JP2017032686A - Image forming apparatus - Google Patents

Abstract

An image forming apparatus capable of appropriately correcting an image density is provided.
An image forming apparatus includes an image density correction unit. The image density correction unit 61 includes a patch image forming unit 62, a derivation unit 64, and a setting unit 65. The deriving unit 64 determines the image density of the solid patch image and the image density of the half patch image from the relationship between the toner amount of the solid patch image and the half patch image calculated by the toner amount calculation unit 63, the exposure amount, and the development bias value. The relationship between the exposure amount and the developing bias value when correcting the above is derived. Based on the relationship derived by the deriving unit 64, the setting unit 65 sets both the exposure amount and the development bias value when correcting the image density of the solid patch image and the image density of the half patch image.
[Selection] Figure 5

Description

  The present invention relates to an image forming apparatus.

  In an image forming apparatus typified by a multifunction peripheral or the like, after an image of a document is read by an image reading unit, light is irradiated on the photoconductor provided in the image forming unit based on the read image, An electrostatic latent image is formed on the surface. Thereafter, a developer such as charged toner is supplied onto the formed electrostatic latent image to form a visible image, and then transferred to a sheet, fixed, and discharged outside the apparatus.

  Here, in an image forming apparatus capable of forming a full-color image, a color image is formed by superimposing each color of yellow, magenta, cyan, and black on a primary transfer body such as a transfer belt. There is. In such an image forming apparatus, it is necessary to correct the image density at a predetermined timing in order to improve color developability and color reproducibility.

  When correcting the image density, a pattern image composed of a plurality of patch images for correcting the image density is formed by each color image forming unit and transferred onto the transfer belt. Then, the toner amount of a plurality of patch images transferred onto the transfer belt is detected and calculated, and the exposure amount and the like are adjusted so as to be the target toner amount. The pattern image is usually composed of a plurality of patch images with different image densities. Specifically, based on the calculated toner amount, the image density is corrected by adjusting the exposure amount of the laser beam to be applied to the photoconductor and the developing bias value applied to the developing roller during development. Yes.

  Japanese Patent Application Laid-Open No. 2009-93007 (Patent Document 1) discloses a technique relating to image density correction of an image forming apparatus using a patch image. According to Patent Document 1, when the exposure amount determined by the determination process does not fall within the range from the predetermined lower limit exposure amount to the upper limit exposure amount, the exposure amount determined by the determination process is set to a value that falls within the same range. Correction processing is performed to correct the development bias value determined in the determination processing to a value corresponding to the exposure amount falling within the same range.

JP 2009-93007 A

  In the technique disclosed in Patent Document 1 described above, the exposure amount is fixed to an upper limit value or a lower limit value within a predetermined range, and then adjusted with the development bias value. As a result, the image density is adjusted only by the development bias value. With such a configuration, it is difficult to appropriately correct the image density. In particular, when an image is formed using a two-component developer, both the development bias value and the exposure amount affect the solid image and the half image, which is not preferable.

  An object of the present invention is to provide an image forming apparatus capable of appropriately correcting an image density.

  In one aspect of the present invention, the image forming apparatus can form a color image on a recording medium using a plurality of colors of toner. The image forming apparatus includes an image creator, an exposure unit, a primary transfer body, and an image density correction unit. The image forming device includes an image forming unit for each color including a photoconductor corresponding to each color and a developing roller that supplies toner to each photoconductor. The exposure unit irradiates the photoconductor with light. The primary transfer member rotates in one direction, and the visible image formed by the toner formed by each image forming unit is primarily transferred thereon. The image density correction unit corrects the image density of the visible image by the toner formed by the imager at a predetermined timing. The image density correction unit includes a patch image forming unit, a toner amount detection sensor, a toner amount calculation unit, a derivation unit, and a setting unit. The patch image forming unit applies a surface potential to the photoconductor, and changes the exposure amount of light irradiated by the exposure unit and the development bias value applied to the developing roller within a predetermined range, respectively. A solid patch image that is a patch image and a half patch image that is a halftone patch image are formed. The toner amount detection sensor detects the amount of toner in the solid patch image and the half patch image that are primarily transferred onto the primary transfer body. The toner amount calculation unit calculates the toner amount of each color based on the toner amount of the solid patch image and the half patch image detected by the toner amount detection sensor. The deriving unit corrects the image density of the solid patch image and the image density of the half patch image based on the relationship between the toner amount of the solid patch image and the half patch image calculated by the toner amount calculation unit, the exposure amount, and the development bias value. The relationship between the exposure amount and the developing bias value is derived. The setting unit sets both the exposure amount and the developing bias value when correcting the image density of the solid patch image and the image density of the half patch image based on the relationship derived by the deriving unit.

