GB2208495A

GB2208495A - Multi-colour printer

Info

Publication number: GB2208495A
Application number: GB8818873A
Authority: GB
Inventors: Makoto Tomoyori; Keiichi Akiyama
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 1987-08-10
Filing date: 1988-08-09
Publication date: 1989-04-05
Anticipated expiration: 2008-08-09
Also published as: JPS6442664A; GB8818873D0; GB2208495B

Abstract

A printer has a belt-like latent image carrier (21) for carrying latent images thereon. A plurality of developer units (28C, 28M, 28Y and 28B) are provided for independently supplying toners having different colours. A plurality of latent image carrier moving mechanisms (39C, 39M, 39Y and 39B) are arranged facing respective developer units but with the latent image carrier (21) interposed therebetween. The latent image carrier may be photosensitive, electrostatic or magnetographic. For example, optical write head (27) applies a single line of characters to carrier (21) after charging (26); the appropriate moving mechanism is selectively displaced to develop the images; developed images are transferred to sheet (2) at transfer station (32); and the cycle repeated for another colour while sheet remains stationary. <IMAGE>

Description

PRINTERS The present invention relates to printers.

Printers form characters, symbols, figures, etc. onto a sheet of paper. There is a demand for printers which are compact and capable of effecting colour printing.

Recently, a page printer such as typically, a laser printer has widely used as this type of printer.

It is an object of the present invention to provide an improved printer.

According to the present invention, there is provided in a printer having a belt-like latent image carrier for forming latent images thereon and a developer unit for depositing toners onto the latent images to form toner images, the improvement wherein the developer unit comprises a plurality of developers for independently supplying the toners having different colours and a plurality cf latent image carrier moving means arranged in opposed relationship to the developer units with the latent image carrier interposed therebetween, said latent image carrier moving means being adapted to move the latent image carrier so as to selectively approach the same to any one of the developer units.

In the printer embodying the invention and described hereinafter a latent image for a first colour is formed on the belt-like latent image carrier along the advancing direction thereof according to a printing pattern. Then, a toner of the first colour is deposited on the latent image by feeding the latent image carrier to the developer unit for the first colour by means of the latent image carrier moving means, thus forming ti +ir^+ toner image. Then, the toner image ls moved together with the latent image carrier to a position facing a sheet, and the toner image is transferred onto the sheet. Then, while the sheet remains still at this position, the latent image carrier only is moved to remove a residual toner from the carrier.Thereafter, toner images for the subsequent colours are transferred on the sheet in the same manner as the above. Finally, when a toner image for the final colour is transferred onto the paper, all the colours are mixed to obtain a multiple colour print. After the final transfer is ended, the sheet is fed by one line corresponding to a width of the latent image carrier to carry out the next cycle of printing for the next one line. Thus, such a printing operation is repeated to print the entire image on to the sheet.

A printer embodying the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings in l-sh ^h: Figure 1 is an elevation in sctiC.n OÏ a printer embodying the present invention; Figure 2 is a cross section taken along the line II-II in Figure 1; Figure 3 is a cross section taken along the line Ill-Ill in Figure 1; Figure 4 is a block diagram of printer of Figure 1; Figure 5 and 6 are block diagrams of modified printers; and Figures 7 and 8 are schematic sectional side views of previously proposed printers.

Figure 7 shows a previously proposed printer. As shown a stack of sheets 2 having a standardized size such as E5 of A4 is contained in a paper supply cassette 1, and the sheets 2 are extracted one by one by a hopping roll 3. While a sheet of paper 2 is fed along a paper feeding path 4, characters or the like corresponding to a printing pattern are formed on the paper 2 by means of a mechanism section including a photosensitive drum 5 and other devices. The photosensitve dum 5 has an axial length greater than the maximum width of the sheet 2 and is arranged to be rotated in the sense of the associated arrow A. As the drum rotates it is uniformly charged by a charger 6 located around the photosensitive drum 5.An electrostatic latent image corresponding to a printing pattern is formed on the photosensitive drum 5 by means of an optical writing head 7. Toner is deposited on the latent image written on the photosensitive drum 5 by means of a developer 8 to thereby form a toner image. When the toner image reaches a position of a transferer 9 (during rotation of the photosensitive drum 5), it is transferred onto the sheet 2 by the electrostatic attracting force of the transferer 9. Thereafter, the sheet 2 is peeled off from the photossltive drum 5, end is fed to a fixing device 10, where the toner image is fixed on the paper 2 with heat; or under pressure. Then, the sheet 2 is A & .U cntc paper tray 11.The photosensitive drum 5 having passed the transferer 9 reaches a position of an eraser 12, where any residual charge on the photosensitve drum 5 is removed. Thereafter, any residual toner deposited on the photosensitive drum 5 is removed by a cleaner 17.

