AU2021100388A4

AU2021100388A4 - A general structure construction method of three-dimensional assembly model based on conjugate subgraph

Info

Publication number: AU2021100388A4
Application number: AU2021100388A
Authority: AU
Inventors: Hu QIAO
Original assignee: Xian Technological University
Current assignee: Xian Technological University
Priority date: 2021-01-21
Filing date: 2021-01-21
Publication date: 2021-04-15
Anticipated expiration: 2029-01-21

Abstract

The invention relates to the technical field of three-dimensional model reuse, in particular to a general structure construction method of three-dimensional assembly model based on conjugate subgraph. Firstly, with the common structure of three-dimensional assembly model as the carrier, the assembly feature matching problem of three-dimensional assembly model is transformed into the assembly feature matching problem based on conjugate subgraph based on attributes such as assembly features and matching relationship. Secondly, on the basis of ullmann algorithm, combined with the definition of conjugate subgraph and related optimization operations, the conjugate subgraph matching problem based on vertex screening is proposed. Finally, the construction process of general structure is put forward, and the general structure of three-dimensional assembly model is established. The method can integrate three-dimensional assembly model information with similar structures, reduce the matching times in the process of information reuse, and improve the design reuse efficiency of the three-dimensional assembly model. -1/5 f g h Fig. 1 A set of three-dimensional assembly models of a certain series of machine tool fixtures, in which (a)-(h) respectively correspond to fixture 1-fixture 8.

Description

-1/5

f

g

h

Fig. 1

A set of three-dimensional assembly models of a certain series of machine tool fixtures,

in which (a)-(h) respectively correspond to fixture 1-fixture 8.

A GENERAL STRUCTURE CONSTRUCTION METHOD OF THREE DIMENSIONAL ASSEMBLY MODEL BASED ON CONJUGATE SUBGRAPH TECHNICAL FIELD

The invention relates to the technical field of three-dimensional model reuse, in particular

to a general structure construction method of three-dimensional assembly model based on

conjugate subgraph.

BACKGROUND

With the development of information science and technology and related knowledge of

product modeling, CAD model has made a qualitative leap in its ability to describe

information from both connotation and extension. In the current environment, there are

numerous existing models, and a large number of new models still appear every day.

When an enterprise develops a new product, it is not a total innovation, but 40%

improves the design history appropriately, 40% optimizes the design history, and only

% is the result of design innovation. With the rapid development of manufacturing

industry, the design reuse technology of three-dimensional assembly model information

has gradually become a research hotspot. Excavating model information supporting reuse

from different angles and aspects, reducing design cycle and improving design efficiency,

plays a key role in large-scale design and manufacturing.

Traditional model retrieval takes single models as units, and multiple model retrieval

requires multiple matching. Constructing the general structure of three-dimensional assembly model and expressing several three-dimensional assembly models with similar structures in a unified way can reduce the retrieval times in the process of model reuse and further improve the efficiency of model retrieval.

A construction method of general structure takes brake products as an example. Firstly,

the expression specification of attribute connection graph is constructed, and then the

general design unit is obtained based on clustering algorithm and frequent subgraph

algorithm, so as to realize assembly model information excavation.

A general structure construction method is to construct a graph-based three-dimensional

assembly model descriptor, which represents the corresponding model elements, defines

related attributes, and realizes bidirectional mapping between the model and the graph.

Then, based on distance calculation, the local differences of parts are fused. Finally, the

frequent subgraph algorithm is used to extract the corresponding general structure. The

limitation of the above methods is that these two methods only extract the common parts

of the three-dimensional assembly model, and only obtain part of the model structure

when reusing the design, thus affecting the design efficiency.

SUMMARY

The purpose of the invention is to reduce the times of graph matching in design reuse of a

three-dimensional assembly model, and realize corresponding universal expression on the

basis of a group of model structures with design commonness. That is, based on the

common structure of three-dimensional assembly model, combined with other

components that are not classified into the common structure, a graph model

representation with comprehensive expression and diverse functional types is formed, which is the unified expression of this group of models, thus a general structure construction method of three-dimensional assembly model based on conjugate subgraph is proposed.

