JP2011133771A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can efficiently reduce the unevenness of density in a main scanning direction without using an expensive density meter or without repeating visual density correction work a plurality of times. <P>SOLUTION: A sheet on which a plurality of toner patches 97 are formed in a main scanning direction by an image forming section is used as a test print 93. The density in the main scanning direction is corrected on the basis of the density information of the toner patches 97 of the test print 93 conveyed along a conveying path 67 detected by the density sensor 9 when the test print 93 is fed to the conveying path while a direction in which the plurality of toner patches are formed in the main scanning direction is oriented toward a conveying direction. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a color copying machine or a color printer.

  In an image forming apparatus using an electrophotographic system, uneven charging due to deterioration of a charger for charging a photosensitive drum, uneven exposure of a laser scanner or the like that writes a latent image on the photosensitive drum, or a latent image formed on the photosensitive drum Development unevenness of a developing device for developing the toner.

  These unevenness causes density unevenness in the main scanning direction of the image formed on the sheet (the sheet width direction orthogonal to the sheet conveying direction).

  Therefore, a technique has been proposed in which a sheet on which a plurality of toner patches are printed in the main scanning direction is output as a test print, and the density of the toner patches in the test print is read with a handy densitometer or the like (Patent Document 1).

  In this proposal, the density information of the toner patch read by a handy densitometer or the like is input to the image forming apparatus, the amount of density unevenness is calculated by the control unit of the image forming apparatus, and the main scanning direction is calculated based on the calculation result. By controlling the laser emission characteristics, density unevenness in the main scanning direction is reduced.

  Further, when the densitometer is not used, a plurality of operations for visually judging the density of the toner patch of the test print, inputting density correction information based on the judgment result to the image forming apparatus, and outputting the test print again are performed. By repeating the process repeatedly, density unevenness in the main scanning direction is reduced.

JP 2004-163216 A

  However, in the above prior art, in order to reduce the density unevenness in the main scanning direction, it is necessary to purchase an expensive densitometer or to repeat the density correction work visually when the densitometer is not used. It is difficult to reduce density unevenness in the main scanning direction efficiently.

  Therefore, the present invention provides an image forming apparatus capable of efficiently reducing density unevenness in the main scanning direction without using an expensive densitometer or repeating visual density correction work a plurality of times. With the goal.

  In order to achieve the above object, an image forming apparatus according to the present invention includes an image forming unit that forms an image on a sheet that is transported through a transport path, and the transport path is transported after the image is formed by the image forming unit. An image forming apparatus comprising: a density detecting unit configured to detect a density of an image of the sheet to be printed; and a test print using a sheet on which images of a plurality of toner patches are formed in the main scanning direction by the image forming unit. , When the sheet is fed to the transport path with the direction in which the plurality of toner patches are formed in the main scanning direction facing the transport direction, the test detected by the density detector and transported through the transport path Control means for correcting the density in the main scanning direction based on density information of the toner patch of the print is provided.

  According to the present invention, it is possible to efficiently reduce density unevenness in the main scanning direction without using an expensive densitometer or repeating visual density correction work a plurality of times.

1 is a schematic cross-sectional view of an image forming apparatus using an electrophotographic method according to a first embodiment of the present invention. It is sectional drawing for demonstrating a density | concentration sensor. It is a figure which shows an example of the light-receiving part of a charge storage type sensor. It is a figure which shows an example of a test print. It is a graph which shows the relationship between a laser power conversion value and a density | concentration difference. It is a graph which shows the laser power of the main scanning direction set based on a laser power conversion value.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic cross-sectional view of an image forming apparatus using an electrophotographic system according to a first embodiment of the present invention.

  As shown in FIG. 1, an image forming apparatus 100 according to this embodiment includes a photosensitive drum 1 as an image carrier that rotates at a constant speed.

