JPH11295941A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely perform density control of a toner image by an image forming device. SOLUTION: This device is allowed to precisely detect a position of a photoreceptor drum 1 surface by forming phase mark M1 on the photoreceptor drum 1 surface, and detecting same by a phase sensor. Since the device is made possible to form plural toner images (patch) for measuring the density on the photoreceptor drum 1 surface, and to correct the density data base on the base data corresponding to that patch, the density control can be precisely performed. As a result, in the image forming device adopting a process cartridge, the need of providing extensive memory in the process cartridge is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as an electrophotographic copying machine and a laser printer.

[0002]

2. Description of the Related Art FIG. 6 shows a schematic configuration of a conventional color image forming apparatus.

A photosensitive drum 1 as an image carrier is driven to rotate in a direction of an arrow R 1 by a driving means (not shown), and is uniformly charged by a primary charger 2. The photosensitive drum 1 is
As shown in FIG. 7, an organic photoconductor layer (OPC) is formed on the outer peripheral surface of a grounded conductive drum base 20 made of aluminum or the like.
Is formed by coating a photosensitive layer consisting of The photosensitive layer is
In order from the inside, there are four layers: an undercoat layer (CPL) 21, an injection blocking layer (UCL) 22, a charge generation layer (CGL) 23, and a charge transport layer (CTL) 24.

Next, a laser beam L based on yellow image information is irradiated from the exposure device 3 onto the photosensitive drum 1,
An electrostatic latent image is formed on the surface of the photosensitive drum 1. When the photosensitive drum 1 further rotates in the direction of the arrow R1, the electrostatic latent image is developed by the developing device 4. The developing device 4 includes a rotary support 4a and four developing devices mounted thereon, that is, developing devices 4Y, 4M, 4C, and 4Bk in which yellow, magenta, and cyan black toners are stored, respectively. . Among these developing devices, a yellow developing device 4Y is arranged at a developing position facing the photosensitive drum 1 by rotation of the rotary support 4a, and causes yellow toner to adhere to the electrostatic latent image on the photosensitive drum 1. Develop as a toner image.

[0005] The intermediate transfer belt 5 (transfer member) includes a primary transfer roller 5a, a driving roller 5b, and a secondary transfer opposing roller 5a.
c, the driving roller 5
With the rotation of b, the photosensitive drum 1 rotates in the direction of arrow R5 at substantially the same speed. The toner image on the photosensitive drum 1 is primarily transferred onto the outer peripheral surface of the intermediate transfer belt 5 by a primary transfer bias applied to a primary transfer roller 5a. At this time, the toner (primary transfer residual toner) remaining on the surface of the photosensitive drum 1 without being transferred to the intermediate transfer belt 5 is removed by the cleaning device 6.

By performing the above-described series of image forming processes, that is, charging, exposure, development, primary transfer, and cleaning, for magenta, cyan, and black other than yellow, a plurality of colors are formed on the intermediate transfer belt 5. The toner images are superimposed.

Next, the transfer material P is fed from the transfer material cassette 8 by the pickup roller 9 at a predetermined timing. At the same time, a secondary transfer bias is applied to the secondary transfer roller 7, and a plurality of toner images on the intermediate transfer belt 5 are collectively and secondarily transferred onto the transfer material P. The transfer material P after the transfer of the toner image is transported by the transport belt 10 to the fixing device 11, where it is fused and fixed. Thereby, a color image is obtained. Note that toner (secondary transfer residual toner) remaining on the intermediate transfer belt 5 without being transferred to the transfer material P
Is removed by the intermediate transfer belt cleaner 13.

