DEVICE FOR CLEANING XEROGRAPHIC CYLINDERS
United States Patent 3712734
A device for wiping clean xerographic cylinders using a web of cloth-like material maintained in contact with the drum as it rotates. The contact area covers a considerable angular extent of the drum for substantially its entire width and when compared to similar prior art devices, provides greater cleaning action, uses less web material per drum revolution, and reduces drum wear due to web contact.
US Patent References:
Xerographic plate cleaning method utilizing the relative movement of a cleaning web
Graff et al. - June 1965 - 3186838
Web cleaner apparatus
Eichorn et al. - August 1963 - 3099856
CLEANING APPARATUS FOR ELECTROSTATIC COPYING MACHINES
Dimond et al. - September 1970 - 3526457
Xerographic plate cleaning method utilizing the relative movement of a cleaning web
Graff et al. - June 1965 - 3186838
Web cleaner apparatus
Eichorn et al. - August 1963 - 3099856
CLEANING APPARATUS FOR ELECTROSTATIC COPYING MACHINES
Dimond et al. - September 1970 - 3526457
Application Number:
05/127162
Publication Date:
01/23/1973
Filing Date:
03/23/1971
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
15/1.510
International Classes:
G03G21/00; G03G15/22
Field of Search:
355/3,15 15/1.5,256.52
Primary Examiner:
Matthews, Samuel S.
Assistant Examiner:
Braun, Fred L.
Claims:
What is claimed is
1. In an electrophotographic reproducing apparatus employing a rotating xerographic drum having a series of processing stations disposed about it including a drum cleaning station wherein residual developer material is removed from the drum surface after transfer of the developed image to the copy has been completed, the improvement in the drum cleaning station comprising
2. An electrophotographic apparatus having an improved drum cleaning station in accord with claim 1 wherein said pressure roller is biased toward said drum to maintain a pressure of between 1/2 and 11/2 pounds per lineal inch of pressure roller length.
3. In an electrophotographic reproducing apparatus employing a rotating xerographic drum having a series of processing stations disposed about it including a drum cleaning station wherein residual developer material is removed from the drum surface after transfer of the developed image to the copy has been completed, the improvement in the drum cleaning station comprising
1. In an electrophotographic reproducing apparatus employing a rotating xerographic drum having a series of processing stations disposed about it including a drum cleaning station wherein residual developer material is removed from the drum surface after transfer of the developed image to the copy has been completed, the improvement in the drum cleaning station comprising
2. An electrophotographic apparatus having an improved drum cleaning station in accord with claim 1 wherein said pressure roller is biased toward said drum to maintain a pressure of between 1/2 and 11/2 pounds per lineal inch of pressure roller length.
3. In an electrophotographic reproducing apparatus employing a rotating xerographic drum having a series of processing stations disposed about it including a drum cleaning station wherein residual developer material is removed from the drum surface after transfer of the developed image to the copy has been completed, the improvement in the drum cleaning station comprising
Description:
BACKGROUND OF THE INVENTION
The field of the invention is generally related to xerography and more particularly to improvements in the method of cleaning the xerographic drum after the transfer of the developed image to a paper copy.
In the branch of electrophotography commonly known as xerography, an electrostatic image is formed by first charging and then exposing a photoconductive insulating surface to a light pattern. The electrostatic image is converted to a visible image by a development step wherein fine colored particles, called toners, are caused to adhere to the electrostatic image on the photoconducting insulating surface. The developed image is then transferred to a paper carrier and fixed and the entire process is ready for repetition, except for one problem. Unfortunately, when the developed image is transferred to the paper carrier, the transfer is not absolutely complete. Some of the toner particles are left adhering to the photoconducting insulating surface after the transfer, and must be removed if they are not to reduce the contrast of subsequent copies. It is with respect to this cleaning cycle that the invention is directed.
In many if not most of the modern xerographic copying machines, the photoconducting insulating surface is a plate arranged into cylindrical form. In the majority of such machines continuous cleaning is accomplished by one or more rotating fur-like brushes in contact with the rotating drum. Supplemental vacuuming action often aids cleaning in this type of device. However, the fur is relatively expensive and has a relatively short working life; 40-60 hours of operation being a typical life. Since this life is relatively limited and other expensive components are needed such as the vacuuming system, it would be desirable to clean the drum in a manner that is less expensive to implement and with a longer service life. One such device that is less expensive is the Web Cleaner Apparatus described in the U.S. Pat. No. 3,099,856 of Eichorn et al. However, even though Eichorn's device is less costly to implement than the prior art cleaning system, it, like its predecessors, suffered from a shorter working life than desired.