  Around the photosensitive drum 1, a pre-exposure lamp 6 that performs static elimination of the photosensitive drum 1, a charger 7 that uniformly charges the surface of the photosensitive drum 1, and a laser that forms a latent image on the surface of the photosensitive drum 1. An exposure optical system 2 is arranged. Around the photosensitive drum 1, there is disposed a rotating type developing body 5 that attaches toner to a latent image formed on the surface of the photosensitive drum 1 and develops it as a toner image. The toner image formed on the surface of the photosensitive drum 1 is sequentially transferred to the intermediate transfer member 3, and the residual toner remaining on the surface of the photosensitive drum 1 after the transfer is removed by the cleaning device 4.

  The rotary developer 5 includes a black developer 5K, a yellow developer 5Y, a magenta developer 5M, and a cyan developer 5C. The rotary developer 5 can rotate around the rotation axis in the direction of arrow a in the drawing to move the developing device of a desired color to a developing position facing the photosensitive drum 1.

  When forming an image, the photosensitive drum 1 is rotated, and the surface of the photosensitive drum 1 after being neutralized by the pre-exposure lamp 6 is uniformly charged by the charger 7, and the laser exposure optical system 2 applies the first color laser. A light image E is irradiated to form a latent image on the surface of the photosensitive drum 1.

  Next, the latent image formed on the surface of the photosensitive drum 1 is developed as a toner image by the first color developing device of the rotary developer 5, and then the toner image on the surface of the photosensitive drum 1 is transferred to the intermediate transfer member 3. Primary transfer.

  When the development of the first color is completed, the rotary developer 5 is rotated by 60 ° in the direction of arrow a in the drawing, and the developer of the second color is moved to the development position facing the photosensitive drum 1.

  After the primary transfer of the first color toner image from the photosensitive drum 1 to the intermediate transfer body 3 is finished, the photosensitive drum 1 from which the remaining toner on the surface is removed by the cleaning device 4 is similar to the first color. The third color, fourth color and latent image, development, and primary transfer are repeated. As a result, the toner images of the respective colors are sequentially superimposed on the intermediate transfer body 3 and primarily transferred.

  On the other hand, the sheets stored in the storage units 61, 62, 63, 64 are selectively fed one by one to the transport path by the respective feed rollers 71, 72, 73, 74, and are registered rollers (hereinafter referred to as “registration rollers”). The skew is corrected at 75).

  The sheet whose skew has been corrected is conveyed to the secondary transfer unit 76 at a predetermined timing, and the toner images of the respective colors superimposed and transferred to the intermediate transfer body 3 are secondarily transferred collectively. The sheet on which the toner image of each color is secondarily transferred by the secondary transfer unit 76 passes through the conveyance unit 77, and is fixed on the toner image by the fixing device 8, and is then discharged to the discharge tray 65 by the discharge roller 79. .

  When images are formed on both sides of the sheet, the sheet passes through the fixing unit 8 and is once guided to the reverse path 66 by the first switching guide 80. The sheet guided to the reversing path 66 is conveyed in the opposite direction with the trailing edge when it is fed in the opposite direction by the reverse rotation of the reversing roller 78, and sent to the duplex conveying path 67 via the second switching guide 81. After that, it is conveyed to the registration roller 75.

  Thereafter, as described above, the skew of the sheet is corrected by the registration roller 75, and then the sheet is conveyed to the secondary transfer unit 76, and the toner images of the respective colors superimposed and transferred to the intermediate transfer body 3 are collectively transferred to the secondary transfer unit 76. After that, the sheet is discharged to the discharge tray 65 through the conveyance unit 77, the fixing device 8, and the discharge roller 79.

  Here, in the present embodiment, as shown in FIG. 2, a density sensor 9 that detects the density of the toner patch 97 of the test print 93 conveyed on the double-sided conveyance path 67 is disposed above the double-sided conveyance path 67. ing.

  A roller 94 is disposed below the duplex conveyance path 67 so as to face the density sensor 9. The roller 94 presses the test print 93 against the upper conveyance guide 95 of the upper and lower conveyance guides 95 and 96 constituting the double-sided conveyance path 67 to keep the distance between the test print 93 and the density sensor 9 constant. It is. The density sensor 9 and the roller 94 are existing ones that are arranged to detect the density in the sub-scanning direction of an image formed on a normal sheet.

