JP7236047B2 - Curling device, sheet conveying device and image forming device - Google Patents

Description

The present invention relates to a curl straightening device, a sheet conveying device, and an image forming apparatus.

Conventionally, it is arranged in the discharge path for discharging the sheet that has passed through the fixing device to the outside of the image forming apparatus, and corrects the curl of the sheet by passing the sheet through a nip formed by bringing a pair of conveying members into contact. Curl straighteners are known.

Japanese Laid-Open Patent Publication No. 2002-100003 discloses a curl straightening device in which two conveying members having different hardnesses are brought into contact with each other, and a fixing device is installed in a curved nip portion formed by the high-hardness conveying member biting into the low-hardness conveying member. It is described that the curl of the sheet is corrected by allowing the sheet to pass through.

However, the curl straightening device described in Patent Document 1 may not be able to straighten the curl of the sheet.

In order to solve the above-described problems, the present invention provides a nip formed by bringing a pair of conveying members into contact with each other and arranged in a discharge path for discharging a sheet that has passed through a fixing device to the outside of an image forming apparatus. In a curl correcting device for correcting the curl of a sheet by causing the sheet to pass through, a heating means for heating one of the pair of conveying members from the outside , and a surface temperature of the conveying member heated by the heating means is detected. a temperature detection sensor; control means for controlling the heating means based on a detection result of the temperature detection sensor; and pushing means for pushing one of a pair of conveyance members into the other conveyance member. wherein the control means changes the pushing amount of the pushing means and the target temperature of the surface of the conveying member, which is the target for controlling the heating means, according to the type of the sheet to be conveyed. and

According to the present invention, curls can be corrected satisfactorily.

1 is a schematic configuration diagram showing an example of a cross section of a printer main body according to an embodiment of the invention; FIG. FIG. 2 is a cross-sectional view showing the configuration of a fixing device; FIG. 2 is a schematic perspective view showing a paper ejection path from a fixing device to a curl straightening device; FIG. 2 is a schematic cross-sectional view showing a paper discharge path from a fixing device to a curl straightening device; FIG. 4 is a diagram for explaining curl correction by a curl correction device; FIG. 4 is a diagram for explaining the arrangement of heating portions of a decal heater; FIG. 4 is a diagram for explaining the relationship between the diameter of a soft roller and the diameter of a hard roller; FIG. 2 is a schematic configuration diagram showing an example of a pushing adjustment mechanism; 10 is a graph showing the temperature of paper when it enters the decal nip and the effect of reducing the amount of curl. FIG. 2 is a control block diagram of the printer according to the embodiment; FIG. 5 is a control flow diagram for adjusting the pressing amount of the soft roller with respect to the hard roller and the surface temperature of the hard roller according to the type of paper. FIG. 10 is a control flow diagram for performing lighting control of the decal heater based on lighting control of the halogen heater of the fixing device;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an example of a cross section of a printer main body 1 according to one embodiment of the present invention. As shown in FIG. 1, a printer body 1 as an image forming apparatus is provided with an intermediate transfer belt 16 . The intermediate transfer belt 16 is stretched over a plurality of rollers and can run, and photoreceptors 12 for yellow Y, cyan C, magenta M, and black K are provided on the upper side in the figure. A laser scanning unit 10, a charging device 11, a developing device 13, a primary transfer roller 14, and the like are arranged around each photosensitive member 12 with an intermediate transfer belt 16 interposed therebetween.

A secondary transfer roller 15 is provided below the intermediate transfer belt 16 to secondarily transfer the toner image primarily transferred onto the intermediate transfer belt 16 onto a sheet of paper 20 . A fixing device 17 is provided downstream of the secondary transfer portion in which the secondary transfer roller 15 is provided in the sheet conveying direction. A sheet material position correction device 30 is provided in the center of the printer main body 1 below the secondary transfer portion and the fixing device 17 and in the middle of the transport path 19 along which the paper 20 is transported.

An operation panel 3 is provided on the upper side of the printer main body 1, and a paper discharge tray 4 is provided on the left side thereof. Further, three paper feed trays 5 for stacking paper 20 are provided below the sheet material position correcting device 30 and below the printer main body 1 . Each of the first to third paper feed trays 5 stores paper 20 made of transfer paper or resin film. ˜The third paper feed tray 5 can be selected. Further, a control device is provided as a control means composed of a CPU, a ROM, a RAM, etc., for controlling the printer main body 1 and the like.

When printing is started in the printer main body 1 having the above configuration, first, each photoreceptor 12 is rotationally driven in the counterclockwise direction in the figure, and at this time, the surface of the photoreceptor 12 is charged to a predetermined polarity by the charger 11. . Next, the charged surface of each photoreceptor 12 is irradiated with laser light based on image information from the laser scanning unit 10 for each color, whereby an electrostatic latent image is formed on the photoreceptor 12 . The electrostatic latent image formed on the surface of the photoreceptor 12 is visualized as a toner image by the developing device 13 , and the toner image is transferred to the intermediate transfer belt 16 by the primary transfer roller 14 . After the toner image is transferred, residual toner remaining on the surface of the photoreceptor 12 is removed by a photoreceptor cleaner.

When forming a color image, the image forming operation described above is performed on all of the photoreceptors 12, whereby the yellow toner image, cyan toner image, magenta toner image and black toner image formed on each photoreceptor 12 are intermediately transferred. The images are sequentially superimposed and transferred onto the bell 16 .

