DEAD ZONE OPTIMISATION IN A HEIGHT CONTROL SYSTEM OF A FIELD SPRAYER

Abstract

Simple on-off control algorithms are often found back in practice. These algorithms compare the target value with a reference value and based on that, there is switched to one or the other direction. Such type of controller drives the system in limit cycle behaviour. Therefore, a dead band is placed around the reference value in order to stop the oscillations. A disadvantage of the dead band is that the accuracy is reduced. As the amplitude of the oscillations is a function of the system parameters, this amplitude can be minimised with respect to system parameters. A methodology based on the describing function technique is developed, estimating the amplitude of the oscillation during limit cycle behaviour and applied to the height control system of field sprayer. By tuning the filter constant of the ultrasonic sensor, measuring the height above the crop, the amplitude of the oscillations during limit cycle behaviour can be reduced, minimising the required dead zone in the control, such that the accuracy of the control system is improved.