Mechanical transmission for a robotic device

Abstract

Mechanical transmission device (1) for a robotic device, comprising: - a transmission element (4) intended to be diverted between an input direction (d1) and an output direction (d2), - an input pulley (2) configured to rotate about a first rotation axis (a1) orthogonal to the input direction (d1) and at least partially wound by the transmission element (4), - an output pulley (3) configured to rotate about a second rotation axis (a2) orthogonal to the output direction (d2) and at least partially wound by the transmission element (4), the second rotation axis (a2) being non-parallel to the first rotation axis (a1), wherein the first rotation axis (a1) and the second rotation axis (a2) form between them a deflection angle (a) having a predetermined width, - at least one intermediate pulley (5) positioned between the input pulley (2) and the output pulley (3) and configured to rotate about a third rotation axis (a3) lying in one of the planes defined by the axes (a1, a2) and inclined by an angle (b) with respect to one of the rotation axes (a1, a2), the width of this angle (b) being less than the width of the deflection angle (a), and this at least one intermediate pulley being partially wound by the transmission element (4), and wherein the rotation planes of the pulleys (2, 3, 5) are non-parallel.

Description

Technical Field

[0001] This invention relates to a mechanical transmission device for use in robotic devices. Specifically, this invention relates to a mechanical transmission device in which the input and output shafts of the pulleys constituting the mechanical transmission device are not parallel to each other.

[0002] This invention finds preferred, but not exclusive, applications in the field of robotic devices, and particularly in those devices that physically interact with humans, such as collaborative robots and actuated exoskeletons. The latter are characterized by their ability to mimic the complex movements of human joints in order to provide physical assistance to the user's movements. Background Technology

[0003] Such devices typically consist of multiple joints connected to each other via rigid components (or "links"). These joints allow related movements between the links via rotary joints or prismatic joints, and can even have multiple degrees of freedom. Specifically, in robotic devices, we can identify:

[0004] - Fixed (or base) link: typically attached to the bottom frame;

[0005] - End link: Typically connected to an end effector suitable for performing a specific activity (such as grasping an object);

[0006] - The intermediate link between the base link and the end link.

[0007] One or more actuators are connected to the joint via appropriate mechanical drive devices to move the joint in space and generate torque and / or interaction forces with the external environment. Typically, the actuators are placed directly at the joint to be moved; however, this leads to problems in terms of space and weight for so-called moving links, namely end links and intermediate links.

[0008] Therefore, the implementation of drive systems is well-known, allowing actuators to be placed on fixed links (referred to in the art as "remotization") to reduce the space and mass / inertia of moving links, offering significant benefits in terms of the dynamic performance of robotic devices and the safety of operators located within their workspace or physically interacting with them (e.g., in the case of collaborative robots or actuated exoskeletons). Furthermore, this solution implies a reduction in the torque requirements of some actuators, primarily those closer to the fixed links, as the latter need not support the weight and inertia of other actuators arranged on their downstream links.

[0009] However, the remote operation of actuators requires the implementation of “long” mechanical drives capable of transmitting the torque / force generated by each actuator to the associated joint to be moved. Therefore, these drives must span the joint between the joint to be actuated and the actuator, following and accompanying them across the entire width of their movement.

[0010] There are various solutions for manufacturing long mechanical drive units.

[0011] The first known solution involves using gears coupled to the drive shaft. However, these components, in addition to being heavy, require tight machining tolerances to ensure low operating friction and clearance, which unfavorably increases production costs.

[0012] Another well-known solution involves systems using gear belts and / or chains. However, this type is also very inconvenient, characterized by fluctuations in the transmission ratio.

[0013] Another solution involves using cables guided by a flexible sheath (called "bowdencables"), which, due to their flexibility, can follow the movement of the linkage. However, these mechanical actuators do have several drawbacks, as they require sufficient space to allow the sheath to bend excessively even at the robot's extreme postures. Furthermore, these actuators are characterized by non-negligible friction, which varies depending on the sheath's bending during joint movement. Additionally, variations in sheath bending and cable tension create gaps in the actuator, primarily due to changes in the cable surface in contact with the guiding sheath.

[0014] At least for the reasons mentioned above, providing a solution using tension cables is more efficient because it allows for the creation of mechanical drives that can relatively easily traverse even complex joints (e.g., those with non-parallel axes) and can transmit relatively high forces and power with high stiffness, zero backlash, and very low friction.

