JP2008009062A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain skewing of sheet material at a transfer nip part. <P>SOLUTION: In order to reduce the difference between right and left of toner amount depending on an image pattern, the difference of conveying force is reduced by a means for reducing the difference between the right and left of the toner amount, when the difference between the right and left of the printing rate in development of an image is equal to or higher the predetermined one. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming method for reducing a conveyance failure caused by a printed image in an electrophotographic image forming apparatus such as a laser beam printer or a copying machine that forms an image on a sheet material, and the apparatus.

  FIG. 7 is a diagram illustrating a configuration of a conventional printer device. In FIG. 7, reference numeral 100 denotes a host computer that generates an image information source for the printer, and 101 denotes a printer main body. The printer main body 101 includes a controller unit 102 and an engine unit 106 that receives image data output from the controller unit 102 and prints it on recording paper.

  The controller unit 102 is a computer interface unit 103 connected to the host computer 100, and an image processing unit 104 that performs bitmap conversion of video RGB image data and code data transferred from the host computer 100 into image data for a printer. It comprises a buffer memory 104a for storing map data and a video interface unit 105a connected to the engine 106.

  Furthermore, the engine unit 106 includes a video interface unit 105b connected to the controller unit 102, and an engine control unit 107 that controls various controls of the engine unit. The engine control unit 107 houses a CPU 107a. The engine 106 holds a cassette for storing the transfer material S, 120 is a pickup roller, 121 is a sheet material separating / conveying roller pair, and 122 is a conveying roller. Reference numeral 123 denotes a registration roller pair that conveys the transfer material S to the transfer portion at a predetermined timing, 124 a photosensitive drum, 129 an intermediate transfer belt, and 125 a developer. A transfer roller 126 performs a transfer process, and a laser scanner 128 performs an exposure process.

  The operation of the conventional printer 101 having the above configuration will be described.

  First, conversion of image data into a video signal will be described. The image data input from the host computer 100 is converted into bitmap data by the image processing unit 104 via the interface unit 103 and held in the buffer memory 104a. In the case of a full-color image, the input data is converted into YMCK, which is a signal format handled by the engine unit 106, and held in the buffer memory 104a. During the printing operation, the image data is read from the buffer memory 104a, and the image processing circuit (not shown) in the video interface block 105a performs conversion in consideration of the process characteristics of the engine unit 106, that is, toner characteristics, development bias. Optimized masking processing and UCR (Under Color Removal) based on the result of the density characteristics are performed. Then, the image data that has undergone image processing by the video controller unit 102 is sent as a video signal to the engine control unit 107 via the video interface block 105b on the engine side.

  Next, the printing operation in the engine from paper supply to paper discharge will be described. The uppermost sheet of the sheet material stored in the sheet feeding cassette S is fed by the pickup roller 120, and the sheet material being multifed by the separation roller 121 is separated. The sheet material is conveyed by the conveyance roller 122, the skew is corrected by the registration roller 123, and sent to the transfer unit. In the exposure process, for example, a latent image is formed on the photosensitive drum 124 by a laser beam from a scanner unit 128 in which a semiconductor laser (not shown) is accommodated. The developing device 125 is divided into YMCK four-color stations, and performs a developing process on the latent image on the photosensitive drum 124 for each color. The developed toner images of the respective colors are transferred onto the intermediate transfer belt 129, and the four color superimposed color toner images are transferred onto the sheet material by the transfer unit. The sheet material is conveyed by the transfer roller 126, and the toner is fixed on the sheet material by a fixing unit (not shown) and discharged.

  An image forming apparatus using an electrophotographic method, such as a laser beam printer, fixes a toner image onto a sheet material in synchronization with the transfer of the toner image to the sheet material, and the sheet material passes through the transfer portion. A transfer process is performed. Therefore, when the sheet material is obliquely fed, the inclined transfer image is transferred to the sheet material and skew is generated. In addition, when the skew feeding is large, the sheet material is not limited to the transfer portion, but the sheet material may come into contact with a portion other than the contact portion of the conveyance design such as an end portion of the conveyance path, and the sheet material may be damaged and a jam may occur.

  Conventionally, in order to suppress the oblique feeding of the sheet material, the sheet material side is regulated by the sheet feeding unit, or the sheet material position reference is provided in the direction perpendicular to the conveyance, and the sheet material is not damaged at the reference portion. It has been carried out to convey the sheet material while pressing it to the extent, or to regulate the inclination of the sheet material with a resist roller.

  Hereinafter, as an example of skew feeding correction, skew feeding correction by the registration roller method will be described with reference to FIG.

