JPH02230265A - Image forming device - Google Patents

Abstract

PURPOSE:To increase the image forming speed while holding the accuracy of each detecting operation high by isolating a density detecting means and a surface potential detecting means at least at right angles to the moving direction of the photosensitive surface of a photosensitive body. CONSTITUTION:A photosensor 35-6-1 is arranged on the downstream side of a developing unit 31-15 and a surface potential sensor 35-7-1 is provided on its upstream side while shifting in position in the axial direction of the photosensitive body 31-13. By this arrangement, the detection range of the photosensor 35-6-1 and the detection range of the surface potential sensor 35-7-1 are set on the surface of the photosensitive body 31-13 as two belts which are isolated at a sufficient axial interval for the removal of mutual interference. Therefore, the interval of electrostatic latent images for image formation is only set according to one area which is longer in the moving direction. Consequently, the image forming speed can be increased while the accuracy of each detecting operation is held high.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus that forms an electrostatic latent image on the photosensitive surface of a photoreceptor, develops it, and transfers it to a recording medium, and in particular, The present invention relates to a technique for detecting the surface potential of a photoreceptor and the concentration of a developer.

■Prior art Electrostatic transfer type image forming apparatuses consist of a photoreceptor, a charging device that uniformly charges the photoreceptor surface of the photoreceptor, and a latent image that forms an electrostatic latent image on the charged photoreceptor surface in accordance with recorded information. It is equipped with an image forming device, a developing device that develops the electrostatic latent image, and a transfer device that transfers the developed image to recording paper, and sequentially performs image forming processing while moving the photosensitive surface. There is.

In this case, the uniformity of charging on the photosensitive surface and the stability of the developer concentration in the developing device greatly influence the quality of the reproduced image on the recording paper. Therefore, it is effective to monitor the charged potential of the photosensitive surface and the developer concentration.

FIG. 9 shows a portion of a printer that monitors the charging potential of the photosensitive surface and the developer concentration of this type. This system is equipped with a surface potential sensor and a photosensor that face the photoreceptor, and adjusts the charged potential by comparing the surface potential of the photosensitive surface detected by the surface potential sensor with a reference potential, and The developer concentration is adjusted by comparing the density of the developed image corresponding to the pattern with a reference density.

Of course, the area detected by the surface potential sensor on the photosensitive surface and the area detected by the photosensor are set between the front and rear latent latent images that contribute to recording, and these developed images are not transferred to the recording paper. do not have.

(2) Problems to be Solved by the Invention In the conventional example described above, the surface potential sensor and the photosensor are arranged in series with respect to the moving direction of the photosensitive surface. Here, the area where the surface potential sensor detects the surface potential (hereinafter referred to as the potential detection area) is a predetermined area immediately below the area A, and the area where the photo sensor detects the developed image density (hereinafter referred to as the density detection area). ) is a predetermined area B immediately below it, then areas A and B must be separated in the direction of movement of the photosensitive surface to avoid interference with each other. That is, as shown in FIG. 10a, a density detection area is spaced apart in the direction of movement of the photosensitive surface between the rear end of the latent image corresponding to the previous image and the front end of the latent image corresponding to the subsequent image. and a potential detection area is set.

Currently, for detection with sufficient reliability, 20 mI
Assume that a concentration detection area with a length of I+ (referring to the length in the moving direction of the photosensitive surface) and a potential detection area with a length of 50 mm are required. In this case, if the moving speed of the photosensitive surface is 901III18 and 10 sheets of A4 paper are printed per minute, the distance between the rear end of the first latent image and the front end of the next latent image will be 120 m. As shown in FIG. 10a, each area can be set with sufficient margin.

However, when the printing speed is increased to 10 sheets per minute, the spacing becomes 60 mm, and the regions interfere with each other as shown in FIG. 10b.

That is, in the past, printing speed had to be sacrificed in order to increase the accuracy of potential detection and density detection, and the accuracy of potential detection and density detection had to be sacrificed in order to increase the printing speed.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that has high accuracy in detecting the density of a developed image corresponding to a predetermined pattern and detecting the surface potential of the photosensitive surface of a photoconductor, and has a high image forming speed.

