MBD-based assembly error automatic modeling method

Abstract

The invention relates to the field of computer-aided engineering, in particular to an MBD-based assembly error automatic modeling method. The method comprises the steps that firstly, an assembly relation graph is used for storing the assembly relation, the assembly sequence and the assembly hierarchy of parts in an assembly body; secondly, the geometric feature positioning relation graph is used for determining a reference-target relation between feature surfaces in the parts in the assembly relation graph; then, establishing a reference coordinate system of each geometric feature, and defining correct positions of the geometric features under the reference coordinate system according to the theoretical size; and finally, converting the graph into an error propagation chain according to the geometric feature position hierarchical system, determining the actual position of the geometric feature, and calculating a spatial dimension chain according to the actual position. The method provides a solution for realizing 3D tolerance analysis based on the model, and has the advantages of less man-machine interaction operation, high calculation precision and the like. The tolerance can be conveniently defined and managed in CAD software, and the establishment of a tolerance model is realized.

Description

Technical Field

[0001] This invention belongs to the field of computer-aided tolerance analysis (CAE), specifically a method for automatic modeling of assembly errors based on MBD. Background Technology

[0002] Computer-aided tolerance analysis is an important component of computer-integrated manufacturing (CIMM). Currently, traditional assembly tolerance analysis methods are generally based on a two-dimensional plane. This involves transforming the critical dimension transfer process of the assembly into planes in various directions, establishing the dimensional chain equations on the transformed planes, and completing the tolerance analysis. This method is inefficient, requires most operations to be performed manually, has low automation, and poor readability. Even with the rapid development of CAD / CAM technology, computer-aided tolerance design still cannot be integrated with CAD systems. Therefore, there is an urgent need for a highly automated assembly tolerance analysis method oriented towards CAD systems, simplifying the workload of manufacturing personnel in predicting product accuracy, improving calculation accuracy, and shortening product manufacturing cycles. Summary of the Invention

[0003] To address the aforementioned problems, the present invention aims to provide a spatial dimension chain establishment method based on MBD annotation, thereby solving the problems of cumbersome process, error-proneness, poor readability, and low degree of automation in traditional tolerance analysis design using manual methods.

[0004] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0005] An automatic assembly error modeling method based on MBD includes the following steps:

[0006] 1) Based on the 3D model of the assembled parts, establish a directed graph of assembly relationships for the assembly;

[0007] 2) Establish a diagram showing the positioning relationships of the geometric features within the part;

[0008] 3) Determine the transformation relationship between adjacent geometric features in the geometric feature positioning relationship diagram based on the geometric feature position hierarchy system;

[0009] 4) Based on the transformation relationship, calculate the transformation relationship from the target feature to the global reference feature.

[0010] Step 1) includes the following steps:

[0011] 1.1) In CAD, select the analysis target and reference target for the 3D model of the assembly parts;

[0012] 1.2) Obtain the part containing the analysis target, all assembly constraint information of the part, all mating parts, and the assembly sequence of the part, and create the first node in the assembly relationship diagram, and store the part attributes, assembly order, and assembly matrix in the data domain;

[0013] 1.3) Compare the assembly order of mating parts. If the assembly priority of the mating part is higher than that of the current part, then the mating part is the positioning part of the current part and is pushed onto the stack. If the assembly priority of the mating part is lower than that of the current part, then the mating part is the assembly part.

[0014] 1.4) Get the top element of the stack, check if there is a mating part node in the assembly relationship diagram. If it exists, pop the next top element of the stack. If it does not exist, create a node in the assembly relationship diagram and store the attributes of the positioning part, the assembly order of the positioning part, and the assembly matrix of the positioning part in the data field.

[0015] 1.5) Create an edge that stores the constraint types and mating surfaces of the locating part and the assembly part. The direction of the edge is from the locating part to the assembly part.

[0016] 1.6) If no assembly priority higher than the current part can be found in the assembly constraint information, that is, the current part has no positioning part, then pop the top element of the stack and repeat steps 1.4) to 1.6) until the stack is empty, and obtain the directed graph of assembly relationship.

