JP5884627B2 - Image forming apparatus and misalignment correction method - Google Patents

Description

  The present invention relates to an image forming apparatus and a positional deviation correction method.

  In an image forming apparatus such as a copier or a printer, misregistration may occur during duplex printing. Conventionally, in order to correct misregistration, marks are printed on both sides of a sheet, and the print start position is adjusted according to the amount of misalignment of the marks (see, for example, Patent Document 1). As a method for detecting misalignment, there are disclosed a method for detecting misalignment between a mark on the front surface and a mark on the back surface that shows through, and a method of using a punch hole in the paper and using it as a reference position for the misalignment of the mark. Has been.

  In addition to misregistration, a method for correcting misalignment due to scanner distortion is disclosed (for example, see Patent Document 2). According to Patent Document 2, a method is disclosed in which grid lines are printed on the entire surface of a sheet using a correction chart, and a positional deviation at a specific point where each grid line intersects is detected.

JP 2003-173109 A JP 2006-345367 A

  Either method can detect misregistration with high accuracy, but the misregistration amount is not always a constant amount, but fluctuates. Therefore, an accurate misregistration cannot be detected only by using one sheet. . Practically, about 10 sheets are used, and correction is performed with an average value of the amount of misalignment detected on each sheet.

  However, the correction by the average value may obtain an average correction effect as a whole, but it cannot cope with the fluctuation itself, and there are not a few misregistrations that cannot be corrected in individual sheets. . In order to further improve the accuracy of correction, it is not sufficient to use about ten sheets, and it is necessary to print marks for detecting misregistration on more sheets, but the cost for the printing increases.

  The subject of this invention is correct | amending the position shift of a printing position accurately.

According to the invention of claim 1,
A printing unit for printing the detection pattern on a plurality of sheets;
A positional deviation amount measuring unit for measuring the positional deviation amount of the detection pattern;
The positional deviation amount is arranged in accordance with the time when the detection pattern is printed to calculate a temporal change in the positional deviation amount, and a periodic component of the positional deviation amount is calculated based on the temporal change in the calculated positional deviation amount. A periodic component extraction unit that extracts at least one and averages residual components;
A correction value calculation unit that calculates a correction value of misregistration based on at least the average value of the residue components;
An image forming apparatus is provided.

According to invention of Claim 2,
The correction value calculation unit predicts a positional deviation amount of a printing position periodically generated based on the periodic component, and uses the predicted positional deviation amount and a positional deviation amount obtained by totaling the average values of the residual components. 2. An image forming apparatus according to claim 1, wherein a correction value for misregistration is calculated.

According to invention of Claim 3,
The printing unit prints the detection pattern on both sides of a plurality of sheets of paper,
The positional deviation amount measuring unit measures the positional deviation amount of the detection pattern printed on both sides,
3. The image forming apparatus according to claim 1, wherein the periodic component extraction unit extracts a periodic component by arranging a positional deviation amount in accordance with a time when the detection pattern is printed.

According to invention of Claim 4,
The image forming apparatus according to claim 3, wherein the correction value is a correction value for a front-back displacement.

According to the invention of claim 5,
5. The image forming apparatus according to claim 1, wherein when extracting a plurality of periodic components, the periodic component extracting unit first extracts a long-period component and then extracts a short-period component. 6. Provided.

According to the invention of claim 6,
When extracting the short cycle component, the periodic component extraction unit extracts the short cycle component from the positional deviation amount in units of paper, and averages the short cycle components of each sheet by matching the phases of the extracted short cycle components. An image forming apparatus according to claim 5 is provided.

According to the invention of claim 7,
A positional deviation amount measuring step for measuring a positional deviation amount of a detection pattern printed on a plurality of sheets;
The positional deviation amount is arranged in accordance with the time when the detection pattern is printed to calculate a temporal change in the positional deviation amount, and a periodic component of the positional deviation amount is calculated based on the temporal change in the calculated positional deviation amount. Extracting at least one and averaging the residual components; and
A correction value calculating step for calculating a correction value for misregistration based on at least the average value of the residue components;
Is provided.

