JP2018031813A - Image forming apparatus and method for controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can even correct a large positional shift in a main scanning direction of colors (color shift), and a method for controlling the same.SOLUTION: An image forming apparatus 100 comprises: a first image forming unit 4K that forms a first image; a second image forming unit 4Y that forms a second image; third image forming units 4M, 4C, and 4W that form third images; a detection part 17 that detects the amount of first positional shift UXY between the first image and second image; and a control part that determines the amounts of second positional shift UXM, UXC, and UXW between the first image and third images on the basis of the amount of first positional shift UXY, and corrects the positions of the third images on the basis of the amounts of second positional shift UXM, UXC, and UXW.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus and a control method thereof.

  The color misregistration correction of the electrophotographic image forming apparatus in the conventional printer, copying machine, facsimile machine, multifunction machine, etc. is transferred by superimposing two color toner images on the transfer belt, and the density of reflection of the superposed patch is 2 There is one that detects the amount of misregistration between colors (for example, see Patent Document 1). There is also a multicolor image forming apparatus in which color expressions are diversified by adding special color toners such as white and clear (for example, see Patent Document 2).

JP 2001-134041 A Japanese Patent Laying-Open No. 2015-176032

  However, the multicolor image forming apparatus to which the special color toner is added tends to be larger in the transfer belt conveyance direction than the conventional small image forming apparatus or the general four color image forming apparatus. There is a tendency for the amount of color misregistration (color misregistration amount) that is far from each other in the transport direction to increase. In particular, the positional deviation in the direction orthogonal to the transfer belt conveyance direction, that is, the main scanning direction is remarkable. Further, since the weight of the apparatus increases as the size of the apparatus increases, there is a problem in that the amount of displacement is further increased due to distortion of the installation surface of the apparatus.

  When the amount of misregistration increases as described above, a color misregistration correction method in the same range as that of a conventional small image forming apparatus or a general four-color image forming apparatus is applied. I was unable to respond. In consideration of this, it has been necessary to greatly expand the range of detection and correction of possible misregistration. As a result, there is a problem that extra toner consumption and correction time are required for detection.

  The present invention has been made to solve the above-described problems, and provides an image forming apparatus capable of performing correction even when a positional shift (color shift) in the main scanning direction of each color is large, and a control method thereof. The purpose is to do.

  An image forming apparatus according to an aspect of the present invention includes a first image forming unit that forms a first image, and a first direction that is a medium transport direction with respect to the first image forming unit. A second image forming unit disposed at a distance of 1 to form a second image, and a second image forming unit longer than the first distance with respect to the first image forming unit in the first direction. A third image forming unit arranged at a distance of 2 to form a third image, and a second orthogonal to the first direction between the first image and the second image A second detecting unit configured to detect a first misregistration amount in the direction, and a second in the second direction between the first image and the third image based on the first misregistration amount. A positional deviation amount is determined, and the second direction is determined based on the second positional deviation amount. And having a control unit for correcting the position of definitive the third image.

  According to one aspect of the present invention, there is provided a method for controlling an image forming apparatus, comprising: forming a first image by a first image forming unit; and forming the first image in a first direction that is a medium transport direction. Forming a second image with a second image forming unit disposed at a first distance relative to the unit; and, in the first direction, the first image forming unit with respect to the first image forming unit. Forming a third image by a third image forming unit disposed at a second distance longer than the first distance; and the first image between the first image and the second image. A detection step of detecting a first misregistration amount in a second direction orthogonal to the first direction, and based on the first misregistration amount, between the first image and the third image. Second position in the second direction Determining a shift amount, based on said second positional deviation amount, and having the steps of: correcting the position of the third image in the second direction.

  According to the present invention, it is possible to provide an image forming apparatus capable of performing correction even when a positional deviation (color deviation) of each color in the main scanning direction is large, and a control method therefor.

