Patent Publication Number: US-11662679-B2

Title: Image heating apparatus and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an image heating apparatus such as a fixing apparatus provided in an electrophotographic-recording image forming apparatus such as a copier and a printer, and a gloss applying device which improves the glossiness of a toner image fixed to a recording material by reheating the toner image. 
     Description of the Related Art 
     One form of a fixing apparatus mounted in an image forming apparatus such as a copier and a printer has a cylindrical film which transfers heat to a recording material, a heater which has a ceramic substrate having a heat-generating resistor thereon and which is provided in contact with the inner surface of the film, and a roller which forms a nip portion together with the heater via the film. The fixing apparatus has a roller driven to rotate by driving unit such as a gear provided at one end of the roller, and the film is driven to rotate while sliding on the heater. A configuration is proposed for such a fixing apparatus, in which the heat-generating region of the heater is divided into a plurality of regions in the longitudinal direction of the heater, a thermistor as a temperature detecting element is formed on the substrate for each of the heat-generating regions, and a temperature is detected for each of the heat-generating regions (Japanese Patent Application Publication No. 2017-054071). 
     SUMMARY OF THE INVENTION 
     The heater disclosed in Japanese Patent Application Publication No. 2017-054071 includes a plurality of conductors each connected to each temperature detecting element and a plurality of electric contacts connected to a plurality of conductors respectively. The plurality of electric contacts are connected to a control substrate by electric wires. When a flexible sheet such as an FPC (Flexible Printed Circuit) and an FFC (Flexible Flat Cable) is used as electric wiring for electrical connection to the plurality of electric contacts of the heater, electric wire routing can be easily carried out. Therefore, improvement of assembling of the fixing apparatus can be expected. 
     The flexible sheet may be extended from the electric contact at the heater end to the control substrate in a direction same as the longitudinal direction of the heater. However, since the driving unit is provided at one end of a roller, the driving unit has to be apart from the heater end and the flexible sheet in order to prevent the flexible sheet and the driving unit from contacting each other. In this case, the size of the fixing apparatus increases in the longitudinal direction of the heater, which may increase the size and cost of the apparatus. 
     When a support component or a heater connected with the flexible sheet is inserted into the cylindrical film, the inside of the film and the flexible sheet may come into contact with each other and can be damaged. 
     It is an object of the present invention to provide a configuration which can prevent damage to a sheet member such as a flexible sheet and a film without increasing the size of an apparatus. 
     In order to achieve the above object, an image heating apparatus for heating an image formed on a recording material, according to the present invention includes 
     a first rotating member; 
     a second rotating member provided in contact with an outer surface of the first rotating member to form a nip portion which sandwiches the recording material between the first rotating member and the second rotating member; 
     a heater unit provided inside the first rotating member and having a heater for heating the image formed on the recording material sandwiched by the nip portion; and 
     a flexible sheet member including a flexible printed circuit or a flexible flat cable provided to overlap a part of the heater and electrically connected to the heater, 
     wherein the flexible sheet member includes a first flexible sheet member connected to one end of the heater in a longitudinal direction of the heater and a second flexible sheet member connected to the other end of the heater, 
     wherein the first flexible sheet member extends from the one end of the heater in a direction crossing the longitudinal direction, and 
     wherein the second flexible sheet member extends from the other end of the heater in the longitudinal direction. 
     In order to achieve the above object, an image forming apparatus according to the present invention includes 
     an image forming portion which forms an image on a recording material, the image forming portion includes a photosensitive member, a charging device for charging the photosensitive member, a scanner unit for scanning the photosensitive member with a light in accordance with an image information, a developing device for developing an electrostatic latent image formed on the photosensitive member with toner, and a transfer unit for transferring the image to the recording material; and 
     a fixing portion which fixes an image, formed by the image forming portion, on the recording material, 
     wherein the fixing portion is the image heating apparatus according of the present invention. 
     According to the present invention, damage to a sheet member such as a flexible sheet connected to a heater and a film can be prevented without increasing the size of the apparatus. 
