Abstract
In this paper, the hysteresis characteristics of a commercial direct drive hydraulic servovalve are investigated experimentally in cases by adding dither into a low speed driving signal, a PWM drive and with fluid flowing through the valve. It is considered that hysteresis is caused by Coulomb friction between the spool and the sleeve. In the case of adding a dither signal, computer simulation was also conducted. Simulation results show that the average friction force approaching zero is an important factor in hysteresis reduction. Experimental results show that the fiction characteristic obtained under a semi-static condition changes because of spool vibration in a radial direction, which is caused by dither, PWM or oil flow through the valve. For a direct drive hydraulic servovalve, it is considered that a dither's hysteresis reducing effect can not be discussed by focusing only on velocity amplitude.