In order to achieve the purpose of the invention, the technical scheme provided by the

invention is as follows:

A general structure construction method of three-dimensional assembly model based on

conjugate subgraph, which is characterized in that: firstly, based on the common structure

of three-dimensional assembly model, and based on the attributes of assembly features

and matching relations, and combining the idea of conjugate, the matching problem of

assembly features of three-dimensional assembly model is transformed into the matching

problem of assembly features based on conjugate subgraph. Secondly, on the basis of

ullmann algorithm, combined with the definition of conjugate subgraph and related

optimization operations, the conjugate subgraph matching problem based on vertex

screening is proposed. Finally, the construction process of general structure is put

forward, and the general structure of three-dimensional assembly model is established.

The method comprises the following steps:

Step 1: defining n universal sets (n is the number of parts in the common structure of

three-dimensional assembly model), and initializing them, which are respectively used to

store attribute adjacency graphs that satisfy conjugate matching with the parts in the

matching process.

Step 2: inputting the common structure of the three-dimensional assembly model and the

attribute adjacency graph atlas respectively corresponding to the component to be matched, wherein the atlas mainly stores the attribute adjacency graph corresponding to each component in the model respectively.

Step 3: traversing all parts in the common structure of the three-dimensional assembly

model based on the vertex screening conjugate subgraph matching algorithm, and

performing conjugate subgraph matching on each component in the current component

atlas to be matched with the attribute adjacency graph of the current part in turn. For the

k-th part in the common structure:

1) If conjugate matching is satisfied, adding the attribute adjacency graph corresponding

to the component to the universal set corresponding to the k-th part, updating the added

general structure state of the three-dimensional assembly model, and selecting the next

component to be matched to continue conjugate subgraph judgment.

2) If conjugate matching is not satisfied, skip directly, and selecting the next component

to be matched to continue conjugate subgraph judgment.

Step 4: until all the components in the current component atlas to be matched are

traversed, the universal set corresponding to the part is constructed, the part in the next

common structure is selected, and stepping into step 3.

Step 5: repeating the above steps until each part in the common structure of the three

dimensional assembly model is traversed to obtain a universal set corresponding to each

part, so that the general structure of the three-dimensional assembly model is constructed.

Furthermore, the conjugate subgraph matching algorithm based on vertex screening in

step 3 specifically includes the following steps:

(3-a) Pretreatment.

(3-b) Initializing VI and V2 to make VI = 0 and V2 = 0. VI and V2 are vertex sets, and

the function of these two sets is to store vertices that satisfy conjugate matching during

the running of the algorithm.

(3-c) Start traversing from the first row of the mapping matrix (M). If the element mrc=

1, adding the vertex corresponding to the element to VI and V2 respectively, and set the

occupation mark (OC) of the c column as true, initializing the regression mark (B) as

false, and the row count (L) as r.

(3-d), r+1, traverse matrix M, if B is false, enter the row and run step (3-e). Otherwise, go

back to r row and run step (3-f).

(3-e), traverse the i-th row in m, starting from the 0-th column:

1) if mij = 1 and the column is not occupied, add matched vertices to VI and V2

respectively, and make conjugate subgraph matching judgment. If the conditions such as

the same conjugate subgraph structure, the same vertex plane type and vertex matching

requirements, the opposite vertex plane normal vectors and the opposite edge attributes

are met, Oj is set to be true, and execute step (3-d). Otherwise, delete the matching

vertex, L+I.

2) Otherwise, L+1.

(3-f), if OC in row r is false, delete the matching vertex, and traverse the i-th row of the

matrix from column c+1:

1) if mij = 1 and the column is not occupied, add matched vertices to VI and V2

are met, then set Oj as true and B as false, and execute step (3-d). Otherwise, delete the

matching vertex, L+ 1.

2) Otherwise, L+1.

(3-g), if the number of columns of L and M is equal, or the number of columns of c+1

and M in step (3-f) is equal, set B as true, and go back one row. Otherwise, go to the next

row.

(3-h), after traversing M, if VI and V2 sets are not empty sets, the vertices in the sets are

matched conjugate subgraphs and output. Otherwise, the algorithm ends and the subgraph

is not conjugate.

