JP4684804B2 - Image heating device - Google Patents

Description

  The present invention provides an endless belt stretched over a plurality of members, electromagnetic induction heating means arranged to face the outer surface of the belt and generating heat from the belt, and a nip portion formed in pressure contact with the belt. And an image heating apparatus that sandwiches and conveys and heats a recording material carrying an image at the nip portion.

  2. Description of the Related Art Conventionally, in an image forming apparatus employing an electrophotographic method, various types of fixing devices have been proposed as a fixing device that heats and fixes an unfixed toner image.

  For example, Patent Document 1 discloses a fixing device using an induction-heated fixing belt as one of such fixing devices. This fixing device has a configuration in which a fixing belt is supported by two rollers, and an induction heating coil is disposed outside the fixing belt. The purpose is to shorten the warm-up time.

  In the fixing device disclosed in Patent Document 2, an induction heating coil, which is an induction heating source, is arranged to face the fixing belt via a recording material passage. The object is to increase the heating time of the recording material.

  Further, in the fixing device disclosed in Patent Document 3, an induction heating coil is disposed outside the fixing belt, and the fixing belt and the heat generating roller are heated simultaneously. The purpose is to shorten the warm-up time while making the temperature distribution of the belt uniform.

Patent Document 4 discloses a mechanism for releasing the tension of the fixing belt in a fixing device using the fixing belt.
Japanese Patent Laid-Open No. 1-144084 JP-A-10-74004 Japanese Patent Laid-Open No. 2003-215556 JP 2003-43848 A

  According to the above-described prior art, a method of directly heating a fixing belt having a low heat capacity by electromagnetic induction heating is effective for shortening the warm-up time. At that time, by disposing the electromagnetic induction coil so as to face the outer surface of the fixing belt, it is possible to prevent the coil temperature from becoming high. Heating the fixing belt with the electromagnetic induction heating means arranged on the outer side in this way is an effective configuration for shortening the warm-up time and preventing the coil from being heated.

  However, according to the above-described prior art, there are the following problems.

  That is, at least a metal layer is required for the fixing belt in order to generate heat using the electromagnetic induction heating. In full color image formation, at least an elastic layer is required for the fixing belt in order to obtain high image quality. Without the elastic layer, the fixing belt becomes high in hardness, and the fixing is not performed following the shape of the toner, resulting in fixing unevenness, and the dot shape becomes large because the toner is crushed more than necessary. It may cause image degradation.

  If a fixing belt having such an elastic layer is stretched between a plurality of members for a long time, a problem arises in that a compression set is generated in the elastic layer of the fixing belt and a history of stretching remains. As a result, uneven rotation occurs in the fixing belt, and uneven fixing occurs in accordance with the rotation of the fixing belt.

  In order to prevent this compression set, Patent Document 4 discloses that the tension of the fixing belt is released during non-image formation.

  However, a fixing belt that generates heat by electromagnetic induction as described in Patent Documents 1 to 3 has at least a metal layer. Therefore, when the tension is released, the shape of the fixing belt changes to a cylindrical shape. Here, if the electromagnetic induction heating means is disposed in close proximity to the outer surface of the fixing belt, there arises a new problem that the fixing belt and the electromagnetic induction heating means come into contact with each other. The surface layer of the fixing belt is made of an elastic material such as silicone rubber or a resin such as PFA. When this surface comes into contact with the coil of the electromagnetic induction heating means, the surface of the fixing belt is scratched, resulting in an image defect. It becomes.

  Therefore, the present invention provides an electromagnetic induction heating type fixing device that can perform high-speed fixing, has a short warm-up time, can prevent the induction heating coil from rising in temperature, and further prevents deformation of the fixing belt and scratches on the surface. Is to provide.

In order to achieve the above object, a typical configuration of an image heating apparatus according to the present invention includes an endless belt having a metal layer, a plurality of stretching members that stretch the belt, and an outer surface of the belt. An electromagnetic induction heating means that generates magnetic flux for generating heat from the belt, a pressure means that presses against the belt to form a nip portion, and a release means that releases the tension of the belt. in the image heating apparatus for heating a recording material bearing an image by the nip nipped and conveyed, with the release of the tension of the belt, a moving means for moving the front Symbol electromagnetic induction heating means or the tension member, and having a abutment means abutting on the non-paper passing area of the belt in order to prevent the said belt during release of tension and the electromagnetic induction heating means is in contact

  According to the above-described fixing device configuration according to the present invention, it is possible to shorten the warm-up time and to prevent deformation and scratches of the fixing belt.

(1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration model diagram of an example of an image forming apparatus. This image forming apparatus is a tandem type full-color printer using an electrophotographic process.

  Y, M, C, and B are first to fourth color toner image forming stations arranged in order from right to left on the drawing. Each station has an electrophotographic process mechanism having a rotating drum type electrophotographic photosensitive member 51 as an image carrier, a charging device 52, an exposure device 53 such as a laser scanner or an LED array, a developing device 54, a cleaning device 55, and the like. It is. The photoreceptor 51 is driven to rotate at a predetermined peripheral speed in the clockwise direction of the arrow.

