JP4696815B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device that fixes unfixed toner on a recording medium such as paper and an image forming apparatus including the fixing device, and more particularly to a technique for suppressing deformation of a heating roller.

  2. Description of the Related Art Image forming apparatuses such as copying machines, facsimile machines, and printers use a fixing device that fixes an unfixed toner image transferred to a recording medium such as paper. The fixing device generally includes a heating roller for heating a toner image and a pressure roller pressed against the heating roller. In the fixing device, a pressure contact portion is formed between the heating roller and the pressure roller, and the toner image is heated and melted and fixed to the recording medium while the recording medium passes through the pressure contact portion.

  The heating roller includes a heater, and generally consumes a large amount of power during operation. In order to reduce the power consumption of the heating roller, it is effective to reduce the size or thickness of the heating roller for the purpose of reducing the heat capacity. In addition, the first copy time can be shortened by realizing a low heat capacity. However, if the heating roller is downsized or the wall thickness is reduced, the rigidity of the heating roller is reduced. Therefore, the heating roller to which the pressure roller is pressed may be bent by the pressing force, and the shape of the pressing portion may change accordingly. As a result, a defect in the conveyance of the recording medium occurs, such as fixing failure of the toner image or wrinkles on the recording medium.

In order to suppress such bending of the heating roller, there has been proposed a fixing device including a deformation preventing roller that presses the heating roller from the side opposite to the pressure roller (see Patent Document 1).
JP-A-8-234608

  However, in the above conventional fixing device, although the deflection of the heating roller is suppressed, there is a case where the fixing property of the toner image is not sufficient because there is only one pressure contact portion through which the recording medium passes.

  The present invention has been made in view of the above problems, and an object thereof is to provide a fixing device and an image forming apparatus capable of improving the fixability of a toner image while suppressing the bending of a heating roller. It is in.

  In order to solve the above problems, a fixing device according to the present invention is a fixing device that fixes an unfixed toner image transferred to a recording medium to the recording medium, the recording medium being in contact with an outer peripheral surface, A heating roller that heats the recording medium; and at least two pressure rollers that are in pressure contact with a contact area on the outer peripheral surface of the heating roller that contacts the recording medium, the at least two pressure rollers from the heating roller to the heating roller Each pressure roller is pressed against the heating roller so that the applied pressing force is balanced, and the recording medium passes through each of the pressure contact portions between the heating roller and each pressure roller, The toner image is fixed.

  Here, the recording medium is a recording medium capable of fixing a toner image, such as paper, a resin-made OHP sheet, or a postcard. In addition, when the pressure contact force applied to the heating roller from at least two pressure rollers is balanced, the resultant force of the pressure contact force changes not only when the resultant force of the pressure contact force becomes zero, but also in the shape of the heating roller. This includes cases where the size is too small.

  According to the present invention, since the recording medium passes through the pressure contact portion between at least two pressure rollers and the heating roller, the fixability of the toner image is improved. In addition, since the pressing force applied to the heating roller from at least two pressing rollers is balanced, bending of the heating roller due to the pressing of the pressing roller is suppressed.

  In one embodiment of the present invention, the at least two pressure rollers are arranged at equal intervals in a circumferential direction of the heating roller.

  According to this aspect, since the at least two pressure rollers are arranged at equal intervals in the circumferential direction of the heating roller, each pressure roller is arranged so as to sandwich the heating roller, and stably heats the pressure roller. It can be pressed against the roller.

  In order to solve the above problems, the present invention is a fixing device for fixing an unfixed toner image transferred to a recording medium to the recording medium, the recording medium being in contact with an outer peripheral surface, and the recording medium being A heating roller for heating, at least two pressure rollers pressed against the contact position of the outer peripheral surface of the heating roller with the recording medium, and a non-contact region of the recording medium on the outer peripheral surface of the heating roller A pressure roller, and the pressure roller and each pressure roller are pressed against the heating roller so that the pressure contact force applied to the heating roller from the pressure roller and the at least two pressure rollers is balanced, The recording medium passes through each pressure contact portion between the heating roller and each pressure roller, and the toner image is fixed.

  According to the present invention, since the pressure contact portion between the at least two pressure rollers and the heating roller passes, the fixability of the toner image is improved. In addition, since the pressure contact force applied to the heating roller from the at least two pressure rollers and the pressure roller is balanced, bending of the heating roller due to the pressure contact of the pressure roller is suppressed.

