# Path Tracking of Agricultural Vehicles Based on 4 WIS-4 WID Structure and Fuzzy Control
## 1 Introduction  
Path-tracking control at low speeds is one of the critical technologies of unmanned agricultural machines contributing to the quality and efficiency of machinery operations. Influenced by the structure of conventional tractors, researchers tend to pay more attention to the front wheel corner speed constraint, which influences path-tracking accuracy [1; 2; 3]. Advanced controller response using aiming pursuit is a commonly adopted path-tracking approach. However, constrained by the minimum steering radius, agricultural machines often take longer to converge to the desired path when the initial deviation is significant, limiting their application in tight facilities such as greenhouses. With the evolution of facility agriculture, the structure of agricultural robots is also innovating and breaking through. The pure pursuit algorithm proposed for the autonomous navigation of a centered articulated robot applied in a cotton field obtained 0.04 m, 0.06 m, and 0.09 m mean absolute error (MAE) through three tests [4]. Using an input map with predefined geospatial coordinates, the pure pursuit algorithm for an articulated steering vehicle platform determines the future heading direction and appropriate coordinates from the input map based on Global Positioning System coordinates and corresponding heading data. It calculates the required steering radius to achieve the looking-ahead distance [5]. A path-tracking controller for a tractor-trailer robot is designed through a purely geometric path-tracking approach [6]. Slip-free motion is achieved by controlling velocity, lateral deviation, and heading deviation. The quality of path tracking is ensured by a linear, time-invariant, decoupled controller for tracking straight or circular paths at a constantvelocity. Proportion Integration Differentiation (PID-control) and state feedback techniques can determine the gain. Path generation and the motion control of a tractor-trailer are implemented for autonomous maneuvers on the farmland and verified with an experimental trailer hooked to mobile power; at the end of each row, a reverse turn is automatically generated to connect the subsequent reference trajectory that can perform the maneuver automatically [7]. Based on an improved dual arc path planning algorithm, an autonomous path-tracking control method is proposed for a combined harvester with rear-wheel steering [8]. A dual DQN-based path-tracking method is proposed for crop-row agricultural machinery with a differential steering mechanism [9]. In addition to the machinery structures mentioned earlier, such as articulated, traction, and rear-wheel steering, agricultural machinery with four-wheel independent steering and four-wheel independent drive (4 WIS-4 WID) structure was studied and applied for its flexibility of steering and driving characteristics. Aiming to realize the dynamic switch of three steering modes in a four-wheel independent steering (4 WIS) rescue vehicle without stopping, the steering control strategy is investigated, and the wheel steering trajectory is optimized based on two objectives: to minimize the sudden change of dynamic parameters and to minimize the energy consumption in the steering process [10]. Coordinated regulation of the vehicle's sway and deflection angles is required for smoother WIS steering. Up-to-date control techniques such as fuzzy and model predictive control have been applied to study direct deflection control [11; 12; 13]. The path-tracking controller introduced in [14] shows that four-channel autoturbation control (ADRC) could achieve performance like anti-side wind, anti-skid, and anti-rollover in path tracking of four-wheel steering (4 WS) agricultural vehicles. Simulation results show that the 4 WS autonomous vehicle with this controller has good anti-side wind, anti-skid, and anti-rollover performance in path tracking, even on curves with minor steering radius or low adhesion. A robust differential steering control system (DSCS) for an independent four-wheel drive (4 WID) electric vehicle is investigated.