps S201 to S214 in process S200 are the same as S101 to S114 in process S100, except for points that are not specifically mentioned, so their explanation is omitted.

[0074] After step S214, process S200 proceeds to step S215. In step S215, the bending resistance control unit 101 increases the bouncing angle from the normal first angle (e.g., 10°) used in step S205 to a second angle (e.g., 60°). The second angle is greater than the first angle.

[0075] In step S216, the knee angle sensor 60 obtains the knee angle θ after the change in the bouncing angle. When the user stands up from a seated position, the knee angle θ at this point will decrease.

[0076] In step S217, the state determination unit 102 determines whether the knee angle θ has reached the second angle. If the knee angle θ has reached the second angle (Y in step S217), process S200 proceeds to step S218. If the knee angle θ has not reached the second angle (N in step S217), process S200 returns to step S216.

[0077] In step S218, the bending resistance control unit 101 performs bouncing control. Note that extension movement is not restricted even during bouncing control, so the user can stand up.

[0078] In step S219, the state determination unit 102 determines whether the knee angle θ has reached the first angle. If the knee angle θ has reached the first angle (Y in step S219), process S200 proceeds to step S220. If the knee angle θ has not reached the first angle (N in step S219), the state determination unit 102 continues the determination until the knee angle θ reaches the first angle.

[0079] In step S220, the bending resistance control unit 101 terminates the bouncing control and returns the bouncing angle to the first angle. After step S220, process S100 returns to step S201.

[0080] As described above, the prosthetic leg 10 of the second embodiment includes a seating determination unit 104 that determines whether the user is seated, and the rotational resistance control unit 100 changes the bouncing angle from a first angle to a second angle which is greater than the first angle when it is determined that the user is seated, and executes bouncing control when the user transitions from a state in which it is determined that the user is seated to a state in which it is determined that the user is not seated and the knee angle θ becomes the second angle. With this configuration, the flexion resistance increases at an early stage after the user attempts to stand up, so even users with weak standing strength can easily stand up from a seated position without their knees bending again.

[0081] Alternatively, the load sensor detection result may be acquired between steps S214 and S221, and the processes S101 to S114 in process S100 may be performed in parallel. This allows for a smooth transition of control when a user who has tried to stand up tries to sit down again.

[0082] Modifications of the present invention will be described below.

[0083] In this embodiment, a knee angle sensor 60, a load sensor 70, and an inertia sensor 75 were used as sensors for controlling the flexion of the knee joint 20. However, only the knee angle sensor 60 and the load sensor 70 may be used, or only the inertia sensor 75 may be used. Furthermore, other sensors may be used as long as they are suitable for the purpose.

[0084] In this embodiment, two strain sensors are arranged on the toe side and heel side as the load sensor 70, but it is not limited to this, and two or more strain sensors may be arranged on the toe side and heel side. Also, three strain sensors may be provided, including the center of gravity position of the ankle, or a strain sensor may be placed only at the center of gravity position of the ankle. Furthermore, if suitable for the purpose, other sensors such as torque sensors may be used instead of strain sensors.

[0085] In this embodiment, the load sensor 70 is provided at the lower end of the lower leg portion 21, but it may also be provided at the thigh connection portion 22, the knee portion between the thigh connection portion 22 and the lower leg portion 21, or the foot portion 12. Also, in this embodiment, the temperature sensor 80 for measuring the oil temperature inside the cylinder 30 is provided on the outer wall of the cylinder 30, but it may also be attached to the inner wall of the cylinder 30.

[0086] In this embodiment, the termination range is defined as the toe side of the prosthetic leg 10 from the viewpoint of suppressing misjudgment, but it is not limited to this. For example, from the viewpoint of convenience, it may be defined as the heel side of the prosthetic leg 10 (the range from the reference position of the ankle to the heel side (rear side)). Since users often use the prosthetic leg 10 with their weight centered on the heel side, defining the termination range as the heel side of the prosthetic leg 10 makes it easier for the user to sit down with smooth movements. Furthermore, the termination range may be defined as the range on one side or both sides in the left-right direction of the prosthetic leg 10, or it may be defined as at least one of the toe side, heel side, or one side or both sides in the left-right direction of the prosthetic leg 10.

[0087] In this embodiment, the load position is any position on the side where the strain sensor that detects a larger load moment relative to the reference position is installed is used as the load position. However, the system is not limited to this, and the center of gravity of the load detected by the load sensor 70 may be used as the load position. For example, the load distribution is determined from the loads measured by each load sensor 70, and the center of gravity of the load detected by the load sensor 70 is determined based on the load distribution. Whether or not to terminate the bouncing control may be determined based on whether or not this center of gravity of the load is within the termination range.

[0088] In this embodiment, the decision to terminate the bouncing control was made based on the load applied to the lower leg portion 21, but it is not limited to this, and the decision to terminate the bouncing control may also be made based on the load applied to the thigh connection portion 22, the foot portion 12, or the prosthetic leg 10. In this case, the load applied to the thigh connection portion 22, the foot portion 12, and the prosthetic leg 10 may be measured by providing load sensors 70 on the thigh connection portion 22 and the foot portion 12.

[0089] In this embodiment, a hydraulic circuit was used as the mechanism for generating rotational resistance of the knee axis 23, but other mechanisms such as magnetic fluid or mechanical valves may also be used.

[0090] This invention allows users with knee joints on both legs to release the bouncing state through a natural posture.

[0091] The present invention has been described above based on embodiments. The embodiments are illustrative, and it will be understood by those skilled in the art that various modifications are possible in combinations of their components and processing processes, and that such modifications also fall within the scope of the present invention.

