JP5530982B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image (toner image) by scanning and exposing a photosensitive drum with a laser device.

  Conventionally, there is an image forming apparatus in which a laser beam is reflected on a polygon mirror rotated by a polygon motor, and an electrostatic latent image is formed on a photosensitive drum using a lens or a mirror. Here, the position of the pixel in the main scanning direction of the photosensitive drum due to the incident angle of the laser beam to the photosensitive drum, the change in the transmittance of the lens due to the incident angle, and the change in the reflectance of the mirror due to the incident angle. As a result, a difference may occur in the energy (light quantity) given to the photosensitive drum by the beam. In such a case, when the scanning exposure of the photosensitive drum is performed with the output light emission level of the laser device constant, the density of the toner image varies depending on the position in the main scanning direction. Therefore, Patent Document 1 describes an invention that corrects the light amount of a laser device in accordance with the position in the main scanning direction.

  Specifically, Patent Document 1 discloses a correction output that drives a laser whose output light is scanned on a scanning target surface via a scanning optical system and corrects output fluctuations according to an incident angle with respect to the scanning target surface. A generating means for generating a value, a multiplying means for multiplying a reference output value by a corrected output value from the generating means, and a constant current source whose current value is controlled based on a multiplication result of the multiplying means, the constant current source A first generating means for generating a modulation current obtained by modulating the current flowing through the image data in accordance with the image data, and a linear portion corresponding to the laser emission region in the laser driving current versus output light quantity characteristic is removed to an axis indicating zero light quantity. A second generating means for generating a threshold current having a current value in the vicinity of the spontaneous light emission region at an extrapolation point that is an intersection with the axis when inserted; and a current generated from the first and second current sources. To drive the laser based on Laser drive and means have been described. With this configuration, it is intended to accurately correct the output light fluctuation according to the incident angle (see Patent Document 1: Claim 2, paragraphs [0006], [0014], [0015], etc.).

JP 11-291548 A

  In recent years, color image forming apparatuses have been widely used. Some color image forming apparatuses have a plurality of photosensitive drums (sometimes referred to as a tandem type). When a plurality of photosensitive drums are provided, a plurality of laser devices, mirrors, and lenses are mounted according to the number of photosensitive drums.

  Here, when the invention described in Patent Document 1 is applied to a color image forming apparatus, the configuration of the invention described in Patent Document 1 (for example, the generating means, the multiplying means, the constant in Patent Document 1) is applied to each photosensitive drum. One current source, first generation means, second generation means, addition means, etc.) must be mounted on the image forming apparatus. As a result, in order to perform light amount correction on each photosensitive drum, a large number of parts, circuits, and the like are required, which increases the manufacturing cost of the image forming apparatus.

  If the configuration of the invention described in Patent Document 1 is shared by a plurality of photosensitive drums, the correction may not be sufficient because correction cannot be performed in consideration of individual differences in sensitivity among the photosensitive drums. Therefore, there is also a problem that correction for a plurality of photosensitive drums cannot be performed accurately.

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to enable correction of a laser apparatus that is inexpensive and has few errors in an image forming apparatus having a plurality of laser apparatuses.

To achieve the above object, an image forming apparatus according to claim 1 emits a plurality of photosensitive drums as an image carrier, and a beam for scanning and exposing the photosensitive drum, and the photosensitive drum. A laser device provided separately, an optical unit that causes a beam emitted from the laser device to reach the photosensitive drum, and performs scanning and exposure along a main scanning direction of the photosensitive drum, and the photosensitive device A correction output value indicating a light emission level of a beam for correcting an energy difference received by the photosensitive drum according to a position of the body drum in the main scanning direction, and correction data common to the laser devices; A storage unit that stores a reference output value for determining and correcting a light emission level that serves as a reference of the light amount of the beam irradiated to the photoconductive drum for each photoconductive drum, and before the correction data A first drive unit that changes an output current supplied to each laser device in accordance with a position in the main scanning direction according to a magnitude of the correction output value, and changes a light emission level of the beam in the main scanning direction; A second driving unit that is individually provided for each of the laser devices, and outputs a current of a certain magnitude to be supplied to the corresponding laser device according to the size of the reference output value. The laser device emits a beam upon receiving a current obtained by combining the output current of the first drive unit and the output current of the second drive unit, and the storage unit scans and exposes the laser device at a maximum light emission level. wherein a first correction pattern shows the change of the correction output value corresponding to the position in the main scanning direction of the first ideal correction data predetermined as an ideal the correction data of the maximum level at which, the laser device minimum Scanning a light level, ideal second correction pattern shows the change of the correction output value corresponding to the position in the main scanning direction of the second ideal correction data predetermined as the correction data of the minimum level at which the exposure The correction data in which the correction output value corresponding to the position in the main scanning direction is determined is stored.

  According to this configuration, each laser device emits a beam upon receiving supply of a current obtained by combining the output current of the first drive unit and the output current of the second drive unit. As a result, only one current source is required to supply each laser device with a current that corrects the energy difference of the beam irradiated to each pixel in the main scanning direction of the photosensitive drum. Therefore, only one correction is required to make the amount of energy received by each pixel in the main scanning direction on each photosensitive drum one, and the manufacturing cost of the image forming apparatus can be reduced.

  Further, according to this configuration, the storage unit is positioned at the position in the main scanning direction of the first ideal correction data that is predetermined as ideal correction data at the maximum level for scanning and exposing the laser device at the maximum light emission level. A first correction pattern indicating a change in the corresponding correction output value and a main scanning direction of second ideal correction data predetermined as ideal correction data at the minimum level for scanning and exposing the laser device at the maximum light emission level. The correction data in which the correction output value corresponding to the position in the main scanning direction is determined within the range of the second correction pattern indicating the change of the correction output value corresponding to the position is stored. Thereby, the light emission level of the beam irradiated to each pixel in the main scanning direction of each photoconductive drum can be corrected by correction data that draws a correction pattern limited within a certain range. Therefore, even if the correction data is one and a common current is supplied to each laser device by the first driving unit, the ideal emission level of the beam to be irradiated to each pixel in the main scanning direction of each photosensitive drum is large. Without being separated (while suppressing errors), the light emission level of the laser device can be corrected according to the position in the main scanning direction, and the balance of each color can be reduced.

  According to a second aspect of the present invention, in the first aspect of the invention, the storage unit includes a maximum total value obtained by adding a maximum value of the correction output value in the correction data and a predetermined reference standard value, and the The correction data determined so that the ratio between the minimum value of the correction output value in the correction data and the minimum total value obtained by adding the reference standard values becomes a predetermined ideal ratio is stored.

  The reference emission level of the beam to be irradiated for each photosensitive drum varies depending on sensitivity characteristics and manufacturing errors. In consideration of reflectance and transmittance, the difference between the maximum value and the minimum value of the correction output value in the correction data is preferably made different according to the light emission level that is the reference of the beam. Therefore, according to this configuration, the storage unit refers to the maximum total value obtained by adding the maximum value of the correction output value in the correction data and the predetermined reference standard value, and the minimum value of the correction output value in the correction data. Correction data determined so that the ratio of the reference value to the minimum total value becomes a predetermined ideal ratio is stored. Thereby, even if the correction data is one and a common current is supplied to each laser device by the first drive unit, the correction data is set so that the ratio between the maximum total value and the minimum total value is optimal. Therefore, it is possible to make the irradiation amount (irradiation energy) of the beam uniform for each pixel in the main scanning direction of the photosensitive drum.

  According to a third aspect of the invention, in the second aspect of the invention, the photosensitive drum is provided for four colors of black, cyan, magenta, and yellow, and the storage unit corresponds to the photosensitive drum of each color. The reference output value is stored for each of the second drive units, and the maximum total value and the minimum total value when a value between any two reference output values other than black is used as the reference reference value The correction data determined so that the ratio to the ideal ratio is stored.

  Color balance loss, color unevenness, and differences from the original are easily recognized when toner images other than black relating to saturation, hue, and the like are superimposed. Therefore, according to this configuration, the storage unit stores the reference output value for each second driving unit corresponding to the photosensitive drum of each color and refers to a value between any two reference output values other than black. Correction data determined such that the ratio between the maximum total value and the minimum total value when the reference value is used is an ideal ratio is stored. As a result, even if one correction data is supplied and a common current is supplied to each laser device by the first driving unit, an error from an ideal correction output value for each pixel is averaged for cyan, magenta, and yellow. Less correction data. Therefore, even if the toner images of the respective colors are superimposed, the color balance can be reduced, and an inexpensive and high-quality image forming apparatus can be provided.

  According to a fourth aspect of the present invention, in the second aspect of the invention, the storage unit uses an average value of at least two of the reference output values among the plurality of reference output values as the reference reference value, and the reference. The correction data determined so that the ratio between the maximum total value and the minimum total value at the reference value becomes the ideal ratio is stored.

  According to this configuration, the storage unit uses, as a reference standard value, an average value of at least two standard output values among a plurality of standard output values, and an ideal ratio between the maximum total value and the minimum total value of the reference standard values. Correction data determined to be a ratio is stored. As a result, even if a single correction data is supplied and a common current is supplied to each laser device by the first drive unit, correction data that reduces an error from an ideal correction output value for each pixel between at least two colors is obtained. Determined. Therefore, even if the toner images of the respective colors are superimposed, the color balance can be reduced, and an inexpensive and high-quality image forming apparatus can be provided.

  The invention according to claim 5 is the invention according to claim 2, wherein the storage unit refers to an average value of the maximum reference output value and the minimum reference output value among the plurality of reference output values. The correction data determined to be the reference value and stored so that the ratio between the maximum total value and the minimum total value at the reference reference value becomes the ideal ratio is stored.

  According to this configuration, the storage unit uses the average value of the maximum standard output value and the minimum standard output value among the plurality of standard output values as the reference standard value, and the maximum total value and the minimum total value at the reference standard value The correction data determined so that the ratio to the ideal ratio is stored. As a result, even if one correction data is supplied and a common current is supplied to each laser device by the first drive unit, an error from an ideal correction output value for each pixel is seen from the entire output range of the laser device. A small amount of correction data is determined on average. Therefore, even if the toner images of the respective colors are superimposed, the color balance can be reduced, and an inexpensive and high-quality image forming apparatus can be provided.

  According to a sixth aspect of the present invention, in the first aspect of the present invention, the storage unit is correction data in which a predetermined reference standard value is determined as a minimum value in the correction data, and the correction data The maximum total value obtained by adding the largest reference output value among the plurality of reference output values, the minimum value in the correction data, and the largest reference output value among the plurality of reference output values. A first ratio with a minimum total value, a maximum value in the correction data and a maximum total value obtained by adding the smallest reference output values among a plurality of the reference output values, a minimum value in the correction data, and a plurality of the Correction data in which correction output values are determined so that the difference between the second ratio and the minimum total value obtained by adding the smallest reference output values among the reference output values is equal or minimized is stored.