On the other hand, among the first to third paper feed trays 5 provided at the bottom of the printer main body 1, the user selects the paper feed tray 5 by operating the operation panel 3 or an input terminal such as a PC. A paper 20 made of transfer paper, resin film, or the like is fed. The fed paper 20 is sent toward the registration roller 18, and the front end of the paper 20 hits the stopped registration roller 18.例文帳に追加After the paper 20 is thus aligned, the registration roller 18 feeds the paper 20 toward the secondary transfer portion of the intermediate transfer belt 16 provided with the secondary transfer roller 15 at a timing that coincides with the toner image.

Then, the toner image on the intermediate transfer belt 16 is transferred to the paper 20 by the secondary transfer roller 15 . The paper 20 with the toner image transferred thereon is sent to the fixing device 17 , and after the unfixed toner image is fixed thereon, curl is corrected by the curl correction device 40 to be described later, and the paper 20 is discharged to the paper discharge tray 4 . After the transfer of the toner image, the transfer residual toner adhering to the surface of the intermediate transfer belt 16 is removed by a cleaner for the intermediate transfer belt.

When the user operates the operation panel 3 or an input terminal such as a PC to select double-sided printing of the paper 20 , the paper 20 with an image formed on the first side can be printed on both sides by switching the conveying path with the bifurcation claw 23 . It is conveyed to the path and sent out to the reversing rollers 21 . The paper 20 sent out to the reversing roller 21 by the branching claw 23 is conveyed to the double-sided roller 35 (see FIG. 2 described later) of the sheet material position correcting device 30 by the forward and reverse rotation of the reversing roller 21 . At this time, the front and back sides of the paper 20 with respect to the conveying direction are reversed from those during image formation on the first surface. After the paper 20 is conveyed from the relay rollers 22 to the registration rollers 18 , the image is formed on the second surface in the same process as described above, and then the paper is discharged to the paper discharge tray 4 .

For the printer main body 1 configured as described above, the user can optionally connect a paper feed bank capable of feeding a large amount of paper, or install a finisher capable of stapling and folding instead of the paper output tray 4. It is also possible to connect

FIG. 2 is a sectional view showing the configuration of the fixing device 17. As shown in FIG.
The fixing device 17 shown in FIG. 2 has a fixing belt 171 as a fixing member and a pressure roller 172 as a pressure member. A halogen heater 173, which is a heat source, is provided in the fixing belt 171, so that the fixing belt 171 is directly heated from the inner peripheral side by radiant heat. The halogen heater 173 has three halogen lamps 173a, 173b, and 173c filled with a gas mainly composed of xenon and krypton as an inert gas in a glass tube.

In addition, a nip forming member 176 that forms a nip with the pressure roller 172 via the fixing belt 171 is arranged on the side of the fixing belt 171 facing the pressure roller 172 , and the fixing belt 171 and the inner peripheral surface of the fixing belt 171 are arranged. It slides directly or indirectly via a sliding sheet. In order to reduce wear between the fixing belt 171 and the nip forming member 176, fluorine oil or fluorine grease is applied to the inner peripheral surface of the fixing belt 171 as a lubricant. The lubricant may be fluorine grease or silicone grease containing fluorine particles as a thickening agent. Further, a surface layer of a fluorinated material may be provided on the surface of the fixing belt 171 that contacts the nip forming member 176 .

The shape of the fixing nip portion N is such that the central portion in the sheet conveying direction protrudes toward the nip forming member 176 side. As a result, the separation of the paper 20 from the fixing belt 171 is improved, thereby suppressing the occurrence of jams.

The fixing belt 171 is an endless belt (or film) using a metal belt such as nickel or SUS or a resin material such as polyimide. The surface layer of the fixing belt 171 has a release layer made of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA) or tetrafluoroethylene resin (PTFE), and has a release property so that toner does not adhere. I have An elastic layer made of silicone rubber or the like may be provided between the base material of the fixing belt 171 and the release layer. If there is no elastic layer, the heat capacity is reduced and the fixability is improved. There is a possibility that an image portion may have uneven luster like citron skin (a citron skin image). In order to improve this, an elastic layer of silicone rubber having a thickness of 100 [μm] or more is provided. Deformation of the elastic layer absorbs minute unevenness, and the yuzu skin image can be improved.

Further, a stay 177, which is a support member for supporting the fixing nip portion N, is provided inside the fixing belt 171 to suppress bending of the nip forming member 176 that receives pressure from the pressure roller 172, thereby A uniform nip width can be obtained in the direction (perpendicular to the paper surface). The stay 177 is made of metal material to ensure rigidity. The stay 177 is held and fixed by side plates at both ends in the axial direction and positioned. Since the nip forming member 176 has a complicated shape, it is preferable to use an injection-molded product made of a heat-resistant resin. is desirable. Further, a reflecting member 179 is provided between the halogen heater 173 and the stay 177 to reflect the radiant heat from the halogen heater 173, thereby suppressing the waste of energy due to the stay 177 being heated by the radiant heat. . Here, instead of providing the reflecting member 179, the surface of the stay 177 may be heat-insulated or mirror-finished to obtain the same effect.