[0092] The functional configurations of each device described in the embodiments can be realized using hardware resources, software resources, or through the cooperation of hardware and software resources. Hardware resources can include processors, ROMs, RAMs, and other LSIs. Software resources can include operating systems, applications, and other programs.

[0093] In the embodiments disclosed herein, those in which multiple functions are provided in a distributed manner may have some or all of those multiple functions integrated into a single unit, and conversely, those in which multiple functions are integrated may have some or all of those functions provided in a distributed manner. Whether the functions are integrated or distributed, the configuration should be such that the objective of the invention can be achieved.

[0094] This invention relates to prosthetic limb technology.

[0095] 10 Prosthetic leg, 11 Socket, 20 Knee joint, 21 Lower leg, 22 Thigh joint, 23 Knee axis, 30 Cylinder, 34 Piston rod, 35 Piston, 40 Control mechanism, 43 Extension valve, 45 Flexion valve, 50 Control unit, 60 Knee angle sensor, 70 Load sensor, 75 Inertia sensor, 100 Rotational resistance control unit, 101 Flexion resistance control unit, 102 State determination unit, 103 Counting unit, 104 Seating determination unit, 110 Knee angle acquisition unit, 111 Thigh angle calculation unit, 120 Angular velocity acquisition unit, 121 Thigh angular velocity acquisition unit, 122 Shin angular velocity acquisition unit, 130 Load acquisition unit.

Claims

1. A prosthetic leg comprising: a thigh connection portion provided on the thigh side; a lower leg portion connected to the thigh connection portion and rotatable around a knee axis; a load acquisition portion for acquiring the load applied to the prosthesis via the thigh portion; a knee angle acquisition portion for acquiring the knee angle formed by the axis of the lower leg portion and the axis of the thigh portion; and a rotational resistance control portion for controlling the rotational resistance of the knee axis, wherein the rotational resistance control portion performs bouncing control to strengthen the rotational resistance to limit further increases in the knee angle when the knee angle exceeds a predetermined bouncing angle; the rotational resistance control portion determines whether the position of the load is in a predetermined end position state within a predetermined end range based on the load acquired by the load acquisition portion while the bouncing control is being performed, and terminates the bouncing control when the duration of the end position state exceeds a predetermined time.

2. The end range is the toe-side range of the prosthesis, as described in claim 1.

3. The end range is the heel side range of the prosthesis, as described in claim 1.

4. The prosthetic leg according to any one of claims 1 to 3, comprising a seating determination unit for determining whether a user is seated, wherein the rotational resistance control unit executes the bouncing control when the knee angle becomes the bouncing angle after it has been determined that the user is seated.

5. The prosthetic leg according to any one of claims 1 to 3, comprising a seating determination unit for determining whether a user is seated, wherein the rotational resistance control unit changes the bouncing angle from a first angle to a second angle greater than the first angle when it is determined that the user is seated, and executes the bouncing control when the user transitions from a state in which it is determined that the user is seated to a state in which it is determined that the user is not seated and the knee angle becomes the second angle.

6. The prosthetic leg according to claim 5, wherein the rotational resistance control unit changes the bouncing angle to the first angle when the user transitions from a state in which it is determined that the user is seated to a state in which it is determined that the user is not seated, and the knee angle reaches the second angle, and then the knee angle reaches the first angle.

7. A knee joint comprising: a thigh connecting portion provided on the thigh side; a lower leg portion connected to the thigh connecting portion and rotatable around a knee axis; a load acquisition portion for acquiring the load applied to the lower leg portion via the thigh portion; a knee angle acquisition portion for acquiring the knee angle formed by the axis of the lower leg portion and the axis of the thigh portion; and a rotational resistance control portion for controlling the rotational resistance of the knee axis, wherein the rotational resistance control portion performs bouncing control to increase the rotational resistance to limit further increases in the knee angle when the knee angle exceeds a predetermined bouncing angle; the rotational resistance control portion determines whether the position of the load is in a predetermined end position state within a predetermined end range based on the load acquired by the load acquiring portion while the bouncing control is being performed, and terminates the bouncing control when the duration of the end position state exceeds a predetermined time.

8. A control method for a knee joint comprising: a thigh connecting portion provided on the thigh side; a lower leg portion connected to the thigh connecting portion and rotatably provided around a knee axis; a load acquisition portion for acquiring the load applied to the lower leg portion via the thigh portion; a knee angle acquisition portion for acquiring the knee angle formed by the axis of the lower leg portion and the axis of the thigh portion; and a rotational resistance control portion for controlling the rotational resistance of the knee axis, the control method comprising: a step of performing bouncing control to strengthen the rotational resistance to limit further increase of the knee angle when the knee angle exceeds a predetermined bouncing angle; a step of determining whether the position of the load is in an end position state within a predetermined end range based on the load acquired by the load acquisition portion while the bouncing control is being performed; and a step of terminating the bouncing control when the duration of the end position state exceeds a predetermined time.

9. A control program for a knee joint comprising: a thigh connecting portion provided on the thigh side; a lower leg portion connected to the thigh connecting portion and rotatable around a knee axis; a load acquisition unit for acquiring the load applied to the lower leg portion via the thigh portion; a knee angle acquisition unit for acquiring the knee angle formed by the axis of the lower leg portion and the axis of the thigh portion; and a rotational resistance control unit for controlling the rotational resistance of the knee axis, the control program causing a computer to perform: a bouncing control that strengthens the rotational resistance to limit further increase of the knee angle when the knee angle exceeds a predetermined bouncing angle; a step of determining whether the position of the load is in a predetermined end position state within a predetermined end range based on the load acquired by the load acquisition unit while the bouncing control is being performed; and a step of terminating the bouncing control when the duration of the end position state exceeds a predetermined time.

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