JPS60189766A - Image density controller - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an image density control device for an electrophotographic copying machine.

(Prior Art) When copying using an electrophotographic copying machine, if the original original image is light, it is necessary to copy it darker than usual. A typical electrophotographic copying machine is provided with an adjustment device for this purpose. Image density or copy density varies depending on many factors, such as charge amount, exposure amount, development bias voltage, transfer voltage, developer characteristics, photoreceptor characteristics, etc. In a normal electrophotographic copying machine, the exposure amount or developing bias voltage value is changed by moving an adjustment knob provided on the operation section to adjust the "k'"-density. However, the microcopy density Once set appropriately, it will not remain that way forever.Especially when continuous copying is being performed, the photoreceptor may become fatigued due to temperature rise, etc., and as the number of copies increases, The image density decreases.For this reason, conventionally, in addition to a manual copy density adjustment device using an operation unit, there has been a method for detecting photoreceptor fatigue, as described in Japanese Patent Laid-Open No. 52-110046, for example. Therefore, devices have been proposed that automatically control the exposure amount, developing bias, etc. according to the degree of fatigue of the photoreceptor.However, in such conventional image density control devices, the parameters representing photoreceptor fatigue are Since there are several parameters such as temperature, photoconductor residual potential, and number of copies, photoconductor fatigue cannot be correctly corrected by controlling only one of them, and if a plurality of parameters are used, the control becomes complicated.

Recently, electrophotographic copying machines have also become available on the market in which the developing section is unitized and developers of different colors can be exchanged for each unit, allowing copies to be made in any color other than black, such as red, blue, or yellow. When copies are made using such a copying machine, background stains are most noticeable in black, while yellow and other stains are hardly noticeable. On the other hand, colors such as yellow must be developed a little darker, otherwise the image will be thin and hard to see. Therefore, better quality images can be obtained by developing at a high bias for black development and at a low bias for yellow development than by developing at the same development bias. Apart from this, since the physical properties of different colors of developers will naturally differ, the amount of charge on the toner will vary depending on the developer, and developing with the same bias voltage will not produce the optimal image density. I can't do it. Therefore, in such a copying machine, it is necessary to readjust the developing bias according to each color, and if you add the above-mentioned correction due to photoreceptor fatigue, the control becomes difficult! It has to become complicated.

(Object of the Invention) The main object of the present invention is to provide an improved image density control device for an electrophotographic copying machine that can maintain an initially set image density for a long time while correcting deterioration due to photoreceptor fatigue, etc. It is in.

Another object of the present invention is to provide an electrophotographic copying machine in which developers of different colors can be interchangeably used, and which can control the developing bias and/or exposure amount and charge amount for each color to obtain an appropriate image density. An object of the present invention is to provide an image density control device.

(Structure of the Invention) An image density control device according to the present invention reproduces a reference density pattern consisting of a high density area and a low density area provided in a non-image area of a document table on a non-image area of a photoreceptor, and reproduces the image. In addition to photoelectrically detecting the density, the developing bias voltage is controlled according to the difference or ratio between the output ratio of the image density of the high density area and the image density of the low density area and a predetermined reference value. ing.

An embodiment of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, an original 2 to be copied is placed on the upper surface of the original platen glass 1, and a reference density pattern 3 consisting of a high density area 3a and a low density area 3b is placed on the lower surface of the non-image area on the side thereof. It is provided. An exposure optical system 10 consisting of a thermal light lamp 4, a mirror 5, 6, 7, 8, a lens 9, etc. is disposed below the document table glass 1, and below the exposure optical system 10, an exposure optical system 10 having a photoconductive insulating layer on the surface is arranged. A photosensitive drum 11 is arranged.

When the photosensitive drum 11 rotates at a constant speed in the direction of the arrow, its surface is first uniformly charged to a predetermined polarity by the charging charger 12, and then the surface is charged to the original platen glass 1 by the exposure optical system 1o.
Exposure scanning of the upper original 2 is performed, and the original image is transferred to the photoreceptor 1.
The images are sequentially projected onto one surface. As a result, the electrical charge on the photoreceptor 11 is selectively dissipated depending on the brightness of the original image.
An electrostatic charge pattern corresponding to the original image, that is, an electrostatic latent image, is formed there. On the surface of the photoreceptor 11, undischarged charges remain in the image area other than the used original 2, so this is the erase lamp 1.
After being erased by step 3, the electrostatic latent image formed is transferred to developing device 1.
The image is developed with the developer 15 supplied from 4. The developer 15 is a two-component developer consisting of toner and carrier, which is mixed and stirred by an impeller 16, transferred to a developing roller 17, and supplied to the surface of the photoreceptor 11. Development is performed by attracting only the toner in the developer 15 to the electrostatic latent image, and new toner is replenished from the toner replenishing device 18 in an amount corresponding to the consumed toner. The toner image formed on the photoreceptor 11 by the development is then transferred to a transfer paper by a transfer device (not shown), the residual toner on the photoreceptor 11 is removed by a cleaning device, and the residual potential is erased by a static eliminator. be done.

