JPH09244313A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an output image of the desired gradation by selecting a comparative dot image of the desired area ratio, and controlling the image forming condition based on the area ratio of the selected comparative dot image and the reference dot image by a sensor. SOLUTION: A solid reference image is formed on a photosensitive body 1 at the reference surface potential and the reference developing bias potential, and the toner adhesion is detected to set the developing bias potential of the desired adhesion. The comparative dot image of the specified area ratio is formed on the photosensitive body 1 through an operation panel 20 in the set developing bias potential and the standard surface potential, and the area ratio is detected based on the output of an image sensor 10. Then, the reference dot image is formed to detect the area ratio. Difference in the area ratio between the comparative dot image and the reference dot image is obtained, a look-up table which is stored in a memory 14 in advance is referred to, and the surface potential is set based on the difference in the area ratio so that the area ratio of the comparative dot image is same as that of the reference dot image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus such as a digital full-color copying machine which employs an electrophotographic system, which expresses gradations based on the density of dots and lines. The present invention relates to image density control of an apparatus.

[0002]

2. Description of the Related Art Before an image is actually formed on a sheet of paper in an image forming apparatus, an image stabilization process is performed for the same image data so that the density of the image formed on the sheet of paper becomes a constant level. What is known is. The image stabilization process is performed, for example, by forming a reference toner image on the photoconductor, detecting the density of the formed reference toner image with a density sensor, and based on the detection value of the density sensor, the charge amount of the photoconductor and the light source. And the values of parameters such as the developing bias potential used in the image forming process are controlled.

[0003]

The gradation characteristic (brightness) of the output image obtained by the image stabilization process may not be satisfied by some users. In the case where gradation is expressed in terms of density of dots and lines, in order to adjust the gradation characteristics, the size (diameter) of the dots formed on the photoconductor and the toner adhesion amount per unit area ( It is necessary to change the thickness). When the developing bias potential is changed to change the toner adhesion amount, the dot size also changes, and the area ratio of the halftone dot image changes. Further, when the surface potential value is changed to correct the dot size, the transfer efficiency changes accordingly, and the density of the output image becomes unstable. As described above, it is difficult to obtain the gradation desired by the user in the image forming apparatus that expresses gradation by the density of dots and lines.

An object of the present invention is to provide an image forming apparatus that controls gradation of image forming conditions so that a desired gradation can be obtained in the image forming apparatus that expresses gradation by the density of dots and lines. Is.

[0005]

