JP2010271504A - Fixing device and image forming apparatus including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which prevents paper wrinkles by appropriately setting the entering angle of a paper sheet to a fixation nip, according to types of paper sheets. <P>SOLUTION: The fixing device 22 includes: a heat roller (heating member) 25 and a pressure roller (pressure member) 26 which rotate in contact with each other; an entrance guide 31 for guiding the paper sheet to the fixation nip N formed between the heat roller 25 and the pressure roller 26; and a pressurizing force switching mechanism of switching pressurizing force of the pressure roller 26 to the heat roller 25; wherein the angle of the guide surface of the entrance guide 31 is changed linked with the switching operation of the pressurizing force switching mechanism. Specifically, the tilt angle β of the guide surface of the entrance guide 31 when a pressure reduction mode is selected as a fixation mode, is set larger than that when a normal pressure mode is selected. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fixing device capable of switching a pressing force (fixing pressure) of a pressure member to a heating member, and an image forming apparatus including the same.

  In an image forming apparatus such as a copying machine or a printer that forms an image on a sheet by electrophotography, the electrostatic latent image formed on the image carrier is developed by a developing device and visualized as a toner image. The image is transferred onto the paper. The sheet onto which the toner image has been transferred is conveyed to a fixing device, and after the toner image is fixed by heat and pressure by the fixing device, it is discharged out of the apparatus, thereby completing a series of image forming operations. .

  By the way, the fixing device is provided with a heating member and a pressure member that rotate in contact with each other, and a predetermined fixing pressure (nip pressure) is secured between them by pressing the pressure member against the heating member. Like to do.

  When passing an envelope through such a fixing device, the envelope is excessively pressurized with the fixing pressure when passing ordinary plain paper, causing problems such as wrinkles on the envelope that has passed through the fixing nip. To do.

  Therefore, a fixing device that can switch the fixing mode to the normal pressure mode or the pressure reduction mode has been proposed (see, for example, Patent Document 1). In such a fixing device, when an envelope is passed through, a pressure is applied. The fixing pressure is set low by switching to the reduction mode.

  Incidentally, an inlet guide for guiding the paper to the fixing nip is provided upstream of the fixing nip, which is a contact portion between the heating member and the pressure member of the fixing device, in the paper conveyance direction. The inclination angle is fixed at a constant value, and therefore the angle of entry of the sheet into the fixing nip is also constant.

  However, depending on the type of paper, the approach angle to the fixing nip may not be appropriate, and in such a case, the generation of paper wrinkles may be induced.

  In Patent Document 2, the inlet guide is rotatably supported, and the inlet guide is rotated in conjunction with the movement of the core of the pressure roller due to a change in the durability of the pressure roller. There has been proposed a fixing device that adjusts the angle of entry of a sheet guided along the fixing nip.

JP-A-9-034299 JP-A-8-254913

  However, in the fixing device proposed in Patent Document 2, the entry angle of the paper into the fixing nip is adjusted in accordance with a change in the durability of the pressure roller, and the adjustment amount is very small. Therefore, there is a problem that it cannot cope with the type of paper. For example, an envelope is more likely to wrinkle than plain paper, and it is necessary to adjust the angle of entry of both of them into the fixing nip to an appropriate value that does not cause wrinkle. When passing through the envelope, the pressure reduction mode is selected, and the pressing force switching mechanism switches the pressing force of the pressure member to reduce the fixing pressure. May not be enough.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its object is to fix a paper wrinkle that can be prevented by appropriately setting the angle of entry of the paper into the fixing nip according to the type of paper. The present invention provides an apparatus and an image forming apparatus including the apparatus.

  In order to achieve the above object, the invention described in claim 1 includes a heating member and a pressure member rotating in contact with each other, an inlet guide for guiding a sheet to a fixing nip between the heating member and the pressure member, In the fixing device including a pressure switching mechanism that switches the pressure applied to the heating member by the pressure member, the angle of the guide surface of the inlet guide is changed in conjunction with the switching operation of the pressure switching mechanism. Features.

