Towards a standardized cost measure of assembly operations

A statistical measure of the cost of assembling two mating features is presented. It is based on how well the geometry of the task compensates, during the assembly, the uncertainties associated with the mating features: manufacturing tolerances and the pose uncertainty. The latter is due either to the accumulation of tolerances and clearances between mating features that are previously assembled or to the positioning errors of an assembly robot. The proposed measure allows a systematic evaluation of the assembly cost for a given assembly sequence, thus providing a method for evaluating assembly sequences and selecting an optimal one from the assembly point of view. The influence of different sources of uncertainties and the assembly procedure can also be evaluated with the proposed cost index. The paper includes an example to illustrate the use of the proposed cost measure