JPS6131458B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a copying apparatus that scans an original and projects and exposes the original image onto a moving photoreceptor, the copying apparatus comprising means for converting the projection magnification of the original image. This invention relates to a variable magnification copying device.

In general, variable-magnification copying devices are often used that can select between full-size copying and reduced-size copying of an original, but in the past, when changing the copying magnification, the scanning speed of the original was changed. For example, when converting from a full-size copy to a reduced copy, the document scanning speed becomes faster than the reciprocal of the reduction magnification compared to the same-size copy. Therefore, in a device that scans a document by moving an optical member such as a mirror, the quality of the parts related to the optical member (particularly the driving force transmission means such as gears and belts, bearings, supporting members, etc.) It is necessary to increase the rigidity,
This is one of the causes of increased costs. Alternatively, it becomes necessary to make the run-up distance of the scanning optical member extra long. Furthermore, in order to cause the scanning optical member to scan faster during reduction copying than when copying at full size, the power consumption of the motor driving the scanning optical member increases.

Second, if a conventional variable magnification copying machine were to be equipped with a sheet document feeder, a speed changeover clutch would be required for the sheet document feeder in addition to the speed changeover clutch for the scanning optical member, which would be unnecessary. It's the economy. Furthermore, as the number of clutches increases, the reliability of the device also decreases. Furthermore, if the feeding speed of such a sheet document feeding device changes, it becomes difficult for the operator to operate the device, especially when feeding a single sheet of document.

Furthermore, no matter what method is used to scan a document, if the document scanning speed changes, there is a problem in that images are likely to be blurred.

SUMMARY OF THE INVENTION Therefore, the main object of the present invention is to provide a copying apparatus that can easily solve the various disadvantages mentioned above.

The variable magnification copying apparatus of the present invention is a copying apparatus that scans an original and projects and exposes the image of the original onto a moving electrophotographic photoreceptor, and is capable of selecting reduction copying in addition to full-size copying. In the photoreceptor,
A photoconductor speed changing means for moving the photoconductor at a lower speed during reduction copying than during full-size copying, a means for charging or neutralizing the photoconductor for forming a latent image, and a photoconductor having a selected electric field strength between the photoconductors. The apparatus is characterized in that it includes a photoreceptor potential control means that changes the intensity to correspond to the speed of movement.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment of a variable magnification copying machine equipped with an automatic sheet document feeder to which the present invention is applied. 1st
In the figure, we will first give an overview of the same size copy. A thick original 1 such as a book is placed on a fixed original table 2 that constitutes an original placing surface. This manuscript is illumination lamp 3
and is optically scanned by a first mirror 4 that moves integrally with this lamp 3, and a second mirror 5 that moves in the same direction at 1/2 the speed of this first mirror 4, Then, by an optical system consisting of a fixed in-mirror lens 6 and a fixed mirror 7, the image is formed on a drum 8 rotating in the direction of the arrow. The surface of the drum 8 is an electrophotographic photosensitive surface formed by laminating an electrically grounded conductive layer, a photoconductive layer, and a surface insulating layer, and a well-known method can be used to form a latent image thereon. . For example, the residual charge on the surface of the drum 8 is uniformly erased by the pre-charger 9,
Then, it is uniformly charged by a primary charger 10,
Next, when reaching the image forming section 11, the original image is exposed to light as described above, and at the same time, the static electricity is removed by the static eliminator 12.Then, the entire surface is exposed by the full surface exposure lamp 13, and an electrostatic latent image is formed on the drum surface. It is formed. Next, the latent image on the drum surface is visualized by a developing roller 15 to which an antifogging bias voltage is applied, which is disposed in a developing device 14 using a liquid developer.

