JP5055842B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms a color image on a recording medium.

  In general, as an image forming apparatus for forming a color image on a recording medium, an image forming apparatus for forming a color image by forming a plurality of images of different colors and superimposing the formed images of the respective colors is known. Yes. In this image forming apparatus, in order to obtain a high-quality image, it is required to superimpose the images of each color without deviation. For example, the expansion / contraction of the recording medium, the positional deviation of various optical components, change with time, etc. As a result, the position where the image of each color is formed may deviate from the original position, and thus color misregistration may occur when superimposed.

Therefore, a color registration mark is formed for each color at a predetermined position on the recording medium, the color registration mark of each color formed is detected, the amount of positional deviation of the image of each color is calculated, and based on the calculated amount of positional deviation A technique for correcting a position where an image of each color is formed is known (see, for example, Patent Document 1 and Patent Document 2). This technique calculates and corrects the positional deviations in the print writing direction (main scanning direction) and the printing paper feed side direction (sub-scanning direction).
JP-A-8-272176 JP-A-8-50385

  However, in the above conventional technique, it is necessary to provide a plurality of detection units for detecting the color registration marks of each color in order to calculate the positional deviation of each color in the main scanning direction and the sub-scanning direction.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of correcting a misalignment of a formed image in a main scanning direction and a sub scanning direction with a simple configuration. And

In order to achieve the above object, an image forming apparatus according to the present invention is based on a plurality of image forming units provided for each color for forming a color image on a recording medium by performing main scanning and sub-scanning, and image data. The plurality of image forming units are controlled so that a new image is formed, and a first registration mark in which a deviation in the main scanning direction does not appear in the sub-scanning direction and a first registration mark in which the deviation in the main scanning direction appears in the sub-scanning direction Each of the first registration mark and the second registration mark includes a reference color mark and a mark of another color different from the reference color spaced apart from the reference color mark by a predetermined distance in the sub-scanning direction. A control unit that controls the plurality of image forming units so that the provided registration mark is formed a plurality of times at a predetermined timing; a first registration mark formed on the recording medium; A reading unit for reading the second registration mark, and based on a reading result of the reading unit, a deviation amount in the sub-scanning direction of the mark of the other color with respect to the reference color mark for the first registration mark is used. First correction means for calculating a correction amount in the sub-scanning direction, and sub-marks of the other color marks based on the reference color mark for the first registration mark based on the reading result of the reading means. A correction amount in the main scanning direction is calculated by using a deviation amount in the scanning direction and a deviation amount in the sub scanning direction of the mark of the other color with respect to the reference color mark for the second registration mark. Calculating means, and image forming position correcting means for correcting the image forming position based on the image data based on the correction amounts calculated by the first calculating means and the second calculating means, Serial control means, the first time, the first magnitude the first registration mark and the second registration mark of the form, the second and subsequent times, and the correction of the first sub scanning direction calculated by the calculating means When the amount is equal to or smaller than a predetermined value in the sub-scanning direction, and the correction amount in the main scanning direction calculated by the second calculating unit is equal to or smaller than a predetermined value in the main scanning direction The plurality of image forming means are controlled so that a first registration mark and a second registration mark having a second size smaller than the first size are formed.

It said control means, for controlling said plurality of image forming means so that the first registration mark and the second registration mark in the sub scanning direction is formed is effective.

As described above, the first registration mark and the second registration mark are formed in the sub-scanning direction, so that the reading unit can easily read the first registration mark and the second registration mark. .

  As described above, according to the present invention, the positional deviation of the formed image in the main scanning direction and the sub-scanning direction can be corrected with a simple configuration, so that an image with high quality can be obtained. can get.

  FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus 10 according to the present embodiment. The image forming apparatus 10 is a tandem printer that forms an image on the continuous paper 11 at a high speed.

  In the image forming apparatus 10, yellow (Y), magenta (M), cyan (C), and black (K) toner images of respective colors are sequentially transferred onto the continuous paper 11, and the printing units 12 </ b> Y for superimposing the respective color toner images, 12M, 12C, and 12K (hereinafter, referred to as print units 12Y to 12K) are sequentially arranged from the upstream side in the transport direction. A paper transport unit 14 that transports the continuous paper 11 to the print units 12Y to 12K is provided on the upstream side in the transport direction of the print units 12Y to 12K. Further, on the downstream side in the transport direction of the printing units 12Y to 12K, the fixing unit 16 that fixes the unfixed toner image transferred by the printing units 12Y to 12K to the continuous paper 11, and the continuous paper 11 that has passed through the fixing unit 16 are discharged. A paper discharge unit 17 for paper is provided.

