JP2010000720A - Image adjusting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mechanism capable of easily performing image adjustment without requiring complicated mechanical adjustment for image adjustment of an image forming apparatus.
An image digitally corrected based on actual measurement is measured again, and distortion of each laser scanning image is calculated based on the re-measured positional deviation amount and the positional deviation amount previously measured by actual measurement. The correction information for canceling is calculated.
[Selection] Figure 3

Description

  The present invention relates to an image adjustment technique for digitally correcting image distortion.

  In recent years, in order to increase the image forming speed in an electrophotographic color image forming apparatus, the same number of developing devices and photosensitive drums as the number of color materials are provided, and images of different colors are sequentially placed on an image conveying belt or a recording medium. The number of tandem color image forming apparatuses that transfer images is increasing. In this tandem color image forming apparatus, it is already known that there are a plurality of factors that cause registration deviation, and various countermeasures have been proposed for each factor.

  One factor is the non-uniformity of the lens of the optical laser unit, the mounting position shift, and the mounting position shift of the optical laser unit to the color image forming apparatus main body. In that case, the scan line is inclined or bent, and the degree of the change differs for each color, resulting in registration shift.

  As a method for dealing with this registration deviation, Patent Document 1 discloses that an optical sensor is used in an assembly process of an optical laser unit to measure the amount of bending of the scanning line, and the lens is mechanically rotated to rotate the lens. There has been proposed a method of correcting (adjusting) bending and fixing with an adhesive.

  Further, Patent Document 2 discloses a method of measuring an inclination of a scanning line using an optical sensor, adjusting an inclination of the scanning line by mechanically inclining an optical laser unit, and then assembling the main body on a color image forming apparatus main body. Has been proposed.

  Further, in Patent Document 3, in order to simplify the initial adjustment of the optical scanning device, a plurality of optical elements are simultaneously and independently arranged so that the scanning lens can be accessed from the upper surface of the optical box and desired optical characteristics can be obtained. An adjustment method for adjusting from the direction has been proposed.

  Further, Patent Document 4 proposes a configuration in which beam spots of a plurality of light beams are substantially linear on the surface to be scanned, and the linear beam spots have a predetermined angle with respect to the main scanning direction. Has been.

  Further, Patent Document 5 proposes a method of executing a divided writing method in which image data of each scanning line is written by correcting the scanning line curvature. Specifically, in an optical scanning device that optically scans a surface to be scanned with a light spot, an effective scanning region is divided into a plurality of regions: Di (i = 1, 2,...) According to scanning line bending characteristics. . Then, image data suitable for optical scanning of each region: Di is selected from the image data in a plurality of scanning lines for each optical scanning.

Further, Patent Document 6 proposes a method of measuring the inclination of a scanning line and the size of a curve using an optical sensor, correcting bitmap image data so as to cancel them, and forming the corrected image. ing. Since this method electrically corrects image data by processing it, it is described in Patent Documents 1, 2, 3, and 4 in that a mechanical adjustment member and an adjustment step during assembly are not required. Registration deviation can be dealt with at a lower cost than the method. This electrical registration error correction is divided into correction for each pixel and correction for less than one pixel. In the correction in units of one pixel, as shown in FIG. 13, the pixels are offset in the sub-scanning direction in units of one pixel in accordance with the correction amount of inclination and curvature. For correction of less than one pixel, as shown in FIG. 14, the gradation value of the bitmap image data is adjusted by pixels before and after in the sub-scanning direction. By performing the correction of less than one pixel, it is possible to eliminate an unnatural step at the offset boundary caused by the correction in units of one pixel and smooth the image.
JP 2002-116394 A JP 2003-241131 A JP 2005-054771 A JP 2004-148645 A JP 2003-322811 A JP 2004-170755 A

  However, the conventional example has the following drawbacks.

  In the assembly process of the optical laser unit, a method of measuring the amount of bending of the scanning line using an optical sensor, mechanically rotating the lens to correct (adjusting) the bending of the scanning line, and then fixing with an adhesive is It takes time and effort. In the case of a configuration having a plurality of lenses and a folding mirror as in a color image forming apparatus, the above-described adjustment takes a very long time, and the cost is accordingly increased.

  In addition, in the method proposed in Patent Document 5, although time and effort as in Patent Documents 1 to 4 can be reduced, the image quality is not sufficient in terms of image quality, and the linearity of an image such as a straight line is particularly poor. May not be enough.

  Further, the methods proposed in Patent Documents 5 and 6 have problems such as errors and distortions when the optical laser unit is attached to the image forming apparatus, or the inclination of the laser scanning surface to the image carrier. In other words, the laser scanning may be further distorted with respect to the measured tilt and curve data, and in this case, the registration shift of each color may not be sufficiently improved.

  On the other hand, as in Patent Documents 5 and 6, when digital correction is performed on a printed image that is not corrected for laser scanning, the adjustment range of the image forming apparatus is generally defined by the number of bits that can be calculated and the register range. The

  However, in order to cope with the bending and inclination of the laser scanning image exceeding the adjustment range, it is necessary to take a measure such as greatly expanding the calculation range. In order to achieve this, the cost of the configuration itself becomes expensive.

The present invention has been devised in view of the above points, and a plurality of laser beam generating means for generating a laser beam based on a laser scanning image, and each image carrier corresponding to the laser beam generated by the laser beam generating means. An optical laser unit having one or more rotary polygon mirrors to be deflected and scanned, and an electrostatic latent image is formed on each of the plurality of image carriers by the laser beam, and the electrostatic latent image on each image carrier A color misregistration adjustment method related to an image forming apparatus, comprising: a developing unit corresponding to a plurality of colors developed by a developer; and a unit for sequentially transferring a plurality of color images formed by each developing unit, The laser scanning output from the optical laser unit is measured by the irradiation position measuring means at three or more positions, and the measurement result is set as the first measurement result. A first calculation step of calculating a first correction information for eliminating the distortion of 査 image, based on the first correction information, a first digital correction step for correcting each laser scanning images,
An image for remeasurement is formed on the basis of each laser scanning image corrected in the first digital correction step, and laser scanning is performed at three or more positions using the formed image for remeasurement. A re-measurement step for re-measurement, and the re-measured measurement result as a second measurement result, based on the second measurement result and the first measurement result, for eliminating distortion of each laser scanning image It has a 2nd calculating process which calculates 2nd correction information, and a 2nd digital correction process which corrects each laser scanning picture based on the 2nd correction information.