  Station Y forms a yellow component toner image of a full-color image on the surface of photoconductor 51. Station M similarly forms a magenta component toner image on the surface of photoconductor 51. Station C also forms a cyan component toner image on the surface of photoconductor 51. Then, station B forms a black toner image on the surface of photoconductor 51. Since the electrophotographic image forming principle and process in each station are known, the description thereof will be omitted.

  A transfer belt 56 is suspended around a plurality of support rollers 57, and is arranged under the stations Y, M, C, and B so as to extend over all stations. The transfer belt 56 is rotationally driven in a counterclockwise direction indicated by an arrow at a peripheral speed corresponding to the peripheral speed of the photoconductor 51.

  Reference numeral 58 denotes a transfer roller, and at each station Y, M, C, and B, a transfer nip portion is formed by press-contacting the lower surface of the photoreceptor 51 with the transfer belt 56 interposed therebetween.

  Reference numeral 59 denotes a recording material feeding path. A sheet-like recording material (transfer material, paper) P separated and fed from a sheet feeding mechanism (not shown) is fed to the first station Y side of the transfer belt 56. Feed to the end. The transfer belt 56 electrostatically attracts and holds the fed recording material P, or grips it with a chuck, and sequentially conveys it to the transfer nip portion of each station Y, M, C, and B. As a result, the yellow toner image, the magenta toner image, the cyan toner image, and the black toner image are sequentially superimposed and transferred in the aligned state on the surface of the same recording material P, and an unfixed full-color toner image is synthesized and formed. .

  The recording material P that has been transported and passed through the transfer nip portion of the fourth station B is separated from the transfer belt 56, introduced into the fixing device F, subjected to heat fixing processing of the unfixed toner image, and discharged and transported.

(2) Fixing device F
FIG. 2 is an enlarged cross-sectional side view of a main part of the fixing device F and a block diagram of a control system. The fixing device F is an electromagnetic induction heating type / belt heating type fixing device (IH fixing device). In the following description, the longitudinal direction of the fixing device or a member constituting the fixing device is a direction parallel to the direction orthogonal to the recording material conveyance direction in the recording material conveyance path surface. The width or the width direction (short direction) is a dimension in the recording material conveyance direction or a direction parallel to the recording material conveyance direction. The upstream side and the downstream side are the upstream side and the downstream side in the recording material conveyance direction.

  Reference numeral 1 denotes a fixing belt unit as fixing means, and 2 denotes a pressure belt unit as pressing means. A fixing nip portion N is formed between the fixing unit 1 and the pressing unit 2 by arranging the pressing unit 2 and the pressing unit 2 in pressure contact with each other. Reference numeral 3 denotes an induction heating coil unit (induction heating source of the fixing belt) as electromagnetic induction heating means (hereinafter referred to as heating means), which is disposed on the upper side of the fixing means 1.

[Fixing means 1]
In the fixing unit 1, reference numerals 4 and 5 denote a tension roller and a fixing roller arranged in parallel on the upstream side and the downstream side. Reference numeral 6 denotes an endless, flexible fixing belt that is stretched between the two rollers 4 and 5.

  The tension roller 4 is a hollow iron roller. The fixing roller 5 is an elastic roller in which a silicon rubber layer is provided on an iron alloy core. The cored bar has a tapered shape in which the diameter of the longitudinal center is larger than the diameter of both ends. The reason why the mandrel is tapered is to make the width of the pressure contact portion with the pressure roller 10 uniform in the longitudinal direction even when the fixing roller 5 is bent when the pressure is applied by the pressure roller 10 described later. .

  FIG. 3 is a cross-sectional model view showing the layer structure of the fixing belt 6. Reference numeral 6a denotes a metal layer (hereinafter referred to as a base layer) made of a magnetic metal material as an electromagnetic induction heat generating layer. In this embodiment, an endless belt-like nickel layer having a thickness of 50 μm manufactured by an electroforming method is used as the base layer 6a. An elastic layer 6b is provided on the outer surface (outer peripheral surface) of the base layer 6a. In this embodiment, the elastic layer 6b is a heat-resistant silicone rubber layer, and the thickness can be selected in the range of 100 to 1000 μm. In consideration of obtaining a fixed image suitable for fixing a color image by reducing the heat capacity of the fixing belt 6 to shorten the warm-up time, in this embodiment, the elastic layer 6b has a thickness of 300 μm. . The silicone rubber of the elastic layer 6b has a hardness of 20 degrees according to JIS-A, and the thermal conductivity λ2 is 0.4 W / mK. Further, a fluororesin layer (for example, PFA or PTFE) is provided on the outer periphery of the elastic layer 6b with a thickness of 30 μm as the surface release layer 6c. In order to improve the slidability on the inner surface of the base layer 6a, a resin material such as polyimide may be coated. In this embodiment, a polyimide layer 6d is provided on the inner surface of the base layer 6a. When the inner member (inclusion) such as a fixing roller or a tension roller that contacts the inner surface of the fixing belt 6 is conductive, the inner surface of the fixing belt 6 is electrically insulated in order to effectively induce an induced current through the base layer 6a of the fixing belt 6. It is desirable to have a layer. As a magnetic metal material constituting the electromagnetic induction heat generating layer of the fixing belt 6, iron alloy, copper, silver or the like can be appropriately selected in addition to nickel. Moreover, the structure of laminating | stacking these metal layers on a resin base layer may be sufficient. The thickness of the base layer 6a or the metal layer may be adjusted according to the frequency of the high-frequency current passed through the induction heating coil, which will be described later, and the permeability / conductivity of the base layer 6a or the metal layer, and is set between about 5 and 200 μm. To do.

