METHOD FOR CONTROLLING AN ARTIFICIAL KNEE JOINT

Abstract

The invention relates to a method for controlling an artificial knee joint which includes an upper part having an anterior side and a posterior side; a lower part mounted on the upper part so as to be pivotable about a knee axis and having an anterior side and a posterior side; a foot part arranged on the lower part; at least one sensor; a control device connected to the at least one sensor; and an actuator which is coupled to the control device and by means of which an achievable knee angle (KAmax) between the posterior side of the upper part and the posterior side of the lower part in the swing phase can be set by the control device.

Claims

1. A method for controlling an artificial knee joint comprising an upper part with an anterior face and a posterior face, a lower part which is mounted on the upper part so as to be pivotable about a knee axis and has an anterior face and a posterior face, a foot part arranged on the lower part, at least one sensor, a control device connected to the at least one sensor, and an actuator which is coupled to the control device and via which an achievable knee angle (KAmax) between the posterior face of the upper part and the posterior face of the lower part in the swim, phase can be set by the control device, characterized in that, on the basis of sensor data from the at least one sensor, it is concluded that a height difference (ΔH) of the foot part relative to a foot or a foot part of the contralateral side of a patient in their stance phase, or relative to the immediately preceding stance phase of the foot part during walking, is to be overcome, and the knee angle (KAmax) achievable in the swing phase is adjusted.

2. The method as claimed in claim 1, characterized in that, when a height difference (AH) increases counter to the direction of gravity (G), the achievable knee angle (KAmax) is reduced.

3. The method as claimed in claim 1, wherein the height difference (AH) is calculated or estimated from the trajectory of a trunk, a pelvis, hips and/or the knee axis of a leg aided by the artificial knee joint.

4. The method as claimed in claim 1. wherein the height difference (AH) is calculated or estimated over the vertical path of a hip joint of a leg aided by the artificial knee joint, over the vertical path of the knee axis (15) and/or the vertical path of the foot part (30).

5. The method as claimed in claim 1, wherein the height difference (ΔH) is determined via a hip angle (HA) of a leg aided by the artificial knee joint or the spatial orientation of the upper part and/or their time profiles.

6. The method as claimed in claim 1, wherein the height difference (ΔH) is determined via the time profile of the knee angle of a leg aided by the artificial knee joint.

7. The method as claimed in claim 1. wherein the height difference (ΔH) is calculated or estimated from the ratio of a horizontal movement of a trunk, a pelvis, the hip or the knee axis of a leg aided by the artificial knee joint to the hip angle (HA) or the spatial orientation of the upper part.

8. The method as claimed in claim 1, wherein the height difference (ΔH) is calculated from a determined knee angle (KAD) and a determined hip angle (HA).

9. The method as claimed in claim 1. wherein the achievable knee angle (KAmax) is set via an adjustable mechanical or hydraulic extension stop or a change in the movement resistance against knee extension.

10. The method as claimed in claim 1, wherein the spatial orientation of the lower part is used as a parameter for the achievable knee angle (KAmax).

11. The method as claimed in claim 1. wherein the height difference (ΔH) is determined or estimated from a knee angle (KAD) measured with a knee angle sensor on the artificial knee joint and/or a spatial position of the upper part and/or lower part measured via a spatial position sensor.

12. The method as claimed in claim 1, wherein the achievable knee angle (KAmax) is set in the swing phase and is maintained until a predetermined spatial position and/or movement of the lower part and/or upper part is reached, until an ankle joint angle (AA) and/or a force application point (PF) into the foot part is reached, and/or over a predetermined period of time.

13. The method as claimed in one of the preceding claims claim 1, wherein, after reaching a minimum hip angle (HA) and a movement reversal, the spatial orientation of the lower part is kept constant until detection of an initial contact, an axial force (FA) on the lower part and/or a change in an ankle joint angle (AA).

14. The method as claimed in claim 1, wherein walking up an incline, climbing stairs or otherwise negotiating a height difference during walking is detected via the time profile of the upper part orientation and/or the ratio of the upper part orientation to a translational horizontal movement of the knee axis, and the achievable knee angle (KAmax) is adjusted on the basis of the profile and/or the ratio.

15. The method as claimed in claim 1, wherein a flexion resistance in the swing phase, after reversal of the direction of movement of the lower part, is set to a level higher than when walking on level ground.

16. The method as claimed in claim 1, wherein, upon detection of walking up an incline, climbing stairs or otherwise negotiating a height difference (ΔH) during walking, the maximum achievable knee angle (KAmax) is reduced by 10° to 25°.

17. The method as claimed in claim 1. wherein the movement resistance against an extension movement of the knee joint is reduced continuously in the swing phase.

18. The method as claimed in claim 1, wherein the height difference (AH) is used as a parameter for the achievable knee angle (KAmax), and the actuator is activated or deactivated on the basis of this parameter.

