JP2013050636A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent streaks generated on dithering patterns from standing out.SOLUTION: An image forming device comprises: a light emitting array 41 constituted of a plurality of light emitting chips CH; an image forming section 30 for forming an image on a recording medium to be recorded by using an electrostatic latent image formed on a photoreceptor 53 exposed by the light emitting array 41; and light emission controlling devices 100 and 110 for indicating gradation of the image to light emitting elements P of the light emitting array 41 and forming dithering patterns that are aggregates of dots having regularity in which the dots are inclined in one direction. The light emission control device 100 and 110 control lighting timing of the light emitting elements P constituting the light emitting chips CH in a light emitting chip unit or a control unit smaller than the light emitting chip unit such that the aggregates of the dots formed by the light emitting elements P of each of the light emitting chips CH are close to a straight line.

Description

  The present invention relates to a technique for making an image stripe inconspicuous.

  Japanese Patent Application Laid-Open No. 2004-151620 discloses a technique for making white stripes inconspicuous by correcting the light amount of the light emitting element at the boundary according to the distance between the LED chips. Patent Document 2 below proposes a technique in which the gradation of an image is represented by a dither pattern composed of a repetitive pattern of diagonal lines.

JP 2001-080111 A JP 2004-364084 A

  In order to improve the image quality, it is preferable to make the streaks such as white streaks as inconspicuous as possible, and further improvement has been demanded.

  The present invention has been completed based on the above-described circumstances, and an object thereof is to make an image streak inconspicuous.

  An image forming apparatus disclosed in the present specification includes a light emitting array formed of a plurality of light emitting chips arranged in a main scanning direction by forming a plurality of light emitting elements on a semiconductor substrate, and a photosensitive exposed by the light emitting array. An image forming unit that forms an image on a recording medium using an electrostatic latent image formed on the photosensitive member, and the light emitting elements of the light emitting array indicate the gradation of the image in one direction. A light emission control device that forms a dither pattern, which is a set of dots having regularity that inclines, and the light emission control device is arranged so that a set of dots formed by light emitting elements of each light emitting chip approaches a straight line. Timing control is performed to control the lighting timing of the light-emitting elements constituting the light-emitting chip in a light-emitting chip unit or a control unit smaller than the light-emitting chip unit.

  The “arranged in the main scanning direction” includes a pattern in which the light emitting chips are arranged in a line in the main scanning direction and a pattern in which the light emitting chips are arranged in a staggered pattern in the main scanning direction.

  In addition, as shown in FIG. 20, a plurality of lines La and Lb form a set of sets UT to form a set UT, as shown in FIG. The case where each line La and Lb approaches a straight line is included. The white circles in the figure indicate the positions before correction.

  According to the image forming apparatus disclosed in the present specification, since the aggregate of dots formed by each light emitting chip is adjusted so as to approach a straight line, white stripes and color stripes formed in the dither pattern can be made inconspicuous. This makes it possible to improve the image quality.

In the image forming apparatus, the following is preferable.
The distance between two light emitting elements located at the seam of the second light emitting chip adjacent to the right side of the first light emitting chip and the first light emitting chip is a reference. When the inclination direction is larger in the main scanning direction and the distance between the two light emitting elements located at the joint between the first light emitting chip and the second light emitting chip is smaller than the reference value. Among these, in at least any one of the cases, the light emission control device delays the light emission timing of the light emitting elements constituting the second light emitting chip from the normal light emission timing when the distance is the reference value. In order to “make the light emission timing of the light emitting element constituting the second light emitting chip slower than the normal light emission timing when the distance is a reference value”, the light emission control device sets the light emission timing in units of light emitting chips. The case of delaying and the case of delaying by a control unit smaller than the light emitting chip unit are included.

The distance between the two light emitting elements located at the joint of the first light emitting chip and the second light emitting chip adjacent to the right of the first light emitting chip is a reference value. A case in which the direction of inclination is lowering to the right in the main scanning direction and the distance between two light emitting elements located at the joint between the first light emitting chip and the second light emitting chip is smaller than a reference value. In at least one of the cases, the light emission control device delays the light emission timing of the light emitting elements constituting the first light emitting chip from the reference light emission timing when the distance is a reference value. In order to “make the light emission timing of the light emitting element constituting the first light emitting chip later than the normal light emission timing when the distance is a reference value”, the light emission control device sets the light emission timing in units of light emitting chips. The case of delaying and the case of delaying by a control unit smaller than the light emitting chip unit are included.

The light emission control device increases the delay amount of the light emission timing with respect to the normal light emission timing as the distance between the two light emitting elements becomes larger than a reference value.

The light emission control device increases the delay amount of the light emission timing with respect to the regular light emission timing as the inclination angle increases.

The light emission control device is configured such that the distance between two light emitting elements located at the joint of the first light emitting chip and the second light emitting chip adjacent to the right side of the first light emitting chip is out of a reference value. Of the two light emitting chips, the light emitting timing of the light emitting element constituting one light emitting chip is made slower than the normal light emitting timing when the distance is the reference value, and the light emitting timing of the light emitting element constituting the other light emitting chip is It is earlier than the regular light emission timing.

