JP2008145854A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce degradation in conveyance, resulting from sudden removal of moisture from a sheet material, by eliminating a big difference between one-sided printing and both-sided printing in terms of the amount of moisture held in a sheet material. <P>SOLUTION: (1) In a one-sided printing process, a conveyance path for conveying a sheet material into a heat fixing device more than one time is provided. (2) In a both-sided printing process, a conveyance roller warmed by the residual heat of the heat fixing device reheats the sheet material in a both-sided conveyance path after printing on one side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus having a sheet material moisture amount adjusting means for transferring and recording a document image in an image forming apparatus such as a printer having a heat fixing device.

  An image forming apparatus according to the prior art will be described with reference to the sheet material conveying apparatus of FIG.

  The sheet material P loaded on the paper cassette 101 and discharged from the sheet feeding device 102 is sequentially conveyed by each sheet material conveying device 100.

  In the image forming unit 105, the sheet material P on which the document image is transferred and recorded is again conveyed by the sheet material conveying device and conveyed to the fixing device 103.

  In the fixing device 103, the original image on the sheet material is fixed, and then the sheet material is directly discharged to the paper discharge unit 106 b through the paper discharge conveyance path 106 a of the paper discharge conveyance device 106.

  As a fixing device, a heat fixing device using a heater or the like is generally known. By heating by the fixing device, a transfer image by toner or the like is fixed to the sheet material, and the moisture contained in the sheet material by the heating is fixed. Is evaporated to dryness.

  When the difference in moisture content of the sheet material before and after passing through the heat fixing device is large, the sheet curls greatly to the side of the heating element where drying is promoted, and the conveyance performance is remarkably lowered. In addition, if the water content distribution of the sheet material is uneven, it will cause wrinkles. In addition, the amount of elongation of the sheet material increases due to the heating by the heat fixing device, which becomes a large variation factor with respect to the printing in the image forming unit, so that the printing magnification accuracy is deteriorated.

  In order to solve this problem, a method has been devised in which a sheet heating element is provided in a paper cassette, a sheet material is heated and dried, and the moisture content is adjusted or reduced to a constant level. In order to remove the curl, a means for providing a curl removing roller is realized.

  However, when a sheet heating element is provided in a paper cassette, a large-capacity heating element is required to dry the entire sheet material, and drying unevenness easily occurs. In addition, the power supply to the heating element must be performed at all times, and there are safety problems and installation cost problems.

  Further, as shown in FIG. 5, the paper cassette is not used, and there is a problem that it cannot be applied to the image forming apparatus of the tray stacking type paper feeding device 107 provided with the paper feeding tray 107a.

  As disclosed in Japanese Patent Laid-Open No. 6-83221, a proposal has been made to dry the sheet material by transporting the heat generated by the heat fixing device to the paper cassette using a duct instead of the sheet heating element. However, there have been problems such as a problem in machine arrangement and a problem that it does not function unless it is in operation even though it does not dry in a short time.

  Regarding curling rollers, there is a problem in installation that it is not effective unless it passes through the heat fixing device, the limit for mechanically correcting the sheet material, damage to the sheet material, and the direction of curling to correct. There was a problem.

In addition, as proposed in Japanese Patent Laid-Open No. 1-267254, there has been a proposal to reduce the mechanical stress by providing a heating means in the decurling roller part, but this also requires a separate heating device. There was an installation cost problem that had to be done.
JP-A-6-83221 Japanese Unexamined Patent Publication No. 1-267254

  (1) Due to the moisture absorption state of the sheet material, the amount of curl increases when the sheet is passed through the heat fixing device, which impedes the conveyance of the sheet material.

  (2) Depending on the moisture absorption state of the sheet material, when the heat fixing device is passed through, the elongation amount of the sheet material fluctuates, an error in the set magnification accuracy occurs, and the printing magnification accuracy deteriorates. In addition, the difference in printing magnification accuracy between single-sided printing and double-sided printing also increases.

  (1) In the single-sided printing process, a conveyance path for conveying the sheet material a plurality of times into the heat fixing apparatus is provided.

