Development of a computer program for the path generation of tractor hitch points

In the vertical longitudinal plane of a tractor, the three-point hitch system is a six-bar mechanism that can be designed and modelled as two distinct four-bar linkages sharing two links. A Newton–Raphson solution for the four-bar linkage has been applied to a three-point hitch system of tractor to determine the range of movement of the lift arm and generate the path of motion of lower and upper hitch points in the movement range of the hitch. The algorithm was executed as a program in MATLAB. The program has the ability to generate the path of motion of lower; upper and virtual hitch points, determine the geometric performance parameters of the hitch system, and identify the variations in the quality of force transmission by the linkage system throughout the range of hitch movements for 165 different groups of hitch dimensions available in the Nebraska tractor test reports. Application of the program for searching improved design solutions for the existing hitch system of a tractor was demonstrated. The program has the potential to be used in any search-based techniques for optimisation of the dimensions of three-point hitch systems for tractors. In addition, variations in length of links and spatial location of their pivot points were studied for various categories of hitches. The range of values of link lengths and the spatial location of their pivot points reported here can be used for defining the design space during the optimal dimensional synthesis of tractor three-point hitch systems.

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► Newton–Raphson solution for the four-bar linkage applied to tractor three-point hitch system.
► Algorithm implemented in MATLAB generated paths of motion of upper, lower and virtual hitch points.
► Application of program for the identification of improved design solutions demonstrated.
► Program has the potential for use in optimal dimensional synthesis of tractor hitch system.
► Variations in dimensions of linkage geometry of various categories of hitch were studied.