CA1038019A - Electrostatic sheet transport system - Google Patents
Electrostatic sheet transport systemInfo
- Publication number
- CA1038019A CA1038019A CA211,158A CA211158A CA1038019A CA 1038019 A CA1038019 A CA 1038019A CA 211158 A CA211158 A CA 211158A CA 1038019 A CA1038019 A CA 1038019A
- Authority
- CA
- Canada
- Prior art keywords
- copy sheet
- alternating
- supporting surface
- charged
- pattern
- 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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H5/00—Feeding articles separated from piles; Feeding articles to machines
- B65H5/02—Feeding articles separated from piles; Feeding articles to machines by belts or chains, e.g. between belts or chains
- B65H5/021—Feeding articles separated from piles; Feeding articles to machines by belts or chains, e.g. between belts or chains by belts
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/65—Apparatus which relate to the handling of copy material
- G03G15/6529—Transporting
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S271/00—Sheet feeding or delivering
- Y10S271/901—Magnetic operation
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Electrostatic Charge, Transfer And Separation In Electrography (AREA)
- Paper Feeding For Electrophotography (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A transport for paper or other copy sheets consisting of a photoconductive belt which is corona charged and then optically exposed to a fine pattern of closely spaced alterna-ting adjacent light and dark areas to provide a correspondingly fine electrostatic pattern of alternating charged and discharged areas on the belt. This provides a fine pattern of fringe fields for electrostatically holding either charged or uncharged paper on the belt. The charge pattern spacing is preferably that of the paper thickness or less so that the system may be utilized for the transport of a copy sheet through a xerographic transfer station without affecting image transfer.
A transport for paper or other copy sheets consisting of a photoconductive belt which is corona charged and then optically exposed to a fine pattern of closely spaced alterna-ting adjacent light and dark areas to provide a correspondingly fine electrostatic pattern of alternating charged and discharged areas on the belt. This provides a fine pattern of fringe fields for electrostatically holding either charged or uncharged paper on the belt. The charge pattern spacing is preferably that of the paper thickness or less so that the system may be utilized for the transport of a copy sheet through a xerographic transfer station without affecting image transfer.
Description
~3~
The present invention relates to a sheet transport system utilizing an optically controlled electrostatic sheet retaining charge.
The accurate and reliable transport of sheets, particularly cut paper or other copy sheets (or original documents) utilized in electrostatographic copying systems is a particular problem due to the variable nature of such materials. Various sheet transporting devices such as mech-anical grippers, vacuum transport belts, feed rollers, etc., are well known.
It is also known that a cop~ sh~et can be trans-ported on a belt or other member which has been charged by an electrostatic charge pattern. The following U. S. Patents are exemplary of this art of electrostatic tacking of paper ; 15 to a paper transport belt by uniform or non-uniform electro-static charging of the belt or paper: 2,576,882 to P. Koole et al, 3,357,325 to R. H. Eichorn, 3,642,362 to D. Mueller, 3,690,646 to J. A. Kolivis, 3,717,801 to M. Silverberg, and 3,7~5,957 to ~. Weigl. However, these charged transport belts are dielectric or conductive rather than photoconductive.
This presents serious practical problems in impressing thereon a sufficiently closely spaced electrostatic charge pattern of alternating charged and uncharged, or opposite polarity areas.
Corona charging techniques are not practically capable oE
producing a Eine (closely spaced) variable charge pattern. A
fine charge pattern can be provided on a dielectric surEace by a fine conductive grid therein or by direct contact of a conductive or semi-conductive biased electrode or roller which has a sufficiently finely textured or roughened surface to ~L~3~
apply by electrical contact transfer a fine charge pattern on the dielectric surface. However, it will be appreciated that the placing of fine charge patterns on a dielectric surface by direct contact by an electrode is dificult, due to surface contact problems, variations in the surface to be charged, contamination, etc. Thus, a non-contacting method of charging of a copy sheet transport supporting surface is generally pre~erable.
