JP2009205024A - Image forming apparatus, control method for image forming apparatus and control program for image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of appropriately adjusting an image. <P>SOLUTION: An image ratio showing a ratio of pixels to which toner is stuck to pixels to which toner is not stuck in each main scanning line is calculated. Each main scanning line extends in a subscanning direction in accordance with the image ratio. Since the image is formed on paper in such a way that its length in the subscanning direction is shortened as the image ratio is higher due to change in a friction coefficient between a photoreceptor and the paper, the pixel of each line is made to extend in accordance with the image ratio. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, an image forming apparatus control method, and an image forming apparatus control program, and more particularly to an image forming apparatus capable of appropriately adjusting an image, an image forming apparatus control method, and image formation. The present invention relates to a device control program.

  Electrophotographic image forming apparatuses (MFP (Multi Function Peripheral), printers, facsimile machines, copiers, etc.) include monochrome and color printing methods.

  As a typical example of a transfer unit (transfer device) of a monochrome image forming apparatus, there is a configuration in which a toner image on a photosensitive member is transferred to a sheet while the sheet is sandwiched and conveyed by a photosensitive member and a transfer roller. In such a configuration, the sheet conveyance speed is determined by the surface speed of the photoconductor, the surface speed of the transfer roller, and the transfer nip width.

  Typical printing methods for color image forming apparatuses include a 4-cycle method and a tandem method. The tandem system includes an intermediate transfer tandem system (intermediate transfer belt system) using an intermediate transfer belt, and a direct transfer tandem system (direct transfer belt system) using a direct transfer belt.

  The tandem method has an advantage that the printing speed is faster than the four-cycle method. However, the use of an intermediate transfer belt or a direct transfer belt has a disadvantage in terms of cost reduction.

  Further, a tandem system that does not use a belt (beltless tandem system) can be considered. The belt-less color printer does not use an intermediate transfer belt or a direct transfer belt. In the beltless tandem system, a plurality of pairs of photoconductors and transfer rollers are arranged. The toner on the photoconductor is transferred onto the paper while the paper is sandwiched and conveyed only by the pair of the photoconductor and the transfer roller.

  Patent Document 1 below discloses an image forming apparatus that changes a driving rotation speed of a transfer unit according to a ratio of an image transferred to a sheet. This is to adjust the change in the image length by the rotational speed of the transfer unit driving device.

  Patent Document 2 below discloses an image forming apparatus in which the rotation speed of a polygon motor is changed according to the ratio of an image transferred to a sheet and the sheet size to be fed. This adjusts the change in the image length by the rotational speed of the polygon motor.

Patent Document 3 below discloses an image forming apparatus in which the rotation speed of a main motor is changed between the first half and the second half of a sheet based on the sheet size and image data. This adjusts the change in the image length by the rotation speed of the main motor.
JP 2002-156871 A JP 2002-202691 A Japanese Patent Laid-Open No. 2003-307989

  In actuality, toner is interposed between the photosensitive member and the paper in the transfer section of the monochrome image forming apparatus, so that the paper transport speed is affected by the amount of toner adhesion. When the paper conveyance speed changes in the transfer section, the image length (overall magnification, partial magnification) on the paper deviates from the target length.

  In the primary transfer portion of an intermediate transfer tandem color printer, the conveyance speed of the intermediate transfer belt is not easily affected by the amount of toner adhesion. This is because, in the primary transfer portion, the conveyance speed of the intermediate transfer belt when toner is transferred from the photoreceptor to the intermediate transfer belt is strongly influenced by the surface speed of the drive roller that is a drive source. However, in the secondary transfer section, the sheet conveyance speed is affected by the toner adhesion amount. This is because the toner image on the intermediate transfer belt is transferred to the sheet while the sheet is sandwiched and conveyed by the intermediate transfer belt and the transfer roller. Therefore, the same problem as the above-described monochrome image forming apparatus occurs even in the intermediate transfer tandem color printer.

  Even in the belt-less color printer, the sheet conveyance speed changes depending on the amount of toner adhering to the photoreceptor. The change in the sheet conveyance speed changes the image length on the sheet at the position of each photoconductor. That is, the change in the paper conveyance speed causes a problem that the color registration accuracy is deviated and color misregistration occurs. Therefore, there are many problems regarding the accuracy of color alignment. Visually, the occurrence of color misregistration has a greater effect on the image quality seen by the user than the change in image length.

  In a direct transfer tandem type color printer, the toner image on the photosensitive member is transferred while the sheet is conveyed while being sufficiently held by the direct transfer belt. The sheet conveyance speed is not affected by the toner adhesion amount. However, the direct transfer tandem type color printer has a drawback in that the cost increases due to the provision of the direct transfer belt.

  As a method for solving the change in the image length of the monochrome image forming apparatus, the method of changing the rotational speed of the transfer unit driving device in Patent Document 1, the method of changing the rotational speed of the polygon motor in Patent Document 2, and Patent Document 3 There has been proposed a method of changing the rotation speed of the main motor. When these methods are used, it is possible to execute correction of the paper conveyance speed in a large range, such as adjusting the deviation of the overall magnification of the image. However, these methods are not suitable for correcting local image length changes. This is because even if the rotation speed of the motor is changed, the response is poor. That is, the response cannot catch up with the correction of the paper conveyance speed in a small range.

  The present invention has been made to solve such problems, and provides an image forming apparatus, an image forming apparatus control method, and an image forming apparatus control program capable of appropriately adjusting an image. The purpose is that.

  In order to achieve the above object, according to one aspect of the present invention, an image forming apparatus includes an image carrier that carries a toner image, a member that is disposed to face the image carrier, and that sandwiches a sheet together with the image carrier, An image writing unit for drawing an image on the image carrier, and an image data processing unit for sending image data to the image writing unit. The image data processing unit has an amount for attaching toner to the image carrier. Accordingly, the image length of the image data in the sub-scanning direction is changed.

