Optimal Digital Hydraulic Feed-Forward Control Applied to Simple Cylinder Drives
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Proceedings of the Eight Workshop on Digital Fluid Power Tampere, Finland
So far, optimal feed-forward hydraulic switching control has been investigated by the authors mainly to find out the performance limitations of this technology. Requiring time optimality is a trick to enforce a bang-bang type result for a basically continuous valve, in other words, to obtain an input which can be realized by switching valves. The results of these previous studies showed the feasibility of the approach for a few types of linear hydraulic drives.
The intention of this paper is to give a short and clear insight into the basics of this principle. This includes a discussion of the idea of this approach as well as a discussion of different solution techniques. Possibilities, challenges and limitations of the approach and these different solution techniques are summarized. Simple examples are stated in order to demonstrate the results.
To this end, a quite simple system composed of a differential cylinder in plunger mode with a mass and one or two digital half bridges of different size and dynamics are subject of this investigation. For this simple example, with multiple inputs, a switching feed-forward could be found. Finally, a dual chamber cylinder is actuated using different kinds of digital valves. First, each fluid chamber is connected to a 3-3 way valve; second, each chamber is connected to a digital half bridge consisting of two 2-2- way valves; and third, the cylinder is actuated using a single 4-3 way valve connected to both fluid chambers. The optimisation problems for all these examples could be solved and the resulting feed-forward commands are realizable by switching valves.