CA1116227A - Controlled corona for charging electrostatic photocopy paper having zno binder layer - Google Patents

Abstract

CONTROLLED CORONA FOR CHARGING ELECTROSTATIC PHOTOCOPY PAPER
HAVING ZnO BINDER LAYER

Abstract of Disclosure The invention provides a corona control circuit, especially for use in photocopy machines using an electrostatically chargeable paper. The corona forming circuit charges the surface of the paper at different levels of energy, which level is selected as a function of charging polarity and width of the copy paper.

Description

This invention is related to the structure shown in U.S. Patent 3,899,248, granted August 12, 1975 and assigned to the assignee of the present invention. Since much of the present machine has already been described in the patent, its description herein will be brief.
The present invention in general relates to an apparatus for projecting a positive or negative image on a screen for viewing purposes and thereafter for projecting the image onto a charged sensitive paper, in order to obtain a printed image, which may also be either a positive or a negative.
The above-identified patent 3,899,248 describes a reader-printer for forming images upon a paper having a zinc oxide (ZnO) binder-layer which has previously been electro-statically charged. Unfortunately, this type of paper sometimes takes on a gray background, and the images are printed upon that gray background. Most of the gray back-ground is caused by layer defects which accept higher electrostatic charging potentials than the surrounding area.
This background can be controlled by the corona discharge device.
The ZnO paper is initially charged by a corona and after exposure, the paper is brought into contact with toner made of particles which are attracted to or repelled by the charge. The toner particles can be considered as probes sensing the electric field distribution near the ZnO-binder layer surface. These "probes" follow that distribution, and cling to the paper in order to form a background having an ;

optical density which is proportional to the field strength of the corona. A gradient of the surface potential results in toner deposition at the points of lower positive potential (when positive toner is used).

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Unequal charging of the ZnO-binder layer agglomerations can resul-t from the roughness of the surface and non-uniform distribution of corona current. S-trong fields tend to push away weak fields so that the latter will not eause toner deposition. Since strong fields produce a faster deposition of toner particles than weak fields, the number of particles is important. Sometimes the ZnO-binder layer material is lacking ~-at pinholes. Assuming a uniform charge density, the potentials of the pinholes are less than the charge density of the surrounding areas. Sometimes the binder layer is thinner than average, and the capaeitance is diminished. The reduced layer thickness also leads to dielectric breakdown during charging, so that the charge already stored is further diminished.

To reduce visible gray background deposits on layers of the ZnO-type of photocopy paper, eorona eharging shouId be eontrolled. Sinee the gray tone is primarily caused by small areas of excessively high potentlal, the maximum surface potential of the electrostatic charge shouId be limited, without ~ preventing a sufficient level of electrostatic eharging in order ; 20 to aehieve a desired eontxast.
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Hence, there is a problem of providing a charging eorona whieh is strong enough to print a picture, with aeeeptable eontrast, but not so strong that it eaused gray ; baekground deposits. The present invention provides a single apparatus whieh may be used for either or both reading and printing responsive to a microfilm image.

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.,. , , - ~ . . . . -The present invention provides a microfilm reader, printer or reader~printer using paper which is sensitized by an electrostatic charge, on the surface of a ZnO-binder layer. In greater detail, a corona unit electrostatically charges a 2nO-binder layer at either of two energy levels depending upon the amount of the imprinted surface which is to receive the ink or toner.
In particular, the pxesent invention comprehends a microfilm reader-printer which makes positive prints on zinc oxide binder paper from either positive or negative microfilm images. The reader-printer comprises a potential source means having two polarities. A polarity-responsive electronic switch means selectively switches the potential i source between the two polarities which respectively attract or repel toner. The potential source energizes corona forming means via the switch means for charging the zinc oxide binder surface of the paper to either a high or a low level of electro-static charge. The high level charge is a potential which attracts toner to charged areas on the binder surface and the low level charge is a potential which is high enough to repel toner from charged areas on the binder surface. The low level charge is low enough to preclude speckles which form a gray tone owing to discontinuities on the surface of zinc oxide binder paper. The reader-printer further comprises a light source means for exposing the charged binder surface ; to an image of light in the visible spectrum.
The nature of the preferred embodiment of the invention may be understood best from a study of the attached drawing, wherein:

