A parallel robot mechanism with three motion mode RCMs

Abstract

The application provides a kind of RCM parallel robot mechanism with three kinds of motion modes, which has simple structure, convenient processing and high rigidity, and is suitable for more scenes. The moving pair of the moving platform and the rotating pair of the branch chain are combined together and used as the connection structure of the moving platform and the top of the branch chain. By adjusting the moving pair, the position of the rotating pair at the top of the branch chain is changed, the positional relationship between the axes of several rotating pairs at the top of the branch chain is controlled, and the relationship between the axis of the rotating pair at the top of the branch chain and the fixed platform is controlled, so that three different motion modes are realized.

Description

Technical Field

[0001] This invention relates to the fields of mechanics and robotics, specifically to an RCM parallel robot mechanism with three motion modes. Background Technology

[0002] A telecentric mechanism is a parallel mechanism in which the end effector of a surgical instrument used in minimally invasive surgery can move based on a single telecentric point; this movement is called telecentric motion. Most telecentric parallel mechanisms have only one degree of freedom and lack versatility. For example, if a patient only needs to undergo a simple puncture procedure, an end effector with only 1R1T degrees of freedom is sufficient. Using an end effector with multiple degrees of freedom would increase the difficulty of the surgery. For complex surgeries, a single-degree-of-freedom end effector is insufficient.

[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 limitations of existing RCM parallel robot structures due to their difficult manufacturing process and low rigidity, which restricts their application scenarios, this invention provides an RCM parallel robot mechanism with three motion modes. 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 solution of the present invention is as follows: an RCM parallel robot mechanism with three motion modes, comprising: a fixed base and a moving platform, characterized in that: the fixed base and the moving platform are connected by N parallel branches, wherein N≥3; all branches have the same branch structure, which is an RRRRR branch; The moving platform includes N moving platform connecting rods of equal length; each moving platform connecting rod has a plate-like structure with a through groove in the middle serving as a moving platform slide groove; at least one end of each moving platform connecting rod is set in an arc shape; on the upper surface of the arc end, an arc-shaped slider is provided that protrudes upward and is perpendicular to the plate surface of the moving platform connecting rod along the arc shape of the end, while the lower surface of the arc end has a concave arc-shaped slide groove along the arc shape of the end, and the shape and size of the arc-shaped slide groove are adapted to the shape and size of the arc-shaped slider; The moving platform includes: N revolute joints and N prismatic joints for the moving platform; N moving platform connecting rods are inserted together from top to bottom based on the arc-shaped sliding groove and the arc-shaped slider to form N coaxial rotating pairs for the moving platform; The top end of each branch is connected to the moving platform via a sliding joint, and the bottom end is connected to the fixed base via the bottommost revolute joint; the branches are evenly arranged on the circumference formed by the connection points between the bottom end of the branch and the fixed base. The point of intersection of the rotation axes of the lowest rotating joints of the N branches is the centroid.

[0006] Its further features are: The structure of the branch includes four branch links connected sequentially from bottom to top: the first link, the second link, the third link, and the fourth link; One end of the first connecting rod forms a first revolute joint with the fixed base, and the other end forms a second revolute joint with one end of the second connecting rod. The other end of the second connecting rod forms a third revolute joint with one end of the third connecting rod, and the other end of the third connecting rod forms a fourth revolute joint with one end of the fourth connecting rod. The other end of the fourth connecting rod is provided with a protruding cylindrical slider, the diameter of which is adapted to the size of the moving platform groove opened on the moving platform connecting rod. The cylindrical slider is movably inserted into the moving platform groove, forming a sliding joint of the moving platform and also forming a fifth revolute joint of the chain. The axes of rotation of the second, third, and fourth revolute joints are parallel to each other; The axes of rotation of the first revolute joint and the fifth revolute joint are neither parallel nor collinear; at the same time, the axes of rotation of the first revolute joint and the fifth revolute joint are perpendicular to the axes of rotation of the second revolute joint, the third revolute joint and the fourth revolute joint, respectively. The rotation axis of the rotating joint of the moving platform is perpendicular to the plane in which the moving platform is located; It also includes: a drive pair, the drive pair including a drive pair for platform transformation and a drive pair for branching; The driving joint for the moving platform includes: N moving joints; The drive pair for the branch includes: a first revolute joint and a second revolute joint on each branch; The structure of the first connecting rod includes: an annular connector, a straight connector, and a rod body. The straight connector is disposed at one end of the rod body in a direction perpendicular to the rod body, and the annular connector is disposed at the other end of the rod body. The axis of the annular connector is perpendicular to both the rod body and the straight connector. The second and third connecting rods have the same mechanism, comprising: a U-shaped connector, a straight connector, and a rod body. One end of the rod body is provided with the closed end of the U-shaped connector, and the two open ends of the U-shaped connector have through holes in a direction perpendicular to the rod body. The straight connector is provided at the other end of the rod body in a direction parallel to the axes of the two through holes. The diameter of the straight connector is adapted to the inner diameter of the through holes. The fourth link further includes: a rod body and a U-shaped connector, one end of the rod body is provided with the closed end of the U-shaped connector, and the two open ends of the U-shaped connector are provided with through holes in a direction perpendicular to the rod body. The slider is perpendicular to both the rod body and the axis of the two through holes. The fixed base is a cross-shaped structure, a star-shaped structure, a frame-shaped structure, or a ring-shaped structure; A U-shaped connector is provided on the fixed base. The closed end of the U-shaped connector is connected to the fixed base. The two open ends of the U-shaped connector are provided with a horizontal axis in a direction parallel to the plane of the fixed base. The diameter of the horizontal axis is adapted to the inner diameter of the annular connector on the first connecting rod. The number of branches, N, is 4.

