JPS6389887A - Copying machine - Google Patents

Abstract

PURPOSE:To inexpensively and surely remove an unnecessary electrostatic latent image by providing the titled machine with a timing detecting means, an electrifier control means, and so on. CONSTITUTION:The timing detecting means detects timing required for the scanning of the leading end of an original by an original scanning means during the period required when a photosensitive body 2 is moved from a charger 4 to an exposure point based on an original rear end scanning timing. On the other hand, the electrifier control means stops the operation of the charger 4 when the timing detecting means detects the timing. Accordingly when the operation of the electrifier 4 is stopped and the rear end of a charge area formed on a photosensitive body 2 reaches the exposure point, electrifier 4 coincides with the timing for scanning the rear end of the original by the original scanning means. Even if the original scanning means continues scanning from the rear end of the original by a fixed distance, only an optical image is led into an uncharged area on the photosensitive body 2 and no electrostatic latent image is formed. Thereby, unnecessary toner is not stucked by a developing device 6.

Description

[Detailed description of the invention] (AL industrial application field The present invention relates to an electrostatic electrophotographic copying machine.

(b1 Summary of the Invention The copying machine according to the present invention includes a photoreceptor, a charger placed close to the photoreceptor, and a document placed on a document table that is scanned and an optical image of the document is charged by the charger. A so-called electrostatic electrophotographic copying machine is provided with a document scanning means for forming an image on an exposed point on the surface of a photoconductor, and the present invention is particularly applicable to an area other than the area where the document image is formed on the photoconductor. The present invention relates to a copying machine that prevents unnecessary toner images from being formed.

(C) Conventional technology In a copying machine that forms a latent image of an original on a photoreceptor by scanning the original, no unnecessary electrostatic latent image is formed on the photoreceptor after the original scanning means scans to the rear edge of the original. We are trying to do this. Conventionally, for this purpose, a white reflective plate was attached to the rear edge of the document table to prevent an electrostatic latent image from being formed on the photoreceptor even if the document was scanned a certain distance past the rear edge of the document. In such a method, if an original smaller than the maximum size that can be copied is placed on the original table, the original is a book, and the original is copied with the original cover open. In this case, as the document scanning means scans the trailing edge of the document, an electrostatic latent image is not continuously formed on the photoreceptor, and as a result, a large amount of toner is wasted.

Therefore, we limited the range of document scanning according to the document size.
There is also a copying machine in which the document scanning means returns immediately after scanning to the rear end of the document. However, even in this case, the document scanning means cannot be stopped immediately at the rear edge of the document, and the photoreceptor moves a certain amount before returning past the rear edge of the document, resulting in unnecessary static movement in that section. A latent image is formed.

In order to completely remove such unnecessary electrostatic latent images, a static elimination lamp is placed between the charger and the developing device to selectively eliminate static electricity from the surface of the photoreceptor, and the static electricity removal lamp is arranged between the charger and the developing device, and the static electricity removal lamp is arranged between the charger and the developing device to selectively eliminate static electricity from the surface of the photoreceptor. There is a method for removing static electricity from an electrostatic latent image formed behind the trailing edge of a document, and a method for removing static electricity using a reflective plate using the irradiation light of a copy lamp, as shown in Figure 6 (A) and (B). be.

6(A) and 6(B) are schematic diagrams of the optical system of the copying machine, and FIG. 6(A) shows a state in which the middle of the document placed on the document table 10 is being scanned, and the document is The light is irradiated by the copy lamp 11, and a light image of the original is formed on the photoreceptor 2 by the lens 13. The document is scanned together with the document table 10 in the direction of the arrow in the figure, and when the document is scanned to the rear end of the document as shown in FIG. The photoreceptor 2 is moved to eliminate static electricity. By providing the reflector S in this way, the document table 10
Even if the document is scanned by passing over the rear end of the document, no unnecessary electrostatic latent image is formed on the photoreceptor.

(d) Problems to be Solved by the Invention However, the above-mentioned method using a static elimination lamp requires a dedicated static elimination lamp and a drive control circuit to drive and control the lamp, resulting in a problem of high cost. Further, in the method using the reflector described above, the mechanism for moving the reflector at high speed is complicated, and high accuracy is required for the angle of the reflector. This invention solves these conventional problems and provides a copying machine that does not require a dedicated static elimination lamp or reflector, is low cost, and can reliably remove unnecessary electrostatic latent images. is intended to provide.

