DK142634B - Copier for copying publishers of various sizes. - Google Patents

Description

(11) PUBLICATION 142634 DENMARK (51), nt · C | · 3 Q 03 g 15 / o a «(21) Application No 505/75 (22) Filed on the 12th of bold).

(24) Race day 12. bold). 1975 (44) The application submitted increase the petition published on the 1st fteC. 1 98θ

DIRECTORATE OF

PATENT AND TRADEMARKET SYSTEM (30) P "0" ** referred dw

Feb 14 1974, 442555, US

(71) INTERNATIONAL BUSINESS MACHINES CORPORATION, Armonk, New York 10504, (js.

(72) Inventor: Sterrltt R. Fuller, 1509 Roanoke Rd., Lexington, KY 40504, US: Howard E. Munzel, ^ 142 Montavesta Rd., Lexington, KY 02, US: Carl A. Queener, 70TJ Cromwell Way, Lexington , KY 40505, US.

(74) Plenipotentiary in the proceedings:

The engineering firm Budde, Schou & Co._, (54) Photocopier for copying publishers of various sizes.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a photocopier having a station for constructing an electrostatic image for powder image development, which includes means for progressively scanning a narrow strip of a slide reflected from an exposure window to subsequent portions of the photoconductive surface, a discharge means. disposed between an exposure station and a developing station which can assume an active and an inactive state, which discharge means over a delay means is controlled by drum position sensors to completely discharge the photoconductive surface between consecutive image areas.

In such apparatus, the powder image transferred to a copied sheet is usually used for fixing a so-called contact firing apparatus in which the copied sheet with the powder image transmitted thereto is heated so that the powder melts and thereby adheres to the sheet.

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Contact fastening devices are effective, compact and flexible devices for fixing images of thermoplastic powder on support sheets. Appropriate construction methods and special care in heat transfer and material selection make it possible to provide a contact fastening apparatus which fires the thermoplastic image and presses it against a carrier sheet without even adhering thereto. The attachment of pigment to the contact surface of the retaining member may cause staining on subsequent copies and, in the worst case, may cause an adhesion of the copy sheet to the retaining surface causing a paper jam. It has been found that there is a maximum tendency for adhesion between a copy subjected to burning and a heated burner roller in a contacting burner when burning a wide portion of a very dense image. The problem of the tendency to stick is greatest when the wide, dense image is found near the leading edge of the copy sheet, where the separation of the copy sheet from the heated burner roller must be initiated.

When copying ordinary publishers, such as letters, drawings and even photographs, it is not unusual to take large coherent black image areas at one edge of the publisher. When a copy image is produced by exposure with light reflected from the publisher, the absence of a light reflective publishing area produces a dense, black image over the entire corresponding area of the copy sheet. For this reason, photocopiers that work with reflected light are usually provided with a publisher cover that has a white background and which is placed above those publishers smaller than the photocopier's exposure window. However, an overlaid white backing does not perform its function when copying a page in a thick document collection, e.g. in a book, or in other cases where the operator cannot close the lid or cover. Books whose pages are significantly smaller than the copier display window pose a risk of making copies with one or more contiguous black border areas. If one of these edge areas comprises the leading edge of a copy sheet as it passes through the copying process, there is a high probability of a paper feed failure in a contact fastener.

According to the present invention, the apparatus is configured with a light sensor for sensing the instantaneous mean intensity of the reflected light from a representative portion of said strip of the light and a detector means associated with the light sensor and arranged to cooperate. with the purpose of detecting an increase in the mean intensity of the reflected light above a predetermined threshold and, through a delay means whose delay corresponds to the time required for a point on the photoconductive surface to move from the exposure station to the discharge means; controlling a means for changing the density of the evoked image. In such an apparatus, the erasure means known in principle will activate the discharge means in e.g. a deletion lamp at the beginning of a copy cycle to prevent the development of a photoconductor within specific regions outside the preset image area.

During the exposure scan, the sensed mean light intensity is compared to a preset threshold. When the sensed reflected light exceeds the threshold, corresponding to the scanning strip of light striking an edge on a light surface, e.g. a page in a book smaller than the exposure window turns off the unloader and the copying process usually continues. The resulting copy is then given an impeccable white edge which readily passes through the contact combustion apparatus. Moreover, pigment consumption is reduced and the requirement for cleaning is reduced.

