Exoskeleton device for the hand

DESCRIPTION Field of the invention

The present invention relates to the field of wearable exoskeletons for neuro-motor and orthopedic rehabilitation assisted by robot and for the guidance and assistance to the movement of the limbs during the course of everyday activities.

In particular, the invention relates to the an exoskeleton for rehabilitation, the guidance and the assistance to the movement of flexion/extension of the fingers of a hand, also during the cylindrical gripping of objects.

Description of the prior art

As well known, a problem faced by many mechanical devices wearable (haptic or exoskeleton devices) is to provide an outer kinematic coupling with the human hand and at the same time allowing an exchange of physic actions (forces/torques) with the phalanxes of the hand itself: all this in conditions of efficiency and of maximum safety for the human user. One reason for inefficiency in the transmission of forces from the exoskeletal structure to the phalanx can be represented by the implementation of points of attachment by means of contact surfaces with the phalanx that require the transmission of forces by friction tangentially to the same contact surfaces. The transmission of the motion by means of these frictional forces can be inefficient due to possible sliding between exoskeletal structure and phalanx, both for possible deformations of the skin of the phalanx, both for a coefficient of friction not appropriate for the extent of the forces that are acting. Moreover, this type of transmission of motion can be uncomfortable because of a deformation or a slight abrasion of the skin.

In the more restrictive case of care and rehabilitation, where typically there is a muscular hypertonia during the movements of opening of the hand and consequent resistance offered to the movement, the exoskeleton structure must be able to withstand substantial external loads and transmit them in a comfortable, safe and efficient way to the phalanges and to the articular joints, without causing overloads on the human joints. In fact, the coupling of the human kinematic structure with a sufficiently rigid exoskeletal structure can lead to a non-efficient functioning of the mechanism, as a result of various factors, such as misalignment of the axes of robotic joints with human joints and the variability of the outer conformation of human limb. The particular case of the hand presents these problems in a very extended form, because of its large mobility and small size of its segments. However, the search for solutions to this problem is very desirable in the rehabilitative clinical environments, where the therapies mediated by robotic devices are increasingly being used for their great potential: at the technical level, this need is realized in the request of wearable mechanical devices that allow assistance to individual anatomical joints of the patient's fingers, without interfering with their natural movements and without causing undue discomfort.

The greatest interest is focused on the functional rehabilitation of the grips, such as the cylindrical grip or the precision grip. For this reason it is necessary that the device should not interfere with the hand palm area, as well as it should allow a control of the patient's wrist flexion to maintain the posture of the hand relative to the arm during the anatomically correct grip. Furthermore, the use of underactuated systems allows to modulate the distribution of the forces on the various phalanges so as to adapt to the grasped object geometry, although using a limited number of actuators to reduce the weight of the device worn.

The document WO2014033613 describes an exoskeleton for rehabilitation of the metacarpal-phalangeal joint of the hand, in particular the thumb and the forefinger. In particular, the exoskeleton above allows the assistance to the flexion-extension of joints of a hand by means of pure torques which do not generate parasitic forces on the phalangeal and metacarpal-phalangeal joints, moving them for their entire natural workspace. In addition, the exoskeleton is adjustable and adaptable to the different anthropometric measurements of the patient's hand.

However, this exoskeleton has two main critical issues.

The first relates to a reduced accuracy in assisting the gripping of an object. In fact, being connected only with the proximal phalanx of the finger, the exoskeleton is very stiff in the distal phalanges and therefore not very effective during the gripping of complex objects and with dimensions not known a priori .

A second aspect relates to the presence of perpendicular reactions on the joints, on the plane of flexion-extension, in correspondence of the connection between the exoskeleton and phalanx. Although reduced, these reactions may cause a limitation to the movement of the fingers and, in the long run, also the onset of articular damages .

The documents ES2558024 and US20100305717 also have two exoskeleton devices for hand rehabilitation.

However, in both documents use is made of circular guides that define the axis of rotation of the phalanges.

This implies that, for a proper operation, the center of the guides must coincide with the metacarpo/phalangeal joints (MCP) and proximal interphalangeal (PIP) of the finger. In particular, the device described in ES2558024 requires the adjustment on the metacarpo/phalangeal joint (MCP) , the latter having to coincide with the center of the first circular guide. The device described in US20100305717, instead, requires the alignment with the finger joints of both circular guides, acting on linear dovetail guides lockable via screws.

This alignment has several disadvantages, including a long time to wear the device, a procedure dependent by the operator and the possible presence of non-controllable loads on the joints, due to a non-perfect alignment.

The device described in ES2558024 ensures that the force transmitted to the phalanges is perpendicular only on the first phalanx, and only if there are no errors in the alignment of the circular waveguide with the MCP joint of the finger. On the second phalanx the alignment with the PIP joint is automatic, but torques on the phalanx are applied.

