JP6617580B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus equipped with the fixing device.

  In recent years, market demands for energy saving and high speed have been increasing for image forming apparatuses such as printers, copiers, and facsimiles.

  Among the image forming devices, the fixing device consumes a lot of power and has a lot of room for energy saving.Therefore, various proposals have been made.For example, a thin endless belt in the form of a film with a low heat capacity is used as a metal heat that also serves as a support. There has been known a fixing device that can directly heat without using a conductor and can obtain good fixing performance even when mounted on a high-production image forming apparatus (see, for example, Patent Document 1). In this fixing device, a pressure roller disposed on the outer peripheral side of an endless fixing belt and a nip forming member fixedly disposed inside the fixing belt (in the loop) are brought into pressure contact with each other via the fixing belt, thereby fixing the fixing nip. Is forming.

  On the other hand, recording materials of various sizes are used in the image forming apparatus. In order to handle recording materials of various sizes, the fixing belt, which is a non-sheet-passing part, is used when fixing a small size recording material when the length of the fixing heat source (heater) of the fixing device is adjusted to the maximum size of the recording material. / The temperature of the roller end rises. Since the end is excessively heated during continuous paper feeding, it is necessary to reduce the productivity by, for example, slowing the recording material conveyance speed.

  In order to cope with this problem, inside the fixing belt / roller, for example, a halogen heater having a dense light distribution in the center so as to correspond to an A4 longitudinal paper width (210 mm), and A4 longitudinal paper among A3 longitudinal paper widths. There is known a fixing device including a halogen heater having a dense light distribution near an end portion excluding a portion corresponding to the paper width (that is, excluding a central 210 mm portion of a 297 mm width). In the case of a recording material of a small size, this fixing device performs fixing by turning on only a halogen heater having a dense light distribution in the center, and in the case of a recording material larger than a small size, turning on both halogen heaters. .

  The fixing device using such a plurality of heat sources has the following problems. FIG. 14 is a schematic diagram illustrating a fixing device including two halogen heaters as heat sources. The halogen heater 50 </ b> A is a central heater that heats the longitudinal center portion of the fixing belt 60, and the halogen heater 50 </ b> B is a side heater that heats both longitudinal portions of the fixing belt 60. As shown in FIG. 14, since the two halogen heaters 50 are arranged in parallel, the radiant heat of one halogen heater heats the other halogen heater, and the heating efficiency decreases. In particular, when the endless fixing belt is reduced in size with the downsizing of the fixing device and the distance between the halogen heaters in the cross section of the fixing device is shortened, such a problem is serious. Further, since the two heaters are arranged inside the fixing belt having a reduced diameter so as to be surrounded by the reflecting member disposed on the surface of the support member, the irradiation angle of the heater to the fixing belt is narrowed. In this respect, the heating efficiency is lowered.

  On the other hand, for example, Patent Document 2 discloses a configuration in which a plurality of halogen heaters are disposed on both sides sandwiched by reflectors to prevent thermal interference between the plurality of halogen heaters that are heated to each other.

  On the other hand, there is a market need to create an image on a recording material (so-called nobi paper) wider than the A3 longitudinal paper width (297 mm). However, if the distribution of light distribution of the halogen heater used is matched to the width of the Nobi paper, when the image is formed on a recording material of A3 longitudinal paper or less, the non-paper passing portion at the end of the fixing belt / roller is The temperature rises excessively, so that it is necessary to adjust productivity and the throughput is lowered.

  Therefore, a fixing device is known that heats the fixing belt / roller from the A3 longitudinal paper width (297 mm) to both ends with a resistance heating element disposed in a fixing nip. In this fixing device, concave portions are formed at both ends of a nip forming member that forms a fixing nip, a resistance heating element is disposed there, and the nip forming member and the resistance heating element are substantially at the same height, and heat transfer assistance is provided thereon. The fixing belt is heated through the heat transfer assisting member by bringing the members into contact with each other.

  As a result, when the so-called nobi paper is passed through the fixing device, the halogen heater and the resistance heating element are turned on to maintain a high temperature up to the end of the fixing belt / roller. It can be handled by heating only with a heater. This eliminates the need for productivity adjustment and avoids a decrease in throughput.

  However, in the case of a fixing device that heats the fixing belt / roller from the A3 longitudinal paper width (297 mm) to both ends with a resistance heating element arranged in the fixing nip, the energization to the resistance heating element is controlled, and the resistance heating element In order to maintain the heated fixing belt / roller at a desired temperature, it is necessary to install a temperature detecting member for the fixing belt / roller.

  A contact-type thermistor is known as an inexpensive temperature detection member, but if it is brought into direct contact with the outside of the fixing belt, the fixing belt will be damaged, resulting in uneven gloss and streaky abnormal images. It is not used in the color printer. Also known is a technique in which a contact type thermistor abuts from the inside of the fixing belt. However, in a fixing device having a halogen heater inside the fixing belt, the inside of the fixing belt becomes high temperature. I can't.

  Therefore, an NC sensor or a thermopile is used as a non-contact temperature detecting member. Thereby, gloss unevenness and abnormal images do not occur, but the cost increases.

  The present invention has been made in view of such a current situation, and controls the energization of the resistance heating element using an inexpensive temperature detection member, and does not generate uneven gloss and streak-like abnormal images. An object is to maintain an image quality image.