The present invention can be practiced in several ways different from the preferred embodiment mentioned above. The image area at the leading edge need not be completely erased to obtain the advantages of the present invention. Thus, by increasing the electrical bias on a magnetic brush in the developer station, a low density image can be provided within the leading edge region, thereby preserving information found on a publisher having a close image near the leading edge. The leading edge image area may also be brightened or eliminated by controlling the transfer station or, if the timing conditions allow, the corona discharge means providing the sensitivity. Although it is preferred that the sensing of the mid-light intensity is effected by means of a light-detecting arrangement mounted on a part with a specific position relative to the scanning area for reflected light, e.g. a scanning lens, other arrangements for the midlight measurement can be used. However, it is important that only light reflected from at least one representative sample of a small cross-scan section across the document window is able to reach the light detector to ensure an accurate time relationship between the threshold detection and the copying process that is the subject of management. It is also possible, albeit more costly and less reliably, to detect the mean light intensity using multiple light detectors located close to the exposure window itself, providing an average circuit for electrically combining the output signals of all detectors prior to the threshold comparison.

The invention will be explained in more detail below with reference to the drawing, in which: FIG. Figure 1 shows a simplified design of an electrophotographic photocopier or printing apparatus utilizing cutting edge density control in accordance with the present invention; 2 is a block diagram of the controller in accordance with the present invention; FIG. 3 is a perspective view of a separate light sensing device in accordance with the invention; and FIG. 4 is a diagram of a suitable threshold detector which can be used in the embodiment of FIG. 2.

FIG. 1 shows an electrophotographic photocopier 10 containing a rotatable image generation drum 11 having a photoconductive peripheral surface 12 movable along a copy generation path 12a past electrostatic imaging means comprising a sensitizing charging corona means 13, an image exposure station 40, a magnetic exposure station 14, powder image 15 on the surface 12, and a transfer corona station 16, where the powder image 15 is transferred to a copy sheet 17. At a cleaning station 18, any remaining pigment particles are removed from the photoconductive surface 12 before being re-fed past the sensitizing charge corona member 13.

At the exposure station 14, a scanning lens 20 inside a light-tight housing 30 transmits a strip of progressive light reflected from a publisher 19 on the exposure window 31 to the photoconductive surface 12 synchronously with its movement along the path 12a. This progressive image is produced. by movement of e.g. a lens 21, along a scan path 21a which is parallel to one axis of the exposure window 31. The lens 21 is mounted on a carriage 22 which enables scanning, and is carried by suitable rails or tracks 23. The carriage 22 is driven at appropriate speed to provide the advancing image synchronously with the drum 11 via a transmission 24. A flexible membrane 32 surrounds the lens 21 and ensures that only light passing through the lens 21 can reach the photoconductive surface 12. Two normally stationary mirrors 33 and 34 redirect the light received from the lens 21 to the photoconductive surface 12.

To achieve maximum light effect and minimal effect of the curvature of the photoconductive surface 12, only a very narrow strip 25 of the exposure window 31 is projected through the lens 21 at any given time. This is done by means of a stationary incandescent lamp 35 which directs a narrow transverse beam of light via a stationary mirror 36 and a moving mirror 26 towards the exposure wine fly 31 to illuminate only the narrow strip 25. The moving mirror 26 is carried by a carriage 27: and suitable rails or tracks 28 for movement thereof through the transmission 24 and at an appropriate rate for progressive scanning with the illuminated strip 25 through successive portions or image areas of the window 31, in optical terms synchronous with the movement of the lens 21 and the photoconductive surface 12.

At the magnetic brush developing station 40, electroscopic pigment powder is fed to a latent electrostatic charge image produced at the exposure station 14. The developing station 40 contains a magnetic brush assembly 42 with an electrically biased conductive cylinder 44 which acts as a developing electrode and is thus capable of night time operation. to reproduce both halftone areas and large, completely black areas, as well as lines formed images.

The powder image 15 developed at the developing station 40 is transferred to the copy sheet 17 which is applied synchronously with the motion and position of the photo-conductive surface 12. The copy sheet 17 is conveyed from the transfer station 16 by means of a pneumatic conveyor 50 via an image-fixing contact fixing apparatus 51 in which the powder image is permanently attached to the copy sheet. Output feeder drums 52 guide the finished copy sheet to an output pocket 53 for removal. The contact solder 51 consists of a heated solder drum 54 with a built-in heat source and a heated surface 55 which is made of a deformable silicone elastomer with little adhesion to the thermoplastic pigment material in the powder image 15. The solder 51 further includes an auxiliary heater or 56 which guides the copy sheet 17 with the associated powder image in close contact with the heated surface 55.