19. A method for controlling an artificial knee joint, including the steps of: providing a knee joint comprising an upper part with an anterior face and a posterior face, a lower part with an anterior face and a posterior face, the lower part being mounted on the upper part so as to be pivotable about a knee axis, a foot part arranged on the lower part, at least one sensor, a control device connected to the at least one sensor, and an actuator which is coupled to the control device and via which an achievable knee angle (KAmax) between the posterior face of the upper part and the posterior face of the lower part in the swing phase can be set by the control device, wherein: obtaining sensor data from the at least one sensor; determining from the sensor data that a height difference (AH) of the foot part relative to a foot or a foot part of the contralateral side of a patient in their stance phase, or relative to the immediately preceding stance phase of the foot part during walking, is to be overcome; and adjusting the knee angle (KAmax) achievable in the swing phase, wherein when the height difference increases counter to the direction of gravity (G), the achievable knee angle (KAmax) is reduced.

20. A method for controlling an artificial knee joint, including the steps of: providing a knee joint comprising an upper part with an anterior face and a posterior face, a lower part with an anterior face and a posterior face, the lower part being mounted on the upper part so as to be pivotable about a knee axis, a foot part arranged on the lower part, at least one sensor, a control device connected to the at least one sensor, and an actuator which is coupled to the control device and via which an achievable knee angle (KAmax) between the posterior face of the upper part and the posterior face of the lower part in the swing phase can be set by the control device, wherein: obtaining sensor data from the at least one sensor; determining from the sensor data that a height difference (ΔH) of the foot part relative to a foot or a foot part of the contralateral side of a patient in their stance phase, or relative to the immediately preceding stance phase of the foot part during walking, is to be overcome via the time profile of the knee angle of a leg aided by the artificial knee joint; and adjusting the knee angle (KAmax) achievable in the swing phase, wherein when the height difference increases counter to the direction of gravity (G), the achievable knee angle (KAmax) is reduced.

Description

[0052] Illustrative embodiments are explained in more detail below with reference to the accompanying figures, in which:

[0053] FIG. 1 shows a schematic representation of a prosthetic leg;

[0054] FIG. 2 shows a representation of different phases and situations when negotiating a height difference;

[0055] FIG. 3 shows a representation of a fitted prosthesis, with angles;

[0056] FIG. 4 shows a sequence diagram of walking up an incline;

[0057] FIG. 5 shows a sequence diagram of negotiating a step;

[0058] FIG. 6 shows trajectories of the ankle joint axis, the knee joint axis and the greater trochanter when walking on level ground;

[0059] FIG. 7 shows trajectories of the ankle joint axis, the knee joint axis and the greater trochanter when walking up an incline;

[0060] FIGS. 8a and 8b show representations of the height difference;

[0061] FIG. 9 shows representations of different heel strike situations;

[0062] FIG. 10 shows the dependence of the knee angle on the height difference when walking up an incline;

[0063] FIG. 11 shows the dependence of the knee angle on the height difference when negotiating a step;

[0064] FIG. 12 shows knee angle profiles for different height differences over the relative time;

[0065] FIG. 13 shows the profile of a thigh orientation over a stride cycle;

[0066] FIG. 14 shows the relationship of the thigh orientation in relation to the horizontal path of the hip;

[0067] FIG. 15 shows a possible auxiliary variable for estimating the stride height;

[0068] FIG. 16 shows the knee angle profile KA in over a stride cycle;

[0069] FIG. 17 shows different control profiles of a stance phase extension;

[0070] FIG. 18 shows two different knee angle profiles over phases of the gait cycle;

[0071] FIG. 19 shows a resistance profile in the case of passive control;

[0072] FIG. 20 shows a variant of FIG. 19;

[0073] FIG. 21 shows the profile of a lower leg angle in relation to the thigh angle;

[0074] FIG. 22 shows the profile of the knee angle in relation to the thigh angle; and

[0075] FIG. 23 shows a definition of the leg chords.

[0076] FIG. 1 shows a schematic representation 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 respective artificial knee joint is then arranged medially and/or laterally on the natural joint. In the illustrative embodiment shown, the artificial knee joint 1 is in the form of a prosthetic knee joint having an upper part 10 with an anterior face 11, i.e. a front face in the walking direction, and a posterior face 12 lying opposite the anterior face 11. A lower part 20 is mounted on the upper part 10 so as to be pivotable about a pivot axis 15. The lower part 20 also has an anterior face 21 and a posterior face 22. In the illustrative embodiment shown, the knee joint 1 is designed as a monocentric knee joint. It is also possible in principle to control a polycentric knee joint correspondingly. At the distal end of the lower part 20, a foot part 30 is arranged which can be connected to the lower part either as a rigid foot part 30 with an immovable ankle or with a pivot axis 35, in order to permit a sequence of movement akin to the natural sequence of movement.

[0077] The knee angle KA is measured between the posterior face 12 of the upper part 10 and the posterior face 22 of the lower part 20. The knee angle KA can be measured directly via a knee angle sensor 25, which can be arranged in the region of the pivot axis 15. An inertial angle sensor 51 is arranged on the upper part 10 and measures the spatial position of the upper part 10, for example in relation to a constant force direction, for example the force of gravity G, which is directed vertically downward. An inertial angle sensor 52 is likewise arranged on the lower part 20 in order to determine the spatial position of the lower part during the use of the prosthetic leg.

[0078] In addition to the inertial angle sensor 53, a force sensor or moment sensor 54 can be arranged on the lower part 20 or the foot part 30, in order to determine an axial force FA acting on the lower part 20.

