JP2010256618A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which performs calibration without reducing productivity with inexpensive constitution. <P>SOLUTION: In the image forming apparatus which performs the calibration, an image for print and a toner pattern for calibration are formed simultaneously, and the calibration is implemented by using the toner pattern, when it is determined that an image to be formed for print next is equal to or under predetermined size, and implementation of the calibration is required. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus such as a printer or a color copying machine.

  In recent years, colorization of copying machines, printers, fax machines, and the like that handle documents has progressed rapidly, and documents in offices have been colored. Devices that handle these color documents tend to be further accelerated in the future. As an apparatus that handles color documents, for example, an image forming unit including an exposure device, a photoconductor, a developing device, and the like for each color of black (K), yellow (Y), magenta (M), and cyan (C) is provided. There is a so-called tandem color printer.

  The exposure apparatus of the tandem color printer forms a latent image on the photosensitive member for each color by using an image writing start signal as a trigger, and forms the toner image for each color by developing the latent image with a developing device. . Then, the toner images for each color are sequentially transferred onto the sheet conveyed by the transfer belt. As a result, a full-color toner image is formed.

  Such a tandem color image forming apparatus has higher print productivity than a developing machine switching type color image forming apparatus, and has become the mainstream in recent color image forming apparatuses.

  However, in such a tandem-type color image forming apparatus, a shift in the transfer position between colors, that is, a color shift occurs due to a shift in the optical scanning position in each exposure apparatus, and a significant deterioration in image quality occurs. There is a risk. Therefore, in the color image forming apparatus, it is necessary to perform color misregistration correction every predetermined period.

  In a color image forming apparatus, a color misregistration correction pattern is used to detect and correct color misregistration. The color misregistration correction pattern includes each color toner image pattern, and is formed on a moving body such as a paper transport belt. The color misregistration correction pattern is read by a sensor, the position of each toner image pattern is calculated by an arithmetic processing unit, a position difference (color misregistration amount) between the respective colors is detected, and the image writing timing of each color according to the color misregistration amount By adjusting, color misregistration is detected and corrected.

  As techniques relating to color misregistration correction using the color misregistration correction pattern as described above, the following has been proposed.

  In Patent Document 1, each color mark row (toner image pattern) created on the entire surface of a transfer belt is read by a sensor, a scanning position is specified and stored in a memory, and the scanning position is adjacent to the specific reading signal in the memory. There has been proposed a color image forming apparatus that reliably detects the mark position by calculating the mark position based on the scanning position of the data group belonging to the change area.

  In Patent Document 2, when forming a color misregistration correction pattern on the entire surface of a moving body such as an intermediate transfer belt, the color misregistration correction is performed by reducing the interval between the color marks of the color misregistration correction pattern for each detection. A color image forming apparatus that can be performed with high accuracy has been proposed.

  Further, in Patent Document 3, a distance between sheets is calculated from a sheet to be used, a linear velocity, and the like, a color misregistration correction pattern that fits between the sheets is selected, and a photoconductor is included in an interval of image formation processing on a recording medium. An image forming apparatus that forms a color misregistration correction pattern between printing papers by transferring each toner image pattern formed on the transfer belt between papers, and detects the color misregistration amount of the color misregistration correction pattern Has been proposed.

  In Patent Document 4, a plurality of image output means outputs a color misregistration measurement pattern outside the maximum paper area allowed by the image forming apparatus of the transfer belt in parallel with the print cycle, and corrects color misregistration. An image forming apparatus that can be performed with high accuracy has been proposed.

JP 2002-174936 A JP 2004-46001 A JP 2006-171352 A JP 2003-295560 A

  The above-described technology has the following problems.

  In the techniques described in Patent Document 1 and Patent Document 2, since the color misregistration correction pattern is formed on the entire surface of the transfer belt in order to perform color misregistration correction, the normal image forming process must be stopped, and the image forming process is produced. The nature will decline.

  In the technique described in Patent Document 3, image formation processing and color misregistration correction can be performed at the same time, so productivity of the image formation processing does not decrease. However, in Patent Document 3, since two or more color misregistration correction patterns are formed in the main scanning direction in the inter-sheet space of each sheet, a sensor for reading the pattern is required for that column, resulting in an increase in cost. Further, in an image forming apparatus having a short sheet interval, there are few color misregistration correction patterns that can be formed within the sheet interval.

