CA1066758A - Drum cleaning process and apparatus for electrophotography - Google Patents
Drum cleaning process and apparatus for electrophotographyInfo
- Publication number
- CA1066758A CA1066758A CA263,156A CA263156A CA1066758A CA 1066758 A CA1066758 A CA 1066758A CA 263156 A CA263156 A CA 263156A CA 1066758 A CA1066758 A CA 1066758A
- Authority
- CA
- Canada
- Prior art keywords
- photoconductive member
- light
- drum
- unit
- light source
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G21/00—Arrangements not provided for by groups G03G13/00 - G03G19/00, e.g. cleaning, elimination of residual charge
- G03G21/0005—Arrangements not provided for by groups G03G13/00 - G03G19/00, e.g. cleaning, elimination of residual charge for removing solid developer or debris from the electrographic recording medium
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Discharging, Photosensitive Material Shape In Electrophotography (AREA)
- Cleaning In Electrography (AREA)
Abstract
Abstract of the Disclosure Charging, imaging, developing and transfer units are operatively arranged about the circumference of a rotary photoconductive drum, the developing unit comprising a magnetic brush. A discharge unit is disposed between the transfer unit and the developing unit and comprises a light source and a corona discharge element to simultaneously illuminate the drum causing photoconduction and expose the drum to an electric field thereby neutralizing any residual charge on the drum and residual toner particles remaining on the drum after the transfer operation. The residual toner is subse-quently removed by the magnetic brush of the developing unit.
Description
The present invention relates to a drum cleaning process and apparatus for electrostatic photography by which residual toner particles are thoroughly removed from a photoconductive element after a transfer operation.
In a well known dry type electrophotographic process, a photoconductive drum or belt is electrostatically charged, radiated with a light image to cause local photoconduction and produce an electrostatic image, developed by applying a toner substance thereto to form a toner image and subjected to a transfer operation in which the toner image is trans-ferred to a copy sheet. In practical application, it is impossible to transfer the toner image to the copy sheet completely, and residual toner remains on the drum after the transfer operation.
In order to utilize the drum for successive copying operations of different original documents, it is necessary to remove this residual toner ~rom the drum, since double printing would occur if it were not removed.
`` In a wet electrophotographic process, a scraper bladeis used to remove the residual toner. However, this expedient is not applicable to a dry electrophotographic process since abrasion of the delicate photoconductive surface layer on the drum would occur due to dry friction.
In order to remove the residual toner, it is necessary to dissipate the electrostatic image on the drum which $ strongly binds the residual toner to the drum surface. For ~-- ~ this reason, most conventional dry electrophotographic machines comprise a coro~a discharge unit to apply an electric field OppoQite in polarity to the initial electrostatic charge to ; 30 neutralize the electrostatic image on the drum, and a light
In a well known dry type electrophotographic process, a photoconductive drum or belt is electrostatically charged, radiated with a light image to cause local photoconduction and produce an electrostatic image, developed by applying a toner substance thereto to form a toner image and subjected to a transfer operation in which the toner image is trans-ferred to a copy sheet. In practical application, it is impossible to transfer the toner image to the copy sheet completely, and residual toner remains on the drum after the transfer operation.
In order to utilize the drum for successive copying operations of different original documents, it is necessary to remove this residual toner ~rom the drum, since double printing would occur if it were not removed.
`` In a wet electrophotographic process, a scraper bladeis used to remove the residual toner. However, this expedient is not applicable to a dry electrophotographic process since abrasion of the delicate photoconductive surface layer on the drum would occur due to dry friction.
In order to remove the residual toner, it is necessary to dissipate the electrostatic image on the drum which $ strongly binds the residual toner to the drum surface. For ~-- ~ this reason, most conventional dry electrophotographic machines comprise a coro~a discharge unit to apply an electric field OppoQite in polarity to the initial electrostatic charge to ; 30 neutralize the electrostatic image on the drum, and a light
-2-~066758 source to subsequently illuminate the drum surface to cause photoconduction and further discharge of the drum.
` Since the electrostatic force between the residual toner anddrum is reduced substantially, the residual toner may be more readily removed from the drum by a magnetic brush or the like.
A drawback exists in this prior art expedient in that the corona discharge is performed in the absence of light.
The conductivity of the photoconductive layer in the dark is high, and it is impossible to dissipate the electrostatic charge in the lowermost portion of the layer. Even the subsequent exposure to light does not produce complete dis-charge, and the problem of double printing is not effectively solved.
It is an object of the present invention to provide a process for completely removing residual toner from a photo- !
conductive member of an electrophotographic apparatus after a toner image transfer operation.
It is another object of the present invention to provide an electrophotographic apparatus embodying the process.