[0079] An actuator 40 is arranged between the upper part 10 and the lower part 20 in order to influence a pivoting movement of the lower part 20 relative to the upper part 10. The actuator 40 can be designed as a passive damper, as a drive or as a so-called semi-active actuator 40, with which it is possible to store kinetic energy and release the latter again at a later point in time in order to slow down or support movements. The actuator 40 can be designed as a linear or rotary actuator. The actuator 40 is connected to a control device 60, for example by a wired or a wireless connection, which in turn is coupled to at least one of the sensors 25, 51, 52, 53, 54. The control device 60 processes the signals, transmitted from the sensors, electronically using processors, arithmetic 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 is available for processing data. After the sensor data have been processed, an activation or deactivation command is issued, with which the actuator 40 is activated or deactivated. By activation of the actuator 40, a valve can be opened or closed, for example, in order to change a damping behavior.

[0080] A prosthesis socket, which serves to receive a thigh stump, is secured on the upper part 10 of the prosthetic knee joint 1. The prosthetic leg is connected to the hip joint via the thigh stump. A hip angle HA is measured on the anterior face of the upper part 10, which angle is taken between a vertical line through the hip joint and the longitudinal extent of the upper part 10 and the connecting line between the hip joint and the knee joint axis 15 on the anterior face 11. If the thigh stump is raised and the hip joint flexed, the hip angle HA decreases, for example when sitting down. Conversely, the hip angle HA increases in the event of an extension, for example when standing up or performing similar movements.

[0081] During a gait cycle when walking on level ground, the foot part 30 is first set down with the heel; the first contact of the heel or of a heel part of the foot part 30 is called heel strike. Plantar flexion then takes place until the foot part 30 rests completely on the ground. As a rule, the longitudinal extent of the lower part 10 is then behind the vertical that runs through the ankle joint axis 35. While walking on level ground, the center of gravity of the body is then shifted forward, the lower part 20 pivots forward, the ankle angle AA decreases, and there is increasing loading of the forefoot. The ground reaction force vector migrates forward from the heel to the forefoot. At the end of the stance phase, toe-off takes place, followed by the swing phase in which the foot part 30, when walking on level ground, is shifted behind the center of gravity or the hip joint of the ipsilateral side while reducing the knee angle KA, in order then to be rotated forward after a minimum knee angle KA is reached, in order to then reach heel contact again with a generally maximally extended knee joint 1. The force application point PF thus migrates from the heel to the forefoot during the stance phase and is shown schematically in FIG. 1.

[0082] Walking on level ground differs from walking up an incline, climbing stairs or otherwise negotiating a height difference. The human gait is essentially defined by a coordinated movement of both legs. To take a stride, for example, the supporting leg has to take over the movement of the center of gravity of the body and generate forward progression, while the swing leg positions the contralateral foot in such a way that balance is maintained and an efficient weight transfer is possible.

[0083] The movement of both sides or of both legs is therefore functionally linked and can be observed during the most varied of movements. The functional linking of movements is simulated by modeling, and the functional linking of the components on the ipsilateral side and also on the contralateral side can be used to determine any missing information concerning individual segments from the behavior or the states of other segments. The method provides that the linking of the respective segments of the aided, ipsilateral side is used in order to simulate or control the leg movement and to recognize an intention and derive setpoint profiles and target values. The invention proposes, without a sensor system on the contralateral side, to analyze the movement and intended movement and to generate a control on the basis of this evaluation. While it is possible, with bilateral fittings, to obtain the movement of the respective contralateral side through sensors located on the prosthesis, orthosis or the exoskeleton or also via biosignals such as muscle activity or the like, this possibility is not available with unilateral fittings. Here, additional sensors would have to be arranged on the unaided, contralateral side, which would make the overall system much more complex. It is therefore proposed to use a model to determine the missing variables from the existing measured variables on the ipsilateral side, in order thereby to manage without instrumentation on the contralateral side. Even with sensors on the ipsilateral side alone, it is possible to obtain information about the movement of the contralateral leg in its stance phase, namely about the translational knee or hip movement, without these variables on the contralateral side being explicitly calculated. Sensors in the orthopedic device that receives the artificial knee joint record the states of the orthopedic device on the aided, ipsilateral side, and, optionally, individual variables on the contralateral side can be derived from these sensor values. With the aid of a model, the movement variables on the contralateral side are estimated from the measured data. In the case of a mechanical model, the boundary conditions and constraints can depend on the particular gait situation. For the control of the actuators, both the measured data, i.e. the sensor values, and the estimated variables are used to activate or deactivate the actuator.

