Abstract:
Agricultural machine automatic navigation is one of the key technologies in precision agriculture technology system, the in-depth study is important in scientific research, application and social values. In this paper, we investigated the navigation problems in the application of the farm work, including slow on-line speed, bad on-line stability, and poor adaptability of bumpy complex road surface. These problems can be summarized as the speed and stability problems of track tracking in the case of large position deviation or large course deviation. Through the analysis of the work principle and control parameters function of the navigation, a conclusion is made that the correct speed and stability of the position deviation and course deviation of agricultural machinery can be improved by allocating the weight of the position deviation wheel angle decision quantity and course deviation wheel angle decision quantity reasonably. Then in this paper, we developed the navigation control algorithm based on the agricultural machine kinematics model and the pole optimal configuration theory. Because of the small angle linearization of course deviation angle and wheel angle during the deducing, the control law can achieve good control effect only in the ideal straight path tracking control with small position deviation, course deviation, and wheel angle. Based on this, a path tracking control method of aiming pursuit model for agricultural machine navigation was proposed aiming at improving the on-line speed, stability and adaptability to complex road surface of the automatic navigation system of agricultural machine. In this method, we selected a tracking target point on the planning path of agricultural machine ahead, and tracked the target point by controlling the steering wheel angle. The direction of the agricultural machine vehicle center point to the target point was called as the aiming course. The desired steering angle would be larger when the deviation was larger between the course of agricultural machine and the aiming course, with a rapid correction of aiming course deviation to achieve the goal of fast tracking the target path. On the other hand, the desired steering angle would be smaller when the deviation was smaller between the course of agricultural machine and the aiming course, with a stable tracking to aiming path to achieve the goal of stable tracking the target path. In this model, the steering wheel angle was designed to be K times of the aiming course deviation and K was called as control gain. The length of the projection of the agricultural machine vehicle center to the target point vector on the planning path was named as the preview distance. The control gain and the preview distance were two important parameters that affected the control effect of the model. In this paper, there were three steps to prove the feasibility of the method. The control gain K and the preview distance were set up by referring to the result of the pole optimal configuration method based on the kinematic model of agricultural machine. By comparing two methods formula, the position deviation wheel angle decision quantity had a linear relationship with the position deviation in the kinematics model method and the position deviation wheel angle decision quantity had an inverse tangent function relationship with the position deviation. The inverse tangent function relation was more beneficial to maintain proper weight of position deviation wheel angle decision quantity and course deviation wheel angle decision quantity that would make the path tracking control of agricultural machinery navigation more rapid and stable. Simulation analysis results of aiming pursuit model algorithm in different position and different course deviation showed that the proposed method had a fast and stable path tracking performance and good robustness and adaptability to the navigation path tracking. The test results of agricultural machine showed that the control method proposed in this paper had a good effect in the rapid responsibility and line tracking performance. In the case of 0.5, 1, 1.5 m initial position error, the on-line time was 6.8, 8.2, 9.4 s, respectively, the corresponding travelling distance was 6.73, 8.11 and 9.33 m, respectively and the corresponding overshoot was 5.2, 7.0, 8.5 cm, respectively. The maximum error of straight-line path tracking for bumpy uneven field was not more than 4.23 cm, the mean value of the absolute value of the error was 1 cm, and the standard deviation was 1.25 cm, which satisfied the operation requirements of agricultural machine.