Optimized Pulse Modulation: A Novel Idea of a Digital Control Method for On/Off Valves

Hydraulic control with switching valves can excite undesirable hydraulic and mechanical oscillations; hence, control performance is inadequate. There are different ways to cope with such oscillations. One way is to change the design or to add some damping elements which improve the attenuation of the oscillations. Another way is to actuate the system in an appropriate way -so that almost no unwanted oscillations are excited. This article illustrates that optimal feedforward control theory can be used to obtain a realisable switching valve command which avoids ongoing oscillations for the case of a fast position step. A system composed of a dual-stroke cylinder with its piston chamber connected to the switching valves by some pipeline and its rod chamber to pre-pressurised accumulators for counterbalancing is modelled as a discrete dynamical system of order 9. The optimal control problem is conditioned such that the resulting valve signals can be approximately realised by the existing switching valves. For this realisation, the so-called ballistic mode of switching valves plays an important role. The theoretical results are tested experimentally on a proper test rig.

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“…An introduction of this actuation mode can be found in Flor et al 16 (pp. 6-7) and Schepers and Weber 17 (pp. 104-105).…”

Section: Resultsmentioning

confidence: 99%

Optimal feed-forward control of a digital hydraulic drive

Haas

Lukachev

2016

Proceedings of the Institution of Mechanical Engineers, Part I:

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“…That is rarely used in the digital hydraulic valve systems. Some theoretical analyses are presented [7] and [8]. Paper [7] presented an extensive analysis of digital control methods for one switching valve.…”

Section: Improving Flow Resolution With Pfmmentioning

confidence: 99%

“…Some theoretical analyses are presented [7] and [8]. Paper [7] presented an extensive analysis of digital control methods for one switching valve. PFM was the only control method by which small average openings could be realised without a ballistic mode.…”

Section: Improving Flow Resolution With Pfmmentioning

confidence: 99%

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Equal Coded Digital Hydraulic Valve System – Improving Tracking Control with Pulse Frequency Modulation

Paloniitty

Linjama

Huhtala

2015

Procedia Engineering

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Previous research on digital fluid power indicates down-scaling to be beneficial to the characteristics of digital valves. This theoretical aspect yields to use equal size on/off valves in digital hydraulic valve systems. A simple miniaturized on/off valve, having orifice diameter of 0.7 mm, have been developed to study the feasibility of this approach. A manifold manufacturing technology also has been developed to facilitate a compact framework for the valve system containing dozens of the miniature valves. The first equal coded valve system prototype contains 16 miniature valve prototypes. A natural modulation method for an equal coded valve system is Pulse Number Modulation (PNM), where the output depends on the number of activated valves. With this modulation method, resolution of the output is equivalent to the number of the valves in the control edge. Limited resolution hampers the tracking control performance especially at low velocity where small steps in flow rate are required. The main purpose of this paper is to study the feasibility of Pulse Frequency Modulation (PFM) to improve the controllability of the equal coded valve system at the velocities below the minimum velocity of PNM control. Poor controllability at low velocities is one of the main challenges of the digital hydraulic valve systems. Characteristics of the PFM method are analysed and an experimental study is carried out to measure the improvement of the PFM method on the tracking control performance. The study indicates that the PFM method is an effective way to improve tracking control performance at low velocity.

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“…Belforte et al 12 used two PWM valves connected in parallel in a pneumatic system with different PWM frequencies to improve the dynamic performance of the system. Schepers et al 13 developed an optimal control method that utilized ballistic modes to realize flow rates that are unattainable with the typical PWM control. In the ballistic mode, the valve opens but the duration of the control pulse is shorter than the valve needs to open fully.…”

Section: Introductionmentioning

confidence: 99%

High-linear digital hydraulic valve control by an equal coded valve system and novel switching schemes

Paloniitty

Linjama

2018

Proceedings of the Institution of Mechanical Engineers, Part I:

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This study proposes a novel digital hydraulic valve system using multiple equal size on/off valves and a circulating switching control, with an aim to increase the resolution and the linearity of the digital hydraulic valve systems. The solution is founded on the equal coded valve system concept which represents a recent development in the digital hydraulic valve technology. The circulating switching control algorithm is used to overcome nonlinearities occurring in the typical noncirculating switching control and to decrease the operating frequency of single on/off valves. As a result, a substantial improvement in tracking control performance is demonstrated with 8 + 8 parallel connected valves. The results verify that compact, robust, and high-performance valve control can be realized.

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Optimized Pulse Modulation: A Novel Idea of a Digital Control Method for On/Off Valves

Cited by 3 publications

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Optimal feed-forward control of a digital hydraulic drive

Optimal feed-forward control of a digital hydraulic drive

Equal Coded Digital Hydraulic Valve System – Improving Tracking Control with Pulse Frequency Modulation

High-linear digital hydraulic valve control by an equal coded valve system and novel switching schemes

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