JP2007072282A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correspond to a case when calibration of a sensor reading a color shift compensation pattern is not carried out correctly due to having the reading based on one part of transfer material. <P>SOLUTION: The calibration (Vsg adjustment) of the pattern sensor is carried out (S102 to 104) before compensation for color shift is executed after reading correction pattern. As a result of this adjustment, service lives of a light emitting element and a transfer belt are checked (S105) based on light emitting element current value to be set and texture of the transfer belt is read under a reading condition after the adjustment and whether or not the calibration is correct is checked (S106 to 109). According to the result of checking the correctness of the calibration in each sensor in a configuration in which each sensor is attached to a central part and both end parts in a scanning direction of the transfer belt, only a compensating action which can be carried out correctly is executed making a read value of a normal acting sensor effective. When execution is not carried out, a compensating action is omitted and transition is made to a next job without repeating the same action. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus (for example, a laser printer, a copying machine, a facsimile machine, etc.) that performs image composition after writing an image of each color component onto a photoreceptor by light beam scanning, and more specifically. The present invention relates to an image forming apparatus provided with a color registration error detecting means.

In image forming apparatuses such as printers, copiers, and facsimile machines that perform image formation by electrophotography, in recent years, a method of writing an image on a photosensitive member by light (laser or the like) beam scanning has been mainstream. In this system, laser light whose lighting is controlled by a video signal (line image signal) is periodically scanned in the main scanning direction by a scanning means such as a polygon mirror, and the scanned surface of the photosensitive member is sub-scanned. The image is moved in the direction (usually orthogonal to the main scanning direction), and a two-dimensional image is written on the photoreceptor by such exposure scanning.
When a color image is formed by such a light beam scanning method, a photosensitive member (a method using a single photosensitive member or a so-called tandem method using a plurality of photosensitive members of each color) is used for each color component by exposure scanning. The created electrostatic latent image is developed with toner, and then a color image is synthesized in the transfer process from the transfer body to the recording (transfer) paper, and the formed color image is output through a fixing process. A flow is typical.
As described above, the photosensitive member is exposed and scanned for each color component, and then color synthesis is performed. Therefore, it is necessary to manage the image forming process so that no deviation occurs between the synthesized color component images. For this purpose, an image forming state of each color component system is detected as a color registration error, and a color registration error (color shift) is corrected according to the detection result, thereby obtaining an appropriate image output.

As a method for detecting a color registration error, a test pattern (hereinafter referred to as a “correction pattern”) is actually formed by each color component system, and a pattern shift is detected by reading the formed correction pattern with a sensor. The method is used. The following Patent Documents 1 and 2 show conventional examples employing this method.
The color misregistration detection method disclosed in Patent Document 1 reads a transfer belt surface by a sensor used for color misregistration detection before detecting a detection pattern, detects a scratch on the transfer belt, and based on the detection result, It is characterized in that a detection pattern is imaged in an area having no defect and erroneous detection occurs due to scratches (noise) when the detection pattern is detected.
Moreover, the detection method of patent document 2 is characterized by the following (1) to (4). That is, (1) the registration sensor is arranged on the transfer belt conveyance roller with little fluctuation of the transfer belt surface, and the test pattern is stably detected. (2) The above sensor detects the position of the scratch on the transfer belt, and the test pattern is not marked at the position of the scratch to obtain a stable sensor output without being affected by the scratch. (3) A normal binarized output is obtained by lowering the threshold level of the comparator that detects the pattern in response to a decrease in the reflectance of the transfer belt. (4) The reflectance of the transfer belt is measured, and the time when the reflectance of the toner is substantially equal is displayed as the belt replacement time.
Japanese Patent Laid-Open No. 10-73981 Japanese Patent No. 3234878