  According to the present invention, the image quality of the output image of the image forming apparatus can be improved without significantly increasing the cost of the image forming apparatus main body.

Example 1
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

(Cross section of color laser beam printer)
FIG. 1 is a cross-sectional view showing the configuration of a color laser beam printer (hereinafter referred to as a color laser printer) which is an image forming apparatus according to the present invention. 201 is a color laser printer used in the present invention, and 202 is a host computer. The color laser printer used in the present invention includes a four-color image forming unit to form a color image in which images of four colors (yellow: Y, magenta: M, cyan: C, black: BK) are superimposed. Yes.

  The image forming unit 201 includes toner cartridges 207 to 210 having photosensitive drums 301 to 304 as image carriers. Also included is an optical laser unit (hereinafter referred to as a scanner unit) 205 having a laser diode for generating a laser beam as a light source for image exposure. Among these, the toner cartridge has one for each of the four colors. The scanner unit 205 will be described in detail later.

  The color laser printer 201 receives image data from the host computer 202. A print image generation unit 203 in the color laser printer 201 incorporates a CPU and develops received image data into desired video signal formation data (for example, bitmap data) to generate a video signal for image formation. The print image generation unit 203 and the image formation control unit 204 perform serial communication to transmit and receive information. The image formation control unit 204 also has a built-in CPU to control the image formation process of the laser printer. The video signal is transmitted to the image formation control unit 204, and the image formation control unit 204 drives a laser diode (not shown) in the scanner unit 205 in accordance with the video signal. Then, electrostatic latent images are formed on the photosensitive drums 301 to 304 (on the image carrier) in the toner cartridges 207 to 210, respectively.

  The photosensitive drums 301 to 304 are used to form an electrostatic latent image of 301, black, 302, cyan, 303, magenta and 304, respectively.

  The photosensitive drums 301 to 304 form toner images on the photosensitive drums 301 to 304 by visualizing the electrostatic latent images (developing with a developer) with the respective toner cartridges 207 to 210. Although not shown, it is assumed that there are multiple colors for developing the developer on the photosensitive drum.

  In the toner images of the respective colors developed on the photosensitive drums 301 to 304, first, a yellow (Y) image is transferred to the intermediate transfer belt 211, and then magenta (M), cyan (C), black ( BK) are sequentially transferred. As a result, a color image is formed on the intermediate transfer belt 211.

  The recording paper in the cassette 314 is fed to the registration roller 319 by the paper feeding roller 316, and the recording paper is conveyed in synchronization with the image on the intermediate transfer belt 211 at the driving timing of the registration roller 319. The color image is secondarily transferred from the intermediate transfer belt 211 to the recording paper by the transfer roller 318. The recording paper onto which the secondary transfer image has been transferred is fixed on the recording paper by heat and pressure by a fixing device 313 and then discharged onto a paper discharge tray 317 at the top of the printer.

  There is also a registration detection sensor 212 that monitors the registration position of the image on the intermediate transfer belt 211. This sensor reads the position of each color image formed on the intermediate transfer belt 211 at a desired timing other than during image formation, and feeds back the data to the print image generation unit 203 or the image formation control unit 204. This adjusts the image registration position of each color to prevent color misregistration.

(Detailed illustration of the scanner unit)
FIG. 2 is a diagram showing details of the scanner unit 205 in FIG.
In FIG. 2, reference numerals 101, 102, 103, and 104 denote laser diodes that scan the photosensitive drums 301, 302, 303, and 304 using video signals output via the image formation control unit 204. For convenience, 101 is referred to as a first laser diode (LD1), 102 is referred to as a second laser diode (LD2), 103 is referred to as a third laser diode (LD3), and 104 is referred to as a fourth laser diode (LD4). Reference numeral 105 denotes a polygon mirror (rotating polygon mirror), which is rotated at a constant speed in the direction of arrow A in the figure by a motor (not shown), and performs deflection scanning while reflecting the beams from the laser diodes LD1, LD2, LD3, and LD4. A motor (not shown) that drives the polygon mirror 105 is controlled to rotate at a constant speed by an acceleration signal and a deceleration signal of a speed control signal from the image formation control unit 204 and rotates.

  An optical sensor 110 is on the scanning path of the laser diode LD1 and generates a signal when a laser beam is incident to generate a horizontal synchronizing signal, and is called a BD (BeamDetect) sensor. In the present invention, the BD sensor 110 is only on the scanning path of the laser diode LD1, and does not exist on the scanning path of other laser diodes. The laser beam emitted from the laser diode LD1 is scanned by the rotation of the polygon mirror 105 while being reflected by the polygon mirror 105, is further reflected by the folding mirror 106, and the laser beam scans on the photosensitive drum 301 from left to right.

  In practice, the laser beam passes through various lens groups (not shown) in order to focus on the photosensitive drum or to convert the laser beam from diffused light to parallel light.

  Usually, the print image generation unit transmits a video signal to the image formation control unit 204 a predetermined time after detecting the output signal of the BD sensor 110. As a result, the main scanning start position of the image by the laser beam on the photosensitive drum always coincides.

  On the other hand, the laser diodes LD2, LD3, and LD4 also form electrostatic latent images on the photosensitive drums 302, 303, and 304, respectively, similarly to the laser diode LD1.

  Since the color laser printer used in the present invention does not have a BD sensor on the scanning path of the laser diodes 102, 103, and 104 for detecting BD, the write reference signal for the laser diodes LD2, LD3, and LD4 is used to generate a print image. The unit 203 generates. In the following description, the laser-side writing reference signal that does not have the BD sensor will be referred to as a pseudo BD signal. In this configuration, the pseudo BD signal is generated by the print image generation unit 203.

