JP4492315B2 - Image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly to an electrophotographic image in which a toner image formed for each color by an image forming unit is superimposed on an intermediate transfer member such as a transfer belt. The present invention relates to color misregistration correction control of a system image forming apparatus.

  In recent years, image forming apparatuses such as copiers, printers, and facsimiles have been colorized, and for example, toner images for each color of yellow (Y), magenta (M), cyan (C), and black (K) are used. A tandem method in which an image forming unit (also referred to as image forming means) to be formed is provided along a transfer belt (intermediate transfer member), and toner images of respective colors are superimposed on the transfer belt and then transferred onto a transfer paper such as paper. Such an image forming apparatus is well known.

  In such an image forming apparatus, the toner images of the respective colors are formed by the respective image forming units and are superimposed on the transfer belt. Therefore, when the toner images are formed by the respective image forming apparatuses, Alternatively, when the toner images formed by the respective image forming apparatuses are transferred to the transfer belt, the toner images of the respective colors are shifted and overlapped due to mechanical and electrical error factors. When a phenomenon called this occurs and the color of the image blurs due to this color shift, there arises a problem that a high-quality and beautiful color image cannot be formed.

In order to eliminate such color misregistration, when printing an image, the toner image formed on the photosensitive drum of the image forming unit is transferred to the image area of the transfer belt, and is also outside the image forming area of the transfer belt. A reference pattern for measuring color misalignment is formed, and this reference pattern is measured by a sensor such as a CCD to determine whether the misregistration amount is greater than or equal to the reference value. For example, the timing of writing image information to the photosensitive drum of the image forming unit is adjusted temporarily, and then the toner image formed on the photosensitive drum of the image forming unit is again transferred to the image area of the transfer belt. In addition to transferring, a reference pattern for measuring color misregistration is formed outside the image forming area of the transfer belt, and this reference pattern is measured by a sensor such as a CCD. Back manner technologies have been disclosed (e.g., see Patent Document 1).
JP-A-8-6347

  However, in recent years, in addition to the color misregistration based on the error factors such as the above-described mechanical error and electrical operation timing, for example, depending on the amount of toner on the photosensitive drum of the image forming unit, the transfer belt, There is a difference in the frictional force between the image forming unit and the member in contact with the photosensitive drum, which causes a slight difference in the rotational speed of the photosensitive member and the transfer belt. As a result, the toner image is transferred from the photosensitive drum to the transfer belt. It has been found that there is a new color misregistration phenomenon that is considered to cause color misregistration when transferring the image.

  Therefore, in Japanese Patent Application Laid-Open No. 2004-133260, although the color misregistration based on the error factors such as the mechanical error and the electrical operation timing described above can be eliminated, a means for eliminating a new color misregistration phenomenon related to the amount of toner. However, there is a problem that it has not been considered yet.

  Further, in Patent Document 1, in order to correct color misregistration, complicated control such as creating and measuring a reference pattern outside the image forming area of the transfer belt together with a toner image to be printed every time is performed. There is a problem that the control for correcting the deviation becomes complicated.

  In view of the above problems, the present invention provides a high-definition, high-definition color image that is free from color misregistration related to the amount of toner, color misregistration based on error factors such as mechanical errors and electrical operation timing, and the like. An object of the present invention is to provide an image forming apparatus capable of forming images.

This invention can achieve the said objective by taking the following structure.
(Claim 1)
A plurality of image forming means for forming images of different colors,
Each of the plurality of image forming units includes a photoreceptor.
Based on the image information, an image is formed on the photoreceptor for each color,
In an image forming apparatus for forming a multiple image on an intermediate transfer member,
Measuring a reference pattern formed on the intermediate transfer member by the image forming means;
A deviation amount calculating means for calculating a color deviation amount for each color;
A printing rate correction value storage means for preliminarily storing a color misregistration correction value corresponding to each of a plurality of printing rates as a printing rate correction value;
A printing rate calculation unit that calculates the printing rate of an image for each color from image information in units of one page on which an image is formed by the image forming unit;
When the image forming unit forms an image based on the image information of one page unit,
According to the printing rate correction value read from the printing rate correction value storage unit corresponding to the printing rate calculated by the printing rate calculation unit,
An image forming apparatus comprising: a color misregistration correcting unit that corrects the misregistration amount for each color calculated by the misregistration amount calculating unit.
(Claim 2)
The color misregistration correction means includes
For image forming means for forming an image of a preset reference color,
A distance distance in the direction along the intermediate transfer body with an image forming unit that forms an image of each other color is provided as a coefficient.
By the printing rate correction value and the coefficient,
The image forming apparatus according to claim 1, wherein the shift amount for each color calculated by the shift amount calculation unit is corrected.
(Claim 3)
The deviation amount calculating means includes:
Comprising a sensor for measuring the passage time of a reference pattern for each color formed on the intermediate transfer member;
A passing time for each color of the reference pattern detected by the sensor;
Compare with the preset reference time of each color,
While calculating the difference as the amount of deviation for each color,
Depending on the amount of deviation for each color,
The image forming apparatus according to claim 1, wherein an amount of misregistration of another color with respect to a preset reference color is calculated.
(Claim 4)
The printing rate correction value storage means includes
4. The image forming apparatus according to claim 1, wherein a plurality of printing ratios and a plurality of color misregistration correction values are stored in advance as a matrix.
(Claim 5)
The image forming unit includes:
Based on the shift amount for each color corrected by the color shift correction means,
5. The image forming apparatus according to claim 1, further comprising a writing timing adjustment unit that adjusts a writing timing of an exposure unit that writes the image information on a photosensitive member.

  According to the present invention, when image information is printed by an image forming apparatus, a printing rate for each page of image information to be printed is obtained, and a printing rate correction value stored in advance is calculated in accordance with the obtained printing rate. Since the read and detected misregistration amount for each color is corrected by the read printing rate correction value, it is possible to correct the color misalignment that is considered to occur due to the amount of toner, that is, the change of the printing rate, An image forming apparatus capable of always forming a high-definition and high-quality color image can be provided.

  In addition, color misregistration correction is performed in consideration of the distance of the image forming unit, using the distance between the image forming unit that forms an image of a reference color set in advance and the image forming unit that forms an image of each color as a coefficient. High-quality and high-definition color can be corrected by absorbing error factors such as mechanical and electrical timing for the intermediate transfer member (transfer belt) when transferring the toner image formed by each color image forming means. An image forming apparatus capable of providing an image can be provided.

  Further, since the color misregistration is corrected with respect to a preset reference color, it is possible to provide an image forming apparatus that can easily perform color misregistration correction control.

  In addition, the color misregistration correction value corresponding to each of the plurality of printing rates is stored in advance as the printing rate correction value, and the color misregistration amount for each color is obtained prior to image formation. Therefore, it is not necessary to provide a reference pattern for color misregistration correction outside the image area of the transfer belt, and it is not necessary to increase the width of the transfer belt, so that a small image forming apparatus can be provided.

