JP7414548B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine using an electrophotographic method or an electrostatic recording method.

2. Description of the Related Art Conventionally, some image forming apparatuses using an electrophotographic method or the like include an endless belt (hereinafter also simply referred to as a "belt") as an image carrier that carries a toner image. Examples of such a belt include, for example, a second belt that transports a toner image that has been primarily transferred from a photoreceptor as a first image carrier to a sheet-like recording material such as paper. There is an intermediate transfer belt as an image carrier. Hereinafter, an image forming apparatus that employs an intermediate transfer method having an intermediate transfer belt will be mainly described as an example.

In an intermediate transfer type image forming apparatus, a toner image formed on a photoreceptor or the like in an image forming section is primarily transferred onto an intermediate transfer belt in a primary transfer section. Further, the toner image that has been primarily transferred to the intermediate transfer belt is secondarily transferred to a recording material at a secondary transfer section. Intermediate transfer is performed by an internal material (secondary transfer internal material) provided on the inner peripheral surface of the secondary transfer belt and an external material (secondary transfer external material) provided on the external peripheral surface of the secondary transfer belt. A secondary transfer nip is formed as a secondary transfer portion, which is a contact portion between the belt and the external material. As the internal member, an inner roller, which is one of a plurality of tension rollers that tension the intermediate transfer belt, is used. As the outer member, an outer roller is often used, which is disposed at a position facing the inner roller with the intermediate transfer belt interposed therebetween. Then, for example, by applying a secondary transfer voltage having a polarity opposite to the charging polarity of the toner to the outer roller, the toner image on the intermediate transfer belt is secondarily transferred onto the recording material in the secondary transfer nip. Generally, a conveyance guide for guiding the recording material to the secondary transfer nip is provided upstream of the secondary transfer nip in the conveyance direction of the recording material.

Here, depending on the shape of the secondary transfer nip, the behavior of the recording material in the upstream vicinity and downstream vicinity of the secondary transfer nip changes with respect to the conveyance direction of the recording material. In addition, in recent years, there has been a demand for support for various recording materials that have different stiffness due to differences in thickness and surface properties. The behavior of the recording material near the downstream changes. For example, when the recording material is "thin paper", which is an example of a recording material with low rigidity, the intermediate transfer belt and the recording material may stick together near the downstream of the secondary transfer nip in the conveyance direction of the recording material, causing the intermediate transfer A jam (paper jam) may occur due to poor separation of the recording material from the belt. This phenomenon becomes noticeable when the stiffness of the recording material is low because the recording material tends to stick to the intermediate transfer belt due to its weak stiffness. On the other hand, for example, when the recording material is "cardboard" which is an example of a recording material with high rigidity, when the rear end of the recording material in the transport direction passes through the transport guide, the rear end of the recording material in the transport direction may collide with the intermediate transfer belt. Then, the posture of the intermediate transfer belt near the upstream side of the secondary transfer nip with respect to the recording material conveyance direction is disturbed, resulting in image defects (stripes extending in a direction substantially perpendicular to the recording material conveyance direction) at the rear end of the recording material conveyance direction. image disturbances, etc.) may occur. This phenomenon becomes noticeable when the recording material has a high stiffness because the stiffness of the recording material makes it easier for the rear end of the recording material in the conveying direction to collide with the intermediate transfer belt with a strong force. To address this problem, a configuration has been proposed in which the width of the secondary transfer nip in the rotational direction of the intermediate transfer belt is changed depending on the type of recording material (Patent Document 1).

In addition, there are other issues as follows. In other words, the posture of the recording material conveyed from the conveyance guide to the secondary transfer nip changes depending on the rigidity of the recording material. For example, when the recording material is "cardboard", a gap is likely to occur between the intermediate transfer belt and the recording material near the entrance of the secondary transfer nip due to the high rigidity of the recording material. Then, under the influence of the transfer electric field, discharge occurs in the gap, and the toner image may scatter, resulting in image defects ("splatters"). To address this problem, a configuration has been proposed in which a pressing member is provided that contacts the inner peripheral surface of the intermediate transfer belt near the entrance of the secondary transfer nip to reduce the gap near the entrance of the secondary transfer nip. (Patent Document 2).

Japanese Patent Application Publication No. 2014-134718 Japanese Patent Application Publication No. 2002-82543

As mentioned above, in order to improve the separation of the recording material from the intermediate transfer belt and to suppress image defects caused by collision of the trailing edge of the recording material in the transport direction with the intermediate transfer belt, it is necessary to It is effective to change the width of the secondary transfer nip (the position of the secondary transfer nip) with respect to the rotational direction of the intermediate transfer belt. The width of the secondary transfer nip is changed by moving the inner roller or the outer roller and changing the relative position between the inner roller and the outer roller in the circumferential direction of the inner roller, thereby changing the position of the secondary transfer nip. This can be done by

On the other hand, in order to suppress image defects ("splatters") caused by discharge near the entrance of the secondary transfer nip, it is effective to provide a pressing member that contacts the inner peripheral surface of the intermediate transfer belt near the entrance of the secondary transfer nip. It is.

However, as a result of study by the present inventors, it has been found that when attempting to improve the separability, suppress image defects caused by the collision, and suppress image defects ("splatters") caused by the discharge by employing both of the above measures, , the following issues were found. In other words, for example, when the recording material is switched from "thick paper" to "thin paper", the intermediate transfer belt on the upstream side of the secondary transfer nip with respect to the conveyance direction of the recording material changes due to the change in the relative position of the inner roller and the outer roller. The contact area with the recording material becomes larger. This may cause image defects, so-called "roughness", in which the toner image is mechanically disturbed due to friction between the toner image on the intermediate transfer belt and the recording material.

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 exists regarding the toner image transfer section.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image forming apparatus that can improve transferability to each of a plurality of types of recording materials having different stiffnesses.

The above object is achieved by an image forming apparatus according to the present invention. To summarize, the present invention provides a rotatable endless belt for conveying a toner image, a plurality of tension rollers for tensioning the belt, and an inner roller and a plurality of tension rollers for stretching the belt. an upstream roller disposed adjacent to the inner roller upstream from the inner roller; an outer roller forming a transfer portion that transfers a toner image onto a recording material; and an outer roller that is capable of contacting the inner circumferential surface of the belt upstream of the inner roller and downstream of the upstream roller with respect to the rotational direction of the belt; A pressing member capable of pressing the belt from the inner circumferential surface side to the outer circumferential surface side, and the position of at least one of the inner roller or the outer roller is changed so that the inner roller and the outer roller with respect to the circumferential direction of the inner roller are changed. a first position changing mechanism that changes the position of the transfer unit by changing the relative position of the pressing member; a second position changing mechanism that changes the position of the pressing member; a control unit that controls the position change mechanism of No. 2, and in a cross section substantially orthogonal to the rotational axis direction of the inner roller, a common control unit of the inner roller on the side around which the belt is wound and the upstream roller; A tangent line is a reference line L1, a straight line passing through the rotation center of the inner roller and substantially orthogonal to the reference line L1 is an inner roller center line L2, and a straight line passing through the rotation center of the outer roller and substantially orthogonal to the reference line L1 is an outer roller. center line L3, the distance between the inner roller center line L2 and the outer roller center line L3 is set by an offset amount If the offset amount X is a first offset amount When the amount X is a second offset amount X2 (>0) that is larger than the first offset amount X1, the second position changing mechanism moves the pressing member away from the inner peripheral surface of the belt. This is an image forming apparatus characterized by controlling.

According to the present invention, it is possible to improve transferability to each of a plurality of types of recording materials having different stiffnesses.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus. It is a schematic side view which shows an offset mechanism and a press mechanism. It is a schematic side view which shows an offset mechanism and a press mechanism. FIG. 3 is a schematic side view showing a mechanism for moving the outer rollers toward and away from each other. FIG. 2 is a schematic block diagram showing a control mode of main parts of the image forming apparatus. FIG. 2 is a flowchart diagram showing an outline of a job operation procedure. FIG. 7 is a schematic side view showing another example of an offset mechanism and a pressing mechanism. It is a schematic side view which shows another example of an external material. FIG. 3 is a schematic diagram for explaining the behavior of a recording material near a secondary transfer nip. FIG. 3 is a schematic cross-sectional view for explaining an offset amount. FIG. 3 is a schematic cross-sectional view for explaining the amount of penetration.

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 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem-type multifunction machine (having the functions of a copying machine, a printer, and a facsimile machine) that employs an intermediate transfer method. The image forming apparatus 100 can, for example, form a full-color image on a sheet-like recording material (transfer material, sheet material) S such as paper using an electrophotographic method in response to an image signal transmitted from an external device. can.

The image forming apparatus 100 includes four image forming sections 10Y, 10M, which form yellow (Y), magenta (M), cyan (C), and black (K) images, respectively, as a plurality of image forming sections (stations). It has 10C and 10K. These image forming units 10Y, 10M, 10C, and 10K are arranged in series along the moving direction of a substantially horizontally arranged image transfer surface of an intermediate transfer belt 31, which will be described later. For elements with the same or corresponding functions or configurations in each image forming unit 10Y, 10M, 10C, 10K, the suffix Y, M, C, K of the code indicating that the element is for one of the colors is omitted. This may be explained comprehensively. In this embodiment, the image forming section 10 includes photosensitive drums 11 (11Y, 11M, 11C, 11K), chargers 12 (12Y, 12M, 12C, 12K), and exposure devices 13 (13Y, 13M, 13C, 13K), which will be described later. ), developing device 14 (14Y, 14M, 14C, 14K), primary transfer roller 35 (35Y, 35M, 35C, 35K), cleaning device 15 (15Y, 15M, 15C, 15K), etc. .

The photosensitive drum 11, which is a rotatable drum-shaped (cylindrical) photosensitive member (electrophotographic photosensitive member) serving as a first image carrier that carries a toner image, is rotated in the direction of arrow R1 (counterclockwise) in the figure. Rotationally driven. The surface of the rotating photosensitive drum 11 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charger 12 as a charging means. The charged surface of the photosensitive drum 11 is scanned and exposed according to an image signal by an exposure device 13 serving as an exposure means (electrostatic image forming means), and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 11. It is formed. In this embodiment, the exposure device 13 is constituted by a laser scanner device that irradiates the photosensitive drum 11 with a laser beam modulated according to an image signal. The electrostatic image formed on the photosensitive drum 11 is developed (visualized) by supplying toner as a developer by a developing device 14 serving as a developing means, and a toner image (developer image) is formed on the photosensitive drum 11. be done. In this embodiment, the exposed area (image area) on the photosensitive drum 11, whose absolute value has decreased by being exposed to light after being uniformly charged, has the same polarity as the charged polarity of the photosensitive drum 11 (in this embodiment). In this example, negatively charged toner is attached (reversal development).