[0015] In current configurations, actuators with tension cables typically include a cable, a drive pulley, a driven pulley, and possibly an idler pulley. The drive pulley receives a predetermined torque from the actuator, causing a traction force to be applied to the cable to move it. The idler pulley internally orients the cable appropriately towards the linkage and joint to allow its movement. The driven pulley receives the force transmitted by the cable and applies the corresponding torque to the joint to be actuated.

[0016] Since a taut cable can only transmit traction force, in order to generate torque in both directions, the taut cable must form a closed loop with forward and return branches.

[0017] Such bidirectional actuators with tensioned cables are typically equipped with a device for pre-tensioning (or preloading) the cable to prevent excessive slack in the unloaded branch, which could cause the cable to slip off the pulley (i.e., detach from its guide surface). Furthermore, to maintain a constant preload value, the total length of the closed loop must remain constant as the robot's posture changes. Therefore, mechanical transmissions that need to cross joints must ensure that the loop length remains unchanged. One possible solution to achieve this is to wind the forward and return branches onto idler wheels with axes coinciding with the joint's rotational axis (see Figure 1), thus ensuring that both branches are in contact with these pulleys in all postures achieved by the device.

[0018] There are different types of transmission devices used for tensioning cables. In this case, a first type of transmission device and a second type of transmission device can be defined.

[0019] The first type of transmission device is, for example, a transmission device in which cable deflection occurs on a single plane and is partially wound around one or more pulleys having axes of rotation parallel to each other.

[0020] Figure 1 illustrates an example of a first type of transmission mechanism used in a general-purpose robot device A with two parallel rotational degrees of freedom. Specifically, device A is provided with an intermediate link B, which is connected at its ends to a base link C and an end link D by means of first and second rotational torques having rotational axes that are parallel to each other.

[0021] Device A also includes a bidirectional drive with a tension cable, wherein a forward branch E and a return branch F necessary for transmitting torque in both directions are identified, and an idler wheel G is arranged such that its axis of rotation coincides with the axis of the first rotational torque, so as to ensure that the length of the tension cable loop remains constant.

[0022] As can be seen from Figure 1, the winding angle of the forward branch on the idler wheel G is relatively small, and the additional clockwise rotation of the intermediate link B will cause the cable to disengage from the idler wheel G, thus no longer ensuring the constant condition of the cable loop length. To increase the permissible angle range of the intermediate link B, an additional idler wheel can be used, wherein the axis of rotation is locked to the base link C and / or the intermediate link B, and is properly positioned to increase the winding angle of the branch driving the cable.

[0023] Conversely, the second type of transmission device spans joints with two or more degrees of freedom, and generally their axes are not parallel. In this case, the loop made of taut cable is not contained within a single plane.

[0024] For the second type of transmission device, the deflection angle can be defined as the angle between the rotation axis of the input pulley and the rotation axis of the output pulley.

[0025] In the second type of transmission device where the axes of rotation of the input and output pulleys intersect each other, the clearance is defined as the minimum distance between the side surfaces of adjacent pulleys. In practice, this clearance must be greater than zero to prevent the pulleys from contacting and generating interaction forces due to machining tolerances and deformation caused by operating loads.

[0026] Transmission devices with intersecting axes are known, wherein the rotation axes of pulleys intersect at a point called the "transmission device center".

[0027] For example, US4903536A describes a second type of transmission device having a pair of pulleys with intersecting axes of rotation. The transmission device is configured to deflect a taut cable by a 90° deflection angle through a portion of the cable wound between the pulleys.

[0028] Figure 2 illustrates an example of a second type of transmission device H with intersecting axes according to a known solution. This transmission device can be used in a robotic device having a base link I connected to an end link M via an intermediate link L. The intermediate link L is connected to both the base link I and the end link M via a first rotational torque and a second rotational torque, respectively, the latter being arranged such that their axes intersect and are orthogonal to each other. Therefore, the transmission device H includes a first idler pulley N and a second driven pulley O, the first idler pulley N being arranged such that its axis of rotation coincides with the axis of the first rotational torque, and the second driven pulley O being arranged such that its axis of rotation coincides with the axis of the second rotational torque.

[0029] Transmission via pulleys forces the cable path to deviate substantially from a straight line, corresponding to a configuration of minimum potential energy; however, this would cause the cable to slip off the pulley. According to existing technology, slippage from the pulley can be prevented by ensuring the gap has a size smaller than the cable's diameter.

[0030] However, the force exerted on the pulley by the drive cable at the gap may increase its value, causing the cable to slip off the pulley towards the interior of the transmission. This, in turn, leads to a loss of drive functionality and a potential hazard to user safety.

