JP2009265513A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive and effective image forming apparatus which can stabilize and equalize image density without using a high precision member or a high strength member. <P>SOLUTION: The image forming apparatus is constituted so that an electrostatic latent image is formed on a surface of a photoreceptor 1 by image exposure on a charged photoreceptor 1 by an exposure means 3 for which multiple steps of exposure strength can be set, and toner developing is performed by developing a bias from a developing bias source 39 and a toner image is formed on the photoreceptor 1, and the chromaticity of a test pattern for the toner image which is transferred on the photoreceptor 1 or an intermediate transfer belt 5 is detected by three units or more of test pattern sensors 24 arranged in a long direction of the photoreceptor 1, and the developing the bias over the whole length of a developing means 4 by the chromaticity of the test pattern on the charged photoreceptor 1, or at the intermediate transfer belt 5, and exposure strength in the vicinity of spots in the test pattern on the photoreceptor 1 or the intermediate transfer belt 5 can be set. A detection means 38 for detecting a rotational position of the photoreceptor 1 is included in the image forming apparatus. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that sequentially transfers a toner image on an image carrier onto a recording paper carried on a transfer belt or an intermediate transfer member.

In recent years, demand for high productivity for color image forming apparatuses has increased, and as an image forming method, an image forming unit including a plurality of image bearing members and a developing device is arranged in parallel at a position facing a transfer belt or an intermediate transfer member. A color image forming apparatus called a tandem system in which a toner image on an image carrier is sequentially transferred onto a recording paper carried on a transfer belt or an intermediate transfer member has become the mainstream.
In addition, the demand for high image quality is very high as is the case with high productivity. In particular, the image density gradation, the uniformity of the image density on the transfer paper, and the uniformity of the image density between the transfer papers are sensuously good and bad. It is a big factor to judge.
In order to stabilize these, fine image filling by reducing the particle size of the toner and carrier, development-photoreceptor gap uniformity by developing sleeves with high precision and strength, and toner density upstream and downstream of the developer in the developing unit. And the like, and the amount of developer pumped up, the stability of the transfer process for intermediate transfer and paper transfer, etc. are required, and various proposals have been made in order to improve these (for example, Patent Document 1). And 2).

In Patent Documents 1 and 2, a color image forming apparatus called a tandem system and a development gap of 0.4 mm or less are configured to sequentially transfer a toner image on an image carrier onto a recording paper carried on a transfer belt or an intermediate transfer body. An image forming apparatus is disclosed.
Although not a conventional example, in the prior application (Japanese Patent Application No. 2007-81426) of the present applicant, for example, the development gap is larger than the phenomenon in which the central development gap becomes wider than both ends due to the bending due to the nip pressure of the development roller. Proposes uniform technology.
Further, for example, in another prior application (Japanese Patent Application No. 2008-029095) of the present applicant, a technique for increasing the pumping amount in the central portion in order to compensate for the developing roller bending due to the nip pressure and the reduction in developing capacity with respect to both ends. Has proposed.
In addition, with respect to fluctuations in toner density, techniques for optimizing the number of rotations of the developer agitating / conveying screw and increasing the toner replenishment resolution can be cited. The effects of these techniques are high, and the contribution to high image quality in recent years is large. However, on the other hand, an increase in cost for achieving component accuracy and a decrease in production yield are inevitable, and the use of a high-strength material inevitably increases the cost due to the high material.
In response to such a technical problem, although not a conventional example, in another prior application (Japanese Patent Application No. 2007-093168) of the present applicant, three or more on the photosensitive member or the intermediate transfer member in the longitudinal direction of the photosensitive member. A technology that forms a test pattern, uses an optical test pattern sensor, performs image density control based on the measurement result of the toner adhesion amount, and simultaneously corrects the image density in the longitudinal direction of the photosensitive member with laser power. Proposed.
JP 2001-356541 A JP 2003-323050 A

However, a narrow development gap has been advanced due to a demand for high image quality, and in this case, a flare component at a circumferential pitch of the developing roller and the photoreceptor is a major cause of image quality degradation. In order to reduce the flare, it is inevitable that the yield is reduced and the cost is increased due to the higher precision of the parts.
Accordingly, an object of the present invention is to provide an inexpensive and effective image forming apparatus that can stabilize and equalize the image density without using a high-precision member or a high-strength member in consideration of the above-described circumstances. There is to do.