  In the technique described in Patent Document 4, image formation processing and color misregistration correction can be performed simultaneously as in Patent Document 3, so that productivity of the image formation processing does not decrease, but the color on the transfer belt is not reduced. Since the position for forming the deviation correction pattern is outside the maximum sheet area allowed by the image forming apparatus, it is necessary to increase the width of the transfer belt more than necessary, resulting in an increase in cost.

  Further, calibration using a correction pattern includes density correction in addition to color misregistration correction. This density correction has the same problem as in Patent Document 1 and Patent Document 2.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that performs calibration accurately without reducing productivity in an inexpensive configuration.

In order to achieve the above object, the first invention according to the present application,
Image forming means having an optical part and a photoreceptor for each toner color;
Primary transfer means for transferring an image formed by the image forming means to an intermediate transfer belt;
A paper size determining means for determining a paper size on which an image formed by the image forming means is to be transferred;
Calibration execution determining means for determining execution of calibration using a toner pattern;
When the paper size determining means determines that the next image to be formed for printing is smaller than a predetermined size and the calibration execution determining means has issued a calibration execution request, it forms for printing. Simultaneously with the image, a printing toner pattern forming means for forming a calibration toner pattern on the intermediate transfer belt outside the area of the predetermined size;
Calibration execution means for executing calibration using the printing toner pattern;
It is characterized by having.

In order to achieve the above object, the second invention according to the present application is the first invention,
The predetermined size described in the first invention is determined by a position of a toner pattern at the time of printing formed by the toner pattern forming unit.

In order to achieve the above object, the third invention according to the present application is the first invention,
The calibration toner pattern described in the first invention uses all colors of toner used in the image forming means.

In order to achieve the above object, a fourth invention according to the present application is the first to third inventions,
The calibration described in the first invention is for performing color misregistration correction control.

In order to achieve the above object, a fifth invention according to the present application is the first to fourth inventions,
The color misregistration correction control according to a third aspect of the invention includes a toner pattern detection unit that reads a calibration toner pattern formed by the toner pattern formation unit during printing with a sensor;
An arithmetic processing unit for calculating a color misregistration amount using data read from the toner pattern detecting unit;
Image writing timing adjusting means for adjusting the image writing timing of each color according to the amount of color misregistration;
It is characterized by having.

In order to achieve the above object, a sixth invention according to the present application is the first to third inventions,
The calibration described in the first invention is for performing density correction control.

In order to achieve the above object, the seventh invention according to the present application is the first to third and sixth inventions,
A toner pattern detecting means for reading a calibration toner pattern formed by the printing toner pattern forming means with a sensor;
An arithmetic processing unit for creating a lookup table using data read from the toner pattern detection unit;
It is characterized by having.

  As described above, according to the present invention, the paper size determination unit determines that the image to be formed next for printing is smaller than the predetermined size, and the calibration execution determination unit issues a calibration execution request. In this case, a calibration toner pattern is formed outside a predetermined size area on the intermediate transfer belt at the same time as an image to be formed for printing, and calibration is executed using the toner pattern. Calibration can be executed without reducing productivity.

1 is a schematic perspective view illustrating an example of a color image forming apparatus showing an embodiment of the present invention. It is a block diagram of a detection means for detecting a toner pattern. FIG. 2 is a block diagram illustrating a configuration of the color image forming apparatus illustrated in FIG. 1. FIG. 6 is a schematic diagram of a toner pattern for color misregistration correction for performing color misregistration correction control. 1 is a diagram showing an internal configuration of a color image forming apparatus showing an embodiment of the present invention. 3 is a flowchart showing a control flow of Embodiment 1 of the present invention. FIG. 2 is a schematic diagram of an image formed during printing in Embodiment 1 of the present invention. It is a flowchart which shows the control flow of Embodiment 2 of this invention. It is a schematic diagram of the image formed at the time of printing in Embodiment 2 of this invention. FIG. 4 is a schematic diagram of a toner pattern for density correction for performing density correction control.

Example 1
Hereinafter, the present invention will be described in detail based on the illustrated embodiments.