[0031] To mitigate this drawback, the pulley support elements must be significantly reinforced, which increases the overall size and cost of the entire transmission system.

[0032] By using a pulley equipped with a retaining element, such as a groove formed along the side surface of the pulley, the cable is more effectively prevented from sliding from the pulley toward the center of the transmission device. The retaining element is characterized by its geometry to prevent the cable from shifting in a direction parallel to the axis of rotation of the pulley.

[0033] However, in the second type of transmission device manufactured according to the prior art, this solution has some limitations related to the fact that the cable needs free space to be transferred from one pulley to another, whereby the cable cannot be supported by any retaining element. In fact, the retaining element formed on the pulley cannot occupy the space required for the cable to be transferred from one pulley to another, thus making it impossible to mate the pulley with a retaining element that prevents the cable from slipping from the pulley toward the center of the transmission device.

[0034] For example, this solution cannot be used when the deflection angle is equal to or greater than 90 degrees. In fact, as shown in Figure 3, the cable will interfere with these retaining elements as it is passed from one pulley to another.

[0035] To better understand this situation, Figure 3 shows a cross-section on a plane containing the axis of the pulley of the second type of transmission device according to Figure 2 of the prior art. This transmission device has a first pulley P having a vertical axis intersecting the horizontal axis of the second pulley Q. Figure 3 also shows an enlarged view of the transmission device at the area where the cable passes between the two pulleys, where a protrusion is shown in the cross-section of the portion of the cable wound on pulley P, indicated by regions R and U in the figure. Therefore, it is clear that any retaining element present on pulley Q occupying region U will interfere with the cable itself, resulting in premature wear of the cable and retaining material. The same consideration applies to any retaining element formed on pulley P.

[0036] Therefore, since it is impossible to install sufficiently effective retaining elements on the surface of the pulleys to prevent them from slipping off, existing solutions require ensuring a clearance value significantly smaller than the cable diameter under all operating conditions. As mentioned above, maintaining a minimum clearance is particularly difficult due to the potential deformation of the shaft supporting the pulley and / or the clearance of the associated bearings supporting the pulley.

[0037] Finally, regarding the overall dimensions of the transmission device, it should be noted that they are uniquely determined by the radii of pulleys P and Q; the larger the radii of pulleys P and Q, the larger the radius of the transmission device. Summary of the Invention

[0038] In view of the above problems, the present invention makes the transmission device more robust by adding one or more intermediate pulleys, that is, more effective in preventing cable slippage, and at the same time more compact. These advantages are achieved without the need for expensive support elements that insert pulleys.

[0039] Therefore, the present invention relates to a mechanical transmission device for a robot device, which can overcome the disadvantages of the prior art. Attached Figure Description

[0040] Other features and advantages of the invention will become more apparent from the description of a preferred, but not exclusive, embodiment of the mechanical transmission device, which is illustrated in the accompanying drawings by way of illustrative but not limiting example, wherein:

[0041] Figures 1, 2, and 3 are schematic diagrams of some existing solutions;

[0042] Figure 4 This is a schematic diagram of a possible embodiment of the mechanical transmission device according to the present invention;

[0043] Figure 5 It shows Figure 4 The schematic diagram shows that the prior art solutions are represented by superimposed shading lines, indicating that the size of the transmission device covered by the present invention is smaller than that of the prior art transmission devices;

[0044] Figure 6 Another schematic diagram of the mechanical transmission device covered by the present invention is shown, which illustrates how the size of the component is maintained by changing the tilt angle between two consecutive pulleys;

[0045] Figure 7 It is an orthogonal view of the plane defined by the axis of the transmission device covered by the present invention, wherein only one branch of the drive device exists;

[0046] Figure 8 This is a perspective view of an embodiment of the transmission device covered by the present invention, relating to a case with multiple drives having tension cables;

[0047] Figure 9 It is an orthogonal view of a plane defined by the axis of the transmission device covered by the present invention, relating to the case of multiple drives having tension cables;

[0048] Figure 10 This is a perspective view of an exoskeleton equipped with the mechanical transmission device covered by the present invention. Detailed Implementation

[0049] Referring specifically to these figures, reference numeral 1 generally indicates a mechanical transmission device for a robotic device configured for torque / force drive as covered by the present invention.

