JP2023160677A - Image forming apparatus - Google Patents

Abstract

To obtain good transferability regardless of the amount of pressing of a pressing member while preventing shock image disturbance, in a configuration that transfers a toner image from a first belt to a recording material by using a second belt and can vary the amount of pressing of the pressing member against the first belt.SOLUTION: An image forming apparatus comprises: a second belt that is in contact with a first belt to form a transfer part N2; a plurality of second belt tension rollers; a first driving unit that drives the first belt; a second driving unit that drives the second belt; a pressing member that can press the first belt; a moving mechanism that can change the amount of pressing of the pressing member against the first belt; and a control unit that performs control so that the peripheral speed of the second belt becomes faster than the peripheral speed of the first belt, and performs control to change the difference in peripheral speed between the first belt and the second belt in transferring a toner image to a recording material based on settings of the position of the pressing member made by the moving mechanism in transferring the toner image to the recording material.SELECTED DRAWING: Figure 7

Description

The present invention relates to an image forming apparatus such as a printer using an electrophotographic method or an electrostatic recording method, a printing machine, a copying machine, a facsimile machine, or a multifunctional device having multiple functions among these.

Conventionally, for example, in an image forming apparatus using an electrophotographic method, a toner image has been electrostatically transferred from an image bearing member such as a photoreceptor or an intermediate transfer member to a recording material such as paper using a transfer member. be exposed.

As in the image forming apparatus proposed in Patent Document 1, a plurality of tension racks are used as a transfer member (secondary transfer member) that performs secondary transfer of a toner image from an intermediate transfer belt serving as an intermediate transfer member to a recording material. Some use a secondary transfer belt that is rotated around rollers. In this configuration, the secondary transfer inner roller, which is one of the plurality of tension rollers of the intermediate transfer belt, and the plurality of tension rollers of the secondary transfer belt are connected via the intermediate transfer belt and the secondary transfer belt. One of them, the secondary transfer outer roller, contacts to form a secondary transfer portion.

Further, like the image forming apparatus proposed in Patent Document 2, a configuration includes a pressing member (backup sheet) that presses the inner circumferential surface of the intermediate transfer belt upstream of the secondary transfer section in the conveyance direction of the intermediate transfer belt. There is. The pressing member includes a secondary transfer inner roller arranged to face the secondary transfer belt via the intermediate transfer belt, and an upstream roller arranged adjacent to the secondary transfer inner roller upstream in the conveying direction of the intermediate transfer belt. The intermediate transfer belt is pressed from the inner circumferential surface side toward the outer circumferential surface side between.

Note that with respect to the recording material, the terms "leading edge" and "trailing edge" refer to the leading edge and the trailing edge, respectively, in the conveying direction of the recording material, even if not specified. Further, the upstream side of the secondary transfer section in the conveyance direction of the intermediate transfer belt is also simply referred to as "upstream of the secondary transfer section".

Japanese Patent Application Publication No. 2021-124682 JP2017-9767A

In recent years, in order to meet the desired high productivity (number of output sheets per unit time), it has become necessary to further increase the process speed (transport speed of the intermediate transfer belt).

Here, when the process speed is increased, the transferability may deteriorate particularly in the concave portions (for example, 80 to 140 μm in depth) of a recording material such as embossed paper that has an uneven surface. This is due to the following reasons. In other words, the voltage applied to the inner secondary transfer roller (or outer secondary transfer roller) during secondary transfer increases, and the recording material ``Gap discharge'' occurs in the recesses. This is because, due to this discharge, the toner becomes difficult to secondary transfer on the intermediate transfer belt before entering the secondary transfer section. For example, the image may appear to be scattered. On the other hand, with smooth recording materials such as high-quality paper (or plain paper) and coated paper, increasing the process speed has little effect.

On the other hand, when using embossed paper, if the inner circumferential surface of the intermediate transfer belt is pushed by the aforementioned pressing member, the recording material and the intermediate transfer belt will come into close contact with each other up to a point upstream from the secondary transfer section. . Therefore, gap discharge in the recessed portions of the recording material is suppressed, and transferability is improved.

However, if the pressing amount (pushing amount) of the pressing member against the belt is increased, a phenomenon called "shock image disturbance" may become apparent, especially at the leading end of the recording material. According to studies by the present inventors, it has been found that this is due to the speed difference between the intermediate transfer belt and the secondary transfer belt, and that the shock image disturbance tends to worsen when the speed difference is large.

In other words, in order to maintain stability in the conveyance speed of the intermediate transfer belt and the secondary transfer belt, the image forming apparatus is designed to have a speed difference between the conveyance speed of the intermediate transfer belt and the conveyance speed of the secondary transfer belt. Sometimes. This is to prevent the zero speed difference from being inadvertently crossed due to fluctuations in the conveyance speed of the intermediate transfer belt or the secondary transfer belt. If the speed difference exceeds zero, the conveyance speed of the intermediate transfer belt or the secondary transfer belt may become unstable due to changes in the meshing locations of the gears in the drive train. Then, when the intermediate transfer belt is pressed from the inner peripheral surface side toward the outer peripheral surface side by the pressing member, the contact area between the intermediate transfer belt and the secondary transfer belt increases, so that the drive load on the secondary transfer belt increases. If the recording material rushes in in this state and load fluctuation occurs, the behavior of the recording material will become unstable. The load fluctuation when the recording material enters tends to increase as the speed difference between the intermediate transfer belt and the secondary transfer belt increases. To explain further, when the recording material enters the secondary transfer section due to unevenness in the surface properties of the recording material (unevenness in frictional force within the surface of the recording material), load fluctuations on the secondary transfer belt occur. This load fluctuation tends to increase as the speed difference between the intermediate transfer belt and the secondary transfer belt increases. As mentioned above, when the intermediate transfer belt is pushed by the pressing member and the driving load of the secondary transfer belt increases, the influence of this load fluctuation tends to become noticeable, and the leading edge of the recording material is pushed into the secondary transfer section. When it enters, the conveyance speed of the recording material increases momentarily. When the behavior of the recording material becomes unstable in this way, the intermediate transfer belt upstream of the secondary transfer section may flap (the distance to the recording material may fluctuate). Furthermore, since the intermediate transfer belt pressed by the pressing member approaches the recording material upstream of the secondary transfer section, the toner image on the intermediate transfer belt is disturbed in front of the secondary transfer section, resulting in a shock image. Disturbances become apparent.

On the other hand, for high-quality paper (or plain paper) and coated paper, which are often used recording materials, if the amount of pressure of the pressing member is adjusted to improve the transferability to embossed paper, the following phenomenon will occur. becomes more likely to occur. In other words, the contact distance between the intermediate transfer belt and the recording material upstream of the secondary transfer section is longer, which causes a phenomenon called "image rubbing" in which the intermediate transfer belt and recording material rub against each other, causing image distortion. This may occur. Embossed paper is less affected by this phenomenon due to differences in visibility due to surface irregularities. In addition, if the pressing amount of the pressing member is kept as is, which is adjusted to improve transferability for embossed paper that is used relatively infrequently, creep deformation of the tip of the pressing member that is in contact with the intermediate transfer belt will be accelerated. There is also the problem.

Therefore, for example, the pressure of the pressing member can be changed depending on whether embossed paper is used, high-quality paper (or plain paper), coated paper, etc. It is desirable to have a configuration in which the amount is variable.

However, when using high-quality paper (plain paper), coated paper, etc., if the amount of pressure from the pressing member is reduced, the transfer performance may deteriorate depending on the conveyance speed of the intermediate transfer belt and the conveyance speed of the secondary transfer belt. There is. Therefore, it is not desirable to simply reduce the speed difference between the intermediate transfer belt and the secondary transfer belt by considering only the suppression of the shock image disturbance as described above.

The conventional problems have been explained above using as an example the secondary transfer section, which is the section where toner images are transferred from the intermediate transfer belt to the recording material. A similar problem may occur with respect to the toner image transfer portion.

Therefore, it is an object of the present invention to transfer a toner image from a first belt to a recording material using a second belt, and to suppress shock image disturbances in a configuration in which the amount of pressure of a pressing member on the first belt is variable. The objective is to obtain good transferability regardless of the amount of pressure applied by the pressing member.

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention includes a rotatable endless first belt carrying a toner image, and a plurality of first belt stretching rollers that stretch the first belt, the inner roller and the first belt stretching rollers stretching the first belt. a plurality of first belt tension rollers including an upstream roller disposed upstream of the inner roller and adjacent to the inner roller with respect to the rotational direction of the first belt; a rotatable endless second belt forming a transfer section for transferring a toner image from one belt to a recording material; and a plurality of second belt tension rollers that stretch the second belt, the first belt an outer roller that contacts the inner roller via the belt and the second belt to form the transfer section; a tension roller that applies tension to the second belt; a plurality of second belt tension rollers including a drive roller disposed upstream of the tension roller and downstream of the tension roller and transmitting a driving force to the second belt; a first drive unit that drives the first belt; a second drive unit that drives a second belt; the second drive unit is capable of contacting the inner circumferential surface of the first belt upstream of the inner roller and downstream of the upstream roller with respect to the rotational direction of the first belt; a pressing member capable of pressing one belt from an inner peripheral surface side toward an outer peripheral surface side; a moving mechanism capable of changing the position of the pressing member to change the amount of pressure the pressing member presses against the first belt; Controlling at least one of the first drive section and the second drive section so that the circumferential speed of the second belt is faster than the circumferential speed of the first belt when transferring the toner image onto the recording material. At the same time, based on the setting of the position of the pressing member by the moving mechanism when transferring the toner image onto the recording material, the circumferential speed of the first belt and the second belt when transferring the toner image onto the recording material are determined. and a control section that controls at least one of the first drive section and the second drive section so as to change a circumferential speed difference between the circumferential speed of the image forming apparatus and the circumferential speed of the image forming apparatus.