1 is a diagram illustrating a schematic configuration of a printer as an image forming apparatus according to an embodiment of the present invention. 3 is a block diagram illustrating a configuration of a printer control unit according to the embodiment. FIG. It is a circuit block diagram which shows the structure around the density | concentration detection sensor in embodiment. 1 is a perspective view illustrating a schematic configuration of a printer according to an embodiment. (a) is a figure which shows the position shift of the main scanning direction about the apparatus A of a structure with high rigidity of an apparatus upper surface, (b) is the figure of the main scanning direction about the apparatus B of a structure with low rigidity of an apparatus upper surface. It is a figure which shows position shift. 6 is a graph showing the amount of positional deviation in the main scanning direction of each color with respect to the distortion level of apparatus A. It is a table | surface which shows the value of the coefficient A of each color in embodiment. It is a graph which shows the relationship between the offset amount of each color in an embodiment, and a distortion level. (A) And (b) is a figure which shows the patch pattern for detecting the positional offset amount of each color in embodiment. It is a graph which shows the relationship between the positional offset amount of each color after offset in an embodiment, and the distortion level of an apparatus. It is the figure which showed the correction value of the position shift of each color in the state without the distortion of the apparatus detected at the time of the apparatus shipping inspection in embodiment. It is a top view which shows the schematic structure of the LED head in embodiment.

  Hereinafter, an image forming apparatus and a control method thereof according to an embodiment of the present invention will be described with reference to the drawings. In the figure, an xyz orthogonal coordinate system is shown for easy understanding of the relationship between the figures. In the figure, the x-axis is shown as a coordinate axis parallel to the main scanning direction of the image forming apparatus. In the figure, the y-axis is shown as a coordinate axis parallel to the sub-scanning direction of the image forming apparatus. In the drawing, the z-axis is shown as a coordinate axis parallel to the vertical direction of the image forming apparatus.

<< 1 >> Configuration FIG. 1 is a diagram showing a schematic configuration of a printer 100 as an image forming apparatus according to an embodiment of the present invention. The image forming apparatus is, for example, a printer, a copier, a facsimile, or the like, and may be any apparatus that can be used for image formation. In the description of the embodiment, the image forming apparatus will be described as a printer 100 that employs an electrophotographic system. In the following description, the image forming apparatus may be referred to as apparatus A or apparatus B. In addition, the image forming apparatus according to the embodiment can be regarded as a control method of the image forming apparatus.

  As shown in FIG. 1, the printer 100 includes a paper cassette 2 that stores a print medium 3. In addition, the printer 100 includes a paper feed roller 31 as a means for feeding and transporting the print medium 3, paper sensors 37 and 38 for detecting the transport position of the print medium 3, the secondary transfer roller 21, and the backup roller 14. And a pair of conveying rollers 18 and 19 for conveying the printing medium 3 and a fixing means 50 for fixing the toner image of the printing medium 3 with heat and pressure. A discharge roller pair 36 is provided on a route for discharging the print medium 3 after passing through the fixing unit 50. The fixing unit 50 includes, for example, a heat roller 53 that is heated by a heater 51 such as a halogen heater, a pressure roller 52, and a temperature sensor 54 that detects the surface temperature of the heat roller 53.

  As shown in FIG. 1, the printer 100 includes, as elements for forming a secondary transfer image, an intermediate transfer belt 11 as an intermediate transfer medium, a belt driving roller 13 that drives the intermediate transfer belt 11 to rotate, and an intermediate transfer belt. 11 and a belt tension roller 12 that stretches the belt 11. The intermediate transfer belt 11 is conveyed in the arrow direction in FIG. The printer 100 also includes an image drum unit 4K (black) as a first image forming unit that forms a first image, and an image drum unit 4Y (yellow) as a second image forming unit that forms a second image. And image drum units 4W (white), 4C (cyan), and 4M (magenta) as third image forming units for forming a third image (hereinafter referred to as ID units). As shown in FIG. 1, the ID units 4W, 4C, 4M, 4Y, and 4K are arranged at regular intervals (first and second distances) in the sub-scanning direction (y-axis direction). .

  As shown in FIG. 1, the printer 100 includes LED heads 6W, 6C, 6M, 6Y, 6K that form electrostatic latent images of ID units 4W, 4C, 4M, 4Y, 4K, and ID units 4W, 4C, Each of the transfer rollers 5W, 5C, 5M, 5Y, and 5K is configured to primarily transfer the toner images formed by 4M, 4Y, and 4K to the intermediate transfer belt 11. In addition, the printer 100 includes a blade 15 that scrapes off a residual transfer toner slightly remaining on the intermediate transfer belt 11 after the secondary transfer of the primary transferred toner image to the print medium 3, and a collection container 16. The printer 100 includes a density detection sensor 17 that measures the amount of primary transfer toner on the intermediate transfer belt 11.

