JP2023166157A - Image forming apparatus - Google Patents

Abstract

To prevent the occurrence of a failure in image transfer when the thickness of a recording medium is equal to or more than a predetermined thickness.SOLUTION: An image forming apparatus comprises: an image carrier 8 that carries an image; a transfer rotating body 71 that is in contact with the image carrier 8 to form a transfer nip, and transfers the image on the image carrier 8 to a recording medium conveyed to the transfer nip; an arithmetic unit 91 that calculates the difference between the length in a conveyance direction of an image with a low image area ratio transferred to the recording medium and the length in the conveyance direction of an image with a high image area ratio transferred to the recording medium; a speed difference adjustment unit 96 that adjusts the relative difference in the rotation speed of the transfer rotating body 71 relative to the image carrier 8 so as to reduce the absolute value of the difference calculated by the arithmetic unit 91; and a speed correction unit 97 that, when the thickness of the recording medium is equal to or more than a predetermined thickness, decreases the rotation speed of the transfer rotating body 71 compared with the rotation speed of the transfer rotating body 71 based on the speed difference adjusted to reduce the absolute value of the difference.SELECTED DRAWING: Figure 12

Description

The present invention relates to an image forming apparatus.

Image forming apparatuses such as printers and copying machines are known in which a transfer rotating body such as a transfer belt or a transfer roller is brought into contact with an image bearing member such as an intermediate transfer belt or a photosensitive drum to form a transfer nip. .

In such an image forming apparatus, when a recording medium such as paper is conveyed to a transfer nip, an image on an image carrier is transferred to the recording medium at the transfer nip.

Incidentally, depending on the image area ratio of the image transferred from the image carrier to the recording medium, the length of the transferred image on the recording medium in the conveyance direction may change. Specifically, when the image area ratios differ, the frictional state between the recording medium and the image carrier in the transfer nip changes depending on the respective image area ratios, which causes variations in the conveyance speed of the recording medium in the transfer nip. This variation causes the image to expand or contract in the transport direction during transfer.

In order to suppress the variation in the length of the transferred image in the transport direction due to the difference in image area ratio as described above, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2021-176010), the transfer rotation body is A method has been proposed in which at least one of the relative linear velocity difference and the contact pressure of the transfer rotor against the image carrier in the transfer nip is adjusted.

However, as described above, even if at least one of the linear velocity difference and the contact pressure in the transfer nip is adjusted according to the image area ratio, if the thickness of the recording medium is more than a predetermined thickness, Band-shaped image transfer defects (transfer unevenness) sometimes occurred across the width direction.

In order to solve the above problems, an image forming apparatus according to the present invention includes an image bearing member that carries an image, a transfer nip formed by contacting the image bearing member, and a transfer nip formed on the recording medium conveyed to the transfer nip. On the other hand, the transfer rotary body that transfers the image on the image carrier, the length in the transport direction of the image with a low image area ratio transferred to the recording medium, and the length of the image with a high image area ratio transferred to the recording medium. a calculation unit that calculates a difference with the length in the transport direction; and adjusting a relative rotational speed difference of the transfer rotating body with respect to the image carrier so that the absolute value of the difference calculated by the calculation unit is small. a speed difference adjusting section; when the thickness of the recording medium is equal to or greater than a predetermined thickness, the rotational speed of the transfer rotary body is based on the speed difference adjusted so that the absolute value of the difference is small; The image forming apparatus is characterized in that it includes a speed correction section that makes the rotation speed slower than the rotation speed of the transfer rotary body.

According to the present invention, it is possible to suppress the occurrence of image transfer defects when the thickness of the recording medium is greater than or equal to a predetermined thickness.

1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. 1 is a diagram illustrating a configuration of an image forming section included in an image forming apparatus according to an embodiment. 1 is a diagram illustrating the configuration of an intermediate transfer belt and its vicinity included in an image forming apparatus according to an embodiment; FIG. FIG. 2 is a block diagram showing the configuration of a control section according to the present embodiment. FIG. 2 is a diagram showing the configuration of a secondary transfer device and a control section thereof included in the image forming apparatus according to the present embodiment. 3A and 3B are diagrams showing images formed in the adjustment mode, in which (A) is a diagram showing an image with a low image area ratio formed on the front side of the sheet, and (B) is a diagram showing an image with a high image area ratio formed on the back side of the sheet. FIG. It is a flowchart which shows control in adjustment mode. A table showing the relationship between the difference in length in the conveyance direction between the first image pattern and the second image pattern and the rotational speed difference between the intermediate transfer belt and the secondary transfer belt in the secondary transfer nip for each sheet with different thickness. It is. 9 is a graph showing the relationship shown in FIG. 8 with the vertical axis representing the difference in length in the transport direction and the horizontal axis representing the rotational speed difference. It is a table showing the rotational speed difference for each type of sheet when the rotational speed of the secondary transfer belt is extracted so that the difference in length in the transport direction is 0 [mm]. 3 is a table showing whether or not image transfer defects occur for each sheet thickness. FIG. 3 is a diagram showing the configuration of a control section that corrects the rotational speed of a secondary transfer belt. 7 is a flowchart showing control when correcting rotational speed. 7 is a table showing the results of a test to determine whether band-like image transfer defects occur before and after the rotation speed is corrected. 7 is a table showing the difference in the length of the transferred image in the transport direction before and after the rotation speed is corrected. It is a flow chart which shows control concerning other embodiments of the present invention.

Hereinafter, the present invention will be explained based on the accompanying drawings. In addition, in each drawing for explaining the present invention, components such as members and components having the same function or shape are given the same reference numerals as much as possible so that they can be distinguished. Omitted.

First, an embodiment of an image forming apparatus according to the present invention will be described based on FIGS. 1 to 5.

FIG. 1 is a schematic configuration diagram of the entire image forming apparatus according to the present embodiment, and FIG. 2 is a diagram showing the configuration of an image forming section included in the image forming apparatus according to the present embodiment. Further, FIG. 3 is a diagram showing the configuration of an intermediate transfer belt and its vicinity included in the image forming apparatus according to the present embodiment, and FIG. 4 is a diagram showing the configuration of a control section included in the image forming apparatus according to the present embodiment. FIG. 5 is a block diagram showing the configuration of a secondary transfer device included in the image forming apparatus according to the present embodiment.

As shown in FIG. 1, an intermediate transfer belt 8 (intermediate transfer body) serving as an image carrier is arranged at the center of the image forming apparatus 100. Further, image forming units 6Y, 6M, 6C, and 6K corresponding to each color (yellow, magenta, cyan, and black) are arranged in parallel so as to face the intermediate transfer belt 8.

As shown in FIG. 2, the image forming section 6Y corresponding to yellow includes a photoconductor drum 1Y as a photoconductor, a charging section 4Y arranged around the photoconductor drum 1Y, a developing section 5Y, a cleaning section 2Y, It includes a lubricant supply device 3, a static eliminator, and the like. Then, an image forming process (charging process, exposure process, development process, transfer process, cleaning process, static elimination process) is performed on the photoconductor drum 1Y, and a yellow image is formed on the photoconductor drum 1Y.

Note that the other three image forming sections 6M, 6C, and 6K have almost the same configuration as the image forming section 6Y corresponding to yellow, except that the color of toner used is different. Therefore, images corresponding to the respective toner colors are also formed in these image forming units 6M, 6C, and 6K. Hereinafter, description of the other three image forming sections 6M, 6C, and 6K will be omitted as appropriate, and only the image forming section 6Y corresponding to yellow will be explained.

As shown in FIG. 2, the photosensitive drum 1Y is rotationally driven in a counterclockwise direction by a drive motor. Then, the surface of the photoreceptor drum 1Y is uniformly charged at the position of the charging section 4Y (charging step). Thereafter, the surface of the photoreceptor drum 1Y reaches the irradiation position of the laser beam L emitted from the exposure section 7, and at this position, the surface of the photosensitive drum 1Y reaches the width direction (the direction perpendicular to the paper plane of FIGS. 1 and 2, and the main scanning direction). ), an electrostatic latent image corresponding to yellow is formed by exposure scanning (exposure step).

The surface of the photoreceptor drum 1Y on which the electrostatic latent image is formed reaches a position facing the developing section 5Y, and at this position, toner is supplied from the developing section 5Y to the electrostatic latent image on the photoreceptor drum 1Y. As a result, the electrostatic latent image on the photoreceptor drum 1Y is developed, and a yellow toner image is formed (developing step). Thereafter, the surface of the photoreceptor drum 1Y reaches a position facing the intermediate transfer belt 8 and the primary transfer roller 9Y, and at this position the toner image on the photoreceptor drum 1 is primarily transferred to the surface of the intermediate transfer belt 8 ( primary transfer process).

