Three-mode parallel robot mechanism based on adjustable branch chain motion center

Abstract

According to the three-mode parallel robot mechanism based on the adjustable branch chain motion center, the position of the rotation center of each branch chain can be adjusted through a second universal hinge rotation pair R22, and then adjustment of the motion state of the movable platform is achieved; the positions of the axes of a plurality of rotating pairs R21 are controlled by controlling a second universal hinge rotating pair R22 in each branch chain, and then three different motion modes are achieved by controlling the position relation between the axes of the rotating pairs R21 at the top ends of the branch chains and the position relation between the axes of the rotating pairs R21 at the top ends of the branch chains and the fixed platform. The three rotation modes are respectively three rotation modes and have telecentric point immovable characteristics, two rotation modes and one movement mode and have telecentric point immovable characteristics, and one rotation mode and one movement mode and have telecentric point immovable characteristics.

Description

Technical Field

[0001] This invention relates to the fields of mechanics and robotics, specifically to a three-mode parallel robot mechanism based on an adjustable branch motion center. Background Technology

[0002] A remote motion center (RCM) mechanism refers to a surgical instrument end effector used in minimally invasive surgery that can continuously rotate around a fixed point located at the distal end of the mechanism within space; this motion is called telecentric motion. However, existing RCM parallel mechanisms have only one degree of freedom and lack versatility. In recent years, due to the rapid development of the medical field, the demand for surgeries that can be performed quickly for different diseases has increased, leading to widespread attention to multi-mode parallel mechanisms. Given the varying surgical needs, multi-mode RCM parallel mechanisms can perform multiple surgeries without assembly. For example, when a patient only needs to undergo simple procedures around the puncture point, such as intravenous puncture or nasopharyngoscopy, a 1R1T degree-of-freedom actuator end effector is sufficient. Using a multi-degree-of-freedom actuator end effector would increase the difficulty of the surgery. For complex surgeries, a single-degree-of-freedom end effector is insufficient; for example, a 2R1T degree-of-freedom RCM parallel mechanism is required for novel vitreoretinal surgeries to treat retinal diseases, while a 3R1T degree-of-freedom RCM parallel mechanism is required for vitrectomy. Therefore, it is necessary to introduce the multi-mode concept into the RCM mechanism to achieve a single RCM mechanism with multiple degrees of freedom of motion characteristics in order to meet the needs of surgeries of different difficulty.

[0003] Technicians are exploring the need to incorporate reconfigurable concepts into Remote Center of Motion (RCM) mechanisms to achieve a single RCM with multiple degrees of freedom. Given the varying surgical requirements, reconfigurable RCM parallel mechanisms can perform multiple surgeries without requiring reassembly. Existing reconfigurable parallel robots, such as the patent with publication number CN109009448A, disclose a parallel surgical robot with a remote center of motion; however, it uses curved guide rails to implement the RCM, which are difficult to manufacture and have low rigidity. This structural complexity and cost limit its application scenarios. Summary of the Invention

[0004] To address the issues of complex motion platforms, difficult manufacturing, and limited application scenarios in existing RCM parallel robot mechanisms with three motion modes, this invention provides a three-mode parallel robot mechanism based on an adjustable branch motion center. This mechanism is simple in structure, easy to manufacture, and has high rigidity, making it suitable for a wider range of applications.

[0005] The technical scheme of the present application is as follows: a three-mode parallel robot mechanism based on adjustable branch motion center, comprising a fixed base, a moving platform and a branch; the fixed base and the moving platform are connected through parallel N branches; It is characterized in that: The number N of the branches is greater than or equal to 3, all the branches have the same structure and are equal in length; all the branches are uniformly arranged on the circumcircle of the moving platform and the fixed base; The structure of the branch is a URRU branch; each branch comprises, from bottom to top, a first universal hinge, a first revolute pair, a second revolute pair and a second universal hinge; The structure of the branch comprises, from bottom to top, three connecting rods connected in sequence: a first connecting rod, a second connecting rod and a third connecting rod; the bottom end of the first connecting rod is connected to the fixed base based on the first universal hinge, and the top end of the fourth connecting rod is connected to the moving platform through the second universal hinge; adjacent connecting rods are connected to each other through revolute pairs, and the rotation axes of the two revolute pairs are parallel to each other; The first universal hinge comprises two revolute pairs intersecting with each other: revolute pair R11 and revolute pair R12, the two revolute pair axes are perpendicular to each other and parallel to the fixed base, wherein the revolute pair R11 axis points to the center of the fixed base; the intersection point of the four revolute pair R11 axes is the telecentric point.