  The density sensor 9 corresponds to an example of the density detection means of the present invention, and as shown in FIG. 2, a white LED 91 and a charge storage sensor 92 with RGB on-chip filter (hereinafter simply referred to as “charge storage sensor 92”). .). The white LED 91 irradiates the toner patch 97 of the test print 93 conveyed through the double-sided conveyance path 67 from light at an angle of 45 °, and the charge accumulation type sensor 92 receives the intensity of irregularly reflected light in the 0 ° direction. The charge storage type sensor 92 outputs a signal corresponding to the received light amount to a control unit (not shown).

  As shown in FIG. 3, the light receiving unit of the charge accumulation type sensor 92 has R, G, and B independent pixels, and the charge accumulation amount can be changed by arbitrarily changing the output or integration time of the white LED 91. It is adjusted to obtain a desired dynamic range.

  The charge accumulation sensor 92 can measure the toner density of the test print 93 with high accuracy from the amount of reflected light by performing the above adjustment using a reference index in advance. Based on three different outputs from the charge storage sensor 92 obtained by this, for example, R, G, and B pixel outputs, the control unit identifies C, M, Y, and K, and detects the density. can do.

  The charge storage type sensor 92 may be a photodiode, or may be a set of three sets of R, G, and B pixels. Further, the density sensor 9 may have an incident angle of light emitted from the white LED 91 of 0 ° and a reflection angle of light reflected by the test print 93 of 45 °. Furthermore, the density sensor 9 may be constituted by an LED that emits three colors of R, G, and B and a light receiving sensor without a filter.

  FIG. 4 is a diagram illustrating an example of the test print 93.

  As shown in FIG. 4, the test print 93 has a plurality of (seven in the figure) toner patches 97 formed in the main scanning direction (longitudinal direction) of the sheet. In this embodiment, four test prints 93 each formed with toner patches 97 of four colors C, M, Y, and K are discharged onto the discharge tray 65 by the above-described image forming operation on the sheet.

  Of the seven toner patches 97, the central toner patch 97 has an optical density set to 0.3, and the other six toner patches 97 are printed at the same data level. Therefore, when there is density unevenness in the main scanning direction, the density of each toner patch 97 is different.

  By the way, when the test print 93 forms an image of seven toner patches 97 in the main scanning direction on the sheet, the sub scanning direction (short direction: arrow A direction in FIG. 4) perpendicular to the main scanning direction. To the discharge tray 65. On the other hand, the density sensor 9 is disposed at the upper position of the double-sided conveyance path 67 in the center portion in the main scanning direction.

  Therefore, when the seven toner patches 97 of the test print 93 are read by the density sensor 9, the test print 93 is fed by being inclined by 90 ° with respect to the conveyance direction when the seven toner patches 97 are formed on the sheet. There is a need to.

  That is, when the seven toner patches 97 of the test print 93 are read by the density sensor 9, the seven toner patches 97 are formed on the test print 93 in the main scanning direction (longitudinal direction: arrow B direction in FIG. 4). It is necessary to feed the paper in the direction of conveyance.

  The test print 93 has seven marks 98 indicating the conveyance direction so that the user does not mistake the conveyance direction (paper feeding direction) of the test print 93 when reading the toner patch 97 by the density sensor 9. Printed on both sides of the toner patch 97.

  The reading operation of the toner patch 97 by the density sensor 9 is started, for example, when the user selects a density correction mode in the main scanning direction using an operation unit (not shown) and presses a reading start button. In the present embodiment, the test print 93 is fed from the storage unit 64 (manual feed tray) with the image forming surface of the toner patch 97 facing up in the main scanning direction.

  That is, when a reading start button (not shown) is pressed, referring to FIG. 1, the test print 93 is fed from the storage unit 64 to the conveyance path, and the registration roller 75, the secondary transfer unit 76, the conveyance unit 77, and the fixing unit. After passing through the container 8, the first switching guide 80 guides the reversing path 66. The test print 93 guided to the reversing path 66 is transported in the opposite direction with the trailing edge when fed in as a leading edge by the reverse rotation of the reversing roller 78, and is sent to the duplex transport path 67 via the second switching guide 81. And conveyed to the density sensor 9.

