WEARABLE ASSISTIVE DEVICE

Abstract

The present invention relates to a wearable assistive device.

Claims

1. A wearable assistive device comprising first and second parts, configured to be wearable proximal and distal of a limb joint of a limb respectively and having an articulated interconnection and a tendon interconnection, guided from the first part to the second part and adapted to exert an assistive force on the limb joint when tensioned; wherein the articulated interconnection is configured to be provided unilaterally, on the lateral side of the limb joint, the tendon interconnection is configured to be provided unilaterally, on the lateral side of the limb joint, and counter-torsion means adapted to generate forces counteracting torsion of the first and second parts relative to the limb by tensioning the tendon interconnection are provided.

2. The wearable assistive device according to claim 1, wherein a motor is provided adapted to tension the tendon interconnection.

3. The wearable assistive device according to claim 2, wherein the motor adapted to tension the tendon interconnection is provided at a torso and a tendon of the tendon interconnection is guided from the torso to the first part or the second part.

4. The wearable assistive device according to claim 1, wherein a control is provided to tension a tendon of the tendon interconnection in a manner stabilizing a posture and/or in a manner supporting an extension of the limb.

5. The wearable assistive device according to claim 1, wherein the first and second parts are adapted to be wearable proximal and distal of a knee joint and the assistive device is adapted to assist in stance stabilization and/or leg extension.

6. The wearable assistive device according to claim 1, wherein at least one of the first and second parts comprises a solid plate adapted to be nestled in use to the limb and a strap arrangement comprising one or more straps adapted for attaching the solid plate on the limb.

7. The wearable assistive device according to claim 6, wherein the strap arrangement is adapted for attaching the plate on the limb such that at least one strap extends from one side of the plate, around a posterior part of the limb and to an opposite side of the plate.

8. The wearable assistive device according to claim 6, wherein the strap arrangement is adapted for attaching the plate on the limb such that at least one strap is self-tensioning so as to implement a counter-torsion means.

9. The wearable assistive device according to claim 8, wherein the at least one self-tensioning strap is adapted to be guided from one side of the plate, around a posterior part of the limb, to an opposite side of the plate, and to the tendon interconnection.

10. The wearable assistive device according to claim 9, wherein the tension generated within the self-tensioning strap upon tensioning the tendon interconnection, during use, generates a counter-torsional moment acting on the limb via the solid plate.

11. The wearable assistive device according to claim 6, wherein a tendon of the tendon interconnection is guided through a guiding member having a flexibility higher than that of the solid plate of the first part and/or the second part and lower than that of the tendon, the guiding member being fixedly attached to a strap of the strap arrangement.

12. The wearable assistive device according to claim 6, wherein the solid plate of the first part or the second part is adapted to be positioned in use on proximal anterior and lateral sides of a shank of the limb.

13. The wearable assistive device according to claim 6, wherein the solid plate of the first part or the second part is adapted to be worn at distal anterior and lateral sides of a thigh.

14. The wearable assistive device according to claim 6, wherein the solid plate has a base part made of plastic material.

15. The wearable assistive device according to claim 1, wherein the limb joint is a knee joint, and wherein the articulated interconnection is provided at the lateral side of the knee joint.

16. The wearable assistive device according to claim 15, wherein the articulated interconnection is provided in the form of a hinge joint having a center of rotation aligned, in use, at least approximately with that of the knee joint, wherein any deviation is compensated in use by the compression of the device and/or by the compression of the tissue of the user limb.

17. The wearable assistive device according to claim 16, wherein the first and second parts both comprise a solid plate adapted to be nestled in use to the limb and a strap arrangement comprising one or more straps adapted for attaching the solid plate on the limb, wherein the hinge joint is connected to first and second solid plates, wherein the first plate is positioned distal to the limb joint and the second plate is positioned proximal to the limb joint, wherein the distal first plate is adapted to guide a tendon of the tendon interconnection and extends anteriorly from a joint axis when viewed in a sagittal plane.

