JP2008242260A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of maintaining excellent gradation characteristic regardless of whether engine characteristic is good or bad when transferring a reference gradation pattern to paper. <P>SOLUTION: The image forming apparatus is equipped with: an image forming means to form the reference gradation pattern on an image carrier and transfer it to recording paper; a first density adjusting means to generate a gradation conversion table based on a result obtained by adjusting the solid density of the read reference gradation pattern to be target density; and a second density adjusting means to form a test pattern based on the gradation conversion table on the image carrier or an intermediate transfer belt and correct developing bias and the gradation conversion table so that the density value of the test pattern read by a density sensor may be the target density. The first density adjusting means generates the gradation conversion table so that the adjusted solid density out of the formed reference gradation pattern may be the maximum value of the input image data. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention provides an image forming means for forming a reference gradation pattern on an image carrier and transferring it to a recording paper, and reading the density of the reference gradation pattern formed on the recording paper by an image reading means, so that the solid density is a target. A first density adjusting unit that adjusts the density (on the surface and the developing bias) and generates a gradation conversion table based on the result; and the gradation conversion table on the image carrier or the intermediate transfer belt. And a second density adjusting means for correcting the developing bias or the gradation conversion table so that the test pattern density is read by a density sensor and the value becomes a target density. The present invention relates to an image forming apparatus.

  Conventionally, in an image forming apparatus such as a color digital copying machine, a reference gradation pattern is transferred to a recording sheet after the power switch of the apparatus is turned on and a warm-up is completed to shift to a state where a normal image forming process is possible. Then, the reference gradation pattern on the recording paper is read by an image reading device such as a scanner, and the input data is numerically converted based on the read information of the reference gradation pattern, so that output data having desired gradation characteristics is obtained. Has been generated.

  However, when the image forming apparatus is used for a long period of time, an optimal image may not always be obtained in the generated gradation conversion table due to a change in the adhesion characteristics of the toner to the image carrier. all right.

  Therefore, in Patent Document 1, a reference gradation pattern is formed on an image carrier, and a forming unit that forms a gradation pattern image by transferring an image corresponding to the reference gradation pattern onto a recording paper, and the recording A determination unit that reads a gradation pattern image formed on paper and determines a density correction characteristic of the forming unit; a holding unit that holds the density correction characteristic determined by the determination unit; and the image carrier with the density correction characteristic Storage means for storing the density of the image formed on the body, the density stored by the storage means, and the density of the image formed on the image carrier at a predetermined timing, There has been proposed an image processing apparatus having an adjustment unit that adjusts the density correction characteristic held in the holding unit.

In the image processing apparatus of Patent Document 1, the adjustment unit compares the density of the image formed on the image carrier with the density of the reference image stored by the storage unit at a predetermined timing. Since the density correction characteristic is adjusted so that the two densities coincide with each other, even if the image forming apparatus is used for a long period of time and an optimum image cannot be obtained with the first density correction characteristic, the density after adjustment is adjusted. With the correction characteristics, an optimum image can be obtained.
JP 2000-238341 A

  However, like the image processing apparatus of Patent Document 1, a gradation conversion table as a density correction characteristic is generated based on the density of the reference gradation pattern on the recording paper read by a scanner or the like, and is formed on the image carrier. When using the method of adjusting the gradation conversion table based on the density of the obtained image, there are the following problems.

  That is, when transferring a reference gradation pattern to a recording sheet, an image forming unit that forms a toner image of the reference gradation pattern and transfers it to the recording sheet, a fixing unit that fixes a sheet onto which the toner image has been transferred, etc. The characteristics of the engine part of the surface are due to machine differences including variations in the components of the image forming part and assembly errors, and the surface of the intermediate transfer belt due to wear and scratches caused by repeated execution of the image forming process. It is not always a good state due to a change in state or the like.

  The gradation conversion table generated or corrected based on the gradation pattern transferred to the recording sheet in a state where the characteristics of the engine unit are not good exhibits the following characteristics, for example.

  That is, when the density of the patch having the highest density in the gradation pattern, that is, the solid density is higher than the target density, the relationship between the input data, the output data, and the toner density is as shown in FIG. Therefore, even if the entire range of the input data is included, the portion of the predetermined range A of the output data cannot be reproduced.

