JP2009169031A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce downtime for an apparatus due to processing control for an image formation using a test pattern; and to obtain a stable image quality while employing an intermediate transfer method with high image superposing accuracy. <P>SOLUTION: A test pattern A and a test pattern B are formed outside an image region on both sides of the image region; a correction value for an image processing condition is calculated which is determined on the basis of the detected results by an image processing condition A and an image processing condition B which are each determined on the basis of each of the detected result of the test pattern A and the test pattern B arranged outside the image region; an image processing condition C for execution is calculated by using these; a test pattern D is created in the image forming region and an image processing condition D for reference is calculated on the basis of the detected result; and then whether or not the image forming process condition C is suitable is decided on the basis of the condition D. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a fax machine, and more particularly to process control of image formation.

A widely known method is to create a test pattern outside the print area on the photoconductor or transfer belt, and to control the image process conditions related to image density, image position, etc. by inferring density and position information from the reflectance data. Yes.
In this type of image process condition control (image process control), when the test pattern has been read, the created test pattern is not discharged as a printed image. Therefore, it is discarded by a belt cleaner or the like, or a recycling apparatus is used in combination. Will be reused.
Further, known image process control includes a method for creating a test pattern during a preparation period from when the power is turned on until printing is possible, and a method for creating a test pattern in a non-image area being printed.

In recent years, in order to improve the granularity, the particle size of the toner is reduced, or the particle diameter is made spherical and uniform by using a production method such as a polymerization method toner. It is generally known that these small particle toner and spherical toner are difficult to clean, and toner that is not properly cleaned remains on the image carrier and is generated on the transfer material as an abnormal image. In order to prevent such poor cleaning and improve the cleaning performance per time, it is necessary to increase the contact pressure with a blade cleaning device. In this case, however, the load on the belt and the cleaning blade Increase in blade wear due to the increase, misalignment, generation of jitter, and the like occur.
In addition, if it is bias roller cleaning, it is necessary to provide a plurality of rollers, and both types have an effect on cost reduction and space saving. Further, a method of improving the cleaning property by rotating the transfer belt a plurality of times has been taken, but this method increases the downtime of the apparatus.
In addition, a color image forming apparatus that forms a color image by superimposing a plurality of images includes a direct transfer method in which a plurality of photosensitive member images are transferred to a transfer material on a transfer / conveyance belt, and a plurality of photosensitive member images are temporarily transferred to a transfer belt. There is an intermediate transfer method in which the image is transferred onto the transfer material after being overlaid on top. However, since the intermediate transfer method forms a color image once on the transfer belt, the image overlay accuracy is high, and the thickness of the transfer material and the tolerance for the material Is advantageous.

However, in the intermediate transfer system, a primary transfer device (a primary transfer belt as an example) that superimposes images in a transfer process and a secondary transfer device (a secondary transfer roller as an example) that transfers an image onto a transfer material such as paper. There is an intermediate transfer system using two transfer devices. In the intermediate transfer method using these two transfer devices, a device capable of contacting and separating the primary transfer belt and the secondary transfer roller is necessary so that the test pattern is not transferred to the secondary transfer roller, and the test pattern is transferred to the secondary transfer roller. It must be separated before reaching the roller. For this reason, a contact / separation mechanism is required. For this reason, there are problems such as an increase in apparatus cost, an increase in apparatus, and an increase in layout restrictions. In particular, when it is necessary to create a test pattern during a printing operation, performing the contact / separation during the printing operation is used to change the load on an image carrier such as a transfer belt or a photoconductor or to form a latent image. Since image shift or jitter occurs due to a shock to the exposure apparatus or the like, there is a restriction that the contact cannot be separated from the start of exposure for printing to the end of primary transfer, and throughput is reduced.
On the other hand, if the mechanism does not contact and separate the secondary transfer roller, the test pattern is inevitably transferred to the secondary transfer roller, thereby requiring a cleaning device for the secondary transfer roller. Furthermore, since the test pattern needs to be read before being transferred to the secondary transfer roller, the layout of the reading device is limited (the reading device needs to be arranged upstream of the secondary transfer roller). .

In addition, as a known technique, in an image forming apparatus provided with a detection unit that detects the toner adhesion amount of a toner image for adhesion amount detection from each transferred photoreceptor, and a toner adhesion amount control unit that controls image formation conditions, Transfer where X <Z−Y, where X is the length in the axial direction of the transfer paper, Y is the length in the axial direction of the toner image for detecting the toner adhesion amount, and Z is the length in the axial direction of the printable area. 2. Description of the Related Art There is an image forming apparatus that includes a toner image creating unit that creates a toner image for toner adhesion amount detection outside a printing area when printing is performed in a paper size (for example, see Patent Document 1).
For example, in the case of A4 longitudinal paper, since a margin is formed in the axial direction on the intermediate transfer belt, a test pattern is formed at that portion. However, a test pattern cannot be formed because there is no margin in a mode that uses the image area in the entire axial direction, such as A4 landscape paper.
JP 2006-17868 A JP 2001-36747 A Japanese Patent Laid-Open No. 8-15943 Japanese Unexamined Patent Publication No. 07-096645 Japanese Patent No. 3078421 JP-A-2005-250311 JP 2003-098771 A JP 2002-040742 A Japanese Patent No. 3390283 JP 2003-248361 A JP 2003-241478 A JP-A-2005-250311 Japanese Patent Laid-Open No. 10-142880

  The present invention has been made in consideration of the above circumstances, and while employing an intermediate transfer method with high image overlay accuracy, realizing a reduction in cost and space saving of a cleaning device, and a test pattern was used. An object of the present invention is to reduce the downtime of the apparatus by process control for image formation and to obtain stable image quality.

In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention includes a plurality of image carriers, a charging device that charges each image carrier, an exposure device that forms a latent image on each image carrier, A developing device that develops a latent image formed on each image carrier with toners of different colors, and a transfer position where the image formed on each image carrier is opposed to each image carrier. A first transfer device that obtains a color image by superimposing and transferring the image on a second image carrier that moves, and a second that transfers the image transferred and formed on the second image carrier to a transfer material. Transfer device, a test pattern generating device capable of forming a test pattern image formed on each image carrier and transferred onto the second image carrier, and a test capable of detecting the state of the test pattern A pattern detector and a test pattern detection result And image process control means for determining image process conditions for performing at least one of process control for changing image forming conditions and toner density control for changing toner replenishment amount, and the second transfer device is included in the first transfer device. In the image forming apparatus configured such that the test pattern is not transferred to the second transfer device while being always in contact, the test pattern can be created at a plurality of locations, and in the rotation direction of the first transfer device, An image process in which a test pattern A and a test pattern B are created outside the image areas on both sides of the image area, and each is determined based on the detection results of the test patterns A and B arranged outside the image area. Image process condition correction determined based on detection results of condition A and image process condition B Based on this image process condition correction value, an execution image process condition C for use in forming an image in the image area is calculated, and a test pattern D is created and detected in the image formation area. A reference image process condition D is calculated based on the detection result, and whether or not the image forming process condition C is appropriate is determined based on the image process condition D.
By adopting such a configuration, while adopting an intermediate transfer method with high image overlay accuracy, it is possible to reduce the cost and space of the cleaning device, and to control the process for image formation using a test pattern Therefore, it is possible to reduce the downtime of the apparatus and maintain stable image quality.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the determination criterion for the determination is a correspondence between the image process condition C for execution and the image process condition D for reference. It is characterized in that it is appropriate when the difference in the values of items to be performed is equal to or less than a predetermined value. Since the difference between [the image process condition C determined from the image process condition A and the image process condition B] and [the image process condition D determined from the detection result of the pattern D] is set to a predetermined value or less as the determination criterion, the image When the calculation accuracy of the process condition C is high, it is possible to determine the image forming condition with high accuracy without depending on the test pattern D accompanied by a defect that requires a cleaning process and causes downtime. If the calculation system of the image process condition C is lowered, the image process condition necessary for image formation can be determined with high accuracy by image formation / detection of the test pattern D in the image area. That is, the toner adhesion amount closer to the target can be obtained by comparing the difference with the image process condition D in the image region to be detected.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, when the process condition C is determined to be appropriate according to the result of the determination, the image process condition C is set as the image forming condition. And when the process condition C is determined to be inappropriate, the test pattern A and the test pattern B are newly created, and the image process condition correction value is updated based on the test pattern A and the test pattern B. To do.
According to the invention of claim 3, according to the determination result in the image forming apparatus of claim 1, in the case of <OK>, the image process condition C determined from the image process condition A and the image process condition B is set as an image. On the other hand, in the case of <NG>, since the image process condition correction value is updated and the image formation condition is appropriately switched in accordance with the determination result so as to calculate a more accurate image process condition. It is possible to always set appropriate image forming conditions and maintain stable image quality.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the image process condition A determined based on the detection result of the test pattern A and the image process condition B determined based on the detection result of the test pattern B On the other hand, from the difference from the image process condition D determined by the detection result of the test pattern D, the image process condition correction value when each of the test patterns A or B is used is calculated as image process condition correction value A = [image process Condition A]-[Image Process Condition D] and Image Process Condition Correction Value B = [Image Process Condition B]-[Image Process Condition D]. As described above, since the image process condition correction values of the test patterns A and B are derived from the test pattern D imaged and detected in the image area, the image process condition with high accuracy is provided in the invention of claim 4. A and image process condition B can be calculated, and stable image quality can be maintained.