[0017] Step 2) includes the following steps:

[0018] 2.1) Push all the positioning surfaces of the current part in the assembly onto the stack;

[0019] 2.2) Obtain the top element of the stack, create a node in the geometric feature localization relationship graph, and store the geometric entity attributes, CAD coordinate system, and all GD&T annotations attached to the geometric entity in the node data field;

[0020] 2.3) Obtain the datum designations from all GD&T annotations, obtain the geometric features to which the datum designations are attached through the datum annotations, and push them onto the stack in sequence;

[0021] 2.4) Query whether the current geometric feature node exists in the geometric feature positioning relationship diagram. If it exists, pop the top element of the stack. If it does not exist, create the node in the geometric feature positioning relationship diagram and store the attributes of the reference feature, CAD coordinate system, and GD&T annotation in the node data field.

[0022] 2.5) If the GD&T annotation cannot be obtained on the reference feature, pop the top element of the stack and repeat steps 2.2) to 2.4). Otherwise, obtain the GD&T annotation of the reference feature and execute steps 2.3) to 2.4) until the stack is empty, and obtain the geometric feature localization relationship map.

[0023] Step 2.3) specifically refers to:

[0024] If the obtained GD&T annotation type is geometric tolerance, then the datum feature is obtained directly based on the datum symbol;

[0025] If the obtained GD&T annotation type is dimensional tolerance, then the datum-target relationship is determined according to rule 1;

[0026] If the obtained GD&T annotation type is dimension annotation, then determine the feature datum-target relationship according to rule 2-7;

[0027] If the datum-target relationship of the feature surfaces within a part cannot be determined through geometric tolerances and rules 1-7, then the dimensions and geometric tolerances of the part are considered incomplete or missing.

[0028] Rules 1-7 are specifically as follows:

[0029] Rule 1: If the annotation is a geometric tolerance annotation, the datum element of the current geometric element shall be determined directly based on the datum given by the geometric tolerance.

[0030] Rule 2: When the base datum feature of a part is a feature related to dimensional tolerances, the base datum feature is the datum feature, and the other feature is the target feature;

[0031] Rule 3: For two geometric features with dimensional tolerances, the feature that appears earlier in the order of face → line → point is the reference feature, and the feature that appears later in the order is the target feature. If they are the same, additional judgment is made according to other rules.

[0032] Rule 4: The central element is the reference element of the group of elements, and the member elements are the target elements. The group of elements represents the positioning of the central element relative to the member elements, and the error propagation direction is: central element → member element.

[0033] Rule 5: The fully located element is the reference element, and the incomplete element is the target element. If the position of a geometric element is fully constrained, that is, there are no extra degrees of freedom, the geometric element is the reference element, and the other element is the target element.

[0034] Rule 6: When labeling a baseline, the feature containing the baseline is the reference feature, and all other features are the target features;

[0035] Rule 7: The two ends of consecutively labeled elements are successively used as the reference element and the target element.

[0036] Step 3) includes the following steps:

[0037] 3.1) Based on the geometric feature positioning relationship diagram, obtain the initial geometric elements of the starting part and the geometric elements that participate in the positioning of other elements together with this element;

[0038] 3.2) Extract the CAD coordinate system, change it to the actual position according to the SDT model, and combine the reference geometric elements to establish a composite reference, i.e., the reference reference frame;

[0039] 3.3) Calculate the ideal position based on the nominal dimensions of the target feature within the reference frame;

[0040] 3.4) Obtain the geometric elements that participate in the datum function according to the assembly relationship diagram, and repeat steps 3.2) to 3.4) until the first assembly positioning surface of the part is reached;

[0041] 3.5) After the geometric feature position hierarchy of the reference part is established, the assembly part is obtained according to the assembly relationship diagram, and the transformation matrix from the global coordinate system of the assembly part to the actual position of the first assembly positioning surface of the positioning part is determined according to the mating relationship and the contact surface type.

[0042] 3.6) Repeat steps 3.1) to 3.5) and establish the geometric feature hierarchy positioning system of each part one by one according to the assembly order based on the transformation matrix. When the last installation part, i.e. the terminal part, is established, only steps 3.1) to 3.4) are executed to complete the establishment of the geometric feature hierarchy relationship.