  In order to solve this problem, a rotatable endless fixing member, a pressure member abutting from the outer peripheral side of the fixing member, an inner side of the fixing member, and the pressure member via the fixing member A nip forming member that forms a fixing nip, a first heat source and a second heat source that have different light distributions in the longitudinal direction and heat the fixing member from the inside, and the first heat source and the second heat source. The first temperature detection member for detecting the temperature of the fixing member heated by the heat, and the heat transfer for moving the heat of the fixing member in the longitudinal direction, sandwiched between the nip forming member and the inner periphery of the fixing member An auxiliary member, a resistance heating element provided at both ends of the nip forming member and heating the fixing member via the heat transfer auxiliary member, and a temperature of the fixing member heated by the resistance heating element are detected. Second temperature And the second temperature detecting member is in contact with the fixing member at the outer side in the longitudinal direction from the maximum image guarantee width, and the first temperature detecting member or the second temperature member is selected depending on the recording material size. A fixing device is proposed in which a temperature detected by a temperature detecting member is selected, and energization to the resistance heating element is controlled based on the selected detected temperature.

  By bringing the second temperature detection member into contact with the fixing member on the outer side in the longitudinal direction from the maximum guaranteed image width, the detection member can be reduced in cost. In addition, by detecting the heat and temperature of the fixing member spread to the outside in the longitudinal direction by the heat transfer auxiliary member by the second temperature detecting member and controlling the temperature of the resistance heating element, within the width of the recording material used by the user The fixing member is not damaged, and a high-quality image free from uneven gloss and streaky abnormal images can be maintained.

1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention. 1 is a schematic cross-sectional configuration diagram illustrating an embodiment of a fixing device. It is a perspective view which shows the basic composition of a nip formation unit. It is a perspective view which shows the structure of a nip formation unit and a halogen heater. It is a schematic diagram which shows arrangement | positioning of a 1st temperature detection member and a 2nd temperature detection member. FIG. 6 is a diagram illustrating a temperature distribution in the longitudinal direction of the fixing belt when the fixing device is warmed up. FIG. 6 is a diagram illustrating a temperature distribution of a fixing belt for each elapsed time from the start of paper feeding. It is a schematic diagram which shows arrangement | positioning of the heat-emitting part of a halogen heater and an edge part heater. It is a schematic diagram which shows the positional relationship of each heat-emitting part of a halogen heater and an edge part heater. It is a graph (1st pattern) which shows the heating output of a 2nd halogen heater. It is a graph which shows the state of each heating output of the halogen heater which has a heat generating part near the center, and the halogen heater which has a heat generating part near the end. It is a graph (2nd pattern) which shows the heating output of a 1st, 2nd halogen heater. It is a graph (3rd pattern) which shows another example of the heating output of a 1st, 2nd halogen heater. It is a schematic diagram which shows the fixing device which concerns on a prior art provided with two halogen heaters as a heat source.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 1 is a color laser printer. In the center of the printer body, four image forming units 4Y, 4C, 4M, and 4K are provided in parallel along the extending direction of the intermediate transfer belt 30. Yes. Each of the image forming units 4Y, 4C, 4M, and 4K contains developers of different colors of yellow (Y), cyan (C), magenta (M), and black (K) corresponding to the color separation components of the color image. Other than that, the configuration is the same.

  Specifically, each of the image forming units 4Y, 4C, 4M, and 4K constituting the image station includes a drum-shaped photoreceptor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoreceptor 5, and A developing device 7 for supplying toner to the surface of the photoreceptor 5 and a cleaning device 8 for cleaning the surface of the photoreceptor 5 are provided. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are assigned color codes, and the other image forming units 4 </ b> Y, 4 </ b> C, and 4 </ b> M The reference numerals are omitted.

  Below the image forming units 4Y, 4C, 4M, and 4K, an exposure device 9 that exposes the surface of the photoreceptor 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.

  A transfer device 3 is disposed above the image forming units 4Y, 4C, 4M, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as a transfer body, four primary transfer rollers 31 as primary transfer means, and a secondary transfer roller 36 as secondary transfer means. Further, the transfer device 3 includes a secondary transfer backup roller 32, a cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35.

  The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, when the secondary transfer backup roller 32 is driven to rotate, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. In addition, each primary transfer roller 31 is connected to a power source of a printer main body, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to each primary transfer roller 31. .

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Similarly to the primary transfer roller 31, the secondary transfer roller 36 is also connected to the power source of the printer main body, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has come to be.

The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30.
A bottle container 2 is provided in the upper part of the printer main body, and four toner bottles 2Y, 2C, 2M, and 2K containing replenishing toner are detachably attached to the bottle container 2. As is well known, a replenishment path is provided between each toner bottle 2Y, 2C, 2M, 2K and each developing device 7, and each development from each toner bottle 2Y, 2C, 2M, 2K is performed via this replenishment path. The toner is supplied to the device 7.

  On the other hand, a lower portion of the printer main body is provided with a paper feed tray 10 that stores paper P as a recording material, a paper feed roller 11 that carries the paper P out of the paper feed tray 10, and the like. Here, in addition to plain paper, the recording material includes thick paper, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, and the like. Further, as is well known, a manual paper feed mechanism may be provided.

  In the printer main body, a transport path R is provided for discharging the paper P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of registration rollers 12 serving as transport means for transporting the paper P to the secondary transfer nip is disposed upstream of the position of the secondary transfer roller 36 in the paper transport direction.

  Further, a fixing device 20 for fixing the unfixed image transferred onto the paper P is disposed downstream of the position of the secondary transfer roller 36 in the paper transport direction. Further, a pair of paper discharge rollers 13 for discharging the paper to the outside of the apparatus is provided downstream of the fixing device 20 in the paper conveyance direction of the conveyance path R. In addition, a paper discharge tray 14 for stocking paper discharged outside the apparatus is provided on the upper surface of the printer main body.

