JP2009294541A - Image forming apparatus and control method for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which corrects potential unevenness generated when a photoreceptor drum is charged, in an image forming position as well as a position where the image is not formed at high speed, and to provide a control method for the image forming apparatus. <P>SOLUTION: The image forming apparatus corrects the exposure amount in an exposure device so that the potential unevenness caused by exposure of the charged photoreceptor and the potential unevenness in non-exposure. In addition, the potential unevenness in the exposure and the potential unevenness in the non-exposure are measured in a region obtained by dividing the surface of the photoreceptor drum into a plurality of regions. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an apparatus for scanning a photosensitive member with a laser beam, and more particularly to an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, and a control method thereof.

  An electrophotographic image forming apparatus is an image input / output apparatus having a function of copying a document image, a function of printing a computer-generated electronic image as a visible image on paper, a function of transmitting / receiving an image as a FAX, and the like. Widely used in the office and light printing fields. The electrophotographic technology that enables image output in this way forms a visible image on a sheet by the following mechanism. First, the photosensitive drum is uniformly charged, and the photosensitive drum is irradiated with laser light corresponding to the image. Subsequently, for example, in the case of a process of developing only a portion irradiated with laser light with toner, a toner image corresponding to the image is formed on the photosensitive drum. The toner image on the photosensitive drum is transferred onto a sheet, and a permanent visible image is formed by fixing the toner on the sheet on the sheet by applying pressure and temperature with a fixing device. By controlling this series of operations with high accuracy, for example, a high-quality copy image equivalent to a document image can be created.

  However, in order to create a high-quality image with the above-described mechanism, it is necessary to uniformly charge the photosensitive drum. This is because if the photosensitive drum is not uniformly charged and the charging potential varies depending on the surface of the photosensitive drum, for example, when a halftone image is printed over the entire area of the paper, a high-quality image with a constant halftone image density is not obtained due to potential unevenness. Because. That is, in order to create a high-quality image, it is necessary to suppress the occurrence of potential unevenness on the photosensitive drum or to correct the generated potential unevenness.

For example, when the photosensitive drum is uniformly charged at −500 V and the potential of the photosensitive drum is measured, it is necessary to be −500 V at any portion. However, it is very difficult in terms of production technology to equalize the charging characteristics over the entire surface as the characteristics of the photosensitive drum, and potential unevenness occurs at present. In order to solve this problem, for example, Patent Document 1 proposes a mechanism for measuring a two-dimensional potential on the entire surface of the photosensitive drum. Patent Document 2 proposes a mechanism for changing the charging potential according to the potential unevenness characteristic. Furthermore, Patent Document 3 proposes a mechanism for changing the amount of laser light at the time of laser emission corresponding to an image in accordance with the characteristic of potential unevenness.
JP 05-165295 A JP 2002-207350 A JP 2004-223716 A

  However, the conventional techniques have the following problems. For example, when measuring the two-dimensional potential unevenness and sensitivity unevenness of the photosensitive drum and changing the charging potential according to the measurement result, the response and charging of the high voltage generation circuit required for charging the photosensitive drum It is difficult to correct the charged potential at high speed due to the responsiveness of the charger or the photosensitive drum. On the other hand, the laser element and the drive circuit can realize high-speed responsiveness, and the potential unevenness of the photosensitive drum can be reduced by changing the light amount according to the measurement result of the potential unevenness of the photosensitive drum at the time of laser emission corresponding to the image. It is possible to correct. However, it is impossible to correct the potential unevenness of the photosensitive drum in a portion where there is no image data. The unevenness of the potential of the photosensitive drum where there is no image data is a portion that is not developed at the time of toner development, but depending on the process characteristics of the apparatus, a phenomenon such as fog in which a minute toner is developed in an unintended portion outside the image area. Is generated. Furthermore, due to the difference in the potential difference between the image edge part exposed with the laser beam and the non-exposed part for each region, a phenomenon such as blurring of the character edge part occurs due to the difference in edge sharpness when developing toner. Resulting in.

  The present invention has been made in view of the above problems, and corrects at high speed not only the image forming position but also the potential non-image forming position among the potential unevenness generated when the photosensitive drum is charged. An object of the present invention is to provide an image forming apparatus and a control method thereof.

  The present invention includes, for example, an image carrier, a charging unit that charges the image carrier, an exposure unit that exposes the charged image carrier with a light amount according to image data, and an image carrier that is exposed to light. It can be realized as an image forming apparatus including a developing unit that develops the formed electrostatic latent image with toner. The image forming apparatus includes a first potential in a state where the charged image carrier is exposed by an exposure unit and a second potential in an unexposed state in a divided region obtained by dividing the surface of the image carrier into a plurality of regions. Measuring means for measuring the first correction means for correcting the exposure amount with respect to the exposure position in order to eliminate the potential unevenness of the exposure position according to the image data of the image to be formed based on the measured first potential; And a second correction unit that corrects an exposure amount with respect to the non-exposure position based on the measured second potential in order to eliminate potential unevenness at the non-exposure position according to the image data.

  The present invention also provides an image carrier, a charging unit that charges the image carrier, an exposure unit that exposes the charged image carrier with a light amount corresponding to image data, and an image carrier by exposure. This can be realized as a control method of an image forming apparatus including a developing unit that develops the formed electrostatic latent image with toner. In the control method, in the divided region obtained by dividing the surface of the image carrier into a plurality of regions, the first potential in a state where the charged image carrier is exposed by the exposure means and the second potential in a state where the image carrier is not exposed are set. A measurement step for measuring, a first correction step for correcting the exposure amount with respect to the exposure position in order to eliminate potential unevenness at the exposure position according to the image data of the image to be formed, based on the measured first potential, and measurement And a second correction step of correcting the exposure amount with respect to the non-exposure position so as to eliminate the potential unevenness at the non-exposure position according to the image data based on the second potential.

  The present invention can provide, for example, an image forming apparatus and a control method therefor that can rapidly correct potential unevenness not only at an image forming position but also at a position where no image is formed, among potential unevenness generated when a photosensitive drum is charged.

  An embodiment of the present invention is shown below. The individual embodiments described below will help to understand various concepts, such as superordinate concepts, intermediate concepts and subordinate concepts of the present invention. Further, the technical scope of the present invention is determined by the scope of the claims, and is not limited by the following individual embodiments.

<First Embodiment>
<Configuration of image forming apparatus>
The first embodiment will be described below with reference to FIGS. 1 to 7 and FIG. FIG. 1 is a diagram illustrating a partial hardware configuration of the image forming apparatus according to the first embodiment. Reference numeral 101 denotes a photosensitive drum as an image carrier, which is charged by the primary charger 102 at a predetermined charging voltage of −700 V, for example. Reference numeral 103 denotes laser scanning light. The laser scanning light 103 is scanned in the axial direction of the photosensitive drum 101 from the front to the back in the drawing. Reference numeral 104 denotes a potential sensor, which is a measuring device that measures the charging voltage of the photosensitive drum 101.

  Here, a mechanism for converting laser light into scanning light will be described. Reference numeral 105 denotes a semiconductor laser, which generates laser light according to image data. Reference numeral 106 denotes a polygon mirror, which converts laser light from the semiconductor laser 105 into scanning light in the drum axis direction. Reference numeral 107 denotes an fθ lens, which optically corrects the scanning light so that the laser spot is focused on the image region dg of the photosensitive drum 101. Reference numeral 109 denotes a BD sensor, which detects the laser beam scanning light on the laser irradiation surface of the polygon mirror 106 and generates a BD signal 110 that is a reference signal for main scanning.

  When forming an image, first, the photosensitive drum 101 is uniformly charged, and the photosensitive drum 101 is irradiated with laser light according to the image. Thereby, an electrostatic latent image is formed on the photosensitive drum 101. By developing the electrostatic latent image with toner, a toner image corresponding to the image is formed on the photosensitive drum 101. The formed toner image is transferred onto a sheet, and a permanent visible image is created by fixing the toner on the sheet on the sheet by applying pressure and temperature with a fixing device.

  However, when the photosensitive drum 101 is uniformly charged by the primary charger 102, there is a problem that the formed image quality is deteriorated due to generation of potential unevenness. Further, this potential unevenness occurs in the entire photosensitive drum 101. That is, potential unevenness occurs not only at the image formation position (position where development is performed with toner) but also at a position where image formation is not performed (position where development is not performed using toner). Therefore, as is conventionally done, even if the potential unevenness at the image forming position is improved, problems such as image fogging and blurring of the image edge occur. Therefore, in order to further improve the image quality, the image forming apparatus according to the present embodiment reduces potential unevenness generated on the photosensitive drum 101 not only at the image forming position but also at a position where no image formation is performed. This improves the image quality.

  When measuring the potential unevenness of the photosensitive drum 101, first, the photosensitive drum 101 is rotated at a predetermined rotational speed at which charging is stabilized, and is charged by the primary charger 102 to −700 V, for example. The potential sensor 104 is movably disposed at an arbitrary position in the main scanning direction. Therefore, for example, when it is desired to measure the potential of 50 blocks of the main scanning 5 blocks and the sub-scanning 10 blocks on the two-dimensional surface of the photosensitive drum 101, the potential sensor 104 is moved to a block position where the main scanning is performed. Thereafter, the block is measured for 10 sub-scanning blocks. If this operation is performed for each block of main scanning, the charged potentials on the photosensitive drums 101 of all 50 blocks on the two-dimensional surface can be measured. As described above, in the image forming apparatus according to the present embodiment, the surface potential is measured in a divided region obtained by dividing the surface of the photosensitive drum into a plurality of regions. Further, regarding the potential unevenness when the laser is turned on (exposure position), the photosensitive drum 101 is charged by the primary charger 102, the image area dg is exposed by the semiconductor laser 105 at a predetermined exposure amount, and the same measurement as described above is performed. It can be measured by executing the operation.

<Measurement method of potential unevenness>
Next, with reference to FIGS. 2A and 2B, a method for measuring the two-dimensional surface of the photosensitive drum 101 will be described. FIG. 2A is a diagram illustrating a configuration example of the periphery of the photosensitive drum according to the first embodiment.