[0050] Figure 10 A transmission device 1 according to a first embodiment is shown, which is installed inside an anthropomorphic exoskeleton for a user's upper limb, and its purpose is to change the direction of the transmission element 4 by a predetermined deflection angle α. Specifically, the exoskeleton includes a support frame configured to support, for example, a plurality of pulleys oriented parallel to a rotation axis and the transmission device 1 covered by the present invention. In detail, the transmission device 1 is configured to receive at least one transmission element 4 and to steer it between an input direction d1 located on an input plane and an output direction d2 located on an output plane.

[0051] The transmission device 1 includes an input pulley 2 at the input direction d1 and an output pulley 3 at the output direction d2 of the transmission element 4. The input pulley 2 is configured to rotate about a first rotation axis a1 orthogonal to the input direction d1 and is at least partially wound by the transmission element 4. The output pulley is configured to rotate about a second rotation axis a2 orthogonal to the output direction d2 and is at least partially wound by the transmission element 4. Specifically, the second rotation axis a2 is not parallel to the first rotation axis a1.

[0052] Specifically, each pulley 2, 3 has a peripheral surface adapted to be at least partially wound by a transmission element 4, which can be, for example, a cable, belt, or any flexible tie rod. Preferably, the cable is of a metallic type.

[0053] Preferably, pulleys 2 and 3 are arranged such that their axes of rotation a1 and a2 are inclined to each other at a predetermined angle defined as a deflection angle α. In other words, the first axis of rotation a1 and the second axis of rotation a2 form a deflection angle α with a predetermined width between them. Specifically, the planes of rotation of the input pulley 2 and the output pulley 3 are respectively arranged to be substantially parallel to the input plane and the output plane of the transmission device 1.

[0054] Advantageously, the transmission device 1 includes at least one intermediate pulley 5 positioned between the input pulley 2 and the output pulley 3 and configured to rotate about a third rotation axis a3, which lies in one of the planes defined by axes a1 and a2.

[0055] In one or more variations, the third rotation axis a3 lies in one of the planes defined by the first rotation axis a1 and the second rotation axis a2.

[0056] In one or more variations, the third rotation axis a3 lies in one of the planes defined by the first rotation axis a1 or the plane defined by the second rotation axis a2.

[0057] The intermediate pulley 5 is configured to be partially wound by the transmission element 4.

[0058] Advantageously, the intermediate pulley 5 is configured to rotate about its own axis of rotation a3, which is tilted at an angle β relative to one of the two axes of rotation a1 and a2, the width of which is smaller than the width of the deflection angle α. Furthermore, the planes of rotation of pulleys 2, 3, and 5 are not parallel.

[0059] Preferably, the intermediate pulley 5 is oriented such that the angle β of the third rotation axis a3 has a value between 30% and 70% of the deflection angle α, preferably 50%.

[0060] Preferably, the transmission device 1 has intersecting axes, that is, pulleys 2, 3, and 5 are arranged such that their rotation axes a1, a2, and a3 intersect substantially at the intersection point O (the so-called "center of the transmission device").

[0061] Preferably, the intermediate pulley 5 is spaced apart from each adjacent pulley 2, 3 by a gap G, the size of which is smaller than the diameter of the cable 4. Specifically, the term "gap" refers to the minimum distance between the peripheral surfaces of two consecutive pulleys.

[0062] like Figure 7 and Figure 8 As shown, pulleys 2, 3, and 5 can have a basically conical shape, but the possibility of manufacturing a transmission device with cylindrical pulleys cannot be ruled out.

[0063] exist Figure 8 and Figure 9 In some embodiments, pulleys 2, 3, and 5 may have a substantially conical or truncated conical shape. Thus, the gap G between the intermediate pulley 5 and the input pulley 2 and output pulley 3 can be substantially constant along the entire length of the generatrix (generator) of pulleys 2, 3, and 5 located in a plane containing the two axes of the transmission device.

[0064] Preferably, each pulley 2, 3, 5 is wound by only one branch of the drive unit (e.g., the forward branch).

[0065] Preferably, in order to make the transmission device simpler and more compact, each pulley 2, 3, 5 can be wound by both the forward branch and the return branch of the same drive device.

[0066] However, according to alternative embodiments, pulleys 2, 3, and 5 may also have different shapes, for example, substantially disc-shaped or cylindrical. The plane in which the cables of the drive branches on pulleys 2 and 3 lie allows the drive distance of the transmission device 1 to be defined, i.e., the distances L1 and L2 between the plane in which they lie and the center of the transmission device 1 (see...). Figure 7 ).

[0067] Preferably, each pulley 2, 3, 5 may include one or more retaining elements 6 configured to retain the cable 4 at least partially wound on a plane orthogonal to the axis of rotation of the pulley 2, 3, 5.

