Assembly cost evaluation based on necessary adjustments due to tolerances

An assembly task, whether robotic or manual, may involve adjusting the positions of already assembled parts when a new part is assembled, due to tolerance and position uncertainties of the parts. Such an adjusting operation can increase the cost of the product because of the adjusting time, fixturing costs, additional operations, etc. In this paper, a statistical approach to evaluate the cost of assembly is proposed. The cost is measured according to the number of objects that must be moved in order to successfully assemble the product. The approach uses a statistical analysis of the accumulated tolerances, the local clearances, and the possible adjustable zones due to clearances between the already assembled parts, to calculate the minimum number of objects that must be adjusted to complete the assembly. Special attention is given to the assembly of parallel chains. The complete procedure and simulation results are given.