JP6476961B2 - Image forming apparatus, image forming control method, and image forming control program - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer, an image forming control method, and an image forming control program, and in particular, an image forming having a function of scanning a light beam from a light source and writing it on a recording medium such as an image carrier. It relates to control of the device.

  As an image forming apparatus, while driving an image carrier such as an image carrier drum or an image carrier belt in a first direction (sub scanning direction), one line in a second direction (main scanning direction) corresponding to image data It is known to perform two-dimensional (every one page) image formation by repeatedly performing image formation for each of a plurality of lines.

As an example, in an electrophotographic image forming apparatus, an image carrier (image carrier drum) which scans a light beam modulated according to image data in the main scanning direction and rotates in the sub scanning direction in parallel with this (Image carrier belt), an image is formed by the light beam.
In order to realize such main scanning of the light beam, a rotating polygon mirror (polygon mirror) having a plurality of rotating reflecting surfaces is used.

It is desirable that each reflecting surface of this polygon mirror is ideally a perfect plane. However, due to an accuracy error of machining, fine unevenness (for example, several nm to several tens of nm in height difference from the reference surface) may be locally present along the main scanning direction.
By the way, in the underfield optical system, a light beam of a beam spot system smaller than the length in the main scanning direction of the polygon mirror is used. In this underfield optical system, the position (reflection position) in the plane of the polygon mirror to which the light beam is irradiated changes as the polygon mirror rotates.

  In this case, since the reflection position moves in the main scanning direction as the polygon mirror rotates, it may overlap with fine irregularities on the reflection surface of the polygon mirror, and the beam spot shape of exposure on the image carrier may change momentarily. That is, at a certain moment, not only the dot position to be originally exposed but also the proximity dot position which should not be originally exposed may be exposed on the surface of the image carrier.

  And, the change of the beam spot shape of the exposure caused by such fine unevenness of the reflecting surface of the polygon mirror occurs in a different state depending on the position of the reflecting surface of the polygon mirror. For this reason, the finally obtained image is degraded in a state including partial density unevenness. The minute unevenness on the reflecting surface of the polygon mirror and the change of the beam spot shape based on the unevenness will be described in detail in the embodiment with reference to a specific example.

  Further, various adjustments in the case of forming an image by scanning with a light beam are described in Patent Document 1 below.

JP-A-7-164674

In the above-mentioned Japanese Patent Application Laid-Open No. 7-164674, there is proposed a technique for controlling the influence of the beam spot of exposure on peripheral pixels to reduce the resolution and the gradation.
Here, the fine irregularities on the reflecting surface of the polygon mirror described above exist in different situations depending on the reflecting surface and the reflection position in each reflection. Therefore, the change of the beam spot shape and the deterioration of the image quality also occur under different conditions depending on the reflection surface of the polygon mirror and the reflection position in each reflection.

However, in this Japanese Patent Application Laid-Open No. 7-164674, the control is uniform, and the contents do not correspond to the beam spot shape based on the fine unevenness of the reflecting surface which is different for each main scanning position and for each polygon surface. For this reason, the subject which the inventor of this application is examining can not be solved.
The present invention has been made to solve the above-described problems, and an image forming apparatus, an image forming control method, and an image forming control method capable of reducing deterioration in image quality due to fine unevenness on the reflecting surface of a polygon mirror. An object of the present invention is to realize an image formation control program.

An image forming apparatus, an image formation control method, and an image formation control program in which one aspect of the present invention is reflected are configured as follows.
(1) An image forming apparatus in which one aspect of the present invention is reflected comprises: an image carrier on which an image is formed by light beam exposure; a light source for generating the light beam emitting light according to image data; A light scanning unit for scanning the light beam in a first scanning direction on the image carrier by a plurality of reflecting surfaces of a rotary polygon mirror rotationally driven by a source; and a second scanning direction orthogonal to the first scanning direction At each position of each surface of the rotating polygon mirror, a second scanning direction drive unit for relatively moving the image carrier and the light beam, a reflecting surface identification unit for identifying each reflecting surface of the rotating polygon mirror, and A storage unit for storing irradiation shape information generated from the irradiation shape of the reflected light beam on the image carrier surface, and the irradiation shape information of the adjacent pixels, the exposure intensity of the target pixel on the image carrier surface is original Corresponds to the pixel value Image processing of correcting the pixel value of the target pixel of the image data with reference to the irradiation shape information and the pixel value of the adjacent pixel so as to be in the state, and supplying the corrected image data to the light source A portion, and the irradiation shape information includes information on the position and intensity of secondary irradiation around the target irradiation position on the image carrier surface .

An image forming control method according to one aspect of the present invention includes an image carrier on which an image is formed by light beam exposure, a light source generating the light beam emitting light according to image data, and a rotational drive source. A light scanning unit that scans the light beam in a first scanning direction on the image carrier by a plurality of reflective surfaces of a rotary polygon mirror that is rotationally driven; and the image bearing in a second scanning direction that is orthogonal to the first scanning direction A second scanning direction drive unit for relatively moving the body and the light beam, a reflecting surface identification unit for identifying each reflecting surface of the rotating polygon mirror, and reflection at each position of each surface of the rotating polygon mirror Storage unit for storing irradiation shape information generated from the irradiation shape of the light beam on the image carrier surface and including information on the position and intensity of secondary irradiation around the target irradiation position on the image carrier surface And the image day And correcting the pixel value of the target pixel, and controlling the image formation of the image forming apparatus including the image processing unit for supplying the corrected image data to the light source. Based on the shape information, the irradiation shape information and the pixel value of the adjacent pixel are referred to so that the exposure intensity of the pixel of interest on the image carrier surface corresponds to the original pixel value, and the image data Correct the pixel value of the target pixel.

