JP5422763B2 - Fixing device and image forming apparatus having the same - Google Patents

Description

  The present invention relates to a fixing device that switches the angle of an approach guide in conjunction with a fixing pressure switching operation, and an image forming apparatus including the fixing device.

  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. Transfer the image 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. .

  The fixing device includes a heating member and a pressure member that rotate in contact with each other. By pressing the pressure member against the heating member, a predetermined fixing pressure (nip pressure) is secured between them. I have to.

  For example, when an envelope is passed through such a fixing device, the envelope is manufactured by folding and bonding the paper, and this causes distortion when passing through the fixing nip between the heating member and the pressure member. It is easy to generate my own. For this reason, when passing an envelope, it is common to make the fixing pressure as small as possible, and a fixing device having a fixing pressure switching mechanism that switches the fixing pressure manually or automatically depending on the type of paper. Has been proposed (see, for example, Patent Documents 1 and 2).

JP 2004-279702 A JP-A-6-337612

  Incidentally, an entrance guide for guiding the paper to the fixing nip is provided on the upstream side in the paper conveyance direction of the fixing nip formed by the heating member and the pressure member of the fixing device, but the thickness is relatively thin. When passing plain paper, the angle of the entrance guide is set so that the curvature of the conveyance line at the fixing nip is larger, so that the amount of winding of the plain paper around the heating member equipped with a heat source becomes larger and fixing is performed. It is preferable because the properties are improved.

  However, since the envelope is manufactured by folding and bonding paper as described above, if the angle of the entrance guide is set to a value that provides high fixability when plain paper passes, the fixing nip is The curvature of the envelope that passes through becomes large, and even if the fixing pressure is lowered, the curvature difference between the front side and the back side of the envelope becomes large and wrinkles are likely to occur.

  The present invention has been made in view of the above problems, and the object of the present invention is to change the angle of the entry guide in conjunction with the fixing pressure switching operation without requiring manual operation by the user, thereby wrinkling the envelope. It is an object of the present invention to provide a fixing device capable of stably fixing an image without generating it, and an image forming apparatus including the same.

In order to achieve the above-mentioned object, the invention described in claim 1 includes a heating member and a pressure member that rotate in contact with each other, and a fixing nip formed by the heating member and the pressure member on the upstream side in the paper conveyance direction. A rotatable approach guide provided; a fixing pressure switching mechanism for switching the fixing mode to a high pressure mode with a high fixing pressure or a low pressure mode with a low fixing pressure; and the fixing pressure switching operation by the fixing pressure switching mechanism. In a fixing device having an approach guide switching mechanism for switching the angle of the approach guide,
A pressure lever that pivotally supports the pressure member, and a biasing means that biases the pressure lever in a direction in which the pressure member is pressed against the heating member; Comprising a first cam that is rotated by a motor to switch the pressing force of the pressing member to the heating member by the biasing means;
The entry guide switching mechanism is integrated with the first cam, an urging means for urging the entry guide in one rotation direction, an entry guide switching lever that is slidably held and has one end abutting against the entry guide, and the first cam. And a second cam that contacts the other end of the entry guide switching lever .

When the high pressure mode is selected as the fixing mode, the second cam comes into contact with the entry guide switching lever and slides the entry guide switching lever, thereby setting the angle of the entry guide to the value in the high pressure mode. Set,
When the low pressure mode is selected as the fixing mode, the second cam is separated from the entry guide switching lever, and the entry guide switching lever is slid in the direction opposite to that in the high pressure mode, thereby moving the entry guide. The angle is set to a value in the low pressure mode.

According to a second aspect of the invention, in the invention according to the first aspect, as well as binding the said first cam shaft is rotated the second cam and actuator by said motor, PI in the vicinity of the actuator A sensor is arranged, and the light that travels from the light emitting portion to the light receiving portion of the PI sensor is blocked by the actuator rotated by the motor via the shaft, thereby detecting that the fixing mode is the low pressure mode. Features.

An image forming apparatus according to a third aspect includes the fixing device according to the first or second aspect.
The entry so that the curvature of the conveyance line of the paper passing through is smaller than the curvature in the high pressure mode

  According to the present invention, when the envelope is passed through, the fixing mode is switched to the low pressure mode by the fixing pressure switching mechanism to lower the fixing pressure, and the envelope is passed through the fixing nip by the entry guide switching mechanism. Since the angle of the approach guide is switched so that the curvature of the line is smaller than the curvature in the high pressure mode, the difference in curvature between the front and back sides of the envelope is reduced, and the envelope is wrinkled along with the effect of lowering the fixing pressure. This makes it difficult to stably fix the image on the envelope.

