JP2009093155A - Color image forming apparatus and color misregistration correction method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus receiving a diffuse reflected light component and performing registration correction while using the color of a developer with less reflection component of diffuse reflected light such as black as a reference color. <P>SOLUTION: A light emitting part 200 emits light to a superimposed pattern in Figure 4 in which a black developer (Bk) is superimposed on a color developer (Y, M, C) as a background color, and reflected diffuse reflected light is detected by a light receiving part 201. Based on the detection result, positional deviation among the colors is computed using the black developer (Bk) as the reference color to adjust image forming conditions. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a mechanism for correcting a registration shift (color shift) between colors in an electrophotographic color image forming apparatus.

  Conventionally, a color image forming apparatus having an independent image carrier is designed so that images of all colors overlap without shifting, but it is very difficult to completely eliminate variations in parts and assembly. Therefore, a means for adjusting the registration deviation is necessary. As one of the adjusting means, as disclosed in Patent Document 1, it is known to form a pattern for detecting a registration deviation and detect the position of the formed pattern to correct the deviation amount.

  In Patent Document 1, black is used as a reference color, and a pattern detection unit for detecting a pattern is configured to receive a regular reflection component of light emitted from a light emitting unit by a light receiving unit. Then, the measurement color is sandwiched between the reference colors, and the position shift amount is calculated from the shift amount obtained by comparing the center position of the two reference color patterns sandwiching the measurement color with the center position of the measurement color pattern. Based on the calculation result, it is possible to correct the registration deviation amount between the respective colors by correcting the image writing conditions such as the image writing timing and the image clock.

  On the other hand, as one method for reducing the cost of the color image forming apparatus, there is a method of scanning light from a plurality of laser diodes with a single polygon mirror in the configuration in the scanner unit. A configuration is also known in which the number of sensors for detecting a beam for forming a horizontal synchronizing signal is reduced. In a configuration in which the number of sensors for generating a horizontal synchronization signal is reduced, it is known that a pseudo-generated horizontal synchronization signal (pseudo BD signal) is used for image formation of a color having no sensor. For example, Patent Document 2 discloses the configuration.

In a configuration in which the number of beam detection sensors for generating a horizontal synchronization signal is reduced, it is important which color the sensor is attached to. Color image forming apparatuses with mono print mode (printing only in black) and full color mode are known, but many images are output in mono print mode, and the character quality is an important item required by the user. one of. Here, when the pseudo BD signal is generated, an error is superimposed with accuracy such as calculation and sampling. That is, this superposition causes variations in the writing position in the main scanning direction, and as a result, a so-called jitter problem occurs. Therefore, it is desirable to use the horizontal synchronization signal (BD signal) formed with the highest accuracy for black print synchronization. Further, it is desirable that black (Bk) formed with high accuracy be a reference color in registration correction.
Japanese Patent Laid-Open No. 2002-023445 JP 2004-102276 A

  In recent years, for the purpose of further cost reduction measures, as a technique to make full use of an inexpensive intermediate transfer member, a method of correcting the registration by receiving a diffuse reflected light component independent of the surface state of the intermediate transfer member at the light receiving portion has been studied. ing.

  However, for example, when black is used as a reference color as described above, the sensor output for beam detection provided for black is used as a BD signal, and pseudo-BD is used for other colors, diffuse reflected light may be applied. However, a problem that the black pattern cannot be detected occurs. This has its origin in that black is a developer that has a small amount of reflection component of diffuse reflected light. However, if the black pattern cannot be read, registration correction cannot be performed in the first place.

  On the other hand, in recent years, in color image forming apparatuses, there is a case where further downsizing is required, or efficient registration correction is required, for example, toner consumption is reduced with registration correction. .

  The present invention has been made in view of the above problems, and is a color capable of efficiently performing registration correction using a diffuse reflection component while using a developer color such as black that has a small reflection component of diffuse reflection. An object is to provide an image forming apparatus.

  In order to achieve the above object, a color image forming apparatus according to the present invention comprises a forming means for forming an image on an image carrier using a color developer and a black developer, and an image formed on the image carrier. A color image forming apparatus comprising a transfer means for transferring to a transfer material and a fixing means for fixing an image transferred onto the transfer material by the transfer means. A control unit for forming a superimposed pattern on which the pattern is superimposed on the image carrier by the forming unit; a detecting unit for irradiating the superimposed pattern with light and detecting reflected diffused reflection; and The position of the pattern and the position of the pattern of the black developer are obtained based on the detection result of the diffuse reflected light from the superimposed pattern by the detecting means, and the pattern of the color developer is obtained. Characterized in that it has a calculating means for calculating a relative positional deviation amount of the pattern of over emissions and black developer, and adjusting means for adjusting an image forming condition based on the calculation result by the calculating means.

