JP2017177682A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device that can improve image quality by reducing influences of defocus.SOLUTION: The image forming device comprises a reference value setting portion 111 that sets a reference value for determining movement amounts of an end part 43b of a line head 43 on the basis of an exposure width of the line head 43 adjusted by an adjusting portion 110. The reference value setting portion 111 sets the reference value so that the maximum value of angles which are formed between a plurality of line heads 43 moved by a line head moving portion 116 and a shaft direction of an image carrier 41 becomes the smallest.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus that exposes the surface of an image carrier with a line head including a light emitting element.

  Conventionally, an LED array (line head) in which a plurality of LEDs are arranged is used as an exposure unit of an electrophotographic image forming apparatus. However, because the line head can have a difference in the exposure width in the longitudinal direction of the line head due to manufacturing errors, etc., when using multiple line heads, it is necessary to adjust the exposure width in the main scanning direction on the photoreceptor. It becomes.

  As a method of matching the exposure width in the main scanning direction on the photoconductor, the line head is attached so as to be swingable with respect to the rotation direction of the photoconductor, and the end of the line head is moved so that the photoconductor of each line head. A technique for adjusting the exposure width in the main scanning direction is known (Patent Document 1).

JP 2006-82522 A

 However, in the method described in the above document, the distance between the end of the line head and the surface of the photoreceptor changes before and after the end of the line head is moved. For this reason, depending on the amount of movement of the line head, a defocused state in which the focus on the photosensitive member is deviated occurs near the end of the line head after the movement, resulting in a problem that the quality of the image is deteriorated.

  An object of the present invention is to reduce the influence of defocusing in the case where the exposure width in the main scanning direction on the image carrier is matched by moving the end of the line head in consideration of the above-mentioned problems, An object of the present invention is to provide an image forming apparatus that improves quality.

  In order to solve the above problems and achieve the object of the present invention, an image forming apparatus according to the present invention includes a plurality of cylindrical image carriers and a plurality of light emitting elements arranged in a straight line, and the surface of the image carrier. A line head that forms a latent image by exposing in the main scanning direction, a line head moving unit that supports the end of the line head so as to be movable in a direction perpendicular to the axial direction of the image carrier, An adjustment unit that adjusts the exposure width of the line head by adjusting the light emission number of the light emitting element, and a reference for determining the amount of movement of the end of the line head based on the exposure width of the line head adjusted by the adjustment unit A reference value setting unit for setting a value. The reference value setting unit sets the reference value so that the maximum value of the angle between the plurality of line heads moved by the line head moving unit and the axial direction of the image carrier is minimized.

Furthermore, in order to solve the above-described problems and achieve the object of the present invention, the image forming apparatus of the present invention also includes an image carrier comprising a cylindrical image carrier and a plurality of light emitting elements arranged linearly. A line head that exposes the surface of the image in the main scanning direction to form a latent image, a line head moving unit that supports the end of the line head so as to be movable in a direction perpendicular to the axial direction of the image carrier, and a line An adjustment unit that adjusts the exposure width of the line head by adjusting the number of light emission of the light emitting element of the head, and
Length of image carrier in main scanning direction: A
The exposure width of the line head adjusted by the adjusting unit: A ′
Radius of image carrier: B
Allowable length of movement of the line head in the direction perpendicular to the axial direction of the image carrier and toward the line head: C
And satisfying the following relationship: C> B− (B ² −A ′ ² + A ² ) ^0.5
It is configured as follows.

  According to the image forming apparatus of the present invention, it is possible to improve the image quality by reducing the influence of the deferred on the image carrier.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. It is the schematic diagram seen from the upper part at the time of rocking | fluctuating the line head which concerns on embodiment of this invention. FIG. 2 is a block diagram illustrating a hardware configuration of each unit of the image forming apparatus according to the embodiment of the present invention. 4A to 4C are explanatory diagrams for explaining the operation of matching the exposure widths on the photosensitive members of the plurality of line heads according to the embodiment of the present invention. FIG. 5A is a front cross-sectional view schematically showing the positional relationship between the line head and the photoconductor according to this example, and FIG. 5B shows the movement of the line head above a partial area W of the photoconductor in FIG. 5A. It is a schematic diagram showing a possible region Z 6A is a front sectional view schematically showing the positional relationship between the line head and the photoconductor according to this example, and FIG. 6B is a diagram showing the movement of the line head above a partial area W of the photoconductor in FIG. 6A. 3 is a schematic diagram showing a possible region Z. FIG. FIG. 7B is a front sectional view schematically showing the positional relationship between the line head and the photoconductor according to this example, and FIG. 7B is a movable area Z ′ of the line head above a partial area W of the photoconductor in FIG. 7A. It is the schematic diagram which showed. FIG. 6 is a front sectional view schematically showing the positional relationship between a line head and a belt-like image carrier according to a modification.

