Model Based Compensator Design for Pitch Plane Stability of a Farm Tractor with Implement

摘要

An agricultural tractor finds extensive application in agriculture and is used with various types of implements. When it is driven with an implement attached to its rear, on-road or on uneven terrain, it experiences excessive vibrations in the pitch plane, which results in front wheel lift-off as an extreme scenario. The objective of this paper is to minimize these vibrations caused due to road disturbances by automatically controlling the lifting and lowering of the implement with the help of a hydraulic actuator. Using a Linear Time Invariant (LTI) approximation, a model relating the current input and the force variation output on the implement was developed based on the analysis of frequency response and time response. The data used in this process were acquired from an experimental setup consisting of control valves, hydraulic actuator and hitch system. Since the lifting and lowering of the implement is controlled by separate solenoid valves, individual models were obtained for each of them. These models were the used to design a lag compensator in order to reduce the gain of the system in the desired frequency range while maintaining the control variable (current) within its design limits. Results showed that the designed lag compensator exhibited a positive performance by reducing the variation of force on the hitch point by 95.8% during lifting and 87.2% during lowering.