The distributed controller architecture for a masterarm and its application to teleoperation with force feedback

Abstract

For-robot teleoperation, a lot of researches have been done to control the slave robot from remote site using a master arm. To make the master feel the same force as the slave robot, force feedback is important for precise control dealing with unknown environments. External motion capturing devices or joint angle measuring sensors are usually used to generate position commands from the master and the measured forces from the slave robot are fed back to the operator. Time-delay problem, which frequently occurs between the master and the slave, has been extensively studied so far, but not too much on the controller architecture of the masterarm. A new concept of the distributed controller architecture for the masterarm is introduced in this paper. To reduce possible non-uniform time delay and to have higher position command update rate, the host controller with the distributed satellite controllers are developed. Each satellite controller measures the corresponding joins angle, while the host controller performs initial calibration, inverse kinematics calculation, and position commands generation. The host controller and the satellite controllers are networked via SPI (Serial Peripheral Interface) protocol, with maximum speed of 5Mbps. For force feedback, the host controller solves the joint torque relations based on kinematics of the masterarm and the satellite controller controls each joint's torque. This distributed controller greatly reduces calculation and control loads and makes the electrical wiring very simple. For teleoperation of the KIST humanoid robot which has two arms, the masterarm controller with one host controller and 14 satellite controllers is implemented. Force feedback with less than 2msec update rate is achieved. The experimental results show not only the performance of the distributed controller but the possibility of applying it to the robot motion controller which has large number of joints.