JP2016012091A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that certainly stabilizes half-tone density by optimizing image formation conditions.SOLUTION: An image forming apparatus 100 comprises a storage section 210, an engine section 110, a density detection section 230, an image reading section 90, and a control section 200. The storage section 210 stores first image data and second image data for forming a first test toner image and a second test toner image which include a plurality of areas which gradually change the density of each area. At the time of executing calibration processing, the control section 200 causes the density detection section 230 to detect first density of the first test toner image formed on a photoreceptor drum 31 by the engine section 110. The control section 200 compares the first density with second density of read image data which is obtained by reading a sheet having the first test toner image formed thereon by the image reading section 90. The control section 200 determines an area in which the first density is approximate to the second density as the second test toner image and updates the second image data.

Description

  The present invention relates to an image forming apparatus that adjusts image forming conditions such as exposure conditions by an exposure unit, developing conditions by a developing unit, transfer conditions by a transfer unit, and fixing conditions by a fixing unit.

  In an electrophotographic image forming apparatus, an electrostatic latent image is formed on the surface of a photosensitive member by an exposure unit, a toner is supplied to the electrostatic latent image by a developing unit, and a toner image is formed. The toner image is directly or indirectly transferred from the surface of the body to the paper, and the toner image is fixed on the paper by the fixing unit, thereby forming an image on the paper. The image forming apparatus cannot obtain good image quality due to aging or contamination of various units. In order to obtain good image quality, the halftone density is stabilized by adjusting the image forming conditions such as the exposure conditions by the exposure unit, the development conditions by the development unit, the transfer conditions by the transfer unit, and the fixing conditions by the fixing unit. Process control processing must be performed periodically.

  In the process control process, each time an image is formed on a predetermined number of sheets, a test toner image whose density changes stepwise is formed on the surface of the photoconductor, and is detected from the surface of the photoconductor by the density detector. Some image forming conditions are adjusted based on the density of a test toner image (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 9-134044

  However, the concentration detection unit may cause a measurement error at a predetermined concentration due to variations in sensitivity due to individual differences. For this reason, if the image forming conditions are optimized based on the density at which the measurement error has occurred, the halftone density becomes unstable.

  An object of the present invention is to provide an image forming apparatus that can reliably stabilize halftone density by optimizing image forming conditions.

  The image forming apparatus of the present invention includes a storage unit, an image forming unit, a density detecting unit, an image reading unit, and a control unit. The storage unit stores first image data, second image data, and a correction table. The first image data and the second image data are formed as a first test toner image and a second test toner image such as a gray scale or a color scale having a plurality of regions and the density of each region varies stepwise. Is to do. The correction table is for adjusting the halftone density. The image forming unit forms a toner image on an image carrier and forms it on a sheet. The density detection unit detects the density of the toner image formed on the image carrier. The image reading unit reads an image from a sheet. The control unit controls calibration processing and process control processing. Calibration process C is a process for adjusting the halftone density by adjusting the correction table using the first test toner image, which is performed at the time of factory shipment or when the power is turned on. Specifically, in the calibration process, a first test toner image formed on the paper using the first image data by the image forming unit is read as read image data by the image reading unit, and the first image data and the read image are read. The correction table is adjusted based on the data comparison result. The process control process is performed every predetermined number of processed images, and is a process for stabilizing the halftone density by adjusting the image forming conditions of the image forming unit using the second image data. Specifically, in the process control process, the density of the second test toner image formed on the image carrier using the second image data by the image forming unit is detected by the density detection unit, and the second test use is performed. The image forming conditions of the image forming unit are adjusted based on the density of the toner image. The control unit detects the first density of the first test toner image formed on the image carrier by the image forming unit when the calibration process is performed, and detects the first density and the read image data. The second image data is updated based on the comparison result of the second density.

  In this configuration, when executing the calibration process, the control unit, in addition to the normal calibration process, based on the comparison result between the first density and the second density of the read image data, uses the second control process. Update the image data. The control unit performs process control processing using the updated second image data in the calibration processing.

  Further, it is preferable that the control unit updates the second image data so as to form a second test toner image having a region in which the first density and the second density are approximated when the calibration process is executed.

  The control unit updates the second image data so as to form a second test toner image having a region in which the first density and the second density are approximated, thereby measuring the density due to the sensitivity variation of the density detection unit. The process control process can be performed using the second test toner image formed of a region where an error is unlikely to occur. Thus, the image forming apparatus can reliably stabilize the halftone density by optimizing the image forming conditions in the process control process.

