JP2021135374A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can prevent "scattering" and "image rubbing" even when using a recording material with high rigidity, such as high rigidity thick paper.SOLUTION: An image forming apparatus 100 has: a pressing member 26 that can be in contact with an inner peripheral surface of a belt 7 on the upstream of an inner roller 21 and on the downstream of an upstream roller 24 with respect to a direction of rotation of the belt 7, and can press the belt 7 against an outer peripheral surface from the inner peripheral surface side; a pressing mechanism 16 that can change the amount of pressing of the pressing member 26 against the belt 7; a control unit 200 that controls the pressing mechanism 16; and environment detection means 13 that outputs a signal correlating with the water content in the environment. The control unit 200 can control the pressing mechanism 16 so as to change the amount of pressing of the pressing member 26 based on an output value from the environment detection means 13.SELECTED DRAWING: Figure 4

Description

The present invention relates to an image forming apparatus such as a copier, a printer, and a facsimile apparatus using an electrophotographic system or an electrostatic recording system.

Conventionally, some image forming apparatus using an electrophotographic method or the like has an endless belt (hereinafter, also simply referred to as “belt”) as an image carrier for supporting a toner image. As such a belt, for example, a second toner image primaryly transferred from a photoconductor or the like as a first image carrier is conveyed for secondary transfer to a sheet-like recording material such as paper. There is an intermediate transfer belt as an image carrier. Hereinafter, an image forming apparatus adopting an intermediate transfer method having an intermediate transfer belt will be mainly described as an example.

In the image forming apparatus of the intermediate transfer method, the toner image formed on the photoconductor or the like in the image forming portion is first transferred to the intermediate transfer belt in the primary transfer portion. Further, the toner image primaryly transferred to the intermediate transfer belt is secondarily transferred to the recording material by the secondary transfer unit. An inner member (secondary transfer inner member) provided on the inner peripheral surface side of the intermediate transfer belt and an outer member (secondary transfer outer member) provided on the outer peripheral surface side of the intermediate transfer belt form an intermediate transfer belt. A secondary transfer nip as a secondary transfer portion, which is a contact portion with the outer member, is formed. As the inner member, an inner roller, which is one of a plurality of tensioning rollers for tensioning the intermediate transfer belt, is used. As the outer member, an outer roller arranged at a position facing the inner roller with the intermediate transfer belt interposed therebetween is often used. 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 at the secondary transfer nip.

In recent years, the entry into the printing market of electrophotographic image forming apparatus has been progressing. Along with this, it is required to use a high-rigidity thick paper as a recording material, which has been difficult to perform stable transfer in the past.

Generally, the transfer speed of the recording material by the resist roller arranged upstream of the secondary transfer nip is set slightly faster than the transfer speed of the recording material in the secondary transfer nip. .. As a result, if the recording material has a certain degree of rigidity, a loop of the recording material is formed between the resist roller and the secondary transfer nip, and the outer peripheral surface (toner image supporting surface) of the intermediate transfer belt and the recording material are separated from each other. Can be brought into close contact. Here, the contact distance between the outer peripheral surface of the intermediate transfer belt and the recording material with respect to the moving direction of the intermediate transfer belt is defined as the adhesion distance. At this time, if the close contact distance is shorter than the discharge region of the outer roller, discharge occurs with a gap between the outer peripheral surface of the intermediate transfer belt and the recording material. As a result, the toner is not transferred to the original position on the recording material, and a part of the toner is transferred to the state of being scattered around the original position, which causes an image defect called "scattering". When a recording material with high rigidity such as thick paper with high rigidity is used, the carrying force of the resist roller loses to the strength of the recording material, so a loop of the recording material is formed between the resist roller and the secondary transfer nip. It is difficult to form, and it may not be possible to obtain a sufficient adhesion distance.

To solve this problem, a pressing member is provided on the inner peripheral surface (the surface opposite to the toner image supporting surface) side of the intermediate transfer belt to press the intermediate transfer belt from the inner peripheral surface side and project it toward the outer roller side. The provided configuration has been proposed (Patent Document 1).

Further, since the close contact distance changes depending on the type (rigidity) of the recording material, a configuration in which the pressing amount of the pressing member is changed according to the type of the recording material has also been proposed (Patent Document 2).

Japanese Unexamined Patent Publication No. 2002-82543 Japanese Unexamined Patent Publication No. 2015-215594

As described in Patent Document 1, when the intermediate transfer belt is pressed by the pressing member, the contact pressure between the intermediate transfer belt and the recording material increases as the amount of protrusion of the intermediate transfer belt by the pressing member increases, and recording is performed. The material and the intermediate transfer belt may rub against each other. When the recording material and the intermediate transfer belt are strongly rubbed, the unfixed toner image supported on the intermediate transfer belt is disturbed, and an image defect called "image rubbing" occurs on the recording material after the toner image is transferred. I have something to do.

Therefore, as described in Patent Document 2, it is conceivable to obtain the optimum contact distance and contact pressure according to the type of recording material by changing the pressing amount of the pressing member according to the type of recording material. Be done. However, a recording material having a high rigidity such as a thick paper having a high rigidity, which is difficult to form a close contact distance, tends to have a larger contact pressure between the intermediate transfer belt and the recording material. Therefore, even if the pressing amount of the pressing member is changed according to the type of the recording material, it may be difficult to suppress both "scattering" and "image rubbing" at the same time.

Therefore, an object of the present invention is to provide an image forming apparatus capable of suppressing "scattering" and "image rubbing" even when a recording material having high rigidity such as thick paper having high rigidity is used. ..

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises a rotatable endless belt that conveys a toner image and a plurality of tension rollers that stretch the belt, the inner roller and the inner roller with respect to the direction of rotation of the belt. A plurality of tension rollers including an upstream roller arranged adjacent to the inner roller upstream of the inner roller, and a plurality of tension rollers arranged so as to face the inner roller, contacting the outer peripheral surface of the belt, and from the belt. The outer member forming the transfer portion for transferring the toner image to the recording material can come into contact with the inner peripheral surface of the belt upstream of the inner roller and downstream of the upstream roller in the rotation direction of the belt. A pressing member capable of pressing the belt from the inner peripheral surface side to the outer peripheral surface side, a pressing mechanism capable of changing the pressing amount of the pressing member against the belt, a control unit controlling the pressing mechanism, and the amount of water in the environment. It has an environment detecting means for outputting a correlated signal, and the control unit can control the pressing mechanism so as to change the pressing amount based on the output value of the environment detecting means. It is an image forming apparatus.

According to another aspect of the present invention, there is a rotatable endless belt that conveys a toner image, and a plurality of tension rollers that stretch the belt, the inner roller and the inner roller with respect to the rotation direction of the belt. A plurality of tension rollers including an upstream roller arranged adjacent to the inner roller upstream of the roller and a plurality of tension rollers arranged to face the inner roller and abutting on the outer peripheral surface of the belt to abut the belt. The outer member forming a transfer portion for transferring the toner image from the recording material to the recording material, and the inner roller and the outer member with respect to the circumferential direction of the inner roller by changing the position of at least one of the inner roller or the outer member. The control unit has a position change mechanism for changing the relative position, a control unit for controlling the position change mechanism, and an environment detection means for outputting a signal correlating with the amount of water in the environment. The control unit detects the environment. An image forming apparatus is provided, characterized in that the position changing mechanism can be controlled so as to change the relative position based on the output value of the means.

According to the present invention, it is possible to suppress "scattering" and "image rubbing" even when a recording material having high rigidity such as thick paper having high rigidity is used.

It is a schematic cross-sectional view of an image forming apparatus. It is a graph for demonstrating the difference in the amount of pressing which can form a good image on the thick paper with high rigidity due to the difference in the absolute moisture content of the environment, and the difference in the range of the position of the inner roller. It is a schematic side view which shows the pressing mechanism. It is a schematic side view for demonstrating the operation of a pressing mechanism. It is a schematic block diagram which shows the control mode of the main part of the image forming apparatus of Example 1. FIG. It is a flowchart of the control of Example 1. FIG. It is a schematic side view which shows the offset mechanism. It is a schematic side view for demonstrating the operation of an offset mechanism. It is a schematic block diagram which shows the control mode of the main part of the image forming apparatus of Example 2. FIG. It is a flowchart of the control of Example 2. FIG. It is the schematic sectional drawing for demonstrating the offset amount. It is the schematic sectional drawing for demonstrating the pressing amount (penetration amount). It is a schematic cross-sectional view for demonstrating the close contact distance and contact pressure. It is a schematic cross-sectional view for demonstrating the action by changing the position of an inner roller.

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

[Example 1]
1. 1. Overall configuration and operation of the image forming apparatus FIG. 1 is a schematic cross-sectional view of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem type compound machine (having the functions of a copying machine, a printer, and a facsimile device) that employs an intermediate transfer method. The image forming apparatus 100 uses, for example, an electrophotographic method to perform a full-color image on a sheet-like recording material (transfer material, sheet material, recording medium, medium) P such as paper in response to an image signal transmitted from an external device. Can be formed.

The image forming apparatus 100 has four image forming units 10Y and 10M that form yellow (Y), magenta (M), cyan (C), and black (K) images as a plurality of image forming units (stations), respectively. It has 10C and 10K. These image forming portions 10Y, 10M, 10C, and 10K are arranged in series along the moving direction of the image transfer surface which is arranged substantially horizontally of the intermediate transfer belt 7 described later. For elements having the same or corresponding functions or configurations in each image forming unit 10Y, 10M, 10C, and 10K, Y, M, C, and K at the end of the code indicating that the elements are for any color are omitted. And there is a general explanation. In this embodiment, the image forming unit 10 includes a photosensitive drum 1 (1Y, 1M, 1C, 1K), a charger 2 (2Y, 2M, 2C, 2K), and an exposure device 3 (3Y, 3M, 3C, 3K), which will be described later. ), Developer 4 (4Y, 4M, 4C, 4K), primary transfer roller 5 (5Y, 5M, 5C, 5K), cleaning device 6 (6Y, 6M, 6C, 6K) and the like. ..

The photosensitive drum 1, which is a rotatable drum-shaped (cylindrical) photoconductor (electrophotographic photosensitive member) as the first image carrier that carries the toner image, is a drum drive motor 111 (FIG. 5) as a drive source. ), And the driving force is rotationally driven in the direction of arrow R1 (counterclockwise) in the figure. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative electrode property in this embodiment) by a charger 2 as a charging means. During the charging process, a predetermined charging voltage is applied to the charging device 2 by a charging power source (not shown). The surface of the charged photosensitive drum 1 is scanned and exposed by an exposure apparatus 3 as an exposure means (electrostatic image forming means) according to an image signal, and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 1. It is formed. In this embodiment, the exposure apparatus 3 is composed of a laser scanner apparatus that irradiates the photosensitive drum 1 with a laser beam modulated according to an image signal (image information). The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by supplying toner as a developer by the developer 4 as a developing means, and a toner image (developer image) is formed on the photosensitive drum 1. Will be done. In this embodiment, the exposed portion (image portion) on the photosensitive drum 1 whose absolute potential value is lowered by being exposed after being uniformly charged has the same polarity as the charging polarity of the photosensitive drum 1 (this embodiment). In the example, the charged toner adheres to the negative polarity) (reversal development). The developing device 4 has a developing roller which is a rotatable developing agent carrier which carries a developing agent and conveys it to a developing position which is a portion facing the photosensitive drum 1. The developing roller is rotationally driven, for example, by transmitting a driving force from the driving system of the photosensitive drum 1. Further, at the time of development, a predetermined development voltage is applied to the development roller by a development power source (not shown).