[0043] Step 4) specifically involves:

[0044] The transformation matrix from the actual position to the ideal position, the transformation matrix from the reference frame to the actual position of the first reference, the transformation matrix from the ideal position to the reference frame, and the matrix of the global coordinate system of the assembly part relative to the first assembly positioning surface are obtained sequentially. Each group of four matrices is accumulated from left to right in a sequential order to obtain the position variation matrix of the target element relative to the global reference of the assembly.

[0045] An automatic assembly error modeling system based on MBD includes:

[0046] The assembly relationship diagram construction module is used to build a directed graph of assembly relationships based on the 3D model of the assembly parts.

[0047] The geometric feature positioning relationship diagram construction module is used to establish the geometric feature positioning relationship diagram within a part;

[0048] The geometric feature location hierarchy construction module is used to determine the transformation relationship between adjacent geometric features in the geometric feature location relationship diagram based on the geometric feature location hierarchy.

[0049] The target-global feature transformation module is used to calculate the transformation relationship from target features to global baseline features based on the transformation relationship.

[0050] An automatic assembly error modeling device based on MBD includes a memory and a processor; the memory is used to store a computer program; the processor is used to implement the automatic assembly error modeling method based on MBD when the computer program is executed.

[0051] A computer-readable storage medium storing a computer program that, when executed by a processor, implements the MBD-based automatic assembly error modeling method.

[0052] The present invention has the following beneficial effects and advantages:

[0053] 1. The tolerance modeling process is performed directly on the 3D model, which is seamlessly integrated with the CAD system. No data conversion is required, eliminating the need for manual interpretation of the engineering semantics of drawings using traditional engineering drawings during the tolerance modeling process;

[0054] 2. It can perform various geometric tolerance calculations with minimal manual operation and high calculation accuracy;

[0055] 3. This invention establishes a tolerance model through data structures such as assembly relationship diagrams and geometric feature positioning relationship diagrams, which has high adaptability and high accuracy for error transmission methods of different assemblies. Attached Figure Description

[0056] Figure 1 This is a flowchart of the method described in this invention;

[0057] Figure 2 This is an isometric view of an assembly according to an embodiment of the present invention;

[0058] Figure 3 This is an exploded view of an assembly according to an embodiment of the present invention;

[0059] Figure 4 This is an assembly relationship diagram of the parts of the assembly in step 1 of an embodiment of the present invention;

[0060] Figure 5 This is a diagram showing the positioning relationship of geometric elements within the assembly parts in step 2 of an embodiment of the present invention.

[0061] Figure 6 This is a flowchart illustrating the process of establishing the positioning relationship diagram of geometric elements within the assembly parts in step 2 of an embodiment of the present invention.

[0062] Figure 7 This is a diagram illustrating the calculation process of the geometric feature positioning relationship of part 3 in step 4 of an embodiment of the present invention;

[0063] Figure 8 This is a diagram illustrating the assembly error calculation process between parts 3 and 4 in step 4 of an embodiment of the present invention.

[0064] Wherein: 1-Part 1, 101-Part 1 first basic datum element, 102-Part 1 first positioning datum element, 103-Part 1 second positioning datum element; 2-Part 2, 201-Part 2 first assembly datum element, 202-Part 2 second assembly datum element, 203-Part 2 first positioning datum element, 204-Part 2 second positioning datum element; 3-Part 3, 301-Part 3 first assembly datum element, 302-Part 3 second assembly datum element, 303-Part 3 first positioning datum element, 304-Segment 3 second positioning datum element; 4-Part 4, 401-Part 4 first assembly datum element, 402-Part 4 second assembly datum element, 403-Part 4 first positioning datum (analysis target). Detailed Implementation

[0065] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0066] An automatic assembly error modeling method based on MBD, such as Figure 1 As shown, it includes 4 steps:

[0067] Step 1: Create an assembly relationship diagram;

[0068] Step 2: Establish a diagram showing the positioning relationships of the geometric features within the part;

[0069] Step 3: Determine the transformation relationships between geometric features in the geometric feature positioning relationship diagram based on the geometric feature position hierarchy system;

[0070] Step 4: Calculate the transformation relationship from the target feature to the global reference feature;

[0071] Because of the manufacturing process of the parts, the geometric elements must be manufactured in a certain order. Errors will be transmitted from the reference to the target in the geometric features within the parts, and from the positioning parts to the assembly parts through the assembly contact surfaces between the parts.

