A parallel mechanism with six degrees of freedom for pose decoupling

Abstract

This invention discloses a six-degree-of-freedom (DOF) pose-decoupled parallel mechanism, belonging to the field of mechanics. The parallel mechanism includes a fixed platform, a moving platform, and two sets of branch groups arranged in parallel between the fixed and moving platforms. Each branch group contains at least three branches; each branch contains five sequentially connected rotating components, connected to a base and the moving platform respectively through rotating components at both ends. The parallel mechanism proposed in this invention possesses six degrees of freedom, enabling translational and rotational motions of the moving platform relative to the fixed platform. The translational motion is entirely controlled by the rotating components of one set of transmission components. When the position is fixed, the rotational motion can be controlled by the rotating components of the other set of transmission components, thus achieving decoupling of position and attitude control. All the rotating components controlling the input of this invention are directly connected to the base, allowing the drive module to be fixed to the base, thereby reducing the dynamic mass of the mechanism.

Description

Technical Field

[0001] This invention belongs to the field of mechanics, and particularly relates to the field of robot mechanics and parallel robot technology, specifically to a parallel mechanism with six degrees of freedom of pose decoupling. Background Technology

[0002] Compared to serial mechanisms, parallel mechanisms, with their advantages of high rigidity, high precision, and high load-bearing capacity, have become a core configuration in high-end equipment. Among them, six-DOF parallel mechanisms can achieve precise six-DOF motion within a limited space and are widely used in key areas such as precision machining, surgical robots, and flight simulators. However, the development of this type of mechanism still faces significant challenges: firstly, real-time solution of forward kinematics (position forward kinematics) is difficult; secondly, the reliance on high-precision composite kinematic pairs such as ball joints leads to high manufacturing costs, difficulty in completely eliminating motion errors, and limited workspace. These bottlenecks severely restrict further improvement in their overall performance and large-scale engineering applications.

[0003] Currently, typical six-degree-of-freedom parallel mechanism configurations mainly include:

[0004] 1. Gough-Stewart platforms based on symmetrical branches and their variants: such as 6-SPS and 6-UPS configurations with six identical branches, and their derivatives (e.g., 6-PUS and 6-RUS). These configurations are intuitive and simple. However, their inherent drawbacks include: highly complex forward kinematics solutions with a lack of analytical solutions; the existence of various singular configurations affecting control stability; and the high precision machining difficulty of key kinematic pairs such as ball joints, making it difficult to guarantee the high-precision motion requirements of the end effector.

[0005] 2. A symmetrical configuration with three composite branches: such as 3-PPPS, 3-PPSR, etc. This type of scheme usually requires two drive sources to be arranged on a single branch, causing the motor providing the drive to become part of the load of the moving platform, significantly increasing the system inertia, and thus impairing the high-speed dynamic performance of the mechanism (reduced maneuverability).

[0006] 3. Asymmetric branch scheme: This type of scheme is usually a modification design of the branch of the Gough-Stewart platform. Although it can change the distribution of singular configurations to a certain extent, it fails to fundamentally solve the core problems that are common in the aforementioned schemes, such as processing costs, error accumulation, and workspace limitations.

[0007] Crucially, the existing solutions generally share a common shortcoming: the difficulty in effectively decoupling mechanism position control from attitude control. This strong motion coupling not only exacerbates the complexity of kinematic analysis but also significantly reduces real-time control efficiency, becoming a key factor hindering performance optimization and application expansion. Summary of the Invention

[0008] To overcome the shortcomings of existing technologies, this invention provides a six-degree-of-freedom pose decoupling parallel mechanism. Based on a bilateral symmetrical branched structure and employing pure revolute joints, this mechanism effectively decouples the position and attitude control of the moving platform. Simultaneously, the actuators can be arranged on a fixed platform, significantly reducing the load and inertia of the moving platform, simplifying the manufacturing and assembly of the joint structure, and contributing to improved overall motion accuracy.

