JP7435194B2 - Back curl straightening device, drying device, fixing device and image forming device - Google Patents

Description

The present invention relates to a backcurl correction device, a drying device, a fixing device, and an image forming apparatus equipped with the backcurl correction device.

An image forming apparatus using an electrophotographic method passes a sheet member carrying an unfixed toner image through a first nip (fixing nip) between a heating member and a pressure member of a fixing device. At one nip portion, the unfixed toner image is pressed and heated to be fixed on the sheet member.

Conventionally, it has been known that a sheet member curls back toward the back side due to a temperature difference between a heating member and a pressure member. If paper is ejected with large back curl, it may not be possible to eject the specified number of sheets onto the paper ejection tray, or the stacked state on the paper ejection tray may be disturbed.

In order to eliminate back curls, a back curl correction device has been proposed in Patent Document 1 (Japanese Patent No. 6,543,977). This backcurl correction device includes a drive roller, a driven roller, and a guide member disposed on the downstream side of a first nip portion (fixing nip portion) of a fixing device, and includes a drive roller, a driven roller, and a guide member formed between the drive roller and the driven roller. The sheet member after fixing is passed through the second nip portion (auxiliary nip portion). Then, the back curl is corrected by bending the leading end of the sheet member coming out of the second nip portion in the opposite direction to the back curl (toward the driven roller side) using the guide member.

However, in the back curl correction device of Patent Document 1, when the tip of the sheet member comes into contact with the guide member, dents and scratches may occur at the tip of the sheet member, or worse, the tip of the sheet member may buckle, resulting in poor conveyance. I found out that it does. Therefore, an improved back curl correction device (Patent Document 2: Japanese Unexamined Patent Publication No. 2016-177063) has been proposed. In this improved type, the position and angle of the guide member have been devised to prevent dents and buckling of the tip of the sheet member, but the back curl correction effect is insufficient due to the low quality sheet material with poor paper quality. There was a problem that the stacking condition on the paper output tray was disordered.

The present invention has been made in view of this situation, and an object of the present invention is to achieve both a backcurl correction effect on a sheet member and suppression of occurrence of dents and buckling at the leading end of the sheet member.

In order to solve the above problems, the back curl correction device of the present invention includes a first nip portion formed between a heating member and a pressure member for conveying a sheet member, and a first nip portion downstream of the first nip portion in the conveying direction. a second nip portion formed between the driving roller and the driven roller; and a guide member movable so as to be able to come into contact with the leading end portion of the sheet member conveyed downstream in the conveying direction from the second nip portion. In the back curl correction device, the guide member has a first position in which it does not block an imaginary tangent extending downstream in the conveyance direction through the second nip portion, and a second position in which it protrudes so as to block the imaginary tangent; It is characterized in that it is movable to a third position protruding from the second position so as to interrupt the virtual tangent.

According to the present invention, it is possible to ensure the back curl correction effect of the sheet member, and to suppress the occurrence of dents and buckling at the leading end of the sheet member.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic configuration diagram of a fixing device according to an embodiment of the present invention before a job starts; FIG. FIG. 3 is a schematic configuration diagram of the fixing device according to the embodiment of the present invention at the time of starting back curl correction. FIG. 2 is a schematic configuration diagram of the fixing device during backcurl correction according to the embodiment of the present invention. This shows the positional relationship between the sheet member coming out of the second nip portion and the guide member, (a) at the start of back curl correction, (b) during the first half of back curl correction, (c) during the second half of back curl correction, (d ) is a diagram at the time of waiting for next sheet correction. 3 is a flowchart for moving the guide member to the first to fourth positions. 3 is a flowchart for moving the guide member to the first to third positions. FIG. 2A is a view of the pressure-side separation member and the drive roll guide member as viewed in the direction of arrow IV. FIG. 3 is a perspective view of a part of the fixing device viewed from the conveyance path side when the exit guide member is in the first position according to an embodiment of the present invention. FIG. 7 is an enlarged perspective view of a part of the fixing device seen from the conveyance path side when the exit guide member is in the second position according to an embodiment of the present invention. FIG. 7 is a diagram of a part of the fixing device viewed from the conveyance path side when the exit guide member moving means is activated and the exit guide member is in the second position according to an embodiment of the present invention. FIG. 3 is a front view of a part of the fixing device viewed from the conveyance path side when the exit guide member is in the first position according to an embodiment of the present invention. FIG. 7 is a front view of a part of the fixing device viewed from the conveyance path side when the exit guide member is in the second position according to an embodiment of the present invention. FIG. 3 is a perspective view showing an arrangement of a branch member and an exit guide member according to an embodiment of the present invention. FIG. 6 is a diagram illustrating a plurality of paper conveyance paths by combining the positions of branching members and exit guide members according to an embodiment of the present invention.

(Overall configuration of image forming apparatus)
DESCRIPTION OF THE PREFERRED EMBODIMENTS A fixing device and an image forming apparatus (color laser printer) according to embodiments of the present invention will be described below with reference to the drawings. A laser printer is an example of an image forming apparatus, and it goes without saying that the image forming apparatus is not limited to a laser printer. That is, the image forming apparatus can be configured as a copying machine, a facsimile machine, a printer, a printing press, and an inkjet recording apparatus, or as a multifunction device that combines at least two or more of these.

Note that the same or corresponding parts in each figure are denoted by the same reference numerals, and overlapping explanations thereof will be simplified or omitted as appropriate. In addition, the dimensions, materials, shapes, relative arrangement thereof, etc. in the description of each component are merely illustrative, and the scope of the present invention is not intended to be limited thereto unless specifically stated.

In the following embodiments, a sheet member that is a recording medium may be described as a "paper," but the "sheet member" is not limited to paper. "Sheet member" includes not only paper but also OHP sheets, fabrics, metal sheets, plastic films, and prepreg sheets in which carbon fibers are pre-impregnated with resin.

A medium to which a developer or ink can be attached, a sheet member, and a recording sheet are all included in the term "sheet member." In addition to plain paper, "paper" also includes cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and the like.