  Preferably, the image data processing unit changes the image length in the sub-scanning direction in the main scanning line of the image data.

  Preferably, the image data processing unit changes the image length of the main scanning line in the sub-scanning direction according to the toner adhesion amount in each main scanning line of the image data.

  Preferably, the image data processing unit changes the image length of the main scanning line in the sub-scanning direction according to the toner adhesion amount at a position corresponding to the nip portion between the photosensitive member and the transfer roller in the image data.

  Preferably, the image data processing unit performs image processing based on at least one of paper type, paper thickness, paper width, image formation on the first or second surface, environmental temperature, and environmental humidity. The length in the sub-scanning direction is changed.

  Preferably, the image writing means is capable of writing in the sub-scanning direction at a resolution n times (n = 2 or greater) the resolution of the image data in the sub-scanning direction.

  Preferably, a plurality of image carriers are provided, and a member for sandwiching the paper is provided for each of the plurality of image carriers, and the paper is provided between the plurality of image carriers and a member for sandwiching the plurality of papers. The image data processing unit adheres the toner on the image carrier and the toner on the upstream image carrier in each of the plurality of image carriers. The image length of the image data in the sub-scanning direction is changed according to the amount.

  According to another aspect of the present invention, an image carrier that carries a toner image, a member that is disposed opposite to the image carrier, and holds a sheet together with the image carrier, and an image for drawing an image on the image carrier An image forming apparatus including a writing unit includes: an image adjustment step that changes an image length of image data in a sub-scanning direction according to an amount of toner attached to an image carrier; and an image adjustment step. And a control step of controlling the image writing means based on the adjusted image data.

  According to still another aspect of the present invention, an image carrier that carries a toner image, a member that is disposed to face the image carrier, and holds a sheet together with the image carrier, and for drawing an image on the image carrier. An image forming apparatus including an image writing unit includes: an image adjusting step for changing an image length of image data in a sub-scanning direction according to an amount of toner attached to an image carrier; and an image adjusting step. And a control step for controlling the image writing means based on the image data adjusted in step (b).

  According to these inventions, it is possible to provide an image forming apparatus, an image forming apparatus control method, and an image forming apparatus control program capable of appropriately adjusting an image.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described.

  The image forming apparatus is a tandem color printer that prints all colors of YMCK (yellow, magenta, cyan, black) in one cycle. In a tandem color printer, photoconductors of a plurality of colors are arranged in series. A color image is formed by sequentially transferring the toner images of the respective colors from the photoreceptor to the paper while the paper is being passed and conveyed.

  That is, the image forming apparatus employs a belt-less tandem system that does not use an intermediate transfer belt or a direct transfer belt.

  [First Embodiment]

  FIG. 1 is a diagram illustrating a hardware configuration of the image forming apparatus according to the first embodiment of the present invention.

  Referring to the drawing, an image forming apparatus 1 includes a paper feed cassette 2, a paper feed unit 3, a Y color photoconductor 4A, an M color photoconductor 4B, a C color photoconductor 4C, and a K color photoconductor 4D. Y color transfer roller (transfer portion) 5A, M color transfer roller (transfer portion) 5B, C color transfer roller (transfer portion) 5C, K color transfer roller (transfer portion) 5D, fixing portion 6, A paper discharge unit 7.

  The paper feed cassette 2 contains paper for forming an image. The presence or absence of paper is detected by a sensor. If no paper is set or if paper runs out during printing, the sensor detects the situation and informs the user via a display panel or the like. A paper feed unit 3 is provided in front of the paper feed cassette 2 (on the right side in the figure) to send out the paper in the paper feed cassette 2 to an image forming unit (image writing unit). The image forming apparatus 1 includes a controller (image data processing unit) 51 including a CPU that controls the apparatus.

  The image forming apparatus 1 is used by being connected to a computer directly or via a network. Image data to be printed on paper is transferred from the computer to the controller 51 in the image forming apparatus. The image forming unit forms a latent image on the Y color photoconductor 4A based on the transferred image data. The developing unit forms an image on the Y-color photoconductor 4A with a developer according to the latent image. The image formed by the developer formed on the Y color photoreceptor 4A is transferred to the paper by the Y color transfer roller 5A. This sheet is the sheet in the sheet feeding cassette 2 sent out from the sheet feeding unit 3. The sheet is controlled by the sheet feeding unit 3 so that the position of the image with respect to the sheet is appropriate, and is conveyed to the Y color transfer roller 5A. Similarly, transfer processing by the M color photoconductor 4B and the M color transfer roller 5B, transfer processing by the C color photoconductor 4C and the C color transfer roller 5C, and transfer by the K color photoconductor 4D and the K color transfer roller 5D. Processing is performed for each color continuously. The sheet on which the developer has been transferred by the color transfer rollers 5A to 5D is sent to the fixing unit 6 where heat and pressure are applied. The developer on the paper passes through the fixing unit 6 and develops color as soon as it is fixed on the paper. Thereafter, the paper is discharged to the paper discharge unit 7. Thereby, the image formation is completed.

  FIG. 2 is a diagram showing a configuration for performing a transfer process included in the image forming apparatus of FIG.

  The toner 12 is selectively developed from the developing roller 9 to the photoreceptor 4. The toner 12 on the photoconductor 4 is transferred onto the paper 11 while the paper 11 is sandwiched and conveyed by the photoconductor 4 and the transfer roller 5. The photoreceptor 4 has a function as an image carrier that carries a toner image.

  Here, the photoconductor 4 is one of the color photoconductors 4A to 4D in FIG. The transfer roller 5 is any one of the color transfer rollers 5A to 5D in FIG. When the photoreceptor 4 is a K-color photoreceptor 4D, the transfer roller 5 is a K-color transfer roller 5D. The photoconductor 4 and the transfer roller 5 correspond to each color.

