JP2017049302A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to easily adjust a timing of printing by a print head.SOLUTION: An image forming apparatus comprises: image forming units each including an image carriers, a plurality of writing units disposed partially overlapped with and shifted from each other in the main scanning direction, and a developing unit; transfer units that form developer images as correction images on a transfer medium on the basis of correction data; an image detection part that detects the correction images; and a control part that adjusts a printing timing at which the writing members form electrostatic latent images on the basis of the variable number that changes from formation of the electrostatic latent images at the printing timing to detection of the correction images by the image detection part, and thereby simplifying the correction images and reducing a system down time during which printing cannot be performed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, an image forming apparatus such as a printer, a copier, a facsimile machine, or a multifunction machine using an electrophotographic system, for example, a color printer, includes a plurality of image forming units, and a photosensitive drum disposed in each image forming unit. A toner image of each color is formed on the surface. For this purpose, in each image forming unit, the surface of the photosensitive drum is uniformly charged by a charging roller, exposed by an LED head as a print head, and an electrostatic latent image is formed. Development is performed by the developing roller, and toner images of each color are formed.

  Then, the belt is caused to run along each image forming unit, and the toner images of each color are transferred onto the paper conveyed on the belt by the transfer roller so as to be transferred into a color toner image. Is fixed on the paper in the fixing device.

  By the way, in a printer in which the left and right images formed by two LED heads positioned on the left and right in the width direction of the paper are connected to form one image, the left and right images are shifted, and the image quality is low. It will decline. Therefore, by using two LED heads, a plurality of alignment patterns are formed on the belt by shifting the positions little by little, and the alignment patterns overlapping each other are detected by an optical sensor so that the printing timing by the LED heads is adjusted. Yes.

JP 2011-83905 A

  However, in the conventional color printer, printing cannot be performed while a plurality of alignment patterns are formed on the belt by shifting the positions little by little using two LED heads, resulting in a long system down time. .

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that solves the problems of the conventional color printer and can easily adjust the printing timing of the print head.

  For this purpose, in the image forming apparatus of the present invention, the image carrier and the image carrier are opposed to each other so as to overlap each other in the main scanning direction and to be adjacent to each other in the sub scanning direction. A plurality of writing members each for forming an electrostatic latent image at a predetermined printing timing, a developing device for developing each electrostatic latent image to form a developer image, and each electrostatic latent image by each writing member. In order to adjust the printing timing at which an image is formed, a transfer unit that forms each developer image formed on the basis of the correction data on the transfer medium as a correction image is disposed opposite to the transfer medium, An image detection unit that detects the corrected image, a variable that changes from when an electrostatic latent image is formed based on correction data at the printing timing to when the corrected image is detected by the image detection unit, and the variable Based on the theoretical value, and a control unit for adjusting a print timing of each write member forms a respective electrostatic latent images.

  According to the present invention, in the image forming apparatus, the image carrier and the image carrier are opposed to each other so as to overlap each other in the main scanning direction and to be adjacent to each other in the sub scanning direction. A plurality of writing members each for forming an electrostatic latent image at a predetermined printing timing, a developing device for developing each electrostatic latent image to form a developer image, and each electrostatic latent image by each writing member. In order to adjust the printing timing at which an image is formed, a transfer unit that forms each developer image formed on the basis of the correction data on the transfer medium as a correction image is disposed opposite to the transfer medium, An image detection unit that detects the corrected image, a variable that changes from when the electrostatic latent image is formed based on the correction data at the print timing to when the corrected image is detected by the image detection unit, and the variable Based on the value, and a control unit for the respective write member to adjust the print timing for forming each electrostatic latent image.

  In this case, in order to adjust the printing timing at which each electrostatic latent image is formed by the first and second writing members, each developer image formed based on the correction data is formed on the transfer medium as a corrected image. A variable that changes from when an electrostatic latent image is formed based on the correction data at the printing timing until the correction image is detected by the image detection unit, when the correction image is detected by the image detection unit, Since the printing timing is adjusted based on the theoretical value of the variable, the corrected image can be simplified.

