Reconfiguration Analysis of a Fully Reconfigurable Parallel Robot

Abstract

This paper presents a new method for the combined topological and geometric reconfiguration of a parallel robot to achieve task-based reconfiguration. Using the existing structure of a six degree-of-freedom (DOF) parallel robot, reconfiguration to limited mobility modes, a configuration with less than six degrees-of-freedom, can be achieved easily without the need to remove branches from the robot structure. Branch modules are instead, reconfigured from an unconstrained-active to a constrained-passive state by means of hybrid active/passive motors and reconfigurable universal-to-revolute joints. In doing so, the robot is capable of assuming a configuration in which the number of task-based degrees-of-freedom match the number of controllable actuators within the robot structure. The selection of branch modules for reconfiguration is independent of the limited mobility mode required and leads to multiple isomorphic configurations. A comparative study is thus needed to understand not only the implication of morphing, but also the capabilities of the reconfigured robot. For this purpose, a branch-based mobility analysis is performed and isomorphic configurations are identified. These isomorphic configurations are then compared based on their workspace and kinematic capabilities for which a parametric kinematic constraint formulation is developed. The comparative study evaluates the abilities of each configuration and is used for guidance in selecting an appropriate configuration for a particular task. The developed tools can also be used for design evaluation purposes.