SUMMARY OF THE INVENTION An image forming apparatus of the present invention comprises an exposing means for exposing a uniformly charged surface of a photosensitive member with a predetermined amount of light, and an exposing means for emitting light before an image forming operation. First image forming means for forming a halftone dot reference image composed of various dots on the photoconductor, and a plurality of coarse dots formed by causing the exposing means to emit light at a value obtained by increasing the predetermined amount of light. Selecting means for selecting one of the comparative halftone dot images and the comparative halftone dot image selected by the selecting means,
Except for the amount of light emitted by the exposing means, the first image forming means forms a halftone dot reference image on the photoreceptor under the same image forming conditions as the second image forming means, and the first image forming means exposes the light. The area ratio of the halftone dot reference image formed on the body,
The image forming conditions are set so that there is no difference between the area ratio of the comparative halftone dot image formed on the photoconductor by the second image forming means and the area ratio detected by the detecting means. And control means for controlling. Excluding the amount of light emitted by the exposing means, the area ratio of the halftone dot reference image formed by fine dots formed with a predetermined surface potential and a predetermined developing bias, and the coarse dots selected by the selecting means. By controlling the image forming conditions such as the surface potential so as to eliminate the difference with the area ratio of the halftone dot image, an output image having the brightness corresponding to the area ratio of the selected comparative halftone dot image can be obtained.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described with reference to the accompanying drawings. (1) Configuration of Copying Machine FIG. 1 is a so-called area gradation in which an electrophotographic system, which is an embodiment of the image forming apparatus of the present invention, is used to express the gradation of an image in terms of density of dots and lines. It is a sectional view of a copying machine which adopts the method. A photoconductor 1 as an image carrier having a surface coated with an organic photoconductive material (OPC) is rotatably provided in the direction of arrow A. Further, around the photosensitive member 1, along the rotation direction thereof, the charging brush 2, the surface potential detecting sensor 12, the laser exposure device 3, the developing device 4 having the developing sleeve 15, the image sensor 10, the intermediate transfer member 5,
Also, a cleaner unit 6 is provided. The surface of the photoconductor 1 is charged to a uniform potential by using the charging brush 2 to which a voltage is applied by the charging power supply 7 as the photoconductor 1 rotates. Then, the surface potential detection sensor 12 detects the surface potential V ₀ of the charged photoconductor. The laser exposure device 3 is turned on / off based on the image data, and exposes the uniformly charged surface of the photoconductor 1. An electrostatic latent image is formed on the exposed surface of the photoconductor 1. Developing device 4
Is a developing unit for four colors of cyan, magenta, yellow, and black. Under the control of the printer controller 11, first, the developing unit for cyan is selected to develop the electrostatic latent image formed on the photoconductor 1. To do. The intermediate transfer member 5 is
It is composed of a conductive resin belt, and a transfer voltage V _T having a polarity opposite to that of the toner is applied from a transfer power supply 14 via a current detector 13. The toner image formed on the photoconductor 1 is conveyed to the transfer portion and transferred to the intermediate transfer member 5. Intermediate transfer member 5
The toner remaining on the photoconductor 1 without being transferred to the toner is collected by the cleaner unit 6. The current detector 13
Is used when measuring the resistance value of the intermediate transfer member 5. The steps of charging and exposing the photoconductor 1 and developing in the developing device 4 are repeatedly executed in the order of cyan, magenta, yellow, and black, and the intermediate transfer member 5 is overcoated with toner images of four colors. The toner image formed as a multicolor image on the intermediate transfer member 5 is electrostatically transferred onto a transfer material by a final transfer member (not shown) and is conveyed to a fixing device (not shown), where the multicolor image is transferred. The toner image is fixed on the transfer material. Although an image is formed by the above-described structure, when forming an image, in order to always obtain the same image density for the same data, the surface potential V ₀ of the photoconductor 1 and the developing sleeve are set. Development bias potential V _B applied to the surface of 15
It is necessary to control image forming conditions such as. Therefore, in the present case, the solid reference image 91 and the halftone dot reference image 92 are formed on the photoconductor before the image forming operation, and the image sensor 10 causes the area ratio of the halftone dot reference image 91 (the ratio of dots per unit area to be occupied). ) And the toner adhesion amount (thickness) of the solid reference image 92. The printer control unit 11 controls the surface potential V ₀ of the photoconductor 1 and the developing bias potential V _B based on the detected values and various look-up tables stored in the memory 16 in advance. The configuration of the image sensor 10 and the control of image forming conditions based on the detection value of the image sensor 10 will be described later. Based on the operation of the operation panel 20, the printer control unit 11 sets the overall density of the output image formed on the paper to the input image to be lighter or darker. As will be described later, this density control is performed by changing the area ratio (the ratio of dots per unit area) of the comparative halftone dot image used when executing the control processing of the image forming conditions. That is, the printer control unit 11 sets a predetermined reference image 9 (a solid reference image 92, a halftone dot reference image 91, and a comparison halftone dot having a predetermined area ratio) in the non-developed area on the photoconductor 1 before the image forming process. The image sensor 10 detects the area ratio of halftone dots of the reference image 9 and the toner adhesion amount (thickness) by the image sensor 10. Then, based on the respective detected values and various tables stored in advance in the memory 14, the surface potential V ₀ of the photoconductor 1 and the value of the developing bias potential V _B are set to appropriate surface potential V ′ ₀ and setting the developing bias potential V _'B.

(2) Operation Panel FIG. 2 is a front view of the operation panel 20. Operation panel 2
0 is a display panel 21 that displays the number of copies and the operation status.
A numeric keypad 22 for inputting the number of copies, a start key 23 for starting the copying operation, and keys 24, 25 for setting the area ratio of the comparative halftone dot image used for adjusting the gradation of the output image. And 26. When the key 24 is pressed, the area ratio of the comparative halftone dot image is set to 60% in order to darken the density of the output image as a whole. When the key 25 is pressed, the area ratio of the comparative halftone dot image is set to 50% in order to output an image of standard brightness. When the key 26 is pressed, the area ratio of the comparative halftone dot image is set to 40% in order to brighten the density of the output image as a whole. The details of the adjustment of the gradation of the output image using the comparative halftone image of the set area ratio will be described later.

