Research Papers

Fault-Tolerant Actuating Pressure Controller Design for an Electrohydrostatic Actuator Experiencing a Leaky Piston Seal

[+] Author and Article Information
Guangan Ren

School of Mechanical Engineering
and Automation,
Northeastern University,
Shenyang 110819, China
e-mail: 369220424@163.com

Jinchun Song

School of Mechanical Engineering
and Automation,
Northeastern University,
Shenyang 110819, China
e-mail: jchsong@mail.neu.edu.cn

Nariman Sepehri

Department of Mechanical Engineering,
University of Manitoba,
Winnipeg, MB R3T 5V6, Canada
e-mail: nariman.sepehri@umanitoba.ca

1Currently a Ph.D. student at the University of Manitoba.

2Corresponding author.

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received May 7, 2016; final manuscript received November 21, 2016; published online March 22, 2017. Assoc. Editor: M. Porfiri.

J. Dyn. Sys., Meas., Control 139(6), 061004 (Mar 22, 2017) (8 pages) Paper No: DS-16-1237; doi: 10.1115/1.4035348 History: Received May 07, 2016; Revised November 21, 2016

Electrohydrostatic actuators (EHAs), as a class of pump-controlled hydraulic actuators, are known for energy efficiency and easy maintainability. Thus, they can be widely used in the situations where actuating pressure/force control of hydraulic actuators is essential. Examples are automotive active suspension, deep-drawing press, molding machine, and vibration isolation. However, a leaky piston seal in an EHA system can be especially problematic as it is not visually detectable, but causes internal leakage flowing across actuator chambers impairing the performance. This paper employs quantitative feedback theory (QFT) to design a robust fixed-gain linear actuating pressure controller that is tolerant to actuator internal leakage. Since QFT captures uncertainties by templates, representing frequency responses of the plant on Nichols chart, the first step, to design a QFT controller, is to establish plant templates. In doing so, a set of offline parametric system identifications are implemented, and the family of identified models, providing frequency responses, are used to design the QFT fault-tolerant controller. The controller also satisfies the prescribed design tolerances on tracking, stability and sensitivity (disturbance rejection at plant output) under different conditions, including various levels of actuator internal leakage, environmental stiffnesses, and load masses. The ability of the controller to maintain actuating pressure within the acceptable response envelope is demonstrated in experiments. The experimental results show that the system specifications are satisfied despite internal leakage up to 12 L/min.

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Fig. 1

Experimental setup: (a) photograph of experimental test bench and (b) detailed schematic of test rig: 1: servomotor; 2: fixed-displacement hydraulic pump; 3: air pump source; 4: accumulator; 5: check valve; 6: actuator; 7: ball valve; 8: flow meter; 9: needle valve; 10: load; 11: spring; 12: tank

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Fig. 3

Experimental data of actuator movement against a 125 kN/m spring in the presence of actuator internal leakage of 4.8 L/min on average and load mass of 15 kg: (a) input chirp excitation, (b) actuating pressure response, and (c) internal leakage

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Fig. 4

The results of CIFER identification for the experiment shown in Fig. 3: (a) magnitude, (b) phase, and (c) measured coherence

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Fig. 5

Two degrees-of-freedom (DOFs) feedback system structure

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Fig. 6

Plant templates at selected frequencies on Nichols chart

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Fig. 7

QFT bounds B(ω) and nominal loop transmission L(,α0)

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Fig. 8

Verification of QFT controller considering various levels of actuator internal leakage, environmental stiffnesses and load masses: (a) normalized tracking specification (time domain), (b) tracking specification (frequency domain), (c) stability specification, and (d) sensitivity specification

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Fig. 9

Experimental response to a 3 MPa step input for actuator working under normal (no leak) condition, moving a load mass of 12 kg against a 125 kN/m spring: (a) actuating pressure (normalized), (b) control signal, and (c) actuating pressure error

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Fig. 10

Experimental response to a 3 MPa square-wave input for actuator working against a 125 kN/m spring and moving a mass of 12 kg in the presence of increasing leakage flow: (a) actuating pressure (normalized), (b) control signal, (c) actuating pressure error, and (d) leakage flow

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Fig. 11

Experimental responses to various step inputs in the presence of different levels of actuator internal leakage. The experiments include motions against a 125 kN/m spring and a 82 kN/m spring for an actuator moving load masses of 12 kg and 15 kg: (a) actuating pressure, (b) control signal, (c) actuating pressure error, and (d) leakage flow.




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