  A tension roller shift unit 8 serves as a tension application / release unit for the fixing belt 6. Although the specific configuration of the shift means 8 is omitted in the drawing, for example, the rotation of a cam connected to a motor or solenoid causes the tension roller 4 to move away from the fixing roller 5 for fixing. The shift is shifted between a first position where the belt 6 is tensioned and a second position where the belt 6 is moved closer to the fixing roller 5 to release the tension of the fixing belt 6. In this embodiment, when the tension roller 4 is shifted to the first position, the fixing belt 6 is in a state where a tension of about 100 N is applied. The shift means 8 is controlled by a control circuit unit 100 as control means.

  M1 is a fixing roller driving means (motor). When the fixing belt 6 is tensioned by the tension roller 4, the fixing roller 5 is driven to rotate clockwise by the driving unit M <b> 1, so that the silicone rubber surface of the fixing roller 5 and the inner surface polyimide layer of the fixing belt 6 are rotated. It is rotationally driven in the same direction as the rotation of the fixing roller 5 by friction with 6d.

[Pressure means 2]
In the pressurizing means 2, 9 and 10 are a tension roller and a pressure roller arranged in parallel on the upstream side and the downstream side. Reference numeral 11 denotes an endless and flexible pressure belt that is stretched between the two rollers 9 and 10.

  The tension roller 9 is a hollow iron roller. The pressure roller 10 is a solid roller made of an iron alloy, and has a tapered shape in which the diameter of the central portion in the longitudinal direction is larger than the diameter of both end portions. The taper shape is used for the same reason as the fixing roller 5 in order to make the width of the pressure contact portion with the fixing roller 5 uniform in the longitudinal direction even when the pressure roller 10 is bent when pressed. The pressure roller 10 is harder than the fixing roller 5 and greatly deforms the fixing belt 6 at a pressure contact portion between the fixing roller 5 via the fixing belt 6 and the pressure roller 10 via the pressure belt 11. This is because the recording material on which the toner image is formed can be easily peeled off from the fixing belt 6.

  FIG. 4 is a cross-sectional model diagram showing the layer structure of the pressure belt 11. The pressure belt 11 has a base layer 11a made of a polyimide resin having a thickness of 50 μm. The reason why the polyimide resin is used for the base layer 11a is that there is no need to use a metal base layer because the pressure belt 11 is not heated by induction heating. However, a metal base layer may be used as in the fixing belt 6. A heat resistant silicone rubber layer is provided as an elastic layer 11b on the outer periphery of the base layer 11a. The thickness of the elastic layer 11b can be selected in the range of 100 to 1000 μm, and in this embodiment, the thickness is 300 μm. The silicone rubber used for the elastic layer 11b has a hardness of JIS-A 20 degrees, and the thermal conductivity λ3 is 0.1 W / mK. Further, on the outer periphery of the elastic layer 11b, a fluororesin layer (for example, PFA or PTFE) is provided as a surface release layer 11c with a thickness of 30 μm. A heat insulating layer may or may not be provided on the inner surface of the base layer 10a.

  A tension roller shift unit 13 serves as a tension application / release unit for the pressure belt 11. Although the specific configuration of the shift unit 13 is not shown in the drawing, as in the shift unit 8 in the fixing unit 1, for example, the tension roller 9 is controlled by controlling the rotation of a cam connected to a motor or a solenoid. Is moved in a direction away from the pressure roller 10 to apply tension to the pressure belt 11, and moved in a direction closer to the pressure roller 10 to release tension of the pressure belt 11. And shifts in a switching manner. This shift means 13 is also controlled by the control circuit unit 100.

  M2 is a pressure roller driving means (motor). The pressure belt 11 is rotated at a predetermined speed by the pressure roller 10 being rotated counterclockwise by the driving means M2 in a state where the tension roller 9 is applied with tension.