Furthermore, in step (3-a) initializes M according to the related properties of conjugate

subgraph, and mainly judges the element with a value of 1in M to see if it can be set as 0.

Because the number of elements in M is limited, the preprocessing steps are limited until

no element in M can be set to 0.

Furthermore, the step (3-a) includes the following steps:

If the attributes of vertices in two graphs do not conform to the same attributes of nodes

corresponding to conjugate subgraphs, the elements corresponding to vertices in matrix

M are set to 0.

After initialization, vertex screening is performed, and conjugate subgraph matching is

exited if the following conditions are met. If not, proceed to step (3-b).

(i), in M, if all the elements in a row is not 1, it means that a node in the matched

subgraph does not exist in the large graph to be retrieved.

(ii), in M, r > c means that the matched subgraph is larger than the large graph to be

retrieved.

(iii), the number of a node in the matched subgraph is larger than the number of similar

nodes in the large graph to be retrieved.

Compared with the prior art, the invention has the beneficial effects that:

The method is based on attributes such as assembly features, matching relations and the

like, combines conjugate ideas, improves efficiency based on related optimization means

such as conjugate subgraph correlation characteristics and preprocessing, and uses a

conjugate subgraph matching algorithm based on vertex screening to solve the matching

problem of assembly features in a three-dimensional assembly model. In the algorithm,

according to the principle that subgraphs formed by vertex set VI on the matched small

picture and V2 on the matched large picture must also be isomorphic, judging whether

subgraphs composed of VI and V2 are isomorphic or not, and whether the attributes of

edges corresponding to corresponding vertices conform to the opposite properties of

edges corresponding to conjugate subgraphs, so as to judge the validity of newly found

columns, effectively eliminate invalid matches and improve matching accuracy and

efficiency.

The general structure of the three-dimensional assembly model constructed by the

invention can reflect reusable common structure information such as functions,

structures, attributes and the like in a group of three-dimensional assembly models, meet

public demands, and provide designers with the general structure of the group of models,

relevant functions, attributes, design experience and other information. It can also reflect

the relevant information of many non-common structures, and include as many qualified

structures as possible, so as to meet various individualized needs of designers at different

stages and under different conditions, and provide comprehensive and detailed reusable

information for designers in design and manufacturing. Therefore, in the process of

design reuse, the matching times are reduced and the reuse efficiency is improved.

DESCRIPTION OF THE FIGURES

The scheme of the present invention will be further explained with reference to the

figures and embodiments.

Fig. 1 shows a set of three-dimensional assembly models of a certain series of machine

tool fixtures, in which (a)-(h) respectively correspond to fixture 1-fixture 8.

Fig. 2 shows the common structure of three-dimensional assembly model.

Fig. 3 shows the hydraulically driven piston cylinder and piston rod.

Fig. 4 is an example diagram of the universal set of three-dimensional assembly models.

Fig. 5 shows the general structure of three-dimensional assembly model.

DESCRIPTION OF THE INVENTION

The present invention will be described in detail with reference to figures and

embodiments.

According to the technical scheme provided by the invention, a general structure

construction method of three-dimensional assembly model based on conjugate subgraph

comprises the following steps: firstly, based on the model representation method in the

patent A methodfor discovering common structure based on three-dimensionalassembly

model (CN110399657A) and the common structure obtained by excavation, excavating

the corresponding common structure. Taking the common structure as the carrier, based

on the attributes of assembly features and matching relations, and combining the idea of

conjugation, the assembly feature matching problem of three-dimensional assembly

model is transformed into the assembly feature matching problem based on conjugate

subgraph. Secondly, on the basis of ullmann algorithm, combined with the definition of

conjugate subgraph and related optimization operations, the conjugate subgraph matching

problem based on vertex screening is proposed. Finally, the construction process of

general structure is put forward, and the general structure of three-dimensional assembly

model is established, so as to achieve the purpose of design reuse. The common structure

of three-dimensional assembly model is different with different frequency thresholds, and

the excavation results under any threshold are corresponding to the corresponding

common structure.