-The said light emission control apparatus does not perform the said timing control, when the inclination of the said inclination is below a predetermined value.
The light emission control device includes the timing control for controlling the lighting timing of the light emitting elements that constitute the light emitting chip so that the aggregate of dots formed by the light emitting chips approaches a straight line, and the position at the joint between the light emitting chips. The light quantity control for correcting the light quantity of the light emitting elements to be corrected according to the distance between the light emitting elements is also used.
The light emission control device does not execute the timing control when the dither pattern is not included in the image.

  According to the present invention, it is possible to make the lines that can be formed into a dither pattern inconspicuous.

FIG. 3 is a side sectional view of a main part of the color printer according to the first embodiment. Enlarged view of LED unit and process cartridge LED unit viewed from the exposure side Block diagram of light emission control unit and control device Diagram showing the suppression principle of white stripes (when tilting downward to the right) Diagram showing the principle of suppression of color streaks (when tilting downward to the right) The figure which shows the relationship between the error U, movement amount (DELTA), and angle (theta). The figure which shows the relationship between the error U, movement amount (DELTA), and angle (theta). The figure which shows the level difference which can be done by correcting the sub scanning position Diagram showing the suppression principle of white stripes (when tilting upward to the right) Diagram showing the suppression principle of color streaks (when tilting upward to the right) Diagram showing batch movement of multiple line segments Diagram showing the principle of light intensity correction Diagram showing correction value data Diagram showing correction table The flowchart figure which shows the flow of the processing performed at the time of power activation The flowchart figure which shows the flow of the process performed at the time of print data reception The flowchart figure which shows the flow of the process performed at the time of print data reception in Embodiment 2. The figure which shows the correction pattern of the subscanning position in Embodiment 3. Diagram showing another example of dither pattern

<Embodiment 1>
Embodiment 1 will be described with reference to FIGS.
1. As shown in FIG. 1, an electrophotographic color printer 1 is fed into a main body housing 10 with a paper feeding unit 20 that feeds paper S, which is an example of a recording medium, and the paper is fed. An image forming unit 30 that forms an image on the sheet S, a sheet discharge unit 90 that discharges the sheet S on which the image is formed, and a control device 100 that controls the operation of each unit are provided. In the following description, the direction will be described with reference to the user when using the color printer. That is, in FIG. 1, the left side toward the paper surface is “front side”, the right side toward the paper surface is “rear side”, the rear side toward the paper surface is “left side”, and the front side toward the paper surface is “right side”. To do. The main scanning direction is the “X direction” and the sub-scanning direction is the “Y direction”.

  An upper cover 12 that can be opened and closed relative to the main body housing 10 is provided on the upper portion of the main body housing 10 so as to be rotatable up and down around a hinge 12A provided on the rear side. An upper surface of the upper cover 12 serves as a paper discharge tray 13 for accumulating the paper S discharged from the main body housing 10, and an LED unit 40 serving as an exposure device is provided below the upper cover 12.

  Further, a cartridge drawer 15 that detachably accommodates each process cartridge 50 is provided in the main body housing 10. The cartridge drawer 15 is provided with a pair of metal side plates 15A (only one side is shown) provided on the left and right and a cross member 15B connecting the pair of side plates 15A on the front and rear. The side plates 15A are members that are disposed on both sides of the LED array 41 as the exposure head of the LED unit 40 in the left-right direction, and directly or indirectly support and position the photosensitive drum 53. Light emission of the LED array 41 is controlled by the control device 100 and the light emission control unit 110. The control device 100 and the light emission control unit 110 are examples of the light emission control device of the present invention. The photosensitive drum 31 is an example of the photosensitive member of the present invention.

  The paper feeding unit 20 is provided in the lower part of the main body housing 10, and is a paper feeding tray 21 that is detachably attached to the main body housing 10, and a paper that conveys the paper S from the paper feeding tray 21 to the image forming unit 30. A supply mechanism 22 is mainly provided. The paper supply mechanism 22 is provided on the front side of the paper feed tray 21 and mainly includes a paper feed roller 23 and a separation roller 24.

  In the paper feed unit 20 configured as described above, the paper S in the paper feed tray 21 is separated one by one and sent upward, and is turned backward through the transport path 28 to the image forming unit 30. Supplied.

  The image forming unit 30 includes four LED units 40, four process cartridges 50, a transfer unit 70, and a fixing unit 80. The four LED units 40 and the four process cartridges 50 correspond to four colors of black, yellow, magenta, and cyan.

  The process cartridge 50 is arranged side by side in the front-rear direction between the upper cover 12 and the paper feeding unit 20, and as shown in FIG. 2, the drum unit 51 and the developing unit 61 that is detachably attached to the drum unit 51. And. The side plate 15 </ b> A supports the process cartridge 50, and the process cartridge 50 supports the photosensitive drum 53. Each process cartridge 50 has the same configuration except that the color of the toner stored in the toner storage chamber 66 of the developing unit 61 is different.

  The drum unit 51 mainly includes a drum frame 52, a photosensitive drum 53 as an example of a photosensitive member rotatably supported by the drum frame 52, and a scorotron charger 54.