  According to a second aspect of the present invention, in the first aspect of the present invention, the pressurizing lever according to the first aspect of the present invention is configured to rotate the pressurizing force switching mechanism about a fulcrum and rotatably support the pressurizing member, and the pressurizing lever A pressure spring that biases the pressure member toward the heating member, and a pressure that presses the pressure lever in a direction that selectively contacts the anti-fulcrum side end of the pressure lever and pulls the pressure member away from the heating member. The inlet guide is pivotably supported, and a part thereof is engaged with the fulcrum side end of the pressure lever.

  According to a third aspect of the present invention, the sensor according to the second aspect of the present invention is provided with a sensor that detects the operation of the pressing member of the pressure switching mechanism, and the inlet is in a pressure reducing mode in which the pressing member presses the pressure lever. The inclination angle of the guide surface of the guide is set larger than that in the normal pressure mode in which the pressing member is separated from the pressure lever.

  An image forming apparatus according to a fourth aspect includes the fixing device according to any one of the first to third aspects.

  According to the first aspect of the present invention, the angle of the guide surface of the inlet guide is changed in accordance with the switching operation of the pressure switching mechanism, that is, the type of the paper, so that the paper guided along the inlet guide can be changed. The angle of entry into the fixing nip can be set optimally according to the type of the paper, thereby reliably preventing the occurrence of paper wrinkles.

  According to the second aspect of the present invention, when the pressure member is brought into contact / separated with the pressure lever in the pressure switching mechanism according to the type of paper and the pressure of the pressure member is switched, the pressure lever is a fulcrum. However, when the pressure lever is rotated in this way, the inlet guide engaged with the fulcrum side end is rotated and the angle of the guide surface is switched. Accordingly, the entrance angle of the paper guided along the entrance guide to the fixing nip is optimally set according to the type of the paper, and the generation of paper wrinkles is surely prevented.

  According to the third aspect of the invention, the operation of the pressing member of the pressure switching mechanism (the operation of contacting / separating to the pressure lever), that is, whether the pressure reduction mode is selected as the fixing mode or the normal pressure mode Is selected by the sensor. For example, when the pressure reducing mode is selected when passing through an envelope, the normal pressure mode when passing the plain paper through the inclination angle of the guide surface of the inlet guide Since the angle of entry of the paper guided along the entrance guide to the fixing nip is optimally set according to the type of the paper, the generation of paper wrinkles is surely prevented. It is.

  According to the fourth aspect of the present invention, generation of paper wrinkles in the fixing device is prevented regardless of the type of paper, and a high-quality image without image displacement can be stably obtained.

1 is a cross-sectional view of a color laser printer according to the present invention. FIG. 3 is a schematic diagram illustrating a state in a normal pressure mode of the fixing device according to the present invention. FIG. 4 is a schematic diagram illustrating a state in a pressure reduction mode of the fixing device according to the present invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

[Image forming apparatus]
FIG. 1 is a cross-sectional view of a color laser printer as an embodiment of an image forming apparatus according to the present invention. The illustrated color laser printer is a tandem type, and a magenta image forming unit is provided at the center of the main body 100. 1M, a cyan image forming unit 1C, a yellow image forming unit 1Y, and a black image forming unit 1K are arranged in tandem at regular intervals.

  Each of the image forming units 1M, 1C, 1Y, and 1K is provided with photosensitive drums 2a, 2b, 2c, and 2d, which are image carriers, and a charger 3a is disposed around each of the photosensitive drums 2a to 2d. 3b, 3c, 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d and drum cleaning devices 6a, 6b, 6c, 6d, respectively.

  Here, the photosensitive drums 2a to 2d are drum-shaped photosensitive members, and are driven to rotate at a predetermined process speed in a direction indicated by an arrow (clockwise) by a driving motor (not shown). The chargers 3a to 3d uniformly charge the surfaces of the photosensitive drums 2a to 2d to a predetermined potential by a charging bias applied from a charging bias power source (not shown).

  Further, the developing devices 4a to 4d contain magenta (M) toner, cyan (C) toner, yellow (Y) toner, and black (K) toner, respectively, and are formed on the photosensitive drums 2a to 2d. In addition, the toner of each color is attached to each electrostatic latent image to visualize each electrostatic latent image as a toner image of each color.