  In addition, since it is not necessary to obtain the amount of color misregistration every time an image based on the image information of the document is formed, the amount of toner for creating the reference pattern can be reduced, and there is no operation for obtaining the amount of color misregistration. The productivity of the image forming operation in the image forming apparatus can be improved.

  Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. In addition, in each drawing, the thing of the same code | symbol shall show the same thing, and shall be demonstrated in detail suitably with reference to other related drawings.

  1 is a schematic diagram of an image forming apparatus according to the present invention, FIG. 2 is a block diagram showing a circuit configuration of the image forming apparatus according to the present invention, FIG. 3 is a basic pattern diagram according to color misregistration correction control of the present invention, and FIG. Is a schematic diagram of a detection signal according to the color misregistration correction control of the present invention, FIG. 5 is a diagram showing a relationship between the printing rate and the correction value according to the color misregistration correction control of the present invention, and FIG. 6 is a diagram of the color misregistration correction control of the present invention. It is a flowchart which shows a procedure.

  The configuration of the image forming apparatus according to the present invention will be described with reference to FIG.

  The image forming apparatus 20 in the embodiment of the present invention is an electrophotographic copying machine. Since the electrophotographic copying machine is well known, the parts not directly related to the present invention will be described briefly.

  Reference numeral 20 denotes an image forming apparatus, and 30 denotes an automatic document feeder (ADF) mounted on the image forming apparatus 20.

  In the image forming apparatus 20, a manual feed tray 2 for supplying a relatively small amount of transfer material P is provided on the right side surface portion of the housing 1, and a paper discharge tray 3 is provided on the left side surface portion.

  On the paper discharge tray 3, a transfer material P, which is supplied from a paper feed cassette 12 and a manual tray 2 described later and on which an image is formed, is discharged and stacked.

  The transfer material P includes normal transfer paper made of plain paper and special transfer paper made of OHP sheet or the like, but in this embodiment, normal transfer made of plain paper is used unless otherwise specified. Paper (also simply referred to as transfer paper P) is used.

  A plurality of rollers (also referred to as casters) 4 for enabling the image forming apparatus 20 to move are provided on the bottom surface of the housing 1.

  A control panel CP as a display unit and an operation input unit for operating the image forming apparatus 20 is provided in the upper part of the front surface of the housing 1.

  The control panel CP includes a liquid crystal display device as the display means DP, or a touch panel type liquid crystal display device in which a touch panel or the like is incorporated in the liquid crystal display device.

  In addition, a numerical value or the like is input for inputting various image forming conditions such as whether the copy (printing, printing, or printing) is color or black and white, and control-related information such as the number of copies and the number of copies. An operation input means including a keyboard KB and a start button (also referred to as a copy button) SK for executing a series of image forming operations such as copying is provided as an input device.

  In particular, the touch panel type display means DP allows the user to input information such as selection and setting of information displayed on the display unit when the user touches a pattern such as a button on which a number, character, symbol, or the like is displayed on the display unit. For example, it also serves as an input means for an item that requires selection and setting such as an operation mode such as a single-side mode or a double-side mode.

  The single-side mode refers to a single-sided copy mode in which an image is formed by transferring a toner image formed by the image forming unit 11 to only one side of the transfer paper P based on image data. Incidentally, the duplex mode refers to a duplex copy mode in which images are formed on both sides of a transfer sheet.

  Although details will be described later, in the present embodiment, a color misregistration correction mode for performing color misregistration correction control is provided, and the color misregistration correction control is performed by operating the control panel CP according to a preset procedure. Whether to execute or not can be selected and set.

  Inside the housing 1 are provided a control means EC, a transfer separating means 8, a fixing device 10, an image forming means 11, an image reading means 13, a paper supply / discharge means 14, an intermediate transfer member 16, and the like.

  The control means EC, also called a control circuit, is a means for controlling all operations of the image forming apparatus 20, and is composed of an electric circuit composed of a CPU (Central Processing Unit) or the like. Based on a control program or control data stored in advance in the CPU, all means constituting the image forming apparatus 20 are driven and controlled.

  Further, when an accessory device such as the ADF 30 is connected to the image forming apparatus 20, similarly, the control unit EC operates smoothly as a system of the image forming apparatus 20 in cooperation with these accessory devices. The drive is controlled to

  Further, even when connected to a personal computer or other information equipment via a LAN (local area network), etc., the control means EC cooperates with these equipment to provide information necessary for operation. It shall be possible to smoothly control drive without any problems including memory and transfer.

  The image forming unit 11 is a unit for forming an image based on image information of a document. This embodiment is called a tandem system, and an image forming unit 11Y that forms a yellow (Y) image, an image forming unit 11M that forms a magenta (M) image, and an image forming unit that forms a cyan (C) image. 11C, image forming units 11K that form black (K) images are arranged in the image forming apparatus 20 in order from the top to the bottom in the vertical direction.

  Since the image forming units 11Y, 11M, 11C, and 11K constituting the image forming unit 11 perform the same operation except for the color of the toner used, the image forming unit 11Y that forms a yellow (Y) image is used here. Detailed description will be made with only the symbols attached.

  For example, the image forming unit 11Y uniformly includes a photosensitive drum (also referred to as a photosensitive member) 5Y and a photosensitive drum 5Y that rotate in an image forming direction (for example, counterclockwise) set in advance by a driving source such as a motor. The charging means 6Y for charging the light, the exposure light EY for forming an electrostatic latent image on the photosensitive drum 5Y, which is converted into a signal based on the image information (also referred to as image data) of the original, and the electrostatic latent image formed on the photosensitive drum 5Y. Development means 7Y that visualizes the image as a toner image, transfer separation means 8Y (also referred to as primary transfer means) that transfers the toner image formed on the photosensitive drum 5Y to the intermediate transfer body 16, and the toner image that is intermediate transfer A cleaning means 9Y for scraping off toner, paper dust, and the like remaining on the photosensitive drum 5Y after being transferred to the body 16 is constituted.

  The toner images formed by the respective image forming units are sequentially transferred and superimposed on, for example, a belt-like intermediate transfer body 16 (also referred to as a transfer belt) that rotates clockwise.

  The toner images of the respective colors transferred to the intermediate transfer body 16 are imparted to the transfer paper P with a charge opposite in polarity to the polarity of the toner image by the transfer roller 8 as the contact transfer means 8 (also referred to as transfer separation means). Then, it is transferred from the intermediate transfer body 16 to the transfer paper P by electrostatic force.

  The transfer paper P onto which the toner image has been transferred is melt-fixed (fixed) in the process of passing through the fixing device 10, and the transfer paper P on which the color image with Y, M, C, and K toners is formed Thereafter, the paper is discharged to the paper discharge tray 3.

  As in the present embodiment, an image forming apparatus using an intermediate transfer member can superimpose toner images formed by the respective image forming units on the intermediate transfer member. Widely used. The intermediate transfer member is not limited to the transfer belt as long as it can transfer the toner image formed by the image forming unit, and may be a photosensitive drum.

