WO2012042416A2

WO2012042416A2 - Device to relieve the articular efforts resulting from the weight of a human limb

Info

Publication number: WO2012042416A2
Application number: PCT/IB2011/053986
Authority: WO
Inventors: Fabio Salsedo; Massimo Bergamasco; Marco Fontana
Original assignee: Scuola Superiore S. Anna
Priority date: 2010-09-11
Filing date: 2011-09-12
Publication date: 2012-04-05
Also published as: EP2613753A2; WO2012042416A3; ITPI20100102A1; IT1402610B1; EP2613753B1

Abstract

A device (1) for carrying out rehabilitation exercises, or training, of a limb, for example of the upper limb (40), of an operator (150). The device (1) comprises a fixed base (10) and a movable interaction element (60) arranged in contact and integral to a medial segment (42, 142), of the limb (40, 140), of the operator (150). In case of the upper limb (40) the medial segment, i.e. the forearm (42) of the operator (150), is set between elbow articulation (E) and the wrist articulation (W). The movable interaction element (60) and the base (10) are connected by a mechanism comprising a primary section Si equipped with, for example, of six pivot joints (21-26), connected by rigid links (12-16) and for moving the movable interaction element (60) in a workspace with respect to the fixed base (10). Furthermore, is provided a secondary section (S₂), kinematically depending to the primary section (S₁). The device (1) comprises, furthermore, a means for generating a vertical load (C) substantially fixed at a point (O₃') integral to a link of the secondary section (S₂). More in detail, the means (30') of generating the load (C) and said mechanism are adapted to apply a force vertical F proportional to the load (C), and therefore fixed, in a predetermined balance point (45).

Description

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TITLE

DEVICE TO RELIEVE THE ARTICULAR EFFORTS RESULTING FROM THE WEIGHT OF A HUMAN LIMB

DESCRIPTION Field of the invention

The present invention relates to the field of motor rehabilitation and, in particular, it relates to a sensorized device that can be used in combination with a system for generating virtual environments, that is able to reduce or even to eliminate articulation stresses deriving from the weight of human limbs (arms and legs) , in a workspace substantially coincident to the natural workspace of the human limbs, in order to assist the user in the execution of a wide variety of physical exercises, necessary to recover the motor ability, compromised after cerebrovascular (e.g. stroke) or orthopaedic traumas.

Description of the prior art

In the last decade, studies conducted from many research laboratories have shown the efficiency of innovative rehabilitation techniques which use robotic devices in combination with systems for generating virtual environments.

These techniques provide the use of mechatronic interfaces (i.e., normally, actuated, sensorized and controlled) , which physically interact with an invalid limb of a user, for supporting, guiding, assisting or reacting the execution of a motor task, whereas the system for generating virtual environments displays a scenario consisting of objects that can be manipulated by the user, by means of the interface that acquires the movement of the limb. The adoption of robotic technologies has unquestionable advantages with respect to the traditional practices, because of the repetitiveness of the motor tasks of rehabilitation.

Furthermore, it ensures a higher repetitiveness between the different executions of the same task and an objective measure of the motor performances of the user (angular excursion of the different articulations, degree of coordination, forces/torques exercised, etc.), not obtainable with the traditional practices.

Finally, the possibility of varying the dependency between the force exercised by the robot and the posture/movements of the limb with a high flexibility, allows to investigate and to test new methodologies of rehabilitation, with the target of identifying methods that allow to define the better motor tasks for the particular requirements of the patients.

The combination of the robotic device with a virtual environment allows, moreover, to improve the motivations of the user during the execution of the motor task, that, instead, tends to reduce in the traditional practices, because of the repetitiveness of the movements. Virtual reality, in fact, allows to implement a practically infinite range of scenarios, populated by objects more or less fantastic, with which the user can actively interact. From this point of view, the whole system, i.e. the robot seen as the interface of interaction and the system for generating virtual environments, is completely comparable to the common videogames the capacity of which is well known to keep high the attention of the user also for hours . Recently, in order to improve the degree of intrinsic safety of the devices reducing in the meantime the cost of the technology, systems of virtual reality have been investigated having mechanical interface not actuated, but only sensorized (passive interface) . The clinical results obtained with these systems have shown recoveries of the motor functionality of the upper limb completely comparable to those obtainable with actuated interface (active interface) , especially in case of rehabilitation in post-acute phase.

However, the need of alleviate the weight of the arm of the user in order to assist the execution of a motor task, requires the use of passive balancing techniques, which can complicate the mechanics of the device, as well as considerably limit the amplitude of the allowable movement .

In FR2541574 a device is described for reducing the articular stresses deriving from the weight of the arm of an user, in order to assist the user in the execution of the rehabilitative exercises. The device consists of a fixed base and of a movable interaction element which is adapted to be located integrally to the medial segment of the arm of the patient (forearm) , and of a mechanism comprising a plurality of kinematical couples connected to each other by respective rigid links, that is adapted to operatively connect the movable interaction element with the base. The mechanism, by means of said plurality of kinematical couples, provides to the movable interaction element three translational degrees of freedom and three rotational degrees of freedom with respect to said fixed base. Furthermore, the device comprises a counterweight that allows to generate a substantially fixed vertical load at a point integral to the medial segment of the arm of the patient. However, since the translational degrees of freedom are obtained using an articulated parallelogram and two turning pairs having vertical axis and serially connected to each other wherein the first is serially connected to the articulated parallelogram, only the movement of the latter is capable of producing the vertical movement of the application point of the fixed force to the medial segment.

Therefore, if a relatively great variation is requested for the vertical height of the application point of the force, it is necessary to use very long links of the parallelogram, which are, therefore, subject to relatively high mechanical stresses and require relatively high transverse dimensions of the links. High dimensions of the links of the parallelogram, both longitudinal and transversal, however, do not permit making a compact device and involve a higher inertia of the device, which is perceived by the patient at the medial segment of the arm. In conclusion, the mechanism of the device described in FR2541574, which has a single degree of freedom for the vertical movement of the application point of the force on the medial segment of the arm, when it has to be sized to allow a big variation of the vertical height of the application point of the force, is cumbersome and not very transparent to the movement of the patient, and also it is characterised by relatively high perceived inertia.

If, instead, the dimensions of the links of the parallelogram are kept relatively small for containing the size and the inertia of the device, the variation of the vertical height of the application point of the force is relatively small and, then, it is not enough to completely cover the natural workspace of a human arm.