  According to such an image forming apparatus, the relationship between the exposure amount and the development bias value when adjusting the image density of the solid patch image and the image density of the half patch image is derived. Based on these relationships, since both the exposure amount and the development bias value for correcting the image density of the solid patch image and the image density of the half patch image are set, more appropriate image density correction can be performed. It can be carried out.

1 is a schematic diagram illustrating an appearance of a multifunction peripheral when an image forming apparatus according to an embodiment of the present invention is applied to the multifunction peripheral. FIG. 2 is a block diagram illustrating a configuration of the multifunction machine illustrated in FIG. 1. FIG. 2 is an external view illustrating a schematic configuration of an image forming unit. FIG. 3 is an external view illustrating a schematic configuration of a toner amount detection sensor. It is a block diagram which shows the structure of a control part. It is a figure which shows the some patch image which comprises a pattern image. 6 is a flowchart showing the contents of processing when image density is corrected using the multifunction peripheral according to the embodiment of the present invention. It is a graph which shows the relationship between ID and a development bias value. It is a graph which shows the relationship between ID and exposure amount. It is a graph which shows the relationship between an exposure amount and a development bias value. It is a graph which shows the relationship between the exposure amount at the time of changing the surface potential in the case of a half patch image, and the post-exposure potential. It is a graph which shows the relationship between the exposure amount at the time of changing the surface potential in the case of a solid patch image, and post-exposure potential.

  Embodiments of the present invention will be described below. FIG. 1 is a schematic diagram showing an external appearance of a multifunction peripheral when an image forming apparatus according to an embodiment of the present invention is applied to the multifunction peripheral. FIG. 2 is a block diagram illustrating a configuration of the multifunction peripheral illustrated in FIG.

  With reference to FIGS. 1 to 2, a multifunction machine 11 as an image forming apparatus according to an embodiment of the present invention includes a control unit 12, an operation unit 13, an image reading unit 14, an image forming unit 15, A paper setting unit 19, a hard disk 16 as a storage unit for storing data, a facsimile communication unit 17, and a network interface unit 18 for connecting to a network 25 are provided.

  The control unit 12 controls the entire multifunction machine 11. The operation unit 13 includes a display screen 21 that displays information transmitted from the multifunction peripheral 11 side and user input contents. The operation unit 13 inputs image forming conditions such as the number of copies to be printed and gradation, and power on / off. The image reading unit 14 includes an ADF (Auto Document Feeder) 22 as a document transport device that transports a document set at the set position to the read position. The image reading unit 14 reads an image of a document set on the ADF 22 or a mounting table (not shown). The paper setting unit 19 includes a manual feed tray 28 for manually setting paper as a recording medium and a paper feed cassette group 29 that can store a plurality of sheets of different sizes. The image forming unit 15 forms an image on the conveyed paper based on the image data read by the image reading unit 14 and the image data transmitted via the network 25. The sheet on which the image is formed by the image forming unit 15 is discharged to the discharge tray 30. The hard disk 16 stores transmitted image data, input image forming conditions, and the like. The facsimile communication unit 17 is connected to the public line 24 and performs facsimile transmission and facsimile reception.

  The multi-function device 11 includes a DRAM (Dynamic Random Access Memory) for writing and reading image data, and the illustration and description thereof are omitted. In addition, arrows in FIG. 2 indicate the flow of data regarding control signals, control, and images. As shown in FIG. 1, in this embodiment, the sheet cassette group 29 includes three sheet cassettes 23a, 23b, and 23c.

