中英文翻译原文

Proceedings of the 7th ICFDM2006

International Conference on Frontiers of Design and Manufacturing

June 19-22, 2006, Guangzhou, China

Pages 1-6

RAPID CREATIVE DESIGN METHODOLOGY FROM CONCEPTUAL

DESIGN TO VIRTUAL ENTITY DESIGN

Wang Yuxin

Department of Mechanical Engineering, Tongji University, Shanghai 200092, P.R. China

Abstract:Along with the development towards global manufacture of products and competitive intensification of the market, it is needed urgently that enterprises can develop their products to meet the requirements of markets. So, increasing competitiveness of products and reducing design life cycle of products are two key problems to be solved for design engineers. Since most 3d software is parametric and feature-based, under 3d design platform, the technical characteristics of structures, assembly rationality and manufacture property for products can be evaluated and modified easily during the design processes, and through simulation of virtual prototype and inspection of interferences among the elements of products, the design scheme of products can be perfected as soon as possible. However, 3d software can’t support the conceptual designs of mechanical devices. Based on the regeneration conceptual design method, in this paper, a systematic and automatic design method, for mechanical devices from conceptual design to virtual entity design is presented. With this method, all the design processes of products from the conceptual design to the structure design, the virtual assembly and simulation, and to the virtual entity prototype can be carried out automatically. Keywords: Creative design, Virtual design

1. Introduction

With the development towards global manufacture of products and competitive intensification of the market, it is needed urgently that enterprises can develop their products to meet the requirements of markets at first time. The parametric technology and feature-based design have been applied by most of commercial CAD software. The main advantage of designing products under 3D developing environment is that the technical characteristics of structures, assembly rationality and manufacture property for products can be evaluated and modified easily at real time. With the support of assembly tools of 3D software, the virtual prototype of products can be given out. Through simulation of this virtual prototype and inspection of interferences among the elements of products, the design scheme of products can be perfected as soon as possible. The capability of the integration of CAD/CAM/CAE and CAPP in a uniform design platform by API technique and data translate interface makes it possible to speed up the process of design and manufacture of products. However, 3D software can't support the conceptual designs of mechanical devices. Considering the advantage of 3D software in speeding up the process of design and manufacture of products, based on a series of our previous research works [1-8], in this paper, a conceptual design supported automatic virtual prototype design method for mechanical devices is presented. In this method, the regeneration method is adopted to generate conceptual schemes of mechanical devices, which are expressed by character strings. After identifying the structure of the scheme, the kinematic analysis process is automatically carried out by matching Barranov chains. On the other hand, the recognized element in the structure is built up in virtual entity form after selecting the type of the element with the aid of API technique supplied by 3D software. Using the background pre-placement assembly method, the mechanical device represented by the scheme is assembled automatically in virtual entity form. Therefore, with the method presented in this paper, all the design processes, from the conceptual design to the structure design, the simulation, the virtual assembly and the virtual entity prototype design, can be carried out automatically.

2. The Method 2.1. Methodology Figure 1 is a flow chart of the rapid creative design system for mechanical systems. The system consists of conceptual design process, identification of symbol schemes process, kinematic analysis process, 3D virtual entity design (or 3D structural design) process, automatic assembly process, virtual simulation process, modification, and space layout design of products. At the end of the rule-based conceptual design, a series of conceptual design results, which are expressed by symbolic schemes, for instance GCBKHEZIF(36), are produced. These symbolic schemes then can be decomposed into a number of basic mechanisms, such as gears, linkages, cams and so on, and connections among them. After carrying out kinematic analysis and virtual structure design to basic mechanisms, the spatial layout of thecomplex mechanical system corresponding with the symbol scheme can be calculated based on structures of basic mechanisms and their connections. With pre-assembly technique, virtual basic mechanisms are posed at specific spatial position in 3-D space according to the spatial layout results. Transforming the kinematic analysis data in plane into

spatial kinematic data where the basic mechanisms locate, finally, we can get a virtual prototype of the complex mechanical system relative to the conceptual design result

expressed by the symbol scheme. Since all the design processes can be carried out automatically, and design results and data in above design processes can be made use by the current design process, this system can fulfill the total design progress from the conceptual design to virtual entity prototype automatically,

efficiently and systematically. By this system, it is possible to evaluate the performances of conceptual design results in virtual entity forms rather than only in economic value angles. Simultaneously, through writing down the design rules at the conceptual design phase, the solutions of conceptual designs can be exploited as lager as possible. By this way, some innovative conceptual design results can possibly be found from whole

conceptual design results. As a result, with aid of this system, we cannot only obtain innovative designs with excellent performances, but also reduce the design time and the cost of product developments.

