JP2016008984A - Image forming apparatus and image density correction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to correct image density with high accuracy.SOLUTION: An image forming apparatus operates as follows: measuring a CTD value of each of first patch images formed (S12); calculating a development bias voltage ΔV corresponding to a target CTD value after measuring the CTD value of the first patch image (S13); forming a second patch image by use of the development bias voltage set as a temporary ΔV (S14); detecting a CTD value again on each of the second patch images formed accordingly (S15); calculating an average of the obtained CTD values (S16); calculating a difference between the average and the first CTD value (S17); calculating a final target CTD value by adding the calculated difference to the first CTD value (S18); and calculating a final ΔV corresponding to the final target CTD value (S19).

Description

  The present invention relates to an image forming apparatus and an image density correction method, and more particularly, to an image forming apparatus that performs development using toner and an image density correction method.

  In an image forming apparatus typified by a digital multifunction peripheral or the like, after an image of a document is read by an image reading unit, an electrostatic latent image is formed on a photoreceptor provided in the image forming unit based on the read image. Thereafter, a toner charged on the formed electrostatic latent image is supplied from the developing device to form a visible image, transferred to a sheet, fixed, and discharged outside the device. In this way, an image is formed. Also, there is a configuration in which a transfer belt is provided as an intermediate transfer member when transferring from a photosensitive member to a sheet.

  Here, from the viewpoint of maintaining an image to be formed with high image quality, in response to changes in the environment in which the image forming apparatus is installed, changes over time in members constituting the image forming apparatus, etc. It becomes necessary to correct the initial set values and adjust the image density and image quality. Japanese Patent Application Laid-Open No. 2011-154146 (Patent Document 1) discloses correction relating to image density, that is, technology relating to density correction.

  In Patent Document 1, when executing high density correction, a plurality of toner patch images are formed on a photoconductor based on the development potential obtained by the high density correction executed immediately before, and images of the plurality of toner patch images are obtained. An image forming apparatus is disclosed in which a development potential for obtaining a target image density is set based on the density.

JP 2011-154146 A

  In the technique disclosed in Patent Document 1, in the correction of the high density image density, a toner patch image is formed using the development voltage obtained in the immediately preceding high density correction, and the target density is determined based on the image density. The development voltage for obtaining the image density is set. However, the technique disclosed in Patent Document 1 may have insufficient correction accuracy.

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

  Another object of the present invention is to provide an image density correction method capable of correcting an image density with high accuracy.

  The inventor of the present application pays attention to the relationship between the image density and the developing bias voltage for the correction of the image density, and has found that the relationship between the image density and the developing bias voltage has the following tendency. That is, regarding the relationship between the image density and the development bias voltage, even when the development bias voltage is the same, the variation in the measured image density is compared between when the voltage is increased and when the voltage is decreased. I found it big. And this inventor earnestly examined and came to the structure of this invention.

  In other words, the image forming apparatus according to the present invention includes a developing device that forms a visible image with toner, and a transfer body onto which the visible image with toner is transferred. The developing device applies a predetermined developing bias voltage to form a patch image for density correction with toner on the surface of the transfer member, and measures the toner density of the patch image formed by the patch image forming unit. The toner density measuring unit and the patch image forming unit assign and apply different development bias voltages to form a plurality of first patch images in different regions on the surface of the transfer member, and the toner density measuring unit Temporary development bias voltage for measuring the toner density corresponding to the first patch image of the image and calculating the temporary development bias voltage corresponding to the target toner density as a target from the relationship between the assigned development bias voltage and a plurality of toner densities The temporary development bias voltage calculated by the temporary development bias voltage calculation unit is calculated by the calculation unit and the patch image forming unit, respectively. In addition, a plurality of second patch images are formed in different areas on the surface of the transfer body, and the toner density corresponding to the plurality of second patch images is measured by the toner density measuring unit, and each measured toner is measured. Calculates the average density, calculates the difference between the calculated average toner density and the target toner density, and adds the difference calculated by the difference calculation section to the target toner density to calculate the final target toner density And a final development bias voltage calculation unit for calculating a final development bias voltage corresponding to the final target toner density from the relationship between the assigned development bias voltage and a plurality of toner densities.