  The conveyance speed of the paper 11 is determined mainly by the peripheral speed of the photoconductor 4 and the transfer roller 5. However, since the toner 12 is interposed between the photoconductor 4 and the paper 11, the friction coefficient between the photoconductor 4 and the paper 11 changes. As a result, the conveyance speed of the paper 11 changes.

  As a paper transport method, the peripheral speed of the transfer roller 5 is made to follow the peripheral speed of the photoconductor 4 and the paper 11 is transported, and the peripheral speed of the transfer roller 5 is set faster than the peripheral speed of the photoconductor 4. In this case, a method of conveying the paper 11 can be considered.

  When the peripheral speed of the transfer roller 5 is made to follow the peripheral speed of the photoconductor 4, the rotation of the photoconductor 4 is a driving source for the conveyance of the paper 11. When the toner 12 is interposed between the photoconductor 4 and the paper 11, the friction coefficient between the photoconductor 4 and the paper 11 is lowered. When the friction coefficient is lowered, it becomes easier to slide between the photosensitive member 4 as a driving source and the paper 11, so that the paper 11 becomes difficult to convey. Thereby, the conveyance speed of the paper 11 is lowered.

  When the peripheral speed of the transfer roller 5 is set faster than the peripheral speed of the photoconductor 4, the main drive source of the paper 11 is the transfer roller 5. It can be said that the rotation of the photosensitive member 4 serves as a brake against the conveyance of the paper 11. Since the toner 12 is interposed between the photoconductor 4 and the paper 11, the friction coefficient between the photoconductor 4 and the paper 11 is lowered. When the coefficient of friction between the photosensitive member 4 and the sheet 11 is lowered, the sheet 11 is easily conveyed according to the rotation of the transfer roller 5 that is a driving source. Thereby, the conveyance speed of the paper 11 is increased.

  The image forming apparatus according to the present embodiment employs a system in which the sheet 11 is conveyed by causing the peripheral speed of the transfer roller 5 to follow the peripheral speed of the photoconductor 4.

  FIG. 3 is a control block diagram of the image forming apparatus according to the first embodiment.

  Referring to the drawing, the image forming apparatus includes a controller 51 that controls the entire apparatus, an operation panel 103 that displays information to the user and receives information input from the user, and data between the external devices. An input interface (I / F) 105 for exchanging data, various motors 107 for rotating the photoconductor, transfer roller, paper feed roller, paper transport roller, fixing roller, etc. at a predetermined speed, and a latent image on the photoconductor A laser diode 109 for writing, a charging device 111 for charging the photosensitive member, and various solenoids 113 for operating each part of the device are provided. The laser diode 109 or the like functions as an image writing unit for drawing an image on the photosensitive member 4 that is an image carrier.

  An instruction input by the user is sent from the operation panel 103 to the controller 51. A computer connected to the image forming apparatus 1 via a network sends an instruction to the controller 51 through the input interface 105.

  In response to the instruction, the controller 51 controls the various motors 107, the laser diode 109, the charging device 111, and the various solenoids 113.

  When printing is performed, image data is sent from the input interface 105 to the controller 51. Each device is controlled by the image data.

  The laser diode 109 may be of a type in which a plurality of light emitting elements are arranged in series, and an electrostatic latent image is written on the photosensitive member by controlling lighting and extinguishing of each element, or a motor. It is also possible to employ a type that scans the photosensitive member via a rotating polygon mirror.

  FIG. 4 is a diagram illustrating the relationship between the image ratio (toner adhesion amount) and the sheet conveyance speed.

  In the graph of the figure, the horizontal axis represents the image ratio (%), and the vertical axis represents the actual paper conveyance speed. Here, the “image ratio” indicates the ratio of the number of pixels to which toner is attached in the total pixels of one main scanning line. When there is no pixel to which toner adheres to one main scanning line, the image ratio is 0%, and when toner adheres to all main scanning one line, the image ratio is 100%. That is, the image ratio is calculated from the toner adhesion amount of each main scanning line.

  From FIG. 4, it can be seen that the higher the image ratio (the larger the toner adhesion amount), the lower the paper conveyance speed. This is because, as described above, as the amount of toner increases, the coefficient of friction between the photosensitive member and the sheet decreases, and the sheet becomes difficult to be conveyed.

  FIG. 5 is a diagram illustrating the relationship between the image ratio (toner adhesion amount) and the image length.

  In the graph of the figure, the horizontal axis indicates the image ratio (%), and the vertical axis indicates the length in the sub-scanning direction (paper conveyance direction) of the image of one line when one main scanning line is printed. .

  From this figure, it can be seen that the higher the image ratio (the larger the toner adhesion amount), the shorter the image length. This is because, as described above, as the amount of toner increases, the coefficient of friction between the photosensitive member and the sheet decreases and the sheet becomes difficult to be transported, so that the area where the toner adheres to the sheet is shortened. That is, the length of the toner image formed on the sheet in the sheet conveyance direction is shorter than the length of the toner image formed on the sheet in the sheet conveyance direction.

  As described above, the image ratio affects the sheet conveyance speed and the image length. When the paper transport speed decreases, the image on the paper shrinks in the paper transport direction (sub-scanning direction).

  In the present embodiment, by correcting the shrinkage of the image retroactively to the image data, a print image having an appropriate length can be obtained. A method for adjusting the image data will be described below.

  FIG. 6 is a diagram for explaining the image data conversion method executed by the controller.

  The original image data is shown on the left of FIG. On the right, the converted image data is shown. Here, for simplification, an example of image data in which the main scanning direction is 10 pixels × the sub-scanning direction (paper transport direction) is 10 lines is shown.