  Reference numeral 102 denotes a shift means as a pressure contact / separation means of the pressure means 2 with respect to the fixing means 1. Although the specific configuration of the shift unit 102 is not shown in the drawing, for example, when the cam connected to the motor or the solenoid is controlled to rotate, the pressurizing unit 2 is pushed up with respect to the fixing unit 1 and pressed. A shift is made in a switching manner between the first position brought into contact and the second position (retracted position) pulled down from the fixing means 1 and spaced apart by a predetermined distance. This shift means 102 is also controlled by the control circuit unit 100.

  In this embodiment, when the pressure unit 2 is shifted to the first position, the pressure roller 10 is pressurized toward the fixing roller 5 at 284 N (30 kgf). Further, the tension roller 9 is pressurized toward the tension roller 4 by 147N (15 kgf). Further, a pressure member 7 disposed between the tension roller 4 and the fixing roller 5 on the fixing unit 1 side, and a pressure member 12 disposed between the tension roller 9 and the pressure roller 10 on the pressure unit 2 side. Is pressed between the fixing belt 6 and the pressure belt 11. As a result, the fixing belt 6 and the pressure belt 11 come into contact with each other between the tension rollers 4 and 11 and between the fixing roller 5 and the pressure roller 10 to form a fixing nip portion N. The fixing belt 6 and the pressure belt 11 are pressurized at the fixing nip portion N by the pressure members 7 and 12, respectively, and apply nip heat and pressure to the recording material.

  The pressure members 7 and 12 are made of an elastic material such as silicone rubber, or a resin such as PPS, and the surface that comes into contact with the fixing belt 6 or the pressure belt 11 is coated with a glass fiber cloth with a fluororesin, Friction resistance is reduced by using a polyimide sheet or the like devised to reduce the contact area by providing unevenness, and slipping of the fixing belt 6 or the pressure belt 11 is prevented.

[Heating means 3]
The heating means 3 is an induction heating source for the fixing belt 6, and is arranged close to the outer surface of the fixing belt 6 by a predetermined small constant distance on the side opposite to the pressure means 2 side of the fixing means 1. ing. The heating means 3 includes a magnetic core (hereinafter abbreviated as core) 14 and an induction heating coil (hereinafter abbreviated as coil) 15. The core 14 is formed from, for example, a ferrite core or a laminated core. The coil 15 is configured, for example, by winding a copper wire having a fusion layer and an insulating layer on the surface a plurality of times. More specifically, the heating means 3 uses, for example, a litz wire as the electric wire of the coil 15. This is a horizontally long and thin plate member in which a coil 15 formed by winding a horizontally long and flat sheet-like spiral coil and a core 14 covering the coil 15 are integrally molded with an electrically insulating resin. More specifically, the coil 15 is covered with the core 14 so that the generated magnetic field does not leak to any part other than the base layer 6 a that is the electromagnetic induction heating layer of the fixing belt 6. Further, the coil 15 and the core 14 are integrally molded by an electrically insulating resin. The fixing belt 6 and the coil 15 are electrically insulated by a 0.5 mm mold, and the distance between the fixing belt 6 and the coil 15 is 1.5 mm (the distance between the mold surface and the fixing belt surface is 1.0 mm) and constant. Yes, the fixing belt 6 is heated uniformly. The coil 15 has a length along the sheet passing width direction of the recording material P (a direction perpendicular to the conveying direction of the recording material P) longer than the sheet passing width of the recording sheet P having the maximum sheet passing width used for image formation. It is formed to be long.

Reference numeral 103 denotes a shift unit as a proximity / separation unit of the heating unit 3 with respect to the fixing unit 1. Although the specific structure of the shift unit 103 is omitted in the drawing, for example, the rotation of a cam connected to a motor or a solenoid controls the heating unit 3 to a predetermined small fixed distance from the fixing unit 1. The shift is switched between a first position that is closely spaced and a second position (retracted position) that is lifted from the first position and separated from the fixing unit 1 by a predetermined distance. This shift means 103 is also controlled by the control circuit unit 100.

[During fixing operation]
FIG. 2 shows the state of the fixing device F during a fixing operation for fixing the unfixed toner image T on the recording material P introduced into the fixing device F.

  That is, the control circuit unit 100 controls the shift unit 8 for the fixing unit 1 to hold the tension roller 4 shifted to the first position where the fixing belt 6 is tensioned (tension−). ON). The fixing roller 5 is rotationally driven by the driving means M1 so that the fixing belt 6 is rotated (belt-rotation).

  With respect to the pressure belt unit 2, the shift means 13 is controlled to hold the tension roller 9 in a state shifted to the first position where tension is applied to the pressure belt 116 (tension-ON). The pressure roller 10 is rotated by the driving means M2 to rotate the pressure belt 11 (belt-rotation). Further, the shift means 102 is controlled so that the pressure means 2 is brought into pressure contact with the fixing means 1 to be shifted to the first position where the fixing nip portion N is formed (added). Pressure means-wearing).

