METHOD FOR CONTROLLING AN ARTIFICIAL ORTHOTIC OR PROSTHETIC KNEE JOINT

Abstract

A method for controlling an artificial orthotic or prosthetic knee joint, on which a lower-leg component is arranged and with which a resistance device is associated, the bending resistance (R) of which resistance device is changed in dependence on sensor data that are determined by means of at least one sensor during the use of the orthotic or prosthetic knee joint, wherein a linear acceleration (a.sub.F) of the lower-leg component is determined, the determined linear acceleration (a.sub.F) is compared with at least one threshold value, and, if a threshold value of the linear acceleration (a.sub.F) of the lower-leg component is reached, the bending resistance (R) is changed.

Claims

1-13. (canceled)

14. A method for controlling an artificial orthotic or prosthetic knee joint, the orthotic or prosthetic knee joint including a resistance device, at least one sensor, and a below-knee component, the method comprising: determining sensor data via the at least one sensor during use of the orthotic or prosthetic knee joint; determining at least one of a linear acceleration of the below-knee component, an extended stride position of a prosthesis or orthosis having the artificial prosthetic or orthotic knee joint, a knee angle, a knee angle velocity, and/or an angular velocity of the below-knee component with the sensor data; comparing at least one of the determined linear acceleration, the determined extended stride position, the determined knee angle, the determined knee angle velocity, and/or the determined angular velocity with at least one threshold value therefor; reducing a flexion resistance if the threshold value is reached; determining an absolute angle of the below-knee component in order to detect a terminal stance phase; and reducing the flexion resistance if a predefined limit value for the absolute angle of the below-knee component is exceeded.

15. The method as claimed in claim 14, wherein determining at least one of a linear acceleration of the below-knee component, an extended stride position of a prosthesis or orthosis having the artificial prosthetic or orthotic knee joint, a knee angle, a knee angle velocity, and an angular velocity of the below-knee component with the sensor data comprises determining the extended stride position of a prosthesis or orthosis having the artificial prosthetic or orthotic knee joint, and reducing the flexion resistance when the extended stride position is present.

16. The method as claimed in claim 14, wherein determining at least one of a linear acceleration of the below-knee component, an extended stride position of a prosthesis or orthosis having the artificial prosthetic or orthotic knee joint, a knee angle, a knee angle velocity, and an angular velocity of the below-knee component with the sensor data comprises determining the linear acceleration of the below-knee component, and reducing the flexion resistance when the extended stride position is present, and wherein the threshold value is zero acceleration in a horizontal direction.

17. The method as claimed in claim 14, further comprising measuring the absolute angle of the below-knee component from an absolute angle of a thigh component and a knee angle or directly with an inertial angle sensor.

18. The method as claimed in claim 14, wherein determining at least one of a linear acceleration of the below-knee component, an extended stride position of a prosthesis or orthosis having the artificial prosthetic or orthotic knee joint, a knee angle, a knee angle velocity, and an angular velocity of the below-knee component with the sensor data comprises determining the knee angle via the at least one sensor, and reducing the flexion resistance if a predefined limit value for the knee angle is not reached.

19. The method as claimed in claim 14, wherein determining at least one of a linear acceleration of the below-knee component, an extended stride position of a prosthesis or orthosis having the artificial prosthetic or orthotic knee joint, a knee angle, a knee angle velocity, and an angular velocity of the below-knee component with the sensor data comprises determining the knee angle velocity, and reducing the flexion resistance only when a limit value is exceeded.

20. The method as claimed in claim 14, wherein determining at least one of a linear acceleration of the below-knee component, an extended stride position of a prosthesis or orthosis having the artificial prosthetic or orthotic knee joint, a knee angle, a knee angle velocity, and an angular velocity of the below-knee component with the sensor data comprises calculating or detecting the angular velocity of the below-knee component via the at least one sensor, and reducing the flexion resistance only when the angular velocity is below a limit value.

21. The method as claimed in claim 14, wherein, after a reduction of the flexion resistance, the method further comprising increasing the flexion resistance again if, within a predefined time interval, no bending of the knee joint took place, or if, within an enclosed knee angle, a limit value for an acceleration is exceeded.