According to the present invention, in a configuration in which a toner image is transferred from a first belt to a recording material using a second belt, and the amount of pressure of a pressing member on the first belt is variable, while suppressing shock image disturbance, Good transferability can be obtained regardless of the amount of pressure applied to the member.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus. FIG. 3 is a schematic cross-sectional view of the vicinity of the secondary transfer section. FIG. 3 is a schematic cross-sectional view of the vicinity of the secondary transfer section. FIG. 3 is a schematic cross-sectional view of a pressing member. FIG. 3 is a schematic cross-sectional view for explaining the amount of pressure applied by a pressing member. FIG. 2 is a schematic block diagram showing a control mode of the image forming apparatus. FIG. 3 is a flowchart of control in the first embodiment. FIG. 3 is a flowchart of control in Example 2. FIG. It is a table showing evaluation results showing the effects of Examples.

Hereinafter, the image forming apparatus according to the present invention will be explained in more detail with reference to the drawings.

[Example 1]
1. Overall Configuration and Operation of Image Forming Apparatus FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 according to the present embodiment (a cross section approximately perpendicular to the rotational axes of the photosensitive drum 1 and the tension roller of the intermediate transfer belt 6, etc., which will be described later). ). The image forming apparatus 100 of this embodiment is a tandem printer that uses an intermediate transfer method. The image forming apparatus 100 uses an electrophotographic method to form a sheet-like recording material such as paper (transfer material, sheet, recording medium, media, paper, etc.) in response to an image signal transmitted from an external device such as a personal computer. ) A full color image can be formed on 7.

The image forming apparatus 100 includes four image forming sections SY, SM, and a plurality of image forming sections (stations) that form yellow (Y), magenta (M), cyan (C), and black (K) images, respectively. Has SC and SK. These image forming units SY, SM, SC, and SK are arranged in a line along the moving direction of a substantially horizontally arranged image transfer surface of an intermediate transfer belt 6, which will be described later. For elements with the same or corresponding functions or configurations in each image forming unit SY, SM, SC, SK, the suffix Y, M, C, K is omitted to indicate that the element is for one of the colors. This may be explained comprehensively. In this embodiment, the image forming section S includes photosensitive drums 1 (1Y, 1M, 1C, 1K), charging devices 2 (2Y, 2M, 2C, 2K), and exposure devices 3 (3Y, 3M, 3C, 3K), which will be described later. ), a developing device 4 (4Y, 4M, 4C, 4K), a primary transfer roller 5 (5Y, 5M, 5C, 5K), a cleaning device 11 (11Y, 11M, 11C, 11K), etc. .

A photosensitive drum 1, which is a rotatable drum-shaped (cylindrical) photosensitive member (electrophotographic photosensitive member) serving as a first image carrier, rotates in the direction of arrow R1 (counterclockwise direction) in FIG. Driven. The photosensitive drum 1 is rotated at a predetermined circumferential speed (process speed) by receiving a driving force from a drum driving device (not shown) serving as a photosensitive member driving means. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charging device 2 serving as a charging means. During the charging process, a predetermined charging voltage (charging bias) is applied to the charging device 2 by a charging power source (not shown). The charged surface of the photosensitive drum 1 is scanned and exposed based on image information (image signal) by an exposure device 3 serving as an exposure means, and an electrostatic latent image (electrostatic image) corresponding to the image information is formed on the photosensitive drum 1. formed on top. In this embodiment, the exposure device 3 is constituted by a laser scanner device that irradiates the photosensitive drum 1 with laser light that is modulated according to image information.

The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by supplying toner as a developer by a developing device 4 serving as a developing means, and a toner image (toner image, developer image) is formed. The developing devices 4Y, 4M, and 4C contain chromatic toners of yellow (Y), magenta (M), and cyan (C), respectively, and the developing device 4K contains toner of black (K) color. Contains toner. In this embodiment, the charged polarity of the photosensitive drum 1 is applied to the exposed area (image area) of the electrostatic latent image on the photosensitive drum 1 whose absolute value has decreased by being exposed to light after being uniformly charged. Toner of the same polarity (negative polarity in this embodiment) is attached (reversal development method). During development, a predetermined development voltage (development bias) is applied to a development roller as a developer carrier included in the development device 4 by a development power source (not shown). In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner during development, is negative polarity.

An intermediate transfer belt (a first belt) 6 is arranged. The intermediate transfer belt 6 is wound around a tension roller 19 as a plurality of tension rollers (first belt tension roller), a pre-secondary transfer roller 20, an inner secondary transfer roller 21, and a drive roller 22. It is stretched with a tension of . The tension roller 19 applies a predetermined tension to the intermediate transfer belt 6 and controls the tension of the intermediate transfer belt 6 to be constant. The tension roller 19 is rotated from the inner circumferential surface side of the intermediate transfer belt 6 to the outer circumferential surface side by a tension spring 41 configured of a compression coil spring or the like, which is a biasing member serving as a biasing means, at both ends in the rotational axis direction. is being energized towards. The pre-secondary transfer roller 20 forms a surface of the intermediate transfer belt 6 near the upstream side of the secondary transfer portion N2 with respect to the conveyance direction (surface movement direction, rotation direction) of the intermediate transfer belt 6. The inner secondary transfer roller (inner member) 21 forms a secondary transfer portion N2 in cooperation with an outer secondary transfer roller 9, which will be described later. In this embodiment, a secondary transfer voltage is applied to the secondary transfer inner roller 21. Drive roller 22 transmits driving force to intermediate transfer belt 6 . The drive roller 22 is rotationally driven by a driving force transmitted from an intermediate transfer belt drive device (first drive unit) 61 (FIG. 6) serving as a drive means. The intermediate transfer belt drive device 61 includes an intermediate transfer belt drive motor 61a (FIG. 1) as a drive source, a drive transmission member, and the like. As a result, the intermediate transfer belt 6 receives the driving force from the drive roller 22, and moves in the direction of arrow R2 (clockwise direction) in FIG. Rotate (move around). In this embodiment, the intermediate transfer belt 6 rotates at a peripheral speed (moving speed of the outer peripheral surface) of 600 to 650 mm/sec. Further, on the inner circumferential surface (inner surface, back surface) side of the intermediate transfer belt 6, a roller-type primary transfer member 1 serving as a primary transfer means is provided corresponding to each photosensitive drum 1Y, 1M, 1C, and 1K. Next transfer rollers 5Y, 5M, 5C, and 5K are arranged. The primary transfer roller 5 presses the intermediate transfer belt 6 toward the photosensitive drum 1 to form a primary transfer portion (primary transfer nip) N1 that is a contact area between the photosensitive drum 1 and the intermediate transfer belt 6. . The tension roller 19 , the pre-secondary transfer roller 20 , the inner secondary transfer roller 21 , and each of the primary transfer rollers 5 are driven to rotate as the intermediate transfer belt 6 rotates. Further, on the inner peripheral surface side of the intermediate transfer belt 6, a pressing member (backup member) 28 is provided upstream of the secondary transfer inner roller 21 and downstream of the secondary transfer pre-roller 20 in the conveying direction of the intermediate transfer belt 6. is located. The pressing member 28 will be further explained later.

The toner image formed on the photosensitive drum 1 as described above is transferred (primary transfer) onto the rotating intermediate transfer belt 6 at the primary transfer portion N1. During the primary transfer, the primary transfer roller 5 is charged with a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) by a primary transfer power source (not shown) serving as a primary transfer voltage applying means. A primary transfer voltage (primary transfer bias) which is a DC voltage is applied. For example, when forming a full-color image, toner images of yellow, magenta, cyan, and black formed on each photosensitive drum 1 are sequentially superimposed on the same image forming area on the intermediate transfer belt 6. Next to be transferred. In this embodiment, the primary transfer portion N1 is an image forming position where a toner image is formed on the intermediate transfer belt 6. The intermediate transfer belt 6 is an example of a rotatable endless belt that conveys the toner image carried at the image forming position.

A secondary transfer device 10 is disposed on the outer peripheral surface (outer surface, front surface) side of the intermediate transfer belt 6 at a position facing the inner secondary transfer roller 21 . The secondary transfer device 10 has a rotatable secondary transfer belt (second belt) 15 configured as an endless belt so as to come into contact with the outer peripheral surface of the intermediate transfer belt 6 . The secondary transfer belt 15 functions as a recording material carrier that supports and conveys the recording material 7. The secondary transfer belt 15 is wound around a secondary transfer outer roller 9 as a plurality of tension rollers (second belt tension rollers), a separation roller 24, a tension roller 25, an auxiliary roller 26, and a drive roller 27. , is stretched with a predetermined tension. The outer secondary transfer roller (external material) 9 cooperates with the inner secondary transfer roller 21 to form a secondary transfer portion N2. That is, the secondary transfer outer roller 9 sandwiches the intermediate transfer belt 6 and the secondary transfer belt 15 with the secondary transfer inner roller 21, and the secondary transfer belt 6 and the secondary transfer belt 15 are in contact with each other. A certain secondary transfer portion (secondary transfer nip) N2 is formed. In this embodiment, the secondary transfer outer roller 9 is electrically grounded (connected to the ground). The separation roller 24 curvature-separates the recording material 7 from the secondary transfer belt 15 after passing through the secondary transfer portion N2. Tension roller 25 applies a predetermined tension to secondary transfer belt 15 . The tension roller 25 is moved from the inner circumferential surface side of the secondary transfer belt 15 to the outer circumferential surface side by means of tension springs 42 made up of compression coil springs and the like, which are biasing members serving as biasing means, at both ends in the rotational axis direction. is being energized towards. Drive roller 27 transmits driving force to secondary transfer belt 15 . The drive roller 27 is rotationally driven by a driving force transmitted from a secondary transfer belt drive device (second drive unit) 63 (FIG. 6) serving as a drive means. The secondary transfer belt drive device 63 includes a secondary transfer belt drive motor 63a (FIG. 1) as a drive source, a drive transmission member, and the like. As a result, the secondary transfer belt 15 receives a driving force from the drive roller 27, and rotates (circularly moves) in the direction of arrow R3 (counterclockwise direction) in FIG. The outer secondary transfer roller 9 , the separation roller 24 , the tension roller 25 , and the auxiliary roller 26 rotate in accordance with the rotation of the secondary transfer belt 15 . In this embodiment, the conveyance speed (peripheral speed) of the secondary transfer belt 15 is faster than the conveyance speed (peripheral speed) of the intermediate transfer belt 6 (for example, +0.4 to +0.9% faster conveyance speed). It is set so that The conveyance speed of the secondary transfer belt 15 will be further explained later.