In addition the devices described in ES2558024 and US20100305717 are all mechanisms with a single degree of freedom. This implies having to manually impose the angle of both the MCP and PIP joints, leading to further possible misalignments between anatomical and mechanical joints, and therefore to unwanted parasitic forces, and to constrain the movements of flexion/extension of the phalanges on an imposed trajectory that fixes the relations between the angles of the MCP and PIP joints.

Summary of the invention

It is therefore a feature of the present invention to provide an exoskeleton device that allows to reduce unwanted stresses on anatomical joints.

It is also a feature of the present invention to provide a said exoskeleton device that allows a dedicated and more precise attuation for each single phalanx of the fingers, in order to adapt during the grip of objects with shape and size not known a priori .

It is a further feature of the present invention to provide a said exoskeleton device that is safe, comfortable and quick to wear, without requiring initial operations of adjustment or calibration.

It is still a feature of the present invention to provide a said exoskeleton device that is adaptable to different anthropometric measurements of the anatomical limbs of a user.

These and other objects are achieved by an exoskeleton device arranged to assist the movement of at least one phalangeal articulation of a finger in a flexion/extension plane Γ of the articulation, said exoskeleton device arranged to pass between an open configuration and a closed configuration during a rotation 6 ₁ ,6 ₂ of the phalangeal articulation about an axis substantially orthogonal to the flexion/extension plane Γ, said exoskeleton device comprising :

- a metacarpal support arranged to be integral to a metacarpal portion of a hand;

- a first support having engagement means arranged to engage the first support to a first phalanx of the finger;

- a kinematic chain arranged to connect the metacarpal support and the first support; said kinematic chain comprising:

- an linear actuator constrained to the metacarpal support by a first rotational joint and arranged to carry out a stroke x in a radial direction with respect to the rotational joint;

- a first stiff link connected to linear actuator by a second rotational joint;

- a second stiff link connected to the metacarpal support by a fourth rotational joint and connected to the first stiff link by a fifth rotational j oint ;

- a first slide connected to the first support and arranged to carry out a translation with respect to it along an axis y, said first slide being also connected to the first stiff link by a third rotational joint;

said first slide and said third rotational joint being configured for avoiding the generation of forces parallel to the axis y on the first phalanx of the finger, when the exoskeleton device passes between the open configuration and the closed configuration, whose main feature is that the exoskeleton device comprises a second support having engagement means arranged to engage said second support (170) to a second phalanx of said finger,

and that said kinematic chain comprises furthermore:

- a third stiff link connected to the second stiff link by a sixth rotational joint;

- a fourth stiff link connected to the third stiff link by a seventh rotational joint and connected to the first stiff link by an eighth rotational j oint ;

- a second slide connected to the second support and arranged to carry out a translation with respect to it along a axis y' , said second slide being connected to the fourth stiff link by a ninth rotational joint;

said second slide and said ninth rotational joint being configured for avoiding the generation of forces parallel to the axis y' on the second phalanx of the finger, when the exoskeleton device passes between the open configuration and the closed configuration.

In this way, the transmission of motion between the exoskeletal structure and phalangeal joint increases its effectiveness and user comfort, since it does not rely on the transmission of tangential forces between the contact surfaces, which may be unreliable and uncomfortable due to slippage between said surfaces in case of high magnitude forces. In addition, the exoskeleton device, once worn on each finger, is a labile structure with 2 degrees of freedom. Being equipped with a single actuator, said exoskeleton device is configured so as an underactuated system with a degree of underactuation . This implies that the movement of the single actuator takes to the variation of both θι and Θ ₂ , at the same time allowing the finger to place itself in any position without generating forces parallel to the axes y and y' . In this way, you have therefore a distribution of the loads on the different phalanges, allowing a better adaptation to the object to be grasped. Moreover, the fact of not requiring a second actuator reduces the weight, the cost and complexity of the exoskeleton.

Advantageously, the third rotational joint lays on the axis y, in order to reduce the friction in the mechanism and to make more fluid the rotation θι. Advantageously, the ninth rotational joint lays on the axis y' , in order to reduce the friction in the mechanism and to make more fluid the rotation Θ ₂ .

This way, jammings of the mechanism during the transition between closed and open position are avoided.

Advantageously, the second stiff link has a L shape configured to avoid that there is an overlap between it and other components of the kinematic chain, when the exoskeleton device passes in the closed configuration. In particular, you avoid the interference of the second stiff link with the eighth rotational joint and with the first and the fourth stiff link.

Advantageously, the fourth stiff link has a Y shape configured to avoid that there is an overlap between it and other components of the kinematic chain, when the exoskeleton device passes in the closed configuration. In particular, you avoid the interference of the fourth stiff link with the proximal interphalangeal articulation and with the slides.