  According to the present invention, it is possible to accurately detect a positional shift that fluctuates periodically. By extracting the periodic component of the positional deviation and acquiring the average value of the residual components, it is possible to accurately detect and correct the positional deviation that occurs in units of paper. In addition, it is possible to predict the amount of misalignment that periodically varies from the extracted periodic component and add it to the average value of the residual component to calculate a correction value. It becomes possible.

1 is a functional block diagram of an image forming apparatus according to the present embodiment. It is a schematic block diagram of a printing part. It is a flowchart of a position shift correction process. An example of a detection pattern is shown. It is a figure showing the relationship between the printing pattern of double-sided printing, and the time when the detection pattern was printed. It is a figure showing the measured value of the amount of position shifts for every fixed time. The image figure of the amount of position shift which arises by the factor of paper dependence is shown. The image figure of the amount of position shift which arises by the factor of paper dependence is shown. The period of a long period component and a short period component is shown.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an image forming apparatus and a positional deviation correction method of the present invention will be described below with reference to the drawings.

FIG. 1 is a functional block diagram of an image forming apparatus 1 according to the present embodiment.
As shown in FIG. 1, the image forming apparatus 1 includes a control unit 21, a storage unit 22, an operation unit 23, a display unit 24, an IF 25, an image reading unit 3, an image processing unit 4, a misregistration correction unit 5, and an image memory 6. The printing unit 7 is provided.

  The control unit 21 reads a program stored in the storage unit 22, controls the operation of each unit of the image forming apparatus 1 in cooperation with the program, and executes various processes such as a printing process. The control unit 21 can be configured by a CPU (Central Processing Unit) and a RAM (Random Access Memory).

The storage unit 22 stores a program executed by the control unit 21, data necessary for executing the program, and the like. As the storage unit 22, for example, a hard disk or the like can be used.
The storage unit 22 stores detection patterns. The detection pattern is used for detecting a positional deviation of the printing position.

The operation unit 23 includes operation keys, a touch panel, and the like, and outputs operation signals corresponding to these operations to the control unit 21.
The display unit 24 includes a display and displays an operation screen and the like according to instructions from the control unit 21. The display is configured by itself or integrally with the touch panel.
The IF 25 is an interface such as a USB (Universal Serial Bus). Two image forming apparatuses 1 can be connected via the IF 25, and a computer apparatus for maintenance can also be connected.

The image reading unit 3 includes a scanner and reads an original by optical scanning. The read signal (analog signal) is output to the image processing unit 4.
The image processing unit 4 performs signal processing on the read signal from the image reading unit 3, generates image data by A / D conversion, and stores the image data in the image memory 6. For example, a DRAM (Dynamic RAM) or the like can be used as the image memory 6.

The image processing unit 4 reads image data from the image memory 6 and performs various image processing. Examples of image processing include color conversion processing, enlargement / reduction processing, and screen processing. The image data after the image processing is stored in the image memory 6 and then output to the printing unit 7.
When measuring the displacement amount of the printing position, the detection pattern stored in the storage unit 22 is printed on the paper by the printing unit 7. When the paper is read by the image reading unit 3, the image processing unit 4 generates image data of a detection pattern from the read signal. The image data is stored in the image memory 6 and then output to the misalignment correction unit 5.

  The misregistration correction unit 5 analyzes the image data of the detection pattern, calculates a misregistration correction value for the printing position, and outputs the correction value to the printing unit 7. The misregistration correction unit 5 includes a misregistration amount measurement unit 51, a periodic component extraction unit 52, and a correction value calculation unit 53 as shown in FIG.

  The misregistration amount measurement unit 51 analyzes the image data of the detection pattern and measures the misregistration amount of the print position of the detection pattern.

  The periodic component extraction unit 52 extracts at least one periodic component of the positional deviation amount measured by the positional deviation amount measurement unit 51. After extraction, the periodic component extraction unit 52 averages the residual components of the positional deviation amount.

