The human wrist contributes greatly to the mobility of the arm/hand system, empowering dexterity and manipulation capabilities. However, both robotic and prosthetic research communities tend to favor the study and development of end-effectors/terminal devices (hands, grippers, etc.) over wrists. Wrists can improve manipulation capabilities, as they can orient the end-effector of a system without imparting significant translational motion. In this paper, we review the current state of the art of wrist devices, ranging from passive wrist prostheses to actuated robotic wrist devices. We focus on the mechanical design and kinematic arrangements of said devices and provide specifications when available.

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.