Joint device for a robot

Abstract

This invention discloses a joint device for a robot. The joint device includes: a first axis; a second axis configured perpendicular to the first axis; a first friction wheel and a second friction wheel rotatably supported at both ends of the first axis; a drive device for rotating each of the first and second friction wheels; and a third friction wheel rotatably supported at an end of the second axis and in contact with the first and second friction wheels, wherein when the first and second friction wheels rotate in the same direction, the third friction wheel rotates in a pitch direction, and when the first and second friction wheels rotate in opposite directions, the third friction wheel rotates in a roll direction.

Description

Technical Field

[0001] This disclosure relates to a joint device for a robot, and more specifically, to a joint device for a robot having bidirectional rotational degrees of freedom using friction wheels. Background Technology

[0002] The joint structures used in robots can be manufactured by sequentially combining multiple rotational axes. Specifically, joints for robots can have serial structures where motors are directly connected to each rotational axis, linkage structures where heavy-duty motors are concentrated at the lower end of a mechanism using wires or links, or interference drive structures where multiple degrees of freedom are connected in parallel.

[0003] Interference drive structures can efficiently distribute weight by placing the drive source near the upper axis. They are simple in structure and can be modularized on an axis-by-axis basis, so they are widely used as joint structures for robots.

[0004] In existing technologies, interference drive structures primarily utilize bevel gears or wire. However, using bevel gears presents challenges due to the need for high-precision machining, resulting in very high production costs and difficulty in supporting axial loads. Furthermore, using wire presents issues such as increased assembly and maintenance complexity and a larger overall structural volume, as the wire requires a specific radius of curvature. Summary of the Invention

[0005] Technical issues

[0006] This disclosure provides a joint device for a robot with bidirectional rotational degrees of freedom using friction wheels.

[0007] Technical solution

[0008] According to one aspect of this disclosure, a joint device for a robot includes: a first axis; a second axis configured to be perpendicular to the first axis; a first friction wheel rotatably supported by a first end of the first axis; a second friction wheel rotatably supported by a second end of the first axis; a drive mechanism configured to rotate each of the first and second friction wheels; and a third friction wheel rotatably supported by a first end of the second axis and in contact with the first and second friction wheels, wherein the third friction wheel rotates in a pitch direction when the first and second friction wheels rotate in the same direction, and rotates in a roll direction when the first and second friction wheels rotate in opposite directions.

[0009] Each of the first, second, and third friction wheels may have a frustoconical shape, and the side surface of the third friction wheel contacts the side surface of each of the first and second friction wheels.

[0010] The third friction wheel can contact the first friction wheel along the first line, and the third friction wheel can contact the second friction wheel along the second line. The first line and the second line can intersect at the intersection point between the central axis of the first shaft and the central axis of the second shaft.

[0011] The joint device may further include: a first pressing member for pressing the first friction wheel toward the third friction wheel; and a second pressing member for pressing the second friction wheel toward the third friction wheel.

[0012] Each of the first pressing member and the second pressing member may include a disc spring mounted on the first shaft.

[0013] The joint device may further include: a first nut, fitted at a first end of the first shaft to support the end of the first pressing member; and a second nut, fitted at a second end of the first shaft to support the end of the second pressing member.

[0014] The joint device may further include: a first bearing inserted between the first shaft and the first friction wheel; and a second bearing inserted between the first shaft and the second friction wheel.

[0015] Each of the first and second bearings can be an angular contact ball bearing.

[0016] The joint device may further include: a first pressing member for pressing the first friction wheel toward the third friction wheel; and a second pressing member for pressing the second friction wheel toward the third friction wheel. The first bearing may include an inner ring in contact with the first pressing member and an outer ring in contact with the first friction wheel, and the second bearing includes an inner ring in contact with the second pressing member and an outer ring in contact with the second friction wheel.

[0017] The first pressing member may have a convex shape toward the inner ring of the first bearing, and the second pressing member may have a convex shape toward the inner ring of the second bearing.

[0018] The drive device may include: a first motor configured to rotate a first friction wheel; and a second motor configured to rotate a second friction wheel.

[0019] The drive unit may further include: a first pulley connected to a first friction wheel; a second pulley connected to a second friction wheel; a first timing belt configured to provide driving force of a first motor to the first pulley; and a second timing belt configured to provide driving force of a second motor to the second pulley.