Brief description of the drawings

Further characteristic and/or advantages of the present invention are more bright 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 side view of an exemplary embodiment of the exoskeleton device in the open configuration;

- Fig. 2 shows a side view of the exemplary embodiment of Fig. 1 in the closed configuration;

- Fig. 3 shows a perspective view of the exemplary embodiment of Fig. 1 in the open configuration and applied to four fingers of the hand;

- Fig. 4 shows a perspective view of the exemplary embodiment of Fig. 3 in the closed configuration;

- Fig. 5 shows a perspective view of an exemplary embodiment alternative to that of Fig. 3, where the exoskeleton device is mounted even at the thumb ;

- Fig. 6 shows in a first side view the exemplary embodiment of Fig. 5;

- Fig. 7 shows in a second side view the exemplary embodiment of Fig. 5.

Description of a preferred exemplary embodiment

With reference to Figs. 1, 2. 3 and 4 the exoskeleton device 100 according to the present invention is adapted to assist the movement of the two phalangeal articulations 50 and 60 of a finger 200 located in a flexion/extension plane Γ.

In particular, the exoskeleton device 100 is adapted to pass between an open configuration and a closed configuration during a rotation θι of the phalangeal articulation 50 about an axis substantially orthogonal to the flexion/extension plane Γ and a rotation Θ2 of the phalangeal articulation 60 about an axis substantially orthogonal to the flexion/extension plane Γ.

Advantageously, the exoskeleton device 100 comprises a metacarpal support 150 integral to a metacarpal portion of a hand, for example the back, and a first support 160 that can be fixed to a first phalanx of the finger 200, for example the proximal phalanx.

Among the metacarpal support 150 and the first support 160 a kinematic chain is provided comprising a linear actuator 101 constrained to the metacarpal support 150 itself from a first rotational joint 111. The actuator 101 is adapted to carry out a stroke x in a radial direction with respect to the rotational joint 111. The chain comprises then a first stiff link 121, connected to the actuator 101 by a second rotational joint 112, and a second stiff link 122, connected to the metacarpal support 150 by a fourth rotational joint 114 and connected to the first stiff link 121 by a fifth rotational joint 115. The chain also comprises a first slide 131 connected to the first support 160 and arranged to carry out a translation with respect to it along an axis y. The slide 131 is also connected to the first stiff link 121 by a third rotational joint 113. In this configuration, a combination of the first slide 131 with the third rotational joint 113 causes that they can not make forces parallel to the axis y when the exoskeleton

100 passes in the closed configuration, i.e. tangentially directed to the phalanx on which the device is worn.

In this exemplary embodiment, therefore, the actuator

101 can bring in rotation the phalangeal articulation 50, without generating forces tangential with respect to the surface of the phalanx of the finger 200, increasing remarkably the comfort of a user during the use and the efficiency of the transmittion of the forces. In fact, the transmission by friction of forces tangential to the phalanx can result both not much efficient, and not much comfortable, owing to possible relative slipping between the exoskeleton structure and the phalanx itself, in case that the forces are to big. The present invention overcomes this drawback since it does not need such tangential forces for transmitting the motion .

The exoskeleton device 100 is also arranged to assist the movement of the phalangeal articulation 60 of the finger 200 always in the flexion/extension plane Γ.

In particular, the exoskeleton device 100 is adapted to pass between an open configuration and a closed configuration during a rotation Θ2 of the phalangeal articulation 60 about an axis substantially orthogonal to the flexion/extension plane Γ.

Advantageously, the exoskeleton device 100 comprises a first support 160 that can be fixed to a first phalanx of the finger 200, for example to the intermediate phalanx.

Furthermore, the kinematic chain comprises a third stiff link 123, connected to the second stiff link 122 by a sixth rotational joint 116, and a fourth stiff link 124, connected to the third stiff link 123 by a seventh rotational joint 117 and connected to the first stiff link 121 by a eighth rotational joint 118.

The kinematic chain comprises then a second slide 132 connected to the second support 170 and arranged to carry out a translation with respect to it along an axis y' . The second slide 132 is also connected to the fourth stiff link 124 by a ninth rotational joint 119.

Similarly to what happens for the articulation 50, a combination of the second slide 132 with the ninth rotational joint 119 causes that they can not make forces parallel to the axis y' when the exoskeleton 100 passes in the closed configuration .

In this exemplary embodiment, once worn on the finger, the exoskeleton device 100 defines a labile kinematic structure with 2 degrees of freedom. This would cause that the variation of the coordinate x by the actuator 101 brings to a variation both of θι and of Θ2, allowing at the same time the finger of place itself in any position not generating forces parallel to axes y and y' .