[0007] This application provides an RCM parallel robot mechanism with three motion modes. It combines the prismatic joints of the moving platform and the revolute joints of the branches as a connection structure between the moving platform and the top of the branches. By adjusting the prismatic joints, the position of the revolute joints at the top of the branches is changed, controlling the positional relationship between the axes of the revolute joints at the top of the branches, and controlling the relationship between the axes of the revolute joints at the top of the branches and the fixed platform, thus achieving three different motion modes: three rotations and one prismatic joint with a stationary telecentric point, two rotations and one prismatic joint with three rotations and a stationary telecentric point, and one rotation and one prismatic joint with a stationary telecentric point. This application achieves motion mode reconstruction without changing the kinematic joints within the branches, reducing the complexity of mode reconstruction. Based on the three-mode parallel mechanism in this application, the motion mode switching method is easy to control, using only single-degree-of-freedom kinematic joints and avoiding complex kinematic joints. It has low requirements for the stiffness and assembly accuracy of the mechanism components, a simple structure, and is easy to modularize and manufacture. It is applicable to production and assembly tasks requiring multiple motion modes. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the overall structure of this application; Figure 2 This is a schematic diagram of the structure of the first branch; Figure 3 This is a structural diagram of the moving platform; Figure 4 A schematic diagram of the connecting rod of the moving platform; Figure 5 This is a schematic diagram of the first link; Figure 6 This is a schematic diagram of the second link; Figure 7 This is a structural diagram of the fourth link; Figure 8 This is an example of a general posture where the organization in this application is located under the pattern; Figure 9 This is a general example of the organization in this application being located in Mode 2; Figure 10 This is a general posture example of the organization in this application under Mode 3.

[0009] In the picture: 1 First branch; 11 First link of first branch; 12 Second link of first branch; 13 Third link of first branch; 14 Fourth link of first branch; 2 Second branch; 21 First link of second branch; 22 Second link of second branch; 23 Third link of second branch; 24 Fourth link of second branch; 3 Third branch; 31 First link of third branch; 32 Second link of third branch; 33 Third link of third branch; 34 Fourth link of third branch; 4 Fourth branch; 41 First link of fourth branch; 42 Second link of fourth branch; 43 Third link of fourth branch; 44 Fourth link of fourth branch; 5 Reconfigurable moving platform; 51 First link of moving platform; 52 Second link of moving platform; 53 Third link of moving platform; 54 Fourth link of moving platform; 511 Link body of moving platform; 512 Slide groove of moving platform; 513 Support arc plate; 514 Arc-shaped slider; 515 Arc-shaped slide groove; 6. Fixed base; 61. U-shaped connector for base; 7. Rod body; 8. Straight connector; 9. Ring connector; 10. U-shaped connector; 101. Through hole; 102. Columnar slider; 1-1 First revolute joint of the first branch; 1-2 Second revolute joint of the first branch; 1-3 Third revolute joint of the first branch; 1-4 Fourth revolute joint of the first branch; 1-5 Fifth revolute joint of the first branch; 2-1 First revolute joint of the second branch; 3-1 First revolute joint of the third branch; 4-1 First revolute joint of the fourth branch; 2-2 Second revolute joint of the second branch; 3-2 Second revolute joint of the third branch; 4-2 Second revolute joint of the fourth branch; 51-1 Moving platform rotary joint one, 52-1 Moving platform rotary joint two, 53-1 Moving platform rotary joint three, 54-1 Moving platform rotary joint four; 51-2 Moving sub-unit 1, 52-2 Moving sub-unit 2, 53-2 Moving sub-unit 3, 54-2 Moving sub-unit 4. Detailed Implementation