It is another object of the present invention to provide an electrophotographic process in which an electro-static attractive force between residual toner particles and a photoconductive drum is dissipated through simultaneous illumination of the drum surface with light and exposure of the drum surface to an electric field thereby effecting complete discharge of the drum and toner.
It is another object of the present invention to provide an electrophotographic process in which complete discharge of a photoconductive drum is produced by simulta-neous illumination of the drum surface by light and exposure--3_ of the drum surface to an electric field, the effect of said steps in combination being greater than the aggregate effect of said steps performed sequentially.
It is another object of the present invention to provide an electrophotographic apparatus in which a magnetic brush which is used to apply toner substance to a photocon-ductive drum for development is also used to remove residual toner from the drum after a discharge operation comprising the simultaneous steps of illuminating the drum surface with light and exposing the drum to an electric field.
It is another object of the present invention to provide an electrophotographic apparatus in which a photo-~;~ conductive drum is rotated adjacent to a light source and a corona discharge unit which simultaneously operate on the drum to dissipate an electrostatic charge thereon, the area of radiation of light on the drum surface overlapping the area of the electric field on the drum surface and extending downstream of the area of the electric field in the direction of rotation of the drum.
It is another object of the present invention to ~`
provide a generally improved electrophotographic process and apparatus embodying the process.
Other objects, together with the foregoing, are attained in the embodiments of the present invention described in the following description and shown in the accompanying ~
drawings. ~`
Figure 1 is a schematic view of an electrophotographic apparatus embodying the present invention;
Figure 2 is an enlarged schematic view illustrating an important aspect of the present invention; and . ~. .
Figures 3 to 5 are fragmentary schematic views illustrating respective modifications of the present electrophotographic apparatus.
While the electrophotographic apparatus of the invention is susceptible of numerous physical embodiments, depending upon the environment and requirements of use, substantial numbers of the herein shown and described embodi-ments have been made, tested and used, and all have performed in an eminently satisfactory manner.
Referring now to Figure 1, an electrophotographic apparatus 11 embodying the present invention comprises an electrically grounded rotary drum 12 formed with a photo-conductive dielectric surface layer (not designated) and which is supported by a drive shaft 13. Drive means (not shown) rotate the shaft 13 and thereby the drum 12 clockwise at constant speed. A corona charging unit 14 is disposed adja-cent to the periphery of the drum 12 and operative to electro-statically charge the surface of the drum 12 in the absence of light. A light source 16 is arranged to illuminate an original document 17 which is moved by a scanning system (not shown) in the direction of an arrow 18 at a speed equal to the tangential speed of the surface of the drum 12 in such a manner that an imaging system, shown in simplified form as a converging lens 19, radiates a light image of the document 17 onto the surface of the drum 12. The highlight areas of the light image cause the photoconductive layer of the drum 12 to conduct thereby dissipating the electrostatic charge in these areas and forming an electrostatic image of the docu-ment 17. A developing unit 21 which will be described in detail below applies a powdered toner substance to the drum 12 which is electrostatically attracted to the areas of the photoconductive layer in which the electrostatic charge is high, which correspond to the dark or background areas of the document 17. The developing unit 21 thereby forms a toner image of the document 17 on the drum 12.
At a transfer unit 22 comprising a corona charging unit 23 similar to the corona charging unit 14, a copy sheet 24 is fed in synchronized contact with the drum 12 and an electrostatic force is applied to the back of the sheet 24 thereby attracting and effecting transfer of the toner image to the sheet 24. A fixing unit (not shown) subsequently fixes the toner image by heat, pressure or both to the copy sheet 24.
A discharge unit 26 then completely discharges the drum 12 - and any residual toner is removed by the developing unit 21 as will be described in detail below.
The developing unit 21 comprises a hopper 31 which is filled with a powdered developing or toner substance preferably ~ - -in the form of tiny granules or particles. Each granule comprises at least one particle of black carbon and at least one particle of iron, said particles being rigidly held together by a resin binder. A magnetic brush 32 is disposed ; closely adjacent to the surface of the drum 12 below an opening in the hopper 31 and comprises a magnetic core 33 surrounded by a non-magnetic sleeve 34, the core 33 and sleeve ~ 25 34 being coextensive with the length of the drum 12. Either one or both of the core 33 and sleeve 34 are rotated so that toner from the hopper 31 is magnetically attracted to the magnetic brush 32 to form an accumulation of toner particles on the surface of the sleeve 34 and rotates in the direction of an arrow 36 which brushingly engages with the surface of ; ` -6-.
the drum 12. A doctor 37 is provided at the opening of the hopper 31 to limit the thickness of the toner substance on the sleeve 34 to a required value. Due to the brushing engagement of the toner on the magnetic brush 32 with the surface of the drum 12, the toner is applied to the drum 12 to effect development of the electrostatic image into the toner image. The magnetic force of the magnetic core 33 is selected so that it is less than the electrostatic attraction betwean the electrostatic image on the drum 12 so that the toner may be transferred from the magnetic brush 32 to the drum 12 for development.
