Optics: measuring and testing – By shade or color – With color determination by light intensity comparison
Reexamination Certificate
2001-08-27
2004-08-10
Smith, Zander V. (Department: 2877)
Optics: measuring and testing
By shade or color
With color determination by light intensity comparison
C399S030000
Reexamination Certificate
active
06774999
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the printing and xerographic arts. It finds particular application in conjunction with the monitoring and control of developer materials, and will be described with particular reference thereto. However, it is to be appreciated that the present invention will also find application in other printing and xerographic systems where the concentration of toner or other materials or chemicals used in the printing process is advantageously calibrated, monitored, or controlled.
In many printing and xerography systems, images are formed on paper or another medium using electrophotographic printing. In this method, a photoreceptive surface is uniformly electrostatically charged, and the image is transferred to the photoreceptive surface through selective exposure to light or other electromagnetic radiation. The light discharges the exposed areas of the photoreceptive surface to form an electrostatic charge pattern known as the latent image. The latent image is developed by exposure to a developer material that selectively coats the charged surface areas. A typical two-component developer includes toner particles comprising a polymer or resin with a color agent, and carrier beads comprising resin-coated spheres of steel or another material. The carrier beads are usually several times larger than the toner particles. The toner particles triboelectrically bond to the larger, spherical carrier beads to form composite developer particles. In the vicinity of the electrostatically charged regions of the latent image, the toner particles are attracted away from the carrier beads and attach onto the photoreceptor due to the greater electrostatic attraction of the photoreceptor versus the triboelectric bonding to the carrier beads. The thusly developed latent image is known as the toner image. The toner image is transferred to the paper or other print medium using a corona discharge to effectuate transfer of the toner particles from the toner image onto the paper. Finally, a fusing process employing heat and pressure permanently affixes the toner onto the paper to form the final printed image.
In the case of color printing, several toner stations are employed, e.g. in the case of CMYK printing separate toner stations for printing the cyan, magenta, yellow, and black (K) image components. A full color toner image is thus produced which is transferred to the final print medium and fused in a manner similar to that just described. An electrophotographic printing apparatus typically includes additional components to monitor the electrostatic potentials, image characteristics, and other aspects of the complex printing process.
An important system parameter for obtaining consistently high quality electrophotographic printing is control of the developer composition. The toner concentration is typically defined as the ratio of the weight of the toner to the weight of the carrier in the developer. During printing, toner is gradually depleted whereas the carrier beads do not transfer to the paper. Thus, the toner concentration in the developer decreases over time with usage.
With reference to
FIG. 1
, a developer housing
10
that stores, maintains, and applies the developer is described. A mixing wheel
12
rotates in a direction
13
and mixes toner particles
14
and carrier beads
16
in a developer sump
18
. Under the action of the mixing wheel
12
, the toner particles
14
triboelectrically bond to the carrier beads
16
to form composite developer particles
20
, each of which includes a plurality of toner particles
14
surrounding a single carrier bead
16
. Note that the toner particles
14
and the carrier beads
16
are shown schematically in FIG.
1
and are not drawn to scale. In a typical developer, the carrier beads
16
are several times larger than the toner particles
14
, and both are much smaller than they are shown in
FIG. 1. A
magnetic roll
22
comprising a hollow tube
24
and fixed magnets
26
applies the developer particles
20
to the photoreceptor
28
(shown in part). The hollow tube
24
of the magnetic roll
22
rotates in a direction
29
as shown and the magnets
26
attract the metallic cores of the carrier beads
16
of the developer particles
20
onto the tube
24
. As the hollow tube
24
rotates the attached developer particles
20
are brought into close vicinity with the photoreceptor
28
where the toner particles
14
are pulled off the carrier beads
16
and onto the charged portions comprising the latent image
30
. The photoreceptor
28
is typically embodied in the form of a continuous belt loop that rotates in a direction
31
so as to develop the entire latent image
30
. The toner coating thus formed comprises the toner image
32
. In order to control the thickness of the developer coating on the roll
22
, a baffle or metering blade
34
removes excess developer from the roll
22
.
As a consequence of the developing process, toner particles
14
are removed from the developer sump
18
to form the toner image
32
. As a result, the toner concentration in the developer sump
18
decreases over time and is advantageously replenished. A toner dispenser
36
includes a toner brush
38
that dispenses toner in a controlled fashion from a toner reservoir
40
into the developer sump
18
.
The prior art discloses several methods for determining when to replenish the toner, and to determine how much toner to add. In some printing systems, toner dispensing occurs on a fixed schedule, i.e. by a pre-determined use factor, such as one minute of dispensing for every ten minutes of printing. Of course, this type of system rather inflexible. Many printing systems use some sort of automatic dispensing system in which the toner concentration is monitored in some way and toner replenishment occurring responsive to the monitoring. The monitoring process can take place either in the developer housing
10
or on the photoreceptor
28
, e.g. by printing a test patch that is characterized by optical reflectance or other means. Monitoring on the photoreceptor
28
has the disadvantage of introducing additional factors which can affect the toner image
32
, such as variations in electrostatic charge of the photoreceptor
28
. Monitoring in the developer housing
10
involves measurement of the toner concentration in the developer sump
18
. The prior art discloses use of an in situ magnetic permeability sensor, commonly known as a packer sensor (not shown in FIG.
1
), for monitoring the toner concentration in the developer sump
18
. The packer sensor detects changes in the magnetic permeability of the developer material due to changes in the average spacing of the metallic cores of the carrier beads
16
due to changes in the toner concentration. The packer sensor has the disadvantage of being a relative sensor. There remains an unfulfilled need in the art for a convenient method and apparatus for obtaining absolute quantitative information on the toner concentration in a developer which can be used, for example, to calibrate a packer sensor.
The present invention contemplates a new and improved method and apparatus therefor which overcomes the above-referenced problems and others.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, an apparatus for measuring toner concentration in a developer contained in a developer housing is disclosed. A developer sample container receives a portion of developer extracted from the developer housing. A spectrophotometer measures spectrophotometric data for the portion of the developer in the developer sample container. A processor estimates the toner concentration based on the measured spectrophotometric data and a pre-determined relationship between the spectrophotometric data and the toner concentration.
In accordance with another aspect of the present invention, a method for measuring toner concentration in a developer is disclosed. A sample of the developer is extracted. Color characteristics of the developer sample are measured. The toner con
Franzen James J.
Garsin Paul A.
Gross Eric M.
Smith, Jr. Edward W.
Fay Sharpe Fagan Minnich & McKee LLP
Smith Zander V.
Stock, Jr. Gordon J.
Xerox Corporation
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