JP4898259B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer that forms an image using an electrophotographic system or an electrostatic recording system.

  In general, an image forming apparatus using an electrophotographic system or an electrostatic recording system has a step of developing an electrostatic latent image formed on the surface of an image carrier using a developer called toner.

  In the developing process, a phenomenon called sweeping occurs. This is a phenomenon in which the developing toner amount at the rear end portion of the latent image is larger than the developing toner amount at the latent image plane portion. This phenomenon increases the density of the rear end of the image, or widens the width of the toner image relative to the electrostatic latent image at the rear end of the image, causing problems in terms of image uniformity and latent image reproducibility. Arise.

As a control method for sweeping, there is a method for correcting sweeping by performing correction processing on image data and adjusting the exposure amount (see Patent Document 1 and Patent Document 2). Further, a method has been proposed in which a density difference between an image plane portion and an image edge portion is detected by a patch detection sensor, and correction is performed according to the result (see Patent Document 3). Furthermore, there is also a method (see Patent Document 4) that is effective not only for sweeping but also for thinning of density in the image plane portion, etc., by correcting the AC bias applied during development according to changes in environmental conditions. Proposed.
JP 2003-345076 A JP-A-9-272224 JP 2003-330232 A JP-A-7-134479

  However, the conventional method has a problem that the sweeping cannot be appropriately corrected depending on the image pattern.

  Specifically, in FIG. 15A, there is a problem that a new sweep 24 is generated upstream of the correction region 23 indicated by the broken line in the sub-scanning direction due to the effect of correcting the sweep region 22.

  Further, as shown in FIG. 15B, when an image exists in the vicinity of the target image on the downstream side in the sub-scanning direction, the following problem occurs. That is, there is a problem that the density reduction region 25 in which the image density is partially lowered due to overcorrection occurs, or a problem that the image density remains partially high due to insufficient correction.

  These problems are prominently observed in a system in which development is performed mainly in a state where the image carrier and the developer carrier are in contact with each other or very close to each other.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of correcting the influence of sweeping and forming a high-quality image having a uniform image density and excellent latent image reproducibility regardless of the image pattern.

The above object is achieved by the image forming apparatus according to the present invention. In summary , according to one aspect of the present invention , a rotatable image carrier, charging means for uniformly charging the image carrier, and image data for the uniformly charged image carrier. An exposure unit that performs exposure based on the image; and a developing unit that develops the electrostatic latent image formed on the image carrier by the exposure of the exposure unit using a developer conveyed by a rotatable developer carrier. In an image forming apparatus comprising:
The developer carrier rotates in the same direction as the image carrier at a position facing the image carrier,
The peripheral speed of the developer carrier is greater than the peripheral speed of the image carrier,
The developing means performs development by bringing the developer carrier and the image carrier into contact with each other,
The higher the image density, the larger the pixel data value.
In the development area, which is the area where the electrostatic latent image is developed, the width that the developer carrier overtakes the image carrier in the sub-scanning direction is defined as the overtaking width.
The data value of the target pixel on the image data is compared with the data value of the specific pixel located downstream of the target pixel by the overtaking width in the sub-scanning direction, and the data value of the target pixel> the data of the specific pixel When the value is a value, an image forming apparatus is provided that includes a calculation unit that corrects the data value of the target pixel so that the density of the image of the target pixel is low .
According to another aspect of the present invention, a rotatable image carrier, charging means for uniformly charging the image carrier, and exposure based on image data for the uniformly charged image carrier. And exposure means for developing the electrostatic latent image formed on the image carrier by exposure of the exposure means using a developer conveyed by a rotatable developer carrier. In the image forming apparatus,
The developer carrier rotates in the same direction as the image carrier at a position facing the image carrier,
The peripheral speed of the developer carrier is greater than the peripheral speed of the image carrier,
The developing means performs development in a state in which the distance between the image carrier and the developer carrier is close to 200 [μm] or less,
The higher the image density, the larger the pixel data value.
In the development area, which is the area where the electrostatic latent image is developed, the width that the developer carrier overtakes the image carrier in the sub-scanning direction is defined as the overtaking width.
The data value of the target pixel on the image data is compared with the data value of the specific pixel located downstream of the target pixel by the overtaking width in the sub-scanning direction, and the data value of the target pixel> the data of the specific pixel When the value is a value, an image forming apparatus is provided that includes a calculation unit that corrects the data value of the target pixel so that the density of the image of the target pixel is low.