The discharge unit 26 comprises a housing 41 which acts as a light and electrical shield, the housing 41 being opaque, electrically conductive and electrically grounded. The housing 41 is coextensive with the length of the drum 12 and is formed with an opening 42 facing the drum 12. A light source 43 such as a fluorescent bulb is disposed in the housing 41 such " that light from the light source 43 is radiated onto the surface of the drum 12 through the opening 42. A corona dis-charge electrode 44 is further disposed in the housing 41 such that an electric field of opposite polarity to that of the charging unit 14 is applied to the surface of the drum 12 through the opening 42.
As shown in Figure 2, the housing 41 comprises, ` 25 adjacent to the opening 42, an upstream wall 41a and a down-stream wall 41b, the designations upstream and downstream `~
referring to the direction of movement of the surface of the drum 12. The end of the downstream wall 41b adjacent to the drum 12 is cut away to define an opening 41c, and an electri-cally conductive transparent plate 41d formed of, for example . . :
. `~
1066'758 NESA (trademark) glass, is fitted in the opening 41c.
In Figure 2 the photoconductive surface layer of the drum 12 is designated as 12a and toner particles attracted to the surface layer 12a are shown as circles but are not designated by reference numerals. Due to the electrical shielding effect of the walls 41a and 41b, the electric field from the corona discharge electrode 44 is applied to the layer 12a in an area bounded by lines A and D as indi-cated by dashed lines leading from the electrode 44 to the layer 12a. The light from the light source 43 is radiated onto the layer 12a in an area bounded by lines B and E as indicated by dot-dash lines leading from the light source 43 to the layer 12a. It will be noted that the light passes through the plate 41d whereas the electric field is blocked or shielded thereby.
- The light from the light source 43 and the electric field produced by the corona discharge electrode 44 are superimposed on the layer 12a in an area bounded by the lines `~ B and D such that the layer 12a is simultaneously irradiated by light and electrically discharged in this position. The polarity of the corona discharge electrode 44 is opposite to that of the corona charging unit 14 so that the electro-static image on the drum 12 is neutralized. The light causes photoconduction in the layer 12a so that any remaining charge ` 25 on the layer 12a is shorted to ground due to the high conduc~
tivity of the layer 12a. In this manner, the charge on both the layer 12a and toner particles is completely removed, a `
result which cannot be achieved by corona discharge followed by exposure to light.
Assuming that the charge applied to the layer 12a by the charging unit 14 is negative in polarity, the polarity of the discharge electrode 44 is positive. The negative charge at the surface of the layer 12a produces electrostatic polarization of the toner particles so that they are positive at their ends next to the layer 12a and negative at their ends away from the layer 12a, thereby being electrostatically attracted to the layer 12a. A similar magnetic phenomenon attracts the toner particles to the magnetic brush 32 of the developing unit 31.
As viewed in Figure 2, the electric field of the electrode 44 extends further upstream than the light from the light source 43, such that only the electric field exists in an area bounded by the lines A and B. This is of no practical consequence, and the housing 41 may be designed so that the electric field and light extend the same distance upstream or the light extends further upstream than the electric field. What is important, however, is that the electric field does not extend further downstream than the light.
If the plate 41d were opaque, the light from the light - source 43 would be confined to an area on the layer 12a between the line B and a line C, as indicated by a solid line 46 leading from the light source 32 to the layer 12a, and only the electric field would exist in an area bounded by the ` 25 lines C and D. As a result, the layer 12a would be electro-statically charged with a positive polarity, thereby inducing electrostatic polarization in the toner particles opposite to the normal polarity. The toner particles would be caused to be attracted to the layer 12a by the action of the discharge electrode 44, thereby defeating the purpose of the discharge ~066758 unit 26. Since the toner particles would be attracted to the layer 12a as a result of the operation of the discharge electrode 44, it would~be impossible for the magnetic brush 32 to completely remove the residual toner particles from ` 5 the drum 12. However, due to the provision of the plate 41d, the light extends further downstream than the electric field and the problem of reverse charging of the layer 12a and toner particles is eliminated.