  According to such an image forming apparatus, a temporary developing bias voltage is once calculated in the developing device, and a plurality of second patch images are formed using the temporary developing bias voltage. Here, when forming a plurality of second patch images, the same temporary development bias voltage is applied and formed, so that the temporary development bias can be increased without increasing or decreasing the development bias voltage. A voltage can be applied. As a result, it is possible to suppress variations in toner image density due to an increase or decrease in the developing bias voltage, and it is possible to accurately measure the toner image density corresponding to the temporary developing bias voltage. Further, since the patch image is formed a plurality of times, the number of samples for calculating the correction value can be increased. Therefore, such an image forming apparatus can correct the image density with high accuracy.

  In another aspect of the present invention, the image density correction method allocates and applies different development bias voltages to form a plurality of first patch images in different regions on the surface of the transfer body, and Temporary development bias voltage calculation step of measuring the toner density corresponding to one patch image and calculating the temporary development bias voltage corresponding to the target toner density as a target from the relationship between the assigned development bias voltage and a plurality of toner densities And applying the provisional development bias voltage calculated in the provisional development bias voltage calculation step to form a plurality of second patch images in different regions on the surface of the transfer body, corresponding to the plurality of second patch images. Each toner density to be measured, and the average of the measured toner densities is calculated, and the difference between the calculated average toner density and the target toner density is calculated. And calculating the final target toner density by adding the difference calculated in the difference calculation process to the target toner density, and calculating the final target toner density from the relationship between the assigned development bias voltage and the plurality of toner densities. And a final development bias voltage calculating step for calculating a final development bias voltage corresponding to.

  According to such an image density correction method, highly accurate image density correction can be performed.

  According to such an image forming apparatus, a temporary developing bias voltage is once calculated in the developing device, and a plurality of second patch images are formed using the temporary developing bias voltage. Here, when forming a plurality of second patch images, the same temporary development bias voltage is applied and formed, so that the temporary development bias can be increased without increasing or decreasing the development bias voltage. A voltage can be applied. As a result, it is possible to suppress variations in toner image density due to an increase or decrease in the developing bias voltage, and it is possible to accurately measure the toner image density corresponding to the temporary developing bias voltage. Further, since the patch image is formed a plurality of times, the number of samples for calculating the correction value can be increased. Therefore, such an image forming apparatus can correct the image density with high accuracy.

  Further, according to such an image density correction method, it is possible to correct the image density with high accuracy.

1 is a schematic perspective view illustrating an external appearance of a digital multifunction peripheral when an image forming apparatus according to an embodiment of the present invention is applied to the digital multifunction peripheral. 1 is a block diagram illustrating a configuration of a digital multifunction peripheral when an image forming apparatus according to an embodiment of the present invention is applied to the digital multifunction peripheral. FIG. 2 is a schematic cross-sectional view illustrating a part of an image forming unit provided in the digital multifunction peripheral. 6 is a flowchart showing a flow of processing when correcting the setting of the developing bias voltage using the digital multi-functional peripheral according to one embodiment of the present invention. It is a figure which shows an example of the 1st patch image formed on the surface of a transfer belt. It is a graph which shows the relationship between the development bias voltage allocated to 4 levels, and a CTD value. It is a figure which shows an example of the 2nd patch image formed on the surface of a transfer belt. It is a graph which shows the relationship between the development bias voltage allocated to 4 levels, and a CTD value.

  Embodiments of the present invention will be described below. First, the configuration of an image forming apparatus according to an embodiment of the present invention will be described. FIG. 1 is a schematic perspective view showing an external appearance of a digital multi-function peripheral when an image forming apparatus according to an embodiment of the present invention is applied to the digital multi-function peripheral. In the state shown in FIG. 1, the side on which an operation unit, which will be described later, is arranged is the front side of the digital multifunction peripheral, and the opposite side is the rear side of the digital multifunction peripheral. FIG. 2 is a block diagram showing a configuration of the digital multifunction peripheral when the image forming apparatus according to the embodiment of the present invention is applied to the digital multifunction peripheral.