By the way, as shown in the conventional example described above, in order to prevent the belt surface state (scratches, change in reflectance, etc.) from affecting the deviation correction, at least a portion of the belt surface forming the correction pattern is patterned in advance. It is necessary to perform processing such as reading with a sensor, detecting scratches, etc., and forming a pattern so as not to be affected by the scratches. These operations take extra time and are a negative factor for speeding up the processing. In addition, hardware resources necessary for processing must be secured.
Therefore, a method of detecting the state of the belt surface by performing a detection operation of several seconds (detection of the background on a small part of the transfer belt) necessary for the calibration of the pattern sensor is adopted. Here, the calibration of the pattern sensor is an operation of adjusting the output to a predetermined value with respect to fluctuations in the reflectance of the belt and the light emission amount of the light emitting element that affect the sensor output. In the case of this conventional method, it is necessary to take a countermeasure for scratches.
However, since the calibration operation of the conventional method usually ends in a few seconds and immediately enters the reading operation of the correction pattern, the fluctuation of the reading signal of the entire transfer belt is not checked after calibration. According to such an operation, if the read value of the belt surface that has been calibrated does not accidentally show a normal value, there may be a problem when the correction pattern is read.
The present invention provides a pattern for correcting a color registration error (color misregistration) generated in a composite image in an image forming apparatus that performs image composition on a photoconductor after writing an image of each color component on a photoconductor. This problem has been made in view of the above-described problems of the related art relating to the calibration of the pattern sensor to be detected, and the problem to be solved is based on the read signal of one part of the transfer body. It is possible to cope with the case where it has not been performed, and it is possible to suppress the deterioration of the image quality of the output image due to the color shift occurring between the respective color images, and the calibration method of the conventional method in which only one part of the transfer body can be read. It is in taking advantage of the benefits.

  According to the first aspect of the present invention, in an image forming apparatus having a transfer body to which an image of each formed color component is transferred through writing in a two-dimensional scanning method, image forming conditions for each color component are corrected on the transfer body. A correction pattern image forming unit for forming a correction pattern image for reading, a pattern sensor for reading a correction pattern image on a transfer member formed by the correction pattern image forming unit, and the correction pattern by the pattern sensor. An image correcting unit that reads an image and corrects an image forming condition based on the obtained read signal, a sensor adjusting unit that calibrates the pattern sensor, and the transfer performed by the pattern sensor adjusted by the sensor adjusting unit. The surface of the body on which the correction pattern image is formed is read, and it is checked whether the obtained read signal is within a predetermined fluctuation range. Tsu by providing a click to read condition propriety check section, is intended to solve the above problems.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, in which the transfer member is a transfer belt, the reading condition suitability checking unit reads one rotation of the transfer belt and uses the obtained read signal as a reading signal. The present invention is characterized in that it is a means for checking the reading conditions. By doing so, the above-mentioned problems are solved.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, in which the transfer body is a transfer belt, the pattern sensor is disposed on a flat portion of the transfer belt. By doing so, the above-mentioned problems are solved.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the sensor for reading the center and both ends of the direction intersecting the moving direction of the transfer body is provided as the pattern sensor. The image correction means, as a check result of the pattern sensor by the read condition suitability check means, the sensor provided at the center is not an appropriate reading condition, and the sensors provided at both ends are appropriate reading conditions, The present invention is characterized in that the color misregistration is corrected based on the reading signals of the sensors provided at both ends, and by doing so, the above-mentioned problems are solved.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the sensor for reading the center and both ends of the direction intersecting the moving direction of the transfer body is provided as the pattern sensor. The image correction means is characterized in that, as a result of checking the pattern sensor by the read condition suitability check means, correction of color misregistration is omitted when the sensors provided at both ends are not in proper read conditions. In this way, the above-described problems are solved.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, it is determined whether or not a set value after adjustment by the sensor adjusting unit exceeds a predetermined allowable limit value. And a means for notifying to the outside when it is determined that the allowable limit value is exceeded as a determination result by the allowable limit determination means. This solves the above problem.

According to the present invention, since the calibration of the pattern sensor is performed based on the signal obtained by reading a part of the transfer body, even if the adjustment is wrong, the reading is performed from the read signal when the transfer body is read after the adjustment. Since the correctness of the conditions is checked, correct color registration error (color misregistration) correction operation can be ensured, there is no image quality degradation of the output image due to misalignment, and the calibration operation is performed by reading a part of the transfer body. Enable the benefits of doing it. In addition, when the transfer body is a transfer belt, the entire belt is read and the read signal obtained is checked for suitability of the reading conditions. A check can be made (Claim 2). In addition, even if the pattern sensor is laid out on the flat surface of the transfer belt, proper operation can be ensured. Further, when laid out on the flat surface, the reading accuracy of the sensor is easier to obtain than in the case of laying out on the cylindrical surface, and the part cost, etc. (Claim 3).
In addition, when the pattern sensor provided at the center is not in proper reading conditions and the pattern sensors provided at both ends are in proper reading conditions, color deviation is corrected based on the reading signals of the pattern sensors provided at both ends. Therefore, even if the signal detected by the pattern sensor provided at the center is not normal, the loss time can be eliminated by correcting the range that can be performed without performing the same operation again (claim 4). .
In addition, when the pattern sensors provided at both ends are not in proper reading conditions, correction of color registration error (color misregistration) is omitted, so the next operation is not performed again. By entering the operation, loss time can be eliminated (claim 5).
In addition, the pattern sensor is calibrated, and when it is determined that the set value after adjustment exceeds a predetermined allowable limit value, the fact is notified to the outside. Downtime can be reduced by accurately informing the user of the time for maintenance such as body and sensor replacement.

