GB2165962A - Electrophotographic apparatus - Google Patents

Abstract

A selective editing arrangement for an electrophotographic apparatus includes an array (50) of light- emitting diodes (LED's) (51) which extend across the entire width of the photoconductive imaging surface (1) between the imaging station (3) and the development station (4). A programmable control means operated from the keyboard of the apparatus is used to energise individual LED's so that selected areas of the original information may be deleted from the copy. <IMAGE>

Description

SPECIFICATION Electrophotographic apparatus This invention relates to an electrophotographic apparatus including a recirculating photoconductive imaging surface upon which electrostatis latent images of object information are formed for development and transfer to copy sheets.

In making copies of documents, it is often desirable to be able to produce copies on which only selected portions of the information on the original document are reproduced.

This may be achieved by, for example, placing pieces of blank paper over the document so as to cover those portions of the document which it is not desired to copy. This can be a tedious process, requiring the cutting of blank paper sheets of the appropriate size and shape and ensuring that they are in the correct place relative to the document during copying. An alternative approach is to cover the portions which it is desired to delete with a white paint, or to fix blank pieces of paper to the document. This, of course, suffers from the advantage that it spoils the original document. Various mechanical devices have been used to provide a form of selective editing of documents, and these typically include overlays for use in conjunction with the document being copied.Apart from the added complication which they introduce, these devices have the disadvantage that it is possible to delete (or add) matter only in predetermined areas of a copy, as determined by a particular overlay.

It would clearly be a desirable feature of an electrophotographic copying apparatus to be able to selectively edit the information on an original to be copied without the need to resort to the above described methods. It is an object of the present invention to enable such selective editing. Accordingly, the electrophotographic apparatus of the invention is characterised in that it includes a selective editing arrangement which comprises an array of closely-spaced light sources extending across the entire width of the imaging surface generally transversely of the process direction, and programmable control means for selectively energising individual ones of the light sources so as to discharge corresponding portions of the imaging surface and thereby delete selected areas of the object information from the developed image.

An electrostatographic apparatus in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic cross-sectional view of a xerographic copying machine incorporating the invention; Figure 2 is an enlarged view of the xerographic drum of Fig. 1 together with its closely associated parts of the machine; Figure 3 is an enlarged cross-sectional view of an array of light emitting diodes used in a preferred embodiment of the invention; Figure 4 is a cross-sectional view on a diameter of the xerographic drum, showing the array of light emitting diodes; and Figure 5 is a circuit diagram of an arrangement for activating individual light-emitting diodes in the array.

Referring first to Figs. 1 and 2 there is shown a xerographic copying machine incorporating the present invention. The machine includes a photoreceptor drum 1 mounted for rotation (in the clockwise direction as seen in Fig. 1) to carry the photoconductive imaging surface of the drum sequentially through a series of xerographic processing stations: a charging station 2, an imaging station 3, a development station 4, a transfer station 5, and a cleaning station 6.

The charging station 2 comprises a corotron which deposits a uniform electrostatic charge on the photoreceptor, typically of selenium, After charging a potential of around +900V remains on the photoreceptor surface. A document to be reproduced is positioned on a platen 13 and scanned by means of a moving optical scanning system to produce a flowing light image on the drum at 3. The optical image selectively discharges the photoconductor in image configuration, whereby an electrostatic latent image of the object is laid down on the drum surface. Discharged areas of the photoreceptor typically retain a potential of around +200V. At the development station 4, the electrostatic latent image is developed into visible form by bringing into contact with it toner particles which deposit on the charged areas of photoreceptor.Cut sheets of paper are moved into the transfer station 5 in synchronous relation with the image on the drum surface and the developed image is transferred to a copy sheet at the transfer station 5, where a transfer corotron 7 provides an electric field to assist in the transfer of the toner particles thereto. The copy sheet is then stripped from the drum 1, the detachment being assisted by the electric field provided by a de-tack corotron 8. The copy sheet carrying the development image is then carried by a transport belt system 9 to a fusing station 10.

After transfer of the development image from the drum, some toner particles usually remain on the drum, and these are removed at the cleaning station 6. After cleaning, any electrostatic charges remaining on the drum are removed by an erase corotron 11. The photoreceptor is then ready to be charged again by the charging corotron 2, as the first step in the next copy cycle.