[0072] The specific content of step 1 in this invention is as follows:

[0073] (1) Users select the analysis target and reference target of the 3D model by using the mouse in CAD.

[0074] (2) Obtain the part where the analysis target is located, all assembly constraint information of the part, all mating parts, and the assembly sequence of the part, and create the first node in the assembly relationship diagram, and store the part attributes, assembly order, and assembly matrix in the data domain;

[0075] The assembly sequence of each part is provided by the CAD model sequence or specified by the human-computer interaction method;

[0076] (3) Compare the assembly order of mating parts. If the assembly priority is higher than the current part, push it onto the stack.

[0077] (4) Get the top element of the stack, check if the part node exists in the diagram. If it exists, pop the next top element of the stack. If it does not exist, create the node in the assembly relationship diagram and store the attributes of the positioning part, the assembly order of the positioning part, and the assembly matrix of the positioning part in the data field.

[0078] (5) Create an edge and store the constraint type and mating surface of the positioning part and the assembly part on the edge. The direction of the edge is from the positioning part to the assembly part.

[0079] (6) If an assembly with a higher priority than the current part cannot be found in the assembly constraint information, that is, the current part has no positioning part, pop the top element of the stack and execute (4) to (6) until the stack is empty to obtain the assembly relationship diagram.

[0080] Once the directed graph of assembly relationships is established, a geometric feature positioning relationship graph is created within each part node in the graph. The creation process is carried out according to the following steps:

[0081] (1) Push all the current part's positioning surfaces onto the stack. Only push the analysis target onto the stack for the part where the analysis target is located. All the part's positioning surfaces are obtained through all the adjacent edges of the part in the assembly relationship diagram.

[0082] (2) Obtain the top element of the stack, create a node in the geometric feature positioning relationship diagram, and store the geometric entity attributes, CAD coordinate system, and all GD&T annotations attached to the geometric entity in the node data field;

[0083] (3) Obtain the datum designations in all GD&T annotations, obtain the geometric features to which the datum designations are attached through the datum annotations, and push them onto the stack in sequence.

[0084] (4) Check if the node exists in the geometric feature positioning relationship diagram. If it exists, pop the top element of the stack. If it does not exist, create the node in the geometric feature positioning relationship diagram and store the attributes of the reference feature, CAD coordinate system, and GD&T annotation in the node data field.

[0085] (5) If the GD&T annotation cannot be obtained on the reference feature, pop the top element of the stack and repeat steps (2) to (5). Otherwise, obtain the GD&T annotation of the reference feature and execute steps (3) to (5) until the stack is empty to obtain the geometric feature positioning relationship diagram.

[0086] If the obtained GD&T annotation type is geometric tolerance, the datum feature can be directly obtained based on the datum symbol. If the GD&T annotation is dimensional tolerance, the datum-target relationship is determined according to the following rules:

[0087] Rule 1: If the annotation is a geometric tolerance annotation, the datum feature of the current geometric feature shall be determined directly based on the datum given by the geometric tolerance.

[0088] If the tolerance is a dimension annotation, the feature datum-target relationship is determined according to the following rules:

[0089] Rule 2: When the basic datum feature of a part is a feature related to dimensional tolerances, the basic datum feature is the datum feature, and the other feature is the target feature. The basic datum feature defines the position of other features on the part and is also the contact surface between the part and the positioning parts during assembly.

[0090] The basic datum feature is the global datum plane of the part. The position or tolerance zone of other surfaces on the part is also based on this. It is usually the first assembly datum plane when assembling the part, but it can also be specified by the user.

[0091] Rule 3: Use complex geometric elements as the baseline and simple geometric elements as the target. For example, with line elements and point elements, the line element is the baseline element and the point element is the target element.

[0092] Rule 4: The central element serves as the baseline for the group of elements, while the member elements serve as the target. The group of elements represents the positioning of the central element relative to the member elements, and the error propagation direction is: central element → member element.

[0093] Rule 5: Fully positioned elements are reference elements, and incompletely positioned elements are target elements. If the position of a geometric element is fully constrained, i.e., there are no extra degrees of freedom, the geometric element is the reference element, and the other element is the target element.

