An Automatic Visual Design Method for the Topology of Parallel Mechanisms

Abstract

The present invention discloses an automatic visualization design method for the topology of a parallel mechanism, comprising the following steps: building a three-dimensional simulation environment; creating a component library; expressing the topology of the parallel mechanism to be visualized in matrix form; establishing the conversion relationship between the topology and constraints; establishing a parallel mechanism in the three-dimensional simulation environment; detecting the correctness of the constraints on the topological structure; performing effective three-dimensional display of the parallel mechanism; and completing the three-dimensional visualization design of the topology of the parallel mechanism. The present invention does not need to rely on existing commercial software, has strong scalability, can perform drag-and-drop operations on the parallel mechanism, and has good interactivity; the mechanism rods can be saved parametrically, and the complex axis geometric relationships between the rods are described in common spatial orientations, which is applicable to general mechanisms; it meets the requirements of high automation, and the entire visualization process is independently completed by the system without the guidance of professionals, which can effectively reduce the design difficulty of the parallel mechanism, shorten the design cycle of the parallel mechanism, and reduce the development cost of the parallel robot.

Description

Technical Field

[0001] The present invention belongs to the technical field of three-dimensional visualization design, and particularly relates to an automatic visualization design method for the topology of a parallel mechanism. Background Art

[0002] Parallel robots have been widely used in the industrial field. Their topological structures greatly affect the performance of parallel robots. During the design process of the topological structures of parallel robots, three-dimensional visualization of the topological configurations can help researchers intuitively understand the motion characteristics of the mechanisms, solve problems in the design, manufacturing, and operation of robots in advance, greatly reduce research costs, and provide convenience for the research of robots.

[0003] Currently, there is a lack of relevant mature simulation software for the three-dimensional visualization of the topology of parallel mechanisms. The visualization construction of topological structures relies on commercial computer-aided modeling and analysis software, mostly for secondary development based on software such as SOLIDWORKS and Pro / E, which cannot meet the large demand for robot research. The current three-dimensional visualization process of the topology of parallel mechanisms has the following deficiencies:

[0004] Firstly, due to the complex geometric relationships of the joint axes of parallel mechanisms and the variable and non-universal shapes of components, traditional visualization design of parallel mechanisms requires individual modeling of each component. The modeling process involves a large amount of repetitive work, affecting the design cycle of parallel robots and greatly increasing the time cost. For example, the construction of the Stewart mechanism described in Chinese Patent CN112580167A requires drawing a three-dimensional model with the aid of SOLIDWORKS software, and the operation is cumbersome.

[0005] Secondly, the degree of automation is not high and requires professional personnel to participate. However, due to the complex theoretical knowledge of parallel mechanisms, designers need rich design experience and a large amount of professional knowledge accumulation, resulting in low efficiency and being prone to errors. For example, the construction of a parallel mechanism described in Chinese Patent 114638072A requires first establishing a kinematic model of the target mechanism through the closed-loop vector method, and the design difficulty is great.

[0006] Thirdly, the visualization design of the topology of parallel mechanisms relies on CAD / CAE commercial software, having problems of insufficient scalability and poor interactivity.

[0007] Fourthly, it is mainly for building virtual prototypes and simulations, unable to perceive the topological structure and lacking a mechanism for judging the rationality of the mechanism.

[0008] In summary, the existing visualization methods for the topology of parallel mechanisms cannot meet the requirements of the above application fields. Summary of the Invention

[0009] The present invention is proposed to solve the problems existing in the prior art, and its purpose is to provide an automatic visualization design method for the topology of a parallel mechanism.

[0010] The technical solution of the present invention is: an automatic visualization design method for the topology of a parallel mechanism, comprising the following steps:

[0011] ⅰ. Build a three-dimensional simulation environment;

[0012] ⅱ. Create a component library based on the three-dimensional simulation environment;

[0013] ⅲ. Express the topology of the parallel mechanism to be visualized in matrix form;

[0014] ⅳ. Establish the conversion relationship between topology and constraints;

[0015] ⅴ. Establish a parallel mechanism in the three-dimensional simulation environment;

[0016] ⅵ. Detect the correctness of constraints on the topological structure;

[0017] ⅶ. Perform effective three-dimensional display of the parallel mechanism;

[0018] ⅷ. Complete the three-dimensional visualization design of the topology of the parallel mechanism.