2.2 Regeneration of Conceptual Schemes The conceptual design process is based rules-based conceptual design method, which had been presented in Ref. [2]. The regeneration procedure is mainly composed of three parts: definition of design problem, selection of topological carriers of creative designs, and regeneration. In the procedure of the definition of design problem, by analyzing existing designs or novel design requirements, designers make certain the topological characteristics of mechanisms and design requirements, and write down the

regeneration rules and evaluation rules for the design problem. The design rules are in the following form: A (B )[C ︱D …!E ︱F …]

Regeneration rules and evaluation rules can be the description of behaviors of design requirements, such as kinematic functions, and can also be the topological characteristics of mechanisms, such as the freedom and/or

structures of mechanisms and etc. If trying to find

solutions of the design problem as much as possible, the regeneration rules should only include the rules that describe the kinematic functions requirements; if trying to select more detail and optimized solutions to meet specific design requirements from all solutions above, the evaluation rules should be added. The more the evaluation

rules are added in, the more exiguity the solutions are, and the better the solutions meet special design requirements.

For a design problem, the regeneration rules and evaluation rules can be interchangeable. For convenience, we call both regeneration rules and evaluation rules as

design rules.

After regeneration procedure, a set of mechanisms expressed by the character string embodied by design

rules, such as GE000KBC(1)(P12), 0EGCBK00(3) (P23)

and etc. are given out. These character strings are called

regeneration codes, or symbol schemes.

2.3 Identification of Symbol Schemes

At the end of the conceptual design with rule-based

conceptual design method, the conceptual design results

are expressed in the form of symbolic schemes, for example, Gc = CE000ZGDF(9). Since this scheme coincides with the graphical carrer, in order to mark the status of each link in the graphical carrer, the state array of links is introduced: G[n ]={1，2，3，4，5，6，7…n } In this array, the initial elements are serial numbers of the graphical carrer. During identification of the basic mechanisms, if a basic mechanism is identified, then the elements in G[n] corresponding the links, which compose of the basic mechanism, should be set -1. After finishing the identification process for the symbolic scheme, the state array should be in following form:

G[n ]={-1，-1，-1，-1，-1，-1，-1…-1} If some elements in this array can not be set -1 yet, it indicates that the symbolic scheme cannot be divided into the combination of basic mechanisms.

There are three processes for identification of basic mechanisms: ① Identification of basic mechanisms; ② Identification of driving mechanisms ；③ Identification of the other basic mechanisms 。The basic mechanisms

here are Cam mechanism, Gear mechanism, Geneva wheel mechanism, Four-bar mechanism and its evolutive mechanisms, Five-bar mechanism, Assur II and Assur III. Driving mechanism stands for that the basic mechanism contains one or more driving elements ，i.e. the driving links exist in the basic mechanism. The other links are those links whose state numbers in G[n ] are not set to -1 yet. Structure Design Pre-assembly Kinematic Analysis Symbol Scheme (Comfit packing mechanism)Virtual Prototype GCBKHEZIF(36) Figure 1: The rapid creative design systems

For instance, the symbolic scheme NKJHFBCGZ (29) is a mechanism with two DOFs. The state array is:

G[9]={1，2，3，4，5，6，7，8，9}

The final identification result is

D ataStr =“B8912B8765W58234 [G8C79]” (1)

The expression (1) is called the basic mechanisms string. It can be divided into two parts: the main part and the secondary part. Here, the main part is

B8912B8765W58234, and the secondary part is G8C79. The information of basic mechanisms and their connections have been included in the main part. In this example, the mechanism is composed of two Cam mechanisms, B8912 and B8765, and a Five-links mechanism W58234. The information of driving links and ground link have been contained in the secondary part. In the secondary part, the capital letter is the function code, and there are G,C and P. G and C represent that at the right of the capital letter, the numerical number are the ground link or the driving links. P represents that at the right of the letter, two numerical numbers are two elements to consist of a sliding pair. For instance, in [G2C1P21], link 2 and link 1 consists of a slider pair.