The optical image at imaging station 3 is formed by optical system 12. A document (not shown) to be copied is placed on platen 13, and is illuminated by a lamp 14 that is mounted on a scanning carriage 15 which also carries a mirror 16. Mirror 16 is the full-rate scanning mirror of a full and half-rate scanning system. The full-rate mirror 16 reflects an image of a strip of the document to be copied onto the half-rate scanning mirror 17. The image is focussed by a lens 18 onto the drum 1, being deflected by a fixed mirror 19. In operation, the full-rate mirror 16 and lamp 14 are moved across the machine at a constant speed, while at the same time the half-rate mirrors 17 are moved in the same direction at half that speed. At the end of a scan, the mirrors are in the position shown in a broken outline at the left hand side of Fig. 1.These movements of the mirrors maintain a constant optical path length, so as to maintain the image on the drum in sharp focus throughout the scan.

At the development station 4, a magnetic brush developer system 20 develops the electrostatic latent image. Toner is dispensed from a hopper 21 by means of a rotating foam roll dispenser 22, into developer housing 23. Housing 23 contains a 2-component de developer mixture comprising a magnetically attractable carrier and the toner, which is brought into developing engagement with drum 1 by a magnetic brush developing arrangement.

The developed image is transferred, at transfer station 5, from the drum to a sheet of copy paper (not shown) which is delivered into contact with the drum by means of a paper supply system 25. Paper copy sheets are stored in two paper trays, an upper, main tray 26 and a lower, auxiliary tray 27. The top sheet of paper in either one of the trays is brought, as required, into feeding engagement with a common, fixed position, sheet feeder 28. Sheet feeder 28 feeds sheets around curved guide 29 for registration at a registration point 30. Once registered, the sheet is fed over a baffle member 42 into contact with the drum in synchronous relation to the image so as to receive the image at transfer station 5.Baffle member 42 comprises a sheet guiding portion 44 and a corona discharge limiting portion 43 which defines a limit to the extent of the corona generated by the transfer corotron 7.

The copy sheet carrying the transferred image is transported, by means of vacuum transport belt 9, to fuser 10, which is a heated roll fuser. The image is fixed to the copy sheet by the heat and pressure in the nip between the two rolls of the fuser. The final copy is fed by the fuser rollers along output guides 31 into catch tray 32, which is suitably an offsetting catch tray.

After transfer of the developed image from the drum to the copy sheet, the drum surface is cleaned at cleaning station 6. At the cleaning station, a housing 33 forms with the drum 1 an enclosed cavity, within which is mounted a doctor blade 34. Doctor blade 34 scrapes residual toner particles off the drum, and the scraped off particles then fall into the bottom of the housing, from where they are removed by an auger 35.

Between the emitting station 3 and the development station 4 there is located a fadeout unit 50 (Fig. 2). This unit, illustrated in greater detail in Figures 3 and 4, is used to selectively discharge the photoreceptor, thereby controlling those areas of the copy sheet which carry an image. The fade-out unit comprises an array of light-emitting diodes (LED's) 51 equally spaced apart over the entire usable width of the photoreceptor. For example, in a copying machine which will take copy paper of B4 size, the maximum copy width is about 364mm. In these circumstances, 86 LED's are used, i.e. 85 pitches, with a spacing (pitch) of 4.3mm. This spacing corresponds with the standard line spacing of typwritten material.

The LED's 51 in the array are mounted side by side on a strip 52 of, for example, printed circuit board material, the rear face of the strip being used for establishing electrical connections to the individual diodes, for example by means of a matrix arrangement. One suitable such arrangement is illustrated in the circuit diagram of Fig. 5. By means of appropriate digital inputs in the input wires 53, the desired pattern of diodes may be illuminated.

In the arrangement shown, groups of 10 LED's are controlled by way of integrated circuits 54 (e.g. Sprague ICM5810). The array of LED's is mounted within a housing 55 that is mounted adjacent the drum surface. One suitable form of housing 55 is a hollow plastic extrusion formed with internal slots to accommodate the strip 52. The light emitting portions of the LED's 51 are situated adjacent the lower end of the casing 55, which is closed by a transparent window 56.

