Method and apparatus employing variable pressure to clean a substrate in a printing apparatus

An electrostatic printer employing a cleaning blade that applies a variable amount of pressure on a photoreceptor substrate. The printer detects an amount of toner on the substrate, and varies the cleaning blade pressure as an increasing function of the detected amount of toner.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to method and apparatus for cleaning a 
substrate in a printing apparatus, and, more particularly, to a method and 
apparatus for cleaning the substrate by applying variable pressure to the 
substrate. 
2. Discussion of the Related Art 
A typical document copier includes an electrostatic printer with a belt 
having a photoconductive surface. To transfer an image onto a sheet of 
paper, the printer charges the belt to a uniform potential, and 
subsequently exposes the belt to a pattern of light corresponding to the 
image. Parts of the belt exposed to the light are discharged, resulting in 
an electrostatic latent image being formed on the belt. The portion of the 
belt having the electrostatic image then passes a development station that 
deposits toner on the belt in the pattern of the image, resulting in a 
toner powder image being formed on the belt. A piece of paper is then 
tacked to the belt and then removed from the belt, resulting in an image 
being formed on the paper. 
In a printing process of this type, some residual toner particles will 
remain on the photoconductive surface after the toner image has been 
transferred to the paper. In addition to the residual toner, other 
residual particles, such as paper debris, additives and plastic, are left 
behind on the surface after image transfer. The residual particles should 
be mostly removed prior to the next printing cycle to avoid their 
interference with production of another image. 
Various methods may be used for removing residual particles, such as 
methods employing a cleaning brush, a cleaning web, or a cleaning blade of 
a rubber-like material such as polyurethane. Blade cleaning scrapes or 
wipes across the belt to remove the residual particles from the belt. 
Blade cleaning is a desirable method for removing residual particles due 
to its simplicity and economy. Blade cleaning entails frictional contact 
with the belt, however, which degrades the blade over a period of time. 
A conventional blade cleaning method applies a constant blade pressure 
against the substrate. The constant pressure is chosen based on the many 
contingencies that might affect cleaning performance. The resulting 
constant pressure is more than is needed under some conditions, thereby 
accelerating the wear rate of the blade. If an over-pressured blade is 
configured in "doctor mode," the blade will be more susceptible to 
fold-under, resulting in immediate destruction of the blade and perhaps 
even damage to the belt. More particularly, lesser amounts of residual 
toner to be cleaned results in increased friction and adhesion between the 
blade and the belt. The increase in the friction and adhesion cause the 
blade to be drawn further downstream in the process direction, with an 
increase, therefore, in the pressure of the blade against the belt. This 
increase in pressure initiates a positive feedback mechanism which 
increases the friction and adhesion, which increases the pressure, etc. 
Thus, excessive frictional contact results from excessive pressure on the 
blade, leading to premature blade failure. Insufficient pressure on the 
blade, however, leads to insufficient cleaning of the substrate. 
The following disclosures may be relevant to various aspects of the present 
invention and may be briefly summarized as follows: 
U.S. Pat. No. 3,918,809 to Hwa discloses an apparatus for cleaning liquid 
developer from an upwardly moving support surface, such as a reusable 
surface for carrying latent electrostatic images. Cleaning blades clean 
the support surface. Separate members hold the cleaning blades in contact 
with the support surface. 
U.S. Pat. No. 5,034,774 to Higginson et al. discloses an apparatus for 
applying toner for developing an electrostatic latent image formed on the 
charge retaining surface of a moving recording medium. The apparatus 
includes compliant cleaning blades for contacting a drying roller to 
prevent agglomeration of papers fibers and toner particles on the 
interface between the roller and the scraper blade. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of the invention to provide a printing apparatus having an 
improved substrate cleaning system. 
It is another object of the present invention to provide a printing 
apparatus that regulates pressure applied to a cleaning member. 
Additional objects and advantages of the invention will be set forth in 
part in the description which follows and in part will be obvious from the 
description, or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and attained by means of 
the instrumentalities and combinations particularly pointed out in the 
appended claims. 