An intermediate transfer belt, which is a rotatable intermediate transfer body composed of an endless belt, serves as a second image carrier that carries a toner image and faces the four photosensitive drums 11Y, 11M, 11C, and 11K. 31 are arranged. The intermediate transfer belt 31 is wound around a plurality of drive rollers 33 as tension rollers (support rollers), a tension roller 34, a pre-secondary transfer roller 37, and an inner roller (secondary transfer opposing roller, inner material) 32. It is stretched with a predetermined tension. Drive roller 33 transmits driving force to intermediate transfer belt 31 . The tension roller 34 applies a predetermined tension to the intermediate transfer belt 31. The pre-secondary transfer roller 37 forms a surface of the intermediate transfer belt 31 near the upstream side of the secondary transfer nip N2 (described later) with respect to the rotational direction (running direction) of the intermediate transfer belt 31. The inner roller 32 functions as a member (counter electrode) facing the outer roller 41 (described later). The intermediate transfer belt 31 rotates (circularly moves) in the direction of arrow R2 (clockwise) in the figure as the drive roller 33 is rotationally driven. In this embodiment, the intermediate transfer belt 31 is driven to rotate at a circumferential speed of 400 mm/sec, for example. Among the plurality of support rollers, the support rollers other than the drive roller 33 are driven to rotate as the intermediate transfer belt 31 rotates. On the inner peripheral surface side of the intermediate transfer belt 31, primary transfer rollers 35Y, 35M, which are roller-shaped primary transfer members serving as primary transfer means, are provided corresponding to the respective photosensitive drums 11Y, 11M, 11C, and 11K. 35C and 35K are placed. The primary transfer roller 35 presses the intermediate transfer belt 31 toward the photosensitive drum 11 to form a primary transfer nip N1 as a primary transfer portion, which is a contact portion between the photosensitive drum 11 and the intermediate transfer belt 31. . The toner image formed on the photosensitive drum 11 as described above is primarily transferred onto the rotating intermediate transfer belt 31 by the action of the primary transfer roller 35 in the primary transfer nip N1. During the primary transfer, a primary transfer power source (not shown) applies a primary DC voltage to the primary transfer roller 35, which is a DC voltage of opposite polarity to the normal charging polarity of the toner (the charging polarity of the toner during development). A transfer voltage is applied. For example, when forming a full-color image, toner images of yellow, magenta, cyan, and black formed on each photosensitive drum 11 are sequentially superimposed on the same image forming area on the intermediate transfer belt 31. Next to be transferred. In this embodiment, the primary transfer nip N1 is an image forming position where a toner image is formed on the intermediate transfer belt 31. The intermediate transfer belt 31 is an example of a rotatable endless belt that conveys the toner image carried at the image forming position.

On the outer peripheral surface side of the intermediate transfer belt 31, an outer roller (secondary transfer roller, external member) 41, which is a roller-shaped secondary transfer member serving as a secondary transfer means, is arranged at a position facing the inner roller 32. ing. The outer roller 41 is pressed toward the inner roller 32 via the intermediate transfer belt 31, and forms a secondary transfer nip N2 as a secondary transfer portion, which is a contact portion between the intermediate transfer belt 31 and the outer roller 41. The toner image formed on the intermediate transfer belt 31 as described above is transferred to the recording material being conveyed while being sandwiched between the intermediate transfer belt 31 and the outer roller 41 by the action of the outer roller 41 in the secondary transfer nip N2. Secondary transfer is performed on S. In this embodiment, during secondary transfer, a secondary transfer voltage, which is a DC voltage with a polarity opposite to the normal charging polarity of the toner, is applied to the outer roller 41 by a secondary transfer power source (not shown). . In this embodiment, the inner roller 32 is electrically grounded (connected to the ground). The inner roller 32 is used as a secondary transfer member to which a secondary transfer voltage having the same polarity as the normal charging polarity of the toner is applied, and the outer roller 41 is used as a counter electrode and is electrically grounded. Good too.

The recording material S is conveyed to the secondary transfer nip N2 in synchronization with the toner image on the intermediate transfer belt 31. That is, the recording material S stored in the recording material cassettes 61, 62, and 63 is sent out by rotation of any one of the feeding rollers 71, 72, and 73. The recording material S is conveyed through the feeding conveyance path 81 to a registration roller (registration roller pair) 74, which is a conveyance member serving as a conveyance means, and is temporarily stopped. The recording material S is produced by rotationally driving the registration rollers 74 so that the toner image on the intermediate transfer belt 31 and the desired image forming area on the recording material S coincide with each other in the secondary transfer nip N2. It is fed into the secondary transfer nip N2. With respect to the conveyance direction of the recording material S, a conveyance guide 83 that guides the recording material S to the secondary transfer nip N2 is provided downstream of the registration rollers 74 and upstream of the secondary transfer nip N2. The conveyance guide 83 includes a first guide member 83a that can make contact with the front surface of the recording material S (the surface on which the toner image is transferred immediately after passing through the conveyance guide 83), and a back surface of the recording material S (the surface on which the toner image is transferred immediately after passing through the conveyance guide 83). and a second guide member 83b that can come into contact with the opposite surface). The first guide member 83a and the second guide member 83b are arranged to face each other, and the recording material S passes between these two members. The first guide member 83a restricts the movement of the recording material S in the direction approaching the intermediate transfer belt 31. The second guide member 83b restricts the movement of the recording material S in the direction away from the intermediate transfer belt 31.

The recording material S onto which the toner image has been transferred is transported by a transport belt 42 to a fixing device 50 as a fixing means. The fixing device 50 fixes (melts, fixes) the toner image on the surface of the recording material S by heating and pressurizing the recording material S carrying the unfixed toner image. Thereafter, the recording material S with the toner image fixed thereon is discharged (output) through the discharge conveyance path 82 to a discharge tray 64 provided outside the apparatus main body 100a of the image forming apparatus 100.

On the other hand, toner remaining on the photosensitive drum 11 after the primary transfer (primary transfer residual toner) is removed from the photosensitive drum 11 and collected by a cleaning device 15 serving as a cleaning means. Further, toner remaining on the intermediate transfer belt 31 after the secondary transfer (secondary transfer residual toner) and deposits such as paper dust attached from the recording material S are removed from the intermediate transfer belt 31 by a belt cleaning device 36 serving as an intermediate transfer member cleaning means. It is removed from the transfer belt 31 and collected.

In this embodiment, the intermediate transfer belt 31 stretched around a plurality of tension rollers, each primary transfer roller 35, a belt cleaning device 36, a frame supporting these, etc. are used as a belt conveyance device. An intermediate transfer belt unit 30 is configured. The intermediate transfer belt unit 30 is removable from the apparatus main body 100a for maintenance or replacement.

Here, as the intermediate transfer belt 31, one made of a resin material having a single layer or multilayer structure can be used. Further, as the intermediate transfer belt 31, it is preferable to use a belt having a thickness of 40 μm or more, a Young's modulus of 1.0 GPa or more, and a surface resistivity of 1.0×10 ⁹ to 5.0×10 ¹³ Ω/□. Can be done.

Further, in this embodiment, the inner roller 32 is configured by providing an elastic layer (rubber layer) made of a rubber material as an elastic material on the outer periphery of a metal core (base material). This elastic layer can be formed of, for example, EPDM rubber (which may contain a conductive agent). In this embodiment, the inner roller 32 is formed to have an outer diameter of 20 mm and an elastic layer thickness of 0.5 mm. Further, in this embodiment, the hardness of the elastic layer of the inner roller 32 is set to, for example, 70° (JIS-A). Note that the inner roller 32 may be a metal roller made of a metal material such as SUM or SUS. Note that the pre-secondary transfer roller 37 can have the same configuration as the inner roller 32.

In addition, in this embodiment, the outer roller 41 has a conductive elastic layer (solid rubber layer) formed of a conductive rubber material as a conductive elastic material on the outer periphery of a metal core (base material). Alternatively, a sponge layer (foamed elastic material layer) may be provided. This elastic layer can be formed of, for example, NBR rubber or EPDM rubber containing a conductive agent such as a metal complex or carbon. In this embodiment, the outer roller 41 is formed such that the core metal has an outer diameter of 12 mm, the elastic layer has a thickness of 6 mm, and the outer roller 41 has an outer diameter of 24 mm. Further, in this embodiment, the hardness of the elastic layer of the outer roller 41 is set to, for example, 28° (Asker C). Further, in this embodiment, the outer roller 41 is held at a predetermined level with respect to the inner roller 32 with the intermediate transfer belt 31 in between by a pressing spring 44 (FIG. 2) which is a biasing member (elastic member) serving as a biasing means. They are urged into contact by pressure.

Note that in this embodiment, the respective rotation axis directions of the tension roller of the intermediate transfer belt 31 including the inner roller 32 and the outer roller 41 are substantially parallel to each other. The support structure of the inner roller 32 and outer roller 41 will be further explained later.

2. Offset FIG. 9A is a schematic cross-sectional view (a cross-section substantially perpendicular to the rotational axis direction of the inner roller 32) for explaining the behavior of the recording material S in the vicinity of the secondary transfer nip N2. Note that in FIG. 9A, elements having the same or corresponding functions or configurations as those of the image forming apparatus 100 of this embodiment are given the same reference numerals.

As mentioned above, depending on the shape of the secondary transfer nip N2 (the position of the secondary transfer nip N2) and the rigidity of the recording material S, recording may occur near the upstream or downstream of the secondary transfer nip N2 in the conveying direction of the recording material S. The behavior of material S changes. For example, if the recording material S is "thin paper", which is an example of a recording material S with low rigidity, a jam may occur due to poor separation of the recording material S from the intermediate transfer belt 31. . This phenomenon becomes noticeable when the stiffness of the recording material S is small because the stiffness of the recording material S is weak and the recording material S tends to stick to the intermediate transfer belt 31.

That is, in the cross section shown in FIG. 9(a), a tension line T is a line indicating the tension surface of the intermediate transfer belt 31 formed by being stretched between the inner roller 32 and the pre-secondary transfer roller 37. The pre-secondary transfer roller 37 is an example of an upstream roller that is disposed upstream of the inner roller 32 in the rotational direction of the intermediate transfer belt 31 and adjacent to the inner roller 32 among the plurality of tension rollers. Further, in the same cross section, a straight line passing through the rotation center of the inner roller 32 and the rotation center of the outer roller 41 is defined as the nip center line Lc. Further, in the same cross section, a line substantially orthogonal to the nip center line Lc is defined as a nip line Ln. Note that FIG. 9A shows that the rotation center of the outer roller 41 is offset to the upstream side in the rotation direction of the intermediate transfer belt 31 than the rotation center of the inner roller 32 in the direction along the tension wire T. Indicates the condition.

At this time, when the recording material S is held between the inner roller 32 and the outer roller 41 in the secondary transfer nip N2, it tends to maintain its posture substantially along the nip line Ln. Therefore, in general, when the rotation center of the inner roller 32 and the rotation center of the outer roller 41 are close to each other in the direction along the tension wire T, the recording material S is ejected as shown by the broken line A in FIG. 9(a). The angle θ becomes smaller. In other words, the leading edge of the recording material S in the conveyance direction is in a posture such that it is discharged near the intermediate transfer belt 31 when it is discharged from the secondary transfer nip N2. This makes it easier for the recording material S to stick to the intermediate transfer belt 31. On the other hand, generally speaking, the more the rotation center of the outer roller 41 is located upstream in the rotation direction of the intermediate transfer belt 31 than the rotation center of the inner roller 32 in the direction along the tension line T, the more the a) As shown by the solid line in the middle, the discharge angle θ of the recording material S increases. That is, the leading edge of the recording material S in the conveyance direction is in a posture such that it is discharged in a direction away from the intermediate transfer belt 31 when it is discharged from the secondary transfer nip N2. This makes it difficult for the recording material S to stick to the intermediate transfer belt 31.