A particular sheet transport problem is the accura-te and positive transporting of sheets into, throw~h, and out oE a xerographic trans~er station. The copy sheet must be maintAined in accurate registration with the toner image to be transferred from the imaging surface onto the copy sheet at the transfer station. ~he sheet typically ac~uires a tacking electrostatic 15 charge and the imaging surface has a charge on it as well.
Thus, the sheet must be either mechanically or electrostatically stripped from the imaging surface at the exit of the transfer station or process. The stripping device if it takes the con-20 ventional form of an air puffer, gripper, or stripper finger,can cause some disturbance of the transferred toner image, which is typically unfused at that point.
Thus, ideally, it is desirahle to fully support and positively retain the copy sheet on a transport through the 25 transfer station. This can be done by a vacuum belt as disclosed ; in U. S. Patent No. 3,647,292 to D. J. Weikel, for example.
The present invention provides a different means for continuously positively retaining, and thereby stripping the copy sheet from the photoreceptor, in the transfer station. The present system 30 utilizes purely electrostatic forces for this function and does not require a vacuum system, although it will be appreciated that ~3~9 a vacuum may be additionall~ applied in combination therewith if so desired.
It will be noted that the use of a fine charge pattern produced on the imaging surface itself for increased toner reten-kion by fringe field effectc~, e. g., for improved "half-tone"
solid area image reproduction, is known. The fine charge pattern may be placed on the photoreceptor imaging surface by an optical screen, or by the photoreceptor construction itself, or by contact with a charging roller having a patterned or textured surface for transferring a fine e:Lectrical pattern to th~ photoreceptor.
For example, t~e imaging s~lrface ma~ be patt~rn c~a~ocl ~ ~
contacting electrically chargecl wire screen or knurled conducting rubber roller at a suitable voltage. ~Iowever, this type of structure is utilized for increasing the quantity or uniformity of toner retained on a given area of the photoreceptor prior to its transfer to the copy sheet, and not for retention of a copy sheet. Thus, it affects the transfer by changing the image which is transferred. In contrast, the copy sheet transport system of the invention does not affect the imaging surface and does not affect the transfer process or the transferred image pattern.
The sheet transport system of the invention may be utilized in any desired path or configuration. It may be utilized for transfer with an imaging surface which has any desired con-figuration, such as a cylinder or a belt. Belt imaging surfacephotoconductors in electrographic copying systems are exemplified by U. S. Patent Nos. 3,093,039 to Rheinfrank, 3,707,13~ to Cartright, and 3,719,165 to Trachienberg, et al.
-~03~0la In the conventional transfer station in xerography, toner is transferred from the photoreceptor (the original support and imaging surface) to the copy paper ~the final support surface). Such development material transfers are also required in other electrostatographic processing steps, such as electrophoretic development. In xerography, developer transfer is most commonly achieved by electrostatic ~orce fields created by D. C. charges applied to the back of the copy paper (opposite from the side contacting the toner-bearing photoreceptor) sufficient to overcome the charges holding the toner to the photoreceptor and to attract mo~t o~ the toner to tran~fer onto the paper. These xerographic trans~er ~ields are generally provided in on~ of two w~y~, by ion emisqion from a transfer corotron onto the paper, as in U. S. Patent No. 2,807,233, or by a D. C. biased transfer roller or belt rolling along the back of the paper. Examples of bias roller transfer systems are described in U. S. Patent Nos. 2,807,233;
3,043,684; 3,267,840; 3,598,580; 3,625,146; 3,630,591;
3,691,993; 3,702,482; and 3,684,364. The copy sheet is typically electrostatically tacked to the photoreceptor until it is subsequently mechanically or electrostatically stripped off as previously noted, i. e., the tacking forces must be overcome in some manner for the copy sheet to be removed from the imaging surface.
