MECHANISM AND METHOD FOR PERFORMING FORCE IMPULSES IN TENDON SYSTEMS

Description

This nonprovisional application is a continuation of International Application No. PCT/EP2023/081756, which was filed on Nov. 14, 2023, and which claims priority to Patent Application No. P-202200226, which was filed in Slovenia on Nov. 14, 2022, and which are both herein incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The subject of the invention is a mechanism and method for the application of assistive or resistive forces or force impulses in tendon systems during walking or standing, which enables the implementation of the established method of training the maintenance of dynamic balance while standing and walking. The proposed mechanism and method improve the quality of the interaction between the user and the tendon system for the application of assistive or resistive forces or force impulses in the intervals between individual applications of force, while at the same time ensure the appropriate tension of the tendons or preventing their loosening in the moments before the applications of assistive or resistive forces or force impulses.

Description of the Background Art

Perturbation-based training (PBT) is an established method of maintaining dynamic balance during standing and/or walking on a treadmill, in which external disturbing or supporting forces or force impulses are applied to body segments. Particularly interesting are systems that use a tendon system to transmit a disturbing or supporting force or an impulse of force from the actuator—the source of force-to the selected body segment (example: A-TPAD system, Aprigliano F, Martelli D, Kang J, Kuo S H, Kang U J, Monaco V, Micera S, Agrawal S K. Effects of repeated waist-pull perturbations on gait stability in subjects with cerebellar ataxia. J Neuroeng Rehabil. 2019 Apr. 11; 16(1):50. doi: 10.1186/s12984-019-0522-z. PMID: 30975168; PMCID: PMC6460671). With tendon systems, the person does not carry the entire system, but the actuators—the sources of forces—are placed on the external frame, and only the tendons that are attached to the selected body segment and which transmit the force to the selected body segment lead to the person. Tendon systems are therefore light, and the added weight and inertia is less than, for example, with systems that use rigid segments to transfer force to the user (example: BART system, Olenšek, A., Zadravec, M. & Matjačić, Z. A novel robot for imposing perturbations during overground walking: mechanism, control and normative stepping responses. J NeuroEngineering Rehabil 13, 55 (2016). https://doi.org/10.1186/s12984-016-0160-7), or with exoskeletons (example: Lokomat system).

In general, the tendon system is composed of an actuator, usually a motor, which is the source of an assistive or a resistive force or an impulse of force, and a tendon (for example, a string, a steel cable, etc.), which is at one—distal (as viewed by the user)—end attached to an axis of the motor either directly or via a pulley, and is attached on the other-proximal (as viewed by the user)—end, to the attachment point on the selected segment of the user's body. Upon application of a assistive or resistive force or an impulse of force, the motor rotates to pull the tendon, which then transmits the pulling force to the selected body segment (example: 3DCaLT system, Wu M, Kim J, Wei F. Facilitating Weight Shifting During Treadmill Training Improves Walking Function in Humans With Spinal Cord Injury: A Randomized Controlled Pilot Study. Am J Phys Med Rehabil. 2018 August; 97 (8): 585-592. doi: 10.1097/PHM.0000000000000927. PMID: 29547448; PMCID: PMC6051897).

In order for such tendon systems to transmit an assistive or a resistive force or impulse of force at selected intervals from the source of force—the actuator—to the selected body segment of the user, they must ensure that the tendon is taut at the moment of application of the assistive or resistive force or impulse of force (i.e. prevent its looseness). Therefore, the tendon systems must provide tension/prevent slack in the tendons in the intervals between applications of assistive or resistive forces or force pulses. This is considered to be one of the main challenges of tendon systems, since the body segments as well as the attachment points of the tendons on the selected body segment move in 3D space, which requires that the proximal ends of the tendons track the movements of the body segments. This results in a situation where the selected body segment and the attachment point of the tendon (proximal end of the tendon) on the selected body segment move in the direction of the tendon away from the actuator, which reflects in a tendon pull. If the selected segment is to move in the desired direction, then the tendon must follow it—the length of the tendon must lengthen accordingly. If this does not occur, an unwanted external force acts on the user. Conversely, when the selected body segment and attachment point of the tendon (proximal end of the tendon) move in the direction of the tendon but towards the actuator, this reflects in tendon looseness-without proper correction, the tendon becomes loose. If the tendon is to remain taut, then its length must decrease accordingly. If this does not occur, the tendon is slack/not taut when applying an assistive or a resistive force or an impulse of force. Ideally, you would want the tendon length to be adjusted so that there is minimal tension and the tendon attachment points on the selected segments perfectly follow the movement of the user's body segments, with no force between the body segment and the tendon. This is referred to as the transparency of the interaction between the tendon and the selected segment of the body, which should be as small as possible, i.e. the force with which the tendon is stretched.

