JP5834842B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus including an exposure apparatus having an exposure head in which a plurality of light emitting points are arranged in the main scanning direction.

  In an electrophotographic image forming apparatus, an electrostatic latent image is formed on a photosensitive member by exposing the photosensitive member with a beam. As an exposure apparatus used for this exposure, in recent years, an exposure apparatus having an exposure head in which a plurality of light emitting points such as LEDs are arranged in the main scanning direction (direction orthogonal to the direction in which the paper is conveyed) may be used.

  In this type of exposure head, an LED array chip (light emitting chip) in which LED light emitting elements are finely arranged in a line by a semiconductor process in one semiconductor chip is arranged in the main scanning direction on a circuit board. More specifically, the light emitting chips are arranged in the main scanning direction on the circuit board, and the light emitting point at one end of one light emitting chip and the other end of the light emitting chip adjacent thereto (the end close to the one light emitting chip). In order to prevent the occurrence of a gap in the main scanning direction with respect to the light emitting point, adjacent LED chip arrays are arranged so as to be shifted in the sub scanning direction orthogonal to the main scanning direction. Since a plurality of light emitting chips are arranged in one exposure head in this way and adjacent light emitting chips are arranged shifted in the sub-scanning direction, the light emitting point of the LED is a straight line in the main scanning direction. Therefore, the points exposed on the photoconductor (exposure points) are aligned in a straight line (Patent Document 1). In order to perform such correction, generally, a reference line extending in the main scanning direction is set on the exposure head or the image forming apparatus main body, and the amount of deviation of the light emitting point from the reference line in the sub-scanning direction is measured. Is stored in the exposure apparatus or the image forming apparatus main body.

JP-A-11-0770697

  However, in order to store the amount of deviation of each light emitting point in the sub-scanning direction as a digital value, if a quotient obtained by simply dividing the amount of deviation by a quantization unit is a digitized (quantized) amount of deviation, a reference line Depending on the degree of deviation of the light emitting point from the light source, the amount of deviation in the sub-scanning direction between adjacent light emitting points may become unexpectedly large when light is emitted at the corrected timing. In other words, if the correction is performed successfully, the amount of deviation in the sub-scanning direction between adjacent exposure points can be considered to be less than half of the quantization unit. , There is a problem that the amount of deviation of the exposure point may be partially larger than half of the quantization unit.

  In particular, in an exposure apparatus in which a plurality of light emitting chips as described above are arranged, an error (displacement) in arrangement occurs not only in the sub-scanning direction but also in the main scanning direction between the chips. When a gap in the sub-scanning direction is formed between the light emitting point at one end of the light emitting chip and the light emitting point at the other end of the light emitting chip adjacent thereto, a gap in the main scanning direction is also added, so that a large image is formed. There may be gaps (unevenness).

  Therefore, the present invention has been made in view of the above background, and by improving the method for determining the correction amount of the light emission timing of the light emission point, the unevenness of the image based on the shift of the light emission point between the light emitting chips in the sub-scanning direction. The purpose is to suppress image quality and improve image quality.

  An image forming apparatus disclosed in the present specification includes an exposure apparatus having an exposure head in which a plurality of light emission points are arranged in the main scanning direction, and a photoreceptor on which an electrostatic latent image is formed by exposure by the exposure apparatus. An electrophotographic image forming apparatus comprising: a control device that controls light emission of the exposure device; and a storage device that stores a shift amount C of a light emission point with respect to a reference line extending in a main scanning direction. The exposure apparatus includes a plurality of light emitting chips having a plurality of light emitting points arranged in the main scanning direction, and the light emitting chips adjacent to each other in the main scanning direction are sub-scanned perpendicular to the main scanning direction. The control device is arranged so that the exposure points by the light emission points are arranged in a line in the main scanning direction on the photoconductor, and the timing for emitting each light emission point is quantized. As A A light emission timing determination unit that determines the light emission point, and an exposure head drive unit that emits light by shifting each light emission point from a reference time by a time corresponding to the correction amount. The provisional determination process for provisionally determining the correction amount A based on the quotient divided by D, the difference ΔC between the deviation amounts C of the two light emitting chips B, and the difference ΔA between the correction amounts A of the two light emitting points A to the quantization unit A value obtained by multiplying D is ΔE, and | ΔE−B | <first threshold condition 1 is satisfied between the light emitting point at one end of the nth light emitting chip and the light emitting point at the other end of the (n + 1) th light emitting chip. If not, an inter-chip correction amount adjustment process for determining the correction amount A by shifting the value of the correction amount A for the light emitting point at the other end of the (n + 1) th light emitting chip to satisfy the condition 1, and a correction amount The light emitting point at the other end of the (n + 1) th light emitting chip with A shifted And | ΔE−B | <second threshold condition 2 is not satisfied between the light emitting point adjacent to the light emitting point at the other end and the condition 2 is satisfied between the two light emitting points. In the case where the processing for shifting the correction value of the light emitting point is performed in the n + 1th light emitting chip and the condition 2 cannot be satisfied only in the n + 1th light emitting chip. In addition, the process of shifting the value of the correction amount of the light emitting point is performed as a correction amount readjustment process outside the chip performed within the (n + 2) th light emitting chip, and the correction amount readjustment process outside the chip is the (n + 1) th correction process. When the condition 2 is not satisfied in the inter-chip correction amount adjustment process executed for the (n + 2) th light-emitting chip and the inter-chip correction amount adjustment process for the (n + 1) th and n + 2th light-emitting chips, Realized for n + 2 light emitting chip Wherein the includes a correction amount re-adjusting process in the chip.

  In the image forming apparatus disclosed in this specification, it is determined whether or not the exposure point shift | ΔE−B | between the adjacent nth and n + 1th light emitting chips is larger than the first threshold value. The light emission point correction amount A is adjusted (correction amount adjustment processing between chips) so that the deviation | ΔE−B | of the exposure point is smaller than the first threshold value. For this reason, it is possible to reduce the deviation of the exposure point between the light emitting chips where the deviation of the exposure point is conspicuous, thereby suppressing the unevenness of the image and improving the image quality.

  In addition, as a result of the correction amount adjustment processing between the chips, there may be a portion where the deviation of the exposure point becomes large in the (n + 1) th light emitting chip. In the present embodiment, in the (n + 1) th light-emitting chip, a set of adjacent light-emitting points with a relatively small exposure point shift is searched for, and the correction amount of the light-emitting point in the portion where the shift is small is shifted to perform in-chip adjustment. Therefore, the deviation of the adjacent exposure points in the sub-scanning direction can be made inconspicuous and the image quality can be improved as a whole image (correction amount readjustment processing in the chip).

  Furthermore, if the correction amount readjustment within the chip cannot find a set of adjacent light emitting points with relatively small exposure point deviations, a correction amount readjustment process outside the chip is performed. Then, a set of adjacent light emitting points having a relatively small exposure point shift is searched, and adjustment is performed by shifting one correction amount of the light emitting points in a portion where the shift is small. For this reason, even when it is difficult to suppress the deviation of the exposure point in the sub-scanning direction only by adjusting the correction amount within the chip, it is possible to suppress the deviation of the exposure point in the sub-scanning direction. Therefore, the image quality can be improved (correction amount readjustment processing outside the chip).

