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This paper introduces the hydraulic control system of a novel tube straightener, in which the position of the rolls is controlled by the proportional valves controlled cylinders through a PLC in order to adjust the gap and compensate the deviation automatically. This hydraulic control system enables the straighter to have the characteristic of a high degree of automation and accuracy. This article focuses on the study of the symmetrical proportional direction valve controlled unsymmetrical cylinder since it is more difficult to be controlled than the symmetrical ones. In this article, firstly, the model of the symmetrical valve controlled unsymmetrical cylinder is built using DSHplus and the effectiveness is tested by referring to the practical measured value. Then, the characteristic of the model is discussed further by comparing with the model of the symmetrical valve controlled symmetrical cylinder. Finally, two common used compensation methods that are applied to the symmetrical valve controlled unsymmetrical cylinder system are analyzed separately and their effectiveness is compared. This is meaningful for hydraulic designers to select the proper compensation ways in the design.