The second goal for identification of symbolic schemes is to identify the connections among basic mechanisms.

The identification approach is as following:

① Estimate the connections between two driving mechanisms (marked as

i

A).

Mechanisms with the compound connection III, the postposition mechanism should be a differential mechanism with two input degrees and it only has one driving link. For two driving mechanisms with the parallel connection II, if the second mechanism is a differential mechanism, two driving links must be existed.

② Estimate the connections among all driven basic mechanisms and the driving mechanism in ①.

For two basic mechanisms with series connection I, the postposition mechanism should be a single input basic mechanism. However, for two basic mechanisms with compound connection I or series connection II, the postposition mechanism should be a difference mechanism. But, for two basic mechanisms with feedback connection, the postposition mechanism should not be a difference mechanism.

③ Identification of connections among the driven basic mechanisms

The connections among driven basic mechanisms can be the parallel connection I, the parallel connection II, the parallel connection III, compound connection III and superposed connection. The method to identify connections is the same with step ②.

It should be mentioned that all identification rules are based assumption that, in the current combination of mechanisms, there is at lest one driving basic mechanism. Obviously, this above assumption can not be satisfied in common cases. For satisfying the assumption, in the processes of identification of connections among driven basic mechanisms, the replacement of driving basic mechanisms should be taken. The replacement method is as follows: let the connecting links

i

B and

i

A obtained

in the step ② be the current driving link, and

i

B be the current driving basic mechanism, then judge the

connections among all of

i

B.

④ Regard all

i

B are new

i

A，and prepare the next cycle.

⑤C ount+1.

Through the identification process, the symbolic scheme GCBKHEZIF(36), for instance, is divided into basic mechanisms and their connections, as shown in Fig.2.

2.4 Kinematic Analysis of Symbol Schemes

In order to estimate the dynamic behaviors and to simulate the syytem, the kinematic analysis process is necessary. The kinematic analysis methods applied by the system are kinematic chain based method and basic mechanism based method. Here, the kinematic chain based method is taken as an example.

If fixing the input link with the ground link in the mechanism with 1-DOF, the mechanism will become a rigid structure with 0-DOF. This rigid structure can be generally divided into basic Barranov trusses. When fixing the input link with the output link for 1-DOF mechanisms with N links (N<=8), there are five kinds of Barranov trusses presented in Ref. [4]. The displacement functions of these Barranov trusses can be set up by the condition that two joints of a link must remain a fixed distance apart.

Kinematic analyses for these Barranov trusses have been programmed and capsulated in a series of functions with VC++.

The displacement analysis of planar mechanisms with 1-DOF will be easily solved if we can automatically change a mechanism into a set of Barranov trusses by

Fig.2 Identify the symbolic schemes into basic mechanisms and their connections

fixing the ground link with the input link. The modeling process can be decomposed into the following steps:

(1) Input the generation code Gc;

(2) Input kinematic parameters;

(3) Form a rigid structure;

(4) Matching Barranov trusses.

2.5 Automatic Assembly

The possible structures that make up of the complex mechanical devices have been stored in the database of the system. In the database, the structures are modeled under 3D environment. With the aid of API tools applied by 3D software, these 3D structures are encapsulated with VC++ by the feature-based interface. These structures can be binary link, ternary link, quaternary link, cam, gear, Geneva element and even special defined structure of mechanical devices.