  According to this configuration, the storage unit is correction data in which a predetermined reference standard value is determined as the minimum value in the correction data, and the largest standard among the maximum value and the plurality of reference output values in the correction data. A first ratio of the maximum total value obtained by adding the output values, the minimum value in the correction data, and the minimum total value obtained by adding the largest reference output value among the plurality of reference output values, and the maximum value in the correction data and the plurality of values The difference between the second ratio between the maximum total value obtained by adding the smallest reference output value among the reference output values, the minimum value in the correction data, and the minimum total value obtained by adding the smallest reference output value among the plurality of reference output values. Correction data in which correction output values are determined so as to be equal or minimized. As a result, the correction data in which the error between the maximum correction output value in the correction data of the color having the largest reference output value and the color having the smallest reference output value and the maximum correction output value in the correction data is reduced is obtained. Even if a single correction data is stored and a common current is supplied to each laser device by the first drive unit, the correction data reduces an error from an ideal correction output value of each pixel of each photosensitive drum. Is determined.

According to a seventh aspect of the present invention, in the second aspect of the invention, a density information input unit that receives input of information indicating the density of each color density toner image formed on each of the photosensitive drums; Based on the information input to the density information input unit, the deviation of the toner image of each color from the ideal density is grasped, and for the color darker than the ideal density, the reference output value is reduced. A control unit that updates the reference output value of the storage unit and updates the reference output value of the storage unit so as to increase the reference output value for colors lighter than the ideal density.

  Due to aged deterioration due to use or the like, a deviation between the density of the actually formed toner image and the density of the ideal toner image occurs (for example, becomes thinner). However, according to this configuration, the control unit grasps the deviation from the ideal density of the toner image of each color based on the information input to the density information input unit, and for colors that are darker than the ideal density. The reference output value of the storage unit is updated so as to reduce the reference output value, and the reference output value of the storage unit is updated so as to increase the reference output value for colors lighter than the ideal density. Thereby, each reference output value indicating the light emission level as a reference of each laser device is corrected. Therefore, the deviation from the ideal toner image caused by use can be corrected as a whole.

The invention according to claim 8 is the invention of claim 7, wherein the photosensitive drum, black, cyan, magenta, provided four colors of yellow, the controller may update the reference output value of each color when the ratio of the minimum sum and the maximum sum value when the value was the reference standard value between any two of the reference output value other than black has been determined so that the ideal ratio The correction data is generated and stored in the storage unit.

  According to this configuration, when the reference output value of each color is updated, the control unit sets the maximum total value and the minimum total value when a value between any two standard output values other than black is used as a reference standard value. The correction data determined so that the ratio is the ideal ratio is generated and stored in the storage unit. As a result, with the update of the reference output value for each color, correction data with an average small error from the ideal correction output value for each pixel is determined for cyan, magenta, and yellow. Accordingly, it is possible to provide an image forming apparatus in which the color balance is not disturbed and high image quality is maintained even when the reference output value of each color is updated.

  The invention according to claim 9 is the invention according to claim 7, wherein, when the control unit updates the reference output value, an average value of at least two of the reference output values of the reference output values of each color. Is generated as the reference standard value, the correction data is generated so that the ratio of the maximum total value and the minimum total value in the reference standard value is the ideal ratio, and the correction data generated in the storage unit is I decided to update it.

  According to this configuration, when the standard output value is updated, the control unit uses the average value of at least two standard output values among the standard output values of each color as the reference standard value, and the maximum total value of the reference standard values Correction data is generated so that the ratio to the minimum total value becomes an ideal ratio, and the generated correction data is updated in the storage unit. Thereby, correction data in which an error from an ideal correction output value of each pixel of each photosensitive drum is reduced is generated with the update of the reference output value of each color. Accordingly, it is possible to provide an image forming apparatus in which the color balance is not disturbed and high image quality is maintained even when the reference output value of each color is updated.

  According to a tenth aspect of the present invention, in the seventh aspect of the invention, when the control unit updates the reference output value, the maximum reference output value and the minimum reference output value among the reference output values of each color are updated. An average value of standard output values is set as the reference standard value, and the correction data is generated so that a ratio between the maximum total value and the minimum total value in the reference standard value becomes the ideal ratio, and the storage unit stores the correction data. The generated correction data is updated.

  According to this configuration, when the standard output value is updated, the control unit uses the average value of the maximum standard output value and the minimum standard output value among the standard output values of each color as the reference standard value, The correction data is generated so that the ratio between the maximum total value and the minimum total value becomes an ideal ratio, and the generated correction data is updated in the storage unit. As a result, with the update of the reference output value for each color, correction data with an average small error from the ideal correction output value for each pixel is generated as seen from the entire output range of the laser device. Accordingly, it is possible to provide an image forming apparatus in which the color balance is not disturbed and high image quality is maintained even when the reference output value of each color is updated.

  The invention according to claim 11 is the invention according to claim 7, wherein the control unit is correction data in which a predetermined reference standard value is determined as a minimum value in the correction data, and the standard for each color is determined. When the output value is updated, the maximum value in the correction data and the maximum total value obtained by adding the largest reference output values among the plurality of updated reference output values, the minimum value in the correction data, and the updated value The first ratio with the minimum total value obtained by adding the largest reference output values among the plurality of reference output values, the smallest value after updating among the maximum value in the correction data and the plurality of reference output values The difference between the second sum of the maximum total value obtained by adding the output values, the minimum value in the correction data, and the minimum total value obtained by adding the smallest updated reference output value among the plurality of reference output values is equal. Or to be minimized Generates the correction data corrected output value has been determined, it was decided to update the correction data generated in the storage unit.

  According to this configuration, the control unit is correction data in which a predetermined reference standard value is determined as the minimum value in the correction data, and when the standard output value of each color is updated, the maximum value in the correction data is The maximum total value obtained by adding the largest reference output value among the plurality of updated reference output values, the minimum value in the correction data, and the minimum total value obtained by adding the largest reference output value among the plurality of updated reference output values. The first sum ratio, the maximum value in the correction data and the maximum total value obtained by adding the smallest reference output value after the update among the plurality of reference output values, the minimum value in the correction data, and the plurality of reference output values The correction data in which the correction output value is determined so that the difference from the second ratio with the minimum total value obtained by adding the smallest reference output value after the update is equal or minimized is generated, and the correction generated in the storage unit Update the data. As a result, correction data in which an error from the ideal correction output value of each pixel of each photosensitive drum is reduced is determined with the update of the reference output value of each color.

  According to a twelfth aspect of the present invention, in the first to eleventh aspects of the invention, the correction data is obtained from a pixel at a center position in the main scanning direction of the photosensitive drum to an end portion in the main scanning direction of the photosensitive drum. The correction output value is set so as to increase toward the pixel.

  According to this configuration, the correction data is set so that the correction output value increases as it goes from the pixel at the center position in the main scanning direction of the photosensitive drum to the pixel at the end in the main scanning direction of the photosensitive drum. . As a result, the correction output value is increased as the end position of the photosensitive drum is such that the incident angle of the beam to the member included in the photosensitive drum or the optical unit becomes an acute angle. Accordingly, it is possible to appropriately correct the energy difference of the beam applied to each pixel in the main scanning direction of the photosensitive drum.

According to a thirteenth aspect of the present invention, in the first to twelfth aspects of the invention, the first ideal correction data includes a maximum value of the correction output value and a maximum reference output value within the first ideal correction data. a total value of the ratio of the total value of the minimum and maximum of the reference output value of the corrected output value in the first the ideal correction data are determined so that a predetermined ideal proportions are as hereinbefore, the second ideal correction data, the second ideal correction data in the correction of the maximum value and the total value of the minimum of the reference output value of the correction output value in the second the ideal correction data in and then that the ratio of the total value of the minimum value and the minimum of the reference output value of the output value is determined so as to become an ideal a predetermined ratio.

  According to this configuration, the first ideal correction data includes the maximum value of the correction output value in the first ideal correction data, the sum of the maximum reference output values, and the minimum value of the correction output value in the first correction data. The second ideal correction data is a correction output value within the second ideal correction data, and the ratio of the total of the maximum reference output values is determined to be a predetermined ideal ratio. The ratio between the total value of the maximum value and the minimum reference output value and the minimum value of the correction output value and the total value of the minimum reference output value in the second ideal correction data is a predetermined ideal ratio. It is determined as follows. Thereby, when the reference light emission level of the beam is maximum, the difference between the maximum value and the minimum value in the correction output value in the first ideal correction data is increased, and when the reference light emission level of the beam is minimum, The difference between the maximum value and the minimum value in the correction output value in the first ideal correction data is reduced. Accordingly, the first ideal correction data and the second ideal correction data are determined at an optimum ratio according to the reference emission level of the beam.

  According to the present invention, in an image forming apparatus having a plurality of laser devices, it is possible to correct a light emission level of a beam that is inexpensive and has few errors.

1 is a schematic front cross-sectional view illustrating an example of a multifunction machine. It is an expanded model sectional view of an image forming unit. It is a schematic diagram which shows an example of exposure apparatus. 2 is a block diagram illustrating an example of a hardware configuration of a multifunction peripheral. FIG. It is a block diagram which shows an example of the hardware constitutions of exposure apparatus. It is a graph which shows an example of the energy (light reception amount) which a photosensitive drum receives at each position in the main scanning direction. It is a graph which shows an example of the output ratio of a laser apparatus when correcting the light emission level according to the position of the photoconductor drum in the main scanning direction. It is a graph for demonstrating an example of how to determine correction data It is a graph for demonstrating an example of how to determine correction data It is a graph for demonstrating the method of defining correction data (1st Embodiment). It is a flowchart which shows an example of the flow of a scanning and exposure with correction | amendment of the light emission level of each laser apparatus in a multi function device. It is a flowchart which shows an example of the flow of control in density calibration. 6 is an explanatory diagram illustrating an example of a toner image generated by density calibration. FIG. It is a graph for demonstrating the method of defining correction data (2nd Embodiment). It is a graph for demonstrating the method of determining correction data (3rd Embodiment). It is a graph for demonstrating the method of determining correction data (4th Embodiment).

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 13 by taking a multifunction peripheral 100 (corresponding to an image forming apparatus) as an example. First, the 1st Embodiment of this invention is described using FIGS. However, each element such as configuration and arrangement described in this embodiment does not limit the scope of the invention and is merely an illustrative example.

(Outline of image forming apparatus)
First, an outline of the multifunction peripheral 100 according to the first embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic front cross-sectional view illustrating an example of the multifunction peripheral 100. FIG. 2 is an enlarged schematic cross-sectional view of the image forming unit 21.

  As shown in FIG. 1, the multifunction peripheral 100 according to the embodiment has a document cover 100 a at the top, and the main body of the multifunction peripheral 100 includes an operation panel 1 a, an image reading unit 1 b, a paper feeding unit 1 c, a conveyance path 1 d, An image forming unit 2 (including the exposure device 4), an intermediate transfer unit 3a, a fixing unit 3b, and the like are provided.

  First, as indicated by a broken line in FIG. 1, the operation panel 1 a is provided on the upper front side of the multifunction device 100. The operation panel 1a includes a liquid crystal display unit 11 that displays the state of the multifunction peripheral 100 and various messages. The liquid crystal display unit 11 can display one or a plurality of keys for performing function selection, setting, and the like. Further, a touch panel unit 12 (for example, a resistive film type) is provided on the upper surface of the liquid crystal display unit 11. The touch panel unit 12 detects the position and coordinates of the portion pressed by the liquid crystal display unit 11. The operation panel 1a is also provided with various input hard keys such as a numeric keypad 13 for inputting numbers and a start key 14 for instructing start of execution of various functions such as copying.

