Note: Descriptions are shown in the official language in which they were submitted.
TOMEP. CONCENT~ATION SENSOR
This invention relates to the monitoring of electrostatic image
development and, in particular, to an image development sensor for deter-
mining the concentration of toner on a photoreceptor surface by optically
sensing the amount of toner that is triboelectrically attracted to a portion of
the photoreceptor surface.
In accordance with well known electrostatic printing processes, a
surfa~e bearing a latent electrostatic image is developed by selectively
applying a developer mix comprising toner and a carrier medium to the image.
With repeated use of the developer mix, toner is gradually consumed until
there is no longer a sufficient concentration of toner in the mix to develop
high ~uality, dense images. Also, the toner concentration may be insufficient
due to an unsuitable electrical bias on the developing system.
The prior art systems of monitoring toner concentration generally
follow two schemes of measurement, electrical and optical. Electrical sytems
depend upon measurements such as measuring the changes in resistance in the
mix as the high resistivity toner component varies in relation to the con-
ductive carrier component or measuring the change in inductance in a coil
through which the carrier and toner components are conveyed. In the optieal
systems, a test pattern is established either in the developer housing or on thephotoreceptive surface itself. The concentration of toner in the mix is then
correlated to the toner concentration as determined by an optical sensing
device measuring the amount of toner on the test pattern.
For example, prior art systems such as disclosed in U.S. Patent
Nos. 3,348,522; 3,348,523 and 3,376,853 disclose a reflective type sensor. In
particular, a clean drum signal is compared to a signal reflected from a test
pattern formed on the drum. Separate sensors are used for detecting each
signal and the outputs of the sensors are compared by a bridge circuit to
provide an error signal. The error signal represents the degree of toner
concentration.
In systems as shown in U.S. Patent Nos. 3,873,002 and 4,065,0319 an
electrically biased transparent electrode disposed on the photoreceptor
surface is conveyed past the development station to attract toner particles.
Light is transmitted t rom within the photoreceptor surface through the
transparent electrode and detected by a photosensor surface. The photosensor
-2~ 7B
provides a signal indicative of the density of toner particles on the transparent
electrode. A disadvantage with systems of this type is the relative cost due to
the complexity and number of components required.
Other systems measure toner concentration in the developer mix-
5 ture contained in a developer housing or resevoir. For example, U.S. Patent
Nos. 3,233,781 and 3,8~6,106 disclose reflecting a light beam from the
developer mixture. The measure of the reflectivity of the mixture manifests
the proportion of the toner to carrier concentration in the mixture. Disadvan-
tages with systems of this type are due in part to noise generated in the
10 system, due to the fact that the system is only an analog of the amount of
toner actually applied to the photoreceptor surface, and inclependent of the
effects of photoreceptor bias and exposure intensity, and due to the
dependence of the system to the constituents of the developer mixture.
Other examples of analog control are U.S. Patent 3,968,926
15 teaching the use of a funnel in the developer apparatus to collect developingmaterial. An inductance coil is wound about the funnel and connected to a
bridge circuit. The reactance of the inductance coil varies in accordance to
percentage of toner contained in the developing material.
A difficulty with many of the above mentioned toner monitoring
20 systems is that the accuracy of the systems depends upon a well controlled
distance between the measuring instrument and the photoreceptor surface. In
other words, the output of the sensing devices can vary considerably as the
distance between the sensing device and the photoreceptor surface varies.
This is particularly true in xerographic reproduction machines using belt
25 photoreceptors rather than drum photoreceptors. Except for locations very
near the drive rolls, the position of a belt in a belt system will vary during use.
In particular, the flutter and ripple of the belt, dynamic oscillations, and
localized deformations induced in the coating process can cause the distance
between the belt and the sensor to vary. Since the toner sensor voltage
30 fluctuations due to a photoreceptor spacing and misalignment are indistin-
guishable from those due to different developed toner masses, a device that is
insensitive to these variables is very advantageous.
It would be desirable therefore, to provide ~ simple inexpensive
densitometer or toner sensor for use in a xerographic processing machine that
35 provides a stable output signal for varying distances from the densitometer to
the surface under test.
