DOCUMENT COPIER WITH AUTOMATIC IMAGE QUALITY CONTROL

Abstract: Occasionally, a sheet of a document stack will have a contrast or density which when copied by a copier in normal operation will produce a poor copy. In this case the practice has been to remove the sheet from the document stack and copy it individually, making an intermediate or master copy. The copy master is then returned to the appropriate position in the document stack and the production run is undertaken. A problem with this arrangement is that during the production ran when the copy master is copied, image quality may be unavoidably degraded. In accordance with the invention, contrast and density of copies of particular document sheets of a multi-sheet document is adjusted during production runs but without making copy masters. Before the production ran, an operator designates the use of either a halftone screen (13') and/or other process parameter information for controlling the contrast and density of a copy for a particular document sheet having a copy characteristic that is substantially different from the other document sheets of the document stack. This information is stored in a memory (32) located in the copier. During a production ran the logic and control device (31) causes the document feeder (50) to sequentially transport document sheets S to the exposure platen (2) of the copier where they are copied and in accordance with the stored information activates a halftone screen (13') and/or otherwise adjusts the copier process parameters for producing improved copy contrast and density of the copies of the particular document sheet.

Description: DOCUMENT COPIER WITH AUTOMATIC IMAGE QUALITY CONTROL The present invention relates to copiers having automatic document feeders for producing production runs (i.e. multiple collated copies) of multisheet documents. More particularly, it relates to apparatus for automatically adjusting copier parameters, during a production run, to compensate for variations in image quality of the document sheets being copied. High-speed document copiers having automatic document feeders are currently used for making multiple collated copies of multisheet documents. In some such copiers, a recirculating document feeder automatically feeds document sheets, one at a time, from the bottom of a stack, to the exposure platen of the copier, and returns each sheet, after it is copied, to the top of the document stack. In returning each sheet to the stack its original orientation is maintained. Since the copy sheets are delivered from the copier in the same order as that in which the original document sheets are stacked, collation of the copy sheets by a sorter accessory is unnecessary. Occasionally, one or more sheets of the multisheet document will have an image quality (e.g. contrast, density and/or continuous tone) which differs substantially from that of the other sheets in the stack. For example, one sheet in the stack may be a photograph having continuous tones of varying density, while the other sheets are typewritten text. Obviously, when the parameters of the copier are adjusted to achieve optimum copy quality for the typewritten sheets, the copy quality of the "different" document sheet (i.e. the photograph) will be somewhat less than optimum. To alleviate this problem, the normal practice is to remove the "different" document sheets from the document stack and to copy them individually, adjusting the copier process parameters, to the extent possible, so that the image quality of the copies is as similar to the majority of the document sheets as possible. These copies of the "different" document sheets are then substituted for the original sheets in the stack and the production run is undertaken in the normal manner. The problem with this technique is that, during the production run when the substituted copies are copied, the image quality of the copies of such substituted copies is still less than optimum because copies are being made from copies. In view of the foregoing, an object of this invention is to eliminate the need for making copies of copies in order to compensate for differences in image quality of the individual document sheets which compose a multisheet document to be copied. In accordance with the present invention, the image quality of copies of each of the individual document sheets of a multisheet document is automatically adjusted during a production run in accordance with information stored in a memory device (e.g. the memory of a microprocessor) . Before a production run, an operator determines the copier process parameters (e.g. in the case of an electrophotographic copier, the initial voltage V and exposure E applied to the photoconductive recording element, the development bias Vg, and/or the voltage V- applied to lamps which illuminate a halftone screen) which produce optimum image quality for each of the document sheets. Information corresponding to such copier process parameters is stored in the memory device, together with information representative of the position of each document sheet in the stack and the number of times each document sheet is to be copied. Logic and control means, responsive to the stored information, controls the operation of a document feeder and adjusts the copier parameters to produce the desired image quality for each of the document sheets copied. The invention will be better understood from the ensuing detailed description of a preferred embodiment, reference being made to the accompanying drawings in which: Fig. 1 is a schematic side elevational view of an electrophotographic copier incorporating the present invention; Fig. 2 is a block diagram of the logic and control unit shown in Fig. 1; Fig. 3 shows an enlarged cross-section of the photoconductive recording element