  A drum driving motor 201 directly drives the photosensitive drum 101. Normally, the motor to the rotating shaft of the photosensitive drum 101 is driven while being decelerated via a gear or a belt. However, uneven rotation of the gear pitch or uneven rotation of the belt meshing pitch occurs on the shaft of the photosensitive drum 101. As a result, density unevenness due to pitch unevenness may also occur in the image, so it is desirable to use direct drive.

  Reference numeral 207 denotes a drum HP (home position) sensor, which is a reflective sensor for detecting the HP mark 208 provided outside the image area of the photosensitive drum 101. The drum HP sensor 207 generates a signal indicating the origin of the rotational phase of the photosensitive drum. Therefore, since the photosensitive drum 101 is driven at a predetermined constant rotational speed by the drum drive motor 201, the sub-scan of the two-dimensional surface of the photosensitive drum 101 is measured by measuring the output time of the signal from the drum HP sensor 207. You can know the position of the direction.

  A stepping motor 202 is a drive source for moving the potential sensor 104 in the main scanning direction. When the drive shaft of the stepping motor 202 is rotated counterclockwise (CCW), the potential sensor 104 moves to the main scanning direction 111 side. When the drive shaft of the stepping motor 202 is rotated clockwise (CW), the potential sensor 104 moves in the CW direction of the main scanning direction.

  Reference numeral 205 denotes an HP sensor as a potential sensor, which is a transmissive photo interrupter. When the photo interrupter 205 detects the HP flag 206, the movement of the potential sensor 104 is stopped at a predetermined reference position other than the image area dg in the main scanning direction.

  When measuring the potential unevenness of the photosensitive drum 101, the potential sensor 104 is moved by the stepping motor 202 to the main scanning position where the potential unevenness is to be detected. Before starting the measurement, a home position operation for reliably moving the potential sensor 104 to the reference position is performed. In this operation, the potential sensor 104 is moved by the stepping motor 202, and the potential sensor 104 is reliably stopped at the reference position by stopping the motor while the photo interrupter 205 detects the HP flag 206 during CCW rotation. Can be in a state.

  The predetermined distance in the main scanning direction from the reference position can be realized by driving the stepping motor 202 by the number of pulses corresponding to the distance. The operation of the stepping motor 202 has a characteristic that, for example, the drive shaft rotates 0.36 degrees with one drive pulse. In the moving mechanism of the potential sensor 104 according to this embodiment, since the potential sensor 104 moves according to the rotation angle of the gear attached to the motor drive shaft, the potential sensor 104 changes according to the rotation speed and rotation angle of the stepping motor 202. The distance traveled is fixed. Therefore, the distance between the plurality of potential measurement points from the photo interrupter 205 in the main scanning direction is determined in advance, and the number of rotations of the stepping motor 202 corresponding to the distance and the number of drive pulses corresponding to the rotation angle are calculated in advance, thereby The potential at any position can be measured.

  FIG. 2B is a diagram for explaining a method of measuring potential unevenness for one rotation in the photosensitive drum according to the first embodiment. The drum driving motor 201 that directly drives the photosensitive drum 101 includes an encoder, and the rotation speed and phase information of the motor driving shaft are output from the encoder. The drum drive motor 201 is controlled so that the motor drive shaft rotates at a constant rotation according to the speed and phase information. Since the motor drive shaft and the photosensitive drum shaft are directly connected because of the direct drive motor, the photosensitive drum 101 always has a constant rotational speed and a constant phase. The movement distance D (mm) in the sub-scanning direction on the drum surface from the reference position is a predetermined drum rotation speed V (mm / sec) and a reference after the HP mark 208 is detected by the drum HP sensor 207. It is obtained by multiplying the time t (sec) from the position signal.

D (mm) = V (mm / sec) × t (sec) (1)
Therefore, the time from the reference position to an arbitrary position in the sub-scanning direction is
t (sec) = D (mm) / V (mm / sec) (2)
It becomes. Therefore, the potential unevenness at the predetermined position D (mm) in the sub-scanning direction of the photosensitive drum 101 from the reference position is the potential of the photosensitive drum 101 by the potential sensor 104 after t (sec) obtained from the reference signal by the equation (2). Should be sampled.

  Reference numeral 221 denotes a state where the reference position of the photosensitive drum 101 is developed on a two-dimensional surface. 224 indicates the main scanning direction, and 225 indicates the sub-scanning direction. Reference numeral 220 denotes a reference position. Here, the two-dimensional surface of the photosensitive drum 101 is divided into five regions with addresses 1 to 5 in the main scanning direction and 10 regions with addresses A to J in the sub-scanning direction, and 50 as 1A to 5J as two-dimensional surfaces. It is divided into areas.

  As described above, the method for measuring the potential unevenness in the photosensitive drum 101 has been described here. However, instead of measuring the potential unevenness, previously measured potential unevenness information may be stored in advance. An example of a method for acquiring previously measured drum potential unevenness information is shown in FIG.

  FIG. 18 is a diagram illustrating a method of acquiring potential unevenness information measured in advance. Reference numeral 1801 denotes a barcode attached to the photosensitive drum 101. The bar code 1801 holds identification information of the photosensitive drum 101. Using this identification information, it is possible to identify which photosensitive drum the potential unevenness information corresponds to.

  Specifically, when potential unevenness data on the photosensitive drum 101 is measured, drum identification information is read by the barcode reader 1802, and potential unevenness information is stored in the data server 1803 together with this identification information. Thereafter, the barcode reader 1808 reads the barcode 1807 attached to the drum when the drum is incorporated into the image forming apparatus 100, acquires the corresponding potential unevenness information from the data server 1803 via the LAN 1804, and the image forming apparatus. 100. With the mechanism described above, potential unevenness information measured in advance can be acquired, and potential unevenness correction can be easily performed.

  3A and 3B are diagrams showing the results of measuring the potential unevenness on the two-dimensional surface of the photosensitive drum. Reference numeral 301 in FIG. 3A indicates potential unevenness in the main scanning direction at the sub-scanning addresses D and H on the two-dimensional surface of the drum when the photosensitive drum 101 is charged to 550 V and laser light is not scanned. Horizontal axes 302 and 306 indicate main scanning addresses of the two-dimensional drum surface. The vertical axis 305 indicates the measured drum potential (V). Reference numeral 308 denotes a laser drive current amount.

  As a characteristic of the semiconductor laser 105, it has a reference current Ith of laser emission, and shows a characteristic of an LED emission region at a current of Ith320 or less and a laser emission region at a current of Ith or more. That is, since the laser drive current 307 is equal to or less than Ith320 over the entire main scanning address on the two-dimensional drum surface, the semiconductor laser 105 does not emit laser light. Therefore, in FIG. 3A, the measurement result is obtained when the photosensitive drum 101 is not exposed to the laser beam.

  In this state, if the charging sensitivity of the photosensitive drum 101 is the same over the entire two-dimensional surface, if charging is performed at 550 V, the charging voltage is 550 V over the entire two-dimensional surface of the drum, and the measurement result of the potential sensor is also 550 V. is there. However, if there is uneven charging sensitivity, for example, in the measurement result 303 at the sub-scanning address D on the two-dimensional surface of the drum, the charging characteristics differ depending on the region, such as 520 V at the main scanning address 1 and 550 V at the main scanning address 3. This characteristic is different for each region of the two-dimensional surface. For example, in the measurement result 304 at the sub-scanning address H of the drum two-dimensional surface, it varies depending on the region, such as 500 V for the main scanning address 1 and 520 V for the main scanning address 3.

  Reference numeral 309 in FIG. 3B indicates potential unevenness in the main scanning direction at the sub-scanning addresses C and H on the two-dimensional surface of the drum when the photosensitive drum 101 is charged to 550 V and laser light is scanned. Horizontal axes 310 and 314 indicate main scanning addresses of the two-dimensional drum surface. The vertical axis 313 indicates the measured drum potential (V). The vertical axis 316 indicates the amount of laser drive current.

  As a characteristic of the semiconductor laser 105, it has a reference current Ith of laser emission, and shows a characteristic of an LED emission region at a current of Ith320 or less and a laser emission region at a current of Ith or more. That is, since the laser drive current 315 is equal to or greater than Ith320 over the entire main scanning address on the two-dimensional surface of the drum, laser light emission is performed and the photosensitive drum 101 is exposed with the laser light.

  In this state, if the charging sensitivity of the photosensitive drum 101 is the same over the entire two-dimensional plane, for example, 200V is uniform, and the measurement result of the potential sensor is also 200V. However, if there is uneven charging sensitivity, for example, in the measurement result 311 at the sub-scanning address C on the two-dimensional surface of the drum, the charging characteristics differ depending on the region, such as 170 V for the main scanning address 1 and 200 V for the main scanning address 3. This characteristic is different for each region of the two-dimensional surface. For example, in the measurement result 312 at the sub-scanning address H of the drum two-dimensional surface, it varies depending on the region, such as 150 V for the main scanning address 1 and 165 V for the main scanning address 3.

  Accordingly, the photosensitive drum 101 is charged with a predetermined potential, and the potential of the two-dimensional surface of the drum when laser light is emitted is measured, and the potential of the two-dimensional surface of the drum when no laser light is emitted is measured. Unevenness characteristics can also be measured.

<Correction method for potential unevenness>
4A and 4B are diagrams illustrating potential unevenness correction in the laser non-exposed portion of the photosensitive drum according to the first embodiment. Reference numeral 401 in FIG. 4A shows a method for correcting drum potential (second potential) unevenness which is a laser non-lighting portion (non-exposure position) without image data at the sub-scanning address D on the two-dimensional drum surface. Horizontal axes 403 and 407 indicate main scanning addresses on the two-dimensional drum surface. The vertical axis 402 represents the measured drum potential (V). The vertical axis 406 represents the laser drive current. Reference numeral 404 denotes a measurement result when the photosensitive drum 101 is charged at 550 V and the laser is not lit. That is, it is a measurement result in the case of a laser drive current 409 that is equal to or less than Ith.