[0084] The ipsilateral leg movement must be sufficiently determined from a technical point of view. For a cross-knee orthopedic device, for example, an inertial angle sensor 52 on the lower part, which records the absolute angle and the horizontal accelerations, and an angle sensor 25 for recording the knee angle KA between the upper part 10 and the lower part 20 are sufficient. To estimate the contralateral leg angle, for example, the ipsilateral leg movement is recorded, the hip translation is calculated from this, and a conclusion regarding the contralateral leg movement is drawn from the hip translation. For determining the translational movement of the hip, the translational movement of a point on the aided side, i.e. on the orthopedic device, for example the movement of the knee axis, is used. The translational movement of the knee axis, for example, is determined in particular via a double integration of measured linear accelerations with the appropriate initial conditions. In the further course of the process, the kinematic chain as far as the hip is followed using absolute angles and relative angles. The initial conditions of the integration can be determined using a kinematic model, wherein the start of the integration advantageously lies in the late stance phase. The roll-off point of the foot part, also called the center of rotation (COR), can be formulated as a function of load and position and included in the calculation. The segment lengths required for the calculation are measured and stored in the system, or assumptions are made based on statistical values. Since prosthetic fittings in particular are often custom-made, the individual segment lengths are known, since these necessarily have to be recorded in order to select components when assembling the prosthesis system. Alternatively, using anthropometric models, segment lengths can be determined with sufficient accuracy from characteristic lengths, e.g. the knee-ground dimension, or amputation features such as the amputation height, by means of scaling. Thus, from the measured acceleration of a fixed point of the orthopedic system, for example the position of the pivot axis, the trajectory of this point can be determined by double integration. By way of the kinematic chain, the hip trajectory is then defined as a function of the relative degrees of freedom and segment lengths. The translational movement of the hip is already a good measure for evaluating the intended movement; in particular, the horizontal component of the hip movement represents the proportion of the forward progression that is generated by the supporting leg. By virtue of the coordination of swing leg movement and supporting leg movement, the relationship of the ipsilateral swing leg movement to the hip translation permits a classification of the movement and a control of the prosthesis behavior. To identify which movement is being carried out or is intended, a combination of orientation of the upper part and hip translation or translation of the knee axis and hip translation is particularly suitable, since these variables can be determined entirely using the sensors in the orthopedic device.

[0085] In order to be able to estimate the leg angle of the contralateral side, wherein the leg angle between the hip joint and the set-down point at heel strike is measured in relation to the direction of gravity, two assumptions are made, namely that the contralateral foot is in contact with the ground and thus the relative movement between the foot and the ground surface is equal to 0, and that at least at one point in time in the double support phase, i.e. when both feet or foot parts are on the ground, an inertial leg angle of the contralateral side can be determined. One admissible assumption here would be that the leg angle on the contralateral side corresponds to the negative leg angle on the prosthesis side. Proceeding from this initial condition, the change in position of the contralateral leg angle can be calculated using trigonometric functions from the segment lengths and the relative translation of the hip. If the contralateral leg angle in its stance phase and the spatial orientation of the ipsilateral upper part in its swing phase are put in relation, the ratio can provide information on whether the user wishes to walk up an incline or climb stairs with the aided side or intends in some other way to negotiate a height difference ΔH when walking. Typical of such an intended gait behavior is a strong rearward inclination of the angle of the ipsilateral upper part at the middle of the swing phase, with a relatively low heel strike of the contralateral side in the stance phase. In other words, the contralateral side remains almost vertical, which means that the translational hip movement is small, while the upper part or the thigh is raised and flexed strongly.

[0086] If, when walking up an incline, the artificial knee joint 1 is stopped in the flexed position at the end of the swing phase, the extent of such a preflexion can be determined such that the ipsilateral and contralateral leg angles are in a harmonious relationship to each other when the aided side makes contact with the ground. The flexion and extension resistances in the form of setpoint values of the actuator 40 are then set in the orthopedic device in the swing phase such that a harmonious relationship is established between the leg angle on the contralateral side in the stance phase and the leg angle on the ipsilateral side in the swing phase. The setpoint values of the actuator 40 and thus also the flexion resistances and extension resistances are set such that the maximum achievable knee angle KA.sub.max is adjusted according to the determined or estimated height difference ΔH of the foot part on the ipsilateral side, wherein the height difference ΔH is applied to a foot or a foot part on the contralateral side of a patient.

[0087] If walking up an incline, climbing stairs or stepping over an obstacle by negotiating a height difference ΔH is detected, the maximum extension of the lower part 20 relative to the upper part 10 is limited, such that the maximum achievable knee angle KA.sub.max is reduced. The lower part 20 is stopped at a specific angle of the lower part 20. FIG. 2 illustrates such control using three states of an orthopedic device. If the lower part 20 were to be extended to the maximum extent when negotiating a height difference ΔH in a manner unchanged from walking on level ground, such that the achievable knee angle KA.sub.max is approximately 180°, the foot part 30′ would be set down very far forward and with a large sole angle, and the patient would have to rotate the hip about the set-down point over the entire leg chord length, which would lead to a non-physiological sequence of movements. According to the invention, by contrast, provision is made that the extension of the lower part 20 at a specific maximum knee angle or with a specific orientation of the lower part, which can be detected by the inertial angle sensor 52 for example, is stopped even before the maximum extension is reached, such that the foot part 30″ at the end of the extension movement is located above the ledge or step or at the end of the movement is located at the determined or estimated height difference ΔH. Subsequently, in the further course of movement, the thigh or the upper part 10 is lowered, wherein the orientation of the lower part 20 is preferably kept constant, i.e. the spatial position of the lower part 20 does not change, until the foot part 30′″ has touched the ground. This can be detected, for example, by the axial force sensor 54 detecting the occurrence of an axial force. If such an axial force FA is detected, it is to be assumed that the swing phase has ended and, in order to negotiate the height difference ΔH, both the hip angle HA is increased and the knee angle KA is increased, at least not decreased, so that, due to the variable knee angle setting and a preflexion, the effective leg chord length is shortened at set-down and less energy is required to negotiate the height difference ΔH.

