Control of a passive prosthetic knee joint with adjustable damping

Abstract

Systems and methods for controlling a passive prosthetic knee joint with adjustable damping in the direction of flexion such that a prosthetic unit attached to the knee joint can be adapted for climbing stairs.

Claims

1. A method for controlling a passive prosthetic knee joint in a prosthetic unit, the prosthetic unit comprising: the passive prosthetic knee joint; a prosthetic leg unit coupled to the passive prosthetic knee joint; a prosthetic foot coupled to the prosthetic leg unit; a plurality of sensors; the method for controlling the passive prosthetic knee joint comprising: determining that the passive prosthetic knee joint is straight or approximately straight by detecting a knee angle of the passive prosthetic knee joint with at least one of the plurality of sensors; determining that an axial force in the prosthetic leg unit is zero or approximately zero with at least one of the plurality of sensors; initiating a stair-climbing mode of the passive prosthetic knee joint based upon the passive prosthetic knee joint being straight or approximately straight and based upon the axial force in the prosthetic leg unit being zero or approximately zero; activating a flexion resistance control of the passive prosthetic knee joint upon initiation of the stair-climbing mode; activating an extension resistance control of the passive prosthetic knee joint upon initiation of the stair-climbing mode; wherein the flexion resistance control includes adjusting a flexion damping of the passive prosthetic knee joint, and wherein adjusting the flexion damping includes lowering the flexion damping to a minimum value; wherein the flexion resistance control further includes: minimizing a flexion resistance after initiation of the stair-climbing mode; determining that the passive prosthetic knee joint is in a hip straightening phase or has experienced an extension movement; maintaining the minimum flexion resistance until the passive prosthetic knee joint is determined to be in a hip-straightening phase or experiences an extension movement; and increasing the flexion resistance to a maximum value based upon the passive prosthetic knee joint being in the hip-straightening phase or experiencing the extension movement to avoid an unintended flexion movement resulting from an insufficient hip straightening torque.

2. The method of claim 1, wherein the prosthetic unit comprises an upper element coupled to the passive prosthetic knee joint, the upper element also being configured to receive a stump, and wherein the upper element and the passive prosthetic knee joint form a rigid structure from a location where the passive prosthetic knee joint rotates to a location where the upper element is configured to be coupled to the stump.

3. The method of claim 1, comprising maintaining the minimum value of the flexion damping until the axial force in the prosthetic leg unit increases as detected by the at least one of the plurality of sensors.

4. The method of claim 1, wherein the prosthetic unit comprises a control unit that detects the stair-climbing mode of the prosthetic foot.

5. The method of claim 1, comprising determining that the prosthetic leg unit is accelerating vertically, and initiating the stair-climbing mode of the passive prosthetic knee joint based upon the prosthetic leg unit accelerating vertically.

6. The method of claim 1, comprising maintaining the minimum value of flexion damping until a predetermined minimum knee angle is detected by the at least one of the plurality of sensors.

7. The method of claim 1, comprising determining that the prosthetic foot is in a foot placement phase with at least one of the plurality of sensors, and increasing an extension damping level to a level above that used for walking on level ground based upon the prosthetic foot being in the foot placement phase.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An illustrative embodiment is explained in more detail below with reference to the figures.

(2) FIGS. 1 to 6 are schematic depictions showing the sequence involved in alternating stair-climbing with a passive knee joint prosthesis.

DETAILED DESCRIPTION

(3) FIG. 1 shows a prosthesis wearer 1 with a knee joint prosthesis 2 which is secured by upper attachment elements to a femoral stump. The prosthetic leg 20 stands with the healthy contralateral leg 4 in front of a step.