(3) Configuration of Image Sensor FIG. 3 is a configuration diagram of the image sensor 10. The image sensor 10 is an LED 101 that is a light emitting element that illuminates a reference image formed on the photoconductor 1 at a predetermined angle.
And a photo sensor 102 that is a light receiving element that receives specularly reflected light from the LED 101, and a photo sensor 103 that receives scattered light. Printer control unit 11
Forms the halftone dot reference image 91 shown in FIG. 4 and the solid reference image 92 shown in FIG. 5 in order to control the density of the image forming apparatus. The halftone dot reference image 91 shown in FIG. 4 is a halftone dot image formed by switching the laser exposure device 3 to ON / OFF at a predetermined cycle at the reference surface potential V _0ref and the reference developing bias potential V _Bref . It is a dot image. The area ratio is the ratio of halftone dots (dots) per unit area. The solid reference image 92 shown in FIG. 5 has a reference surface potential V _0ref and a reference development bias potential V _Bref .
It is a solid image formed by keeping the laser exposure device 3 always on. First, in order to detect the thickness of the toner adhered on the photoconductor 1, a solid reference image 92 is formed, and the LED 1
The scattered light of 01 is detected by the photo sensor 103. Then, in order to detect the area ratio of the halftone dot image, the halftone dot reference image 91 is formed on the photoconductor 1 and the specularly reflected light from the LED 101 is detected by the photosensor 102. That is,
The solid reference image 92 is formed by the first rotation of the photoconductor, and the scattered light is detected by the photosensor 103, thereby detecting the toner adhesion amount with respect to the solid reference image. The halftone dot reference image is formed by the second rotation of the photoconductor, and the area ratio of the halftone dot reference image is detected by detecting the specularly reflected light by the photosensor 102.

The detection of the area ratio of the halftone dot reference image 91 will be described below. FIG. 6 is a diagram for explaining that the intensity of specular reflection light generated by irradiation by the LED 101 changes depending on the size of the dots forming the halftone dot reference image 91. As the dot size increases in the order of (a), (b) and (c), the amount of specular reflection light decreases as indicated by the width of the arrow in (d), (e) and (f). This is because the light incident from the LED 101 is hardly scattered on the surface of the photoconductor on which toner is not adhered, and most of the light is specularly reflected, whereas most of the toner image is scattered and toner adheres. This is based on the characteristic that the amount of light in the specular reflection direction is smaller than that of the surface of the photoconductor that is not provided.
That is, most of the light detected by the photo sensor 102 is
This is specular reflection light from the surface of the photoconductor 1 on which the toner of the halftone dot reference image 91 is not attached. Therefore, the photo sensor 10
It is possible to check the area ratio of the halftone dot reference image 91 based on the detected value of 2. Note that if the measurement range of the photosensor 102 is limited, the detected value greatly varies depending on the position of the measurement range. In order to stably detect specularly reflected light for more dots, the LED 101 and the photo sensor 102 do not have much directivity, and
It is preferable to widen the incident angle of 101 with respect to the normal to the photoconductor 1.

The detection of the thickness (adhesion amount) of the toner attached to the photosensitive member 1 will be described below. 7A and 7B are diagrams illustrating that the intensity of scattered light generated by irradiation with the LED 101 changes depending on the thickness of the toner. The directions and lengths of a plurality of arrows shown in the figure indicate the direction and intensity of the reflected light. (A) shows that a large amount of light is diffusely and uniformly reflected when the toner adhesion amount is large, and (b) shows that a large amount of light is reflected in the regular reflection direction when the toner adhesion amount is small. It indicates that the remaining slight amount of light is diffusely reflected. The amount of specularly reflected light tends to decrease and the amount of scattered light tends to increase as the toner adhesion amount increases. Therefore, it is considered that the toner thickness of the solid reference image 92 can be detected based on the amount of regular reflection light detected by the photo sensor 102. However, the photo sensor 1
The light detected at 02 is the sum of specularly reflected light and scattered light. As described above, the amount of specular reflection light decreases as the toner adhesion amount increases, but the amount of scattered light increases conversely. Unlike the halftone dot reference image 91, in the solid reference image 92, the value of these sums changes only slightly with an increase in the toner adhesion amount. Therefore, it is conceivable to give the photosensor 102 directivity and detect only the amount of specular reflection light. This is against the condition required for the photosensor 102 when detecting the area ratio of the halftone dot reference image 91. Is.
Therefore, the image sensor 10 is provided with the photosensor 103 for the purpose of accurately detecting only the scattered light, and the toner thickness is obtained based on the detected value of the scattered light of the solid reference image 92. Note that the photo sensor 103 detects only scattered light and eliminates the influence of specular reflection light as much as possible.
The LED 10 inside the angle formed by 101 and the normal line of the photoconductor 1
It is placed at a position closer to 1.