  The document cover 100a has a fulcrum in the depth direction of FIG. 1 and can be opened and closed in the vertical direction of the page. The document cover 100a presses the document placed on the placement reading contact glass 15 when the document is copied. The image reading unit 1b reads a document and forms image data of the document. The image reading unit 1b is provided with optical system members (not shown) such as an exposure lamp, a mirror 45, a lens 41, and an image sensor (for example, CCD). Instead of the document cover 100a, a document conveying device that automatically and continuously conveys documents one by one toward the reading position of the image reading unit 1b may be provided.

  Then, using these optical system members, the original placed on the placement reading contact glass 15 is irradiated with a beam, and the output value of each pixel of the image sensor receiving the reflected beam of the original is A / D converted. Then, image data is generated. The multi-function device 100 can perform printing based on image data obtained by reading (copy function).

  The paper feed unit 1c accommodates various types of paper such as copy paper, OHP sheets, and label paper. The paper feeding unit 1c feeds the paper to the transport path 1d by a paper feeding roller 16 that is rotated by a driving mechanism (not shown) such as a motor. The conveyance path 1d conveys the sheet in the multifunction peripheral 100 and guides the sheet supplied from the sheet feeding unit 1c to the discharge tray 17 through the intermediate transfer unit 3a and the fixing unit 3b. The conveyance path 1d is provided with a conveyance roller pair 18 and a registration roller pair 19 that waits for the conveyed paper in front of the intermediate transfer unit 3a and sends it in time.

  As shown in FIGS. 1 and 2, the multifunction peripheral 100 includes an image forming unit 2 as a part for forming a toner image based on image data of an image to be formed. The image forming unit 2 includes an image forming unit 21 and an exposure device 4 for four colors. Specifically, the MFP 100 includes, as the image forming unit 21, an image forming unit 21Bk that forms a black image, an image forming unit 21Y that forms a yellow image, and an image forming unit 21C that forms a cyan image. And an image forming unit 21M for forming a magenta image.

  Here, the image forming units 21Bk to 21M will be described in detail with reference to FIG. Each of the image forming units 21Bk to 21M has basically the same configuration except that the color of the toner image to be formed is different. Therefore, in the description below, the symbols Bk, Y, C, and M in each image forming unit 21 are omitted unless specifically described.

  Each photosensitive drum 22 provided in each image forming unit 21 (black 22Bk, cyan 22C, magenta 22M, yellow 22Y, four colors in total, four in the following description, Bk, C , M, and Y are omitted) carry a toner image on the peripheral surface. Each photosensitive drum 22 has a photosensitive layer on the outer peripheral surface, and is rotated at a predetermined process speed by a driving device (not shown). Each charging device 23 charges the photosensitive drum 22 at a constant potential. The exposure device 4 below each image forming unit 21 receives the input of the color-separated image signal and converts it into a signal indicating turning on / off of the beam. Then, the exposure apparatus 4 outputs a laser beam (illustrated by a broken line) on and off based on the converted signal. In this way, the exposure device 4 performs scanning exposure of each photosensitive drum 22 after charging to form an electrostatic latent image. Each developing device 24 stores a developer of a corresponding color. Each developing device 24 supplies toner to the electrostatic latent image on the photosensitive drum 22 and develops it. Each cleaning device 25 cleans the photosensitive drum 22.

  Returning to FIG. The intermediate transfer unit 3a receives the primary transfer of the toner image from the photosensitive drum 22 and performs the secondary transfer on the paper. The intermediate transfer unit 3a includes primary transfer rollers 31Bk to 31M, an intermediate transfer belt 32, a drive roller 33, driven rollers 34a to 34c, a secondary transfer roller 35, a belt cleaning device 36, and the like. Each primary transfer roller 31 </ b> Bk to 31 </ b> M sandwiches the corresponding photosensitive drum 22 and the endless intermediate transfer belt 32. A transfer voltage is applied to each of the primary transfer rollers 31Bk to 31M. As a result, the toner image is transferred to the intermediate transfer belt 32.

  The intermediate transfer belt 32 is stretched around a driving roller 33 and the like, and rotates around the driving roller 33 connected to a driving mechanism (not shown) such as a motor. The drive roller 33 and the secondary transfer roller 35 sandwich the intermediate transfer belt 32. The toner images (black, yellow, cyan, and magenta colors) formed by the image forming units 21 are sequentially superimposed without deviation and are primarily transferred to the intermediate transfer belt 32 and then applied with a predetermined voltage. The image is transferred onto the paper by the secondary transfer roller 35.

  The fixing unit 3b is disposed downstream of the secondary transfer roller 35 in the sheet conveyance direction, and fixes the toner image secondarily transferred to the sheet by heating and pressing. The fixing unit 3b is mainly composed of a fixing roller 37 having a built-in heat generation source and a pressure roller 38 pressed against the fixing roller 37, and forms a nip. Then, the paper on which the toner image is transferred passes through the nip and is heated and pressurized, and as a result, the toner image is fixed on the paper. The fixed sheet is discharged to the discharge tray 17 and the image forming process is completed.

(Configuration of exposure apparatus 4)
Next, an example of the exposure apparatus 4 according to the first embodiment will be described with reference to FIG. FIG. 3 is a schematic diagram showing an example of the exposure apparatus 4. In FIG. 3, the configuration for one color is shown.

  First, the outline of scanning / exposure of the photosensitive drum 22 using the exposure apparatus 4 will be described with reference to FIG. As shown in FIG. 3, the exposure device 4 is provided with a laser device 5 (for example, a laser diode). One laser device 5 is provided for the photosensitive drum 22 of each image forming unit 21 (5Bk for black, 5Y for yellow, 5C for cyan, and 5M for magenta. See FIG. 5). Therefore, the exposure apparatus 4 of this embodiment is provided with a total of four laser apparatuses 5 (only one is shown in FIG. 3 for convenience).

  Then, a lens 41 (corresponding to the optical unit) provided between the laser device 5 and the polygon mirror 43, which reflects the laser beam as an optical unit for causing the laser beam (laser light) emitted from each laser device 5 to reach the photosensitive drum 22. A polygon mirror 43 (corresponding to the optical unit) that has a plurality of planar reflecting surfaces to be rotated at high speed by the polygon motor 42, and an fθ lens 44 (corresponding to the optical unit) for making the scanning speed of the laser beam on the photosensitive drum 22 constant. ), A mirror 45 (corresponding to an optical unit) for reflecting the laser beam toward each photosensitive drum 22 is provided.

  In the present embodiment, four laser devices 5 (5Bk to 5M) are provided for the four photosensitive drums 22. In the following description, the symbols Bk, Y, C, and M may be omitted. A combination of a polygon mirror 43 and a polygon motor 42 is provided for each of the four laser devices 5. In addition, the combination of the polygon mirror 43 and the polygon motor 42 may not be provided in each laser device 5, but one combination of the polygon mirror 43 and the polygon motor 42 may be provided, for example, and all the laser devices 5 may be shared. Further, two combinations of the polygon mirror 43 and the polygon motor 42 may be provided, and the two laser apparatuses 5 may share the combination of one polygon mirror 43 and the polygon motor 42.

  The lens 41, the fθ lens 44, the mirror 45, and the like are provided for each color (for four colors) (only one color is shown for convenience in FIG. 3). Then, the laser beam is irradiated to each photoconductor drum 22 from the exposure device 4, and an electrostatic latent image combined with image data is formed on each photoconductor drum 22.

  The exposure device 4 is provided with a light receiving unit 46 within the irradiation range (scanning range) of the laser beam by the polygon motor 42 and outside the irradiation range of the photosensitive drum 22. The light receiving unit 46 changes its output current (output voltage) depending on whether or not the laser beam is irradiated. The light receiving unit 46 is a circuit including a light receiving element (for example, a photodiode). Then, the timing of exposure (writing) to the photosensitive drum 22 is taken based on the output of the light receiving unit 46.

(Hardware configuration of MFP 100)
Next, based on FIG. 4, the hardware configuration of the multifunction peripheral 100 according to the embodiment of the present invention will be described. FIG. 4 is a block diagram illustrating an example of a hardware configuration of the multifunction peripheral 100.

  As shown in FIG. 4, the multifunction peripheral 100 according to the present embodiment includes a main control unit 6 inside. The main control unit 6 controls each unit of the multifunction device 100. For example, the main control unit 6 includes a CPU 61, a storage device 62, an image processing unit 63, and the like.

  The CPU 61 is a central processing unit, and controls and performs each part of the multifunction peripheral 100 based on a control program stored in the storage device 62 and developed. The storage device 62 is configured by a combination of nonvolatile and volatile storage devices such as ROM, RAM, and flash ROM. For example, the storage device 62 stores a control program, control data, and the like for the multifunction peripheral 100.

  The main control unit 6 is communicably connected to an engine control unit 20 that controls a portion related to printing (print engine unit). Based on an instruction from the main control unit 6, the engine control unit 20 performs image formation, ON / OFF of a motor or the like that rotates various rotating bodies, and the like. The engine control unit 20 actually controls the operations of the paper feed unit 1c, the conveyance path 1d, the image forming unit 2, the exposure device 4, the intermediate transfer unit 3a, the fixing unit 3b, and the like.

  The main control unit 6 is connected to a computer 200 (for example, a personal computer or a server) via a network or a cable. Print data including image data to be printed and setting data for printing is input from the computer 200 to the main control unit 6. Further, the image data of the original read by the image reading unit 1b is input to the main control unit 6. The image processing unit 63 performs various types of image processing such as enlargement, reduction, density conversion, and data format conversion on the image data from the computer 200 and the image reading unit 1b according to the setting. Then, the image processing unit 63 sends the image data after the image processing to the exposure device 4. The exposure device 4 receives this image data and performs scanning and exposure.

  The main control unit 6 is connected to the operation panel 1a, the image reading unit 1b, and the like. The operation panel 1a is provided, for example, at the upper front of the multifunction peripheral 100, has a liquid crystal screen, and displays various setting information, warnings, and the like. Based on the setting made on the operation panel 1a, the main control unit 6 appropriately forms an image based on image data obtained by reading the document of the image reading unit 1b and a control program and data of the storage device 62. The operation of each part is controlled.

  The image processing unit 63 performs image processing on the received image data and transmits the processed image data to the exposure device 4. The exposure device 4 forms an electrostatic latent image on the photosensitive drum 22 based on the image data.

(Control of exposure apparatus 4)
Next, an outline of control of the exposure apparatus 4 according to the first embodiment will be described based on FIG. FIG. 5 is a block diagram showing an example of the hardware configuration of the exposure apparatus 4.

  As shown in FIG. 5, in the multifunction peripheral 100 of this embodiment, the engine control unit 20 controls the exposure apparatus 4. For example, the engine control unit 20 turns on / off the laser devices 5 (black laser device 5Bk, yellow laser device 5Y, cyan laser device 5C, magenta laser device 5M) of each color based on the image data. Control. The exposure device 4 is provided with one first drive unit 7 and a plurality of second drive units 8 that supply current to the laser device 5.