In the image forming apparatus, the following is preferable.
A plurality of continuous light emitting point groups in the light emitting chip are defined as one light emitting point block, and light emitting points in the light emitting chip are divided into a plurality of light emitting point blocks, and the deviation amount is determined for each light emitting point block. One value is stored in the storage device, and the light emission point correction amount A is determined by the light emission timing determination unit as determination of the light emission point block correction amount A.

The light emission timing determining unit determines the correction amount A for each light emitting point of the (n + 1) th and subsequent light emitting chips when the correction amount readjustment processing outside the chip does not satisfy the condition 2; A batch adjustment process is performed in which the correction amount is uniformly shifted in the direction in which the correction amount is shifted with respect to the light emitting point at the other end.

The light emission timing determination unit executes the batch adjustment process in common for the exposure heads of the respective colors.

  According to the present invention, it is possible to suppress image unevenness due to a shift in the sub-scanning direction of light emitting points between light emitting chips.

1 is a cross-sectional view illustrating an overall configuration of a color printer as an example of an image forming apparatus according to a first exemplary embodiment. It is an enlarged view of an LED unit and a process cartridge. It is the figure which looked at the LED unit from the exposure surface side. It is an enlarged view which shows arrangement | positioning and the light emission point of the LED array chip arrange | positioned at the exposure surface of an LED unit. It is an enlarged view of the exposure surface of a LED unit explaining the deviation | shift amount of a light emission point. It is an enlarged view explaining the light emission point block of a LED array chip. It is a functional block diagram of a control device and an LED unit. It is a figure explaining the shift | offset | difference of light emission points. It is a figure explaining the case where the clearance gap between the exposure points after correction | amendment becomes comparatively large by quantization error. It is a figure which shows the positional relationship of a light emission point when the light emission timing of the light emission point of FIG. It is a figure explaining the correction amount readjustment processing in a chip. It is a figure explaining the correction amount readjustment process outside a chip | tip. It is a flowchart which shows the adjustment sequence of the correction amount A. It is a figure which shows the batch adjustment process of Embodiment 2. FIG. It is explanatory drawing explaining generation | occurrence | production of color misregistration. It is explanatory drawing which performs the batch adjustment process in common with respect to the exposure head of each color.

  <Embodiment 1>

A first embodiment will be described with reference to FIGS.
1. Overall Configuration of Color Printer As shown in FIG. 1, an electrophotographic color printer 1 as an example of an image forming apparatus of the present invention includes a paper supply unit 20 that supplies paper S in a main body housing 10, and a paper supply unit. An image forming unit 30 that forms an image on the paper S that has been formed, a paper discharge unit 90 that discharges the paper S on which an image has been formed, and a control device 100 that controls the operation of these units 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. In addition, the vertical direction toward the page is defined as the “vertical 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. The 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 as an example of an exposure device is provided on the lower surface.

  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 head 41 as an example of the exposure head in the left-right direction, and directly or indirectly support and position the photosensitive drum 53. The light emission of the LED head 41 is controlled by the control device 100. The photosensitive drum 53 is an example of a photosensitive member.

  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, a separation roller 24, and a separation pad 25.

  In the paper feed unit 20 configured in this way, the paper S in the paper feed tray 21 is separated one by one and sent upward, and passes through between the paper dust removal roller 26 and the pinch roller 27 in the process. After the powder is removed, the direction is changed backward through the conveyance path 28 and supplied to the image forming unit 30.

  The image forming unit 30 mainly includes four LED units 40, four process cartridges 50, a transfer unit 70, and a fixing unit 80.

  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 a layer thickness regulating blade 65. The developing unit 61 includes a toner storage chamber 66 that stores toner. Yes. 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 head 41 at the lower end is inserted into the exposure hole 55. Details of the LED head 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 arranged in parallel in a spaced manner in the front-rear direction, and a conveyance belt 73 formed of an endless belt is stretched between them. 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 head 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.

  In addition, the toner in the toner storage chamber 66 is supplied to the developing roller 63 by the rotation of the supply roller 64, and enters between the developing roller 63 and the layer thickness regulating blade 65 by the rotation of the developing roller 63 and has a constant thickness. It is carried on the developing roller 63 as a thin layer.

  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.

<Configuration of LED head>
The LED head 41 is a member in which a plurality of light emitting points are arranged in the main scanning direction (a direction orthogonal to the transport direction of the paper S, in the left-right direction in the present embodiment). As shown in FIG. 3, the LED head 41 has a plurality of LED array chips CHn (CH1 to CH20, where n is the number of the LED array chip) as an example of the light emitting chip on the downward exposure surface facing the photosensitive drum 53. An arranged circuit board CB is provided. Each LED array chip CHn has a fine LED element formed on the surface by a semiconductor process. In the present embodiment, 20 LED array chips CHn are arranged on the circuit board CB.

  In each LED array chip CHn, as shown in FIG. 4, light emitting points P are densely arranged in a line by LED elements in the main scanning direction. Each LED array chip CHn is provided with, for example, 256 light emitting points P in the main scanning direction. In manufacturing the LED array chip CHn, the light emitting point P cannot be formed up to the edge of the LED array chip CHn. Therefore, the LED array chips CHn are not arranged in a straight line in the main scanning direction, but adjacent LED array chips CHn are arranged so as to be shifted in the sub-scanning direction. As a result, the light emitting point at one end (right end) of the LED array chip CHn (for example, the light emitting point indicated by symbol P1 in FIG. 4) and the other end of the LED array chip CHn + 1 adjacent to the LED array chip CHn on one end side ( The leftmost light emission point (for example, the light emission point indicated by reference numeral P2 in FIG. 4) can be arranged so as to be shifted by one pitch in the positional relationship in the main scanning direction. In the present embodiment, adjacent LED array chips CHn are alternately shifted back and forth and are arranged in a zigzag pattern, but it is not always necessary to arrange them in a zigzag pattern. The three positions may be shifted so as to take one of the three positions. Further, the deviation in the sub-scanning direction of the light emitting chip referred to in the present invention is not limited to including both the intentional deviation and the assembly error as in the present embodiment, but includes the case of including only the assembly error. Including.

  As shown in FIG. 4 or FIG. 5, the LED array chip CHn on the circuit board CB is an odd-numbered LED array chip CHn arranged in a line on the front side, and the even-numbered LED array chip CHn is an odd-numbered LED array chip. They are shifted to the rear side so as to be arranged in a line at a fixed distance from CHn. However, when actually arranged, an assembly error occurs during manufacturing. Therefore, even-numbered LED array chips CHn cannot be arranged so that the light emitting points P are completely aligned, and are slightly inclined. Or shifted in the main scanning direction and the sub-scanning direction. The odd-numbered LED array chip CHn is also difficult to be accurately placed at a fixed distance from the even-numbered LED array chip CHn, and the distance varies, and the direction in which the light emitting points P are arranged also differs from the main scanning direction. It can be slightly diagonal.