  Referring to FIGS. 1 and 2, a digital multifunction peripheral 11 as an image forming apparatus according to an embodiment of the present invention transmits a control unit 12 that controls the entire digital multifunction peripheral 11 and the digital multifunction peripheral 11 side. A display screen 21 that displays information to be input and user input contents, an operation unit 13 for inputting image forming conditions such as the number of copies and gradation, and power on / off, and a reading unit that automatically reads a set original. Including an ADF (Auto Document Feeder) 22 that transports the image to an image, an image reading unit 14 that reads an image of the document, and a developing device 23 that performs development using toner, and an image that has been read or transmitted via the network 25 An image forming unit 15 that forms an image based on data, and a hard disk that stores transmitted image data, input image forming conditions, and the like 16, a facsimile communication unit 17 that is connected to the public line 24 and performs facsimile transmission and reception, and a network interface unit 18 for connection to the network 25. The digital multi-function peripheral 11 includes a DRAM (Dynamic Random Access Memory) that writes and reads image data, a paper transport unit that transports a paper on which a visualized image formed by a developer is transferred, and the like. The illustration and description are omitted. In addition, arrows in FIG. 2 indicate the flow of data regarding control signals, control, and images.

  The digital multifunction peripheral 11 operates as a copying machine by forming an image in the image forming unit 15 using the original read by the image reading unit 14 and printing the image on a sheet. In addition, the digital multifunction peripheral 11 forms an image in the image forming unit 15 using image data transmitted from the computers 26a, 26b, and 26c connected to the network 25 through the network interface unit 18, and prints it on a sheet. It works as a printer. That is, the image forming unit 15 operates as a printing unit that prints the requested image. Further, the digital multifunction peripheral 11 forms an image in the image forming unit 15 via the DRAM using the image data transmitted from the public line 24 through the facsimile communication unit 17, and also by the image reading unit 14. The image data of the read original is transmitted to the public line 24 through the facsimile communication unit 17, thereby operating as a facsimile apparatus. That is, the digital multifunction peripheral 11 has a plurality of functions such as a copying function, a printer function, and a facsimile function with respect to image processing. Further, each function has functions that can be set in detail. Note that the digital multifunction machine 11 includes a so-called quad-tandem image forming unit 15 and can perform full-color printing.

  The image forming system 27 including the digital multifunction peripheral 11 includes the digital multifunction peripheral 11 and a plurality of computers 26a, 26b, and 26c. Specifically, the image forming system 27 includes the digital multifunction peripheral 11 having the above-described configuration and a plurality of computers 26 a, 26 b, and 26 c connected to the digital multifunction peripheral 11 via the network 25. In this embodiment, three computers 26a to 26c are shown. Each of the computers 26 a to 26 c can print by making a print request to the digital multi-function peripheral 11 via the network 25. The digital multi-function peripheral 11 and the computers 26a to 26c may be connected by wire using a LAN (Local Area Network) cable or the like, or may be connected wirelessly. A configuration in which a digital multifunction peripheral or a server is connected may be used.

  Next, the configuration of the image forming unit 15 will be briefly described. FIG. 3 is a schematic cross-sectional view showing a part of the image forming unit 15 provided in the digital multifunction peripheral 11. In FIG. 3, a part of hatching is omitted from the viewpoint of easy understanding.

  Referring to FIG. 3, the image forming unit 15 includes four developing devices 23 corresponding to four colors such as yellow, magenta, cyan, and black, and a transfer belt 41 to which a visible image formed by each color is transferred. Including. That is, the image forming unit 15 included in the digital multi-function peripheral 11 includes a developing device 23 that forms a visible image using toner, and a transfer belt 41 as a transfer body to which the visible image using toner is transferred. Visible images are formed by the four developing devices 23 corresponding to the respective colors, and the visible images formed by the respective colors are transferred onto the surface 42 of the transfer belt 41 to form a full-color image. The full-color image formed on the surface 42 of the transfer belt 41 is transferred to a sheet, and the full-color image is fixed on the sheet by a fixing unit (not shown) and discharged outside the apparatus. Here, a description will be given using one developing device 23 that forms a yellow color.

The developing device 23 includes a cylindrical photoreceptor 31 that forms an electrostatic latent image on the surface 32 thereof. Photoreceptor 31 rotates in the direction of the arrow R ₁ in FIG. After the surface 32 of the photoreceptor 31 is charged by a charging unit (not shown), light is irradiated from an exposure device (not shown). An electrostatic latent image is formed on the surface 32 of the photoreceptor 31 by the irradiated light.