  The density sensor 9 emits light from the white LED 91 at a predetermined timing toward the toner patch 97 of the test print 93 that has been conveyed under the control of the control unit, and the charge accumulation sensor 92 receives the reflected light. To do. The charge storage type sensor 92 outputs a signal corresponding to the amount of received light to the control unit as density information.

  The test print 93 that has passed through the density sensor 9 is discharged to the discharge tray 65 via the registration roller 75, the secondary transfer unit 76, the transport unit 77, the fixing device 8, and the discharge roller 79.

  The control unit converts the signal value as the density information output from the charge storage sensor 92 using the density conversion table, and calculates all the densities for the seven toner patches 97. Further, the control unit calculates the difference in density with respect to the central toner patch 97 for each of the other six toner patches 97 using the density of the central toner patch 97 among the seven toner patches 97 as a reference value.

  Then, the control unit controls the laser power in the main scanning direction of the laser light image E irradiated from the laser exposure optical system 2 to the surface of the photosensitive drum 1 based on the calculated density difference of the toner patch 97.

  FIG. 5 is a graph showing the relationship between the laser power converted value and the density difference. In FIG. 5, the density of the central toner patch 97 among the seven toner patches 97 is the median value (0), and the laser power conversion value corresponding to the median value is the reference value.

  As shown in FIG. 5, when the density is low with respect to the median (− direction), the control unit sets the laser power conversion value stronger than the reference value according to the density difference, and conversely, with respect to the median. If the density is high (in the + direction), the laser power conversion value is set to be weaker than the reference value according to the density difference.

  FIG. 6 is a graph showing the laser power in the main scanning direction set based on the laser power converted value set as described above.

  Based on the laser power converted values of the seven toner patches 97, the control unit sets the laser power in units of pixels in the main scanning direction by linear interpolation of values between the points. The control unit switches the laser power for each pixel when the laser exposure optical system 2 irradiates the surface of the photosensitive drum 1 with the laser light image E during actual image formation.

  By performing the above-described processing on the four test prints 93 on which the four color toner patches 97 of C, M, Y, and K are formed, the density in the main scanning direction of all colors is corrected to reduce density unevenness. be able to.

  As described above, in the present embodiment, it is possible to efficiently reduce density unevenness in the main scanning direction without using an expensive densitometer or repeating visual density correction work a plurality of times.

  In this embodiment, the density is corrected by switching the laser power for each pixel in the main scanning direction. However, the present invention is not limited to this. For example, the image data for image formation may be converted using a LUT (Look Up Table) having a data conversion table corresponding to each pixel to correct the density in the main scanning direction.

  In this embodiment, the laser power is set for each pixel in the main scanning direction by linear interpolation. However, interpolation with higher accuracy may be obtained by performing nonlinear interpolation such as spline conversion.

(Second Embodiment)
Next, an image forming apparatus using an electrophotographic system according to a second embodiment of the present invention will be described. In addition, the part which overlaps with respect to the said 1st Embodiment is demonstrated using a figure and a code | symbol.

  In the present embodiment, when the user feeds the test print 93 in the wrong conveyance direction (paper feeding direction), a warning is issued, and reading failure of the toner patch 97 by the density sensor 9 is prevented.

  Optical sensors (not shown) are arranged on both sides of the density sensor 9 in the main scanning direction (axial direction of the roller 94). The optical sensor corresponds to an example of a mark detection unit of the present invention, and is arranged at a position corresponding to the conveyance mark 98 of the test print 93 when the test print 93 is conveyed in a normal direction.

  Based on the output of the optical sensor, the control unit can detect the non-passed / passed test print 93 and the unprinted / printed part of the test print 93.

  Specifically, when the test print 93 is conveyed to the density sensor 9, the control unit determines that the sheet has been switched from non-passing paper based on the output of the optical sensor.

  The control unit determines that the conveyance mark 98 does not pass through the optical sensor when the printing unit is not detected by a change in the output of the optical sensor within a predetermined time from the timing when switching from non-sheet passing to sheet passing. .