  The embodiment of the present invention shows an image forming apparatus having image forming means of four colors, that is, yellow Y, magenta M, cyan C, and black Bk. FIG. 1 shows an electrophotographic color image forming apparatus. FIG. 2 is a cross-sectional view of a tandem color image forming apparatus employing an intermediate transfer member 103 as an example. The operation of the image forming unit in the electrophotographic color image forming apparatus will be described with reference to FIG.

  FIG. 1 is a schematic perspective view illustrating an example of a color image forming apparatus showing a first embodiment of the present invention. For example, four colors, that is, yellow (hereinafter referred to as Y), magenta (hereinafter referred to as M), cyan (hereinafter referred to as “color”) are illustrated. , C), and black (hereinafter referred to as Bk) image forming means (image forming stations).

  In the figure, 101 (101a, 101b, 101c, 101d) is a photosensitive drum for forming an electrostatic latent image (101a, 101b, 101c, 101d are photosensitive drums for Bk, C, M, Y, respectively), 102 (102a). , 102b, 102c, and 102d) are laser scanners (102a, 102b, 102c, and 102d for Bk, C, M, and Y, respectively) that perform exposure according to image signals and form an electrostatic latent image on the photosensitive drum 101. (Laser scanner) 103 is an endless transport belt that also serves as a transfer belt for sequentially transporting paper to each color image forming section, and sequentially transports print paper to each color image forming section by a belt motor (not shown). The drive roller 104 is driven to rotate.

  The driving roller 104 is connected to a driving unit including a motor and a gear (not shown), and drives the conveyor belt 103 at a predetermined speed. Reference numeral 105 denotes a roller that is driven to rotate and rotates according to the movement of the conveyance belt 3 and applies a certain tension to the conveyance belt 103. 106 (106a, 106b) are a pair of optical sensors that detect the calibration toner pattern 107 (107a, 107b) formed on the conveyor belt 3, and are installed in the vicinity of the driving roller 104. Yes.

  A controller 111 includes a CPU, a RAM, and a ROM as shown in FIG. 3, which will be described later. By executing a control program stored in the ROM, a sensor signal and image data input via an input port (not shown). The image forming apparatus drive control, the laser scanner 102 drive control, and the like are performed.

  In addition, as shown in FIG. 3 to be described later, data to be printed is sent to the engine from a reading unit such as a host computer (personal computer, workstation) or scanner, and image formation according to the engine method is completed and printing is possible. Then, a sheet material is supplied from a paper feed cassette (not shown) and reaches the conveyance belt 103, and the conveyance belt 103 sequentially conveys the paper to the image forming units for each color.

  Then, in synchronization with the conveyance of the sheet material by the conveyance belt 103, image signals of the respective colors are sent to the respective laser scanners 102, and electrostatic latent images are formed on the photosensitive drums 101. It is developed and transferred onto a sheet by a transfer unit (not shown).

  In FIG. 1, images are sequentially formed in the order of Y, M, C, and Bk. Thereafter, the sheet material is separated from the conveyance belt 103, and the toner image is fixed on the paper by heat by a fixing device (not shown) and discharged to the outside.

  3 is a block diagram for explaining the configuration of the color image forming apparatus shown in FIG. 1, and the same components as those in FIG. 1 are denoted by the same reference numerals.

  In the figure, reference numeral 301 denotes a printer CPU (hereinafter simply referred to as a CPU), which is a system based on a control program stored in a program ROM of a ROM 302 or a control program stored in an external memory 303 or other storage medium (not shown). Access to various devices connected to the bus 312 is comprehensively controlled, and an image signal as output information is output to the printing unit 308 connected via the printing unit interface 313.

  The font ROM of the ROM 302 stores font data used when generating the output information. In the case of a printer that does not have the external memory 303 such as a hard disk in the data ROM of the ROM 302, it is stored on the host computer. Stores information used in The CPU 301 can communicate with the host computer via the input unit 305, is configured to notify the host computer of information in the program, etc., and can acquire image information to be output from the host computer. .

  Further, the CPU 301 can input image information to be output from the reading unit 314 via the reading unit interface 304.