[0010] like Figure 1As shown, the present invention includes an RCM parallel robot mechanism with three motion modes, comprising: a fixed base 6 and a reconfigurable moving platform 5. The fixed base 6 and the moving platform 5 are connected by N parallel branches, wherein N≥3; in this embodiment, the number of branches N is 4, and a total of 4 branches are provided, namely: first branch 1, second branch 2, third branch 3 and fourth branch 4.

[0011] like Figure 3 and Figure 4 As shown, the moving platform 5 includes N moving platform links of equal length. The number of moving platform links is the same as the number of branches. In this embodiment, four moving platform links are provided: moving platform first link 51, moving platform second link 52, moving platform third link 53, and moving platform fourth link 54. The moving platform links have the same structure, as shown... Figure 4 As shown, taking the first link 51 of the moving platform as an example, the structure of the moving platform link is explained.

[0012] The moving platform connecting rod includes a plate-shaped moving platform connecting rod body 511. A through groove is formed in the middle of the moving platform connecting rod body 511 as a moving platform slide groove 512. At least one end of the moving platform connecting rod body 511 is set in an arc shape. In this embodiment, both ends of the moving platform connecting rod body 511 are set in an arc shape, and correspondingly, both ends of the moving platform slide groove 512 in the length direction are also semi-circular arc shapes. On the upper surface of one arc end of the moving platform connecting rod body 511, a support arc plate 513 is provided along the arc shape of the end. The support arc plate 513 is perpendicular to the moving platform connecting rod plate surface, and an arc-shaped slider 514 is provided at the top of the support arc plate 513. At the same time, the lower surface of the arc end where the support arc plate 513 is located is formed along the arc shape of the end with a concave arc-shaped slide groove 515. The shape and size of the arc-shaped slide groove 515 are adapted to the shape and size of the arc-shaped slider 514.

[0013] The moving platform 5 includes N revolute joints and N prismatic joints. The N moving platform connecting rods are connected from top to bottom based on arc-shaped grooves 515 and arc-shaped sliders 514, forming N coaxial revolute joints. In this embodiment, there are four revolute joints: revolute joint one 51-1, revolute joint two 52-1, revolute joint three 53-1, and revolute joint four 54-1. The revolute joints are coaxial, and their rotation axes are perpendicular to the plane of the moving platform 5.

[0014] All branches have the same branch structure, which is RRRRR branch. In the initial configuration, all branches are symmetrically distributed on the fixed base 6, where R represents a revolute joint.

[0015] The structure of the branch chain consists of four branch links connected sequentially from bottom to top: the first link, the second link, the third link, and the fourth link.

[0016] like Figure 5 As shown, the structure of the first connecting rod includes: an annular connector 9, a straight connector 8, and a rod body 7. The straight connector 8 is arranged at one end of the rod body 7 in a direction perpendicular to the rod body 7, and the annular connector 9 is arranged at the other end of the rod body 7. The axis of the annular connector 9 is perpendicular to both the rod body 7 and the straight connector 8.

[0017] The mechanisms of the second and third links are the same. For example... Figure 6 As shown, taking the second connecting rod as an example, the specific structure includes: a U-shaped connector 10, a straight connector, and a rod body 7. One end of the rod body 7 is provided with the closed end of the U-shaped connector 10, and the two open ends of the U-shaped connector 10 are provided with through holes 101 in a direction perpendicular to the rod body 7; the straight connector 8 is provided at the other end of the rod body 7 in a direction parallel to the axis of the two through holes 101; the diameter of the straight connector 8 is adapted to the inner diameter of the through holes 101.