  The characteristic of the photosensitive drum 101 is a characteristic in which the charged potential is lowered by exposing the photosensitive drum 101 with laser light, and the amount of potential reduction is determined according to the amount of laser light. According to this embodiment, after measuring all the potentials of the two-dimensional surface of the photosensitive drum 101 when the laser is not lit, the laser driving current is set so that the potential of the photosensitive drum 101 is adjusted to the lowest voltage of the measurement result, here, 500V. Increase. Thereby, potential unevenness when the laser is not turned on can be eliminated. That is, the potential is corrected to 500 V by exposing a minute laser beam to a region having potential unevenness of 500 V or more.

  Therefore, in order to cause the laser to emit a small amount of light according to the potential unevenness data on the two-dimensional drum surface, the laser is driven in the laser emission region with a correction current 408 equal to or greater than Ith even in the non-laser emission region according to the image data. . As a result, the measurement result 404 including the potential unevenness can be corrected like a 500V uniform charging potential 405.

  Reference numeral 410 in FIG. 4B denotes a method for correcting drum potential unevenness in which there is no image data at the sub-scanning address H on the two-dimensional drum surface, which is a laser non-lighting portion. The horizontal axes 412 and 416 indicate main scanning addresses on the two-dimensional drum surface. The vertical axis 411 represents the measured drum potential. The vertical axis 415 indicates the laser drive current. Here, reference numeral 414 denotes a measurement result when the photosensitive drum 101 is charged at 550 V and the laser is not lit. That is, it is a measurement result in the case of the laser drive current 418 that is equal to or less than Ith.

  Similar to FIG. 4A, after all the potentials of the two-dimensional surface of the photosensitive drum 101 when the laser is not turned on are measured, the laser driving current is corrected so that the potential of the photosensitive drum 101 is adjusted to the lowest voltage of the measurement result, here 500V. To do. That is, the laser drive current is increased.

  Therefore, the laser is driven with a correction current 417 equal to or greater than Ith even in the non-laser emission region according to the image data so that the laser emits a minute amount of light according to the potential unevenness data on the two-dimensional drum surface. As a result, the measurement result 414 including the potential unevenness can be corrected like a 500V uniform charging potential 413. 4A and 4B is an example of the control in the second correction unit.

  As a method for correcting the potential unevenness due to the laser light, the potential unevenness may be corrected by reading out the potential unevenness data when the laser on the two-dimensional surface of the drum is not lit from a memory or the like storing the potential unevenness measured in advance. . In this case, for example, since the drum characteristic is such that the potential decreases according to the exposure amount with the laser beam, it is desirable to obtain the laser light emission amount according to the amount of potential unevenness from the minimum potential with reference to the minimum potential. In addition, in order to set the charging potential to 500 V for each of the two-dimensional regions, the laser current is increased stepwise for a predetermined region, and the laser current read by the potential sensor 104 becomes 500 V. A correction amount for the region may be used.

  5A and 5B are diagrams illustrating potential unevenness correction in the laser exposure unit of the photosensitive drum according to the first embodiment. Reference numeral 501 in FIG. 5A indicates a method for correcting drum potential (first potential) unevenness, which has image data at the sub-scanning address C on the two-dimensional surface of the drum and is a laser lighting portion (exposure position). Horizontal axes 503 and 507 indicate main scanning addresses on the two-dimensional drum surface. The vertical axis 502 indicates the measured drum potential. The vertical axis 506 represents the laser drive current. Here, reference numeral 504 denotes a measurement result at the time of laser lighting after the photosensitive drum 101 is charged at 550V. That is, it is a measurement result in the case of a laser drive current 508 that is equal to or less than Ith.

  According to this embodiment, after all the potentials of the two-dimensional surface of the photosensitive drum 101 at the time of laser lighting are measured, the laser drive current is set so that the potential of the photosensitive drum 101 is adjusted to the highest voltage of the measurement result, here 200V. to correct. In other words, in the region having the potential unevenness of 200 V or less, the laser light potential on all the drum surfaces is corrected to 200 V by reducing the laser light quantity. Thereby, potential unevenness at the time of laser lighting can be eliminated.

  Therefore, the laser is driven with the correction current 509 in the laser emission region in order to correct the laser light amount in accordance with the potential unevenness data on the two-dimensional drum surface. As a result, the measurement result 505 including the potential unevenness can be corrected like a charging potential 504 having a uniform voltage of 200V.

  Reference numeral 510 in FIG. 5B shows a method for correcting drum potential unevenness, which has image data at the sub-scanning address H on the two-dimensional drum surface and is a laser lighting portion. Horizontal axes 512 and 516 indicate main scanning addresses on the two-dimensional surface of the drum. The vertical axis 511 represents the measured drum potential. The vertical axis 515 indicates the laser drive current. Here, reference numeral 514 denotes a measurement result when the photosensitive drum 101 is charged at 550 V and the laser is not turned on. That is, it is a measurement result in the case of the laser drive current 517 that is equal to or less than Ith.

  Similarly to FIG. 5A, after all the potentials of the two-dimensional surface of the photosensitive drum 101 at the time of laser lighting are measured, the laser light quantity is lowered so that the potential of the photosensitive drum 101 is adjusted to the highest voltage of the measurement result, here 200V. That is, the laser drive current is reduced.

  Accordingly, the laser is driven with the correction current 518 in the laser emission region in order to correct the laser light amount according to the potential unevenness data of the two-dimensional drum surface. As a result, the measurement result 514 including the potential unevenness can be corrected like a 200 V uniform charging potential 513. As described above, the potential unevenness correction method of FIGS. 5A and 5B is an example of control in the first correction unit.

  As a method for correcting potential unevenness due to laser light, potential unevenness may be corrected by reading out potential unevenness data at the time of laser lighting of the two-dimensional drum surface from a memory or the like that stores previously measured potential unevenness. In this case, for example, since the drum characteristic is such that the potential decreases according to the exposure amount with the laser beam, it is desirable to obtain the laser light emission amount according to the amount of potential unevenness from the maximum potential with reference to the maximum potential. Further, in each two-dimensional region, in order to set the charging potential to 200 V, the laser current amount at the time of laser lighting in each region may be obtained. Specifically, the laser current is increased stepwise in a region where the measurement result of potential unevenness is lower than 200V, and the laser current whose potential read by the potential sensor 104 becomes 200V is corrected for that region. It may be an amount.

<Laser drive unit>
FIG. 6 is a diagram illustrating a configuration example of the laser driving unit according to the first embodiment. As a laser drive unit that has been used in a conventional image forming apparatus, a bias current control unit that is equal to or less than Ith to a semiconductor laser, and a drive current control unit that controls a current added to the bias current and controls a laser emission amount. It was the composition of. However, the laser drive unit 3 according to this embodiment includes two drive current control units, and determines which drive current control unit is used according to image data.

  Reference numeral 601 in FIG. 6 denotes a Laser_ON signal corresponding to the image signal. When the Laser_ON signal 601 is “L”, the switch 608 is turned on and the switch 609 is turned off. Therefore, the current amount ib + iL (mA), which is the sum of the current iL (mA) and the bias current ib (mA) flowing in the constant current circuit 607 controlled at a constant current according to the current setting voltage VL603, is the current mirror. The circuit 610 flows. In this case, since the current iP (mA) flowing through the semiconductor laser 105 is controlled to the same current, iP (mA) = ib + iL (mA).

  When the Laser_ON signal 601 is “H”, the switch 609 is turned on and the switch 608 is turned off. Therefore, ib + iD (mA), which is the sum of the current iD (mA) and the bias current ib (mA) flowing through the constant current circuit 612 controlled at a constant current according to the current setting voltage VD604, is the current mirror. The circuit 610 flows. In this case, since the current iP (mA) flowing through the semiconductor laser 105 is controlled to the same current, iP (mA) = ib + iD (mA).

  Here, the current setting voltage VL603 for setting the current iL is set to a voltage corresponding to the correction current amount corresponding to the drum potential unevenness when the laser is turned off. Further, as the correction voltage, a voltage corresponding to the drum potential unevenness amount at the time of laser OFF at the phase of the drum is sequentially set according to the rotation phase from the drum HP. Therefore, even in a region where the laser is turned off according to the image data, in this embodiment, the laser driving current can be controlled according to the potential unevenness characteristic of the drum.

  The current setting voltage VD 604 for setting the current iD is set to a voltage corresponding to the correction current amount corresponding to the drum potential unevenness when the laser is ON. Further, as the correction voltage, a voltage corresponding to the amount of drum potential unevenness at the time of laser ON at the phase of the drum is set in accordance with the rotation phase from the drum HP. Therefore, even in a region where the laser is turned on according to the image data, the laser driving current can be controlled according to the potential unevenness characteristic of the drum.

  FIG. 7 is a timing chart of the laser driving unit according to the first embodiment. The vertical axis 701 indicates the laser drive current, and the horizontal axis 702 indicates the main scanning address. In FIG. 7, the current amount when the laser is OFF is 704 and the current amount when the laser is ON is 703 for correcting the drum potential unevenness corresponding to the main scanning address in the sub-scanning address portion on the two-dimensional drum surface. It is shown that.

  The corrected laser drive current 704 is a current ib + iL (mA) obtained by adding the bias current ib and the correction current iL when the laser is OFF, and the laser is driven with this current amount when the laser is OFF according to the main scanning address. The corrected laser drive current 703 is a current ib + iD (mA) obtained by adding the bias current ib and the correction current iD when the laser is ON, and the laser is driven with this amount of current when the laser is ON according to the main scanning address.

  Reference numeral 705 denotes Video_CLK, which is a reference signal for the main scanning address. Reference numeral 706 denotes a Laser_ON signal, which is a signal for performing exposure control for forming an image by controlling ON / OFF of the laser in accordance with the image with respect to the main scanning address. Vb707 is a reference voltage for controlling the bias current. Normally, the Ith current changes in the semiconductor laser 105 due to the long-period temperature characteristics, but the bias current set to be equal to or less than the Ith current is controlled so as to always be a predetermined value or less with respect to Ith. In this embodiment, scanning of one line with a short cycle is shown as an example. Since there is no change in Ith, the bias current is also constant, so Vb 707 is also constant.

