A four-degree-of-freedom parallel robot

Abstract

The present invention discloses a four-degree-of-freedom parallel robot comprising a fixed frame, a first branch chain, a second branch chain, and a dual-motion platform assembly. The first branch chain and the second branch chain are respectively connected to the fixed frame and the dual-motion platform assembly to form a spatially closed loop structure. Through the linear drive motion of each module in the first and second branches, the dual-motion platform assembly can achieve four degrees of freedom: three degrees of freedom of translation and rotation about a vertical axis. This invention can expand the parallel robot's translational and rotational workspace, improve positioning accuracy, and enable adaptive assembly of the end-movement platform and eliminate internal stress in the connecting rod.

Description

Technical Field

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

[0002] SCARA robots are four-degree-of-freedom robots, encompassing three-dimensional translation and rotation about the Z-axis. They are widely used in automation applications such as handling and palletizing. However, their serial structure leads to drawbacks such as insufficient load-bearing capacity, poor rigidity, low precision, and relatively slow speed. Parallel robots, due to their structural characteristics, are more suitable for high-speed, high-precision, and high-load applications. The Delta parallel robot, currently the most widely used, achieves three degrees of freedom in translation through three kinematic branches. In practice, since the direction of materials generally requires adjustment, a rotational axis is typically added to the Delta robot's dynamic platform to adjust the material's orientation.

[0003] Patent CN201610303555.2 proposes a new type of four-degree-of-freedom parallel mechanism. Through two kinematic branches, the dynamic platform can achieve translation in three directions and rotation around the Z axis. However, there are problems such as a small and fixed translational workspace and a maximum rotation angle around the Z axis of only ±90°. In addition, the cumulative error of the connecting rod makes it difficult to assemble the end of the dynamic platform, and internal stress is generated inside the connecting rod. In response to some of the above problems, Patent CN202121911821.2 proposes a biased parallelogram mechanism design to extrapolate the local singular positions of the mechanism, thereby expanding the translational workspace of the parallel mechanism to a certain extent. However, other problems still exist.

[0004] Therefore, it is necessary to improve the problems of the above-mentioned existing four-degree-of-freedom robots, such as small working space, low positioning accuracy, difficult assembly of the platform end, and internal stress generated inside the connecting rod. Summary of the Invention

[0005] The main purpose of the present invention is to provide a four-degree-of-freedom parallel robot that can expand the translational and rotational working space, improve positioning accuracy, enable adaptive assembly of the end moving platform, and eliminate internal stress in the connecting rod.

[0006] To achieve the aforementioned purpose of the invention, the technical solution adopted by the present invention includes: a four-degree-of-freedom parallel robot, including a fixed frame, a first branch chain, a second branch chain and a double-action platform assembly, the first branch chain and the second branch chain are both fixed to the fixed frame, and the two are respectively located on both sides of the double-action platform assembly in a first direction, and both 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 and second directions. The device is extended, 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-action 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-action platform assembly; during operation, when the parallelogram mechanisms of the first branch chain and the second branch chain move synchronously in the same direction along their respective third modules, the double-action platform assembly moves horizontally along the third direction, and when moving synchronously in the opposite direction, the double-action platform assembly moves horizontally along the first direction; when the third modules of the first branch chain and the second branch chain move synchronously in the same direction along their respective second modules, the double-action platform assembly moves horizontally along the second direction, and when moving synchronously in the opposite direction, the double-action 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 is rigidly connected to the double-action platform assembly, and the parallelogram mechanism of the second branch is floatingly connected to the double-action platform assembly.

[0009] In a preferred embodiment, the parallel robot further comprises a joint bearing assembly, and the parallelogram mechanism of the second branch chain is floatingly connected to the double-motion platform assembly via the joint 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, 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 both offset in the first direction and the third direction, and 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 both offset in the first direction and the third direction.