The correction value calculation unit 53 calculates a correction value for misregistration based on the average value of the residual components obtained by the periodic component extraction unit 52.
In addition, the correction value calculation unit 53 predicts the amount of misregistration of the printing position that periodically occurs based on each periodic component extracted by the periodic component extraction unit 52, and averages the residual component to the estimated amount of misregistration. It is also possible to calculate a misalignment correction value by adding the values.

The printing unit 7 prints a toner image on a sheet based on the image data.
FIG. 2 is a schematic configuration diagram of the printing unit 7.
As shown in FIG. 2, the printing unit 7 includes a rotating intermediate transfer belt 71 and image forming units 72c, 72m, 72y, and 72k arranged in series on the intermediate transfer belt 71.

  The image forming units 72c, 72m, 72y, and 72k form toner images of colors C (cyan), M (magenta), Y (yellow), and K (black) on the intermediate transfer belt 71, respectively. The image forming units 72c, 72m, 72y, and 72k are different in toner color but have the same configuration, and include an exposure unit u1, a developing unit u2, a photosensitive drum u3, and the like. Each image forming unit 72c, 72m, 72y, 72k forms an electrostatic latent image by the exposure unit u1, develops it by the developing unit u2, forms a toner image on the photosensitive drum u3, and intermediately transfers the toner image. Transfer onto the belt 71.

  The printing unit 7 includes a secondary transfer roller 73 downstream of the rotation direction of the intermediate transfer belt 71, and transfers the toner image from the intermediate transfer belt 71 onto the paper by the secondary transfer roller 73. The printing unit 7 includes a sensor 76 immediately before the transfer position, detects the leading edge of the sheet conveyed from the sheet feeding tray by the sensor 76, and controls the sheet feeding timing to the transfer position.

  The printing unit 7 includes a fixing device 74, and the fixing device 74 fixes the paper on which the toner image is transferred. The printing unit 7 discharges the paper after the fixing process in the case of single-sided printing, but conveys the paper to the reversing mechanism 75 in the case of double-sided printing. The reversing mechanism 75 has a conveyance path that reverses the front and back of the paper when passing, and guides the paper whose front and back are reversed to the transfer position again.

FIG. 3 is a flowchart of misalignment correction processing executed by the image forming apparatus 1.
As shown in FIG. 3, the printing unit 7 prints the detection pattern on both surfaces of a plurality of sheets (step S1). The printing pattern of double-sided printing is not particularly limited, and printing can be performed while reversing the front and back of each sheet, or the back surface can be continuously printed after the front surface is continuously printed in units of a plurality of sheets.

FIG. 4 shows an example of the detection pattern.
In the detection pattern, as shown in FIG. 4, cross images called register marks are arranged at regular intervals. Note that the content of the detection pattern is not particularly limited as long as it is a pattern that can detect misalignment.

After printing, both sides of each sheet are read, but may be read by the image reading unit 3, or may be read by the line sensor provided immediately after the fixing device 74. The image processing unit 4 generates image data from the read signal and outputs it to the misalignment correction unit 5.
The misregistration correction unit 5 analyzes the image data on the front and back of each sheet by the misregistration amount measurement unit 51, and measures the misregistration amount of the print position of the detection pattern (step S2).

  Although the method for measuring the amount of misalignment is not particularly limited, in the case of the detection pattern shown in FIG. 4, the misalignment amount measuring unit 51 measures the distances x1 and y1 from the edge of the paper to the crosshairs of each registration mark. The difference between the distances x1 and y1 and the preset reference distances x0 and y0 can be acquired as the amount of positional deviation. (X0-x1) is the amount of positional deviation in the main scanning direction, and (y0-y1) is the amount of positional deviation in the sub-scanning direction.

  If a measurement value suddenly differs greatly from other measurement values, the measurement value is deleted and the paper on which the measurement value is obtained is discharged as scraped paper to prevent a reduction in correction accuracy. It is preferable to do. The number of splinter sheets may be counted, and maintenance may be urged when a certain number is reached.

