Measuring and testing – Liquid level or depth gauge – Immersible electrode type
Reexamination Certificate
1998-06-25
2001-09-25
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Immersible electrode type
C702S052000, C340S620000, C361S284000
Reexamination Certificate
active
06293144
ABSTRACT:
The invention concerns the monitoring of the consumption of a normally electrically conductive product contained in a reservoir made of electrically non-conductive material. It applies notably, but not exclusively, to the monitoring of the consumption of a marking product in an image forming device, for example that of an ink in a printing device.
The principal aim of monitoring the consumption of product is to be able to inform the user of the equipment including the reservoir about the residual quantity of product it has available: in that way the user can estimate in advance the moment to replace the reservoir, and secondarily the moment to obtain a replacement reservoir to do this.
This monitoring is notably useful in printing devices: ink level detection is then commonly referred to.
Various methods of ink level detection in devices using ink-jet technology are already known.
In particular, the document EP-A2-0 028 399 describes a method of detecting a minimum ink level in a reservoir which uses a resonating resonant circuit, the capacitance of which is formed by two metal plates between which the ink reservoir is located. This ink behaves as a dielectric whose value changes as the ink level decreases; likewise the capacitance of the resonant circuit changes with this ink level. It is indicated that this resonant circuit is calibrated so that its resonant frequency, and therefore the maximum level of voltage at its resistance, is achieved when the ink level has fallen to a predetermined minimum level, for example equal to 20%. When crossing of this threshold is detected, an optical or acoustic signal is emitted.
Detection of a given threshold of ink appears to correspond to detection of the crossing of a voltage threshold for the frequency which has been defined beforehand as being the resonant frequency for the quantity of residual ink it is being attempted to detect.
It must be noted that this method is of the all or nothing type, depending on whether the threshold has been crossed or not, and is not concerned with monitoring the quantity of ink prior to the crossing of this threshold.
In fact it must be noted that, the smaller the quantity of ink defining the capacitance, the smaller the voltage peak, in consequence of which this voltage peak is all the more difficult to detect since it corresponds to a small quantity of residual ink in the reservoir. This is doubtless one of the reasons which explains why this document provides for a minimum threshold as high as 20%.
Moreover, the crossing of the voltage threshold by the electrical signal which is detected appeared to correspond to quite scattered values of the quantity of residual ink actually available in the reservoir. This is doubtless another reason for which the manufacturers of printing equipment choose substantial safety margins in their indications of a “zero” level of residual ink which is supposed to lead the user to replace the reservoir.
One consequence of the choice of so high a safety margin is that, in order to guarantee that the user will not be prematurely short of ink, the reservoir is discarded while there is sometimes still an appreciable quantity of useable ink remaining.
The same situation is found more generally in relation to reservoirs containing a marking product, whether ink or not, and more generally in relation to reservoirs made of an electrically non-conductive material containing a product which is electrically conductive, and therefore able to be integrated into a capacitive arrangement.
One reason for the aforementioned scatter certainly lies in the existence of noise which is added to the measurement signal. Such noise is notably to be feared in the presence of sources of sizeable electromagnetic waves situated in proximity to the reservoir, or when mounting or mechanical configuration requirements do not allow the plates to be placed in sufficient proximity to the reservoir, which increases the sensitivity of the measurements with regard to the environment.
The object of the invention is to overcome the aforementioned drawbacks by allowing continuous monitoring of the consumption of a product contained in a reservoir, combined with an improved accuracy as regards detection of the moment when the residual quantity of this product crosses a minimum threshold, with the consequence of allowing, with complete security for the user, a lowering of this threshold and therefore a fuller use of the product contained in the reservoir before the latter is discarded. The invention aims to achieve this object without a modification of the reservoir being necessary (such a modification is of course possible while remaining within the scope of the invention).
More particularly, the invention aims to reduce the noise liable to spoil the accuracy of the measurements, simply and reliably, but without resulting in any notable cost. It aims in effect to be able to achieve the aforementioned objects within the context of mass production.
To that end the invention applies to a method of monitoring the consumption of an electrically conductive product contained in a reservoir made of an electrically non-conductive material having a storage chamber connected to one end of a product output channel, according to which
the storage chamber is disposed in a capacitive arrangement;
a measurement procedure is defined, having an excitation step consisting of applying an electrical excitation signal to that capacitive arrangement and an acquisition step consisting of taking an output signal from that capacitive arrangement and of supplying a measurement signal, this electrical excitation signal having a frequency chosen so that this measurement signal has a characteristic whose amplitude varies substantially with the quantity of product contained in that chamber;
a filtering procedure is defined, having a step of multiplying the measurement signal by a reference signal having a frequency at least approximately equal to the frequency of the electrical excitation signal, and the multiplied signal is applied to a low-pass filter with cut-off frequency greater than the difference between the frequencies of the excitation signal and the reference signal, so as to obtain a filtered signal;
a processing procedure is defined, having an identification step consisting of determining, in the filtered signal, the value of the amplitude of a characteristic of the same kind as the said characteristic of the measurement signal, and a conversion step consisting of deducing the value of information representing the quantity of product available in the reservoir from the said value of this amplitude; and
at least one measurement cycle is carried out, having steps consisting of monitoring the measurement procedure, the filtering procedure and the processing procedure and of acquiring the instantaneous value of the said information.
It must be noted here that the product of two periodic, notably sinusoidal, terms, is the sum of a first term whose frequency is the difference between the frequencies of the multiplied terms and a second term whose frequency is the sum of these frequencies. If the two terms have substantially the same frequency, the result of this is that the signal obtained by multiplication has a term with a substantially zero frequency and a term whose frequency is twice the common frequency of the original terms: by filtering this obtained signal with a simple low-pass filter, a signal substantially cleared of its noise components whose frequency is different from the frequency of the original terms can therefore be obtained. Such a multiplication is here without any consequence which interferes with the remainder of the processing, since the concern here is with an amplitude of the measurement signal and this amplitude is located, except for a multiplying factor defined by the chosen reference signal, in the filtered signal.
Preferentially, the capacitive arrangement is formed by disposing the said storage chamber between two electrically conductive plates, the excitation step consisting of applying the excitation s
Coudray Pascal
Froger Marie-Helene
Lorgeoux Mickael
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Loo Dennis
Williams Hezron
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