Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
This invention relates to an improved photo-
conductive drum cleaning apparatus for use with an electro-
static copier.
There exist, in the prior art, a number of systems
designed to remove toner particles and other materials which
accumulate on the photoconductive imaging surface and which,
if allowed to remain on the imaging surface, would result in
dirty copies and possible machine malfunction. Generally,
these systems comprise belts, rollers, blades, and the like.
While these systems have enjoyed some success, they have
generated their own problems, one of which is buildup of
toner fluid or other material on the cleaning surface them-
selves. This buildup impairs cleaning action of the system
and may in time damage the photoconductive surface.
SUMMARY OF THE INVENTION
Broadly speaking the present invention overcomes
the problems of the prior art by providing an electrophoto-
graphic copying machine including in combination a recix-
culating imaging surface; intermittently actuated means for
sequentially moving the imaging surface in the course of a
single circuit through an exposure station at which the
surface is provided with an electrostatic latent image of an
original, through a developing station at-,which liquid
de~eloper is applied to the surface to form a developed
toner image, through a transfer station at which the developed
image is transferred to a copy sheet, and then through a
cleaning station spaced from the developing station; a
cleaning member at the cleaning station; means for retracting
3C the cleaning member from the imaging surface while the surface
is stationary; and means for moving the cleaning member into
engagement with the surface when a predetermined period less
than the period required to traverse an entire circuit has
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elapsed following initaition of movement of the surface,
the predetermined period being sufficient to permit the
arrival at the cleaning station of an imaging surface
portion that has been wetted by liquid developer at the
developing station.
More specifically, our invention contemplates a
photoconductive drum cleaning apparatus comprising a
rotating foam roller and a self-cleaning squeegee blade
sequentially arranged adjacent to and in contact with the
photoconductive surface at a location beyond that at which
image transfer takes place and ahead of the charging station.
The self-cleaning squeegee blade is formed by a driven
endless rubber or polyurethane belt supported by pulleys
located outboard of the drum so that the belt extends com-
pletely across the photoconductive surface. The belt is
so disposed as to contact the photoconductive surface at
an
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angle to a tangent to the drum so that an edge portion of
the belt engages the photoconductive surface. The endless
belt is itself cleaned as it is driven past a cleaning
station located away from the photoconductive surface. In
various embodiments of the invention, the endless belt
contacts the photoconductive surface at a right ang~e or
at an acute angle to a tangent to the photoconductive
surface.
Our cleaning apparatus substantially avoids the
problem of cleaning system clogging and the attendan-t risk
of damage to the photoconductive surface. The foam roller,
which rotates in the same direction as the photoconductive
surface and is supplied with liquid developer during the
course of a copying operation, provides the basic cleaning
action. The self-cleaning squeegee blade enhances the
cleaning action and, in addition, wipes the photoconductive
surface dry. Because the squeegee blade is itself being
continually cleaned by its auxiliary cleaning system, there
is little danger of toner buildup on the blade scratching
the photoconductive surface. While the preferred embodi-
ment of our invention is described in relation to a copying
machine employing a drum, our cleaning apparatus is equally
adaptable to a machine employing a photoconductive surface
of the endless ~elt type.
In the machine for which our apparatus is designed,
developer is supplied to the developer applicator when ~he
machine is turned on and to the cleaning apparatus upon
initiation of a copying operation.
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Our invention further comprises means for main-
taining the cleaning apparatus out of engagement with
the photoconductive surface while the surface is
stationary and moving the apparatus into engagement
with the surface after the surface portion initially
at the developing station has advanced to a position
adjacent to the cleaning apparatus. In this manner, we
ensure that the cleaning apparatus contacts the photo-
conductive surface only after the surface has been
wetted by liquid developer in the developing station
and thus avoid the possibility of scratching the sur-
face by contacting it while it is dry.
BRIEF DESCRIPTION OF THE DRAWINGS
.
In the accompanying drawings which form part of
the instant specification and which are to be read in
conjunction therewith and in which like reference numer-
als are used to indicate like parts in the yarious views:
FIGURE 1 is a rear elevation of our clearling appar-
atus, with parts broken away.
FIGURE 2 is a section of our cleaning apparatus
taken along line 2- 2 of FIGURE 1.
FIGURE 3 is a top plan of the roller subassembly
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~f our cleaning apparatus, with parts broken away.
~ IGURE 4 is a side elevation o~ the blade assembly
of our cleaning apparatus.
