Liquid temperature control for a hydraulic turning machine

The Stanford´s Quiet Hydraulic precision lathe was designed to use an exclusively hydraulic approach and equipped with an open liquid circulation system. By using a temperature-controlled liquid for a liquid shower, as well as for machine actuation, a uniform temperature environment can easily be maintained and the machining accuracy level can be assured. The liquid temperature is regulated by a commercially available cross-flow type heat exchanger. Due to the inherent time-varying and long time-delay characteristics, regulation of liquid temperature variation at the shower point down to m°C level is a very challenging problem. Successive feedback loops with Smith predictor and disturbance feedforward are implemented to regulate both the heat exchanger outlet and shower point temperature. Satisfactory long duration control results are obtained through this approach. In order to extend system bandwidth, the use of a Smith predictor with intentional temporal mismatch has been studied. It is found that the system performance can be improved by introducing an intentional mismatch for certain systems. The results are also verified by experimental observations