An image forming control program reflecting one aspect of the present invention includes an image carrier on which an image is formed by light beam exposure, a light source generating the light beam emitting light according to image data, and a rotational drive source. A light scanning unit that scans the light beam in a first scanning direction on the image carrier by a plurality of reflective surfaces of a rotary polygon mirror that is rotationally driven; and the image bearing in a second scanning direction that is orthogonal to the first scanning direction A second scanning direction drive unit for relatively moving the body and the light beam, a reflecting surface identification unit for identifying each reflecting surface of the rotating polygon mirror, and reflection at each position of each surface of the rotating polygon mirror Storage unit for storing irradiation shape information generated from the irradiation shape of the light beam on the image carrier surface and including information on the position and intensity of secondary irradiation around the target irradiation position on the image carrier surface And the picture And an image processing unit that corrects the pixel value of a target pixel of data and supplies the corrected image data to the light source. Thus, the target pixel of the image data is referred to with reference to the irradiation shape information and the pixel value of the adjacent pixel such that the exposure intensity of the target pixel on the image carrier surface corresponds to the original pixel value. Correct the pixel value of.

  (2) In the above (1), when the exposure intensity of the light beam of the pixel of interest on the surface of the image carrier is affected by the peripheral characteristics of the irradiation shape of the light beam of the adjacent pixels, The pixel value of the target pixel of the image data is corrected using the peripheral characteristic included in the irradiation shape information of the pixel.

(3) In the above (1) to (2), in the image processing unit, the exposure intensity on the surface of the image carrier based on the pixel value of the target pixel depends on the peripheral characteristics of the irradiation shape of the light beam of the adjacent pixels. If smaller than the influence, the pixel value of the adjacent pixel is corrected .

( 4 ) In the above (1) to ( 3 ), the image processing unit corrects the pixel value of the pixel in the main scanning direction of the image data.

The following effects can be obtained by the image forming apparatus, the image formation control method, and the image formation control program in which one aspect of the present invention is reflected.
(1) In the present invention, the irradiation shape information and the pixel value of the proximity pixel are referred to so that the exposure intensity on the image carrier surface of the pixel of interest corresponds to the original pixel value by the irradiation shape information of the proximity pixel. Then, the pixel value of the target pixel of the image data is corrected.

As a result, even if fine irregularities are present on the reflective surface of the rotating polygon mirror and even near dot positions that should not be exposed on the surface of the image carrier are exposed, the pixel value of the pixel of interest is corrected. Thus, the same state as when exposed with the original pixel value can be maintained. That is, it is possible to reduce the deterioration of the image quality due to the fine unevenness on the reflecting surface of the rotating polygon mirror.
In addition, since the irradiation shape information includes information on the position and intensity of the secondary irradiation around the target irradiation position on the image carrier surface, the influence from peripheral pixels to the pixel of interest can be correctly calculated, and the polygon polygon mirror It is possible to reduce the deterioration of the image quality caused by the fine irregularities on the reflective surface of the lens.

(2) In the above (1), when the exposure intensity on the image carrier surface of the light beam of the pixel of interest is affected by the peripheral characteristics of the irradiation shape of the light beam of the near pixel, it is included in the irradiation shape information of the near pixel. The pixel value of the target pixel of the image data is corrected using the peripheral characteristic.
As a result, even if fine irregularities are present on the reflective surface of the rotating polygon mirror and even near dot positions that should not be exposed on the surface of the image carrier are exposed, the pixel value of the pixel of interest is corrected. Thus, the same state as when exposed with the original pixel value can be maintained. That is, it is possible to reduce the deterioration of the image quality due to the fine unevenness on the reflecting surface of the rotating polygon mirror.

  (3) In the above (1) to (2), when the exposure intensity on the image carrier surface based on the pixel value of the pixel of interest is smaller than the influence of the peripheral characteristics of the irradiation shape of the light beam of the adjacent pixels Correct the pixel value of the adjacent pixel. As a result, even when correction can not be performed by the correction of the pixel value of the pixel of interest, the same state as exposure with the original pixel value can be maintained. That is, it is possible to reduce the deterioration of the image quality due to the fine unevenness on the reflecting surface of the rotating polygon mirror.

( 4 ) In the above (1) to ( 3 ), by correcting the pixel values for the pixels in the main scanning direction of the image data, it is possible to correctly calculate the influence from peripheral pixels in the exposure using the rotating polygon mirror It is possible to reduce the deterioration of the image quality caused by the fine unevenness on the reflecting surface of the rotating polygon mirror.

