A Six-Axis Asymmetric Parallel Manipulator Co-Driven by Direct-Drive and Geared Motors for Enhanced Force-Sensing Capability

This article introduces a novel six-axis parallel manipulator co-driven by motors with and without geared reducers. The design leverages the high stiffness provided by the geared motors and the high force-sensing capability of the direct drives. When the geared motors move synchronously with their direct-drive counterparts, the manipulator mimics a Delta robot's spatial translation, while the direct drives double as high-performance force sensors. An asymmetric design of the manipulator is proposed to allocate a larger portion of torque to the geared motors, raising the overall stiffness of the mechanism. Relations between the external force to the driving torque are derived and the torque redistribution effect of the asymmetric design is illustrated numerically. Experimental results on prototypes of both the symmetric design and the asymmetric design show that direct drives consistently exhibit much higher linearity in the force-to-torque relationship compared to the geared drives, and also confirm that asymmetric design alleviates the torque burden on the direct drives. (c) 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.