Hereinafter, embodiments of the image forming apparatus of the present invention will be described. In the embodiment described below, LD (Laser Diode) optical writing is performed on a photosensitive member by a main / sub two-dimensional scanning method according to the present invention relating to an image forming apparatus provided with a color registration error (color shift) detection unit. An example applied to an electrophotographic color image forming apparatus will be described. An image forming apparatus having a transfer body to which an image of each formed color component is transferred. Also, in this example, each type of photoconductor is typical of this type of apparatus and formed on each color photoconductor. A so-called tandem apparatus for synthesizing a color image on an intermediate transfer member (transfer belt) to which an image is transferred is shown. However, the present invention is not limited to this method, and a method using a single photoconductor for each color or a method of synthesizing a color image by a transfer process from an intermediate transfer member can be implemented in the same manner as in this example.
FIG. 1 shows a schematic configuration of a color image forming apparatus according to an embodiment of the present invention.
In FIG. 1, each of the photosensitive drums 2 to 5 is subjected to processing of an image forming unit that forms an image by LD light writing or an electrophotographic process (not shown), and each color component constituting a color image (usually, Magenta: M, cyan: C, yellow: Y, black: K) toner images are formed. Since writing is performed on the photosensitive drum by the main / sub two-dimensional scanning method, the drum is rotated in the sub scanning direction (indicated by an arrow in FIG. 1).
The toner images formed on the photosensitive drums 2 to 5 are transferred to a transfer belt 6 as an intermediate transfer member. The transfer belt 6 is an endless belt wound around a driving roller for applying a driving force and a driven roller that is driven to rotate. The transfer belt 6 moves in the direction indicated by the arrow in FIG. 1 in synchronization with the photosensitive drums 2 to 5. .

In the present embodiment, the respective color component images are superimposed on the transfer belt 6 at the time of transfer from the respective photosensitive drums 2 to 5 and color synthesis is performed.
Accordingly, the LD writing timing to each of the photosensitive drums 2 to 5 previously performed is set so that the image of each color does not shift based on the specifications of the arranged drums and the LD writing system. In practice, however, color misregistration occurs due to the accuracy of the machine and the variation of the LD writing system on the drum. For this purpose, color registration is performed to adjust the timing of image writing to each of the photoconductive drums 2 to 5 so as not to cause color misregistration.
The color image synthesized on the transfer belt 6 after receiving the transfer from each of the photosensitive drums 2 to 5 is transferred to the transfer paper 7 fed at a predetermined timing. The transfer paper 7 onto which the image has been transferred is conveyed to the fixing unit 12, where it is pressed by a roller heated to a high temperature, undergoes a fixing process by thermocompression, and the image forming process is completed.

Here, the color registration for adjusting the image writing timing to each of the photosensitive drums 2 to 5 will be further described.
The color registration is caused by a change over time such as a change in the position of the components in the writing unit and the photosensitive drum depending on the temperature when the continuous printing operation is performed in the image forming apparatus having the configuration as shown in FIG. As a result, a registration error (color misregistration) occurs. Therefore, a timing at which a change is expected (for example, when starting from a sleep state such as when the power is turned on, when a predetermined number of prints are output, or It is necessary to correct the color misregistration when a temperature change occurs that causes a change in the state of the LD writing system or the like. The color misregistration is corrected by adjusting the sub-scanning resist, the inclination (skew), the main scanning resist, and the main scanning magnification.
As a method for detecting registration error (color misregistration), the above-described sub-scanning resist, inclination (skew), main-scanning resist, and a correction pattern for obtaining correction values for main-scanning magnification are actually used for the image forming unit for each color. By operating, forming on the transfer belt 6, and reading the correction pattern, the state of registration error (color misregistration) is detected and quantitatively grasped. A pattern sensor 1 for reading the correction pattern on the transfer belt 6 is provided to face the image surface of the transfer belt 6 as shown in FIG.

