Data processing: measuring – calibrating – or testing – Measurement system – Measured signal processing
Reexamination Certificate
1998-06-25
2001-02-06
Shah, Kamini (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Measured signal processing
C702S189000, C702S190000, C347S007000, C347S014000
Reexamination Certificate
active
06185515
ABSTRACT:
The invention concerns the detection of a threshold for filling, with an electrically conducted product, a reservoir made of electrically insulating material. It relates notably, but not exclusively, to the detection of a threshold for filling, with a marking product, a reservoir designed to be integrated into an image formation device, for example for an ink in a printing apparatus. The filling threshold can be zero, corresponding to the case of a reservoir which no longer contains any available product.
The main aim of detecting when a filling threshold has been crossed is to be able to inform the user of the appliance including the reservoir that it will shortly be time to replace the reservoir.
Such detection is notably useful in printing appliances: this is then normally referred to as ink level detection.
Various methods of detecting an ink level in devices using inkjet technology are already known.
In particular the document EP-A2-0 028 399 describes a method of detecting a minimum level of ink in a reservoir which uses a resonating resonant circuit whose capacitance is formed by two metal plates between which the ink reservoir is situated. This ink behaves like a dielectric whose value changes as the ink level decreases; likewise the capacitance of the resonant circuit changes with this ink level. This resonant circuit is calibrated so that its resonant frequency, and therefore the maximum level of the voltage at its resistor, is achieved when the ink level has dropped to a predetermined minimum level, for example 20%. When it is detected that this threshold has been crossed, a visual or audible signal is emitted.
The detection of a given ink threshold appears to correspond to the detection of the crossing of a voltage threshold for the frequency which has previously been defined as being the resonant frequency for the residual quantity of ink which is to be detected.
In fact, it should be noted that, the lower the quantity of ink defining the capacitance, the lower the voltage peak, as a consequence of which this voltage peak is all the more difficult to detect when it corresponds to a small residual quantity of ink in the reservoir. This is no doubt one of the reasons which explains why this document provides for a minimum threshold as high as 20%.
In addition, the crossing of the voltage threshold by the electrical signal which is detected appeared to correspond to fairly scattered values of the residual quantity of ink actually available in the reservoir. This is no doubt another reason why the manufacturers of the printing equipment choose substantial safety margins in their indications of a “zero” residual ink level, supposed to cause the user to replace the reservoir.
One consequence of the choice of such a high safety margin is that, in order to guarantee that the user will not be prematurely short of ink, the reservoir is scrapped when there sometimes still remains a not insignificant quantity of usable ink.
The same situation prevails more generally with regard to reservoirs containing a marking product, whether or not it is a case of ink, and more generally with regard to reservoirs made of electrically insulating material containing an electrically conductive product, which can therefore be integrated into a capacitive arrangement.
One reason for the aforementioned scatter lies certainly in the existence of noise which is added to the measuring signal. Such noise is notably to be feared in the presence of significant sources of electromagnetic waves situated close to the reservoir, or when requirements for installation or mechanical configuration do not make it possible to place the plates sufficiently close to the reservoir, which reinforces the sensitivity of the measurements vis-a-vis the environment.
The object of the invention is to mitigate the aforementioned drawbacks by affording an improved accuracy of the time when the residual quantity of an electrically conductive product contained in an electrically insulating reservoir crosses a minimum threshold, with the consequence of allowing, in complete safety for the user, a lowering of this threshold and therefore a more complete utilisation of the product contained in the reservoir before scrapping the latter. The invention aims to achieve this object without any modification of the reservoir being necessary (such a modification is of course possible whilst remaining within the scope of the invention). The invention also aims to determine the absence of product in the outlet channel of the reservoir (zero filling threshold), notably the absence of ink in a duct connected to a print head, whilst doing away with ambient noise.
More particularly the invention aims to reduce noise liable to impair the accuracy of the measurements, in a simple and reliable fashion, but without giving rise to appreciable cost. It aims in fact to be able to achieve the aforementioned objects in the context of mass production.
The invention relates to this end to a method of detecting a predetermined threshold for filling, with an electrically conductive product, a reservoir made of electrically insulating material having a storage cavity containing this product connected to a product outlet channel, according to which
the storage cavity is disposed in a capacitive arrangement;
a measuring procedure is defined having an excitation step consisting of applying, in periodic square waves, an electrical excitation signal to this capacitive arrangement and a capture step consisting of taking off a measurement signal from this capacitive arrangement, this electrical excitation signal being chosen so that this measurement signal has a characteristic varying substantially when the quantity of product contained in this cavity reaches this filling threshold;
a conversion procedure is defined, including steps consisting of identifying an instantaneous value (for example a peak to peak amplitude) of a quantity representing the said characteristic, comparing it with a reference threshold representing the filling threshold, and deriving therefrom a first binary signal representing the situation of the said instantaneous value with respect to the reference threshold;
a digital filtering procedure is defined, including a convolution step consisting of generating a third binary signal whilst effecting the convolution product of this first binary signal and a second binary signal derived from the first binary signal by introducing a delay equal to a multiple of at least one of the period of the square waves;
a processing procedure is defined including a test step consisting of deriving from the mean value of this third binary signal a binary value representing the situation of the quantity of product with respect to the filling threshold; and
at least one measuring cycle is effected, including steps consisting of monitoring the measuring procedure, the conversion procedure, the filtering procedure and the processing procedure and capturing the said binary value.
It should be noted here that the measurement signal must normally be zero outside the square waves, that is to say when there is no excitation signal; when the measurement signal is not zero this may be due to noise, but an effective way of eliminating the noise is to seek the part of the measurement signal which is periodic with a period equal to that of the excitation square waves and to eliminate the remainder of the signal. It is this result that the convolution product makes it possible to produce very simply. The most simple delay is a delay equal to the period of the square waves, but it is of course possible to choose longer delays, for example in order to eliminate the periodic noises of short duration.
In so far, however, as this digital filtering does not make it possible to eliminate any part of the noise which has a frequency of occurrence substantially equal to the frequency of the square waves, it may be advantageous to combine this digital filtering with a filtering of another nature, for example a frequency filtering, so as also to exclude the noise being repeated at t
Coudray Pascal
Froger Marie-Helene
Lorgeoux Mickael
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Shah Kamini
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