Kinematic Optimization of a Novel Partially Decoupled Three Degree of Freedom Hybrid Wrist Mechanism

Abstract

This paper discusses the kinematic design and geometric optimization of a novel hybrid three degree-of-freedom (DOF) wrist mechanism. The architecture consists of a one prismatic-revolute-universal linkage and one prismatic-spherical-spherical linkage in parallel with a revolute-universal linkage. This architecture is capable of spherical motion identical to that of a pitch-yaw-roll wrist. Moreover, this mechanism is considered to be partially decoupled, as not all actuators contribute to motion in an arbitrary direction. The forward and inverse kinematics of the parallel 2-DOF mechanism are presented. The 2-DOF mechanism is geometrically optimized over its design parameters to maximize a global transmission index, which measures the motion and torque transmissibility of particular wrist configuration over its workspace. The decoupled nature of the mechanism allows the pitch and yaw mechanism to be optimized separately, greatly reducing the parameter search space and allowing a much larger number of mechanism configurations to be simulated. We leverage this increase in simulated configurations to examine the effect of size constraints on the resulting mechanisms as well.