After operation on the drum 12 by the discharge unit 26, the magnetic brush 32 removes the residual toner particles from the drum 12 through physical contact. Since the electro-static attractive force between the drum 12 and toner parti-- cles is reduced to substantially zero by the discharge unit26, the magnetic attractive force of the magnetic brush 32 is effective in effecting complete transfer of the residual toner ~; particles to the magnetic brush 32~
For each copying operation, the drum 12 is rotated through two revolutions. During the first revolution the copying operation is performed and the discharge unit 26 operates on the drum 12. During the second revolution, the charging unit 14 and light source 16 are de-energized so that the drum 12 is operated on by the magnetic brush 32 for removal of the residual toner after operation thereon by the discharge unit 26. Of course, if a second magnetic brush (not shown) is provided between the discharge unit 26 and charging unit 14, the entire copying and drum cleaning opera-tion may be performed during one revolution of the drum 12, with the magnetic brush 32 serving only the developing function.
Figures 3 to 5 illustrate alternative forms of the housing 41 which provide the same function. In these Figures, . , : .
:
~10667S8 a solid line 50 indicates the downstream limit of radiation of the light from the light source 43 and a dashed line 60 indicates the downstream limit of the electric field from the discharge electrode 44. Since the light source 43 and discharge electrode 44 are identical in all forms, the same reference numerals are utilized.
In Figure 3 a housing Sl comprises an upstream wall 51a and a downstream wall ~Ib which have formed therebetween an opening 51c facing the drum 12. The downstream wall 51b is formed with an opening 51d in which is fitted an electri-cally conductive screen 51e. The screen 51e is substantially transparent to light but acts as a shield to the electric field, and serves the same function as the plate 41d.
In ~igure 4 a housing 61 comprises an upstream wall 61a and a downstream wall 61b which have formed therebetween - an opening 61c facing the drum 12. The downstream wall 61b is perforated and bent outwardly to define an opening 61d which allows light to extend further downstream from the housing 61 than the electric field as indicated.
Figure 5 shows a housing 71 which differs in construc-tion from the housing 41 and comprises an upstream wall 71a and a downstream wall 71b. Whereas in the housing 41 the dis-charge electrode 44 is disposed between the light source 43 and the drum 12, in the housing 71 the light source 43 is arranged downstream of the discharge electrode 44. A parti-tion wall 71c is provided in the housing 71 between the light source 43 and discharge electrode 44 and cut away at its bottom end to define an opening 71d. The walls 71a and 71c have formed therebetween an opening 71e facing the drum 12 and the walls 71b and 71c have formed therebetween an opening 1~66758 71f facing the drum 12. The opening 71d is formed in such a manner that the electric field extends into the opening 71f but the light extends further downstream than the elec-tric field.
Many modifications of the preferred embodiments shown and described within the scope of the invention will become possible for those skilled in the art after receiving the teaching of the present disclosure. For example, the inven-tion is practically operable if the discharge electrode 44 is adapted to apply an alternating electric field to the drum 12 rather an electric field of opposite polarity to that of the charging unit 14.
; 15 - :.
. .
. .
:
.
` Since the electrostatic force between the residual toner anddrum is reduced substantially, the residual toner may be more readily removed from the drum by a magnetic brush or the like.
A drawback exists in this prior art expedient in that the corona discharge is performed in the absence of light.
The conductivity of the photoconductive layer in the dark is high, and it is impossible to dissipate the electrostatic charge in the lowermost portion of the layer. Even the subsequent exposure to light does not produce complete dis-charge, and the problem of double printing is not effectively solved.
It is an object of the present invention to provide a process for completely removing residual toner from a photo- !
conductive member of an electrophotographic apparatus after a toner image transfer operation.
It is another object of the present invention to provide an electrophotographic apparatus embodying the process.
It is another object of the present invention to provide an electrophotographic process in which an electro-static attractive force between residual toner particles and a photoconductive drum is dissipated through simultaneous illumination of the drum surface with light and exposure of the drum surface to an electric field thereby effecting complete discharge of the drum and toner.
It is another object of the present invention to provide an electrophotographic process in which complete discharge of a photoconductive drum is produced by simulta-neous illumination of the drum surface by light and exposure--3_ of the drum surface to an electric field, the effect of said steps in combination being greater than the aggregate effect of said steps performed sequentially.
It is another object of the present invention to provide an electrophotographic apparatus in which a magnetic brush which is used to apply toner substance to a photocon-ductive drum for development is also used to remove residual toner from the drum after a discharge operation comprising the simultaneous steps of illuminating the drum surface with light and exposing the drum to an electric field.
It is another object of the present invention to provide an electrophotographic apparatus in which a photo-~;~ conductive drum is rotated adjacent to a light source and a corona discharge unit which simultaneously operate on the drum to dissipate an electrostatic charge thereon, the area of radiation of light on the drum surface overlapping the area of the electric field on the drum surface and extending downstream of the area of the electric field in the direction of rotation of the drum.