The image forming sequence of the image forming apparatus described above is based on the top mark M provided on the intermediate transfer belt 5.
Is detected by the top sensor S, and the signal is used as a timing signal for controlling the operation of the image forming apparatus. In the image forming sequence, the top mark M on the intermediate transfer belt 5 is detected by the top sensor S, and a first color electrostatic latent image is formed on the photosensitive drum 1 from the exposure device 3 at this timing. This electrostatic latent image is primarily transferred as a first color toner image onto the intermediate transfer belt 5 through the above-described development and primary transfer processes. After this process, the top mark M on the intermediate transfer belt 5 passes through the top sensor again, and in accordance with this timing, similarly to the first color, the second color toner image is formed on the intermediate transfer belt 5 by the first color toner image. The primary transfer is performed so as to overlap the image.

As described above, when the toner images are superimposed, there is an advantage that the registration between the colors at the time of the superposition can be minimized by taking the image forming timing from the medium on which the superposition is actually performed. In particular, in the case of superimposing transfer on a medium such as the intermediate transfer belt 5 in which the expansion and contraction cannot be ignored, since the driving speed of the intermediate transfer belt 5 is constant, the expansion and contraction of the intermediate transfer belt 5 becomes apparent as a one-cycle deviation. . For this reason, when a timing signal is detected from a part other than the intermediate transfer belt 5, the deviation of the period directly becomes the deviation of the registration between the colors, so that it is necessary to take the image forming timing from the intermediate transfer belt 5 where the superposition is actually performed. It is considered that the color image forming apparatus is the best.

In the main body of the above-described color image forming apparatus, an optical density sensor 1 is provided so as to face the photosensitive drum 1.
2 are provided. In general, in an electrophotographic image forming apparatus, characteristic fluctuations due to the use environment, the number of printed sheets (image formation sheets) of a developing device and a photosensitive drum, variations in sensitivity during the manufacture of a photosensitive drum, and frictional charging during the manufacture of a toner. The density characteristics of the printed image fluctuate due to variations in the characteristics and the like.

It is difficult to sufficiently stabilize these change and fluctuation characteristics. In particular, in a color image forming apparatus, in order for a user to obtain a desired density and color balance, image forming conditions for four colors of Y, M, C, and Bk must be adjusted. Therefore, prior to normal image formation, a toner image for density measurement (hereinafter, referred to as “patch”) is formed on the photosensitive drum 1 and its optical characteristics are measured, and based on the result, image forming conditions are controlled. Many methods are used.

More specifically, as shown in FIG.
A plurality of patches A are formed on the surface of the photosensitive drum 1 while changing a developing bias which is an image forming condition, and the optical characteristics of these patches A are measured by a density sensor 12 including a light emitting element (LED) 12a and a light receiving element 12b. Detected, the CPU (not shown) calculates the density of each patch based on the detection result, and calculates the developing bias for obtaining a desired density.

(Development Bias Control) A constant halftone pattern is used for the above-described patch A, and control is performed to obtain a development bias so that the optical density D becomes, for example, D = 1.0. Using a constant halftone pattern in this way makes it easier to detect changes in the developing device, photosensitive drum, etc., than when using a solid image for patch A,
This is because it is an effective method for obtaining the uniformity of the line width, and has been widely known.

In addition, using the developing bias obtained by the above-described developing bias control, a patch A having a variable halftone pattern (that is, a patch A having a different exposure light amount or an averaged latent image potential) is developed. A method of measuring the density of each patch A by the density sensor 12 in a similar manner to obtain a γ curve of the light intensity of the photosensitive drum 1 versus the (VS) density and stabilizing the gradation property, so-called γ control. Many are used together.

The γ control is useful for faithfully reproducing a natural image or graphic data in which the density gradually changes. Further, since human eyes are sensitive to the color difference of the intermediate density, it is essential to stabilize the image characteristics of the intermediate density, and from such a viewpoint, these control methods are very effective.

The above-described density control (development bias control and γ control) is performed when the power of the image forming apparatus main body is turned on, when each cartridge (process cartridge, developing device cartridge, etc.) is replaced, at every predetermined number of prints, and the like. .

