Dynamic Modelling and Performance of a Two Stage Piezoelectric Servovalve

Abstract

This paper describes the design, simulation and testing of a piezoelectrically-actuated two stage spool valve. The first stage is a small spool controlled by a piezoelectric ring bender and the second stage is a closed loop position controlled main spool. A dynamic mathematical model of the valve has been derived.Step response tests for both the first stage and second stage are presented, and experimental second stage frequency response results are shown. The mathematical models for the amplifier, first stage and second stage spool behaviour are validated against experimental data. The second stage spool behaviour is found to be very sensitive to the first stage flow characteristics. In addition, the displacement of the hydraulic fluid by the piezoelectric ring bender, from one side of the piezoelectric ring bender to the other, had a significant impact on the valve characteristics.

A Review of Electro-Hydraulic Servovalve Research and Development

“…Analytical models are also available in the literature to calculate K t and K m (see, e.g., Gordić et al 2004). With reference to Figure 3, assuming that the main spool (having mass M ) moves with a displacement denoted by X, the following equations can be applied to analytically study the main stage valve (Gordić et al, 2004, Persson et al, 2016, Li et al, 2018. The overall actuation force acting on the main spool is to be calculated as the product of the pressure difference between the left and right control chambers (p l − p r ) and the spool area A.…”

“…In (Persson et al, 2015) and (Persson et al, 2016), a two stage servovalve was designed in which the first stage is composed of a four-way three-position small spool controlled by a piezoeletric ring bender. The flow through the small spool is capable of controlling the spool of a main stage according to the hydraulic scheme shown in Figure 21a.…”

A dual lane piezoelectric ring bender actuated nozzle-flapper servo valve for aero engine fuel metering

“…In a recent valve prototype, a ring bender was used as the pilot stage actuator [15][16][17]. This time the pilot stage was a miniature spool with some overlap used to minimize pilot stage leakage flow.…”

“…In comparison with actuators used in the previous designs summarised in table 1, a ring bender is a light and compact actuator providing a combination of force and displacement ranges which is very suitable for this application. High performance multi-layer ring benders have only become commercially available in the last few years, and only used previously in a servovalve application by Persson et al [16]. However, unusually, the pilot flow in Persson's valve is controlled by a miniature spool, and for which driving actuator would normally be expected to be able to supply a high 'chip shear force' (typically ∼100 N) to prevent jamming by contaminant particles in the fluid, which is not easy to achieve with a ring bender.…”

Non-linear Control of a Piezoelectric Two Stage Servovalve

“…In order to deflect the ring bender in both directions the electrodes are combined into three groups, as shown in fig. 1 (b) [8].…”