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Research Papers

A Complete Analysis and a Novel Solution for Instability in Pump Controlled Asymmetric Actuators

[+] Author and Article Information
Hakan Çalışkan

Mechanical Engineering Department,
Middle East Technical University,
Çankaya, Ankara 06800, Turkey
e-mail: chakan@metu.edu.tr

Tuna Balkan

Mechanical Engineering Department,
Middle East Technical University,
Çankaya, Ankara 06800, Turkey
e-mail: balkan@metu.edu.tr

Bülent E. Platin

Mem. ASME
Mechanical Engineering Department,
Middle East Technical University,
Çankaya, Ankara 06800, Turkey
e-mail: platin@metu.edu.tr

1Corresponding author.

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received September 19, 2014; final manuscript received May 1, 2015; published online June 24, 2015. Assoc. Editor: Heikki Handroos.

J. Dyn. Sys., Meas., Control 137(9), 091008 (Sep 01, 2015) (14 pages) Paper No: DS-14-1380; doi: 10.1115/1.4030544 History: Received September 19, 2014; Revised May 01, 2015; Online June 24, 2015

This paper addresses the stability problem of pump controlled asymmetric hydraulic actuators and proposes a physical solution for it. The system under consideration utilizes a shuttle valve to compensate for unequal flow rates due to the asymmetry in the actuator. Possible hydraulic circuit configurations resulting from various valve positions are defined on the load pressure versus velocity plane and a generalized linear model of the system is derived. The investigation shows that there exists a critical load pressure region in which any equilibrium point requiring a partially open spool position is unstable during the retraction of the actuator. A particular valve underlap is proposed in order to avoid the instability and a shuttle valve selection guide is presented. Theoretical findings are validated by both numerical simulations and experimental tests. Results show that the undesired pressure oscillations are removed up to certain actuator velocities with the use of an underlapped shuttle valve.

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References

Figures

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Fig. 3

Shuttle valve with a closed center spool

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Fig. 4

Possible valve positions and asymptotic stability limit in the critical load pressure region

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Fig. 2

Working principle of the proposed hydraulic system

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Fig. 1

Pump controlled circuit concept for an asymmetric actuator

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Fig. 5

Possible circuit configurations for partially opened valve positions

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Fig. 6

Simulation model responses: asymptotically stable operation range of underlapped shuttle valve

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Fig. 7

Simulation model repose and experimental test results comparison

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Fig. 8

Experimental test setup

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Fig. 9

Open-loop pressure responses to external load and pump speed inputs with an overlapped shuttle valve

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Fig. 10

Open-loop pressure responses to external load and pump speed inputs with an underlapped shuttle valve

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