  When passing plain paper with a relatively thin thickness other than the envelope, the fixing mode is switched to the high pressure mode by the fixing pressure switching mechanism, and the fixing pressure is increased. Because the angle of the entrance guide is switched so that the curvature of the conveyance line of plain paper passing through the paper becomes larger than the curvature in the low pressure mode, the amount of winding of plain paper around the heating member increases, and the effect of increasing the fixing pressure In combination with this, the fixability of the image on plain paper is improved.

1 is a cross-sectional view of a color laser printer according to the present invention. FIG. 2 is a cross-sectional view of the fixing device portion of the color laser printer according to the present invention (enlarged detailed view of a portion X in FIG. 1). 1 is a perspective view of a fixing device according to the present invention. FIG. 3 is an exploded perspective view of a fixing device according to the present invention. FIG. 3 is a cross-sectional view illustrating a state in a high pressure mode of the fixing device according to the present invention. FIG. 3 is a cross-sectional view illustrating a state in a low pressure mode of the fixing device according to the present invention. FIG. 6 is an explanatory diagram illustrating a relationship between a change in angle of an approach guide and a change in a sheet conveyance line in 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, and charging rollers 3a, 3b, 3c, and 3d are disposed around the photosensitive drums 2a to 2d. 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d and drum cleaning devices 6a, 6b, 6c, 6d are arranged, respectively.

  Here, the photosensitive drums 2a to 2d are drum-shaped photosensitive members, and are rotationally driven at a predetermined process speed in the direction of the arrow (clockwise) by a motor (not shown). The charging rollers 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 are provided to feed one by one to the transport path L.

  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 transport path L, another transport path L ′ used for forming an image on both sides of the sheet is formed, and a plurality of transport roller pairs 20 are appropriately used in the transport 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 discharge roller pair 23 are provided. A front cover 101 that can be opened and closed is provided on the front surface of the main body 100. When the paper is jammed in the fixing device 22 or the like, the front cover 101 is opened as shown in FIG. Processing such as removal is performed.

  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 photosensitive drums 2a to 2d are driven to rotate at a predetermined process speed in the direction of the arrow (clockwise) in the image forming units 1M, 1C, 1Y, and 1K, and these photosensitive drums 2a. ˜2d are uniformly charged by the charging rollers 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 to complete a series of image forming operations. 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.

  2 is a cross-sectional view of the fixing device portion of the color laser printer (enlarged detailed view of portion X in FIG. 1), FIG. 3 is a perspective view of the fixing device, FIG. 4 is an exploded perspective view of the identification wearing device, and FIG. FIG. 6 is a cross-sectional view showing the state of the identification apparatus in the low-pressure mode, and FIG. 7 is an explanatory view showing the relationship between the change of the angle of the entrance guide and the change of the paper transport line. It is.

  As shown in FIG. 2, the fixing device 22 includes a heating roller 24 that rotates in contact with each other, a pressure roller 25, and a tension roller 26 disposed below the pressure roller 25. The pressure roller 25 and the tension roller 26 are arranged in parallel and rotatable along the direction perpendicular to the plane of FIG. An endless fixing belt 27 is wound between the pressure roller 25 and the tension roller 26. The pressure roller 25 is connected to the heating roller 24 via the fixing belt 27 by a pressure mechanism described later. By applying pressure, a fixing nip N having a predetermined pressure (fixing pressure) is formed between the rollers 24 and 25.

  In addition, two heaters 28 on the upper and lower sides are passed through the hollow heating roller 24 in the direction perpendicular to the paper surface of FIG. 2, and the outer periphery of the heating roller 24 is for detecting the surface temperature of the heating roller 24. Thermistor 29 is provided.

  Further, on the upstream side of the fixing nip N formed by the heating roller 24 and the pressure roller 25 in the sheet conveying direction (lower side in FIG. 2), an entry guide 30 for guiding the sheet to the fixing nip N can be rotated ( The angle can be adjusted).

  Thus, as described above, the sheet on which the full-color toner image is secondarily transferred collectively from the intermediate transfer belt 7 by the secondary transfer roller 10 is conveyed to the fixing device 22, and the fixing device 22 is heated. A full color toner image is fixed by being heated and pressed in the process of being nipped and conveyed in the fixing nip N between the roller 24 and the pressure roller 25. Then, the sheet on which the toner image is fixed is discharged to the discharge tray 21 by the discharge roller pair 23 (see FIG. 1).