An intermediate transfer belt, which is a rotatable intermediate transfer body composed of an endless belt as a second image carrier that supports a toner image so as to face the four photosensitive drums 1Y, 1M, 1C, and 1K. 7 is arranged. The intermediate transfer belt 7 is hung around a drive roller 22 as a plurality of tension rollers (support rollers), an upstream auxiliary roller 23a, a downstream auxiliary roller 23b, a tension roller 25, a secondary transfer pre-roller 24, and an inner roller 21. It is stretched with a predetermined tension. The drive roller 22 transmits a driving force to the intermediate transfer belt 7. The tension roller 25 applies a predetermined tension to the intermediate transfer belt 7 and controls the tension of the intermediate transfer belt 7 to be constant. The secondary transfer pre-roller 24 forms a surface of the intermediate transfer belt 7 in the vicinity of the upstream of the secondary transfer nip N2 (described later) with respect to the rotation direction (movement direction, traveling direction) of the intermediate transfer belt 7. The inner roller (secondary transfer facing roller, inner member) 21 functions as a facing member (opposing electrode) of the outer roller 9 (described later). The upstream auxiliary roller 23a and the downstream auxiliary roller 23b form an image transfer surface that is arranged substantially horizontally. By transmitting the driving force from the belt drive motor 112 (FIG. 5) as the drive source, the drive roller 22 is rotationally driven to rotate (clockwise) in the direction of arrow R2 (clockwise) in the drawing. In this embodiment, the intermediate transfer belt 7 is rotationally driven so that the peripheral speed is 150 to 470 mm / sec. Of the plurality of tension rollers, the tension rollers other than the drive roller 22 drive and rotate as the intermediate transfer belt 7 rotates. On the inner peripheral surface side of the intermediate transfer belt 7, the primary transfer rollers 5Y, 5M, which are roller-shaped primary transfer members as the primary transfer means, correspond to the photosensitive drums 1Y, 1M, 1C, and 1K. 5C and 5K are arranged. The primary transfer roller 5 presses the intermediate transfer belt 7 toward the photosensitive drum 1 to form a primary transfer nip N1 as a primary transfer portion which is a contact portion between the photosensitive drum 1 and the intermediate transfer belt 7. .. Further, on the inner peripheral surface side of the intermediate transfer belt 7, a pressing member 26 is provided upstream of the inner roller 21 and downstream of the secondary transfer pre-roller 24 in the rotation direction of the intermediate transfer belt 7. The pressing member 26 can come into contact with the inner peripheral surface of the intermediate transfer belt 7 and press the intermediate transfer belt 7 from the inner peripheral surface side to the outer peripheral surface side. As a result, the pressing member 26 covers the tension surface T (FIG. 3) of the intermediate transfer belt 7 formed between the inner roller 21 and the secondary transfer pre-roller 24 from the inner peripheral surface side of the intermediate transfer belt 7. It can be projected to the surface side. The pressing member 26 and the pressing mechanism 16 for changing the position of the pressing member 26 will be further described later.

The toner image formed on the photosensitive drum 1 as described above is primarily transferred onto the rotating intermediate transfer belt 7 by the action of the primary transfer roller 5 in the primary transfer nip N1. At the time of primary transfer, the primary transfer roller 5 has a polarity opposite to the normal charging polarity of the toner (charging polarity of the toner during development) (positive polarity in this embodiment) due to the primary transfer power supply (not shown). The primary transfer voltage, which is the DC voltage of), is applied. For example, when forming a full-color image, the toner images of each color of yellow, magenta, cyan, and black formed on each photosensitive drum 1 are sequentially superimposed on the same image forming region on the intermediate transfer belt 7. Next transcribed. In this embodiment, the primary transfer nip N1 is an image forming position that forms a toner image on the intermediate transfer belt 7. The intermediate transfer belt 7 is an example of a rotatable endless belt that conveys a toner image supported at an image forming position.

On the outer peripheral surface side of the intermediate transfer belt 7, at a position facing the inner roller 21, an outer roller (secondary transfer roller, outer member) which is a roller-shaped secondary transfer member (transfer rotating body) as a secondary transfer means. ) 9 is arranged. The outer roller 9 is pressed toward the inner roller 21 via the intermediate transfer belt 7 to form a secondary transfer nip N2 as a secondary transfer portion which is a contact portion between the intermediate transfer belt 7 and the outer roller 9. The toner image formed on the intermediate transfer belt 7 as described above is a recording material that is sandwiched and conveyed between the intermediate transfer belt 7 and the outer roller 9 by the action of the outer roller 9 in the secondary transfer nip N2. Secondary transcription is performed on P. In this embodiment, during the secondary transfer, the outer roller 9 is controlled by the secondary transfer power supply (high voltage applying means) 18 to have a constant voltage control having a polarity opposite to the normal charging polarity of the toner (positive electrode property in this embodiment). The secondary transfer voltage, which is the DC voltage, is applied. In this embodiment, for example, a secondary transfer voltage of +1 to +7 KV is applied and a secondary transfer current of +40 to +120 μA is passed, so that the toner image on the intermediate transfer belt 7 is secondarily transferred onto the recording material P. Will be done. In this embodiment, the inner roller 21 is electrically grounded (connected to the ground). The inner roller 21 is used as a secondary transfer member, a secondary transfer voltage having the same polarity as the normal charging polarity of the toner is applied to the inner roller 21, and the outer roller 9 is used as a counter electrode to electrically ground the inner roller 21. May be good.

The recording material P is conveyed to the secondary transfer nip N2 at the same timing as the toner image on the intermediate transfer belt 7. That is, the recording material P stored in the recording material cassette 11 as the recording material storage unit is a resist roller (resist roller) which is a transport member as a transport means by a feed roller or the like which is a feed member as a feed means. Pair) It is transported to 8 and temporarily stopped. Then, in the secondary transfer nip N2, the resist roller 8 is rotationally driven so that the toner image on the intermediate transfer belt 7 and the desired image forming region on the recording material P coincide with each other. It is sent to the secondary transfer nip N2.

Regarding the transport direction of the recording material P, a transport guide 14 for guiding the recording material P to the secondary transfer nip N2 is provided downstream of the resist roller 8 and upstream of the secondary transfer nip N2. The transport guide 14 includes a first guide member 14a that can come into contact with the front surface of the recording material P (the surface on which the toner image is transferred immediately after passing through the transport guide 14) and the back surface (front surface) of the recording material P. Is configured to have a second guide member 14b, which can come into contact with the opposite surface). The first guide member 14a and the second guide member 14b are arranged so as to face each other, and the recording material P passes between the two members. The first guide member 14a regulates the movement of the recording material P in the direction approaching the intermediate transfer belt 7. The second guide member 14b restricts the movement of the recording material P in the direction away from the intermediate transfer belt 7.

The recording material P to which the toner image is transferred is conveyed to the fixing device 40 as the fixing means by the pre-fixing transport device 41. The pre-fixing transport device 41 is a belt body formed of a rubber material such as EPDM having a width of 100 to 110 mm and a thickness of 1 to 3 mm in the central portion in a direction substantially orthogonal to the transport direction of the recording material P. Is rotatable. The pre-fixing transport device 41 carries the recording material P on the belt body. This belt body has a hole with a diameter of 3 to 7 mm, and by sucking air from the inner peripheral surface side, the carrying force of the recording material P is enhanced, and the transportability of the recording material P is stabilized. .. The fixing device 40 fixes (melts, fixes) the toner image on the surface of the recording material P by heating and pressurizing the recording material P carrying the unfixed toner image. After that, the recording material P on which the toner image is fixed is discharged to a discharge tray 15 provided outside (outside the machine) of the apparatus main body 110 of the image forming apparatus 100 by a discharge roller or the like which is a discharge member as a discharge means. (Output).

On the other hand, the toner remaining on the photosensitive drum 1 after the primary transfer (primary transfer residual toner) is removed from the photosensitive drum 1 by the cleaning device 6 as a cleaning means and recovered. Further, the toner (secondary transfer residual toner) remaining on the intermediate transfer belt 7 after the secondary transfer and the deposits such as paper dust adhering from the recording material P are intermediated by the belt cleaning device 12 as the intermediate transfer body cleaning means. It is removed from the transfer belt 7 and recovered. In this embodiment, the belt cleaning device 12 electrostatically collects and cleans the deposits such as the secondary transfer residual toner on the intermediate transfer belt 7.

In this embodiment, an intermediate transfer belt 7 stretched on a plurality of tension rollers, each primary transfer roller 5, a belt cleaning device 12, a frame supporting these, and the like are provided as a belt transfer device. The intermediate transfer belt unit 20 is configured. The intermediate transfer belt unit 20 is removable from the device main body 110 for maintenance or replacement.

Here, as the intermediate transfer belt 7, one made of a resin-based material having a single-layer or multi-layer structure, a multi-layer structure having an elastic layer made of an elastic material, or the like can be used. The intermediate transfer belt 7 preferably has 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 used.

Further, in this embodiment, the primary transfer roller 5 is configured by providing an elastic layer made of ionic conductive foam rubber on the outer periphery of a metal core metal (core material). Further, in this embodiment, the primary transfer roller 5, the outer diameter of 15 to 20 mm, the electric resistance value is 23 ° C., 1 × 10 ⁵ as measured by applying a voltage of 2kV at 50% RH environment ~ 1 × 10 ⁸ Ω.

Further, in this embodiment, the outer roller 9 is configured by providing an elastic layer of ion conductive foam rubber on the outer periphery of a metal core metal (core material). Further, in this embodiment, the outer roller 9 has an outer diameter of for example 20 to 25 mm, the electric resistance value is 23 ℃, 1 × ¹⁰ 5 ~ when measured by applying a voltage of 2kV at 50% RH environment It is 1 × 10 ⁸ Ω. Further, in the present embodiment, both ends of the outer roller 9 in the direction of the rotation axis are rotatably supported by bearings 9a (FIG. 3). The bearing 9a is slidable in the direction toward the inner roller 21 and in the opposite direction, and is a pressing spring 9b composed of a compression spring which is an urging member (elastic member) as an urging means (FIG. 3). Is pressed toward the inner roller 21. As a result, the outer roller 9 abuts on the inner roller 21 with a predetermined pressure across the intermediate transfer belt 7 to form the secondary transfer nip N2.