According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, [Image Process Condition A] <[Image Process Condition D] and [Image Process Condition B] <[Image Process Condition D], or In the case of any of image process condition A]> [image process condition D] and [image process condition B]> [image process condition D], the average of image process condition A and image process condition B as the image forming condition Control is performed such that the image process condition C obtained as a value is not used.
According to the fifth aspect of the present invention, in the image forming apparatus of the first aspect, [Image Process Condition A] <[Image Process Condition D] and [Image Process Condition B] <[Image Process Condition D], or With respect to the image process conditions outside the image area at both ends, such as “condition A]> [image process condition D] and [image process condition B]> [image process condition D]” When it is detected that the process condition is higher or lower, it is determined that the toner adhesion amount of the test pattern does not have a deviation that increases or decreases in the order of before, after, and after that, the image process condition A and the image process condition B The image process condition C obtained as an average value is not used. In other words, in a situation where the image process condition in the image area cannot be correctly calculated from the image process condition outside the image area, it is not performed, and accordingly, an inappropriate value is set as the image process condition. It is avoiding that.

According to a sixth aspect of the present invention, in the image forming apparatus according to the first aspect, the test pattern includes a pattern for detecting the amount of toner adhesion and a pattern for detecting the image position. Is. According to a seventh aspect of the present invention, in the image forming apparatus according to the first aspect, the image carrier in the first transfer device is in a belt shape, and the second transfer device is in a belt shape or It is a roller-shaped one.
According to an eighth aspect of the present invention, in the image forming apparatus according to the first aspect, the image formation / detection timing of the test pattern D is set to a predetermined number of sheets. As a result, the frequency of downtime such as cleaning associated with the image formation of the test pattern D can be reduced as much as possible, and problems that hinder the user's operation are suppressed.
According to a ninth aspect of the present invention, in the image forming apparatus according to the first aspect, the image formation / detection timing of the test pattern D is immediately after power-on. This makes it possible to reduce the frequency of downtime as much as possible by duplicating the downtime that occurs for the start-up of fixing and the downtime that occurs during cleaning associated with image formation of the test pattern D. The problem that prevents the operation is suppressed.

According to a tenth aspect of the present invention, in the image forming apparatus according to the first aspect, the image formation / detection timing of the test pattern D is a case where a print command is not received for a predetermined time or more. . As described above, since the image formation / detection timing of the test pattern D in the image forming apparatus according to claim 1 is limited to a case where a print command is not received for a predetermined time or more, cleaning associated with the image formation of the test pattern D is performed. Downtime occurs at times when the user is not using it. As a result, it is possible to suppress problems that hinder user operations.
According to an eleventh aspect of the present invention, in the image forming apparatus according to the first aspect, after the image formation / detection of the test pattern D, the second image carrier is cleaned. . As a result, the test pattern D is prevented from being transferred and soiled on the back surface of the transfer material.

  According to the present invention, while adopting an intermediate transfer method with high image overlay accuracy, it is possible to reduce the cost and space saving of a cleaning device, and to control the apparatus by process control for image formation using a test pattern. It is possible to reduce downtime and obtain stable image quality.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. This embodiment is an application example to a tandem type full-color electrophotographic printer (hereinafter simply referred to as “printer”) as an image forming apparatus.
First, an outline of the configuration of the printer of this embodiment will be described. FIG. 1 is a schematic configuration diagram (hereinafter referred to as a process engine unit) showing an image forming process part that performs exposure, charging, development, transfer, and fixing in the printer of this embodiment. In addition to FIG. 1, the printer includes a print controller (410 in FIG. 5) that processes image data sent from a PC or the like and converts it into exposure data, a high pressure generator (416 in FIG. 5) that generates high pressure, and an image. A main body control unit (406 in FIG. 5) for controlling the forming operation, a paper feeding device (not shown) for supplying the transfer paper 113 as a recording material, a manual feed tray (not shown) for manually feeding the transfer paper 113, and an image A paper discharge tray (not shown) for discharging the formed transfer paper 113 is provided.

In FIG. 1, an endless belt-like intermediate transfer belt 105 as a second image carrier is provided in the main body as a first transfer device. The intermediate transfer belt 105 has a three-layer structure including a base layer, an elastic layer, and a coat layer. The base layer is configured, for example, by combining a fluorine resin having a small elongation or a rubber material having a large elongation with a material that is difficult to stretch, such as a canvas. The elastic layer is made of, for example, fluorine rubber or acrylonitrile-butadiene copolymer rubber, and is formed on the base layer. The coat layer is formed by coating the surface of the elastic layer with, for example, a fluorine resin. The intermediate transfer belt 105 is rotationally driven by the drive roller 112 in the counterclockwise direction in FIG. 2 while being stretched around the four support rollers.
There are four image forming units of yellow, cyan, magenta, and black in the transfer belt stretching portion, and the image forming units are the photoreceptor units 103Y, 103C, 103M, and 103K and the developing units 102Y, 102C, 102M, and 102K, respectively. They are arranged side by side. Under these image forming units, an exposure device 109 is provided. Based on the image information, a semiconductor laser is driven from a laser exposure unit (not shown) provided in the exposure device 109 to write light. For forming electrostatic latent images on the photosensitive drums 101Y, 101C, 101M, and 101K as image carriers provided in the respective photosensitive units. Here, the emission of the writing light is not limited to the laser, but may be, for example, an LED (Light Emitting Diode).

The configuration of the image forming unit will be described. In the following description, an image forming unit that forms a black toner image will be described as an example, but other image forming units have the same configuration.
[Image forming unit]
In the image forming unit, a charging device 301, a developing device 102, and a photoconductor cleaning device 302 are provided around the photoconductor drum 101. Further, a primary transfer device 106 is provided at a position facing the photosensitive drum 101 via the intermediate transfer belt 105.
The charging device 301 is of a contact charging type employing a charging roller, and uniformly charges the surface of the photosensitive drum 101 by applying a voltage in contact with the photosensitive drum 101. As the charging device 301, a non-contact charging type using a non-contact scorotron charger or the like can be used.

  The developing device 102 uses a two-component developer composed of a magnetic carrier and a nonmagnetic toner. As the developer, a one-component developer may be used. The developing device 102 can be roughly divided into an agitating unit 303 and a developing unit 304 provided in the developing case. In the agitation unit 303, a two-component developer (hereinafter simply referred to as “developer”) is conveyed while being agitated and supplied onto a developing sleeve 305 as a developer carrier. The stirring unit 303 is provided with two parallel screws, and a partition plate is provided between the two screws 306 for partitioning so that both ends communicate with each other. A toner density sensor 103 for detecting the toner density of the developer in the developing device 102 is attached to the developing case. On the other hand, in the developing unit 304, the toner in the developer attached to the developing sleeve 305 is transferred to the photosensitive drum 101. The developing unit 304 is provided with a developing sleeve 305 that faces the photosensitive drum 101 through the opening of the developing case, and a magnet (not shown) is fixedly disposed in the developing sleeve 305. A doctor blade 307 is provided so that the tip approaches the developing sleeve 305. In the present embodiment, the distance at the closest portion between the doctor blade 307 and the developing sleeve 305 is set to 0.9 mm.

  In the developing device 102, the developer is conveyed and circulated while being stirred by two screws 306, and is supplied to the developing sleeve 305. The developer supplied to the developing sleeve 305 is drawn up and held by a magnet. The developer pumped up by the developing sleeve 305 is conveyed as the developing sleeve 305 rotates, and is regulated to an appropriate amount by the doctor blade 307. The regulated developer is returned to the stirring unit 303. The developer transported to the developing area facing the photosensitive drum 101 in this manner is brought into a spiked state by a magnet and forms a magnetic brush. In the developing region, a developing electric field that moves the toner in the developer to the electrostatic latent image portion on the photosensitive drum 101 is formed by the developing bias applied to the developing sleeve 305. As a result, the toner in the developer is transferred to the electrostatic latent image portion on the photosensitive drum 101, and the electrostatic latent image on the photosensitive drum 101 is visualized to form a toner image. The developer that has passed through the developing region is transported to a portion where the magnetic force of the magnet is weak, thereby leaving the developing sleeve 305 and being returned to the stirring unit 303. When the toner concentration in the stirring unit 303 becomes light by repeating such an operation, the toner concentration sensor 103 detects this, and toner is supplied to the stirring unit 303 based on the detection result.

A primary transfer roller is employed as the primary transfer device 106 and is installed so as to be pressed against the photosensitive drum 101 with the intermediate transfer belt 105 interposed therebetween. Further, both end portions of the primary transfer roller are in contact with the portion of the axial range 203 in FIG. The primary transfer device 106 may not be a roller shape, but may be a conductive brush shape, a non-contact corona charger, or the like. The axial range 203 is set so that the transfer sheet 115 of the transfer paper 115 having the longest length in the direction perpendicular to the rotation direction of the transfer belt is sandwiched between the primary transfer device 106 and the intermediate transfer belt 105. ing.
The photoconductor cleaning device 308 includes a cleaning blade 309 made of, for example, polyurethane rubber, which is disposed so that the front end is pressed against the photoconductor drum 101. In this embodiment, in order to improve the cleaning performance, a conductive fur brush 310 that contacts the photosensitive drum 101 is also used. A bias is applied to the fur brush 310 from a metal electric field roller (not shown), and the tip of a scraper (not shown) is pressed against the electric field roller. The toner removed from the photosensitive drum 101 by the cleaning blade 309 or a fur brush (not shown) is accommodated in the photosensitive member cleaning device 308 and collected by a waste toner collecting device (not shown).