  In addition, when it is necessary to distinguish YMCK, it explains by adding any of Y, M, C, and K after the code, and when it is not necessary to distinguish YMCK, Y, M, C, and K are changed. Omitted.

  The paper transport unit 14 includes a main drive roll 18 around which the continuous paper 11 is wound. The main drive roll 18 is driven by a paper conveyance motor (not shown) that is a stepping motor, and an IOT controller (76 in FIG. 2) that controls the entire image forming apparatus 10 controls the number of pulses of the paper conveyance motor. Thus, the feed amount of the continuous paper 11 is controlled.

  Further, idle rolls 19A and 19B around which the continuous paper 11 is wound are provided on the upstream side in the conveyance direction of the main drive roll 18 of the paper conveyance unit 14, and the continuous paper is provided on the downstream side in the conveyance direction of the main drive roll 18. An idle roll 19D around which 11 is wound is disposed. Further, the idle roll 19E is in pressure contact with the main drive roll 18. The idle roll 19E and the main drive roll 18 sandwich and convey the continuous paper 11.

  A transport guide 26 and an aligning roll 27 are disposed between the idle roll 19A and the idle roll 19B. The conveyance guide 26 is formed with a U-shaped curved surface around which the continuous paper 11 is wound, and a guide rib (not shown) that guides one end of the continuous paper 11 in the width direction (a direction orthogonal to the conveyance direction). ing.

  Further, the aligning roll 27 is a roll having a significantly narrower roll width than the idle rolls 19A, 19B, 19D, and 19E and having a rotation axis that obliquely intersects the conveyance direction of the continuous paper 11, and the width of the continuous paper 11 The continuous paper 11 is pressed against one end in the width direction by coming into contact with one end in the direction. As a result, one end in the width direction of the continuous paper 11 is abutted against a guide rib (not shown), and the skew of the continuous paper 11 is corrected.

  Also, the registration mark detection unit 70 reads registration marks (not shown) formed in advance on the continuous paper 11 and instructs the printing units 12Y to 12K to start image formation for each page.

  The main drive roll 18, idle rolls 19A, 19B, 19D, and 19E, a paper transport motor (not shown), a transport guide 26, and an aligning roll 27 are attached to the paper transport frame 22 directly or via a support member. It is supported. The paper transport frame 22 is supported on the base 23.

  The printing units 12Y to 12K each include a photoconductor 20, and around the photoconductor 20, the transfer roll 24, the cleaning device 28, and the like are arranged in the order of rotation of the photoconductor 20 (the direction of arrow A shown in FIG. 1). A charger 30, an LED 32, and a developing device 34 are disposed. The print units 12Y to 12K include print frames 38Y to 38K that support the photoreceptor 20, the cleaning device 28, the charger 30, and the LEDs 32, respectively. Adjacent print frames 38Y to 38K are connected by connecting bases 40 that support the print frames 38Y to 38K so as to be movable up and down with bolts and nuts (both not shown), and connecting the print frames 38Y to 38K. This is done by positioning and screwing through a plate (not shown). The base 40 that supports the print frame 38 </ b> Y is connected to the base 23 that supports the paper transport frame 22.

  The transfer roll 24 abuts on the upper surface of the photoconductor 20 and sandwiches and conveys the continuous paper 11 together with the photoconductor 20. At this time, the toner image formed on the photoconductor 20 is transferred to the continuous paper 11 by the developing device 34. Let

  The charger 30 charges the surface of the photoconductor 20, and the LED 32 is controlled to emit light based on the image data, and the surface of the photoconductor 20 is line-exposed to form a latent image. The developing unit 34 forms a toner image by attaching toner to the latent image formed on the surface of the photoconductor 20. Further, the cleaning device 28 scrapes off and removes untransferred residual toner remaining on the surface of the photoconductor 20 without being transferred to the continuous paper 11.

  Further, the print unit 12K is provided with a color registration mark detection unit 72, which is formed by the print units 12Y to 12K with a reflection type sensor (90 in FIG. 2) provided in the color registration mark detection unit 72. The color registration marks (81Y to K and 83Y to 83K in FIG. 8) are read.

  On the other hand, the fixing unit 16 includes a plurality of fixing devices 52 including, for example, eight flash lamps 48, idle rolls 54 </ b> A, 54 </ b> B, 54 </ b> D, and a paper discharge roll 56. The idle rolls 54A, 54B, 54D, the fixing device 52, and the paper discharge roll 56 are sequentially arranged along the conveyance direction, and both end portions in the direction orthogonal to the conveyance direction are supported by the fixing frame 58. Yes.

