Abstract
This paper is a thorough review of innovative architectures of electro-hydraulic servovalves that exploit actuation systems based on piezo-electric materials. The use of commercially available piezo-electric actuators, namely, piezo stacks, amplified piezo stacks, rectangular benders, and ring benders, is very promising for the actuation of the main stages and of the pilot stages of servovalves given the fast response and low weight of piezoelectric materials. The use of these actuators can also allow novel designs to be developed, thus helping manufacturers to overcome the typical drawbacks of commercial servovalves, such as the high complexity and the high internal leakage of the pilot stages of two-stage servovalves as well as the large size and weight of direct-drive servovalves. First, the piezoelectric actuators that can be used for driving servovalves are presented in the paper, and their characteristics are thoroughly discussed. The main novel architectures present in the literature are then explained and compared with the commercial ones, and their performance parameters are discussed to draw conclusions on the prospect that some of these architectures can be used by manufacturers as future designs.
Highlights
Concerning two-stage servovalves, there is sensitivity to contamination in the pilot stage, which can cause premature wear and failure, and a significant quiescent flow in the pilot stage, which consumes a significant part of the input power since oil continuously flows through the pilot stage even when the spool is in the neutral position [1,2,3,4]
The cost of the amplified piezo stack actuators with a diamond amplification mechanism is currently high [23]; the cost could be reduced in the future by the large-scale production of these actuators
The designs in which a bimorph bender is used to actuate the pilot stage of a two-stage servovalve might have an issue concerning the very low actuation force generated by these piezo actuators
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Concerning two-stage servovalves, there is sensitivity to contamination in the pilot stage, which can cause premature wear and failure, and a significant quiescent flow in the pilot stage, which consumes a significant part of the input power since oil continuously flows through the pilot stage even when the spool is in the neutral position [1,2,3,4] Another issue concerned with two-stage servovalves is the complexity of the torque motor, which is made up of many sensitive mechanical and Energies 2021, 14, 4858 electrical parts, such as the flexure tube, being manufactured very accurately in order to achieve the required stiffness. Their operating principles will be introduced, and their performance parameters will be discussed in detail
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