TheResearchofInd_省略_MechanicalDesign_PHY.pdf

_ Received Date: September 29, 2010 Biography: PHYO Wai Lin (1978-), male, born in Shwebo, Myanmar. Ph.D candidate, main research field is independent knowledge based design. kophyobuaa 1 Introduction Product design procedure depends on designers experience seriously. By using designers knowledge and experience, product manufacturers can reduce product cost and produce high quality products. Designer must, however, draw upon experiential engineering knowledge such as past experiences, specific design rules and procedures. Most designers need to get the correct geometric information, parameters and find non- geometric feature information from the mechanical design handbook manually which are pretty time- consuming. Parametric modeling CAD systems are based on the geometrical relationships between parts. Parts can be transformed by varying dimensions easily. However, non-geometrical knowledge about the product design cannot be managed easily1. Some commercial CAD systems ignore this issue. Therefore Knowledge-based engineering (KBE) has been presented to meet the demands of engineering design methods since the last of 1980s. KBE is a subset of knowledge Base System (KBS) which is a spin-off from artificial intelligence (AI). KBE is the methodology for The Research of Independent Knowledge Based Mechanical Design PHYO Wai Lin, XI Ping, ZHANG Bao-yuan, CHEN Rui-zhi (School of Mechanical Engineering and Automation, Beijing University of Aeronautics and Astronautics, Beijing 100191, China) Abstract: Most of KBE systems applied by previous researchers are dependent on some CAD software, which makes knowledge hard to be reused to other CAD software. Independent knowledge based system is independent of CAD software; therefore knowledge can be reused freely. This paper describes independent knowledge based system for mechanical design. A detailed discussion about typical design is put forward including design process implementation based on knowledge engineering, independent knowledge based design architecture. The main principal of knowledge driven engineering is explained. The implementation of KBE on the design of worm reducer is studied as a case. Independent knowledge based reducer design system is realized. The usage of independent knowledge based system makes KBE system work independent of CAD software, which enhances their portability and fertilizes the collaborative work of heterogeneous CAD systems. Keywords: knowledge-based engineering; independent knowledge base; reducer; Knowledge Interpreter (KI) CLC Number: TP 391 Document Code: A Article ID: 1003-4951(2010)02-0001-07 Vol.20 No.2 CADDM December 2010 capturing and structuring knowledge which is used to define engineering methods and procedures2. Typical knowledge-based system is based on object- oriented programming language and is tightly integrated with a geometric modeling tool, AI, designers experience, database and so on. Fig. 1 is the typical KBE design architecture. Fig. 1 KBE design architecture In recent years, the application of CAx, AI and KBE technologies have been developing for design and manufacturing systems. Richard Curran, Wim J. C. Verhagen, Ton H. van der Laan and MJT van Torren incorporated the Knowledge Optimized Manufacture and design (KNOMAD) methodology within KBE3 for the analytical utilization of manufacturing knowledge. C.B. Chapman, Martyn Pinfold describes a knowledge based engineering system (KBES) to extend the current capabilities of automotive body-in-white (BIW) engineer4. Pablo Bermell-Garcia and Ip-Shing Fan applied KBE system for the design and manufacturing of a wind tunnel testing model of aircraft nacelles by adoption and combination of the production rules and the object-oriented knowledge representation5. Most of the KBE systems applied by previous researchers are dependent on some CAD software, which makes them quite inconvenient for the knowledge to be reused to other CAD software. Independent knowledge based system is independent of CAD software; therefore knowledge can be reused freely in various CAD software such as UG, CATIA, Solidworks etc. 2 Goal of Knowledge Modeling Goal of this research is to get knowledge driven parametric model by using independent knowledge based system. Therefore the relationship between geometrical and non-geometrical attribute is basic concept for the framework of knowledge model. The Geometric description is only one piece of information about the total product model6. Fig. 2 is the relation of geometric and non- geometric attribute. In the parametric modeling of the product, entities are associated with geometric parameter such as a boolean primitive, a line or arc in a wireframe, or a filleting operation. These parameters control and play the various geometric attributes such as height, width, length, volume and area of the model. They