In order to solve the above problems, the invention according to claim 1 is directed to an electrostatic latent image formed on the surface of the photosensitive member by image exposure by an exposure unit capable of setting a multi-step exposure intensity on the charged photosensitive member. And developing the electrostatic latent image with a developing roller to which toner is attached by a developing bias from a developing bias source that generates a potential difference necessary to move the toner to the electrostatic latent image; and The color of the test pattern of the toner image formed on the photosensitive member and transferred onto the photosensitive member or the intermediate transfer belt by a test pattern sensor arranged at least three in the longitudinal direction of the photosensitive member. The development bias over the entire length of the developing means and the test pattern location of the photoconductor or the intermediate transfer belt are detected according to the chromaticity of the test pattern on the photoconductor or the intermediate transfer belt. In the image forming apparatus can be set and the exposure intensity of the near, and wherein the image forming apparatus having a detecting means for detecting a rotational position of the photosensitive member.
According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, further comprising detection means for detecting a rotational position of the developing roller.
According to a third aspect of the present invention, in the image forming method according to the first or second aspect, the developing bias is set according to the chromaticity of the test pattern disposed substantially at the center where the exposure intensity is changed stepwise. Features the device.
According to a fourth aspect of the present invention, the exposure intensity is set from chromaticity and exposure intensity of a test pattern other than the central portion in the set development bias. The image forming apparatus is characterized.
According to a fifth aspect of the present invention, the chromaticity of the test pattern obtained from the set developing bias and the exposure intensity is measured at the developing roller rotating position and / or the photosensitive member rotating position. 5. The image forming apparatus according to claim 3, wherein the exposure intensity at the rotational position is set.

The invention according to claim 6 is the image forming apparatus according to any one of claims 1 to 5, wherein three or more test pattern sensors arranged in the longitudinal direction of the photosensitive member are reflection density detection sensors. And
According to a seventh aspect of the present invention, there is provided photoconductor surface potential measuring means for measuring a potential between the test pattern sensor arranged in the longitudinal direction of the photoconductor and the surface of the photoconductor substantially at the same position. 6. The image forming apparatus according to any one of 6 above.
The invention according to claim 8 is an image forming apparatus according to claim 7, wherein an exposure intensity in the vicinity of the test pattern is set from the photoconductor surface potential measured by the photoconductor surface potential measuring means and the test pattern. It is characterized by.
According to a ninth aspect of the present invention, a developing gap between the photosensitive member and the developing roller is in a range of 0.2 to 0.5, and a developing bias applied to the developing roller is a direct current component. 9. An image forming apparatus according to claim 1, wherein the image forming apparatus is any one of the image forming apparatuses.
The invention according to claim 10 is the image forming apparatus according to any one of claims 1 to 9, comprising a plurality of the photoreceptor, a charging unit for charging the photoreceptor, and a developing unit. Features.
In the invention according to claim 11, the shape factor SF-1 of the toner used for the toner development is in the range of 100 to 180, and the shape factor SF-2 is in the range of 100 to 180. 11. An image forming apparatus according to any one of items 1 to 10.

