MODELING AND CONFIGURATION-INDEPENDENT CONTROL OF A SELF-MOBILE SPACEMANIPULATOR

The Self-Mobile Space Manipulator (SM(2)) is a 5-DOF, 1/3-scale, labor atory version of a robot designed to walk on the trusswork and other e xterior surfaces of Space Station Freedom. It will be capable of routi ne tasks such as inspection, parts transportation and simple maintenan ce and repair. We have designed and built the robot and gravity compen sation system to permit simulated zero-gravity experiments. The contro l of SM(2) is challenging because of significant structural flexibilit y, relatively high friction at the joints, positioning error amplified from joint errors due to the long reach, and high performance require ments for general 3-D locomotion. In this paper, we focus on the model ing of the robot system and the design of the control system based on the model. We address the kinematics and dynamic modeling of the 3-D m otion of SM(2) and demonstrate the simulation and experimental modal a nalysis results. The robot dynamic characteristics vary significantly when the robot configuration changes. To consider this effect, we deve lop a control system that is composed of two basic parts, the model-ba sed part and the servo part. The model-based loop can be updated based on the off-line dynamic model, and the servo control loop is updated by a gain schedule according to the off-line relationship between the closed-loop frequency and the modal frequency estimated from the off-l ine dynamic model. By taking dynamic variation into account in the con troller, the control system is independent of the robot configuration, and the motion performance of SM(2) is greatly enhanced in implementa tion.