(A) study on analysis and design of a poppet type electropneumatic servovalve

Abstract

Pneumatic drives are becoming increasingly popular as they offer an attractive alternative to hydraulic and electromechanical actuation for low to medium power requirements. Because of low cost and ease of maintenance electropneumatic servo systems are used in new applications such as small robots and manipulators. They are also clean, reliable, and lightweight. In such systems, servovalves are essential components, as they serve as amplifiers of the fluid power. Spool-sleeve type valves have been traditionally used as servovalves for pneumatic power control. The spool-sleeve type valves must have a close matching tolerance for small air leakages. Therefore, the machining cost for such valves rises, and air contamination becomes a sensitive problem. There is also large leakage of the air flowing through the radial clearance between the spool and the sleeve at null. In this study, A new poppet type electropneumatic servovalve is proposed, which utilizes a poppet in the metering stage, and is controlled by a digital controller. The valve actuator is of a moving-coil type, and a capacitance-type position sensor is developed to sense the position of the poppet. Compared to the existing spool-sleeve type valves, the proposed valve can be fabricated at low cost; it is also insensitive to air contamination, and does not have the problem of air leakage at null. However, the proposed valve has relatively larger friction than spool-sleeve type valves because O-rings are installed in the peripheral grooves of the balance pistons of the poppet to prevent external leakage. This friction is a dominant factor that limits the performance of the poppet position control. Since flow control in the valve is achieved by positioning the poppet, valve performance can be improved by friction compensation control. As the valve is controlled by a digital controller, if the friction is precisely modeled the friction force can be compensated in the controller by inputting the signal corre...