■Means for Solving the Problems In order to achieve the above objects, the present invention includes: a photoreceptor; a charging means for uniformly charging the photosensitive surface of the photoreceptor;
A latent image forming means for forming an electrostatic latent image according to recorded information on a charged photosensitive surface; a developing means for developing the electrostatic latent image; and a transfer means for transferring the developed image onto a recording medium; In an image forming apparatus that sequentially performs image forming processing while moving a photosensitive surface, an electrostatic latent image corresponding to a predetermined pattern is formed on a portion of the photosensitive surface of the photoreceptor that is uniformly charged by the charging means. A pattern latent image forming means for forming a pattern latent image forming means for forming an electrostatic latent image corresponding to the predetermined pattern by movement of the photosensitive surface of the photoreceptor; a density detection means for detecting the density of a developed image formed on the surface of the photoreceptor; surface potential detection means for detecting the surface potential of the opposing surfaces;

(2) Effect According to this, since the concentration detection means and the surface potential detection means are separated at least in the direction perpendicular to the moving direction of the photosensitive surface of the photoreceptor, the detection means of each detection means is parallel to the moving direction. You can set an area for In other words, the length of either region in the moving direction. Since it is only necessary to set the interval between electrostatic latent images that contribute to image formation based on the one with the longest value, it is possible to increase the image formation speed while ensuring high accuracy in each detection.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

ΦEmbodiment FIG. 1 shows a color copying apparatus to which the present invention is applied. This color copying apparatus consists of three large blocks: a scanner 1, an image processing section 2, and a printer 3.

(1) Scanner 1: A device that reads a document by dividing it into pixels, and includes a contact glass l1, an illumination lamp 12, and reflection mirrors 13-1 to 13-.
3, a condenser lens 14, a dichroic prism 15, photoelectric conversion elements 1G-1 to 16-3, and a drive control device (not shown).

The illumination lamp 12 illuminates the original placed on the contact glass 11, and each of the reflecting mirrors 13-1 to I3-3 guides the reflected light to the condenser lens 14. The condenser lens 14 condenses the light, and the dichroic prism 15 separates the light into red (R), green (G) and blue (B) and converts it into photoelectric conversion elements 16-1, 16-2 or 16-. 3
irradiate. Each photoelectric conversion element outputs an electric signal corresponding to the intensity of the illuminated light in pixel units, and this electric signal is digitally converted by an A/D converter (not shown) to the image processing unit 2 as read image data of each color. given to.

(2) Image processing section 2: The image processing section 2 processes the read image data of each color to generate reproduced image data of yellow (Y), magenta (M), cyan (C), and black (BK). Both of these data are binary data indicating whether or not each color is recorded in a pixel section, and a description of the generation process will be omitted here.

(3) Printer 3: The printer 3 is a device that reproduces the original image on recording paper based on the reproduction image data of each color.
C, M, Y) image forming systems 3l-1 to 31-4, paper feeding system 32
, transfer system 33, fixing sheet discharge system 34 and control system 35 (second
Figure) etc.

a. Image forming systems 31-1 to 31-4: Since the image forming systems for each reproduction color have the same configuration, the BK image forming system 31-1 will be described here.

The BK imaging system 3l-1 includes a laser emitter 31-1.1 (
(see Figure 2), polygon mirror 31-12, photoreceptor 31
-13. It consists of a charger 31-14, a developer 31-15, a cleaner 31-16, etc. The laser emission Il:i31-11 is controlled on/off based on the BK reproduction image data, and the laser beam is input to the polygon mirror 31-12 via a collimator lens, a cylindrical drill lens, etc. (not shown). The polygon mirror 31-12 is rotated by a motor 31-12-1 and deflects the laser beam in the axial direction of the photoreceptor 31-13 to perform main scanning.

The charger 31-14 is connected to the photoreceptor 3 which rotates in the direction of the arrow]. −
The surface potential of 13 is uniformly charged, and the main scanning forms an electrostatic latent image on that part by exposure and neutralization. Developing device 31-1
Step 5 develops the electrostatic latent image with BK toner.

The cleaner 31-16 removes toner and the like remaining on the surface of the photoreceptor 31-13.

b9 Paper feed system 32: The paper feed system 32 has two stages, upper and lower. In this case, when the upper paper feed is selected, the topmost sheet of recording paper held in the paper feed cassette 32-11 is extracted by the paper feed roller 32-12, and when the lower paper feed is selected, The topmost sheet of recording paper held in the paper feed cassette 32-21 is extracted by the paper feed rollers 32-22 and sent to the registration rollers 32-3. The registration roller 32-3 passes the fed recording paper to the transfer system 33.