[0020] The joint device may further include: a fourth friction wheel, rotatably supported by a second end of a second shaft intersecting the first shaft, and the fourth friction wheel being contactable with each of the first and second friction wheels.

[0021] The joint device may further include: a frame that rotatably supports a first end and a second end of the first shaft.

[0022] The first shaft and the second shaft can be integrally formed. When the first friction wheel and the second friction wheel rotate in the same direction, the first shaft, the second shaft and the third friction wheel can rotate around the first shaft. When the first friction wheel and the second friction wheel rotate in different directions, the third friction wheel can rotate around the second shaft. Attached Figure Description

[0023] Figure 1 This is a perspective view of a joint device for a robot according to an embodiment of the present disclosure;

[0024] Figure 2 yes Figure 1 Exploded perspective view of a joint device used in a robot;

[0025] Figure 3 It is an exploded perspective view of the components assembled on the first axis;

[0026] Figure 4 It is along Figure 1 A cross-sectional view of the joint device used in the robot, taken from line AA;

[0027] Figure 5 This is a view showing the state of the third friction wheel rotating in the rolling direction; and

[0028] Figure 6 This is a view showing the state of the third friction wheel rotating in the pitch direction. Detailed Implementation

[0029] It should be understood that the embodiments described below are provided illustratively to aid in understanding this disclosure, and that this disclosure may be modified in various ways, differing from the embodiments described herein. However, in the following description of this disclosure, detailed descriptions and specific illustrations of relevant known functions or components will be omitted if it is determined that such detailed descriptions would unnecessarily obscure the gist of this disclosure. Furthermore, the drawings are not necessarily shown to scale, but the dimensions of some components may be enlarged to aid in understanding this disclosure.

[0030] The terminology used in the specification and claims is general terminology chosen with regard to the functionality of this disclosure. However, these terms may vary depending on the intent of those skilled in the art, legal or technical interpretation, the emergence of new technologies, etc. Furthermore, some terms may be chosen arbitrarily by the applicant. These terms are to be interpreted as meaning as defined in the specification, and unless specifically defined, may be interpreted based on the entire specification and common technical knowledge in the art.

[0031] In the specification, the use of terms such as "has", "may have", "includes", "may include" indicates the presence of the stated features (e.g., numbers, functions, operations, or components such as parts), but does not exclude the presence of additional features.

[0032] Furthermore, the specifications describe the components required to describe each embodiment of this disclosure, but the components are not necessarily limited thereto. Therefore, some components may be changed or omitted, and other components may be added. Additionally, the components may be arranged in a distributed manner in different independent devices.

[0033] Furthermore, embodiments of this disclosure will now be described in detail with reference to the accompanying drawings and the descriptions therein; however, this disclosure is not limited to or constrained by these embodiments.

[0034] The present disclosure will be described in more detail below with reference to the accompanying drawings.

[0035] Figure 1 This is a perspective view of a joint device for a robot according to an embodiment of the present disclosure. Figure 2 yes Figure 1 An exploded perspective view of a joint device used in a robot. Figure 3 It is an exploded perspective view of the components assembled on the first axis. Figure 4 It is along Figure 1 A cross-sectional view of the joint device used in the robot, taken from line AA.

[0036] Reference Figures 1 to 4 According to embodiments of the present disclosure, a joint device 1 for a robot may include a first axis 100, a second axis 200, a first friction wheel 300, a second friction wheel 400, a third friction wheel 500, and a drive device 600.

[0037] The first shaft 100 can rotatably support the first friction wheel 300 and the second friction wheel 400 at opposite ends of the first shaft 100, respectively. Therefore, the first friction wheel 300 and the second friction wheel 400 can rotate about the first shaft 100 with the same axis of rotation.

[0038] The first shaft 100 can be arranged parallel to the Y-axis. That is, the rotation axes of the first friction wheel 300 and the second friction wheel 400 can be parallel to the Y-axis. The first shaft 100 can have a cylindrical shape.

[0039] The second shaft 200 can rotatably support the third friction wheel 500 at one end of the second shaft 200. Therefore, the third friction wheel 500 can rotate about the second shaft 200.

[0040] The second shaft 200 may be arranged perpendicular to the first shaft 100. For example, the second shaft 200 may be arranged parallel to the X-axis. That is, the rotation axis of the third friction wheel 500 may be parallel to the X-axis. Similar to the first shaft 100, the second shaft 200 may have a cylindrical shape.