  On the other hand, when the solid density is lower than the target density, the relationship between the input data, the output data, and the toner density is as shown in FIG. 7B, and the density of the predetermined range B of the input data. Cannot be reproduced.

  That is, in the gradation conversion table generated or corrected based on the gradation pattern transferred to the recording paper in a state where the characteristics of the engine unit are not good, either of FIGS. 7A and 7B is applicable. However, a density that cannot be reproduced occurs, that is, the gradation width becomes narrow. When the image processing apparatus is used for a long time using such a gradation conversion table, a correct gradation is not always obtained.

  In other words, the image formed on the image carrier when correcting the gradation conversion table is an image formed based on the gradation conversion table generated by the poor engine characteristics, and the gradation width is narrower than usual. The gradation conversion table corrected based on the image density may have an unfavorable characteristic such as a smaller gradation width than before the correction. Then, when the image forming process is repeated and the gradation conversion table is adjusted many times based on the density of the image formed on the image carrier, for example, the narrowing ratio of the gradation width increases. As a result, the density that cannot be reproduced increases, and the quality of the output image may deteriorate.

  In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of maintaining good gradation characteristics regardless of whether engine characteristics are good or bad when a reference gradation pattern is transferred to a sheet. is there.

  In order to achieve the above object, the image forming apparatus according to the present invention is characterized in that a reference gradation pattern is formed on an image carrier and transferred to a recording sheet as described in claim 1 of the claims. The image forming means to read and the density of the reference gradation pattern formed on the recording paper are read by the image reading means, adjusted so that the solid density becomes the target density, and a gradation conversion table is generated based on the result A test pattern based on the gradation conversion table is formed on the first density adjusting means and the image carrier or intermediate transfer belt, the test pattern density is read by a density sensor, and a development bias or a value is set so that the value becomes a target density. An image forming apparatus configured to include a second density adjusting unit configured to correct the gradation conversion table, wherein the first density adjusting unit is formed by the image forming unit. Of the reference gradation patterns, as solid density after adjustment is the maximum value of the input image data, in terms of generating the gradation conversion table.

  According to the above-described configuration, even if the engine characteristics of the image forming apparatus are not good, the gradation conversion table is set so that the solid density after the adjustment becomes the maximum value of the input image data at the time of adjustment by the first density adjusting unit. Since the full gradation is ensured by the generation, correction of the developing bias and the like is performed by a test pattern based on a gradation conversion table in which the full gradation is not ensured at the subsequent density adjustment by the second density adjusting unit. Therefore, it is possible to prevent the gradation width from being reduced and maintain good gradation characteristics.

  As described above, according to the present invention, it is possible to provide an image forming apparatus capable of maintaining good gradation characteristics regardless of whether engine characteristics are good or bad when a reference gradation pattern is transferred to a sheet. It became so.

  Hereinafter, an embodiment using a tandem color digital copying machine as an image forming apparatus according to the present invention will be described.

  As shown in FIGS. 1 and 2, the color digital copying machine includes a color CCD, image reading means 1 that reads an original image by photoelectric conversion, and RGB component image data read by the image reading means 1. Is subjected to image processing such as gradation conversion, color adjustment, and magnification conversion, and converted to output image data of each component of YMCK, and based on the output image data converted by the image processing means 2 An image forming unit 3 for forming a toner image of each color component of YMCK, a sheet feeding unit 4 for supplying a sheet as a recording medium to the image forming unit 3, and a transfer unit for transferring the toner image to the fed sheet. 5, a fixing unit 6 for fixing the sheet on which the toner image is transferred, a sheet discharging unit 7 for discharging the sheet, a plurality of menu setting keys for setting various menus, and the like. A work unit 8 is configured by a control unit 9 for controlling them.

  As shown in FIG. 2, the image forming unit 3 is provided with M (magenta), C (cyan), Y (yellow), and K (black) colors arranged along an intermediate transfer belt 51 as an image carrying unit. Development unit comprising a charging device, an exposure head, a developing roller, a magnetic roller, and the like along the circumferential direction of a photosensitive member 31 as an image carrier. Devices, cleaners, static elimination lamps, etc. are arranged.