of the copier shown in Fig. 1; and Fig. 4 shows copier controls for operating the copier shown in Fig. 1. To assist in understanding the present invention, it will be useful to consider an electrophotographic copier having a logic and control unit, and a recirculating document feeder. At the outset, it will be noted that although this invention is suitable for use with a recirculating feeder, it also can be used with other types of feeders. Whenever the term "document sheet" is used, it refers to particular mediums such as sheets having images to be copied. The term "document" refers to a plurality of document sheets that are to be copied during a production run. The term "copy" refers to the output of the copier such as a copy sheet having a fixed toner image. In Fig. 1, a recirculating feeder 50 is positioned on top of an exposure platen 2 of a copier 1. The recirculating feeder may be similar to that disclosed in commonly assigned U.S. Patent No. 4,076,408, issued February 28, 1979, wherein a plurality of document sheets S having images only on first sides of such sheets can be repeatedly fed seriatim from a stack of such sheets to the exposure platen 2. The feeder 50 includes feed rollers 51 which transport a document sheet S across the exposure platen 2 to document registration blocks 60 and 61, which stop and register the document on the exposure platen. The platen 2 is constructed of transparent glass. When energized, two xenon flashlamps 3 and 4 flash illuminate the document sheet S. By means of an object mirror 6, lens system 7, and an image mirror 8, an image of the illuminated document sheet is optically stopped on discrete image areas of a moving photoconductive recording element, shown as an endless web 5. After a document sheet is illuminated, the blocks 60 and 61 are withdrawn from the path of travel and the document sheet is returned to the top of the document stack in a tray. Fig. 3 illustrates a partial cross-section of the photoconductive web 5 which includes a flexible transparent support 12' , a halftone screen- 13', a conductive layer 14', and a photoconductive layer 16'. The support 12' provides mechanical strength to the other layers of the web and makes it suitable for use in electrophotographic copying machines. The support 12' may be fabricated of almost any flexible transparent material, either conductive or insulating, and may be made of polyethylene, polyethylene terephthalate or the like. Although a transparent support is used in this illustrative embodiment of the invention, other types of support w can be used, especially in circumstances where the photoconductive layer 16' is exposed to the halftone screen (as described below) other than through the support. In the disclosed embodiment, immediately adjacent to the transparent support 12' is the halftone screen 13', which is made up of a number of finely divided, alternating, opaque and transparent areas. This screen is used to form charge islands on the photoconductive layer 16' (which assist in the production of high quality copies of original sheets bearing continuous tone images) . The screen pattern of opaque and transparent areas may be a convenional dot pattern or line pattern of the type used for the fabrication of halftone plates for newspaper printing. The alternating opaque and transparent areas of the screen pattern may be of almost any shape, including round dots, elliptical dots, lines and the like. The spacings of the pattern may also vary so that the pattern is regular, irregular, or random. The pattern may also be varied in size from dot-to-dot or line-to-line. Since the screen pattern is utilized only for forming charge islands, the screen may be either electrically conducting or insulating. Immediately adjacent to the halftone screen 13' is the conductive layer 14 which may, for example, be composed of a very thin transparent layer of tin oxide, nickel, cermet, or copper iodide. The photoconductive layer 16' may be composed of any of the photoconductive insulating materials generally used in electrophotography, and may include such diverse materials as vitreous selenium, aggregate photoconductive layers of the type disclosed in U.S. Patent No. 3,615,414 to Light or any one of many other organic photoconductor OMPI £ y layers including multilayer photoconductive structures having separate charge generating and charge transport functions. Returning to Fig. 1, the endless photoconductive web 5 is trained about six transport rollers 10, 11, 12, 13, 14, and 15. Roller 10 is coupled to a drive motor M in a conventional manner. Motor M is connected to a source of potential V when a switch SW is closed by a logic and control unit (LCU) 31. When the switch SW is closed, the roller 10 is driven by the motor M and moves the web 5 in clockwise direction, as indicated by arrow. This movement causes successive image areas of the web 5 to sequentially pass a series of electrophotographic work stations of the copier. For the purpose of the instant disclosure, several copier work stations are shown along the web's path. These stations will be briefly described. For more complete disclosures of them, see commonly assigned U.S. Patent No. 3,914,047. First, a charging station 17 is provided at which the photoconductive surface 9 of the web 5 is sensitized by applying to such surface an electrostatic charge of a predetermined voltage. The station 17 includes an A.C. charger shown as a three wire A.C. charger. The output of the charger is controlled by a grid 17A connected to a programmable power supply 17B. The supply 17B is in turn controlled by the LCU 31 to adjust the voltage level V applied onto the surface 9 by the charger 17 in accordance with a designated set value as will be described later. For some exemplary values, the grid voltage can be