The pressure roller 172 is composed of a core metal, an elastic rubber layer provided on the core metal, and a release layer (PFA or PTFE layer) provided on the surface to obtain release properties. The pressure roller 172 rotates clockwise as indicated by an arrow in FIG. 2 when a driving force is transmitted through gears from a driving source such as a motor provided in the printer body 1 . Further, the pressure roller 172 is pressed against the fixing belt 171 side by a spring or the like, and has a predetermined nip width due to the elastic rubber layer being crushed and deformed.

The pressure roller 172 may be a hollow roller, and may have a heat source such as a halogen heater inside the pressure roller 172 . The elastic rubber layer may be made of solid rubber, but if there is no heater inside the pressure roller 172, sponge rubber may be used. The use of sponge rubber is more desirable because it enhances heat insulation and makes it difficult for the fixing belt 171 to lose heat.

The fixing belt 171 is rotated counterclockwise by the pressure roller 172 as indicated by the arrow in FIG. In the case of the fixing device 17 of FIG. 2, the pressure roller 172 is rotated by a drive source, and the fixing belt 171 rotates as the driving force is transmitted to the fixing belt 171 at the fixing nip portion N. As shown in FIG. The fixing belt 171 rotates while being nipped by the fixing nip portion N, and travels while being guided by flanges at both ends except for the fixing nip portion. The paper 20 is heated and pressurized while passing through the fixing nip portion N, and the fixing process is performed.
With the above configuration, it is possible to realize a fixing device that is inexpensive and warms up quickly.

Further, the nip forming member 176 has a protruding portion 178 protruding toward the pressure roller at the downstream end portion of the nip forming member 176 in the paper transport direction. The fixing belt 171 is curved toward the pressure roller so that the fixing belt 171 does not contact the pressure roller 172 . As a result, the curvature of the fixing belt 171 on the nip exit side can be increased, and the separation of the sheet 20 from the fixing belt 171 after passing through the fixing nip portion N can be enhanced.

The paper 20 passing through the fixing nip portion N is heated by the fixing device 17, and moisture contained in the paper 20 evaporates. . Therefore, in this embodiment, as shown in FIG.

FIG. 3 is a schematic perspective view showing the paper discharge path 70 from the fixing device 17 to the curl straightening device 40, and FIG. 4 is a schematic cross-sectional view.
The curl correcting device 40 is arranged downstream in the paper transport direction from the transport roller pair 71 that transports the paper that has passed through the fixing nip portion N. As shown in FIG.
The curl straightening device 40 has a hard roller 42 made of metal and a soft roller 41 having a diameter larger than that of the hard roller 42 and having at least a rubber layer or a sponge layer as an elastic layer. It also has a decal heater 43 as heating means for heating the hard roller 42 from the outside, and a temperature detection sensor 44 for detecting the surface temperature of the hard roller 42 . The decal heater 43 is provided with heating portions 43a at one end and the other end in the width direction. The decal heater 43 is connected to the controller 100 , and the controller 100 controls the decal heater 43 based on the detection result of the temperature sensor 44 .

The hard roller 42 is a driving roller that is rotationally driven by a driving force transmitted from a driving source, and the soft roller 41 is a driven roller that rotates together with the hard roller 42 . The hard roller 42 is in contact with the soft roller 41 so as to bite into it, forming a curved decal nip D. As shown in FIG.

The smaller the diameter of the hard roller 42, the greater the curvature of the decal nip D and the more the curl straightening effect is enhanced. preferable.

In addition, it is preferable to provide a release layer on the surface of the hard roller 42 or to perform a surface treatment to enhance the release property. This is because the paper 20 is reheated by the curl straightening device 40 , so there is a risk that the toner will be retransferred from the paper to the hard roller 42 . By applying a release layer or a surface treatment that enhances releasability to the surface of the hard roller 42, it is possible to make it difficult for toner to adhere to the hard roller 42, and to suppress toner retransfer to the hard roller 42. can.

Further, a release layer may be provided on the surface of the soft roller 41, or a surface treatment may be performed to enhance the release property. By providing a release layer on the surface of the soft roller 41 or applying a surface treatment that enhances the release property, the toner fixed on the first surface of the paper is retransferred to the soft roller 41 during double-sided printing. can be suppressed.

As shown in FIG. 4, the curl straightening device 40 is arranged such that the center O1 of the rotation axis of the pressure roller 172 and the center O2 of the rotation axis of the soft roller 41 are separated by X [mm].

FIG. 5 is a diagram for explaining curl correction by the curl correction device 40. As shown in FIG.
The paper 20 is curled as it passes through the fixing nip portion N while moisture contained in the paper 20 is evaporated by heating by the fixing device 17 . In this embodiment, as described above, the fixing belt 171 is curved toward the pressure roller by the protrusion 178 on the nip exit side. As a result, the paper 20 that has passed through the fixing nip portion N curves toward the pressure roller together with the fixing belt 171, so that the paper 20 curls toward the pressure roller.

The paper 20 curled toward the pressure roller side enters the decurling nip D of the curl straightening device 40 . The curl correcting device 40 has the soft roller 41 arranged on the pressure roller side and the hard roller 42 arranged on the fixing belt 171 side across the paper conveying path, so that the decal nip D is formed on the paper that has passed through the fixing device 17 . The nip shape is curved in the direction opposite to the direction of curvature of the pressure roller (curl on the pressure roller side). As a result, the paper 20 that has entered the decurling nip D is subjected to a bending force in the direction opposite to the direction in which it was curled, as indicated by the arrow α in the figure, and the curl of the paper 20 is corrected.

