Tether Based Locomotion for Astronaut Support Robot Introduction of Robot Experiment on JEM

An astronaut support robot called Astrobot will conduct tasks to reduce workloads of astronauts and risks of hazardous incidents that include astronauts. To realize Astrobot, new technologies must be developed such as robot locomotion capability to move robot’s location so that it arrives at required workplace and returns to its storage position. We are proposing a new type of robot locomotion method that uses tethers. JAXA is conducting experiments called Robot Experiment on Japanese Experiment Module or REX-J, to evaluate the usefulness of these new technologies. This paper discusses REX-J’s tether based locomotion control. This proposed tether locomotion control is defined as an under-actuated cable driven parallel manipulator. This system is difficult to control because tethers easily become slack in microgravity environment in orbit, which instantly changes their state. To cope with this problem, model-based control method using statics analysis is proposed as slackless control in microgravity environment. The proposed sequential tether length and tension control were tested using a breadboard model. REX-J onboard equipment was transported to the ISS/JEMin July 2012 and many experiments are now being conducted.