Further, a small amount of untransferred toner remains on the photoreceptor drum 1Y after the primary transfer. Therefore, when the surface of the photoreceptor drum 1Y reaches a position facing the cleaning section 2Y, the untransferred toner remaining on the photoreceptor drum 1Y at this position is removed by the cleaning blade 2a and collected into the cleaning section 2Y. (cleaning process).

Here, a lubricant supply device 3 (photoconductor lubricant supply device) including a lubricant supply roller 3a, a solid lubricant 3b, a compression spring 3c, etc. is provided inside the cleaning section 2Y. Then, the lubricant is scraped little by little from the solid lubricant 3b by the lubricant supply roller 3a rotating clockwise in FIG. 2, and the lubricant is supplied to the surface of the photoreceptor drum 1Y by the lubricant supply roller 3a. . Thereafter, the surface of the photoreceptor drum 1Y reaches a position facing the static eliminating section, and the residual potential on the photoreceptor drum 1 is removed at this position. In this way, a series of image forming processes performed on the photosensitive drum 1Y are completed.

Note that the above-described image forming process is performed in the other image forming sections 6M, 6C, and 6K in the same manner as in the yellow image forming section 6Y. That is, as shown in FIG. 1, a laser beam L based on image information is emitted from the exposure section 7 arranged above the image forming section onto the photoreceptor drums 1M, 1C of the respective image forming sections 6M, 6C, 6K. , 1K upward. Specifically, the exposure section 7 emits laser light L from a light source, and irradiates the photoreceptor drum with the laser light L through a plurality of optical elements while scanning the laser light L with a rotationally driven polygon mirror. Note that as the exposure section 7, a plurality of LEDs arranged side by side in the width direction may be used.

Thereafter, the toner images of the respective colors formed on the respective photoreceptor drums 1M, 1C, and 1K through a developing process by the respective developing units 5M, 5C, and 5K are primarily transferred onto the intermediate transfer belt 8 in an overlapping manner. In this way, a color image is formed on the intermediate transfer belt 8.

Here, the intermediate transfer belt 8 as an image carrier is stretched and supported by a plurality of roller members 16 to 22, 80 (see FIG. 3), and one roller member is driven by a drive motor Mt1 (see FIG. 3). The drive roller 16 rotates (endlessly moves) in the direction of the arrow in FIG. 3 due to the rotational drive of the drive roller 16. The four primary transfer rollers 9Y, 9M, 9C, and 9K sandwich the intermediate transfer belt 8 with the photosensitive drums 1Y, 1M, 1C, and 1K, respectively, to form primary transfer nips. Then, a transfer voltage (primary transfer bias) having a polarity opposite to that of the toner is applied to the primary transfer rollers 9Y, 9M, 9C, and 9K. In this state, the intermediate transfer belt 8 rotates in the direction of the arrow in FIG. 3 and sequentially passes through the primary transfer nips of the primary transfer rollers 9Y, 9M, 9C, and 9K. As a result, the toner images of each color on the photoreceptor drums 1Y, 1M, 1C, and 1K are primarily transferred onto the surface of the intermediate transfer belt 8 in an overlapping manner (primary transfer step).

Thereafter, the intermediate transfer belt 8 reaches a position facing the secondary transfer belt 71 as a transfer rotating body. At this position, the secondary transfer opposing roller 80 and the secondary transfer roller 72 sandwich the intermediate transfer belt 8 and the secondary transfer belt 71, forming a secondary transfer nip (transfer nip). The four-color toner images formed on the intermediate transfer belt 8 are secondarily transferred onto a sheet P such as paper as a recording medium that is conveyed to the position of this secondary transfer nip (secondary transfer process ).

Furthermore, untransferred toner that has not been transferred to the sheet P remains on the surface of the intermediate transfer belt 8 after the secondary transfer. Therefore, when the intermediate transfer belt 8 reaches the position of the intermediate transfer cleaning section 10, the intermediate transfer cleaning section 10 removes the untransferred toner and other deposits on the intermediate transfer belt 8 at this position. Further, the intermediate transfer belt 8 reaches the position of a lubricant supply device 30 as an intermediate transfer lubricant supply device, and at this position, lubricant is supplied from the lubricant supply device 30 to the surface of the intermediate transfer belt 8. In this way, a series of transfer processes performed on the intermediate transfer belt 8 are completed.

Here, referring to FIG. 1, the sheet P conveyed to the position of the secondary transfer nip is fed from the paper feed section 26 disposed below the apparatus main body to the paper feed roller 27 and the registration roller pair 28 (timing It is conveyed via a pair of rollers) or the like. Specifically, the paper feed section 26 stores a plurality of sheets P as recording media stacked one on top of the other. Then, when the paper feed roller 27 is rotationally driven in the counterclockwise direction in FIG. Ru.

Thereafter, the sheet P reaches the pair of registration rollers 28 and once stops at the roller nip position of the pair of registration rollers 28 whose rotational drive has been stopped. Then, the registration roller pair 28 is rotationally driven in synchronization with the color image on the intermediate transfer belt 8, and the sheet P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the sheet P.

Thereafter, the sheet P is transported by the secondary transfer belt 71 and separated from the secondary transfer belt 71, and then transported to the position of the fixing section 50 by the transport belt 60. Then, at this position, the color image transferred to the surface is fixed onto the sheet P by heat and pressure from the fixing belt and the pressure roller (fixing step).

Thereafter, the sheet P is discharged from the apparatus by a pair of paper discharge rollers via the second conveyance path K2. The sheets P discharged from the apparatus by the pair of paper discharge rollers are sequentially stacked on the stack section as an output image.

In this way, a series of image forming processes (printing operations) in the image forming apparatus are completed. Note that a line sensor 95 used in the adjustment mode is disposed downstream of the fixing unit 50 and upstream of the branching point between the second conveyance path K2 and the third conveyance path K3. will be explained in detail later.

Here, as shown in FIG. 1, in the image forming apparatus 100 according to the present embodiment, a toner image is transferred to the back surface of the sheet P after the toner image is transferred to the front surface in the secondary transfer nip (transfer nip). In order to transfer the toner image on the transfer belt 8, a double-sided conveying device 40 is arranged to convey the sheet P toward the secondary transfer nip.

Specifically, when the "double-sided printing mode" that prints on both sides (front side and back side) of the sheet P is selected, the sheet P after the fixing process on the front side is Instead of being ejected as is when the "single-sided printing mode" is selected, the paper is guided to the third conveyance path K3 in the duplex conveyance device 40, and after the conveyance direction is reversed, it is transferred to the fourth conveyance path K4. The image is conveyed again toward the position of the secondary transfer nip (secondary transfer device 70). Then, image formation (secondary transfer) is performed on the back surface of the sheet P by the same image forming process (image forming operation) as described above at the position of the secondary transfer nip, and then the fixing unit 50 fixes the image. After the process, it is discharged from the image forming apparatus 100 via the second conveyance path K2.

Next, with reference to FIG. 2, the configuration and operation of the developing section 5Y (developing device) in the image forming section will be described in more detail.

As shown in FIG. 2, the developing section 5Y includes a developing roller 51Y facing the photoreceptor drum 1Y, a doctor blade 52Y facing the developing roller 51Y, and two conveyance screws 55Y arranged in the developer storage section. , a concentration detection sensor 56Y for detecting the toner concentration in the developer, and the like. The developing roller 51Y includes a magnet fixed inside, a sleeve rotating around the magnet, and the like. A two-component developer G consisting of carrier and toner is accommodated in the developer accommodating portion.

The developing section 5Y configured in this manner operates as follows.

When the sleeve of the developing roller 51Y rotates in the direction of the arrow in FIG. 2, the developer G carried on the developing roller 51Y by the magnetic field formed by the magnet moves on the developing roller 51Y as the sleeve rotates. Here, the developer G in the developing section 5Y is adjusted so that the ratio of toner (toner concentration) in the developer G is within a predetermined range. Specifically, when the density detection sensor 56Y detects that the toner density is low, new toner is replenished from the toner container 58 into the developing section 5Y so that the toner density falls within a predetermined range. .

Thereafter, the toner supplied from the toner container 58 into the developer accommodating section is mixed and stirred together with the developer G by the two conveyance screws 55Y, and circulates through the two isolated developer accommodating sections (see FIG. 2). (This is a movement perpendicular to the page.) The toner in the developer G is attracted to the carrier by frictional charging with the carrier, and is supported on the developing roller 51Y together with the carrier by the magnetic force formed on the developing roller 51Y.

