JP2017087687A - Optical writing device and image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus which can suppress reduction in image quality due to inclination of an LPH (LED Print Head) in the zigzag arrangement with respect to the main-scanning direction at a low cost.SOLUTION: In an optical writing device in which light-emitting elements are arranged in the zigzag shape, light-emitting element arrays on both ends in the short side direction of the zigzag arrangement are end arrays, and another light-emitting element array is a center array. When the overlapping between exposure regions on a photoreceptor of the farthest light-emitting elements from the center in the short side direction becomes larger as an inclination angle with respect to the main-scanning direction of the longitudinal direction of the zigzag arrangement becomes larger with the axial direction of the photoreceptor drum to which optical writing is performed by the optical writing device as the main-scanning direction, the light emission amount of the light-emitting elements is reduced and the light emission amount of the other light-emitting elements is increased, thereby periodical moire generated due to the inclination when all the light-emitting elements are tuned on can be reduced.SELECTED DRAWING: Figure 13

Description

  The present invention relates to an optical writing apparatus and an image forming apparatus, and more particularly to a technique for reducing deterioration in image quality due to a mounting error of a print head in which light emitting elements are arranged in a staggered manner at low cost.

  In an electrophotographic image forming apparatus, an electrostatic latent image is formed by exposing an outer peripheral surface of a uniformly charged photosensitive drum by an optical writing device. In particular, an LED (Light Emitting Diode) array type optical writing device (LPH: LED Print Head) performs exposure for each line by individually turning on or off a large number of LEDs arranged in a line. In LPH, in order to ensure a sufficient exposure amount, as illustrated in FIG. 16, one pixel is formed by a square lattice array in which a plurality of LEDs having the same position in the longitudinal direction of the line are connected in the sub-scanning direction. A multiple exposure method has been developed for exposing the above.

  However, the longitudinal direction of the square lattice arrangement in the multi-exposure LPH is inclined with respect to the main scanning direction (axial direction of the photosensitive drum) due to problems in the manufacturing process such as displacement of the LPH attachment position. In this case, the positions of the plurality of LEDs that are supposed to expose the same pixel on the outer peripheral surface of the photosensitive drum by shifting the position in the main scanning direction are shifted from each other in the main scanning direction.

Then, since the exposure areas of these LEDs are shifted from each other in the main scanning direction, one pixel spreads in the main scanning direction, and further, pixels adjacent to each other in the main scanning direction overlap each other, resulting in a blurred image. Decreases.
To deal with such a problem, for example, among the LED arrays arranged in the longitudinal direction in the square lattice array, the LED array located in the center in the short direction increases the light emission amount, and the other LED arrays decrease the light emission amount. The technique which performs is proposed (for example, refer patent document 1). By reducing the exposure amount at the location where the pixels spread in this way, it is possible to reduce the blurring of the image due to the inclination of the LPH attachment position.

JP 2004-330472 A

  The arrangement of LEDs in the LPH includes not only a square lattice but also a staggered arrangement. In the staggered arrangement, a plurality of LED rows extending in the longitudinal direction of the LPH are arranged in the short direction, and the LED rows are arranged at positions slightly shifted in the longitudinal direction. In this way, these LEDs are separated in the short direction so that the light emitting areas of adjacent LEDs do not interfere with each other at a short pitch in the longitudinal direction. Therefore, since the adjacent exposure regions on the outer peripheral surface of the photosensitive drum are arranged at high density at equal intervals so as to partially overlap each other, high resolution can be realized.

When such a staggered arrangement of LPHs is attached to be inclined with respect to the main scanning direction, the spacing between the LEDs in the main scanning direction becomes coarse and dense in accordance with the inclination angle. When the exposure operation is performed in such a state where the density is high and low, pixels are blurred in the square lattice arrangement LPH, and striped moire is generated according to the density cycle, so that the print quality is remarkably deteriorated. .
However, by applying the above-described conventional technique to the LPH in a staggered arrangement, among the LED arrays arranged in the longitudinal direction in the square lattice array, the LED array located in the center in the short direction increases the light emission amount, Even if the amount of light emitted from the LED array is reduced, the amount of light is not corrected according to the density of the LED intervals in the main scanning direction (in other words, the density of the pixels on the printed image), but the image quality is further deteriorated. .

Further, if a rotation mechanism for precisely rotating the LPH is provided, it is possible to eliminate the deterioration of the image quality by correcting the tilt angle with respect to the main scanning direction, but the cost for adding the rotation mechanism occurs.
The present invention has been made in view of the above-described problems, and can reduce image quality degradation caused by tilting the staggered LPH with respect to the main scanning direction at low cost. An object is to provide an optical writing device and an image forming apparatus.

  In order to achieve the above object, the image forming apparatus according to the present invention includes three or more light emitting element rows in which a plurality of light emitting elements are arranged at an equal pitch in the first direction, and the staggered light emitting elements between adjacent light emitting element rows. An optical writing device that is arranged in a second direction that intersects the first direction and performs light writing on the photosensitive member by controlling light emission of the light emitting element arrays, wherein the first direction Detecting means for detecting an inclination state with respect to the main scanning direction, and when the first direction is inclined with respect to the main scanning direction, the first direction is inclined with respect to the main scanning direction. And a light emission amount determining means for determining a light emission amount different from the light emission amount for each light emitting element by a light amount corresponding to the tilted state as a light emission amount for each light emitting element.

In this way, it is possible to reduce image quality degradation caused by the staggered arrangement of LPHs being inclined with respect to the main scanning direction at low cost.
In this case, the light emission amount determining means may determine the light emission amount for each light emitting element, depending on which of the light emitting element columns the light emitting element belongs to.
Further, the light emission amount determining means may determine the light emission amount of the light emitting element according to a distance from a center in a short direction of the staggered arrangement to the light emitting element row.