[0011] In a preferred embodiment, the double-moving 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, and the first connecting member is rotationally connected to the first moving platform in the third direction through the first rotating shaft, the second connecting member is rotationally connected to the first moving platform in the third direction through the second rotating shaft, the second moving platform is rotationally connected to the third rotating shaft arranged on the first moving platform, the first gear is fixedly connected to the first rotating shaft, the third gear is fixedly connected to the third rotating shaft, and is meshed with 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 movable platform is ±90°, and the maximum rotation angle of the second movable platform is ±180°.

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

[0014] In a preferred embodiment, the double-moving 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.

[0015] In a preferred embodiment, the joint bearing assembly includes a bearing outer ring and a bearing inner ring, the inner surface of the bearing outer ring and the outer surface of the bearing inner ring are spherically connected to form a ball pair, the bearing inner ring is connected to the double-action platform assembly, and the bearing outer ring is connected to the parallelogram mechanism of the second branch chain.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The present invention introduces the first module to make the distance between the branches on both sides of the parallel mechanism adjustable, thereby increasing the working space in the first direction and making the working space of the parallel mechanism highly flexible and adaptable to various different needs.

[0018] 2. The present invention adopts a double-action platform design, which can greatly expand the terminal rotation angle of the parallel mechanism by adjusting the planetary transmission gear ratio, and is not subject to the original maximum ±90° rotation angle limit.

[0019] 3. The present invention can eliminate the transmission gap of the planetary gears and improve the positioning accuracy of the parallel mechanism by adding the second anti-backlash gear. At the same time, it forms a symmetrical transmission structure together with the first fixed gear and the third planetary gear, which is conducive to force balance.

[0020] 4. The dynamic platform assembly of the present invention is rigidly connected to the first branch chain and is floatingly connected to the second branch chain via a joint bearing assembly, thereby enabling the dual dynamic platform assembly to achieve adaptive assembly and eliminate internal stress in the connecting rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 is a three-dimensional view of a four-degree-of-freedom parallel robot according to an embodiment of the present invention;

[0023] Figure 2 2. It is a front view of a four-degree-of-freedom parallel robot according to an embodiment of the present invention;

[0024] Figure 3 is a perspective view of a double-action platform assembly according to an embodiment of the present invention;

[0025] Figure 4 is a cross-sectional view of a double-action platform assembly according to an embodiment of the present invention;

[0026] Figure 5 is a bottom view of the double-action platform assembly of an embodiment of the present invention with the cover plate removed;

[0027] Figure 6 yes Figure 5 The view after rotating 45°;

[0028] Figure 7 yes Figure 2 Magnified view of point Ⅰ in the middle;

[0029] Figure 8 This is a top view of the parallel robot after the dual-action platform assembly is rotated 45°;

[0030] Figure 9 yes Figure 8 corresponding stereoscopic views;

[0031] Reference numerals:

[0032] 100, first branch chain; 1001, first module; 1002, second module; 1003, third module; 1004, parallelogram mechanism; 10041, first connecting rod; 10042, second connecting rod; 10043, first support; 10044, second support;

[0033] 200, second branch;

[0034] 300, double-moving 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;

[0035] 400, fixed frame; 4001, first bracket; 4002, second bracket;

[0036] 500, spherical plain bearing assembly; 5001, bearing outer ring; 5002, bearing inner ring; 5003, bearing gland; 5004, shaft end gland. DETAILED DESCRIPTION

[0037] The present invention will be more fully understood through the following detailed description, which should be read in conjunction with the accompanying drawings. Detailed embodiments of the present invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the present invention, which can be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but rather as a basis for the claims and as a representative basis for teaching those skilled in the art to employ the present invention in various ways in virtually any appropriately detailed embodiment.

[0038] Combine 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 dual-motion platform assembly 300 and a joint bearing assembly 500. The first branch chain 100 and the second branch chain 200 are respectively connected to the fixed frame 400 and the dual-motion platform assembly 300 to form a spatial closed-loop structure.

[0039] like Figure 1 As 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 in the second direction (ie, the Y direction), and both extend along the first direction (ie, the X direction).

