Optimum Tolerancing of Planar Mechanisms Based on an Error Sensitivity Analysis

This paper presents an analytical procedure to determine the optimum set of tolerance bands of the dimensions of a planar mechanism. Optimum tolerance bands are those which allow the largest values of dimensional tolerances, while ensuring that the desired output motion is kept within acceptable deviations form the output that would be generated by an ideal mechanism having no errors in dimensions. The analysis technique presented permits identification of the most sensitive link dimension, the most sensitive combination of input errors, and the most sensitive period within the entire cycle, which make the largest contribution to the output error. The optimum tolerancing procedure is then presented. Examples applied to single and multiple loop mechanisms are included.