  Further, the inclined state is an inclination angle of the first direction with respect to the main scanning direction, and as the inclination angle of the longitudinal direction with respect to the main scanning direction increases, the light emitting element farthest from the center in the lateral direction. When the overlap between the exposure areas on the photoconductor increases, the light emission amount of the light emitting element is decreased, the light emission amount of the other light emitting elements is increased, and the inclination angle in the longitudinal direction with respect to the main scanning direction is increased. If the overlap between the exposed areas on the photoreceptor due to the light emitting element farthest from the center in the short direction becomes smaller as the value becomes larger, the light emitting amount of the light emitting element is increased and the light emitting amount of the other light emitting elements is increased. Less is preferable.

Further, when there is a light emitting element group in which a predetermined number or more of light emitting elements to be emitted according to the optical writing data are continuous in the main scanning direction, the light emission amount determining means emits light from a light emitting element that does not belong to the light emitting element group. Prohibiting means for prohibiting the correction of the amount may be provided.
An image forming apparatus according to the present invention has a light emitting element array in which light emitting elements are arranged in a zigzag pattern, and three or more light emitting element columns in which the light emitting elements are arranged in a longitudinal direction in the zigzag array. A color image forming apparatus for each color having an optical writing device for performing optical writing on the photosensitive member using the light emitting element array, wherein the zigzag for the main scanning direction of the photosensitive member is provided for each optical writing device of each color. Detecting means for detecting the state of inclination in the longitudinal direction of the array, and when the longitudinal direction is inclined with respect to the main scanning direction for each color optical writing device, And a light emission amount determining means for determining the light emission amount for each light emitting element by correcting the light emission amount for each of the light emitting elements when the longitudinal direction is not inclined according to the inclined state. And

  In this case, for each optical writing device of each color, optical writing is performed so that the electrostatic latent image by the optical writing stands upright in the main scanning direction according to the inclination angle in the longitudinal direction with respect to the main scanning direction. You may provide the optical writing data correction | amendment means which correct | amends data.

1 is a diagram illustrating a main configuration of an image forming apparatus according to an embodiment of the present invention. It is sectional drawing which shows the main structures of LPH100 unit. 2 is a plan view schematically showing a staggered arrangement of OLEDs 201 on an OLED panel 200. FIG. It is a schematic plan view of the OLED panel 200, and a sectional view taken along line BB ′ and a sectional view taken along line CC ′ are also shown. 3 is a block diagram showing a main functional configuration of the LPH unit 100. FIG. FIG. 3 is a circuit diagram showing main configurations of a pair of selection circuits 501 and a light emitting block 502. 2 is a block diagram illustrating an interface between a controller unit 101 and an LPH unit 100. FIG. 5 is a flowchart showing processing for reducing periodic moire caused by the inclination of the LPH unit 100. It is a figure which illustrates the toner patch for detecting inclination-angle (theta). It is a figure which illustrates a correction ratio table. It is a figure which shows the characteristic dimension of the LPH unit 100 for determining the correction ratio c. It is a figure which compares the exposure amount distribution of the LPH unit 100 which is not inclined with respect to the main scanning direction, and the exposure amount distribution of the LPH unit 100 which is inclined with respect to the main scanning direction, taking a solid image as an example. It is a figure which shows exposure amount distribution after light quantity correction | amendment in the LPH unit 100 inclined with respect to the main scanning direction for a solid image as an example. It is a block diagram explaining the structure of the controller part 101 which concerns on the modification of this invention. It is a flowchart which shows the light quantity correction process which concerns on the modification of this invention. It is a figure which illustrates LPH which arranged LED in the square lattice shape.

Embodiments of an optical writing device and an image forming apparatus according to the present invention will be described below with reference to the drawings.
[1] Configuration of Image Forming Apparatus First, the configuration of the image forming apparatus according to the present invention will be described.
As shown in FIG. 1, the image forming apparatus 1 is a so-called tandem color printer. The image forming units 110Y, 110M, 110C, and 110K included in the image forming apparatus 1 receive toner images of respective colors Y (yellow), M (magenta), C (cyan), and K (black) under the control of the control unit 102. Form.

In the image forming unit 110Y, the charging device 112 uniformly charges the outer peripheral surface of the photosensitive drum 111. An LPH (LED Print Head) unit 100 performs optical writing on the outer peripheral surface of the photosensitive drum 111 to form an electrostatic latent image.
The developing device 113 supplies toner to the outer peripheral surface of the photosensitive drum 111 and develops (visualizes) the electrostatic latent image to form a Y-color toner image. The primary transfer roller 114 electrostatically transfers (primary transfer) the toner image from the outer peripheral surface of the photosensitive drum 111 to the outer peripheral surface of the intermediate transfer belt 103. The toner remaining on the outer peripheral surface of the photosensitive drum 111 after the primary transfer is removed by the cleaner 115.

  The intermediate transfer belt 103 is stretched around the secondary transfer roller pair 104 and the driven roller 105, and rotates in the direction of arrow A while carrying the toner image. Similarly to the case where the image forming unit 110Y forms a Y color toner image, the MCK color toner images formed by the image forming units 110M, 110C, and 110K are synchronized with the rotation of the intermediate transfer belt 103, and The toner image is primarily transferred onto the toner carrying surface of the intermediate transfer belt 103 so as to overlap with the color toner image to form a color toner image.

  As the intermediate transfer belt 103 conveys the color toner image to the secondary transfer roller pair 104, the recording sheet S supplied from the paper feed cassette 120 is also conveyed to the secondary transfer roller pair 104. The secondary transfer roller pair 104 electrostatically transfers (secondary transfer) the toner image on the intermediate transfer belt 103 onto the recording sheet S. The recording sheet S to which the toner image has been transferred is thermally fixed on the toner image by the fixing device 106 and then discharged onto the discharge tray 108 by the discharge roller 107.