FIGURE 5 is a bottom plan of the blade assembly
shown in FIGURE 4.
FIGURE 6, appearing on the same sheet as FIGURE 2,
is a section of the blade assembly of our cleaning apparatus
taken along line 6-6 of FIGURE 1.
FIGURE 7, appearing on the same sheet as EIGURE 2,
is a section of an alternative embodiment of the blade
assembly which contacts the photoconductive surface along
one transverse only.
FIGURE 8 is a side elevation, shown partly in section,
of a copying machine employing our cleaning apparatus.
FIGU~E 9 is a schematic of the control circuit
associated with the machine shown in FIGURE 1.
DESCRIPTION OF THE PREFERRED E~30DIMENTS
. _ _
Referring to FIGURES 1 to 6 and 8j our cleaning
apparatus, indicated generally by the reference numeral 10,
is intended to be used with a cylindrical drum 32 having a
photoconductive outer surface 30. The drum 32 is supported
by a shaft 138 which is driven by a motor 140 in a counter-
clockwise direction, as seen in FIGURE 8, past a plurality
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of processing stations, as is known in the prior art.
These stations include a corona charging station 142
at which the photoconductive surface 30 is uniformly
electrostatically charged, an exposure station 144 at
which the surface is exposed to a light image of an
original to form an electrostatic latent image, a
developing station 145 at which a liquid developer
is applied from a developing tank 146 to foxm a
visible image, and an image transfer station 148 at
which the developed image is transferred to a sheet
of paper 150. Shaft 138 carries for rotation there-
with a cam 152 which momentarily closes the contacts
of a switch 154 as the cam moves through a predetermined
angular position, for a purpose to be more fully describ-
ed.
The cleaning apparatus 10 includes a cylindrical
roller indicated generally by the reference character 12
having an aluminum core 14 and a covering layer 16 of
polyurethane foam or the like. The roller 12 is mounted
on stub shafts 18 and 20 which are supported by bearings
22 and 24 located respectively in roller support brackets
26 and 28. When in use, the roller 12 contacts the photo-
conductive surface 30 of the drum 32 at a location between
the transfer station 148 and the charging station 142.
Pivot screws 38 and 40 mount the roller support
brackets 26 and 28 on cleaner support brackets 34 and 36
for movement of roller 12 toward and away from the surface
30 of drum 32. Tension springs 42 and 44 e~tending between
brackets 34 and 36 and brackets 26 and 28 urge roller 12
to move away from drum 32 to a limit position defined by
adjusting scxews 46 and 48. Screws 46 and 48 can be
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turned to adjust the position o~ roller 12 and thus
the pressure exerted by the roller on the surface 30
of drum 32. A pair of rods 50 and 52, extending res-
pectively between the roller support brackets 26 and
28 and cleaner support brackets 34 and 36~ giye the
roller subassembly torsional rigidity.
Bearings 54 and 56 pivotally mount cleaner
support brackets 34 and 36 on a main drive shaft 58
driven by a motor 59. The entire cleaning apparatus
10 is thus mounted on the shaft 58 for movement toward
and away from drum 32. We form suppo~t brackets 34
and 36 with upwardly extending arms 156 and 158. The
cleaning apparatus 10 I$ normally biased away from the
drum surface 30 against a pair of stops 161 (FIGU~E 2)
by means of tension sprin~s 162 extending between the
respective arms 156 and 158 and a fixed frame portion
164. Actuation of a pair of solenoids 166 and 168 coup-
led to the respective arms 156 and 158 causes the appar-
atus 10 to move into engagement with the surface 30,
the limit position being determined by a second pair
of stops 169 (FIGURE 2).
Bearings 62 and 64 on cleaner suppcrt hrackets
34 and 36 rotatablY support an intermediate drive shaft
60. A sprocket wheel 66 mounted on the main drive shaft
58 drives a chain 68 which drives a second sprocket
wheel 70 carried by the intermediate drive shaft 6Q. The
intermediate driye shaft 60 and the roller stub shaft
20 are coupled by means of a chain 72 which engages the
teeth of sprocket wheels 74 and 76 located on the respec-
tive shafts. Rotation of the main drive shaft 58 will
thus drive both the intermediate drive shaft 60 and the
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roller 12 with the roller 12 moving in a direction
opposite to that of the drum surface 30 at the point
of tangency.