C. Transfer system 33: The transfer system 33 includes a transfer belt 33-1 and a transfer device 33-21.
33-24, a static eliminator 33-3, etc.

The transfer belt 33-1 electrostatically attracts the recording paper passed from the paper feed system 32 and conveys it from right to left in the figure. Each transfer device 33
-21 to 33-24 are located directly below the photoreceptor drums of each color image forming system, and when the recording paper passes over them, the toner images on each photoreceptor drum are transferred to the recording paper.

The static eliminator 33-3 removes residual charges on the transfer belt 33-1 and charges generated by transfer. d. Fixing paper discharge system 34: The fixing paper discharge system 34 includes a fixing device 34-1 and a paper discharge roller 34.
-2 magnitude.

When the fixing device 34-1 receives the recording paper on which the toner image has been transferred from the transfer system 33, it heat-fixes it and transfers it to the wandering paper roller 3.
4-2 discharges the recording paper after fixing.

e. Control system 35: The control system 35 consists of a main control section 35-1, a video control section 35-2, various drivers, a high-voltage power supply, and sensors. (.) Video control unit 35-2: The video control unit 35-2 has an independent microprocessor, and under the instructions of the main control unit 35-1, each image forming unit is controlled via the laser driver 35-21. system laser emitter 3
1-11 to 31-41, and motor driver 35-
22, the motors 31-12-1 to 31-42-1 for driving polygon mirrors of each image forming system are controlled.

In this, the control of each laser emitter is as follows. Image processing section 2
The reproduction image data of each color generated by the main control unit 35
This is done based on the pattern data for toner density detection stored in -1, but each control timing is shifted based on the interval between each photoreceptor and the moving speed of the recording paper.
Further, each motor is controlled based on a line synchronization signal and a pixel synchronization signal of reproduced image data.

(b) Various drivers: a motor driver 35-3-1 that energizes the motors for driving the photoreceptors 31-13 to 31-43 of each image forming system and the transfer belt 33-1, the fixing device 34- A heater driver 35-3-2 that energizes the heater No. 1, and clutches 31-15-3 to 31, 45-3 for replenishing toner provided in developing devices 31-15 to 31-45 of each image forming system. There is a clutch driver 35-3-3 etc. that applies the force. (c) Various high voltage power supplies: Charging high voltage power supplies 35-4-1 that energize the chargers 31-14 to 31-44 of each image forming system. Transfer device 3 for each color of transfer system 33
Transfer high voltage electricity g35-4 that energizes 3-21 to 33-24
-2. Transfer devices 33-21 to 33-2 for each color of the transfer system 33
Transfer high voltage power supply 35-4-2. Transfer belt static elimination high-voltage power supply 35 that energizes the static eliminator 33-3 of the transfer system 33
-4-3, a developing bias high voltage power supply 35-4 that applies a developing bias to the developing sleeves 31-15-1 to 31-45-1 provided in the developing devices 31-15 to 31-45 of each image forming system;
-4, and a replenishment bias high voltage power supply 35-4-5 that applies a replenishment bias to the toner replenishment rollers 31-15-2 to 31-45-2 of each of the developing units 31-15 to 31-45.

(d) Various sensors: Thermistor 35-5- that detects the temperature of the fixing device 34-1
1. Wandering paper sensor 35-5-2 that detects paper discharge, paper feed system 3
Paper end sensor 35- for detecting the paper end of No. 2
5-3. Registration sensor 35- for detecting paper feed registration
5-4, a cassette size sensor 35-5-5 for detecting the recording paper size of each paper cassette of the paper feeding system 32; Photo sensor 35 for detecting toner density of each image forming system
-6-1 to 35-6-4. And each photoreceptor 31-13
A surface potential sensor 35 that detects the surface potential of ~31-43
-7-1 to 35-7-4, etc.

Here, the photo sensor 35-6, which is closely related to the present invention, will be described.
-1 to 35-6-4 and surface potential sensor 35-7
Add explanations for -1 to 35-7-4. however,
Explanations regarding these are common to each imaging system, so
Photo sensor 35- provided corresponding to K image forming system 31-1
6-1 and surface potential sensor 35-7-1 will be replaced with the respective explanations.

The photo sensor 35-6-1 consists of an infrared emitting LED and a phototransistor, as shown in FIGS. 4a and 4b, and the LED is connected to the photoreceptor 31 according to pattern data.
The patterned toner image formed on -13 is illuminated, and the phototransistor receives the reflected light. At this time, the output signal of the phototransistor corresponds to the density of the toner image, that is, the toner density in the developing device 31-15.

