METHOD FOR CONTROLLING A PROSTHESIS OR ORTHESIS

Abstract

The invention relates to a method for controlling a prosthesis or orthesis of the lower extremity, the prosthesis or orthesis comprising an upper part (10) and a lower part (20) which is connected to the upper part (10) via a knee joint and is mounted so as to be pivotable relative to the upper part (10) about a joint pin (15); wherein an adjustable resistance device (40) is situated between the upper part (10) and the lower part (20), by means of which resistance device a resistance (Rf) is modified on the basis of sensor data; wherein state information is detected by sensors, a cyclical movement different from walking is determined and the resistance (Rf) is adjusted to a low level during the cyclical movement; wherein determining the cyclical movement comprises the following steps: a. detecting the flexion angle (α.sub.K) and at least one absolute angle (αS) of the lower part (20) and/or the upper part (10) over at least one movement cycle, b. identifying the cyclical movement from the relative movement of the upper part (10) and the lower part (20) and the absolute movements of the upper part (10) and/or the lower part (20) in space.

Claims

1. A method for controlling a prosthesis or orthosis of the lower extremity, the prosthesis or orthosis having an upper part (10) and a lower part (20) which is connected to the upper part (10) via a knee joint and is mounted so as to be pivotable relative to the upper part (10) about a joint axis (15), wherein an adjustable resistance device (40) is arranged between the upper part (10) and the lower part (20), by means of which resistance device (40) a resistance (Rf) is modified on the basis of sensor data, wherein state information is detected via sensors, a cyclical movement different than walking is determined, and the resistance (Rf) is adjusted to a low level during the cyclical movement, characterized in that the determination of the cyclical movement comprises the following steps: a. detecting the flexion angle (α.sub.K) and at least one absolute angle (α.sub.S) of the lower part (20) and/or of the upper part (10) over at least one movement cycle, b. identifying the cyclical movement from the relative movement of upper part (10) and lower part (20) and from the absolute movements of upper part (10) and/or lower part (20) in space.

2. The method as claimed in claim 1, characterized in that the reduction of the resistance (Rf) takes place only when a flexion angle change (ΣΔα.sub.K), in particular the amount of the flexion angle change, added up over an interval in which certain conditions are met, is greater than a specified limit value, in particular greater than 240°.

3. The method as claimed in claim 1, characterized in that a cyclical movement is ascertained only if the flexion angle (α.sub.K) is greater than a limit value, in particular greater than 10°, in particular greater than 15°.

4. The method as claimed in claim 1, characterized in that a cyclical movement is ascertained only if the angle of inclination (α.sub.S) of the lower part (20) and/or the flexion angle (α.sub.K) does not exceed and/or fall below certain limit values.

5. The method as claimed in claim 1, characterized in that a cyclical movement is ascertained only if the angle of inclination (α.sub.S) of the lower part (20) forward relative to the vertical (G) is less than a limit value, in particular less than 5°.

6. The method as claimed in claim 1, characterized in that the end of the cyclical movement is identified from the fact that the lower part (20) is relieved of an axial force (FA) for a predetermined period of time and the axial force (FA) falls below a predetermined limit value and the flexion angle (α.sub.K) falls below a limit value or the inclination (α.sub.S) of the lower part (20) to the vertical (G) exceeds a limit value.

7. The method as claimed in claim 1, characterized in that, when the cyclical movement is interrupted while the lower part (20) is simultaneously subjected to an axial force (FA), an extension of the knee joint (1) below a specified flexion angle (α.sub.K) is prevented and the flexion resistance (Rf) increased and, after an end stop is reached, followed by flexion and renewed extension, the resistance is set anew for the cyclical movement.

8. The method as claimed in claim 1, characterized in that, in order to determine the cyclical movement, the angular velocities of the flexion angle (α.sub.K) and of the angle of inclination (α.sub.S) are calculated, and the quotient of the angular velocities is determined in specified time segments.

9. The method as claimed in claim 8, characterized in that changes in the quotient of the angular velocities are determined as tangent slopes in specified time segments.