The above-cited and other re~erences teach details of various suitable exemplary xerographic structures, materials and functions to those skilled in the art. Further examples are disclosed in the books Electrophotoqraphy by R. M. Schaffert, and Xeroqraphy and Related Processes by John H. Dessauer and Harold E. Clark, both first published in 1965 by Focàl Press Ltd., London, England.
~(~38~
. . . .
In accordance with this invention there is provided ,~ in an electrostatographic copying system in which an image is formed on an imaging surface and trans~erred at a transfer station to a copy sheet, the improvement comprising copy sheet transport means including a copy sheet supporting surface, said supporting sur~ace being photoconductively electrically dischargeable, support means for said transport means ~or moving said supporting surface intimately past said imaging surface, charging means for electric-ally charging said supporting surface, and optical means for opti-cally imaging a fine liyht pattern o~ closely alternating adjacent light and dark areas on said supporting surface, sub~equent to said electrical charging thereo~ by said charging m~an~, Eor photo-conductively discharging said supporting sur~ace into a Eine charge pattern of alternating closely adjacent charged and discharged areas on said supporting surface providing copy sheet retaining electrical I ~ringe fields.
This invention will be better understood by reference to -the following description and to the drawing forming a part thereof, wherein:
The Figure is a schematic perspective view of an exemplary sheet transport system in accordance with the present inven~ion, including a conventional xerographic copying system.
Referring to the Figure, there is schematically shown a sheet transport system 10 which is an exemplary embodi~ent Oe the present învention. Since the conventional details thereof are well known and fully described in the above-cited and other references relating to copy sheet handling, transfer and xerography, these details, for improved clarity, will not be described herein.
~o~o~
The system 10 here com~rises a copy sheet transport belt 12 ~hich is supported and rotatably driven between rollers 14 and 16. The transport belt 12, unlike conventional sheet transport belts, is photoconductive. It may be constructed of the same photoconductive materialq and structure as other photoconductive belts utilized ~or xerographic imaging surfaces, such as those previously cited herein. Adaitional U. S. Patents disclosing the construction of photoconductive belts are :
- 6a -~3~ 9 3,697,285 and 3,713,821~
The photoconductive transport belt 12 positively supports and carries the copy sheet 18 into and out of contact with an imaging surface 20 of a xerographic copying system 22 S at a trans~er station 24. T.rans~er is conventionally provided at the transfer station 2~ by a bias transfer roller, here comprising the roller 19. The xerographic copying system 22 shown h.ere also includes the conventional stations for optical imaging, cleaning, charging, and development of the imaging surface 20.
The kransport belt 12, by the eleck.rostatic ~.r.inge field charge pattern de~cr:ibed herein, provides pos.itive retention o~ the copy sheet 18 at all desired points along the path o~ the transport belt 12, until it is desired to strip the copy sheet therefrom by any suitable conventional sheet stripping means. With the disclosed system the copy sheet 18 can be positively retained through the entire transfer station 24 wlthout affecting the normal xerographic : transfer in any way.
To provide the copy sheet retaining charge pattern ; on the transport belt 12, the belt ~which may be previously conventionally neutralized or grounded electrically or optically) is first uniformly conventionally corona charged by a non-contacting conventional corona charging device 26 extending laterally across the width of the transport belt 12, i.e., transversely of the direction of motion of the belt~ Subse~uent to this electrical charging of the copy sheet supporting surface of the transport belt 12, optical means are provided for selectively optically discharging discrete, but closely Q~
adjacent, areas of the transport belt surface across the belt, at a belt discharging station 30.
The discharging station 30 includes an optical system or optically imaging a fine light pattern of closely alternating adjacent light and dark areas on the copy sheet supporting surface of the belt, so as to photoconductively discharge this supporting surface into a fine charge pattern of alternating closely adjacent charged and discharged areas which will provide copy sheet retaining electrical fringe fields. This may be provided as shown by sequentially ~lash imaging on the belt 12, as it advances, an ori~:inal image pattern 32 o~ alternating closely adjacent light and dark areas through a conventional imaging lens 34 onto the supporting surface. This original image pattern 32 may be either an opaque or transparent pattern or any othex suitable means for forming the desired image pattern on the transport belt, such as a scanning laser beam pattern or the like.