  A specific setting of the image forming unit will be described. The diameter of the photosensitive drum 101 is 40 mm, and the photosensitive drum 101 is driven at a linear speed of 200 mm / s. The developing sleeve 305 has a diameter of 25 mm, and the developing sleeve 305 is driven at a linear speed of 564 mm / s. Further, the charge amount of the toner in the developer supplied to the development region is preferably in the range of about − (minus) 10 to −30 μC / g. The development gap, which is the gap between the photosensitive drum 101 and the development sleeve 305, can be set in the range of 0.5 to 0.3 mm, and the development efficiency can be improved by reducing the value. Further, the thickness of the photosensitive layer of the photosensitive drum 101 is 30 μm, the beam spot diameter of the optical system of the exposure apparatus 109 is 50 × 60 μm, and the amount of light is about 0.47 mW. As an example, the surface of the photosensitive drum 101 is uniformly charged to −700 V by the charging device 301, and the potential of the electrostatic latent image portion irradiated with the laser by the exposure device 109 is −120 V. On the other hand, the developing bias voltage is set to -470V, and a developing potential of 350V is secured. Such process conditions are changed as appropriate according to the result of the potential control.

  In the image forming unit of FIG. 3 having the above configuration, the surface of the photosensitive drum 101 is first uniformly charged by the charging device 301 as the photosensitive drum 101 rotates. Next, based on image information from the print controller, laser light is irradiated from the exposure device 109 to form an electrostatic latent image on the photosensitive drum 101. Thereafter, the electrostatic latent image is visualized by the developing device 102 to form a toner image. The toner image is primarily transferred onto the intermediate transfer belt 105 by the primary transfer device 106. The transfer residual toner remaining on the surface of the photoconductive drum 101 after the primary transfer is removed by the photoconductive cleaning device and used for the next image formation.

  Next, as shown in FIG. 2, a secondary transfer roller 108, which is a secondary transfer device, is provided at a position facing the third support roller 112 among the support rollers. When the toner image on the intermediate transfer belt 105 is secondarily transferred onto the transfer paper 115, the secondary transfer roller 108 is pressed against the portion of the intermediate transfer belt 105 wound around the third support roller 112. Next transfer is performed. A roller cleaning unit 116 that cleans toner adhering to the secondary transfer roller 108 is in contact with the secondary transfer roller 108. The secondary transfer device (secondary transfer member) is not limited to the configuration using the secondary transfer roller 108, but may be configured to use, for example, a transfer belt or a non-contact transfer charger. The axial width (image carrier width) of the intermediate transfer belt 105 in the first transfer device is the axial width (second transfer device width) of the secondary transfer roller 108 (or transfer belt or the like) as the second transfer device. ) And the maximum width of the transfer material is equal to or smaller than the width of the second transfer device, and the test is performed in a region (outside of the image region) of the dimensional difference between the image carrier width and the second transfer device width. A pattern is formed.

  A fixing device 111 for fixing the toner image transferred onto the transfer paper 115 is provided downstream of the secondary transfer roller 108 in the transport direction of the transfer paper 115. The fixing device 111 has a configuration in which a pressure roller 118 is pressed against a heating roller 117. Photo sensors 109F and 109R (hereinafter referred to as P / TM sensor 109) for estimating the density and relative position of the test pattern are provided at positions facing the third support roller 112 among the support rollers of the intermediate transfer belt 105. It is provided at two locations on the front side and the back side in the axial direction. Further, a belt cleaning device 110 is provided at a position facing the second support roller 113 among the support rollers of the intermediate transfer belt 105. The belt cleaning device 110 is for removing residual toner remaining on the intermediate transfer belt 105 after the toner image on the intermediate transfer belt 105 is transferred to the transfer paper 115.

  FIG. 4 is a schematic diagram of the P / TM sensor 109. The P / TM sensor 109 includes a specular reflection light receiving element 603 and a diffuse reflection light receiving element at two locations, one infrared light LED and a position where it can receive the light specularly reflected on the intermediate transfer belt 105 and a position where it does not receive specular reflection light. 604 is provided. As the light emitting element, a laser light emitting element or the like may be used. Further, although phototransistors are used for the light receiving elements 603 and 604, photodiodes may be amplified and used. A condensing lens 605 is provided in the middle of the optical path. In this configuration, a diffused light receiving unit and a regular reflection light receiving unit are provided as the light receiving elements 603 and 604, but either one may be used depending on the object to be detected and necessary information.

FIG. 5 is a block diagram showing an electrical connection of each unit provided in the printer of this embodiment. As shown in FIG. 5, the printer according to the present embodiment includes a main body control unit 406 having a computer configuration, and the main body control unit 406 controls driving of each unit. A main body control unit 406 includes a ROM (Read Only Memory) 405 that stores in advance fixed data such as a computer program via a bus line 409 in a CPU (Central Processing Unit) 402 that executes various calculations and drive control of each unit. A RAM (Random Access Memory) 403 that functions as a work area for storing various data in a rewritable manner is connected.
The ROM 405 stores the test pattern formation position and density information necessary for generating the test pattern, the bias condition for forming the test pattern gradation, and the TM / P sensor output for estimating the test pattern adhesion amount. The adhesion amount conversion LUT is stored.
A print controller 410 is connected to the main body control unit 406, and the print controller 410 transmits image information from a PC, FAX, scanner, or the like as unified image data to the main body control unit 406. Further, an A / D conversion circuit 401 that converts various sensor information into digital data, a drive circuit that drives a motor and a clutch, a high-voltage generator that generates a voltage necessary for image formation, and the like are also connected.

Next, a known image forming operation in the printer of this embodiment will be described. When printing from a PC using a printer having the above-described configuration, first, image information is transmitted using a printer driver on the PC. The print controller 410 receives print information from the printer driver and sends an exposure signal to the laser exposure device 109.
Upon receiving the print command, the main body control unit 406 drives a drive motor (not shown) so that the support roller 112 is rotated and the intermediate transfer belt 105 is rotated. At the same time, the photosensitive drums 101Y, 101C, 101M, and 101K of each image forming unit are also rotated. Thereafter, based on information from the print controller, the exposure device 109 irradiates writing light onto the photosensitive drums 101Y, 101C, 101M, and 101K of each image forming unit. As a result, electrostatic latent images are formed on the respective photosensitive drums 101Y, 101C, 101M, and 101K, and are visualized by the developing devices 102Y, 102C, 102M, and 102K. Then, yellow, cyan, magenta, and black toner images are formed on the photosensitive drums 101Y, 101C, 101M, and 101K, respectively.

The respective color toner images formed in this way are primarily transferred by the primary transfer devices 106Y, 106C, 106M, and 106K so as to sequentially overlap the intermediate transfer belt 105. As a result, a composite toner image in which the toner images of the respective colors overlap is formed on the intermediate transfer belt 105. The transfer residual toner remaining on the intermediate transfer belt 105 after the secondary transfer is removed by the belt cleaning device 17.
In response to the image information, a paper feed roller of a paper feed device (not shown) corresponding to the transfer paper 105 selected by the user rotates, and the transfer paper 105 is sent out from one of the paper feed cassettes (not shown). The transferred transfer paper 105 is separated into one sheet by a separation roller (not shown), enters a paper feed path (not shown), and is conveyed by a conveyance roller 47 to a conveyance path 48 in the printer main body 100. The transfer paper 105 conveyed in this way is stopped when it hits the registration roller 107. When the transfer paper 105 not set in the paper feed cassette (not shown) is used, the transfer paper 105 set on the manual feed tray (not shown) is fed by a paper feed roller (not shown) and separated into one sheet by a separation roller (not shown). Thereafter, the sheet is conveyed through a manual sheet feeding path (not shown). Then, it stops when it hits the registration roller 107.

  The registration roller 107 starts to rotate in accordance with the timing at which the composite toner image formed on the intermediate transfer belt 105 as described above is conveyed to the secondary transfer unit facing the secondary transfer roller 108. Here, in general, the registration roller 107 is often used while being grounded, but a bias may be applied to remove the paper dust of the transfer paper 105. The transfer paper 105 sent out by the registration roller 107 is sent between the intermediate transfer belt 105 and the secondary transfer roller 108, and the composite toner image on the intermediate transfer belt 105 is transferred onto the transfer paper 105 by the secondary transfer roller 108. Secondary transfer is performed. Thereafter, the transfer paper 105 is conveyed to the fixing device 111 while being attracted to the secondary transfer roller 108, and heat and pressure are applied by the fixing device 111 to perform a toner image fixing process. The transfer sheet 105 that has passed through the fixing device 111 is discharged and stacked on a discharge tray (not shown) by a discharge roller (not shown). When image formation is also performed on the back surface of the surface on which the toner image is fixed, the transfer direction of the transfer paper 105 that has passed through the fixing device 111 is switched by a switching claw (not shown) and sent to a paper reversing device (not shown). The transfer paper 105 is reversed there and guided to the secondary transfer roller 108 again.

