JP2009271324A - Fixing device and image forming apparatus with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device czpable of immediately detecting the overrun of a heat source and securely stopping the supply of electric power to the heat source, thereby avoiding a serious damage. <P>SOLUTION: The fixing device is configured such that a thermocut 26 is disposed outside an endless belt 25 which is not stretched as a heat member, a heater (heat source) 28 is disposed inside the endless belt 25, a toner image held on paper passed through a fixing nip between the endless belt 25 and a pressure roller (pressing member), disposed in contact with the endless belt, is heated by the heater 28 and fixed on paper, and supply of power to the heater 28 is stopped when the thermocut 26 detects overrun of the heater 28. In the fixing device, a bimetal (thermal deforming member) 33 is disposed inside the endless belt 25. If the heater overruns, the bimetal 33 deforms, pushes the endless belt 25 up toward the thermocut 25 such that the endless belt 25 is brought near the thermocut 26. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fixing device that heats a toner image carried on a sheet passing through a fixing nip formed between an endless belt, which is a heating member, and a pressure member abutting on the belt, and fixes the toner image on the sheet by a heat source. The present invention relates to an image forming apparatus provided.

  In an image forming apparatus such as a copying machine or a printer that employs an electrophotographic system, paper is fed to an image forming unit, and a toner image formed on an image carrier in the image forming unit is placed on a recording material such as paper. After the transfer, an image is formed through a process of fixing the toner image onto a recording material by a fixing device. In recent years, however, the image forming device is required to further reduce the warm-up time from the viewpoint of energy saving.

  In order to shorten the warm-up time, it is essential to reduce the heat capacity of the heating means of the fixing device. However, if the heat capacity of the heating means is reduced, the rate of temperature rise will increase, so the power supply to the heater will be cut off only when the heater runs away. It becomes difficult to do.

In order to quickly detect the runaway of the heater, Patent Document 1 proposes a configuration in which a heat concentration member having high thermal conductivity is disposed facing the fixing roller and the heat concentration member is provided with a runaway prevention device. Yes.
JP 200603030917 A

  However, when a heater runs away in a fixing device using an endless belt that is not suspended as a heating member, thermal expansion of the endless belt becomes uneven due to a local temperature difference, and the endless belt is dented. . When a local dent is generated in the endless belt, the endless belt surface and the runaway detection member are separated from each other, thereby causing a problem that the detection of the runaway of the heater is delayed.

  The present invention has been made in view of the above problems, and the object of the present invention is to quickly detect when the heat source is out of control and reliably cut off the power supply to the heat source to avoid serious damage. It is an object of the present invention to provide a fixing device and an image forming apparatus having the same.

  In order to achieve the above object, the invention according to claim 1 is characterized in that a thermo-cut is disposed outside an endless belt that is not suspended as a heating member, and a heat source is disposed inside the endless belt. A toner image carried on a sheet passing through a fixing nip formed between contacting pressure members is heated and fixed on the sheet by the heat source. When the thermocut detects a runaway of the heat source, power supply to the heat source is cut off. In the fixing device configured as described above, a heat deformation member is disposed inside the endless belt, and when the heat source runs away, the heat deformation member is deformed and pushes the endless belt to the thermo-cut side, and the endless belt is thermo-cut. It is characterized by being close.

  The invention according to claim 2 is characterized in that, in the invention according to claim 1, the thermally deformable member is arranged at a position facing the thermo-cut with the endless belt interposed therebetween.

  A third aspect of the invention is characterized in that, in the first aspect of the invention, a plurality of the heat-deformable members are arranged at non-opposing positions of the thermocut across the endless belt.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the thermally deformable member is made of a bimetal.

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

  According to the present invention, even if a partial dent occurs in the endless belt due to a local temperature difference caused by a heat source runaway, the heat-deformable member is deformed and pushes the endless belt to the thermo-cut side. Since it is close to the cut, the thermo-cut can quickly detect the heat source runaway without time delay and can reliably cut off the power supply to the heat source, thereby avoiding serious damage due to the heat source runaway.

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

[Image forming apparatus]
FIG. 1 is a side sectional view of a laser printer as an embodiment of an image forming apparatus according to the present invention.

  In the illustrated laser printer 1, an inclined concave discharge tray 3 is provided at the center of the upper surface of a box-shaped main body (housing) 2. An openable and closable manual feed tray 4 is provided at the upper part of the front surface of the main body 2 (the right side in FIG. 1 is the front). The manual feed tray 4 and a manual feed tray rotatably provided in the main body 2 at the back of the manual feed tray 4 are provided. The paper feed roller 5 constitutes a manual paper feed unit 6.

