Onboard assembling of a large space structure by a torque-controlled space robot

摘要

On Earth orbit, astronomical observation is in very good condition that is free from any absorptions or disturbances by the Earth's atmosphere. Therefore, some large space telescopes and large space radio telescopes are planned. Diameter of payload bay of launch vehicle might be restriction for the size of such telescopes. That is the reason why structures larger than the payload bay have to be deployed or assembled onboard. Onboard assembling structure is better in surface accuracy and rigidity than deployable structure. We present a constitution of on-board assembling telescope reflector structure and its connecting mechanisms suitable for robot tasks. For assembling of such large structure, space robot has to move around on the structure. Power/signal lines, its connectors and grapple fixtures are needed on the structure for providing power/signal and foot restraints to the mobile robot arm. Compliant motions of robot are needed for constrained motion tasks such as grasping, attaching and mobile inchworm motion of onboard structure assembling. A new control method, active limp control of the robot arm joints, has high response and high stability because of their sensor/actuator collocation. So they are adequate to space robots for onboard assembling tasks. Constitutions of on-board assembling structure, a scenario of its assembling and control methods of the space robot are described in this paper. Characteristics of the new control methods and its suitability for onboard assembling tasks were confirmed by testing with using a prototype joint mechanism and its control system. The testing results and evaluation are also described in this paper.