FIG. 2 is an explanatory view showing a configuration of a main part of an image forming apparatus according to an embodiment of the present invention. It is explanatory drawing which shows the mode of the planarity (fine unevenness) of each reflective surface of a polygon mirror. It is explanatory drawing which shows the mode of the planarity (fine unevenness) of each reflective surface of a polygon mirror. It is explanatory drawing which shows the beam spot shape in one of the reflective positions of a polygon mirror. It is explanatory drawing which shows the beam spot shape in one of the reflective positions of a polygon mirror. It is explanatory drawing which shows the beam spot shape in one of the reflective positions of a polygon mirror. It is explanatory drawing which shows the beam spot shape in one of the reflective positions of a polygon mirror. It is explanatory drawing which shows the beam spot shape in one of the reflective positions of a polygon mirror. It is explanatory drawing which shows the beam spot shape in one of the reflective positions of a polygon mirror. It is explanatory drawing which shows the beam spot shape in one of the reflective positions of a polygon mirror. It is a flowchart which shows operation | movement of the image forming apparatus of one Embodiment of this invention. FIG. 7 is an explanatory view showing the image quality deterioration eliminating operation of the image forming apparatus of the embodiment of the present invention; FIG. 7 is an explanatory view showing the image quality deterioration eliminating operation of the image forming apparatus of the embodiment of the present invention; FIG. 7 is an explanatory view showing the image quality deterioration eliminating operation of the image forming apparatus of the embodiment of the present invention; FIG. 7 is an explanatory view showing the image quality deterioration eliminating operation of the image forming apparatus of the embodiment of the present invention; FIG. 7 is an explanatory view showing the image quality deterioration eliminating operation of the image forming apparatus of the embodiment of the present invention; FIG. 7 is an explanatory view showing the image quality deterioration eliminating operation of the image forming apparatus of the embodiment of the present invention; FIG. 7 is an explanatory view showing the image quality deterioration eliminating operation of the image forming apparatus of the embodiment of the present invention;

Hereinafter, the best mode (embodiment) for carrying out the present invention will be described in detail with reference to the drawings.
Device Configuration of Embodiment
Hereinafter, the configuration of the main part of the image forming apparatus 100 according to the present embodiment will be described in detail based on FIG. The image forming apparatus 100 is controlled by the image forming control program, and the image forming control method is executed. Further, in this embodiment, the general and well-known components of the electrophotographic image forming apparatus 100 are omitted.

  Here, an overall control portion of the image forming apparatus 100 that forms an image of four color images of four colors Y (yellow), M (magenta), C (cyan), and K (black) by light beam irradiation; The light beam irradiation control part is mainly shown. However, it is also possible to use colors other than these YMCKs, and it is also possible to form an image with more or less colors.

  The image forming apparatus 100 shown in FIG. 1 includes an overall control unit 101, a storage unit 103, an operation display unit 105, an image data storage unit 110, an image processing unit 120, a correction value calculation unit 125, and laser driving. It comprises a section 130, a print engine 140, and an optical system 170.

Here, the overall control unit 101 is configured by a CPU or the like in order to control each part of the image forming apparatus 100, and performs various controls regarding image formation.
The storage unit 103 stores various programs such as an image forming program and an adjustment program, and various parameters such as adjustment pattern data. In this embodiment, the storage unit 103 stores irradiation shape information generated from the irradiation shape on the image carrier surface of the light beam reflected at each position on each surface of the polygon mirror. The irradiation shape information includes information on the position and intensity of the secondary irradiation around the target irradiation position on the image carrier surface.

The operation display unit 105 notifies the overall control unit 101 of an operation input signal according to the operation input by the user, and performs various information display according to an instruction from the overall control unit 101.
The image data storage unit 110 stores image data from a scanner, an external device, a print controller, and the like until the start of image formation.

The image processing unit 120 subjects the image data read from the image data storage unit 110 to image processing necessary for image formation based on an instruction from the overall control unit 101.
The correction value calculation unit 125 may change the exposure intensity on the image carrier surface of the pixel of interest on the surface of the image carrier 181 according to the irradiation shape information of the adjacent pixels. In such a case, the image carrier of the pixel of interest is also carried A correction value for correcting the pixel value of the target pixel is calculated so that the exposure intensity on the body surface corresponds to the original pixel value. The calculation of the correction value in the correction value calculation 125 is performed with reference to the irradiation shape information stored in the storage unit 103 and the pixel value of the adjacent pixel. Also, the calculated correction value is supplied to the image processing unit 120, and the image processing unit 120 executes correction of the pixel value of the target pixel.

The laser drive unit 130 controls the drive state so that the light source emits a light beam according to the image data based on the control of the overall control unit 101.
Here, the laser drive unit 130 drives the laser drive for laser drive for Y, the laser drive unit 130M for laser drive for M, the laser drive unit 130C for laser drive for C, and K for laser drive. And a laser driving unit 130K to be performed.

Each of the laser drive units 130Y to 130K includes a phase synchronization signal generation unit 131, a write clock phase generation unit 133, a laser control unit 134, and an LD drive unit 135.
The phase synchronization signal generation unit 131 generates a phase synchronization signal (index signal) based on the light beam detection signal at a predetermined position on the scan start side. The write clock phase generation unit 133 generates a pixel clock for writing (hereinafter, simply referred to as a “pixel clock”) in which the start timing, the phase, and the frequency are corrected with reference to the index signal and the correction data. The laser control unit 134 receives the pixel clock and the image data, and generates a laser control signal for driving laser emission according to the signal value of the image data along the timing of the pixel clock. The LD driving unit 135 receives the laser control signal and generates a laser driving signal for driving the laser diode to emit light.