Figure 8 shows another previously proposed printer capable of effecting colour printing on a sheet 2. In Figure 8 parts similar to those in Figure 7 are similarly referenced. ~ Referring to Figure 8 the developing station to be located around the photosensitive drum 5 is constructed of independent developer units 8C, 8M and 8Y for supplying toners for having the colours of cyan, magenta and yellow, respectively. A transfer drum 14 for transferring toner images for these colours onto the sheet 2 is provided in such a manner that the paper 2 is wrapped around and separated from the transfer drum 14. The transfer drum 14 contains a transferer 9.

In operation a latent image for yellow is formed on the photosensitive drum 5 according to the printing pattern by means of the optical writing unit 7. Then, a toner for yellow is supplied to the latent image for yellow by the developer unit 8Y to form a yellow toner image. The yellow toner image formed on the photosensitive drum 5 is transferred onto the sheet 2 taken out from the paper supply cassette 1 and wrapped around the transfer drum 14, by means of the transferer 9. The paper 2 on which the yellow toner image is transferred is rotated with the transfer drum 14. The photosensitive drum 5 after passing the transferer 9 reaches the position of the eraser 12, and any residual charge on the drum 5 is removed by the eraser 12.

Furthermore any residual yellow toner deposited on the drum 5 is removed by the cleaner 13.

Thereafter, the drum 5 is charged again by the charger 6, and a latent image for magenta is formed on the photosensitive drum 5 by the optical writing unit 7. Then, a magenta toner image is formed on the drum 5 by the developer SN. The magenta toner image is transferred to a proper position on the sheet 2 wrapped around the transfer drum 14, by means of the transferer 9. The same series cf operations is carried out for producing a cyan toner image, thus obtaining a desired colour print with the colours of yellow, magenta and cyan mixed.

After the transferring of the cyan toner image is ended, the sheet 2 is separated from the transfer drum 14, and the colour image on the paper 2 is fixed by the fixing device 10. Finally, the paper 2 is ejected onto the paper tray 11.

With such printers since the axial length of the photosensitive drum 5 is greater than the width of the sheet 2, it is necessary to make axial lengths of various devices located around the photosensitive drum 5, namely, the charger 6, the optical writing unit 7, the developer units 8, 8C, 8M and SY, the transferer 9, the eraser 12, the cleaner 15 and the transfer drum 14, substantially equal to the axial length of the photosensitive drum 5. As a result, the printer is rendered generally large in size, and the manufacturflng cost is increased.

To cope with this problem, an improved printer has been proposed employing a belt-like latent image carrier designed to run across the width of the sheet 2, in place of the photosensitive drum 5 having an axial length greater than the width of the sheet 2. This printer has been intended to reduce the size and the manufacturing cost and improve a printing quality.

The printer shown in Figures 1 to 4 includes an electrophotographic process unit cartridge 20 formed of synthetic resin. The electrophotogaphic process unit cartridge 20 houses an endless belt-like latent image carrier 21 such as OPC belt extending between a drive roller 2= an3 driven roller 25. The OPC belt 21 is driven by the driving force of the drive roller 22 in the direction of the arrow A across the width of a sheet 2 (in a direction perpendicular to a feeding direction of the sheet 2).A transfer unit is provided between the drive roller 22 and the driven roller 25, and the sheet 2 is allowed to pass from an elongate slit 24 in the transfer unit through the electrophotographic process unit cartridge 20.

Toner is deposited on an outer surface of the OPC belt 21, and a toner image is transferred onto the paper 2. A charger 26 for uniformly charging the OPC belt 21 is located outside the OPC belt 21 at a left hand end portion of the cartridge 20. An optical writing head 27 is located downstream of the charger 26 along the advancing direction of the OPC belt 21. The optical writing head 27 comprises an BED head having a plurality of light emitting elements arranged in a direction perpendicular to the advancing direction of the OPC belt 21. The optical writing head 27 serves to form an electrostatic latent image cor-.esponånng te each colour of a printing pattern onto the OPO tlt 21.