Hereinafter, an exemplary embodiment of an image forming apparatus according to the present invention (hereinafter referred to as the present example) will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected to the common member in each figure.
FIG. 1 is an overall configuration diagram showing the image forming apparatus of this example.

  As shown in FIG. 1, the image forming apparatus 1 forms an image on a sheet by an electrophotographic method, and has four colors of yellow (Y), magenta (M), cyan (C), and black (Bk). This is a tandem color image forming apparatus that superimposes toner. The image forming apparatus 1 includes a document transport unit 10, a paper storage unit 20, an image reading unit 30, an image forming unit 40, an intermediate transfer belt 50, a secondary transfer unit 70, and a fixing unit 80. .

  The document transport unit 10 includes a document feed table 11 on which a document G is set, a plurality of rollers 12, a transport drum 13, a transport guide 14, a document discharge roller 15, and a document discharge tray 16. Yes. The documents G set on the document feeder 11 are conveyed one by one to the reading position of the image reading unit 30 by the plurality of rollers 12 and the conveying drum 13. The conveyance guide 14 and the document discharge roller 15 discharge the document G conveyed by the plurality of rollers 12 and the conveyance drum 13 to the document discharge tray 16.

  The image reading unit 30 reads an image of the document G transported by the document transport unit 10 or the document placed on the document table 31 and generates image data. Specifically, the image of the original G is irradiated by the lamp L. The reflected light from the document G is guided in the order of the first mirror unit 32, the second mirror unit 33, and the lens unit 34 and forms an image on the light receiving surface of the image sensor 35. The image sensor 35 photoelectrically converts incident light and outputs a predetermined image signal. The output image signal is created as image data by A / D conversion.

  The image reading unit 30 has an image reading control unit 36. The image reading control unit 36 performs processing such as shading correction, dither processing, and compression on the image data created by the A / D conversion, and stores it in the RAM 103 (see FIG. 3). The image data is not limited to data output from the image reading unit 30 and may be data received from an external device such as a personal computer connected to the image forming apparatus 1 or another image forming apparatus.

  The paper storage unit 20 is disposed at the lower part of the apparatus main body, and a plurality of paper storage units 20 are provided according to the size and type of paper. The sheet is fed by the sheet feeding unit 21 and sent to the transport unit 23, and is transported by the transport unit 23 to the secondary transfer unit 70 having a transfer position. That is, the transport unit 23 functions to transport the paper fed from the paper feed unit 21 to the secondary transfer unit 70 and forms a transport path for transporting the paper. Further, a manual feed portion 22 is provided in the vicinity of the paper storage portion 20. From the manual feed section 22, paper of a size not stored in the paper storage section 20, tag paper having a tag, special paper such as an OHP sheet is sent to the transfer position. In FIG. 1, a sheet S fed by the sheet feeding unit 21 is denoted by a symbol “S”.

  An image forming unit 40 and an intermediate transfer belt 50 are disposed between the image reading unit 30 and the paper storage unit 20. The image forming unit 40 includes four image forming units 40Y, 40M, 40C, and 40K in order to form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (Bk). .

  The first image forming unit 40Y forms a yellow toner image, and the second image forming unit 40M forms a magenta toner image. The third image forming unit 40C forms a cyan toner image, and the fourth image forming unit 40K forms a black toner image. Since these four image forming units 40Y, 40M, 40C, and 40K have the same configuration, only the first image forming unit 40Y will be described here.

  The first image forming unit 40Y includes a drum-shaped photoconductor 41, a charging unit 42 arranged around the photoconductor 41, a line head 43 as an exposure unit, a developing unit 44, and a cleaning unit 45. doing. The photoreceptor 41 is rotated by a drive motor (not shown). The charging unit 42 applies a charge to the photoconductor 41 and uniformly charges the surface of the photoconductor 41. The line head 43 performs spot scanning on the photoreceptor 41 by performing exposure scanning on the surface of the photoreceptor 41 based on image data generated by the image reading unit 30 or image data transmitted from an external device. An electrostatic latent image having a shape is formed.

FIG. 2 is a schematic view when the line head 43 of this example is swung as viewed from above.
As shown in FIG. 2, the line head 43 includes LEDs 200 as a plurality of light emitting elements arranged linearly along the longitudinal direction of the line head 43. The resolution of the line head 43 is represented by dpi (dots per inch), and the size of one dot corresponding to the LED 200 is represented by 25.4 / dpi. The line head 43 performs line exposure on the surface of the photoreceptor 41 while the exposure timing and exposure amount of the LED 200 are controlled by an instruction from the CPU 101 described later. In this example, the line head 43 is provided for each of the image forming units 40Y, 40M, 40C, and 40K.

