CAD system with product assembly/disassembly planning function

Abstract

Assembly design of mechanical products is one of the most important subjects in the CAD/CAM systems of the near future. The product model (geometric model) is the input in many CAD/CAM systems in order to determine the assembly/disassembly sequence. Disassembly is executed with cooperation between the computer system and the designer. The kinematic simulation should support the designer; however, most simulation systems do not have enough functions to do this. There are many problems left, mainly caused by the lack of functionality of the kinematic simulation of mechanical products. When product designers are requested to consider product assembly and extract the fundamental assembly plan from their design solutions, the kinemati simulation and evaluation functions, to obtain the product assembly plan, are most important in CAD systems. This paper deals with a kinematic simulation system used in assembly planning that simulates physical phenomena including the effect of gravity, and a prototype simulator is developed. An evaluation method for the ease of assembly/disassembly based on the kinematic simulation system is also proposed, which gives a decision support tool. Here, the assembly sequence is considered as the reverse of the disassembly sequence, which is justified through taking the kinematic simulation into consideration. The part to be removed is decided by comparing the evaluation standard values of candidate parts when several parts can be removed at the same time. With the use of the product model presented by 3-D solid geometry, possible movements of each part in the product are calculated, and the removal possibilities from the product can be searched. When there are several ways to remove the part from the product, the best disassembly operation for the part is selected on the basis of shortest distance of part movement. In the evaluation, the effect of gravity is considered, which may cause the next assembly/disassembly operation to be difficult. The developed simulation system is also effective in detecting the necessity for jigs or fixtures in the assembly sequence. Through a case study, it is shown that the developed system is valid and effective in enabling product designers to obtain product assembly plans.