Patent Publication Number: US-8971735-B2

Title: Image heating apparatus configured to detect breakages of lateral end portions of an endless belt

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image heating apparatus configured to heat a toner image on a sheet. The image heating apparatus may be used, for example, in an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction peripheral having a plurality of functions of those apparatuses. 
     2. Description of the Related Art 
     Conventionally, there has been proposed a fixing apparatus (image heating apparatus) configured to fix a toner image formed on a sheet by using a heating belt (endless belt). 
     In the fixing apparatus, repetitive bending of the heating belt may cause a fatigue failure of the heating belt, or some accident may cause a breakage of a lateral end portion of the heating belt (partial breakage may occur from the lateral end portion to a lateral inner side of the heating belt). In case such a breakage occurs in the heating belt, the breakage needs to be immediately detected. 
     In view of such circumstances, Japanese Patent Application Laid-Open No. 2011-33832 discloses a belt position detecting device for belt lateral movement control, which is provided at one lateral end of the heating belt and configured to detect a breakage on the one lateral end of the heating belt. Furthermore, a breakage on the other lateral end of the heading belt is detected by using the belt position detecting device. To this end, a link mechanism extending from the one lateral end to the other lateral end of the heating belt is provided on the side of the outer surface of the heating belt. 
     With this, in the image heating apparatus described in Japanese Patent Application Laid-Open No. 2011-33832, the breakages of the heating belt can be properly detected. 
     However, in an apparatus structure in which a large installation space cannot be secured on the side of the outer surface of the heating belt, it is difficult to employ the belt breakage detecting mechanism described in Japanese Patent Application Laid-Open No. 2011-33832. 
     SUMMARY OF THE INVENTION 
     The present invention provides an image heating apparatus configured to easily detect breakages of lateral end portions of an endless belt without requiring a large installation space on the side of an outer surface of the endless belt. 
     According to an exemplary embodiment of the present invention, there is provided an image heating apparatus including: (i) an endless belt configured to heat a toner image on a sheet; (ii) a heating device configured to heat the endless belt; (iii) an electric power source configured to supply electric power to the heating device; (iv) a fuse configured to shut off the electric power supplied to the electric power source; and (v) a detecting mechanism configured to detect a breakage of one lateral end of the endless belt, the detecting mechanism including, (v-i) a rocking arm configured to rock about a rocking center and be electrically grounded; (v-ii) an urging member configured to urge the rocking arm to cause one end of the rocking arm to contact to an inner surface, adjacent to the one lateral end, of the endless belt; and (v-iii) an electric element provided between the electric power source and the fuse and configured to contact to the other end of the rocking arm with displacement of the one end of the rocking arm toward an outer side of the endless belt with respect to the endless belt. 
     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 structural view of an image forming apparatus according to a first embodiment. 
         FIG. 2  is a structural view of an image heating apparatus according to the first embodiment. 
         FIG. 3  is a perspective view of a belt lateral movement control mechanism according to the first embodiment. 
         FIG. 4A  is a perspective view of a belt lateral movement detecting sensor portion according to the first embodiment. 
         FIG. 4B  is a table showing control operations in response to signals from the belt lateral movement detecting sensor portion. 
         FIG. 4C  is a structural view of another belt lateral movement detecting sensor portion according to the first embodiment. 
         FIG. 5  is a flowchart illustrating lateral movement control on a heating belt according to the first embodiment. 
         FIG. 6A  is a perspective view of a belt failure detecting mechanism according to the first embodiment. 
         FIG. 6B  is a block diagram illustrating how heating is stopped in response to detection of a belt failure. 
         FIG. 7A  is a view illustrating a state of the belt failure detecting mechanism during a normal operation. 
         FIG. 7B  is a view illustrating a state of the belt failure detecting mechanism at the time of the belt failure. 
         FIG. 8  is a view illustrating a state of a belt failure detecting mechanism according to a second embodiment during a normal operation. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     First Embodiment 
     A first embodiment of the present invention will be described in detail with reference to the drawings.  FIG. 1  is a structural view of an image forming apparatus having an image heating apparatus mounted thereto according to the first embodiment. 