FIG. 2 shows the relationship between the correction pattern on the transfer belt 6 and the pattern sensor 1 in more detail.
As shown in FIG. 2, a part of the correction pattern 10 formed on the transfer belt 6 is shown. A pattern composed of four horizontal lines and four diagonal lines for each color of K, Y, C, and M in FIG. 2 is set as one set, and this set is a transfer belt moving direction (that is, a sub-scanning direction, and an arrow in FIG. ) Are formed at a plurality of sets (for example, 8 sets) at the detection positions of the pattern sensors 22, 23, and 24 arranged at three positions in the direction (ie, the main scanning direction) orthogonal to the center), that is, two positions at the center and both ends. And a pattern string.
The configuration of the pattern sensors 22, 23, 24 is such that a detection component in which the light emitting unit 20 and the light receiving unit 21 are paired is placed on the central part 23 and both end parts 22, 24 in the main scanning direction on the substrate of the pattern sensor 1, respectively. Installed.
The reason why the pattern row is composed of a plurality of sets of patterns is that the phase is taken into consideration so that errors in pattern formation and detection are minimized, and the average of these detection results is calculated to increase detection accuracy. Because. For example, eight sets of K, Y, C, and M horizontal line and diagonal line patterns are read by the pattern sensors 22, 23, and 24, thereby causing skew with respect to the reference color (usually K), sub-scanning resist deviation, main-scanning resist deviation, It is possible to calculate the main scanning magnification error, and it is possible to perform correction by reflecting the correction amount obtained from these deviation amounts in the writing timing on the photosensitive drums 2 to 5 (for example, each sensor). The shift amount due to the magnification deviation in the main scanning direction is corrected to be inconspicuous by shifting the image in the opposite direction to the position shift direction by 1/2 of the maximum position shift amount obtained from the read value). Note that the method of calculating the correction amount from the reading value of the pattern sensor can be implemented by applying a conventional technique (for example, see Japanese Patent Application Laid-Open No. 2004-101567), and therefore, detailed description thereof is omitted here. To do.

Next, calibration of the pattern sensor 1 according to the present embodiment will be described.
In order to correct the above-described color misregistration, the pattern sensor 1 reads the correction pattern 10 formed on the transfer belt 6, and usually performs sensor calibration before performing this pattern reading. That is, the sensor is adjusted in order to perform proper reading with respect to fluctuations in reading conditions such as the state of the background on the transfer belt 6 and variations in the light emitting unit 20 and the light receiving unit 21 constituting the pattern sensor 1.
The calibration is performed by driving the light source (light emitting element) of the light emitting unit 20 of the pattern sensor 1 with a predetermined setting, irradiating the transfer belt 6 with the emitted light, and receiving the reflected light from the ground surface of the transfer belt 6. Detection is performed by the light receiving element of the unit 21. At this time, the reading conditions fluctuate due to the temporal change of the light emitting element and the transfer belt 6, and the value detected by the light receiving element changes. Therefore, even if the reading condition fluctuates, the set value on the light emitting unit 20 side is adjusted so that the value detected by the light receiving unit 21 becomes a constant value (Vsg value).
FIG. 3 is a diagram showing the characteristics of the sensor used as the pattern sensor 1. In FIG. 3, the horizontal axis represents the light emitting element current value, and the vertical axis represents the detected voltage value of the light receiving element.
As can be seen from the characteristics of FIG. 3, even if the light-emitting element current flowing during driving is increased, the detected voltage value of the light-receiving element becomes a constant value (Vsg value) when the current exceeds a certain value.
Therefore, at the time of calibration, the light emitting element current value that sets the detection voltage value of the light receiving element to a constant value (Vsg value) is usually set as small as possible with a predetermined margin.
However, as described above, since the light receiving element receives the light emitted from the light emitting element as reflected light from the belt surface, the characteristics differ from pattern sensor to pattern sensor, and changes with time are also added. Therefore, a constant value (Vsg value) is obtained. The set value of the light-emitting element current to be changed also differs depending on the individual pattern sensor and the time of use.
Therefore, before reading the correction pattern 10 formed on the transfer belt 6, the pattern sensor 1 is calibrated, and the registration error (color misregistration) correction pattern 10 is read according to the adjusted reading conditions. To do. In this way, reading can be performed under appropriate conditions regardless of variations in the pattern sensor 1 and the transfer belt 6 and changes with time.

