JP2012093488A - Image forming apparatus and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that accurately detects the toner adhesion amount on a sheet and maintains good tone reproduction characteristics on a sheet, irrespective of the types of sheets to be used.SOLUTION: Test patches (tone patches) having different tone characteristics are formed on a photoreceptor, and each of the toner amount P is detected by a sensor. The formed test patches are again transferred to sheets, and each of the transfer residual toner amount D is detected by a sensor. The toner amount before transfer and the transfer residual toner amount of respective tone patches are compared, and each of the toner residual amount on a sheet is determined. Here, the difference between the toner amount before transfer and the transfer residual toner amount is defined as the toner adhesion amount on a sheet.

Description

  The present invention relates to an image forming apparatus and an image forming method such as a copying machine, a facsimile, and a printer using an electrophotographic system.

  In an electrophotographic image forming apparatus, it is difficult to avoid variations in gradation due to changes in toner charge amount due to changes in temperature and humidity, deterioration of durability of parts, and the like. Therefore, in the digital electrophotographic system, the density of the high gradation portion is maintained by the potential control, and the gradation property of the halftone region is corrected and controlled using the gradation correction conversion lookup table (LUT) itself as an operation amount. The method is known. In the case of a copying machine equipped with a scanner, a configuration is often employed in which a test chart for gradation correction is printed on paper, and the result read by the scanner is fed back to the conversion LUT.

  As a gradation correction method in a printer without a scanner, a configuration for correcting the conversion LUT based on the density detection results of toner patches of different gradations formed on an image carrier is already known.

  For example, Japanese Patent Laid-Open No. 2005-331658 (Patent Document 1) detects the density of a plurality of toner patches of different gradations formed on an image carrier for the purpose of maintaining gradation reproducibility, A configuration for correcting the gradation control conversion LUT based on the density of the toner patch is disclosed.

  However, with the conventional gradation correction control on the image carrier, the gradation on the image carrier can be ensured, but due to the effect of transfer efficiency depending on the area ratio, the target gradation reproduction is not necessarily performed on the paper. There is a problem that sex cannot be maintained. In order to solve this problem, a method for directly detecting the toner on the paper by arranging a sensor on the paper conveyance path is conceivable. However, the same toner detection accuracy is ensured for various types of paper. There was a problem that it was difficult.

The method disclosed in Patent Document 1 cannot always maintain the tone reproducibility on the paper in a target state, and the above problem cannot be solved.
The present invention solves the above-mentioned problems in the conventional image forming apparatus, accurately detects the toner adhesion amount on the paper, regardless of the paper type used, and maintains good gradation reproducibility on the paper. It is an object of the present invention to provide an image forming apparatus that can perform the above-described process.

  According to the present invention, there is provided an image carrier that carries a toner image, a transfer unit that transfers the toner image carried on the image carrier to a recording medium, and a toner adhesion amount on the image carrier. A toner adhesion amount detection means for detecting the toner adhesion amount of a predetermined toner patch carried on the image carrier by the toner adhesion amount detection means, and the predetermined toner patch by the transfer means. This is solved by providing a toner amount calculation unit on the recording medium that calculates the toner amount on the recording medium based on the result of detection of the toner adhesion amount after being transferred to the recording medium by the toner adhesion amount detection unit.

  And a cleaning unit that cleans the surface of the image carrier. The toner adhesion amount detection unit is disposed between a transfer unit where the toner patch is transferred to a recording medium by the transfer unit and the cleaning unit. And preferred.

  And a transfer restricting unit that restricts transfer of the toner image from the image carrier to the recording medium, and the toner adhesion amount of the toner patch on the image carrier with the transfer restricted by the transfer restricting unit. A first detection mode for detecting by the detection means, and a second detection mode for detecting residual toner remaining on the image carrier after the toner patch is transferred to a recording medium by the toner adhesion amount detection means. The toner amount calculation unit on the recording medium preferably calculates the toner amount on the recording medium by comparing the detection result in the first detection mode with the detection result in the second detection mode.

The transfer restricting unit preferably restricts transfer of the toner image to the recording medium by separating the image carrier and the transfer unit.
The image forming apparatus further includes a cleaning unit that cleans the surface of the image carrier, and the toner adhesion amount detection unit is a first toner adhesion amount that is disposed upstream of the transfer unit of the transfer unit in the moving direction of the image carrier. It is preferable that the detection unit includes a second toner adhesion amount detection unit disposed between the transfer unit and the cleaning unit.

