Research on autonomous driving technology for a robot vehicle in mountainous farmland using the Quasi-Zenith Satellite System

Abstract

The centimeter-level augmentation service (CLAS) provided by Michibiki (also known as the Quasi-Zenith Satellite System (QZSS)) can be utilized as a navigation sensor for a robot vehicle in orchards, which are often located in mountainous areas with steep slopes. Buildings, windbreaks, and the inclination of the antenna affected the CLAS less than they did the virtual reference station real-time kinematic (VRS-RTK) method, which is one of the most common navigation sensors for autonomous driving in agriculture. The time to first fix (TTFF) of the CLAS was 60 s earlier near buildings and 90 s earlier in case of a tilted antenna compared to that of the VRS-RTK. Moreover, the CLAS does not depend on an internet signal such as that provided for mobile broadband, since it uses augmentation information from the QZSS. A positioning test in a real vineyard, where grapevines are trained over vertical trellises, revealed that the CLAS could acquire FIX solutions constantly, whereas the VRS-RTK could not because of weak internet signals. The accuracy of the CLAS was less than 6.4 cm for a 95% confidence interval at static positioning and less than 3 cm root mean square (RMS) at dynamic positioning. A robot vehicle navigated by the CLAS autonomously traveled two paths, including a turning maneuver, with less than 9 cm RMS and less than 20 cm MAX. The results showed that the CLAS enabled the robot vehicle to work autonomously without any collisions in an actual vineyard.