  The developing unit 61 includes a developing frame 62, a developing roller 63 and a supply roller 64 that are rotatably supported by the developing frame 62, and includes a toner storage chamber 66 that stores toner. In the process cartridge 50, the developing unit 61 is mounted on the drum unit 51, whereby an exposure hole 55 is formed between the developing frame 62 and the drum frame 52 so as to face the photosensitive drum 53 from above. The LED unit 40 holding the LED array 41 at the lower end is inserted into the exposure hole 55. Details of the LED array 41 will be described later.

  As shown in FIG. 1, the transfer unit 70 is provided between the paper feeding unit 20 and each process cartridge 50, and mainly includes a drive roller 71, a driven roller 72, a conveyance belt 73, and a transfer roller 74.

  The driving roller 71 and the driven roller 72 are spaced apart and arranged in parallel in the front-rear direction, and a conveyor belt 73 is stretched therebetween. The outer surface of the conveyor belt 73 is in contact with each photosensitive drum 53. In addition, four transfer rollers 74 that sandwich the conveyor belt 73 between the photosensitive drums 53 are arranged inside the conveyor belt 73 so as to face the photosensitive drums 53. A transfer bias is applied to the transfer roller 74 by constant current control during transfer.

  The fixing unit 80 is disposed on the back side of each process cartridge 50 and the transfer unit 70, and includes a heating roller 81 and a pressure roller 82 that is disposed to face the heating roller 81 and presses the heating roller 81.

  In the image forming unit 30 configured as described above, first, the surface (photosensitive surface 53A) of each photosensitive drum 53 is uniformly charged by the scorotron charger 54 and then irradiated from each LED array 41. It is exposed by LED light. As a result, the potential of the exposed portion is lowered, and an electrostatic latent image based on the image data is formed on each photosensitive drum 53.

  Further, the toner in the toner storage chamber 66 is supplied and carried on the developing roller 63 by the rotation of the supply roller 64. The toner carried on the developing roller 63 is supplied to the electrostatic latent image formed on the photosensitive drum 53 when the developing roller 63 comes into contact with the photosensitive drum 53. As a result, the toner is selectively carried on the photosensitive drum 53 to visualize the electrostatic latent image, and a toner image is formed by reversal development.

  Next, the sheet S supplied onto the conveyance belt 73 passes between each photosensitive drum 53 and each transfer roller 74 disposed inside the conveyance belt 73, thereby forming on each photosensitive drum 53. The toner image thus transferred is transferred onto the paper S. Then, as the sheet S passes between the heating roller 81 and the pressure roller 82, the toner image transferred onto the sheet S is thermally fixed.

  The paper discharge unit 90 mainly includes a paper discharge side transport path 91 formed so as to extend upward from the exit of the fixing unit 80 and to be reversed to the front side, and a plurality of pairs of transport rollers 92 that transport the paper S. I have. The sheet S on which the toner image has been transferred and heat-fixed is transported along a paper discharge side transport path 91 by a transport roller 92, discharged outside the main body housing 10, and accumulated in the paper discharge tray 13.

2. Configuration of LED Array As shown in FIG. 3, the LED array 41 has a plurality of light emitting elements P arranged in the main scanning direction orthogonal to the paper feeding direction (vertical direction in FIG. 3). Specifically, 20 LED array chips CH are arranged in a staggered pattern on the circuit board CB. Each LED array chip CH is obtained by forming a plurality of light emitting diodes as light emitting elements P on a semiconductor substrate by a semiconductor process. The LED array 41 receives a light emission signal from a light emission control unit 110 to be described later, so that the scanning start side (for example, the left side in FIG. 3) in the main scanning direction to the scanning end side (for example, the right side in FIG. 3). The light is emitted toward the light and the photosensitive drum 53 is exposed. In the present embodiment, the light emitting elements P constituting the LED array 41 are controlled to emit light at the light emitting elements P in units of control within the LED array chip CH, and are simultaneously lit between the LED array chips CH.

  In this example, as shown in FIG. 3, each LED array chip CH is staggered in the sub-scanning direction orthogonal to the main scanning direction on the circuit board CB. This is because the chip cannot be formed up to the chip edge. That is, the staggered arrangement allows the distance Dx between the light emitting elements at the joint between the chips CH to coincide with the reference pitch.

3. Description of Control Device 100 and Light Emission Control Unit 110 The control device 100 controls the entire color printer 1, and includes an arithmetic control unit 100A including a CPU, a RAM 100B, and a ROM 100C. . The light emission control unit 110 controls the light emission of each light emitting element P of the LED array 41 together with the control device 100. The light emission control unit 110 includes an ASIC 120 as shown in FIG. Four sets of LED arrays 41 are commonly connected to the light emission control unit 110, and the ASIC 120 of the light emission control unit 110 is configured to control the light emission of the four sets of LED arrays 41.

  Each LED array 41 is provided with an EEPROM 43 as a nonvolatile storage means. The EEPROM 43 stores the following data necessary for light emission timing control and light amount correction described below.