(4) To reach the next step up, a prosthetic foot 6 has to be guided over the step edge. An active bending of the hip, as is indicated by the arrow 7, assists the passive bending of the knee, which is shown by the arrow 8 and which, because of the mass inertia both of the prosthetic foot 6 and also of the connection element 3, occurs from the prosthetic knee joint 2 to the prosthetic foot 6. For this purpose, a minimum extension damping is required to ensure that, after a flexion of the hip, the prosthetic foot 6 does not swing forward and is not moved against the riser or under the step 5. In the lift phase, as shown in FIG. 2, the prosthetic foot 6 is guided upward, as far as possible in a perpendicular manner, this possibly being initiated by a slight rearward movement. The lift is detected with at least one sensor 10 (see FIGS. 1-3) via the flexion angle a between the connection element 3 and the thigh or via a reduction of the axial force in the connection element 3, without flexion of the prosthetic foot 6. It is also possible to detect the stair-climbing mode, and thus the lowering of the flexion damping to a value below the normal swing phase control, preferably to the minimum value, via a horizontal rearward movement of the prosthetic foot 6 in conjunction with a bending of the hip.

(5) After the step edge has been negotiated and the lift phase completed, as is shown in FIG. 2, a secure positioning of the prosthetic foot 6 on the step is required. For this purpose, the prosthetic foot 6 has to be moved forward, which can be achieved by extension as a result of the force of gravity. For this purpose, an extension damping can be reduced, if this has not already been done in the lift phase. A prosthetic knee joint 2 that is sufficiently damped in flexion and extension prior to straightening allows the prosthesis wearer 1 to position the prosthetic foot 6, by changing the hip angle. In the lowering and hip-straightening phase, the flexion and extension are preferably strongly damped to control the foot placement, and to prevent a spontaneous backward fall in the event that the hip-straightening torque is insufficient. The extension remains damped so as to be able to control the speed of straightening of the hip and knee. This is shown in FIG. 3.

(6) in FIG. 4, the foot placement phase is completed. The prosthesis wearer 1 can initiate straightening of the knee with a hip-straightening torque. The straightening of the knee can be assisted by an extension of the healthy foot.

(7) FIG. 5 shows the increasing straightening of the knee through application of a hip torque. The increasing straightening of the knee shortens the effective lever and facilitates the straightening of the knee through the straightening of the hip.

(8) FIG. 6 shows the complete extension of the leg provided with the knee joint prosthesis 2. The contralateral leg 4 is moved past the prosthetic leg 20 and placed on the next step up, such that alternating climbing of stairs is possible with the passive knee joint prosthesis.

(9) Accordingly, the control is configured in such a way that, during the lift of the prosthetic foot 6 a flexion resistance is set that results in a knee angle a, which allows the prosthetic foot 6 to be placed on the next step. Flexion support by spring mechanisms may facilitate the lifting movement and make it easier to negotiate the step height.

(10) If no action is to take place after the stair-climbing mode has been triggered by detection of a low-torque lift, a free extension is set, said free extension being set in a time-dependent manner. The time function can also be mechanical. The low-torque lift can be detected via the mass inertia, if the healthy leg is first set down and only the second step is intended to be negotiated by the leg provided with the prosthesis. If the prosthetic foot is first unloaded and the prosthetic knee joint then bent, the stair-climbing mode is set. Damping both in the direction of extension and also in the direction of flexion after the lift phase, that is to say during the hip-straightening phase, is maintained until a complete extension of the prosthetic knee joint is reached or detected.

(11) P1. A control of a passive prosthetic knee joint with adjustable damping in the direction of flexion such that a prosthetic unit, with upper attachment elements and with a connection element to an artificial foot, can be adapted for climbing stairs, said control involving the following steps: detecting a low-torque lift of the prosthetic food, and lowering the flexion damping in a lift phase to below a level that is suitable for walking on level ground.

(12) P2. The control in paragraph P1, characterized in that the extension and/or flexion damping, in a foot placement and hip-straightening phase, is increased to a level above a damping of a swing phase control for walking on level ground.

(13) P3. The control in paragraph P2, characterized in that the flexion damping in the foot placement phase is increased to a maximum value.