  According to the present invention, it is possible to realize a color image forming apparatus that can efficiently perform registration correction using a diffuse reflection light component while using a developer color having a small reflection component of diffuse reflection light such as bublack.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the constituent elements described in this embodiment are merely examples, and are not intended to limit the scope of the present invention only to them.

[Example 1]
First, FIG. 1 shows a schematic configuration diagram of a color image forming apparatus. Reference numeral 100 denotes a color image forming apparatus, and 202 denotes a host computer. The color image forming apparatus used in the present embodiment includes a four-color image forming unit to form a color image in which images of a plurality of colors (yellow: Y, magenta: M, cyan: C, black: Bk) are superimposed. I have. In the following, a four-color image forming apparatus will be described, but it goes without saying that the present invention can be applied to various known multi-color image forming apparatuses such as six colors.

  The image forming unit includes process cartridges 207 to 210 having photosensitive drums 301 to 304 and a scanner unit 205 having a laser diode for generating a laser beam as a light source for image exposure.

  When print data from the host computer 202 is received, the print data received by the video controller 203 in the color image forming apparatus 100 is developed into desired video signal formation data (for example, bitmap data), and a video signal for image formation is displayed. Generate. The video controller 203 and the engine controller 204 perform serial communication to transmit and receive information. The video signal is transmitted to the engine controller 204 by transmitting and receiving this information. Further, the engine controller 204 drives a laser diode (not shown) in the scanner unit 205 in accordance with the video signal, and is statically placed on the photosensitive drums 301 to 304 in the process cartridges 207 to 210 charged by the chargers 305 to 308. An electrostatic latent image is formed. The engine controller 204 also functions as a control unit that forms a pattern shown in FIG. 4 to be described later with a process cartridge that functions as a forming unit. 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 electrostatic latent images formed on the photosensitive drums 301 to 304 are visualized by the process means built in the respective process cartridges 207 to 210 at the positions of the developing rollers 309 to 312, and the toner is formed on the photosensitive drums 301 to 304. Form an image. The process means includes a charging roller, a developing roller, a cleaning roller, etc., but detailed description thereof is omitted here. In the toner images of the respective colors formed on the photosensitive drums 301 to 304, first, a yellow (Y) image is transferred to the intermediate transfer member 103, which is an image carrier, and then magenta (M), cyan ( C) and black (Bk) are sequentially transferred in this order. By this sequential transfer, a multicolor image is formed on the intermediate transfer member 103 (on the image carrier).

  Further, the transfer material in the cassette 314 is fed to the registration roller 319 by the paper feed roller 316, and the transfer material is conveyed in synchronization with the image on the intermediate transfer body 103 at the drive timing of the registration roller 319. The multicolor image is transferred from the intermediate transfer member 103 onto the transfer material by the transfer roller 318. The transfer material on which the image has been transferred is fixed on the transfer material by heat and pressure by the fixing device 313. Then, the paper is discharged to a paper discharge tray 317 at the top of the color image forming apparatus.

  Reference numeral 120 denotes a color misregistration detection pattern detection sensor for registration detection, which is a sensor for detecting a color registration pattern formed on the intermediate transfer member. Then, the position of each color image formed on the intermediate transfer member 103 is read at a desired timing other than during image formation, and the data is fed back to the video controller 203 or the engine controller 204 to adjust the image registration position for each color. To do. Thereby, it is possible to prevent color misregistration while ensuring usability.

  Next, a schematic configuration of the scanner unit 205 will be described with reference to FIG. Reference numerals 101, 102, 103, and 104 denote laser diodes that generate laser beams that scan the photosensitive drums 301, 302, 303, and 304, respectively, based on video signals generated by the engine controller 204. Here, 101 is called a first laser diode (LD1), 102 is called a second laser diode (LD2), 103 is called a third laser diode (LD3), and 104 is called a fourth laser diode (LD4). A polygon mirror 105 is rotated at a constant speed in the direction of arrow A in the figure by a motor (not shown), and scans while reflecting the laser beams from the laser diodes LD1, LD2, LD3, and LD4. The motor for driving the polygon mirror 105 is controlled and rotated by the engine controller 204 so as to have a constant speed by the acceleration signal and the deceleration signal of the speed control signal. Reference numerals 106, 107, 108, and 109 are reflection plates for guiding the laser beams from the laser diodes LD 1, LD 2, LD 3, and LD 4 reflected by the polygon mirror 105 to the photosensitive drums 301, 302, 303, and 304. 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 (Beam Detect) sensor. In this embodiment, the BD sensor 110 is disposed only on the scanning path of the black laser diode LD1, and does not exist on the scanning paths of the other laser diodes. Here, the reason why the BD sensor 110 is disposed only on the scanning optical path of the laser diode LD1 is to prevent deterioration of character quality in a single black print that is most used by the user.