The control unit 102 has a built-in controller unit 101, and executes image processing and control of the LPH unit 100 as described later. In addition, an operation panel (not shown) is connected to the control unit 102 and presents information to the user of the image forming apparatus 1 or receives an instruction input from the user.
An IDC sensor (Image Density Control Sensor) 130 detects toner patches carried on both ends of the intermediate transfer belt 103. In particular, the inclination angle of the LPH unit 100 with respect to the main scanning direction is estimated by detecting the upstream end (ON edge) of the toner batch in the conveyance direction of the intermediate transfer belt. In this specification, the main scanning direction refers to the rotation axis direction of the photosensitive drum 111.

[2] Configuration of LPH Unit 100 Next, the configuration of the LPH unit 100 will be described.
As illustrated in FIG. 2, the LPH unit 100 includes an OLED panel 200 and a rod lens array 202 accommodated in a holder 203, and the OLED 201 is mounted on the OLED panel 200. The light beam L emitted from the OLED 201 is condensed on the outer peripheral surface of the photosensitive drum 111 by the rod lens array 202. The rod lens array 202 is an optical element in which a large number of rod lenses are integrated. An SLA (SLA: Selfoc Lens Array; Selfoc is a registered trademark of Nippon Sheet Glass Co., Ltd.) may be used, or an MLA (Micro Lens Array). ) May be used. Note that cables and the like for connecting to necessary portions of the image forming apparatus 1 are not shown.

  As shown in FIG. 3, the OLEDs 201 are arranged in a zigzag pattern with the four OLEDs 201 as a set on the OLED panel 200. In this embodiment, four OLEDs 201 are set as one set, and 3,750 sets of OLEDs 201 are arranged in the main scanning direction. In the present embodiment, a set of four OLEDs 201 are all arranged in a line in a direction inclined with respect to the sub-scanning direction. Needless to say, the number of OLEDs 201 constituting one set is not limited to four, but three or less or five or more may be one set.

FIG. 4 is a schematic plan view of the OLED panel 200, and a cross-sectional view taken along the line BB ′ and a cross-sectional view taken along the line CC ′ are also shown. Moreover, the state which removed the sealing plate 501 mentioned later is shown in the schematic plan view part.
As shown in FIG. 4, the OLED panel 200 includes a TFT substrate 400, a sealing plate 401, a driver IC (Integrated Circuit) 402, and the like. On the TFT substrate 400, 15,000 OLEDs 201 are arranged in a staggered pattern along the main scanning direction. These OLEDs 201 have a focusing point of 21.2 μm pitch (1200 dpi) on the outer peripheral surface of the photosensitive drum 111.

Further, the substrate surface of the TFT substrate 400 on which the OLED 201 is disposed is sealed in a state where a sealing plate 401 is attached with a spacer frame 403 sandwiched so as not to be exposed to the outside air, and dry nitrogen or the like is sealed. Has been.
A driver IC 402 is mounted outside the sealing region of the TFT substrate 400. The control unit 102 inputs a digital luminance signal (video data) to the driver IC 402 via a card electric wire (FFC: Flexible Flat Card) 410. The controller 102 generates a digital luminance signal in the controller unit 101. The card electric wire 410 is deformed according to the inclination angle of the OLED panel 200 with respect to the main scanning direction, and the connection state between the control unit 102 and the driver IC 402 is maintained.

The driver IC 402 converts the digital luminance signal into an analog luminance signal and inputs it to the driving circuit for each OLED 201. The drive circuit supplies a drive current corresponding to the analog luminance signal to the OLED 201. The analog luminance signal may be a current signal or a voltage signal.
As shown in FIG. 5, in the TFT substrate 400, 15,000 OLEDs 201 are grouped into 150 light emitting blocks 502 in units of 100. Accordingly, each light emitting block 502 includes 25 sets of four OLEDs 201. The driver IC 402 includes 150 DACs (Digital to Analogue Converter) 500, which correspond to the light-emitting blocks 502 on a one-to-one basis, and supply analog luminance signals.

  When the driver IC 402 receives a digital luminance signal from the controller unit 101 built in the control unit 102, the analog luminance signal corresponding to the digital luminance signal is distributed to each DAC 500 by 100 pixels every scanning period. A selection circuit 501 is disposed on the circuit from the DAC 500 toward the light emission block 502. The DAC 500 sequentially inputs analog luminance signals to the light emitting blocks 502 selected by the selection circuit 501 among the 100 light emitting blocks 502 under its control by so-called rolling driving.

As described above, one DAC is time-shared by 100 OLEDs 201, and the light emission level of the OLED 201 is changed by changing the level of the analog luminance signal.
As shown in FIG. 6, the light emitting block 502 includes 100 light emitting pixel circuits, and each light emitting pixel circuit has a capacitor 621, a driving TFT 622, and an OLED 201. The selection circuit 501 includes a shift register 611 and 100 selection TFTs 612.

The shift register 611 is connected to the gate terminals of the 100 selection TFTs 612, and sequentially turns on the selection TFTs 612. The source terminal of the selection TFT 612 is connected to the DAC 500 via the write wiring 630, and the drain terminal is connected to the first terminal of the capacitor 621 and the gate terminal of the driving TFT 622.
With the shift register 611 turning on the selection TFT 612, the analog luminance signal from the DAC 500 is input to the first terminal of the capacitor 621, and a voltage corresponding to the analog luminance signal is held. The first terminal of the capacitor 621 is also connected to the gate terminal of the driving TFT 622, and the second terminal of the capacitor 621 is connected to the source terminal of the driving TFT 622 and the power supply wiring 631.

