Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Reexamination Certificate
1998-10-09
2002-01-15
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
C324S071100
Reexamination Certificate
active
06339335
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, for example by measuring a resistance representing this quantity, preferably even when the reservoir is in a noise environment.
Methods have already been proposed for detecting the residual quantity of available ink contained in ink reservoirs within printing devices.
Some of these methods are based on a measurement of resistance variation.
Thus the document EP-A-0 370 765 describes a method for detecting the presence of an electrically conductive ink in the ink discharge pipe which connects a storage cavity of the reservoir to an ejection or print head. Two electrodes are placed in this pipe: an absence of ink in the pipe (because of the exhaustion of the ink contained in the cavity or because this ink has dried in the pipe, notably) is easily detectable by the abrupt increase in resistivity between the electrodes.
The document EP-A-0 509 747 for its part discloses disposing two electrodes in two zones of a porous body contained in the reservoir and soaked with the ink in question, these two zones being chosen so as to have different capillarities. The variations in the concentration of ink within the porous body has an influence on the resistivity of the area of the porous body between the electrodes, which makes it possible to detect the quantity of ink.
These methods have a certain number of defects, the main one of which is that installing the electrodes requires an adaptation of the reservoir (the term cartridge is sometimes used to designate the exchangeable assembly of which the reservoir forms part), namely its cavity or its discharge pipe. This gives rise to a certain degree of complexity and therefore an increase in the cost of producing the reservoirs or cartridges.
Moreover, these electrodes are in direct contact with the ink, which is often corrosive, which obliges the manufacture to use noble materials (gold, etc), which are therefore expensive.
Finally, the first aforementioned document does not afford a true determination of the residual ink, since it monitors only the resistive state of the pipe through which the ink flows, whilst the second document discloses only detecting the passing of a threshold or residual ink level without the user being able to know the quantity of ink remaining in the reservoir as long as this threshold has not been passed.
Other methods involve a measurement of apparent capacitance.
Thus for example the document EP-A-0 028 399 describes a 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.
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 (greater or not) of this level with respect to the 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 20% of the ink remains in the reservoir. By using an analogue to digital converter, determining the level of ink in the reservoir continuously could be considered, 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. 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 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.
The ink plotters such as the one mentioned in the description 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 a series or parallel configuration.
Likewise, conventional wound inductors 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.
In any event, the known solutions are not suitable for dealing with cases where, at the time of the measurements, the reservoir and the associated detection means are in a noisy environment and because of that suffer interference leading to erroneous measurements.
A first object of the invention is to mitigate the aforementioned drawbacks by virtue of a method or device which allows the detection, at least within an operating range including preferably the low values, of the residual quantity of an electrically conductive product contained in a reservoir made of electrically insulating material, in a simple, precise and reliable fashion, by measuring a resistance characterising the reservoir when the latter is included in a resonant circuit, without having to modify the latter in any way.
A second object of the invention is to mitigate the aforementioned drawbacks by virtue of a method or device which allows the detection, at least within an operating range preferably including low values, of the residual quantity of an electrically conductive product contained in a reservoir made of electrically insulating material, in a simple, precise and reliable fashion, in particular by eliminating the effects of the environment, such as electromagnetic noise, and this by means of measurements which require no modification to the reservoir in order to fit electrodes.
Additionally (but these aspects can be taken into consideration independently of each other and of the aforementioned object) the invention aims to achieve this object:
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;
while easily allowing the detection also of situations where there is no product in a duct delivering product to a 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 a storage cavity of this reservoir 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).
According to a first aspect, the invention proposes a method of determining the qu
Coudray Pascal
Froger Marie-Helene
Lorgeoux Mickaël
Brown Glenn W.
LeRoux Etienne
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