In-line color electrophotographic printer

Abstract

 A multi-color electrophotographic printer (10) is illustrated in the accompanying drawing for printing a multi-color image on a sheet (12). The sheet is first fed past a plurality of image formation and transfer stations (14-17) to successively receive a plurality of separate mono-color images that are superimposed on each other to form a composite multi-color image. The sheet is then moved past an image fixing station (20) to fix the formed composite multi-color image to the sheet. Each station (14-17) has an image formation and transfer device (28) forming a separate mono-color image and for transferring the separate image to the sheet. Each device (28) includes (1) a photoconductive drum (30) having a cylindrical photoconductive surface (32), (2) an electrostatic charging member (34), (3) an electroluminescent edge emitting line array member (36), (4) a toner developing member (38), (5) a transfer member (42) and (6) a surface cleaning member (44). The downstream fixing station (20) has heated fixing rollers (48) and (50). Transfer of plural color images to the sheet take place simultaneously.

Description

FIELD OF THE INVENTION

[0001] This invention relates to color electrophotographic printers and methods for color electrophotographic printing.

BACKGROUND OF THE INVENTION

[0002] Generally multi-color electrophotographic printers are much slower than mono-color electrophotographic printers. Generally such multi-color electrophotographic printers utilize laser technology with a large diameter photoconductive drum or belt that has a circumference or surface dimension, parallel with the path of the sheet, that is equal to or greater than the length of the sheet so that a full length image may be formed on the photoconductive drum. Such printers require that the sheet make several passes over the photoconductive surface; usually one pass per color. Consequently, four color printing is generally four times slower than mono-color printing. Sometimes an intermediate image transfer drum or belt is utilized, as illustrated in U.S. Patent No. 5,314,774, granted May 24, 1994 to Thomas Camis.

[0003] It has been recognized that a large in-line laser printer could be constructed utilizing a series of separate in-line photoconductive surfaces with each surface being coextensive with the length of a sheet. Such a multi-color laser printer could conceivably print at the same speed or sheet rate as a mono-color electrophotographic printer. However, the cost and size of such a laser printer system makes it impractical.

[0004] One of the principal objects of this invention is to provide an in-line multi-color electrophotographic printer that is small in size and capable of printing multi-color images on sheets at a rate comparable to mono-color electrophotographic printers.

[0005] These and other objects and advantages of this invention will become apparent to a person of ordinary skill in this art upon studying the following detailed description of a preferred embodiment.

SUMMARY OF THE INVENTION

[0006] One aspect of the invention concerns a color electrophotographic printer that has a print medium drive or feed for moving the print medium past a plurality of spaced image formation and transfer stations and then past a downstream image fixing station. Each image formation and transfer station has a device for forming a separate color image and for transferring the separate color image to the print medium to form with the other devices a composite multi-color image on the print medium as the print medium moves past the image formation and transfer stations.

[0007] Each device includes (1) a photoconductor member having an electrostatically chargeable photoconductive surface, (2) a photoconductive charge member, (3) an electroluminescent edge emitting line array member for selectively exposing the photoconductive surface to produce a latent electrostatic image on the photoconductive surface, (4) a toner developing member for placing a layer of toner of a selected color on the photoconductive surface to form a selected color image on the photoconductive surface, and (5) a transfer member for transferring the selected color image from the photoconductive surface to the print medium as the print medium passes the image formation and transfer station. An image fixing apparatus is positioned at the image fixing station for fixing the composite color image to the print medium as the print medium passes the image fixing station.

[0008] Another aspect of the invention is a color electrophotographic method for printing a multi-color image on a print medium. The print medium is moved past a plurality of image formation and transfer stations and a downstream image fixing station. A separate color image is formed at each of the image formation and transfer stations by charging the surface of a moving photoconductive member and then selectively exposing the moving photoconductive surface to produce a latent electrostatic image thereon. Color toner is then applied to the surface to form a separate color image on the moving photoconductive surface. Each separate color image is then transferred to the print medium to form a composite multi-color image on the print medium as the print medium moves past the image formation and transfer stations. The composite multi-color image is then fixed on the print medium as the print medium passes the image fixing station.

DESCRIPTION OF THE DRAWINGS

[0009] A preferred embodiment of the invention is described below with reference to the accompanying drawing, which illustrates the embodiment in schematic diagram form.