It will be appreciated that the light utilized may be either visible or invisible radiant energy, depending on the radiant energy sensitivity of the photoconductive material on the transport belt. It will also be appreciated that the image pattern 32 as shown is merely exemplary. The image pattern may be in the form of a pattern of closely spaced dots rather than lines. Alternatively, with a line of alternating closely spaced light and dark spots, or lines extending in the direction of motion of the belt, it may be possible with a stable belt support to utilize continuous imaging rather than intermittent flash exposure to form a continuous overall pattern.
8 _ An important desired feature of the optical image pattern formed on the photoreceptor belt is the alternating light and dark areas are sufficiently closely spaced, i.e., sufficiently fine, such that the corresponding alternating adjacent charged and discharged areas on the belt sur~ace form a very fine fringe field electrostatic pattern which will not affect the image transfer at the transfer station. Preferably the spacing of the alternating charged and discharged areas is not substantially greater than the thickness of the copy sheet. Such close or fine spacing will cause the fringe fields to extend mainly inside the copy sheet Erom the supported back surEace thereo~, and not extend appr~ciably outs:Lde oE
the Eront or image receiving surEace Oe the copy ~he~t. For most conventional copy sheet thicknesses the preferred charge pattern is thus approximately 0.13 millimeters (5 mils) in spacing between the charged and uncharyed areas. With this spacing the fringe fields on the underlying transport belt 12 will not significantly affect the transfer fields in the transfer nip of the transfer station, and thereby will not affect the transfer of toner to the upper or exposed surface of the copy sheet 18. Further, they will not disturb the toner once it is transferred to the copy sheet. This substantially eliminates the chances for any observable toner '~print-out'r of the transport belt charge pattern onto the copy sheet.
It will be noted that the exposed or discharged areas of the transport belt 12 do not have to be fully discharged, nor do the unexposed or undischarged areas have to be fully unexposed (i.e., remain at their total initial charge). It is only necessary for this system that the discharged areas be g _ ~3t~0~9 discharged to a different, i~ e., lower, voltage le~el than the undischarged areas, so as to create fringe fields between different adjacent voltage levels of appropriate intensity for retention of the particular copy sheets.
Another important advantage in using a photocon-ductive transfer belt is that the transfer fields can be tailored, even for a single potential transfer electrode, by using light sources shining light into selected regions in and past the transfer nip. This will reduce the belt resis-tivity in these regions, which can make the pr~-nip Eields smaller than the nip or post-nip fields iE a thick photocon-ductive belt is used. ~his i5 basically a diEEerent way of making an electrically "relaxable" belt material, but with a less critical resistivity specification. The requirement is a dark rela~ation time for charge flow near the transfer nip much longer than the time spent near the nip. The minimum corresponding dark resisti~ity of the photoconductor to ensure this depends on process speed, belt thickness, and system geometry but is typically near 1011 ohm-cm. The light resistivity must be such that the relaxation time for charge flow in the nip is less than the nip time (typically 10~ ohm-cm but dependent on process speed, belt thickness, and geometry.
The sheet transport system disclosed herein is presently considered to be pre~erred; however~ it is contem-plated that further variations and modifications within the purview of those skilled in the art can be made herein. The followin~ claims are intended to cover all such variations and modifications as fall within the true spirit and scope of the invention.
The present invention relates to a sheet transport system utilizing an optically controlled electrostatic sheet retaining charge.
The accurate and reliable transport of sheets, particularly cut paper or other copy sheets (or original documents) utilized in electrostatographic copying systems is a particular problem due to the variable nature of such materials. Various sheet transporting devices such as mech-anical grippers, vacuum transport belts, feed rollers, etc., are well known.