  According to the present invention, a test pattern is formed in a section longer than one turn of the photosensitive member or one turn of the developing roller, and obtained by the detecting means for detecting the rotation position of the developing roller and the rotating position of the photosensitive member. The laser power in the recording paper conveyance direction is optimized based on the correlation between the chromaticity and the rotation position, so that the image density can be stabilized and made uniform at low cost without using high-precision or high-strength members. Can be possible.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing an image forming portion of a tandem type color copying machine as an image forming apparatus. In FIG. 1, a plurality of photoconductors 1a, 1b, 1c, and 1d arranged side by side along the intermediate transfer belt 5 are provided with developing devices 4a, 4b, 4c, and 4d, respectively, and the photoconductors 1a, 1b, A so-called tandem type color copier A that forms single-color toner images on 1c and 1d, sequentially transfers the single-color toner images, and records a composite color image on a sheet (not shown) as transfer paper. The image forming part is shown.
Further, the structure will be described. Charging means (in the figure, the latent images are optically written by the writing means 3 on the photoconductors 1a, 1b, 1c, and 1d uniformly charged by the charging rollers 2a, 2b, 2c, and 2d by the writing means 3). 3b, 3c, and 3d, and visualized toner images are formed by the developing units 4a, 4b, 4c, and 4d.
The toner images formed on the photoreceptors 1a, 1b, 1c, and 1d are once transferred to the intermediate transfer belt 5 by intermediate transfer belt transfer means (primary transfer rollers) 12a, 12b, 12c, and 12d. The toner image on the intermediate transfer belt 5 is transferred onto the transfer paper by the paper transfer belt 7 serving as a paper transfer means onto the transfer paper that has been transferred. The toner image transferred to the transfer paper is conveyed to the fixing means 8 by the transfer paper transfer belt 7, and the toner image on the transfer paper is fixed by heat and discharged.
Untransferred toner that has not been transferred to the intermediate transfer belt 5 on each of the photoreceptors 1a, 1b, 1c, and 1d is scraped off from the photoreceptors 1a, 1b, 1c, and 1d by the photoreceptor cleaning blades 9a, 9b, 9c, and 9d. It is. Residual charges on these photoreceptors 1a, 1b, 1c and 1d are neutralized by a neutralizing means (not shown) to prepare for the next image forming operation.
Untransferred toner scraped off by the cleaning blades 9a, 9b, 9c, and 9d passes through the recovery toner transport paths 14a, 14b, 14c, and 14d indicated by dotted lines, and is used for untransferred toner and process control on the intermediate transfer belt 5. The pattern image is scraped off from the intermediate transfer belt 5 by the intermediate transfer cleaning blade 13 and is also stored in the waste toner storage container 15 through the recovered toner transport path 14e.

Next, replenishment of new toner to the developing devices 4a, 4b, 4c, and 4d will be described. New toner filled in the toner cartridge is supplied to the toner hoppers 11a, 11b, 11c, and 11d on the rear side of the machine main body indicated by the dotted line by the toner supply devices 10a, 10b, 10c, and 10d.
The toner stored in the toner hoppers 11a, 11b, 11c, and 11d is transferred to the developing devices 4a, 4b, 4c, and 4d by toner density detecting means (denoted by reference numeral 21 in FIG. 2) in the developing devices 4a, 4b, 4c, and 4d. When it is determined that the toner density in the toner is low, a toner replenishing screw (not shown) in the toner hoppers 11a, 11b, 11c, and 11d is rotated to put an appropriate amount of toner in the toner hoppers 11a, 11b, 11c, and 11d. To the developing devices 4a, 4b, 4c and 4d.
Toner remaining amount detection of the toner bottles of the toner hopper portions 11a, 11b, 11c, and 11d is provided with a toner presence / absence detection sensor (not shown) in the toner hopper portions 11a, 11b, 11c, and 11d, and the toner presence / absence detection sensor has no toner. Is detected, toner supply devices 10a, 10b, 10c, and 10d are requested to supply toner. If the presence of toner is not detected even if requested for a predetermined time, it is determined that there is no toner.