Summary of the invention It is therefore a feature of the present invention to provide a device to relieve the articular efforts resulting from the weight of a human limb that is not actuated and that allows to follow the movements (tracking) of the limb in a workspace substantially coincident to the natural limb workspace, and, in particular, which allows relatively large vertical movements to the limb and at the same time creates lever- arms of the various rigid links substantially shorter than the prior art, obtaining considerable reductions of encumbrance and of inertia perceived by the user.

It is also a feature of the invention to provide a device to relieve the articular efforts that provides a constant level of reduction of the articular stresses in a workspace substantially coincident to the natural limb workspace, and, then considerably wider than similar devices of the prior art.

It is a further feature of the present invention to provide a device to relieve the articulation efforts of human limbs that allows a better contact pressure distribution and then a better ergonomics with respect to known devices.

It is another feature of the present invention to provide a device to relieve the proper weight of human limbs that does not require any type of setting for correctly positioning the device with respect to a user' s limb .

It is a further feature of the present invention to provide a device to relieve the proper weight of human limbs structurally easier and cheaper with respect to the devices of the prior art.

These and other features are accomplished with one exemplary device to relieve the proper weight of a human limb, said limb comprising a proximal segment articulated to a trunk by a proximal articulation, a medial segment articulated to the proximal segment by a medial articulation and a distal segment articulated to the medial segment by a distal articulation, said device comprising :

- a fixed base;

- a movable interaction element comprising a means for engaging said medial limb integrally to said movable interaction element;

- a mechanism comprising a plurality of kinematic pairs connected to each other by respective rigid links, said mechanism arranged to operatively connect said movable interaction element with said base, wherein said mechanism, by said plurality of kinematic pairs, provides to said movable interaction element three translational degrees of freedom and three rotational degrees of freedom with respect to said fixed base in a workspace substantially coincident to the natural medial segment workspace;

- a means for generating a substantially constant vertical load at a predetermined point integral to a link of said mechanism; wherein said means for generating and said mechanism are arranged to apply a vertical force, which is proportional to said load and therefore substantially constant in said workspace, at a balance point that is integral to said medial segment of the limb and that lays on the junction line of the medial articulation with the distal articulation, whose main feature is that said mechanism provides the above described degrees of freedom to the movable interaction element in such a way that at least two of said degrees of freedom contribute to generate a variation of the vertical position of the balance point.

Advantageously, said mechanism provides to the element said two degrees of freedom that contribute to generate a variation of the vertical position of the balance point by means of two hinges having horizontal axis, and, in particular, at least one of the two hinges is not a hinge of an articulated parallelogram.

The device is, in particular, configured in such a way that the balance point is located at a distance xp from said medial articulation that is set between 80 mm and 130 mm.

Advantageously, distance x_F of the balance point from the medial articulation is set between 85 and 125 mm.

Preferably, distance x_F of the balance point from the medial articulation is set between 88 and 120 mm.

In particular, distance xp is substantially defined responsive to the anthropometric dimensions of the limb of the user and of the mass of segments Of the limb according to the following formula:

where

- I_IUA is . the distance between the proximal articulation and . the barycentre of the proximal segment;

- 1_2UA is the distance between the medial articulation and the barycentre of the proximal segment;

- I_IFA is the distance between the medial articulation and the barycentre of the set consisting of the medial segment and of the distal segment;

- P_p is the weight of the proximal segment;

- P_d is the weight of the set consisting of the medial segment and of the distal segment.

Advantageously, an adjustable means is provided for fastening the medial segment to said interaction element that is configured to adjust said distance x_F between said balance point and said medial articulation.

Advantageously, the mechanism comprises a primary section, comprising at least 6 independent kinematic pairs, said primary section arranged to allow the full mobility, i.e. 3 translational degrees of freedom and 3 rotational degrees of freedom, in said workspace of said movable element with respect to said fixed base, and a secondary section, that is arranged to transmit said vertical load to said interaction element, transforming, normally, intensity and direction, and then generating said vertical force at said balance point so that it is fixed in said workspace, said secondary section being kinematically depending on said primary section, i.e. not adding degrees of freedom to said mechanism.

Preferably, the primary section of said mechanism comprises 6 independent pivot joints (degrees of freedom) .

In particular, the six pivot joints of the primary section are combined in pairs, in order to form a first, a second and a third combination of pivot joints, such that:

- the rotation axes of the pivot joints of each combination of two pivot joints are orthogonal to each other and incident in three respective different points Oi, Q>2, 0₃;

- the intersection point Oi of the rotation axes of the first combination of two pivot joints is integral to said fixed base;

- the intersection point 0₃ of the rotation axes of the third combination of two pivot joints lays on the junction line of the centre of the distal articulation with the centre of the medial articulation of the arm, at a distance Xf from the medial articulation;

- the intersection point 0₃ is arranged at a variable distance D from the intersection point Oi of the rotation axes of the first combination of two pivot joints and in such a way to lay on the junction line of the medial articulation with the distal articulation of said limb;

- said means for generating a substantially constant vertical load generates said load in said predetermined point (0₃' ) integral to a link of said mechanism, such that 0₃' is arranged on the line 0₃0i opposite to 0₃ with respect to Oi, and in such a way that the equation: Oi0₃'=K-D, K being a constant, is true .

In particular, said K is less than 1.

In particular, the movement of at least two of the first four pivot joints contribute to the variation of the vertical height of the application point of force 0₃.

In a preferred embodiment, the following can be provided :

- the axis of the first pivot joint of the first combination of two pivot joints is arranged in a vertical direction and, then, the axis of the second pivot joint of the first combination of two pivot joints is arranged in a horizontal direction;

- the intersection point O2 of the rotation axes of the second combination of two pivot joints is arranged at an invariant distance L_x from the intersection point Ol of the rotation axes of the first combination of two pivot joints;

- the intersection point 0₃ of the rotation axes of the third combination of two pivot joints is arranged at an invariant distance L₂ from the intersection point 0₂ of the rotation axes of the second pair;

- the axis of the third pivot joint, i.e. the first one of the second combination of two pivot joints, is arranged parallel to the axis of the second pivot joint, i.e. the second pivot joint of the first combination of two pivot joints, and, then is arranged in a horizontal direction;

- the axis of the fifth pivot joint, i.e. the first pivot joint of the third combination of two pivot joints, is arranged orthogonal and incident with the axis of the fourth pivot joint, i.e. the second pivot joint of the second combination of two pivot joints;

- said movable interaction element is integral to the movable part of the sixth pivot joint, i.e. the second pivot joint of the third combination of two pivot joints and configured in such a way that, when connected to the medial segment of the limb of the user, said intersection point O3 falls on the junction the medial articulation and of the distal articulation of the limb.