The latent image on the drum is usually visualized by toner contained in the developer, but in order to increase the adsorption power of this toner to the drum surface, a weak corona discharge is applied immediately after development to coat the drum surface. A post charger 16 for charging is provided. The visible image on the drum is sent from the paper feed section 18 or 19 by a transfer charger 17, and the copy paper is fed out by register rollers 20, 21 so that its leading edge coincides with the leading edge of the visible image on the drum. 22. The transferred copy paper is separated from the drum by a separating section 23, guided to a fixing section 24, fixed thereon, and then discharged onto a tray 25. On the other hand, the drum surface is pressed against the drum surface and rotates in the opposite direction to the drum. It is pre-cleaned by the cleaning roller 26 and then completely cleaned by the cleaning blade 27, making it possible to perform the next cycle again.

The solid line positions of the first mirror 4 and the second mirror 5 indicate the travel start positions for document scanning, and the two-dot chain line positions 4' and 5' indicate the positions when the maximum size document is scanned. When the scanning of the original on the original platen 2 is completed, the mirrors 4 and 5 move back from the positions 4' and 5' to the above-mentioned starting position.

Next, the automatic sheet document feeding section 37 will be described. When a sheet original copy command is received, the first mirror 4
The second mirror 5 moves to a position where a standard white plate 35 (described later) can be exposed onto the drum 8, and immediately returns to the starting position when the exposure is completed. By exposing the standard white plate 35, the bias value of the developing roller 15 is set as described later. Thereafter, the second mirror 5 is moved to the position 5'' in the figure, and the optical path for exposing the original image on the original platen 2 is eliminated, and an optical path for exposing the sheet original image is formed.The sheet original 38 is placed on the sheet original mounting table. The sheet original 38 is placed with the copy side facing down on the sheet document 39.The sheet original 38 is fed one by one from above by feeding rollers 40, 41.Feeding rollers 40, 4
The sheet original fed by 1 enters the window 42 facing the lens 6, is illuminated by the illumination lamp 43, and its image is projected onto the in-mirror lens 6 and the fixed mirror 7 (in the case of reduction copying, the in-mirror lens 6' and the fixed mirror). The drum is exposed to light at the exposure section 11 via an optical path consisting of 7'). That is, the sheet original is conveyed through the window section 42 and optically scanned. For forming a latent image on the drum, the same method as when copying a thick original using the original platen 2 can be used. After that, the sheet original is placed in tray 44.
discharged inside. When the entire sheet original 38 has been copied, the second mirror returns to the 5'' position.

The sheet document is placed in the window 4 in the sheet document feeding device mentioned above.
2 is conveyed speed (scanning speed of sheet original)
The scanning speed of the document on the table 2 (the forward movement speed of the first mirror 4) is the same.

In the apparatus described above, when a reduction copy command is issued using a copy button or the like (not shown), the in-mirror lens 6 is selected instead of the in-mirror lens 6, and the in-mirror lens 6 is placed at the top of the drawing (or at the front). (rear) side, and an in-mirror lens 6' is placed in the optical path. That is, the in-mirror lenses 6 and 6' are fixed to one member movable in a direction perpendicular to the drawing. In this embodiment, the in-mirror surfaces of the in-mirror lenses 6 and 6' are on the same plane, and the optical path center of the in-mirror lens 6' is arranged in advance so as to be located slightly below the in-mirror lens 6. Simultaneously with the movement of the in-mirror lens, the fixed mirror 7 comes to the position 7' while keeping the mirror surfaces parallel. In this way, the first mirror 4, the second mirror 5, the in-mirror lens 6', and the fixed mirror 7' operate the optical system for reducing and copying the original on the original platen 2. When the mirror 5 is rotated to the 5'' position, The in-mirror lens 6' and the fixed mirror 7' constitute an optical system for reduction copying when the sheet original feeding device 37 is used.

The difference in light amount between the normal magnification and reduction can be solved by making the in-mirror lens 6' darker than the in-mirror lens 6 in advance.

After the reduction copying optical system is configured as described above, when copying the original 1 on the stand 2, the mirror 4,
5 travels as described above, and when copying the sheet original 38, the mirror 5 is retracted to the 5'' position and each feeding roller of the feeding device 37 rotates to convey the sheet original as described above. The image of the desired original is exposed onto the photosensitive drum 8, but in both cases, the original scanning speed is the same as when copying at the same size.In other words, regardless of the selected copying magnification, the mirror 4 .