  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, further reflected by the folding mirror 106, and scanned on the photosensitive drum 301 from left to right (main scanning direction). To do. 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.

  Normally, the video controller 203 transmits a video signal to the engine controller 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. As for the position detection of the laser beam, since there is no BD sensor on the scanning path of the laser diodes 102, 103, 104, it is necessary to take horizontal synchronization by some means. When all the stations do not have a BD sensor, a pseudo BD signal or horizontal synchronization adjusted in advance by a predetermined time based on the BD signal or horizontal synchronization signal which is the output of the BD sensor of the station having the BD sensor. A signal is generated by the video controller 203. More specifically, a horizontal synchronizing signal is generated at the same timing as LD1 for LD2 scanned on the same surface as LD1 having a BD sensor. Further, for LD3 and LD4 that are always scanned on a different surface from LD1 having a BD sensor, it is common to generate a horizontal synchronization signal at a timing corrected by the surface jitter of the polygon mirror 105. In the following description, among the laser diodes that do not have the BD sensor, the horizontal synchronization signal used in the laser diodes LD3 and LD4 that are scanned on the surface of the polygon mirror 105 that is scanned is different from the laser diode LD1 is simulated. This is called a BD signal.

  In this way, a black (Bk) image is formed on the photosensitive drum 301 by the laser diode LD 1 having the BD sensor 110. Further, yellow (Y), magenta (M), and cyan (C) 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. Formation takes place.

  In addition, the color image forming apparatus 100 according to the present exemplary embodiment superimposes a mono print mode in which an image is formed only with a black developer and a plurality of developers (color developer and black developer) to form a multicolor image. It has a print mode of the color print mode to be formed. In particular, the mono print mode is often used for printing business texts, and character quality is regarded as important. On the other hand, since the full color mode is used for printing photographic images and the like, color reproducibility is regarded as important, and in order to improve color reproducibility, overlay accuracy (color shift accuracy) of a plurality of developers is important.

<Description of registration sensor>
An example of a circuit for detecting the color misregistration detection pattern is shown in FIG. Here, the color misregistration amount means a registration misregistration amount between colors, and the color misregistration amount detection pattern may be called a registration misregistration amount detection pattern. Hereinafter, description will be made using the term “color misregistration amount”. The pattern detection sensor 120 (sensor 120) includes a light emitting unit 200 (for example, an LED) and a light receiving unit 201 (for example, a phototransistor). The light receiving unit 201 detects diffusely reflected light, which is emitted (irradiated) from the light emitting unit 200 and diffusely reflected by the intermediate transfer body 103, and the light receiving unit 201 performs IV conversion on the detected light to the engine controller 204. A signal is sent to a certain comparator 211. The comparator 211 binarizes the analog signal sent from the light receiving unit 201 with reference to a predetermined threshold voltage and sends it to the signal detection unit 212. The signal detection unit is configured by a function such as a CPU or ASIC that can capture and store signals in time series. Note that ASIC is an abbreviation for Application Specific Integrated Circuit. The output of the signal detection unit 212 is taken into a controller 204 such as a CPU and used as registration deviation detection data.

<Description of registration pattern>
Next, the configuration of one set of color misregistration amount detection pattern, the outline of the color misregistration amount detection pattern formed on the intermediate transfer body 103 when color misregistration correction control is performed, and the color misregistration correction method will be sequentially described. .

  FIG. 4 shows a configuration example of one set of color misregistration amount detection patterns. It is formed under the control of the engine controller 204. Each of the color misregistration detection patterns shown in FIG. 4 has a parallelogram shape, and each color in the main scanning direction and the sub-scanning direction depends on how much the color misregistration detection pattern is deviated from the original position. The deviation can be calculated. The width in the moving direction of the first developer pattern (Y, M, C) is longer than the width of the second developer pattern (Bk) in the moving direction. Assuming the maximum shift amount between the positions of the reference color (Bk) and the measurement colors (Y, M, C), and the maximum shift occurs, the width of the measurement color in the moving direction becomes short. Even in such a situation, the width in the moving direction of the pattern (Y, M, C) of the first developer is set longer in order to ensure a pattern width that matches the reading performance of the sensor. Thus, reliable registration correction can be realized.

  The color misregistration detection pattern shown in FIG. 4 has the measurement colors yellow (Y), magenta (M), and cyan (C) shown in FIG. The pattern of black (Bk) which is the reference color shown in FIG. This pattern is called a superimposed pattern. In this embodiment, the black developer is referred to as a second developer as a class of developer in which the diffuse reflected light cannot be sufficiently detected (detected) by the sensor 120, while the diffuse reflected light such as yellow (Y) is used. Is called a first developer as a class of developer that can be detected (detected) by the sensor 120. Then, the overlapping pattern moves from left to right (or from right to left), and passes under the sensor 120 in this order of the first developer, the second developer, and the first developer, Superimposition pattern detection (detection) is performed by diffuse reflection detection (detection).

