Distributed-Torque-Based Independent Joint Tracking Control of a Redundantly Actuated Parallel Robot With Two Higher Kinematic Pairs

A redundantly actuated parallel robot of the 6RSS mechanism involving two point-contact higher kinematic pairs (HKPs) has been developed for the evaluation of food texture changes during the process of mastication. To accomplish this, a fundamental capability of reproducing complex mandibular motions of human subjects in a biomimetic manner is required. In this paper, first, the mechanism and experimental setup of the robot are described, followed by five performance criteria proposed for the torque distribution across the robot. Second, the distributed torque is employed as a feedforward to enhance the independent joint control for the tracking of the mandibular movement. The frictional effects are compensated for to further improve the tracking accuracy. Finally, experiments are carried out to evaluate and compare the proposed control algorithms with the robot being commanded to reproduce a real human mandibular motion in free chewing, chewing a silicone gel, and chewing a wooden stick. The results illustrate that the robot is able to emulate complex mandibular motions, the distributed-torque-based joint control significantly enhances the motion tracking accuracy, and the friction compensation can further improve the motion tracking performance.