(3) Control of image forming conditions This copying machine adopts an area gradation method. The laser exposure device 3 uses the image data that has been subjected to the area gradation processing to perform
Value exposure is performed. Here, the size (diameter) of each dot forming the halftone dot reference image formed on the photoconductor may become larger or smaller than a desired value depending on changes in temperature and humidity. When the dot size is large, the ratio of halftone dots per unit area, that is, the area ratio increases and the image becomes dark. The density of the halftone dot reference image also changes depending on the thickness of the dots, that is, the amount of toner adhered per unit area. If the dot size is the same,
The thicker the image on which the toner adheres, the higher the density. FIG.
FIG. 3 is a diagram showing a potential distribution generated on the surface of the photoconductor 1 by exposure by the laser exposure device 3, and illustrates the size and thickness of dots formed on the photoconductor 1 by exposure. The size of the dot and its thickness are
Surface potential V _{0 of the} photoconductor 1 charged by the charging brush 2.
Then, the developing bias power source 8 controls the developing bias potential V _B applied to the surface of the developing sleeve 13.
Before the exposure by the laser exposure device 3, the photoreceptor 1 has a negative surface potential V ₀ , and the surface of the developing sleeve 13 of the developing device 4 has a low potential negative bias voltage V _B (however, | V _B | < ｜
V ₀ | is satisfied) is given. As the photosensitive member rotates, the portion charged to the surface potential V ₀ reaches the portion facing the laser exposure device 3 and when exposed by the laser exposure device 3, the surface potential V ₀ is attenuated to the potential V _I. To do. FIG.
As shown in (a) of, the exposure amount of the laser exposure device 3 is
The surface potential of the photoconductor 1 is adjusted to a value that attenuates to a predetermined maximum attenuation potential V _I. The surface potential V ₀ is detected by the V ₀ sensor 12, which is a surface electrometer. The toner adhesion amount increases in proportion to the developing voltage ΔV = | V _B −V _I |. For example, the toner adhesion amount can be increased by changing the value of the developing bias potential V _B to V ′ _B. Further, as shown in FIG. 8A, when the surface potential V ₀ is increased to V ′ ₀ , the slope of potential change due to exposure becomes steep. When the value of the developing voltage ΔV is constant, the size of the dots formed on the photoconductor 1 changes depending on the value of the surface potential V ₀ .
As shown in FIG. 8B, the diameter of the dot 202 formed when the surface potential is set to V ′ ₀ is smaller than the diameter of the dot 201 formed when the surface potential is V ₀ .
That is, when the developing bias potential V _B is constant, the dot size can be controlled by the value of the surface potential V ₀ . Based on the above characteristics, the printer control unit 11 detects the toner adhesion amount of the solid reference image developed under the predetermined image forming condition and the area ratio of the halftone dot reference image with the image sensor 10, and based on the detected value. To adjust the developing bias V _B and the surface potential V ₀ ,
Stabilize image density.

FIG. 9 is a diagram showing a potential distribution generated on the surface of the photoconductor 1 by the exposure by the laser exposure device 3. The exposure amount of the laser exposure device 3 is adjusted to a value that attenuates the surface of the photoconductor 1 to the maximum attenuation potential V _I. When the exposure amount is further increased without changing the value of the surface potential V ₀ , the region where the potential is attenuated by the exposure is widened in the direction of increasing the size of the dot (the width where the potential becomes the developing bias potential V _B or less). Direction) and becomes, for example, a region indicated by a dotted line. FIG. 10 is a comparative halftone dot image 911 with an area ratio of 50% formed when the exposure amount of the laser exposure device 3 is increased more than usual at the reference surface potential V _0ref and the reference development bias potential V _Bref . As described above, the size of the dot is not limited to the surface potential, but the laser exposure device 3
It can also be controlled by the exposure amount of.