[0094] Rule 6: When labeling baselines, the feature containing the baseline is the reference, and all other features are the targets.

[0095] Rule 7: The two ends of consecutively labeled elements are successively used as the reference and target elements.

[0096] Some points need clarification here: When two parts are assembled, one is a locating part, and the other is an assembly part. During assembly, the first contact surface on the assembly part is called the assembly datum feature, and the first contact surface on the locating part is called the locating datum feature. Assembly errors are transmitted to the assembly datum features of the locating parts through the locating datum features of the locating parts. For the frame parts of the assembly, which have no locating parts, their first basic datum feature is the assembly datum feature. For the top-level part, the manually selected analysis target is its locating datum feature.

[0097] The content in step 3 defines the positional hierarchy of geometric elements, including the following:

[0098] The ideal position of a geometric element is generated by the geometric tolerance, which controls the actual position.

[0099] The ideal position of geometric elements is defined according to the correct dimensions within the measurement reference frame;

[0100] The measurement reference frame is established based on the actual location of the reference elements;

[0101] The actual position of the benchmark feature is generated by the variation of the ideal position of the benchmark feature;

[0102] The assembly relationship diagram uses pointers or variables to index the geometric feature positioning relationship diagram. The geometric feature positioning relationship diagram completes all the information in the assembly relationship diagram and, in the sense of error propagation, indicates the direction of error propagation within the part.

[0103] The process of establishing the geometric feature position hierarchy in step 3 is as follows: (1) According to the assembly relationship diagram obtained in step 2, obtain the starting geometric element of the starting part and the geometric element that participates in the positioning of other elements together with the element; (2) Extract the CAD coordinate system, i.e. the ideal position coordinate system; (3) According to the SDT model, change to the actual position and combine the reference geometric elements to establish a combined reference, i.e., the reference reference frame; (4) Calculate the ideal position according to the nominal size of the target element under the reference reference frame; (5) Then, according to the assembly relationship diagram, obtain the geometric elements that participate in the reference function together, and repeat steps (2) to (5) until the first assembly positioning surface of the part is reached; When two parts are assembled, the mating surfaces on the positioning parts are called the first assembly positioning surface, the second assembly positioning surface, etc. in order of positioning function (or order); the mating surfaces on the assembly parts are called the first assembly reference surface, the second assembly reference surface, etc. in order of contact sequence (or order). (6) After the geometric feature position hierarchy of the reference part is established, the assembly part is obtained according to the assembly relationship diagram. The transformation matrix from the global coordinate system of the assembly part to the actual position of the first assembly positioning surface of the positioning part is determined according to the mating relationship and the contact surface type. (7) After the assembly matrix is ​​established, repeat steps (1) to (6) and establish the geometric feature position hierarchy of each part one by one according to the assembly order. When the last installation part, i.e. the terminal part, is established, only steps (1) to (5) are executed, and the geometric feature hierarchy relationship is established.

[0104] The first assembly datum plane is the starting geometric element of the terminal part, and the final target element is the manually selected analysis target; the starting geometric element of the intermediate part is the first assembly datum plane, and the final target element is the first assembly positioning plane; the starting geometric element of the datum part is the manually selected datum, and the final target element is the first assembly positioning plane.

[0105] The transformation matrix from the global coordinate system of the assembly part to the first assembly positioning surface of the positioning part is an assembly matrix that describes the assembly position of the assembly part relative to the positioning part. It is related to the mating relationship, the type of mating surface, and the number of mating surfaces. Due to the large number of assembly relationships, this paper only involves the assembly method of cylindrical rotary parts.

[0106] In actual execution, the ideal position is obtained through the API of the CAD software, and the actual position is calculated by the tolerance representation model. The establishment of the combined datum, i.e. the datum reference frame, is carried out in accordance with the ASME standard. The transformation matrix from the actual position to the ideal position, the transformation matrix from the datum reference frame to the actual position of the first datum, the transformation matrix from the ideal position to the datum reference frame, and the matrix of the global coordinate system of the assembly part relative to the first assembly positioning surface are obtained in sequence. Every four matrices are grouped together and accumulated from left to right according to the geometric element error transmission relationship diagram to obtain the position variation matrix of the target element relative to the global datum of the assembly. This position variation is the result of the combined effect of part manufacturing error and assembly error.