The developing device 23 includes a mag roller 33 and a developing sleeve 34. The mag roller 33 is also called a magnetic roller. Inside the mag roller 33, N poles and S poles are alternately formed in the circumferential direction. The mag roller 33 carries on its surface 35 a developer composed of toner and carrier. The magnet roller 33 supplies toner to the developing sleeve 34 from the developer carried while rotating. A thin layer of toner is formed on the surface 36 of the developing sleeve 34. The thickness of the thin toner layer formed on the surface 36 of the developing sleeve 34 is controlled by a doctor blade (not shown). Developing sleeve 34 while rotating in the direction of the arrow R ₂ in FIG. 3, for supplying toner to the surface 32 of the photoconductor 31. When toner is supplied to the electrostatic latent image formed on the surface 32 of the photoconductor 31, a visible image by the toner is formed on the surface 32 of the photoconductor 31. Both the mag roller 33 and the developing sleeve 34 are disposed in a developing container 37 partially illustrated. The developer container 37 is filled with a developer (not shown). The toner consumed by the development is supplied into the developing container 37 as needed. The developing container 37 is also provided with a stirring roller (not shown) that stirs toner and developer.

  The developing device 23 includes a voltage applying unit 38 that applies a voltage to each of the mag roller 33 and the developing sleeve 34. There is a difference between the voltages applied to the mag roller 33 and the developing sleeve 34. That is, the voltage value applied to the mag roller 33 is different from the voltage value applied to the developing sleeve 34. Here, the developing bias voltage refers to a potential difference between the mag roller 33 and the developing sleeve 34. That is, the voltage application unit 38 applies a developing bias voltage formed between the mag roller 33 and the developing sleeve 34. The amount of toner supplied from the mag roller 33 to the developing sleeve 34 is adjusted according to the magnitude of the developing bias voltage, and then the visible image formed on the surface 32 of the photoreceptor 31 and further the transfer belt. This affects the image quality of the visible image 43 transferred to the surface 42 of 41. The developing bias voltage is also controlled by the control unit 12 that controls the image forming unit 15. The development bias voltage is changed and corrected from the initial set value in accordance with the secular change of the members constituting the image forming unit 15 or the change of the environment where the digital multifunction peripheral 11 is installed.

The image forming unit 15 includes the above-described endless transfer belt 41 as an intermediate transfer member. The outer surface 42 of the transfer belt 41 is in contact with the surface 32 of the photoreceptor 31. During development, transfer belt 41 is rotating, in the abutting area between the surface 32 of photoreceptor 31, moving in the direction of arrow D ₁ of the in Figure 3. A transfer roller 39 is provided on the inner side of the transfer belt 41 in a region in contact with the surface 32 of the photoconductor 31. A voltage is also applied to the transfer roller 39, and the visible image 43 is transferred from the surface 32 of the photoconductor 31 to the surface 42 of the transfer belt 41 due to a potential difference between the photoconductor 31 and the transfer roller 39. The transfer roller 39 also has a mechanism for rotating the transfer belt 41. The four developing devices 23 described above are arranged side by side along the direction in which the transfer belt 41 moves.

  Further, the developing device 23 includes a toner concentration measuring unit 40 that measures the toner concentration of the visible image 43 transferred to the surface 42 of the transfer belt 41. The toner density measuring unit 40 is constituted by, for example, a photosensor, and irradiates light on an image portion formed by the formed toner, receives the reflected light, and transfers the transferred toner according to the amount of reflected light received. Measure the concentration.

  Next, a case where the digital multifunction peripheral 11 is used to correct the setting of the developing bias voltage in the developing device 23 will be described. In this case, a numerical value of 910 is set as a target CTD (Color Toner Density) value that is a target toner density. This value CTD is unitless. When the target CTD is set to 910 in the current configuration of the digital multi-function peripheral 11, an appropriate development bias voltage corresponding to the target CTD is derived and the setting of the development bias voltage is corrected.

  FIG. 4 is a flowchart showing the flow of processing when correcting the setting of the developing bias voltage using the digital multi-function peripheral 11 according to one embodiment of the present invention. Referring to FIG. 4 and the like, when correcting the setting of the developing bias voltage, first, the developing bias voltage is assigned to four levels, and the first patch image for density correction with toner is formed on the surface 42 of the transfer belt 41. (In FIG. 4, step S11, hereinafter, “step” is omitted). Here, the image forming unit 15 or the like operates as a patch image forming unit. In this embodiment, the four levels of voltages are 170V (volts), 240V, 310V, and 380V. There is a difference of 70V between each level.