Further, in this embodiment, the inner roller 21 is configured by providing an elastic layer of electronically conductive rubber on the outer periphery of a metal core metal (core material). Further, in this embodiment, the inner roller 21 has an outer diameter of, for example, 10 to 22 mm (16 mm as an example), and is measured by applying a voltage of 50 V in an environment where the electric resistance value is 23 ° C. and 50% RH. It is 1 × 10 ⁵ to 1 × 10 ⁸ Ω. The secondary transfer pre-roller 24 may have the same configuration as the inner roller 21, for example.

Further, in this embodiment, the rotation axis directions of the tension roller and the outer roller 9 of the intermediate transfer belt 7 including the inner roller 21 are substantially parallel to each other.

Further, in this embodiment, an environment sensor (temperature / humidity sensor) 13 for detecting the internal environment of the apparatus main body 110 is provided inside the apparatus main body 110 of the image forming apparatus 100. In this embodiment, the environment sensor 13 can measure the absolute water content (absolute humidity) of the atmosphere inside the apparatus main body 110, particularly the atmosphere of the image forming portion including the vicinity of the secondary transfer nip N2. It is configured. The environment sensor 13 is an environment detecting means that can be used to acquire at least information on the amount of water in the atmosphere inside or outside the image forming apparatus 100 as information on the environment (printing environment) of the image forming apparatus 100. This is an example. In this embodiment, the environmental sensor 13 detects the temperature and humidity of the atmosphere, obtains the absolute water content of the atmosphere based on the detected temperature and humidity, and controls the information (signal) regarding the obtained absolute water content. Enter in 200 (Fig. 5). Alternatively, the environmental sensor 13 detects the temperature and humidity of the atmosphere, inputs information (signal) regarding the detection result to the control unit 200, and the control unit 200 absolutely of the atmosphere based on the information regarding the temperature and humidity. The amount of water may be calculated.

2. "Splattering", "Image rubbing"
FIG. 13 is a schematic cross-sectional view (direction of the rotation axis of the inner roller 21) for explaining the close contact distance between the recording material P and the intermediate transfer belt 7 and the contact pressure of the recording material P with respect to the intermediate transfer belt 7. It is a cross section that is substantially orthogonal to.

In this embodiment, the transfer speed of the recording material P by the resist roller 8 arranged upstream of the secondary transfer nip N2 in the transfer direction of the recording material P is higher than the transfer speed of the recording material P in the secondary transfer nip N2. Is set a little earlier. As a result, a loop of the recording material P is formed between the resist roller 8 and the secondary transfer nip N2, and the outer peripheral surface (toner image supporting surface) of the intermediate transfer belt 7 and the recording material P can be easily brought into close contact with each other. ..

As shown in FIG. 13, the outer peripheral surface and recording of the intermediate transfer belt 7 with respect to the moving direction of the intermediate transfer belt 7 in the vicinity of the inlet of the secondary transfer nip N2 (near the upstream of the inner roller 21 with respect to the rotation direction of the intermediate transfer belt 7). The distance of contact with the material P is defined as the close contact distance. More specifically, this close contact distance is determined by the contact start position between the inner roller 21 and the intermediate transfer belt 7 and the contact start position between the recording material P and the intermediate transfer belt 7 with respect to the moving direction of the intermediate transfer belt 7. The distance between. At this time, as described above, if the close contact distance is shorter than the discharge region of the outer roller 9, discharge occurs with a gap between the outer peripheral surface of the intermediate transfer belt 7 and the recording material P. As a result, the toner is not transferred to the original position on the recording material P, and a part of the toner is transferred to the state of being scattered around the original position, which causes an image defect called "scattering". When a recording material P having a high rigidity such as a thick paper having a high rigidity is used, the carrying force of the resist roller 8 may be defeated by the strength of the recording material P. Therefore, it is difficult to form a loop of the recording material P between the resist roller 8 and the secondary transfer nip N2, and a sufficient close contact distance may not be obtained.

To solve this problem, as shown in FIG. 13, the intermediate transfer belt 7 is placed on the inner peripheral surface (the surface opposite to the toner image supporting surface) side of the intermediate transfer belt 7 near the upstream side of the secondary transfer nip N2. It is effective to provide a pressing member 26 that presses the material from the inner peripheral surface side and projects it toward the outer roller 9 side.

However, when the intermediate transfer belt 7 is pressed by the pressing member 26, when the overhanging amount of the intermediate transfer belt 7 by the pressing member 26 increases, the contact pressure between the intermediate transfer belt 7 and the recording material P increases, and the recording material P increases. And the intermediate transfer belt 7 may rub strongly. As described above, when the recording material P and the intermediate transfer belt 7 are strongly rubbed, the unfixed toner image supported on the intermediate transfer belt 7 is disturbed, and the unfixed toner image is transferred onto the recording material P after the toner image is transferred. Image defects called "image rubbing" may occur.

Here, since the adhesion distance changes depending on the type (rigidity) of the recording material P, the pressing amount of the pressing member 26 is changed according to the type of the recording material P, and the optimum adhesion distance according to the type of the recording material P. And the contact pressure. However, the contact pressure between the intermediate transfer belt 7 and the recording material P tends to be larger in a recording material having a high rigidity such as a thick paper having a high rigidity in which it is difficult to form a close contact distance. Therefore, even if the pressing amount of the pressing member 26 is changed according to the type of the recording material P, it may be difficult to suppress both "scattering" and "image rubbing" at the same time.

When a recording material P having a high rigidity such as a thick paper having a high rigidity is used, the reason why it is difficult to suppress both "scattering" and "image rubbing" is considered as follows. In other words, the fact that the environmental fluctuation factors that are disadvantageous to each of "scattering" and "image rubbing" are different has a great influence. Since "scattering" is caused by the discharge phenomenon in the secondary transfer nip N2, it is disadvantageous in a low humidity environment where the absolute humidity is low. On the other hand, "image rubbing" is caused by rubbing between the intermediate transfer belt 7 and the recording material P, so that the toner is hard to be charged, the electrostatic adhesion to the intermediate transfer belt 7 is small, and the absolute humidity is high. It is disadvantageous in a high humidity environment.

Therefore, in this embodiment, the control unit 200 (FIG. 5) controls the pressing mechanism 16 (FIG. 3) based on the output value (detection result of the absolute water content) of the environmental sensor 13, and is intermediate between the pressing members 26. The amount of pressure applied to the transfer belt 7 is changed (adjusted). Generally, in a low humidity environment, the pressing amount of the pressing member 26 is increased to increase the contact distance between the intermediate transfer belt 7 and the recording material P. This makes it possible to suppress the occurrence of "scattering". Further, generally, in a high humidity environment, the pressing amount of the pressing member 26 is reduced, and the contact pressure between the intermediate transfer belt 7 and the recording material P upstream of the secondary transfer nip N2 is reduced. This makes it possible to suppress the occurrence of "image rubbing". Hereinafter, it will be described in more detail.

3. 3. Pressing amount and offset amount Here, the pressing amount of the pressing member 26 against the intermediate transfer belt 7 will be further described. The amount of pressure of the pressing member 26 against the intermediate transfer belt 7 can be expressed by the amount of penetration of the pressing member 26 against the intermediate transfer belt 7. The amount of penetration is roughly determined by the tension surface (tension surface) T of the intermediate transfer belt 7 formed by the pressing member 26 being stretched by the inner roller 21, the outer roller 9, and the secondary transfer pre-roller 24. On the other hand, it is an amount that causes the intermediate transfer belt 7 to project outward. The secondary transfer pre-roller 24 is an example of an upstream roller arranged adjacent to the inner roller 21 upstream of the inner roller 21 in the rotation direction of the intermediate transfer belt 7 among the plurality of tension rollers. More specifically, the definition of the intrusion amount changes depending on the offset amount indicating the relative positions of the inner roller 21 and the outer roller 9 in the circumferential direction of the inner roller 21.

First, the offset amount will be described. FIG. 11 is a schematic cross-sectional view (abbreviated as the rotation axis direction of the inner roller 21) in the vicinity of the secondary transfer nip N2 for explaining the definition of the offset amount X indicating the relative positions of the inner roller 21 and the outer roller 9. Orthogonal cross section). In the cross section shown in FIG. 11, the common tangent line between the inner roller 21 and the secondary transfer pre-roller 24 on the side on which the intermediate transfer belt 7 is hung is defined as the reference line L1. The reference line L1 corresponds to the tension surface T of the intermediate transfer belt 7 when the intermediate transfer belt 7 is not projected toward the outer peripheral surface side by the pressing member 26. Further, in the same cross section, a straight line passing through the center of rotation of the inner roller 21 and substantially orthogonal to the reference line L1 is defined as the inner roller center line L2. Further, in the same cross section, a straight line passing through the rotation center of the outer roller 9 and substantially orthogonal to the reference line L1 is defined as the 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 set to the offset amount X (however, the outer roller center line L3 is more in the rotation direction of the intermediate transfer belt 7 than the inner roller center line L2). When it is on the upstream side of, it is defined as a positive value). 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 rotation direction of the intermediate transfer belt 7 is widened to the upstream side in the rotation direction of the intermediate transfer belt 7. That is, the rotation of the intermediate transfer belt 7 in the contact region between the outer roller 9 and the intermediate transfer belt 7 is more than the upstream end in the rotation direction of the intermediate transfer belt 7 in the contact region between the inner roller 21 and the intermediate transfer belt 7. The end on the upstream side in the direction will be located on the upstream side. In this way, the position of at least one of the inner roller 21 and the outer roller 9 is changed, and the relative positions of the inner roller 21 and the outer roller 9 are changed with respect to the circumferential direction of the inner roller 21 to change the secondary transfer nip (transfer). Part) The position of N2 can be changed.

Next, the amount of intrusion will be described. 12 (a) and 12 (b) are schematic cross-sectional views (rotational axis of the inner roller 21) in the vicinity of the secondary transfer nip N2 for explaining the definition of the penetration amount Y of the pressing member 26 with respect to the intermediate transfer belt 7. A cross section substantially orthogonal to the direction). The definition of the intrusion amount Y differs depending on whether the offset amount X is positive or 0 or negative. Generally, the tension surface T of the intermediate transfer belt 7 without being pressed by the pressing member 26 is formed by the inner roller 21 and the secondary transfer pre-roller 24, or by the outer roller 9 and the secondary transfer pre-roller 24. This is because whether it is formed depends on the offset amount X. FIG. 12A shows a case where the offset amount X is 0 or a negative value (particularly a negative value), and FIG. 12B 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. In the cross section shown in FIG. 12A, the common tangent line between the inner roller 21 on the side on which the intermediate transfer belt 7 is hung and the secondary transfer pre-roller 24 is defined as the reference line L1. Further, in the same cross section, the tangent line of the intermediate transfer belt 7 that contacts the outer peripheral surface of the intermediate transfer belt 7 in the region where the pressing member 26 contacts the intermediate transfer belt 7, which is substantially parallel to the reference line L1, is defined as the pressing portion tangent line L4. .. At this time, when the offset amount X is 0 or a negative value, the distance (vertical distance) between the reference line L1 and the tangent line L4 of the pressing portion is set to the intrusion amount Y of the pressing member 26 with respect to the intermediate transfer belt 7 (however, pressing). It is defined as a positive value when the partial tangent line L4 is closer to the outer peripheral surface side of the intermediate transfer belt 7 than the reference line L1). This intrusion amount Y can take a positive value of 0.