  Next, the positional deviation correcting unit 5 extracts at least one periodic component of the positional deviation amount by the periodic component extracting unit 52. Since the time when the detection pattern is printed on the front and back of each sheet differs depending on the printing pattern at the time of double-sided printing, the periodic component extraction unit 52 arranges the positional deviation amount according to the time when the detection pattern is printed, Extract. The printing time is the time when the toner image is transferred onto the paper, and can be calculated from the time when the leading edge of the paper is detected by the sensor 76 and the paper conveyance speed.

  As shown in FIG. 5, when the detection patterns printed on the front and back sides of each sheet are arranged according to the printing time, when the double-sided printing is performed by inverting the front and back for each sheet, the arrangement is shown by the print pattern a. However, when two-sided printing is performed with the front and back reversed in units of three sheets, the arrangement shown by the print pattern b is obtained. In FIG. 5, the time on the horizontal axis indicates the time during which the image forming apparatus 1 is performing the printing operation. When the printing operation is stopped, the time during which the printing operation is performed is excluded except for the stop time. Since the print patterns a and b have different printing times on the respective sheets, the amount of misregistration at different time points is observed depending on whether the print pattern a or the print pattern b. Therefore, in order to extract the periodic component, the measurement values of the positional deviation amount are arranged in accordance with the time when each registration mark is printed, and the positional deviation amount is evaluated on a common time axis.

  For the extraction of the periodic component, the measured values of all the dragonflies can be used. As shown in FIG. 5, observation points pn (n is an integer) are set at regular intervals, and dragonflies corresponding to the respective observation points pn are set. Only measured values of can be used. The registration mark closest to the observation point pn can be selected as the registration mark corresponding to the observation point pn, or two registration marks located before and after the observation point pn are selected, and the average value of the respective displacement amounts is calculated as the registration mark. It can also be obtained as a displacement amount at the observation point pn. Like the observation point p7, for the observation point pn located between the sheets, it is sufficient to interpolate and use the positional deviation amounts of two register marks that are close to each other in the preceding and succeeding sheets.

FIG. 6 shows a diagram in which the amount of positional deviation corresponding to the observation point pn is arranged. The vertical axis represents the amount of displacement and the horizontal axis represents time. The time on the horizontal axis is the time during which the image forming apparatus 1 is performing the printing operation as described above.
As shown in FIG. 6, the positional deviation amount has periodicity and includes a plurality of periodic components. This is because the periodicity of the amount of positional deviation differs depending on the cause of the positional deviation. For example, in the case where the intermediate transfer belt 71 is a factor, a long-period position shift appears across the sheets in accordance with the distance of one round of the belt. Further, when the paper conveyance roller, the photosensitive drum u3, or the like is a factor, a short-cycle position shift corresponding to the distance corresponding to one rotation appears. When the positional deviation occurs after the toner images of the respective colors are superimposed on the intermediate transfer belt 71, the periodicity is common to the respective colors, but when it occurs before that, the periodicity is different from each other.

  When extracting a plurality of periodic components, the periodic component extracting unit 52 first extracts a long-period component (step S3). By extracting the long period component first, the accuracy of extracting the subsequent short period component is improved.

  The method for extracting the periodic component is not particularly limited, but a specific periodic component can be extracted by, for example, Fourier transforming the measured value of the positional deviation amount. After that, the extracted periodic component is subjected to inverse Fourier transform to acquire information on the period of the extracted periodic component, that is, information on the amount of positional deviation that is time and amplitude that is a phase. When the phase and the like of each periodic component can be specified in advance depending on the cause of positional deviation, it can also be extracted using a bandpass filter that can extract the neighboring components.

  After extracting the long cycle component, the cycle component extraction unit 52 similarly extracts the short cycle component of the positional deviation amount (step S4). When extracting short-period components, it is preferable to use the measurement values of all the register marks or increase the number of observation points pn in order to accurately grasp the phase. Although the phase may gradually shift, if the phase shift between the sheets is too large, it is difficult to accurately extract the short period component from the measured value of each sheet. In this case, it is preferable to extract a short period component of the amount of misalignment in units of paper, and after averaging these phases, averaging is performed. Thereby, more accurate information on the cycle of the short cycle component can be obtained.