  The basic operation of the printer according to this embodiment is as follows. When the image forming operation is started, the photoconductors 5 in the image forming units 4Y, 4C, 4M, and 4K are rotationally driven clockwise in the drawing, and the surface of each photoconductor 5 is set to a predetermined polarity by the charging device 6. Uniformly charged. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5. At this time, the image information to be exposed on each photoconductor 5 is single-color image information obtained by separating a desired full-color image into color information of yellow, cyan, magenta, and black. In this way, toner is supplied to each electrostatic latent image formed on each photoconductor 5 by each developing device 7, whereby the electrostatic latent image is visualized (visualized) as a toner image. .

  When the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, and the intermediate transfer belt 30 is caused to run in the direction indicated by the arrow in the figure. Then, a constant voltage or a constant current controlled voltage having a polarity opposite to the charging polarity of the toner is applied to each primary transfer roller 31. As a result, a transfer electric field is formed in the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

  Thereafter, when each color toner image on the photoconductor 5 reaches the primary transfer nip as each photoconductor 5 rotates, the toner image on each photoconductor 5 is formed by the transfer electric field formed in the primary transfer nip. The images are sequentially superimposed and transferred onto the intermediate transfer belt 30. Thus, a full color toner image is carried on the surface of the intermediate transfer belt 30. Further, the toner on each photoconductor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Thereafter, the surface of each photoconductor 5 is neutralized, and the surface potential is initialized.

  In the lower part of the image forming apparatus, the paper feed roller 11 starts to rotate, and the paper P is sent out from the paper feed tray 10 to the transport path R. The sheet P sent to the conveyance path R is timed by the registration roller 12 and is sent to the secondary transfer nip between the secondary transfer roller 36 and the secondary transfer backup roller 32. At this time, a transfer voltage having a polarity opposite to the toner charge polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip.

  Thereafter, when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 rotates, the toner image on the intermediate transfer belt 30 is generated by the transfer electric field formed in the nip. Are collectively transferred onto the paper P. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the paper P is removed by the belt cleaning device 35, and the removed toner is conveyed to a waste toner container placed in the printer body. To be recovered.

Thereafter, the paper P is conveyed to the fixing device 20, and the toner image on the paper P is fixed to the paper P by the fixing device 20. Then, the paper P is discharged out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.
The above description is an image forming operation when a full-color image is formed on a sheet. A single color image can be formed using any one of the four image forming units 4Y, 4C, 4M, and 4K. Two or three image forming units can be used to form a two-color or three-color image.

  FIG. 2 is a schematic cross-sectional configuration diagram showing an embodiment of the fixing device 20. The fixing device 20 includes a fixing belt 21 that is a thin, flexible, rotatable endless and cylindrical fixing member, and a pressure roller 22 that is a pressure member that abuts from the outer peripheral side of the fixing belt 21. And have. The fixing belt 21 is heated by the radiant heat of halogen heaters 23A and 23B (hereinafter also referred to as first halogen heater 23A and second halogen heater 23B) as a plurality of fixing heat sources arranged inside (in the loop). The halogen heater represents a radiant heat source as a fixing heat source which is a main heat source.

  Further, a nip forming member 24 that forms a fixing nip N with the pressure roller 22 via the fixing belt 21 and a stay member 25 (support member) that supports the nip forming member 24 are arranged inside the fixing belt 21. Has been. The nip forming member 24 arranged across the width direction of the fixing belt 21 is fixedly supported by the stay member 25, thereby preventing the nip forming member 24 from being bent by the pressure from the pressure roller 22, A uniform nip width is obtained over the axial direction (longitudinal direction) of the pressure roller 22. The nip forming member 24 is a heat-resistant member having high mechanical strength and a heat-resistant temperature of 200 ° C. or more, particularly heat-resistant resins such as polyimide (PI) resin, polyether ether ketone (PEEK) resin, and reinforced them with glass fiber. Is made up of. This prevents deformation of the nip forming member 24 due to heat in the toner fixing temperature range, ensures a stable fixing nip state, and stabilizes the output image quality. Further, the stay member 25 and the halogen heaters 23A and 23B are fixed and held at both ends in the longitudinal direction to a side plate of the fixing device 20 or a separately provided holder. End heaters 26 a and 26 b different from the main heat source (fixing heat source) are integrally attached to both ends in the longitudinal direction of the nip forming member 24, and both ends in the longitudinal direction of the fixing belt 21 are heated. The end heat source is located within the range of the fixing nip N in the circumferential direction of the fixing belt 21. As the end heater, a contact heat transfer type heat source that is a resistance heating element such as a ceramic saver is generally used.

  A heat transfer auxiliary member 27, also referred to as a soaking member, that facilitates heat transfer in the longitudinal direction of the fixing belt, has each surface facing the inner peripheral surface of the fixing belt 21 of each of the nip forming member 24 and the end heater 26. The cover belt is arranged so as to prevent heat from staying in the end region of the fixing belt 21 when passing small-size paper or when the end heater 26 is turned on, and thus positively in the width direction of the fixing belt 21, that is, The heat is transferred in the longitudinal direction of the heat transfer assisting member 27 to eliminate the temperature non-uniformity in the longitudinal direction. Therefore, the heat transfer auxiliary member 27 is formed of a material having high thermal conductivity that enables heat transfer in a short time, such as copper or aluminum. In the depiction in FIG. 2, the surface of the heat transfer assisting member 27 that faces the inner peripheral surface of the fixing belt 21 is a surface that directly contacts the fixing belt 21 and is a nip forming surface that is formed flat. However, it may be a concave shape or other shapes. When the nip forming surface has a concave shape, the discharge direction at the front end of the sheet is closer to the pressure roller, the separation is improved, and jamming is suppressed.