To achieve the objects and in accordance with the purpose of the invention, 
as embodied and broadly described herein, a method of operating an 
apparatus having a substrate and a cleaning member contacting the 
substrate, comprises the steps of moving the substrate relative to the 
cleaning member; detecting residual particles on the substrate; and 
causing the cleaning member to apply a variable pressure to the substrate, 
the variable pressure being an increasing function of an amount of 
residual particles detected by the detecting step. 
According to another aspect of the present invention, a method of operating 
an apparatus having a substrate and a cleaning member contacting the 
substrate, comprises the steps of moving the substrate relative to the 
cleaning member; detecting residual particles at a location downstream 
from the cleaning member; and causing the cleaning member to apply a 
variable pressure to the substrate, the variable pressure being an 
increasing function of an amount of residual particles detected by the 
detecting step. 
According to yet another aspect of the present invention, an apparatus 
comprises a substrate; a cleaning member configured to remove residual 
particles from the substrate; means for moving the substrate relative to 
the cleaning member; means for generating a signal indicating an amount of 
residual particles on the substrate; and means, responsive to the signal, 
for causing the cleaning member to apply a variable pressure to the 
substrate. 
According to yet another aspect of the present invention, an apparatus 
comprises a substrate; a cleaning member configured to remove residual 
particles from the substrate; means for moving the substrate relative to 
the cleaning member; means for generating a signal indicating an amount of 
residual particles at a location downstream from the cleaning member; and 
means, responsive to the signal, for causing the cleaning member to apply 
a variable pressure to the substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1 the exterior of a preferred copier 100, including an 
electrostatic printer, of the preferred embodiments of the present 
invention is shown to include a document feeder 105 for transporting an 
original document to a platen where the copier scans the original 
document. Copier 100 then duplicates the original document image onto a 
piece of paper and transports the piece of paper to paper output tray 180. 
The interior of the copier 100, as shown in FIG. 2, includes a 
photoreceptor belt 110 has a photoconductive surface 111. Belt 110 moves 
in the direction of arrow 12 to advance successive portions of belt 110 
through various processing stations sequentially disposed about the path 
of movement of belt 110. Belt 110 is entrained about a stripping roller 
114, a tension roller 16, and a drive roller 20 driven by a motor 121. A 
pair of springs (not shown) maintain belt 110 in tension by resiliently 
urging tension roller 16 against belt 110. Both stripping roller 114 and 
tension roller 16 are rotatably mounted. 
Initially, a portion of belt 110 passes through charging station A, where a 
corona device 122 charges a portion of belt 110 to a relatively high, 
substantially uniform, potential, either positive or negative. 
At exposure station B, flash lamps 132 illuminate an original document on 
transparent platen 30. Lens 133 projects light rays reflected from the 
original document onto the charged portion of belt 110 to selectively 
dissipate the charge on belt 110. This selective discharging records an 
electrostatic latent image, corresponding to an image on the original 
document, on belt 110. Alternatively, a laser may be provided to 
selectively discharge belt 110 in accordance with stored electronic 
information. 
Belt 110 then advances the electrostatic latent image to development 
station C. Development station C includes two developer housings 134 and 
136 for contacting belt 110 to develop the electrostatic latent image. 
Cams 138 and 140 move housings 134 and 136 into and out of a developing 
position. Motor 121 selectively drives cams 138 and 140. Each developer 
housing 134 and 136 supports a developing system including brush rolls 142 
and 144, each of which includes a rotating magnetic member for advancing 
developer mix, carrier beads and toner, into contact with the 
electrostatic latent image. The electrostatic latent image attracts toner 
particles from the carrier beads to form a toner powder image on belt 110. 
If only one color of developer material is required, the second developer 
housing may be omitted. 
A sheet of paper 149 advances from supply tray 50 to transfer station D 
along conveyor 156. Belt 110 advances the toner powder image to transfer 
station D, where the sheet of paper contacts the powder image on belt 110. 
A corona generator 146 charges the paper to a potential such that the 
paper becomes tacked to belt 110 and the toner powder image is attracted 
from belt 110 to the paper. A corona generator 148 then charges the paper 
such that the paper becomes detached from belt 110, allowing stripping 
roller 114 to remove the paper from belt 110. 
