Improving the Dynamic Response of a Linear Hydraulic Drive using a Digital Valve Control
Sprache des Titels:
Proceedings of the Tenth Workshop on Digital Fluid Power
Hydraulic cylinders are mostly used for linear drive actuation of heavy loads because of their high force density. Furthermore, servo valves are often used in a closed loop control in order to achieve a high dynamic movement of the drive system. In case of huge loads the natural frequency of the drive is rather low, which in turn slows down the closed loop response in spite of the use of fast servo valves. This problem is shown by simulations for the step control of wrapper rolls in a down coiler in hot rolling mills. In order to overcome the limited bandwidth of the closed loop servo valve control in this paper a digital valve control is presented, which achieves the maximum physical dynamic response of a linear hydraulic drive. It is a type of feedforward control, which is designed to the natural frequency of the drive such that almost no oscillations of the wrapper roll will remain. The original problem of the wrapper roll was transferred to a linear drive axis with similar dynamics. Measurements on a laboratory test rig show a significant improvement in the dynamic response with the high dynamic digital control compared to a digital single pulse control. The results and relevant effects are discussed and, finally, a conclusion and an outlook for next steps in development are provided.