In this embodiment, as described above, the secondary transfer inner roller 21 is used as a voltage applying member to apply a secondary transfer voltage having the same polarity as the normal charging polarity of the toner, and the secondary transfer outer roller 21 is 9 is used as a counter electrode and electrically grounded. However, the secondary transfer outer roller 9 is used as a voltage applying member to apply a secondary transfer voltage having a polarity opposite to the normal charging polarity of the toner, and the secondary transfer inner roller 21 is used as a counter electrode to apply an electrical voltage. It may be grounded to

In this embodiment, as the intermediate transfer belt 6, an endless belt made of resin such as polyimide or polycarbonate, or various rubbers containing an appropriate amount of carbon black as an antistatic agent is used. Further, as the intermediate transfer belt 6, one having a volume resistivity of 5×10 ⁺⁸ to 5×10 ⁺¹² [Ω·cm] and a thickness of 0.070 to 0.400 [mm] can be suitably used. Further, as the intermediate transfer belt 6, one having a hardness of 55 to 100° in terms of IRHD hardness can be suitably used. Further, as the intermediate transfer belt 6, it is preferable to use a belt whose outer circumferential surface has a static friction coefficient (static friction coefficient with respect to the SUS surface) of 0.2 to 0.6 as measured using HEIDON Tribogear Muse Type: 94i. Can be done.

Further, in this embodiment, as the secondary transfer belt 15, an endless belt made of resin such as polyimide or polycarbonate, or various rubbers containing an appropriate amount of carbon black as an antistatic agent is used. Further, as the secondary transfer belt 15, one having a volume resistivity of 1×10 ⁺⁸ to 1×10 ⁺¹¹ [Ω·cm] and a thickness of 0.07 to 0.1 [mm] can be suitably used. . Further, as the secondary transfer belt 15, one whose outer circumferential surface has a static friction coefficient (static friction coefficient with respect to the SUS surface) measured using HEIDON Tribogear Muse Type: 94i of 0.15 to 0.50 is preferably used. be able to.

Further, in this embodiment, as the secondary transfer outer roller 9, a roller configured with a core metal and an elastic layer of ion conductive foam rubber (NBR rubber) formed around the core metal is used. used. In addition, in this embodiment, the secondary transfer outer roller 9 has an outer diameter of 23 to 25 mm and a resistance value of 1× when measured by applying 2 kV in an N/N (23° C., 50% RH) environment. A roller of 10 ⁺⁵ to 5×10 ⁺⁸ Ω was used.

Further, in this embodiment, as the primary transfer roller 5, a roller configured with a core metal and an elastic layer of ion conductive foam rubber (NBR rubber) formed around the core metal is used. did. In addition, in this embodiment, the primary transfer roller 5 has an outer diameter of 16 to 20 mm and a resistance value of 1×10 when measured by applying 2 kV in an N/N (23° C., 50% RH) environment. ⁺⁵ to 1×10 ⁺⁸ Ω rollers were used.

Further, in this embodiment, as the secondary transfer inner roller 21, a roller configured with a core metal and an elastic layer of electronically conductive rubber (EPDM) formed around the core metal is used. did. In addition, in this embodiment, the secondary transfer inner roller 21 has an outer diameter of 19 to 22 mm and a resistance value of 1× when measured by applying 50 V in an N/N (23° C., 50% RH) environment. A transfer roller of 10 ⁺⁵ to 1×10 ⁺⁸ Ω was used.

Note that the rotation axes of the tension roller of the intermediate transfer belt 6 and the tension roller of the secondary transfer belt 15 are substantially parallel to each other.

Further, in this embodiment, the intermediate transfer belt unit includes the intermediate transfer belt 6 stretched across a plurality of tension rollers, each primary transfer roller 5, a belt cleaning device 28, a frame supporting these, and the like. It is configured. The intermediate transfer belt unit is removable from the main body of the image forming apparatus 100 for maintenance or replacement.

The recording material 7 is conveyed from the feeding section 80 to the secondary transfer section N2. The feeding section 80 includes a recording material cassette 81 as a recording material storage section, a feeding roller 82 as a feeding member as a feeding means, and the like. Note that a plurality of recording material cassettes 81 and a plurality of feeding rollers 82 may be provided. The recording material 7 is stored in a recording material cassette 81. The recording material 7 stored in the recording material cassette 81 is sent out from the recording material cassette 81 by a feeding roller 82 or the like. Further, upstream of the secondary transfer portion N2 with respect to the conveying direction of the recording material 7, a pair of registration rollers 8, which is a conveyance member serving as a conveyance means, and is composed of a pair of registration rollers 8a and 8b is arranged. The recording material 7 fed out from the recording material cassette 81 by the feeding roller 82 is conveyed to the pair of registration rollers 8 and is temporarily stopped. The pair of registration rollers 8 nip and convey the recording material 7 in the direction of the arrow in FIG. 1 by rotationally driving at least one of the pair of registration rollers 8a and 8b by a registration roller drive device (not shown). The registration roller pair 8 transports the recording material 7 to the secondary transfer section N2 in synchronization with the transport of the toner image on the intermediate transfer belt 6 to the secondary transfer section N2.

The toner image formed on the intermediate transfer belt 6 as described above is transferred ( secondary transfer). When the recording material 7 passes through the secondary transfer portion N2, the secondary transfer inner roller 21 is charged with the same polarity as the normal charging polarity of the toner image ( In this embodiment, a secondary transfer voltage (secondary transfer bias) which is a DC voltage of negative polarity is applied. For example, the toner image on the intermediate transfer belt 6 is transferred to the recording material 7 by applying a secondary transfer voltage and flowing a current of -80 to -95 μA.

The recording material 7 onto which the toner image has been transferred is conveyed to the position of the separation roller 24 and separated from the secondary transfer belt 15 by curvature. The recording material 7 separated from the secondary transfer belt 15 is conveyed to a fixing device 13 as a fixing means. The fixing device 13 fixes (melts, fixes) the toner image on the recording material 7 by heating and pressurizing the recording material 7 carrying an unfixed toner image by sandwiching and conveying the recording material 7 with a pair of fixing rotors. The recording material 7 with the toner image fixed thereon is discharged (output) to the outside of the image forming apparatus 100 (outside the machine).

On the other hand, deposits such as toner (primary transfer residual toner) remaining on the photosensitive drum 1 after passing through the primary transfer section N1 are removed from the photosensitive drum 11 by a cleaning device 11 serving as a cleaning means and collected. be done. Further, deposits such as toner (secondary transfer residual toner) remaining on the intermediate transfer belt 6 after passing through the secondary transfer section N2 are removed by a belt cleaning device (electrostatic brush cleaning device) as an intermediate transfer member cleaning means. It is removed from the intermediate transfer belt 6 by the device) 12 and collected. The belt cleaning device 12 collects toner using fur brushes 16a and 16b. Then, the belt cleaning device 12 electrostatically transfers the toner on the fur brushes 16a and 16b to the metal rollers 17a and 17b, and scrapes and removes the toner on the metal rollers 17a and 17b with cleaning blades 18a and 18b. .

2. Secondary Transfer Process The secondary transfer process in this example will be further described with reference to FIG. 2. FIG. 2 is a schematic cross-sectional view showing the vicinity of the secondary transfer portion N2 in this embodiment (a cross section approximately perpendicular to the rotational axis direction of the photosensitive drum 1, the inner secondary transfer roller 21, the outer secondary transfer roller 9, etc.). be.

As described above, in this embodiment, the conveyance speed (peripheral speed) of the secondary transfer belt 15 is set to be faster than the conveyance speed (peripheral speed) of the intermediate transfer belt 6. In this embodiment, the conveying speed of the intermediate transfer belt 6 and the conveying speed of the secondary transfer belt 15 are designed so that the speed difference does not straddle zero. Thereby, as described above, the stability of the conveyance speed of the intermediate transfer belt 6 and the secondary transfer belt 15 is maintained.

Furthermore, by increasing the conveyance speed of the secondary transfer belt 15 with respect to the conveyance speed of the intermediate transfer belt 6, the secondary transfer belt 15 is moved to the outer peripheral surface side (intermediate transfer belt 6 side) on the upstream side of the secondary transfer portion N2. ) so that the recording material 7 can be supported from the back side of the recording material 7. In other words, in this embodiment, with respect to the conveyance direction (surface movement direction, rotation direction) of the secondary transfer belt 15, the drive roller 27 of the secondary transfer belt 15 is the secondary transfer outer roller forming the secondary transfer portion N2. 9 and downstream of the tension roller 25 that applies tension to the secondary transfer belt 15. Therefore, when the secondary transfer belt 15 is driven by the drive roller 27 at a conveyance speed faster than the conveyance speed of the intermediate transfer belt 6, especially in the range up to the drive roller 27 on the upstream side of the secondary transfer portion N2, The next transfer belt 15 is bent toward the outer peripheral surface (towards the intermediate transfer belt 6). In particular, in this embodiment, the drive roller 27 of the secondary transfer belt 15 is arranged adjacent to the upstream side (that is, immediately upstream) of the inner secondary transfer roller 9 with respect to the conveyance direction of the secondary transfer belt 15. There is. Therefore, the above-mentioned deflection is more likely to occur. This reduces the possibility of the recording material 7 falling away from the intermediate transfer belt 6 upstream of the secondary transfer section N2, and allows "pre-transfer" due to a weak transfer electric field upstream of the secondary transfer section N2. can be suppressed from occurring. Pre-transfer is a phenomenon in which toner is transferred from the intermediate transfer belt 6 to a region other than a predetermined area on the recording material 7 (a position different from the position to which it should originally be transferred) due to the weak transfer electric field.

