Four-degree-of-freedom parallel robot

Abstract

The invention discloses a four-degree-of-freedom parallel robot which comprises a fixed rack, a first branch chain, a second branch chain and a double-acting platform assembly, the first branch chain and the second branch chain are connected with the fixed rack and the double-acting platform assembly respectively to form a space closed-loop structure, and through linear driving movement of all modules in the first branch chain and the second branch chain, the four-degree-of-freedom parallel robot is formed. And four-degree-of-freedom movement of three-degree-of-freedom translation and rotation around a vertical shaft of the double-acting platform assembly can be realized. The translation and rotation working space of the parallel robot can be expanded, the positioning precision is improved, the tail end movable platform is self-adaptively assembled, and the internal stress of the connecting rod is eliminated.

Description

Technical Field

[0001] The present invention belongs to the technical field of robots, and particularly relates to a four-degree-of-freedom parallel robot. Background Art

[0002] SCARA robots are four-degree-of-freedom robots, which include four degrees of freedom of translation in three directions and rotation about the Z-axis. They are widely used in automation fields such as handling and palletizing. However, due to their serial structure, they have defects such as insufficient load-bearing capacity, poor rigidity, low precision, and relatively slow speed. Parallel robots are more suitable for applications with high speed, high precision, and high load-bearing due to their structural characteristics. The most widely used Delta parallel robot at present realizes three translational degrees of freedom of the moving platform through three kinematic chains. In actual applications, since the direction of the material generally needs to be adjusted, a rotating axis is generally added to the moving platform of the Delta robot to adjust the direction of the material.

[0003] Patent CN201610303555.2 proposed a new type of four-degree-of-freedom parallel mechanism, which can realize the functions of translation in three directions of the moving platform and rotation about the Z-axis through two kinematic chains. However, there are problems such as a small and fixed translational workspace and a maximum rotation angle about the Z-axis of only ±90°. And due to the cumulative error of the connecting rods, it is difficult to assemble the end of the moving platform, and internal stresses are generated inside the connecting rods. Patent CN202121911821.2 addressed some of the above problems by designing a mechanism based on an offset parallelogram mechanism to extrapolate the local singular positions of the mechanism, thereby expanding the translational workspace of the parallel mechanism to a certain extent, but the remaining problems still exist.

[0004] Therefore, it is necessary to improve the problems existing in the above-mentioned existing four-degree-of-freedom robots, such as small workspace, low positioning accuracy, difficulty in assembling the end of the platform, and generation of internal stresses inside the connecting rods. Summary of the Invention

[0005] The main object of the present invention is to provide a four-degree-of-freedom parallel robot that can expand the translational and rotational workspaces, improve the positioning accuracy, and enable the end moving platform to be adaptively assembled and eliminate the internal stresses of the connecting rods.

[0006] To achieve the foregoing invention object, the technical solution adopted by the present invention includes: a four-degree-of-freedom parallel robot, comprising a fixed frame, a first branch chain, a second branch chain and a double-acting platform assembly. The first branch chain and the second branch chain are both fixed on the fixed frame, and are respectively located on both sides of the double-acting platform assembly in a first direction. Both of them include a first module, a second module, a third module and a parallelogram mechanism. The first module is fixed on the fixed frame and extends along the first direction. The second module is slidably connected to the first module and extends along a second direction perpendicular to the first direction. The third module is slidably connected to the second module and extends along a third direction perpendicular to both the first direction and the second direction. One end of the parallelogram mechanism of the first branch chain is slidably connected to its third module, and the other end is connected to the double-acting platform assembly. One end of the parallelogram mechanism of the second branch chain is slidably connected to its third module, and the other end is connected to the double-acting platform assembly. During operation, when the parallelogram mechanisms of the first branch chain and the second branch chain move synchronously and in the same direction along their respective third modules, the double-acting platform assembly moves translationally along the third direction. When they move synchronously and in the opposite direction, the double-acting platform assembly moves translationally along the first direction. When the third modules of the first branch chain and the second branch chain move synchronously and in the same direction along their respective second modules, the double-acting platform assembly moves translationally along the second direction. When they move synchronously and in the opposite direction, the double-acting platform assembly rotates around the third direction.