In this way, a black (BK) color image is formed on the photosensitive drum 301 by the laser diode LD 1 having the BD sensor 110. Further, cyan (C), magenta (M), and yellow (Y) color images are formed on the photosensitive drums 302, 303, and 304 by the laser diodes LD2, LD3, and LD4 that do not have the BD sensor 110, respectively.
The above is a series of processes for image formation by laser scanning.

(Laser scanning line correction)
Next, the main concept of this embodiment will be described with reference to FIG.

  S1 in FIG. 3A is one laser beam scanning image S1 among arbitrary laser beams output from the scanner unit 205. Note that the image forming apparatus used in the present invention has the laser scanning images of the four laser diodes LD1 to LD4, but in order to make the description of the present embodiment easier to understand, only one laser diode LD1 will be described. The ideal laser beam scanned image S1 should be arranged in a straight line at the position 0 of the main scanning, but actually, it is like the laser beam scanned image S1 in FIG. 3A unless high-precision adjustment is performed. . The laser beam scanning image S1 generally has a quadratic curve characteristic as shown in FIG.

  First, in order to derive an approximate expression of the quadratic curve of the laser beam scanning image S1, as shown in FIG. 9, the CCD sensor 403 is positioned at three positions -D, 0, and D at the irradiation position in the main scanning direction shown in FIG. , 401, 402 is attached as a tool. Thereby, the irradiation position in the sub-scanning direction of the laser scanning image at each position is measured. Here, the CCD sensors are arranged corresponding to the positions of the three points, but it goes without saying that it is possible to implement the sensor with three or more points.

  In practice, the laser diode 101 (LD1) emits light, and is scanned by being reflected by the rotating polygon mirror 105, and the laser scanning image S1 further reflected by the folding mirror 106 is measured by the CCD sensors 403, 401, and 402. . By this measurement, the sub-scanning deviations ΔL, ΔC, ΔR are measured.

  The sub-scanning deviations ΔL, ΔC, and ΔR that are the measurement results are not transferred to the laser scanning reference positional deviation amount storage unit 410 that stores the laser scanning reference positional deviation amount for each color included in the image forming unit 203 shown in FIG. Sent via the illustrated external interface. Then, the laser scanning reference positional deviation amount storage means 410 stores each sent color as L_ *, C_ *, R_ * (first measurement result).

  Then, the following quadratic curve approximation formula is derived based on the stored L_ *, C_ *, and R_ *. Although the storage unit 410 is described as being provided in the print image generation unit 203 in the color laser printer 201, various calculations may be performed by an external computer or the like.

  Hereinafter, the correction information calculation for eliminating the distortion of the laser scanning image will be described in detail based on the first measurement result. In the following description, −f (x) is first calculated, and −f (x) ′ is further calculated, so that the first calculation and the second calculation are distinguished from each other.

First, the positional deviation amount with respect to the sub-scanning direction is expressed by a general quadratic curve equation f (x) = ax ² + bx + c (1)
It is defined as

Therefore, the sub-scanning deviations ΔL, ΔC, ΔR in FIG. 3A are expressed by the following equations (2) to (4).
f (−D) = a (−D) ² + b (−D) + c = ΔL (2)
f (0) = a (0) ² + b (0) + c = ΔC (3)
f (D) = a (D) ² + b (D) + c = ΔR (4)
In order to obtain a quadratic curve, the coefficients a, b, and c need to be obtained from the above equations (2) to (4).
First, from equation (3), c = ΔC (5)
Can be obtained. Furthermore, from equation (2), equation (4) and equation (5), b = (ΔR−ΔL) / (2 × D) (6)
a = (ΔR + ΔL− (2 × ΔC)) / (2 × D ² ) (7)
Can be obtained.

  Then, based on the deviation amount obtained from the storage means 410 shown in FIG. 10, the calculation result of the laser scanning reference position deviation correction amount calculation means 411 that calculates the correction amount for each laser scanning image by the above equation is stored as an arithmetic expression correction coefficient. The color is stored in the means 412 for each color.

Therefore, an image file is created with a correction profile of −f (x) for the quadratic curve f (x) ((1)) in the sub-scanning direction calculated as described above. This -f (x) is referred to as first correction information in order to distinguish it from -f (x) 'obtained by re-positioning measurement and calculation, which will be described in detail later. f (x) ′ is referred to as second correction information. The created image file is schematically displayed in S2 of (b). The sub-scanning deviations ΔL ′, ΔC ′, and ΔR ′ in FIG. 3B are ΔL ′ = − ΔL ′.
ΔC ′ = − ΔC ′
ΔR ′ = − ΔR ′
It is.

  In order to perform digital correction based on the above-mentioned quadratic curve coefficient, the digital correction means capable of correcting the laser scanning reference position deviation in units of less than one pixel for each laser scanning image in FIG. 450 is transferred from the interface unit 413. By this delivery, the digital correction unit 450 executes image correction and creates an image file (laser scanning image) reflecting the correction. In order to distinguish from the case of creating an image file (laser scanning image) reflecting the correction based on -f (x) ', which will be described in detail later, these are called first digital correction and second digital correction, respectively. Distinguish. Here, the first digital correction is based on the first correction information (−f (x)) described above, and the second digital correction is based on the second correction information (−f (x) ′) described above. Based.

  In the present embodiment, the image generation unit 203 is described as being included in the color laser beam printer, but the present invention is not limited to this, and the host computer 202 or a controller (not shown) may be used.

  In the image file created above, for example, a linear image as shown in FIG. 11A is subjected to digital correction as shown in FIG. 11B based on the correction profile −f (x). It becomes an image.

  As described above, the ideal laser scanning image should be S3 of (c) by creating an image file with the correction profile -f (x) for the laser scanning image S1. However, in reality, when the scanner unit is assembled and imaged on the image forming apparatus, there are many cases where an image as shown in S4 of (d) is produced due to assembly variations and various other factors.