18. The wearable assistive device according to claim 1, wherein the tendon interconnection comprises a ribbon or a non-bowden cable having a radius of curvature smaller than 1 cm.

19. The wearable assistive device according to claim 1, wherein each of the first and second parts comprises a solid plate adapted to be nestled in use to the limb, and wherein routing means are provided to route the tendon interconnection from a hinge joint between the two solid plates towards an anterior central point of the solid plate of the proximal part.

20. The wearable assistive device according to claim 19, wherein the limb joint is a knee joint, and wherein the tendon interconnection is adapted to be routed such that the tendon is guided laterally from a distal position below the knee joint to a more medial position proximal of the knee joint at an angle BETA between 5° and 45° to a collinear path so as to implement a counter-torsion means.

Description

[0056] The present invention will now be disclosed with reference to the drawings by way of non-limiting examples. In the drawings,

[0057] FIG. 1 shows a leg to which the wearable assistive device is attached in a front view, a side view and a back view;

[0058] FIG. 2 shows the lower plate without tendon and without straps;

[0059] FIG. 3 shows a thigh plate used in FIG. 1;

[0060] FIG. 4 shows a simplified scheme of the human leg with one degree of freedom;

[0061] FIG. 5 shows the model usable in a virtual work analysis;

[0062] FIG. 6 shows the relation between a knee angle and the knee moment;

[0063] FIG. 7 shows the relation between a hip moment and the knee angle;

[0064] FIG. 8 explains a preferred detail of a wearable assisting device wherein a spring as resilient elastic element provided in series with a tendon which in turn is fixed to a plate attached to a limb;

[0065] FIG. 9 shows a frontal plane view of a thigh brace of a wearable device according to a preferred embodiment of the present invention in order to display the transverse, sagittal and frontal planes;

[0066] FIG. 10 schematically shows the moments generated within the transverse plane without self-tensioning strap; and

[0067] FIG. 11 schematically shows the moments generated within the transverse plane with a preferred embodiment of a self-tensioning strap.

[0068] According to FIG. 1, a wearable assistive device 1 comprises two parts 2, 3 wearable proximal (cf. part 2) and distal (cf. part 3) of a limb joint 4, respectively, and having an articulated interconnection 5 (cf. also FIG. 3) and a tendon interconnection 6 guided from the first part to the second part and exerting an assistive force F.sub.reaction on the limb joint 4 when tensioned as indicated by R.sub.tendon, wherein the articulated interconnection 5 is provided unilaterally, the tendon interconnection 6 is provided unilaterally and counter torsion means 7 adapted to generate forces counteracting torsion of the wearable parts 2, 3 on tensioning the tendon interconnection are provided.

[0069] In the embodiment shown in FIG. 1, the wearable assistive device is a leg assistive device and the limb joint 4 is a knee. The wearable assistive device 1 is an active wearable assistive device wherein the tendon of the tendon interconnection 5 is actuated by a DC motor provided at a breast or back plate on the torso of a user (not shown). The tendon is routed across the hip to the motor.

[0070] The two parts wearable proximal and distal of the knee comprise plates 2 and 3, each plate being attachable to the leg with 2 straps 2a, 2b and 3a, 3b, respectively.

[0071] As can be estimated from the three views shown in FIG. 1, the components of the wearable assistive device attached to the leg do not extend far away from the leg and therefore, these parts of the wearable assistive device can be worn underneath a trouser or the like. Accordingly, the wearable assistive device is unobtrusive.

[0072] Thigh plate 2 as shown in FIG. 3 has a front part having a plurality of holes to reduce transpiration and increase comfort to the user. Thigh plate 2 is shaped and sized to be worn anterior with straps extending posterior from the left side of the plate to the right side at two positions, namely a proximal and a more distal position. Note that the thigh part provides a stiff pivot support, designated as (R1) and that the calf part also provides stiff pivot support designated as (R2).