[0006] It is further characterized in that: The second universal hinge comprises: revolute pair R21 and revolute pair R22 intersecting with each other, the axis of revolute pair R22 is always perpendicular to the axis of revolute pair R21; revolute pair R21 is connected to the third connecting rod, and revolute pair R22 is connected to the moving platform; The revolute pair R22 of the second universal hinge is parallel or coplanar to the moving platform; The rotation axis of the revolute pair R12 of the first universal hinge, the rotation axis of the first revolute pair and the rotation axis of the second revolute pair are parallel to each other; The rotation axis of the revolute pair R11 of the first universal hinge and the rotation axis of the revolute pair R21 in the second universal hinge are not parallel and not collinear to each other; at the same time, the rotation axis of the revolute pair R11 of the first universal hinge and the rotation axis of the revolute pair R21 in the second universal hinge are respectively perpendicular to the rotation axes of the revolute pair R12 of the first universal hinge, the first revolute pair and the second revolute pair; Three driving pairs are arranged in each branch: the revolute pair R11 of the first universal hinge, the revolute pair R12 of the first universal hinge and the revolute pair R22 in the second universal hinge; The moving platform is arranged in a cross shape, and the number of the branches is arranged as four; A U-shaped connector is arranged on each branch of the cross-shaped moving platform, and the two ends of the revolute pair R22 of the second universal hinge in each branch are rotatably connected to the U-shaped connector. The base is a cross structure, a star structure or a circular ring structure. A moving pair is arranged at the lower end of the cross-shaped central position of the moving platform. The first connecting rod and the second connecting rod are structurally identical, and are both provided with a U-shaped connecting head at one end and a T-shaped head at the other end; the third connecting rod is provided with U-shaped connecting heads at both ends, and the opening ends of the U-shaped connecting heads at both ends are perpendicular to each other.

[0007] The application provides a three-mode parallel robot mechanism based on adjustable branch chain motion centers, the position of the rotation center of each branch chain can be adjusted through a second universal hinge rotation pair R22, and then the motion state of the moving platform is adjusted; the position of the axis of the several rotation pairs R21 is controlled by respectively controlling the second universal hinge rotation pair R22 in each branch chain, and then the positional relationship between the axes of the top rotation pairs R21 of the several branch chains and the positional relationship between the axes of the top rotation pairs R21 of the branch chains and the fixed platform are controlled, so that three different motion modes are realized, which are three rotations with a fixed telecentric point, two rotations and one movement with a fixed telecentric point, and one rotation and one movement with a fixed telecentric point; the application does not need to change the internal motion pairs of the branch chains to realize the reconstruction of the motion modes, and the complexity of the mode reconstruction is reduced. The branch chain in the RCM mechanism in the application is a URRU branch chain, which not only has good rigidity and the characteristic of a fixed telecentric point in each motion mode, but also has a simple structure and is convenient to process, and can be applied to more scenes. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 Fig. 1 is a schematic diagram of the overall structure of the parallel robot mechanism of the application; Figure 2 Fig. 2 is a schematic diagram of the first branch chain structure; Figure 3 Fig. 3 is a general attitude example of the mechanism of the application in mode one; Figure 4 Fig. 4 is a general attitude example of the mechanism of the application in mode two; Figure 5 Fig. 5 is a general attitude example of the mechanism of the application in mode three; Figure 6 Fig. 6 is a schematic diagram of the overall structure of the application, which is an example 2; Figure 7 Fig. 7 is an example of the first connecting rod and the second connecting rod; Figure 8 Fig. 8 is an example of the third connecting rod. DETAILED DESCRIPTION

[0009] As Figures 1-8As shown, the present application comprises a three-mode parallel robot mechanism based on adjustable branch motion center, which comprises a moving platform 1, a fixed base 2 and a branch; the fixed base 2 and the moving platform 1 are connected by parallel N branches.

[0010] The number of branches N is greater than or equal to 3, all branch structures are the same and equal in length; all branches are uniformly arranged on the circumcircle of the moving platform 1 and the fixed base 2; the structure of the branch is a URRU branch, where R is a rotary pair and U is a universal hinge. Each branch includes, from bottom to top: a first universal hinge U1, a first rotary pair 1-1, a second rotary pair 1-2 and a second universal hinge U2.

[0011] In this embodiment, the moving platform 1 is set to a cross shape, and the number of branches is set to 4. A U-shaped connector is arranged on each branch of the cross-shaped moving platform 1, and the two ends of the rotary pair R22 in the second universal hinge U2 of each branch are rotatably connected to the U-shaped connector. The base is a cross structure, a star structure or a circular ring structure. In this embodiment, the fixed base 2 is a cross structure with equal length branches, the four branches are symmetrically arranged, and are uniformly arranged on the circumcircle of the cross structure of the moving platform 1 and the fixed base 2. The four branches are respectively: a first branch 3, a second branch 4, a third branch 5 and a fourth branch 6.