Next, image process control related to the present invention and performed by the CPU 402 according to the present embodiment based on a computer program will be described with reference to FIG. FIG. 6 is a flowchart showing the flow of execution of image process control.
The image process control determines whether it is necessary when the power switch of the main body is turned on or when printing is started, and is executed if necessary (S502, S503). Immediately after the power is turned on, the heating time of the fixing heater and the preparation time of the print controller are necessary, and the image processing control should be performed because it may be left until then or the usage environment may change. There is. Also, during the printing operation, toner supply and consumption, and changes in the characteristics of the photoconductor and transfer belt may occur, and image process control may be performed. Immediately after power-on, image process control is executed when the stop time of the photosensitive member is 6 hours or more, the temperature in the apparatus has changed by 10 ° C. or more, or the relative humidity in the apparatus has changed by 50% or more. . Among the above, the stop time of the photosensitive member is obtained as follows. When the photosensitive member stops, time information is acquired from the real-time clock held by the print controller 410 and stored in the RAM 403. Similarly, at the time of power-on, time information is acquired from the real-time clock, and the photosensitive member stop time is obtained from the difference. The temperature and humidity changes are obtained by acquiring temperature information and relative humidity information from the in-machine temperature / humidity sensor 414 when the photosensitive member is stopped, and acquiring temperature information and relative humidity information from the temperature / humidity sensor 414 in the same manner at power-on. The temperature change amount and the relative humidity change amount are obtained from the difference. During printing, a test pattern is created when the number of printed sheets reaches a predetermined interval. The interval in this case is determined by the amount of process variation obtained in advance through experiments or the like. In addition to the number of prints, the travel distance of the developing sleeve 305 and the intermediate transfer belt 105 may be set as a threshold value.

Next, if it is determined that image process control is necessary, a test pattern is formed (S504). A state diagram in which the test pattern is formed on the transfer belt is shown in each of FIGS.
FIGS. 7A and 7B are top views of the intermediate transfer belt 105 that forms a test pattern during the test pattern creation operation in the image forming apparatus of FIG. 1. FIGS. 7A and 7B show a case where the test pattern is formed outside the image area. FIG. 7B is a diagram for explaining the timing for forming (forming) a test pattern on the non-image forming area 710 during printing, and FIG. 7C is for forming the test pattern at the center in the image area. Shows the case.
201 in each figure shows a test pattern (P pattern) for detecting the toner adhesion amount. Reference numeral 202 in FIG. 7 denotes a test pattern (TM pattern) for detecting the image position. The P pattern and the TM pattern are formed on the near side and the far side in the axial direction, and the near side P pattern is denoted by 201F, the far side P pattern is denoted by 201R, the near side TM pattern is denoted by 202F, and the far side TM pattern is denoted by 202R. Image process control includes potential potential control, toner density target value correction control, and alignment correction control, and the test pattern formation conditions differ depending on which control is performed.

[Potential potential control]
First, conditions for forming a test pattern for controlling potential potential will be described. The test pattern 201 is used for potential potential control. Of the test patterns 201, only 201F is formed, but if necessary, only 201R may be formed, and both 201F and 201R may be formed. 201F and 201R are formed to have a size of 10 mm in the axial direction (main scanning) and 15 mm in the traveling direction of the intermediate transfer belt 105 (sub scanning). The size in the main scanning direction includes the irradiation range (spot diameter) of the P / TM sensor 109 on the intermediate transfer belt 105, the conditions under which the test pattern is stably formed in the process (a region where no edge effect or the like occurs), and the main size. It is determined from the maximum scanning position deviation amount. The size in the sub-scanning direction needs to be the same as that in the main scanning. However, when the sampling frequency and gradation pattern of the A / D conversion circuit are formed with the developing bias variable, the rise time of the high voltage generator 416 is increased. Etc. need to be considered. The exposure amount is the same as that for printing, and is 0.47 mW in this embodiment. The development bias is switched to about 50 msec immediately before the test pattern exposure unit comes on the photosensitive member 101 and the developing sleeve 305. This switching timing is set in consideration of the response of the high voltage generation circuit. Five types of test patterns are formed, and the values of the developing bias are switched from the first to −100V, −150V, −200V, −250V, and −300V, respectively. The charging bias is set so as to always maintain a potential of 200 V with respect to the developing bias. In this case, the charging bias is set to -300 V, -350 V, -400 V, -450 V, and -500 V. In this case, the test pattern for controlling the potential potential is formed by changing the developing bias and cannot be executed simultaneously with the printing operation. Therefore, the test pattern is formed at the timing of the non-image forming area 710 during printing shown in FIG. 7B. However, when the exposure energy is made variable in order to obtain a gradation (development γ) by the development potential of the test pattern, the test pattern may be formed simultaneously with printing. Toner density target value correction control is also performed using the same test pattern as this potential potential control.

  Next, test pattern formation conditions for alignment correction control will be described. In the alignment correction control, test patterns 202F and 202R are used. 202F and 202R are formed by tilting 45 °, which is the same size as 10 mm in the main scanning direction and 1 mm in the sub-scanning direction. The size in the sub-scanning direction is determined by the irradiation range (spot diameter) of the P / TM sensor 109 on the intermediate transfer belt 105. Each color is formed in order as K, M, C, and Y. The exposure value is the same as that for printing (0.47 mW in this embodiment), but a dedicated exposure pattern may be used. The development bias and the charging bias are the same as those for printing. However, if the toner adhesion amount of the test pattern portion is a condition that the surface of the intermediate transfer belt 105 is covered, if it is not simultaneous with printing, it can be set individually. Good. Details of the positional deviation correction control will be described later.

  Next, a test pattern detection method and calculation method for potential potential control will be described. Before the test pattern formed first passes through the P / TM sensor 109, the light emission amount adjustment (Vsg adjustment) of the light emitting elements 603 of the P / TM sensor 109F and P / TM sensor 109R is performed. The Vsg adjustment only needs to be completed before the test pattern passes through the P / TM sensor 109. The Vsg adjustment will be described. When Vsg adjustment starts, turn on the LED. As the current PWM value at this time, the previous adjustment value (IF) stored in the RAM 403 is used. Next, the output data of the regular reflection output element 603 is read. The sampling time interval at this time is 2 msec, and 10 points are sampled to obtain the average value so as not to be affected by the uneven reflection of the intermediate transfer belt 105. This average value is referred to as Vsg_REG. If Vsg_REG is within 4.0V ± 0.5V, IF is not updated and the previous value is maintained. If Vsg_REG is not within 4.0V ± 0.5V, adjustment operation is performed. An IF that makes Vsg_REG closest to 4.0 V is detected using a two-part search method as the adjustment operation. If the IF is found, the IF data on the RAM 403 is updated. If the IF is not found, an adjustment abnormality is detected, the abnormality is notified to the print controller 410, and the abnormality is displayed on the printer driver or the operation unit of the main body. Further, when Vsg_REG is detected using the final IF, the output voltage of the diffuse reflection light receiving element 604 is also detected at the same time. This value is called Vsg_DIF. Next, Vsg_REG and Vsg_DIF are stored in the RAM 403. When the P / TM sensor LED is continuously turned on, the test pattern reaches the light irradiation portion position of the intermediate transfer belt 105 of the P / TM sensor 109. The output is sampled every 2 msec at the timing when the test pattern reaches the P / TM sensor 109 and converted into digital data by the A / D conversion circuit 401. The digitally converted data is returned to analog output data by a conversion formula preset in the ROM 405. In the CPU 402, since the size of the sub-scan of the test pattern is 15 mm and the linear velocity is 200 mm / sec, the sampling is (15/200 × 1000) / 2≈38 data. In order to remove noise, 10 pieces of sampled data are removed from a large value and 10 pieces from a small value, an average value of the remaining data is obtained, and the first test pattern regular reflection output data (Vsp [1 ] _REG). Similarly, the output data of the diffusion light receiving element is also obtained as Vsp [1] _DIF. The same applies to the second and subsequent test patterns (Vsp [2-5] _REG, Vsp [2-5] _DIF).

Next, a method for converting (Vsp [n]) data into toner adhesion amount data will be described. FIG. 8A shows the relationship between the color toner adhesion amount and the output voltage of the regular reflection light receiving element 603. FIG. 8B shows the relationship between the color toner adhesion amount and the output voltage of the diffuse reflection light receiving element 604. FIG. 8C shows the relationship between the black toner adhesion amount and the output voltage of the regular reflection light receiving element 603. Since the black toner does not have a diffuse reflection component, the diffuse reflection light receiving element 604 is not used for detecting the black toner. In this embodiment, a case where only the regular reflection light receiving element 603 is used for conversion of the color toner adhesion amount will be described. The following sensitivity correction coefficient (K2) of the regular reflection light receiving element 603 is obtained from the relationship of the data Vsp [1-5] _REG and Vsp [1-5] _DIF obtained first. K2 is obtained from the following equation (1).
K2 = MIN (Vsp [n] _REG / Vsp [n] _DIF) Expression (1)

Next, an expression (2) for obtaining a value (K [n]) obtained by removing the toner diffuse reflection component from the output voltage of the regular reflection light receiving element 603. This value represents a regular reflection light component from the intermediate transfer belt 105 in the test pattern portion.
K [n] = (Vsp [n] _REG−Vsp [n] _DIF × K2) / (Vsg [n] _REG−Vsg [n] _DIF × K2) (2)
Next, the diffuse reflection component from the intermediate transfer belt 105 is removed from the output voltage of the diffuse reflection light receiving element 604, and only the diffuse reflection component from the color toner is separated. This separation method is obtained by the following equation (3).
Vsp [n] _DIF_dush = Vsp [n] _DIF−Vsg [n] _DIF × K [n] — Expression (3)

Next, gain adjustment is performed to correct variations in the toner output of the diffuse reflection light receiving element 604. This gain adjustment is performed by obtaining a gain adjustment coefficient K5. Equation (4) shows how to obtain K5.
K5 = 1.63 / (α × 0.15 ^ 2 + β × 0.15 × γ) (4)
In equation (4), α, β, and γ are square terms obtained by quadratic approximation when the test axis is K [n] on the X axis and Vsp [n] _DIF_dush of each test pattern is on the Y axis. Coefficient, coefficient of the first power term, and y-intercept. The approximate straight line is obtained by the method of least squares. In addition, the constant in the equation (4) is a value obtained in advance by experiments or the like.
Next, normalization calculation is performed. An equation for obtaining the normalized value (R [n]) is shown in Equation (5).
R [n] = K5 × Vsp [n] _DIF_dush (5)
At this point, the sensor attachment and individual variation of the detection system and the reflection characteristic change of the intermediate transfer belt 105 are substantially canceled and determined uniquely. Next, the toner adhesion amount MA [n] is obtained from the LUT and R [n] shown in FIG.