  By the way, in the fixing device 22 according to the present embodiment, the fixing mode is automatically switched to the high pressure mode in which the fixing pressure (the pressure applied to the heating roller 24 by the pressure roller 25) is high or the low pressure mode in which the fixing pressure is low. A pressure switching mechanism and an approach guide switching mechanism for switching the angle of the approach guide 30 as shown in FIGS. 5 to 7 in conjunction with the fixing pressure switching operation by the fixing pressure switching mechanism are provided. The configurations of the fixing pressure switching mechanism and the approach guide switching mechanism will be described below with reference to FIGS.

  That is, both ends in the axial direction of the rotary shaft 31 of the pressure roller 25 are swingably supported by a pair of left and right side plates (not shown) via bearings 32 (only one is shown in the figure). An intermediate portion of each of the pair of left and right pressure levers 33 whose one end 33a is rotatably supported by a side plate (not shown) is in contact with the outer periphery. Therefore, if each pressure lever 33 is rotated about one end 33 a to press the bearing 32, the pressure roller 25 is pressed against the heating roller 24 via the fixing belt 27, and between the rollers 24, 25. A fixing nip N having a predetermined pressure is formed.

  The other end of each pressure lever 33 is connected to the upper ends of a pair of left and right pressure plates 34 bent in an L shape by pins 35, and the front cover is located near each pressure plate 34. A pair of left and right open / close levers 37 that rotate about a shaft 36 in conjunction with the open / close operation of 101 (see FIG. 1) are provided on the left and right side plates. The upper end is connected. Here, the pair of left and right rods 38 penetrates the pressure plate 34 and extends downward. A pressure spring 39 as an urging means is interposed between the opening / closing lever 37 and the pressure plate 34 on the outer periphery of each rod 38.

  Further, a shaft 40 is disposed in the vicinity of the tension roller 26 so as to be rotatable along the axial direction of the tension roller 26 and the pressure roller 25, and a pair of left and right cams 41 are provided at both ends of the shaft 40 in the axial direction. It is bound. Each cam 41 is divided into right and left straddling the rod 38. As shown in FIGS. 5 and 6, each cam 41 has a large first cam 41A and a small second cam 41B. It is integrally formed with a phase difference of 90 °.

  Each of the cams 41 is rotated when the fixing mode is switched to the low pressure mode, abuts against the pressure plate 34 as shown in FIG. 6, and pressurizes the pressure plate 34 to pressurize as will be described later. This is for reducing the pressure (fixing pressure) of the pressure roller 25 by the spring 39. As shown in FIG. 3, a gear G1 and a plate-like actuator 42 are bound to one end of the shaft 40. .

  Further, as shown in FIG. 3, a DC motor 43 is vertically arranged on the side where the gear G1 is provided, and the pinion G2 connected to the output shaft of the DC motor 43 is a gear train G. And is connected to the gear G1. Therefore, when the DC motor 43 is driven, the rotation of the output shaft is transmitted to the shaft 40 while being decelerated through the pinion G2, the gear train G, and the gear G1, and the pair of left and right attached to the shaft 40 is connected to the shaft 40. The cam 41 and the actuator 42 are simultaneously rotated.

  Further, in the vicinity of the actuator 42, a PI sensor 44 for optically detecting the position of the cam 41, specifically, the position where the applied pressure of the pressure roller 25 is reduced in the low pressure mode is arranged. .

  Next, the configuration of the approach guide switching mechanism will be described.

  As shown in FIG. 4, rotation shafts 45 extending outward are attached to the lower left and right ends of the entry guide 30, and each rotation shaft 45 is pivotally supported by the left and right side plates. 5 and FIG. 6 by springs 46 (see FIGS. 3 and 4) which are urging means wound around the respective rotating shafts 45 and are supported rotatably on the left and right side plates around the lower end thereof. It is urged clockwise.

  In addition, an approach guide switching lever 47 is slidable in a direction perpendicular to the rotating shaft 45 (the left and right direction in FIGS. 5 and 6) at the left and right ends of the back side of the approach guide 30 (the right side in FIGS. 5 and 6). A hemispherical protrusion 47a is provided on the surface of the entry guide switching lever 47 that faces the entry guide 30, and a rectangular block-like protrusion 47b is provided on the opposite surface. The one guide 47a of the entry guide switching lever 47 is in contact with the entry guide 30 urged clockwise by the spring 46 about the rotation shaft 45 in FIGS. 5 and 6, and the other projection 47b. Is in contact with a second cam 47B formed on the cam 41.

