JP2016224144A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus which can obtain a high quality image.SOLUTION: A digital composite machine comprises: a photoreceptor made of amorphous silicon; an exposure device; a development roller; a magnetic roller; a peripheral velocity ratio change part 60; an intermediate transfer body; a toner amount measurement part; a first voltage application part; a second voltage application part; a patch image formation part 56; a difference calculation part 57; a determination part 58; and a potential difference derivation part 59. The difference calculation part 57 calculates the difference in toner amounts between the plurality of first patch images. The determination part 58 determines whether or not there are a prescribed number or more of data on the toner amounts of the first patch images whose difference is within a prescribed range. The potential difference derivation part 59 derives the potential difference for adhering the target toner amount to the intermediate transfer body from the data on the toner amounts of the first patch images when the determination part 58 determines that there are the prescribed number or more of data.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus.

  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, light is irradiated to the photoconductor provided in the image forming unit based on the read image, and the photoconductor An electrostatic latent image is formed thereon. 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, a technique relating to image formation in the image forming apparatus is disclosed in Japanese Patent Application Laid-Open No. 2005-308821 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2003-270873 (Patent Document 2).

  In Patent Document 1, a magnetic brush made of a magnetic carrier and toner is formed on the outer periphery of a supply roller that encloses a fixed magnetic pole member, and the magnetic brush is rubbed against the development roller while responding to a potential difference between the supply roller and the development roller. A developing device is disclosed in which toner is transferred to a developing roller to form a thin toner layer on the developing roller for development. The developing device includes a pattern forming unit that forms a density detection pattern as a toner image from a plurality of thin toner layers formed at different potential differences by changing the potential difference, and detects the density of each density detection pattern to detect image density. And a potential difference determining means for determining a set potential difference in accordance with the toner amount of the toner thin layer for each potential difference and the image density for each potential difference.

  Patent Document 2 discloses an exposure unit that exposes a surface of a charged photoreceptor to a light beam to form an electrostatic latent image, a developing unit that exposes the electrostatic latent image with toner to form a toner image, and a developing unit. A toner image formed on the photosensitive member by the means or a toner image formed by transferring the toner image onto a transfer medium as a patch image, a density detecting means for detecting the image density, and a predetermined detection based on the detection result of the density detecting means. An image forming apparatus including a control unit that obtains an image forming condition necessary for forming a toner image having a target density as an optimum condition is disclosed. The control means provided in the image forming apparatus forms a patch image having a density lower than the target density under each image forming condition while changing the image forming conditions in multiple stages, and sets the optimum conditions based on the image density of the patch images. It is characterized by seeking.

JP 2005-308821 A JP 2003-270873 A

  In order to form a high-quality image, it is necessary to adjust the toner density with high accuracy. In this case, it is necessary to accurately detect the toner amount of the patch image formed on the intermediate transfer member for image adjustment. For the measurement of the toner amount of the patch image formed on the intermediate transfer member, an optical sensor is often used as disclosed in Patent Document 1. That is, the patch image formed with toner is irradiated with light, the amount of irradiated light, the amount of reflected light reflected by the patch image, and the reflected light from the surface of the intermediate transfer member to which no toner is attached The amount of toner is calculated based on the amount of light.

  According to the calculation of the toner amount using such an optical sensor, the toner amount in the low density to medium density region is calculated with high accuracy because the difference in the amount of reflected light is relatively large. Can do. However, with respect to the toner amount in the high density region, it is difficult to calculate the toner amount with high accuracy because the difference in the amount of reflected light is very small. This tendency is particularly remarkable for black toner.

  In this case, as shown in Patent Document 2, it is conceivable that a contrast potential for developing a toner amount that neutralizes an electric field on an electrostatic latent image is calculated and set as a developing bias. However, when an amorphous silicon photoconductor is used from the viewpoint of extending the life, the development amount changes based on the gap fluctuation between the developing roller and the photoconductor because the relative dielectric constant of amorphous silicon is relatively high. large. Therefore, the method disclosed in Patent Document 2 cannot be adopted.

  An object of the present invention is to provide an image forming apparatus capable of obtaining a high-quality image.