[0088] The greater the height difference ΔH to be negotiated, which can be determined for example on the basis of a reduced heel strike on the contralateral side or a detected maximum spatial position of the upper part 10, the maximum achievable knee angle KA.sub.max is reduced, i.e. the preflexion is increased and the extension stop is shifted forward. The extension stop can be shifted forward by a motorized adjustment of a mechanical stop or by suitable opening and closing of valves in a hydraulic or pneumatic control system within the actuator 40.

[0089] The vertical path of the knee axis, i.e. the difference in height against the direction of gravity G, can be calculated from the absolute angle of the upper part 10, if the vertical path of the hip is known, or is determined as an estimate. The vertical path of the foot part can be calculated or estimated from a combination of the spatial orientation of the upper part 10 in conjunction with the relative angle or knee angle KA, which can be determined via the knee angle sensor 25. The knee angle sensor 25 allows the determined knee angle KAD to be determined and, if sensor data are available on the hip angle in conjunction with the segment lengths, serves to calculate the height difference ΔH. The achievable knee angle KA.sub.max is set in the swing phase of the ipsilateral leg and is maintained until a predetermined spatial position of the lower part and/or upper part is reached. Likewise, the setting with regard to the achievable knee angle KA.sub.max can be maintained, when monitoring the ankle joint angle AA, until a predetermined ankle joint angle AA is reached, which is defined for example as the angle that arises after the foot part 30 is lifted at the end of the stance phase, when the foot part 30 is in a neutral position. If the foot part 30 is then set down, the ankle joint angle AA changes, which is a sign that a change in the maximum achievable knee angle KA.sub.max is now possible. Alternatively, by determining the force profile along the longitudinal extent of the foot part, the position of the force application point can be determined and, depending on this position, the actuator 40 can be controlled accordingly in order to block further extension up to a certain point in time and only then to permit an extension of the knee joint 1. Alternatively or in addition, a timer element can be used to set a specific time period that limits a maximum extension.

[0090] Reaching a minimum hip angle HA can be detected by monitoring the spatial orientation of the upper part 10. If the thigh or the upper part 10 is maximally flexed, the longitudinal extent of the upper part 10 is at a maximum inclination relative to the direction of gravity G. If the upper part 10 is then pivoted downward about the hip joint and the longitudinal extent of the upper part 10 approaches the direction of gravity G, a minimum hip angle HA is reached and a movement reversal has taken place. After the detection of the movement reversal, the maximum knee angle or, for example, the spatial orientation of the lower part 20 can be kept constant until a set-down of the foot part 30 on the ground is determined, for example by detecting an axial force FA or by a change in the ankle joint angle KA. While the maximum achievable knee angle KA.sub.max is set by changing the extension resistance in order to set the foot part 30 down in the correct orientation with an angled leg, it is advantageous, for the further course of movement, if the flexion resistance in the swing phase of the ipsilateral side after a movement reversal of the lower part 20 in the vertical direction, i.e. when the lower part is lowered, is kept at a high level, at a level that is higher than the flexion resistance when walking on level ground, in order to facilitate lifting the body of the user of the orthopedic device when walking up an incline, climbing stairs or the like and to avoid unwanted flexion and bending of the knee joint 1.

[0091] In FIG. 3, the respective angles and spatial orientations and the respective reference values are shown in order to clarify the respective relationships among one another. The direction of gravity is denoted by the arrow g; the gravity orientation essentially corresponds to a vertical orientation. The spatial orientation of the upper part 10 is defined by the angle φ.sub.T, the spatial orientation of the lower part 20 is represented by the angle φs, in each case measured from the direction of gravity g. The hip angle HA is measured between the longitudinal orientation of the trunk and the longitudinal orientation of the upper part 10 on the front side in the g direction; the knee angle KA is measured between the longitudinal extent of the upper part 10 and the longitudinal extent of the lower part 20 about the knee axis 15.

[0092] FIG. 4 is an illustration of a sequence of movement when walking up an incline. The sequence of movement begins at t.sub.0 for the aided leg with the upper part 10, the lower part 20 and the prosthetic foot 30, in which the prosthetic foot 30 still just touches the ground and is at the end of the stance phase. The unaided, contralateral leg is fully placed on the ground and slightly flexed. At the time t.sub.1, the aided leg is raised and is in a maximally flexed position with a minimal knee angle KA. At the time t.sub.2, the foot part 30 is moved toward the ground and lowered, the lower part 20 is at the end of a swing phase extension movement and is braked, for example by activating a brake, increasing a damping rate or adjusting an extension stop, with which the achievable knee angle is changed. At the time t.sub.3, the foot part 30 of the aided leg is set down with a flexed knee joint 1; the contralateral, unaided leg is unloaded and moved forward. At the same time, a stance phase extension is carried out for the aided leg, which is completed in the phase at the time t3. The center of gravity of the body is then moved forward in the walking direction via the knee pivot axis 15. With an extended knee joint, the lower part 20 performs a forward rotation about a support point or pivot point on the ground side and, in the illustrative embodiment, is arranged in the region of the tip of the prosthetic foot 30. The movement cycle then begins again.