Embodiment: in this paper, a set of three-dimensional assembly models of a series of

machine tool fixtures shown in Fig. 1 is taken as an example, and there are 8 fixtures in this embodiment. Set the minimum frequency threshold to 1, and build the corresponding general structure with the common structure as shown in Fig. 2. Among them, the "a" code in the figure means that the connection relationship between the two parts that cooperate with each other is "welding", and the contact type of the mating surface is

"plane-plane contact". The meaning represented by "b2" code is that the connection

relationship between the two parts that cooperate with each other is "threaded

connection", and the contact type of the mating surface is "cylinder-cylinder contact".

The meaning represented by "d2" code is that the connection relationship between the

two parts that cooperate with each other is "contact connection", and the contact type of

the mating surface is "cylinder-cylinder contact". 1 stands for bottom plate. 2 stands for

positioning plate. 3 stands for pressure plate. 5 stands for strutting piece 1. 6 stands for

nut. 9 stands for strutting piece 2. It can be seen that the common structure of this set of

fixtures under this threshold value at least includes pressure plate, bottom plate, strutting

piece, nut, positioning block and other parts. Parts are connected by welding, thread

connection, contact connection, etc.

conjugate subgraph, which specifically comprises the following steps:

matching process.

attribute adjacency graph atlas respectively corresponding to the component to be

matched, wherein the atlas mainly stores the attribute adjacency graph corresponding to

each component in the model respectively.

model based on the vertex screening conjugate subgraph matching algorithm, and

k-th part in the common structure:

The conjugate subgraph matching algorithm based on vertex screening specifically

includes the following steps:

(3-a) Pretreatment.

The specific content of preprocessing is to initialize M according to the related properties

of conjugate subgraph, which is mainly to judge the element with the value of 1 in M to

see if it can be set as 0. Because the number of elements in M is limited, the

preprocessing steps are limited until no elements in M can be set to 0. The specific steps

are as follows:

M are set to 0.

exited if the following conditions are met. If not, proceed to step (3-b).

subgraph does not exist in the large graph to be retrieved.

retrieved.

nodes in the large graph to be retrieved.

the running of the algorithm.

false, and the row count (L) as r.

back to r row and run step (3-f).

(3-e), traverse the i-th row in m, starting from the 0-th column:

1) if mij = 1 and the column is not occupied, add matched vertices to VI and V2

requirements, the opposite vertex plane normal vectors and the opposite edge attributes are met, Oj is set to be true, and execute step (3-d). Otherwise, delete the matching vertex, L+1.

2) Otherwise, L+1.

matrix from column c+1:

1) if mij = 1 and the column is not occupied, add matched vertices to VI and V2

matching vertex, L+ 1.

2) Otherwise, L+1.

row.

is not conjugate.

For the k-th part in the common structure of three-dimensional assembly model:

1) If conjugate matching is satisfied, add the attribute adjacency graph corresponding to

the component to the universal set corresponding to the k-th part, update the added general structure state of the three-dimensional assembly model, and select the next component to be matched to continue conjugate subgraph judgment.

2) If conjugate matching is not satisfied, skip directly, and select the next component to

be matched to continue conjugate subgraph judgment.

Take one piston cylinder part and four piston rod parts of hydraulic transmission in a

machine tool accessory shown in Fig. 3 as an example to build a universal set. Keep the

assembly feature information, simplify the non-assembly feature information, construct

the adjacency graph of the attributed assembly feature corresponding to each part, and

construct the general structure to get the corresponding universal set as shown in Fig. 4.

In which, 1 in the figure represents piston rod 1. 2 represents piston rod 2. 3 represents

piston rod 3. 4 represents piston rod 4. 5 represents piston cylinder. The part circled by

the coil is the related content represented by the universal set. Shaded parts are parts of

assembly features where parts cooperate, and virtual and real lines used for connecting

conjugate nodes represent edges with opposite attributes in assembly features of parts.

Step 4, until all the components in the current component atlas to be matched are

common structure is selected, and proceed to step 3.