[0018] like Figure 7 As shown, the fourth connecting rod includes: a rod body 7, a U-shaped connector 10, and a cylindrical slider 102. One end of the rod body 7 has the closed end of the U-shaped connector 10. The two open ends of the U-shaped connector 10 have through holes 101 in a direction perpendicular to the rod body 7. The slider is perpendicular to both the axis of the rod body 7 and the axes of the two through holes 101. The diameter of the cylindrical slider 102 is adapted to the size of the moving platform groove 512 on the moving platform connecting rod.

[0019] The connection method between the branch and the fixed base 6 is as follows: a base U-shaped connector 61 is provided on the fixed base 6, the closed end of the base U-shaped connector 61 is used to fix the base 6, and the two open ends of the base U-shaped connector 61 are provided with a horizontal axis (not marked in the figure) in a direction parallel to the plane of the fixed base 6. The diameter of the horizontal axis is adapted to the inner diameter of the annular connector 9 on the first link. The annular connector 9 on the first link of each link is fitted onto the horizontal axis to form a rotating pair of each branch, realizing the connection between the bottom of the branch and the fixed base 6.

[0020] The connection between the branch and the east platform 5 is as follows: the cylindrical slider 102 on the fourth link is movably inserted into the sliding groove 512 of the moving platform from top to bottom, forming a sliding joint of the moving platform 5 and also forming the fifth rotating joint of each branch. In this application, through structural design, the sliding joint of the moving platform and the rotating joint of the branch are combined together as the connection structure between the top of the moving platform and the branch.

[0021] The connections between the four links of the branch, the connection between the branch and the moving platform, and the connection between the branch and the fixed base are all the same, such as... Figure 2 As shown, the explanation will be based on the first branch 1 as an example.

[0022] The annular connector of the first link 11 of the first branch and the fixed base 6 form the first rotating joint 1-1 of the first branch; the straight connector of the first link 11 of the first branch and the U-shaped connector of the second link 12 of the first branch form the second rotating joint 1-2 of the first branch; the straight connector of the second link 12 of the first branch and the U-shaped connector of the third link 13 of the first branch form the third rotating joint 1-3 of the first branch; the straight connector of the third link 13 of the first branch and the U-shaped connector of the fourth link 14 of the first branch form the fourth rotating joint 1-4 of the first branch; the cylindrical slider 102 of the fourth link 14 of the first branch is movably inserted into the moving platform slide groove 512 opened in the moving platform connecting rod 511, forming the moving joint 51-2 of the moving platform 5, and also forming the fifth rotating joint 1-5 of the first branch of the branch.

[0023] The axes of rotation of the second, third, and fourth revolute joints in each branch are parallel to each other; the axes of rotation of the first and fifth revolute joints are neither parallel nor collinear; simultaneously, the axes of rotation of the first and fifth revolute joints are perpendicular to the axes of rotation of the second, third, and fourth revolute joints, respectively. For example... Figure 2 As shown, the axes of rotation of the second revolute joint 1-2, the third revolute joint 1-3, and the fourth revolute joint 1-4 of the first branch are parallel to each other; the axis of rotation of the first revolute joint 1-1 of the first branch is perpendicular to the axes of rotation of the second revolute joint 1-2, the third revolute joint 1-3, and the fourth revolute joint 1-4 of the first branch; the axis of rotation of the fifth revolute joint 1-5 of the first branch is perpendicular to the axes of rotation of the second revolute joint 1-2, the third revolute joint 1-3, and the fourth revolute joint 1-4 of the first branch; at the same time, the axes of rotation of the fifth revolute joint 1-5 of the first branch and the first revolute joint 1-1 of the first branch are neither parallel nor collinear.

[0024] In practical applications, in order to ensure that the fifth revolute joint of each branch and the sliding joint of the moving platform 5 can be realized, the height difference between the supporting arc plate and the moving platform connecting rod body must be greater than or equal to the thickness of the fourth connecting rod body 7; at the same time, the thickness of the columnar slider 102 must be adapted to the depth of the moving platform slide groove 512 to ensure that the superimposed fourth connecting rods do not affect each other during sliding and rotation, and to ensure that the columnar slider 102 of each branch can move along the moving platform slide groove to the center point of the moving platform 5.