Data on the pitch “Dx” in the main scanning direction between the light emitting elements at the joint portion between the chips (see FIG. 3).
Data on the pitch “Dy” in the sub-scanning direction between the light emitting elements at the joint portion between the chips (see FIG. 3).
Correction value data X and correction value table (see FIGS. 14 and 15)

4). Light emitting timing correction The light emitting elements P on the LED array 41 are arranged at a constant reference pitch Dp in the main scanning direction, specifically, at a pitch of 42 μm when the image resolution is 600 dpi. And also about the joint of each LED array chip CH, LED array chip CH is arrange | positioned so that the distance Dx between light emitting elements may become the reference pitch Dp. The distance in the sub-scanning direction of the joint portion is 52.3 μm. The reference pitch Dp is an example of the “reference value” in the present invention.

  However, when mounting each LED array chip CH on the circuit board CB, the mounting position may deviate from the normal position. At the joint between the LED array chips, a one-dot chain line frame (A part, B part, As shown by the three parts of part C), the distance Dx between the light emitting elements may increase or decrease with respect to the reference pitch Dp. When the distance Dx between the light emitting elements increases or decreases with respect to the reference pitch Dp, as shown in FIGS. 5 and 6, the line segment constituted by the dots formed by each light emitting element P and inclined with respect to the main scanning direction is repeated. When the image is printed using the dither pattern Z, the image is likely to be streaked.

  That is, when the distance Dx between the light emitting elements coincides with the reference pitch Dp (in the case of A portion in FIG. 3), as shown in the left hand of FIG. 5 and FIG. Absent. However, when the distance Dx between the light emitting elements is larger than the reference pitch Dp (in the case of B portion in FIG. 3), as shown in the center of FIG. Further, when the distance Dx between the light emitting elements is smaller than the reference pitch Dp (in the case of C portion in FIG. 3), as shown in the center of FIG.

  Therefore, in the present embodiment, when the distance Dx between the light emitting elements at the joint of each LED array chip CH is out of the reference pitch Dp, the light emission timing of the LED array chip CH is shifted from the normal light emission timing, and the dither pattern Z By showing the seam of the line in a straight line, the occurrence of color streaks and white streaks is suppressed. Each line segment constituting the dither pattern Z is an example of the “dot aggregate” of the present invention.

  The dither pattern Z is used when gradation is applied to an image. Four patterns corresponding to four color toners, that is, four kinds of dither patterns Z having different oblique line angles θ with respect to the main scanning direction are used. Is provided. In the present embodiment, four dither patterns Z having diagonal lines θ with respect to the main scanning direction of “+ 27 °”, “−27 °”, “+ 63 °”, and “−63 °” are used. The dither pattern Z is changed for each color so that the dither patterns Z do not overlap each other.

  Hereinafter, the method of suppressing the stripes generated in the image will be described separately for the case where the dither pattern Z is inclined downward to the right and the upward inclination to the right in the main scanning direction.

<When dither pattern Z is inclined downward to the right with respect to the main scanning direction>
As shown in FIG. 5, when the distance Dx between the light emitting elements is larger than the reference pitch Dp, the light emission timing of the right LED array chip CHR among the two LED array chips CHL and CHR adjacent to the left and right is set to the normal light emission. Slow from timing. As a result, the sub-scanning position of the line segment LR formed by the right-side array chip CHR is shifted downward in the figure with respect to the normal sub-scanning position. Therefore, as shown on the right side in FIG. The line segment LR formed by the LED array chip CHR on the right side overlaps the extended line of the line segment LL formed by CHL, and both line segments LL and LR are arranged on the same straight line.

  In this way, the two line segments LL and LR created by the two LED array chips CHL and CHR approach a straight line. For this reason, the white stripes are not noticeable.

  Next, as shown in FIG. 6, when the distance Dx between the light emitting elements is smaller than the reference pitch Dp, the light emission timing of the left LED array chip CHL among the two LED array chips CHL and CHR adjacent to the left and right is Delay from the normal emission timing. As a result, the sub-scanning position of the line segment formed by the left array chip CHL is shifted downward in the figure with respect to the normal sub-scanning position, so that the right LED array chip CHR is shown as shown on the right side in FIG. The line segment LL formed by the left LED array chip CHL overlaps the extension line of the line segment LR formed by, and both line segments LL and LR are arranged on the same straight line.

  In this way, the two line segments LL and LR created by the two LED array chips CHL and CHR approach a straight line. For this reason, the color streak becomes inconspicuous.

  The regular light emission timing means the light emission timing of each LED array chip CH when the distance Dx between the light emitting elements is the reference pitch Dp. The normal sub-scanning position means the sub-scanning position of each line segment when each LED array chip CH is caused to emit light at the normal light emission timing.

  Further, if the angle θ of the dither pattern Z is the same, the delay amount with respect to the normal light emission timing may be increased as the error U of the distance Dx between the light emitting elements with respect to the reference pitch Dp is increased. If the error U is the same, the delay amount with respect to the normal light emission timing may be increased as the angle θ of the dither pattern Z is increased.