  In one aspect of the present invention, an image forming apparatus includes an image forming unit that performs image formation. The image forming apparatus includes an amorphous silicon photosensitive member, an exposure device, a developing roller, a magnetic roller, a peripheral speed ratio changing unit, an intermediate transfer member, a toner amount measuring unit, a first voltage applying unit, A second voltage applying unit, a patch image forming unit, a difference calculating unit, a determining unit, and a potential difference deriving unit. The exposure apparatus irradiates the photoconductor with light to form an electrostatic latent image on the surface of the photoconductor. The developing roller supplies toner to the photoconductor to form a visible image with toner from the electrostatic latent image. The magnetic roller holds the two-component developer and supplies toner constituting the two-component developer to the developing roller. The peripheral speed ratio changing unit changes the peripheral speed ratio between the developing roller and the photosensitive member. In the intermediate transfer member, a visible image formed on the photosensitive member is primarily transferred thereon. The first voltage application unit applies a first voltage to the developing roller. The second voltage application unit applies a second voltage to the magnetic roller. The patch image forming unit assigns a plurality of potential differences between the first voltage and the second voltage by using the peripheral speed ratio between the photosensitive member and the developing roller as the first peripheral speed ratio at the time of image formation. Then, a first patch image for toner amount adjustment is formed on the intermediate transfer member by the image forming unit. The toner amount measuring unit measures the toner amount of the first patch image formed by the patch image forming unit. The difference calculation unit calculates a difference in toner amount between the plurality of first patch images. The determination unit determines whether there is a predetermined number or more of data regarding the toner amount of the first patch image whose difference is within a predetermined range. The potential difference deriving unit derives a potential difference that causes the target toner amount to adhere to the intermediate transfer member from the data related to the toner amount of the first patch image if the determination unit determines that the predetermined number or more is present.

  According to such an image forming apparatus, the toner amount can be accurately adjusted over a wide range from a low density area to a high density area. Therefore, such an image forming apparatus can obtain a high-quality image.

1 is a schematic diagram showing 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. It is a block diagram which shows the structure of a control part. FIG. 2 is a schematic diagram illustrating a configuration of an image forming unit included in the digital multifunction peripheral illustrated in FIG. 1. FIG. 2 is a cross-sectional view illustrating a schematic configuration of a black developing unit. FIG. 3 is a schematic diagram illustrating a configuration of a toner amount detection sensor. It is a flowchart which shows the flow of a process in the case of adjusting the potential difference (DELTA) V between a magnetic roller and a developing roller using a digital multi-function peripheral. It is a figure which shows each patch image formed on the surface of a transfer belt. 6 is a graph showing a relationship between a potential difference ΔV and a detected toner amount in different developing devices. 6 is a graph showing a relationship between a peripheral speed ratio of a developing roller to a photoreceptor and a detected toner amount. 6 is a graph showing a relationship between a potential difference ΔV and a detected toner amount when materials of a developing roller are different.

  Embodiments of the present invention will be described below. FIG. 1 is a schematic diagram showing 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. 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, the digital multifunction peripheral 11 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 discharge tray 30, a toner. A quantity detection sensor 51, a hard disk 16 as a storage unit, 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 digital multi-function peripheral 11. The operation unit 13 includes a display screen 21 that displays information transmitted from the digital 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 the mounting table. The paper setting unit 19 includes a manual feed tray 28 for manually setting paper and a paper feed cassette group 29 that can store a plurality of different sizes of paper. The paper setting unit 19 sets paper to be supplied to the image forming unit 15. The image forming unit 15 includes an image forming unit 33 that forms a visible image with toner. The image forming unit 15 forms an image on the conveyed paper based on the image 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 digital multi-function peripheral 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 digital multifunction machine 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. Further, the digital multifunction peripheral 11 forms an image in the image forming unit 15 and prints it on a sheet using image data transmitted from the computers 26a, 26b, and 26c connected to the network 25 through the network interface unit 18. It works as a printer. That is, the image forming unit 15 operates as a printing unit that prints the requested image. The digital multifunction machine 11 forms an image in the image forming unit 15 through the DRAM using the image data transmitted from the public line 24 through the facsimile communication unit 17 and is read by the image reading unit 14. By transmitting the image data of the original document to the public line 24 through the facsimile communication unit 17, the facsimile apparatus operates. The digital 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.

