Robust control of a hydraulically driven flexible arm using backstepping technique

In this paper, a new robust controller is proposed to regulate both flexural vibrations and rigid body motion of a hydraulically driven flexible arm. The proposed controller combines backstepping, sliding mode, and pole placement techniques to arrive at a controller capable of dealing with a nonlinear system with uncertainties. The sliding mode technique is used to achieve an asymptotic joint angle and vibration regulation in the presence of payload uncertainty by providing a virtual torque input at the joint while the backstepping technique is used to regulate the spool position of a hydraulic valve to provide the required torque. The pole placement design methodology is applied to attain a good dynamic response by placing the poles of the sliding plane in the desired location. It is shown that in contrary to conventional use of sliding mode controllers, there is no chatter in the hydraulic valve which results in smoother and noiseless operation of the system.