Further, in this embodiment, the pair of registration rollers 8a and 8b constituting the registration roller pair 8 are configured so that they can be moved toward and away from each other by a registration roller separating device 64. The registration roller separation device 64 includes a separation drive source (such as a solenoid) 64a and a separation movement section 64b that moves at least one of the pair of registration rollers 8a and 8b. The registration roller separating device 64 can switch the pair of registration rollers 8a and 8b between a state in which they are in contact with each other and a state in which they are separated from each other. In this embodiment, the image forming apparatus 100 performs a separating operation of the pair of registration rollers 8 at the timing when the recording material 7 reaches the secondary transfer section N2, so that the recording material 7 is nipped and conveyed at the secondary transfer section N2. It looks like this. This suppresses the loop of the recording material 7 caused by the difference between the conveyance speed of the recording material 7 at the secondary transfer section N2 and the conveyance speed of the recording material 7 at the pair of registration rollers 8, and The influence of the pair of registration rollers 8 on the posture of the recording material 7 can be reduced. More specifically, the timing of separating the pair of registration rollers 8 is desirably approximately at the same time as, immediately before, or immediately after the recording material 7 reaches the secondary transfer portion N2. However, if the influence of the registration roller pair 8 on the posture of the recording material 7 upstream of the secondary transfer section N2 can be sufficiently reduced, the recording material 7 can be moved at any timing when it passes through the secondary transfer section N2. The pair of registration rollers 8 can be separated. In this way, the registration roller separating device 64 as a switching unit can switch the recording material 7 between the first state where the pair of registration rollers 8, which sandwich the recording material 7 and convey it to the secondary transfer section N2, can sandwich the recording material 7, and the first state where the recording material 7 can be sandwiched. is switched to the second state where it cannot be pinched. Then, the registration roller separation mechanism 64 brings the pair of registration rollers 8 into the second state when the recording material 7 passes through the secondary transfer portion N2.

3. Pressing Member Next, the pressing member 28 in this embodiment will be explained. FIG. 3 is a schematic cross-sectional view showing the vicinity of the secondary transfer part N2 in this embodiment on a larger scale (approximately perpendicular to the rotation axis direction of the photosensitive drum 1, the secondary transfer inner roller 21, the secondary transfer outer roller 9, etc.). (cross section). Note that FIG. 3 shows a state in which the intermediate transfer belt 6 is removed, and the tension surface of the intermediate transfer belt 6 without the pressing member 28 is shown by a broken line (common tangent line L1 to be described later). FIG. 4 is a schematic cross-sectional view showing the pressing member 28 and the supporting member 29a of the pressing member 28 in this embodiment (in the direction of the rotation axis of the photosensitive drum 1, the secondary transfer inner roller 21, the secondary transfer outer roller 9, etc.). (approximately perpendicular cross section). Further, FIG. 5 is a schematic cross-sectional view of the vicinity of the pressing member 28 (photosensitive drum 1, inner secondary transfer roller 21, outer secondary transfer roller 9, etc.) for explaining the pressing amount (pushing amount) of the pressing member against the belt. (a cross section substantially perpendicular to the direction of the rotational axis).

As shown in FIG. 3, in this embodiment, the intermediate transfer belt 6 is stretched between the secondary transfer inner roller 21 and the pre-secondary transfer roller 20 among the plurality of tension rollers of the intermediate transfer belt 6. A pressing member (backup member) 28 is arranged which contacts the inner peripheral surface and presses the intermediate transfer belt 6 from the inner peripheral surface side to the outer peripheral surface side. The pressing member 28 is provided close to the secondary transfer inner roller 21 upstream of the secondary transfer portion N2. In other words, the pressing member 28 can contact the inner circumferential surface of the intermediate transfer belt 6 upstream of the secondary transfer inner roller 21 and downstream of the secondary transfer pre-roller 20 with respect to the rotational direction of the intermediate transfer belt 6. It is arranged like this. In particular, in this embodiment, the pressing member 28 is arranged so as to be able to come into contact with the inner circumferential surface of the intermediate transfer belt 6 in a range overlapping with the secondary transfer belt 15 with respect to the conveyance direction of the recording material 7 .

In this embodiment, during image formation (secondary transfer), the inner peripheral surface of the intermediate transfer belt 6 and the tip of the pressing member 28 are in contact with each other. The pressing member 28 can contact the inner peripheral surface of the intermediate transfer belt 6 and press the intermediate transfer belt 6 from the inner peripheral surface side to the outer peripheral surface side. As a result, the pressing member 28 moves the tension surface of the intermediate transfer belt 6 formed between the inner secondary transfer roller 21 and the pre-secondary transfer roller 20 from the inner circumferential surface side to the outer circumferential surface side of the intermediate transfer belt 6. It can be extended to. In this embodiment, the pressing member 28 is formed of a flexible plate-like member made of resin, and the pressing member 28 elastically biases the intermediate transfer belt 6 by utilizing bending elasticity. Therefore, the shape (the amount of deflection, the amount of deformation) or the position of the pressing member 28 is the position (or shape). The position of the pressing member 28 determines the shape (posture) of the intermediate transfer belt 6 upstream of the secondary transfer portion N2. Further, in this embodiment, the image forming apparatus 100 is provided with a pressing member driving device 62 as a moving mechanism capable of changing the position of the pressing member 28. As a result, in this embodiment, the image forming apparatus 100 is configured to be able to control the position of the pressing member 28, that is, the shape (posture) of the intermediate transfer belt 6 upstream of the secondary transfer section N2. There is.

In this embodiment, the pressing member 28 as a whole has a longitudinal direction that is arranged substantially parallel to the width direction of the intermediate transfer belt 6 (a direction that is substantially orthogonal to the conveyance direction), and a lateral direction that is substantially orthogonal to the longitudinal direction. and a plate-like (sheet-like) member (backup sheet) each having a predetermined length and a predetermined thickness and having a substantially rectangular shape in plan view. The length of the pressing member 28 in the longitudinal direction is equivalent to the length of the intermediate transfer belt 6 in the width direction. The pressing member 28 has a free end (tip end) that is one end in the transverse direction (the end on the downstream side with respect to the rotational direction of the intermediate transfer belt 6), and extends over substantially the entire width of the intermediate transfer belt 6. 6 and can press the intermediate transfer belt 6 . Further, in this embodiment, the pressing member 28 has a part on the fixed end (base end) side which is the other end in the transverse direction (the end on the upstream side with respect to the rotational direction of the intermediate transfer belt 6). , are fixed to the support member 29a. Here, the pressing member 28, more specifically, the free end (tip) side of the pressing member 28 in the lateral direction (herein also simply referred to as the "tip") is connected to the secondary transfer inner roller 21. It is desirable to be placed as close as possible to the However, the pressing member 28 is arranged so as not to come into contact with the secondary transfer inner roller 21. The pressing member 28 is located, for example, at a position that is approximately 2 mm or more, typically approximately 10 mm or more, upstream in the conveying direction of the intermediate transfer belt 6 from the position where the secondary transfer inner roller 21 and the intermediate transfer belt 6 contact. It is arranged so as to be in contact with the inner circumferential surface of the intermediate transfer belt 6. Further, the pressing member 28 is located, for example, at a position that is approximately 40 mm or less, typically approximately 25 mm or less, upstream in the rotational direction of the intermediate transfer belt 6 from the position where the secondary transfer inner roller 21 and the intermediate transfer belt 6 contact. The intermediate transfer belt 6 is disposed so as to be in contact with the inner circumferential surface of the intermediate transfer belt 6.

As shown in FIG. 4, in this embodiment, the pressing member 28 is composed of a first sheet 28a and a second sheet 28b. In this embodiment, the first sheet 28a is attached to the support member 29a with double-sided tape so that the free length Jb is 12.5 to 14.5 mm. Furthermore, the surface of the first sheet 28a on the intermediate transfer belt 6 side is adjusted so that the amount of displacement Ja of the leading edge of the second sheet 28b with respect to the leading edge of the first sheet 28a is 2 to 4 mm. is attached with double-sided tape. In this embodiment, the second sheet 28b is attached to the first sheet 28a with double-sided tape in a region that does not cover the free length Jb. Note that the first sheet 28a and the second sheet 28b may be fixed by other fixing means such as adhesion or fastening. The pressing member 28 contacts the inner peripheral surface of the intermediate transfer belt 6 at the leading end of the first sheet 28a and the leading end of the second sheet 28b.

In this embodiment, a sheet-like member made of a resin material such as polyester and having a thickness of about 0.4 to 0.6 mm is used as the first sheet 28a. Further, in this embodiment, as the second sheet 28b, a sheet-like member having a thickness of about 0.2 to 0.3 mm is used, which is made of the same resin material as the first sheet 28a. In this embodiment, in order to stabilize the state of contact with the intermediate transfer belt 6, the pressing member 28 is made by pasting together two sheet-like members, the first sheet 28a and the second sheet 28b. Configured. However, the pressing member 28 is not limited to the configuration of this embodiment, and may be composed of a sheet-like member corresponding to the first sheet 28a in this embodiment, and the second sheet 28b in this embodiment. does not need to be provided. Note that as the resin material constituting the pressing member 28, PPS (polyphenylene sulfide), PEEK (polyether ether ketone), PET (polyethylene terephthalate), etc. can be used.