[0068] exist Figure 9 In the illustrated embodiment, each pulley 2, 3, 5 includes a pair of retaining elements 6 configured to receive two branches 4 (forward branch and return branch) of the drive device.

[0069] like Figure 4 and 9 As shown, the retaining element 6 may include at least one groove 7 formed along the peripheral surface of the pulley and configured to receive and support the drive cable 4. For this purpose, the groove 7 has a profile that is substantially complementary to the cross-sectional shape of the drive cable. However, the possibility of using different retaining elements 6, such as attachments, flanges, or suitable portions formed on the surface to achieve connection through the shape between the cable 4 and the pulley, cannot be ruled out.

[0070] refer to Figure 9 In the example, each groove 7 includes a lower edge 7a and an upper edge 7b respectively arranged at the proximal and distal positions of the center O of the transmission device 1.

[0071] In detail, at least the lower edge 7a of the intermediate pulley 5 is arranged at the corresponding gap to be substantially aligned with the lower edges 7a of the input pulley 2 and the output pulley 3, so that the cable 4 can pass between the pulleys 2, 3 and 5.

[0072] As described above, the groove 7 should be configured to allow the cable 4 to pass from one pulley to another. Specifically, the groove 7 is characterized by its depth P, which is defined as the distance between the bottom of the groove 7 and the projection of its lower edge 7a onto the rotation plane of the respective pulleys 2, 3, 5.

[0073] The groove 7 can be made to allow the cable 4 to pass from one pulley to another. The maximum depth P depends on the tilt angle between the rotation axes of the consecutive pulleys: specifically, the smaller the tilt angle between two consecutive pulleys, the greater the depth P of the groove 7.

[0074] Advantageously, according to the invention, the introduction of one or more intermediate pulleys 5 allows for a reduction in the tilt angle between the rotation axes of the consecutive pulleys, compared to the prior art. Thus, with the same deflection angle, a deeper groove 7 can be formed, making the transmission extremely robust. Figure 6 It is shown that the size of the retaining element decreases as the deflection angle increases. Specifically, it is determined that a decrease in the deflection angle corresponds to an increase in the size of the retaining element 6.

[0075] In a preferred embodiment, the axes of pulleys 2, 3, and 5 are substantially located in the same plane.

[0076] exist Figure 7 , Figure 8 and Figure 9 In one embodiment shown, the transmission device 1 has a deflection angle α that is substantially greater than or equal to 90°.

[0077] In this embodiment, preferably, the intermediate pulley 5 is arranged such that the rotation axis a3 is inclined at an angle β of approximately 45° relative to the rotation axis a2. In different embodiments, the rotation axis a3 is inclined at an angle β relative to one of the two axes, the width of which is always less than the width of the deflection angle α.

[0078] Preferably, each pulley 2, 3, 5 rotates relative to the corresponding shaft by, for example, using one or more bearings.

[0079] In use, the cable 4 is alternately partially wound around the pulleys 2, 3, and 5. For example, the cable 4 can be wound clockwise around the first pulley 2 and the second pulley 3, and counterclockwise around the middle pulley 5.

[0080] In one or more embodiments not shown in the figures, the transmission device 1 may include a plurality of intermediate pulleys 5 located between the input pulley 2 and the output pulley 3. In this case, the intermediate pulleys 5 are arranged consecutively between the input pulley 2 and the output pulley 3. Preferably, each intermediate pulley 5 is arranged such that its own axis of rotation a3 is tilted at an angle relative to the axis of rotation of one of the adjacent pulleys, and this angle is preferably between 30% and 70% of the deflection angle α. For example, if the deflection angle is 90° and a pair of intermediate pulleys 5 is included, the pair of intermediate pulleys 5 may be arranged such that the axis of rotation a3 is tilted at approximately 30° relative to the axis of rotation of one of the adjacent pulleys.

[0081] Figure 10 An anthropomorphic exoskeleton for the upper limb is shown, with details illustrating the portion connected to the shoulder joint. The exoskeleton comprises at least one first limb and one second limb, connected to each other by at least one rotational torque allowing the second limb to perform at least one rotational movement within a predetermined plane of rotation. Figure 10 In the illustrated embodiment, the two limbs are connected by a joint with three rotational degrees of freedom.

[0082] The exoskeleton is also equipped with at least one actuator for moving the joints, which is connected to the joints via one or more transmission elements 4.

[0083] In the part related to the shoulder joint, two transmission devices 1 are manufactured according to the present invention.