Next, how to determine the black toner adhesion amount will be described. In the case of black toner, it is determined only by the regular reflection light reflectance from the intermediate transfer belt 105 and the light absorption characteristics of the toner, so the relationship of the following equation (6) may be obtained.
R [n] [Bk] = Vsp_REG / Vsg_REG Formula (6)
When R [n] [Bk] is obtained, the LUT and R [n] shown in FIG. The toner adhesion amount MA [n] [Bk] is obtained from [Bk].
When the adhesion amount MA [n] is obtained, the relationship between the developing bias Vb [n] of the test pattern and the adhesion amount MA [n] is linearly approximated. The linear approximation is obtained by the least square method. Next, the optimum developing bias Vb is obtained from the target value (MA_REF) of the adhesion amount obtained in advance and the approximate linear equation, and stored in the RAM. The charging bias Vc is determined by the relationship of Vc = Vb + 200 (V) and is similarly stored in the RAM. The determined Vc and Vb are used in the next printing operation. The toner density target value correction control is performed using the slope data of an approximate linear equation. Since the inclination of the approximate linear equation is an alternative characteristic of development γ (the inclination when the Y-axis is the toner adhesion amount on the photoconductor and the X-axis is the development potential), toner supply control is performed with respect to the approximate linear inclination target value. Control the target value.

[Position correction control]
Next, the process of positional deviation correction control will be described with reference to Japanese Patent Application Laid-Open No. 2002-207338 of Patent Document 10. (FIG. 10 to FIG. 18 show the contents of “color matching” (CPA). When proceeding to this “color matching” (CPA), the CPU 402 first performs “test pattern formation and measurement” (PFM). As shown in FIG. 10, start marks Msr and Msf and 8 sets of test patterns are formed on the intermediate transfer belt 105 at the rear r and front f, and the marks are detected by the P / TM sensors 109F and 109R. Then, the mark detection signals Sdr and Sdf are converted into digital data, that is, mark detection data Ddr and Ddf by the A / D conversion circuit 401 and read, and the position of the center point of each mark on the intermediate transfer belt 105 ( Furthermore, the rear side 8 sets of average patterns (average group of mark positions) and the same front side 8 sets of average patterns are calculated. That. The contents of this "formation of the test pattern and measurement" (PFM) will be described later with reference to FIG. 13 below.
When the average pattern is calculated, the image forming deviation amount by each of the Bk, Y, C, and M image forming units is calculated based on the average pattern (DAC), and adjustment for eliminating the deviation based on the calculated deviation amount is performed. (DAD).

  FIG. 11 shows a flowchart of “test pattern formation and measurement” (PFM). When proceeding to this process, as shown in FIG. 10, the CPU 402 simultaneously, for example, in the y direction of the mark on each of the rear side R and front side f surfaces of the intermediate transfer belt 105 driven at a constant speed of 200 mm / sec. Formation of start marks Msr, Msf and 8 sets of test patterns having a width w of 1 mm, a length A in the x-direction of 10 mm, a pitch d of 6 mm, and an interval c between the sets of 9 mm, for example, was started. A timer Tw1 with a time limit value Tw1 for starting the timing immediately before MsR and Msf arrives immediately below the P / TM sensors 109F and 109R is started (1) and waits for the timing. That is, it waits for the timer Tw1 to time out (2). When the timer Tw1 is over, this time, the timer Tw2 whose time limit is Tw2 is used to determine when the last of the eight test patterns in the rear and front ends through the P / TM sensors 109F and 109R. Start (3).

When the Bk, Y, C, or M mark is not present in the field of view of the P / TM sensors 109F and 109R, the detection signals Sdr and Sdf of the P / TM sensors 109F and 109R are at a high level H (about 4V) and the mark is present. The mark detection signal Sdr has a level fluctuation as shown in FIG. 14 due to the low level L (about 1 V) and the intermediate transfer belt 105 moving at a constant speed. A part of the fluctuation is enlarged and shown in FIG. In this case, the descending area where the level of the mark detection signal is reduced corresponds to the leading edge area of the mark, and the ascending area where the mark is rising corresponds to the trailing edge area of the mark. Between these is the area of the mark width w.
In step 4 of FIG. 11, in the process where the start marks Msr and Msf arrive at the field of view of the P / TM sensors 109F and 109R and the detection signals Sdr and Sdf change from H to L, the window comparator 39r or 39f of FIG. The detection signal Sdr or Sdf waits until the detection signal Swr = L or Swf = L indicating that the detection signal Sdr or Sdf is 2 to 3V. That is, it is monitored whether at least one edge region of the start marks Msr and Msf has arrived in the visual field of the P / TM sensors 109F and 109R.

  When the timer arrives, the timer Tsp whose time limit value is Tsp (for example, 50 μsec) is started. When the timer Tsp expires, the “timer Tsp interrupt” (TIP) shown in FIG. 10 is executed, and the timer interrupt is permitted (5). Then, the sampling number value Nos of the sampling number register Nos is initialized to 0, and writing to the r memory (rear side mark read data storage area) and the f memory (front side mark read data storage area) allocated to the FIFO memory in the CPU 402 is performed. The addresses Noar and Noaf are initialized to the start address (6). Then, it waits for the timer Tw2 to time out. That is, it waits for all the eight sets of test patterns to finish passing through the fields of view of the P / TM sensors 109F and 109R (7).

Here, with reference to FIG. 10, the content of the “interrupt of timer Tsp” (TIP) will be described. It should be noted that this process is executed every time the timer Tsp whose time limit value is Tsp expires. At the beginning of this process, the CPU 402 restarts the timer Tsp (11) and instructs the A / D conversion circuit 401 to perform A / D conversion (12). That is, the instruction signals Scr and Scf are temporarily set to the A / D conversion instruction level L. Then, the sampling number value Nos in the sampling number register Nos, which is the number of instructions, is incremented by one (13).
As a result, the elapsed time since Nos × Tsp detected the leading edge of the start mark Msr or Msf (= the belt movement direction y along the surface of the intermediate transfer belt 105 based on the start mark Msr or Msf). This represents the current detected position on the intermediate transfer belt 105 by the P / TM sensors 109F and 109R.

  Then, it is checked whether the detection signal Swr of the window comparator 39R is L (P / TM sensor 20R is detecting the edge portion of the mark, 2V ≦ Sdr ≦ 3V) (14). The sampling number value Nos of the sampling number register Nos and the A / D conversion data Ddr (value of the mark detection signal Sdr of the P / TM sensor 109R) are written to the memory address Noar as write data (15). Then, the write address Noar of f memory is incremented by 1 (16). When the detection signal Swr of the window comparators 39R and 39f is H (Sdr <2V or 3V <Sdr), data is not written to the r memory. This is for reducing the amount of data written to the memory and simplifying subsequent data processing.

  Next, similarly, it is checked whether the detection signal Swf of the window comparator 39f is L (P / TM sensor 109f is detecting the edge portion of the mark and is 2V ≦ Sdf ≦ 3V) (17). Then, the sampling number value Nos of the sampling number register Nos and the A / D conversion data Ddf (value of the mark detection signal Sdf of the P / TM sensor 109f) are written as write data in the address Noaf of the f memory (15). Then, the write address Noaf of the f memory is incremented by 1 (19).

Since such interrupt processing is repeatedly executed in the Tsp cycle, when the mark detection signals Sdr and Sdf of the P / TM sensors 109F and 109R change to high and low as shown in FIG. In the r memory and the f memory allocated to the FIFO memory, only the digital data Ddr and Ddf of the detection signals Sdr and Sdf within the range of 2V to 3V shown in FIG. And stored together. Since the sampling number value Nos of the sampling number register Nos is incremented by 1 in the Tsp cycle, and the intermediate transfer belt 105 moves at a constant speed, the number value Nos is based on the detected start mark as the intermediate transfer belt 105. It shows the y position along the top surface.
It should be noted that, as shown in FIG. 15B, the center position a of the descending area where the level of the mark detection signal is reduced and the center position of the ascending area which is rising next is within the range of 2V to 3V. The middle point Akrp of b is the center position of one mark Akr in the y direction, and similarly, the center position c of the descending region where the level of the mark detection signal that appears next to the mark is lowered, and the next rise The middle point Ayrp of the center position d of the rising area is the center position in the y direction of another mark Ayr. These mark center positions Akrp, Ayrp,... Are calculated by calculation CPA (FIG. 11, FIG. 13) of the mark center point position described later.

  Reference is again made to FIG. After the last mark of the last 8th set in the test pattern passes the P / TM sensors 109F and 109R, the timer Tw2 times out. Then, the CPU 402 prohibits interruption of the timer Tsp (7, 8). Thereby, the A / D conversion of the detection signals Sdr and Sdf in the Tsp cycle shown in FIG. 12 is stopped. The CPU 402 calculates the center position of the mark (CPA) based on the detection data Ddr and Ddf in the R memory and f memory in the FIFO memory, and each of the eight sets of patterns of the rear R and the front f. The appropriateness of the distribution of the detected mark center point position is verified, the inappropriate detection pattern (set) is deleted (SPC), and the average pattern of the appropriate detection pattern is obtained (MPA).