FIG. 5 is a diagram showing an example of the first patch image formed on the surface 42 of the transfer belt 41 in this case. Note that an arrow D ₁ in FIG. 5 is a rotation direction that is a circumferential direction of the transfer belt 41. Direction indicated by the arrow D ₂ in FIG. 5 is a direction toward the front side from the rear side of the digital multifunction peripheral 11 in the main scanning direction.

  Referring to FIG. 5, a yellow first patch image 46a, a magenta first patch image 47a, and a front side of the most upstream region 44a indicated by a dotted line on the surface 42 of the transfer belt 41, A first patch image group 45a composed of four first patch images 46a, 47a, 48a, 49a such as a cyan first patch image 48a and a black first patch image 49a is formed. Each of the first patch images 46a to 49a is formed in a rectangular shape, and is formed so as to be adjacent from the upstream side toward the downstream side. The first patch image group 45a is formed by setting the developing bias voltage to 170V. Also, a yellow first patch image 46b, a magenta first patch image 47b, a cyan first patch image 48b, and a black first patch image 49b formed by setting the same developing bias voltage to 170V. Is formed on the rear side of the surface 42 of the transfer belt 41 in the same circumferential region 44a as the first patch image group 45a formed on the front side.

  Further, the yellow region formed by setting the developing bias voltage to 240 V in the region 44b downstream in the rotation direction of the transfer belt 41 with respect to the region 44a where the first patch image group 45a on the front side is formed. A first patch image group 45c including a first patch image 46c, a magenta first patch image 47c, a cyan first patch image 48c, and a black first patch image 49c is formed. Similarly, the yellow formed by setting the developing bias voltage to 240 V in the area 44b downstream in the rotation direction of the transfer belt 41 with respect to the area 44a in which the first patch image group 45b on the rear side is formed. A first patch image group 45d including a first patch image 46d, a magenta first patch image 47d, a cyan first patch image 48d, and a black first patch image 49d is formed. . Similarly, the yellow formed by setting the developing bias voltage to 310 V in the region 44 c downstream in the rotation direction of the transfer belt 41 with respect to the region 44 b in which the first patch image group 45 c on the front side is formed. The first patch image 46e, the first patch image 47e of magenta, the first patch image 48e of cyan, and the first patch image 49e of black are formed. . Similarly, the yellow formed by setting the developing bias voltage to 310 V in the region 44 c on the downstream side in the rotation direction of the transfer belt 41 with respect to the region 44 b in which the first patch image group 45 d on the rear side is formed. First patch image 46f, magenta first patch image 47f, cyan first patch image 48f, and black first patch image 49f are formed as a first patch image group 45f. . Similarly, the yellow formed by setting the developing bias voltage to 380 V in the region 44d downstream in the rotation direction of the transfer belt 41 with respect to the region 44c in which the first patch image group 45e on the front side is formed. First patch image 46g, magenta first patch image 47g, cyan first patch image 48g, and black first patch image 49g are formed as a first patch image group 45g. . Similarly, the yellow formed by setting the developing bias voltage to 380 V in the region 44d downstream in the rotation direction of the transfer belt 41 with respect to the region 44c in which the rear first patch image group 45f is formed. First patch image 46h, magenta first patch image 47h, cyan first patch image 48h, and black first patch image 49h are formed. . That is, a total of eight first patch image groups 45a to 45h are formed.

  Next, the CTD values of the formed first patch images 46a and the like are measured (S12). The measurement of the CTD value is performed by the toner density measuring unit 40 described above. Here, mainly the yellow image will be described, but the process flow for magenta, cyan, and black is the same as that for yellow.

  After measuring the CTD value of the first patch image 46a and the like, a developing bias voltage ΔV corresponding to 910 set as the target CTD value is calculated (S13). The calculated development bias voltage ΔV is determined as a temporary ΔV that is a temporary development bias voltage. A method of determining the temporary ΔV will be briefly described.

