This paper presents an experimental evaluation of four regulators in task space using unit quaternions to represent the end-effector orientation. We address the problem of regulation, that is, when the desired pose is constant. We present experimental results of the following control schemes: the resolved acceleration control, damped resolved acceleration control, hybrid damped resolved acceleration control, and transpose Jacobian-based control. All the controllers are tested on a three degrees-of-freedom spherical wrist.

Resolved acceleration control is a method for motion control of robot manipulators in task space where a desired end-effector pose trajectory is specified. We consider the orientation part of the pose given by the Euler parameters or unit quaternion. The main contribution is a novel proof of asymptotic stability based in the use of a strict Lyapunov function. This is a one stage procedure which improves previously reported analysis where two-stage mechanisms are in general invoked: first demonstrating stability and then convergence.