  The transfer rollers 5a to 5d are arranged so as to be able to contact the photosensitive drums 2a to 2d via the intermediate transfer belt 7 in the respective primary transfer portions. Here, the intermediate transfer belt 7 is stretched between the secondary transfer counter roller 8 and the tension roller 9 and is disposed on the upper surface side of each of the photosensitive drums 2a to 2d. The roller 8 is disposed so as to be in contact with the secondary transfer roller 10 via the intermediate transfer belt 7 in the secondary transfer portion. A belt cleaning device 11 is provided in the vicinity of the tension roller 9.

  Incidentally, toner containers 12a, 12b, 12c, and 12d for supplying toner to the developing devices 4a to 4d are arranged in a line above the image forming units 1M, 1C, 1Y, and 1K in the apparatus main body 100. It is installed.

  In addition, a laser scanner unit (LSU) 13 is disposed below the image forming units 1M, 1C, 1Y, and 1K in the apparatus main body 100, and a paper feed cassette 14 is detachably attached to the bottom of the main body 100 below the image forming units. is set up. A plurality of sheets of paper (not shown) are stacked and accommodated in the paper feed cassette 14, and a pickup roller 15 for picking up paper from the paper feed cassette 14 and a picked up paper are placed near the paper feed cassette 14. A feed roller 16 and a retard roller 17 that are separated and fed one by one to the transport path L are provided.

  Further, the conveyance path L extending in the vertical direction on the side of the apparatus main body 100 includes a conveyance roller pair 18 that conveys the sheet, and the secondary transfer counter roller 8 and the second transfer opposing roller 8 at a predetermined timing after the sheet is temporarily held. A registration roller pair 19 is provided to be supplied to a secondary transfer portion which is a contact portion with the next transfer roller 10. Next to the conveyance path L, another conveyance path L ′ used for forming an image on both sides of the sheet is formed, and a plurality of reversing roller pairs 20 are appropriately used for the conveyance path L ′. Are provided at regular intervals.

  By the way, the conveyance path L arranged in the vertical direction on one side of the apparatus main body 100 extends to the paper discharge tray 21 provided on the upper surface of the apparatus main body 100, and in the middle thereof, the fixing according to the present invention. A device 22 and a pair of paper discharge rollers 23 and 24 are provided.

  Next, an image forming operation by the color laser printer having the above configuration will be described.

  When an image formation start signal is issued, the respective photosensitive drums 2a to 2d are rotationally driven in the image forming units 1M, 1C, 1Y, and 1K in a direction indicated by arrows (clockwise) at a predetermined process speed, and these photosensitive drums 2a. ˜2d are uniformly charged by the chargers 3a to 3d. The laser scanner unit 13 emits a laser beam modulated by a color image signal for each color, irradiates the surface of each photosensitive drum 2a to 2d with the laser beam, and each color is applied to each photosensitive drum 2a to 2d. An electrostatic latent image corresponding to the color image signal is formed.

  First, magenta toner is attached to the electrostatic latent image formed on the photosensitive drum 2a of the magenta image forming unit 1M by the developing device 4a to which a developing bias having the same polarity as the charged polarity of the photosensitive drum 2a is applied. The electrostatic latent image is visualized as a magenta toner image. This magenta toner image is moved in the direction of the arrow in the figure by the action of the transfer roller 5a to which a primary transfer bias having a polarity opposite to that of the toner is applied in the primary transfer portion (transfer nip portion) between the photosensitive drum 2a and the transfer roller 5a. Primary transfer is performed on the intermediate transfer belt 7 that is rotationally driven.

  The intermediate transfer belt 7 on which the magenta toner image has been primarily transferred as described above moves to the next cyan image forming unit 1C. In the cyan image forming unit 1C as well, the cyan toner image formed on the photosensitive drum 2b is transferred to the magenta toner image on the intermediate transfer belt 7 in the primary transfer portion in the same manner as described above.

  Similarly, yellow and black toners respectively formed on the photosensitive drums 2c and 2d of the yellow and black image forming units 1Y and 1K on the magenta and cyan toner images superimposed and transferred on the intermediate transfer belt 7, respectively. The images are sequentially superimposed at each primary transfer portion, and a full-color toner image is formed on the intermediate transfer belt 7. The transfer residual toner which is not transferred onto the intermediate transfer belt 7 and remains on the photosensitive drums 2a to 2d is removed by the drum cleaning devices 6a to 6d, and the photosensitive drums 2a to 2d are prepared for the next image formation. It is done.