[0025] In this application, all branch structures are identical and of equal length. The top of each branch is connected to the moving platform 5 via a sliding joint, and the bottom is connected to the fixed base 6 via a rotating joint at the very bottom. The fixed base 6 can be a cross structure, a star structure, or a ring structure, with the specific structure selected according to actual needs. The branches are evenly arranged on the circumference formed by the connection points between the bottom of the branch and the fixed base 6. In this embodiment, the fixed base 6 is a cross structure with branches of equal length, and the four branches are symmetrically arranged in pairs, evenly distributed on the circumference of the outer circle of the cross structure.

[0026] In this application, the point where the rotation axes of the lowest rotating joints of the N branches intersect is the centroid. For example... Figure 8 , Figure 9 and Figure 10 As shown, the axes of motion of the first revolute joint 1-1 of the first branch, the first revolute joint 2-1 of the second branch, the first revolute joint 3-1 of the third branch, and the first revolute joint 4-1 of the fourth branch always intersect at a single point, and all axes lie in the same plane. This point is the centroid.

[0027] The drive pairs include drive pairs for the transformation of the moving platform and drive pairs for the branches. The drive pairs for the moving platform include N prismatic joints; that is, in this embodiment, four prismatic joints of the moving platform—prismatic joint 1 51-2, prismatic joint 2 52-2, prismatic joint 3 53-2, and prismatic joint 4 54-2—are set as drive pairs to control the configuration changes of the reconfigurable moving platform. In practical applications, the displacement changes of the prismatic joints are achieved by driving them using linear drive modules such as linear cylinders. The drive pairs for the branches include a first revolute joint and a second revolute joint on each branch, which are driven by a motor to achieve rotation.

[0028] By adjusting the positional relationship between the top of each branch and the fifth rotary joint connected to the moving platform 5, the mechanism can be controlled to enter different telecentric motion modes. The mechanism of this application supports three different motion modes: three rotations and one movement (3T1R) with a fixed telecentric point, two rotations and one movement (2T1R) with a fixed telecentric point, and one rotation and one movement (1T1R) with a fixed telecentric point.

[0029] The initial state of the mechanism in this application is a motion mode of three rotations (R) and one translation (T) with a fixed telecentric point. In this mode, among the four moving platform links of the reconfigurable moving platform 5, the ends of all branches on the plane of the moving platform coincide with the center of the reconfigurable moving platform. Figure 8The illustrated embodiment shows four reconfigurable moving platform links 5 connected layer by layer. The axes of the rotating joints of the four moving platform links are on the same straight line L. The axes of the fifth rotating joints of the four branches L1, L2, L3, and L4 coincide with axis L. In the figure, the red arrows represent the three rotating axes of the moving platform 5 in this mode: R1, R2, and R3. The blue arrows indicate the movable direction T of the moving platform 5. The movable direction T is located on the circumferential line L and coincides with one of the rotating axes R.

[0030] exist Figure 8 As shown in the 3T1R configuration with a fixed telecentric point, by driving the first revolute joint 1-1 of the first branch, the first revolute joint 2-1 of the second branch, the first revolute joint 3-1 of the third branch, the first revolute joint 4-1 of the fourth branch, the second revolute joint 1-2 of the first branch, the second revolute joint 2-2 of the second branch, the second revolute joint 3-2 of the third branch, and the second revolute joint 4-2 of the fourth branch, the mechanism achieves a motion mode of three rotations and one movement with a fixed telecentric point. For example, by driving the first revolute joint 1-1 of the first branch, the first revolute joint 2-1 of the second branch, the first revolute joint 3-1 of the third branch, the first revolute joint 4-1 of the fourth branch, and the second revolute joint 2-2 of the second branch, the second revolute joint 3-2 of the third branch, and the second revolute joint 4-2 of the fourth branch to rotate simultaneously in the same direction, the moving platform 5 can achieve rotation in the R3 direction with L as the axis. Drive one or more of the following components to rotate: the first branch second revolute joint 1-2, the second branch second revolute joint 2-2, the third branch second revolute joint 3-2, and the fourth branch second revolute joint 4-2, while locking the first revolute joint, thus enabling movement in the T direction.