[0073] It is noted that a large distance between the two straps attached to plate 2 (and, similarly a large distance between the two straps 3a, 3b attached to plate 3) helps to prevent rotation or other movement of the plate relative to the leg when exerting forces by tensioning the tendon interconnection. The straps 2a, 2b are flexible enough to be comfortable, but are tight enough to still keep the plates in their position without major movements. It will be understood that plate 2—and, similarly, plate 3, will be padded to increase the comfort to the user. The padding may allow diffusion to increase breathability; also, it is preferred to not cover the entire inner area of the plate with padding but to leave one or more cutouts. In particular, the padding can have a large central opening. Similar padding is provided for plate 3. Also note that in a lightweight arrangement, plates 2 and 3 may have a central cutout as well.

[0074] As can be seen in FIG. 1, (cf. the back view), the upper strap 2a, that is the most proximal strap on the thigh, has an anchor strap 2c through which the tendon is guided in a manner such that, when the tendon is tensioned, the strap is pressed against the skin of a user to a higher degree. Accordingly, the strap is self-tensioning and the self-tensioning of the strap counteracts twisting or torsion in use so that the anchor strap 2c can be considered a counter torsion means. A counter-torsion means based on such self-tensioning will be explained in more detail further below with reference to FIGS. 9-11.

[0075] It is noted that the straps will have some flexibility and that they preferably can be replaced easily. Accordingly, a Velcro-like attachment to the plate is preferred on at least one side of the plate.

[0076] Tendon 6 is guided in a trench-like structure 2d along the edge of the plate. Furthermore, the through-holes on the front side of the plate not only serve to increase breathability, but may also be used to insert studs, screws or other structures that allow to guide the tendon sideways towards the center of the leg, that is closer to the knee cap. Through-holes suitable for this are indicated as 2e1, 2e2, 2e3.

[0077] As will be seen in FIG. 1, tendon 6 is routed in a manner that leads to an angle β of the tendon relative to a plane comprising the joint 5 and the lateral edge of the knee cap and the lateral edge of the knee cap. The angle β helps to reduce any tendency of relative twist or torsion between upper and lower plate on tensioning the tendon and hence serves as a counter torsion means. This can be done in a manner selecting a through-hole 2e1 or 2e2 or 2e3 suitable for a given user to insert a tendon deflecting stud.

[0078] Whereas plate 2 is made of plastics material, for example in a practical embodiment made of polyamide, the joint 5 made of metal, produced separately and attached to the plate 2 with screws or the like. Note that plate 3 is also made of plastic material.

[0079] It will be understood that the plate 2 has a thickness and shape allowing some deformation so that a ready-made plate can be used without customization for every user. The same holds, obviously, for plate 3.

[0080] It is noted that the straps could be tensioned by suitable tensioning mechanisms such as shown by reference numeral 2f showing a tensioning mechanism commonly known in the art; however, such tensioning mechanism is not deemed vital.

[0081] The joint 5 is arranged such that for an average user, the axis of joint 5 is collinear with an axis of a knee joint movement. Note that given the anatomical shape of the thigh (having a large circumference closer to the hip compared to the circumference closer to the knee), and given the anatomical form of the calf, the parts of the joint 5 will not have to extend laterally beyond a general contour tangent to the outermost parts of the thigh and the calf, respectively. Accordingly, the wearable assistive device can be worn below underneath normal clothing, in particular in view of the fact that soft tendons 6 requiring no stiff sheaths can be used.

[0082] It will be understood that tendons having a minimum radius of curvature below 3 cm are highly preferred. A preferred embodiment may use Dyneema tendons.

[0083] Regarding plate 3, straps 3a and 3b are arranged such that the upper strap is routed above the gastrocnemius muscle and the lower strap is routed below the muscle insertion, right above where the Achilles tendon typically is visible. It is noted that the anatomical form of the calf helps to position the lower plate using such a strap arrangement and to keep the lower plate correctly positioned.

[0084] Furthermore, as can be seen in FIG. 2, shank plate 3 comprises a tendon guide element 3c which in use extends anterior of joint axis 5. However, guide 3c does not need extend beyond the front of lower plate 3 divided as indicated by dashed line 3d.

