Mechanical design of the Carpal wrist: a parallel-actuated, singularity-free robotic wrist

Parallel robotic manipulators offer potential advantages over the more conventional serial manipulators, such as a higher stiffness-to-weight ratio and more precise control. However, their use as base manipulators and robotic wrists has been limited by their more complicated kinematic solutions and, especially in the case of a wrist, severely limited work spaces. Due to these shortcomings, robotic wrists in existence today are typically built as serial kinematic chains that provide large, spherical work spaces but suffer from lower stiffness, higher mass, and interior singularities. A parallel mechanism consisting of three sets of serial-chains can be manufactured that possesses characteristics suitable for use as a robotic wrist. As a result of its parallel structure, it provides for the high strength and low weight of a parallel manipulator, while its novel configuration gives it a workspace comparable to that of serial-type wrists. Additionally, the configuration of the links allows the wrist to have a large open center through which cables or hoses supplying the end-effector can be routed. This tunnel-like similarity to a human wrist's carpal tunnel leads to its name, the Carpal wrist. This thesis discusses the characteristics of the Carpal wrist and develops simple tools for its design. A simple force analysis is developed and used to solve for the required input forces and resulting internal forces in the wrist. Computer algorithms are developed that facilitate the solution of both the kinematic and force equations resulting from the analysis of the wrist. Using these tools, a prototype wrist is designed such that it may serve as a proof-of-concept model capable of denl0nstrating both the kinematic function and load-carrying capability of this device.