Design of cam shape for maximum stiffness variability on a novel compliant actuator using differential evolution

Abstract

In this paper, a particular cam shape was found for maximizing the range of stiffness variability of a novel adjustable compliant actuator called BAFSA. On one hand, this cam shape had to maximize the area corresponding to the curves of the stiffness–torque relationship of such actuator. On the other hand, it had to match with some parameters involved in the design of the BAFSA, in order to guarantee its feasibility of operation as a knee joint actuator on a human exoskeleton. To cope with all these conditions at a time, a differential evolution (DE) technique was applied. A DE algorithm was programmed, introducing a graphical approach based on Bézier curves to define the cam shape. Multiple runs were performed to test up to 10 configurations of the algorithm, progressively applying different constraints and cost functions. Such DE approximation proved to be very effective to design cam shapes, taking into account parameters of the mechanism in which the cam will perform. Finally, the best cam shape was selected from the different cases studied. Such a solution successfully complies with all the design criteria and constraints initially established.