  After extracting the periodic components, the periodic component extracting unit 52 averages the residual components (step S5). The residual component includes non-periodic components such as paper-dependent positional deviation and noise. As factors of the sheet-dependent positional deviation, for example, the following factors 1 to 3 can be cited.

Factor 1 is the expansion and contraction of the paper due to the fixing process. During double-sided printing, the paper expands and contracts due to the fixing process on the front surface, and the paper size varies between the front and back surfaces. This paper size shift appears as a positional shift, and the positional shift amount varies depending on the moisture content of the paper, the amount of toner adhesion, and the like.
Factor 2 is erroneous detection or error of the paper size. During double-sided printing, the leading edge of the paper is switched by reversing the front and back, but the paper feed timing to the transfer position is determined by the detection of the leading edge of the paper by the sensor 76, so it is necessary to correctly detect the paper size. . If the paper size is erroneously detected, or the paper size (for example, A4 size) is correctly detected, but the paper size has an error during cutting (for example, slightly smaller than the specified size), the front and back sides In this case, the sheet feeding timing is shifted and the position is shifted.
Factor 3 is an error in the paper transport position. When transporting paper to the transfer position, there is an adjustment mechanism that aligns one side of the front edge of the paper in the main scanning direction. However, if the front edge is changed by reversing the front and back during double-sided printing, the parallelism of the front edge alignment is shifted between the front and back. It may appear as a gap. For example, when the two sides of the leading and trailing edges of the sheet are not parallel due to the cutting error of the sheet, change with time, external force, humidity, etc., the parallelism of the front and back leading edge alignment shifts and a positional shift occurs.

7 and 8 show image diagrams of misalignment amounts caused by factors 1 to 3. FIG. 7 shows the amount of misalignment in the case of the print pattern a, and FIG. 8 shows the amount of misalignment in the case of the print pattern b.
As shown in FIGS. 7 and 8, the misregistration due to the factors 1 to 3 shows a specific misregistration amount depending on whether the printing surface is the front or the back. Further, the positional deviation due to the factors 1 to 3 occurs only on the paper, so that the paper is interrupted between the papers, and the positional deviation amount is not continuous between the papers because the positioning is repeated for each paper. All the residual components of each sheet may be averaged and may be a constant value regardless of the front and back of the sheet. However, as described above, a specific positional deviation amount appears depending on the front and back of the sheet. And as shown in FIG. 8, the average value of a residue component can also be calculated about each front and back of each paper. Note that the average value is obtained by averaging the residual components in a specific identical position area of each sheet. As a simple example, there is a case where the amount of misregistration is obtained for the four corners of the paper. In this case, the residual components of the misregistration amounts existing in the four corner regions may be averaged. Of course, if the expansion and contraction of the paper can be ignored and the overall positions of the front and back images only need to match, the residual components of the amount of positional deviation on the entire paper surface may be averaged.

Information on the average value of each periodic component and residual component of the positional deviation amount is stored in the storage unit 22.
When correcting the positional deviation between the front and the back in double-sided printing, the positional deviation correction unit 5 reads at least the average value of the residue component from the storage unit 22, and the correction value calculation unit 53 based on the average value of the residual component causes A correction value for deviation is calculated (step S6).

  The correction value calculation unit 53 reads out each periodic component of the misregistration amount from the storage unit 22, predicts the misregistration amount of the printing position that periodically occurs based on each periodic component, and predicts the misregistration amount and the residue A misregistration correction value can also be calculated using the misregistration amount obtained by summing up the average values of the components. According to this correction value, it is possible to perform correction corresponding to not only a positional deviation that occurs in units of paper but also a cyclically changing positional deviation.