     As illustrated in  FIG. 1 , an image forming apparatus  1  according to the embodiment includes four image forming portions U (UY, UM, UC, and UK) corresponding to yellow (Y), magenta (M), cyan (C), and black (K), respectively. In each of the image forming portions U, a photosensitive drum (image bearing member)  2  charged by a charging roller  3  is subjected to exposure with a laser beam emitted from a laser scanner  4  according to image information output from an external host device  23 . In this way, an electrostatic latent image is formed on the photosensitive drum  2 . 
     The electrostatic latent image thus formed is developed into a toner image of corresponding one of the colors by a developing device  5  with a toner of the corresponding one of the colors. The formed toner images of the corresponding colors are transferred onto an intermediate transfer belt  8  by corresponding primary transfer rollers  6 . In this way, a full-color toner image is formed on the intermediate transfer belt  8 . 
     Meanwhile, sheets (recording materials) S stored in cassettes  15  and  16  are each conveyed through a conveying path  17  by feed roller pairs  11 , conveyer roller pairs  12 , and a registration roller pair  18  toward a nip portion (secondary transfer portion) between the intermediate transfer belt  8  and a secondary transfer roller (transfer unit)  14 . The sheet S conveyed to the secondary transfer portion is subjected to secondary transfer of the full-color toner image, and conveyed to a fixing apparatus (image heating apparatus)  100  through a conveying path  19 . The fixing apparatus  100  heats and pressurizes the sheet S so as to fix the full-color toner image to the sheet S, and discharges the sheet S onto a discharge tray  21  through a discharge roller pair  20 . 
     (Fixing Apparatus  100 ) 
       FIG. 2  is a structural view of the fixing apparatus  100  having a function of the image heating apparatus. As illustrated in  FIG. 2 , the fixing apparatus  100  includes a heating unit A, a pressure unit B, and an IH heater (heating mechanism)  170 . The heating unit A includes a heating belt (endless belt)  105  and a plurality of support rollers configured to support the heating belt  105  in a rotatable manner from an inner surface thereof, that is, a fixing roller  131  and a tension roller  132 . The IH heater  170  includes an exciting coil configured to heat the heating belt  105  with induction heating. The pressure unit B includes an endless pressure belt  120 , and a pressure roller  121  and a tension roller  122  over which the pressure belt  120  passes. 
     A driving mechanism M ( FIG. 2 ) including a motor and a gear train drives and rotates the fixing roller  131  so as to rotate the heating belt  105 . Further, the pressure belt  120  is rotated by the rotation of the heating belt  105 . 
     The heating belt  105  is liable to be laterally moved (belt lateral movement) to one side or the other side in a lateral direction orthogonal to a sheet conveying direction V during a rotation process thereof. Similarly, the pressure belt  120  which is caused to press-contact to the heating belt  105  so as to form a fixing nip portion N is also liable to be laterally moved. 
     As a countermeasure, in the embodiment, as described below, there is provided a belt lateral movement control mechanism configured to regulate a travel range in the lateral direction of the heating belt  105  to fall within a predetermined zone. Note that, although not described, the pressure belt  120  also includes a similar belt lateral movement control mechanism. 
     (Belt Lateral Movement Control Mechanism) 
       FIG. 3  is a perspective view of the belt lateral movement control mechanism.  FIG. 4A  is a perspective view of a belt lateral movement detecting sensor portion (detecting device)  150 .  FIG. 4B  is a table showing the relationships between a lateral position of an end surface of the heating belt  105  and ON/OFF signals output from sensors  150   a  and  150   b , and how to control the position of the end surface of the heating belt  105 . 
     As illustrated in  FIG. 3 , at one lateral end of the heating belt  105  of the heating unit A, as the belt lateral movement control mechanism, there are provided a stepping motor  155 , a worm  157 , a worm wheel  152 , a fork plate  161 , a pin  151 , and a support arm  154 . 