also control the locations of these entities within the model. Knowledge- model Design parameterNon - geometric Geometric parameter Geometric Knowledge driven Parameter driven Fig. 2 Geometric and non-geometric attributes Power, weight, material, life, speed ratio, load and manufacturability are included in the non- geometric attributes that mean they are design parameter. Geometric and non-geometric attributes are interrelated. For example, the pitch-line velocity of the worm is Vw=dwnw /12. Geometric properties dw (pitch diameter) and non-geometric properties Vw (pitch-line velocity) are dependent to each other. The inputs to the KBE model contain geometric and non-geometric attributes which can include design specifications, design practices, engineer expertise, material properties and structural analysis. The key 2 PHYO Wai Lin, XI Ping, ZHANG Bao-yuan, CHEN Rui-zhi CADDM research content of KBE is to get geometric parameters out from non-geometric parameters. The output is knowledge model which meets customers demands. 3 Knowledge Acquisition and Representation Knowledge Acquisition KA is the transformation of knowledge from the form in which it exists (be tacit or explicit) into forms that can be used in a knowledge-based system. The process of collecting domain knowledge and transforming the knowledge into a computerized representation: KA includes the elicitation, collection, analysis, modeling and validation of knowledge for knowledge engineering and knowledge management projects3 and involves breaking down, grouping, structuring, chaining up and controlling the knowledge. An important problem is how to extract knowledge from an expert and how to represent the elicited knowledge in a knowledge-based system. KA can solve that problem by considering the purpose and function of the desired information. KBE systems use a combination of the “production rules” and “the object-oriented knowledge representation” as the representation paradigms. Fig. 3 is the knowledge representation chart of research work to control and modify knowledge that needs a collection of various forms of knowledge, including Mathematical formulas, Rules, experience, parametric model, form and chart for mechanical design parametric model. Knowledge implementation for typical design model, design knowledge can be categorized as follows: (1) Mathematical formula: In the mechanical design, there are many areas of mathematical forms of knowledge. Many design parts such as size, material, strength and so on need the complex mathematical calculations and derivation to get their appropriate values. Mathematical formulas including expressions (arithmetic expressions, logical expression, etc.), differential equations and integral equation and so on that is used for the design MathematicalCalculation Chart Table Parametric Model Expertise Rule ( IF - THEN ) Fig. 3 Knowledge representation of the transmission parts to get a certain constraint relations. For example: the mathematical formula of worm allowable contact stress is s HPHPvN Z Z= and stress cycles equation is 1 60 Lh Nnt= . (2) Class rules: The knowledge-driven model behind knowledge-based engineering (KBE) is based on a language tailored for capturing engineering rules. If the worm head is equal to 1, the estimated range of efficiency is 0.65 to 0.75; when the worm head is equal to 2, the efficiency of the range of 0.75 085; when the worm head is greater than 2, the effective range 0.85. If the condition part is satisfied, then the conclusion part December 2010 The Research of Independent Knowledge Based Mechanical Design 3 is executed. The sample of worm gear class rule expression is as follows: If (worm_z=1)Efficiency = “0.650.75”; If (worm_z=2)Efficiency = “0.750.85”; If (worm_z2)Efficiency = “0.85”; (3) Design tables: There are many engineering knowledge of standard parts often exists in table form, Fig. 4 is a table of the relationship of module, worm diameter and worm diameter factor which is used to determine dimensional families of product. Fig. 4 The relationship of module and diameter Table data are discrete binary mapping that can be store in a relational database according to certain rules using a scripting language. This scripting language related to syntax and language interpreter to explain the mapping table, represent to use the form. (4) Expertise: Expertise plays the role to fill the knowledge gap between the detail stage and the conceptual stage, assist the designers to make decision. For example, expertise tells which working temperature range should be more eligible, higher than 95 or less than 95. (5) Parametric model: Parametric model files (such as UG .Prt file) store the history of product modeling, modeling process contain the carrier of expertise and knowledge. Parametric model provides the knowledge modeling process. Therefore geometric model can be change