  Specifically, the correction value calculation unit 53 obtains the phase and amplitude of each periodic component, and identifies the period of each periodic component as shown in FIG. The correction value calculation unit 53 calculates a predicted time when the leading edge of each sheet reaches the transfer position during double-sided printing, and acquires misregistration amounts z1 and z2 corresponding to the predicted time from the period of each periodic component. Regardless of whether the printing surface is front or back, the periodic component is misaligned depending on the time during which the printing operation is performed. Therefore, the periodic component occurs during printing regardless of the printing pattern a or the printing pattern b. The predicted misregistration amount can be acquired.

  Since the phase of each periodic component may gradually shift, it is preferable to detect a phase shift every fixed period and correct the shift by correcting the shift by a certain amount from the viewpoint of improving correction accuracy. For example, a registration mark for phase confirmation is printed on the nobby portion of the paper, and the period is shifted along the time axis in accordance with the positional deviation of the registration mark.

  Moreover, the correction value calculation part 53 acquires the average value z3 of a residue component. When the residual components are averaged for each front and back of the sheet as shown in FIGS. 7 and 8, the correction value calculation unit 53 acquires an average value z3 corresponding to the printing surface.

  The correction value calculation unit 53 calculates the correction value of the front and back positional deviation using the positional deviation amount (z1 + z2 + z3) obtained by adding the positional deviation amounts z1 and z2 of the respective periodic components and the average value z3 of the residual components. The correction value calculation unit 53 can also calculate correction values for correcting the positional deviation of the front and back surfaces of each sheet according to the reference position, and correct the positional deviation of the rear surface according to the amount of positional deviation of the front surface. A correction value can also be calculated. For example, when the positional deviation amount at the specific position on the front surface of the first sheet is +5, the positional deviation amount at the position corresponding to the back side of the specific position on the back surface of the first sheet is +2, and correction is performed according to the reference position. The correction value for the front surface of the first sheet is −5, and the correction value for the back surface of the first sheet is −2. When correcting according to the front surface, the correction value of the first front surface is 0, and the correction value of the first back surface is +3.

  Since the misregistration amount is measured in each of the main scanning direction and the sub scanning direction, the misregistration correction unit 5 uses the misregistration amount in each direction to correct the correction value in the main scanning direction and the correction value in the sub scanning direction. May be calculated.

  Based on the correction value output from the misalignment correcting unit 5, the printing unit 7 corrects misalignment (step S7). For example, the printing unit 7 adjusts the paper feeding timing to the transfer position according to the correction value. Further, as the correction of the positional deviation, the image processing unit 4 may adjust the magnification of the image data according to the correction value, and the image data is partially converted so that the positional deviation at each position in the sheet can be corrected. You may deform | transform into.

  As described above, according to the present embodiment, the image forming apparatus 1 includes the printing unit 7 that prints the detection pattern on a plurality of sheets, and the misregistration amount measurement unit 51 that measures the misregistration amount of the detection pattern. A periodic component extraction unit 52 that extracts at least one periodic component of the positional deviation amount and averages the residual component, and a correction value calculation unit that calculates a positional deviation correction value based on at least the average value of the residual component 53.

As a result, it is possible to accurately detect a positional shift that periodically varies. By extracting the periodic component of the positional deviation and acquiring the average value of the residual components, it is possible to accurately detect and correct the positional deviation that occurs in units of paper. In addition, it is possible to predict a positional deviation amount that periodically varies from the extracted periodic component and add it to the average value of the residual component to calculate a correction value, and it is also possible to perform correction corresponding to the periodic variation. .
If there is a measured value that can identify the phase, the periodic component of the positional deviation amount can be accurately detected even if the measured value of the positional deviation amount is less than one period, for example, half a period. it can. Therefore, consumption of toner and paper can be suppressed when measuring the amount of misalignment, and costs can be reduced.

The above embodiment is a preferred example of the present invention, and the present invention is not limited to this. Modifications can be made as appropriate without departing from the spirit of the present invention.
For example, when a sudden error such as a jam occurs, the positional relationship between the intermediate transfer belt and the photosensitive drum may shift, and the periodicity of the positional deviation amount may change. Therefore, when an error occurs, it is preferable to print the detection pattern and update the periodic component information of the positional deviation amount.