  Reference numeral 708 denotes a reference voltage of a constant current circuit corresponding to the amount of laser light for correcting drum potential unevenness when the laser is OFF. By setting the reference voltage VL708 according to the drum potential unevenness when the laser is OFF, the laser drive current is corrected as indicated by 704. Reference numeral 709 denotes a reference voltage of a constant current circuit corresponding to the amount of laser light for correcting drum potential unevenness when the laser is on. By setting the reference voltage VD 709 according to the drum potential unevenness when the laser is ON, the laser driving current is corrected as indicated by 703.

  Reference numeral 710 denotes the laser drive current amount after the laser drive currents 703 and 704 are selected in response to the Laser_ON signal 706. When the Laser_ON signal 706 is “L”, the laser drive current 704 is selected, and when the Laser_ON signal 706 is “H”, the laser drive current 703 is selected. This realization can be realized for the first time with the configuration of the laser drive unit 3 in FIG. 6 described above, and cannot be executed by a conventional laser drive unit.

  Reference numeral 711 denotes the laser light amount after the drum potential unevenness correction is performed in accordance with the Laser_ON signal 706. Conventionally, even in the region indicated by 712 in which the Laser_ON signal 706 is “L” and OFF, in this embodiment, the laser is caused to emit a small amount of light to correct drum potential unevenness. Further, even in a region 713 where the Laser_ON signal 706 is “H” and ON 713, the laser light quantity is changed according to the drum potential unevenness to correct the potential unevenness.

  As described above, the image forming apparatus according to the present embodiment reduces the exposure amount of the exposure apparatus so as to eliminate the potential unevenness when the charged photosensitive drum is exposed and the potential unevenness when the photosensitive drum is not exposed. to correct. Further, the potential unevenness in the exposed state and the potential unevenness in the unexposed state are measured in a divided region obtained by dividing the surface of the photosensitive drum into a plurality of regions. As a result, the image forming apparatus measures the potential unevenness at a high speed and also eliminates the potential unevenness at a position where the toner is not developed (non-exposed position). As a result, it is possible to reduce blurring of edges such as image fog and characters.

<Second Embodiment>
Next, a second embodiment will be described with reference to FIGS. 8A to 11. In the present embodiment, 8-bit multi-value data is used as image data, the laser lighting pulse width is adjusted with a 256 pulse width from 0 (h) to FF (h), and potential unevenness is corrected.

  8A and 8B are diagrams illustrating measurement results of potential unevenness on the two-dimensional surface of the photosensitive drum. Reference numeral 801 in FIG. 8A indicates potential unevenness in the main scanning direction at the sub-scanning addresses D and H on the two-dimensional surface of the drum when the photosensitive drum 101 is charged to 550 V and laser light is not scanned. Horizontal axes 802 and 806 indicate main scanning addresses of the two-dimensional drum surface. The vertical axis 805 represents the measured drum potential (V). The vertical axis 308 indicates the laser lighting pulse width.

  As indicated by reference numeral 807, since the laser lighting pulse width is “0” over the entire main scanning address on the two-dimensional surface of the drum, the photosensitive drum 101 is not exposed to the laser beam without laser emission. In this state, if the charging sensitivity of the photosensitive drum 101 is the same throughout the two-dimensional surface, if charging is performed at 550 V, the charging voltage is 550 V in the entire region of the two-dimensional surface of the drum, and the measurement result of the potential sensor 104 is also 550 V. It becomes. However, if there is uneven charging sensitivity, for example, in the measurement result 803 of the sub-scanning address D on the two-dimensional drum surface, the charging characteristics differ depending on the region, such as 520 V for the main scanning address 1 and 550 V for the main scanning address 3. This characteristic is different for each region of the two-dimensional surface. For example, in the measurement result 804 of the sub-scanning address H of the drum two-dimensional surface, it varies depending on the region, such as 500 V for the main scanning address 1 and 520 V for the main scanning address 3.

  Reference numeral 809 in FIG. 8B indicates potential unevenness in the main scanning direction at the sub-scanning addresses C and H on the two-dimensional surface of the drum when the photosensitive drum 101 is charged to 550 V and laser light is scanned. Horizontal axes 810 and 814 indicate main scanning addresses of the two-dimensional drum surface. The vertical axis 813 represents the measured drum potential (V). The vertical axis 816 represents the laser lighting pulse width.

  As shown at 815, the laser lighting pulse width is “FF” over the entire area of the main scanning address on the two-dimensional surface of the drum (the laser is always on in the entire area of the main scanning address). The photosensitive drum 101 is exposed with a laser beam. In this state, if the charging sensitivity of the photosensitive drum 101 is the same over the entire two-dimensional plane, for example, 200V is uniform, and the measurement result of the potential sensor 104 is also 200V. However, when there is uneven charging sensitivity, for example, in the measurement result 811 at the sub-scanning address C on the two-dimensional drum surface, the charging characteristics differ depending on the region, such as 170 V for the main scanning address 1 and 200 V for the main scanning address 3. This characteristic is different for each region of the two-dimensional surface. For example, in the measurement result 812 of the sub-scanning address H of the drum two-dimensional surface, it varies depending on the region, such as 150 V for the main scanning address 1 and 165 V for the main scanning address 3.

  Accordingly, the photosensitive drum 101 is charged with a predetermined potential, and the potential of the two-dimensional surface of the drum when laser light is emitted is measured, and the potential of the two-dimensional surface of the drum when no laser light is emitted is measured. Unevenness characteristics can also be measured.

  FIGS. 9A and 9B are diagrams illustrating potential unevenness correction of the laser non-exposed portion of the photosensitive drum according to the second embodiment. Reference numeral 901 in FIG. 9A indicates correction of drum potential unevenness that is a laser non-lighting portion when the image data at the sub-scanning address D on the two-dimensional surface of the drum is “0 (h)”. Horizontal axes 903 and 907 indicate main scanning addresses on the two-dimensional drum surface. The vertical axis 902 indicates the measured drum potential (V). The vertical axis 906 indicates the laser lighting pulse width. Here, reference numeral 904 denotes a measurement result when the photosensitive drum 101 is charged at 550 V and the laser is not lit. That is, it is a measurement result when the laser lighting pulse width 909 is “0 (h)”.

  Similar to the first embodiment, in the present embodiment, when the image data that is a non-laser emission region is “0 (h)” in order to cause the laser to emit a small amount of light according to the potential unevenness data of the two-dimensional drum surface. Also, the laser is driven with the correction pulse width 908. As a result, the measurement result 904 including the potential unevenness can be corrected like a charging potential 905 having a uniform voltage of 500V.

  Reference numeral 910 in FIG. 9B indicates correction of drum potential unevenness that is a laser non-lighting portion when the image data at the sub-scanning address H on the two-dimensional surface of the drum is “0 (h)”. Horizontal axes 912 and 916 indicate main scanning addresses on the two-dimensional drum surface. The vertical axis 911 indicates the measured drum potential (V). The vertical axis 915 indicates the laser lighting pulse width. Here, reference numeral 914 denotes a measurement result when the photosensitive drum 101 is charged at 550 V and the laser is not lit. That is, this is a measurement result when the laser lighting pulse width 918 is “0 (h)”.

  Similar to the first embodiment, in the present embodiment, when the image data that is a non-laser emission region is “0 (h)” in order to cause the laser to emit a small amount of light according to the potential unevenness data of the two-dimensional drum surface. Also, the laser is driven with the correction pulse width 917. As a result, the measurement result 914 including the potential unevenness can be corrected like a 500 V uniform charging potential 913.

  As a method for correcting the potential unevenness due to the laser light, the potential unevenness may be corrected by reading out the potential unevenness data when the laser on the two-dimensional surface of the drum is not lit from a memory or the like storing the potential unevenness measured in advance. . In this case, for example, since the drum characteristic is such that the potential decreases according to the exposure amount with laser light, it is desirable to obtain the laser emission pulse width according to the amount of potential unevenness from the minimum potential with reference to the minimum potential. Further, in order to set the charging potential to 500 V for each of the two-dimensional regions, the laser light emission pulse width is increased stepwise for a predetermined region, and the laser light emission with the potential read by the potential sensor 104 becomes 500 V. The pulse width may be a correction amount for the region.

  10A and 10B are diagrams illustrating potential unevenness correction in the laser exposure unit of the photosensitive drum according to the second embodiment. 10A in FIG. 10A indicates correction of drum potential unevenness that is a laser lighting portion when the image data at the sub-scanning address C on the two-dimensional surface of the drum is “FF (h)”. Horizontal axes 1003 and 1007 indicate main scanning addresses on the two-dimensional surface of the drum. The vertical axis 1002 indicates the measured drum potential (V). The vertical axis 1006 indicates the laser lighting pulse width. Here, reference numeral 1005 denotes a measurement result at the time of laser lighting with the photosensitive drum 101 charged at 550V. That is, it is a measurement result when the laser lighting pulse width 1008 is “FF (h)”.

  Therefore, in the present embodiment, the laser lighting pulse width is corrected to the pulse width 1009 in order to perform laser light amount correction according to the potential unevenness data on the two-dimensional drum surface. As a result, the measurement result 1005 including the potential unevenness can be corrected like a charging potential 1004 having a uniform voltage of 200V.

  10B in FIG. 10B indicates correction of drum potential unevenness that is a laser lighting portion when the image data at the sub-scanning address H on the two-dimensional surface of the drum is FF (h) ". The horizontal axes 1012, 1016 are on the two-dimensional surface of the drum. The vertical axis 1011 indicates the measured drum potential (V), and the vertical axis 1015 indicates the laser lighting pulse width, where 1014 indicates a laser in which the photosensitive drum 101 is charged at 550V. The measurement result at the time of lighting is shown, that is, the measurement result when the laser lighting pulse width 1017 is “FF (h)”.

  Therefore, in the present embodiment, the laser lighting pulse width is corrected to the pulse width 1018 in order to perform laser light amount correction according to the potential unevenness data on the two-dimensional drum surface. As a result, the measurement result 1014 including the potential unevenness can be corrected like a charging potential 1013 having a uniform voltage of 200V.

