Back structure for exoskeleton

Abstract

One aspect of the invention relates to a back structure (100) for an exoskeleton comprising: a beam (110) having a length (115) and a cross-section, the cross-section having a major dimension and a minor dimension, a first fixed connection (120) with the exoskeleton located at a first end (113) of the beam (110), and a second connection (130) with the exoskeleton located at a second end (114) of the beam (110) of the sliding pivot type. Figure to be published with the abbreviation: Figure 1

Description

Title of the invention: Back structure for exoskeleton TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of walking assistance exoskeletons.

[0002] The present invention relates to a dorsal structure for an exoskeleton. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] An exoskeleton is a device fixed to one or more limbs of the human body to restore its mobility or increase its physical capabilities.

[0004] Exoskeletons can assist a human in various tasks such as carrying heavy loads, walking, running, etc. Numerous applications are possible, for example in the medical, industrial, or military fields.

[0005] Depending on the intended applications, exoskeletons differ greatly. Thus, it is possible to divide exoskeletons into two main categories.

[0006] A first category concerns passive exoskeletons. Passive exoskeletons are not motorized. Passive exoskeletons incorporate materials and equipment that store and release energy during the user's movement. The term "user" refers to the person wearing the exoskeleton. This person can be a man or a woman of any age. Passive exoskeletons are often used for ergonomic purposes, to prevent repetitive strain injuries, or to assist in lifting tools or equipment. Thus, passive exoskeletons, such as the one disclosed in patent application WO2014109799A1, are primarily intended to assist able-bodied individuals in performing repetitive and / or traumatic tasks.

[0007] A second category of exoskeletons concerns active exoskeletons. Active exoskeletons rely on systems such as motors, hydraulic or pneumatic systems, capable of increasing human strength or reducing the body's energy consumption. An active exoskeleton consists of one or more actuators, which could be an electric motor, for example. The actuator actively increases the power of the human body.

[0008] Generally speaking, active exoskeletons are heavier than passive exoskeletons due to the amount of equipment and accessories they incorporate. The weight of the active exoskeleton makes it uncomfortable to use. Furthermore, active exoskeletons, such as the one shown in US patent 11185460B2, generally greatly limit the user's mobility.

[0009] Active walking assistance exoskeletons actively participate in the flexion and extension of the user's hip. These exoskeletons include an actuator located near the hip that generates a torque around the hip flexion / extension axis. These exoskeletons also include a belt to which the actuators are attached. In addition, a harness worn around the torso is known. The harness transmits the hip assistance reaction forces generated by the actuators. The resulting simplified force is a near-normal force exerted on the user's torso in the sagittal plane, forward or backward depending on the direction of assistance. Transmitting the force to the belt and torso, rather than solely to the belt, increases the lever arm and thus reduces the equivalent perceived effort.

[0010] To connect the harness and the exoskeleton's belt, US patent 10766134B2 proposes a dorsal structure inspired by the functioning of the human spine. This dorsal structure comprises a plurality of vertebral elements, stacked one on top of the other, and a flexible connecting element linking the vertebral elements together. This structure has several drawbacks. First, due to the large number of parts it comprises, it is complex and expensive to manufacture. Furthermore, this dorsal structure is heavy. Finally, it greatly limits lateral flexion movements, also called abduction and / or adduction, of the torso, as well as torso torsion. This dorsal structure is therefore not suitable for use in an exoskeleton designed to provide assistance during walking, and particularly during mountain hiking.