Adequate tracking of the tendon attachment point on a selected segment of the user's body and ensuring sufficient tension of the tendons prior to the application of an assistive or resistive force or force impulse is most often solved by using a servo-motor drive with appropriate rated forces/torques and powers that properly winds or unwinds the tendon at the distal end (viewed from the side user) on its axis or on the pulley on its axis. In this way, it decreases or increases the effective length of the tendon according to the movement of the attachment points of the tendons on selected body segments. This type of control is usually used in combination with: force sensors that measure the force with which the tendon is tensioned, and the control of tendon length is responding to the force measurement; measuring the position of the attachment point—the position of the proximal end of the tendon—and/or body segments (e.g. with optical systems, potentiometers, . . . ) and the control of the effective length of the tendon is responding to the measurement of the position; elastic elements, which are added in series with the rigid tendon-in this way, the elastic elements ensure that the tendons are always taut, and at the same time, the tension force of the tendons can be estimated, if the elongation of the elastic elements is measured and the result is also used to control the servo-motor drive, (examples: A-TPAD system, Aprigliano F, Martelli D, Kang J, Kuo S H, Kang U J, Monaco V, Micera S, Agrawal SK. Effects of repeated waist-pull perturbations on gait stability in subjects with cerebellar ataxia. J Neuroeng Rehabil. 2019 Apr. 11; 16(1):50. doi: 10.1186/s12984-019-0522-z. PMID: 30975168; PMCID: PMC6460671 and 3DCaLT system: Wu M, Kim J, Wei F. Facilitating Weight Shifting During Treadmill Training Improves Walking Function in Humans With Spinal Cord Injury: A Randomized Controlled Pilot Study. Am J Phys Med Rehabil. 2018 August; 97(8):585-592. doi: 10.1097/PHM.0000000000000927. PMID: 29547448; PMCID: PMC6051897). The implementation of such control in the intervals between the applications of individual assistive or resistive forces or force impulses is very demanding from a mechanical and control point of view and does not allow full transparency of the interaction with the user. Furthermore, undesirable dynamic properties of servo-motor drives, such as friction and inertia, are also transmitted via the tendons to the body segments, which further worsen the transparency of the interaction between the user and the tendons.

The latter can be reduced to a large extent if the source of force (e.g. electric motor) and the distal end of the tendon (the end closer to the source of force) are mechanically connected to the electromagnetic clutch only during the application of assistive or resistive forces or force impulses, but are otherwise mechanically separated in the intermediate intervals (example: KEES system, patent application MATJAČIĆ, Zlatko, OLENŠEK, Andrej. Modularna naprava za generiranje motilnih ali podpornih sunkov sile med hojo po tekočem traku: patent SI 26153 A, 2022 Sep. 30. Ljubljana: Urad RS za intelektualno lastnino, 2022. 17 str., 7 str. pril., ilustr. https://worldwide.espacenet.com/patent/search/family/083444923/publication/SI2 6153A?q=pn%3DSI26153A, http://www3.uil-sipo.si/PublicationServer/documentpdf.jsp?iDocId=51499&iepatch=.pdf. [COBISS. SI-ID 125461251], patent family: P-202100048, 2021 Mar. 19). In this case, tensioning of the tendon in the intervals between applications of individual assistive or resistive forces or force impulses is provided either by a counterweight or by an elastic element at the distal end of the tendon, which pulls the tendon away from the point of attachment, thus applying tension. Although in this way the unwanted dynamic properties of the actuator are eliminated and the transparency of the interaction with the user is improved, the dynamic properties (friction, moment of inertia) of the electromagnetic clutch and passive mechanical components (shafts, pulleys, counterweights) are still transmitted to the selected body segment of the user via the tendon. Unwanted forces acting on the selected body segment have a particularly significant effect in cases involving the manipulation of a body segments that reach higher velocities during movement.