  According to the present invention, appropriate sweep correction can be performed, and an image without sweeping can be obtained regardless of the image pattern.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
First, the operation of the image forming apparatus in the first embodiment of the present invention will be described with reference to FIG.

  In this embodiment, the image forming apparatus includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1 that is an image carrier. The surface of the photosensitive drum 1 is uniformly charged by a charging device 2 such as a charging roller as charging means. The uniformly charged photosensitive drum 1 is then exposed with an exposure amount of light based on image data by an image exposure device 7 such as a laser beam scanner device as an image exposure means. Thereby, an electrostatic latent image is formed on the surface of the photosensitive drum 1. At this time, the image calculation unit 9 performs a sweep correction process on the image data read from the host computer 8.

  In this embodiment, the image forming apparatus includes a CPU 10 that controls the entire apparatus, and a memory 11 that includes an image memory 11a and an LUT 11b. The image memory 11a is a memory for developing image data to be printed out. On the other hand, the LUT 11b is a look-up table, and stores data such as process condition values and correction amounts that are acquired by measurement in the apparatus or set in advance. The correction amount is calculated in advance according to the data value of the pixel on the image data, each process condition, environmental condition, and the like.

  The developing device 3 as developing means includes a toner container for storing and storing a developer (hereinafter referred to as “toner”) 12 and a developing roller 30 as a developer carrier. In this embodiment, a non-magnetic one-component toner is used as a developer, but the present invention is not limited to this.

  In this embodiment, the toner supplied to the developing roller 30 is regulated in its layer thickness by a regulating blade 31 as a toner layer thickness regulating member, and is simultaneously charged. Then, the toner which is regulated to a predetermined layer thickness and is given a predetermined charge is conveyed to the developing region 14 by the developing roller 30.

  The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed with the toner 12 conveyed to the development area 14 by the developing roller 30. The toner image formed on the surface of the photosensitive drum 1 is transferred onto the transfer material P by the transfer device 4 at the transfer position T. The toner image transferred onto the transfer material P is conveyed to the fixing device 6 and is fixed by heat and pressure in the fixing device 6 to form an image.

  On the other hand, the toner 12 remaining on the surface of the photosensitive drum 1 without being transferred onto the transfer material P at the transfer position T is removed by the cleaning device 5. The surface of the photosensitive drum 1 from which the toner 12 has been removed is charged again by the charging device 2, and the above steps are repeated.

  Next, with reference to FIG. 2, the developing method in this embodiment will be described.

  In this embodiment, the photosensitive drum 1 and the developing roller 30 are in contact with each other, and the photosensitive drum 1 and the developing roller 30 have different peripheral speeds (peripheral speed of the photosensitive drum 1: about 100 [mm / sec]. The peripheral speed of the developing roller 30 is about 150 [mm / sec]).

  Further, a DC voltage (about −300 [V]) is applied as a developing bias from the power source 32 between the photosensitive drum 1 and the developing roller 30, and the polarity of the developing bias depends on the charging of the surface of the photosensitive drum 1. It is set to the same polarity as the potential.

  In the above configuration, the toner 12 thinned on the developing roller 30 is conveyed to a region where the photosensitive drum 1 and the developing roller 30 are in contact with each other, and the electrostatic latent image formed on the surface of the photosensitive drum 1 Develop.

  Next, the principle on which the present invention is based will be described.

  Conventionally, as a cause of the sweeping phenomenon, as shown in FIG. 3, an electric field wraparound effect generated at the boundary between two regions having different surface potentials, such as the boundary between the exposed portion and the charged portion on the image carrier. (Hereinafter referred to as the “edge effect”).