22. A method to control an artificial orthotic or prosthetic knee joint, the method comprising: providing an inertial measurement system, a below-knee component positioned on the orthotic or prosthetic knee joint, and a resistance device, the below-knee component including a sole member; determining sensor data via the inertial measurement system during use of the orthotic or prosthetic knee joint; determining a linear acceleration at a level of the sole member, an extended stride position of a prosthesis or orthosis having the artificial prosthetic or orthotic knee joint, a knee angle, a knee angle velocity, and an angular velocity of the below-knee component with the sensor data; comparing at least one of the determined linear acceleration, the determined extended stride position, the determined knee angle, the determined knee angle velocity, and the determined angular velocity with at least one threshold value; reducing a flexion resistance if the threshold value is reached; determining an absolute angle of the below-knee component in order to detect a terminal stance phase; and reducing the flexion resistance if a predefined limit value for the absolute angle of the below-knee component is exceeded.

23. The method as claimed in claim 22, wherein determining at least one of a linear acceleration of the below-knee component, an extended stride position of a prosthesis or orthosis having the artificial prosthetic or orthotic knee joint, a knee angle, a knee angle velocity, and an angular velocity of the below-knee component with the sensor data comprises determining the extended stride position of a prosthesis or orthosis having the artificial prosthetic or orthotic knee joint, and reducing the flexion resistance when the extended stride position is present.

24. The method as claimed in claim 22, wherein determining at least one of a linear acceleration of the below-knee component, an extended stride position of a prosthesis or orthosis having the artificial prosthetic or orthotic knee joint, a knee angle, a knee angle velocity, and an angular velocity of the below-knee component with the sensor data comprises determining the linear acceleration of the below-knee component, and reducing the flexion resistance when the extended stride position is present, and wherein the threshold value is zero acceleration in a horizontal direction.

25. The method as claimed in claim 24, further comprising measuring the absolute angle of the below-knee component from an absolute angle of a thigh component and a knee angle or directly with an inertial angle sensor.

26. The method as claimed in claim 22, wherein determining at least one of a linear acceleration of the below-knee component, an extended stride position of a prosthesis or orthosis having the artificial prosthetic or orthotic knee joint, a knee angle, a knee angle velocity, and an angular velocity of the below-knee component with the sensor data comprises determining the knee angle via the at least one sensor, and reducing the flexion resistance if a predefined limit value for the knee angle is not reached.

27. The method as claimed in claim 22, wherein determining at least one of a linear acceleration of the below-knee component, an extended stride position of a prosthesis or orthosis having the artificial prosthetic or orthotic knee joint, a knee angle, a knee angle velocity, and an angular velocity of the below-knee component with the sensor data comprises determining the knee angle velocity, and reducing the flexion resistance only when a limit value is exceeded.

28. The method as claimed in claim 22, wherein determining at least one of a linear acceleration of the below-knee component, an extended stride position of a prosthesis or orthosis having the artificial prosthetic or orthotic knee joint, a knee angle, a knee angle velocity, and an angular velocity of the below-knee component with the sensor data comprises calculating or detecting the angular velocity of the below-knee component via the at least one sensor, and reducing the flexion resistance only when the angular velocity is below a limit value.

29. The method as claimed in claim 22, wherein, after a reduction of the flexion resistance, the method further comprising increasing the flexion resistance again if, within a predefined time interval, no bending of the knee joint took place, or if, within an enclosed knee angle, a limit value for an acceleration is exceeded.

30. The method as claimed in claim 22, wherein the threshold value is zero acceleration in a horizontal direction.

31. The method as claimed in claim 22, wherein the inertial measurement system includes an inertial sensor and an acceleration sensor.

32. The method as claimed in claim 14, wherein the at least one sensor includes an inertial sensor and an acceleration sensor.

33. A method to control an artificial orthotic or prosthetic knee joint, the method comprising: providing at least one sensor, a below-knee component positioned on the orthotic or prosthetic knee joint, and a resistance device, the below-knee component including a sole member, the at least one sensor including an inertial sensor and an acceleration sensor; determining sensor data via the at least one sensor during use of the orthotic or prosthetic knee joint; changing a flexion resistance applied by the resistance device using the sensor data; determining a linear acceleration at a level of the sole member with the sensor data; reducing the flexion resistance if the linear acceleration is zero in a horizontal direction; determining an absolute angle of the below-knee component in order to detect a terminal stance phase; and reducing the flexion resistance if a predefined limit value for the absolute angle of the below-knee component is exceeded.

