| This research presents the problems of assembly sequence planning for constrained environments. The constrained environments under consideration refer to the limitation of system resources, such as robot arms, grippers, tools and fixtures in the assembly systems. A gap between assembly sequence planning and task planning, along with the consideration of constrained environments for assembly planning bring up the importance of system resources and the necessity of considering feasibility and quality issues in the early stages of the assembly planning process.;A decomposition approach is applied to generate the sequence plans by decomposing the final assembly into separated parts. By performing feasibility testing and assessing the quality of the assembly operations at each iteration of the decomposition process, it is possible to construct the best feasible sequence plan for further task planning and execution.;A set of feasibility conditions is proposed which includes the constraints imposed by the geometry of the assembly, as well as the availability of the resources in the assembly cell. These conditions are tested during the generation process to assure the feasibility of the assembly operations in the sequence plan. Both resource-independent and resource-dependent conditions for testing feasibility are presented, such as mechanical feasibility, geometric feasibility, resource compatibility, resource accessibility and subassembly stability.;In addition, operation-related criteria, as well as sequence-related criteria, are proposed to assess the quality of assembly operations and sequence plans based upon the complexity of the assembly operations and their demands on system resources. Five evaluation criteria, such as direction index, fixture complexity, direction change, tool change and fixture reconfiguration are presented together with the integration of the complexity measures for the selection process.;Finally, a prototype system has been developed based on the decomposition process to implement the sequence planning for assembly under constrained environments: Several applications are presented to illustrate the process of feasibility testing, evaluation, selection and decomposition for assembly sequence planning problems. |