-3~
It is therefore an object of an aspect of the
present invention to obtain improved toner concentration
sensing by using a toner concentration sensor providing a
relatively constant output signal regardless of the distance
between the sensor and the phot~receptor surface.
Further advantages of the present invention will
become apparent as the following description proceeds, and
the features characterizing the invention will be characterized
with particularity in the claims annexed to and forming a
part of this specification.
Briefly, the present invention in one aspect is
concerned with apparatus for monitoring toner concentration
on a photoreceptor surface. The apparatus includes a light
emitting diode (LED), a phototransistor, a beam splitter,
and a lens disposed between the beam splitter and the photo-
receptor surface to collimate -the light beam between the
lens and the photoreceptor surface. A portion of the light
emitted from the LED is transmitted through the beam splitter
and the lens to the photoreceptor surface. Collimated light
is reflected from the photoreceptor surface back through
the lens and reflected from the beam splitter to the photo-
transistor. The output signal from the phototransistor,
because of the reflected collimated light beam, is not depend-
ent upon the distance of the lens to the photoreceptor surface.
Alternately, a second lens is disposed between the beam splitter
and the phototransistor to enhance the overall resolution
of the system.
Other aspects of this invention are as follows:
- An electrophotographic reproduction machine including
a photoreceptor surface,
an optical system for projecting images of objects
onto the photoreceptor surface,
a developer ~or applying toner particles to the
latent image on the photoreceptor surface and an optical
densitometer for monitoring toner density on a portion of
the photoreceptor surface, the optical densitometer comprising
-3a-
a light emitting diode (LED), a beam splitter, a lens, a portion of
the light from the LED being transmitted through the beam splitter and the
lens to the photoreceptor surface,
a phototransistor, a portion of the light transmitted from the LED
to the photoreceptor surface through the beam splitter and the lens being
reflected from the photoreceptor surface baclc through the lens to the beam
splitter, and reflected from the beam splitter to the phototransistor whereby
a signal is provided representative of the concentration of toner on the
photoreceptor sur~ace, the signal being independent of the distanca from the
lens to the photoreceptor surface.
Apparatals for monitoring toner concentration on a photorecep-
tor surface independent of the apparatus to surface distance including
a. a light source
b. a photcconductor and
c. a lens disposed between the light source and the photoreceptor
surfa¢e for collimating the light from the light source, a portion of the light
from the light source being transmitted through the lens to the photoreceptor
surface, a portion of the light reflected from the photoreceptor surface being
collimated and reflected to the photoconductor.
2 0 Apparatus for monitoring toner concentration on a photo-
receptor surface including
a. a Iight source
b. a first photoconductor,
c. a photoreceptor surface,
d. a first lerLs disposed between the light source and the photo-
receptor surface, a second lens disposed between the photoreceptor surface
and the photoconductor, a portion OI the light from the light source
transmitted through the first lens to the photoreceptor surface, a portion of
the light reflected from the photoreceptor surface being transmitted back
3 0 through the second lens to the photoconductor.
-3b-
An electrophotographic reproduction machine including a
photoreceptor surface,
an optical system for projecting images of objects onto the
photoreceptor surface,
a developer for spplying toner particles to the latent image on the
photoreceptor surface snd an optical densitometer for monitoring toner
density on a portion of the photoreceptor surface, the optical densitometer
comprising
a light emitting diode (LED), a beam splitter, a first lens for
collimating th~ light from the LED, a portion of the light from the LED being
transmitted through the beam splitter and the lens to the photoreceptor
surface, a second lens,
a phototransistor, a portion of the light transmitted from the LED
to the photoreceptor surface through the beam splitter and the first lens
being reflected from the photoreceptor surface back through the first lens to
the beam splitter, and reflected from the beam splitter through the second
lens to the phototransistor whereby a signal is provided representative of the
concentration of toner on the photoreceptive surface, the signal being
independent of the distance from the lens to the phototreceptor surface.
Apparatus for monitoring toner concentration including
a. a light emitting diode (LED)
b. a first phototransistor,
c. a photoreceptor surface,
d. a beam splitter in communication with the LED and the
phototransistor,
e. a first lens disposed between the beam splitter and the photo-
receptor surface for collimating the light from the LED, a portion of the
light from the LED transmitted through the beam splitter and the lens to the
photoreceptor surface, a portion of the collimated light reflected from the
photoreceptor surface being transmitted back through the first lens and
reflected from the beam splitter to the phototransistor to compensate for
variable distance between the first lens and the photoreceptor surf~ce.