  Thus, the laser printer 1 transfers the paper P as a recording material along the transport path L provided in the main body 2 to the paper P based on image data transmitted from a terminal (not shown). An image is formed, and the conveyance path L is substantially L-shaped in a side view and extends to the paper discharge tray 3.

  Further, the laser printer 1 includes a cassette paper feeding unit 7 provided at a lower portion of the main body 2, an image forming unit 8 provided at a substantially central portion in the main body 2 above the cassette paper feeding unit 7, and the image forming unit. A fixing device 9 disposed behind the unit 8 and a concave paper discharge unit 10 provided on the upper surface of the main body 2 above the fixing device 9 are provided.

  The cassette paper feeding unit 7 stacks and accommodates a plurality of sheets of paper P in a rectangular box-shaped paper feeding cassette 11 having an open upper surface, and picks a roller 12 that picks up the paper P in the paper feeding cassette 11 one by one. And a feed roller 13 and a retard roller 14 for separating the taken paper P one by one and feeding them to the transport path L. The transport path L has a predetermined length after the fed paper P is temporarily held. A registration roller pair 15 is provided to be supplied to the image forming unit 8 at this timing.

  The image forming unit 8 forms an image on the paper P supplied from the manual paper feeding unit 6 or the cassette paper feeding unit 7, and is an image carrier that is rotatably arranged at a substantially central portion in the main body 2. A photosensitive drum 16 as a body, a charger 17 disposed around the photosensitive drum 16, a developing device 18 as a developing means, a transfer roller 19 as a transfer means, and a cleaning device 20, and a laser scanner unit (above them) LSU) 21, toner hopper 22 and the like.

  The fixing device 9 is for fixing the toner image transferred onto the paper P in the image forming unit 8 to the paper P, and the details of the configuration will be described later.

  The paper discharge unit 10 is for discharging the paper P on which the toner image is fixed in the fixing device 9 to the outside of the main body 2, and a paper discharge roller pair 23 provided at the end of the transport path L; A plurality of vertical rib-shaped conveyance guide ribs 24 for guiding the paper P conveyed on the conveyance path L to the paper discharge roller pair 23 and the paper discharge tray 3 for stacking the paper P discharged to the outside of the main body 2. It has.

  Next, an image forming operation of the laser printer 1 having the above configuration will be described.

  For example, when a print start signal is transmitted to the laser printer 1 from a terminal such as a personal computer (personal computer), the photosensitive drum 16 is moved in the direction indicated by the arrow (clockwise) in FIG. ) And the surface thereof is uniformly charged to a predetermined potential by the charger 17. Then, when laser light based on image data transmitted from the terminal is output from the laser scanner unit 21 and irradiated onto the photosensitive drum 16, an electrostatic latent image is formed on the photosensitive drum 16. Then, the electrostatic latent image formed on the photosensitive drum 16 is developed by the developing device 18 using toner as a developer to be visualized as a toner image.

  By the way, when cassette feeding is performed, the paper P stored in the paper feeding cassette 11 of the cassette paper feeding unit 7 is picked up one by one from the uppermost one by the pick roller 12, and the feed roller 13 and the retard roller 14. Are separated one by one and conveyed to the registration roller pair 15.

  In the registration roller pair 15, the paper P is temporarily in a standby state and then supplied to the image forming unit 8 at a predetermined timing synchronized with the toner image on the photosensitive drum 16.

  In the image forming unit 8, the sheet P supplied to the transfer nip between the photosensitive drum 16 and the transfer roller 19 is conveyed while being pressed against the photosensitive drum 16 by the transfer roller 19, so that the surface (transfer) The toner image on the photosensitive drum 16 is transferred onto the surface. Then, the sheet P on which the toner image is transferred is conveyed to the fixing device 9 where the toner image is fixed by being heated and pressed by the fixing device 9. Incidentally, the toner (transfer residual toner) remaining on the surface of the photosensitive drum 16 after the transfer of the toner image onto the paper P is removed by the cleaning device 20.

  Thus, the sheet P on which the toner image is fixed on the surface by the fixing device 9 is conveyed upward along the conveyance path L and guided along the conveyance guide rib 24 to the sheet discharge roller pair 23, and the sheet discharge roller. The pair 23 is discharged and stacked on the discharge tray 3 at the top of the main body 2 to complete a series of image forming operations.

  When the user manually feeds the paper, the paper P set on the manual tray 4 of the manual paper feeder 6 is supplied to the registration roller pair 15 by the paper feed roller 5, and thereafter the same as described above. An image is formed on the paper P through the process.

