Internet enabled fixture design system using case based reasoning technology

INTERNET-ENABLED FIXTURE DESIGN SYSTEM USING CASE-BASED REASONING TECHNOLOGY FAN LIQING (B Eng.) A THESIS SUBMITTED FOR THE DEGREE OF MASTERS OF ENGINEERING DEPARTMENT OF MEACHANICAL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2003 Acknowledgements First and foremost I would like to express his sincere thanks and appreciation to my supervisor, Associate Professor A Senthil Kumar, for guidance, for his involvement in this research, for the technical discussions and particularly for his support throughout the course of my Master studies I wouldn’t have finished this thesis without his support and drive Thanks to my colleague, Fathianathan Mervyn, for his error check for this thesis and for the suggestion and discussion with him at the research project I am also very grateful to fellow graduate students for encourage and discussion in study: Wang Zhigang, Wu Yifeng, Zhang Wei, Wang Binfang, Chen Xiaolong, and Lu Cong I would also like to acknowledge financial support provided by National University of Singapore and to thank Laboratory for Concurrent Engineering and Logistics (LCEL) for providing facility to complete my research Last but not least, I would like to express my deep sense of gratitude to my wife, Chen Hui, for her understanding, moral support and love My son Fan Ziqian gave me great spiritual support and encouraged me throughout this difficult but exciting journey I thank my mother, my brother and my sister for all of their support and love i Table of Contents Acknowledgements i Table of Contents ii Summary vi List of Figures viii List of Tables x Chapter Introduction 1.1 Fixture 1.2 Case-based Reasoning 1.3 Internet-enabled Manufacturing Environment 1.4 Organization of the Thesis Chapter Research Background and Literature Review 2.1 Fixture Design Fundamentals 2.1.1 Fixture Design Principle 2.1.2 The 3-2-1 Locating Principle 10 2.1.3 Modular Fixture Systems 11 2.2 Introduction to Case Based Reasoning 13 2.2.1 Overview 13 2.2.2 Case-Based Reasoning Cycle 14 2.2.3 Areas of CBR Applications 15 2.3 Case-Based Reasoning for Design 16 2.3.1 Issues in Developing CBD systems 16 ii 2.3.2 Case Representation and Memory Organization 17 2.3.3 Indexing and Case Retrieval 19 2.3.4 Case Adaptation 20 2.4 Distributed CBR 21 2.5 Related Research Works 23 2.5.1 Case-Based Reasoning in Mechanical Engineering 23 2.5.2 Case-Based Reasoning in Fixture Design 25 2.6 Discussion 26 2.7 Research Objective and Scopes 27 Chapter System Architecture 29 3.1 Distributed CBR Architecture 29 3.1.1 Three-tier Architecture Model 29 3.1.2 Architecture for Distributed CBR 31 3.2 Architecture of the System 32 3.2.1 Server 32 3.2.2 Client 33 3.2.3 Repository 35 3.3 Summary 36 Chapter Knowledge Representation for Fixture Design 37 4.1 Introduction 37 4.2 Case Representation using XML 39 4.2.1 Case Structure 39 4.2.2 Part Representation 40 4.2.3 Fixture Design Representation 42 4.2.4 Setup Representations 44 iii 4.2.5 XML Schema for Modeling 45 4.3 Case Base Organization 46 4.4 Summary 47 Chapter Case-Based Fixture Design Process 48 5.1 Design Process using Case-based Reasoning 48 5.2 Distributed CBR in Fixture Design 50 5.3 Case Indexing 51 5.4 Case Retrieval 53 5.4.1 Geometrical Similarity Metric 55 5.4.2 Non-geometrical Similarity 61 5.4.3 Mass Case Filter 62 5.4.4 Ranking of Cases 63 5.5 Adapting Cases 63 5.5.1 Workpiece Adaptation 64 5.5.2 Baseplate Adaptation 66 5.5.3 Locating Elements Adaptation 68 5.5.4 Supporting Elements Adaptation 69 5.5.5 Clamping Element Adaptation 72 5.6 Case Storage 74 5.7 Summary 74 Chapter Case Study 75 6.1 Information Input 75 6.1.1 Feature Information Input 75 6.1.2 Setup Information Input 77 6.2 Retrieval 78 iv 6.3 Adaptation 83 6.4 Case Storage 87 6.5 Summary 88 Chapter Conclusions and Future Works 89 7.1 Research Contributions 89 7.2 Recommendation for Future Work 91 References 92 v Summary The primary objective of the research in this thesis is to develop an Internet-enabled computer-aided fixture design system This system is implemented in a new environment that utilizes Case-Based Reasoning (CBR) paradigm, an approach derived from instance based previous solutions of similar problems The main issues for the system are case representation and process control issue that includes case indexing and retrieval, case adaptation, and case storing Case representation for fixture design is composed of three parts: part representation, fixture representation and setup representation They are described in XML (eXtensible Markup Language) using Unified Modeling Language (UML) notation A featurebased similarity measure is adopted for case indexing and case retrieval in this system There are two major perspectives in a part considered in the similarity: geometric shape and material In addition, a filter method is introduced to reduce the retrieval time based on the size and shape of parts when the size of