JP2008026552A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of stably maintaining highly precise image density characteristics over a long period of time. <P>SOLUTION: Upon an instruction to adjust gradation (SP1), a gradation pattern image is formed on recording paper (SP2), a gradation pattern image is read from the recording paper (SP4), and image density correction characteristics for correcting a gradation characteristic are calculated (SP5). Next, the maximum density value on the gradation characteristic is detected, and it is determined whether the maximum density value is equal to or greater than a predetermined value or not. If it is equal to or greater than the predetermined value, the gradation characteristic of the maximum density value is stored (SP7). If it is less than the predetermined value, the gradation characteristic of the image forming section, until that time, is held (SP8). Thus, the optimum gradation characteristic of the image forming section can be obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus capable of adjusting gradation characteristics.

  When the image forming apparatus is used as a copying machine, the electrostatic latent image formed on the photoreceptor is visualized by attaching toner, and the visible image is transferred to a sheet and output. When the image forming apparatus is used for a long period of time, the gradation characteristics of the output image, that is, the so-called shading degree may change due to fatigue of the photoreceptor or developer. In such a case, the gradation characteristic table is corrected in accordance with the usage status of the image forming apparatus, and an optimum gradation characteristic table is created. An image is formed using the table of gradation characteristics.

In JP 2000-238341 A (Patent Document 1), for example, a gradation pattern image is formed on a recording sheet by transferring an image corresponding to the gradation pattern onto the recording sheet at startup. It describes that a gradation pattern image is read, and automatic gradation correction is performed so that the gradation of the read image signal matches the gradation recorded on the recording paper. In Patent Document 1, after that, a patch is created on the photosensitive drum to detect the density value, the density value is stored as a reference density value, and the density value of the patch formed on the photosensitive drum at a predetermined timing is stored. It also describes that the detected density value is matched with the reference density value.
JP 2000-238341 A (summary, FIG. 27)

  However, the method of creating a gradation pattern by transferring to a recording paper as in Patent Document 1 does not necessarily provide optimum image formation due to changes in the adhesion characteristics of the developing toner with respect to the potential of the photosensitive drum due to long-term use. It cannot be said that the condition is obtained. For example, the charging potential of the photosensitive drum may increase to change the adhesion characteristics of the developing toner, or the amount of developer may be low, and the image forming unit is maintained under conditions that are not optimal image forming conditions. When an image is formed with certain gradation characteristics, correct gradation cannot be obtained.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of stably maintaining accurate image density characteristics over a long period of time.

  The present invention includes an image forming unit that forms a gradation pattern image on a recording sheet, a reading unit that reads a gradation pattern image formed on the recording sheet by the image forming unit, and a floor for the image forming unit to form an image. A storage means for storing tonal characteristics; an image density value detecting means for detecting a density value of an image formed by the image forming means based on a gradation pattern image read by the reading means; and an image density value detection Control means for determining whether or not to change the gradation characteristics stored in the storage means according to whether or not the maximum density value of the gradation pattern image detected by the means is greater than or equal to a predetermined value. .

  In one embodiment, if the maximum density value of the gradation pattern image read by the reading unit is greater than or equal to a predetermined value, the control unit may convert the gradation characteristics stored in the storage unit to the gradation read by the reading unit. Change to characteristics. In another embodiment, if the maximum density value of the gradation pattern image read by the reading means is less than a predetermined value, the control means maintains the previous gradation characteristics stored in the storage means.

  Specifically, the image forming unit forms a color image. The gradation pattern image is an image pattern of a plurality of colors whose density changes continuously.

  According to the present invention, the gradation characteristics of the stored image forming means are changed depending on whether or not the maximum density value of the gradation pattern image detected by reading the gradation pattern image is greater than or equal to a predetermined value. Since the tone characteristics of the image forming means are matched with the read tone characteristics, the optimum tone characteristics at that time can be obtained, so accurate image density characteristics are stable over a long period of time. Can be maintained.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a digital multifunction peripheral 10 when an image forming apparatus according to an embodiment of the present invention is applied to the digital multifunction peripheral 10.

  Referring to FIG. 1, a digital multifunction device 10 includes a control unit 11 that operates as a control unit that controls the entire digital multifunction device 10, a DRAM 12 that writes and reads image data and the like, and a digital multifunction device 10. An operation unit 13 that serves as an interface with the user in the digital multi-function peripheral 10, an image reading unit 15 that operates as a reading unit that reads an image of a document at a predetermined reading position, and an image An image forming unit 16 that operates as an image forming unit that forms an image from a document read by the reading unit 15, a hard disk 17 that operates as a storage unit that stores image data and the like, and a FAX connected to the public line 20 A communication unit 18 and a network IF (interface) unit 19 for connecting to the network 21 Obtain.

  The operation unit 13 includes a gradation adjustment key operated when performing gradation adjustment, a reading key for instructing reading by the image reading unit 15, and the like. The control unit 11 compresses and writes the original data supplied from the image reading unit 15 in the DRAM 12, reads the data written in the DRAM 12, decompresses and encodes the data, and outputs it by the image forming unit 16.

