Abstract
The development of implement control systems has been greatly influenced by the pattern set by the Te20 Ferguson tractor, and most three-point linkage draught control systems operate on the same principle. Such designs, whilst adequate for most purposes on level going, display poor depth control behaviour when traversing undulating ground. A full understanding of these systems has been limited by the absence of a mathematical theory capable of predicting their behaviour. This paper sets out to examine the problem in control theory terms.
An experimental hydraulic control system has been built using pure draught force sensing, and its behaviour has been studied both mathematically and experimentally in the laboratory and in the field. To enable theoretical predictions of system behaviour to be made a second rig was constructed to study the transfer functions of implements. This rig can also serve as a simulator of field surface disturbances. The performance of the experimental system was compared with a popular commercial system using the second rig as a simulator and the results indicate that pure draught control sensing as used in the experimental system is feasible in practice. The paper concludes with a short discussion of alternative control strategies.
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