BRIEF SUMMARY OF THE INVENTION
It is accordingly a principal object of the invention to provide an improved device for cleaning xerographic drums.
Yet another object of the invention is to provide a xerographic drum cleaning device having improved service life over that of prior art devices.
Still another object of the invention is to provide a xerographic drum cleaning device having improved cleaning properties over those of prior art devices.
The foregoing and other objects are achieved in the xerographic cylinder cleaning device of the invention which employs a moving clothlike web pressed against the rotating cylinder. The web is biased against the drum by two rollers and contacts the cylinder over a surface segment of considerable angular extent.
BRIEF DESCRIPTION OF THE DRAWING
The drawing illustrates in schematic form the functional processing areas disposed about a xerographic drum and the inventive cleaning device in respect thereto.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The various processing stations employed in xerography are shown in the drawing disposed about the circumference of a xerographic drum 10 arranged to rotate about axis 16 in the direction of arrow 17. The angular extent of each station is approximately correct for most xerographic processing machines but those shown are exemplary only, the purpose being to show the relative location of the cleaning area and device in the station sequence. As shown, the cleaning station occupies that area between the "transfer" and "charge" area segments. As there shown, the cleaning sector has an angular extent of approximately 120°. This is approximately the maximum area available and is only achieved with relatively large diameter cylinder or drums -- on the order of 14-16 inches in diameter. Since the hardware space requirements to implement each station do not decrease appreciably for smaller drums, as drum size is made smaller, the space for the cleaning station decreases. For a cylinder/drum diameter of 7-9 inches, the cleaning station is typically limited to a 75°-105° sector. It is a feature of the invention that almost all of this sector is used for the cleaning station and, as a result of the novel arrangement and features of the cleaning device, the xerographic drum is cleaned more effectively than heretofore possible.
As shown, a web 18 of cleaning material is maintained in contact with the drum over a large angular sector of the drum surface. The web 18 is fed from supply roll 14 in the direction of arrow 19 until it contacts the drum at 39. Thence, it is conducted across the surface of the drum in a direction of arrow 20 to line 21 where it contacts pressure-roller 13. From pressure roller 13, the web 18 is fed in the direction of arrow 22 to takeup roller 15. Roller 15 is coupled to drum 10 by means of a gear train (not shown). The gear train is selected to drive take up roller 15 at a rate in the range of 1/50 to 1/100 that of drum 10, the particular speed depending on several factors as discussed further below.
In all embodiments of the cleaning device, the principal web drive is through take up roller 15. Generally I find that no power should be applied to pressure roller 13 and that supply roll 14 should either have a friction brake about its axle 27 or, that a garter spring drive from takeup roller 15 under driving supply roll 14 can be used to cause braking action. The axle 27 for supply roll 14 is mounted on swinging arm 23 which in turn rotates about pivot 24. The supply roll is lightly spring biased against drum 10. In practice, the amount of this bias is made as small as possible consistent with maintaining contact of the web with drum when the system is not operating. Advantageously, the spring bias is provided by an over-center spring arrangement, the spring 28 connected between a spring stud 29 and swinging arm 23. With this arrangement, I have found that maintaining a force of the supply roll against the drum of between 4-8 ounces generally is satisfactory.
Pressure roller 13 is mounted for rotation about axle 30 which, in turn is secured to swinging arm 25. Arm 25 rotates about pivot 26. The pressure of roller 13 against the drum is considerably higher than that of the supply roll since the pulling action of the web tends to pull the pressure roller away from the drum. This pressure is maintained by springs (not shown) connected to arm 25. The springs are chosen to maintain a pressure of 1/2 to 11/2 pounds per lineal inch of feed roll length while the drum and web are moving relative to each other. This pressure is considerably less than that used in other web type cleaning devices and, as a consequence, results in reduced wear on the xerographic drum. Nevertheless, even though there is less pressure, the cleaning action is superior by virtue of the large angular contact sector used in the inventive device compared to the substantially line contact of prior art web type cleaning devices.
