Nozzle Pressure Response Characteristics of Variable Rate System for Unmanned Aerial Applications

Abstract

As interest in the variable rate application (VRA) increases, it is necessary to study the characteristics of the nozzle pressure applied for unmanned aerial applications. In this study, therefore, we analyzed the performance of nozzle pressure responses to the ground velocity in an unmanned rotorcraft test bed. Then, the responses using air chamber and Kalman filter were compared for reducing the pulsation and time delay. For the VRA system test, an unmanned agricultural rotorcraft with a commercial controller was used as a test bed for the VRA of the aerial pesticide application. The VRA system responses with air chamber and Kalman filter were measured when the system was switched on and off during flight maneuvers. Then, the lag time and pulsation were determined. Pulsation of nozzle pressure has been conventionally relieved using an air chamber, but the response of the nozzle pressure is delayed by 2.6–3.8 s. This delay could lead to a significant error in the application rate and uniformity in the case of high spraying speeds. Therefore, the air chamber method was excluded from the use in variable control applications. As an alternative, the pressure response was gently induced by employing the Kalman filter in the control S/W. The optimal covariances of the Kalman filter were found to be R = 100 and Q = 1, and the response time of the nozzle pressure was estimated to be less than 0.1 s. To alleviate the time lag and pulsation of nozzle pressure, it was necessary to reduce the variation of the pulse width modulation (PWM) voltage relative to the ground velocity. The VRA system with Kalman filter would be implemented in unmanned rotorcraft for aerial application purpose. Consequently, the adaptation of Kalman filter technology enables to improve spray uniformity along the flight trajectory.