  FIG. 2 is a block diagram illustrating a configuration of the printer control unit 60 according to the embodiment. The printer control unit 60 in the embodiment detects a shift in the printing position in the main scanning direction and the sub-scanning direction in the image forming apparatus 100 and performs an operation for correcting the shift.

  As shown in FIG. 2, the printer controller 60 includes a mechanism controller 61, a high voltage controller 62, a motor controller 63, an LED head controller 64, a high voltage power supply 65, an image processor 66, And an operation panel 67. The mechanism control unit 61 includes a CPU 61a, a timer 61b, a counter 61c, and a storage device (first and second storage units) 61d that stores programs and correction values. The high voltage controller 62 is connected to a high voltage power supply 65 and controls the voltage for image formation of the ID units 4W, 4C, 4M, 4Y, and 4K which are printing mechanisms. The motor control unit 63 rotationally drives a belt motor that rotationally drives the transfer belt, a drum motor that drives the photosensitive drums of the ID units 4W, 4C, 4M, 4Y, and 4K, a feed motor that conveys the print medium 3, and the like.

  As shown in FIG. 2, the LED head control unit 64 is connected to the LED heads 6W, 6C, 6M, 6Y, and 6K that are electrostatic latent image exposure means of the image forming units for each color, and is input from the image processing unit. The LED heads 6W, 6C, 6M, 6Y, and 6K are controlled based on the bitmap image. The LED head control unit 64 is connected to the mechanism control unit 61 and controls exposure timing in the sub-scanning direction and the main scanning direction in the image forming apparatus 100 while synchronizing with the feed motor and the belt motor. As shown in FIG. 2, the printer control unit 60 includes a density detection sensor 17 as a detection unit that detects positional color misregistration between colors. The density detection sensor 17 is controlled by the mechanism control unit 61.

  FIG. 3 is a circuit block diagram showing a configuration around the density detection sensor 17 in the embodiment. As shown in FIG. 3, the density detection sensor (reflection intensity detection mechanism) 17 includes a light emitting unit 17a, a light receiving unit 17b, a limiting resistor 17c, and a power source 17d. A mechanism control unit 61 is connected to the density detection sensor 17 to control the density detection sensor 17. Infrared light is emitted from the light emitting portion 17a, reflected by the intermediate transfer belt 11, and the reflected light reflected is received by the light receiving portion 17b. The reflection intensity of the reflected light received by the light receiving unit 17b is converted into a minute current.

  As shown in FIG. 3, the mechanism control unit 61 connected to the concentration detection sensor 17 includes a voltage / current conversion circuit 61e, a D / A converter (digital / analog conversion circuit) 61f, a storage device 61d, a CPU (central). a processing unit) 61a, a signal amplification circuit 61g, and an A / D converter (analog-digital conversion circuit) 61h.

  The voltage-current conversion circuit 61e and the D / A converter 61f adjust the light emission amount of the light emitting unit 17a of the concentration detection sensor by adjusting the current of the light emitting unit 17a of the concentration detection sensor 17. The signal amplifying circuit 61g receives the light received by the light receiving unit 17b of the concentration detection sensor 17, amplifies the converted minute current, and outputs the amplified current to the A / D converter 61h.

  The A / D converter 61h converts the direct current input from the signal amplification circuit 61g into an alternating current and outputs the alternating current to the CPU 61a so that the CPU 61a can perform computation. The CPU 61a, the storage device 61d, the D / A converter 61f, and the A / D converter 61h may not have different configurations. For example, as the CPU 61a, a CPU 61d, a D / A converter 61f, and an A / D converter 61h can be used.

<< 2 >> Operation Hereinafter, the operation of the printer 100 in the present embodiment will be described. First, the relationship between the distortion applied to the apparatus (distortion) and the positional shift (color shift) of each color in the main scanning direction will be described with reference to FIGS. The distortion applied to the apparatus is, for example, a distortion generated in the shape of the entire apparatus due to distortion on the installation surface on which the printer 100 is installed. The positional deviation in the main scanning direction is a positional deviation (color deviation) in the main scanning direction between the LED heads 6W, 6C, 6M, 6Y, and 6K and the intermediate transfer belt 11. The main scanning direction is the x-axis direction in FIG. The sub-scanning direction is the y-axis direction in FIG.