  In this embodiment, the transfer separating unit 8 is configured as a transfer roller 8 by a contact transfer method, and is disposed at a transfer position facing the intermediate transfer member 16, and a toner image formed on the intermediate transfer member 16. Is a means for applying a charge having a polarity opposite to the polarity of the toner image to the transfer paper P and transferring it with electrostatic force.

  Note that 8Y, 8M, 8C, and 8K (symbols are attached only to 8Y) are used to transfer the toner images formed by the image forming units 11Y, 11M, 11C, and 11K to the intermediate transfer member 16. It is a transfer separation means used.

  The cleaning unit 9 removes toner, paper dust, and the like remaining on the intermediate transfer member 16, and is configured by a blade, a brush roller, or the like. 9Y, 9M, 9C, and 9K (symbols are attached only to 9Y) are cleaning units that are used to clean the photosensitive drums of the image forming units 11Y, 11M, 11C, and 11K with the same configuration.

  Although not shown, the fixing device 10 includes, for example, a heating roller including a heater, a pressure roller, and the like. The toner image transferred to the transfer paper P is heated (for example, about 200 ° C.), pressure, and the like. It is a means for melting and fixing (fixing).

  The image reading unit 13 includes a reading optical system including a light source LT, a mirror group MR, an imaging lens LZ, and the like, and a reading device ES including an electric circuit including a CCD (solid-state imaging device).

  The reading device ES reads image information of a document placed on a platen glass (not shown) provided on the upper portion of the housing 1 or a document conveyed to a reading position by the automatic document feeder 30 and digitally reads the image information. The image data is stored in a storage means provided in the control means EC.

  Further, when the document conveyed by the ADF 30 is read by the image reading unit 13, the light source LT irradiates the document conveyed to the reading position, and the reflected light from the document is reflected by the imaging lens LZ via the mirror group MR. An image is formed on the CCD surface of the reading device ES, and image information output from the CCD is stored as image data.

  The paper supply / discharge means 14 is configured as a paper supply cassette 12 and a paper supply / discharge conveyance device (transfer paper conveyance means) comprising a motor as a drive source and a plurality of rollers.

  The paper feed cassette 12 includes, for example, a cassette 12a that stores special transfer paper, a cassette 12b that stores plain paper, and the like.

  The paper supply / discharge conveyance device as the paper supply / discharge means 14 selects a special transfer paper or plain paper according to an instruction from the control means EC, and then rotates a motor as a drive source to thereby provide a plurality of roller groups, etc. , And is fed to the intermediate transfer member 16 from the paper feed cassette 12 at an appropriate timing. After the toner image is melted and fixed (fixed) by the fixing device 10 and an image is formed, the paper discharge tray 3 is discharged and conveyed.

  The intermediate transfer member 16 is also called a transfer belt, and is composed of a belt-like object stretched around a plurality of rollers. In the present embodiment, the intermediate transfer member 16 is rotated clockwise by a drive source such as a motor (not shown). It is designed to rotate.

  When using an intermediate transfer member, the electrical characteristics (volume resistivity, surface resistivity, etc.), thickness, structure (for example, the number of layers such as single layer, two layers, three layers, etc.), material, material, etc. It is desirable to select and use various appropriate ones according to image forming conditions.

  The entire ADF 30 is covered with an ADF casing 31, and the ADF 30 is provided with a document table 32 and a paper discharge unit 33 outside the ADF casing 31.

  On the document placement table 32, a plurality of documents WP with the document surface (front surface) of the first page at the top is placed. The placed document WP is conveyed to a reading position by a document conveying device including a plurality of rollers and the like, read by a reading device ES, and discharged to a paper discharge unit 33.

  The document conveying device is operated in conjunction with the control means EC of the image forming apparatus 20 by a drive control circuit (not shown).

  The circuit configuration of the image forming apparatus according to the present invention will be briefly described with reference to FIG. In the present embodiment, the case where the image forming apparatus is a copying machine as described above will be described.

  Reference numeral 100 denotes a configuration of various means and circuits of the entire image forming apparatus 20. Reference numeral 110 denotes a CPU that controls the entire image forming apparatus, and stores various mode programs for controlling the image forming apparatus 20, data necessary for executing the programs, and the like.

  An information control circuit 120, an image processing circuit 140, a drive control circuit 150, a power supply circuit 400, and the like are connected to the CPU 110. These circuits constitute the control means EC shown in FIG. 1 so that the entire image forming apparatus 20 can be controlled.

  The information control circuit 120 is connected to the external information device 500 via an interface (I / F) 130 according to an instruction from the CPU 110 to set image information such as characters and images, density and magnification necessary for image formation, and the like. Information is input and stored in the storage means 160. The setting information stored in the storage unit 160 is output to the image processing circuit 140, the drive control circuit 150, the display unit 300, or the like.

  The information control circuit 120 is necessary for the operation of circuits and various means including the image processing circuit 140 and the drive control circuit 150 in addition to JOB information including image information and setting information input from the external information device 500. For example, information related to the instruction information, for example, various information input by the operation input unit 200, information indicating an operation state output during operation of various units of the apparatus, and the like are determined so as not to hinder the operation of the image forming apparatus. It has a function of smoothly and appropriately transmitting information to each circuit and various means of the image forming apparatus.

  The external information device 500 is mainly a computer or an Internet server, but in some cases, it can output other image forming apparatuses on a local area network (LAN), a digital camera, or measured information. Information equipment such as a measuring device is assumed.

  In the present embodiment, the information control circuit 120, which is also a color misregistration correction unit, performs color misregistration correction control when the color misregistration correction mode is selected. The details will be described later. For example, when power is supplied to the image forming apparatus, a reference pattern formed on the intermediate transfer body 16 at a predetermined printing rate is measured by a sensor (sensor means) including a CCD (solid-state imaging device) (not shown). The deviation amount calculating means obtains the difference (deviation amount) between the detected signal of the reference pattern measured and detected and the preset reference signal for each color, and the deviation amount for each color is determined at a predetermined printing rate. The storage unit 160 stores the correction amount for each color.

  On the other hand, when the image forming apparatus is regularly inspected or when the image forming unit 11 or the like is replaced for some reason, a correction value (printing value) related to the printing rate is obtained so that an appropriate image forming condition is obtained each time. Color misregistration correction control for updating the ratio correction value is also performed.

  When obtaining a correction value related to the printing rate, a reference pattern is formed on the intermediate transfer body 16 so as to obtain a predetermined printing rate, and the detection signal measured and detected and the reference signal for each color as described above are used. By calculating the difference (deviation amount), setting this deviation amount as a correction value corresponding to a predetermined printing rate, and determining the relationship between the predetermined printing rate and the correction value for a plurality of printing rates, for example, the printing rate and the correction The relationship of values is made into a matrix and stored as a printing rate correction value in the storage unit 160 which is also a printing rate correction value storage unit.