  The toner amount calculation unit on the recording medium carries the step of carrying a toner patch on the image carrier and the toner patch before passing through the transfer unit is detected by the first toner adhesion amount detection unit. A step of transferring the toner patch onto the recording medium by the transfer unit, and a step of detecting the toner patch remaining on the image carrier after the transfer by the second toner adhesion amount detection unit. It is preferable to calculate the toner amount on the recording medium.

  The toner amount calculation unit on the recording medium preferably calculates the toner amount on the recording medium based on a difference in toner amount on the image carrier before and after the transfer detected by the toner adhesion amount detection unit.

Further, it is preferable to use a plurality of toner patches having different image area ratios as the toner patches.
Gradation processing means for performing gradation processing on the input image signal, and gradation control of the halftone area by the gradation processing means are controlled by operating a gradation correction conversion lookup table. It is preferable that a gradation correction unit is provided, and the gradation correction unit operates the gradation correction conversion lookup table based on a calculation result of the toner amount calculation unit on the recording medium.

  Further, according to the present invention, there is provided a result of detecting a toner adhesion amount of a predetermined toner patch carried on an image carrier by a toner adhesion amount detecting unit and transferring the predetermined toner patch to a recording medium. The toner amount on the recording medium is calculated based on the result of detection of the toner adhesion amount of the subsequent image carrier by the toner adhesion amount detecting means, and the gradation correction is performed based on the calculated toner amount on the recording medium. It is solved by an image forming method.

  According to the image forming apparatus of the present invention, since the toner amount is detected on the image carrier, the calibration of the toner detection sensor may be performed on the image carrier, and the surface state of the image carrier is compared with that of paper. Since it is extremely stable, the toner amount can be detected with high accuracy. Therefore, it is possible to accurately detect the toner adhesion amount on the paper regardless of the paper type used in the image forming apparatus, and gradation correction control is performed based on the toner adhesion amount on the paper detected with high accuracy. By doing so, it is possible to maintain the tone reproducibility on the paper in a targeted state, and it is possible to maintain a high-quality output image over time.

According to the second aspect of the present invention, the toner adhesion amount can be detected before the transfer residual toner after the toner patch is transferred to the recording medium is cleaned by the cleaning means.
According to the configuration of the third aspect, it is possible to easily detect the toner adhesion amount before and after the transfer of the toner patch to the recording medium.

According to the fourth aspect of the present invention, the toner adhesion amount before transfer can be easily detected by separating the image carrier and the transfer unit.
According to the configuration of the fifth aspect, it is not necessary to provide transfer limiting means such as a contact / separation mechanism of the transfer means, and the apparatus configuration can be simplified.

According to the configuration of the sixth aspect, the toner amount on the recording medium can be accurately calculated.
With the configuration of the seventh aspect, it is possible to accurately calculate the toner amount on the recording medium.

According to the configuration of the eighth aspect, by using a plurality of gradation patches having different image area ratios, there is no influence of a difference in transfer efficiency due to the gradation (image area ratio) of the test patch.
With the configuration according to claim 9, gradation correction control is performed based on the toner adhesion amount detected on the paper with high accuracy regardless of the type of paper used, so that gradation reproducibility on the paper is maintained in a targeted state. This makes it possible to maintain a high-quality output image over time.

  According to the image forming method of the tenth aspect, since the toner adhesion amount on the paper can be detected with high accuracy regardless of the type of paper to be used, based on the toner adhesion amount on the paper detected with high accuracy. By performing the gradation correction control, it is possible to maintain the gradation reproducibility on the paper in a targeted state, and it is possible to realize maintaining a high-quality output image over time.

1 is a cross-sectional configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention. It is a flowchart which shows the process of the gradation correction control in 1st Embodiment. It is a schematic diagram explaining the gradation patch used for specific gradation correction control. It is a block diagram which shows the structure of the part in connection with the gradation correction control in 1st Embodiment. It is a cross-sectional block diagram which shows the image forming apparatus of 2nd Embodiment of this invention. It is a flowchart which shows the process of the gradation correction control in 2nd Embodiment. It is a cross-sectional block diagram which shows the image forming apparatus of 3rd Embodiment of this invention. It is a flowchart which shows the process of the gradation correction control in 3rd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention. The image forming apparatus shown in FIG. 1 is configured as a tandem type direct transfer type color printer, and an endless belt-like transfer belt 120 is provided at substantially the center of the apparatus main body 100. Along the upper side of the transfer belt 120, process cartridges 102a to 102d for monochrome black and three colors (for example, cyan, magenta, and yellow) are arranged in parallel to constitute a tandem image forming unit. In the present embodiment, the process cartridges 102 a to 102 d are detachably attached to the image forming apparatus main body 100.