Case Base is large A derivational replay method is mainly adopted to adapt a retrieved case This adaptation process is fully integrated with the CAD system; it can interact with solid models on the Java3D canvas This process involves with five modules: workpiece adaptation, base-plate adaptation, locator adaptation, support adaptation and clamp adaptation It creates a new solution using the same procedure vi This is one of the first Internet-enabled design systems that are implemented using distributed case-based reasoning methodology A distributed CBR engine is developed as client-server model and it is implemented to integrate with existing internet-enabled fixture design system using Java3D technology and Java programming language so that the system can run on any platform that supports Java The system has been tested and demonstrated with case study for fixture design in a distributed design environment vii List of Figures Figure 2.1 Twelve degrees of freedom Figure 2.2 The 3-2-1 method of location 11 Figure 2.3 Modular Fixture Systems 12 Figure 2.4 The typical CBR cycle [Aamodt & Plaza, 1994] 15 Figure 2.5 Memory organization 18 Figure 3.1 A typical three-tier client-server architecture 30 Figure 3.2 Architecture for distributed CBR engine 31 Figure 3.3 System Architecture 33 Figure 4.1 Unified modeling language notation 39 Figure 4.2 Case structure 40 Figure 4.3 Part representation in UML notation 41 Figure 4.4 Inheritance in the Hole class 42 Figure 4.5 Example of XML file for part representation 43 Figure 4.6 Fixture Design Representation Model in UML Notation 43 Figure 4.7 Fixture design and its XML schema 44 Figure 4.8 Setups in UML notation 45 Figure 4.9 Structure of a facet data XML file 46 Figure 4.10 Case Base organizations 47 Figure 5.1 Design process using case-based reasoning 49 Figure 5.2 Work flow of CBR on fixture design 51 Figure 5.3 Flow chart of case retrieval 56 viii Figure 5.4 An example of workpiece 57 Figure 5.5 Adapting cases process 65 Figure 5.6 Base-plate classification 66 Figure 5.7 Flow chart of baseplate adaptation 67 Figure 5.8 Flowchart of locating elements adaptation 70 Figure 5.9 Flowchart of support adaptation 71 Figure 5.10 Flowchart of clamping element adaptation 73 Figure 6.1 Load a workpiece into system 76 Figure 6.2 Input the property information of the workpiece 76 Figure 6.3 Input parameters for selected feature 77 Figure 6.4 Group features into existing features and to-be-machined features 77 Figure 6.5 Examples of parts in database 78 Figure 6.6 The retrieved part names and their similarity value 81 Figure 6.7 One of retrieved parts and its fixture 81 Figure 6.8 Tree views of features and fixture design of one of retrieved parts 82 Figure 6.9 The new workpiece and fixture designs of its similar parts 82 Figure 6.10 Face selection for supporting faces 84 Figure 6.11 The input part and existing fixture 84 Figure 6.12 A locating face is selected for re-positioning the highlighted locator 85 Figure 6.13 A locator is selected from Database to replace the highlighted locator 85 Figure 6.14 A new point is selected to re-locate the highlighted support 86 Figure 6.15 A top-clamp element is selected to clamp the workpiece 86 Figure 6.16 A side-clamp is selected to clamp the workpiece 87 Figure 6.17 The final fixture design of the new workpiece 87 Figure 6.18 The storing option 88 ix Chapter Case Study 6.3 Adaptation After a fixture design is selected from the list of similar parts of the new workpiece, the adaptation process begins The system first prompts a dialog to ask the user to select the supporting faces for support (Figure 6.10), and then the workpiece in the selected fixture design is replaced by the new workpiece that is adjusted at appropriate position in the existing fixture design If the area of the baseplate is satisfied with the requirement, a message dialog is prompted at the center of application to show the baseplate is satisfied After that, all fixture elements are parsed and displayed in the design window The collision occurred between the input part and existing fixture elements can be also observed (Figure 6.11) In following steps, locators, supports and clamps will be highlighted to be replaced, repositioned, or deleted with the aid of designer In the process, designer is asked to select faces and points for locating, supporting or clamping based on requirement The locating elements are adapted in two ways, either to be re-positioned (Figure 6.12) or to be replaced by new ones (Figure 6.13) The supporting elements are also modified in these two ways When a support is relocating, it is highlighted (Figure 6.14) and the user is asked to select a new position Figure 6.15 and Figure 6.16 show that a topclamping element and a side-clamping element are selected from the list to clamp the workpiece respectively Figure 6.17 shows the final fixture design for the input part 83 Chapter Case Study Selected face Figure 6.10 Face selection for