  Further, the image forming means 3 is provided with a developing bias adjusting means controlled by a control means 9 which will be described later, and the developing bias adjusting means applies at least a predetermined low-voltage bias voltage to the developing device. Thus, the development is performed so that the density of a later-described reference gradation pattern formed on the photoconductor 31 becomes a target density, and the density of a test pattern read by a density sensor described later becomes a target density. A developing bias that is a bias voltage applied to the apparatus is adjusted.

  The transfer means 5 includes an endless intermediate transfer belt 51 supported by three rollers 50, a primary transfer roller disposed on the opposite side of the photoreceptor 31 with the intermediate transfer belt 51 interposed therebetween, and A secondary transfer roller 52 arranged in contact with the intermediate transfer belt 51 is provided, and M (magenta), C (cyan), Y (yellow), and K (black) formed by the photosensitive unit 30. ) Are primarily transferred onto the intermediate transfer belt 51 by the action of the transfer voltage applied to the primary transfer roller, and the paper feeding means is applied by the action of the transfer voltage applied to the secondary transfer roller 52. 4 is secondarily transferred to the paper fed from 4.

  The control means 9 includes a CPU, a ROM that stores a control program executed by the CPU, a RAM that stores control data, and the like. The hardware implements a predetermined function for causing the color digital copying machine to execute an image forming process.

  By the way, the image forming means 3 is configured to form a reference gradation pattern on the photoconductor 31 and transfer it to a recording sheet.

  More specifically, the image forming unit 3 is provided in the image processing unit 2 by being controlled by the control unit 9 when a reference gradation pattern output key provided in the operation unit 8 is operated. The pixel data of the reference gradation pattern stored in the ROM is read, and the read pixel data is formed on the surface of the photoreceptor 31 as the reference gradation pattern of the toner image, and the formed reference gradation The toner image of the pattern is transferred from the photoreceptor 31 to the recording paper via the intermediate transfer belt 51.

  Here, the reference gradation pattern has the image forming unit 3 transfer pixel data composed of a plurality of test patches with different gradation patterns arranged in a preset order to the intermediate transfer belt 51. In other words, the toner image is composed of a plurality of test patches having different image densities. An example of the reference pattern is shown in FIG.

  Hereinafter, the image processing means 2 will be described. The function of the image processing means 2 described below is realized by a CPU provided in the control means 9 or a control program executed by the CPU provided in the image processing means 2.

  In other words, the image processing unit 2 reads the density of the reference gradation pattern formed on the recording paper by the image forming unit 3 by the image reading unit 1, and the surface potential and the development so that the solid density becomes the target density. A first density adjusting unit 21 that adjusts a bias or the like and generates a gradation conversion table 22 based on the result, and a test pattern based on the gradation conversion table 22 is formed on the intermediate transfer belt 51, and the test pattern The image forming apparatus includes a second density adjusting unit 23 that reads the density with the density sensor and corrects the developing bias or the gradation conversion table 22 so that the value becomes the target density.

  The first density adjusting unit 21 will be described. First, the gradation conversion table 22 is a look-up table for performing numerical conversion so that the output image data can secure a desired gradation property with respect to the input image data. For example, the gradation characteristics shown in FIG. It is something that has The gradation conversion table 82 is stored in a ROM provided in the control unit 9 or the image processing unit 2, and the gradation conversion table 22 is provided for each color component constituting the input image data. Is provided.

  The processing operation of the first density adjusting means 21 will be described in detail. The operator of the color digital copying machine sets the reference gradation pattern transferred to the recording paper as a document on the document placing portion of the color digital copying machine. When the gradation conversion table generation key of the operation unit 8 is operated, the reference gradation pattern is read by the image reading unit 1. At this time, the first density adjusting unit 21 receives the density information of the reference gradation pattern read by the image reading unit.

  The first density adjusting unit 21 compares the solid density, which is the density of the test patch having the highest density among the received test patches of the reference gradation pattern, with a preset target density, and When the solid density is lower than the target density, adjustment is performed to increase the surface potential of the photoconductor 31 and / or the developing bias in order to increase the solid density, and the solid density is higher than the target density. Adjusts to reduce the surface potential and / or the developing bias in order to reduce the solid density.