  One first drive unit 7 is provided for each laser device 5 (laser device 5Bk to laser device 5M). The first drive unit 7 outputs a current for correcting the light emission level of the irradiated beam according to the position (each pixel) in the main scanning direction of the photosensitive drum 22, and the same current (in FIG. (shown as i1) is supplied to each laser device 5. When the photosensitive drum 22 is exposed, the engine control unit 20 gives a value (corrected output value) indicating the magnitude of the current to be output to the first driving unit 7. The first drive unit 7 outputs a current corresponding to the corrected output value instructed from the engine control unit 20. In the present embodiment, the engine control unit 20 provides the first drive unit 7 with a corrected output value as a digital value. Therefore, the first drive unit 7 is, for example, a digital-analog converter (DAC) that outputs a current in accordance with the magnitude of the correction output value.

  The correction data (data indicating the correction output value of each pixel) indicating what correction output value is given according to the position of the photosensitive drum 22 in the main scanning direction (according to the pixel) is the engine control unit. 20 (which may be built in the engine control unit 20) is stored in a memory 9 (corresponding to a storage unit, for example, a flash ROM). When the photosensitive drum 22 is exposed, the engine control unit 20 acquires correction data from the memory 9 and sequentially supplies correction output values to the first drive unit 7 based on the correction data.

  In addition, one second drive unit 8 is provided for each laser device 5 (laser device 5Bk to laser device 5M) (four in total). In FIG. 5, among the second drive units 8, the black one is given an 8 Bk code, the yellow one is given an 8 Y code, the cyan one is given an 8 C code, and magenta. An 8M code is attached to the product for use. For convenience of explanation, the second drive unit 8 may be simply referred to as the second drive unit 8 by omitting the symbols Bk, 8Y, 8C, and 8M. Each of the second drive units 8 (second drive unit 8Bk to second drive unit 8M) determines and corrects the light emission level (light quantity) that serves as a reference of the laser beam applied to the corresponding photosensitive drum 22 (is used as a reference). A current (indicating the emission level) is output and supplied to the corresponding laser device 5.

  When performing exposure of each photosensitive drum 22 during printing (toner image formation), the engine control unit 20 gives a value (reference output value) indicating the magnitude of the current to be output to the second drive unit 8. . The second drive unit 8 outputs a current corresponding to the reference output value instructed from the engine control unit 20. As a result, each laser device 5 emits a laser beam at a light emission level (reference output, reference light quantity) that is a reference that is predetermined for each photosensitive drum 22. In the present embodiment, the engine control unit 20 gives a reference output value to each second drive unit 8 as a digital value. Therefore, each second drive unit 8 is also a digital-analog converter (DAC) that outputs a current according to the magnitude of the reference output value, for example. Therefore, the first drive unit 7 and the second drive unit 8 may be the same circuit (same type).

  A reference output value determined for each laser device 5 (each photosensitive drum 22) is stored in the memory 9. When performing exposure of the photosensitive drum 22, the engine control unit 20 acquires the reference output value of each second drive unit 8 from the memory 9 and gives the reference output value to each second drive unit 8.

  As shown in FIG. 5, each laser device 5 is given a current obtained by superimposing the current i <b> 1 output from the first drive unit 7 on the current output from the corresponding second drive unit 8. When performing this current reception, scanning of the photosensitive drum 22, and exposure, each laser device 5 (laser device 5Bk to laser device 5M) outputs a laser beam.

  Further, the output of each light receiving unit 46 is input to the engine control unit 20. For example, the engine control unit 20 determines the writing start timing for each laser device 5 with reference to the light receiving unit 46 for black. By using the output change of one light receiving unit 46 as a signal for synchronization, the writing position of each line can be matched.

  The engine control unit 20 controls ON / OFF of the polygon motor 42 (when a plurality of polygon motors 42 are provided, the engine control unit 20 controls the rotation of each polygon motor 42 (only one is shown in FIG. 5 for convenience)). The engine control unit 20 gives an instruction to the drive signal generation unit 47 that generates a signal (for example, a clock signal) for rotating the polygon motor, and controls the ON / OFF and rotation speed of the polygon motor 42. The engine control unit 20 rotates the polygon motor 42 when scanning and exposing the photosensitive drum 22, and stops the polygon motor 42 when the print job is completed.

  In the present embodiment, an example in which the engine control unit 20 controls the exposure apparatus 4 will be described. However, the operation of the exposure apparatus 4 is actually controlled in the exposure apparatus 4 upon receiving an instruction from the engine control unit 20. A controller may be provided. Further, instead of the engine control unit 20, the main control unit 6 may perform scanning and exposure control of the exposure device 4 and light emission level control of each laser device 5 described later. As described above, the engine control unit 20, the controller, and the main control unit 6 can also function as a control unit that controls light emission of each laser device 5 of the exposure apparatus 4.

(Outline of laser beam emission level correction)
Next, an example of correcting the light emission level (light emission amount) of each laser device 5 according to the first embodiment will be described with reference to FIGS. 6 and 7. FIG. 6 is a graph showing an example of energy (amount of received light) received by the photosensitive drum 22 at each position in the main scanning direction. FIG. 7 is a graph showing an example of the output ratio of the laser device 5 when the light emission level is corrected according to the position of the photosensitive drum 22 in the main scanning direction.

  First, with reference to FIG. 6, a description will be given of fluctuations in energy (light reception amount) received by the photosensitive drum 22 at each position in the main scanning direction. In the exposure device 4, a polygon mirror 43, an fθ lens 44, a mirror 45, and the like are provided to allow the laser beam to reach the photosensitive drum 22 from each laser device 5.

  As a premise, basically, it causes color unevenness and the like, and it is desirable that the energy received by the photosensitive drum 22 (the amount of laser beam received) is uniform in the main scanning direction (the horizontal line in FIG. 6). ). Here, in the exposure apparatus 4 of the present embodiment, the polygon mirror 43 is provided corresponding to the center position of the photosensitive drum 22 in the main scanning direction. Therefore, the laser beam is incident on the fθ lens 44, the mirror 45, and the photosensitive drum 22 at an inclined angle as the distance from the center position of the photosensitive drum 22 in the main scanning direction increases. The reflectance of the mirror 45 changes depending on the incident angle of the laser beam, and the transmittance (attenuation rate) of the fθ lens 44 also changes depending on the incident angle of the laser beam.

  Therefore, when a constant current is applied to the laser device 5 to emit light (when scanning is performed with a constant laser beam emission level), as shown by the upwardly convex line in FIG. 6, depending on the position in the main scanning direction, The energy (amount of received light) received by the photosensitive drum 22 varies. Specifically, the energy received by the photosensitive drum 22 decreases toward the end of the photosensitive drum 22.

  Therefore, the engine control unit 20 according to the present embodiment performs correction to increase the current supplied to the laser device 5 toward the end of the photosensitive drum 22, as shown in FIG. As a result, as shown by the horizontal line in FIG. 6, the energy received by the photosensitive drum 22 (the amount of laser beam received) is made uniform in the main scanning direction. The correction of the light emission level of the laser device 5 in accordance with the exposure position of the photosensitive drum 22 in the main scanning direction is performed by the engine control unit 20 scanning the first driving unit 7 in the main scanning direction based on the correction data. This is done by changing the current output during the period.

(Correction data)
Next, correction data in the laser apparatus 5 according to the first embodiment will be described with reference to FIGS. 8 and 9 are graphs for explaining an example of how to determine correction data.

  First, with reference to FIG. 8, the point that the ideal correction data differs depending on the intensity of the light emission level used as the reference of the laser device 5 will be described. The vertical axis in FIG. 8 indicates the total value (output value) of the digital value given to the first drive unit 7 and the digital value given to the second drive unit 8. The horizontal axis indicates the position of the photosensitive drum 22 in the main scanning direction.

  And the thick broken line in FIG. 8 shows the light emission level used as the reference | standard of the laser apparatus 5. FIG. For example, in the first drive unit 7 and the second drive unit 8 of the present embodiment, the laser device 5 is used as a reference in the range of the black arrow, for example, in accordance with individual differences in sensitivity of the photosensitive drum 22. The light emission level can be varied. In the example of FIG. 8, the engine control unit 20 gives a reference output value in the range of 70 to 130 to the second drive unit 8 in terms of output value, and varies the light emission level serving as a reference in each laser device 5. Can be made.

  For example, in the multifunction peripheral 100 of the present embodiment, the second drive unit 8 generates a current for causing each laser device 5 to emit light at a reference light emission level. For example, in terms of the output value of the laser device 5, when the light is emitted at the reference level of 70, the engine control unit 20 gives the second drive unit 8 a digital value of 70 (reference output value). It should be noted that a part of the digital value given to the second drive unit 8 is added to all correction output values in the correction data, and the correction data and each photoconductor are biased so as to bias the output value of the first drive unit 7 with the correction data. A reference output value for the drum 22 may be determined. Note that the fluctuation range of the light emission level as a reference varies depending on the current limit value of the laser device 5 and the output current value per step of the first drive unit 7 and the second drive unit 8, and is limited to the above example. Absent.

  As shown in FIG. 8, the correction data is stored in the photosensitive drum 22 such that the first drive unit 7 increases the current supplied to each laser device 5 toward the end of the photosensitive drum 22 in the main scanning direction. It is determined according to the position in the main scanning direction. For example, the correction data is data that defines a value (correction output value) indicating a current to be output by the first drive unit 7 for each pixel. Specifically, in the correction data of this embodiment, the light emission level of each laser device 5 becomes the highest at the start of scanning and exposure in the main scanning direction, and the light emission level gradually increases as the scanning position goes to the center of the photosensitive drum 22. As the light emission level decreases, the light emission level becomes equal to the reference light emission level at the center position (0 mm point) of the photoconductive drum 22 in the main scanning direction, and the scanning position is the end of the photoconductive drum 22 (rear pixels in the main scanning direction). ), The light emission level gradually increases, and the current supplied by the first drive unit 7 changes so that the light emission level of each laser device 5 becomes the highest at the end of scanning and exposure in the main scanning direction. Determined.

  Here, the reflectance and transmittance are changed depending on the incident angle to the photosensitive drum 22, the fθ lens 44, and the mirror 45. Therefore, in order to equalize the amount of energy given by the laser beam at any position in the main scanning direction of the photosensitive drum 22, the total value (output value) of the digital values given to the first driving unit 7 and the second driving unit 8 is used. ) (The ratio of the total value of the reference output value and the corrected output value at the end of the photosensitive drum 22 and the total value of the reference output value and the corrected output value at the center of the photosensitive drum 22). ) Is preferably constant.

  Then, the ideal light emission level of the laser device 5 to be increased from the center to the end of the photosensitive drum 22 in accordance with the reference light emission level (light emission amount) (the current amount that the first drive unit 7 should increase). Changes. In other words, the width (difference) between the maximum value (maximum total value) and the minimum value (minimum total value) of the total value (output value) of the digital values given to the first drive unit 7 and the second drive unit 8 is the reference and Depending on the light emission level (light emission amount, in this embodiment, the minimum total value).