  An image forming system 27 including a digital multifunction peripheral 11 according to an embodiment of the present invention includes a digital multifunction peripheral 11 having the above-described configuration and a plurality of computers 26 a and 26 b connected to the digital multifunction peripheral 11 via a network 25. 26c. 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 control unit 12 will be described. FIG. 3 is a block diagram illustrating a configuration of the control unit 12. With reference to FIG. 3, the control unit 12 includes a peripheral speed ratio changing unit 60, a patch image forming unit 56, a difference calculating unit 57, a determining unit 58, and a potential difference deriving unit 59. The peripheral speed ratio changing unit 60 changes the peripheral speed ratio between the developing roller and the photoconductor. The patch image forming unit 56 uses the peripheral speed ratio changing unit 60 to set the peripheral speed ratio between the photoconductor and the developing roller as the first peripheral speed ratio at the time of image formation, and the potential difference between the first voltage and the second voltage. A plurality of images are allocated, and a first patch image for adjusting the toner amount is formed on the intermediate transfer member by the image forming unit 15. The difference calculation unit 57 calculates a difference in toner amount between the plurality of first patch images. The determination unit 58 determines whether there is a predetermined number or more of data regarding the toner amount of the first patch image whose difference is within a predetermined range. If the determination unit 58 determines that there is a predetermined number or more, the potential difference deriving unit 59 derives a potential difference for attaching the target toner amount on the intermediate transfer member from the data regarding the toner amount of the first patch image. These configurations will be described later.

  Next, the configuration of the image forming unit 15 provided in the digital multifunction peripheral 11 will be described in more detail. FIG. 4 is a schematic cross-sectional view illustrating a schematic configuration of the image forming unit 15 provided in the digital multifunction peripheral 11. From the viewpoint of easy understanding, the members are not hatched in FIG. FIG. 4 is a cross-sectional view of the digital multifunction machine 11 cut along a plane extending in the vertical direction.

  Referring to FIG. 4, the image forming unit 15 includes four photosensitive members 31a, 31b, 31c, and 31d corresponding to four colors of yellow, magenta, cyan, and black, and four developing units 32a, 32b, 32c, An image forming unit 33 including 32d, an LSU (Laser Scanner Unit) 34 as an exposure device, a transfer belt 35 as an intermediate transfer member, and a primary transfer unit 37 including four primary transfer rollers 36a, 36b, 36c, and 36d. A secondary transfer roller 38, a cleaning blade 39, and a toner amount detection sensor 51. From the viewpoint of extending the life, all of the photoconductors 31a to 31d are made of amorphous silicon. About LSU34, it has shown roughly with the dashed-dotted line. The toner amount detection sensor 51 is schematically indicated by a two-dot chain line. The digital multi-function peripheral 11 includes a so-called quad tandem image forming unit 15. In FIG. 4, the developing units 32a to 32d are schematically shown.

  The LSU 34 exposes the four photoconductors 31a to 31d based on the images read by the image reading unit 14, respectively. Electrostatic latent images are formed on the photoreceptors 31a to 31d based on the exposed light of the components of each color. Each color toner is supplied from the developing units 32a to 32d to the electrostatic latent images formed on the photoreceptors 31a to 31d. The toner is agitated in the developing units 32a to 32d and charged, for example, to have a positive charge. The charged toner is supplied to the photoconductors 31a to 31d, and visible images are formed on the photoconductors 31a to 31d. The visible images of the toner formed on the photoreceptors 31 a to 31 d in this way are primarily transferred to the transfer belt 35.

The transfer belt 35 is endless. The transfer belt 35 is rotated in one direction by the driving roller 41a and the driven roller 41b. Rotational direction of the transfer belt 35 is indicated by an arrow D ₁ of the in FIG. That is, the rotation direction of the transfer belt 35 is the direction from the left side to the right side in the lower area where the photoconductors 31a to 31d are provided, and the direction from the right side to the left side in the opposite upper area. In the rotation direction of the transfer belt 35, among the developing units 32a to 32d, the yellow developing unit 32a is disposed on the most upstream side, and the black developing unit 32d is disposed on the most downstream side. Note that the transfer belt 35 rotates from the upstream side toward the downstream side.

  The four primary transfer rollers 36 a to 36 d are arranged at positions facing the photoconductors 31 a to 31 d of the respective colors via the transfer belt 35. The primary transfer unit 37 primarily transfers a visible image with toner formed by the four color developing units 32 a to 32 d of yellow, magenta, cyan, and black onto the transfer belt 35. Specifically, by applying a bias to each of the primary transfer rollers 36 a to 36 d, visible images of toner formed on the photoreceptors 31 a to 31 d by the developing units 32 a to 32 d are formed on the surface 42 of the transfer belt 35. Primary transcription. At this time, the images of the respective colors are superimposed on the transfer belt 35 to form a full color image on the transfer belt 35.

