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EXPERIMENTAL RESEARCH ON A DIGITAL HYDRAULIC CYLINDER

Ioan Pavel

Abstract

The development of computer science in recent years has enabled researchers in the field of hydraulic drive systems to address the concept of ?digital hydraulics?. Digital hydraulics refers to systems that use binary parallel-connected components or switching control elements which have discrete input values and can actively control the system. The concept of ?digital hydraulics? implies that the operation of digital hydraulic devices is based on the on/off principle, meaning that active area or nominal opening are discretized, divided sections can have two states: active or inactive (0 or 1), and the combination of sections and states produces an active speed / rotational speed or force / torque output control. Digital hydraulics is a newly developed alternative replacing actuation with servo valves or proportional directional valves, devices which are expensive and compelling as to the hydraulic oil contamination degree. Digital hydraulics results in hydraulic systems that have at least one hydraulic component ensuring discrete, accurately and actively controlled outputs. To meet these challenges, the authors of this paper have found through experimental research that, for an active cylinder control, when speaking of digital hydraulic cylinders it is more convenient to vary the piston surface than the pressure or flow. Piston surface is divided into several concentric different-sized working areas which are, individually or cumulatively, supplied with constant pressure, generating levels of force, which can be actively controlled by selecting area combinations according to system requirements. The test results were obtained on an experimental model of a digital cylinder and a specialized stand, developed by the authors at INOE 2000 ? IHP, comprising: a power station, a distribution block, data acquisition board and LabVIEW- programmed virtual instrument software with embedded control logic for supplying the digital hydraulic cylinder chambers and the system that performs data acquisition for the measured signals (force, displacement, pressure, flow rate). The digital hydraulic cylinder under laboratory tests, having its piston surface divided into three functionally independent annular areas, has been supplied with constant pressure, and by selecting the combinations of active areas seven levels of force resulted; they could be controlled using a distribution block and dedicated software.

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DOI resolver: doi.org/10.5593/sgem2019/2.1/s07.036

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