[0019] The process of step ⅰ of building a three-dimensional simulation environment is as follows:

[0020] First, build a three-dimensional simulation environment

[0021] The three-dimensional simulation environment refers to a virtual environment generated by computer technology with real-time model rendering function and establishing rigid body constraints. Users can perform operations such as creating, modifying, and deleting models through the internal API interface;

[0022] Then, call the rigid body constraint function in the three-dimensional simulation environment;

[0023] The rigid body constraint function refers to a built-in function in the three-dimensional simulation environment that can add motion restrictions between rigid body models;

[0024] Finally, expand and encapsulate the rigid body constraint function into a kinematic pair assembly function;

[0025] The parameters of the rigid body constraint function are not easy to obtain. Expand and encapsulate the rigid body constraint function into a kinematic pair assembly function with a common axis as the parameter for easy use.

[0026] The process of step ⅱ of creating a component library based on the three-dimensional simulation environment is as follows:

[0027] First, determine the basic components of the parallel mechanism, and save each basic component as a three-dimensional model library. The basic components at least include a static platform, a connecting rod, and a connecting joint;

[0028] Then, a static platform component library and a moving platform component library are established using a series of disk-shaped geometric bodies with different radii respectively;

[0029] After that, a connecting rod component library is established using a series of rod-shaped geometric bodies with square cross-sections and different lengths;

[0030] After that, a revolute pair (R pair) component library is established using cylindrical rotating shafts with dimensions adapted to the connecting rods;

[0031] After that, a prismatic pair (P pair) component library is established using cuboid sliders with dimensions adapted to the connecting rods;

[0032] Finally, a Hooke's joint (U pair) component library and a spherical joint (S pair) component library are established using spherical connecting joints with dimensions adapted to the connecting rods.

[0033] Step ii: Based on the 3D simulation environment, create a component library, which also includes establishing a reference coordinate system for the basic component parts in the component library. The specific process is as follows:

[0034] First, define a basic reference coordinate system for each type of component in the component library, including the static and moving platforms, connecting rods, and connecting joints. For the static and moving platforms, use the circular cross-section as the O-xy plane, the normal direction of the cross-section as the O-z axis, and the geometric center of the static and moving platforms as the origin of the coordinate system to establish the reference coordinate system;

[0035] Then, for the connecting rod, use the square cross-section as the O-xy plane, the direction along the rod length as the O-z axis, and the geometric center of the connecting rod as the origin of the coordinate system to establish the reference coordinate system;

[0036] After that, for the cylindrical revolute pair joint, use its own axis as the joint axis direction;

[0037] Finally, for the cuboid prismatic pair slider, use its own axis as the joint axis direction.

[0038] Step iii: Express the topology of the parallel mechanism to be visualized in matrix form. The specific process is as follows:

[0039] First, define the diagonal elements of the matrix. Define 0, 1, 2, and 3 in the diagonal elements of the matrix as revolute pair (R pair), prismatic pair (P pair), Hooke's joint (U pair), and spherical joint (S pair) respectively;

[0040] Then, define the non-diagonal elements of the matrix. Define 1, 2, 3, 4, 5, and 6 in the non-diagonal elements of the matrix as relative position relationships of parallel, perpendicular, orthogonal, collinear, intersecting, and skew respectively;

[0041] After that, express the topology of the parallel mechanism in matrix form for digital representation, which can clearly and completely describe the topological structure of the parallel mechanism;

[0042] Finally, the matrix form expression of the parallel mechanism topology is obtained.

[0043] Step ⅳ: Establish the conversion relationship between topology and constraints. The specific process is as follows:

[0044] First, consider the combination type of kinematic pairs and the positional relationship between the axes of kinematic pairs of two adjacent linkages;

[0045] Then, obtain the mapping relationship between the matrix elements and the constraint parameters;

[0046] Finally, convert the elements in the matrix into the constraint parameters required for establishing constraints through the mapping relationship.

[0047] Step ⅴ: Establish a parallel mechanism in a 3D simulation environment. The specific process is as follows:

[0048] First, add a static platform and a moving platform in the 3D simulation environment;

[0049] Then, add the first connecting linkage and connecting joint assembled with the static platform to the simulation environment;

[0050] Next, obtain the constraint parameters according to the matrix elements extracted from the matrix and the mapping relationship between the matrix elements and the constraint parameters;

[0051] Next, establish the constraint connection between the connecting linkage and the static platform according to the constraint parameters;

[0052] Next, assemble the connecting linkages according to the extracted matrix elements until a constraint connection with the moving platform is established, and one branch chain of the parallel mechanism is completed;

[0053] Finally, repeat the above process to establish the remaining branch chains.

[0054] Step ⅵ: Detect the constraint correctness of the topological structure, including scale correctness detection and topological correctness detection.

