CA1074180A - Transfer system for electrostatic reproduction machine - Google Patents

Transfer system for electrostatic reproduction machine

Info

Publication number
CA1074180A
CA1074180A CA253,107A CA253107A CA1074180A CA 1074180 A CA1074180 A CA 1074180A CA 253107 A CA253107 A CA 253107A CA 1074180 A CA1074180 A CA 1074180A
Authority
CA
Canada
Prior art keywords
transfer
charge
photoreceptor
corona generating
sheet
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
Application number
CA253,107A
Other languages
French (fr)
Inventor
J. William Ladrigan
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Xerox Corp
Original Assignee
Xerox Corp
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Priority to US60249675A priority Critical
Priority to US05/602,497 priority patent/US4027960A/en
Application filed by Xerox Corp filed Critical Xerox Corp
Application granted granted Critical
Publication of CA1074180A publication Critical patent/CA1074180A/en
Expired legal-status Critical Current

Links

Classifications

    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03GELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00Apparatus for electrographic processes using a charge pattern
    • G03G15/14Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base
    • G03G15/16Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer

Abstract

ABSTRACT OF THE DISCLOSURE

An improved transfer system for transferring a developed electrostatic image from a photoreceptor to a transfer member includes an electrically biased transfer roll, and a transfer corona generating device. Preferably, the corona generating device is an ultra-high field device having an instantaneous turn-on time.
The transfer member is first fed between the photoreceptor and the transfer roll whereby transfer is initiated and the transfer member is electrostatically tacked to the photoreceptor, and then the transfer member moves beneath the transfer corona generating device whereby transfer is completed. The transfer roll applies a first charge to the transfer member, and the transfer corona generating device then applies a second but higher charge to the transfer member.

Description

BACKGROUND OF T~E IN~ENTION
The present invention relate~ to an improved transfer ~y~tem for transferring a developed electrostatic image from a Xerographic plate to a transfer member such as a sheet f ~aper. More particularly, the invention is directed to a transfer system including an electrically biased transfer roll and a transfer corona generating device having an improved turn-on time.
In conventional xerogrzlphy, a xerographic plate comprising a layer of photosensitive insulating material af~ixed to a conductive backing i9 used to support electro-static latent images. In the xerographic process, the photo~
sensitive sur~3ce is electrostatically charged, and the charged surface is then exposed to a light pattern of the image being reproduced to thereby discharge the surface in the areas where light strikes the surface. The undischarsed areas of the surface thus form an electrostatic charge pattern (an electrostatic latent imaga) conforming to the original pattarn. The latent image is then developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner".
Toner is held on the image areas by the electrostatic charge on the surace. Where the charge is greater, a greater amount of toner is depvsited. Thus, a toner image is produced in conformity with a light image of the copy ~eing reproduced.
Generally, the developed image is then transferred to a suitable tran~fer member (e.g~, paper), and the image is af~ixed thereto to form a permanent record of the original documentO
In the practice of xerography, the transfer member is caused to move in synchronized contact with the p~oto-sensitive surface during the transfer operation, and an electrical potential opposite from the polarity of the toner is applied
2-to the ~ide of the paper remote ~rom the photosen~itive surace to electro tatically attract the toner image from the surface to the paperO
~ modern high ~peed duplicatirly machine sometimes utilizes an electrically biased transfer roll to effect the image transfer~ Although a ~iased transfer roll system ~ffects very good to excellent copy quality, certain copy quality deects are still produced. These copy quality deficiencies may be classified into two general catagories, poor transfer of ima~es (hollow characters and blotchy solids), and the redistribution of toner in and around images (toner disturbances, Lichtenburg figures, and blur). These deficiencies are present to some exten~ in other prior art trans~er systems.
Also high ~peed duplicating machines utilize numerous corona generating devices for applyin-J various charges to either a photoreceptor or a transfer member such as a sheet of paper. In many instances, it is necessary to turn the device on as instantly as possible. Prior art arrangements do not permit these devices to be actuated as rapidly as desired~
SUMMARY OF THE INVENTION
The present invention i~ primarily directed to an improved transfer system for overcoming the a~ove mentioned problems. The transfer system includes an electrically biased transer roll in combination with a transfer corona generating device, preferably an ultra-high field device. A sheet of `:
paper or other transfer member is fed between the transfer ~ roll ~nd the photosensitive suxface whereby transfer is - ~ partially effacted, and the sheet is electrostat~cally tacked to the photosensitive surface. Transfer of the developed electrostatic image to the sheet is completed as the latter
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1 ~ 7 ~i ~0 passe.s under -the transfer corona generat.iny device. In passiny unde.r the transfer corona yenera-ting device, however, the lead edge of the sheet preEerably is not charged; only the body and trail edge of the sheet are charged.
After the transfer operation, the sheet passes under a detack corona generating device in order to lessen the electrostatic attraction between the photosensitive surface and the sheet so that the latter can be rernoved and transported to a fusiny device. When passing under the detack corona generating device, the body and trail edge of the sheet prefer-~ ably receive a charge which is of a smaller magnitude than the charge deposited on the lead edge of the sheet in order ko prevent the developed image from being retransferred from the she~t to the photosen~itive surface.
In order that the transfer corona generating device can be up to full effectiveness almost instantaneously, a j dummy or standby electrical load is provided together with a switching arrangement to switch the power supply from standby load directly to the corona generating device~
; 20 In accordance with one aspect of -this invention there is provided an improved transfer system for transferring a developed electrostatic image from a charged photoreceptor to a transfer member, the improvement comprising the combination : ~ of a transfer roll in contact with the photoreceptor, and a transfer corona generating device located adjacent to both the ~ ~ photoreceptor and the transfer roll, and means for applying a first charge to the transfer member with the transfer roll, ~. ~ and for subsequently applyiny a second charge to the transfer ~ ~ member with the transfer corona generating device, the first and second charges each being of the same polarity as the charge on the photoreceptor.