  As a method for correcting potential unevenness due to laser light, potential unevenness may be corrected by reading out potential unevenness data at the time of laser lighting of the two-dimensional drum surface from a memory or the like that stores previously measured potential unevenness. In this case, for example, since the drum characteristic is such that the potential decreases according to the exposure amount with the laser beam, it is desirable to obtain the laser emission pulse width according to the amount of potential unevenness from the maximum potential with reference to the maximum potential. In addition, for each two-dimensional region, in order to set the charging potential to 200 V, measurement may be performed in each region to obtain the laser emission pulse width when the laser is turned on. Specifically, the laser light emission pulse width is gradually increased in a region where the measurement result of potential unevenness is lower than 200 V, and the laser light emission pulse width at which the potential read by the potential sensor 104 becomes 200 V is determined for the region. It may be a correction amount.

  11A to 11C are diagrams illustrating a configuration example of a laser driving unit according to the second embodiment. In a laser driving unit used in a conventional image forming apparatus, a density obtained by exposing a photosensitive drum with laser light and developing with toner according to image data is linear with respect to input image data. The laser lighting control was performed by correcting the pulse width with the LUT table. Therefore, conventionally, when the image data (8 bits) is “0 (h)”, the pulse width in one pixel is “0”.

  As shown in FIG. 11A, the laser driving unit 1100 according to the present embodiment passes the potential unevenness LUT1102 after gradation correction by the γ-LUT 1101, thereby increasing the pulse width when the image data is “0 (h)”. Correction is performed for each two-dimensional drum area. Furthermore, the pulse width at the time of FF (h) is also corrected, and the input pulse width region of 0 to 100% is set to the offset pulse width of 00 (h) according to the potential unevenness characteristic of the drum, and the input 100 The maximum output pulse width for% pulse width can be set. Thereby, the offset and the slope of the pulse width characteristic can be varied arbitrarily.

  FIG. 11B shows image data on the horizontal axis and the pulse width before correction on the vertical axis. 1116 is a value defined in the γLUT 1101. In the γ-LUT 1101, since the image data is 8-bit multi-value data, the input image data is 256 data from 0 (h) to FF (h).

  In FIG. 11C, the horizontal axis represents the γLUT output pulse width, and the vertical axis represents the corrected pulse width. Here, the γ characteristic of the laser drive pulse width with respect to the input image data is shown. This γ characteristic is set to a pulse width characteristic such that the toner density characteristic by laser exposure becomes linear with respect to the input image data. Reference numeral 1118 denotes a correction pulse width corrected by the potential unevenness LUT1102. Here, correction data characteristics for correcting the potential unevenness from the potential unevenness data when the laser is OFF and when the laser FF is turned on are shown.

  In this embodiment, when a γ input pulse width of 00 (h) is input according to the drum potential unevenness characteristic, the pulse width is corrected to 10 (h) and the γ input pulse width of FF (h) is If it is input, it is corrected to E0 (h). Therefore, the offset and the inclination are corrected so that the γ input pulse width of 00 (h) to FF (h) is 10 (h) to E0 (h). Thereafter, a pulse width signal is output to the laser driver 1103 and the laser 1104 is driven.

  As described above, even when the image data is “00 (h)” and the laser is not turned on, the potential unevenness of the drum can be corrected by emitting the laser with a minute pulse width. Further, even in a region where the laser is turned on with a pulse width corresponding to the image data in a region other than 00 (h) in the image data, the laser light quantity can be corrected according to the drum potential unevenness. Thereby, even when the image data is “00 (h)”, the potential unevenness of the photosensitive drum 101 can be corrected.

<Third Embodiment>
Next, a third embodiment will be described with reference to FIGS. FIG. 12 is a diagram for explaining an interpolation mechanism according to the third embodiment. Reference numeral 1202 denotes a main scanning direction which is an axial direction of the photosensitive drum 101, and 1203 denotes a sub-scanning direction which is a rotation direction of the photosensitive drum 101. Reference numeral 1204 denotes a reference signal for the rotational position of the photosensitive drum 101. This reference signal is generated every rotation of the photosensitive drum 101. The radius of the photosensitive drum 101 is r. 1201 is a development view of a two-dimensional drum surface. The main scanning direction of the two-dimensional surface indicates the maximum width of image writing. For example, in this embodiment, the image writing width is dg. The video clock is 700 clocks. The length 1206 in the sub-scanning direction is 2πr where r is the radius of the photosensitive drum 101. The number of scans for one rotation of the drum is equivalent to 600 lines. Therefore, the time conversion is 700 × VIDEO_CLK1 period time in the main scanning direction and 600 lines × 1h scanning time in the sub-scanning direction. The 1h scanning time indicates an interval between BD signals that are scanning reference signals.

  Reference numeral 1208 denotes one correction area having a two-dimensional surface 1201 on the photosensitive drum 101. Here, an example is shown in which the region of the main scanning address: 1 and the sub scanning address: H is further subdivided by interpolation. In order to correct the potential unevenness of the photosensitive drum 101, it is necessary to measure the potential of the photosensitive drum 101. However, as the measurement area on the two-dimensional surface of the drum increases, more accurate correction is possible, but a great amount of measurement time is required. appear. On the other hand, the smaller the measurement area, the lower the correction accuracy, but the measurement time can be reduced.

  However, as a product, it is necessary to solve a conflicting technical problem that high correction accuracy is required with a short measurement time. Therefore, in the present embodiment, as the measurement area, a plurality of sample areas capable of reproducing at least the potential unevenness profile in the drum main scanning direction and a plurality of sample areas capable of reproducing at least the potential unevenness profile in the sub-scanning direction. Measure the number. For example, as shown in 1201, the measurement is performed in 50 regions in which the main scanning direction is divided into five and the sub-scanning direction is divided into ten. However, when the drum potential unevenness is measured by dividing the main scanning direction into 5 parts, for example, the correction level greatly changes between the region 1 and the region 2, so even if potential unevenness correction is performed, this region is switched. Abrupt changes in concentration may occur. Therefore, in this embodiment, in order to realize highly accurate potential unevenness correction, a linear interpolation is performed between the measurement areas on the two-dimensional surface of the photosensitive drum 101, and a predetermined number of interpolation data is added.

FIG. 13 is a diagram illustrating an interpolation method according to the third embodiment. The vertical axis represents the set potential (V), and the horizontal axis represents the sub-scan interpolation address. Vα and Vβ indicate voltages obtained by actually measuring the drum potential at α and β of the sub-scanning address, respectively. V1, V2, and V3 indicate voltages interpolated from Vα and Vβ, respectively. Thus, if two points of Vα and Vβ are actually measured, potential unevenness between them can be predicted, interpolation data can be created, and data for smoothly correcting potential unevenness can be created. This interpolation mechanism will be described in detail below. If the number of interpolation data between measurement areas is n and m = n + 1,
V (n) = Vα + {(Vβ−Vα) / m} × n (3)
It is possible to perform linear interpolation by applying Therefore, V1 in FIG. 13 is assumed that n = 3 and m = 4. V1 = Vα + {(Vβ−Vα) / 4} × 1 (4)
V2 is n = 3 and m = 4 V2 = Vα + {(Vβ−Vα) / 4} × 2 (5)
V3 is assumed that n = 3 and m = 4. V3 = Vα + {(Vβ−Vα) / 4} × 3 (6)
Interpolation data can be created as Here, an example of creating interpolation data between drum potential measurement data has been described. However, exposure amount correction data at the time of exposure of the photosensitive drum 101 is created from the drum potential measurement data, and interpolation data is generated for the exposure correction data. You may create it.

  FIG. 14 is a circuit block diagram for creating interpolation data according to the third embodiment. Reference numeral 1401 denotes a sub-scanning address counter. The Drum_HP signal 1410 is a drum reference position signal, and is output once per drum rotation. Sub-scanning address counter 1401 counts the input of BD signal 1411 after the input of the reference position signal. The BD signal 1411 is a signal that is output once in one scan of the above laser scanner, and one scan is normally one pixel (600 dpi = about 42 μm). Therefore, by counting the number of times the BD signal 1411 is input after the Drum_HP signal 1410 is input, the rotational position from the drum reference position can be grasped. The sub scanning address counter 1401 outputs a sub scanning address 1407 that is a rotation position signal from the drum reference position.

  Reference numeral 1402 denotes a main scanning address counter. The main scanning enable signal (ENB) 1414 is a signal indicating the start of image writing, and is the leading signal of the image area portion of the photosensitive drum 101 when the semiconductor laser 105 performs laser scanning. After the input of the main scanning enable signal 1414, the input of Video_CLK 1413 is counted by the main scanning address counter 1402. Video_CLK 1413 has a cycle of one clock for one pixel (600 dpi = about 42 μm) of main scanning. Accordingly, by counting the number of times Video_CLK 1413 is input after the main scanning enable signal 1414 is input, the main scanning scanning position in the image area on the photosensitive drum 101 can be grasped. The main scanning address counter 1402 outputs a main scanning address 1408 that is a scanning position signal on the photosensitive drum 101.

  The interpolation unit 1403 interpolates between the drum potential unevenness measurement data 1404 based on the main scanning interpolation division number 1418 and the sub scanning interpolation division number 1417 based on the main scanning address 1408 and the sub scanning address 1407 of the photosensitive drum 101. To do. The interpolated data is input to the DA converter 1405 through the highlight portion potential unevenness LUT1421 that defines the relationship between the potential unevenness of the laser OFF portion and the potential unevenness correction laser current amount, and is supplied to the reference voltage VL1419 of the laser OFF side constant current circuit. Is generated.

  Further, the interpolated data is input to the DA converter 1406 through the dark portion potential unevenness LUT1422 that defines the relationship between the potential unevenness of the laser ON portion and the potential unevenness correction laser current amount, and the reference voltage of the laser ON-side constant current circuit. A VD 1420 is generated. As described above, smooth potential unevenness correction can be executed in a minute region that is larger than the measurement data by interpolating the result of measuring the potential unevenness for the entire region of the photosensitive drum 101.

  FIG. 15 is a timing chart for creating interpolation data according to the third embodiment. Reference numeral 1521 denotes a measurement timing of potential unevenness, and 1522 denotes a creation timing of correction data.