Furthermore, "image formation" used in the following description means not only adding images such as characters and figures to a medium, but also adding patterns such as patterns to the medium.

FIG. 1 shows a color laser printer 1 as an image forming apparatus. , a pair of reversing rollers 16, a duplex unit 17, and the like.

The image forming section A includes four image forming sections 4Y, 4M, 4C, and 4K, an exposure device 9, a transfer device 3, and the like, which will be described later. The image forming apparatus 1 is characterized in that the fixing device 20 includes a backcurl correction device C. This will be explained in detail below.

Four image forming sections 4Y, 4M, 4C, and 4K are provided at the center of the image forming apparatus main body of the image forming apparatus 1. Each of the image forming units 4Y, 4M, 4C, and 4K accommodates developers of different colors, yellow (Y), magenta (M), cyan (C), and black (K), corresponding to the color separation components of a color image. The configuration is the same except for the

Specifically, each of the image forming units 4Y, 4M, 4C, and 4K includes a drum-shaped photoreceptor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoreceptor 5, and a charging device 6 that charges the surface of the photoreceptor 5. It includes a developing device 7 that supplies toner and a cleaning device 8 that cleans the surface of the photoreceptor 5. In FIG. 1, only the photoreceptor 5, charging device 6, developing device 7, and cleaning device 8 included in the black image forming section 4K are labeled, and the other image forming sections 4Y, 4M, and 4C are designated by reference numerals. , has the same configuration as the black image forming section 4K, so its reference numeral is omitted.

An exposure device 9 for exposing the surface of the photoreceptor 5 is provided below each of the image forming units 4Y, 4M, 4C, and 4K. The exposure device 9 includes a laser light source (not shown), a polygon mirror 51a, an f-theta lens 51b, a plurality of reflective mirrors 51c, etc., and irradiates the surface of each photoreceptor 5 with laser light based on image data, An electrostatic latent image is formed on the surface of 5.

Furthermore, a transfer device 3 is disposed above each image forming section 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as an intermediate transfer body, four primary transfer rollers 31 as a primary transfer mechanism, a secondary transfer roller 36 as a secondary transfer mechanism, and a secondary transfer backup roller 32. A cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35 are provided.

The intermediate transfer belt 30 is an endless belt, and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, by rotationally driving the secondary transfer backup roller 32, the intermediate transfer belt 30 is configured to travel around (rotate) in the direction indicated by the arrow in the figure.

The four primary transfer rollers 31 each sandwich the intermediate transfer belt 30 with each photoreceptor 5 to form a primary transfer nip. Further, a power source is connected to each primary transfer roller 31, and a predetermined direct current voltage (DC) or a predetermined alternating current voltage (AC) is applied to each primary transfer roller 31.

The secondary transfer roller 36 and the secondary transfer backup roller 32 sandwich the intermediate transfer belt 30 to form a secondary transfer nip. Further, like the primary transfer roller 31, the secondary transfer roller 36 is also connected to a power source so that a predetermined direct current voltage (DC) or alternating current voltage (AC) is applied to the secondary transfer roller 36. It has become.

The belt cleaning device 35 includes a cleaning brush and a cleaning blade that are arranged to come into contact with the intermediate transfer belt 30. The waste toner collected by the belt cleaning device 35 is stored in a waste toner container via a waste toner transfer hose.

A bottle accommodating section 2 is provided at the top of the main body of the image forming apparatus, and four toner bottles 2Y, 2M, 2C, and 2K for accommodating replenishment toner are removably attached to the bottle accommodating section 2. ing. Toner is supplied from each toner bottle 2Y, 2M, 2C, 2K to each developing device 7 via a supply path (not shown) provided between each toner bottle 2Y, 2M, 2C, 2K and each developing device 7. Ru.

On the other hand, a paper feed section B is provided at the bottom of the image forming apparatus main body. The paper feed section B includes a paper feed tray 10 that accommodates a sheet member P as a recording medium, a paper feed roller 11 that carries out the sheet member P from the paper feed tray 10, and the like.

Note that the sheet member P as a recording medium includes, in addition to plain paper, cardboard, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, and the like. Further, a manual paper feeding mechanism may be provided. In this embodiment, cardboard refers to paper with a basis weight of 160 g/m ² or more.

A conveyance path R is provided within the main body of the image forming apparatus for discharging the sheet member P from the paper feed tray 10 through the secondary transfer nip and out of the apparatus. In the conveyance path R, on the upstream side in the conveyance direction of the sheet member P from the position of the secondary transfer roller 36, there is a pair of registration rollers 12 as timing rollers that measure the conveyance timing and convey the sheet member P to the secondary transfer nip. It is arranged.

Further, downstream of the position of the secondary transfer roller 36 in the conveyance direction of the sheet member P, there is a fixing device that pressurizes and heats the sheet member P carrying an unfixed toner image to fix the toner image on the sheet member P. 20 are arranged. Furthermore, a pair of paper discharge rollers 13 for discharging the sheet member P out of the apparatus is provided downstream of the fixing device 20 in the conveyance direction of the sheet member P on the conveyance path R. Further, a paper discharge tray 14 for storing sheet members P discharged outside the apparatus is provided on the upper surface of the main body of the image forming apparatus.

(Double-sided paper feeding mode)
Further, a branching member 15 is provided between the paper ejection roller 13 and the fixing device 20. The branching member 15 is in the first state shown in FIG. 1 in the single-sided paper passing mode, and on the other hand, in the double-sided paper passing mode, the branching member 15 is in the second state closed in the direction of the arrow from the first state shown in FIG. It is fixed to the main body so that it can rotate.

In other words, the branching member 15 is connected to an external discharge path (path passing through the paper discharge roller 13) for discharging the sheet member P conveyed downstream of the fixing device 20 to the paper discharge tray 14 outside the machine, and a reversal path for double-sided printing. Since it is configured to switch the route (a route passing through the inside of the duplex unit 17 described later), it constitutes a sheet member P conveyance route branching mechanism of the present invention. Further, a back curl correction device C, which will be described later, is provided between the branching member 15 and the fixing device 20.