[0012] The structure of the four branches and the connection mode of each branch to the moving platform 1 and the fixed base 2 are the same, as shown in Figure 2 , which is described by taking the first branch 31 as an example.

[0013] The structure of the branch includes three connecting rods connected in turn from bottom to top: a first connecting rod 31, a second connecting rod 32 and a third connecting rod 33; adjacent connecting rods form a rotary pair, and three connecting rods form two rotary pairs: a first rotary pair 1-1 and a second rotary pair 1-2, the rotary axes of the two rotary pairs are parallel to each other; the bottom end of the first connecting rod 31 is connected to the fixed base 2 based on the first universal hinge U1, and the top end of the fourth connecting rod is connected to the moving platform 1 through the second universal hinge U2.

[0014] The first universal hinge U1 includes two rotary pairs intersecting each other: rotary pair R11 and rotary pair R12, the two rotary pair axes are perpendicular to each other and parallel to the fixed base 2, wherein the rotary pair R11 axis points to the center of the fixed base 2; the intersection of the four rotary pair R11 axes is the remote center point O.

[0015] The second universal joint U2 includes two intersecting revolute joints: revolute joint R21 and revolute joint R22. The axis of revolute joint R22 is always perpendicular to the axis of revolute joint R21. Revolute joint R21 is connected to the fourth link, and revolute joint R22 is connected to the moving platform 1. Revolute joint R22 is parallel or coplanar with the moving platform 1. In this embodiment, in order to simplify the structure and reduce the manufacturing difficulty, revolute joint R22 and moving platform 1 are set to be coplanar.

[0016] A U-shaped connector is provided on the fixed base 2. The two ends of the rotating joint R11 of the first universal joint U1 are rotatably connected to the U-shaped connector of the fixed base 2 to realize the connection between the branch and the fixed base 2.

[0017] like Figure 7 As shown, Figure 7 The first link 31 and the second link 32 have the same structure, both with a U-shaped connector at one end and a T-shaped connector at the other end; for example Figure 8 As shown, both ends of the third link 33 are U-shaped connectors, and the lines connecting the open ends of the U-shaped connectors at both ends are perpendicular to each other. The two ends of the revolute joint R12 of the first universal joint U1 are rotatably connected to the U-shaped connector of the first link 31; the T-shaped head at the other end of the first link 31 and the U-shaped connector of the second link 32 form the first revolute joint 1-1, and the T-shaped head of the second link 32 and one U-shaped connector of the third link 33 form the second revolute joint 1-2. U-shaped connectors are provided on the moving platform 1, and the two ends of the revolute joint R22 of the second universal joint U2 are rotatably connected to the U-shaped connector of the moving platform 1, and the two ends of the revolute joint R21 of the second universal joint U2 are rotatably connected to the other U-shaped connector of the third link 33, thus connecting the branch to the moving platform 1.

[0018] The axes of rotation of the first universal joint U1's revolute joint R12, the first revolute joint 1-1, and the second revolute joint 1-2 are parallel to each other; the axes of rotation of the first universal joint U1's revolute joint R11 and the second universal joint U2's revolute joint R21 are neither parallel nor collinear; at the same time, the axes of rotation of the first universal joint U1's revolute joint R11 and the second universal joint U2's revolute joint R21 are perpendicular to the axes of rotation of the first universal joint U1's revolute joint R12, the first revolute joint 1-1, and the second revolute joint 1-2, respectively.

[0019] The branched chain in the present application is composed of two universal hinges and two rotating pairs to form a branched chain of URRU structure. The reason why the cross structure universal hinge is used in the branched chain instead of other structures is that the cross-axis universal hinge can provide two degrees of freedom of rotation, and the structure is simpler, more rigid, more efficient, and easier to manufacture. In addition, the cross structure universal hinge structure is compact and occupies less space, ensuring that the robot mechanism of the present application is suitable for more scenarios. The moving platform 1 is only composed of a cross structure platform, and the moving platform 1 does not need to be assembled, and the structure is simple. At the same time, although the rotation angle of the cross structure universal hinge is limited, it is suitable for the application scenario of the RCM mechanism without large angle rotation.

[0020] Three driving pairs are arranged on each branched chain: the rotating pair R11 of the first universal hinge U1, the rotating pair R12 of the first universal hinge U1, and the rotating pair R22 of the second universal hinge U2 are set as driving pairs; each driving pair is driven to rotate based on a motor.

