Parallel Mechanisms for Multiscale Motion Using Twisted Wire Actuation: Designing for Microworkspace and Dexterity

This article presents an exploratory study of a new family of parallel mechanisms with multiscale (micro/macro) motion capabilities. These composite serial-in-parallel mechanisms use kinematic redundancy and two sets of macro and micro actuators to achieve multiscale motion. Use of twisted wire actuators (TWAs) is considered as a low-cost alternative for achieving micromotion. A kinematically redundant 3RRPR planar parallel robot is used as a case study for task-based design of these robots with considerations of macro and micromotion workspace, dexterity, minimal motion resolution, and end-effector error considering the use of low-cost TWAs for achieving micromotion. Task-based considerations for the microworkspace are used to illustrate the effect of the TWAs on the micromotion kinematics. An experimental study shows that, because of the use of TWAs, it is possible to achieve motion resolutions on the order of a few micrometers despite using low-cost manufacturing techniques and actuators. The use of TWAs is shown to also significantly alter the kinematic characteristics of the robot at the microscale. The modeling framework of this article can guide designers in key design considerations for parallel robots with multiscale motion capabilities. Results of this article can be used to guide users in the selection of TWAs and in determining the threshold when the robot should switch from macro to micromotion and to facilitate a smooth transition via redundancy resolution.