On the other hand, as described above, if the recording material S is, for example, "cardboard" which is an example of a recording material S with high rigidity, when the rear end of the recording material S in the transport direction passes through the transport guide 83, , the rear end of the recording material S in the conveyance direction may collide with the intermediate transfer belt. As a result, image defects may occur at the rear end of the recording material S in the conveyance direction. This phenomenon becomes noticeable when the stiffness of the recording material S is large, because the stiffness of the recording material S makes the rear end of the recording material S in the conveying direction more likely to collide with the intermediate transfer belt 31 with strong force. .

That is, as described above, in the cross section shown in FIG. 9(a), the recording material S is approximately aligned with the nip line Ln when it is held between the inner roller 32 and the outer roller 41 in the secondary transfer nip N2. There is a tendency to try to maintain a consistent posture. Therefore, in general, the more the rotation center of the outer roller 41 is disposed on the upstream side in the rotational direction of the intermediate transfer belt 31 than the rotation center of the inner roller 32 in the direction along the tension line T, the more the nip line Ln is It will be shaped like a T. As a result, when the rear end of the recording material S in the transport direction passes through the transport guide 83, as shown by the broken line B in FIG. 31, and image defects are likely to occur at the rear end of the recording material S in the conveyance direction. On the other hand, in general, if the rotation center of the inner roller 32 and the rotation center of the outer roller 41 are made close to each other in the direction along the tension wire T, when the rear end of the recording material S in the conveyance direction comes out of the conveyance guide 83, Collision with the intermediate transfer belt 31 is suppressed. As a result, image defects at the rear end of the recording material S in the transport direction are less likely to occur.

As a countermeasure to this problem, it is effective to change the relative position of the inner roller 32 and the outer roller 41 in the circumferential direction of the inner roller 32 (rotation direction of the intermediate transfer belt 31) depending on the type of recording material S. It is. FIG. 10 is a schematic cross-sectional view of the vicinity of the secondary transfer nip N2 for explaining the definition of the relative position between the inner roller 32 and the outer roller 41 (a cross section approximately perpendicular to the rotational axis direction of the inner roller 32). It is. Note that in FIG. 10, elements having the same or corresponding functions or configurations as those of the image forming apparatus 100 of this embodiment are given the same reference numerals.

In the cross section shown in FIG. 10, a common tangent between the inner roller 32 on the side around which the intermediate transfer belt 31 is wound and the pre-secondary transfer roller 37 is defined as a reference line L1. The reference line L1 corresponds to the tension line T when the intermediate transfer belt 31 is not extended to the outer peripheral surface side by a pressing member 39, which will be described later. Further, in the same cross section, a straight line passing through the center of rotation of the inner roller 32 and substantially perpendicular to the reference line L1 is defined as an inner roller center line L2. Further, in the same cross section, a straight line passing through the center of rotation of the outer roller 41 and substantially orthogonal to the reference line L1 is defined as an outer roller center line L3. At this time, the distance (vertical distance) between the inner roller center line L2 and the outer roller center line L3 is offset by an amount positive value when it is on the upstream side of The offset amount X can take a negative value, 0, or a positive value. By increasing the offset amount X, the width of the secondary transfer nip N2 with respect to the rotational direction of the intermediate transfer belt 31 becomes wider upstream in the rotational direction of the intermediate transfer belt 31. That is, the rotation of the intermediate transfer belt 31 in the contact area between the outer roller 41 and the intermediate transfer belt 31 is higher than the upstream end in the rotation direction of the intermediate transfer belt 31 in the contact area between the inner roller 32 and the intermediate transfer belt 31. The end on the upstream side of the direction is located further upstream. In this way, the position of at least one of the inner roller 32 or the outer roller 41 is changed, and the relative position of the inner roller 32 and the outer roller 41 is changed in the circumferential direction of the inner roller 32, thereby forming a secondary transfer nip (transfer Part) The position of N2 can be changed.

In FIG. 10, the outer roller 41 is shown virtually touching the reference line L1 (tension wire T) without being deformed. However, as described above, the outermost layer of the outer roller 41 is made of an elastic material such as rubber or sponge, and is actually pressed in the direction toward the inner roller 32 (in the direction of the white arrow in the figure) by the pressing spring 44. It's deformed. The outer roller 41 is arranged offset to the upstream side in the rotational direction of the intermediate transfer belt 31 with respect to the inner roller 32, and is pressed by a pressure spring 44 so as to sandwich the intermediate transfer belt 31 between the outer roller 41 and the inner roller 32. Then, a substantially S-shaped secondary transfer nip N2 is formed. The posture of the recording material S guided by the conveyance guide 83 is also determined according to the shape of the secondary transfer nip N2. The larger the offset amount X is, the more the recording material S is bent. Therefore, as described above, when the recording material S is "thin paper", for example, by increasing the offset amount X, the recording material S is separated from the intermediate transfer belt 31 after passing through the secondary transfer nip N2. can improve sex. However, if the offset amount X is large, as described above, if the recording material S is "thick paper", the recording material The rear end in the direction collides with the intermediate transfer belt 31. This becomes a factor that deteriorates the image quality at the rear end portion of the recording material S in the transport direction. Therefore, in this case, the offset amount X may be reduced.

3. Pressing Member FIG. 9(b) is a schematic cross-sectional view (a cross-section substantially orthogonal to the rotational axis direction of the inner roller 32) for explaining the conveying posture of the recording material S in the vicinity of the secondary transfer nip N2. . Note that in FIG. 9B, elements having the same or corresponding functions or configurations as those of the image forming apparatus 100 of this embodiment are given the same reference numerals. In addition, FIG.9(b) has shown the state where the rotation center of the inner roller 32 and the rotation center of the outer roller 41 are arrange|positioned at the substantially same position with respect to the direction along the tension wire T.

As described above, the posture of the recording material S conveyed from the conveyance guide 83 to the secondary transfer nip N2 changes depending on the rigidity of the recording material S. For example, when the recording material S is "cardboard", a gap G is likely to occur between the intermediate transfer belt 31 and the recording material S near the entrance of the secondary transfer nip N2, and "scattering" is likely to occur. .

That is, in FIG. 9B, the intermediate transfer belt 31 and the recording are performed along the moving direction of the intermediate transfer belt 31 near the entrance of the secondary transfer nip N2 (near the upstream of the inner roller 32 with respect to the rotational direction of the intermediate transfer belt 31). The distance in which the material S is in contact with the material S is defined as the contact distance D. More specifically, the contact distance D is defined as the contact start position between the inner roller 32 and the intermediate transfer belt 31 and the contact start position between the recording material S and the intermediate transfer belt 31 in the moving direction of the intermediate transfer belt 31. is the distance between. For example, when the recording material S is "cardboard", the recording material S has a high rigidity and is difficult to bend near the entrance of the secondary transfer nip N2, so that the contact distance D becomes small. Therefore, a gap G is generated between the intermediate transfer belt 31 and the recording material S, and discharge occurs in the gap G due to the influence of the transfer electric field, which may cause the toner image to scatter and cause image defects ("splatter"). .

As a countermeasure to this problem, it is possible to reduce the gap G near the entrance of the secondary transfer nip N2 by providing a pressing member that contacts the inner peripheral surface of the intermediate transfer belt 31 near the entrance of the secondary transfer nip N2. is valid.

FIG. 11 is a schematic cross-sectional view (a cross section substantially perpendicular to the rotational axis direction of the inner roller 32) for explaining the definition of the amount of penetration of the pressing member into the intermediate transfer belt 31. Note that in FIG. 11, elements having the same or corresponding functions or configurations as those of the image forming apparatus 100 of this embodiment are given the same reference numerals.

In the example shown in FIG. 11, the image forming apparatus 100 has a sheet-like sheet near the entrance of the secondary transfer nip N2 that presses the inner circumferential surface of the intermediate transfer belt 31 and causes the intermediate transfer belt 31 to protrude toward the outer circumferential surface. A pressing member (backup sheet) 39 is provided. The pressing member 39 is arranged to contact the inner circumferential surface of the intermediate transfer belt 31 upstream of the inner roller 32 and downstream of the pre-secondary transfer roller 37 with respect to the rotational direction of the intermediate transfer belt 31. . The pressing member 39 presses the intermediate transfer belt 31 from the inner peripheral surface side toward the outer peripheral surface side, and causes the intermediate transfer belt 31 to extend toward the outer peripheral surface side. That is, the pressing member 39 comes into contact with the intermediate transfer belt 31 with a predetermined amount of penetration into the intermediate transfer belt 31 . This intrusion amount is approximately the tension line T that indicates the tension surface of the intermediate transfer belt 31 formed by the pressing member 39 being stretched between the inner roller 32 or the outer roller 41 and the pre-secondary transfer roller 37. In contrast, this is the amount by which the intermediate transfer belt 31 is made to protrude outward. Note that the definition of the amount of intrusion Y (the amount of intrusion of the pressing member 39 into the intermediate transfer belt 31) differs depending on whether the offset amount X is positive or 0 or negative. FIG. 11A shows a case where the offset amount X is 0 or a negative value (particularly a negative value), and FIG. 11B shows a case where the offset amount X is a positive value.

First, a case where the offset amount X is 0 or a negative value will be described. As shown in FIG. 11(a), in a cross section substantially orthogonal to the rotational axis direction of the inner roller 32, a common tangent line between the inner roller 32 on the side around which the intermediate transfer belt 31 is wound and the pre-secondary transfer roller 37 is the reference line L1. Further, in the same cross section, a tangent to the intermediate transfer belt 31 that contacts the outer circumferential surface of the intermediate transfer belt 31 in a region where the pressing member 39 contacts the intermediate transfer belt 31, which is substantially parallel to the reference line L1, is defined as a pressing part tangent L4. . At this time, if the offset amount It is defined as a positive value when the tangent line L4 is closer to the outer peripheral surface of the intermediate transfer belt 31 than the reference line L1. The amount of intrusion Y can take a value of 0 or a positive value.

Next, a case where the offset amount X is a positive value will be explained. As shown in FIG. 11(b), in a cross section substantially orthogonal to the rotational axis direction of the inner roller 32, a common tangent line between the outer roller 41 on the side around which the intermediate transfer belt 31 is wound and the pre-secondary transfer roller 37 is the reference line L1'. In addition, in the same cross section, the tangent line of the intermediate transfer belt 31 that contacts the outer peripheral surface of the intermediate transfer belt 31 in the area where the pressing member 39 contacts the intermediate transfer belt 31, which is substantially parallel to the reference line L1', is the pressing part tangent line L4'. shall be. At this time, if the offset amount X is a positive value, the distance (vertical distance) between the reference line L1' and the pressing part tangent L4' is calculated as It is defined as a positive value when the pressing portion tangent L4' is closer to the outer peripheral surface of the intermediate transfer belt 31 than the reference line L1'. The amount of intrusion Y can take a value of 0 or a positive value.

As shown in FIGS. 11(a) and 11(b), by causing the intermediate transfer belt 31 to protrude toward the outer circumferential surface side by the pressing member 39, the contact distance D is increased, and the intermediate transfer belt 31 near the entrance of the secondary transfer nip N2 is The gap G between the transfer belt 31 and the recording material S can be reduced. Thereby, "scattering" can be suppressed.

