Frictionless control of robot arm with sliding mode observer

In this paper, the authors consider a one-link robot arm, and the purpose of this study is to realize a frictionless joint of the arm of a robot. In order to do so, compensation of not only friction but also spring effect in harmonic gear which is set on the motor shaft is required. For their compensation, the authors consider a nonlinear sliding mode disturbance observer, and removing the effect of the disturbance by the observer, the parameters of the system are identified by a GA (genetic algorithm). The disturbance observer is also implemented in a controller in an online manner, so that frictionless jointing of the arm of the robot is realized. In order to verify the frictionless joint by compensation of the disturbance, the authors try to set the spring characteristics for the joint by a control design. The effectiveness of their proposal is verified by simulation and experimental results.