Further, the surface potential sensor 35-7-1 is a non-contact potential probe, and detects the surface potential of the photoreceptor 3143.

Here, since the potential (VO) of the unexposed portion of the surface of the photoreceptor 31-13 is detected,
Based on the detection signal, the charging strength caused by the charger 31-14 can be evaluated. In this way, the photosensor 35
-6-1 and the surface potential sensor 35-7-1 detect different information even if they detect the surface of the photoreceptor 31-13. It is necessary to set conditions for this. For this reason, the arrangement of each sensor has been devised.

That is, as shown in FIG.
-1 is a surface potential sensor 35 downstream of the developing device 31-15.
-7-1 is provided upstream thereof, and is also disposed offset in the axial direction of the photoreceptor 31-13, as shown in FIG. With this arrangement, on the surface of the photoreceptor 31-13, the range that can be detected by the photosensor 35-6-1 and the range that can be detected by the surface potential sensor 35-7-1 are arranged so that mutual interference can be eliminated in the axial direction. Two bands (hereinafter referred to as detection bands) separated by a sufficient interval are set.

Since the state of the parts of the surface of the photoreceptor 31-13 that belong to each detection band is independent from the state of the parts that belong to the other detection band, even if the projections in the axial direction overlap, the states of the parts of each detection band Conditions for detection of the photosensor 35-6-1 or the surface potential sensor 35-7-1 can be set.

In order to assist in a more specific understanding, reference will be made to a schematic diagram (an example) showing the developed surface of the photoreceptor 31-13 shown in FIG. In this drawing, the surface speed of the photoreceptor 31-13 is 90 m.
m/m, when printing 20 A4 sheets per minute, approximately 60 mm width between the rear edge of the previous image area and the front edge of the subsequent image area (the width of the surface of the photoreceptor 31-13). A region (hereinafter referred to as a concentration detection region) in which conditions contributing to detection by the photosensor 35-6-1 are set within the region (width in the moving direction).

) and a region (hereinafter referred to as a VO detection region) for setting conditions contributing to detection by the surface potential sensor 35-7-i.
This shows that the settings are made without overlapping. In other words, even if the interval between each image area becomes small due to high-speed printing, sufficient density detection areas and vo detection areas are set for each detection. (e) Main control unit 35-1: The main control unit 35-1 controls the video control unit 3s-2, various drivers, high-voltage power supply, etc. while monitoring each unit using the various sensors described above. Therefore, although the control contents are diverse, it should be understood that the explanation here will be limited to the l/ner replenishment control and charging potential control, which are closely related to the present invention. In this case as well, the same type of control is performed for each image forming system, so B
We believe that the explanation of the control corresponding to the K image forming system 31-1 is sufficient.

As described above, the video control unit 35-2 controls the laser emitter 31-11 on/off based on the BK reproduction image data given from the image processing unit 2 under instructions from the main control unit 35-1. At the same time, the polygon mirror 3 is synchronized with the line synchronization signal and pixel synchronization signal of the image data.
1-12 drive motor 31-12-1 is energized and controlled. During this time, the main control unit 35-1 rotates the photoreceptor 31-13 at a predetermined speed in the direction of the arrow in FIG. 1, so that the main scanning and sub-scanning of the laser beam output from the laser emitter 31-11 are repeated. B of the original image is placed on the photoreceptor 31-13.
An electrostatic latent image (hereinafter referred to as a print latent image) corresponding to the K component.
) is formed.

On the other hand, the main control section 35-1 instructs the video control section 35-2 to perform exposure using pattern data for toner density detection every time a predetermined number of sheets are printed. As a result, the video control section 35-2 reads out the internally stored pattern data for toner density detection and controls the laser emitter 31-11 on/off.
An electrostatic latent image (hereinafter referred to as a pattern latent image) corresponding to the pattern is formed on the top. In this case, exposure according to the pattern data is performed only on the detection band of the photo sensor 35-6-1, and the V is applied to a portion whose projection in the axial direction is equal to the detection band of the photo sensor 35-6-1. The detection area is set. Therefore, as shown in the timing chart of FIG. 6a, when the VO detection area moves directly below the surface potential sensor 35-7-1, the V. After detection is performed and a pattern latent image having the same axial projection is developed by a developing device H-15, when the latent image is moved directly below the photo sensor 35-6-1, the density is detected by the sensor. A more detailed explanation of the formation of the pattern latent image will be given with reference to FIG. 6b. A beam detection sensor (see Figure 3) is provided at the near end of the photoreceptor 31-13, and when a laser beam is irradiated thereon, a main scanning synchronization detection signal is output, and from the fall of the signal, main scanning synchronization is detected. The signal is set.

