JPS5922934B2 - copying device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a copying apparatus that performs a multi-sheet copying operation in which a plurality of copies are obtained from one electrostatic latent image.

Conventionally, various methods have been proposed for copying apparatuses to obtain a plurality of copies from one electrostatic latent image. but,
In such a copying device, the surface potential of the photoreceptor normally decreases as the number of edge copies increases from when an electrostatic latent image is formed, as shown in FIG. In this case, the image quality of the copy deteriorates, resulting in an undesirable copy. The decrease in the surface potential of the photoreceptor is usually thought to be due to dark decay of the surface potential of the photoreceptor, charge leakage during development, charge leakage during transfer, etc.
Changes in the surrounding environment such as humidity and power supply voltage fluctuations, deterioration of the exposure lamp, dirt on the exposure mirror, etc. may cause the image to become as shown by the dotted line in Figure 1. Therefore, the number of copies with good image quality obtained from one electrostatic latent image also varies, which poses a practical problem. The object of the present invention is to provide a copying apparatus which eliminates the above-mentioned drawbacks and can produce any number of copies with good image quality.

An embodiment of the present invention will be described below with reference to the drawings.

In a copying apparatus that performs a multi-sheet copying operation in which copies are obtained from one electrostatic latent image by multiple repetitions of development and transfer,
The limit at which a desirable image density can be obtained as a copy image is when the surface potential of the photoreceptor is V. As shown in Fig. 1, normally nb copies with a desirable image density can be obtained, but only one copy can be obtained. There is an undesirable difference in image density between the second copy and the nbth copy.

As shown in FIG. 2, there is not much difference in the image density of the copies when the surface potential of the photoreceptor is V2 or higher. Therefore,
If the lifespan of the electrostatic latent image is set to the time until the surface potential of the photoreceptor reaches V2, copies with good image quality can be obtained as long as this lifespan exists, regardless of changes in the decreasing characteristic of the surface potential of the photoreceptor.
In this example, each time the life of the electrostatic latent image set in this way ends, a new same electrostatic latent image is automatically formed, and a desired number of high-quality copies can be obtained from the same original. This will be explained next with reference to FIG.
A document is placed on the document table 1, and the number P of the document to be copied is set in the preset counter 2.

The detector 3 may be one that detects the surface potential on the photoconductor 4. For example, it may detect the surface potential at the end of the photoconductor 4, which is an unexposed, non-image area, or detect the surface potential of a large area area. There is a method that detects the average value of the surface potential and then uses a photoelectric detection device to detect the toner image on the photoconductor after development or the toner image on transfer paper after transfer to detect the reflection density of the toner image. Can be used as appropriate. The life end detection device 5 detects the end of the life of the electrostatic latent image from the output signal of the detector 3, and compares the output signal of the detector 3 with a reference potential VR corresponding to the surface potential 2, for example. in this case,
The reference potential Vs can be arbitrarily set within a range equal to or greater than the value corresponding to 1 above. Further, the detector 3 may be configured to detect the density of the toner image on the photoreceptor or the image yield of the copy. The preset counter 2 is counted or subtracted each time a copy is obtained, and the control device 6 uses signals from the preset counter 2, end-of-life detection device 5, print switch, etc. Each device in the device is controlled to perform the following operations. If the surface potential on the photoreceptor 4 is s when forming an electrostatic latent image, then if the number of copies obtained by the time s reaches V2 is greater than P, then when the print switch is pressed, the photoreceptor 4 is rotated in the direction of the arrow shown in the figure.