11 and 13 show the contents of “calculation of mark center point position” (CPA). Here, “calculation of mark center point position of rear r” (CPAr) and “calculation of mark center point position of front f” (CPAf) are executed.
In “calculation of mark center point position of rear r” (CPAr), the CPU 402 first initializes the read address RNoar of the r memory allocated to the FIFO memory in the first, and the data of the center point number register Noc is set to the first edge. It is initialized to 1 which means (21). Then, the data Ct of the one-edge region sample number register Ct is initialized to 1, and the data Cd and Cu of the descending number register Cd and the ascending number register Cu are initialized to 0 (22). Then, the read address RNoar is written in the edge area data group start address register Sad (23). The above is preparation processing for data processing of the first edge region.

  Next, the CPU 402 sends data (y position Nos: N · RNoar, detection level Ddr: D · RNoar) from the r memory address RNoar, and data (y position Nos: N · (RNoar + 1) from the next address RNoar + 1. ), The detection level Ddr: D · (RNoar + 1)) is read, and first, whether the y position difference between the two data is E (for example, E = w / 2 = for example, a value corresponding to 1/2 mm) or less (on the same edge region). Check (24). If so, check whether the mark detection data Ddr is in a downward trend or an upward trend (25). If the mark detection data Ddr is in a downward trend, the data Cd in the downward count register Cd is incremented by 1 (27). If the tendency is upward, the data Cu of the upward number register Cu is incremented by 1 (26). Then, the data Ct in the one-edge sample number register Ct is incremented by one (28). Then, it is checked whether the r memory read address RNoar is the end address of the r memory (29). If the r memory read address RNoar is not the end address, the memory read address RNoar is incremented by 1 (30), and the above processing (24-30) is performed. )repeat.

  When the y position (Nos) of the read data changes to that of the next edge region, the position difference between the position data of the front and rear memory addresses checked in step 24 is larger than E, and the CPU 402 starts from step 24 in FIG. Proceed to step 31. Here, all the sampling data in one mark edge (leading edge or trailing edge) area have been checked for a downward and upward tendency. Therefore, it is checked whether the sample number data Ct in the one-edge sample number register Ct at this time is an equivalent value in one edge region (in the range of 2V to 3V). That is, it is checked whether F ≦ Ct ≦ G (31). F is a lower limit (setting of the number of times of writing the sample value Ddr to the r memory while the detection signal Sdr is 2 V or more and 3 V or less when the leading edge or the trailing edge of the mark formed normally is detected. Value) and G are upper limit values (set values).

  If Ct is F ≦ Ct ≦ G, the correctness / incorrectness of the data of one mark edge that has been normally read and stored is completed, and the result is “appropriate”. It is checked whether the obtained detection data group has a downward trend or an upward trend as a whole of the edge region (2V or more and 3V or less) (32, 34). In this embodiment, if the data Cd of the descending number register Cd is 70% or more of the sum Cd + Cu of the data Cu of the descending number register Cu and the data Cu of the ascending number register Cu, the memory edge No. If the address Down is written to the address addressed to Noc (33), and the data Cu in the ascending number register Cu is 70% or more of Cd + Cu, the memory edge No. Information Up indicating an increase is written in the address addressed to Noc (35). Further, the average value of the y position data of the edge region, that is, the center point position of the edge region (a, b, c, d,... Write to the address addressed to Noc (36).

Next, the edge No. It is checked whether Nos has become 130 or more, that is, calculation of the center positions of the leading edge area and trailing edge area of all of the start mark Msr and the eight sets of mark patterns has been completed. If this has been completed, or if all of the stored data has been read from the r memory, the mark center point position is calculated based on the edge center point position data (y position calculated in step 36). (39). That is, the memory edge No. The address data (falling / rising data & edge center point position data) is read, and the position difference between the center point position of the preceding falling edge area and the center point position of the immediately following rising edge area is the width of the mark in the y direction. It is checked whether it is within the range corresponding to w, and if it is out, these data are deleted. If it is within the range, the average value of these data is set as the center point position of one mark. Write to memory. If mark formation, mark detection and detection data processing are all appropriate, with respect to rear r, start mark Msr and 8 sets of marks (1 set 8 marks x 8 sets = 64 marks), 65 mark center points in total Position data is obtained and stored in memory.
Next, the CPU 402 executes “calculation of the mark center point position of the front f” CPAf, and performs the data processing of the above-mentioned “calculation of the mark center point position of the rear r” CPAr similarly to the measurement data in the f memory. carry out. With respect to the front f, if mark formation, measurement, and measurement data processing are all appropriate, start mark Msf and 8 sets of marks (64 marks), a total of 65 mark center point position data are obtained and stored in memory. Is done.

Reference is again made to FIG. When the mark center point position is calculated as described above (CPA), the CPU 402 displays the mark center point position data group written in the memory in the next “verification of pattern of each set” (SPC) as shown in FIG. The central point distribution corresponding to the mark distribution is verified. Here, data deviating from the mark distribution equivalent to that shown in FIG. 10 is deleted in units of sets, and only the data set corresponding to the mark distribution shown in FIG. leave. If all are appropriate, 8 sets of data remain on the rear r side and 8 sets of data remain on the front f side.
Next, the CPU 402 changes the center point position data of the first mark in each set after the second set to the first center point position of the first set in the rear r-side data set. The center point position data of the second to eighth marks are also changed by the changed difference value. That is, the center point position data group of each set after the second set is changed to a value shifted in the y direction so that the top of each set is aligned with the top of the first set. Similarly, the center point position data in each set after the second set on the front f side is also changed.

Next, the CPU 402 calculates average values Mar to Mhr (FIG. 16) of the center point position data of each mark of all sets on the rear r side by “calculation of average pattern” (MPA), and also on the front f side. Average values Maf to Mhf (FIG. 16) of the center point position data of each mark of all sets are calculated. These average values are distributed as shown in FIG. 16, virtual average position marks MAkr (representative of Bk rear orthogonal marks), MAyr (representative of Y rear orthogonal marks), MAcr (rear orthogonal marks of C). Representative), MAmr (representative of M rear orthogonal mark), MBkr (representative of Bk rear oblique mark), MByr (representative of Y rear oblique mark), MBcr (representative of C rear oblique mark), And MBmr (representative of M rear oblique mark), MAkf (representative of front orthogonal mark of Bk), MAyf (representative of front orthogonal mark of Y), MAcf (representative of front orthogonal mark of C), MAmf (Representative of M front orthogonal mark), MBkf (representative of Bk front oblique mark), MByf (representative of Y front oblique mark), MBcf (representative of C front flow mark) Representative DOO diagonal mark), and indicates the center point position of MBmr (representative of front diagonal mark of M).
The above is the content of “Test Pattern Formation and Measurement” (PFM) shown in FIG.

Reference is again made to the flowchart of FIG. See also the graph of FIG. In the displacement amount calculation (DAC) shown in FIG. 18, the CPU 402 calculates the image formation displacement amount as follows. The calculation (Acy) of the image forming deviation amount of Y is specifically shown below.
Sub-scanning shift amount dyy: The shift amount of the difference (Mbr−Mar) between the center point positions of the Bk orthogonal mark MAkr and the Y orthogonal mark MAyr on the rear r side with respect to the reference value d (FIG. 10),
dyy = (Mbr−Mar) −d
Main scanning deviation amount dxy: deviation amount with respect to the reference value 4d (FIG. 10) of the difference (Mfr−Mbr) in the center point position between the orthogonal mark MAyr on the rear r side and the oblique mark MByr,
dxyr = (Mfr−Mbr) −4d
And a deviation amount of the difference (Mff−Mbf) between the center point positions of the orthogonal mark MAyf on the front f side and the oblique mark MByf with respect to the reference value 4d (FIG. 10),
dxyf = (Mff−Mbf) −4d,
And the average value,
dxy = (dxyr + dxyf) / 2 = (Mfr−Mbr + Mff−Mbf−8d) / 2
Skew dSqy: difference in center point position between the orthogonal mark MAyr on the rear R side and the orthogonal mark MAyf on the front f side,
dSqy = (Mbf−Mbr)
Main scanning line length shift amount dLxy: Skew dSqy = (Mff−Mfr) is subtracted from the difference (Mff−Mfr) between the center point positions of the rear r side oblique mark MByr and the front f side oblique mark MByf. value,
dLxy = (Mff−Mfr) −dSqy = (Mff−Mfr) − (Mbf−Mbr)
The other C and M image formation shift amounts are calculated in the same manner as the calculation related to Y (Acc, Acm). Although Bk is substantially the same, in this embodiment, since color matching in the sub-scanning direction y is based on Bk, the positional deviation amount dyk in the sub-scanning direction is not calculated for Bk (Ack). .

In the shift adjustment (DAD) shown in FIG. 18, the CPU 402 adjusts the image forming shift amount of each color as follows. The Y shift amount adjustment (Ady) is specifically shown below.
Adjustment of sub-scanning deviation amount dy: The start timing of image exposure (latent image formation) for forming a Y toner image is set by shifting the calculated deviation amount dyy from the reference timing (y direction).
Adjustment of main scanning deviation amount dxy: The image data at the head of the line to the exposure laser modulator of exposure apparatus 109 for the line synchronization signal representing the head of the line in image exposure (latent image formation) for Y toner image formation. The sending timing (x direction) is set to be shifted from the reference timing by the calculated shift amount dxy.