According to the known state of the art, there is a need for a more effective solution that would improve the transparency of the interaction between the selected segment of the user's body and the tendons of the system for the application of assistive or resistive forces or force impulses (in the intermediate intervals when the assistive or resistive forces or force impulses between the tendon system and selected segments of the user are not applied).

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a mechanism that improves the quality of the interaction between the user and the tendon system for the application of assistive or resistive forces or force impulses in the intervals between individual applications, while at the same time, before the applications of assistive or resistive forces or force impulses, it ensures the appropriate tension of the tendons or prevents their loosening, so that during force application, the force is transferred from the source of force to the selected segment of the user's body via the tendon.

In an example, the main mechanical features of the proposed mechanism are i) the attachment of a rigid tendon at its distal end by an elastic element of weak stiffness directly or via light pulleys to a fixed point and ii) a mechanism for winding the tendon, which is formed of a source of rotation (for example, a servo-motor drive) and a reel, to which, during the application of assistive or resistive forces or force impulses, the distal end of the tendon is first clamped and then wound, and in the intervals between the applications of assistive or resistive forces or force impulses, the distal end of the tendon is unwound from the reel and mechanically separated from the source of rotation and the reel until the next application of force.

The main functional characteristic of the proposed mechanism is that in the intervals between individual applications of assistive or resistive forces or force impulses, unwanted static and dynamic properties of the mechanical drive components such as friction, mass, inertia and moment of inertia of the motor, clutch, drive shafts, pulleys and belts, pulleys/pulleys, counterweights, are not transferred to the selected segment of the user's body, due to the mechanical separation of the tendon from the source of force. At the same time, the elastic element, which is attached at one end to the distal end of the rigid tendon, and at the other end to a fixed point and which has a weak stiffness, ensures tensioning of the tendon with the minimum necessary force. Since both the tendon and the elastic element have a small mass, the influence of their static and dynamic properties on the selected segment of the user's body is small. Both functional characteristics significantly improve the transparency of the interaction between the selected segment of the user's body and the tendon system for the application of assistive or resistive forces or force impulses, resulting in minimal impact on the user's movement.

Compared to similar devices, the proposed mechanism does not need sensors or complex control schemes that would properly adjust the lengths of the tendons so that they are properly tensioned with the smallest possible force in the intervals between the applications of assistive or resistive forces or force impulses. To control the proposed mechanism, it is sufficient to alternately engage and disengage the rotational energy source (for example, servo-motor drive, flywheel . . . ). During the application of an assistive or resistive forces or force impulses electronic circuit that functions as a switch makes sure that the rotational energy is transferred to the reel from a source of rotational energy (for example, a servo-motor drive, flywheel, etc.), which rotates the reel so that the tendon gets clamped and wound. During the interval between successive applications of assistive or resistive forces or force impulses, unwinding of the tendon from the reel is ensured: automatically: the electronic circuit, that functions as a switch, turns off the supply of rotational energy, and the tendon is automatically unwound and mechanically separated from the reel due to the tensioning force created as a combination of the tendon's pull due to the movement of the user's body segment and the pull of the elastic element; and/or automatically with the support of a rotary actuator: with an electronic circuit that functions as a switch, it briefly changes the direction of the rotary energy, so that the reel rotates in the reverse direction to the starting position which unwinds, and mechanically separates the tendon from the reel.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes, combinations, and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

FIG. 1 is a schematic representation of the structural design of the tendon length modulation mechanism in concrete use,

FIGS. 2a to 2e show schematic representations of the principle of operation by application of assistive or resistive forces or force impulses by the tendon winding,

FIGS. 3a to 3d show schematic representations of the principle of operation by the mechanical separation of the tendon from the source of force in the intervals between application of assistive or resistive forces or force impulses,

FIGS. 4a to 4d show schematic representations of the possible implementations of the device,

FIGS. 5a to 5b show examples of the winding reel,

FIG. 6 is a schematic representation in which a tension element is fixed with its distal end on a storage reel, and

FIG. 7 shows a pelvis translation during walking shown as a trajectory in space and shown as projections in all three planes of movement.