The anode terminal of the OLED 201 is connected to the drain terminal of the driving TFT 622 to form a series circuit. The cathode terminal of the OLED 201 is connected to the ground wiring 632. The power supply wiring 631 is connected to the constant voltage source Vpwr received from the power supply unit 612, and the ground wiring 632 is connected to the ground terminal GND.
The constant voltage source Vpwr is a supply source of the drive current supplied to the OLED 201, and the drive TFT 622 supplies a drain current corresponding to the holding voltage of the capacitor 621 to the OLED 201 as a drive current. For example, when a signal corresponding to Hi is written in the capacitor 621, the driving TFT 622 is turned on, and the OLED 201 emits light with a light amount corresponding to the driving current.

Therefore, the light emission amount of the OLED 201 can be controlled by changing the analog luminance signal. When a signal corresponding to Low is written to the capacitor 621, the driving TFT 622 is turned off and the OLED 201 does not emit light.
Note that a reset circuit 640 is connected to the DAC 500. When the reset circuit 640 is turned on, the wiring from the DAC 500 to the selection TFT 612 is reset to a predetermined voltage. This predetermined voltage may be a constant voltage Vdd or a ground voltage GND. The reset circuit 640 may be built in the driver IC 402, or the polarity of the current DAC may be changed between reset and write.

Note that although the case where the driving TFT 622 is a p-channel is described as an example in this embodiment mode, it is needless to say that an n-channel driving TFT 622 may be used.
[3] Interface between Controller Unit 101 and LPH Unit 100 Next, an interface between the controller unit 101 and the LPH unit 100 will be described.

FIG. 7 is a block diagram illustrating an interface between the controller unit 101 and the LPH unit 100. In FIG. 7, the LPH unit 100Y is particularly described in detail, and the LPH units 100M, 100C, and 100K have the same configuration as the LPH unit 100Y, and thus are not described.
(3-1) Controller unit 101
As shown in FIG. 7, the controller unit 101 includes an LPH control unit 700, an image processing unit 710, a memory unit 711, a power supply unit 712, and a backup EEPROM (Electric Erasable Programmable Read Only Memory) 713. The LPH control unit 700 may be a so-called ASIC (Application Specific Integrated Circuit).

  When executing a print job, the controller unit 101 performs PDL (Page Description Language) language analysis and rasterization processing in the image processing unit 710 to generate, for example, 1200 dpi binary video data. The memory unit 711 is, for example, a DDR SDRAM (Double-Data-Rate Synchronous Dynamic Random Access Memory), and stores data necessary for the operation of the LPH control unit 700, particularly video data.

  The LPH control unit 700 receives video data from the image processing unit 710 by the video data receiver unit 701. The inclination angle acquisition unit 703 acquires the inclination angle with respect to the main scanning direction for each of the LPH units 100Y, 100M, 100C, and 100K. The rotation processing unit 702 rotates the video data of each color of YMCK with a rotation angle obtained by inverting the sign of the inclination angle acquired by the inclination angle acquisition unit 703.

  The LPH interface unit 705 causes the LVDS (Low Voltage Differential Signaling) unit 706 to transmit video data of each color of YMCK to the LPH units 100Y, 100M, 100C, and 100K. The LVDS unit 706 transmits video data at a high speed through a clock-synchronized data bus of about 80 MHz. The LVDS unit 706 is connected to each YHCK color LPH unit 100 by an 8-bit signal line, and transmits a clock signal (LVDS_CLK), a strobe signal (LVDS_STB), and a 6-bit data signal (LVDS_Data [5: 0]). To do.

A TG (Timing Generator) unit 707 inputs a horizontal synchronization signal (HSYNC) representing the synchronization timing of main scanning to the LPH unit 100 for each color of YMCK.
The light emission amount correction unit 704 calculates a DAC setting value for causing each OLED 201 to emit light with a target light amount for each OLED column arranged in the longitudinal direction in accordance with the inclination angle acquired by the inclination angle acquisition unit 703, and sends it to the driver IC 402. Send. In this case, the light emission amount correction unit 704 performs serial communication with the driver IC 402 and the EEPROM 722 mounted in the backup EEPROM 713 and the LPH unit 100 for each color of YMCK. For example, an I ² C (Inter-Integrated Circuit) system can be used as the serial communication system.

The backup EEPROM 713 is a non-volatile memory for backing up data written to the EEPROM 722 by serial communication. The power supply unit 712 has a built-in DC / DC converter or a low voltage unit, and supplies low voltage power to the LPH unit 100 for each color of YMCK.
(3-2) LPH units 100Y, 100M, 100C and 100K
Next, the LPH units 100Y, 100M, 100C, and 100K will be described. Since the LPH units 100Y, 100M, 100C, and 100K all have the same configuration, only the LPH unit 100Y will be described below.

The LPH unit 100Y includes a selection circuit 501, a light emission block 502, and an EEPROM 722 in addition to the driver IC 402 described above.
The driver IC 402 incorporates a light emission amount setting RAM (Random Access Memory) 721 and operates by receiving power from the power supply unit 712. The light emission amount setting RAM 721 is a volatile memory that receives and stores the DAC setting value of each OLED 201 from the light emission amount correction unit 704. When the driver IC 402 receives one line of video data from the LPH control unit 700, the driver IC 402 refers to the DAC setting value stored in the light emission amount setting RAM 721 and synchronizes the DAC setting value corresponding to the video data with the horizontal synchronization signal. And output.

  The driver IC 402 generates a timing signal by dividing and counting the clock signal (LVDS_CLK) output by the LVDS unit 706 of the controller unit 101. For this reason, since it is not necessary to provide an oscillation circuit in the driver IC 402, the circuit scale of the driver IC 402 can be reduced. Therefore, it is possible to reduce the cost and improve the chip size by improving the yield at the time of manufacturing the driver IC 402.