After completing the formation of a predetermined print latent image, the main control section 35-1 sets a mode for performing toner replenishment control and charging potential control when a predetermined number of main scanning synchronization signals are counted. In this mode, the pattern control signal is turned to H level for a time period of t3 seconds after t2 seconds from the rise of the main scanning synchronization signal. This pattern control signal is given to the video control section 35-2, and the video control section 35-2 receives the pattern control signal.
2 reads pattern data while it is at H level and controls on/off of the laser emitter 31-11.

The above t2 seconds corresponds to the time for the main scanning of the laser beam to move from the far end of the beam detection sensor to the near end of the detection band of the photo sensor 35-6-1, and the above t3 seconds corresponds to the time when the main scanning of the laser beam moves from the far end of the beam detection sensor to the near end of the detection band of the photo sensor 35-6-1. This corresponds to the time it takes to move from the near end to the far end of the detection band 31-1. Formed on 3.

FIG. 7 is a flowchart showing charging potential control performed by the main control section 35-1. As shown in this,
When the main control unit 35-1 detects the potential detection timing at which the VO detection area moves directly below the surface potential sensor 35-7-1 by counting the main scanning synchronization signal, the main control unit 35-1 controls the output of the surface potential sensor 35-7-1. When the reading is lower than the reference charging potential, the charging high voltage power supply 35-4-1 is instructed to increase the output, and when it is higher than the reference charging potential, 'r
;Instructs the high voltage power supply 35-4-1 to reduce its output. Further, FIG. 8 is a flowchart showing toner replenishment control performed by the main control section 35-1. As shown in this figure, when the main control unit 35-1 detects the density detection timing at which the density detection area in which the toner image corresponding to the pattern data is formed moves directly below the photo sensor 35-6-1, the main control unit 35-1 LED of photo sensor 35-6-1
Turn it on, read its output, and compare it with the value corresponding to the standard toner density. If it is determined that the toner concentration detected by this comparison is lower than the reference toner concentration, the clutch driver 35-3-3 is connected to the clutch 31 for replenishing BK toner. ．． 15-3 is instructed to be energized, and if it is determined to be high, it is instructed to de-energize it. After this, the photo sensor 35-6-
Turn off LED 1 and end the process. ■Effects of the Invention As explained above, the present invention includes: a photoreceptor; a charging means for uniformly charging the photosensitive surface of the photoreceptor;
A latent image forming means for forming an electrostatic latent image according to recorded information on a charged photosensitive surface; a developing means for developing the electrostatic latent image; and a transfer means for transferring the developed image onto a recording medium; In an image forming apparatus that sequentially performs image forming processing while moving a photosensitive surface, an electrostatic latent image corresponding to a predetermined pattern is formed on a portion of the photosensitive surface of the photosensitive member that is uniformly charged by the charging means. A pattern latent image forming means for forming a pattern latent image forming means for forming an electrostatic latent image corresponding to the predetermined pattern by movement of the photosensitive surface of the photoreceptor; a density detection means for detecting the density of a developed image formed on the surface of the photoreceptor; It is equipped with a surface potential detection means that detects the surface potential of the opposing surface. That is, by applying the present invention, the concentration/detection means and the surface potential detection means are separated at least in the direction perpendicular to the moving direction of the photosensitive surface of the photoreceptor, so that the respective detecting means are arranged in parallel with the moving direction. The area for detection can be set. Therefore, it is only necessary to set the interval between electrostatic latent images that contribute to image formation based on the longer length in the movement direction of either region, while ensuring high accuracy in each detection. , the image forming speed can be increased.