[0055] In the scale correctness detection of the constraint correctness detection of the topological structure in Step ⅵ, the specific process is as follows:

[0056] First, during the process of adding connecting linkages to establish constraints, record two connection marker points at the connection points of the two connecting linkages respectively;

[0057] Then, when establishing the constraints, these two connection marker points coincide. After the parallel mechanism is established, extract the positions of the marker points of each pair of constraints;

[0058] Next, detect whether each pair of the above marker points is separated;

[0059] Finally, if the marked points are separated, it indicates that there is a break between the connecting rods, and the dimensions of the parallel mechanism are incorrect; conversely, if the marked points coincide and are not separated, the dimensions of the parallel mechanism are correct, achieving the detection of dimensional correctness.

[0060] The beneficial effects of the present invention are as follows:

[0061] The present invention does not need to rely on existing commercial software, has strong scalability, can perform drag operations on the parallel mechanism, has good interactivity, can intuitively check whether the designed configuration is reasonable, the mechanism rods can be saved parametrically, and the complex axis geometric relationship between the rods is described in common spatial orientations, which is applicable to general mechanisms; it meets the requirements of high automation, and the entire visualization process is independently completed by the system without the guidance of professionals, which can effectively reduce the design difficulty of the parallel mechanism, shorten the design cycle of the parallel mechanism, and reduce the development cost of the parallel robot. Description of the Drawings

[0062] Figure 1 is a schematic framework diagram of the present invention;

[0063] Figure 2 is the self-reference coordinate system of the rod in the present invention;

[0064] Figure 3 is the corresponding diagram of matrix elements and constraint parameters in the present invention;

[0065] Figure 4 is the PRS chain with the R-axis tangentially arranged in the present invention;

[0066] Figure 5 is the PRS chain with the R-axis radially arranged in the present invention;

[0067] Figure 6 is the flow chart of constraint correctness detection in the present invention;

[0068] Figure 7 is that the topological incorrectness of the PRS chain axis offset is detected by the topological correctness detection algorithm in the present invention;

[0069] Figure 8 is the 3-PRS parallel mechanism detected by the constraint correctness detection in the present invention. Detailed Embodiment

[0070] Hereinafter, the present invention will be described in detail with reference to the drawings and embodiments:

[0071] As Figures 1 to 8 shown, an automatic visualization design method for the topology of a parallel mechanism includes the following steps:

[0072] ⅰ. Build a three-dimensional simulation environment;

[0073] ii. Create a component library based on the 3D simulation environment;

[0074] iii. Express the topology of the parallel mechanism to be visualized in matrix form;

[0075] iv. Establish the conversion relationship between topology and constraints;

[0076] v. Establish a parallel mechanism in the 3D simulation environment;

[0077] vi. Detect the correctness of the constraints on the topological structure;

[0078] vii. Perform effective 3D display of the parallel mechanism;

[0079] viii. Complete the 3D visualization design of the parallel mechanism topology.

[0080] Step i: Set up the 3D simulation environment. The specific process is as follows:

[0081] First, set up the 3D simulation environment

[0082] The 3D simulation environment refers to a virtual environment generated by computer technology with real-time model rendering function and establishment of rigid body constraints. Users can perform operations such as creating, modifying, and deleting models through the internal API interface;

[0083] Then, call the rigid body constraint function in the 3D simulation environment;

[0084] The rigid body constraint function refers to a built-in function in the 3D simulation environment that can add motion restrictions between rigid body models;

[0085] Finally, expand and encapsulate the rigid body constraint function into a kinematic pair assembly function;

[0086] The parameters of the rigid body constraint function are not easy to obtain. Expand and encapsulate the rigid body constraint function into a kinematic pair assembly function with a common axis as the parameter for easy use.

[0087] The kinematic pair assembly function can simulate the motion constraint function of kinematic pair entities in the 3D simulation environment, facilitating the subsequent establishment of the mechanism model.

[0088] Step ii: Create a component library based on the 3D simulation environment. The specific process is as follows:

[0089] First, determine the basic components of the parallel mechanism and save each basic component as a 3D model library. The basic components at least include a static platform, connecting rods, and connecting joints;

[0090] Then, establish a static platform component library and a moving platform component library with a series of disk-shaped geometric bodies with different radii respectively;

[0091] Subsequently, a connecting rod member library is established with a series of rod-shaped geometric bodies having square cross-sections of different lengths;

[0092] Subsequently, a revolute pair (R pair) member library is established with a cylindrical rotating shaft whose dimensions are adapted to the connecting rod;

[0093] Subsequently, a prismatic pair (P pair) member library is established with a cuboid slider whose dimensions are adapted to the connecting rod;

[0094] Finally, a Hooke's joint (U pair) member library and a spherical joint (S pair) member library are established with spherical connection joints whose dimensions are adapted to the connecting rod.