  As is well known, a separation member 41 that separates the paper P from the fixing belt 21 is disposed downstream of the fixing device 20 in the paper conveyance direction. Further, releasable pressure means for pressing the pressure roller 22 to the fixing belt 21 is also provided.

  In order to reduce the heat capacity, the endless fixing belt 21 which is thin and small in diameter like a film is composed of a base material on the inner peripheral side formed of a metal material such as nickel or SUS, or a resin material such as polyimide, and a PFA. It is constituted by a release layer on the outer peripheral side formed of (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) or PTFE (polytetrafluoroethylene). An elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer. When the thickness of the elastic layer is about 100 μm, when the unfixed toner is crushed and fixed, minute irregularities on the belt surface can be absorbed by the elastic deformation of the elastic layer, and uneven gloss can be avoided. From the viewpoint of reducing the heat capacity, the fixing belt 21 is set to a thickness of 1 mm or less and a diameter of 20 to 40 mm as a whole. The thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in a range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is preferably 0.2 mm or less, more preferably 0.16 mm or less, and the diameter is 30 mm. The following is desirable.

  The stay member 25 having a T-shaped cross section has an upright portion 25a that is upright on the side opposite to the fixing nip N side. One of the halogen heaters 23A and 23B has a heat generating portion at a longitudinal center portion corresponding to a small size paper, and the other has a heat generating portion at both longitudinal end portions corresponding to a large size paper. The halogen heaters 23A and 23B are configured to generate heat by being output controlled by a power supply unit provided in the printer body, and the output control is performed by belts such as sensors 46a and 46b provided outside the fixing belt 21. This is performed based on the temperature detection result of the surface. By such heater output control, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature. The heater output control based on the temperature detection result of the belt surface by the sensor will be described later.

  Reflecting members 28A and 28B are disposed between the stay member 25 and the halogen heaters 23A and 23B. Accordingly, the heating efficiency of the halogen heaters 23A and 23B with respect to the fixing belt 21 can be increased, and wasteful energy consumption due to the stay member 25 being heated by the radiant heat from the halogen heaters 23A and 23B can be suppressed. The same effect can be obtained by performing heat insulation or mirror treatment on the surface of the stay member 25 instead of providing the reflecting members 28A and 28B.

  The pressure roller 22 includes a cored bar, an elastic layer made of foamable silicone rubber or fluororubber provided on the surface of the cored bar, and a release layer made of PFA, PTFE, etc. provided on the surface of the elastic layer. It is configured. At a location where the pressure roller 22 is pressed against the fixing belt 21 by a pressing means such as a spring and is pressed against the fixing belt 21, the elastic layer of the pressure roller 22 is crushed to form a fixing nip N having a predetermined width. The The pressure roller 22 is rotationally driven by a driving source such as a motor provided in the printer main body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 through the fixing nip N, and the fixing belt 21 is driven to rotate. The fixing belt 21 is sandwiched and rotated at the fixing nip N, and travels while being guided by side plate flanges disposed at both ends except for the fixing nip N.

  In the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. In that case, a heat source such as a halogen heater may be disposed inside the pressure roller 22. The elastic layer may be solid rubber, but if there is no heat source inside the pressure roller, sponge rubber may be used. Sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away.

  FIG. 3 is a perspective view showing a basic configuration of the nip forming unit. As shown in FIG. 3, the nip forming unit includes a nip forming member 24, a stay member 25, a heat transfer assisting member 27, and end heaters 26a and 26b. In the nip forming unit, the surface of the nip forming member 24 opposite to the fixing nip N side is integrated with the plane of the stay member 25 on the fixing nip N side. At this time, uneven shapes such as bosses and pins may be formed on the respective surfaces, and these may be fitted in a shape-constrained manner. The heat transfer assisting member 27 is fitted and integrated so as to cover the surface of the substantially rectangular parallelepiped nip forming member 24 facing the inner peripheral surface of the fixing belt 21. The heat transfer assisting member 27 and the nip forming member 24 may be integrated with each other by providing a claw or the like, but may be bonded or the like. Concave portions 24a and 24b as stepped portions are formed at both ends in the longitudinal direction of the nip forming member 24, and end heaters 26a and 26b are accommodated and fixed at these portions. The positional relationship between the end heaters 26a and 26b and the halogen heaters 23A and 23B will be described later.

  The surface of the heat transfer assisting member 27 that faces the inner peripheral surface of the fixing belt 21 is configured as a belt sliding contact surface 27a. However, in terms of mechanical strength, the nip forming surface substantially becomes the nip forming surface. This is a surface 24 c facing the pressure roller 22.

  As described above, in the present embodiment, the end heaters 26 a and 26 b are integrally provided on the nip forming member 24 necessary for forming the fixing nip, so that the end heaters 26 a and 26 b are provided on the fixing belt 21. It can be placed inside with space saving.

  In addition, the surface of the end heaters 26a and 26b that faces the inner surface of the fixing belt 21 and the surface of the nip forming member 24 that faces the fixing belt 21 are positioned at the same height (on the same plane). Sufficient pressure is applied through the heat transfer assisting member 27.

  As a result, the fixing belt 21 is in a state of being in intimate contact with the end heaters 26a and 26b, so that stable belt traveling can be performed. Further, the fixing belt 21 and the end heaters 26a and 26b are in contact with each other with a sufficient contact pressure, and good heating is maintained. With these configurations, the reliability of the fixing device 20 is improved.