[0007] In a preferred embodiment, the first branch chain and the second branch chain share the first module.

[0008] In a preferred embodiment, the parallelogram mechanism of the first branch chain is rigidly connected to the double-acting platform assembly, and the parallelogram mechanism of the second branch chain is floatingly connected to the double-acting platform assembly.

[0009] In a preferred embodiment, the parallel robot further includes a spherical plain bearing assembly. The parallelogram mechanism of the second branch chain is floatingly connected to the double-acting platform assembly through the spherical plain bearing assembly.

[0010] In a preferred embodiment, the parallelogram mechanism includes a first connecting rod, a second connecting rod, a first support and a second support. Both ends of the first connecting rod are respectively connected to the first support and the second support. Both ends of the second connecting rod are also respectively connected to the first support and the second support. And the end of the first connecting rod connected to the first support and the end of the second connecting rod connected to the first support are offset in both the first direction and the third direction. The end of the first connecting rod connected to the second support and the end of the second connecting rod connected to the second support are also offset in both the first direction and the third direction.

[0011] In a preferred embodiment, the double-acting platform assembly includes a first connecting member, a second connecting member, a first moving platform, a first gear, a second gear, a third gear, and a second moving platform. The first connecting member and the second connecting member are respectively connected to the parallelogram mechanisms of the first branch chain and the second branch chain. The first connecting member is rotationally connected to the first moving platform in the third direction through a first rotating shaft, and the second connecting member is rotationally connected to the first moving platform in the third direction through a second rotating shaft. The second moving platform is rotationally connected to a third rotating shaft disposed on the first moving platform. The first gear is fixedly connected to the first rotating shaft, and the third gear is fixedly connected to the third rotating shaft and meshes with both the first gear and the second gear. By adjusting the transmission speed ratio of the first gear and the third gear, the second moving platform can obtain a larger rotation angle than the first moving platform.

[0012] In a preferred embodiment, the maximum rotation angle of the first moving platform is ±90°, and the maximum rotation angle of the second moving platform is ±180°.

[0013] In a preferred embodiment, the second gear, the first gear, and the third gear together form a symmetric transmission structure. The second gear is a backlash-eliminating gear and is rotationally connected to the second rotating shaft through an elastic element.

[0014] In a preferred embodiment, the double-acting platform assembly further includes a connecting plate, which is located above the first moving platform and is connected to both the first rotating shaft and the second rotating shaft. [[ID=—11]]

[0015] In a preferred embodiment, the articulated bearing assembly includes an outer bearing ring and an inner bearing ring. The inner surface of the outer bearing ring and the outer surface of the inner bearing ring are connected through a spherical surface to form a spherical pair. The inner bearing ring is connected to the double-acting platform assembly, and the outer bearing ring is connected to the parallelogram mechanism of the second branch chain.

[0016] Compared with the prior art, the beneficial effects of the present invention are at least as follows: 1. By introducing the first module, the present invention enables the distance between the two branch chains of the parallel mechanism to be adjustable, thereby making the working space height of the parallel mechanism highly flexible and variable on the basis of increasing the working space in the first direction, and can adapt to various different requirements.

[0017] 2. The present invention adopts a double-acting platform design. By adjusting the planetary transmission gear speed ratio, the rotation angle of the end of the parallel mechanism can be greatly expanded, without being limited by the original maximum rotation angle of ±90°.

[0018] 3. By adding a second backlash-eliminating gear, the present invention can eliminate the clearance of the planetary gear transmission, improve the positioning accuracy of the parallel mechanism, and at the same time form a symmetric transmission structure together with the first fixed gear and the third planetary gear, which is beneficial to force balance.