-3c ~ 7~3
For a better understanding of the present invention, reference may
be had to the accompanying drawings wherein the same reference numerals
have been applied to like parts and wherein:
Figure 1 is a schematic elevational view of an electrophotographic
5 printing machine incorporating the features of the present invention;
Figure 2 is a collimated infrared densitometer or toner sensor in
accordance with the present invention; and
Figure 3 is an infrared line densitometer in accordance with
another feature of the present invention.
With reference to Figure 1, there is illustrated an electrophoto-
grahic printing machine having a belt 10 with a photoconductive surface 12
moving in the direction of arrow 16 to advance the photoconductive surface 12
sequentially through various processing stations~ At charging station A, a
corona generating device 26 electrically connected to high voltage power
15 supply 32 charges the photoconductor surface 12 to a relatively high substan-
tially uniform potential. Next, the charged portion of the photoconductive
surface 12 is advanced through exposure station B. At exposure station B, an
original document 34 is positioned upon a transparent platen 36. Lamps 38
illuminate the original document and the light rays reflected from the original
document 34 are transmitted through lens 40 onto photoconductive surface 12.
The exposure station B also includes test area generator 42 comprising a light
source providing two different output levels. The two different output levels
provide different intensity test light images projected onto the photocon-
ductive surface 12 to record two test areas. Each of the test area recorded on
the photoconductive surface 12 is rectangular and about 10 mm by 8 mm in
size. Each of these test areas will be developed with toner particles at
development station C.
A magnetic brush development system ~4 advances a developer
material into contact with the electrostatic latent image in the test areas at
lS development station C. Preferably, the magnetic brush development system
44 includes two magnetic brush developer rollers 46 and 48. Each developer
roller forms a brush comprising carrier granules and toner particles. The
latent image and test areas attract toner particles from the carrier granules
forming a toner powder image on the latent image and a pair of developed
mass areas corresponding to each of the test areas.
A toner particle dispenser 50 is arranged to furnish additional toner
particles to housing 52. In particular, a foam roller 56 disposed in a sump 58
dispenses toner particles into an auger 60 comprising a helical spring mounted
in a tube having a plurality of apertures. Motor 62 rotates the helical member
of the auger to advance the toner particles to the housing 52. The developed
test areas pass beneath a collimated infrared densitometer or toner sensor 64.
The infrared densitometer 64 is positioned adjacent the photoconductor
surface 12 between the developer station C and transfer station D and
generates electrical signals proportional to the developed toner mass of the
test areas.
At the transfer station D, a sheet of support material 66 is moved
into contact with the toner powder image. The sheet of support material is
advanced to the transfer station by sheet feeding apparatus 68, preferably
including a feed roll 70 contacting the uppermost sheet of stack 72. Feed roll
70 rotates so as to advance the uppermost sheet from stack 72 into chute 74.
The ehute 74 directs the advancing sheet of support material into contact with
--5--
the photoconductive surface 12 in timed sequence in order that the toner
powder image developed thereon contacts the advancing sheet of support
material at the transfer station.
Transfer station D includes a corona generating device 76 for
5 spraying ions onto the underside of sheet 66. This attracts the toner powder
image from photoconductive surface 12 to sheet 66. After transferJ the sheet
continues to move onto a conveyor (not shown) which advances the sheet to
fusing station ~.
Fusing station E includes a fuser assembly 80 for permanently
10 affixing the transferred powder image to sheet 66. Preferably, the fuser
assembly comprises a heated fuser roller 82 and a backup roller 84. The sheet
66 passes between the fuser roUers with the toner powder image contacting
fuser roller 82. After fusing, the chute 86 drives the advancing sheet 66 to
catch tray 88 for removal from the printing machine by the operator.