[0011] There is therefore a need to provide a dorsal structure for an exoskeleton that limits the aforementioned disadvantages. Summary of the invention

[0012] The invention offers a solution to the problems mentioned above by providing a back structure adapted for use within an exoskeleton. The back structure comprises a beam that transmits the reaction forces of the hip assistance generated by the exoskeleton's actuators while allowing sufficient freedom of movement to the user's torso. Indeed, due to its large dimension, the beam is sufficiently rigid in the user's sagittal plane to ensure efficient transmission of the forces generated by the exoskeleton's actuators. Furthermore, due to its small dimension, the beam allows for lateral flexion of the user's torso and, to a lesser extent, torsion of the user's torso.The sliding-type link located at one end of the beam also ensures sufficient mobility when the exoskeleton user bends forward or when performing a movement. hip flexion. The sliding type connection finally allows the dorsal structure to adapt to any size difference between different users of the exoskeleton.

[0013] One aspect of the invention relates to a dorsal structure for an exoskeleton comprising: • a beam having a length and a cross-section, the cross-section having a larger dimension and a smaller dimension, • a first fixed connection with the exoskeleton located at one end of the beam, and • a second connection with the exoskeleton located at a second end of the sliding-type beam.

[0014] The back structure according to the invention is adapted for use within an exoskeleton. In one example, the back structure according to the invention is adapted for use within an exoskeleton designed to assist walking, and in particular to assist mountain hiking. Thus, the back structure according to the invention is comfortable, notably because it is lightweight, allowing for intensive walking lasting several hours. Furthermore, the back structure according to the invention allows the user to maintain freedom of movement during walking assistance. Finally, the back structure is reliable and simple to manufacture so that it can be used by a large number of amateur athletes.

[0015] In addition to the characteristics mentioned in the preceding paragraph, the dorsal structure according to one aspect of the invention may have one or more complementary characteristics from among the following, considered individually or according to all technically possible combinations: • the second connection is of the sliding pivot type, • the second joint includes a rotational degree of freedom adapted to allow rotation around a joint axis of the second joint between -45° and 45°, • the axis of connection of the second connection also forms an angle between 120° and 180° with the length of the beam, the angle formed being in a longitudinal section of the beam, • The beam has a first bending resistance in the plane perpendicular to the face of the larger dimension of between 5 and 50 newtons and a second bending resistance in the plane perpendicular to the face of the smaller dimension of between 50 and 300 newtons, • The larger dimension of the beam is between 10 and 50 millimeters, and the smaller dimension of the beam is between 1 and 10 millimeters. • The beam length is between 50 millimeters and 300 millimeters, • The second connection is implemented by a plain or ball bearing coupled to a smooth-ground cylinder of revolution, • The length of the smooth-ground cylinder of revolution is between 50 and 400 millimeters, • The beam (110) is made of composite material with: • carbon fibers, or • fiberglass, or • Kevlar fibers, or • flax fibers.

[0016] Another aspect of the invention relates to a user's walking assistance exoskeleton comprising: • Right and left actuators assisting a flexion and extension movement of the user's right and left hips respectively, the right and left actuators being attached to a lumbar belt adapted to encircle the user's waist, • A chest harness designed to fit snugly around the user's torso, and • A back structure according to any one of the preceding claims, the back structure being connected to the lumbar belt by the first connection and to the chest harness by the second connection.

[0017] The exoskeleton according to the invention is adapted for assisting walking, and in particular for mountain hiking. Specifically, thanks to the presence of a back support structure according to the invention, the exoskeleton allows for the distribution of the forces associated with assisting walking. Thus, the equivalent perceived effort is distributed between the lumbar belt and the chest harness. This improves the user comfort of the exoskeleton. Furthermore, the presence of the back support structure according to the invention in the exoskeleton also allows the user to maintain freedom of movement, particularly for lateral flexion of the torso.

[0018] In addition to the characteristics just mentioned in the preceding paragraph, the exoskeleton according to one aspect of the invention may have a chest harness comprising a rigid plate linked to the second connection.

