A Predictive Control Strategy to Offset-Point Tracking for Agricultural Mobile Robots

TL;DR

This paper introduces a predictive control method for agricultural robots that models attached implements as offset points, significantly improving path-tracking accuracy and safety.

Contribution

It extends existing control strategies by explicitly modeling implement offset points and accounts for slip and lever-arm effects in Ackermann vehicles.

Findings

Reduces median tracking error by 24% to 56%.

Decreases peak errors during curvature transitions by up to 70%.

Enhances operational safety near crop rows.

Abstract

Robots are increasingly being deployed in agriculture to support sustainable practices and improve productivity. They offer strong potential to enable precise, efficient, and environmentally friendly operations. However, most existing path-following controllers focus solely on the robot's center of motion and neglect the spatial footprint and dynamics of attached implements. In practice, implements such as mechanical weeders or spring-tine cultivators are often large, rigidly mounted, and directly interacting with crops and soil; ignoring their position can degrade tracking performance and increase the risk of crop damage. To address this limitation, we propose a closed-form predictive control strategy extending the approach introduced in [1]. The method is developed specifically for Ackermann-type agricultural vehicles and explicitly models the implement as a rigid offset point, while accounting for lateral slip and lever-arm effects. The approach is benchmarked against state-of-the-art baseline controllers, including a reactive geometric method, a reactive backstepping method, and a model-based predictive scheme. Real-world agricultural experiments with two different implements show that the proposed method reduces the median tracking error by 24% to 56%, and decreases peak errors during curvature transitions by up to 70%. These improvements translate into enhanced operational safety, particularly in scenarios where the implement operates in close proximity to crop rows.