  Therefore, in order to perform exposure on the photosensitive drum 53 in a straight line in the main scanning direction at these light emission points P, the light emission timing of each light emission point P is set in consideration of the arrangement error of the LED array chip CHn. It needs to be adjusted. Therefore, a shift amount C in the sub-scanning direction of each light emitting point P with respect to the reference line L extending in the main scanning direction is stored, and each light emitting point P is shifted from the reference time by a time corresponding to the shift amount C. By emitting light, accurate exposure is performed. This deviation amount C includes the deviation amount CX of each light emitting point P from the reference line L1 with the LED head 41 as a reference, and the deviation amount CY with respect to the reference position of the main body housing 10 (in this embodiment, two locations on the left and right ends). Therefore, the reference line L1 is connected to the reference position of the main body housing 10 (the straight line connecting the reference position of the main body shown in FIG. 5 as the reference line L of the main body). The shift amount C of each light emitting point P is determined by adding the shift amount CX from the reference line L1. The shift amount CX determined by the LED head 41 itself is measured for each LED head 41 and stored in the storage device 49 (see FIG. 7) of the LED head 41. The shift amount C is stored in the storage device 109 including an assembly error of the LED unit 40 with respect to the reference line L when the LED unit 40 is assembled to the main body of the color printer 1.

  In the present embodiment, the reference line L1 includes the leftmost light emitting point of the leftmost LED array chip CH1 and the rightmost light emitting point of the rightmost LED array chip CH19 among the chips arranged in the same front row as the LED array chip CH1. A straight line connecting the lines is defined as a reference line L1. That is, the reference line L1 is determined with reference to two light emitting points determined after the LED array chip CHn is arranged on the circuit board CB. However, the method of determining the reference line L1 is not limited to this method.

  Since each light emitting point P emits light at a different timing according to the deviation amount C as described above, this timing deviation is stored in the storage device as the correction amount A. The correction amount A can be stored in a storage device arranged at an arbitrary position in the color printer 1, and is stored in, for example, the storage device 109 in the control device 100 shown in the block diagram of FIG. .

  The control device 100 includes a light emission timing determination unit 110, an LED unit drive unit 120, and a storage device 109 as functional units related to the light emission control of the LED unit 40. The control device 100 includes a CPU, a ROM, a RAM, and an input / output interface, and implements each unit by executing a program stored in advance.

  The LED unit driving unit 120 is an example of an exposure head driving unit, and is a unit that causes each light emitting point P to emit light by shifting from the reference time by a time corresponding to the correction amount A. In this embodiment, the reference time is a time when a light emitting point at one end defining the reference line L1 is caused to emit light.

  The storage device 109 stores the above-described deviation amount C and deviation amount CY in addition to various constants, parameters, print data, and the like necessary for the overall operation of the color printer 1. The deviation amount C is calculated in consideration of the deviation amount CY to the deviation amount CX stored in the storage device 49 of the LED unit 40. Since the shift amount CY slightly changes each time the cover 2 is opened and closed, the reference line L1 is defined when performing a known patch test conventionally performed for color shift correction after the cover 2 is closed. It can be obtained by emitting light emission points P at substantially both ends and performing an exposure test.

2. Process Regarding Adjustment of Correction A The light emission timing determination unit 110 executes the following four processes.
(1) Temporary determination processing for provisionally determining correction amount A (2) Inter-chip correction amount adjustment processing for adjusting correction amount between chips after provisional determination of correction amount A (3) After inter-chip correction amount adjustment processing Correction amount readjustment processing within the chip to readjust the correction amount within the chip (4) After correction amount readjustment processing within the chip, the correction amount readjustment outside the chip is readjusted after the correction amount readjustment processing inside the chip Adjustment process

<Provisional determination of correction amount A>
The correction amount A is provisionally determined based on the quotient obtained by dividing the shift amount C by the quantization unit D. For example, when the deviation amount C is “45” μm and the quantization unit D is “10.6” μm, the quotient is “4”. In this case, the correction amount A is “4”. .

  The correction amount A may be determined on a one-to-one basis for each light emitting point P, and may be stored. However, since the number of light emitting points P is very large, a plurality of light emitting points P are grouped into one group. The handling process is simpler. Specifically, as shown in FIG. 6, one LED array chip CHn may be divided into a plurality of groups in the main scanning direction. As an example, in the present embodiment, 256 light emitting points P included in one LED array chip CHn are divided into eight groups (that is, 32 each), and each is divided into light emitting point blocks BLn_i (i = 1 to 8). And

  Here, “n” corresponds to the number n of the LED array chip CHn, and “i” represents the number of the light emitting point block in the LED array chip CHn. As described above, since the arrangement of the light emitting points P in each LED array chip CHn is accurate, there is little deviation in the sub-scanning direction, and even if the 32 light emitting points P are handled together, Since the length in the main scanning direction is small, the shift in the sub scanning direction due to the inclination of the LED array chip CHn is also small.

  Therefore, even if a plurality of light emitting points P are simultaneously emitted, there is no substantial influence. Therefore, one correction amount A is assigned to each light emitting point block BLn_i, and each light emitting point block BLn_i uses this correction amount A. It is supposed to emit light simultaneously by applying. That is, in the present embodiment, a plurality of continuous light emitting point groups in the LED array chip CHn are defined as one light emitting point block BLn_i, and light emitting points in the LED array chip CHn are divided into a plurality of light emitting point blocks BLn_i. As the correction amount A, one value is stored in the storage device for each light emission point block BLn_i.

<Description of correction error due to quantization>
As shown in FIG. 8, the LED array chips CHn and CHn + 1 arranged on the circuit board CB may be arranged so that adjacent ones are shifted in the sub-scanning direction. Note that the fringes by broken lines in the drawing are lines drawn at equal intervals with the pitch of the quantization unit D with reference to the reference line L, and the light emission point P is sub-scanned during exposure according to the quantized correction amount A. It is displayed so that the pitch for emitting light by shifting in the direction can be visually understood. In this specification, for the sake of convenience, the stripes indicated by broken lines are referred to as “quantization unit stripes”.

  As an example, the quantization unit D is 10.6 μm, the right emission point P1 of the eighth emission point block BLn_8 of the nth LED array chip CHn, and the first emission point block of the n + 1th LED array chip CHn + 1. Assume that the difference ΔC (= | C1−C2 |) in the amount of deviation in the sub-scanning direction from the leftmost light emitting point P2 of BLn + 1_1 is 55 μm.

  Then, the exposure point can be shifted by a multiple of 10.6 μm by shifting the light emission timings of the two light emission points P1 and P2 according to the quantized correction amount A. On the other hand, since the remainder obtained by dividing “55” which is the difference ΔC of the deviation amount C by “10.6” is 2, the deviation of the exposure point after correction is expected to be about 2 μm.