  (2) In the double-sided printing process, after single-sided printing, the sheet material is reheated in the double-sided conveyance path by the conveyance roller heated by the residual heat of the heat fixing device.

As described above, the present invention allows the sheet material to pass through the heat fixing device a plurality of times in the single-sided printing process, and adjusts or reduces the moisture absorption amount of the sheet material to a constant value.
(1) It has become possible to eliminate the occurrence of curling and the like that significantly reduce the sheet material conveyance performance.

  (2) The printing magnification accuracy can be improved without being affected by the paper quality, environment and printing surface.

  (3) In addition, in order to adjust or reduce the moisture absorption amount of the sheet material to a certain level, the use of a heat fixing device can be realized without adding a new device. For this reason, it has become possible to apply the present invention to a tray-stacking type paper feeding device that does not use a paper cassette.

  (4) The image fixing temperature of the heat fixing device during the first conveyance can be set low, and since the sheet material has already been warmed the second time, the amount of heat taken away by the fixing device by the sheet material is low, so an energy saving effect can also be realized. It was.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

  FIG. 1 shows an image forming apparatus according to a first embodiment of the present invention.

  The sheet material conveying operation by the sheet material conveying device of the image forming apparatus of the present invention will be described with reference to FIG.

  The sheet material P loaded on the paper cassette 2 and discharged from the sheet feeding device 7 in the direction a is sequentially conveyed by each sheet material conveying device 1.

  In the image forming unit 5, an image such as toner formed on the photoreceptor 5 a through a predetermined process is transferred and recorded on the sheet material P according to the document image.

  The sheet material P on which an image such as toner is electrostatically adsorbed is further conveyed by the sheet material conveying device 1 and sent to the heat fixing device 3.

  In the heat fixing device 3, reference numeral 3a denotes a pressure roller that functions as a driving roller and rotates clockwise. The sheet material P is nipped and conveyed by the pressure roller 3a and the driven fixing roller 3b. On the other hand, the original image on the sheet material P is fixed by the fixing roller 3 b, and then the sheet material P is conveyed to the fixing paper discharge conveyance unit 9. In the case of single-sided printing, the paper is discharged in the direction b by the transport roller pair 6c of the paper discharge transport device 6 through the paper discharge transport path 6b without changing the transport direction, and is stacked on the paper discharge stacking portion 6a.

  On the other hand, in the case of double-sided printing, the sheet material P is moved in the direction of discharge b by the transport roller pair 6 c of the paper discharge transport device 6, and the rear end of the sheet material P is transported by paper discharge after the fixing paper discharge transport unit 9 After passing through the switching mechanism 10 provided in the path 6b, the rotation of the transport roller pair 6c of the paper discharge transport device 6 stops and starts to feed the sheet material in the c direction opposite to the sheet material feed direction of the image forming unit. The sheet material P is selected on the duplex conveyance path 4a of the duplex conveyance device 4 by switching the sheet material guide surface of the switching mechanism 10. The sheet material P is conveyed to the double-sided conveying device 4 and is again guided to the conveying path of the heat fixing device 3.

  The sheet material P is reheated by the pressure roller 3a at the conveyance roller pair position including the pressure roller 3a and the fixing conveyance roller 3c of the heat fixing device 3. By this reheating, the image fixing temperature of the heat fixing device during single-sided printing conveyance can be set low.

  A pair of conveyance rollers composed of the pressure roller 3a and the fixing conveyance roller 3c of the heat fixing device 3 functions as a partial conveyance device of the double-sided conveyance device 4, and the sheet material P is conveyed again in the d direction to the double-sided conveyance path 4b. Is done.

  The sheet material P is changed to the e direction by the U-turn path 4c, and is guided to the resist conveyance device 8 including the registration lower roller 8a and the registration upper roller 8b.

  The resist conveying device 8 and thereafter take the same conveying form as in the case of single-sided printing, and are finally discharged to the paper discharge stacking portion 6a of the paper discharge conveying device 6 to complete a series of image forming processes.

  FIG. 2 shows an image forming apparatus according to the second embodiment of the present invention.