DETAILED DESCRIPTION OF THE INVENTION

[0010] This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws "to promote the progress of science and useful arts". U.S. Constitution, Article 1, Section 8.

[0011] An in-line color electrophotographic printer, generally identified with numeral 10 in the accompanying drawing, is provided for printing a multi-color image on a print medium 12 such as sheet paper. The printer 10 includes a print medium drive or feed, generally designated with the numeral 22, for moving a sheet or page 12 first past a series of in-line image formation and transfer stations 14, 15, 16 and 17 to form a composite color image thereon and then to pass the sheet 12 past an image fixing station 20 to fix the composite color image to the print medium 12. Preferably there are four stations each representing a different color, such as yellow, cyan, magenta and black.

[0012] The sheets 12 are conveyed from a sheet stack supported in a sheet tray or cartridge 26 along a print medium path, generally designated by the numeral 24, past the stations 14-17 and 20. Although the length of the sheets 12 may be of different sheet lengths, it is preferred that the sheets each have a length of eleven inches to fourteen inches.

[0013] Each image formation and transfer station 14-17 has a separate image formation and transfer device 28 for forming a selected separate color image and for transferring the formed separate color image to the print medium 12 to compose, in cooperation with the other devices 28, a composite multi-color image on the sheet 12 as the sheet is moved past the stations 14-17.

[0014] Each separate image formation and transfer device 28 has its respective photoconductive member 30 with a photoconductive surface 32 on which a latent electrostatic image may be formed. Preferably the photoconductive member 30 is in the form of a roller or cylinder that is mounted for rotation about an axis that is normal to the print medium path with a segment of the surface 32 being substantially tangent to the print medium path 12.

[0015] Each device 28 includes an electrostatic charging member 34 adjacent to and angularly spaced about the surface 32 for uniformly electrostatically charging the surface 32 as the member 30 is rotated.

[0016] Each device 28 further includes an electroluminescent edge emitting line array member 36 angularly spaced downstream of the charging member 34 for selectively exposing the photoconductive surface 32 to produce a latent electrostatic image on the photoconductive surface 32 as the member 32 is rotated. The line array member 36 extends transverse to the print medium path 24 and has a plurality of closely spaced electroluminescent edge emitting pixel elements, each of which selectively transmits light onto an axial segment of the photoconductive surface 32 to selectively expose the surface 32 as the roller 30 is rotated. Preferably the spacing between the pixel elements is such that the resulting image has a resolution of at least 300 dpi (dots per inch). Examples of an electroluminescent edge emitting line arrays are illustrated and described in: (1) an article entitled "Thin Film Electroluminescent Edge Emitters for Solid State Imaging", authored by Mr. Zoltan K. Kum, that was published in the July 1988 issue of the technical journal Solid State Technology, at pages 77-85; (2) an article entitled "The Construction and Characterization of a 400-dpi Thin-Film Electroluminescence Edge Emitter", authored by Messrs. Leksell, Kum and Machiko, published in the Proceedings of the SID, Vol. 29/2, 1988, pages 147-150; and (3) U.S. Patent No. 5,328,808 issued to Mr. Koichiro Sakamoto on July 12, 1994. Such articles and patent are incorporated herein by reference concerning the structure and operation of such electroluminescent edge emitter line arrays.

[0017] Each device 28 includes a toner developing member 38 adjacent the photoconductive surface 32 downstream of the electroluminescent edge emitting line array member 36 for placing a layer of toner of a selected color on the photoconductive surface 32 to form a separate color image on the photoconductive surface 32 corresponding to the latent electrostatic image as the photoconductive member 30 is rotated. Preferably, each toner developing member 38 places a layer of dry mono-color toner powder on the surface 32, selected from the colors of yellow, cyan, magenta and black. Such toner developing members 38 are rather conventional and will not be discussed in any detail to minimize the length of this document.