  Therefore, an image for measurement (for remeasurement) subjected to the primary digital correction is created from the digital correction means 450 in FIG. 10, and it is output, and S4 sub-scanning deviations ΔL ″ and ΔC ′ in FIG. ', ΔR' 'is measured again at the positions of -D, 0, D in the main scanning direction. As for the measurement method, an image scanner 500 as shown in FIG. 12 is used, and images at positions 502, 501, and 503 that are opposite to the positions -D, 0, and D in the main scanning direction of the measurement image on FIG. Measurement is performed by reading. ΔL ″, ΔC ″, ΔR ″ obtained by the calculation of the external calculation means 510 in FIG. 12 based on the measurement result (second measurement result) are the secondary correction laser scanning reference position deviation amount storage means. Store it in 414. An example of the calculation method of ΔL ″, ΔC ″, ΔR ″ will be described later with reference to FIG.

Based on the sub-scanning deviations ΔL ″, ΔC ″, ΔR ″ newly obtained by the measurement, a laser scanning image in the image forming apparatus can obtain the following new quadratic curve as an approximate expression.
f (x) ′ = a′x ² + b′x + c ′ (8)
By adding the measurement result to the above equation (8) and the original data, the result is as follows.
f (−D) ′ = a ′ (− D) ² + b ′ (− D) + c ′ = ΔL + ΔL ″ (9)
f (0) ′ = a ′ (0) ² + b ′ (0) + c ′ = ΔC + ΔC ″ (10)
f (D) ′ = a ′ (D) ² + b ′ (D) + c ′ = ΔR + ΔR ″ (11)
From equations (9) to (11), the quadratic curve of the laser scanning image of the scanner unit 205 in the image forming apparatus can be approximated by obtaining the coefficients a ′, b ′, and c ′.

  The coefficients a ′, b ′, and c ′ are calculated by the calculation correction coefficient storage unit 415 after the calculation result of the secondary correction laser scanning reference position deviation correction amount calculation unit 411 in FIG. 2 Create an image file as -f (x) 'which is correction information. With this created image file, the laser scanning image becomes S5 in FIG.

  Although the above equations (9) to (11) are measured at the same position and the approximate expression of the quadratic curve is calculated, the measurement is performed at different positions other than -D, 0, D when measuring on the image. May be. In this case, since the coefficients are obtained by the equations (5) to (7), the equation (9) is calculated using ΔL, ΔC, and ΔR that are calculated by combining the first calculated x with the position of the image measurement unit. ) To (11) are of course good.

  Further, whether to calculate −f (x) ′ or whether to use the calculated −f (x) ′ as correction information depends on the sub-scanning deviations ΔL ″, ΔC ″, ΔR ″. You may make it respond | correspond only when it is outside. That is, if the sub-scanning deviations ΔL ″, ΔC ″, ΔR ″ are within the allowable range, the image file (laser scanning image) may be corrected using only −f (x).

  As described above, by using the ΔL ″, ΔC ″, ΔR ″ obtained from the external calculation means 510 in FIG. 12, the coefficients a ′, b ′, c ′ of the quadratic curves of the respective colors according to the above calculation formula. Can be calculated. Based on this calculation result and the shift amount obtained from the storage unit 414 shown in FIG. 10, the calculation result of the calculation unit 415 that calculates the correction amount for each laser scanning image by the above formula is stored in the storage unit 412 for each color. Remember it.

(Sub-scanning deviation calculation method)
Next, FIG. 4 shows an example of an image for calculating the sub-scanning deviations ΔL ″, ΔC ″, ΔR ″ used in the present embodiment from the image.

  4, 0, 1-1 to N-4 in the left part are reference straight lines, and in this embodiment, the recording is performed using recording paper on which the reference straight lines are previously printed at equal intervals. The interval between the reference straight lines is printed in consideration of the range that can be corrected by the image forming apparatus.

  The short lines 1-1L to N-1L, 1-2L to N-2L, 1-3L to N-3L, and 1-4L to N-4L are print images obtained by laser scanning. Moreover, 1-1C-N-1C, 1-2C-N-2C, 1-3C-N-3C, 1-4C-N-4C, 1-1R-N-1R, 1-2R-N-2R, The short thick lines 1-3R to N-3 and 1-4R to N-4R are also printed images by laser scanning.

  In FIG. 4, the laser scanning images of the laser diode LD1 correspond to 1-1L to N-1L, 1-1C to N-1C, and 1-1R to N-1R. The other LD2 to LD4 also correspond to 2 to 4 of the * portion of 1- * L to N- * L, 1- * C to N- * C, 1- * R to N- * R, respectively. Yes.

A method of calculating the sub-scanning deviation from the image using FIG. 4 will be described below.
With respect to the sub-scanning deviation for LD1, the difference from the reference straight line * -1 is used as the reference straight line 0 starting point, and the sub-scanning deviation measuring means using the scanner shown in FIG. Are temporarily stored in the external computing means 510 while sequentially measuring. Then, based on the stored data, new sub-scanning deviations ΔL ″, ΔC ″, ΔR ″ are calculated by the external calculation means 510 using the following averaging process.

The following calculated (12) to (14) are representative expressions.
ΔL_1 ″ = (Δ1-1L + Δ2-1L +... + ΔN-1L) / N (12)
ΔC_1 ″ = (Δ1-1C + Δ2-1C +... + ΔN-1C) / N (13)
ΔR_1 ″ = (Δ1-1R + Δ2-1R +... + ΔN-1R) / N (14)
Regarding the sub-scanning deviations for LD2 to LD4, all the differences from the reference straight line *-* are sequentially measured at -D, 0, D using the measurement means on the image, and temporarily stored, and then the averaging process is used. The following formulas (15) to (17) are the representative expressions.
ΔL _ * '' = (Δ1- * L + Δ2- * L +... + ΔN- * L) / N (15)
ΔC _ * ″ = (Δ1- * C + Δ2- * C +... + ΔN- * C) / N (16)
ΔR _ * '' = (Δ1- * R + Δ2- * R +... + ΔN- * R) / N (17)
(* Indicates 2-4)
In the present embodiment, the summation averaging process is performed, but it goes without saying that similar calculation results can be obtained by using other averaging processes. In this embodiment, the sub-scanning deviation is calculated using recording paper on which the reference straight line is printed at equal intervals. However, the present invention is not limited to this and may be calculated by other methods.