  FIG. 4 is a perspective view illustrating a schematic configuration of the printer 100 according to the embodiment. As shown in FIG. 4, the printer 100 has a device upper surface 101 and a device bottom surface 102. The positions of the LED heads 6W, 6C, 6M, 6Y, and 6K in FIG. 4 in the main scanning direction are affected by the position and shape of the apparatus upper surface 101 and change in conjunction with the position and shape of the apparatus upper surface 101. For example, when the upper surface 101 of the apparatus is distorted in the vertical direction (z-axis direction in FIG. 4), the LED heads 6W, 6C, 6M, 6Y, and 6K are similarly distorted in the vertical direction (z-axis direction in FIG. 4). The intermediate transfer belt 11 as a primary transfer medium is affected by the position and shape of the apparatus bottom surface 102 and changes in conjunction with the position and shape of the apparatus bottom surface 102. In the embodiment, for example, a case where distortion is applied in the direction of the arrow 200 (+ z axis direction) in FIG. 4 to one corner 102a of the apparatus bottom surface 102 will be described as an example.

  FIGS. 5A and 5B are schematic diagrams for explaining an outline of the positional deviation in the main scanning direction when the printer 100 is distorted in the direction of the arrow 200 in FIG. FIG. 5B is a diagram showing an outline of the positional deviation in the main scanning direction for the apparatus A having a high rigidity on the apparatus upper surface 101, and FIG. 5B shows the apparatus B having a structure on the apparatus upper surface 101 having a low rigidity. It is a figure which shows the outline | summary of the position shift of a main scanning direction.

  As shown in FIG. 5A, in the apparatus A having a configuration in which the apparatus upper surface 101 has high rigidity, even if the apparatus A is distorted, the shape of the apparatus upper surface 101 is not distorted. Therefore, the shape of the device upper surface 101 remains rectangular. At this time, the LED heads 6 </ b> W, 6 </ b> C, 6 </ b> M, 6 </ b> Y, and 6 </ b> K are not distorted similarly to the upper surface 101 of the apparatus. However, the apparatus bottom surface 102 is distorted so as to rotate counterclockwise in FIG. At this time, the position of the intermediate transfer belt 11 provided at the lower part in the printer 100 is also deformed so as to rotate counterclockwise with respect to the upper surface 101 of the apparatus.

  At this time, there is a positional deviation in the main scanning direction between the LED heads 6W, 6C, 6M, 6Y, and 6K and the intermediate transfer belt 11. As shown in FIG. 5A, the conveyance direction (sub-scanning direction) vector of the intermediate transfer belt 11 is 90 indicated by a broken line, whereas the sub-scanning of the LED heads 6W, 6C, 6M, 6Y, and 6K. The vector of the direction is 91 indicated by a solid line, and when the vectors 90 and 91 are shifted, a positional shift (color shift) of each color in the main scanning direction occurs. Specifically, between the image transferred onto the intermediate transfer belt 11 by the LED head 6W and the image transferred onto the intermediate transfer belt 11 by the LED head 6K, the vector shown in FIG. A positional shift (color shift) of the same amount as the shift of 90 and the vector 91 occurs in the main scanning direction.

  As shown in FIG. 5B, in the device B where the rigidity of the device upper surface 101 is low, the device upper surface 101 is distorted with respect to the device bottom surface 102. Further, the shape of the upper surface 101 of the device is also distorted into a rhombus. As the apparatus upper surface 101 is distorted, the LED heads 6W, 6C, 6M, 6Y, and 6K are also distorted so that the arrangement thereof is obliquely shifted. At this time, the conveyance direction (sub-scanning direction) vector of the intermediate transfer belt 11 is 92 indicated by a dotted line, and the vector in the sub-scanning direction of the LED heads 6W, 6C, 6M, 6Y, and 6K is 93 indicated by a solid line. . As shown in FIG. 5B, the position of W (white) in the main scanning direction far from the reference color K (black) of the apparatus B is greatly shifted to the left due to the relationship between the vectors 92 and 93. I understand that

  In an image forming apparatus using a laser light source, the rigidity of a laser unit, which is a precision component, is often set high, and the characteristics of the apparatus A shown in FIG. Therefore, hereinafter, the configuration of the device A shown in FIG. 5A will be described as an example.