As is explained more fully below, preferably
we supply developer liquid to the cleaning roll`er 12
by means of a trough 78 which is disposed abo~e the
roller 12 and is supported between respective end
support brackets 80 and 82. This is not done until
after a copying operation has been ;`nitiated. A
leading edge splash cover 84 mounted on an upper
frame 86 extends across the width of the cleaning
roller 12 at a location just beyond the roller 12 in
the direction of rotation of drum 32. Preferably,
we provide our apparatus with a steel roller 87
rotatably supported on brackets 26 and 28 at a loca-
tion at which it squeezes the foam layer 16to remwe
excess liquid therefrom. This arrangement permits us
to supply a sufficient quantity of deyeloper from
trough 78 to flush roller 12 fully while at the same
time preventing an excessiye amount of liquid from
being thrown from roller 12. Roller 87 may be freély
rotatable or it may be driven to reduce drag on roller
12. We position a tray 88 below roller 87 to collect
liquid being squeezed out of roller 12. Tray 88 directs
the collected liquid to one side of the machine at which
it is fed back to the developer supply system.
The wiper blade assembly of the cleaning system,
indicated generally by the reference character 90, in-
cludes an endless belt 92 which is composed of nitrile
rubber, polyurethane ! or other developer carrier liquid
resistant flexible material. We stretch the belt 92
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between two pulleys 94 and 96 located outboard of
the drum ends. In the preferred embodiment of our
invention, both traverses of the belt 92 contact
the photoconductive surface 30 generally perpendic-
ularly across its width~ as shown, providing addition-
al cleaning action. We mount the pulleys 94 and 96
on shafts 98 and 100 supported by respective bearings
102 and 104 disposed in a support member 106. The
support member 106 is fixedly secured to cleaner support
brackets 34 and 36 by any suitable means such as weld-
ing or the like. Pulley shafts 98 and 100 are coupled
to the intermediate drive shafts 60 through respective
sets of worm gears, one of which is made up of a worm
wheel 108 and a worm 112 and the other of which is made
up of a worm wheel 110 and a worm 114. The belt 92 is
kept in substantially perpendicular engagement with the
photoconductor surface 30 by means of a guide 116 mount-
ed beneath the support member 106 between the pulleys 94
and 96. The guide 116, formed of a suitable low friction
material such as polytetrafluoroethylene copolymer, has
a generally rectangular cross section, and is provided
with grooves 118 and 120 for-receiving the upper portion
of the linear segments of the belt 22.
A pair of wiper blades 122 and 124 are urged
into contact with the endless belt 92 at the left end of
its c7'rcuit. These wiper blades remove the toner and
other material picked up by the endiess belt 92, and are
assisted in their cleaning action by feed pipes 126 and
128, which spray the surface of the belt 92 with jets of
developer liquid through exit orifices 130 and 132.
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Actuation of the various electromechanical devices
used in our cleaning system is controlled by the circuit
shown in FIGURE 9. The circuit includes four flip-flops
170, 172, 174, and 176, which are turned on by applying
signals to the S or "set" inputs and are turned off by
appl~ing signals to the R or "reset" inputs. Flip-flops
170, 172, 174 and 176 are coupled to suitable driver
circuits 178, 180, 182 and 184, which are in turn coupled
to the electromechanical devices. More particularly,
circuit 178 drives the cleaner solenoids 166 and 168 and
the cleaner motor 59. Circuit 180 drives a cleaner pump
186, which controls the flow of liquid developer to the
developer trough 78 and the feed ~ipes 126 and 128. Cir-
cuit 182 drives a developer pump 188, which controls the
flow of li~uid developer to the developing tank at the
developing station 145. Circuit lg4 drives the drum
motor 140.
Cam switch 154 has one of its terminals connected
to a line 190 coupled to a suitable voltage source. The
other terminal of switch 154 is connected to one input
of a two-input AND gate 192 and to the clock-pulse (CP)
or counting input of a counter 194. Line lgO is also coup-
led to one terminal of a copy switch 196 which remains
closed during a copying cycle. The other terminal of
switch 196 is coupled to the second input of AND gate 192,
the R or reset input of counter 194, and the S input of
flip-fl~p 176. AND gate 192 has its output coupled to the
S inputs of flip-flops 170 and 172. Counter 194 provides
a first signal, indicating a count of two, to the R inputs
of flip-flops 172 and 174 and provides a second signal
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indicating a count of five, to the R inputs of flip-
flops 170 and 176 and the S input of flip-flop 174.
Before a copy cycle is started, the drum 32 IS
atrest with the cam 152 oriented as shown in FIGURE 8.