On the other hand, the reference density pattern 3 provided on the lower surface of the non-image area of the document platen glass 1 is scanned simultaneously when the exposure optical system 10 scans the document, and its grayscale image is similarly charged in advance by the band charger 12. The electrostatic charge pattern is projected onto the non-image area of the photoreceptor drum 11, and an electrostatic charge pattern corresponding to the light and shade of the area is formed. This electrostatic charge pattern is similarly developed by being supplied with developer 15 from the developing device 14. The density of each of the developed grayscale images is photoelectrically detected by a reflective photosensor 19 consisting of a light emitting element 19a and a light receiving element 19b.

When the image density to be detected is low, the amount of light emitted from the light emitting element 19a reflected from the surface of the photoreceptor 11 increases accordingly, and the amount of light incident on the light receiving element 19b increases. The current flowing through the photo sensor 19 increases, and a signal at a high voltage level is output from the photosensor 19.

Conversely, when the image density is high, the amount of reflected light decreases and the current flowing through the light receiving element 19b decreases, so that the photosensor 19 outputs a signal at a low voltage level.

Therefore, the density of the developed image on the photoreceptor 11 of the reference density pattern 3 having the high density area 3a and the low density area 3b is detected as a voltage difference that changes over time as shown in FIG. 2(A). . High voltage V corresponding to this low concentration portion 3b
The ratio V1/v2 between the V1 signal and the low voltage V2 signal corresponding to the high density portion 3a exhibits a certain value when the copying machine is properly adjusted and operating properly. Therefore, by using this certain value as a reference value C and comparing this value C with the detected vl value, it is possible to know whether or not the copying machine is operating correctly.

For example, as shown in FIG. 2(B), the value V2 when the developed image density signal voltage V2' corresponding to the high density portion 3a is normal.
When v2 is also high, ■1'/v21 becomes smaller than the reference value C, and conversely, as shown in Figure 2 (C), when ■2〃 is also larger than the normal value v2. , y, //to 8// are larger than the reference value C, so by comparing these, it is possible to know the change in the developed image density. As a result, when V+'/v2'< C, the developing bias voltage is lower than in the normal case to increase the developed image density, and when Vl〃/V2''> C, the developing bias voltage is lower than in the normal case. When V17v21<C, the density on the developed image side is also low, so toner is replenished from the toner replenishing device 18 to the developing device 14 shown in FIG. , ■+"/v2">C, it is preferable not to replenish toner. Note that when comparing V+/V2 and C, the difference between the two may be taken or the ratio may be taken.

By comparing V+/V2 and C in this way,
The influence of other factors affecting concentration changes can be excluded. For example, with density detection using a single density pattern, if the photosensor, lens, mirror, etc. are dirty, even if the developer density or developed image density is low, it may be determined to be appropriate. be. In the present invention, in such a case, the values of both v2 and v2 become high, and the ratio thereof becomes smaller than the reference value C, so it is difficult to accurately know the density decrease of both the developer and the developed image. can.

Such concentration detection and concentration control are performed by a control block shown in FIG. That is, the voltage signals (1) and (v2) from the photosensor 19 are amplified by the amplifier 20, and then converted into digital signals by the A/D converter 21 and sent to the central processing unit CP of the computer.
It is input to U22.

In the CPU 22, the ratio between ■ and v2 is calculated according to a command from the read-only memory lJROM 23, and the ratio is compared with a reference value C. The comparison result is input to the drive circuit 24, and the bias power supply The developing bias voltage value applied to the developing roller 17 at step 25 is changed. It also controls the toner replenishing operation of the toner replenishing device 18 as necessary. As a result, when copying the original 2, development is performed under the changed appropriate developing bias voltage. When developing No. 3, it is necessary to always use the reference developing bias voltage value before being changed. Furthermore, if the copying machine is equipped with a development bias switching type copy density adjustment device, the control of the developing bias value by density detection is based on the bias voltage value when the density is adjusted by the operator at that time. It is necessary to do so. In this control, the bias voltage value at that time is read out at any time and temporarily stored in the write memory 26, and the CPU 22 performs calculations based on this.