As shown in FIG. 7 and FIG. 8, there are the following between the error U, the angle θ of the dither pattern Z, and the movement amount Δ for aligning the two line segments LL and LR: A) The relationship of the formula is established.
Δ = U × tan θ (A)

  For this reason, if the angle θ is the same, the larger the error U, the larger the movement amount Δ, so it is necessary to increase the delay amount with respect to the normal light emission timing. Further, if the error U is the same, the larger the angle θ, the larger the movement amount Δ, and therefore it is necessary to increase the delay amount with respect to the normal light emission timing.

  In the dither pattern Z, the angle θ with respect to the main scanning direction is small (around 30 ° as a guide), and when the error U is about 10 μm, for example, the movement amount Δ is about half that of 5 μm. The value is small. That is, when the angle θ is small, even if the light emission timing is corrected, the effect is small, and the light emission timing may not be corrected. “30 °” is an example of “predetermined value” in “when the inclination of the inclination is not more than a predetermined value” in the present invention.

  On the other hand, when the angle θ with respect to the main scanning direction is large (approximately 60 ° as a guide), when the error U is about 10 μm, for example, the movement amount Δ is about 20 μm and is large. That is, when the angle θ is large, correcting the light emission timing has a large effect, so it is preferable to correct the light emission timing.

  However, since the correction of the light emission timing shifts the sub-scanning direction of the printing position from the normal position, if the light emission timing correction is applied as it is and normal printing not including the dither pattern Z is performed, as shown in FIG. A step ST is created when the horizon is drawn. Since the size of the step ST is proportional to the movement amount Δ, if the movement amount Δ is excessively increased, there is a problem that the image quality during normal printing is deteriorated.

  Therefore, the upper limit value of the movement amount Δ is set to about 1/4 of the size of one dot, for example, about 10 μm, and the light amount correction is performed for the amount that cannot be corrected. In this embodiment, as shown in FIGS. 7 and 8, four light receiving spots S formed by the light emitting element P are overlapped in the sub-scanning direction to form one dot, and the dot is in units of 10 μm. It is possible to move with.

  The light amount correction is a correction that makes the line inconspicuous by correcting the light amount of the light emitting element located at the joint between the LED array chips. This light amount correction will be described in detail later.

<When dither pattern Z is inclined upward to the main scanning direction>
As shown in FIG. 10, when the distance Dx between the light emitting elements is larger than the reference pitch Dp, the light emission timing of the left LED array chip CHL among the two LED array chips CHL and CHR adjacent to the left and right is set to the normal light emission. Slow from timing. As a result, the sub-scanning position of the line segment LL formed by the left array chip CHL is shifted downward in the figure with respect to the normal sub-scanning position, so that the right LED array chip is shown as shown on the right side in FIG. The line segment LL formed by the left LED array chip CHL overlaps the extended line of the line segment LR formed by CHR, and both line segments LL and LR are arranged on the same straight line.

  Next, as shown in FIG. 11, when the distance Dx between the light emitting elements is smaller than the reference pitch Dp, the light emission timing of the right LED array chip CHR among the two LED array chips CHL and CHR adjacent to the left and right is Delay from the normal emission timing. As a result, the sub-scanning position of the line segment LR formed by the right-side array chip CHR is shifted downward in the figure with respect to the normal sub-scanning position. Therefore, as shown on the right side in FIG. The line segment LR formed by the LED array chip CHR on the right side overlaps the extended line of the line segment LL formed by CHL, and both line segments LL and LR are arranged on the same straight line.

  In this way, the two line segments LL and LR created by the two LED array chips CHL and CHR approach a straight line. For this reason, the color streak becomes inconspicuous.

<Correction between line segments>
By the way, the LED array 41 has, for example, 20 LED array chips CH arranged in a staggered manner, and one line is composed of a line segment of “20”.

  Therefore, for example, as shown in the upper part of FIG. 12, when there is a gap that causes white streak between the line segment 1 and the line segment 2, the light emission timing of the LED array chip of the line segment 2 is set to the normal light emission timing. If the position of the line segment 2 is shifted so that the line segment 2 is aligned with the line segment 1, the gap between the line segment 2 and the line segment 3 may be increased as shown in the middle part of FIG.

  In view of this, it is preferable to shift the light emission timings as a group up to a line segment with a small gap between the seams. For example, in the example of FIG. 12, the joint between the line segment 3 and the line segment 4 has a small gap. Therefore, the light emission timings of the LED array chips corresponding to both line segments are collectively shifted as a group of line segment 2 and line segment 3. In this way, as shown in the lower part of FIG. 12, the line segment 2 and the line segment 3 are moved together, so that the gap between the line segment 2 and the line segment 3 is not increased. On the other hand, although a new gap is formed between the line segment 3 and the line segment 4, the size thereof is small. For this reason, since the entire line is substantially close to a straight line, white stripes and color stripes are less likely to occur.

5. Light quantity correction By correcting the light quantity of the light emitting element P at the joint of each LED array chip CH, the occurrence of color streaks and white streaks can be suppressed. For example, as shown in FIG. 13, when the distance Dx between the light emitting elements is larger than the reference pitch Dp, the correction is performed to increase the light amount by extending the light emission time for the two light emitting elements Pa and Pb at the center of the joint. Do. As a result, after the light amount correction, as shown on the right side of FIG. 13, the center portion of the joint is in a state where the lines are connected, and the white streak is less noticeable than in the case where the correction is not performed.