  The secondary transfer roller 38 is provided at a position facing the driven roller 41 b via the transfer belt 35. The image forming unit 15 includes a sheet conveyance path 43 a for conveying a sheet as a recording medium at a position where the secondary transfer roller 38 and the surface 42 of the transfer belt 35 abut. The image forming unit 15 also includes a sheet conveyance path 43b for conveying the second-transferred sheet to a fixing unit (not shown). A sheet is supplied from the upstream sheet conveyance path 43a where the sheet feeding cassettes 23a to 23c are located to a position where the secondary transfer roller 38 and the surface 42 of the transfer belt 35 abut. A bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 38 in accordance with the timing of paper conveyance. By applying a bias to the secondary transfer roller 38, a visible image formed by the toner formed on the surface 42 of the transfer belt 35 is electrically drawn to the supplied paper side and is secondarily transferred to the paper. The sheet on which the visible image is transferred by the toner is conveyed to a fixing unit (not shown) using the sheet conveying path 43b.

  The cleaning blade 39 is provided at a position facing the driving roller 41a with the transfer belt 35 interposed therebetween. The cleaning blade 39 is provided on the upstream side of the yellow developing unit 32a. The cleaning blade 39 is composed of a rubber-like long and narrow plate-like member having elasticity. The cleaning blade 39 is attached so that the main scanning direction of the digital multi-function peripheral 11 is the longitudinal direction. The cleaning blade 39 is disposed so that its tip end is in contact with the surface 42 of the transfer belt 35 in a so-called counter direction. The cleaning blade 39 is fixed at a predetermined location, and physically removes toner adhering to the surface 42 of the transfer belt 35 rotating in one direction. As a material of the cleaning blade 39, for example, urethane rubber is used. After the visible image by the toner is transferred to the paper, the toner remaining on the transfer belt 35 is physically removed by the cleaning blade 39. Then, the next image formation is performed.

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

  Next, the configuration of the black developing unit 32d will be described. FIG. 5 is a cross-sectional view showing a schematic configuration of the black developing unit 32d. With reference to FIG. 5, the developing unit 32 d includes a magnetic roller 45 and a developing roller 46. The magnetic roller 45 is also called a mag roller. The developing roller 46 is also called a developing sleeve.

  Both the magnetic roller 45 and the developing roller 46 are disposed in a developing container 44 partially illustrated. The developing container 44 is filled with a two-component developer (not shown) composed of toner and carrier. The toner consumed by the development is supplied into the developing container 44 as needed. In the developing container 44, a stirring roller (not shown) for stirring the toner and the developer is also provided.

  Inside the magnetic roller 45, N and S poles are alternately formed in the circumferential direction. The magnetic roller 45 holds the two-component developer on the surface 47 thereof. The magnetic roller 45 supplies toner from the two-component developer held on the surface 47 to the developing roller 46 side. A thin layer of toner supplied from the magnetic roller 45 side is formed on the surface 48 of the developing roller 46.

Developing roller 46 while rotating in the direction of the arrow R ₂ in FIG. 5, for supplying the toner to the surface 49 of the black photoreceptor 31d. The photosensitive member 31d rotates in the direction of the arrow _{R 1} in FIG. When toner is supplied to the electrostatic latent image formed on the surface 49 of the photoconductor 31d, a visible image of the toner is formed on the surface 49 of the photoconductor 31d.

  The developing unit 32 d includes a first voltage application unit 50 a that applies a first voltage to the magnetic roller 45. The developing unit 32d includes a second voltage applying unit 50b that applies a second voltage to the developing roller 46. The first voltage application unit 50a and the second voltage application unit 50b are provided separately. There is a difference between the voltages applied to the magnetic roller 45 and the developing roller 46. That is, the first voltage applied to the magnetic roller 45 is different from the second voltage applied to the developing roller 46. Based on the potential difference ΔV between the first voltage and the second voltage, the layer thickness of the toner formed on the developing roller 46 is determined. That is, the potential difference ΔV is made variable to set the toner layer thickness on the developing roller 46.

  Next, the configuration of the toner amount detection sensor 51 will be briefly described. FIG. 6 is a schematic diagram illustrating the configuration of the toner amount detection sensor 51. In FIG. 6, the toner amount detection sensor 51 is schematically indicated by a two-dot chain line.

  Referring to FIGS. 1 to 6, the toner amount detection sensor 51 as a toner amount measuring unit is disposed on the downstream side of the black developing unit 32 d in the rotation direction of the transfer belt 35. The toner amount detection sensor 51 receives light by a light emitting element 52a that irradiates light on the surface 42 side of the transfer belt 35, a light receiving element 52b that receives reflected light reflected from the surface 42 side of the transfer belt 35, and a light receiving element 52b. A toner amount calculation unit 53 that calculates a toner amount from the amount of reflected light. In this embodiment, the light emitting element 52 a and the light receiving element 52 b are installed so as to be symmetrical with respect to a plane 54 extending in a direction perpendicular to the surface 42 of the transfer belt 35. That is, the light receiving element 52b is provided at a position for receiving regular reflection light with respect to the light emitted by the light emitting element 52a. As an example of the light emitting element 52a, specifically, an infrared light emitting diode that irradiates infrared light is employed. As an example of the light receiving element 52b, specifically, an infrared light receiving element is employed.