In this embodiment, in order to perform calibration of the pattern sensor 1 in a short time (for example, a time of several seconds or less), the reading of the transfer belt 6 is set as a part of the background surface of the belt.
By sampling a part of the ground surface in this way, the processing can be speeded up by shortening the time required for calibration. However, since the calibration is intended to adjust the standard value (average background level) of the belt background, it is better to sample the background, but in this example, the scanned background of the belt is one copy. In addition, there is a danger of reading a ground surface (abnormal value) that does not show the target average background level (normal ground surface level). In such a case, proper calibration is not performed. In other words, since the setting is set according to the abnormal value, there is a problem that after the adjustment, the value obtained by reading the normal background is greatly deviated from the value of the constant value (Vsg) or the correction pattern 10 cannot be detected. Get up.
Therefore, in the present embodiment, it is possible to check the suitability of the set value of the light emitting element current set after the adjustment, that is, the suitability of calibration. By this check, if the background level is erroneously detected and an incorrect setting is made in the pattern sensor 1 according to the result, it is possible to avoid the correction operation of the registration error (color shift) (see FIG. 4 to be described later). Detailed in the embodiment shown in the flow).

To check the suitability of calibration, after calibration, the value detected by the pattern sensor 1 that reads the belt surface while the transfer belt 6 rotates once, that is, the detection voltage value of the light receiving unit 21 is checked.
The range to be checked is a predetermined voltage value range, for example, the detection voltage value Vsg of the light receiving unit 21 when the set value of the light emitting element current is determined by the calibration performed previously (although this value is a constant value). As described above, the range is defined based on the individual pattern sensors and based on the point of use. If the detected voltage value of the light receiving unit 21 during one rotation of the transfer belt 6 deviates from the voltage value within the specified range, it is determined that the calibration has not been performed properly. In order to perform this check, it is necessary to save Vsg at the time of calibration in the storage unit.
In addition, since the detection voltage value of the pattern sensor 1 that has read the belt surface of the transfer belt 6 to perform the above check represents the state of the surface, even if the calibration is properly performed, It is possible to know noise due to deterioration, scratches, etc., for example. It can be used to maintain the detection accuracy of the correction pattern 10.

In the present embodiment, means for detecting an abnormality in the reading condition is provided based on the light emitting element current value set in the process of calibrating the pattern sensor 1.
As described above, the light emitting element current value set by the calibration depends on the characteristics of the pattern sensor 1 and the surface state of the transfer belt 6, and the setting value reflects the state at the time of calibration.
Therefore, when calibration is performed, the light source of the light emitting unit 20 of the pattern sensor 1 is deteriorated, and a much larger current than that in the normal state is obtained in order to obtain a light emission amount that makes the light reception voltage of the light receiving unit constant (Vsg). It is necessary to flow, and the surface of the transfer belt 6 is deteriorated so that the reflectance is lowered (the glossy portion is lost), and the light emission amount is set to obtain the light reception amount that makes the light reception voltage constant (Vsg). In any case, the state where the deterioration has progressed beyond the limit appears in the set value of the light emitting element current value.
Therefore, based on the empirical values obtained by testing, etc., prepare the use limit value that appears in the set value of the light emitting element current value as the standard value in advance, prepare the light emitting element current value to be set after performing calibration The service life is checked based on the use limit value, and if the use limit is exceeded, processing such as parts replacement is performed. In addition, about this check process performed after calibration, the Example integrated in the flow of FIG. 4 mentioned later is shown.

Since the calibration of the pattern sensor 1 is based on a sampling value obtained by reading a part of the belt background surface, the calibration may become unstable as described above. In the above, it has been shown that this adjustment failure can be checked by observing a detection voltage value obtained by reading a normal background surface with a sensor after calibration.
Here, an embodiment relating to a method of avoiding the correction operation when the adjustment is not successful and the registration error (color misregistration) cannot be corrected properly according to the above check result will be described.
In this embodiment, the suitability of calibration of each sensor in the configuration in which the sensor is attached to the central portion 23 and both end portions 22 and 24 in the main scanning direction on the substrate of the pattern sensor 1 shown in FIG. In accordance with the check result, the reading value of the sensor that operates normally is validated, and only a correctable correction operation is executed.
That is, when normal reading cannot be performed by the center sensor and normal reading can be performed by the sensors at both ends, the skew and main magnification color misregistration correction is executed based on the reading signals of the sensors at both ends. Correction of color misregistration of the sub-scanning resist and the main scanning resist is omitted. Further, when normal reading cannot be performed by the sensors at both ends, correction of all color misregistration is omitted.
As described above, in any case, a range in which an appropriate correction operation can be performed is executed. However, if the correction operation cannot be performed, the correction operation is omitted and the next operation in the image forming processing flow is started without performing the same operation again. By eliminating the loss time.