[0013] By changing the value of the development bias potential V _B to V _'B, not only the amount of adhering toner (thickness) increases,
The dot size (diameter) also increases. As shown in FIG. 9, when the variation of the dot size when the value of the developing bias potential V _B is changed to V ′ _B is obtained, the normal exposure amount is L _s , and the exposure amount is increased to increase the exposure. When the potential distribution on the body surface is set to the state shown by the dotted line, it becomes L _b , which is smaller than L _s . This is because, as can be seen from the figure, when the exposure amount is increased more than usual, the slope of the decay of the surface potential becomes steeper. FIG. 11 is a graph showing the area ratio of the halftone dot image when the value of the developing bias potential V _B is changed at the reference surface potential V _0ref . At the reference surface potential V _0ref and the reference development bias potential V _Bref , 100 is a graph of a halftone dot reference image 91 having an area ratio of 50% formed of fine dots formed by the laser exposure device 3 emitting a normal amount of light. 101 is a comparative halftone dot image 9 having an area ratio of 50% formed of coarse dots formed by increasing the exposure amount more than usual.
11 is a graph of 11. As is clear from this figure, the halftone dot image formed by the rough dots formed when the light emission amount of the laser exposure device 3 is increased more than usual is the area ratio with respect to the change of the developing bias potential V _B. There are few variables. The area ratio of a fine dot image of dots formed with a normal exposure amount is unstable with respect to changes in other image forming conditions.

The printer controller 11 controls the solid reference image 92.
After the developing bias potential V ′ _B is set based on the toner adhesion amount of the _above , the area ratio of the halftone dot reference image 91 and the comparative halftone dot image 911 formed at the developing bias potential V ′ _B and the reference surface potential V _0ref . Is detected, and the surface potential V ′ ₀ is set based on the difference so that the area ratios of the halftone dot reference image 91 and the comparative halftone dot image 911 are the same (50%). FIG.
4 is a graph showing the relationship between the density of the input image and the density of the output image. Through the above processing, the relationship between the density of the input image and the density of the output image becomes a linear relationship as shown by the graph 200. 12 and 13 are comparative halftone dot images with area ratios of 40% and 60%, which consist of coarse dots formed by increasing the exposure amount more than usual at the reference surface potential V _0ref and the reference development bias potential V _Bref . It is a figure which shows 912 and 913. Regarding the comparative images 912 and 913, changes in the area ratio when the developing bias potential V _B is changed are graphs 103 and 102 in FIG. 11. Here, the above processing is performed using the comparative image 913 having the area ratio of 60% instead of the comparative image 911 having the area ratio of 50%, and the area ratios of the comparative image 913 and the halftone dot reference image 91 at the developing bias potential V ′ _B. When the surface potential V ′ ₀ is set such that the same, the density of the output image becomes dark as a whole as shown by the graph 201 in FIG. On the other hand, when the comparative image 912 having the area ratio of 40% is used instead of the comparative image 911 having the area ratio of 50%, the density of the output image with respect to the input image becomes light as a whole as shown by the graph 202 in FIG. .

(4) Control of Image Forming Condition FIG. 15 is a control flowchart of the image forming condition which the printer control unit 11 executes before the actual image forming process is executed. First, at the reference surface potential V _0ref and the reference development bias potential V _Bref , the laser exposure device 3 is caused to emit light continuously to form a solid reference image 92 on the photoconductor 1 (step S1). Based on the output of the image sensor 10,
The toner adhesion amount of the solid reference image 92 is detected (step S2). Referring to Table 1, which is a look-up table stored in advance in the memory 14, the developing bias potential V ′ _B that gives a desired toner adhesion amount is set (step S
3).

[Table 1] Set developing bias potential V _'B and the reference surface potential V
_{At 0ref} , a comparative halftone dot image (any one of 911, 912, and ₉₁₃₎ of the area ratio specified via the operation panel 20 is formed on the photoconductor 1 (step S4). Here, when the key 24 is pressed, a comparative halftone dot image 913 having an area ratio of 60% is formed in order to darken the density of the entire image. When the key 25 is pressed, the density of the output image is set to the standard, and therefore the comparative halftone dot image 9 with an area ratio of 50% is set.
11 is formed. When the key 26 is pressed, the comparative halftone dot image 912 having an area ratio of 40% is formed in order to lighten the density of the output image as a whole. The area ratio of the comparative halftone dot image formed on the photoconductor 1 is detected based on the output of the image sensor 10 (step S5). At the developing bias potential V ′ _B and the reference surface potential V _0ref , the halftone dot reference image 9
1 is formed on the photoconductor 1 (step S6). The area ratio of the halftone dot reference image 91 formed on the photoconductor 1 is detected based on the output of the image sensor 10 (step S).
7). The difference in area ratio between the comparative halftone dot image (any one of 911, 912, and 913) and the halftone dot reference image 91 is obtained (step S8). By referring to Table 2 which is a look-up table stored in advance in the memory 14, the surface potential V ′ _{0 at} which the area ratio of the comparative halftone dot image and the halftone dot reference image are the same is set based on the difference of the area ratio. (Step S9).