  In the figure, hatched pixels are pixels to which toner adheres, and other pixels are pixels to which toner does not adhere. Assume that the 1, 2, 5, 6, 9, and 10 lines from the top have an image ratio of 0%. The 3rd and 4th lines are assumed to have an image ratio of 50%. The 7th and 8th lines are assumed to have an image ratio of 100%.

  The controller converts the original image data so as to extend the image in the vertical direction (sub-scanning direction) in FIG. 6 in order to compensate for the shrinkage of the image length shown in FIG.

  Specifically, the image ratio is calculated from the number of pixels to which toner in the main scanning direction is attached in each line. Thereafter, as shown in the right figure, the line is elongated in the vertical direction according to the image ratio. Assuming that the vertical length of a line with an image ratio of 0% is a, the vertical length of a line with an image ratio of 50% is b (b> a), and the vertical length of a line with an image ratio of 100% is c (c> b). In this way, the pixels of each line are converted to a length corresponding to each image ratio.

  Alternatively, only the pixels in the line with a high image ratio may be elongated in the vertical direction according to the image ratio. That is, the lines to be subjected to image conversion may be only lines having an image ratio of a certain level or more.

  In the present embodiment, as described with reference to FIG. 5, it is assumed that the higher the image ratio is, the shorter the image length is, and the shorter the image length, the longer the pixels on each line are calculated. Is.

  The photoconductor in the image forming apparatus is exposed according to the converted image data. Thereafter, toner is developed on the photoreceptor in the developing unit. The toner image developed on the photoreceptor is an image stretched in the vertical direction as shown in the right of FIG. The toner image on the photoconductor is transferred onto a sheet. At that time, the friction coefficient between the photosensitive member and the paper decreases due to the toner adhesion amount on the paper, and the paper transport speed decreases. As a result, the image converted to extend in the vertical direction is reduced in the vertical direction on the paper.

  By adjusting the length of the image in the vertical direction and the length that shrinks during transfer to the same amount, the image converted to extend in the vertical direction is the original image length on the paper. Will be reproduced.

  That is, as shown on the left side of FIG. 6, an image having the same length is reproduced on every line regardless of the image ratio.

  As described above, by performing the conversion process on the original image, an image having an appropriate length can be formed on the sheet.

  FIG. 7 is a flowchart showing print processing of the image forming apparatus according to the first embodiment of the present invention.

  In this flowchart, the controller 51 converts image data to be printed, controls each device, and performs processing until printing. As described in FIG. 6, the image data is converted according to the image ratio. Thereafter, development processing and transfer processing are performed based on the converted image data.

  First, in step S101, image data to be printed is input to the controller 51. This image data is data sent from a computer connected to the image forming apparatus 1 via a network, or data read by the image forming apparatus 1. Image data is input to the controller 51 through the input interface 105.

  Thereafter, in step S103, the image ratio in each line is calculated from the toner adhesion amount (the number of pixels to which the toner adheres) in each main scanning line of the image data. The image ratio is calculated by obtaining the ratio of the toner adhesion amount to the total number of pixels in each main scanning line.

  In step S105, the image length in the sub-scanning direction (paper transport direction) in each main scanning line is determined based on the image ratio calculated in step S103. That is, the calculation for extending the length of the image is performed according to the image ratio.

  Based on the image length determined in step S105, in step S107, each apparatus is controlled to print each main scanning line in order. That is, the image is developed on the photoconductor and transferred onto the paper based on the data in which the image length in the sub-scanning direction is converted. An image having an appropriate length similar to the image before conversion is not reproduced on the sheet, but an image whose length is extended in the sub-scanning direction is not reproduced. This is because, as described with reference to FIG. 6, the converted image is formed on the sheet with a reduced length in the sub-scanning direction due to a decrease in the sheet conveyance speed between the photosensitive member and the sheet.

  Note that the process of extending an image as shown in FIG. 6 can be performed by any of the following methods.

  (1) The amount of image expansion for each main scanning line is calculated, and the amount of image expansion for each line is stored in the memory. Based on the stored amount, a mechanism for irradiating the photosensitive member with light is controlled. For example, in the case of an apparatus in which a plurality of light emitting elements are arranged in the main scanning direction to form an image on the photosensitive member, the lighting time of the light emitting elements in each main scanning line is changed based on the amount of image extension. As a result, the length in the sub-scanning direction can be adjusted for each line.

  (2) The amount of image expansion is calculated for each main scanning line, and the image data itself is changed based on the amount of image expansion for each line. That is, the resolution of the image to be processed is increased, and the image data is partially extended. For example, if an image of 600 dpi is to be processed, the length in the sub-scanning direction of one main scanning line can be extended with a resolution of 25% of one line by converting it to 2400 dpi. By further increasing the resolution, the amount of image expansion can be adjusted more finely.

  [Second Embodiment]

  Next, an image forming apparatus according to a second embodiment of the present invention will be described. The hardware configuration of the image forming apparatus in the second embodiment is almost the same as that in the first embodiment. Here, only the differences of the second embodiment from the first embodiment will be described.

  As described above, in the image forming apparatus according to the first embodiment, the sheet is sandwiched and conveyed by the photoreceptor and the transfer roller. In the first embodiment, before the paper contacts the photoconductor, the toner on the photoconductor may jump on the paper, so-called “pre-transfer scattering” may occur.

  In the second embodiment, a pre-transfer guide is attached in the vicinity of the photosensitive member in order to prevent such “scattering before transfer”. As a result, toner scattering and defective image formation are prevented.

  FIG. 8 is a diagram showing a configuration of a portion that performs a transfer process of the image forming apparatus according to the second embodiment of the present invention.