supporting faces Collision occurred Figure 6.11 The input part and existing fixture 84 Chapter Case Study Highlighted locator Selected face Figure 6.12 A locating face is selected for re-positioning the highlighted locator Replaced locator Figure 6.13 A locator is selected from Database to replace the highlighted locator 85 Chapter Case Study Support to be relocated Figure 6.14 A new point is selected to re-locate the highlighted support Figure 6.15 A top-clamp element is selected to clamp the workpiece 86 Chapter Case Study Figure 6.16 A side-clamp is selected to clamp the workpiece Figure 6.17 The final fixture design of the new workpiece 6.4 Case Storage In the final step, the system will ask designer whether to store the repaired design in XML server, i.e the case-base (Figure 6.18) The case-based reasoning system implements the learning mechanism in this way 87 Chapter Case Study Figure 6.18 The storing option 6.5 Summary In this chapter, the detailed fixture design processes, including input information, case retrieval, case adaptation and case storage, are discussed with case study This chapter presents how the system guides a user to design a fixture for a mechanical part with graphical user interface (GUI) 88 Chapter Conclusions and Future Works 7.1 Research Contributions This thesis presents a system that uses case-based reasoning technology to deal with the fixture design problem in mechanical engineering applications This thesis emphasizes on knowledge representation in fixture design domain, and the development of effective methodologies for automotive case retrieval and case adaptation The distributed CBR engine has been constructed and implemented Each of these contributions is described as follows ™ Case Representation and Case Base Organization XML schema is developed for knowledge representation in fixture design domain It comprises of three levels: machining feature representation, fixture design representation and manufacturing resource (setup) representation Each level representation is described in each XML file stored in Apache Xindice XML server Every level of a workpiece is related with one another by workpiece name ™ Retrieval Method In retrieval module of this thesis, a part and cases in Case Base are indexed so that the system can identify the cases efficiently and find out the most similar cases from Case Base The case indexing incorporates geometry, material, and heat-treatment In 89 Chapter Conclusion and Future Works addition, a filter method is introduced to reduce the retrieval time based on the size and shape of parts when the size of Case Base is large The similarity metric that measures the similarity of two parts is developed based on geometric, material and heat-treatment in order to retrieve the most cases from casebase The geometric similarity is developed based on Ramesh's six geometrical feature characteristics to compare similarity of prismatic parts in geometrical shape Finally, all the cases are sorted in a descending order according to the degree of overall similarity Only the first ten cases will be sent back to client side to display ™ Adaptation Process The adaptation process is an assistance to guide the designers to create a new solution by modifying a retrieved case It is fully integrated with CAD system and can interact with solid models on the Java3D canvas This process involves with five modules: workpiece adaptation, base-plate adaptation, locator adaptation, support adaptation and clamp adaptation It creates a new solution using the same procedure ™ Distributed CBR Engine A distributed CBR engine is proposed as client-server model and it is implemented to integrate with existing internet-enabled fixture design system using Java3D technology and Java programming language so that the system can run on any platform that support Java 90 Chapter Conclusion and Future Works 7.2 Recommendation for Future Work Despite several of the achievements mentioned above, some problems remain unsolved in the development of this research work In order to make better the case-based fixture design system, future works can be focused on following aspects: • Retrieval methods issues In the system of this thesis, the similarity matching method of retrieval only focuses on 3D prismatic workpiece So, the similarity matching method should expand to be suitable for not only prismatic type but also other types, e.g cylindrical, flat, box, etc • Feature extraction issues In this system, machining features of a workpiece are input by designer manually This work is time-consuming and not effective for designer since the designer must know all the dimensions or measure them in other CAD system A feature extraction module should be developed to integrate with this system to save designer's time and efforts Thus, CAD system can fully cooperate with textual CBR process • Cross-Domain reasoning issues The system presented in this thesis operates in a very specific