[Fixing device]
Next, an embodiment of the fixing device 9 will be described.

<Embodiment 1>
2 is a cross-sectional view of the fixing device according to the first embodiment of the present invention, FIGS. 3A and 3B are partial front sectional views of the identification fixing device, and FIGS. 4A and 4B are non-bimetallic plates. It is a fragmentary perspective view which shows the state of the guide member at the time of operation | movement and an operation | movement.

  As shown in FIG. 2, the fixing device 9 according to the present embodiment includes a thin cylindrical endless belt 25 that is not suspended as a heating member, and a thermocut 26 is disposed outside the endless belt 25. Has been.

  In addition, a plate-like backup member 27 that is long in the longitudinal direction of the endless belt 25 (left and right direction in FIG. 3) is vertically arranged at the inner central portion of the endless belt 25, and on both left and right sides of the backup member 27 The heaters 28 as heat sources are arranged in parallel with each other along the longitudinal direction of the endless belt 25. An arc-curved belt guide 29 is attached to the lower end of the backup member 27 so as to slidably contact the inner peripheral surface of the endless belt 25 and guide the endless belt 25.

  Here, the endless belt 25 is made of a metal layer such as SUS or Ni having a thickness of 30 to 80 μm as a base material, and further comprises a silicone rubber layer having a thickness of 200 to 500 μm and a fluororesin having a thickness of 30 μm. It is configured by forming a release layer. Further, SUS is used as the material of the backup member 27, and a reflection plate or a reflection film such as aluminum is formed on the surface of the backup member 27 so as to reflect the light from the heater 28. Further, a halogen lamp or a carbon lamp is used for the heater 28 as a heat source.

  On the other hand, a pressure roller 30 is rotatably disposed below the endless belt 25. The pressure roller 30 is pressed against the endless belt 25 by being pressed by the belt guide 29 with the endless belt 25 interposed therebetween. A fixing nip is formed therebetween, and is driven to rotate at a predetermined speed in the direction of the arrow (counterclockwise) in FIG. 2 by a driving means (not shown).

  By the way, in the present embodiment, a channel-like shape in which the lower part opens at a position facing the thermocut 26 across the endless belt 25 at the upper end in the longitudinal direction of the backup member 27 arranged inside the endless belt 25. An arcuate guide member 32 attached to the holder 31 is arranged to be movable up and down. That is, as shown in FIG. 4, the holder 31 is fitted into the upper end of the backup member 27 from above, so that the guide member 32 is attached to the upper end of the backup member 27 so as to be vertically movable. A bimetal 33, which is a heat deformation member, is passed through the holder 31, and this bimetal 33 is placed on the upper surface of the backup member 27 and bent so that both ends in the longitudinal direction are obliquely spread upward when not operating. is doing.

  In the fixing device 9 configured as described above, when the pressure roller 30 is rotationally driven in the direction of the arrow in FIG. 2 by the driving means (not shown) as described above, the endless belt 25 in contact with this is shown in FIG. Rotate following the arrow direction (clockwise). The heater 28 generates heat when energized from a power source (not shown), and heats the endless belt 25 from the inside to a predetermined fixing temperature.

  Thus, when the sheet P on which the toner image has been transferred by the image forming process is sandwiched and passed through the fixing nip between the endless belt 25 and the pressure roller 30, the toner image is heated and pressurized. To be fixed on the paper P.

  Here, when the heater 28 is operating normally, the temperature of the endless belt 25 is maintained at a predetermined fixing temperature. Therefore, the bimetal 33 does not operate, and a guide as shown in FIG. The member 32 maintains a non-contact state with respect to the endless belt 25, and a predetermined gap is formed between them. The distance L1 between the thermo-cut 26 and the endless belt 25 is set to a value that can detect this when the heater 28 runs away and the endless belt 25 is abnormally heated.

  However, in the fixing device 9 using the endless belt 25 that is not suspended as a heating member as described above, if the heater 28 runs away, the thermal expansion of the endless belt 25 becomes uneven due to a local temperature difference. As a result, the endless belt 25 is dented. If a local dent is generated in the endless belt 25, the surface of the endless belt 25 and the thermo-cut 26 are separated from each other, so that the detection of the runaway of the heater 28 is delayed.

