Designing Micromanipulation Systems for Decoupled Dynamics and Control

A new, seven parameter class of micromanipulators is found with decoupled dynamics. The resonant frequencies and damping ratios are found to be simple functions of the parameters, making it possible to design manipulators to meet resonant frequency or damping ratio specifications. Methods for designing the dynamics so that they are amenable to control are derived, which leads to significant increase in the closed-loop performance and robustness. To illustrate the new theory, a manipulator currently used on the International Space Station (ISS) is redesigned to greatly enhance its fault tolerance and closed-loop performance. Even though both manipulators control the same payload over the same bandwidth with exactly the same struts, the H∞ controller for the new manipulator is five times less sensitive to worst case disturbances than the H∞ controller for the existing manipulator. Moreover, the decoupling facilitates the design of Nyquist stable controllers with nonlinear dynamic compensators which give the new decoupled manipulator 100 times higher performance at low frequencies. This greatly increased performance and robustness requires implementation of only the six compensators along the diagonal of the six degree-of-freedom system, versus implementation of all 36 compensators for the ISS manipulator. This performance improvement is achieved with no increase in system cost, mass, or power budget; it is exclusively the result of the new theory presented in this paper.