Static Analysis of Torque and Coupler Driven Spherical Four-Bar Mechanisms With an Applied Load

Spherical four-bar mechanisms are classically designed to be driven via a torque applied to the input link. This paper presents a comparison of the resulting statics associated with this method of actuating a spherical four-bar versus actuating the mechanism with the force applied directly to the coupler. A force may be applied in this fashion via a spherical-prismatic-spherical, or SPS, chain mounted between the ground frame and the coupler with the prismatic joint actuated. The spherical four-bar linkage with the SPS chain connected directly to the coupler defines a spatial analogue to the Stephenson III six-bar mechanism. Moreover, this work builds on previously derived static models of spherical four-bars by considering the additional loading issues associated with links at different radii and the forces that arise from an external load on the coupler.