Emitting element 52a is towards the visible image 40 by the surface 42 or the toner of the transfer belt 35 is irradiated with light 55a such infrared light to the left obliquely upward direction indicated by arrow E ₁ in FIG. When the visible image 40 is not formed with toner, the light emitting element 52 a emits light 55 a toward the surface 42 of the transfer belt 35.

The light receiving element 52b is either one or toner, the reflected light 55b from the surface 42 of the reflected light 55b and the transfer belt 35 from the visible image 40 by the toner toward the lower left direction indicated by the arrow E ₂ in FIG. 6 The reflected light 55b from both the visible image 40 and the surface 42 of the transfer belt 35 is received. If the visible image 40 made of toner completely covers the surface 42 of the transfer belt 35, only the reflected light 55b from the visible image 40 made of toner is received. If the visible image 40 made of toner is not formed on the surface 42 of the transfer belt 35, only the reflected light 55b from the surface 42 of the transfer belt 35 is received. If the visible image 40 made of toner does not completely cover the surface 42 of the transfer belt 35 and the amount of toner in the visible image 40 made of toner is small, the reflection from both the visible image 40 made of toner and the surface 42 of the transfer belt 35 will occur. The light 55b is received.

Toner amount detecting sensor 51, the transfer belt 35 to a visible image 40 is formed by the toner on the surface 42 is irradiated with light 55a in the direction indicated by arrow E ₁ in FIG. The light 55 a is reflected by either the visible image 40 made of toner and the surface 42 of the transfer belt 35, or both the visible image 40 made of toner and the surface 42 of the transfer belt 35. The reflected reflected light 55b is received by the light receiving element 52b. The light receiving element 52b outputs a current corresponding to the amount of received light. The toner amount calculation unit 53 converts the current output from the light receiving element 52b into a voltage value. Then, the toner amount is calculated based on this voltage value. In this way, the toner concentration detection sensor 51 detects the toner amount.

  In the digital multifunction peripheral 11, the above-described potential difference ΔV is adjusted at a predetermined timing. That is, the potential difference ΔV when the target toner amount is attached to the surface 42 of the transfer belt 35 in accordance with the aging of the members constituting the image forming unit 15 or the environment in which the digital multifunction peripheral 11 is installed. Is adjusted from the initial setting value. By accurately adjusting the toner amount over a wide range from the low density area to the high density area, it is possible to maintain high precision image quality.

  Next, a case where the potential difference ΔV between the magnetic roller 45 and the developing roller 46 is adjusted using the digital multifunction machine 11 will be described. FIG. 7 is a flowchart showing the flow of processing when the potential difference ΔV between the magnetic roller 45 and the developing roller 46 is adjusted using the digital multi-function peripheral 11. Here, a case where the potential difference ΔV is adjusted in the black developing unit 32d will be described. In this embodiment, the potential difference ΔV is changed by four levels, and the number of data useful for adjusting the potential difference ΔV is set to four. In the following, a black image will be described, but the processing flow for yellow, magenta, and cyan colors is the same as that for black.

  1 to 7, when adjusting the potential difference ΔV, the control unit 12 first assigns the potential difference ΔV to four levels, and the image forming unit 15 adjusts the toner amount on the surface 42 of the transfer belt 35. The first patch image is formed (in FIG. 7, step S11, hereinafter “step” is omitted). In this case, the peripheral speed ratio S / D between the developing roller 46 and the photoreceptor 31d is the first peripheral speed ratio during normal image formation. An actual first peripheral speed ratio is 1.6, for example. The peripheral speed ratio M / S between the magnetic roller 45 and the developing roller 46 is fixed at a constant value.

In this case, the value of the voltage to the developing roller 46 is fixed, and the value of the voltage applied to the magnetic roller 45 is variable. Specifically, the potential difference ΔV between the respective levels is set to about 100 V to be equal. FIG. 8 shows patch images 61a, 61b, 61c and 61d formed on the surface 42 of the transfer belt 35. FIG. Referring to FIG. 8, patch images 61a to 61d are each configured in a rectangular shape. Further, the patch image 61a~61d, in the transport direction of the transfer belt 35 indicated by the arrow _{D 1,} are provided respectively at an interval.