  However, when the centers of the light emission points P1 and P2 are in the positional relationship of FIG. 8 with respect to the quantization unit stripe, the pixel position on the quantization unit stripe (quantized position indicated by a square) is set. On the other hand, if the centers of the light emission points P1 and P2 are simply assigned, the corrected exposure point may be larger than 2 μm. In the positional relationship of FIG. 8, the light emitting point P1 is shifted 1 μm backward from the boundary line of the quantization unit stripe, and the light emitting point P2 is shifted forward 1 μm from the boundary line of the quantization unit stripe. At this time, since the light emitting points P1 and P2 are shifted by 6 pixels (6 units) as the number of pixels determined by the quantization unit stripe, the correction amount A is set to 6, and the light emitting point block BLn + 1_1 is 6 units at the time of exposure. Shift backward by a minute (it may be considered that the light emission point block BLn_8 is shifted forward by 6 units). Then, as shown in FIG. 9, the light emission point P1 and the light emission point P2 fall within the common stripe of the quantization unit stripe, but the light emission point P1 and the light emission point P2 in the stripe are in the sub-scanning direction. The amount of deviation is 8.6 μm (= 10.6 μm-1 μm-1 μm). That is, it becomes larger than the expected deviation of 2 μm.

<Inter-chip correction amount adjustment processing>
In this case, if the light emitting point block BLn + 1_1 is not shifted backward by 6 units but shifted by 5 units, as shown in FIG. 10, the amount of deviation in the sub-scanning direction between the light emitting point P1 and the light emitting point P2 becomes 2 μm. . Therefore, in the present embodiment, the gap between the light emitting points P between adjacent LED array chips is increased by performing the next inter-chip correction amount adjustment process and adjusting the correction amount A by “1”. Suppress.

In the correction amount adjustment processing between chips (see FIGS. 5 and 8), “B” is calculated based on the following equation (1), and “ΔE” is calculated based on the following equation (2). calculate.
B = | ΔC | = | Cn_8−Cn + 1_1 | (1) Equation ΔE = | ΔA | × D = | An_8−An + 1_1 | × D (2) formula

  Cn_8 is a shift amount C of the light emitting point (light emitting point P1 in FIG. 8) located at the right end of the eighth light emitting point block BLn_8 located at the right end (one end) of the nth LED array chip CHn. On the other hand, Cn + 1_1 is the shift amount C of the light emitting point (light emitting point P2 in FIG. 8) located at the left end of the first light emitting point block BLn + 1 located at the left end (the other end) of the (n + 1) th LED array chip CHn + 1. .

  An_8 is the correction amount of the eighth light emitting point block BLn_8 located at the right end (one end) of the nth LED array chip CHn, and An + 1_1 is 1 located at the left end (the other end) of the n + 1th LED array chip CHn + 1. This is the correction amount of the light emitting point block BLn + 1_1. D is a quantization unit.

Then, from the results of the expressions (1) and (2), the condition of the following expression (3) is determined.
| ΔE−B | <D / 2 (3) Note that “D / 2” is an example of the “first threshold” in the present invention.

  As a result of the determination, if the expression (3) is not satisfied, the correction amount An + 1_1 is shifted by “1” for the first light emitting point block BLn + 1_1 of the (n + 1) th LED array chip CHn + 1 so that the expression (3) is satisfied. To. Whether the correction amount A is shifted to the plus side or the minus side may be determined by calculating both the case where the correction amount A is added and the case where it is subtracted.

  By performing this processing, for example, in the case of FIG. 9, the correction amount of the first light emitting point block BLn + 1_1 of the n + 1th LED array chip is shifted to the front side in the sub-scanning direction (upper side in the drawing). 6 "is adjusted to" 5 ". As a result, as shown in FIG. 10, the deviation of the exposure point between the nth and n + 1th LED array chips, that is, the amount of deviation of the light emitting point P1 and the light emitting point P2 in the sub-scanning direction is improved to 2 μm.

<In-chip correction amount readjustment process>
The first stage in FIG. 11 shows the LED array chips CHn and CHn + 1 shifted by several units, and the second stage in FIG. 11 temporarily determines the correction amount A for each light-emitting point block BLn_i and between the chips. As a result of this correction amount adjustment processing, the light emitting point P1 located at the right end of the eighth light emitting point block BLn_8 of the LED array chip CHn, and the left end of the first light emitting point block BLn + 1_1 of the LED array chip CHn + 1 adjacent thereto. This shows a state in which the amount of deviation of the exposure point of the light emitting point P2 located at is small.

  However, as a result of this inter-chip adjustment, as shown in the second row of FIG. 11, the light-emitting point block BLn + 1_1 in which the correction amount A is adjusted by the inter-chip correction amount adjustment processing, and the light-emitting point block adjacent to the right side thereof Between BLn + 1_2, the deviation of the exposure point, that is, the deviation of the exposure point between the light emission point P3 and the light emission point P4 is large (indicated by a circle in the figure).

  The correction amount readjustment processing within the chip is performed by adjusting the correction amount adjustment processing between the chips, and the deviation of the exposure point that has become large in the (n + 1) th LED array chip is readjusted at a portion where the deviation is relatively small in the chip. It is processing to do.

  Specifically, the “N + 1” th LED array chip CHn + 1 so that “B” obtained from the following equation (4) and “ΔE” obtained from the following equation (5) satisfy the following equation (6): For the second light emitting point block BLn + 1_2, the correction amount A is shifted.

B = ΔC = | Cn + 1_i−Cn + 1_i + 1 | (4) equation ΔE = | An + 1_i−An + 1_i + 1 | × D (5) equation | ΔE−Bn | <D (6) Note that “D” is an example of the “second threshold value” in the present invention.

  Note that Cn + 1_i is the amount of deviation C of the light emitting point located at the end of the “i” th light emitting point block of the LED array chip n + 1, and Cn + 1_i + 1 is the “i + 1” th of the LED array chip CHn + 1. This is the amount of deviation C of the light emitting point located at the end of the light emitting point block.

  This correction amount readjustment processing in the chip satisfies the condition | ΔE−B | <D between the light emission point block whose readjustment amount has been readjusted and the light emission point block which does not readjust the correction amount adjacent thereto. The process is repeated until the number “i” is updated.

  The third row in FIG. 11 is an example in which the correction amount readjustment process in the chip is completed once, that is, only the correction amount A of the second light emitting point block BLn + 1_2 in the LED array chip n + 1 is readjusted. In this example, the boundary between the place where the correction amount A is readjusted and the place where the correction amount A is not readjusted is between the second light-emitting point block BLn + 1_2 and the third light-emitting point block BLn + 1_3.

  In the third row of FIG. 11, the correction amount of the second light emission point block BLn + 1_2 is adjusted to “1” on the front side in the sub-scanning direction (upward in the figure) with respect to the correction amount at the time of adjusting the correction amount between chips. On the other hand, as a result of maintaining the correction amount of the third light emission point block BLn + 3 at the correction amount at the time of adjusting the correction amount between chips, the exposure point between the light emission points P3 and P4 is compared with the second stage of FIG. The deviation is small.

  By performing the correction amount readjustment process in the chip in this way, exposure of the two light emitting points P3 and P4 located between the first and second light emitting point blocks BLn + 1_1 and BLn + 1_2 in the LED array chip CHn + 1 is performed. The point shift can be reduced. Further, since a light emitting point block with a small exposure point deviation is selected as a boundary between a place where the correction amount A is adjusted and a place where the correction amount A is not adjusted, the deviation of the exposure point does not become D or more between the light emitting point blocks serving as the boundary. .