  In one aspect of the present invention, the at least two pressure rollers and the pressing roller are arranged at equal intervals in a circumferential direction of the heating roller.

  According to this aspect, since the at least two pressure rollers and the pressure roller are arranged at equal intervals in the circumferential direction of the heating roller, each pressure roller and the pressure roller are arranged so as to sandwich the heating roller and stably The pressure roller and the pressure roller can be brought into pressure contact with the heating roller.

  In one embodiment of the present invention, the at least two pressure rollers have the same structure.

  According to this aspect, since the fixing device includes the pressure roller having the same structure, it is not necessary to design and produce a plurality of types of pressure rollers, and the productivity of the fixing device is improved.

  In one embodiment of the present invention, the at least two pressure rollers and the pressure roller have the same structure.

  According to this aspect, since the fixing device includes the pressure roller and the pressure roller having the same structure, it is not necessary to design and produce a plurality of types of pressure rollers and pressure rollers, and the productivity of the fixing device is improved.

  In addition, an image forming apparatus for solving the above problems includes any one of the fixing devices described above.

  Here, the image forming apparatus is, for example, a printer, a copying machine, a facsimile, or a multifunction machine having these functions integrally. According to this image forming apparatus, since the fixing device included in the image forming apparatus includes the pressure roller or the pressure roller that is pressed so that the pressing force applied to the heating roller is balanced, the deflection of the heating roller is suppressed. In addition, poor fixing of the toner image due to the deflection of the heating roller is suppressed. Further, since the recording medium passes through the pressure contact portion between the at least two pressure rollers and the heating roller, the fixability of the toner image is improved.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.

  FIG. 1 is an overall configuration diagram showing an outline of an image forming apparatus 1 including a fixing device according to the present embodiment, and FIG. 2 is a cross-sectional view showing an outline of the fixing device 10. In FIG. 1, a two-dot chain line R indicates a conveyance path for the recording medium P.

  As shown in FIG. 1, the image forming apparatus 1 includes a fixing device 10 and an image forming mechanism 20 on the upstream side of the conveyance path of the recording medium P from the fixing device 10. The image forming mechanism 20 includes a photosensitive drum 22, a charging roller 23 disposed around the photosensitive drum 22, an optical scanning device 24, a developing device 25, a transfer roller 27, and a cleaning device 26. ing.

  The photosensitive drum 22 rotates clockwise (direction indicated by α in FIG. 1) when the image forming apparatus 1 operates. The charging roller 23 uniformly charges the surface of the photosensitive drum 22 with a negative charge. The optical scanning device 24 irradiates the surface of the photosensitive drum 22 with a laser beam or LED (Light Emitting Diode) of an image pattern to be output by the image forming apparatus 1, and forms an electrostatic latent image on the surface of the photosensitive drum 22. Form. The developing device 25 attaches toner to the electrostatic latent image and forms a toner image corresponding to the image pattern on the surface of the photosensitive drum 22. The transfer roller 27 transfers the toner image to a recording medium P such as a resinous sheet or paper, and forms an unfixed toner image on the recording medium P. The recording medium P is conveyed to the fixing device 10, and after the unfixed toner image is fixed in the fixing device 10, the recording medium P is discharged to the outside of the image forming apparatus 1. The cleaning device 26 removes residual toner, paper dust, and the like from the surface of the photosensitive drum 22. The recording medium P before being fed is held in the sheet feed tray 4. The recording medium P is transported from the paper feed tray 4 to the downstream side of the transport path R (the image forming mechanism 20 side) by a paper feed mechanism (not shown).

  As shown in FIG. 2, the fixing device 10 includes a heating roller 12 and two pressure rollers 14 and 15 having the same structure. The heating roller 12 has a cylindrical outer peripheral portion 12c and is rotatably supported about an axis perpendicular to the conveyance direction of the recording medium P (direction indicated by β in FIG. 2). During operation of the fixing device 10, the heating roller 12 rotates in the clockwise direction (the direction indicated by A in FIG. 2) about the axis while contacting the recording medium P on the outer peripheral surface thereof. Transport to the downstream side of the transport path R. The heating roller 12 includes a heater 12a, and heats the outer peripheral portion 12c of the heating roller 12 by energizing the heater 12a. A guide member 19 that is curved along the outer peripheral surface of the heating roller 12 is disposed in the vicinity of the outer peripheral surface.

