Efficient pulling motion of a two-link robot arm near singular configuration

This paper discusses the advantages of singular configurations of a two-link robot arm in achieving tasks of pulling or lifting a heavy object. Optimal base location and arm motion for minimizing the joint torques are examined by numerical simulations, and the base location where the robot arm is near a singular configuration at the start time of task is optimal. It is shown analytically that joint torques can supply energy to the system composed of the robot arm and the object efficiently near singular configurations of the arm. The energy supply rates at two singular configurations are derived based on the equations of motion of the system.