[0019] 4. The moving platform component of the present invention is rigidly connected to the first branch chain and is floatingly connected to the second branch chain through a joint bearing component, so that the double moving platform component can achieve adaptive assembly and eliminate the internal stress of the connecting rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 is a three-dimensional view of the four-degree-of-freedom parallel robot according to the embodiment of the present invention; Figure 2 is a front view of the four-degree-of-freedom parallel robot according to the embodiment of the present invention; Figure 3 is a three-dimensional view of the double moving platform component according to the embodiment of the present invention; Figure 4 is a sectional view of the double moving platform component according to the embodiment of the present invention; Figure 5 is a bottom view of the double moving platform component with the cover removed according to the embodiment of the present invention; Figure 6 is Figure 5 the view after rotating 45°; Figure 7 is Figure 2 the enlarged view of part I in; Figure 8 is a top view of the parallel robot after the double moving platform component rotates 45°; Figure 9 is Figure 8 the corresponding three-dimensional view; Reference numerals: 100, the first branch chain; 1001, the first module; 1002, the second module; 1003, the third module; 1004, the parallelogram mechanism; 10041, the first connecting rod; 10042, the second connecting rod; 10043, the first support; 10044, the second support; 200, the second branch chain; 300. Double-acting platform assembly; 3001. Connecting plate; 3002. First moving platform; 3003. Second moving platform; 3004. First connecting member; 3005. Second connecting member; 3006. First rotating shaft; 3007. Second rotating shaft; 3008. Third rotating shaft; 3009. First gear; 30010. Third gear; 30011. Second gear; 30012. Elastic element; 400. Fixed frame; 4001. First bracket; 4002. Second bracket; 500. Spherical plain bearing assembly; 5001. Bearing outer ring; 5002. Bearing inner ring; 5003. Bearing gland; 5004. Shaft end gland. Detailed implementation mode

[0022] The present invention will be more fully understood from the following detailed implementation modes, which should be read in conjunction with the accompanying drawings. Specific embodiments of the present invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the present invention, and the present invention can be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but merely as a basis for the claims and as a representative basis for teaching those skilled in the art to employ the present invention in any suitable detailed embodiment in different ways.

[0023] Combined with Figure 1 And Figure 2 As shown, a four-degree-of-freedom parallel robot disclosed in an embodiment of the present invention mainly includes a fixed frame 400, a first branch chain 100, a second branch chain 200, a double-acting platform assembly 300, and a spherical plain bearing assembly 500. The first branch chain 100 and the second branch chain 200 are respectively connected to the fixed frame 400 and the double-acting platform assembly 300 to form a spatial closed-loop structure.

[0024] As Figure 1 Shown, the fixed frame 400 mainly includes a first bracket 4001 and a second bracket 4002. The first bracket 4001 and the second bracket 4002 are arranged parallel to each other front and back in the second direction (i.e., the Y direction), and both extend along the first direction (i.e., the X direction).

[0025] Both the first branch chain 100 and the second branch chain 200 are fixed to the fixed frame 400, and they are respectively located on both sides of the double-acting platform assembly 300 in the first direction, that is, on the left and right sides of the double-acting platform assembly 300 respectively. As Figure 1As shown, the first branch chain 100 mainly includes a first module 1001, a second module 1002, a third module 1003, and a parallelogram mechanism 1004. Among them, the first module 1001, the second module 1002, and the third module 1003 are perpendicular to each other and arranged in a rectangular coordinate system. Specifically, in this embodiment, corresponding to the number of brackets of the fixed frame, two sets of the first module 1001 are also arranged front and back. One first module 1001 is fixed on each bracket of the fixed frame 400. That is, the two sets of the first module 1001 are also arranged parallel to each other front and back in the second direction (i.e., the Y direction), and both extend along the first direction (i.e., the X direction) and are fixed at both left and right ends to the corresponding brackets. The second module 1002 extends along the second direction (i.e., the Y direction) perpendicular to the first direction, and its two ends are respectively slidably connected to the corresponding ends of the first module 1001, and can reciprocate along the first module 1001 in the first direction. The third module 1003 extends along the third direction (i.e., the Z direction) perpendicular to both the first direction and the second direction, and is slidably connected to the second module 1002, and can reciprocate along the second module 1002 in the second direction. One end of the parallelogram mechanism 1004 is slidably connected to the third module 1003 and can reciprocate along the third module 1003 in the third direction, and the other end is connected to the double-acting platform assembly 300. The above-mentioned first module 1001, second module 1002, and third module 1003 are all linear drive components, and when implemented, various driving methods such as linear motors, gear racks, lead screws, and synchronous belts can be used for driving and transmission.