  Further, the heating portion of the fixing belt 21 by the end heaters 26a and 26b is in the nip region. Therefore, the problem of remelting of unfixed toner (quality degradation) due to heating at a site different from the fixing nip N as in Patent Document 1 does not occur.

  FIG. 4 is a perspective view showing configurations of the nip forming unit and the halogen heater. As shown in FIG. 4, the stay member 25 includes a first member 25 </ b> A and a second member 25 </ b> B having a substantially L-shaped section, and has a substantially T-shaped section. Therefore, the rigidity is high and the nip forming member 24 can be prevented from being bent by the stress from the pressure roller 22. The stay members 25 (the first member 25 </ b> A and the second member 25 </ b> B) extend linearly in the longitudinal direction of the nip forming member 24 and are fixed to the nip forming member 24. Therefore, a good nip forming surface can be maintained over the entire longitudinal direction of the fixing nip N.

  A first halogen heater 23A and a second halogen heater 23B are disposed on both sides of the standing portion 25a in the short direction. That is, the first and second halogen heaters 23A and 23B are shielded from each other by the standing portion 25a. Therefore, unlike the fixing device shown in FIG. 14, since the glass tubes are not heated when the heater is turned on, the heating efficiency is not lowered. Further, since the first and second halogen heaters 23A and 23B are not surrounded by the stay member 25 (the center of each halogen heater 23 is outside the space surrounded by the stay member 25), the irradiation angles α and β (see FIG. 2) becomes obtuse and heating efficiency can be improved.

  The cross-sectional shape of the stay member 25 is not limited to a substantially T shape. The first and second halogen heaters 23A and 23B may be arranged so as to partition each other with the upright portion 25a interposed therebetween, and the first member 25A and the second member 25B extend in a longitudinal direction of the halogen heater. May be. Further, the first member 25A and the second member 25B may be raised in an oblique direction with respect to the nip forming surface of the nip forming member 24.

Next, a temperature control method for the end heater 26 will be described.
In FIG. 2, sensors 46 a and 46 b that are first temperature detection members are arranged to face the halogen heaters 23 </ b> A and 23 </ b> B via the fixing belt 21, and detect the temperature of the fixing belt 21 without contact with the fixing belt 21. . As the non-contact type first temperature detection member, a thermopile with quick response or an NC sensor with low cost is used. The halogen heaters 23A and 23B function as a first heat source and a second heat source for heating the fixing belt 21 from the inside, respectively. The sensors 46a and 46b detect the fixing belt temperature mainly heated by the halogen heaters 23A and 23B. Further, end sensors 36 a and 36 b that are second temperature detecting members are in contact with the lower side of the fixing belt 21. A contact thermistor is used as the second temperature detection member.

FIG. 5 is a schematic diagram showing the arrangement of the first temperature detection member and the second temperature detection member.
As shown in the drawing, the sensor 46a is disposed at the center in the longitudinal direction so as to be located within the light distribution (heat generation region) of the halogen heater 23A. The sensor 46b is arranged on the inner side in the longitudinal direction so as to be located in the light distribution (heat generation region) of the halogen heater 23B. The sensor 46b is located on the outer side in the longitudinal direction from the light distribution of the halogen heater 23A.

  The end sensors 36a and 36b are disposed outside the maximum image guarantee width of the image forming apparatus. For example, when the maximum sheet passing width is A3 Nobi size, it is outside the maximum image guaranteed width for A3 Nobi. This is because if the end sensors 36a and 36b, which are contact thermistors, are brought into contact with the fixing belt 21 within the sheet range, the surface of the fixing belt is damaged, and an abnormal image such as gloss streak or offset occurs in the fixed image. It is. By disposing the end sensors 36a and 36b outside the maximum image guarantee width, the fixing belt is not damaged within the paper width used by the user, and therefore, the fixed image is prevented from being adversely affected. This is the same as the reason why the sensors 46a and 46b are arranged in non-contact with the fixing belt 21. Here, the maximum guaranteed image width is an area in which image quality is guaranteed in the image forming apparatus. For example, when there is a width (image missing width) in which 2 mm on both ends cannot be formed on a sheet having a maximum sheet passing width or image quality cannot be guaranteed (image missing width), the value of the maximum image guaranteed width is the maximum sheet passing width− 4 mm.

FIG. 6 shows a longitudinal temperature distribution of the fixing belt 21 when the fixing device 20 is warmed up. Here, the temperature distribution at the left end in FIG. 5 is shown, and the symmetrical temperature distribution at the right end is omitted.
During warm-up, it is desired to maintain the fixing belt 21 at a uniform temperature in the longitudinal direction within the sheet passing range. However, since the heat is taken away by components (side plates, flanges, etc.) outside the fixing belt 21, the end of the belt The temperature of the part tends to decrease. Therefore, in FIG. 6, the end portion of the fixing belt 21 detected by the end sensor 36a on the outermost side of the A3 Nobi paper width is as equal as possible to the temperature T1 detected by the inner sensor 46b. The energization / heating of the heater 26 is controlled.

  However, in reality, the detection range of the end sensor 36a and the heat generation area of the end heater 26a do not completely coincide with each other in the longitudinal direction, so that there is a difference between the temperature T2 and the temperature Te to be actually maintained. When the end sensor 36a deviates outward in the longitudinal direction from the end heater 26a, the temperature T2 becomes lower than the temperature Te. As shown in FIG. 6, when the end sensor 36a is located outside the heat generating area of the end heater 26a and detects the temperature T2 outside the heat generating area, the difference becomes more remarkable.