  FIG. 6 is a graph showing the relationship between the development bias voltage assigned to the above four levels and the CTD value. The vertical axis in FIG. 6 represents the CTD value, and the horizontal axis in FIG. 6 represents the development bias voltage value (V). Referring to FIG. 6, first, CTD values corresponding to the detected voltage values are plotted against the voltage values assigned to the four levels. Then, a line 53a corresponding to the target CTD value is drawn along the horizontal axis on the line segments 52a, 52b, 52c connecting the adjacent points 51a, 51b, 51c, 51d, and any of the line segments 52a-52c is drawn. And the intersection 54a of the line 53a is a temporary ΔV. The line 53a is indicated by a one-dot chain line. In this case, 300 V is calculated as a voltage value corresponding to the target CTD value 910. The calculated 300V is determined as a temporary ΔV (S13). That is, it is set as a temporary ΔV corresponding to the target CTD value. Steps S11 to S13 are temporary development bias voltage calculation steps. In this case, the control unit 12 or the like operates as a temporary development bias voltage calculation unit.

  Next, using the developing bias voltage set as the temporary ΔV, the second patch image is formed in the same areas 44a to 44d as all the areas 44a to 44d where the first patch image 46a and the like are formed. That is, a second patch image is formed (S14). In this case, provisional ΔV is applied as a developing bias voltage to form a second patch image. That is, without assigning the development bias voltage, assuming that the development bias voltage is 300 V, the four regions 44a to 44d measured by ΔV1 to ΔV4, and further, the front side and the rear side, two places in total, eight places A patch image is formed again.

  FIG. 7 is a diagram showing an example of the second patch image formed on the surface 42 of the transfer belt 41 in this case. FIG. 7 corresponds to FIG. Referring to FIG. 7, on the surface 42 of the transfer belt 41, a yellow second patch image 56a, a magenta second patch image 57a, and a cyan second patch arranged on the front side of the region 44a. A second patch image group 55a composed of the image 58a and the black second patch image 59a is formed. On the surface 42 of the transfer belt 41, a yellow second patch image 56b, a magenta second patch image 57b, a cyan second patch image 58b, and a black second patch image arranged on the rear side of the region 44a. A second patch image group 55b composed of the patch images 59b is formed. On the surface 42 of the transfer belt 41, a yellow second patch image 56c, a magenta second patch image 57c, a cyan second patch image 58c, and a black second patch image arranged on the front side of the region 44b. A second patch image group 55c composed of the patch images 59c is formed. On the surface 42 of the transfer belt 41, a yellow second patch image 56d, a magenta second patch image 57d, a cyan second patch image 58d, and a black second patch image arranged on the rear side of the region 44b. A second patch image group 55d composed of the patch images 59d is formed. On the surface 42 of the transfer belt 41, a yellow second patch image 56e, a magenta second patch image 57e, a cyan second patch image 58e, and a black second patch arranged on the front side of the region 44c. A second patch image group 55e composed of the patch images 59e is formed. On the surface 42 of the transfer belt 41, a yellow second patch image 56f, a magenta second patch image 57f, a cyan second patch image 58f, and a black second patch image arranged on the rear side of the region 44c. A second patch image group 55f composed of the patch images 59f is formed. On the surface 42 of the transfer belt 41, a yellow second patch image 56g, a magenta second patch image 57g, a cyan second patch image 58g, and a black second patch arranged on the front side of the region 44d. A second patch image group 55g composed of the patch images 59g is formed. On the surface 42 of the transfer belt 41, a yellow second patch image 56h, a magenta second patch image 57h, a cyan second patch image 58h, and a black second patch arranged on the rear side of the region 44d. A second patch image group 55h composed of the patch images 59h is formed. The developing bias voltage at the time of forming each second patch image 56a and the like is the same 300V.

  The CTD value is measured again for each second patch image 56a and the like thus formed (S15). In this case, the CTD value is measured using the toner concentration measuring unit 40 as in the step in S13.

  Next, an average is calculated for the measured CTD values (S16). In this embodiment, it is assumed that 890 is calculated as the average CTD value.

  Next, the difference between the calculated average and the first CTD value is calculated (S17). In this case, 910−890 = 20 is calculated. That is, 20 is calculated as the difference from the target CTD value that was initially targeted. The steps S14 to S17 are a difference calculation step. In this case, the control unit 12 or the like operates as a difference calculation unit.

