CA1103302A - Photoconductive drum cleaning apparatus - Google Patents

Abstract

Title of the Invention PHOTOCONDUCTIVE DRUM CLEANING APPARATUS

Abstract of the Disclosure Apparatus for cleaning the photoconductive drum of an electrostatic copier in which a rotating foam roller and a self-cleaning squeegee blade are sequentially arranged adjacent the photoconductive surface at a location follow-ing the station at which the image has been transferred to copy material such as paper. The self-cleaning squeegee blade is formed by a driven endless belt which extends across the entire photoconductive surface and which is so disposed that an edge portion or portions contact the surface of the photoconductor. The endless belt is cleaned by means remote from the photoconductive surface. In various embodiments of the invention the endless belt contacts the photoconductive surface at an acute, a right, and an obtuse angle to a tangent to the photoconductive surface. Means is provided for supplying developer liquid to the developer applicator on start-up of the machine and to the cleaning apparatus upon initiation of a copying operation. To prevent scratching of the photoconductive surface by the cleaning apparatus, the cleaning apparatus is retracted from the photoconductive surface until such time after initiation of a copying operation that the surface portion initially at the developer applicator has advanced to a position adjacent to the cleaning apparatus.

Description

11~33(~z 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 ~, ~
~ sd~ `` ``` -2-11t}3~3~2 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 1~`33~2 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.

Pg/~ - 4 -11~33~2 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 J` 5 -~1~;33~

~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 sd/\~ 6-~- ~

~1~33~;~

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 Pg~ 7 -1~33~Z
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 pg/~ X - 8 -33~

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 pg~ _ g _ ~1~33~2 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.

pg~cl ~ 10 -~1~3~

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 p g/~

~1033~2 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 33~2 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 p~ 13 -~1033~%
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.

.~ . ~
,'~.
p~/~) - 14 -1~33~2 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 ;

p~ 15 -

Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An electrophotographic copying machine including in combination a recirculating imaging surface; intermittently actuated means for sequentially moving said imaging surface in the course of a single circuit through an exposure station at which said surface is provided with an electro-static latent image of an original, through a developing station at which liquid developer is applied to said surface to form a developed toner image, through a transfer station at which said developed image is transferred to a copy sheet, and then through a cleaning station spaced from said develop-ing station; a cleaning member at said cleaning station;
means for retracting said cleaning member from the imaging surface while said surface is stationary; and means for moving said cleaning member into engagement with said surface when a predetermined period less than the period required to traverse an entire circuit has elapsed following initiation of movement of said surface, said predetermined period being sufficient to permit the arrival at said cleaning station of an imaging surface portion that has been wetted by liquid developer at said developing station.

2. Apparatus as in Claim 1 in which said predetermined period is less than the time required for movement of said surface from said exposure station to said cleaning station.

3. Apparatus as in Claim 1 in which said means for re-tracting said cleaning member is a spring.

4. Apparatus as in Claim 1 in which said retracting means is a spring and in which said moving means comprises a solenoid adapted to be energized to overcome the action of said spring.

5. Apparatus as in Claim 1 in which said retracting means comprises a spring and in which said moving means comprises a solenoid adapted to be energized to overcome the action of said spring and time delay means responsive to actuation of said intermittently actuated means for activating said time delay means.

6. Apparatus as in Claim 1 in which said surface moving means comprises a shaft, said retracting means comprises a spring and said moving means comprises a solenoid adapted to be energized to move said cleaning member against the action of said retracting means and means including a cam on said shaft for energizing said solenoid.

7. An electrophotographic copying machine including in combination a recirculating imaging surface; intermittently actuated means for sequentially moving said imaging surface in the course of a single circuit through an exposure station at which said surface is provided with an electrostatic latent image of an original, through a developing station at which liquid developer is applied to said surface to form a developed toner image, through a transfer station at which said developed image is transferred to a copy sheet, and then through a cleaning station spaced from said developing station;
apparatus for removing residual toner particles from said imaging surface at said cleaning station including in combination a roller having a spongy outer surface, means for rotatably mounting said roller at said cleaning station in contact with said imaging surface at a location at which said surface enters said cleaning station, means for driving said roller in a direction of surface movement thereof opposite to that of the imaging surface at the region of contact between the roller and the imaging surface to provide a scrubbing action to remove the major portion of toner particles from said imaging surface, an elongated squeegee blade, means for mounting said squeegee blade at said cleaning station at a location beyond said roller with the length thereof extending across and with an edge thereof in contact with said imaging surface, and means for driving said blade in a direction of its length to wipe said surface dry and to remove and carry away any toner particles which remain thereon following the action of the cleaning roller; means mounting said roller mounting means and said blade supporting means for movement between first positions in which said roller and said squeegee blade are in contact with said surface and second positions in which said roller and said squeegee blade are spaced away from said surface; means for maintaining said roller mounting means and said blade supporting means in said second positions while said surface is stationary; and means for moving said roller mounting means and said blade supporting means into said first positions when a predeter-mined period less than the period required to traverse an entire circuit has elasped following initation of movement of said surface, said predetermined period being sufficient to permit the arrival at said cleaning station of an imaging surface portion that has been wetted by liquid developer at said developing station.

8. Apparatus as in Claim 7 in which said predetermined period is at least equal to the time required for movement of said surface from said developing station to said cleaning station.

9. An electrophotographic copying machine including in combination a recirculating imaging surface; intermittently actuated means for sequentially moving said imaging surface in the course of a single circuit through an exposure station at which said surface is provided with an electrostatic latent image of an original, through a developing station at which liquid developer is applied to said surface to form a developed toner image, through a transfer station at which said developed image is transferred to a copy sheet, and then through a cleaning station spaced from said developing station; a cleaning member at said cleaning station; means for retracting said cleaning member from the imaging surface while said sur-face is stationary; and means for moving said cleaning member into engagement with said surface during the first circuit thereof substantially simultaneously with the arrival at said station of an imaging surface portion that has been wetted by liquid developer at said developing station.