Further, in this embodiment, the hard roller 42 is heated by the decal heater 43 . As a result, the paper 20 passes through the decal nip D while being heated by the hard roller 42 . By heating the paper 20 in this manner, the paper can be softened, the curl correction effect can be enhanced, and the curl can be corrected satisfactorily.

In the present embodiment, as shown in FIG. 3, the decal heater 43 has heating portions 43a at one end and the other end in the width direction so as to heat only the end portion of the sheet which tends to curl. As a result, as shown in FIG. 6(a), power consumption can be reduced compared to the case where the heating portion 43a of the decal heater 43 is arranged over the entire area in the axial direction. In addition, it is necessary to deal with various paper sizes. Therefore, as shown in FIG. 6B, the position of the heating portion 43a on the inner side in the axial direction is set to the inner side of the width L1 of the minimum paper size that can be passed, and the position of the heating portion 43a on the outer side in the axial direction is set to pass through A heating part 43a is provided outside the width L2 of the maximum paper size that can be used.

If the surface temperature of the hard roller 42 is lower than the target temperature, the paper 20 will not be sufficiently softened, and the curl correction effect will not be sufficiently enhanced. On the other hand, if the surface temperature of the hard roller 42 is higher than the target temperature, moisture may evaporate from the paper 20 and the paper 20 may curl toward the hard roller. Therefore, in this embodiment, the temperature detection sensor 44 is provided, and the controller 100 controls the decal heater 43 based on the detection result of the temperature detection sensor 44 so that the surface temperature of the hard roller 42 reaches the target temperature. . As a result, the curl correction effect can be sufficiently enhanced, and the paper 20 that has passed through the decurling nip D can be prevented from curling toward the hard roller.

By arranging the curl straightening device 40 near the fixing device 17, the softened paper immediately after being heated can enter the decal nip D, and the curl can be satisfactorily straightened without providing the decurling heater 43. It is considered possible to do so. However, if the curl correction device 40 is arranged near the fixing device 17, the following problems may occur. That is, the moisture evaporated from the paper 20 heated in the fixing nip portion N may adhere to the hard roller 42 and the like, causing dew condensation. In addition, there is also a risk of being subject to restrictions on the layout of the device. Furthermore, the hard roller 42 may be heated by the paper 20 to a temperature higher than the target temperature for enhancing the curl correction effect, and the paper 20 passing through the decurling nip D may curl toward the hard roller.

On the other hand, in the present embodiment, by providing the decurling device 40 with a decurl heater as a heating means, the decurling device can be arranged at an appropriate position on the paper discharge path of the device without being subject to layout restrictions. can. In addition, since it can be arranged away from the fixing device 17, it is possible to suppress the occurrence of dew condensation on the hard roller 42 and the like. In addition, the temperature of the hard roller 42 can be easily maintained at the target temperature at which the curl straightening effect can be enhanced, and the paper 20 passing through the decurl nip D can be prevented from curling toward the hard roller.

Also, in this embodiment, the decurling heater 43 is arranged outside the hard roller 42 . As a result, the diameter of the hard roller 42 can be shortened compared to the case where the decal heater 43 is arranged inside the hard roller 42 and the hard roller 42 is heated from the inside, and the size of the apparatus can be reduced. . Further, since the diameter of the hard roller 42 can be shortened, the curvature of the decal nip D can be increased, and the curl straightening effect can be enhanced.

The soft roller 41 has a larger diameter than the hard roller 42 , further has an elastic layer made of rubber or sponge, and has a larger heat capacity than the hard roller 42 . Therefore, when heating the soft roller 41, there is a problem that it takes time for the roller to reach the target temperature. Also, the coefficient of thermal expansion of the elastic layer made of rubber material is large. Therefore, as shown in FIG. 6(a), unless the heating portion 43a of the decal heater 43 is arranged in the entire axial direction to uniformly heat the soft roller 41 in the axial direction, there is no difference in the outer diameter in the axial direction. I'm out. As a result, the surface speed of the soft roller 41 in the decal nip varies in the axial direction, and there is a possibility that the sheet 20 may be wrinkled, thus affecting the conveyability.

On the other hand, in this embodiment, by heating the hard roller 42, the roller can be quickly heated to the target temperature. Further, since the hard roller 42 is made of metal and has a lower coefficient of thermal expansion than the soft roller, even if there is some difference in the temperature distribution in the axial direction, the difference in outer diameter is unlikely to occur. As a result, as shown in FIG. 6(b), even if the heating portion 43a is provided only at a portion of the hard roller 42 which is in contact with the widthwise end portion of the paper 20, there is no difference in the outer diameter in the axial direction. It can be suppressed that it does not come out so much and affects the transportability.

FIG. 7 is a diagram for explaining the relationship between the diameter of the soft roller 41 and the diameter of the hard roller 42. As shown in FIG. (a) is a diagram showing an example in which the diameter of the soft roller 41 is larger than the diameter of the hard roller 42, and (b) is an example in which the diameter of the soft roller 41 and the diameter of the hard roller 42 are the same. It is a figure which shows. (c) is a diagram showing an example in which the diameter of the soft roller 41 and the diameter of the hard roller 42 are smaller than each other.

As shown in FIG. 7(c), when the diameter of the soft roller 41 is made smaller than the diameter of the hard roller 42, the nip width of the decal nip D (arc length of the decal nip D) is shortened. As a result, the curl correction time (the time during which a bending force is applied to the paper 20) is short, and the curl correction effect is hardly obtained.