Subsequently, the paper moves in the direction of arrow 60 to fusing 
station E. Fusing station E includes a fuser assembly 170 that permanently 
affixes the transferred toner powder image to the paper. Fuser assembly 
170 includes a heated fuser roller 172 and a backup roller 174 for 
pressure engaging the toner powder image, which contacts fuser roller 172. 
The paper then advances through a chute 162 to paper output tray 180. 
Cleaning station F removes residual particles remaining on photoreceptor 
belt 110 after each copy is made. FIG. 3 shows cleaning station F in more 
detail. A primary cleaning blade 116 is located upstream in the process 
direction from a secondary cleaning blade 118. Primary blade 116 removes 
most of the residual particles from the surface of belt 110. A vacuum 
system transports particles, removed by primary blade 116, to a waste 
particle receptacle. Alternatively, the particles may be transported by an 
auger in front of blade 116, or, if the cleaning station is located under 
the belt, the particles may be transported by gravity. 
Secondary blade 118 accumulates particles not removed by primary blade 116. 
Secondary blade 118 accumulates particles in a location that blocks an 
optical path between light source 160 and photodetector 150, which sends a 
signal to controller 196 to control actuator 120 to vary an amount of 
pressure applied to primary blade 116, as discussed in more detail below. 
FIG. 4 shows a cross-section of cleaning blades 116 and 118, each having an 
edge in frictional contact with the photoreceptor surface 111 at an angle 
.alpha. (where .alpha.=180.degree. (.beta.+90.degree. ). Primary blade 116 
is configured in the "doctoring mode," having an angle .alpha.1 of 
approximately 10.degree. to 25.degree. with a preferred angle of 
approximately 15.degree. when the pressure on primary blade 116 is 
approximately 35 grams/cm. 
Secondary blade 118 is configured in the "wiping mode," having an angle 
.alpha.2 of approximately 65.degree. to 80.degree. with a preferred angle 
.alpha.2 of approximately 75.degree. when the pressure on secondary blade 
118 is approximately 35 grams/cm. In general, the secondary blade pressure 
for a given angle .alpha. will be less than that of the primary blade 
loading, because toner securely fixed on belt 110 acts as a lubricant and 
a secondary blade will see less of this securely fixed toner than the 
primary blade sees. 
Secondary blade 118 accumulates residual particles 130 as copier 100 
operates over a period of time. Copier 100 clears accumulated toner 130 by 
periodically blowing compressed air, by swabbing with a piece of plastic 
foam or other material, or, when copier 100 is not generating copy output, 
by momentarily camming secondary blade 118 away from belt 110, allowing 
the accumulated particles to be carried by belt 100 to the upstream 
primary blade 116. 
A photodetector 150 and light source 160 oppose each other upstream from 
the cleaning edge of secondary cleaning blade 118. Accumulation of toner 
130 blocks the passage of light between light source 160 and photodetector 
150. 
In general, an excessively large amount of toner getting past primary blade 
116 indicates that primary blade 116 should apply additional pressure to 
belt 110. The rate of toner pile growth 130 is an increasing function of 
the rate of toner getting past primary blade 116. The amount of light 
detected by detector 150 is a decreasing function of the size of toner 
pile 130. Thus, if the amount of light received by detector 150 is below a 
certain threshold, a certain amount of time after cleaning blade 118 has 
been cleared of toner, controller 196 causes actuator 120 to apply a 
greater amount of pressure to primary blade 116, resulting in primary 
blade 116's applying a greater amount of pressure to belt 110. 
It is desirable to always have some small level of residual toner passing 
under primary blade 116 to provide lubrication. Thus, an excessively small 
amount of toner getting past primary blade 116 indicates that primary 
blade 116 can, or should, apply less pressure to belt 110. If the amount 
of light detected by detector 150 is above a certain threshold, a certain 
amount of time after cleaning blade 118 has been cleared of toner, 
controller 196 causes actuator 120 to apply a lesser amount of pressure to 
cleaning blade 116, resulting in cleaning blade 116's applying a lesser 
amount of pressure to belt 110. Thus, controller 196 controls actuator 120 
to apply pressure as an increasing function of detected toner. 
In the first preferred copier, controller 196 causes actuator 120 to adjust 
the pressure on blade 116 no more often than every few hours, since the 
particle detection feedback loop operates relatively slowly, as blade 118 
normally accumulates toner relatively slowly. 