  For example, the correction amount readjustment process in the chip is completed three times, that is, the correction amount A of the second to fourth light emitting point blocks BLn + 1_2 to BLn + 1_4 of the “n + 1” -th LED array chip n + 1 is re-read. When adjusted, the boundary between the place where the correction amount A is adjusted and the place where the correction amount A is not adjusted is between the fourth light-emitting point block BLn + 1_4 and the fifth light-emitting point block BLn + 1_5, and the second to fourth light-emitting point blocks BL. Is corrected by “1” in the same direction, and the correction amount of the fifth and subsequent light-emitting point blocks BL is maintained at the correction amount A when adjusting the correction amount between chips.

<Correction amount readjustment process outside the chip>
The reason why the correction amount readjustment processing in the chip is established is that there is a boundary between the place where the correction amount A is readjusted and the place where the readjustment amount is not readjusted in the “n + 1” -th LED array chip CHn + 1. That is, when there is a set of light-emitting point blocks with a small deviation of the exposure point, and when the correction amount is adjusted for one of the light-emitting point blocks, the correction point adjacent to the light-emitting point block that has not readjusted the correction amount Therefore, it is necessary to satisfy the condition of | ΔE−B | <D.

  On the other hand, as shown in the first row of FIG. 12, when the inclination of the “n + 1” -th LED array chip CH that is the object of readjustment processing is large, naturally, the inclination of each light-emitting block BLn + 1 becomes large. . In this case, the LED array chip CHn + 1 does not have a combination of light emitting point blocks with small exposure point deviation, and when the correction amount is readjusted for any one of the light emitting point blocks, the correction amount adjacent thereto is set. There is a possibility that the deviation of the exposure point becomes large with respect to the light emitting point block which has not been readjusted. That is, the condition | ΔE−B | <D may not be satisfied.

  Therefore, in the correction amount readjustment process outside the chip, the deviation of the exposure point cannot be absorbed in the “n + 1” -th LED array chip CHn + 1, that is, the condition of | ΔE−B | <D cannot be satisfied. In addition, the object of readjustment of the correction amount is extended outside the chip, that is, by extending the “n + 1” -th LED array chip CH to the “n + 2” -th LED array chip CH, it is intended to suppress the deviation of the exposure point. To do.

  Specifically, the above-described inter-chip correction amount for the eighth light emitting point block BLn + 1_8 of the “n + 1” th LED array chip CHn + 1 and the first light emitting point block BLn + 2_1 of the “n + 2” th LED array chip CHn + 2. Perform the adjustment process. Then, by executing the inter-chip correction amount adjustment process, a condition of | ΔE−B | <D between the first light emission point block BLn + 2_1 and the second light emission point block BLn + 2_2 of the “n + 2” th LED array chip CHn + 2 Is not satisfied, the in-chip correction amount adjustment process described above is performed on the “n + 2” -th LED array chip CHn + 2. In other words, the correction amount readjustment process outside the chip is a process of updating the number “n” of the LED array chip CH, and performing an interchip correction amount adjustment process and an in-chip correction amount readjustment process. .

  As described above, by expanding the target for readjustment of the correction amount from the inside of the chip to the outside of the chip, it is possible to absorb the deviation of the exposure point at the expansion destination, and a new part with a large deviation of the exposure point Therefore, it is possible to reduce the shift of the exposure point caused by the inter-chip correction amount adjustment process, that is, the shift of the exposure point between the light emission point P3 and the light emission point P4.

  In FIG. 12, in the “n + 2” -th LED array chip CHn + 2, the first and second light-emitting point blocks BLn + 2_1 and BLn + 2_2 are defined as a boundary between a place where the correction amount is readjusted and a place where the readjustment is not readjusted. This is an example in which the correction values A of the eight light emitting point blocks BLn BLn + 1_2 to BLn + 1_8 and BLn + 2_1 located on the left side in the drawing from the boundary position are collectively adjusted to “1” in the upward direction.

3. Correction A Adjustment Sequence Next, a correction amount A adjustment sequence (FIG. 13) executed by the light emission timing determination unit 110 of the control device 100 will be described. First, in S10, an exposure test is performed on the condition that the cover 2 is closed, the shift amount CY is measured, and a process of specifying the shift amount Cn_i of the light emission point block BLn_i with respect to the main body housing 10 (main body) is performed. . This deviation amount Cn_i is stored in the storage device 109.

<Provisional determination of correction amount A>
In subsequent S20, the light emission timing determination unit 110 executes a process of temporarily determining the correction amount An_i of each light emission point block BLn_i. Specifically, the deviation amount Cn_i of the light emitting point block BLn_i calculated in S10 is divided by the quantization unit D, and the obtained quotient is provisionally determined as the correction amount An_i.

  Next, in S30, the light emission timing determination unit 110 performs the following calculation. That is, B = | Cn_8−Cn + 1_1 | and ΔE = | An_8− for the light emitting point block BLn_8 of the “n” th LED array chip CHn and the light emitting point block BLn + 1_1 of the “n + 1” th LED array chip CHn + 1. An + 1_1 | × D is calculated. Since n = 1 in the first calculation, the eighth light emission point block of the first LED array chip CH1 and the first light emission point block of the second LED array chip CH2 adjacent thereto are targeted. The value of “B” and the value of “ΔE” are calculated.

  Thereafter, the process proceeds to S40, and the light emission timing determination unit 110 determines whether or not the condition 1 of | ΔE−B | <D / 2 is satisfied. If | ΔE−B | is smaller than D / 2 (S40, Yes), the value of “n” is incremented by 1, and the process proceeds to S30 again. As a result, since “n” = 2 is set next, the eighth light emitting point block of the second LED array chip CH2 and the first light emitting point block of the third LED array chip CH3 adjacent thereto are targeted. As a result, the value of “B” and the value of “ΔE” are calculated.

  Thereafter, the process proceeds to S40, and the light emission timing determination unit 110 determines whether or not the condition 1 of | ΔE−B | <D / 2 is satisfied. If | ΔE−B | is smaller than D / 2 (S40, Yes), the value of “n” is incremented by 1, and the process proceeds to S30 again. In the determination process in S40, it is determined whether or not the next inter-chip correction amount adjustment process is necessary.

<Inter-chip correction amount adjustment processing>
When | ΔE−B | is larger than D / 2 (S40, No), the process proceeds to S50, and the inter-chip correction amount adjustment processing is performed. That is, the correction amount An + 1_1 of the first light-emitting point block BLn + 1_1 of the “n + 1” th LED array chip CHn + 1 is adjusted by “1” so that | ΔE−B | satisfies D / 2.

  And if the process of S50 is performed, it will transfer to S60 after that. In S60, the light emission timing determination unit 110 calculates “B” for the LED array chip CHn + 1 based on the equation (4), and calculates “ΔE” according to the equation (5).

  Since “i” = 1 in the first calculation, the value of “B” and “ΔE” are set for the first light-emitting point block BLn + 1_1 of the LED array chip CHn + 1 and the second light-emitting point block BLn + 1_2 adjacent thereto. Is calculated.

