Objective To address the issue of unstable stubble height during the machine harvesting in the first quarter of ratoon rice, which damages axillary buds and affects the yield of the ratoon season.

Method This paper proposed an automatic control method for regulating the stubble height of ratoon rice. An online monitoring scheme for the header height above ground was established, primarily utilizing millimeter-wave ranging sensors and displacement sensors. The measurement accuracy of the header height above ground was improved by real-time adjustment of the threshold weights for left and right ranging data of the header via a linear displacement sensor. A raw data processing method for the header height above ground, based on multi-segment thresholds and Kalman filtering, was proposed to solve the problem of inaccurate ranging caused by environmental interference such as field leaves and weeds during the measurement process. A fuzzy PID control model was adopted for the automatic regulation of header height. The effectiveness of the control model was verified through AMESIM and Simulink co-simulation, and field harvesting experiments were conducted.

Results Field test results showed that the standard deviation of the real-time monitoring data for header height above ground was 5.6 mm, the mean absolute error was 4.8 mm, and the root mean square error was 6.7 mm. When the header height control system was activated, the standard deviation of the monitored stubble height was consistently less than 12 mm, and the coefficient of variation was consistently less than 0.1.

Conclusion The automatic control system for header stubble height of ratoon rice proposed in this paper demonstrates high control accuracy and qualified stubble height, meeting the requirement for stubble height consistency in the first crop of ratoon rice.