In accordance with the present invention, the infrared densito-
meter 64 as shown in Figure 2 includes a suitable semiconductor light emitting
diode (LED) 9û, a phototransistor 92, a beam splitter 94 and a double convex
lens 96. The LED 90 can provide, for example, a 9DsO nanometer peak output
wavelength with a 60 nanometer one-half power bandwidth. In a preferred
20 embodiment, the power output is appro~imately 45 +1~ milliwatts. The
phototransistor 92 receives the light rays or beam reflected from the test
areas on the photoconductive surface 12 of belt 10. The phototransistor 92
converts the light ray input to an electrical output signal ranging from about
zero volts to about ten volts. The LFD 90 and phototransistor 92 can be
25 provided with focusing lenses 91 ~nd 93, respectively.
The infrared densitometer 64 is also used perio~ically to measure
the light rays reflected from the bare photoconductive surface, i.e. without
developed toner particles, to provide a reference level for calculation of the
signal ratios. Preferably, a not shown air purge system is associated with the
30 infrared densitometer to prevent the accumulation of particles on the optic
components.
As illustrated in Figure 2 by the solid lines, a collimated light beam
is projected from the lens 96 to the portion of the photoconduetive surface 12
illustrated as the illuminated area. Preferably, the photoconductive surface 12
35 provides a considerable amount of specular reflectance. It should be noted,
~.Ald;.9~ 7~
however, that a surface that is substantially diffuse reflecting will work, but
may diminish the accuraey of the densitometer 64.
A coUimated light beam as shown by the dotted lines is reflected
from the surface 12 back to lens 96. There is a relatively large area of surface12 reflecting light, illustrated as the area of reflected signal. The reflected
light signal or beam is also collimated between the surface 12 and lens 96.
Thus, the illumination and re~lected beams remain relati-rely constant, regard-
less of the gap distace between the lens 96 and the surface 12. This relatively
constant re~lected beam is projected onto the phototransistor 92. In other
words, the output signal from phototransistor 92 is relatively constant
regardless of gap distance.
In operation, the light output or beam from the light emitting diode
90 is projected through the beam splitter 94. Preferably~ the beam splitter 94
is 50 percent transmissive and is positioned to enable both the phototransistor
92 and the LED 90 to be located on the same optical axis. The light beam
transmitted to the beam splitter 94 is then projected through the lens 96 onto
the photoreceptive surface 12. In a preferred embodiment, the lens 96 is an 18
mm focal bi-convex lens. The lens 12 provides collimation of the light beam
onto the photoreceptor surface 12 and focuses the spectrally reflected portion
Of the beam onto the phototransistor 92 through a suitable aperture 97.
Preferably, this arrangement allows approximately 50 percent of
the energy specularly reflected from the photoreceptive surface 12 to be
collected and focused onto the phototransistor 92 independent of the lens 96 to
photoreceptor surface 12 distance. A second phototransistor 98 can be placed
in the path of the light beam initially reflected from the beam splitter 94 as
shown in Figure 2. This will provide a reference signal to compensate for light
output changes due to LED aging and ambient temperature changes.
In accordance with another ~eature of the present invention, a
double convex lens 100 may be inserted between the phototransistor 92 and the
beam splitter 94 or between beam splitter 94 and LED 90 to enhance the
overall resolution of the sensor as shown in Figure 3. The resolution is
approximately inversly proportional to the total system magniEication of the
lenses. For typical values, in a preferred embodiment, the expectant resolution
is of the order of 40 micrometers.
It should be noted that the focal length oE lens 100 is determined by
the average operating gap distance between lens 96 and photoconductive
æ~7~
surface 12 in order to minirnize lens errors. In operation, the effect of lens 100
is to diminish the collimation of the beam reflected from surface 12 in favor ofbetter resolution.
The effect of lens 100 is illustrated in Figure 3, showing in dotted
5 lines an exaggerated diverging beam reflected from a relatively small area of
surface 12. Thus, the resolution is enhanced, illustrated by the relatively small
area of reflected signal, at the expense of a less collimated reflected signal.
An aperture 102 can be included to minimize error in spot size due to lens
errors.
While there has been illustrated and described what is at present
considered to be a preferred embodiment of the present invention, it will be
appreciated that numerous changes and modifications are likely to occur to
those skilled in the art, and it is intended in the appended claims to cover allthose changes and modifications which fall within the true spirit and scope of
15 the present invention.
