A novel piezohydraulic aerospace servovalve. Part 1: design and modelling

Abstract

Servovalves are compact, accurate and high-bandwidth modulating valves widely used in aerospace, defence, industrial and marine applications. However, manufacturing costs are high due to high part count and tight tolerances required, particularly in the first stage of the valve, and due to manual adjustments required as part of the set-up process. In this research, a novel servovalve concept is investigated that has the potential to be more cost-effective. In particular, for the first time, a piezoelectric first-stage actuator is developed to move a servovalve spool using the deflector jet principle; this is especially suited to aerospace actuation requirements. In the new valve, the conventional electromagnetic torque motor is replaced by a multilayer bimorph piezoelectric actuator. The bimorph deflects a jet of fluid to create a pressure differential across the valve spool; hence the spool moves. A feedback wire is used to facilitate proportional spool position control via mechanical feedback. The bimorph is directly coupled to the feedback wire and is immersed in hydraulic fluid. A high-order non-linear model of the valve has been developed and used to predict valve static and dynamic characteristics and is described in this article. This makes use of stiffness constants derived analytically for the bimorph-feedback wire assembly and cross-referenced to finite element analysis predictions. The model of the flow force acting on the deflector is an approximation of the force characteristic found from computation fluid dynamic analysis. The measured characteristics of the prototype valve are in good agreement with the simulation results and prove that the operational concept is viable.

Non-linear control of a hydraulic piezo-valve using a generalised Prandtl–Ishlinskii hysteresis model

“…These valves are distinguished by control based on spool or actuator position feedback provided by electrical position transducers. Conversely, [18] presents an aerospace servovalve where a mechanical feedback wire is retained between the spool and piezoelectric bender, which is currently an industry requirement for safety-critical flight controls.…”

Dynamic Modelling and Performance of a Two Stage Piezoelectric Servovalve

“…Servohydraulic control systems are used in applications where high forces, fast response time and high power to weight ratios are required [1]. A two-stage servovalve converts an electrical signal into the movement of a fluid-metering spool via a hydraulic amplification stage.…”

Open loop control of piezoelectric tube transducer

“…The play operator connects the input signal v with an output z and the relation between them is described by two envelop functions γr, γl and threshold r. The following operators and density functions are changing and dependent on value of jthreshold r described by (4). If the shapes of the increasing and decreasing hysteresis slopes are very similar, simplifying the model by using the same envelop function to describe the increasing and decreasing shapes of the hysteresis can be considered as in (5). The advantages of this approach are faster parameter estimation, a simpler model.…”

“…Precise displacement measurements are executed via a laser displacement sensor optoNCDT 1700 with 0.5 µm resolution and a 2 mm measurement range (2). The number (4) is a two-channel high voltage amplifier with a two-channel control signal input (5). The high voltage amplifier was specially designed for these tests and is based on an APEX P91 high voltage operational amplifier.…”

“…in micro-and nano-positioning stages [1,2], vibration control [3], fluid power pilot valves [4][5][6], energy harvesting [7,8], and other areas in which conventional solutions cannot fulfil the increasing requirements with regard to fast response, high precision, high speed positioning and low energy costs. Piezoelectric actuators use inversed piezoelectric effect which converses applied electrical field to the surface of the material into deformation of the material.…”