  FIG. 6 shows a detection waveform when the pattern detection sensor 120 detects the pattern shown in FIG. At the surface of the intermediate transfer member 103 and the portion where the black (Bk) developer is present, the amount of diffusely reflected light output (irradiated) from the light emitting portion of the pattern detection sensor 120 is received in advance by the light receiving portion. Since it is insufficient to exceed the set threshold, the LOW level is indicated. Further, in the portion where the developer of yellow (Y), magenta (M), and cyan (C) exists, the amount of diffuse reflection of the light output from the light emitting portion of the pattern detection sensor 120 is received by the light receiving portion. The HIGH level is indicated because the amount is sufficient to exceed a preset threshold.

<Overall appearance of color misregistration detection amount pattern>
FIG. 7 shows an example of a color misregistration amount detection pattern formed on the intermediate transfer body 103 when the endless intermediate transfer body 103 is developed. In this example, one set of the color misregistration detection pattern length (Pattern Length) Pl shown in FIG. 4 is formed in the peripheral length RL (Round Length) of the intermediate transfer body 103 at the pattern interval Pi (Pattern Interval). Indicates. Each set of color misregistration detection patterns has a write timing as a position shifted in phase by 72 degrees in the rotation period T of the image carrier as shown in FIG. At this time, the following relationship holds.
RL> 4 × Pi + Pl
Pi> Pl
Pi = N / 5 (N indicates the length of the belt)
When M color misregistration correction patterns are formed on the peripheral length RL of the intermediate transfer member 103,
RL> (M−1) × Pi + Pl
Pi> Pl
Pi = N / M
If this condition is satisfied, it is possible to complete one color misregistration correction control by making the intermediate transfer member 103 make one turn.

<Description of deviation detection method>
Next, referring to FIG. 9, a method for specifying the position of each color image and calculating the registration shift amount between the respective colors based on the detection result (detection result) of the color shift detection pattern (superimposition pattern) will be described. To do. Here, based on the detection result of the diffuse reflected light from the pattern by the first developer (Y, M, C) included in the overlapping pattern, the position of the pattern of the first developer (Y, M, C) and the second The position of the developer (Bk) pattern is obtained. Note that the calculation described below is performed by the controller 801 including the CPU or ASIC in FIG. 3 described above.

  The method for calculating the amount of registration deviation of the measurement color with respect to the reference color from the result detected by the signal detection unit 212 is that the center value of the pattern of the reference color (Bk) and the pattern of the measurement color (Y or M or C) is shifted Judging from the amount. A center value deviation amount calculation method between the reference color (Bk) pattern and the measurement color (Y, M, or C) pattern will be described with reference to FIG.

FIG. 9 shows an example of a color shift amount detection pattern and a detection signal detected by the pattern detection sensor 120 and binarized by the comparator 211. When the time (time) corresponding to the rise and fall of the detection signal is t _Y11 , t _Y12 , t _Y21 , and t _Y22 as shown in FIG. 9, the center value t _KY1 of the reference color and the center value of the measurement color t _Y1 is represented by the following formula, respectively. Note that “t” indicates an elapsed time from a certain reference (start of timer measurement), and in this embodiment, this time is converted into a distance (equivalent) to obtain a position. In other words, the time position is obtained. Incidentally, at this time, there is a reference (timer measurement start), for example to 10 to be described later may be timing first pattern is detected (TY11 in FIG. 9), or from t _Y11 in FIG. 9 May be the previous timing. The pattern position means a general term for the center position of the pattern, the position of the end of the pattern, and the like. T _Y11 indicates the start of detection of the first developer, and t _Y22 indicates the end of detection. Further, the position of the pattern by the second developer (Bk) is indirectly specified by detecting t _Y12 and t _Y21 indicating the end of detection of the first developer and the start of detection.
t _Y1 = (t _Y22 + t _Y11 ) / 2
_tKY1 = ( _tY21 + _tY12 ) / 2
Similarly, as shown in FIG. 10, the center values of all patterns in a set of color misregistration detection patterns are obtained, and the color misregistration amount, which is the relative misregistration amount between colors, is calculated as follows.
Sub-scanning color misregistration amount Bk-Y sub-scanning color misregistration amount = (t _Y1 −t _KY1 + t _Y2 −t _KY2 ) / 2
Bk-M sub-scanning color misregistration amount = (t _M1 −t _KM1 + t _M2 −t _KM2 ) / 2
Bk-C sub-scanning color misregistration amount = (t _C1 −t _KC1 + t _C2 −t _KC2 ) / 2
A main scanning color misregistration amount between Bk and Y in the main scanning direction = (t _Y1 −t _KY1 −t _Y2 + t _KY2 ) / 2
Bk-M main scanning color shift amount = (t _M1 −t _KM1 −t _M2 + t _KM2 ) / 2
Bk-C main scanning color misregistration amount = (t _C1 −t _KC1 −t _C2 + t _KC2 ) / 2
The amount of color misregistration at the writing position for sub-scanning and main scanning is calculated by performing the above calculation for each pattern set and calculating the average of all sets. By taking an average in the pattern set in which the phase of the writing timing is shifted, it is possible to average the color misregistration amount due to the rotation unevenness of the image carrier.

