A Generalized Approach for Sensitive Analysis of Four- Bar Mechanism and Identifying Sensitive Link/s Tolerances Using Relative Velocity Method

Abstract

The performance of a mechanism is defined as ratio of difference between calculated angular velocity ratio and ideal angular velocity ratio to the ideal angular velocity ratio. The angular velocity ratio can be calculated from velocity diagram. The paper uses a crank – rocker mechanism, a type of simple four bar mechanism in which crank rotates 3600 and rocker oscillates. In the presence of manufacturing errors like manufacturing tolerances, thermal deformation, deflection of links, human errors, machine defects, etc., it is impossible to maintain a constant performance of the mechanism in bulk manufacturing. There will be slight variation in the performance due to variation in one or more links. Any manufacturing process is associated with dimensional tolerances that leads to variation in part dimensions and generally cost of manufacturing increases exponentially for closer tolerances to all links of the mechanism. The aim of the paper is to discuss an approach to determine maximum and minimum performance variation and identify links which causes maximum performance variation. The closer tolerances should be given to that link/s only which will permit to designer to give slightly loose tolerances on remaining links.