  In registration alignment, the registration roller pair 123 is stopped, and the conveyance roller 122 is driven for a certain period of time, and the leading edge of the sheet material S sent through the conveyance path hits the nip portion of the registration roller pair 123. The line is corrected and controlled to be parallel to the registration roller pair 123. Thereafter, at a predetermined timing, the registration roller pair 123 is driven at a timing when the driving force of the conveyance system is required by a clutch means (not shown), etc., is switched from the stopped state to the rotating state, and conveys the sheet material again. To do.

As another conventional example, Patent Document 1 can be cited.
Japanese Patent Laid-Open No. 10-186876

  However, in the conveyance path from the transfer process to the fixing process, it is impossible to provide a portion that positively corrects skew because of the influence on the unfixed image on the sheet material. It depends on the stability of the conveying force of the rollers. Therefore, there is no correction means for the skew that occurs in the transfer nip due to the transfer roller conveyance force difference caused by the difference between the left and right toner application amounts of the print image. Here, the oblique feeding mechanism at the transfer nip portion resulting from the print image will be described with reference to the cross section of the transfer nip, FIGS. 8 and 9.

  FIG. 8 is a sectional view of the transfer nip when toner is present, and FIG. 9 is a sectional view of the transfer nip when toner is not present. In FIG. 8, 140 is a toner layer, and 141 is a rotation shaft of the transfer roller 126.

  The sheet material is conveyed by the rotation of the transfer roller 126, and the conveyance distance of the sheet material has a ratio of R ′: R with and without the toner layer. For example, when the transfer roller 126 has a radius of 5 mm, the sheet material S has a thickness of 100 μm, and the toner layer 140 has a thickness of 20 μm, the difference in distance from the rotation axis 141 of the transfer roller due to the thickness of the toner layer is A3. When one size sheet material is transported, a transport distance difference of about 1.7 mm is generated.

  Therefore, a difference in conveying force in the transfer longitudinal direction occurs depending on the presence or absence of toner on the left and right sides of the image, so that the sheet material is obliquely fed to the fixing nip while being skewed, the unfixed portion comes into contact with the conveyance guide, An image defect occurs due to entering.

  Therefore, the present invention reduces the left-right difference in the toner amount due to the image pattern. Therefore, when the left-right difference in the printing rate at the time of image development is greater than or equal to a predetermined value, the means for reducing the left-right difference in the toner amount is used. And to prevent skewing at the transfer nip.

  As described above, the present invention has the following effects.

  1. It is possible to suppress and reduce skew, paper wrinkles, and image defects.

  2. Toner can be saved.

  Next, details of the present invention will be described in accordance with the description of the embodiments.

  In this embodiment, when the left / right difference in the printing rate is greater than or equal to a predetermined value when the image is developed, the left / right difference in the toner amount is realized by means for adjusting the developing toner amount to be small.

  A first embodiment will be described with reference to FIGS. FIG. 1 is a schematic diagram of this embodiment. The controller 102 shown in FIG. 7 of the image forming apparatus shown in the conventional example is read from the contents of the buffer memory 104a in the image processing unit 104 to calculate the printing rate. The printing rate difference judgment unit 1 is added. The parts common to those in FIG. FIG. 2 is a flow regarding determination.

  Image data input from the host computer 100 is converted into bitmap data by the image processing unit 104 via the interface unit 103 and held in the buffer memory 104a. In the case of a full-color image, the input RGB image data is converted into YMCK, which is a signal format handled by the engine unit 106, and held in the buffer memory 104a.

  Here, the determination unit 1 that performs determination regarding the left / right difference of the printing rate refers to the bitmap data in the buffer memory 104a. The bitmap data of the image is divided into left and right areas at the center of the image, the presence / absence of printing is confirmed for each pixel, and the number of print dots is integrated in each of the left and right areas. In the case of a color image, the same processing is performed for each color data of YMCK, and pixels of all colors are integrated in the left and right areas. The determination value is the integrated value or the difference in the ratio of the integrated value to the total number of pixels in the page. If this determination value exceeds a predetermined value, it is determined that the toner application amount operation is necessary, and the engine control unit 107 of the printer engine 106 is controlled via the video interface block 105 so as to control the toner application amount. Tell. If the determination value is less than the predetermined value, no special control is performed. The above flow is illustrated in FIG.

  The engine control unit 107 that has received the status of the applied toner amount operation adjusts the developing bias applied to a developing roller (not shown), reduces the potential difference between the developing roller and the photosensitive drum 124, and develops toner, for example. Reduce the amount.

  Further, a developing toner amount adjusting unit that adjusts the amount of laser light of the scanner to be small may be used.

  The effect of the present embodiment is that by reducing the developing toner amount in the page, the difference in the left and right toner amounts is reduced, the left and right difference in the conveying force is reduced, and skew feeding can be suppressed.