Next, a case where the offset amount X is a positive value will be described. In the cross section shown in FIG. 12B, the common tangent line between the outer roller 9 on the side on which the intermediate transfer belt 7 is hung and the secondary transfer pre-roller 24 is defined as the reference line L1'. Further, in the same cross section, the tangent line of the intermediate transfer belt 7 that contacts the outer peripheral surface of the intermediate transfer belt 7 in the region where the pressing member 26 contacts the intermediate transfer belt 7, which is substantially parallel to the reference line L1', is tangent to the pressing portion L4'. And. At this time, when the offset amount X is a positive value, the distance (vertical distance) between the reference line L1'and the pressing portion tangent line L4' is set as the intrusion amount Y of the pressing member 26 with respect to the intermediate transfer belt 7 (however, pressing). It is defined as a positive value when the partial tangent line L4'is closer to the outer peripheral surface side of the intermediate transfer belt 7 than the reference line L1'). This intrusion amount Y can take a positive value of 0.

Here, the intrusion amount Y as described above is also simply referred to as a pressing amount of the pressing member 26.

4. Change in pressing amount FIG. 2 shows the pressing amount of the pressing member 26 capable of forming a good image on high-rigidity thick paper (Garley rigidity 64 mN or more) and the inner roller for each absolute moisture content of the environment in the configuration of this embodiment. It is a graph which shows the range of the position of 21 (here, also simply referred to as "OK range"). The high-rigidity cardboard (Garley rigidity of 64 mN or more) is an example of a recording material P having high rigidity. In FIG. 2, the vertical axis represents the pressing amount (intrusion amount Y) of the pressing member 26, and the horizontal axis represents the position of the inner roller 21. The position of the inner roller 21 indicates that the + direction is located on the downstream side in the moving direction of the intermediate transfer belt 7 and the − direction is located on the upstream side in the moving direction of the intermediate rolling belt 7. The reference position of the inner roller 21 is set in advance as, for example, a position for setting the above-mentioned offset amount X to a predetermined offset amount X. When the predetermined offset amount X is 0 mm, the value at the position of the inner roller 21 matches the value of the offset amount X.

In FIG. 2, when the upper limit of the OK range is exceeded, an image defect of “image rubbing” occurs, and when the lower limit of the OK range is exceeded, an image defect of “scattering” occurs. The OK range in a low humidity environment with an absolute moisture content of 3 g / m ^{3 or less and the OK range in a high humidity environment with an absolute moisture content of 13 g / m 3} or more are shifted up and down. Both the pressing amount of the pressing member 26 and the position of the inner roller 21 have component tolerances. Therefore, in order to set the pressing amount of the pressing member 26 and the position of the inner roller 21 in the OK range in consideration of the tolerance, it is desired to aim at the center under each environment.

Consider a case where the position of the inner roller 21 is fixed to a reference position and the pressing amount of the pressing member 26 is changed. Stationary environment (absolute water content is greater than 3 g / ^{m 3,} a small range of environment than 13 g / ^{m 3)} under, by a pressing amount 1.9 mm, can be set at the center of the OK range. On the other hand, in a low humidity environment with an absolute water content of 3 g / m ³ or less, the pressing amount of 2.1 mm makes it possible to set the center of the OK range. Further, in a high humidity environment with an absolute water content of 13 g / m ³ or more, the pressing amount of 1.7 mm makes it possible to set the center of the OK range.

Further, consider a case where the pressing amount of the pressing member 26 is fixed to 1.9 mm and the position of the inner roller 21 is changed. Stationary environment (absolute water content is greater than 3 g / m ^3, a small range of environment than 13 g / m ³⁾ under the position of the inner roller 21 is assumed to be the position of the reference. In a low humidity environment with an absolute moisture content of 3 g / m ³ or less, the position of the inner roller 21 is set to the center of the OK range by moving the position of the inner roller 21 to the downstream side in the moving direction of the intermediate transfer belt 7 by 0.3 mm with respect to the reference position. It becomes possible to do. Further, in a high humidity environment with an absolute moisture content of 13 g / m ³ or more, by moving the position of the inner roller 21 to the upstream side in the moving direction of the intermediate transfer belt 7 by 0.3 mm with respect to the reference position, it is within the OK range. It is possible to set it in the center.

In the configuration of this embodiment, for the recording material P having a garley rigidity smaller than 64 mN, the OK range of FIG. 2 can be made wider, so that the pressing amount of the pressing member 26 and the position of the inner roller 21 can be determined. No need to move. That is, in this case, "scattering" is suppressed and "image" is suppressed without changing the pressing amount of the pressing member 26 or the position of the inner roller 21 based on the output value (detection result of the absolute water content) of the environmental sensor 13. It is possible to achieve both suppression of "rubbing".

Further, as described above, regardless of which of the pressing amount of the pressing member 26 and the position of the inner roller 21 is changed, it is possible to suppress both "scattering" and "image rubbing". Is. However, since the position accuracy of the inner roller 21 also affects the transportability of the recording material P in the secondary transfer nip N2, it is desirable to change the pressing amount of the pressing member 26.

In this embodiment, a thick paper with high rigidity (Garley rigidity of 64 mN or more) is used as the recording material P, and the position of the inner roller 21 is fixed to a reference position (as an example, a position where the offset amount X is −1.3 mm). The case where the pressing amount of the pressing member 26 is changed will be described.

5. Pressing member, pressing mechanism Next, the pressing member 26 in this embodiment and the pressing mechanism 16 for changing the position of the pressing member 26 will be described. FIG. 3 is an outline of a main part in which the vicinity of the secondary transfer nip N2 in this embodiment is viewed from one end side (front side of the paper surface in FIG. 1) of the inner roller 21 in the rotation axis direction substantially parallel to the rotation axis direction. It is a side view. FIG. 3 shows the configuration of one end portion of the inner roller 21 in the rotation axis direction, but the configuration of the other end portion is also the same (substantially symmetrical with respect to the center of the inner roller 21 in the rotation axis direction).

In this embodiment, the image forming apparatus 100 has a sheet-shaped pressing member (backup sheet) 26. The pressing member 26 can press the inner peripheral surface of the intermediate transfer belt 7 in the vicinity of the inlet of the secondary transfer nip N2 to cause the intermediate transfer belt 7 to project toward the outer peripheral surface side. The pressing member 26 is arranged so as to be in contact with the inner peripheral surface of the intermediate transfer belt 7 in the rotation direction of the intermediate transfer belt 7 upstream of the inner roller 21 and downstream of the secondary transfer pre-roller 24. There is. In particular, in this embodiment, the pressing member 26 is located upstream of the inner roller 21 and downstream of the tip of the transport guide 14 (first guide member 14a) on the downstream side in the transport direction of the recording material P. It is arranged so that it can come into contact with the inner peripheral surface of the intermediate transfer belt 7 corresponding to the above.

The pressing member 26 can be formed by using a resin material. As the resin material forming the pressing member 26, for example, a polyester resin such as PET resin can be preferably used. In this embodiment, the pressing member 26 is arranged in a longitudinal direction substantially parallel to the width direction of the intermediate transfer belt 7 (a direction substantially orthogonal to the moving direction of the surface) and a lateral direction substantially orthogonal to the longitudinal direction. , Each of which has a predetermined length and is composed of a plate-shaped member having a predetermined thickness. The length of the pressing member 26 in the longitudinal direction is equivalent to the length of the intermediate transfer belt 7 in the width direction. The free end of the pressing member 26, which is one end in the lateral direction (the end on the downstream side in the rotation direction of the intermediate transfer belt 7), covers substantially the entire width of the intermediate transfer belt 7 and is formed by the intermediate transfer belt 7. It can contact the inner peripheral surface and can press the intermediate transfer belt 7. Further, as an example, the thickness of the pressing member 26 is about 0.4 mm to 0.6 mm.

For example, when a PET resin sheet is used as the pressing member 26, if a PET resin sheet having an electric resistance too low is used, a current flows through the pressing member 26 as the secondary transfer voltage is applied to the outer roller 9, and the transfer is performed. May cause defects. On the other hand, if a PET resin sheet having too high electrical resistance is used, static electricity (triboelectric charging) is generated due to friction between the pressing member 26 and the intermediate transfer belt 7, and the intermediate transfer belt 7 is attracted to the pressing member 26 to attract the intermediate transfer belt 7. It may interfere with the rotation of 7. Therefore, as the pressing member 26, it is preferable to use a PET resin sheet adjusted to a medium resistance electrical resistance (for example, a volume resistivity of 1 × 10 ⁵ to 1 × 10 ^{9 Ω · cm).}

Then, in this embodiment, the image forming apparatus 100 has a pressing mechanism 16 that changes the position of the pressing member 26 to change the pressing amount of the pressing member 26 against the intermediate transfer belt 7. The pressing member 26 is supported by a pressing member holder 28 as a supporting member. The pressing member 26 has a fixed end that is one end in the lateral direction (the end on the upstream side in the rotation direction of the intermediate transfer belt 7) and is fixed to the pressing member holder 28 over substantially the entire width in the longitudinal direction. The pressing member holder 28 is supported by a frame or the like of the intermediate transfer belt unit 20 so as to be rotatable about the pressing member rotating shaft 28a. In this way, the position of the pressing member 26 is changed by rotating the pressing member holder 28 around the pressing member rotating shaft 28a and rotating the pressing member 26 around the pressing member rotating shaft 28a. Can be done. Thereby, the pressing amount of the pressing member 26 against the intermediate transfer belt 7 can be changed. The pressing member holder 28 is configured to rotate by the action of the pressing cam 27 as an operating member. The pressing cam 27 is supported by a frame or the like of the intermediate transfer belt unit 20 so that the pressing cam 27 can rotate about the pressing cam rotating shaft 27a. The pressing cam 27 is driven by the pressing cam drive motor 211 as a drive source and rotates about the pressing cam rotation shaft 27. Further, the pressing cam 27 is in contact with the cam follower 28b provided on the pressing member holder 28. The pressing member holder 28 may be configured to be constantly urged by the tension of the intermediate transfer belt 7 so that the cam follower 28b rotates in the direction of engaging with the pressing cam 27. Alternatively, the pressing member holder 28 is moved by a rotating spring composed of a tension spring or the like, which is an urging member (elastic member) as an urging means, so that the cam follower 28b rotates in the direction of engaging with the pressing cam 27. It may be configured to be urged. Further, in the present embodiment, the image forming apparatus 100 is pressed by the image forming apparatus 100 as a position detecting means for detecting the position of the pressing cam 27 in the rotating direction, particularly, in the present embodiment, the home position (HP) in the rotating direction. A cam position sensor (cam HP sensor) 212 is provided. The pressing cam position sensor 212 can be configured to include, for example, the pressing cam 27 or a flag as an indicating unit provided coaxially with the pressing cam 27, a photo interrupter as a detecting unit, and the like. As described above, in this embodiment, the pressing mechanism 16 includes the pressing member holder 28, the pressing cam 27, the pressing cam drive motor 211, the pressing cam position sensor 212, and the like.