The developer G supported on the developing roller 51Y is conveyed in the direction of the arrow in FIG. 2 and reaches the position of the doctor blade 52Y. After the amount of developer G on the developing roller 51Y is adjusted to an appropriate amount at this position, it is conveyed to a position (developing area) facing the photoreceptor drum 1Y. Then, the toner is attracted to the electrostatic latent image formed on the photoreceptor drum 1Y by the electric field formed in the development area. Thereafter, the developer G remaining on the developing roller 51Y reaches above the developer storage section as the sleeve rotates, and leaves the developing roller 51Y at this position. Note that the toner container 58 is configured to be detachable (replaceable) from the developing section 5Y (image forming apparatus 100). When the toner container 58 is emptied of the new toner contained therein, it is removed from the developing section 5Y (image forming apparatus 100) and replaced with a new one.

Next, with reference to FIG. 3, the intermediate transfer belt device according to the present embodiment will be described in detail.

As shown in FIG. 3, the intermediate transfer belt device includes an intermediate transfer belt 8 as an image carrier, four primary transfer rollers 9Y, 9M, 9C, 9K, a drive roller 16, a driven roller 17, a pre-transfer roller 18, Tension roller 19, cleaning opposing roller 20, lubricant opposing roller 21, backup roller 22, intermediate transfer cleaning section 10, lubricant supply device 30 as an intermediate transfer lubricant supply device, secondary transfer opposing roller 80, secondary transfer device 70 etc.

The intermediate transfer belt 8 forms a primary transfer nip by contacting the four photoreceptor drums 1Y, 1M, 1C, and 1K, each carrying a toner image of each color. The intermediate transfer belt 8 mainly includes eight roller members (a driving roller 16, a driven roller 17, a pre-transfer roller 18, a tension roller 19, a cleaning opposing roller 20, a lubricant opposing roller 21, a backup roller 22, and a secondary transfer opposing roller). 80).

In this embodiment, the intermediate transfer belt 8 is made of a single layer or multiple layers of PVDF (vinyldene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), etc. It is a belt member in which a conductive material such as carbon black is dispersed. The intermediate transfer belt 8 is adjusted so that the volume resistivity is in the range of 10 ⁶ to 10 ¹³ Ωcm, and the surface resistivity on the back side of the belt is in the range of 10 ⁷ to 10 ¹³ Ωcm. Further, the intermediate transfer belt 8 is set to have a thickness in the range of 20 to 200 μm. In this embodiment, the thickness of the intermediate transfer belt 8 is set to about 60 μm, and the volume resistivity is set to about 10 ⁹ Ωcm.

In this embodiment, the intermediate transfer belt 8 is provided with an elastic layer made of a rubber material or the like as an intermediate layer. As a result, even when a sheet P having an uneven surface is passed through, the transfer performance in the secondary transfer nip is unlikely to deteriorate. Note that a release layer may be coated on the surface of the intermediate transfer belt 8 if necessary. At that time, the materials used for the coating are ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinyldene fluoride), PEA (perfluoroalkoxy fluororesin), FEP (tetrafluoroethylene copolymer), Fluororesins such as ethylene fluoride-propylene hexafluoride copolymer), PVF (vinyl fluoride), and the like can be used, but are not limited thereto.

The primary transfer rollers 9Y, 9M, 9C, and 9K are in contact with the corresponding photoreceptor drums 1Y, 1M, 1C, and 1K via the intermediate transfer belt 8, respectively. Specifically, the transfer roller 9Y for yellow contacts the photoreceptor drum 1Y for yellow via the intermediate transfer belt 8, and the transfer roller 9M for magenta contacts the photoreceptor drum 1Y for magenta via the intermediate transfer belt 8. 1M, the cyan transfer roller 9C contacts the cyan photosensitive drum 1C via the intermediate transfer belt 8, and the black transfer roller 9K contacts the cyan photosensitive drum 1C via the intermediate transfer belt 8. It is in contact with the photosensitive drum 1K for black (black). The primary transfer rollers 9Y, 9M, 9C, and 9K are elastic rollers in which a conductive sponge layer with an outer diameter of about 16 mm is formed on a core metal with a diameter of about 10 mm, and have a volume resistivity of 10 ⁶ to 10. It is adjusted to be in the range of 10 ¹² Ω (preferably 10 ⁷ to 10 ⁹ Ω).

The drive roller 16 is mounted on the inner circumference of the intermediate transfer belt 8 with the intermediate transfer belt 8 being wound at a winding angle of about 120 degrees at a position on the downstream side in the rotational direction of the intermediate transfer belt with respect to the four photosensitive drums. placed in contact with the surface. The drive roller 16 is rotated clockwise in FIG. 3 by a drive motor Mt1 controlled by the control unit 90. As a result, the intermediate transfer belt 8 rotates in a predetermined rotation direction (clockwise in FIG. 3).

The driven roller 17 is positioned on the upstream side in the rotational direction of the intermediate transfer belt 8 with respect to the four photoconductor drums, and the driven roller 17 rotates inside the intermediate transfer belt 8 in a state where the intermediate transfer belt 8 is wound at a winding angle of about 180 degrees. It is arranged so as to be in contact with the peripheral surface. In the intermediate transfer belt 8, a portion from the driven roller 17 to the drive roller 16 is set to be a substantially horizontal surface. The driven roller 17 rotates clockwise in FIG. 3 as the intermediate transfer belt 8 rotates.

Tension roller 19 is in contact with the outer peripheral surface of intermediate transfer belt 8 . On the other hand, the pre-transfer roller 18 , the cleaning opposing roller 20 , the lubricant opposing roller 21 , the backup roller 22 , and the secondary transfer opposing roller 80 are in contact with the inner peripheral surface of the intermediate transfer belt 8 . An intermediate transfer cleaning section 10 (cleaning blade) is arranged between the secondary transfer opposing roller 80 and the lubricant opposing roller 21 so as to be in contact with the cleaning opposing roller 20 via the intermediate transfer belt 8 .

Furthermore, a lubricant supply device 30 (intermediate transfer lubricant supply device) that contacts the lubricant counter roller 21 via the intermediate transfer belt 8 is arranged between the cleaning counter roller 20 and the tension roller 19 . The lubricant supply device 30 is equipped with a lubricant supply roller, a solid lubricant, a compression spring, etc., like the lubricant supply device 3 for photoreceptor drums. Then, the lubricant is scraped little by little from the solid lubricant by the lubricant supply roller rotating counterclockwise in FIG. 3, and the lubricant is supplied to the surface of the intermediate transfer belt 8 by the lubricant supply roller. All of the roller members 17 to 22 and 80 except the drive roller 16 are driven to rotate as the intermediate transfer belt 8 rotates.

As shown in FIG. 4, the control section 90 includes a CPU (Central Processing Unit) 201, a memory 202, an I/O port 203, and a bus line 204. The CPU 201 is an arithmetic device that sequentially executes branching, repeating processing, etc. by executing programs stored in the memory 202. Memory 202 is a storage device that stores programs and various data. The I/O port 203 controls a control signal for controlling a power supply unit 93 (see FIG. 3) and a motor 92 (see FIG. 5), which will be described later and rotates the secondary transfer roller 72, via a motor driver. This is an interface that outputs control signals for The bus line 204 is an address bus, a data bus, etc. for electrically connecting each component such as the CPU 201.

Next, with reference to FIG. 5, the configuration of the secondary transfer device and its control unit according to the present embodiment will be described.

As shown in FIG. 5, the secondary transfer opposing roller 80 is in contact with the secondary transfer roller 72 via the intermediate transfer belt 8 and the secondary transfer belt 71. The secondary transfer counter roller 80 is made of NBR having a volume resistance of about 10 ⁷ to 10 ⁸ Ω and a hardness (JIS-A hardness) of about 48 to 58 degrees on the outer peripheral surface of a cylindrical core made of stainless steel or the like. An elastic layer (layer thickness is about 5 mm) made of rubber is formed.

Further, in this embodiment, the secondary transfer opposing roller 80 is electrically connected to a power supply section 93 (see FIG. 3) as a bias output means, and is supplied with a voltage of about -5 kV from the power supply section 93 under the control of the control section 90. A secondary transfer bias that is a high voltage is applied. The secondary transfer bias applied to the secondary transfer opposing roller 80 is for secondary transferring the toner image on the intermediate transfer belt 8 onto the sheet P conveyed to the secondary transfer nip. The secondary transfer bias (DC voltage) has the same polarity as the polarity (negative polarity in this embodiment). As a result, the toner carried on the toner carrying surface (outer peripheral surface) of the intermediate transfer belt 8 is electrostatically moved from the secondary transfer opposing roller 80 side toward the secondary transfer device 70 side by the secondary transfer electric field.

The secondary transfer device 70 includes a secondary transfer belt 71 as a transfer rotating body, a secondary transfer roller 72, a separation roller 73, a tension roller 74, a brush opposing roller 75, a brush roller 78, a first blade opposing roller 76, a first It includes a blade 85, a lubricant application roller 79, a second blade facing roller 77, a second blade 86, and the like.