The second embodiment of the present invention differs from the first 
preferred embodiment in the manner in which the amount of residual 
particles on belt 110 is detected. FIG. 5 shows the toner detection system 
of the second preferred copier. Laser 594 directs a light beam towards 
belt 110. If the light beam impinges on belt 110 on an area containing no 
residual particles, the light beam will be reflected to mirror 515, which 
is positioned approximately one inch above belt 110. Mirror 515 then 
reflects the light beam back to belt 110. Thus, the light beam reflects 
off of belt 110 multiple times before reaching detector 584. 
If the light beam impinges on an area of belt 110 containing one or more 
residual particles, the amount of light received by detector 584 
decreases. 
Detector 584 sends a signal to low pass filter 582, which generates a 
smoothed version of the signal from detector 584, and sends the smoothed 
signal to controller 596. Low pass filter 582 compensates for the rapid 
movement of toner particles, fixed on moving belt 110, relative to laser 
594 and detector 584. Controller 596 causes actuator 120 to apply pressure 
to belt 110 as a decreasing function of the smoothed signal from low pass 
filter 582. 
Thus, the toner detection method of the second embodiment does not rely on 
accumulation of toner by a blade downstream from the primary blade. 
Laser 594 is angled such that the light beam will impinge onto belt 110 a 
certain amount of times. A higher angle of incidence results in more 
reflections off belt 110 and a greater sensitivity of the system, 
resulting from an increased probability that the light beam will impinge 
on an area of belt 110 containing a toner particle. If the angle of 
incidence of a light beam is too high, however, the light signal 
ultimately received by detector 584 will be decreased, resulting from 
increased absorption of belt 110 due to the increased angle of incidence 
and resulting from the increased number of reflections from belt 110 and 
mirror 515 before the light beam ultimately impinges on detector 584. 
Mirror 515 should be separated from belt 110 by a sufficient distance so 
that mirror 515 is not overly susceptible to contamination by toner 
particles. Further, to reduce toner particle contamination, bias voltage 
generator 592 charges mirror 515 with the same polarity as the toner 
particles to repel the toner particles. Further, air streams sweep across 
mirror 515, detector 584, and laser 594 to keep mirror 515, detector 584, 
and laser 594 relatively free of particles. 
Thus, the preferred embodiments of the present invention employ a method 
for determining an amount of loading of a cleaning blade to clean a 
photoreceptor and to increase the reliability and life expectancy of a 
blade cleaning system. 
The preferred embodiments of the present invention may be modified in 
various ways. If the substrate is sufficiently translucent, rear 
illumination of part or all of the width of the substrate is advantageous, 
because detection of transmitted light is relatively insensitive to 
surface scratches. The photodetector could be located at a fixed position 
along the width of the substrate, could span the entire rear-illuminated 
width, or could be scanned back and forth along the width. 
FIG. 6 is a flow chart illustrating a method of operating an apparatus 
having a substrate and a cleaning member contacting the substrate in 
accordance with another embodiment of the invention. As illustrated this 
method includes step 602 of moving the substrate relative to the cleaning 
member, step 604 of detecting residual particles and step 606 of causing 
the cleaning member to apply a variable pressure to the substrate, wherein 
the variable pressure is an increasing function of an amount of residual 
particles detected by the detecting step 604. As shown in FIG. 6, the 
detecting step 604 further includes the steps of directing light toward 
the substrate and detecting an amount of light transmitted through the 
substrate. Additionally the detecting of step 604 may be at a location 
downstream from the cleaning member. 
Detection of the residual toner densities upstream of the primary blade 
would allow the system to adjust blade pressure before the detected toner 
levels reach the primary blade. 
Although a photoreceptor belt is shown, the proposed invention is 
applicable to drum type photoreceptors as well. 
Additional advantages and modifications will readily occur to those skilled 
in the art. The invention in its broader aspects is therefore not limited 
to the specific details, representative apparatus, and illustrative 
examples shown and described. Thus, various modifications and variations 
can be made to the present invention without departing from the scope or 
spirit of the invention, and it is intended that the present invention 
cover the modifications and variations provided they come within the scope 
of the appended claims and their equivalents.