  In this case, since there is a high possibility that the conveyance direction of the test print 93 is wrong and the correction based on the density signal read by the density sensor 9 is not properly performed, the control unit does not correct the density and The operator is notified by a display on an operation unit (not shown) or the like. As a result, when the user feeds the test print 93 in the wrong conveyance direction (paper feeding direction), a warning is issued, and reading failure of the toner patch 97 by the density sensor 9 can be prevented. Other configurations and operational effects are the same as those of the first embodiment.

(Third embodiment)
Next, an image forming apparatus using an electrophotographic system according to a third embodiment of the present invention will be described. In addition, the part which overlaps with respect to the said 1st Embodiment is demonstrated using a figure and a code | symbol.

  In this embodiment, since the density sensor 9 reads the four test prints 93 each having the four color toner patches 97 of C, M, Y, and K, the same operation is performed four times. At that time, there is a possibility that the density of the test print 93 of the toner patch 97 of the same color is corrected or the correction is forgotten due to an operation error or the like.

  Therefore, in this embodiment, when the density sensor 9 determines that the reading of the toner patch 97 has been properly completed in the second embodiment, an end mark is printed on the test print 93.

  Specifically, the control unit conveys the test print 93 that has been properly read by the density sensor 9 to the registration roller 75 and waits for the photosensitive drum 1 during the same image forming operation. A toner image of the end mark is formed.

  Then, the control unit drives the registration roller 75 to convey the test print 93 in synchronization with the transfer timing of the toner image from the photosensitive drum 1 to the intermediate transfer member 3, and tests the end mark by the secondary transfer unit 76. Transfer to print 93.

  The test print 93 to which the end mark is transferred passes through the conveyance unit 77, and after the toner image is fixed by the fixing device 8, is discharged to the discharge tray 65 by the discharge roller 79. As a result, it is possible to reduce operation mistakes during density correction in the main scanning direction.

  In this embodiment, the end mark is transferred to the back surface of the test print 93. However, the density sensor 9 is disposed below the duplex conveyance path 67 and the roller 94 is disposed above the duplex conveyance path 67. Thus, the end mark can be transferred to the printing surface of the toner patch 97. In this case, the test print 93 is fed with the main scanning direction facing the transport direction with the image forming surface of the toner patch 97 facing down from the storage unit 64 (manual feed tray). Other configurations and operational effects are the same as those of the first and second embodiments.

  In addition, this invention is not limited to what was illustrated by said each embodiment, In the range which does not deviate from the summary of this invention, it can change suitably.

9 Density sensor 67 Double-sided conveyance path 93 Test print 94 Roller 97 Toner patch 98 Conveying mark 100 Image forming apparatus

Claims (4)

Image forming means for forming an image on a sheet conveyed through the conveyance path;
An image forming apparatus comprising: a density detecting unit that detects a density of an image of a sheet conveyed through the conveyance path after an image is formed by the image forming unit;
A sheet on which images of a plurality of toner patches are formed in the main scanning direction by the image forming unit is used as a test print, and the test print is formed with the direction in which the plurality of toner patches are formed in the main scanning direction facing the transport direction. Control means for correcting the density in the main scanning direction based on the density information of the toner patch of the test print transported through the transport path detected by the density detection means when the paper is fed to the transport path. Prepare
An image forming apparatus. The image forming unit forms, together with the toner patch image, an image serving as a mark indicating the test print conveyance direction when forming a plurality of toner patch images in the main scanning direction of the sheet.
The image forming apparatus according to claim 1. A mark detecting means for detecting an image of the mark of the test print conveyed in the conveyance path;
The control means performs a process of notifying the warning without correcting the density in the main scanning direction when the image of the mark is not detected by the mark detecting means,
The image forming apparatus according to claim 2. When the mark detection unit detects the mark image, the control unit displays a mark image indicating that the density detection of the toner patch by the density detection unit is completed for the test print. Controlling the image forming means to form,
The image forming apparatus according to claim 3.

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