Friction compensation of a Schilling hydraulic robot

Illustrates the application of a model-based friction compensation scheme to an industrial six degrees of freedom Schilling Titan II hydraulic manipulator. The dynamic friction model and the control structure studied in Canudas de Wit et al. (1995) are used as a basis for this work. First, a low level nonlinear torque controller is developed to provide a high bandwidth and performance torque response of the hydraulic actuators. This inner loop controller is based on a nonlinear model of the servovalve and the hydraulic actuator. Friction compensation is then developed. An off line identification method for the estimation of the different friction model parameters is proposed. Then an adaptative friction compensation presented in Canudas de Wit and Lischinsky (1997) is applied to the hydraulic manipulator, assuming that the nominal identified model is suitably structured. Both the torque control capabilities and the friction compensation efficiency are largely illustrated through experimental results.