As described above, in this embodiment, the image forming apparatus 100 includes the pressing member driving device 62 that changes the position of the pressing member 28 (FIG. 3). The pressing member driving device 62 can control the shape (posture) of the intermediate transfer belt 31 upstream of the secondary transfer portion N2 by changing the position of the pressing member 28. In other words, the pressing member driving device 62 controls the amount of penetration of the pressing member 28 into the intermediate transfer belt 6 (H, which will be described later) by changing the position of the pressing member 28, thereby controlling the amount of the pressing member 28 against the intermediate transfer belt 6. The amount of pressure (I to be described later) can be controlled. Further, the pressing member driving device 62 may be configured to be able to change the state of contact or separation of the pressing member 28 with respect to the intermediate transfer belt 6 by changing the position of the pressing member 28. Note that changing the pressing amount of the pressing member 28 includes changing the state of contact or separation of the pressing member 28 with respect to the intermediate transfer belt 6.

In this embodiment, the pressing member driving device 62 includes an eccentric cam 30 as an acting part that acts on the support member 29a as a moving part, and a cam drive motor (stepping motor) 31 as a drive source that drives the eccentric cam 30. , and is configured with the following. The support member 29a is rotatable around a rotation axis substantially parallel to the width direction of the intermediate transfer belt 6, with the rotation shaft portions 29b at both ends in the longitudinal direction being the center. It is supported by a frame (not shown) of the main body of the device. In this way, by rotating the support member 29a around the rotation axis substantially parallel to the width direction of the intermediate transfer belt 6, the pressing member 28 is rotated around the rotation axis, and the pressing member 28 The position of can be changed. In this embodiment, changing the position of the pressing member 28 means, more specifically, the position of the tip of the pressing member 28 assuming that there is no intermediate transfer belt 6 (hereinafter also simply referred to as "tip position"). ). Specifically, in this embodiment, changing the position of the pressing member 28 means changing the position of the supporting member 29a by the pressing member driving device 62. The eccentric cam 30 is in contact with the support member 29a and has a stepless surface whose radius from the center of rotation changes uniformly depending on the rotation angle. Therefore, as the eccentric cam 30 rotates, the support member 29a rotates about the rotation shaft portion 29b. Note that in this embodiment, the support member 29a is urged to rotate in a direction in which it engages with the eccentric cam 30. The support member 29a is biased by the tension of the intermediate transfer belt 6 via the pressing member 28, and may also be provided with a spring or the like as a biasing member serving as a biasing means for biasing the support member 29a. . Thereby, the pressing member 28 can be separated from the intermediate transfer belt 6.

The control unit 50, which will be described later, is capable of detecting the home position (HP position) of the eccentric cam 30 based on a signal from a cam position sensor (not shown) composed of an optical sensor or the like. Further, the memory 52 of the control unit 50, which will be described later, stores information indicating the relationship between the amount of penetration H (or the amount of pressing I) of the pressing member 28 and the number of pulses input to the cam drive motor 31 (number of input pulses). remembered. Then, the control unit 50 moves the support member 29a to an arbitrary position by inputting an arbitrary number of pulses to the cam drive motor 31 from the home position of the eccentric cam 30 (that is, the home position of the pressing member 28). The pressing member 28 can be moved to any desired position. Thereby, the penetration amount H (or the pressing amount I) of the pressing member 28 can be variably controlled.

The pressing amount (pushing amount) of the pressing member 28 against the intermediate transfer belt 6 will be described with reference to FIGS. 3 and 5. The pressing amount of the pressing member 28 against the intermediate transfer belt 6 is roughly determined by the amount of pressure applied by the pressing member 28 to the tension surface of the intermediate transfer belt 6 formed by being stretched between the inner secondary transfer roller 21 and the pre-secondary transfer roller 20. On the other hand, it is the amount by which the intermediate transfer belt 6 protrudes outward. The pre-secondary transfer roller 20 is an example of an upstream roller that is disposed adjacent to the second inner transfer roller 21 upstream of the second inner transfer roller 21 in the rotational direction of the intermediate transfer belt 6 among the plurality of tension rollers. It is. In other words, in FIG. 5, a common tangent between the inner secondary transfer roller 21 and the pre-secondary transfer roller 20 that are in contact with the intermediate transfer belt 6 is defined as a common tangent L1. At this time, the pressing amount I of the pressing member 28 is the normal distance from the common tangent L1 to the tip of the pressing member 28 (between the common tangent L1 and a line passing through the tip of the pressing member 28 and parallel to the common tangent L1). distance). Note that depending on the relative position of the secondary transfer inner roller 21 and the secondary transfer outer roller 9 with respect to the rotational direction of the intermediate transfer belt 6, the secondary transfer outer roller 9 (more specifically, the secondary transfer belt 15 above it) The tension surface of the intermediate transfer belt 6 upstream of the secondary transfer portion N2 may be formed by being stretched between the intermediate transfer belt 6 and the pre-secondary transfer roller 20. In this case, in the same manner as above, a common tangent between the secondary transfer outer roller 9 (more specifically, the secondary transfer belt 15 thereon) and the secondary transfer pre-roller 20 on the side in contact with the intermediate transfer belt 6 is applied. The amount of pressure can be defined. In this embodiment, the amount of pressure of the pressing member 28 against the intermediate transfer belt 6 can be controlled by the amount of penetration of the pressing member 28 into the intermediate transfer belt 6 (the position of the tip of the pressing member 28). As shown in FIG. 3, the intrusion amount H of the pressing member 28 into the intermediate transfer belt 6 is determined by the normal distance (common (distance between the tangent line L1 and a line that passes through the tip of the pressing member 28 and is parallel to the common tangent line L1 when the intermediate transfer belt 6 is not stretched). In this embodiment, by rotating the eccentric cam 30, the penetration amount H (FIG. 3) can be set from 1.5 to 3.8 mm during image formation (secondary transfer). By setting the penetration amount H of the pressing member 28 in this way, the amount by which the tension surface of the intermediate transfer belt 6 is changed by the pressing member 28, that is, the pressing amount I (FIG. 5), is set to 1.0 to 3. It was set to about 0 mm.

Note that the pressing amount I of the pressing member 70 only needs to be a desired value while the recording material 7 is passing near the entrance of the secondary transfer section N2 and through the secondary transfer section N2. More specifically, the vicinity of the entrance of the secondary transfer section N2 is the intermediate transfer belt 6 between the position where the pressing member 28 contacts the intermediate transfer belt 6 and the secondary transfer section N2 in the conveying direction of the recording material 7. This area corresponds to the area of . For example, when the image forming apparatus 100 is in a standby state (power ON and waiting for job input), power OFF state, or sleep state, the pressing member 28 may be placed in a position separated from the intermediate transfer belt 6 or simply in contact with the intermediate transfer belt 6. (the penetration amount H is 0 mm in both cases). Thereby, deformation of the pressing member 70 when the image forming apparatus 100 is left unattended can be suppressed. In this embodiment, the home position of the pressing member 28 is determined either when the pressing member 28 is separated from the intermediate transfer belt 6, or when the pressing member 28 is at an intermediate position with a smaller penetration amount H (for example, 0 to 1 mm) than during image formation (secondary transfer). It is set at a position where it contacts the transfer belt 6. In this embodiment, when the image forming apparatus 100 is in a standby state, power OFF state, or sleep state, the pressing member 28 is placed at the home position.

In FIG. 3, a straight line passing through the rotation center of the secondary transfer inner roller 21 and perpendicular to the common tangent line L1 (a perpendicular line drawn from the rotation center of the secondary transfer inner roller 21 to the common tangent line L1) is the inner roller center line L2. shall be. In addition, in FIG. 3, a straight line passing through the rotation center of the secondary outer transfer roller 9 and perpendicular to the common tangent line L1 (a perpendicular line drawn from the rotation center of the secondary transfer outer roller 9 to the common tangent line L1) is an outer roller center line L3. shall be. At this time, in this embodiment, the secondary transfer outer roller 9 is arranged such that the outer roller center line L3 is located downstream of the inner roller center line L2 with respect to the conveyance direction of the secondary transfer belt 15. There is. In particular, in this embodiment, the secondary transfer roller 9 is arranged such that the distance E between the inner roller center line L2 and the outer roller center line L3 is 1.5 to 2.5 mm. In such a configuration, the contact distance between the intermediate transfer belt 6 and the recording material 7 tends to be easily changed due to the action of the secondary transfer belt 15. There is a tendency to easily obtain the effect of changing the speed difference. However, the present invention is not limited to such a configuration, and may include a configuration in which the inner roller center line L2 and the outer roller center line L3 are at the same position, or the outer roller center line L3 is closer to the inner roller center line L2 than the inner roller center line L2. may be located on the upstream side.

4. Control Mode FIG. 6 is a schematic block diagram showing a control mode of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 is provided with a control section 50. The control section 50 includes a CPU 51 as an arithmetic processing means, a memory 52 as a storage means, an input/output section (not shown) for inputting and outputting signals to the control section 50, and the like. The memory 52 is composed of ROM, RAM, nonvolatile memory, and the like. The control unit 50 controls each part of the image forming apparatus 100 by the CPU 51 according to a control program stored in the ROM, using the RAM as a work area, and based on input signals from various sensors included in the image forming apparatus 100. Can be centrally controlled. For example, the control unit 50 is connected to an intermediate transfer belt drive device 61 (specifically, the intermediate transfer belt drive motor 61a), a pressing member drive device 62 (specifically, the cam drive motor 31), and the like. The control unit 50 also includes a secondary transfer belt drive device 63 (specifically, a secondary transfer belt drive motor 63a), a registration roller separation device 64 (specifically, a separation drive source 64a), and an image forming unit S. Control devices for each part are connected to it. Further, an operation unit (user interface (UI)) 70 provided in the image forming apparatus 100 is connected to the control unit 50 . The operation unit 70 includes a display unit (display means) that is controlled by the control unit 50 and displays information, and an input unit (input unit) that inputs information to the control unit 50 through operations by an operator such as a user or a service person. has. The operation unit 70 may include a touch panel that functions as a display means and an input means. Further, an external device such as a personal computer, an image reading device, etc. may be connected to the image forming apparatus 100.