[0026] Combined Figure 1 and as Figure 2 As shown, in this embodiment, the parallelogram mechanism 1004 specifically includes a first connecting rod 10041, a second connecting rod 10042, a first support 10043, and a second support 10044. Among them, the first support 10043 is slidably connected to the third module 1003, the second support 10044 is connected to the double-acting platform assembly 300, both ends of the first connecting rod 10041 respectively form two rotating pairs with the first support 10043 and the second support 10044, and both ends of the second connecting rod 10042 also respectively form two rotating pairs with the first support 10043 and the second support 10044. And the end of the first connecting rod 10041 connected to the first support 10043 and the end of the second connecting rod 10042 connected to the first support 10043 are offset in both the first direction and the third direction. The end of the first connecting rod 10041 connected to the second support 10044 and the end of the second connecting rod 10042 connected to the second support 10044 are also offset in both the first direction and the third direction, so as to expand the rotation angle of a part of the parallelogram mechanism 1004, thereby expanding the working space of the parallel robot moving in the first direction.

[0027] The structure of the second branch chain 200 is exactly the same as that of the first branch chain 100, that is, it also includes a first module 1001, a second module 1002, a third module 1003 and a parallelogram mechanism 1004. The parallelogram mechanism 1004 also specifically includes a first connecting rod 10041, a second connecting rod 10042, a first support 10043 and a second support 10044. Preferably, in this embodiment, the first branch chain 100 and the second branch chain 200 share the first module 1001, so as to make the structure compact and save costs. The description of other structures of the second branch chain 200 can refer to the description of the first branch chain 100 above, and will not be elaborated here.

[0028] Combined Figure 3 with Figure 4 As shown, the double-acting platform assembly 300 is located between the first branch chain 100 and the second branch chain 200, and mainly includes a first connecting member 3004, a second connecting member 3005, a first moving platform 3002, a first gear 3009, a second gear 30011, a third gear 30010 and a second moving platform 3003. Among them, the first moving platform 3002 respectively forms a rotating pair with the first connecting member 3004 and the second connecting member 3005 to form a first rotating shaft 3006 and a second rotating shaft 3007. Specifically, in this embodiment, both the first rotating shaft 3006 and the second rotating shaft 3007 are vertically arranged in the third direction, and the first connecting member 3004 is rotationally connected to the first rotating shaft 3006 and connected to the second support 10044 of the first branch chain 100, and the second connecting member 3005 is rotationally connected to the second rotating shaft 3007 and connected to the second support 10044 of the second branch chain 200 through a joint bearing assembly 500. A third rotating shaft 3008 is provided at the center of the first moving platform 3002, and the second moving platform 3003 is located below the first moving platform 3002 and is coaxially and rotationally connected to the third rotating shaft 3008.

[0029] In this embodiment, the first moving platform 3002 of the double-acting platform assembly 300 is a hollow structure inside, and the above-mentioned first gear 3009, second gear 30011, and third gear 30010 are all arranged inside the first moving platform 3002, finally forming a closed structure, so as to play multiple roles such as reducing noise, sealing grease, safety protection, and aesthetics. Among them, the first gear 3009 is a fixed gear and is fixedly connected to the lower end of the first rotating shaft 3006. The third gear 30010 is a planetary gear, which is fixedly connected to the third rotating shaft 3008, and is located between the first gear 3009 and the second gear 30011 and meshes with both the first gear 3009 and the second gear 30011. The second gear 30011 is a backlash elimination gear, and is preferably rotationally connected to the lower end of the second rotating shaft 3007 through an elastic element 30012.