  Therefore, the print timing can be easily adjusted, and the corrected image can be formed on the transfer medium in a short time, so that the system down time during which printing cannot be performed can be shortened.

It is a control block diagram which shows the control apparatus of the printer in embodiment of this invention. 1 is a conceptual diagram of a printer in an embodiment of the present invention. It is a figure for demonstrating the relationship of an LED head, a correction pattern, and an optical sensor when the intermediate transfer belt in this Embodiment is expand | deployed. It is a time chart for demonstrating operation | movement of the control apparatus in embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this case, a color printer as an electrophotographic image forming apparatus will be described.

  FIG. 2 is a conceptual diagram of the printer in the embodiment of the present invention.

  In the figure, reference numeral 10 denotes a printer. The printer 10 has white (W), yellow (Y), magenta (M), cyan (C), and black (Bk) developer images as special colors. Image drum units (ID units) for forming toner images, that is, image forming units 12W, 12Y, 12M, 12C, and 12Bk are detachably disposed on the main body of the printer 10, that is, the apparatus main body. Since the image forming units 12W, 12Y, 12M, 12C, and 12Bk have the same structure, only members of the image forming unit 12W will be described in detail with reference to the drawings.

  In the printer 10, a plurality of left and right images are formed in the width direction of the sheet P as a medium and as a first transfer medium in the present embodiment, and the two images are joined together. As a result, one image is formed.

  For this purpose, each of the image forming units 12W, 12Y, 12M, 12C, and 12Bk includes a photosensitive drum 15 as an image carrier that is rotatably arranged, and above each photosensitive drum 15, the photosensitive drum. In the present embodiment, two LED heads (print heads) 20 and 21 as exposure apparatuses and as first and second writing members are arranged in the main scanning direction. In a staggered configuration, that is, a part of the photosensitive drums 15 are overlapped (overlapped) in the axial direction of the photosensitive drum 15 and shifted adjacent to each other in the sub-scanning direction. By exposing the drum 15, an electrostatic latent image as a latent image is formed on the surface of the photosensitive drum 15.

  Each of the image forming units 12W, 12Y, 12M, 12C, and 12Bk includes the photosensitive drum 15, a charging roller 16 as a charging device, a developing roller 18 as a developer carrier, a toner supply roller 17 as a developer supply member, A toner cartridge 14 as a developer accommodating portion, a plate-shaped cleaning blade 19 as a first cleaning member, and the like are provided. The charging roller 16 and the developing roller 18 are in contact with the photosensitive drum 15, and the toner supply roller 17. Is rotatably disposed in contact with the developing roller 18 and is rotated by driving an ID motor (not shown) as a drive unit for image formation in the forward direction. The toner supply roller 17 and the developing roller 18 constitute a developing device.

  The charging roller 16 uniformly charges the surface of the photosensitive drum 15 to a negative polarity by applying a negative polarity voltage for charging.

  Further, the developing roller 18 is applied with a negative polarity voltage for development, so that the toner as a developer adheres to the photosensitive drum 15, and the electrostatic latent image formed on the surface of the photosensitive drum 15. The image is developed to form a toner image. The toner supply roller 17 is rotated in the same rotation direction as the rotation direction of the developing roller 18, and supplies toner to the developing roller 18 while the electrostatic latent image is being developed. The toner is triboelectrically charged to a negative polarity.

  The toner cartridge 14 is detachably disposed on the main body of the image forming units 12W, 12Y, 12M, 12C, and 12Bk, that is, the main body of the image forming unit, and stores toner supplied to the toner supply roller 17. To do.

  The cleaning blade 19 is disposed with its tip in contact with the photosensitive drum 15, and after the toner image is transferred to an intermediate transfer belt 30 as a second transfer medium, which will be described later, the surface of the photosensitive drum 15. The residual toner, that is, the residual toner is removed by scraping.

  Below each of the image forming units 12W, 12Y, 12M, 12C, and 12Bk, a primary toner image for primary transfer for forming a color toner image by sequentially transferring toner images of each color on the intermediate transfer belt 30 in a superimposed manner. And a second transfer unit u2 for secondary transfer for transferring the color toner image formed on the intermediate transfer belt 30 onto the paper P.