  The calculated sub-scanning deviations ΔL ″, ΔC ″, ΔR ″ are notified to the print image forming unit 203 via an interface (not shown) as shown in FIG.

  The sub-scanning deviation in the image forming apparatus of the laser scanning image in each of the laser diodes LD1 to LD4 obtained by the above formulas (12) to (17) is again calculated and calculated by the above formulas (9) to (11). By doing so, an approximate expression of a new quadratic curve can be calculated. Then, by correcting the image file based on the calculated approximate expression as shown in FIG. 11, the sub-scanning deviation of each laser scanning image is canceled.

  In the image forming apparatus used in the present invention, the digital correction unit 450 shown in FIG. 10 can selectively output a primary correction image file or a secondary correction image file in accordance with an instruction from the image forming apparatus. It is a possible configuration.

  Therefore, in the image in which the sub-scanning deviation is canceled, the laser scanning images of the laser diodes LD1 to LD4 have almost no registration deviation and partial sub-scanning deviation as shown in FIG. 4B. High image quality can be provided.

(Example 2)
Next, a second embodiment of the present invention will be described with reference to FIG.

  S7 and S8 in FIG. 5A are two laser beam scanning images S7 and S8 among arbitrary laser beams output from the scanner unit 205. Note that the image forming apparatus used in the present embodiment has the laser scanning images of the four laser diodes LD1 to LD4. However, in order to make the description of the present embodiment easier to understand, the description will be made with two laser diodes LD1 and LD2. The ideal laser beam scanned images S7 and S8 should be arranged in a straight line at the position 0 of the main scanning, but in practice, unless high-precision adjustment is performed, as in the first embodiment, FIG. ) Laser beam scanning images S7 and S8. The laser beam scanning image S7 generally has a quadratic curve characteristic as shown in FIG. 5A as in the above-described embodiment. Therefore, first, an approximate expression of a quadratic curve of the laser beam scanning images S7 and S8 is obtained. Since the method of deriving the quadratic curve approximation formula as the first correction information has been described in the first embodiment, a detailed description thereof will be omitted in this embodiment.

  Sub-scanning deviations ΔL_1, ΔC_1, ΔR_1ΔL_2, ΔC_2, and ΔR_2 of the laser scanning images S7 and S8 are measured by a sub-scanning irradiation position measuring unit 400 including CCD sensors 403, 401, and 402 as shown in FIG. The measured sub-scanning deviations ΔL_1, ΔC_1, ΔR_1, ΔL_2, ΔC_2, and ΔR_2 are stored as L_ *, C_ *, and R_ * for each color via the external interface (not shown) in the storage unit 410 shown in FIG.

  Based on the stored L_ *, C_ *, and R_ *, sub-scanning deviations ΔL_1, ΔC_1, ΔR_1ΔL_2, ΔC_2, and ΔR_2 are used to derive respective quadratic curve approximation formulas.

  As described above, the laser scanning images S7 and S8 should be S11 in (c) by creating an image file with a correction profile of −f (x). However, in reality, when the scanner unit is assembled and imaged on the image forming apparatus, there are many cases where an image such as S12 and S13 in (d) is generated due to assembly variations and various other factors.

  Therefore, the sub-scanning deviation is measured from the measurement image output from the image forming apparatus 201 for the image data subjected to the primary correction by the print image generating unit 203 in the image forming apparatus of FIG. More specifically, the S12 sub-scanning deviations ΔL_1 ″, ΔC_1 ″, ΔR_1 ″ and the S13 sub-scanning deviations ΔL_2 ″, ΔC_2 ″, ΔR_2 ″ of FIG. Is used to measure at positions -D, 0, D in the main scanning direction of the measurement image.

  Based on the measurement result, ΔL_ * ″, ΔC_ * ″, ΔR_ * ″ obtained by the calculation of the external calculation unit 510 in FIG. 12 are stored in the secondary correction laser scanning reference position deviation amount storage unit 414. Remember. Since an example of data transfer of ΔL_ * ″, ΔC_ * ″, and ΔR_ * ″ has been described in the first embodiment, description thereof is omitted here.

  An example of a method of calculating the sub-scanning deviations ΔL_ * ″, ΔC_ * ″, ΔR_ * ″ will be described later.

Based on the sub-scanning deviations ΔL_ * ″, ΔC_ * ″, ΔR_ * ″ newly obtained by the measurement, the laser scanning image of the laser diode LD2 combined with the laser diode LD1 in the image forming apparatus is as follows. A quadratic curve can be obtained as an approximate expression.
f (x) ″ = a ″ x ² + b ″ x + c ″ (18)
The result obtained by adding the measurement result to the above equation (18) and the original data is as follows.
f (−D) ″ = a ″ (− D) ² + b ″ (− D) + c ″ = ΔL — 2 + ΔL — 2 ″ −ΔL — 1 ″ (19)
f (0) ″ = a ″ (0) ² + b ″ (0) + c ″ = ΔC_2 + ΔC_2 ″ −ΔC_1 ″ (20)
f (D) ″ = a ″ (D) ² + b ″ (D) + c ″ = ΔR — 2 + ΔR — 2 ″ −ΔR — 1 ″ (21)
From the equations (19) to (21), the quadratic curve of the laser scanning image of the scanner unit 205 in the image forming apparatus can be approximated by obtaining the coefficients a ″, b ″, and c ″. .

  After calculating the coefficients a ″, b ″, and c ″, an image file is created with −f (x) ″ as the second correction information, and a laser scanning image is shown in FIG. The laser scanning image S15 of the laser diode LD2 is aligned with the laser scanning image S14 of the laser diode LD1.