In performing such density control, factors that guarantee the stability include the accuracy of the density sensor 12 and the stabilization of the density of the photosensitive drum 1 as a base included in the density data of the patch A. can give.

In particular, it is difficult to maintain the initial performance of the density sensor 12 when the light emission amount due to the deterioration of the LED 12a is reduced as compared with the initial state, or when the measurement surface of the sensor becomes dirty with toner or the like. Therefore, the reflectance of the photosensitive drum 1 with respect to infrared light is set to a predetermined value in advance, and the density sensor 12 is calibrated by periodically measuring the density. Such a method is a conventionally known technique for guaranteeing the above-mentioned guarantee factor, and is disclosed in, for example, JP-A-7-36230.

In order to calibrate the density sensor 12 and to stabilize the background density included in the density data of the patch A, the photosensitive drum 1 has the density (infrared light reflectance). It is necessary to stably manufacture the photosensitive drum 1, and thus the cost of the photosensitive drum 1 has to be increased.

In order to solve this problem, a storage means is provided in the process cartridge, and the density fluctuation of the photosensitive drum 1 is recorded in advance at the time of manufacturing, and the density information of the photosensitive drum 1 is read out at the time of density control. There has been proposed an image forming apparatus in which the optical density sensor 12 described above is calibrated in accordance with information on the density, and the contribution of the base is corrected from the density data of the patch A.

[0021]

However, according to the above-mentioned prior art, the following problems occur.

Partial Density Fluctuation in Photosensitive Drum The reflection density information of the photosensitive drum at the time of manufacture is a difference between lots, and the partial density fluctuation in the same drum is buried in the leveled information. Therefore, the reflection density information of the photosensitive drum at the time of manufacturing in the process cartridge is:
This is effective for a routine that converges the value while performing feedback, such as calibration of a density sensor. However, it is also used when calculating the density change of patch A from the obtained density output as follows. There was a problem. That is, in the above-described density control, if the partial variation in the density of the photosensitive drum is negligibly small compared to the density difference between the patches A, no problem occurs. However, for example, when the above-described γ control is performed, However, there is a problem that the density difference between the adjacent density patches A cannot be captured, and the density inversion phenomenon occurs.

Variations in Density Control by Optical Memory Similarly, another problem that cannot be captured in the delicate patch A density variation is the variation in patch A density due to the optical memory of the photosensitive drum. Although the problem exists to some extent in any photosensitive drum, the previously exposed part is
When exposure is performed again after the first primary charging, there is a phenomenon that the potential of the exposed portion (exposed portion potential _VL fluctuates by several%) depending on whether or not the previous exposure was performed. Therefore, the image forming apparatus gradually recovers after a pause, so that the rate of change at the start of the image forming apparatus is the largest, and the rate of change decreases exponentially with respect to the number of exposures. Therefore, in the density control performed at the time of starting the image forming apparatus main body, for example, a plurality of patches A having close gradations are formed over a plurality of rotations of the photosensitive drum to control the gradation. If a part of the patch A is formed at a place where the exposure is performed the last time and a place where it is not, the density of the patch A, which changes monotonously, is reversed, and normal gradation control is not performed. There has been a problem to say.

Therefore, according to the present invention, the density of each toner image is corrected in accordance with the partial density of a portion of the surface of the image carrier on which a plurality of toner images for density measurement are formed, thereby achieving high accuracy. It is an object of the present invention to provide an image forming apparatus which performs density control.

[0025]

According to a first aspect of the present invention, there is provided an image forming apparatus, comprising: an image carrier; an exposure device for forming an electrostatic latent image on the image carrier; An image forming apparatus including: a developing device that attaches toner to the electrostatic latent image to develop the toner image as a toner image; and an optical density sensor that detects a reflection density of the toner image on the image carrier.
Forming a plurality of toner images for density measurement on the image carrier surface, measuring the densities of these toner images with the density sensor, and forming the plurality of toner images on the image carrier surface, respectively. The correction is performed based on the partial density of the portion where the image is present.