When the pressing cam 27 is driven by the pressing cam drive motor 211 and rotates clockwise, the pressing member holder 28 rotates counterclockwise around the pressing member rotating shaft 28a. Thereby, the pressing amount of the pressing member 26 can be increased. Further, the pressing cam 27 is driven by the pressing cam drive motor 211 and rotates counterclockwise, so that the pressing member holder 28 rotates clockwise around the pressing member rotation shaft 28a. Thereby, the pressing amount of the pressing member 26 can be reduced.

Here, although not limited to this, from the viewpoint of suppressing "scattering" and "image rubbing", the initial setting value (predetermined) of the pressing amount (penetrating amount Y) of the pressing member 26 against the intermediate transfer belt 7 is set. The pressing force) is preferably about 1.0 to 3.0 mm. Further, it is desirable that the pressing member 26 is as close as possible to the inner roller 21, but it is desirable that the pressing member 26 be arranged so as not to come into contact with the inner roller 21. The pressing member 26 is located at a position separated from the position where the inner roller 21 and the intermediate transfer belt 7 are in contact with the upstream side in the rotation direction of the intermediate transfer belt 7 by, for example, about 2 mm or more, and the inner peripheral surface of the intermediate transfer belt 7 and the pressing member. It can be arranged so that it comes into contact with the tip of 26. Further, the pressing member 26 presses against the inner peripheral surface of the intermediate transfer belt 7 at a position separated from the position where the inner roller 21 and the intermediate transfer belt 7 come into contact with the upstream side in the rotation direction of the intermediate transfer belt 7 by about 40 mm or less. It is preferable that the member 26 is arranged so as to be in contact with the tip of the member 26. Typically, the pressing member 26 can contact the inner peripheral surface of the intermediate transfer belt 7 within 25 mm from the region where the inner roller 21 and the intermediate transfer belt 7 contact to the upstream side in the rotation direction of the intermediate transfer belt 7. Arranged like this.

FIG. 4 is an enlarged side view of the vicinity of the pressing member 26 as viewed from the same direction as in FIG. 3 for explaining the position of the pressing member 26 and the operation of the pressing mechanism 16 under each environment. Note that FIG. 4 shows the position of the pressing member 26 when a thick paper having a high rigidity (Garley rigidity of 64 mN or more) is used as the recording material P.

4 (a) is stationary environment (absolute water content is greater than 3 g / ^{m 3,} a small range of environment than 13 g / ^{m 3)} shows the vicinity of the pressing member 26 under. In this embodiment, as described above, the pressing amount of the pressing member 26 in the steady environment is set to 1.9 mm.

FIG. 4B shows the vicinity of the pressing member 26 in a low humidity environment with an absolute water content of 3 g / m ^{3 or less.} In a low humidity environment, it is necessary to increase the pressing amount of the pressing member 26 as compared with the steady environment in order to suppress "scattering". As shown in FIG. 4B, the pressing amount of the pressing member 26 can be increased by rotating the pressing cam 27 clockwise from the state of FIG. 4A. In this embodiment, as described above, the pressing amount of the pressing member 26 in a low humidity environment is set to 2.1 mm. This makes it possible to suppress "scattering" in a low humidity environment.

Further, FIG. 4C shows the vicinity of the pressing member 26 in a high humidity environment having an absolute water content of 13 g / m ^{3 or more.} In a high humidity environment, it is necessary to reduce the pressing amount of the pressing member 26 as compared with the steady environment in order to suppress "image rubbing". As shown in FIG. 4 (c), the pressing amount of the pressing member 26 can be reduced by rotating the pressing cam 27 counterclockwise from the state of FIG. 4 (a). In this embodiment, as described above, the pressing amount of the pressing member 26 in a high humidity environment is set to 1.7 mm. This makes it possible to suppress "image rubbing" in a high humidity environment.

6. Control mode FIG. 5 is a schematic block diagram showing a control mode of a main part of the image forming apparatus 100 of this embodiment. The control unit 200 as a control means includes a CPU as an arithmetic control means which is a central element for performing arithmetic processing, a memory (storage medium) such as a ROM and a RAM as a storage means, an interface unit (input / output circuit), and the like. It is composed of. The RAM, which is a rewritable memory, stores information input to the control unit 200, detected information, calculation results, and the like, and the ROM stores a control program, a data table obtained in advance, and the like. Data can be transferred and read from each other between the CPU and the memory. The interface unit controls the input / output (communication) of signals between the control unit 200 and the device connected to the control unit 200.

Each part of the image forming apparatus 100 (an image forming unit 10, an intermediate transfer belt 7, a driving device of a member related to the transfer of the recording material P, various power sources, etc.) is connected to the control unit 200. In relation to the present embodiment, the control unit 200 has a calculation unit 201, a drive control unit 210, and a storage unit 220 as functional blocks. The calculation unit 201 and the drive control unit 210 are realized by operating the CPU according to a predetermined program. The storage unit 220 is realized by the above memory. The drive control unit 210 is connected to drive means of each part of the image forming apparatus 100, such as a drum drive motor 111, a belt drive motor 112, and a pressing cam drive motor 211. The drive control unit 210 operates each unit according to a command from the calculation unit 201. The storage unit 220 stores the absolute water content information 221 acquired from the environment sensor 13 and the pressing cam position information 222 acquired from the pressing cam position sensor 212 that detects the home position (HP) of the pressing cam 27. Further, the storage unit 220 stores a pressing amount conversion table 223 for rotationally driving the pressing cam 27 to a predetermined position in order to obtain an optimum image according to the absolute water content information 221.

Further, an operation unit (operation panel) 101 provided in the image forming apparatus 100 is connected to the control unit 200. The operation unit 101 has a display means for displaying information under the control of the control unit 200, and an input means for inputting information to the control unit 200 by an operation by an operator such as a user or a service person. The operation unit 101 may be configured to have a touch panel having the functions of a display means and an input means. Further, the control unit 200 includes an image reading device (not shown) provided in the image forming device 100 or connected to the image forming device 100, or an external device such as a personal computer connected to the image forming device 100 (not shown). (Not shown) may be connected.

The control unit 200 controls each unit of the image forming apparatus 100 based on the job information to perform the image forming operation. The job information includes information (command signal) regarding image formation conditions such as a start instruction (start signal) input from the operation unit 101 or an external device, and a type of recording material P. Further, the job information includes image information (image signal) input from the image reading device, the external device, or the operation unit 101. The information on the type of recording material P (also simply referred to as "information on recording material") is based on general characteristics such as plain paper, high-quality paper, glossy paper, coated paper, embossed paper, thick paper, and thin paper. Includes arbitrary information that can distinguish recording materials, such as attributes (so-called paper type category), basis weight, thickness, size, rigidity, and other numerical values and numerical ranges, or brands (including manufacturer, product number, etc.). Is what you do. Further, in this embodiment, the control unit 200 controls the operation of changing the position of the pressing member 26 by controlling the pressing cam drive motor 211 of the pressing mechanism 16.

The image forming apparatus 100 executes a job (print job, print job) which is a series of operations of forming and outputting an image on a single or a plurality of recording materials P, which is started by one start instruction. The job generally includes an image forming step (image forming operation, printing operation, printing operation), a front rotation step, a paper-to-paper step when forming an image on a plurality of recording materials P, and a back rotation step. The image forming step is a period during which an electrostatic image of an image actually formed and output on the recording material P is formed, a toner image is formed, a primary transfer of the toner image is performed, and a secondary transfer is performed, and the image is formed (image). The formation period) means this period. More specifically, the timing at the time of image formation differs depending on the position where each of the steps of forming the electrostatic image, forming the toner image, and performing the primary transfer and the secondary transfer of the toner image is performed. The pre-rotation step is a period during which the preparatory operation before the image forming step is performed from the input of the start instruction to the actual start of forming the image. The inter-paper process is a period corresponding between the recording material P and the recording material P when image formation is continuously performed on the plurality of recording materials P (continuous image formation). The back rotation step is a period for performing an organizing operation (preparation operation) after the image forming step. The non-image forming period (non-image forming period) is a period other than the image forming period, and is from the pre-rotation step, the inter-paper step, the post-rotation step, and further, when the power of the image forming apparatus 100 is turned on or in the sleep state. It includes a pre-multi-rotation process, which is a preparatory operation at the time of recovery. The sleep state (hibernate 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 200 (or a part thereof) is stopped, and the power consumption is less than that in the standby state. Is.

7. Control procedure Next, the job control procedure in this embodiment will be described. FIG. 6 is a flowchart showing an outline of a job control procedure in this embodiment. Here, a case where the operator causes the image forming apparatus 100 to execute one job from the operating unit 101 of the apparatus main body 110 will be described as an example. Further, here, it is assumed that a cardboard having a high rigidity (Garley rigidity of 64 mN or more) is used as the recording material P. Note that FIG. 6 shows an outline of a control procedure focusing on an operation of changing the position of the pressing member 26, and many other operations normally required for executing a job and outputting an image are shown. It has been omitted.

First, when the job information is input, the control unit 200 acquires the absolute water content information 221 of the environment detected by the environment sensor 13 before starting the image forming operation (S101). Next, the control unit 200 sends a command to the pressing cam drive motor 211 based on the pressing cam position information 222 detected by the pressing cam position sensor 212, and drives the pressing cam 27 to rotate to the HP position (S102). Further, the control unit 200 sends a command to the pressing cam drive motor 211 based on a preset pressing amount conversion table 223 based on the rotation amount of the pressing cam 27 from the HP, etc., and is optimized according to the absolute water content. The pressing cam 27 is rotationally driven to a predetermined position in order to obtain an image. As a result, the control unit 200 moves the pressing member 26 to a predetermined position (S103). As described above, in this embodiment, the constant environment (absolute water content is greater than 3 g / ^{m 3,} a small range of environment than 13 g / ^{m 3)} In the case of the pressing amount of the pressing member 26 is a 1.9mm NS. Further, in the case of a low humidity environment with an absolute water content of 3 g / m ³ or less, the pressing amount of the pressing member 26 is 2.1 mm. Further, in the case of a high humidity environment having an absolute water content of 13 g / m ³ or more, the pressing amount of the pressing member 26 is 1.7 mm. After that, the control unit 200 sends a command to each unit of the image forming apparatus 100 to perform an image forming operation (S104). In S104, the control unit 200 sends a command to each unit of the image forming apparatus 100 such as the drum drive motor 111 and the belt drive motor 112 to start the image forming preparation operation (pre-rotation step). Then, as soon as the predetermined image formation preparation operation is completed, a command is sent to each part of the image forming device 100 such as the exposure device 3 and the driving device of the member related to the transportation of the recording material P, and the image forming operation is started.