The control unit 50 controls each unit of the image forming apparatus 100 to execute an image forming operation based on job information input from an external device or the operation unit 70. The job information includes a start instruction (start signal), information regarding image forming conditions (command signal) such as information regarding the recording material 7, and image information (image signal). Note that the information regarding the recording material 7 (recording material information) refers to attributes based on general characteristics (so-called, Includes any information that can distinguish the recording material 7, such as paper type category), numerical value or numerical range such as basis weight, thickness, and rigidity, or brand (including manufacturer, product name, product number, etc.) It is something to do. It can be considered that each type of recording material 7 is classified by the information regarding the recording material 7. Further, the information regarding the recording material 7 may be included in print mode information that specifies the operation settings of the image forming apparatus 100, such as "plain paper mode" or "embossed paper mode", or may be substituted with print mode information. You can also

The image forming apparatus 100 executes a job (print job), which is a series of operations for forming and outputting an image on one or more recording materials 7, which is started in response to a single start instruction. A job generally includes an image forming process (image forming operation), a pre-rotation process, a paper-interval process when forming images on a plurality of recording materials 7, and a post-rotation process. The image forming process is a period during which the electrostatic image of the image to be actually formed on the recording material 7 and output, the formation of the toner image, the primary transfer, and the secondary transfer of the toner image are performed. Formation period) refers to this period. More specifically, the timing of image formation differs depending on the position where each of the steps of electrostatic image formation, toner image formation, toner image primary transfer, and secondary transfer is performed. The pre-rotation process is a period from when a start instruction is input until actually starting to form an image, during which preparatory operations are performed before the image forming process. The inter-paper process (inter-recording material process, inter-image process) is a period corresponding to the interval between recording materials 7 when images are formed on a plurality of recording materials 7 in succession (continuous image formation). be. The post-rotation process is a period in which organizing operations (preparatory operations) are performed after the image forming process. The non-image forming period (non-image forming period) is a period other than the image forming period, and includes the following periods. That is, it includes a pre-rotation process, a paper interval process, a post-rotation process, and a pre-multi-rotation process which is a preparatory operation when the image forming apparatus 100 is turned on or returned from a sleep state. It also includes a power OFF state, a sleep state, a standby state, a period from the standby state until starting the pre-rotation process or the pre-multi-rotation process. In this embodiment, the image forming apparatus 100 can perform an operation of setting (adjusting) the position of the pressing member 28 when not forming an image.

5. Control of the Present Embodiment Referring to FIG. 7, job operations in the present embodiment will be described. FIG. 7 is a flowchart showing an outline of the job procedure in this embodiment.

When a job starts, the control unit 50 causes the pressing member driving device 62 to move the pressing member 28 to a position where the amount of penetration H into the intermediate transfer belt 6 is 1.5 to 2.2 mm (S1). Next, the control unit 50 controls the intermediate transfer so that the conveying speed (peripheral speed) of the secondary transfer belt 15 is +0.35 to +0.45% faster than the conveying speed (peripheral speed) of the intermediate transfer belt 6. The belt 6 and the secondary transfer belt 15 are driven (S2). Note that in S2, other elements such as the photosensitive drum 1 are also driven. Here, the difference between the conveying speed (peripheral speed) of the secondary transfer belt 15 and the conveying speed (peripheral speed) of the intermediate transfer belt 6 (if the conveying speed (peripheral speed) of the secondary transfer belt 15 is faster, the difference is positive). value) is also simply referred to as the "circumferential speed difference." This "circumferential speed difference" may be anything that represents a difference in circumferential speed, and does not simply mean a difference, but also includes a speed ratio as in this embodiment. Next, the control unit 50 determines whether the recording material 7 on which the next image is to be formed (passed) is embossed paper based on the job information (S3). If the control unit 50 determines in S3 that the paper is not embossed paper, it outputs the image using the same intrusion amount H and the peripheral speed difference (S8, S9). Next, the control unit 50 determines whether all images of the job have been output (S6). When the control unit 50 determines that the process has ended in S6, the control unit 50 causes the pressing member driving device 62 to move the pressing member 28 so that it does not come into contact with the intermediate transfer belt 6 or the intrusion amount H is 0 to 1.0 mm. It is evacuated to the home position (HP position) (S7) and the job is ended. While waiting for a job, the tip of the pressing member 28 can be prevented from entering (merely contacting) the intermediate transfer belt 6, entering by a smaller amount than during image formation, or retracting to a position where it does not come into contact with the intermediate transfer belt 6. The creep deformation of can be further reduced. Further, if the control unit 50 determines that the process has not ended in S6, the process returns to S3.

On the other hand, if the control unit 50 determines that the paper is embossed paper in S3, the control unit 50 causes the pressing member driving device 62 to move the pressing member 28 to a position where the amount of penetration H into the intermediate transfer belt 6 is 3.0 to 3.8 mm. (S4). Next, the control unit 50 controls the present implementation so that the conveying speed (peripheral speed) of the secondary transfer belt 15 is faster than the conveying speed (peripheral speed) of the intermediate transfer belt 6 by +0.05 to +0.15%. In the example, the driving speed of the secondary transfer belt 15 is changed (S5). Thereafter, the control unit 50 proceeds to the processing of S6 and S7 in the same manner as described above. Note that in order to change the circumferential speed difference, either the conveyance speed of the intermediate transfer belt 6 or the conveyance speed of the secondary transfer belt 15 may be changed, or both may be changed. However, from the viewpoint of the influence on the image, it is preferable to change the conveyance speed of the secondary transfer belt 15.

In this example, as the embossed paper, special paper Lezac 66 with a basis weight of 151 g/m ² was used. Further, in this example, Canon GF-C081 was used as plain paper other than embossed paper.

FIG. 9 is a table showing evaluation results for explaining the effects of the control of this embodiment. The evaluation items are "shock image disturbance", "transferability", and "image rubbing" when embossed paper or plain paper is used as the recording material 7. Regarding the transferability, embossed paper was evaluated for deterioration in transferability due to gap discharge, and plain paper was evaluated for deterioration in transferability due to pre-transfer. The evaluation results for each evaluation item are shown as follows. “〇 (Good)” indicates a case where no image defect was confirmed for each evaluation item. Moreover, "Δ (slightly poor)" indicates that some image defects for each evaluation item occur, which may become a practical problem depending on the case. "× (Poor)" indicates that an image defect for each evaluation item has occurred and may pose a practical problem in many cases.

As shown in FIG. 9, when the penetration amount H of the pressing member 28 is set to 3.0 to 3.8 mm (S4), the recording material 7 and the intermediate transfer belt 6 are brought into close contact upstream of the secondary transfer portion N2. Become. Therefore, gap discharge in the recesses on the surface of the recording material 7 is suppressed and transferability is improved, so that transferability to embossed paper is improved.

However, if the penetration amount H is set to 3.0 to 3.8 mm (S4) and the circumferential speed difference is kept at +0.35 to +0.45% (S9), the following will occur. In other words, in addition to the pressure from the pressing member 28, the deflection of the secondary transfer belt 15 causes the contact area between the intermediate transfer belt 6 and the secondary transfer belt 15 to increase. Therefore, the driving load on the secondary transfer belt 15 increases, and if the recording material 7 rushes into the secondary transfer section N2 in this state and a load fluctuation occurs, the same applies to both embossed paper and plain paper as described above. Shock image disturbances become apparent. As described above, the behavior of the recording material 7 has become unstable due to the load fluctuation, and the recording material 7 is approaching the intermediate transfer belt 6 that has been pushed into the press backup sheet upstream of the secondary transfer section N2. It's for a reason. Therefore, in order to suppress the above load fluctuation, the speed difference between the intermediate transfer belt 6 and the secondary transfer belt 15 is reduced, and the peripheral speed is set to +0.5 to +0.15% (S5). As a result, it is possible to prevent the behavior of the recording material 7 from becoming unstable due to the load fluctuations, and it is possible to reduce shock image disturbances for both embossed paper and plain paper.

On the other hand, if the penetration amount H is set to 3.0 to 3.8 mm (S4), image rubbing may occur on plain paper, and transferability may deteriorate. This is because, as mentioned above, the contact distance between the intermediate transfer belt 6 and the recording material 7 upstream of the secondary transfer section is long, and the intermediate transfer belt 6 and the recording material 7 rub against each other, causing the image to deteriorate. This is because it may be disrupted. Due to differences in visibility due to surface irregularities, the effect of this phenomenon is less with embossed paper, but can become noticeable with plain paper. Further, if the penetration amount H is continued to be used at 3.0 to 3.8 mm, the creep deformation of the tip of the pressing member 28 that is in contact with the intermediate transfer belt 6 will be accelerated.

Therefore, in the case of plain paper, even if the intrusion amount H is set to 1.5 to 2.2 mm (S8), if the peripheral speed difference is +0.05 to +0.15% (S5), the pre-transfer Transferability begins to deteriorate. On the other hand, according to the inventor's intensive studies, in the case of plain paper, even if the penetration amount H of the pressing member 28 is 1.5 to 2.2 mm (S8), the peripheral speed difference is +0.35 mm. If it is set to +0.45% (S9), transferability can be ensured. This is because, as described above, the deflection of the secondary transfer belt 15 supports the recording material 7 from the back surface of the recording material 7, thereby ensuring the contact distance between the intermediate transfer belt 6 and the secondary transfer belt 15.