  FIG. 6 shows the temperature distribution when the heat transfer assisting member 27 is installed and when it is not installed. In the absence of the heat transfer auxiliary member 27, the heat generated by the end heater 26a is difficult to spread in the longitudinal direction, and the temperature T3 detected by the end sensor 36a is greatly reduced, and is large between the temperature T3 and the temperature Te. There is a difference. In such a situation, even if the temperature T3 slightly changes, the temperature Te changes greatly (that is, the sensitivity of the change in the temperature T3 is poor with respect to the change in the temperature Te), and is based on the temperature detected by the end sensor 36a. The energization control of the end heater 26a becomes difficult.

  However, when the heat transfer assisting member 27 is present, the heat generated by the end heater 26a is sufficiently spread outward in the longitudinal direction, and the difference between the temperature Te and the temperature T2 detected by the end sensor 36a is reduced. Therefore, it is possible to control the temperature Te to the target temperature by performing energization control of the end heater 26a while monitoring the temperature T2 by the end sensor 36a.

  As described above, the difference between T2 and Te is caused by the difference in the position in the longitudinal direction between the end sensor 36a and the end heater 26a. Therefore, the set position of the end sensor 36a is set to the end heater 26a as much as possible. It can also be reduced by approaching the heat generation range. Therefore, in FIG. 5, the end sensors 36a and 36b are disposed outside the maximum image guarantee width in the longitudinal direction and within the maximum sheet passing width.

  Incidentally, since various sizes of paper are passed through the fixing device 20, it is necessary to change the temperature sensor used for temperature control of the end heaters 26a and 26b according to the paper size. That is, the temperature detected by the sensors 46a, 46b or the end sensors 36a, 36b is selected according to the paper size, and the energization to the end heater is controlled based on the selected detected temperature. This will be described below. The sensor selection and the energization to the end heater are controlled by a power supply unit provided in the printer main body.

  When a sheet of A3 size or less that fits in the heat generation area of the halogen heater 23B is passed, the portion of the fixing belt 21 that is mainly heated by the end heater 26 is not deprived of heat by the sheet P. Since the difference between Te and temperature T2 is also small, it is possible to control the energization of the end heaters 26a and 26b based on the detected temperatures of the end sensors 36a and 36b.

  On the other hand, when a sheet larger than the A3 size is passed, the end heaters 26a and 26b have a high energization rate because the sheet P is deprived of heat at the fixing belt 21 where the end heaters 26a and 26b mainly heat. is necessary. However, since the installation positions of the end sensors 36a and 36b are outside the sheet passing range, the fixing belt 21 in this portion is not deprived of heat by the paper P, and the temperature T2 detected by the end sensors 36a and 36b is high. The difference between the temperature Te to be actually maintained and the temperature T2 becomes small. Therefore, based on this temperature T2, the end heaters 26a and 26b require only a low energization rate, and as a result, the end heaters 26a and 26b are controlled at a low energization rate. For this reason, the fixing belt temperature (temperature Te) at the end of the A3 Nobi sheet is lowered, and an abnormal image such as a cold offset occurs.

  In order to prevent the occurrence of such an abnormal image, the end heaters 26a and 26b are energized based on the temperature detected by the sensor 46b that detects the location of the fixing belt 21 that is deprived of heat by the paper P. Control. As a result, the end heaters 26a and 26b generate heat at a high energization rate to compensate for the amount of heat deprived of the paper, and maintain the fixing belt temperature (temperature Te) at the end of the A3 Nobi paper sufficiently high. Can do.

  This is because the heat generation density of the halogen heater 23B and the end heater 26 (wattage when converted per 1 mm in the longitudinal direction) is substantially the same. This is because the temperature Te becomes substantially the same. The heat generation density of the halogen heater 23B and the end heater 26 is substantially the same, so that both heaters reach the desired temperature in the same amount of time during warm-up, thereby reducing wasted power and heating time. It is also for the purpose.

  By the way, when the end heaters 26a and 26b are controlled based on the detection results of the end sensors 36a and 36b when a sheet of A3 size or less is passed, the end sensor It is necessary to change the control target temperatures of 36a and 36b. This will be described below.

FIG. 7 shows the temperature distribution of the fixing belt 21 for each elapsed time from the start of paper feeding. The horizontal axis indicates the length of the fixing belt in the longitudinal direction, and the vertical axis indicates the temperature. In the figure, t1 <t2 <t3. Time t1 indicates the time immediately after the start of paper feeding.
At time t1 immediately after the start of paper passing, heat is taken away by components (side plates, flanges, etc.) outside the fixing belt 21, so that the temperature at the belt end tends to decrease, and a large difference occurs between the temperature Te and the temperature T2. However, the difference becomes smaller at times t2 and t3. This is because the parts outside the fixing belt 21 are also gradually warmed, so that the amount of heat taken away by the parts is reduced. Therefore, the temperature T2 for keeping the temperature Te constant needs to be increased as time passes from the start of paper feeding. Although the temperature T2 to be controlled is low at time t1, the temperature T2 to be controlled is increased every time time t2 and t3. That is, when the energization to the end heater 26a is controlled based on the temperature detected by the end sensor 36a, the target temperature of the detected temperature of the end sensor 36a is increased every time after the start of paper feeding. If the temperature T2 is controlled and fixed at the same temperature immediately after the start of paper feeding, the temperature Te becomes lower with the passage of time (the difference between the temperature Te and the temperature T2 becomes smaller), and an abnormal image such as a cold offset occurs. End up.