In particular, the fastening means for fastening the medial segment to the interaction element can comprise a knob that can be grasped by the hand of the user, where said knob can be integral to said interaction element and approachable/movable away with respect to the rotation axis of said sixth pivot joint of the primary section of the mechanism.

Advantageously, in case of the upper limb, the primary section of the mechanism comprises, furthermore, a seventh and an eight pivot joint.

In particular, the seventh and the eighth pivot joint have the following features:

- the respective rotation axes are incident and orthogonal at a point O4, substantially coincident with the wrist articulation and, then, arranged at a predetermined distance L₃ from O3, adjustable responsive to the anthropometric size of the user;

- the fixed part of the seventh pivot joint is integral to said movable interaction element; - the axis of the seventh pivot joint is orthogonal and incident to the junction line of the elbow articulation with that of the wrist;

- the movable part of the eighth pivot joint is integral to a knob that can be grasped by the hand of the user.

This way, the device allows to detect also the movement of the hand with respect to the forearm, increasing the variety of movements that can be executed.

Preferably, the axis of the seventh pivot joint is substantially coincident with the axis of the flexion- extension wrist articulation.

Preferably, the axis of the eighth pivot joint is substantially coincident with the axis of abduction- abduction wrist articulation.

Advantageously, said movable interaction element has a surface shaped as a cradle, said cradle arranged to receive said medial segment._. The kinematic arrangement as above described, allows to follow completely and without limits all the movements of the user's upper limbs and, in particular, the movements of the forearm with respect to a fixed reference point and the movements of the hand with respect to the forearm. In fact, the first six degrees of freedom allow to follow any position and orientation assumed by the forearm with respect to a fixed reference, whereas the seventh and eighth degrees of freedom allow to follow a desired orientation of the hand with respect to the forearm.

Advantageously, the secondary section of said mechanism is a pantograph comprising an articulated parallelogram. In particular, the articulated parallelogram comprises :

- four secondary pivot joints having respective rotation axes, said rotation axes being parallel to the rotation axis of the second pivot joint of said primary section, where the axis of the first secondary pivot joint of the articulated parallelogram passes through for point 0₂;

- four secondary rigid links that connect in pairs the secondary pivot joints.

In particular, the first secondary rigid link of said four secondary rigid links is integral to the junction line of said points Oi and 0₂ of said primary section, and the second secondary rigid link of said four secondary rigid links is integral to the junction line of said points 0₂ and 03 of said primary section.

In particular, the axis of the second secondary pivot joint of the above described four secondary pivot joints of the articulated parallelogram is configured to cut the junction line of said points Oi and 0₂ of said primary section of said mechanism at a point 0₂' opposite to the first secondary pivot joint with respect to point Oi.

Furthermore, the line of minimum distance between the axis of the second secondary pivot joint and of the third secondary pivot joint is parallel to the junction line of said points 0₂ and 0₃ of said primary section of said mechanism.

The third secondary rigid links, connecting the second secondary pivot joint with the third secondary pivot joint of the articulated parallelogram, is provided with a load point O3' located on the line of minimum distance between the second secondary pivot joint and the third secondary pivot joint and such that the junction line O3-O3' passes through point Oi .

The line of minimum distance between the axis of the third secondary pivot joint and the axis of the fourth secondary pivot joint is parallel to the junction line of said points Oi and 0₂ of said primary section of said mechanism.

The fourth secondary rigid links connects the third secondary pivot joint with the fourth secondary pivot joint.

This way, due to the geometric features of the pantograph, the ratio of segments O3-O1 and O1-O3' is constant in all the configurations assumed by the pantograph. Then, the application in O3' of a constant vertical balancing load directed downwards, produces in 0₃ a constant vertical balancing force directed upwards proportional to it.

Advantageously, said means for generating a substantially constant vertical load comprises a counterweight .

Alternatively, said means for generating comprises an elastic element, for example a helical traction spring, having a first end connected to point 03' and a second end connected to a fixed point of the device.

Advantageously, the elastic element has a high pliability and is appropriately pre-loaded.

Advantageously, at least one of the two first combinations of two pivot joints of the primary section of said mechanism is loaded as a torsion-flexion joint. Preferably, said, or each, torsion-flexion joint comprises a central body, a balancing element rotating with respect to said central body about a flexion axis and a shaft rotating with respect to said central body about a torsion axis, said flexion axis being orthogonal and incident with said torsion axis.

Advantageously, said shaft and said balancing element are hollow in such a way to allow the passage of possible electric cables in the torsion-flexion joint.

Advantageously, the implementation of the fifth and of the sixth pivot joint of said primary section of said mechanism is obtained using a mechanism having a remote centre of rotation, whose movable part incorporates the bearings of the sixth pivot joint. Such exemplary embodiment has the advantage to not need the insertion of the medial segment of the limb of the user in the structure of the device, operation that can result troublesome especially for people who have a low motor ability .

Preferably, the mechanism having the centre remote of rotation comprises a first and a second articulated parallelogram, where the second articulated parallelogram is kinematically depends from the first articulated parallelogram.

Advantageously, furthermore, a means is provided for instantly measuring the angular position of said pivot joints of said primary section of said mechanism. This way, a sensorized device is obtained that is adapted to be used in combination with a system for generating virtual environments, to assist the execution of rehabilitation or training exercises, and to monitor such exercises and to provide sensory feedbacks to the user/patient.

Preferably, the means for instantly measuring the angular position of each pivot joint comprises a sensor of magnetic field, such as a Hall effect sensor, and a permanent magnet for each joint.

In particular, each pivot joint comprises a first member and a second member pivotally connected to each other .

Advantageously, the means for measuring the position of each pivot joint comprises a magnet integral to the first member of a pivot joint and a Hall effect sensor integral to the second member of the same pivot joint.

Preferably, the magnet has a cylindrical geometry, said cylindrical geometry having a longitudinal axis.

In particular, the cylindrical geometry of the magnet can be selected from the group consisting of:

- a full cylindrical geometry;

- an annular cylindrical geometry.

In particular, the axis of the magnet is parallel to the rotation axis of the pivot joint to which it is associated.

Advantageously, the axis of the magnet is arranged at a predetermined distance from the rotation axis of the second member.

Advantageously, the magnet is magnetized in a diametrical direction.

