JPS58179855A - Pattern forming method in controlling image density of electrophotographic copying machine - Google Patents

Abstract

PURPOSE:To eliminate a detection error due to the difference in size of patterns and to simplify control, by rendering same the positions, shapes, and sizes of the patterns to be formed on a photoreceptor. CONSTITUTION:A sensor pattern 2 has a size of 20mm. in the direction parallel to the axis of a photosensitive drum 8 and 28mm. in its peripheral direction, and when contraction copying is carried out in a magnification of 0.65, a lens 7 is moved toward the drum 8, and the projected image of the pattern 2 on the drum 8 is contracted from an image 15 having 20mm. width at a magnification of 1 to an image 16 having 13mm. width. On the other hand, as for the peripheral direction of the drum 8, the peripheral drum speed is raised from 120mm./sec at a magnification of 1 to 185mm./sec, and the projected image is contracted from 28mm. length of the image 15 to 18mm. length of the image 16. The image 15 is shown by full lines and the image 16 with chain lines, and when it is developed as it is, the difference in pattern size occurs and causes detection errors, so the range hatched (13mm.X13mm.) is set as an image forming range, and its outside parts are destaticized with an eraser 10 to eliminate the difference of the patterns and detection errors.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a pattern on a photoreceptor to control image density in an electrophotographic copying machine.

In an electrophotographic copying machine, one method of controlling the density of a copied image to a desired density is to provide a standard density sensor pattern on the same plane as the document placement surface, and use this as a light source for exposing the document image. The image is exposed to light on the photoconductor using an exposure device, and this is visualized using a developing device for image development. There is a method of controlling the image density by detecting the image as a specific output and using this output to control the amounts that affect the image density, such as the toner density of the developer, exposure, developing bias, and charging conditions. The photoelectric element used in this method is called a P-sensor element and the pattern is called a P-sensor pattern.

The pattern on the photoreceptor used in this control method is created by the same means and process as those used to create an image on the photoreceptor, so it is not suitable as an image control method. However, if the mounting position and dimensional accuracy of the sensor pattern is not good, the position and dimensions of the pattern imaged on the photoreceptor will deviate from the predetermined position and dimensions.
When variable-magnification copying is performed, the size of the pattern is also reduced or enlarged at a variable magnification rate, and there is a drawback that errors occur when density is detected with a photoelectric element provided at a fixed position.

This invention eliminates the above-mentioned drawbacks of the pattern image forming method in the conventional P-sensor image density control method, and makes it possible to maintain the same position, shape and size of the pattern on the photoconductor not only during full-size copying but also during variable-magnification copying. It is an object of the present invention to provide a method for forming a pattern for controlling image density.

Hereinafter, the present invention will be explained in detail based on drawings showing embodiments thereof.

FIG. 1 is a diagram showing an exposure device and the vicinity of a photoreceptor in an embodiment of an electrophotographic copying machine that forms a pattern image by the method of the present invention.

Image tip position 1 of Tact Gates L, the container on which the original is placed
Sensor pattern 2 having a reference density in contact with the lower surface of a
is installed. A known exposure and scanning optical system consisting of a light source 3, a mirror 4, 5, 6 and a lens 7 is provided below the contact glass 1, the scanning range of which extends over the sensor pattern 2 mentioned above. Around the photoreceptor drum 8, in the order of the direction of rotation indicated by the arrow in the figure, there are a charging charger 9, an eraser (partial static eliminator) 1O1, an image exposure position 11. Developing device 12. A P sensor element 13 and a transfer/separation charger 14 are arranged. The rest of the equipment is the same as a conventional general electrophotographic copying machine and will therefore be omitted. In the above erase 10, a light source is provided inside the casing, and static electricity is removed by light irradiation.

The entire surface of the photosensitive drum 8 charged by the charger 9 is irradiated with light by erasing lO except for the image area and a predetermined image forming area of a pattern for image density control, and only that portion is neutralized. At this time, the erase light may also be used for other purposes such as front and rear end erase and site erase.

As described above, an image of the sensor pattern 2 is first formed by the exposure system at the exposure position 11 on the photoreceptor 8, which has been entirely charged by the charging charge 9 and has been neutralized except for the image area and the pattern image forming area. However, since the outside of the predetermined pattern image forming area has been neutralized, if the sensor pattern 2 is made considerably larger than the predetermined dimensions of the pattern on the photoreceptor, even if its mounting position is slightly shifted, Even when the image of the pattern is enlarged or reduced during reduction copying, charges will remain in accordance with the density of the sensor pattern 2 only in a predetermined pattern image forming area that is in a charged state.