     Further, the heating unit A also includes the belt lateral movement detecting sensor portion  150  (refer to  FIG. 4A ) provided at the one lateral end of the heating belt  105 . 
     As illustrated in  FIG. 4A , the sensor portion  150  includes two sensors  150   a  and  150   b , a sensor flag  150   c , a sensor arm  150   d , and a sensor spring  150   e . The sensor spring  150   e  generates an urging force to press and cause the sensor arm  150   d  to contact the end surface of the heating belt  105  (one lateral end of the belt). With this, the sensor arm  150   d  is operated in association with the movement in the lateral direction of the heating belt  105 . 
     When the sensor arm  150   d  is moved in the belt lateral direction by the heating belt  105 , the sensor flag  150   c  pivots to a position at which the sensor flag  150   c  turns ON and OFF the sensors  150   a  and  150   b . Based on combinations of ON/OFF signals of each of the sensors  150   a  and  150   b , the position in the belt lateral direction of the sensor arm  150   d  is detected. In this way, the position of the heating belt  105  is detected. 
     A signal representing a position of an end portion of the heating belt  105  (position of the laterally moved belt), which is detected by the sensor portion  150 , is sent to a control portion (controller)  10  (refer to  FIG. 1 ). 
     As shown in  FIG. 4B , based on detection results of the position of the end portion of the heating belt  105 , the control portion  10  rotates the stepping motor  155  in a forward rotation direction (CW) or a reverse rotation direction (CCW) by a predetermined number of revolutions. With this, through intermediation of the worm  157 , the worm wheel  152 , the fork plate  161 , and the pin  151 , the support arm  154  is pivoted (displaced) by a predetermined control amount in an upward direction or a downward direction about a shaft  131   a  of the fixing roller  131 . 
     This causes a shaft  132   a  of the tension roller  132  to move upward or downward, and inclination in the lateral direction of the tension roller  132  varies. As a result, the heating belt  105  is moved in the lateral direction. In this way, lateral movement control of the heating belt  105  is performed. 
     In the embodiment, the lateral movement of the heating belt  105  is stabilized within a predetermined lateral movement range by the swing type lateral movement control. Specifically, the swing type lateral movement control causes the tension roller  132  to be inclined in a direction opposite to a lateral movement direction of the heating belt  105  when the sensor portion  150  detects that the belt position is moved from a lateral central portion by a predetermined amount or more. 
     Repetition of the swing type lateral movement control causes the heating belt  105  to be periodically moved from one lateral side to the other lateral side, and hence the lateral movement of the heating belt  105  can be stably controlled. In other words, the heating belt  105  is reciprocable in the lateral direction orthogonal to the conveying direction V of the sheet S. 
     Note that, a transmission type non-contact sensor  196  illustrated in  FIG. 4C  may be provided instead of the belt lateral movement detecting sensor portion  150  so as to detect the lateral position of the end surface of the heating belt  105 . 
       FIG. 5  is a flowchart illustrating the lateral movement control on the heating belt  105 . As shown in  FIGS. 4B and 5 , in a case where a meandering motion of the heating belt  105  in a central area (S 1 ) occurs, when the sensor  150   a  is turned OFF and the sensor  150   b  is turned ON (S 2 ), a position of +1.0 mm from a central position to a far side is detected. In response to a signal of the detection result, the stepping motor  155  is driven in the clockwise (CW) direction so as to incline the tension roller  132  at an angle of −2° to the fixing roller  131  (S 3 ). In other words, the tension roller  132  is displaced. 
     In contrast, when the sensor  150   a  is turned ON and the sensor  150   b  is turned OFF (S 2 ), a position of −1.0 mm from the central position to a near side is detected. Then, the stepping motor  155  is driven in the counterclockwise (CCW) direction so as to incline the tension roller  132  at an angle of +2° to the fixing roller  131  (S 3 ). With this, the heating belt  105  is moved in a direction in which the heating belt  105  returns to the central area. In this way, the lateral movement control is performed. 