  In addition, the periodic component of the positional deviation amount is obtained for each paper type and stored in the storage unit 22, and the periodic component of the positional deviation amount corresponding to the paper type of the paper to be printed or its tray is read from the storage unit 22 to obtain a correction value. Is preferably calculated. Although the periodicity of the positional deviation amount may differ depending on the paper type, the positional deviation can be corrected corresponding to the different periodicity in this case as well.

  Further, the processing content of the positional deviation correction unit 5 is programmed, and the control unit 21 executes the program, whereby the positional deviation correction processing can be realized by software. As a computer-readable medium for such a program, a non-volatile memory such as a ROM and a flash memory, and a portable recording medium such as a CD-ROM can be applied. In addition, a carrier wave is also included as a medium for providing program data via a communication line.

  The processing content of the misalignment correction unit may be executed by an external computer device instead of the image forming apparatus 1. The computer apparatus can acquire the image data of the detection pattern printed by the image forming apparatus 1, calculate a correction value for misregistration, and provide it to the image forming apparatus 1.

  In addition, when a plurality of image forming apparatuses are connected and different image forming apparatuses print the front and back surfaces of the paper, the misalignment can be corrected in the same manner. Each image forming apparatus prints the detection pattern, calculates a correction value of the positional deviation from the reference position, and can correct the positional deviation. In addition, the image forming apparatus that performs printing on the back side can calculate a correction value of the positional deviation from the printing position on the front surface and correct the positional deviation according to the printing position on the front surface.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 21 Control part 22 Storage part 31 Storage part 3 Image reading part 4 Image processing part 5 Misalignment correction part 51 Misalignment amount measurement part 52 Periodic component extraction part 53 Correction value calculation part 6 Image memory 7 Printing part

Claims (7)

A printing unit for printing the detection pattern on a plurality of sheets;
A positional deviation amount measuring unit for measuring the positional deviation amount of the detection pattern;
The positional deviation amount is arranged in accordance with the time when the detection pattern is printed to calculate a temporal change in the positional deviation amount, and a periodic component of the positional deviation amount is calculated based on the temporal change in the calculated positional deviation amount. A periodic component extraction unit that extracts at least one and averages residual components;
A correction value calculation unit that calculates a correction value of misregistration based on at least the average value of the residue components;
An image forming apparatus comprising:   The correction value calculation unit predicts a positional deviation amount of a printing position periodically generated based on the periodic component, and uses the predicted positional deviation amount and a positional deviation amount obtained by totaling the average values of the residual components. The image forming apparatus according to claim 1, wherein a correction value for misregistration is calculated. The printing unit prints the detection pattern on both sides of a plurality of sheets of paper,
The positional deviation amount measuring unit measures the positional deviation amount of the detection pattern printed on both sides,
The image forming apparatus according to claim 1, wherein the periodic component extraction unit extracts a periodic component by arranging positional shift amounts in accordance with a time when the detection pattern is printed.   The image forming apparatus according to claim 3, wherein the correction value is a correction value for a front-back displacement.   5. The image forming apparatus according to claim 1, wherein when extracting a plurality of periodic components, the periodic component extracting unit first extracts a long-period component and then extracts a short-period component.   When extracting the short cycle component, the periodic component extraction unit extracts the short cycle component from the positional deviation amount in units of paper, and averages the short cycle components of each sheet by matching the phases of the extracted short cycle components. The image forming apparatus according to claim 5. A positional deviation amount measuring step for measuring a positional deviation amount of a detection pattern printed on a plurality of sheets;
The positional deviation amount is arranged in accordance with the time when the detection pattern is printed to calculate a temporal change in the positional deviation amount, and a periodic component of the positional deviation amount is calculated based on the temporal change in the calculated positional deviation amount. Extracting at least one and averaging the residual components; and
A correction value calculating step for calculating a correction value for misregistration based on at least the average value of the residue components;
Correction method including misalignment.

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