Patent Publication Number: US-8983313-B2

Title: Image heating device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image heating device that heats an image on a sheet. 
     2. Description of the Related Art 
     An image forming apparatus, such as a printer, a copying machine, a facsimile machine, or a multi-functional apparatus of these machines, which includes a fixing device (an image heating device) of a belt heating type using a fixing belt (an endless belt) has hitherto been put into practical use. In such a fixing device, a toner image, which is formed and born on a sheet (a recording material) by an image forming method such as an electrophotographic process or an electrostatic recording process, is fixed on a surface of the recording material by heating. 
     Since such a fixing device of the belt heating type uses a thin fixing belt having low heat capacity and high thermal responsiveness, the temperature of the fixing belt can reach a fixing temperature in a short time from power-on. This greatly contributes to power saving of the image forming apparatus. 
     However, the thin fixing belt may be broken owing to deformation or a flaw caused by any external force. If the fixing belt is broken, not only an image defect may be caused, but also a broken part may contact and break other components. Therefore, if the fixing belt is broken, it is preferable to immediately understand the fact and to prohibit a fixing process (an image heating process). A technique for that purpose is proposed in Japanese Patent Laid-Open No. 2002-287542. 
     Specifically, in a fixing device described in Japanese Patent Laid-Open No. 2002-287542, a belt mark is put on a fixing belt, and an optical sensor is disposed on a side opposed thereto. With this structure, it is determined that the fixing belt is broken when the optical sensor does not detect the belt mark for a fixed time. 
     However, in the fixing device described in Japanese Patent Laid-Open No. 2002-287542, if a flaw is made on the belt mark or a foreign substance adheres to the belt mark, the amount of light (amount of reflected light) received by the optical sensor decreases and becomes unstable. Hence, a breakage of the fixing belt may be detected erroneously. 
     SUMMARY OF THE INVENTION 
     Aspects of the present invention provide an image heating device including a belt configured to heat an image on a sheet, a wire stretched from one widthwise end to the other widthwise end of the belt near a peripheral surface of the belt, a moving member movably fixed to one end of the wire, a biasing member configured to bias the moving member, a detection unit configured to detect that the moving member is moved by a biasing force of the biasing member with being cut of the wire, and a control unit configured to control, according to an output of the detection unit with regard to detecting that the moving member is moved, whether or not to prohibit an image heating process. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of a fixing device. 
         FIG. 2  is a schematic configuration view of an image forming apparatus including the fixing device. 
         FIG. 3  is a side view of the fixing device. 
         FIG. 4  is a side view of the fixing device, illustrating a suspended member. 
         FIG. 5  is an exploded perspective view illustrating the interior of a fixing unit. 
         FIGS. 6A and 6B  are perspective views of a cut detection mechanism, respectively, illustrating a set state before cut detection and a state at the time of cut detection. 
         FIG. 7  is a control flowchart. 
         FIGS. 8A and 8B  are perspective view of another cut detection mechanism, respectively, illustrating a set state before cut detection and a state at the time of cut detection. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     An embodiment of the present invention will be described below with reference to the drawings. While an image heating device of the embodiment is applied to a fixing device that fixes an unfixed toner image onto a sheet (a recording material), the present invention is also applicable to a heat treatment device that heats a recording material bearing a fixed image or a semi-fixed image to adjust the surface texture of the image. The dimensions, materials, shapes, and relative arrangements of the constituent components adopted in the embodiment should be appropriately changed according to the configuration and various conditions of the device to which the present invention is applied, and are not intended to be limited to the following embodiment. 
     First, an electrophotographic color printer serving as an image forming apparatus will be described with reference to  FIG. 2 .  FIG. 2  is a cross-sectional view of the electrophotographic color printer, taken along a sheet conveying direction. In the following description of the embodiment, the electrophotographic color printer will be simply referred to as a “printer.” 