     When the end surface of the heating belt  105  is moved to a position of +3 mm from the central position or a position of −3 mm from the central position and the lateral movement control is lost, both the sensors  150   a  and  150   b  are turned OFF (S 4 ). Simultaneously, the image forming apparatus  1  determines that some abnormality, such as breakage of the lateral end portion of the heating belt  105 , has occurred (S 5 ), and stops heating in the fixing apparatus  100  and the rotation of the heating belt  105  (S 6 ). In other words, based on outputs from the sensors  150   a  and  150   b , the control portion (controller)  10  stops supply of an electric power to the IH heater (heating mechanism)  170  and the supply of an electric power to the driving mechanism M ( FIG. 2 ) configured to drive and rotate the heating belt  105 . As a result, in accordance with the stopping of the rotation of the heating belt  105 , the rotation of the pressure belt  120  to be rotated by the rotation of the heating belt  105  is also stopped. 
     (Detection of Failure of Heating Belt  105 ) 
       FIG. 6A  is a perspective view of a belt failure detecting mechanism  190  according to the embodiment.  FIG. 6B  is a block diagram illustrating how heating is stopped in response to detection of a belt failure. 
     In the embodiment, a failure (breakage) of the one lateral end of the heating belt  105  can be detected by the belt lateral movement control mechanism described above. As a counterpart, a detecting mechanism configured to detect a failure (breakage) of the other lateral end of the heating belt  105  is required. In view of the circumstance, as illustrated in  FIG. 6A , the belt failure detecting mechanism  190  configured to detect the failure of the other lateral end of the heating belt  105  is provided at the other lateral end of the heating belt  105 . 
     The belt failure detecting mechanism  190  includes a rocking arm (arm member)  191  electrically connected to a ground contact portion G, an arm end portion  191   a , a pivot shaft  192 , an abutment member  193 , an urging member  194 , and a detection switch  195 . The rocking arm  191  is pivotable (rockable) about the pivot shaft (rocking center)  192 . The arm end portion  191   a  is provided at one end of the rocking arm  191 , and the abutment member  193  is provided at the other end of the rocking arm  191 . 
     The rocking arm  191 , the arm end portion  191   a , and the pivot shaft  192  are each formed of a conductive member such as SUS. The abutment member  193  contacts to an inner surface of the heating belt  105  and is rotated by the rotation of the heating belt  105 . Rotary members excellent in smoothness and rollability, such as a rotatable member made of tetrafluoroethylene (PFA) and a bearing are desirable as the abutment member  193 . In the embodiment, a PFA rotatable member having a diameter of 3 mm is used. 
     The urging member  194  is a compression spring, and urges the abutment member  193  against the inner surface of the heating belt  105  with a force of 100 gf. The detection switch (electric element, or excessive temperature rise preventing element)  195  is a (bimetallic) thermostat switch. As illustrated in  FIG. 6B , an electric power is supplied from a main electric power source  168  to an IH electric power source  171  via a current fuse  169  and the detection switch  195 . The IH electric power source  171  activates the IH heater  170 . 
       FIG. 7A  is a view illustrating a state of the belt failure detecting mechanism  190  during a normal operation.  FIG. 7B  is a view illustrating a state of the belt failure detecting mechanism  190  at the time of the belt failure. 
     As illustrated in  FIG. 7A , during the normal operation in which the failure or an abnormality of excessive lateral movement of the heating belt  105  does not occur, the end portion of the heating belt  105  is located on an outside of a heat generating area of the IH heater  170 . In other words, none of the fixing roller  131  and the tension roller  132  is exposed in the heat generating area of the IH heater  170 . During the normal operation, the rocking arm  191  is located at a first urging position, and the urging member  194  holds the abutment member  193  in contact with the inner surface of the heating belt  105 . Meanwhile, the arm end portion  191   a , which is electrically grounded, does not contact to the detection switch  195 . 