  The image forming apparatus according to the second embodiment has a sheet material conveyance mode in which the function of the paper feeding device is added to the sheet material conveyance unit of the paper discharge conveyance device with respect to the image forming apparatus according to the first embodiment. It is a thing.

  When the sheet material P loaded on the tray 7a of the paper supply / discharge port detects a paper feed signal, the sheet material conveyance device 1 including the heat fixing device 3 is driven, and the sheet material P is circulated by the circulation conveyance device 4. Via a conveyance path 4a, the heat is fed to a pair of conveyance rollers including a pressure roller 3a and a fixing conveyance roller 3c of the heat fixing device 3.

  A heating device such as a heater of the heat fixing device 3 only needs to be provided on the image printing surface side, and the sheet material P is dried by the pressure roller 3a heated by the heating device 3b. The sheet material P is dried by evaporating moisture absorbed in the heat fixing device 3, and then conveyed to the circulation conveyance path 4 b of the circulation conveyance device 4. The conveyance direction is changed by the U-turn path 4 c, and the sheet material P is guided to the resist conveyance device 8. To the image forming unit 5.

  In the image forming unit 5, an image such as toner formed on the photoreceptor 5 a through a predetermined process is transferred and recorded on the sheet material P according to the document image.

  The sheet material P on which an image such as toner is electrostatically adsorbed is further conveyed by the sheet material conveying device 1 and sent to the heat fixing device 3.

  Since the moisture content of the sheet material P has already been dried, the amount of elongation of the sheet material at the time of image fixing is small, and the occurrence of curling is also small.

  After fixing, the sheet material P is discharged by a pair of conveyance rollers 7c of the paper supply / discharge conveyance device 7 through a discharge conveyance path 7b and stacked on the discharge stacking portion 7d.

  On the other hand, in the case of double-sided printing, the paper discharge stacking unit 7d, the tray 7a, the separation unit, etc. are withdrawn, and are separated from the sheet material P stacked on the tray 7a of the paper supply / discharge port. After being ejected by the pair 7 of transport rollers 7c, it is moved to the paper feed position.

  When the paper feed signal is detected, the sheet material conveying device 1 including the heat fixing device 3 is driven, and the sheet material P passes through the circulation conveying path 4a of the circulation conveying device 4 and is fixed to the pressure roller 3a of the heat fixing device 3. It is sent to a pair of conveyance rollers comprising a conveyance roller 3c.

  Thereafter, through the same process as the single-sided printing process, the sheet material P is stacked on the paper discharge stacking unit 7d, and the series of operations is completed.

  FIG. 3 shows an image forming apparatus according to the third embodiment of the present invention.

  In the image forming apparatus according to the third embodiment, the sheet material P is reciprocally conveyed along the same conveyance path of the heat fixing apparatus and circulated with respect to the image forming apparatus according to the second embodiment. It is.

  When the sheet material P stacked on the tray 7a of the sheet feeding device 7 detects a sheet feeding signal, the sheet material conveying device 1 including the heat fixing device 3 is driven, and the sheet material P is fed and conveyed to form an image. Sent to part 5.

  In the image forming unit 5, an image such as toner formed on the photoreceptor 5 a through a predetermined process is transferred and recorded on the sheet material P according to the document image.

  The sheet material P on which an image such as toner is electrostatically adsorbed is further conveyed by the sheet material conveying device 1 and sent to the heat fixing device 3.

  An image such as toner on the sheet material P is fixed on the sheet material by the heat fixing device 3.

  The sheet material P after fixing is discharged to the supply / discharge port 6a by the conveyance roller pair 6c of the sheet supply / discharge conveyance device 6.

  On the other hand, in the case of double-sided printing, the sheet material conveying apparatus 1 stops driving before the rear end (relative to the conveying direction) of the sheet material P is discharged by the conveying roller pair 6c. It remains in a state of being sandwiched between the transport roller pair 6c.

  Thereafter, the sheet material conveying device 1 including the heat fixing device 3 is driven in the opposite direction to the previous direction, and the sheet material P is sent to the heat fixing device 3 again. By this reheating, the image fixing temperature of the heat fixing device during single-sided printing conveyance can be set low.