  Then, the image processing circuit 140 serving as a printing rate calculation unit obtains a printing rate for the transfer sheet from the image data for each page when forming an image based on the image data, and the amount of misregistration for each color at the above-described predetermined printing rate ( Color to be corrected by obtaining a correction value related to the printing rate and a ratio (coefficient) of the distance between the target image forming unit and the image forming unit of the target color. A deviation correction amount is calculated. Corresponding to the obtained color misregistration correction amount, for example, the image forming unit having the function of adjusting the writing timing adjusts the writing timing when the photosensitive drum is exposed by laser light or the like based on the image data. Therefore, highly accurate color misregistration correction control is performed.

  It should be noted that the printing rate refers to a printed image (letters, numbers, symbols, etc.) for an image forming area (area) in units of one page formed on one side of a predetermined paper, for example, A4 size transfer paper. This is the percentage of the total.

  The interface (I / F) 130 is information exchange means, and is configured to be connected to the above-described computer, other image forming apparatuses, and external information equipment 500 such as an Internet server via various networks.

  The operation input unit 200 is an input device provided on the control panel CP of the image forming apparatus 20. The above-described liquid crystal display device DP, keyboard KB, start button SK, etc., which are touch panel type display means, are assumed.

  For example, by operating the keyboard KB, the number and type of output materials (also referred to as transfer paper) (for example, index paper, thick paper, plain paper, thin paper, recycled paper, OHP sheet, etc.), enlargement / reduction, etc. Setting information such as magnification and output image density can be input.

  In some cases, the operation input unit 200 sets various operation modes of the image forming apparatus 20, such as a color mode, a monochrome mode, a single-side mode, and a double-side mode, which are selected and set when performing a copy operation. It becomes an input means for doing.

  In particular, in the present embodiment, it is possible to select and set whether or not to execute the color misregistration correction mode by operating the control panel CP as the operation input unit 200.

  The display means 300 is configured by the above-described liquid crystal display device, or a display device DP in which a touch panel or the like is incorporated in a liquid crystal display unit.

  The display means 300 includes an operation procedure when inputting information with the operation input means 200, a list display of various information, a display of information stored in the storage means 160, a status display during operation of the image forming apparatus 20, and a warning. Display etc. are displayed.

  The image processing circuit 140 digitally converts the image information of the document read by the image reading unit 13 in accordance with an instruction from the CPU 110 and stores the image information in the storage unit 160 as image data or the image data stored in the storage unit 160. This is a circuit for converting data, signals and the like suitable for the image forming method of the image forming means 11 when the image forming means 11 forms an image.

  In particular, in the present embodiment, the image processing circuit 140 performs color misregistration correction control as a printing rate calculation unit. For example, when the image processing circuit 140 performs image formation in units of one page on one side of a predetermined sheet, for example, image information of a document. Based on the above, a printing rate calculation process for obtaining a printing rate in units of one page for a predetermined sheet from the image data stored in the storage unit 160 is performed.

  The drive control circuit 150 cooperates with the image processing circuit 140 in response to an instruction from the CPU 110, and the contact transfer unit 8, the fixing unit 10, the image forming unit 11, the image reading unit 13, the paper supply / discharge unit 14, the ADF 30, and the like. Is a circuit for operating an image forming operation at an appropriate timing based on a preset operation mode.

  Since the contact transfer unit 8, the fixing unit 10, the image forming unit 11, the image reading unit 13, the paper supply / discharge unit 14, and the ADF 30 have been described above, the items related to the circuit will be briefly described here.

  The image reading unit 13 is operated by the drive control circuit 150 and reads the image information of the document conveyed to the reading position by the reading device ES. The read image information is converted into digital image data by the image processing circuit 140, for example. And is stored in the storage means 160.

  The image forming unit 11 is operated by the drive control circuit 150 according to an instruction from the CPU 110, and the image processing circuit 140 is based on the image data stored in the storage unit 160 in each of the image forming units 11Y, 11M, 11C, and 11K. Each color toner image is formed on an image carrier (photosensitive drum 5), and the formed toner image is transferred to the intermediate transfer member 16.

  The contact transfer means (transfer roller) 8 is operated by a drive control circuit 150 and applies an electric charge having a polarity opposite to the polarity of the toner image superimposed on the intermediate transfer body 16 to transfer the toner image onto the transfer paper P. Is supposed to do. 8Y, 8M, 8C, and 8K are image forming units 11Y, 11M, 11C, and 11K, and perform an operation of transferring the toner image formed on the photosensitive drum 5 to the intermediate transfer body 16.

  The fixing device 10 is configured to melt and fix (fix) the toner image transferred onto the transfer paper P by heat and pressure or the like according to an instruction from the drive control circuit 150.

  The paper supply / discharge unit 14 is operated in cooperation with the contact transfer unit 8, the fixing device 10, the image forming unit 11, and the like by the drive control circuit 150 based on a program preset in the CPU 110, and transfers the transfer paper P. Performs smooth and timely transport operation.

  As shown in FIG. 1, the automatic document feeder (ADF) 30 is a device that automatically conveys documents placed on a document placing table 32 to a reading position one by one by a document conveying device. The CPU 110 operates in cooperation with the drive control circuit 150 according to the instruction of the CPU 110.

  The storage unit 160 stores JOB information including image data necessary for forming an image, setting conditions for controlling the image forming apparatus 20, JOB data related to the jOB information, programs for various setting modes, and the like. Information is memorized.

  In the present embodiment, as described above, the amount of deviation (correction amount) for each color at a predetermined printing rate, which is measured and calculated by the information control circuit 120, and the correction value (printing rate correction value) related to the printing rate. Alternatively, the printing rate in units of one page calculated by the image processing circuit 140 is further stored. Of course, it goes without saying that storage means may be provided separately depending on the type of information to be stored.

  When a power switch (not shown) is turned on by a user's operation, the power supply circuit 400 is appropriately energized from the power source to the entire image forming apparatus. When the power switch is shut off, the power supply is shut off. It has become so.

  Even when the power switch is turned on (ON), for example, in the power saving mode for setting the image forming apparatus in a standby state, the CPU 110 instructs the memory 110 to temporarily store the memory contents. Only necessary energization is continued, and other energization such as a heater of the fixing device can be cut off.

  In addition, even when the power is turned off (OFF) by the power switch, the CPU 110 and the like are operated instead of shutting off all the power as in the power saving mode in which the image forming apparatus is in a standby state. The image forming operation or the like may be started quickly in response to, for example, a case where the power supply necessary for this is performed and the power switch is turned on (ON) or image information is input via the LAN.

  Here, the image forming operation in the present embodiment will be briefly described with reference to FIGS.

  In the single-side mode in which an image is formed on one side of the transfer paper P, the drive control circuit 150 is actuated by an instruction from the CPU 110 and image data read by the image reading unit 13 shown in FIG. A yellow (Y) toner image is formed by the screen on the basis of the image data stored in the storage means, and is transferred to the intermediate transfer member 16 by the operation of the well-known electrophotographic image forming unit 11Y. .

  Similarly, magenta (M), cyan (C), and black (K) toner images are formed by the image forming units 11M, 11C, and 11K, and transferred to the intermediate transfer member 16.