  An exposure device 103 is disposed on the tandem image forming unit in which the process cartridges 102a to 102d are arranged. Further, the lowermost part of the apparatus main body 100 is configured as a paper feed unit, and a paper feed tray 104 is disposed.

  Each of the process cartridges 102a to 102d has the same structure except for the color of the toner to be handled. The charging unit 110, the developing unit 111, the transfer unit 101 (the loop of the transfer belt 120) are arranged around the photosensitive member 108 as an image carrier. The equipment necessary for the electrophotographic process such as (inside) is arranged.

  In the present embodiment, the image carriers 108a to 108d (hereinafter simply referred to as the photoconductor 108 unless otherwise required) are cylindrical photoconductor drums and are driven to rotate at a linear speed of 50 mm / s. A roller-shaped charger 110 serving as charging means is pressed against the surface of the photoconductor 108 and is driven to rotate by the rotation of the photoconductor 1008. A bias in which AC is superimposed on DC or DC by a high voltage power source (not shown). Is applied, the photosensitive member 108 is uniformly charged to a substantially uniform surface potential.

  Subsequently, the photosensitive member 108 is exposed to image information by an exposure unit 103 which is a latent image forming unit, and an electrostatic latent image is formed. This exposure process is performed by a laser beam scanner or LED using a laser diode. Reference numeral 111 denotes a one-component contact developing device as developing means, which visualizes the electrostatic latent image formed on the photoconductor 1008 as a toner image by a predetermined developing bias supplied from a high voltage power source (not shown). The developing device 111 initially stores one-component toner.

  In the tandem image forming unit in which the process cartridges 102a to 102d are disposed, visible images are formed in the order of black, cyan, magenta, and yellow during full color image formation. A transfer electric field is formed by applying a predetermined transfer bias +400 to +2500 V supplied from an unillustrated high-voltage power source for each color (not shown) to the transfer roller 101 arranged to face the toner image on the photoconductor 108 as a recording medium. A full-color image is formed by sequentially transferring to a sheet, and then the sheet is discharged after being fixed on the sheet by heat and pressure by the fixing unit 106. Further, the transfer residual toner remaining on the photoconductor 108 after the transfer is collected and discarded by the cleaning units 127a to 127d (hereinafter, simply referred to as the cleaning unit 127 unless otherwise required). In addition, there is a cleanerless system in which the transfer unit toner is collected by the developing unit without providing the cleaning unit on the photosensitive member 108, and various known cleaning units can be employed in the present invention.

  A sheet as a recording medium is stored in a paper feed tray 104, fed by a paper feed roller 105, conveyed to a registration roller pair 107, and at a timing when the leading end of the toner image on the photoconductor 108 reaches the transfer portion. They are sent out together and enter the transfer section.

  The transfer belt 120 is stretched by a drive roller 122, a transfer roller 101, and a tension roller 121, and is rotationally driven via the drive roller 122 by a drive motor (not shown). Further, pressure is applied by a spring on both sides of the tension roller 121 as belt tension. The tension roller 121 is an aluminum pipe shape having a diameter of Φ19 and a width of 231 mm. A flange (not shown) is press-fitted into both ends to serve as a regulating member that regulates the meandering of the transfer belt 120.

  Each roller that stretches the transfer belt 120 is supported from both sides of the transfer belt 120 by a transfer belt unit side plate (not shown). Further, the photoconductor 108 and the transfer belt 120 can be separated at an arbitrary timing by a contact / separation mechanism (not shown).

  As the driving roller 122 of the transfer belt 120, polyurethane rubber (wall thickness: 0.3 to 1 mm), thin layer coating roller (wall thickness: 0.03 to 0.1 mm), or the like can be used. A urethane coating roller (thickness 0.05 mm, Φ19) having a small diameter change due to was used.

  A conductive sponge roller or a conductive solid roller can be used as the transfer roller 101 which is a transfer means. In the case of a conductive sponge roller, a conductive core is made of 10 ^ 4 to 10 ^ 13Ω on a metal core such as SUS. It is configured by covering an elastic body adjusted to a resistance value. As the material, an ion conductive roller (urethane + carbon dispersion, NBR, hydrin), an electronic conductive type roller (EPDM) or the like is used, and generally has an Asker C hardness of 35 ° to 60 °. The toner image on the photoconductor 108 is transferred to the transfer belt 120.