[0041] The second shaft 200 may be integrally formed with the first shaft 100. Specifically, the first shaft 100 and the second shaft 200 may be formed together as an integral shaft with a "T" or "X" shape to rotatably support the first friction wheel 300, the second friction wheel 400, and the third friction wheel 500. However, the first shaft 100 and the second shaft 200 may be formed separately, rather than integrally.

[0042] The first friction wheel 300 and the second friction wheel 400 can rotate while they are mounted on the first shaft 100. The first friction wheel 300 and the second friction wheel 400 can have a frustoconical shape.

[0043] The first friction wheel 300 and the second friction wheel 400 may be arranged symmetrically with respect to the second axis 200. Specifically, the first friction wheel 300 and the second friction wheel 400 may be configured to have a cross-section that decreases as they approach the second axis 200.

[0044] The third friction wheel 500 can rotate while it is mounted on the second shaft 200. The third friction wheel 500 may have a frustoconical shape. Specifically, the third friction wheel 500 may be configured to have a cross-section that decreases as it approaches the first shaft 100.

[0045] The third friction wheel 500 can simultaneously contact the first friction wheel 300 and the second friction wheel 400 at different positions. Therefore, due to the frictional force generated in the parts that contact the first friction wheel 300 and the second friction wheel 400, the third friction wheel 500 can be passively rotated by the rotational force transmitted from the first friction wheel 300 and the second friction wheel 400.

[0046] The first friction wheel 300, the second friction wheel 400, and the third friction wheel 500 can be made of aluminum, but their materials are not limited to this. This allows for a lighter joint device 1 for the robot and a reduction in the overall size of the joint device 1 for the robot.

[0047] Furthermore, the first friction wheel 300, the second friction wheel 400, and the third friction wheel 500 can rotate smoothly without noise because they are in continuous contact with each other and no teeth are formed on their surfaces, which does not cause backlash. In addition, the first friction wheel 300, the second friction wheel 400, and the third friction wheel 500 can be manufactured at a lower cost than gears and require fewer parts than wires, thereby reducing maintenance costs.

[0048] Specifically, the side surface of the third friction wheel 500 can simultaneously contact the corresponding side surfaces of the first friction wheel 300 and the second friction wheel 400. Specifically, the third friction wheel 500 can contact the first friction wheel 300 along a first line L1 and the second friction wheel 400 along a second line L2. Furthermore, the first line L1 and the second line L2 intersect at the intersection point between the central axis C1 of the first shaft 100 and the central axis C2 of the second shaft 200.

[0049] When the first friction wheel 300 and the second friction wheel 400 rotate in the same direction, the third friction wheel 500 can rotate in the pitch direction because the third friction wheel 500 receives frictional forces from the first friction wheel 300 and the second friction wheel 400 in the same direction. The pitch direction can be the direction of rotation relative to a rotation axis parallel to the Y-axis.

[0050] When the first friction wheel 300 and the second friction wheel 400 rotate in opposite directions, the third friction wheel 500 can rotate in the tumbling direction because the third friction wheel 500 receives frictional forces from the first friction wheel 300 and the second friction wheel 400 in different directions. The tumbling direction can be the direction of rotation relative to a rotation axis parallel to the X-axis.

[0051] In other words, the third friction wheel 500 can be passively rotated by the rotational force transmitted from the first friction wheel 300 and the second friction wheel 400, and can have two rotational degrees of freedom depending on the rotational direction of the first friction wheel 300 and the second friction wheel 400. (Refer to...) Figure 5 and Figure 6 The process of the third friction wheel 500 rotating based on two rotational degrees of freedom is described in detail.

[0052] The connecting plate 510 may be disposed on the front surface of the third friction wheel 500. The connecting plate 510 may have a disc shape and may be coupled to the third friction wheel 500 to rotate integrally with the third friction wheel 500.

[0053] Any of the various robot structures can be connected to the connecting plate 510. For example, any of the various parts of the robot, such as the arm, hand, foot, leg, and head, can be connected to the connecting plate 510 to rotate together with the third friction wheel 500.

[0054] Bearings 501 and 502 may be disposed between the third friction wheel 500 and the second shaft 200. Although two bearings 501 and 502 are shown, the number of bearings is not limited thereto.

[0055] Bearings 501 and 502 may be angular contact ball bearings, but the bearing type is not limited to this. Bearings 501 and 502 enable the third friction wheel 500 to rotate easily relative to the stationary second shaft 200.