As shown in FIG. 7B, when the diameter of the soft roller 41 and the diameter of the hard roller 42 are the same, the layer thickness of the elastic layer of the soft roller 41 is thin and the compressibility of the elastic layer is small. Therefore, the hard roller 42 cannot be sufficiently bitten into the soft roller 41, and in FIG. is not sufficiently obtained.

On the other hand, as shown in FIG. 7A, in the present embodiment in which the diameter of the soft roller 41 is larger than that of the hard roller 42, the thickness of the elastic layer of the soft roller 41 can be sufficiently thickened. The compressibility of the elastic layer can be increased, and the hard roller 42 can be sufficiently bitten into the soft roller 41 . As a result, the nip width of the decal nip D (arc length of the decal nip D) can be sufficiently increased, and a good curl correction effect can be obtained.

In addition, a push-in adjustment mechanism is provided to adjust the pushing amount of pushing the soft roller into the hard roller so that the nip width of the decal nip D (arc length of the decal nip D) can be adjusted according to the type of paper 20 (material and paper thickness). can be

FIG. 8 is a schematic configuration diagram showing an example of a pushing adjusting mechanism 50 as pushing means.
The pushing adjustment mechanism 50 has a lever member 51 whose one end is rotatably supported and which supports the soft roller 41 so as to adjust the pushing amount of the hard roller 42, and the other end of the lever member 51 that is urged downward in the figure. It has a spring 53 as an urging means, a cam member 52 for moving the lever member 51 toward the hard roller against the urging force of the spring 53, a cam motor 54 for driving the cam member 52, and the like.

The lever member 51 abuts on a bearing 55 that receives the shaft 41 a of the soft roller 41 . FIG. 8 shows the state of the cam member when the push adjustment mechanism 50 is at the maximum adjustable push amount. When the cam motor 54 is controlled by the control unit 100 and the cam member 52 rotates from the state shown in FIG. Then, the soft roller 41 moves away from the hard roller 42 due to the reaction force from the hard roller 42, and the pressing amount of the soft roller 41 against the hard roller 42 is reduced.

FIG. 9 is a graph showing the temperature of the paper when entering the decal nip D and the effect of reducing the amount of curl. FIG. 9(a) is a graph showing the paper temperature when entering the decal nip D when the nip width of the decal nip D is α mm, and the effect of reducing the amount of curl. 10 is a graph showing the paper temperature at the time of entry into the decal nip D and the effect of reducing the amount of curl when the nip width is β mm (α<β). FIG. 9(c) is a graph showing the paper temperature when entering the decal nip D when the nip width of the decal nip D is γ mm (β<γ) and the effect of reducing the amount of curl.

FIGS. 9A to 9C show the results of using paper stored in a high humidity environment for several days. Further, in FIG. 9, as the temperature of the paper heated by the hard roller 42 in the decurl nip D, the temperature of the paper immediately before entering the decurl nip is used. Specifically, the temperature of the paper immediately before entering the decal nip was measured with a temperature sensor. Also, the temperature of the fixing device was adjusted to adjust the temperature of the paper when entering the decal nip D. Paper A, paper B, and paper E are papers made of different materials and having a basis weight of 70 [gsm]. again. The curl amount reduction effect is a value obtained by subtracting the curl amount before passing through the decal nip from the curl amount after passing through the decal nip D. As for the amount of curl, the curl on the back side of the paper (pressure roller side) is negative, and the curl on the front side of the paper (hard roller side) is positive.

As shown in FIGS. 9A to 9C, it can be seen that the curl reduction effect tends to increase as the temperature increases. In addition, as shown in FIG. 9(a), it can be seen that the curl reduction effect is more strongly affected by the temperature as the nip width of the decal nip D is narrower for thin paper (low grammage). Therefore, it can be seen that, for thin paper (low basis weight), the surface temperature of the hard roller 42 can be suppressed by narrowing the nip width, and a sufficient curl reduction effect can be obtained.

On the other hand, it can be seen that the curl reduction effect tends to increase as the nip width of the decal nip D increases for thick paper (large basis weight). Therefore, it is preferable to increase the pressing amount of the soft roller 41 with respect to the hard roller 42 to increase the nip width of the decal nip D when the paper is thick (has a large basis weight). Also, as with the paper J shown in FIG. 9C, depending on the material of the paper, even if the basis weight is not so large, the curl reduction effect may be enhanced by widening the nip width of the decal nip D. be.

In this way, the nip width of the decal nip D, which effectively obtains the curl reduction effect, and the paper temperature, differ depending on the paper thickness and paper material. It is preferable to change the nip width of the decal nip D and the paper temperature by adjusting the pressing amount of the hard roller 41 and the surface temperature of the hard roller.

FIG. 10 is a control block diagram of the printer of this embodiment.
FIG. 10 illustrates a configuration necessary for controlling the decal heater 43 and the cam motor 54 of the pressing adjustment mechanism 50. As shown in FIG.
As shown in FIG. 10, the printer includes a control section 100 that controls the decal heater 43 and the cam motor 54 of the pressing adjustment mechanism 50 . Connected to the control unit 100 are the operation panel 3, the temperature detection sensor, the decal heater 43, the storage unit 101 as nonvolatile storage means, the cam motor 54 of the pressing adjustment mechanism 50, the halogen heater 173 of the fixing device 17, and the like. .