[0095] Step ii: Based on the 3D simulation environment, a component library is created, which also includes establishing a reference coordinate system for the basic components in the component library. The specific process is as follows:

[0096] First, a basic reference coordinate system is defined for each type of component in the component library, including the static platform, the connecting rod, and the connection joint. For the static platform and the moving platform, a circular cross-section is used as the O-xy plane, the cross-section normal is used as the O-z axis, and the geometric center of the static platform and the moving platform is used as the origin of the coordinate system to establish the reference coordinate system;

[0097] Then, for the connecting rod, a square cross-section is used as the O-xy plane, the direction along the rod length is used as the O-z axis, and the geometric center of the connecting rod is used as the origin of the coordinate system to establish the reference coordinate system;

[0098] Subsequently, for the cylindrical revolute pair joint, its own axis is used as the joint axis direction;

[0099] Finally, for the cuboid prismatic pair slider, its own axis is used as the joint axis direction.

[0100] Step iii: The topology of the parallel mechanism to be visualized is expressed in matrix form. The specific process is as follows:

[0101] First, the diagonal elements of the matrix are defined. The numbers 0, 1, 2, and 3 in the diagonal elements of the matrix are defined as revolute pair (R pair), prismatic pair (P pair), Hooke's joint (U pair), and spherical joint (S pair) in sequence;

[0102] Then, the non-diagonal elements of the matrix are defined. The numbers 1, 2, 3, 4, 5, and 6 in the non-diagonal elements of the matrix are defined as the relative position relationships of parallel, perpendicular, orthogonal, collinear, intersecting, and skew in sequence;

[0103] Subsequently, the topology of the parallel mechanism is digitally expressed in matrix form, which can clearly and completely describe the topological structure of the parallel mechanism;

[0104] Finally, the matrix form expression of the topology of the parallel mechanism is obtained.

[0105] Step iv: Establish the conversion relationship between topology and constraints. The specific process is as follows:

[0106] First, consider the combination type of kinematic pairs between adjacent two link members and the positional relationship between the axes of kinematic pairs;

[0107] Then, obtain the mapping relationship between matrix elements and constraint parameters;

[0108] Finally, convert the elements in the matrix into the constraint parameters required for establishing constraints through the mapping relationship.

[0109] Step ⅴ Establish a parallel mechanism in a three-dimensional simulation environment, and the specific process is as follows:

[0110] First, add a static platform and a moving platform in the three-dimensional simulation environment;

[0111] Then, add the first connecting link member and connecting joint assembled with the static platform to the simulation environment;

[0112] After that, obtain the constraint parameters according to the matrix elements extracted from the matrix and the mapping relationship between matrix elements and constraint parameters;

[0113] After that, establish a constrained connection between the connecting link member and the static platform according to the constraint parameters;

[0114] After that, assemble the connecting link members according to the extracted matrix elements until a constrained connection is established with the moving platform, and one branch chain of the parallel mechanism is generated;

[0115] Finally, repeat the above process to establish the remaining branch chains.

[0116] Step ⅵ Detect the constraint correctness of the topological structure, including scale correctness detection and topological correctness detection.

[0117] In the scale correctness detection in the constraint correctness detection of the topological structure in Step ⅵ, the specific process is as follows:

[0118] First, during the process of adding connecting link members to establish constraints, record two connection marked points at the connection points of the two connecting link members respectively;

[0119] Then, when establishing constraints, these two connection marked points coincide, and extract the positions of the marked points of each pair of constraints after the parallel mechanism is established;

[0120] After that, detect whether each pair of the above marked points is separated;

[0121] Finally, if the marked points are separated, it indicates that there is a break point between the connecting link members, and the scale of the parallel mechanism is incorrect; on the contrary, if the marked points coincide and are not separated, the scale of the parallel mechanism is correct, and the scale correctness detection is realized.

[0122] Specifically, for the topological correctness detection in step ⅵ, the specific process is as follows:

[0123] First, during the process of adding connecting rods to establish constraints, a pair of marked axes are set between the constraints.

[0124] Then, after the parallel mechanism is established, the positions and directions of the marked axes of each pair of constraints are extracted.

[0125] Finally, after the parallel mechanism is established, the angular difference between the marked axes is extracted to detect whether there is an offset of the axes, so as to realize the topological correctness detection.