  Reference numeral 306 denotes a RAM that functions as a main memory, a work area, and the like of the CPU 301. The RAM 306 can be expanded by an optional RAM connected to an expansion port (not shown). The RAM 306 is used as an output information expansion area, environment data storage area, NVRAM, and the like. Access to the above-described external memory 303 such as a hard disk or ID card is controlled by a memory controller (MC) 307.

  The CPU 301 executes various control processes based on a program stored in the program ROM of the ROM 302, the external memory 303, or other storage medium (not shown).

  Here, FIG. 2 shows a configuration of a sensor corresponding to 106 in FIG. 1 which is a calibration toner patch detecting means in this embodiment. An infrared light emitting element 201 such as an LED, a light receiving element 202 such as a photodiode, an IC (not shown) that processes received light data, and a holder (not shown) that accommodates these elements. The light receiving element 202 detects the intensity of reflected light from the toner pattern 203. Although FIG. 2 is configured to detect regular reflection light, the present invention is not limited to this, and irregular reflection light may be detected. An optical element such as a lens (not shown) may be used for optical coupling between the light emitting element 201 and the light receiving element 202.

  In the present embodiment, as the calibration, color misregistration correction control for detecting and correcting the color misregistration amount by the sensor shown in FIG. 2 is performed.

  Hereinafter, color misregistration correction control of this type of color image forming apparatus will be described with reference to FIG.

  FIG. 4 is a schematic diagram illustrating an example of a color misregistration detection pattern in color misregistration correction control of this type of color image forming apparatus.

  Reference numerals 106 (106 a, 106 b) are a pair of sensors that detect a toner pattern for color misregistration detection formed on the conveyance belt 103, and are installed in the vicinity of the driving roller 104.

  Reference numerals 401 (401a to 401d) and 402 (402a to 402d) denote patterns for detecting a color misregistration amount in the print paper conveyance direction (sub-scanning direction), and 403 (403a to 403d) and 404 (404a to 404d) denote This is a pattern for detecting the amount of color misregistration in the main scanning direction orthogonal to the print paper conveyance direction. In this example, a, b, c, and d are black (Bk) and cyan (C) with an inclination of 45 degrees, respectively. , Magenta (M) and yellow (Y). tsf1 to tsf4, tmf1 to tmf4, tsr1 to tsr4, tmr1 to tmr4 indicate the detection timing of each pattern, and the arrows indicate the rotation direction of the conveyor belt 103.

The moving speed of the conveyance belt 103 is v (mm / s), the theoretical distance between each color misregistration detection pattern in the print sheet conveyance direction and the Bk pattern is dsC (mm), dsM (mm), dsY (mm), The measured distances between the color misregistration detection pattern in the print paper conveyance direction and the color misregistration detection pattern in the main scanning direction are dmfK (mm), dmfC (mm), dmfM (mm), dmfY (mm), and dmrK (mm), respectively. ), DmrC (mm), dmrM (mm), and dmrY (mm). These theoretical distances are all equal. With Black as a reference color, the color misregistration amount δes of each color in the sub-scanning direction is
δesY = v × {(tsf4-tsf1) + (tsr4-tsr1)} / 2-dsY (Equation 1)
δesM = v × {(tsf3−tsf1) + (tsr3−tsr1)} / 2−dsM (Expression 2)
δesC = v × {(tsf2−tsf1) + (tsr2−tsr1)} / 2−dsC (Equation 3)
It becomes.

The color misregistration amounts δemf and δemr for the left and right colors in the main scanning direction
dmfK = v × (tmf1−tsf1) (Formula 4)
dmfC = v × (tmf2−tsf2) (Formula 5)
dmfM = v × (tmf3-tsf3) (Formula 6)
dmfY = v × (tmf4-tsf4) (Expression 7)
When,
dmrK = v × (tmr1−tsr1) (Equation 8)
dmrC = v × (tmr2−tsr2) (Formula 9)
dmrM = v × (tmr3-tsr3) (Formula 10)
dmrY = v × (tmr4-tsr4) (Formula 11)
Than,
δemfY = dmfY−dmfK (Equation 12)
δemfM = dmfM−dmfK (Equation 13)
δemfC = dmfC−dmfK (Formula 14)
When,
δemrY = dmrY−dmrK (Equation 15)
δemrM = dmrM−dmrK (Equation 16)
δemrC = dmrC−dmrK (Equation 17)
Thus, the direction of color misregistration can be determined from the sign of the calculation result, the main scanning writing position is corrected from δemf, and the main scanning width is corrected from δemr−δemf. If there is an error in the main scanning width, the main scanning writing position is calculated not only by δemf but also by taking into account the amount of change in the image clock frequency that has been changed with the main scanning width correction. When a plurality of sets of color misregistration toner patterns are formed, the color misregistration amounts of the respective colors in the main scanning direction and the sub scanning direction are calculated by averaging the color misregistration amounts.