     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 sectional view of a general structure of an image forming apparatus to which the present invention can be applied; 
         FIG.  2    is a sectional view of a fixing nip structure according to an embodiment of the present invention; 
         FIG.  3    is a perspective view of the fixing nip structure according to the embodiment of the present invention; 
         FIGS.  4 A to  4 E  are views of a heater structure according to the embodiment of the present invention; 
         FIG.  5    is a perspective view of a heater fixed to a heater holding member; 
         FIG.  6    is a perspective view for illustrating how a heater unit is inserted into a film; and 
         FIG.  7    is a schematic perspective view of a fixing apparatus according to the embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, a description will be given, with reference to the drawings, of embodiments (examples) of the present invention. However, the sizes, materials, shapes, their relative arrangements, or the like of constituents described in the embodiments may be appropriately changed according to the configurations, various conditions, or the like of apparatuses to which the invention is applied. Therefore, the sizes, materials, shapes, their relative arrangements, or the like of the constituents described in the embodiments do not intend to limit the scope of the invention to the following embodiments. 
     First Embodiment 
     General Structure of Image Forming Apparatus 
       FIG.  1    is a view (a longitudinal section) of an exemplary electrophotographic image forming apparatus according to an embodiment of the invention. The present invention is applicable to printers and copiers based on electrophotographic and electrostatic recording methods, and an example of application of the invention to a laser printer will be described. 
     A cassette  2  is retractably stored at the lower part of a printer  1 . A manual paper feed portion  3  is provided on the right side of the printer  1 . Recording materials P are loaded and stored at the cassette  2  and the manual paper feed portion  3 . The loaded recording materials P are separated on a sheet basis and fed to resist rollers  4 . The printer  1  includes an image forming portion  5  including transversely aligned image forming stations  5 Y,  5 M,  5 C, and  5 K corresponding to yellow, magenta, cyan, and black. 
     The image forming portion  5  includes photosensitive drums  6 Y,  6 M,  6 C, and  6 K (hereinafter collectively referred to as photosensitive drums  6 ) as image bearing members and charging devices  7 Y,  7 M,  7 C, and  7 K which uniformly charge the surfaces of the photosensitive drums  6 . The apparatus also includes a scanner unit  8  which performs laser beam irradiation on the basis of image information to form an electrostatic latent image on a photosensitive drum  6 , and developing devices  9 Y,  9 M,  9 C, and  9 K which develop toner images by sticking toner to the electrostatic latent image. Primary transfer portions  11 Y,  11 M,  11 C, and  11 K (hereinafter collectively referred to as primary transfer portions  11 ) are provided to transfer the toner images on the photosensitive drums  6  to an electrostatic transfer belt  10 . The toner images transferred on the transfer belt  10  by the primary transfer portions  11  are transferred to the recording material P by a secondary transfer portion  12 . Then, when passing through a fixing apparatus (an image heating apparatus)  100  as the fixing portion (the image heating portion), the transferred images are conveyed while being sandwiched and heated between a heating unit  101  and a pressure roller  102  in pressure-contact with the heating unit  101  and fixed on the recording material P. Thereafter, the conveyance path is arbitrarily switched by a double-sided flapper  13 , and the material is conveyed to a pair of discharge rollers  14  or a pair of reverse rollers  15 . The recording material P conveyed to the side of the reverse rollers  15  is reversed and conveyed by the reverse rollers  15  in prescribed timing to pass between the resist rollers  4  and the secondary transfer portion  12  again, so that an image is formed on the backside surface of the recording material. After passing through the fixing apparatus  100 , the recording material is conveyed to the pair of discharge rollers  14 . Finally, after passing through the pair of discharge rollers  14 , the recording material P is discharged to a recording material P loading portion  16 , which completes the duplex printing. 
     Although the full-color laser beam printer having the plurality of photosensitive drums  6  is described as an exemplary image forming apparatus, the invention is also applicable to a fixing apparatus for use in a monochrome copier or printer including a single photosensitive drum  6 . 