  The multifunction device 11 operates as a copying machine by forming an image in the image forming unit 15 using the image data of the document read by the image reading unit 14. Further, the multifunction machine 11 forms an image in the image forming unit 15 and prints it on a sheet using the image data transmitted from the computers 26a, 26b, and 26c connected to the network 25 through the network interface unit 18. It operates as a printer. That is, the image forming unit 15 operates as a printing unit that prints the requested image. The MFP 11 uses the image data transmitted from the public line 24 through the facsimile communication unit 17 to form an image in the image forming unit 15 via the DRAM and is read by the image reading unit 14. The image data of the original is transmitted to the public line 24 through the facsimile communication unit 17, thereby operating as a facsimile apparatus. The multifunction machine 11 has a plurality of functions such as a copying function, a printer function, and a facsimile function regarding image processing. Further, each function has functions that can be set in detail.

  The image forming system 27 including the multifunction peripheral 11 according to an embodiment of the present invention includes the multifunction peripheral 11 having the above-described configuration and a plurality of computers 26a, 26b, and 26c connected to the multifunction peripheral 11 via the network 25. Prepare. In this embodiment, three computers 26a to 26c are shown. Each of the computers 26 a to 26 c can make a print request to the multi-function peripheral 11 via the network 25 to perform printing.

  Next, the configuration of the image forming unit 15 provided in the digital multifunction peripheral 11 will be described in more detail. FIG. 3 is a cross-sectional view showing a schematic configuration of the digital multi-function peripheral 11 according to the embodiment of the present invention. From the viewpoint of easy understanding, the members are not hatched in FIG. FIG. 3 is a cross-sectional view of the digital multifunction machine 11 cut along a plane extending in the vertical direction.

  Referring to FIG. 3, the image forming unit 15 develops supplying toner to the photoconductors 31 a, 31 b, 31 c, 31 d corresponding to the four colors of yellow, cyan, magenta, and black, and the photoconductors 31 a to 31 d. An image forming unit 33 including image forming units 32a, 32b, 32c, and 32d for each color including rollers 39a, 39b, 39c, and 39d, and an LSU (Laser Scanner Unit) as an exposure unit that irradiates light to the photoreceptors 31a to 31d. 34, a transfer belt 35 as a primary transfer member that rotates in one direction and primarily transfers a visible image formed by the respective image forming units 32a to 32d thereon, and a primary transfer onto the transfer belt 35. Secondary transfer roller (not shown) for secondary transfer of the visible image formed by the toner onto the paper as the recording medium And a transfer belt cleaning unit 37 for removing toner remaining on the transfer belt 35 with a blade or the like. About LSU34, it has shown roughly with the dashed-dotted line. The transfer belt cleaning unit 37 is also schematically shown.

The transfer belt 35 is endless, and is a visible image formed by image forming units 32a to 32d of four colors of yellow, cyan, magenta, and black while being rotated in one direction by a driving roller 36b and a driven roller 36a. Is transcribed. Rotational direction of the transfer belt 35 is indicated by an arrow D ₁ of the in Figure 3. Of the image forming units 32a to 32d, the yellow image forming unit 32a is disposed on the most upstream side, and the black image forming unit 32d is disposed on the most downstream side in the rotation direction of the transfer belt 35. . The transfer belt cleaning unit 37 is disposed upstream of the yellow image forming unit 32a.

  The visible image formed by the toner transferred onto the transfer belt 35 is transferred to the conveyed paper and fixed on the paper by a fixing unit (not shown). After fixing, the sheet is discharged out of the digital multifunction peripheral 11, specifically, the discharge tray 30. After the visible image by the toner is transferred to the paper, the toner remaining on the transfer belt 35 is removed by the transfer belt cleaning unit 37. Then, the next image formation is performed.

  The digital multifunction peripheral 11 can perform monochrome printing using only the black image forming unit 32d. The digital multi-function peripheral 11 can perform color printing using at least one of a yellow image forming unit 32a, a magenta image forming unit 32b, and a cyan image forming unit 32c.