It is another object of the present invention to ~`
provide a generally improved electrophotographic process and apparatus embodying the process.
Other objects, together with the foregoing, are attained in the embodiments of the present invention described in the following description and shown in the accompanying ~
drawings. ~`
Figure 1 is a schematic view of an electrophotographic apparatus embodying the present invention;
Figure 2 is an enlarged schematic view illustrating an important aspect of the present invention; and . ~. .
Figures 3 to 5 are fragmentary schematic views illustrating respective modifications of the present electrophotographic apparatus.
While the electrophotographic apparatus of the invention is susceptible of numerous physical embodiments, depending upon the environment and requirements of use, substantial numbers of the herein shown and described embodi-ments have been made, tested and used, and all have performed in an eminently satisfactory manner.
Referring now to Figure 1, an electrophotographic apparatus 11 embodying the present invention comprises an electrically grounded rotary drum 12 formed with a photo-conductive dielectric surface layer (not designated) and which is supported by a drive shaft 13. Drive means (not shown) rotate the shaft 13 and thereby the drum 12 clockwise at constant speed. A corona charging unit 14 is disposed adja-cent to the periphery of the drum 12 and operative to electro-statically charge the surface of the drum 12 in the absence of light. A light source 16 is arranged to illuminate an original document 17 which is moved by a scanning system (not shown) in the direction of an arrow 18 at a speed equal to the tangential speed of the surface of the drum 12 in such a manner that an imaging system, shown in simplified form as a converging lens 19, radiates a light image of the document 17 onto the surface of the drum 12. The highlight areas of the light image cause the photoconductive layer of the drum 12 to conduct thereby dissipating the electrostatic charge in these areas and forming an electrostatic image of the docu-ment 17. A developing unit 21 which will be described in detail below applies a powdered toner substance to the drum 12 which is electrostatically attracted to the areas of the photoconductive layer in which the electrostatic charge is high, which correspond to the dark or background areas of the document 17. The developing unit 21 thereby forms a toner image of the document 17 on the drum 12.
At a transfer unit 22 comprising a corona charging unit 23 similar to the corona charging unit 14, a copy sheet 24 is fed in synchronized contact with the drum 12 and an electrostatic force is applied to the back of the sheet 24 thereby attracting and effecting transfer of the toner image to the sheet 24. A fixing unit (not shown) subsequently fixes the toner image by heat, pressure or both to the copy sheet 24.
A discharge unit 26 then completely discharges the drum 12 - and any residual toner is removed by the developing unit 21 as will be described in detail below.
The developing unit 21 comprises a hopper 31 which is filled with a powdered developing or toner substance preferably ~ - -in the form of tiny granules or particles. Each granule comprises at least one particle of black carbon and at least one particle of iron, said particles being rigidly held together by a resin binder. A magnetic brush 32 is disposed ; closely adjacent to the surface of the drum 12 below an opening in the hopper 31 and comprises a magnetic core 33 surrounded by a non-magnetic sleeve 34, the core 33 and sleeve ~ 25 34 being coextensive with the length of the drum 12. Either one or both of the core 33 and sleeve 34 are rotated so that toner from the hopper 31 is magnetically attracted to the magnetic brush 32 to form an accumulation of toner particles on the surface of the sleeve 34 and rotates in the direction of an arrow 36 which brushingly engages with the surface of ; ` -6-.
the drum 12. A doctor 37 is provided at the opening of the hopper 31 to limit the thickness of the toner substance on the sleeve 34 to a required value. Due to the brushing engagement of the toner on the magnetic brush 32 with the surface of the drum 12, the toner is applied to the drum 12 to effect development of the electrostatic image into the toner image. The magnetic force of the magnetic core 33 is selected so that it is less than the electrostatic attraction betwean the electrostatic image on the drum 12 so that the toner may be transferred from the magnetic brush 32 to the drum 12 for development.
The discharge unit 26 comprises a housing 41 which acts as a light and electrical shield, the housing 41 being opaque, electrically conductive and electrically grounded. The housing 41 is coextensive with the length of the drum 12 and is formed with an opening 42 facing the drum 12. A light source 43 such as a fluorescent bulb is disposed in the housing 41 such " that light from the light source 43 is radiated onto the surface of the drum 12 through the opening 42. A corona dis-charge electrode 44 is further disposed in the housing 41 such that an electric field of opposite polarity to that of the charging unit 14 is applied to the surface of the drum 12 through the opening 42.