FIG. 2 is a schematic view showing an image forming unit of a single color image forming apparatus in which only one process cartridge is arranged. Next, the image forming unit will be described with reference to FIG. The process cartridge of FIG. 2 is a process cartridge in which the photosensitive member 1, the developing device 4, the charging unit 2 (charging roller in this embodiment), and the cleaning unit 9 (cleaning blade in this embodiment) are integrated.
The developing device 4 has a developing roller 16 for forming a toner visualized image on a latent image on the photosensitive member 1 optically formed at a writing position 3 ′ by a writing means (not shown) on the photosensitive member 1. On the upstream side of the developing area of the developing roller 16, there is a regulating member 17 (hereinafter referred to as a developing doctor 17) that regulates the amount of developer on the developing roller 16 to a certain fixed amount.
A two-component developer in which toner particles and magnetic particles (carriers) are mixed is stored in the developing tank section 4a in the developing device 4, and this developer has two conveying screws, that is, a first conveying screw 18 and It is circulated by the second conveying screw 19. In addition, a toner concentration sensor 21 is disposed below the second conveying screw 19, and the toner concentration in the developing tank is measured at any time and controlled so as to be within an appropriate value.

The toner from the toner replenishing unit is temporarily stored in a sub hopper unit (not shown), and when the toner concentration value in the developing tank is detected as low by the toner concentration sensor 21, the time converted by a predetermined conversion formula The toner replenishing screw 22 is rotated as much as possible, and an appropriate amount of toner is replenished to the developing toner supply port 23.
Further, an inlet seal 20 is disposed on the right side of the developing doctor 17 to prevent toner scattering from the developing nip portion. The distance between the developing roller 16 and the surface of the photosensitive drum 1 as a photosensitive member is called a developing gap.
Although FIG. 1 shows an example of a full-color image forming apparatus in which four process cartridges are arranged, a single-color image forming apparatus in which only one process cartridge in FIG. 2 is arranged or a two-color image forming apparatus in which two process cartridges are arranged is also applicable. is there.
Image density control will be described. Image density control is performed mainly when the power is turned on or whenever a fixed number of images are created. As a special pattern, there are cases where a test pattern is created between images when conditions are created.

As shown in FIG. 2, the test pattern sensor 24 forms a test pattern 25 on the developing roller 16 by the writing means 3 with an arbitrary laser power, and obtains a developing potential and a developing bias for obtaining an arbitrary image density.
In the present invention, variation in the longitudinal direction of the developing potential is caused by the relationship between the plurality of test pattern sensors 24 arranged in the longitudinal direction of the photosensitive drum and the developing roller rotational position and the photosensitive body rotational position detecting means (encoder, etc.). Image uniformity is achieved by finely adjusting the variation in the paper transport direction with the laser power.
More specifically, as shown in FIG. 1, the test pattern sensor 26 is arranged at three or more locations in the longitudinal direction of the photoconductor 1 (for example, above the test pattern 27 on the intermediate transfer belt 5), for example, on the intermediate transfer belt 5. It is arranged in a total of three places, approximately the center and one place before and after that.
The development bias is set at a pattern arranged approximately at the center of the pattern sensors 24 arranged at three or more locations in the longitudinal direction of the developing roller 16 of the developing means 4 (for example, approximately the center and a total of three locations before and after that). It is calculated from the chromaticity obtained from the sensor 24.
In this state, the image density in the recording paper is substantially stabilized, but the image density is made uniform by optimizing the laser power in the vicinity of each test pattern for further fine adjustment. Then, a test pattern is formed in a section longer than one turn of the photosensitive member 1 or one turn of the developing roller 16, and is obtained by a detecting unit that detects the rotational position of the developing roller 16 and the rotational position of the photosensitive member 1. The laser power in the recording paper conveyance direction is optimized from the correlation between the chromaticity and the rotation position.

