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TECHNICAL PAPERS

Modeling and Control of a Wheel Loader With a Human-in-the-Loop Assessment Using Virtual Reality

[+] Author and Article Information
Roger Fales

Virtual Reality Applications Center,  Iowa State University, Ames, IA 50014falesr@missouri.edu

Erik Spencer, Kurt Chipperfield, Frank Wagner, Atul Kelkar

Virtual Reality Applications Center,  Iowa State University, Ames, IA 50014

J. Dyn. Sys., Meas., Control 127(3), 415-423 (Sep 07, 2004) (9 pages) doi:10.1115/1.1985437 History: Received February 26, 2004; Revised September 07, 2004

This paper presents dynamic modeling, controller design, and virtual reality (VR)-based human-in-the-loop real-time simulation for a wheel loader control system. In particular, a loader with electrohydraulic actuation is considered. A detailed nonlinear dynamic model is developed for the hydraulic system and the loader linkage. The hydraulic model includes a load sensing pump, valves, and cylinders. The linkage model represents a two degree of freedom loader with lift and tilt functions. A linear quadratic Gaussian based robust controller is designed for automatic bucket leveling to assist the operator by keeping the angle of the bucket leveled while the boom is in motion. The closed-loop control system design is tested with a nonlinear model in a real-time VR simulation. In the VR simulation, the operator interacts with the model using a joystick input. The loader linkage geometry is displayed to the operator in real time using a VR display. The controller performance was assessed in the VR environment. As expected, the controller was found to provide a significant improvement in the accuracy of the bucket leveling, particularly in the case of a novice operator controlling the linkage motion. While prototypes cannot be eliminated, the VR simulation combined with realistic physics and control dynamics provided a useful tool for evaluating hydraulic systems and controls with less reliance on prototype machines.

Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 2

Tilt valve schematic

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Figure 3

Lift valve schematic

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Figure 4

Load sensing pump schematic

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Figure 5

Diagram of the loader linkage

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Figure 7

Closed-loop system with LQG controller/estimator

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Figure 8

Tracking of reference lift position and tilt position with the linear model and LQG controller

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Figure 9

Tracking of reference lift and tilt positions and with the nonlinear model and LQG controller

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Figure 10

Tilt error and lift position output of the VR simulation controlled by a novice operator

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Figure 11

Tilt error and lift position output of the VR simulation with the level lift controller aiding the operator

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Figure 12

Ramp input simulation result using the LQG controller design and the linear model

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Figure 13

Level lift simulation result using the LQG controller design and the nonlinear model

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Figure 14

VR interface block diagram

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Figure 15

VR communication function subprogram flow chart

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Figure 16

VR display from inside the operator’s cabin

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Figure 17

VR display from the side of the machine

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