  A Drum_HP signal 1501 is output once every time the photosensitive drum 101 rotates once. Reference numerals 1502 and 1508 denote BD signals that are output once per laser scanner scan. The BD counters 1503 and 1509 are reset by Drum_HP, and the number of BD inputs from the Drum_HP signals 1501 and 1506 is counted. Reference numeral 1504 denotes an address division number which is the number of BDs / the number of measurements in one rotation of the drum in which the drum potential unevenness in the sub-scanning direction is measured. Reference numerals 1505 and 1507 denote divided sub-scan address areas. The sub-scanning interpolation count value 1510 indicates a value counted by the sub-scanning interpolation counter. Reference numeral 1511 denotes Vα in the above-described formula (3), 1512 denotes Vβ, and 1513 denotes m. Reference numeral 1514 denotes an interpolation output.

  As shown by 1521, in the case of this embodiment, 1000 shots of BD are input by one rotation of the drum. The address division number 1504 is set to BD number (= 1000) / measured number (= 10) per rotation of the drum in which the drum potential unevenness in the sub-scanning direction is measured. In the present embodiment, 100 (D) is set. Is done. Therefore, as the sub-scanning address 1505, the address of the potential unevenness measurement region is output. In the case of this embodiment, since 10 areas A to J are divided as measurement areas for sub-scanning, 10 areas 1 to 10 are output for sub-scanning addresses.

  The interpolation timing when the sub-scanning address is 1 to 2 will be described with reference to 1522. The sub-scanning interpolation BD counter is reset by switching the sub-scanning address and counts BD. Then, the count is increased by the value set in the area division number m1513, and the value obtained by counting the count UP signal by the sub-scan interpolation counter is a sub-scan interpolation count value 1510. This sub-scanning interpolation count value 1510 corresponds to n in the above equation (3). Further, based on the drum measurement potential Vα 1511 in region 1 and the drum measurement potential Vβ 1512 in region 2, an interpolation output 1514 corresponding to the sub-scanning interpolation count value 1510 is generated. Here, the interpolation timing of the measurement data of the sub-scan has been described, but the interpolation can be performed at the same timing in the main scan.

  As described above, the image forming apparatus according to the present embodiment measures the potential in the exposed state and the potential in the unexposed state in each divided region obtained by dividing the surface of the photosensitive drum into a plurality of regions. Is corrected by correcting the drive current of the semiconductor laser. Furthermore, this image forming apparatus can realize smooth correction at high speed by interpolating between measured data. Further, correction data generated from measured data may be interpolated.

<Fourth Embodiment>
Next, a fourth embodiment will be described with reference to FIGS. FIG. 16 is a circuit block diagram for creating interpolation data according to the fourth embodiment. Here, only the blocks different from FIG. 14 will be described. Therefore, the same blocks as those in the circuit block diagram of FIG.

  The interpolated potential unevenness data 1602 when the laser is OFF is input to the corrected γLUT generation unit 1601 through the highlight portion potential unevenness LUT1421 in which the relationship between the potential unevenness of the laser OFF portion and the correction pulse width of the image data 00h of the γLUT is defined. Is done. Further, the interpolated potential unevenness data 1603 at the time of laser ON is passed through the dark portion potential unevenness LUT 1422 in which the relationship between the potential unevenness of the laser ON portion and the correction pulse width of the image data FFh of the γLUT is defined. Entered.

  The correction γLUT generation unit 1601 creates a new γLUT table from the correction data of 00h and FFh. Then, by exposing the photosensitive drum 101 with the pulse width converted by passing the image data through the γLUT, it is possible to perform smooth potential unevenness correction in a region where the potential unevenness of the photosensitive drum 101 is smaller than the measurement data.

  FIG. 17 is a timing chart for creating interpolation data according to the fourth embodiment. Reference numeral 1721 denotes a measurement timing of potential unevenness, and 1722 denotes a creation timing of correction data.

  Reference numeral 1701 denotes a Drum_HP signal, which is output once every time the photosensitive drum 101 rotates once. Reference numerals 1702 and 1708 denote BD signals that are output once per laser scanner scan. The BD counters 1703 and 1709 are reset by Drum_HP, and the number of BD inputs from the Drum_HP signals 1701 and 1706 is counted. Reference numeral 1704 denotes an address division number which is the number of BDs / the number of measurements in one rotation of the drum in which the drum potential unevenness in the sub-scanning direction is measured. Reference numerals 1705 and 1707 denote divided sub-scan address areas. The sub-scanning interpolation count value 1710 indicates a value counted by the sub-scanning interpolation counter. Reference numeral 1711 denotes Vα in the above-described formula (3), 1712 denotes Vβ, and 1713 denotes m. Reference numeral 1714 denotes an interpolation output.

  As shown in 1721, in the case of the present embodiment, 1000 BDs are input by one rotation of the drum. The address division number 1704 is set to BD number (= 1000) / measured number (= 10) in one rotation of the drum in which the drum potential unevenness in the sub-scanning direction is measured. In the present embodiment, 100 (D) is set. Is done. Therefore, the potential unevenness measurement area address is output as the sub-scanning address 1705. In the case of this embodiment, since 10 areas A to J are divided as measurement areas for sub-scanning, 10 areas 1 to 10 are output for sub-scanning addresses.

  The timing of interpolation when the sub-scanning address is 1 to 2 will be described with reference to 1722. The sub-scanning interpolation BD counter is reset by switching the sub-scanning address and counts BD. Then, the count is increased by the value set in the area division number m1713, and a value obtained by counting the count UP signal by the sub-scan interpolation counter is a sub-scan interpolation count value 1710. This sub-scanning interpolation count value 1710 corresponds to n in the above-described equation (3). Further, based on the drum measurement potential Vα 1711 in region 1 and the drum measurement potential Vβ 1712 in region 2, an interpolation output 1714 at the time of laser OFF corresponding to the sub-scan interpolation count value 1710 is generated. Similarly, an interpolation output 1715 when the laser is ON is also output. Here, the interpolation timing of the measurement data of the sub-scan has been described, but the interpolation can be performed at the same timing in the main scan.

  As described above, the image forming apparatus according to the present embodiment measures the potential in the exposed state and the potential in the unexposed state in each divided region obtained by dividing the surface of the photosensitive drum into a plurality of regions. Is corrected by correcting the drive pulse width of the semiconductor laser. Furthermore, this image forming apparatus can realize smooth correction at high speed by interpolating between measured data. Further, correction data generated from measured data may be interpolated.

<Fifth Embodiment>
Next, a fifth embodiment will be described with reference to FIGS. 19A to 24B. In the present embodiment, a more specific correction method for correcting potential unevenness occurring on the photosensitive drum 101 will be described. The hardware configuration according to this embodiment is the same as the hardware configuration shown in FIG. Here, the semiconductor laser 105 shown in FIG. 1 is described as the semiconductor laser 4.

<Control Configuration of Image Forming Apparatus>
First, the control configuration of the image forming apparatus according to the present embodiment will be described with reference to FIG. 19A. FIG. 19A is a schematic diagram illustrating a control configuration of the image forming apparatus according to the fifth embodiment. Here, the configuration related to the present invention will be mainly described. Therefore, the image forming apparatus according to the present invention may be realized including other configurations.

  The image forming apparatus 100 mainly includes an engine control unit 17, an image control unit 18, a laser driving unit 3, and a backup memory 16 as a control configuration. The engine control unit 17 controls the image control unit 18 to store the data signal 31 output from the EEPROM 5 included in the laser driving unit 3 in the backup memory 16. Further, the engine control unit 17 calculates a correction approximate value 25 of the light amount correction data output from the EEPROM 5 using the correction approximate expression stored in the backup memory 16. Further, the engine control unit 17 generates the light amount adjustment value 24 based on the input result of the light amount sensor included in the image forming apparatus 100 in order to control the laser driving current so that a predetermined laser is irradiated onto the photosensitive drum 101. To do. Further, the engine control unit 17 generates a sensitivity correction formula 26 based on sensitivity data stored in the EEPROM 8 provided in the photosensitive drum 101.

  The image control unit 18 reads out the data signal 31 of the EEPROM 5 and controls the state of the laser driving circuit 6 via the image control signal 23 from the engine control unit 17. The image control unit 18 also includes a correction data generation unit 19 that generates switching current (Isw) correction data 27 and bias current (Ib) correction data 28. Here, the switching current indicates a modulation driving current for driving the modulation unit of the semiconductor laser 4. Details regarding the correction data generation unit 19 will be described later with reference to FIG.

  The laser drive unit 3 includes a laser drive circuit 6, a correction current control circuit 9, and an EEPROM 5 in order to control the amount of light emitted from the semiconductor laser 4. The laser drive circuit 6 controls the drive current of the semiconductor laser 4 to cause the semiconductor laser 4 to emit light constantly with a predetermined light amount (intensity). The correction current control circuit 9 will be described later with reference to FIG. The semiconductor laser 4 includes a laser diode (hereinafter referred to as “LD”) 4a and a photodiode (hereinafter referred to as “PD”) 4b that monitors laser light output from the LD 4a. The PD 4b outputs a current corresponding to the amount of laser beam to be monitored.

  Next, a detailed configuration example of the laser drive circuit 6 shown in FIG. 19A will be described with reference to FIG. 19B. FIG. 19B is a block diagram illustrating a configuration example of a laser driving unit according to the fifth embodiment.

  Reference numeral 7 denotes a light amount adjustment variable resistor for adjusting the LD 4a to emit light with a predetermined light amount. The PD current (Im) corresponding to the light amount of the laser beam output from the PD 4 b is converted into a voltage by the light amount adjustment variable resistor 7 and output as a PD voltage signal 71. The PD voltage signal 71 is input to a light amount control circuit (APC CTL) 74 together with a reference voltage 73 generated by a reference voltage generation circuit (Vref) 72.

  The light amount control circuit 74 compares the PD voltage signal 71 with the reference voltage 73 when the light amount adjustment mode is set in the mode control circuit (MODE CTL) 78 by the mode control signal 10 input from the image control unit 18. To do. Furthermore, the semiconductor laser 4 is adjusted to a predetermined light quantity by controlling the switching current (Isw) set value 14 in an adjustable manner. Similarly, for example, the light emission start current of the semiconductor laser 4 is obtained from the drive current when 1/4 of the predetermined light quantity is set, and the current obtained by dividing or subtracting the predetermined current from the light emission start current is determined as the bias current (Ib ) Set value 20 is output. Further, when the current holding mode is set in the mode control circuit 78 by the mode control signal 10, the light amount control circuit 74 sets the switching current (Isw) setting value 14 based on the result obtained when the light amount adjustment mode is set. Hold.