  On the other hand, one sheet of transfer paper P taken out from the paper feed cassette 12 is temporarily stopped at the position of the roller R2 provided in the vicinity of the intermediate transfer body 16 from the X1 direction by the paper supply / discharge means 14, and then at an appropriate timing. Thus, the transfer paper P is conveyed in the direction of the intermediate transfer body 16 by the roller R2.

  When the transfer sheet P approaches the intermediate transfer body 16, the transfer roller 8 operates in a direction in contact with the intermediate transfer body 16, and thereafter, at the transfer position where the intermediate transfer body 16 and the transfer roller 8 face each other, the intermediate transfer body 16. When the transfer paper P passes between the transfer roller 8 and the transfer roller 8, a charge having a polarity opposite to the polarity of the toner image is applied, and the electrostatic force causes the toner image on the intermediate transfer member 16 to be transferred to the transfer paper P. Is transferred to the second surface (surface).

  The transfer paper P onto which the toner image has been transferred passes through the fixing device 10 to melt and fix the toner image, is conveyed in the X4 direction, and is discharged onto the paper discharge tray 3 shown in FIG. When an image is formed on one side of a plurality of transfer sheets P, this operation is repeated.

  When performing double-sided copying (double-sided mode), first, the CPU 110 of the controller EC causes the drive control circuit 150 to perform an operation of forming an image on one side of the transfer paper P described above.

  Then, the transfer paper P on which an image is formed on one side passes through the fixing device 10 and is then conveyed in the direction of the paper discharge tray 3 (arrow X4 direction), and the rear end of the transfer paper P passes through a pair of rollers HR. The control means EC stops the rotation of the roller HR just before the operation.

  Subsequently, the roller HR is rotated in the reverse direction to be conveyed in the X3 direction, the front and back of the transfer sheet are reversed, and conveyed to the conveyance path A through the conveyance paths C and D.

  The transfer paper P that has entered the transport path A again is temporarily stopped at the position of the roller R2, and then transported in the direction of the intermediate transfer body 16 at an appropriate timing, and formed on the first surface (back surface) by the image forming means 11. The toner image is transferred from the intermediate transfer body 16 to the transfer paper P by the transfer roller 8 as in the case of single-sided copying.

  Then, after passing through the fixing device 10, the transfer sheet P is conveyed in the X4 direction toward the sheet discharge tray 3 and discharged without causing the roller HR to stop. Finish copying. Therefore, this process is repeated when a plurality of double-sided copies are made.

  In general, the transfer path of the transfer paper is often provided with a guide member for appropriately transferring the transfer sheet, a switching means for switching the transfer path, and the like. In order to simplify the explanation, illustration and explanation of these members are omitted.

  Next, the operation of color misregistration correction control will be described. In the present embodiment, color misregistration correction control is performed when the color misregistration correction mode is selected.

  In the color misregistration correction control, details will be described later, but first, the CPU 110 of the control circuit EC operates the image forming units 11Y, 11M, 11C, and 11K based on the color misregistration correction control program stored in advance to perform main scanning. A preset reference pattern is formed so that the amount of color misregistration in the direction and the sub-scanning direction can be detected.

  The reference pattern is formed as a toner image of each color of Y, M, C, and K. For example, the image is formed in parallel with the conveyance direction of the intermediate transfer member (transfer belt) 16 and in the width direction of the intermediate transfer member 16. Transfer to both ends of the area.

  Next, the reference pattern of each color formed on the rotating intermediate transfer body 16 is detected and measured by a sensor means (not shown) including a fixed CCD (solid-state imaging device) or the like. A shift amount between the reference signal and the reference pattern detection signal for each color is calculated in the scanning direction and the sub-scanning direction.

  Regarding the amount of misalignment in the main scanning direction, when the photosensitive drum of each color is exposed based on the image data, the writing timing in the main scanning direction is adjusted by an amount corresponding to the amount of misalignment according to an instruction from the information processing circuit 120. It is corrected by.

  Next, with respect to the amount of deviation in the sub-scanning direction, in order to perform correction that is considered to be caused by the amount of toner, that is, the printing rate, the printing rate is calculated from image information in units of one page when forming an image. The printing rate correction value corresponding to the obtained printing rate is obtained from the relationship between the correction value (printing rate correction value) relating to the printing rate that is obtained and stored in advance, and the above-described measurement is performed using this printing rate correction value. Correction is performed for the shift amount for each color.

  Further, in the present embodiment, in consideration of correction of mechanical and electrical error factors related to toner image transfer, image formation of a color to be corrected with respect to an image forming unit of a reference color set in advance is performed. By performing correction according to the ratio (coefficient) of the distance to the unit, more accurate color misregistration correction is performed.

  It should be noted that when the amount of misregistration (color misregistration) is indicated, it is easy to understand if the misregistration amount is converted into a length (mm) and expressed as, for example, a misalignment of 0.05 mm or 50 μm. Actually, when correcting the deviation amount, the timing of writing the image data by laser light or the like when exposing the image data to the photosensitive drum of each color is adjusted, so the deviation amount is set in units of time. It is preferable to calculate and store.

  A basic pattern diagram according to color misregistration correction control of the present invention will be described.

  FIG. 3 is a schematic diagram showing a state in which the reference patterns BP1 and BP2 are formed on the transfer belt 16 that is an intermediate transfer member. PS indicates a predetermined paper, for example, an A4 size paper area, and PA indicates a paper area in consideration of mechanical or electrical error factors so that an image can be reliably formed on the paper area PS. An image forming area provided with a small margin inside the PS is shown.

  BP indicates a reference pattern, and the reference patterns BP1 and BP2 are the same pattern having the same shape. In the reference pattern BP, “F” -shaped unit patterns are arranged in the same direction as the transfer belt 16 indicated by an arrow from the top, for example, four by four, K1, K2, K3, K4 (particularly reference numerals are attached). 16), a total of 16 colors of Y, M, C, and K are formed by repeating equally. The reference pattern BP1 is formed as a toner image on a straight line in the order of K, C, M, and Y from the top, and at both ends in the width direction of the image area PA in the direction orthogonal to the conveyance direction of the transfer belt 16 indicated by an arrow. And BP2 are arranged.

  S is a sensor means, and S1 and S2 are fixedly provided opposite to the reference patterns BP1 and BP2, respectively. Each unit pattern of “F” shape is measured one by one, for example, the passing time is detected. The detection signal for doing this is output.

  The reference pattern BP is used to detect color misregistration in the image forming apparatus and may be any color pattern that can detect color misregistration. The shape and number of the reference patterns shown in the present embodiment, and the arrangement of each color It is not limited to such as.

  The sensor means S is also the same. In the present embodiment, for the sake of simplicity of explanation, an example in which two sensors comprising CCDs are provided is shown. When color deviation is detected by the reference pattern, or image recognition is used, for example, by recognizing an image of a “F” -shaped unit pattern and simultaneously detecting a deviation in the main scanning direction and the sub-scanning direction with respect to the reference. In the case of detecting the color misregistration amount, it is preferable to use a line sensor including a plurality of CCDs.

