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Agricultural production mode has been required for the intelligence and digitization of agricultural machinery. An automatic control system has gradually been the research interest of agricultural machinery in recent years. Among them, the navigation system with path tracking control can be expected to improve the accuracy of the agricultural machinery and the adaptability to the environment. Specifically, the accuracy and efficiency of agricultural production can be improved to realize more complex tasks, in order to avoid the wide crop coverage due to leakage testing. In this review, the types of agricultural machinery models were evaluated with/without the navigation path tracking control system. Three categories were also divided into the path-tracking control system with the kinematic or dynamic models, as well as the model-independent path-tracking control. Agricultural machinery was assumed as a rigid or single rigid body system for control with the kinematic model. The kinematic model of agricultural machinery included pure tracking, linear quadratic optimal control, and the model predictive control. By contrast, the dynamic model of agricultural machinery considered the influence of the mass and inertia of agricultural machinery on the control, particularly with the sliding mode variable structure control. The path-tracking control method unrelated to the agricultural machinery model was utilized to directly extract the features from the sensor data or visual information. The PID, and fuzzy control were the widely-used path-tracking control systems in the path-tracking control methods unrelated to the agricultural machinery model. The optimal path-tracking control of the agricultural machinery was achieved to correct the control system using the error between the sensor feedback and reference input values. The pros and cons of various control methods were clarified to evaluate the existing solutions. The current research progress was reviewed on the general and specific existing solutions to the navigation path tracking control of agricultural machinery. The applicability of various control methods was also evaluated for the current development status of agricultural machinery navigation products. The development prospects were then proposed for a navigation path tracking control of agricultural machinery. Some recommendations were as follows: (1) The current model was limited to describing the motion process of agricultural machinery. There was a high demand for the high precision model research of agricultural machinery; (2) In order to improve the adaptability and robustness of the control method, the research should be extended from the conventional to extreme and complex conditions; (3) The single control method was confined in the navigation path tracking control method of agricultural machinery. It can be expected to require the development trend of multi-method fusion control. This finding can provide strong references for subsequent research on the path-tracking control methods, particularly for the intelligent development of agricultural machinery in China. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agricultural Science & Technology (1008-0864) is the property of Journal of Agricultural Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The generation of power shift tractor promotes the automatic driving of agricultural machinery to the direction of unmanned, and the automatic obstacle avoidance of agricultural machinery has become a key issue to be solved. Most of the existing obstacle avoidance path planning adopts the shortest tangent method, which has the advantages of fast and simple path generation and short track, but the curvature of the path curve is discontinuous and there are corner inflection points, which make the tractor front wheel angle suddenly change and affect the obstacle avoidance accuracy. In this paper, for the curvature discontinuity of the shortest tangent path curve, poor tracking control accuracy and low precision of agricultural machinery model, the third-order bezier curve optimization method was used to form a continuous smooth agricultural machine obstacle avoidance path. The optimized curve curvature was continuous and the obstacle avoidance path was smooth with no turning points, which was conducive to the control of agricultural machinery driving. The linear control model of agricultural machinery movement was established by chain control theory, and the PI controller was used for corner compensation to improve the accuracy of agricultural machinery obstacle avoidance. The simulation of the path tracking control method was completed. The simulation results showed that the heading error angle of the agricultural machinery was mostly in the range of - 0.06-0.06 rad, the lateral position error was less than 13 cm, and the front wheel steering angle changed gently with no significant mutation, indicating that the control method of the obstacle avoidance path control method had a high precision, and the agricultural machinery can drive according to the preset trajectory. The ploughing operation test was carried out, and the Dongfanghong LF954-C power shift tractor was used, which can automatically start, stop, shift, and implement the lifting operation of the farm. The tractor was equipped with the Beidou agricultural autopilot with the straight running accuracy of ±2.5 cm. Ultrasonic radar and image recognition technology were used to perceive obstacles in the working environment. The farm implement was a 250 cm wide plow. A haystack obstacle was set on the machine working path with a contour radius smaller than the minimum turning radius of the tractor. The results of the plowing operation test showed that the machine can automatically complete the straight-line driving, farm implement lifting, automatic obstacle avoidance, farm implement falling, and continuous straight-line operation. The obstacle avoidance accuracy of the bezier curve was 5.21 cm, and the tracking control effect of the curve path was well. The accuracy of the agricultural machine continuing to travel in a straight line after obstacle avoidance was 1.98 cm, which indicated that the path tracking control method can ensure the tractor straight-line automatic driving after obstacle avoidance. The above results showed that the obstacle avoidance path and control method showed good robustness and adaptability in uneven ploughing land and can meet the obstacle avoidance requirements of tractor operation. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)