Proportional pneumatic fin actuator system without feedback control

Abstract

An actuator system having a motor that drives a pneumatic spool valve to a known position based upon the number of step commands delivered to it. Valve ports or passages uncovered by the net position difference between the spool valve and a piston create gas flow to or from a control chamber. This gas flow causes a pressure differential across the face of the piston, inducing the piston to follow the spool valve. In this two-stage system, the piston acts as a force amplifier so that large forces and/or inertias may be actuated by positioning the motor. During steady state conditions, the piston achieves the same position as the spool valve is. Proportional control and very accurate positioning of the piston are provided without active position or position rate feedback control.