  The first transfer unit u1 includes a driving roller 22 as a first roller for primary transfer, a driven roller 23 as a second roller for primary transfer, and a backup roller 24 as a third roller for primary transfer. An intermediate transfer belt 30 as a belt member stretched by the drive roller 22, driven roller 23, and backup roller 24, and is rotatably disposed to face each photosensitive drum 15 via the intermediate transfer belt 30. Further, a transfer roller 25 as a transfer member for primary transfer, a first cleaning device 31 disposed to face the driven roller 23 with the intermediate transfer belt 30 interposed therebetween, and a medium conveyance path Rt1 in the intermediate transfer belt 30 The correction pattern Pt1 is arranged on the lower surface opposite to Pt1 and detects correction patterns Pt1 and Pt2 (FIG. 3) as correction images to be described later. Comprising an optical sensor 55 such as an image detector. The driving roller 22 is rotated by driving a belt traveling motor 73 (FIG. 1) as a belt traveling driving unit described later. The correction patterns Pt1 and Pt2 adjust the printing timing when there is a deviation in the printing timing at which the electrostatic latent image is formed due to an attachment error of the LED heads 20 and 21 to the apparatus body, looseness of the mounting member, or the like. Therefore, the intermediate transfer belt 30 is formed. The intermediate transfer belt 30 is an endless belt made of, for example, a high-resistance semiconductive plastic film, and travels in the direction of arrow A as the driven roller 23 rotates.

  The first cleaning device 31 is disposed with its tip abutting against the intermediate transfer belt 30, and removes the adhering material such as toner of the toner image formed on the intermediate transfer belt 30 by scraping. A plate-shaped cleaning blade 40 as a second cleaning member, and a cleaner container 26 for storing scraped deposits are provided.

  Further, the optical sensor 55 includes a light emitting unit and a light receiving unit (not shown). The optical sensor 55 emits light toward the intermediate transfer belt 30 from the light emitting unit, irradiates the correction patterns Pt1 and Pt2 on the intermediate transfer belt 30, and reflects the reflected light. Is received by the light receiving unit, and the correction patterns Pt1 and Pt2 are detected.

  The second transfer unit u2 is a secondary transfer unit rotatably disposed so as to face the backup roller 24 via the backup roller 24 and the intermediate transfer belt 30 as secondary transfer rollers. A transfer roller 50 serving as a transfer member, and a second cleaning device 32 disposed to face the transfer roller 50. The transfer roller 50 includes, for example, a metal shaft and a rubber layer made of a conductive rubber material. The shaft is grounded to the casing Cs of the printer 10.

  The second cleaning device 32 is made of a metal roller rotatably disposed in contact with the transfer roller 50, and a third cleaning device that scrapes off adhering substances such as toner adhering to the transfer roller 50. A cleaning roller 33 as a member, a plate-shaped cleaning blade as a fourth cleaning member which is disposed with its tip abutting against the cleaning roller 33 and removes adhering matter such as toner adhering to the cleaning roller 33 by scraping off. 34 and a cleaner container 35 for storing the scraped deposits.

  A sheet cassette 51 serving as a medium accommodating portion for accommodating the sheets P in a stacked state is attached to and detached from the apparatus main body below the first and second transfer units u1 and u2, that is, at the bottom of the printer 10. A hopping roller 36 is provided at the front end of the paper cassette 51 as a feeding member that feeds the paper P in the paper cassette 51 one by one to the medium transport path Rt1.

  A pair of registration rollers Tr1 is used to convey the paper P fed from the paper cassette 51 to the medium conveyance path Rt1 and send it to a contact portion (nip portion) between the intermediate transfer belt 30 and the transfer roller 50 at a predetermined timing. , And a pair of conveying rollers Tr2 and Tr3 disposed downstream of the pair of registration rollers Tr1. A sensor 45 serving as a medium position sensor that detects the presence or absence of the paper P is disposed between the pair of transport rollers Tr2 and Tr3.