[0093] FIG. 5 shows a corresponding sequence of movement for negotiating a step, wherein a further movement stage for negotiating a step is designated in FIG. 5 as t.sub.4 and lies between the time segments and t4 in the sequence shown in FIG. 4. At the time t.sub.4 in FIG. 5, the unaided, contralateral leg is raised and at a height just above the step to be negotiated, and the knee on the contralateral side has not yet been moved in front of the knee axis 15 of the prosthetic knee joint 1.

[0094] In FIG. 6, the trajectories of the ankle joint A at the height of the ankle joint axis 35, those of the knee K at the height of the knee joint axis 15 and those of the trochanter Tr, as a prominent point of the thigh bone in the region of the hip joint, are plotted. The orientations of upper part 10 and lower part 20 in the sagittal plane are shown between the trajectories shown in solid lines. The trajectories and likewise the orientations reflect walking on level ground; the arrow directions indicate the forward movement. At the start of the swing phase, at toe-off TO, the ankle joint A is slightly raised, compared to being straight during standing. After the toe-off, the knee joint K is brought forward and raised slightly, creating a whiplash effect in which the ankle joint A is raised and the greater trochanter remains at an almost unchanged level. With a further forward movement, the knee joint K is raised further and moved forward, the ankle joint A overtakes the knee joint after about 40% of the gait cycle until the knee joint K is in a maximally extended position, which is the case with heel contact or heel strike. This gait phase is marked with the solid line and the reference sign IC for initial contact. Due to the elasticity of the foot, the ankle joint axis sinks slightly and the leg rolls forward around the foot 30 or the ankle joint axis 35 in the walking direction, wherein the knee joint is slightly bent because this is a stance phase flexion. At about 70% of the gait cycle, the greater trochanter overtakes the knee joint axis, and the hip is brought in front of the knee joint and a forward movement is initiated. Each individual dashed line marks one tenth of a gait cycle.

[0095] FIG. 7 shows the trajectories of ankle A, knee K and greater trochanter Tr when walking up an incline, for example on a ramp. It can be seen from the different trajectories that the ankle joint A has the same trajectory shape, but that it is inclined upward. The lower leg orientation upon initial contact is different than when walking on level ground, as also is the orientation of lower part to upper part, namely bent in contrast to a maximally extended position when walking on level ground. All the trajectories end at a higher level than they began, which is the nature of things when walking up an incline.

[0096] On the basis of FIG. 8, the stride height between the contralateral, unaided leg and the ipsilateral foot part 30 of the aided leg can be defined. For example, the distance H.sub.1 from the ground to a prominent point of the hip, for example the greater trochanter, is determined at the level of the supporting leg, the distance H.sub.2 is the distance between the ground and the hip or the greater trochanter on the leading side, in the example shown on the aided side. The height difference HΔ then results from the difference between H1 and H2. Accordingly, a definition of the height difference ΔH applies for walking on a ramp. FIG. 8b shows the definition of a height difference ΔH* in which the negotiated height is measured from ipsilateral to ipsilateral, i.e. the height difference between the lifting of the aided leg and the setting back down, which corresponds to the height difference between the toe-off of the aided leg and the initial contact.

[0097] FIG. 9 illustrates the difference to the patient, when seeking to negotiate a height difference, between using the aided leg with a flexed knee joint and a leg with an extended knee joint. In the left-hand view, a preflexed configuration is shown, while the right-hand view shows an extended configuration in which the knee angle KA.sub.2 is greater than in the preflexed configuration with a knee angle KA.sub.1. Due to the preflexion, the heel strike L.sub.1 is less than when setting down with an extended leg. The center of gravity COM of the body must be moved forward in order to achieve gait progress. To do this, the lever L.sub.*1 must be used as the distance between the center of mass COM and the vertical from the contact point, in order to move the center of gravity of the body. The lower the lever L.sub.*1, the less the effort that the patient has to make via the thigh muscles and the hip extensor. In the view on the right, in which the heel strike is L2>L1, the lever L.sub.*2 is also much larger, even with a user leaning forward, so that considerably greater force is required to negotiate the height difference. In the case of an extended configuration as in the view on the right, the height difference LE must be achieved using a larger heel strike L.sub.2 compared to a preflexed configuration. The usual compensation is effected by a forward inclination of the upper body, which attempts to reduce the lever L.sub.* between the set-down point and the center of mass COM. In addition, there is an increased plantar flexion of the trailing supporting leg, which cannot be seen in the illustration.

[0098] FIG. 10 shows the dependence of the knee angle KA on the height difference ΔH or the stride height. The greater the stride height or the height difference ΔH to be negotiated, the smaller the knee angle KA becomes, in particular if the lower leg orientation is to be the same at set-down. FIG. 11 shows this relationship for negotiating a step; FIG. 10 shows it for walking up an incline on a ramp.