  The print engine 140 is an image forming unit that forms an image, and a process unit (not shown) that charges, develops, and transfers an image carrier 181 that receives a light beam scan, an optical system 170 that performs exposure, The apparatus is configured to include a transport unit that transports a sheet in the sub-scanning direction. The optical system 170 causes the laser diode to emit light in response to the laser drive signal to generate a light beam, scans the light beam in the main scanning direction, and exposes the surface of the image carrier 181 according to the image data. .

  Here, the optical system 170 includes an optical system 170 Y that scans a light beam for Y, an optical system 170 M that scans a light beam for M, an optical system 170 C that scans a light beam for C, and And an optical system 170K for scanning a beam. Each of the optical systems 170Y to 170K includes a laser diode 171, a polygon mirror 172, a reflection surface detection unit 173, a scanning lens 174, and an index sensor 175.

  The laser diode 171 receives a laser drive signal to generate a light beam. The polygon mirror 172 reflects the light beam so as to scan it in the main scanning direction on the rotating reflecting surface. The reflection surface detection unit 173 generates a reflection surface detection signal for detecting which surface of the polygon mirror 172 reflects the light beam by referring to the surface identification mark attached to the polygon mirror 172 and the like. The scanning lens 174 optically corrects the light beam reflected by the polygon mirror 172 so that it has a constant velocity on the image carrier 181. The index sensor 175 detects the light beam at a predetermined position on the scan start side and generates a light beam detection signal.

The spot diameter of the light beam irradiated from the laser diode 171 to the polygon mirror 172 is smaller than the length in the main scanning direction of each reflecting surface of the polygon mirror 172, and constitutes an underfield optical system.
When the light beam is scanned in the main scanning direction (first scanning direction) on the image carrier 181, a direction (sub scanning direction) perpendicular to the main scanning direction (first scanning direction) of the image carrier 181 Subscanning is performed by rotating in the second scanning direction).

Here, the polygon mirror 172 which scans the light beam in the main scanning direction is a light scanning unit. Further, a drive source (not shown) for rotationally driving the image carrier 181 in the sub scanning direction is a second scanning direction drive unit for relatively moving the image carrier 181 and the light beam in the second scanning direction.
An electrostatic latent image of each color is formed on the image carrier 181 by such main scanning and sub scanning. The electrostatic latent image is developed by a developing unit (not shown) and converted into a toner image. Then, the toner images of the respective colors on the image carrier 181 are superimposed on an intermediate transfer member (not shown) to form a color toner image. Further, this color toner image is transferred to the sheet by a transfer unit (not shown). The color toner image on the sheet is converted to a stable color image by heat and pressure of a fixing unit (not shown).

[Description of image quality deterioration]
Hereinafter, a mechanism that causes deterioration of the image quality due to the fine unevenness on the reflection surface of the polygon mirror 172, which is the problem of the present embodiment, will be described.
FIGS. 2 and 3 show the asperity characteristics of the reflecting surface of the polygon mirror. Here, ± 10 mm of the horizontal axis indicates the position of the reflective surface of the polygon mirror 172 in the main scanning direction. Further, in FIG. 2 and FIG. 3, ± 60 nm of the vertical axis is an error with respect to the reference plane in the direction perpendicular to the reflecting surface at each position in the main scanning direction of the reflecting surface of the polygon mirror 172 Is shown.

C1 in FIG. 2 represents the asperity characteristic of the reflecting surface having ideal smoothness of the polygon mirror 172. Here, fine irregularities are not present on the reflective surface.
On the other hand, C2 in FIG. 3 represents a state in which fine asperities caused by processing errors of the reflection surface of the polygon mirror 172 exist.

  In FIG. 4, the beam spot shape irradiated from the laser diode 171 to the polygon mirror 172 and scanned by the polygon mirror 172 having the above-described ideal reflection surface characteristic C1 (FIG. 2) is exposed to the image carrier 181 It shows. FIG. 5 is a beam spot shape characteristic diagram showing the exposure intensity of the beam spot shape of FIG. 4 described above measured in the main scanning direction and the maximum value normalized to 1. FIG. 6 is an explanatory view schematically showing dots formed on the image carrier 181 by the exposure of FIG. 4 described above.

  In the beam spot shapes shown in FIG. 4 and FIG. 5 above, side lobes (sub-irradiation) occur at a position near 60 μm from the center due to optical diffraction, interference, etc. around the central region. However, this secondary irradiation is at a sufficiently low level, and as shown in FIG. 6, in the image carrier 181, dots are formed only at the central portion.

  In FIG. 7, a laser diode 171 irradiates a polygon mirror 172, which is reflected and scanned in a reflection surface area C2b of the polygon mirror 172 having the reflection surface characteristic C2 (FIG. 3) having the above-described fine asperities. Shows the shape of the beam spot to be exposed. FIG. 8 is a beam spot shape characteristic diagram showing the exposure intensity of the beam spot shape of FIG. 7 described above measured in the main scanning direction and the maximum value normalized to 1. FIG. 9 is an explanatory view schematically showing the dots formed on the image carrier 181 by the exposure of FIG. 7 described above.