  The idle rolls 54A, 54B, 54D are disposed on the back side of the image forming surface of the continuous paper 11, and the idle roll 54D is disposed above the idle roll 54B. For this reason, the continuous paper 11 wound around the idle rolls 54A, 54B, 54D is reversed and conveyed with the image forming surface facing upward.

  The fixing device 52 is disposed on the image forming surface side of the continuous paper 11 conveyed with the image forming surface facing upward, and irradiates the image forming surface of the continuous paper 11 with flash light. As a result, the unfixed toner on the continuous paper 11 is heated and melted, and then solidified and fixed on the continuous paper 11.

  The paper discharge roll 56 discharges the toner-fixed area of the continuous paper 11 from the image forming apparatus 10, but the continuous paper 11 that has passed through the fixing device 52 is once discharged from the fixing unit 16 and discharged from the paper discharge unit 17. , The paper returns to the fixing unit 16 and is discharged to the outside of the image forming apparatus 10 by the paper discharge roll 56.

  In the paper discharge unit 17, an idle roll 59A, a tension applying roll 60, a sub drive roll 61, an idle roll 59B, a conveyance guide 62, an aligning roll 63, and an idle roll 59D are arranged in order along the conveyance direction. These are supported by the paper discharge frame 65 directly or via a support member or the like at both ends in a direction orthogonal to the transport direction. The paper discharge frame 65 is connected to the print frame 38K and the fixing frame 58.

  The sub drive roll 61 is disposed above the idle roll 59A, and the continuous paper 11 wound around the idle roll 59A and the sub drive roll 61 is redirected and conveyed upward. The idle roll 59 </ b> B is in pressure contact with the sub drive roll 61, rotates following the rotation of the sub drive roll 61, and sandwiches and conveys the continuous paper 11 together with the sub drive roll 61.

  In addition, a tension applying roll 60 is disposed between the idle roll 59A and the sub drive roll 61, and the continuous paper 11 is disposed between the idle roll 59A and the tension applying roll 60, and between the tension applying roll 60 and the sub drive. It is meandered between the rolls 61 and conveyed.

  The tension applying roll 60 is supported at both ends in the main scanning direction so as to be swingable by arms (not shown). Further, the arm is urged toward the continuous paper 11 by an urging means (not shown) such as a spring, whereby tension is applied to the continuous paper 11.

  Further, the position of the arm is detected by a sensor (not shown), and the rotation speed of the sub drive roll 61 is controlled so that the position of the arm is always at a fixed position.

  Further, a conveyance guide 62 and an aligning roll 63 are disposed on the downstream side of the sub drive roll 61 in the conveyance direction. The transport guide 62 and the aligning roll 63 have the same configuration as the transport guide 26 and the aligning roll 27 provided in the paper transport unit 14 and correct the skew of the continuous paper 11.

  An idle roll 59D is disposed downstream of the conveyance guide 62 in the conveyance direction. The continuous paper 11 is wound around the idle roll 59 </ b> D, and the direction is changed toward the paper discharge roll 56 of the fixing unit 16.

  FIG. 2 is a block diagram of a control system of the image forming apparatus 10 according to the present embodiment. Here, only one of the four colors of YMCK is shown as a representative.

  An IOT controller 76 is connected to the image formation control unit 74, and a user interface 77 is connected to the IOT controller 76, and an instruction regarding image formation and the like is given by a user operation, and information at the time of image formation is displayed. It informs the user. Further, the IOT controller 76 is connected to a network line with an external host computer (not shown) so that image data is input. When the image data is input, the IOT controller 76 analyzes, for example, the print instruction information included in the image data and the image data, converts the data into a format suitable for the image forming apparatus (for example, bitmap data), Image data is transmitted to the image formation control unit 74.

  The image formation control unit 74 includes a memory 78 that stores image data of the first color registration mark and the second color registration mark in advance, an optical scanning system control unit 33, a drive system control unit 21, and a charger control. The unit 31, the developing device control unit 35, and the cleaning device control unit 29 are connected, and these are synchronously controlled based on the image data to execute image formation.

  Furthermore, a color registration mark detection unit 72 is connected to the image formation control unit 74, and the color registration mark detection unit 72 includes a reflection type sensor 90, a first color registration mark, and a second color registration mark. A memory 92 and a CPU 94 for storing in advance a predetermined interval between each reference color mark and another color mark are provided.

  Next, a process for correcting misalignment of images formed by the printing units 12Y to 12K executed in the image forming apparatus 10 according to the present embodiment will be described with reference to FIGS.

  FIG. 3 shows the overall flow of the processing of the control routine for correcting image misregistration. For example, this is executed when an instruction to execute printing is input from the IOT controller 76 to the image forming control unit 74. Is done.