[0040] The first branch chain 100 and the second branch chain 200 are both fixed on the fixed frame 400, and are respectively located on both sides of the double-action platform assembly 300 in the first direction, that is, respectively located on the left and right sides of the double-action platform assembly 300. Figure 1 As shown, the first branch chain 100 primarily comprises a first module 1001, a second module 1002, a third module 1003, and a parallelogram mechanism 1004. The first, second, and third modules 1001, 1002, and 1003 are perpendicular to each other and arranged in rectangular coordinates. Specifically, in this embodiment, corresponding to the number of brackets on the fixed frame, two sets of first modules 1001 are provided, one in front and one behind. A first module 1001 is affixed to each bracket of the fixed frame 400. Thus, the two sets of first modules 1001 are also arranged parallel to each other in the second direction (i.e., the Y direction). Both extend along the first direction (i.e., the X direction), with their left and right ends fixed to corresponding brackets. The second module 1002 extends in a second direction (i.e., the Y direction), perpendicular to the first direction, with its ends slidably connected to the corresponding first modules 1001, allowing reciprocating movement along the first module 1001 in the first direction. The third module 1003 extends in a third direction (i.e., the Z direction) perpendicular to both the first and second directions and is slidably connected to the second module 1002, enabling reciprocating movement along the second module 1002 in the second direction. One end of the parallelogram mechanism 1004 is slidably connected to the third module 1003, enabling reciprocating movement along the third module 1003 in the third direction, while the other end is connected to the dual-action platform assembly 300. The first module 1001, second module 1002, and third module 1003 are all linear drive components, and various drive methods, such as linear motors, rack and pinion gears, lead screws, and synchronous belts, can be employed in implementation.

[0041] Combine Figure 1 He Ru Figure 2As 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, wherein the first support 10043 is slidingly connected to the third module 1003, the second support 10044 is connected to the double-action platform assembly 300, and the two ends of the first connecting rod 10041 respectively form two rotating pairs with the first support 10043 and the second support 10044, and the two ends of the second connecting rod 10042 also form two rotating pairs with the first support 10043 and the second support 10044. One end of the first link 10041 connected to the first support 10043 and one end of the second link 10042 connected to the first support 10043 are offset in the first direction and the third direction, and one end of the first link 10041 connected to the second support 10044 and one end of the second link 10042 connected to the second support 10044 are also offset in the first direction and the third direction. By expanding the local rotation angle of the parallelogram mechanism 1004, the working space of the parallel robot moving horizontally along the first direction is expanded.

[0042] The structure of the second branch chain 200 is identical to that of the first branch chain 100, namely, 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, thereby achieving a compact structure and reducing costs. The description of other structures of the second branch chain 200 can be found in the description of the first branch chain 100 above and will not be repeated here.

[0043] Combine Figure 3 and Figure 4As shown, the dual-moving platform assembly 300 is located between the first branch chain 100 and the second branch chain 200 and primarily includes a first connector 3004, a second connector 3005, a first movable platform 3002, a first gear 3009, a second gear 30011, a third gear 30010, and a second movable platform 3003. The first movable platform 3002 forms a rotational pair with the first connector 3004 and the second connector 3005, respectively, to form a first rotating shaft 3006 and a second rotating shaft 3007. Specifically, in this embodiment, the first rotating shaft 3006 and the second rotating shaft 3007 are both vertically disposed along the third direction. The first connector 3004 is rotationally coupled to the first rotating shaft 3006 and connected to the second support 10044 of the first branch chain 100. The second connector 3005 is rotationally coupled to the second rotating shaft 3007 and connected to the second support 10044 of the second branch chain 200 via the joint bearing assembly 500. A third rotating shaft 3008 is provided at the center of the first movable platform 3002 . The second movable platform 3003 is located below the first movable platform 3002 and is coaxial with the third rotating shaft 3008 and is rotationally connected thereto.