Upon receiving the DAC signal and timing signal from the driver IC 402, the selection circuit 501 and the subordinate light emitting block 502 cause the OLED 201 to emit light at the light amount corresponding to the DAC signal and the light emission timing corresponding to the timing signal.
[4] Correction of Image Quality Degradation Due to Inclination of LPH Unit 100 Next, processing for correcting image quality deterioration due to the inclination of the LPH unit 100 will be described.

As shown in FIG. 8, when the control unit 102 reaches a predetermined timing at which the inclination angles θy, θm, θc, and θk of the LPH units 100Y, 100M, 100C, and 100K should be reached (S801: YES), the LPH unit The inclination angles θy, θm, θc, and θk of 100Y, 100M, 100C, and 100K are detected (S802).
The predetermined timing may be when the image forming apparatus 1 is turned on or during image stabilization processing. In addition, for example, when the inclination angle of the LPH units 100Y, 100M, 100C, and 100K is likely to fluctuate, such as when the image forming apparatus 1 is installed in a place where mechanical vibration is intense, the inclination angle every time a print job is received. θy, θm, θc, and θk may be detected.

  When detecting the inclination angles θy, θm, θc, and θk, as shown in FIG. 9, the control unit 102 forms rectangular toner patches 901 and 902 for each color of YMCK at both ends of the intermediate transfer belt 103. The IDC sensor 130 is used to detect the ON edges of the toner patches 901 and 902. The inclination angles θy, θm, θc, and θk of the LPH units 100Y, 100M, 100C, and 100K can be obtained from the time difference (T1−T2) between the ON edge detection timings T1 and T2 between the both ends.

  For example, the following formula (1) may be used.

ここで、ｖは中間転写ベルト１０３の走行速度であり、Ｌはトナーパッチ９０１、９０２の間隔である。
制御部１０２は、印刷ジョブを受け付けると（Ｓ８０３：ＹＥＳ）、傾斜角θｙ、θｍ、θｃ及びθｋを確認して、ＹＭＣＫ各色のうち傾斜角θが０でない色がある場合には（Ｓ８０４：ＹＥＳ）、回転処理部７０２にて当該色のビデオデータを−θ度だけ回転させる（Ｓ８０５）。

Here, v is the traveling speed of the intermediate transfer belt 103, and L is the interval between the toner patches 901 and 902.
When the control unit 102 receives the print job (S803: YES), the control unit 102 checks the inclination angles θy, θm, θc, and θk, and if there is a color whose inclination angle θ is not 0 among the YMCK colors (S804: YES). ), The rotation processing unit 702 rotates the video data of the color by −θ degrees (S805).

  Since the color with the inclination angle θ of 0 is originally erect, if only the video data of the color with the inclination angle θ not 0 is rotated by −θ degrees, the video data can be erect with all colors. it can. Therefore, it is possible to prevent color misregistration due to the difference in the inclination angle θ between the LPH units 100Y, 100M, 100C, and 100K. The light amount correction is not necessary for the LPH unit having the inclination angle θ of 0, and if it is performed only for the LPH unit having the inclination angle θ of 0, the periodic moire can be reduced for the LPH unit.

When the video data is rotated, the gradation value at each coordinate after rotation is obtained from the original video data. For this reason, assuming that each lattice point (a point where each coordinate value is an integer) corresponds to one pixel, first, from each coordinate (x _t , y _t ) after rotation, the coordinate (x, y) is obtained by equation (2).

式（２）を用いて算出された座標（ｘ，ｙ）が整数値である場合には、その座標における階調値を回転後の座標（ｘ_t，ｙ_t）の画素の階調値とする。また、算出された座標（ｘ，ｙ）が整数値でない場合には、ビデオデータにおける直近の４つの整数座標（ｘ₁，ｙ₁）、（ｘ₁，ｙ₂）、（ｘ₂，ｙ₁）及び（ｘ₂，ｙ₂）の各画素の階調値Ｇ₁₁、Ｇ₁₂、Ｇ₂₁及びＧ₂₂から当該座標（ｘ，ｙ）における階調値Ｇを算出する。

If coordinates calculated using equation (2) (x, y) is an integer value, the tone value of the pixel of coordinates after rotation gradation value at the coordinates (x _t, y _t) To do. Further, when the calculated coordinates (x, y) are not integer values, the four most recent integer coordinates (x ₁ , y ₁ ), (x ₁ , y ₂ ), (x ₂ , y ₁ ) in the video data. ) And (x ₂ , y ₂ ), the gradation value G at the coordinates (x, y) is calculated from the gradation values G ₁₁ , G ₁₂ , G ₂₁ and G ₂₂ of each pixel.

ここで、

here,

である。上記の処理をすべての座標（ｘ_t，ｙ_t）について実行すれば、回転後のビデオデータを生成することができる。
次に、制御部１０２は、発光量補正部７９４にて、すべてのＯＬＥＤ２０１について個別にステップＳ８０６からＳ８０８の処理を実行する。すなわち、ＯＬＥＤ２０１毎に、千鳥状配列における短手方向の位置を特定する（Ｓ８０６）。図３においては、当該ＯＬＥＤ２０１が第１列から第４列までの何れの列に属しているかを特定する。

It is. If the above processing is executed for all coordinates (x _t , y _t ), the video data after rotation can be generated.
Next, the control unit 102 causes the light emission amount correction unit 794 to execute the processing of steps S806 to S808 individually for all the OLEDs 201. That is, the position in the short direction in the staggered arrangement is specified for each OLED 201 (S806). In FIG. 3, it is specified which column from the first column to the fourth column the OLED 201 belongs to.