[0019] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0020] The figures are presented for illustrative purposes only and are in no way limiting of the invention. • Figures 1, 2 and 3 show a schematic representation, from different points of view, of an example of a dorsal structure according to the invention. • Fig. 4 shows a schematic representation of an example of a sliding pivot type connection included in the dorsal structure according to the invention. • Fig. 5 shows a schematic representation of an example of an exoskeleton according to the invention. • Fig. 6 shows a schematic representation of an example of a beam according to the invention. DETAILED DESCRIPTION

[0021] Figure 1 shows a schematic representation from a first viewpoint of an example of a dorsal structure 100 according to the invention. Figure 2 shows a schematic representation from a second viewpoint of an example of a dorsal structure 100 according to the invention. Figure 3 shows a schematic representation from a third viewpoint of an example of a dorsal structure 100 according to the invention.

[0022] The back structure 100 comprises a beam 110 having a length 115 and a cross-section. The term "length" may, in this application, refer to the principal or longitudinal axis of an element such as the beam. The term "principal axis" refers, in this application, to the principal axis of inertia. The cross-section is a plane surface perpendicular to the length 115 of the beam. The shape of the cross-section may be any geometric shape that can be characterized by the size of a first dimension and the size of a second dimension. The two dimensions are measured in two non-parallel directions and preferably in two orthogonal directions. The cross-section may, for example, be a polygon or an ellipse. When the cross-section is a polygon, it may be a polygon inscribed in an ellipse or, preferably, a convex polygon inscribed in an ellipse.The cross-section can, for example, be a polygon such as a rectangle or a parallelogram. When the cross-section is a rectangle, the first dimension can be the length of the rectangle and the second dimension can be the width of the rectangle. When the cross-section is a parallelogram, the first dimension can be the base of the parallelogram and the second dimension can be the height of the parallelogram. The cross-section can also be a triangle or a polygon with at least five sides. When the cross-section is an ellipse, the first dimension can be the major axis of the ellipse and the second dimension can be the minor axis of the ellipse. The cross-section can also vary along the length of the beam. In other words, depending on its distance from a first end 113 of the beam, the cross-section can vary. The variation in the cross-section can involve the size of the first dimension and / or the size of the second dimension. The size variation can be proportionally the same for both dimensions or different. Alternatively, the variation can involve the type of geometric shape of the beam. For example, the cross-section can be a rectangle at the first end 113 and a hexagon or an ellipse at the second end 114. The variation in the size of the dimensions and / or the type of geometric shape can be proportional to the distance from the first end 113.Alternatively, the variation in the size of the dimensions and / or type of geometric shape can be carried out in a non-proportional manner with respect to the distance to the first endpoint 113 or even abruptly, that is to say without transition from one dimension to another or from one type of geometric shape to another.

[0023] The beam has a first end 113 and a second end 114. The term "end" refers to the portions of the beam 110 located at the ends of the beam along its length. In one example, illustrated in [Fig. 1], consistent with the preceding examples, the beam comprises a first end 113 and a second end 114. For example, the first end 113 is the end of the beam near the user's pelvis, and the second end 114 is the end near the user's shoulder blades. As illustrated in [Fig. 1], the beam 110 can be adapted so that its length extends along the spine of an exoskeleton user. Thus, the direction of the beam 110 along its length can be substantially vertical when the user is in the anatomical reference position.The term "substantially vertical" means that the length of beam 110 is vertical, with a maximum error of 20°. In other words, the length of beam 110 can be substantially parallel to the main axis of the torso when the user is in the anatomical reference position. The term "substantially parallel" means that the length of beam 110 is parallel to the main axis of the torso, with a maximum error of 20°, preferably 10°. The anatomical reference position is the reference posture used by international convention in descriptive human anatomy. Beam 110 can also be adapted so that its longer dimension is parallel to the sagittal plane of an exoskeleton user and its shorter dimension is perpendicular to the sagittal plane of the exoskeleton user.In an example consistent with the previous one, beam 110 is a parallelepiped. Thus, in this example, beam 110 has six faces. Figure 6 shows a schematic representation of beam 110. One type of face of beam 110 is called the "large face". dimension” in the present application and is denoted 111 in [Fig. 6]. One face of the larger dimension has two edges 118 that are parallel to the larger dimension of the cross-section of the beam and two edges 119 that are parallel to the length 115 of the beam. A second type of face of the beam 110 is called the “face of the smaller dimension” in the present application and is denoted 112 in [Fig. 6]. One face of the smaller dimension has two edges 117 that are parallel to the smaller dimension of the cross-section of the beam and two edges 119 that are parallel to the length 115 of the beam. A third type of face is called the “face of the side section” and is denoted 116 in [Fig. 6]. One face 116 of the lateral section has two edges 117 and two edges 118. The beam 110 has two faces 111 of the large dimension, two faces 112 of the small dimension and two faces 116 of the lateral section.Beam 110 is preferably a rectangular parallelepiped, otherwise known as a cuboid, and thus has six rectangular faces, all of whose angles are right angles.