  Then, the pickup from the paper feed cassette 14 is performed in accordance with the timing at which the front end of the full color toner image on the intermediate transfer belt 7 reaches the secondary transfer portion (transfer nip portion) between the secondary transfer counter roller 8 and the secondary transfer roller 10. The sheet fed to the conveyance path L by the roller 15, the feed roller 16 and the retard roller 17 is conveyed to the secondary transfer unit by the registration roller pair 19. Then, a full-color toner image is collectively transferred from the intermediate transfer belt 7 to the sheet conveyed to the secondary transfer unit by the secondary transfer roller 10 to which a secondary transfer bias having a polarity opposite to that of the toner is applied. .

  Thus, the sheet on which the full-color toner image has been transferred is conveyed to the fixing device 22, and the sheet on which the full-color toner image has been fixed by being heated and pressurized and thermally fixed on the surface of the sheet. Then, the paper is discharged onto the paper discharge tray 21 by the paper discharge roller pair 23 and 24, and a series of image forming operations is completed. The transfer residual toner that is not transferred onto the sheet and remains on the intermediate transfer belt 7 is removed by the belt cleaning device 11, and the intermediate transfer belt 7 is prepared for the next image formation.

[Fixing device]
Next, details of the fixing device 22 according to the present invention will be described with reference to FIGS.

  FIG. 2 is a schematic diagram showing a state of the fixing device according to the present invention in a normal pressure mode, and FIG. 3 is a schematic diagram showing a state of the identification wearing device in a pressure reduction mode.

  The fixing device 22 includes a heating roller 25 and a pressure roller 26 that rotate in contact with each other. The pressure roller 26 disposed below the heating roller 25 has a shaft 26a disposed substantially horizontally. By receiving a concave bearing portion 27 a formed on the pressure lever 27, the pressure lever 27 is rotatably supported. A fixing nip N is formed at a contact portion between the heating roller 25 and the pressure roller 26.

  Further, a fulcrum P and a pressure spring 28 are provided at substantially equal distances on both sides of a bearing portion 27a which is a support portion of the pressure roller 26 of the pressure lever 27, and the pressure lever 27 is a fulcrum. It is supported so as to be pivotable about P, and is urged in a direction (counterclockwise in FIGS. 2 and 3 centering on the fulcrum P) to be pressed against the heating roller 25 by the pressure spring 28. A V-groove 27b that opens upward is formed at the end of the pressure lever 27 opposite to the fulcrum P with respect to the bearing portion 27a that is the support portion of the pressure roller 26, and this V-groove 27b. A pressing member 29 is arranged above and below the pressing member 29, and in the vicinity of the pressing member 29, the operation of the pressing member 29 (the fixing mode is the normal pressure mode or the pressure reduction mode as will be described later). The sensor 30 which detects ()) is arranged. The tip end (lower end) 29a of the pressing member 29 is formed in a tapered shape in accordance with the shape of the V groove 27a of the pressure lever 27, and the tip 29a is formed in the V groove 27a as shown in FIG. The end of the pressure lever 27 is pushed down by abutting engagement.

  Thus, the pressurizing lever 27, the pressurizing spring 28, and the pressing member 29 described above constitute a pressurizing force switching mechanism.

  On the other hand, on the upstream side (left side in FIGS. 2 and 3) of the sheet in the conveyance direction (right direction in FIGS. 2 and 3), the upstream side (left side in FIGS. 2 and 3) of the fixing nip N that is the contact portion between the heating roller 25 and the heating roller. An inlet guide 31 that guides the toner to the fixing nip N is disposed in a state where its end is pivotally supported by a shaft 32. And in the longitudinal direction intermediate part of the lower surface of this inlet guide 31, the convex part 27c projectedly provided by the edge part (left edge part of FIG.2 and FIG.3) by which the fulcrum P of the pressurization lever 27 was provided is provided. Is engaged.

  In the fixing device 22 configured as described above, the pressure lever 27 is urged upward by the pressure spring 28, whereby the pressure roller 26 supported by the pressure lever 28 is moved to the heating roller 25. When pressed, a fixing nip N having a predetermined pressure (fixing pressure) is formed between the heating roller 25 and the pressure roller 26.