     [Printer] 
     As illustrated in  FIG. 2 , a printer  1  includes a printer main body  4 . The printer main body  4  includes image forming sections  10  corresponding to Y (yellow), M (magenta), C (cyan), and Bk (black) colors. Each of the image forming sections  10  includes a photosensitive drum  11 , and a charger  12 , a laser scanner  13 , a developing unit  14 , a primary transfer blade  17 , and a cleaner  15  that are arranged in order in a rotating direction of the photosensitive drum  11 . 
     In each of the image forming sections  10 , the photosensitive drum  11  is charged by the charger  12  beforehand, and an electrostatic latent image is formed thereon by the laser scanner  13 . The electrostatic latent image is developed into a visible toner image by the developing unit  14 . Toner images formed on the photosensitive drums  11  corresponding to the colors are each sequentially transferred by the primary transfer blade  17  onto an intermediate transfer belt  31  serving as an image bearing member so as to form a color toner image. After this transfer, toner remaining on each photosensitive drum  11  is removed by the cleaner  15 . Hence, a surface of the photosensitive drum  11  is cleaned and can prepare for the next image forming operation. 
     In contrast, recording materials P are fed one by one from a first sheet cassette  20   a , a second sheet cassette  20   b , or a multipurpose sheet tray  25  provided on one side of the printer  1 , and a fed recording material P is sent between a pair of registration rollers  23 . The registration rollers  23  temporarily receive the recording material P and correct skew feeding. Then, the registration rollers  23  send the recording material P into a secondary transfer nip between the intermediate transfer belt  31  and a secondary transfer roller  35  in synchronization with the toner image on the intermediate transfer belt  31 . The intermediate transfer belt  31  is supported by tension rollers  18 ,  19 , and  34  to be rotatable in a direction of arrow A. 
     The color toner image on the intermediate transfer belt  31  is transferred onto the recording material P by the secondary transfer roller  35  serving as a transfer member. After that, the recording material P is heated and pressed by a fixing device  40 , and a toner image t (see  FIG. 1 ) is fixed on the recording material (sheet) P. In  FIG. 2 , reference numeral  2  denotes a pre-fixing guide that guides the recording material P to the fixing device  40  before fixing. 
     When a toner image is to be formed on one side of the recording material P, a conveyance path is switched by a switch member (flapper)  61  according to the condition. When the recording material P is to be discharged face up (the toner image faces up), it is discharged via sheet discharge rollers  63  onto a sheet discharge tray  64  disposed on a side surface of the printer  1 . In contrast, when the recording material P is to be discharged face down (the toner image faces down), it is discharged onto a sheet discharge tray  65  disposed in an upper part of the printer  1 . 
     When a toner image is to be formed on each side of the recording material P, after a toner image is fixed on one side of the recording material P by the fixing device  40 , the recording material P is guided upward by the switched switch member  61 , and is turned upside down by being switched back into a switchback conveyance path  73  when a trailing edge of the recording material P reaches a reverse point R. After that, the recording material P is conveyed through a duplex conveyance path  70 , and a toner image is formed on the other side of the recording material P through a process similar to that for one-sided image formation. Then, the recording material P is discharged onto the sheet discharge tray  64  or the sheet discharge tray  65 . A section constituted by the switch member  61 , the switchback conveyance path  73 , etc. is an example of a reversing unit. 
     [Fixing Device] 
     Next, the fixing device  40  will be described with reference to  FIGS. 1 and 3 .  FIG. 1  is a schematic cross-sectional view of the fixing device  40 , taken along the sheet conveying direction, and  FIG. 3  is a side view of the fixing device  40 , as viewed from a right side of  FIG. 1 . 
     The fixing device  40  is an example of a belt heating type fixing device. The fixing device  40  includes a pressing roller  106  serving as a driving rotating member or a rotating member, and a fixing unit  41  opposed to the pressing roller  106  and serving as an image heating member. The fixing unit  41  includes a ceramic heater  100  serving as a heating mechanism therein. The pressing roller  106  serving as the driving rotating member forms a fixing nip (nip) N in cooperation with a fixing belt  101  serving as an endless belt, and drives the fixing belt  101 . 
