A pulse-frequency controlled hydraulic drive for the elastic deformation of a structure

Sprache des Vortragstitels:

Englisch

Original Tagungtitel:

9th International Fluid Power Conference (9th IFK)

Sprache des Tagungstitel:

Englisch

Original Kurzfassung:

Various control strategies in digital hydraulics have been studied and published in the last years. Pulse
Frequency Control (PFC) which ? opposite to PWM ? uses the pulse repeating frequency and not the pulse width
as control input, is a fairly new control concept in digital hydraulics. PFC may be to be preferred if the hydraulic
switching device can realize a very particular pulse in a favourable way, e.g. concerning energetic efficiency,
simplicity and cost of components, or ease of component or control standardization.
This paper deals with the application of PFC to the control of a hydraulic drive. It is assumed that a digital flow
unit (e.g. digital pump) can realize only one particular flow pulse which can be repeated any time but not before
the previous pulse is finished. As a consequence, the relative control resolution of a PFC-system is limited
because of the fixed pulse quantity and the maximum repeating frequency. Since this pulsing may interact with
the dynamics of the plant, the dynamics of the whole system with the PFC needs to be analyzed.
In a previous paper, authors investigated a system comprising a digital flow unit and a hydraulic cylinder with an
attached mass and a constant load. They found that oscillation can be largely reduced, if either the single pulse?s
duration or the time span of two pulses is tuned to the natural frequencies of the drive. In this paper additional
degrees of freedom in form of an elastic structure (e.g. an elastic beam) are added to the linear hydraulic drive
which is pulse-frequency controlled. The dynamical response characteristics of such a multi degree of freedom
system in PFC, the switching effort, and the achievable position accuracy in two different operating scenarios ? a
stepwise motion with one and two PFC drives - are analyzed by mathematical modelling, simulation, analysis,
and reasoning.