The double-sided reversing path 40 includes a reversing roller 16 that switches back the sheet member P provided on the downstream side of the branching member 15, and a double-sided unit 17 between the reversing roller 16 and the registration roller 12. This duplex unit 17 includes conveyance rollers 42 to 44 to form a reversal path for double-sided printing, and the sheet member P that has been fixed on the first side is switched back by the reversal roller 16 and transferred via the conveyance rollers 42 to 44. and is conveyed to the registration rollers 12.

(Basic operations of image forming apparatus)
Next, the basic operation of the image forming apparatus 1 according to the embodiment of the present invention will be explained. First, when an image forming operation is started, each photoreceptor 5 in each image forming section 4Y, 4M, 4C, 4K is rotated clockwise in the figure, and the surface of each photoreceptor 5 is charged to a predetermined level by a charging device 6. Uniformly charged with polarity. The charged surface of each photoreceptor 5 is irradiated with laser light from the exposure device 9, and an electrostatic latent image is formed on the surface of each photoreceptor 5.

At this time, the image information exposed to each photoreceptor 5 is monochrome image information obtained by separating a desired full-color image into yellow, magenta, cyan, and black color information. By supplying toner from each developing device 7 to the electrostatic latent image formed on each photoreceptor 5 in this manner, the electrostatic latent image is developed (visualized) as an image.

Further, when the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, causing the intermediate transfer belt 30 to travel around in the direction indicated by the arrow in the figure.

Further, by applying a constant voltage or constant current controlled voltage having a polarity opposite to the charging polarity of the toner to each primary transfer roller 31, a primary transfer nip between each primary transfer roller 31 and each photoconductor 5 is formed. A transfer electric field is formed at.

Thereafter, as each photoreceptor 5 rotates, when each color image on the photoreceptor 5 reaches the primary transfer nip, the image on each photoreceptor 5 is transferred to an intermediate position by the transfer electric field formed in the primary transfer nip. The images are transferred onto the transfer belt 30 in a superimposed manner.

In this way, a full-color image is carried on the surface of the intermediate transfer belt 30. Furthermore, the toner on each photoreceptor 5 that has not been completely transferred to the intermediate transfer belt 30 is removed by the cleaning device 8 . Then, the surface of each photoreceptor 5 is neutralized by a static eliminating device, and the surface potential is initialized.

At the bottom of the printer, the paper feed roller 11 starts rotating, and the sheet member P is sent out from the paper feed tray 10 to the conveyance path R. The conveyance of the sheet member P sent out to the conveyance path R is temporarily stopped by the registration rollers 12.

Thereafter, rotational driving of the registration rollers 12 is started at a predetermined timing, and the sheet member P is conveyed to the secondary transfer nip in accordance with the timing when the image on the intermediate transfer belt 30 reaches the secondary transfer nip. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip.

Then, the images on the intermediate transfer belt 30 are transferred onto the sheet member P all at once by this transfer electric field. Further, at this time, residual toner on the intermediate transfer belt 30 that has not been completely transferred to the sheet member P is removed by a belt cleaning device 35 and conveyed to a waste toner container.

After that, the sheet member P is conveyed to the fixing device 20, and the image on the sheet member P is fixed to the sheet member P by the fixing device 20. The sheet member P conveyed from the fixing device 20 is guided in the ejection direction and the paper refeeding direction via a branching member 15 for switching between a path for ejecting the sheet member P out of the device and a double-sided reversal path. .

In the single-sided sheet feeding mode, the branching member 15 is opened and the sheet member is conveyed to the outside of the apparatus by a pair of sheet ejection rollers 13 for ejection, and the sheet member ejected to the outside of the apparatus is provided on the upper surface of the image forming apparatus main body. The paper is discharged to a paper discharge tray 14 for stocking paper P.

In the double-sided paper passing mode, the branching member 15 closes in the direction of the arrow, so that the sheet member P after the first side fixing is guided to the double-sided reversing path 40. The sheet member P guided to the duplex reversing path 40 is switched back by a pair of reversing rollers 16, is conveyed to a duplex unit 17, is conveyed again to a pair of registration rollers 12, and is re-fed. Similarly to the first side, the second side image is printed on the back side of the sheet member P. Then, the sheet member P is discharged out of the apparatus by the paper discharge roller 13 and is stocked on the paper discharge tray 14.

The above explanation is about the image forming operation when forming a full color image on the sheet member P, but a monochrome image is formed using any one of the four image forming units 4Y, 4M, 4C, and 4K. It is also possible. It is also possible to form a two-color or three-color image using two or three image forming sections.

(Fixing device)
Next, the fixing device 20 having the backcurl correction device C according to the embodiment of the present invention will be described in detail with reference to FIGS. 2A to 2C. As shown in FIGS. 2A to 2C, the fixing device 20 is used to fix the transferred toner image T carried on the sheet member P by melting and permeating it with heat and pressure. A flexible fixing belt 21 that can run endlessly is provided.

The fixing device 20 passes the sheet member P onto which the toner image has been transferred in the image forming section A through a first nip section N1 that is a fixing nip section, and applies heat and pressure to the first nip section N1 to fix the toner image. It is fixed on the sheet member P.

In addition to the endless fixing belt (fixing member) 21, the fixing device 20 has an endless fixing belt (fixing member) 21, and a first nip portion N1 is formed by applying pressure between the fixing belt 21 and the fixing belt 21 in an abutting state. A pressure roller (pressure member) 22, which is a counter rotating body, is provided. A heater (heat source) 23 including a plurality of halogen lamps 23a and 23b that heats the inner surface of the fixing belt 21 at locations other than the first nip portion N1 is provided inside the fixing belt 21.

Inside the fixing belt 21, there is a nip forming member 24 that is a base member for forming a nip disposed inside the fixing belt 21, a stay 25 that supports the nip forming member 24, and light emitted from the heater 23. A reflecting member 26 is provided to reflect the light onto the fixing belt 21.

The nip forming member 24, which is a base member for forming a nip, has a sliding sheet (low friction sheet) wrapped around a base pad, although details are not shown.