  Here, the target density is a density such that the solid density after adjustment for increasing or decreasing the surface potential and / or the developing bias described above corresponds to the maximum value of the input image data. That is, the first density adjusting unit 21 adjusts the gradation conversion table 22 so that the solid density after the adjustment becomes the maximum value of the input image data among the reference gradation patterns formed by the image forming unit 3. Is generated.

  For example, if the input pixel data value corresponding to the solid density before adjustment is smaller than the maximum value of the input image data as shown by the broken line in FIG. A gradation conversion table 22 as shown by the solid line in (a) is generated, and the value of the input pixel data corresponding to the solid density before adjustment is the maximum of the input image data as shown by the broken line in FIG. When the value is larger than the value, the gradation conversion table 22 as shown by the solid line in FIG. As a result, the solid density after adjustment corresponds to the maximum value of the input image data in both cases of FIGS.

  Hereinafter, the second density adjusting means 23 will be described. The second density adjusting unit 23 reads out pixel data of a test pattern stored in a ROM provided in the image processing unit 2 at a predetermined timing, and generates a floor generated by the first density adjusting unit 23. After application to the tone conversion table, the pixel data of the applied test pattern is transferred to the intermediate transfer belt 51 by the image forming unit 3 to form a test pattern as a toner image.

  Here, the predetermined timing is, for example, the timing when the processing operation of the first density adjusting unit 21 is completed, the timing when a certain time elapses after the power switch of the color digital copying machine is turned on, or the color digital There is a timing when an output value from a temperature sensor, a humidity sensor or the like provided in the copying machine reaches a predetermined value.

  In addition, the test pattern is obtained by using the image forming unit 3 to generate pixel data consisting of a plurality of test patches having different gradation patterns arranged in a preset order in the same way as the reference gradation pattern. This is a toner image composed of a plurality of test patches each having a different image density transferred to the transfer belt 51. Note that the order of test patches and the gradation pattern used in the test pattern may be the same as or different from the reference gradation pattern.

  The reference gradation pattern is transferred to a recording sheet, output from the color digital copying machine, and read by the image reading unit 1 while the density information read by the first density adjusting unit 21 is used. For the test pattern, the density information read by the density sensor provided in the image forming unit 3 is used by the second density adjusting unit 23.

  Here, as shown in FIG. 2, the density sensor 32 is provided on the downstream side of the photoreceptor unit 30 along the circumferential direction of the intermediate transfer belt 51.

  More specifically, the density sensor 32 projects a single polarized light at a predetermined tilt angle with respect to the normal direction of the intermediate transfer belt 51 as shown in FIG. In addition, the reflected light from the intermediate transfer belt 51 is different from the first polarized light and the projected light that are disposed on the opposite side of the light projecting unit 321 with respect to the normal direction. The reflection-type density is configured to include a polarization separation unit 322 that separates into the second polarized light, and first and second light-receiving units 323 that receive the first and second polarized light. The density value detected by the sensor 32 is 1 when the surface of the intermediate transfer belt 51 where the toner image is not formed is detected, and the density value becomes lower as the density of the toner image becomes higher.

  The second density adjusting means 23 compares the density read by the density sensor 32 with a preset target density. Here, the target density is set for at least one test patch of the formed test pattern, for example, only for the test patch with the highest density or for all test patches. Although the target density differs depending on the apparatus, as an example, there is a configuration in which the target density of the test patch having the highest density is set to ID 1.6.

  As a result of comparing the densities, if the read density is lower than the target density, the second density adjusting unit 23 performs adjustment to increase the developing bias in order to increase the read density, and the read density Is higher than the target density, adjustment is performed to reduce the developing bias in order to increase the density to be read.

  Further, the second adjusting means 23 may be configured to correct the gradation conversion table instead of adjusting the developing bias or in addition to adjusting the developing bias. More specifically, when the read density is low, the gradation conversion table data is corrected and read so that the gradient of the gradation characteristics of the gradation conversion table is large, that is, the toner density is high. When the density is high, the table data of the gradation conversion table is corrected so that the gradient of the gradation characteristic becomes small, that is, the toner density becomes low.

  Hereinafter, the generation and correction of the gradation conversion table of the color digital copying machine according to the present invention will be described with reference to the flowchart shown in FIG.