[0085] Note that guide 3c is integral with the guide plate and thus built from plastic material. The same holds for a hinge cover that covers hinge 5 such that during movement of the hinge, no textile material from clothing worn above the wearable assistive device can be pinched or jam the movement of the joint. The tendon is guided on the outer perimeter of the cover, which however does not extend anterior of the leg. From the analysis below, it will be understood that sufficient support can be provided to the leg despite this small dimension.

[0086] For anchoring the tendon, at the lower part of the plate 3, through-hole 3e is provided, through which the tendon can be guided and to which the tendon can be fixed using a knot.

[0087] In a preferred embodiment, it is possible to provide a resilient elastic element in series with a tendon and to then fix the resilient elastic element to the through-hole 3e. This will be described below with reference to FIG. 8. In more detail, it is possible to implement a preferred embodiment that has a transparency mode and/or provides other advantages. In more detail, we herein incorporate DE 10 2018 215 163.6 and/or any family member claiming priority thereof. Note that FIG. 8 is derived from DE 10 2018 215 163.6. In DE 10 2018 215 163.6, a wearable active assisting device has been suggested having a selectable minimum degree of assistance, which can be close to zero limb assistance, by actuating the motors usually assisting the limb in a manner so that the elongation of the force transmission element is tightly controlled according to a model derived based on the plurality of sensor signals. This allows selecting minimum assistance without decoupling the actuators, motors and the like from of the tendons. In particular, it is possible that the minimum degree of limb assistance is selected not by the user wearing the wearable active assisting device himself but by a physical therapist, physiotherapist, medical doctor and so forth, in particular even without the patient noticing. As the motor continues to elongate or shorten at least one force transmission element, even where no actual support is provided, a user hearing the motor will have the impression of being supported. Thus, a placebo effect of the wearable active assisting device can easily be tested, in particular where a patient has to rebuild confidence in his (or her) own muscles. What is more is that by modeling elongation and by shortening and/or elongating the at least one force transmission element, in case where it turns out that assistance must still be provided for certain movements in spite of the expectation of the physiotherapist or the like, assistance can and will immediately be available. It should be noted that for the purpose of the present invention, a limb assistance degree selection input is adapted so that with the unit switched on at least 2 different degrees of support are selectable, the minimum degree of limb assistance being one of these degrees selectable even where this minimum degree corresponds to zero assistance.

[0088] It has also been suggested in the document incorporated herein, that it is highly preferred to allow that the wearable active assisting device can be used without determining dedicated physical parameters for each single user overly exact. The same holds for the present invention. In a highly preferred embodiment disclosed in the reference incorporated, between the limb and a motor, a resilient element is provided in series with the force transmission element to be elongated or shortened. Using such a resilient element, for example a coil spring, allows small errors in the determination of an elongation or shortening of the force transmission element currently needed to remain undetectable to a user. This can be done in the present application as well. Accordingly, in a preferred embodiment of the present invention, it is preferred that a restrictor is provided that limits or restricts the elongation of the resilient element, for example restricts the elongation of the spring to a maximum allowed elongation, and that takes up any additional forces else applied to the spring or other resilient element without allowing further elongation thereof. For example, a specific length of a cord or wire could be provided within a coil spring. The cord could be attached at the same points as the ends of the spring, so that the restrictor also would be placed between the limb and a motor used for assisting the limb when actuated. Given that the rope shall be longer than the spring coil as long as the spring coil is not extended, all forces exerted on the force transmission element, for example due to the mismatch between model and user, will lead to an extension of the spring to a certain degree. A corresponding example is shown in FIG. 8. Note that in FIG. 8, a cuff drawn as a closed ring like structure is shown that would be attached to a limb, but that in a practical embodiment, the cuff would of course be replaced by the plate/straps-arrangement shown in FIG. 1.