  The heating means 3 is held in a state where it is shifted to the first position where the heating means 3 is controlled by the shift means 103 so as to be located close to the fixing means 1 by a predetermined small fixed distance. Heating means-proximity). Further, a high frequency current of 20 to 50 kHz is passed from the excitation circuit 101 to the coil 15 to cause the base layer 6a of the fixing belt 6 to generate induction heat (heating-ON). That is, the magnetic flux supplied to the fixing belt 6 is generated by energization of the coil 15. This magnetic flux is absorbed by the base layer 6a, which is the heat generating layer of the fixing belt 6, in a region where the heating means 3 and the fixing belt 6 are opposed, and a vortex-induced current is generated in the base layer 6a. Fever. In this way, an induction current is generated in the fixing belt 6 by the high-frequency current flowing through the coil 13, and the fixing belt 6 itself is heated by electromagnetic induction. The surface temperature of the fixing belt 6 is detected by a temperature sensor TH such as a thermistor, and the detected temperature information is fed back to the control circuit unit 100. The control circuit unit 100 outputs the high-frequency current output from the excitation circuit 101 so that the detected temperature information from the temperature sensor TH is kept constant at, for example, 170 ° C., which is the target temperature of the fixing belt 6 (target fixing temperature). The temperature of the fixing belt 6 is adjusted by controlling the power input to the coil 15 by changing the frequency of.

  In the state as described above, the recording material P having the unfixed toner image T is guided by the entrance guide member 16 and introduced into the fixing nip portion N with the toner image carrying surface side facing the fixing belt 6 side. The recording material P is sufficiently in close contact with the outer peripheral surface of the fixing belt 6 by the pressure members 7 and 12 and is nipped and conveyed together with the fixing belt 6 through the fixing nip portion N. As a result, the heat of the fixing belt 6 is applied, and the unfixed toner image T is fixed to the surface of the recording material P by the pressure applied by the fixing nip portion N. The recording material P that has passed through the fixing nip portion N is separated from the outer peripheral surface of the fixing belt 6 by the deformation of the exit portion of the fixing nip portion N and is conveyed outside the fixing device.

  The fixing belt 6 and the pressure belt 11 are rotationally driven without wrinkles at substantially the same peripheral speed as the conveying speed of the recording material P conveyed to the fixing device F. In the case of this embodiment, the surface rotation speed of the fixing belt 6 and the pressure belt 11 is 160 mm / sec, and it is possible to fix 40 A4 size full-color images per minute.

  In this way, by using the pressure means 2 with a belt stretched around a roller, the fixing nip portion N can be formed widely between the fixing belt 6 and the pressure means 2, and the speed of the apparatus is increased. Even when the speed is increased, a sufficient time for heat transfer to the recording material P can be secured, so that sufficient fixability can be obtained.

  Since the coil 15 is disposed outside the fixing belt 6 that is at a high temperature, the temperature of the coil 15 is unlikely to be high, so that an inexpensive heat-resistant grade coil material can be used. Further, since the coil 15 does not reach a high temperature, there is an advantage that the loss due to Joule heat generation is reduced even when a high frequency current is passed without increasing the electrical resistance.

[Standby]
At the time of standby for waiting for the image formation start signal, the control circuit unit 100 controls the shift unit 102 for the pressurizing unit 2 to pull it down from the fixing unit 1 and separate it to a predetermined position as shown in FIG. (The pressurizing means is removed). In this state, the fixing belt 6 and the pressure belt 11 are held in a tensioned state, and are both driven to rotate (tension-ON, belt-rotation). A high frequency current is passed through the coil 15 so that the fixing belt 6 is heated to a predetermined fixing temperature (heating means—proximity, heating—ON).

  During standby, as described above, the fixing belt 6 and the pressure belt 11 are separated from each other, so that heat of the fixing belt 6 is not conducted to the pressure belt 11, so that the thermal economy is good. Further, the warming up time of the fixing device can be made faster than in the case where the fixing belt 6 and the pressure belt 11 are in pressure contact.

[When the power is off and in power saving mode]
When the power is turned off or the power saving mode when the apparatus is not turned on, the control circuit unit 100 controls the shift unit 102 for the pressurizing unit 2 to pull it down from the fixing unit 1 as shown in FIG. Is held in a state shifted to the second position separated from each other (pressurizing means-desorption). The rotation of the pressure roller 10 is turned off (belt-stop). The shift means 13 is controlled to hold the tension roller 9 in a state shifted to the second position where the tension of the pressure belt 11 is released (tension-release).

  About the heating means 3, the energization with respect to the coil 15 is turned off (heating-OFF). The shift unit 103 is controlled to hold the heating unit 3 in a state shifted to a second position that is separated from the fixing unit 1 by a predetermined distance (heating unit-retreat). In other words, the shift unit 103 is controlled to move the heating unit relative to the fixing belt 6 so as not to come into contact therewith.

  For the fixing unit 1, the rotation of the fixing roller 5 is turned off (belt-stop). The shift means 8 is controlled to hold the tension roller 4 in a state shifted to the second position where the tension of the fixing belt 6 is released (tension-release).