[0099] FIG. 12 shows the knee angle profile for different height differences ΔH. When walking on level ground, where ΔH=0, the toe-off TO.sub.1 results in a reduction of knee angle KA down to a minimum knee angle. The foot is then brought forward, the knee angle KA increases until almost complete extension at heel strike or initial contact IC. A preflexion is set so that stance phase flexion can be performed. The stance phase flexion increases up to the point in time t/T=1.05 and then decreases until the maximum extension at t/T=1.4, which corresponds more or less to the rollover. Then, at the end of the stance phase, a preflexion is carried out to initiate the swing phase. With increasing height differences ΔH, it can be seen that the preflexion increases with the height difference ΔH in the event of a heel strike or initial contact IC; the stance phase flexion may decrease or be suppressed as the height difference ΔH increases. The knee angle KA is plotted over the dimensionless time by the proportion of the gait cycle; the subdivisions each correspond to 10% of a gait cycle.

[0100] FIG. 13 shows the profile of a thigh orientation ϕ.sub.T in ° over a stride cycle with the subdivision into the respective proportion of the gait cycle, applied from a first initial contact or heel strike IC as far as a second initial contact IC2 or heel strike. The dashed line shows the profile of the thigh orientation φ.sub.T for walking on level ground, the solid line for walking up an incline or climbing stairs with ΔH>0. In order to detect ascent, the height difference ΔH can be deduced from the profile of the thigh orientation φ.sub.T on the basis of the greater range of motion or the greater pivoting in the period from the increase in hip flexion at T.sub.1 to T.sub.3, which is expressed in a greater Δφ.sub.T1, from the greater hip flexion between T.sub.2 and T.sub.3 in the form of Δφ.sub.T2 or the ratio of hip extension to hip flexion

[00001]$\left(\frac{\mathrm{\phi \Delta }T2}{\left(\mathrm{\phi \Delta }T1-\mathrm{\phi \Delta }T2\right)}\right)$

or the ratio of flexion to range of motion

[00002]$\left(\frac{\mathrm{\phi \Delta }T2}{\mathrm{\phi \Delta }T1}\right).$

The corresponding adjustment commands from the control device for adapting the damping and/or the stops then result from the calculation or estimation.

[0101] FIG. 14 shows the ratio of the thigh orientation φ.sub.T in relation to the horizontal path of the hip or of the greater trochanter X.sub.H for different height differences of the ΔH. Walking on level ground with ΔH1 results in a comparatively small range of motion; with increasing height difference ΔH, there is an increasing increase in the thigh orientation φ.sub.T with a shortening stride length or a shortening horizontal path of the hip. From such a relationship, it can be deduced whether the person is stepping over an obstacle or walking up an incline and whether and to what extent an adjustment of the extension stop or damping devices should be undertaken. The adjustment of the extension stop or of the damper device can then take place in the swing phase, for example when a threshold value stored in the control unit for this ratio is reached.

[0102] FIG. 15 illustrates a possible auxiliary variable for estimating the stride height or the height difference ΔH to be negotiated, namely the ratio of the thigh orientation φ.sub.T to the horizontal path of the hip X.sub.H. A rising inclination K indicates an increasing stride height ΔH; the greater the stride height ΔH, the greater also is the inclination of the ratio of thigh orientation φ.sub.T to a horizontal path X.sub.H of the hip, for example of the greater trochanter.

[0103] FIG. 16 shows the knee angle profile KA in ° over a stride cycle, starting with toe-off TO, with a heel strike HS or initial contact IC at 1 and a second toe-off TO at 1.6. In the different gait phases, different goals are pursued via the control of the resistances or the stops. In region A, the swing phase extension is braked in a controlled manner or the knee joint is actively extended as far as the respectively desired preflexion angle. In phase B, the stance phase flexion is checked, for example bending under a high flexion resistance in order to limit or prevent excessive stance phase flexion. In phase C, the stance phase extension is influenced, for example via the extension rate, such that the rollover behavior and extension behavior can be influenced. In phase D, the stance phase extension is slowed down, in order to avoid a hard stop in the extension stop when the rollover has taken place and the maximum knee angle is reached.

[0104] An example of the application of an energy store, which can be integrated in an active or semi-active actuator, lies in the use of the energy store in selected gait phases. The kinetic energy can in particular be stored during the stance phase extension, that is to say during phases C and D, within these phases in particular during the braking in the stance phase extension, which corresponds to phase D. To support the swing phase flexion, especially directly after the initiation of the swing phase, the stored energy is released again. It is likewise possible that the kinetic energy is stored during the stance phase extension in phase D, in order to release it again during the swing phase extension in phase A, there in particular in the second half of the stance phase extension. The correct positioning of the foot is supported in this way. In principle, it is also possible to store the kinetic energy in other movement phases and to release it again in other movement phases.

[0105] It is not necessary for all of the stored kinetic energy to be released again immediately; amounts of stored energy can also be accumulated, for example over several movement phases of a stride or over several strides in different or in the same movement phases.

[0106] FIG. 17 shows different control profiles of a stance phase extension over the lower leg angle cps. The knee extension can be controlled in such a way that, with a profile according to A, the lower leg or the lower part 10 maintains an approximately constant orientation during the knee extension movement. Alternatively, according to profile B, a certain amount of forward rotation of the lower part 20 and the lower leg can be allowed, and a forward rotation speed can be set to a defined level. The profile C provides a certain amount of rearward rotation or a rearward rotation speed. All three control variants may depend on the walking speed, the stride height, the stride length and the degree of knee flexion. The lower leg angle cps is again plotted over the phases of a gait cycle from the initial contact IC to the beginning of the swing phase at toe-off TO.

