Robust μ-Controller for Hydraulic Spool Valve, Pilot Operated with Switching Micro Valves

Jordan Kralev,Alexander Mitov,Tsonyo Slavov

doi:10.3390/en14164817

Abstract

Hydraulic spool valve, pilot operated with bi-state switching micro valves is a low-cost alternative to the conventional proportional and high-response valves. However, high-frequency switching causes variations in the control flow which limits achievable spool tracking error. This paper presents the design of a robust μ-controller for the spool position reference tracking synthesized with D-K iterative procedure. Furthermore, in order to reduce wind-up effects in the closed-loop, the μ-controller is decomposed to a canonical observer and state feedback components which allows explicit introduction of the saturated control signal in the controller equations. The uncertainty model required for the μ-synthesis is inferred from the nonlinear hydraulic model by identification of a Box–Jenkins model set characterized by its parameter covariance matrix. The regulator is implemented in a 32-bit programmable logic controller (PLC) and its performance is experimentally verified on a laboratory test bench of electro-hydraulic power steering system.

Highlights

The purpose of the article is to design a μ-controller for the spool position tracking of a proportional spool valve, pilot operated by switching micro valves such that closed-loop control system to ensure robust stability and robust performance in presence of uncertain dynamic response of the spool model
The implemented test rig layout includes a MC012-022 microcontroller, a programmable joystic (JS6000) for supplying operator commands, and the spool valve, pilot operated with switching micro valves, which drives a hydraulic servo cylinder
The main contribution of the article is successful design and application of a high-order robust controller to control the position of a spool valve through switching digital valves

Summary

Introduction

A well-recognized benefit of using fluid power actuators compared to electrical actuators is the fast response time over large bandwidth, ability to produce extremely high forces or torques, high power density, relatively small and compact dimensions, and high reliability and durability. There are numerous applications fields for the hydraulic actuators such as in automotive, aerospace and manufacturing. Work of the authors is mainly focused on the electro-hydraulic steering units for low speed mobile machines. The steering unit is essentially a hydraulic servo system which demands fast and precise reference tracking of the machine operator commands. The classical design of the hydraulic servo units is as a direct or pilot operated proportional spool valve. The position of the spool valve is sensed by a linear transnational differential transducer and manipulated with the help of a proportional solenoid [1]

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