The main scanning overall magnification color misregistration amount is calculated for each pattern set formed facing the left and right sides of the intermediate transfer member 103 shown in FIG. 7 based on the main scanning color misregistration amount.
N-th set main scanning overall magnification color shift n-th set Bk-Y overall magnification color shift amount = n-th set (right) Bk-Y main-scanning color shift amount-n-th set (left) Bk -Y main scanning color misregistration amount n-th set Bk-M overall magnification color misregistration amount = n-th set (right) Bk-M main-scanning color misregistration amount-n-th set (left) Bk-M Main scan color misregistration amount n-set Bk-C overall magnification color misregistration amount = n-th set (right) Bk-C main scan color misregistration amount-n-th set (left) Bk-C main scan color Here, when the calculation result is positive, it means that writing of the measurement color is slow with respect to the reference color (the image width of the measurement color is wider than the reference color at the overall magnification). On the other hand, when the calculation result is negative, it indicates that the measured color is written quickly with respect to the reference color (the image width of the measured color is narrower than the reference color at the overall magnification).

  After executing the color misregistration correction control, the color image forming apparatus 100 corrects the image forming conditions determined before performing the color misregistration correction control. More specifically, correction is performed by adding (or subtracting) the amount of deviation obtained by calculation to the setting of main scanning writing timing, sub-scanning writing timing, and main scanning overall magnification as image forming conditions. As described above, the image forming conditions can be appropriately adjusted based on the calculation result relating to the color misregistration, and can be set to be adopted from the next time. Note that the adjustment of the image forming condition based on the calculated color misregistration amount (registration misregistration amount) can employ a well-known technique, and detailed description thereof is omitted here.

<Effect of Example 1>
As described above, it is possible to realize a color image forming apparatus that can receive a diffuse reflected light component and efficiently perform registration correction while using a developer color such as black that has a small reflected component of diffuse reflected light. Further effects will be described. Now, a color misregistration detection pattern as shown in FIG. 15 is assumed. In the color misregistration detection pattern of FIG. 15, the reference color is black (Y), the measurement colors are yellow (Y), magenta (M), and cyan (C), and the sensor 120 that detects the diffusely reflected light described above. Shall be detected. In this case, since diffuse reflection light cannot be detected by black (Bk), pattern formation is performed by superimposing black (Bk) on yellow (Y) as a base. In this way, a resist is provided even in a mode in which a BD sensor is provided for black (Bk), a pseudo BD is employed for other measurement colors, and diffused reflected light is detected (the intermediate transfer belt is made inexpensive). Correction.

  Here, the further effect that the length of the whole pattern can be shortened by adopting the superposition pattern shown in FIG. 4 as compared with the superposition pattern shown in FIG. 15 will be specifically described. First, on the performance of the sensor response, resolution, etc., the width required to detect the measurement color (assuming the moving speed is assumed to be a certain speed) is 1 and the width required for black (Bk) is d. Further, in order to set the registration accuracy to the same condition, the number of measurement colors is set to six (Y, Y, Y, M, Y, C in FIG. 15).

  Then, in the pattern illustrated in FIG. 15, a length of at least (12l + 12d) is required for one set of overlapping patterns. On the other hand, according to the pattern of FIG. 4, (12l + 6d) is obtained, the width required for the reference color black (Bk) can be shortened, and the amount of toner used for black (Bk) can be reduced. There are cases where the color image forming apparatus is centered on monoprints, which is useful in such cases.

  Registration correction is required to reduce downtime, and it is desired that all patterns be accommodated within one round of the intermediate transfer member (belt). It is also necessary to form a certain number of patterns in order to ensure a certain registration correction accuracy. In such a case, by adopting a pattern as shown in FIG. 4, the color misregistration amount detection pattern width per set can be shortened. As a result, while maintaining a certain registration correction accuracy, the intermediate transfer body (belt ) Can be shortened.

[Example 2]
Example 2 will be described with reference to FIGS. An example of the overall configuration of the color image forming apparatus to which the second embodiment is applied is the same as that shown in the first embodiment, and a description thereof will be omitted. Here, the configuration of one set of color misregistration amount detection patterns in the second embodiment, the configuration of the color misregistration amount detection pattern formed on the intermediate transfer member 103 when performing color misregistration correction control, and the color misregistration correction method are sequentially described. explain.