Switches 15~ and 196 are open; flip-flops 170, 172, and
176 are off; and flip-flop 174 is on so as to energize
the developer pump 188. Closure of the copy switch 196
at the beginning of a copy cycle causes voltage to be
applied from line 190 to the S terminal of flip-flop
176, turning on that flip-flop to start the drum motor
140. As the surface of the drum rotates counterclockwise
through the developing station 145, it becomes coated
with liquid developer. When the wetted portion of the
drum surface reaches the cleaning apparatus 10, ca,m
152 has rotated to a position at which it closes the
switch 154. AND gate 192 then provides a signal to the
S input of flip-flop 170 to turn on that flip-flop and
actuate the cleaner motor 59 and the cleaner solenoids
166 and 168, which move the cleaning apparatus 10 into
engagement with the wetted drum surface 30, AND gate
192 also turns on flip-flop 172, which actuates the
cleaner pump 186 to cause developer liquid to be supplied
to the toner trough 78.
As the drum 32 rotates in a counterclockwise dir-
ection to carry the surface from the image transfer station
into the cleaning station, the foam-covered roller 12,
the surface of which is moving in a direction opposite
to that of the drum surface along the line of contact,
scrubs the surface to loosen adhering toner particles
' 30 and the like~ Developer flowing onto the roller 12 prevents
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agglomeration of toner particles on the roller. After
the surface 30 leaves the roller 12, it is enga~ed
by an edge portion of belt 92, which acts to complete
the cleaning process by removing any remaining toner
particles from the surface 30 while at the same time
wiping the surface dry. Any materials carried away
from the surface 30 are removed from the belt through
the action of wipers 122 and 124 and developer jets
from pipes 126 and 128.
At the end of the copy cycle, switch 196 re-
opens to remo~e the potential from the R input of
counter 194, allowing the counter to be clocked by
sNccessive closings of the cam switch 154. While
the counter 194 is being clocked, operation of the
cleaning system is continued to clean the drum surface
completely and to allow the belt and sponge roller to
be thoroughly flushed with developer. After two rotat-
tions of the drum or about six seconds, assuming a
rotation period of three seconds, counter 194 provides
a signal on the 2 line to reset flip-flops 180 and 182,
turning off the cleaner pump 186 and the developer
pump 188. Cutting off the supply of developer and
cleaner liquid in this manner permits the roller 12 to
squeeze out excess liquid and the belt 92 to clear the
excess developer liquid from in front of the squeegee
point. After another three drum rotations or about nine
seconds, counter 194 provides a signal on the 5 line to
reset flip-flops 170 and 176 and set flip-flop 174. As
a result, cleaner solenoids 166 and 168 are deactuated,
permittin~ the cleaning apparatus to move away from the
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drum, and the cleaner and drum motors are also de-
actuated so that the drum comes to rest in the origin-
al position shown in FIGURE 1. At the same time, the
developer pump 188 is reactuated to ensure a supply
of developer liquid when the next copy cycle is
begun. It is to be understood that the particular
logic circuitry we have shown is by way of example
only. Any suitable arrangement may be used which
ensures that the cleaning system is not brought into
contact with the drum until a wetted portion of the
drum surface arrives at the cleaning station.
Referring now to FIGURE 7, we show an alter-
native embodiment of our blade assembl~ desIgned to
contact the photoconductive surfac,e along only one
edge of the endless belt. This embodiment is sub-
stantially identical to the first embodiment except
that guide means, comprising an inner guide wall 130
having an L-shaped cross-section and an outer guide
wall 136, enclose~ only one traverse of the belt 92.
The blade assembly 90 is also inclined with respect
to the photoconductive surface 30 to provide a suit-
able contacting angle. The contacting edge of the
belt 92 may be inclined either into or against the
direction of the rotation of the drum 32.
It will be seen from the foregoing description
that we have accomplished the objects of our invention.
Our cleaning apparatus effectively cleans the photo-
conductive surface. It does not scratch the photo-
conductive surface. Our cleaning apparatus minimizes
clogging.
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It will be understood that certain features
and subcombinations are of utility and may be employed
without reference to other features and subcombinations.
This is contemplated by and is within the scope of our
claims. It is further obvious that Various changes
may be made in details within the scope of our claims
without departing from the spirit of our invention.
It is, therefore, to be understood that our invention
is not to be limited to the specific details shown and
described.
Having thus described our invention, what we claim
is ;
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