DETAILED DESCRIPTION

FIG. 1 shows a schematic representation of the construction of the proposed mechanism for the implementation of assistive or resistive forces or force impulses on a selected body segment while standing or walking on a treadmill for tendon systems with a demonstration of concrete use.

The mechanism for applying assistive or resistive forces or force impulses to a body is characterized in that a tension element is connectable with its proximal end to the body and with its distal end to a fixed point 12. A deflecting element is provided and adjustable between a location or orientation, in which the tension element is free of an impingement, and a location or orientation, in which the tension element is deflected to cause a force or a force impulse to the body.

In the example shown in the figures, the deflecting device is formed as a rotating body, namely, as a winding reel 5, whereby the tension element is crossing the axis 3 of rotation.

FIG. 5b shows an example, where the tension element is guided radially through a hole of the winding reel 5, whereas FIG. 5a and also FIG. 1 refers to an example, where the winding reel 5 is formed of a central roller 5′ and at least one side plate 20 extending radially over the central roller 5′. The embodiment shown in the FIG. 5a has two side plates 20. Eccentrically with respect to the axis 3 of rotation of the winding reel 5 a tensioning roller 5″ is installed in a fixed manner on the side plates 20, whereby through the gap between the central roller 5′ and the tension roller 5″ passes and moves freely in the tangential direction relative to the central roller 5′ the tension element, when the winding reel 5 is in the location or orientation, in which the tension element is free of an impingement. The examples in the FIGS. 1 to 4 show embodiments, where the central roller 5′ and the tension roller 5″ of the winding reel 5 are concentrically embraced by cylinders 6, 7, each of which can rotate freely around its own roller 5′, 5″.

Source 1 of rotational mechanical energy, e.g. electric rotary actuator, is mechanically connected to the mechanical axis 3 through the axis coupling 2, to which the rotary energy source 1 transfers the rotary mechanical energy to rotate it, when necessary. The source 1 of rotational mechanical energy is any device capable of generating rotational mechanical energy on the mechanical axis 3, e.g. an electric motor or a servo motor 15 (e.g. FIG. 4a) with or without a transmission 16 (e.g. FIG. 4b), which transfers the mechanical rotational energy to the mechanical axis 3 directly by means of a mechanical coupling or indirectly via a belt 19 (e.g. FIG. 4d) or an electromagnetic coupling. The mechanical axis 3 is supported by bearings 4, preferably in two places, and the winding reel 5 is fixed to it in such a way that the mechanical axis 3 passes through the central roller 5′ of the winding reel 5. Between the sides of the winding reel 5, eccentrically with respect to the axis of rotation of the reel, there is the tension roller 5″, which is displaced from the common axis of rotation of the winding reel 5 and the mechanical axis 3 so that the tendon 8 passes between the central roller 5′ and the tension roller 5″ and that it moves freely in the tangential direction with respect to the central roller 5′, when the application of assistive or resistive forces or force impulses does not take place. The central roller 5′ and the tension roller 5″ of the winding reel 5 concentrically surround the cylinders 6 and 7 respectively, each of which can rotate freely around its own roller.

Rigid tendon 8, e.g. a rigid cord or braided wire is attached at one end to the attachment point on the cuff 14, which embraces the selected body segment of the user while walking on the treadmill 13. The attachment of the tendon 8 to the cuff 14 can also be realized with an intermediate elastic coupling of suitable stiffness. The opposite end of the rigid tendon 8 is routed through the gap between the central roller 5′ and the tension roller 5″ and is connected with a connecting joint 9, e.g. a mechanical or chemical joint by an elastic element 10 of weak stiffness, e.g. an elastic cord that stretches the tendon. The elastic element 10 is attached at the opposite end to the fixed point 12 directly or indirectly via the pulley 11. The tensioning of the rigid tendon 8 can also be carried out in such a way that instead of the elastic element 10, the rigid tendon 8 is directly connected either to an elastic element of constant stiffness or is a weight suspended on it via a pulley.