The secondary transfer belt 71 (transfer rotating body) has six rollers (secondary transfer roller 72, separation roller 73, tension roller 74, brush facing roller 75, first blade facing roller 76, second blade facing roller 77). It is an endless belt that is stretched and supported, and is made of substantially the same material as the intermediate transfer belt 8. The secondary transfer belt 71 (transfer rotating body) contacts the intermediate transfer belt 8 (image carrier) to form a secondary transfer nip as a transfer nip, and also conveys the sheet P sent out from the secondary transfer nip. It also functions as a belt member. Note that in this embodiment, the secondary transfer belt 71 may be provided with an elastic layer made of a rubber material or the like as an intermediate layer.

The secondary transfer roller 72 and the secondary transfer opposing roller 80 sandwich the intermediate transfer belt 8 and the secondary transfer belt 71 to form a secondary transfer nip. The secondary transfer roller 72 has an elastic layer having a hardness (Asker C hardness) of about 70 degrees formed (covered) on a hollow metal core made of stainless steel, aluminum, or the like. The elastic layer of the secondary transfer roller 72 is made of a rubber material such as polyurethane, EPDM, or silicone, in which a conductive filler such as carbon is dispersed, or an ionic conductive material is contained therein. can be formed into In this embodiment, the volume resistance of the elastic layer is set to about 10 ^6.5 to 10 ^7.5 Ω in order to suppress concentration of transfer current. Note that in this embodiment, the secondary transfer roller 72 is grounded.

Further, the secondary transfer roller 72 is rotationally driven by a motor 92 (see FIG. 5) that is a driving source. By rotationally driving the secondary transfer roller 72 in the counterclockwise direction in FIG. 5, the secondary transfer belt 71 rotates (travels) in the counterclockwise direction in FIG. Along with this, the roller members 73 to 77 that contact the inner circumferential surface of the secondary transfer belt 71 are driven to rotate counterclockwise in FIG. 5, and the brush roller 78 that contacts the outer circumferential surface of the secondary transfer belt 71 and the lubricant application roller 79 are driven to rotate clockwise in FIG. The motor 92 is a variable rotation speed motor, and is configured such that the rotation speed of the secondary transfer roller 72 (the rotation speed of the secondary transfer belt 71) can be adjusted under control by the control unit 90.

The separation roller 73 is disposed at a downstream position in the conveyance direction of the sheet P with respect to the secondary transfer nip. The sheet P sent out from the secondary transfer nip is conveyed along the secondary transfer belt 71 rotating counterclockwise in FIG. It is separated from the secondary transfer belt 71 (curvature separation) by the secondary transfer belt 71 having a curved surface formed as shown in FIG.

A cleaning bias having a polarity opposite to the toner polarity is applied to the brush roller 78 in order to remove toner adhering to the surface of the secondary transfer belt 71 .

The first blade 85 comes into contact with the surface of the secondary transfer belt 71 and removes foreign matter such as toner and paper dust adhering to the surface of the secondary transfer belt 71.

The lubricant application roller 79 applies lubricant to the surface of the secondary transfer belt 71 in order to reduce wear of the first blade 85 and the like.

The second blade 86 contacts the surface of the secondary transfer belt 71 to thin the lubricant applied to the surface of the secondary transfer belt 71.

By the way, in conventional image forming apparatuses, when a toner image on an image carrier is transferred to a sheet such as paper, the length of the transferred image in the conveying direction depends on the image area ratio of the transferred toner image. It may change. That is, the image magnification in the transport direction when an image is transferred from the image carrier to the sheet may change depending on the image area ratio. Note that the "image area ratio" herein refers to the ratio of the image area (portion on which the toner image is formed) per unit area of the sheet. Therefore, when the sheet is blank and no image is formed at all, the image area ratio is 0%; when a solid image is formed on the entire surface of the sheet, the image area ratio is 100%; The image area ratio when a tone image is formed is 25%.

Therefore, in image formation according to the present embodiment, in order to suppress fluctuations in the length of the transferred image in the transport direction (image magnification) due to the difference in image area ratio of the toner images as described above, An adjustment mode is performed to adjust the relative rotational speed difference (linear speed difference) of the transfer rotary body.

The adjustment mode in this embodiment will be explained below.

<Adjustment mode>
As described above, in the image forming apparatus 100 according to the present embodiment, a transfer rotating body that contacts the intermediate transfer belt 8, which serves as an image carrier carrying a toner image, and forms a transfer nip (secondary transfer nip) is used. A secondary transfer belt 71 is provided. This secondary transfer belt 71 (transfer rotating body) is for transferring the toner image on the intermediate transfer belt 8 to the sheet P conveyed to the secondary transfer nip.

Further, the control unit 90 of the image forming apparatus 100 according to the present embodiment controls the relative relationship between the secondary transfer belt 71 (transfer rotating body) and the intermediate transfer belt 8 (image carrier) in the secondary transfer nip (transfer nip). It has a speed difference adjustment section 96 (see FIG. 5) that adjusts the rotational speed difference (linear speed difference).

The speed difference adjustment unit 96 adjusts the rotational speed of the secondary transfer belt 71 by controlling the motor 92 (see FIG. 5) that rotationally drives the secondary transfer roller 72. Further, the speed difference adjustment unit 96 controls the motor 92 based on the variation in length in the transport direction of the transferred image due to the difference in image area ratio, so that the variation is reduced. That is, the speed difference adjustment unit 96 adjusts the rotational speed difference (V2-V1) between the rotational speed V1 of the intermediate transfer belt 8 in the secondary transfer nip and the rotational speed V2 of the secondary transfer belt 71 in the secondary transfer nip. Adjustments are made so that variations in the length of the transferred image in the transport direction are reduced.

The variation in the length of the transferred image in the transport direction caused by the difference in the image area ratio is calculated by the calculation section 91 (see FIG. 5) included in the control section 90. The calculation unit 91 calculates variations in the length of the transferred image in the transport direction based on image information on the sheet P read by a line sensor 95 (see FIG. 1) serving as an image reading unit.

Specifically, in this embodiment, a first image pattern M with a low image area ratio (an image with a small image area ratio) formed on the front side PA of the sheet P shown in FIG. A second image pattern N with a high image area ratio (an image with a high image area ratio) formed on the back surface PB of the sheet P shown in (B) is read by the line sensor 95. Then, based on each image information of the first image pattern M and the second image pattern N read by the line sensor 95, the calculation unit 91 calculates the conveyance direction length H1 and the length H1 of the first image pattern M in the secondary transfer nip. The difference (H2-H1) between the length H2 in the transport direction of the two image patterns N, that is, the variation in length in the transport direction is calculated.

Next, a series of controls in the adjustment mode will be described with reference to the flowchart shown in FIG.

First, when the adjustment mode is executed, one sheet P is fed from the paper feed unit 26, and at the position of the secondary transfer nip, the front surface PA of the sheet P has a low level shown in FIG. 6(A). A first image pattern M having an image area ratio and four detection marks R1, R2, R1', and R2' are formed. The four detection marks R1, R2, R1', and R2' are cross-shaped images formed at the four corners of the sheet surface, respectively. The first image pattern M is an image having a lower image area ratio than the second image pattern N formed on the back surface PB. In this embodiment, the image area ratio of the first image pattern M is set to 0%. Therefore, only four detection marks R1, R2, R1', and R2' are formed on the front surface PA. Note that the first image pattern M and each of the detection marks R1, R2, R1', and R2' are formed through the same process as the image forming process described above.

When the sheet P on which the four detection marks R1, R2, R1', and R2' (and the first image pattern M) are formed on the front surface PA reaches the position of the line sensor 95 after the fixing process, the line sensor 95 Detection marks R1 and R2 (R1', R2') separated in the sub-scanning direction (conveyance direction) are read by. Then, the calculation unit 91 multiplies the reading time difference of the line sensor 95 by the transport speed of the sheet P to calculate the length H1 (H1') of the first image pattern M on the sheet P in the transport direction (Fig. 7: Step S1). Note that the length H1 in the transport direction of the first image pattern M that is finally determined is the length H1 in the transport direction calculated based on the detection marks R1 and R2 at one end in the main scanning direction, and the length H1 in the transport direction at the other end in the main scanning direction. This is the average value of the length H1' in the transport direction calculated based on the side detection marks R1' and R2'.

