Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
1998-10-09
2002-02-26
Assouad, Patrick (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C347S007000
Reexamination Certificate
active
06351716
ABSTRACT:
The invention concerns a method and a device for determining the quantity of product contained in a reservoir, for example in an ink reservoir for a printer.
In known printing devices, methods have already been proposed for detecting the residual quantity of available ink (this is then sometimes referred to as ink level monitoring or detection).
By way of example the document EP-A2-0 028 399 describes an ink level detection method using an resonant circuit with which the reservoir to be monitored is integrated. More precisely, the capacitor of this resonant circuit has two metal plates forming electrodes defining a dielectric space in which the storage cavity of the ink reservoir is situated.
The ink thus behaves as a dielectric whose value changes as the ink reserve decreases. Consequently the capacitance of the resonant circuit also changes.
The latter is calibrated so that its resonant frequency, and therefore the maximum voltage at its resistor, is reached when the level of the ink reserve has dropped to a predetermined value. When this threshold is passed, a signal is activated.
This method has a certain number of defects.
First of all, when the ink level decreases, the voltage at the terminals of the resistor varies up to a certain threshold. The only information given by this device is therefore an indication on the situation (above or below) of the ink level with respect to the said threshold.
Only the information relating to the amplitude of the measurement signal is taken into account and compared with a threshold; this type of detector indicates only one type of information: when there is 20% of the ink remaining in the reservoir. By using an analogue to digital converter, it would be possible to think of determining the level of ink in the reservoir continuously, but this type of component has a high cost.
In addition, when it is wished to measure the quantity of ink present in small reservoirs or when the capacitance is of low value (a few picofarads), the resonant frequency then becomes extremely high, which appreciably increases the cost of the components used and may generate electromagnetic interference or disturbances. One solution would consist of using inductors of very high value (1 henry for example). These would reduce the frequency, but they are very difficult to produce and in any case are bulky.
It is briefly mentioned in this document that it is possible to use a parallel circuit but it is added that a series circuit is preferable; in any event everything which is described and shown concerns a series circuit.
The ink plotters such as the one mentioned in the description of EP-A-0028399 have a reservoir and a recorder. The reservoir and recorder are not electrically connected to the printing device, which of course makes it possible to place the capacitor consisting of metal plates and ink reservoir in either a series or a parallel configuration.
The same applies to conventional wound inductors, which can be placed equally well in a series or parallel configuration.
It must nevertheless be noted that:
if the recorder is for example connected to a potential, for example earth, the series resonant circuit cannot be produced; this case is however increasingly usual;
if the capacitance is very small, it is necessary to produce inductors with very high values if it is desired to remain within low frequencies, which cannot be achieved in conventional technologies.
A first object of the invention is to mitigate the drawbacks of the known solutions by virtue of a method or device which makes it possible to detect, preferably at least within an operating range preferably including the low values, the residual quantity of an electrically conductive product contained in a reservoir made of an electrically insulating material in a simple and reliable fashion, by identifying an easily measurable characteristic of a resonant circuit including the reservoir, without having to modify the latter in any way, without for all that using expensive components in the processing of the measurement signals.
An other object of the invention (but these aspects can be taken into consideration independently of each other and of the aforementioned object) is to detect the residual quantity of an electrically conductive product contained in a reservoir made of an electrically insulating material in a simple and reliable manner:
even when the technological constraints of location and operation of the system receiving the reservoir allow the formation only of a resonant circuit of the parallel type (in particular when the reservoir includes, or cooperates with, a print head whose operation requires an electrical connection of the said head to a predetermined potential, which prevents any series connection);
at a moderate cost and within a moderate size, in particular without using components which are difficult to produce and/or expensive in the resonant circuit itself or in the generator designed to deliver excitation signals to this resonant circuit);
which easily allows, by means of minor adaptations, the detection also of situations where there is no product in the duct through which the product flows to the print or ejection head (therefore minimizing the additional components to be provided when it is desired not only to detect the quantity of product in the storage chamber but also to check, in real time, that there is indeed, in the delivery duct, product in a normal state, that is to say electrically conductive).
To this end the invention first proposes a method of determining the quantity of an electrically conductive product contained in a reservoir made of electrically insulating material having at least one storage cavity, according to which:
a resonant circuit is formed having a capacitive arrangement comprising at least part of this reservoir;
this resonant circuit is connected to an excitation signal generator;
a measurement procedure is defined according to which a plurality of excitation signals is applied to this resonant circuit having different frequencies included in a predetermined frequency range and a plurality of measurement signals are taken off at a measuring point in response to these excitation signals, this frequency range being chosen so as to contain the frequencies at which the resonant circuit is in resonance for a plurality of values of the quantity of product within a predetermined operating range;
a processing procedure is defined consisting of identifying the instantaneous resonant frequency of the resonant circuit from this plurality of measurement signals, measuring the width, for a given amplitude level, of the resonance peak and deriving therefrom an item of information representing the quantity of product contained in the storage cavity, this amplitude level being chosen so that there exists a univocal correlation law between the width of the resonance peak and this item of information when the quantity of product is within the said operating range;
at least one determination cycle is effected, consisting of triggering the measurement procedure and the processing procedure, and capturing the instantaneous value of the said item of information.
It may be appreciated that the invention thus makes provision for detecting the resonant frequency of a resonant circuit in which a capacitive element consists of at least part of the reservoir, which is easy to achieve at a moderate cost, and to derive a value representing the residual quantity of product from the width of the resonance peak, which requires only the use of a simple comparator, of a cost very much less than that of an analogue to digital converter. However, it became clear that it was possible, for electrically conductive products, notably printing inks, to establish a univocal correlation law between the width of such a resonance peak and the quantity of product at which resonance occurs.
One of the possible sources of cost in implementing the method of the invention lies in the need to be able to generate excitation signals able to result in measurement signals of sufficiently hig
Coudray Pascal
Froger Marie-Helene
Lorgeoux Mickaël
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