     In other words, as long as the arm end portion  191   a  is located at the first urging position, the detection switch  195  and the ground contact portion G are kept out of contact with each other, and the electric power continues to be supplied from the IH electric power source  171 . In this way, the IH heater  170  is operated. 
     Meanwhile, as illustrated in  FIG. 7B , when the failure or the abnormality of excessive lateral movement of the heating belt  105  occurs, the end portion of the heating belt  105  comes into the heat generating area of the IH heater  170 . In other words, the fixing roller  131  or the tension roller  132  is exposed in the heat generating area of the IH heater  170 . In this state, the abutment member  193  cannot contact the heating belt  105  so that the abutment member  193  is pushed up by the urging member  194 . In this way, the rocking arm  191  pivots about the pivot shaft  192  up to a second urging position, and the arm end portion  191   a , which is electrically grounded, contacts the detection switch  195 . In other words, one end of the rocking arm  191 , specifically, the abutment member  193 , shifts to the side of an outer surface of the heating belt  105  with respect to the heating belt  105 , and the other end of the rocking arm  191 , specifically, the arm end portion  191   a , contacts the detection switch  195 . 
     As long as the arm end portion  191   a  is located at the second urging position, the arm end portion  191   a  connected to the ground contact portion G is held in contact with the detection switch  195  and remains short-circuited. As a result, the supply of the electric power to the IH electric power source  171  is stopped, and hence the operation of the IH heater  170  is stopped. Specifically, when the arm end portion  191   a  contacts the detection switch  195 , the current fuse  169  provided to the fixing apparatus  100  is blown. In this way, heating of the image heating apparatus  100  can be stopped. Further, in a circuit configuration of the embodiment, when the current fuse  169  is blown, the supply of the electric power from the IH electric power source  171  to the driving mechanism M for the heating belt  105  is also automatically shut off. In other words, the rotation of the pressure belt  120  to be rotated by the rotation of the heating belt  105  is also stopped. 
     According to the embodiment, even when a large installation space cannot be secured on the outer surface of the heating belt  105 , the breakage of each of the lateral end portions of the heating belt  105  can be easily detected. 
     Further, the belt failure detecting mechanism  190  of the embodiment is provided with a safeguard independent of a CPU of the control portion  10 . Thus, even in case the CPU fails and loses control, the heating of the fixing apparatus  100  and the rotation of the heating belt  105  can be stopped. 
     Second Embodiment 
     Next, an image heating apparatus and an image forming apparatus according to a second embodiment of the present invention will be described with reference to the drawings. The same parts as those described above in the first embodiment are denoted by the same reference symbols, and description thereof is omitted.  FIG. 8  is a view illustrating a state of belt failure detecting mechanisms  190  and  190 B according to the embodiment during a normal operation. 
     As illustrated in  FIG. 8 , the fixing apparatus  100  as the image heating apparatus of the embodiment is different from the fixing apparatus  100  of the first embodiment described above in that a belt failure detecting mechanism  190 B is provided instead of the belt lateral movement detecting sensor portion  150 . 
     Similarly to the belt failure detecting mechanism  190  of the first embodiment described above, the belt failure detecting mechanism  190 B includes the rocking arm  191 , the arm end portion  191   a , the pivot shaft  192 , the abutment member  193 , and the urging member  194 , and detects a failure of the other end of the heating belt  105 . The belt failure detecting mechanisms  190  and  190 B detect failures of both the lateral end portions of the heating belt  105 , respectively. With this, states of both the lateral ends of the heating belt  105  can be detected. 
     According to the embodiment, even when a large installation space cannot be secured on the side of the outer surface of the heating belt  105 , the breakage of each of the lateral end portions of the heating belt  105  can be easily detected. 
     The components of the image heating apparatus of the present invention, which are described above in each of the first embodiment and the second embodiment, may be replaced with various other known components within the spirit of the present invention. 
     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. 2012-097326, filed Apr. 23, 2012, which is hereby incorporated by reference herein in its entirety.