     The fixing unit  41  includes a cylindrical fixing film (hereinafter referred to as a fixing belt)  101  serving as an endless belt, and a guide member  103  that forms the fixing nip N with the pressing roller  106  such that the fixing belt  101  is located therebetween. The guide member  103  extends long to have a length nearly equal to an axial length of the fixing belt  101  and the pressing roller  106 . The fixing belt  101  is heated by the ceramic heater  100  (heating member) and is supported to be rotatable in a circumferential direction. The pressing roller (rotating member)  106  is rotatably supported while forming the fixing nip (nip) N by contact with the fixing belt  101 . 
     The fixing unit  41  further includes fixing flanges  104  and a stay  102 . The fixing flanges  104  are disposed at both axial ends of the fixing belt  101 , respectively, to regulate a circumferential track of the fixing belt  101 . The stay  102  is disposed on an inner surface side of the fixing belt  101  to ensure strength of the guide member  103 . 
     The fixing device  40  includes a controller  45  formed by a CPU and serving as a control unit, a detection unit  118  serving as a cut detection unit connected to the controller  45 , and a driving unit  24 , such as a motor, connected to the controller  45  to rotationally drive the pressing roller  106 . The detection unit  118  also functions as a detection unit for detecting a conductive state of a wire  111 , and the controller  45  functions as a prohibition unit. The controller  45  serving as the prohibition unit prohibits an image heating process when the detection unit  118  detects that the wire  111  is in a non-conductive state. For example, the controller  45  prohibits the image heating process by at least one of a method of stopping a heating operation with a heating member, such as the ceramic heater  100 , and a method of stopping driving of the pressing roller  106 . 
     The members will be described in detail below. First, the members that constitute the fixing unit  41  will be described. 
     The fixing belt  101  in the fixing unit  41  is formed by a heat-resistant cylindrical member that transfers heat to a recording material P, and is loosely fitted on the guide member  103 . For example, the fixing belt  101  can be formed by a thin metal film having a thickness within the range of 20 to 100 μm, preferably to 50 μm. As the thin metal film, a composite-layer film obtained by coating an outer peripheral surface of SUS with PTFE, PFA, or FEP, can be used, for example. 
     On an inner side of the fixing belt  101 , the guide member  103  is disposed to extend long with a length slightly more than the longitudinal length of the fixing belt  101 . The guide member  103  is formed of a heat-resistant and heat-insulating material. As this material, a material that has high insulation and high heat resistance, such as phenol resin, polyimide resin, polyamide resin, polyamideimide resin, PEEK resin, PES resin, PPS resin, PFA resin, PTFE resin, or LCP resin, can be used. The guide member  103  is in pressure contact with the pressing roller  106  to assist pressurization at the fixing nip N formed between the fixing belt  101  and the pressing roller  106  and to function as a guide for stabilizing the rotation of the fixing belt  101 . 
     In a lower surface of the guide member  103  in  FIG. 1 , a fitting groove  103   a  extends in the longitudinal direction. The ceramic heater  100  having a length nearly equal to the length of the fitting groove  103   a  is fitted and supported in the fitting groove  103   a . The ceramic heater  100  is a heating member having a low heat capacity, and is increased in temperature with a totally steep rise characteristic by energization of a heating resistor layer. For example, in the ceramic heater  100 , an energizing heating resistor layer is provided on a ceramic substrate shaped like an elongated thin plate. 
     The stay  102  is disposed on the guide member  103 . The stay  102  has a length nearly equal to the longitudinal length of the guide member  103 . The stay  102  is pressed against a back surface of the guide member  103  made of comparatively soft resin to impart longitudinal strength to the guide member  103  and to correct the guide member  103 . 
     The fixing flanges  104  and  104  are fitted in both longitudinal ends of the stay  102 , respectively. These fixing flanges  104  have side wall portions that guide the circumferential rotation of the fixing belt  101  and function as thrust stops for regulating movement of the fixing belt  101  in the widthwise direction (right-left direction in  FIG. 3 ). The fixing flanges  104  are fitted in and held by side plates  108  disposed at both axial ends of the fixing belt  101  and the pressing roller  106 , respectively. This ensures the position of the entire fixing unit  41 . 