Next, the sheet P is conveyed again to the secondary transfer nip position by the double-sided conveyance device 40, and at the secondary transfer nip position, a second image shown in FIG. 6(B) is printed on the back surface PB of the sheet P. A pattern N and the same four detection marks R1, R2, R1', and R2' as in FIG. 6(A) are formed. Note that this second image pattern N and each of the detection marks R1, R2, R1', and R2' are also formed through the same process as the image forming process described above. The second image pattern N is an image with a higher image area ratio than the first image pattern M. In this embodiment, the second image pattern N is formed by superimposing solid images of cyan and magenta, and the image area ratio is set to be 100% or more. Further, the second image pattern N is formed at a position excluding the four detection marks R1, R2, R1', R2' and their surroundings.

When the sheet P on which the four detection marks R1, R2, R1', R2' and the second image pattern N are formed on the back side PB reaches the position of the line sensor 95 after the fixing process, the line sensor 95 detects the back side. Detection marks R1 and R2 (R1', R2') separated in the sub-scanning direction (conveyance direction) of the PB are read. Then, the calculation unit 91 multiplies the reading time difference of the line sensor 95 by the transport speed of the sheet P to calculate the length H2 (H2') of the second image pattern N in the transport direction (FIG. 7: Step S2). . Note that the length H2 in the transport direction of the second image pattern N that is finally determined is the length H2 in the transport direction calculated based on the detection marks R1 and R2 at one end in the main scanning direction, and the length H2 in the transport direction at the other end in the main scanning direction. It is set as the average value of the conveyance direction length H2' calculated based on the side detection marks R1' and R2'.

Then, the calculating section 91 calculates the difference (H2-H1) between the lengths H1 and H2 of the first image pattern M and the second image pattern N in the conveyance direction at the secondary transfer nip, and the speed difference adjusting section 96 calculates It is determined whether the absolute value of the difference (|H2-H1|) is less than or equal to a predetermined value E (FIG. 7: Step S3). Note that this predetermined value E is preset based on the allowable value of the difference in length in the transport direction between the first image pattern M (image with a low image area ratio) and the second image pattern N (image with a high image area ratio). is the value given.

As a result, if it is determined in step S3 of FIG. 7 that the absolute value of the above difference (|H2-H1|) is less than the predetermined value E, the transport direction of the transferred image due to the difference in image area ratio Since the variation in length is small, the rotational speed of the secondary transfer belt 71 is not adjusted (FIG. 7: step S4), and the adjustment mode is ended.

On the other hand, if it is determined in step S3 of FIG. 7 that the absolute value of the difference (|H2-H1|) is not less than or equal to the predetermined value E (exceeds the predetermined value E), the image area ratio Assuming that there is a large variation in the length of the transferred image in the transport direction due to the difference, the speed difference adjustment unit 96 adjusts the rotational speed of the secondary transfer belt 71 (FIG. 7: Step S5).

Here, the reason why the rotational speed of the secondary transfer belt 71 is adjusted is that the fluctuation in the length of the transferred image in the conveying direction due to the difference in image area ratio is This is because it can be reduced by adjusting the rotational speed difference (V2-V1) with the transfer belt 71. That is, by adjusting the rotational speed difference (V2-V1) between the intermediate transfer belt 8 and the secondary transfer belt 71, the first image pattern M (an image with a low image area ratio) and the second image pattern N (an image with a high image area ratio) can be adjusted. The absolute value (|H2−H1|) of the difference in length in the transport direction from the image (area ratio image) can be reduced.

FIG. 8 shows the difference (H2-H1) in the conveyance direction length between the first image pattern M and the second image pattern N for each sheet with different thickness, and the intermediate transfer belt 8 and secondary transfer in the secondary transfer nip. It is a table showing the relationship with the rotational speed difference ((V2-V1)/V1) with the belt 71. FIG. 9 is a graph showing the relationship shown in FIG. 8 with the vertical axis representing the difference in length in the transport direction (H2-H1) and the horizontal axis representing the rotational speed difference ((V2-V1)/V1). In FIGS. 8 and 9, the rotational speed difference between the intermediate transfer belt 8 and the secondary transfer belt 71 is expressed as a ratio ((V2-V1)/V1) [%] to the rotational speed V1 of the intermediate transfer belt 8. represents. Hereinafter, this ratio ((V2-V1)/V1) will be simply referred to as "rotational speed difference." In addition, the "thickness of the sheet" in this specification means the dimension of the sheet in the direction perpendicular to the surface of the sheet on which an image is formed (image forming surface), and generally, the thickness of the sheet The sheet thickness becomes thicker as the basis weight (weight per 1 m ² of sheet area) increases, so in this specification, the sheet thickness is expressed as basis weight [gsm]. In FIG. 9, the solid line is sheet A with a basis weight of 64 [gsm], the dotted line is sheet B with a basis weight of 209 [gsm], the one-dot chain line is sheet C with a basis weight of 279 [gsm], and the two-dot chain line is with a basis weight of 360 [gsm]. ] sheet D is shown.

As shown in FIGS. 8 and 9, for any type of sheet, when the rotational speed difference ((V2-V1)/V1) changes, the difference in length in the transport direction (H2-H1) also changes. For example, in the case of sheet A in FIG. 8, the rotation speed difference ((V2-V1)/V1) is -1.6 [%], -1.1 [%], -0.6 [%], - When the change is 0.1 [%], the difference in length in the transport direction (H2-H1) is -0.1715 [mm], 0.0052 [mm], 0.1786 [mm], 0.7224 [mm] ].

From the relationship between the rotational speed difference ((V2-V1)/V1) and the difference in length in the conveyance direction (H2-H1) for each type of sheet shown in FIGS. 8 and 9, the difference in length in the conveyance direction The rotational speed of the secondary transfer belt 71 at which the absolute value of (|H2−H1|) is small is extracted. In this embodiment, the rotational speed Z of the secondary transfer belt 71 when the difference in length in the transport direction (H2-H1) is 0 [mm] is extracted (FIG. 7: Step S5). Note that this extraction of the rotational speed Z is performed by the arithmetic unit 91 or the like.

FIG. 10 shows the rotational speed difference ((V2- V1)/V1).

If the rotational speed difference ((V2-V1)/V1) for each type of sheet is adjusted to the value shown in FIG. It is possible to suppress fluctuations in the length of the transferred image in the transport direction (image magnification) due to differences in image area ratio. Therefore, in this embodiment, the rotational speed V2 of the secondary transfer belt 71 is adjusted so that the rotational speed difference ((V2-V1)/V1) becomes the value shown in FIG. That is, the rotation speed of the motor 92 is controlled by the speed difference adjustment unit 96 so that the rotation speed V2 of the secondary transfer belt becomes the rotation speed Z extracted in step S5 of FIG. 7 (FIG. 7: step S6). .

In this embodiment, the rotational speed Z of the secondary transfer belt 71 when the difference (H2-H1) in the length in the transport direction is 0 [mm] is extracted, but the length in the transport direction The difference (H2-H1) is not necessarily limited to 0 [mm], but extracts the rotational speed of the secondary transfer belt 71 when the difference is a value close to 0 [mm] (a value other than 0 [mm]). You may. That is, in addition to the case where the difference in length in the transport direction (H2-H1) is 0 [mm], the rotation speed of the secondary transfer belt 71 is set so that the absolute value of the difference (|H2-H1|) is small. By adjusting, it is possible to suppress fluctuations in the length of the transferred image in the transport direction (image magnification) caused by differences in the image area ratio of the toner images.

Furthermore, in this embodiment, the rotational speed difference ((V2-V1)/V1) is adjusted by adjusting the rotational speed V2 of the secondary transfer belt 71 (transfer rotating body), but the intermediate transfer belt 8 or the rotation speeds V1 and V2 of both the secondary transfer belt 71 and the intermediate transfer belt 8. Also in this case, the relative rotation speed difference ((V2-V1)/V1) of the secondary transfer belt 71 to the intermediate transfer belt 8 can be adjusted. Furthermore, by adjusting the length of the image formed on the photoreceptor drum in the transport direction, it is also possible to suppress fluctuations in the length of the transferred image in the transport direction (image magnification).

Here, in the image forming apparatus in which the rotational speed V2 of the secondary transfer belt 71 was adjusted as described above, images were formed on various sheets by changing the ambient temperature and humidity around the apparatus, as shown in FIG. As shown, for relatively thick sheets C (basis weight 279 [gsm]) and sheet D (basis weight 360 [gsm]), band-shaped image transfer defects (transfer unevenness) across the sheet width direction occur at high temperature and high humidity. Occurred. In FIG. 11, an "x" mark indicates a case where a band-shaped image transfer defect occurs, and an "O" mark indicates a case where a band-like image transfer defect does not occur. In this case, band-like image transfer defects occurred on Sheet C and Sheet D when the temperature was 32° C. and the humidity was 54%, and when the temperature was 27° C. and the humidity was 80%. On the other hand, such image transfer defects did not occur with relatively thin sheets A (basis weight 64 [gsm]) and sheet B (basis weight 209 [gsm]).