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Fig. 1 is a perspective view of an exemplary microfilm reader-printer;

Fig. 2 is a vertical section of the apparatus of Fig. 1 showing the location of the principle components as well as the position of the mirrors to enable viewing of the microfilm image on a screen;

Fig. 3 is another vertical section of the micro-film reader-printer of Fig. 1 with the mirrors positioned to enable a microfilm image to be projected and printed on sensitized paper, appearing with Fig. l;

Fig. 4 is a schematic diagram of a control system for the microfilm reader-printer; appearing with Fig. l;

Fig. 5 is a bottom view of a rotary blade paper cutter embodying the present invention;

Fig. 6 is a side view taken in the direction of the arrows of the paper cutter ol Fig. 5 ' ~

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Fig. 7 is a side view of the paper cutter of Fig~ 5 as , viewed in the direction o~ the arrows;
Fig. 8 is a side view with portions broken away, partly in cross-section, and partly cut a~lay showing a corona unit embodying the present invention;
Fig. 9 is a cross-sectional view of Fig. 8 taken along lines 9 - 9.

A microfilm reader-printer embodying the present invention is shown in Figs. 1 and 2, as having a housing 10 with a translucent screen 11, a microfilm carrier 12, and a control panel. A microfilm 14 on carrier 12 is controllably positioned in an optical path by means of a control arm 15, for selectively projecting any suitable image from the microfilm onto the viewing screen 11.

A dual intensity halogen lamp 16 is mounted in the base of housing 10 and beneath carrier 12. Its light beam is directèd horizontally through a lens 17 to a mirror 18 which directs it upwardly through film 14 to lens assembly 19. ;
Thereafter, the projected light beam is directed vertically to mirro~ 20, anguIarly to mirror 21, and then to the back side of opaque screen ll. There, the image can be viewed. This path of the projected image is shown by the dash lines 22 in Fig. 2.

For printing purposes, the image projection is redirected to the path shown by the dash lines 23 in Fig. 3.
This is accomplished by repositioning mirrors 20 and 21. The angular position of mirror 20 is changed by means of a cam control mechanism, and the mirror 21 is repositioned to shift forwardly into full abutting engagement with the back side of screen 11. -~

All external light is completely blocked by a light tight housing enclosure to enable an exposure of the ZnO-binder 2~
- layer of sensitized paper during an image printing sequence.
This paper comes from a paper roll retainer 25, through a paper cutting device 27, a corona paper charging unit 28, a conveyor 29, a sensitized paper toner and dryer 30 and a paper discharge conveyor and chute 31. The paper roll retainer or spool 25 is rotatably mounted within a compartment 32 in the upper portion of the housing 10.
Paper is withdrawn from the roll 33 over a lead guide bar 50 through engagement with a feed roller 53 which is belt driven by means of a feed motor 52. An idler 51 engages the feed roller 53 so that the paper passes therebetween and into engagement with a guide bar 54 which directs the paper into paper cutter 27. The paper cutter 27 comprises a cutter bar 55 disposed beneath the paper and a rotary cutter blade 56 disposed above the paper. The rotary blade 56 is actuated by means of a solenoid. The paper cutter of the present invention is shown in the accompanying Figures 5 through 7 and is fully described in U.S. patent 3,899,248. Therefore, its description will not be repeated here.
Paper is directed into a guide chute 58 and through a corona paper charging unit 28 where the paper is electrostatically sensitized. The corona unit 28 is energized from a power pack 59 (Figs. 2 and 4) mounted in the housing 10.
Thereafter, the paper is directed through conveyor 29 which is comprised of a series of belts 60 that carry it downwardly to a position where it can be exposed. The belts 60 are mounted on a common drive shaft 62 powered by a drive motor 63 acting through a chain and sprocket mechanism 640 After the exposure cycle has been completed, the exposed sheet of paper is fed downwardly into a well 67 integrally formed in a removable toner tray 68. Prior to the entry of the paper into the well 67, toner fluid is pumped from the lower part of the tray 68 into the well by pump 69. The paper is fully immersed in the fluid during the period while it is passing through the well. A pair o~ rollers 70 force from the paper all of the excess fluid which returns to the well.

