Control Passive Mobile Robots for Object Transportation - Braking Torque Analysis and Motion Control

In this paper, we propose a concept on realizing impedance-based motion control of passive type robots for transporting a single object in coordination with a human operator. In this research, we developed a prototype of passive type robot referred to as passive robot porter or PRP, which consists of three omni-directional wheels with MR Brakes, and on-board computer system. We analyze the singularity of PRP braking torques, and control the brake torque of each wheel based on the brake force/moment constraint so that impedance characteristics is realized on PRP with human´s pushing. This allows a PRP to track a 2D path which includes motion perpendicular to human´s pushing direction without using servo motors, and multi-PRPs to work cooperatively on handling a single object with orientation control for avoiding collision with obstacles. Experimental results are shown to illustrate the validity of the proposed concept.