     Fixing Apparatus 
     With reference to  FIGS.  2  and  3   , the fixing apparatus (the image heating apparatus)  100  according to the embodiment of the present invention will be described.  FIG.  2    is a schematic sectional view of the fixing apparatus  100  having the heating unit  101  and the pressure roller  102 , and  FIG.  3    is a schematic perspective view of the fixing apparatus  100 . The heating unit  101  includes a tubular film  103  as a first rotating member and a heater unit  111  in contact with the inner surface of the film  103 . 
     The heater unit  111  includes a heater  200  in contact with the inner surface of the film  103  on a sliding surface layer  207 , a heater holding member  105  which holds the heater  200 , a metal stay member  104 , and flange members  109  attached to the stay member  104  to support the opposed ends of the film in a rotatable manner. The heater  200  includes a substrate  201 , a heat-generating member provided on the surface of the substrate  201  (hereinafter referred to as the backside surface) opposite to the surface facing the film  103 , and the sliding surface layer  207  provided at the surface of the substrate  201  facing the film  103 . Heat from the heat-generating member is transferred to the film  103  through the substrate  201  and the sliding surface layer  207 . The heat-generating member includes a first heat-generating resistor  202   a  and a second heat-generating resistor  202   b.    
     The pressure roller  102  as a second rotating member has an elastic layer made for example of a metallic core portion and silicone rubber. The flange members  109  and the stay member  104  are biased toward the pressure roller  102  by pressurizing unit (not shown), and the heater holding member  105  is biased toward the pressure roller  102  by this force. 
     More specifically, the heating unit  101  is biased toward the pressure roller  102 , and the heating unit  101  and the pressure roller  102  form the fixing nip portion which sandwiches the conveyed recording material P therebetween. A driving member (gear)  108  provided at the end of the pressure roller  102  is driven to rotate by driving unit (a motor) which is not shown, so that the pressure roller  102  rotates. As the pressure roller  102  rotates, the film  103  is driven in the rotation direction R. 
     Heater 
     With reference to  FIGS.  4 A to  4 E , the feature of the heater according to the embodiment will be described.  FIG.  4 A  shows a section of the heater  200  when the heater  200  is viewed in the longitudinal direction of the heater  200  (the direction orthogonal to the direction in which the recording material P is conveyed). The heater  200  is heated by the first heat-generating resistor  202   a  and the second heat-generating resistor  202   b  provided at a current-passing layer on the ceramic substrate  201 , the longitudinal direction of which is orthogonal to the direction in which the recording material P is conveyed. The current-passing layer is provided with a first conductor  203  and a second conductor  204  in the longitudinal direction of the heater. The first conductor  203  branches into  203   a  and  203   b  respectively upstream and downstream of the direction in which the recording material P is conveyed. The second conductor  204  is provided between the first heat-generating resistor  202   a  and the second heat-generating resistor  202   b.    
     An insulating protection layer  206  covering the two heat-generating resistors  202   a  and  202   b  and the conductors  203  and  204  is provided at the backside surface of the heater  200 . The sliding surface layer  207  of a coating for example of glass or polyimide having high slidability is provided on the sliding surface side (on the side of the surface opposed to the film  103 ) of the heater  200  on which the heater  200  and the film  103  slide on each other. 
       FIGS.  4 B,  4 C, and  4 D  are plan views of the layers (the protection layer in  FIG.  4 B , the current-passing layer in  FIG.  4 C , and the sliding surface layer in  FIG.  4 D ) of the heater  200 . A plurality of heat-generating blocks including the second conductor  204 , the first heat-generating resistor  202   a , and the second heat-generating resistor  202   b  are arranged in the longitudinal direction of the heater  200  in the current-passing layer of the heater  200 . The heater  200  according to the embodiment has five heat-generating blocks in total in the longitudinal direction of the heater  200 . 
     A first heat-generating block  202 - 1  includes a first heat-generating resistor  202 - 1   a  and a second heat-generating resistor  202 - 1   b  formed symmetrically with respect to the transverse direction of the heater  200 , a conductor  204 - 1  as a part of the second conductor  204 , and an electrode  205 - 1  which will be described. The second to fifth heat-generating blocks  202 - 2  to  202 - 5  are similarly formed. 