FIGS. 2 and 3 shows the principle of operation of the proposed mechanism. Depending on whether the proposed mechanism works in the phase of application of an assistive or a resistive force or force impulse, or in the intermediate intervals when it does not apply any forces, the proposed mechanism can demonstrate two principles of operation. FIG. 2 shows the principle of operation of the proposed mechanism in the phase of application of an assistive or resistive force or force impulse. At the beginning of the application of an assistive or resistive force or force impulse (FIG. 2a), the assembly of the tendon 8 and the elastic element 10 of weak stiffness is tensioned and passes through the gap between the central roller 5′ and the tension roller 5″, and the source 1 of rotary mechanical energy to the mechanical axis 3 begins to transmit rotational energy, due to which the winding reel 5 begins to rotate. When the winding reel 5 is turned, the tendon 8 is clamped against the tension roller 5″ and begins wind on the winding reel 5 (FIG. 2b and FIG. 2c). As a result of winding, both ends of the tendon 8 (the proximal end which is attached to the user and the distal end which is connected to the elastic element) move towards the winding reel 5, which reflects in the pulling of the user in the direction of the tendon 8 towards the winding reel 5 with a force F1 and the pull of the elastic element 10 of weak stiffness towards the winding reel 5 with the force F2, due to which it stretches. The further transfer of rotational energy to the mechanical axis 3 increases the rotation of the winding reel 5 and the length of the tendon 8, which is wound on it from both sides, as a result of which the traction force of the user F1 and the stretching force of the elastic element F2 increase (FIG. 2d and FIG. 2e). During the winding of the tendon on the winding reel 5, the tendon 8 is clamped against the tension roller 5″ at the same place all the time.

FIG. 3 shows the principle of operation of the proposed mechanism in the intermediate intervals when the application is not running. When the transfer of rotational energy to the mechanical axis 3 is discontinued, the tendon 8 is maximally wound on the winding reel 5 (FIG. 3a). Two forces act on it: i) when the user returns to stationary walking, he pulls the tendon 8 on the proximal side away from the winding reel 5 with the force F1, ii) since the tendon 8 is wound on the winding reel 5 also on the distal side, the elongation of the elastic element 10 is then maximal; as a result the elastic element 10 at the distal end of the tendon 8 creates a pull with a force F2 (FIG. 3a). Due to the torque of the two forces, the winding reel 5 automatically rotates in the opposite direction, so that the tendon 8 is completely unwound and mechanically separated from the winding reel 5, and the tendon 8 moves freely through the gap between the central roller 5′ and the tension roller 5″ of the winding reel 5 (FIG. 3b). The tension of the assembly of the tendon 8 and the elastic element 10 of weak stiffness is reduced to the level as was before the application of the assistive or resistive force or force impulse and, due to the weak stiffness, is small but sufficient so that the tendon 8 is tensioned all the time.

If the user moves in the direction of the tendon 8 away from the winding reel 5 (FIG. 3c), the tendon 8 moves freely through the gap between the central roller 5′ and the tension roller 5″ of the winding reel 5 in the direction of the user away from the reel 5. The length of the elastic element 10 of weak stiffness increases slightly, which slightly increases the force with which the tendon 8 and the elastic element 10 are tensioned, F1 and F2 respectively (F1=F2). But due to the weak stiffness of the elastic element 10, the tension remains small.

If the user moves in the direction of the tendon 8 towards the winding reel 5 (FIG. 3d), the tendon 8 moves freely through the gap between the central roller 5′ and the tension roller 5″ of the winding reel 5 in the direction towards the reel 5. The length of the elastic element 10 of weak stiffness is slightly reduced, as a result of which the force with which the tendon 8 and the elastic element 10 are tensioned is slightly reduced, but not so much that the tendon 8 would become loose.

FIG. 4 shows possible implementations of source 1 of rotational energy. The source 1 of rotational mechanical energy is any device capable of generating rotational mechanical energy on the mechanical axis 3, e.g. an electric motor or a servo motor with or without a transmission, which transfers the mechanical rotational energy to the mechanical axis 3 directly by means of a mechanical coupling or indirectly via a belt or an electromagnetic clutch.

In FIG. 4a, an electric motor or a servo motor 15 is used as a source 1 of rotational energy, which transfers rotational energy to the mechanical axis 3 via the axial coupling 2 when it is switched on. Such a direct transfer of energy from the engine to the mechanical axis 3 requires the use of high-torque motor drives if sufficient efficiency is to be achieved.