  Next, a method for calculating the color misregistration amount and the correction amount will be described with reference to FIG.

  FIG. 4A shows the relationship between the detection signal from the sensor S and the “f” -shaped unit pattern of the reference pattern BP. SP indicates a straight line passing through the center of the sensor S, and indicates a relationship of the detection position with the “F” -shaped unit pattern. Each sensor on the “F” -shaped unit pattern (also simply referred to as a unit pattern). S schematically shows a detection unit by the sensor S. BS represents a preset reference signal, and DS represents a detection signal from the sensor S.

  The “F” shape of the unit pattern is composed of a horizontal line part and a hatched part. Although the details will be described later, the horizontal line part is for detecting a shift amount in the sub-scanning direction, and the hatched part is in the main scanning direction. This is for detecting the amount of deviation.

  A description will be given of the measurement of the deviation amount based on the reference pattern.

  First, when detecting the amount of deviation between the main scanning direction and the sub-scanning direction, the reference pattern BP formed on the transfer belt 16 is fixed by the fixed sensor S when the transfer belt 16 is conveyed in the direction indicated by the arrow. Therefore, as shown in FIG. 4A, the sensor S relatively measures the “F” -shaped unit pattern along the straight line SP. A detection signal DS having a signal portion indicating that detection has been performed at two locations of the horizontal line portion and the oblique line portion of the unit pattern is output.

  Therefore, when the reference signal BS and the detection signal DS in FIG. 4A are compared, the time interval LD of the reference signal BS and the time interval LD of the detection signal DS are the same time LD, which is different from the time interval LD. It turns out that there is no match. It can also be seen that the detection signal DS is detected with a delay of ΔX time with respect to the reference signal BS.

  In other words, the time interval LD indicates the time when the sensor S detects the horizontal line portion and the oblique line portion of the unit pattern on the straight line SP. Therefore, if the time interval LD changes between the reference signal BS and the detection signal DS, the main scan is set in advance. Since the unit pattern is formed with a deviation from the writing start timing in the direction, this means that a deviation has occurred in the main scanning direction, and the occurrence of ΔX time has caused a deviation in the sub-scanning direction. Means that.

  Therefore, as a result, in this embodiment, since there is no difference in the time interval (LD), it can be seen that there is no deviation in the main scanning direction, and since a time difference of ΔX has occurred, the sub-scanning direction It can be seen that a deviation amount corresponding to this ΔX occurs.

  The amount of deviation in time units can be converted into the amount of deviation in length units by the conveyance speed (mm / s) of the transfer belt 16 × ΔX (S: seconds).

  In this way, the amount of deviation can be obtained by comparing the reference signal BS of the target color with the detection signal DS of the target color.

  Note that the color misregistration correction in the main scanning direction may be performed by calculating a misregistration amount with respect to the reference signal BS and correcting the writing timing in the main scanning direction described above, for example, by a time corresponding to the misregistration amount. Therefore, in the present embodiment, the color misregistration correction in the sub-scanning direction according to the present invention, which is characterized in how to obtain the correction amount, will be particularly described.

  Next, how to determine the amount of deviation of each color in the sub-scanning direction will be described.

  FIG. 4B shows the case where four “f” -shaped unit patterns of each color of the reference pattern BP are numbered 1 to 4 in order from the head of each color, and the detection signal DS and reference signal BS of the same number for each color. Is a contrast. BL1 to BL4 indicate reference lines of the reference signal BS, and the shift amount of each color can be detected as a difference from the detection signal DS of each color with respect to the reference lines BL1 to BL4.

  First, in order to calculate the shift amount between the colors, a shift amount with respect to the reference signal BS (amount corresponding to the aforementioned ΔX) is obtained. In the present embodiment, the shift amount between the reference signal BS and the detection signal DS is obtained for each of Nos. 1 to 4 of each color, and averaged to obtain the shift amounts ΔXK, ΔXC, ΔXM, and ΔXY of the respective colors. did.

  As shown in FIG. 3, for example, when the reference color is K (black), when obtaining the amount of deviation between the reference color K (black) and other colors, the interval between the colors is When the reference interval is set to BL at equal intervals, the difference LKC, K (interval difference between K (black) and C (cyan) can be obtained by using the above-described shift amounts ΔXK, ΔXC, ΔXM, ΔXY of the respective colors. The distance difference LKM between (black) and M (magenta), the distance difference LKM between (black) and M (magenta), and the distance difference LKY between K (black) and Y (Yetto) are LKC = BL + (ΔXC), LKM = 2 × BL + (ΔXM), LKY = 3 × BL + (ΔXY) can be easily calculated.

  As another calculation method, when there are four unit patterns as in the present embodiment, LKC, LKM, and LKY corresponding to the first to fourth of the reference K (black) are measured four times. Thus, the obtained values may be averaged and calculated as the reference intervals LKC, LKM, LKY.

  Next, correction values related to the printing rate will be described.

  FIG. 5 shows the relationship between the print rate and the print position shift amount (also referred to as the shift amount related to the print rate) where the vertical axis is the shift amount (μm) and the horizontal axis is the print rate (%). It is. In this table, when the reference sheet is, for example, A4 sheet as shown in FIG. 3, the number of reference patterns BP to be formed and the printing rate is calculated in advance. A reference pattern is formed on the transfer belt 16 in accordance with the calculated printing rate, and the result is obtained by repeating the operation of measuring the deviation amount by the measurement method described above for the formed reference pattern BP. .

  In the present embodiment, for example, when the printing rate is changed to 30%, 60%, and 100%, it has been obtained that it is preferable to correct the deviation by about 15 μm, 42 μm, and 55 μm. Therefore, this result is stored in the storage unit 160 with the printing rate and the correction value as a matrix.

  The correction value related to the printing rate shows the amount of deviation that differs depending on the toner used, the transfer belt, the photosensitive drum, etc., so the correction value related to the printing rate obtained as a result of measurement with the image forming device used is used. There is a need to.

Next, a method for calculating the color misregistration correction value will be described.
(1) First, the deviation amounts ΔXK, ΔXC, ΔXM, and ΔXY of each color in the sub-scanning direction are obtained by the method described above. For example, when the sensor S measures the above-described reference pattern BP, a black shift amount ΔXK = 10 μm, a cyan shift amount ΔXC = 40 μm, a magenta shift amount ΔXM = 70 μm, and a yellow shift amount ΔXY = 110 μm are obtained. To do.
(2) Next, a cyan shift amount ΔKC, a magenta shift amount ΔKM, and a yellow shift amount ΔKY with respect to the reference color K (black) when the reference color is K (black) are obtained. Since the shift amounts ΔXK, ΔXC, ΔXM, and ΔXY of each color in the sub-scanning direction are obtained, ΔKC = ΔXC−ΔXK = 30 μm, ΔKM = ΔXM−ΔXK = 60 μm, and ΔKY = ΔXY−ΔXK = 100 μm are obtained.
(3) Next, regarding the image data to be printed, the printing rate of the image data per page is obtained, and a correction value related to the printing rate is obtained. For example, when the image processing circuit 140 obtains the printing rate of the image data of one page to be printed and the printing rate is calculated to be 100% in a state where an image is printed on A4 paper without a margin, 5 indicates that when the printing rate is 100%, the amount of deviation is 55 μm. Therefore, 55 μm is obtained as a correction value when the printing rate is 100%.
(4) A final cyan correction amount ΔC, a magenta correction amount ΔM, and a yellow correction amount ΔY with respect to the reference color K (black) are obtained. The correction value related to the obtained printing rate is distributed by the ratio of the distance from the reference color, and is added to the deviation amounts ΔKC, ΔKM, and ΔKY with respect to the reference color K (black).