  Further, the first image data includes the same image data as the second image data, and the control unit, when executing the calibration process, approximates from the region side where the first density and the second density are not approximated. It is preferable to shift the region of the second test toner image toward.

  The control unit shifts the second test toner image to a region where the measurement error due to the sensitivity variation of the density detection unit is unlikely to occur, so that the control unit does not include a region where the density measurement error is likely to occur due to the sensitivity variation of the density detection unit. Process control processing can be performed using the second test toner image.

  In addition, the first image data includes the same image data as the second image data, and the control unit performs the first density and the second of the plurality of regions of the second test toner image when executing the calibration process. It is preferable to reduce the area where the density is not approximate.

  The control unit includes a region where a density measurement error due to the sensitivity variation of the density detection unit is excluded from the second test toner image by removing a region where the density measurement error is likely to occur due to the sensitivity variation of the density detection unit. The process control process can be performed using the second test toner image that is not present.

  Further, the control unit reduces, when the calibration process is performed, a region where the first density and the second density are not approximated among the plurality of areas of the second test toner image, and the first density and the second density are approximated. It is preferable to compensate for the area to be processed.

  The control unit compensates the area where the density measurement error is likely to occur due to the variation in the sensitivity of the density detection unit of the second test toner image with the area where the measurement error is less likely to occur. The process control process can be performed using the second test toner image in which a measurement error hardly occurs.

  In addition, the density detector detects the density of the first test toner image by irradiating the first test toner image formed on the image carrier with light and measuring the reflected or transmitted light. With this configuration, the control unit determines the amount of light emitted by the density detection unit based on the comparison result between the first density and the second density, instead of updating the second image data, when executing the calibration process. It is preferable.

  The control unit increases the amount of light emitted by the density detection unit when the density detected by the density detection unit is low during the calibration process, and the density detection unit when the density detected by the density detection unit is high. To reduce the amount of light emitted. Thereby, the control unit can make it possible to measure even a region where a measurement error due to the concentration detection unit is likely to occur.

  According to the present invention, the halftone density is reliably stabilized by optimizing the image forming conditions.

1 is a schematic front sectional view of an image forming apparatus according to a first embodiment of the present invention. 2 is a block diagram illustrating functions and configurations of the image forming apparatus. FIG. (A) is an example of a first test toner image stored in the image forming apparatus, and (B) is an example of a second test toner image. 5 is a flowchart of calibration processing by a control unit of the image forming apparatus. (A)-(C) are examples of the second test toner image after the calibration process. It is a flowchart of the process control process by the same control unit. (A)-(C) are examples of the 2nd test toner image after the calibration process which concerns on 2nd-4th embodiment. It is a flowchart of the calibration process by the control part which concerns on 5th Embodiment.

  An image forming apparatus including a developing device according to a first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the image forming apparatus 100 includes an image reading unit 90, an engine unit (corresponding to the image forming unit of the present invention) 110, and a paper feeding unit 80, and is based on instructions from the control unit 200. Then, using the image data read from the original by the image reading unit 90 or the image data input from the external apparatus, a multi-color or single-color image forming process is performed on the paper by an electrophotographic method.

  The image reading unit 90 reads an image from a document that passes on the document table 93 by conveyance of the automatic document conveyance device 120 or a document that is manually placed on the document table 92 with an opening / closing operation of the automatic document conveyance device 120 by an operator. Read data.

  The engine unit 110 includes an exposure unit 1, developing units 21 to 23, photosensitive drums (corresponding to the image carrier of the present invention) 31 to 34, chargers 51 to 54, an intermediate transfer unit 60, and a secondary transfer unit 40. , And a fixing unit 70. The chargers 51 to 54 uniformly charge the surfaces of the photosensitive drums 31 to 34 to a predetermined potential. The exposure unit 1 exposes the surfaces of the photosensitive drums 31 to 34 with laser light modulated with Bk, C, M, and Y image data, thereby forming an electrostatic latent image. The developing devices 21 to 24 supply Bk, C, M, and Y toners and apply a developing bias to convert the electrostatic latent images formed on the photosensitive drums 31 to 34 to Bk, C, M, and Y. The toner image is visualized.

  The intermediate transfer unit 60 includes an intermediate transfer belt 61 and primary transfer rollers 621 to 624, and toner images formed on the peripheral surfaces of the photosensitive drums 31 to 34 are transferred to the surface of the intermediate transfer belt 61 by the primary transfer rollers 621 to 624. Primary transfer. The secondary transfer unit 40 includes a secondary transfer roller 41, and secondarily transfers the toner image on the surface of the intermediate transfer belt 61 onto the paper fed from the paper feed unit 80 by the secondary transfer roller 41. The fixing unit 70 heats and presses the paper on which the toner image is transferred, and firmly fixes the toner image on the surface of the paper. The sheet on which the toner image is fixed is discharged to the paper discharge tray 91.