[0009] The six-degree-of-freedom pose decoupling parallel mechanism of the present invention includes a moving platform, a fixed platform, a URS branch group, and an SRU branch group.

[0010] The URS branch group comprises at least three URS branches with identical structures; each URS branch includes five rotating components connected in series. The first rotating component is connected to the fixed platform via a first R-pair and to the second rotating component via a second R-pair. The axes of the first and second R-pairs intersect at a first common point on the fixed platform, forming a U-pair motion relationship. The second rotating component is connected to the third rotating component via a third R-pair. The fourth rotating component is connected to the third rotating component via a fourth R-pair and to the fifth rotating component via a fifth R-pair. The fifth rotating component is connected to the moving platform via a sixth R-pair. The axes of the fourth, fifth, and sixth R-pairs intersect at a second common point on the moving platform, forming an S-pair motion relationship.

[0011] The SRU branch group contains at least three SRU branches with the same structure; the structure of the SRU branch is exactly the same as that of the URS branch, but its first rotating member is connected to the moving platform through the first R joint, and its fifth rotating member is connected to the fixed platform through the sixth R joint.

[0012] The technical terms S-sub, U-sub, and R-sub used in this invention are all well-known terms in the field, and their meanings are as follows:

[0013] An Spherical Joint (S-joint) is a spherical joint consisting of three rotational axes (three R-joint axes) that intersect at a single point (R∩R∩R).

[0014] A universal joint (U-joint) is a revolute joint (R∩R) formed by two rotation axes (two R-joint axes) intersecting at a single point.

[0015] An R-joint (Revolute Joint) is a revolute joint with one rotational degree of freedom (such as a door hinge).

[0016] The axis of the R-pair refers to the axis of rotation of the R-pair.

[0017] In this invention, the URS branch represents a branch composed of U-joints, R-joints, and S-joints connected sequentially. Similarly, the SRU branch represents a branch composed of S-joints, R-joints, and U-joints connected sequentially. In this invention, the URS and SRU branches have identical structures, both including five rotating components, with their orientations reversed only in the mounting direction between the two platforms. The material of the rotating components is not limited as long as it can transmit motion and remain undeformed; for example, it can be metal (such as stainless steel), engineering plastics, carbon fiber, etc. Provided the aforementioned rotational relationship is satisfied, the size and form of the rotating components are also not required. For example, the rotating components can be in the form of connecting rods, plates, etc., and can be hollow or solid.

[0018] This invention's parallel mechanism is suitable for fields with stringent precision requirements, such as ultra-precision machining, where it serves as a moving platform for machine tools, providing multi-axis linkage milling capabilities for the cutting tools. In the field of minimally invasive surgical robots, it can be equipped with precision tools such as lasers, thus serving as a component of ophthalmic microsurgery or intracranial surgical robot systems, meeting the demands for high precision and high mobility in confined spaces.

[0019] The parallel mechanism of the present invention has the following significant advantages:

[0020] 1. Position and attitude decoupling: The unique bilateral symmetric URS / SRU branch configuration achieves effective decoupling of the position and attitude of the moving platform (the position of the moving platform is determined only by the URS branch group), which significantly simplifies the kinematic model and control algorithm.

[0021] 2. Low load on the moving platform: All drives are located on the fixed platform, which greatly reduces the load and inertia of the moving platform and improves the dynamic response performance of the mechanism.

[0022] 3. Simple manufacturing and assembly: All kinematic pairs are revolute pairs (R-pairs), which are simple and reliable in structure, avoiding the manufacturing of complex sliding pairs or high-precision ball joints, and significantly reducing the difficulty and cost of manufacturing and assembly.

[0023] 4. High motion accuracy: The pure rotating joint structure reduces errors introduced by friction and backlash. Combined with low load inertia and symmetrical design, it effectively improves the overall motion accuracy and repeatability of the mechanism.

[0024] 5. Good stiffness performance: The bilaterally symmetrical structure endows the mechanism with good stiffness characteristics. Attached Figure Description

[0025] Figure 1 This is a simplified kinematic diagram illustrating the motion of a six-degree-of-freedom parallel mechanism in the embodiment.