[0031] The second state of the mechanism in this application is a motion mode of two rotations and one movement with a fixed telecentric point. In this mode, on the plane of the moving platform, the end of the fourth link of at least one branch does not coincide with the center of the reconfigurable moving platform, that is: at least one axis of L1, L2, L3, L4 does not coincide with axis L, but at the same time, all four axes L1, L2, L3, L4 are perpendicular to the plane of the fixed platform. For example, based on Figure 8 In the initial state, the moving joints on the four moving platforms are driven, causing the cylindrical sliders at the top of all branches to slide along the sliding grooves of the moving platform, moving away from the center point of the moving platform 5. Then, the axes L1, L2, L3, and L4 of the fifth rotating joints of the four branches separate from axis L, entering the 2R1T mode. Figure 9 The state of the illustrated embodiment. Figure 9The four moving platform links of the reconfigurable moving platform 5 are connected layer by layer. The axes of the revolute joints of the four moving platform links are the same straight line L. At this time, the axes of the fifth revolute joints of the four branches L1, L2, L3, and L4 do not coincide with the axis L, and the four axes L1, L2, L3, and L4 are all perpendicular to the plane of the fixed platform. At this time, by driving the first and second revolute joints on each branch, the mechanism achieves a motion mode of two rotations and one movement with a fixed telecentric point. Figure 9 The red arrows in the middle indicate the two rotation axes R of the moving platform 5 in this mode, and the blue arrows indicate the movable direction T of the moving platform 5. The moving direction T is located on the circumference line L.

[0032] The mechanism described in this application operates in a motion mode characterized by three rotations and one movement with a fixed centroid. In this mode, the first rotational joint axes of the four moving platform links are aligned with a straight line L. At this time, at least one of the fifth rotational joint axes L1, L2, L3, and L4 of the four branches does not coincide with axis L, and none of the four axes L1, L2, L3, and L4 are perpendicular to the plane of the fixed platform. For example, in... Figure 9 In this state, by simultaneously driving the first rotating joint 1-1 of the first branch, the first rotating joint 3-1 of the third branch, the second rotating joint 2-2 of the second branch, and the second rotating joint 4-2 of the fourth branch to rotate in the direction of the fourth branch 4, the moving platform 5 is driven to deflect in the direction of the fourth branch 4, thus obtaining... Figure 10 The state of the illustrated embodiment. Figure 10 In the middle, the four links of the reconfigurable moving platform 5 are connected layer by layer. The first rotational joint axis of the four links is the same straight line L. At this time, the fifth rotational joint axes L1, L2, L3, and L4 of the four branches do not coincide with the axis L, and the four axes L1, L2, L3, and L4 are not perpendicular to the plane where the fixed platform is located. Figure 10 The red arrow in the middle indicates the rotation axis R of the moving platform 5 in this mode, and the blue arrow indicates the movable direction T of the moving platform 5, with the movement direction T located on the circumferential line L. In this state, the movable mechanism can achieve a motion mode based on the rotation axis R and the movement direction T, which involves rotation and movement with a fixed centroid.

[0033] After using the technical solution of this invention, all branches are connected in parallel between the moving platform 5 and the fixed base 6, and the RCM is realized by the constraint relationship between the branches. Its degree of freedom can be changed according to the change of the branch ends. The degree of freedom of the parallel mechanism is the intersection of all branches. When different branches find the intersection in the movement and rotation, the normal direction of the moving plane and the rotation center play an important role. This patent uses the change of the position of the rotation center of the branch to realize the switching of different degrees of freedom. For example, when the degree of freedom is 3R1T, the rotation centers of all branches coincide. When the degree of freedom is 2R1T, the rotation centers of the branches do not coincide and are all perpendicular to the plane of the fixed platform. When the degree of freedom is 1R1T, the rotation centers of the branches do not coincide and are not perpendicular to the plane of the fixed platform. At the same time, in this application, the parallel mechanism is formed by multiple independent kinematic chains (branches) connecting the moving platform and the stationary platform to form a closed loop structure. The load is shared by multiple branches, resulting in high overall stiffness. It does not use multi-degree-of-freedom kinematic pairs, but only relies on revolute and prismatic joints to achieve RCM. The branch structure is simple, easy to manufacture, and can be applied to more application scenarios.

