Active gravity compensation test bed for a six-DOF free-flying robot
A novel active gravity compensation concept is proposed to simulate space on-orbit microgravity environments for free-flying robots on ground. Here, robots are suspended by active-controlled motion path tracking mechanisms through wires to compensate for gravitational forces. Based on the concept, an experimental test bed was designed and fabricated in laboratory to study on-ground kinematic and dynamic behaviors of a free-flying robot. The experimental fabrication contains an active horizontal motion tracking mechanism composed of primary and secondary active rotating arms. An multi-objective optimization method calculating the tension of the wires to minimize torques on robot joints is approved. The tension of the suspension wires is obtained through passive counterweights using pulley mechanisms. The kinematics and dynamics of a 6-DOF free-flying manipulator were calculated in MATLAB and simulated in MSC Adams under three working conditions: zero-gravity, gravity compensation and gravity. The lowest ratio of the torque compensation reached 80%. Agreements between numerical analyses and simulation results confirm the ability of this gravity compensation concept to simulate the kinematic and dynamic behaviors of free-flying manipulator in space.
Ground-based simulation of space manipulators using test bed with suspension system
An experimental system simulating dynamic behavior of space manipulators is constructed for the purpose of technological demonstration of space robots and evaluation of their dynamic features. The system consists of a space robot with dual manipulators, a suspension system, and a control system. The manipulators are hung by wires at each joint of the manipulators to cancel the effect of the ground gravitational force. The tension of the wires is controlled to be constant to simulate on the ground the dynamic behavior of the manipulators in space. Dynamics of the two-link manipulators is analyzed experimentally employing the present ground facility through inspection of their dynamic features in space. The motion of the manipulator is restricted to a vertical plane as the first step of study. The outline of the experimental system is also briefly introduced. The results of the numerical simulation and the experiments show sufficient capability of the on-ground simulation to study dynamic behavior of the manipulator in space.
Space robotics in Japan
Japan has been one of the most successful countries in the world in the realm of terrestrial robot applications. The panel found that Japan has in place a broad base of robotics research and development, ranging from components to working systems for manufacturing, construction, and human service industries. From this base, Japan looks to the use of robotics in space applications and has funded work in space robotics since the mid-1980's. The Japanese are focusing on a clear image of what they hope to achieve through three objectives for the 1990's: developing long-reach manipulation for tending experiments on Space Station Freedom, capturing satellites using a free-flying manipulator, and surveying part of the moon with a mobile robot. This focus and a sound robotics infrastructure is enabling the young Japanese space program to develop relevant systems for extraterrestrial robotics applications.