  Referring to the figure, in the present embodiment, a pre-transfer guide 13 is attached immediately before the photoreceptor 4 and the transfer roller 5. The sheet 11 is conveyed from left to right in the drawing. The pre-transfer guide 13 has a function of pressing the conveyed paper 11 against the photosensitive member 4. As a result, scattering of toner before transfer is prevented.

  In the first embodiment described above, the photoconductor 4 and the paper 11 are in contact with each other at the line “A” where the photoconductor 4 and the transfer roller 5 are in contact. Therefore, the image length in the sub-scanning direction for forming the “A” line on the photoconductor 4 is determined based on the toner adhesion amount (image ratio in one line) in the “A” line.

  In the second embodiment, the photoreceptor 4 and the sheet 11 are in contact with each other at the transfer nip width D from the “A” line to the “B” line. Thus, in the present embodiment, the image length in the sub-scanning direction formed on the photoconductor 4 is determined based on the toner adhesion amount (image ratio in the transfer nip width D) in the portion having the length of the transfer nip width D. decide. For example, when the line “C” at the center of the transfer nip width D is formed on the photoconductor 4, the toner adhesion amount (transfer nip width D) in the portion where the image length in the sub-scanning direction is the length of the transfer nip width D. Image ratio).

  That is, in order to determine the image length of the “C” line on the left of FIG. 6, the image ratio of the transfer nip width D from the “A” line to the “B” line is used. The image ratio of the transfer nip width D in FIG. 6 is obtained as follows.

  The number of pixels included in the transfer nip width D is 10 × 7 = 70 pixels. Among these, 30 pixels (hatched pixels) to which toner is attached are 30 pixels. Therefore, the image ratio is calculated as 30/70 = 43 [%]. Based on this image ratio, the correction amount of the length in the sub-scanning direction of the image of the “C” line is calculated.

  In the present embodiment, the image forming apparatus includes a configuration (a configuration in which the pre-transfer guide 13 is attached) that prevents scattering before transfer. The image ratio is calculated for each transfer nip width region. Thereby, more effective image conversion can be performed.

  In calculating the image ratio (toner adhesion amount), an area corresponding to the nip width of the photoconductor and the transfer roller may be used, or an area having a length equal to or less than the nip width may be used. Good.

  [Third Embodiment]

  Next, an image forming apparatus according to a third embodiment of the present invention will be described. The hardware configuration of the image forming apparatus in the third embodiment is substantially the same as that in the first and second embodiments. Here, only the differences of the third embodiment from the first and second embodiments will be described.

  In an image forming apparatus that transports a sheet between a photoconductor and a transfer roller, the sheet transport speed changes due to various factors. As described in the first embodiment, in the tandem color printer, the sheet conveyance amount may be different for each color (for example, Y, M, C, K) photoconductor depending on the image ratio. . As a result, if the correction described in the above embodiment is not performed, a problem of color misregistration occurs depending on the image ratio (toner adhesion amount).

  There are other factors that change the paper transport speed. Specifically, if the paper type (plain paper, coated paper, OHP sheet, etc.), paper thickness (thin paper, plain paper, thick paper, etc.), paper width, and duplex printing function are built-in, There are factors such as whether it is the second side (front side or back side) and environmental temperature and humidity.

  In the present embodiment, in addition to the corrections in the first and second embodiments, the image forming apparatus performs image correction by adding factors other than the toner adhesion amount on the paper that change the paper transport speed.

  FIG. 9 is a flowchart showing image data correction processing executed by the image forming apparatus according to the third embodiment of the present invention.

  In this flowchart, the controller 51 converts the original image data D1 to be printed and creates corrected image data D2. The original image data D1 is converted according to the image ratio as in the first and second embodiments, and then corrected by factors other than the toner adhesion amount on the paper. Thereby, corrected image data D2 is created.

  In step S201, calculation for extending the length of the image is performed on the original image data D1 in accordance with the image ratio. The calculation of the conversion amount of the image data is the same as the processing described with reference to FIG.

  In step S203, the conversion amount of the image data is further calculated based on factors other than the toner adhesion amount on the paper. The factors used here are the paper type, paper thickness, paper width, whether the paper is on the first side or the second side, and the ambient temperature and humidity. These factors change the coefficient of friction between the photoconductors 4A to 4D of each color and the paper 11, but since they act in the same way on each color, the problem of color misregistration does not occur. However, since the image length changes in the same way for each color, a problem of magnification shift in the entire sub-scanning direction occurs. For this reason, when calculating the correction amount of the original image data D1 based on the image ratio, more effective image conversion can be performed by correcting these factors together.

  After the conversion amount of the original image data D1 is calculated, the original image data D1 is converted to generate corrected image data D2.

  In order to actually stretch the image, as described in the first embodiment, the lighting time of the light emitting element is changed based on the amount by which the calculated image is stretched, or the calculated image is stretched. Either of the methods of changing the image data itself based on the amount may be adopted. In the former case, the corrected image data D2 in FIG. 9 is composed of a combination of the original image data D1 and the amount by which the image in each main scanning line of the original image data D1 is stretched. In the latter case, the corrected image data D2 in FIG. 9 is image data obtained by locally extending the original image data D1.

  [Fourth Embodiment]

  Next, an image forming apparatus according to a fourth embodiment of the present invention will be described.

  The exposure methods for creating a latent image on the photoreceptor are roughly divided into the following two methods.

  (1) A type in which a single (or multiple) laser beam is scanned line by line with a scanning member such as a polygon scanner

  (2) A line-shaped LED element that has approximately the same length as the paper width and that exposes line by line.

  Considering the writing frequency for each line, in the method (2), the time width allocated to one line can be adjusted electrically. In this method, it is easy to make fine the correction accuracy of the image for locally stretching the image.

  On the other hand, the method (1) usually employs a single scan method in which one line is exposed for each surface of the polygon scanner. In order to correct the image length, as disclosed in JP-A-2002-202691, a method of changing the rotational speed of the polygon motor is conceivable. However, with this method, the responsiveness of the polygon motor must be taken into account, and it is difficult to cope with local changes in the conveyance speed.