  Further, on the side of the first and second transfer units u1 and u2, a fixing device as a fixing device for fixing the color toner image transferred onto the paper P to the paper P and forming a color image. 60 is disposed.

  The fixing device 60 includes a heating roller 61 as a first fixing roller that heats and melts the toner of the color toner image on the paper P by a built-in heater (not shown) as a heating body, and melted toner. Is provided with a pressure roller 62 as a second fixing roller that penetrates the paper P by pressurizing. A thermistor 63 as a temperature detector for detecting the temperature of the heating roller 61 is disposed in the vicinity of the surface of the heating roller 61.

  A discharge roller 41 for discharging the paper P on which the color image is formed to the outside of the printer 10 is disposed on the downstream side of the fixing device 60 in the medium transport path Rt1.

  Next, the operation of the printer 10 will be described.

  In each of the image forming units 12W, 12Y, 12M, 12C, and 12Bk, a negative polarity voltage for charging is applied to the charging roller 16, and the surface of the photosensitive drum 15 is uniformly charged to a negative polarity. When the LED heads 20 and 21 selectively irradiate the photosensitive drum 15 with light at a predetermined printing timing based on the image data above the photosensitive drum 15, an electrostatic latent image corresponding to the image data is formed on the photosensitive drum. It is formed on the surface of the drum 15.

  When a negative polarity voltage is applied to the developing roller 18 and toner adheres to the photosensitive drum 15, the electrostatic latent image is developed with toner, and a toner image is formed on the surface of the photosensitive drum 15. The The toner supply roller 17 receives the toner supplied from the toner cartridge 14, supplies the toner to the developing roller 18 while the electrostatic latent image is being developed, and negatively absorbs the toner by the stirring operation at that time. Triboelectrically charged to the polarity of

  Each color toner image formed on the surface of the photosensitive drum 15 in each of the image forming units 12W, 12Y, 12M, 12C, and 12Bk is transferred to an intermediate transfer belt 30 that runs between the photosensitive drum 15 and the transfer roller 25. The toner images are transferred one after another, and a color toner image is formed on the intermediate transfer belt 30. The cleaning blade 19 removes the toner remaining on the surface of the photosensitive drum 15 after the toner image is transferred to the intermediate transfer belt 30, that is, the residual toner by scraping it off.

  When a predetermined color image is formed on the paper P, the image portion formed by the LED head 20, that is, the left image, and the image portion formed by the LED head 21, that is, the right image are mainly displayed. Since one image is formed by joining in the scanning direction, the print timing when the LED head 20 forms an electrostatic latent image and the print timing when the LED head 21 forms an electrostatic latent image. The toner images formed by developing the electrostatic latent images are transferred to the same portion of the intermediate transfer belt 30 at different printing timings.

  On the other hand, the paper P fed from the paper cassette 51 to the medium transport path Rt1 by the hopping roller 36 is temporarily stopped by the registration roller pair Tr1, and then the intermediate transfer belt by the transport roller pairs Tr2 and Tr3 at a predetermined timing. 30 to the contact portion between the transfer roller 50 and the transfer roller 50. At this time, the color toner image on the intermediate transfer belt 30 is transferred to the paper P, and the paper P on which the color toner image is transferred is sent to the fixing device 60, and the color toner image is transferred to the paper P in the fixing device 60. The color image is fixed.

  By the way, when the left and right images are formed by the LED heads 20 and 21 and the two images are joined to form one image as in the present embodiment, When the image is displaced, the image quality is deteriorated.

  Therefore, in the present embodiment, when the operator of the printer 10 has a deviation between the left and right images, the LED heads 20 and 21 are statically moved in the image forming units 12W, 12Y, 12M, 12C, and 12Bk. By adjusting the printing timing for forming the electrostatic latent image, it is possible to eliminate the image shift.

  Next, the operation of the control device of the printer 10 will be described.

  FIG. 1 is a control block diagram illustrating a printer control apparatus according to an embodiment of the present invention, and FIG. 3 is a diagram illustrating a relationship among an LED head, a correction pattern, and an optical sensor when the intermediate transfer belt according to the present embodiment is developed. is there. In the present embodiment, a case will be described in which the printing timing of the LED heads 20 and 21 is adjusted in the black image forming unit Bk when there is a deviation between the left and right images.