It is therefore an underactuated system that, in addition to reduce the parassite forces on the anatomicalof joints the user, allows also to use a single actuator for handling both the phalanxes and therefore to not need for an actuator dedicated on the articulation 60. This would cause clear benefits both in economic terms and in terms of weight and encumbrance. Furthermore, the underactuation allows a better distribution of the loads on the different phalanxes, allowing a better matching to the object to grip.

With particular reference to Figs. 1 and 2, in this exemplary embodiment the pivot joints 113 and 119 lay, respectively, on the axes y and y' , overlapping to the slides 131 and 132. Such structural aspect causes to avoid jamming of the mechanism during the passage between closed and open configuration, thus making it more fluid the rotation of the joints and more precise the assistance of the exoskeleton 110 to the handling..

Still with reference to Figs. 1 and 2, to avoid mechanical interferences between different components of the kinematic chain during the rotation, the present exemplary embodiment provides some structural solutions. In particular, the L shape of the second stiff link 122 allows it not to overlap, in the closed configuration, to the joint 118 and to the links 121 and 124.

Similarly, the Y shape of the fourth stiff link 124 allows it not to overlap, in the closed configuration, to the proximal interphalangeal articulation and to the slides 131 and 132.

In the exemplary embodiment of Figs. 6, 7 and 8, the exoskeleton device 300 is applied to the thumb 400 of a hand.

Kinematically the human thumb 400 differs from the other four fingers of the hand since its movement is not approximable with a plane movement. The thumb is in fact modelable as a serial kinematical chain composed of 5 pivot joints that have skew axes to each other, but suitably directed according to an anatomical model.

The use of universal joints 311, 312, 314, 315 and 317 and of spherical joints 331, 353 and 357 and the introduction of the rotational joint 323 in the kinematic chain of the exoskeleton for thumb 300 has allowed to obtain a three- dimensional workspace, increasing the number of underactuated degrees of freedom of the exoskeleton device 300 with respect to the plane workspace of the exoskeleton 100 used for other fingers and the only degree of underactuation of this exoskeleton 100. The kinematic chain that forms the exoskeleton for thumb 300 has been designed for being capable, once worn the device, to follow isostatically all the 5 the degrees of freedom (dof) that the thumb has for its kinematic nature. It follows that, all the kinematical system comprising exoskeleton and thumb still has 5 dof. Being operated just one dof of the 5 dof of the system, the latter is underactuated of 4 dof.

Such level of underactuation allows, owing to the particular kinematic chain shown, to guide the thumb in the steps of opening and closing the hand, leaving the finger free to have in each instant the position which more is natural, even if following a conveying direction applied by the device by means of the actuator 301. The device 300 is designed for the application of two forces on the finger thumb 400, one exerted on the metacarpal bone and the other on the distal phalanx. The exoskeleton is in fact constrained to the metacarpal bone by a support 360 suitably shaped and to the distal phalanx by a band 370.

Also in this embodiment 300, as in the exoskeleton 100 for fingers, the forces applied are always perpendicular to the axis of the phalanx on which they are exercitated. This way, all the advantages of comfort and efficiency of transmition of the forces discussed for the embodiment 100 are kept. From the kinematical point of view, in space, this is obtained componmg a spherical hinge with a prismtic joint (prismtic joints are represented by the axes y' and y' ' for the respective supports) . The spherical hinge allows to have as only constraining reaction a force applied to the centre of the hinge itself, whereas the prismtic joint transmits to the slides 341 and 342, to which is integrally constrained, only the components of this reaction having direction perpendicular to the generic translating direction y.

For simplicity the spherical joint 353 centred in the axis y has been made by the kinematic equivalent of an universal joint 313 centred in the axis y and having a rotation axis in a direction y, and a rotational joint 322 having rotation axis perpendicular to the rotation axes of the universal joint 313 and passing through the centre of the universal joint itself. Similarly, the spherical joint 357 centred in the axis y' ' has been made by the kinematic equivalent of a universal joint 316 centred in the axis y' ' and having a rotation axis in a direction y' ' , and a rotational joint 324 having rotation axis perpendicular to the rotation axes of the universal joint 316 and passing through the centre of the universal joint itself.

Finally, the kinematic chain provides that the actuator 301 is mounted between a spherical joint 331 and an universal joint 311, having translational axis always perpendicular to the plane defined by the rotation axes of the universal joint 311. Therefore, the only load which the actuator 301 has to counteract is a force in a direction of the movement, thus preventing possible breaks deriving from the loading of the actuator 301 by means of loads perpendicular to the axis or torques .

The foregoing description some exemplary specific embodiments 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 in various applications the specific exemplary embodiments without further research and without parting from the invention, and, accordingly, it is meant that such adaptations and modifications will have to be considered as equivalent to the specific embodiments. 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 that is employed herein is for the purpose of description and not of limitation .