  Next, a final target CTD value is calculated by adding the calculated difference to the first CTD value (S18). In this case, 910 + 20 = 930 is calculated. That is, 930 is calculated as the final target CTD value.

  Next, a final ΔV corresponding to the final target CTD value is calculated (S19). FIG. 8 is a graph showing the relationship between the development bias voltage assigned to the above four levels and the CTD value. FIG. 8 corresponds to FIG. The vertical axis in FIG. 8 indicates the CTD value, and the horizontal axis in FIG. 8 indicates the development bias voltage value (V). Referring to FIG. 8, a line corresponding to the final target CTD value is drawn along the horizontal axis, and the intersection with the line segment is determined as the final ΔV. The line 53b is indicated by a two-dot chain line. In this case, 350V is calculated as a voltage value corresponding to 930 which is the final target CTD value. This calculated 350V is determined as the final ΔV. That is, it is set as the final ΔV corresponding to the final target CTD value. In this way, the final ΔV is calculated. Steps S18 to S19 are the final development bias voltage calculation step. In this case, the control unit 12 or the like operates as a final development bias voltage calculation unit. The developing bias voltage is corrected based on the final ΔV thus obtained.

  The digital multi-functional peripheral 11 having such a configuration once calculates a temporary development bias voltage in the developing device 23 and forms a plurality of second patch images using the temporary development bias voltage. Here, when forming a plurality of second patch images, the same temporary development bias voltage is applied and formed, so that the temporary development bias can be increased without increasing or decreasing the development bias voltage. A voltage can be applied. As a result, it is possible to suppress variations in toner image density due to an increase or decrease in the developing bias voltage, and it is possible to accurately measure the toner image density corresponding to the temporary developing bias voltage. Further, since the patch image is formed a plurality of times, the number of samples for calculating the correction value can be increased. Therefore, such an image forming apparatus can correct the image density with high accuracy.

  Further, the image density correction method according to the present invention allocates and applies different development bias voltages to form a plurality of first patch images in different regions on the surface of the transfer body, and thereby forms a plurality of first patch images. A temporary development bias voltage calculating step of measuring a corresponding toner density and calculating a temporary development bias voltage corresponding to a target toner density as a target from a relationship between the assigned development bias voltage and a plurality of toner densities; A plurality of second patch images are formed in different regions on the surface of the transfer body by applying the temporary development bias voltages calculated in the voltage calculation step, and toner densities corresponding to the plurality of second patch images are respectively set. Measure difference, calculate the average of each measured toner density, and calculate the difference between the calculated toner density average and the target toner density The final target toner density is calculated by adding the difference calculated in the output process and the difference calculating process to the target toner density, and the final corresponding to the final target toner density is calculated from the relationship between the assigned development bias voltage and the plurality of toner densities. And a final development bias voltage calculation step for calculating a development bias voltage.

  According to such an image density correction method, highly accurate image density correction can be performed.

  In this case, since the position where the first patch image is formed and the position where the second patch image is formed are the same, the developing bias voltage can be corrected with higher accuracy.

  In this case, the provisional development bias voltage calculation unit controls the patch image forming unit to form the first patch image in the front side region and the rear side region of the transfer belt, respectively. The developing bias voltage can be corrected with high accuracy.

  In this case, the temporary development bias voltage calculation unit controls the patch image forming unit to form the first patch images in different regions in the circumferential direction of the transfer belt. The developing bias voltage can be corrected with high accuracy.

  In this case, the provisional development bias voltage calculation unit allocates the development bias voltage at four levels and controls the patch image forming unit to form the first patch image. Therefore, the number of samples is increased and development is performed with high accuracy. The bias voltage can be corrected.

  In the above embodiment, the patch images are formed on both the front side and the rear side. However, the present invention is not limited to this, and a patch image may be formed at the center or in the circumferential direction. A patch image may be formed by allocating a developing bias voltage of 5 levels or more. By doing so, it is possible to correct the image density with higher accuracy. The first patch image and the second patch image may be formed at least one place each. Moreover, the allocation of the voltage of 2 level or 3 level may be sufficient.

  In the above embodiment, the first patch image and the second patch image may be formed at different positions.

  In addition, the transfer belt is used as the transfer body.

  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 high-precision image formation is required.