Next, an embodiment related to a series of color misregistration correction processing, in which the above-described calibration suitability check and component (light emitting unit 20, transfer belt 6) use limit (lifetime) check are performed in the previous stage of color misregistration correction. Indicates.
FIG. 4 shows a flow of color misregistration correction processing according to this embodiment.
In this color misregistration correction process, the calibration of the pattern sensor 1 is performed before the correction pattern 10 is read, the lifetime of the light emitting unit 20 and the transfer belt 6 is checked based on the adjustment result, and calibration adjustment is performed. A process of reading the background of the transfer belt under the reading conditions set as a result and checking the suitability of calibration is performed as a pre-process.
As shown in the processing flow of FIG. 4, when the color misregistration correction operation is started, first, the transfer belt 6 starts to roll (step S101).
When the rotation of the transfer belt 6 is stabilized, the calibration of the pattern sensor 1 is started (step S102). The sensor calibration is performed by adjusting Vsg (see the above [0014] section). That is, the current flowing through the element of the light emitting unit 20 is increased / decreased until the light receiving voltage of the light receiving unit 21 reaches a specified Vsg (steps S103 and S104). If the voltage can be adjusted to Vsg (step S104-YES), the adjustment is performed. As a result, the element current of the light emitting unit 20 when the light reception voltage is adjusted to Vsg is set as the adjusted set value, and the adjustment loop is exited. Also, Vsg at the time of this adjustment is stored and used when checking the suitability of the subsequent calibration.

Next, the set value of the element current of the light emitting unit 20 set by the Vsg adjustment performed in the previous calibration is a range of standard values in which the state of the component reflected in the light emitting element current value is determined in advance as the use limit (life) Is it within? It is checked whether or not (step S105). That is, when the set value of the light emitting element current exceeds the standard value, the surface of the transfer belt 6 is deteriorated and the glossy portion is lost, so that the reflected light is reduced or the light emitting characteristics are deteriorated due to the deterioration of the light emitting element. Is expected to decrease (see paragraph [0017] above).
Therefore, when the standard value is exceeded (step S105-NO), the light emitting unit 20 and the transfer belt 6 have reached the use limit, so that it is time to replace these parts to the user. This is displayed on the operation panel (not shown) of the apparatus (step S111), and the process flow is exited.
On the other hand, if the value exceeds the standard value, there is no problem with these parts, and the process proceeds to a processing step for checking the suitability of the next calibration.

In the process for checking the suitability of calibration (see the above [0016] section), first, data necessary for the check is acquired (step S106). That is, it is set by calibration (Vsg adjustment) in steps S103 and S104 by the pattern sensors at the central portion 23 and both end portions 22 and 24 in the main scanning direction mounted on the substrate of the pattern sensor 1 shown in FIG. The background of the transfer belt 6 is read under the read conditions, and the obtained read value and Vsg stored at the time of Vsg adjustment are acquired as data necessary for the check.
Next, based on the acquired Vsg and the reading value of the background, whether or not the calibration is properly performed is checked. Here, a range in which an appropriate correction operation can be performed is executed based on the check result. However, if the correction operation cannot be performed, the correction operation is omitted, and the next operation in the image forming process flow is started without performing the same operation again. (See paragraph [0018] above).
In the processing flow, when the background readings of all the sensors are normal (step S107-YES), skew, sub-scanning registration, main scanning registration, and main magnification color misregistration correction are executed (step S113), and the processing flow is Exit.
If the background reading of the central sensor 23 is abnormal (YES in step S108), the sub-scanning registration and main scanning registration are omitted, and skew and main magnification color misregistration correction is executed (step S115). Exit.
Further, if the background readings of the sensors 22 and 24 at both ends are abnormal (YES in step S109), all the processing for correcting color misregistration is omitted, and a procedure for immediately proceeding to the next job process is performed (step S117). ), Exit the processing flow.