The paper is thereafter fed through a curved guide 71 and feed forwardly and downwardly into engagement with power driven rollers 72 for delivery into a discharge chute 73 at the front end of housing 10. While the paper is traveling forwardly to the discharge chute, it passes through a stream of air, created by fan 74, to rapidly dry the print. The stream of air also cools lamp 16.

The toner tray 68 is completely self-contained for developing sensitized sheets of paper passing therethrough.
Liquid is normally contained in the bottom of the tray and pumped into the well 67 only during the periods while sheets of paper are actually passing therethrouah. Any liquid remaining in the well automatically drains back into the bottom part of the tray.

Mirrors 20 and 21 are positioned by a power drive, ;
including a timer motor which rotates cam disc 81. For reading ~`
a microfilm, the mirrors are held in the position shown in Fig. 2; for printing they are held in the position shown in Fig. 3. Mirror 20 is supported for pi~otal movement on a shaft 82, and mirror 21 is supported on a shaft 83. ~he mirror 21 is carried on a pair of support arms, one of which is support arm 85 and the other being located directly behind support arm 85 ;`
which are adjustably secured to the shaft 83. A linkage arm 86 is mounted on the end of the shaft externally of the housing ~ -wall. A pin 88 is secured in the arm 86. Because the cam disc 81 is likewise mounted on the exterior of the housing wall, a X

`` 3 ~ 7 connecting arm 89 is disposed to connect the disc 81 and arm 86.
A pin 90 mounted transversely in the disc provides the linkage with the arm 89 while a slot in the arm is disposed to fit over pin 88 in the arm 86. A spring 91 is secured to the end of connecting arm 89 and to the extending end of the pin 88 on the - arm 86 to provide a cushioning effect at the moment when the mirror 20 is moved rearwardly to the extreme position shown in Fig. 2.

When so positioned, a plate 92 supporting the mirror 21 is in abutment with interiorally extending pins 93 and 94 secured to the sidewalls of housing 10. A spring 95 is secured to the bottom of plate 92 and extends upwardly to the pin mounted in the lower ends of each of the support arms. Such ; pins extend through slot 96 in rearwardly extending ears from plate 92. The springs serve to retain the mirror in its uppermost position during the reading mode. At the same time, ; an arm 98 secured to shaft 83 will have ro*ated counter-clockwise so that the arm will engage the back side of mirror 20 and cause it to tilt downwardly to the position shown in Fig. 2.
At this time the microfilm image is pro~ected from the magnifying lens l9 to the mirror 20, deflected to mirror 21, and to the back side of screen 11. `

If the image is the selected one, an initiation of , a printing cycle causes the cam disc 81 to rotate counterclockwise. The arm 89 moves forwardly from the position shown in Fig. 2 to the position shown in Fig. 3. Shaft 83 rotates so that arm 98 is disengaged from the back side of mirror 20. The mirror tilts upwardly to the position shown in Fig. 3. Rotation of shaft 83 likewise causes the support arms 85 to move forward and permit the mirror and backing plate to initially pivot about fixed pins 94. Thus, the mirror tilts forwardly from the reading mode position so ~.