  DESCRIPTION OF SYMBOLS 11 Digital multifunction device, 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, 21 Display screen, 22 ADF, 23 Developing apparatus, 24 Public line , 25 network, 26a, 26b, 26c computer, 27 image forming system, 31 photoconductor, 32, 35, 36, 42 surface, 33 mag roller, 34 developing sleeve, 37 developing container, 38 voltage application unit, 39 transfer roller, 40 Toner density measuring unit, 41 transfer belt, 43 visible image, 44a, 44b, 44c, 44d area, 45a, 45b, 45c, 45d, 45e, 45f, 45g, 45h, 55a, 55b, 55c, 55d, 55e, 55f, 55g, 55h pack Image group, 46a, 46b, 46c, 46d, 46e, 46f, 46g, 46h, 47a, 47b, 47c, 47d, 47e, 47f, 47g, 47h, 48a, 48b, 48c, 48d, 48e, 48f, 48g, 48h 49a, 49b, 49c, 49d, 49e, 49f, 49g, 49h, 56a, 56b, 56c, 56d, 56e, 56f, 56g, 56h, 57a, 57b, 57c, 57d, 57e, 57f, 57g, 57h, 58a , 58b, 58c, 58d, 58e, 58f, 58g, 58h, 59a, 59b, 59c, 59d, 59e, 59f, 59g, 59h patch images, 51a, 51b, 51c, 51d, 54a, 54b, 52a, 52b, 52c, 53a, 53b lines.

Claims (6)

An image forming apparatus comprising: a developing device that forms a visible image with toner; and a transfer body onto which the visible image with toner is transferred.
The developing device includes a patch image forming unit that applies a predetermined developing bias voltage to form a patch image for density correction with toner on the surface of the transfer member;
A toner density measuring unit for measuring the toner density of the patch image formed by the patch image forming unit;
The patch image forming unit assigns and applies different development bias voltages to form a plurality of first patch images in different regions on the surface of the transfer body, and the toner density measuring unit sets a plurality of the first patch images. Temporary development bias voltage calculation that measures the toner density corresponding to each patch image and calculates the temporary development bias voltage corresponding to the target toner density that is the target from the relationship between the assigned development bias voltage and the plurality of toner densities And
The patch image forming unit applies each of the temporary development bias voltages calculated by the temporary development bias voltage calculation unit to form a plurality of second patch images in different regions on the surface of the transfer member, and the toner The density measuring unit measures the toner density corresponding to each of the plurality of second patch images, calculates the average of each measured toner density, and calculates the difference between the calculated average toner density and the target toner density A difference calculating unit to
The difference calculated by the difference calculation unit is added to the target toner density to calculate a final target toner density, and corresponds to the final target toner density from the relationship between the assigned development bias voltage and the plurality of toner densities. An image forming apparatus comprising: a final developing bias voltage calculating unit that calculates a final developing bias voltage. The image forming apparatus according to claim 1, wherein a position where the first patch image is formed and a position where the second patch image is formed are the same. The said temporary image development bias voltage calculation part controls the said patch image formation part so that said 1st patch image may be formed in the area | region of the front side of the said transfer body, and a rear side, respectively. Image forming apparatus. The temporary development bias voltage calculation unit controls the patch image forming unit to form the first patch image in different regions in the circumferential direction of the transfer body, respectively. The image forming apparatus described. The temporary development bias voltage calculation unit controls the patch image forming unit to allocate the development bias voltage at three levels or more to form the first patch image. Image forming apparatus. Different development bias voltages are assigned and applied to form a plurality of first patch images in different areas on the surface of the transfer member, and the toner densities corresponding to the plurality of first patch images are measured and assigned. A temporary development bias voltage calculating step of calculating a temporary development bias voltage corresponding to a target toner density that is a target from the relationship between the development bias voltage and the plurality of toner densities;
A plurality of second patch images are formed in different regions on the surface of the transfer body by applying the temporary development bias voltages calculated in the temporary development bias voltage calculating step, respectively. A difference calculating step of measuring a toner density corresponding to each of the two, calculating an average of each measured toner density, and calculating a difference between the calculated average of the toner density and the target toner density;
The difference calculated in the difference calculating step is added to the target toner density to calculate a final target toner density, and the final target toner density is handled from the relationship between the assigned development bias voltage and the plurality of toner densities. And a final development bias voltage calculation step of calculating a final development bias voltage.

Images