  In the figure, 20 and 21 are LED heads, 55 is an optical sensor, 71 is a control unit, 72 is built in the control unit 71 and is a counter as a counting unit for counting the number of lines in the sub-scanning direction, 73 is a belt running motor, Reference numeral 75 denotes an operation unit disposed in the casing Cs of the printer 10, and 76 denotes a memory as a storage device. Correction pattern data Da <b> 1 and Da <b> 2 as correction data are recorded in the memory 76.

  As shown in FIG. 3, the LED head 20 is on the right side and the LED head 21 is on the left side in the direction of arrow A, which is the traveling direction of the intermediate transfer belt 30. Arranged.

  When the two left and right images are displaced, the operator operates the operation unit 75 to instruct the formation of a correction pattern.

  Accordingly, the control unit 71 reads the correction pattern data Da1 and Da2 from the memory 76, sends the correction pattern data Da1 to the LED head 20, and corrects the intermediate transfer belt 30 in the area Ar1 overlapping the LED head 21 in the LED head 20. The pattern Pt1 is formed, the correction pattern data Da2 is sent to the LED head 21, and the correction pattern Pt2 is formed on the downstream side of the correction pattern Pt1 in the area Ar1 in the LED head 21 overlapping the LED head 20. In the present embodiment, the correction pattern Pt1 is composed of lines m1 to m3 as three image elements that extend in the main scanning direction and are formed in parallel with each other at a predetermined pitch. It consists of lines n1 to n3 as three image elements extending in the scanning direction and formed in parallel with each other at a predetermined pitch.

  The correction patterns Pt1 and Pt2 are detected by the optical sensor 55. Then, the printing timing at which the electrostatic latent image is formed by the LED heads 20 and 21, and the correction patterns Pt1 and Pt2 reach the optical sensor 55 as the intermediate transfer belt 30 travels, and the optical sensor 55 corrects the correction patterns Pt1 and Pt1. The print timing is adjusted based on the timing at which Pt2 is detected.

  Next, the relationship between the formation of the correction patterns Pt1 and Pt2 and the sensor output of the optical sensor 55 will be described.

  FIG. 4 is a time chart for explaining the operation of the control device according to the embodiment of the present invention. Note that the number of lines that change when the intermediate transfer belt 30 is moved in the sub-scanning direction is a variable representing time. In the present embodiment, the number of lines changes in proportion to the time as the time elapses from the timing t0, which is the printing timing at which the electrostatic latent image is formed by the LED head 20, It is counted by the counter 72.

  In this case, the controller 71 changes the number of lines that change from when the electrostatic latent images of the correction patterns Pt1 and Pt2 are formed at the timings t0 and t2 until the correction patterns Pt1 and Pt2 are detected by the optical sensor 55, and Based on the theoretical value of the number of lines, the timings t0 and t2 at which the LED heads 20 and 21 form each electrostatic latent image are adjusted. The theoretical value of the number of lines is determined by the dimensions and specifications of each member of the printer 10.

  First, the control unit 71 reads the correction pattern data Da1 from the memory 76 at the timing t0, sends it to the LED head 20, forms an electrostatic latent image with the LED head 20, and forms a correction pattern on the intermediate transfer belt 30 with the developing roller 18. Pt1 is formed. During this time, the correction pattern data Da1 is turned on in the image output section q1 of 304 [Line], is turned off in the image non-output section q2 of 304 [Line], and is turned on / off three times. Subsequently, when the controller 71 drives the belt running motor 73 at timing t1, the driving roller 22 is rotated and the intermediate transfer belt 30 is caused to run. Accordingly, the optical sensor 55 detects the intermediate transfer belt 30 at timing t1, and generates a belt detection output Qb.

