Energy Efficient Linear Drive Axis Using a Hydraulic Switching Converter

Digital hydraulics uses simple and cheap on/off valves in order to replace expensive proportional valves. Furthermore, with fast switching hydraulic converters the energy efficiency can be raised compared to proportional valve control. The hydraulic buck converter (HBC) represents an energy efficient and cost-effective switched inertance system, because its inductance is realized by a simple pipe. In this paper, a prototype for a hydraulic linear cylinder drive controlled by an HBC is presented. Characteristic for this drive axis is that the HBC is directly mounted on the cylinder, which allows a reduction of the oil transport loss between the axis and the hydraulic power supply unit. Furthermore, piston accumulators are used for decoupling and pressure attenuation. Due to their robustness regarding the prepressure to operating pressure, the load pressure can be controlled arbitrary in the piston-sided chamber. The energy performance and the tracking behavior of the axis with a flatness-based control (FBC) are investigated by steady-state measurements and dynamic trajectories, respectively. The results are discussed and an outlook about further improvements of the concept is provided.