Fuzzy-PID controller with variable universe for tillage depth control on tractor-implement

A control algorithm of fuzzy-PID controller with variable universe (VUFPID) was proposed to realize fast and accurate adjustment of tillage depth control on tractor-implement and adapt to the complex and changeable agricultural environments. The electro-hydraulic hitch system was modeled through transfer functions of the electrically operated hydraulic valve and the hydraulic cylinder. And the VUFPID controller was designed in accordance with the error of tillage depth and the error rate of tillage depth. Then, the designed controller was simulated by comparing with PID controller and fuzzy PID controller. Also, field experiments were conducted to assess stability of the proposed controller. According to the simulation results, the proposed controller can adjust the hitch system to the set depth more quickly and steadily than the other controllers, with the minimum tracking error of 1.13 mm for the simulation with sine signal, and the shortest response time of 0.261 s and lowest overshoot of 12.4% for the simulation with step signal. As for the field experiments, the results are in good agreement with the simulation results, and the proposed controller shows good stability with the maximum error of tillage depth of 7.8% at the set depth of 10–20 cm. The proposed controller has good adaptability and anti-interference in tillage depth control.