  In S70, the light emission timing determination unit 110 determines whether the condition 2 of | ΔE−B | <D is satisfied based on the calculation result of S60. The determination process (initial determination) in S70 is a process of checking the amount of exposure point deviation between the light emitting point blocks after adjusting the correction amount between blocks, and checking the deviation of the exposure points of the light emitting point block BLn + 1_1 and the light emitting point block BLn + 1_2. Is done.

  When the exposure point deviation is small, that is, when the condition of S70 is satisfied, it is not necessary to perform the in-chip correction amount readjustment process. Therefore, after performing the process of adding “1” to the value of n, the process returns to S30. Transition.

<In-chip correction amount readjustment process>
On the other hand, when the deviation of the exposure points is large, that is, when the condition of S70 is not satisfied (S70, No), the correction amount readjustment processing within the chip is performed by the light emission timing determination unit 110. Specifically, in S80, a process of adjusting the correction amount An + 1_i + 1 of the “i + 1” th light emission point block by “1” so as to satisfy the condition 2 of | ΔE−B | <D is performed. Here, the correction amount An + 1_2 of the second light emitting point BLn + 1_2 is adjusted by “1”.

  Thereafter, in S90, a process of adding “1” to “1” is performed, and in subsequent S100, it is determined whether “i” has become larger than the upper limit value (here, “7”). If “i” is not larger than the upper limit value, the process returns to S60 and the values of “B” and “ΔE” are calculated again. Therefore, here, the value of “B” and the value of “ΔE” are recalculated for the second light emitting point block BLn + 1_2 of the LED array chip CHn + 1 and the third light emitting point block BLn + 1_3 adjacent thereto.

  Thereafter, in the second determination of S70, that is, the determination of “i = 2”, does the condition 2 of | ΔE−B | <D be satisfied for the second and third light-emitting point block BLn + 1_2 and light-emitting point block BLn + 1_3? Processing for determining whether or not is performed. Thereby, the deviation of the exposure point between the light emission point block BLn + 1_2 and the light emission point block BLn + 1_3 after the correction amount readjustment process is checked.

  When the exposure point deviation is small, that is, when the condition of S70 is satisfied, the correction amount readjustment process in the chip ends there, and after performing the process of adding “1” to the value of n, the process returns to S30. Transition.

  On the other hand, when the deviation of the exposure point is large, that is, when the condition of S70 is not satisfied (S70, No), the process returns to S80 and the correction amount readjustment process is performed again. That is, a process of adjusting the correction amount An + 1_i + 1 of the “i + 1” th light emitting point block by “1” so as to satisfy the condition 2 of | ΔE−B | <D is performed. Here, the correction amount An + 1_3 of the third light emitting point BLn + 1_3 is adjusted by “1”.

  As described above, in S70, the light-emitting point blocks BL in the “n + 1” -th LED array chip CHn + 1 are sequentially arranged in ascending order of the number “i” until the condition 2 | ΔE−B | <D is satisfied. And the correction amount A of each light-emitting point block BL is readjusted. Then, the process is completed when the condition of S70 is satisfied.

<Correction amount readjustment process outside the chip>
Next, when “i” reaches the upper limit value without satisfying the condition of S70, that is, in S80 (i = 7), | ΔE−B | <D between the seventh and eighth light-emitting point blocks. After performing the process of adjusting the correction amount An + 1_8 of the eighth light emission point block by “1” so as to satisfy the condition 2, the process proceeds to S90, and the value of “i” is added from “7” to “8” In this case, since “i” exceeds the upper limit “7”, YES is determined in S100.

  If YES is determined in S100, then, in S110, a process of determining whether “n” has reached the upper limit value is performed. If the value of “n” has not reached the upper limit value, the value of “n” is updated and the process returns to S30 again.

  Thereafter, in S30 to S50, an inter-chip correction process is performed on the “n + 1” -th and “n + 2” -th LED array chips. Specifically, at S30, the eighth light emission point block BLn + 1_8 of the “n + 1” th LED array chip CHn + 1 and the first light emission point block BLn + 2_1 of the “n + 2” th LED array chip CHn + 2 are processed as B. = | Cn + 1_8−Cn + 2_1 | and ΔE = | An + 1_8−An + 2_1 | × D are calculated.

  Thereafter, the process proceeds to S40, and the light emission timing determination unit 110 determines whether or not the condition 1 of | ΔE−B | <D / 2 is satisfied. When | ΔE−B | is larger than D / 2 (S40, No), the process proceeds to S50, and the inter-chip correction amount adjustment processing is performed. That is, the correction amount An + 2_1 of the first light-emitting point block BLn + 2_1 of the “n + 2” -th LED array chip CHn + 2 is adjusted by “1” so that | ΔE−B | satisfies D / 2.

  And if the process of S50 is performed, it will transfer to S60 after that. In S60, the light emission timing determination unit 110 calculates “B” for the LED array chip CHn + 2 based on the equation (4), and calculates “ΔE” according to the equation (5).

  Here, since “i” = 1, the value of “B” and the value of “ΔE” are targeted for the first light emission point block BLn + 2_1 of the LED array chip CHn + 2 and the second light emission point block BLn + 2_2 adjacent thereto. Is calculated.

  In S70, the light emission timing determination unit 110 determines whether or not the condition 2 | ΔE−B | <D is satisfied based on the calculation result in S60. The determination process (initial determination) in S70 is a process of checking the amount of exposure point deviation between light emitting point blocks after adjusting the correction amount between blocks. Here, the exposure points of the light emitting point block BLn + 2_1 and the light emitting point block BLn + 2_2 are checked. The deviation is checked.

  When the deviation of the exposure point is small, that is, when the condition of S70 is satisfied, it is not necessary to perform the in-chip correction amount readjustment process for the n + 2nd LED array chip CHn + 2, so that correction outside the chip is performed at this time. The amount readjustment process ends.

  On the other hand, when the exposure point deviation is large, that is, when the condition of S70 is not satisfied (S70, No), the correction amount readjustment process in the chip is performed for the n + 2nd LED array chip CHn + 2. Specifically, in S80, a process of adjusting the correction amount An + 2_i + 1 of the “i + 1” th light emission point block by “1” so as to satisfy the condition 2 of | ΔE−B | <D is performed. Here, the correction amount An + 2_2 of the second light emitting point BLn + 2_2 is adjusted by “1”.

  Thereafter, in S90, a process of adding “1” to “1” is performed, and in subsequent S100, it is determined whether “i” has become larger than the upper limit value (here, “7”). If “i” is not larger than the upper limit value, the process returns to S60 and the values of “B” and “ΔE” are calculated again. Accordingly, here, the value of “B” and the value of “ΔE” are recalculated for the second light emitting point block BLn + 2_2 of the LED array chip CHn + 2 and the third light emitting point block BLn + 2_3 adjacent thereto.

  Thereafter, in the second determination of S70, that is, the determination of “i = 2”, does the condition 2 of | ΔE−B | <D be satisfied for the second and third light-emitting point block BLn + 2_2 and light-emitting point block BLn + 2_3? Processing for determining whether or not is performed. Thereby, the deviation of the exposure points of the light emission point block BLn + 2_2 and the light emission point block BLn + 2_3 after the correction amount readjustment process is checked.