The control section 100 controls the halogen heater 173 of the fixing device 17 . Specifically, an upper limit temperature and a lower limit temperature are set around the set temperature for the temperature of the fixing belt 171. When the temperature of the fixing belt 171 reaches the upper limit temperature, the control unit 100 detects the halogen temperature. When the heater 173 is turned off and the temperature of the fixing belt 171 reaches the lower limit temperature, the control unit 100 performs control to turn on the halogen heater 173 .

FIG. 11 is a control flow diagram for adjusting the pressing amount of the soft roller 41 against the hard roller 42 and the surface temperature of the hard roller according to the type of paper (material and thickness).
The storage unit 101 stores the paper information (such as the material of the paper and the basis weight of the paper) of the paper set in the paper feed tray 5 that is input by the user through the operation panel, in correspondence with the paper feed tray 5 . I remember. Alternatively, the brand of paper may be used as the paper information, and the material of the paper and the basis weight of the paper may be specified from the brand of paper.

When forming an image, the control unit 100 reads from the storage unit 101 the information on the paper sheets loaded in the paper feed tray 5 selected by the user by operating the operation panel 3 or an input terminal such as a PC. The type of paper to be printed (material, basis weight, etc.) is specified (S1).

The storage unit 101 stores, for example, a table shown in Table 1 below. Based on the table shown in Table 1, the target temperature of the hard roller and the target pressing force of the soft roller 41 against the hard roller 42 are set. Set the amount (S2).

In Table 1 above, the target temperature (A<B<C) and the target pressing amount (D<E<F) increase as the basis weight of the paper increases. The smaller the basis weight of the paper, the lower the surface temperature of the hard roller 42, the more the paper can be heated to a temperature at which a sufficient curl reduction effect can be obtained. On the other hand, the greater the basis weight of the paper, the greater the heat capacity of the paper. Unless the surface temperature of the hard roller 42 is increased and the amount of heat imparted to the paper from the hard roller 42 is not increased, the curl reduction effect of the paper can be sufficiently obtained. Cannot heat up to paper temperature. Therefore, the target temperature of the hard roller is increased as the grammage of the paper increases. In addition, by lowering the target temperature of the hard roller as the basis weight of the paper decreases, the sheet with the smaller basis weight is overheated, and the sheet passing through the decal nip D curls toward the hard roller. You can prevent it from collapsing.

Further, as the basis weight of the paper increases, the target pressing amount of the soft roller 41 against the hard roller 42 is increased, and the nip width of the decal nip D is widened. can be corrected. In addition, Table 1 is an example, and is not limited to this. Further, in the present embodiment, the target temperature and the target pressing amount are set so that the amount of curl after passing through the curl straightening device 40 is ±10 [mm] or less.

Next, the control unit 100 controls the cam motor 54 of the pressing adjustment mechanism 50 to adjust the pressing amount of the soft roller 41 against the hard roller 42 to the target pressing amount, and adjusts the nip width of the decal nip D according to the type of paper. The nip width is adjusted accordingly (S3). Further, the control unit 100 controls the decal heater 43 based on the detection result of the temperature detection sensor 44 so that the surface temperature of the hard roller 42 reaches the target temperature.

Specifically, the control unit 100 checks whether or not the temperature detected by the temperature detection sensor 44 exceeds the target temperature (S4). to heat the hard roller 42 . On the other hand, when the detected temperature detected by the temperature detection sensor 44 exceeds the target temperature (Yes in S4), the decurler heater is turned off. Thereby, the surface temperature of the hard roller 42 is adjusted to the target temperature.

In this way, by adjusting the surface temperature of the hard roller 42 and the pressing amount of the soft roller 41 against the hard roller 42 according to the type of paper (the material and basis weight of the paper), good printing results can be obtained regardless of the type of paper. curl can be corrected.

In addition, the amount of curling of the paper that has passed through the fixing nip portion N differs depending on the environment. Therefore, the target temperature and the target pressing amount may be set in consideration of the environmental conditions (humidity) in addition to the paper type (material and basis weight).

When the image forming operation is performed while the conveying rollers and guide members that constitute the paper discharge path 70 are cold, the moisture evaporated from the paper when heated by the fixing device 17 moves through the paper discharge path 70 . When it adheres to the transport rollers and guide members, it may be cooled and liquefied, causing dew condensation on these members. In this way, when dew condensation occurs on the transport rollers and guide members that constitute the discharge path 70, there is a risk that the paper will get wet, or that the paper will stick to the guide members and cause a paper jam.

Therefore, it is preferable that the decal heater 43 is turned on not only during image formation, but also when the apparatus is started up when the power is turned on, and when the apparatus returns from the standby state. The decal heater 43 is turned on and the hard roller 42 is rotationally driven at the time of start-up or restoration of the apparatus. As a result, the decal heater 43 can heat the conveying rollers and the guide members that constitute the discharge path 70 . As a result, it is possible to suppress the occurrence of dew condensation on the transport rollers and the guide members that constitute the paper discharge path 70, and it is possible to suppress the occurrence of paper wetting and paper jams. Further, by rotating the hard roller 42, it is possible to prevent the surface of the hard roller 42 from being heated at a predetermined portion.

