| The velocity of agricultural vehicles varies considerably due to the constantly changing ground conditions of the offroad environment in which they operate. It would be desirable to have a controller that can automatically compensate for such variations and allow the operator to focus on other processes taking place around the vehicle. In applications where the system is mass produced there are often variations in the hardware comprising the plant. This leads to varying plant dynamics from vehicle to vehicle which have to be compensated for. Concerns related to operator comfort also apply restraints on the performance of the controller. The vehicle at the focus of this study is a self-propelled windrower with a hydrostatic transmission. A cascade control design incorporating an electrical current controller, cylinder position controller and velocity controller is proposed. The cylinder position controller uses a set of gain scheduled lag compensators in series with a sequence of segmented deadzone inversions. The deadzone inversions compensate for nonlinear valve dynamics. Results from the implementation of a simple PID controller indicated the existence of varying drive train dynamics between acceleration and decceleration. A variable PID controller was designed to compensate for this. Further, two intelligent control strategies, namely supervisory control and adaptive control, are investigated to automatically compensate for individual vehicle to vehicle variation. A stability analysis of the closed loop controllers is performed. Experimental results from a self-propelled windrower are used to demonstrate the effectiveness of the control systems. |
