Optimal design and sensitivity analysis of flexible cam mechanisms

Abstract

The optimum design of cam-follower mechanisms is considered in this paper. The design methodology proposed here leads to optimum values for the following design parameters: cam base-circle radius, follower roller radius, follower offset, cam thickness, return spring stiffness and initial compression for minimum cam volume, for the case in which structural flexibility effects of the cam mechanism are considered. It is shown that an optimal design based only on kinematic motion of the cam mechanism may be unacceptable when implemented on a real cam mechanism due to excitation of structural flexibility effects. These structural flexibility effects lead to large accelerations of the cam-follower which results in excessive surface stresses on the cam and follower roller. Such exceissve stress may lead to premature mechanical failure of the mechanism. To overcome this problem, a design methodology is proposed here to overcome this problem. The design process models the structural flexibility of the cam-follower mechanism and leads to a design which a sufficiently large margin of safety to ensure acceptable performance of the system. While a satisfactory approach to this design problem exists if structural dynamics stiffness and damping coefficients are known, variation in these parameters from their nominal values may lead to an unacceptable design when implemented. To investigate the nature of the effect of uncertainty in these parameters on the cam-follower performance, a sensitivity analysis is performed. The effect of variations in various structural dynamic parameters on the dynamic response of the flexible cam mechanism (displacement, velocity and acceleration of the follower) and also on the minimum and maximum values of the contact force are determined. Numerical simulation results support the results given in this paper.