that its u~per edge leads the lower edge ~s the arms contillue to move until the upper edge of mirror plate 92 encJages the rear side of screell 11. The upper edge of thc plate will strike the screen frames in the vicinity o~ the top edge and permit the plate to slide upwardly untll it rcaches a stop - 97. A continued movement of arms 85 causes the lower por- ¦
; tion of the mirror plate 92 to move forwardly until the entire face o~ the mirror abu-ts the rear face of screen 11.
In this position, mirror 21 precludes light from entering into the housing through the screen. At this time, a micro-film image is projected through the magnifying lens 19 to strike the mirror 20 along the path indicated by the dash lines 23. The image is thus projected onto the sensitized paper, for exposure in the rearward por-tion of the apparatus.
When the apparatus is recycled for its succeeding ~ ;
reading operation, the support arms 85 again move rearwardly -from the position shown in Fig. 3. At that time, the spring, 95 pulls the pin in slot 96 and causes the mirror to return to the same tilted position. The top edge of the mirror becomes disengaged from the stop 97: The mirror 21 moves ! `
rearwardly to the reading positlon.
The operating cycle of the apparatus is controlled by the electrical circuitry shown in the schematlc diagram in Fig. 4. Initially, the circuit is energized responsive . ~`
to a manipulation of switch 100. The fan motor 75 is energized and runs constantly. Simultaneously a circuit is comp]eted through normally closed contacts in a cam actuated Micro- ¦ -switch 101 to selector switch 102.
Dependellt upon the ambient exterior lighting con-dition of the apparatus, the operator will have previously set the switch 102 to project either a low intensity ligllt or a high intensity light OlltO the screen 11. Thus, a circuit is completcd throucJh an appropr~te windincJ within _ 9~ :.

., , , . ~ .~- . ; : : , transformer 103 to the projection lamp 16. S;nce the mirrors 20 and 21 are assumed to be in a readincj posi~ion, it is no~
possible to view an im~cJe on screen 11.
If the operator discovers an incorrect rnicrofilm in the carrier 12, he can replace it or adjust the position of carrier 12 by moving arm i5 until another image is presented on the viewing screen 11.
If a print cycle is initiated, a print switch 104 is manually manipulated. A circui-t is completed frorn the line serving switch 102 to the paper feed motor 52. The feed motor is started to feed paper from roll 33 into the apparatus.
Two normally closed Microswitches are included in the feed motor circuitry. Feed motor switch 105 is cam controlled to interrupt the circuit as the cam disc is rotated, when there is no paper in the machine. The other normally closed Microswitch 106 is mounted on the framework immediately ad~acent the conveyor belt 60 and actuated by the passage of paper, at that point.
Whenever power is applied to the feed motor, a pair of switches 107 and 108 are actuated by solenoids responsive to energization of the feed motor. The closure of normally open switch 108 continuously supplies power to the feed motor. The closure of the normalIy open switch 107 completes a circuit to the drive motor 63, the power pack 59, the pump 69, the timer motor 80, and the cutter solenoid 57. Timer motor 80 rotates cam disc 81 to actuate switch ;
101 and complete a circuit through a normall~ closed micro-switch to the drive motor 63, the power pack 59, the pump 69, timer motor 80 and the cutter solenoid 57. At the same time, the forward edge of the paper from roll 33 engages switch 106 to interrupt the feed motor. When power to the feed motor is discontinued, the switches 107 and 108 open.
However, because the timer motor 80 is still energized, the cam 81 continues to rotate.

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Both switches 109 ancl 110 are mounted on the frame so that their actuating arms arc positioned to be engaged by the leading edge of the paper as it advances on conveyor belts 60. Because the operator will have manipulated a copy length selector switch 111 before the printing cycle is initiated, only one oE these two switches will be eEfective in the circuit. The switch 109 measures short paper~ while switch 110 measures long paper. Thus, the selectar switch ` 111 is here drawn to indica-te that lon~ paper is desired.
Immediately upon the energization oE solenoid, the cutter ; severs the paper at that indicated long length. The sheet of paper can then advance until its edge engages -the actuat-ing arm of Mircoswitch 112, interrupting the circuit to ~he drive motor 63, power pack 59, and solenoid 57. However, because the switch 101 is still positioned as previously described, the pump motor 6g and the timer motor 80 remain ener~ized.
The sensitized paper is exposed in the following manner. The rotation of cam disc 81 causes mirrors 20 and ~ ~
21 to move and project the microfilm image onto mirror 20 ~ `
and rearwardly onto the paper. At the same time, pin 90 extends through the face of the cam disc and engages the actuating arm of the two~positioned Microswitch 115. This completes the circuit from the main line through switch 115 to a dimmer relay 116, transformer 103 and the halogen lamp 16. The dimmer relay is adjusted by manipulating the control knob 117 on the front of housing 10. This adjustment ena~les the operator to obtain a print which has the necessary detail clarity, without over-exposure. It also enables him to compensate for line voltage variations which, in turn, would result in prints of varying clarity.
The light source for projecting the microfilm image onto the sensitized paper remains on only for a period -- 11 -- .