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~ In accorda.lce with another aspect of this invention 'I , ~ . .

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the.re is providecl an improved process ~o~ transferring a developed electrostatic image from a charyed photoreceptor to a transfer men~er, the improvement comprising:
(a) pressing the transEer member into con-tact wlth the developed image while sim-ultaneously applying a first charge to the transfer member o~ the same polarity as the charge on the photoreceptor, the first charge being sufficient to electrostatically tack the transfer memb~r to the photo-receptor; and then (b) applying a second charge to the transfer member of the same polarity as the first charge.
BRIEF DESCRIPTION ~F THE DRAWINGS
Figure 1 is a schematic sectional view of an electro-static reproduction machine emhodying the principles of the present invention.
Figure 2 is a schematic diagram of the circuit for ; controlling both the trans~er and the detack corona generating devices.
DESCRIPTION OF THE INVENTION
0 E'or a general understanding of an electrostatic reproduction machine in which the present invention may be incorporated~ reference is made to Figure 1. As in all `
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electrostatic reproduction machines of the type illustrated, a light image of an original is projected onto the photo~ensitive surfa~e of a xerographic plate to form an electrostatic latent image thereon. Thereafter, the latent image i3 developed with an oppositely charged developing material comprising carrier beads and toner particles triboeLectrirally adhering thereto to form a xerographic powder image corre~ponding to the latent image on the photosensitive surface. The powder image is then electrostatically transferred to a trans~er member such as a sheet of paper to which it may be fixed by a fusing device whe~eby the toner image is caused permanently to adhere to the transfer member.
In the illustrated machine 10, an original 12 to be copied is placed upon a transparent support platen 14 fixedly arranged in an illumination assembly indicated generally by the reference numeral 16. While upon the platen, the illumination assembly flashes light rays upon the original, thereby producing image rays corresponding to the informational areas on the original. The image rays are projected by means vf an optical system 18 to an exposure station 20 for exposing the surface of a moving xeroyraphic plate in the form of a flexible photo-- conductive belt or photoreceptor 2~ In moving in the direction indicated by the arrow, prior to reaching the exposure station 20, that portion of the belt being exposed would have been uniformly charged to approximately ~900 volts by a corona generating device 24 located at a belt run extending between the belt supporting rollers 26 and 28. The exposure station extends between the roller 28 and a third roller 30.
The exposura of the photosensitive surface of the belt to the light image discharges the surface in the areas struck . ~
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: ' ' ': ' 7~by light whereby an electrostatic latent image remains on the belt in image configuration corresponding to the light image projected from the original on the support platen.
As the belt continues its movement, the latent image passes around the roller 30 and through a developing station 32 wh~re a developing apparatus indicated generally by the reference numeral 34 is positioned. The developing apparatus 34 comprises a plurality of magnetic brushes 36 which carry developing material to the surface of the upwardly moving belt 22. As the developing material is applied to the belt~
toner particles in the development material are el0ctrostatically attxacted to the charged photosensitive surface to form a powder image (an electrostatic developed image).
