Stable and robust vehicle steering control using an overhead guide in greenhouse tasks

• Design and construction of an autonomous vehicle for greenhouse tasks.
• Development of a robust and stable control algorithm for steering a vehicle with an overhead guide.
• System stability analysis by analytical formulation and numerical simulation.
• Multibody simulation using MSC.ADAMS to better simulate rough working conditions.
• Proof-of-concept experiments testing the accuracy and stability of the vehicle.

We have developed an autonomous vehicle steering control algorithm to aid with harvesting and spraying tasks in greenhouses to alleviate the problem of shortage of workers. We use an overhead guide constructed in the greenhouse to mark the desired path of the vehicle. A rigid bar is then connected from the guide to the vehicle. The vehicle steers and corrects itself by sensing the angle and distance of the vehicle from the guide. The control algorithm was developed for a two-dimensional kinematic vehicle model which was found to be valid for low-speed vehicles. The steering control was examined by numerical simulation in order to investigate the effects of parameters such as control-point location on stability deviations of the vehicle path. The asymptotic stability of the system was verified analytically and confirmed using numerical simulations. The control system was then simulated using a multibody dynamics simulation in conditions that better simulated an agricultural environment, thus confirming that the control system also maintained stability under rough conditions. Finally, in accordance with the control algorithm and the simulations, a proof-of-concept prototype of the vehicle was developed and the control algorithm was successfully deployed on a set of experiments.