In particular, the magnet has a magnetization direction orthogonal to a eccentricity direction.

Advantageously, the Hall effect sensor has a sensitive point, said sensitive point arranged in the plane orthogonal to said axis of said magnet and passing through the middle line of its height.

In particular, during the rotation of the second member about its rotation axis, the Hall effect sensor describes a circular trajectory about a point 0, said sensor having a direction of sensitivity orthogonal to said circular trajectory.

With respect to the known sensor implementation techniques, the present solution provides an absolute sensorization of the angular position of the pivot joint and then does not require a zeroing procedure of the axes, necessary, for example, in case of use of incremental encoders.

Furthermore, carrying out a continuous transduction of the angular position, the resolution of the sensor is virtually infinite, i.e. only limited by the level of electric noise of the Hall effect sensor and by the electronic of acquisition and analog/digit conversion. With a suitable choice of the Hall effect sensor and an appropriate implementation of the electronic of acquisition and conversion it is possible to obtain resolutions of 15-16 bit on an angular range of 180° (corresponding to 0.1- 0.05 thousand of radian), hardly reachable also by the best absolute encoders. High resolution allows to obtain a higher stability of the graphic representation of the hand/arm in a virtual environment .

A further advantage is shown by the minimum number of components and by the absence of crawling parts, present instead, for example, in the potentiometers. This makes it possible to obtain extremely reliable sensors, with performances unchanged with time.

In addition to what above disclosed, the use of components largely diffused, such as cylindrical/annular magnets and Hall effect sensors, allows to sensibly reduce the cost of the sensor. In particular, with respect to the absolute encoder having a comparable resolution, the cost is of some orders of magnitude lower.

At the end, the minimum number of components and the high measurement flexibility of geometric parameters allows an easy integration in the articulated devices, achieving a high level of compactness.

In particular, the link of said mechanism at which the means for generating generates said substantially constant vertical load is opposite to said movable interaction element with respect to said first pivot joint of said primary section.

Alternatively, the link of said mechanism at which the means for generating generates said substantially constant vertical load is arranged at the same side of said movable interaction element with respect to said first pivot joint of said primary section. In particular, vertical load Can be mounted on the secondary section at a point 0₃" arranged between Oi and 0₃. This way, the mechanism applies a vertical force F directed downwards at point 0₃ and therefore increases the articular stresses on the limb, making it possible the use of the device as a training, or a fitness machine.

In particular, the load is integral to a connection link that is pivotally connected to said first and to said third secondary links. Brief description of the drawings

The invention will be now illustrated with the following description of an exemplary embodiment , thereof, exemplifying but not limitative, with reference to the attached drawings in which:

Fig. 1 shows a kinematic scheme of the device, according to the invention, to relieve the articular efforts resulting from the proper weight of the human limbs ;

Fig. 2 shows a perspective elevational side view of a possible exemplary embodiment of the device, according to the invention, for balancing the proper weight of the human limbs; .

Fig. 3 shows an elevational side view of the device of Fig. 1;

Fig. 4 schematically shows the geometric properties of the pantograph used in the device of Fig. 2;

Fig. 5A shows a possible schematization of the user's upper limbs in 3 segments;

Figs, from 5B to 5D show a possible schematization of the user's upper limbs in 2 segments;

Figs. 6 and 7 show a plan view and in a kinematic scheme of a possible implementation which can be used for the fifth and the sixth pivot joint of the device of Fig. 2;

Fig. 8 shows a perspective view of the device, according to the invention, in an operative configuration;

Fig. 9 shows a cross sectional view of an exemplary embodiment of the invention for a combination of two pivot joints; Fig. 10 shows a principle scheme of a sensorisation technique which can be associated with the device;

Figs. 11 and 12 schematically show, respectively, a perspective view and an elevational side view of a possible exemplary embodiment of the device of Fig. 1, in case of use as a training, or fitness machine.

Detailed description of some exemplary embodiments

In Fig. 1 a device 1 is schematically shown, according to the invention, for carrying out rehabilitation exercises, or training, of a limb, for example of the upper limb 40, of an operator 150.

Device 1 comprises a fixed base 10, for example having a base frame 15 that, in use, rests on a support surface, and a movable interaction element 60.

In particular, movable interaction element 60 is adapted to be arranged in contact and integral to a medial segment 42, or 142, depending on whether it is the upper limb 40, or the lower limb 140, respectively, of operator 150. The medial segment is arranged between a medial articulation and a distal articulation. In case of the upper limb 40, the medial segment corresponds to the forearm of operator 150 arranged between the elbow articulation and the wrist articulation W. If the limb is the lower limb 140 of operator 150, instead, the medial segment corresponds to leg 142, arranged between the knee articulation K and the ankle articulation (Fig. 8).

More in detail, movable interaction element 60 is operatively connected to base 10 by a mechanism comprising a primary section SI, indicated in Fig. 1 with a continuous line, equipped with a plurality of kinematic pairs, for example six pivot joints 21-26, connected by rigid links 12-16. Primary section SI of the mechanism allows to move movable interaction element 60 in a workspace with respect to fixed base 10. The six pivot joints 21-26 provide three translational degrees of freedom and three rotational degrees of freedom to movable interaction element 60 with respect to fixed base 10.

The mechanism comprises, furthermore, a secondary section S2, indicated in Fig. 1 with a broken line, kinematically dependent on primary section Si. Therefore, secondary section S2 does not add degrees of freedom with respect to primary section Si.

Device 1 comprises, furthermore, a means for generating a vertical substantially constant load C at a point O3' integral to a link of secondary section S2. More in detail, the means 30' for generating load C and said mechanism is configured to apply a vertical force F proportional to load C, and therefore constant, in a predetermined balance point 45 that is integral to the medial segment of operator 150, for example to forearm 42, and that lays on the junction line of the medial articulation with the distal articulation, and that is located at a predetermined distance x_F from the medial articulation of the limb.

Therefore, in case of an arm 40, balance point 45 lays on the junction line of the elbow articulation with the wrist articulation W and its distance x_F from the medial articulation is comprised between 80 mm and 130 mm, advantageously between 85 mm and 125 mm, preferably between 88 mm and 120 mm (Fig. 5) . In case of a lower limb 140 the balance point 145 is arranged, instead, on the junction line of the knee articulation K with ankle articulation A (Fig. 8) .

In particular, the position of balance point 45 is substantially defined responsive to the anthropometric size of limb 40, or 140, of operator 150 and of the masses of segments Of the limb.