domain; expansion of this system to other similar design domain is an important area as well • Case evaluation issues The objective of case evaluation is to check how good the adapted case is 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Novice Design Assistant, is another case- based design system developed to assist firefighters to design their own pumper engines 24 Chapter 2 Research Background and Literature Review 2.5.2 Case- Based Reasoning in Fixture Design In fixture design domain, Senthil Kumar et al (1995) and Nee et al (1995) presented a framework for automated fixture concept design using case- based reasoning In the system, ... knowledge domain and project focus 2.3.2 Case Representation and Memory Organization Case representation is the cornerstone of the entire case- based reasoning system A case- based reasoner depends on the knowledge stored in the case library to perform its reasoning The case representation in case- based reasoning systems mainly concerns how to structure cases stored in the case- base to facilitate effective... machining fixtures In addition, the system in this thesis utilizes the dowel-pin -based modular fixture system provided by IMAO Corporation, Japan (a) (b) Figure 2.3 Modular Fixture Systems (a) T-slot -based (b) dowel-pin -based 12 Chapter 2 Research Background and Literature Review 2.2 Introduction to Case Based Reasoning 2.2.1 Overview Case- based reasoning (CBR) is an Artificial Intelligence (AI) technology. .. what is in a design case, how is a design case represented, how is a design case indexed, and how is design case memory organized Control issues concern the general process model of a CBD system This involves 16 Chapter 2 Research Background and Literature Review when and how a design case is retrieved, how is a design case adapted, and how is an adapted design case evaluated Different CBD systems have... the domain As mentioned in last section, fixture design is a complex process and based on past experiences, and its domain knowledge is incomplete and difficult to generalize These features make case- based reasoning approach naturally suitable to the domain of fixture design Fixture design can also benefit from the advantages of case- based reasoning 1.3 Internet- enabled Manufacturing Environment In today's... this research an attempt will be made to develop a fixture design system based on Internet This makes the fixture design system possible to interoperate with other Internet- based manufacturing systems, such as computer-aided process planning (CAPP) and computer-aided numerical control systems This also makes available the database storing fixture design experiences that users around the world could... similarities between hierarchies Attr4: Val4 List of cases Case A Case B Case C … Case AA Attr1: Val1 Attr2: Val2 Case B Case C (A) List of cases Attr1: Val3 Attr3: Val5 Case A Case AA Attr4: Val6 Case D Case F (B) Attribute tree Figure 2.5 Memory organization There are primarily factors considered in case representation strategy and the memory organization in CBD system: flexibility and efficiency Flexibility... & 1993] is the first planner attempted to develop a case- based approach to process planning It combined case- based reasoning with knowledge -based reasoning in cutting process for rotation parts PROCASE [Yang and Lu, 1994] is also a prominent case- based process planning system for machining of rotational parts Besides TOLTEC and PROCASE, other case- based process planners which consider cutting processes... cost in fixture design They also need less storage space compared with dedicated fixtures Hence, manufacturing lead time is shorter, engineering changes are easier to handle, and storage cost is decreased Modular fixture systems are broadly classified into two categories: T-slot -based and dowel-pin -based systems Figure 2.3 are designs of T-slot -based and dowel-pin -based modular fixture design systems... automatically with use of the system The problem solving approach of a case- based design system is based on the retrieve and reuse of specific experiences 2.3.1 Issues in Developing CBD systems There are no general methods to build a case- based reasoning system, but some general issues must be considered when such a system is built The major considerations in a CBR approach to design can be broadly classified ... is to propose a system where a strategy extending case- based reasoning to the Internet, distributed case- based reasoning, is applied in the fixture design domain 1.2 Case- based Reasoning CBR is... CBR systems adopt this mode in the Internet The alternative distributed case- based reasoning system is a hybrid of case- based reasoning with a multi-agent system This system distributes case. .. experiment with the design and implementation of an internetenabled computer-aided fixture design environment The primary objective is to develop a fixture design system using case- based reasoning approach