  Specifically, as shown in FIG. 8, assuming that the ratio of the maximum value (maximum total value) and the minimum value (minimum total value) of the total value (output value) is an ideal ratio, the light emission level (light emission amount) is When scanning and exposure is performed at the maximum level (for example, when the minimum total value is 130), the difference between the maximum total value and the minimum total value (illustrated by the white arrow Δ1) and the light emission level (light emission amount) are set to the minimum level. This is different from the difference between the maximum total value and the minimum total value (illustrated by the white arrow Δ2) when scanning and exposure are performed (for example, when the minimum total value is 70).

  For example, an ideal maximum value (maximum total value) and minimum value (minimum total value) of the total output value of the digital value given to the first drive unit 7 and the digital value given to the second drive unit 8 are ideal. When the ratio is 1.15, when the minimum total value (reference output value) is 130, the ideal maximum total value is 130 × 1.15 at the end of the photosensitive drum 22 as shown in FIG. ≈150 (the difference between the maximum total value and the minimum total value is about 20).

  For example, if the ideal ratio between the ideal maximum value (maximum total value) and the minimum value (minimum total value) is 1.15, and the minimum total value (reference output value) is 70, the photoconductor At the end of the drum 22, as shown in FIG. 8, the ideal maximum total value is 70 × 1.15≈81 (the difference between the maximum total value and the minimum total value is about 11).

  Therefore, as shown in FIG. 9, the first ideal correction data determined in advance as the ideal correction data at the maximum level for scanning and exposing the laser device 5 at the maximum light emission level corresponds to the position in the main scanning direction. A first correction pattern indicating a change in the correction output value and second ideal correction data determined in advance in the main scanning direction as ideal correction data at the minimum level for scanning and exposing the laser device 5 at the minimum light emission level. The correction output value corresponding to the position in the main scanning direction in the correction data is determined so as to be within the range of the second correction pattern indicating the change of the correction output value according to the position. The memory 9 connected to the engine control unit 20 stores the correction data determined in this way.

  Specifically, the first ideal correction data includes the maximum total value obtained by summing the maximum value of the correction output value in the first ideal correction data and the reference output value at the maximum level for scanning and exposure at the maximum light emission level, and the first total value. The ratio between the minimum value of the corrected output value in the correction data and the minimum total value obtained by summing the reference output values at the maximum level for scanning and exposure at the maximum light emission level is determined to be a predetermined ideal ratio. It is what was done. The second ideal correction data includes the maximum total value obtained by summing the reference output values at the minimum level for scanning and exposure at the maximum value of the correction output value and the minimum light emission level in the second ideal correction data, and the second correction data. The ratio between the minimum correction output value and the minimum total value obtained by summing the reference output values at the minimum level for scanning and exposure at the minimum light emission level is determined to be a predetermined ideal ratio. Is.

  More specifically, the correction data includes a maximum total value obtained by adding the maximum value of the correction output value in the correction data and a predetermined reference standard value, the minimum value of the correction output value in the correction data, and the reference standard. The ratio to the minimum total value obtained by adding the values is determined to be a predetermined ideal ratio. The memory 9 stores the correction data determined in this way. Details of the reference standard value will be described later.

(Method for determining correction data)
Next, a method for determining correction data in the first embodiment will be described with reference to FIG. FIG. 10 is a graph for explaining a method for determining correction data in the first embodiment.

  First, in FIG. 10, the total value (maximum total value) of the reference output value of each color determined in advance for the four colors of black, yellow, cyan, and magenta and the maximum value (end of the photosensitive drum 22) in the correction data is shown. The ideal correction data for each color when the ratio of the total value (minimum total value) of the reference output value of each color and the minimum value (center of the photosensitive drum 22) in the correction data is the optimum (ideal ratio) is shown. ing. As shown in FIG. 10, the sensitivity (the degree of excitation with respect to the amount of light) with respect to the laser beam varies depending on each photosensitive drum 22. Therefore, the memory 9 stores a reference output value for each second drive unit 8 corresponding to the photosensitive drum 22 of each color.

  However, in the present embodiment, one first driving unit 7 is provided for the plurality of second driving units 8. The first drive unit 7 outputs the same amount of current (current corresponding to the same correction output value) to each second drive unit 8. For this reason, it is necessary to determine correction data in which an error from ideal correction data (correction pattern) for each color is minimized.

  Therefore, in determining correction data, the minimum total value of each color (in this embodiment, the reference output value. For example, in FIG. 10, black is about 130, yellow is about 110, cyan is about 70, and magenta is about 80. ), The ratio between the maximum total value and the minimum total value when a value between any two minimum total values (standard output values) other than black is used as a reference standard value is an ideal ratio (for example, 1.15). ) Is stored. In the example shown in FIG. 10, an example in which the average value of the standard output values (minimum total value) of yellow and cyan is used as the reference standard value is shown.

  The reference standard value may be an average value (minimum total value) of cyan and magenta standard output values, an average value of yellow and magenta standard output values (minimum total value), or yellow and cyan. The average of the reference output value (minimum total value) of magenta may be used as the reference output value. Thereby, it is possible to reduce errors in correction for a plurality of colors.

  The reference output value is determined for each photoconductor drum 22 measured and confirmed by inspection at the time of manufacture and stored in the memory 9. Further, correction data is determined as described above according to the reference output value (minimum total value) determined for each photosensitive drum 22, and the memory 9 stores the correction data.

(Printing flow)
Next, the flow of scanning and exposure with correction of the light emission level of each laser device 5 in the multifunction machine 100 of the first embodiment will be described with reference to FIG. FIG. 11 is a flowchart showing an example of the flow of scanning and exposure with correction of the light emission level of each laser device 5 in the multi-function device 100.

  The start in FIG. 11 is a point in time when a print job is started (copy) based on image data of a document read by the image reading unit 1b, or a point in time when a print job is started based on image data received from a computer.

  First, the engine control unit 20 reads correction data from the memory 9 (step # 1). Further, the engine control unit 20 reads a reference output value to be given to each second drive unit 8 from the memory 9 (step # 2).

  Then, the engine control unit 20 continues to check whether or not it is the start timing of scanning and exposure of the line in the main scanning direction of the page based on the output of the light receiving unit 46 and the instruction from the main control unit 6 (step #). 3. No of step # 3 → step # 3). At this time, the engine control unit 20 rotates the polygon motor 42 at a predetermined rotation speed during scanning and exposure.

  When the start timing is reached, the engine control unit 20 gives a digital value indicating a current value to be output to the first drive unit 7 based on the correction data for one line in the main scanning direction, and also supplies each second drive unit 8 with each digital value. On the other hand, based on the corresponding reference output value, a digital value to be output by each second drive unit 8 is given (step # 4). As a result, the photosensitive drum 22 is scanned and exposed for one line in the main scanning direction (step # 5). For pixels (dots) that are not scanned and exposed, the engine control unit 20 masks instruction signals (digital values) so as not to output current to the first drive unit 7 and the second drive units 8. ).

  Then, the engine control unit 20 confirms whether the scanning and exposure of the lines in all main scanning directions to be printed by the print job are completed (step # 6). If not completed (No in step # 6), the flow returns to step # 3. Thereby, scanning and exposure of lines in the main scanning direction are continuously performed in the sub-scanning direction, and scanning and exposure of the photosensitive drum 22 for one page or a plurality of pages are performed. If completed (Yes in Step # 6), the engine control unit 20 stops the exposure operation (Step # 7), and this flow ends.

(Calibration of density and update of correction data accompanying calibration)
Next, with reference to FIGS. 10, 12, and 13, density calibration in the multifunction peripheral 100 according to the first embodiment and update of correction data accompanying the calibration will be described. FIG. 12 is a flowchart illustrating an example of a control flow in density calibration. FIG. 13 is an explanatory diagram showing an example of a toner image generated by density calibration.

  When the multi-function device 100 is used, for example, the density of the formed toner image is different from the ideal density due to wear or dirt of the photosensitive drum 22 (aging deterioration). For example, during use, the density of the formed toner image decreases (decreases). Therefore, in the MFP 100 according to the present embodiment, the density calibration operation is performed at a predetermined time point such as when a predetermined number of sheets are printed or when the main power is turned on.

  Therefore, the flow of density calibration will be described with reference to FIG. In FIG. 12, the start is a time point at which density calibration is executed.

  As the density calibration is executed, the engine control unit 20 forms a toner image for density calibration (step # 11). Then, the engine control unit 20 transfers the toner image to the intermediate transfer belt 32 (step # 12). Further, the density sensor 26 (corresponding to the density information input unit) reads the toner image (step # 13).

  FIG. 13 is a diagram illustrating an example of the intermediate transfer belt 32, the density measurement toner image P <b> 1 formed on the intermediate transfer belt 32, and the density sensor 26. Image data for forming the density measurement toner image P1 is stored in, for example, the memory 9, and the engine control unit 20 forms a toner image based on the image data of the density measurement toner image P1, and the intermediate transfer belt 32. Let them transcribe. For example, as shown in FIG. 13, the density measurement toner image P1 is a combination of patches of each color (black, yellow, cyan, magenta). A plurality of density measurement toner images P1 may be formed as shown in FIG.

  A density sensor 26 is provided so that the detection range is on the moving path of the density measurement toner image P1. The density sensor 26 is an optical sensor that reads the density measurement toner image P1. For example, the density sensor 26 is an optical sensor that irradiates light toward the intermediate transfer belt 32, receives reflected light, and has a different output size depending on the amount of reflected light. For example, the density sensor 26 is provided between the black image forming unit 21 and the driving roller 33 so as to face the intermediate transfer belt 32 (see FIG. 1).

  Depending on the density of the density measurement toner image P1, the light absorption rate and light diffusion rate of the toner image are different, the amount of light received by the density sensor 26 is changed, and the output is different. The output of the density sensor 26 is input to, for example, the engine control unit 20 (see FIG. 3). The engine control unit 20 recognizes the output voltage value of the concentration sensor 26.

  The memory 9 stores, for example, a table indicating the density with respect to the output value of the density sensor 26 for each color. The engine control unit 20 recognizes the density of each color patch based on the table of the memory 9 and the output value of the density sensor 26 when the density measurement toner image P1 is formed. In this way, the engine control unit 20 compares the density of each color patch with the ideal density of each color patch (for example, storing data indicating the ideal density of each color patch in the memory 9). A difference between the density in the current printing and the ideal density is recognized (step # 14).

  The engine control unit 20 prints the density measurement toner image P1, reads the printed matter by the image reading unit 1b, and based on the pixel value (density value) of the density measurement toner image P1 in the image data obtained by the reading. However, the difference between the density in the current printing and the ideal density may be recognized. Therefore, instead of the density sensor 26, the image reading unit 1b may be used as a density information input unit that receives input of information indicating the density of the density measurement toner image P1. Further, the service person or the user visually confirms the toner image or the printed matter, and the engine control unit 20 inputs the deviation between the current printing density and the ideal density to the operation panel 1a as a value. You may recognize the shift | offset | difference of the density in the present printing, and an ideal density. Therefore, instead of the density sensor 26, the operation panel 1a may be used as a density information input unit that receives input of information indicating the density of the density measurement toner image P1.

  Then, if necessary, the engine control unit 20 updates the reference output value of each color according to the recognized shift in each color (step # 15). Specifically, the engine control unit 20 updates the reference output value in the memory 9 so that the reference output value is reduced for a color darker than the ideal density, and the reference for the lighter color than the ideal density. The reference output value is updated in the memory 9 so as to increase the output value.

