Tactile feedback of steer-by-wire agriculture machines
University of Delaware
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.