Abstract
Making use of a direct drive servovalve's driving current, which is in proportion to the driving force, and the spool displacement got from the build-in LVDT, it is possible to get the state variables such as flow force, flow rate and load pressure for the purpose of valve control without attaching other transducers on the servovalve. In this paper, experiments are conducted under the conditions of different loads. With PWM driving, no hysteresis appears no matter what the flow rate is. Because of the flow force compensation on the spool of the valve used in the experiment, an empirical equation is made for the calculation of flow rate from the measured flow force. Under different load conditions, the calculated flow rates are in consistence with the measured ones. Then load pressures are obtained from the calculated flow rates, with the flow coefficient acquired by empirical equations. The calculated load pressures show good agreement with the measured results.