FIG. 3 is a block diagram showing an overview of the overall control unit of the image forming apparatus according to the present invention. In FIG. 3, a control unit 30 is a main control that controls the entire image forming apparatus including a CPU 31, a ROM 32 that stores programs executed by the CPU 31, other fixed data, and a RAM 33 that temporarily stores image data and the like. Part 34 is provided.
The overall control unit in FIG. 3 will be described in the form of connecting only the part necessary for the description here to the control unit 30. The main control unit 34 includes the photosensitive member 1, the charging unit 2, the writing unit (exposure unit) 3, the developing device 4, the intermediate transfer belt 5, the test pattern sensor 24, the main scanning unit 35, the sub-scanning unit 36, and the photosensitive unit 1. Surface potential measuring means 37 for measuring the surface potential, detection means (encoder) 38 for detecting the rotational position of the photosensitive member 1, development bias source 39, and detection for detecting the rotational position of the developing roller 16 (FIG. 2) of the developing device 4. A means (encoder) 40 and a test pattern creation unit 41 are connected.
The photosensitive member 1 connected to the main controller 34 is charged by the charging unit 2, and an electrostatic latent image is formed on the surface by image exposure by an exposure unit (writing device) 3 capable of setting multi-step exposure intensity. . The developing means (developing device) 4 and the developing roller 16 develop the electrostatic latent image with a developing bias for obtaining a potential difference necessary for moving the toner to the electrostatic latent image generated from the developing bias source 39, and A toner image is formed on the photoreceptor 1.
Three or more test pattern sensors 24 are arranged in the longitudinal direction of the photoreceptor 1 and detect the chromaticity of the test pattern of the toner image transferred on or after the photoreceptor 1. The tandem type color copier A (FIG. 1), which is an image forming apparatus, sets the developing bias over the entire length of the developing means 4 and the exposure intensity in the vicinity of each test pattern location according to the chromaticity of the test pattern at each location. The rotation position of the photosensitive member 1 is detected by the encoder 38 serving as detection means.

FIG. 4 is a flowchart showing a processing procedure of image density control in the present embodiment. FIG. 5 is a graph showing the relationship between the exposure intensity used for calculating the exposure intensity and the test pattern sensor. FIG. 6 is a graph showing the relationship between the exposure intensity function and the exposure intensity used for developing bias calculation and the distance in the main scanning direction. FIG. 7 is a graph showing the relationship between the position in the sub-scanning direction and the output of the test pattern sensor.
1 to 4, first, a test pattern for process control for deviation adjustment in the main scanning direction is formed (S1). Next, the test pattern is detected by the test pattern sensor 24 (FIG. 2) (S2).
Next, an exposure intensity is calculated so that the output of the test pattern sensor 24 becomes a target value (S3). Next, an exposure intensity function and a development bias are calculated (S4). Next, the test pattern of the process control for period deviation adjustment is formed under a predetermined condition (S5). Finally, the exposure intensity at the time of actual image formation is changed (adjusted) according to the calculation result of the exposure intensity function obtained as described above (S6).
In step (S1), the exposure intensity is changed to 10 levels (n1, n2, n3,..., N10) with a developing bias of 500 V, and an image is formed at the position facing the test pattern sensor 24 (24F, 24C, 24R). That is, the test pattern is formed on the front side (F), the center (C), and the back side (R), which are the positions facing the test pattern sensor 24 (24F, 24C, 24R) in the width direction of the intermediate transfer belt 5. .

In step (S2), each test pattern is detected by the test pattern sensors 24F, 24C, 24R. In this case, the test pattern output is
pF1, pF2, pF3,. . . , PF10
pC1, pC2, pC3,. . . , PC10
pR1, pR2, pR3,. . . , PR10
It is.
In step (S3), as shown in FIG. 5, the exposure intensity (nF (0.5), nC (0.5) such that the output of the test pattern sensor 24 becomes the target value (0.5 in FIG. 4). ), (NR (0.5)), where nF (0.5) calculates the exposure intensity from the linear sensitivity of a total of 6 points before and after the data where pFn is close to 0.5. .
nC (0.5) calculates the exposure intensity from the linear sensitivity of 6 points in total, 3 points before and after the data where pCn is near 0.5. nR (0.5) calculates the exposure intensity from the linear sensitivity of 6 points in total, 3 points before and after the data where pRn is near 0.5.
In step (S4), the development bias calculates VL and appropriate Vb from the average exposure intensity of the exposure intensity (nF (0.5), nC (0.5), (nR (0.5))).