[0026] Figure 2 for Figure 1A simplified kinematic diagram of the URS branch mechanism in a parallel system;

[0027] Figure 3 for Figure 1 A schematic diagram illustrating the positional analysis of a parallel mechanism;

[0028] Figure 4 This is a structural diagram illustrating a six-degree-of-freedom parallel mechanism in the embodiment;

[0029] Figure 5 for Figure 4 A schematic diagram of the URS branch structure of a parallel mechanism;

[0030] Figure 6 for Figure 4 A schematic diagram of the 6-DOF motion of a parallel mechanism.

[0031] In the diagram: Fixed platform 1, Moving platform 2, URS branch chain 3, SRU branch chain 4, Driver 5, First common point 10, Second common point 20, First rotating component 31, Second rotating component 32, Third rotating component 33, Fourth rotating component 34, Fifth rotating component 35, First R sub-axis 301, Second R sub-axis 302, Third R sub-axis 303, Fourth R sub-axis 304, Fifth R sub-axis 305, Sixth R sub-axis 306, URS branch chain driver 51, SRU branch chain driver 52. Detailed Implementation

[0032] The present invention will be further described and illustrated below with reference to specific embodiments. The embodiments described are merely examples of the content of this disclosure and do not limit the scope of the invention. The technical features of each embodiment in the present invention can be combined accordingly, provided that there is no mutual conflict.

[0033] This invention provides a decoupled parallel mechanism based on a bilateral symmetrical branch structure and employing a pure rotating pair. It consists of two symmetrically distributed branches, namely a URS branch group and a SRU branch group. The URS branch group comprises at least three structurally identical URS branches, and the SRU branch group comprises at least three structurally identical SRU branches. Each URS branch includes five rotating members connected in series. The first rotating member is connected to the fixed platform via a first R-pair and to the second rotating member via a second R-pair. The axes of the first and second R-pairs intersect at a first common point on the fixed platform, forming a U-pair motion relationship. The second rotating member is connected to the third rotating member via a third R-pair. The fourth rotating member is connected to the third rotating member via a fourth R-pair and to the fifth rotating member via a fifth R-pair. The fifth rotating member is connected to the moving platform via a sixth R-pair. The axes of the fourth, fifth, and sixth R-pairs intersect at a second common point on the moving platform, forming an S-pair motion relationship. The structure of the SRU branch is exactly the same as that of the URS branch, but its first rotating member is connected to the moving platform via a first R-pair, and its fifth rotating member is connected to the fixed platform via a sixth R-pair.

[0034] like Figure 1 The diagram illustrates a simplified kinematic diagram of a six-degree-of-freedom parallel mechanism in one embodiment. This parallel mechanism includes a fixed platform 1, a moving platform 2, three URS branches 3, and three SRU branches 4. The fixed platform has a rotation center located at a first common point 10; the moving platform has a rotation center located at a second common point 20. (The fixed platform and the moving platform can oscillate or rotate around their respective rotation centers, such as...) Figure 6 (As shown in the diagram, the moving platform moves around the Rx, Ry, and Rz axes.)