adjusted about a nominal value of -500 volts with a 600 hertz A.C. square signal applied to the corona wires. At exposure station 18, the inverse image of a document sheet S is projected onto the photoconductive surface 9 of the web 5. The image dissipates the electrostatic charge at the exposed areas of the photoconductive surface 9 and forms a latent electrostatic image. A programmable power supply 18A, under the supervision of the LCU 31, controls the intensity or duration of light incident upon the web 5 to adjust the exposure level E by the lamps 3 and 4 in accordance with a designated set value as will be described later. For a specific example of such an exposure station and programmable • power supply, see commonly assigned U.S. Patent No. 4,150,324, issued August 8, 1978 to Seil. After being imagewise exposed at exposure station 18, the photoconductive web 5 may optionally be flood illuminated through its transparent support 12' and halftone screen 13' by lamps 83. Such flood exposure may be carried out prior to, simultaneous with, or after image exposure of the photoconductor, the only requirement being that this rear exposure be carried out after charging and prior to development. Lamps 83 are energized by an adjustable power supply 84 which, in turn, is operated by the logic and control unit 31. The output V-, of the power supply can be varied to change the flood exposure provided by the lamps 83. The lamps 83 provide a uniform rear exposure through the screen 13' and serve to at least partially discharge all areas of the photoconductive layer 16' directly opposite transparent areas of the screen 13'. This exposure forms a plurality of very small charge islands on the photoconductive layer 16' . The amount of exposure used to form these charged islands is varied according to a variety of factors including the nature of the photoconductive layer, type of developer, and mode of development, as 'BUkiΞ.4, OMPI . _- WIPO described in detail in the commonly assigned U.S. Application Serial No. 133,077, filed March 24, 1980 in the name of Kasper. A dual magnetic brush developing station 19 includes developer, having iron carrier particles and electroscopic toner particles with an electrostatic charge opposite to that of the latent electrostatic image. The developer is brushed over the photoconductive surface 9 of the web 5 and toner particles adhere to the latent electrostatic image to form a visible toner particle, transferable image. The dual-magnetic brush station 19 includes two rollers, a transport roller 19A, and a developer roller 19B. As is well understood in the art, each of the rollers 19A and 19B include a conductive (non-magnetic) applicator cylinder which may be made of aluminum. In the disclosed embodiment, conductive portions, such as the drive shaft and the applicator cylinder of the transport roller 19A, act as an electrode and are electrically connected to a source of fixed D.C. potential, shown as a battery 19C. Conductive portions of development roller 19B also act as an electrode and are electrically connected to a programmable power supply 19D controlled by the LCU 31. Power supply 19D adjusts the level of V β , the voltage level applied to station electrode and will be discussed later. For a specific disclosure of a dual magnetic brush which can be used in accordance with the invention, see commonly assigned U.S. Patent No. 3,543,720. The copier 1 also includes a transfer station shown as a corona charger 21 at which the toner image on web 5 is transferred to a copy sheet S'; and a cleaning station 25, at which the photoconductive surface 9 of the photoconductive layer 16' is cleaned of any residual toner particles OM ' 3N remaining after the electroscopic images have been transferred and any residual electrostatic is discharged. As shown in Fig. 1, a copy sheet S' is fed from a supply 23 to continuously driven rollers 14, (only one of which is shown) which then urge the sheet against a rotating registration finger 32' of a copy sheet registration mechanism 22. When the finger rotates free of the sheet, the driving action of the rollers 14 and sheet buckle release cause the sheet to move forward onto the web 5 in alignment with a toner image at the transfer station 21. After transfer of the unfixed electroscopic images to a copy sheet S', such sheet is transported to fuser 27 where the image is fixed to it. To coordinate operation of the various work stations 17, 18, 19, 21, and 25 with movement of the image areas on the web 5 past these stations, the web has a plurality of perforations along one of its edges. These perforations generally are spaced equidistantly along the edge of the web member 16. For example, the web member 5 may be divided into six image areas by F perforations; and each image area may be subdivided into 51 sections by C perforations. The relationship of the F and C perforatons to the image areas is disclosed in detail in commonly assigned U.S. Patent No. 3,914,047. At a fixed location along the path of web movement, there is provided suitable means 30 for sensing web perforations. This sensing produces input signals into the LCU 31 which has a digital computer, preferably a microprocessor. The microprocessor has a stored program responsive to the input signals for sequentially actuating then de-actuating the work stations as well as for controlling the operation of many other machine functions as disclosed in U.S. Patent No. 3,914,047. Programming of a number of commercially available microprocessors such as INTEL model 8080 or model 8085 microprocessor (which along with others can be used in accordance with the invention), is a conventional skill well understood in the art. The following disclosure is written to enable a programmer having ordinary skill in the art to produce an appropriate