There are provided above the OPC belt 21 reaweer, the optical writing head 27 and the driven roller 25 four developer supply rollers 28C, 28M, 28Y and 28B for independently supplying toners in the colours of cyan C, magenta M, yellow Y and black B, respectively, onto the electrostatic latent images formed on the OPC belt 21. The rollers 28C, 28N, 28Y and 28B are positioned along the advancing direction of the OPC belt 21. Toner chambers 29C, 29M, 29Y and 293 each have at a central portion thereof an agitator 50 for agitating the toner to supply respective rollers 28C, 28M, 28Y and 28B with toner.Toner cartridges 31C, 31M, 51Y and 51B are detachably mounted on upper openings of the toner chambers 29C, 29M, 29Y and 29B, respectively, so as to replenish the toner developers. Tension rollers 39C, 39M, 39Y and 59B are located opposite the rollers 28C, 28M, 28Y and 28B, respectively, with respect to the OPC belt 21.The tension rollers 39C, 39M, 39Y and 393 serve as a latent image carrier moving mechanism for selectively approaching the OPC belt 21 to any one cf the developer rollers 28C, 28M, 28Y and 283. When a toner image formed on the OPC belt 21 is moved via the driven roller 23 to reach a position above the sheet 2, the toner image is transferred onto the sheet 2 by a transferer 32 provided under the sheet 2 across the width of the paper 2. A static eraser 33 such as an Eli for erasing a residual charge on the OPC belt 21 is provided downstream of the transferer 52 in the advancing direction of the OPC belt 21.A cleaner 34 for removing a residual toner deposited on the OPC belt 21 is provided downstream of the static eraser 33. The cleaner 34 is in the form of a sponge roller 34a for removing the toner from the OPC belt 21. A magnet roller 34b is provided for removing the toner from the sponge roll 34a by a magnetic attracting force, and blade 34c is provided for scraping any toner from the magnet roller 34b into a toner collecting portion 55. The electrophotographic process unit cartridge 20 is formed at its right and left hand ends with male connecting member 35 to be detachably connected to female connecting members 57 formed at upper end portion of a printer body.

In operation, -an image of a one line on a document corresponding to a width of the OPC belt 21 is printed in colour on the sheet 2, and then the sheet 2 is fed by an amount corresponding to the next one line on the document. Then, an image of the next one line is similarly printed in colour on the paper -2.

First, the drive roller 22 is rotated according to a print start command to move the OPC belt 21 in a direction of the arrow A in Figure 1.

Then, the OPC belt 21 is charged by the charger 26, and a latent image for cyan C is formed on the OPC belt 21 by the optical writing head 27 according to a printing pattern. The formation of the cyan latent image by the optical writing head 27 is continuously carried out for every printing of line corresponding to the width of the OPC belt 24. Then until the cyan latent image is moved to a position facing the cyan developer roller 28C the tension roller 399 is moved a predetermined distance in such a direction as to approach the developer roller 28C by means of driving means such as a solenoid (not shown). Accordingly, the latent image on the OPC belt 21 comes into contact with the cyan toner supplied from the developer roller 28C, and a cyan toner corresponding to the latent image is formed on the OPC belt 21. At this time, the other tension rollers 39M, 59Y and 393 remain spaced apart from the respective developer rollers 28M, 28Y and 283, so that the magenta, the yellow and the black toners are prevented from making contact with the OPC belt 21. Accordingly, it is possible to inhibit toners other than the cyan from being deposited onto the OPC belt 21 and so mixing with the other toners.

The toner image for cyan C thus formed on the OPC belt 21 is further advanced until a forward end of the one line is moved via the driven roller 23 to reach a transfer position 58 of the transferring portion, the OPC belt 21 is then stopped. In this position, the toner image for cyan C is electrostatically transferred onto the sheet 2 by means of the transferer 52. Then, while the sheet 2 remains still in this position, the OPC belt 21 only is moved to remove any residual charge from the OPC belt 21 by means of the static eraser 55 and further to remove any residual cyan toner from the OPC belt 21 by means of the cleaner 54.

Thereafter, the other colours of magenta M and yellow Y are printed in the same manner as the above operation for cyan C. Finally, a black toner is tranferred onto the sheet 2, thereby mixing the colours and attaining colour printing.

That is to say, after the residual cyan toner is removed from the OPC belt 21, the OPC belt 21 is charged again by the charger 26, and an electrostatic latent image for the colour magenta M is formed on the OPC belt 21 by the optical writing head 27. During the advancement of the OP belt 21, magenta toner supplied from the devloper roller 28N onto the latent image for magenta M formed or. the OPC belt 21 to thereby form a magenta toner image.

Then, the OPC belt 21 is further advanced to the transfer position 58, and is stopped at this position. The magenta toner formed on the OPC belt 21 is then transferred to the sheet 2 by the transferer 52. Then, while the paper 2 remains still at this position, the OPC belt 21 only is further advanced. Thereafter, the formation of toner images in yellow Y and black B is carried out similarly in a continuous manner. Finally, at the end of transferring of the toner image for black B, the colour print with the four colours mixed is obtained.

