Design and Implementation a Nonlinear H∞ based Tracking Controller for Low Stiffness Flexible Joint Robot with Backlashes Nonlinearities

This paper proposes a nonlinear H∞ controller to control a single link rotary flexible joint robot which has dead zone problem. Dead zone properties are caused by dry friction and gearbox backlashes. The flexibility in setup robot is performed by means of a solenoid spring, which is connected between actuator shaft-out and joint shaft-input in a bilateral connection form. The effect of dead zones and also frictions are highly decreased by a pulsation signal as an extra voltage that is added to the nonlinear H∞ controller signal as an input voltage of motor. In order to use Taylor expansion algorithm, the dynamic of frictions and actuator saturation are modeled by smooth and derivable equations. The control law is produced as a function of end payload by using Taylor expansion. The system parameters, which have tolerance, are modeled as nonlinear H∞ compatible uncertainties. Experimental results show that the effect of dead zones generally and gearbox backlashes on error integrator specially are compensated and also the proposed controller has ability to control single link flexible joint robot with a good performance.