When copying documents onto same size copy paper sheets (i.e. 1:1 copying), it is difficult to achieve a perfect replica of the original because of the shadows of the edges of the document being copied. Even if the document is aligned on the platen with absolute accuracy, it is nevertheless likely that dark edges will appear on the copy. These shadows can be eliminated by using a slight magnification (typically 105%) to ensure that the area of the document which appears on the copy is slightly less than all of the area of the original. This has the disadvantage that on some occasions, information that it is desired to copy is lost, with the further disadvantage that it is not possible to make exactly 1:1 copies. One way to make 1:1 copies while eliminating shadows is to use an edge fadeout device. In such a device, light is directed along the edge zone of the photoreceptor so that no image is formed in, say, the 2 mm strip adjacent the edge of the copy. In copiers where different magnification modes are pro vided, two or more separate fade-out lamps may be used selectively to produce fade-out at the appropriate copy width.

The array described above may be used to provide edge fade-out by selectively illuminating the appropriate LED's at the edges of the array. The width illuminated may be controlled directly in accordance with the magnification mode selected, even if there are a large number of magnification modes. Thus, for example, the array can be used if there is continuously variable magnification, or magnification which can be varied in a large number of discrete steps (such as one percent steps).

Furthermore, it is usual in copying machines to flood illuminate the photoreceptor in the gaps between successive copies. This is because otherwise the gaps would be undischarged and therefore developed as a solid black zone. This is wasteful of developer material, and imposes extra strain on the cleaning system when it is cleaned off the drum. The array described above is ideal for this purpose, since all the LED's can be illuminated together for the appropriate length of time, providing a band of light across the photoreceptor and giving the required flood illumination on rotation of the photoreceptor drum.

In addition to the above described modes of operation of the LED array, which are effected automatically by the logic circuitry which controls the machine, it is possible to employ the array in a further mode, i.e. a selective editing mode. In this mode, the switching on and off of the LED's is under the control of the person operating the machine. Thus, for example, by activating one or more of the LED's in the imaging zone for the duration of a copy cycle, it is possible to discharge the photoreceptor along one or more strips extending in the process direction. With documents whose printed lines extend in this direction, which is common with many copiers, it is accordingly possible to delete one or more lines of text from the copy. Preferably the LED's are spaced, for example as described above, so that each LED permits the deletion of a single line of typwritten text.If selected LED's are switched on and off during a copy cycle, it is also possible to delete selected rectangular areas of the information.

In order to selectively edit the copy, the relevant LED's may be activated from the push button keyboard of the copying machine.

For line editing only, straightforward sets of numbers are used to define the beginnings and ends of strips to be deleted. For area editing, a grid system is set up to enable the operator to use the keyboard to define, for example, one or more corner coordinates of each rectangular area to be deleted. Thus, the area to be deleted might be defined by providing the coordinates of its top left hand corner, and defining with width and height of the area. Alternatively, a pair of sliding cursors may be provided adjacent to the platen so that coordinates may be read off and entered by way of the keyboard. In a further embodiment, sliding cursors may be used to feed electric signals (e.g. by the use of potentiometer circuits) representing coordinates directly into the control system in response to the pressing of a designated key on the keyboard.

Claims (6)

1. Electrophotographic apparatus including a recirculating photoconductive imaging surface upon which electrostatic latent images of object information are formed for development and transfer to copy sheets, characterised in that the apparatus includes a selective editing arrangement which comprises an array of closely-spaced light sources extending across the entire width of the imaging surface generally transversely of the process direction, and programmable control means for selectively energising individual ones of the light sources so as to discharge corresponding portions of the imaging surface and thereby delete selected areas of the object information from a developed image.

2. The apparatus of claim 1 wherein the control means is programmable to energise individual ones of the light sources for the duration of a copy cycle, whereby strips of information extending in the process direction may be selectively deleted.

3. The apparatus of claim 1 wherein the control means is programmable to energise individual ones of the light sources for a time period equal to or less than the duration of a copy cycle, whereby rectangular areas of information within the copy area may be selectively deleted.

4. The apparatus of any one of claims 1 to 3 wherein appropriate ones of the light sources are automatically energised to provide edge fade-out in accordance with copy size and magnification mode.

5. The apparatus of any one of claims 1 to 4 wherein all the light sources are automatically energised for an appropriate length of time to discharge the imaging surface in the gaps between successive latent images.

6. The apparatus of any one of claims 1 to 5 wherein the light sources comprise an array of light-emitting diodes.