  However, in this embodiment, when the heater 28 runs away and the endless belt 25 rises in temperature abnormally, the bimetal 33 operates and reverses as shown in FIGS. 3 (b) and 4 (b). Then, the guide member 32 held so as to be movable up and down by the back-up member 27 is moved up via the holder 31 and comes into contact with the endless belt 25, and the endless belt 25 is pushed up to the thermo-cut 26 side to end the endlay belt 25. Is brought close to the thermo-cut 26. For this reason, the distance L2 between the endless belt 25 and the thermo-cut 26 is reduced (L2 <L1), and the thermo-cut 26 detects the runaway of the heater 28 quickly without time delay and reliably cuts off the power supply to the heater 28. Therefore, serious damage due to the runaway of the heater 28 is avoided.

<Embodiment 2>
Next, a fixing device according to Embodiment 2 of the present invention will be described with reference to FIGS. FIGS. 5A and 5B are partial front sectional views showing the normal state and the heater runaway state of the fixing device according to the second embodiment of the present invention. FIG. ), The same elements as those shown in (b) are denoted by the same reference numerals, and description thereof will be omitted below.

  In the present embodiment, the two guide members 32 attached to the common holder 31 are disposed at the non-opposing positions of the thermocut 26 (the positions on both sides of the thermocut 26 in the longitudinal direction) with the endless belt 25 interposed therebetween. 31 is placed on the upper surface of the backup member 27 through the bimetal 33, and the other configuration is the same as that of the first embodiment.

  Thus, also in the present embodiment, when the heater 28 is operating normally, the temperature of the endless belt 25 is maintained at a predetermined fixing temperature, so that the bimetal 33 does not operate, and FIG. As shown to (a), the guide member 32 is maintaining the non-contact state with respect to the endless belt 25, and the predetermined clearance gap is formed between both.

  When the heater 28 runs away and the endless belt 25 is heated abnormally, the bimetal 33 operates and reverses as shown in FIG. Then, the guide member 32 held so as to be movable up and down by the back-up member 27 is moved up via the holder 31 and comes into contact with the endless belt 25, and the endless belt 25 is pushed up to the thermo-cut 26 side to end the endlay belt 25. Therefore, the thermocut 26 quickly detects the runaway of the heater 28 without a time delay and reliably cuts off the power supply to the heater 28, thereby avoiding serious damage due to the runaway of the heater 28.

<Embodiment 3>
Next, a fixing device according to Embodiment 3 of the present invention will be described with reference to FIGS. 6 (a), 6 (b), 7 and 8. FIG.

  FIGS. 6A and 6B are cross-sectional views showing states of the fixing device according to the third embodiment of the present invention when the heater is normal and when the heater runs away, and FIG. 7 is a partial front sectional view of the identification attachment device. 8 is a perspective view showing a bimetal mounting structure. In these drawings, the same elements as those shown in FIGS. 2 to 4 are denoted by the same reference numerals.

  The present embodiment is characterized in that when the heater 28 runs away, the bimetal 33 itself abuts against the endless belt 25 due to thermal deformation of the bimetal 33 and pushes it up to bring the endless belt 25 closer to the thermocut 26. Yes.

  Here, as shown in FIG. 8, the base of the bimetal 33 is attached to the inclined surface of the triangular prism base 34 fixed to the upper portion of the holder 31, and the holder 31 is placed at the upper center in the longitudinal direction of the backup member 27. By fitting, as shown in FIG. 7, the endless belt 25 is disposed at a position facing the thermocut 26.

  Thus, when the heater 28 is operating normally, the temperature of the endless belt 25 is maintained at a predetermined fixing temperature, so that the bimetal 33 does not operate, and the bimetal 33 is shown in FIG. ) And is curved in a bow shape to maintain a non-contact state with respect to the endless belt 25, and a predetermined gap is formed between the two.

  When the heater 28 runs away and the endless belt 25 rises in temperature abnormally, the bimetal 33 is thermally deformed and reverses and curves in the reverse direction as shown in FIG. Then, as shown in FIG. 6B, the bimetal 33 comes into contact with the endless belt 25 and pushes the endless belt 25 toward the thermocut 26 to bring the endlay belt 25 closer to the thermocut 26. 26 detects the runaway of the heater 28 quickly without delay, and reliably cuts off the power supply to the heater 28, thereby avoiding serious damage due to the 28 runaway of the heater.

<Embodiment 4>
Next, a fixing device according to Embodiment 4 of the present invention will be described with reference to FIGS. 9 (a) and 9 (b). 9 (a) and 9 (b) are partial front sectional views showing the normal state and the heater runaway state of the fixing device according to the fourth embodiment of the present invention, which are shown in FIG. The same elements as those described above are denoted by the same reference numerals, and repetitive description thereof will be omitted below.