  As shown in FIG. 2, the control unit 200 includes a CPU 201, a ROM 202, and a RAM 203, and is connected to a storage unit 210, an operation unit 220, a density detection unit 230, an image reading unit 90, an image processing unit 130, and an engine unit 110. Has been.

  The CPU 201 reads the control program recorded in the ROM 202, and executes the control program using the RAM 203 as a working area.

  The storage unit 210 stores a correction table, various parameters, first image data, and second image data.

  The correction table stores a correction value for adjusting the halftone density. The various parameters are parameters for setting the image forming conditions of the engine unit 110. Specifically, the parameters for setting the charge amounts of the chargers 51 to 54, the parameters for setting the exposure amount of the exposure unit 1, and the exposure unit 1 Are parameters for setting the exposure voltage, parameters for setting the developing bias values of the developing units 21 to 24, parameters for setting the transfer voltage values of the primary transfer rollers 621 to 624 and the secondary transfer roller 41.

  As shown in FIG. 3A as an example, the first image data has 48 regions in which 256 gradations are divided as equally as possible, and the first image data has a density that changes step by step. This is data for forming a test toner image. The first image data is used for calibration processing. The calibration process is performed at the time of factory shipment or when the power is turned on, and is a process for adjusting the correction value of the correction table in order to adjust the halftone density which is the color output characteristic of the image forming apparatus.

  As shown in FIG. 3B as an example, the second image data has 12 areas composed of areas having the same density as some of the plurality of areas of the first test toner image. This is data for forming a second test toner image whose density changes step by step. The second image data is used for process control processing. The process control process is performed every predetermined number of image forming processes (for example, 1000 sheets and 2000 sheets), and is a process for adjusting the image forming conditions of the engine unit 110 in order to stabilize the halftone density. . For example, the first image data and the second image data are gray scale image pattern data. The first test toner image and the second test toner image are not limited to a configuration having 48 and 12 regions.

  The image processing unit 130 performs various image processing on the input image data. For example, the image processing unit 130 adjusts the halftone density of the image data using the correction value of the set correction table.

  The engine unit 110 operates based on various set parameters.

  The density detection unit 230 is, for example, a process control sensor, and is provided in an image forming area in the main operation direction (toner image movement direction). The density detector 230 uses the first test toner image and the second test toner to determine the density of a plurality of areas of the first test toner image and the second test toner image formed on the surface of the photosensitive drum 31. Detect as image density. The density detection unit 230 also detects the density of the first test toner image and the second test toner image transferred to the surface of the intermediate transfer belt 61 (corresponding to the image carrier of the present invention). Good.

  The operation unit 220 receives various operation inputs including an instruction to start image forming processing.

  When a signal indicating that the image forming process start instruction has been received is input from the operation unit 220, the control unit 200 sets the correction value of the correction table in the image processing unit 130 and sets various parameters in the engine unit 110. To do. The control unit 200 performs image processing on the image data read by the image reading unit 90 or image data input from an external device by the image processing unit 130, and outputs the image data after image processing to the engine unit 110, thereby An image is formed on.

  As shown in FIG. 4, the control unit 200 sets the correction value of the correction table in the image processing unit 130 and sets various parameters in the engine unit 110 at the calibration processing execution timing (S11). S12). The control unit 200 performs image processing on the first image data stored in the storage unit 210 by the image processing unit 130 (S13).

  The control unit 200 outputs the first image data after image processing to the engine unit 110 (S14). The engine unit 110 forms a first test toner image having a Bk hue on the surface of the photosensitive drum 31 using the first image data, and the first test toner is formed on the sheet via the intermediate transfer belt 61. Form an image.

  The control unit 200 detects the density of the first test toner image formed on the surface of the photosensitive drum 31 (hereinafter referred to as the first density) by the density detection unit 230 at a predetermined timing (S15).

  When the image reading unit 90 reads an image from the paper on which the first test toner image is formed as read image data (S16), the control unit 200 compares the first image data with the read image data, and compares the correction table. The correction value is adjusted (S17).

  The control unit 200 obtains the density of the read image data (hereinafter referred to as the second density) by digitizing the density (or luminance) of each pixel constituting the read image data (S18).

  The control unit 200 compares the first density with the second density (S19). When the first density and the second density are approximated (S20), the control unit 200 ends the process without updating the second image data. The area where the first density and the second density are approximate is an area where the density difference is less than a predetermined value.