The reason why the belt-like image transfer failure as described above occurs is considered to be that the rotational speed of the secondary transfer belt 72 is faster than the rotational speed of the intermediate transfer belt 8. That is, if the rotational speed of the secondary transfer belt 72 is faster than the rotational speed of the intermediate transfer belt 8, the intermediate transfer belt 8 will be pulled by the sheet in the secondary transfer nip, causing minute wrinkles on the intermediate transfer belt 8. occurs. When such wrinkles occur on the intermediate transfer belt 8, a thin sheet can be deformed by following the wrinkles, but a thick sheet is difficult to deform due to its rigidity and is difficult to follow the wrinkles. It is considered that the adhesion between the sheet and the sheet is reduced, and a belt-like image transfer failure occurs in which the image is not partially transferred in the areas where the adhesion is reduced.

Therefore, in this embodiment, when a thick sheet is used, the rotation speed of the secondary transfer belt 71 is increased in order to suppress the occurrence of the image transfer failure caused by the high rotation speed of the secondary transfer belt 71. I'll try to fix it later. Therefore, as shown in FIG. 12, the control unit 90 of the image forming apparatus 100 according to the present embodiment includes a thickness information acquisition unit 89 that acquires information regarding the thickness of the sheet, and a thickness information acquisition unit 89 that acquires information regarding the thickness of the sheet. It has a speed correction section 97 that corrects the rotational speed of the secondary transfer belt 71 based on information. The speed correction unit 97 corrects the rotation speed of the secondary transfer belt 71 by controlling the motor 92 that rotates the secondary transfer roller 72 .

<Secondary transfer belt speed correction>
Hereinafter, speed correction of the secondary transfer belt 71 in this embodiment will be explained with reference to the flowchart shown in FIG. 13.

In FIG. 13, steps S1 to S5 are the same steps as in the above-mentioned adjustment mode shown in FIG. In this case, in step S5 shown in FIG. 13, after the rotational speed Z of the secondary transfer belt 71 at which the difference (H2-H1) in length in the transport direction becomes small (0 [mm]) is extracted. Information regarding the thickness of the supplied sheet is acquired by the thickness acquisition section 89 (FIG. 13: Step S6). The thickness information acquisition section 89 may, for example, store thickness information for each type of sheet in advance and acquire the thickness information of the sheet based on the type of the supplied sheet, or The thickness information of the sheet may be acquired based on information obtained from a sensor that detects the thickness of the sheet.

Then, based on the information acquired by the thickness information acquisition section 89, the speed correction section 97 determines whether the thickness of the sheet is equal to or greater than a predetermined thickness T (FIG. 13: Step S7). Here, the predetermined thickness T is the thickness of the sheet at which the belt-like image transfer failure as described above is assumed to occur. Specifically, in this embodiment, based on the results shown in FIG. 11 above, the predetermined thickness T is set to the thickness of a sheet having a basis weight of 210 [gsm]. Therefore, in this embodiment, if the supplied sheet is a sheet with a basis weight of 210 [gsm] or more, such as Sheet C and Sheet D, it is assumed that the sheet is a sheet that may cause belt-like image transfer defects. It is determined. Note that the predetermined thickness T is not limited to this value, and can be set as appropriate depending on the material or type of the sheet.

If it is determined in step S7 of FIG. 13 that the thickness of the sheet is equal to or greater than the predetermined thickness T, it is determined that there is a risk of image transfer failure, and the speed correction unit 97 adjusts the speed of the secondary transfer belt 71. The rotation speed is corrected (FIG. 13: Step S8). That is, in step S5 of FIG. 13, the rotation speed Z of the secondary transfer belt 71 is extracted such that the absolute value of the difference in length in the transport direction (|H2-H1|) is 0 [mm] or smaller. The rotational speed of the secondary transfer belt 71 is corrected so as to match the rotational speed. Specifically, in this embodiment, the rotation speed of the secondary transfer belt 71 is corrected to a slow rotation speed Y so that the rotation speed difference ((V2-V1)/V1) is reduced by 0.2%. do. For example, in the case of sheet C, the rotational speed difference ((V2-V1)/V1) when the absolute value of the difference in length in the transport direction (|H2-H1|) is 0 [mm] is 0.2[% ] (see Figure 10), the rotational speed difference ((V2-V1)/V1) is set to be 0.2% smaller than the rotational speed difference ((V2-V1)/V1). ] The rotational speed of the secondary transfer belt 71 is corrected so that Then, the rotational speed of the secondary transfer belt 71 is set to the rotational speed Y corrected in this way (FIG. 13: Step S9).

On the other hand, if it is determined in step S7 of FIG. 13 that the thickness of the sheet is not greater than the predetermined thickness T (less than the predetermined thickness T), it is determined that there is no risk of image transfer failure. The rotational speed of the secondary transfer belt 71 is not corrected (FIG. 13: Step S10). Therefore, in this case, the rotational speed of the secondary transfer belt 71 is extracted such that the absolute value of the difference in length in the transport direction (|H2-H1|) is 0 [mm] or small in step S5 of FIG. The rotational speed Z of the secondary transfer belt 71 is set (FIG. 13: Step S11).

As described above, after the rotation speed of the secondary transfer belt 71 is set (changed or corrected), an image is generated based on the image information of the document read by the document reading device or the print image information instructed to print from the terminal. When the formation starts, an image is formed on each photoreceptor drum 1Y, 1M, 1C, and 1K through the above-described image forming process, and the image is transferred from the intermediate transfer belt 8 to the sheet in the secondary transfer nip. At this time, the sheet is conveyed at the rotational speed of the secondary transfer belt 71 set in step S9 or step S11, and the image is transferred from the intermediate transfer belt 8 to the sheet. After the images on the sheets are fixed in the fixing section 50, the sheets are discharged from the apparatus and stacked on the stack section.

After that, the control unit 90 determines whether there are any sheets to be continuously fed (FIG. 13: Step S12), and if there are no sheets to be continuously fed, the above series of adjustment modes and speed correction flows are performed. finish.

On the other hand, if there are sheets that are continuously supplied, the control unit 90 further determines whether the supplied sheets are of different types (FIG. 13: Step S13), and whether or not the supplied sheets are of the same type. In this case, the rotational speed of the secondary transfer belt 71 set in step S9 or step S11 in FIG. 13 is maintained. On the other hand, if the supplied sheet is of a different type, the flow from step S1 onward in FIG. 13 is repeated, and the rotational speed of the secondary transfer belt 71 is newly set.

As described above, in the image forming apparatus 100 according to the present embodiment, when the thickness of the sheet is equal to or greater than the predetermined thickness T, the rotation speed of the secondary transfer belt 71 is corrected to be low, thereby achieving the above-mentioned This makes it possible to suppress the occurrence of belt-like image transfer defects. In other words, by correcting the rotational speed of the secondary transfer belt 71 to a low value, it becomes possible to suppress the occurrence of wrinkles on the intermediate transfer belt 8 caused by the high rotational speed of the secondary transfer belt 71. Partial adhesion failure between the belt 8 and the sheet can be suppressed, and occurrence of band-like image transfer failure can be suppressed.

FIG. 14 shows the test results of examining the occurrence of band-like image transfer defects on sheets C and D when the rotational speed of the secondary transfer belt 71 was corrected to be slow.

In this test, the rotational speed of the secondary transfer belt 71 was modified to a plurality of different rotational speeds, and in each case, a belt-shaped image was transferred onto the sheet in a high-temperature, high-humidity environment with a temperature of 27°C and a humidity of 80%. We observed whether defects occurred. The rotation speed difference (0.2 [%] for sheet C and 0.0 [%] for sheet D) shown in the uppermost frame in each table for sheet C and sheet D shown in FIG. , is the result before the rotational speed of the secondary transfer belt 71 is corrected. In other words, in the case where the rotational speed difference in sheet C is 0.2 [%] before correction, and in the case where the rotational speed difference in sheet D is 0.0 [%] before correction, as shown in FIG. Similar to the results for Sheet C and Sheet D (see the results when the temperature was 27° C. and the humidity was 80% in FIG. 11), band-shaped image transfer defects occurred in both cases.

The results obtained by correcting the speed with respect to the results before such correction are the results shown in the second and subsequent frames from the top of each table of Sheet C and Sheet D shown in FIG. For seat C, if the rotation speed difference is 0.2 [%] before correction, if it is decelerated to 0.1 [%] after correction, if it is decelerated to 0 [%] after correction, then the difference in rotation speed after correction is In all cases where the speed was reduced to -0.1%, band-like image transfer defects did not occur. In addition, in the table of Sheet D, when decelerating from 0.0 [%], which is the rotational speed difference ((V2-V1)/V1) before correction, to -0.1 [%] after correction, If a band-shaped image transfer defect occurs, but the speed is reduced to -0.2 [%] after correction, or if the speed is reduced to -0.3 [%] after correction, the band-shaped image transfer defect will occur. It did not occur.