  In this embodiment, when the left / right difference in the printing rate is greater than or equal to a predetermined value at the time of image development, the left / right difference in the toner amount is reduced by printing yellow toner in the print margin.

  A second embodiment will be described with reference to FIG. FIG. 3 is a schematic diagram of the controller of the present embodiment, and the description of the same parts as those in FIG. 1 is omitted. FIG. 3 houses the video interface block 11 in the controller unit 102. The video interface block 11 has an image processing circuit 14 that performs masking processing and UCR, and a register circuit 15 that synchronizes the image data sent from the image processing circuit 14 with a clock signal and sends it to the printer engine as a video signal. The video interface block 11 has a function of receiving a toner application amount adjustment status and an image processing circuit 14 that performs image processing according to the status.

  The determination unit 1 determines the left / right difference in the printing rate from the contents of the buffer memory 104a in the image processing unit 104, and transmits the status based on the determination to the video interface block 11. When the determination value exceeds a predetermined value and a status indicating that the applied toner amount needs to be adjusted is transmitted, the image processing circuit 14 discretely arranges pixels to be printed with yellow toner in the margin on the image data, Reduce the difference in the amount of applied toner between the left and right sides of the image. If the determination value is less than the predetermined value, no special control is performed.

  In the present invention, it is selected because yellow has low sensitivity to human vision. However, in order to reduce the difference in the amount of applied toner between the left and right images, the toner color printed on the margin in the data is not particularly limited. For example, a transparent toner may be used.

  The effect peculiar to the present embodiment is that adjustment of the left / right difference in the toner amount can be performed while preventing the density decrease that may occur in the process of reducing the amount of toner to be developed described in the first embodiment, thereby suppressing skew feeding. be able to.

  In this embodiment, when the left / right difference of the printing rate is greater than or equal to a predetermined value at the time of image development, the shadow portion on the side with the lower printing rate is configured by process black with YMC superimposed, so that the left / right difference in toner amount is increased. Reduce.

  The present embodiment will be described with reference to FIGS. FIG. 4 is a schematic diagram of the controller of the present embodiment, and the description of the same parts as those in FIGS. 1 and 3 is omitted. In this embodiment, the image processing unit 20 shown in FIG. 4 has two CMYK conversion tables having different gray color scheme designs. These gray color schemes will be described with reference to FIG. FIG. 5a shows a toner composition of a gray design in a conventional full color printer, and is a CMYK conversion table A. FIG. FIG. 5B is a diagram showing a toner composition of a gray design unique to this embodiment, and is a CMYK conversion table B.

  In a conventional full-color printer using an electrophotographic system, process black mixed with YMC toner and BK toner are used in combination for expression in a halftone shadow portion. Gbk in FIG. 5a is a point at which the blending of the BK toner starts, and the blending amount of the YMC toner decreases toward the shadow part, and the BK toner replaces them. On the other hand, in FIG. 5b, the blending start point Gbk ′ of the BK toner is more than that of the shadow, and b does not blend the BK toner between Gbk and Gbk ′, so that b blends more YMC toner than a. Even when blending of the BK toner is started toward the shadow portion, the blending amount of the BK toner is set to be smaller in b in FIGS. 5A and 5B, and more YMC toner is blended.

  Therefore, the CMYK conversion table B consumes a larger amount of toner in the shadow portion than the conventional CMYK conversion table A.

  When the determination unit 1 sends a status indicating that the determination value exceeds a predetermined value and the toner applied amount adjustment is necessary, the image processing unit 20 reconverts the YMCK bitmap data using the CMYK conversion table B, and Write again to buffer memory.

  The effect peculiar to the present embodiment is that toner is not arranged in the margin part, and therefore the toner amount can be adjusted without changing the color of the margin part.

  In this embodiment, when the left / right difference in the printing rate is greater than or equal to a predetermined value when the image is developed, the left / right difference in the toner amount is reduced by performing toner saving processing on the side where the printing rate is high.

  The configuration of the fourth embodiment is the same as that of the second embodiment and will be described with reference to FIGS.

  The toner saving process is a function that saves toner during printing by thinning data from other than the edge portion so that the shape of the figure or character is not destroyed as much as possible.

  As for the data thinning-out method, if all the dots around the thinned-out portion exist as shown in FIG. 6a, it is determined that it is not an edge portion, and the dots are thinned out as shown in FIG. 6b. If even one of the surrounding dots has white, it is judged as an edge portion and data is not thinned out.

  The image processing circuit 14 that has received the status of the applied toner amount operation from the determination unit 1 performs toner saving processing on the data on the left and right sides of the image with the higher printing rate.

  The effects peculiar to the present embodiment can reduce skew feeding and save toner at the same time.