It is also known that a cop~ sh~et can be trans-ported on a belt or other member which has been charged by an electrostatic charge pattern. The following U. S. Patents are exemplary of this art of electrostatic tacking of paper ; 15 to a paper transport belt by uniform or non-uniform electro-static charging of the belt or paper: 2,576,882 to P. Koole et al, 3,357,325 to R. H. Eichorn, 3,642,362 to D. Mueller, 3,690,646 to J. A. Kolivis, 3,717,801 to M. Silverberg, and 3,7~5,957 to ~. Weigl. However, these charged transport belts are dielectric or conductive rather than photoconductive.
This presents serious practical problems in impressing thereon a sufficiently closely spaced electrostatic charge pattern of alternating charged and uncharged, or opposite polarity areas.
Corona charging techniques are not practically capable oE
producing a Eine (closely spaced) variable charge pattern. A
fine charge pattern can be provided on a dielectric surEace by a fine conductive grid therein or by direct contact of a conductive or semi-conductive biased electrode or roller which has a sufficiently finely textured or roughened surface to ~L~3~
apply by electrical contact transfer a fine charge pattern on the dielectric surface. However, it will be appreciated that the placing of fine charge patterns on a dielectric surface by direct contact by an electrode is dificult, due to surface contact problems, variations in the surface to be charged, contamination, etc. Thus, a non-contacting method of charging of a copy sheet transport supporting surface is generally pre~erable.
A particular sheet transport problem is the accura-te and positive transporting of sheets into, throw~h, and out oE a xerographic trans~er station. The copy sheet must be maintAined in accurate registration with the toner image to be transferred from the imaging surface onto the copy sheet at the transfer station. ~he sheet typically ac~uires a tacking electrostatic 15 charge and the imaging surface has a charge on it as well.
Thus, the sheet must be either mechanically or electrostatically stripped from the imaging surface at the exit of the transfer station or process. The stripping device if it takes the con-20 ventional form of an air puffer, gripper, or stripper finger,can cause some disturbance of the transferred toner image, which is typically unfused at that point.
Thus, ideally, it is desirahle to fully support and positively retain the copy sheet on a transport through the 25 transfer station. This can be done by a vacuum belt as disclosed ; in U. S. Patent No. 3,647,292 to D. J. Weikel, for example.
The present invention provides a different means for continuously positively retaining, and thereby stripping the copy sheet from the photoreceptor, in the transfer station. The present system 30 utilizes purely electrostatic forces for this function and does not require a vacuum system, although it will be appreciated that ~3~9 a vacuum may be additionall~ applied in combination therewith if so desired.
It will be noted that the use of a fine charge pattern produced on the imaging surface itself for increased toner reten-kion by fringe field effectc~, e. g., for improved "half-tone"
solid area image reproduction, is known. The fine charge pattern may be placed on the photoreceptor imaging surface by an optical screen, or by the photoreceptor construction itself, or by contact with a charging roller having a patterned or textured surface for transferring a fine e:Lectrical pattern to th~ photoreceptor.
For example, t~e imaging s~lrface ma~ be patt~rn c~a~ocl ~ ~
contacting electrically chargecl wire screen or knurled conducting rubber roller at a suitable voltage. ~Iowever, this type of structure is utilized for increasing the quantity or uniformity of toner retained on a given area of the photoreceptor prior to its transfer to the copy sheet, and not for retention of a copy sheet. Thus, it affects the transfer by changing the image which is transferred. In contrast, the copy sheet transport system of the invention does not affect the imaging surface and does not affect the transfer process or the transferred image pattern.
The sheet transport system of the invention may be utilized in any desired path or configuration. It may be utilized for transfer with an imaging surface which has any desired con-figuration, such as a cylinder or a belt. Belt imaging surfacephotoconductors in electrographic copying systems are exemplified by U. S. Patent Nos. 3,093,039 to Rheinfrank, 3,707,13~ to Cartright, and 3,719,165 to Trachienberg, et al.