Description

[0024] An illustrative embodiment of the invention is explained in more detail below with reference to the figures, in which:

[0025] FIG. 1 shows a schematic representation of a prosthetic knee joint;

[0026] FIG. 2 shows a schematic representation of an extension stop;

[0027] FIG. 3 shows an example of a control sequence, and

[0028] FIG. 4 shows a schematic representation of a control concept.

[0029] FIG. 1 shows a prosthetic device for patients with a thigh stump and with no knee joint and lower leg. A prosthesis socket 1, also designated as the thigh component of the prosthesis or as the thigh socket, serves to receive the stump (not shown). Arranged on the prosthesis socket 1, there is a prosthetic knee joint 2 which, in the present case, is designed as a monocentric knee joint, and a below-knee component 3 is mounted so as to pivot about a pivot axis, relative to the thigh socket 1. A prosthetic foot 4 is arranged at the distal end of the below-knee component 3. The prosthetic device is shown in a terminal stance phase, the prosthetic foot 4 still located on the ground. Arranged inside the below-knee component 3 there is a resistance device 5, which offers resistance to bending, i.e. flexion, and the resistance device 5 likewise serves for variable adjustment of an extension resistance. The resistance within the resistance device is changed via an actuator which, for example, opens or closes valves or redirects hydraulic flows. Alternatively, it is likewise possible that the actuator changes Theological properties of the hydraulic fluid in order to change the resistance. Alternative changes to resistance are possible, for example the activation of brakes or the conversion of kinetic energy to electrical energy.

[0030] An inertial sensor 31 is arranged on the below-knee component 3 and records the absolute angle φ.sub.US of the below-knee component. The inertial sensor 31 measures the absolute angle φ.sub.US of the below-knee component 3 with respect to the vertical and can be configured as a 2D or 3D magnetic field sensor, a 2D or 3D acceleration sensor or as a gyroscope. The absolute angle φ.sub.US increases as the inclination of the below-knee component 3 in the forward walking direction increases, i.e. during a clockwise pivoting about a distal point of contact with the ground. Moreover, an acceleration sensor 12 is arranged on the below-knee component 3 and can determine a tangential acceleration a.sub.T, i.e. an acceleration tangential to the pivot radius of the below-knee component 3, and a radial acceleration a.sub.R, i.e. an acceleration in the direction of the distal rotation point of the below-knee component 3, of the knee joint 12. With a corresponding sensor, e.g. a 3D acceleration sensor, it is also possible to detect the medial and lateral accelerations in addition or to detect only these accelerations.

[0031] Finally, a knee angle sensor 11 is provided via which the knee angle φk can be detected. The knee angle φ.sub.K is regarded as increasing positively in the flexion direction from the prolongation of the longitudinal extent of the below-knee component 3; the knee angle φ.sub.K is 0 when the longitudinal extent of the prosthesis socket 1 is flush with the axis of the longitudinal extent of the below-knee component 3. A hyperextension is regarded as a negative knee angle φk.

[0032] The prosthetic knee joint 2 can have an elastic extension stop, which is shown schematically in FIG. 2. In addition to the schematic thigh socket 1 and the schematic below-knee component 3, which are mounted pivotably on each other about a joint axis, an abutment 10 is arranged on the upper part of the prosthetic knee joint 2. The abutment 10 is substantially rigid and, in the extended state as shown in FIG. 2, an elastic stop element 30 bears on the rigid abutment 10. A slight hyperextension is permitted by the spring design and, from knowledge of the spring rate of the stop element 30, the knee moment acting in the extension direct on can be calculated from the knee angle φ.sub.K. Of course, it is also possible to arrange the abutment 10 on the below-knee component and to arrange the elastic stop element on the upper part 1.

[0033] To control the enablement of a swing phase, several parameters can be used, namely the forward inclination of the below-knee component 3, i.e. a positive below-knee angle φ.sub.US of the below-knee component 3, a forward rotation of the lower leg in the walking direction, i.e. an increase in the absolute angle φ.sub.US of the below-knee component 3, an acceleration of the knee joint, in order in particular to determine the state of movement of the prosthetic foot 4 at the sole level, and the knee angle φ.sub.K and a knee angle velocity ω.sub.K, which can be calculated from the first time derivative of the knee angle φ.sub.K.

