The design of a three point linkage implement height control system

Abstract

The purpose of this project was to design a height control system that could be applied to a Three Point Linkage mounted implement. Several methods of achieving this goal were investigated. The two methods that were investigated in detail were an electrical over hydraulic system and a mechanical over hydraulic system. The unique operation of the three point linkage implements when lift assist is used presents problems when accurate frame height is required, such as when seeding operations are being performed. The system has been designed so that it is constantly sensing the height of the frame at both ends of the implement. The output from this sensing is used to control a hydraulic valve mechanically or electrically. If a height discrepancy between the front and rear of the implement is detected, this valve will be activated to allow a flow of hydraulic oil to the lift assist system, levelling the implement. The investigation of the electrical control system involved constructing a prototype circuit that was based on a PICAXE microcontroller to provide computing power. This chip was programmed to read the output from two variable resistors and detect any height discrepancies. When a discrepancy was detected, the microcontroller activated a servomechanism that used mechanical motion to correct the position of one of the resistor to match the mechanical position of the two resistors, thus proving the concept of mechanical height control. The mechanical system was designed so that the output from two height sensing wheels was mechanically input into the hydraulic valve to actuate it when the wheels sensed that there was a height discrepancy. This system was modelled using the solid modelling package SolidWorks and basic engineering analysis was performed on the design.