Further, as described above, the upper limit temperature and the lower limit temperature are set around the set temperature of the fixing belt 171. When the temperature of the fixing belt 171 reaches the upper limit temperature, the control unit 100 controls the halogen heater 173 is turned off and the halogen heater 173 is turned on when the temperature of the fixing belt 171 reaches the lower limit temperature. Therefore, the temperature of the paper passing through the fixing nip portion N when the halogen heater is turned off is the same as the temperature of the paper entering the decal nip D after passing through the fixing nip portion N when the halogen heater is turned off. It may be lower than the paper temperature. Therefore, if the decal heater 43 is turned off when the paper passing through the fixing nip portion N when the halogen heater is turned off passes through the decal nip D, the paper cannot be heated to a temperature at which a sufficient curl reduction effect can be obtained. , curl may remain. Therefore, the lighting control of the decal heater 43 may be performed based on the lighting control of the halogen heater 173 of the fixing device 17 .

FIG. 12 is a control flow diagram for performing lighting control of the decal heater 43 based on lighting control of the halogen heater 173 of the fixing device 17 .
As shown in FIG. 12, when the temperature detected by the temperature detection sensor is higher than the target temperature (Yes in S14), the control unit 100 controls the lighting of the halogen heater 173 of the fixing device 17 to turn on the halogen heater t seconds before. Check if the heater 173 was turned off. The above "t seconds" is the time it takes for the paper 20 to reach the decal nip D from the fixing nip portion N. can be calculated from the distance X [mm] between and the paper transport speed V [mm/s] (t=X/V).

If the halogen heater 173 was turned off t seconds before (Yes in S15), the decal heater 43 is turned on. On the other hand, if the temperature detected by the temperature detection sensor is higher than the target temperature (Yes in S14) and the halogen heater 173 was turned on t seconds before (Yes in S15), the decal heater is turned off (S16). .

In this way, by controlling the lighting of the decurling heater 43 based on the lighting control of the halogen heater 173 of the fixing device 17, it is possible to reliably heat the paper to a temperature at which a sufficient curl reduction effect can be obtained. Curls can be corrected well.

What has been described above is only an example, and each of the following aspects has a unique effect.
(Aspect 1)
A pair of conveying members (in this embodiment, a hard roller 42 and a soft In the curl straightening device 40 for correcting the curl of the sheet by passing the sheet through a nip such as the decurl nip D formed by contacting the roller 41), a decurl heater for heating one of the pair of conveying members from the outside. A heating means such as 43 was provided.
According to this, the sheet passing through the nip is heated by one of the pair of conveying members by heating one of the conveying members. As a result, the sheet is softened and the curl correction effect can be enhanced, and even a sheet with a large amount of curl can be corrected satisfactorily.
Further, by heating one of the conveying members from the outside, the outer diameter of the one of the conveying members can be made smaller than when the heating means is provided inside the one of the conveying members to heat the one of the conveying members from the inside. It is possible to reduce the size of the device. As a result, the curl correcting device can be arranged in the paper ejection path without increasing the size of the image forming apparatus.

(Aspect 2)
In mode 1, the pair of conveying members have different hardnesses, and the diameter of the conveying member with low hardness such as the soft roller 41 is larger than the diameter of the conveying member with high hardness such as the hard roller 42 .
According to this, as described in the embodiment, the high-hardness conveying member such as the hard roller 42 can be sufficiently bitten into the low-hardness conveying member such as the soft roller 41, and the nip width ( The arc length of the decal nip D) can be sufficiently increased, and a good curl straightening effect can be obtained.

(Aspect 3)
In mode 2, the low-hardness conveying member such as the soft roller 41 is a roller having an elastic layer, the high-hardness conveying member is a metal roller, and the heating means such as the decal heater 43 is a high-hardness roller. Heat the transport member.
According to this, as described in the embodiment, the conveying member can be quickly heated to the target temperature. In addition, even if there is a slight difference in the temperature distribution in the axial direction, the difference in the outer diameter is unlikely to occur, and it is possible to suppress the influence on the transportability.

(Aspect 4)
In any one of modes 1 to 3, a temperature detection sensor 44 is provided to detect the surface temperature of the conveying member (hard roller 42 in this embodiment) heated by a heating means such as a decal heater 43 .
According to this, the heating means such as the decal heater 43 can be controlled based on the detection result of the temperature detection sensor 44 .

(Aspect 5)
In mode 4, there is provided control means such as the control unit 100 that controls the heating means such as the decal heater 43 based on the detection result of the temperature detection sensor 44 .
According to this, the paper can be heated to an optimum temperature at which a sufficient curl straightening effect can be obtained.

(Aspect 6)
In aspect 5, a pushing means such as a pushing adjusting mechanism 50 for pushing one of the pair of conveying members (soft roller 41 in this embodiment) into the other conveying member (hard roller 42 in this embodiment) is provided. , the control unit 100 or the like controls the pressing amount of the pressing unit and the heating unit such as the decal heater 43 according to the type of sheet being conveyed (such as the material and basis weight of the sheet). and the target temperature of the surface of the conveying member to be changed.
According to this, as described in the embodiment, it is possible to satisfactorily correct the curl of a sheet such as paper regardless of the sheet type (material and basis weight).

(Aspect 7)
In any one of modes 1 to 6, there is provided control means such as the control section 100 that controls heating means such as the decal heater 43 based on ON/OFF control of the heat source of the fixing device 17 such as the halogen heater 173 .
According to this, as described with reference to FIG. 12, it is possible to reliably heat a sheet such as paper to a temperature at which a sufficient curl reduction effect can be obtained, and it is possible to satisfactorily correct curl.