  Thus, the fixing device 22 according to the present embodiment includes a normal pressure mode in which the pressure roller 26 is pressed against the heating roller 25 with a high pressure (fixing pressure) when passing plain paper, and an envelope. The pressure reduction mode can be selected in which the fixing pressure is lowered from the value in the normal pressure mode when the paper is passed, but the selection of the fixing mode is made by contact / separation of the pressing member 29 with the pressure lever 27. The sensor 30 detects the operation (contact / separation) of the pressing member 29, that is, whether the fixing mode is the normal pressure mode or the pressure reduction mode.

Hereinafter, the normal pressure mode and the pressure reduction mode of the fixing device 22 will be described.
(1) Normal pressure mode:
When the normal pressure mode is selected as the fixing mode when passing plain paper, the pressing member 29 is spaced above the pressure lever 27 as shown in FIG. The lever 27 is urged counterclockwise in FIG. 2 about the fulcrum P by the pressure spring 28, and the pressure roller 26 supported by the pressure lever 27 is pressed by the heating roller 25 and both rollers 25, 26 are pressed. A fixing nip N is formed therebetween.

  At this time, the inlet guide 31 that engages with the convex portion 27 c protruding from the end of the pressure lever 27 has an inclination angle of the guide surface set to α shown in FIG. The sheet to be entered enters the fixing nip N at the entrance angle α and receives the fixing of the color toner image. If the entrance angle α of the sheet to the fixing nip N is large and the tip height of the entrance guide 31 is high, there is a possibility of toner fusion to a fixing frame (not shown). α should be set appropriately.

Thus, the plain paper is sandwiched with a predetermined pressure in the fixing nip N between the heating roller 25 and the pressure roller 26 and heated and pressurized, and the color toner image carried thereon is fixed on the plain paper. .
(2) Pressure reduction mode:
When the envelope is passed through, as shown in FIG. 3, the pressing member 29 is lowered, and the leading end 29a abuts and engages with the V-groove 27b formed at the end of the pressure lever 27. One end of the pressure lever 27 is pushed down. Then, the pressure lever 27 rotates in the clockwise direction of FIG. 3 (the direction in which the pressure roller 26 moves away from the heating roller 25) about the fulcrum P against the urging force of the pressure spring 28. The pressure applied to the pressure roller 25 by the pressure roller 26 rotatably supported by the bearing portion 27a of the pressure lever 27 is reduced. In the present embodiment, the pressure lever 27 rotates to such an extent that the urging force applied to the pressure roller 26 by the pressure spring 28 is released, and the pressure force (fixing pressure) of the pressure roller 26 is increased. It is given only by the elastic force of the rubber constituting the pressure roller 26.

  Thus, as described above, when the pressure lever 27 rotates in the clockwise direction in FIG. 3 about the fulcrum P, the inlet guide 31 engaged with the convex portion 27 c of the pressure lever 27 is centered on the shaft 32. Rotating counterclockwise, the inclination angle of the guide surface becomes β shown in the figure, which is set larger than the inclination angle α (see FIG. 2) in the normal pressure mode (β> α), and the inlet guide The tip height of 31 is also set higher than that in the normal pressure mode. Accordingly, the envelope guided by the entrance guide 31 enters the fixing nip N at the approach angle β to receive the fixing of the color toner image, and the approach angle is adjusted to be large in combination with the reduction of the fixing pressure. As a result, the generation of wrinkles on the envelope passing through the fixing nip N is reliably prevented.

  As described above, in the present embodiment, the angle of the guide surface of the inlet guide 31 is changed according to the switching operation of the pressure switching mechanism, that is, the type of paper, so that the guide is guided along the inlet guide 31. The entry angle of the sheet to the fixing nip N can be optimally set in accordance with the type of the sheet, thereby reliably preventing the occurrence of paper wrinkles.