  As for the ratio of the distance from the reference color, as shown in FIG. 1, the image forming apparatus in the present embodiment is called a tandem type, and Y, M, C, and K toner images are obtained from the upper side. The image forming units to be formed are arranged at equal intervals at three intervals, and as is clear from the relationship between LKC, LKM, and LKY in FIG. Thus, 2/3 for the color M and 1/3 for the color C, and the correction amounts ΔY, ΔM, and ΔC are obtained as follows.

ΔY = −ΔKY− (55) × 3/3 = −100−55 = −155 μm
ΔM = −ΔKM− (55) × 2/3 = −60−37 = −97 μm
ΔC = −ΔKC− (55) × 1/3 = −30−18 = −48 μm
When the correction amounts ΔY, ΔM, and ΔC for each color are obtained, the transfer belt conveyance speed (mm / S) at that time can be converted into time, and the writing start timing corresponding to the time can be calculated. By adjusting the writing timing of the image data for each color according to the written writing timing, the color misregistration for each color can be corrected.

  In the present embodiment, the sign (−) of the correction amounts ΔY, ΔM, ΔC, etc. means that the correction is made in the direction of advancing the writing timing when color misregistration correction is performed, and (+) is. This means that the correction is made in the direction of slowing down.

  Further, in the present embodiment, in order to simplify the explanation, when it is necessary to correct the deviation in the sub-scanning direction in the direction of advancing the writing timing, that is, as shown in FIG. Although the case where the deviation occurs in a state where the detection signal DS is detected with a delay of ΔX time with respect to the signal BS has been described as an example, there may be a deviation that needs to be corrected in the direction of delaying the writing timing. An appropriate correction value or the like needs to be obtained after setting in advance in which direction the signs (−) and (+) such as the shift amount and the correction amount are added.

  As described above, the color misregistration correction control according to the present invention has been described. However, with respect to the color misregistration, correction control may be performed so that other colors do not cause color misregistration with respect to the reference color K (black). All may be corrected with respect to the reference signal BS, but in this embodiment, in order to make the color misregistration correction control easier, for example, a reference color K (black) is set, The color misregistration amount of other colors is corrected with respect to the color K (black).

  Therefore, the detected color misregistration amount can be corrected with respect to the reference color K (black) by using the ratio between the correction value related to the printing rate and the distance between the image forming units. The method for obtaining the amount of misalignment of each color is not limited to this.

  Note that, by using the color misregistration correction control in the present embodiment, it is possible to correct all the misregistration amounts for each color with respect to the reference signal BS. In this case, after obtaining the color misregistration amount of the reference color K (black) with respect to the reference signal BS and correcting the color misregistration amount of the reference color K (black) with respect to the reference signal BS by adjusting the writing timing as described above. The color misregistration correction control in this embodiment may be executed.

  Next, the procedure of color misregistration correction control will be described with reference to FIG. As a premise, the image forming apparatus is a copying machine, and will be described in detail with reference to FIGS. 1 to 5 as necessary.

(ST1)
In this step, it is determined whether the image forming apparatus is powered on. When the power is turned on, for example, when the CPU 110 of the control circuit EC activates the information control circuit 120 and confirms that the power is on, the process proceeds to ST2, and when the power is not confirmed, the determination in ST1 is repeated.

(ST2)
This is a step of determining whether or not a periodic inspection is performed. When the power is turned on, for example, the information control circuit 120 determines whether or not the total number of copies exceeds the preset number to instruct periodic inspection. If periodic inspection is to be performed, the process proceeds to ST3, and if it is determined that the periodic inspection is not performed, the process proceeds to ST5.

(ST3)
This is a step of calculating a correction value related to the printing rate. When periodic inspection work, unit replacement work, etc. are performed by a service person etc., the state of the image forming unit etc. of the image forming apparatus changes from the image forming conditions etc. that have been adjusted so far. Therefore, the CPU 110 executes a printing rate correction value calculation program stored in advance.

  When the printing rate correction value calculation program is executed, a reference pattern BP corresponding to a plurality of printing rates set in advance is sequentially formed on the transfer belt 16, and the shift amount is sequentially detected by the sensor S, which can be repeated. Then, measurement is performed to obtain the relationship between the printing rate and the amount of deviation. Then, a new correction value related to the printing rate is obtained and stored in the storage unit 160. When the update of the correction value related to the printing rate is executed in this way, the process proceeds to ST4.

(ST4)
This is a step of measuring and detecting the amount of deviation of each color. This step is always executed when the power is turned on even in the normal state. Accordingly, only a deviation amount (color deviation amount) with respect to a preset printing rate is measured, the measured deviation amount is stored in the storage means 160, and printing based on image data can be executed immediately thereafter. Yes.

  In the present embodiment, the amount of color misregistration obtained in this step is the reference for the amount of color misregistration of the image forming apparatus from when the power of the image forming apparatus is turned on (turned on) to when the power is turned off (shut off). Value. Accordingly, with respect to other printing ratios, the color misregistration amount is corrected based on the correction value relating to the printing ratio obtained in ST3.

  In addition, when the deviation amount in the previous measurement is updated by the current deviation amount measured in this step and stored in the storage unit 160, for example, the information control circuit 120 compares the current deviation amount with the previous deviation amount. If the change range of the preset shift amount is significantly exceeded, an abnormality warning regarding the color shift amount may be issued, or the print rate correction value calculated in ST3 may be calculated again. good.

(ST5)
This is a step of determining whether or not a unit relating to image formation has been replaced. For example, if the entire image forming unit for image formation or the components of the image forming unit is replaced for some reason, even though it is not time for periodic inspections, the image forming conditions that have been adjusted so far If these units and parts are replaced, the process proceeds to ST3 in order to calculate the printing rate correction value again.

  In addition, when the unit is not regularly checked and the unit is not replaced, it indicates that the image forming apparatus application is turned on in the normal state, so that the amount of misregistration of each color in the normal state is detected. , Go to ST4.

(ST6)
This is a step of determining whether or not a print start based on image data has been executed. For example, if the information that the start button SK is pressed or the image data is input to the storage means 160 via the information control circuit 120 via a network such as a LAN and the stored information is obtained, the process proceeds to ST7 and starts. If information such as the press of the button SK cannot be obtained, the process waits until the print start state is reached in ST6.