  Next, the system configuration of the printing unit 308 in FIG. 3 will be described with reference to FIG. The image forming apparatus according to the present exemplary embodiment includes a CPU 501, a system control unit 502, a drive control unit 503, an image forming unit 504, a calibration execution determination unit 505, a sensor control unit 506, and an arithmetic processing unit 507. Composed.

  A system control unit 502 controls the entire engine system. The drive control unit 503 controls each drive device such as a motor and a clutch. The image forming unit 504 performs control for forming an image. The calibration execution determination unit 505 determines whether to execute calibration. The sensor control unit 506 detects the calibration toner pattern on the secondary transfer belt 103 by the sensor 106. The calculation processing unit 507 performs calculation using the detection timing of the calibration toner pattern obtained by the sensor control unit. The CPU 501 performs control control of the entire system.

  The image forming unit 504 includes a print image forming unit 508, a paper size determining unit 509, and a printing toner pattern forming unit 510. The print image forming unit 508 forms an electrostatic latent image for printing sent from the controller on the drum. The paper size determining unit 509 determines whether the size of the electrostatic latent image formed by the print image forming unit 508 in the main scanning direction is smaller than the installation distance of the sensors 106a and 106b. The printing toner pattern forming unit 510 determines that the size of the electrostatic latent image to be formed next for printing in the main scanning direction is smaller than the distance between the sensors by the paper size determining unit 509, and the engine performs calibration. When it is determined that execution is necessary, a toner pattern for color misregistration correction is formed at the center position of each of the sensors 106a and 106b simultaneously with the electrostatic latent image formed for printing.

  In this embodiment, the paper size determination unit 509 determines that the image to be formed for printing is smaller than the distance between the sensors 106a and 106b, and the calibration execution determination unit 505 requests execution of color misregistration correction. In this case, the toner pattern forming unit 510 at the time of printing forms a toner pattern for color misregistration correction on the intermediate transfer belt outside the area of the paper size to be printed next, simultaneously with the image to be printed. By executing the color misregistration correction control using the pattern, the color misregistration correction control is realized without reducing the productivity.

  The control flow in the present embodiment will be described using the flowchart shown in FIG.

  When the printing operation is started, the printing unit 308 (hereinafter referred to as the engine) determines whether or not the color misregistration correction needs to be performed by the calibration execution determining unit 505 (STEP 601 (hereinafter referred to as S601)). Execution of color misregistration correction is required after printing a predetermined number or more, at the time of CRG replacement, or replacement of the intermediate transfer belt. Next, the paper size detecting means 509 detects the paper size on which an image to be formed next is transferred. It is determined whether the detected paper size is smaller than the distance between the sensors on the transfer belt 103 of the printer engine (between 106a and 106b) (S602). An image to be formed for printing when a color misregistration correction execution request is issued in S601 and the paper size is smaller than the distance between the sensors on the transfer belt 103 (between 106a and 106b) in S602. At the same time, a toner pattern for color misregistration correction formed by the engine is reserved (S603). If there is a reservation, an image for printing and a toner pattern for color misregistration correction are formed, and if there is no reservation, only a printing image is formed (S604).

  Next, FIG. 7 shows a conceptual diagram when an image for printing and a toner pattern are simultaneously formed on the intermediate transfer belt 103. In FIG. 7, a toner pattern for calibration is formed on both sides of the image area for printing. When performing calibration, the sensor control unit 506 stores the timings at which the toner patterns 107a and 107b are detected using the sensors 106a and 106b, and the arithmetic processing unit 507 substitutes each detection timing into the above-described equation. The amount of color misregistration is calculated. Then, the color misregistration correction calculated with a plurality of toner patterns is averaged to realize highly accurate color misregistration correction.