  Next, referring to the correction ratio table, the correction ratio c is determined according to the position of the OLED 201 in the short direction and the inclination angle θ (S807). As illustrated in FIG. 10, the correction ratio table stores a correction ratio c for each combination of the tilt angle θ and the position of the OLED 201 in the short direction. 10, the center column refers to the second column and the third column in FIG. 3, and the end column refers to the first column and the fourth column.

For example, when the inclination angle θ is −1 degree and the OLED 201 belongs to the third column, the correction ratio c is −5.4%. When the inclination angle θ is +0.5 degrees and the OLED 201 belongs to the fourth column, the correction ratio c is −2.6%.
The correction ratio c is determined based on LPH design values such as the distances x and y of the OLEDs 201 in the longitudinal direction and the lateral direction, the number of columns of the OLEDs 201 in the lateral direction, and the outer diameter (emission diameter) r of the light emitting region of the OLED 201. (FIG. 11).

  For example, as the interval x between the OLEDs 201 in the longitudinal direction is wider, the end rows are less likely to approach each other when the LPH is inclined in a direction in which the inclination angle θ is positive, while the center rows are more likely to be separated. Accordingly, as the interval x between the OLEDs 201 in the longitudinal direction is wider, the absolute value of the correction ratio c when the LPH is inclined in the direction in which the inclination angle θ is positive is smaller in the end row and larger in the center row.

  Further, as the emission diameter r of the OLED 201 is smaller, the end rows are less likely to approach each other when the LPH is tilted in a direction in which the tilt angle θ is positive, while the center rows are more easily separated. Therefore, the smaller the emission diameter r of the OLED 201, the smaller the absolute value of the correction ratio c when the LPH is inclined in the direction in which the inclination angle θ is positive, and the absolute value of the correction ratio c is larger in the center row.

  In consideration of such characteristics, instead of the table illustrated in FIG. 10, the correction ratio c is a combination of the interval x and y of the OLED 201, the number n of columns of the OLED 201, the emission diameter r of the OLED 201, and the inclination angle θ. A table in which the correction ratio c is associated with may be used. Further, the correction ratio c may be calculated from the intervals x and y of the OLED 201, the number n of rows of the OLED 201, the emission diameter r and the inclination angle θ of the OLED 201.

  The driver IC 402 calculates the target light amount L for each OLED 201 from the target light amount L ′ before correction using the following equation (5).

補正前の目標光量Ｌ´はビデオデータから生成される。
すべてのＯＬＥＤ２０１について目標光量Ｌを求めたら、画像形成装置１は印刷ジョブを実行する（Ｓ８０９）。なお、ＬＰＨユニット１００Ｙ、１００Ｍ、１００Ｃ及び１００Ｋの何れについても傾斜角θが０である場合には（Ｓ８０４：ＮＯ）、目標光量を補正せずに（Ｓ８１０）、印刷ジョブを実行する（Ｓ８０９）。印刷ジョブの実行を終えた後や印刷ジョブを受け付けていない場合には（Ｓ８０３：ＮＯ）、ステップＳ８０１に進んで上記の処理を繰り返す。

The target light amount L ′ before correction is generated from the video data.
When the target light amount L is obtained for all the OLEDs 201, the image forming apparatus 1 executes a print job (S809). When the inclination angle θ is 0 for any of the LPH units 100Y, 100M, 100C, and 100K (S804: NO), the print job is executed without correcting the target light amount (S810) (S809). . After the execution of the print job is completed or when the print job is not received (S803: NO), the process proceeds to step S801 and the above processing is repeated.

[5] Elimination Example of Periodic Moire Next, the exposure amount generated when the LPH units 100Y, 100M, 100C and 100K (hereinafter collectively referred to as “LPH unit 100”) are inclined with respect to the main scanning direction. An example of eliminating periodic moire is shown.
FIG. 12 compares the exposure amount distribution of the LPH unit 100 that is not inclined with respect to the main scanning direction and the exposure amount distribution of the LPH unit 100 that is inclined with respect to the main scanning direction, taking a solid image as an example. FIG. As illustrated in FIG. 12, when the LPH unit 100 is not inclined with respect to the main scanning direction, the exposure position interval for each OLED 201 is equal in the main scanning direction, so that exposure in the main scanning direction is performed. The quantity distribution becomes uniform and no periodic moire occurs.

  When the LPH unit 100 is inclined with respect to the main scanning direction, the interval between the exposure positions for each OLED 201 is not equal in the main scanning direction. As illustrated in FIG. 12, when the sign of the inclination angle θ is positive, the interval between the OLEDs 201 belonging to the end column is narrowed, while the interval between the OLEDs 201 belonging to the center column is belonging to the center column. The interval between the OLED 201 and the OLED 201 belonging to the end row is widened.

In addition, when the sign of the inclination angle θ is negative, the interval between the OLEDs 201 belonging to the end row is widened, while the interval between the OLEDs 201 belonging to the center row or the OLED 201 belonging to the center row belongs to the end row. The distance from the OLED 201 is narrowed.
Thus, when the exposure position intervals for each OLED 201 are not equal in the main scanning direction and the exposure position distribution is sparse and dense, the sparsely distributed areas are dark and the dense areas are bright. The exposure dose distribution in the direction is not uniform, and periodic moire occurs. When periodic moiré occurs, vertical streaky moiré is visually recognized in the printed matter, and image quality deteriorates.