[0024] In an example consistent with the preceding examples, the beam 110 may exhibit a first bending resistance, in the plane perpendicular to a plane including a face of the larger dimension, of between 5 and 50 newtons. This first bending resistance of the beam 110 may be adapted so that the user can easily bend laterally. The terms "bend laterally" mean "perform lateral flexion of the torso" or "perform abduction of the torso." The term "easily" here means that the additional resistance related to the back structure for performing this lateral flexion movement of the torso is low, i.e., a maximum of 50 newtons. The first bending resistance can be evaluated by a bending test in which the end 113 of the back beam 110 is fixed and a force is applied perpendicularly to the face 111 of the larger back beam 110 at the second end 114.The force required to cause a 45-degree bend in the back beam 110 in the plane perpendicular to the large face 111 is the value of the first bending resistance.

[0025] In an example consistent with the preceding examples, the back beam 110 has a second bending resistance, in the plane perpendicular to a plane including the face of the smaller dimension, different from the first bending resistance of the beam 110. The second bending resistance can be evaluated by a bending test in which the end 113 of the back beam 110 is fixed and a force is applied perpendicularly to the face 112 of the smaller back beam 110 at the second end 114. The force required to induce bending of the back beam 110 in the plane perpendicular to the face 112 of the smaller dimension is the value of the second bending resistance. The bending of the beam caused by the force can correspond to any measurable bending, for example, a bending of an angle less than or equal to 2°.

[0026] This second bending resistance of beam 110 can be greater than the first bending resistance of beam 110. For example, the second bending resistance of beam 110 is 2 to 60 times greater than the first bending resistance of beam 110. Preferably, the second bending resistance of beam 110 is 5 to 10 times greater than the first bending resistance of beam 110. This second bending resistance of beam 110 can be between 50 and 300 newtons. This second bending resistance of beam 110 can be adapted to mechanically transmit an applied force, at the level of a first fixed connection 120 of the back structure 110, to a second connection 130 of the back structure 110.The terms "mechanically transmit" in this application mean that the movement from a force exerted at the first joint 120 of the back beam 110 is transmitted to the second joint 130 of the back beam without being transformed, when the transmitted force is less than the second bending resistance, therefore less than a value between 50 and 300 newtons.

[0027] In an example, compatible with the previous examples, the length of the beam 110 is between 50 millimeters and 300 millimeters and preferably between 100 and 200 millimeters.

[0028] In an example consistent with the preceding examples, the larger dimension of beam 110 is 5 to 20 times greater than the smaller dimension of beam 110. Preferably, the larger dimension of beam 110 is 10 times greater than the smaller dimension of beam 110. The larger dimension therefore corresponds to the thickness of the beam in the larger dimension. The smaller dimension therefore corresponds to the thickness of the beam in the smaller dimension. For example, the larger dimension may be between 10 and 50 millimeters, preferably 30 millimeters. The smaller dimension of beam 110 may be between 1 and 10 millimeters, preferably between 2 and 4 millimeters. The larger and smaller dimensions can obviously vary depending on the material used to manufacture the beam.