  FIG. 6 is a graph illustrating the amount of misregistration (color misregistration amount) of each color in the main scanning direction with respect to the distortion level of apparatus A. In FIG. 6, the vertical axis represents the amount of misregistration of each color in the main scanning direction, and the horizontal axis represents the distortion level of apparatus A. In FIG. 6, the unit of the positional deviation amount of each color in the main scanning direction is 1/1200 inch unit, and the direction shifted to the left with respect to the reference color K (black) is positive. Further, the distortion level of the apparatus A is calculated based on the amount of misalignment in the main scanning direction of Y (yellow) closest to the reference color K (black). As shown in FIG. 6, the distance from the reference color K (black) (the distance between the LED heads) and the amount of misregistration of each color in the main scanning direction are approximately proportional. It can be seen that the amount of displacement in the scanning direction tends to increase.

  In FIG. 6, the amount of positional deviation in each main scanning direction when the distortion level of the apparatus A is 0 is represented by 0. In FIG. 6, the upper limit of the detection range and the correction range in the main scanning direction in the conventional small-sized printing apparatus and the general four-color printing apparatus is indicated by max and min. As shown in FIG. 6, the upper limit value (max) of the detection and correction range of the positional deviation amount in the main scanning direction in the conventional apparatus is +20, and the lower limit value (min) is −20.

  As shown in FIG. 6, in C (cyan) and W (white), which are colors separated from the reference color K (black), the positional deviation in the main scanning direction exceeds the upper limit value and the lower limit value. As described above, when the amount of misregistration in the main scanning direction exceeds the upper limit value and the lower limit value described above, it exceeds the detectable range set in advance in the printer 100. Correction) is not performed properly.

The details of the misregistration correction for each color in the present embodiment will be described below. In the present embodiment, attention is first focused on the detected value of the positional deviation amount (first positional deviation amount) in the main scanning direction of Y (yellow) closest to the reference color K (black). As shown in FIG. 6, the amount of misalignment in the main scanning direction of Y (yellow) is within a range of ± 20 regardless of the distortion of any device, and the misalignment can be detected and detected without exceeding the detection range. Correction is possible. Assuming that the distortion level of the apparatus A is X and the expected displacement amount of each color in the main scanning direction is UX, the displacement amount UX is expressed by the following equation (1) using the coefficient A.
UX = A × X (1)

FIG. 7 is a table showing the value of the coefficient A for each color in the embodiment. FIG. 8 is a graph showing the relationship between the offset amount of each color and the distortion level in the embodiment. In the device A in the embodiment, the coefficient A indicating the relationship between the distortion level and the offset amount in each color is as shown in the table shown in FIG. From FIG. 7, when the amount of positional deviation of each color from the reference color K (black) is UXW (white), UXC (cyan), UXM (magenta), UXY (yellow), UXW, UXC, UXM (first) 2) and UXY (first positional deviation amount), the following expressions (2) to (4) are satisfied.
UXW = UXY × 3.0 (2)
UXC = UXY × 2.1 (3)
UXM = UXY × 1.5 (4)

  As shown in FIGS. 7 and 8, the value of the coefficient A is higher as the color is farther from the reference color K (black). This indicates that the position displacement in the main scanning direction increases as the color is farther from the reference color K (black). The coefficient A is obtained in advance as a characteristic of the same model, recorded in the storage device 61d, and used for calculation at the time of correcting the misalignment.

  FIGS. 9A and 9B are diagrams illustrating patch patterns for detecting the amount of misregistration of each color in the embodiment. FIG. 9A shows the case where the positional deviation of each color is 0, and FIG. 9B shows the case where the positional deviation of each color is 2. 9A and 9B, the hatched area indicates the intermediate transfer belt 11, and the white area indicates a patch pattern formed by a color that is a target for detecting the amount of misalignment. Is shown. A region indicated by black indicates a patch pattern formed with the reference color K (black).