The developed electrostatic image is transported by the belt 22 to a transfer station 38 where a sheet of paper is moved at a speed in synchronism with the moving belt in order to effect transfer of the developed image~ Located at the transfer station 38 i~ a transfer roll 40 which is arranged on the frame of the machine to contact the back side of the sheet o paper as the latter is moved or fed between . . , the belt and the transfer roll. The roll 40 is electrically biased with sufficient voltage 90 that the developed image on the belt may be electrostatically attracted to the adjacent side of a sheet of paper as the latter is hrought into contact therewith. The transer is initiated by the transfer roll 40, but is completed by the ultra-high field corona generating device 42. The corona generating device 42 applies a higher charge to the sheet than do~s the transfer roll, the former producing a field of approximately 40 to 60 volts per micron, , ' ~ . .
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the latter producing a ield of approximately 27 to 32 volts per micron. The trans~er roll 40 applies a charge to the entire sheet as it moves between the roll and the belt 22.
Asjwill be explained below, however, the transfer corona generating device 42 does not apply charge to the lead edge of the sheet, but only to the remainder thereof.
A suitable sheet transE)ort mechanism transports sheets of paper seriatim from a E~aper handling mechanism indicated generally by the reference numeral 44 to the developed image on the belt as the same is carxied around the roller 26.
In passing from the paper handling mechanism to the transfer roll 40, each sheet contacts a plurality of registration fingers 46, the operation of which will ~e more fully described below.
As a sheet emerges from the transfer station 38, a charge is deposited thereon by a detack corona genPrating device 48 to lessen theelectrostatic attraction between the belt 22 and the sheet so that the latter can be removed by a vacuum stripping and transport mechanism 50, the device 48 having a plastic shield. The sheet is thereater retained on the underside o~ the vacuum stripping tran~port mechanism 50 for movement into a fuser assembly indicated generally by the reference numeral 52 wherein the powder image on the sheet is permanently affixed thereto. After fusing, the finished copy is discharged at a suitable point ~or collection. The ton~r particles remaining as residue on the belt 22 are carried by the belt to a cleaning apparatus 54. The cleaning apparatus 54 comprises a corona discharge device 56 for neutralizing charyes remaining on the untransferred toner particles, a rotating brush 58 mounted within a housing 60, and a vacuum outlet 62.

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Referring to Figure 2, the operation o~ the pre~ent invention will now be de~cribed in more detail. ~he movement of each sheet fed to the transfer station 38 i5 synchronized so that the sheet contacts the rotating registration fingers 46. As the registration fingers 46 rotate out o~ the path of the sheet, a reset pulse is sent to the timing circuit 64 to reset the latter to zero. ~hle timing circuit now begins to count the clock pulses generated by the detector 660 the latter counting the teeth on the main drive gear 6~ of the machine 10. Since both the numbler of teeth on the gear 68 and the rotation speed o~ the gear are known, and since all the subsystems of the machine 10 are synchronized with the main drive gear, the location of a sheet at any particular time after registration can be accurately determined.
Wnlen the sheet is at the proper location with respect to the transfer roll 40, an output pulse is delivered from the timing cixcuit to a suitable constant current power supply 70 to actuate th0 latter s~ that the transfer roll 40 applies a first charge to ~he entire sheet. When the sheet reaches the proper location with respect to the transfer corona generating device 42, an output pulse is delivered from the timing circuit to the reed relay switch 72 to switch a suitable constant current power supply 74 from the dummy load 76 to the transfer corona generating device 42.
For this particular application, the resistance o~
dummy Ioad 76 equals the resistance from the corona wire of t~e corona generating device 42 to the photoreceptor 22. Since the shield current is returned to the power supply and is not part of the controlled current, the dummy~load resistance is Vo/ip, where V~ LS the power supply voltage and ip is the current .