  The line head 43 is pivotably supported so that one end 43a is rotatably supported and the other end 43b can move in a direction perpendicular to the axial direction G of the photoreceptor (in the direction of arrow S in the figure). ing. The other end portion 43b is rotatably supported by a screw 116 having a screw groove formed on the outer periphery as a line head moving portion. By rotating the screw 116 by a driving portion (not shown), the line head 43 The end 43 b is moved in a direction perpendicular to the axial direction of the photoconductor 41. The configuration of the line head moving unit is not limited to the above configuration as long as the end 43b of the line head 43 can be moved. By moving the end 43b of the line head 43, for example, as shown in FIG. 2, the exposure width of the line head 43 on the photosensitive member 41 in the main scanning direction can be adjusted from L2 to L1.

  The developing unit 44 attaches yellow toner to the electrostatic latent image formed on the photoconductor 41 using, for example, a two-component developer composed of toner and carrier. As a result, a yellow toner image is formed on the surface of the photoreceptor 41.

  The developing unit 44 of the second image forming unit 40M attaches magenta toner to the photoconductor 41, and the developing unit 44 of the third image forming unit 40C attaches cyan toner to the photoconductor 41. Then, the developing unit 44 of the fourth image forming unit 40K adheres black toner to the photoconductor 41.

The toner image formed on the photoreceptor 41 is transferred to the intermediate transfer belt 50. The intermediate transfer belt 50 is formed in an endless shape and is stretched around a plurality of rollers. The intermediate transfer belt 50 is rotationally driven in a direction opposite to the rotation (movement) direction of the photoconductor 41 by a drive motor (not shown).
The cleaning unit 45 removes the toner remaining on the surface of the photoreceptor 41 after the toner image is transferred to the intermediate transfer belt 50.

  A primary transfer portion 51 is provided at a position on the intermediate transfer belt 50 that faces the photoreceptor 41 of each of the image forming units 40Y, 40M, 40C, and 40K. The primary transfer unit 51 primarily transfers the toner image formed on the photoreceptor 41 to the intermediate transfer belt 50 by applying a voltage having a polarity opposite to that of the toner to the intermediate transfer belt 50.

  When the intermediate transfer belt 50 is driven to rotate, the toner images formed by the four image forming units 40Y, 40M, 40C, and 40K are sequentially transferred onto the surface of the intermediate transfer belt 50. As a result, yellow, magenta, cyan, and black toner images are superimposed on the intermediate transfer belt 50 to form a color toner image.

  A toner adhesion amount detection sensor 60 is provided in the vicinity of the intermediate transfer belt 50 and downstream of the four photoconductors 41 in the paper conveyance direction. The toner adhesion amount detection sensor 60 detects the amount of toner adhered to the intermediate transfer belt 50. In accordance with the detection result of the toner adhesion amount detection sensor 60, so-called image stabilization control for changing the control conditions of each process of image formation is appropriately performed.

  A belt cleaning device 53 faces the intermediate transfer belt 50. The belt cleaning device 53 cleans the surface of the intermediate transfer belt 50 that has finished transferring the toner image onto the paper.

  A secondary transfer unit 70 is disposed near the intermediate transfer belt 50 and downstream of the transport unit 23 in the sheet transport direction. The secondary transfer unit 70 secondarily transfers the toner image formed on the outer peripheral surface of the intermediate transfer belt 50 onto a sheet.

  The secondary transfer unit 70 has a secondary transfer roller 71. The secondary transfer roller 71 is in pressure contact with the counter roller 52 with the intermediate transfer belt 50 interposed therebetween. A portion where the secondary transfer roller 71 and the intermediate transfer belt 50 come into contact becomes a secondary transfer nip portion 72. The secondary transfer nip portion 72 is a transfer position where the toner image formed on the outer peripheral surface of the intermediate transfer belt 50 is transferred to the paper S.

  A fixing unit 80 is provided on the paper discharge side of the secondary transfer unit 70. The fixing unit 80 pressurizes and heats the paper to fix the transferred toner image on the paper. The fixing unit 80 includes, for example, a fixing upper roller 81 and a fixing lower roller 82 which are a pair of fixing members. The upper fixing roller 81 and the lower fixing roller 82 are arranged in pressure contact with each other, and a fixing nip portion is formed as a pressing portion at a position where the upper fixing roller 81 and the lower fixing roller 82 are in contact with each other.

  A heating unit is provided inside the fixing upper roller 81. The outer peripheral portion of the fixing upper roller 81 is warmed by the radiant heat from the heating portion. Then, the heat of the fixing upper roller 81 is transmitted to the sheet, whereby the toner image on the sheet is thermally fixed.

  The sheet is conveyed so that the surface on which the toner image is transferred by the secondary transfer unit 70 (the surface to be fixed) faces the fixing upper roller 81 and passes through the fixing nip portion. Accordingly, the sheet passing through the fixing nip portion is pressed by the upper fixing roller 81 and the lower fixing roller 82 and heated by the heat of the upper fixing roller 81.