<Description of registration pattern>
FIG. 11 shows a configuration example of one set of color misregistration detection patterns in the second embodiment. The color misregistration detection pattern shown in FIG. 11 is obtained by superimposing a black (Bk) pattern on one side of a yellow (Y), magenta (M), and cyan (C) pattern, as shown in FIG. The reference color pattern is superimposed on the measurement color pattern formed with a width wider than a predetermined pattern width so that the pattern width of the measurement color becomes a predetermined ideal width.

FIG. 13 shows a detection waveform when the pattern shown in FIG. 11 is detected by the pattern detection sensor 120. In the portion where the surface of the intermediate transfer member 103 and the black (Bk) developer are present, the amount of the diffusely reflected light output from the light emitting portion of the pattern detection sensor 120 received by the light receiving portion is set in advance. Since it is insufficient to exceed the threshold, the LOW level is indicated. On the other hand, in the portion where yellow (Y), magenta (M), and cyan (C) developers are present, the amount of diffuse reflection of light output from the light emitting portion of the pattern detection sensor 120 is received by the light receiving portion is: The HIGH level is indicated because the amount is sufficient to exceed a preset threshold. The conditions for determining the configuration of the color misregistration detection pattern formed on the intermediate transfer body 103 when the endless intermediate transfer body 103 is developed are the same as those in the first embodiment. That is, when M sets of color misregistration patterns are formed on the peripheral length RL (Round Length) of the intermediate transfer body 103 with one set of color misregistration amount detection pattern length (Pattern Length) Pl and pattern interval Pi (Pattern Interval). ,
RL> (M−1) × Pi + Pl
Pi> Pl
Pi = N / M
If this condition is satisfied, it is possible to complete one color misregistration correction control by making the intermediate transfer member 103 make one turn.

  Next, a method for detecting the color misregistration amount using the color misregistration amount detection pattern of this embodiment will be described.

  Since the circuit configuration for detecting the color misregistration amount detection pattern can be implemented by the same configuration as that of FIG. 6 described in the first embodiment, description thereof is omitted. Therefore, a method for calculating the color misregistration amount from the result detected by the signal detection unit will be described below.

The method of calculating the color misregistration amount from the result detected by the signal detection unit 212 is determined from the amount that the reference color (Bk) pattern covers the measurement color (Y, M, or C) pattern (the amount that is superimposed). A method for calculating the color misregistration amount from the amount by which the measurement color is covered with the reference color will be described with reference to FIG. FIG. 14 shows an example of a set of color misregistration detection patterns and detection signals detected by the pattern detection sensor 120 and binarized by the comparator 211. When the time (time) corresponding to the rise and fall of the detection signal in the yellow pattern is t _Y11 , t _Y12 , t _Y21 , t _Y22 as shown in FIG. 14, the center position t _Y1 of each yellow pattern , T _Y2 is represented by the following equation.
t _Y1 = (t _Y11 + t _Y12 ) / 2
t _Y2 = (t _Y21 + t _Y22 ) / 2

Accordingly, the differences Δt _Y1 and Δt _Y2 between the ideal yellow pattern center position P _YW and the measured yellow pattern center positions t _Y1 and t _Y2 are expressed by the following equations. Note that the ideal yellow pattern center position P _YW is a position obtained by adding a distance (time) that is half of (T _Y12 −t _Y11 ) that should originally _exist from t _Y11 in FIG. 14.
Δt _Y1 = t _Y1 −P _YW
Δt _Y2 = t _Y2 −P _YW

Similarly, the difference of the actual pattern width with respect to the ideal pattern width of each measurement color is obtained, and the color misregistration amount that is a relative misregistration amount between colors is calculated by the following equation.
Sub-scanning color misregistration Bk-Y sub-scanning color misregistration amount = (Δt _Y1 + Δt _Y2 ) / 2
Bk-M sub-scanning color shift amount = (Δt _M1 + Δt _M2 ) / 2
Bk-C sub-scanning color misregistration amount = (Δt _C1 + Δt _C2 ) / 2
Color shift amount Bk−Y in the main scanning direction Main scanning color shift amount = (Δt _Y1 −Δt _Y2 ) / 2
Bk-M main scanning color shift amount = (Δt _M1 −Δt _M2 ) / 2
Bk-C main scanning color shift amount = (Δt _C1 −Δt _C2 ) / 2

  The amount of color misregistration at the writing position for sub-scanning and main scanning is calculated by performing the above calculation for each pattern set and calculating the average of all sets. By taking an average in the pattern set in which the phase of the writing timing is shifted, it is possible to average the color misregistration amount due to the rotation unevenness of the image carrier.