As pointed out above, various embodiments of the invention can have variations in the angular sector of the xerographic drum wiped by the cleaning web, available space varying between about 75° and 120°. The area used for wiping contact is chosen based upon several variables including relative speed between the drum and cleaning web, the type of material employed in the web and the amount of interstitial space between fibers of the web; the last factor apparently being of the greatest importance. While conventional cotton cloth, cheese cloth, asbestos cloth and cloths comprised of various artificial fibers have been utilized, the preferred web material is a non-woven cellulose having between 15 and 25 percent open spaces and approximately 7-9 mils thick. With such a material and the speed of the web relative to the drum set between 1/75 and 1/100, the preferred wiping area for a 9 inch diameter drum is a 75° sector or an area 61/4 inches wide by drum length. With these parameters, very high web collection efficiencies are achieved; about 96 percent of the available interstitial space of the web being filled with toner particles as revealed by microscopic inspection. Further, since there is interstitial space remaining in the web when it ceases contact with the drum, there is a reduction in wear of the drum compared to systems where there is insufficient interstitial space and hence, loose toner particles are tumbled between the advancing web and the drum, abrading the drum.
Other web materials yield slightly different optimum results. In general, the softer the web material the greater the collection efficiency of the web. However, there is an optimum point on softness, -- reached when the pressure of the web against the drum in itself compacts the web and thus tends to seal-off the interstitial spaces. In the drawing, the various parts of the inventive apparatus are shown schematically in orthographic projection only. As will be obvious, the various cylinders and rolls in actual practice are supported between main frames that have been omitted from the drawing for simplicity.
The invention has been described in detail herein with particular reference to preferred embodiments thereof. However, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.
The field of the invention is generally related to xerography and more particularly to improvements in the method of cleaning the xerographic drum after the transfer of the developed image to a paper copy.
In the branch of electrophotography commonly known as xerography, an electrostatic image is formed by first charging and then exposing a photoconductive insulating surface to a light pattern. The electrostatic image is converted to a visible image by a development step wherein fine colored particles, called toners, are caused to adhere to the electrostatic image on the photoconducting insulating surface. The developed image is then transferred to a paper carrier and fixed and the entire process is ready for repetition, except for one problem. Unfortunately, when the developed image is transferred to the paper carrier, the transfer is not absolutely complete. Some of the toner particles are left adhering to the photoconducting insulating surface after the transfer, and must be removed if they are not to reduce the contrast of subsequent copies. It is with respect to this cleaning cycle that the invention is directed.
In many if not most of the modern xerographic copying machines, the photoconducting insulating surface is a plate arranged into cylindrical form. In the majority of such machines continuous cleaning is accomplished by one or more rotating fur-like brushes in contact with the rotating drum. Supplemental vacuuming action often aids cleaning in this type of device. However, the fur is relatively expensive and has a relatively short working life; 40-60 hours of operation being a typical life. Since this life is relatively limited and other expensive components are needed such as the vacuuming system, it would be desirable to clean the drum in a manner that is less expensive to implement and with a longer service life. One such device that is less expensive is the Web Cleaner Apparatus described in the U.S. Pat. No. 3,099,856 of Eichorn et al. However, even though Eichorn's device is less costly to implement than the prior art cleaning system, it, like its predecessors, suffered from a shorter working life than desired.
BRIEF SUMMARY OF THE INVENTION
It is accordingly a principal object of the invention to provide an improved device for cleaning xerographic drums.
Yet another object of the invention is to provide a xerographic drum cleaning device having improved service life over that of prior art devices.
Still another object of the invention is to provide a xerographic drum cleaning device having improved cleaning properties over those of prior art devices.
The foregoing and other objects are achieved in the xerographic cylinder cleaning device of the invention which employs a moving clothlike web pressed against the rotating cylinder. The web is biased against the drum by two rollers and contacts the cylinder over a surface segment of considerable angular extent.
BRIEF DESCRIPTION OF THE DRAWING
The drawing illustrates in schematic form the functional processing areas disposed about a xerographic drum and the inventive cleaning device in respect thereto.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The various processing stations employed in xerography are shown in the drawing disposed about the circumference of a xerographic drum 10 arranged to rotate about axis 16 in the direction of arrow 17. The angular extent of each station is approximately correct for most xerographic processing machines but those shown are exemplary only, the purpose being to show the relative location of the cleaning area and device in the station sequence. As shown, the cleaning station occupies that area between the "transfer" and "charge" area segments. As there shown, the cleaning sector has an angular extent of approximately 120°. This is approximately the maximum area available and is only achieved with relatively large diameter cylinder or drums -- on the order of 14-16 inches in diameter. Since the hardware space requirements to implement each station do not decrease appreciably for smaller drums, as drum size is made smaller, the space for the cleaning station decreases. For a cylinder/drum diameter of 7-9 inches, the cleaning station is typically limited to a 75°-105° sector. It is a feature of the invention that almost all of this sector is used for the cleaning station and, as a result of the novel arrangement and features of the cleaning device, the xerographic drum is cleaned more effectively than heretofore possible.