  A transfer belt cleaning blade 123 performs cleaning by scraping off the toner on the transfer belt 120. As the cleaning blade material, urethane rubber having a thickness of 1.5 to 3 mm and a rubber hardness of 65 to 80 ° is used, and is brought into counter contact with the transfer belt 120. The transfer residual toner thus scraped off is stored in the transfer-material waste toner storage section 124 through a toner conveyance path (not shown).

A toner mark sensor (TM sensor) 125 measures each color position on the transfer belt 120 by a regular reflection type sensor and adjusts color matching.
Reference numerals 126a to 126d denote toner amount detection means for detecting the toner amount of the toner patch formed on the photosensitive member 108 (hereinafter, simply referred to as toner amount detection means 126 unless otherwise required). The toner amount detection means 126 is an optical sensor composed of a regular reflection type sensor and a diffuse reflection type sensor in this embodiment. The toner amount detection unit 126 is disposed downstream of the transfer roller 101 and upstream of the cleaning unit 127 in the driving direction of the photoreceptor 108.

  Although a tandem color image forming apparatus has been described as an example here, the present invention can also be applied to a 4-cycle color image forming apparatus or a monochrome image forming apparatus. Further, a developing method using two-component toner may be employed.

  Next, gradation correction control for correcting the gradation correction LUT by calculating the toner adhesion amount on the paper will be described with reference to FIGS. FIG. 2 is a flowchart showing the tone correction control process in the first embodiment, and FIG. 3 is a schematic diagram for explaining a tone patch used for specific tone correction control.

  First, the photoreceptors 108 and the transfer belt 120 are separated from each other by the contact / separation mechanism (step S1). In this state, test patches (tone patches) 200a to 200c having different tone characteristics as shown in FIG. 3 are formed on the photoconductor (step S2). Here, an example in which three patches are used is shown, but the number of gradation patches is not particularly limited, and can be changed as appropriate. At this time, no voltage is applied to the transfer roller 101, and all the toner forming the gradation patch remains on the photoconductor even when it passes between the photoconductor 108 and the transfer roller 101.

  Then, the toner amount of the gradation patch reaching the detection unit is detected by the toner amount detection means 126 (step S3). The gradation patch formation (S2) and detection (S3) are repeated, and when the toner amount detection of all the gradation patches is completed (step S4), the contact / separation mechanism is operated to bring the photoconductor 108 and the transfer belt 120 into contact with each other. (Step S5). At this time, a voltage is applied to the transfer roller 101 and further preparations for conveying the sheet to the transfer unit are made.

  Thereafter, a gradation patch is formed again on the photoconductor (step S6), and the gradation patch is transferred to the sheet (step S7). At this time, the gradation characteristics, size, and number of gradation patches created in step S6 are the same as those formed in step S2.

  When the transfer residual toner of the gradation patch after being transferred to the paper reaches the detection portion, the toner amount of the transfer residual toner is detected by the toner amount detection means 126 (step S8). The gradation patch formation (S6), transfer to paper (S7), and detection (S8) are repeated, and when toner amount detection for all gradation patches is completed (step S9), the toner amount before transfer of each gradation patch ( The toner amount P) detected in step S3 and the residual toner amount (toner amount D detected in step S8) are compared to determine the remaining amount of toner on the paper (step S10). Here, the difference between the amount of toner before transfer and the amount of toner remaining after transfer is defined as the toner adhesion amount on paper.

Then, the tone correction LUT is changed (corrected) based on the toner adhesion amount (toner remaining amount) on the paper calculated in step S10 (step S11).
As described above, in the first embodiment, the toner adhesion amount before and after the transfer is detected on the image carrier (photoconductor 108), and the toner adhesion amount on the sheet is calculated from the results. That is, in order to detect the amount of toner on the image carrier, the toner detection sensor may be calibrated on the image carrier, and the surface state of the image carrier is much more stable than paper. The toner amount can be detected with high accuracy. Therefore, it is possible to accurately detect the toner adhesion amount on the paper regardless of the paper type used in the image forming apparatus, and gradation correction control is performed based on the toner adhesion amount on the paper detected with high accuracy. By doing so, it is possible to maintain the tone reproducibility on the paper in a targeted state, and it is possible to maintain a high-quality output image over time.

  Further, by performing gradation correction control using the result of calculating the toner adhesion amount on the paper of a plurality of gradation patches having different image area ratios, a difference in transfer efficiency depending on the gradation (image area ratio) of the test patch Therefore, it is possible to perform gradation correction control without being influenced by the above, and to perform accurate gradation correction.

