A DSP (digital signal processor) and a feedforward compensation method called ZPETC (zero phase error tracking control) are applied to an electrohydraulic servo system with a nonsymmetrical cylinder to improve on the frequency responses of the system. ZPETC is a control algorithm, rendering the transfer function between the input and actual output close to unity. This algorithm assumes the controlled system to be linear. However, the relationship between the input and flow rate at the servo valve is nonlinear. Another nonlinear factor is added when the cylinder is nonsymmetrical. Therefore, these nonlinearities should be removed. The nonlinearity of the servo valve is compensated for by using the detected load pressure, and the effect of the nonsymmetrical cylinder is compensated for by using the detected sign of the input. The DSP performs the calculations for ZPETC and for linearization. The effects of improving the frequency responses of the system by this digital signal processing technique are investigated.