(ST7)
In this step, image data is input based on the image information of the document and stored in the storage means. For example, when the start button SK is pressed, the automatic document feeder (ADF) 30 is activated, or the document placed on the platen glass is read, and via the information control circuit 120 via a network such as a LAN. When the image data is input and stored in the storage means 160, the process proceeds to ST8.

(ST8)
This is a step of calculating a printing rate. One page of image data to be printed by the image processing circuit 140 is read from the storage means 160, and the printing rate is calculated from the data amount (printing amount) of the image data with respect to the preset image area (area) of the transfer paper to be printed. It is a step to do.

  The printing rate is calculated for each page of the image data to be printed in units of one page and stored in the storage unit 160. Note that the printing rate calculated last time may be updated and stored with the printing rate calculated this time.

(ST9)
This is a step of calculating a correction amount for the color misregistration amount of each color. Since the calculation of the correction amount for the color misregistration amount of each color has already been described in detail in “Calculation method of color misregistration correction value”, the detailed description is omitted here, but the “printing rate in units of one page obtained in ST8”. The correction value corresponding to the printing rate is obtained from the “correction value relating to the printing rate” obtained in advance in ST3, and the ratio of the distance of the image forming unit of the other color to the reference color K (black) is taken into consideration. When the correction amount for the “deviation amount of each color” obtained in ST4 is calculated, the process proceeds to ST10.

(ST10)
This is a step of performing an image forming operation. The amount of color misregistration of each color is converted and corrected by, for example, a writing timing of image data with respect to the photosensitive drum by a laser beam or the like by the correction amount of one page obtained in ST9. When the image forming operation of the image data for one page is executed at the corrected writing timing, the process proceeds to ST11.

(ST11)
In this step, it is determined whether or not predetermined printing has been completed. If printing according to the number of printed sheets or the number of copies in single-sided printing or double-sided printing set in advance on the control panel CP or the like is completed, the process proceeds to ST12, and if not completed, the process returns to ST8 to continue the image forming operation. .

(ST12)
In this step, it is determined whether or not the image forming apparatus is powered off. When the power supply is cut off, for example, the CPU 110 terminates all operations of the image forming apparatus with the energy of the backup power supply. When the power supply is not cut off, the CPU 110 returns to ST6 and waits for the start of printing the next image data. It is like that.

  As described above, in the embodiment of the present invention, when the amount of color misregistration for each color is corrected, when the image information is printed by the image forming apparatus, the printing rate for each page of the image information to be printed is set. Since the print rate correction value stored in advance is read in accordance with the obtained print rate, and the detected shift amount for each color is corrected by the read print rate correction value, It has become possible to correct color misregistration that may occur due to the amount of toner, that is, a change in printing rate.

  In addition, color misregistration correction is performed in consideration of the distance of the image forming unit, using the distance between the image forming unit that forms an image of a reference color set in advance and the image forming unit that forms an image of each color as a coefficient. Thus, it is possible to perform correction by absorbing error factors such as mechanical and electrical timing for the transfer belt when transferring the toner image formed by the image forming means of each color.

  Further, since the color misregistration is corrected with respect to a preset reference color, the color misregistration correction control can be easily performed.

  In addition, the color misregistration correction value corresponding to each of the plurality of printing rates is stored in advance as the printing rate correction value, and the color misregistration amount for each color is obtained prior to image formation. Therefore, it is not necessary to provide a reference pattern for correcting color misregistration outside the image area of the transfer belt, and it is not necessary to increase the width of the transfer belt.

  In addition, since it is not necessary to obtain the amount of color misregistration every time an image based on the image information of the document is formed, the amount of toner for creating the reference pattern can be reduced, and there is no operation for obtaining the amount of color misregistration. The productivity of the image forming operation in the image forming apparatus can be improved.

  The present embodiment has been described by taking a copying machine as an example for the sake of simplicity. However, multiple images, that is, color images, are superimposed on an intermediate transfer member such as a transfer belt by superimposing toner images of respective colors. Needless to say, the image forming apparatus can be applied to an image forming apparatus such as a printer or a facsimile machine.

1 is a schematic view of an image forming apparatus according to the present invention. 1 is a block diagram showing a circuit configuration of an image forming apparatus according to the present invention. Basic pattern diagram according to color misregistration correction control of the present invention FIG. 6 is a schematic diagram of a detection signal according to color misregistration correction control of the present invention. FIG. 6 is a diagram illustrating a relationship between a printing rate and a correction value according to color misregistration correction control of the present invention. 6 is a flowchart illustrating a procedure of color misregistration correction control according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Case 2 Manual feed tray 3 Discharge tray 4 Roller 5 Photoconductor drum 6 Charging means 7 Developing means 8 Transfer separation means 9 Cleaning means 10 Fixing device 11 Image forming means 12 Paper feed cassette 13 Image reading means 14 Feeding / discharging means 16 Intermediate transfer member 20 Image forming device 30 Automatic document feeder

Claims (5)

A plurality of image forming means for forming images of different colors,
Each of the plurality of image forming units includes a photoreceptor.
Based on the image information, an image is formed on the photoreceptor for each color,
In an image forming apparatus for forming a multiple image on an intermediate transfer member,
Measuring a reference pattern formed on the intermediate transfer member by the image forming means;
A deviation amount calculating means for calculating a color deviation amount for each color;
A printing rate correction value storage means for preliminarily storing a color misregistration correction value corresponding to each of a plurality of printing rates as a printing rate correction value;
A printing rate calculation unit that calculates the printing rate of an image for each color from image information in units of one page on which an image is formed by the image forming unit;
When the image forming unit forms an image based on the image information of one page unit,
According to the printing rate correction value read from the printing rate correction value storage unit corresponding to the printing rate calculated by the printing rate calculation unit,
An image forming apparatus comprising: a color misregistration correcting unit that corrects the misregistration amount for each color calculated by the misregistration amount calculating unit. The color misregistration correction means includes
For image forming means for forming an image of a preset reference color,
A distance distance in the direction along the intermediate transfer body with an image forming unit that forms an image of each other color is provided as a coefficient.
By the printing rate correction value and the coefficient,
The image forming apparatus according to claim 1, wherein the shift amount for each color calculated by the shift amount calculation unit is corrected. The deviation amount calculating means includes:
Comprising a sensor for measuring the passage time of a reference pattern for each color formed on the intermediate transfer member;
A passing time for each color of the reference pattern detected by the sensor;
Compare with the preset reference time of each color,
While calculating the difference as the amount of deviation for each color,
Depending on the amount of deviation for each color,
The image forming apparatus according to claim 1, wherein an amount of misregistration of another color with respect to a preset reference color is calculated. The printing rate correction value storage means includes
4. The image forming apparatus according to claim 1, wherein a plurality of printing ratios and a plurality of color misregistration correction values are stored in advance as a matrix. The image forming unit includes:
Based on the shift amount for each color corrected by the color shift correction means,
5. The image forming apparatus according to claim 1, further comprising a writing timing adjustment unit that adjusts a writing timing of an exposure unit that writes the image information on a photosensitive member.

Images