After the transferring of the black toner image is terminated, the sheet 2 is fed by one line corresponding to the width of the OPC belt 21 to carry out similar printing operation for the next one line. Such a printing operation is repeated for every line to print the entire image onto the sheet 2. After all the toner images are transferred, and the sheet 2 is fed, the residual charge on the OPC belt 21 is removed by the static eraser 33, and then the residual toner deposited on the OPC belt 21 is removed by the cleaner 34, thus -preparing the OPC belt 21 for the next cycle of printing.

The toner images transferred on the sheet 2 are fixed on the sheet 2 by a fixing device (not shown) during the feeding operation of the sheet 2.

Figure 4 shows a block diagram of the above-mentioned embodiment employing the optical wr-iting system.

Figures 5 and 6 show block diagram of modifications of the printer of Figures 1 to 4 employing an electrostatic system and 2 magnetic system, respectively.

In the electrostatic system as shown in Figure 5, an electrostatic endless belt is used as the latent image carrier, and a latent image is electrostatically written on the electrostatic belt by means of a multi-needle electrode head. The latent image thus formed is developed by a plurality of developers to form a toner image. Then, the toner image is transferred onto the sheet by means of a transferer. Thereafter, a residual toner deposited on the electrostatic belt is removed by a cleaner, and a residual charge cn the electrostatic belt is erased by a static eraser, thus preparing the electrostatic belt for the next cycle of printing.

In the magnetic system as shown in Figure 6, a magnetic endless belt is used as the latent image carrier, and a latent image is magnetically written on the magnetic belt by means of a magnetic head. The latent image is thus formed is developed by a plurality of developers to form a toner image. Then, the toner image is transferred onto the sheet by mea.ns of a transferer. Thereafter, any residual toner deposited on the magnetic belt is removed by a cleaner, and the magnetic belt I demagnatized by a magnetic eraser, th.e preparing the magnetic belt for the next cycle cf printing

Claims

CLAIMS 1. A printer having a belt-like latent image carrier for forming latent images thereon and a developer unit for depositing toners onto said latent images to form toner images; said developer unit comprising a plurality of developer units for independently supplying toners having different colours and a plurality of latent image carrier moving means arranged to face said developer units with said latent image carrier interposed therebetween, said latent image carrier moving means being arranged to move said latent image carrier selectively so as to selectively displace the carrier towards a selected one of said developer units.

2. A printer according to Claim 1 wherein said latent image carrier comprises an endless photosensitive belt.

5. A printer according to Claim 1 wherein said latent image carrier comprises an Ondless electrostatic belt.

4. A printer according to Claim 1, wherein said latent image carrier comprises an endless magnetic belt.

5. A printer according to Claim 2 including an optical writing head for writing a said latent image on said endless photosensitive belt.

6. A printer according to any preceding claim, wherein said developer units house four toner developers respectively having colours of cyan, magenta, yellow and black.

7. A printer according to any preceding claim, wherein said latent image carrier moving means comprise tension rollers arranged to be driven by a driving means.

8. A printer according to any preceding claim further comprising a transferer for transferring said toner images onto a sheet, said transferer being located under said sheet in such a manner as to extend across a width of said sheet.

9. A printer according to any preceding claim wherein said latent image carrier is arranged to be moved in a direction prependicular to a feeding direction of a paper.

10. An electrophotographic process unit cartridge for use with a printer having a belt-like latent image carrier for forming latent images thereon and a developer unit for depositing toners onto said latent images to form toner images, the developer unit comprising a plurality of developer units for independently supplying toners having different colours, and a plurality of latent image carrier moving means facing said developer units with said latent image carrier interposed therebetween, said latent image carrier moving means being arranged to selectively displace said latent image carrier towards a selected one of said developer units.

11. A multiple colour printing method comprising the steps of: charging a belt-like latent image carrier; forming a latent image for one of a plurality of colours onto said latent image carrier, the formation of said latent image being effected for one line on a sheet corresponding to the width of said latent image carrier; advancing said latent image carrier to a position between a developer unit housing a toner of said one colour and a latent image carrier moving means; moving said latent image carrier moving means towards said developer unit to form a toner image corresponding to said latent image; transferring said toner image onto said sheet in a predetermined rest position; advancing said latent image carrier to an original position under the condition where said sheet remains still; and conducting substantially the same steps as above-mentioned for each of the other ones of said plurality of colours.

12. A printer substantially as hereinbefore described with reference to Figures 1 to 5 in combination with any one of Figures 4 to 6 of the accompanying drawings.

14. A method of printing substantially as hereinbefore described with reference to Figures 1 to 3 in combination with any one of Figures 4 to 6.