  In addition, the digital multi-function peripheral 11 includes a toner amount detection sensor 42 that detects the toner amount in the visible image by the toner transferred onto the transfer belt 35.

  Next, the configuration of the toner amount detection sensor 42 will be briefly described. FIG. 4 is a schematic diagram illustrating a configuration of the toner amount detection sensor 42. In FIG. 3, the toner amount detection sensor 42 is schematically indicated by a two-dot chain line.

  3 and 4, the toner amount detection sensor 42 is disposed on the downstream side of the black image forming unit 32d. The toner amount detection sensor 42 includes a light source 43 that emits light to the transfer belt 35 side, a first polarization unit 44a that divides the light from the light source 43 into polarized light such as P wave and S wave, and a first polarization unit 44a. Reflected light from the visible image 49 by the first polarized light input unit 45a that receives polarized light having the wavelength of the divided S wave and the toner formed on the surface 38 of the transfer belt 35 or the surface 38 of the transfer belt 35 And a second polarization unit 44b that receives the polarized light having the wavelength of the S wave divided by the second polarization unit 44b. And a light receiving unit 46 that receives polarized light having a P-wave wavelength via the second polarization unit 44b.

Toner amount detection sensor 42 is rotated in the direction of arrow D ₁ of the in Figure 4 from the light source 43, the transfer belt 35 to a visible image 49 is formed by the toner on the surface 38, the arrows in FIG. 4 irradiating light 47a obliquely indicated by E _1. Polarizing 47b having a wavelength of P-wave separated by the first polarization unit 44a is reflected in the direction indicated by the arrow E ₃ against the visible image 49 by the toner formed on the surface 38 of the transfer belt 35. The polarized light 47c having the S wave wavelength divided by the first polarizing unit 44a is input to the first polarized light input unit 45a. The reflected light 47d is divided by the second polarization unit 44b, and the polarized light 47e having the wavelength of the P wave is received by the light receiving unit 46. Further, the polarized light 47f having the S wave wavelength divided by the second polarization unit 44b is input to the second polarized light input unit 45b. Toner of each color from the amount of light 47a emitted from the light source 43, the amount of polarized light 47e received by the light receiving unit 46, the amount of polarized light 47c and 47f received by the first and second polarized light input units 45a and 45b, etc. An output value as a substitute value of the amount is calculated and detected as a toner amount.

Here, an example of a specific toner amount calculation method will be described. The coverage with toner as an alternative value of the toner amount can be obtained by the following calculation method. That is, the output when the P wave reflected from the visible image 49 is detected is P ₁ , the output when the S wave reflected from the visible image 49 is detected is S ₁ , and the dark potential of the P wave is P ₀ , S The dark potential of the wave is S ₀ , the output when the P wave reflected from the surface 38 of the transfer belt 35 is detected is Pg, the output when the S wave reflected from the surface 38 of the transfer belt 35 is detected is Sg, When the coefficient for correcting the output values of (S ₁ −S ₀ ) and (Sg−S ₀ ) is K, the toner coverage is obtained by the following calculation formula. The P wave and the S wave are polarized light divided into the first and second polarization units 44a and 44b, respectively.

Coverage = 1 − ((P ₁ −P ₀ ) − (S ₁ −S ₀ ) × K) / ((Pg−P ₀ ) − (Sg−S ₀ ) × K)

  Next, the configuration of the control unit 12 will be described. FIG. 5 is a block diagram illustrating a configuration of the control unit 12. Referring to FIG. 5, control unit 12 includes an image density correction unit 61. The image density correction unit 61 corrects the image density or the like of a visible image by toner formed on the transfer belt 35 by the image forming units 32a, 32b, 32c, and 32d at a predetermined timing. As the specific predetermined timing, the image density correction unit 61, for example, determines the timing when the number of printed sheets reaches a predetermined number, specifically, the timing when the number of image formation is every 1000 sheets, and the driving time is predetermined. In addition, the timing at which the time has reached, the timing at which the environment has changed, for example, the timing at which the temperature or humidity has suddenly changed, or the timing at which a part of the units constituting the multifunction device 11 is replaced. The image density correction unit 61 corrects the density, position, and color shift of the visible image formed on the transfer belt 35 by the image forming units 32a to 32d at a predetermined timing.