  Thus, the entry guide switching lever 47 and the second cam 41B of the cam 41 that slides the entry guide switching lever 47 constitute an entry guide switching mechanism.

  When plain paper is passed through the fixing device 22 configured as described above, the high pressure mode is selected as the fixing mode and the fixing pressure is set high.

  That is, when the front cover 101 is closed as shown in FIG. 1, as shown in FIG. 5, the opening / closing lever 37 is rotated in the direction of the arrow about the shaft 36 by the opening / closing cover 101 to push down the rod 38 as shown. . Here, when the high pressure mode is selected as the fixing mode, as shown in FIG. 5, the first cam 41A of the cam 41 is separated from the pressure plate 34, and the second cam 41B is moved to the entry guide switching lever. 47, the entry guide switching lever 47 is slid in the direction of the arrow in FIG. 5 (leftward), so that the entry guide 30 that is in contact with the projection 47a of the entry guide switching lever 47 is attached to the spring 46. It rotates in the direction of the arrow in FIG. 5 around the rotation shaft 45 against the force, the angle of the entry guide 30 is adjusted, and its position is switched to the position shown in FIG. 5 (position A shown in FIG. 7). .

  Thus, when the rod 38 is pushed down by the open / close lever 37 as shown in FIG. 5 with the first cam 41A of the cam 41 being separated from the press plate 34 as described above, the open / close lever 37 and the press plate The pressure spring 39 interposed between the pressure springs 34 is pressed and contracted, and the reaction force (spring force) is transmitted to the pressure lever 33 via the pressure plate 34, and the other end 33b of the pressure lever 33 is added. It is pushed down by the reaction force of the pressure spring 39. Therefore, the pressure lever 33 rotates about the one end 33 a in the clockwise direction in FIG. 5 to press the bearing 32, so that the pressure roller 25 rotatably supported by the bearing 32 is interposed via the fixing belt 27. As a result, a fixing nip N having a predetermined pressure is formed between the pressure roller 25 and the heating roller 24, and when the plain paper passes through the fixing nip N, the toner image is heated and heated. It is pressed and fixed on plain paper.

  In the high pressure mode, since the entrance guide 30 is at the position shown in FIG. 5 (position A in FIG. 7) as described above, the transport line for plain paper passing through the fixing nip N is indicated by a in FIG. Thus, the curvature of the transfer line a is larger than the curvature of the transfer line b (described later) in the low pressure mode shown in FIG. For this reason, the amount of winding of the plain paper around the heating roller 24 is increased, and the fixability of the toner image on the plain paper is enhanced in combination with the effect of increasing the fixing pressure in the high pressure mode.

  In this high pressure mode, the actuator 42 stands up, and the light traveling from the light emitting portion to the light receiving portion of the PI sensor 44 is not blocked by the actuator 42. Therefore, the PI sensor 44 has the fixing mode in the high pressure mode. Is detected.

  On the other hand, when the envelope is passed while the front cover 101 is closed and the image forming operation is performed, the fixing mode is switched from the high pressure mode to the low pressure mode by a signal to that effect. Then, the DC motor 43 shown in FIG. 3 is driven, and as described above, the rotation of the DC motor 43 is transmitted to the shaft 40, and the shaft 40 and the pair of left and right cams 41 and the actuator 42 attached thereto are angled. Rotate by 90 °.

  When the cam 41 rotates as described above, the first cam 41A formed integrally with the cam 41 abuts against and presses up the pressure plate 34 as shown in FIG. On the other hand, the pressure lever 33 rotates counterclockwise in FIG. 6 about the one end 33a to reduce the pressing force to the bearing 32. As a result, the pressing force applied to the pressure roller 25 by the pressure lever 33 is weakened, the pressure applied to the pressure roller 25 is reduced, and the fixing pressure is lowered. In this embodiment, the fixing pressure is set to 0 when the fixing mode is switched to the low pressure mode.

  In this low pressure mode, since the fixing cam 41 rotates by an angle of 90 °, the second cam 41B is separated from the protrusion 47b of the entry guide switching lever 47, so that the entry guide switching lever 47 is separated from the entry guide 30. It slides in the direction of the arrow (rightward) in FIG. Then, the entrance guide 30 is rotated about the rotation shaft 45 in the direction of the arrow (clockwise) in FIG. 6 by the slide of the entrance guide switching lever 47, and the angle thereof is switched, and the broken line position shown in FIG. The position is switched from the A position shown in FIG. 7 to the solid line position (B position shown in FIG. 7).

