【正文】 utput diagram， the number of alternative curve that describes the future path of hysteresis nonlinearity with nonloca1 memory is infinite. Namely, the future output of the system depends not only on the current output Ya and future input， but also on the past history of input value’s extremum. Hence, the output response of new type of piezoelectric electrohydraulic servo valve to an applied input voltage bees unpredictable. In the system， there exist other nonlinearities such as force of friction and work dead zone of valve, furthermore， damping coefficient and oil temperature are also changed with time． The nonlinearity and uncertainty have seriously effects on the position precision. To improve the performance of the new type of piezoelectric electrohydraulic servo valve system, a valid control method is needed 3 Control algorithm At present, conventional PID controller is widely applied in industrial control domain because of its simple control structure, easy design and inexpensive cost． However, conventional PID controller is difficult to achieve good control performance in the new type of piezoelectric electro, hydraulic servo valve system because the control object has high nonlinearity and uncertainty． Fuzzy controller shows good results in the case of controlling high nonlinear systems. However, conventional fuzzy controller is essentially a kind of nonlinear PD controller, there exists steady state error, which cannot meet the demand of high precise of the system． In this paper, a highprecise fuzzy control algorithm with Preisach 第 頁 2 hysteresis nonlinear model in feedforward loop was proposed． The block diagram of the bined controlis shown in Fig． 3． The control system is posed of a feedforward loop based on Preisach model and a feedback loop of high precise fuzzy controller． Ul( is the output of feedforward loop based on Preisach mode1． As a linear term, it is selected from a Preisach function table based on the given position value． U2( is the output of the high precise fuzzy controller． The sum U(t) of feedforward control voltage f and feedback control voltage U2(t) ， as ultimate control voltage， is acted on new type piezoelectric electrohydraulic servo valve. 3． 1 Feedforward loop based on Preisach model The open loop response of the new type piezoelectric electrohydraulic servo valve system under an arbitrary and noncyclic input signal is shown in Fig． 2． This phenomenon appears as hysteresis nonlinearity with nonlocal memory, which can be predicted by Preisachmode1． The numerical form of Preisach model can be written as foliows： ?? ??? ddtuutf S??? ? )(),()( (1) Eqn.(1) can be used to calculate the response of the new type of piezoelectric electrohydraulic servo valve subject to a known arbitrary input voltage sequence． A series of first order functions 39。39。)( ?nUtU ?? or )(39。 when E or EC are equal to 0, Interpolation algorithm is adopted to calculating the control output U’ instead of quantization. The method of interpolation calculation is shown in . The U(I,j),U(i+1,j),and U(i+1,j+1) are four point in the lookup table ,and the value of U’ can be calculated based on them. 4. Experimental research The position precision of the new type of piezoelectric electrohydraulic servo valve system is significantly reduced due to the effect of nonlinearity and uncertainty． In this paper，the highprecise fuzzy control method with Preisach hysteresis nonlinear model in feedforward loop was developed to solve this problem. To demonstrate the effectiveness of this proposed control method ， a series of experiments were performed on the new type of piezoelectric electrohydraulic servo valve system under various conditions． The experimental setup was built. which consisted of industrial control puter, hydraulic pressure experimental bench ， pumping station ， PES arbitrary waveform generator(Model AG1200， Yokogawa Co． ) and multipurpose FFT analyzer (Model CF5220， Onosokki Co． )． The experiments were conducted under a hydraulic pressure of 7 MPa. Hydraulic pressure experimental bench was used to provide the operational environment for the PESV . Pumping station was used to provide the liquid pressure for hydraulic pressure experimental bench． Waveform generator was used to provide the waveform． Fourier analyzer was used to analyze the experimental result． Industrial control puter was used to receive the position feedback signals and provide control voltage based on the proposed control method． The industrial control puter still includes a 12 bit AD／ DA card (Model PC一 63 l1， Zhongtai Co． )， a power amplifier and program of the proposed control method． Industrial control puter accepts the given signal from waveform generator and position feedback signal through A／ D conversion interface， soon afterwards，