Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-06-24
2001-02-06
Grimley, Arthur T. (Department: 2852)
Incremental printing of symbolic information
Ink jet
Controller
C073S30400R
Reexamination Certificate
active
06183054
ABSTRACT:
The invention relates to a method and a device for determining the quantities of consumable products contained in reservoirs grouped together next to one another. It relates to a type of measurement of the available volumes by capacitive means and concerns more particularly an improvement making it possible to improve the accuracy of different measurements in spite of stray capacitive couplings existing between electrodes associated with the different reservoirs.
By way of a preferred application, the invention also concerns a document printing device using the method indicated above.
A number of ways for detecting a level of ink in a reservoir of a printing device are known. Notably, association with the reservoir is known of a capacitive arrangement to which an excitation signal, generally a high frequency alternating signal, is applied. It is known that the signal transmitted by such a capacitive arrangement varies according to the quantity of ink remaining in the reservoir. This variation can therefore be used to indicate to the user the fill level of the reservoir or at least the fact that a minimum level has been reached. Such information allows the user to refill the reservoir or to change a cartridge comprising such a reservoir often associated with an ink-jet print head. The capacitive arrangement is such that at least one capacitor of relatively small capacitance (a few picofarads) is constituted so that the reservoir is located or can be located at a given instant between electrodes of such a capacitor.
By way of example, document EP 0 028 399 describes a method for detecting the minimum level of ink in a reservoir, using a resonant circuit, the capacitor of which is formed by two metal plates (electrodes) between which the ink reservoir is located. The latter therefore fills the dielectric space of such a capacitor and the quantity of ink has a direct effect on the permittivity of the said dielectric space, and therefore the value of the capacitance. The resonant circuit is calibrated so that its resonant frequency and the maximum voltage at its measurement resistance are reached when the level of ink has fallen to a predetermined value. When resonance is achieved, a signal which can be used for signalling is sent. Consequently, with such a system, the only information available is an indication of the fact that the ink level is or is not above a predetermined low threshold.
When the ink level decreases, the measurements become inaccurate and it is difficult to determine the voltage which corresponds exactly to a total absence of ink. This uncertainty leads to provision of a safety margin taking into account the measurement inaccuracy, in order to guarantee a presence of ink at any instant. For example, it may be chosen to send a message when the level is below 20% of the initial level. Once this message has been sent, it is no longer possible to indicate the instant at which the ink runs out completely. This therefore results in a certain wastage. This problem is accentuated when a number of reservoirs containing different coloured inks or pigmented products are used, for example for colour reproduction. These reservoirs are carried by a carriage constrained to move along a guidance means itself arranged facing a print medium movement mechanism. Each reservoir communicates with an output duct connected to a corresponding print head, itself carried by the carriage. Consequently, the reservoirs are grouped together next to one another and, if metal electrodes are associated with each of them in order to constitute a capacitive arrangement suitable for allowing measurements of level in the different reservoirs, stray capacitances may exist between electrodes normally assigned to different reservoirs, which leads to measurement errors. The lower the level of ink measured in a reservoir, the greater the errors, even if large quantities of ink remain in the neighbouring reservoirs.
The invention aims firstly to correct this type of measurement error.
More particularly, the invention concerns a method of determining quantities of consumable products respectively contained in reservoirs grouped together next to one another, of the type using a capacitive arrangement comprising a number of conductive electrodes associated respectively with the said reservoirs, certain of which may be connected to an excitation signal generator and others of which may be connected to detection and measurement means, in order to respectively apply a signal to the said capacitive arrangement and to detect and process a resulting signal transmitted by the latter and representing a quantity of product contained in one of the reservoirs, characterised in that it consists, for each reservoir in turn, of selecting aforementioned electrodes of the said capacitive arrangement in order to apply such a signal across one of the reservoirs, of detecting and measuring the corresponding transmitted signal, then of correcting each measurement by correction values depending on at least certain of the other measurements.
The aforementioned consumable products are generally different. For example, if different coloured inks or pigmented products are concerned, they may have different densities or viscosities, or in general different characteristics.
According to a currently preferred embodiment, the correction values consist of terms each representing the product of another measurement (that is to say relating to another reservoir) and a predetermined corrective coefficient. In practice, the global correction applied to a measurement is the algebraic sum of such terms relating to the other reservoirs. The corrective coefficients depend on the geometry of the reservoirs and their layout with respect to one another. A matrix of correction coefficients is thus defined, which can be stored once and for all, so that the correction consists, after each series of measurements successively using the conductive electrodes assigned to the different reservoirs and making it possible to form a vector of measurement values (that is to say the uncorrected values resulting from the measurements of the transmitted signals, each time, by the capacitive arrangement), of producing the product of this vector and the matrix of correction coefficients in order to obtain a vector of corrected measurement values. These corrected measurement values can then be displayed to inform the user.
According to another advantageous characteristic of the invention, which applies when the reservoirs contain electrically conductive products flowing towards a device electrically connected to a reference potential (for example earth), the method defined above may be supplemented by a series of additional operations, possibly used after comparison of each of the aforementioned corrected measurements with a threshold value or respective threshold values.
Depending on the result of these comparisons, the excitation signal may be changed and aforementioned electrodes selected again in turn in order to apply a second excitation signal successively across each reservoir.
The corresponding transmitted signal is detected and measured and each of these signals is compared with a new predetermined threshold value, possibly specific, and, depending on these comparisons, a control and/or display command is produced.
More precisely, in the method envisaged above, the excitation signals are high-frequency alternating signals, of different frequencies, and consequently the change of excitation signal consists of a change of frequency. During the first part of the method, a relatively high frequency, for example of the order of 5 MHz, is used, while the second part of the method is implemented with a much lower frequency, for example of the order of 10 kHz.
With this second frequency, which is therefore applied only when the reservoir is almost empty, the transmitted signal is relatively constant except when the electrically conductive product disappears in the duct connecting the reservoir to the using device electrically connected to a reference potential. A r
Coudray Pascal
Froger Marie-Helene
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Grimley Arthur T.
Tran Hoan
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