  A switching current (Isw) control unit 75 outputs a drive signal 77 for the current driver based on the switching current (Isw) set value 14 and the switching correction value 12. A bias current (Ib) control unit 76 generates a bias current (Ib) based on the bias current (Ib) set value 20 and the bias correction value 13, and adds the drive current (Iop) to the current driver 88 output signal. ) 86 to drive the semiconductor laser 4.

  When the data output mode is set in the mode control circuit (MODE CTL) 78 by the mode control signal 10, the drive signal 77 of the current driver corresponding to the switching current (Isw) control unit 75 is output. A differential receiver (LVDS) 81 having a differential input receives a differential data signal input from the image control unit 18. When the sample mode is set in the mode control circuit 78 by the mode control signal 10, the output selection circuit (OUTPUT SELECT) 83 sets the switching signal a84 to ON and sets the switching signal b85 to OFF. When the data output mode is set, the switching signal a84 and the switching signal b85 corresponding to the differential output signal 82 are output.

  Reference numeral 88 denotes a current driver, which has a differential amplification configuration in which the emitter terminals of the transistors 88a and 88b are connected. The transistor 88a performs switching driving of the LD 4a based on the drive signal 77 and the switching signal a84. Similarly, the transistor 88b performs switching drive of the load resistor 89 based on the drive signal 77 and the switching signal b85.

<Configuration of Correction Data Generation Unit and Correction Current Control Circuit>
FIG. 20 is a block diagram illustrating a configuration example of a correction data generation unit and a correction current control circuit according to the fifth embodiment. As illustrated in FIG. 20, the correction data generation unit 19 includes a sensitivity correction coefficient calculation unit 32, a light amount correction value calculation unit 34, a sensitivity correction value calculation unit 36, and an adder 38. The sensitivity correction coefficient calculation unit 32 uses a light amount adjustment value (D) 24 determined by the engine control unit 17 based on an input result of a light amount sensor provided in the image forming apparatus 100 and a sensitivity correction formula 26 to obtain a sensitivity correction coefficient. 33 is generated. The light amount correction value calculation unit 34 calculates a light amount correction value 35 corresponding to the sensitivity correction coefficient 33 based on the correction approximate value 25 generated by the engine control unit 17.

  The sensitivity correction value calculation unit 36 receives the bias current (Ib) set value 20 from the laser drive circuit 6, calculates the sensitivity correction value based on the bias current (Ib) set value 20 based on the sensitivity correction formula 26, and the bias Current (Ib) correction data 28 is output. The bias current (Ib) correction data 28 is input to an adder 38 and a bias current (Ib) correction storage unit 42 described later.

  The adder 38 adds the bias current (Ib) correction data 28 and the light amount correction value 35 and stores the switching current (Isw) correction data 27 in a correction storage unit 40 described later.

  The correction current control circuit 9 includes a switching current (Isw) correction storage unit 40, a bias current (Ib) correction storage unit 42, a multiplier 44, a switching correction value generation unit 46, and a bias correction value generation unit 47. The Isw correction storage unit 40 stores the switching current (Isw) correction data 27 as described above. In addition, bias current (Ib) correction data 28 is input from the sensitivity correction value calculation unit 36 to the bias current correction storage unit 42. The multiplier 44 multiplies the switching current (Isw) set value 14 output from the laser driving circuit 6 by the light amount adjustment value (D) 24 and outputs a switching current (Isw) adjustment value 45. The switching correction value generation unit 46 generates the switching correction value 12 using the switching current (Isw) correction storage data 41 and the switching current (Isw) adjustment value 45 stored in the switching current (Isw) correction storage unit 40. . The bias correction value generation unit 47 uses the bias current (Ib) set value 20 output from the laser driving circuit 6 and the bias current (Ib) correction storage data 43 stored in the bias current (Ib) correction storage unit 42. Thus, the bias correction value 13 is generated.

<Correction method>
Here, the correction method in the present embodiment will be described with reference to FIGS. 21A and 21B. FIG. 21A is a diagram illustrating an image plane distribution characteristic of the photosensitive drum and an approximate expression generation method. FIG. 21B is a diagram illustrating a correction data generation method according to the fifth embodiment. In FIG. 21A, the horizontal axis indicates the image height, and the vertical axis indicates the drum surface light amount. Reference numeral 2101 denotes a fourth-order approximate expression at 100% light emission. Reference numeral 2102 denotes a fourth-order approximation expression at 80% light emission. Reference numeral 2103 denotes a fourth-order approximation expression at 60% light emission. Reference numeral 2104 denotes a fourth-order approximation expression at 40% light emission. Reference numeral 2105 denotes a fourth-order approximation expression at 20% light emission. In FIG. 21B, the horizontal axis represents the image height, and the vertical axis represents the image plane illuminance. Reference numeral 2111 denotes a block for measuring the illuminance on the image plane.

Here, the specifications for generating correction data are
Image height (within image area): ± 150mm
Image surface illuminance measurement / image height: 9 (37.5 mm equally spaced)
Image plane illuminance / approximate order: 4
Number of correction blocks: 25 (12.5 mm equidistant)
Illuminance measurement number: 5 (100%, 80%, 60%, 40%, 20%)
Laser drive current (ILD) resolution: 10 bits
And

  First, the light quantity of the semiconductor laser 4 is adjusted. Specifically, the image height in the image area (± 150 mm) is divided at an equal interval of 37.5 mm, and image plane illuminance measurement is performed at a total of nine locations. However, the intervals between the positions of the image height need not be equal. When the illuminance at the nine image heights is measured, the image height that is the minimum illuminance is detected, and the laser drive unit 3 is set to the light amount adjustment mode so that the illuminance at the image height becomes a predetermined value, thereby adjusting the light amount. The amount of light obtained as described above is defined as 100% light amount, and the laser drive current (ILD) set at this time is defined as 100% light amount drive current.

  Next, the image plane illuminance is measured. Specifically, the image plane illuminance is measured at nine image heights including 20%, 40%, 60%, and 80% light amount drive current with respect to 100% light amount drive current including 100% light amount drive current. .

  Next, an approximate expression is calculated. Specifically, a fourth-order approximate expression is generated from the measured values of image plane illuminance at nine image heights obtained by image plane illuminance measurement.

  Next, a correction value is calculated. Specifically, the illuminance correction value is calculated by a total of 25 correction blocks at an image area internal image height (± 150 mm) at an equal interval of 12.5 mm. The arrangement method of the correction block with respect to the image height may not coincide with the image height at the time of image plane illuminance measurement. From the fourth-order approximation, the image plane illuminance difference (X (k%) n) of the other 24 blocks with respect to the correction block having the lowest illuminance is calculated. Here, as shown in FIG. 21B, the image plane illuminance of the correction block 24 is the minimum illuminance. The image plane illuminance difference (X (k%) n) is quantized using the laser drive current (ILD) as a full scale to obtain correction data. When the resolution of the laser drive current (ILD) is 10 bits, the correction bit ΔX is 100% light amount drive current / 1024.

  Finally, the calculated correction value is stored. By the method described above, the correction count value is calculated with respect to the image plane illuminance when each light amount driving current of the laser driving current is set to 100%, 80%, 60%, 40%, and 20%. The correction count value obtained as a result is stored in the EEPROM 5 via the memory control signal 30.

<Light intensity correction value generation method>
FIG. 22 is a diagram for explaining a light amount correction value generation method in the light amount correction value calculation unit according to the fifth embodiment. In 2201, the horizontal axis indicates the light amount adjustment value D, and the vertical axis indicates the correction data characteristic when the correction data P is used. In 2202, the horizontal axis indicates the image height d, and the vertical axis indicates the correction coefficient ε (d). An nth-order approximation expression represented by a curve 2201 is stored in the backup memory 16. The correction coefficient ε (d) is stored in the backup memory 16. The following is assumed as the correction specification.
Correction specifications nth-order approximation P = 150D (2-D), second order 2. Light intensity adjustment value (D) = 70%
3. Sensitivity coefficient ε (d) Number of blocks = 24
Further, a method for calculating the light amount correction value 35 at the image height d = −125 mm will be described below.

  First, correction data based on an nth-order approximation is calculated. Specifically, the correction data P at the light amount adjustment value D = 70% is 150 × 0.7 × (2−0.7) = 136.5. Subsequently, correction data based on the sensitivity coefficient is calculated. Specifically, when the sensitivity coefficient ε (−125) = 0.8 at the image height d = −125 mm, P ′ = 150 × (0.7 × 0.8) × {2− (0.7 × 0.8)} = 121.0.

  FIG. 23 is a diagram for explaining a photosensitive drum potential correction method according to the fifth embodiment. In 2301, the horizontal axis represents the drive current Iop, and the vertical axis represents the laser light amount Po. Reference numeral 2302 denotes a light amount distribution before correction and a surface potential of the drum. Reference numeral 2303 denotes the light amount distribution after correcting the highlight potential VL and the surface potential of the drum. Reference numeral 2304 denotes a light amount distribution after correcting the highlight potential VL and the dark potential Vd and the surface potential of the drum.

  As a result of correcting the light amount distribution of the photosensitive drum 101 before correction by the light amount correction value 35 generated by the light amount correction value calculation unit 34, only the highlight potential VL becomes uniform as the surface potential. On the other hand, a result obtained by adding the bias current (Ib) correction data 28 generated by the sensitivity correction value calculation unit 36 to the light amount correction value 35 is referred to as switching current (Isw) correction data 27. Further, a drive current (Iop) of the semiconductor laser 4 is generated based on the bias current (Ib) correction data 28. Thereby, the dark potential Vd in the surface potential of the photosensitive drum 101 is corrected.

  Next, a control procedure for generating correction data and current correction values will be described with reference to FIGS. 24A and 24B. FIG. 24A is a flowchart illustrating a correction data generation procedure in the correction data generation unit according to the fifth embodiment.