4. Summary of the problem and the configuration of this embodiment While obtaining good conveyance of the recording material S near the secondary transfer nip N2 for a wide variety of recording materials S with different stiffness such as "thin paper" and "thick paper" In order to suppress image defects occurring near the secondary transfer nip N2 and form a good image, the offset amount X is changed depending on the type of recording material S, and the offset amount It is considered effective to provide a pressing member 39 that contacts the inner circumferential surface of the intermediate transfer belt 31.

However, as shown in FIG. 11(b), for example, when the recording material S is "thin paper", the offset amount If the contact distance D becomes too large, the toner image on the intermediate transfer belt 31 is mechanically disturbed due to friction between the toner image and the recording material S, resulting in an image defect called "roughness". There is.

Therefore, in this embodiment, when the image forming apparatus 100 changes the position of at least one of the inner roller 32 or the outer roller 41 to greatly change the offset amount X, the image forming apparatus 100 changes the position of the pressing member 39 to The structure is such that the amount of penetration Y is changed so that the amount Y becomes smaller. In particular, in this embodiment, the image forming apparatus 100 is configured to change the offset amount X by changing the position of the inner roller 32. Furthermore, in this embodiment, the image forming apparatus 100 is configured to synchronously change the offset amount shall be.

For example, when the recording material S is "thick paper", the inner roller 32 is arranged at the first inner roller position where the offset amount X is the first offset amount X1, and the intrusion amount Y is the first intrusion amount Y1. The pressing member 39 is arranged at the first pressing member position. For example, when the recording material S is "thin paper", the following procedure is performed. The inner roller 32 is arranged at a second inner roller position where the offset amount X is a second offset amount X2 larger than the first offset amount The pressing member 39 is disposed at a second pressing member position having an intrusion amount Y2 of 2. The first offset amount X1 may be a positive value, 0, or a negative value, and the second offset amount X2 is typically a positive value. Further, the first amount of intrusion Y1 may be a positive value, and the second amount of intrusion Y2 may be 0 or a positive value.

Note that changing the offset amount X and the intrusion amount Y in synchronization means the following. Typically, when forming an image on a certain recording material S, if the offset amount X is changed before the recording material S reaches the secondary transfer nip N2, the recording material This means that the amount of penetration Y is also changed before reaching N2. As another example, when performing a predetermined adjustment operation such as applying a secondary transfer voltage to control the secondary transfer voltage, if the offset amount X is changed before the start of the adjustment operation. This means that the amount of penetration Y is also changed before the start of the adjustment operation. Further, for example, when the recording material S is "thin paper" or "thick paper", more specifically, it means when "thin paper" or "thick paper" is passed through the secondary transfer nip N2, respectively.

5. Configuration related to secondary transfer The configuration related to secondary transfer in this embodiment will be explained in more detail. Here, for the sake of simplicity, an example will be described in which information on the basis weight of paper as the recording material S is used as information regarding the type of the recording material S, which is mainly related to the rigidity of the recording material S. As an example of the recording material S with low stiffness, "thin paper" is used, and as an example of the recording material S with high stiffness, "cardboard" is used. However, as will be described later, information regarding the type of recording material S that is related to the rigidity of recording material S is not limited to information about the basis weight of recording material S.

2 and 3 are diagrams showing the vicinity of the secondary transfer nip N2 in this embodiment, viewed from one end side of the rotational axis of the inner roller 32 (the front side of the paper in FIG. 1) and approximately parallel to the rotational axis. FIG. FIG. 2 is a diagram mainly for explaining the configuration and operation of the offset mechanism 1, which will be described later. For ease of understanding, some configurations related to the pressing mechanism 2, which will be described later, are shown with chain double-dashed lines. There is. Further, FIG. 3 is a diagram mainly for explaining the configuration and operation of the pressing mechanism 2, which will be described later. For ease of understanding, some configurations related to the offset mechanism 1, which will be described later, are shown with chain double-dashed lines. has been done. 2(a) and 3(a) show the state in the case of "thick paper", and FIG. 2(b) and FIG. 3(b) show the state in the case of "thin paper".

5-1. Offset Mechanism The offset mechanism 1 in this embodiment will be described with reference to FIGS. 2(a) and 2(b). In this embodiment, the image forming apparatus 100 includes an offset mechanism (offset amount changing means) as a first position changing mechanism that changes the offset amount X by changing the relative position of the inner roller 32 in the circumferential direction of the outer roller 41. ) has 1. 2(a) and 2(b) show the configuration of one end of the inner roller 32 in the direction of the rotational axis, but the configuration of the other end is similar (relative to the center of the inner roller 32 in the direction of the rotational axis). approximately symmetrical).

Both ends of the inner roller 32 in the rotation axis direction are rotatably supported by an inner roller holder 38 as a support member. The inner roller holder 38 is supported by the frame of the intermediate transfer belt unit 30 or the like so as to be rotatable about a first rotation shaft 38a. In this way, by rotating the inner roller holder 38 around the first rotation axis 38a and rotating the inner roller 32 around the first rotation axis 38a, the inner roller 32 is rotated relative to the outer roller 41. The offset amount X can be changed by changing the relative position of.

The inner roller holder 38 is configured to rotate by the action of the first cam 111 as an operating member. The first cam 111 is supported by the frame of the intermediate transfer belt unit 30 or the like so as to be rotatable about the cam rotation shaft 110. More specifically, in this embodiment, a cam rotation shaft 110 is rotatably supported by the frame of the intermediate transfer belt unit 30, and the first cam 111 is fixed to this cam rotation shaft 110. The first cam 111 is rotatable about the cam rotation shaft 110 by being driven by a position change motor 113 serving as a drive source. More specifically, in this embodiment, the first cam 111 fixed to the cam rotation shaft 110 is integrated with the cam rotation shaft 110 as the cam rotation shaft 110 rotates in response to the drive from the position change motor 113. rotate. Further, the first cam 111 is in contact with a first cam follower 38b provided on the inner roller holder 38. In addition, the inner roller holder 38 is configured with a tension spring or the like that is a biasing member (elastic member) as a biasing means so that the first cam follower 38b rotates in the direction in which it engages with the first cam 111. The first rotation spring 114 is biased by the first rotation spring 114. Note that the tension of the intermediate transfer belt 31 or the pressure of the outer roller 41 may provide sufficient moment to rotate the inner roller holder 38 in the direction in which the first cam follower 38b engages with the first cam 111. be. In this case, the first rotation spring 114 may not be provided.

As described above, in this embodiment, the offset mechanism 1 includes the inner roller holder 38, the first cam 111, the cam rotation shaft 110, the position change motor 113, the first rotation spring 114, etc. .

As shown in FIG. 2A, in the case of "cardboard", the first cam 111 is driven by the position change motor 113 and rotates clockwise. As a result, the inner roller holder 38 rotates counterclockwise about the first rotation shaft 38a, and the relative position of the inner roller 32 with respect to the outer roller 41 is determined. As a result, the inner roller 32 is placed at the first inner roller position where the offset amount X is the first offset amount X1, which is relatively small. As a result, as described above, it is possible to suppress the deterioration of the image quality at the rear end of the "cardboard" in the transport direction.

Further, as shown in FIG. 2(b), in the case of "thin paper", the first cam 111 is driven by the position change motor 113 and rotates counterclockwise. As a result, the inner roller holder 38 rotates clockwise about the first rotation shaft 38a, and the relative position of the inner roller 32 with respect to the outer roller 41 is determined. As a result, the inner roller 32 is placed at the second inner roller position where the offset amount X is the second offset amount X2, which is relatively large. As a result, as described above, the separation of the "thin paper" from the intermediate transfer belt 31 after passing through the secondary transfer nip N2 is improved.

5-2. Pressing Mechanism The pressing mechanism 2 in this embodiment will be described with reference to FIGS. 3(a) and 3(b). In this embodiment, the image forming apparatus 100 has a pressing mechanism (as a second position changing mechanism) that changes the position of the pressing member 39 and changes the amount of penetration Y in synchronization with the operation of the offset mechanism 1 described above. Intrusion amount changing means) 2 is included. In particular, in this embodiment, the pressing mechanism 2 changes the position of the pressing member 39 to change the amount of penetration Y in conjunction with the operation of the offset mechanism 1 described above. Although FIGS. 3A and 3B show the configuration of one end of the inner roller 32 in the rotational axis direction, the configuration of the other end is similar (with respect to the center of the inner roller 32 in the rotational axis direction). approximately symmetrical).

In this embodiment, the image forming apparatus 100 includes a sheet-shaped pressing member (backup sheet) 39 similar to that described with reference to FIG. The pressing member 39 presses the inner peripheral surface of the intermediate transfer belt 31 near the entrance of the secondary transfer nip N2 to cause the intermediate transfer belt 31 to protrude toward the outer peripheral surface. The pressing member 39 is arranged to contact the inner circumferential surface of the intermediate transfer belt 31 upstream of the inner roller 32 and downstream of the pre-secondary transfer roller 37 with respect to the rotational direction of the intermediate transfer belt 31. . In particular, in this embodiment, the pressing member 39 is located at a position upstream of the inner roller 32 and downstream of the downstream end of the conveyance guide 83 (first guide member 83a) with respect to the conveyance direction of the recording material S. The intermediate transfer belt 31 is disposed so as to be in contact with the inner circumferential surface of the intermediate transfer belt 31 corresponding to the intermediate transfer belt 31 . The pressing member 39 can be formed using a resin material. As the resin material forming the pressing member 39, for example, polyester resin such as PET resin can be suitably used. In this embodiment, the pressing member 39 has a longitudinal direction that is arranged substantially parallel to the width direction of the intermediate transfer belt 31 (a direction that is substantially orthogonal to the direction of movement of the surface), and a lateral direction that is arranged substantially orthogonal to the longitudinal direction. , each having a predetermined length and a predetermined thickness. The length of the pressing member 39 in the longitudinal direction is equivalent to the length of the intermediate transfer belt 31 in the width direction. The pressing member 39 has a free end, which is one end in the transverse direction (the downstream end in the rotational direction of the intermediate transfer belt 31 ), which extends over substantially the entire width of the intermediate transfer belt 31 . It can contact the inner peripheral surface and press the intermediate transfer belt 31. Further, as an example, the thickness of the pressing member 39 is 0.4 mm to 0.6 mm. For example, when using a PET resin sheet as the pressing member 39, if a PET resin sheet with too low electrical resistance is used, current will flow through the pressing member 39 when the secondary transfer voltage is applied to the outer roller 41, which may cause transfer failure. There is a possibility that it may occur. On the other hand, if a PET resin sheet with too high electrical resistance is used, static electricity (frictional charging) will be generated due to friction between the pressing member 39 and the intermediate transfer belt 31, and the intermediate transfer belt 31 will be attracted to the pressing member 39, causing the intermediate transfer belt to 31 may be prevented from rotating. Therefore, as the pressing member 39, it is preferable to use a PET resin sheet adjusted to have a medium electrical resistance (for example, a volume resistivity of 1×10 ⁵ to 1×10 ⁹ Ω·cm).

