Optics: measuring and testing – For light transmission or absorption – Of fluent material
Patent
1995-02-27
1996-10-29
Rosenberger, Richard A.
Optics: measuring and testing
For light transmission or absorption
Of fluent material
356436, 356440, G01N 2159
Patent
active
055701930
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the field of concentration detection and more particularly to the detection of toner concentration in color liquid developer compositions especially in the presence of contaminants.
BACKGROUND OF THE INVENTION
In liquid developer systems the liquid developer is generally comprised of a carrier liquid and toner particles in a generally constant ratio. During imaging operations the concentration of toner particles is reduced and concentrated toner is added to return the concentration to its desired value.
It is important that the concentration of particles should be kept within a given range in order to realize consistent copy quality. This requirement is especially important in color printers or copiers, where the quality of the images is especially dependent on the color balance and on its stability.
In general, concentration of toner particles in liquid developers is determined by measuring the attenuation of light passing through a given path filled with the liquid developer. Since the particles absorb and scatter light, the attenuation of the light is related to the concentration of the particles.
U.S. Pat. No. 4,579,253 describes a system in which the beam of light is split into two components only one of which is attenuated by the liquid developer. The concentration is determined from the ratio of the attenuated and unattenuated beams.
Such systems work fairly well in single color systems or in multicolor systems in which there is no cross contamination between the colors. In general, the most troublesome cross-contamination is black toner particles in a relatively low attenuation color such as yellow. Since black has an attenuation several times that of yellow, visually negligible black contamination can effect the determination of the color concentration in a way which seriously disturbs the color balance of the system.
Japanese Patent Publication Kokai 1-148943 describes a system in which the attenuation of beams of light having two different colors are sequentially measured. Using these attenuation values, the publication describes a method for determining the concentration of both the black and the color particles.
Generally speaking, measurement of attenuation caused by toner particles is most effective when a large cross-section is viewed, since this increases the signal level for the brightness of light source. This preferred operation requires a detector with a wide field of view.
SUMMARY OF THE INVENTION
The present invention is based on an analysis of the different factors which are operative in the attenuation of light by toner particles dispersed in a carrier liquid.
The two main factors are the absorption of light and the scatter of light by the particles. In general, for black toner particles, the effect of scatter is very small compared to the effect of absorption. On the other hand, for colored toner particles, especially for yellow, the effect of scatter is much greater than that of absorption.
In a preferred embodiment of the invention, the relative sensitivity to scattering measurements is improved by reducing the angle of view of a detector which detects light passing through the dispersion.
When a wide field of view is used much of the light which reaches the detector may be caused by multiple scattering. When black or other mainly absorbing toners are measured this effect is unimportant. However, when colored toners are present this multiple scattering greatly reduces the sensitivity of the system.
For maximum sensitivity, light which is scattered by a colored toner particle should be removed from the system and should not reach the detector. However, when the angle of view of the detector is wide, light which is scattered is generally rescattered and a portion of the rescattered light reaches the detector. The larger the angle the greater the problem.
In a preferred embodiment of the invention the angle of view of the detector is limited to less than .+-.10 degrees, preferably less than .+-.5 degrees. At these angle
REFERENCES:
patent: 3233781 (1966-02-01), Grubbs
patent: 4416538 (1983-11-01), Mueller et al.
patent: 4579253 (1986-04-01), Shenier
patent: 4660152 (1987-04-01), Downing et al.
patent: 4981362 (1991-01-01), deJong et al.
English Language Abstract of JP-62-99774.
English Language Abstract of JP-62-099775.
English Language Abstract of JP-62-140061.
Forgacs Peter
Landa Benzion
Niv Yehuda
Plotkin Michael
Indigo N.V.
Rosenberger Richard A.
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