  However, this is a remarkable phenomenon particularly in a system in which development is performed while keeping the image carrier and developer carrier in non-contact. In a method in which development is performed in a state where the image carrier and the developer carrier are in contact with each other or very close to each other (hereinafter referred to as “proximity development method”), as shown in FIG. Little impact is seen.

  Nevertheless, in practice, sweeping occurs even in the proximity development method. From this, it is considered that the cause of sweeping in the proximity development method is a factor different from the edge effect.

  As a result of investigations by the present inventors, it has been found that the developer on the developer carrier on the rear side in the sub-scanning direction is related to the occurrence of sweeping in the proximity developing method. Hereinafter, the developing method of this embodiment will be described in detail as an example.

  FIG. 5 shows a state where the trailing edge of the electrostatic latent image is developed.

  As described above, the photosensitive drum 1 and the developing roller 30 are in contact with each other, and the peripheral speed relationship is the peripheral speed of the photosensitive drum 1 <the peripheral speed of the developing roller 30. Further, only a DC voltage is used as the developing bias.

  In the development area 14, the electrostatic latent image is developed by the toner conveyed to the development area 14 by the development roller 30 (see FIG. 5A). Further, since the developing roller 30 rotates faster with respect to the photosensitive drum 1, the positional relationship on the surface of both of them constantly deviates. Therefore, when the electrostatic latent image rear end 13 enters the developing region 14, the toner 15 on the developing roller 30 located on the rear side in the sub-scanning direction from the starting position of the developing region 14 The trailing edge 13 of the electrostatic latent image is overtaken before leaving the development area 14 until the development is completed (see FIG. 5B). The toner 15 passing from the rear side in the sub-scanning direction increases the amount of toner supplied to the trailing edge 13 of the electrostatic latent image, and as a result, the development amount of the trailing edge 13 of the electrostatic latent image increases (FIG. 5 ( c)). That is, sweeping occurs.

  As described above, the width at which the toner positioned on the rear side in the sub-scanning direction passes the trailing edge of the electrostatic latent image due to the difference in peripheral speed while the trailing edge of the electrostatic latent image passes through the development region is referred to as “passing width”. I will do it.

  In addition, the above principle is not limited to the development method in which the image carrier and the developer carrier are in contact with each other, and even in a method in which development is performed in a non-contact state, as long as the effect of edge development is small, the effect of the edge effect is small. It holds.

  As a result of the study by the present inventors, the range of proximity development in which the influence of the edge effect is small is when the distance between the image carrier and the developer carrier is 200 [μm] or less, preferably 50 [μm] or less. I found out.

  In the present invention, on the basis of the above principle, the sweeping correction in consideration of the overtaking width determined by the peripheral speed (that is, the moving speed) of the photosensitive drum and the developing roller, the width of the developing area, and the image pattern to be output is performed. Do it on the data.

  Next, sweep correction calculation in the present embodiment will be described.

  In the following, on the image data, the rear side in the sub-scanning direction is expressed as “downstream side in the sub-scanning direction”.

  FIG. 6 shows an operation flow of the image calculation unit 9 shown in FIG. 1 in the present embodiment.

  Referring also to FIG. 1, first, image data is read from the host computer 8 (step S1). Since the image forming apparatus of this embodiment is a reversal development system, exposure is performed on the black image portion. Therefore, when the data value (corresponding to the exposure intensity) in each pixel on the image data is expressed in hexadecimal, the white value is 00h and the black value is FFh.

  Next, the read image data is stored in the image memory 11a (step S2). At the same time, on the other hand, based on the image forming conditions including the process conditions of the apparatus (developing bias, photosensitive drum peripheral speed, developing roller peripheral speed, etc.), the overtaking when the pixel data value is FFh from the overtaking width table of the LUT 11b. The width is acquired (step S3). Here, the overtaking width calculated in advance is stored in the overtaking width table of the LUT 11b based on image forming conditions including pixel data values and apparatus process conditions.

  Next, the following calculation is performed in the image memory 11a.