In the nip forming member 24 shown in FIGS. 2A to 2C, the first nip portion N1 has a flat shape, but the shape is not limited to this. For example, in the case where the first nip portion N1 is formed in a concave shape along the circumferential surface of the pressure roller 22, the leading edge of the sheet member P passing through the first nip portion N1 is closer to the pressure roller 22 side, so that fixing is prevented. There is an advantage that separation from the belt 21 is improved.

The temperature of the fixing belt 21 is detected by a temperature sensor 27 provided on the side where the sheet member P enters the first nip portion N1, and is used for feedback processing of the heater 23. Note that in FIGS. 2A to 2C, arrow F indicates the conveyance direction of the sheet member P.

The fixing belt 21 is an endless belt formed in the shape of a thin and flexible sleeve, and is composed of a base material and a release layer located on the surface of the base material. For the base material, a metal material such as nickel or A-SUS, or a resin material such as polyimide is used. Further, for the release layer, a material such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) or polytetrafluoroethylene (PTFE), which has releasability to toner, is used.

The pressure roller 22 includes a core bar 22a, an elastic layer 22b made of foamable silicone rubber, silicone rubber, fluororubber, etc. provided on the circumferential surface of the core bar 22a, and PFA provided on the surface of the elastic layer 22b. Alternatively, it is configured by a release layer made of PTFE or the like.

The pressure roller 22 is pressed toward the fixing belt 21 by a pressure mechanism (not shown), and is in contact with the fixing belt 21 and in contact with a nip forming member 24 serving as a base member.

At the point where the pressure roller 22 and the fixing belt 21 come into contact, the elastic layer 22b of the pressure roller 22 is crushed, and the nip forming member 24 receives pressure between it and the fixing belt 21 to a predetermined width. The first nip portion N1 is secured.

The pressure roller 22 is configured to be rotationally driven by a drive source such as a motor (not shown) provided in the printer body. When the pressure roller 22 is driven to rotate, the driving force is transmitted to the fixing belt 21 at the first nip portion N1, and the fixing belt 21 is driven to rotate.

In the fixing device 20 according to the present embodiment, the pressure roller 22 is a solid roller, but it may be a hollow roller. In that case, it is also possible to arrange a heat source such as a halogen heater using radiant heat inside the pressure roller 22.

In addition, when there is no elastic layer 22b, the heat capacity is small and the fixing performance is improved, but when unfixed toner is crushed and fixed, minute irregularities on the belt surface are transferred to the image and the solid areas of the image become glossy. Unevenness may occur. To prevent this, it is desirable to provide an elastic layer with a thickness of 100 μm or more.

Aluminum, iron, stainless steel, etc. can be selected as the pipe-shaped metal used for the hollow roller. When a heat source is provided within the pressure roller 22, in order to prevent the support from being heated by radiant heat from the heat source, a heat insulating layer or a mirror-treated heat ray reflecting surface may be provided on the surface of the support. is desirable. The heat source in this case is not limited to the halogen heater described above, but may also be an IH heater, a resistance heating element, or a carbon heater.

In the case of the above-described fixing device 20, since the fixing device has a configuration in which a heating member with a low heat capacity is directly heated, the temperature rises very quickly, and therefore, there is an advantage that the first print can be performed quickly. However, from the viewpoint of back curling on the sheet member P, fixing may be performed before the pressure roller is sufficiently warmed or the fixing temperature may drop during the operation of the fixing device 20. Back curl (for example, the curved shape of the solid line P' shown in FIG. 2C) occurs due to the temperature difference, and this occurs particularly at the rear end portion of the sheet member P.

(separation conveyance mechanism)
On the sheet member P exit side of the fixing device 20, a separating and conveying mechanism is provided that separates the sheet member P that has passed through the first nip portion N1 near the first nip portion N1 and guides the sheet member P in the discharge direction toward the sheet discharge portion. ing.

The separation and conveyance mechanism includes a belt-side separating member 201 having a tip 201a that is close to the fixing belt 21 side on the downstream side in the moving direction of the sheet member P moving from the first nip portion N1, and a swinging member that is close to the pressure roller 22 side. The pressurizing side separation member 202 has a moving end 202a.

The belt-side separation member 201 is provided to separate the sheet member P that is adhesively stuck to the fixing belt 21 from the fixing belt 21 . For this reason, a metal belt-side separation member 201 is used so that the sheet member P stuck to the fixing belt 21 can be accurately positioned at a close position where it can be lifted off the surface of the fixing belt 21. It will be done.

The pressurizing side separating member 202 is made of a resin molded product, and a support rod 202A provided in a part of the pressurizing side separating member 202 is rotatably supported by a housing (not shown). Thereby, the swinging end 202a facing the pressure roller 22 can swing toward and away from the pressure roller 22.

By swinging relative to the pressure roller 22, the pressure-side separating member 202 swings greatly in the direction away from the pressure roller 22, for example, when removing a jammed sheet member P from the first nip portion N1. The hand can be moved to create a space for inserting the hand into the first nip portion N1. Thereby, the sheet member P can be pulled out.

(back curl correction device)
The backcurl correction device C is disposed between the branching member 15 (see FIG. 1) and the fixing device 20. The backcurl correction device C has a driving roller 204, a driven roller 203, a guide member 205, and a guide member moving mechanism D shown in FIGS. 7 and 8.

The driving roller 204 and the driven roller 203 are arranged downstream of the separating members 201 and 202, as shown in FIGS. 2A to 2C. The drive roller 204 is connected to the pressure roller 22 on the side where the sheet member P back curls in the first nip portion N1, that is, on the side opposite to the heater (heat source) 23, with respect to the conveyance path between the fixing device 20 and the branching member 15. Provided on the side.

The driven roller 203 is provided on the side where the sheet member P is heated (the fixing belt 21 side) in the first nip portion N1 with respect to the conveyance path between the fixing device 20 and the branching member 15. The drive roller 204 and the driven roller 203 form a second nip portion N2, roll and rotate, and assist in transporting the sheet member P. The distance between the first nip portion N1 and the second nip portion N2 is set shorter than the length of the sheet member P.