     Pressing springs  105  and  105  are disposed on outer sides of the side plates  108  and  108  at both ends, respectively. These pressing springs  105  and  105  impart a predetermined pressing force to the fixing flanges  104  and  104  at both ends of the fixing belt  101 . The pressing roller  106  located on a lower side of the fixing belt  101  is supported by the side plates  108  provided at both axial ends such that a rotation shaft (a cored bar  107 ) thereof is rotatable. The pressing roller  106  is also pressed toward the fixing belt  101  by an unillustrated pressing mechanism to form the fixing nip N. 
     Next, the pressing roller (rotating member)  106  serving as the pressing member will be described in detail with reference to  FIG. 3 . 
     That is, as illustrated in  FIG. 3 , the pressing roller  106  includes the cored bar  107  that extends in an axial direction (a right-left direction in  FIG. 3 ) to serve as a rotation shaft for the pressing roller  106 , and a roller-shaped covering layer provided around the cored bar  107 . The covering layer is molded integrally and concentrically with the cored bar  107  to cover the cored bar  107 . A release layer is provided on a surface of the pressing roller  106 . The covering layer provided around the cored bar  107  is formed of a heat-resistant elastic material such as silicone rubber, fluoro rubber, or fluoro resin. As the release layer, a material having high releasability and high heat resistance, such as fluoro resin, silicone resin, fluoro silicone rubber, fluoro rubber, silicone rubber, PFA, PTFE, or FEP, can be selected. 
     Unillustrated bearing members formed of a heat-resistant resin, such as PEEK, PPS, or a liquid crystal polymer, are attached to both ends of the cored bar  107 , respectively. These bearing members allow the cored bar  107  to be rotatably held in the side plates  108  and  108 . A gear  109  is attached to one longitudinal end of the cored bar  107 . The pressing roller  106  is rotationally driven by the rotation received from the driving unit  24 , which is controlled by the controller  45  ( FIG. 1 ), to the cored bar  107  via the gear  109 . When the pressing roller  106  rotates, the fixing belt  101  in contact with the pressing roller  106  drags (rotates) along with the rotation of the pressing roller  106 . 
     [Cut Detection Mechanism] 
     Next, a cut detection mechanism for detecting a breakage (cut) of the fixing belt  101  will be described with reference to  FIGS. 4 and 5 .  FIG. 4  is a side view of a wire  111  serving as a suspended member, and  FIG. 5  is an exploded perspective view illustrating an internal structure of the fixing belt  101 . 
     That is, as illustrated in  FIGS. 4 and 5 , the cut detection mechanism includes the wire  111  serving as the suspended member. The wire  111  is laid in the longitudinal direction of the fixing belt  101  such as to be close to an inner peripheral surface of the fixing belt  101 . The detection unit  118  connected to the controller  45  ( FIG. 1 ) is connected to the cut detection mechanism, and detects that the wire  111  is cut. 
     The controller (control unit)  45  controls the members of the fixing device  40 , and determines, on the basis of detection of the detection unit (cut detection unit)  118 , that the fixing belt (endless belt)  101  is broken. The detection unit  118  serves to detect that the wire  111  provided in the fixing belt  101  is cut. When determining, on the basis of the detection of the detection unit  118 , that the fixing belt  101  is broken, the controller  45  stops driving of the driving unit  24  ( FIG. 1 ) to stop the pressing roller  106 , and to stop the rotation of the fixing belt  101 . 
     A fixed-side support member  112  and a movable-side support member  113  serving as a pair of support portions for supporting both ends of the suspended member are disposed at both longitudinal ends of the guide member  103 , respectively. The fixed-side support member  112  is fixedly supported at one end of the guide member  103 , and the movable-side support member  113  is supported at the other end of the guide member  103  such as to be movable in a direction of arrow F. 
