Tactile feedback of steer-by-wire agriculture machines
Date
2009
Authors
Xu, Hong
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
The implementation of control systems in the automotive industry enabled by
electronic actuators is referred to as X-by-wire technique. The application of steerby-
wire technique in agriculture machine simplifies manufacture, decreases machine
costs and increases machine flexibility. Previous study of Applied Controls Laboratory
focused on vehicle velocity control through electrical signals, which leads
to drive-by-wire agriculture machines without tactile feedback. Current research
focuses on the tactile feedback control of steer-by-wire vehicles where the research
goal is to improve the steering maneuverability comparable to traditional mechanical
steering systems. A DC motor is regulated according to the movement status of
the steering wheel to produce a smooth feedback force to the operator. A prototype
windrower provided by Case New Holland LLC is modulated, developed and tested
for the research where a conventional steering input system is modified by being
mounted with a steering input sensor and a DC geared motor. The steering input
system, including the steering wheel, the steering column, the mounted sensor and
the DC geared motor is mathematically modeled. The permitted angle of a steering
wheel has been made up to 720 degrees in both clockwise and counter-clockwise directions
whose big movement range brings a nonlinearity property into the steering
mechanism. Furthermore, an H-bridge circuit has been designed and added to the
control unit to enable the DC geared motor to turn in both directions. To produce
the desired feedback force, two cascaded controllers have been designed. The first
is a hybrid controller with multiple control branches developed to regulate the DC
motor to produce the desired feedback force. Each control branch is a proportional integral (PI) controller. The working ranges of each branch of the controller are
decided according to the angle and angular velocity of the steering wheel. The stability
of the designed closed loop controller is proved by Routh stability criterion
and extensive simulations have been performed to verify the stability of the controller.
The second is a current sense controller which is designed by the root locus
method to regulate the electrical current of the DC geared motor that varies due to
environmental changes. Verified by simulation, an accurate control of the feedback
force can be achieved.