Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Mechanical measurement system
Reexamination Certificate
1998-06-26
2002-08-20
Wachsman, Hal (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Mechanical measurement system
C702S050000, C702S052000, C702S189000, C347S007000
Reexamination Certificate
active
06438500
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a method and a device for detecting the absence of a product in a reservoir. More particularly, the present invention concerns the detection of ink in a removable print cartridge of an image transfer device.
2. Description of the Related Art
For image transfer devices which use ink-jet technology, such as ink-jet printers, many devices and methods have been designed to detect the absence of ink.
A first known type of detection uses the electrical characteristics of the ink by measuring the resistance thereof between two electrodes.
The document EP-A-0 370 765 describes a detection device comprising two electrodes placed in the channel connecting an ink ejection head to the ink reservoir and a means of detecting the electrical resistance between the two electrodes. The first electrode is situated in proximity to the ejection head while the second is remote from it. A potential difference is applied between these two electrodes. The resistance of the ink is measured and the presence or absence of the ink is deduced from the measured resistance value.
This device has many drawbacks.
The two electrodes must necessarily be spaced out by a predetermined distance, which complicates the production of the ink cartridge or the ejection head and increases the production cost. Furthermore, during the printing of a document, the electrodes are subjected to electromagnetic interference which affects the detection of the resistance.
In an image transfer device which uses ink-jet technology, such as an ink-jet printer, a print head has a plurality of ink transfer means in the form of ejection channels, generally identical and parallel, which make it possible to simultaneously eject a number of drops of ink of different pigmentation and thus increase the print speed of the image transfer device.
In the course of their research, the inventors determined that, by transmitting electrical energy to the ink contained in an ejection channel and analyzing the effect produced, it is possible to deduce information on the operation of the channel under consideration.
However, according to the methods and devices for detecting signal presence known in the prior art, for example by rejection filter, detection of the signal transmitted by a channel necessitates positioning the print head in a fixed position, which prevents the detection of ink during the print phases. This constraint considerably reduces the number of pages which can be printed during a predetermined period, or the number of ink detection phases is very limited.
These considerations become all the more significant as the number of ink reservoirs becomes larger, which further increases the constraint for color printers.
The document EP-A-0 028 399 describes a device for detecting a minimum quantity of ink in a reservoir. A resonant circuit has a resistor and a capacitor, the poles of which are formed by two metal plates between which the ink reservoir is located. The reservoir containing the ink forms the dielectric of the capacitor. As the quantity of ink decreases, the value of the capacitance of the capacitor thus formed varies.
The resonant circuit is calibrated so that its resonant frequency corresponds to a predetermined quantity of ink in the reservoir. The maximum voltage at the terminals of the resistor is thus reached for this predetermined quantity of ink which constitutes a threshold.
By measuring the voltage at the terminals of the resonant circuit resistor, the crossing of the threshold is detected, and an alarm signal is activated.
According to this document, only the crossing of one threshold can be measured, and consequently a single quantity of ink can be detected. Under these conditions, this device is of interest if the quantity of ink detected is small, in order to alert the user just before there is no more ink in the reservoir.
However, in particular because of the poor signal detection signal to noise ratio, it is very difficult with this device to determine accurately what voltage exactly corresponds to a small quantity of ink. It is then necessary to provide a safety margin in order to alert the user before the reservoir is empty. This safety margin, for example of the order of 20 percent of the total quantity of ink, leads to a wastage of ink, since the user will change the reservoir while there is ink remaining inside.
The failings described above concerning the transmission of a signal to an ejection channel are also valid with regard to the document EP-A-0 028 399.
Persons skilled in the art may also be induced to cause the sending of a signal in order that the reception thereof is affected by the quantity of product he wishes to detect or measure. He must then use signal detection techniques of known type.
To that end, in the field of signal detection, a device capable of detecting a periodic signal when it is mixed in a set of signals is known through the document U.S. Pat. No. 5,185,783. Such a device comprises a filter capable of selecting only the frequency of the carrier (affected by its tolerance) from a set of signals sent on the telephone line and containing a signal mixed with other signals. The signal at the output of the filter is sampled. The samples are processed as they are taken. By counting them and testing for crossing of a numerical threshold by the number of samples obtained during this counting, an attempt is made to determine the occurrence of a period T
ON
then that of a period T
OFF
. The presence of the signal is validated when one period T
OFF
and one period T
ON
have been detected.
This method is not satisfactory in all cases and the inventor has notably observed the following drawbacks:
the method is highly sensitive to parasitic signals whose frequency is in the frequency band of the signal to be detected. In the case where these signals are too numerous, at least one of the periods T
ON
or T
OFF
is not recognized,
in the case of samples not recognized as belonging to a period T
ON
or T
OFF
, the information contained in these samples, although possibly significant, is lost. There results, at the very least, a delay in detection of the signal.
SUMMARY OF THE INVENTION
The present invention aims to remedy the drawbacks of the prior art by providing a device and a method for determining the absence of product in at least one reservoir, with a satisfactory reliability and accurately, while being simple and economical to implement.
To that end, according to a first aspect, an object of the invention is a method of detecting the absence of a product in a reservoir consisting, during a transmission step, of transmitting a signal affected by the presence of the product in the reservoir, and of detecting the presence of the signal amongst a set of signals, the signal having an occurrence duration T
ON
, comprising notably:
a) a discrimination step, during which the said signal is discriminated from the set of signals, and an output signal is delivered, the level of which represents the result of the said discrimination of the said signal from the said set of signals,
b) a sampling step, during which the said level thus obtained is sampled in In signal samples spread over a duration greater than a repetition period T
a method characterized in that it also comprises:
c) a correlation step, during which, to each sample of rank i varying from 1 to In, a state value B(i) representing its level is mapped and, during at least part of the sampling duration, a true correlation value SR is calculated, by summing, for each pair of samples of ranks i and i+Z, the instantaneous value of correlation between the state value B(i) and the state value B(i+1), the samples of ranks i and i+Z being located at instants displaced by a period T, Z being the number of samples taken during a period T of the signal to be detected.
d) a rate calculation step, during which the rate &rgr; of samples, whose level represents the presence of the said signal, is measured over at least part of the sampling duration, thi
Coudray Pascal
Delumeau François
Dodge Alexandre
Froger Marie-Helene
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Wachsman Hal
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