[0056] The drive unit 600 is rotatable of each of the first friction wheel 300 and the second friction wheel 400. For example, the drive unit 600 may include a first motor 610 and a second motor 620. The first motor 610 is rotatable of the first friction wheel 300, and the second motor 620 is rotatable of the second friction wheel 400.

[0057] The first motor 610 and the second motor 620 can be supported by the frame 700 and can be positioned behind the first friction wheel 300, the second friction wheel 400 and the third friction wheel 500.

[0058] For example, the drive unit 600 may also include a first pulley 630, a second pulley 640, a first synchronous belt 650, and a second synchronous belt 660.

[0059] The first pulley 630 and the second pulley 640 can be mounted on the first shaft 100 to rotate about the first shaft 100. The first pulley 630 can be disposed on the rear surface of the first friction wheel 300, and the second pulley 640 can be disposed on the rear surface of the second friction wheel 400.

[0060] A first synchronous belt 650 may partially surround the circumference of a first pulley 630 to provide the driving force of a first motor 610 to the first pulley 630. Furthermore, the first pulley 630 may be coupled to a first friction wheel 300 to rotate integrally with the first friction wheel 300.

[0061] Similarly, the second synchronous belt 660 may partially surround the circumference of the second pulley 640 to provide the driving force of the second motor 620 to the second pulley 640, and the second pulley 640 may be coupled to the second friction wheel 400 to rotate integrally with the second friction wheel 400.

[0062] However, the above-described structure of the drive device 600 is merely an example, and the structure of the drive device 600 is not limited thereto. The drive device 600 can be implemented in any structure, as long as it is capable of rotating the first friction wheel 300 and the second friction wheel 400.

[0063] The joint device 1 for the robot may further include a first pressing member 310 and a second pressing member 410. The first pressing member 310 can press the first friction wheel 300 toward the third friction wheel 500. The second pressing member 410 can press the second friction wheel 400 toward the third friction wheel 500.

[0064] As a result, the first pressing member 310 and the second pressing member 410 provide a preload to the first friction wheel 300 and the second friction wheel 400, thereby providing sufficient friction to the third friction wheel 500. Therefore, the rotational force of the first friction wheel 300 and the second friction wheel 400 can be easily transmitted to the third friction wheel 500.

[0065] For example, the first pressing member 310 and the second pressing member 410 can be disc springs mounted on the first shaft 100. Even with small displacements, the disc springs can apply pressure to the first friction wheel 300 and the second friction wheel 400 with large elastic forces. Therefore, the rotational force of the first friction wheel 300 and the second friction wheel 400 can be transmitted more effectively to the third friction wheel 500, thereby allowing the joint device 1 used in the robot to be manufactured in a smaller size.

[0066] The joint device 1 for the robot may further include a first nut 320 and a second nut 420. The first nut 320 may be fitted to one end of the first shaft 100 to support one end of the first pressing member 310. The second nut 420 may be fitted to the other end of the first shaft 100 to support one end of the second pressing member 410.

[0067] For example, the first nut 320 and the second nut 420 can be secured by threads formed on the side surface of the first shaft 100. The preload of the first pressing member 310 and the second pressing member 410 can be adjusted according to the degree to which the first nut 320 and the second nut 420 are tightened on the first shaft 100.

[0068] The joint device 1 for the robot may further include a first bearing 330 and a second bearing 430. The first bearing 330 may be disposed between the first shaft 100 and the first friction wheel 300. The second bearing 430 may be disposed between the first shaft 100 and the second friction wheel 400.

[0069] The first bearing 330 and the second bearing 430 enable the first friction wheel 300 and the second friction wheel 400 to rotate easily relative to the stationary first shaft 100.

[0070] The first bearing 330 and the second bearing 430 can be angular contact ball bearings, each capable of transmitting axial loads more easily. Because the straight line connecting the balls to the contact points between the inner and outer rings forms a predetermined angle relative to the radial direction, the angular contact ball bearings can easily transmit loads both axially and radially.

[0071] Therefore, the first bearing 330 makes it easier to transmit the elastic force from the first pressing member 310 to the first friction wheel 300. Similarly, the second bearing 430 makes it easier to transmit the elastic force from the second pressing member 410 to the second friction wheel 400.

[0072] Specifically, the inner ring 331 and outer ring 333 of the first bearing 330 can respectively contact the first pressing member 310 and the first friction wheel 300. Therefore, the elastic force of the first pressing member 310 can be transmitted sequentially through the inner ring 331, the ball 332 and the outer ring 333 of the first bearing 330, and finally transmitted to the first friction wheel 300.