  Next, the toner amounts of the formed first patch images 61a to 61d are measured (S12). The toner amount is measured by the toner amount detection sensor 51 described above. Note that the relationship between the set potential difference ΔV and the toner amount tends to be different for each developing unit.

Here, the relationship between the potential difference ΔV for each different development unit and the toner amount will be described. FIG. 9 is a graph showing the relationship between the potential difference ΔV and the detected toner amount in different developing units. In FIG. 9, the vertical axis indicates the toner amount (mg / cm ² ), and the horizontal axis indicates the potential difference Δ (volt). Three lines 62a to 62c shown in FIG. 9 show three different development units.

  Referring to FIG. 9, as can be seen from lines 62a, 62b, and 62c, even when the potential difference ΔV is the same, the detected toner amount differs for each developing unit. The relationship between the potential difference Δ and the detected toner amount is approximately proportional, although there is a difference between the developing units.

Here, in the case shown in FIG. 9, the relationship between the potential difference Δ and the detected toner amount is linear. Specifically, in the developing unit shown by line 62a, a potential difference ΔV is if the 200V from 100 V, a toner amount of about 0.15 mg / cm ^2, measured with 0.31 mg / cm ^2. Further, the potential difference ΔV is if the 300V from 200V, a toner amount of about 0.31 mg / cm ^2, measured with 0.41 mg / cm ^2. That is, when the potential difference ΔV increases by 100 V, the measured toner amount increases by at least about 0.1 mg / cm ² .

  However, when the potential difference ΔV is high, for example, when the potential difference ΔV is 400 V or more, the measured toner amount may hardly change. That is, there is a situation in which there is almost no change in the toner amount measured by the toner amount detection sensor 51, even though the potential difference ΔV is about 100 V, compared with cases where the potential difference ΔV is relatively high. This corresponds to the potential difference ΔV when a high density image is formed.

Here, the control unit 12 calculates a difference in toner amount between the plurality of first patch images 61a to 61d (S13). Then, the determination unit 58 determines whether or not there is a predetermined number of data relating to the toner amount of the first patch images 61a to 61d in which the calculated difference is within a predetermined range, that is, four or more in this case (S14). When the above-described potential difference ΔV is 100 V, regarding the toner amount difference, there are 4 data relating to the toner amount of the first patch images 61a to 61d in which the detected toner amount is at least 0.1 mg / cm ² as a predetermined range. Determine whether there are more than two.

If it is determined that the number of data is four or more (YES in S14), a linear approximation is performed based on the relationship between the potential difference Δ and the detected toner amount based on the obtained four data, and the target toner The potential difference Δ corresponding to the amount of toner, which is a level that cannot be measured by the toner amount detection sensor 51, is calculated (S15). Then, the calculated potential difference Δ is reflected in the setting for image formation, and the adjustment of the potential difference ΔV is completed (S16). After that, calibration such as light quantity and gamma correction of the LSU 34 is performed. The sensitivity of the toner amount detection sensor 51 is such that the toner amount when the image density ID is 1.2 is 0.4 mg / cm ² . When the target value of the image density ID is 1.4, the toner amount is 0.5 mg / cm ² .

  On the other hand, if it is determined that the number of data is less than 4 (NO in S14), the peripheral speed ratio changing unit 60 changes the peripheral speed ratio between the developing roller 46 and the photoreceptor 31d to the first peripheral speed ratio. To the second peripheral speed ratio (S17). The first peripheral speed ratio is smaller than the second peripheral speed ratio. An actual second peripheral speed ratio is 0.8, for example.

FIG. 10 is a graph showing the relationship between the peripheral speed ratio of the developing roller 46 relative to the photoreceptor 31d and the detected toner amount. In FIG. 10, the vertical axis indicates the toner amount (mg / cm ² ), and the horizontal axis indicates the peripheral speed ratio.

  Referring to FIG. 10, as the peripheral speed ratio is decreased, the measured toner amount is decreased. This is presumably because the amount of toner supplied to the nip portion between the photoreceptor 31d and the developing roller 46 is reduced. Further, the peripheral speed ratio and the toner amount are substantially proportional.

  Then, after setting the second peripheral speed ratio, the potential difference ΔV is again assigned to four levels, and the second patch image for adjusting the toner amount is formed on the surface 42 of the transfer belt 35 using the image forming unit 15. Form (S18). Then, the toner amount of each formed second patch image is measured by the toner amount detection sensor 51 (S19).

