Understanding the true dynamics of space manipulators from air-bearing based ground testing

A space manipulator can easily handle a large payload having a much larger mass than its own mass. However, physical test of such a manipulator handling a large-mass payload in 3D space on the ground is almost impossible due to gravity effect. A commonly used test method is to support the manipulator with air-bearing pads on a horizontal granite surface so that the robot can freely maneuver on the 2D surface as it were floating in a 2D microgravity environment. However, such a test method suffers a major problem: the air-bearing based support equipment is large and massive when the manipulator is long (e.g., 10 m or longer) and/or its payload is heavy (e.g., 500 kg or heavier), which adds significant inertial loading to the robot when it maneuvers. As a result, the manipulator has to make much more effort on a test than it would need in space. This paper describes a study for understanding the true dynamics of a space manipulator from such an air-bearing supported test. A test-data analysis method is developed, which can decouple and remove the dynamics effect of the air-bearing support equipment from tested manipulator system. With such an approach, the true joint torques for the space manipulator to produce a prescribed end-effector motion trajectory can be determined, although the manipulator has to be constrained to a massive air-bearing based support equipment for the testing. The method has been experimentally validated by a specially designed experiment facility.