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Research Papers

A Novel in Field Method for Determining the Flow Rate Characteristics of Pneumatic Servo Axes

[+] Author and Article Information
Paolo Righettini

Department of Engineering,
University of Bergamo,
Dalmine 24044, Italy
e-mail: paolo.righettini@unibg.it

Hermes Giberti

Mechanical Department,
Politecnico di Milano,
Milano 20156, Italy
e-mail: hermes.giberti@polimi.it

Roberto Strada

Department of Engineering,
University of Bergamo,
Dalmine 24044, Italy
e-mail: roberto.strada@unibg.it

Contributed by the Dynamic Systems Division of ASME for publication in the Journal of Dynamic Systems, Measurement, and Control. Manuscript received May 25, 2012; final manuscript received March 6, 2013; published online May 21, 2013. Assoc. Editor: Evangelos Papadopoulos.

J. Dyn. Sys., Meas., Control 135(4), 041013 (May 21, 2013) (8 pages) Paper No: DS-12-1182; doi: 10.1115/1.4024010 History: Received May 25, 2012; Revised March 06, 2013

Several strategies, in order to improve an actuator's control and to increase the bandwidth, consider the relationship between the valve's driving signal and the air flow rate. Such an approach to the control strategy takes advantage of the evaluation of the valve's characteristic parameter, known as sonic conductance. The sonic conductance can be measured following the procedure stated by the standard ISO 6358. Nevertheless, the measurement carried out according to this standard is very expensive in terms of time and air consumption. In this paper, an alternative method to evaluate the sonic conductance is presented. The method is based on a new practical approach: the sonic conductance is evaluated leaving the valve mounted on the actuator and using only the piston's position transducer. The steady state piston's motion allows us to determine the sonic conductance. The new approach allows us to get the conductance in a very short time, without the need to use a proper test bench and pressure transducers. Moreover, performing the measurements directly on the pneumatic axis allows us to characterize not only the valve but the duct connecting the valve to the actuator's chamber too.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

ISO 6358 test rig scheme

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Fig. 2

5/3 proportional directional flow control valve

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Fig. 3

Operational scheme of a pneumatic axis

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Fig. 4

Test rig according to ISO 6358

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Fig. 5

2–3 duct's conductance versus command signal, according to ISO 6358 method

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Fig. 6

Temperature behavior during a set of tests

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Fig. 8

Position versus time (dark lines) and slopes at the stroke's end (light lines)

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Fig. 9

Piston's velocity versus position (black lines) and slopes at the stroke's end (gray lines)

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Fig. 10

Downstream/upstream pressure ratio versus position

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Fig. 11

ΔP versus piston's position

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Fig. 12

Pressure versus piston's position

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Fig. 13

Comparison between the terms of inequality in Eq. (19); P·/P (black lines), (Ax·)/(Ax + V*) (gray lines)

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Fig. 14

Steady state velocity method versus ISO method

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Fig. 15

Percentage variation with respect to ISO method

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