As shown in Figure 2, the housing 41 comprises, ` 25 adjacent to the opening 42, an upstream wall 41a and a down-stream wall 41b, the designations upstream and downstream `~
referring to the direction of movement of the surface of the drum 12. The end of the downstream wall 41b adjacent to the drum 12 is cut away to define an opening 41c, and an electri-cally conductive transparent plate 41d formed of, for example . . :
. `~
1066'758 NESA (trademark) glass, is fitted in the opening 41c.
In Figure 2 the photoconductive surface layer of the drum 12 is designated as 12a and toner particles attracted to the surface layer 12a are shown as circles but are not designated by reference numerals. Due to the electrical shielding effect of the walls 41a and 41b, the electric field from the corona discharge electrode 44 is applied to the layer 12a in an area bounded by lines A and D as indi-cated by dashed lines leading from the electrode 44 to the layer 12a. The light from the light source 43 is radiated onto the layer 12a in an area bounded by lines B and E as indicated by dot-dash lines leading from the light source 43 to the layer 12a. It will be noted that the light passes through the plate 41d whereas the electric field is blocked or shielded thereby.
- The light from the light source 43 and the electric field produced by the corona discharge electrode 44 are superimposed on the layer 12a in an area bounded by the lines `~ B and D such that the layer 12a is simultaneously irradiated by light and electrically discharged in this position. The polarity of the corona discharge electrode 44 is opposite to that of the corona charging unit 14 so that the electro-static image on the drum 12 is neutralized. The light causes photoconduction in the layer 12a so that any remaining charge ` 25 on the layer 12a is shorted to ground due to the high conduc~
tivity of the layer 12a. In this manner, the charge on both the layer 12a and toner particles is completely removed, a `
result which cannot be achieved by corona discharge followed by exposure to light.
Assuming that the charge applied to the layer 12a by the charging unit 14 is negative in polarity, the polarity of the discharge electrode 44 is positive. The negative charge at the surface of the layer 12a produces electrostatic polarization of the toner particles so that they are positive at their ends next to the layer 12a and negative at their ends away from the layer 12a, thereby being electrostatically attracted to the layer 12a. A similar magnetic phenomenon attracts the toner particles to the magnetic brush 32 of the developing unit 31.
As viewed in Figure 2, the electric field of the electrode 44 extends further upstream than the light from the light source 43, such that only the electric field exists in an area bounded by the lines A and B. This is of no practical consequence, and the housing 41 may be designed so that the electric field and light extend the same distance upstream or the light extends further upstream than the electric field. What is important, however, is that the electric field does not extend further downstream than the light.
If the plate 41d were opaque, the light from the light - source 43 would be confined to an area on the layer 12a between the line B and a line C, as indicated by a solid line 46 leading from the light source 32 to the layer 12a, and only the electric field would exist in an area bounded by the ` 25 lines C and D. As a result, the layer 12a would be electro-statically charged with a positive polarity, thereby inducing electrostatic polarization in the toner particles opposite to the normal polarity. The toner particles would be caused to be attracted to the layer 12a by the action of the discharge electrode 44, thereby defeating the purpose of the discharge ~066758 unit 26. Since the toner particles would be attracted to the layer 12a as a result of the operation of the discharge electrode 44, it would~be impossible for the magnetic brush 32 to completely remove the residual toner particles from ` 5 the drum 12. However, due to the provision of the plate 41d, the light extends further downstream than the electric field and the problem of reverse charging of the layer 12a and toner particles is eliminated.
After operation on the drum 12 by the discharge unit 26, the magnetic brush 32 removes the residual toner particles from the drum 12 through physical contact. Since the electro-static attractive force between the drum 12 and toner parti-- cles is reduced to substantially zero by the discharge unit26, the magnetic attractive force of the magnetic brush 32 is effective in effecting complete transfer of the residual toner ~; particles to the magnetic brush 32~
For each copying operation, the drum 12 is rotated through two revolutions. During the first revolution the copying operation is performed and the discharge unit 26 operates on the drum 12. During the second revolution, the charging unit 14 and light source 16 are de-energized so that the drum 12 is operated on by the magnetic brush 32 for removal of the residual toner after operation thereon by the discharge unit 26. Of course, if a second magnetic brush (not shown) is provided between the discharge unit 26 and charging unit 14, the entire copying and drum cleaning opera-tion may be performed during one revolution of the drum 12, with the magnetic brush 32 serving only the developing function.
Figures 3 to 5 illustrate alternative forms of the housing 41 which provide the same function. In these Figures, . , : .
:
~10667S8 a solid line 50 indicates the downstream limit of radiation of the light from the light source 43 and a dashed line 60 indicates the downstream limit of the electric field from the discharge electrode 44. Since the light source 43 and discharge electrode 44 are identical in all forms, the same reference numerals are utilized.