  A switching gate 24 is disposed downstream of the fixing unit 80 in the sheet conveyance direction. The switching gate 24 switches the conveyance path of the sheet that has passed through the fixing unit 80. That is, the switching gate 24 moves the paper straight when performing face-up paper discharge in which the image forming surface is discharged upward in single-sided image formation. As a result, the paper is discharged by the pair of paper discharge rollers 25. Further, the switching gate 24 guides the sheet downward when performing face-down paper discharge and double-sided image formation in which the image forming surface in single-sided image formation is discharged downward.

When face-down paper discharge is performed, after the sheet is guided downward by the switching gate 24, the sheet reverse transport unit 26 reverses the front and back and transports the sheet upward. As a result, the sheet whose front and back sides are reversed and whose image forming surface faces downward is discharged by the pair of discharge rollers 25.
When performing double-sided image formation, after the sheet is guided downward by the switching gate 24, the front and back are reversed by the sheet reversing conveyance unit 26, and sent again to the transfer position of the secondary transfer unit 70 by the refeed path 27.

Next, a control system of the image forming apparatus 1 will be described with reference to FIG.
FIG. 3 is a block diagram illustrating a control system of the image forming apparatus 1.
As shown in FIG. 3, the image forming apparatus 1 is used as, for example, a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102 for storing a program executed by the CPU 101, and a work area of the CPU 101. RAM (Random Access Memory) 103. Further, it has a hard disk drive (HDD) 104 as a mass storage device and an operation display unit 105. As the ROM 102, for example, an electrically erasable programmable ROM is used.

  The CPU 101 is an example of a control unit, and is connected to the ROM 102, the RAM 103, the HDD 104, and the operation display unit 105 via the system bus 107, and controls the entire apparatus including the line head moving unit. The CPU 101 is connected to the image reading unit 30, the image processing unit 106, the image forming unit 40, the paper feeding unit 21, the transport unit 23, the adjustment unit 110, and the reference value setting unit 111 via the system bus 107.

  The HDD 104 stores image data of an image of a document obtained by reading by the image reading unit 30, and stores output image data and the like. The operation display unit 105 is a touch panel including a display such as a liquid crystal display (LCD) or an organic ELD (Electro Luminescence Display). The operation display unit 105 displays an instruction menu for the user, information about the acquired image data, and the like. Furthermore, the operation display unit 105 includes a plurality of keys, receives input of various instructions, data such as characters and numbers, and outputs an input signal to the CPU 101.

  Image data generated by the image reading unit 30 and image data transmitted from a PC (personal computer) 120 which is an example of an external device connected to the image forming apparatus 1 are sent to the image processing unit 106 for image processing. Is done. The image processing unit 106 performs image processing such as shading correction, image density adjustment, and image compression on the received image data as necessary.

  The image forming unit 40 receives the image data image-processed by the image processing unit 106, performs exposure to the photosensitive member 41 by the line head 43 and development by the developing unit 44 based on the image data, and performs an image on the paper S. Form.

  The adjustment unit 110 adjusts the exposure width in the longitudinal direction of the line head 43 by adjusting the number of light emission of the LEDs 200 arranged linearly on the line head 43 based on the initial reference value stored in the ROM 102.

  The reference value setting unit 111 sets a reference value for determining the amount of movement of the line head 43 based on the exposure width in the longitudinal direction of the line head 43 adjusted by the adjusting unit 110. The reference value set by the reference value setting unit 111 is sent to the CPU 101 via the system bus 107.

  For example, the communication unit 108 receives job information transmitted from the PC 120 which is an external information processing apparatus via a communication line. The received job information is sent to the CPU 101 via the system bus 107.

  In this embodiment, an example in which a personal computer is applied as an external device has been described. However, the present invention is not limited to this, and various other devices such as a facsimile device can be applied as the external device. .

  Next, the operation of this example will be described.

  The line head 43 of this example has a slight difference in the length in the longitudinal direction for each line head 43 due to an error in the manufacturing process, that is, a slight difference in the exposure width in the longitudinal direction. For this reason, when a plurality of line heads 43 are used, it is necessary to adjust the exposure width of each line head 43 in the main scanning direction on the photoconductor 41.

4A to 4C are explanatory diagrams for explaining the operation of matching the exposure widths of the plurality of line heads 43 in the main scanning direction on the photosensitive member.
As shown in FIG. 4A, in this example, description will be made using four line heads 431 to 434 in which an error occurs in the length in the longitudinal direction due to an error in the manufacturing process. As four line heads, a line head 431 (hereinafter referred to as a Y line head) used in the image forming unit 40Y, a line head 432 (hereinafter referred to as an M line head) used in the image forming unit 40M, and an image forming unit 40C. A line head 433 (hereinafter referred to as “C line head”) used and a line head 434 (hereinafter referred to as “K line head”) used in the image forming unit 40K are used. When the length of the Y line head 431 is used as a reference, the M line head 432 has a manufacturing error that slightly shortens the length. The C line head 433 has an error that shortens the length, and the K line head 434 is multiplied by an error that increases the length.