  The image forming apparatus according to the present embodiment executes a process of locally changing the image length based on the image ratio or the like, as described in the above-described embodiment, using a polygon scanner.

  The image forming apparatus according to the present embodiment employs a multi-scan method in which one line is created by a plurality of scans using a polygon scanner. By adopting an exposure method based on multi-scan, the correction accuracy can be improved.

  FIG. 10 is a diagram for explaining the image length correction processing by the multi-scan method.

  FIG. 10A is a diagram illustrating an example of image formation in a normal single scan (drawing one line in one scan). The number of the line formed on the horizontal axis is shown, and the exposure amount of the photoreceptor (the amount of light emitted from the laser diode) is shown on the vertical axis. Here, an example in which the second, fifth and eighth lines are exposed is shown.

  FIG. 10B is a diagram illustrating an example of image formation in multi-scanning (drawing one line by a plurality of scans). The number of the line formed on the horizontal axis is shown, and the exposure amount of the photoreceptor (the amount of light emitted from the laser diode) is shown on the vertical axis. Also here, an example is shown in which the second, fifth and eighth lines are exposed.

  In the figure, the exposure amount for each scan is indicated by a plurality of small peaks, and the exposure amount obtained by synthesizing the exposure amounts of the plurality of small peaks is indicated by the large peak. Here, an example is shown in which one main scanning line of the photoconductor is exposed by five scans and an image of one line is formed by five scans.

  That is, the lines Nos. 2, 5 and 8 are exposed by five scans as indicated by the small peaks in the figure. The amount of exposure in one scan is smaller than that in the single scan of FIG. As a result, the combined exposure amount in the five scans is almost equal to the exposure amount in the single scan in the single scan.

  FIG. 10C is a diagram showing an example in which the lengths of the second, fifth and eighth lines are extended by 1/5 line (one scan) in the multi-scan method of FIG.

  Here, in order to extend the length of the second line by 1/5 line, the number of scans for forming the second line is increased by one. That is, the second line is formed by six scans. The same applies to the 5th and 8th lines.

  In this way, compared with FIG. 10B, the image is locally extended in the sub-scanning direction in FIG. 10C.

  As described above, in the present embodiment, by creating one line by n scans, it becomes possible to have a correction resolution of 1 / n line, and more effective image conversion can be performed. That is, the writing resolution in the sub-scanning direction is set to n times (n = 2 or more integer) the resolution of the image data in the sub-scanning direction.

  [Fifth Embodiment]

  Next, an image forming apparatus according to a fifth embodiment of the present invention will be described.

  FIG. 11 is a diagram showing the configuration of the photosensitive member portion of the image forming apparatus according to the fifth embodiment of the present invention.

  The image forming apparatus includes an array of color tandem photoconductors. As the paper is transported from the upstream side (left in the figure) to the downstream side (right in the figure), the paper is composed of the photoconductor 4A and a transfer roller facing the photoconductor 4B, and a transfer roller facing the photoconductor 4B, It passes between the photoreceptor 4C and the transfer roller facing it, and the photoreceptor 4D and the transfer roller facing it. In that order, toners Y, M, C, and K are transferred onto the paper.

  In such a configuration, as described above, the phenomenon that “the image length shrinks according to the image ratio” occurs, and therefore, in each of the Y, M, C, and K image data, the sub-scanning direction (paper transport direction) Then, image conversion for adjusting the image length is performed. At this time, the image length of each line of the color data may be obtained from the image ratio of the data of each color.

  However, the amount of toner that intervenes between the paper and the photoconductor increases as it goes to the right in the figure. For example, when attention is paid to the paper passing between the last-stage photoconductor 4D and the transfer roller facing the photoconductor 4D, not only the K toner transferred by the photoconductor 4D but also each of Y, M, and C toners is transferred to the photoconductor. Between the paper and the paper.

  Therefore, the image ratio of each color of Y, M, and C should be taken into consideration at the position of the photoreceptor 4D. From this point of view, in this embodiment, instead of obtaining the length of the image only from the respective image ratios obtained from the image data of each color, including information on the image ratio of the color up to the previous stage of the color, Find the length of the image. As a result, more effective image conversion is performed. In the configuration of FIG. 11, “color up to the previous stage of the color” is YMC if “the color” is K, YM if C, and Y if M. If “the color” is Y, there is no previous color.

  It is assumed that a pre-transfer guide 13 shown in FIG. 8 is attached to the image forming apparatus in the present embodiment.

  12 to 15 are diagrams showing a state in which the image ratio increases in each stage in the configuration of FIG.

  12 to 15 show image ratios at the time of Y, M, C, and K transfer (from the first transfer to the fourth transfer), respectively. The horizontal axis represents the image No. in the sub-scanning direction. (Line number), and the vertical axis represents the image No. The image ratio is shown. The image ratio assumes that the maximum value for one color is 256, and the maximum value for all four colors is 1024.

  FIG. 12 shows the image ratio calculated from only the Y image, and FIG. 13 shows the image ratio when the M image is superimposed on the Y image. FIG. 14 shows the image ratio when the C image is further superimposed, and FIG. 15 shows the image ratio when the K image is further superimposed.

  In the figure, “average of 7 lines” is an average value of image ratios for 7 lines in the sub-scanning direction. For example, no. The average of 7 lines in No. 4 is 7 lines before and after that line. 1-No. The average of the image ratio of 7 lines is shown.

  In each color shown in FIGS. 12 to 15, the image data of that color is corrected based on “7-line average”.

  FIG. 16 is a flowchart illustrating image correction processing of the image forming apparatus according to the fifth embodiment.