As shown in FIG. 6, n (F, C) uses the distance between F and C and nF (0.5) and nC (0.5) as a function of the distance from the center. For n (C, R), the distance between C and R and nF (0.5) and nC (0.5) are functions of the distance from the center.
In step (S5), the process control test pattern for adjusting the period deviation has predetermined conditions, that is, the exposure intensity is n (F, C), n (C, R), the pattern is 2by2, and the image forming distance is the photoconductor. The image is formed under the condition that the circumference is 2.5 times and the image forming position is C only.
1) Pattern exposure is started (Ts), and the delay time of the pattern sensitivity rise time Tp is calculated. 2) Simultaneously with 1), the output of the photoconductor cycle detection encoder is detected to detect the photoconductor cycle. 3) The function of the photosensitive member cycle detection encoder cycle is approximated to a sine waveform from the average waveform of the two output waveforms of the test pattern sensor 24 and the pattern sensitivity rise time Tp. 4) As shown in FIG. 7, the clothes scanning direction exposure function m (0.5) is an inverse function of 4).
In step (S6), the exposure intensity function during image formation is set to the encoder detection position, (F (d, t) = n (F, C) × m (0.5) (exposure intensity function between FCs), F The exposure intensity is changed based on the calculation result of (d, t) = n (C, R) × m (0.5) (exposure intensity function between C and R)).

FIG. 8 is a diagram schematically showing the shape of the toner in order to explain the shape factor SF1 of the toner. FIG. 9 is a diagram schematically showing the shape of the toner in order to explain the shape factor SF2 of the toner.
In order to obtain the developing ability in the developing gap, a force due to the difference between the photosensitive member surface linear velocity and the developing roller surface linear velocity is used. Generally, the developing roller linear velocity is set to about 1.3 to 2.0 times the photosensitive member surface linear velocity.
In order to suppress the toner adsorbing power to a low level and to suppress the development of unnecessary toner under a narrow gap, it is necessary to set a toner condition for uniform image density. When both SF-1 and SF-2 exceed 180, the amount of toner that is developed only with a narrow gap increases, so the influence of the development gap deviation becomes large.
The toner shape factor SF-1 in FIG. 8 is expressed by the following equation (1). This is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4.
SF-1 = {(MXLNG) 2 / AREA} × (100π / 4) Expression (1)
When the value of SF-1 is 100, the shape of the toner is a true sphere, and becomes irregular as the value of SF-1 increases.

Further, the shape factor SF-2 in FIG. 9 indicates the ratio of unevenness of the toner, and is represented by the following formula (2). A value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner onto the two-dimensional plane by the figure area AREA and multiplying by 100π / 4.
SF-2 = {(PERI) 2 / AREA} × (100π / 4) Expression (2)
When SF-2 is 100, unevenness does not exist on the toner surface, and as the value of SF-2 increases, the unevenness of the toner surface becomes more prominent.
Specifically, the shape factor is measured by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), introducing it into an image analyzer (LUSEX 3: manufactured by Nireco), and analyzing it. calculate.
When the development gap between the photosensitive member and the developing roller is in the range of 0.2 to 0.5, the toner adsorption force can be kept low, and unnecessary toner development under a narrow gap can be suppressed. . If both SF-1 and SF-2 exceed 180, the amount of toner that will be developed increases simply because the gap is narrow, and the influence of the development gap deviation becomes large.
As mentioned above, although this invention was demonstrated by embodiment of illustration, this invention is not limited to this. The number of test pattern sensors arranged in the main scanning direction is not limited to three, and may be four or more. The arrangement of the plurality of test pattern sensors in the main scanning direction is also an example. Further, the place where the test pattern is detected is not limited to the intermediate transfer belt, and it is also possible to detect the test pattern on the photoreceptor.