[0021] By adjusting the position of the axis of the rotating pair R11 of the second universal hinge U2 at the top of each branched chain, the positional relationship between the axis of the rotating pair R11 of each branched chain and the moving platform 1 can be controlled, and the parallel mechanism can be controlled to enter different telecentric motion modes. The parallel mechanism of the present application supports three different motion modes, which are: three rotations 3R with a fixed telecentric point, two rotations and one translation 2T1R with a fixed telecentric point, and one rotation and one translation 1T1R with a fixed telecentric point.

[0022] As shown in Figure 3 The initial state of the mechanism of the present application is shown in the figure, which is a three-rotation (3R) motion mode with a fixed telecentric point. In this mode, the axes of the rotating pairs R21 of the second universal hinges U2 at the top of the four branched chains: L1, L2, L3 and L4 all converge at the telecentric point O. The red arrows in the figure are the three rotation axes R1, R2, R3 of the moving platform 1 in the 3R mode.

[0023] In this mode, locking the revolute joint R22 of the second universal joint U2 and the revolute joint R12 of the first universal joint U1 at the top of the four branches ensures that L1~L4 converge at a single point, and that the convergence point coincides with point O. Driving the two drive joints R11 of the first universal joint U1 in each of the four branches allows rotation about axes R1, R2, and R3 respectively. For example, rotating all four drive joints R11 of the first universal joint U1 clockwise while locking the other drive joints allows for clockwise rotation of the moving platform 1 about axis R1. If the drive joints R11 of the first universal joint U1 in the first branch 3 and the third branch 5 rotate simultaneously in the same direction while locking the other drive joints, rotation of the moving platform 1 about axis R2 is achieved. If the drive joints R11 of the first universal joint U1 in the second branch 4 and the fourth branch 6 rotate simultaneously in the same direction while locking the other drive joints, rotation of the moving platform 1 about axis R3 is achieved.

[0024] In practical applications, under the 3R motion model, a sliding joint can be set at the lower end of the cross-shaped center position of the moving platform 1 according to actual needs; for example... Figure 8 As shown, if a sliding joint 7 is added below the moving platform 1 and the minimally invasive scalpel is placed at the end of the sliding joint 8, the moving platform 1 can realize the 3R1T movement of the scalpel in the 3R mode.

[0025] Based on the 3R mode, the rotational joint R22 of the second universal joint U2 at the top of the four branches is driven so that axes L1, L2, L3, and L4 do not converge at the centroid, and all four axes L1, L2, L3, and L4 are perpendicular to the plane of the fixed platform. Then, the parallel mechanism of this application enters state two, a two-rotation-one-movement (2R1T) motion mode with a fixed centroid. The position of the centroid O remains unchanged, and the corresponding rotation axes R2 and R3, and the moving axis T are as follows: Figure 4 As shown. In 2R1T mode, the rotary joint R22 of the second universal joint U2 at the top of the four branches is locked, so that the angle between L1~L4 and the moving platform 1 will not change. If the R12 of the first universal joint at the bottom of the four branches is driven to swing in the same direction and with the same amplitude at a downward or upward angle, the moving platform 1 will move vertically along the T-axis. If the drive joint R11 of the first universal joint U1 in the first branch 3 and the third branch 5 rotates in the same direction at the same time, the moving platform 1 can rotate about R2. If the drive joint R11 of the first universal joint U1 in the second branch 4 and the fourth branch 6 rotates in the same direction at the same time, and the other drive joints are locked, the moving platform 1 can rotate about R3.

[0026] On the basis of the 2R1T mode, the rotary pair R22 of the second universal joint U2 at the top end of the four branches is driven, so that the axes L1, L2, L3 and L4 are not all convergent to the telecentric point, and the four axes L1, L2, L3 and L4 are not all perpendicular to the plane on which the fixed platform is located. Then the parallel mechanism enters the motion mode of rotation and translation (1R1T) with a fixed telecentric point, and the corresponding rotation axis R3 and translation axis T are as shown in Figure 5 In the 1R1T mode, the rotary pair R22 of the second universal joint U2 at the top end of the four branches is locked, so that the angles of L1-L4 with respect to the moving platform 1 do not change. If the R12 in the first universal pair at the bottom end of the four branches is simultaneously driven to swing in the same direction with the same amplitude of pitch or elevation, the moving platform 1 is moved in the vertical direction along the T axis. If the driving pairs R11 in the first universal joints U1 in the second branch 4 and the fourth branch 6 are simultaneously rotated in the same direction, and the remaining driving pairs are locked, the moving platform 1 can be rotated about the R3 axis.