A detection sensor 230 for detecting the leading end of the sheet member P is arranged between the first nip portion N1 and the second nip portion N2 and at a position close to the second nip portion N2. This detection sensor 230 is arranged at a position where the distance to the second nip portion N2 is S ₀ .

If the time at which the detection sensor 230 detects the leading edge of the sheet member P is _T1 , the time _T2 at which the leading edge of the sheet member P reaches the second nip portion N2 is _T2 = _T1 + ( _S0 / _V1 ) is calculated by the main body control unit based on the calculation formula. V ₁ is the conveyance speed of the first nip portion N1.

As will be described later, even if a speed difference is provided between the conveyance speed V ₁ of the first nip portion N1 and the conveyance speed V ₂ of the second nip portion N2, the above-mentioned T ₂ =T ₁ +(S ₀ /V ₁ ) The calculation formula remains unchanged. The timing for moving the guide member 205 from the first position in FIG. 2A to the second position in FIG. 2B is determined by the main body control unit with reference to the time _T1 . Based on this determined timing, the guide member moving mechanism D that moves the guide member 205 is drive-controlled. Then, when the leading end of the sheet member P leaves the second nip portion N2 and advances downstream by a distance _L1 as shown in FIG. 2B, the leading end of the sheet member P crosses the leading end of the guide member 205 at an angle _θ1. Contact with.

(Jam prevention mechanism)
In this embodiment, in order to prevent jamming of the sheet member P, the following configurations 1) to 3) are adopted.
1) The diameter of the drive roller 204 is set to be larger than the diameter of the driven roller 203 as required.
2) The conveyance speed V ₂ of the sheet member P in the second nip portion N2 is set to be slightly smaller than the conveyance speed V ₁ of the sheet member P in the first nip portion N1.
3) The nip pressure of the second nip portion N2 is set to be smaller than the nip pressure of the first nip portion N1.
With the above configuration, jamming or the like does not occur in the sheet member P between the first nip portion N1 and the second nip portion N2.

The drive roller 204 has at least a roller circumferential surface made of rubber, and the driven roller 203 has at least a roller circumferential surface that is harder than the roller circumferential surface of the drive roller 204 and has releasability. In this embodiment, the drive roller 204 has a high friction coefficient and is made of a core metal 204a (hereinafter referred to as a roller shaft 204a) and a material such as silicone, EPDM, urethane, fluororubber, etc. provided on the surface of the core metal 204a. The sheet member P is made of a solid rubber material 204b, so that the conveying force of the sheet member P can be obtained.

The driven roller 203 has a structure in which a hollow pipe-shaped metal surface is covered with a low-μ tube (thickness: 30 to 300 μm) such as PFA, ETFA, or FEP. The reason why the hollow pipe-shaped metal is used is to prevent water vapor generated by evaporation from the paper during fixing from forming condensation on the driven roller side. This is to keep it warm.

The reason for arranging the low-μ tube on the surface is to make it difficult for a small amount of toner that has not been dissolved after fixing to adhere, and to prevent it from accumulating even if it adheres. That is, since the driven roller 203 side is conveyed while always being in contact with the image surface side, the above-described configuration is achieved.

The driven roller 203 is held in the main body of the image forming apparatus via a holder by a spring member (not shown). By pressing the holder with the spring, the driving roller 204 and the driven roller 203 come into contact with each other and move to the second nip portion. N2 is formed to enable auxiliary conveyance of the sheet member P.

(Guide member)
The guide member 205 is provided so that its center of rotation is coaxial with the roller shaft 204a of the drive roller 204. The guide member 205 is moved to at least the first position in FIG. 2A, the second position (broken line) in FIG. 2B, and the third position in FIG. Moved to position 3.

As shown by the solid line in FIG. 2A, the first position is a position where the guide member 205 does not block the virtual tangent VL passing through the second nip portion N2 and extending downstream in the conveying direction, and the guide member 205 is connected to the sheet member P. This is a retracted position where there is no contact. Here, the virtual tangent line VL is the second nip portion N2 when the driving roller 204 and the driven roller 203 are a perfect circle and the second nip portion N2 between both rollers is a line contact extending in the longitudinal direction of both rollers. This is a tangent line that is perpendicular to the straight line connecting the centers of the drive roller 204 and the driven roller 203.

The second position is a first forward position in which the blade protrudes shallowly so as to barely block the virtual tangent line VL, as shown by the broken line in FIG. 2B. When the guide member 205 in FIG. 2B rotates around the roller shaft 204a from the first position indicated by the solid line to the second position indicated by the broken line, the tip of the sheet member P coming out of the second nip portion N2 is moved to the tip of the guide member 205. soft initial contact with the part at an intersection angle θ1.

The intersection angle θ1 is desirably as close to 180° as possible so as not to damage the tip of the sheet member P. When the crossing angle θ1 is close to 180°, the overlapping angle θ5 at which the leading end of the guide member 205 overlaps the leading end of the sheet member P becomes close to zero. For example, if the overlapping angle θ5<30° (150°<θ1), the impact of the guide member 205 on the tip of the sheet member P can be almost eliminated, thereby preventing the tip of the sheet member P from being dented or buckled. be able to.

Since the distance S ₁ from the detection sensor 230 to the contact portion is S ₁ =S ₀ +L ₁ , if the time when the detection sensor 230 detects the tip of the sheet member P is T ₁ , then the tip of the sheet member P is The time T ₃ at which the tip of the guide member 205 comes into contact is T ₃ =T ₁ +(S ₀ +L ₁ /V ₁ ). The guide member 205 moves from the first position to the second position in time for this time _T3 .

The third position is a second forward position where the guide member 205 rotates further than the second position and protrudes deeply so as to completely block the virtual tangent line VL, as shown by the solid line in FIG. 2C, At this third position, the sheet member P is pressed as required to correct the back curl.

The leading end of the sheet member P contacts the guide member 205 at the second position in FIG. 2B, and then, while being pressed by the guide member 205 rotating from the second position in FIG. 2B to the third position in FIG. The nip conveyance force of the rollers 203 provides auxiliary conveyance. As a result, the guide member 205 presses the sheet member P as required in the direction of curvature (face curl) in which the sheet member P has a concave curved surface on the side opposite to the back curl, thereby correcting the back curl.