[Table 2] When the processing in steps S1 to 9 has not been completed for each of the colors cyan, magenta, yellow, and black included in the developing device 4 (NO in step S10), the processing returns to step S1 and is repeated. When the processes of steps S1 to 9 have been completed for all colors (YES in step S10), the control ends. In addition,
In this case, the comparative halftone dot image has an area ratio of 60% and 4
However, the area ratio is not limited to this. For example, the area ratio of the comparison image may be directly designated by the ten key 22.

[0016]

The image forming apparatus of the present invention selects the comparative halftone dot image having the desired area ratio by the selecting means, and the image is formed based on the area ratios of the selected comparative halftone dot image and the halftone dot reference image by the sensor. Control formation conditions. An output image having a desired gradation can be obtained by combining the area ratios of the halftone dot reference image and the comparative halftone dot image.

[Brief description of drawings]

FIG. 1 is a configuration cross-section of a copying machine according to an exemplary embodiment of the invention.

FIG. 2 is a front view of an operation panel.

FIG. 3 is a configuration diagram of an image sensor.

FIG. 4 is a diagram showing a halftone dot reference image.

FIG. 5 is a diagram showing a solid reference image.

FIG. 6 is a diagram for explaining that the intensity of specular reflection light generated by irradiation with an LED changes depending on the size of a dot forming a halftone dot reference image.

FIG. 7 is a diagram illustrating that the intensity of scattered light generated by irradiation with an LED changes depending on the thickness of toner.

FIG. 8 shows a photoconductor 1 by exposure by a laser exposure device 3.
It is a figure which shows the electric potential distribution produced in the surface of.

FIG. 9 is a photoconductor 1 by exposure by a laser exposure device 3.
It is a figure which shows the electric potential distribution produced in the surface of.

FIG. 10 is a diagram showing a comparative halftone dot image composed of coarse dots and having an area ratio of 50%.

FIG. 11 is a graph showing the area ratio of a halftone dot image when the value of the developing bias potential V _B is changed at the reference surface potential V _0ref .

FIG. 12 is a diagram showing a comparative halftone dot image having an area ratio of 40% composed of coarse dots.

FIG. 13 is a diagram showing a comparative halftone dot image having an area ratio of 60% composed of coarse dots.

FIG. 14 is a graph showing the relationship between the density of an input image and the density of an output image.

FIG. 15 is a control flowchart of image forming conditions executed by the printer control unit before the actual image forming process is executed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Photosensitive member 2 ... Charging brush 3 ... Laser exposure device 4 ... Developing device 5 ... Intermediate transfer member 6 ... Cleaner unit 7 ... Charging power supply 8 ... Development bias power supply 9 ... Reference image 10 ... Image sensor 11 ... Printer control unit 12 ... Surface potential detection sensor 13 ... Developing sleeve 14 ... Memory 20 ... Operation panel 91 ... Halftone dot reference image 92 ... Solid reference image 101 ... LED 102, 103 ... Photosensor 911, 912, 913 ... Rough dot net Dot image

Claims (1)

[Claims] 1. An exposure unit that exposes a uniformly charged surface of a photoconductor with a predetermined amount of light, and the exposure unit is caused to emit light before an image forming operation to expose a halftone dot reference image composed of fine dots. One of a plurality of comparative halftone dot images formed of coarse dots formed by causing the first image forming means to be formed on the body and the exposing means to emit light at a value obtained by increasing the predetermined light amount is selected. The selecting means and the comparative halftone dot image selected by the selecting means are formed on the photoconductor under the same image forming conditions as those for forming the halftone dot reference image by the first image forming means, except for the light emission amount by the exposing means. Area ratio of the second image forming means to be formed, halftone dot reference image formed on the photoconductor by the first image forming means, and area of comparative halftone dot image formed on the photoconductor by the second image forming means And a detection means for detecting the rate. Has been such that the difference of each area ratio is eliminated, the image forming apparatus characterized by a control means for controlling the image forming conditions.