[0044] In this embodiment, the first movable platform 3002 of the dual-action platform assembly 300 has an internally hollowed structure. The first gear 3009, second gear 30011, and third gear 30010 are all disposed within the first movable platform 3002, ultimately forming a closed structure that serves multiple purposes, including noise reduction, grease sealing, safety protection, and aesthetics. The first gear 3009 is a fixed gear fixedly connected to the lower end of the first rotating shaft 3006. The third gear 30010 is a planetary gear fixedly connected to the third rotating shaft 3008. It 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-eliminating gear, preferably rotatably connected to the lower end of the second rotating shaft 3007 via an elastic element 30012.

[0045] 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.

[0046] 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.

[0047] Due to the accumulated errors in manufacturing and assembly, it is difficult for the above-mentioned double-action platform assembly 300 to be rigidly connected to the first branch chain 100 and the second branch chain 200 at the same time. In order to enable the double-action platform assembly 300 to be adaptively connected and assembled and eliminate the stress in 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-action platform assembly 300, and the second support 10044 at the end of the second branch chain 200 is floatingly connected to the second connecting member 3005 of the double-action platform assembly 300 through the joint bearing assembly 500. Figure 7As shown, the spherical bearing assembly 500 specifically includes a bearing outer ring 5001, a bearing inner ring 5002, a bearing pressure cover 5003, and a shaft end pressure cover 5004. The inner surface of the bearing outer ring 5001 and the outer surface of the bearing inner ring 5002 are spherically connected to form a ball pair. The bearing inner ring 5002 is connected to the second connecting member 3005 of the double-action platform assembly 300 via the shaft end pressure cover 5004. The bearing outer ring 5001 is connected to the second support 10044 of the second branch chain 200 via the bearing pressure cover 5003. This allows the double-action platform assembly 300 and the second branch chain 200 to be adaptively connected and assembled when there is an angular error, thereby eliminating stress within the connecting rod.

[0048] The present invention can realize the three-degree-of-freedom translation and the four-degree-of-freedom rotation about the vertical axis (i.e., Z axis) of the dual-action platform assembly 300 through the four linear drive motions of the second module 1002 and the third module 1003 in the first branch chain 100 and the second branch chain 200. Specifically, when the parallelogram mechanisms 1004 of the first branch chain 100 and the second branch chain 200 respectively move synchronously in the same direction along their respective third modules 1003, the double-action platform assembly 300 moves horizontally along 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 respectively move synchronously in opposite directions along their respective third modules 1003, the double-action platform assembly 300 moves horizontally along the first direction (i.e., the X direction) because the thrusts of the two side branches on the platform are in opposite directions; when the third modules 1003 of the first branch chain 100 and the second branch chain 200 respectively move synchronously in the same direction along their respective second modules 1002, the double-action platform assembly 300 moves horizontally along the second direction (Y direction); when the third modules 1003 of the first branch chain 100 and the second branch chain 200 respectively move synchronously in opposite directions along their respective second modules 1002, the double-action platform assembly 300 rotates around the third direction (Z direction).

[0049] Furthermore, the introduction of the first module 1001 of the present invention significantly increases the parallel robot's translational workspace along the first direction, while also making its height (i.e., Z-direction) workspace flexible and variable. The first and second branches 100, 200, can move synchronously left and right as a whole, or independently left and right, in the direction of the first module 1001 (i.e., X-direction). When they move as a whole, the distance between the second modules 1002 of the first branch 100 and 1002 of the second branch 200 remains unchanged. In this case, the parallel robot's height workspace remains unchanged, but its translational workspace along the first direction increases. When they move independently left and right, the distance between the second modules 1002 of the first branch 100 and 1002 of the second branch 200 is variable. This allows the parallel robot to expand its translational workspace in the first direction while also adjusting its height workspace, better meeting the complex working conditions required in real-world situations.