  The difference is calculated again for the measured toner amount (S20), and it is determined whether or not there is a predetermined number of data relating to the toner amount of the second patch image in which the calculated difference is within a predetermined range, here 4 or more. Judgment is made (S21). If it is determined that the number of data is four or more (YES in S21), it is further changed to a third peripheral speed ratio that is smaller than the second peripheral speed ratio (S22). Then, the potential difference ΔV is assigned to four levels, and a third patch image for toner amount adjustment is formed on the surface 42 of the transfer belt 35 by the image forming unit 15 (S23). Then, the toner amount of each formed third patch image is measured by the toner amount detection sensor 51 (S24). In this case, based on FIG. 10 described above, the toner amount decreases as the peripheral speed ratio decreases. Accordingly, regarding the relationship between the measured toner amount and the potential difference ΔV, the number of data regarding the toner amount of the third patch image in which the calculated difference is within a predetermined range is four.

  Then, four data relating to the relationship between the second peripheral speed ratio and the third peripheral speed ratio, the toner amount of the second patch image obtained in the case of the second peripheral speed ratio, and the third peripheral speed ratio. From the four data regarding the toner amount of the third patch image obtained in the case of the speed ratio, the first peripheral speed ratio, that is, the relationship between the peripheral speed ratio during image formation and the second peripheral speed ratio is derived. Further, the relationship between the potential difference ΔV and the toner amount at the first peripheral speed ratio is derived (S25).

  Then, from the relationship between the derived potential difference ΔV at the first peripheral speed ratio and the toner amount, a potential difference ΔV for obtaining a target toner amount is calculated (S15). Then, the calculated potential difference Δ is reflected in the setting for image formation, and the adjustment of the potential difference ΔV is completed (S16).

  If it is determined that the number of data obtained with the second circumferential speed ratio is less than 4 (NO in S19), the circumferential speed ratio is decreased until the number of data becomes 4 or more. Is newly set as the second peripheral speed ratio, and patch image formation and toner amount measurement are similarly performed. That is, the peripheral speed ratio is reduced until four data are obtained, and when four data are obtained, the peripheral speed ratio at that time is set as the second peripheral speed ratio. Then, the patch image is formed and the toner amount is measured again at the third peripheral speed ratio having a lower peripheral speed ratio. Thereafter, the relationship between the second peripheral speed ratio and the third peripheral speed ratio, four data obtained in the case of the second peripheral speed ratio, and 4 obtained in the case of the third peripheral speed ratio. From the two data, the relationship between the potential difference ΔV at the first peripheral speed ratio and the toner amount is derived.

  With this configuration, the toner amount can be accurately adjusted over a wide range from a low density area to a high density area. Therefore, such an image forming apparatus can obtain a high-quality image.

  In addition, when the relationship between the peripheral speed ratio and the toner amount, that is, the correlation data between the peripheral speed ratio and the toner amount is known in advance and this data is stored in the hard disk 16, for example, You may decide to utilize this data, without acquiring the data in the third peripheral speed ratio. In this way, the toner amount can be adjusted more efficiently.

Specifically, if the relationship shown in FIG. 10 can be grasped in advance, the potential difference ΔV and the toner amount at the first peripheral speed ratio are calculated from the relationship between the potential difference ΔV and the toner amount at the second peripheral speed ratio. The relationship can be derived. For example, when the first peripheral speed ratio is 1.6 and the second peripheral speed ratio is 0.8, the toner amount measured at each peripheral speed ratio is about 0.5 mg / cm ^2. About 0.29 mg / cm ² . Using these relationships, the relationship between the potential difference ΔV and the toner amount at the first peripheral speed ratio is derived from the relationship between the potential difference ΔV and the toner amount at the second peripheral speed ratio.

A case where the material of the developing roller 46 is different will be described. FIG. 11 is a graph showing the relationship between the potential difference ΔV and the detected toner amount when the material of the developing roller 46 is different. In FIG. 11, the vertical axis represents the toner amount (mg / cm ² ), and the horizontal axis represents the potential difference Δ (volt). The two lines 63a to 63b shown in FIG. 11 show the case of a developing device using two developing rollers 46 of different materials.

  Referring to FIG. 11, in the developing unit indicated by line 63a, when the potential difference ΔV is less than 100V, the linearity is lost compared to the case of the developing unit indicated by line 63b. Specifically, the amount of toner tends to be measured with respect to the applied potential difference ΔV. In this regard, the developing roller included in the developing unit indicated by the line 63a has a lower electric field followability at a low potential difference ΔV than the developing roller included in the developing unit indicated by the line 63b.

