Contact localization using force/torque measurements

A three-fingered robotic hand manipulation system, employing three Motoman K-3S1 robots as its fingers, and a VME based multiprocessor system with the Vx-work real-time operating system as its control system, has been developed in the Robot Manipulation Laboratory of the Hong Kong University of Science and Technology for the study of dextrous manipulation. One of the major problems we encounter in this study is the determination of contact locations between fingertips and the object to be grasped/manipulated. We propose the use of measurement data supplied by a force/torque sensor mounted at the end of the fingertip for localization of contact. We first give a mathematical formulation of the problem. We incorporate gravitational effects in the model and show how to eliminate the biasing effect during real implementation. Then, we perform an error analysis of the computed results from which we can infer accuracy of the proposed approach. Finally, we give experimental results obtained using a Lord FT335x force/torque sensor mounted at the end of the fingertip. It is shown that force/torque based approach can yield results of good resolution compared with the tactile-based approach, and the former is also easier to implement with commercially available components