[0034] FIG. 3 shows a schematic control sequence. In order to enable a swing phase and to reduce the flexion resistance R of the resistance device 5, the forward inclination is first determined, i.e. the positive absolute angle φ.sub.US of the below-knee component 3 relative to the vertical. If the absolute angle φ.sub.US is above a set limit value, for example 5°, the first condition for enablement of the swing phase is met. If, in addition, a forward rotation in the form of a lower leg angular velocity ω.sub.US is detected, it can be assumed that the lower leg is in movement; a forward rotation of >10°/s, for example, can be assumed as limit value. As soon as these limit values are met or exceeded, a check is made to ascertain whether the knee angle φ.sub.K corresponds to a set limit value. In the terminal stance phase, which is adopted before initiation of the swing phase, the prosthetic knee joint 2 is situated in an extended or almost extended position, and a hyperextension can even occur in the case of an elastic extension stop. If a limit value for the knee angle φ.sub.K, which is <5° and can also assume negative values, is not reached, then a further condition for initiating the enablement of a swing phase is met. The knee moment acting in the extension direction can be calculated using the knee angle φ.sub.K and the known data of the spring device in the elastic extension stop.

[0035] In the case of a negative knee angle φ.sub.Ki.e. in the case of hyperextension, a check is made to ascertain how great the knee angle velocity ω.sub.K is. If the latter is below a limit value, for example below 7°/s, it can be assumed that there is no or only slight knee flexion and knee dynamic, which is likewise characteristic for a terminal stance phase. If there is no hyperextension, a check is made to ascertain whether the negative angular velocity is below a limit value, and the question here is how great is the knee angle velocity in the flexion direction or extension direction. If the determined knee angle velocities ω.sub.K are below the required limit values, the extent of the acceleration a.sub.F at sole level is calculated, which is based on the relative position of the acceleration vector with respect to the prosthetic foot 4. If the acceleration a.sub.F at sole level is below a limit value, for example below 3 m/s.sup.2, it is to be assumed that the kinematic contact conditions between the prosthetic foot 4 and the ground correspond to those of a terminal stance phase and, consequently, the reduction of the resistance R of the resistance device 5 can be initiated.

[0036] The clear decision between forward heel-toe walking via the prosthetic foot 4, i.e. a forward stride, and a rearward swing-through of the prosthesis under the body, for example in the swing phase of a rearward step, all the steps and questions are necessary that follow the establishment of a forward inclination and forward rotation of the below-knee component 3. For this purpose, a hyperextension of the prosthetic knee joint 2 counter to an elastic extension stop 10, 30 or a strongly extending movement at a low knee angle φ.sub.K is needed, which can be measured by the knee angle sensor 11. In addition, the acceleration sensor 12 determines whether the extension moment about the knee joint is applied statically or dynamically. In particular, the linear accelerations of the prosthesis at the sole level are calculated. Assuming that the forward inclination, i.e. the positive absolute angle φ.sub.US, and a forward rotation of the below-knee component are given, case distinctions can be made on the basis or accelerations and knee moments and, on the basis of these case distinctions, the flexion resistance R is either maintained at a high stance phase flexion level or is reduced to a swing-phase level.

[0037] If there is an insufficient extension moment or a sufficient flexion moment about the prosthetic knee joint 1, or if the knee angle velocity ω.sub.K is either extending or the prosthetic knee joint 2 is in hyperextension, there can be no enablement of the swing phase.

[0038] If the prosthetic knee joint experiences an extension moment about the knee axis on account of dynamic forces, for example on account of the inertial forces of the prosthetic foot 4 and of the below-knee component 3, a hyperextension in the knee joint or a stretching movement can be measured. If the below-knee component 3 thus moves, this situation corresponds to that of a pendulum, such that there is no enablement of a swing phase.

[0039] Enablement of a swing phase accordingly takes place when an extension moment about the knee axis is caused by static forces, such as ground reaction force, and stump forces acting on the prosthetic knee joint. In this case, a hyperextension or a greatly stretching movement of the knee joint is measured, but no or only slight acceleration a.sub.F at sole level. Such a situation is characteristic of the terminal stance phase, in which the prosthesis, loaded in the walking direction, rolls heel to toe over the foot. In this situation, the resistance R is reduced.