That is, during the aforementioned original size copying, the peripheral speed of the drum 8 is the same speed as the document scanning speed, but during reduction copying, the peripheral speed of the drum 8 is the speed equal to the original scanning speed multiplied by the reduction copying magnification, that is, the same speed. Converted when the peripheral speed is lower than the peripheral speed during copying. And at the same time copy paper 2
2, for example, rollers 20, 21, etc., convert the copy paper transport speed from the speed for full size copying to the speed for reduced copying.

The conveyance speed of the copy paper 22 is the same as the circumferential speed of the drum 8. To change the speed of the drum 8 and the copy paper conveying device, as shown in FIG. This is achieved by transmitting the information to the paper transport device 49.

In the above-described apparatus, even if the circumferential speed of the photoreceptor changes between full-size copying and reduction copying, the bright and dark potentials of the electrostatic latent image formed on the photoreceptor remain the same when copying the original. On the other hand, both when copying at the same size and when copying at a reduced size,
A means is provided for controlling the surface potential of the photoreceptor so that the respective standard values are the same. In other words, by changing the electric field strength between the corona dischargers 10, 12 and the photoreceptor to an intensity corresponding to the selected photoreceptor speed and controlling the corona discharge applied to the photoreceptor, the photoreceptor speed can be increased. Regardless of the conversion, ie, the process speed, a good copy image of the same quality is always obtained.

As the means and method for controlling the surface potential of the photoreceptor, those already disclosed in detail in Japanese Patent Application No. 53-103038 can be used, so only a brief explanation will be given here. This control method uses a surface potential sensor 28 to measure the surface potential of the photosensitive drum 8 during the previous rotation of the drum, feeds it back, and corrects it to maintain a constant surface potential of the drum when the original image is exposed. This is a method to keep it within the standards. Note that the pre-rotation of the drum 8 refers to rotating the drum 8 a predetermined number of times before scanning the original and projecting and exposing the image onto the photoreceptor when copying the desired number of sheets from the desired original. After this pre-rotation is completed, the original is scanned a set number of times, and the image thereof is exposed to the photoreceptor to obtain the desired number of copies.

Now, in FIG. 3, while rotating the drum 8 at a speed corresponding to the selected copying magnification, a reference current is applied to the primary charger 10 and the static eliminator 11, respectively, to determine the bright and dark potentials of the drum surface. are alternately measured by the sensor 28. The blank exposure lamp 13 is turned on when measuring bright area potential, and is turned off when dark area potential is measured. Signals of bright area potential and dark area potential detected by the sensor 28 are amplified by an amplifier circuit 30 and input to an arithmetic control circuit 31.

The control circuit 31 compares a preset target potential constant 32 with the signal detected by the sensor 28, calculates the difference, and adds a correction current calculated according to a preset correction formula to the reference current. Then, this added current passes through the primary high-voltage power supply 33 and the static eliminator power supply 34 to the primary charger 1, respectively.
0 and is applied to the static eliminator 12.

In this way, of the reference current plus the correction current, one corresponding to the dark potential is applied to the primary charger, and one corresponding to the bright potential is applied to the static eliminator. The reference current plus the correction current becomes the reference current for the next control (the next time the drum front rotates). After repeating the above-mentioned control during the previous rotation of the drum,
Eventually, the surface potential of the drum 8 comes to fall within a predetermined standard. After this state is reached, scanning of the original and projection of its image onto the photoreceptor at the selected magnification is started.

Target potential constant signal generation means 32 in the control device
The signal is converted according to the copying magnification. That is,
This signal is converted so as to reduce the voltage applied to the corona dischargers 10 and 12 by a value corresponding to the reduction magnification compared to when copying at the same size during reduction copying where the photoreceptor speed is slow as described above.