[0107] FIG. 18 shows two different knee angle profiles KA, likewise over phases of the gait cycle, wherein the phase following the initial contact IC here takes place with a relatively rigid preflexion of 20 degrees. Stance phase flexion is suppressed over the profile according to the solid curve A. The profile with the dashed line B permits a further stance phase flexion to 30 degrees, but the extent of the stance phase flexion is monitored and the maximum knee flexion limited. Both variants can be used depending on the walking speed, the stride height, the stride length and the profile of the force application point in the foot part.

[0108] FIG. 19 shows the possible resistance profile with passive control and with suppression of stance phase flexion on the basis of three diagrams. The upper diagram shows the knee angle profile KA, the middle diagram shows the flexion resistance R.sub.flex and the lower diagram shows the extension resistance R.sub.ext over a gait cycle from toe-off 1 to toe-off 2 with the initial contact IC or heel strike at 1.0. All three curves are plotted over the dimensionless time through the proportion of the gait cycle. Before the initial contact IC, the flexion resistance R.sub.flex is increased to a maximum value, such that a maximum flexion resistance is applied at an initial contact IC of the foot part. The increase in phase A takes place during the swing phase extension, the knee joint is locked at initial contact IC. After the initial contact IC, the flexion resistance R.sub.flex to the stance phase extension is reduced again in phase B, for example when a stance phase extension takes place, in order then to permit, at the end of the stance phase, a rapid drop in the extension resistance in order to initiate the swing phase. The extension resistance is increased in phase C before the initial contact IC during the swing phase extension, in order to stop the knee joint at a defined knee angle KA. There does not have to be a complete blocking of the extension movement. By increasing the resistance, the extension movement can be reduced sufficiently to adequately stop the joint. The extension resistance is then reduced, if necessary depending on the walking speed, stride height, stride length, existing knee flexion and the profile of the ground reaction force vector. The extension resistance R.sub.ext is then increased in a controlled manner during the stance phase extension movement, for example by regulating it to a setpoint extension rate of the knee joint or as a function of the lower leg angle φ.sub.s. Finally, the stance phase extension is brought to a stop by a further increase in phase F, in order to avoid a hard stop in the extension or when the desired knee angle KA is reached.

[0109] FIG. 20 corresponds substantially to FIG. 19, but shows different profiles for both the knee angle KA and the respective resistances over the course of a gait cycle. In contrast to the profile in FIG. 19, the flexion resistance R.sub.flex is not increased to a maximum value before the initial contact IC, but instead is reduced to a lower value, after a maximum for slowing down in the swing phase, until after the initial contact IC the flexion resistance R.sub.flex is increased in phase B in order to permit a controlled stance phase flexion. The increase in phase B serves to control the flexion rate or the extent of the stance phase flexion. The extent to which the flexion resistance R.sub.flex is increased depends on the desired maximum flexion angle. The flexion resistance is then reduced again in phase C, analogously to phase B in FIG. 19. The extension resistance R.sub.ext is adjusted as explained in the profile of FIG. 19.

[0110] FIG. 21 shows the profile of the lower leg angle φ.sub.s in relation to the thigh angle φ.sub.T for walking on level ground in the broken line with a height difference AR equal to 0. Here too, the distinctive points of the gait are marked with toe-off TO and the initial contact IC. The solid line shows the ratio of the lower leg angle φ.sub.s to the thigh angle φ.sub.T for walking up an incline or stepping over an obstacle with a height difference ΔH greater than 0. The subdivisions each correspond to 10 percent of a gait cycle. On the basis of the different profiles of the curves, it is possible to estimate how great is the height difference AH that has been overcome or is to be overcome. In particular, from the curve profile after 80 percent of the gait cycle, i.e. after two lines after the toe-off TO or at 0.8, there is a substantially steeper increase for walking on level ground with ΔH equal to 0 than for walking up an incline or stepping over an obstacle with a height difference ΔH greater than 0. For different height differences ΔH, different profiles can be determined or stored, which are then made available to the control device in order to be able to make a corresponding adjustment of the stops and the resistances for adaptation to the respective gait situation.

[0111] FIG. 22 shows the ratio of the knee angle KA to the thigh angle φ.sub.T for walking on level ground with ΔH equal to 0 with the dashed line, and for stepping over an obstacle or walking up an incline with ΔH greater than 0 with the solid line. With a stride cycle of 0.6 at a toe-off, there is likewise a significant difference in the curve profiles in the range of 0.8 of a gait cycle, via which the height difference ΔH is then estimated using comparison algorithms, and a corresponding adaptation of the resistances or stops can be effected with the control.

[0112] In FIG. 23, a definition of the leg chords of an ipsilateral, aided leg and a contralateral, unaided leg is made. The leg chord goes through the hip rotation point and forms a line to the ankle joint. As can be seen from FIG. 23, the length of the leg chord and the orientation φ.sub.L of the leg chords change during the movement, in particular also with different inclines. The height differences ΔH that are to be negotiated can be estimated and predicted or determined via the profile of the change in length and/or orientation of the leg chord. The respective control commands are then derived from this. The respective orientation of the ipsilateral leg chord φ.sub.Li relative to the direction of gravity G and the contralateral leg chord φ.sub.Lk is entered in each case.