WO1988005562A1

WO1988005562A1 - Electrostatic colour copier

Info

Publication number: WO1988005562A1
Application number: PCT/AU1988/000006
Authority: WO
Inventors: George William Browne; Alwin Clements; Gene Kostecki
Original assignee: Malaita Pty. Ltd.
Priority date: 1987-01-14
Filing date: 1988-01-12
Publication date: 1988-07-28

Abstract

The method of producing electrostatic colour copies by charging a photoconductive surface, light imaging the charged surface to represent a selected colour, developing the image with a toner of the selected colour and repeating the steps of charging and light imaging and toning with other selected colours to form a colour image, in which the successive images are produced on a rotating drum (1, 65) synchronised to overlay each colour image on the preceding colour image.

Description

"ELECTROSTATIC COLOUR COPIER"

This invention relates to an electrostatic colour copier and in particular it relates to a copier of the type in which an original to be copied is light scanned to modify an image on a photo-

5. conductive member to be exposed after precharging of the surface, followed by development of the surface in one of a series of colours, the process being continued until colour exposures of different required colours have been effected and developed

10. to provide a final multicolour built-up image corresponding to the original colour image.

Certain problems exist in this type of machine, principle of which is the effecting of correct register of the multiple images in different colours 15. which are superimposed on the sheet successively, and the ability to achieve a correct colour balance.

It is one of the objects of this invention therefore to provide a method of and means of producing colour copies wherein accurate register of the 20. various images is achieved.

It is a further object to provide a means of copying in which development of the various images will be carried out in the correct colours and will be accepted by the previously applied colour.

25. It is a still further object to provide means which will ensure correct fill-in of the developed areas and will be capable of half tone reproduction to maintain correct colour values. It is a further object to provide a colour copy on plain paper.

The objects of the invention are achieved by carrying the membrane on a rotating drum disposed at a

5- position where the image from the material to be copied is projected on to the membrane on the drum by an imaging mechanism, and this drum has associated with it charging means whereby the surface of the xerographic layer is activated

10. prior to light imaging by means of the image projected from the imaging mechanism, and has associated with it also a series of colour stations each of a colour required to produce a final correctly toned coloured image, the basis of operation of

15. the invention being to project the image on to a xerographic surface on, or carried by, the drum and to rotate the drum through a first step to bring the xerographic surface past the charging station and then through the light exposure station to produce a latent

20. electrostatic image corresponding to the first exposure, a colour filter being used to expose to the correct colour value, then subjecting the latent image so produced to a first colour station to develop the image by a developer of the first colour, the drum

25. continuing to rotate to expose the photoconductor surface to a second cycle where a different colour filter is used and a different colour developer is applied, and so on until all of the colours have been reproduced on the surface. The xerographic surface can be on a membrane attached to the drum during the required number of revolutions, or two drums are used, the first having a photo- conductive surface and the second carrying the 5. membrane on to which colour images produced on the photoconductive drum are transferred to provide a colour overlay.

The method of the invention consists in charging a photoconductive surface, light imaging the charged

10. surface to represent a selected colour, developing the image with a toner of the selected colour, and repeating the steps of charging and light imaging and toning with other selected colours to form a coloured image, characterised by producing the

15. successive images on a rotating drum synchronised to overlay each colour image on the preceding colour image.

The means comprise, means to charge a photoconductor and means to light image the photoconductor to

20. a selected colour and ^"means for developing the image with a toner of the selected colour, character¬ ised by a drum mounted on a frame to otate and having a photoconductor on its surface and having the means to charge the photoconductor and light

25. image the charge and develop the light imaged charge arranged around it sequentially, all arranged to produce a first image of a selected colour during a revolution of the drum and further differently coloured images during sucessive revolutions of the

30. drum whereby to overlay the coloured images to produce a multicoloured image. The actual construction of the device can be consider¬ ably varied but we have found that a highly effective machine results when built generally on the system schematically illustrated in the accompanying

5. drawing which shows basically a glass platten which reciprocates over the exposure area and carries the material to be copied, and related to this is a light and double mirror system the first part of which projects the image to a lens

10. and mirror which projects it back to the second mirror system which projects it down on to the drum, but it will be appreciated that other forms of imaging mechanisms can be used by appropriately arranging the system.