The pressing member 39 is supported by a pressing member holder 40 as a support member. The pressing member 39 has a fixed end, which is one end in the transverse direction (an end on the upstream side in the rotational direction of the intermediate transfer belt 31), fixed to the pressing member holder 40 over substantially the entire width in the longitudinal direction. The pressing member holder 40 is supported by the frame of the intermediate transfer belt unit 30 or the like so as to be rotatable about the second rotation shaft 40a. In this way, the position of the pressing member 39 is changed by rotating the pressing member holder 40 around the second rotation axis 40a and rotating the pressing member 39 around the second rotation axis 40a. The amount of penetration Y can be changed by

The pressing member holder 40 is configured to rotate by the action of the second cam 112 as an operating member. The second cam 112 is coaxial with the first cam 111 that constitutes the offset mechanism 1 described above, and is rotatable in conjunction with the first cam 111. More specifically, in this embodiment, the second cam 112 is fixed to a cam rotation shaft 110 that is rotatably supported by the frame of the intermediate transfer belt unit 30 or the like. In this embodiment, when the cam rotation shaft 110 is driven by the position change motor 113 and rotates, the first cam 111 and the second cam 112 fixed to the cam rotation shaft 110 rotate. . Further, the second cam 112 is in contact with a second cam follower 40b provided on the pressing member holder 40. Further, the pressing member holder 40 is configured with a tension spring or the like which is a biasing member (elastic member) as a biasing means so that the second cam follower 40b rotates in a direction in which it engages with the second cam 112. The second rotation spring 115 is biased by the second rotation spring 115.

Here, the first cam 111 and the second cam 112 are arranged in a phase relative to the cam rotation shaft 110 so that the inner roller 32 and the pressing member 39 can be moved in conjunction with each other in a predetermined relationship. is fixedly provided. Thereby, the pressing mechanism 2 can change the amount of penetration Y in conjunction with the operation of the offset mechanism 1 described above. In this manner, in this embodiment, the offset amount X and the intrusion amount Y can be changed synchronously using one (common) drive source. That is, in this embodiment, the offset mechanism 1 and the pressing mechanism 2 can be driven by one (common) actuator. Therefore, it is possible to simplify the configuration of the device and reduce costs.

In this way, in this embodiment, the pressing mechanism 2 includes the pressing member holder 40, the second cam 112, the cam rotation shaft 110, the position change motor 113, the second rotation spring 115, etc. .

As shown in FIG. 3(a), in the case of "thick paper", in conjunction with the offset mechanism 1 placing the inner roller 32 at the first inner roller position (first offset amount X1), The second cam 112 is driven by the position change motor 113 to rotate clockwise. As a result, the pressing member holder 40 rotates counterclockwise around the second rotation axis 40a, and reaches the first pressing member position where the insertion amount Y is the first insertion amount Y1, which is relatively large. , the pressing member 39 is placed. In this embodiment, at this time, the tip of the pressing member 39 comes into contact with the inner peripheral surface of the intermediate transfer belt 31 near the entrance of the secondary transfer nip N2, causing the intermediate transfer belt 31 to protrude toward the outer peripheral surface (the first Intrusion amount Y1>0mm). As a result, as described above, the contact distance D between the intermediate transfer belt 31 and the recording material S near the entrance of the secondary transfer nip N2 can be increased, and "scattering" can be suppressed.

Furthermore, as shown in FIG. 3(b), in the case of "thin paper", the offset mechanism 1 moves the inner roller 32 to the second inner roller position (second offset amount X2). Then, the second cam 112 is driven by the position change motor 113 and rotates counterclockwise. As a result, the pressing member holder 40 rotates clockwise around the second rotation shaft 40a, and the pressing member holder 40 is moved to the second pressing member position where the intrusion amount Y is a relatively small second intrusion amount Y2. The pressing member 39 is now placed. In this embodiment, at this time, the tip of the pressing member 39 separates from the inner peripheral surface of the intermediate transfer belt 31 (second intrusion amount Y2=0 mm).

Here, while the pressing member 39 is placed at the first pressing member position (first intrusion amount Y1) shown in FIG. 3(a), the inner roller 32 is moved to the second pressing member position shown in FIG. 3(b). Consider a case where the roller is placed at the inner roller position (second offset amount X2). In this case, the contact distance D is such that the inner roller 32 is at the first inner roller position (first offset amount X1) and the pressing member 39 is at the first pressing member position (first The contact distance D becomes even larger than the contact distance D when the contact distance is arranged at the intrusion amount Y1). Therefore, an image defect in which the toner image is mechanically disturbed due to friction between the toner image on the intermediate transfer belt 31 and the recording material S, that is, so-called "roughness" occurs. On the other hand, in this embodiment, as shown in FIG. 3(b), the inner roller 32 is disposed at the second inner roller position (second offset amount In conjunction with this, the pressing member 39 is arranged at a second pressing member position (second penetration amount Y2), particularly at a position spaced apart from the intermediate transfer belt 31. Thereby, the contact distance D can be prevented from becoming unnecessarily large, and "roughness" can be suppressed.

In this embodiment, the pressing member 39 is a sheet-like member made of resin, but is not limited to this. The pressing member 39 may be, for example, a sheet-like member made of a thin metal plate. Further, the pressing member 39 may be, for example, an elastic body (pad-like member, etc.) such as sponge or rubber. Further, the pressing member 39 may be a rigid body such as a rotatable roller made of resin or metal, for example. Furthermore, the pressing member 39 is not limited to one that is arranged at a predetermined position and comes into contact with the intermediate transfer belt 31 as in this embodiment. For example, when a rigid body such as the rotatable roller described above is used as the pressing member 39, the pressing member 39 may be urged toward the intermediate transfer belt 31 using a spring or the like as an urging means.

5-3. Approach/Separation Mechanism The approach/separation mechanism 3 for the outer roller 41 in this embodiment will be described. FIG. 4 is a schematic diagram showing a schematic configuration of the detachment mechanism 3. As shown in FIG. Although FIG. 4 shows the configuration of one end of the inner roller 32 in the rotational axis direction, the configuration of the other end is also similar (substantially symmetrical with respect to the center of the inner roller 32 in the rotational axis direction).

Both ends of the outer roller 41 in the rotation axis direction are rotatably supported by bearings 43 . The bearing 43 is supported by the frame of the apparatus main body 100a or the like so that it can slide in a direction toward the inner roller 32 and in the opposite direction along a predetermined direction (for example, a direction substantially perpendicular to the reference line L1 described above). There is. The bearing 43 is pressed toward the inner roller 32 by a pressing spring 44 formed of a compression spring, which is a biasing member (elastic member) serving as a biasing means. As a result, the outer roller 41 comes into contact with the inner roller 32 with the intermediate transfer belt 31 in between, forming a secondary transfer nip N2.

In this embodiment, the image forming apparatus 100 includes a separation mechanism (contact/separation means) 3 for causing the outer roller 41 to separate from and come into contact with the intermediate transfer belt 31. As shown in FIG. 4, the detachment mechanism 3 includes an arm 122, a detachment cam 121, a detachment motor 123, and the like. The arm 122 is supported by the frame of the apparatus main body 100a so as to be rotatable about an arm rotation shaft 122a, and is engaged with a bearing 43. Further, the arm 122 is configured to rotate by the action of the separation cam 121 as an operating member. The separation cam 121 is supported by the frame of the apparatus main body 100a so as to be rotatable about the separation cam rotation shaft 120. The separation cam 121 is rotatable about the separation cam rotation shaft 120 in response to drive from a separation motor 123 serving as a drive source. Further, the separation cam 121 is in contact with a separation cam follower 122b provided on the arm 122. Further, the arm 122 is biased by the pressing spring 44 so that the separable cam follower 122b rotates in the direction in which the separable cam follower 122b engages with the separable cam 121.

The separation mechanism 3 moves the outer roller 41 in a direction away from and in a direction closer to the inner roller 32. As shown by the solid line in FIG. 4, when the outer roller 41 is separated from the intermediate transfer belt 31, the arm 122 is driven by the separation motor 123 and the separation cam 121 rotates counterclockwise, for example. rotates clockwise. As a result, the arm 122 moves the bearing 43 in a direction away from the inner roller 32 (downward) against the biasing force of the pressure spring 44, thereby separating the outer roller 41 from the intermediate transfer belt 31. On the other hand, as shown by the two-dot chain line in FIG. 4, when the outer roller 41 is brought into contact with the intermediate transfer belt 31, the detachment cam 121 is driven by the detachment motor 123 and rotates clockwise, for example. , the arm 122 is rotated counterclockwise by the urging force of the pressing spring 44. As a result, the arm 122 moves the bearing member 43 in a direction closer to the inner roller 32 (upward) and brings the outer roller 41 into contact with the intermediate transfer belt 31 .

In this embodiment, the separation mechanism 3 is configured to prevent toner from being transferred to the recording paper S, such as a test image (patch) for image density correction or color misregistration correction formed on the intermediate transfer belt 31, from the surface of the outer roller 41. The outer roller 41 is spaced apart from the intermediate transfer belt 31 in order to avoid adhesion to the intermediate transfer belt 31. Furthermore, when a jam (paper jam) is handled, the separation mechanism 3 separates the outer roller 41 from the intermediate transfer belt 31. Further, if the outer roller 41 continues to be pressed against the inner roller 32 after a job (described later) is finished, the inner roller 32 and the outer roller 41 may be deformed. Therefore, in this embodiment, the separating mechanism 3 separates the outer roller 41 from the intermediate transfer belt 31 when a job is completed and the image forming apparatus 100 enters a standby state in which it waits for the next job. Even when the image forming apparatus 100 is in a sleep state (described later) or the main power is turned off, the outer roller 41 is maintained separated from the intermediate transfer belt 31.

In this embodiment, the operations of changing the offset amount X by the offset mechanism 1 and changing the intrusion amount Y by the pressing mechanism 2 (herein also simply referred to as "position changing operation") are performed when the outer roller 41 performs intermediate transfer. The outer roller 41 may be in contact with the belt 31 or may be separated from the intermediate transfer belt 31. Further, in this embodiment, the position changing operation may be performed either while the intermediate transfer belt 31 is stopped or while the intermediate transfer belt 31 is rotating. From the viewpoint of reducing wear on the intermediate transfer belt 31 and the outer roller 41 and reducing the driving load of the position changing operation, it is advantageous to perform the position changing operation with the outer roller 41 separated from the intermediate transfer belt 31. In this case, the position changing operation is typically performed while the intermediate transfer belt 31 is stopped. On the other hand, when performing a position change operation while the intermediate transfer belt 31 is rotating in the sheet spacing process (described later), from the viewpoint of shortening the time required for the position change operation, it is necessary that the outer roller 41 It is advantageous to perform this in contact with the transfer belt 31.

5-4. Specific examples of offset amount and intrusion amount ・Specific example 1
In this embodiment (specific example 1), based on the basis weight M of the recording material S, the combination pattern of the offset amount X (X1, X2) and the intrusion amount Y (Y1, Y2) is, for example, as follows. It is set to have two patterns.
(a) M≧52g/m ² :X1=-1.3mm Y1=1.5mm
(b) M<52g/m ² :X2=2.5mm Y2=0mm (separation)

As in this embodiment, when the pressing member 39 is made of resin and has a sheet-like shape, the position of the inner roller 32 and the pressing member 39 in setting (b) above should be set as the home position. is preferred. This is to prevent creep deformation of the pressing member 39 due to continuous pressure from the tension of the intermediate transfer belt 31 for a long period of time. When the pressing member 39 creeps, the amount of penetration Y1 in the case of "cardboard", for example, may become smaller than the above setting of 1.5 mm due to changes over time. Here, the home position refers to the position when the image forming apparatus 100 is in a sleep state or a state in which the main power is turned off.