[0107] After the geometric feature error propagation relationship diagram is established, the initial geometric elements are obtained, and the homogeneous coordinate transformation matrix is ​​sequentially accumulated according to the geometric element coordinate system hierarchy to obtain the position of the target element in the part and the position of the part in the assembly.

[0108] The coordinate system accumulation order is as follows: first geometric feature ideal position coordinate system → actual position coordinate system → measurement reference frame position → second geometric feature ideal position coordinate system, until the final target element.

[0109] Example

[0110] Existing high-end equipment such as Figure 2 As shown, for ease of description, the surface numbers of its parts are as follows: Figure 3As shown. According to step 1 of the present invention, an assembly relationship diagram of the assembly parts is established. The specific process is as follows: the user selects the analysis target element 403, uses the CAD system to obtain the part 4 where the target element 403 is located, and creates a node in the diagram. The first assembly datum element 401 and the second assembly datum element 402 of part 4 are respectively connected to the first positioning datum element and the second positioning datum element of part 3, and the connection methods are coincidence and coaxial, respectively. Therefore, the positioning part - part 3 is obtained, and the node of part 3 is created at the same time. An edge is created, with the direction pointing from part 3 to part 4. After creation, the positioning part 3 is taken as the current part, and the first positioning datum element 203, the second positioning datum element 204, and the body of part 2 are obtained through the first assembly datum element 301 and the second assembly datum element 302 of the positioning part 3. The node of part 2 is created in the diagram, and a connecting edge is established, pointing from part 2 to part 3. This process is repeated until the node of part 1 and the edge between part 1 and part 2 are created, and the assembly relationship diagram of the parts is established. Figure 4 As shown.

[0111] According to step 2 of the present invention, the process of establishing the positioning relationship diagram of the geometric features within the part includes:

[0112] Starting from the positioning datum element 403 of part 4 (analysis target), create the geometric element 403 node inside the node of part 4. Based on the height dimension of part 4, i.e., the distance from the positioning datum element 403 of part 4 to the first assembly datum element 401 of part 4, search for the associated surface 403, create the geometric element node in the drawing, and create an edge pointing from the first assembly datum element 401 to the first positioning datum element 403. The datum element of the analysis target is the first assembly datum element 401 of part 4. At this point, the internal geometric element positioning relationship diagram of part 4 is completed as follows. Figure 6 As shown. The next step starts from the first positioning datum element 303 of part 3 and creates a geometric element 303 node inside the node of part 3. Based on the height dimension of part 3, that is, the distance from the first positioning datum element 303 to the first assembly datum element 301 of part 3, obtain the geometric element 301, and create the geometric element 301 node and edges, with the direction pointing from geometric element 301 to geometric element 303. Since geometric element 301 is the first assembly datum element of part 3, the positioning relationship diagram of the internal geometric elements of part 3 is completed. Repeat this process until the relevant nodes and edges from the first positioning datum element 102 to the first basic datum element 101 of part 1 are completed inside part 1. At this point, the positioning relationship diagram of the internal geometric features of the assembly parts is completed, as shown. Figure 5 As shown.

[0113] The specific process of step 3 according to the present invention is as follows: Obtain the geometric element 403 of part 4 and its positioning elements—surface 401 (first positioning datum) and face 402 (second positioning datum). Based on the SDT screw theory, transform face 401 and face 402 to their true positions according to tolerance markings. Establish a reference frame based on the true positions of face 401 and face 402. Multiply the coordinate system of geometric element 403 with the coordinate system of the reference frame to obtain the position of the geometric element 403's coordinate system under the reference frame description, i.e., the transformation matrix T from the reference reference frame composed of face 401 and face 402 to face 403. DRF→F401 .

[0114]

[0115] In the formula, This indicates the current coordinate system of geometric element 403. This represents the reference frame coordinate system established by combining surfaces 401 and 402. The calculation process is as follows: Figure 7 As shown.

