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Research Papers

Energy Optimal Control of Servo-Pneumatic Cylinders Through Nonlinear Static Feedback Linearization

[+] Author and Article Information
Jihong Wang

School of Engineering,  University of Warwick, Coventry CV4 7AL, UKjihong.wang@warwick.ac.uk

Tim Gordon1

Department of Mechanical Engineering,  University of Michigan, Ann Arbor, MI 48109tjgordon@umich.edu

1

Corresponding author.

J. Dyn. Sys., Meas., Control 134(5), 051005 (Jun 05, 2012) (11 pages) doi:10.1115/1.4006084 History: Received June 14, 2011; Revised January 09, 2012; Published June 05, 2012; Online June 05, 2012

Although pneumatic actuators are widely used in industry, they have two major weaknesses—nonlinearities associated with compressibility of air and low energy efficiency. The former limits its applicability whenever accurate positioning is required, and the latter has a negative impact on users through increased energy costs. This paper addresses these issues with the aim of developing a widely applicable servo control strategy, which combines improved tracking accuracy and energy efficiency. A detailed actuator system model is linearized through nonlinear input–output feedback linearization, and the energy optimal velocity profile is derived. Simulation and experimental studies indicate that energy efficiency improvements of 3–7% are possible, while tracking accuracy can be ensured. The method is suitable for real-time implementation and is cost effective; it requires the implementation of an improved velocity profile, while hardware components do not need to be altered.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Co-ordinate system of a pneumatic cylinder

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Figure 2

The test rig/experimental system: (a) PC-based control system and (b) photograph of the test rig

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Figure 3

Simulated and measured velocities (step response): (a) 20% valve displacement and (b) 80% valve displacement

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Figure 4

Illustration of the sinusoidal and trapezoidal velocity profiles

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Figure 5

Trajectories with the terminal pressures of 2.5 bars

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Figure 6

Chamber pressure with terminal pressures of 2.5 bars

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Figure 7

Comparison with a sine wave profile

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Figure 8

Velocity using energy-efficient velocity profile

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Figure 9

Velocity using trapezoid velocity profile

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Figure 10

CACI curves for both velocity profiles

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Figure 11

Simulation results using the feedback control of Eq. 40

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Figure 12

Simulation results using the feedback control of Eq. 41

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Figure 13

Simulation results using the feedback control of Eq. 43

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Figure 14

Piston velocity using the traditional velocity profile

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Figure 15

Piston velocity using the energy-efficient velocity profile

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Figure 16

Examples of CACI curve with supply pressures: (a) 6 bars and (b) 8 bars

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