The position x_F of the application point of the force F can be measured by applying, for example, to upper limb 40, the technique of balancing as shown hereafter.

According to the used technique of balancing, upper limb 40 of user 150 can be schematically shown as consisting of 3 segments and precisely arm 41 articulated to trunk 155 through the shoulder articulation S, forearm 42 articulated to arm 41 through the elbow articulation and a hand 43 articulated to forearm 42 through the wrist articulation W.

Assuming that the barycentre 41g of arm 41 lays on the junction line SE, and that the amplitude of the movement of hand 43 with respect to forearm 42, and the ratio between the masses of forearm 42 and of hand 43 is such that the barycentre of the segments 42 and 43 falls substantially in a fixed point G arranged on the junction line EW, it is possible . to eliminate the articulation couples necessary to balance the proper weight of upper limb 40 arranging a single constant and vertical force F in a determined point that lays on the junction line EW.

In fact, according to the above described hypothesis, upper limb 40 of user 150 can be schematized with only two segments, i.e. arm 41 and forearm 42 articulated in E to each other, as diagrammatically shown in Figs. 5B, 5C and 5D.

Indicating: with 1_1UA the distance between the proximal articulation and the barycentre of the proximal segment, with 1₂UA the distance between the medial articulation and the barycentre of the proximal segment, with li_FA the distance between the medial articulation and the barycentre of the group of the medial segment and of the distal segment, with P_p the weight of the proximal segment and with P_d the weight of the group of the medial segment and of the distal segment and setting the balance of the two segments, i.e. of arm 41 and of the segment obtained combining forearm 42 with hand 43 with the above described approximations, in the hypothesis of articulation couples equal to zero, it is:

l_lFA ' cosa = F ^« x_F · cos o

R_E + P_d from which:

and

and :

Pd ^*

Pd " pA * lUA +∑2I/ift)

(P_p + P_d) · ί_{1ί Λ} + _ώ · l_2UA

The above balance conditions show that for a determined user it is possible to balance the weight of its upper limb in the whole workspace, using a single fixed vertical force of value defined and applied in a defined point on junction EW, i.e. of the elbow articulation and of the wrist. For studying the variability of these parameters between different patients, is preferred to normalize the expressions previously obtained as given hereafter:

where

and

where.

Assuming that between different users there is a substantial invariance of the anthropometric ratios, it is noted that the balancing force F is directly proportional to the sum of the weights of the forearm and of the hand, whereas its application point xF is directly proportional to the distance of the barycentre of the second segment from the elbow articulation.

However, while the coefficient of proportionality of F is considerably higher than the unity, the x_F coefficient is considerably less than the unity. This condition, together with the relatively reduced size of Li_FA, causes a variability of x_F in absolute terms of about 30 mm from a minimum height of the user of 160 cm to a maximum of 200 cm.

In conclusion, according to the above hypothesis, the articulation couples necessary for balancing the proper weight of the upper limb of a whole population of patients, comprised between a minimum height of 160 cm and a maximum of 200 cm, can be relieved in the whole workspace of the upper limb, by a device that is capable of generating in that workspace a constant vertical force, whose value is modifiable at the beginning of the rehabilitation session, responsive to the weight of the limb of the user and whose application point on the forearm is arranged on the junction line of the elbow articulation with the wrist and that is modifiable in a range of about 30mm.

From the point of view of the implementative complexity of the device, it is important to note that if a solution is adopted that does not allow the change of the position of the application point of the vertical balancing force on the junction line EW, the subsequent unbalancing effects can be made completely negligible with a suitable size of the device.

In fact, if implementative solutions are adopted that do not allow adjusting the distance of the application point of the vertical force with respect to , if this distance is sized for an average height (180cm) of the considered population of patients, the maximum divergence with respect to the ideal position would be about 15mm, to which a maximum unbalancing couple would correspond, in case of maximum balancing force of the arm (about 30 N) , of only 0,45Nm.

The six pivot joints 21-26 having respective rotation axes 101-106 and connected through a plurality of rigid links 12-16 can be combined in pairs, in order to form a first combination of pivot joints 21, 22, a second combination of pivot joints 23, 24 and a third combination of pivot joints 25, 26. The rotation axes 101-102, 103-104 and 105-106 of each combination of pivot joints 21-22, 23- 24 and 25-26 are substantially orthogonal and incident in three respective points Oi, 0₂ and 0₃. More precisely, rotation axis 101 of the first pivot joint 21 is oriented along a substantially vertical direction, whereas rotation axis 102 of second pivot joint 22 is oriented along a horizontal direction. The two axes 101 and 102 of the first combination of pivot joints 21 and 22 are incident in point Oi . Rotation axis 103 of third pivot joint 23 is parallel to axis 102 of second pivot joint 22, whereas axis 104 of fourth pivot joint 24 is orthogonal to axis 103 of third pivot joint 23. The two axes 103 and 104 of the second combination of joints 23 and 24 are incident in point O2 arranged at a predetermined invariant distance LI from point Οχ . Finally, the rotation axes 105 and 106 of the fifth and of the sixth pivot joints 25 and 26 are incident in point O3 arranged at a predetermined invariant distance L₂ from 0₂. In particular, axis 105 of pivot joint 25 is arranged orthogonal and incident with axis 104 of pivot joint 24. Movable interaction element 60 is integral to the movable part of sixth pivot joint 26, i.e. to the second joint of the third combination of pivot joints, and is configured in such a way that when connected to medial segment 42, point 0₃ lays on the junction line of the medial articulation, i.e. of the elbow and, of the distal articulation, i.e. of wrist W.

In an advantageous exemplary embodiment, primary section S_x comprises, furthermore, a seventh and an eight pivot joint 27 and 28 having respective rotation axes 107 and 108 substantially orthogonal. More in detail, the seventh and the eighth pivot joint 27 and 28 are incident at a point 0₄, substantially coincident with the wrist articulation W of operator 150 and, then, located at a determined distance L₃ from 0₃, adjustable responsive to the anthropometric size of the user.

In this case, movable interaction element 60 is integral to the fixed part of pivot joint 27. Axis 107 of pivot joint 27 is, furthermore, orthogonal to the junction line EW of the elbow articulation with that of wrist W whereas the movable part of the eighth pivot joint 28 is integral to a knob 158 that can be grasped by user's hand 43.