When kinematic analysis process is over, the system can automatically identify the structures to make up of the mechanical devices according to matrixes of R m, J sm, and S lm. Under the modeling interface for the structure, after inputting proper parameters, the system will model up 3D entity of the structure automatically. The method to assembly these 3D virtual entities and make up of a complex mechanical device is by hand with the aid of assembly tools supplied by the software. By manual method, if the mechanical device is too complex to assembly, to assembly it will spend much more time. To fulfill automatic assembly of generation schemes, a method called “background pre-placement” assembly technique is adopted. This method is a kind of data-driving assembly method. The data describes the space that the 3D virtual entity should be occupied. With the aid of API tools supplied by software, we program and put this 3D virtual entity to occupy the needed space. For example, if we try to put a 3D virtual entity into a needed space under Mechanical Desktop (AutoDesk) 3D environment, we can do this thing by following commands:

ads_

command(RTSTR,”MOVE”,RTENAME,ent1,RTSTR,””, RT3DPOINT,p1,RT3DPOINT,p2,0);

//Virtual entity moves along the reference point form p1 to p2.

ads_command(RTSTR,”UCS”,RTSTR,”ZA”,RT3DPO

INT,

p2,RT3DPOINT,normal,0);

ads_command(RTSTR,”rotate”,RTENAME,ent1,RTST R,””, TSTR,”

0,0,0”,RTREAL,angnorm,0);

//Virtual entity rotates angnorm angle along the cross

axis of last reference axis and current axis.

ads_ command(RTSTR,”UCS”,RTSTR,”ZA”, RT3DPOINT,p2,

RT3DPOINT,cur _axil_point,0);

By program with VC++, all the virtual 3D entities can

be put or assembled at proper positions. Since the position for the virtual entity to occupy is pre-calculated

in the kinematic analysis process, with the background

pre-placement technique method, the assembly of generation scheme can be carried out automatically. This automatic assembly method is very efficient for modification, space layout and perfection of mechanical devices.

2.6 Spatial Layout

As an important part of the rapid creative design system for mechanical systems, the goal of spatial layouts

is to lay out the mechanical system correlating with the symbolic scheme to occupy minimal 3-D space, and to meet industrial aesthetics requirements. The research of

the layout problem with considering the industrial aesthetics requirements will be presented in the future. Therefore, the layout problem is focused on layout mechanical systems to occupy a minimal spatial space considering connections among basic mechanisms.

To fulfill this goal, at first, several common connecting relations existing in complex mechanical systems are generalized into three kinds of connections, serial connections, parallel connections, and closed connections, and then constrain equations caused by these connections are set up based on transforming matrixes. Then, expressing spatial spaces occupied by basic mechanisms with cuboid model, and dealing with constrains and interferences in mechanical systems with

the fitness function, the spatial layout problem of complex mechanical systems is calculated based on an adaptive genetic algorithm.

Table 1: Basic mechanisms in the symbol scheme (2) (Ground: c; Driving: b)

Number Name String Number Name String

0 Gear Acbrd 4 Gear Acdsl

1 Gear Arcef 5 Groove

Iscmn

2 Cam Begch 6 Gear

Amopc

3 Linkage Pgkjc 7 Gear Aokcr

3 Example

A complex mechanical system, an automatic high-speed

fastener battery assembly device, is taken as an example to

illustrate the efficiency of the algorithm presented in this

paper. According to function requirements to the

automatic high-speed fastener battery assembly devices,

with aid of the automatic conceptual design process

presented in Figure 1, we get 142 conceptual design

schemes in symbolic form. The following symbolic

scheme is one of them. The basic mechanisms in this

symbolic scheme are shown in Table 1.

][GcCb AmopcAokcr AcdslIscmn BegchPgkjc AcbrdArcef (2)

With the automatic identification process in Figure 1,

the connecting relations among these basic mechanisms

can be expressed with matrix form

??????????????????????????=1 1 01 l Symmetrica 001 000 1 0000 1 000 00 100 001111113111S P S S S P S S S C M (3) Where 1S

stands for the serial connection I; 1P stands for the parallel connection I; 3P stands for the

parallel connection III; and “0” stands for no-connection; and “1” stands for basic mechanism himself. After the process of virtual structure design shown design in Figure 1, the layout parameters for each basic mechanism are listed in Table 2. Based on connections in Eq. (3) and layout parameters for each basic mechanism listed in Table 2, with the self-adaptive genetic algorithm presented in this paper, the spatial layout solution for the symbolic scheme expressed in Eq. (2) is obtained after five hundreds generation evolution iterations. The layout result is listed in Table 3 and the virtual spatial layout is shown in Figure 3.