[0040] The characteristic of the elastic hyperextension, in particular the spring characteristic of the elastic extension stop, and the threshold values for the knee angle φ.sub.K, the knee angle velocity ω.sub.K and the admissible accelerations a.sub.F for enablement of a swing phase have to be chosen such that, on the one hand, a clear distinction can be made as to whether a swing phase is enabled and, on the other hand, also a slight hyperextension is achieved, for example by users with low body weight and with small steps and slow walking speeds.

[0041] If, for example, within the first 5° of a knee flexion movement after enablement of the resistance device 5 to a reduced flexion resistance R, an acceleration a.sub.F of a magnitude above a defined threshold is established, for example by striking against an obstacle, it is possible for the flexion resistance R to be immediately switched back to a high level of stance-phase flexion damping, in order to avoid unwanted flexion in an emergency.

[0042] All of the measured signals of the sensors can be filtered in order to be able to compensate for measurement inaccuracies. For the acceleration conditions, asymmetrical limit values can be set in order to be able to perform individual adaptation to the respective gait situation and movement directions.

[0043] The proposed control arrangement does not require direct measurement of forces, and it is therefore possible to do without force sensors that can in some cases be sensitive and difficult to evaluate. The sensors used are exclusively knee angle sensors, inertial angle sensors such as gyroscopes, and acceleration sensors. The moments about the knee axis, particularly in the extension direction, can be easily determined with these sensors, since the parameters of an elastic extension stop are detected and used as a basis for the calculation.

[0044] The easily determinable linear and angular accelerations are used to calculate the state of movement of the prosthesis, in particular to identify the state of movement of the prosthetic foot 4. Through the logical linkage of forces and moments with accelerations, it is possible to distinguish between static forces and dynamic forces and moments, such that this distinction permits detection of the walking pattern. In this way, a distinction can easily be made as to whether a free swing-through or a terminal stance phase is present.

[0045] The control according to the method described moreover also permits the reliable enablement of the swing phase even with slow walking speeds, small strides and on soft ground, for example loose sand or snow. The control is independent of the patient's weight and is able to ensure the patient can safely walk backward.

[0046] FIG. 4 shows a schematic view of a control concept of a prosthetic knee joint, the set-up of the prosthesis corresponding to that of FIG. 1. It is also possible in principle to use the control concept in orthoses, particularly in what is called a KAFO (knee ankle foot orthosis). The prosthesis socket 1 or the thigh component is connected to the below-knee component 3 via the prosthetic knee joint 2. The prosthetic foot 4 arranged at the distal end of the below-knee component 3. The resistance device 5 is likewise situated inside the below-knee component 3. The elastic extension stop, which can be arranged in particular inside the resistance device 5, is shown on the right next to the schematic representation of the prosthetic device. The prosthetic device is located in the extended stride position in the terminal stance phase, which means that, in the front area of the foot, a resting and rotating point 6 is created about which the prosthetic device rotates. On account of the lever between the longitudinal axis of the below-knee component 3 and the resting point 6, an extension moment is applied around the knee joint 2, and this has the effect that the abutment 10, which in this case is movable and part of a hydraulic piston, is pressed against the stop element 30 in the form of a spring. At the same time, it is ascertained whether the prosthetic device has a forward inclination, which is indicated by the curved arrow. If an absolute angle φ.sub.US is present, i.e. an inclination to the vertical in the clockwise direction in the illustrative embodiment shown, and if a forward rotation takes place, i.e. an increase of the absolute angle φ.sub.US in the forward direction of walking, wherein the rotation takes place about the distal resting point 6, further criteria are given for determining the instantaneous state and the phase within a gait cycle or a gait sequence. The extension moment can be calculated from the spring rate of the stop element 30 and the knee angle, in this case the negative knee angle φ.sub.K.

[0047] To rule out the possibility of the below-knee component simply swinging freely about the knee joint 2, the linear acceleration a.sub.F at the contact point 6 is determined. If this acceleration is 0 or very low, it can be assumed that the prosthetic foot 4 and the resting point 6 have ground contact, such that a stationary rotation point is present at the resting point 6. The load is virtually static. In the case of a static load, a forward inclination and forward rotation and, if appropriate, hyperextension, if the knee moment extension moment does not exceed a limit value X, the flexion resistance R of the resistance device 5 is then reduced, such that a bending of the prosthetic knee joint 2 can easily take place.