  When the exposure point shift is large, that is, when the condition of S70 is not satisfied (S70, No), the process proceeds to S80 and the correction amount readjustment process is performed again. That is, a process of adjusting the correction amount An + 2_i + 1 of the “i + 1” -th light emitting point block by “1” so as to satisfy the condition 2 of | ΔE−B | <D is performed. Here, the correction amount An + 2_3 of the third light emitting point BLn + 2_3 is adjusted by “1”.

  As described above, in S70, until the condition 2 | ΔE−B | <D is satisfied, the light emitting point blocks BL in the “n + 2” -th LED array chip CHn + 2 are sequentially arranged in ascending order of the number “i”. And the correction amount A of each light-emitting point block BL is readjusted. Then, the process is completed when the condition of S70 is satisfied.

  FIG. 12 is an example in which the condition 2 of | ΔE−B | <D is satisfied in S70 when the correction amount A is readjusted for the first light emission point block BLn + 2_1 of the “n + 2” -th LED array chip CHn + 2. is there. In this case, as shown in the third row in FIG. 12, among the “n + 2” -th LED array chip CHn + 2, the correction amount is between the first light-emitting point block BLn + 2_1 and the second light-emitting point block BLn + 2_2. The boundary between the readjustment place and the place where no readjustment is made, and the correction values of the eight light emitting point blocks BL of BLn + 1_2 to BLn + 1_8 and BLn + 2_1 located on the left side of the figure from the border position are collectively adjusted by “1”. It will be.

  By performing the correction amount readjustment process outside the chip, the exposure point shift between the light-emitting blocks caused by the inter-chip correction amount adjustment process, for example, FIG. 11, the shift of the exposure points P3 and P4 between the light emission block BLn + 1_1 and the light emission block BLn + 1_2 shown in the second stage can be reduced.

  After the correction amount readjustment process outside the chip is completed (S70: after YES determination), a process of adding “1” to the value of n is performed, and then the process proceeds to S30. The processing after S30 is advanced for the array chip CH.

  As described above, according to the color printer 1 of the present embodiment, it is determined whether or not the deviation of the exposure point between adjacent LED array chips CH is larger than half of the quantization unit D. Since the correction amount A is adjusted (inter-chip correction amount adjustment process) so that the deviation of the exposure point is smaller than half of the quantization unit D, the deviation of the exposure point between the LED array chips where the deviation of the exposure point is easily noticeable. By reducing the size, unevenness of the image can be suppressed and the image quality can be improved.

  Further, as a result of performing the inter-chip correction amount adjustment processing for the nth and n + 1th LED array chips, there may be a portion where the deviation of the exposure point becomes large in the n + 1th LED array chip CHn + 1. In this regard, in the present embodiment, the n + 1-th LED array chip CHn + 1 is searched for a pair of adjacent light-emitting point blocks having a relatively small exposure point shift, and the correction amount A of the light-emitting point block in a portion where the shift is small. Is shifted so as to satisfy the condition 2 of | ΔE−B | <D to absorb the deviation of the exposure point, so that the deviation of the adjacent exposure point in the sub-scanning direction becomes inconspicuous and the image quality is improved as the entire image. (Correction amount readjustment processing in the chip).

  Furthermore, when the correction amount readjustment within the chip cannot find a set of adjacent light emitting point blocks with a relatively small exposure point shift, a correction amount readjustment process outside the chip is performed. Thus, a set of adjacent light emitting point blocks having a relatively small deviation of the exposure point is searched, and the correction amount A of the light emitting point block of the portion where the deviation is small is set to the condition 1 of | ΔE−B | <D / 2 or | ΔE The shift of the exposure point is absorbed by shifting “1” so that the condition 2 of −B | <D is satisfied. For this reason, even when it is difficult to suppress the deviation of the exposure point in the sub-scanning direction only by adjusting the correction amount within the chip, it is possible to suppress the deviation of the exposure point in the sub-scanning direction. Therefore, the image quality can be improved (correction amount readjustment processing outside the chip).

<Embodiment 2>
Next, Embodiment 2 will be described with reference to FIGS.
In the first embodiment, correction amount readjustment processing outside the chip is performed under certain conditions. That is, when the correction amount of the light emitting point block in the “n + 1” -th LED array chip CH cannot be satisfied by satisfying the condition 2 of | ΔE−B | <D, the correction amount is readjusted. The target to be corrected is expanded to the “n + 2” -th LED array chip CH, and the light emission point block is corrected so as to satisfy the condition 1 of | ΔE−B | <D / 2 and the condition 2 of | ΔE−B | <D. By shifting the amount A, the deviation of the exposure point was suppressed.

  However, for example, as shown in the first stage of FIG. 14, when the circuit board CB is attached to the printer in a tilted state, the light emitting blocks BL in each LED array chip CH have a large tilt. Become. For this reason, there is no combination of light emitting point blocks BL with small deviation of the exposure point, and even if correction amount readjustment processing is performed outside the chip, the condition 1 of | ΔE−B | <D / 2 or | ΔE− In some cases, the condition 2 of B | <D cannot be satisfied.

  In the second embodiment, even when correction amount readjustment processing outside the chip is performed, the condition 1 of | ΔE−B | <D / 2 or the condition 2 of | ΔE−B | <D cannot be satisfied. In addition, batch adjustment processing is performed in which the correction amount A of each light emitting point of the “n + 1” and subsequent light emitting chips is shifted by the same amount in the direction in which the correction value is shifted in the inter-chip correction amount adjustment processing.

  For example, as shown in the second row of FIG. 14, in the inter-chip correction amount adjustment process, the correction amount of the first light-emitting point block BLn + 1_1 corresponding to the left end of the “n + 1” -th LED array chip CH is set in the sub-scanning direction. When “1” is adjusted to the upper side in the figure corresponding to the front side, the correction amount of all the light emitting point blocks BL positioned on the right side of the first light emitting point block BLn + 1_1 is uniformly “1” on the upper side in the figure. adjust. In the example of FIG. 14, as shown in the third row in the figure, the correction amounts of all the light emitting point blocks BL from BLn + 1_2 to BLn + 2_8 are uniformly adjusted to “1” on the upper side in the figure. If there is an LED array chip CH of “n + 3” or “n + 4”, the correction amount for these light-emitting point blocks BL is also uniformly adjusted to “1” on the upper side in the drawing.

  In this way, when the deviation of the exposure point in the sub-scanning direction between the “n” -th and “n + 1” -th LED array chips (specifically, between BLn_8 and BLn + 1_1) is large, a new exposure is performed. The shift can be suppressed without creating a place where the shift of the point is large.

  On the other hand, when the batch adjustment process is performed as described above, when exposure is performed on the photosensitive drum 53 in the main scanning direction, the positions of both ends (left end and right end) of the exposure line are changed to the sub positions as shown in FIG. It will shift in the scanning direction.

  In a color printer having four LED heads corresponding to four colors, when such exposure line misalignment occurs only in some LED heads, as shown in the lower part of FIG. There may be a gap in the overlap. In FIG. 15 and FIG. 16, B, Y, M, and C indicate black, yellow, magenta, and C exposure lines, respectively.