  Contrary to the example of FIG. 13, when the distance Dx between the light emitting elements is smaller than the reference pitch Dp, the light emitting time is shortened and the light quantity is reduced for the two light emitting elements at the center of the joint. . Thereby, after the light amount correction, the light amount difference between the central portion of the seam and the peripheral portion is reduced, so that the color streak becomes inconspicuous compared with the case where the correction is not performed.

  The light emission time of each light emitting element P is determined by correction value data X described below, and the set values are different. This is because each light emitting element P of the LED array 41 has a luminance variation, and when the light emitting time and the current value are lit uniformly with the same conditions such as the light emitting time and the current value, a difference in the amount of light occurs, resulting in uneven exposure and image quality. Affects. Therefore, by changing the light emission time according to the luminance value of each light emitting element P, the luminance variation is compensated and the light quantity is made uniform.

  The correction value data X shown in FIG. 14 defines a correspondence relationship to which grade of correction gradation is applied to each light emitting element P on the LED array. The numbers in the frame of FIG. 14, for example, “2”, “1”, “3”, etc., indicate the grade of the correction gradation. On the other hand, the correspondence between the correction gradation grade and the light emission time (specifically, the clock count) is defined in the correction value table of FIG.

  Therefore, the light emission time of each light emitting element can be obtained by referring to the correction value table. In the case of the light emitting element P1 shown in FIG. 14, the correction value data X is “2”. In this case, the grade of the correction gradation is “2”, and the clock count is “29” times, that is, the light emission time is 112.4 sec according to the correction value table. In the case of the light emitting element Pn, the correction value data X is “4”. In this case, the grade of the correction gradation is “4”, and the clock count is “31” times, that is, the light emission time is 120.1 sec according to the correction value table. Here, the clock cycle of the clock for measuring the light emission time is set to “3.875” ns.

  The correction value data “X1” shown in FIG. 14 is obtained by incorporating light amount correction for suppressing the generation of color streaks and white streaks into the correction value data X, and is positioned at the center of the seam with respect to the correction value data “X”. The correction gradation grade of the two light emitting elements Pa and Pb is changed.

6). Light emission control Next, a light emission control example of each light emitting element P constituting the LED array 41 will be described with reference to FIGS. 16 and 17.

<Operation at power-on>
The control device 100 starts up when the power is turned on. Thereafter, the arithmetic control unit 100 </ b> A of the control device 100 reads data from the EEPROM 43 of each LED array 41. Specifically, from the EEPROM 43, data of the pitch “Dx” in the main scanning direction between the light emitting elements at the joint portion between the chips, data of the pitch “Dy” in the sub scanning direction between the light emitting elements at the joint portion between the chips, Data of the correction value data X and data of the correction value table are read (S10).

  Thereafter, the arithmetic control unit 100A determines the angle θ of the dither pattern Z, the data of the pitch “Dx” in the main scanning direction between the light emitting elements, the data of the reference pitch Dp, and the sub-interval between the light emitting elements at the joint portion between the chips. Based on the data of the pitch “Dy” in the scanning direction, the movement amount Δ of the line segment constituting the dither pattern is calculated with 10 μm as the upper limit value. The movement amount Δ of the line segment is calculated for each LED light emitting chip CH.

  In calculating the movement amount Δ, the data of the pitch “Dy” in the sub-scanning direction between the light emitting elements in the joint portion between the chips is taken into consideration. The two line segments LL and LR can be made closer to a straight line. Because. That is, since the pitch “Dy” in the sub-scanning direction has an error with respect to the reference pitch (52.3 μm as an example), similarly to the pitch “Dx” in the main scanning direction, it is better to consider the error. This is because the two line segments LL and LR can be made closer to a straight line.

  When the obtained movement amount Δ exceeds the upper limit value, correction value data “X1” is created from the correction value data “X”. The correction value data X1 is created with each LED array 41 as a unit. The generated movement amount Δ data and correction value data X1 are stored in the RAM 100B of the control device 100. At this time, if no print data is received, the process enters a standby state and the process ends.

<Operation when printing>
Thereafter, when print data is received, print processing is executed according to the flow shown in FIG. Specifically, the arithmetic control unit 100A of the control device 100 first reads the movement amount Δ and the correction value data X1 from the RAM 100B. Then, the read movement amount Δ and the correction value data X1 are sent to the light emission control unit 110 together with the print data (S40).

  Then, the ASIC 120 of the light emission control unit 110 that has received the data calculates the delay amount of the light emission timing from the movement amount Δ, and adjusts the light emission timing of the light emitting element P for each LED array chip. Further, the light emission time of each light emitting element P mounted on the LED array 41 is controlled according to the correction value data X1 (S50).

  Thus, the position in the sub-scanning direction is corrected so that the line segment constituting the dither pattern Z approaches a straight line. Therefore, white stripes and color stripes are not noticeable. Further, when the position correction only in the sub-scanning direction is not sufficient, that is, when the movement amount Δ exceeds 10 μm, the movement amount Δ is kept at 10 μm, and the shortage is compensated by adjusting the light amount of the light emitting element P.