[0126] If the directions of each pair of marked axes should always coincide, the parallel mechanism does not have incorrect topology. However, if a certain offset is detected between the two marked axes, the parallel mechanism has incorrect topology.

[0127] Specifically, in step ⅴ, when establishing a parallel mechanism in a three-dimensional simulation environment, if the target parallel mechanism is a symmetric parallel mechanism, the first established branch chain is copied and evenly distributed on the moving and static platforms according to the number of branch chains, and then the parallel mechanism can be established.

[0128] In the present invention, through steps ⅰ and ⅱ, a simulation environment and a component library are built. The parallel mechanism to be visualized is expressed by the matrix described in step ⅲ, and the matrix elements are converted into constraint parameters in step ⅳ. When multiple groups of constraint axis orientations are obtained from the adjacency matrix in step ⅳ, parallel mechanisms are respectively established through step ⅴ, and then the constraint correctness detection is performed, discarding the parallel mechanisms with incorrect topological scales, and screening out the correct three-dimensional model of the target parallel mechanism.

[0129] Another embodiment

[0130] As Figure 1 shown, taking the topological visualization of a 3-PRS parallel mechanism based on THREE.js as an example, it includes the following steps:

[0131] ⅰ. Build a three-dimensional simulation environment

[0132] The three-dimensional simulation environment refers to a virtual environment generated by computer technology with real-time model rendering function and model constraint establishment. Users can perform operations such as creating, modifying, and deleting models through the internal API interface. The constraint refers to a built-in function in the three-dimensional simulation environment, and by calling it, the movement of the models in the simulation environment can be restricted, simulating the movement constraint function of kinematic pair entities. Here, the THREE.js three-dimensional simulation environment applied to the Web side is used as the virtual scene.

[0133] ⅱ. Create a component library

[0134] The component library is a three-dimensional model library containing the basic components of the parallel mechanism, including the basic static platforms, connecting rods, kinematic pair joints, and moving platforms with different sizes.

[0135] The basic static platform and the moving platform are expressed as a series of disc-shaped geometric bodies with different radii in the component library; the connecting rods are expressed as a series of rod-shaped geometric bodies with square cross-sections and different lengths in the component library; the kinematic pair joints include revolute pairs (R pairs), prismatic pairs (P pairs), Hooke joints (U pairs), and spherical joints (S pairs), which are respectively expressed as cylindrical rotating shafts, cuboid sliders, and spherical connecting joints with dimensions adapted to the connecting rods in the component library; the basic static platform, the moving platform, and the connecting rods included in the component library should have their own reference coordinate system O-xyz: the basic static platform and the moving platform use the circular cross-section as the O-xy plane, the cross-section normal direction as the O-z axis, and the geometric center of the component as the origin of the coordinate system to establish the reference coordinate system.

[0136] As Figure 2 shown, the connecting rod uses the square cross-section as the O-xy plane, the direction along the rod length as the O-z axis, and the geometric center of the component as the origin of the coordinate system to establish the reference coordinate system; the kinematic pair joints included in the component library should have their own joint axis directions: the cylindrical revolute pair joint uses its own axis as the joint axis direction, and the cuboid prismatic pair slider uses its own axis as the joint axis direction.

[0137] ⅲ. Express the topology to be visualized in matrix form

[0138] The matrix is a common expression method of the parallel mechanism topology, which describes the sequence of various kinematic pair types on the limb of the parallel mechanism and the positional relationship between kinematic pairs.

[0139] The diagonal elements of the matrix are represented by 0, 1, 2, and 3 for revolute pairs (R pairs), prismatic pairs (P pairs), Hooke joints (U pairs), and spherical joints (S pairs), respectively, and the non-diagonal elements express the positional relationship between the corresponding kinematic pair axes.

[0140] The six relationships of parallel, perpendicular, orthogonal, collinear, intersecting, and skew are represented by the numbers 1 - 6; expressing the parallel mechanism topology in matrix form digitally can clearly and completely describe the topology structure of the parallel mechanism, and at the same time facilitate computer storage and analysis, which is a necessary condition for subsequent automatic visualization of the parallel mechanism topology.

[0141] The matrix expression of the 3-PRS parallel mechanism is:

[0142]

[0143] The diagonal elements are represented by 1, 0, and 3 for prismatic pairs (P pairs), revolute pairs (R pairs), and spherical joints (S pairs), respectively, and the non-diagonal elements 2 and 0 express the perpendicular and parallel positional relationships between the corresponding kinematic pair axes.