6;~7 :' of time which is sufficient to insure a goo~ print. As the actuating arm of switch 115 becomes disenga~ed from the pin 90, the circui-t is interrupted and the light is ex-tinguished.
However, the actuation of the switch 115 re-establishes a circuit through cam control Microswitch 118, whereby the drive motor 63 is again energized. Thus, the e~posed paper moves downwardly from the belts 60 into the toner and dryer 30. Because the toner pump motor 69 is already energized, the developer fluid in the toner will already have been pumped into well 67 so that the paper passing therethrough is fully immersed. Thereafter, the paper is fed through squeegee rollers 70 and pass fan 74, so that it is dried before it is fed out of the discharged chute 73.
The timer motor 80 continues to drive the cam disc and operate the switch 118 whereby the circuit to the drive motor 63 is interrupted. No sheet of paper remains within the apparatus. The cam disc 81 also operates switch 101 for interrupting the circuit to the timer motor 80 and re-establishing the circuit to the switch 102. The viewing lamp 16 is turned on for microfilm viewing. It should be noted that the operation of the cam disc has also moved the mirrors 20 and 21 to the viewing position.
A further feature of the circuit relates to the ability of the apparatus to use either a positive or nega-tive photographic microfilm and to produce positive prints from either. This feature is made possible by the in~ro-duction of a two-positioned switch 200 in the circuit between power pack 59 and corona 28. The switch 200 is operated responsive to a setting of knob 121 on the front face of the housing, as shown in Fig. 1. The switch effects - a revcrsal in the char~e on the paper p~sing through the corona 28 so tha~ the resulting prints produced by the apparatus will still be of a positive type. Of course, it must be kept in mind that a different type of paper must be used unless the operator has been using paper having bi-chargeable characteristics. Thix feature is particularly desirable when it is nece~sary to work with both positive ; and negative Microfiche films.
When the background of the image to be copied is mainly black (i.e., usually a negative~, the ZnO-binder layer retains a relatively large charge. If the same level of corona activity is used for all images whether mainly black or white, it is necessary to provide controlled ZnO-binder layer charges. Without such controls, the ZnO-binder layer retains such a high charge when the image to be copied is mainly black, that a gray background tone occurs.
The invention overcomes these problems by pro-viding means for tailoring the electrostatic charging to fit the needs of the image. In greater detail, the polarity switcher 200 (Fig. 4) is controlled by an operator who looks at a document to be copied and decides whether it appears to be mainly black or mainly white. Alternatively, a photo-sensor could be used to appraise the image content of the document to be copied.
A large resistor 202 is connected in series be-~ween power pack 59 and the corona forming circuit 28 to reduce the level of the energy supplied to the corona forming circuit. Thus, a low level of electrostatic charge is applied to the ZnO-binder layer for one type of operation wherein the percentage of the surface of th~ paper which is to retain a charge is relatively great.