In Figure 3 a housing Sl comprises an upstream wall 51a and a downstream wall ~Ib which have formed therebetween an opening 51c facing the drum 12. The downstream wall 51b is formed with an opening 51d in which is fitted an electri-cally conductive screen 51e. The screen 51e is substantially transparent to light but acts as a shield to the electric field, and serves the same function as the plate 41d.
In ~igure 4 a housing 61 comprises an upstream wall 61a and a downstream wall 61b which have formed therebetween - an opening 61c facing the drum 12. The downstream wall 61b is perforated and bent outwardly to define an opening 61d which allows light to extend further downstream from the housing 61 than the electric field as indicated.
Figure 5 shows a housing 71 which differs in construc-tion from the housing 41 and comprises an upstream wall 71a and a downstream wall 71b. Whereas in the housing 41 the dis-charge electrode 44 is disposed between the light source 43 and the drum 12, in the housing 71 the light source 43 is arranged downstream of the discharge electrode 44. A parti-tion wall 71c is provided in the housing 71 between the light source 43 and discharge electrode 44 and cut away at its bottom end to define an opening 71d. The walls 71a and 71c have formed therebetween an opening 71e facing the drum 12 and the walls 71b and 71c have formed therebetween an opening 1~66758 71f facing the drum 12. The opening 71d is formed in such a manner that the electric field extends into the opening 71f but the light extends further downstream than the elec-tric field.
Many modifications of the preferred embodiments shown and described within the scope of the invention will become possible for those skilled in the art after receiving the teaching of the present disclosure. For example, the inven-tion is practically operable if the discharge electrode 44 is adapted to apply an alternating electric field to the drum 12 rather an electric field of opposite polarity to that of the charging unit 14.
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Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In an electrophotographic process in which a photo-conductive member is electrostatically charged, radiated with a light image to produce an electrostatic image, developed by application of a toner substance thereto to form a toner image and subjected to a transfer operation in which the toner image is transferred to a copy sheet, an improvement for removing residual toner substance from the photoconductive member after the transfer operation comprising the steps of:
(a) radiating light uniformly onto the photoconductive member to cause photoconduction;
(b) applying an electric field to the photoconductive member to substantially neutralize the electrostatic charge simultaneously with performing step (a); and (c) subsequently applying a magnetic brush to the photoconductive member to remove the residual toner substance.
(a) radiating light uniformly onto the photoconductive member to cause photoconduction;
(b) applying an electric field to the photoconductive member to substantially neutralize the electrostatic charge simultaneously with performing step (a); and (c) subsequently applying a magnetic brush to the photoconductive member to remove the residual toner substance.
2. A process as claimed in claim 1, in which the photo-conductive member moves through a position at which steps (a) and (b) are performed, the light extending further downstream from said position than the electric field in a direction of movement of the photoconductive member.
3. In an electrophotographic apparatus including a photoconductive member, a charging unit for applying an electrostatic charge to the photoconductive member, an imaging unit for radiating a light image onto the photoconductive member to produce an electrostatic image, a developing unit for applying a toner substance to the photoconductive member to form a toner image and a transfer unit for transferring the toner image to a copy sheet, an improvement for removing residual toner substance from the photoconductive member after operation thereon by the transfer unit comprising:
a light source for radiating light uniformly onto the photoconductive member to cause photoconduction;
an electrical discharge unit for applying an electric field to the photoconductive member to substantially neutralize the electrostatic charge thereon simultaneously with the radiation of the light; and a cleaning unit for subsequently removing the residual toner substance from the photoconductive member through contact therewith.
a light source for radiating light uniformly onto the photoconductive member to cause photoconduction;
an electrical discharge unit for applying an electric field to the photoconductive member to substantially neutralize the electrostatic charge thereon simultaneously with the radiation of the light; and a cleaning unit for subsequently removing the residual toner substance from the photoconductive member through contact therewith.
4. An apparatus as claimed in claim 3, in which the developing unit and cleaning unit are integral and comprise a single magnetic brush for applying the toner substance to the photoconductive member to form the toner image and remov-ing the residual toner substance from the photoconductive member.
5. An apparatus as claimed in claims 3, in which the photoconductive member moves through a position at which the light source and discharge unit act thereon, the light from the light source extending further downstream from said posi-tion than the electric field from the discharge unit in a direction of movement of the photoconductive member.
6. An apparatus as claimed in claims 3, 4 or 5, in which the photoconductive member comprises a rotary drum formed with a photoconductive surface, the charging unit, imaging unit, developing unit, transfer unit, light source, discharge unit and cleaning unit being circumferentially arranged adjacent to the surface of drum.