  The numbers 1 to n + 1 used for the line heads 431 to 434 schematically represent the number of LEDs 200 arranged linearly in the longitudinal direction of each line head. For example, n in the figure indicates that the LED 200 is the nth LED 200 that is counted from the LEDs 200 that are arranged at the end 43 a of the line head 43.

  In this example, an initial reference value V for roughly aligning the exposure width in the longitudinal direction of the plurality of line heads 431 to 434 having manufacturing errors as described above is provided in advance. The CPU 101 sets the number of light emission of the LED 200 at the moving side end 43b of each line head 43 so that the exposure width in the longitudinal direction of each line head 43 falls within the range of ± 0.5 dots with respect to the initial reference value V. The exposure width in the longitudinal direction of each line head 43 is adjusted accordingly.

Since the value of the Y line head 431 in this example is the same value as the initial reference value V, the LED 200 is not adjusted. The value of the M line head 432 is a value smaller than the initial reference value V, but is within the range of the initial reference value V−0.5 dots, so that the LED 200 is not adjusted. Since the value of the C line head 433 is smaller than the initial reference value V and exceeds the range of the initial reference value V−0.5 dots, the number of LEDs 200 used for exposure is inserted by one dot. (N + 1), adjustment is made so as to be within the range of the initial reference value V ± 0.5 dots. Since the value of the K line head 433 is larger than the initial reference value V and exceeds the range of the initial reference value V + 0.5 dots, the number of LEDs 200 used for exposure is reduced by one dot (n -1) Adjustment is made so as to be within the range of the initial reference value V ± 0.5 dots.
Thus, in this example, by performing rough adjustment so that the exposure width in the longitudinal direction of the plurality of line heads 431 to 434 having manufacturing errors falls within the range of the initial reference value V ± 0.5 dots, The operation of setting a reference value Y described later can be simplified.

  Next, the setting of the reference value Y for determining the amount of movement of the end 43b of each line head 43 will be described based on FIG. 4B. The reference value Y shown in FIG. 4B is the exposure width in the main scanning direction on the photoreceptor 41 exposed by each line head 43.

Hereinafter, the operation of setting the reference value Y by the reference value setting unit 111 will be described in detail. Table 1 shows an example (Example 1) of an operation for setting the reference value Y.

  The left column of Table 1 shows a difference value between the exposure width in the longitudinal direction of each line head 431 to 434 and the initial reference value V after the adjustment based on the initial reference value V described above. That is, the value of the Y line head 431 after adjustment is +0.2 dots, the value of the M line head 432 is +0.3 dots, and the value of the C line head 433 is −0.4 dots. , The value of the K line head 434 is +0.4 dots.

In the plan 1, the temporary reference value for setting the reference value Y is set to -0.5 dots.
Under this temporary reference value, the value of the Y line head 431 is +0.2 − (− 0.5) = + 0.7 dots. The value of the M line head 432 is +0.3 − (− 0.5) = + 0.8 dots. The value of the C line head 433 is −0.4 − (− 0.5) = + 0.1 dot. The value of the K line head 434 is +0.4 − (− 0.5) = + 0.9 dots. Therefore, in the plan 1, the maximum difference between the exposure width in the longitudinal direction of the four line heads 431 to 434 and the temporary reference value is the case of the K line head 434, and the value is +0.9 dots. It becomes.

  In plan 2, the temporary reference value is set to -0.4 dots. As a result, the value of the Y line head 431 is +0.6 dots, the value of the M line head 432 is +0.7 dots, the value of the C line head 433 is 0 dots, and the value of the K line head 434 is +0.8 dots. Thus, the maximum difference from the provisional reference value in plan 2 is +0.8 dots of the K line head 434.

  In plan 3, the temporary reference value is set to -0.3 dots. As a result, the value of the Y line head 431 is +0.5 dots, the value of the M line head 432 is +0.6 dots, the value of the C line head 433 is -0.1 dots, and the value of the K line head 434 is +0.7. In the case 3, the sign of the value of the C line head 433 becomes negative. When a negative value occurs in this way, a portion where the photoconductor 41 is not exposed is generated in the vicinity of the end portion of the C line head 433. For this reason, in this example, when a negative value occurs when setting the reference value Y, a portion of the LED 200 that is not exposed in the main scanning direction is generated by adding one dot of the LED 200. To prevent. Therefore, in the plan 3, the value of the C line head 433 is −0.1 + 1.0 = 0.9 dots, and as a result, the maximum difference from the temporary reference value in the plan 3 is the value of the C line head 433. +0.9 dot.