Note that the eraser 10 may be provided between the exposure position 11 and the developing device 12. In that case, after the charge in the image area of the sensor pattern 2 is reduced by exposure, the eraser 10 is used to form a predetermined pattern. Since the outside of the imaging range is irradiated with light and the charge is completely removed, the result is the same.

A specific example will be explained below.

The sensor pattern 20 dimension is 2 in the axial direction of the photoreceptor drum.
0, and 28 wings in the circumferential direction of the drum. Since the sensor pattern 2 is placed under the contact glass 1,
Its density (OD) is set to 0.8 so that the amount of light is the same as on glass. Moreover, its mounting position is placed at the center of the optical axis.

Now, if a 0.65x reduction copy is to be made, the lens 7 moves toward the photoreceptor 8 as shown in FIG. The image projected above was an f-elevation 15 with a width of 20 mm at the same size, but is reduced to an image 16 with a width of 13 mm.

On the other hand, in the circumferential direction of the drum, it is 120 ma/se at the same magnification.
When copying is performed by reducing the circumferential speed of drum e to 0,665 times, the speed is increased to 185 W'sec.As shown in Fig. 3, the sensor pattern 2, which has a length of 28 ma in the circumferential direction of the drum, is photosensitive at the same magnification. An image 15 with a length of 28 cm is formed on the body, but when reduced, it becomes an image 16 with a length of 18+u+.

Therefore, as shown in FIG. 4, the image of the sensor pattern projected onto the photoreceptor is 20 r as shown by the solid line 15 at the same magnification.
u X 28 U, 13 y shown by chain line 16 when reduced
X 18U, if it is developed as it is, there will be a difference in the size of the resulting pattern, which will cause a detection error.

Furthermore, if the size of the image when reduced is set to a predetermined size, the image when magnified at 100% will be large, which will place a burden on the IJ=ing unit. When enlarging copying, the size becomes even larger.

However, in the present invention, the range (13 ma x 13 y) shown by /S latching in FIG. Even when reduced, the size of the developed image is 13w x 13m, which eliminates detection errors due to differences in pattern size and reduces the burden on the cleaning device. Furthermore, since the image range is determined by partial static elimination, as long as the erase accuracy is achieved, there is no need to improve other mounting accuracy. Erasing accuracy can be achieved by simply controlling the irradiation timing (on/off accuracy) of the erase light, and as a result, a pattern image of the same shape can always be obtained at the same position. In particular, if the variable magnification mechanism is a mechanism in which only the optical system is changed, the drum rotates at a constant speed, so the on/off timing of the erase light can always be controlled using the same program, making control easier. .

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the main parts of an electrophotographic copying machine that performs cross-turn image formation according to the method of the present invention, and FIGS. be. l...Contact glass (original placement surface) 2...Sensor patterns 3 to 7...Image exposure means 8...Photosensitive drum 9
...Charging charger 10...Erasing (optical static eliminator) 12...Developing device 13...Photoelectric element (P sensor element) Fig. 1 14 Fig. 2 Fig. 3 Fig. 4

Claims (3)

[Claims] (1) A sensor pattern with a reference density is provided on the same plane as the document placement surface, the image is formed and exposed on the photoreceptor using an image exposure means, and this is visualized using an image development means. In the above method for forming a pattern on a photoreceptor in a control method in which the density of the obtained pattern is detected as an electrical output using a photoelectric element and this output is used to control the image density, the entire surface is charged by the charging step. In addition to removing static electricity by irradiating light other than image exposure to areas other than the pattern image forming area at a predetermined position and shape on the photoconductor, the area other than the image area on the photoreceptor is removed by at least the above-mentioned method. 1. A pattern imaging method, comprising: forming an image of a sensor pattern in a pattern forming area using an image exposure means, thereby creating an image of a predetermined shape of a brim pattern at a predetermined position. (2) The pattern image forming method according to claim 1, wherein the time of irradiation with light other than the above-mentioned image exposure to remove static electricity is after the charging step and before the exposure step. (3) The pattern image forming method according to claim 1, characterized in that the time of irradiation with light other than the above-mentioned image exposure to eliminate static electricity is after the exposure step and before the development step.