  In the beam spot shapes shown in FIG. 7 and FIG. 8 above, side lobes (sub-irradiation) C2b_s1 are generated in the vicinity of 60 μm from the center due to optical diffraction, interference or the like around the central region C2b_m. However, the level of the secondary irradiation C2b_s1 shown in FIGS. 7 to 8 is larger than that in the state of FIGS. 4 and 5 due to the influence of the fine asperities on the reflective surface. As a result, as shown in FIG. 9, in the image carrier 181, a secondary dot C2d_s1 by secondary irradiation C2b_s1 is formed in the vicinity of the target dot C2d_m formed by the central region C2b_m. The secondary dot C2d_s1 is a position 60 μm away from the target dot C2d_m, and occurs at a position 3 dots apart in the case of 1200 dpi.

Due to the formation of such sub-dots, the density of the image is not appropriate. That is, by exposing a portion which is not originally exposed, an image may be generated in a portion where the image should not exist, or the density of the image may be increased more than originally.
Although an example in which the secondary irradiation appears at a position separated by 60 μm on the right side in the main scanning direction is described here, the present invention is not limited thereto, and may occur on the left side in the main scanning direction or a place other than 60 μm. I assume.

Further, in the present embodiment, since the light beam and the polygon mirror 172 are used in the underfield optical system, the beam spot shape, that is, the secondary irradiation at the reflection position even on the same reflection surface of the polygon mirror 172. The situation changes.
FIG. 10 shows a beam spot shape which is reflected / scanned by the reflection area C2a and exposed to the image carrier 181 with respect to the polygon mirror 172 having the reflection surface characteristic C2 (FIG. 3) having the fine irregularities described above, and the reflection area It is explanatory drawing which shows the beam spot shape which is reflected and scanned by C2b, and is exposed to the image carrier 181. FIG.

  As shown in FIG. 10, since the reflection area C2a and the reflection area C2b have different unevenness with respect to the reflecting surface characteristic C2 having the fine unevenness described above, the beam spot shape according to the difference in the reflection area in the main scanning direction Is also changing. In one example shown in FIG. 10, how the beam spot shape changes is individually different. Therefore, it is necessary to measure the beam spot shape at each position of each reflecting surface of the polygon mirror 172.

Various known methods can be used for the measurement of the beam spot shape or the secondary irradiation as described above.
For example, in the case of forming 20000 dots at the maximum in the main scanning direction of the image carrier 181, a slit and a sensor for passing only the first dot at a position corresponding to the exposure position of the first dot of the image carrier 181 And scanning the light beam in the main scanning direction, a time waveform corresponding to FIG. 5 or FIG. 8 is obtained. If the time of this time waveform is converted into distance with reference to the scanning speed of the light beam, the characteristic diagram of FIG. 5 or 8 is obtained. Similarly, beam spot shape characteristics at each position (each dot) corresponding to the exposure surface of the image carrier 181 can be obtained by repeating the measurement of the second dot, the third dot,... 20000st dot.

In addition, by performing the measurement of the beam spot shape characteristic described above also for the other surface of the polygon mirror 172, the beam spot shape of the light beam at each position of each reflection surface of the polygon mirror 172 (light beam irradiation shape) Characteristics are obtained.
The control unit 101 causes the storage unit 103 to store, as irradiation shape information, the position and intensity of the secondary irradiation at each position of each of the reflection surfaces in the beam spot shape characteristic thus obtained. If the position of the secondary irradiation is fixed, the control unit 101 causes the storage unit 103 to store the position of the secondary irradiation and the intensity of the secondary irradiation at each position of each reflective surface as irradiation shape information.

  The position of the secondary irradiation included in the irradiation shape information changes with the image formation density, such as 3 dots for 1,200 dots and 6 dots for 2,400 dpi, so the information of absolute values such as 60 μm is left. It is desirable to calculate how many dots are in accordance with the image formation density at the time of formation.

Further, as the intensity of the secondary irradiation included in the irradiation shape information, for example, it is desirable to convert the exposure intensity of the target dot into a numerical value when normalized to the maximum value 255 of 8 bits. Note that 8-bit (maximum value 255) is an example and may be adjusted to the accuracy of image data.
Operation of Embodiment
The operation of the image forming apparatus 100 of the present embodiment, that is, the processing procedure of the image formation control method or the image formation control program will be described below with reference to the flowchart of FIG. 11 and the explanatory diagrams of FIG.

  First, with the polygon mirror 172 rotated, the control unit 101 refers to the reflection surface detection signal from the reflection surface detection unit 173 and reflects the light beam from the laser diode 171 by the polygon mirror 172 for reflection. The face is identified (step S101 in FIG. 11). It is possible to use a known method, such as detecting a mark by the reflection surface detection unit 173, with a specific mark attached to the polygon mirror 172 in advance.

Here, the control unit 101 specifies a reflective surface to be used at the next exposure timing.
Further, the control unit 101 acquires, from the storage unit 103, irradiation shape information on the position and intensity of the secondary irradiation at each position of each of the reflection surfaces for the specified reflection surface (step S102 in FIG. 11). The control unit 101 transmits the acquired irradiation shape information to the correction value calculation unit 125.