  The digital multi-function peripheral 10 operates as a copier by forming an image in the image forming section 16 via the DRAM 12 using the document read by the image reading section 15. The digital multifunction machine 10 forms an image in the image forming unit 16 via the DRAM 12 using the image data transmitted from the personal computer 22 connected to the network 21 through the network IF unit 19, thereby serving as a printer. Operate.

  Further, the digital multifunction peripheral 10 forms an image in the image forming unit 16 through the DRAM 12 using the image data transmitted from the public line 20 through the FAX communication unit 18, and also by the image reading unit 15. The image data of the read original is transmitted to the public line 20 through the FAX communication unit 18 to operate as a facsimile machine.

  In FIG. 1, thick arrows indicate the flow of image data, and thin arrows indicate the flow of control signals or control data.

  Next, a specific configuration of the image forming unit 16 provided in the digital multifunction peripheral 10 illustrated in FIG. 1 will be described.

  FIG. 2 is a diagram showing the configuration of the image forming unit 16, and FIG. 3 is a cross section of the photosensitive drum and the developing machine of the image forming unit 16 shown in FIG. 2 along a plane perpendicular to the rotation axis of the photosensitive drum. It is a schematic sectional drawing at the time of doing. Referring to FIG. 2, the image forming unit 16 includes photosensitive drums 31, 32, 33, and 34 corresponding to four colors of cyan (C), yellow (Y), magenta (M), and black (K). And developing units 35, 36, 37, and 38. A transfer belt 39 is in contact with the photosensitive drums 31, 32, 33, and 34. Developers 35, 36, 37, and 38 are filled with developers corresponding to the respective colors. Each developing device 35, 36, 37, 38 includes a developing roller that supplies toner to each of the photosensitive drums 31, 32, 33, 34. FIG. 3 shows a developing roller 36 included in a cyan developing device 35 as a representative example. The developing roller 36 is rotatable.

  Here, an image forming process in the digital multi-function peripheral 10 will be briefly described. 1 to 3, first, photosensitive drums 31, 32, and 33 to which a high potential is applied by irradiating light based on an image read by the image reading unit 15 shown in FIG. , 34, electrostatic latent images are formed. Next, toner is supplied from the corresponding developing roller onto the photosensitive drums 31, 32, 33, and 34 on which the electrostatic latent image is formed, and the electrostatic latent image is visualized. Thereafter, the obtained visible image is transferred to the transfer belt 39. Four color toners of cyan, yellow, magenta, and black are transferred onto the transfer belt 39. After a full color image is formed on the transfer belt 39, the color image is transferred from the transfer belt 39 to a sheet (not shown), and the sheet is discharged. In this way, a full color image is formed.

  The developer of each color filled in the developing units 35, 36, 37, and 38 is deteriorated in charging performance and the like due to long-term use. In such a case, in order for the image to be formed to have the optimum gradation characteristic, the gradation characteristic table is corrected according to the usage status of the image forming apparatus 10 to create the optimum gradation characteristic table. There is a need to. Then, an image is formed using a table of gradation characteristics adjusted optimally.

  FIG. 4 is a flowchart for explaining an operation for obtaining optimum gradation characteristics in the digital multi-function peripheral 10 as an example of the image forming apparatus according to the embodiment of the present invention.

  The gradation adjustment is performed by a service person. The service person operates the gradation adjustment key of the operation unit 13. The control unit 11 determines whether or not there is an instruction for gradation adjustment in a step (abbreviated as SP in the drawing) SP1 shown in FIG. If it is determined that there is an instruction for gradation adjustment, a gradation pattern image is created on the recording paper 30 as shown in FIG.

  FIG. 5 is a diagram showing a recording paper 30 on which gradation pattern images of cyan, yellow, magenta, and black are created. In the main scanning direction of the recording paper 30 shown in FIG. 5 (the direction shown by the arrow A or the reverse direction), gradation patterns of respective colors are created in the order of cyan, yellow, magenta, and black. In the gradation pattern, the density of each color varies stepwise for each predetermined width in the sub-scanning direction (the direction indicated by arrow B or the reverse direction).

  The service person sets the recording paper 30 on which the gradation pattern image shown in FIG. 5 is recorded in the image reading unit 15 and operates the reading key of the operation unit 13. If it is determined in step SP3 that the recording paper 30 has been set and the reading key has been operated, the gradation pattern image on the recording paper 30 is read by the image reading unit 15 in step SP4. In step SP5, the control unit 11 calculates an image density correction characteristic for correcting the gamma characteristic from the gamma characteristic of the gradation pattern image read from the recording paper 30 by calculation.

  6 is a diagram showing gradation characteristics, an image density correction characteristic curve, and gradation characteristics read from the recording paper 30 shown in FIG. 5, and FIG. 7 is adjusted with the gradation characteristics shown in FIG. FIG.

  As shown in FIG. 6, the gradation characteristic a should increase almost linearly as the number of gradations increases as indicated by a one-dot chain line, but the image density increases with long-term use. As the number of gradations increases, the density becomes saturated as shown in the solid line. This saturation of the density is caused by the fact that the optimum image forming conditions cannot be ensured due to the change in the adhesion characteristics of the developing toner with respect to the charging potential of the photosensitive drum 23 included in the image forming unit 16.