control program for the microprocessor. The particular details of any such program would, of course, depend on the architecture of the designated microprocessor. Turning now to Fig. 2, a block diagram of logic and control unit (LCU) 31 is shown which interfaces with the copier 1 and the feeder 50. Leads 144 (shown in Fig. 1) from feeder 50 provide inputs to and receive outputs from LCU 31 to synchronize the operation of the feeder. For a more detailed disclosure of the operation and the feeder 50, see commonly assigned U.S. Patent No. 4,099,860. The LCU 31 consists of temporary data storage memory 32, central processing unit 33, timing and cycle control unit 34, stored program unit 34, and stored program control 36. Data input and output is performed sequentially under program control. Input data are applied either through input signal buffer 40 to a multiplexer 42 or to interrupt signal processor 44. The input signals are derived from various switches, sensors, and analog-to-digital converters. The output data and control signals are applied to storage latches 46 which provide inputs to suitable output drivers 48 which are directly connected to the work stations and to a copy sheet registration feeding mechanism 22. As shown, interrupt signals" are provided by copy buttons 73, 75, 76, 78, and 80 shown in more detail in Fig. 4, and information representing a particular set of a OMPI matrix array is designated by exposure knob 70 and contrast knob 72 which provide inputs to buffers 40 via their respective analog/digital converters 71. For convenience of illustration, a copier keyboard 35 is shown connected to the interrupt signal processor 44. This keyboard 35 can conveniently be located on the operator control panel. The starred (*) button is used to enter in memory 32 the location of particular document sheets that have a different copy characteristic then other document sheets as will be described later. Returning now to the microprocessor, stored in memory is the matrix array shown in Fig. 11 of the above-identified Fiske et al patent application. This matrix is in a digitized format, located in stored program control 36, provided by one or more conventional Read Only Memories (ROM) . The ROM contains operational programs in the form of binary words corresponding to instructions and values. These programs are permanently stored in the ROM and cannot be altered by the computer operation. The temporary storage memory 32 may be conveniently provided by a conventional, Read/Write memory or Random Access Memory (RAM) . Commonly assigned U.S. Patent No. 4,099,860 to Connin, discloses the operation of a recirculating feeder and a copier controlled by a logic and control unit. The operation will be briefly reviewed. The feeder 50 enables the copier to make either collated or noncollated sheets of copies in a production run. In the feeder, there are a plurality of sensors. As shown in Fig. 1, there is a sensor 67, a microswitch, which is disposed adjacent to feed rollers 51 located near the tray which receives the document stack. When a document sheet passes this position, the switch 67 is closed and applies a signal to the LCU OMPI 31. After a sheet is delivered by the rollers 51 to the exposure platen, it is stopped by registration gates 60, 61 and flash exposed by lamps 3 and 4. Thereafter, it is returned to the top of the document stack. In accordance with the invention, document sheets are transported in the same fashion. However, the input signal buffers 40 receives a signal from its switch 67 as the document passes by such switch. In accordance with the invention, this signal is provided as an input to the central processing unit which counts and provides an input to the temporary memory 32 which stores a cumulative total count. As explained below, when a particular document sheet has an image characteristic which differs from the other sheets, the copy process parameter for optimizing the quality of the copies thereof is stored in temporary memory 32. When the count stored by memory 32. indicates that such sheet has passed switch 67 and is positioned for copying, the microcomputer 31 adjusts the copier process parameters (e.g. V , E , V B and Vg) so that the image quality of the copy thereof is determined by the stored parameters. The document sheet is then exposed and returned to the stack. The LCU 31 then adjusts the copier, returning it to a normal copy making mode of operation. The document sheet feeding and copying process is repeated until all such sheets are copied the desired number of times. For a detailed explanation of the theory of copier contrast and exposure control by controlling V , E , and Vg, reference may be made to the following article: Paxton, Electrophotographic Systems Solid Area Response Model, 22 Photographic Science and Engineering 150 (May/June 1978) . In Fig. 4, the operator controls for the copier include two rotary knobs, exposure knob 70 and contrast knob 72, the special print copy button 74, and the halftone button 73. These controls are in addition to the normal, darken and lighten copy buttons 76, 78, and 80 usually found on copiers. Both knobs 70 and 72 have nine discrete positions. As disclosed in U.S. Application Serial No. 137,149, filed April 4, 1980 in the name of Fiske et al the two control knobs 70 and 72 correspond to eighty-one different sets of Vo. Eo and V-B, which in turn correspond to eighty-one different D ηn D out response curves. As explained in the above-mentioned Fiske et al application, the first knob 70 functions as an exposure control and translates the breakpoint of the Di.n/Dout. curve. When the knob 72 is turned, the slop v e of the Di.n/Dout. curve is changed. Note, "D in " and "D " refer to the image density of the document sheet and copy, respectively. To make single