  In the state shown in FIG. 6, since the fixing belt 6 is in a free state in which the tension is released, deformation of the belt due to the compression set does not occur. Further, since the heating unit 3 is also retracted away from the fixing belt 6, the surface of the fixing belt 6 does not come into contact with the heating unit 3, and the surface of the fixing belt 6 is not damaged. In the pressurizing means 2 as well, the tension roller 9 moves in the direction of loosening the tension of the pressure belt 11, and the tension of the pressure belt 11 is also released.

[Fixing device status control]
FIG. 7 is a control operation flowchart of the fixing device state as shown in FIGS. 2, 5, and 6 described above.

  When the power of the image forming apparatus is turned off, the control circuit unit 100 keeps the fixing device F in the states of [tension-release, belt-stop, pressurizing unit-detached, heating unit-retreat, heating-OFF] in FIG. (Step S1⇔S2).

  When the power is turned on, the control circuit unit 100 switches the fixing device F from the power-off state in FIG. 6 to the standby state in FIG. 5 [tension-ON, belt-rotation, heating means-proximity, heating-ON. , Pressurizing means-deselection] (step S2 → S3). That is, the tension rollers 4 and 9 move in the direction in which the fixing belt 6 and the pressure belt 11 are tensioned, the tension is applied, and the fixing belt 6 and the pressure belt 11 start rotating. At this time, the heating means 3 in the retracted position approaches the fixing belt 6 of the fixing means 1 and starts a heating operation. In this state, the pressure belt 11 is still separated from the fixing belt 6. This is to make it as fast as possible in the warm-up time, and by separating the heat, the heat of the fixing belt 6 is prevented from transferring to the pressure belt 11. Then, while the belts are rotated as they are, the heating operation is performed until the surface temperature of the fixing belt 6 reaches a predetermined value.

  When the temperature sensor TH detects that the surface temperature of the fixing belt 6 has reached a predetermined value, the printable state is entered, and the heating means 3 shifts to ON / OFF control and enters a standby state.

  Next, when an image formation start signal is input and image formation is started, the control circuit unit 100 controls the shift unit 102 to push the pressurizing unit 2 against the fixing unit 1 so as to make a press contact. Further, the pressurizing means-wearing state is set (step S4 → S5). The recording material P having the unfixed toner image T is introduced into the fixing nip portion N, the fixing operation is performed, and the image formation is completed (step S6).

  When the image formation is completed, the pressure belt 11 is separated from the fixing belt 6 again and returns to the standby state while rotating (step S7). From this state, the timer counts the time (step S8), and the fixing belt 6 rotates while the temperature is adjusted until the predetermined time elapses, and the pressure belt 11 also continues to rotate (steps S8 → S9 → S7). The pressure belt 11 may be stopped in this state.

  When an image formation start signal is obtained again in this standby state, the image forming operation is started as described above (steps S8 → S9 → S4).

  If the image formation start signal is not obtained even after a predetermined time has elapsed, the mode is shifted to the power saving mode (steps S8 → S10). In this case, the control circuit 100 changes the state of the fixing device F from the standby state of FIG. 5 to [belt-stop, tension-release, pressurization unit-deletion, heating unit-retreat, heating-OFF] of FIG. Holds converted to state. That is, the energization of the heating unit 3 is interrupted and the heating of the fixing belt 6 is stopped. When the heating is stopped, the driving of the fixing belt 6 is also stopped, and the tension rollers 4 and 9 are moved in the direction of loosening the tension of the fixing belt 6 and the pressure belt 11, and the tension of each belt is released. In accordance with this, the heating means 3 moves to the retracted position and moves away from the fixing belt 6.

  In this state, since the fixing belt 6 and the pressure belt 11 are in a free state in which the tension is released, deformation of the belt due to the compression set does not occur. Further, since the heating unit 3 is also retracted away from the fixing belt 6, the surface of the fixing belt 6 does not come into contact with the heating unit 3, and the surface of the fixing belt 6 is not damaged.

  If the image formation start signal is not obtained in this state, the fixing device is cooled while the heating operation is stopped, and the main body power supply is automatically shut off when a predetermined time elapses. When the image formation start signal is obtained again within this predetermined time, or when the power is turned off after the predetermined time has elapsed, the power is turned on again (steps S1 → S2 → S3). ).

  As described above, in this embodiment, the heating unit 3 can be reduced in size by arranging it outside the fixing belt 6. By supporting the fixing belt 6 by the fixing roller 5 and the tension roller 4, the fixing belt 6 having a small diameter and a small heat capacity can be heated with less wasteful heat conduction, and the warm-up time can be shortened.

  Further, when the fixing belt 6 and the pressure belt 11 are stopped, the tension rollers 4 and 9 are moved and the belt tension is released. Therefore, even when a belt having an elastic layer is used, belt deformation does not occur. . When the tension of the fixing belt 6 is released, the heating unit 3 moves away from the fixing belt 6, so that the fixing belt 6 does not contact the heating unit 3 and the surface of the fixing belt 6 is not damaged.

