KR101439997B1 - System and method for modifying b-rep models using stepwise volume decomposition - Google Patents

Abstract

The present invention relates to a CAD model modification system and method using a stepwise volume decomposition for modifying a shape represented by a boundary representation (b-rep) or a CAD model, A volume correcting unit for changing, deleting and copying a volume which is desired to be corrected among the volumes decomposed in the stepwise volume decomposing unit using movement, rotation, enlargement / reduction transformation, And a volume re-combination unit for re-joining the volumes, using the Boolean union operation.

Description

Technical Field [0001] The present invention relates to a method and system for modifying a CAD model using stepwise volume decomposition,

The present invention relates to a model reconstruction in a CAD system, and more particularly, to a CAD model modification system and method using a stepwise volume decomposition for modifying a shape represented by a boundary representation (b-rep) or a CAD model .

In general, CAD systems adopt a feature-based model as a key expression method to facilitate design change. We use boundary representation (B-rep) as an ancillary representation method for CAD model visualization, geometric calculation, and user interaction.

IGES and STEP AP203 edition 1, which is a representative CAD file exchange format, supports only B-rep model, so if you save CAD model in this file format, feature information will be lost. This makes it difficult to change the design of CAD models exchanged using the IGES and STEP file formats.

In order to overcome the disadvantage that conventional STEP AP203 edition 1 format only supports B-rep model, STEP Parametrics Group established STEP AP203 edition 2 which is a new standard format for exchanging feature-based model.

However, there is no commercial system supporting this.

Similarly, a macro-parametric approach for exchanging macro files that record CAD model creation and change history, and an exchange method based on a universal product representation (UPR) structure capable of accommodating feature information of a commercial CAD system Lt; / RTI >

However, since these methods require feature model information as input information, they can not be applied when the B-rep model is given, and thus the range of application is limited.

More specifically, design changes of CAD systems will be described as follows.

Commercial machine CAD systems employ a hybrid modeling approach that uses both a b-rep model and a procedural model to represent the shape of a CAD model.

The dual procedural model expresses the shape in the order of the modeling operators used to create the shape, called the feature. In a procedural model, the shape can be changed by changing the arguments of the modeling operator or the order of the operators.

Therefore, it is easy to modify the shape in the procedural model. However, since the initial graphics exchange specification (IGES) and the standard for the exchange of product model data (STEP) AP203 edition 1 do not support a procedural model, a CAD model can be stored If the procedural model information is lost.

This makes it difficult to change CAD models stored using the IGES and STEP file formats. In addition, many engineering software still only support boundary representation models, so an effective way to modify the representation represented by the boundary representation model is needed.

To modify a shape or a CAD model represented by a boundary representation method, it is necessary to decompose the shape into components such as points, curves, curved surfaces, vertices, edges, and faces, modify the shape of the part to be corrected, Should be.

Such a process is time-consuming, frequent errors occur in the recombination process, and is difficult to apply when the shape is greatly changed.

The present invention solves the problem of the design change method of the CAD systems of the related art. The CAD model using the stepwise volume decomposition for correcting the shape expressed by the boundary representation (b-rep) or the CAD model And an object of the present invention is to provide a correction system and method.

The present invention provides a CAD model modification system and method using a stepwise volume decomposition that can be applied when modifying a shape represented by a boundary expression method by using a stepwise volume decomposition and to facilitate shape modification even without procedural model information, There is a purpose.

The present invention can significantly reduce the number of concave corners by applying a wraparound operation and a volume partitioning operation, and can process a second-order curve whose decomposition speed is fast and which can not be processed by convex decomposition by volume decomposition method, The present invention provides a system and method for revising a CAD model using a stepwise volume decomposition to generate a volume having a shape and a subtractive shape.

The objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, a CAD model modification system using stepwise volume decomposition according to the present invention includes a stepwise volume decomposition unit for decomposing an original shape represented by a boundary representation model into unit volumes, A volume reconfiguring unit for changing, deleting, and copying a desired volume using a moving, rotating, and zooming conversion; a volume reconciliation unit for reconverting the disassembled volumes, which have been changed by the volume coordinator, using a Boolean union operation; ; And

The stepwise volume decomposer may include a fillet / round / chamfer removal unit that removes a fillet, a round, and a chamfer shape in an original shape represented by a boundary expression model, and a wraparound operation to remove a shape A volume division unit for dividing a shape by applying a volume split operation, and a cell-based decomposition method for finding concave corners of a shape and sharing the same And a volume decomposition unit for decomposing the shape into cells and combining them.

In the fillet / round / chamfer removal, the original shape before the fillet and the round are removed is S, and the shape after the fillet and the round are removed is T, the volume F of the fillet is F = S - ^* T , The volume R of the round is calculated as R = T - ^* S, where - ^* is a regularized Boolean subtract operator.

In order to accomplish another object, a method of modifying a CAD model using stepwise volume decomposition according to the present invention is a method for modifying a shape or a CAD model represented by a boundary expression method (b-rep) Removing the fillet, round and chamfer shapes in the shape, decomposing the shape by applying a wrap-around operation, decomposing the shape by applying a volume split operation, Finding all concave corners of a shape using a cell-based decomposition method, finding and sharing faces sharing the shape, and decomposing and combining the shape into cells, Changing, removing, copying and correcting by using rotation, enlargement / reduction transformation, and reconstructing the decomposed volumes using a Boolean union operation. And a step of summing.

Here, the step of decomposing the shape by applying the wrap-around operation includes: marking a convex inner loop in the original shape; separating all surfaces of the marked original shape Removing the surfaces that do not constitute a solid in the step of recombining all the surfaces again, and removing the solidified surfaces of the solid And combining the original solid and the original solid using a Boolean sum operation.

And the step of resolving the shape by applying the volume split operation comprises the steps of finding a concave inner loop of the shape S and creating a copy F of the face having a concave inner loop Removing the inner loop from the copy F to obtain a non-regularized Boolean union of the shape S and the copy F and dividing the shape into two cells; And dividing the cell of the cell into a volume and decomposing the shape.

V인 경우에, V를 솔리드(S)의 최대 볼륨으로 판단하는 것을 특징으로 한다.Then, in the step of finding all concave corners of the shape using the cell-based decomposition method and finding and expanding the faces to share and decomposing the shape into cells and combining them, The volume condition is satisfied until the volume condition is satisfied. When the volume (V) satisfies the following conditions, ① V ⊆ S and ② V have no concave edge. ③ All halfspaces of V are halfspaces of S. ④ For other volume B that satisfies the above conditions, B

V, it is determined that V is the maximum volume of the solid (S).

The CAD model modification system and method using the stepwise volume decomposition according to the present invention have the following effects.

First, a shape or CAD model represented by a boundary representation (b-rep) can be efficiently modified using volume decomposition.

Second, it is applied to the case of modifying the shape expressed by the boundary expression method by using the stepwise volume decomposition, and it is easy to modify the shape without the procedural model information.

Third, the number of concave corners can be greatly reduced by applying the wraparound operation and the volume division operation, thereby reducing the overall volume decomposition time.

Fourth, the volume decomposition method can process to the second-order surface which has a fast decomposition speed and can not process the convex decomposition, and can generate the volume having the additive form and the subtractive form.

Fifth, it is possible to quickly modify a shape represented by a boundary representation (b-rep) or a shape of a CAD model.