[0084] It has been demonstrated, by incorporating the transmission device covered by this invention into an exoskeleton for the upper limb, that the described invention achieves its intended purpose.

[0085] In fact, the transmission device covered by this invention has demonstrated a greater ability to prevent cable slippage than prior art transmission devices, for at least the following reasons:

[0086] The insertion of intermediate pulleys allows for a reduction in pulley diameter, thus enabling greater stability of the clearance values ​​between successive pulleys with similar clearances and deformations in their supporting elements (primarily shafts and bearings). Consequently, the machining tolerances of the transmission components that determine the clearance between their couplings can be less constrained, and greater deformation of the pulley's supporting elements is permitted. This final condition allows for a reduction in the weight of the components themselves, resulting in significant benefits in terms of the overall size and mass of the transmission, while maintaining the same load applied by the drive. This last aspect is advantageous both from the perspective of reducing the total cost of the transmission and from the perspective of reducing the moving mass.

[0087] The reduced angle between the axes of rotation of the continuous pulleys allows for the manufacture of more efficient retaining elements. Specifically, the presence of the intermediate pulley allows for a pulley geometry arrangement that enables the manufacture of deeper grooves, thereby ensuring greater strength of the transmission against cable slippage.

[0088] Furthermore, the transmission device manufactured according to the present invention allows the use of pulleys with a smaller diameter than those in the prior art, while having the same drive distance and deflection angle, thus making it more compact.

[0089] In practice, the minimum values ​​of these distances are determined by the overall dimensions of the joint components, which must be driven by cables and traversed via a transmission mechanism. Such components can be, for example, the links, shafts, and bearings that make up the joint.

[0090] On the other hand, in existing solutions, the radius of the pulley is determined by the deflection angle and the driving distance. Specifically, when the deflection angle is equal to 90°, a pulley with a radius substantially equal to the driving distance is required.

Claims

1. A mechanical transmission device (1) for a robot device, comprising: - Transmission element (4), which is designed to steer between the input direction (d1) and the output direction (d2), - Input pulley (2), the input pulley (2) is configured to rotate about a first rotation axis (a1) orthogonal to the input direction (d1) and is at least partially wound by the transmission element (4), - Output pulley (3), the output pulley (3) is configured to rotate about a second rotation axis (a2) orthogonal to the output direction (d2) and is at least partially wound by the transmission element (4), the second rotation axis (a2) is not parallel to the first rotation axis (a1) and intersects it at a point. The first rotation axis (a1) and the second rotation axis (a2) form a deflection angle (α) with a predetermined width between them. The mechanical transmission device is characterized in that it comprises: At least one intermediate pulley (5) is positioned between the input pulley (2) and the output pulley (3) and configured to rotate about a third rotation axis (a3), the third rotation axis being located in a plane defined by the first rotation axis (a1) and the second rotation axis (a2) and tilted at an angle (β) relative to one of the rotation axes (a1, a2), the width of the angle (β) being smaller than the width of the deflection angle (α), and the at least one intermediate pulley being partially wound around the transmission element (4). Furthermore, the planes of rotation of the pulleys (2, 3, 5) are not parallel. The pulleys (2, 3, 5) are said to have a conical or truncated conical shape. The intermediate pulley (5) is spaced apart from each of the input and output pulleys (2, 3) by a gap (G), the size of which is smaller than the diameter of the transmission element (4).

2. The mechanical transmission device (1) according to claim 1, characterized in that, The rotation axes (a1, a2, a3) of the pulleys (2, 3, 5) intersect at point (O).

3. The mechanical transmission device (1) according to claim 1 or 2, characterized in that, The intermediate pulley (5) is oriented such that the angle (β) of the third rotation axis (a3) ​​has a value between 30% and 70% of the deflection angle (α).

4. The mechanical transmission device (1) according to claim 1 or 2, characterized in that, The deflection angle (α) has a width greater than or equal to 90°.

5. The mechanical transmission device (1) according to claim 1 or 2, characterized in that, Each of the pulleys (2, 3, 5) includes one or more retaining elements (6) configured to retain the transmission element (4) at least partially wound around a plane orthogonal to the axis of rotation (a1, a2, a3) of the pulley (2, 3, 5).

6. The mechanical transmission device (1) according to claim 5, characterized in that, The retaining element (6) includes at least one groove (7) formed along the peripheral surface of each of the pulleys (2, 3, 5).

7. An exoskeleton comprising a mechanical transmission device (1) according to any one of claims 1-6.

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