  In step S301, a relational expression between the image ratio α of each color and the image length L of each color is set. The Y color image ratio is αy, the M color image ratio is αm, the C color image ratio is αc, and the K color image ratio is αk. The image length in the Y color calculated from the image ratio of the Y color image data is Ly, the image length in the M color calculated from the image ratio of the Y, M color image data is Lym, Y, The image length in C color calculated from the image ratio of M, C color image data is Lymc, and the image length in K color calculated from the image ratio of Y, M, C, K color image data is Lymck. Is written.

  The relational expression of each numerical value is expressed by the following expression.

  Ly = fy (αy)

  Lym = fym (αy, αm)

  Lymc = fymc (αy, αm, αc)

  Lymck = fymck (αy, αm, αc, αk)

  That is, for example, the image length Lymck for K color is calculated by assuming that the image length αm for Y color, the image ratio αm for M color, the image ratio αc for C color, and the image ratio αk for K color are all affected. Is set.

  FIG. 17 is a diagram illustrating the relationship between the image ratio and the image length in the sub-scanning direction.

  The horizontal axis represents the image ratio, and the vertical axis represents the image length. As shown in the figure, every time the image ratio increases, the image length becomes shorter due to the decrease in the friction coefficient.

  In step S303, the moving average line number N is set. In the examples of FIGS. 12 to 15, N = 7. This moving average line number N is the number of lines that is almost equal to the transfer nip width D in FIG.

  In step S305, the reference image ON time Tstd is set. For example, if an image is formed at a resolution of 600 dpi and a sub-scanning speed of 200 mm / sec, the time for forming one line is 0.217 msec (4.72 kHz). This time is set as a reference image ON time Tstd. The reference image ON time Tstd is the image ON time when the image ratio is 0 (when the friction coefficient is not reduced by the toner).

  In step S307, an image ON time for forming a one-line image for each color is calculated. The longer the image ON time, the longer the image formed on the photoconductor is in the sub-scanning direction.

  More specifically, the moving average (7 line average) of the image ratio of the first color (Y) is obtained. That is, the sub-scanning direction image No. Each time, an average is obtained from the image ratio of a total of 7 lines including the 3 lines before and after (FIG. 12). Based on this, the sub-scanning direction image No. Every time, the image ON time for each line is calculated.

  FIG. 18 is a diagram illustrating the relationship between the image ratio and the image ON time.

  The horizontal axis indicates the image ratio, and the vertical axis indicates the value of the image ON time to be set. Each time the image ratio increases, the image length decreases as the friction coefficient decreases. To compensate for this, the image ON time is increased each time the image ratio increases as shown in the figure.

  Further, a moving average (7-line average) of the total image ratios of the first color (Y) and the second color (M) is obtained (FIG. 13). Based on this, the sub-scanning direction image No. Every time, the image ON time for each line is calculated.

  Similarly, the moving average (7-line average) of the total image ratios of the first color (Y), the second color (M), and the third color (C) is obtained (FIG. 14). Based on this, the sub-scanning direction image No. Every time, the image ON time for each line is calculated. Also, a moving average (7-line average) of the total image ratios for the first color (Y), the second color (M), the third color (C), and the fourth color (K) is obtained (FIG. 15). Based on this, the sub-scanning direction image No. Every time, the image ON time for each line is calculated.

  In addition, when calculating | requiring a moving average, a simple moving average may be calculated | required and each line may be weighted and a weighted moving average may be calculated | required.

  In step S309, the image ON time for each color and each line is calculated (for example, rounded off) to be a multiple of the minimum controllable resolution of the writing system (photoreceptor exposure system).

  For example, it is assumed that the basic frequency of writing is 4.72 kHz (600 dpi, 200 mm / sec) when an exposure apparatus that performs writing with an LED array is employed. At this time, if the ON / OFF control of the LED is possible at a frequency (472 kHz) that is 100 times the basic frequency, the image length can be adjusted in units of 1%.

  Further, it is assumed that the basic frequency of writing is 4.72 kHz (600 dpi, 200 mm / sec) when an exposure apparatus that performs writing with an LD (laser diode) and a polygon mirror is employed. At this time, if ON / OFF control is possible at a frequency (23.6 kHz) five times the basic frequency, the image length can be adjusted in units of 20%.

  In the case where an exposure apparatus that performs writing with an LD and a polygon mirror is employed, it is possible to increase the writing frequency by increasing the rotational speed of the polygon mirror or decreasing the photosensitive member rotational speed. . Moreover, you may use the control demonstrated in FIG.

  The above calculation may be performed by either the print server (PC) or the controller 51 in the printer.

  In addition, in order to adjust the image, data with image ON time information added for each line of the original 600 dpi image data may be created, or the number of lines is increased N times only in the sub-scanning direction, and the image ON time is increased. Thus, data in which the number of lines is adjusted may be created.

  [Modification]

  In the above-described embodiment, the method of conveying the paper 11 by causing the peripheral speed of the transfer roller 5 to follow the peripheral speed of the photoconductor 4 has been described. The image adjustment processing in the present invention can also be applied to a system in which the sheet 11 is transported with the peripheral speed of the transfer roller 5 set higher than the peripheral speed of the photoconductor 4. In this case, the higher the image ratio, the easier the paper 11 is conveyed. Therefore, the length of the image formed on the paper 11 may be longer than the original image data. Therefore, when converting the original image data, a process of shortening the image in the vertical direction according to the image ratio is performed. By doing so, an image having the same length as the original image can be reproduced on the paper. That is, the conversion amount of the length of the image data is changed.

  In the above-described embodiment, the image correction when the toner image is directly transferred from the photosensitive member to the paper has been described. However, the present invention also applies to the image correction when the toner image is transferred from the secondary transfer belt to the paper. Can be applied.

