Automatic Assembly Sequence Plan Generation

本研究提出一個能找出建構Petri net所需的反組裝程序的方法。由於Petri net簡單清淅的符號表示及完整的數學特性，它一直是一種廣泛使用的模擬工具。如果能將所有可行的組裝程序以一個Petri net表示，運用它的數學特性，便可快速地找出最佳的組裝程序或反組裝程序。 本研究利用CAD組裝檔的拘束條件及各零件的幾何特徵，找出組裝檔中各零件相對於其他各個零件可行的反組裝方向。利用反組裝方向及可行性測試可以判定每個反組裝步驟是否可行。再利用反組裝步驟建構該組裝檔的Petri net。不同的是，本研究中的反組裝方向可以是一個任意的方向，而非局限於某個直角座標體系的三軸方向。本研究亦採用simplex algorithm演算法，實作運用Petri net的數學特性找出該Petri net所屬的組裝檔的最佳反組裝程序。最後，本研究也以各包含了四個、八個及十二個的組裝檔測試本研究法則之可行性。This thesis describes a method to generate all feasible tasks which are the essential information to build the Petri net of a product. Petri net is a powerful modeling tool because of its well-defined semantics and mathematical properties. With the Petri net of a product, the optimal sequence can be quickly found according to its mathematical properties. The method in this thesis starts from extracting constraints and geometric features of the assembly model of a product. The disassembly orientations of every part relative to the others are obtained from constraints and geometric features. By intersecting related disassembly orientations of a disassembly task and feasible tests, we can gain every practicable disassembly task and hence build the Petri net of the assembly model. What is the most special point is that the disassembly orientations can be arbitrary directions, not merely limited to positive and negative directions of x, y and z axes. The thesis also implemented the searching of the optimal disassembly sequence by employing simplex algorithm. At last, three assembly models which contain four, eight, and twelve parts respectively are employed to verify this method in this thesis.1.1 Background 1 1.2 Assembly sequence 2 1.2.1 Geometric criteria 3 1.2.2 Manufacturing criteria 4 1.2.3 Terminology used 5 1.3 Development platform 6 1.3.1 Assembly model structure 6 1.4 Objective and structure 8 2.1 About the criterion 10 2.1.1 Geometric criteria 11 2.1.2 Manufacturing criteria 12 2.2 About the representation 14 2.2.1 No graph in presentation 14 2.2.2 And/or graph 15 2.2.3 Petri net 16 2.2.4 Disassembly completed graph 21 2.2.5 Genetic algorithm 22 2.2.6 The comparison of algorithms and their representation 23 2.3 Conversion from Petri net into state shift matrix 26 2.4 Linear programming 30 2.4.1 Formulation of searching the optimal sequence 30 2.4.2 Simplex algorithm 30 3.1 Definition of connection graph 32 3.2 Virtual bind 34 3.2.1 Definition of disassembly orientation (DO) 36 3.2.2 Face-to-face contact 37 3.2.3 Coincidence 38 3.3 The procedure of building connection graph 44 3.4 Adding constraints into virtual bind 45 3.5 Disassembly task in connection graph 56 4.1 The procedure of building Petri nets 58 4.2 Connection test 60 4.3 Clash test 63 4.3.1 The infeasibility of disassembly orientations 65 4.3.2 The detection of infeasible disassembly orientations 67 4.4 Complexity of Petri net 71 5.1 The platform of implementation 73 5.2 The dialog of assembly sequence 74 5.3 Flashlight 76 5.4 Robotic arm 79 5.5 Car model 83 6.1 Conclusions 87 6.2 Future work 89 7 Reference 9