That is, when the guide member 205 is located in the third position shown by the solid line in FIG. 2C, the guide member 205 protrudes deeper than the second position in FIG. 2B so as to interrupt the virtual tangent line VL at the intersection angle θ2. When the guide member 205 is held at the third position at a crossing angle θ2, the direction of the sheet member P passing through the second nip portion N2 (the direction of the virtual tangent line VL perpendicular to the line connecting the centers of the roller pair) On the other hand, it is placed at a position that blocks the conveyance path from the same side as the drive roller 204.

As a result, the front portion of the sheet member P passing through the second nip portion N2 in the conveying direction is pressed toward the driven roller 203 by the guide member 205 while slidingly contacting the guide member 205 at the intersection angle θ2. Due to this pressing action, the sheet member P is bent into a concave shape (face curl) in a direction opposite to the back curl.

Furthermore, the distance L ₂ from the second nip portion N2 to the guide member 205 is significantly shortened from L ₁ in FIG. 2B to L ₂ in FIG. 2C. Therefore, the back curl correction of the guide member 205 acts effectively on the sheet member P. By doing so, the sheet member P passing through the guide member 205 can be discharged to the paper discharge tray 14 without the back curl occurring at the first fixing nip portion N1. Note that the distance S ₂ from the contact position of the intersection angle θ2 to the detection sensor 230 is S ₂ =S ₀ +L ₂ .

As described above, based on the detection sensor 230, the leading end of the sheet member P passes through the second nip portion N2, travels the distance _L1 shown in FIG. Wait at position 2. Thereafter, the guide member 205 rotates from the second position shown in FIG. 2B to the third position shown in FIG. 2C, thereby achieving both the effect of correcting the tip dent and the back curl. That is, after the tip of the sheet member P is soft landed on the guide member 205 at the second position in FIG. 2B, the back curl is corrected by increasing the angle while conveying the sheet member P to the third position in FIG. 2C.

FIGS. 3(a) to 3(d) show the rotating state of the guide member 205 step by step after the above-mentioned initial contact. 3(a) to (c) show the rotating state of the guide member 205 during back curl correction, and the angle of the guide member 205 with respect to the virtual tangent VL direction of the second nip portion N2 is θ1 (see FIG. 2b). ) → θ2 (see FIG. 2C) → θ3.

θ3 in FIG. 3(c) is the maximum angle, and this θ3 is the angle when the guide member 205 further rotates leftward from the third position (θ2) in FIG. 2C and moves to the fourth position (θ3). It is. In the fourth position, the guide member 205 rotates further and protrudes more deeply than in the third position so as to block the virtual tangent line VL. Immediately after FIG. 3(c), the rear end portion of the sheet member P passes through the second nip portion N2.

With respect to the rear portion of the sheet member P, as shown in FIGS. 3(b) to 3(c), the bending angle to the second nip portion N2 gradually increases from α to β. Further, the distance from the second nip portion N2 to the guide member 205 is also shortened from L ₂ to L ₃ . Therefore, the back curl correction of the guide member 205 effectively acts on the rear side portion of the sheet member P.

If the job is continuing, the guide member 205 returns to the second position in FIG. 2B for the next seat back curl correction, as shown in FIG. 3(d). When the job is finished, the guide member 205 returns to the first position in FIG. 2A.

(flowchart)
4A and 4B show flowcharts of the method for rotating the guide member 205 described above. FIG. 4A is a flowchart of back curl correction shown in FIGS. 3(a) to 3(d). FIG. 4B is a flowchart of back curl correction in (a), (b), and (d) with (c) of FIG. 3 omitted. FIG. 4B is basically the same as FIG. 4A except that step S5 of FIG. 4A (the guide member 205 is in the fourth position) is not present.

When a print job is started in step S1, the guide member 205 moves from the first position to the second position in FIG. 2B. In the next step S2, the leading edge of the sheet member is detected by the detection sensor 230. At this time, the guide member remains in the second position.

In step S3, after the detection sensor 230 detects the leading edge of the sheet member P, the guide member 205 remains at the second position in FIG. 2B even while the sheet member advances by a distance _S1 . In step S4, when the leading end of the sheet member P reaches the guide member 205 (soft initial contact), the guide member 205 begins to move from the second position to the third position.

In step S5, after the leading end of the sheet member P reaches the downstream branching member 15, the guide member 205 rotates from the third position in FIG. 2C to the fourth position in FIG. 3(c). As a result, the backcurl of the second half of the sheet member P is strongly corrected at a contact angle θ3 (bending angle β).

In step S6, after the detection sensor 230 detects the rear end of the sheet member P, the guide member 205 is held at the fourth position in FIG. 3(c) until the sheet member P advances a distance _S0 . In step S7, when the rear end of the sheet member P passes through the second nip portion N2, the guide member 205 is returned from the fourth position in FIG. 3(c) to the second position in FIG. 3(d). Finally, when the detection sensor 230 detects the leading edge of the next paper in step S8, the process returns to step S3 and the aforementioned steps S3 to S8 are repeated. This is particularly effective for sheet members P such as cardboard that have relatively large back curls and in cold regions.

The flowchart in FIG. 4B omits step S5 in FIG. 4A. That is, the step of correcting the backcurl of the latter half of the sheet member P more strongly than in FIG. 3C by setting the guide member 205 at a large angle θ3 at the fourth position in FIG. 3C is omitted. The flowchart in FIG. 4B is also applicable to sheet members P such as thin paper with relatively little backcurl and in normal temperature regions.

(Guide member moving mechanism)
Next, the configurations of the guide member 205 and the guide member moving mechanism D will be described with reference to FIGS. 5 to 11. As shown in FIG. 5, the drive roller 204 has a roller shaft 204a that is rotatably supported at both ends by the pressure-side separating member 202 via a sliding bearing 208, and a roller shaft 204a that is fitted and fixed at a required distance from the roller shaft 204a. It consists of a plurality of short cylindrical parts 204b made of an elastic material such as rubber.