Here, the control unit 101 sets the initial value to 1 and the maximum value to Nmax for the pixel position N of the target pixel. Note that Nmax is the maximum pixel position Nmax that can be exposed, including chart formation, which is the largest or that is used for image formation (step S103 in FIG. 11).
Then, the process proceeds with the pixel at the pixel position specified by N as the pixel of interest. That is, in response to an instruction from the control unit 101, the image processing unit 120 acquires the pixel value of the target pixel and notifies the correction value calculation unit 125 (step S104 in FIG. 11).

  Further, the correction value calculation unit 125 that has received the instruction from the control unit 101 recognizes the position of the secondary irradiation from the irradiation shape information, and specifies the related proximity pixel. Then, the correction value calculation unit 125 acquires the intensity of the secondary irradiation of the identified close pixel from the irradiation shape information, and acquires the pixel value of the close pixel from the image processing unit 120 (step S105 in FIG. 11). ).

  Here, the correction value calculation unit 125 that has received the instruction from the control unit 101 sets the irradiation shape information and the proximity pixel so that the exposure intensity of the pixel of interest on the surface of the image carrier 181 corresponds to the original pixel value. The correction value for correcting the pixel value of the target pixel is calculated with reference to the pixel value, and the correction value is notified to the image processing unit 120 (step S106 in FIG. 11).

The image processing unit 120 notified of the correction value from the correction value calculation unit 125 corrects the pixel value of the pixel of interest using the notified correction value (step S107 in FIG. 11), and It stores in the position (step S108 in FIG. 11).
The calculation of the correction value and the execution of the correction will be described in detail later using specific numerical values.

  The control unit 101 controls the image processing unit 120 and the correction value calculation unit 125 so that the calculation of the correction pixel for the pixel of interest and the correction execution are repeatedly performed from the initial value 1 to the maximum value Nmax of the pixel of interest. The control is performed (steps S109, S110, and S104 to S108 in FIG. 11).

Then, when correction for one main scanning line is completed, the image processing unit 120 sends image data for one main scanning line to the laser drive unit 130 under the control of the control unit 101, and the laser drive unit 130 performs exposure. It starts (step S111 in FIG. 11).
The control unit 101 further specifies the reflection surface to be used at the next exposure timing (steps S113 and S101 in FIG. 11), and acquires the irradiation shape information of the corresponding reflection surface (step S102 in FIG. 11). The respective units are controlled to execute correction value calculation and correction (steps S103 to S110 in FIG. 11), and the laser driving unit 130 starts exposure using the corrected image data for one line (FIG. 11). Control is performed as in step S111). Then, the control unit 101 controls each unit so as to repeat the above-described operation until image formation for one screen is completed (step S112 in FIG. 11).

In the case of a color image forming apparatus using a plurality of colors, the above processing is performed for each color.
[Specific Example of Embodiment]
FIG. 12 schematically shows the state in the case of performing the exposure with the dot 3 and the dot 6 using the intensity of the beam spot.

Here, it is assumed that the dot 6 (Dot_6) is the pixel of interest and the exposure intensity of the pixel of interest is F1 (the waveform of the solid line in FIG. 12).
However, under the influence of the secondary irradiation intensity E1s of the dot 3 (Dot_3, the waveform of the alternate long and short dash line in FIG. 12) which is a close pixel of the pixel of interest 6 (Dot_6), the exposure intensity of the pixel of interest is higher than F1. It becomes large F1 '(= F1 + E1s) (the characteristic of the broken line in FIG. 12).

Therefore, in the correction value calculation 125, a correction value corresponding to the intensity E1s of the secondary irradiation of the adjacent pixel at the pixel position of the target pixel is calculated, and the exposure intensity of the target pixel is corrected to F1 ′ ′ Solid waveform in 13).
As a result, even if the secondary irradiation intensity E1s of the dot 3 (Dot_3, the waveform of the alternate long and short dash line in FIG. 13) which is the close pixel of the target pixel dot 6 (Dot_6) is affected, the exposure intensity of the target pixel is Finally, the original strength F1 (= F1 "+ E1s) is obtained (the characteristic of the broken line in FIG. 13).

FIG. 14 is an explanatory view showing pixel values of image data of eleven pixels in the main scanning direction of Dot_1 to Dot_11 before correction. Here, it is assumed that the influence of the secondary irradiation appears in the third pixel on the left side in the main scanning direction. Further, it is assumed that the influence of the secondary irradiation affects the focused pixel at an intensity of 5% of the pixel value of the adjacent pixel.
As shown in FIG. 15, when the target pixel is Dot_5, -6 of -5% of the pixel value 127 of the adjacent pixel Dot_2 is a correction value. Therefore, the pixel of interest has a pixel value after correction of Dot_5, that is, 255-6 = 249.

Similarly, if the pixel of interest is Dot_6, -6 of -5% of the pixel value 127 of the adjacent pixel Dot_3 is the correction value. Therefore, the pixel of interest has a pixel value after correction of Dot_6, that is, 127-6 = 121.
Similarly, if the target pixel is Dot_7, -13 of -5% of the pixel value 255 of the adjacent pixel Dot_4 is a correction value. Therefore, the target pixel has a corrected pixel value of Dot_7, that is, 127-13 = 114.