  Subsequently, the control unit 71 reads the correction pattern data Da2 from the memory 76 at a timing t2 when the number of lines reaches 600 [Line] as a theoretical value from the timing t0 which is the printing timing, and sends the correction pattern data Da2 to the LED head 21. As a result, an electrostatic latent image is formed and a correction pattern Pt2 is formed on the intermediate transfer belt 30 by the developing roller 18. During this time, the correction pattern data Da2 is turned on in the image output section q1 of 304 [Line] and turned off in the image non-output section q2 of 304 [Line], and the on / off is 3 as in the correction pattern data Da1. Repeated times.

  Thereafter, at the timing t3 when the number of lines from the start of the formation of the correction pattern Pt1 to the intermediate transfer belt 30 at the timing t0 until the detection of the correction pattern Pt1 by the optical sensor 55 is 15380 [Line] as a theoretical value. When the correction pattern Pt1 is actually detected by the optical sensor 55 before and after (after the timing t3 in the present embodiment), the sensor output of the optical sensor 55 decreases every time the lines m1 to m3 are detected. Become.

  Subsequently, the timing t4 at which the number of lines from the start of the formation of the correction pattern Pt2 on the intermediate transfer belt 30 at the timing t2 to the detection of the correction pattern Pt2 by the optical sensor 55 reaches the theoretical value of 15980 [Line]. When the correction pattern Pt2 is actually detected by the optical sensor 55 before and after (after timing t4 in this embodiment), the sensor output of the optical sensor 55 is output every time the lines n1 to n3 are detected. Lower.

Therefore, in order to obtain the timing at which the correction patterns Pt1 and Pt2 are actually detected, the control unit 71 has a predetermined number of lines from the timing t3 at which the number of lines becomes 15380 [Line] as a theoretical value. , The belt detection output Qb of the optical sensor 55 before detecting the line m1 before 1681 [Line] is read, and by a predetermined number of lines from the timing t3, in this embodiment, only 1361 [Line]. The pattern detection output Qk of the optical sensor 55 after detecting the line m1 is read, and the sensor output of the optical sensor 55 is that of the image output section q1 using the belt detection output Qb and the pattern detection output Qk. Or a threshold value Vth for determining whether the image is in the non-image output section q2
Vth = (Qk + Qb) / 2
Is calculated.

  Note that the values of 1681 [Line] and 1361 [Line] of the number of lines ensure that the belt detection output Qb can be read reliably before the timing t3 and that the pattern detection output Qk can be reliably transmitted after the timing t3. Set to be readable.

Subsequently, the control unit 71 divides the section in which the correction pattern Pt1 is detected into blocks 1 to 4 using the threshold value Vth. That is, after the sensor output of the optical sensor 55 becomes greater than the threshold value Vth at the timing u1 and the line m1 is not detected, the control unit 71 causes the sensor output of the optical sensor 55 to become smaller than the threshold value Vth at the timing u2, and the line m2 Is detected as block 1, and the sensor output of the optical sensor 55 becomes smaller than the threshold value Vth at the timing u2, and after the line m2 is detected, the sensor output of the optical sensor 55 becomes larger than the threshold value Vth at the timing u3. The block until the line m2 is no longer detected is block 2. The sensor output of the optical sensor 55 becomes greater than the threshold value Vth at timing u3, and the line m2 is no longer detected. The block until the line m3 is detected becomes smaller than the threshold value Vth. 3, a block from the time when the sensor output of the optical sensor 55 becomes smaller than the threshold value Vth at the timing u4 and the line m3 is detected until the sensor output of the optical sensor 55 becomes larger than the threshold value Vth at the timing u5 is referred to as a block 4. . When the lengths of the sections from timing t3 to timing u1 to u5 are LL1 to LL5, timings u1 and u2 are the front end and rear end of block 1, and timings u2 and u3 are the front end and rear end of block 2, respectively. Since the timings u3 and u4 are the front and rear ends of the block 3, and the timings u4 and u5 are the front and rear ends of the block 4, the control unit 71 determines the number of lines at the center of each of the blocks 1 to 4. ML1-ML4
ML1 = (LL1 + LL2) / 2
ML2 = (LL2 + LL3) / 2
ML3 = (LL3 + LL4) / 2
ML4 = (LL4 + LL5) / 2
Can be calculated.

