Tracking Control of a Spool Displacement in a Direct Piezoactuator-Driven Servo Valve System

This paper presents tracking control performances of a piezostack direct drive valve (PDDV) operating at various temperatures. As a first step, a spool valve and valve system are designed to be operated by the piezoactuator. In this study, the stacked piezoelectric actuator, which is lead–zirconate–titanate (PZT) ceramic is used for control of spool displacement. An aerogel is used for heat insulation since the PZT piezoelectric actuator has low Curie temperature. After briefly describing the operating principle, the governing equation of the proposed valve system is driven including the piezostack actuator. Subsequently, an experimental apparatus for investigating the effect of temperatures on the performances is set up. The PDDV is installed in a large-size heat chamber equipped with electric circuits and sensors. A classical proportional-integral-derivative (PID) controller is designed and applied to control the spool displacement. In addition, a fuzzy algorithm is integrated with the PID controller to enhance the performance of the proposed valve system. The gain of PID changes to satisfy the target frequency and displacement according to input frequency and operating temperature. Therefore, fuzzy algorithm with two input variables that are frequency and temperature can determine the gain of PID controller. The tracking performance of a spool displacement is tested by increasing the temperature and exciting frequency up to 150°C and 200 Hz, respectively. It is shown that the tracking performance heavily depends on both the operating temperature and the excitation frequency.