  Furthermore, since the reference output value has been updated to a new value, the engine control unit 20 also updates the correction data (step # 16). Specifically, as described above, the engine control unit 20 refers to a value between any two reference output values other than black among the updated reference output values (also referred to as minimum total values) of the respective colors. Correction data determined so that the ratio between the maximum total value and the minimum total value when used as the reference value is an ideal ratio (for example, 1.15) is generated, and the correction data generated in the memory 9 is stored.

  As described above, the image forming apparatus (for example, the multifunction peripheral 100) according to the present embodiment has a plurality of photosensitive drums 22 as image carriers and beams for scanning and exposing the photosensitive drums 22. The laser device 5 separately provided to the photosensitive drum 22 and the beam emitted by the laser device 5 reach the photosensitive drum 22 to perform scanning and exposure along the main scanning direction of the photosensitive drum 22. And a correction output indicating the light emission level of the beam to be increased to correct the energy difference received by the photosensitive drum 22 in accordance with the position of the optical drum (mirror 45, fθ lens 44, etc.) and the photosensitive drum 22 in the main scanning direction. Correction data common to each laser device 5 and a reference output value for determining and correcting a light emission level that serves as a reference for the amount of light emitted to the photosensitive drum 22 The output current supplied to each laser device 5 is changed according to the position in the main scanning direction in accordance with the storage unit (memory 9) stored for each photosensitive drum 22 and the magnitude of the correction output value of the correction data. The first driving unit 7 for changing the light emission level of the beam in the main scanning direction and the laser device 5 are provided individually, and are supplied to the corresponding laser device 5 according to the magnitude of the reference output value. Each of the laser devices 5 is supplied with a current obtained by combining the output current of the first drive unit 7 and the output current of the second drive unit 8. The beam is emitted, and the storage unit performs correction according to the position in the main scanning direction of first ideal correction data that is predetermined as ideal correction data at the maximum level for scanning and exposing the laser device 5 at the maximum light emission level. The first showing the change of the output value Change in correction output value in accordance with the correction pattern and the position in the main scanning direction of second ideal correction data predetermined as ideal correction data at the minimum level for scanning and exposing the laser device 5 at the minimum light emission level The correction data in which the correction output value corresponding to the position in the main scanning direction is determined within the range of the second correction pattern indicating.

  As a result, only one current source is required to supply each laser device 5 with a current for correcting the energy difference of the beam irradiated to each pixel of the photosensitive drum 22 in the main scanning direction. Accordingly, only one correction is required to make the amount of energy received by each pixel in the main scanning direction on each photosensitive drum 22 one, and the manufacturing cost of the image forming apparatus (for example, the multifunction peripheral 100) can be reduced. Can be reduced. Further, the light emission level of the beam irradiated to each pixel in the main scanning direction of each photoconductive drum 22 can be corrected by correction data that draws a correction pattern limited within a certain range. Therefore, even if one correction data is supplied and a common current is supplied to each laser device 5 by the first drive unit 7, ideal light emission of a beam to be irradiated to each pixel in the main scanning direction of each photosensitive drum 22 The light emission level of the laser device 5 can be corrected according to the position in the main scanning direction without greatly separating from the level (suppressing errors), and the balance of each color can be reduced.

  Further, the reference emission level of the beam to be irradiated for each photosensitive drum 22 varies depending on sensitivity characteristics, manufacturing errors, and the like. In consideration of reflectance and transmittance, the difference between the maximum value and the minimum value of the correction output value in the correction data is preferably made different according to the light emission level that is the reference of the beam. Therefore, the storage unit (memory 9) has a maximum total value obtained by adding the maximum value of the correction output value in the correction data and a predetermined reference standard value, the minimum value of the correction output value in the correction data, and the reference standard value. Correction data determined so that the ratio to the minimum total value obtained by adding to the predetermined ideal ratio is stored. Thereby, even if there is one correction data and a common current is supplied to each laser device 5 by the first drive unit 7, the correction data is set so that the ratio between the maximum total value and the minimum total value is optimal. . Accordingly, it is possible to make uniform the irradiation amount (irradiation energy) of the beam to each pixel of the photosensitive drum 22 in the main scanning direction.

  Also, color balance loss, color unevenness, and difference from the original are easily recognized when toner images other than black relating to saturation, hue, and the like are superimposed. Therefore, in the image forming apparatus of the present embodiment (for example, the multifunction peripheral 100), the photosensitive drums 22 are provided for four colors of black, cyan, magenta, and yellow, and the storage unit (memory 9) is a photosensitive body for each color. A reference output value is stored for each second drive unit 8 corresponding to the drum 22, and a maximum total value and a minimum total value when a value between any two reference output values other than black is used as a reference reference value, The correction data determined so that the ratio is the ideal ratio is stored. As a result, even if a single correction data is supplied and a common current is supplied to each laser device 5 by the first drive unit 7, an error from an ideal correction output value for each pixel is detected for cyan, magenta, and yellow. A small amount of correction data is determined on average. Therefore, even if the toner images of the respective colors are superimposed, the color balance can be reduced, and an inexpensive and high-quality image forming apparatus (for example, the multifunction peripheral 100) can be provided.

  Further, due to aging deterioration due to use, etc., a deviation between the density of the actually formed toner image and the ideal density of the toner image occurs (for example, becomes thinner). In view of this, the multifunction peripheral 100 of this embodiment has a density information input unit (a density sensor 26, an image reading unit) that receives input of information indicating the density of the density measurement toner image P1 of each color formed on each photosensitive drum 22. Part 1b, operation panel 1a, etc.) and the information inputted to the density information input part, the deviation of the toner image of each color from the ideal density is grasped, and the reference output is output for a color darker than the ideal density A control unit that updates the reference output value of the storage unit (memory 9) to reduce the value, and updates the reference output value of the storage unit to increase the reference output value for a color lighter than the ideal density. An engine control unit 20). Thereby, each reference output value indicating the light emission level as a reference of each laser device 5 is corrected. Therefore, the deviation from the ideal toner image caused by use can be corrected as a whole.

  The photosensitive drum 22 is provided for four colors of black, cyan, magenta, and yellow. When the control unit (engine control unit 20) updates the reference output value of each color, any two of the standards other than black are provided. Correction data determined so that the ratio between the maximum total value and the minimum total value when the value between the output values is the reference standard value is an ideal ratio is generated and stored in the storage unit (memory 9). As a result, with the update of the reference output value for each color, correction data with an average small error from the ideal correction output value for each pixel is determined for cyan, magenta, and yellow. Accordingly, it is possible to provide an image forming apparatus (for example, the multifunction peripheral 100) in which the color balance is not lost and the high image quality is maintained even when the reference output value of each color is updated.

  The correction data is set so that the correction output value increases as it goes from the pixel at the center position of the photosensitive drum 22 in the main scanning direction to the pixel at the end of the photosensitive drum 22 in the main scanning direction. As a result, the corrected output value is increased as the end position of the photosensitive drum 22 is such that the incident angle of the beam to the members included in the photosensitive drum 22 and the optical unit (mirror 45, fθ lens 44, etc.) becomes sharper. . Accordingly, it is possible to appropriately correct the energy difference of the beam applied to each pixel of the photosensitive drum 22 in the main scanning direction.

  The first ideal correction data includes the sum of the maximum correction output value and the maximum reference output value in the first ideal correction data, the minimum value and the maximum reference of the correction output value in the first correction data. The ratio of the output value to the total value is determined to be a predetermined ideal ratio, and the second ideal correction data is the maximum value of the correction output value in the second ideal correction data. The ratio between the total value of the minimum reference output values and the minimum value of the corrected output values in the second ideal correction data and the total value of the minimum reference output values is determined to be a predetermined ideal ratio. It is a thing. Thereby, when the reference light emission level of the beam is maximum, the difference between the maximum value and the minimum value in the correction output value in the first ideal correction data is increased, and when the reference light emission level of the beam is minimum, The difference between the maximum value and the minimum value in the correction output value in the first ideal correction data is reduced. Accordingly, the first ideal correction data and the second ideal correction data are determined at an optimum ratio according to the reference emission level of the beam.

(Second Embodiment)
Next, a second embodiment of the present invention will be described based on FIG. FIG. 14 is a graph for explaining a method for determining correction data in the second embodiment.

  The second embodiment differs from the first embodiment in how to define correction data, but the other points may be the same. Therefore, except for the case where it is specifically described, the parts common to the first embodiment can be used, and thus the description and illustration are omitted.

  In FIG. 14, the total value (maximum total value) of the reference output value of each color predetermined for four colors of black, yellow, cyan, and magenta and the maximum value (end of the photosensitive drum 22) in the correction data, and each color. The ideal correction data when the ratio of the total value (minimum total value) of the reference output value and the minimum value (center of the photosensitive drum 22) in the correction data is set to the optimum (ideal ratio) is shown. As shown in FIG. 14, each photoconductor drum 22 has a different sensitivity (degree of excitation with respect to the amount of light) with respect to the laser beam, so that optimum correction data (correction pattern) for each color is different. Therefore, the memory 9 stores a reference output value for each second drive unit 8 corresponding to the photosensitive drum 22 of each color.

  In this embodiment, when determining correction data, the minimum total value of a plurality of colors (in this embodiment, a reference output value. For example, in FIG. 14, black is about 130, yellow is about 110, cyan is about 70, magenta. Is an average of a plurality of (at least two) standard output values (minimum total value) as a reference standard value, and the maximum total value and minimum total value (= reference standard value) of the reference standard value The correction data is determined so that the ratio to () becomes an ideal ratio.

  Specifically, FIG. 14 shows an example in which an average value of four standard output values (all standard output values) of black, yellow, cyan, and magenta is used as a reference standard value (specifically, see The reference value is, for example, about 97 to 98). It should be noted that an average of the standard output values (minimum total values) of three colors among the four colors may be obtained and the average may be determined as the reference standard value. Note that an average of the standard output values for two specific colors among the four colors may be obtained, and the average may be determined as a reference standard value. Then, the correction data is determined so that the ratio between the maximum total value and the minimum total value (= reference standard value) in the reference standard value becomes an ideal ratio.

  Further, even in the case of the present embodiment, the correction data may be updated when the reference output value is updated in accordance with the density calibration. Specifically, the engine control unit 20 uses, as a reference standard value, an average value of at least two standard output values (minimum total value) among a plurality of standard output values (minimum total value), and the maximum of the reference standard values. Correction data is generated so that the ratio between the total value and the minimum total value becomes an ideal ratio. Similarly to FIG. 14, the engine control unit 20 uses the average value of all the standard output values (minimum total value) among the plurality of updated standard output values (minimum total value) as a reference standard value. The correction data may be generated so that the ratio between the maximum total value and the minimum total value at the reference value becomes an ideal ratio.

  Thus, in the present embodiment, the storage unit (memory 9) uses the average value of at least two standard output values among the plurality of standard output values as the reference standard value, and the maximum total value of the reference standard values and Correction data determined so that the ratio to the minimum total value becomes the ideal ratio is stored. As a result, even if a single correction data is supplied and a common current is supplied to each laser device 5 by the first drive unit 7, the correction is performed by reducing an error from an ideal correction output value for each pixel between at least two colors. Data is defined. Therefore, even if the toner images of the respective colors are superimposed, the color balance can be reduced, and an inexpensive and high-quality image forming apparatus (for example, the multifunction peripheral 100) can be provided.