The main scanning overall magnification color misregistration amount is calculated for each pattern set formed facing the left and right sides of the intermediate transfer member 103 shown in FIG. 7 based on the main scanning color misregistration amount.
N-th set main scanning overall magnification color shift n-th set Bk-Y overall magnification color shift amount = n-th set (right) Bk-Y main-scanning color shift amount-n-th set (left) Bk -Y main scanning color misregistration amount n-th set Bk-M overall magnification color misregistration amount = n-th set (right) Bk-M main-scanning color misregistration amount-n-th set (left) Bk-M Main scan color misregistration amount n-set Bk-C overall magnification color misregistration amount = n-th set (right) Bk-C main scan color misregistration amount-n-th set (left) Bk-C main scan color Deviation amount

  Here, when the calculation result is positive, it indicates that writing of the measurement color is slow with respect to the reference color (the image width of the measurement color is wider than the reference color at the overall magnification). On the other hand, when the calculation result is negative, it indicates that the measured color is written quickly with respect to the reference color (the image width of the measured color is narrower than the reference color at the overall magnification). Then, the color image forming apparatus 100 executes the color misregistration correction control and then adjusts the image forming condition based on the calculated color misregistration amount (registration misregistration amount), as in the first embodiment.

<Effect of the second embodiment>
As described above, even when the color misregistration detection pattern shown in FIG. 11 is used, the diffuse reflected light component is efficiently received while using the developer color with a small reflected component of diffuse reflected light such as black. A color image forming apparatus capable of performing registration correction can be realized.

  Further, the applicant's experimental results revealed that nine sets of the color misregistration amount detection patterns shown in FIG. 11 are necessary to perform registration correction with the same accuracy as the color misregistration amount detection patterns shown in FIG. did. In this case, as in the first embodiment, assuming that the width required to detect the measurement color (assuming the moving speed is assumed to be 1) is 1 and the width required for black (Bk) is d, the color shift shown in FIG. In the amount detection pattern, a length of (54l + 54d) is required. This length is at least shorter than (60l + 60d), which is the length of 5 sets of patterns in FIG. 15, which is (12l + 12d) × 5, and the image carrier can be further miniaturized as in the first embodiment. Can do.

[Example 3]
In the first and second embodiments, the case where the BD sensor 110 is disposed only on the scanning path of the black laser diode LD1 and does not exist on the scanning path of the other laser diodes has been described. However, the present invention can also be applied to a case where a laser beam detector for generating a horizontal synchronizing signal is provided for each color laser diode in the color image forming apparatus. Even in this case, it is possible to realize a color image forming apparatus capable of receiving the diffuse reflected light component and correcting the registration while using the developer color having a small reflected component of diffuse reflected light such as black as a reference color. Further, black (Bk) has been described as an example of the first developer that cannot detect the position by the diffuse reflected light. However, if the developer cannot detect the position by the diffuse reflected light inherent in the color image forming apparatus, It is also possible to apply to other colors.

[Other Embodiments]
Although various embodiments have been described in detail above, the present invention may be applied to a system constituted by a plurality of devices, or may be applied to an apparatus constituted by one device. For example, a computer system including a printer, a facsimile, a PC, a server, and a client.

  The present invention supplies a software program that implements the functions of the above-described embodiments directly or remotely to a system or apparatus, and a computer included in the system reads and executes the supplied program code. Can also be achieved.

  Accordingly, since the functions and processes of the present invention are implemented by a computer, the program code itself installed in the computer also implements the present invention. That is, the computer program itself for realizing the functions and processes is also one aspect of the present invention.

  In this case, the program may be in any form as long as it has a program function, such as an object code, a program executed by an interpreter, or script data supplied to the OS.

  Examples of the recording medium for supplying the program include a flexible disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, and CD-RW. Examples of the recording medium include a magnetic tape, a non-volatile memory card, a ROM, a DVD (DVD-ROM, DVD-R), and the like.

  The program may be downloaded from a homepage on the Internet using a browser on a client computer. That is, the computer program itself of the present invention or a compressed file including an automatic installation function may be downloaded from the home page to a recording medium such as a hard disk. It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer may be a constituent requirement of the present invention.

  Further, the program of the present invention may be encrypted and stored in a storage medium such as a CD-ROM and distributed to users. In this case, only the user who cleared the predetermined condition is allowed to download the key information to be decrypted from the homepage via the Internet, decrypt the program encrypted with the key information, execute it, and install the program on the computer May be.

  Further, the functions of the above-described embodiments may be realized by the computer executing the read program. Note that an OS or the like running on the computer may perform part or all of the actual processing based on the instructions of the program. Of course, also in this case, the functions of the above-described embodiments can be realized.