10. The method as claimed in claim 8, characterized in that the cyclical movement is ascertained when the time profile of the tangent slopes is increasing monotonically.

11. The method as claimed in claim 8, characterized in that an evaluation of the angular velocities takes place only when a limit value of the flexion angle velocity is exceeded.

12. The method as claimed in claim 1, characterized in that the phase space of two angle parameters and/or their derivatives is used to determine the cyclical movement, in particular the direction of rotation in the phase space is determined and used.

13. The method as claimed in claim 1, characterized in that the trajectory of the foot part (30) and/or its derivatives relative to a determined hip rotation point is determined from the knee angle (KA) and/or absolute angles of upper part (10) and lower part (20) and is used for the determination of the cyclical movement.

Description

[0023] An exemplary embodiment of the invention is discussed in more detail below with reference to the figures, in which:

[0024] FIG. 1 shows a schematic illustration of a prosthetic leg;

[0025] FIG. 2 shows a schematic illustration of a pedaling movement;

[0026] FIG. 3 shows a common illustration of a flexion angle and of a roll angle;

[0027] FIG. 4 shows a schematic illustration of the calculation of a tangent slope;

[0028] FIG. 5 shows a comparison of measured and calculated angular velocities;

[0029] FIG. 6 shows the profile of the slope of a connection line in the diagram according to FIG. 5;

[0030] FIG. 7 shows a data record for setting off and the activation of a cycling function, and

[0031] FIG. 8 shows an illustration of an orthosis.

[0032] FIG. 1 shows a schematic illustration of an artificial knee joint 1 in an application on a prosthetic leg. As an alternative to an application on a prosthetic leg, a correspondingly designed artificial knee joint 1 can also be used in an orthosis or an exoskeleton. Instead of replacing a natural joint, the artificial knee joint is then arranged medially and/or laterally on the natural joint. In the exemplary embodiment shown, the artificial knee joint 1 is in the form of a prosthetic knee joint having an upper part 10 with a side 11, which is anterior or situated to the front in the walking direction, and a posterior side 12, which is located opposite the anterior side 11. A lower part 20 is arranged on the upper part 10 so as to be pivotable about a pivot axis 15. The lower part 20 also has an anterior side 21 or front side and a posterior side 22 or rear side. In the exemplary embodiment shown, the knee joint 1 is designed as a monocentric knee joint; it is in principle also possible to control a polycentric knee joint in a corresponding manner. At the distal end of the lower part 20 there is arranged a foot part 30 which can be connected to the lower part either in the form of a rigid foot part 30 with a fixed foot joint or by a pivot axis 35, in order to make possible a movement sequence that emulates the natural movement sequence.

[0033] Between the posterior side 12 of the upper part 10 and the posterior side 22 of the lower part 20, the knee angle KA is measured. The knee angle KA can be measured directly by means of a knee angle sensor 25, which can be arranged in the region of the pivot axis 15. The knee angle sensor 25 can be coupled to a torque sensor or can have such a sensor, in order to detect a knee moment about the joint axis 15. On the upper part 10 there is arranged an inertial angle sensor or an IMU 51, which measures the spatial position of the upper part 10, for example in relation to a constant force direction, for example the gravitational force G, which is directed vertically downward. An inertial angle sensor or an IMU 53 is likewise arranged on the lower part 20 in order to determine the spatial position of the lower part while the prosthetic leg is in use.

[0034] In addition to the inertial angle sensor 53, an acceleration sensor and/or transverse force sensor 53 can be arranged on the lower part 20 or on the foot part 30. By means of a force sensor or torque sensor 54 on the lower part 20 or foot part 30, an axial force FA acting on the lower part 20 or an ankle moment acting about the ankle joint axis 35 can be determined.