  The above equations (19) to (21) were measured at the same position, and an approximate expression of a quadratic curve was calculated. However, when the measurement is performed on the image at different positions, the following may be used. That is, since the coefficients are obtained by the equations (5) to (7) described in the first embodiment, ΔL_ *, ΔC_ *, which are calculated by combining the first calculated x with the position of the image measurement unit. It goes without saying that the equations (19) to (21) are obtained using ΔR_ * (* indicates 2 to 4). Next, FIG. 6 shows an example of an image for calculating the sub-scanning deviations ΔL_ * ″, ΔC_ * ″, ΔR_ * ″ (* indicates 2 to 4) used in the present embodiment from the image.

  In FIG. 6, 1L, 1C, and 1R in FIG. 6 are equally spaced images at −D, 0, and D portions using the laser diode LD1 as a predetermined laser scanning image. The image interval of the LD 1 is printed in consideration of the range that can be corrected by the image forming apparatus. 1L, 1-2L to N-2L, 1-3L to N-3L, 1-4L to N-4L, 1C, 1-2C to N-2C, 1-3C to N-3C, 1-4C to N- The short thick lines 4C, 1R, 1-2R to N-2R, 1-3R to N-3, and 1-4R to N-4R are printed images by laser scanning.

  The images in FIG. 6 correspond to the laser scanning images of the laser diode LD1 corresponding to 1L, 1C, and 1R, and the other LD2 to LD4 are also 1- * L to N- * L, 1- * C to N- *. C, 1- * R to N- * R correspond to 2 to 4 in the * part, respectively.

  A method for calculating the sub-scanning deviation from the image shown in FIG. 6 will be described below.

In the present embodiment, regarding the sub-scanning deviations relating to LD2 to LD4, differences from 1L, 1C, and 1R equally spaced laser scanning images formed by LD1 are all calculated. Starting from the laser-scanned image S14 of LD1, the sub-scanning deviation measuring unit (not shown) is used to sequentially measure and temporarily store the portions of -D, 0, D, and then calculate using the averaging process. (22) to (24) are representative expressions.
The sub-scanning deviation of the laser scanning image of the laser diode LD2 is ΔL_2 ″ = (Δ1-2L +... + ΔN-2L) / N (22)
ΔC — 2 ″ = (Δ1-2C +... + ΔN-2C) / N (23)
ΔR_2 ″ = (Δ1-2R +... + ΔN-2R) / N (24)
More obtained.

Differences from the laser scanning images of 1L, 1C, and 1R equally spaced are also calculated for all sub-scanning deviations of LD3 to LD4, and -D, 0, and D are measured using measurement means on the image (not shown). Measure in order and store temporarily. Then, the following formulas (25) to (27) are representative expressions for the averaging process.
ΔL _ * ″ = (Δ1- * L + Δ2- * L +... + ΔN- * L) / N (25)
ΔC _ * ″ = (Δ1- * C + Δ2- * C +... + ΔN- * C) / N (26)
ΔR _ * ″ = (Δ1- * R + Δ2- * R +... + ΔN- * R) / N (27)
(* Indicates 2-4)
In the present embodiment, the summation averaging process is performed, but it goes without saying that similar calculation results can be obtained by using other averaging processes. In this embodiment, the sub-scanning deviation of another laser scanning image is calculated based on the laser scanning image of the laser diode LD1, but there is no problem even if it is obtained from the laser scanning image of an arbitrary laser diode. Furthermore, in the present embodiment, the pattern is not limited to the pattern shown in FIG. 6, and it is of course possible to calculate using a pattern that provides the same result.

  The sub-scanning deviation in the image forming apparatus of the laser scanning image in each of the laser diodes LD2 to LD4 obtained by the above equations (22) to (27) is calculated and calculated again using the above equation f (x) ''. Thus, an approximate expression for a new quadratic curve can be calculated. Then, by correcting the image file based on the calculated approximate expression, the sub-scanning deviation of each laser scanning image is aligned with the laser scanning image of the laser diode LD1.

  Therefore, in the image aligned with the laser scanning image of the laser diode LD1, the laser scanning images of the laser diodes LD1 to LD4 have almost no registration shift and partial sub-scanning shift as shown in FIG. 6B. High quality images can be provided.

(Example 3)
Next, a third embodiment of the present invention will be described with reference to FIG.

  S21 and S22 in FIG. 7A are two laser beam scanning images S21 and S22 among arbitrary laser beams output from the scanner unit 205. Note that the image forming apparatus used in the present embodiment has the laser scanning images of the four laser diodes LD1 to LD4. However, in order to make the description of the present embodiment easier to understand, the description will be made with the two laser diodes LD1 and LD2.

  The ideal laser beam scanned images S21 to S22 should be arranged in a straight line at the main scanning 0 position, but in practice, unless high-precision adjustment is performed, as in the first embodiment, FIG. ) Laser beam scanned images S21 to S22.

  The laser beam scanning images S21 to S22 generally have a quadratic curve characteristic as shown in FIG. Among them, in the present embodiment, the laser diode LD1 is adjusted with high accuracy, and the distortion as shown in S21 is minimized.

  This corrects all image files from the quadratic curve approximation formula, and can provide a high quality image with almost no positional deviation between the laser scanning images and partial sub-scanning deviation. There is also a concern that the digital correction part will be conspicuous for the fine line.

  In order to improve this concern, in this embodiment, as described above, the laser diode LD1 is adjusted with high accuracy, and the laser scanning image of the LD1 is not digitally corrected. Thus, an object of the present invention is to provide a high-quality image with almost no registration shift and partial sub-scan shift between laser scanning images.