  Furthermore, the program read from the recording medium may be written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Based on the instructions of the program, a CPU or the like provided in the function expansion board or function expansion unit may perform part or all of the actual processing. In this way, the functions of the above-described embodiments may be realized.

1 is a diagram illustrating a schematic configuration in a color image forming apparatus. It is a figure which shows schematic structure of a scanner unit. It is a figure which shows an example of the detection circuit of a color shift amount detection pattern. It is a figure which shows an example of a color shift amount detection pattern. FIG. 6 is a diagram showing an example of a color misregistration amount detection pattern classified by color. It is a figure which shows the detection waveform at the time of detecting a color shift amount detection pattern. FIG. 6 is a diagram illustrating a state of a color misregistration detection pattern formed on an intermediate transfer body (on an image carrier). It is a figure which shows the relationship between the phase of an image carrier, and the write-out timing of a color shift amount detection pattern. It is a figure for demonstrating the calculation method of the deviation | shift amount of the position of the measurement color by a 1st developer, and the position of the reference color by a 2nd developer. It is a figure which shows the mode of a position detection for 1 set of color shift amount detection patterns. It is a figure which shows an example of a color shift amount detection pattern. FIG. 6 is a diagram showing an example of a color misregistration amount detection pattern classified by color. It is a figure which shows the detection waveform at the time of detecting a color shift amount detection pattern. It is a figure which shows the mode of a position detection for 1 set of color shift amount detection patterns. It is a figure for demonstrating the effect in an Example.

Claims (12)

Forming means for forming an image on an image carrier using a color developer and a black developer; transfer means for transferring an image formed on the image carrier to a transfer material; and A color image forming apparatus comprising: a fixing unit that fixes a transferred image;
A control unit that forms a superimposed pattern on the image carrier by the forming unit with a color developer pattern as a base and a black developer pattern superimposed thereon;
Detecting means for irradiating the superposed pattern with light and detecting diffuse reflection light reflected;
The position of the color developer pattern and the position of the black developer pattern are obtained based on the detection result of diffuse reflected light from the superimposed pattern by the detection means, and the color developer pattern and the black developer pattern Calculating means for calculating the relative positional deviation amount of
A color image forming apparatus comprising: an adjusting unit that adjusts an image forming condition based on a calculation result by the calculating unit.   The calculation means obtains the position of the color developer pattern and the position of the black developer pattern based on the detection result of diffuse reflected light from the pattern by the color developer included in the superimposed pattern. The color image forming apparatus according to claim 1.   The color image forming apparatus according to claim 1, wherein the calculation unit specifies the position of the pattern by the black developer based on the start and end of detection of the color developer.   The control means is arranged such that the color developer, the black developer, and the color developer pass through the detection means in order from one overlapping pattern along the pattern moving direction. 4. The color image forming apparatus according to claim 1, wherein a superimposed pattern is formed by superimposing the black developer on a color developer as a base. 5.   5. The color image forming apparatus according to claim 1, wherein a width in the moving direction of the color developer pattern is longer than a width in the moving direction of the black developer pattern. 6.   6. The color image forming apparatus according to claim 1, wherein the black is a reference color for calculating the amount of relative positional shift. Forming means for forming an image on an image carrier using a color developer and a black developer; transfer means for transferring an image formed on the image carrier to a transfer material; and A color misregistration correction method in a color image forming apparatus comprising a fixing means for fixing a transferred image,
A control step of forming a superimposed pattern in which a pattern of a color developer is used as a base and a pattern of a black developer is superimposed on the image carrier by the forming unit;
A detection step by a detecting means for irradiating the superposed pattern with light and detecting the reflected diffuse reflected light; and
The position of the color developer pattern and the position of the black developer pattern are obtained based on the detection result of diffuse reflected light from the superimposed pattern in the detection step, and the relative positions of the color developer and the black developer A calculation process for calculating the deviation amount of
A color misregistration correction method comprising: an adjustment step of adjusting an image forming condition based on a calculation result of the calculation step.   In the calculation step, the position of the color developer pattern and the position of the black developer pattern are obtained based on the detection result of diffuse reflected light from the pattern by the color developer included in the superimposed pattern. The color misregistration correction method according to claim 7.   The color misregistration correction method according to claim 7, wherein in the calculation step, the position of the pattern by the black developer is specified based on the start and end of detection of the color developer.   In the control step, the color developer, the black developer, and the color developer are passed through the detection unit in order from the superimposed pattern along the pattern moving direction. The color misregistration correction method according to claim 7, wherein a superimposed pattern is formed by superimposing the black developer on a color developer.   11. The color misregistration correction method according to claim 7, wherein a width in the moving direction of the color developer pattern is longer than a width in the moving direction of the black developer pattern.   The color misregistration correction method according to any one of claims 7 to 11, wherein the black is a reference color for calculating the relative positional misalignment amount.

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