  First, when a print instruction is input to the image forming control unit 74, in step 100, the first color registration mark and the second color registration mark of the initial value size are given to the printing units 12Y to 12K at predetermined timing for each print page. Instruct the formation of the mark. Thereby, the color registration marks 81Y to 81K and the color resist marks 83Y to 83K are sequentially formed at predetermined intervals on the same page of the continuous paper 11 by the printing units 12Y to 12K. In the present embodiment, the printing units 12Y to 12K form the color registration marks 81Y to 81K and the color registration marks 83Y to 83K for each page.

  The color registration mark will be described with reference to FIG. FIG. 4 shows the color registration marks 80Y to 80K and color registration marks 82Y to 82K formed on the continuous paper 11 when there is no image displacement (reference state). The horizontal direction in which the color registration marks in FIG. 4 are arranged is the sub-scanning direction and the reading direction of the reflective sensor 90. The direction perpendicular to the sub-scanning direction is the main scanning direction. A line indicated by a straight line L is a reading line indicating the reading direction of the reflective sensor 90, and is along the sub-scanning direction.

  The color registration marks 80 </ b> Y to 80 </ b> K are first color registration marks for detecting misalignment in the sub-scanning direction, and are formed in an elongated rectangular shape, and the length direction is in the main scanning direction of the continuous paper 11. It is formed along. For this reason, even if a deviation occurs in the main scanning direction, the position in the sub-scanning direction where the first color registration mark intersects with the reading line (straight line L) of the reflective sensor does not change, so the deviation in the main scanning direction does not occur. Does not appear in the sub-scanning direction. The color registration marks 82 </ b> Y to 82 </ b> K are second color registration marks for detecting misalignment in the main scanning direction, are formed in an elongated rectangular shape, and the length direction is the sub-scanning direction of the continuous paper 11. And a predetermined angle θ (for example, 45 °). For this reason, when a deviation x occurs only in the main scanning direction, the position in the sub-scanning direction where the second color registration mark and the straight line L intersect changes by x / tan θ. It appears as x / tan θ in the scanning direction (details will be described later in FIG. 10). When θ = 45 °, the amount of deviation in the main scanning direction is equal to the amount of deviation in the sub-scanning direction. In the present embodiment, the black (K) color registration marks 80K and 82K are used as reference color marks, and the color registration mark 80K and other color marks (color registration marks 80C, M, and Y) are separated by a predetermined interval VPDi. Is formed. Further, the color registration mark 82K and other color marks (color registration marks 82C, M, Y) are formed at a predetermined interval HPAdi. Further, predetermined timings for forming the color registration marks 80Y to 80K and the color registration marks 82Y to 82K at the predetermined intervals are stored in the memory 78 in advance. Note that the size of the color registration marks 80Y to 80K and the color registration marks 82Y to 82K and the predetermined intervals VPDi, HPDi and the predetermined angle θ for forming the color registration marks 82Y to K are the deviation of the image forming position in advance through experiments or the like. In order to prevent the color registration marks from overlapping each other when they occur, the positional deviation amounts in the sub-scanning direction and main scanning direction of the image forming positions generated in the printing units 12Y to 12K are obtained and determined based on this. The intervals between the color registration marks 80Y to 80K and the color registration marks 82Y to 82K may be equal intervals or different intervals. Further, the color registration marks 80Y to 80K and the color registration marks 82Y to 82K are preferably formed on the same straight line along the sub-scanning direction so as to be read by the reflective sensor 90 at a time.

  In the next step 102, the color registration mark detector 72 is instructed to read the formed color registration marks 81Y to 81K and the color registration marks 83Y to 83K, and in the next step 104, the formed color registration marks 81Y to 81K. In addition, the size information of the color registration marks 83Y to 83K is output. In this case, signals indicating initial value sizes are output as the sizes of the color registration marks 81Y to 81K and the color registration marks 83Y to 83K. As a result, the color registration mark detection unit 72 reads the color registration marks 81Y to 81K and the color registration marks 83Y to 83K based on the input information, and details the correction amount VPOSi (i = c, m). , Y) and the correction amount HPOSi (i = c, m, y) are calculated and output to the image formation controller 74 (FIG. 7).