In this way, both when copying at the same size and when copying in reduced size, the bright area potential of the latent image for the same original is the bright area potential, and the dark area potential is within the specified standard range, so that a good copied image is always obtained. is obtained.

In FIG. 1, in both the case of copying the original on the stand 2 and the case of copying the original by the feeding device 37, the standard white plate 35 is moved to the lamp 3 immediately before scanning the original and exposing it to the photoreceptor.
The photoreceptor is irradiated with a standard exposure amount, and the surface potential at this time is measured by the sensor 28. Based on this measured value, the control circuit 31 calculates a voltage that will not cause fogging on the drum during development. , is applied to the developing roller 15 via a developing bias power supply 36 (see FIG. 3). It should be noted that this developing bias control is performed both when copying at the same size and when copying at reduced size.

In the embodiment shown in FIG. 1, the configuration is such that one type of reduction copy can be performed for the same-size copy, but the present invention is not particularly limited to this, and two or more types can be used. Stepless reduction is possible by changing the configuration of the optical system, etc.

In the embodiment shown in FIG. 1, the table 2 on which the thick original 1 is placed is fixed, and the original is scanned by moving the mirrors 4 and 5.
may be fixed, and the document 1 may be scanned by moving the table 2. Furthermore, the present invention is not limited to a transfer type so-called plain paper copying device, but can also be applied to a copying device that uses photosensitive paper and fixes a toner image directly onto the paper.

As described above, according to the present invention, it is possible to adopt a power-saving motor or the like as a drive source because it is only necessary to assume that the load during full-size copying is the maximum. Furthermore, since the circumferential speed of the photoreceptor decreases during reduction copying, the copying paper feeding speed naturally decreases, and the heat source of the fixing device can also be reduced accordingly.

Furthermore, since it is sufficient to consider in advance that the maximum load is applied to the transmission means such as gears, chains, belts, etc., and bearings, etc. during full-size copying, there is no need to increase the special strength as in conventional machines. Despite this, high quality reproduction images can be obtained with high reliability. Furthermore, since the document scanning speed is not changed, image blurring can be easily prevented. Furthermore, since the run-up distance of the scanning optical member is exactly the same when magnified and reduced, there is no need to provide an extra run-up distance even if a reduction function is added, and there is no need to increase the size of the main body.

Furthermore, in the case of a copying machine that uses a sheet document feeder as described above, the document scanning speed has conventionally been changed in accordance with the selected copy magnification, so it is necessary to change the optical member traveling speed for scanning thick documents. Although both a clutch and a clutch for changing the feeding speed of the sheet original were required, according to the present invention, only a clutch for changing the speed of the photoreceptor is required (the copy paper conveyance device is linked to the photoreceptor). ) is very economical. Moreover, since the number of clutches is reduced, the stability of the device is improved.

[Brief explanation of the drawing]

FIG. 1 shows one embodiment of a variable magnification copying machine equipped with an automatic sheet document feeder using the present invention.
The figure is a diagram for explaining speed switching, and FIG. 3 is a diagram for explaining potential control on the drum surface. 4...First mirror, 5...Second mirror, 6,
6'...In-mirror lens, 7...Fixed mirror,
8...Photosensitive drum, 10...Primary charger, 12...
...Static eliminator, 15...Developing roller, 28... Potential sensor, 31... Arithmetic control circuit, 37... Sheet original feeding device.

Claims (1)

[Scope of Claims] 1. A variable-magnification copying device that scans an original and projects and exposes the original image onto a moving electrophotographic photoreceptor, in which reduction copying can be selected in addition to full-size copying. , means for changing the speed of the photoreceptor for moving the photoreceptor at a lower speed during reduction copying than for full size copying; means for charging or neutralizing the photoreceptor for forming a latent image; and means for controlling the electric field strength between the photoreceptor. A variable magnification copying apparatus comprising: photoconductor potential control means for changing the intensity to a level corresponding to a selected photoconductor movement speed.