Similarly, if the target pixel is Dot_8, -13 of -5% of the pixel value 249 of the adjacent pixel Dot_5 is a correction value. Therefore, the pixel of interest has a pixel value after correction of Dot_8, that is, 255-13 = 242.
The image processing unit 120 that has received the notification of the correction value from the correction value calculation unit 125 performs the above-described correction for each main scanning line before the exposure is performed.

The image data in FIG. 14 and FIG. 15 are aligned in the main scanning direction, and it is possible to use a line memory in the main scanning direction for such processing.
FIG. 16 shows a toner image after transfer onto the image carrier 181 surface or transfer paper obtained when using the polygon mirror 172 having an ideal reflecting surface when exposure is performed with the pixel values shown in FIG. The situation of is schematically shown.

However, as described above, in the case of using a polygon mirror having fine irregularities on the reflecting surface, the final exposure intensity may change due to the influence of the secondary irradiation of the adjacent pixels, and the image quality may be deteriorated. .
Here, it is assumed that fine irregularities of the reflective surface exist only on the second surface (Line_2) of the polygon mirror 172, and the influence of the secondary irradiation as shown in FIG. 15 needs to be corrected. Here, in FIG. 17, when exposure is performed with the corrected pixel value shown in FIG. 15, the toner after transfer to the surface of the image carrier 181 or a transfer sheet in a state not affected by the secondary irradiation It schematically shows the appearance of the image.

Actually, fine irregularities of the reflecting surface exist on the second surface (Line_2) of the polygon mirror 172, and the influence of the secondary irradiation occurs, so that a toner image as shown in FIG. 16 is finally obtained. It will be.
[Other Embodiments (1)]
In the above description, there are cases where the exposure intensity in the image carrier 181 based on the pixel value of the pixel of interest is smaller than the influence of the peripheral characteristics of the irradiation shape of the light beam of the neighboring pixels. In such a case, it is not possible to cope with the correction of the pixel of interest. For example, (a) (b) (c) in Figure 18 corresponds to this state. In such a case, the pixel value of the adjacent pixel is corrected. For example, by slightly reducing the pixel values of dot_6 which is a close pixel for dot_9 and dot_7 which is a close pixel for dot_10 and dot_7 which is a close pixel for dot_10, the influence caused to dot_9 to dot_11 can be reduced. It is possible.

[Other Embodiments (2)]
In the above description, although the influence of the main scanning direction is described as a specific example as the influence of the proximity pixel to the target pixel, the present invention is not limited to this. For example, it is also possible to correct in consideration of the influence of the sub scanning direction as the influence of the proximity pixel on the target pixel.

  In this case, the calculation and correction of the correction value shown in the main scanning direction in FIG. 15 can be coped with by executing in the sub scanning direction as well. For this purpose, processing can be performed by preparing several lines of line memories in the main scanning direction as shown in FIG. For example, assuming that the influence of the secondary irradiation appears at a position separated by three pixels in the sub scanning direction, correction in the sub scanning direction can be realized by preparing a line memory for a total of seven lines.

[Other Embodiments (3)]
Further, in multi-beam image formation in which a plurality of light beams are irradiated to the same surface of the polygon mirror 172, the above-described processing is performed on image data in the main scanning direction using the same surface. can do. In this case, processing is performed by preparing line memories for the number of beams for each color.

[Other Embodiments (4)]
Further, although it is preferable to use the above embodiment for an electrophotographic image forming apparatus using a light beam, various other laser imagers such as a laser imager which exposes a printing paper using a light beam may be used. It is possible to apply each embodiment of the present invention to an image forming apparatus of the present invention, and it is possible to obtain good results.

Moreover, it is possible to apply even when it is a case where other light sources other than a laser diode (LD) are used as a light source.
[Effect Obtained by Embodiment]
(1) In the present embodiment, the irradiation shape information and the pixel value of the adjacent pixel are set such that the exposure intensity of the image carrier 181 of the target pixel corresponds to the original pixel value according to the irradiation shape information of the adjacent pixel. And correct the pixel value of the target pixel of the image data. As a result, even if fine irregularities are present on the reflecting surface of the polygon mirror 172 and even near dot positions that should not be exposed on the surface of the image carrier are exposed, the pixel value of the pixel of interest is corrected. Thus, the same state as when exposed with the original pixel value can be maintained. That is, it is possible to reduce the deterioration of the image quality due to the fine unevenness on the reflection surface of the polygon mirror 172.

  (2) In the above (1), when the exposure intensity in the image carrier 181 of the light beam of the pixel of interest is affected by the peripheral characteristics of the irradiation shape of the light beam of the adjacent pixels, it is included in the irradiation shape information of the adjacent pixels The pixel value of the target pixel of the image data is corrected using the peripheral characteristic. As a result, even if fine irregularities are present on the reflecting surface of the polygon mirror 172 and even near dot positions that should not be exposed on the surface of the image carrier are exposed, the pixel value of the pixel of interest is corrected. Thus, the same state as when exposed with the original pixel value can be maintained. That is, it is possible to reduce the deterioration of the image quality due to the fine unevenness on the reflection surface of the polygon mirror 172.

  (3) In the above (1) to (2), when the exposure intensity of the image carrier 181 based on the pixel value of the pixel of interest is smaller than the influence of the peripheral characteristics of the irradiation shape of the light beam of the adjacent pixels The pixel value of the adjacent pixel is corrected. As a result, even when correction can not be performed by the correction of the pixel value of the pixel of interest, the same state as exposure with the original pixel value can be maintained. That is, it is possible to reduce the deterioration of the image quality due to the fine unevenness on the reflection surface of the polygon mirror 172.