[0018] Each device 28 further includes an image transfer member 42, preferably in the form of a roller, that is positioned adjacent the photoconductive member 30 downstream of the toner developing member 38 for transferring the selected color image from the photoconductive surface to the print medium as the print medium passes the respective image transfer station. Specifically the image transfer member 42 opposes the photoconductive member 30 relative to the print medium path 24 to bias the sheet against the photoconductive surface 32 to facilitate the transfer of the selected color image from the photoconductive surface 32 to the sheet as the sheet moves along the path 24 past the respective image transfer station. Preferably the image transfer members 42 rotate as idlers in relation to the rotation of the associated photoconductive members 30. The image transfer members 42 also serve to stabilize and maintain the alignment of the sheets relative to the photoconductive surfaces 32 as the sheets are fed through the printer.

[0019] Each device 28 also includes a surface cleaning member 44 downstream of the image transfer member 42 for cleaning the photoconductive surface 32 to remove any foreign particles or untransferred toner so that the photoconductive surface may be reused without image contamination from foreign particles or unused toner.

[0020] Preferably the photoconductive member 30 has a circumferential dimension, in a direction parallel with the direction of the path 24, that is less than the length of the sheet. Preferably, the diameter of the photoconductive member 30 is between one and one-half inches with the circumferential dimension being several times less than the length of the sheet 12. The roller 30 produces and carries only a portion of a sheet image at one time. The roller 30 forms one portion of the image as another portion is being transferred to the sheet.

[0021] Preferably, the accumulated total center-to-center distance between the stations 14-17 along the path 24 is less than twice the length of the sheet, so that at least two separate images are being laid up, in an overlapping relationship, on the sheet at one time. Desirably, the center-to-center distance between adjacent stations 14-17 is four inches or less to minimize the length of the path 24 and the size of the printer. It is an important objective to be able to print a three or four color composite image in about the same time that it takes to print a mono-color image. Although each color layer or image is successively laid up on the sheet 12, one layer on top of the another prior to fixing, each layer is also being laid up simultaneously with other layers. Most preferably all three or four separate layers are being simultaneously laid up in overlapping relationships with the first station 14 laying up the trailing end of its image while the last station 17 is laying up the leading end of its image. This requires that the total center-to-center distances between the stations 14-17 be equal or less than the length of the sheet 12.

[0022] As shown in the accompanying drawing, the sheet 12 is initially removed or picked from the sheet storage tray 26 and then sequentially directed past the image formation and transfer stations 14-17. At station 14, a separate yellow color image is first progressively formed and progressively transferred to the sheet; starting adjacent the leading edge of the sheet and proceeding to the trailing sheet edge. At station 15, a separate cyan color image is progressively formed and progressively transferred to the sheet, overlaying the yellow color image; starting adjacent the leading edge of the sheet and proceeding to the trailing sheet edge. It should be noted that the cyan color image is transferred to the sheet at the same time that the yellow color image is applied to the sheet. A separate magenta color image is progressively formed and progressively transferred to the sheet at station 16, overlaying both the yellow color image and the cyan color image; starting adjacent the leading edge of the sheet and proceeding to the trailing sheet edge. It should be noted that the magenta color image is transferred to the sheet at the same time that the cyan color image is transferred to the sheet. A separate black color image is progressively formed and progressively transferred to the sheet at station 17, overlaying the yellow, cyan and the magenta color images, starting adjacent the leading edge of the sheet and proceeding to the trailing edge of the sheet 12. It should be noted that black color image is transferred to the sheet at the same time that the magenta color image is transferred to the sheet. Preferably, the black color is transferred to the sheet at the same time that both the cyan and magenta color images are transferred to the sheet.

[0023] After the composite multi-colored image has been formed on the sheet, the sheet 12 is then moved along the path of the image fixing station 20 to fix the composite multi-colored image to the sheet 12. A fixing apparatus 46 in the form of heated rollers 48 and 50 is located at the image fixing station 20. Roller 48 serves as the driven roller and roller 50 serves as an idler nip roller. Various types of heating or melting systems may be utilized as long as the desired throughput is maintained.

[0024] The sheet drive 22 preferably is operatively connected to the photoconductive members 30 and the driven roller 48 to rotate the same at the same peripheral speeds to maintain sheet control and alignment.

[0025] In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.