An image forming apparatus according to a second aspect is the first aspect.
, A detachable process cartridge having an image carrier, and an image carrier main body to which the process cartridge is mounted, wherein the plurality of toner images for density measurement are formed on the surface of the image carrier. And a storage means for storing the partial density of the portion in the process cartridge.

According to a third aspect of the present invention, there is provided the image forming apparatus according to the first aspect.
In the surface of the image carrier, the partial density of the portion where the plurality of toner images for density measurement are formed is measured prior to the density measurement of the plurality of toner images for density measurement, and the measurement is performed. The measurement values of the plurality of toner images for density measurement are corrected in accordance with the values.

[0028] The image forming apparatus according to the fourth aspect is the first aspect.
4. The image forming apparatus according to claim 3, further comprising: a transfer body onto which the toner images are transferred so as to overlap each other, wherein the transfer body has a top mark serving as a reference of an image forming sequence, and the transfer body rotates along with the rotation of the transfer body. When an image forming apparatus that forms an image using the top mark rotation count is encountered, a plurality of toner images for density measurement are formed on the surface of the image carrier, and the densities of these toner images are measured by the density sensor. In the density control sequence for controlling the image forming conditions based on the measurement result, the top mark rotation count is not used.

According to a fifth aspect of the present invention, in the image forming apparatus according to the first, second, third or fourth aspect, prior to the density measurement of the plurality of toner images for density measurement, The exposure is performed by the exposure device.

[0030] The image forming apparatus according to the sixth aspect is the fifth aspect of the invention.
In the step of exposing the image carrier with the exposure device, the step of forming a plurality of toner images for density measurement on the surface of the image carrier, and measuring the densities of these toner images with the density sensor Is performed.

[Operation] The main operation (operation according to claim 1) based on the above configuration is as follows.

The measured density values of the plurality of toner images for density measurement are calculated based on the partial densities of the portions of the surface of the image carrier on which the plurality of toner images for density measurement are formed.
By correcting based on the background density of the portion where a plurality of toner images are formed, the density of the toner image can be accurately detected even when the surface of the image carrier fluctuates.

[0033]

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

First Embodiment FIG. 1 shows an example of an image forming apparatus according to a first embodiment. FIG. 6 is a longitudinal sectional view showing a schematic configuration of the laser printer.
The same reference numerals are given to the same members and the like as those of the conventional example shown in FIG. 1 and the overlapping description is omitted, and the parts different from the conventional example are mainly described.

The image forming apparatus shown in FIG. 1 includes an electrophotographic drum-type photosensitive member (photosensitive drum) 1 as an image carrier. In the vicinity of the photosensitive drum 1, a phase sensor S1 is provided as means for grasping the phase of the photosensitive drum so as to face the surface of the photosensitive drum 1. A phase mark M1 is provided in a non-image portion on the surface of the photosensitive drum 1, which is a surface facing the phase sensor S1.

In the present invention, when measuring the density of patch A,
The measurement is performed while linking the density data and the phase data of the patch A. Therefore, prior to patch A density measurement,
If the relationship between the background data and the phase data for the surface of the photosensitive drum 1 has been created in advance, the density of each patch A can be corrected with an accurate background density by checking the data link.

The relationship between the background data and the phase data is as follows:
It only has to exist as data when detecting the density of patch A,
For example, this data may be stored in the process cartridge from the time of manufacture. However, prior to density detection, the density on the photosensitive drum 1 on which the patch A has not been formed is measured by a density detection sensor, and the density of the background and the phase are measured. A data table may be created. When this method is used, there is no need to prepare a large amount of data in the process cartridge, so that there is an advantage that the memory capacity can be reduced.

By using the above-described configuration, each patch A can be corrected by the density at the position where the patch A is actually formed on the surface of the photosensitive drum 1. The above-mentioned problem caused by the density fluctuation can be solved.