Since the center line numbers ML1 to ML4 of the blocks 1 to 4 from the timing t3 are theoretical values and are 456 [Line], 760 [Line], 1064 [Line], and 1368 [Line], respectively, the controller 71 Are the deviations BL1 to BL4 with respect to the theoretical values of the calculated number of lines ML1 to ML4 in the center of each of the blocks 1 to 4.
BL1 = (LL1 + LL2) / 2-456 [Line]
BL2 = (LL2 + LL3) / 2-760 [Line]
BL3 = (LL3 + LL4) / 2-1064 [Line]
BL4 = (LL4 + LL5) / 2−1368 [Line]
Can be calculated.

Therefore, the control unit 71 determines the average value AVBL of the deviation amounts BL1 to BL4.
AVBL = (BL1 + BL2 + BL3 + BL4) / 4
ZL between the theoretical timing at which the correction pattern Pt1 is formed and the timing at which the correction pattern Pt1 is actually formed
ZL = AVBL
= (BL1 + BL2 + BL3 + BL4) / 4 can be calculated.

  Similarly, the control unit 71 divides a section in which the correction pattern Pt2 is detected into blocks 1 to 4 using the threshold value Vth. That is, after the sensor output of the optical sensor 55 becomes larger than the threshold value Vth at the timing v1 and the line n1 is not detected, until the sensor output of the optical sensor 55 becomes smaller than the threshold value Vth at the timing v2 and the line n2 is detected. , The sensor output of the optical sensor 55 becomes smaller than the threshold value Vth at the timing v2 and the line n2 is detected, and then the sensor output of the optical sensor 55 becomes larger than the threshold value Vth at the timing v3. The block until no longer is detected is block 2, and the sensor output of the optical sensor 55 becomes larger than the threshold value Vth at timing v3, and the sensor output of the optical sensor 55 becomes smaller than the threshold value Vth at timing v4 after the line n2 is not detected. The section until the line n3 is detected is block 3, and the optical Sensor output capacitors 55 becomes smaller than the threshold value Vth at the timing v4, since the line n3 is detected, the sensor output of the optical sensor 55 and block 4 a section up to greater than the threshold value Vth at the timing v5.

When the lengths of the sections from timing t4 to timings v1 to v5 are LR1 to LR5, timings v1 and v2 are the front end and rear end of block 1, and timings v2 and v3 are the front end and rear end of block 2, respectively. Since the timings v3 and v4 are the front and rear ends of the block 3, and the timings v4 and v5 are the front and rear ends of the block 4, the control unit 71 is connected to the center line of each of the blocks 1 to 4. Number MR1-MR4
MR1 = (LR1 + LR2) / 2
MR2 = (LR2 + LR3) / 2
MR3 = (LR3 + LR4) / 2
MR4 = (LR4 + LR5) / 2
Can be calculated.

Since the center line numbers MR1 to MR4 of the blocks 1 to 4 from the timing t4 are theoretical values and are 456 [Line], 760 [Line], 1064 [Line], and 1368 [Line], respectively, the control unit 71 Are the shift amounts BR1 to BR4 with respect to the theoretical values of the center line numbers MR1 to MR4 of the blocks 1 to 4.
BR1 = (LR1 + LR2) / 2-456 [Line]
BR2 = (LR2 + LR3) / 2-760 [Line]
BR3 = (LR3 + LR4) / 2-1064 [Line]
BR4 = (LR4 + LR5) / 2−1368 [Line]
Can be calculated.

Therefore, the control unit 71 determines the average value AVBR of the deviation amounts BR1 to BR4.
By AVBR = (BR1 + BR2 + BR3 + BR4) / 4, a shift ZL between the theoretical timing at which the correction pattern Pt2 is formed and the timing at which it is actually formed
ZL = AVBR
= (BR1 + BR2 + BR3 + BR4) / 4 can be calculated.

In the present embodiment, since the LED head 20 is used as a reference print head for adjusting the image deviation, the electrostatic latent image is generated by the LED head 21 based on the deviations ZL and ZR of the correction patterns Pt1 and Pt2. The print timing when the image is formed
ΔZ = ZL-ZR
By correcting with, image shift in the sub-scanning direction can be eliminated.