In the same procedure, when the maximum value of the difference from the temporary reference value is obtained for the cases 4 to 11 in which the value of the temporary reference value is changed by 0.1 dots, the value of the temporary reference value is set to +0. In scheme 8 set to 2 dots, the maximum value of the difference is 0.4. That is, in Plan 8, the value of the Y line head 431 is 0 dot, the value of the M line head 432 is +0.1 dot, the value of the C line head 432 is +0.4 dot, and the value of the K line head 434 is +0.2. The maximum value of the difference from the provisional reference value in case 8 is +0.4 dots of the C line head 433.
Therefore, in the first embodiment, the value of the maximum difference from the temporary reference value is the smallest at +0.4 dots in the plan 8, so the reference value setting unit 111 sets the temporary reference value in the plan 8 +0.2 dot is set as the reference value Y.

Table 2 shows another example (Example 2) in which the reference value setting unit 111 sets the reference value Y.

  The left column of Table 2 shows the difference between the exposure width in the longitudinal direction of each line head 431 to 434 after adjustment and the initial reference value V. That is, after the adjustment, the value of the Y line head 431 is −0.1 dot, the value of the M line head 432 is +0.3 dot, and the value of the C line head 433 is −0.4 dot. Yes, the value of the K line head 434 is +0.4 dot.

  When the value of the tentative reference value is changed by 0.1 dot in the same procedure as in Table 1 and the maximum difference between the tentative reference value and the tentative reference value 11 is obtained, In the case 9 in which is set to +0.3 dots, the maximum value is +0.6 dots, and the value of the maximum value of the difference from the temporary reference value is the smallest in the case of +0.6 dots in the case 9. Therefore, in the second embodiment, the reference value setting unit 111 sets the +0.3 dot of the temporary reference value in the plan 9 as the reference value Y.

  The CPU 101 controls the line head moving unit 116 based on the reference value Y set by the reference value setting unit 111 to move the line heads 431 to 434. That is, as shown in FIG. 4C, even when a plurality of line heads 431 to 434 are used, the exposure widths of the plurality of line heads 431 to 434 on the photoconductor 41 in the main scanning direction can be matched. If the line head 43 is moved in this manner, the exposure position becomes oblique with respect to the axial direction of the photoconductor 41. Therefore, the CPU 101 adjusts the exposure (light emission) timing of the LED 200 so that the exposure position is photosensitive. Correction is made so as to coincide with the main scanning line of the body 41.

  Further, according to this example, by adjusting the exposure width as described above, the maximum of a plurality of angles that can be formed between the longitudinal direction of the moved line heads 431 to 434 and the axial direction of the photoreceptor 41 is achieved. The value can be minimized. As a result, the maximum distance that can be formed between the end 43b of the line head 43 after movement and the surface of the photoconductor 41 can be minimized, so that the influence of the deferred generated near the end 43b of the line head 43. Can be reduced, and the image quality can be improved.

Next, another embodiment of the present invention (hereinafter referred to as another example) will be described.
FIG. 5A is a front sectional view schematically showing the positional relationship between the line head 43 and the photoconductor 41 according to another example, and FIG. 5B is a line above a partial region W of the photoconductor 41 of FIG. 5A. 5 is a schematic diagram showing a movable region Z of a head 43. FIG.

  In FIG. 5A, the radius of the photoreceptor 41 is B. Further, the difference between the distance C1 between the opposed surface 43c ′ of the line head 43 ′ after movement and the surface of the photosensitive member 41 and the distance C2 between the opposed surface 43c of the line head 43 before movement and the surface of the photosensitive member 41 is expressed as a line head. It is defined as 43 allowable + direction lengths C. Here, the + direction is a direction perpendicular to the axial direction of the photoconductor 41 and refers to a direction in which the line head 43 is arranged from the center of the photoconductor 41. Further, let X be the maximum movable distance between the line head 43 before movement and the line head 43 ′ after movement in the direction perpendicular to the axial direction of the photoconductor 41.

  In FIG. 5B, let A be the exposure width in the longitudinal direction of the line head 43 before movement, and let A ′ be the exposure width in the longitudinal direction of the line head 43 ′ adjusted based on the initial reference value V after movement.