[0027] After the technical solution of the application is used, the RCM is realized by the constraint relationship between the branches, and the degree of freedom can be changed according to the change of the end of the branch. The degree of freedom of the parallel mechanism is the intersection of all the branches, and the normal direction of the moving plane and the rotation center play an important role in the intersection of the moving and rotating motions. In this scheme, the rotation axis of the branch is controlled to change the position of the rotation center of the branch, so that the switching of different degrees of freedom can be realized. The parallel mechanism of the application is driven and supported by multiple independent motion branches, and the external load (such as cutting force and weight of workpiece) is evenly distributed to each branch, so that each branch only bears a part of the total load, which greatly reduces the stress and deformation of a single branch. In addition, the moving platform 1, the static platform and each branch of the parallel mechanism form multiple closed-loop motion chains. In the closed-loop structure, the deformation of each link is limited by adjacent links and joints, forming a “mutual restraint” constraint relationship, which effectively suppresses the bending, torsion and other elastic deformations of the links.

Claims

1. A three-mode parallel robot mechanism based on an adjustable branched motion center, comprising: A fixed base, a moving platform, and branches; the fixed base and the moving platform are connected by N parallel branches; Its features are: The number of branches N is greater than or equal to 3, all branches have the same structure and are of equal length; all branches are evenly arranged on the outer circumference of the moving platform and the fixed base. The structure of the branch is an URRU branch; each branch includes, from bottom to top: a first universal joint, a first revolute joint, a second revolute joint, and a second universal joint; The branch structure includes three links connected sequentially from bottom to top: a first link, a second link, and a third link; the bottom end of the first link is connected to the fixed base based on a first universal joint, and the top end of the fourth link is connected to the moving platform through a second universal joint; adjacent links are connected to each other through revolute joints, and the rotation axes of the two revolute joints are parallel to each other; The first universal joint includes two intersecting revolute joints: revolute joint R11 and revolute joint R12. The axes of the two revolute joints are perpendicular to each other and parallel to the fixed base. The axis of revolute joint R11 points to the center of the fixed base. The intersection of the axes of the four revolute joints R11 is the centroid.

2. The three-mode parallel robot mechanism based on adjustable branch motion centers according to claim 1, characterized in that: The second universal joint includes: a rotating joint R21 and a rotating joint R22 that intersect each other, wherein the axis of the rotating joint R22 is always perpendicular to the axis of the rotating joint R21; the rotating joint R21 is connected to the third link, and the rotating joint R22 is connected to the moving platform.

3. The three-mode parallel robot mechanism based on adjustable branch kinematic centers according to claim 2, characterized in that: The second universal joint revolute R22 is parallel or coplanar with the moving platform.

4. The three-mode parallel robot mechanism based on adjustable branch kinematic centers according to claim 1, characterized in that: The rotation axes of the first universal joint's revolute joint R12, the first revolute joint's rotation axis, and the second revolute joint's rotation axis are parallel to each other. The axis of rotation of the first universal joint R11 and the axis of rotation of the second universal joint R21 are neither parallel nor collinear; at the same time, the axis of rotation of the first universal joint R11 and the axis of rotation of the second universal joint R21 are perpendicular to the axes of rotation of the first universal joint R12, the first universal joint, and the second universal joint, respectively.

5. The three-mode parallel robot mechanism based on adjustable branch motion centers according to claim 2, characterized in that: Each branch is provided with three drive pairs: the first universal joint's revolute joint R11, the first universal joint's revolute joint R12, and the second universal joint's revolute joint R22.

6. The three-mode parallel robot mechanism based on adjustable branch kinematic centers according to claim 1, characterized in that: The moving platform is configured in a cross shape, and the number of branches is set to 4; A U-shaped connector is provided on each branch of the cross-shaped moving platform, and the two ends of the rotating joint R22 in the second universal joint of each branch are rotatably connected to the U-shaped connector.

7. The three-mode parallel robot mechanism based on adjustable branch kinematic centers according to claim 1, characterized in that: The base can be a cross, star, or ring structure.

8. The three-mode parallel robot mechanism based on an adjustable branch kinematic center as described in claim 6, characterized in that: A sliding pair is provided at the lower end of the cross-shaped center position of the moving platform.

9. The three-mode parallel robot mechanism based on adjustable branch motion centers according to claim 1, characterized in that: The first and second links have the same structure, with a U-shaped connector at one end and a T-shaped connector at the other end; the third link has U-shaped connectors at both ends, and the lines connecting the open ends of the U-shaped connectors at both ends are perpendicular to each other.

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