[0030] Preferably, the third gear 30010 of the dual-action platform assembly 300 performs planetary motion around the first gear 3009, both rotating and revolving, thereby increasing the speed and rotation angle of the third gear 30010. The second moving platform 3003 is connected to the third gear 30010, thereby increasing the rotation angle of the second moving platform 3003 around the Z axis. By adjusting the transmission ratio of the first gear 3009 and the third gear 30010, the second moving platform 3003 can obtain a larger rotation angle than the first moving platform 3002. At the same time, the second gear 30011 can eliminate the gap in the gear transmission to improve positioning accuracy. Figure 5 This is a view when the first moving platform 3002 does not rotate. At this time, the first moving platform 3002 and the second moving platform 3003 are parallel, that is, the angle between them is 0°. Figure 6 、 Figure 8 and Figure 9 As shown, the first movable platform 3002 rotates around the Z axis by the movement of the first branch chain 100 and the second branch chain 200, and the rotation angle is α. At this time, the second movable platform 3003 rotates by an angle β. , where Z1 and Z3 are the number of teeth of the first gear 3009 and the third gear 30010 respectively. In this embodiment, Z1=Z3, so , Figure 6 middle , In this embodiment, the maximum rotation angle of the first movable platform 3002 is ±90°, while the maximum rotation angle of the second movable platform 3003 is expanded to ±180°. A larger rotation angle can be obtained by adjusting the gear ratio of the first gear 3009 and the third gear 30010. In addition, the second gear 30011 is connected to the third gear 30010 with a certain preload force through the elastic element 30012, thereby eliminating the backlash in the gear transmission to improve the positioning accuracy of the parallel robot terminal and forming a symmetrical gear transmission structure, which is conducive to force balance.

[0031] Combine Figure 3 and Figure 4 As shown, in addition, in order to improve the rigidity of the above-mentioned double-moving platform assembly 300, the double-moving platform assembly 300 also includes a connecting plate 3001, which is located above the first moving platform 3002, and is connected to the upper end of the first rotating shaft 3006 and the upper end of the second rotating shaft 3007, and moves synchronously with the first moving platform 3002, thereby avoiding a cantilever structure.

[0032] Due to the cumulative errors in manufacturing and assembly, it is difficult for the above-mentioned double-acting platform assembly 300 to be rigidly connected to the first branch chain 100 and the second branch chain 200 simultaneously. In order to enable the double-acting platform assembly 300 to adaptively connect and assemble and eliminate the internal stress of the connecting rod. In this embodiment, the second support 10044 at the end of the first branch chain 100 is rigidly connected to the first connecting member 3004 of the double-acting platform assembly 300, and the second support 10044 at the end of the second branch chain 200 and the second connecting member 3005 of the double-acting platform assembly 300 are floatingly connected through a spherical plain bearing assembly 500. As shown in Figure 7 As shown, the spherical plain bearing assembly 500 specifically includes an outer ring 5001, an inner ring 5002, a bearing gland 5003 and a shaft end gland 5004. Among them, the inner surface of the outer ring 5001 and the outer surface of the inner ring 5002 are connected by a spherical surface to form a spherical pair. The inner ring 5002 is connected to the second connecting member 3005 of the double-acting platform assembly 300 through the shaft end gland 5004, and the outer ring 5001 is connected to the second support 10044 of the second branch chain 200 through the bearing gland 5003, so that when there is an angular error between the double-acting platform assembly 300 and the second branch chain 200, they can adaptively connect and assemble to eliminate the internal stress of the connecting rod.