  As shown in FIGS. 9A and 9B, the position shift amount of each color in the main scanning direction in this embodiment is detected between the reference color K (black) and the color from which the position shift amount is detected. The density detection sensor 17 detects the density of reflection when the patch pattern is superimposed on the transfer belt 11. The patch pattern to be detected is as shown in FIGS. 9A and 9B, and the amount of displacement is calculated from the patch number of the portion having the highest diffuse reflection intensity. When there is no position shift, the diffuse reflection intensity is highest at the center 0, and therefore the position shift amount is calculated as 0. When the color (color) that is the target of the positional deviation detection is shifted by 2 to the left with respect to the reference color K (black), the diffuse reflection intensity is highest in the two portions 2 to the left of the center. The positional deviation amount is calculated as 2.

When the positional deviation amount of Y (yellow) in the main scanning direction is detected as 10 in this positional deviation amount detection operation, the distortion level of the apparatus is set to 10, and the position of each color in the main scanning direction is calculated from the above equation (1). The amount of deviation is calculated as follows. In order to make the detected value an integer, the decimal point is rounded off.
M: 15
C: 21
W: 30

  When the position correction is not applied, the position of the color in the main scanning direction is shifted from the reference color K (black) due to the distortion of the apparatus A. Therefore, at the time of patch generation at the time of detecting misalignment of M (magenta), C (cyan), and W (white), the LED head controller 64 sets dots in the main scanning direction for the LED head corresponding to each color. LED exposure is performed with a numerical offset.

  FIG. 10 is a graph showing the relationship between the amount of positional deviation of each color after offset and the distortion level of the apparatus in the embodiment. In FIG. 10, the vertical axis represents the amount of misregistration of each color in the main scanning direction, and the horizontal axis represents the distortion level of apparatus A. In FIG. 10, the unit of the positional deviation amount of each color in the main scanning direction is 1/1200 inch unit, and the direction shifted to the left with respect to the reference color K (black) is positive.

  As shown in FIG. 10, it can be seen that the amount of misregistration of each color after the offset is within the range of the upper limit value and the lower limit value (+20 to −20) for any distortion level of the apparatus. Before the offset for each color, as shown in FIG. 6, the amount of misregistration of each color exceeds the upper limit value and the lower limit value (+20 to −20). As a result, the color is greatly shifted. 9A and 9B, there is a patch in which the reflected light is maximum at a portion close to 0 in FIGS. 9A and 9B, and as shown in FIG. Can fall within the range of the upper limit value and the lower limit value (+20 to −20). As a result, the amount of misalignment of each color (M, C, W) can be detected within the same detectable range as when the amount of misalignment of Y (yellow) is detected. For Y (yellow), there is no need to offset, and the value has already been detected for the patch.

  Based on the above detection results, the positional deviation correction value at the time of final printing is the positional deviation amount (UXY) calculated from the positional deviation of Y (yellow), and the patch after offset as shown in FIG. The detected value is added. With this misalignment correction, each color dot is offset in the main scanning direction during printing.

  The above has described the case where the positional deviation amount of each color is 0 when the distortion level of the apparatus is 0. In practice, due to variations in manufacturing of each device, even if the distortion level of the device is 0, the displacement amount of each color is often 10 or more. Therefore, it is desirable to detect the amount of positional deviation of each color of each device in a state where there is no distortion of the device in advance, calculate the correction value, and add it to the correction value described above.

  FIG. 11 is a diagram illustrating correction values for the positional deviation of each color in a state where there is no distortion of the apparatus detected at the time of apparatus shipment inspection in the embodiment (a state where the distortion level is 0). As shown in FIG. 11, in the shipping inspection mode at the time of the shipping inspection of the apparatus, a positional deviation (measured positional deviation amount) of each color in a state where there is no distortion of the apparatus is detected, and the detection result is obtained as a correction value FXW, FXC for each color. , FXM, FXY are recorded in the storage device 61d.

  When Y is detected, a patch is output with an offset in the main scanning direction by FXY (first measured positional deviation amount). The distortion level of the apparatus is not added with FXY, but is set as a color misregistration detection value by a patch as described above. Based on the detection result of the distortion level of the apparatus, when generating detection patches of other colors, the main scanning is performed by adding the FXW, FXC, FXM (second measured displacement amount) of the other colors shown in FIG. 10 to the UX. Offset the dot in the direction. As for the final dot offset at this time, with respect to Y, FXY is added to the positional deviation amount detection value by the patch.