  First, in step S2401, the correction data generation unit 19 reads the light amount adjustment value 24 from the engine control unit 17 by the sensitivity correction coefficient calculation unit 32. Further, in step S2402, the correction data generation unit 19 reads the sensitivity correction formula 26 from the engine control unit 17 by the sensitivity correction coefficient calculation unit 32. Thereafter, in step S 2403, the correction data generation unit 19 calculates the sensitivity correction coefficient 33 using the light amount adjustment value 24 and the sensitivity correction formula 26 by the sensitivity correction coefficient calculation unit 32.

  In step S <b> 2404, the correction data generation unit 19 calculates a light amount correction value 35 using the sensitivity correction coefficient 33 and the correction approximate value 25 by the light amount correction value calculation unit 34.

  In step S <b> 2405, the correction data generation unit 19 reads the bias current (Ib) set value 20 from the laser driving circuit 6 by the sensitivity correction value calculation unit 36. Subsequently, in step S2406, the correction data generation unit 19 reads the sensitivity correction formula 26 from the engine control unit 17 by the sensitivity correction value calculation unit 36, and calculates the sensitivity correction value 28 by calculating the bias current (Ib) set value 20. Is generated. Hereinafter, the sensitivity correction value 28 is also referred to as bias current (Ib) correction data 28.

  In step S <b> 2407, the correction data generation unit 19 adds the sensitivity correction value 28 to the light amount correction value 35 by the adder 38 to generate the switching current (Isw) correction data 27.

  In step S 2408, the correction data generation unit 19 stores the switching current (Isw) correction data 27 in the switching current (Isw) correction storage unit 40. In step S 2409, the correction data generation unit 19 stores the bias current (Ib) correction data 28 in the bias current (Ib) correction storage unit 42.

  FIG. 24B is a flowchart illustrating a procedure for generating a current correction value in the correction current control circuit according to the fifth embodiment.

  First, in step S 2411, the correction current control circuit 9 multiplies the light amount adjustment value 24 and the switching current (Isw) setting value by the multiplier 44 to generate a switching current (Isw) adjustment value 45.

  In step S 2412, the correction current control circuit 9 reads the switching current (Isw) correction storage data 41 from the Isw correction storage unit 40 by the switching correction value generation unit 46. In step S <b> 2413, the correction current control circuit 9 generates the switching correction value 12 by subtracting the switching current (Isw) correction stored data 41 from the switching current (Isw) adjustment value 45 by the switching correction value generation unit 46.

  In step S <b> 2414, the correction current control circuit 9 reads the bias current (Ib) set value 20 from the laser driving circuit 6 by the bias correction value generation unit 47. Subsequently, in step S <b> 2415, the correction current control circuit 9 reads the bias current (Ib) correction storage data 43 by the bias correction value generation unit 47. In step S 2416, the correction current control circuit 9 generates the bias correction value 13 by adding the bias current (Ib) set value 20 and the bias current (Ib) correction storage data 43 by the bias correction value generation unit 47. .

FIG. 2 is a diagram illustrating a partial hardware configuration in the image forming apparatus according to the first embodiment. FIG. 3 is a diagram illustrating a configuration example around a photosensitive drum according to the first embodiment. It is a figure for demonstrating the measuring method of the electrical potential nonuniformity for 1 round in the photosensitive drum which concerns on 1st Embodiment. , It is a figure which shows the result of having measured the electrical potential nonuniformity of the two-dimensional surface of a photosensitive drum. , It is a figure which shows the electric potential nonuniformity correction | amendment in the laser non-exposure part of the photosensitive drum which concerns on 1st Embodiment. , It is a figure which shows the electric potential nonuniformity correction | amendment in the laser exposure part of the photosensitive drum which concerns on 1st Embodiment. It is a figure which shows the structural example of the laser drive part which concerns on 1st Embodiment. It is a timing chart of the laser drive part concerning a 1st embodiment. , It is a figure which shows the measurement result of the electrical potential nonuniformity in the two-dimensional surface of a photosensitive drum. , It is a figure which shows the electric potential nonuniformity correction | amendment of the laser non-exposure part of the photosensitive drum which concerns on 2nd Embodiment. , It is a figure which shows the electric potential nonuniformity correction | amendment in the laser exposure part of the photosensitive drum which concerns on 2nd Embodiment. , , It is a figure which shows the structural example of the laser drive part which concerns on 2nd Embodiment. It is a figure explaining the mechanism of the interpolation which concerns on 3rd Embodiment. It is a figure which shows the interpolation method which concerns on 3rd Embodiment. It is a circuit block diagram which creates the interpolation data concerning a 3rd embodiment. It is a timing chart of interpolation data creation concerning a 3rd embodiment. It is a circuit block diagram which creates the interpolation data concerning a 4th embodiment. It is a timing chart of interpolation data creation concerning a 4th embodiment. It is a figure which shows the acquisition method of the electrical potential nonuniformity information measured beforehand. FIG. 10 is a schematic diagram illustrating a control configuration of an image forming apparatus according to a fifth embodiment. It is a block diagram which shows the structural example of the laser drive part which concerns on 5th Embodiment. FIG. 10 is a block diagram illustrating a configuration example of a correction data generation unit and a correction current control circuit according to a fifth embodiment. It is a figure which shows the image surface distribution characteristic and approximate expression production | generation method of a photosensitive drum. It is a figure which shows the production | generation method of the correction data which concerns on 5th Embodiment. It is a figure for demonstrating the production | generation method of the light quantity correction value in the light quantity correction value calculating part which concerns on 5th Embodiment. It is a figure for demonstrating the electric potential correction method of the photosensitive drum which concerns on 5th Embodiment. It is a flowchart which shows the production | generation procedure of the correction data in the correction data generation part which concerns on 5th Embodiment. It is a flowchart which shows the production | generation procedure of the current correction value in the correction current control circuit which concerns on 5th Embodiment.

Explanation of symbols

101: photosensitive drum 102: primary charger 103: laser scanning light 104: potential sensor 105: semiconductor laser 106: polygon mirror 107: fθ lens 109: BD sensor 110: BD signal

Claims (11)

An image carrier, charging means for charging the image carrier, exposure means for exposing the charged image carrier with a light amount corresponding to image data, and exposure are formed on the image carrier. An image forming apparatus comprising: a developing unit that develops the electrostatic latent image with toner;
In a divided region obtained by dividing the surface of the image carrier into a plurality of regions, a first potential in a state where the charged image carrier is exposed by the exposure unit and a second potential in a state where the image carrier is not exposed are measured. Measuring means to
First correcting means for correcting the exposure amount with respect to the exposure position in order to eliminate the potential unevenness of the exposure position according to the image data of the image to be formed based on the measured first potential;
An image comprising: second correction means for correcting an exposure amount with respect to the non-exposure position based on the measured second electric potential in order to eliminate potential unevenness at the non-exposure position according to the image data. Forming equipment.   The image forming apparatus according to claim 1, further comprising an interpolation unit that adds a predetermined number of interpolation data in order to linearly interpolate between measurement data measured in each divided region.   Interpolation means for adding a predetermined number of interpolation data to linearly interpolate between exposure amount data corrected by the first correction means and the second correction means based on measurement data measured in each divided region The image forming apparatus according to claim 1, further comprising: The first correction unit and the second correction unit are:
4. The image formation according to claim 1, wherein the exposure amount is corrected by correcting a current amount of a drive current according to the image data input to the exposure unit. 5. apparatus. The exposure means includes
A semiconductor laser emitting a laser;
A laser driving means for driving the semiconductor laser according to the driving current based on the modulation driving current for driving the modulation unit of the semiconductor laser and the bias current of the semiconductor laser;
The first correction means corrects the modulation drive current based on the measured first potential,
The image forming apparatus according to claim 4, wherein the second correction unit corrects the bias current based on the measured second potential. Sensitivity correction coefficient calculating means for calculating a sensitivity correction coefficient for correcting the modulation drive current or the bias current in order to eliminate the potential unevenness in the measured first potential or the second potential. ,
6. The image forming apparatus according to claim 5, wherein the first correction unit and the second correction unit correct the modulation drive current or the bias current using the calculated sensitivity correction coefficient. The first correction unit and the second correction unit are:
4. The image formation according to claim 1, wherein the exposure amount is corrected by correcting a pulse width of a driving pulse in accordance with the image data input to the exposure unit. 5. apparatus. The exposure means reduces the charged potential at the exposure position by exposing the charged image carrier according to the image data,
The first correction unit reduces the exposure amount in other divided regions so as to match the highest potential among the first potentials measured in each divided region,
8. The method according to claim 1, wherein the second correction unit increases an exposure amount in another divided region so as to match the lowest potential among the second potentials measured in each divided region. The image forming apparatus according to claim 1. A storage means for storing the value of the first potential and the value of the second potential measured in advance;
The first correction unit and the second correction unit are:
The exposure amount using the first potential value and the second potential value stored in the storage means instead of the first potential value and the second potential value measured by the measuring means. The image forming apparatus according to claim 1, wherein: Input means for inputting the value of the first potential and the value of the second potential;
The first correction unit and the second correction unit are:
Instead of the first potential value and the second potential value measured by the measuring means, the first potential value and the second potential value input by the input means are used to determine the exposure amount. The image forming apparatus according to claim 1, wherein correction is performed. An image carrier, charging means for charging the image carrier, exposure means for exposing the charged image carrier with a light amount corresponding to image data, and exposure are formed on the image carrier. A control method for an image forming apparatus comprising: a developing unit that develops an electrostatic latent image with toner,
In a divided region obtained by dividing the surface of the image carrier into a plurality of regions, a first potential in a state where the charged image carrier is exposed by the exposure unit and a second potential in a state where the image carrier is not exposed are measured. Measuring step to
A first correction step of correcting an exposure amount with respect to the exposure position in order to eliminate potential unevenness of the exposure position according to the image data of the image to be formed based on the measured first potential;
And a second correction step of correcting an exposure amount with respect to the non-exposure position in order to eliminate potential unevenness at the non-exposure position according to the image data based on the measured second potential. Control method of forming apparatus.

Images