As described above, in the present embodiment, the image forming apparatus 100 includes a pressing mechanism 16 capable of changing the pressing amount of the pressing member 26 against the intermediate transfer belt 7, a control unit 200 for controlling the pressing mechanism 16, and an environmental moisture content. It has an environment sensor 13 that outputs a signal that correlates with the above. Then, in this embodiment, the control unit 200 can control the pressing mechanism 16 so as to change the pressing amount of the pressing member 26 based on the output value of the environmental sensor 13. When the water content of the environment indicated by the output value of the environment sensor 13 is the first water content, the control unit 200 sets the pressing amount of the pressing member 26 as the first pressing amount, and the environment indicated by the output value of the environment sensor 13 When the amount of water in the pressing member 26 is larger than the first amount of water, the pressing mechanism 16 is set so that the amount of pressing of the pressing member 26 is the second amount of pressing smaller than the first amount of pressing. It is controllable. In particular, in this embodiment, when the water content of the environment indicated by the output value of the environmental sensor 13 is smaller than the predetermined range, the control unit 200 determines the water content of the environment indicated by the output value of the environmental sensor 13. The pressing mechanism 16 can be controlled so that the pressing amount of the pressing member 26 is larger than that within the range. Further, in the present embodiment, when the water content of the environment indicated by the output value of the environmental sensor 13 is larger than the predetermined range, the control unit 200 determines the water content of the environment indicated by the output value of the environmental sensor 13. The pressing mechanism 16 can be controlled so that the pressing amount of the pressing member 26 is smaller than that within the range. Here, in this embodiment, the pressing amount of the pressing member 26 is changed to three stepwise according to the absolute water content of the environment, but two stepwise or continuously depending on the absolute water content of the environment. Alternatively, it may be changed to four or more. Further, the pressing amount of the pressing member 26 is the pressing amount of the pressing member 26 according to the absolute water content of the environment when the recording material P passes through the secondary transfer nip N2 (during the secondary transfer). Just do it.

Although not shown in FIG. 6 because the case where a thick paper having high rigidity is used as the recording material P is taken as an example, the control unit 200 provides information on the type of recording material P related to the rigidity of the recording material P. Control can be switched based on. That is, when the control unit 200 receives the job information, it acquires the information regarding the type of the recording material P used for the image forming operation, which is included in the job information. The control unit 200 acquires information regarding the type of recording material P directly input (including selecting from a plurality of options) from the operation unit 101 (or an external device) by the operation of the operator. Can be done. Further, the control unit 200 relates to the type of the recording material P based on the information of the recording material cassette 11 that sends out the recording material P in the job, which is input from the operation unit 101 (or an external device) by the operation of the operator. You can also get information. In this case, the control unit 200 acquires information on the type of the recording material P from, for example, information on the type of the recording material P stored in the storage unit 220 in relation to each of the plurality of cassettes 11. be able to. Then, the control unit 200 uses a predetermined recording material P for the job (that is, a predetermined recording material P) based on the information regarding the recording material P input by the operation unit 101 or the like as an input unit for inputting the information regarding the recording material P. In the case of (transferring to the recording material P), it is possible to control to change the pressing amount of the pressing member 26 based on the output value of the environmental sensor 13. Here, in the present embodiment, the predetermined recording material P is a recording material P having a rigidity equal to or higher than a predetermined rigidity. On the other hand, when a recording material P other than the predetermined recording material P (for example, a recording material P having a rigidity less than the predetermined rigidity) is used for the job, the pressing amount of the pressing member 26 is based on the output value of the environmental sensor 13. It is not necessary to control to change. In this embodiment, the pressing amount of the pressing member 26 in this case is arbitrary, but can be fixed regardless of the type of the recording material P, or can be changed according to the type of the recording material P, for example. .. In particular, when a recording material P having a low rigidity such as a thin paper having a low rigidity is used as the recording material P, "scattering" is unlikely to occur. It may be 0 mm (the pressing member 26 may be separated from the intermediate transfer belt 7).

As described above, according to the present embodiment, even when a recording material P having a high rigidity such as a thick paper having a high rigidity is used, both "scattering" and "image rubbing" are suppressed, and a good image is obtained. Can be obtained.

[Example 2]
Next, other examples 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 Example 1. Therefore, in the image forming apparatus of the present embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of the first embodiment are designated by the same reference numerals as those of the first embodiment, and detailed description thereof will be omitted. do.

1. 1. Outline of this Example As described in Example 1 with reference to FIG. 2, by changing the position (offset amount X) of the inner roller 21, "scattering" can be suppressed and "image rubbing" can be achieved depending on the environment. It is possible to achieve both the suppression of "". This point will be further described with reference to FIG. FIG. 14 is a schematic cross-sectional view (cross section substantially orthogonal to the rotation axis direction of the inner roller 21) for explaining the behavior of the recording material P in the vicinity of the secondary transfer nip N2.

In the cross section shown in FIG. 14, the line indicating the tension surface (tension surface) of the intermediate transfer belt 7 formed by being stretched by the inner roller 21 and the secondary transfer pre-roller 24 is referred to as a tension wire T. Further, in the same cross section, a straight line passing through the rotation center of the inner roller 21 and the rotation center of the outer roller 9 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 referred to as a nip line Ln. Note that in FIG. 14, the pressing member 26 is not shown. At this time, when the recording material P is sandwiched between the inner roller 21 and the outer roller 9 by the secondary transfer nip N2, the recording material P tends to maintain its posture substantially along the nip line Ln. Therefore, in general, the more the outer roller 9 is arranged on the upstream side in the rotation direction of the intermediate transfer belt 7 (the larger the offset amount X), the more the nip line Ln becomes. It has a shape that cuts into the overhead wire T (one-dot chain line in FIG. 14). As a result, the close contact distance between the intermediate transfer belt 7 and the recording material P can be increased. On the contrary, the smaller the offset amount X, the smaller the contact pressure between the intermediate transfer belt 7 and the recording material P (broken line in FIG. 14).

Therefore, instead of changing the pressing amount of the pressing member 26 in the first embodiment, by changing the position (offset amount X) of the inner roller 21, "scattering" can be suppressed and "image rubbing" can be achieved according to the environment. It is possible to achieve both the suppression and the suppression of.

Therefore, in this embodiment, the control unit 200 (FIG. 9) controls the offset mechanism 17 (FIG. 7) based on the output value (detection result of the absolute water content) of the environmental sensor 13 to control the inner roller 21. Change (adjust) the position (offset amount X). Generally, in a low humidity environment, the position of the inner roller 21 is moved to the downstream side in the moving direction of the intermediate transfer belt 7 (the offset amount X is made relatively large). Then, the transport direction of the recording material P in the secondary transfer nip N2 is changed to increase the close contact distance between the intermediate transfer belt 7 and the recording material P upstream of the secondary transfer nip N2. This makes it possible to suppress the occurrence of "scattering". Further, roughly, in a high humidity environment, the position of the inner roller 21 is moved to the upstream side in the moving direction of the intermediate transfer belt 7 (the offset amount X is made relatively small). Then, the transport direction of the recording material P in the secondary transfer nip N2 is changed to reduce the contact pressure between the intermediate transfer belt 7 and the recording material P upstream of the secondary transfer nip N2. This makes it possible to suppress the occurrence of "image rubbing".

2. Offset Mechanism With reference to FIG. 7, the offset mechanism 17 in this embodiment will be described. FIG. 7 shows the vicinity of the secondary transfer nip N2 for explaining the offset mechanism 17 from one end side (front side of the paper surface in FIG. 1) of the inner roller 21 in the rotation axis direction substantially parallel to the rotation axis direction. It is a schematic side view of the main part.

In this embodiment, the image forming apparatus 100 has an offset mechanism 17 as a position changing mechanism that changes the relative position of the inner roller 21 with respect to the circumferential direction of the outer roller 9 to change the offset amount X. FIG. 7 shows the configuration of one end portion of the inner roller 21 in the rotation axis direction, but the configuration of the other end portion is also the same (substantially symmetrical with respect to the center of the inner roller 21 in the rotation axis direction).

Both ends of the inner roller 21 in the direction of the rotation axis are rotatably supported by the inner roller holder 30 as a support member. The inner roller holder 30 is supported by a frame or the like of the intermediate transfer belt unit 20 so as to be rotatable about the inner roller rotation shaft 30a. In this way, the inner roller holder 30 is rotated around the inner roller rotation shaft 30a, and the inner roller 21 is rotated around the inner roller rotation shaft 30a, so that the inner roller 21 is relative to the outer roller 9. The offset amount X can be changed by changing the position. The inner roller holder 30 is configured to rotate by the action of the offset cam 29 as an operating member. The offset cam 29 is supported by a frame or the like of the intermediate transfer belt unit 20 so that the offset cam 29 can rotate about the offset cam rotation shaft 29a. The offset cam 29 is driven by the offset cam drive motor 213 as a drive source and rotates about the offset cam rotation shaft 29a. Further, the offset cam 29 is in contact with the cam follower 30b provided on the inner roller holder 30. Further, the inner roller holder 30 is a rotating spring composed of a tension spring or the like which is an urging member (elastic member) as an urging means so that the cam follower 30b rotates in a direction in which the cam follower 30b engages with the offset cam 29. May be urged by. The tension of the intermediate transfer belt 7 or the pressing by the outer roller 9 may provide a sufficient moment to rotate the inner roller holder 30 in the direction in which the cam follower 30b engages with the offset cam 29. In this case, the rotary spring may not be provided. Further, in the present embodiment, the image forming apparatus 100 has an offset cam position sensor (as a position detecting means for detecting the position of the offset cam 29 in the rotation direction, particularly the home position (HP) in the rotation direction). A cam HP sensor) 214 is provided. The offset cam position sensor 214 can be configured to include, for example, an offset cam 29 or a flag as an indicator provided coaxially with the offset cam 29, a photo interrupter as a detection unit, and the like. As described above, in this embodiment, the offset mechanism 17 includes an inner roller holder 30, an offset cam 29, an offset cam drive motor 213, an offset cam position sensor 214, and the like.

The offset cam 29 is driven by the offset cam drive motor 213 and rotates clockwise, so that the inner roller holder 30 rotates clockwise around the inner roller rotation shaft 30a. As a result, the inner roller 21 can be moved to the downstream side in the moving direction of the intermediate transfer belt 7 to increase the offset amount X. Further, the offset cam 29 is driven by the offset cam drive motor 213 and rotates counterclockwise, so that the inner roller holder 30 rotates counterclockwise around the inner roller rotation shaft 30a. As a result, the inner roller 21 can be moved to the upstream side in the moving direction of the intermediate transfer belt 7 to reduce the offset amount X.