(e) Means for Solving the Problems The copying machine of the present invention includes a photoreceptor, a charger placed close to the photoreceptor, and an S! A copying machine comprising: a document scanning means for scanning a placed document and forming an optical image of the document on an exposure point on the surface of a photoreceptor charged by the charger, based on the document trailing edge scanning timing; , a timing detection means for detecting a scanning timing before the photoreceptor moves from the charger to the exposure point, and a charger control means for stopping the operation of the charger when the detection means detects the timing. (If the configuration has more than one function, the timing detection means scans the front side by the time the photoreceptor moves from the charger to the exposure point, based on the scanning timing of the rear edge of the document. The timing is detected.Meanwhile, the charger control means stops the operation of the charger when the timing detection means detects the timing.Therefore, the charger stops its operation and the charged area formed on the photoreceptor is When the trailing edge reaches the exposure point, the document scanning device scans the trailing edge of the document. In this case, a light image is only guided to an uncharged area, and no electrostatic latent image is formed.Therefore, unnecessary toner is not deposited by the developing device.

FIG. 5 is a conceptual diagram showing the optical system of the copying machine of the present invention. If the distance on the circumference between the position P1 of the charger 4 placed close to the photoreceptor 2 and the exposure point P2 is L, then the scan timing before the photoreceptor moves L based on the scanning timing of the trailing edge of the document is as follows. P3 is located a distance of L/a from the rear edge of the document. Here, a represents the copy magnification. Therefore, by stopping the output of the charger 4 at the timing when the original scanning means scans these 23 points, when the original scanning means scans the rear end of the original, the rear end of the charged area is located at the exposure point P2. .

(Bright Embodiment FIG. 2 is a schematic side sectional view of a copying machine according to an embodiment of the present invention. At approximately the center of the copying machine 1, there is a photosensitive drum formed in the shape of a drum for forming a copy image. The photoreceptor 2 is rotatably held in the figure and rotated clockwise by a drive mechanism (not shown). A static eliminator 3, a charger 4, a developing device 6, a transfer device 7, and a cleaning device 8 are arranged along the rotational direction.

Copy lamp 1 is placed on the top of copying machine 1 after placing the original.
A document table 10 for exposure at step 1 is movably arranged. This document table 10 is scanned left and right by a drive device (not shown). A light image obtained by irradiation by a copy lamp 11 enters a lens 13 from a mirror 12 in an optical lens unit 15, and is projected by a mirror 14 onto a photoconductive layer on the surface of a photoreceptor drum. In addition, lens 1
3 moves as shown by the broken line according to the selected magnification by switching the movement operation means provided in the operation section. As a result, the original image is formed as an electrostatic latent image on the surface of the photoreceptor 2 at a selected magnification, and this latent image is visualized as a toner image by the developing device 6.

Paper 17 is stored in a paper feed cassette 16 and fed out by a paper feed roller 18. The paper feeding timing is determined by a signal from the document scanning means. Then, it is transported from the U-turn transport section 19 to the PS board 23 by transport rollers 22 . In addition, 20 is a manual insertion slot, and paper entry sensor 2
When the leading edge of the paper is detected at step 1, the conveyance roller 22 is driven to rotate, and the manually inserted paper is conveyed to the PS plate 23. Thereafter, at the timing when the leading edge of the toner image and the leading edge of the paper coincide, the PS plate 23 is opened and conveyance of the paper is started. The toner image is transferred onto the paper sent from the conveyance path 24 by the transfer device 7.

Thereafter, the paper is peeled off by a peeling device 25, and the paper is peeled off from the conveyance path 2.
6 to a fixing device 27, where the toner image is fixed onto the paper. Then, the paper is discharged onto the paper discharge tray 28.

In the copying machine configured as described above, timing control of the charger 4 is performed as follows. Figure 4 is on the manuscript table! 3
FIG. 3 is a diagram showing the relationship between a 2M original and scanning points of the original. In this example, in consideration of tolerances, misalignment, and looseness of various parts such as the document scanning system and the photoreceptor, we moved the rear end of the ideal document by a distance of 10 from the rear end of the ideal document (hereinafter referred to as This point is simply referred to as the trailing edge of the document, and the scanning timing is detected and determined based on this point before the photoreceptor moves from the charger to the exposure point. Specifically, the detection is performed as follows.

If the distance from the home position HP of the document table 10 to the above-mentioned 23 points is A, and the distance from the HP point to the rear edge of the document is 0, then it is expressed as A = O-L / a, and the document table can change this distance A. The time t required for moving is expressed by the following formula.

t+=Aa/V = (0-1,/a) a/V = (Oa-L)/V Here, ■ is the moving speed of the photoconductor, a is the copying magnification, and L is the exposure from the charger to the exposure point. Each represents the distance on the body. In this way, the time from the start of document scanning until the charger is stopped can be determined in advance according to the copying magnification.