  When the operator of the color digital copying machine operates the gradation conversion table generation key in a state where the recording paper on which the reference gradation pattern is transferred in the image forming means 3 is set in the color digital copying machine (S1), image reading is performed. The means 1 reads the reference gradation pattern of the recording paper (S2).

  The first density adjusting unit 21 adjusts the density so that the solid density becomes the target density based on the density information of the reference gradation pattern received from the image reading unit 1 (S3). A key conversion table is generated (S4).

  Thereafter, the second density adjusting unit 23 forms a test pattern on the intermediate transfer belt 51 at a predetermined timing (S5), and reads the density of the formed test pattern with the density sensor 32 (S7). The development bias or the gradation conversion table is corrected so that the read value becomes the target density (S8).

  Hereinafter, another embodiment will be described. In the above-described embodiment, the color digital copying machine as the image forming apparatus includes the intermediate transfer belt 51, and the toner image formed on the photoconductor 31 is transferred onto the recording paper via the intermediate transfer belt 51. The second density adjusting means 23 has been described with respect to a configuration in which a test pattern based on the gradation conversion table 22 is formed on the intermediate transfer belt 51. However, the color digital copying machine 1 does not include the intermediate transfer belt 51. The toner image may be directly transferred from the photoreceptor 31 (image carrier) to the paper.

  That is, the second density adjusting unit 23 may be configured to form a test pattern based on the gradation conversion table 22 on the photoconductor 31 (image carrier).

  In the above-described embodiment, the configuration has been described in which the image forming unit 3 forms the reference gradation pattern and transfers it to the recording sheet by operating the reference gradation pattern output key provided in the operation unit 8. The image forming unit 3 may be configured to form the reference gradation pattern and transfer it to a recording sheet regardless of the operation of the operation unit 8. For example, the image forming means 3 forms a reference gradation pattern at a predetermined time before the completion of warming up when the power switch of the color digital copying machine is turned on and a normal image forming process is possible. It may be configured to transfer to a recording sheet.

  In the above-described embodiment, the color digital copying machine is used as the image forming apparatus according to the present invention. However, the image forming apparatus is not limited to the color digital copying machine. For example, an embodiment using a monochrome digital copying machine, a color or monochrome analog copying machine, a printer, a facsimile machine, a multifunction machine, or the like as the image forming apparatus may be used.

  The above-described embodiments are merely examples of the present invention, and the scope of the present invention is not limited by the description, and the specific configuration of each part is appropriately changed within the scope of the effects of the present invention. It goes without saying that it can be done.

Block diagram of color digital copier (image forming device) Internal explanatory diagram of a color digital copying machine (image forming apparatus) (A) shows a reference gradation pattern, (b) is an explanatory view showing a density sensor. Illustration of gradation conversion table (A) shows the relationship between input pixel data and density when the value of the input image data corresponding to the solid density before adjustment is smaller than the maximum value of the input image data, and (b) corresponds to the solid density before adjustment. Graph showing the relationship between input image data and density when the value of input image data is greater than the maximum value of input image data Flowchart for explaining generation and correction of gradation conversion table of color digital copying machine according to the present invention. (A) shows the relationship between input data, output data, and toner density when the solid density is higher than the target density, and (b) shows input data when the solid density is lower than the target density. , Graph showing the relationship between output data and toner density

Explanation of symbols

1: image reading means 2: image processing means 21: first density adjusting means 22: gradation conversion table 23: second density adjusting means 3: image forming means 32: density sensor 51: intermediate transfer belt

Claims (1)

An image forming unit that forms a reference gradation pattern on an image carrier and transfers it to a recording sheet, and the density of the reference gradation pattern formed on the recording sheet is read by the image reading unit so that the solid density becomes a target density. First density adjusting means for generating a gradation conversion table based on the result, a test pattern based on the gradation conversion table is formed on the image carrier or the intermediate transfer belt, and the density of the test pattern is determined. An image forming apparatus configured to include a development bias or a second density adjusting unit that corrects the gradation conversion table so that a value read by a sensor becomes a target density;
The first density adjusting unit generates the gradation conversion table so that the adjusted solid density becomes the maximum value of the input image data among the reference gradation patterns formed by the image forming unit. apparatus.