  [Effects of the embodiment]

  According to the above-described embodiment, in an image forming apparatus that transfers a toner image onto a sheet while sandwiching and transporting the sheet with a photoconductor and a transfer roller, an image is calculated based on an image ratio calculated from image data to be printed. Image data with a converted length is created. That is, expansion (or compression) is performed on the image length in the paper conveyance direction from the image ratio data. As a result, even when the paper conveyance speed fluctuates due to the size of the image ratio (the amount of toner adhesion), the image can be transferred to an ideal position on the paper. For this reason, an image magnification shift in the sub-scanning direction (paper transport direction) (a shift in the overall image magnification and a local partial magnification shift) caused by a change in the paper conveyance speed at the transfer unit, an image length It is possible to prevent changes in color and color misregistration. That is, the image position accuracy and color alignment accuracy in the sub-scanning direction can be improved.

  In addition, it should be thought that the said embodiment is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a diagram illustrating a hardware configuration of an image forming apparatus according to a first embodiment. FIG. 2 is a diagram illustrating a configuration for performing a transfer process included in the image forming apparatus of FIG. 1. FIG. 3 is a control block diagram of the image forming apparatus in the first embodiment. FIG. 6 is a diagram illustrating a relationship between an image ratio (toner adhesion amount) and a sheet conveyance speed. It is a figure which shows the relationship between an image ratio (toner adhesion amount) and image length. It is a figure for demonstrating the conversion method of the image data which a controller performs. 3 is a flowchart illustrating print processing of the image forming apparatus according to the first embodiment. FIG. 10 is a diagram illustrating a configuration of a portion that performs a transfer process of an image forming apparatus according to a second embodiment. 10 is a flowchart illustrating image data correction processing executed by an image forming apparatus according to a third embodiment. It is a figure for demonstrating the correction process of the image length by a multiscan system. It is a figure which shows the structure of the part of the photoreceptor of the image forming apparatus in 5th Embodiment. FIG. 12 is a diagram illustrating a state in which the image ratio increases in each stage in the configuration of FIG. 11. FIG. 12 is a diagram illustrating a state in which the image ratio increases in each stage in the configuration of FIG. 11. FIG. 12 is a diagram illustrating a state in which the image ratio increases in each stage in the configuration of FIG. 11. FIG. 12 is a diagram illustrating a state in which the image ratio increases in each stage in the configuration of FIG. 11. 10 is a flowchart illustrating image correction processing of an image forming apparatus according to a fifth embodiment. It is a figure which shows the relationship between an image ratio and the image length of a subscanning direction. It is a figure which shows the relationship between an image ratio and image ON time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Paper feed cassette 3 Paper feed part 4 Photoconductor 4A Y color photoconductor 4B M color photoconductor 4C C color photoconductor 4D K color photoconductor 5 Transfer part 5A Y color transfer roller (transfer part)
5B M color transfer roller (transfer section)
5C C color transfer roller (transfer section)
5D K color transfer roller (transfer section)
6 Fixing unit 7 Paper discharging unit 9 Developing roller 11 Paper 12 Toner 13 Pre-transfer guide 51 Controller 107 Various motors 109 Laser diode

Claims (9)

An image carrier for carrying a toner image;
A member that is disposed opposite to the image carrier and sandwiches a sheet together with the image carrier;
Image writing means for drawing an image on the image carrier;
An image data processing unit for sending image data to the image writing means,
The image forming apparatus, wherein the image data processing unit changes an image length of the image data in a sub-scanning direction according to an amount of toner attached to the image carrier.   The image forming apparatus according to claim 1, wherein the image data processing unit changes an image length in a sub-scanning direction in a main scanning line of the image data.   The image forming apparatus according to claim 1, wherein the image data processing unit changes an image length of the main scan line in the sub-scanning direction according to a toner adhesion amount in each main scan line of the image data. .   The image data processing unit changes the image length in the sub-scanning direction on the main scanning line according to the toner adhesion amount at a position corresponding to the nip portion between the photoconductor and the transfer roller in the image data. The image forming apparatus according to claim 1.   The image data processing unit determines whether the image is formed based on at least one of a paper type, a paper thickness, a paper width, whether the image is formed on the first or second surface, an environmental temperature, and an environmental humidity. The image forming apparatus according to claim 1, wherein the length in the sub-scanning direction is changed.   6. The image writing unit according to claim 1, wherein writing in the sub-scanning direction is possible at a resolution n times (n = 2 or greater) the resolution of the image data in the sub-scanning direction. Image forming apparatus. A plurality of the image carriers are provided,
A member for sandwiching the paper is provided for each of the plurality of image carriers,
The paper passes between the plurality of image carriers and a member sandwiching the plurality of papers in order from upstream to downstream,
In each of the plurality of image carriers, the image data processing unit is configured to select the image in accordance with an amount of toner attached to the image carrier and an amount of toner attached to an upstream image carrier. The image forming apparatus according to claim 1, wherein the image length in the sub-scanning direction of data is changed. An image carrier for carrying a toner image;
A member that is disposed opposite to the image carrier and sandwiches a sheet together with the image carrier;
A control method for an image forming apparatus comprising an image writing means for drawing an image on the image carrier,
An image adjustment step of changing an image length in the sub-scanning direction of the image data in accordance with an amount of toner attached to the image carrier;
And a control step of controlling the image writing means based on the image data adjusted in the image adjustment step. An image carrier for carrying a toner image;
A member that is disposed opposite to the image carrier and sandwiches a sheet together with the image carrier;
A control program for an image forming apparatus comprising image writing means for drawing an image on the image carrier,
An image adjustment step of changing an image length in the sub-scanning direction of the image data in accordance with an amount of toner attached to the image carrier;
A control program for an image forming apparatus, which causes a computer to execute a control step for controlling the image writing unit based on the image data adjusted in the image adjustment step.

Images