  As described above, the gradation characteristic a read from the recording paper 30 is saturated at a high gradation, so that an appropriate density cannot be obtained according to the number of gradations. Therefore, the image density correction characteristic curve b is calculated so as to obtain the gradation characteristic c indicated by a straight line, and the gradation characteristic a is corrected by the image density correction characteristic b.

  In step SP6, the image forming unit 16 detects the maximum density value from the read gradation characteristic a, and determines whether or not the maximum density value is a predetermined value, for example, ID (Image Density) = 1.0 or more. To do. If the maximum density value is ID = 1.0 or more, the gradation characteristic of the maximum density value is stored in the hard disk 17 in step SP7. If the maximum density value is less than ID = 1.0, the gradation characteristics up to that of the image forming unit 16 stored in the hard disk 16 are held in step SP8.

  For example, it is assumed that ID = 1.1 is obtained as the maximum density value from the gradation characteristic a shown in FIG. In this case, since ID = 1.0 or more, the gradation characteristic c having the maximum density value of ID = 1.1 is changed as the gradation characteristic of the image forming unit 16 as shown in FIG. If only ID = 0.9 is obtained as the maximum density value from the gradation characteristic a, the gradation characteristic d shown in FIG. 7 of the image forming unit 16 until then is held as the gradation characteristic of the image forming unit 16. To do.

  As described above, according to this embodiment, when performing gradation adjustment, a gradation pattern image is created on the recording paper 30, and the gradation pattern image is read to obtain an optimum gradation characteristic. The correction characteristic is calculated, and the gradation characteristic is corrected by the image density correction characteristic to obtain an appropriate gradation characteristic. If the maximum density value is detected from the read tone characteristics and the maximum density value is ID = 1.0 or more, which is a predetermined value, the tone characteristics of the image forming unit 16 are maintained at the maximum density value. Thereby, an accurate image density characteristic with a density corresponding to the target number of gradations can be stably maintained over a long period of time. If the maximum density value is less than ID = 1.0, an image is formed with the gradation characteristics held so far.

  In the above description, the present invention is applied to the full-color digital multi-function peripheral 10 composed of four colors of cyan, yellow, magenta, and black. However, the present invention is not limited to this example. You may apply this invention to a machine.

  In the above description, the present invention is applied to the digital multifunction peripheral 10, but the present invention may be applied to a single device such as a copying machine, a printer, and a facsimile.

  As mentioned above, although embodiment of this invention was described with reference to drawings, this invention is not limited to the thing of embodiment shown in figure. Various modifications and variations can be made to the illustrated embodiment within the same range or equivalent range as the present invention.

1 is a block diagram illustrating a configuration of a digital multifunction peripheral when an image forming apparatus according to an embodiment of the present invention is applied to the digital multifunction peripheral. 2 is a diagram illustrating an overall configuration of an image forming unit. FIG. FIG. 2 is a schematic cross-sectional view of the image forming unit illustrated in FIG. 1. 6 is a flowchart for explaining an operation of creating a reference density in the digital multi-function peripheral as an example of the image forming apparatus according to the embodiment of the present invention. FIG. 4 is a diagram showing a recording sheet on which gradation pattern images of cyan, yellow, magenta, and black are created. FIG. 6 is a diagram illustrating gradation characteristics read from the recording paper illustrated in FIG. 5, an image density correction characteristic curve, and corrected gradation characteristics. It is a figure which shows the corrected gradation characteristic shown in FIG. 6, and the adjusted gradation characteristic.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Image forming apparatus, 11 Control part, 12 DRAM, 13 Operation part, 15 Image reading part, 16 Image forming part, 17 Hard disk, 18 FAX communication part, 19 Network IF part, 20 Public line, 21 Network, 22 Personal computer, 31 , 32, 33, 34 Photosensitive drum, 35, 36, 37, 38 Developer, 36 developing roller, 39 transfer belt.

Claims (5)

Image forming means for forming a gradation pattern image on recording paper;
Reading means for reading a gradation pattern image formed on the recording paper by the image forming means;
Storage means for storing gradation characteristics for the image forming means to form an image;
An image density value detecting means for detecting a density value of an image formed by the image forming means based on the gradation pattern image read by the reading means;
Control for determining whether to change the gradation characteristics stored in the storage means according to whether the maximum density value of the gradation pattern image detected by the image density value detection means is a predetermined value or more. And an image forming apparatus.   If the maximum density value of the gradation pattern image read by the reading unit is equal to or greater than the predetermined value, the control unit may convert the gradation characteristics stored in the storage unit to the gradation read by the reading unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is changed to a characteristic.   The control means maintains the previous gradation characteristics stored in the storage means if the maximum density value of the gradation pattern image read by the reading means is less than the predetermined value. The image forming apparatus described in 1.   The image forming apparatus according to claim 1, wherein the image forming unit forms a color image.   The image forming apparatus according to claim 4, wherein the gradation pattern image is an image pattern of a plurality of colors whose density continuously changes.

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