On the other hand, in the present embodiment, as illustrated in FIG. 13, when the inclination angle θ is +1 degree, the target light amount in the end row, that is, the first row and the fourth row is 5. Decrease by 4%, and increase the target light quantity in the middle row, that is, the second row and the third row by 5.4%.
In this way, at locations where the exposure positions of the OLEDs 201 belonging to the end row are close to each other in the main scanning direction, an increase in the exposure amount is suppressed by reducing the light amount of the OLED 201. In addition, in locations where the exposure positions of the OLEDs 201 belonging to the central row approach in the main scanning direction, or locations where the exposure positions of the OLED 201 belonging to the central row and the exposure positions of the OLED 201 belonging to the end row approach each other in the main scanning direction. By decreasing the amount of light of the OLED 201, a decrease in the exposure amount is suppressed.

In this way, brightness unevenness due to the density of the exposure position of the OLED 201 in the main scanning direction is reduced, so that periodic moire is reduced.
Not only in the example of FIG. 13, as shown by the sign of the correction ratio c in FIG. 10, when the sign of the inclination angle θ is positive, the light amount of the OLED 201 belonging to the end row is reduced and the center row is reduced. It is desirable to increase the light quantity of the OLED 201 belonging to the above. Further, when the sign of the inclination angle θ is negative, the density of the exposure distribution is reversed as compared with the case where the inclination angle θ is positive, so that the light amount of the OLED 201 belonging to the end row is increased. It is desirable to reduce the light amount of the OLED 201 belonging to the central row.

Further, the absolute value of the inclination angle θ can be considered as follows.
When the sign of the inclination angle θ is positive, the larger the inclination angle θ, the closer the exposure positions of the OLEDs 201 in the end row are, and the more the exposure amount increases, and the exposure positions of the OLEDs 201 in the center row are different. The exposure position of the OLED 201 in the center row and the exposure position of the OLED 201 in the end row are separated from each other, and the amount of exposure is significantly reduced.

When the sign of the inclination angle θ is negative, the exposure position of the OLED 201 in the end row is separated and the exposure amount is decreased as the inclination angle θ is smaller and accordingly the absolute value of the inclination angle θ is larger. The exposure amount of the OLED 201 in the center row, the exposure position of the OLED 201 in the center row, and the exposure position of the OLED 201 in the end row approach each other so that the amount of exposure increases significantly.
For this reason, as shown in FIG. 10, if the absolute value of the correction ratio c is increased as the absolute value of the inclination angle θ is increased, it is effective in reducing the periodic moire.

  It should be noted that the exposure regions on the outer peripheral surface of the photosensitive drum 111 exposed by the OLEDs 201 adjacent in the main scanning direction may overlap with each other when the LPH unit 100 is not inclined. In such a case, when the exposure positions are close to each other, the overlapping portion between the exposure regions is large, and when the exposure positions are separated from each other, the overlapping portion between the exposure regions is small. FIG. 12 and FIG. 13 illustrate the case where the exposure areas overlap.

  Further, although the shape and size of the light emitting region of the OLED 201 varies, it is considered sufficient to reduce the periodic moire if the correction ratio c is determined assuming an average shape and size. It is done. The average shape is a circle, and the average size is the outer diameter of the circle. In addition, the light amount distribution in the light emitting region of one OLED 201 may be uniform, and the change in the light emission diameter caused by the light amount correction and the change in the light amount distribution in the light emitting region are also intended to reduce periodic moire. In light of the above, it is considered negligible.

Further, when the LPH unit 100 is inclined due to an attachment error or vibration of the LPH unit 100, the inclination angle θ is smaller than the angle formed by the arrangement direction of the OLED 201 in the short direction and the short direction on the LPH unit 100. It is considered to be. In that sense, the range of the tilt angle θ has a limit, and the absolute value of the tilt angle θ also has an upper limit.
[6] Modifications As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications can be implemented. .

  (1) In the above embodiment, the case where the light amount is corrected for all the OLEDs 201 in accordance with the inclination angle θ of the LPH unit 100 has been described as an example, but it goes without saying that the present invention is not limited to this. Instead, it may be as follows. In addition, when there exists a member corresponding to the said embodiment below, the code | symbol common to the said embodiment is used.

  Since the OLED 201 is turned on / off according to the video data, periodic moiré is more noticeable when the lit OLED 201 is continuous in the main scanning direction, whereas when the number of continuous OLEDs 201 is small, the periodic moiré is generated. It becomes invisible. Focusing on this point, if the light amount correction is performed only when the periodic moire is conspicuous, the image quality deterioration due to the periodic moire is suppressed while suppressing the processing load for the light amount correction compared to the case where the light amount correction is performed for all the OLEDs 201. Can be reduced.

  As shown in FIG. 14, the LPH control unit 700 according to this modification includes a dot count processing unit 1401. The dot count processing unit 1401 counts the number of OLEDs 201 included in the block for each block in which the OLEDs 201 to be lit are continuous for each line in the video data, and the number is equal to or greater than a predetermined number. It is determined whether or not.

As shown in FIG. 15, the processing from step S806 to S808 is executed only for the OLED 201 belonging to a block in which a predetermined number or more of OLEDs 201 are included.
Specifically, the light emission amount correction unit 704 refers to the determination result of the dot count processing unit 1401 and performs light amount correction only for the OLED 201 belonging to a block in which a predetermined number or more of OLEDs 201 are included. In this way, since the light amount correction is performed only for the OLED 201 that contributes to periodic moire, the image forming speed of the image forming apparatus 1 can be improved by reducing the processing load for the light amount correction.

Instead of the dot count, it may be determined whether or not the OLED 201 contributes to periodic moire when performing PDL language analysis or rasterization processing of the print job.
(2) In the above embodiment, the case where the light emitting element mounted on the LPH unit 100 is the OLED 201 has been described as an example. However, it goes without saying that the present invention is not limited to this, and a semiconductor LED is used instead of the OLED. Even if it is used, the same effect can be obtained.