  In the next step 106, it is determined whether or not the correction amount VPOSi and the correction amount HPOSi are input from the color registration mark detection unit 72. If the determination is negative, the process enters a standby state. If the determination is affirmative, the process proceeds to step 108. In step 108, the printing units 12Y to 12K are instructed to correct the deviation of the image forming position in the sub-scanning direction. The correction in the sub-scanning direction is performed by, for example, instructing the optical scanning system control unit 33 and controlling the timing at which the exposure of the photosensitive member 20 is started by the LED 32. In this case, as shown in FIG. 5, the exposure is started from the position where the correction amount VPOSi of the photoconductor 20 is shifted. The degree of correction (unit) depends on the exposure resolution, but as an example of a specific numerical value, it is 7 μm at 1/3600 dpi. Note that the method of correcting the deviation in the sub-scanning direction is not limited to this. For example, the driving system control unit 21 may rotate the photoconductor 20 in advance to correct the position where exposure is started. .

  In the next step 110, the printing units 12Y to 12K are instructed to correct the deviation of the image forming position in the main scanning direction. The correction in the main scanning direction is performed by, for example, instructing the optical scanning system control unit 33 to control the light emitting element that starts writing the LED 32. In this case, as shown in FIG. 5, the light emission of the element is started from the position where the correction amount HPOSi of the LED 32 is shifted. The degree of correction (unit) depends on the LED resolution, but as an example of a specific numerical value, it is 21 μm at 1/1200 dpi. Note that the method of correcting the deviation in the main scanning direction is not limited to this, and may be implemented by, for example, moving the LED 32 in advance and correcting the position where printing is started (relative position with respect to the photoreceptor 20). Good.

In the next step 112, it is determined whether or not to end printing. The determination as to whether or not to end printing is made, for example, based on whether or not a predetermined number of prints have been completed or whether or not a print end instruction has been input from the IOT controller 76. In the case of negative determination, the process proceeds to step 114, and it is determined whether or not the correction amounts in the sub-scanning direction of all colors (C, M, Y) to be corrected are equal to or less than the predetermined value VPOS ₀ . Thereby, it is determined whether or not the operation of the image forming apparatus 10 is stable. In the case of negative determination, since the operation is not yet stable, the process returns to step 100, the first color registration mark and the second color registration mark having the initial size are formed, and the process of correcting the image forming position is repeated. . On the other hand, when the operation is stable, the determination is affirmative and the routine proceeds to step 116. In step 116, it is determined whether or not the correction amounts in the main scanning direction of all colors (C, M, Y) to be corrected are equal to or less than the predetermined value HPOS ₀ . As in step 114, this determines whether the operation of the image forming apparatus 10 has stabilized. If a negative determination is made, the process returns to step 100, while an affirmative is made when the operation is stable, and the process proceeds to step 118. Note that the default value VPOS ₀ and the default value HPOS ₀ are obtained in advance by experimentally determining the amount of misalignment in the sub-scanning direction and the main scanning direction of the image forming position caused by changes over time when the operation of the image forming apparatus 10 is stable. It is determined based on.

  In step 118, the image formation control unit 74 sets the first color registration mark and the second color smaller than the initial value size formed in step 100 at a predetermined timing for each print page in the printing units 12Y to 12K. The formation of registration marks (color registration marks 84Y to 84K, 86Y to 86K illustrated in FIG. 6) is instructed. As described above, when the operation of the image forming apparatus 10 is stabilized, the amount of misregistration of the image forming position caused by a change with time or the like is, for example, from when the operation is unstable immediately after the image forming apparatus 10 is turned on or immediately after printing is started. Therefore, the first color registration mark and the second color registration mark can be reduced in size. The specific size can be determined in advance based on the amount of displacement in the sub-scanning direction and the main-scanning direction of the image forming position, which is caused by changes over time when the operation of the image forming apparatus 10 is stable, through experiments or the like. That's fine. Further, as shown in FIG. 6, a predetermined interval VPAD′i between the reference color mark (color registration mark 84K) and the other color mark (color registration mark 84C, M, Y) and the reference color mark (color registration mark 86K). ) And other color marks (color registration marks 86C, M, and Y) at predetermined intervals HPAD′i when the first color registration mark and the second color registration mark are formed at step 100. It may be shorter than the predetermined interval HPDi. As for the specific interval, similarly to the size of the color registration mark, the amount of misregistration in the sub-scanning direction and the main scanning direction of the image forming position caused by a change over time when the operation of the image forming apparatus 10 is stabilized is obtained in advance by experiments or the like. It may be determined based on this. When the first color registration mark and the second color registration mark having a small size are formed, the process returns to step 102 and the correction process for correcting the image forming position is repeated. On the other hand, if the determination in step 112 is affirmative, this process ends. As described above, according to this process, the color registration marks 81Y to 81K and the color registration marks 83Y to 83K are formed, and the printing units 12C, M, and Y are formed based on the correction amounts input from the color registration mark detection unit 72. The image forming position can be corrected according to the image forming position of the printing unit 12K.