  The other color is a value obtained by adding the detection value (FXW, FXC, FXM) corresponding to each color and the UX of each color calculated above to the positional deviation amount detection value by the patch. As described above, it is possible to perform positional deviation correction (color misregistration correction) corresponding to the distortion of the apparatus at the time of shipment of the apparatus by setting the amount of positional deviation when the distortion level of the apparatus in the factory-shipped state is 0. it can.

  Next, a method for correcting the positional deviation in the main scanning direction caused by the inherent deviation amounts of the LED heads 6W, 6C, 6M, 6Y, and 6K will be described. LED heads 6W, 6C, 6M, 6Y, and 6K are components that can be replaced after shipment of the apparatus and cause large positional deviation in the main scanning direction. FIG. 12 is a plan view showing a schematic configuration of the LED head 6K in the embodiment. Since the other LED heads (6W to 6Y) have the same configuration as the LED head 6K, description thereof is omitted here. As shown in FIG. 12, the LED head 6 </ b> K includes a light emitting element 70, a storage device 71, and a fitting reference point 72.

  The LED head 6K needs to correct the light amount in units of dots in the main scanning direction so that the printing density unevenness is not conspicuous. The dot light correction value is recorded in an EEPROM (Electrically Erasable Programmable Read-Only Memory) which is a storage device 61d in the LED head 6K. Further, the distortion of the light emission position in the sub-scanning direction is measured for each dot in the main scanning direction of the LED head 6K, and is recorded in the storage device 61d as the distortion amount.

  In the measurement of the light emission position, the absolute position from the fitting reference point 72 between the LED head 6K and the printer 100 main body can be measured, and the positions of all dots are detected. An average value of the deviation amounts of all dots from the reference position in the main scanning direction is obtained and recorded as the deviation amount X in the storage device 61d. The shift amount X may not be an average value of all dots, but may be a specific one dot or a shift amount of two or more dots.

  For the LED heads 6W, 6C, 6M, 6Y, and 6K for all colors including the reference color K (black), a dot offset amount in the main scanning direction is set in advance by the LED head control unit 64 at the time of color misregistration detection and printing. . It is assumed that the deviation amount X recorded in the storage device 61d of each LED head 6W, 6C, 6M, 6Y, 6K is read by the mechanism control unit 61 when the printer 100 is activated. Even when the LED head (6W to 6K) is replaced by component replacement or the like, the positional deviation in the main scanning direction due to the inherent deviation amount X of the LED heads 6W, 6C, 6M, 6Y, and 6K is almost 0. Can be.

<< 3 >> Effect As described above, according to the printer 100 according to the embodiment, the interval from the reference color (for example, black) to the farthest color (for example, white) is wide in the sub-scanning direction (y-axis direction). In an image forming apparatus that is particularly large and has added special colors such as white and clear, the entire surface of the apparatus is distorted due to distortion on the installation surface of the apparatus, and misalignment of each color in the main scanning direction occurs. In such a case, it is possible to perform misalignment correction without changing the conventional misalignment detection pattern. As a result, the amount of misregistration can be detected and corrected without increasing the toner consumption and correction time associated with the correction, and printing can be performed without causing any color misregistration of each color.

  According to the printer 100 according to the embodiment, the positional deviation in the main scanning direction of each color in a state where there is no distortion of the apparatus is detected in advance, and the detection result is set as the correction value FXW, FXC, FXM, FXY of each color, and the storage device 61d. The position deviation correction is performed in consideration of the detection result. As a result, it is possible to take into account misregistration based on individual differences at the time of manufacturing the apparatus, and to improve the accuracy of misregistration correction (color misregistration correction).

<< 4 >> Modifications In the above embodiment, an example in which the present invention is applied to an intermediate transfer type image forming apparatus has been described. However, the present invention is directed to a direct transfer type image forming apparatus that directly transfers a toner image to a recording medium. It is possible to apply also to. Further, although the LED array head has been described as the exposure means, the present invention can be applied to a printing apparatus using laser light.