142634 6

The problem which is intended to be solved by the present invention first arises when a copying publisher is placed on the exposure window 31 such that there is an uncovered portion 29 near the edge of the window 31 which is first searched by the lens 21 A document holder lid 37 is pivotally mounted in connection with the exposure window 31 and has a white background surface portion 38 adapted to cover such areas as the area 24 when placed over a publisher in the form of a thin document on the exposure window. Accordingly, the uncovered edge portion 29 of the exposure window 31 appears most frequently when copying smaller publishers, e.g. a page in a small book, and the thickness of the book prevents the closure of the lid 37. When no document or white background part is available that reflects light from the mirror 36, the lens 21 only projects low light onto the photoconductive surface 12, so that the still heavily charged photoconductive surface 12 arrives at the developing station 40 where it is developed as a large, coherent black area. Without using the present invention, this black area would be transferred to the copy sheet 17 in alignment with its leading edge. A large, black area across the leading edge of the copy sheet has been found to cause a tendency for the sheet to adhere to the firing roller surface 55. When a copy is not properly separated from the firing roller surface 55, paper jams occur, resulting in the disabling of the entire machine 10. Large, dark areas at copy locations 17 other than at the leading edge are less important. Namely, as soon as a proper separation of the leading edge has begun between the output feed rollers 52, the copy sheet can be pulled away from the combustion roll surface 55 if there is a tendency for sticking.

It is known to provide a light source for deleting regions of a photoconductive surface between consecutive image areas for reducing pigment consumption and increasing the life of a filter unit which may form part of a cleaning station 18. According to the present invention For example, an elongated discharge or deletion lamp 60 is disposed between the exposure station 14 and the developing station 40. This discharge lamp 60 is usually intended to "provide the known function of deleting or discharging the photoconductor 12 within the area following the trailing edge of the a first copy and appears in front of the edge of the image area for a subsequent copy.

Insofar as the leading and trailing edges of copies always appear at the same locations of the surface of the drum 11, the control of the discharge lamp 60 may conveniently be provided by a drum position sensor such as e.g. a cam 61 with associated switches 62 and 63. The cam 61 is adapted to close the switch 62 until the front edge of the image area of the photoconductor surface 12 aligns with the discharge lamp 60. The switch 63 is closed until the rear edge of the image area of the photoconductor surface. 12, the discharge lamp 60 passes. As shown in FIG. 2, a switch 64 responds to the closure of the switch 63 by activating the discharge lamp 60. When, as discussed below, the switch 65 senses that the cover 37 has fallen down by being placed in the dotted position shown, the switch 64 responds by closing the switch 62 representative of the leading edge of the car joint to extinguish the discharge lamp 60 so that that this one becomes inactive.

In the present invention, the image density at the leading edge of a copy produced at transfer station 16 is controlled by providing an alternate control of the deactivation of lamp 60. The alternative control according to the invention is preferably selected in that the switch 65 which senses the closure of the lid is placed in the position shown in full lines in FIG. 2 to indicate that the document cover 37 is open. According to the invention, a further sensing means 70 is used for the intensity of the reflected light, which sensing means includes a circuit 80 for detecting the intensity increase of the reflected light up above a preset threshold value for inputting a signal for resetting the switch 64 and deactivating the discharge lamp. 60, after a period measured by a delay circuit 66, which is a measure of the time required for a point on the photoconductor surface 12 at the exposure station 14 to be aligned with the discharge lamp 60.

When the lid 37 is in its upper or open position and the switch 65 is in the fully drawn line position according to FIG. 2, the lamp 60 will remain connected past the leading edge of the image area of the photoconductive surface 12, usually defined by the closure of the switch 62.

The light intensity sensor 70 will sense a low level of light as long as the mirror 26 projects light through the window 31 in areas where light is not reflected by a publisher 19 on the window. When the scanning strip of light from the mirror 26 reaches the left edge or for the edge of the document 19 /, the light intensity perceived by the sensing means 70 grows rapidly, producing a signal to the delay circuit 66.

The lamp 60 remains operative for discharging the photoconductor surface 12 until the delay time has elapsed, at which time the electrostatic image of the left edge of the publisher 19 reaches a location outside the discharge lamp 60. At the expiration of the delay time, the cut-off signal is transmitted to the lock switch 64, which turns off lamp 60 and lets the copying process continue in the normal way. Since the leading edge of the image area of the photoconductor surface 12 is discharged by lamp 60, no pigment material will be developed on the photoconductor surface at developing station 40, and no image will be transmitted to the leading edge of copy sheet 17 at transfer station 16. The unpigmented leading edge of the copy will readily pass through the contact burner 51.

Using the switch 65, it becomes possible to copy the entire area of thin documents that may contain dark parts near the leading edge scan area of the exposure window 31.