  Note that the sizes of the first color registration mark and the second color registration mark and the predetermined intervals between the reference color mark and other color marks are prepared in advance, and are adjusted in accordance with the stability of the operation of the image forming apparatus 10. May be formed.

  When a print instruction is input from the IOT controller 76, the first color registration mark of the initial value (large) size and the first color registration mark until the operation of the image forming apparatus 10 is stabilized before the image of the input image data is formed. 2 color registration marks are formed, and the image forming positions of the printing units 12Y to 12K are corrected, and after the operation is stabilized, the first color registration marks and the second color registration marks having small sizes are formed and input. An image of the processed image data may be formed.

  Furthermore, the upper limit value of the correction amount that can be corrected by each of the printing units 12C, 12M, 12Y is determined as a default value, and if the input correction amount is equal to or greater than the upper limit value, an error display is output. Error processing may be performed and this processing may be terminated.

  Next, a correction amount calculation process based on the first color registration mark and the second color registration mark formed by the process shown in FIG. 3 executed in the color registration mark detection unit 72 will be described with reference to FIG. This will be described in detail. When an instruction to read the first color registration mark and the second color registration mark (output in step 102 in FIG. 3) is input, in step 200, the formed first color registration mark and second color registration mark are formed. It is determined whether or not the size information has been input (output in step 104 in FIG. 3), and the process waits until it is input.

  In step 202, the first color registration mark and the second color registration mark are read. In reading the first color registration mark and the second color registration mark, the reflective sensor 90 is scanned in the direction opposite to the conveying direction of the continuous paper 11 and is read all at once. Note that the reflective sensor 90 itself may be moved or may be read as the continuous paper 11 is conveyed without being moved. Reading of the first color registration mark and the second color registration mark will be described with reference to FIG. FIG. 8A shows a first registration mark (color registration marks 81Y to 81K) and a second color registration mark (color registration marks 83Y to 83K) formed on the continuous paper 11, and is shown by a straight line L. The indicated line is a line indicating the reading direction of the reflective sensor 90. FIG. 8B shows the output of the reflective sensor 90 corresponding to FIG. The output value is high at the portion corresponding to the blank paper of the continuous paper 11 and low at the portion corresponding to the color registration mark.

  In the next step 204, the center values of the color registration marks 81Y to 81K and the color registration marks 83Y to 83K are calculated. Specifically, the edge of the sensor output (FIG. 8B) (position where the output high and low are switched) is detected, and the center value (position indicated by the dotted line L ′ in FIG. 8) of the portion where the output is low is detected. calculate. In the present embodiment, this center value is the position of each color registration mark 81Y-K and color registration mark 83Y-K.

  In the next step 206, the interval VADRi (i = c, m, y) between the reference color mark (color registration mark 81K) and the other color mark (color registration mark 81C, M, Y) is calculated. The distance HADRi (i = c, m, y) between the reference color mark (color registration mark 83K) and the other color mark (color registration mark 83C, M, Y) is calculated and stored in the memory 92.

  In the next step 208, predetermined intervals (predetermined intervals VPADi, HPDi) corresponding to the size information of the color registration marks 81Y to K and color registration marks 83Y to 83K input in step 200 are read from the memory 92.

  In the next step 210, correction amounts VPOSc, VPOSm, and VPOSy in the sub-scanning direction of the image forming positions of the printing units 12C, M, and Y are calculated by the equation (1) and stored in the memory 92.

VPOSi = α (VADRi−VPADi) (i = c, m, y) (1)
α is a coefficient for converting the shift amount Xi (i = c, m, y) in the sub-scanning direction into a correction amount in the sub-scanning direction of the image forming positions of the printing units 12C, M, Y. Is obtained when the operation of the image forming apparatus 10 is stable. (VADRi−VPADi) is a difference obtained by subtracting a predetermined interval from the read value, and corresponds to a shift amount Xi in the sub-scanning direction. In this embodiment, when the interval between the reference color mark and the mark of the other color is shorter than the predetermined interval, the correction amount is negative (−). When the interval is longer than the predetermined interval, the correction amount is Become positive (+).

