Speed control of an autonomous electric vehicle for orchard spraying

• We developed an electric robot sprayer in orchards and vineyards by converting a powertrain system for automobiles. • We examined rolling resistance coefficients on asphalt, gravel, soil, and grass surfaces to apply to the speed controller. • The proposed speed controller compensated for traveling resistance and improved control performance on off-roads. We developed an autonomous electric vehicle for orchard spraying, termed a spraying robot. Traveling resistance varies depending on vehicle weight, the front sideslip angle, and surface slope. The vehicle weight must change while traveling, especially for the spraying robot. To adapt to changes in those resistances, it is necessary to develop a speed controller. This research focused on rolling and slope resistance as a traveling resistance, which depends on the vehicle weight. We modeled the resistance and developed a feedforward controller with a proportional-integral-derivative (PID) feedback controller. The developed controller (FF-PID) was compared with a simple PID controller in simulation. The FF-PID was verified to be more rapid and stable response than the PID. Moreover, the FF-PID responded adaptively when the vehicle weight changed. Compared to the PID, the FF-PID reduced the error to the target speed by 50 % during sideslip angle changes and by 48 % during slope angle changes. Finally, we simulated a spraying task based on actual traveling data in a vineyard, factoring in the vehicle weight, steering angle, and slope angle change. The results showed that the FF-PID reduced error by 32 %. This research improved the performance of the spraying robot’s speed controller by modeling traveling resistance in an orchard environment.