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between the corona wire and the photoreceptor. This arrangement lessens the turn-on time considerably since this time is a function of the resonse time of the power supply. As stated above, the transfer corona generating device 42 preferably apI~lies a second charge to all but the lead edge of the sheet, the second charge being of a greater magnitude than the first charge applied by the transfer roll 40. By not applying a charge to the lead edge of the sheet with the corona generating device 42, the sheet is~easier to detack. The same output pulse used to switch the reed relay switch 72 is also delivered to the pulse delay unit 78 where it is delayed for a pre-determined time before being delivered to the power supply 80.
In this manner, the transfer roll 40, and the corona generating devices 42 and 48 are actuated at the proper times so that the appropriate charges are deposited on the sheets passing there-under. Preferably, the detack corona generating device is actuated so as to apply a larger detacking charge to the lead edge of a sheet than to the remainder of the sheet as described in U. S. Patent Number 3,970,381, issued July 20th, 1976 and assigned to Xerox Corporation. If desirad, however, ; the same detacking charge may be applied to the entire sheet.
The ultra-high transfer corona generating device augments the transfer roll, the latter now serving to apply -! a charge to the entire sheet to initiate transfer as well as . .
~ to tack the sheet to the photosensitive surface of the belt.
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Since each sheet is now rolled into contact with and electro-:' statically tacked to the photosensitive surface of the ~elt by the transfer roll~ the ultra-high field transfer corona generating device very effectively completes the transfer operation to produce a very stable unfused image on the sheet, : _g , .

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~n image much more stable than can be pro~uced with a prior art transfer system utilizing a transfer roll only.
If enough of a charge i8 placed on a sheet of paper, thçn an electric fi01d large enough for air breakdown is generated. Air breakdown takes place (according to Paschen's Law) in the region with the largest paper to photoreceptor gap. Because each sheet of paper has been rolled into contact with and electrostatically tacked to the photosensitive surface of the belt before the application o~ the ultra-high ield, ~elective air breakdown occurs, i.e, the breakdown occurs in the background regions adjacent to toner imayes; thuQ, each sheet is in contact wlth the developed image and this tends to prevent breakdown in image areas and confines the breakdown to background areas. This results in a negative charge on the image sic~e of the sheet of paper which tends to reduce the electrostatic toner repulsion forces. As a result, a very stable unfused image is produced on each sheet, and little or no redistribution of toner in and around images occurs. In addition, the image produced by the present transfer system is less sensitive to paper resistivity. Thus, a wider selection of copy paper is available~for use with the present transfer system~ In addition to stabilizing the unfused image on each sheet of paper, the air breakdown that occurs tends to decrease the net charge on the background toner, thus resulting in reduced backgxound transfer.
In acldition, in utilizing the present transfer system as compared to one utiliæing a trans~er roll only, the requirements relatîng to temperature, humidity, and transfer roll material can be relaxed somewhat because the present system i5 not as dependent on the transfer roll.

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Also, tests have indicated thak the present transfer system reduces photoreceptor filming as compared to a txansfer system utilizing a transfer roll only; filming life can be extended by at least a factor of 1:hree. Although the filming process is a very complicated interaction between various machine subsystems, the most important interaction iR believed to be that between ~ine toner parlicles (less than 4 micron~) and the cleaning brushr The present transer system txansfers significantly more o~ the fine toner particles, thus, decrea~ing the number of ~ine toner particles on the cleaning brush;
consequently; the photoreceptor ~ilming rate is substantially .
reduced. AlsoO because increased brush speed or increased brush interference with the photoreceptor increases the filming .
rate, it may be possible to decrease both the speed and the interference by utilizing the present invention.
While the invention has been described with reference to the structure disclosed, it is not confined to the details set forth, but, is intended to cover such modifications or changes as may come within the scope of the following ~laim~.

