High resolution control system for a pressure-responsive positioning device

摘要

Two magnetic valves, one of which reduces the pressure and the other one of which increases the pressure by which the displacement of a positioning member is controlled, only one of them operated at a time in accordance to the sign of the error signal, are operated in a pulsed mode with variable pulse width when the error signal is within a range of low absolute value and in a continuous mode of operation when the error signal has a higher absolute value. Variation of the magnitude of the error signal within the intermittent valve operation range controls pulse width variation. Hysteresis is provided in a transition between operating modes of a valve by a time delay of the mode change after the error signal has risen or fallen past a threshold value of signal. High displacement resolution is obtained as well as independence from effect of temperature drifts and magnetic valve characteristics.