Note that the area detected by the surface potential detection means does not have to be limited to the black level (unexposed level) as shown in the example, and an electrostatic latent image corresponding to a certain pattern is formed. Also good. In this case, the charging potential is evaluated by comparison with a reference potential corresponding to the pattern.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the configuration of a color copying apparatus to which the present invention is applied. 2 is a block diagram showing a part of the electrical configuration of the color copying apparatus shown in FIG. 1. FIG. 3 is a perspective view showing the external appearance of a part of the color copying apparatus shown in FIG. It is a diagram. 4a is a front view showing the external appearance of the photo sensor 35-6-1 provided in the color copying machine shown in FIG. 1, FIG. 4b is a circuit diagram showing its configuration, and FIG. 1
FIG. 3 is a schematic diagram showing the haze distribution of each latent image by developing the photosensitive surface of the photoreceptor 31-13 provided in the color copying apparatus shown in the figure. 6a and 6b are timing charts for explaining potential detection and density detection executed by the main control section 35-1 included in the color copying apparatus shown in FIG. The figure shows the main control section 35-1.
3 is a flowchart for explaining charging potential control and toner replenishment control executed by. FIG. 9 is a perspective view showing the structure of a conventional electrostatic transfer type image forming apparatus near a photoreceptor. Figures 10a and 1
Figure 0b shows the developed photosensitive surface of the photoreceptor shown in Figure 9. FIG. 3 is a schematic diagram showing the arrangement of each 'R image. 1: Scanner 11: Contact glass 12: Illumination lamps 13-1 to 13-3: Reflecting mirror 14: Condensing lens 14 15: Dichroic prisms 16-1 to 16-3: Photoelectric conversion element 2: Image processing unit 3: Printer 31-1 to 31-4: Imaging systems 31-11 to 31-41: Laser emitters 31-12 to
31-41: Polygon mirror-31-12-1 to 31-
42-1: Motor 31-11 to 31-41.31-1
2 to 3+-41: (electrostatic latent image forming means, pattern latent image forming means) 31-13 to 31-43: Photoreceptor (photoreceptor) 31-14 to 31-44: Charger (charging means) 31
-15~31. ．． ．． 45: Developing device (developing means) 31-1
6 to 31-46: Cleaner 32: Paper feeding system 32-11. 32-22: Paper feeding cassette 32-12.
32-22: Paper feed roller 32-3: Registration roller 33: Transfer system (transfer means) 33-1 Transfer belt 33-21 to 33-24: Transfer device 33-3: Static eliminator 34: Fixing paper discharge system 34- 1: Fuser 34-2: Paper ejection roller 35: Control system 35-1: Main control section 35-2: Video control section 35-3-1: Motor & driver (driving means) 35-
3-2.35-3-3: Driver 35-4-1 to 35
-4-5: High voltage power supply 35-5-1 to 35-5-5:
Various sensors 35-6-1 to 35-6-4: Photo sensor (concentration detection means) 35-7-1 to 35-7-4: Surface potential sensor 35-
7-1 ~ (Surface potential detection means)

Claims (3)

[Claims] (1) Photoreceptor; driving means for moving the photoreceptor surface of the photoreceptor; charging means for opposing the photoreceptor surface and uniformly charging the opposing surface; charging the photoreceptor surface of the photoreceptor; A latent image forming means that forms an electrostatic latent image according to recorded information on a portion uniformly charged by the means; a developing means that develops the electrostatic latent image formed by the latent image forming means to form a developed image. and a transfer means for transferring the developed image developed by the developing means to a predetermined recording medium; an image forming apparatus comprising: a portion of the photosensitive surface of the photoreceptor that is uniformly charged by the charging means; pattern latent image forming means for forming an electrostatic latent image corresponding to a predetermined pattern; by movement of the photosensitive surface of the photoreceptor, the pattern latent image forming means can be opposed to a region where an electrostatic latent image corresponding to the predetermined pattern is to be formed; a density detection means for detecting the density of a developed image formed on an opposing photosensitive surface; and a density detection means that is separated from the density detection means at least in a direction perpendicular to the moving direction of the photosensitive surface of the photoreceptor. , a surface potential detection means that faces the photosensitive surface of the photoconductor and detects the surface potential thereof; An image forming apparatus characterized by comprising: (2) Assume that there are two strip-shaped areas on the photosensitive surface of the photosensitive member that extend in the direction of movement and do not overlap with each other, one of which is
when the other band is referred to as a second band, the pattern latent image forming means forms an electrostatic latent image corresponding to the predetermined pattern on a part of the first band, and the surface potential detecting means forms an electrostatic latent image corresponding to the predetermined pattern on a part of the first band. The image forming apparatus according to claim 1, wherein the image forming apparatus faces a portion belonging to the band. (3) Regarding the movement of the photosensitive surface of the photosensitive member, the density detection means is provided downstream of the developing means, and the surface potential detection means is provided upstream of the developing means. The image forming apparatus according to item (1).