In order to increase the torque on the mechanical axis, a motor drive with a transmission 16 can be used as a source 1 of rotary mechanical energy (FIG. 4b).

In FIG. 4c and FIG. 4d, the flywheel 17—the body that stores the rotational energy—is used as the source 1 of rotational mechanical energy, which is connected to the mechanical axis by the electromagnetic clutch 18. When the clutch is activated, the rotational energy from the flywheel 17 is transferred to the mechanical axis 3. Here, an electric motor or servo motor 15 can be used to provide the rotational energy to the flywheel 17, which increases the rotational energy of the flywheel 17 either directly (FIG. 3c) or indirectly via the belt/chain 19 (FIG. 4d).

FIG. 5 shows the possible implementations of the winding reel 5. FIG. 5a shows the solution when the cylinders 6 and 7 are removed from the winding reel 5, which otherwise concentrically embrace the central cylinder 5′ and the tension cylinder 5″ of the winding reel 5. Omitting cylinders 6 and 7 improves the adhesion of the tendon 8 when it is clamped against the tension roller 5″ during the application of an assistive or resistive force or force impulse, and at the same time slightly increases the friction between the tendon 8 and the winding reel 5 when the force is not applied and the tendon 8 only slides through the gap between the central 5′ and the tension 5″ roller.

In the second embodiment (FIG. 5b), the tendon 8 is guided radially through the axis of rotation of the winding reel 5. The tension roller 5″ is unnecessary in this case, since upon application of an assistive or resistive force or force impulse, the winding reel 5 rotates and the tendon 8 is clamped against the central cylinder 5′ of the winding reel 5. In the intervals between the applications of an assistive or resistive force or force impulse, the tendon 8 moves freely through the hole in the winding reel 5.

FIG. 6 refers to an example, where the tension element is fixed with its distal end on a storage reel 22 as the fixed point 12, on which is acting a spring 23 to provide a tensioning force, which is suited to ensure, that the tension element is taut. The storage reel 22 is supported on a storage reel-axis 24, on which the spring 23 in the embodiment of a worm spring or torque spring acts. Furthermore, on the storage reel-axis 24 a decoder 21 is arranged to detect the orientation of the storage reel 22. The storage reel-axis 24 is supported by at least one bearing 4.

It is to mention that in the drawing examples are shown with only one mechanism for performing force impulses on the walking human body, however, more than one mechanism can be used, especially also four mechanisms acting on the coupling for the connecting to the body like the cuff in four directions, e.g. right and left and forward and rearward. These directions can be tilted around the body axis of the human.

Furthermore, the use of the decoder 21 can also improve the application of the force to the body, since the decoder 21 monitors the turning of the storage reel 22, which is directly related to the phase of each step of the walking person. This gait detection analyses for example the movement of the hip.

A sensor is provided to monitor the periodic displacement of the tension element whereby a control element is provided to use the changes in the direction of the movement of the tension element for triggering the application of force impulse. The sensor can be optical encoder attached to the pulley 11. A plurality of sensors can be used to improve reliability and robustness of triggering the application of force impulse.

During walking on a treadmill or overground all body segments undergo cyclical movement. The pelvis for example is displaced and rotates in all directions. By monitoring the length of the tensional element attached to the side (or any other point) of the pelvis a characteristic and periodic signal is obtained a shown in FIG. 7. By detecting the change of direction of the movement of the pelvis one can extract distinct gait events during the gait cycle. For example, the peak lateral displacement of the pelvis occurs in the middle of the gait cycle. It is straight forward to estimate other events such as heel strike or toe-off from the duration of gait cycle as determined from consecutive peak displacement.

Similar is the situation if the tensional element is attached to the knee or the ankle of a leg. Also, in this case a periodic signal, similar to those shown in FIG. 7 is obtained and by detecting the change of direction of tensional element (identifications of peaks of movement) heel strike event (direction of tensional element movement changes from forward to backward) is detected or toe-off event (direction of tensional element movement changes from backward to forward) is detected.

When the tensional element or tendon is attached to the left side of the body (left side of the pelvis or the knee or the ankle of the left leg) left heel strike, left toe-off are determined. The opposite holds for the right side.

These distinct gait events can then be used to trigger and generate a perturbing force impulse.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.