quickly, can be viewed as an instance of a class of geometric models; Object-oriented method can be used to organize and express this knowledge. For example, the design of the worm geometric model has several geometric parameters as shown in Table 1. Table 1 Worm modeling geometry Module m Pitch circle diameter d Addendum circle diameter d1 Tooth root diameter d2 Pressure angle a Length L (6) Chart: Chart is a common engineering knowledge express with two-dimensional coordinated system in which the data is represented by symbols, such as bars in a bar chart, lines in a line chart and so on. Therefore knowledge is implemented in various forms including engineering rules, formulas, geometric models, design tables and charts to construct independent knowledge based system. It also describes the representation of geometric properties including part complexity and the automation of the design processes. 4 Independent Knowledge Based Design Architecture Mechanical design engineers are always faced with the problem to get the correct geometric information, parameters and need to find non- geometric feature information from the mechanical design handbook manually. Information is difficult to communicate verbally and formalize for the purpose of designing a knowledge base7. Knowledge interpreter can be solved these problems. Knowledge Interpreter (KI) is constructed based on knowledge representation explained in section (3) to get parametric model that mean knowledge driven parametric model. The principle structure of knowledge interpreter (KI) is shown in Fig. 5. Knowledge interpreter can parse 4 PHYO Wai Lin, XI Ping, ZHANG Bao-yuan, CHEN Rui-zhi CADDM knowledge document files just like computer compiler parsing source code files. For example, in C language the source code written using C, but we can automatically save as. CPP format and then the compiler can generates an executable file after compilation. Fig. 5 Knowledge interpreter (KI) KI solve to get geometric parameters by integrating mechanical engineering design parameters and knowledge document. Some of the design parameters of typical design are power, speed, speed ration and life and so on, knowledge document include if-than rule expressed in section (2) and engineering knowledge, geometrical parameters are pressure angle, pitch cycle diameter of worm gear, module and so on. Independent knowledge based design architecture is divided into three layers as shown in Fig. 6. Core layer is the main layer of modeling system and links the user layer and geometric modeling layer. Knowledge and experiences are stored in the knowledge base in the form of knowledge documents and database files. Knowledge base feeds to the knowledge operation module for knowledge managing. Knowledge reasoning module gets values of non-geometric parameters from user layer and gives out values of geometric parameters according to knowledge stored in the knowledge base. CAD support module uses modeling function of the CAD software to communicate with it according to the output values of geometric parameters from core layer. Then geometric modeling layer updates CAD models. Fig. 6 Independent knowledge based design architecture 5 Case Study The case selected in this KBE implementation is a worm reducer. The complete product assembly includes features such as worm wheel, worm shaft etc. The implementation tools used in this project are UG/Open API and C+ development system for user interface, MFC and Microsoft Access for database. Modeling and assembly are realized on UGNX 3.0 platform. When click on “FileExecuteNX OPEN” and select the specified path of .dll file, user interface will pop up as shown in Fig. 7, and enter design parameter, independent knowledge based system will automatically execute the design process of the reducer with the geometry based method and process based method by determining speed, power and life. Table 2 and Table 3 is the input design parameters and output geometric parameters of typical design. Fig. 8 is the process of Independent knowledge based reducer design. December 2010 The Research of Independent Knowledge Based Mechanical Design 5 Fig. 7 User interface of reducer design system Table 2 Design parameters Design parameters Value Description Power (p) 75 kW Speed (n) 1450 Rev/min Speed ratio (i) 20 - Table 3 Output geometric parameters Fig. 8 Independent knowledge based reducer design 6 Conclusions Most of the KBE systems are dependent on some CAD software which makes knowledge reuse hard to realize. This paper put forward independent knowledge based system to avoid this disadvantage. After explaining the principle of knowledge driven engineering, independent knowledge based design architecture is constructed. Eventually, independent knowledge based reducer design system is realized. The usage of independent knowledge based system changes the KBE systems dependence