1 is a block diagram of a CAD model modification system using stepwise volume decomposition according to the present invention.
2 is a detailed block diagram of a stepped volume decomposition unit according to the present invention.
Fig. 3 is an exploded view of the shape according to the fillet / round /
4 is a flowchart illustrating a CAD model modification method using stepwise volume decomposition according to the present invention.
5A is a diagram illustrating a configuration of a shape decomposition according to an operation in a wrap-
FIG. 5B is a flowchart showing a shape decomposition procedure according to an operation in the wrap-
FIG. 5C is a diagram illustrating a configuration of the shape decomposition according to the wrap-
FIG. 6A is a configuration explaining the volume decomposition operation of the volume decomposition unit
6B is a flowchart showing a shape decomposition procedure according to a volume division operation of the volume decomposition unit
7 is a block diagram illustrating a volume decomposition process using cell-based decomposition.
FIG. 8 is a block diagram illustrating a CAD model modification process using stepwise volume decomposition according to an embodiment of the present invention.
9 is a diagram showing an example of modification of a shape by CAD model modification using stepwise volume decomposition

Hereinafter, a preferred embodiment of a CAD model modification system and method using stepwise volume decomposition according to the present invention will be described in detail as follows.

The features and advantages of the CAD model modification system and method using the stepwise volume decomposition according to the present invention will be apparent from the following detailed description of each embodiment.

1 is a block diagram of a CAD model modification system using stepwise volume decomposition according to the present invention.

And FIG. 2 is a detailed block diagram of a stepwise volume decomposing unit according to the present invention.

The present invention can be applied to the case of modifying the shape expressed by the boundary expression method by using the stepwise volume decomposition, and the shape can be easily modified even without the procedural model information.

In order to modify a shape or a CAD model represented by the boundary expression method, a step volume decomposition unit 10 for decomposing an original shape represented by a boundary expression model into a small simple volume, as shown in FIG. 1, A volume modifying unit 20 for modifying, deleting and copying a volume that is desired to be modified among the volumes to be modified by using the movement, rotation, and enlargement / reduction transformation, and a volume restoring unit 20 for reassembling the changed resolved volumes by using a Boolean union operation And a volume reconverting unit (30).

2, the stepwise volume decomposing unit 10 includes a fillet / round / chamfer removing unit 11 for removing a fillet, a round, and a chamfer shape in an original shape represented by a boundary expression model A wrap-around operation unit 12 for decomposing a shape by applying a wraparound operation, a volume dividing unit 13 for decomposing a shape by applying a volume split operation, And a volume decomposition unit 14 for finding all concave corners of the shape by using a cell-based decomposition method and finding and extending faces sharing the shape to decompose and combine the shape into cells.

The fillet / round / chamfer remover 11 removes fillet, round and chamfer shapes in the shape, which is accomplished using the known technique (Zhu H. et al.).

Fig. 3 is an exploded configuration diagram of the fillet / round / chamfer removal device.

Let S be the original shape before the fillet and round are removed and T be the shape after the fillet and round are removed. The volume F of the fillet is F = S - ^* T and the volume R of the round is R = T - ^* S is calculated.

Where - ^* is a regularized Boolean subtract operator. Using this, the original shape S is decomposed as shown in FIG.

A method of modifying a shape or a CAD model represented by the boundary expression method in the CAD model modification system using the stepwise volume decomposition according to the present invention is as follows.

4 is a flowchart illustrating a CAD model modification method using stepwise volume decomposition according to the present invention.

First, when an original shape represented by a boundary expression model is input to the stepwise volume decomposition unit 10 in step S401, the fillet / round / chamfer removal unit 11 removes fillet, round, and chamfer shapes in the shape. S402)

Then, a wrap-around operation is applied in the wrap-around operation unit 12 to decompose the shape (S403)

Then, the volume dividing unit 13 applies a volume split operation to decompose the shape (S404)

Then, the volume decomposing unit 14 finds all concave corners of the shape by using a cell-based decomposition method, finds faces sharing the shape, and expands the shape to decompose and combine the shape into cells. (S405)

In step S406, the volume correction unit 20 modifies, deletes, copies, and modifies a volume that is desired to be modified among the volumes decomposed by the movement, rotation,

Subsequently, the volumes reconstructed by the volume recombining unit 30 are reassembled by using a Boolean union operation (S407)

A specific process in each step of the CAD model modification system and method using the stepwise volume decomposition according to the present invention will be described as follows.