Note that even if the drive control is stopped, the document table cannot be stopped immediately, and a blank running distance occurs depending on the scanning speed. Therefore, in this embodiment, the document table is stopped tl earlier than the document is scanned to the rear end.

Therefore, the time t2 from when the charger is stopped to when the document table is stopped is determined by the following equation.

t z = t, / v t * Here, ta represents the blank running distance of the document table determined according to the copying magnification.

Further, the copy lamp is turned off when the original is scanned to the rear end of the original. Therefore, the time t3 from when the charger is turned off to when the copy lamp is turned off is determined by the following 2.

t 3 = L / V FIG. 1 shows a block diagram of a control section of a copying machine according to an embodiment of the present invention. The entire control is performed by the program processing of the CPU 50, and the program is stored in the ROM 51.
is written in advance.

The RAM 52 is used as a timer, which will be described later, when executing the program, and as a working area for calculating the various delay times described above depending on the copying magnification. 11053 is a boat that inputs and outputs signals to various input/output devices.

The cassette sensor 54 is a sensor that detects the type of paper feed cassette, the paper position sensor 63 is a sensor that detects when the document table has reached the start position, and the paper entry sensor 21 is a sensor installed in the manual insertion slot. be. The feed solenoid 56 is a solenoid that operates a clutch that drives the document table 10 in the document scanning direction, and the return solenoid 57 is a solenoid that operates a clutch that moves the document table 10 in the return direction. The driver 58 is a circuit that drives these two solenoids. The main motor 59 is a motor that drives the document table, the photoreceptor, other conveyance rollers, etc., and is controlled on and off by a motor controller 60. The copy lamp 11 is controlled on and off by a lamp controller 61, and is controlled by the CPU 50.
outputs a control signal to the lamp controller 61 at necessary timing. The charger 4 is a charger controller 6
2, and the CPU 50 similarly controls the start and stop of the operation at the required timing.

Next, the operating procedure of the CPU 50 will be explained.

FIG. 3 shows the flowchart. First, as mentioned above, the time 1. and calculate t2 (
nl). Note that the size of the document can be determined from the type of paper feed cassette and the copying magnification. After that, the photoreceptor starts rotating and the charger is turned on (n2→n3). Further, the paper is fed to the PS board, the copy lamp is turned on, and scanning of the original is started (n4→n5→n6). When it is detected that the document table has reached the home position, the timer TM is reset and the timer operation is started (n7→n8). When this timer TM reaches the paper transport start timing, paper transport is started (n9→n10). After that, timer T
M continues the timer operation, and stops driving the charger when the value reaches the already calculated value of 1 or more (n11→n
12). Here, the TM is reset again and the timer operation is started (n13). When the timer TM reaches a value of t2 or more, the document table is stopped, and the timer operation is continued thereafter.

When the value of the timer TM reaches the value above L3, that is, when the document has been scanned to the rear edge of the document, the copy lamp is turned off and the return solenoid is driven to return the document table (n17→n18). .

After starting document scanning as described above, the charger is turned off at a specific timing, the document table is stopped, and the copy lamp is turned off.

In the embodiment, the timer is started after the document table has passed the home position to obtain the necessary timing, but it is possible to obtain the necessary timing by using a microswitch, a timing pulse disk, etc. that is linked to the scanning means such as the document table. It is also possible to configure the system so that the necessary timing signals can be obtained by

(h) Effects of the Invention As described above, according to the present invention, even if the document scanning means scans beyond the rear end of the document, the optical image is only formed on the uncharged area of the photoreceptor. , no electrostatic latent image is formed, and wasteful toner consumption is eliminated.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a control section of a copying machine according to an embodiment of the present invention, FIG. 2 is a schematic side sectional view of the copying machine, FIG. 3 is a flowchart showing the processing procedure of the control section, and FIG. 4 5 is a diagram for explaining the timing of document scanning in a copying machine according to an embodiment of the present invention, FIG. 5 is a diagram for explaining the invention in detail, and FIGS. 1 is a diagram illustrating a copying machine equipped with an unnecessary exposure prevention device in the copying machine.

Claims (1)

[Claims] (1) A photoconductor, a charger placed close to the photoconductor, and a document placed on a document table are scanned and an optical image of the document is projected onto an exposure point on the surface of the photoconductor charged by the charger. A copying machine comprising: a document scanning means for forming an image; A copying machine comprising charger control means for stopping the operation of the charger when the means detects the timing.