  In addition, when the first density and the second density are not approximated, the control unit 200 determines an area where the first density and the second density are approximated as a second test toner image (S21). As shown in FIG. 5A, the area determined as the second test toner image is an area where the first density and the second density are averaged and approximated, and is shown in FIG. 5B. Thus, the first density and the second density are averaged and approximated, and are continuous at a predetermined interval. Further, as shown in FIG. 5C, a plurality of regions in which the first density and the second density are approximated on average and are continuous at a predetermined interval may be used.

  The control unit 200 updates the second image data, which is the image data of the second test toner image, to the storage unit 210 (S22), and ends the process.

  As described above, the control unit 200 updates the second image data based on the comparison result between the first density and the second density when performing the calibration process. As a result, the image forming apparatus 100 can update the second image data to image data for forming a second test toner image including a region in which measurement errors due to variations in sensitivity of the density detection unit 230 are unlikely to occur. it can.

  Also, as shown in FIG. 6, when the predetermined number of image forming processes is reached (S31), the control unit 200 sets the correction value of the correction table in the image processing unit 130 and sets various parameters in the engine unit 110. Set (S32). The control unit 200 performs image processing on the second image data stored in the storage unit 210 by the image processing unit 130 (S33).

  The control unit 200 outputs the second image data after the image processing to the engine unit 110 (S34). The engine unit 110 forms a second test toner image having a Bk hue on the surface of the photosensitive drum 31 using the second image data.

  The control unit 200 detects the density of the second test toner image formed on the surface of the photosensitive drum 31 at a predetermined timing by the density detection unit 230 (S35), and based on the density of the second test toner image. Then, various parameters are corrected (S36).

  As described above, the control unit 200 adjusts the image forming condition of the engine unit 110 by using the second test toner image that includes a region in which a measurement error due to the sensitivity variation of the density detection unit 230 hardly occurs. As a result, the image forming apparatus 100 can reliably stabilize the halftone density by optimizing the image forming conditions by the process control process.

  The image forming apparatus 100 according to the second embodiment differs from the image forming apparatus according to the first embodiment in the method of determining the second test toner image in S20 when the calibration process shown in FIG. 4 is executed. Only the differences will be described below.

  The case where the first concentration and the second concentration are not approximated in the region of BK30 to BK32 will be described as an example. As shown in FIG. 6A, the control unit 200 deletes the area (BK30 to BK32) where the first density and the second density are not approximated, and continues to the area (BK21) opposite to the area not approximated. The number of deleted areas (BK18 to BK20) is added. That is, the control unit 200 shifts the area of the second test toner image from the area side where the first density and the second density are not approximated to the area side where the first density and the second density are approximated.

  As described above, the control unit 200 shifts the second test toner image to a region where a measurement error due to the variation in sensitivity of the density detection unit 230 hardly occurs. As a result, the image forming apparatus 100 can perform the process control process using the second test toner image that does not include a region in which the density measurement error is likely to occur due to the sensitivity variation of the density detection unit 230.

  The image forming apparatus 100 according to the third embodiment differs from the image forming apparatus according to the first embodiment in the method of determining the second test toner image in S20 when the calibration process shown in FIG. 4 is executed. Only the differences will be described below.

  The case where the first concentration and the second concentration are not approximated in the region of BK30 to BK32 will be described as an example. As shown in FIG. 6B, the control unit 200 deletes a region (BK30 to BK32) where the first density and the second density are not approximated. That is, the control unit 200 reduces a region where the first density and the second density are not approximated from the second test toner image.

  As described above, the control unit 200 reduces, from the second test toner image, an area where a density measurement error is likely to occur due to the sensitivity variation of the density detection unit 230. As a result, the image forming apparatus 100 can perform the process control process using the second test toner image that does not include a region in which the density measurement error is likely to occur due to the sensitivity variation of the density detection unit 230.

  The image forming apparatus 100 according to the fourth embodiment differs from the image forming apparatus according to the first embodiment in the method of determining the second test toner image in S20 when the calibration process shown in FIG. 4 is executed. Only the differences will be described below.

  The case where the first concentration and the second concentration are not approximated in the region of BK30 to BK32 will be described as an example. As shown in FIG. 6C, the control unit 200 deletes the areas (BK30 to BK32) where the first density and the second density are not approximated, and between the areas (BK26 to BK29) in the vicinity of the deleted area. The gradation area (BK26.5, BK27.5, BK28.5) is compensated. BK26.5 is a gradation between BK26 and BK27, BK27.5 is a gradation between BK27 and BK28, and BK28.5 is a gradation between BK28 and BK29. That is, the control unit 200 reduces the area where the first density and the second density are not approximated from the second test toner image, and compensates the area where the first density and the second density are approximated.