Next, an embodiment relating to the arrangement of the pattern sensor 1 with respect to the transfer belt 6 will be described.
The transfer belt 6 is an endless belt wound around a driving roller and a driven roller that is driven to rotate. The transfer belt 6 is made of a thin material such as polyimide and rotates at a constant speed in a certain direction. Since the material of the transfer belt 6 is thin, undulation may occur in the belt during rotation, and the generated undulation becomes an obstacle when reading by the reflective pattern sensor 1, thereby causing erroneous detection.
As a countermeasure against this erroneous detection, as shown in FIG. 5, the pattern sensor 1 is arranged so that the position where the transfer belt 6 of the roller 25 is wound is used as a detection unit, and the influence of undulation generated on the belt is affected. It is a method that has been conventionally employed to prevent the reception (see Patent Document 2 above).
However, as shown in FIG. 5, since the detection surface is a cylinder, the accuracy of the sensor 1 and the roller 25 is required, leading to an increase in cost in terms of components, or a jig or the like being required for assembly. .
Therefore, by disposing the detection surface on the flat surface of the belt without using a roller surface, the above-described problems such as accuracy, cost increase, jig, and the like are solved. In the present embodiment, even if an accidental undulation occurs, it is possible to avoid erroneous detection by performing a process for checking the suitability of calibration in correction of color misregistration as described above. Yes, proper operation can be secured.

1 shows a schematic configuration of a color image forming apparatus according to an embodiment of the present invention. The relationship between the correction pattern on the transfer belt of the color image forming apparatus (FIG. 1) and the pattern sensor is shown in more detail. The characteristic line figure of the pattern sensor which consists of a light emission part and a light-receiving part of a color image forming apparatus (FIG. 1) is shown. 2 shows a flow of color misregistration correction processing in a color image forming apparatus (FIG. 1). The prior art example of arrangement | positioning of the pattern sensor with respect to a transfer belt is shown.

Explanation of symbols

1 ... Pattern sensor 2, 3, 4, 5 ... Photosensitive drum (for each color component), 6 ... Transfer belt, 7 ... Transfer paper, 10 ... Correction pattern, 20 ... Light emitting part, 21 ··Light receiving section.

Claims (6)

A transfer body to which an image of each color component formed is transferred through writing in a two-dimensional scanning method;
A correction pattern image forming means for forming a correction pattern image for correcting an image forming condition for each color component on the transfer member;
A pattern sensor for reading a correction pattern image on a transfer body formed by the correction pattern image forming unit;
Image correction means for reading the correction pattern image by the pattern sensor and correcting image forming conditions based on the obtained read signal;
Sensor adjustment means for calibrating the pattern sensor;
Reading condition suitability checking means for reading a surface of the transfer body on which the correction pattern image is formed by the pattern sensor adjusted by the sensor adjusting means and checking whether or not the obtained reading signal is within a predetermined fluctuation range; An image forming apparatus. The image forming apparatus according to claim 1, wherein the transfer body is a transfer belt.
The image forming apparatus according to claim 1, wherein the read condition suitability check means is a means for reading one rotation of the transfer belt and checking the read condition for the obtained read signal.   The image forming apparatus according to claim 1, wherein the transfer body is a transfer belt, and the pattern sensor is disposed on a flat portion of the transfer belt. 4. The image forming apparatus according to claim 1, wherein the pattern sensor includes a sensor that reads a center and both ends in a direction intersecting a moving direction of the transfer body. 5.
The image correction means, as a check result of the pattern sensor by the read condition suitability check means, the sensor provided at the center is not an appropriate reading condition, and the sensors provided at both ends are appropriate reading conditions, An image forming apparatus, wherein color misregistration is corrected based on reading signals of sensors provided at both ends. 5. The image forming apparatus according to claim 1, wherein the pattern sensor includes a sensor that reads a center and both ends in a direction intersecting a moving direction of the transfer body.
The image correction unit is characterized in that, as a result of checking the pattern sensor by the reading condition suitability checking unit, correction of color misregistration is omitted when sensors provided at both ends are not in proper reading conditions. Image forming apparatus. The image forming apparatus according to claim 1,
An allowable limit determination means for determining whether the set value after adjustment by the sensor adjustment means exceeds a predetermined allowable limit value;
An image forming apparatus comprising: means for notifying the outside when it is determined that the allowable limit value is exceeded as a determination result by the allowable limit determination means.

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