[0073] Similarly, the inner ring 431 and outer ring 433 of the second bearing 430 can respectively contact the second pressing member 410 and the second friction wheel 400. Therefore, the elastic force of the second pressing member 410 can be transmitted sequentially through the inner ring 431, the ball 432 and the outer ring 433 of the second bearing 430, and finally transmitted to the second friction wheel 400.

[0074] In other words, the first pressing member 310 and the second pressing member 410 can press the inner ring 331 of the first bearing 330 and the inner ring 431 of the second bearing 430, which are stationary together with the first shaft 100. Therefore, since the object pressed by the first pressing member 310 and the second pressing member 410 is stationary, wear caused by friction can be minimized.

[0075] Furthermore, the first pressing member 310 and the second pressing member 410 may have convex shapes facing the inner ring 331 of the first bearing 330 and the inner ring 431 of the second bearing 430. For example, the first pressing member 310 and the second pressing member 410 may be conical disc springs, each conical disc spring having an opening in its central portion.

[0076] Therefore, the shapes of the first pressing member 310 and the second pressing member 410 make it possible to press only the stationary inner rings 331 and 431 without pressing the rotating outer rings 333 and 433.

[0077] The frame 700 may be positioned at the rear of the joint device 1 for the robot to support the first axis 100 and the drive device 600. However, this is just an example, and the shape and arrangement of the frame 700 are not limited thereto.

[0078] Furthermore, the joint device 1 for the robot may also include a fourth friction wheel 800. The fourth friction wheel 800 may be rotatably supported at the other end of the second axis 200 that intersects with the first axis 100.

[0079] The fourth friction wheel 800 may contact each of the first friction wheel 300 and the second friction wheel 400. For example, the fourth friction wheel 800 may have a frustoconical shape, and the side surface of the fourth friction wheel 800 may simultaneously contact the side surfaces of the first friction wheel 300 and the second friction wheel 400 at different locations.

[0080] The fourth friction wheel 800 may have a shape symmetrical with respect to the first shaft 100 and the third friction wheel 500. Specifically, the fourth friction wheel 800 may have a truncated cone shape with a cross-section that gradually decreases toward the first shaft 100.

[0081] The fourth friction wheel 800 can face the third friction wheel 500 and can rotate in the opposite direction to the third friction wheel 500.

[0082] Furthermore, the fourth friction wheel 800 can support the area of ​​each of the first pressing member 310 and the second pressing member 410 on its rear side. Therefore, due to the elasticity of the first pressing member 310 and the second pressing member 410, the fourth friction wheel 800 can prevent the first friction wheel 300 and the second friction wheel 400 from deforming or from misaligning the rotation axes of the first friction wheel 300 and the second friction wheel 400.

[0083] Figure 5 This is a view showing the third friction wheel rotating in the rolling direction. (Refer to...) Figure 5 The first friction wheel 300 and the second friction wheel 400 can rotate in different directions.

[0084] For example, when the first friction wheel 300 rotates in the R1 direction and the second friction wheel 400 rotates in the R2 direction, the third friction wheel 500 rotates about the second axis 200 in the R4 direction. At this time, in contrast to the third friction wheel 500, the fourth friction wheel 800 can rotate about the second axis 200 in the R3 direction.

[0085] Conversely, when the first friction wheel 300 rotates in the R2 direction and the second friction wheel 400 rotates in the R1 direction, the third friction wheel 500 can rotate about the second axis 200 in the R3 direction. At this time, opposite to the third friction wheel 500, the fourth friction wheel 800 can rotate about the second axis 200 in the R4 direction.

[0086] In other words, when the first friction wheel 300 and the second friction wheel 400 rotate in different directions, the third friction wheel 500 can rotate around the second axis 200 in the rolling direction.

[0087] Figure 6 This is a view showing the third friction wheel rotating in the pitch direction. (Refer to...) Figure 6 The first friction wheel 300 and the second friction wheel 400 can rotate in the same direction.

[0088] For example, when the first friction wheel 300 and the second friction wheel 400 are both rotating in the R1 direction, the third friction wheel 500 can rotate in the R1 direction around the first axis 100. At this time, in contrast to the third friction wheel 500, the fourth friction wheel 800 can rotate in the R2 direction around the first axis 100.