-~03~0la In the conventional transfer station in xerography, toner is transferred from the photoreceptor (the original support and imaging surface) to the copy paper ~the final support surface). Such development material transfers are also required in other electrostatographic processing steps, such as electrophoretic development. In xerography, developer transfer is most commonly achieved by electrostatic ~orce fields created by D. C. charges applied to the back of the copy paper (opposite from the side contacting the toner-bearing photoreceptor) sufficient to overcome the charges holding the toner to the photoreceptor and to attract mo~t o~ the toner to tran~fer onto the paper. These xerographic trans~er ~ields are generally provided in on~ of two w~y~, by ion emisqion from a transfer corotron onto the paper, as in U. S. Patent No. 2,807,233, or by a D. C. biased transfer roller or belt rolling along the back of the paper. Examples of bias roller transfer systems are described in U. S. Patent Nos. 2,807,233;
3,043,684; 3,267,840; 3,598,580; 3,625,146; 3,630,591;
3,691,993; 3,702,482; and 3,684,364. The copy sheet is typically electrostatically tacked to the photoreceptor until it is subsequently mechanically or electrostatically stripped off as previously noted, i. e., the tacking forces must be overcome in some manner for the copy sheet to be removed from the imaging surface.
The above-cited and other re~erences teach details of various suitable exemplary xerographic structures, materials and functions to those skilled in the art. Further examples are disclosed in the books Electrophotoqraphy by R. M. Schaffert, and Xeroqraphy and Related Processes by John H. Dessauer and Harold E. Clark, both first published in 1965 by Focàl Press Ltd., London, England.
~(~38~
. . . .
In accordance with this invention there is provided ,~ in an electrostatographic copying system in which an image is formed on an imaging surface and trans~erred at a transfer station to a copy sheet, the improvement comprising copy sheet transport means including a copy sheet supporting surface, said supporting sur~ace being photoconductively electrically dischargeable, support means for said transport means ~or moving said supporting surface intimately past said imaging surface, charging means for electric-ally charging said supporting surface, and optical means for opti-cally imaging a fine liyht pattern o~ closely alternating adjacent light and dark areas on said supporting surface, sub~equent to said electrical charging thereo~ by said charging m~an~, Eor photo-conductively discharging said supporting sur~ace into a Eine charge pattern of alternating closely adjacent charged and discharged areas on said supporting surface providing copy sheet retaining electrical I ~ringe fields.
This invention will be better understood by reference to -the following description and to the drawing forming a part thereof, wherein:
The Figure is a schematic perspective view of an exemplary sheet transport system in accordance with the present inven~ion, including a conventional xerographic copying system.
Referring to the Figure, there is schematically shown a sheet transport system 10 which is an exemplary embodi~ent Oe the present învention. Since the conventional details thereof are well known and fully described in the above-cited and other references relating to copy sheet handling, transfer and xerography, these details, for improved clarity, will not be described herein.
~o~o~
The system 10 here com~rises a copy sheet transport belt 12 ~hich is supported and rotatably driven between rollers 14 and 16. The transport belt 12, unlike conventional sheet transport belts, is photoconductive. It may be constructed of the same photoconductive materialq and structure as other photoconductive belts utilized ~or xerographic imaging surfaces, such as those previously cited herein. Adaitional U. S. Patents disclosing the construction of photoconductive belts are :
- 6a -~3~ 9 3,697,285 and 3,713,821~
The photoconductive transport belt 12 positively supports and carries the copy sheet 18 into and out of contact with an imaging surface 20 of a xerographic copying system 22 S at a trans~er station 24. T.rans~er is conventionally provided at the transfer station 2~ by a bias transfer roller, here comprising the roller 19. The xerographic copying system 22 shown h.ere also includes the conventional stations for optical imaging, cleaning, charging, and development of the imaging surface 20.
The kransport belt 12, by the eleck.rostatic ~.r.inge field charge pattern de~cr:ibed herein, provides pos.itive retention o~ the copy sheet 18 at all desired points along the path o~ the transport belt 12, until it is desired to strip the copy sheet therefrom by any suitable conventional sheet stripping means. With the disclosed system the copy sheet 18 can be positively retained through the entire transfer station 24 wlthout affecting the normal xerographic : transfer in any way.