The drive roller 204 is configured such that the rotational driving force from the guide member moving mechanism D shown in FIG. 7 is transmitted to the drive gear 210 fixed to the end of the roller shaft 204a via the idler gear 211 at the left end in FIG. It is rotatable. As shown in FIGS. 5 to 8, the guide member 205 is fixed to a support shaft 205a whose both ends are supported by the upper ends of a pair of bracket arms 206. As shown in FIGS.

The pair of bracket arms 206 are fitted onto the outer diameter portion of the sliding bearing 208 and are rotatable. A plurality of guide members 205 are provided on each of the plurality of bosses 205b that are fitted and fixed to the support shaft 205a.

The guide member 205 has its base end fixed to the boss 205b, and its protruding end extends to cover the downstream side of the drive roller 204. The guide member 205 is configured to be stopped at a position where the stopper portion 206b of the bracket arm 206 comes into contact with a part of the pressure-side separation member 202. The posture position of the guide member 205 corresponding to this position becomes the third position at which the angle of the sheet member P discharged from the second nip portion N2 is changed.

As shown in FIGS. 6 to 8, the guide member moving mechanism D includes a solenoid 220 as a driving source, a link mechanism 207 that swings due to the operation of the solenoid 220, and a tension spring 209. The solenoid 220 has a housing fixed to the main body of the image forming apparatus. The extension rod 220a of the solenoid 220 is configured to be extendable and retractable in multiple stages, and in this embodiment, it is extendable and retractable in three or four stages. In the third stage, the guide member 205 moves from the first position to the third position, and in the fourth stage, the guide member 205 moves from the first position to the fourth position.

The tension spring 209 has one end locked to the side surface of the pressure-side separation member 202. The other end of the tension spring 209 is locked in the middle of the arm portion 206a of the bracket arm 206. As a result, the tension force of the tension spring 209 is constantly applied to rotate the bracket arm 206 in the direction in which the guide member 205 protrudes to the third position in FIG. 2C.

As shown in FIG. 8, the link mechanism 207 has one horizontal end 207a supported by a fixed pin shaft 207A. Further, the other end of the link mechanism 207 in the horizontal direction, an operating end 207b, is brought into contact with the tip of the arm portion 206a of the bracket arm 206 so as to surround it from below. An elongated hole 207d provided at the upper end of an upwardly extending portion 207c extending upward from the horizontal midway point of the link mechanism 207 is connected to an extension rod 220a of a solenoid 220 with a pin.

As shown by the broken line in FIG. 8, when the extension rod 220a of the solenoid 220 is extended downward, the operating end 207b of the link mechanism 207, shown by the broken line in FIG. Downward and far apart.

When current flows through the internal coil of the solenoid 220 from the state shown by the broken line in FIG. 8 based on the control signal from the control device, the extension rod 220a of the solenoid 220 retires as shown by the solid line in FIG. As a result, the link mechanism 207 is rotated upward against the tensile force of the tension spring 209, and its operating end 207b lifts the tip of the arm portion 206a of the bracket arm 206. This causes the guide member 205 to retreat from the third position shown in FIGS. 2C and 9 to the first position shown in FIGS. 2A and 10. Furthermore, by applying a current to another internal coil of the solenoid 220, the guide member 205 protrudes to the second position shown by the broken line in FIG. 2B.

On the other hand, when the current in the solenoid 220 is cut off based on the control signal from the control device from the state shown in FIG. It is adapted to protrude into the third position shown in FIG.

In the above configuration, the gap between the drive roller 204 and the guide member 205 can be configured such that the buildup of dimensional tolerances of the parts is minimized. In other words, only the radial distance tolerance from the axis center of each component can be set, and the guide member 205 can be moved while the gap between the drive roller 204 and the guide member 205 is kept constant with high precision. Become.

(branching member)
As shown in FIG. 11, the branch members 15 are arranged in the shape of a plurality of claws corresponding to the width direction perpendicular to the conveyance direction of the sheet member P, and the guide members 205 are also arranged in the width direction perpendicular to the conveyance direction of the sheet member P. They are arranged in a plurality of claw shapes corresponding to the width direction orthogonal to each other. Moreover, the branch members 15 and the guide members 205 are arranged alternately. As a result, even if the swing area of the branching member 15 and the swing area of the guide member 205 overlap on the conveyance line of the sheet member P when viewed from the axial direction, the swing area of the branch member 15 and the swing area of the guide member 205 are allowed to swing independently from each other. It is designed to guide you.

FIGS. 12A to 12D show four ways of conveying the sheet member P formed by the combination of the first and second positions of the branching member 15 and the first and third positions of the guide member 205. Show the route. The first position of the branching member 15 is the one-sided sheet passing mode position shown in FIG.

The second position of the branching member 15 is the position rotated in the direction of the arrow in FIG. 1 for the double-sided paper passing mode. A dashed line in the figure indicates a conveyance path of the sheet member P passing through the second nip portion N2 formed by the drive roller 204 and the driven roller 203.

FIG. 12A shows the transport path of the sheet member P in the thin paper single-sided printing mode, with the branching member 15 in the first position and the guide member 205 in the third position. The guide member 205 comes into contact with the back surface (back curl side surface) of the sheet member P passing through the second nip portion N2, curves it (face curl) to form a concave surface in the opposite direction to the back curl, and ejects the sheet member P. It is designed to be guided to a paper roller 13.

FIG. 12(b) shows the transport path of the sheet member P in the single-sided printing mode for thick paper, in which the branching member 15 is in the first position and the guide member 205 is also in the first position. The guide member 205 does not contact the back surface of the sheet member P that does not cause back curl while passing through the second nip portion N2, and the branching member 15 gently curves the sheet member P and guides it to the paper ejection roller 13. It looks like this.