[0089] Conversely, when the first friction wheel 300 and the second friction wheel 400 both rotate in the R2 direction, the third friction wheel 500 can also rotate in the R2 direction around the first axis 100. At this time, opposite to the third friction wheel 500, the fourth friction wheel 800 can rotate in the R1 direction around the first axis 100.

[0090] Specifically, the frame 700 can rotatably support both ends of the first shaft 100, and the first shaft 100 and the second shaft 200 can be integrally formed. In this case, when the first friction wheel 300 and the second friction wheel 400 rotate in the same direction, the first shaft 100, the second shaft 200 and the third friction wheel 500 can rotate around the first shaft 100 in the R1 or R2 direction.

[0091] In other words, when the first friction wheel 300 and the second friction wheel 400 rotate in the same direction, the third friction wheel 500 can rotate around the first axis 100 in the pitch direction.

[0092] Therefore, the third friction wheel 500 can be passively rotated with two rotational degrees of freedom according to the rotational directions of the first friction wheel 300 and the second friction wheel 400.

[0093] Although embodiments of this disclosure have been shown and described, this disclosure is not limited to the specific embodiments described above, and various modifications can be made by those skilled in the art to which this disclosure pertains without departing from the spirit of this disclosure as claimed in the appended claims. Such modifications fall within the scope of the claims.

Claims

1. A joint device for a robot, the joint device comprising: First axis; The second axis is set to be perpendicular to the first axis; The first friction wheel is rotatably supported by the first end of the first shaft; The second friction wheel is rotatably supported by the second end of the first shaft; The drive mechanism is configured to rotate each of the first friction wheel and the second friction wheel; as well as The third friction wheel is rotatably supported by the first end of the second shaft and is in contact with the first and second friction wheels. When the first and second friction wheels rotate in the same direction, the third friction wheel rotates in the pitch direction, and When the first and second friction wheels rotate in different directions, the third friction wheel rotates in the rolling direction. The joint device further includes: The first pressing component presses the first friction wheel toward the third friction wheel; The second pressing component presses the second friction wheel toward the third friction wheel; A first angular contact ball bearing is inserted between the first shaft and the first friction wheel; and The second angular contact ball bearing is inserted between the first shaft and the second friction wheel. The first angular contact ball bearing includes an inner ring that contacts the first pressing member and an outer ring that contacts the first friction wheel. The second angular contact ball bearing includes an inner ring that contacts the second pressing member and an outer ring that contacts the second friction wheel.

2. The joint device according to claim 1, wherein, Each of the first, second, and third friction wheels has a truncated conical shape, and The side surface of the third friction wheel contacts the side surface of each of the first and second friction wheels.

3. The joint device according to claim 2, wherein, The third friction wheel contacts the first friction wheel along the first line. The third friction wheel contacts the second friction wheel along the second line, and The first line and the second line intersect at the intersection point between the central axis of the first axis and the central axis of the second axis.

4. The joint device according to claim 1, wherein, Each of the first pressing member and the second pressing member includes a disc spring mounted on the first shaft.

5. The joint device according to claim 1, further comprising: The first nut is fitted at the first end of the first shaft to support the end of the first pressing member; as well as The second nut is fitted at the second end of the first shaft to support the end of the second pressing member.

6. The joint device according to claim 1, wherein, The first pressing member has a convex shape toward the inner ring of the first angular contact ball bearing, and the second pressing member has a convex shape toward the inner ring of the second angular contact ball bearing.

7. The joint device according to claim 1, wherein, The driving device includes: A first motor is configured to rotate a first friction wheel; and The second motor is configured to rotate the second friction wheel.

8. The joint device according to claim 7, wherein, The drive device further includes: The first pulley is connected to the first friction wheel; The second pulley is connected to the second friction wheel; A first synchronous belt is configured to provide driving force from a first motor to a first pulley; and The second synchronous belt is configured to provide the second motor with driving force to the second pulley.

9. The joint device according to claim 1, further comprising: The fourth friction wheel is rotatably supported by the second end of the second shaft, which intersects with the first shaft. The fourth friction wheel contacts each of the first and second friction wheels.

10. The joint device according to claim 1, further comprising: The frame rotatably supports the first and second ends of the first shaft.

11. The joint device according to claim 10, wherein, The first and second axes are formed integrally. When the first friction wheel and the second friction wheel rotate in the same direction, the first shaft, the second shaft, and the third friction wheel rotate around the first shaft, and When the first friction wheel and the second friction wheel rotate in different directions, the third friction wheel rotates around the second axis.

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