  In the first embodiment, by using the configuration and the control method as described above, it is possible to execute the printing operation and the color misregistration correction control at the same time, and perform the calibration without reducing the productivity.

(Example 2)
In the first exemplary embodiment, the paper size determining unit 509 determines that the image to be formed for printing is smaller than the distance between the sensors 106a and 106b, and the calibration execution determining unit 505 requests execution of color misregistration correction. In this case, the toner pattern forming means 510 at the time of printing forms a toner pattern for color misregistration correction on the intermediate transfer belt outside the area of the paper size to be printed next, simultaneously with the image to be printed. By executing the color misregistration correction control using the toner pattern, the color misregistration correction was realized without reducing the productivity.

  In the second embodiment, during the continuous printing, if it is determined that the image formed for printing is smaller than the distance between the sensors 106a and 106b, the two items that the calibration execution determination unit requests execution of color misregistration are set. An embodiment in which more accurate color misregistration correction is realized by forming a toner pattern for color misregistration at the same time as a normal print image as long as it is satisfied and by continuing to form a toner pattern for color misregistration correction between papers. Will be described. Since Embodiment 2 is implemented in the same configuration as Embodiment 1, only the difference is described.

  The control flow in the present embodiment will be described using the flowchart shown in FIG.

  When the printing operation is started, the printing unit 308 (hereinafter referred to as the engine) determines whether the color misregistration correction needs to be executed by the calibration execution determination unit 505 (S801). Next, the paper size detecting means 509 detects the paper size on which an image to be formed next is transferred. It is determined whether the detected paper size is smaller than the distance between the sensors (106a and 106b) on the transfer belt 103 of the engine (S802). An image formed for printing when a color misregistration correction execution request is issued in S801 and the sheet size is smaller than the distance between the sensors on the transfer belt 103 (between 106a and 106b) in S802. At the same time, a toner pattern for color misregistration correction formed by the engine is reserved (S803). Further, a reservation is made to form a toner pattern for color misregistration correction between sheets. (S804) When the two reservations are made, the image for printing and the toner pattern for color misregistration correction are simultaneously formed, and the toner pattern for color misregistration correction is also formed between the sheets (S805). ). If there is no reservation, only the image for printing is formed (S805). Next, it is determined whether there is a continuous print request (S806). If there is a request for continuous printing, the process is repeated again from S801 again, and image formation for color misregistration correction is continued as long as the conditions of S801 and S802 are satisfied.

  Next, FIG. 9 shows a conceptual diagram when an image for printing and a toner pattern are simultaneously formed on the intermediate transfer belt 103. In FIG. 8, a calibration toner pattern is formed on both sides of the image area for printing. When performing calibration, the sensor control unit 506 stores the timings at which the toner patterns 107a and 107b are detected using the sensors 106a and 106b, and the arithmetic processing unit 507 substitutes each detection timing into the above-described equation. The amount of color misregistration is calculated. In the second embodiment, since more color misregistration toner patterns are formed than in the first embodiment, the calculation result of a larger amount of color misregistration is averaged, so that the color misregistration correction can be performed with higher accuracy than in the first embodiment. .

(Example 3)
In the first exemplary embodiment, the paper size determining unit 509 determines that the image to be formed for printing is smaller than the distance between the sensors 106a and 106b, and the calibration execution determining unit 505 requests execution of color misregistration correction. In this case, the toner pattern forming means 510 at the time of printing forms a toner pattern for color misregistration correction on the intermediate transfer belt outside the area of the paper size to be printed next, simultaneously with the image to be printed. By executing the color misregistration correction control using the toner pattern, the color misregistration correction was realized without reducing the productivity.

  In the second embodiment, during continuous printing, if it is determined that the image to be formed for printing is smaller than the distance between the sensors 106a and 106b, the calibration execution determining unit determines that it is necessary to perform color misregistration correction. As long as the two items are satisfied, a color misregistration toner pattern is formed at the same time as a normal print image, and by continuing to form a color misregistration correction toner pattern between papers, more accurate color misregistration correction can be achieved. It was realized.