15. To enable the invention to be. appreciated, an embodiment thereof will now be described with reference to the accompanying drawings in which:-

FIG. 1 is a schematic longitudinal section of one form of such a machine using a photoconductive 20. membrane on a drum to receive the colour image,

-FIG. 2 shows schematically a membrane turning assembly which can receive sheets and invert them,

FIG. 3 is an enlarged sectional detail of colour units and showing the units sectioned at different 25. planes to better show the assembly. FIG. 4 is a sectional plan of the end colour station shown in FIG. 3, and

FIG. 5 is a view similar to FIG. 1 but showing a plain paper colour copier using an image transfer 5. assembly.

Referring first to FIGS. 1, 2, 3 and 4 the drum 1 is rotated synchronously with the movement of the glass platten 2 so that a correct image is produced on the drum, and as both drum 1 and platten 10. 2 are moving, a substantial breadth of image can be projected over the width of the platten 2 to allow adequate time for correct exposure.

The drum 1 consists of a metal or conductive inner section.3 shown as having a resilient facing 4 on it 15. such as a relatively soft rubber, which however may be omitted, the facing being electrically conductive or allowing a field to pass therethrough to the conductive inner section.

The charger 5 can be of any usual or approved 20. type generally referred to as a corona discharge device preferably consisting of wires positioned to extend across but spaced from the drum 1 and having the necessary high voltage applied thereto and is disposed adjacent to the exposure station 25. 6 in a position where the photoconductive surface is charged prior to it reaching the exposure station

6, the membrane being supported around the drum

1. Referring to the developer unit, a frame is mounted on suitable means to reciprocate to bring each colour developer into effect at the appropriate time when a selected developer is to be applied, the four developer units 7, 8, 9 and 10 being shown with a fifth unit 11 providing a roller to ensure that correct paper drive continues after release by the normal holding means of the drum.

Each of the developer units 7, 8, 9 and 10, comprises

10 a developer well 14 supporting in it a developer roller 15 and this well is provided with inlet means 16 and outlet means 17 to allow used developer to flow through the well, each developer roller 15 having Its shaft 18 supported in bearings 19

15. operating between guides 20 and urged outwardly by means of a resilient pad 21 which loads the developer roller 15 against the receiving membrane carried on the drum 1, the pad 21 being disposed between the bearings 19 and the base of the developer

20. well 14.

Developer is pumped to inlet means 16 of each well and flows to a transverse distributor channel 22. Over the distributor channel is disposed a developer flow control plate 23 to the upper

25. surface of which developer is sμpplied through a series of open ducts 24 communicating with a transverse chamber 25 which opens through a gap 26 Into the upper part of an extension 27 of the well 14 in which the developer rollers 15 are

30. disposed, this arrangement ensuring that the developer flows from the remote channel gap 26 over the downwardly sloping face of the developer flow control plate 23 to the nip between the associated developer roller 15 and the image receiving membrane 5. on the drum 1. In this way a developer pool 28 is formed over which the image receiving membrane moves to the developer roller 15.

The developer wells 14 are formed in a frame 29 which moves to bring the developer rollers 15 10. sequentially to the development locality beneath the drum 1.

Each roller 15 has a scraper 28 disposed adjacent it in the well 14 to keep the face of the roller clean, and if the drum 1 or 65 is of metal, the rollers 15 15. will at least have a resilient surface such as a surface of rubber.

The fifth station comprises only a roller 15 and its resilient support 21, the components of which are similarly numbered to the components of the 20. developer units 7, 8, 9 and 10, and this roller 15 serves to press the membrane to the drum 1 to continue the membrane drive after the last selected colour developer has been supplied.

Referring to the image receiving membrane feed 25. this may, as shown in FIG. 1, be taken from a reel 30 past feed rollers 31 and a guillotine 32^' and thence between further feed rollers 33 to the drum 1 which has means to grip the end of the Image receiving membrane and cause it to be carried around by the drum as it is rotated, but such a mechanism will be described later herein with reference to the embodiment illustrated in 5. FIG. 5.

In operation the charging station 5 charges the surface of the photoconductor on the image receiving membrane and during rotation of the drum 1 the image receiving membrane moves past the exposure 10. station 6 and is continually exposed during the required part of the revolution and is then carried to the first colour developer unit 7 to print the required colour.

The drum 1 rotates until all the colours have 15. been printed the colours being overlaid to complete the colour rendition, after which the image receiving membrane is released from the drum 1 and is moved to a discharge position.

The flow control plate 23 is removably held to each 20. developer unit by a bolt 35 engaging a threaded unit or bracket 36; a sealing washer 37 preventing loss of developer from the well.