[0029] In an example, consistent with the preceding examples, the dorsal beam 110 is made of composite material with: • carbon fibers, or • fiberglass, or • Kevlar fibers, or • flax fibers.

[0030] Preferably, the material used to manufacture the back beam 110 is flexible and / or has a low density. Furthermore, it is advantageous for the material to be ductile. The term "ductile" in this application means "having high tensile strength". A carbon fiber composite material is particularly Adapted. Furthermore, it is clear that the dimensions of the previously mentioned beam 110 depend on the material used to manufacture the beam. Indeed, the material's flexural strength must be taken into account so that the first and second flexural strengths of the back beam 110 are suitable, for example, within the values ​​presented previously. For cost reasons, it is also possible to use a plastic-type material, a metal, or a plant-based material such as wood or one containing plant fibers.

[0031] The back structure 100 also includes two joints 120 and 130 located at each end of the beam 113 and 114. At the first end 113 of the beam 110, the first joint 120 is fixed. The second joint 130 is a sliding joint. A sliding joint allows for guiding rectilinear translational movement along the principal, or longitudinal, axis of the slide. The sliding joint may include a part having a variable shape, such as a cylinder, parallelepiped, rectangular parallelepiped, or rectangular prism. In one example, the back structure 100 further includes other joints. For example, the back structure 100 further includes at least one other pivot joint, preferably between one and three other pivot joints.In this example, at least one other pivot-type joint allows rotation around the length 115 of the beam and / or around an axis parallel to the main axis of the sliding-type joint.

[0032] Figure 4 is an enlarged view of an example of the second joint 130 of the backbone structure 100. The second joint 130 is located at the second end 114 of the beam 110. In this example, the second joint 130 is a sliding pivot joint. A sliding pivot joint models a cylindrical contact of revolution. At the second joint 130, as illustrated in the example in Figure 4, the second joint 130 comprises a cylinder of revolution 133, or cylindrical axis 133, and a component 132. A cylinder of revolution is the surface generated by the revolution, around a fixed axis, of a straight line parallel to that axis. It is common to characterize the dimensions of a cylinder by its radius and the height of a truncated cylinder. In the example illustrated in [Fig.4], all the points of contact between the cylinder 133, having a fixed axis of connection 131, and the component 132 belong to the cylinder 133 of revolution.Thus, the contact normals between cylinder 133 and component 132 all intersect the connecting axis 131 of cylinder 133. Furthermore, the height of cylinder 133 corresponds to the segment formed by the ends 134 and 135 of cylinder 133. In the example illustrated in [Fig. 4], component 132 is a part with a cylindrical opening, the diameter of which is greater than the diameter of cylinder 133. It should be noted that the diameter of the opening in component 132 is adapted so that the second connection is of the sliding pivot type. The sliding pivot connection thus allows the user's torso to twist.

[0033] In one example, consistent with the preceding examples, the second connection 130 is implemented by a plain or ball bearing coupled to a smooth-ground cylinder 133. A plain bearing provides rotational and translational guidance of the component 132 along the cylinder 133 by sliding or rolling. When the bearing is a ball bearing, the guidance is provided by the rolling elements, i.e., the balls.

[0034] In an example consistent with the preceding examples, the cylinder 133 is a cylinder having a diameter between 5 and 30 millimeters, preferably between 10 and 15 millimeters. The diameter of the cylinder 133 is adapted to ensure that the cylinder is sufficiently strong. The diameter of the cylinder is therefore adapted to prevent any breakage of the cylinder 133 during the use of the dorsal structure 100.