  That is, when the pressing force of the pressure roller 26 is switched by the contact / separation of the pressing member 29 with the pressing lever 27 in the pressing force switching mechanism depending on the type of paper, the pressing lever 27 is centered on the fulcrum P. When the pressure lever 27 rotates in this way, the inlet guide 31 that engages with the convex portion 27c protruding from the end portion on the fulcrum P side rotates about the shaft 32 and rotates. Since the angle of the guide surface is switched, the entry angle of the paper guided along the entrance guide 31 to the fixing nip N is optimally set according to the type of the paper, and the generation of paper wrinkles is surely prevented. .

  Specifically, the operation of the pressing member 29 of the pressing force switching mechanism (operation of contact / separation with the pressure lever 27), that is, the pressure reduction mode is selected as the fixing mode or the normal pressure mode is selected. When the pressure reduction mode is selected when the envelope is passed, for example, when the envelope is passed, the inclination angle β of the guide surface of the inlet guide 31 is set to pass the plain paper as shown in FIG. Since the inclination angle α (see FIG. 2) in the normal pressurizing mode is set to be larger (β> α), the approach angle β is adjusted to be large in combination with the reduction of the fixing pressure. As a result, the generation of wrinkles on the envelope 0 passing through the fixing nip N is reliably prevented.

  Therefore, in the color laser printer shown in FIG. 1 provided with the fixing device 22, the generation of paper wrinkles in the fixing device 22 is prevented regardless of the type of paper, and a high-quality image without image displacement can be stably obtained. .

  In the above embodiment, the embodiment in which the present invention is applied to a fixing device that employs a roller system that uses a heating roller and a pressure roller as a heating member and a pressure member has been described. Of course, the present invention can be similarly applied to a fixing device employing a film system using an endless fixing film as a heating member.

1M Magenta image forming unit 1C Cyan image forming unit 1Y Yellow image forming unit 1K Black image forming unit 2a to 2d Photosensitive drum 3a to 3d Charger 4a to 4d Developing device 5a to 5d Transfer roller 6a to 6d Drum cleaning device 7 Intermediate transfer belt 8 Secondary transfer counter roller 9 Tension roller 10 Secondary transfer roller 11 Belt cleaning device 12a to 12d Toner container 13 Laser scanner unit (LSU)
DESCRIPTION OF SYMBOLS 14 Paper feed cassette 15 Pickup roller 16 Feed roller 17 Retard roller 18 Transport roller pair 19 Registration roller pair 20 Transport roller pair 21 Paper discharge tray 22 Fixing device 23, 24 Paper discharge roller pair 25 Heating roller (heating member)
26 Pressure roller (Pressure member)
27 Pressure Lever 27a Pressure Lever Bearing 27b Pressure Lever Vc 27c Pressure Lever Protrusion 28 Pressure Spring 29 Pressure Member 29a Pressure Member Tip 30 Sensor 31 Entrance Guide 32 Entrance Guide Shaft 100 Image Formation Main body L, L 'Conveyance path N Fixing nip P Support point α Inclination angle of guide surface of inlet guide in normal pressure mode β Inclination angle of guide surface of inlet guide in pressure reduction mode

Claims (4)

A heating member and a pressure member that rotate in contact with each other, an inlet guide that guides a sheet to a fixing nip between the heating member and the pressure member, and a pressure that switches the pressure force of the pressure member to the heating member. In a fixing device equipped with a pressure switching mechanism,
The fixing device, wherein the angle of the guide surface of the inlet guide is changed in conjunction with the switching operation of the pressure switching mechanism.   The pressurizing force switching mechanism is configured to rotate about a fulcrum and support the pressurizing member rotatably, a pressurizing spring that biases the pressurizing lever toward the heating member, and the pressurizing member. A pressure member that selectively contacts the end of the pressure lever on the side opposite to the fulcrum and presses the pressure member in a direction to separate the pressure member from the heating member, and the inlet guide is pivotally supported. The fixing device according to claim 1, wherein a part thereof is engaged with a fulcrum side end of the pressure lever.   A sensor for detecting the operation of the pressing member of the pressurizing force switching mechanism is provided, and in the pressure reducing mode in which the pressing member presses the pressure lever, the inclination angle of the guide surface of the inlet guide is separated from the pressure lever. 3. The fixing device according to claim 2, wherein the fixing device is set to be larger than that in the normal pressure mode.   An image forming apparatus comprising the fixing device according to claim 1.

Images