  First, virtual image data B is created by translating the original image data A to the upstream side in the sub-scanning direction by the acquired overtaking width (see step S4, FIG. 7).

  Then, the difference between the original image data A and the virtual image data B subjected to the parallel movement process is taken to obtain virtual image data C (see step S5, FIG. 8). At this time, in the virtual image data C, the portion where the pixel data value is greater than 00h (see the black portion on the virtual image data C in FIG. 8) indicates the density variation portion during image output.

  Next, the correction area is calculated from the pixel on the rear end side of the virtual image data C (step S6). Here, there is a problem that density fluctuations are newly generated in another pixel although the degree is reduced due to the influence of correction on the pixel. Therefore, processing for setting a pixel in which density variation occurs as a correction area and processing for suppressing the occurrence of density variation in another pixel are performed.

  Specifically, when the target pixel is a density fluctuation portion, the pixel is set as a correction area (see FIGS. 9A and 9B). Then, re-correction processing is performed in which a pixel located upstream in the sub-scanning direction by the overtaking width from the pixel set as the correction region is further set as the correction region (see FIG. 9C). Further, this re-correction process is repeated (see FIG. 9D).

  However, when calculating the correction area, if several pixels with density fluctuations continue in the main scanning direction, the number of repetitions of the re-correction processing is set to a different number for each predetermined interval in the main scanning direction. To do. This is because, as described above, density fluctuations are newly generated in another pixel due to the correction. Therefore, by repeating the re-correction process, the density fluctuation level is gradually reduced, but the density fluctuation itself is eliminated. Because you can't. In particular, when pixels in which density fluctuations occur continue in the main scanning direction, the density fluctuations newly generated by the correction become horizontal line-shaped density irregularities and the like.

  Therefore, as described above, by changing the number of re-correction processing repetitions at predetermined intervals, the position of the density fluctuation newly generated by the correction is shifted in the sub-scanning direction so that the density fluctuation is not noticeable.

  As a result of the study by the present inventors, the predetermined interval in the main scanning direction is at least 150 [μm] or less, preferably 100 [μm] or less, and the re-correction processing repetition number in the sub-scanning direction is at least 4 times. It has been found that the number of times is less than, preferably twice.

  Since the image forming apparatus according to the present embodiment has a resolution of 600 dpi, the predetermined interval in the main scanning direction is 2 dots (about 84 [μm]), and the re-correction processing repetition number in the sub-scanning direction is 2 ( (See FIG. 10).

  In the image forming apparatus of the present embodiment, for example, when the correction area is calculated for uniform density fluctuations in the main scanning direction at the rear end of the image (see the □ portion of the output image in FIG. 10), a staircase correction area is obtained. (See the corrected image in FIG. 10). However, if the above conditions are satisfied and the density fluctuation is not conspicuous, for example, a comb-shaped correction region as shown in FIG. Other than that.

  Further, as described above, by changing the number of repetitions of the re-correction process or the re-correction process at predetermined intervals in the main scanning direction, for example, an image that has been corrected under a certain condition due to variations in process conditions, etc. Even when the overtaking width is deviated from the data by about 100 [μm], the density fluctuation can be made inconspicuous.

  Returning to the operation flow of FIG. 6, next, the correction amount is determined from the pixels in the correction area on the rear end side of the image data, and the data value of the original image data A is corrected (step S7 in FIG. 6). The correction amount is based on the data value of the pixel to be corrected in the original image data A, the data value of the pixel located on the downstream side in the sub-scanning direction by the overtaking width, and the image forming conditions including the process conditions of the apparatus. And obtained from the data correction table of the LUT 11b. At this time, the corrected data value is used as the data value of the pixel located downstream of the pixel to be corrected in the original image data A by the overtaking width by the downstream side in the sub-scanning direction. Further, the process condition of the apparatus is a developing bias.

  The following information is stored in the data correction table of the LUT 11b. In other words, the pixel value to be corrected is generated from the data value of the pixel to be corrected, the data value of the pixel located on the downstream side in the sub-scanning direction by the overtaking width, and the image forming conditions including the process conditions of the apparatus. A correction amount calculated in advance by predicting an excessive development amount.