  The image density correction unit 61 includes a patch image forming unit 62, a toner amount calculation unit 63, a derivation unit 64, and a setting unit 65.

  The patch image forming unit 62 corrects the image density by forming a plurality of patch images constituting a pattern image for adjusting the image density of each color. The patch image forming unit 62 applies a surface potential to the photoconductors 31a to 31d, and the exposure amount of light irradiated by the LSU 34 and the development bias value (applied to the development rollers 39a to 39d, respectively) within a predetermined range. In the following, the solid patch image that is a solid patch image and the half patch image that is a halftone patch image are formed. As described above, the toner amount calculation unit 63 calculates the toner amount of each color based on the toner amounts of the solid patch image and the half patch image detected by the toner amount detection sensor 42. The deriving unit 64 corrects the image density of the solid patch image and the image density of the half patch image based on the relationship between the toner amount of the solid patch image calculated by the toner amount calculation unit 63, the exposure amount, and the development bias value. The relationship between the exposure amount and the development bias value is derived. Based on the relationship derived by the deriving unit 64, the setting unit 65 sets both the exposure amount and the development bias value when correcting the image density of the solid patch image and the image density of the half patch image. Setting unit 65 includes a surface potential changing unit 66. The surface potential changing unit 66 sets the surface potential applied to the photoconductors 31a to 31d in the patch image forming unit 62 so that both the exposure amount and the developing bias value do not become the upper limit value and the lower limit value within a predetermined range, respectively. change.

  Here, an example of the patch image formed by the patch image forming unit 62 will be described. FIG. 6 is a diagram illustrating an example of a plurality of patch images.

  Referring to FIG. 6, a pattern image 52 including eight patch images 51a, 51b, 51c, 51d, 51d, 51e, 51f, 51g, and 51h is formed on the surface 38 of the transfer belt 35. The eight patch images 51 a to 51 h are formed by the patch image forming unit 62. Specifically, the patch image 51a is a black solid patch image 51a, and the patch image 51b is a black half patch image 51b. The patch image 51c is a magenta solid patch image 51c, and the patch image 51d is a magenta half patch image 51d. The patch image 51e is a cyan solid patch image 51e, and the patch image 51f is a cyan half patch image 51f. The patch image 51g is a yellow solid patch image 51g, and the patch image 51h is a yellow half patch image 51h. The solid patch images 51a, 51c, 51e, and 51g are images configured to have an image density of 100%. Further, the half patch images 51b, 51d, 51f, and 51h are images configured to be a halftone having an image density of 25%. A pattern image 52 composed of these eight patch images 51 a to 51 h is formed at a position that can be detected by the toner amount detection sensor 42.

  Next, a case where the image density is corrected using the multifunction machine 11 according to an embodiment of the present invention will be described. FIG. 7 is a flowchart showing the contents of the processing when the image density is corrected using the multifunction machine 11 according to the embodiment of the present invention.

  Referring to FIG. 7, the multi-function device 11 detects that the predetermined timing has been reached, for example, that the number of images formed has reached 1000 (YES in step S11 in FIG. 6). , “Step” is omitted). Then, image density correction is started.

  In this case, the exposure amount and Vdc are shifted to three levels, and the respective pattern images 52 as shown in FIG. 6 are formed (S12). For example, 70%, 100%, and 130% are selected as the three levels of exposure. Here, the exposure amount 100% is a reference light amount. Further, 200V, 300V, and 400V are selected as the three levels of Vdc. A total of nine pattern images 52 are formed. Details of each of the nine conditions and the image density described later are shown in Table 1. Table 1 also shows the surface potential. The surface potential is a value obtained by adding 150 V as a reference to Vdc.

  In this case, the lower limit value of the exposure amount is 70%. The upper limit of the exposure amount is 130%. The lower limit value of Vdc is 200V. The upper limit value of Vdc is 400V. These lower limit value and upper limit value are set in consideration of the influence on the specifications of the high voltage power source used in the multifunction machine 11, the LD performance, and the image.