FIG. 4 is a block diagram showing a configuration of a portion related to the gradation correction control.
The gradation processing unit 402 refers to the gradation correction conversion LUT 404 and converts the input image signal 401 into the output image signal 403. The gradation correction conversion LUT changing unit 405 corrects the gradation correction conversion LUT 404 based on the toner amount on the sheet of the gradation patch 407 detected by the sheet adhesion amount detection (calculation) unit 406.

  The gradation patch 407 may be a combination of images having a predetermined image area ratio determined in advance, or an image formed based on an output image signal obtained by converting a predetermined input image signal by the gradation correction conversion LUT 404. But you can. For each of the gradation patches 407 thus formed, the toner amount detection unit 408 measures the toner amount before transfer and after transfer.

  Note that the gradation processing unit 402 is a unit that performs gradation processing on the input image signal. The gradation correction conversion LUT changing unit 405 is a unit that controls the gradation of the halftone area by the gradation processing unit 402 by operating the gradation correction conversion LUT 404, and detects the adhesion amount on the sheet. Based on the calculation result of the (calculation) means 406, the gradation correction conversion LUT 404 is operated.

Next, a second embodiment of the present invention will be described.
FIG. 5 is a cross-sectional configuration diagram illustrating an image forming apparatus according to a second embodiment of the present invention. The image forming apparatus shown in this figure is configured as a tandem-type intermediate transfer type color printer, and an endless belt-like intermediate transfer belt 520 is provided substantially at the center of the apparatus main body 500. Along the upper side of the intermediate transfer belt 520, monochrome process cartridges 502a to 502d for black and three colors (for example, cyan, magenta, and yellow) are arranged in parallel to constitute a tandem image forming unit. In the present embodiment, the process cartridges 502 a to 502 d are detachably attached to the image forming apparatus main body 100.

  An exposure device 503 is disposed on the tandem image forming unit in which the process cartridges 502a to 502d are arranged. Further, the lowermost part of the apparatus main body 500 is configured as a paper feed unit, and a paper feed tray 504 is disposed.

  Each of the process cartridges 502a to 502d has the same configuration except that the color of the toner to be handled is different. A charging unit 510, a developing unit 511, and a primary transfer unit 501 (intermediate transfer belt 520) are arranged around a photosensitive member 508 as an image carrier. The equipment necessary for the electrophotographic process is arranged in the loop.

  In this embodiment, the image carriers 508a to 508d (hereinafter, simply referred to as the photoconductor 508 unless otherwise required) are cylindrical photoconductor drums and are rotated at a linear speed of 150 mm / s. A roller-shaped charger 510 serving as a charging unit is pressed against the surface of the photosensitive member 508 and is driven to rotate by the rotation of the photosensitive member 508. A bias in which AC is superimposed on DC or DC by a high voltage power source (not shown). Is applied, the photoreceptor 508 is uniformly charged to a substantially uniform surface potential.

  Subsequently, the photosensitive member 508 is exposed to image information by an exposure unit 503 which is a latent image forming unit, and an electrostatic latent image is formed. This exposure process is performed by a laser beam scanner or LED using a laser diode. Reference numeral 511 denotes a one-component contact developing device as developing means, which visualizes the electrostatic latent image of the photosensitive member 508 as a toner image by a predetermined developing bias supplied from a high voltage power source (not shown). The developing unit 511 initially stores one-component toner.

  In the tandem image forming unit in which the process cartridges 502a to 502d are disposed, visible images are formed in the order of black, cyan, magenta, and yellow when forming a full-color image, and the visible images of the respective colors are formed on the photoreceptor 508. By applying a predetermined transfer bias +400 V to +1200 V supplied from an unillustrated high voltage power source (not shown) to the primary transfer roller 501 arranged oppositely, a transfer electric field is formed, and the toner image on the photoreceptor 508 is transferred to the intermediate transfer belt. By sequentially transferring to 520, a full color image is formed on the intermediate transfer belt 520. The full-color image on the intermediate transfer belt 520 is collectively transferred to the paper fed from the paper feed tray 504 by the action of the transfer roller 525 as a secondary transfer unit, and then the paper is fed by the fixing unit 506 by heat and pressure. The paper is ejected after being fixed on.

  Note that the transfer residual toner remaining on the photosensitive member 508 after the transfer to the intermediate transfer belt 520 is collected and discarded by a cleaning unit (not shown). There is also a cleaner-less system in which the transfer means toner is collected by the developing means without providing the cleaning means on the photoconductor 508, and various known cleaning means can be employed in the present invention.