     The stay  102  disposed to cover an upper part of the guide member  103  has long grooves  102   a  and  102   b  at both longitudinal ends, respectively. A distal end portion of the fixed-side support member  112  and a distal end portion of the movable-side support member  113  penetrate the long grooves  102   a  and  102   b , respectively. In this state, the wire (suspended member)  111  is laid between the fixed-side support member  112  and the movable-side support member  113  such as to be located slightly above the stay  102 . That is, the wire  111  is stretched from one widthwise end to the other widthwise end of the fixing belt  101  near the peripheral surface of the fixing belt  101 . 
     Thus, in a state in which the wire  111  is suspended between both widthwise ends of the fixing belt  101  to pass near the inner peripheral surface of the fixing belt  101 , it can be cut when the fixing belt  101  breaks and a broken part thereof contacts the wire  111 . The strength of the wire  111  is set at a degree such that the wire  111  is cut when the broken part of the fixing belt  101  contacts the wire  111 . 
     In the above-described support structure, the wire  111  supported by the fixed-side support member  112  and the movable-side support member  113  is disposed to extend over the entire longitudinal range of the fixing belt  101 . Thus, the wire  111  can be cut even when the fixing belt  101  is broken at any longitudinal position. 
     By changing the support structure including the fixed-side support member  112  and the movable-side support member  113 , the wire  111  can be suspended between both widthwise ends of the fixing belt  101  to pass near an outer peripheral surface of the fixing belt  101 . In this case, although the wire  111  is cut on the outer peripheral side of the fixing belt  101  when the fixing belt  101  is broken, advantages similar to the following advantages can be obtained. 
     The members will be described in detail below with reference to  FIGS. 5 ,  6 A, and  6 B.  FIG. 6A  is a perspective view illustrating a set state of the cut detection mechanism before cut detection, and  FIG. 6B  is a perspective view illustrating a state at the time of cut detection. 
     That is, the wire  111 , which is laid near the inner peripheral surface of the fixing belt  101  and is cut, for example, by contact with a belt broken surface when the fixing belt  101  is broken, can be formed by a fine metallic wire of aluminum, copper, iron, or SUS having a diameter of 30 to 100 μm. Instead of the fine metallic wire, a heat-resistant fine resin wire or a sheet material can be used as the wire. 
     That is, while a wire-shaped conductive member is used as the wire  111  serving as the suspended member in this embodiment, an insulating member having insulation properties can also be used. Since any of the conductive member and the insulating member can be used as the suspended member in this way, the degree of flexibility in selecting the material to be used increases, and this provides a structural advantage of the device. Preferably, the wire  111  is formed by an electrically insulating member so as not to disturb the electric potential of the fixing belt  101 . 
     As illustrated in  FIG. 5 , a suspension guide  110  is attached to the guide member  103  such as to extend in the longitudinal direction of the guide member  103 . The fixed-side support member  112  holds one end of the wire  111  while being provided integrally with the suspension guide  110 . 
     In contrast, as illustrated in  FIGS. 6A and 6B , the movable-side support member  113  is fixed to a distal end portion (right end portion in  FIGS. 6A and 6B ) of a slider  115  serving as a moving member. The slider  115  is movably received in a guide groove  110   a  provided in a side of the suspension guide  110  close to the movable-side support member  113 . Thus, the movable-side support member  113  is supported to be slidable in the longitudinal direction of the fixing belt  101 . In the center of the guide groove  110   a , a wall portion  110   b  is provided. The wall portion  110   b  has a through hole (not illustrated) that the slider  115  penetrates slidably. 
     While being fixed to the slider  115  penetrating the through hole, the movable-side support member  113  is biased by a coil-shaped compression spring  114  serving as a biasing member to apply tensile force to the wire  111  with a predetermined load F. The compression spring  114  is compressed between the wall portion  110   b  and a lower part of the movable-side support member  113 . The compression spring  114  has an outer diameter more than an inner diameter of the through hole. The movable-side support member  113  is formed of an insulating material such as resin. The slider  115  that can slide in the longitudinal direction together with the movable-side support member  113  is formed by a conductive metallic member. 