  When the standard output value is updated, the control unit (engine control unit 20) sets the average value of at least two standard output values of the standard output values of each color as the reference standard value, and the maximum total of the reference standard values. Correction data is generated so that the ratio between the value and the minimum total value becomes an ideal ratio, and the generated correction data is updated in the storage unit (memory 9). As a result, with the update of the reference output value for each color, correction data in which an error from the ideal correction output value of each pixel of each photosensitive drum 22 is reduced is generated. Accordingly, it is possible to provide an image forming apparatus (for example, the multifunction peripheral 100) in which the color balance is not lost and the high image quality is maintained even when the reference output value of each color is updated.

  In addition, the storage unit (memory 9) uses a mean value of all standard output values as a reference standard value, and a correction determined so that the ratio between the maximum total value and the minimum total value in the reference standard value becomes an ideal ratio. Store the data. As a result, even if one correction data is provided and a common current is supplied to each laser device 5 by the first drive unit 7, correction data having an average error from an ideal correction output value for each pixel is determined. It is done. Therefore, even if the toner images of the respective colors are superimposed, the color balance can be reduced, and an inexpensive and high-quality image forming apparatus (for example, the multifunction peripheral 100) can be provided.

  Further, when the control unit (engine control unit 20) updates the standard output value, the average value of all the standard output values is used as the reference standard value, and the ratio between the maximum total value and the minimum total value in the reference standard value is Correction data is generated so that the ideal ratio is obtained, and the generated correction data is updated in the storage unit (memory 9). As a result, with the update of the reference output value for each color, correction data with a small average error from the ideal correction output value for each pixel is generated for all colors. Accordingly, it is possible to provide an image forming apparatus (for example, the multi-function peripheral 100) that maintains high image quality with little color balance disruption even when the reference output value of each color is updated.

(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 15 is a graph for explaining a method of determining correction data in the third embodiment.

  The second embodiment differs from the first and second embodiments in how to define correction data, but the other points may be the same. Therefore, except for the case where it is specifically described, the parts common to the first embodiment can be used, and thus the description and illustration are omitted.

  In FIG. 15, the total value (maximum total value) of the reference output value of each color predetermined for four colors of black, yellow, cyan, and magenta and the maximum value (end of the photosensitive drum 22) in the correction data, and each color. The ideal correction data when the ratio of the total value (minimum total value) of the reference output value and the minimum value (center of the photosensitive drum 22) in the correction data is set to the optimum (ideal ratio) is shown. As shown in FIG. 14 and FIG. 15, the sensitivity data (the degree of excitation with respect to the amount of light) varies with the respective photosensitive drums 22, so that the optimum correction data (correction pattern) differs for each color. Therefore, the memory 9 stores a reference output value for each second drive unit 8 corresponding to the photosensitive drum 22 of each color.

  In this embodiment, when determining correction data, the minimum total value of a plurality of colors (in this embodiment, a reference output value. For example, in FIG. 14, black is about 130, yellow is about 110, cyan is about 70, magenta. Is an average of a plurality of (at least two) standard output values (minimum total value) as a reference standard value, and the maximum total value and minimum total value (= reference standard value) of the reference standard value As with the second embodiment, the correction data is determined so that the ratio to () becomes an ideal ratio.

  In this embodiment, as shown in FIG. 15, the correction data includes the maximum reference output value (black 130 in the example of FIG. 15) and the minimum among the plurality of reference output values (minimum total value). The average value of the reference output values (cyan 70 in the example of FIG. 15) is the reference standard value (100 in the example of FIG. 15), and the ratio between the maximum total value and the minimum total value in the reference standard value is the ideal ratio. You may decide to become.

  As described above, the correction data determined based on the average value of the reference output values is stored in the memory 9. Then, as described with reference to FIG. 11 in the first embodiment, the correction data is used for scanning and exposure of the photosensitive drums 22 of the respective colors.

  Further, even in the case of the present embodiment, the correction data may be updated when the reference output value is updated in accordance with the density calibration. Specifically, the engine control unit 20 uses, as a reference standard value, an average value of at least two standard output values (minimum total value) among a plurality of standard output values (minimum total value), and the maximum of the reference standard values. Correction data is generated so that the ratio between the total value and the minimum total value becomes an ideal ratio. Similarly to FIG. 15, the engine control unit 20 calculates the average of the maximum reference output value (minimum total value) and the minimum reference output value (minimum total value) among the plurality of reference output values (minimum total value). The correction data may be generated so that the ratio between the maximum total value and the minimum total value in the reference standard value becomes an ideal ratio using the value as a reference standard value.

  Thus, in the present embodiment, the storage unit (memory 9) uses the average value of the maximum standard output value and the minimum standard output value among the plurality of standard output values as the reference standard value, and uses the reference standard value as the reference standard value. Correction data determined such that the ratio between the maximum total value and the minimum total value is an ideal ratio is stored. As a result, even if one correction data is supplied and a common current is supplied to each laser device 5 by the first driving unit 7, the ideal correction output value for each pixel can be obtained from the entire output range of the laser device 5. Correction data with a small average error is determined. Therefore, even if the toner images of the respective colors are superimposed, the color balance can be reduced, and an inexpensive and high-quality image forming apparatus (for example, the multifunction peripheral 100) can be provided.

  In addition, when the standard output value is updated, the control unit (engine control unit 20) uses the average value of the maximum standard output value and the minimum standard output value among the standard output values of each color as a reference standard value, and the reference standard Correction data is generated so that the ratio between the maximum total value and the minimum total value in terms of values is an ideal ratio, and the generated correction data is updated in the storage unit (memory 9). As a result, with the update of the reference output value for each color, correction data with a small average error from the ideal correction output value for each pixel is generated as seen from the entire output range of the laser device 5. Accordingly, it is possible to provide an image forming apparatus (for example, the multifunction peripheral 100) in which the color balance is not lost and the high image quality is maintained even when the reference output value of each color is updated.

(Fourth embodiment)
Next, based on FIG. 16, a fourth embodiment of the present invention will be described. FIG. 16 is a graph for explaining a method for determining correction data in the fourth embodiment.

  The fourth embodiment differs from the first to third embodiments in how to define correction data, but the other points may be the same. Therefore, unless otherwise specifically described, portions common to the first and second embodiments can be used, and thus description and illustration are omitted.

  In FIG. 16, the total value (maximum total value) of the reference output value of each color predetermined for four colors of black, yellow, cyan, and magenta and the maximum value (end of the photosensitive drum 22) in the correction data, and each color The ideal correction data when the ratio of the total value (minimum total value) of the reference output value and the minimum value (center of the photosensitive drum 22) of the correction data is the optimum (ideal ratio) is indicated by a broken line. In FIG. 16, an example of (fixed) correction data common to each color is indicated by a solid line.

  In this embodiment, one first driving unit 7 is provided for the plurality of second driving units 8, and the first driving unit 7 supplies the same amount of current (same correction) to each second driving unit 8. Current) corresponding to the output value. For this reason, an error between one fixed correction data and ideal correction data (correction pattern) for each color appears as much as Δ4 to Δ7 in FIG. In this embodiment, the reference standard value for the correction data is provided between the maximum standard output value (minimum total value) and the minimum standard output value (minimum total value). Further, the reference standard value may be a value obtained by averaging a plurality of standard output values (minimum total value).

  Therefore, in the present embodiment, the correction data is a correction data in which a predetermined reference standard value is determined as a minimum value in the correction data, and the correction data has a maximum reference output value among a maximum value and a plurality of reference output values. The first ratio between the added maximum total value, the minimum value in the correction data, and the minimum total value obtained by adding the largest reference output value among the plurality of reference output values, and the maximum value in the correction data and the plurality of reference output values The difference between the second total ratio of the maximum total value obtained by adding the smallest reference output value and the minimum value in the correction data and the minimum total value obtained by adding the smallest reference output value among the plurality of reference output values is equal or The corrected output value is determined so as to be minimized.

  This will be specifically described with reference to FIG. First, as shown in FIG. 16, the largest reference output value (minimum total value) is assumed to be 130, and the smallest reference output value (minimum total value) is assumed to be 70. It is assumed that the reference standard value of the correction data is 100 and the ideal ratio is 1.15. Then, the total value of the correction data based on the reference standard value and the ideal ratio and the reference standard value is 115 (maximum total value, photosensitive drum 22 end) −100 (photosensitive drum 22 center) −115 (maximum total value, End of the photosensitive drum 22). The ratio between the maximum total value and the minimum total value is 1.15.

  When the difference between the maximum total value and the minimum total value is 15 when the reference output value (minimum total value) is 130, the total value of the correction output value of the correction data and the reference output value is 145 (maximum total value, photosensitivity). Photosensitive drum 22 end) -130 (photosensitive drum 22 center) -145 (maximum total value, photoconductive drum 22 end). Therefore, the ratio between the maximum total value and the minimum total value is 145 / 130≈1.12, and the difference from the ideal ratio 1.15 is 0.03.

  On the other hand, if the difference between the maximum total value and the minimum total value is 15 when the reference output value (minimum total value) is 70, the total value of the correction output value of the correction data and the reference output value is 85 (maximum total value, photosensitivity). Photosensitive drum 22 end) -70 (photosensitive drum 22 center) -85 (maximum total value, photoconductive drum 22 end). Therefore, the ratio between the maximum total value and the minimum total value is 85 / 70≈1.21, and the difference from the ideal ratio 1.15 is 0.06. Then, the sum of the ratio differences is 0.09.

  Thus, even if the difference between the maximum total value and the minimum total value (each reference output value) is the same, the ratio between the maximum total value and the minimum total value differs depending on whether the reference output value (minimum total value) is large or small. .

  Therefore, in the present embodiment, the correction data is determined so that the difference in the ratio between the maximum total value and the minimum total value is reduced. Specifically, the smaller the reference output value, the greater the influence on the ratio between the maximum total value and the minimum total value, so it is conceivable to reduce the maximum value of the correction output value in the correction data.

  For example, in the above example, the ratio is assumed to be 1.13. Then, the total value of the correction data based on the reference standard value and the ideal ratio and the reference standard value is 113 (maximum total value, photosensitive drum 22 end) −100 (photosensitive drum 22 center) −113 (maximum total value, The difference between the maximum value and the minimum value is 13. When the difference between the maximum total value and the minimum total value is 12 at the reference output value 130, the total value of the correction output value of the correction data and the reference output value is 143 (maximum total value, end of the photosensitive drum 22). ) -130 (photosensitive drum 22 center) -143 (maximum total value, photosensitive drum 22 end). Therefore, the ratio between the maximum total value and the minimum total value is 143 / 130≈1.1, and the difference from the ideal ratio 1.15 is about 0.04. On the other hand, if the difference between the maximum total value and the minimum total value is 13 when the reference output value is 70, the total value of the correction output value of the correction data and the reference output value is 83 (maximum total value, end of the photosensitive drum 22). ) -70 (photosensitive drum 22 center) -83 (maximum total value, photosensitive drum 22 end). Therefore, the ratio between the maximum total value and the minimum total value is 83 / 70≈1.18, and the difference from the ideal ratio 1.15 is about 0.03. Then, the sum of the ratio differences is 0.07.