  In the third embodiment, as the calibration, density correction control for detecting and correcting the reflection density by the sensor shown in FIG. 2 is performed. Since the third embodiment is implemented in the same configuration and the same control as the first and second embodiments, only the difference is described.

  In the density correction control, after obtaining an appropriate development bias, the density is corrected by changing the lookup table so that the input image data and the halftone image density have good linearity.

  Hereinafter, density control of this type of color image forming apparatus will be described with reference to FIG.

  FIG. 10 is a schematic diagram illustrating an example of a density detection pattern in density control of the color image forming apparatus.

  Reference numeral 103 denotes an endless transport belt that also serves as a transfer belt that sequentially transports the paper to the image forming units for each color, and is driven by a belt motor (not shown) to sequentially transport the print paper to the image forming unit for each color.

  Reference numeral 106 (106a, 106b) denotes a sensor that detects the density of the density detection pattern formed on the conveyor belt 103, and is a direction orthogonal to the conveyance direction of the conveyor belt 103 (indicated by an arrow in the figure). It is installed on the belt end side in the (main scanning direction).

  1001 (1001a, 1001b, 1001c, 1001d), 1002 (1002a, 1002b, 1002c, 1002d), 1003 (1003a, 1003b, 1003c, 1003d) are density detection patterns, each of which has a different density, a , B, c, and d represent black (Bk), cyan (C), magenta (M), and yellow (Y), respectively.

  In density correction control, after developing bias is optimized, a plurality of image data (halftone density detection patterns 1001 (1001a, 1001b, 1001c, 1001d), 1002 (1002a, 1002b, 1002c, 1002d), 1003 (1003a, 1003b) , 1003c, 1003d), and the density detection sensor 106 (106a, 106b) detects the reflection density and changes the look-up table so that the input image data and the halftone image density have good linearity. To optimize the concentration.

  In the third embodiment, by applying the above-described density correction control to the color misregistration correction control in the first and second embodiments, the printing operation and the density correction control are executed at the same time, and the calibration is executed without reducing the productivity. It is possible to do.

DESCRIPTION OF SYMBOLS 101 Laser scanner unit 102 Photosensitive drum 103 Intermediate transfer belt 104 Driving roller 105 Driven roller 106 Sensor 107 Calibration toner pattern 111 Controller 201 Light emitting element 202 Light receiving element 203 Toner pattern 401/402 Toner pattern 401 for correcting color misregistration in the sub-scanning direction 404 Toner pattern for color misregistration correction in the main scanning direction 1001 to 1003 Toner pattern for density correction

Claims (7)

Image forming means having an optical part and a photoreceptor for each toner color;
Primary transfer means for transferring an image formed by the image forming means to an intermediate transfer belt;
A paper size determining means for determining a paper size on which an image formed by the image forming means is to be transferred;
Calibration execution determining means for determining execution of calibration using a toner pattern;
In an image forming apparatus having
When the paper size determining means determines that an image to be formed next for printing is not larger than a predetermined size, and the calibration execution determining means determines that calibration execution is necessary, the paper size is determined for printing. Simultaneously with the image, a printing toner pattern forming means for forming a calibration toner pattern on the intermediate transfer belt outside the area of the predetermined size;
Calibration execution means for executing calibration using the printing toner pattern;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the predetermined size according to claim 1 is determined by a position of a calibration toner pattern formed by the toner pattern forming unit.   The image forming apparatus according to claim 1, wherein the toner pattern forming unit uses all colors of toner used in the image forming unit.   The image forming apparatus according to claim 1, wherein the calibration according to claim 1 is for performing color misregistration correction processing. The color misregistration correction processing according to claim 4 includes: a toner pattern detecting unit that reads a calibration toner pattern formed by the toner pattern forming unit during printing with a sensor;
An arithmetic processing unit for calculating a color misregistration amount using data read from the toner pattern detecting unit;
The image forming apparatus according to claim 1, further comprising:   The image forming apparatus according to claim 1, wherein the calibration according to claim 1 is for performing density correction processing. The density correction processing according to claim 6 includes:
A toner pattern detecting means for reading a calibration toner pattern formed by the printing toner pattern forming means with a sensor;
An arithmetic processing unit for creating a lookup table using data read from the toner pattern detection unit;
The image forming apparatus according to claim 1, wherein the image forming apparatus is used.