By the way, as mentioned above, in a copying machine that has a unitized developing device and is configured so that developers of different colors can be used interchangeably, each color of developer has a different reflectance. Even when the image density is appropriate, the detection voltage varies. For example, the detection voltage for a black image as shown in FIG.
As shown in FIG. 3(B), the detection voltage V2 of the high density area 3a becomes higher, and in the case of a yellow image, the detection voltage V2 of the high density area 3a becomes even higher as shown in FIG. 3(C). Therefore, even if the density is appropriate, the above V+ for each color is
/Vz is different, so there is a reference value C unique to each color, and by using this, it is possible to determine the color of the developer currently being developed.

In addition, each developer has a different amount of charge even at the same charging voltage due to the difference in physical properties due to the difference in pigment, and therefore the development density changes even with the same development bias voltage, so the development bias can be controlled individually for each color. There is a need to.

FIG. 4 shows the relationship between developer colors, reference voltage ratios (c=Vl/V2) for each color, and appropriate reference bias voltages. Since the reference voltage ratio increases in the order of yellow, blue, red, and black, the reference bias voltage needs to be increased in the order of yellow, blue, red, and black. Such a relationship is stored in the ROM 23 in FIG. The detection voltage V for that color and the ratio of the v2 signal and the reference value C are compared.

Even in this case, in the case of a copying machine equipped with a developing bias switching type copy density adjustment device, the developing bias control according to the present invention is performed based on the developing bias voltage value selected by the operator at that time. will be carried out. Since the density of the shredded copy also changes depending on the amount of charge and the amount of exposure, it is also possible to control the charge amount or exposure amount instead of the development bias control for each development cut, or to perform a combination of these controls. Good too.

(Effects of the Invention) As described above, the image density control device according to the present invention reproduces a reference density pattern consisting of a high density area and a low density area provided in the non-image area of the document table in the non-image area of the photoreceptor. The image density is photoelectrically detected, and the developing bias voltage is controlled according to the difference or ratio between the output ratio of the image density of the high density area and the image density of the low density area and a predetermined reference value. Therefore, it is possible to correct image quality deterioration due to photoreceptor fatigue and maintain the initially set good image quality for a long time. Further, since it is possible to detect the developer concentration as well as the developed image density, it is possible to perform highly accurate image density control with a simple structure and at low cost. Furthermore, if this invention is applied to a copying machine in which the developer can be replaced with a different color, the color of the developer currently in use can be determined without a special sensor, and the developing bias voltage most suitable for that color can be determined. can be controlled.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an electrophotographic copying machine to which an embodiment of the present invention is applied, FIG. 2 is a graph illustrating the density detection function in an embodiment of the present invention, and FIG. FIG. 4 is a graph illustrating the developer color discrimination function in another embodiment of the present invention. FIG. 4 is a graph showing the relationship between the developer color, reference voltage ratio, and reference bias voltage in another embodiment of the present invention. It is. 1... Original plate glass, 2... Original, 3... Reference density pattern, 3a... High density area, 3b... Low density area, 10
...Exposure optical system, 11...Photosensitive drum, 12...
・Charger, 13...Erase lamp, 14・
・Developing device, 17 ・Developing roller, 18 Toner supply device, 19... Photo sensor

Claims (1)

[Claims] 1. A reference density pattern consisting of a high density area and a low density area provided in a non-image area of a document table; and projecting the reference density pattern onto a non-image area of a pre-charged photoreceptor; A means for developing the resulting electrostatic charge pattern to form a reference density image, which is the same image forming means as the means for forming the original image, and a means for photoelectrically detecting high-density areas and low-density areas of the reference density image, respectively. and a control means for controlling a developing bias voltage value when forming the original image according to the difference or ratio between the output ratio and a predetermined reference value. Device. 2. When developing the reference density electrostatic charge pattern,
An image density control device according to claim 1, which performs the image density control using a predetermined standard developing bias voltage value. 3. In an electrophotographic copying machine equipped with a copy density adjustment device by switching the developing bias value, the developing bias voltage value is controlled based on the bias voltage value at the current copy density set by the operator. An image density control device according to claim 1. 4. In an electrophotographic copying machine in which development is performed by exchanging developers of a plurality of colors, the control of the developing bias voltage value is based on a ratio of the outputs specific to each color and a predetermined reference value. 2. The image density control device according to claim 1, wherein the image density control device performs the image density control based on the difference or ratio of . 5. A patent claim for controlling the amount of charge on a photoreceptor or the amount of exposure during image formation on a document based on the difference or ratio between the output ratio specific to each color and a predetermined reference value. The image density control device according to scope 4.