[0035] Between the upper part 10 and the lower part 20 there is arranged a resistance device 40, in order to influence a pivoting movement of the lower part 20 relative to the upper part 10. The resistance device 40 can be in the form of a passive damper, in the form of a drive, or in the form of what is called a semi-active actuator with which it is possible to store movement energy and deliberately release it again at a later time in order to slow or assist movements. The resistance device 40 can be in the form of a linear or rotary resistance device. The resistance device 40 is connected to a control device 60, for example in a wired manner or via a wireless connection, which in turn is coupled to at least one of the sensors 25, 51, 52, 53, 54. The control device 60 electronically processes the signals transmitted by the sensors, using processors, computing units or computers. It has an electrical power supply and at least one memory unit in which programs and data are stored and in which a working memory for processing data is provided. After the sensor data have been processed, an activation or deactivation command is output, with which the resistance device 40 is activated or deactivated. By activation of an actuator in the resistance device 40 it is possible, for example, to open or close a valve or to generate a magnetic field, in order to change a damping behavior.

[0036] To the upper part 10 of the prosthetic knee joint 1 there is fastened a prosthesis socket, which serves to receive a thigh stump. The prosthetic leg is connected to the hip joint 16 by way of the thigh stump. On the anterior side of the upper part 10, a hip angle HA is measured, which is marked on the anterior side 11 between a vertical line through the hip joint 16 and the longitudinal extent of the upper part 10 and the connecting line between the hip joint 16 and the knee joint axis 15. If the thigh stump is lifted and the hip joint 16 flexed, the hip angle HA decreases, for example when sitting down. Conversely, the hip angle HA increases in the case of an extension, for example when standing up or in the case of similar movement sequences, for example when pushing down on a pedal during cycling.

[0037] The prosthetic leg with the artificial knee joint between the upper part 10 and the lower part 20 is shown schematically in FIG. 2. The prosthetic foot 30 is placed on a pedal 2 and performs a circular movement along the pedal path. In the position shown, the lower part 20, or the longitudinal extent of the lower part 20, is located in a vertical position, the inclination of the lower part 20 to the vertical G is therefore 0°, and the roll angle is therefore 0. The flexion angle α.sub.K, which results from the pivoting of the upper part 10 relative to the lower part 20 about the knee axis, is the change to the fully extended or straightened prosthetic leg. The flexion angle α.sub.K is calculated from the difference between 180° and the knee angle KA. When performing a pedaling movement, as is necessary when riding a bicycle to propel the bicycle, cyclical movements are performed. Forces from the foot part 30 to the pedals 20 are introduced at the force application point PF, which is shown in FIG. 1. As a rule, these are compressive forces, since it is only with difficulty that a prosthesis user or an orthosis user with limited motor skills in the muscles can apply forces that act against the direction of gravity. Due to the lack of muscle connections to the lower part 20, no forces that act in the horizontal direction can generally be applied to the pedals 2. Since, for safety reasons, the foot part 30 is not fixed on the pedal 2, no forces acting against the direction of gravity, for example by activation of the hip flexor muscle, are transmitted. During the pedaling movement, flexion resistances and extension resistances are therefore undesirable, since these oppose a rotary movement of the pedals 2 about the axis of rotation of the pedal crank.

[0038] Provision is therefore made that at least the resistance, in particular flexion resistance and possibly also an extension resistance, is reduced depending on the detection of a cyclical movement when riding a bicycle. This detection and reduction of the resistance is to be carried out as quickly as possible without the user of the artificial knee joint having to take any further measures apart from carrying out the cycling movement. Once the cyclical movement sequence associated with riding a bicycle is detected, the cycling mode remains set until a change in parameters or sensor values is detected that indicates cessation of cycling, which may not necessarily be accompanied by cessation of the cyclical movement.

[0039] FIG. 3 shows the flexion angle α.sub.K and the roll angle α.sub.s as the angle of inclination of the lower part 20 in space. The illustration on the left shows that both angles run substantially cyclically during cycling and run through a uniform change at a constant speed of the pedals. The illustration on the right shows both values in an X-Y diagram. The pedal movement results in a closed, convex, two-dimensional curve, with the flexion angle α.sub.K being plotted on the x-axis and the lower-leg angle α.sub.s on the y-axis. If a uniform and cyclical movement has been detected, specifically over a specified period of time, for example over two pedal revolutions, the resistance of the resistance device is reduced. When riding a bicycle, the curve in the right-hand illustration of FIG. 3 is traversed counterclockwise, the time profile of the tangent slope of the curve, as illustrated in FIG. 4, being read to the right and therefore increasing monotonically. The slope k.sub.1 at a specific point in time t.sub.1 is calculated from the quotient of the horizontal component and the vertical component; the slope k.sub.2 of the tangent at a later point in time t.sub.2 is greater in the illustrated exemplary embodiment. The tangent slope is the quotient of the changes in the X and Y components, i.e. the quotient of the angular velocities of the flexion angle as and the inclination angle as of the lower part 20.