<Embodiment 2> FIG. 2 is a timing chart of a sequence of density control in Embodiment 2,
5 shows a timing chart of a conventional density control sequence. In the density sequence of the present embodiment, unlike the conventional density control sequence, a top mark (top signal) on the intermediate transfer belt 5 is included in a top signal that is a basis of each operation such as exposure, development, and density detection. Not from
A pseudo top signal (pseudo clock) obtained by integrating an internal clock (internal timer) in the control device (CPU) is used. For this pseudo top signal, the frequency of the internal clock in the CPU is used, and a value equal to three cycles of the photosensitive drum 1 is used. The above-mentioned problem is not a problem if the density control target has a means for grasping the position, since the position of the patch A to be created can be accurately grasped. However, as described above, the operation control of the image forming apparatus is not performed. If the reference top mark does not exist on the object (photosensitive drum 1, intermediate transfer drum 5, etc.) for which density control is to be performed, it is difficult to specify the position. Such a defect is particularly remarkable in the case where the size of the top mark changes due to durability, such as the intermediate transfer belt 5, and the gear ratio of each of the drive units of the object having the density control and the member having the top mark is an integer. Even if it has a double rotation period, the phase gradually shifts due to a change in the circumference of the object. Therefore, the above problem cannot be solved unless the phase of the object to be controlled is permanently equal to that of the object to be controlled. Is required separately, resulting in an increase in the size of the apparatus and an increase in cost.

FIG. 3 shows how a patch A is formed on the photosensitive drum 1 according to the present embodiment.

FIG. 3 shows a patch A which is rotated from an arbitrary position on the photosensitive drum 1 in the circumferential direction and formed according to the sequence shown in FIG. In the figure, the dotted line in the vertical direction represents the cycle of an arbitrary position developed in the circumferential direction, and the first and second rounds of the photosensitive drum 1, respectively.
Is equivalent to

In this embodiment, a method is used in which a 14 mm × 14 mm patch A is formed on the photosensitive drum 1 having a diameter of 46.7 mm such that the distance between adjacent patches is 2 mm.
A method of creating nine patches A per circumference is used.
Prior to the patch creation, the background density is read over three revolutions of the photosensitive drum 1. First, in the first round, the average value of the background density over the entire circumference of the photosensitive drum 1 during production stored in the storage means in the process cartridge is equal to the value of the density sensor in the image forming apparatus main body. Is used to automatically correct the density sensor so that after the second week, the background density data corresponding to the portion where the patch A is actually formed is converted to a color toner having a different optical characteristic with respect to infrared light. It is used to measure each of the black toners.

The formation of a similar patch A is performed by using a center length of 440 m.
m, when the intermediate transfer belt 5 having an error of ± 2 mm including the permanent distortion is formed based on the conventional top signal, the top signal 1 ( Since the timing is taken from FIG. 2), the error of the intermediate transfer belt 5 is not included. Therefore, the position of the photosensitive drum 1 can be accurately grasped. However, in the fifth and subsequent weeks thereafter, a deviation of the circumference error of the intermediate transfer belt 5 ± 2 mm occurs, and the partial density fluctuation is corrected. Requires the phase sensor S1 as described above. The deviation is remarkable especially in the case where the size of the top mark changes due to durability, such as the intermediate transfer belt 5, and the gear ratio of each of the drive units of the object having the density control and the member having the top mark is an integral multiple. Even if it has a rotation cycle, the phase gradually shifts and becomes larger due to a change in the circumference. Therefore, unless the phase of the object whose concentration is to be controlled is permanently equal,
The phase sensor S1 is required. Although FIG. 7 shows an example in which the belt is stretched, when the belt is contracted, the position of the patch A is shifted in the opposite direction.

On the other hand, in the present embodiment, since the operation is performed even after the fourth week based on the pseudo top signal equal to three periods of the photosensitive drum, the position of the patch A to be actually produced and the position of the patch A prior to this are described. Deviation from the background position where the density was measured is less likely to occur.