Although this photoreceptor 4 is formed in the shape of a drum, it may also be formed in the shape of a belt or the like. During the first rotation, the photosensitive body 4 is charged by the charging device 7, and the exposure device 8 exposes the document image to form an electrostatic latent image. The exposure device 8 is, for example, a slit exposure device consisting of a document table 1 having a rack 9, a pinion 101 that meshes with the rack 9, a lamp 11, mirrors 12 to 14, and an in-mirror lens 15. 11 lights up and Haraakidai 1
At the same time, the pinion 10 is rotationally driven by the motor 16 to move the document table 1 in the direction of the arrow shown in the figure, and the image of the document is sequentially exposed to the photoreceptor 4 via the mirrors 12 to 14 and the in-mirror lens 15. An electrostatic latent image is formed. Next, the photoconductor 4 is developed by a developing device 17. This developing device may be a two-component developing device using an insulating carrier to suppress the attenuation of the electrostatic latent image, or a dry developing device using a magnetic field toner with medium resistance or higher. A device is preferred. The photoreceptor is then moved from the paper feeder 18 to the guide members 19 to 22 and the roller 2.
Transfer device 27 to the copy paper fed through 3 to 26
transfer the toner image. After the toner image is transferred to the copy paper, the copy paper is conveyed by a belt 28, the toner is fixed by a fixing device 29, and the copy paper is discharged onto a paper discharge tray 30 as a copy. Transfer device 2
For example, the copying paper 7 is pressed against the photoreceptor 4 by a roller 31 to transfer a toner image. In order to reduce attenuation of the electrostatic latent image on the photoreceptor 4, the roller dielectric surface of the roller 31 is charged by a charging device 32 to a predetermined potential of the same polarity as the surface potential of the photoreceptor 4 before the transfer position. The static electricity is removed by a corona charger 33 on the rear side of the transfer position, and a cleaning device 35 using a blade 34
The toner is removed by cleaning. on the other hand,
As devices for cleaning the photoreceptor 4, a static elimination lamp 36, a cleaning device 37 for removing residual toner, and a static elimination corona charger 38 are used, but at this time they are inactive. Next, after the second rotation of the photoconductor 4, the electrostatic latent image forming device consisting of the charging device 7 and the exposure device 8 becomes inactive, and no electrostatic latent image formation operation is performed on the photoconductor 4. A copy is obtained from the electrostatic latent image formed during the first rotation. That is, each time the photoreceptor 4 rotates once, the toner image on the photoreceptor 4 is developed by the electrostatic latent image device 17 on the photoreceptor 4, and the toner image on the photoreceptor 4 is transferred by the transfer device 27 to a copy paper from the paper feeder 18, and a copy is made. The toner is fixed on the paper by the fixing device 29, and the paper is discharged onto the paper discharge tray 30. When the number of copies obtained in this way reaches the set number P, the static elimination lamp 36, the cleaning device 37, and the static elimination corona charger 3
8 operates and the photoreceptor 4 is swept in the R direction, and then the copying operation is completed. Also, the number N of copies obtained until Vs becomes 2
If is less than or equal to P, the same operation as described above is performed until the number of copies reaches N, but when the number of copies reaches N, Vs=2.
When this happens, an output signal is applied from the life end detection device 5 to the control device 6.

Therefore, the static eliminating lamp 36, the cleaning device 37, and the static eliminating corona charger 38 operate to eliminate static from the photoreceptor 4, erase the electrostatic latent image, and remove residual toner. Thereafter, the charging device 7 and the exposure device 8 operate to form the same electrostatic latent image on the photoreceptor 4, and a copy is obtained from this electrostatic latent image in the same manner as described above. In other words, the static elimination lamp 3
6, cleaning device 37, corona charger for static elimination 38,
The charging device 7 and the exposure device 8 become stationary, and each time the photoreceptor 4 rotates, an electrostatic latent image is developed by the developing device 17, and transferred onto copy paper from the paper feeder 18 by the transfer device 27 on the photoreceptor 4. The upper toner image is transferred. The toner is fixed on this copy paper by a fixing device 29 and the copy paper is discharged onto a paper discharge table 30. In this way, each time s=2 and the life of the electrostatic latent image expires, a new electrostatic latent image is formed, and the operation of obtaining multiple copies from that electrostatic latent image is performed according to the set number P. is repeated. When the number of copies reaches the set number, the static elimination lamp 36, the cleaning device 37, and the static elimination corona charger 38 operate to clean the photoreceptor 4, and then the copying operation is completed. It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be applied to, for example, an electrostatic latent image transfer method, and can be implemented with arbitrary modifications without changing the gist.

As described above, the copying apparatus according to the present invention performs a multi-sheet copying operation in which a plurality of copies are obtained from one electrostatic latent image by repeating development and transfer, and the potential of the electrostatic latent image is
The density of the copy image is detected by detecting the density of the toner image or the image density of the copy, and the end of the life of the electrostatic latent image is detected from the output thereof, and a new electrostatic latent image is formed again. It is easy to obtain any number of copies with good image quality, and moreover, it is not affected by the drop in photoreceptor surface potential.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the relationship between the surface potential of the photoconductor and the number of copies, Figure 2 is a characteristic diagram showing the relationship between the surface potential of the photoconductor and the image density of the copy, and Figure 3 is a characteristic diagram showing the relationship between the surface potential of the photoconductor and the number of copies. FIG. 1 is a configuration explanatory diagram of an embodiment of the invention. 3...detector, 4...photoreceptor, 5...
... Life end detection device, 6... Control device.

Claims (1)

[Claims] 1. A photoconductor, an electrostatic latent image forming device that forms an electrostatic latent image on the photoconductor, and development of one electrostatic latent image formed on the photoconductor by the electrostatic latent image forming device and onto copy paper. A copying apparatus comprising: a means for repeatedly performing the transfer to obtain a plurality of copies; and a photoconductor cleaning device that removes static electricity from the photoconductor and cleans it after copying is completed, and a detector for detecting the density of the copy image; and a device that detects the end of the life of the electrostatic latent image from the output of the detector and operates the photoconductor cleaning device and the electrostatic latent image forming device to form a new electrostatic latent image on the photoconductor. A copying device characterized by: