Abstract
The effects of the unevenness of the underlaps of a 4-way valve on the gain constant and the natural frequency of a valve-controlled cylinder and on a pneumatic servo are investigated. Special emphasis is placed on studying parasitic oscillations which occur in a highpressure pneumatic servo with an uneven-underlap 4-way valve. It is observed that when the supply pressure (ps) to the pneumatic servo is high, parasitic oscillations are apt to occur at low load-port pressures (much lower than 0.8ps), but they don't occur at high loadport pressures (higher than 0.8ps). However, the resolution of the pneumatic servo deteriorates as the loadport pressure approaches to the supply pressure. The mechanisms of these phenomena are cleared theoretically. Applying an appropriate dither signal, the pneumatic servo nay be stabilized, and so the parasitic oscillation may disappear, and the resolution of the servo may be also improved. The wave forms of parasitic oscillation obtained by the theoretical analysis resemble the measured ones. The analog computer results agreed well to the measured wave forms.