First, a process of decomposing a shape by applying a wrap-around operation in a wrap-around operation unit is as follows.

FIG. 5A is a configuration explaining the configuration of the wrap around operation unit according to the operation, and FIG. 5B is a flowchart illustrating the shape decomposition procedure of the wrap around operation unit.

And Fig. 5C is a configuration explaining the shape decomposition according to the wraparound calculation.

The process of decomposing a shape by applying a wrap-around operation in a wrap-around operation unit first finds a convex inner loop in the original shape as shown in FIG. 5A (a). S501)

Then, all the surfaces of the original shape are separated as shown in (b) of FIG. 5A. (S502)

Then, as shown in FIG. 5 (c), the inner loop marked on the separated plane is found and removed (S503)

Then, as in (d) of FIG. 5A, all the surfaces are recombined again (S504). At this time, a surface which does not constitute a solid is generated.

Then, as shown in (e) of FIG. 5A, the surfaces that do not constitute a solid are removed (S505)

Then, as shown in (f) of FIG. 5A, the recombined solid and the original solid are combined using a Boolean sum operation (S506)

When the wraparound operation is applied as described above, the shape is decomposed as shown in FIG. 5C.

Then, the process of decomposing the shape by applying the volume split operation in the volume partitioning section is as follows.

FIG. 6A is a configuration explaining the configuration of the volume decomposition unit according to the volume decomposition operation, and FIG. 6B is a flowchart showing the decomposition procedure of the volume decomposition unit according to the volume decomposition operation.

First, as shown in FIG. 6A, a concave inner loop of the shape S is searched. (S601)

Then, as in (b) of FIG. 6A, a copy F of the face with the concave inner loop is generated (S602)

As shown in (c) of FIG. 6A, the inner loop is removed from F, a non-regularized Boolean union of S and F is obtained, and the shape is divided into two cells (S603)

Subsequently, as shown in Fig. 6 (d), each cell is divided into volumes, and the shape is decomposed as shown in Fig. 6 (e) (S604)

The volume decomposition in the volume decomposition unit uses a cell-based decomposition method proposed by Sakurai H.

7 is a block diagram illustrating a volume decomposition process using cell-based decomposition.

As shown in FIG. 7 (a), in order to decompose a shape in cell-based decomposition, all concave corners of a shape are searched, and as in (b) do. Then, as shown in (c) (d), the cells are combined until the maximum volume condition is satisfied.

The maximum volume conditions are as follows.

When volume V satisfies the following condition, V is called the maximum volume of solid S:

① V ⊆ S

② V does not have a concave edge.

③ All halfspaces of V are halfspaces of S.

V④ For other volume B that satisfies the above conditions, B

V

Figure 7 illustrates volume decomposition using cell-based decomposition.

After such stepwise volume decomposition, the original shape is decomposed into simple volumes.

The user changes, deletes and copies a volume that is desired to be modified among the volumes that were resolved through the volume modification unit by using the movement, rotation, enlargement / reduction transformation, and if the change is completed, the volume decomposed through the volume reconnection unit is Boolean union. And then recombine again using the operation.

FIG. 8 is a diagram illustrating a process of modifying a CAD model using stepwise volume decomposition according to an exemplary embodiment of the present invention, and FIG. 9 is a diagram illustrating an example of modification of a shape by CAD model modification using stepwise volume decomposition.

The present invention decomposes a shape into a simple shape using stepwise volume decomposition, corrects the disassembled shape, and then recombines again.

FIG. 8 illustrates a stepwise volume decomposition of an example shape using a CAD model modification system and method using stepwise volume decomposition according to the present invention.

Fig. 9 shows an example in which the shape is modified after applying the stepwise volume decomposition.

Fig. 9 (a) shows an original shape, and Fig. 9 (b) shows an example in which a part of the hole on the top surface is removed. (c) shows an example in which two side pockets are moved.