Feed means 41 to feed the Image receiving membrane from the dr/um 1 with the image on it can conveniently 25. comprise a vacuum box 42 having a series of belts

43 extending across it side by side, passing around pulleys 44, the belts 43 passing over an apertured face 45 on the vacuum box 42 in a manner such that as a membrane is pushed off the surface of the drum 1 in a manner later described herein, the membrane passes beneath the apertured face 45 but is conveyed across it by the belts 43 as these space the membrane from the apertured face 45 sufficiently to cause the friction between the belts 43 and the 5. membrane to move the membrane forward, the membrane being discharged into an outlet 46.

From the outlet 46 the image receiving membrane preferably passes to ironing rollers 47 and 48 shown particularly in FIG. 2 where they are associated

10. with means for inverting the imaged membrane to have it right-way-up, this comprises a first polished deflector plate 49 which directs the membrane downwardly to cause its leading edge to contact a surface 50 adjacent a wall 51 and as the paper

15. feed continues by the ironing rollers 47 and 48 the membrane is bowed outwardly as shown in the illustration, the bowing out continuing until the copy sheet falls down onto the paper tray 52.

A drier 55 is shown which can be positioned at^' 20. any convenient location and can obtain some of its heat from the lamps 56 which provide illumination for exposure of the material which is to be colour copied, but obviously the drier can be positioned on any part of the drum 1 such as adjacent to 25. the area through which the paper moves after being exposed with the latent electrostatic image.

The means for feeding the developer to the developer stations, not shown, can comprise any convenient form such as tanks fed with developer of the required 30. colour from which the developer is forced by pumps, the developer units 7, 8, 9 and 10 which of course move longitudinally beneath the drum 1 to reach the correct position to apply the developer of the required colour, can have the developer feed 5. from the pumps connected to the inlet means 16 by flexible tubes and similarly the outlet means 17 from the developer wells 14 in which the developer rollers 15 are positioned! can similarly pass back the developer to the tanks through flexible tubes .

10. As stated earlier, the invention need not necessarily be constructed to embody all of the details referred to in this specification but it has been found that the assembly allows effective development in that the receiving sheet on which the copy

15. is to be produced can be firmly locked onto the drum 1 which Is revolved the necessary number of times to bring the membrane past the various stations in proper sequence, and as the drum 1 can rotate continually, the various actions of

20. the selection of the filters, the selection of the developer colour, the feed of the membrane and the discharge of the membrane can readily be effected by timing means such as by wellknown electronic devices, accurate register of the images

25. occurring because the material which is being copied makes the required number of passages synchron¬ ously with the glass platten 2.

The transparent platten 2 on which the data sheet 58 to be copied is supported, moves the data sheet 30. past the exposure station 6 where the image is projected via a double mirror system 59 and mirror lens 60 through the filter bank 61, a variable slit 62 regulating the amount of light reaching the charged image receiving membrane. The variable filter bank is moved to bring the necessary colour filter into 5. position.

Development may be aided by applying a potential between the drum 1 and the rollers 15.

In the above described embodiment the image is produced directly on the image receiving membrane 10. and the colours are superimposed one on the other by sequential charging and exposure as the drum 1 rotates the required number of revolutions and the membrane with the compound colour image thereon is then discharged from the copier.

15. Timing mechanisms can be computerised to control each revolution of the drum 1 and the positioning of the appropriate filters of the filter bank 61 and colour^' developer units 7, 8, 9 and 10.

In the form shown in FIG. 5, which uses a developer 20. transfer system the single drum 1 of FIG. 1 is replaced by a pair of drums 65 and 66, the first drum 65 having a photoconductive surface 67.

The second drum 66 is adapted to carry the membrane on to which transfer is to be effected, the drum 25. 66 having a resilient surface 68.

The drums 65 and 66 are loaded toward each other ^■ and are synchronously driven in opposite directions and a developer image transfer potential is applied between the drums 65 and 66 by high voltage means 69.

A cleaner mechanism 70 for the drum 65 is Indicated which can take any desired form but serves to 5. ensure that any remaining image not transferred

Is removed to present a clean surface for recharging and for the next colour reception.

It will be appreciated that in the machine illustrated in FIG. 5, each colour image is produced independently

10. on the photoconductive surface on the first drum

65 and transferred to the image receiving membrane on the second drum 66 in the form of an overlay, the timing of the paper feed being adjusted so that as the developed image reaches the transfer

15. position, the membrane is in place to receive the image.

