Measuring and testing – Liquid level or depth gauge – Immersible electrode type
Reexamination Certificate
1998-01-08
2002-02-12
Patel, Harshad (Department: 2855)
Measuring and testing
Liquid level or depth gauge
Immersible electrode type
C347S007000
Reexamination Certificate
active
06345532
ABSTRACT:
The present invention concerns in general terms a method and device for determining the quantity of product present in a reservoir, and more particularly for determining the quantity of ink present in the reservoir of an image formation device. The present invention also concerns a product reservoir, notably an ink reservoir for an image formation device. It also concerns a device for processing electrical signals intended to be used in a device for determining the quantity of product present in a reservoir.
For image formation devices, such as printers, which use ink jet technology, numerous devices and methods have been designed for determining the quantity of ink present in the reservoir.
The document U.S. Pat. No. 4,700,754 describes a device for detecting the quantity of liquid ink in a flexible reservoir contracting as the ink level decreases. The external bottom wall is coated with a conductive layer constituting one pole of a capacitor. The wall of the reservoir serves as a dielectric of the capacitor thus produced whilst the ink surface in contact with the bottom wall constitutes the second pole of the capacitor. A measuring electrode placed at the centre of the reservoir connects the ink to a measuring device. When the ink level decreases, the surface area of ink facing the conductive layer coated on the wall decreases, and therefore the value of the equivalent capacitance also decreases. The fact that the reservoir is flexible enables the measuring electrode to remain in contact with the ink.
This type of detection is used for a cartridge having flexible walls and cannot be applied to rigid cartridges. This is because contact between the measuring circuit and the ink can be made only if the top wall, when it is crushed, forces the measuring electrode to be in contact with the ink.
In addition, it is necessary to provide an electrode in contact with the ink in the reservoir, which complicates the manufacture of the reservoir and increases the cost thereof.
Moreover, it is difficult to know the ink level if the latter is below a level lying between the measuring electrode and the bottom wall. This is because the measuring electrode cannot go down as far as the base of the reservoir. The measurement range is thus limited in the lower values. However, it is precisely when there is very little ink remaining in the reservoir that it is advantageous to be alerted so as to change the reservoir or fill it.
The document EP-A-0 028 399 describes a device for detecting a minimum quantity of ink in a reservoir. A resonant circuit includes a resistor and a capacitor whose poles are formed by two metal plates between which the ink reservoir is situated. 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 achieved for this predetermined quantity of ink which constitutes a threshold.
By measuring the voltage at the terminals of the resistor of the resonant circuit, the passing of the threshold is detected, and a warning signal is activated.
According to this document, only the passing of a threshold is measurable, and consequently only a quantity of ink can be detected. Under these circumstances, this device is of interest if the quantity of ink detected is small, in order to alert the user just before the end of the reservoir.
However, it is very difficult with this device to determine accurately what voltage corresponds exactly 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 around 20 per cent of the total quantity of ink, results in a waste of ink, since the user will change the reservoir whilst there is still ink inside.
The present invention aims to remedy the drawbacks of the prior art by providing a device and method for determining the quantity of product present in a reservoir, which detects, with satisfactory reliability and with precision, a predetermined quantity of product, whilst being simple and economical to implement.
The invention starts from the idea according to which generating an electrical field in the reservoir produces a signal representing the quantity of product in the reservoir. However, the inventors have found that this signal can be used only in a limited range of quantities.
This is because, with certain types of alternating electrical fields characterised by a frequency of around 0.5 to 2 MHz, the representation of the quantity of product as a function of the signal is biunivocal within a product quantity range; the signal can therefore be used directly in this range in order to determine the quantity of product. However, the representation of the quantity of product as a function of the signal is not biunivocal outside this range; outside this range, there is therefore uncertainty about the quantity of product.
The inventors then discovered that, by increasing the frequency, the representation was biunivocal for all the quantity values (from 0 to 100%). However, for certain types of reservoir the inventors once again found a scatter in the electrical characteristics of the reservoirs from one example to another, thereby giving rise to uncertainty about the quantity outside a range in which the signal is usable.
In this context, the invention proposes a method for determining the quantity of product present in a reservoir, characterised in that it includes the steps of:
establishing, through the product present in the reservoir, a first electrical field, and a second electrical field which is differentiated from the first electrical field by at least one characteristic,
measuring the said first and second electrical fields passing through the product, in order to produce first and second electrical signals respectively representing the first and second electrical fields, and
processing the first electrical signal in order to produce a first information signal able to take a plurality of values representing the quantity of product then present in the reservoir,
taking into account, in order to determine the quantity of product, at least one range of quantities in which this representation is directly usable, and
processing the second electrical signal in order to produce, at the appropriate time, a second information signal representing at least one predetermined quantity outside the said range.
The present invention resolves the above-mentioned problems and makes it possible to obtain a usable measurement of the quantity of product in a reservoir over all the quantity values (from 0 to 100%).
In particular, providing a second electrical field differentiated by at least one characteristic from the first, advantageously removes the uncertainties mentioned above outside the range in which the first information signal is directly usable, whether these uncertainties are due to the fact that the representation is not biunivocal outside this range, or whether they are due to the scatter in electrical behaviour observed from one reservoir to another.
In general terms, the invention applies to any product, notably a consumable product used in a given device.
The invention preferably applies to ink contained in the reservoir of an image formation device. “Ink” here means any liquid, solid, gaseous or powder product designed to modify an optical or physical factor of the printing medium.
The present invention also has the advantage of being adaptable to a large number of existing devices.
The invention applies to cases where several interchangeable reservoirs can be used in succession. This occurs for example for image formation devices in which ink reservoirs of different colours can be used successively. The user fits the reservoir of the desired colour at a given moment and makes as many changes of reservoir as necessary.
In fact, the
Coudray Pascal
Froger Marie-Helene
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Patel Harshad
LandOfFree
Method and device for determining the quantity of product... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for determining the quantity of product..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for determining the quantity of product... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2968881