That is, in the case of sheet C, if the rotational speed V2 of the secondary transfer belt 71 is reduced by 0.1% or more in terms of rotational speed difference ((V2-V1)/V1), The occurrence of belt-like image transfer defects can be avoided, and in the case of sheet D, the rotational speed V2 of the secondary transfer belt 71 is converted to a rotational speed difference ((V2-V1)/V1) of 0.2%. By slowing down to a value smaller than this, it was possible to avoid band-like image transfer defects. Based on these results, in this embodiment, the rotational speed difference ((V2-V1)/V1) is set to 0.2[%] so that the occurrence of image transfer defects can be suppressed for both sheets C and D. ] The rotational speed V2 of the secondary transfer belt 71 is corrected so that it becomes smaller.

Note that the amount of deceleration when correcting the rotational speed V2 of the secondary transfer belt 71 may be changed as appropriate depending on the thickness of the sheet or the ambient temperature and humidity. Therefore, the amount of deceleration when correcting the rotational speed V2 of the secondary transfer belt 71 may be a value other than 0.2% when converted to the rotational speed difference ((V2-V1)/V1). . Furthermore, if the amount of deceleration (absolute value) of the rotational speed V2 of the secondary transfer belt 71 is too small, it will not be possible to effectively suppress the occurrence of band-like image transfer defects, and on the other hand, if it is too large, other problems may occur. Therefore, the ratio of the rotation speed difference to the rotation speed of the intermediate transfer belt 8 (image carrier) ((V2-V1)/V1) is 0.1 [%] or more and 0.3 [%] or less. It is preferable that there be.

Further, FIG. 15 shows the difference (H2-H1) in the conveyance direction length H2 of the transferred image between the sheet C and the sheet D before and after the secondary transfer belt rotational speed is corrected.

As shown in FIG. 15, for sheet C, the difference (H2-H1) in the conveyance direction length of the transferred image before the rotation speed correction was 0.020101 [mm], but after the rotation speed correction The difference in transport speed length (H2-H1) of the transferred image was -0.09031 [mm]. That is, after the rotational speed of the secondary transfer belt 71 was corrected, the toner image was transferred in a slightly smaller size than before the correction. Also, for sheet D, the difference in length in the transport direction (H2-H1) is from 0.03661 [mm], which is the difference before the rotation speed correction, to -0.16926 [mm], which is the difference after the rotation speed correction. ], resulting in the toner image being transferred with some shrinkage. As described above, in this embodiment, as a result of correcting the rotational speed of the secondary transfer belt to a lower value (as a result of reducing the rotational speed difference by 0.2%), the image after transfer is slightly shrunk in the transport direction. However, in either case, the difference in length in the transport direction (H2-H1) is less than the practically allowable difference of 0.2 [mm], so it can be used without any major problems. Therefore, according to the present invention, it is possible to suppress the occurrence of defective image transfer while suppressing variations in the length of transferred images in the conveyance direction in sheets having a predetermined thickness or more.

<Other embodiments>
Next, an embodiment of the present invention that is different from the above-described embodiment (first embodiment) will be described. In the following description, parts that are different from the above embodiment will be mainly described, and since the other parts have basically the same configuration, the description will be omitted as appropriate.

FIG. 16 is a flowchart showing operations in the adjustment mode and speed correction according to the second embodiment of the present invention.

In the control according to the above-described embodiment (first embodiment), in extracting the rotational speed Z of the secondary transfer belt 71 when the difference in length in the transport direction (H2-H1) is 0 [mm], Using information (information shown in FIGS. 8 and 9) showing the relationship between the rotational speed difference ((V2-V1)/V1) and the difference in length in the transport direction (H2-H1) obtained in advance through experiments etc. However, such information is not used in the second embodiment of the present invention. Therefore, in the second embodiment of the present invention, the rotational speed Z of the secondary transfer belt 71 when the difference in length in the transport direction (H2-H1) is 0 [mm] is extracted as follows. That's what I do.

First, when one sheet P is fed from the paper feed section 26, the sheet is conveyed at the rotational speed F1 of the secondary transfer belt 71, which is initially set for each sheet type, and the The difference (first difference value: H2-H1) between the transport direction length H1 of the image with the image area ratio and the transport direction length H2 of the image with the high image area ratio is calculated by the calculation unit 91 (FIG. 16: Step S1). At this time, each image with a low image area ratio and a high image area ratio formed on the sheet includes the first image pattern M formed on the front surface PA of the sheet P and the four detection images, which are the same as in the above-described embodiment. Marks R1, R2, R1', R2' (see FIG. 6(A)), a second image pattern N formed on the back surface PB of the sheet P, and four detection marks R1, R2, R1', R2' (See FIG. 6(B)). The methods and operations for forming these images, reading image information, and calculating the difference in length in the conveying direction (H2-H1) are the same as in the above-described embodiment, and therefore descriptions thereof will be omitted.

Next, the initially set rotational speed F1 of the secondary transfer belt 71 is changed by the speed difference adjustment section 96, and the rotational speed difference ((V2-V1)/V1) between the intermediate transfer belt 8 and the secondary transfer belt 71 is changed. is changed. In this embodiment, if the difference in length in the transport direction (first difference value: H2-H1) calculated at the time of the initial setting is a positive value, the rotational speed of the secondary transfer belt 71 is It is decelerated by 0.5% when converted to the difference ((V2-V1)/V1), and conversely, the difference in length in the transport direction (first difference value: H2-H1) calculated at the time of initial setting above is If it is a negative value, the rotational speed of the secondary transfer belt 71 is increased by 0.5% in terms of the rotational speed difference ((V2-V1)/V1). Then, the difference in length in the conveying direction (second The difference value: H2-H1) is calculated by the calculation unit 91 (FIG. 16: Step S2). Note that the methods and operations for forming each image with a low image area ratio and a high image area ratio, reading image information, and calculating the difference in length in the transport direction (H2-H1) are also the same as in the above-described embodiment. It's the same.

In this way, by calculating the first difference value of the length in the transport direction at the time of initial setting and the second difference value of the length in the transport direction after changing the speed, the rotation speed difference ((V2-V1)/V1 ) and the difference in length in the transport direction (H2-H1) can now be obtained. In other words, there are two points on the graph showing the relationship between the rotational speed difference ((V2-V1)/V1) and the length difference in the transport direction (H2-H1), one for the initial setting and one after the speed has been changed. Therefore, the relational expression of the graph shown in FIG. 9 can be calculated from these two points. Furthermore, in this embodiment, when the first difference value is a positive value, the rotational speed difference ((V2-V1)/V1) is reduced by 0.5%; is a negative value, by increasing the rotation speed difference ((V2-V1)/V1) by 0.5 [%], the difference in length in the transport direction (H2-H1) becomes 0 [mm]. You will get two points that straddle the point. Note that the amount of decrease or increase in the rotational speed difference ((V2-V1)/V1) to be changed is not limited to 0.5%, and may be any other predetermined amount. As a result, in the present embodiment, it is possible to extract the rotational speed Z of the secondary transfer belt 71 such that the difference in length in the transport direction (H2-H1) is 0 [mm] from the calculated relational expression (Fig. 16 :Step S3).

Note that the rotational speed Z extracted in step S3 in FIG. ] may be the rotational speed of the secondary transfer belt 71 when the value is other than . That is, in this embodiment as well, the difference in length in the transport direction (H2-H1) is not only 0 [mm], but also the secondary transfer in which the absolute value of the difference (|H2-H1|) is small. Any rotational speed of the belt 71 may be used.

After that, the thickness information of the sheet is acquired by the thickness information acquisition unit 89 (FIG. 16: Step S4), and if the thickness of the sheet is equal to or greater than the predetermined thickness T, the same secondary transfer as in the above embodiment is performed. A correction is made to the rotational speed of the belt. The steps after that (FIG. 16: Step S4 to Step S11) are the same as the steps after Step S6 in FIG. 13, so the explanation will be omitted.

As described above, in the second embodiment of the present invention, even if there is no information indicating the relationship between the rotation speed difference ((V2-V1)/V1) and the conveyance direction length difference (H2-H1), , Obtaining the relational expression between the rotational speed difference ((V2-V1)/V1) and the difference in length in the transport direction (H2-H1) from the information calculated between the initial setting rotational speed and the changed rotational speed. Can be done. This makes it possible to adjust the relative rotational speed difference (linear speed difference) between the secondary transfer belt 71 and the intermediate transfer belt 8, and the length of the transferred image in the transport direction (image fluctuations in magnification) can be suppressed. Also, in the second embodiment of the present invention, if the thickness of the sheet is equal to or greater than the predetermined thickness T, the speed of the secondary transfer belt is corrected in the same manner as in the above embodiment. It is possible to suppress the occurrence of wrinkles in the intermediate transfer belt 8 due to the high rotational speed of the belt 72, and it is possible to suppress the occurrence of band-like image transfer defects.