[0116] The assembly method for parts 4 and 3 is as follows: the first positioning datum coincides with the first assembly datum, and the second positioning datum and the second assembly datum are fitted with a hole and shaft perpendicular to the direction of the first datum. After assembly, the remaining degree of freedom is the radial offset along the plane of the first positioning datum. The assembly motion transformation matrix is:

[0117]

[0118] Where, d x d is the offset along the x-axis. y This represents the offset along the axis.

[0119] The assembly calculation process for parts 3 and 4 is as follows: Figure 8 As shown.

[0120] Repeat this process until geometric element 101 of part 1 is calculated. Based on step 4, obtain the variation matrix from the analysis target to the baseline target:

[0121] T 1-n =ΠT Part T assemble

[0122] Among them, T Part T is the variation matrix within the part. assemble T represents the error propagation matrix caused by the assembly relationship between parts. 1 -n It is a variation matrix from the reference position to the target position, which includes the entire process of part manufacturing error and assembly error.

[0123] The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, extensions, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. An automatic assembly error modeling method based on MBD, characterized in that, Includes the following steps: 1) Based on the 3D model of the assembled parts, establish a directed graph of assembly relationships for the assembly; 2) Establish a diagram showing the positioning relationships of the geometric features within the part; 3) Determine the transformation relationship between adjacent geometric features in the geometric feature positioning relationship diagram based on the geometric feature position hierarchy system; 4) Based on the transformation relationship, calculate the transformation relationship from the target feature to the global reference feature.

2. The automatic assembly error modeling method based on MBD according to claim 1, characterized in that, Step 1) includes the following steps: 1.1) In CAD, select the analysis target and reference target for the 3D model of the assembly parts; 1.2) Obtain the part containing the analysis target, all assembly constraint information of the part, all mating parts, and the assembly sequence of the part, and create the first node in the assembly relationship diagram, and store the part attributes, assembly order, and assembly matrix in the data domain; 1.3) Compare the assembly order of mating parts. If the assembly priority of the mating part is higher than that of the current part, then the mating part is the positioning part of the current part and is pushed onto the stack. If the assembly priority of the mating part is lower than that of the current part, then the mating part is the assembly part. 1.4) Get the top element of the stack, check if there is a mating part node in the assembly relationship diagram. If it exists, pop the next top element of the stack. If it does not exist, create a node in the assembly relationship diagram and store the attributes of the positioning part, the assembly order of the positioning part, and the assembly matrix of the positioning part in the data field. 1.5) Create an edge that stores the constraint types and mating surfaces of the locating part and the assembly part. The direction of the edge is from the locating part to the assembly part. 1.6) If no assembly priority higher than the current part can be found in the assembly constraint information, that is, the current part has no positioning part, then pop the top element of the stack and repeat steps 1.4) to 1.6) until the stack is empty, and obtain the directed graph of assembly relationship.

3. The automatic assembly error modeling method based on MBD according to claim 1, characterized in that, Step 2) includes the following steps: 2.1) Push all the positioning surfaces of the current part in the assembly onto the stack; 2.2) Obtain the top element of the stack, create a node in the geometric feature localization relationship graph, and store the geometric entity attributes, CAD coordinate system, and all GD&T annotations attached to the geometric entity in the node data field; 2.3) Obtain the datum designations from all GD&T annotations, obtain the geometric features to which the datum designations are attached through the datum annotations, and push them onto the stack in sequence; 2.4) Query whether the current geometric feature node exists in the geometric feature positioning relationship diagram. If it exists, pop the top element of the stack. If it does not exist, create the node in the geometric feature positioning relationship diagram and store the attributes of the reference feature, CAD coordinate system, and GD&T annotation in the node data field. 2.5) If the GD&T annotation cannot be obtained on the reference feature, pop the top element of the stack and repeat steps 2.2) to 2.4). Otherwise, obtain the GD&T annotation of the reference feature and execute steps 2.3) to 2.4) until the stack is empty, and obtain the geometric feature localization relationship map.

4. The automatic assembly error modeling method based on MBD according to claim 3, characterized in that, Step 2.3) specifically refers to: If the obtained GD&T annotation type is geometric tolerance, then the datum feature is obtained directly based on the datum symbol; If the obtained GD&T annotation type is dimensional tolerance, then the datum-target relationship is determined according to rule 1; If the obtained GD&T annotation type is dimension annotation, then determine the feature datum-target relationship according to rule 2-7; If the datum-target relationship of the feature surfaces within a part cannot be determined through geometric tolerances and rules 1-7, then the dimensions and geometric tolerances of the part are considered incomplete or missing.