Adjustment of the skew dSqy: The rear r side of the axially extending mirror that reflects the laser beam modulated by the Y image data facing the photosensitive drum 101 and projects it onto the photosensitive drum 101 of the exposure device 109 is supported by a fulcrum. The front f side is supported by a block slidable in the y direction. The skew dSqy can be adjusted by moving this block back and forth in the y direction with a y drive mechanism mainly composed of a pulse motor and a screw. In “adjustment of skew dSqy”, the pulse motor of this y driving mechanism is driven to drive the block from the reference y position by an amount corresponding to the calculated skew dSqy.
Adjustment of main scanning line length shift amount dLxy: The frequency of the pixel synchronization clock for allocating image data in units of pixels on the line is set to reference frequency × Ls / (Ls + dLxy). Ls is the reference line length.

The other adjustments of C and M image forming deviation amounts are adjusted in the same manner as the adjustment related to Y (Adc, Adm). Although Bk is generally the same, in this embodiment, since color matching in the sub-scanning direction y is based on Bk, the positional deviation amount dyk in the sub-scanning direction is not adjusted for Bk (Adk). . Until the next “color matching”, a color image is formed under the adjusted conditions.
In addition, as shown in FIG. 7A, based on the detection results of the test patterns 201F and 201R formed outside the image area of the intermediate transfer belt 105, the determined image process conditions (charge application voltage, development bias voltage, or exposure) are determined. There is also a method of feeding back the result of the following arithmetic processing instead of feeding back the power) as it is. Hereinafter, these methods will be described in detail.

[Method of obtaining average value]
The image process conditions determined by the detection of the test pattern 201F are the charging application voltage: Vc (F), the development bias voltage: Vb (F), and the image process conditions determined by the detection of the test pattern 201R are the charging application voltage: Assuming that Vc (R) and development bias voltage: Vb (R), when a density deviation of the test pattern occurs in the axial direction of the driving roller of the intermediate transfer belt, the above Vc (F), Vc (R), Vb (F) and Vb (R) have different values.
For example, when the toner adhesion amount of the test pattern 201F is larger than the toner adhesion amount of the test pattern 201R created under the same test pattern imaging conditions, the image area that is originally desired to be controlled is located between the two. The average value of the image process conditions determined from the test pattern detection result is fed back.
That is, the image process conditions are Vc = {Vc (F) + Vc (R)} / 2 and Vb = {Vb (F) + Vb (R)} / 2.
As a result, even if a test pattern formed outside the image area has a larger or smaller amount of toner adhesion than in the image area without hindering the normal image forming operation, it is possible to assume an appropriate The image process conditions are determined. Incidentally, the above-described density deviation often occurs due to deviations in the direction of each unit rotation axis such as development ability deviation and intermediate transfer ability deviation.

[Method of obtaining correction values and using them as appropriate]
The image process conditions determined by the detection of the test pattern 201F are the charging application voltage: Vc (F), the development bias voltage: Vb (F), and the image process conditions determined by the detection of the test pattern 201R are the charging application voltage: Assuming that Vc (R) and development bias voltage: Vb (R), when a density deviation of the test pattern occurs in the axial direction of the driving roller of the intermediate transfer belt, the above Vc (F), Vc (R), Vb (F) and Vb (R) have different values.
For example, when the toner adhesion amount of the test pattern 201F is larger than the toner adhesion amount of the test pattern 201R created under the same test pattern imaging conditions, the image area that is originally desired to be controlled is located between the two. The average value of the image process conditions determined from the test pattern detection results of image process conditions Vc = {Vc (F) + Vc (R)} / 2, Vb = {Vb (F) + Vb (R)} / 2.
At this time, the difference between the image process condition in the image region and the test pattern 201F and the test pattern 201R is set as a correction value of the image process condition obtained from each test pattern detection result.
That is,
Vc correction value (F) = Vc−Vc (F), Vb correction value (F) = Vb−Vb (F),
It is assumed that Vc correction value (R) = Vc−Vc (R) and Vb correction value (R) = Vb−Vb (R).

The Vc correction value (F), Vb correction value (F), Vc correction value (R), and Vb correction value (R), which are the above correction values, are stored in the storage device RAM (FIG. 5-403) of the main body. To do.
Each correction value stored here is, for example, an image process to be fed back by correcting the Vc correction value (F) and the Vb correction value (F) with respect to the image process condition obtained from the detection result of the test pattern 201F. Determine as a condition. Similarly, in the case of the test pattern 201R, the Vc correction value (R) and the Vb correction value (R) are corrected. By using each of these correction values, it is not necessary to always create and detect the test pattern with both the test pattern 201F and the test pattern 201R, and the image process condition in the image area can be determined by only one of the test pattern detection results. Is determined to an appropriate value.

When the image process condition correction value is obtained, pattern image formation and detection are required at two locations of the test pattern 201F and the test pattern 201R outside the image area as described above. As compared with the case where only a test pattern is formed, the toner consumption associated with the test pattern image formation is doubled, resulting in unnecessary toner consumption, an increase in the amount of waste toner, intermediate transfer belt cleaning, and photoconductor cleaning. There are concerns about the occurrence of problems such as increased load.
Therefore, in the present embodiment, one of the test pattern 201F and the test pattern 201R is imaged and detected except when the image process condition correction value is determined from the above viewpoint. Further, the image formation / detection operation of the test pattern 201F or the test pattern 201R is switched at a timing at which the integration number of either one of the test pattern image formation and detection operations is an integral multiple of 10.

The timing for determining the image process condition correction value is set when the developing unit is replaced or when the intermediate transfer belt or the intermediate transfer device is replaced, assuming that there is a high possibility that the image density deviation in the rotation direction of the intermediate transfer belt is changed. It is also implemented when the P / TM sensor is replaced.
When developing is replaced, development is automatically performed by developing unit replacement detection means (such as a non-contact type ID chip or a method of detecting a mechanical protrusion using a sensor installed in the main unit). By determining that the unit has been replaced and setting a unit replacement flag in the RAM 403, image formation / detection is performed at a plurality of locations in the test pattern 201F and the test pattern 201R during the next test pattern image formation.

Further, when the intermediate transfer belt or the intermediate transfer device is replaced and the P / TM sensor is replaced, a unit replacement flag is set in the RAM 403 by setting manually from the main body operation unit. As a result, at the next test pattern image formation, image formation / detection is performed at a plurality of locations of the test pattern 201F and the test pattern 201R.
The density deviation between the test pattern 201F and the test pattern 201R may change depending on the use state of the image forming apparatus main body such as the image area ratio to be used, the print volume, and the installation environment. In order to cope with these changes, In addition to the unit replacement described above, the determination of the image process condition correction value is executed at a timing at which the integration number of test pattern imaging and detection operations is an integral multiple of 20.

Based on the image forming apparatus of the embodiment described above and the process control that can be executed by the apparatus, the novel control of the image process condition according to the present invention will be described in detail below with a specific example.
In the process control according to the present invention, the process conditions described above are obtained, and further, another test pattern D is created in the image forming area, and this is similarly detected (evaluated) to determine the reference image process conditions. Based on this reference image process condition, it is determined whether or not other (scheduled execution) image forming process conditions are appropriate. Only when a determination result is obtained as appropriate, actual process control is performed in accordance with prescribed execution scheduled image forming process conditions. If it is determined that the scheduled execution image forming process condition is not appropriate, the scheduled execution image forming process condition is discarded and a new scheduled execution image forming process condition and a reference image process condition are obtained again. The above determination process is repeated anew.
That is, in the same manner as described above, the difference between the image process condition in the image area and the test pattern 201F and the test pattern 201R is obtained by using the correction value of the image process condition obtained from each test pattern detection result. ,
Vc = Vc (F) + Vc correction value (F), Vb = Vb (F) + Vb correction value (F),
Vc = Vc (R) + Vc correction value (R), Vb = Vb (R) + Vb correction value (R)
For each Vc and Vb

As shown in FIG. 2B and FIG. 7C, the comparison result is Vc− when compared with Vc (D) and Vb (D) determined based on the detection result of the test pattern D imaged and detected in the image region. When Vc (D) ≦ 20v and Vb−Vb (D) ≦ 20v, it is determined that the image process condition setting value after correction is “normal”, and the image process condition using the correction value is set as image formation. Use as a condition.
On the other hand, if the comparison result is Vc−Vc (D)> 20v or Vb−Vb (D)> 20v, it is determined that the corrected image process condition setting value is “abnormal”, and the correction value Perform reconfiguration (update).
The image process condition correction values at this time are obtained as follows, and the Vc correction value (F), Vb correction value (F), Vc correction value (R), and Vb correction value (R), which are the correction values, are stored in the main body. Stored in the storage device RAM (FIG. 5-403) and updated.
Vc correction value (F) = Vc (D) −Vc (F), Vb correction value (F) = Vb (D) −Vb (F),
Vc correction value (R) = Vc (D) −Vc (R), Vb correction value (R) = Vb (D) −Vb (R)

Similarly to the method described above, the developing bias voltage Vb obtained as an average value from Vb (F) and Vb (R), and the charging bias voltage Vc obtained as an average value from Vc (F) and Vc (R). Is used as the image forming condition, Vc (D) is related to the image process condition D (Vc (D) and Vb (D)) determined based on the test pattern D imaged and detected in the image area. F), Vc (D), Vc (R) and Vb (F), Vb (D), Vb (R)
Vc (F) <Vc (D), Vc (R) <Vc (D) and Vb (F) <Vb (D), Vb (R) <Vb (D),
Or
Vc (F)> Vc (D), Vc (R)> Vc (D) and Vb (F)> Vb (D), Vb (R)> Vb (D),
In this case, the magnitude relationship among Vc (F), Vc (D), Vc (R) and Vb (F), Vb (D), Vb (R) is as shown in FIGS. 22A and 22B.
That is,
Vc (F) <Vc (D) <Vc (R) and Vb (F) <Vb (D) <Vb (R))
Or Vc (F)> Vc (D)> Vc (R) and Vb (F)> Vb (D)> Vb (R)
The image process condition C determined as an average value based on the image process condition A and the image process condition B is not adopted as the image forming condition. .

