Pushing operation by flexible manipulator taking environmental information into account

Vibration suppression in a motion-control system is an important problem in industry applications. Recently, a number of studies about flexible manipulators have been reported. However, there is little published on pushing operation by flexible manipulators. Contact motion to an unknown environment is difficult, because the motion system should recognize the environmental stiffness and adapt to it at the time of collision. This paper proposes a pushing control by a flexible manipulator based on a resonance ratio control. The environmental information is estimated more accurately by using a position sensitive device. The proposed method is composed of three modes: 1) approaching; 2) touching; and 3) pushing. In the approaching mode, the resonance ratio control is applied to suppress the torsional vibration. Compliance control is installed in order to relax an impact force in the touching mode. Finally, a two-step controller is proposed for the pushing mode. In the first step, friction effects are identified by a friction-torque observer. Then, the pushing operation with compensation of the stick-slip friction is controlled based on the identification results in the second step. It is possible to remove an object to a desired position. The experimental results show viability of the proposed method.