  In this way, by adjusting the maximum value of the correction output values of the correction data, as a whole, the ratio of the maximum total value and the minimum total value in the reference output value of each color and the correction output value of the correction data, and the ideal ratio The overall difference can be reduced.

  Specifically, a plurality of types of correction data having different maximum and minimum correction output values are stored in the memory 9 in advance. Then, the engine control unit 20 adds, for each correction data, a maximum total value obtained by adding a maximum value of correction output values of correction data and a plurality of maximum reference output values, a minimum value of correction output values of correction data, and a plurality of correction data. Among them, the ratio of the minimum total value obtained by adding the maximum reference output value, the maximum value of the correction output value of the correction data, and the maximum total value of the minimum reference output value among a plurality and the minimum value of the correction output value of the correction data And the ratio of the minimum total value obtained by adding the minimum reference output values among the plurality of correction data, and the correction data that minimizes the sum of errors from the ideal ratio may be selected and determined as the correction data to be used. .

  Further, even in the case of the present embodiment, the correction data may be updated when the reference output value is updated in accordance with the density calibration. Specifically, a plurality of types of correction data are stored in the memory 9 in advance. Then, the engine control unit 20 adds, for each correction data, a maximum total value obtained by adding the maximum reference output value of the correction output value of the correction data and the updated reference output value, and the correction output value of the correction data. The ratio of the minimum total value obtained by adding the maximum reference output value of the minimum value and the updated reference output value, and the minimum reference output value of the corrected output maximum value and the updated reference output value The sum of the error from the ideal ratio is calculated by calculating the ratio of the minimum total output value obtained by adding the minimum reference output value of the updated reference output value and the minimum reference output value after the update. The smallest correction data may be selected and determined as the correction data to be used.

  In this way, in the present embodiment, the storage unit (memory 9) is correction data in which a predetermined reference standard value is determined as the minimum value in the correction data, and the maximum value in the correction data and a plurality of values. A first ratio of a maximum total value obtained by adding the largest reference output value among the reference output values, a minimum value in the correction data, and a minimum total value obtained by adding the largest reference output value among a plurality of reference output values, and correction The maximum total value obtained by adding the maximum value in the data and the smallest reference output value among the plurality of reference output values, and the minimum sum value obtained by adding the minimum value in the correction data and the smallest reference output value among the plurality of reference output values The correction data in which the correction output value is determined so that the difference from the second ratio is equal or minimized is stored. As a result, the correction data in which the error between the maximum correction output value in the correction data of the color having the largest reference output value and the color having the smallest reference output value and the maximum correction output value in the correction data is reduced is obtained. Even if one correction data is stored and a common current is supplied to each laser device 5 by the first driving unit 7, an error from an ideal correction output value of each pixel of each photosensitive drum 22 is reduced. Correction data is determined.

  The control unit (engine control unit 20) is correction data in which a predetermined reference standard value is determined as the minimum value in the correction data, and when the standard output value for each color is updated, the maximum in the correction data is obtained. The maximum total value obtained by adding the largest reference output value among the updated reference output values and the minimum value in the correction data and the minimum value obtained by adding the largest reference output value among the updated reference output values The first ratio with the total value, the maximum value in the correction data, and the maximum total value obtained by adding the smallest updated reference output value among the plurality of reference output values, the minimum value in the correction data, and the plurality of reference output values Correction data in which the correction output value is determined so that the difference from the second ratio with the minimum total value obtained by adding the smallest updated reference output value is equal or minimized is generated, and the storage unit (memory 9) The generated correction data Further to new and, thereby, with the updating of the reference output value of each color, correction data is determined with a reduced error between the ideal correction output value of each pixel of the photosensitive drum 22.

  The embodiment of the present invention has been described above, but the scope of the present invention is not limited to this, and various modifications can be made without departing from the spirit of the invention.

  The present invention is applicable to an image forming apparatus that forms an image by performing exposure.

100 MFP (image forming apparatus) 1b Image reading unit (density information input unit)
1a Operation panel (concentration information input unit) 20 Engine control unit (control unit)
22 Photosensitive drum 26 Density sensor (Density information input unit)
44 fθ lens (optical part) 45 mirror (optical part)
5 Laser equipment 5Bk Laser equipment (for black)
5Y laser device (for yellow) 5C laser device (for cyan)
5M laser device (for magenta) 7 1st drive unit 8 2nd drive unit 8Bk 2nd drive unit (for black)
8Y Second drive unit (for yellow) 8C Second drive unit (for cyan)
8M Second drive unit (for magenta) 9 Memory (storage unit)

Claims (13)

A plurality of photosensitive drums as image carriers;
A laser device that emits a beam for performing scanning and exposure of the photosensitive drum, and is individually provided for the photosensitive drum;
An optical unit that causes the beam emitted by the laser device to reach the photosensitive drum, and performs scanning and exposure along a main scanning direction of the photosensitive drum;
A correction output value indicating a light emission level of a beam for correcting an energy difference received by the photosensitive drum according to the position of the photosensitive drum in the main scanning direction is determined, and correction data common to the laser devices. A storage unit that stores a reference output value for each photosensitive drum for determining and correcting a light emission level that serves as a reference for the amount of light emitted to the photosensitive drum;
According to the magnitude of the correction output value of the correction data, the output current supplied to each laser device is changed according to the position in the main scanning direction, and the light emission level of the beam in the main scanning direction is changed. One drive unit;
A second driving unit that is individually provided for each of the laser devices, and outputs a current of a certain magnitude to be supplied to the corresponding laser device according to the magnitude of the reference output value,
Each of the laser devices emits a beam upon receiving a supply of a current that combines the output current of the first drive unit and the output current of the second drive unit,
The storage unit performs the correction output according to the position of the first ideal correction data predetermined as ideal correction data at the maximum level for scanning and exposing the laser device at the maximum light emission level in the main scanning direction. a first correction pattern shows the change in value, the scanning laser device at the minimum emission level, the second ideal correction data predetermined as an ideal the correction data of the minimum level at which the exposure in the main scanning direction and to store said correction data to which the correction output value is determined in accordance with the position in the main scanning direction within the said corrected output value second correction pattern shows the change in corresponding to the position Image forming apparatus.   The storage unit includes a maximum total value obtained by adding a maximum value of the correction output value in the correction data and a predetermined reference standard value, a minimum value of the correction output value in the correction data, and the reference standard value. The image forming apparatus according to claim 1, wherein the correction data is stored such that a ratio with a minimum total value obtained by adding is a predetermined ideal ratio. The photosensitive drum is provided for four colors of black, cyan, magenta, and yellow,
The storage unit stores the reference output value for each of the second driving units corresponding to the photosensitive drums of each color, and sets a value between any two of the reference output values other than black as the reference reference value 3. The image forming apparatus according to claim 2, wherein the correction data determined so that a ratio between the maximum total value and the minimum total value is the ideal ratio is stored.   The storage unit uses an average value of at least two of the plurality of standard output values as the reference standard value, and a ratio between the maximum total value and the minimum total value in the reference standard value is The image forming apparatus according to claim 2, wherein the correction data determined to be the ideal ratio is stored.   The storage unit uses, as the reference standard value, an average value of the maximum standard output value and the minimum standard output value among the plurality of standard output values, and the maximum total value and the minimum value in the reference standard value The image forming apparatus according to claim 2, wherein the correction data determined so that a ratio to a total value is the ideal ratio is stored.   The storage unit is correction data in which a predetermined reference standard value is determined as a minimum value in the correction data, and the maximum reference value is the largest of the maximum value in the correction data and the plurality of reference output values. A first ratio of a maximum total value obtained by adding values, a minimum value in the correction data, and a minimum total value obtained by adding the largest reference output value among a plurality of reference output values, and a maximum value in the correction data And a maximum total value obtained by adding the smallest reference output values among the plurality of reference output values, a minimum value in the correction data, and a minimum total value obtained by adding the smallest reference output values among the plurality of reference output values. The image forming apparatus according to claim 1, wherein correction data whose correction output value is determined so that a difference from the second ratio is equal or minimized is stored. A density information input unit that receives input of information indicating the density of each color density toner image formed on each of the photosensitive drums;
Based on the information input to the density information input unit, the deviation of the toner image of each color from the ideal density is grasped, and for the color darker than the ideal density, the reference output value is reduced. A control unit that updates the reference output value of the storage unit and updates the reference output value of the storage unit so as to increase the reference output value for a color lighter than an ideal density. The image forming apparatus according to claim 2 . The photosensitive drum is provided for four colors of black, cyan, magenta, and yellow,
Wherein, when updating the reference output value of each color, the maximum total value when the value was the reference standard value between any two of the reference output value other than black and said minimum sum value the image forming apparatus according to claim 7 in which the ratio of generating the correction data defined such that the ideal ratio, and characterized in that stored in the storage unit.   When the control unit updates the reference output value, an average value of at least two of the reference output values among the reference output values of each color is set as the reference reference value, and the maximum total value at the reference reference value The image forming apparatus according to claim 7, wherein the correction data is generated so that a ratio of the total sum to the minimum total value becomes the ideal ratio, and the correction data generated in the storage unit is updated.   When the control unit updates the reference output value, among the reference output values of each color, the average value of the maximum reference output value and the minimum reference output value is set as the reference reference value, and the reference reference value 8. The correction data is generated so that a ratio between the maximum total value and the minimum total value in the case becomes the ideal ratio, and the correction data generated in the storage unit is updated. The image forming apparatus described.   The control unit is correction data in which a predetermined reference standard value is determined as a minimum value in the correction data, and when the standard output value of each color is updated, the maximum value in the correction data and the updated value are updated. The maximum total value obtained by adding the largest reference output values among the plurality of reference output values, the minimum value in the correction data, and the largest reference output value among the plurality of updated reference output values are added. A first ratio with the minimum total value, a maximum value in the correction data, a maximum total value obtained by adding the smallest updated reference output value among the plurality of reference output values, and a minimum value in the correction data The correction data in which the correction output value is determined so that the difference from the second ratio with the minimum total value obtained by adding the smallest updated reference output value among the plurality of reference output values is equal or minimized. Produces the above The image forming apparatus according to claim 7, wherein the to update the correction data generated in 憶部.   The correction data is set so that the correction output value increases as it goes from a pixel at a central position in the main scanning direction of the photosensitive drum to a pixel at the end of the photosensitive drum in the main scanning direction. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. Said first ideal correction data, and the total value of the maximum value and the maximum of the reference output value of the corrected output value in the first the ideal correction data, the correction output value in the first the ideal correction data is intended the ratio between the total value of the minimum and maximum of the reference output value is determined as an ideal a predetermined ratio,
Said second ideal correction data, the second ideal correction data within the corrected output value of the maximum value and the minimum of the reference output value of the total value and the minimum value of the corrected output value in the second the ideal correction data minimum according to any one of claims 1 to 12 ratio between the total value of the reference output value, characterized in that defined as an ideal a predetermined ratio and Image forming apparatus.

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