In this case the second drum 66 carries the image receiving membrane and is fitted with a membrane- holding and membrane—discharge control device 71 which 20. can similarly be used In the form shown in FIGS. 1 to 4. Similar components used in FIGS. 1 to 4 are given similar reference numerals .

In both illustrated forms the image receiving membrane is preferably held to the drum by the control 25. device 71 which comprises fingers 72 on members 73 carried by a shaft 74 having an actuating roller 75 on it engaging a cam, not shown, which Is appropriately supported to actuate the fingers 72 at selected times, the fingers 72 being associated with a blade 76 which slides in and out under control of the cam to form a stop for the membrane when feeding the image receiving membrane to the drum 1. A discharge member 77 similarly slides in and out to discharge 5. the leading edge of the image receiving membrane from the drum after a colour image has been completed.

The cam is synchronised so that the fingers 72, the blade 76 and the discharge member 77 are actuated only when a image receiving membrane is first fed 10. to the drum 1 and again when the image receiving membrane is to be discharged.

By the mechanism described the leading edge of the image receiving membrane is held to the drum 1- so that the image receiving membrane is then 15. carried round by the drum and lies flat on the drum during the revolutions of the drum, guides being used if required to ensure that the image receiving membrane remains in contact with the drum.

20. The fingers 72 for holding the leading edge of the image receiving membrane and associated blade

76 and discharge member 77 are carried by the drum and at A in FIG. 5 are shown in the position where the blade 76 is clear of the drum with the

25. blade projected to act as a register stop for the image receiving membrane. The discharge member

77 is retracted.

At B is shown the position of the fingers 72 and the blade 76 and the discharge member 77 when 30. holding and carrying the image receiving membrane around. At C is shown the discharge position, the fingers 72 being moved away from the drum 1, the blade 76 retracted, but the discharge member 77 projected to push the leading edge of the image receiving 5. membrane away from the drum 1 and into the discharge locality.

The means to feed the membrane to the drum 66 can take any approved form, a guide roller 78 being shown. To receive the membrane from the drum 66 a pair of feed 10. rollers 79 are used.

In the drawings the image receiving membrane has not been shown, but the path of the membrane is indicated by the chain line 80.

From the foregoing it will be seen that simple 15. and effective machines are envisaged which will overcome the problems which have previously existed and will result in a relatively simple and effective colour coDiers.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. The method of producing electrostatic colour copies which consists in charging a photoconductive surface, light imaging the charged surface to represent a selected colour, developing the image

5. with a toner of the selected colour and repeating the steps of charging and light imaging and toning with other selected colours to form a colour image, characterised by producing the successive images on a rotating drum (1,65) synchronised to overlay each 10. colour image on the preceding colour image.

2. The method of claim 1 wherein an image receiving photoconductive membrane is attached to the drum (1) to rotate with the drum, and the successive colour images are superimposed one on the other during

15. continued rotation of the drum (1).

3. The method of claim 1 wherein a photoconductive surface (67) is supported on a first drum (65) , and transferring each successive colour image produced on the first drum (65) to a receiving membrane on a

20. second drum (66) rotated at the same peripheral speed as the first drum (65) .

4. The method of claim 2 wherein a data sheet (58) to be copied is scanned by a light beam and the light beam is directed to the photoconductive

25. membrane on the drum (1) through a selected filter of a filter bank (61) while rotating the drum (1) to produce a latent colour image on the photo conductive membrane, developing the latent colour Image with a selected colour developer applied by a selected developer roller of a series of developer rollers to produce an Image in one colour, repeating to overlay differently coloured developed 5. images, and removing the photoconductive membrane from the drum (1) .

5. The method of claim 2 or 4 wherein the photo¬ conductive membrane is moved from the drum (1) after the colour image is completed after the

10. required number of revolutions of the drum (1) by belt means (43) by driving the belt means (43) over an apertured face (45) of a vacuum box (42) whereby to carry the photoconductive membrane to a discharge locality by holding the membrane-

15. to the belts (43) by the -induced suction.

