JP2004093570A - Concentration sensor for color toner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a concentration sensor for color toner capable of sensing the toner concentration in a color liquid developer when black toner particles cause a pollution. <P>SOLUTION: The sensing method based on this concentration sensor includes a process preparing dispersion of color toner particles arbitrarily polluted by black toner particles, a process illuminating this dispersion, a process detecting volume of light passing through this dispersion at a view angle of less than ±10 degrees, and a process using the detected volume of light to determine concentration of color toner particles. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to the field of density detection, and more particularly, to the field of toner density detection in color liquid developers, especially when contamination is present.

In liquid developer systems, the liquid developer generally consists of a fixed ratio of carrier liquid and toner particles. During the imaging operation, the toner particle concentration drops, so dark toner is added to return this concentration to its desired value.
It is important that this particle concentration be kept within a given range in order to achieve a certain copy quality. This requirement is particularly important in color printers or copiers where the quality of the image depends in particular on the color balance and its stability.
In general, the concentration of toner particles in a liquid developer is determined by measuring the attenuation of light passing through a given path filled with the liquid developer. As these particles absorb and scatter light, the attenuation of this light is related to the concentration of these particles.

U.S. Pat. No. 6,077,064 describes a system in which a light beam is split into two components, only one of which is attenuated by a liquid developer. The density is determined from the ratio between the attenuated beam and the non-attenuated beam.
Such systems work quite well in single color systems or in multicolor systems where there is no cross-contamination between the colors . Generally, the most troublesome cross-contamination is black toner particles in relatively low attenuation colors such as yellow. Since the black decay is several times that of yellow , visually negligible black contamination can affect color density determination to the extent that it seriously disrupts the color balance of the system.

U.S. Pat. No. 6,077,064 describes a system for sequentially measuring the attenuation of two differently colored light beams. Using these attenuation values, this publication describes a method for determining the density of both black and color particles.
Generally speaking, measuring attenuation caused by toner particles is most useful when looking at large cross sections. This is because it increases the signal level for the brightness of the light source. This preferred operation requires a wide field of view detector.

U.S. Pat. No. 4,579,253

JP-A-1-148943

The present invention is based on the analysis of different factors affecting light attenuation by toner particles dispersed in a carrier liquid.
The two main factors are light absorption and light scattering by the particles. Generally, for black toner particles, the effect of scattering is much smaller than the effect of absorption. On the other hand, for color toner particles, especially yellow, the effect of scattering is much greater than that of absorption.

In a preferred embodiment of the present invention, the relative sensitivity for measuring scattering is improved by reducing the angle of view (viewing angle) of a detector that detects light passing through the dispersion of the toner.
With a wide viewing angle, much of the light reaching this detector can be due to multiple scattering. This effect is not significant when measuring black or other predominantly absorbing toners, but when color toners are present, this multiple scattering greatly reduces the sensitivity of the system.
For maximum sensitivity, light scattered by the color toner particles should be removed from the system and not reach the detector. However, when the angle of view of the detector is large, the scattered light is generally further re-scattered, after which a portion of the re-scattered light reaches the detector. The greater the angle of view, the greater the problem.
In a preferred embodiment of the invention, the angle of view of the detector is limited to less than ± 10 °, preferably less than ± 5 °. At these angles, the relative sensitivity of the color to black increases. Since the total signal received by the detector decreases with decreasing angle, the only lower limit on angle is the brightness of the light source.

Accordingly, in a preferred embodiment of the present invention, there is provided an apparatus for detecting the concentration of color toner particles in the presence of black or other absorbing toner particles,
light source,
A photodetector having a field of view of less than about ± 10 °, preferably less than about ± 5 °,
Means for supplying a dispersion of color toner particles between the light source and the detector, optionally containing improper contamination by black toner particles; and using the output from the photodetector to determine the concentration of the color toner particles. An apparatus is provided that includes a computing circuit component operative to determine.