  As described above, the control unit 200 compensates a region where a density measurement error is likely to occur due to a variation in sensitivity of the second test toner image density detection unit 230 with a region where the measurement error is unlikely to occur. As a result, the image forming apparatus 100 can perform the process control process using the second test toner image that is less likely to cause a density measurement error due to the sensitivity variation of the density detection unit 230.

  The image forming apparatus 100 according to the fifth embodiment differs from the image forming apparatus according to the first embodiment in the processing after S21 in FIG. Only the differences will be described below.

  The density detection unit 230 detects the density of the toner image by irradiating the toner image formed on the photosensitive drum with light and measuring reflected light or transmitted light of the irradiated light.

  As shown in FIG. 7, the control unit 200 ends the process as it is when the first density and the second density are approximated (S20). When the first density and the second density are not approximated, the control unit 200 adjusts the irradiation light amount of the density detection unit 230 (S41). Specifically, when the first density is lower than the second density, the control unit 200 increases the irradiation light amount of the density detector 230, and when the first density is higher than the second density, the density detector The amount of irradiation light 230 is reduced.

  As described above, the control unit 200 can make it possible to measure a region where a measurement error due to the concentration detection unit 230 is likely to occur by adjusting the amount of light emitted from the concentration detection unit 230.

  In the above-described embodiment, the second image data includes not only the image data itself but also data that can create the second image data. For example, it may be information indicating an area of the second test toner image from the area of the first test toner image.

  In the above-described embodiment, the first test toner image and the second test toner image having the Bk hue are formed. However, the first test toner image and the second test toner image for each of the Bk, C, M, and Y hues are formed. A test toner image may be formed. In this case, the first image data and the second image data are, for example, gray scale or color scale image pattern data. The image forming apparatus 100 needs to include a density detection unit 230 for each hue because the sensitivity of density differs for each hue.

  In the above-described embodiment, the first test toner image and the second test toner image are formed in one row. However, the first test toner image and the second test toner image are formed in a plurality of rows. May be. When the first test toner image and the second test toner image formed of two rows are formed, the image forming apparatus 100 needs to include two density detection units 230.

  The above description of the embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

90 ... Image reading unit 110 ... Engine unit 200 ... Control unit 210 ... Storage unit 230 ... Density detection unit

Claims (6)

First image data and second image data for forming a first test toner image and a second test toner image having a plurality of areas and the density of which changes stepwise for each area, and halftone density A storage unit for storing a correction table for adjustment;
An image forming unit that forms a toner image on an image carrier and forms it on a sheet;
A density detector for detecting the density of a toner image formed on the image carrier;
An image reading unit that reads an image from paper as image data;
The first test toner image formed on the sheet using the first image data by the image forming unit is read by the image reading unit as read image data, and a comparison result between the first image data and the read image data A calibration process for adjusting the correction table based on the second image data, and a density detection of the density of the second test toner image formed on the image carrier using the second image data by the image forming unit. A process control process for adjusting the image forming condition of the image forming unit based on the density of the second test toner image detected by the unit, and a control unit for controlling the process control process.
The control unit detects a first density of the first test toner image formed on the image carrier by the image forming unit when the calibration process is performed, and detects the first density of the first test toner image. An image forming apparatus that updates the second image data based on a comparison result between one density and a second density of the read image data.   The control unit updates the second image data so as to form the second test toner image having a region in which the first density and the second density are approximated when the calibration process is executed. The image forming apparatus according to claim 1. The first image data includes the same image data as the second image data,
The control unit shifts a region of the second test toner image from an area side where the first density and the second density are not approximated toward an approximated area side when the calibration process is executed. The image forming apparatus according to 2. The first image data includes the same image data as the second image data,
3. The image formation according to claim 2, wherein when the calibration process is performed, the control unit reduces an area where the first density and the second density are not approximated among a plurality of areas of the second test toner image. apparatus.   The controller reduces, when the calibration process is performed, a region where the first density and the second density are not approximated among a plurality of areas of the second test toner image, thereby reducing the first density and the first density. The image forming apparatus according to claim 2, wherein an area close to two densities is compensated. The density detector irradiates light to the first test toner image formed on the image carrier and measures reflected light or transmitted light of the first test toner image. The concentration of
The controller controls the amount of light emitted by the density detector based on a comparison result between the first density and the second density instead of updating the second image data when the calibration process is executed. The image forming apparatus according to claim 1, wherein the image forming apparatus is determined.

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