[0040] A variant of the calculation or determination of the tangent slopes is shown in FIGS. 5 and 6. FIG. 5 shows the angular velocities both of the measurements and of filtered measurements. The angular velocity V.sub.S of the lower part and the angular velocity V.sub.A of the flexion angle have interference signals, for example due to vibrations or measurement errors, which are identified by the uneven curve progressions. The filtered angular velocity signals V.sub.SF and V.sub.AF are also plotted. In the right-hand illustration, the values are shown in the X-Y diagram with the origin of the coordinates at the cross. Here too, the differences between the comparatively smooth curves and the uneven curves are clear. The slope of the connection line between the origin X and the respective point on the curve in the X-Y diagram at time t.sub.1 and time t.sub.2 is calculated using the rule according to FIG. 4. At a knee angular velocity V.sub.A=0, the sign would jump from plus infinity to minus infinity. Such a value is excluded from the analysis since the evaluation only takes place when a limit value for the flexion angle velocity is exceeded. In principle, smaller deviations from the monotony condition, as explained above, may also be permissible in order to continue to regard the uniformity criterion as fulfilled.

[0041] In order to identify whether the cyclical movement of cycling is being carried out, the amount of the flexion angle changes ΣΔα.sub.K is added up, the flexion angle and the roll angle and/or the orientation of the upper part in space being considered. The course of the flexion angle α.sub.K at the start of cycling is recorded in the diagram in FIG. 7. Starting with an extended leg, flexion with subsequent extension and again flexion and extension is carried out. The resistance Rf initially remains at a high level. The count value ΣΔα.sub.K is always increased when there is a sufficient absolute knee angle velocity, i.e. a sufficiently large change in the flexion angle α.sub.K. In the region of movement reversal with a reduced change in the flexion angle, the count value is not updated, in order not to jeopardize the sufficient safety in identifying the cycling movement. The same applies to the run after calculating a maximum extension, i.e. a lower relative minimum of the flexion angle α.sub.K. If the counter reaches the specified limit value, for example a change in the flexion angle of 240°, which can be seen from the horizontal progression of the counter ΣΔα.sub.K, the resistance Rf is reduced to the desired value, for example dropped to almost 0. The counter value is not updated any further, since the uniformity criterion is sufficiently met.

[0042] FIG. 8 shows a schematic illustration of an exemplary embodiment of an orthosis with an upper part 10 and a lower part 20 mounted thereon so that it can pivot about a pivot axis 15, with which orthosis the method can also be carried out. An artificial knee joint 1 is formed between the upper part 10 and the lower part 20 and is arranged laterally with respect to a natural knee joint in the illustrated exemplary embodiment. In addition to an arrangement of upper part 10 and lower part 20 on one side relative to a leg, two upper parts and lower parts can also be arranged medially and laterally with respect to a natural leg. At its distal end, the lower part 20 has a foot part 30 which is pivotable about an ankle joint axis 35 with respect to the lower part 20. The foot part 30 has a foot plate on which a foot or shoe can be placed. Fastening devices for securing to the lower leg and thigh are arranged on the lower part 20 and on the upper part 30, respectively. Devices for securing the foot on the foot part 30 can also be arranged on the foot part 30. The fastening devices can be in the form of buckles, straps, clasps or the like, in order to be able to fit the orthosis on the user's leg in a releasable manner and to remove it again without destroying it. The resistance device 40 is fastened to the upper part 10, is supported on the lower part 20 and on the upper part 10 and provides an adjustable resistance to pivoting about the pivot axis 15. The sensors and the control device, which were described above in connection with the exemplary embodiment of the prosthesis, are also accordingly present on the orthosis.