Therefore, in this embodiment, the penetration amount H of the pressing member 28 is set to 3.0 to 3.8 mm (S4) only when the surface of the recording material 7 is embossed paper, and in that case, the circumferential It was decided to reduce the speed difference to +0.05 to +0.15%. Thereby, it is possible to obtain good transferability on plain paper while suppressing shock image disturbance on embossed paper. Furthermore, since the penetration amount H is increased only for recording materials 7 that are used relatively infrequently, such as embossed paper with uneven surfaces, the progress of creep deformation at the tip of the pressing member 28 is suppressed. At the same time, it is possible to reduce shock image disturbance when the pressing member 28 is pushed further.

As described above, in this embodiment, the image forming apparatus 100 includes a rotatable endless first belt 6 that carries a toner image, and a plurality of first belt tension rollers that stretch the first belt. , an inner roller 21 , and a plurality of first belt tension rollers including an upstream roller 20 disposed adjacent to the inner roller 21 upstream of the inner roller 21 with respect to the rotational direction of the first belt 6 , and the first belt 6 . A rotatable endless second belt 15 forming a transfer portion N2 that contacts the outer peripheral surface of the first belt 6 to transfer the toner image from the first belt 6 to the recording material 7; An outer roller 9 which is a two-belt tension roller and contacts the inner roller 21 via the first belt 6 and the second belt 15 to form the transfer portion N2, and a tension roller 42 which applies tension to the second belt 15. , and a plurality of second belt tension rollers including a drive roller 27 that is disposed upstream of the outer roller 9 and downstream of the tension roller 42 with respect to the rotational direction of the second belt 15 and transmits driving force to the second belt 15. , a first drive unit 61 that drives the first belt 6 , a second drive unit 63 that drives the second belt 15 , upstream of the inner roller 21 and downstream of the upstream roller 20 with respect to the rotational direction of the first belt 6 A pressing member 28 that can contact the inner peripheral surface of the first belt 6 and press the first belt 6 from the inner peripheral surface side toward the outer peripheral surface side and the position of the pressing member 28 are changed to perform the pressing. A moving mechanism 62 that can change the amount of pressure of the member 28 against the first belt 6 and a mechanism that allows the circumferential speed of the second belt 15 to be higher than the circumferential speed of the first belt 6 when transferring a toner image onto the recording material 7 are provided. At least one of the first drive unit 61 and the second drive unit 63 is controlled so that the toner image is transferred to the recording material 7 based on the position setting of the pressing member 28 by the moving mechanism 62. The first drive section 61 or the second drive section 63 is configured to change the circumferential speed difference between the circumferential speed of the first belt 6 and the circumferential speed of the second belt 15 when transferring the toner image onto the material 7. It has a control section 50 that controls at least one side.

In this embodiment, the control unit 50 sets the position of the pressing member 28 at the first position when transferring the toner image onto the recording material 7 to a second position where the pressing amount is larger than the first position. At least one of the first drive section 61 and the second drive section 63 is controlled so that the circumferential speed difference is smaller in the case of the position. Further, in this embodiment, the first drive unit 61 and the second drive unit 63 are configured to control the circumferential speed of the first belt 6 and the second belt 15 when transferring the toner image onto the recording material 7. The first belt 6 and the second belt 15 are respectively driven to prevent reverse rotation. Further, in the present embodiment, the image forming apparatus 100 includes a conveyance member 8 that pinches the recording material 7 and conveys it to the transfer section N2, a first state in which the conveyance member 8 can pinch the recording material 7, and a first state in which the recording material 7 is and a switching section 64 that switches the conveying member 8 to a second state in which it cannot be nipped, and the switching section 64 sets the conveying member 8 to the second state when the recording material 7 passes through the transfer section N2. In addition, in this embodiment, in a cross section substantially perpendicular to the rotational axis of the inner roller 21, the common tangent between the inner roller 21 on the side that contacts the first belt 6 and the upstream roller 20 is L1, and the common tangent between the inner roller 21 and the upstream roller 20 is L1. When a straight line passing through the center of rotation and perpendicular to the common tangent line L1 is taken as the inner roller center line L2, and a straight line passing through the rotation center of the outer roller 9 and perpendicular to the common tangent line L1 is taken as the outer roller center line L3, the rotation direction of the second belt 15 is The outer roller center line L3 is located downstream of the inner roller center line L2. Further, in this embodiment, the control unit 50 is configured such that the position of the pressing member 28 when waiting for an instruction to start image formation is higher than the position of the pressing member 28 when transferring the toner image onto the recording material 7. The moving mechanism 62 is controlled so that the amount of pressure is small. Further, in this embodiment, the control unit 50 sets the position of the pressing member 28 by the moving mechanism 62 when transferring the toner image to the recording material 7 based on the type of the recording material 7 to which the toner image is transferred. However, when transferring the toner image to the second type of recording material 7, which has a larger surface unevenness than the first type of recording material P, the above-mentioned pressing amount is lower than when transferring the toner image to the first type of recording material P. The position of the pressing member 28 is set so that the value becomes large. Further, in this embodiment, the drive roller 27 is disposed adjacent to the outer roller 9 upstream of the outer roller 9 with respect to the rotational direction of the second belt 15 .

As described above, in this embodiment, the image forming apparatus 100 transfers a toner image from the intermediate transfer belt 6 to the recording material 7 using the secondary transfer belt 15, and presses the pressing member 28 against the intermediate transfer belt 6. The configuration is such that the amount of pressure can be varied. According to this embodiment, with such a configuration, it is possible to suppress shock image disturbance and obtain good transferability regardless of the amount of pressure applied by the pressing member 28.

[Example 2]
Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of Embodiment 1 are designated by the same reference numerals as in Embodiment 1, and detailed explanations are omitted. do.

Referring to FIG. 8, job operations in this embodiment will be described. FIG. 8 is a flowchart showing an outline of the job procedure in this embodiment. In the procedure of FIG. 8, the same step numbers (S1 to S9) are assigned to processes similar to the procedure of FIG. 7 described in the first embodiment. In the procedure of FIG. 8, the process of S10 is added, and if it is determined that all images of the job have not been outputted in S6 ("No"), the process of S4 is performed instead of the process of S3. The procedure differs from the procedure shown in FIG. 7 in that it returns.

In other words, in this embodiment, the control unit 50 outputs the image while keeping the intrusion amount H at 1.5 to 2.2 mm and the peripheral speed difference at +0.35 to +0.45% when the paper is not embossed. After that (S8, S9), it is determined in S10 whether all images of the job have been output. If the control unit 50 determines that the job has ended in S10, it retracts the pressing member 28 to the home position (HP position) (S7) and ends the job. Further, if the control unit 50 determines that the process has not ended in S10, the process returns to S3.

On the other hand, in the present embodiment, in the case of embossed paper, the control unit 50 outputs the image by setting the penetration amount H to 3.0 to 3.8 mm and the peripheral speed difference to +0.05 to +0.15%. (S4, S5), and in S6 it is determined whether all images of the job have been output. If the control unit 50 determines that the job has ended in S6, it retracts the pressing member 28 to the home position (HP position) (S7) and ends the job. Further, if the control unit 50 determines that the process has not ended in S6, the process returns to S4, skips the determination of the type of recording material 7, and determines the intrusion amount H and the circumference regardless of the type of recording material 7. Maintain speed difference.

As in Example 1, the embossed paper in this example was made of special paper Lezac 66 with a basis weight of 151 g/m ² . Further, in this example, Canon GF-C081 was used as plain paper other than embossed paper.

The control of this embodiment also provides the same effect as that described in the first embodiment with reference to FIG. However, in this embodiment, when embossed paper is selected during a job, the intrusion amount H is 3.0 to 3.8 mm and the peripheral speed difference is +0.05 to +0.15% until the job is finished. continues to be output (S4, S5, S6). Therefore, the time period during which the amount of penetration H of the pressing member 28 is increased may be longer than in the first embodiment. As a result, creep deformation of the tip of the pressing member 28 may be accelerated. However, in this embodiment as well, the amount of penetration H is increased only when a recording material 7 that is used relatively infrequently, such as embossed paper, is selected. Therefore, most jobs involve a loop of S3, S8, S9, and S10, and the creep deformation of the tip of the pressing member 28 can also be suppressed in this embodiment.

In other words, in the first embodiment, as shown in FIG. 7, during a job in which plain paper and embossed paper are mixed, the type of recording material 7 is always identified for each sheet, and the intrusion amount H and peripheral speed difference are calculated. Set (S3→...S6→S3→...). In contrast, in this embodiment, as shown in FIG. 8, embossed paper is selected during a job, and after setting the intrusion amount H and circumferential speed difference for the embossed paper (S3, S4, S5), The type of the remaining recording material 7 is not identified. Then, until it is determined that the job is finished and the intrusion amount is set to the HP position (S7), the remaining images of the job are continued to be output with the same intrusion amount H and the peripheral speed difference. If embossed paper is not selected even once during the job, the process is repeated (S3→S8→S9→S10→S3→...). In this embodiment, since the time period during which the amount of penetration H of the pressing member 28 is increased may be longer than that in the first embodiment, creep deformation of the tip of the pressing member 28 may be accelerated. However, in this embodiment, it is possible to reduce time loss due to changes in the amount of penetration and peripheral speed difference during a job. Therefore, the control according to this embodiment is effective when prioritizing productivity until the end of one job. In addition, since the penetration amount H is increased only in the case of a recording material S that is used relatively infrequently, such as embossed paper, most jobs involve a loop of S3, S8, S9, and S10, and even in this embodiment. Creep deformation of the tip of the pressing member 28 is suppressed. Note that the control of the first embodiment and the control of the present embodiment may be configured such that the operator can arbitrarily select and set them, for example, as an image quality priority mode and a productivity priority mode, respectively, from the operation unit 70 or an external device. good.