     The above-described structure can remove slack from the wire  111 , and can maintain a uniform gap between the fixing belt  101  and the wire  111  in the longitudinal direction. The detection unit (cut detection unit)  118  can detect a cut of the wire (suspended member)  111  from an operation in which one of the fixed-side support member  112  and the movable-side support member  113  serving as a pair of support portions (movable-side support member  113 ) separates from the other (fixed-side support member  112 ). 
     While the suspension guide  110  supports the fixed-side support member  112  and supports the movable-side support member  113  slidably in the embodiment, it may be replaced with an appropriate structure having this function. 
     Next, a structure for detecting a breakage of the fixing belt  101  will be described with reference to  FIGS. 1 ,  3 ,  5 ,  6 A, and  6 B. 
     As illustrated in  FIG. 5 , the wire  111  is supported at both ends by the fixed-side support member  112  and the movable-side support member  113 , and the movable-side support member  113  receives a predetermined tensile force F from the compression spring  114 . The movable-side support member  113  is formed of an insulating material such as resin. 
     The slider  115  serving as the moving member (slide member), which slides together with the movable-side support member  113 , penetrates the fixing flange  104  (see  FIG. 3 ), and extends to a position near a photointerrupter  120  disposed on an outer side of the side plate  108  (see  FIG. 3 ). 
     A flag (light shielding member)  119  fixed to the distal end of the slider  115  is protruded toward the photointerrupter  120  by a sliding action of the movable-side support member  113 , and obstructs an optical path  121  (shields light). The optical path  121  is a path through which laser light emitted from a light emitting part  120   a  to an opposed light receiving part  120   b  in the photointerrupter  120  passes. 
     The photointerrupter  120  is connected to the detection unit  118  serving as the cut detection unit. When the detection unit  118  detects, on the basis of a sensor signal issued when the optical path  121  is obstructed by the flag  119 , that the wire  111  is cut, it sends a detection signal to the controller  45 . Thus, the controller  45  serving as the control unit recognizes (determines), according to the detection signal from the detection unit  118 , that the fixing belt  101  is broken. 
     In a normal state in which the fixing belt  101  is not broken, the movable-side support member  113  stays at a predetermined position against the force of the compression spring  114  because the wire  111  is suspended ( FIG. 6A ). In this state, the flag  119  is located at a position such as not to obstruct the optical path  121 . When the detection unit  118  detects that the photointerrupter  120  is not shielded from light, the controller  45  recognizes that the fixing belt  101  is not broken. 
     In contrast, when the fixing belt  101  is broken, a broken part contacts and cuts the wire  111  (a crossed portion in  FIG. 6B ). Hence, the movable-side support member  113  is slid in a direction of arrow C in  FIG. 6B  by the biasing force of the compression spring  114 . Since the flag  119  moves in the same direction and obstructs the optical path  121 , the detection unit  118  detects that the photointerrupter  120  is shifted into a light shield state. 
     Then, the controller  45  recognizes the occurrence of a breakage of the fixing belt  101  on the basis of the detection of the detection unit  118 , and sends, to the driving unit  24  ( FIG. 1 ), a command to stop the driving of the pressing roller  106 . 
     Next, an operation of recognizing a breakage of the fixing belt  101  will be described with reference to  FIG. 7 .  FIG. 7  is a flowchart showing an operation of the image forming apparatus. 
     First, when a job start command is issued by the controller  45  formed by the CPU, breakage detection information (a breakage detection flag) stored in a memory is checked (Step S 1 ). When the breakage detection information is “1”, error display is performed (S 2 ), reception of a job is prohibited, and the operation is finished. 
     In contrast, when the breakage detection information is “0”, the controller  45  turns on the driving unit  24  to rotate the pressing roller  106 , turns on the ceramic heater  100  to start heating (S 3 ), and starts a job (S 4 ). 