Further, among the functions of the embodiments described above, the portions executed by the control section 90 can be realized by one or more processing circuits. Here, the "processing circuit" in this specification refers to a processor programmed to perform each function by software, such as a processor implemented by an electronic circuit, or a processor designed to perform each function described above. This includes devices such as an ASIC (Application Specific Integrated Circuit), a DSP (digital signal processor), an FPGA (field programmable gate array), or a conventional circuit module.

To summarize the aspects of the present invention described above, the present invention includes an image forming apparatus having at least the following configuration.

[First configuration]
A first configuration includes an image carrier that carries an image, a transfer nip that is formed by contacting the image carrier, and an image on the image carrier that is transferred to the recording medium that is conveyed to the transfer nip. A calculation for calculating the difference between the transfer rotary body to be transferred, the length in the transport direction of the image with a low image area ratio transferred to the recording medium, and the length in the transport direction of the image with a high image area ratio transferred to the recording medium. a speed difference adjustment unit that adjusts a relative rotational speed difference of the transfer rotary body with respect to the image carrier so that the absolute value of the difference calculated by the calculation unit is small; When the thickness is greater than or equal to a predetermined thickness, the rotation speed of the transfer rotor is made slower than the rotation speed of the transfer rotor based on the speed difference adjusted so that the absolute value of the difference is smaller. The image forming apparatus includes a speed correction unit that performs the following steps.

[Second configuration]
In a second configuration, in the first configuration, the absolute value of the deceleration amount of the transfer rotary body to be slowed down when the thickness of the recording medium is equal to or more than the predetermined thickness is the rotation of the image carrier. In the image forming apparatus, the ratio of the rotational speed difference to the speed is 0.1% or more and 0.3% or less.

[Third configuration]
A third configuration, in the first or second configuration, includes an image reading unit that reads each image of the low image area ratio and the high image area ratio on the recording medium, and the calculation unit is configured to read the images of the low image area ratio and the high image area ratio on the recording medium, and Based on the information read by the reading unit, the difference in length in the transport direction of each image of the low image area ratio and the high image area ratio is calculated, and the speed difference adjustment unit Adjusting the relative rotational speed difference of the transfer rotary body with respect to the image carrier so that the absolute value is small, and when the thickness of the recording medium is a predetermined thickness or more, the speed correction unit In the image forming apparatus, the rotation speed of the transfer rotor is made slower than the rotation speed of the transfer rotor based on the speed difference adjusted such that the absolute value of the difference is small.

[Fourth configuration]
A fourth configuration, in the first or second configuration, includes an image reading unit that reads each image of the low image area ratio and the high image area ratio on the recording medium, and the calculation unit is configured to read the images of the low image area ratio and the high image area ratio on the recording medium, Based on the information read by the reading section, a first difference value between the lengths in the transport direction of each image of the low image area ratio and the high image area ratio is calculated, and then the speed difference adjustment section While changing the relative rotational speed difference of the transfer rotary body with respect to the carrier, the image reading unit detects the low image area ratio and the high image area ratio on the recording medium obtained after changing the rotational speed difference. The calculating section reads each image of the low image area ratio and the high image area ratio based on the information read by the image reading section after changing the rotational speed difference, and calculates the length in the transport direction of each image of the low image area ratio and the high image area ratio. The speed difference adjustment unit calculates the second difference value of The rotational speed difference is adjusted so that the absolute value of the difference is small, and when the thickness of the recording medium is equal to or greater than a predetermined thickness, the speed correction section adjusts the rotational speed of the transfer rotary body to the In the image forming apparatus, the rotational speed of the transfer rotary body is made slower than the rotational speed of the transfer rotary body based on the speed difference adjusted so that the absolute value of the difference becomes small.

[Fifth configuration]
In a fifth configuration, in the fourth configuration, when the first difference value is a positive value, the speed difference adjustment unit changes the rotational speed difference to become smaller, and the first difference value is a negative value, the rotational speed difference is changed by the speed difference adjustment unit to become larger, and the calculation unit, based on the information read by the image reading unit after changing the rotational speed difference, The image forming apparatus calculates the second difference value between the lengths in the transport direction of each image having the low image area ratio and the high image area ratio.

[Sixth configuration]
A sixth configuration is an image forming apparatus in which the low image area ratio is 0% and the high image area ratio is 100% or more in any one of the first to fifth configurations.

8 Intermediate transfer belt (image carrier)
38 Drum (image carrier)
61 Transfer belt (transfer rotating body)
71 Secondary transfer belt (transfer rotating body)
91 Arithmetic unit 95 Line sensor (image reading unit)
96 Speed difference adjustment section 97 Speed correction section 100 Image forming apparatus

Japanese Patent Application Publication No. 2021-176010

Claims (6)

an image carrier that carries an image;
a transfer rotating body that contacts the image carrier to form a transfer nip and transfers the image on the image carrier to the recording medium conveyed to the transfer nip;
a calculation unit that calculates a difference between a length in a transport direction of an image with a low image area ratio transferred to the recording medium and a length in the transport direction of an image with a high image area ratio transferred to the recording medium;
a speed difference adjustment unit that adjusts a relative rotational speed difference of the transfer rotary body with respect to the image carrier so that the absolute value of the difference calculated by the calculation unit is small;
When the thickness of the recording medium is a predetermined thickness or more, the rotation speed of the transfer rotor is adjusted based on the speed difference such that the absolute value of the difference becomes small. a speed correction section that makes the speed slower than the speed;
An image forming apparatus comprising: The absolute value of the amount of deceleration of the transfer rotor to be slowed down when the thickness of the recording medium is equal to or greater than the predetermined thickness is 0 when converted into the ratio of the rotational speed difference to the rotational speed of the image carrier. The image forming apparatus according to claim 1, wherein the amount is .1% or more and 0.3% or less. comprising an image reading unit that reads each image of the low image area ratio and the high image area ratio on the recording medium,
The calculation unit calculates the difference in length in the transport direction of each image of the low image area ratio and the high image area ratio based on the information read by the image reading unit,
The speed difference adjustment unit adjusts a relative rotational speed difference of the transfer rotary body with respect to the image carrier so that the absolute value of the calculated difference becomes small;
When the thickness of the recording medium is equal to or greater than a predetermined thickness, the speed correction section adjusts the rotational speed of the transfer rotary body based on the speed difference adjusted so that the absolute value of the difference becomes small. The image forming apparatus according to claim 1 or 2, wherein the rotation speed is slower than the rotation speed of the transfer rotary member. comprising an image reading unit that reads each image of the low image area ratio and the high image area ratio on the recording medium,
The calculation unit calculates a first difference value between the lengths in the transport direction of each image of the low image area ratio and the high image area ratio, based on the information read by the image reading unit,
Thereafter, the speed difference adjustment section changes the relative rotational speed difference of the transfer rotary body with respect to the image carrier, and the image reading section adjusts the relative rotational speed difference of the transfer rotary body to the image carrier, and the image reading section adjusts the rotational speed difference between the rotational speed difference and the recording medium obtained after changing the rotational speed difference. reading each image of the low image area ratio and the high image area ratio,
The calculation unit calculates a second difference value between the lengths in the transport direction of each image of the low image area ratio and the high image area ratio based on information read by the image reading unit after changing the rotational speed difference. Calculate,
The speed difference adjustment unit adjusts the rotational speed difference so that the absolute value of the difference becomes small based on the relationship obtained based on the rotational speed difference before and after the change, the first difference value, and the second difference value. Adjust the rotation speed difference,
When the thickness of the recording medium is equal to or greater than a predetermined thickness, the speed correction section adjusts the rotational speed of the transfer rotary body based on the speed difference adjusted so that the absolute value of the difference becomes small. The image forming apparatus according to claim 1 or 2, wherein the rotation speed is slower than the rotation speed of the transfer rotary member. If the first difference value is a positive value, the speed difference adjustment unit changes the rotational speed difference to become smaller;
When the first difference value is a negative value, the rotational speed difference is changed by the speed difference adjustment unit to increase the rotational speed difference,
The calculation unit calculates the second difference value of the length in the transport direction of each image of the low image area ratio and the high image area ratio, based on information read by the image reading unit after changing the rotational speed difference. The image forming apparatus according to claim 4, wherein the image forming apparatus calculates . The image forming apparatus according to claim 1 or 2, wherein the low image area ratio is 0% and the high image area ratio is 100% or more.

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