[0144] ⅳ. Establish the conversion relationship between the topology and the constraints, and obtain the constraint parameters required for establishing the constraints from the matrix elements; in step ⅲ, the topology is expressed in matrix form. Since there are many and difficult orientation elements of the components in the parallel mechanism, it is necessary to extract the topology information in the matrix elements and convert it into the parameters required for establishing the constraints in the THREE.js environment in step ⅰ. The specific conversion method is as follows:

[0145] Considering the combination type of the kinematic pairs between adjacent two link members and the positional relationship between the axes of the kinematic pairs, establishing the constraints between the link members requires the corresponding constraint types and the orientation of the constraint axes. The constraint types include the current joint type and the previous joint type, which are expressed as the combination of the kinematic pair types.

[0146] The PRS branch chain contains two kinematic pair combinations: the PR and RS combinations. Here, only the R pair and the P pair need to be distinguished because when establishing the corresponding constraints for the S pair and the U pair, no complex axis relationship is required. For the S pair, only a spherical hinge constraint needs to be added at the end of the link member. The U pair subtracts a rotational degree of freedom around the link member based on the S pair, and the constraints can be correctly added without considering the corresponding axis relationship.

[0147] The orientation of the said constraint axis refers to one of the x, y, and z coordinate axes directions with reference to the self-coordinate system of the link member.

[0148] Such as Figure 3 shown, it appears in pairs in each constraint, which is the direct condition for establishing the constraints. It is obtained by judging the positional relationship and the constraint type between the kinematic pairs represented by the non-diagonal elements of the adjacency matrix. The judgment rules are as Figure 3 , in the figure, axis 1 and axis 2 respectively represent the orientation of the axes of the kinematic pairs of the front and rear link members of the constraint. " / " indicates that the positional relationship between the kinematic pairs under this constraint type is incorrect or has no practical significance. "Same as ××" indicates that the orientation of the constraint axis when the positional relationship between the kinematic pairs is the same as that when it is ××. "Same as / Perpendicular to the R1 axis" indicates that the constraint axis is the same as or perpendicular to the axis of the previous R kinematic pair. Through the above Table 1 in step 1, it is judged that the constraint axis combination corresponding to the PR kinematic pair combination is axis 1: x / y, axis 2: x.

[0149] Thus, by summarizing the mapping relationship between the matrix elements and the constraint parameters, the elements in the matrix can be converted into the constraint parameters required for establishing the constraints accordingly.

[0150] ⅴ. Establish a parallel mechanism in the three-dimensional simulation environment

[0151] Add the base static platform and the moving platform to the THREE.js scene built in step ⅰ. Subsequently, add rods to the static platform and establish the constrained connection between the rods and the static platform according to the constraint parameters, that is, extract the matrix elements from the matrix in step ⅲ, and obtain the constraint parameters according to the mapping relationship between the matrix elements in step ⅳ and the constraint parameters. Assemble the rods according to the extracted constraint information until the constrained connection with the moving platform is established, and one branch chain of the parallel mechanism is completed. Then, establish the remaining branch chains of the parallel mechanism in turn. If the target parallel mechanism is a symmetric parallel mechanism, copy this branch chain and evenly distribute it on the static and moving platforms according to the number of branch chains, and the parallel mechanism can be established.

[0152] It should be noted that the results judged by the adjacent joint position relationship in the adjacency matrix are not unique in some cases, because there are some position relationships that may correspond to multiple constraint axis orientations.

[0153] Taking the PRS branch chain as an example, the axis of the first P pair joint is perpendicular to the static platform. When the relationship between the two kinematic pairs is perpendicular, the orientation of its adjacent axis cannot be clearly explained. For the second R pair to maintain a perpendicular relationship with the axis of the P pair joint, its axis can be arranged tangentially or radially along the static platform. The tangential arrangement belongs to the common PRS branch chain such as Figure 4 , the constraint axis combination is axis 1: x, axis 2: x, and it can be complemented to a correct symmetric parallel mechanism. However, for the second radial arrangement method such as Figure 5 , the constraint axis combination is axis 1: y, axis 2: x, and the moving platform cannot be correctly complemented to a symmetric parallel mechanism due to the influence of the constraint. This situation is a topological incorrectness caused by the wrong judged constraint axis relationship.

[0154] In addition, when establishing the parallel mechanism, the rod length is temporarily set to a fixed value. In some cases, due to the rod being too long or too short, an error may occur that the rods cannot establish a constrained connection when adding multiple branch chains. This situation is a scale incorrectness caused by the inappropriate rod length. Therefore, after establishing the parallel mechanism according to the above rules, it is necessary to detect the topological and scale correctness of its constraints.