Next, the arrangement of heat sources that can be used for recording materials of special sizes such as A3 Novi will be described.
FIG. 8 is a schematic diagram showing the arrangement of the heating portions of the halogen heater and the end heater. As shown in FIG. 8, a first halogen heater 23A having a dense light distribution at the center in the longitudinal direction and a second halogen heater 23B having a dense light distribution at both ends in the longitudinal direction are arranged. Yes. That is, the first halogen heater 23 </ b> A heats the central range of the fixing belt 21, and the second halogen heater 23 </ b> B heats the side range of the fixing belt 21.

  The heat generating portion 40A of the first halogen heater 23A corresponds to a small size recording material such as A4 vertical size, for example, and the heat generating portion 40B of the second halogen heater 23B is A3 vertical size that cannot be covered by the first halogen heater 23A. Covers the side area of the largest standard size recording material that can be used. That is, the heat generating unit 40 including the heat generating units 40A and 40B of both halogen heaters corresponds to the maximum standard size paper width and does not cover the nobi size paper width larger than the maximum standard size.

  On the other hand, the end heaters 26a and 26b have heating portions 42a and 42b that are located at positions corresponding to both ends in the longitudinal direction of the second halogen heater 23B and heat both ends of the nobi size paper width larger than the maximum regular size. Further, part of the heat generating portions 42a and 42b of the end heaters 26a and 26b overlaps the heat generating portion 40B of the halogen heater 23B. As a result, the fixing device 20 can cope with both ends of the nobi size paper width larger than the maximum standard size.

  Here, the amount of heat (heating output) actually output from the halogen heater and the end heater will be described. FIG. 9 is a schematic diagram showing the positional relationship between the heat generating parts of the second halogen heater 23B and the end heater 26b and the heating output of each heater. The upper part of FIG. 9 shows the state of the right end of the heat generating part of the second halogen heater 23B, and the lower part of FIG. 9 shows the state of the left side of the heat generating part of the end heater 26b.

  Generally, in the halogen heater, the heating output is reduced at the longitudinal end portion of the heat generating portion (portion where the filament is spirally wound). This also changes depending on the winding density of the filament, and is more likely to decrease if the winding density is sparse. As shown in the upper part of FIG. 9, the heat generating part 40B of the second halogen heater 23B ranges from a part that outputs a predetermined heating output of 100 (%) to a part where the heat output is reduced and the heating output becomes 50%. It is common to define.

  Further, as shown in the lower part of FIG. 9, the end heater 26 b also has a reduced heating output at the longitudinal end portion of the heat generating portion 42 b (the portion where the heat generating pattern 37 is provided). In other words, 100% of the predetermined heating output is not output at the end, and the heating output is sag.

  For this reason, when a drop in heating output occurs at the ends of the second halogen heater 23B and the end heater 26b, good fixing is performed particularly at the end of a recording material having a larger size than the maximum standard size. There is a risk of not.

  Therefore, in this embodiment, as shown in FIG. 9, the boundary Bh at which the heating output at the heat generating portion 40B of the second halogen heater 23B starts to decrease and the boundary Bc at which the heating output at the heat generating portion 42b of the end heater 26b starts to decrease. To match. In an actual apparatus, the second halogen heater 23B and the end heater 26b are spaced apart from each other in the space, so that the boundaries Bh and Bc coincide with each other in the longitudinal direction when projected. The same applies to the other end heater 26a.

  Thereby, in the area | region where the halogen heater 23B and the both-ends heaters 26a and 26b overlap, the heating output does not decrease and 100% of the predetermined heating output can be maintained. Therefore, it is possible to guarantee good fixing particularly at both ends of a recording material having a nobi size larger than the maximum standard size.

  As described above, in the present embodiment, the boundary Bh of the second halogen heater 23B and the boundary Bc of the end heater 26b are matched. However, as described above, since the nip forming unit has the heat transfer assisting member 27 with good thermal conductivity, it is possible to level out a certain decrease in heating output. Therefore, a predetermined allowable range may be provided in the arrangement of the boundary where the heating output of the both end heaters 26a and 26b starts to decrease.

  Next, how to set the end of the end heater near the center of the heat generating portion (boundary Bc where the heating output starts to decrease) will be described in three patterns using a graph of the heating output. The position where the boundary Bc is set has a predetermined allowable range.

(First pattern)
FIG. 10 is a graph showing the heating output of the second halogen heater. The depiction of the graph shows the output at one end for convenience of explanation. In FIG. 10, the vertical axis represents the output ratio (%) with respect to the predetermined heating output, and the horizontal axis represents the position in the longitudinal direction of the second halogen heater 23B. The graph of the heating output draws a curve having a convex peak in the longitudinal direction.

  In the case of the heating output shown in FIG. 10, the boundary Bc of the end heater 26 (the boundary where the heating output near the center in the longitudinal direction in the heat generating portion 42b starts to decrease) is closer to the end in the longitudinal direction in the second halogen heater. It is set to a range (a range indicated by A in the figure) from a location where the peak heating output is 40% to a location where the peak heating output is located 80% of the peak heating output. If the boundary Bc of the end heater 26 is set in such a range, the heating output at the end portions of the end heater 26 and the second halogen heater 23B can be within an allowable range.

(Second pattern)
FIG. 11 is a graph showing the heating output states of a halogen heater having a heat generating part in the central range and a halogen heater having a heat generating part in the side range. The heating output of the halogen heater having the heat generating portion in the central range corresponding to the first halogen heater 23A is shown by a broken line graph, and the heating output of the halogen heater having the heat generating portion in the side range corresponding to the second halogen heater 23B is shown by the solid line It shows with. A plurality of halogen heaters having different light distributions in the longitudinal direction and thus having different heating output patterns can have different patterns of total heating output.