In a preferred embodiment of the invention, the light source includes a lamp and a collimator lens. The light detector preferably includes a focusing lens.
In a preferred embodiment of the invention, this field of view is limited by the size of the detector, the size of the focusing lens and / or the stop.
This lamp is preferably a laser diode or other laser light source. Alternatively, preferred light sources are LEDs or high intensity lamps.
In a preferred embodiment of the present invention, the amount of black contamination can be determined. In this embodiment, there is further provided a second photodetector having a large field of view and a computing circuit component operative to use the output from the second photodetector to determine the concentration of the black toner particles. You.

Further, according to a preferred embodiment of the present invention, a method for detecting the concentration of color toner particles in the black toner particles thus contaminated dispersed,
Preparing a dispersion of color toner particles contaminated with black toner particles, illuminating this dispersion,
A method is provided that includes detecting the amount of light passing through the dispersion at a viewing angle of less than ± 10 °, and using the detected amount of light to determine the concentration of the color toner particles.
The present invention will be better understood from the following detailed description of a preferred embodiment of the invention, taken in conjunction with the accompanying drawings.

Reference is now made to FIG. 1 which shows a concentration detector constructed and operative according to an embodiment of the present invention.
The concentration detector typically includes a light source 10, such as a lamp or laser diode, and a collimator lens 12 that collimates the light from the lamp and passes it through a dispersion 14 of toner understanding in the carrier liquid. In order to improve the collimation, that is, to reduce the angle of the light, it is preferable to include the aperture 11. Preferably, the dispersion 14 flows through a channel between the lens 12 and the focusing lens 16. The focusing lens 16 focuses the light passing through the dispersion 14 onto a detector element 18, such as a photodiode or a photoresistor. The system optionally includes an aperture 20 at the focal point of this light to limit the field of view of the detector element 18. Alternatively or additionally, by increasing the distance from lens 16 and detector element 18, the size of the utilization area of detector element 18 will limit the field of view to the desired angle.

In a preferred embodiment of the present invention, the light source 10 is a high-intensity laser diode or LED, and a light source that effectively constitutes a point light source may be used, and the aperture 11 may be omitted. A bright point light source significantly reduces the viewing angle and allows the invention to be optimally applied.
In a preferred embodiment of the present invention, detector element 18 is a photodiode with a very small photosensitive area and aperture 20 may not be necessary.
In a preferred embodiment of the present invention, the angle of view of detector 18 is limited to less than about ± 10 °, and more preferably, to less than about ± 5 °. As will be seen below, the smaller this angle , the greater the selectivity of the system for changes in color toner density compared to black toner contamination . The only practical limitations on angle are the light source intensity and detector sensitivity.

In another, particularly preferred embodiment of the invention, a collimator is provided behind the laser light source 10 so that the lenses 12 and 16 are replaced by planar transparent elements and illuminate only a relatively limited area of the dispersion 14. Is placed . In this embodiment, the viewing angle is limited as described above, but the elimination of double scattered light is greatly improved. In essence, the requirement that light come from small areas of dispersion and arrive at small angles of incidence greatly enhances yellow sensitivity. Preferably, a stop 20 is included to further reduce the illumination angle of the light source 10 and to further reduce the scattered light received by the detector 18.

The inventor has discovered that decreasing the viewing angle of the detector 18 increases the sensitivity to color toner, defined as the percentage change of the signal for a given change in color toner density divided by the nominal signal. The sensitivity to black depends almost exclusively on the viewing angle.
In this way, as the angle decreases, the measurement of the color toner density becomes much less sensitive to contamination by black particles than in a wide field of view.

In particular, in a typical wide-angle system for measuring yellow toner particle concentration, the sensitivity to black stain is about 50 times that for yellow. For this reason, even very small and visually insignificant amounts of black toner contamination can cause large errors in yellow density measurements. If this angle is limited to about ± 5 ° to ± 10 °, the relative sensitivity is reduced to about 3 and 10, respectively , depending on the angle of view. For measurements of magenta toner particles, the relative sensitivity is reduced from about 30 to about 2-5, depending on the angle.