Further, the transfer residual toner remaining on the intermediate transfer belt 520 after the transfer to the paper is collected by the cleaning unit 523 and discarded.
The intermediate transfer belt 520 is stretched by a drive roller 522, a transfer roller 501, and a tension roller 521, and is rotationally driven via a drive roller 522 by a drive motor (not shown). Further, the belt tension is applied by springs on both sides of the tension roller 521. The tension roller 521 is an aluminum pipe shape having a diameter of Φ19 and a width of 231 mm. A flange (not shown) is press-fitted to both ends to serve as a regulating member that regulates meandering of the transfer belt 520.

Each roller that stretches the intermediate transfer belt 520 is supported from both sides of the transfer belt 520 by a transfer belt unit side plate (not shown).
As the driving roller 522, polyurethane rubber (wall thickness: 0.3 to 1 mm), thin layer coating roller (wall thickness: 0.03 to 0.1 mm), or the like can be used. A small urethane coating roller (thickness 0.05 mm, Φ19) was used.

  Materials used for the intermediate transfer belt 520 include PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), TPE (thermoplastic elastomer), and carbon black. In this example, a surface resistance of 9 to 10 logΩ, a volume resistance of 9 to 10 logΩ, a tensile modulus of 1000 to 2500 MPa, and a thickness of 90 to 160 μm are used. A belt having a circumference of 650 mm was used.

  A cleaning blade 523 for the intermediate transfer belt 520 performs cleaning by scraping off the toner on the intermediate transfer belt 520. As the cleaning blade material, urethane rubber having a thickness of 1.5 to 3 mm and a rubber hardness of 65 to 80 ° is used, and is brought into counter contact with the transfer belt 120. The transfer residual toner thus scraped off is stored in a transfer toner waste toner storage section 524 through a toner conveyance path (not shown).

  The secondary transfer roller 525 is configured by coating an elastic body such as urethane adjusted to a resistance value of 10 ^ 6 to 10 ^ 10Ω with a conductive material on a metal core metal such as SUS of φ6. As the material, an ion conductive roller (urethane + carbon dispersion, NBR, hydrin), an electronic conductive type roller (EPDM) or the like is used. In this embodiment, a urethane roller having Φ20 and Asker C hardness of 35 to 50 °. Was used.

  The recording paper is fed by the paper feeding / conveying roller 505 and the registration roller pair 507 at the timing when the leading edge of the toner image on the surface of the intermediate transfer belt 520 reaches the secondary transfer position, and a predetermined transfer bias is supplied by a high voltage power source (not shown). Is applied, the toner image on the intermediate transfer belt 520 is transferred to the recording paper. In this configuration, the paper feed takes a vertical path. The recording sheet is separated from the intermediate transfer belt 520 by the curvature of the secondary transfer counter roller 525, and the toner image transferred to the recording sheet is fixed by the fixing unit 506 and then discharged.

  Reference numeral 526 denotes toner amount detection means for detecting the toner amount of the toner patch formed on the intermediate transfer belt 520, and is an optical sensor composed of a regular reflection type sensor and a diffuse reflection type sensor. The toner amount detection unit 526 is disposed downstream of the secondary transfer unit and upstream of the cleaning blade 523 in the driving direction of the intermediate transfer belt 520.

The secondary transfer roller 525 can be separated from the intermediate transfer belt 520 at an arbitrary timing by a contact / separation mechanism (not shown).
Next, tone correction control in the second embodiment will be described with reference to the flowchart of FIG.

  First, the intermediate transfer belt 520 and the secondary transfer roller 525 are separated by the contact / separation mechanism (step S21). In this state, test patches (tone patches) 200a to 200c having different tone characteristics as shown in FIG. 3 are formed on the intermediate transfer belt 520 (step S22). That is, the test patch 200 formed on the photoconductor is transferred from the photoconductor 508 onto the intermediate transfer belt 520 and carried. At this time, no voltage is applied to the secondary transfer roller 525, and all of the toner forming the gradation patch remains on the intermediate transfer belt 520 even after passing through the secondary transfer portion.

  Then, the toner amount of the gradation patch reaching the detection unit is detected by the toner amount detection means 526 (step S23). The gradation patch formation (S22) and detection (S23) are repeated, and when the toner amount detection of all the gradation patches is completed (step S24), the contact / separation mechanism is operated to move the intermediate transfer belt 520 and the secondary transfer roller 525. (Step S25). At this time, a voltage is applied to the secondary transfer roller 525, and further preparations for conveying the sheet to the secondary transfer unit are made.