  FIG. 12 is a graph showing the heating output of the combined state of the first and second halogen heaters. As shown in FIG. 12, in the graph of the heating output, the output ratio rises to 100% in the vicinity of both ends, and is gentle at almost 100% in the central region in the longitudinal direction.

  Here, the range where the heating output is approximately 100% is defined as length (B), and the range where the output ratio is approximately 100% to 40% is defined as length (C). At this time, the boundary Bc of the end heater 26 is arranged in a range from a position where the output ratio is 40% of the heating output to a length D that satisfies (C + B × 1/10) toward the center in the longitudinal direction. . If the boundary Bc of the end heater 26 is arranged in such a range, the heating output at the ends of the end heater 26 and the second halogen heater 23B can be within an allowable range.

(Third pattern)
FIG. 13 is a graph showing another example of the heating output of the first and second halogen heaters. As shown in FIG. 13, the central area of the graph is gentle, but both ends thereof are higher than the central area. When the filament of the heat generating part of the second halogen heater 23B is wound more densely than the filament of the heat generating part of the first halogen heater 23A, such a shape is obtained.

  Here, a range sandwiched between both ends where the heating output is approximately 100% is defined as length (B '), and a range where the output ratio is approximately 100% to 40% is defined as length (C). At this time, the boundary Bc of the end heater 26 is within a range from a position where the output ratio is 40% of the heating output to a length D ′ that satisfies (C + B ′ × 1/10) toward the center in the longitudinal direction. Be placed. If the boundary Bc of the end heater 26 is arranged in such a range, the heating output at the ends of the end heater 26 and the second halogen heater 23B can be within an allowable range.

Next, an advantageous configuration of the fixing device of the present invention will be described.
Since the heat transfer assisting member 27 is in sliding contact with the inner surface of the fixing belt 21, if a metal material such as copper or aluminum is used as it is, the friction coefficient increases. If the friction coefficient is large, the unit torque becomes large, causing problems such as shortening the life of the apparatus.

  Therefore, it is desirable that the belt sliding contact surface 27a (see FIG. 3) facing (contacting) the fixing belt 21 of the heat transfer assisting member 27 is smooth and further subjected to a low friction process. Specifically, the friction between the heat transfer assisting member 27 and the inner surface of the fixing belt 21 is reduced by applying fluorine-based paint or coating such as PFA or PTFE. It is also desirable to apply a lubricant such as fluorine grease or silicone oil between the heat transfer assisting member 27 and the inner surface of the fixing belt 21, and the friction can be further reduced.

  The present invention has been described based on the embodiments. The present invention is not limited to the embodiments, and can be appropriately changed within the scope of the present invention. The image forming apparatus provided with the fixing device of the present invention is not limited to a copying machine or a printer, but may be a facsimile machine or a multifunction machine having a plurality of functions.

20 fixing device 21 fixing belt (fixing member)
22 Pressure roller (Pressure member)
23A Halogen heater (first heat source)
23B Halogen heater (second heat source)
24 Nip forming members 26a, 26b End heater (resistance heating element)
27 Heat transfer auxiliary members 36a, 36b End sensor (second temperature detection member)
46a, 46b Sensor (first temperature detection member)
N fixing nip P paper (recording material)

JP 2010-32631 A JP 2010-78839 A

Claims (6)

A rotatable endless fixing member;
A pressure member abutting from the outer peripheral side of the fixing member;
A nip forming member disposed inside the fixing member and forming a fixing nip with the pressure member via the fixing member;
A first heat source and a second heat source each having a different light distribution in the longitudinal direction and heating the fixing member from the inside;
A first temperature detection member for detecting a temperature of the fixing member heated by the first heat source and the second heat source;
A heat transfer auxiliary member that is sandwiched between the nip forming member and the inner periphery of the fixing member and moves heat of the fixing member in the longitudinal direction;
A resistance heating element that is provided at both ends of the nip forming member and heats the fixing member via the heat transfer auxiliary member;
A second temperature detection member that detects the temperature of the fixing member heated by the resistance heating element,
The second temperature detection member is in contact with the fixing member on the outer side in the longitudinal direction from the maximum guaranteed image width,
A detection temperature at the first temperature detection member or the second temperature detection member is selected according to a recording material size, and energization to the resistance heating element is controlled based on the selected detection temperature. A fixing device characterized.   When the recording material to be passed is less than or equal to a predetermined size, energization to the resistance heating element is controlled based on the temperature detected by the second temperature detection member, and the recording material to be passed is smaller than the predetermined size. 2. The fixing device according to claim 1, wherein energization to the resistance heating element is controlled based on a temperature detected by the first temperature detection member when the temperature is large.   When the energization to the resistance heating element is controlled based on the temperature detected by the second temperature detection member, the target temperature of the detection temperature of the second temperature detection member is increased every time after the start of sheet passing. The fixing device according to claim 1, wherein the fixing device is a fixing device.   The first temperature detection member is in non-contact with the fixing member, and is not in contact with the temperature detection member disposed so as to be positioned within the light distribution of the first heat source, and the fixing member. The fixing device according to claim 1, wherein the fixing device is a temperature detection member disposed so as to be positioned within a light distribution of two heat sources.   5. The fixing device according to claim 1, wherein the second temperature detection member is arranged outside in the longitudinal direction and within the maximum sheet passing width with respect to the maximum image guarantee width. 6. . An image forming apparatus comprising the fixing device according to claim 1.

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