[0033] Through the four linear driving motions of the second module 1002 and the third module 1003 in the first branch chain 100 and the second branch chain 200, the present invention can realize the four-degree-of-freedom motion of the double-acting platform assembly 300, including three-degree-of-freedom translation and rotation about the vertical axis (i.e., the Z-axis). Specifically: when the parallelogram mechanisms 1004 of the first branch chain 100 and the second branch chain 200 move synchronously and in the same direction along their respective third modules 1003, the double-acting platform assembly 300 translates in the third direction (i.e., the Z-direction); when the parallelogram mechanisms 1004 of the first branch chain 100 and the second branch chain 200 move synchronously and in the opposite direction along their respective third modules 1003, due to the opposite thrust directions of the two side branches on the platform, the double-acting platform assembly 300 translates in the first direction (i.e., the X-direction); when the third modules 1003 of the first branch chain 100 and the second branch chain 200 move synchronously and in the same direction along their respective second modules 1002, the double-acting platform assembly 300 translates in the second direction (Y-direction); when the third modules 1003 of the first branch chain 100 and the second branch chain 200 move synchronously and in the opposite direction along their respective second modules 1002, the double-acting platform assembly 300 rotates about the third direction (Z-direction).

[0034] In addition, the introduction of the first module 1001 of the present invention greatly increases the translational working space of the parallel robot in the first direction, and at the same time makes the working space of the parallel robot flexible and variable in the height direction (i.e., the Z direction). The first branch chain 100 and the second branch chain 200 can move synchronously left and right as a whole or move left and right independently in the direction of the first module 1001 (i.e., the X direction); when they move as a whole, the distance between the second module 1002 of the first branch chain 100 and the second module 1002 of the second branch chain 200 remains unchanged. At this time, the working space of the parallel robot in the height direction remains unchanged, but the translational working space in the first direction increases; when they move left and right independently, the distance between the second module 1002 of the first branch chain 100 and the second module 1002 of the second branch chain 200 is variable. Thus, on the basis of expanding the translational working space in the first direction of the parallel robot, the working space of the parallel robot in the height direction can also be changed, which can better meet the complex working conditions in actual situations.

[0035] In summary, a four-degree-of-freedom parallel robot disclosed by the present invention mainly has the following advantages: (1) By introducing the first module, the present invention makes the distance between the two branch chains on both sides of the parallel mechanism adjustable, so that on the basis of increasing the working space in the first direction, the height of the working space of the parallel mechanism is flexible and variable, and it can adapt to a variety of different requirements; (2) The present invention adopts a double moving platform design. By adjusting the planetary transmission gear ratio, the rotation angle of the end of the parallel mechanism can be greatly expanded, and it is not limited by the original maximum rotation angle of ±90°; (3) By adding a second backlash-eliminating gear, the present invention can eliminate the clearance of the planetary gear transmission, improve the positioning accuracy of the parallel mechanism, and at the same time form a symmetric transmission structure together with the first fixed gear and the third planetary gear, which is beneficial to force balance; (4) The moving platform assembly of the present invention is rigidly connected to the first branch chain and is floatingly connected to the second branch chain through a joint bearing assembly, so that the double moving platform assembly can achieve adaptive assembly and eliminate the internal stress of the connecting rod.

[0036] All aspects, embodiments, features and examples of the present invention should be considered illustrative in all respects and are not intended to limit the present invention. The scope of the present invention is only defined by the claims. Without departing from the spirit and scope of the claimed invention, those skilled in the art will appreciate other embodiments, modifications and uses.

[0037] In the present invention, the use of titles and chapters does not mean to limit the present invention; each chapter can be applied to any aspect, embodiment or feature of the present invention.

