Wrench and Twist Capability Analysis for Cable-Driven Parallel Robots With Consideration of the Actuator Torque–Speed Relationship

Abstract

The wrench feasibility and twist feasibility are the workspace conditions that indicate whether the mobile-platform (MP) of the cable-driven parallel robots (CDPRs) can provide a sufficient amount of wrench and twist. Traditionally, these two quantities are evaluated independently from the actuator's torque and speed limits, which are assumed to be fixed in the literature, but they are, indeed, coupled. This results in a conservative usage of the actuator capability and, hence, hinders the robot's actual feasibility. In this study, new approaches to analyzing and commanding CDPRs by considering the coupling effect are proposed. First, the required wrench of the MP is mapped into the twist space by the motors' torque–speed relationship and becomes the wrench-dependent available twist set. Then, a new workspace condition and a new metric are introduced based on the available twist set. The metric shows the maximum allowable MP speed map of the workspace. Finally, a varying speed trajectory is designed based on the metric to optimize the total MP traveling time. This study shows the potential of robot wrench–twist capability and enhances the robot hardware effectiveness without any hardware changes.