A Method of Gravity Offloading with a SCARA Manipulator

This paper presents a mechanism and control law which is currently under development that is intended to provide gravitational compensation so that lunar bound systems can be terrestrially tested in a simulated lunar gravitational field. The mechanism is a selective compliant articulated robotic arm (SCARA) manipulator. The object to be tested is rigidly attached to the end of the manipulator. The control scheme makes use of a copy of the test-object´s dynamical model. This is integrated in real-time and includes the response due to any externally applied forces and torques. The result of this integration is a trajectory in the task-space. The inverse kinematic model of the manipulator is utilized to generate a trajectory in the joint-space and an exponentially stable tracking controller is implemented to drive the manipulator joints along this trajectory.