Rotation axis 107 of seventh pivot joint 27 is substantially coincident with the axis of the flex- extension movement of the wrist, whereas rotation axis 108 of eighth pivot joint 28 is substantially coincident with the abduction-adduction axis of the wrist. This exemplary embodiment of device 1 allows to detect also the movement of hand 43 with respect to forearm 42, enlarging the variety of the movement that can be executed. In an exemplary embodiment, knob 158 can be configured to approach/move away with respect to rotation axis 106 of sixth pivot joint 26 of primary section SI of the mechanism.

Interaction element 60 can be provided with a surface shaped as a cradle. The cradle shape allows a better distribution of the contact pressures and then a better ergonomics of interaction element 60.

In a particular advantageous exemplary embodiment, secondary section S2 comprises an articulated parallelogram 100. With reference to Figs. 2 and 3, articulated parallelogram 100 comprises four secondary pivot joints 61-64 having respective rotational secondary axes 201-204 and connected in pairs by 4 rigid links 71- 74. In particular, rotational secondary axes 201-204 are parallel to rotation axis 102 of second pivot joint 22 of the primary section of the mechanism and the pivot joint 61 passes through point 02.

Rigid link 71 is integral to the junction line of points Oi and 0₂ of the primary section and rigid link 72 is integral to the junction line of points 0₂ and O3.

Rotation axis 202 of second pivot joint 62 of articulated parallelogram 100 is configured to cut the junction line of points Oi and 0₂ of primary section SI at a point 0₂' opposite to the first pivot joint 61 with respect to point Oi _.. Furthermore, the line of minimum distance 252 between axis 202 of second pivot joint 62 and axis 203 of third pivot joint 63 is parallel to the junction line of points 0₂ and 0₃.

Third secondary rigid link 73 connects second secondary pivot joint 62 with third secondary pivot joint 63 of the articulated parallelogram and has a load point 0₃' arranged on the line of minimum distance 252 between secondary pivot joint 62 and third secondary pivot joint 63, such that junction line O3-O3' passes through point 0±.

The line of minimum distance 254 between axis 203 of third secondary pivot joint 63 and axis 204 of fourth secondary pivot joint 64 is parallel to the junction line of points Oi and 0₂ of the primary section of said mechanism.

Fourth secondary rigid link 74 connects third secondary pivot joint 63 with fourth secondary pivot joint 64.

Device 1 provides a counterweight 35, in particular at 0₂' , that is arranged to balance the weight of the parts both of primary section SI and of secondary section S₂. This way, due to the geometric features of such pantograph, the ratio of segments O3-O1 and O1-O3' is constant in all the configurations that are reached by pantograph 100. Then, the application in 0₃' of a constant vertical load C directed downwards produces in 0₃ a force F which is constant, vertical and directed upwards in all the workspace, and that is proportional to load C.

The constant vertical load C can be obtained using a counterweight 30' mounted in O3' , or, alternatively, using an elastic element, for example a helical pulling spring at high pliability, not shown in the figures. In particular, the elastic element can be suitably pre^¬ loaded. In this case, the spring is provided having a first end connected to point 0₃' and a second end connected to a fixed point of device 1.

Device 1 made as above described, and shown in Figs, from 1 to 9, allows to follow completely and without limits all the movements of user's limb 150. In particular, in the case of upper limb 40, it is possible to follow the movement of forearm 42 with respect to a fixed reference and the movements of hand 43 with respect to forearm 42. In fact, the first six degrees of freedom, i.e. those determined by the first six pivot joints 21-26, allow to follow a desired position and orientation assumed by forearm 42 with respect to a fixed reference, whereas the seventh and eighth degrees of freedom, i.e. the two degrees of freedom defined by pivot joints 27 and 28, allow to follow any orientation of hand 43 with respect to forearm 42. Therefore, using device 1 as above described, it is possible to follow all the possible movements of upper limb 40 of operator 150 and to reduce/eliminate the articulation couples necessary to balance the proper weight in the natural workspace of the limb.

From a kinematic point of view, the device described is equivalent to the device shown in Fig. 4, provided with a pivot point Oi with respect to a fixed base, by an application point of the force on the medial segment of the limb of the patient 0₃ and by an application point of a constant vertical load 0₃' , and characterised by geometric properties that, for each configuration, points Oi, 0₃, 0₃' lay on a line, the distance 0i0₃ and 0_X0₃' are variable, and their ratio is constant.

This geometric property guarantee that, if the applied force C in 0₃' is constant, then also the force F applied in 0₃ is constant. In fact for the balance to the rotation of the device about the point of articulation Oi, it must be :

C · 0θ₃'· sin(a) = F · 0^Q_Z- sin(a) from which:

Therefore, for the geometric properties of the mechanism, F and C are always proportional to each other according to factor K for any configuration of the device.

In a particular advantageous exemplary embodiment, as shown in detail in Figs. 6 and 7, the fifth pivot joint 25 is obtained by means of a mechanism with remote centre of rotation, such that rotation axis 105 coincides with the rotation axis of forearm 42 of operator 150. In particular, as shown in Fig. 7, the movable part of the mechanism with remote centre of rotation incorporates the bearings of sixth pivot joint 26. Such exemplary embodiment has the advantage to not need the insertion of the end portion of upper limb 40 of operator 150 in the structure of the device, which can result troublesome especially for people that have a low motor ability.

With reference to Fig. 9, in a particular exemplary embodiment, the first two combinations of two pivot joints 21, 22 and 23, 24 of primary section SI of the mechanism are implemented in the same way by means of two respective torsion-flexion joints 250.

In particular, each torsion-flexion joint 250 comprises a central body 251, a balancing element 252 rotating with respect to the central body 251 about a flexion axis 253 and a shaft 254 arranged to rotate with respect to the central body 251 about a torsion axis 255. In particular, flexion axis 253 is orthogonal to and incident with torsion axis 255.

In particular, shaft 254 and balancing element 252 can be hollow in order to allow the passage of possible electric cables within torsion-flexion joints 250. The use of torsion-flexion joints 250, as above described, and shown in Fig. 9, allows to considerably simplify device 1 and to considerably reduce the production costs.

Device 1 comprises, furthermore, a means for instantly measuring the angular position of the pivot joints 21-28 of primary section SI of the mechanism. In particular, the means for instantly measuring the position of the pivot joints 21-28 can comprise a Hall effect sensor 81-88 that is arranged to measure the position of a respective magnet 91-98.

More precisely, each pivot joint 21-28 comprises a first member 21a-28a and a second member 21b-28b . pivotally connected to it.