  Therefore, first, an approximate expression of a quadratic curve of the laser beam scanning image S22 is obtained. Since the method of deriving the quadratic curve approximate expression is outlined in the first embodiment, detailed description thereof is omitted in this embodiment. The sub-scanning deviations ΔL_ *, ΔC_ *, and ΔR_ * (* are indicated by 2 to 4) of the laser scanning image S22 and S23 and S24 (not shown) are respectively measured by the sub-scanning irradiation position measuring unit 400 of FIG. The irradiation position of the laser scanning image in the sub-scanning direction is measured. The measured sub-scanning deviations ΔL_1, ΔC_1, ΔR_1, ΔL_2, ΔC_2, and ΔR_2 are stored as L_ *, C_ *, and R_ * for each color via the external interface (not shown) in the storage unit 410 of FIG. The storage unit 410 is a unit that stores a laser scanning reference position shift amount for each color included in the image forming unit 203.

  Based on the stored L_ *, C_ *, and R_ *, sub-scanning deviations ΔL_ *, ΔC_ *, and ΔR_ * (* indicates 1 to 4) are used to derive the following quadratic curve approximation formulas. .

The sub-scanning deviations ΔL_ *, ΔC_ *, ΔR_ * (* indicates 2 to 4) of the laser scanning image S22 of the laser diode LD2 and the laser scanning images S23 and S24 of the LD3 and LD4 (not shown) in FIG. The following equations (30) to (38) are obtained.
f_2 (−D) = a_2 (−D) ² + b_2 (−D) + c_2 = −ΔL_1 + ΔL_2 (30)
f_2 (0) = a_2 (0) ² + b_2 (0) + c_2 = −ΔC_1 + ΔC_2 (31)
f_2 (D) = a_2 (D) ² + b_2 (D) + c_2 = −ΔR_1 + ΔR_2 (32)
f_3 (−D) = a_3 (−D) ² + b_3 (−D) + c_3 = −ΔL_1 + ΔL_3 (33)
f_3 (0) = a_3 (0) ² + b_3 (0) + c_3 = −ΔC_1 + ΔC_3 (34)
f_3 (D) = a_3 (D) ² + b_3 (D) + c_3 = −ΔR_1 + ΔR_3 (35)
f_4 (−D) = a_4 (−D) ² + b_4 (−D) + c_4 = −ΔL_1 + ΔL_4 (36)
f_4 (0) = a_4 (0) ² + b_4 (0) + c_4 = −ΔC_1 + ΔC_4 (37)
f_4 (D) = a_4 (D) ² + b_4 (D) + c_4 = −ΔR_1 + ΔR_4 (38)
As described above, the laser scanning image S22 and S23 and S24 (not shown) create an image file with a correction profile of −f _ * (x) (* indicates 2 to 4). The image should be aligned with S21 'of (c). However, in reality, when the scanner unit is assembled and imaged on the image forming apparatus, due to the assembly variation and various other factors, an image like S30 and S26 of (d) and S27 and S28 (not shown) is obtained. There are many cases. Therefore, the sub-scanning deviations ΔL_2 ″, ΔC_2 ″, ΔR_2 ″ of S30 and S26 in FIG. 7D are measured from the output image at positions −D, 0, and D in the main scanning direction. Further, the sub-scanning deviations ΔL_3 ″, ΔC_3 ″, ΔR_3 ″ and the sub-scanning deviations ΔL_4 ″, ΔC_4 ″, ΔR_4 ″ of S27 and S28 (not shown) are −D, 0, D in the main scanning direction. Measure at position.

  Since the method for calculating the sub-scanning deviation of the laser scanning images of the laser diodes LD2 to LD4 is the same as that in the second embodiment, the description thereof is omitted in this embodiment.

  Next, FIG. 8 shows an example of an image for calculating the sub-scanning shifts ΔL_ * ″, ΔC_ * ″, ΔR_ * ″ (* indicates 2 to 4) used in this embodiment from the image. The image interval of the LD 1 in FIG. 8 is printed in consideration of the range that can be corrected by the image forming apparatus.

  Accordingly, the image data subjected to the primary correction is output, and the output measurement image (corresponding to S12 in FIG. 5D) is output using an image scanner as shown in FIG. Measurements are made at positions -D, 0, D in the main scanning direction. Specifically, the sub-scanning deviations ΔL_1 ″, ΔC_1 ″, ΔR_1 ″ and the S13 sub-scanning deviations ΔL_2 ″, ΔC_2 ″, ΔR_2 ″ are image scanners as shown in FIG. Is used to measure at positions -D, 0, D in the main scanning direction of the measurement image.

  Based on the measurement result, ΔL_ * ″, ΔC_ * ″, ΔR_ * ″ obtained by the calculation of the external calculation unit 510 in FIG. 12 are stored in the secondary correction laser scanning reference position deviation amount storage unit 414. Remember. Since an example of data transfer of ΔL_ * ″, ΔC_ * ″, and ΔR_ * ″ has been described in the first embodiment, description thereof is omitted here.

  An example of a method for calculating the sub-scanning deviations ΔL_ * ″, ΔC_ * ″, and ΔR_ * ″ has been described in the second embodiment, and thus description thereof is omitted here.

  From the above, based on the sub-scanning deviations ΔL_ * ″, ΔC_ * ″, ΔR_ * ″ newly obtained by measurement, the laser scanning image of the laser diode LD2 combined with the laser diode LD1 in the image forming apparatus is The following new quadratic curve can be obtained as an approximate expression.

Based on the result of measurement and calculation of the sub-scanning deviation from the image of FIG. 8A, the laser scanning images of the laser diodes LD2 to LD4 combined with the laser diode LD1 in the image forming apparatus are as follows: Become.
f _ * (x) ″ = a _ * ″ x ² + b _ * ″ x + c_ * ″ (* indicates 2 to 4) (39)
The result obtained by adding the measurement result to the above equation (18) and the original data is as follows.
f _ * (− D) ″ = a _ * ″ (− D) ² + b _ * ″ (− D) + c _ * ″ = ΔL _ * + ΔL _ * ″ − ΔL — 1 (40)
f _ * (0) '' = a _ * '' (0) ² + b _ * '' (0) + c _ * '' = ΔC _ * + ΔC _ * '' − ΔC_1 (41)
f _ * (D) ″ = a _ * ″ (D) ² + b _ * ″ (D) + c _ * ″ = ΔR _ * + ΔR _ * ″ − ΔR_1 (42)
From equations (40) to (42), the quadratic curves of the laser scanning images of the scanner unit 205 in the image forming apparatus are coefficients a_ * '', b_ * '', c_ * '' (* is 2 to 4). An approximate expression can be derived by obtaining (shown).