[0089] In the arrangement shown in FIG. 8, while the extension of the spring (shown as a coil spring) remains low, no forces are taken up by the restrictor shown as a central wire running within the coil. However, once the spring is extended to an allowed maximum, any additional forces will be taken up by the restrictor and will thus not allow further extension of the resilient spring. In other words, the restrictor restricts elongation to a specific maximum allowed in particular where actual support or assistance is provided. By properly selecting an adequate maximum allowed elongation of the resilient spring element and a suitable modulus of resilience, care can be taken that any deviation between the model and an extension actually needed for a specific user will neither impair the intended behavior of the present wearable active assisting device during actual assistance nor will it render the device sensible during a transparency mode.

[0090] In a preferred embodiment, the resilient element has a modulus of resilience such that for a maximum residual force acceptable in a selected minimum degree of limb assistance, the resilient element is elongated by no more than the maximum allowed deviation between a standardized model and the correct extension for a given user.

[0091] In this context, it will be obvious that despite not having to take very precise measures of a user, it is possible and will be preferred to provide a plurality of resilient elements differing both in resilience and maximum allowed length. In a typical situation, the maximum allowed deviation may be a few centimeters, for example 1 to 7 cm. This distance can easily be overcome even in case of an emergency change of limb assistance given standard motor speeds. These maximum allowable lengths that are preferred in turn allow residual forces due to the extension of the resilient element when mismatched to the model that are hardly detectable by a user and will ensure that a mismatch remains undetected most or all of the time.

[0092] As indicated above, it is possible to determine a phase in current movement identified and to output a motor actuation signal in response to a modeled elongation. While it would be possible to predict the actual extension, however, it should be noted that for the transparency mode provided by a wearable active assisting device according to the present invention, neither knowledge of for example a gait phase is needed nor does the system rely on an accurate gait cycle, since the actuation profile is not predefined. In particular, it should be noted that instead of relying on specific gait phases, other parameters such as a continuous force scaling depending on the knee angle asf. can be used.

[0093] However, nonetheless, the control may be adapted to identify certain activities such as walking, standing, walking uphill or downhill, ascending or descending a stair and so forth. As indicated above, even where the control of the transparency mode itself need not rely on the determination of the precise current activity, safety of the device can be increased.

[0094] Accordingly, it can be seen that in a preferred embodiment, it is desirable to use the resilient element as explained with respect to FIG. 8 so as to use general parameters and to elongate or shorten the tendon only to a precision such that the spring is not fully extended during a mode so that a transparency mode can be implemented. Only when actual assistance is needed, for example because a patient becomes exhausted, the tendon will be shortened so much that the element central within the spring coil is no longer slack. As the distance the tendon has to be reeled in will be extremely small during such a transparency mode, active assistance can be provided almost immediately and without causing a shock or jerk to the limb supported.

[0095] It should thus be noted that one possible embodiment can be a wearable active assisting device comprising an actuator in use to provide a limb assistance and coupled to a limb to be actively assisted via at least one force transmission element to be elongated or shortened by the actuator; and a control having an input for signals from a plurality of sensors, a signal processing stage for processing input signals from the plurality of sensors, and an output stage for outputting a motor actuation signal in accordance with the processed sensor signals; wherein the control further has a limb assistance degree selection input for selecting a degree of limb assistance; and wherein the signal processor stage is adapted to continuously model an elongation of the at least one force transmission element to be elongated or shortened corresponding to a movement or posture currently detected by the plurality of sensors to output a continuous actuator actuation signal according to a modeled elongation of the at least one force transmission element to be elongated or shortened and in response to a selected minimum degree of limb assistance. In other words, the device of the preferred embodiment can be used in a transparency mode.

[0096] It will be understood that the wearable assistive device of the present invention is an active wearable assistive device having one or more motor, a control and several sensors that allow the control to energize the motor as necessary to provide assistance to the user.