Note that in this embodiment, the pressing member 39 can be separated from the inner circumferential surface of the intermediate transfer belt 31, but the pressing member 39 is not limited to this. When the amount of penetration Y is 0, the pressing member 39 may be in contact with the intermediate transfer belt 31. Furthermore, the second amount of intrusion Y2 only needs to be smaller than the first amount of intrusion Y1, and the configuration may be such that the amount of intrusion Y does not take zero. For example, when the influence of creep deformation is sufficiently small or absent, such as when the pressing member 39 is a thin metal plate or a rotatable roller, it is easy to adopt a configuration in which the amount of penetration Y does not take zero. For example, based on the basis weight M of the recording material S, the combination patterns of the offset amount X (X1, X2) and the intrusion amount Y (Y1, Y2) are set to be the following two patterns. Good too.

・Specific example 2
(a) M≧52g/m ² :X1=-1.3mm Y1=1.5mm
(b) M<52g/m ² :X2=2.5mm Y2=0.5mm

Further, in the above specific examples 1 and 2, the case where the value of the intrusion amount Y1 is a constant value for each offset amount X (X1, X2) has been described as an example, but the present invention is not limited to this. For example, for each offset amount X (X1, X2), the intrusion amount Y may be changed depending on the basis weight. Specifically, the amount of penetration Y may be set as follows.

・Specific example 3
(a) M≧300g/m ² :X1=-1.3mm Y1=1.5mm
(b) 52g/m ² ≦M<300g/m ² :X1=-1.3mm Y1=0.5mm
(c) M<52g/m ² :X2=2.5mm Y2=0mm (separation)

・Specific example 4
(a) M≧300g/m ² :X1=-1.3mm Y1=1.5mm
(b) 100g/m ² ≦M<300g/m ² :X1=-1.3mm Y1=0.5mm
(c) 52g/m ² ≦M<100g/m ² :X2=2.5mm Y2=0.1mm
(d) M<52g/m ² :X2=2.5mm Y2=0mm (separation)

As in specific example 4, when the value of the intrusion amount Y1 is changed for each offset amount X (X1, X2), the maximum value of the intrusion amount Y that is set when the offset amount X2 (>0) (here, Y2=0.1 mm) is smaller than the minimum value of the intrusion amount Y (here, Y1=0.5 mm) set when the offset amount is X1.

The offset amount X, the penetration amount Y, and the type of recording material S (here, the basis weight of the recording material S) assigned to each combination of the offset amount X and the penetration amount Y are limited to the above-mentioned specific example. It's not a thing. These can be set as appropriate through experiments, etc., from the viewpoint of improving the separability of the recording material S from the intermediate transfer belt 31 as described above and suppressing image defects that occur near the secondary transfer nip N2. Although not limited to this, the offset amount X is preferably about -3 mm to +3 mm. Further, although not limited thereto, the pressing member 39 is located within 25 mm of the intermediate transfer belt 31 upstream in the rotational direction of the intermediate transfer belt 31 from the area where the inner roller 32 and the intermediate transfer belt 31 contact. It is preferable that it be arranged so that it can come into contact with the inner circumferential surface. With such settings, good transferability can be obtained. Although not limited to this, the amount of penetration Y is preferably about 3.5 mm or less. If the amount of penetration Y is larger than 3.5 mm, the load applied to the contact surface between the pressing member 39 and the intermediate transfer belt 31 increases, which may make it difficult for the intermediate transfer belt 31 to rotate smoothly.

Furthermore, in this embodiment, the switching of the offset amount X (the position of the inner roller 32) has been described using an example of a two-stage case, but the present invention is not limited to this. The offset amount X (position of the inner roller 32) may be changed in three or more steps or steplessly.

Note that when the offset amount X can be changed in three or more stages, the intrusion amount Y does not necessarily have to be made smaller as the offset amount X becomes larger. For example, when the amount of change in the offset amount X is small, or when the offset amount X is changed in a negative range, the above-mentioned variation in the contact distance D is small. In this case, the amount of penetration Y does not necessarily have to be made small.

Further, if there is a setting where the intrusion amount Y is 0 in a setting in which the offset amount X is changed in three or more steps, it is preferable to use that setting as the home position setting for the same reason as described above. The settings may be settings that are not used during image formation but are used only when the image forming apparatus 100 is in a sleep state or when the main power is turned off.

6. Control Mode FIG. 5 is a schematic block diagram showing a control mode of main parts of the image forming apparatus 100 of this embodiment. The control unit 150 as a control unit includes a CPU 151 as an arithmetic control unit which is a central element that performs arithmetic processing, a memory (storage medium) 152 such as ROM and RAM as a storage unit, an interface unit 153, etc. be done. The RAM, which is a rewritable memory, stores information input to the control unit 150, detected information, calculation results, etc., and the ROM stores control programs, predetermined data tables, etc. The CPU 151 and the memory 152 are capable of transferring and reading data to each other. The interface section 153 controls signal input/output (communication) between the control section 150 and devices connected thereto.

The control section 150 is connected to each section of the image forming apparatus 100 (the image forming section 10, intermediate transfer belt 31, drive devices for members related to conveyance of the recording material S, various power supplies, etc.). In relation to this embodiment, in particular, the control unit 150 is connected to a position change motor 113 that is a drive source for the offset mechanism 1 and the pressing mechanism 2, a detachment motor 123 that is a drive source for the detachment mechanism 3, etc. ing. Further, an operation section (operation panel) 160 provided in the image forming apparatus 100 is connected to the control section 150. The operation unit 160 includes a display unit as a display unit that displays information under the control of the control unit 150, and an input unit as an input unit that inputs information to the control unit 150 through operations by an operator such as a user or a service person. have The operation unit 160 may include a touch panel having the functions of a display unit and an input unit. The control unit 150 also includes an image reading device (not shown) provided in the image forming apparatus 100 or connected to the image forming apparatus 100 , and an external device 200 such as a personal computer connected to the image forming apparatus 100 . may be connected.

The control unit 150 controls each unit of the image forming apparatus 100 to perform image formation based on job information. The job information includes a start instruction (start signal) input from the operation unit 160 or the external device 200, and information (command signal) regarding image forming conditions such as the type of recording material S. Further, the job information includes image information (image signal) input from the image reading device or the external device 200. Information regarding the type of recording material (also simply referred to as "information regarding recording material") refers to attributes based on general characteristics such as plain paper, high-quality paper, glossy paper, coated paper, embossed paper, thick paper, and thin paper. (so-called paper type category), numerical values or numerical ranges such as basis weight, thickness, size, or brand (including manufacturer, product number, etc.), which includes any information that can distinguish recording materials. be. In this embodiment, the information regarding the type of the recording material S includes information regarding the type of the recording material S that is related to the rigidity of the recording material S, and in particular, information about the basis weight of the recording material S as an example.

Here, the image forming apparatus 100 executes a job, which is a series of operations for forming and outputting an image on a single or multiple recording materials S, which is started by one start instruction. A job generally includes an image forming process (printing operation), a pre-rotation process, a paper-interval process when forming images on a plurality of recording materials S, 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 S 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-sheet process is a period corresponding to a period between recording materials S when images are formed on a plurality of recording materials S in succession (continuous image formation). 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, including the above-mentioned pre-rotation process, paper interval process, post-rotation process, and even when the image forming apparatus 100 is turned on or from the sleep state. This includes a pre-multi-rotation step, which is a preparatory operation for the return. Note that the sleep state (hibernation state) is, for example, a state in which the supply of power to each part of the image forming apparatus 100 other than the control unit 150 (or a part thereof) is stopped, and power consumption is lower than in the standby state. It is. In this embodiment, the above-mentioned "position change operation" is executed during non-image formation.

7. Control Procedure FIG. 6 is a flowchart showing an outline of the job control procedure in this embodiment. Here, it is assumed that the types of recording materials S used for image formation in one job are the same. Further, here, a case will be described as an example in which the operator causes the image forming apparatus 100 to execute a job from the external device 200. Note that FIG. 6 shows an outline of the control procedure focusing on the position change operation, and many other operations that are normally required to execute a job and output an image are omitted.

When job information (image information, image forming condition information, start instruction) is input from the external device 200, the control unit 150 reads information regarding the type of recording material S used for image formation, which is included in the job information. Acquire (S101). In this embodiment, the information regarding the type of the recording material S includes at least information about the basis weight of the recording material S. Note that the control unit 150 acquires information regarding the type of recording material S that is directly input (including selection from a plurality of options) from the external device 200 (or the operation unit 160) through the operation of the operator. be able to. Further, the control unit 150 controls the recording material S based on the information of the cassettes 61, 62, and 63 that send out the recording material S in the job, which is input from the external device 200 (or the operation unit 160) through the operation of the operator. You can also get information about the type of. In this case, the control unit 150 determines the type of recording material S stored in each cassette 61, 62, 63, which is stored in the memory 152 in advance in association with each cassette 61, 62, 63. Information regarding the type of S can be obtained. Here, when registering the information regarding the type of recording material S, the corresponding information is selected from a list of types of recording material S stored in advance in the memory 152 or a storage device connected to the control unit 150 through the network. It would be nice to be able to select

The control unit 150 creates a pattern of combinations of the position of the inner roller 32 (offset amount X) and the position of the pressing member 39 (intrusion amount Y) (here, (also simply referred to as a "position pattern") is determined (S102). The memory 152 stores in advance information on position patterns according to the basis weight of the recording material S, as in the specific example described above. Therefore, the control unit 150 determines the position pattern corresponding to the recording material S used in the current job from the position pattern information stored in the memory 152 based on the information regarding the type of recording material S acquired in S101. do.

As a specific example, in this embodiment (specific example 1), information about a predetermined threshold value of the basis weight of the recording material S (eg, the aforementioned 52 g/m ² ) is stored in the memory 152. Then, if the basis weight of the recording material S used in the current job is equal to or greater than the threshold value, the control unit 150 controls the position of the first inner roller where the offset amount X is the first offset amount X1, which is relatively small. The first pressing member position where the amount Y is the first intrusion amount Y1 is determined to be relatively large. Further, if the basis weight of the recording material S used in the current job is less than the threshold value, the control unit 150 controls the second inner roller position where the offset amount X is a relatively large second offset amount X2, and the intrusion The second pressing member position is determined so that the amount Y is a relatively small second intrusion amount Y2. As mentioned above, when three or more position patterns are set, for example, the basis weight corresponding to each position pattern is set such that as the offset amount X increases, the penetration amount Y decreases. A plurality of threshold information may be set to define the range.

Next, the control unit 150 determines whether or not the current position pattern of the inner roller 32 and the pressing member 39 needs to be changed based on the position pattern determined in S102 (S103). As described above, in this embodiment, the position pattern in which the offset amount X is the second offset amount X2 which is relatively large and the intrusion amount Y is the second intrusion amount Y2 which is relatively small is set as the home position. has been done. Therefore, for example, when the image forming apparatus 100 enters a sleep state after the previous job, the position pattern is the home position regardless of the position pattern in the previous job. The control unit 150 converts information on the current position pattern of the inner roller 32 and the pressing member 39 into information on the position pattern stored in the memory 152 at the end of the previous job, or information on whether or not the sleep state has entered. It can be obtained from etc.