As shown, a web 18 of cleaning material is maintained in contact with the drum over a large angular sector of the drum surface. The web 18 is fed from supply roll 14 in the direction of arrow 19 until it contacts the drum at 39. Thence, it is conducted across the surface of the drum in a direction of arrow 20 to line 21 where it contacts pressure-roller 13. From pressure roller 13, the web 18 is fed in the direction of arrow 22 to takeup roller 15. Roller 15 is coupled to drum 10 by means of a gear train (not shown). The gear train is selected to drive take up roller 15 at a rate in the range of 1/50 to 1/100 that of drum 10, the particular speed depending on several factors as discussed further below.
In all embodiments of the cleaning device, the principal web drive is through take up roller 15. Generally I find that no power should be applied to pressure roller 13 and that supply roll 14 should either have a friction brake about its axle 27 or, that a garter spring drive from takeup roller 15 under driving supply roll 14 can be used to cause braking action. The axle 27 for supply roll 14 is mounted on swinging arm 23 which in turn rotates about pivot 24. The supply roll is lightly spring biased against drum 10. In practice, the amount of this bias is made as small as possible consistent with maintaining contact of the web with drum when the system is not operating. Advantageously, the spring bias is provided by an over-center spring arrangement, the spring 28 connected between a spring stud 29 and swinging arm 23. With this arrangement, I have found that maintaining a force of the supply roll against the drum of between 4-8 ounces generally is satisfactory.
Pressure roller 13 is mounted for rotation about axle 30 which, in turn is secured to swinging arm 25. Arm 25 rotates about pivot 26. The pressure of roller 13 against the drum is considerably higher than that of the supply roll since the pulling action of the web tends to pull the pressure roller away from the drum. This pressure is maintained by springs (not shown) connected to arm 25. The springs are chosen to maintain a pressure of 1/2 to 11/2 pounds per lineal inch of feed roll length while the drum and web are moving relative to each other. This pressure is considerably less than that used in other web type cleaning devices and, as a consequence, results in reduced wear on the xerographic drum. Nevertheless, even though there is less pressure, the cleaning action is superior by virtue of the large angular contact sector used in the inventive device compared to the substantially line contact of prior art web type cleaning devices.
As pointed out above, various embodiments of the invention can have variations in the angular sector of the xerographic drum wiped by the cleaning web, available space varying between about 75° and 120°. The area used for wiping contact is chosen based upon several variables including relative speed between the drum and cleaning web, the type of material employed in the web and the amount of interstitial space between fibers of the web; the last factor apparently being of the greatest importance. While conventional cotton cloth, cheese cloth, asbestos cloth and cloths comprised of various artificial fibers have been utilized, the preferred web material is a non-woven cellulose having between 15 and 25 percent open spaces and approximately 7-9 mils thick. With such a material and the speed of the web relative to the drum set between 1/75 and 1/100, the preferred wiping area for a 9 inch diameter drum is a 75° sector or an area 61/4 inches wide by drum length. With these parameters, very high web collection efficiencies are achieved; about 96 percent of the available interstitial space of the web being filled with toner particles as revealed by microscopic inspection. Further, since there is interstitial space remaining in the web when it ceases contact with the drum, there is a reduction in wear of the drum compared to systems where there is insufficient interstitial space and hence, loose toner particles are tumbled between the advancing web and the drum, abrading the drum.
Other web materials yield slightly different optimum results. In general, the softer the web material the greater the collection efficiency of the web. However, there is an optimum point on softness, -- reached when the pressure of the web against the drum in itself compacts the web and thus tends to seal-off the interstitial spaces. In the drawing, the various parts of the inventive apparatus are shown schematically in orthographic projection only. As will be obvious, the various cylinders and rolls in actual practice are supported between main frames that have been omitted from the drawing for simplicity.
The invention has been described in detail herein with particular reference to preferred embodiments thereof. However, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.