  Therefore, when performing the batch adjustment process, it is preferable to execute the batch adjustment process in common for the LED heads 41 of the respective colors. For example, with respect to the black LED head 41, as shown in FIG. 14, correction of all the light emitting point blocks BL positioned on the right side when viewed from the first light emitting point block BLn + 1_1 of the “n + 1” th LED array chip CH. It is assumed that the amount is uniformly adjusted to the upper side in the figure.

  In this case, for the remaining three color LED heads 41, as in the case of the black LED head 41, all the light emitting points located on the right side when viewed from the first light emitting point block BLn + 1_1 of the “n + 1” th LED array chip CH. The correction amount of the block BL is uniformly adjusted to the upper side in the figure. In this way, as shown in FIG. 16, it is possible to suppress the occurrence of deviation in color overlap at the end of the line.

<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, a plurality of light emission points are set as one light emission point block, and the correction amount A is set for each light emission point block. However, even if the correction amount A is set for each light emission point, Good. The storage device that stores the correction amount A and the shift amounts CX, CY, and C can be provided in any member of the image forming apparatus, and these may be stored in a distributed manner.

(2) In the above embodiment, the shift amount CY is measured every time the cover 2 is closed. However, the shift amount CY may be measured every time printing is started. Further, if the LED unit 40 is not fixed to a movable member such as the cover 2 but is once fixed to a member whose position does not change once the image forming apparatus is assembled, the deviation amount CY is measured. Is not necessary, and the shift amount C may be determined based on a reference line determined based on the LED unit 40.

(3) In the above embodiment, the reference line L1 of the LED unit 40 is defined as a straight line connecting the leftmost light emitting point P of the LED array chip CH1 and the rightmost light emitting point P of the LED array chip CH19. The method of determining the reference line of the unit 40 is not limited to this.

(4) In the above embodiment, the light emitting chip is realized by using a plurality of LED elements as light emitting points, but light emitting elements other than LEDs can also be used.

(5) In the above embodiment, the photosensitive drum 53 is shown as an example of the photosensitive member. However, the photosensitive member may have a belt shape.

(6) In the above embodiment, the color printer 1 has been described as an example of the image forming apparatus. However, the present invention can also be applied to a monochrome printer, a copying machine, a multifunction machine, and the like.

(7) In the embodiment described above, the first threshold value that is the determination value of Condition 1 is set to “D / 2” in the inter-chip correction amount adjustment process (step S40 in FIG. 13). Further, in the correction amount readjustment processing in the chip, the second threshold value that is the determination value of condition 2 is set to “D” (step S70 in FIG. 13). The first threshold and the second threshold are not limited to “D / 2” or “D” exemplified in the embodiment, and may be set in relation to image quality. For example, when the required image quality is high, the first threshold or the second threshold is set slightly smaller than “D / 2” or “D”, and vice versa, the first threshold or the second threshold is set to “ It may be set slightly larger than “D / 2” or “D”.

1. Color printer (an example of the “image forming apparatus” of the present invention)
30: Image forming unit 40: LED unit (an example of the “exposure device” of the present invention)
41... LED head (an example of the “exposure head” in the present invention)
49: Storage device 50: Process cartridge 53 ... Photosensitive drum (an example of the “photosensitive member” of the present invention)
DESCRIPTION OF SYMBOLS 100 ... Control apparatus 109 ... Memory | storage device 110 ... Light emission timing determination part 120 ... LED unit drive part CH ... LED array chip (an example of the "light emission chip" of this invention)

Claims (4)

An exposure apparatus having an exposure head in which a plurality of light emission points are arranged in the main scanning direction; a photoconductor on which an electrostatic latent image is formed by exposure by the exposure apparatus; and a control apparatus for controlling light emission of the exposure apparatus; An electrophotographic image forming apparatus comprising: a storage device for storing a shift amount C with respect to a reference line extending in the main scanning direction of the light emitting point;
The exposure apparatus includes a plurality of light emitting chips having a plurality of light emitting points arranged in the main scanning direction, and the plurality of light emitting chips are arranged such that light emitting chips adjacent to each other in the main scanning direction are perpendicular to the main scanning direction. Arranged in the scanning direction,
The control device determines a light emission timing for determining a light emission timing of each light emission point as a quantized correction amount A so that exposure points by the light emission points are arranged in a line in the main scanning direction on the photoconductor. And
An exposure head drive unit that emits light by shifting each light emitting point from a reference time by a time corresponding to the correction amount,
The light emission timing determining unit
A provisional determination process for provisionally determining the correction amount A based on a quotient obtained by dividing the shift amount C by the quantization unit D;
The difference ΔC between the deviation amounts C of the two light emitting chips is B, and a value obtained by multiplying the difference ΔA between the correction amounts A of the two light emitting points by the quantization unit D is ΔE, and the light emitting point at one end of the nth light emitting chip is Between the light emitting point at the other end of the (n + 1) th light emitting chip,
| ΔE−B | <If the first threshold condition 1 is not satisfied,
An inter-chip correction amount adjustment process for determining the correction amount A by shifting the value of the correction amount A for the light emitting point at the other end of the (n + 1) th light emitting chip to satisfy the condition 1;
Between the light emitting point at the other end of the (n + 1) th light emitting chip with the correction amount A shifted, and the light emitting point adjacent to the light emitting point at the other end,
| ΔE−B | <If the second threshold condition 2 is not satisfied,
A correction amount readjustment process in the chip, which is performed in the (n + 1) th light emitting chip, to shift the value of the correction amount of the light emitting point so as to satisfy the condition 2 between the two light emitting points,
When the condition 2 cannot be satisfied only in the (n + 1) th light emitting chip, the process of shifting the correction value of the light emitting point is performed as a correction amount readjustment process outside the chip performed in the (n + 2) th light emitting chip. And
Correction amount readjustment processing outside the chip,
the inter-chip correction amount adjustment processing executed for the (n + 1) th and (n + 2) th light emitting chips,
The correction amount readjustment in the chip executed for the n + 2th light emitting chip when the condition 2 is not satisfied in the interchip correction amount adjustment processing for the n + 1th and n + 2th light emitting chips. And an image forming apparatus.   A plurality of continuous light emitting point groups in the light emitting chip are defined as one light emitting point block, and light emitting points in the light emitting chip are divided into a plurality of light emitting point blocks, and the shift amount is 1 for each light emitting point block. 2. The value according to claim 1, wherein one value is stored in the storage device, and the light emission point correction amount A is determined by the light emission timing determination unit as determination of the light emission point block correction amount A. Image forming apparatus. The light emission timing determining unit
When the condition 2 is not satisfied in the correction amount readjustment process outside the chip,
A collective adjustment process is performed in which the correction amount A of each light emitting point of the (n + 1) th and subsequent light emitting chips is uniformly shifted in a direction in which the correction amount is shifted with respect to the light emitting point at the other end in the inter-chip correction amount adjustment process. The image forming apparatus according to claim 1 or 2. The light emission timing determining unit
The image forming apparatus according to claim 3, wherein the batch adjustment process is executed in common for the exposure heads of the respective colors.

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