As described above, in this embodiment, the control unit 50 controls the position of the pressing member 28 by the moving mechanism 62 when transferring the toner image onto the recording material 7, based on the type of the recording material 7 to which the toner image is transferred. During continuous image formation in which toner images are transferred to a plurality of recording materials 7, the position of the pressing member 28 is set from the first position to the first position based on the type of recording material 7 to which the toner image is transferred. When changing to the second position where the pressing amount of the pressing member 28 against the first belt 6 is larger than that of the first position, the setting of the position of the pressing member 28 when transferring the toner image to the recording material 7 in the subsequent continuous image formation is as follows. , the recording material 7 is controlled to be maintained at the second position regardless of the type thereof.

As explained above, according to this embodiment, it is possible to obtain the same effects as in the first embodiment while ensuring productivity by reducing time loss due to changes in the penetration amount and circumferential speed difference during a job. can. As described above, according to this embodiment as well, it is possible to appropriately suppress the progress of creep deformation at the tip of the pressing member 28 while reducing shock image disturbance when the pressing member 28 is pushed further.

[others]
Although the present invention has been described above with reference to specific examples, the present invention is not limited to the above-mentioned examples.

In the embodiments described above, the information regarding the recording material is obtained from the job information input from the operation unit or external device, but the present invention is not limited to this embodiment. For example, it is also possible to provide a detection means for detecting the thickness and surface properties of the recording material in the image forming apparatus, and perform control based on information about the thickness and surface properties of the recording material detected by the detection means. For example, a known media sensor using an ultrasonic wave or an optical sensor can be used. Note that the index value regarding the surface properties of the recording material is not limited to a value converted to a value according to a predetermined standard such as Bekk smoothness, but has a correlation with the surface smoothness and surface roughness of the recording material. Any value is fine.

Furthermore, as in the above-described embodiment, when information regarding the recording material is input from the operation unit or an external device, the information regarding the recording material is input directly from the operation unit (including selecting from multiple options). It is not limited to this. For example, when a predetermined recording material cassette is selected from a plurality of recording material cassettes, information regarding the recording material stored in the recording material cassette, which is associated with the recording material cassette and stored in the storage section in advance, is may be obtained.

Furthermore, as described above, job information such as information regarding recording materials is not limited to being input from the operation unit of the image forming apparatus, but from an external device communicably connected to the image forming apparatus. May be entered. In this case, the input/output section described above functions as an input section that inputs information to the control section.

Further, in the above-described embodiments, the pressing member was described as being made of a flexible planar sheet material, but the present invention is not limited to such a structure. The pressing member may include, for example, a contact member that contacts the intermediate transfer belt upstream of the secondary transfer section and an elastic member such as a spring, and may be configured to elastically urge the intermediate transfer belt. For example, the intermediate transfer belt may be elastically biased by biasing a contact member made of a relatively rigid sheet metal with an elastic member (biasing member) made of a compression coil spring, a tension spring, or the like. . In this case, the moving mechanism can be configured to move a pressing member that includes a contact member and an elastic member (for example, move the elastic member). As the contact member, for example, a roller made of an elastic body such as sponge or rubber, or a roller made of a rigid body such as resin or metal may be used. However, since it is easy to arrange the pressing member sufficiently close to the secondary transfer section, it is preferable that the pressing member is made of a planar sheet material. Further, the pressing member may be made of a thin metal plate, but from the viewpoint of suppressing wear of the intermediate transfer belt and leakage of transfer current, it is preferable that the pressing member be made of a resin material.

Furthermore, in the above embodiment, when plain paper or the like is used, the amount of penetration (or amount of pressure) is reduced to press the belt. The amount of penetration may be set to 0 mm.

Furthermore, in the above embodiment, the setting of the penetration amount (or pressing amount) and peripheral speed difference was changed in two steps, but it may be changed in more steps depending on, for example, the depth of the unevenness of the embossed paper. It's okay. In this case, for example, the deeper the unevenness, the larger the pressing amount and the smaller the circumferential speed difference.

Furthermore, in the above embodiment, the case where the belt-shaped image bearing member is an intermediate transfer belt has been described, but the image bearing member may be an endless belt that conveys the toner image carried at the image forming position. If there is, the present invention can be applied. Examples of such a belt-shaped image carrier include, in addition to the intermediate transfer belt in the above embodiment, a photoreceptor belt and an electrostatic recording dielectric belt.

Further, the present invention can be implemented in other embodiments in which part or all of the configurations of the above-described embodiments are replaced with alternative configurations. Therefore, as long as the image forming apparatus uses a belt-like image carrier, it can be implemented without distinction between tandem type/single drum type, charging method, electrostatic image forming method, developing method, transfer method, and fixing method. In the above-described embodiments, the main parts related to toner image formation/transfer have been mainly explained, but the present invention can be applied to printers, various printing machines, copying machines, FAX machines by adding necessary equipment, equipment, and housing structure. It can be implemented in various applications such as , multifunction devices, etc.

1 Photosensitive drum 6 Intermediate transfer belt 7 Recording material 8 Registration roller pair 9 Secondary transfer outer roller 15 Secondary transfer belt 25 Tension roller of secondary transfer belt 27 Drive roller of secondary transfer belt 28 Pressing member (backup sheet)

Claims (9)

a rotatable endless first belt carrying a toner image;
a plurality of first belt tensioning rollers that tension the first belt, including an inner roller and an upstream roller disposed adjacent to the inner roller upstream of the inner roller with respect to the rotational direction of the first belt; a plurality of first belt tension rollers including rollers;
a rotatable endless second belt that forms a transfer portion that contacts the outer peripheral surface of the first belt and transfers the toner image from the first belt to the recording material;
a plurality of second belt tensioning rollers that stretch the second belt, the outer roller contacting the inner roller via the first belt and the second belt to form the transfer portion; a tension roller that applies tension to the second belt; and a plurality of driving rollers that are arranged upstream of the outer roller and downstream of the tension roller with respect to the rotational direction of the second belt and transmit driving force to the second belt. a second belt tension roller;
a first drive unit that drives the first belt;
a second drive unit that drives the second belt;
contactable with the inner circumferential surface of the first belt upstream of the inner roller and downstream of the upstream roller with respect to the rotation direction of the first belt, and moving the first belt from the inner circumferential side to the outer circumferential side. a pressing member capable of pressing toward the
a moving mechanism capable of changing the position of the pressing member to change the amount of pressure the pressing member presses against the first belt;
Controlling at least one of the first drive section and the second drive section so that the circumferential speed of the second belt is faster than the circumferential speed of the first belt when transferring the toner image onto the recording material. At the same time, based on the setting of the position of the pressing member by the moving mechanism when transferring the toner image onto the recording material, the peripheral speed of the first belt and the second belt when transferring the toner image onto the recording material are determined. a control unit that controls at least one of the first drive unit and the second drive unit to change a circumferential speed difference between the circumferential speed of the
An image forming apparatus comprising: The control unit sets the position of the pressing member when transferring the toner image onto the recording material to a second position where the pressing amount is larger than the first position. The image forming apparatus according to claim 1, wherein at least one of the first drive section and the second drive section is controlled so that the circumferential speed difference is smaller. The first drive unit and the second drive unit are arranged so that the circumferential speed of the first belt and the circumferential speed of the second belt are not reversed in magnitude when transferring the toner image onto the recording material. The image forming apparatus according to claim 1, wherein the first belt and the second belt are respectively driven. a conveyance member that sandwiches the recording material and conveys it to the transfer section;
a switching unit that switches between a first state in which the conveyance member can sandwich a recording material and a second state in which it cannot sandwich a recording material;
has
The image forming apparatus according to any one of claims 1 to 3, wherein the switching unit sets the conveyance member to the second state when the recording material passes through the transfer unit. In a cross section substantially perpendicular to the rotational axis of the inner roller, a common tangent between the inner roller on the side in contact with the first belt and the upstream roller is a common tangent L1, and the common tangent L1 passes through the rotation center of the inner roller. The inner roller center line L2 is a straight line perpendicular to the inner roller center line L2, and the outer roller center line L3 is a straight line passing through the rotation center of the outer roller and orthogonal to the common tangent line L1. 4. The image forming apparatus according to claim 1, wherein the outer roller center line L3 is located downstream of the outer roller center line L2. The control unit is configured such that the position of the pressing member when waiting for an instruction to start image formation is a position where the pressing amount is smaller than the position of the pressing member when transferring the toner image onto the recording material. 4. The image forming apparatus according to claim 1, further comprising controlling the moving mechanism. The control unit sets the position of the pressing member by the moving mechanism when transferring the toner image to the recording material, based on the type of recording material to which the toner image is transferred, and sets the position of the pressing member by the moving mechanism when transferring the toner image to the recording material, and sets the position of the pressing member on the first type of recording material. The pressing member is pressed so that the amount of pressure is greater when transferring the toner image to the second type of recording material, which has a larger surface irregularity than the first type. The image forming apparatus according to any one of claims 1 to 3, wherein a position is set. The control unit sets the position of the pressing member by the moving mechanism when transferring the toner image to the recording material, based on the type of recording material to which the toner image is transferred, and transfers the toner image to a plurality of recording materials. During continuous image formation to transfer the toner image, the position of the pressing member is set based on the type of recording material to which the toner image is transferred, from the first position to the second position where the pressing amount is larger than the first position. In the case where the pressing member is changed to the second position, the position of the pressing member when transferring the toner image to the recording material in the continuous image formation is controlled to be maintained at the second position regardless of the type of the recording material. The image forming apparatus according to any one of claims 1 to 3, characterized in that: The driving roller according to any one of claims 1 to 3, wherein the driving roller is disposed upstream of the outer roller and adjacent to the outer roller with respect to the rotational direction of the second belt. Image forming device.

Images