The light intensity sensor 70 is clearly shown in FIG. 3. This sensing means includes a phototransistor 90 mounted under a collecting lens 71 on a printed circuit surface 72 within a housing 73. The housing 73 includes screen walls 74 and 75 which limit the light supply to the interior of the housing 73 to prevent light from the lamp. 35, see FIG. 1, the phototransistor 90 directly engages. The inclined screen walls 75 limit the extent of the phototransistor 90's field of view in the lateral direction. This field of view should be sufficiently large to provide a usable representative sample of the light reflected from the exposure window 31 to distinguish the presence and absence of a window on the window.

Due to the design of the scanning arrangement, an opening 76 in the side wall 77 of the housing 73 enables the phototransistor 90 to receive reflected light during the entire scanning movement of the lens 21 and the mirror 26. To facilitate the light acquisition from a wide area of the exposure window 31, the lens 71 is mounted directly above Thus, the light collected from a wide area represents a mean intensity of the narrow illumination strip 25 which is particularly well suited to distinguish the presence and absence of a publisher on the exposure window 57.

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As is well known, an incandescent lamp, such as lamp 35, produces a substantial amount of infrared light along with visible light. Preferably, a mirror 36 is used which only reflects the visible light on the exposure window 31, which decreases the tendency for heating publishing 19 on the exposure window 31. The infrared light simply passes through the mirror 36 and is reflected inside the optical arrangement housing 30. The housing 30's inner walls are lined with a smooth black material to minimize internal reflections, but the large amount of infrared light produced by lamp 35 is not completely absorbed. For the purpose of reducing undesired optical interference effects produced by this infrared light, there is a blue filter 78 disposed over the lens 71 which prevents the transmission of infrared light to the phototransistor 90.

The threshold detector 80 carried by the printed circuit board 72 inside the housing 73 is shown in FIG. 4. The detector circuit 80 is provided with a positive energy supply input 81, a negative energy supply input 82 and a ground input 83. The positive input energy is filtered by a resistor 84 and a capacitor 85 and fed to similar circuit branches 91 and 92 to provide corresponding voltages. on wires 93 and 94 which form inputs to an operating amplifier 86 connected via a resistor 87, such as a Schmitt trigger to produce an accurate, fast output signal on a line 88. A circuit branch 91 contains the phototransistor 90 whose mode of operation is changed relative to the applied light intensity, voltage divider resistors 91a and 91b, a base resistor 95 and a load resistor 96. The resistor 91b has an outlet 97 of a variable potentiometer, whereby the threshold for which the circuit 80 responds can be controlled. Thus, a voltage level is provided on line 93 which is a function of the light level intensity delivered to the phototransistor 90 and a specific setting of the threshold control potentiometer output 97. The branch 92 contains voltage divider resistors 92a and 92b as well as a load resistor 98 in addition to a diode 99 which provides forward direction which varies with the ambient temperature in a manner similar to the temperature variation voltage drop across the phototransistor 90, thereby compensating for the effect of the ambient temperature on the signals occurring via lines 93 and 94.

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During operation, the output line 88 usually has a positive voltage as long as the light received by the phototransistor 90 is below the threshold determined by the setting of the potentiometer outlet 97. As the light level rises to and above the threshold, the amplifier 86 negates the voltage of the output line 88, thereby detecting the passage of the threshold. The potentiometer outlet 97 is made adjustable to allow tuning of the individual circuit components used, while at the same time allowing the threshold level of a particular machine to be adjusted after installation thereof, taking into account the general light level in the room immediately near the machine.

The delay circuit 66 may consist of a simple monostable multivibrator whose time constant is set to correspond to the time required by a point on the photoconductor surface 12 to pass from the exposure station 14 to the lamp 60. For such a predictable, constant speed machine, such arrangement satisfactorily. A maximum accuracy can be obtained by using a shear sensing means which operates synchronously with the drum 11 to provide a delay which is measured directly by the motion of the photoconductor 12.

Instead of using the erase lamp, it is possible to reduce the density at the leading edge of a copy being developed by increasing the bias of the magnetic brush roll 42 to a level approaching the charge level of the photoconductive surface 12. It is also possible to selectively control the transfer corona member 16 such that there is no transfer of the heavily pigmented leading edge portion of a copy originating from a small publishing house. The photosensitive arrangement can also be placed other than on a moving lens. Even a stationary light sensing arrangement works satisfactorily if it is arranged so that it substantially uniformly receives a representative sample of the reflected light from the illuminated area of the exposure window 31.