  Thereafter, a gradation patch is formed again on the intermediate transfer belt 520 (step S26), and the gradation patch is transferred to the sheet (step S27). At this time, the gradation characteristics, size, and number of gradation patches created in step S26 are the same as those formed in step S22.

  When the transfer residual toner of the gradation patch after being transferred to the paper reaches the detection unit, the toner amount of the transfer residual toner is detected by the toner amount detection means 526 (step S28). The gradation patch formation (S26), transfer to the sheet (S27), and detection (S28) are repeated, and when the toner amount detection of all the gradation patches is completed (step S29), the toner amount before transfer of each gradation patch ( The toner amount P) detected in step S23 is compared with the residual toner amount (toner amount D detected in step S28) to determine the remaining amount of toner on the paper (step S30). Here, the difference between the amount of toner before transfer and the amount of toner remaining after transfer is defined as the toner adhesion amount on paper.

Then, the tone correction LUT is changed (corrected) based on the toner adhesion amount (toner remaining amount) on the paper calculated in step S30 (step S31).
As described above, in the second embodiment, the toner adhesion amount before and after the transfer is detected on the image carrier (intermediate transfer belt 520), and the toner adhesion amount on the sheet is calculated from the results. That is, in order to detect the amount of toner on the image carrier, the toner detection sensor may be calibrated on the image carrier, and the surface state of the image carrier is much more stable than paper. The toner amount can be detected with high accuracy. Therefore, it is possible to accurately detect the toner adhesion amount on the paper regardless of the paper type used in the image forming apparatus, and gradation correction control is performed based on the toner adhesion amount on the paper detected with high accuracy. By doing so, it is possible to maintain the tone reproducibility on the paper in a targeted state, and it is possible to maintain a high-quality output image over time.

Next, a third embodiment of the present invention will be described.
FIG. 7 is a cross-sectional configuration diagram illustrating an image forming apparatus according to a third embodiment of the present invention. The image forming apparatus according to the second embodiment described with reference to FIG. 5 has the same configuration except that the pre-secondary transfer toner amount detection unit 527 is added, and therefore, the configuration and operation of the portion related to image formation are duplicated. Description to be omitted is omitted. The contact / separation mechanism for the secondary transfer roller 525 may be omitted.

FIG. 8 is a flowchart showing the tone correction control process in the third embodiment. The gradation correction control will be described with reference to the flowchart.
Test patches (tone patches) 200a to 200c having different tone characteristics as shown in FIG. 3 are formed on the intermediate transfer belt 520 (step S41). That is, the test patch 200 formed on the photoconductor is transferred from the photoconductor 508 onto the intermediate transfer belt 520 and carried. Then, the toner amount P of the gradation patch before the secondary transfer is detected by the toner amount detection means 527 before the secondary transfer (step S42), and the gradation patch is transferred to the sheet (step S43).

  Next, the secondary transfer residual toner amount detection means 526 detects the toner amount D of the transfer residual toner (step S44). Formation of gradation patches (S41), detection of toner amount P (S42), transfer to paper (S43), detection of toner amount D (S44) are repeated, and toner amount detection of all gradation patches is completed ( In step S45), the toner amount P before transfer of each gradation patch is compared with the residual toner amount D to determine the remaining amount of toner on the sheet (step S46). Here, the difference between the pre-transfer toner amount P and the untransferred toner amount D is defined as the toner adhesion amount on paper.

Then, the gradation correction LUT is changed (corrected) based on the toner adhesion amount (toner remaining amount) on the paper calculated in step S46 (step S47).
In this way, in the third embodiment, the toner adhesion amount before and after the transfer is detected on the image carrier (intermediate transfer belt 520) without providing the contact / separation mechanism of the secondary transfer means, and based on the results. The toner adhesion amount on the paper is calculated. That is, in order to detect the amount of toner on the image carrier, the toner detection sensor may be calibrated on the image carrier, and the surface state of the image carrier is much more stable than paper. The toner amount can be detected with high accuracy. Therefore, it is possible to accurately detect the toner adhesion amount on the paper regardless of the paper type used in the image forming apparatus, and gradation correction control is performed based on the toner adhesion amount on the paper detected with high accuracy. By doing so, it is possible to maintain the tone reproducibility on the paper in a targeted state, and it is possible to maintain a high-quality output image over time.

  As mentioned above, although this invention was demonstrated by the example of illustration, this invention is not limited to this. For example, an appropriate configuration / system can be used as the toner amount detection means. In addition, the gradation patch can have appropriate gradation characteristics, size, shape, number, and the like.

