IMPROVING CHARACTERISTICS OF ELECTROHYDRAULIC SERVO SYSTEM WITH NONSYMMETRICAL CYLINDER USING DSP

抄録

The DSP (digital signal processor) and the feedforward compensation called ZPETC (zero phase error tracking control) are applied to an electrohydraulic servo system with a nonsymmetrical cylinder, and frequency responses of the system are greatly improved. ZPETC is a control algorithm which renders the transfer function between an input and an actual output close to unity. To use this algorithm, it is assumed that the controlled system is linear. However the relationship between load pressure and flow rate at the servo valve is highly 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 using the detected load pressure, and the effect of nonsymmetrical cylinder is compensated using the detected sign of the input. DSP performs the calculations for ZPETC and for linearization of the system. The effect of improving the frequency responses of the system by this digital signal processing technique is investigated.