If the control unit 150 determines that a change is necessary in S103, it sends a control signal to the position change motor 113 to change the position of the inner roller 32 (offset amount X) and the position of the pressing member 39 (intrusion amount Y). (“Position change operation”) (S104). On the other hand, if the control unit 150 determines that no change is necessary in S103, the control unit 150 performs the processing in S105 without changing the position of the inner roller 32 (offset amount X) and the position of the pressing member 39 (intrusion amount Y). Proceed to. Then, the control unit 150 performs a printing operation in a position pattern according to the recording material S used in the current job (S105). Note that the position changing operation is completed by the time the recording material S reaches the secondary transfer nip N2. As described above, the position changing operation may be performed either with the outer roller 41 in contact with the intermediate transfer belt 31 or with it separated from the intermediate transfer belt 31. Further, as described above, the position changing operation may be performed while the intermediate transfer belt 31 is stopped or rotating. When starting a job, typically, the outer roller 41 is separated from the intermediate transfer belt 31, the intermediate transfer belt 31 is stopped, and before feeding of the recording material S is started. Then, a position change operation is performed. Further, for example, when a plurality of types of recording materials S are mixed in the recording materials S used in one job, a position change operation can be performed in the paper spacing process. In this case, typically, after the preceding recording material S finishes passing through the secondary transfer nip N2 while the outer roller 41 is in contact with the intermediate transfer belt 31 and the intermediate transfer belt 31 is rotating, The position changing operation is performed before the subsequent recording material S reaches the secondary transfer nip N2.

8. Effects As explained above, according to this embodiment, it is possible to improve the separation property of the recording material S from the intermediate transfer belt 31 when the recording material S is "thin paper" and to suppress "roughness", and when the recording material S is the "thin paper". It is possible to suppress the "splatter" of. Therefore, for a wide variety of recording materials S, while obtaining good conveyance of the recording material S near the secondary transfer nip N2, image defects occurring near the secondary transfer nip N2 can be suppressed. Images can be formed. In other words, good transfer performance for various recording materials S can be obtained.

[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 will be given the same reference numerals as those of Embodiment 1, and detailed descriptions will not be provided. Omitted. Further, in this embodiment, as in the first embodiment, a case will be described in which "thin paper" is used as an example of the recording material S with low stiffness, and "cardboard" is used as an example of the recording material S with high stiffness.

In the first embodiment, the image forming apparatus 100 is configured to change the offset distance X by changing the position of the inner roller 32. In contrast, in this embodiment, the image forming apparatus 100 is configured to change the offset amount X by changing the position of the outer roller 41.

7(a) and 7(b) show the vicinity of the secondary transfer nip N2 in this embodiment from one end side of the rotation axis direction of the inner roller 32 (the front side of the paper in FIG. 1) substantially parallel to the rotation axis direction. FIG. 7(a) and (b) show the configuration of one end of the inner roller 32 in the direction of the rotational axis, but the configuration of the other end is similar (relative to the center of the inner roller 32 in the direction of the rotational axis). approximately symmetrical). FIG. 7(a) shows the state in the case of "thick paper" and FIG. 7(b) shows the state in the case of "thin paper".

In this embodiment, the outer roller 41 is moved in a direction toward the inner roller 32 along a predetermined first direction (for example, a direction substantially perpendicular to the reference line L1 described above) as in the first embodiment (see FIG. , (b) in the direction of the white arrow) and in the opposite direction. Furthermore, in this embodiment, the outer roller 41 is moved in a predetermined second direction that intersects with the first direction (for example, a direction substantially parallel to the reference line L1 described above), independently of the first direction. It is possible to slide along the direction toward the downstream side of the conveyance direction of the recording material S (the direction of the black arrow in FIG. 7(a)) and the opposite direction (the direction of the black arrow in FIG. 7(b)).

In this embodiment, the support member 132 that supports the bearing 43 of the outer roller 41 so as to be slidably movable along the first direction is attached to the frame of the main body 100a of the apparatus so that the bearing 43 of the outer roller 41 is slidably movable in the second direction. It is supported by etc. Further, the support member 132 is configured to slide by the action of the third cam 131 as an operating member. The third cam 131 is supported by the frame of the apparatus main body 100a so as to be rotatable about the third cam rotation shaft 130. The third cam 131 is rotatable about the third cam rotation shaft 130 by being driven by an offset motor 133 as a drive source. Further, the third cam 131 is in contact with a third cam follower 132a provided on the support member 132. Further, the support member 132 is configured with a compression spring or the like which is a biasing member (elastic member) as a biasing means so that the third cam follower 132a slides in the direction in which it engages with the third cam 131. It is biased by an offset spring 134. As described above, in this embodiment, the offset mechanism 1 includes the support member 134, the third cam 131, the third cam rotating shaft 130, the offset motor 133, the offset spring 134, and the like.

In addition, in this example, the pressing mechanism 2 includes a pressing member holder 40, a second cam 112, a second cam rotation shaft (corresponding to the cam rotation shaft in Example 1) 110, and a pressing motor, as in Example 1. (corresponding to the position change motor in the first embodiment) 113 and the like. Further, in this embodiment, the control unit 150 sends a control signal to the press motor 113 and the offset motor 133 to cause them to execute a position change operation. In this way, the offset mechanism 1 and the pressing mechanism 2 can be driven by separate actuators.

As shown in FIG. 7A, in the case of "cardboard", the third cam 131 is driven by the offset motor 133 and rotates counterclockwise, for example. Then, the support member 132 slides in the downstream direction in the conveying direction of the recording material S (in the direction of the black arrow in the figure) by the biasing force of the offset spring 134, and the relative position of the outer roller 41 with respect to the inner roller 32 is determined. It will be done. As a result, the outer roller 41 is placed at the first outer roller position where the offset amount X is the first offset amount X1, which is relatively small. As a result, as described in Example 1, it is possible to suppress the deterioration of the image quality at the rear end of the "cardboard" in the transport direction. In addition, in synchronization with the operation of the offset mechanism 1, the pressing mechanism 2 operates in the same manner as in the first embodiment, and moves the pressing member to the first pressing member position where the intrusion amount Y is the first intrusion amount Y1, which is relatively large. , the pressing member 39 is placed. In this embodiment, at this time, the tip of the pressing member 39 comes into contact with the inner peripheral surface of the intermediate transfer belt 31 near the entrance of the secondary transfer nip N2, causing the intermediate transfer belt 31 to protrude toward the outer peripheral surface (the first Intrusion amount Y1>0mm). As a result, as explained in Example 1, "scattering" can be suppressed.

Further, as shown in FIG. 7B, in the case of "thin paper", the third cam 131 is driven by the offset motor 133 and rotates, for example, clockwise. Then, the support member 132 slides in the direction (black arrow in the figure) toward the upstream side in the conveying direction of the recording material S against the biasing force of the offset spring 134, and the relative position of the outer roller 41 with respect to the inner roller 32 is moved. can be determined. As a result, the outer roller 41 is placed at the second outer roller position where the offset amount X is the second offset amount X2, which is relatively large. As a result, as described in Example 1, the separation of the "thin paper" from the intermediate transfer belt 31 after passing through the secondary transfer nip N2 is improved. Further, in synchronization with the operation of the offset mechanism 1, the pressing mechanism 2 operates in the same manner as in the first embodiment, and moves the pressing member to the second pressing member position where the intrusion amount Y is the second intrusion amount Y2, which is relatively small. , the pressing member 39 is placed. In this embodiment, at this time, the tip of the pressing member 39 separates from the inner peripheral surface of the intermediate transfer belt 31 (second intrusion amount Y2=0 mm).

Here, while the pressing member 39 is placed at the first pressing member position (first intrusion amount Y1) shown in FIG. 7(a), the outer roller 41 is moved to the second pressing member position shown in FIG. 7(b). Consider the case where the roller is placed at the outer roller position (second offset amount X2). In this case, the distance between the pressing member 39 and the outer roller 41 becomes short, and the intermediate transfer belt 31 and the recording material S are sandwiched between the pressing member 39 and the outer roller 41. As a result, a so-called "roughness" occurs, which is an image defect in which the toner image is disturbed due to frictional force before the recording material S enters the secondary transfer nip N2. On the other hand, in this embodiment, as shown in FIG. 7(b), the pressing member 39 is disposed at a second pressing member position (second intrusion amount Y2), particularly at a position spaced apart from the intermediate transfer belt 31. This prevents the intermediate transfer belt 31 and the recording material S from being sandwiched between the outer roller 41 and the pressing member 39, thereby suppressing "roughness".

Note that, as described in the first embodiment, the pressing member 39 is not limited to a sheet-like member, and the settings of the offset amount X and the intrusion amount Y are not limited to those of this embodiment. do not have.

As explained above, the same effects as in the first embodiment can be obtained with the configuration of this embodiment. However, in this embodiment, since the outer roller 41 needs to be movable in two directions, the configuration of Embodiment 1 is more advantageous in simplifying and downsizing the device configuration compared to the configuration of this embodiment. It can be said that

[Example 3]
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 will be given the same reference numerals as those of Embodiment 1, and detailed descriptions will not be provided. Omitted.

In the first embodiment, the outer roller 41 that directly contacts the outer peripheral surface of the intermediate transfer belt 31 is used as an outer member that forms the secondary transfer nip N2 together with the inner roller 32 as an inner member. In contrast, in this embodiment, an outer roller and a secondary transfer belt stretched between the outer roller and another roller are used as the external member.

FIG. 8 is a schematic view of the main part of the vicinity of the secondary transfer nip N2 in this embodiment, viewed from one end side of the inner roller 32 in the direction of the rotation axis (the front side of the paper in FIG. 1) and approximately parallel to the rotation axis direction. FIG. In this embodiment, the image forming apparatus 100 includes, as external members, a tension roller 46, an outer roller 41, and a secondary transfer belt 45 stretched between these rollers. Then, the outer roller 41 comes into contact with the outer peripheral surface of the intermediate transfer belt 31 via the secondary transfer belt 45 . That is, the intermediate transfer belt 31 and the secondary transfer belt 45 are sandwiched between the inner roller 32 that contacts the inner peripheral surface of the intermediate transfer belt 31 and the outer roller 41 that contacts the inner peripheral surface of the secondary transfer belt 45. A secondary transfer nip N2 is formed by this. In this embodiment, the contact portion between the intermediate transfer belt 31 and the secondary transfer belt 45 is a secondary transfer nip N2 serving as a secondary transfer portion.

Also in this embodiment, the offset amount X is defined by the relative position of the inner roller 32 and the outer roller 41, as in the first embodiment. Further, the intrusion amount Y is also determined by the reference line L1 and the pressing part tangent line L4 formed by the inner roller 32 and the pre-secondary transfer roller 37, or the reference line L1 formed by the outer roller 41 and the pre-secondary transfer roller 37. ' and the pressing part tangent L4' are defined in the same manner as in Example 1. Furthermore, the configuration and operation of the offset mechanism 1 and the pressing mechanism 2 in this embodiment are similar to those in the first embodiment. Also, in this embodiment, as in the first embodiment, the outer roller 41 is moved away from and toward the inner roller 32, and the secondary transfer belt 45 is moved away from and in contact with the intermediate transfer belt 31. A separating/separating mechanism 3 may be provided.