5. The automatic assembly error modeling method based on MBD according to claim 4, characterized in that, Rules 1-7 are specifically as follows: Rule 1: If the annotation is a geometric tolerance annotation, the datum element of the current geometric element shall be determined directly based on the datum given by the geometric tolerance. Rule 2: When the base datum feature of a part is a feature related to dimensional tolerances, the base datum feature is the datum feature, and the other feature is the target feature; Rule 3: For two geometric features with dimensional tolerances, the feature that appears earlier in the order of face → line → point is the reference feature, and the feature that appears later in the order is the target feature. If they are the same, additional judgment is made according to other rules. Rule 4: The central element is the reference element of the group of elements, and the member elements are the target elements. The group of elements represents the positioning of the central element relative to the member elements, and the error propagation direction is: central element → member element. Rule 5: The fully located element is the reference element, and the incomplete element is the target element. If the position of a geometric element is fully constrained, that is, there are no extra degrees of freedom, the geometric element is the reference element, and the other element is the target element. Rule 6: When labeling a baseline, the feature containing the baseline is the reference feature, and all other features are the target features; Rule 7: The two ends of consecutively labeled elements are successively used as the reference element and the target element.

6. The automatic assembly error modeling method based on MBD according to claim 1, characterized in that, Step 3) includes the following steps: 3.1) Based on the geometric feature positioning relationship diagram, obtain the initial geometric elements of the starting part and the geometric elements that participate in the positioning of other elements together with this element; 3.2) Extract the CAD coordinate system, change it to the actual position according to the SDT model, and combine the reference geometric elements to establish a composite reference, i.e., the reference reference frame; 3.3) Calculate the ideal position based on the nominal dimensions of the target feature within the reference frame; 3.4) Obtain the geometric elements that participate in the datum function according to the assembly relationship diagram, and repeat steps 3.2) to 3.4) until the first assembly positioning surface of the part is reached; 3.5) After the geometric feature position hierarchy of the reference part is established, the assembly part is obtained according to the assembly relationship diagram, and the transformation matrix from the global coordinate system of the assembly part to the actual position of the first assembly positioning surface of the positioning part is determined according to the mating relationship and the contact surface type. 3.6) Repeat steps 3.1) to 3.5) and establish the geometric feature hierarchy positioning system of each part one by one according to the assembly order based on the transformation matrix. When the last installation part, i.e. the terminal part, is established, only steps 3.1) to 3.4) are executed to complete the establishment of the geometric feature hierarchy relationship.

7. The automatic assembly error modeling method based on MBD according to claim 1, characterized in that, Step 4) specifically involves: The transformation matrix from the actual position to the ideal position, the transformation matrix from the reference frame to the actual position of the first reference, the transformation matrix from the ideal position to the reference frame, and the matrix of the global coordinate system of the assembly part relative to the first assembly positioning surface are obtained sequentially. Each group of four matrices is accumulated from left to right in a sequential order to obtain the position variation matrix of the target element relative to the global reference of the assembly.

8. An automatic assembly error modeling system based on MBD, characterized in that, include: The assembly relationship diagram construction module is used to build a directed graph of assembly relationships based on the 3D model of the assembly parts. The geometric feature positioning relationship diagram construction module is used to establish the geometric feature positioning relationship diagram within a part; The geometric feature location hierarchy construction module is used to determine the transformation relationship between adjacent geometric features in the geometric feature location relationship diagram based on the geometric feature location hierarchy. The target-global feature transformation module is used to calculate the transformation relationship from target features to global baseline features based on the transformation relationship.

9. An automatic assembly error modeling device based on MBD, characterized in that, It includes a memory and a processor; the memory is used to store a computer program; the processor is used to implement, when executing the computer program, an automatic assembly error modeling method based on MBD as described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, The storage medium stores a computer program, which, when executed by a processor, implements an automatic assembly error modeling method based on MBD as described in any one of claims 1-7.

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