  Therefore, as shown in FIG. 9, the amount of deviation of the sub-scanning position when normal printing not including the dither pattern Z is performed, for example, when the horizontal line is drawn as shown in FIG. . Therefore, even if the light emission timing correction is applied to normal printing, the image quality does not deteriorate, or the image quality deterioration can be suppressed.

  In the first embodiment, the light emission timing of the light emitting element P is adjusted to be delayed with respect to the normal light emission timing. The control for delaying the light emission timing has a merit that the control is easy because it can be easily performed with fewer restrictions than the control for speeding up the light emission.

<Embodiment 2>
In the first embodiment, an example in which light emission timing correction is performed both in the case of gradation printing in which the image includes the dither pattern Z and in the case of normal printing in which the dither pattern Z is not included is described.

  In the second embodiment, the light emission timing correction is performed only in the case of gradation printing in which the image includes the dither pattern Z, and the light emission timing correction is not performed in the case of normal printing in which the image does not include the dither pattern Z. Is.

  More specifically, as shown in FIG. 18, when print data is received, the arithmetic control unit 100A of the control device 100 analyzes whether the dither pattern Z is included in the print data.

  When the dither pattern Z is included in the print data (S110: YES), the arithmetic control unit 100A sends gradation print data to the light emission control unit 110 (S120). Specifically, the movement amount Δ data and the correction value data X1 are sent together with the print data.

  Then, the ASIC 120 of the light emission control unit 110 that has received the data executes light emission timing correction. That is, the delay amount of the light emission timing is calculated from the movement amount Δ, and a part of the light emitting elements P is turned on with the light emission timing shifted from the normal light emission timing. Further, the light emission time of each light emitting element P mounted on the LED array 41 is controlled according to the correction value data X1.

  Thus, the position in the sub-scanning direction is corrected so that the line segment constituting the dither pattern Z approaches a straight line. Therefore, white stripes and color stripes are not noticeable. If the position correction in the sub-scanning direction is not sufficient, the light amount adjustment of the light emitting element P is executed (S140).

  On the other hand, if the dither pattern Z is not included in the print data (S110: NO), the arithmetic control unit 100A sends data for normal printing to the light emission control unit 110 (S120). Specifically, the correction value data X is sent together with the print data. Then, the ASIC 120 of the light emission control unit 110 that has received the data does not execute the light emission timing correction and lights each light emitting element at the normal light emission timing. Further, the light emission time of each light emitting element P is controlled according to the correction value data X (S140).

  As described above, in the second embodiment, the control pattern of the light emitting element P is divided between gradation printing and normal printing, and the light emission timing correction is executed only during gradation printing, and is not executed during normal printing. Therefore, when normal printing is performed, there is no step difference when the amount of deviation of the sub-scanning position, for example, a horizontal line is drawn as shown in FIG. Therefore, there is no deterioration in image quality during normal printing.

<Embodiment 3>
In Embodiments 1 and 2, when the distance Dx between the light emitting elements at the joint of each LED array chip CH is out of the reference pitch, the light emission timing of the LED array chip is shifted from the normal light emission timing, and the joint of the dither pattern Z The appearance of color streaks and white streaks was suppressed by making the lines appear straight.

  Specifically, when a white line or a color line is formed between the two line segments LL and LR, the position in the sub-scanning direction is set so that one of the line segments coincides with the extension line of the other line segment. Shifted.

  The third embodiment is different from the first and second embodiments in the way of shifting the line segment. When white stripes or color stripes are formed between the two line segments LL and LR, the two line segments LL, The position in the sub-scanning direction is changed so that the LRs are close to each other. For example, in the case of FIG. 19, for the line segment LL, the light emission timing is advanced with respect to the normal light emission timing, and the sub-scanning position is shifted upward in FIG. On the other hand, for the line segment LR, the light emission timing is delayed with respect to the normal light emission timing, and the sub-scanning position is shifted downward in FIG. Thereby, both line segments LL and LR can be brought close to each other, and two line segments LL and LR can be arranged on the same straight line.

  In this way, as shown in the middle stage of FIG. 19, the positional deviation amount D1 between the two line segments LL and LR with respect to the reference line V in the sub-scanning direction becomes small. Therefore, when normal printing that does not include the dither pattern Z is performed, there is no deterioration in image quality, or there is little deterioration in image quality.

  The lower part of FIG. 19 shows a positional deviation amount D2 of the line segment LR with respect to the reference line V when the sub-scanning position is corrected only on the LR side of the two line segments LL and LR as a comparative example. . It can be understood that the positional deviation amount D1 is reduced to about ½ times the positional deviation amount D2.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.

  (1) In the above embodiment, an LED array using a light emitting diode as a light emitting element is illustrated as an example of the light emitting array. However, an organic EL array using an organic EL (electroluminescence) element as the light emitting element may be used. Is possible.