  (3) In the above embodiment, the inclination angle θ of the LPH unit 100 is determined from the time difference between the ON edge detection timings T1 and T2 when the toner patches 901 and 902 formed on the intermediate transfer belt 103 are detected by the IDC sensor 130. Although the present invention has been described by way of example, it goes without saying that the present invention is not limited to this. Instead, an acceleration sensor or the like is mounted on the LPH unit 100, and the inclination angle θ of the LPH unit 100 is directly determined from the detected value. It may be calculated. Regardless of the method of detecting the tilt angle θ, the effect of the present invention is the same.

(4) In the above embodiment, as shown in FIG. 3, the case where the first row to the fourth row are sequentially shifted with respect to the longitudinal direction has been described as an example, but the present invention is limited to this. Needless to say, the effect of the present invention is the same even if the shift amount (distance) between adjacent columns and the sign of the shift amount differ from the shift amount and the sign illustrated in FIG.
However, when the sign of the deviation amount is different from that in FIG. 3, it is desirable that the correction ratio c of the light emission amount is also different from the sign of the correction ratio c illustrated in FIG. Needless to say, the correction ratio c is not limited to the value illustrated in FIG. 10, and it is desirable to select an appropriate correction ratio c according to the amount of deviation.

(5) In the above-described embodiment, the case where all the OLEDs 201 belonging to the end rows are corrected for light quantity at the same correction ratio c has been described as an example. However, it goes without saying that the present invention is not limited to this. It may be as follows.
That is, of the 15,000 OLEDs 201, two OLEDs 201 located at both ends in the main scanning direction are not adjacent to the OLEDs 201 belonging to the end row in the main scanning direction, and are only adjacent to the OLEDs 201 belonging to the central row. To do. Therefore, for the two OLEDs 201, if the light amount is corrected at the same correction ratio c as that of the OLEDs 201 belonging to the central row, it is effective to eliminate periodic moire.

  (6) In the above embodiment, the case where the image forming apparatus 1 is a tandem type color printer has been described as an example. However, it goes without saying that the present invention is not limited to this, and other than the tandem type. The present invention may be applied to a color printer or a monochrome printer. The same effect can be obtained even if the present invention is applied to a copying machine equipped with a scanner, a facsimile machine equipped with a communication function, and a multi-function peripheral (MFP) equipped with these functions. .

  The optical writing apparatus and the image forming apparatus according to the present invention are useful as an apparatus for reducing deterioration in image quality due to a mounting error of a print head in which light emitting elements are arranged in a staggered manner at a low cost.

1 ... Image forming apparatus 100 ... LPH unit 101 ... Controller unit 201 ... OLED
402 ... Driver IC
702 ... Rotation processing unit 703 ... Inclination angle acquisition unit 704 ... Light emission amount correction unit

Claims (7)

A plurality of light emitting element rows in which a plurality of light emitting elements are arranged at an equal pitch in the first direction, and a second crossing the first direction in a state where the light emitting elements are staggered between adjacent light emitting element rows. Is an optical writing device that performs light writing on the photosensitive member by controlling light emission of these light emitting element arrays,
Detecting means for detecting an inclination state with respect to the main scanning direction of the first direction;
When the first direction is inclined with respect to the main scanning direction, the light emission amount and the inclination for each light emitting element in the case where the first direction is not inclined with respect to the main scanning direction. An optical writing apparatus comprising: a light emission amount determining unit that determines a light emission amount that differs by a light amount according to a state as a light emission amount for each of the light emitting elements. 2. The optical writing device according to claim 1, wherein the light emission amount determination unit determines the light emission amount for each light emitting element according to which of the light emitting element rows the light emitting element belongs to. 3. The light according to claim 2, wherein the light emission amount determining unit determines the light emission amount of the light emitting element according to a distance from a center in a short direction of the staggered arrangement to the light emitting element row. Writing device. The tilt state is a tilt angle with respect to the main scanning direction of the first direction,
The greater the inclination angle in the longitudinal direction with respect to the main scanning direction, the greater the overlap between the exposure areas on the photoreceptor due to the light-emitting elements farthest from the center in the short-side direction. While reducing the amount of light emission of other light emitting elements,
In the case where the overlapping of the exposure areas on the photoreceptor due to the light emitting element farthest from the center in the short direction becomes smaller as the inclination angle in the longitudinal direction with respect to the main scanning direction becomes larger, the light emission amount of the light emitting element is reduced. The optical writing device according to claim 3, wherein the optical writing device reduces the amount of light emitted from other light emitting elements while increasing the amount. If there is a light emitting element group in which a predetermined number or more of light emitting elements to be emitted according to the optical writing data are continuous in the main scanning direction, the light emission amount determining means determines the light emission amount of a light emitting element that does not belong to the light emitting element group. The optical writing apparatus according to claim 1, further comprising a prohibiting unit that prohibits the correction. A light emitting element array in which the light emitting elements are arranged in a zigzag pattern and three or more light emitting element arrays in which the light emitting elements are arranged in the longitudinal direction in the zigzag array is provided, and is photosensitive using the light emitting element array. A color image forming apparatus provided with an optical writing device for optical writing on a body for each color,
Detecting means for detecting the inclination state of the staggered arrangement in the longitudinal direction with respect to the main scanning direction of the photoconductor for each color optical writing device;
When the longitudinal direction is inclined with respect to the main scanning direction for each color optical writing device, light emission for each light emitting element when the longitudinal direction is not inclined with respect to the main scanning direction An image forming apparatus comprising: a light emission amount determining unit that determines a light emission amount for each of the light emitting elements by correcting an amount according to the tilt state. For each optical writing device of each color, the optical writing data is corrected so that the electrostatic latent image by the optical writing is erected in the main scanning direction according to the inclination angle of the longitudinal direction with respect to the main scanning direction. The image forming apparatus according to claim 6, further comprising an optical writing data correction unit.

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