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The middle and lower reaches of the Yangtze River are the main producing areas of winter rapeseed in China. However, due to the effects of harvesting agricultural crops, heavy soil compaction, small field, the mechanization level of rapeseed is low. The level of intelligent seeding needs to be improved. In this paper, a navigation controller for small crawler-type seeder based on immune PID was designed to solve the problem of intelligent seeding in the middle and lower reaches of the Yangtze River where the soil is sticky, the field is small. The small crawler-type rape seeder automatic navigation control system was designed. It used the small crawler-type rape seeder as the platform, and its steering system was modified by electromagnet. The high-precision BeiDou positioning module and the electronic compass was used for combined navigation to obtain the position and heading information of the crawler-type rape seeder as the input of the navigation controller. The immune PID controller was a nonlinear P controller that could adjust the proportional coefficient according to the feedback in real time. The control process was as follows. First, the plane coordinates of the start and end points of the straight path to be tracked are artificially set, and the main controller automatically calculated the distance of the target heading the start point and the end point. The weighted average algorithm was used to filter the longitude and latitude coordinates collected four times to get the current position. The controller calculated the distance deviation from the current position to the set route by the point-to-line distance formula. Taking the filtered distance deviation as an input, the target heading was calculated using the target heading correction formula distance deviation. Then, the course deviation (the deviation between the corrected target heading and the heading acquired by the electronic compass in real time) is used as an input of the immune PID controller, and the immune PID controller determines the Duty Ratio as the output u to act on the steering mechanism, achieving control of the steering of the track-type seeder. In addition, According to the characteristics of the tracked vehicle, the steering of the small crawler-type rape seeder was analyzed, and its steering model and steering angle transfer function were established. The immune PID controller was verified by Matlab simulation and experiment. Under the same parameters, the simulation showed that, compared with the conventional PID control, the immune PID control had the characteristics of fast response, small overshoot and small average tracking error. The pavement experiment showed that when the vehicle speed was 0.50 m/s, the average absolute deviation of the linear tracking of the immune PID controller was 4.2 cm, and the maximum deviation was not more than 12.0 cm. The field experiment showed that when the vehicle speed was 0.50 m/s, the average absolute deviation of the linear tracking of the immune PID controller was 5.8 cm, and the maximum deviation was not more than 15.2 cm, which was 32.6% and 18.1% higher than the conventional PID. It could better meet the requirements of the seeder navigation operation. This research provides a technical reference for the autonomous navigation of the crawler-type rape seeder. [ABSTRACT FROM AUTHOR]

Thinning is required in fruit tree production to ensure high quality fruit and proper fruit size, which is one of the most labor-intensive practices. Mechanical blossom thinning is an environmental friendly alternative to chemical blossom thinning. Good tree training techniques are required to get high-level blossom removal for mechanical thinning. Electric flexible thinner can realize blossom thinning by rotating flexible strings. There is a challenge in mechanical thinning due to the varying shape of tree canopy. To improve the adaptability of the electric flexible thinner on fruit tree variety, canopy shape and size, it is important to develop a profiling control system. In this paper, the structure of the actuators for profiling action of the electric flexible thinner was proposed. The flexible thinner was suspended on the rear three-point hitch of a tractor and consisted of a vertical rotating spindle attached with several segments of nylon cords in horizontal direction. The spindle was rotated by a brushless direct current motor and its spatial position could be adjusted by translational screw and profile adjusting screw. The ball screws were driven and controlled via stepper motors, which could control the offset into the trees and the angle of the thinner. With the ball screws, the thinning spindle could be stretched and tilted to conform to the height and inclination of the tree canopy. The range measuring rod could map the canopy as it passed and was placed ahead of the spindle to avoid sensor collision with rotating cords. Two pairs of ultrasonic sensors suspended on the range measuring rod could provide the angle and lateral offset sensing of the flexible thinner position by sending infrared laser pulses out and measuring the round-trip flight time to the trees. The spindle rotation speed, screw displacement and thinning angle were adjusted by the electric motors. During the blossom thinning process, the centrifugal force on the panicles of the fruit tree was used to cause rotating nylon cords to thin blossom. The intensity of thinning could be controlled by changing the spindle rotation speed, tractor speed and string arrangement and other parameters. To get the key parameters of profiling control, the geometric relationship between flexible thinner and canopy edge was analyzed. Using the modular structure, the hardware and software of profiling control system were developed. The controller performed the planning task and calculated the number of pulses for stepper motors of ball screws between the current position of the thinner and the currently measured canopy. All field tests with the electric flexible thinner were conducted at a tractor speed of 1.93 km/h. The field test results of single litchi plant illustrated the position servo control performance of two ball screws of the electric flexible thinner. The measured dynamic mean errors of the translational screw and profile adjusting screw were 0.17 and 0.07 cm respectively. To improve the performance of profiling controller, it required to move the thinner quickly without affecting thinning speed and to reduce the control latency to acceptable levels. The experimental results show that the actuators have good position adjusting accuracy and the proposed profiling control system can meet the requirements of real-time control. [ABSTRACT FROM AUTHOR]