  The sheet material P is evaporated and dried again by the heat-fixing device 3 and then transported to the circulation conveyance path inlet 4a and the circulation conveyance path 4b of the circulation conveyance device 4, and the conveyance direction is changed by the U-turn path 4c. It is guided to the conveying device 8 and sent to the image forming unit 5 again.

  Thereafter, through the same process as the single-sided printing process, the sheet material P is discharged to the paper supply / discharge port 6a of the paper supply / discharge conveyance device 6 and the series of operations is completed.

  It is also possible to insert a sheet material from the paper supply / discharge port 6a of the paper supply / discharge conveyance device 6 and execute a series of processes.

  When the sheet material P inserted from the paper supply / discharge port 6a is detected by a sheet material detection sensor 6e provided in front of the conveyance roller pair 6c, the sheet material conveyance device 1 including the conveyance roller pair 6c is driven. The sheet material P is sent to the heat fixing device 3.

  The sheet material P is dried by evaporating moisture absorbed in the heat fixing device 3, and then conveyed to the circulation conveyance path inlet 4a and the circulation conveyance path 4b of the circulation conveyance device 4, and the conveyance direction is changed by the U-turn path 4c, and the resist conveyance is performed. It is guided to the apparatus 8 and sent to the image forming unit 5.

  The heating amount of the heating and fixing device 3 at this time is only the amount of heat necessary for drying the sheet material P, and can be kept lower than when the transfer image such as toner is fixed.

  After the image formation, the same process as described above is performed. Finally, the sheet material P is discharged to the paper supply / discharge port 6a and the series of processes is completed.

  In the image forming apparatus of FIG. 3, the inlet 4 a to the circulation conveyance path 4 is provided in the middle of the conveyance path between the heat fixing device 3 and the image forming unit 5. 3 can also be provided in the middle of the conveyance path between the two. In that case, after the sheet material P conveyed from the sheet feeding device 7 is dried in the heat fixing device 3, the sheet material P is transferred to the circulation conveyance path 4 without changing the driving rotation direction of the heat fixing device 3. Can lead.

1 is a schematic configuration diagram of an image forming apparatus including a sheet material conveying device according to a first embodiment of the present invention. FIG. 6 is a schematic configuration diagram of an image forming apparatus including a sheet material conveying device according to a second embodiment of the present invention. FIG. 10 is a schematic configuration diagram of an image forming apparatus including a sheet material conveying device according to a third embodiment of the present invention. 1 is a schematic configuration diagram of an image forming apparatus provided with a sheet material conveying apparatus using a paper cassette according to a conventional technique. FIG. 6 is a schematic configuration diagram of an image forming apparatus including a sheet material conveying device using a stacking tray according to a conventional technique.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sheet material conveying apparatus 2 Paper cassette 3 Heat fixing apparatus 4 Circulation (double-sided) conveying apparatus 5 Image forming part 6 (Feeding) Discharge conveying apparatus 7 Paper feeding apparatus

Claims (6)

  Depending on the original image, the image formed on the photoconductor through a predetermined process is transferred and recorded, and the sheet is printed multiple times in the single-sided printing process of the image forming apparatus that uses heat to fix the image on the surface of the sheet material. An image forming apparatus having a conveyance path for conveying a material into a heat fixing device.   It has a first conveyance path for fixing an unfixed image after image formation on a sheet material, and a second conveyance path for reheating the sheet material in the double-sided conveyance path after fixing the unfixed image. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 2, wherein the pressure roller of the heat fixing device is a part of the conveying device of the double-sided conveying path.   2. The image forming apparatus according to claim 1, wherein the sheet material is passed through a heat fixing device before the image is formed on the surface of the sheet material.   The image forming apparatus according to claim 4, wherein the image forming is performed through the circulation type conveyance path after the sheet material is passed through the heat fixing device before the image is formed on the surface of the sheet material.   2. The image forming apparatus according to claim 1, wherein after the image is formed on the surface of the sheet material, the sheet material is reciprocally conveyed to the heat fixing device.

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