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diode 204 is conllectecl in parallel with rcsis~or 202 to cause tlle resistor to be in the circuit when the s~itcher 200 applies a voltage,-to the corona 28 in one polarity orientation. ~hen the polarity switcher 200 operates to reverse the polarity of the potential applied to ~he corolla, tlle diode 204 conducts to short circuit the resis-tor 202.
This removal of the short circuit increases the level of the energy supplied to the corona Eorming circuit 28. As a result, corona circuit 28 applies a greater charge to the paper when there is a smaller percentage of the surface of the paper is to be toned. Thus, -the electrostatic charge appearing on the ZnO-binder layer is tailored to the re-quiremellts of a document which is to be copied.
The foregoing description supposes that the polarity of the corona is reversed for different forms of fil~ or for different printing conditions. However, it is a simple matter to select an appropriate polarity for controlling the corona according to any suitable operation that may be desired. While the drawing shows and the foregoing des-cription refers to only two levels of energy (i.e., resistor 202 in or out of the circuit~, it should be understood that any suitable number of levels may be provided.
Figs. 8 and 9 show the corona unit 28 for elec-tro-statically charging a ZnO-binder layer on a copy paper. The corona unit 28 comprises a pair of parallel, spaced assemhlies 160 and 161, each of which includes supporting posts 171, 172 and terminatlng post 175, 176, respectively. Each of the corona unit assemblies also includes an elongated aluminum housing having a U-shaped cross section. The assemblies are arranged so that one is the mirror image of the other, with thc suppor~illg posts alld termina~ g post~ facillg e-lcl other.

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As shown in ~ig. 8, one side 164, 165 of each of the U-shaped cross-sectional housirl~ is shorter than the other side 166, 167. Wh~n the two assemblies are fitted together, the short sides 164, 1~5 form a large opening 168 for receiving the copy paper. High voltage tunysten corona wires 169, 170 extend generally across each half of the corona unit housings. The wires 169, 170 are looped around the facing supporting posts 171, 172 and secured to the main cover. They include integral spring members 173, 174 The ends of the corona wires 169, 170 are secured to the facing terminating posts 176, 175, respectively. Insulating plastic monofilaments 177, 178 are wound about each corona housing to keep the corona wire from touching the copy p~per.
The remaining details of these corona units may be understood from a study of the parent patent 3,899,248.
While a particular embodiment of the invention has been shown and described, those skilled in the art will perceive changes and modifications which may be made without departing from the invention. Therefore, the aim in the appended claims is to cover all equivalents falling within the true spirit and scope of the invention.

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Claims (4)

1. A microfilm reader-printer which makes positive prints on zinc oxide binder paper from either positive or negative microfilm images, said reader-printer comprising a potential source means having two polarities, switch means comprising a polarity-responsive electronic switch means for selectively switching said potential source between said two polarities which respectively attract or repel toner, corona-forming means energized from said potential source via said switch means for charging the zinc oxide binder surface of said paper to either a high or a low level of electrostatic charge, the high level charge being a potential which attracts toner to charged areas on said binder surface and the low level charge being a potential which is high enough to repel toner from charged areas on said binder surface and low enough to preclude speckles which form a gray tone owing to discon-tinuities on the surface of zinc oxide binder paper, and light source means for exposing said charged binder surface to an image of light in the visible spectrum.

2. The reader-printer of claim 1 and means for operating said light source at either a bright or a dim level, said light source normally being maintained at said dim level, and means for momentarily operating said light source at said bright level for the duration of an exposure time period.

3. The reader-printer of claim 1 wherein said switch means comprises a resistor having a relatively large resistance and electronic switch means comprising a diode bypassing at least part of said resistor and poled to insert said bypassed part of said resistor into a circuit extending between said switch means and said corona-forming means for energizing and charging said binder surface to said high level when the polarity selected by said switch means coincides with the direction in which said diode conducts and for charging said binder surface to said low level when the polarity selected by said switch means coincides with the direction in which said diode does not conduct.

4. A circuit for controlling the formation of speckles which forms a gray tone background on a zinc oxide binder surface of paper used in electrostatic printers, said speckles forming when any initial pre-exposure charge on said binder surface has the same polarity as toner used to print on said surface, said circuit comprising a source of potential having two polarities, switch means, a corona-forming means connected through said switch means to said source of potential, said switch switching said corona-forming means between the two polarities of said potential source, and resistor means at least partially bypassed by a diode interposed between said switch means and said corona-forming means, the resistor means reducing the potential at said corona to charge said zinc oxide binder surface to a level which does not form speckles when said binder surface is charged in the same polarity as the toner whereby residual surface discontinuities do not form high-charge areas for attracting toner which should be repelled.