[0155] ⅵ Constraint correctness detection

[0156] Such as Figure 6As shown in the figure, the flowchart of constraint correctness detection first performs scale correctness detection on the 3D model of the parallel mechanism. If the system detects that there is an incorrect scale situation, the scale of the rod is adjusted to an appropriate range through the scale adjustment algorithm. Subsequently, topological correctness detection is performed on it. If the system detects that there is an incorrect topological situation in the parallel mechanism, then this axis combination is discarded and a parallel mechanism model is re-established based on the remaining constraint parameter combinations obtained by conversion in step ⅳ, and topological and scale correctness detections are performed. On the contrary, if no incorrect topology is detected and the scale of the parallel mechanism is appropriate, the correct 3D display of the parallel mechanism is obtained.

[0157] The so-called scale correctness detection refers to the scale correctness detection algorithm embedded in the system background. The specific implementation method is as follows: During the process of adding rods to establish constraints, two connection marker points are respectively recorded at the connection points of the two rods. When establishing the constraint, these two connection marker points coincide. After the parallel mechanism is established, the positions of the marker points of each pair of constraints are extracted, and it is detected whether the two marker points are separated, so as to realize the scale correctness detection. If there is no incorrect scale in the parallel mechanism, these two marker points should always coincide. However, if there is an incorrect scale, there will be a certain displacement between the two marker points.

[0158] The topological correctness detection is similar to the scale correctness detection, referring to the topological correctness detection algorithm embedded in the system background. When establishing the constraint, a pair of marked axes are set, and after the parallel mechanism is established, the angular difference between the marked axes is extracted to detect whether there is an axis offset.

[0159] In this visualization example of the 3-PRS parallel mechanism, through step ⅴ, the system establishes two parallel mechanisms with different axis distributions: namely, the R joint axis is radially arranged and the R joint axis is tangentially arranged. First, the situation where the R joint axis is radially arranged is detected. No disconnection phenomenon is detected at the rod connection, and the scale of each rod is appropriate. Subsequently, topological correctness detection is performed on it.

[0160] As Figure 7 shown, it is detected that there is an axis offset in the combination where the R pair axis is radially arranged. Then this axis combination is discarded, and the situation where the R joint axis is tangentially arranged in the next axis combination is detected, and step ⅴ is re-executed to establish a parallel mechanism model, and topological and scale correctness detections are performed.

[0161] As Figure 8 shown, at this time, no incorrect topology is detected and the scale of the parallel mechanism is appropriate, so the correct 3D display of the parallel mechanism is obtained.

[0162] The present invention does not need to rely on existing commercial software, has strong scalability, can perform dragging operations on parallel mechanisms, has good interactivity, can intuitively check whether the designed configuration is reasonable, the mechanism rods can be saved parametrically, and the complex axis geometric relationships between the rods are described in common spatial orientations, which is applicable to general mechanisms; it meets the requirements of high automation, and the entire visualization process is completed independently by the system without the guidance of professionals, which can effectively reduce the design difficulty of parallel mechanisms, shorten the design cycle of parallel mechanisms, and reduce the development cost of parallel robots.

Claims

1. An automatic visualization design method for the topology of a parallel mechanism, characterized in that: It includes the following steps: (i) Build a three-dimensional simulation environment; (ii) Create a component library based on the three-dimensional simulation environment; (iii) Express the topology of the parallel mechanism to be visualized in matrix form; (iv) Establish the conversion relationship between topology and constraints; (v) Establish a parallel mechanism in the three-dimensional simulation environment; (vi) Detect the correctness of the constraints on the topological structure; (vii) Perform effective three-dimensional display of the parallel mechanism; (viii) Complete the three-dimensional visualization design of the parallel mechanism topology; In step (iii), the topology of the parallel mechanism to be visualized is expressed in matrix form, and the specific process is as follows: First, define the diagonal elements of the matrix, and define 0, 1, 2, and 3 in the diagonal elements of the matrix as revolute pair, prismatic pair, Hooke's joint, and spherical joint in sequence; Then, define the non-diagonal elements of the matrix, and define 1, 2, 3, 4, 5, and 6 in the non-diagonal elements of the matrix as relative position relationships of parallel, perpendicular, orthogonal, collinear, intersecting, and skew in sequence; Then, express the topology of the parallel mechanism in matrix form digitally, which can clearly and completely describe the topological structure of the parallel mechanism; Finally, obtain the matrix form expression of the parallel mechanism topology.