[0035] In an example consistent with the preceding examples, the component for implementing the connection 130, such as the cylinder 133, has a length between 50 and 400, preferably between 100 and 250 millimeters. Furthermore, the sum of the length of the component for implementing the connection 130 and the length of the back beam 110 can be adapted to correspond to the distance between the user's posterior iliac crests and the prominent vertebra, i.e., the base of the upper thoracic vertebrae. For example, the sum of the length of the component for implementing the connection 130 and the length of the back beam 110 can be equal to 540 millimeters for a person measuring 182 centimeters.

[0036] In an example consistent with the preceding examples, the second link 130 further includes a rotational degree of freedom having an axis of rotation which is the principal axis of the cylinder 133, also called the link axis 131. When the second link does not include a cylinder, the link axis 131 corresponds to the longitudinal or principal axis of the second link 130. Thus, the rotational degree of freedom allows the component 132 to pivot about the cylinder 133. Therefore, the rotational degree of freedom allows the component 132 of the second link 130 to form an angle, denoted 140 in Figures 2 and 4, between -45° and 45° with the cylinder 133 of the second link 130. The value of 0° of the angle 140 corresponds to the relative orientation of the component 132 with respect to the cylinder 133 as illustrated in Figures 1 to 5.A positive value of angle 140 can correspond to a clockwise rotation of component 132 relative to cylinder 133. In one example, consistent with the previous examples, the axis of rotation of the second link 130 is offset between the link axis 131 and the main axis of the user's torso. The offset axis of rotation can be parallel, with a maximum margin of error of 30°, to the link axis 131.

[0037] In one example, consistent with the preceding examples, the second connection 130 is adapted so that the connection axis 131 further forms an angle 150 between 120° and 180°, or equivalently between 0° and 60°, with the length 115 of the beam 110 in a longitudinal section of the beam, i.e. in a plane including the length of the beam 110. The angle 150 is contained in a plane parallel to the plane including the large face 111 of the beam 110. In other words, the second connection 130 is adapted so that the connection axis 131 also forms an angle 150 between 120° and 180°, or equivalently between 0° and 60°, with the length 115 of the beam 110. For example, the second connection can be adapted so that the connection axis 131 of the cylinder 133 is parallel to an axis defined by the user's pelvis and the base of the user's cervical spine.

[0038] In one example, consistent with the previous examples, the dorsal structure 110 has a weight of less than 2000 grams, and preferably less than 800 grams.

[0039] A second aspect of the invention relates to a walking assistance exoskeleton, and in particular to a mountain hiking assistance exoskeleton. Figure 5 illustrates an example of an exoskeleton 200 according to the invention. The exoskeleton 200 includes, in particular, the dorsal structure 100 according to the invention. The exoskeleton 200 also includes a lumbar belt 230 and a chest harness 240. The lumbar belt is adapted to encircle the user's waist. The waist is the part of the body located between the ribs, or thorax, and the user's hips. The term "encircle the user's waist" means, for example, that the lumbar belt 230 is fixedly fastened around the user at the level of the lumbar vertebrae, i.e., at the level of the user's lower back. The chest harness 240 is adapted to encircle the user's torso. The term "to enclose" means that the harness can be fixed to the user's torso, for example, using straps.The dorsal structure 100 is fixedly connected to the lumbar belt 230 by the first link 120. The harness 240 is connected to the dorsal beam 110 by the second link 130. For example, as illustrated in [Fig. 5], the harness 240 can be attached to component 132 of the dorsal structure 100.

[0040] In one example, consistent with the preceding examples, the chest harness 240 includes a rigid plate 250. The rigid plate 250 can be connected to the second link 230. For example, as illustrated in [Fig. 5], the rigid plate 250 can be attached to component 132 of the back structure 100. This rigid plate 250 can be in contact with an area of ​​the user's back located between the user's shoulder blades. For improved comfort, a soft material can be added to the face of the rigid plate in contact with the user's back.