or multiple copies (non-production run condition) of a document sheet and to obtain a copy representative of the conditions designated by the exposure and contrast knobs, and screening, the special print copy button 74 must be depressed. To energize lamps 83 and thereby make use of the halftone screen 13', an operator first depresses halftone button 73. Thereafter he depreses the special print button 74. The depression of button 74 also causes the copy to be produced in accordance with the E 0 Λ , V0 Λ and V D D conditions specified by the knobs 70 and 72. In their respective positions .23 and 3.0, shown in Fig. 4, they are set to provide for a normal copy. The knobs 70 and 72 can be adjusted to change the copy contrast and density whether or τiot it is desired to use the screen 13' . If one of the normal, darken or lighten copy buttons is depressed, the computer ignores positions of the knobs 70 and 72, and a - ) -ι n /- ) QUt - response curve corresponding to the normal, darken or lighten copy button designated will be produced. By means of this arrangement, a casual operator can choose to make copies by the conventional normal, darken or lighten copy button selection method. In operation, let us assume a special case where only one document sheet in a document stack- needs special consideration for contrast and density control. An operator would remove this sheet from the document stack and depress the page number select button 75 (Fig. 4). He then depresses the appropriate numbered buttons on the keyboard 35 which enters in memory 32 the position of the sheet in the document stack. In a document feeder which feeds last document sheet first, this position information is the position from the bottom of the document stack. Alternatively, the page number (from the top of the document stack) may be specified, along with the number of pages in the document so that position from the bottom of the document stack can be calculated by the LCU 31. Alternatively, the feeder may cycle through the document once for counting purposes. The operator then would make a copy of the document as previously described. If the document sheet is, for example, a photograph, he may decide that the half toning is appropriate. It, of course, may not be desirable. Let us assume, in this example, this improves the contrast but the copy still has some objectionable background; he then adjusts knobs 70 and 72 and makes another copy. Assuming now that the copy has the desired contrast and density, the operator would then press the starred (*) button of the keyboard 35. The LCU 31 now enters into temporary memory 32 all the processing parameter information for the particular document, i.e. its position in the stack, whether or not the halftone screen is to be used, and what values of V , E and V\, are to be used, as determined by the positions of knobs 70 and 72. In a more general case, if there were other document sheets that needed special consideration, the above iterative process would be repeated for each of them. The operator now returns the removed document sheet to its initial position in the document stack and places the stack in the feeder 50. He also returns knobs 70 and 72 to their normal position, if it is desired to make the other copies at this setting. The special print selection button is now depressed, and the feeder 50 and copier operate as previously described to produce a production run of collated copies of the multisheet document with each the copy corresponding to the particular document sheet having contrast and density in accordance with the stored process information and the remaining copies having normal contrast and density. The invention has been described with particular reference to a preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. For example, rather than storing in memory the copy process parameters of only one or two sheets of a multisheet document and copying all of the remaining sheets using the "normal" parameters, the operator could, if he chose to, optimize the copy quality of each and every document sheet in the stack. In this case, he would carry out the above-described procedure for each sheet. The position of each of the document sheets in the stack, whether or not a halftone screen is to -16- be used, and the values corresponding to the optimum Vo, Eo and VB Ώ levels for each sheet are then stored in memory in accordance with the procedure described above.

Claims: -17- CLAIM In apparatus for producing copies of a multisheet document which includes at least one sheet having an image characteristic that is substantially different from the other sheets, said copier including adjustable control means for varying at least one copier process parameter to change the image quality of copies produced, and means for feeding seriatim the sheets of a multisheet document to a copying position to produce copies of the document, characterized in that there is provided: a) memory means (32) for storing information corresponding to (i) the number of copies to be made of a multisheet document, (ii) the copy process parameters for said multisheet document including the variation in said one copy process parameter to achieve a desired image quality for said • one sheet, and (iii) the position of said one sheet in the multisheet document; and b) logic and control means responsive to said signals for operating said feeding means to sequentially feed the sheets of said multisheet document to said copying position and for setting said adjustable control means prior to copying said one sheet to produce copies of the document, with each copy of a document sheet having a desired image quality. OiV.PI

Inventors: PAXTON K
Applicants: EASTMAN KODAK CO
Application year: 1981
Main classification: G03G15
IPC codes: G03B27, G03G15, G03G21