  After calculating the coefficients a_ * ″, b_ * ″, and c_ * ″, an image file is created as −f _ * (x) (* indicates 2 to 4). As a result, the laser scanning image becomes the laser scanning images S31 to 32 of the laser diodes LD2 to LD4 aligned with the laser scanning image S30 of the laser diode LD1 shown in FIG. 7E and S33 and S34 (not shown).

  In addition, each laser scanning image was measured in the same position by said Formula (40)-(42), and the approximate expression of the quadratic curve was computed. On the other hand, when the measurement is performed on the image at different positions, the coefficients are obtained by the equations (30) to (38). Therefore, the equations (40) to (42) are obtained by using ΔL_ *, ΔC_ *, ΔR_ * (* indicates 2 to 4) obtained by calculating and calculating the first calculated x together with the position of the image measurement unit. Of course it is good. In the present embodiment, the calculation is not limited to the pattern shown in FIG. 8, and the calculation may be performed using a pattern that provides a similar result.

  The sub-scanning deviation in the image forming apparatus of the laser scanning image in each of the laser diodes LD2 to LD4 obtained by the above formulas (40) to (42) is expressed by the above formula f _ * (x) '' (* is 2 to 4). By calculating the coefficient again in (shown), a new approximate expression of a quadratic curve can be calculated. Then, by correcting the image file based on the calculated approximate expression, the sub-scanning deviation of each laser scanning image is aligned with the laser scanning image S30 'of the laser diode LD1.

  Accordingly, in the image aligned with the laser scanning image of the laser diode LD1, the laser scanning images of the laser diodes LD1 to LD4 have almost no registration deviation and partial sub-scanning deviation as shown in FIG. 8B. High image quality can be provided. Furthermore, since digital correction is not applied to the laser scanning image of the laser diode LD1, a laser scanning image of the laser diode LD1 with very good linearity can be provided.

1 is a cross-sectional view of an image forming apparatus. It is a perspective view of a scanner unit. 6 is a diagram illustrating an image correction method according to the first exemplary embodiment. FIG. 3 is an example of a sub-scanning deviation measurement image in Embodiment 1. FIG. 10 is a diagram illustrating an image correction method in Embodiment 2. 7 is an example of a sub-scanning deviation measurement image in Example 2. FIG. 10 is a diagram illustrating an image correction method in Embodiment 3. 12 is an example of a sub-scanning deviation measurement image in Example 3. It is a figure which shows an example of a structure of an irradiation position measurement means. FIG. 3 is a diagram illustrating interfaces of each part of digital correction means in a print image generation unit 203. It is a figure which shows an example of digital image correction. It is a figure which shows the structure which reads the measurement image for secondary correction | amendment. It is a figure explaining the method of the registration shift correction | amendment per pixel in a prior art example. It is a figure explaining the method of the registration shift correction of less than 1 pixel in a prior art example.

Explanation of symbols

101 to 104 Laser diode 105 Bolgon mirror 106 to 109 Folding mirror 110 BD sensor 210 Image forming apparatus (color laser printer)
DESCRIPTION OF SYMBOLS 203 Print image production | generation part 204 Image formation control part 205 Scanner unit 211 Intermediate transfer belt 212 Registration detection sensor 301-304 Photosensitive drum 302 Photosensitive drum 410 Laser scanning reference position shift amount memory | storage means 411 Laser scanning reference position shift correction amount calculation means 412 Calculation Expression correction coefficient storage means 413 Interface section 414 Secondary correction laser scanning reference position deviation amount storage means 415 Secondary correction laser scanning reference position deviation correction amount calculation means 450 Digital correction means

Claims (4)

A plurality of laser beam generating means for generating a laser beam based on a laser scanning image, and one or a plurality of rotating polygon mirrors for deflecting and scanning the laser beam generated by the laser beam generating means on each corresponding image carrier An optical laser unit, and a developing unit corresponding to a plurality of colors for forming an electrostatic latent image on each of the plurality of image carriers by the laser beam, and developing the electrostatic latent image on each image carrier with a developer, And a color misregistration adjustment method relating to an image forming apparatus comprising: means for sequentially transferring a plurality of color images formed by each developing means;
The laser scanning output from the optical laser unit is measured by an irradiation position measuring means at three or more positions, and the measurement result is set as a first measurement result. Based on the first measurement result, distortion of each laser scan image is determined. A first calculation step of calculating first correction information to be eliminated;
A first digital correction step of correcting each laser scanning image based on the first correction information;
An image for remeasurement is formed on the basis of each laser scanning image corrected in the first digital correction step, and laser scanning is performed at three or more positions using the formed image for remeasurement. A re-measurement process to re-measure by
The second measurement result is calculated as second measurement result, and second correction information for eliminating distortion of each laser scanning image is calculated based on the second measurement result and the first measurement result. A calculation process;
And a second digital correction step of correcting each laser scanning image based on the second correction information.   In the second calculation step, the second digital correction step is performed when the deviation from the laser scanning reference position outside the allowable range is measured by the second measurement by the irradiation position measuring means. The image adjustment method according to claim 1.   In the first digital correction step and the second digital correction step, another laser scanning image is corrected so as to align with a predetermined laser scanning image in each laser scanning image. The image adjustment method according to claim 1 or 2.   In the digital correction step and the second digital correction step, each of the other laser scanning images is matched with the laser scanning image in which the distortion of the laser scanning image is corrected in the optical laser unit among the laser scanning images. The image adjustment method according to claim 1, wherein the correction is performed.

Images