Here, as in the first embodiment, a case where a high-rigidity thick paper (Garley rigidity of 64 mN or more) is used as the recording material P will be described. Further, in this embodiment, the position of the pressing member 26 is fixed at a predetermined position. As an example, in this embodiment, the position of the pressing member 26 is fixed at a position where the pressing amount is 1.9 mm. Further, in this embodiment, the reference position of the inner roller 21 is a position where the offset amount X is −1.3 mm. Then, the position of the inner roller 21 is changed with respect to the reference position.

Here, although not limited to this, the offset amount X is preferably about -3 mm to +3 mm. In particular, when a recording material P having a high rigidity such as a thick paper having a high rigidity is used as the recording material P, the rear end of the recording material P in the transport direction when the rear end of the recording material P in the transport direction passes through the transport guide 14. The shock caused by the portion colliding with the intermediate transfer belt 7 may increase. Therefore, the offset amount X is preferably 0 mm or less in order to suppress image defects due to this. On the other hand, when a recording material P having a low rigidity such as a thin paper having a low rigidity is used as the recording material P, the pressing amount of the pressing member 26 is less than 0 mm from the viewpoint of separability of the recording material P from the intermediate transfer belt 7. It is preferable to increase the size.

FIG. 8 is an enlarged side view of the vicinity of the inner roller 21 as viewed from the same direction as in FIG. 7 for explaining the position of the inner roller 21 and the operation of the offset mechanism 17 under each environment. Note that FIG. 8 shows the position of the pressing member 26 when a thick paper having a high rigidity (Garley rigidity of 64 mN or more) is used as the recording material P.

8 (a) is stationary environment (absolute water content is greater than 3 g / ^{m 3,} a small range of environment than 13 g / ^{m 3)} showing the vicinity of the inner roller 21 under. In this embodiment, the position of the inner roller 21 shown in FIG. 8A is used as a reference position. As described above, in this embodiment, the offset amount X at this time is −1.3 mm.

FIG. 8B shows the vicinity of the inner roller 21 in a low humidity environment with an absolute water content of 3 g / m ^{3 or less.} In a low humidity environment, it is necessary to move the position of the inner roller 21 to the downstream side in the moving direction of the intermediate transfer belt 7 with respect to the reference position in order to suppress "scattering". As shown in FIG. 8 (b), by rotating the offset cam 29 clockwise from the state of FIG. 8 (a), the position of the inner roller 21 is set to the reference position (two-dot chain line in FIG. 8 (b)). ), The intermediate transfer belt 7 is moved by 0.3 mm to the downstream side in the moving direction. As a result, the transport direction of the recording material P in the secondary transfer nip N2 can be changed to increase the adhesion distance, and "scattering" in a low humidity environment can be suppressed.

Further, FIG. 8C shows the vicinity of the inner roller 21 in a low humidity environment having an absolute water content of 13 g / m ^{3 or more.} In a high humidity environment, it is necessary to move the position of the inner roller 21 to the upstream side in the moving direction of the intermediate transfer belt 7 with respect to the reference position in order to suppress "image rubbing". As shown in FIG. 8 (c), by rotating the offset cam 29 counterclockwise from the state of FIG. 8 (a), the position of the inner roller 21 is set to the reference position (two points in FIG. 8 (c)). The intermediate transfer belt 7 is moved by 0.3 mm to the upstream side in the moving direction with respect to the chain line). As a result, the transport direction of the recording material P in the secondary transfer nip N2 can be changed to reduce the contact pressure, and "image rubbing" in a high humidity environment can be suppressed.

3. 3. Control mode FIG. 9 is a schematic block diagram showing a control mode of a main part of the image forming apparatus 100 of this embodiment. The control mode of the image forming apparatus 100 of this embodiment is the same as that of the image forming apparatus 100 of Example 1 shown in FIG. 5, but in this embodiment, the control unit 200 includes an offset cam drive motor 213 and an offset. The cam position sensor 214 is connected. Then, in this embodiment, the drive control unit 210 can operate the offset cam drive motor 213 by a command from the calculation unit 201. Further, in the present embodiment, the storage unit 220 stores the offset cam position information 224 acquired from the offset cam position sensor 214 that detects the home position (HP) of the offset cam 29. Further, in the present embodiment, the storage unit 220 stores an inner roller position conversion table 225 for rotationally driving the offset cam 29 to a predetermined position in order to obtain an optimum image according to the absolute water content. Further, in this embodiment, the control unit 200 controls the operation of changing the position of the inner roller 21 by controlling the offset cam drive motor 213 of the offset mechanism 17.

4. Control procedure Next, the job control procedure in this embodiment will be described. FIG. 10 is a flowchart showing an outline of a job control procedure in this embodiment. Here, a case where the operator causes the image forming apparatus 100 to execute one job from the operating unit 101 of the apparatus main body 110 will be described as an example. Further, here, it is assumed that a cardboard having a high rigidity (Garley rigidity of 64 mN or more) is used as the recording material P. Note that FIG. 10 shows an outline of the control procedure focusing on the operation of changing the position of the inner roller 21, and many other operations normally required for executing a job and outputting an image are shown. It has been omitted.

First, when the job information is input, the control unit 200 acquires the absolute water content information 221 of the environment detected by the environment sensor 13 before starting the image forming operation (S201). Next, the control unit 200 sends a command to the offset cam drive motor 213 based on the offset cam position information 224 detected by the offset cam position sensor 214, and rotationally drives the offset cam 29 to the HP position (S202). Further, the control unit 200 sends a command to the offset cam drive motor 213 based on the inner roller position conversion table 225 set in advance based on the rotation amount of the offset cam 29 from the HP and the like. Then, the offset cam 29 is rotationally driven to a predetermined position in order to obtain an optimum image according to the absolute water content. As a result, the control unit 200 moves the inner roller 21 to a predetermined position (S203). As described above, in this embodiment, the constant environment (absolute water content is greater than 3 g / m ^3, a small range of environment than 13 g / m ³⁾ For the position of the inner roller 21 is a position of the reference .. Further, in the case of a low humidity environment having an absolute water content of 3 g / m ³ or less, the position of the inner roller 21 is set to be a position moved by 0.3 mm to the downstream side in the moving direction of the intermediate transfer belt 7 with respect to the reference position. Further, in the case of a high humidity environment having an absolute water content of 13 g / m ³ or more, the position of the inner roller 21 is set to be a position moved by 0.3 mm upstream of the moving direction of the intermediate transfer belt 7 with respect to the reference position. After that, the control unit 200 sends a command to each unit of the image forming apparatus 100 to perform an image forming operation (S204). The operation in S204 is the same as in the first embodiment.

As described above, in the present embodiment, the image forming apparatus 100 includes an offset mechanism 17 that changes the relative positions of the inner roller 21 and the outer roller 9 with respect to the circumferential direction of the inner roller 21, and a control unit 200 that controls the offset mechanism 17. And an environment sensor 13 that outputs a signal that correlates with the amount of water in the environment. Then, in this embodiment, the control unit 200 can control the offset mechanism 17 so as to change the relative position based on the output value of the environment sensor 13. When the water content of the environment indicated by the output value of the environment sensor 13 is the first water content, the control unit 200 sets the relative position as the first relative position and sets the relative position to the first relative position, and the control unit 200 sets the relative position to the first relative position and the water content of the environment indicated by the output value of the environment sensor 13. When the second water content is larger than the first water content, the inner roller 21 is located upstream of the first relative position in the rotation direction of the intermediate transfer belt 7 with respect to the outer roller 9. The offset mechanism 17 can be controlled so as to be a second relative position to be located. In particular, in this embodiment, when the water content of the environment indicated by the output value of the environmental sensor 13 is smaller than the predetermined range, the control unit 200 determines the water content of the environment indicated by the output value of the environmental sensor 13. The offset mechanism 17 can be controlled so that the inner roller 21 is located downstream of the outer roller 9 in the rotation direction of the intermediate transfer belt 7 rather than the relative position in the range. .. Further, in the present embodiment, when the water content of the environment indicated by the output value of the environmental sensor 13 is larger than the predetermined range, the control unit 200 determines the water content of the environment indicated by the output value of the environmental sensor 13. The offset mechanism 17 can be controlled so that the inner roller 21 is located upstream of the outer roller 9 in the rotation direction of the intermediate transfer belt 7 rather than the relative position in the range. .. Here, in this embodiment, the position (offset amount X) of the inner roller 21 is changed to three stepwise according to the absolute water content of the environment, but is stepwise or continuous depending on the absolute water content of the environment. It may be changed to two or four or more. Further, the position of the inner roller 21 (offset amount X) is the position of the inner roller 21 according to the absolute water content of the environment when the recording material P passes through the secondary transfer nip N2 (during the secondary transfer). It suffices if it is (offset amount X).

Although not shown in FIG. 10 because the case where a thick paper having high rigidity is used as the recording material P is taken as an example, the control unit 200 provides information on the type of recording material P related to the rigidity of the recording material P. Control can be switched based on. That is, when the control unit 200 receives the job information, it acquires the information regarding the type of the recording material P used for the image forming operation, which is included in the job information. Then, the control unit 200 uses a predetermined recording material P for the job (that is, a predetermined recording material P) based on the information regarding the recording material P input by the operation unit 101 or the like as an input unit for inputting the information regarding the recording material P. When transferring to the recording material P), it is possible to control to change the relative position based on the output value of the environmental sensor 13. Here, in the present embodiment, the predetermined recording material P is a recording material P having a rigidity equal to or higher than a predetermined rigidity. On the other hand, when a recording material P other than the predetermined recording material P (for example, a recording material P having a rigidity less than the predetermined rigidity) is used for the job, the relative position is changed based on the output value of the environmental sensor 13. No control is required. In this embodiment, the relative position in this case is arbitrary, but for example, it can be fixed regardless of the type of the recording material P, or can be changed according to the type of the recording material P. In particular, when a recording material P having a low rigidity such as a thin paper having a low rigidity is used as the recording material P, the offset amount X of the pressing member 26 is 0 mm from the viewpoint of the separability of the recording material P from the intermediate transfer belt 7. Can be larger.

Further, in the present embodiment, the image forming apparatus 100 is configured to change the offset distance X by changing the position of the inner roller 21, but the offset amount X is changed by changing the position of the outer roller 9. It may be configured to be changed. Further, the configuration is not limited to moving either the inner roller 21 or the outer roller 9, and the offset amount X may be changed by moving both the inner roller 21 and the outer roller 9.

As described above, the same effect as that of the first embodiment can be obtained by changing the position (offset amount X) of the inner roller 21 as in the present embodiment. However, as described above, considering the influence of the position accuracy of the inner roller 21 on the transportability of the recording material P in the secondary transfer nip N2, it is better to change the pressing amount of the pressing member 26 as in the first embodiment. desirable.