To provide the copy sheet retaining charge pattern ; on the transport belt 12, the belt ~which may be previously conventionally neutralized or grounded electrically or optically) is first uniformly conventionally corona charged by a non-contacting conventional corona charging device 26 extending laterally across the width of the transport belt 12, i.e., transversely of the direction of motion of the belt~ Subse~uent to this electrical charging of the copy sheet supporting surface of the transport belt 12, optical means are provided for selectively optically discharging discrete, but closely Q~
adjacent, areas of the transport belt surface across the belt, at a belt discharging station 30.
The discharging station 30 includes an optical system or optically imaging a fine light pattern of closely alternating adjacent light and dark areas on the copy sheet supporting surface of the belt, so as to photoconductively discharge this supporting surface into a fine charge pattern of alternating closely adjacent charged and discharged areas which will provide copy sheet retaining electrical fringe fields. This may be provided as shown by sequentially ~lash imaging on the belt 12, as it advances, an ori~:inal image pattern 32 o~ alternating closely adjacent light and dark areas through a conventional imaging lens 34 onto the supporting surface. This original image pattern 32 may be either an opaque or transparent pattern or any othex suitable means for forming the desired image pattern on the transport belt, such as a scanning laser beam pattern or the like.
It will be appreciated that the light utilized may be either visible or invisible radiant energy, depending on the radiant energy sensitivity of the photoconductive material on the transport belt. It will also be appreciated that the image pattern 32 as shown is merely exemplary. The image pattern may be in the form of a pattern of closely spaced dots rather than lines. Alternatively, with a line of alternating closely spaced light and dark spots, or lines extending in the direction of motion of the belt, it may be possible with a stable belt support to utilize continuous imaging rather than intermittent flash exposure to form a continuous overall pattern.
8 _ An important desired feature of the optical image pattern formed on the photoreceptor belt is the alternating light and dark areas are sufficiently closely spaced, i.e., sufficiently fine, such that the corresponding alternating adjacent charged and discharged areas on the belt sur~ace form a very fine fringe field electrostatic pattern which will not affect the image transfer at the transfer station. Preferably the spacing of the alternating charged and discharged areas is not substantially greater than the thickness of the copy sheet. Such close or fine spacing will cause the fringe fields to extend mainly inside the copy sheet Erom the supported back surEace thereo~, and not extend appr~ciably outs:Lde oE
the Eront or image receiving surEace Oe the copy ~he~t. For most conventional copy sheet thicknesses the preferred charge pattern is thus approximately 0.13 millimeters (5 mils) in spacing between the charged and uncharyed areas. With this spacing the fringe fields on the underlying transport belt 12 will not significantly affect the transfer fields in the transfer nip of the transfer station, and thereby will not affect the transfer of toner to the upper or exposed surface of the copy sheet 18. Further, they will not disturb the toner once it is transferred to the copy sheet. This substantially eliminates the chances for any observable toner '~print-out'r of the transport belt charge pattern onto the copy sheet.
It will be noted that the exposed or discharged areas of the transport belt 12 do not have to be fully discharged, nor do the unexposed or undischarged areas have to be fully unexposed (i.e., remain at their total initial charge). It is only necessary for this system that the discharged areas be g _ ~3t~0~9 discharged to a different, i~ e., lower, voltage le~el than the undischarged areas, so as to create fringe fields between different adjacent voltage levels of appropriate intensity for retention of the particular copy sheets.
