Hydraulic Switching Control – Concepts, Challenges, Solutions

Digital hydraulics – the control of hydraulic system by on-off valves – has a sub-class doing control by a repeated operation of a single or a few valves at relatively high frequencies, e.g., by pulse-width modulation. This class is called hydraulic switching control. Most prominent are switching converters, sometimes called switched inertance hydraulics. But numerous other concepts for switching control have been proposed, studied, or are already applied in practice. They offer different advantages, like, for instance, low cost, simplicity, high precision, or energy efficiency. This paper shows examples of such drives, starting from the hydraulic buck converter to quite specific solutions as a micro-positioning device or a hydraulic stepper drive. For each case existing or potential applications, challenges, and state of the art are reported or discussed, respectively.