[0035] Further as Figure 2 and Figure 3 As shown, the URS branch includes five rotating parts (the first to the fifth rotating parts) connected in series. This invention... Figures 1-3 Different rotating components are indicated by different colors: the first rotating component corresponds to purple, the second to blue, the third to cyan, the fourth to green, and the fifth to yellow. The first rotating component 31 is connected to the fixed platform via a first revolute joint (R-joint) and to the second rotating component 32 via a second revolute joint (R-joint). The axes 301 and 302 of the first and second R-joints intersect at a first common point 10 on the fixed platform, forming a U-joint motion relationship. The second rotating component 32 is connected to the third rotating component 33 via a third revolute joint (R-joint), forming a third R-joint axis 303. The third R-joint axis of each branch is always perpendicular to the line connecting the first and second common points, and the distance between the third R-joint axis and the first common point 10 of the fixed platform is [distance missing]. The fourth rotating member 34 is connected to the third rotating member via a fourth revolute joint (R-joint), and to the fifth rotating member via a fifth revolute joint (R-joint), forming a fourth R-joint axis 304 and a fifth R-joint axis 305. The fifth rotating member 35 is connected to the moving platform 2 via a sixth revolute joint (R-joint), forming a sixth R-joint axis 306. The fourth R-joint axis 304, the fifth R-joint axis 305, and the sixth R-joint axis 306 intersect at a second common point 20 on the moving platform 2, constituting an S-joint motion relationship. The second common point 20 of the moving platform is at a distance from the third R-joint axis 303. .

[0036] See Figure 1 and Figure 3 The SRU branch 4 is the same as the URS branch 3, but its connection direction is reversed. That is, the first rotating member 31 is connected to the moving platform 2 through the first R pair, and the two R pair axes of its U pair (composed of the first R pair and the second R pair) intersect at the second common point 20 on the moving platform; the fifth rotating member 35 is connected to the fixed platform 1 through the sixth R pair, and the two R pair axes of the S pair of the SRU branch 4 (composed of the fourth R pair, the fifth R pair and the sixth R pair) intersect at the first common point 10 on the fixed platform.

[0037] Figure 1 This diagram illustrates a parallel structure in a specific embodiment of the present invention. In this parallel structure, the fixed platform and the moving platform are identical, and the structures of the URS branches and SRU branches are identical. There are three URS branches and three SRU branches, which are staggered and evenly distributed circumferentially. That is, in the circumferential direction, one SRU branch is staggered between two URS branches (and similarly, one URS branch is staggered between two SRU branches). The connection methods of the URS branches and SRU branches are reversed. Overall, this parallel mechanism is a symmetrical structure. It should be noted that the parallel mechanism of the present invention can also be an asymmetrical structure, that is, the structures of the fixed platform and the moving platform can be different, and the rotating parts of the SRU branch group and the URS branch group can have the same or different structures.

[0038] like Figure 3As shown, in a preferred embodiment of the present invention, the structure of each branch is designed as follows: the second R-sub-axis 302 and the third R-sub-axis 303 are perpendicular to each other and intersect at point M; simultaneously, the third R-sub-axis 303 and the fourth R-sub-axis 304 intersect at point N, and a line segment NM located on the third R-sub-axis is taken, with a length of d, satisfying that NM is perpendicular to the line connecting point M and the second common point. Based on this, it can be deduced that the third R-sub-axis is always perpendicular to the plane formed by the second R-sub-axis and the second common point. Therefore, the third R-sub-axis is always perpendicular to the line connecting the first common point and the second common point located in this plane. That is, the line connecting the first common point and the second common point is always perpendicular to the third R-sub-axis of each branch.

[0039] like Figure 4 and Figure 5 As shown, in one embodiment of the present invention, a connecting rod is used to specifically realize the rotating parts of each branch in the decoupled parallel mechanism of the present invention. The R-axis of each branch connected to the fixed platform 1 (i.e., the first R-axis 301 of the URS branch and the sixth R-axis 306 of the SRU branch) is evenly distributed in a ring around the first common point 10; the R-axis of each branch connected to the moving platform (i.e., the sixth R-axis 306 of the URS branch and the first R-axis 301 of the SRU branch) is evenly distributed in a ring around the second common point 20; the number of URS branches and SRU branches is the same, and they are interspersed on the platform. Figure 4 As shown, in a preferred embodiment of the present invention, the R-axis of all connecting branches on the fixed platform is coplanar; the R-axis of all connecting branches on the moving platform is also coplanar. Figure 4 As shown, in a preferred embodiment of the present invention, both the URS branch group and the SRU branch group have 3 branches. Six actuators 5 are arranged on a fixed platform, respectively driving the first rotating member 31 of the URS branch to move around its first R-axis and driving the fifth rotating member 35 of the SRU branch to move around its sixth R-axis. In this scheme, the actuators 5 do not increase the mass of the moving platform at all, and there are no passively driven branches in the mechanism.