[0097] The motor(s), control and sensors are not shown, as the highly flexible tendon allows to use a known arrangement attachable e.g. to the torso of a user. However, the control must be adapted to provide a required level of assistance. To this end, it has already been generally suggested that active wearable assistive device model a necessary elongation or shortening of a tendon in view of a current posture, gait phase and an expected or detected movement. Once the model has predicted a necessary elongation or shortening of a tendon, it is possible for the control to energize the motor correspondingly. It will be understood that for the active wearable assistive device, a control can be implemented in this manner. To this end, a possible model is disclosed hereinafter with respect to FIGS. 4-7.

[0098] With respect to this model, the following is noted. Previously, the significance of the Knee Moment Arm (KMA) has been attributed to the moment produced around the knee joint. In such previous model, the moment around hip and ankle joints were ignored. Also, previously, a swing double pendulum model was used for the system. In such case, the moment generated around the knee is a crucial component of the knee extension.

[0099] However, the present inventions has realized that the situation in a stance phase changes the arrangement of the double pendulum system, locking the ankle and hip joints. The extension of the knee joint thus becomes a result of assistive moments generated around the hip and ankle joints.

[0100] For the model, it is assumed that assistance of the active part of the wearable assistive device is provided during the stance phase only. It has been found that in such a case, the size of the KMA is no longer that critical to the moments generated around the hip and ankle joints in view of the following analysis.

[0101] For the purpose of the analysis, the human body was simplified to a 1DOF frame as shown in FIG. 4.

[0102] In FIG. 4, A is the ankle joint (X-Y supported), H is the hip joint (X-supported) and K is the knee joint. KF is the knee moment arm. Thip and Tshank are the tendons above and below the Knee-Moment-Arm, respectively. x and y subscripts are for x and y components of the respective tendons.

Using this terminology, a virtual work method can be used for an analysis. In more detail, the virtual work model shown in FIG. 5 was used.

[0103] Using this approach, the moment that needs to be generated in order to resist the kinematic change in the H system induced by the sum of hip and thigh tendon forces around K can be determined.

[0104] Consider that dx and dy show the migration of K due to an infinitely small deformation in the system corresponding to work done by Mhip. Mhip will then perform work equal to:

U=Mhip*d(aHKA),

where aHKA is the knee angle and d(aHKA) is the change in the knee angle. Other forces that would perform external work on the system would be the vertical and horizontal projections of the tendon forces around the K:

(Tshank,x+Thip,x)*dx and (Tshank,y+Thip,y)*dy

[0105] Accordingly, the total virtual work equation can be shown to become:

0=−M.sub.hip*δ(aHKA)+(T.sub.shank,y−T.sub.hip,y)*δ(Y)+(T.sub.shank,x+T.sub.thigh,x)*δ(x)

[0106] Note that the negative sign before hip moment is because the work done by that moment is negative; in other words, it is putting work into the system. The negative sign of the vertical hip force is due to the negative direction of the force.

[0107] Having established the total work equation, the d(y) and d(x) parts of the equation can be expressed using the knee angle (d(aHKA)) and accordingly, having the common partial derivative, the equation can be solved for Mhip.

[0108] It can be deduced that the size of the KMA influences the moment generated around the hip as shown in FIGS. 6 and 7, representing knee moment vs knee angle generated at different knee angles, showing the impact of different moment arms and hip mopment vs. knee angle for different moment arms respectively.

[0109] The wearable assistive device assists in a manner particularly useful for a large number of users. To understand this, it is important to realize that in walking, different phases can be differentiated, i.e. stance or swing phase, to provide the optimal support to the user. During stance phase the leg carries the user's weight and a closed kinematic chain is created. Once the foot is lifted from the ground and the leg is swinging forward, it acts like a pendulum swinging around the hip joint and knee joint. In contrast, during swing phase, there is no fixation available and the extension support of the knee is mainly dependent on the moment arm anterior to the knee joint.

[0110] Also, during movements with the foot firm on the ground, the muscles in the human body generate an extension moment that moves the entire body mass (e.g. walking, stair climbing, standing up from a chair). The extension pattern can be supported by a reaction force Freaction (cf. FIG. 1) due to the routing of the tendon (Ft).