  The pressure rollers 14 and 15 have cylindrical surface elastic body layers 14b and 15b. The pressure rollers 14 and 15 are arranged in parallel to the axis of the heating roller 12 and are arranged at equal intervals in the circumferential direction of the heating roller 12. That is, one pressure roller is located on the opposite side to the other pressure roller across the axis of the heating roller 12, and the axis of the pressure rollers 14 and 15 and the axis of the heating roller 12 are on the same plane. The pressure roller 14 is arranged on the upstream side (image forming mechanism 20 side) in the conveyance path R of the recording medium P from the pressure roller 15.

  The pressure rollers 14 and 15 are respectively pressed against the outer peripheral surface of the heating roller 12, and nip portions that heat and press the recording medium P between the outer peripheral surface of the pressure rollers 14 and 15 and the outer peripheral surface of the heating roller 12. (Press contact part) 14a and 15a are formed. The pressure contact force applied by the pressure rollers 14 and 15 to the heating roller 12 is balanced. That is, the magnitude of each pressure contact force is equal, and the directions are opposite to each other. Therefore, the pressure contact forces of the pressure roller 14 and the pressure roller 15 cancel each other, and the resultant force is zero.

  Note that the pressure rollers 14 and 15 are in pressure contact with a contact area 12 b of the outer peripheral surface of the heating roller 12 that is in contact with the recording medium P. That is, the recording medium P is in contact with the semi-cylindrical outer peripheral surface (contact region 12 b) among the cylindrical outer peripheral surfaces of the heating roller 12 during conveyance in the fixing device 10. The pressure roller 14 is in pressure contact with the most upstream position of the conveyance path R in the contact region 12b, and the pressure roller 15 is in pressure contact with the most downstream position.

  During the operation of the fixing device 10, the pressure rollers 14 and 15 rotate in the direction opposite to the heating roller 12 (directions indicated by B and C in FIG. 2) around the axis while being pressed against the heating roller 12. The recording medium P onto which the unfixed toner image has been transferred has the nip portion 14a and the nip portion from the upstream side (image forming mechanism 20 side) of the conveyance path R by the rotation of the heating roller 12 and the pressure rollers 14 and 15. It is drawn into 15a. The recording medium P is heated and pressurized when passing through the nip portions 14a and 15a, and the unfixed toner image is heated and melted and fixed on the recording medium P.

  According to the fixing device 10 described above, the pressure rollers 14 and 15 are pressed against the heating roller 12 so that the pressing force against the heating roller 12 is balanced. The bending of the heating roller 12 due to is suppressed. Further, since the recording medium P passes through the two nip portions 14a and 15b, the fixability of the toner image is improved.

  The present invention is not limited to the fixing device 10 described above, and various modifications can be made. For example, the fixing device 10 includes more pressure rollers, and the pressure rollers are in pressure contact with the outer peripheral surface of the heat roller 12 so that the pressure contact forces of the pressure rollers with respect to the heat roller 12 are balanced. It may be. For example, the fixing device 10 a shown in FIG. 3 includes three pressure rollers 14, 15, 16, and the pressure contact force of the pressure rollers 14, 15, 16 with respect to the heating roller 12 is equal. The direction of the pressure contact force is in the direction of canceling each other, and these pressure contact forces are balanced.

  That is, in the fixing device 10a, the pressure rollers 14, 15, 16 are arranged in this order at equal intervals in the circumferential direction of the heating roller 12, and the axis of the heating roller 12 and the axis of each of the pressure rollers 14, 15, 16 are The angles formed by the planes including each other are all equal (here, 120 degrees). The pressure contact force of the pressure rollers 14, 15, 16 to the heating roller 12 is directed in a direction perpendicular to the outer peripheral surface of the heating roller 12. Therefore, the pressure contact forces cancel each other, and the resultant force is zero.

  In the fixing device 10 a as well, the pressure rollers 14, 15, and 16 are all in pressure contact with the contact area 12 b on the outer peripheral surface of the heating roller 12 where the recording medium P contacts. The recording medium P passes through the nip portions 14a, 15a, and 16a formed between the outer peripheral surface of the heating roller 12 and the outer peripheral surfaces of the pressure rollers 14, 15, and 16, so that the recording medium P passes through. Compared with the case where there is only one nip portion, the fixability of the toner image is improved.