  As described above, in the present embodiment, the developer images formed based on the correction pattern data Da1 and Da2 in order to adjust the printing timing at which the electrostatic latent images are formed by the LED heads 20 and 21. Are formed on the intermediate transfer belt 30 as correction patterns Pt1 and Pt2, the correction patterns Pt1 and Pt2 are detected by the optical sensor 55, and the control unit 71 performs static correction based on the correction pattern data Da1 and Da2 at the printing timing. Since the print timing is adjusted based on the number of lines that change from when the electrostatic latent image is formed to when the correction patterns Pt1, Pt2 are detected by the optical sensor 55, and the theoretical value of the number of lines, the correction patterns Pt1, Pt2 can be simplified.

  Therefore, the printing timing can be easily adjusted, and the correction patterns Pt1 and Pt2 can be formed in the intermediate transfer belt 30 in a short time, so that the system down time during which printing cannot be performed can be shortened. .

  In this embodiment, one image is formed using two LED heads 20 and 21 in the printer 10, but one image is formed using three or more LED heads. be able to. In that case, the print timing at which the electrostatic latent image is formed by a predetermined LED head is used as a reference, and the print timing at which the electrostatic latent image is formed by another LED head is adjusted.

  In the present embodiment, when the two left and right images are misaligned, the operator operates the operation unit 75 to instruct the formation of the correction pattern. When the printer 10 is turned on, or when the cover of the printer 10 is opened and closed, the control unit 71 can instruct the formation of a correction pattern.

  In the present embodiment, the color printer 10 is described. However, the present invention can be applied to a single-color printer, and further applied to an image forming apparatus such as a copying machine, a facsimile machine, and a multifunction machine. can do.

  In addition, this invention is not limited to the said embodiment, It can change variously based on the meaning of this invention, and does not exclude them from the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Printer 15 Photosensitive drum 17 Toner supply roller 18 Developing roller 20, 21 LED head 30 Intermediate transfer belt 55 Optical sensor 71 Controller Da1, Da2 Correction pattern data Pt1, Pt2 Correction pattern u1 First transfer unit

Claims (6)

(A) an image carrier;
(B) Opposed to the image carrier, are arranged to partially overlap each other in the main scanning direction and are adjacent to each other in the sub-scanning direction, and electrostatic latent images are respectively formed at predetermined printing timings. A plurality of writing members to be formed;
(C) a developing device for developing each electrostatic latent image to form a developer image;
(D) a transfer unit that forms each developer image formed based on the correction data on the transfer medium as a correction image in order to adjust the printing timing at which each electrostatic latent image is formed by each writing member; ,
(E) an image detection unit that is disposed to face the transfer medium and detects the corrected image;
(F) Variables that change from the formation of the electrostatic latent image based on the correction data at the printing timing to the detection of the corrected image by the image detection unit, and each writing based on the theoretical value of the variable An image forming apparatus comprising: a control unit that adjusts a printing timing at which a member forms each electrostatic latent image.   The image forming apparatus according to claim 1, wherein the control unit eliminates a shift of an image formed by each writing member by adjusting a printing timing.   The image forming apparatus according to claim 1, wherein the corrected image is formed in a region where the writing members overlap in the main scanning direction.   The image forming apparatus according to claim 1, wherein the variable that changes from the printing timing until the corrected image is detected by the image detection unit is the number of lines in the sub-scanning direction.   The control unit calculates a shift amount of a printing timing at which an electrostatic latent image is formed by each writing member based on the variable and a theoretical value of the variable, and the electrostatic latent image is generated by a predetermined writing member. The image forming apparatus according to any one of claims 1 to 4, wherein a printing timing at which an electrostatic latent image is formed by another writing member is corrected by the shift amount with reference to a printing timing to be formed. (A) The corrected image is composed of a plurality of image elements,
(B) The image detection unit detects each image element of the corrected image to generate a pattern detection output,
(C) The image forming apparatus according to any one of claims 1 to 5, wherein the control unit adjusts print timing based on the pattern detection output.

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