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TECHNICAL PAPERS

Impact Control in Hydraulic Actuators

[+] Author and Article Information
P. Sekhavat, Q. Wu

Experimental Robotics and Teleoperation Laboratory, Department of Mechanical and Manufacturing Engineering, The University of Manitoba, Winnipeg, Manitoba R3T 5V6, Canada

N. Sepehri1

Experimental Robotics and Teleoperation Laboratory, Department of Mechanical and Manufacturing Engineering, The University of Manitoba, Winnipeg, Manitoba R3T 5V6, Canadanariman@cc.umanitoba.ca

1

Author to whom all correspondence should be addressed.

J. Dyn. Sys., Meas., Control 127(2), 197-205 (Oct 25, 2004) (9 pages) doi:10.1115/1.1898231 History: Received October 10, 2002; Revised October 25, 2004

Every manipulator contact task that begins with a transition from free motion to constraint motion may exhibit impacts that could drive the system unstable. Stabilization of manipulators during this transition is, therefore, an important issue in contact task control design. This paper presents a discontinuous controller to regulate the transition mode in hydraulic actuators. The controller, upon sensing a nonzero force, positions the actuator at the location where the force was sensed, thus, exerting minimal force on a nonmoving environment. The scheme does not require force or velocity feedback as they are difficult to measure throughout the short transition phase. Also, no knowledge about the environment or hydraulic parameters is required for control action. Due to the discontinuity of the control law, the control system is nonsmooth. First, the existence, continuation and uniqueness of Filippov’s solution to the system are proven. Next, the extension of Lyapunov stability theory to nonsmooth systems is employed to guarantee the global asymptotic convergence of the entire system’s state towards the equilibrium point. Complete dynamic characteristics of hydraulic functions and Hertz-type contact model are included in the stability analysis. Experiments are conducted to verify the practicality and effectiveness of the proposed controller. They include actuator collisions with hard and soft environments and with various approach velocities.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Actuator-environment configuration

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Figure 2

Schematic of the experimental test rig

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Figure 3

Low velocity impact response (2.5in.∕s); — Aluminum, --- Wood.

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Figure 4

Low velocity impact response (6in.∕s); — Aluminum, --- Wood.

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Figure 5

Frequency profile of control signal

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