As is clear from FIG. 5A, the relationship between the radius B of the photoconductor, the maximum movable distance X, and the length C can be expressed as follows using the three-square theorem.
B ² = (B−C) ² + X ² (1)

Further, as is clear from FIG. 5B, the relationship between the exposure width A, the exposure width A ′, and the maximum movable distance X can be expressed by the following three square theorem.
A ′ ² = A ² + X ² (2)

Therefore, considering that the relationship of radius B> length C of the photoconductor is satisfied, the length C satisfies the following relationship when the length C is solved using the equations (1) and (2). You can see that
^{C> B- (B 2 -A '} 2 + A 2) 0.5 ··· (3)

  According to this example, when the exposure width in the longitudinal direction of the line head 43 is adjusted, the line C after movement is adjusted by adjusting the length C within a range that satisfies the relationship of the above formula (3). The distance that can be formed between the end 43b of the head 43 ′ and the surface of the photoreceptor 41 can be made as small as possible. Thereby, the influence of defocusing in the vicinity of the end 43b of the line head 43 'after movement can be suppressed, and the image quality can be improved.

  6A is a front sectional view schematically showing the positional relationship between the line head 43 and the photoconductor 41 according to another example, and FIG. 6B is a line above a partial region W of the photoconductor 41 in FIG. 6A. 5 is a schematic diagram showing a movable region Z of a head 43. FIG.

  In this example, in FIG. 6B, the exposure width A ′ in the longitudinal direction of the moved line head 43 ′ is A + 25.4 / dpi (the size of one dot corresponding to the LED 200). That is, the adjustment of the exposure width in the longitudinal direction of the line head 43 based on the initial reference value V is performed with a length of 1 dot.

As is apparent from FIG. 6A, the relationship between the radius B, the maximum movable distance X, and the length C of the photosensitive member can be expressed as follows by the three-square theorem.
B ² = (B−C) ² + X ² (4)

Further, as is clear from FIG. 6B, the relationship between the exposure width A, the exposure width A ′, and the maximum movable distance X can be expressed by the following three square theorem.
(A + 25.4 / dpi) ² = A ² + X ² (5)

Accordingly, considering that the relationship of radius B> length C of the photosensitive member is satisfied, the length C satisfies the following relationship when the length C is solved using the equations (4) and (5). You can see that
C> B− (B ² − (50.8 A / dpi) + (25.4 / dpi) ² ) ^0.5 (6)

  According to this example, when the exposure width in the longitudinal direction of the line head 43 is adjusted, the line C after movement is adjusted by adjusting the length C within a range that satisfies the relationship of the above formula (6). The distance that can be formed between the end 43b of the head 43 ′ and the surface of the photoreceptor 41 can be reduced. Thereby, the influence of defocusing in the vicinity of the end 43b of the line head 43 'after movement can be suppressed, and the image quality can be improved.

  FIG. 7A is a front sectional view schematically showing the positional relationship between the line head 43 and the photoconductor 41 according to another example, and FIG. 7B is a line above a partial region W of the photoconductor 41 in FIG. 7A. 5 is a schematic diagram showing a movable region Z ′ of a head 43. FIG.

  The center part of the line head 43 of this example is supported rotatably. Accordingly, the line head 43 has both end portions 43a and 43b movable in a direction perpendicular to the axial direction of the photosensitive member 41 around the central rotation shaft 43c, and has a movable region Z as shown in FIG. 7B. ing.

  In FIG. 7B, let A be the exposure width in the longitudinal direction of the line head 43 before movement, and let A ′ be the exposure width in the longitudinal direction of the line head 43 ′ adjusted based on the initial reference value V after movement.

As is clear from FIG. 7A, the relationship between the radius B, the maximum movable distance X, and the length C of the photoconductor can be expressed as follows by the three square theorem.
B ² = (B−C) ² + X ² (7)

Further, as is apparent from FIG. 7B, the relationship between the exposure width A, the exposure width A ′, and the maximum movable distance X can be expressed by the following three square theorem.
(A ′ / 2) ² = (A / 2) ² + X ² (8)

Therefore, considering that the relationship of radius B> length C of the photosensitive member is satisfied, the length C satisfies the following relationship when the length C is solved using the equations (7) and (8). You can see that
C> B- (B ² − (A ′ / 2) ² + (A / 2) ² ) ^0.5 (9)

  According to this example, when the exposure width in the longitudinal direction of the line head 43 is adjusted, the exposure width A ′ is adjusted within a range in which the length C satisfies the relationship of the above formula (9). The distance that can be formed between the end 43b of the moved line head 43 ′ and the surface of the photoreceptor 41 can be made as small as possible. Thereby, the influence of defocusing in the vicinity of the end 43b of the line head 43 'after movement can be suppressed, and the image quality can be improved.

Next, another modification will be described.
FIG. 8 is a front sectional view schematically showing the positional relationship between the line head 43 and the belt-like image carrier 141 in another modification.

  The belt-shaped image carrier 141 of this example is stretched by four rollers 142, and a plane portion is formed between adjacent rollers 142. Moreover, the line head 43 of this example is arrange | positioned in the position facing the plane part 141a formed in the upper part.