  Next, the toner amounts of the formed solid patch images 51a, 51c, 51e, 51g and the half patch images 51b, 51d, 51f, 51h are calculated (S13). In this case, as described above, the toner amount is detected using the toner amount detection sensor 42. Then, based on the detected toner amount, the toner amount calculation unit 63 calculates in the form of ID (Image Density).

  Thereafter, the deriving unit 64 calculates the toner amount, the exposure amount, and the developing bias value of the solid patch images 51a, 51c, 51e, and 51g and the half patch images 51b, 51d, 51f, and 51h calculated by the toner amount calculating unit 63. From the relationship, the relationship between the exposure amount and the developing bias value when correcting the image density of the solid patch images 51a, 51c, 51e, 51g and the image density of the half patch images 51b, 51d, 51f, 51h is derived (S14). . In this case, the relationship is derived from both the solid patch images 51a, 51c, 51e, and 51g and the half patch images 51b, 51d, 51f, and 51h.

  FIG. 8 is a graph showing the relationship between the exposure amount and Vdc when the solid patch images 51a, 51c, 51e, and 51g are used as a reference. In FIG. 8, the vertical axis represents ID, and the horizontal axis represents Vdc. The line 55a is an exposure amount of 70%, the line 55b is an exposure amount of 100%, and the line 55c is an exposure amount of 130%. A dotted line 54a indicates ID = 1.3 which is the target image density of the solid patch images 51a, 51c, 51e, and 51g. Referring to FIG. 8, the following linear equation (1) is calculated from the relationship between three levels of exposure amounts at which ID = 1.3 and Vdc. Here, y represents Vdc, and x represents the exposure amount.

  y = −3.3333x + 533.33 (1)

  FIG. 9 is a graph showing the relationship between the exposure amount and Vdc when the half patch images 51b, 51d, 51f, and 51h are used as a reference. In FIG. 9, the vertical axis represents ID, and the horizontal axis represents the exposure amount. The line 56a is for Vdc400V, the line 56b is for Vdc300V, and the line 56c is for Vdc200V. A dotted line 54b indicates ID = 0.6, which is the target image density of the half patch images 51b, 51d, 51f, and 51h. Referring to FIG. 9, the following linear equation (2) is calculated from the relationship between three levels of exposure amounts with ID = 0.6 and Vdc. Here, y represents Vdc, and x represents the exposure amount.

  y = −6.6667x + 866.67 (2)

  Next, the setting unit 65 corrects the image density of the solid patch images 51a, 51c, 51e, and 51g and the image density of the half patch images 51b, 51d, 51f, and 51h based on the relationship derived by the derivation unit 64. Both exposure amount and Vdc are set. Specifically, simultaneous equations are solved from these two linear equations (1) and (2). In this way, the setting unit 66 sets both an appropriate exposure amount and Vdc (S15).

  FIG. 10 is a graph showing the relationship between the Vdc and the exposure amount in the solid patch images 51a, 51c, 51e, 51g and the half patch images 51b, 51d, 51f, 51h. In FIG. 10, the vertical axis represents Vdc, and the horizontal axis represents the exposure amount. A line 57a indicates the linear equation (1), and a line 57b indicates the linear equation (2).

  Referring to FIG. 10, the intersection of line 57a and line 57b indicates an appropriate Vdc and exposure amount. That is, in this case, Vdc is set to 300 V and the exposure amount is set to 100% as appropriate values. Then, the image density is corrected with the set exposure amount and Vdc (S16).

  According to such a multi-function peripheral 11, the relationship between the exposure amount and the developing bias value when adjusting the image density of the solid patch images 51a, 51c, 51e, and 51g and the image density of the half patch images 51b, 51d, 51f, and 51h. To derive. Based on these relationships, both the exposure amount and the developing bias value for correcting the image density of the solid patch images 51a, 51c, 51e, and 51g and the image density of the half patch images 51b, 51d, 51f, and 51h are calculated. Since it is set, more appropriate image density correction can be performed.