[0050] In summary, the four-degree-of-freedom parallel robot disclosed in the present invention has the following advantages: (1) The present invention introduces the first module to make the distance between the two side branches of the parallel mechanism adjustable, thereby increasing the working space in the first direction and making the working space of the parallel mechanism highly flexible and variable, which can adapt to a variety of different needs; (2) The present invention adopts a double-action platform design, which can greatly expand the rotation angle of the end of the parallel mechanism by adjusting the speed ratio of the planetary transmission gear, and is not subject to the original maximum ±90° rotation angle limit; (3) The present invention can eliminate the planetary gear transmission gap by adding a second anti-backlash gear, thereby improving the positioning accuracy of the parallel mechanism, and at the same time, together with the first fixed gear and the third planetary gear, it forms a symmetrical transmission structure, which is conducive to force balance; (4) The dynamic platform assembly of the present invention is rigidly connected to the first branch and is floatingly connected to the second branch through the joint bearing assembly, so that the double-action platform assembly can achieve adaptive assembly and eliminate the stress in the connecting rod.

[0051] The various aspects, embodiments, features and examples of the present invention should be considered as illustrative in all respects and are not intended to limit the present invention, the scope of which is defined solely by the claims. Other embodiments, modifications and uses will be apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0052] The use of headings and sections in this disclosure is not meant to limit the disclosure; each section may apply to any aspect, embodiment, or feature of the disclosure.

Claims

1. A four-degree-of-freedom parallel robot, characterized by: The parallel robot includes a fixed frame, a first branch chain, a second branch chain and a double-action 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-action platform assembly in a first direction, and both 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 and second directions, the parallelogram of the first branch chain One end of the parallelogram mechanism is slidably connected to its third module, and the other end is connected to the double-action 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-action platform assembly. During operation, when the parallelogram mechanisms of the first branch chain and the second branch chain move synchronously in the same direction along their respective third modules, the double-action platform assembly moves horizontally along the third direction, and when moving synchronously in the opposite direction, the double-action platform assembly moves horizontally along the first direction; when the third modules of the first branch chain and the second branch chain move synchronously in the same direction along their respective second modules, the double-action platform assembly moves horizontally along the second direction, and when moving synchronously in the opposite direction, the double-action platform assembly rotates around the third direction.

2. A four-degree-of-freedom parallel robot according to claim 1, characterized in that: 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-action platform assembly, and the parallelogram mechanism of the second branch chain is floatingly connected to the double-action platform assembly.

4. The four-degree-of-freedom parallel robot according to claim 3, characterized in that: The parallel robot further includes a joint bearing assembly, and the parallelogram mechanism of the second branch chain is floatingly connected to the double-motion platform assembly via the joint bearing assembly.

5. The 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 both offset in the first direction and the third direction, and 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 both offset in the first direction and the third direction.

6. The four-degree-of-freedom parallel robot according to claim 1, characterized in that: The double-moving 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, and the first connecting member is rotationally connected to the first moving platform in the third direction through the first rotating shaft, the second connecting member is rotationally connected to the first moving platform in the third direction through the second rotating shaft, the second moving platform is rotationally connected to the third rotating shaft arranged on the first moving platform, the first gear is fixedly connected to the first rotating shaft, the third gear is fixedly connected to the third rotating shaft, and is meshed with 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. The four-degree-of-freedom parallel robot according to claim 6, characterized in that: The maximum rotation angle of the first movable platform is ±90°, and the maximum rotation angle of the second movable platform is ±180°.

8. The 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 symmetrical transmission structure. The second gear is a backlash-eliminating gear and is rotationally connected to the second rotating shaft via an elastic element.

9. The four-degree-of-freedom parallel robot according to claim 6, characterized in that: The double-moving 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. The four-degree-of-freedom parallel robot according to claim 4, characterized in that: The joint bearing assembly includes a bearing outer ring and a bearing inner ring. The inner surface of the bearing outer ring and the outer surface of the bearing inner ring are spherically connected to form a ball pair. The bearing inner ring is connected to the double-action platform assembly, and the bearing outer ring is connected to the parallelogram mechanism of the second branch chain.

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