As described above, the image formation and detection of the test pattern D within the image area means that the test pattern toner is applied to the secondary transfer roller that is always in contact with the primary transfer belt while the transfer conditions remain the same as those during image formation. Is transferred, and the stain is transferred to the back surface of the next entering transfer paper.
Therefore, immediately after the image formation / detection of the test pattern D, a cleaning operation for the secondary transfer roller is required.
Here, the repulsive bias voltage applied to the secondary transfer roller from the primary transfer roller during image formation is applied by switching between positive and negative, thereby making it difficult to transfer the test pattern on the primary transfer belt to the secondary transfer roller. At the same time, the test pattern transferred to the secondary transfer roller is gradually reversely transferred to the surface of the primary transfer belt to eliminate toner contamination on the surface of the secondary transfer roller. At this time, in order to completely clean the surface of the secondary transfer roller, it is necessary to rotate the secondary transfer roller 5 times or more, and a cleaning operation time of about 2 seconds is required.
Since the image formation / detection of the test pattern D is performed within the image area, the detection accuracy is higher than when the test pattern is imaged / detected outside the image area, and it is reliable for stabilizing the image quality. Although it is high, it is accompanied by the occurrence of the downtime as described above. Therefore, it is desirable that the frequency of image formation / detection of the test pattern D is as low as possible.

In the present invention, the image pattern detection / detection frequency of the test pattern D is executed together with the test pattern A and the test pattern B when the image process condition is checked when the number of printed sheets reaches 1000 or more.
In addition, the main unit of the image forming apparatus that requires time to cool the fixing unit is turned on as an execution timing that does not affect the user operation or can suppress the influence as much as possible due to the downtime associated with the image formation / detection of the test pattern D. This is set when the print output signal does not come for a long time (3 hours or more in the present invention) in anticipation of the time or when the user is not using the image forming apparatus.
The present invention has been described with reference to the embodiment. However, the above-described embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto, and departs from the gist thereof. Various modifications can be made without departing from the scope.

1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. (A) is a perspective view of the image forming apparatus in FIG. 1 during a test pattern creation operation, and (b) is a perspective view when a test pattern detected by an optical sensor is also created in the center of the image area. FIG. It is a front view of an image forming unit. It is a block diagram of a P / TM sensor. 1 is an overall schematic diagram of an image forming process control system. 3 is a flowchart of image forming process control. FIG. 2 is a top view of the image forming apparatus in FIG. 1 during a test pattern creation operation. FIG. 2 is a top view of the image forming apparatus in FIG. 1 during a test pattern creation operation. FIG. 2 is a top view of the image forming apparatus in FIG. 1 during a test pattern creation operation, in which a test pattern is also created at the center in the image area. FIG. 5A is a characteristic diagram when the amount of color toner adhesion of a test pattern on an intermediate transfer belt is detected by a regular reflection light receiving element, and FIG. The characteristic figure at the time of detecting by. FIG. 6C is a characteristic diagram when the black toner adhesion amount of the test pattern on the intermediate transfer belt is detected by the regular reflection light receiving element. FIG. 6 is a diagram showing a table (LUT) used when converting normalized values into toner adhesion amounts. FIG. 2 is a plan view schematically showing the intermediate transfer belt shown in FIG. 1 and each color mark formed outside the surface image area. FIG. 19 is a flowchart showing the contents of a “test pattern formation and measurement” PFM shown in FIG. 18; FIG. It is a flowchart which shows the content of the interruption process permitted at step 5 shown in FIG. 12 is a flowchart showing a part of the content of “calculation of mark center point position” CPA shown in FIG. FIG. 3 is a diagram side by side showing a time chart showing a distribution of color marks formed on the intermediate transfer belt shown in FIG. 2 and a change in mark detection signal level of an optical sensor. (A) is a time chart showing a part of the time chart of the detection signal Sdr shown in FIG. 14, and (b) is an A / D conversion data of the detection signal shown in (a). 6 is a time chart showing only the range written in the FIFO memory inside the CPU 41 shown in FIG. Steps shown in FIG. 11: “Calculation of average pattern” Average value data (Mar,...) Calculated by the MPA and virtual marks (MAkr,...) At which they are center point positions, that is, average value data It is a top view which shows the mark row | line | column represented by a group. FIG. 6 is a graph showing the distribution of test patterns formed in one circumference of the intermediate transfer belt in the embodiment of the present invention, together with the mark formation position deviation corresponding to the rotation angle of the photosensitive drum. It is a flowchart which shows the outline | summary of "color matching" CPA. It is a block diagram which shows the structure of a part of main body control part shown in FIG. FIG. 12 is a flowchart showing the remainder of the “calculation of mark center point position” CPA shown in FIG. 11. FIG. 10 is a diagram illustrating that a deviation also occurs in an appropriate value of a developing bias voltage with respect to a detected toner adhesion amount deviation in a test pattern portion. FIG. 5 is a diagram illustrating a developing bias voltage that is determined when the detected toner adhesion amount deviation of the test pattern portion does not tend to increase or decrease linearly in the front-rear direction. FIG. 5 is a diagram illustrating a developing bias voltage that is determined when the detected toner adhesion amount deviation of the test pattern portion does not tend to increase or decrease linearly in the front-rear direction.

Explanation of symbols

101Y, 101C, 101M, 101K Photosensitive drum (first image carrier), 102Y, 102C, 102M, 102K Developing device, 105 (constituting the first transfer device) Intermediate transfer belt, 106Y, 106C, 106M, 106K primary transfer device (constituting the first transfer device), 108 secondary transfer roller (second transfer device), 200 exposure device, 201 test pattern (P pattern), 201F near side P pattern, 201R back side P pattern, 202F Front side TM pattern, 202R Back side TM pattern, 202 Test pattern (TM pattern), 301 Charging device

Claims (11)

A plurality of image carriers, a charging device that charges each image carrier, an exposure device that forms a latent image on each image carrier, and a latent image formed on each image carrier from toners of different colors. A developing device for developing with a plurality of color toners;
A first transfer device that obtains a color image by superimposing and transferring an image formed on each image carrier on a second image carrier that moves at a transfer position facing each image carrier;
A second transfer device for transferring an image transferred and formed on the second image carrier onto a transfer material;
A test pattern generator capable of forming a test pattern image formed on each image carrier and transferred onto the second image carrier;
A test pattern detection device capable of detecting the state of the test pattern;
Image process control means for determining image process conditions for performing at least one of process control for changing image formation conditions and toner density control for changing toner replenishment amount according to the detection result of the test pattern;
With
In the image forming apparatus, the test pattern is not transferred to the second transfer device while the second transfer device is always in contact with the first transfer device.
The test pattern can be created at a plurality of locations, and the test pattern A and the test pattern B are created outside the image area on both sides of the image area in the rotation direction of the first transfer device. The image process condition correction value determined based on the detection result of the image process condition A and the image process condition B respectively determined based on the detection result of each of the test pattern A and the test pattern B arranged in Based on the process condition correction value, an image process condition C for execution to be used when forming an image in the image area is calculated,
A test pattern D is created and detected in the image forming area, and a reference image process condition D is calculated based on the detection result,
An image forming apparatus that determines whether or not the image forming process condition C is appropriate based on the image process condition D. The determination criteria for the determination are:
2. The image formation according to claim 1, wherein the image forming condition is suitable when a difference between corresponding item values of the image processing condition C for execution and the image processing condition D for reference is equal to or less than a predetermined value. apparatus. Depending on the result of the determination,
When it is determined that the process condition C is appropriate, image formation is performed using the image process condition C as an image formation condition,
2. The process according to claim 1, wherein if the process condition C is determined to be inappropriate, the test pattern A and the test pattern B are newly created, and the image process condition correction value is updated based on the test pattern A and the test pattern B. Image forming apparatus. The image process condition A determined based on the detection result of the test pattern A and the image process condition D determined based on the detection result of the test pattern D with respect to the image process condition A determined based on the detection result of the test pattern B. From the difference, the image process condition correction value when each of the test patterns A or B is used,
Image process condition correction value A = [Image process condition A] − [Image process condition D],
Image process condition correction value B = [Image process condition B] − [Image process condition D]
The image forming apparatus according to claim 3, wherein: [Image process condition A] <[Image process condition D] and [Image process condition B] <[Image process condition D],
Or
[Image process condition A]> [Image process condition D] and [Image process condition B]> [Image process condition D]
2. The control according to claim 1, wherein the image process condition C obtained as an average value of the image process condition A and the image process condition B is not used as the image forming condition. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the test pattern includes a pattern for detecting an adhesion amount of toner and a pattern for detecting an image position.   The image forming apparatus according to claim 1, wherein the image carrier in the first transfer device is in a belt shape, and the second transfer device is in a belt shape or a roller shape.   The image forming apparatus according to claim 1, wherein the image formation / detection timing of the test pattern D is set to a predetermined number of sheets.   The image forming apparatus according to claim 1, wherein the image formation / detection timing of the test pattern D is set immediately after the power is turned on.   The image forming apparatus according to claim 1, wherein the image formation / detection timing of the test pattern D is a case where a print command is not received for a predetermined time or more.   2. The image forming apparatus according to claim 1, wherein after the image formation / detection of the test pattern D, the second image carrier is cleaned.

Images