  However, the data value of the pixel to be corrected is compared with the data value of the pixel located downstream in the sub-scanning direction by the overtaking width (or the corrected data value if corrected). If the pixel data value ≦ the downstream pixel data value, no correction is performed.

  Based on the result obtained by the above calculation, the exposure amount is corrected so as to eliminate the density fluctuation in the density fluctuation portion (step S8 in FIG. 6).

  The conventional method and the present invention are applied to various image patterns shown in FIG. As a result, although it was difficult to perform proper sweep correction with the conventional method, an image without sweeping could be obtained according to the present invention.

  Further, in this embodiment, when the density fluctuation is determined in the sweep correction calculation in the image calculation unit 9 in FIG. 1 (steps S3 to S5 in FIG. 6), the entire image data is collectively processed as a processing region. Was processed. However, the present invention is not limited to this method. For example, a method of performing sequential processing for each pixel of image data can also be implemented. Furthermore, the means for reflecting the correction result to the image data in the exposure may be exposure time control such as PWM control.

Example 2
Next, a second embodiment of the present invention will be described.

  FIG. 13 shows an image forming apparatus of this embodiment. This is an image forming apparatus for full-color printing in which toners of different colors are used in the image forming apparatus of Embodiment 1 and arranged for four colors.

  In the present embodiment, the full-color image forming apparatus 100 includes four independent image forming units UN (UNa, UNb, UNc, UNd) arranged in series in the same configuration as the image forming apparatus of the first embodiment. Yes. In this embodiment, the image forming units UN (UNa, UNb, UNc, UNd) constitute image forming means for cyan toner, yellow toner, magenta toner, and black toner, respectively.

  Each of the image forming units UN (UNa, UNb, UNc, UNd) has a rotating drum type electrophotographic photosensitive member that is repeatedly used as an image carrier, that is, a photosensitive drum 1 (1a, 1b, 1c, 1d). . Around each photosensitive drum 1, a charging device 2 (2a, 2b, 2c, 2d) as a charging unit, a developing device 3 (3a, 3b, 3c, 3d) as a developing unit, and a developer collecting unit As a cleaning device 5 (5a, 5b, 5c, 5d) is arranged. Further, at the transfer position T (Ta, Tb, Tc, Td) of each image forming unit UN, a transfer device 4 (4a, 4b, 4c, 4d) is arranged facing the photosensitive drum 1.

  Also, below each image forming unit UN, there is disposed a transfer belt 40 as a transfer material carrying and conveying means that is wound around rollers 41 and 42 and is rotatable in the direction of the arrow. The transfer material P is fed from a paper feed unit (not shown), and is carried and transferred by the transfer belt 40 to the transfer position T (Ta, Tb, Tc, Td) of each image forming unit UN.

  Developer images (that is, toner images) of different colors formed by the image forming unit UN are transferred onto the transfer material P carried and conveyed by the transfer belt 40 by the transfer device 4 (4a, 4b, 4c, 4d). The images are transferred one after another. As a result, a full-color image is formed on the transfer material P.

  The full color image formed on the transfer material P is fixed by the fixing device 6 and then discharged to a paper discharge tray (not shown).

  As described above, cyan, yellow, magenta, and black toner are used from the right side device on the transfer material P as the toner. Further, in the image forming unit UNd that uses the black toner that consumes the largest amount of toner, the image forming units UNa, UNb, and the like that use the other three (cyan, yellow, and magenta) toners in order to reduce the toner consumption. The circumferential speed ratio of the developing roller to the photosensitive drum is made smaller than UNc.

  Specifically, the peripheral speed ratio of the developing roller 30d to the photosensitive drum 1d in the image forming unit UNd using black toner is about 150%, and in the other three image forming units UNa, UNb, and UNc, about 200%. %.