[0111] In the arrangement shown, the knee is “pushed” posteriorly, generating moments that depend on the length of the shank and thigh segments rather than on the artificial moment arm that is anterior to the knee joint. As these moment arms are very large, they have a high influence on movement or posture, given that length shank and thigh element=app. 0.245*body height.

[0112] This is helpful, as the length of the artificial knee moment arm is a limiting factor of the practicability in everyday life scenarios. In the present invention, any artificial moment arm can be minimized, as the impact in supporting leg extension is small.

[0113] Also, the more the knee is bent, the more force is typically needed to assist the user in the extension movement, while less support is usually needed when the person is standing with straight legs and the tendon angles are bigger.

[0114] In the present invention, body positions with bent knees increase Freaction due to the sharp tendon angle around the knee. This can be seen in the generated knee moment. Especially when the leg is bent, larger moments are generated with smaller moment arms.

[0115] Only when the leg is almost straight, configurations with large moment arms generate larger knee moments, but this can be compensated by higher tendon forces. In contrast, during standing, the support moments required are low since the body weight is balanced in a stable configuration.

[0116] In view of this, FIG. 1 shows how Freaction can be used in an embodiment to support knee extension. By creating the reaction forces, the rigid elements attached to the thigh and shank rotate around R1 and R2. The straps 3 and 4 counteract the generated forces and transmit these forces to the segments of the user's limb. Straps 1 and 2 are making use of the conical limb shapes to prevent upwards and downwards shifting of the mechanical structure.

[0117] Now, since the forces are only transmitted laterally, the whole structure would tend to rotate around the vertical limb axis due to Freaction and rrot (FIG. 1). The invention suggest that this can be prevented by suitable counter-torsion means, e.g. a snug fit (induced e.g. by a self-tightening thigh strap) or by changing the tendon routing such that rrot is minimized (angle β).

[0118] As the application of forces can be easily timed appropriately using a suitable control mechanism, for example a control mechanism implementing a model as described above, several benefits to a user to the knee joint can be implemented when applied, namely at least assistance in extension during the early stance phase of the gait cycle or during a sit-to-stand transition—becoming effectively an additional external muscle during the concentric knee extension movement; and knee stabilization during the mid-stance phase of the gait cycle or during standing, preventing the knee from collapsing

[0119] Support for the knee extension can be implemented such that a component positioned on the distal lateral and anterior sides of the thigh and a similar component positioned on the proximal anterior and lateral sides of the shank is provided. More specifically, the anterior thigh component shall rest on the posterior part of the quadriceps muscle, just above the quadriceps tendon. Similarly, the anterior part of the shank piece shall cover the area around tibial tubercle. To keep the piece attached to the leg segments, a strap system shall be used. The straps shall extend from the anterior parts of the two components and loop around the segments with an attachment point on posterior—lateral side of the stiff structures.

[0120] As disclosed, the two aforementioned structures are laterally connected by a hinge joint whose center of rotation generally aligns with that of the knee joint, noting that such general alignment need only be approximate. The two sections of the hinge joint extend but slightly from the two leg segment parts of the mechanism, as described above. The hinge joint has but a small protrusion that routes the tendon and extends anteriorly from the thigh half of the joint axis when viewed in sagittal plane. The tendon then continues from the hinge joint laterally over the thigh structure, posteriorly over the thigh (through a structure that sits on the thigh straps) and is attached to a force producing device such as a motor energized in accordance with control signals from a suitable control.

