Nonconventional processing of noisy signals in the adaptive control of hydraulic differential servo cylinders

Hydraulic differential electric servo cylinders are strongly nonlinear, coupled multivariable electromechanical tools applicable for driving, e.g., manipulators. Since they have considerable advantages in comparison with electric drives, it would be desirable to extend their application to dynamic continuous path (CP) control, too. From this point of view these systems have the following specialties: a) the most important phenomena influencing their behavior as, e.g., warming up of the sliding surfaces, are determined by local effects, and cannot be controlled globally; b) the friction forces show discontinuous variation at the zero transition of the piston´s velocity that is a locally nonlinearizable nonlinearity. A common proportional, integral, and derivative (PID) controller may generate a noise-like acceleration signal due to feeding back the effects of such fluctuations. Warming up of the working fluid during operation influences these friction properties, too. Dynamic interaction between the system and its environment neither measured nor modeled by the controller is another agent influencing the system´s observable behavior. For this purpose a special controller was elaborated. It implements certain adaptivity to compensate the effects of the inaccurate model and the unknown external disturbances, and also contains a nonconventional noise filtering technique to reduce the effect of the fluctuating friction forces. In the paper the control method is described, and then its capabilities are illustrated via simulation results.