     In a normal state in which the fixing belt  101  is not broken, the job is executed until a job end signal is sent from the controller  45 . When the job end signal is sent (S 5 ), the rotation of the pressing roller  106  is stopped by the driving unit  24 , heating with the ceramic heater  100  is stopped (S 6 ), and the operation is finished. 
     In contrast, when the detection unit  118  detects a breakage of the fixing belt  101  between the job start (S 4 ) and the job end (S 5 ), the controller  45  determines that the fixing belt  101  is broken (S 7 ), and stores breakage detection information “1” in the memory (S 8 ). Then, the active job is immediately interrupted (S 9 ), the driving unit  24  is turned off to stop the rotation of the pressing roller  106 , the ceramic heater  100  is turned off to stop heating (S 10 ), error display is performed (S 11 ), and the operation is finished. 
     As described above, the embodiment adopts the flag (light shielding member)  119 , and the photointerrupter (photosensor)  120  that is brought into a light shielded state when the flag  119  enters the photointerrupter  120  and into a light receiving state when the flag  119  separates from the photointerrupter  120 . The detection unit (cut detection unit)  118  detects a cut of the wire  111  on the basis of the fact that the photointerrupter  120  is brought into the light shielded state when the flag  119  moves relative to the photointerrupter  120 . The movement relationship between the flag  119  and the photointerrupter  120  can be the reverse of the above. Even when the photointerrupter  120  is moved relative to the flag  119  by changing the support structure, similar advantages can be obtained. 
     While the occurrence of a breakage of the fixing belt  101  is detected by the flag  119  and the photointerrupter  120  in the embodiment, it is satisfactory as long as the structure can detect that the movable-side support member  113  is moved, and a structure illustrated in  FIGS. 8A and 8B  can also be adopted.  FIGS. 8A and 8B  are perspective views of a cut detection mechanism, respectively, illustrating a set state before cut detection and a state at the time of cut detection. Members having functions similar to those in  FIGS. 6A and 6B  are denoted by the same reference numerals, and detailed descriptions thereof are skipped. 
     For example, when the slider  115  slides with the cut of the wire  111  (when a state of  FIG. 8A  is shifted to a state of  FIG. 8B ), a distal end portion  130  of the slider  115  pushes a microswitch  140  serving as a detector, whereby a breakage of the fixing belt  101  is determined. In this case, the microswitch  140  is connected to the controller (CPU)  45  via a signal line. When pushed, the microswitch  140  outputs a corresponding signal to the controller  45 . The controller  45  controls the members along with the control flow of  FIG. 7 , similarly to the above. Other sensors may be used instead of the microswitch. 
     According to the above-described embodiment, the simple structure using the wire  111  as the suspended member can quickly and reliably detect a breakage of the fixing belt  101  only by detecting a cut of the wire  111 . Thus, it is possible to immediately stop the rotation of the fixing belt  101  and to avoid trouble of the device due to the breakage of the fixing belt  101 . Therefore, it is possible to make a prompt response when the breakage of the fixing belt  101  is detected, for example, it is possible to quickly stop the print operation or to quickly replace the fixing belt  101 . 
     In the embodiment, the ceramic heater  100  for directly heating the fixing nip N is used as the heating mechanism. Alternatively, the fixing belt  101  can be heated by radiant heat from a halogen heater. Further alternatively, an IH (electromagnetic induction heating) type heating mechanism can be used to subject the fixing belt  101  to electromagnetic induction heating. In the IH type, a magnetic-flux generation mechanism, which generates magnetic flux for subjecting the fixing belt  101  to electromagnetic induction heating, serves as the heating mechanism. 
     In this way, even when any of the above-described mechanisms is used as the heating mechanism, the present invention can be applied by disposing the wire  111  near the peripheral surface of the fixing belt  101  and providing the detection unit  118  for detecting that the wire  111  is cut. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2013-056225 filed Mar. 19, 2013, which is hereby incorporated by reference herein in its entirety.