  As shown in the figure, also in the present embodiment, as in the first embodiment, the image forming apparatus 100 includes a CPU 10 that controls the entire apparatus, and a memory 11 including an image memory 11a and an LUT 11b. The image memory 11a is a memory for developing image data to be printed out. On the other hand, the LUT 11b is a process condition value acquired by measurement in the apparatus, or a preset data value such as a pixel data value and a correction amount calculated in advance according to each process condition, environmental condition, etc. Is a lookup table storing

  FIG. 14 is an output image when the sweep correction is not performed. FIG. 14A shows an output image by only the image forming unit UNd using black toner, and FIG. 14B shows an output image by the other image forming units.

  As shown in FIGS. 14A and 14B, it was found that the region where sweeping occurs differs when the peripheral speed relationship between the photosensitive drum 1 and the developing roller 30 is different. Therefore, in each image forming unit, it is necessary to correct sweeping in accordance with the peripheral speed relationship between the photosensitive drum and the developing roller.

  In this embodiment, the sweep correction calculation method is the same as that in the first embodiment. However, in this embodiment, the overtaking width calculated in advance is stored in the overtaking width table based on the pixel data value, the developing bias, and the peripheral speed relationship between the photosensitive drum and the developing roller. Then, the above three items used for the calculation of the overtaking width are used as reference parameters for data acquisition from the overtaking width table (see step S3 in FIG. 6).

  The data correction table stores a correction amount. However, the correction amount in this embodiment includes the data value of the pixel to be corrected, the data value of the pixel located downstream in the sub-scanning direction by the overtaking width, the developing bias, the photosensitive drum, and the developing roller. Thus, the excessive development amount generated in the correction target pixel is predicted from the peripheral speed relationship, and is calculated in advance.

  Similarly to the case of acquiring the overtaking width data, the above four items used for calculating the correction amount are used as reference parameters when acquiring data from the data correction table (see step S7 in FIG. 6). As a result, it is possible to perform sweep correction in consideration of the peripheral speed relationship between the photosensitive drum and the developing roller.

  Various image patterns shown in FIG. 12 were output as images from the respective image forming units having different developing roller-to-photosensitive drum peripheral speed ratios. As a result, also in this embodiment, appropriate sweep correction can be performed on various image patterns shown in FIG. Furthermore, it was confirmed that a high-quality image without sweeping can be obtained not only when outputting an image in a single color but also when outputting an image by combining a plurality of colors.

  In this embodiment, the peripheral speed relationship set for each image forming unit is read and used as a reference parameter. However, for example, when the printing speed setting is variable, the result of measuring the peripheral speed of the photosensitive drum or the developing roller can be used. Furthermore, according to the present invention, by using the result of γ correction by density detection or the temperature and humidity measurement result by an environmental sensor as the reference parameter, sweeping according to endurance fluctuation or long-term change in use environment, etc. Can also be corrected.

FIG. 2 is a schematic configuration diagram of an image forming apparatus for explaining an operation of the image forming apparatus in the first embodiment. It is a schematic block diagram of the developing device for explaining the operation of the developing device in the first embodiment. It is a figure explaining the mode of the electric field in the electrostatic latent image edge part in a state where an image carrier and a developer carrier are not in contact. It is a figure explaining the mode of the electric field in the electrostatic latent image edge part in a state where the image carrier and the developer carrier are in contact with or very close to each other. FIG. 4 is a diagram for explaining the principle of sweeping in a method in which development is performed in an area where an image carrier and a developer carrier are in contact with each other. It is a figure explaining the operation | movement flow of the image calculating part in a 1st Example. It is a figure explaining the parallel movement calculation of the image calculating part in a 1st Example. It is a figure explaining the difference calculation of the image calculating part in a 1st Example. It is a figure explaining calculation of the amendment field of the image operation part in the 1st example. It is a figure explaining the conditions of the amendment field in the 1st example. It is a figure explaining the example of the correction | amendment area | region which satisfy | fills the conditions where a density fluctuation is not conspicuous. It is a figure explaining the image pattern used for image evaluation. It is a schematic block diagram of the image forming apparatus explaining the operation of the image forming apparatus in the second embodiment. FIG. 10 is a diagram illustrating sweeping when the peripheral speed relationship between the photosensitive drum and the developing roller is different. It is a figure explaining the problem of the conventional sweep correction method.

