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Technical Briefs

Passivity-Based Impact and Force Control of a Pneumatic Actuator

[+] Author and Article Information
Yong Zhu

Department of Mechanical Engineering, Vanderbilt University, Nashville, TN 37235

Eric J. Barth

Department of Mechanical Engineering, Vanderbilt University, Nashville, TN 37235eric.j.barth@vanderbilt.edu

J. Dyn. Sys., Meas., Control 130(2), 024501 (Feb 29, 2008) (7 pages) doi:10.1115/1.2837430 History: Received March 24, 2006; Revised July 19, 2007; Published February 29, 2008

To carry out stable and dissipative contact tasks with an arbitrary environment, it is critical for a pneumatic actuator to be passive with respect to a supply rate consisting of the spool valve position input and the actuation force output. A pseudo-bond graph model with the inner product between spool valve position input and actuation force output as a pseudo-supply rate is developed. Using this pseudo-bond graph model, an open-loop pneumatic actuator controlled by a four-way proportional valve can be proven to not be passive with respect to the pseudo-supply rate. Conversely, it can also be proven to be passive with respect to the pseudo-supply rate under a closed-loop feedback control law. The passivity of the closed-loop pneumatic actuator is verified in impact and force control experiments. The experimental results also validate the pseudo-bond graph model. The pseudo-bond graph model is intended for passivity analysis and controller design for pneumatic actuation applications where contact stability (such as robotic assembly) and/or stable interaction with a passive environment (such as human-robot interaction) is required.

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Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Bond graph models for (a) a hydraulic actuator and (b) a pneumatic actuator

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Figure 2

A spring-mass system

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Figure 3

Passive valve-actuation schematic. The system produces power when the product of the actuation force Fa and spool position xv is positive (as shown). Feedback is indicated as a virtual link between the actuator force and the valve spool position.

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Figure 8

Impact and force control with the dissipative term. (a) Sensor force, (b) velocity, (c) pressure, and (d) control voltage.

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Figure 7

Impact and force control without the dissipative term. (a) Sensor force, (b) velocity, (c) pressure, and (d) control voltage.

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Figure 6

Experimental setup for impact and force control

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Figure 5

Illustration of passive force control

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Figure 4

Closed-loop feedback control structure

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