During calibration, the dispersion of one or more of the color toner particles is tested and the resulting detector output is measured. Based on these measurements, a sensitivity curve for the system and / or a signal level at which additional dark toner is to be added to the system is determined. This value and other points on the calibration curve are stored in a computing circuit component 24 having a computer such as a microprocessor or dedicated analog and / or digital circuitry. In operation, in a preferred embodiment of the present invention, the computing circuitry 24 compares the output of the detector 18 to a stored value and applies dark toner to the system when the signal is above a threshold.
It will be seen that the reverse of this preferred embodiment, ie, using a wide angle detector in close proximity to the liquid flow, reduces sensitivity to color particles and increases it to black. By placing this detector near the flow, the sensitivity to black can be several times higher than that to yellow .

In one embodiment of the invention, two measurements are made. In the first stage, the black density is determined as described in the previous section. In the second stage, narrow angle measurements are taken and corrections for these results are made for black contamination. Such a correction would be based on a measure of the previous effect of the various black stain levels on narrow angle measurements.
This wide angle measurement can be performed with another light source, or in the preferred embodiment of the invention shown in FIG. 2, a second detector 26 that observes this dispersion is placed near the lens 16. If the detector is small, it will block very little light from the detector 18 and have a wide viewing angle of dispersion. For this configuration, the distance between lenses 12 and 16 must be maximized to reduce sensitivity to yellow.
For those skilled in the art, the present invention is not limited to what has been particularly shown and described, but is only defined by the claims .

FIG. 1 is a schematic diagram of a concentration detector configured and operating according to an embodiment of the present invention. FIG. 9 is a schematic diagram of a concentration detector configured and operated according to a second embodiment of the present invention.

Explanation of reference numerals

10 light source (lamp); 12 collimator lens; 14 dispersion; 16 focusing lens; 18 detector element; 20 aperture stop; 24 arithmetic circuit component

Claims (15)

A method for detecting the concentration of color toner particles in a dispersion improperly contaminated by black toner particles, comprising:
Providing a substantial amount of dispersion of color toner particles optionally contaminated with black toner particles,
Illuminating this dispersion,
Detecting a quantity of light passing through the dispersion at a viewing angle of less than ± 10 °, and using the detected quantity of light to determine the concentration of the color toner particles. The method of claim 1, wherein the preparing step includes determining the sensitivity of the detected light to color toner particles of known density. A method according to claim 1 or claim 2, wherein the viewing angle is less than about ± 5 °. (4) The method according to any one of (1) to (3), comprising a step of correcting black toner particle contamination during the dispersion. The method according to any one of claims 1 to 4, wherein
A method further comprising detecting the amount of light passing through the dispersion at a high viewing angle, and using the detected amount of light to determine the concentration of black toner particles. An apparatus for detecting the concentration of color toner particles in the presence of black or other absorbent toner particles,
Light source (10),
A photodetector (18) having a field of view of less than about ± 10 °,
Means for providing a dispersion (14) of color toner particles between the light source and the detector, optionally including undesired contamination by black toner particles, and using the output from the photodetector to produce the color toner particles Apparatus comprising a computational circuit component (24) operative to determine the concentration of the. 7. The device according to claim 6, wherein the light source comprises:
A device including a laser diode and a collimator (12). The device according to claim 6 or 7, wherein the photodetector comprises a focusing lens (16). The device according to claim 8, wherein the field of view is limited by the size of the detector. The apparatus according to claim 8 or 9, wherein the field of view is limited by the size of the lens. 11. Apparatus according to any one of claims 6 to 10, wherein the photodetector comprises an aperture (20) to limit the field of view. An apparatus according to any one of claims 6 to 11, comprising means for determining the sensitivity of the detected light to color toner particles of known density. 13. The device according to any one of claims 6 to 12, wherein the viewing angle is less than about ± 5 °. 14. Apparatus according to any one of claims 6 to 13, comprising means for determining the concentration of black toner particles contaminating the dispersion. 14. Apparatus according to any one of claims 6 to 13, wherein a second photodetector (26) having a large field of view and the black toner using an output from the second photodetector. An apparatus comprising a computing circuit component (24) operative to determine a concentration of a particle.

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