Claims

1. A four-degree-of-freedom parallel robot, characterized in that: The parallel robot includes a fixed frame, a first branch chain, a second branch chain and a double-acting platform assembly. The first branch chain and the second branch chain are both fixed to the fixed frame, and are respectively located on both sides of the double-acting platform assembly in the first direction. Both of them include a first module, a second module, a third module and a parallelogram mechanism. The first module is fixed to the fixed frame and extends along the first direction. The second module is slidably connected to the first module and extends along a second direction perpendicular to the first direction. The third module is slidably connected to the second module and extends along a third direction perpendicular to both the first direction and the second direction. One end of the parallelogram mechanism of the first branch chain is slidably connected to its third module, and the other end is connected to the double-acting platform assembly. One end of the parallelogram mechanism of the second branch chain is slidably connected to its third module, and the other end is connected to the double-acting platform assembly. During operation, when the parallelogram mechanisms of the first branch chain and the second branch chain move synchronously and in the same direction along their respective third modules, the double-acting platform assembly translates along the third direction. When they move synchronously and in opposite directions, the double-acting platform assembly translates along the first direction. When the third modules of the first branch chain and the second branch chain move synchronously and in the same direction along their respective second modules, the double-acting platform assembly translates along the second direction. When they move synchronously and in opposite directions, the double-acting platform assembly rotates around the third direction.

2. The four-degree-of-freedom parallel robot according to claim 1, wherein: The first branch chain and the second branch chain share the first module.

3. The four-degree-of-freedom parallel robot according to claim 1, characterized in that: The parallelogram mechanism of the first branch chain is rigidly connected to the double-acting platform assembly, and the parallelogram mechanism of the second branch chain is floatingly connected to the double-acting platform assembly.

4. A four-degree-of-freedom parallel robot according to claim 3, characterized in that: The parallel robot further includes a spherical plain bearing assembly. The parallelogram mechanism of the second branch chain is floatingly connected to the double-acting platform assembly through the spherical plain bearing assembly.

5. A four-degree-of-freedom parallel robot according to claim 1, characterized in that: The parallelogram mechanism includes a first connecting rod, a second connecting rod, a first support and a second support. The two ends of the first connecting rod are respectively connected to the first support and the second support. The two ends of the second connecting rod are also respectively connected to the first support and the second support. And the end of the first connecting rod connected to the first support and the end of the second connecting rod connected to the first support are offset in both the first direction and the third direction. The end of the first connecting rod connected to the second support and the end of the second connecting rod connected to the second support are also offset in both the first direction and the third direction.

6. A four-degree-of-freedom parallel robot according to claim 1, characterized in that: The double-acting platform assembly includes a first connecting member, a second connecting member, a first moving platform, a first gear, a second gear, a third gear, and a second moving platform. The first connecting member and the second connecting member are respectively connected to the parallelogram mechanism of the first branch chain and the parallelogram mechanism of the second branch chain. The first connecting member is rotationally connected to the first moving platform in the third direction through a first rotating shaft, and the second connecting member is rotationally connected to the first moving platform in the third direction through a second rotating shaft. The second moving platform is rotationally connected to a third rotating shaft provided on the first moving platform. The first gear is fixedly connected to the first rotating shaft, and the third gear is fixedly connected to the third rotating shaft and meshes with both the first gear and the second gear. By adjusting the transmission speed ratio of the first gear and the third gear, the second moving platform can obtain a larger rotation angle than the first moving platform.

7. A four-degree-of-freedom parallel robot according to claim 6, characterized in that: The maximum rotation angle of the first moving platform is ±90°, and the maximum rotation angle of the second moving platform is ±180°.

8. A four-degree-of-freedom parallel robot according to claim 6, characterized in that: The second gear, the first gear, and the third gear together form a symmetric transmission structure. The second gear is a backlash-eliminating gear and is rotationally connected to the second rotating shaft through an elastic element.

9. A four-degree-of-freedom parallel robot according to claim 6, characterized in that: The double-acting platform assembly further includes a connecting plate, which is located above the first moving platform and is connected to both the first rotating shaft and the second rotating shaft.

10. A four-degree-of-freedom parallel robot according to claim 4, characterized in that: The articulated bearing assembly includes an outer bearing ring and an inner bearing ring. The inner surface of the outer bearing ring and the outer surface of the inner bearing ring are connected by a spherical surface to form a spherical pair. The inner bearing ring is connected to the double-acting platform assembly, and the outer bearing ring is connected to the parallelogram mechanism of the second branch chain.

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