[0040] like Figure 6As shown, the parallel mechanism for pose decoupling proposed in this invention has six degrees of freedom, enabling the moving platform to translate and rotate relative to the fixed platform along the x, y, and z axes. The translational motion is entirely controlled by the rotating components connected to the fixed platform via the URS branch group. With the position fixed, the rotational motion is controlled by the rotating components connected to the fixed platform via the SRU branch group, thus achieving decoupling of position and attitude control. Three URS branches (active branches) in the URS branch group are equipped with drivers, which are located on the fixed platform and drive the first rotating components of each of the three URS branches. If the number of branches in the URS branch group is more than three, the additional URS branches, acting as driven branches, do not require drivers. Similarly, three SRU branches (active branches) in the SRU branch group are equipped with drivers, which are located on the fixed platform and drive the fifth rotating components of each of the three SRU branches. Likewise, if the number of branches in the SRU branch group is more than three, the additional SRU branches, acting as driven branches, do not require drivers.

[0041] This invention also provides a method for solving the analytical solution of the forward kinematics of the position of a moving platform, comprising the following steps:

[0042] 1. Read the driver input parameters to obtain the angles of the first rotating component of each active branch (three URS branches driven by drivers) relative to the fixed platform. Establish a reference coordinate system on the fixed platform and solve for the coordinates of point M on each active branch. , , ;

[0043] 2. Connect the first common point of the fixed platform and the second common point of the moving platform. Draw a perpendicular line from point M to this line, intersecting at point O. Let the vector from the first common point of the fixed platform to point O be denoted as . This vector Perpendicular to , , The plane formed satisfies the system of equations:

[0044]

[0045] The matrix equation is obtained by rearranging:

[0046]

[0047] And there are:

[0048]

[0049] in, For point , , The radius of the circumcircle forming the triangle (which can be solved using the sine theorem). The vector can be obtained from the above formula. :

[0050]

[0051] 3. Second public point of the dynamic platform Located in vector The above, its modulus length is obtained from geometric relationships:

[0052]

[0053] Therefore, the second common point of the dynamic platform The coordinates can be represented as:

[0054]

[0055] Therefore, the forward kinematics formula for calculating the position of the second common point of the moving platform is obtained:

[0056]

[0057] Compared to traditional numerical iterative methods, this method offers a faster and more reliable solution process.

[0058] In practical applications, the parallel mechanism of this invention can achieve precise translational and deflection movements with full degrees of freedom within a limited space. For example, Figure 5 The parallel mechanism composed of the branched structures shown can achieve Figure 6The system illustrates six degrees of freedom motion. Specifically, in this system, the position of the moving platform is controlled by only three URS branches. By adjusting the URS branch driver 51, the second common point of the moving platform can be moved. Simultaneously, adjusting all three URS branch drivers enhances the movement of the moving platform in the x, y, or z-axis directions, while canceling out movements in other directions, thus achieving translational motion along the x, y, and z axes. Simultaneously, the three SRU branch drivers 52 must be adjusted to ensure that the attitude of the moving platform remains unchanged relative to its original attitude. Furthermore, the attitude of the moving platform is controlled by only three SRU branches. By fixing the URS branch driver 51 and adjusting the SRU branch driver 52, the moving platform can rotate around the second common point. Simultaneously adjusting all three SRU branch drivers enhances the deflection effect of the moving platform in the x, y, or z-axis directions, while canceling out effects in other directions, thus achieving rotation around the x, y, and z axes. Through these steps, the moving platform achieves six degrees of freedom motion, and the decoupling of translational and rotational motions is realized. The moving platform can be equipped with high-speed rotating cutting tools for ultra-precision machining, providing multi-axis linkage milling capabilities; or it can be equipped with precision tools such as lasers to provide a motion platform for ophthalmic microsurgery or intracranial surgery; the actuator can also be replaced with a torsion spring device, so that the parallel mechanism can be used as a passive follow-up adjustment platform, which can be equipped with contact non-destructive testing and imaging equipment, providing multi-degree-of-freedom pose adjustment capabilities, adaptively adjusting the relationship between the equipment and the object being tested, preventing damage to the surface of the object being tested and ensuring stable and reliable test results.