2. The automatic visualization design method for a parallel mechanism topology according to claim 1, characterized in that: In step (i), build a three-dimensional simulation environment, and the specific process is as follows: First, build a three-dimensional simulation environment The three-dimensional simulation environment refers to a virtual environment generated by computer technology with real-time model rendering function and establishing rigid body constraints. Users can perform operations of creating, modifying, and deleting models through the internal API interface; Then, call the rigid body constraint function in the three-dimensional simulation environment; The rigid body constraint function refers to a built-in function in the three-dimensional simulation environment that can add motion restrictions between rigid body models; Finally, expand and encapsulate the rigid body constraint function into a kinematic pair assembly function; It is difficult to obtain the parameters of the rigid body constraint function. Expand and encapsulate the rigid body constraint function into a kinematic pair assembly function with a general axis as the parameter for easy use.

3. The automatic visualization design method for a parallel mechanism topology according to claim 1, characterized in that: In step (ii), create a component library based on the three-dimensional simulation environment, and the specific process is as follows: First, determine the basic component parts of the parallel mechanism, and save each basic component part as a three-dimensional model library. The basic component parts include at least a static platform, connecting rods, and connecting joints; Then, establish a static platform component library and a moving platform component library with a series of disk-shaped geometric bodies with different radii respectively; Then, establish a connecting rod component library with a series of rod-shaped geometric bodies with square cross-sections and different lengths; Then, establish a revolute pair component library with cylindrical rotating shafts whose sizes are adapted to the connecting rods; Then, establish a prismatic pair component library with cuboid sliders whose sizes are adapted to the connecting rods; Finally, establish a Hooke's joint component library and a spherical joint component library with spherical connecting joints whose sizes are adapted to the connecting rods.

4. The automatic visualization design method for a parallel mechanism topology according to claim 1, characterized in that: In step (ii), creating a component library based on the three-dimensional simulation environment also includes establishing a reference coordinate system for the basic component parts in the component library, and the specific process is as follows: First, define a basic reference coordinate system for each type of component in the component library, including the static platform, connecting rods, and connecting joints. For the static platform and the moving platform, use the circular cross-section as the O-xy plane, the cross-section normal as the O-z axis, and the geometric center of the static platform and the moving platform as the origin of the coordinate system to establish the reference coordinate system; Then, take the connecting rod member with a square cross-section as the O-xy plane, the O-z axis along the rod length direction, and the geometric center of the connecting rod member as the coordinate origin to establish a reference coordinate system; After that, take the axis of the cylindrical revolute joint as the joint axis direction; Finally, take the axis of the cuboid prismatic joint slider as the joint axis direction.

5. The automatic visualization design method for a parallel mechanism topology according to claim 1, characterized in that: Step (ⅳ) Establish the conversion relationship between topology and constraints. The specific process is as follows: First, consider the combination type of kinematic pairs between two adjacent rod members and the positional relationship between the kinematic pair axes; Then, obtain the mapping relationship between the matrix elements and the constraint parameters; Finally, convert the elements in the matrix into the constraint parameters required for establishing constraints through the mapping relationship.

6. The automatic visualization design method for a parallel mechanism topology according to claim 1, characterized in that: Step (ⅴ) Establish a parallel mechanism in a three-dimensional simulation environment. The specific process is as follows: First, add a static platform and a moving platform to the three-dimensional simulation environment; Then, add the first connecting rod member and the connecting joint assembled with the static platform to the simulation environment; After that, obtain the constraint parameters according to the matrix elements extracted from the matrix and the mapping relationship between the matrix elements and the constraint parameters; After that, establish a constraint connection between the connecting rod member and the static platform according to the constraint parameters; After that, assemble the connecting rod members according to the extracted matrix elements until a constraint connection is established with the moving platform, and one branch chain of the parallel mechanism is completed; Finally, repeat the above process to establish the remaining branch chains.

7. The automatic visualization design method for a parallel mechanism topology according to claim 1, characterized in that: Step (ⅵ) Detect the constraint correctness of the topological structure, including scale correctness detection and topological correctness detection.

8. The automatic visualization design method for a parallel mechanism topology according to claim 7, characterized in that: In the scale correctness detection in the constraint correctness detection of the topological structure in Step (ⅵ), the specific process is as follows: First, during the process of adding connecting rod members to establish constraints, record two connection marker points at the connection points of the two connecting rod members respectively; Then, when establishing the constraints, these two connection marker points coincide. After the parallel mechanism is established, extract the positions of the marker points of each pair of constraints; After that, detect whether each pair of the above marker points is separated; Finally, if the marker points are separated, it means that there is a break between the connecting rod members, and the scale of the parallel mechanism is incorrect; on the contrary, if the marker points coincide and are not separated, the scale of the parallel mechanism is correct, and the scale correctness detection is realized.

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