Claims

1. A parallel RCM robot mechanism with three motion modes, comprising: A fixed base and a moving platform, characterized in that: the fixed base and the moving platform are connected by N parallel branches, wherein N≥3; all branches have the same branch structure, which is an RRRRR branch; The moving platform includes N moving platform connecting rods of equal length; each moving platform connecting rod has a plate-like structure with a through groove in the middle serving as a moving platform slide groove; at least one end of each moving platform connecting rod is set in an arc shape; on the upper surface of the arc end, an arc-shaped slider is provided that protrudes upward and is perpendicular to the plate surface of the moving platform connecting rod along the arc of the end, while the lower surface of the arc end has a concave arc-shaped slide groove along the arc of the end, and the shape and size of the arc-shaped slide groove are adapted to the shape and size of the arc-shaped slider; The moving platform includes: N revolute joints and N prismatic joints for the moving platform; N moving platform connecting rods are inserted together from top to bottom based on the arc-shaped sliding groove and the arc-shaped slider to form N coaxial rotating pairs for the moving platform; The top end of each branch is connected to the moving platform via a sliding joint, and the bottom end is connected to the fixed base via the bottommost revolute joint; the branches are evenly arranged on the circumference formed by the connection points between the bottom end of the branch and the fixed base. The point of intersection of the rotation axes of the bottommost rotating joints of the N branches is the centroid. The structure of the branch includes four branch links connected sequentially from bottom to top: the first link, the second link, the third link, and the fourth link; One end of the first connecting rod forms a first revolute joint with the fixed base, and the other end forms a second revolute joint with one end of the second connecting rod. The other end of the second connecting rod forms a third revolute joint with one end of the third connecting rod, and the other end of the third connecting rod forms a fourth revolute joint with one end of the fourth connecting rod. The other end of the fourth connecting rod is provided with a protruding cylindrical slider, the diameter of which is adapted to the size of the moving platform groove opened on the moving platform connecting rod. The cylindrical slider is movably inserted into the moving platform groove, forming a sliding joint of the moving platform and also forming a fifth revolute joint of the chain. The axes of rotation of the second, third, and fourth revolute joints are parallel to each other; The axes of rotation of the first revolute joint and the fifth revolute joint are neither parallel nor collinear; simultaneously, the axes of rotation of the first revolute joint and the fifth revolute joint are perpendicular to the axes of rotation of the second, third, and fourth revolute joints, respectively. The rotation axis of the rotating joint of the moving platform is perpendicular to the plane in which the moving platform is located.

2. The RCM parallel robot mechanism with three motion modes according to claim 1, characterized in that: It also includes: a drive pair, the drive pair including a drive pair for platform transformation and a drive pair for branching; The driving joint for the moving platform includes: N moving joints; The drive joint for the branch includes: a first revolute joint and a second revolute joint on each branch.

3. The RCM parallel robot mechanism with three motion modes according to claim 1, characterized in that: The first connecting rod includes an annular connector, a straight connector, and a rod body. The straight connector is disposed at one end of the rod body in a direction perpendicular to the rod body, and the annular connector is disposed at the other end of the rod body. The axis of the annular connector is perpendicular to both the rod body and the straight connector.

4. The RCM parallel robot mechanism with three motion modes according to claim 1, characterized in that: The second link and the third link have the same mechanism, which includes: a U-shaped connector, a straight connector, and a rod body. One end of the rod body is provided with the closed end of the U-shaped connector, and the two open ends of the U-shaped connector are provided with through holes in a direction perpendicular to the rod body. The straight connector is provided at the other end of the rod body in a direction parallel to the axis of the two through holes. The diameter of the straight connector is adapted to the inner diameter of the through holes.

5. The RCM parallel robot mechanism with three motion modes according to claim 1, characterized in that: The fourth link further includes: a rod body and a U-shaped connector. One end of the rod body is provided with the closed end of the U-shaped connector. The two open ends of the U-shaped connector have through holes in a direction perpendicular to the rod body. The slider is perpendicular to both the rod body and the axes of the two through holes.

6. The RCM parallel robot mechanism with three motion modes according to claim 1, characterized in that: The fixed base can be a cross-shaped structure, a star-shaped structure, a frame-shaped structure, or a ring-shaped structure.

7. The RCM parallel robot mechanism with three motion modes according to claim 1, characterized in that: A U-shaped connector is provided on the fixed base. The closed end of the U-shaped connector is connected to the fixed base. The two open ends of the U-shaped connector are provided with a horizontal axis in a direction parallel to the plane of the fixed base. The diameter of the horizontal axis is adapted to the inner diameter of the annular connector on the first connecting rod.

8. The RCM parallel robot mechanism with three motion modes according to claim 1, characterized in that: The number of branches, N, is 4.

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