Note that even when an outer roller and a secondary transfer belt stretched between the outer roller and another roller are used as the external material as in this embodiment, the outer member is attached to the inner roller 32 as in the second embodiment. The offset amount X can be changed by changing the position of the material.

As explained above, the same effects as those of the first and second embodiments can be obtained also with the configuration of this embodiment. Furthermore, in this embodiment, it is possible to improve the conveyance of the recording material S passing through the secondary transfer nip N2.

[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 above embodiment, information on the basis weight of the recording material is used as information regarding the type of recording material that is related to the rigidity of the recording material, but the present invention is not limited to this. If the paper type category (for example, paper type category based on surface properties such as plain paper, coated paper, etc.) or brand (including manufacturer, product number, etc.) is the same, the basis weight and thickness of the recording material are often in a substantially proportional relationship (the greater the thickness, the greater the basis weight). Further, when the paper type category or brand is the same, the stiffness of the recording material and the basis weight or thickness of the recording material are often in a substantially proportional relationship (the greater the basis weight or thickness, the greater the stiffness. ). Therefore, for example, for each paper type category, each brand, or each combination of paper type category and brand, position patterns (combinations of offset amount and intrusion amount) are pattern) can be set. Then, the control unit responds to the recording material based on information such as the paper type category and brand input from the operation unit or external device, and information such as the basis weight, thickness, and stiffness of the recording material. The offset mechanism and the pressing mechanism can be operated synchronously so that a position pattern is obtained. Furthermore, the information regarding the type of recording material is not limited to quantitative information such as the basis weight, thickness, or stiffness of the recording material. As information regarding the type of recording material, for example, only qualitative information such as a paper type category, a brand, or a combination of a paper type category and a brand can be used. For example, position patterns can be set according to the paper type category, brand, or a combination of paper type category and brand, and the control unit will respond to information such as the paper type category and brand input from the operation unit or external device. The position pattern can be determined accordingly. In this case as well, position patterns are assigned based on the difference in stiffness of each recording material. The stiffness of the recording material can be represented by Gurley stiffness (MD/vertical grain) [mN], and can be measured with a commercially available Gurley stiffness tester. For example, the Gurley stiffness (MD) of an example of "thin paper" used as a recording material having a basis weight of less than the threshold value of 52 g/m ² in the above embodiment may be about 0.3 mN. Further, in the above-described embodiment, the Gurley stiffness (MD) of "plain paper" (basis weight about 80 g/ ^m2 ), which is an example of the recording material having a basis weight of 52 g/ ^m2 or more, is about 2 mN, and "thick paper" The Gurley stiffness (MD) of an example (with a basis weight of about 200 g/m ² ) may be about 20 mN.

Furthermore, in the above-described embodiment, the control unit acquires information regarding the type of recording material based on the input from the operation unit operated by the operator or the external device, but information regarding the type of recording material It may also be acquired based on the input of the detection result of the detection means that detects. For example, a basis weight sensor can be used as basis weight detection means for detecting an index value that correlates with the basis weight of the recording material. As a basis weight sensor, for example, a basis weight sensor that utilizes attenuation of ultrasonic waves is known. This basis weight sensor includes an ultrasonic wave generator and an ultrasonic receiver, which are arranged to sandwich the recording material conveyance path. The basis weight sensor receives the ultrasonic waves generated from the ultrasonic generator and attenuated by passing through the recording material, and determines the basis weight of the recording material based on the amount of attenuation of the ultrasonic waves. Detect index values that are correlated with Note that the basis weight detection means may be anything that can detect an index value that correlates with the basis weight of the recording material, and is not limited to one that uses ultrasonic waves, for example, one that uses light. Good too. Further, the index value correlated with the basis weight of the recording material is not limited to the basis weight itself, but may be the thickness corresponding to the basis weight. Furthermore, a surface quality sensor can be used as a smoothness detection means that detects an index value that correlates with the smoothness of the surface of a recording material that can be used to detect paper type categories. As a surface sensor, a regular reflection light sensor is known in which a recording material is irradiated with light and the intensity of specularly reflected light and diffusely reflected light is read by a light amount sensor. If the surface of the recording material is smooth, the specularly reflected light will be strong, and if it is rough, the diffusely reflected light will be strong. Therefore, the surface quality sensor can detect an index value that correlates with the smoothness of the surface of the recording material by measuring the amount of specularly reflected light and the amount of diffusely reflected light. Note that the smoothness detection means may be of any type as long as it can detect an index value that correlates with the smoothness of the surface of the recording material, and is not limited to one that uses the above-mentioned light amount sensor; for example, it may use an image sensor. It may be something you have. The index value that correlates with the smoothness of the surface of the recording material is not limited to a value converted to a value that conforms to a predetermined standard such as Bekk smoothness, but also a value that correlates with the smoothness of the surface of the recording material. That's fine. These detection means can be arranged, for example, adjacent to the recording material conveyance path upstream of the registration rollers in the recording material conveyance direction. Furthermore, for example, a sensor (media sensor) in which the above-mentioned basis weight sensor, surface quality sensor, etc. are configured as one unit may be used.

Further, in the above-described embodiment, an actuator that operates a movable part using a cam is used as the offset mechanism, pressing mechanism, and separation mechanism, but the present invention is not limited to this. The offset mechanism, the pressing mechanism, and the separation mechanism may each be of any type as long as they can realize the operations according to the above-described embodiments, and for example, an actuator that operates the movable part using a solenoid may be used.

Further, in the above-described embodiment, a configuration in which either the inner roller or the outer roller is moved has been described, but the offset amount may be changed by moving both the inner roller and the outer roller.

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 Offset mechanism 2 Pressing mechanism 3 Separation mechanism 31 Intermediate transfer belt 32 Inner roller 37 Pre-secondary transfer roller 39 Pressing member 41 Outer roller 83 Conveyance guide S Recording material X Offset amount Y Intrusion amount

Claims (17)

a rotatable endless belt that conveys the toner image;
A plurality of tension rollers for tensioning the 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 belt. A tension roller,
an outer roller that is disposed opposite to the inner roller, contacts the outer peripheral surface of the belt, and forms a transfer section that transfers the toner image from the belt to the recording material;
a pressing member capable of contacting the inner peripheral surface of the belt upstream of the inner roller and downstream of the upstream roller with respect to the rotational direction of the belt, and capable of pressing the belt from the inner peripheral surface side to the outer peripheral surface side; ,
A first method of changing the position of the transfer section by changing the position of at least one of the inner roller or the outer roller to change the relative position of the inner roller and the outer roller in the circumferential direction of the inner roller. a position change mechanism;
a second position changing mechanism that changes the position of the pressing member;
a control unit that controls the first position change mechanism and the second position change mechanism;
has
In a cross section substantially perpendicular to the rotational axis direction of the inner roller, a common tangent line between the inner roller on the side on which the belt is wound and the upstream roller is a reference line L1, and the line passing through the rotation center of the inner roller is the reference line L1. A straight line substantially perpendicular to line L1 is an inner roller center line L2, a straight line passing through the rotation center of the outer roller and substantially orthogonal to the reference line L1 is an outer roller center line L3, and the inner roller center line L2 and the outer roller center line L3 is the offset amount X (a positive value when the outer roller center line L3 is upstream of the inner roller center line L2 in the rotational direction of the belt),
The control unit is configured such that when the offset amount X is a first offset amount X1, the pressing member presses the inner peripheral surface of the belt, and the offset amount X is larger than the first offset amount X1. The image forming apparatus is characterized in that when the second offset amount is X2 (>0), the second position changing mechanism is controlled so that the pressing member moves away from the inner circumferential surface of the belt. 2. The image forming apparatus according to claim 1, wherein when the offset amount X is the first offset amount X1, an intrusion amount Y of the pressing member into the belt can be changed. The image forming apparatus according to claim 1 or 2, wherein the first offset amount X1 is a negative value. an input unit for inputting information regarding the recording material;
4. The control unit controls the first position change mechanism and the second position change mechanism based on information regarding the recording material input by the input unit. The image forming apparatus according to item (1). The control unit is configured to adjust the offset amount X to the first offset amount when the basis weight of the recording material is a first basis weight, based on information on the basis weight of the recording material inputted by the input unit. X1, when the basis weight of the recording material is a second basis weight smaller than the first basis weight, the first position changing mechanism is adjusted so that the offset amount X becomes the second offset amount X2; The image forming apparatus according to claim 4 , wherein the image forming apparatus controls the image forming apparatus. The control unit determines that the offset amount X is the first offset amount when the thickness of the recording material is a first thickness, based on information on the thickness of the recording material input by the input unit X1, when the thickness of the recording material is a second thickness smaller than the first thickness, controlling the first position changing mechanism so that the offset amount X becomes the second offset amount X2; The image forming apparatus according to claim 4 , characterized in that: The control unit is configured to determine, based on the information on the stiffness of the recording material inputted by the input unit, that the offset amount X is the first offset amount X1, the offset amount X is the first offset amount If the stiffness of the recording material is a second stiffness smaller than the first stiffness, the first position changing mechanism is controlled so that the offset amount X becomes the second offset amount X2. The image forming apparatus according to claim 4 . The control unit is configured to determine, based on the information of the category of the recording material inputted by the input unit, that the offset amount X is the first offset amount X1, the offset amount X is the first offset amount If the category of recording material is a second category having lower rigidity than the recording material of the first category, the first position changing mechanism is controlled so that the offset amount X becomes the second offset amount X2. The image forming apparatus according to claim 4 , characterized in that: The control unit is configured to determine, based on information on the brand of the recording material inputted by the input unit, that the offset amount X is the offset amount X1 when the brand of the recording material is a first brand. If the brand is a second brand of recording material having lower rigidity than the first brand of recording material, the first position changing mechanism is controlled so that the offset amount X becomes the second offset amount X2. The image forming apparatus according to claim 4 . The image forming apparatus according to any one of claims 1 to 9 , wherein the outer roller directly contacts an outer circumferential surface of the belt. 10. The outer roller contacts the outer peripheral surface of the belt via another endless belt stretched between the outer roller and another roller. The image forming apparatus described in . When the image forming apparatus is in a sleep state or the main power is OFF, the position of the pressing member is a position where the offset amount is the second offset amount X2. The image forming apparatus according to any one of claims 1 to 11 . 13. The first position changing mechanism changes the position of the inner roller to change the relative position between the inner roller and the outer roller in a circumferential direction of the inner roller. The image forming apparatus according to any one of the items. The image forming apparatus according to claim 13 , wherein the first position change mechanism and the second position change mechanism are driven by one drive source. a rotatable first support member that supports the inner roller and a first cam that rotates the first support member, which constitutes the first position change mechanism;
a rotatable second support member that supports the pressing member and a second cam that rotates the second support member, which constitutes the second position change mechanism;
a rotatable rotation shaft to which the first and second cams are fixed, constituting the first and second position changing mechanisms;
has
The image forming apparatus according to claim 14 , wherein the drive source generates a drive force that rotates the rotation shaft. 16. A guide member for guiding the recording material to the transfer section is provided upstream of the transfer section with respect to the conveyance direction of the recording material, according to any one of claims 1 to 15 . Image forming device. 2. The belt is an intermediate transfer member that transports the toner image that has been primarily transferred from the image carrier to the recording material at the transfer section. 17. The image forming apparatus according to any one of 16 to 16 .

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