6. The method of claim 3 wherein a data sheet (58) to be copied is scanned by a light beam and the light beam is directed to the photoconductive

. surface (67) on the first drum (65) through a 20. selected filter of a filter bank (61) while rotating the drum to produce a latent colour image on the photoconductive surface (67), develops the latent electrostatic colour image with a selected colour developer applied by a selected developer of a 25. series of developer rollers to produce an Image in one colour, transferring the colour image to a receiving membrane on the second drum (66) during synchronous rotation of the drums, repeating rotation of the drums to overlay successively produced 30. developed colour images, and removing the receiving membrane from the second drum (66). 7. An electrostatic colour copier comprising means to charge a photoconductor and means to light image the photoconductor to a selected colour and means for developing the image with a toner of the selected colour, characterised by a drum (1,65) mounted on a frame to rotate and having a photoconductor on its surface and having the means to charge the photoconductor and light image the charge and to develop the light imaged latent

10 electrostatic charge arranged sequentially around the drum (1,65) , all arranged to produce a first image of a selected colour during a revolution of the drum (1,65) and to produce further differently coloured images during successive revolutions ¹⁵ • of the drum (1,65) .

8. An electrostatic copier according to claim 7 comprising a drum (1) arranged to rotate, means (72-77) on the drum (1) to hold at least the leading edge of a photoconductive membrane to the drum

20- to rotate with the drum, means (5) adjacent the drum to charge the photoconductive membrane, means (56-62) to light image the photoconductive membrane with one of a series of selectable colours, means (7-29) to develop the electrostatic latent light

25. modified image on the photoconductive membrane with a colour compatible with the selected latent electrostatic light modified image on the photo¬ conductive membrane. 9. An electrostatic copier according to claim 8 wherein the drum (1) comprises a conductive inner section (3) having a resilient facing (4) which is electrically conductive.

5- 10. An electrostatic copier according to claim

8 or 9 wherein feed of the photoconductive membrane to the drum (1) comprises a supply reel (30), feed rollers (31,33) and a guillotine (32), and means on the drum (1) comprising fingers (72)

10 adapted to engage the leading edge of the photo¬ conductive membrane and press the leading edge to the drum (1).

11. An electrostatic copier according to claim

6 wherein the photoconductive membrane is- moved 15. from the drum (1) by belt means ^'(43) moving over an apertured face (45) in a vacuum box (42) .

12. An electrostatic copier according to claim

7 comprising a first drum (65) and second drum

(66) arranged to rotate oppositely and urged toward 20. each other, a photoconductive coating on the first drum (65), said first drum (65) being adapted to have a series of differently coloured images produced thereon sequentially as the drum is rotated, said second drum being adapted to support a receiving 25. membrane arranged to receive the successive images in superimposed register as the drums (65,66) rotate in register. 13. An electrostatic copier according to claim 12 wherein the second drum (66) has means (72-77) to hold at least the leading edge of the photo¬ conductive membrane to the drum to rotate with

5. the drum.

14. An electrostatic copier according to claim

7 or 11 wherein the developer means (7-29) comprise a series of developer units (7,8,9,10) each having a well (14) to contain a selected colour developer,

10. a developer roller (15) in each well (14), developer inlet means (16) and outlet means (17) for each well (14), and means (21) to urge the developer rollers (15) toward the drum (1) whereby to apply developer to the latent electrostatic light modified

15. images.

15. An electrostatic copier according to claim

14 wherein the means to urge the developer rollers (15) toward the drum (1) comprise bearings (19) engaging shafts (18) on the rollers (15) , the 20. said bearings (19) fitting between guides (20) and urged toward the drum (1) by resilient pads (21).

16. An electrostatic copier according to claim

14 or 15 wherein each developer well (14) contains 25. a control plate (23) mounted adjacent to the developer roller (15), a transverse distributor channel (22) communicating with developer inlet means (16), said transverse distributor channel (22) communicating with a transverse chamber (25) through a series of open ducts (24), said transverse chamber (25) opening through a gap (26) disposed to cause developer to flow over the said control plate (23) toward the roller (15) to form a developer 5. pool (28).

17. An electrostatic copier according to claim 10 or 13 characterised in that means to hold the membrane to the drum (1,66) comprise the said fingers ^'(72) , further characterised by blade (76)

10. mounted to project from the face of the said drum or to be withdrawn into the drum to form a stop for the leading edge of the membrane when feeding the membrane to the drum (1,66) and by a discharge member (77) also mounted to project from the face

15. of the drum or to be withdrawn into the drum to discharge the leading edge of the membrane from the drum after the fingers (72) have released the leading edge of the membrane.

18. An electrostatic copier according to any 20. one of preceding claims 7 ^"to 15 characterised by turn over means from the membrane comprising a deflector- plate (49) in the path of sheets of membrane to direct the membrane downwardly to a surface (50) adjacent a wall (51) to stop forward 25. movement of the leading edge of the membrane to bow the membrane outwards to fall into a tray (52) when the membrane is released by the means urging it forward.