[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-described embodiment, the outer roller that directly contacts the outer peripheral surface of the intermediate transfer belt is used as the outer member that forms the secondary transfer nip together with the inner roller as the inner member. On the other hand, as the outer member, an outer roller and a secondary transfer belt stretched between the outer roller and another roller may be used. That is, the image forming apparatus may have, as an outer member, a tension roller, an outer roller, and a secondary transfer belt stretched between these rollers. Then, the outer roller can be brought into contact with the outer peripheral surface of the intermediate transfer belt via the secondary transfer belt. That is, the secondary transfer nip is formed by sandwiching the intermediate transfer belt and the secondary transfer belt between the inner roller that contacts the inner peripheral surface of the intermediate transfer belt and the outer roller that contacts the inner peripheral surface of the secondary transfer belt. It can be formed. In this case, the contact portion between the intermediate transfer belt and the secondary transfer belt is the secondary transfer nip as the secondary transfer portion. In this case as well, the offset amount X is defined by the relative position between the inner roller and the outer roller, as described above. Further, the penetration amount Y is also the reference line L1 formed by the inner roller and the pre-secondary transfer roller and the tangent line L4 of the pressing portion, or the reference line L1'formed by the outer roller and the pre-secondary transfer roller and the pressing portion. It is defined in the same manner as described above using the tangent line L4'.

Further, the information regarding the type of recording material related to the rigidity of the recording material is not limited to the information of the rigidity of the recording material itself. If the paper type category (for example, paper type category based on surface properties such as plain paper and coated paper) or brand (including manufacturer, product number, etc.) is the same, the basis weight of the recording material and the thickness of the recording material Are often in a substantially proportional relationship (the larger the thickness, the larger the basis weight). Further, when the paper type category or brand is the same, the rigidity of the recording material and the basis weight or thickness of the recording material are often in a substantially proportional relationship (the larger the basis weight or thickness, the greater the rigidity. ). Therefore, for example, the pressing amount according to the environment is changed based on the basis weight, thickness, or rigidity of the recording material for each paper type category, each brand, or each combination of the paper type category and the brand. Multiple controls such as whether or not can be set. Then, the control unit can switch the control based on the information such as the paper type category and the brand input from the operation unit or the external device and the information such as the basis weight, thickness, and rigidity of the recording material. .. Further, the information regarding the type of recording material is not limited to using, for example, quantitative information such as the basis weight, thickness, or rigidity of the recording material. As information on 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, it is possible to set a plurality of controls such as whether or not to change the pressing amount or the like according to the environment according to the paper type category, the brand, or the combination of the paper type category and the brand. Then, the control unit can switch the control according to the information such as the paper type category and the brand input from the operation unit or the external device. In this case as well, a plurality of controls are set based on the difference in the rigidity of each recording material. The rigidity of the recording material can be represented by Garley rigidity (MD / vertical grain) [mN], and can be measured with a commercially available Garley rigidity tester. For example, the Garley rigidity (MD) of an example of "thin paper" as a recording material having a basis weight threshold of ^{less than 52 g / m 2 may be about 0.3 mN.} In addition, the Garley rigidity (MD) of an example of "plain paper" (basis weight of ^{about 80 g / m 2} ) as a recording material having a basis weight threshold of 52 g / m ² or more is about 2 mN, and "thick paper" (basis weight of about 200 g / m 2). The Garley rigidity (MD) of an example (about m ^{2) may be 20 mN or more.}

Further, the control unit is not limited to acquiring information on the type of recording material based on the input from the operation unit or the external device operated by the operator, and is a detection means for detecting the information on the type of recording material. It may be acquired based on the input of the detection result. For example, a basis weight sensor can be used as a basis weight detecting means for detecting an index value that correlates with the basis weight of the recording material. As the basis weight sensor, for example, a basis weight sensor using the attenuation of ultrasonic waves is known. Further, a surface sensor can be used as a smoothness detecting means for detecting an index value that correlates with the smoothness of the surface of the recording material that can be used for detecting the paper type category. As a surface sensor, a specularly reflected light sensor is known in which a recording material is irradiated with light and the intensity of the specularly reflected light and the diffusely reflected light is read by a light amount sensor.

Further, as the pressing mechanism and the offset mechanism, an actuator for operating the movable portion by a cam is used, but the present invention is not limited to this. The pressing mechanism and the offset mechanism may be any as long as they can realize operations similar to those described above, and for example, an actuator that operates a movable portion by using a solenoid may be used.

Further, the case where the belt-shaped image carrier is an intermediate transfer belt has been described, but the present invention can be used as long as the image carrier is composed of an endless belt that conveys the toner image supported at the image forming position. Can be applied. Examples of such a belt-shaped image carrier include a photoconductor belt and an electrostatic recording dielectric belt, in addition to the above-mentioned intermediate transfer belt.

The present invention can also be implemented in another embodiment in which a part or all of the configuration of the above-described embodiment is replaced with an alternative configuration thereof. Therefore, if it is an image forming apparatus using a belt-shaped image carrier, it can be carried out without distinction between a tandem type / 1 drum type, a charging method, an electrostatic image forming method, a developing method, a transfer method, and a fixing method. In the above-described embodiment, the main part related to the formation / transfer of the toner image has been mainly described, but the present invention includes a printer, various printing machines, a copying machine, and a fax machine by adding necessary equipment, equipment, and a housing structure. , Multifunction machine, etc., can be implemented in various applications.

7 Intermediate transfer belt 9 Outer roller 13 Environmental sensor 16 Pressing mechanism 17 Offset mechanism 21 Inner roller 26 Pressing member 100 Image forming device 200 Control unit

Claims (15)

A rotatable endless belt that conveys the toner image,
A plurality of tensioning rollers for tensioning the belt, including an inner roller and an upstream roller arranged adjacent to the inner roller upstream of the inner roller in the rotation direction of the belt. With a tension roller
An outer member which is arranged to face the inner roller and abuts on the outer peripheral surface of the belt to form a transfer portion for transferring a toner image from the belt to a recording material.
With a pressing member capable of contacting the inner peripheral surface of the belt with respect to the rotation direction of the belt upstream of the inner roller and downstream of the upstream roller, and pressing the belt from the inner peripheral surface side to the outer peripheral surface side. ,
A pressing mechanism capable of changing the pressing amount of the pressing member against the belt,
A control unit that controls the pressing mechanism and
Environmental detection means that outputs a signal that correlates with the amount of water in the environment,
Have,
The image forming apparatus is characterized in that the control unit can control the pressing mechanism so as to change the pressing amount based on the output value of the environment detecting means. When the water content of the environment indicated by the output value of the environment detecting means is the first water content, the control unit sets the pressing amount as the first pressing amount and sets the pressing amount of the environment indicated by the output value of the environment detecting means. When the amount of water is a second amount of water larger than the first amount of water, the pressing mechanism can be controlled so that the amount of pressing is a second amount of pressing smaller than the first amount of pressing. The image forming apparatus according to claim 1, wherein the image forming apparatus is characterized by the above. When the water content of the environment indicated by the output value of the environment detecting means is smaller than the predetermined range, the control unit is more than when the water content of the environment indicated by the output value of the environment detecting means is within the predetermined range. The image forming apparatus according to claim 1, wherein the pressing mechanism can be controlled so as to increase the pressing amount. When the water content of the environment indicated by the output value of the environment detecting means is larger than a predetermined range, the control unit is more than when the water content of the environment indicated by the output value of the environment detecting means is within the predetermined range. The image forming apparatus according to claim 1, wherein the pressing mechanism can be controlled so as to reduce the pressing amount. It has an input section for inputting information about recording materials.
The control unit controls to change the pressing amount based on the output value of the environment detecting means when performing the transfer to a predetermined recording material based on the information about the recording material input by the input unit. The image forming apparatus according to any one of claims 1 to 4, wherein the image forming apparatus is performed. The image forming apparatus according to claim 5, wherein the predetermined recording material is a recording material having a rigidity equal to or higher than a predetermined rigidity. A rotatable endless belt that conveys the toner image,
A plurality of tensioning rollers for tensioning the belt, including an inner roller and an upstream roller arranged adjacent to the inner roller upstream of the inner roller in the rotation direction of the belt. With a tension roller
An outer member which is arranged to face the inner roller and abuts on the outer peripheral surface of the belt to form a transfer portion for transferring a toner image from the belt to a recording material.
A position changing mechanism that changes the position of at least one of the inner roller or the outer member to change the relative position between the inner roller and the outer member with respect to the circumferential direction of the inner roller.
A control unit that controls the position change mechanism and
Environmental detection means that outputs a signal that correlates with the amount of water in the environment,
Have,
The image forming apparatus is characterized in that the control unit can control the position changing mechanism so as to change the relative position based on the output value of the environment detecting means. When the water content of the environment indicated by the output value of the environment detecting means is the first water content, the control unit sets the relative position as the first relative position and sets the relative position of the environment indicated by the output value of the environment detecting means. In the case of a second water content in which the water content is larger than the first water content, the inner roller is upstream of the first relative position in the rotational direction of the belt with respect to the outer member. The image forming apparatus according to claim 7, wherein the position changing mechanism can be controlled so as to be a second relative position located on the side. When the water content of the environment indicated by the output value of the environment detecting means is smaller than the predetermined range, the control unit is used when the water content of the environment indicated by the output value of the environment detecting means is within the predetermined range. The claim is characterized in that the position changing mechanism can be controlled so that the inner roller is located downstream of the outer member in the rotational direction of the belt with respect to the relative position. Item 7. The image forming apparatus according to item 7. When the water content of the environment indicated by the output value of the environment detecting means is larger than the predetermined range, the control unit is used when the water content of the environment indicated by the output value of the environment detecting means is within the predetermined range. The claim is characterized in that the position changing mechanism can be controlled so that the inner roller is located upstream of the outer member in the rotational direction of the belt with respect to the relative position. Item 7. The image forming apparatus according to item 7. It has an input section for inputting information about recording materials.
The control unit controls to change the relative position based on the output value of the environment detecting means when the transfer is performed to a predetermined recording material based on the information about the recording material input by the input unit. The image forming apparatus according to any one of claims 7 to 10, wherein the image forming apparatus is performed. The image forming apparatus according to claim 11, wherein the predetermined recording material is a recording material having a rigidity equal to or higher than a predetermined rigidity. The image forming apparatus according to any one of claims 7 to 12, wherein the position changing mechanism changes the position of the inner roller to change the relative position. A pressing member capable of contacting the inner peripheral surface of the belt and pressing the belt from the inner peripheral surface side to the outer peripheral surface side in the direction of rotation of the belt upstream of the inner roller and downstream of the upstream roller. The image forming apparatus according to any one of claims 7 to 13, wherein the image forming apparatus has. Any one of claims 1 to 14, wherein the belt is an intermediate transfer body that transports a toner image primaryly transferred from an image carrier for secondary transfer to a recording material by the transfer unit. The image forming apparatus according to the section.

Images