For example, with reference to Fig. 9, in the hypothesis that the torsion-flexion joint 250 is relative to the combination of pivot joint 21 and of pivot joint 22, magnet 91 is mounted integral to the member 21a of pivot joint 21 and Hall effect sensor 81 is mounted integral to member 21b of pivot joint 21 same.

In a preferred exemplary embodiment, magnet 91 has a full, or annular, cylindrical shape and the axis of the magnet 191 is parallel to rotation axis 101 of joint 21, but arranged in a position eccentric to it. The magnetization direction of magnet 91, furthermore, is provided orthogonal to the eccentricity direction.

As diagrammatically shown in Fig. 10, during the rotation of movable member 91b-98b about the respective axis 101-108, the Hall effect sensor 81-88 describes a circular trajectory 181-188 about a point 0 and has a direction of sensitivity 81' -88' orthogonal to said circular trajectory, the sensitive point of the Hall effect sensor 81 lays in the plane orthogonal to the axis of the magnet and passing through the middle line of its height.

In the figures 11 and 12 an application is shown of device 1 as a training, or fitness machine. In particular, applying a load C at a link arranged between point Or and movable interaction element 60, a force F' is produced in 0₃ that is directed downwards, i.e. a force that increases the articular stresses on limb 40.

In particular, vertical load C can be hanged at the secondary section at a point O3" arranged between 01 and 03. In this case, load C can be integral to a connection link 170 pivotally connected to link 71 and to link 73 of secondary section S2.

The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation .

Claims

1. Device to relieve the proper weight of a human limb

(40) , said limb (40) comprising a proximal segment articulated to a trunk by a proximal articulation

(41) , a medial segment (42) articulated to the proximal segment by a medial articulation and a distal segment articulated to the medial segment by a distal articulation, said device comprising:

- a fixed base;

- a means for generating a substantially constant vertical load at a predetermined point integral to a link of said mechanism;

wherein said means for generating and said mechanism are arranged to apply a vertical force, which is proportional to said fixed vertical load and therefore substantially constant in said workspace, at a balance point that is integral to said medial segment and that lays on a junction line of the medial articulation with the distal articulation,

characterised in that

said mechanism provides said degrees of freedom to said movable interaction element in such a way that at least two of said degrees of freedom contribute to generate a variation of the vertical position of said balance point and that said balance point is arranged at a distance xp from said medial articulation comprised between 80 mm and 130 mm.

Device, according to claim 1, wherein said mechanism provides to said movable interaction element said two degrees of freedom that contribute to generate a variation of the vertical position of the balance point by means of two hinges having horizontal axis, and, in particular, at least one of the two hinges is not a hinge of an articulated parallelogram.

Device, according to claim 1, wherein said mechanism comprises :

- a primary section comprising at least 6 independent kinematic pairs, or degrees of freedom, said primary section arranged to allow the full mobility, i.e. 3 translational degrees of freedom and 3 rotational degrees of freedom, in said workspace of said interaction element with respect to said fixed base;

- a secondary section that is arranged to transmit said vertical load to said interaction element transforming its intensity and direction, and then by arranging said vertical force at said balance point, such that said vertical force is fixed in said workspace, said secondary section being kinematically depending from said primary section, i.e. not adding degrees of freedom to said mechanism.

4. Device, according to claim 3, wherein said primary section of said mechanism comprises six pivot joints.

5. Device, according to claim 4, wherein said six pivot joints of said primary section are combined in pairs, in order to form a first, a second and a third combination of pivot joints that are orthogonal in pairs .

6. Device, according to claim 5, wherein:

- the rotation axes of the pivot joints of each combination of two pivot joints are orthogonal to each other and incident in three respective different points Oi, 0₂, 0₃;

- the intersection point 0₃ of the rotation axes of the third combination of two pivot joints lays on the junction line of the centre of the distal articulation with the centre of the medial articulation of the arm, at a distance xp from the medial articulation, said intersection point 0₃ arranged at a variable distance D from said intersection point Oi of the rotation axes of the first combination of two pivot joints and in order to lay on the junction line of the medial articulation with the distal articulation of said limb; - said means for generating a substantially constant vertical load generating said load in said predetermined point 0₃' integral to a link of said mechanism such that 0₃' is arranged on the line 0₃0i opposite to 0₃ with respect to Oi, and that the equation: Οιθ₃ ^,=Κ·0, being K fixed, is true.

7. Device, according to claim 6, wherein K is less than 1.

8. Device, according to claim 6, wherein the movement of at least two of the first four pivot joints contribute to the variation of the vertical height of the application point of force 0₃.

9. Device, according to claim 6, wherein

- the axis of the first pivot joint of the first combination of two pivot joints is arranged in a vertical direction and, therefore, the axis of the second pivot joint of the first combination of two pivot joints is arranged in a horizontal direction;

- the intersection point 0₂ of the rotation axes of the second combination of two pivot joints is arranged at an invariant distance Li from the intersection point Oi of the rotation axes of the first combination of two pivot joints;

- the intersection point 0₃ of the rotation axes of the third combination of two pivot joints is arranged at an invariant distance L₂ from the intersection point 0₂ of the rotation axes of the second couple;

- the axis of the third pivot joint, i.e. the first of the second combination of two pivot joints, is arranged parallel to the axis of the second pivot joint, i.e. the second pivot joint of the first combination of two pivot joints, and, then is arranged in a horizontal direction;

- the axis of the fifth pivot joint, i.e. the first pivot joint of the third combination of two pivot joints, is arranged orthogonal . and incident with the axis of the fourth pivot joint, i.e. the second pivot joint of the second combination of two pivot joints;

- said movable interaction element being integral to the movable part of the sixth pivot joint, i.e. the second pivot joint of the third combination of two pivot joints and configured in such a way that, when connected to the medial segment of the limb of the user, said intersection point 0₃ lays on the junction line of the medial articulation with the distal articulation of the limb.

10. Device, according to claim 3, wherein, furthermore, a adjustable means is provided for fastening said medial segment to said interaction element in order to adjust said distance x_F between said balance point and said medial articulation.

11. Device, according to claim 10, wherein said adjustable means for fastening said medial segment to said interaction element comprises a knob that can be grasped by the hand of said user, said knob being integral to said interaction element and being approachable/moveable away with respect to the rotation axis of said sixth pivot joint of the primary section of the mechanism.

12. Device, according to claim 1, wherein said interaction movable element is provided with a surface having a cradle shape, said cradle arranged to receive said medial segment.

13. Device, according to claim 5, wherein, if said limb is the upper limb, said primary section of said mechanism comprises, furthermore, a seventh and an eight pivot j oint .