The applicants have determined errors in driving the photosensitive drum 1, the accuracy of the pseudo top created from the frequency division of the internal clock in the CPU, the positional accuracy between the density sensor in the image forming apparatus main body and the photosensitive drum 1, and the like. And the deviation between the position of the patch A and the measurement position of the base in the present embodiment was verified. As a result, it was found that the deviation was within about 100 μm at the maximum. This value corresponds to the edge of the square patch A,
When the density measurement is actually performed, this corresponds to a part to be ignored in order to exclude the fluctuation due to the edge effect at the time of development.

<Embodiment 3> According to the above-described Embodiment 2, partial density fluctuation on the photosensitive drum 1 can be excluded and accurate density control can be performed. However, after the image forming apparatus has been left for a long time, only if the density was controlled, because the initial fluctuation of the exposed portion potential V _L as described above is large, it does not solve the problem that the concentration of the image printed by a continuation of this control will deviate from the predetermined concentration. The problem is, for example,
When the density control was performed with Y, M, C, and Bk, the fluctuation range during the density control of Y and M was large, and the influence of the C and Bk on the density control was negligible.

The applicant measured the virgin drum (new photosensitive drum 1) in a low-temperature and low-humidity environment where the potential variation was the largest, and as a result, the difference between the first and second exposure portion potentials _VL was about 30 V The second and third times are about 8
V, about 3 V for the third and fourth times, and 1 V or less thereafter. Further, after the photosensitive drum 1 in which the fluctuating potential is 1 V or less is left for 30 minutes, 1 hour, 4 hours, 8 hours, 12 hours, and 24 hours, respectively, the difference between the first and second exposure unit potentials _VL is calculated. As a result of the measurement,
V or less (30 minutes), 1V, 2V, 3V, 7V, 14V
(24 hours), and the fluctuation of the exposure portion potential _VL until about 8 hours later does not affect the image control, that is,
When the density control was performed on the photosensitive drum 1 in a state where the fluctuation was 1 V or less, the result was found to be effective even when printing was performed after about 8 hours.

Therefore, the idle state of the image forming apparatus is 8
As long as the time does not elapse, if the surface of the photosensitive drum 1 is exposed three times or more by any method before the density control, a good image can always be obtained.

Therefore, in the present embodiment, as shown in FIG. 4, prior to the step of performing image control, the exposure device is forcibly turned on for three rotations of the photosensitive drum 1 to change the exposure portion potential _VL . Was suppressed. Further, if printing is not performed for a maximum of 4 hours or more, for example, a so-called energy-saving mode or sleep mode is provided in which power other than reception of a signal from the host computer is shut off. Added sequence. Further, the use status of the process cartridge can be stored in the storage device in the process cartridge, and the CPU of the image forming apparatus main body determines whether the process cartridge has been used before. Density control was performed.

As a result, it is possible to solve the problem that has occurred immediately after the virgin drum and the state of a long-term pause.

<Embodiment 4> Since the forcible lighting of the exposure apparatus in the above-mentioned Embodiment 4 may be performed before the patch A is produced, there is no problem when the potential of the photosensitive drum 1 becomes _VL. If there is no situation, you may do it at any time. Therefore, as shown in FIG. 5, when the background density of the photosensitive drum 1 is measured, the forced exposure can be performed in parallel (see sensor correction of density detection, color toner base in FIG. 5). As a result, the time for performing the density control can be reduced, and the walk-up time required until the start of the image forming apparatus can be reduced. Of course, when this method is used, it is desirable to use a method such as applying a holding bias and separating the developing device so that the toner does not fly from the developing device.

[0052]

As described above, according to the present invention,
By correcting the densities of a plurality of density-measuring toner images (patches) based on the partial densities of the portions of the image carrier that form the patches, the respective patch density data correspond to the patches. Since the correction can be made based on the background data, the density control can be performed with high accuracy. Thus, in the image forming apparatus using the process cartridge, it is not necessary to provide a huge memory in the process cartridge.