1 is a schematic view showing an image forming portion of a tandem type color copying machine that is an image forming apparatus. FIG. FIG. 3 is a schematic diagram illustrating an image forming unit of a single color image forming apparatus in which only one process cartridge is disposed. 1 is a block diagram illustrating an overview of an overall control unit of an image forming apparatus according to the present invention. It is a flowchart which shows the process sequence of the image density control in this Embodiment. It is a figure which shows the relationship between the exposure intensity used for exposure intensity calculation, and a test pattern sensor with a graph. It is a figure which shows the relationship between the exposure intensity used for exposure intensity function and development bias calculation, and the distance in a main scanning direction with a graph. It is a figure which shows the relationship between the position of a subscanning direction, and the output of a test pattern sensor with a graph. FIG. 6 is a diagram schematically showing the shape of a toner in order to explain a toner shape factor SF1. FIG. 6 is a diagram schematically illustrating the shape of a toner in order to explain a toner shape factor SF2.

Explanation of symbols

A image forming apparatus, 1 photoconductor, 2 charging means, 3 writing means (exposure means), 3a writing position, 4 developing apparatus, 5 intermediate transfer belt, 16 developing roller, 24 test pattern sensor, 25 test pattern, 26 test pattern Sensor, 27 test pattern, 30 control unit, 34 main control unit, 35 main scanning unit, 36 sub-scanning unit, 37 surface potential measuring unit, 38 detection unit (encoder), 39 developing bias source, 40 detection unit (encoder), 41 Test pattern generator

Claims (11)

An electrostatic latent image is formed on the surface of the photosensitive member by image exposure by an exposure means capable of setting multi-step exposure intensity on the charged photosensitive member, and is necessary for moving toner to the electrostatic latent image. The electrostatic latent image is developed with a developing roller to which toner is attached by a developing bias from a developing bias source that generates a potential difference, and a toner image is formed on the photosensitive member. Three or more test pattern sensors are used to detect the chromaticity of the test pattern of the toner image transferred onto the photosensitive member or the intermediate transfer belt, and to detect the test pattern on the photosensitive member or the intermediate transfer belt. In the image forming apparatus in which the developing bias over the entire length of the developing unit and the exposure intensity in the vicinity of the test pattern portion of the photoreceptor or the intermediate transfer belt can be set according to chromaticity,
An image forming apparatus comprising: a detecting unit that detects a rotational position of the photosensitive member.   The image forming apparatus according to claim 1, further comprising a detection unit configured to detect a rotation position of the developing roller.   3. The image forming apparatus according to claim 1, wherein the developing bias is set according to chromaticity of the test pattern disposed substantially at the center where the exposure intensity is changed stepwise.   4. The image forming apparatus according to claim 1, wherein the exposure intensity is set from chromaticity and exposure intensity of a test pattern other than a central portion in the set developing bias. 5.   Measure the chromaticity of the test pattern obtained from the set developing bias and the exposure intensity at the developing roller rotation position and / or the photosensitive member rotation position, and set the exposure intensity at the rotation position. The image forming apparatus according to claim 3, wherein:   6. The image forming apparatus according to claim 1, wherein three or more test pattern sensors arranged in the longitudinal direction of the photosensitive member are reflection density detection sensors.   7. The photoconductor surface potential measuring means for measuring a potential between the test pattern sensor arranged in the longitudinal direction of the photoconductor and the surface of the photoconductor at substantially the same position. The image forming apparatus described.   8. The image forming apparatus according to claim 7, wherein an exposure intensity in the vicinity of the test pattern is set from the photoconductor surface potential measured by the photoconductor surface potential measuring means and the test pattern.   9. A developing gap between the photosensitive member and the developing roller is in a range of 0.2 to 0.5, and a developing bias applied to the developing roller is a direct current component. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, comprising a plurality of the photosensitive members, a charging unit that charges the photosensitive members, and a developing unit.   The shape factor SF-1 of the toner used for the toner development is in the range of 100 to 180, and the shape factor SF-2 is in the range of 100 to 180. The image forming apparatus according to Item.

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