FIG. 12C shows the conveyance path of the sheet member P with the first side passing in the double-sided printing mode for thin paper, with the branching member 15 at the second position and the guide member 205 at the first position. The guide member 205 lightly contacts the back surface (second surface) of the sheet member P whose back curl has been slightly corrected at the second nip portion N2 and is passing through the second nip portion N2, and the branching member 15 is in the second position. The sheet member P is guided to the reversing roller 16.

FIG. 12(d) shows the transport path of the sheet member P with the second side passing in the double-sided printing mode for thin paper, in which the branching member 15 is in the first position and the guide member 205 is also in the first position. The guide member 205 does not contact the back surface (first surface) of the sheet member P that does not cause back curl while passing through the second nip portion N2, and the branching member 15 softly moves the sheet member P at the first position. The sheet is curved and guided to the sheet discharge roller 13.

Note that, as shown in FIG. 5, the guide member 205 has a plurality of rib shapes along its length, and the rib-shaped branch member 15 is inserted between the guide members 205. As shown in FIG. In order to obtain the curl correction effect, it is necessary to bring the tip of the guide member 205 close to the second nip portion N2. For this reason, the plurality of rubber parts of the drive roller 204 are provided so as to be spaced apart from each other, and the guide member 205 is configured to fit between the rubber parts.

As explained above, the image forming apparatus according to the present invention has the advantage of being able to reduce back curl caused by fixing heat and stabilize conveyance, and also reduce damage to sheet member P and toner images. and is useful for image forming apparatuses.

Although the present invention has been specifically described above based on the embodiments, the present invention is not limited to the above-described embodiments, and can be modified in various ways within the scope of the technical idea described in the claims. Needless to say. For example, in the embodiment described above, the fixing belt 21 is heated by the halogen heater 23, but it is also possible to use an electromagnetic induction heater or a planar heater as the heat source. The planar heater is disposed on the fixing belt 21 side of the nip forming member 24 or on the side opposite to the fixing belt 21 . Further, the present invention is not only applicable to a fixing device, but also to a drying device installed in an inkjet type image forming apparatus, for example, in order to dry ink applied to paper.

1: Image forming device 2Y, 2M, 2C, 2K: Toner bottle 3: Transfer device 4Y, 4M, 4C, 4K: Image forming section 5: Photoreceptor 6: Charging device 7: Developing device 8: Cleaning device 9: Exposure device 10: Paper feed tray 11: Paper feed roller 12: Registration roller 13: Paper ejection roller 14: Paper ejection tray 15: Branching member 16: Reversing roller 17: Duplex unit 20: Fixing device 21: Fixing belt (fixing member) 22: Pressure roller (pressure member)
22a: Core metal 22b: Elastic layer 23: Halogen heater (heat source) 23a, 23b: Halogen lamp 24: Nip forming member 25: Stay 26: Reflective member 27: Temperature sensor 30: Intermediate transfer belt 31: Primary transfer roller 32: Second Next transfer backup roller 33: Cleaning backup roller 34: Tension roller 35: Belt cleaning device 36: Secondary transfer roller 40: Double-sided reversing path 42-44: Conveyance roller 51a: Polygon mirror 51b: f-theta lens 51c: Reflection mirror 201 : Belt side separation member 202: Pressure side separation member 202A: Support rod 202a: Swing end 203: Followed roller 204: Drive roller 204a: Core metal 204a: Roller shaft 204b: Solid rubber material 204b: Short cylindrical portion 205: Guide member 205a: Support shaft 205b: Boss 206: Bracket arm 206a: Arm portion 206b: Stopper portion 207: Link mechanism 207A: Fixed pin shaft 207a: One end 207b: Working end 207c: Upper extending portion 207d: Long hole 208: Slip bearing 210 : Drive gear 211: Idler gear 220: Solenoid 220a: Extension rod 230: Detection sensor A: Image forming section B: Paper feeding section C: Back curl correction device D: Guide member moving mechanism N1: First nip section N2: Second nip Part P: Sheet member VL: Virtual tangent

Patent No. 6543977 Japanese Patent Application Publication No. 2016-177063

Claims (8)

A first nip portion formed between a heating member and a pressure member for conveying a sheet member, and a second nip portion formed between a driving roller and a driven roller downstream of the first nip portion in the conveying direction. A back curl correction device comprising: a guide member that is movable so as to be able to come into contact with the leading end of the sheet member transported from the second nip portion to the downstream side in the transport direction ; and a guide member moving mechanism that moves the guide member. In the device,
The guide member has a first position where the guide member does not block the virtual tangent extending downstream in the conveying direction through the second nip portion, a second position where the guide member protrudes so as to block the virtual tangent, and a second position where the guide member protrudes so as to block the virtual tangent. movable to a third position protruding from the second position ;
A detection sensor for detecting the tip of the sheet member is provided between the first nip portion and the second nip portion, and the guide member is moved based on the time when the detection sensor detects the tip of the sheet member. A back curl correction device characterized in that a mechanism moves the guide member to the second position and the third position . The guide member has a rotation center coaxial with the roller axis of the drive roller, and rotates between the first position and the third position about the rotation center. The back curl correction device according to claim 1 . The guide member moving mechanism moves the guide member to the second nip portion after the rear end of the preceding sheet member passes through the second nip portion and before the front end of the subsequent sheet member reaches the second nip portion. 3. The guide member is returned to the second position from the third position, and the guide member is made to wait at the second position before the leading end of the subsequent sheet member reaches the second nip portion. The back curl correction device described in . The guide member moves from the second position to the second position after the leading end of the sheet member contacts the guide member at the second position and before the rear end of the sheet member exits the second nip portion. The back curl correction device according to any one of claims 1 to 3 , characterized in that the device moves to a third position. The guide member may move from the third position to a fourth position protruding from the third position so as to interrupt the virtual tangent before the rear end of the sheet member exits the second nip portion. The back curl correction device according to claim 4 , characterized by: A drying device comprising the backcurl correction device according to any one of claims 1 to 5 , and heating and drying a sheet member in the first nip portion. A fixing device comprising the backcurl correction device according to any one of claims 1 to 5 , and heating and fixing the unfixed toner image carried on the sheet member at the first nip portion. An image forming apparatus comprising the fixing device according to claim 7 .

Images