  In the above embodiment, the correction value of each color is calculated using the detected value (UXY) of the positional deviation amount in the main scanning direction of Y (yellow), which is the closest color to the reference color K (black), as the reference value. It is also possible to calculate a correction value for each color using the detected value (UXM) of the positional deviation amount in the main scanning direction of the reference color K (black) and the second closest color (for example, M (magenta)) as a reference value. is there. At this time, the positional deviation amount of the reference color K (black) and the second closest color (for example, M (magenta)) in the main scanning direction is within the range of the upper limit value and the lower limit value (+20 to −20). There is a need.

  In the above embodiment, an example in which the present invention is applied to an image forming apparatus using five color toners (W, C, M, Y, K) has been described. However, the present invention uses three or more color toners. The present invention can be similarly applied to an image forming apparatus.

  2 paper cassette, 3 print medium, 4W, 4C, 4M, 4Y, 4K image drum unit, 5W, 5C, 5M, 5Y, 5K transfer roller, 6W, 6C, 6M, 6Y, 6K LED head, 11 intermediate transfer belt, 12 Belt tension roller, 13 belt drive roller, 14 backup roller, 15 blade, 16 collection container, 17 density detection sensor, 18, 19 transport roller pair, 21 secondary transfer roller, 31 paper feed roller, 36 discharge roller pair, 37, 38 Paper sensor, 50 fixing means, 51 heat generating heater, 52 pressure roller, 53 heat roller, 54 temperature sensor, 60 printer control unit, 61a CPU, 61b timer, 61c counter, 61d storage device, 61 mechanism control unit, 62 high pressure Control unit, 63 motor control unit, 64 LED head control unit, 65 high voltage power supply, 66 image processing unit, 67 operation panel, 90, 91, 92, 93 vector, 100 printer, 101 device top surface, 102 device bottom surface, 102a corner .

Claims (8)

A first image forming unit for forming a first image;
A second image forming unit that is disposed at a first distance with respect to the first image forming unit in a first direction, which is a medium transport direction, and forms a second image;
A third image forming unit disposed in the first direction at a second distance longer than the first distance with respect to the first image forming unit to form a third image;
A detection unit for detecting a first positional shift amount in a second direction orthogonal to the first direction between the first image and the second image;
Based on the first displacement amount, a second displacement amount in the second direction between the first image and the third image is determined, and the second displacement amount is determined as the second displacement amount. Based on the control unit for correcting the position of the third image in the second direction;
An image forming apparatus comprising: A first storage unit that stores in advance a coefficient indicating a relationship between the first positional deviation amount and the second positional deviation amount;
The image forming apparatus according to claim 1, wherein the control unit determines the second misregistration amount from the first misregistration amount by a calculation formula using the coefficient.   The image forming apparatus according to claim 2, wherein the calculation formula determines the second misregistration amount by multiplying the first misregistration amount by the coefficient.   The correction by the control unit is performed by offsetting the third image formed by the third image forming unit in the second direction based on the second displacement amount. The image forming apparatus according to claim 3.   The said control part correct | amends the position in the said 2nd direction of the said 2nd image formed by the said 2nd image formation unit based on the said 1st positional offset amount. The image forming apparatus according to claim 1. The first actually measured displacement amount measured in advance in the second direction between the first image and the second image, and the first image and the third image between the first image and the second image. A second storage unit that stores a second actually measured displacement amount measured in advance in the second direction;
The controller corrects the position of the second image formed by the second image forming unit in the second direction based on the first actually measured positional deviation amount, and performs the second actual measurement. 6. The position of the third image formed by the third image forming unit in the second direction is corrected based on a positional deviation amount. The image forming apparatus described.   The first measured positional deviation amount and the second measured positional deviation amount are positional deviation amounts based on at least one of distortion of the image forming apparatus and distortion of the LED head due to individual differences during manufacturing. The image forming apparatus according to claim 6. Forming a first image by a first image forming unit;
Forming a second image by a second image forming unit disposed at a first distance with respect to the first image forming unit in a first direction which is a medium conveying direction;
Forming a third image by a third image forming unit disposed at a second distance longer than the first distance with respect to the first image forming unit in the first direction; When,
A detection step of detecting a first positional deviation amount in a second direction orthogonal to the first direction between the first image and the second image;
Determining a second displacement amount in the second direction between the first image and the third image based on the first displacement amount;
Correcting the position of the third image in the second direction based on the second displacement amount;
A control method for an image forming apparatus, comprising:

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