Development of a Direct-Drive Servo Valve With High-Frequency Voice Coil Motor and Advanced Digital Controller

There is increasing demand for the hydraulic direct-drive valve (DDV) due to its higher reliability than conventional two-stage servo valves. The objective of this paper is to propose a new DDV with high-frequency voice coil motor (VCM) and advanced digital controller. A permanent magnet Halbach array is employed in the design of VCM to generate high flux density in the air gap, and thus increase force output. Both finite-element analysis and experiments are conducted to validate the performance improvements of VCM. A digital controller based on DSP and field-programmable gate array is developed to control the valve motion. A hybrid controller based on disturbance observer and sliding model control (SMC) scheme with a state-space observer is proposed for the DDV system. The static testing indicates that the discrete-time SMC with unmodeled load compensator improves the control accuracy and robustness of the system. The dynamic response testing indicates that the frequency bandwidth of the system is up to 450 Hz for 25% of full stroke. It is higher than existing commercial VCM-DDVs.