  In this example, since the line head 43 is moved within a range facing the flat portion 141a of the belt-shaped image carrier 141, the opposed surface 43c ′ of the moved line head 43 ′ and the surface of the belt-shaped image carrier 141 are moved. And the distance C2 between the surface 43c of the line head 43 before the movement and the surface of the photoreceptor 41 can be made the same. As a result, the occurrence of defocusing in the vicinity of the end 43b of the line head 43 'after movement can be prevented, and the image quality can be improved.

  The present invention is not limited to the embodiments described above and shown in the drawings, and various modifications can be made without departing from the spirit of the invention described in the claims. For example, in this example, an image forming apparatus having four colors Y, M, C, and K has been described as an example, but the present invention can also be applied to an image forming apparatus such as a laser printer having three colors or less.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 40 ... Image forming part, 41, 141 ... Image carrier, 43 ... Line head, 101 ... CPU, 102 ... ROM, 103 ... RAM , 116: line head moving unit, 110: adjusting unit, 111: reference value setting unit, 200: LED (light emitting element)

Claims (7)

A plurality of cylindrical image carriers;
A line head that forms a latent image by exposing the surface of the image carrier in a main scanning direction by a plurality of light emitting elements arranged linearly;
A line head moving unit that supports the end of the line head so as to be movable in a direction perpendicular to the axial direction of the image carrier;
An adjusting unit for adjusting the exposure width of the line head by adjusting the number of light emission of the light emitting elements of the line head;
A reference value setting unit that sets a reference value for determining the amount of movement of the end of the line head based on the exposure width of the line head adjusted by the adjusting unit;
The reference value setting unit sets the reference value so that a maximum value of an angle between the plurality of line heads moved by the line head moving unit and an axial direction of the image carrier is minimized. Image forming apparatus. The image forming apparatus according to claim 1, wherein the adjustment of the exposure width of the line head by the adjustment unit is performed within a range of ± 0.5 dots of the light emitting element with respect to a preset initial reference value. When setting the reference value, if the exposure width of the line head is less than the reference value newly set by the reference value setting unit, the adjustment of the exposure width of the line head by the adjustment unit, The image forming apparatus according to claim 1, which is performed by adding one dot of the light emitting element to the reference value. A cylindrical image carrier;
A line head that forms a latent image by exposing the surface of the image carrier in a main scanning direction by a plurality of light emitting elements arranged linearly;
A line head moving unit that supports the end of the line head so as to be movable in a direction perpendicular to the axial direction of the image carrier;
An adjustment unit that adjusts the exposure width of the line head by adjusting the number of light emission of the light emitting elements of the line head,
Length of the image carrier in the main scanning direction: A
The exposure width of the line head adjusted by the adjusting unit: A ′
Radius of the image carrier: B
Length that allows movement of the line head in a direction perpendicular to the axial direction of the image carrier and toward the line head: C
And satisfying the following relationship: C> B− (B ² −A ′ ² + A ² ) ^0.5
An image forming apparatus. A cylindrical image carrier;
A line head that forms a latent image by exposing the surface of the image carrier in a main scanning direction by a plurality of light emitting elements arranged linearly;
A line head moving unit that holds both ends of the line head so as to be movable in a direction perpendicular to the axial direction of the image carrier;
An adjustment unit that adjusts the exposure width of the line head by adjusting the number of light emission of the light emitting elements of the line head,
Length of the image carrier in the main scanning direction: A
The exposure width of the line head adjusted by the adjusting unit: A ′
Radius of the image carrier: B
Length that allows movement of the line head in a direction perpendicular to the axial direction of the image carrier and toward the line head: C
And satisfying the following relationship C> B− (B ² − (A ′ / 2) ² + (A / 2) ² ) ^0.5
An image forming apparatus. A cylindrical image carrier;
A line head that forms a latent image by exposing the surface of the image carrier in a main scanning direction by a plurality of light emitting elements arranged linearly;
A line head moving unit that supports the end of the line head so as to be movable in a direction perpendicular to the axial direction of the image carrier;
An adjustment unit that adjusts the exposure width of the line head by adjusting the number of light emission of the light emitting elements of the line head,
Length of the image carrier in the main scanning direction: A
Radius of the image carrier: B
Length that allows movement of the line head in a direction perpendicular to the axial direction of the image carrier and toward the line head: C
When the resolution of the line head is expressed using dpi, the following relationship is satisfied: C> B− (B ² − (50.8 A / dpi) + (25.4 / dpi) ² ) ^0.5
An image forming apparatus. An image carrier having a planar portion;
A line head that is provided so as to face the flat portion of the image carrier, and that exposes the surface of the image carrier in a main scanning direction by a plurality of light emitting elements arranged in a straight line to form a latent image;
A line head moving unit that supports the end of the line head so as to be movable in a direction perpendicular to the axial direction of the image carrier;
An adjusting unit for adjusting the exposure width of the line head by adjusting the number of light emission of the light emitting elements of the line head;
An image forming apparatus.

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