  When both the exposure amount and the development bias value to be set are an upper limit value and a lower limit value within a predetermined range, respectively, the surface potential is changed by the surface potential changing unit 66 to thereby adjust the exposure amount and the development. Both of the bias values may not be the upper limit value and the lower limit value within a predetermined range.

  FIG. 11 is a graph showing the relationship between the exposure amount and the post-exposure potential when the surface potential is changed in the case of the half patch images 51b, 51d, 51f, and 51h. In FIG. 11, the vertical axis indicates the post-exposure potential (V), and the horizontal axis indicates the exposure amount. The line 58a is a surface potential of 350V, the line 58b is a surface potential of 450V, and the line 58c is a surface potential of 550V.

  FIG. 12 is a graph showing the relationship between the exposure amount and the post-exposure potential when the surface potential is changed in the case of the solid patch images 51a, 51c, 51e, and 51g. In FIG. 12, the vertical axis indicates the post-exposure potential (V), and the horizontal axis indicates the exposure amount. The line 59a is a surface potential of 350V, the line 59b is a surface potential of 450V, and the line 59c is a surface potential of 550V.

  Referring to FIGS. 11 and 12, the higher the surface potential, the higher the potential after exposure. Accordingly, when the surface potential changing unit 66 forms at least one of the solid patch images 51a, 51c, 51e, and 51g and the half patch images 51b, 51d, 51f, and 51h by the deriving unit 64, the developing bias value is a predetermined value. If the upper limit value is within the range, the surface potential applied to the photoconductors 31a to 31d is set lower. Specifically, the applied surface potential is set to Vdc + 100V with respect to the reference Vdc + 150V. Further, when the surface potential changing unit 66 forms at least one of the solid patch images 51a, 51c, 51e, and 51g and the half patch images 51b, 51d, 51f, and 51h by the deriving unit 64, the exposure amount is within a predetermined range. If the upper limit value is reached, the surface potential applied to the photoconductors 31a to 31d is set lower.

  On the other hand, when the surface potential changing unit 66 forms at least one of the solid patch images 51a, 51c, 51e, and 51g and the half patch images 51b, 51d, 51f, and 51h by the deriving unit 64, the developing bias value has a predetermined value. If the lower limit value is within the range, the surface potential applied to the photoreceptor is increased and set. Specifically, the applied surface potential is set to Vdc + 200V with respect to the reference Vdc + 150V. Further, the surface potential changing unit has an exposure amount within a predetermined range when the deriving unit forms at least one of the solid patch images 51a, 51c, 51e, 51g and the half patch images 51b, 51d, 51f, 51h. If the lower limit value is reached, the surface potential applied to the photoreceptor is increased and set.

  In the above-described embodiment, the patch images are formed on a total of nine conditions using three three-level images. However, the present invention is not limited to this. A patch image may be formed under one condition. Of course, you may use the thing of 4 levels or more.

  In the above embodiment, the image density correction may be retried after the exposure amount and the development bias value are set, or the exposure amount and the development bias value set at the next correction are reflected. You may do it.

  In the above embodiment, the image density of the half patch image is 25%. However, the present invention is not limited to this. For example, an image density of 30% or 45% may be set as the half patch image.

  In addition, the pattern images constituting the plurality of patch images are formed in a line in one direction. However, the present invention is not limited to this. For example, when a plurality of toner amount detection sensors are provided in the main scanning direction, A pattern image may be formed over a plurality of columns at a position in the main scanning direction where the toner amount detection sensor is provided, and the image density may be corrected.

  It should be understood that the embodiments and examples disclosed herein are illustrative in all respects and are not restrictive in any respect. The scope of the present invention is defined by the scope of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims.

  The image forming apparatus according to the present invention is particularly effectively used when an appropriate image density correction is required.