  The configuration of each part of the image forming apparatus is also arbitrary, and the arrangement order of the color process cartridges in the tandem type is arbitrary. In addition to the tandem type, a configuration in which a plurality of developing devices are arranged around a single photosensitive member, or a configuration using a revolver type developing device is also possible. The present invention can also be applied to a full color machine using three color toners, a multicolor machine using two color toners, or a monochrome apparatus. Of course, the image forming apparatus is not limited to a printer or a copying machine, but may be a facsimile machine or a multifunction machine having a plurality of functions.

DESCRIPTION OF SYMBOLS 100 Main body 120 Transfer belt 102 Process cartridge 108 Photoconductor (image carrier)
101 Transfer means 127 Cleaning means 126 Toner amount detection means 200 Test patch (tone patch)
402 gradation processing means 404 gradation conversion LUT
405 gradation correction conversion LUT changing means 406 adhering amount detection (calculation) means 520 intermediate transfer belt (image carrier)
525 secondary transfer roller (secondary transfer means)
523 Cleaning means 526 Toner amount detection means 527 Toner amount detection means before secondary transfer

JP 2005-331658 A

Claims (10)

An image carrier that carries a toner image, a transfer unit that transfers the toner image carried on the image carrier to a recording medium, and a toner adhesion amount detection unit that detects the toner adhesion amount on the image carrier. And
The result of detecting the toner adhesion amount of the predetermined toner patch carried on the image carrier by the toner adhesion amount detection unit, and the toner adhesion amount after the predetermined toner patch is transferred to the recording medium by the transfer unit An image forming apparatus comprising: a toner amount calculation unit on a recording medium that calculates a toner amount on the recording medium based on a result detected by the toner adhesion amount detection unit. A cleaning means for cleaning the surface of the image carrier;
The image forming apparatus according to claim 1, wherein the toner adhesion amount detection unit is disposed between a transfer unit where the toner patch is transferred to a recording medium by the transfer unit and the cleaning unit. Transfer restriction means for restricting transfer of the toner image from the image carrier to the recording medium,
A first detection mode for detecting the toner patch on the image carrier by the toner adhesion amount detection means in a state where transfer is restricted by the transfer restriction means;
A second detection mode in which residual toner remaining on the image carrier after the toner patch is transferred to a recording medium is detected by the toner adhesion amount detection unit;
The toner amount calculation unit on the recording medium calculates a toner amount on the recording medium by comparing a detection result in the first detection mode with a detection result in the second detection mode. The image forming apparatus according to claim 1 or 2.   The image forming apparatus according to claim 3, wherein the transfer restriction unit restricts transfer of the toner image onto a recording medium by separating the image carrier and the transfer unit. A cleaning means for cleaning the surface of the image carrier;
The toner adhesion amount detection means is arranged between a first toner adhesion amount detection means arranged upstream of the transfer portion by the transfer means in the image carrier moving direction, and between the transfer portion and the cleaning means. The image forming apparatus according to claim 1, further comprising a second toner adhesion amount detection unit. The toner amount calculation unit on the recording medium includes:
Carrying a toner patch on the image carrier;
Detecting the toner patch before passing through the transfer portion by the first toner adhesion amount detecting means;
Transferring the toner patch onto a recording medium by the transfer means;
The toner amount on the recording medium is calculated through a step of detecting the toner patch remaining on the image carrier after the transfer by the second toner adhesion amount detection unit. Image forming apparatus. The toner amount calculation unit on the recording medium includes:
7. The toner amount on the recording medium is calculated based on a difference in toner amount on the image carrier before and after the transfer detected by the toner adhesion amount detecting unit. The image forming apparatus described in 1.   The image forming apparatus according to claim 1, wherein a plurality of toner patches having different image area ratios are used as the toner patches. Gradation processing means for performing gradation processing on the input image signal;
Gradation correction means for correcting and controlling the gradation of the halftone area by the gradation processing means by operating a conversion table for gradation correction;
9. The gradation correction unit operates the gradation correction conversion lookup table based on a calculation result of the toner amount calculation unit on the recording medium. Image forming apparatus. The toner adhesion amount of the predetermined toner patch carried on the image carrier is detected by the toner adhesion amount detection means, and the toner adhesion amount of the image carrier after the predetermined toner patch is transferred to the recording medium An image forming method, comprising: calculating a toner amount on a recording medium based on a result detected by an adhesion amount detecting unit; and performing gradation correction based on the calculated toner amount on the recording medium.

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