  In this embodiment, an example in which the tension is released in conjunction with the interruption of the energization to the heating unit 3 is shown. However, the present invention is not necessarily limited to this. For example, after the energization to the heating unit 3 is interrupted, the fixing belt The tension may be released when the sensor TH detects a temperature drop of 6. That is, the tension of the fixing belt is released in conjunction with whether or not the heating unit 3 is energized. Alternatively, the fixing belt tension is released in conjunction with the fixing belt temperature.

  FIG. 8 is a control operation flowchart of the fixing device state in this embodiment. In this flowchart, in addition to the control operation flow shown in FIG. 7 in the first embodiment, a control operation when a conveyance failure (jam) of the recording material occurs after the start of image formation is added.

  That is, if no recording material conveyance failure is detected in step S11 inserted between steps S5 and S6, the image formation is completed normally, and the standby state is again entered as in the first embodiment (step S6 → S7). However, if a recording material conveyance failure or the like occurs between steps S5 and S6 and a jam is detected by a sensor (not shown) in the main body, the control circuit unit 100 forms an image in the image forming apparatus including the fixing device. Stop operation.

  For the fixing device F, from the state at the time of fixing operation of FIG. 2 to the state at the time of power OFF or power saving mode of FIG. 7 [belt-stop, tension-release, pressurizing means-deletion, heating means-retreat, heating- The state is switched to the OFF state (steps S11 → S12). That is, the tension of the fixing belt is released when the recording material is not normally conveyed.

  When the jam processing in the main body is completed, the state is again switched to the standby state [tension-ON, belt-rotation, heating means-proximity, heating-ON, pressurization means-deletion] in step S3 (FIG. 5) (step S3). S12 → S3).

  As described above, in the present embodiment, the heating unit 3 can be reduced in size by being disposed outside the fixing belt 6. By supporting the fixing belt 6 by the fixing roller 5 and the tension roller 4, the fixing belt 6 having a small diameter and a small heat capacity can be heated with less wasteful heat conduction, and the warm-up time can be shortened.

  Further, when the fixing belt 6 and the pressure belt 11 are jammed, the tension rollers 4 and 9 are moved and the tension of the belt is released. Therefore, even when a belt having an elastic layer is used, belt deformation does not occur.

  When the tension of the fixing belt 6 is released, the heating unit 3 moves away from the fixing belt 6, so that the fixing belt 6 does not contact the heating unit 3 and the surface of the fixing belt 6 is not damaged.

  Further, when the jam occurs, the fixing belt 6 and the pressure belt 11 are separated from each other, the respective belt tensions are released, and the heating unit 3 is retracted away from the fixing belt 6. Processing becomes easy.

In this embodiment, the distance between the fixing belt 6 and the heating unit 3 is maintained at a certain level or more even when the tension of the fixing belt 6 is released in the fixing device of the first or second embodiment. FIG. 9 is a state diagram during the fixing operation of the fixing device in the present embodiment, and FIG. 10 is a state diagram when the power is turned off or in the power saving mode.

In the present embodiment, a plurality of roller members 17 (contacting means) are provided in the vicinity of the fixing belt 6 of the heating unit 3 with respect to the fixing device shown in the first or second embodiment. This is in contact with the fixing belt 6.

The roller member 17 is made of metal or heat-resistant resin, is rotatable, and is in contact with the non-sheet passing region of the fixing belt 6. Here, the size of the roller member 17 is adjusted in accordance with the distance at which the efficiency of electromagnetic induction heating is increased so that the distance between the fixing belt 6 and the heating means 3 becomes a certain distance or more .

  By having such a roller member 17, as shown in FIG. 10, the tension roller 4 is moved to a position where the tension of the fixing belt 6 is relaxed as in the first and second embodiments, and the tension of the fixing belt 6 is released. In this case, the heating unit 3 receives a force upward due to the tension of the fixing belt 6 and moves its position.

  However, even in this case, since the distance between the heating unit 3 and the fixing belt 6 is regulated to be constant by the roller member 17, the heating unit 3 moves while maintaining a constant distance from the fixing belt 6. And the heating means 3 are not in contact with each other.

  Note that the tension release operation sequence of the fixing belt 6 when this fixing device is used may be performed when the power is turned off or a jam occurs, as in FIG. 7 or FIG. 8, and the description thereof is omitted in this embodiment.

  In this embodiment, by defining the moving direction of the tension roller 4 of the fixing belt 6, the tension of the fixing belt 6 is released without changing the position of the heating means 3.

  FIG. 11 shows a state during the fixing operation, which is the same as the state of FIG. FIG. 12 is a state diagram when the power is turned off or in the power saving mode. In the present embodiment, the operation at the time of releasing the tension is different from the first and second embodiments. In this embodiment, when releasing the tension, the pressure belt 11 is separated from the fixing belt 6, the tension rollers 4 and 9 are moved to a position where the tension of the fixing belt 6 and the pressure belt 11 is relaxed, and the fixing belt 6 and The tension of the pressure belt 11 is released. The position of the heating means 3 is fixed and does not retract in a direction away from the fixing belt 6.