The CAD model modification system and method using the stepwise volume decomposition according to the present invention can reduce the number of concave corners by applying the wraparound operation and the volume division operation, thereby reducing the overall volume decomposition time, It is possible to process volumes up to a quadratic surface that is fast and can not be processed by convex decomposition, and to create volumes with additive and subtractive shapes.

As described above, it will be understood that the present invention is implemented in a modified form without departing from the essential characteristics of the present invention.

It is therefore to be understood that the specified embodiments are to be considered in an illustrative rather than a restrictive sense and that the scope of the invention is indicated by the appended claims rather than by the foregoing description and that all such differences falling within the scope of equivalents thereof are intended to be embraced therein It should be interpreted.

10. Stepwise volume decomposition part 20. Volume correction part
30. The volume recombination unit

Claims (7)

A stepwise volume decomposition unit for decomposing the original shape represented by the boundary expression model into unit volumes;
A volume modifying unit for modifying, deleting and copying a volume that is desired to be modified among the volumes decomposed in the stepwise volume decomposing unit by using the movement, rotation, and enlargement / reduction transformation;
And a volume re-combination unit for re-merging the decomposed volumes, which have been changed by the volume modifier, using a Boolean union operation. 2. The apparatus of claim 1,
A fillet / round / chamfer removal section for removing fillet, round and chamfer shapes in the original shape represented by the boundary expression model,
A wrap-around operation unit for decomposing the shape by applying a wrap-around operation,
A volume dividing unit for dividing a shape by applying a volume split operation,
And a volume decomposition unit for finding concave corners of the shape by using a cell-based decomposition method and finding and extending faces sharing the shape to decompose and combine the shape into cells. CAD Model Modification System Using Decomposition. 3. The method of claim 2, wherein in the fillet / round / chamfer removal,
Let S be the original shape before the fillet and round are removed and T be the shape after the fillet and round are removed. The volume F of the fillet is F = S - ^* T and the volume R of the round is R = T - ^* S, where - ^* is a regularized Boolean subtract operator. In order to modify the shape or CAD model represented by the boundary expression method (b-rep)
Removing the fillet, round and chamfer shapes in the shape when the original shape represented by the boundary representation model is input;
Applying a wrap-around operation to decompose the shape;
Dividing the shape by applying a volume split operation;
Finding all concave corners of a shape using a cell-based decomposition method and finding and extending faces sharing the shape to decompose and combine the shape into cells;
Changing, deleting and copying the volume to be modified among the decomposed volumes by using the movement, rotation, and enlargement / reduction transformation;
And reconstructing the disassembled volumes using the Boolean union operation after the modification is completed. 5. The method of claim 4, wherein the step of decomposing the shape by applying the wrap-around operation comprises:
Marking and locating a convex inner loop in the original shape,
Separating all sides of the original shape to be marked,
Locating and removing the marked inner loops in a separate plane,
Recombining all the surfaces again,
Removing the faces that do not constitute a solid in the step of recombining all the faces again,
And combining the re-combined solid and the original solid using a Boolean sum operation. 5. The method of claim 4, wherein the decomposing the shape by applying the volume split operation comprises:
Finding a concave inner loop of the shape S,
Creating a copy (F) of a face with a concave inner loop,
Removing the inner loop from the copy F and obtaining a non-regularized Boolean union of the shape S and the copy F and dividing the shape into two cells;
Dividing each cell into volumes and decomposing the shape of each cell into volumes, and modifying the CAD model using stepwise volume decomposition. 5. The method of claim 4, wherein, in the step of finding all concave corners of the shape using the cell-based decomposition method and finding and expanding the surfaces sharing the shape to decompose and combine the shape into cells,
The combination of cells proceeds until the maximum volume condition is satisfied, and the maximum volume condition is satisfied when the volume V satisfies the following condition:
① V ⊆ S
② V does not have a concave edge.
③ All halfspaces of V are halfspaces of S.
④ For other volume B that satisfies the above conditions, B

V,
V is determined as the maximum volume of the solid (S).

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