[0059] Those skilled in the art can readily make various changes and modifications based on the provided textual description, drawings, and claims, without departing from the spirit and scope of the invention as defined by the claims. Any modifications or equivalent variations made to the above embodiments based on the technical concept and essence of the invention fall within the protection scope defined by the claims of this invention.

Claims

1. A parallel mechanism for six-degree-of-freedom pose decoupling, characterized in that, It includes a dynamic platform, a fixed platform, a URS branch group, and an SRU branch group. The URS branch group comprises at least three URS branches with identical structures; each URS branch includes five rotating components connected in series. The first rotating component is connected to the fixed platform via a first R-pair and to the second rotating component via a second R-pair. The axes of the first and second R-pairs intersect at a first common point on the fixed platform, forming a U-pair motion relationship. The second rotating component is connected to the third rotating component via a third R-pair. The fourth rotating component is connected to the third rotating component via a fourth R-pair and to the fifth rotating component via a fifth R-pair. The fifth rotating component is connected to the moving platform via a sixth R-pair. The axes of the fourth, fifth, and sixth R-pairs intersect at a second common point on the moving platform, forming an S-pair motion relationship. The SRU branch group contains at least three SRU branches with the same structure; the structure of the SRU branch is exactly the same as that of the URS branch, but its first rotating member is connected to the moving platform through the first R joint, and its fifth rotating member is connected to the fixed platform through the sixth R joint.

2. The parallel mechanism for six-degree-of-freedom pose decoupling according to claim 1, characterized in that, In each URS branch and SRU branch, the second R sub-axis intersects with the third R sub-axis; and the third R sub-axis intersects with the fourth R sub-axis.

3. The parallel mechanism for six-degree-of-freedom pose decoupling according to claim 1, characterized in that, In each URS branch and SRU branch, the third R sub-axis is perpendicular to the second R sub-axis and perpendicular to the line connecting the intersection of the second R sub-axis and the third R sub-axis with the second common point of the moving platform.

4. The parallel mechanism for six-degree-of-freedom pose decoupling according to claim 1, characterized in that, In the URS branch group and the SRU branch group, the axes of the R pairs connecting the fixed platform of each branch are evenly distributed in a ring around the first common point; the axes of the R pairs connecting the moving platform of each branch are evenly distributed in a ring around the second common point.

5. The parallel mechanism for six-degree-of-freedom pose decoupling according to claim 1, characterized in that, The number of URS branches is the same as the number of SRU branches.

6. The parallel mechanism for six-degree-of-freedom pose decoupling according to claim 5, characterized in that, URS branches and SRU branches are interspersed and evenly distributed in the circumferential direction. That is, in the circumferential direction, an SRU branch is interspersed between any two adjacent URS branches.

7. The parallel mechanism for six-degree-of-freedom pose decoupling according to claim 1, characterized in that, Both the URS branch group and the SRU branch group have 3 branches.

8. The parallel mechanism for six-degree-of-freedom pose decoupling according to claim 1, characterized in that, The axes of all R-joints connecting branches on the fixed platform are coplanar; the axes of rotation of all R-joints connecting branches on the moving platform are also coplanar.

9. The parallel mechanism for six-degree-of-freedom pose decoupling according to claim 1, characterized in that, In the URS branch group, three URS branches are equipped with drivers, which are arranged on a fixed platform and drive the first rotating component of each of the three URS branches; in the SRU branch group, three SRU branches are equipped with drivers, which are arranged on a fixed platform and drive the fifth rotating component of each of the three SRU branches.

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