[0041] The exoskeleton 200 also includes two hip actuators 210 and 220 attached to the lumbar belt 230. The right actuator 210 assists the flexion and extension movements of the user's right hip. The left actuator 220 assists the flexion and extension movements of the user's left hip. Each actuator generates a torque around the flexion / extension axis of its respective hip to assist the user's gait. Thus, each actuator transmits the assistance force to the thigh through a structure following the movements of The thigh. The dorsal structure 100 thus transmits the reaction forces generated by the walking assistance provided by the actuators. The resulting simplified force is almost a normal force for the user's torso, forward or backward depending on the direction of assistance. Transmitting the force to the harness 240 rather than solely to the lumbar belt increases the lever arm, and therefore reduces the equivalent perceived effort. The walking assistance provided by the exoskeleton is therefore more comfortable than with an exoskeleton without a harness.

[0042] Unless otherwise specified, the same element appearing on different figures has a unique reference.

Claims

1.

2.

3.

4. Demands Back structure (100) for a user's walking assistance exoskeleton comprising: - a beam (110) having a length (115) and a cross-section, the cross-section having a larger dimension (118) and a smaller dimension (117), - a first fixed connection (120) with the exoskeleton located at a first end (113) of the beam (110), - a second connection (130) with the exoskeleton located at a second end (114) of the sliding-type beam (110), and the dorsal structure (100) being characterized in that the large dimension of the beam is adapted to ensure efficient transmission of forces generated by the exoskeleton actuators and the small dimension of the beam is adapted to allow lateral flexion mobility of the user's torso. Back structure according to claim 1 in which the second link (130) is of the sliding pivot type. Back structure according to claim 2, wherein: - the second link (130) includes a rotational degree of freedom adapted to allow rotation around a link axis (131) of the second link (130) between -45° and 45°, and / or - the connecting axis (131) of the second connection (130) also forms an angle (150) between 120° and 180° with the length (115) of the beam (110), the angle formed (150) being in a longitudinal section of the beam. Back structure according to any one of the preceding claims, wherein the beam (110) has: - a first resistance to bending such that a first bending force with a magnitude between 5 and 50 newtons causes a 45-degree bend in the back beam (110) in the plane perpendicular to the large face (111) when the first bending force is applied perpendicularly to the large face (111) at the second end (114) with the end (113) of the back beam (110) which is fixed, and - a second bending resistance such that a second bending force of magnitude between 50 and 300 newtons causes a bending of less than or equal to 2 degrees of the back beam (110) in the plane perpendicular to the small face (112) when the second bending force is applied perpendicular to the small face (112) at the level of the second end (114) with the end (113) of the back beam (110) which is fixed.

5. Back structure according to any one of the preceding claims wherein the larger dimension (118) of the beam (110) is between 10 and 50 millimeters and the smaller dimension (117) of the beam (110) is between 1 and 10 millimeters.

6. Back structure according to any one of the preceding claims wherein the length (115) of the beam (110) is between 50 millimeters and 300 millimeters.

7. Back structure according to any one of the preceding claims in which the second linkage (130) is formed by a plain or ball bearing coupled to a smooth ground cylinder (133) of revolution.

8. Back structure according to the preceding claim in which a height of the smooth rectified cylinder (133) of revolution is between 50 and 400 millimeters.

9. Back structure for exoskeleton according to any one of the preceding claims wherein the beam (110) is made of composite with: - carbon fibers, or - glass fibers, or - kevlar fibers, or - flax fibers.

10. A user walking assistance exoskeleton (200) comprising: - right (210) and left (220) actuators assisting a flexion and extension movement of the user's right and left hips respectively, the actuators right and left (210, 220) being attached to a lumbar belt (230) adapted to encircle a user's waist, - A chest harness (240) adapted to encircle a user's torso, and - A back structure (100) according to any one of the preceding claims, the back structure (100) being linked to the lumbar belt (230) by the first linkage (120) and to the chest harness (240) by the second linkage (130).

11. Exoskeleton according to claim 10 in which the chest harness (240) comprises a rigid plate (250) linked to the second linkage (230).

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