  The present embodiment is characterized in that the two bimetals 33 are arranged at the non-opposing positions of the thermocut 26 with the endless belt 25 in between (the positions on both sides of the thermocut 26 in the longitudinal direction). It is the same as that of Form 3.

  Thus, also in the present embodiment, when the heater 28 is operating normally, the temperature of the endless belt 25 is maintained at a predetermined fixing temperature, so the bimetal 33 does not operate, and FIG. As shown to (a), the bimetal 33 is maintaining the non-contact state with respect to the endless belt 25, and the predetermined clearance gap is formed between both.

  When the heater 28 runs away and the endless belt 25 is heated abnormally, the bimetal 33 is thermally deformed and reverses and bends in the opposite direction as shown in FIG. 9B, so that the endless belt 25 is pushed up by the bimetal. And is brought close to the thermo cut 26. For this reason, the thermo-cut 26 detects the runaway of the heater 28 quickly without delay, and reliably cuts off the power supply to the heater 28, thereby avoiding serious damage due to the runaway of the heater 28.

  In this embodiment, the embodiment in which the present invention is applied to a laser printer and a fixing device provided in the laser printer has been described. However, the present invention is not limited to a printer, a copying machine, a facsimile, or a complex machine thereof. Of course, the present invention can be similarly applied to any image forming apparatus and a fixing device provided in the image forming apparatus.

  In the above embodiment, bimetal is used as the heat deformable member, but other shape memory alloys or the like may be used.

1 is a side sectional view of an image forming apparatus (laser printer) according to the present invention. 1 is a cross-sectional view of a fixing device according to Embodiment 1 of the present invention. (A), (b) is the fragmentary front sectional view of the fixing device which concerns on Embodiment 1 of this invention. (A), (b) is a partial perspective view which shows the state of the guide member at the time of bimetal non-operation and operation | movement. (A), (b) is the fragmentary front sectional view which shows the state at the time of the heater normal time and heater runaway of the fixing device which concerns on Embodiment 2 of this invention. (A), (b) is a cross-sectional view which shows the state at the time of the normal heater of a fixing device according to Embodiment 3 of this invention, and a heater runaway. FIG. 6 is a partial front sectional view of a fixing device according to a third embodiment of the present invention. It is a perspective view which shows the attachment structure of a bimetal. (A), (b) is the fragmentary front sectional view which shows the state at the time of the heater normal time of the fixing device which concerns on Embodiment 4 of this invention, and a heater runaway.

Explanation of symbols

1 Laser printer (image forming device)
DESCRIPTION OF SYMBOLS 2 Printer main body 3 Paper discharge tray 4 Manual feed tray 5 Paper feed roller 6 Manual paper feed part 7 Cassette paper feed part 8 Image forming part 9 Fixing device 10 Paper discharge part 11 Paper feed cassette 12 Pick roller 13 Feed roller 14 Retard roller 15 Resist Roller pair 16 Photosensitive drum (image carrier)
17 Charging Device 18 Developing Device 19 Transfer Roller 20 Cleaning Device 21 Laser Scanner Unit (LSU)
22 toner hopper 23 discharge roller pair 24 conveyance guide rib 25 endless belt (heating member)
26 Thermo-cut 27 Backup member 28 Heater (heat source)
29 Belt guide 30 Pressure roller (Pressure member)
31 Holder 32 Guide member 33 Bimetal (thermal deformation member)
34 Base L Conveyance path L1, L2 Distance between thermo-cut and endless belt P Paper

Claims (5)

A sheet that passes through a fixing nip formed between an endless belt and a pressure member that abuts the endless belt, with a thermo-cut disposed outside the endless belt that is not suspended as a heating member, and a heat source disposed inside the endless belt In the fixing device configured to heat the toner image carried by the heat source and fix the toner image on the paper, and to cut off the power supply to the heat source when the thermocut detects the runaway of the heat source,
A heat deformation member is arranged inside the endless belt, and when the heat source goes out of control, the heat deformation member is deformed and pushes the endless belt to the thermo-cut side so that the endless belt approaches the thermo-cut. Fixing device to do.   The fixing device according to claim 1, wherein the thermally deformable member is disposed at a position facing the thermo-cut with the endless belt interposed therebetween.   The fixing device according to claim 1, wherein a plurality of the heat-deformable members are arranged at positions where the thermo-cut is not opposed to the endless belt.   The fixing device according to claim 1, wherein the heat-deformable member is made of a bimetal.   An image forming apparatus comprising the fixing device according to claim 1.

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