4 Conclusion

Figure 3: Spatial layout for a high-speed fastener battery automatic assembly device

Table 2: Layout parameters of the basic mechanisms

Gear Worm Cam Link

-

Slide

Bevel Gear Groov e Gear Inside Gear s k 168 71 66 97 0 84 90 25

k α0 90 180 270 90 180 180 180

L k 370 105 110 115 138 218 218 207

B k 30 160 80 30 122 30 37 18

H k 210 60 105 110 127 128 128 207

a k

15 50 15 21.545 10 15 10 b k

80 26 60 9 60 52 45 55 c k 100 26 25 101 60 52 60 95

Table 3: Layout results for the automatic assembly device of high-speed fastener battery

Mech. Gear Worm Cam Link-Slide Bevel Gear

Groove Gear Inside Gear k β(O) 0 90 270 0

0 180 180 270 k d （mm ） 0 182 5.935.746.5

7.515.5 26

This paper presents an automatic virtual prototype

design method with conceptual design supported for mechanical devices. Based on the creative design theory, after identifying the design problem, all possible novel solutions for creative conceptual design of mechanical devices with complex function requirements can be obtained. The conceptual design results are expressed by a series of symbol schemes. Through automatic identification of the symbol scheme, the structure and composition of the scheme can be recognized, and then the kinematic analysis process will be carried out for this scheme automatically. On the other hand, by selecting of the structure and form of components to make up the scheme, the virtual entity of the component can be drawn out. Based on “background pre-placement” assembly technique, the scheme can be assembled automatically in the prototype form. And with the technique of spatial layout, all sub-mechanisms have been put in special space. Therefore, the method presented in this paper can support not only the conceptual design, but also all the design processes, from the conceptual design to the structure design, the simulation, the virtual assembly and the virtual entity prototype design can be carried out automatically.

Since the method presented in this paper is conceptual design supported and virtual entity design supported, with this method, we can obtain conceptual design schemes as many as possible and give out their simulations in three dimensional virtual entity form automatically. Through simulations, we can select one or more schemes from them for detail designs.

Acknowledgements

The authors gratefully acknowledge the support provided by the Teaching and Research Award program for Outstanding Young Teachers in Higher Education Institutions of MOE, P.R. China (No.1999076). The authors also gratefully acknowledge the support provided by the Shanghai emphases constructing subject foundation. References

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[3] Wang Y. X. Automatic identification of symbolic scheme based on basic mechanisms, Mechanism and Machine Theory, 2006 CIRP, Canada

[4] Wang, Y. X., Automatic displacement analysis of planar mechanisms with matching BKC method, Chinese J. of mechanical engineering, 2003, 39(1): 23-29

[5] Wang, Y. X. and Wang, L. J., Automatic conceptual design of mechanical devices based on reasoning the design rules, 2002 ASME, DETC2002, Canada

[6] Jiang Shan, Wang Y.X. and Li Naihua. Research on automatic transforming symbol scheme to 3D mechanism, J. Computer Aided Design & Computer Graphics, 2002, 14(1): 962-966

[7] Wang Y. X., Tai Xiaomei and Jiang Shan. Conceptual design of mechanical product under the 3 D virtual design environment, China Mechanical Engineering, 2001,12(3): 256-258

[8] Wang Y.X., Wang Yongshan, Alex Duffy. Research on Spatial Layout of Complex Mechanical Systems, Mechanism and Machine Theory, 2005 ASME DETC/2005, USA

[9] Yan, H. S., Creative design of mechanical devices, Springer-Verlag, Singapore 1998.

[10] Yang Tingli, Basic theory of mechanical system, Industry public house, Beijing, 1996.

Contact Info :

e-mail: Wang_Yuxin@https://www.360docs.net/doc/be14645462.html,