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Charging device (charging means)
3 Development device (developing means)
30 Development roller (developer carrier)
4 Transfer device 5 Cleaning device 6 Fixing device 7 Image exposure device (exposure means)
8 Host computer 9 Image calculation unit 10 CPU
11 memory 11a image memory 11b LUT
12 Toner 13 Electrostatic latent image trailing edge 14 Development area 15 Overtaking toner P Transfer material

Claims (8)

A rotatable image carrier;
Charging means for uniformly charging the image carrier;
Exposure means for performing exposure based on image data for the uniformly charged image carrier;
A developing means for developing with the developer conveyed by the rotatable developer carrying member to the electrostatic latent image formed on the image bearing member by exposure of said exposure means,
In an image forming apparatus comprising:
The developer carrier rotates in the same direction as the image carrier at a position facing the image carrier,
The peripheral speed of the developer carrier is greater than the peripheral speed of the image carrier,
The developing means performs development by bringing the developer carrier and the image carrier into contact with each other,
The higher the image density, the larger the pixel data value.
In the development area, which is the area where the electrostatic latent image is developed, the width that the developer carrier overtakes the image carrier in the sub-scanning direction is defined as the overtaking width.
The data value of the target pixel on the image data is compared with the data value of the specific pixel located downstream of the target pixel by the overtaking width in the sub-scanning direction, and the data value of the target pixel> the data of the specific pixel An image forming apparatus comprising: an arithmetic unit that corrects the data value of the target pixel so that the density of the image of the target pixel is low . A rotatable image carrier;
Charging means for uniformly charging the image carrier;
Exposure means for performing exposure based on image data for the uniformly charged image carrier;
Developing means for developing the electrostatic latent image formed on the image carrier by exposure of the exposure means using a developer conveyed by a rotatable developer carrier;
In an image forming apparatus comprising:
The developer carrier rotates in the same direction as the image carrier at a position facing the image carrier,
The peripheral speed of the developer carrier is greater than the peripheral speed of the image carrier,
The developing means performs development in a state in which the distance between the image carrier and the developer carrier is close to 200 [μm] or less,
The higher the image density, the larger the pixel data value.
In the development area, which is the area where the electrostatic latent image is developed, the width that the developer carrier overtakes the image carrier in the sub-scanning direction is defined as the overtaking width.
The data value of the target pixel on the image data is compared with the data value of the specific pixel located downstream of the target pixel by the overtaking width in the sub-scanning direction, and the data value of the target pixel> the data of the specific pixel An image forming apparatus comprising: an arithmetic unit that corrects the data value of the target pixel so that the density of the image of the target pixel is low. The data value of the pixel that has been corrected is used as the corrected data value.
The calculation means compares the corrected data value with the data value of a specific pixel located upstream of the corrected pixel by the overtaking width by an amount corresponding to the overtaking direction. When the data value <the data value of the specific pixel on the upstream side, recorrection processing is performed to correct the data value of the specific pixel on the upstream side so that the image density of the specific pixel on the upstream side becomes low. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. When the data of the specific pixel on the upstream side is corrected, the calculation means compares the corrected data value of the specific pixel on the upstream side with the data value of the specific pixel on the upstream side, The image forming apparatus according to claim 3, wherein the correction process is repeatedly performed. 5. The image formation according to claim 4, wherein when the target pixels to be corrected are continuous in the main scanning direction, the number of repetitions of the re-correction processing is set to a different number for each predetermined interval in the main scanning direction. apparatus. The image forming apparatus according to claim 5, wherein the predetermined interval is 150 μm or less. 7. The image forming apparatus according to claim 1, wherein the means for reflecting the correction to the image data in exposure is control of exposure time or exposure amount. The overtaking width is determined based on at least one of a peripheral speed of the developer carrier and the image carrier, and a voltage applied between the image carrier and the developer carrier. The image forming apparatus according to claim 1.

Images