Another important advantage in using a photocon-ductive transfer belt is that the transfer fields can be tailored, even for a single potential transfer electrode, by using light sources shining light into selected regions in and past the transfer nip. This will reduce the belt resis-tivity in these regions, which can make the pr~-nip Eields smaller than the nip or post-nip fields iE a thick photocon-ductive belt is used. ~his i5 basically a diEEerent way of making an electrically "relaxable" belt material, but with a less critical resistivity specification. The requirement is a dark rela~ation time for charge flow near the transfer nip much longer than the time spent near the nip. The minimum corresponding dark resisti~ity of the photoconductor to ensure this depends on process speed, belt thickness, and system geometry but is typically near 1011 ohm-cm. The light resistivity must be such that the relaxation time for charge flow in the nip is less than the nip time (typically 10~ ohm-cm but dependent on process speed, belt thickness, and geometry.
The sheet transport system disclosed herein is presently considered to be pre~erred; however~ it is contem-plated that further variations and modifications within the purview of those skilled in the art can be made herein. The followin~ claims are intended to cover all such variations and modifications as fall within the true spirit and scope of the invention.
Claims (6)
1. In an electrostatographic copying system in which an image is formed on an imaging surface and transferred at a transfer station to a copy sheet, the improvement comprising:
copy sheet transport means including a copy sheet supporting surface, said supporting surface being photoconductively electrically dischargable;
support means for said transport means for moving said supporting surface intimately past said imaging surface;
charging means for electrically charging said supporting surface, and optical means for optically imaging a fine light pattern of closely alternating adjacent light and dark areas on said supporting surface, subsequent to said electrical charging thereof by said charging means, for photoconductively discharging said supporting surface into a fine charge pattern of alternating closely adjacent charged and discharged areas on said supporting surface providing copy sheet retaining electrical fringe fields.
copy sheet transport means including a copy sheet supporting surface, said supporting surface being photoconductively electrically dischargable;
support means for said transport means for moving said supporting surface intimately past said imaging surface;
charging means for electrically charging said supporting surface, and optical means for optically imaging a fine light pattern of closely alternating adjacent light and dark areas on said supporting surface, subsequent to said electrical charging thereof by said charging means, for photoconductively discharging said supporting surface into a fine charge pattern of alternating closely adjacent charged and discharged areas on said supporting surface providing copy sheet retaining electrical fringe fields.
2. The copying system of Claim 1 wherein said optical means includes an original image pattern of alternating closely adjacent light and dark areas, and lens means for imaging said original image pattern over said supporting surface.
3. The copying system of Claim 1 wherein said copy sheet is moved on said support surface into and out of engage-ment with said imaging surface at said transfer station, retained on said support surface by said fine charge pattern of alternating closed adjacent charged and discharged areas.
4. The copying system of Claim 3 wherein said spacing of said alternating charged and discharged areas is sufficiently fine that said image transfer at said transfer station is unaffected.
5. The copying system of Claim 3 wherein said spacing of said alternating charged and discharged areas is not sub-stantially greater than the thickness of said copy sheet.
6. The copying system of Claim 3 wherein said spacing of said alternating charged and uncharged areas is less than approximately 0.13 millimeters.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US00421179A US3846020A (en) | 1973-12-03 | 1973-12-03 | Electrostatic sheet transport system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1038019A true CA1038019A (en) | 1978-09-05 |
Family
ID=23669497
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA211,158A Expired CA1038019A (en) | 1973-12-03 | 1974-10-10 | Electrostatic sheet transport system |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US3846020A (en) |
| CA (1) | CA1038019A (en) |
| GB (1) | GB1477534A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3981498A (en) * | 1975-03-24 | 1976-09-21 | Xerox Corporation | Non-uniform charging of sheet material |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3642362A (en) * | 1969-06-02 | 1972-02-15 | Xerox Corp | Apparatus for conveying sheet material |
-
1973
- 1973-12-03 US US00421179A patent/US3846020A/en not_active Expired - Lifetime
-
1974
- 1974-10-10 CA CA211,158A patent/CA1038019A/en not_active Expired
- 1974-11-14 GB GB4938674A patent/GB1477534A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US3846020A (en) | 1974-11-05 |
| GB1477534A (en) | 1977-06-22 |
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