[0121] It is noted that a few rules of force flow preferably are followed around the knee joint in order to only induce a beneficial stabilization force in the system: When viewed in the frontal plane, the path of the force transmitting member preferably lies collinearly with the lateral edge of the knee joint. This ensures that no rotation of the structure takes place in the frontal plane. By a tight fight of the thigh plate, this can be easily warranted (cf. FIG. 1, anchor straps). Additionally and/or alternatively, a change in routing can be implemented to help in a compensation of forces (cf. FIG. 1, alternative path using β)

[0122] Furthermore, whereas—as has been described- to ensure that a large variety of user sizes can be accommodated by a single mechanism or very few parts, some degree of flexibility in the thigh and shank anterior component is typically provided. In view of the fact that this might lead to torsion due to the moment arm between the anterior pivot points of the two halves and the knee-aligned joint), that is relative torsional deformation occurring between the shank and thigh parts of the mechanism when tensile forces are applied to the tendon, the tendon as force transmitting member is typically and preferably routed from the hinge joint towards the anterior central point of the stiff thigh component

[0123] Also, the posterior routing is preferably guided around the thigh area through a semi-stiff member that attaches in a fixed manner to the thigh straps. This ensures that the force is transmitted in line with the humeral joint, when viewed in the frontal plane, ensuring that no hip abduction moment is induced.

[0124] Accordingly, due to the mechanical arrangement and the control thereof, moment arms required that exploit a closed kinematic chain and thus, the device of the present invention in particular to be worn underneath clothes.

[0125] Also, high tangential forces are prevented by the small moment arm and the pivot points R1 and R2. Counteracting normal forces or pressure is generated by the corresponding straps (FIG. 1), also preventing the structure from slipping upwards. It is to be noted that the length of the limb segment components preferably is at least 4 times bigger than the distance of the tendon to the center of Rotation (CoR). This reduces the pressure created by the strap. In addition,

rotation around y-axis can prevented, inter alia due to a self-tightening mechanism (cf. anchor strap of FIG. 1) and an additional force routing that minimizes rrot using the angle β.

[0126] It is noted that despite transmission of high forces, the unilateral knee joint of the present invention provides inherent safety since in contrast to other devices known it does not lock the spanned joint any longer once the kinematic chain is opened (e.g. foot is lifted from the ground.

[0127] Therefore, as can be seen from the above text, the arrangement of the present invention is advantageous compared to designs that require almost perfect alignment with the knee joint (e.g. exoskeletons).

[0128] The working principle of a self-tensioning strap as one example for counter-torsion means according to the present invention will now be explained in more detail with reference to FIGS. 9-11. In order to visually display the functionalities of the counter-torsional mechanism and the self-tightening mechanism consider the example where the force is routed from the medial lower-back region of the user to the proximal lateral side of the thigh brace (from where it may then be further routed over the knee moment arm mechanism to the shank piece of the brace).

[0129] FIG. 9 shows a frontal plane view of such a thigh brace having a solid plate 2 of a wearable device according to a preferred embodiment of the present invention in order to display the transverse, sagittal and frontal planes.

[0130] FIG. 10 schematically shows the moments generated within the transverse plane (through a cross-section of the user's thigh 8) without self-tensioning strap: if no counter-torsion means are provided, a moment Ma is generated in the transverse plane around the center A of the user's thigh 8. This moment Ma can be expressed in terms of the tension force T1 generated in the tendon 6 times the distance d1 from the centre A of the user's thigh 8 in the transversal plane: Ma=d1*T1

[0131] If the proximal thigh strap 2c extending in the thigh brace shown in FIG. 10 from a first anchoring point S1 of the stiff brace structure 2, i.e. the solid plate 2, to a second anchoring point S2 of the solid plate 2 is then further extended from the second anchoring point S2 to interface the tensioned tendon 6 at interface or connection 9 (in order to act as a pulley), a looped strap 2c is formed and the diagram shown in FIG. 11 can be generated.

[0132] As the tension in the tendon 6 is increased, the resultant tension force component is generated within the looped strap 2c. This force provides a “self-tensioning” mechanism for the proximal thigh strap 2c. The higher the tension force in the tendon 6, the more apparent is the “self-tensioning” in the thigh proximal strap 2c as its internal tension force (T3) is linearly proportional to the tension force of the tendon 6. The looped strap 2c now generates a counter-torsional moment around the user's center A of the thigh 8. The net moment around point A in the transversal plane can then be calculated as:

Ma=d2*T2−d3*T3