  DESCRIPTION OF SYMBOLS 11 MFP, 12 Control part, 13 Operation part, 14 Image reading part, 15 Image formation part, 16 Hard disk, 17 Facsimile communication part, 18 Network interface part, 19 Paper setting part, 21 Display screen, 22 ADF, 23a, 23b , 23c Paper feed cassette, 24 Public line, 25 Network, 26a, 26b, 26c Computer, 27 Image forming system, 28 Manual feed tray, 29 Paper feed cassette group, 30 Discharge tray, 31a, 31b, 31c, 31d Photoconductor, 32a , 32b, 32c, 32d Image forming unit, 33 Imager, 34 LSU, 35 Transfer belt, 36a Driven roller, 36b Drive roller, 37 Transfer belt cleaning unit, 38 Surface, 39a, 39b, 39c, 39d Developing roller , 42 Toner amount detection sensor, 43 Light source, 44a, 44b Polarizing unit, 45a, 45b Polarized light input unit, 46 Light receiving unit, 47a, 47d Light, 47b, 47c, 47e, 47f, Polarized light, 49 Visible image, 51a, 51b , 51c, 51d, 51e, 51f, 51g, 51h Patch image, 52 pattern image, 54a, 54b, 55a, 55b, 55c, 56a, 56b, 56c, 57a, 57b, 58a, 58b, 58c, 59a, 59b, 59c Line, 61 Image density correcting unit, 62 Patch image forming unit, 63 Toner amount measuring unit, 64 Deriving unit, 65 Setting unit, 66 Surface potential changing unit.

Claims (6)

An image forming apparatus capable of forming a color image on a recording medium using a plurality of color toners,
An image forming device including a photoconductor corresponding to each color and an image forming unit of each color including a developing roller that supplies toner to each of the photoconductors;
An exposure unit for irradiating light to the photoreceptor;
A primary transfer body that rotates in one direction and primarily transfers a visible image formed by the toner formed by each of the image forming units thereon;
An image density correction unit that corrects an image density of a visible image by the toner formed by the imager at a predetermined timing;
The image density correction unit
A solid patch image obtained by applying a surface potential to the photoconductor and changing the exposure amount of light irradiated by the exposure unit and the developing bias value applied to the developing roller within a predetermined range, respectively. A patch image forming unit that forms a solid patch image and a half patch image that is a halftone patch image;
A toner amount detection sensor that detects an amount of the toner in the solid patch image and the half patch image that are primarily transferred onto the primary transfer body;
A toner amount calculation unit that calculates the toner amount of each color based on the toner amount of the solid patch image and the half patch image detected by the toner amount detection sensor;
From the respective relationships between the toner amount of the solid patch image and the half patch image calculated by the toner amount calculation unit, the exposure amount, and the development bias value, the image density of the solid patch image and the image of the half patch image A derivation unit for deriving a relationship between the exposure amount and the development bias value when correcting the density;
A setting unit that sets both the exposure amount and the development bias value when correcting the image density of the solid patch image and the image density of the half patch image based on the relationship derived by the deriving unit; An image forming apparatus. The setting unit sets the surface potential applied to the photoconductor in the patch image forming unit so that both the exposure amount and the development bias value do not become an upper limit value and a lower limit value within the predetermined range, respectively. The image forming apparatus according to claim 1, further comprising a surface potential changing unit to be changed. If the developing bias value is an upper limit value within the predetermined range when the surface potential changing unit forms at least one of the solid patch image and the half patch image by the deriving unit, the photoconductor The image forming apparatus according to claim 2, wherein the surface potential applied to the substrate is set to be lowered. The surface potential changing unit may cause the photoconductor to form the photosensitive member if the exposure amount reaches an upper limit value within the predetermined range when the derivation unit forms at least one of the solid patch image and the half patch image. The image forming apparatus according to claim 2, wherein the applied surface potential is lowered. If the developing bias value is a lower limit value within the predetermined range when the surface potential changing unit forms at least one of the solid patch image and the half patch image by the deriving unit, the photoconductor The image forming apparatus according to claim 2, wherein the surface potential applied to the surface is set by increasing the surface potential. The surface potential changing unit is arranged on the photoconductor if the exposure amount becomes a lower limit value within the predetermined range when the derivation unit forms at least one of the solid patch image and the half patch image. The image forming apparatus according to claim 2, wherein the surface potential applied is set by increasing.

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