7. An apparatus as claimed in claim 5, further comprising .
a housing enclosing the light source and discharge unit and constituting a light and electrical shield, the housing being formed with an opening facing the photoconductive member and means for causing the light from the light source to extend further downstream from said position than the electric field from the discharge unit in the direction of movement of the photoconductive member.
a housing enclosing the light source and discharge unit and constituting a light and electrical shield, the housing being formed with an opening facing the photoconductive member and means for causing the light from the light source to extend further downstream from said position than the electric field from the discharge unit in the direction of movement of the photoconductive member.
8. An apparatus as claimed in claim 7, in which said means comprises a downstream wall of the housing formed with a secondary opening oriented such that light from the light source propagates therethrough onto the photoconductive member.
9. An apparatus as claimed in claim 8, in which said means further comprises a secondary electrical shield mounted in the secondary opening, the secondary electrical shield being substantially transparent to the light.
10. An apparatus as claimed in claim 9, in which the secondary electrical shield comprises an electrically conduc-tive screen.
11. An apparatus as claimed in claim 9, in which the secondary electrical shield comprises an electrically conductive plate.
12. An apparatus as claimed in claim 7, in which the light source is disposed downstream of the discharge unit in the housing, said means comprising a secondary electrical shield disposed between the light source and discharge unit.
13. An apparatus as claimed in claim 12, in which at least part of the secondary electrical shield is transparent to the light.
14. An apparatus as claimed in claim 12, in which the secondary electrical shield is formed with an opening.
15. An apparatus as claimed in claim 3, in which the discharge unit comprises a corona discharge unit.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14141075A JPS5265450A (en) | 1975-11-26 | 1975-11-26 | Method and apparatus for removing electricity for cleaning means of li ght sensitive body |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1066758A true CA1066758A (en) | 1979-11-20 |
Family
ID=15291346
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA263,156A Expired CA1066758A (en) | 1975-11-26 | 1976-10-12 | Drum cleaning process and apparatus for electrophotography |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS5265450A (en) |
| CA (1) | CA1066758A (en) |
| DE (1) | DE2644521C3 (en) |
| GB (1) | GB1557719A (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS51119229A (en) * | 1975-04-11 | 1976-10-19 | Minolta Camera Co Ltd | Electrophotography |
| JPS5446044A (en) * | 1977-09-19 | 1979-04-11 | Mita Industrial Co Ltd | Cleaning of residual toner in transfer type electrostatic copying machine |
| JPS5532051A (en) * | 1978-08-28 | 1980-03-06 | Ricoh Co Ltd | Destaticizer of copying machine |
| JPS5911909B2 (en) * | 1979-02-20 | 1984-03-19 | コニカ株式会社 | electrophotographic copying device |
| JPS59112256U (en) * | 1983-12-27 | 1984-07-28 | シャープ株式会社 | Corona discharge device |
| JPS6251375U (en) * | 1986-09-05 | 1987-03-30 | ||
| JPS6291674U (en) * | 1986-09-05 | 1987-06-11 | ||
| JPS6291675U (en) * | 1986-09-05 | 1987-06-11 | ||
| JP2589718B2 (en) * | 1987-12-25 | 1997-03-12 | 松下電器産業株式会社 | Color electrophotographic method |
| JPH01219881A (en) * | 1988-02-29 | 1989-09-01 | Alps Electric Co Ltd | Cleaning method and device |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1139256A (en) * | 1965-08-11 | 1969-01-08 | Konishiroku Photo Ind | Electrophotographic process and device |
| US3580673A (en) * | 1968-08-26 | 1971-05-25 | Xerox Corp | Cleaning apparatus |
| JPS4943337B1 (en) * | 1970-09-03 | 1974-11-20 | ||
| US3797927A (en) * | 1971-05-20 | 1974-03-19 | Canon Kk | Electrophotographic copying machine |
| US3884572A (en) * | 1972-12-26 | 1975-05-20 | Ibm | Cleaning apparatus |
| JPS49123628A (en) * | 1973-03-31 | 1974-11-26 | ||
| JPS5079337A (en) * | 1973-11-12 | 1975-06-27 |
-
1975
- 1975-11-26 JP JP14141075A patent/JPS5265450A/en active Granted
-
1976
- 1976-09-17 GB GB3851276A patent/GB1557719A/en not_active Expired
- 1976-10-01 DE DE19762644521 patent/DE2644521C3/en not_active Expired
- 1976-10-12 CA CA263,156A patent/CA1066758A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5533075B2 (en) | 1980-08-28 |
| DE2644521A1 (en) | 1977-06-02 |
| DE2644521B2 (en) | 1980-09-11 |
| DE2644521C3 (en) | 1981-06-11 |
| JPS5265450A (en) | 1977-05-30 |
| GB1557719A (en) | 1979-12-12 |
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