  (2) In the above embodiment, the light amount is corrected by adjusting the light emission time of each light emitting element P. However, the light amount is adjusted by adjusting the current value flowing through each light emitting element P, that is, adjusting the luminance. May be corrected. An example of a method for adjusting the current value is a method of changing the resistance value.

  (3) In the above embodiment, the light emission timing of the light emitting elements P constituting the LED array chip CH is shifted from the normal light emission timing, and the seam of the dither pattern Z is shown as a straight line, thereby suppressing the occurrence of color streaks and white streaks. An example is shown. The light emission timing is controlled in units of LED array chips (corresponding to “light emitting chip units” in the present invention). The present invention only needs to control the lighting timing of the light emitting elements constituting the LED array chip CH to make the joint of the dither pattern Z look straight, and the lighting timing is controlled by a control unit smaller than the LED array chip unit. You may go on. The control unit is a group of light emitting elements whose lighting timing is uniformly controlled among the light emitting elements constituting the LED array chip. Therefore, for example, when the control unit is composed of eight light emitting elements, the seam of the dither pattern Z may be shown as a straight line by adjusting the light emission timing with eight light emitting elements as one unit.

  (4) In the above embodiment, the distance Dx in the main scanning direction is exemplified as the distance between the light emitting elements, but is not limited to the main scanning direction. That is, it may be a distance in two directions (XY direction) of the main scanning direction (X direction) and the sub-scanning direction (Y direction).

1. Printer (an example of the “image forming apparatus” of the present invention)
DESCRIPTION OF SYMBOLS 30 ... Image formation part 40 ... LED unit 41 ... LED array (an example of "light emitting array" of this invention)
53. Photosensitive drum (an example of the “photosensitive member” of the present invention)
100... Control device (an example of the “light emission control device” of the present invention)
110... Light emission control unit (an example of the “light emission control device” of the present invention)
CH ... LED array chip (an example of the “light emitting chip” of the present invention)
P ... Light-emitting element Z ... Dither pattern

Claims (9)

A plurality of light emitting elements formed on a semiconductor substrate, and a light emitting array comprising a plurality of light emitting chips arranged in the main scanning direction;
A photoreceptor exposed by the light emitting array;
An image forming unit that forms an image on a recording medium using an electrostatic latent image formed on the photoreceptor;
A light emission control device for forming a dither pattern, which is a set of dots having regularity that inclines in one direction, on the light emitting elements of the light emitting array;
The light emission control device is configured such that the lighting timing of the light emitting elements constituting the light emitting chip is a light emitting chip unit or a control unit smaller than the light emitting chip unit so that an aggregate of dots formed by the light emitting elements of each light emitting chip approaches a straight line. An image forming apparatus that performs timing control. The distance between two light emitting elements located at the joint of the second light emitting chip adjacent to the right side of the first light emitting chip and the first light emitting chip is the reference value. A case in which the direction of inclination is ascending to the right in the main scanning direction and the distance between two light emitting elements located at the joint between the first light emitting chip and the second light emitting chip is smaller than a reference value. , At least in either case
2. The image forming apparatus according to claim 1, wherein the light emission control device delays the light emission timing of a light emitting element constituting the second light emitting chip from a normal light emission timing when the distance is a reference value. The distance between the two light emitting elements located at the joint of the first light emitting chip and the second light emitting chip adjacent to the right side of the first light emitting chip is higher than the reference value. In the case where it is large, or when the direction of the inclination is downward to the right in the main scanning direction and the distance between the two light emitting elements located at the joint of the first light emitting chip and the second light emitting chip is smaller than a reference value, In at least one of the cases
The image forming apparatus according to claim 1, wherein the light emission control device delays the light emission timing of the light emitting elements constituting the first light emitting chip from a reference light emission timing when the distance is a reference value.   4. The image forming apparatus according to claim 2, wherein the light emission control device increases a delay amount of the light emission timing with respect to the normal light emission timing as the distance between the two light emitting elements becomes larger than a reference value. 5.   The image forming apparatus according to claim 2, wherein the light emission control device increases a delay amount of the light emission timing with respect to the regular light emission timing as the inclination angle increases.   When the distance between two light emitting elements located at the joint of the first light emitting chip and the second light emitting chip adjacent to the right side of the first light emitting chip is out of the reference value, Among the chips, the light emission timing of the light emitting element constituting one light emitting chip is delayed from the normal light emission timing when the distance is a reference value, and the light emission timing of the light emitting element constituting the other light emitting chip is set to the regular light emission. The image forming apparatus according to claim 1, wherein the image forming apparatus is earlier than the timing.   The image forming apparatus according to claim 1, wherein the light emission control device does not execute the timing control when the inclination of the inclination is a predetermined value or less. The light emission control device includes:
The timing control for controlling the lighting timing of the light emitting elements constituting the light emitting chip so that the aggregate of dots formed by each light emitting chip approaches a straight line;
The image forming apparatus according to any one of claims 1 to 7, wherein the image forming apparatus is used in combination with a light amount control for correcting a light amount of a light emitting element located at a joint between the light emitting chips according to a distance between the light emitting elements.   The image forming apparatus according to claim 1, wherein the light emission control device does not execute the timing control when the image does not include the dither pattern.

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