  The configuration for reducing the left-right difference in the toner loading amount has been described by giving an example. However, the configuration is not limited to those of the first to fourth embodiments, and a configuration in which these are combined may be used. By combining them, a further effect can be expected in reducing the difference in left and right toner loading.

  Also, an example in which the video controller is held in the printer main body has been described. However, even for a host-based printer that performs processing for converting image data into a video signal on the host computer, the determination of the print rate left-right difference is performed in the host computer. Similar effects can be achieved with different configurations.

The figure which shows the structure of the printer apparatus of this specification Image left / right difference judgment flow Schematic of the controller in the second embodiment Schematic of controller in Example 3 Graph showing the amount of toner blended in gray scale design Schematic diagram of toner saving process The figure which shows the structure of the conventional printer apparatus Cross section of transfer nip Cross section of transfer nip

Explanation of symbols

1 Print rate difference judgment circuit
11 Video interface block
14 Image processing circuit
15 Register circuit
20 Image processing section
100 host PC
101 Printer body
102 Controller section
103 Computer interphase section
104 Image processing unit
104a Buffer memory
105 Video interphase section
106 engine
107 Engine control unit
107a CPU
120 Feed roller
121 Separation roller
122 Conveyor roller
123 Registration roller
124 Photosensitive drum
125 Development unit
126 Transfer roller
128 Scanner unit
129 Intermediate transfer member
140 Toner layer
141 Transfer roller rotating shaft S Sheet material

Claims (13)

  In an image forming apparatus using an electrophotographic system having a printing rate in-page left / right difference detecting unit and a toner amount adjusting unit capable of adjusting a toner amount for each page, the printing rate is detected by the in-page left / right difference detecting unit. An image forming apparatus that adjusts a toner amount for each page by the toner amount adjusting means when a difference between left and right in-page printing ratio reaches a predetermined value or more.   In the image forming apparatus having a video controller, the determination unit that reads the bitmap data in the image data holding medium included in the video controller and calculates the left / right difference of the in-page printing rate as the in-page left / right difference detection unit of the printing rate. An image forming apparatus having in a video controller, wherein the printing rate difference determination unit sends status information for identifying a left / right difference in printing rate within a page.   In a host computer-based image forming apparatus that does not have a video controller, the image bit map data in the recording medium of the host computer is read and the left-right difference in the page print rate is calculated as means for detecting the left-right difference in the print rate. An image forming apparatus comprising: a determination unit configured to be included in a recording medium included in the host computer, wherein the print rate difference determination unit transmits status information for identifying a left / right difference in an in-page print rate.   4. The image forming apparatus according to claim 2, wherein status information for identifying a left-right difference within a page is sent to an engine control unit included in the image forming apparatus.   5. The image forming apparatus according to claim 4, wherein the developing bias is adjusted for each page when the in-page printing rate left / right difference detected by the in-page left / right difference detecting unit of the printing rate reaches a predetermined value or more. Image forming apparatus.   5. The image forming apparatus according to claim 4, wherein when the in-page printing rate left / right difference detected by the in-page left / right difference detecting unit of the printing rate reaches a predetermined value or more, the exposure light amount of the exposure unit is adjusted. Image forming apparatus.   The image forming apparatus according to claim 2, further comprising: a circuit that performs image processing on the image data between an image data holding medium of a bitmap included in a video controller and an interface that transmits the image data to the image forming apparatus as a video signal. An image forming apparatus, wherein a process for adjusting a printing rate is performed by a circuit that performs image processing on the image data based on status information that identifies a left-right difference in a page of the image forming apparatus.   4. The image forming apparatus according to claim 3, wherein CMYK image data in a recording medium included in the host computer is processed according to status information for identifying a left-right difference in the page, and processing for adjusting a printing rate is performed. Forming equipment.   The image forming apparatus according to claim 7 or 8, wherein the process of adjusting the printing rate is realized by printing yellow toner in a non-printing area in a direction to reduce a left / right difference of the printing rate. An image forming apparatus.   The image forming apparatus according to claim 7 or 8, wherein the process of adjusting the printing rate is realized by printing a transparent toner in a non-printing area in a direction to reduce a left / right difference of the printing rate. An image forming apparatus.   9. The image forming apparatus according to claim 7, wherein the process for adjusting the printing rate is a toner saving process in a direction to reduce a left / right difference in the printing rate.   12. The image forming apparatus according to claim 11, wherein the toner saving process is performed by thinning out printing at a portion other than an edge portion of the image.   9. The image forming apparatus according to claim 7, wherein the process of adjusting the printing rate includes a plurality of CMYK printing data pixels formed of black toner in the CMYK image data holding medium in a direction to reduce a left / right difference of the printing rate. An image forming apparatus that converts CMYK image data to be printed with a mixed color toner.

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