  (4) In the above (1) to (3), since the irradiation shape information includes information on the position and intensity of the secondary irradiation around the target irradiation position on the image carrier 181, the peripheral pixel to the target pixel The influence can be correctly calculated, and it is possible to reduce the deterioration of the image quality due to the fine unevenness on the reflection surface of the polygon mirror 172.

  (5) In the above (1) to (4), by correcting the pixel value for the pixel in the main scanning direction of the image data, it is possible to correctly calculate the influence from peripheral pixels in the exposure using the polygon mirror 172 It is possible to reduce the deterioration of the image quality caused by the fine unevenness on the reflection surface of the polygon mirror 172.

100 image forming apparatus 101 overall control unit 103 storage unit 105 operation display unit 110 image data storage unit 120 image processing unit 125 correction value calculation unit 130 laser drive unit 140 print engine 170 optical system

Claims (6)

An image carrier on which an image is formed by light beam exposure;
A light source generating the light beam which emits light according to image data;
A light scanning unit which scans the light beam in a first scanning direction on the image carrier by a plurality of reflecting surfaces of a rotary polygon mirror rotationally driven by a rotary drive source;
A second scanning direction drive unit for relatively moving the image carrier and the light beam in a second scanning direction orthogonal to the first scanning direction;
A reflecting surface identification unit that identifies each reflecting surface of the rotating polygon mirror;
A storage unit for storing irradiation shape information generated from the irradiation shape on the image carrier surface of the light beam reflected by each position of each surface of the rotary polygon mirror;
With reference to the irradiation shape information and the pixel value of the adjacent pixel, the irradiation shape information of the adjacent pixel makes the exposure intensity of the target pixel on the image carrier surface correspond to the original pixel value. An image processing unit that corrects the pixel value of the target pixel of the image data and supplies the corrected image data to the light source;
Equipped with
The irradiation shape information includes information on the position and intensity of secondary irradiation around the target irradiation position on the image carrier surface.
An image forming apparatus characterized by The image processing unit is included in the irradiation shape information of the adjacent pixel when the exposure intensity of the light beam of the target pixel on the image carrier surface is affected by the peripheral characteristics of the irradiation shape of the light beam of the adjacent pixel. Correcting the pixel value of the target pixel of the image data using the peripheral characteristic;
The image forming apparatus according to claim 1, When the exposure intensity on the surface of the image carrier based on the pixel value of the target pixel is smaller than the influence of the peripheral characteristics of the irradiation shape of the light beam of the near pixel, the image processing unit Correct the value,
The image forming apparatus according to any one of claims 1-2, The image processing unit corrects pixel values of pixels in the main scanning direction of the image data.
The image forming apparatus according to any one of claims 1 to 3, characterized in that: An image carrier on which an image is formed by light beam exposure;
A light source generating the light beam which emits light according to image data;
A light scanning unit which scans the light beam in a first scanning direction on the image carrier by a plurality of reflecting surfaces of a rotary polygon mirror rotationally driven by a rotary drive source;
A second scanning direction drive unit for relatively moving the image carrier and the light beam in a second scanning direction orthogonal to the first scanning direction;
A reflecting surface identification unit that identifies each reflecting surface of the rotating polygon mirror;
The position of the secondary irradiation around the target irradiation position on the image carrier surface, generated from the irradiation shape on the image carrier surface of the light beam reflected at each position on each surface of the rotary polygon mirror, and A storage unit that stores irradiation shape information including intensity information;
An image processing unit that corrects a pixel value of a target pixel of the image data and supplies the corrected image data to the light source;
An image forming control method for controlling an image forming of an image forming apparatus comprising
With reference to the irradiation shape information and the pixel value of the adjacent pixel, the irradiation shape information of the adjacent pixel makes the exposure intensity of the target pixel on the image carrier surface correspond to the original pixel value. Correcting the pixel value of the target pixel of the image data;
Images forming control how to characterized in that. An image carrier on which an image is formed by light beam exposure;
A light source generating the light beam which emits light according to image data;
A light scanning unit which scans the light beam in a first scanning direction on the image carrier by a plurality of reflecting surfaces of a rotary polygon mirror rotationally driven by a rotary drive source;
A second scanning direction drive unit for relatively moving the image carrier and the light beam in a second scanning direction orthogonal to the first scanning direction;
A reflecting surface identification unit that identifies each reflecting surface of the rotating polygon mirror;
The position of the secondary irradiation around the target irradiation position on the image carrier surface, generated from the irradiation shape on the image carrier surface of the light beam reflected at each position on each surface of the rotary polygon mirror, and A storage unit that stores irradiation shape information including intensity information ;
An image processing unit that corrects a pixel value of a target pixel of the image data and supplies the corrected image data to the light source;
An image forming control program that causes an image forming apparatus having the
With reference to the irradiation shape information and the pixel value of the adjacent pixel, the irradiation shape information of the adjacent pixel makes the exposure intensity of the target pixel on the image carrier surface correspond to the original pixel value. An image forming control program that causes an image forming apparatus to function so as to correct the pixel value of the target pixel of the image data.