  Therefore, even when using such a developing roller, that is, a developing roller with low electric field followability, the relationship between the potential difference ΔV and the toner amount is derived as described above, and the toner amount corresponding to the target image density The potential difference ΔV corresponding to can be calculated.

  In the above-described embodiment, the voltage applied to the developing roller 46 is fixed and the voltage applied to the magnetic roller 45 is changed. The voltage may be fixed and the voltage applied to the developing roller 46 may be changed.

  In the above embodiment, the number of data is four. However, the number of data is not limited to this, and may be at least two useful data necessary for obtaining a linear relationship. That is, the predetermined number of data may be configured to be 2 or more.

  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 it is required to obtain a high-quality image.

  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, 19 Paper setting part, 21 Display screen, 22 ADF, 23a, 23b, 23c Paper 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 Developing unit, 33 Image forming unit, 34 LSU, 35 Transfer belt, 36a, 36b, 36c, 36d Primary transfer roller, 37 Primary transfer unit, 38 Secondary transfer roller, 39 Cleaning braid , 41a Driving roller, 40 visible image, 41b driven roller, 42, 47, 48, 49 surface, 43a, 43b paper transport path, 44 developing container, 45 magnetic roller, 46 developing roller, 50a, 50b voltage application unit, 51 toner Quantity detection sensor, 52a Light emitting element, 52b Light receiving element, 53 Toner amount calculation part, 54 Plane, 55a, 55b Light, 56 Patch image forming part, 57 Difference calculation part, 58 Judgment part, 59 Potential difference deriving part, 60 Peripheral speed ratio Change part, 61a, 61b, 61c, 61d patch image, 62a, 62b, 62c, 63a, 63b line.

Claims (4)

An image forming apparatus including an image forming unit that performs image formation,
An amorphous silicon photoreceptor,
An exposure apparatus that irradiates light to the photoreceptor to form an electrostatic latent image on the surface of the photoreceptor;
A developing roller that supplies toner to the photoreceptor and forms a visible image with toner from the electrostatic latent image;
A magnetic roller that holds the two-component developer and supplies the toner constituting the two-component developer to the developing roller;
A peripheral speed ratio changing unit for changing a peripheral speed ratio between the developing roller and the photosensitive member;
An intermediate transfer member on which the visible image formed on the photosensitive member is primarily transferred;
A first voltage application unit for applying a first voltage to the developing roller;
A second voltage application unit for applying a second voltage to the magnetic roller;
The peripheral speed ratio changing unit assigns a plurality of potential differences between the first voltage and the second voltage, with the peripheral speed ratio between the photoconductor and the developing roller as a first peripheral speed ratio during image formation. A patch image forming unit that forms a first patch image for toner amount adjustment on the intermediate transfer member by the image forming unit;
A toner amount measuring unit for measuring the toner amount of the first patch image formed by the patch image forming unit;
A difference calculating unit that calculates a difference in toner amount between the plurality of first patch images;
A determination unit that determines whether or not there is a predetermined number or more of data regarding the toner amount of the first patch image in which the difference is within a predetermined range;
A potential difference deriving unit for deriving the potential difference for adhering a target toner amount on the intermediate transfer member from data relating to the toner amount of the first patch image if the determination unit determines that the predetermined number or more exists; An image forming apparatus. The peripheral speed ratio changing unit changes the peripheral speed ratio until it is determined that the predetermined number is greater than or equal to the predetermined number if the determination unit determines that the predetermined number or greater is not present.
The patch image forming unit allocates a plurality of potential differences between the first voltage and the second voltage as the second peripheral speed ratio changed by the peripheral speed ratio changing unit, and the image forming unit Forming a second patch image for toner amount adjustment on the intermediate transfer member,
The toner amount measuring unit measures the toner amount of the second patch image;
The difference calculation unit calculates a difference in toner amount between the plurality of second patch images,
The potential difference deriving unit derives the potential difference from data regarding the second peripheral speed ratio, the first peripheral speed ratio, and the toner amount of the second patch image changed by the peripheral speed ratio changing unit. The image forming apparatus according to claim 1. A storage unit for storing correlation data between the peripheral speed ratio and the toner amount;
The image forming apparatus according to claim 2, wherein the potential difference deriving unit derives the potential difference based on correlation data between the peripheral speed ratio and the toner amount stored in the storage unit. The image forming apparatus according to claim 1, wherein the predetermined number is two.

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