Here, the moving direction of the tension roller 4 will be described in detail. As shown in FIG. 11, when the tension roller 4 moves on a line A connecting the axial centers of the tension roller 4 and the fixing roller 5 as in the first to third embodiments, the fixing belt 6 comes into contact with the heating unit 3 as usual. End up. Therefore, in this embodiment, as shown in FIG. 12, the tension roller 4 is further moved away from the heating unit 3 to prevent the heating unit 3 and the fixing belt 6 from contacting each other. That is, the moving direction of the tension roller 4 is a direction in which vectors of a line direction A connecting the axis centers of the tension roller 4 and the fixing roller 5 and a line direction B connecting the axis centers of the tension roller 4 and the tension roller 9 are combined ( Direction) . The tension roller 4 moves in the direction C to release the tension of the fixing belt 6 as shown in FIG. 12, and the fixing belt 6 moves away from the heating unit 3, and the fixing belt 6 comes into contact with the heating unit 3. Disappear. Since this moving distance varies depending on the size of the apparatus, it may be designed so that the fixing belt 6 and the heating means 3 do not come into contact with each other.

  The sequence in which the tension release operates is the same as in the first to third embodiments.

  By doing in this way, compared with Example 1 thru | or Example 3, in this Example, since the moving mechanism (103) of the heating means 3 is not required, simplification of an apparatus, cost reduction, and space saving can be achieved. .

  Here, in the first to fourth embodiments, the fixing belt 6 and the pressure belt 11 may be configured to be suspended from three or more support members. Further, the pressure means 2 is not limited to the pressure belt configuration, and may be a pressure roller configuration.

  Note that the fixing device of the present invention includes an image heating device that presupposes an unfixed image on a recording material, an image heating device that heats a recording material carrying an image, and modifies surface properties such as gloss. Is done.

Schematic model diagram of an example of an image forming apparatus Expanded cross-sectional side view of main part of fixing device (during fixing operation) and control system block diagram Cross-sectional model diagram showing layer structure of fixing belt Cross-sectional model diagram showing the layer structure of the pressure belt Diagram showing the status of the fixing device during standby The figure which showed the state of the fixing device at the time of power-off or power saving mode Control operation flow chart of fixing device status Flow chart of control operation of fixing device state in embodiment 2 FIG. 6 is an enlarged cross-sectional side view of the main part of the fixing device according to the third embodiment (at the time of fixing operation) and a block diagram of a control system. The figure which showed the state of the fixing device at the time of power-off or power saving mode Fig. 4 is an enlarged cross-sectional side view of the main part of the fixing device according to the fourth embodiment (during fixing operation) and a block diagram of a control system. The figure which showed the state of the fixing device at the time of power-off or power saving mode

Explanation of symbols

  F: fixing device, 1: fixing means (fixing belt unit), 2: pressure means (pressure belt unit), 3: heating means (electromagnetic induction heating means), 4 · 9: tension roller, 5 · 10: fixing Roller and pressure roller, 6 · 11: fixing belt and pressure belt, 7 · 12: pressure member, 8 · 13: shift means, 14: magnetic core, 15: induction heating coil, 17: roller member, 100 : Control means (control circuit section), 101: excitation circuit, 102/103: shift means, TH: temperature sensor (thermistor), P: recording material, T: toner image

Claims (7)

An endless belt having a metal layer, a plurality of stretching members that stretch the belt, an electromagnetic induction heating means that is disposed opposite to an outer surface of the belt and generates a magnetic flux for generating heat from the belt; An image heating apparatus that includes a pressurizing unit that presses against a belt to form a nip portion, and a release unit that releases the tension of the belt, and sandwiches and conveys a recording material carrying an image at the nip portion and heats the recording material In
Said belt in order to prevent the with the release of the tension of the belt, a moving means for moving the front Symbol electromagnetic induction heating means or the stretching members, which said belt during release of tension and the electromagnetic induction heating means is in contact And an abutting means for abutting against the non-sheet passing portion region . Said abutment means, an image heating apparatus according to claim 1, wherein a roller member rotatable mounted to the electromagnetic induction heating unit. The belt is an image heating apparatus according to claim 1 or claim 2 characterized in that it has an elastic layer on the metal layer. The release of the belt tension, the image heating apparatus according to any one of claims 1 to 3 conveying the recording material, characterized in that made in the case of unsuccessful. The release of the belt tension, the image heating apparatus according to any one of claims 1 to 4, characterized in that linked to the presence or absence of energization of the electromagnetic induction heating unit.   6. The image heating apparatus according to claim 1, wherein the release of the tension of the belt is interlocked with a belt temperature. And means for separating the said pressing means from said belt, before releasing the tension of the belt, either of claims 1 to 6, characterized in that for separating the pressurizing means from the belt The image heating apparatus according to claim 1.