Claims

1. A color electrophotographic printer (10) for printing a multi-color image on a print medium (12), comprising:

a) medium transfer (22) for moving the print medium (12) in a path (24) sequentially past a plurality of in-line spaced image formation and transfer stations (14-17) and a downstream image fixing station (20);

b) each image transfer station (14-17) having an image formation and transfer device (28) for forming a selected separate color image and for transferring the selected separate color image to the print medium 12) to form, in cooperation with the other image formation and transfer devices, a composite multi-color image on the print medium (12) as the print medium (12) moves past the image formation and transfer stations (14-17);

c) wherein each image formation and transfer device (28) includes:

(1) a separate photoconductive member (30) having an electrostatically chargeable photoconductive surface (32);

(2) an electrostatic charge member (34) adjacent the photoconductive member (30) for electrostatically charging the photoconductive surface (32);

(3) an electroluminescent edge emitting line array member (36) adjacent the photoconductive member (30) for selectively exposing the photoconductive surface (32) to produce a latent electrostatic image on the photoconductive surface (32);

(4) a toner developing member (38) adjacent the photoconductive member (30) for placing a layer of toner of a selected color on the photoconductive surface (32) of the photoconductive member (30) to form a selected color image on the photoconductive surface (32);

(5) a transfer member (42) opposing the photoconductive member (30) relative to the print medium path (24) for transferring the selected color image from the photoconductive surface (32) to the print medium (12) as the print medium (12) passes the image transfer station (20); and

d) an image fixing apparatus (46) at the image fixing station (20) for fixing the composite color image to the print medium (12) as the print medium (12) passes the image fixing station (20).

2. The color electrophotographic printer as defined in claim 1 wherein the print medium (12) has a prescribed sheet length and wherein each photoconductive surface (32) has an image formation length parallel with the print medium path (24) that is substantially less than the prescribed sheet length.

3. The color electrophotographic printer as defined in claim 2 wherein the photoconductive surface (32) is formed on a drum having a circumference that is substantially less than the prescribed sheet length.

4. The color electrophotographic printer as defined in claim 1 wherein the print medium (12) has a prescribed sheet length and wherein the combined center-to-center spacing of two or more image formation and transfer devices (28) along the print medium path (24) is less than the prescribed sheet length.

5. The color electrophotographic printer as defined in claim 1 wherein the center-to-center spacing between the image formation and transfer devices (28) along the print medium path (24) is such that at least two color images are transferred simultaneously to the print medium (12) as the print medium (12) moves past the image formation and transfer stations (14-17).

6. A color electrophotographic printing method for printing a multi-color image on a print medium (13), comprising:

a) moving the print medium in a path (24) sequentially past a plurality of image formation and transfer stations (14-17) and a downstream image fixing station (20);

b) forming a separate color images at each image formation and transfer station by:

(1) moving a photoconductive surface (32) in relation with the movement of the print medium (12);

(2) electrostatically charging the moving photoconductive surface (32);

(3) selectively exposing the photoconductive surface (32) to produce a latent electrostatic image on the moving photoconductive surface (32) using an electroluminescent edge emitting line array member (36);

(4) placing toner of a selected color on the photoconductive surface (32) of the photoconductive member (30) to form a separate color image on the moving photoconductive surface (32);

c) transferring the separate color images from the respective moving photoconductive surfaces (32) to the print medium (12) to form a composite multi-color image on the print medium (12) as the print medium (12) moves past the image formation and transfer stations (14-17); and

d) fixing the composite multi-color image to the print medium as the print medium passes the image fixing station (20).

7. The color electrophotographic printing method as defined in claim 6 wherein at least two of the separate color images are transferred simultaneously to the print medium (12) as the print medium (12) moves past the image formation and transfer stations (14-17) to form the composite multi-color image prior to passing the image fixing station (20).

8. The color electrophotographic printing method as defined in claim 5 wherein there are at least three image formation and transfer stations (14-17) for forming at least three separate color images and wherein at least three of the separate color images are transferred simultaneously to the print medium as the print medium moves past the image formation and transfer stations (14-17) to form the composite multi-color image prior to passing the image fixing station (20).

9. The color electrophotographic printing method as defined in claim 5 wherein the print medium (12) has a prescribed sheet length and wherein each photoconductive surface (32) has an image formation length parallel with the print medium path (24) that is substantially less than the prescribed sheet length.

10. The color electrophotographic printing method as defined in claim 5 wherein the print medium (12) has a prescribed sheet length and wherein the image formation and transfer stations (14-17) are positioned in-line along the path (24) of the print medium a distance less than the prescribed sheet length.

Drawing