  In the embodiment described above, the recording medium P is transported downstream of the transport path R so as to be in contact with the outer peripheral surface of the heating roller 12 between the nip portions. For example, the fixing shown in FIG. As in the apparatus 10b, the recording medium P may be separated from the outer peripheral surface of the heating roller 12 between the nip portion 14a and the nip portion 15a. In this case, the area where the recording medium P and the outer peripheral surface of the heating roller 12 are in contact with each other decreases, and the amount of heat transferred from the heating roller 12 to the recording medium P decreases, so that the temperature drop of the heating roller 12 is suppressed.

  Furthermore, in the embodiment described above, the pressure roller is provided so as to be pressed against the contact region 12b on the outer peripheral surface of the heating roller 12 with which the recording medium P is in contact. A roller (pressing roller) that is pressed against a non-contact area where the recording medium P is not in contact with the outer peripheral surface of the heating roller 12 may be provided to suppress the bending of the heating roller 12 due to the pressing. A fixing device 10c shown in FIG. 5 is an example of a fixing device according to this embodiment.

  The fixing device 10 c includes three pressure rollers 14, 15, and 16 that press the recording medium P, and is disposed in parallel to the axis of the heating roller 12. The recording medium P is in contact with the outer peripheral surface of the heating roller 12. A pressing roller 17 is provided in pressure contact with the non-contact area 12d. The pressure rollers 14, 15, 16 and the pressure roller 17 are in pressure contact with the outer peripheral surface of the heating roller 12. The magnitudes of the pressure contact forces are equal, and the directions of the pressure contact forces cancel each other, and the pressure contact forces are balanced.

  That is, the pressure rollers 14, 15, 16 and the pressure roller 17 are arranged in this order at equal intervals in the circumferential direction of the heat roller 12, and the axis of the heat roller 12 and the pressure rollers 14, 15, 16 or the pressure roller 17 are arranged. The angles formed by the planes including the axis of each other are all equal (90 degrees here). The pressing force of each pressure roller and the pressure roller 17 against the heating roller 12 is in a direction perpendicular to the outer peripheral surface of the heating roller 12. Therefore, the pressure contact force of the pressure roller 14 cancels out the pressure contact force of the pressure roller 16 disposed on the opposite side of the pressure roller 14 across the axis of the heat roller 12, and the pressure contact force of the pressure roller 15 is The pressure contact force of the pressing roller 17 disposed on the opposite side of the pressure roller 15 across the axis of the heating roller 12 is offset. In the fixing device 10c, the pressure roller 17 has a surface elastic layer 17b, and the pressure rollers 14, 15, 16 and the pressure roller 17 have the same structure.

  In the embodiment described above, the pressure contact force applied to the heating roller 12 from the pressure rollers 14, 15, 16 or the pressure roller 17 is all equal, but the pressure contact force is not uniform. It may be made to become. In this case, the pressing force can be balanced by changing the pressing direction of the pressure rollers 14, 15, 16 or the pressing roller 17 with respect to the outer peripheral surface of the heating roller 12.

1 is an overall configuration diagram illustrating an outline of an image forming apparatus including a fixing device according to an embodiment of the present invention. 1 is a cross-sectional view of a fixing device according to an embodiment of the present invention. It is sectional drawing of the fixing device which concerns on other embodiment of this invention. It is sectional drawing of the fixing device which concerns on other embodiment of this invention. It is sectional drawing of the fixing device which concerns on other embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Image forming device, 4 Paper feed tray, 10 Fixing device, 12 Heating roller, 14, 15, 16 Pressing roller, 17 Pressing roller, 19 Guide member, 20 Image forming mechanism, 22 Photosensitive drum, 23 Charging roller, 24 Optical scanning device, 25 developing device, 26 cleaning device, 27 transfer roller, P recording medium, R transport path.

Claims (3)

A fixing device for fixing an unfixed toner image transferred to a recording medium to the recording medium,
A heating roller that contacts the outer peripheral surface and heats the recording medium;
At least two pressure rollers in pressure contact with the contact position on the outer peripheral surface of the heating roller with which the recording medium comes in contact;
A pressing roller pressed against a non-contact area of the recording medium on the outer peripheral surface of the heating roller,
The pressing roller and each pressing roller are pressed against the heating roller so that the pressing force applied to the heating roller from the pressing roller and the at least two pressing rollers is balanced,
The recording medium passes through each of the pressure contact portions between the heating roller and the pressure rollers, and the toner image is fixed.
A fixing device. The fixing device according to claim 1 ,
The at least two pressure rollers and the pressure roller are arranged at equal intervals in the circumferential direction of the heating roller.
A fixing device. An image forming apparatus including a fixing device according to claim 1 or 2.

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