In addition, only when the density control is performed, the operation of the image forming apparatus is controlled based on the integration of the internal timer in the control device without using the top mark on the transfer body (the intermediate transfer drum 5 in the above description). , The position of the object to be controlled (image carrier such as a photosensitive drum) can be grasped with high accuracy, thereby solving the problem of density control due to the fluctuation of the background density for each patch with a simpler configuration and at lower cost. can do.

Further, by forcibly exposing the image carrier in advance before performing the density control, it is possible to improve the potential fluctuation caused when the image forming apparatus returns from the long-term sleep state.

As described above, accurate density control can be performed with a simple configuration (low cost), and high-quality images can be stably supplied at low cost.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment.

FIG. 2 is a diagram showing a density control sequence according to a second embodiment.

FIG. 3 is a diagram illustrating a patch creation position according to the second embodiment;

FIG. 4 is a diagram showing a density control sequence according to a third embodiment.

FIG. 5 is a diagram showing a density control sequence according to a fourth embodiment.

FIG. 6 is a longitudinal sectional view showing a schematic configuration of a conventional image forming apparatus.

FIG. 7 is a longitudinal sectional view showing a part of the photosensitive drum.

FIG. 8 is a longitudinal sectional view showing a configuration of a density sensor.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Image carrier (photosensitive drum) 2 Primary charger 3 Exposure device 4 Developing device 5 Transfer member (intermediate transfer belt) 6 Cleaning device 7 Secondary transfer roller 11 Fixing device 12 Density sensor A Density measurement toner image (patch) M Top mark M1 Phase mark S Top sensor S1 Phase sensor

Claims (6)

[Claims] An image bearing member, an exposure device for forming an electrostatic latent image on the image bearing member, a developing device for attaching toner to the electrostatic latent image and developing the electrostatic latent image as a toner image; An image forming apparatus comprising: an optical density sensor for detecting a reflection density of a toner image on a body; forming a plurality of toner images for density measurement on the surface of the image carrier; An image forming apparatus that measures by a density sensor and corrects based on a partial density of a portion of the surface of the image carrier where each of the plurality of toner images is formed. 2. A method according to claim 1, further comprising: a detachable process cartridge having an image carrier; and an image carrier main body on which the process cartridge is mounted, wherein the plurality of toner images for measuring the density on the surface of the image carrier. 2. The image forming apparatus according to claim 1, further comprising: a storage unit configured to store a partial density of a portion where the image is formed, in the process cartridge. 3. A partial density of a portion of the surface of the image carrier on which the plurality of toner images for density measurement are formed,
2. The method according to claim 1, wherein the measurement is performed prior to the density measurement of the plurality of toner images for density measurement, and the measured values of the plurality of toner images for density measurement are corrected according to the measured values. The image forming apparatus as described in the above. 4. A transfer member on which a toner image is transferred so as to be superimposed, the transfer member having a top mark serving as a reference of an image forming sequence, and a rotation count of the top mark accompanying the rotation of the transfer member. An image forming apparatus for forming an image by using a plurality of toner images for forming a plurality of toner images for density measurement on the surface of the image carrier, measuring the density of these toner images by the density sensor, based on the measurement result 4. The image forming apparatus according to claim 1, wherein, during a density control sequence for controlling image forming conditions by using the top mark, a round count of the top mark is not used. 5. 5. The image according to claim 1, wherein the image carrier is exposed by the exposure device before the density measurement of the plurality of toner images for density measurement. Forming equipment. 6. A step of exposing the image carrier with the exposure device, wherein a plurality of toner images for density measurement are formed on the surface of the image carrier, and the densities of the toner images are measured by the density sensor. The image forming apparatus according to claim 5, wherein the image forming apparatus is performed in parallel with the step.