(14) P4. The control in paragraphs P2 or P3, characterized in that the flexion damping in the foot placement and hip-straightening phase is maintained until the hip is fully straightened.

(15) P5. The control in one of paragraphs P2 through P4, characterized in that the flexion damping is increased as a function of the change of the knee angle.

(16) P6. The control in one of the preceding paragraphs (P1-P5), characterized in that the flexion damping is increased or lowered as a function of the axial force acting on the lower leg shaft.

(17) P7. The control in one of the preceding paragraphs (P1-P6), characterized in that an extension damping is set during the lift phase and also during the foot placement and hip-straightening phase.

(18) P8. The control in one of the preceding paragraphs (P1-P7), characterized in that the low-torque lift is detected by a force or torque sensor.

(19) P9. The control in one of the preceding paragraphs (P1-P8), characterized in that the low-torque lift is detected by measuring a horizontal acceleration of the prosthetic foot and by recording a bending in the prosthetic knee joint.

(20) P10. The control in one of the preceding paragraphs (P1-P9), characterized in that a low-torque lift is detected by recording a torque at the front of the prosthetic foot.

(21) P11. The control in one of the preceding paragraphs (P1-P10), characterized in that the flexion in the lift phase is supported via a pretensioned spring mechanism.

(22) P12. The control in one of the preceding paragraphs (P1-P11), characterized in that the increase in the flexion and extension damping is initiated when the prosthetic foot, after being lifted, is placed down again.

(23) P13. The control in paragraph P12, characterized in that the foot placement is detected by an axial force measurement in the lower leg shaft or in the prosthetic foot.

(24) P14. The control in one of the preceding paragraphs (P1-P13), characterized in that the flexion damping in the lift phase is lowered to a minimum value.

(25) P15. The control in one of the preceding paragraphs (P1-P14), characterized in that, after the flexion damping has been lowered, a free extension is set with time control.

(26) P16. The control in paragraph P15, characterized in that the free extension is spring-assisted.

(27) P17. The control in paragraph P15 or P16, characterized in that the time control is effected mechanically or electronically.

(28) P18. A method for initiating and implementing a stair-climbing mode in a passive prosthetic knee joint connected to a prosthetic leg unit including a prosthetic foot comprising: detecting a low-torque lift of the prosthetic foot; initiating a lift phase, in which a flexion damping level of the knee joint is reduced to a level below that which is used for walking on level ground; detecting a placement of the prosthetic foot; and initiating a lowering phase, in which the flexion damping level is increased to a level above that which is used for walking on level ground.

(29) P19. The method of paragraph P18, wherein in the lowering phase, an extension damping level is increased to a level above that which is used for walking on level ground.

(30) P20. The method of paragraph P19, wherein the flexion damping and extension damping are increased to maximum levels in the lift phase.

(31) P21. The method of paragraph P18, wherein the flexion damping is reduced to a minimum level in the lift phase.

(32) P22. The method of paragraph P18 further comprising the step of, during the lowering phase, maintaining the flexion damping level until a straightened hip is detected.

(33) P23. The method of paragraph P18, further comprising the step of, during the lowering phase, detecting a knee angle and establishing, the flexion damping level as a function of the detected knee angle.

(34) P24. The method of paragraph P18 wherein at least one of the detecting steps comprises the step of detecting an axial force along the prosthetic unit.

(35) P25. The method of paragraph P18 wherein an extension damping level is established during each of the lifting and lowering phases.

(36) P26. The method of paragraph P18 wherein the step of detecting the low torque lift comprises measuring a horizontal acceleration of the prosthetic foot and by detecting a bend in the knee joint.

(37) P27. The method of paragraph P18 wherein the step of detecting the low torque lift comprises detecting a torque at the front of the prosthetic foot.

(38) P28. The method of paragraph P18 wherein the step of detecting the placement of the foot comprises measuring an axial force measurement along the prosthetic unit.

(39) P29. The method of paragraph P18 wherein after initiating the lifting phase, a time controlled free extension is set.