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Claims (9)

WHAT IS CLAIMED IS:
1. An improved transfer system for transferring a developed electrostatic image from a charged photoreceptor to a transfer member, the improvement comprising the combination of a transfer roll in contact with the photoreceptor, and a transfer corona generating device located adjacent to both the photoreceptor and the transfer roll, and means for applying a first charge to the transfer member with the transfer roll, and for subsequently applying a second charge to the transfer member with the transfer corona generating device, the first and second charges each being of the same polarity as the charge on the photoreceptor.
2. An improved transfer system according to claim 1, wherein the second charge is of a larger magnitude than the first charge.
3. An improved transfer system according to claim 2, wherein the transfer member has a lead edge, and further including means for preventing the second charge from being applied to the lead edge of the transfer member.
4. An improved transfer system according to claim 3, in combination with means for applying a third charge to the transfer member subsequent to applying the second charge, the third charge being of a magnitude and polarity sufficient to lessen the electrostatic attraction between the photoreceptor and transfer member.
5. An improved transfer system according to claim 3, in combination with means for applying both a third charge to the lead edge of the transfer member and a fourth charge to the remainder of the transfer member subsequent to the application of the second charge.
6. An improved transfer system according to claim 1, wherein said means for applying a second charge includes a power supply connected to said corona generating device and means for switching said power supply between said corona generating device and a standby electrical load.
7. An improved transfer system according to claim 6, wherein said load is an impedance which is substantially equal to the impedance of said corona generating device.
8. An improved process for transferring a developed electrostatic image from a charged photoreceptor to a transfer member, the improvement comprising:
(a) pressing the transfer member into contact with the developed image while simultaneously applying a first charge to the transfer member of the same polarity as the charge on the photoreceptor, the first charge being sufficient to electrostatically tack the transfer member to the photo-receptor; and then (b) applying a second charge to the transfer member of the same polarity as the first charge.
9. An improved process according to claim 6, wherein the second charge is of a greater magnitude than the first charge.
CA253,107A 1975-08-06 1976-05-21 Transfer system for electrostatic reproduction machine Expired CA1074180A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US60249675A true 1975-08-06 1975-08-06
US05/602,497 US4027960A (en) 1975-08-06 1975-08-06 Transfer system for electrostatic reproduction machine

Publications (1)

Publication Number Publication Date
CA1074180A true CA1074180A (en) 1980-03-25

Family

ID=27084156

Family Applications (1)

Application Number Title Priority Date Filing Date
CA253,107A Expired CA1074180A (en) 1975-08-06 1976-05-21 Transfer system for electrostatic reproduction machine

Country Status (8)

Country Link
JP (1) JPS5220034A (en)
CA (1) CA1074180A (en)
DE (1) DE2624796A1 (en)
FR (1) FR2320586B1 (en)
GB (1) GB1550124A (en)
IT (1) IT1068105B (en)
NL (1) NL7608722A (en)
PT (1) PT65335B (en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5562465A (en) * 1978-11-02 1980-05-10 Daito Kk Electronic copier
US4823152A (en) * 1987-12-11 1989-04-18 Moore Business Forms, Inc. Transfer corona shield

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3620615A (en) * 1968-12-31 1971-11-16 Xerox Corp Sheet stripping apparatus
JPS5441904B2 (en) * 1971-09-20 1979-12-11
US3832053A (en) * 1973-12-03 1974-08-27 Xerox Corp Belt transfer system

Also Published As

Publication number Publication date
FR2320586B1 (en) 1982-07-30
CA1074180A1 (en)
FR2320586A1 (en) 1977-03-04
GB1550124A (en) 1979-08-08
PT65335B (en) 1978-01-06
IT1068105B (en) 1985-03-21
JPS5220034A (en) 1977-02-15
DE2624796A1 (en) 1977-02-17
NL7608722A (en) 1977-02-08
PT65335A (en) 1976-08-01

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