Step 5, repeating the above steps until each part in the common structure of the three

dimensional assembly model is traversed to obtain a general set corresponding to each

The invention takes the part 9 (strutting piece 2) as an example, and its construction result

is shown in Fig. 5.Among them, the "dl" code in the figure means that the connection relationship between the two parts that cooperate with each other is "contact connection", and the contact type of the mating surface is "plane-cylinder contact".

In the figure, 1 represents bottom plate. 2 represents positioning plate. 3 represents

pressure plate. 4 represents handle. 5 represents strutting piece 1. 6 represents nut. 7

represents spring. 8 represents spring protection sleeve. 9 represents strutting piece 2. 10

represents cylindrical pin. 11 represents rotating member. 12 represents connecting rod.

13 represents swing rod. 14 represents sleeve. 15 represents screw. The structure

displayed outside the coil is the general structure of the three-dimensional assembly

model, which represents the general composition of the model components, while the part

inside the coil is the universal set corresponding to the part 9 (strutting piece 2) in the

general structure of the three-dimensional assembly model.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS

1. A general structure construction method of three-dimensional assembly model based

on conjugate subgraph, which is characterized in that: firstly, based on the common

structure of three-dimensional assembly model, and based on the attributes of assembly

features and matching relations, and combining the idea of conjugate, the matching

problem of assembly features of three-dimensional assembly model is transformed into

the matching problem of assembly features based on conjugate subgraph. Secondly, on

the basis of ullmann algorithm, combined with the definition of conjugate subgraph and

related optimization operations, the conjugate subgraph matching problem based on

vertex screening is proposed. Finally, the construction process of general structure is put

2. The general structure construction method of three-dimensional assembly model based

on conjugate subgraph according to claim 1, characterized in that the method comprises

the following steps:

matching process.

each component in the model respectively.

model based on the vertex screening conjugate subgraph matching algorithm, and

k-th part in the common structure:

component to be matched to continue conjugate subgraph judgment.

to be matched to continue conjugate subgraph judgment.

common structure is selected, and stepping into step 3.

3. The general structure construction method of three-dimensional assembly model based

on conjugate subgraph according to claim 1, characterized in that the conjugate subgraph

matching algorithm based on vertex screening in step 3 specifically comprises the

following steps:

(3-a) Pretreatment.

the running of the algorithm.

false, and the row count (L) as r.

(3-d) r+1, traverse matrix M, if B is false, enter the row and run step (3-e). Otherwise, go

back to r row and run step (3-f).

(3-e) Traverse the i-th row in m, starting from the 0-th column:

1) if mij = 1 and the column is not occupied, add matched vertices to VI and V2

vertex, L+I.

2) Otherwise, L+1.

matrix from column c+1:

1) if mij = I and the column is not occupied, add matched vertices to VI and V2

respectively, and make conjugate subgraph matching judgment. If the conditions such as the same conjugate subgraph structure, the same vertex plane type and vertex matching requirements, the opposite vertex plane normal vectors and the opposite edge attributes are met, then set Oj as true and B as false, and execute step (3-d). Otherwise, delete the matching vertex, L+ 1.

2) Otherwise, L+1.

row.

is not conjugate.

4. The general structure construction method of three-dimensional assembly model based

on conjugate subgraph according to claim 1, characterized in that the step (3-a) initializes

M according to the related properties of conjugate subgraph, and mainly judges the

element with a value of 1 in M to see if it can be set as 0. Because the number of

elements in M is limited, the preprocessing steps are limited until no element in M can be

set to 0.

5. The general structure construction method of three-dimensional assembly model based

on conjugate subgraph according to claim 1, characterized in that the step (3-a) comprises

the following steps:

M are set to 0.

exited if the following conditions are met. If not, proceed to step (3-b).

subgraph does not exist in the large graph to be retrieved.

retrieved.

nodes in the large graph to be retrieved.

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Fig. 1

in which (a)-(h) respectively correspond to fixture 1-fixture 8.

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Fig. 2

the common structure of three-dimensional assembly model.

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Fig. 3

The hydraulically driven piston cylinder and piston rod.

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Fig. 4

An example diagram of the universal set of three-dimensional assembly models.

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Fig. 5

The general structure of three-dimensional assembly model.