  The correction amount VPOSi in the sub-scanning direction will be described with reference to FIG. 9A shows the first color resist marks (color resist marks 80Y to 80K) and the second color resist marks (color resist marks 82Y to 82K) formed in the reference state, and FIG. 9B shows the reference state. Is an example of the first color registration mark (color registration marks 81Y to 81K) and the second color registration mark (color registration marks 83Y to 83K) formed in a state other than the above (state in which the image is misaligned). For convenience of explanation, the print unit 12C is displaced in the main scanning direction and the sub-scanning direction from the image forming position of the print unit 12K, and the print unit 12M is displaced only in the sub-scanning direction. In the print unit 12Y, a position shift is generated only in the main scanning direction. The correction amount in the sub-scanning direction is calculated based on the position of the first color registration mark. Specifically, the displacement Xc of the color registration mark 81C in the sub-scanning direction is VADRc−VPADc (positive value), and the displacement Xm of the color registration mark 81M in the sub-scanning direction is VADRm−VPADm (negative value). A deviation Xy in the sub-scanning direction of the color registration mark 81Y is VADRy−VPADy (0: no deviation). A value obtained by multiplying the deviation Xi in the sub-scanning direction by the coefficient α is the correction amount VPOSi in the sub-scanning direction of the corresponding print unit 12C, M, Y.

  Further, in the next step 212, correction amounts HPOSc, HPOSm, HPOSy in the main scanning direction of the image forming positions of the printing units 12C, 12M, 12Y are calculated according to the equation (2) and stored in the memory 92.

HPOSi = β (HADRi− (VADRi−VPADi) −HPDi) (i = c, m, y) (2)
β is a coefficient for converting the shift amount Zi (i = c, m, y) in the sub-scanning direction into a correction amount in the main scanning direction of the image forming positions of the printing units 12C, M, Y. Is obtained when the operation of the image forming apparatus 10 is stable. In the present embodiment, when other color marks are formed at the upper position in FIG. 9 than the reference color mark, the correction amount is negative (−) and is formed at the lower position. If it is, the correction amount is positive (+).

  The correction amount HPOSi in the main scanning direction will be described with reference to FIG. The correction amount HPOSi in the main scanning direction is calculated based on the first color registration mark and the second color registration mark. In the second color registration mark, the deviation in the main scanning direction appears in the sub-scanning direction, and the deviation in the sub-scanning direction is the same between the first color registration mark and the second color registration mark. The difference obtained by subtracting the predetermined interval (HADRi-HPDi) includes two shift amounts, a shift Xi in the sub-scanning direction obtained from the first color registration mark and a shift Zi in the sub-scanning direction based on the shift in the main scanning direction. It is out. The shift Zi in the sub-scanning direction based on the shift in the main scanning direction is, for example, a color registration mark 83Y illustrating a case where no shift in the sub-scanning direction is generated in FIG. This is a shift Zy in the sub-scanning direction that occurs in the sub-scanning direction due to fluctuation of the shift Wy.

  Therefore, specifically, the shift Zc in the sub-scanning direction of the color registration mark 83C is HADRc-Xc-HPADc (negative value), and the shift Zm in the sub-scanning direction of the color registration mark 83M is HADRm-Xm-HPADm ( 0: No deviation), and the deviation Zy of the color registration mark 83Y in the sub-scanning direction is HADRy-Xy-HPADy (positive value). A value obtained by multiplying the shift Zi in the sub-scanning direction by the coefficient β is the correction amount HPOSi in the main scanning direction of the corresponding printing units 12C, 12M, and 12Y.

  In the next step 214, the correction amount VPOSi in the sub-scanning direction and the correction amount HPOSi in the main scanning direction calculated in step 210 and step 212 are output to the image formation control unit 74 (step 106 in FIG. 3), and this processing is performed. finish. As described above, according to the present process, the amount of deviation in the sub-scanning direction can be calculated based on the result of reading the formed first color registration mark and the predetermined interval. The correction amount in the main scanning direction can be obtained based on the result of reading the second color registration mark, the predetermined interval, and the amount of deviation in the sub-scanning direction.

  In addition to the reflective sensor, other sensors may be used as long as they can detect the distance between the color registration marks. However, from the viewpoint of downsizing and speeding up of the image forming apparatus, it is small and capable of high-speed response. A reflective sensor is preferred.

  In this embodiment, the black (K) color registration mark is used as the reference color mark, but a mark of a color other than black may be used as the reference color mark.

  As described above, in the image forming apparatus according to the present embodiment, the first color registration mark in which the deviation in the main scanning direction does not appear in the sub-scanning direction and the second color in which the deviation in the main scanning direction appears in the sub-scanning direction. Each registration mark is formed at a predetermined interval from the color registration mark of the reference color, and the correction amount in the sub-scanning direction and the main scanning direction is calculated from the result read by the reflective sensor, and each print unit is calculated based on the calculated correction amount. Since the position of the image formed in the above is corrected, the image forming position in the main scanning direction and the sub-scanning direction of each print unit can be corrected with a simple configuration, and thus a high-quality image can be obtained.