(Aspect 8)
In any one of Modes 1 to 7, the heating means such as the decal heater 43 heats the end portion side of the conveying member more than the central portion thereof in the axial direction.
According to this, it is possible to make the sheet width direction end portion having a large amount of curl higher in temperature than the center portion, and it is possible to satisfactorily correct the curl of the sheet.

(Aspect 9)
In any one of modes 1 to 8, the pair of conveying members rotates and the conveying members are heated by the heating means such as the decal heater 43, even when the image forming apparatus is not performing the image forming operation.
According to this, it is possible to heat the conveying rollers and the guide members constituting the paper discharge path 70 by the heating means such as the decal heater 43 . As a result, it is possible to suppress the formation of condensation on the conveying rollers and guide members that constitute the paper ejection path 70 due to moisture evaporated from the sheet that has passed through the fixing device during the image forming operation.

(Mode 10)
In any one of modes 1 to 9, the surface of at least one of the pair of conveying members is provided with a release layer, or the surface is subjected to a surface treatment that enhances releasability.
According to this, as described in the embodiment, retransfer of toner from a sheet such as paper to the conveying member can be suppressed.

(Aspect 11)
A discharge path such as a sheet discharge path 70 for discharging the sheet that has passed through the fixing device 17 to the outside of the image forming apparatus, and curl correction means such as a curl correction device 40 provided in the discharge path for correcting the curl of the sheet. , the curl straightening device according to any one of modes 1 to 10 is used as the curl straightening means.
According to this, it is possible to satisfactorily correct the curl while suppressing an increase in the size of the sheet conveying device.

(Aspect 12)
Image forming means for forming an image on a sheet such as the paper 20, a fixing device 17 for fixing the image formed on the sheet, and a paper discharge path 70 for discharging the sheet that has passed through the fixing device 17 to the outside of the machine. In an image forming apparatus provided with a curl correcting device such as the curl correcting device 40 for correcting the curl of a sheet, the curl correcting device according to any one of Modes 1 to 10 is used as the curl correcting device.
According to this, it is possible to satisfactorily correct the curl while suppressing the enlargement of the image forming apparatus.

1 : Printer body 3 : Operation panel 4 : Paper discharge tray 5 : Paper feed tray 17 : Fixing device 40 : Curling device 41 : Soft roller 41a : Shaft 42 : Hard roller 43 : Decal heater 43a : Heating unit 44 : Temperature detection Sensor 50 : Push adjustment mechanism 51 : Lever member 52 : Cam member 53 : Spring 54 : Cam motor 55 : Bearing 70 : Discharge path 71 : Conveyance roller pair 100 : Control unit 101 : Storage unit 171 : Fixing belt 172 : Pressure roller 173: Halogen heater 176: Nip forming member 178: Projection

JP-A-2000-247526

Claims (9)

A curl correction device is arranged in the discharge path for discharging the sheet that has passed through the fixing device to the outside of the image forming apparatus. in the device,
heating means for heating one of the pair of conveying members from the outside ;
a temperature detection sensor that detects the surface temperature of the conveying member heated by the heating means;
a control means for controlling the heating means based on the detection result of the temperature detection sensor;
a pushing means for pushing one of the pair of conveying members into the other conveying member;
The control means is characterized in that the pushing amount of the pushing means and the target temperature of the surface of the conveying member, which is the target temperature for controlling the heating means, are changed according to the type of the sheet to be conveyed. curl straightening device. The curl straightening device according to claim 1,
the pair of conveying members have hardnesses different from each other,
A curl straightening device, wherein the diameter of the low-hardness conveying member is larger than the diameter of the high-hardness conveying member. In the curl straightening device according to claim 2,
The low-hardness conveying member is a roller having an elastic layer, and the high-hardness conveying member is a metal roller,
The curl straightening device, wherein the heating means heats a conveying member having a high hardness. In the curl straightening device according to any one of claims 1 to 3 ,
The curl straightening device, wherein the control means controls the heating means based on ON/OFF control of a heat source of the fixing device. In the curl straightening device according to any one of claims 1 to 4 ,
The curl straightening device, wherein the heating means heats an end portion of the conveying member more than a central portion thereof in an axial direction. In the curl straightening device according to any one of claims 1 to 5 ,
A curl straightening device, wherein the pair of conveying members are rotated and the conveying members are heated by the heating means in addition to the image forming operation of the image forming apparatus. The curl straightening device according to any one of claims 1 to 6 ,
A curl straightening device, wherein a release layer is provided on the surface of at least one of the pair of conveying members, or the surface is subjected to a surface treatment that enhances releasability. . a discharge path for discharging the sheet that has passed through the fixing device to the outside of the image forming apparatus;
A sheet conveying device provided in the discharge path and including curl correcting means for correcting curl of the sheet,
A sheet conveying apparatus, wherein the curl correcting device according to any one of claims 1 to 7 is used as the curl correcting means. an image forming means for forming an image on a sheet;
a fixing device for fixing the image formed on the sheet;
An image forming apparatus comprising: a curl correcting means for correcting curl of a sheet provided in a discharge path for discharging the sheet that has passed through the fixing device to the outside of the apparatus;
An image forming apparatus, wherein the curl straightening device according to any one of claims 1 to 8 is used as the curl straightening means.

Images