  When the position of the approach guide 30 is switched from the A position shown in FIG. 7 to the B position in the low pressure mode as described above, the envelope conveyance line passing through the fixing nip N becomes as shown in FIG. The curvature of the transfer line b is smaller than the curvature of the transfer line a in the high pressure mode. For this reason, the difference in curvature between the front side and the back side of the envelope is reduced, and as described above, combined with the effect of lowering the fixing pressure in the low pressure mode, the envelope is less likely to wrinkle and the envelope is wrinkled. Therefore, the toner image can be stably fixed.

  When the fixing mode is switched to the low pressure mode and the cam 41 rotates to reduce the pressure (fixing pressure) of the pressure roller 25, the actuator 42 that rotates together with the shaft 40 as shown in FIG. Blocks the light traveling from the light emitting portion to the light receiving portion of the PI sensor 44, so that the PI sensor 44 detects the position of the first cam 41A of the cam 41 so that the user knows that the fixing mode is in the low pressure mode. be able to.

  In the above, the embodiment in which the present invention is applied to the color laser printer and the belt-type fixing device provided in the color laser printer has been described. However, the present invention is applied to a monochrome image forming apparatus and a fixing device provided in the monochrome image forming apparatus. Of course, the present invention can be similarly applied. The fixing device may be a roller type other than the belt type.

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 Charge roller 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 Conveyance roller pair 19 Registration roller pair 20 Conveyance roller pair 21 Paper discharge tray 22 Fixing device 23 Paper discharge roller pair 24 Heating roller (heating member)
25 Pressure roller (Pressure member)
26 Tension roller 27 Fixing belt 28 Heater 29 Thermistor 30 Entrance guide 31 Rotating shaft of pressure lever 32 Bearing 33 Pressure lever 33a, 33b End of pressure lever 34 Pressure plate 35 Pin 36 Opening lever shaft 37 Opening lever 38 Rod 39 Pressure spring 40 Shaft 41 Cam 41A First cam 41B Second cam
42 Actuator 43 DC motor 44 PI sensor 45 Rotating shaft of entry guide 46 Spring (biasing means)
47 Entrance guide switching lever 47a, 47b Projection guide switching lever projection 43 Switch 100 Image forming apparatus main body 101 Front cover A Position of entrance guide in high pressure mode B Position of entrance guide in low pressure mode a Paper transport line in high pressure mode b Paper transport line in low pressure mode G Gear train G1 Gear G2 Pinion N Fixing nip

Claims (3)

A heating member and a pressure member rotating in contact with each other, a rotatable approach guide provided upstream of the fixing nip formed by the heating member and the pressure member in the paper conveyance direction, and fixing the fixing mode A fixing device having a fixing pressure switching mechanism for switching to a high pressure mode with a high pressure or a low pressure mode with a low fixing pressure, and an approach guide switching mechanism for switching the angle of the approach guide in conjunction with a fixing pressure switching operation by the fixing pressure switching mechanism In
A pressure lever that pivotally supports the pressure member, and a biasing means that biases the pressure lever in a direction in which the pressure member is pressed against the heating member; Comprising a first cam that is rotated by a motor to switch the pressing force of the pressing member to the heating member by the biasing means;
The entry guide switching mechanism is integrated with the first cam, an urging means for urging the entry guide in one rotation direction, an entry guide switching lever that is slidably held and has one end abutting against the entry guide, and the first cam. A second cam that is formed in contact with the other end of the entry guide switching lever ,
When the high pressure mode is selected as the fixing mode, the second cam comes into contact with the entry guide switching lever and slides the entry guide switching lever, thereby setting the angle of the entry guide to the value in the high pressure mode. Set,
When the low pressure mode is selected as the fixing mode, the second cam is separated from the entry guide switching lever, and the entry guide switching lever is slid in the direction opposite to that in the high pressure mode, thereby moving the entry guide. A fixing device characterized in that an angle is set to a value in a low pressure mode. Thereby binding the said first cam shaft is rotated the second cam and the actuator by the motor, the PI sensor is disposed in the vicinity of the actuator, toward the light receiving portion from the light emitting portion of the PI sensor 2. The fixing device according to claim 1 , wherein the fixing mode is detected as a low-pressure mode by blocking light from the actuator rotated by the motor through the shaft . An image forming apparatus comprising the fixing device according to claim 1.

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