14. Device, according to claim 13, wherein said seventh and said eight pivot joint. have the following features :

- the respective rotation axes are incident and orthogonal at a point 0 , substantially coincident to the wrist articulation and, then located at a determined distance L₃ from 0₃, adjustable responsive to the anthropometric size of the user;

- the fixed part of the seventh pivot joint is integral to said movable interaction element;

- the axis of the seventh pivot joint is orthogonal and incident to the junction the elbow articulation with that of the wrist;

15. Device, according to claim 13, wherein said seventh pivot joint has a rotation axis that is substantially coincident to the axis of the articulation of flexion- extension of the wrist and said eight pivot joint has a rotation axis that is substantially coincident to the axis of the articulation of abduction-abduction of the wrist.

16. Device, according to claim 3, wherein said secondary section of said mechanism is a pantograph comprising an articulated parallelogram.

17. Device, according to claim 16, wherein said articulated parallelogram comprises:

- four secondary pivot joints having respective rotation axes, said rotation axes being parallel to the rotation axis of the second pivot joint of said primary section, where the axis of the first secondary pivot joint of the articulated parallelogram passes through point 0₂;

- four secondary rigid links junction in pairs the secondary pivot joints.

18. Device, according to claim 16, wherein said articulated parallelogram has at least one of the following features:

- the first secondary rigid link of said four secondary rigid links is integral to the junction line of said points Oi and 0₂ of said primary section and the second secondary rigid link of said four secondary rigid links is integral to the junction line of said points 0₂ and O3 of said primary section;

- the axis of said second secondary pivot joint of the above described four secondary pivot joints of the articulated parallelogram is configured to cut the junction line of said points Oi and 0₂ of said primary section of said mechanism at a point 0₂' that is located opposite to the first secondary pivot joint with respect to point Ο_χ; - the line of minimum distance between the axis of the second secondary pivot joint and of the third secondary pivot joint is parallel to the junction line of said points 0₂ and 0₃ of said primary section of said mechanism;

- the third secondary rigid links connecting the second secondary pivot joint with the third secondary pivot joint of said articulated parallelogram, has a load point 0₃' located on the line of minimum distance between the second secondary pivot joint and the third secondary pivot joint and such that the junction line 0₃-0₃' passes through point Oi;

- a line of minimum distance between the axis of the third secondary pivot joint and the axis of the fourth (40) secondary pivot joint is parallel to the junction line of said points Οχ and 0₂ of said primary section of said mechanism;

- the fourth (40) secondary rigid links connects the third secondary pivot joint with the fourth (40) secondary pivot joint;

- the geometric features of the pantograph are such that the ratio of segments 0₃-Oi and O1-O3' is fixed in all the configurations assumed by the pantograph such that the application in 0₃' of a vertical constant load directed downwards produces in 0₃ a constant vertical balancing force directed upwards proportional to it .

Device, according to claim 1, wherein said means for generating a substantially constant vertical load is selected from the group consisting of: - a counterweight;

- an elastic element having a first end connected to said point 0₃' and a second end connected to a fixed point of said device.

20. Device, according to claim 5, wherein at least one of said first and second combinations of two pivot joints of said primary section of said mechanism is loaded as a torsion-flexion joint, said, or each, torsion- flexion joint comprising a central body, a balancing element arranged to rotate with respect to said central body about a flexion axis and a shaft rotating with respect to said central body about a torsion axis, said flexion axis being orthogonal and incident with said torsion axis.

21. Device, according to claim 20, wherein said shaft and said balancing element are hollow to allow the passage of electric cables inside of said torsion-flexion j oint .

22. Device, according to claim 3, wherein said fifth and said sixth pivot joints of said primary section of said mechanism are obtained using a mechanism with centre remote of rotation, whose movable part incorporates the bearings of said sixth pivot joint.

23. Device, according to claim 22, wherein said mechanism with centre remote of rotation comprises a first and a second articulated parallelogram, wherein said second articulated parallelogram is kinematically depending from said first articulated parallelogram.

24. Device, according to claim 3, wherein, furthermore, a means is provided for instantly measuring the angular position of said pivot joints of said primary section of said mechanism, to provide a sensorized device that is arranged to be used in combination with a system of generating virtual environments, to assist the execution of rehabilitation or training exercises, for monitoring such exercises and for providing the sensory feedbacks to the user/patient.

25. Device, according to claim 24, wherein said means for instantly measuring the angular position of each pivot joint comprises a sensor of magnetic field and a permanent magnet for each joint.

26. Device, according to claim 24, wherein each pivot joint comprises a first member and a second member pivotally connected to each other and said means for measuring the position of each pivot joint comprises a magnet integral to the first member of a pivot joint and a Hall effect sensor integral to the second member of the same pivot joint.

27. Device, according to claim 26, wherein said magnet has a cylindrical geometry, said cylindrical geometry of said magnet having a longitudinal axis and selected from the group consisting of:

- a full cylindrical geometry;

- an annular cylindrical geometry.

28. Device, according to claim 26, wherein said magnet integral to said first member of said pivot joint has at least one of the following features:

- said axis of said magnet is parallel to the rotation axis of the pivot joint to which it is associated; - said axis of said magnet is arranged at a predetermined distance from. the rotation axis of said second member;

- said magnet is magnetized in a diametrical direction;

- said magnet has a magnetization direction orthogonal to the eccentricity direction;

29. Device, according to claim 26, wherein said Hall effect sensor has a sensitive point, said sensitive point arranged in the plane orthogonal to said axis of said magnet and passing through the middle line of its height, during the rotation of said second member about its rotation : axis said Hall effect sensor describing a circular trajectory about a point 0, said sensor having a direction of sensitivity orthogonal to said circular trajectory.

30. Device, according to claim 3, wherein said link of said mechanism at which the means for generating generates said substantially constant vertical load is located opposite to said movable interaction element with respect to said first pivot joint of said primary section .

31. Device, according to claim 3, wherein said link of said mechanism at which the means for generating generates said substantially constant vertical load is arranged at the same side of said movable interaction element with respect to said first pivot joint of said primary section.

32. Device, according to claim 1, wherein said vertical load is mounted on said secondary section at a point 0₃" arranged between O_x and 0₃, such that the device, at point 0₃ generates a vertical force F directed downwards and therefore increases the articulation stresses on the limb, making it possible the use of the device as a training, or fitness, machine in particular a connection link being provided between the second load and the secondary section, said connection link being pivotally connected to said first and to said third secondary links.