  Further, in the image forming apparatus of the present embodiment, all of the first color registration mark and the second color registration mark are formed on the same straight line in the sub-scanning direction, so that all are read at once by the reflective sensor. Since each color registration mark interval can be easily detected and the correction amount in the sub-scanning direction and the main scanning direction can be obtained, the image forming position of each printing unit can be quickly determined with a simpler configuration. Corrections can be made.

  Furthermore, in the image forming apparatus of the present embodiment, when the operation of the image forming apparatus is stable, the sizes of the first color registration mark and the second color registration mark to be formed are set, for example, when the image forming apparatus is turned on or printed. Since it can be made smaller than when the operation is unstable at the start or the like, for example, even when the color registration mark is printed on the continuous paper during printing of the continuous paper, it is not noticeable. Further, it is possible to reduce the amount of toner used for forming the color registration mark.

It is a figure which shows the main structures of the image forming layer apparatus which concerns on embodiment of this invention. 2 is a block diagram of a control system of the image forming apparatus according to the embodiment of the present invention. FIG. 5 is a flowchart showing the overall processing flow of a control routine for controlling image positional deviation executed by the image forming apparatus according to the embodiment of the present invention. It is explanatory drawing of the color registration mark formed with the image forming apparatus which concerns on embodiment of this invention. FIG. 6 is an explanatory diagram of image misalignment correction executed by the image forming apparatus according to the embodiment of the present invention. It is explanatory drawing of the size of the color registration mark formed with the image forming apparatus which concerns on embodiment of this invention. 6 is a flowchart showing a processing flow of a control routine executed by a color registration mark detection unit of the image forming apparatus according to the embodiment of the present invention. It is explanatory drawing of the output of the reflection type sensor of the color registration mark detection part of the image forming apparatus which concerns on embodiment of this invention. It is explanatory drawing of the shift | offset | difference of the formation position of the color registration mark formed with the image forming apparatus which concerns on embodiment of this invention. FIG. 6 is an explanatory diagram of a shift in the main scanning direction of a color registration mark formed by the image forming apparatus according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Continuous paper 12Y-K Print part 72 Color registration mark detection part 74 Image formation control part 90 Reflective sensor 80Y-K Color registration mark 82Y-K Color registration mark

Claims (3)

A plurality of image forming means provided for each color for forming a color image on a recording medium by performing main scanning and sub-scanning;
The plurality of image forming units are controlled so that an image based on image data is formed, a first registration mark in which a deviation in the main scanning direction does not appear in the sub scanning direction, and a deviation in the main scanning direction are sub scanning. A second registration mark that appears in a direction, and each of the first registration mark and the second registration mark is different from a reference color mark and a reference color that is spaced from the reference color mark by a predetermined distance in the sub-scanning direction. Control means for controlling the plurality of image forming means so that a registration mark having a color mark is formed a plurality of times at a predetermined timing;
Reading means for reading the first registration mark and the second registration mark formed on the recording medium;
Based on the reading result of the reading means, the correction amount in the sub-scanning direction is calculated using the shift amount in the sub-scanning direction of the mark of the other color with respect to the reference color mark for the first registration mark. First calculating means;
Based on the reading result of the reading means, the shift amount of the other color mark in the sub-scanning direction with respect to the reference color mark for the first registration mark, and the reference color for the second registration mark Second calculating means for calculating a correction amount in the main scanning direction using a deviation amount in the sub-scanning direction of the mark of the other color with respect to the mark;
An image forming position correcting unit that corrects an image forming position based on the image data based on the correction amount calculated by the first calculating unit and the second calculating unit;
And the control means forms the first registration mark and the second registration mark of the first size for the first time, and the sub-scan calculated by the first calculation means after the second time. The direction correction amount is equal to or less than a predetermined value in the sub-scanning direction, and the correction amount in the main scanning direction calculated by the second calculating unit is equal to or less than a predetermined value in the main scanning direction. In some cases, the image forming apparatus controls the plurality of image forming units so that a first registration mark and a second registration mark having a second size smaller than the first size are formed. It said control means, the image forming apparatus according to claim 1 for controlling the plurality of image forming means so that the first registration mark and the second registration mark is formed in the sub-scanning direction. The control means has a correction amount in the sub-scanning direction calculated by the first calculation means that is equal to or smaller than a predetermined value in the sub-scanning direction, and the main calculation calculated by the second calculation means. When the correction amount in the scanning direction is equal to or smaller than a predetermined value in the main scanning direction, the first registration mark and the second registration mark are formed so that the predetermined interval is smaller than in other cases. The image forming apparatus according to claim 1 , wherein the image forming apparatus controls a plurality of image forming units.

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