     The first conductor  203  is provided in the longitudinal direction of the heater  200  and includes the conductors  203   a  and  203   b . The conductor  203   a  is connected to the first heat-generating resistors  202 - la ,  202 - 2   a ,  202 - 3   a ,  202 - 4   a , and  202 - 5   a  of the heat-generating blocks. The conductor  203   b  is connected to the second heat-generating resistors  202 - 1   b ,  202 - 2   b ,  202 - 3   b ,  202 - 4   b , and  202 - 5   b  of the heat-generating blocks. 
     Here, the conductor  203   a  as the first conductor electrically connects electrodes  205 C 1  and  205 C 2  and the upper ends of the first heat-generating resistors  202 - la  to  202 - 5   a  shown in  FIG.  4 C  in the heat-generating blocks. The conductor  203   b  as the second conductor electrically connects the electrodes  205 C 1  and  205 C 2  and the lower ends of the second heat-generating resistors  202 - 1   b  to  202 - 5   b  shown in  FIG.  4 C  in the heat-generating blocks. The second conductor  204  is divided into five conductors  204 - 1 ,  204 - 2 ,  204 - 3 ,  204 - 4 , and  204 - 5  connected to the corresponding heat-generating blocks. The conductors  204 - 1  to  204 - 5  electrically connect electrodes  205 - 1  to  205 - 5  shown in  FIG.  4 B  and the lower ends of the first heat-generating resistors  202 - la  to  202 - 5   a  shown in  FIG.  4 C . Similarly, the conductors  204 - 1  to  204 - 5  electrically connect the electrodes  205 - 1  to  205 - 5  and the upper ends of the second heat-generating resistors  202 - 1   b  to  202 - 5   b  shown in  FIG.  4 C . 
     The electrodes  205 C 1 ,  205 C 2 ,  205 - 1 ,  205 - 2 ,  205 - 3 ,  205 - 4 , and  205 - 5  are provided on the same surface as the surface provided with the protection layer in order to supply power to the first heat-generating resistor  202   a  and the second heat-generating resistor  202   b . The electrodes  205 C 1 ,  205 C 2 , and  205 - 1  to  205 - 5  are provided and exposed at openings in the protection layer  206  shown in  FIG.  4 B . The electrode  205 C 1  as a first electric contact portion is provided near a longitudinal end of the substrate, and the electrode  205 C 2  as a second electric contact portion is provided near the other longitudinal end of the substrate. The electrodes  205 C 1  and  205 C 2  are common electrodes for supplying power to the five heat-generating blocks  202 - 1  to  202 - 5  through the conductors  203   a  and  203   b . The electrodes  205 - 1  to  205 - 5 , on the other hand, are electrodes for supplying power to the corresponding heat-generating blocks  202 - 1  to  202 - 5 . The electrodes  205 - 1  to  205 - 5  provided between the electrodes  205 C 1  and  205 C 2  correspond to third electric contact portions in the heat-generating blocks. A contact member  300  connected to the power supply is allowed to contact the electrodes  205 - 1  to  205 - 5  for conduction to supply power to the first to fifth heat-generating blocks connected in parallel to the conductor  203   a  and the conductor  203   b . The terminals of power supply connectors  106   a  are in contact with the electrodes  205 C 1  and  205 C 2  (see  FIGS.  6  and  7   ). 
     When the power supply ratio to the divisional heat-generating blocks  202 - 1  to  202 - 5  of the heater  200  is varied, the temperature increase at the ends of a non-passing region may be reduced depending on the width size of the recording material P. For example, when fixing is performed to a recording sheet having a width corresponding to the heat-generating block  202 - 3 , power supplied to the heat-generating block  202 - 3  is maintained, and power supplied to the other heat-generating blocks is lowered, so that the temperature increase at the ends of the non-passing region may be reduced. 
     Temperature Detection Configuration 
     With reference to  FIG.  4 D , the feature of the temperature detection configuration according to the embodiment will be described. At the sliding surface layer of the heater  200 , thermistors Tp 1  to Tp 5  and Ts 1  to Ts 5  as temperature detecting elements are provided in the heat-generating blocks. These thermistors each detect the temperature of a corresponding heat-generating block, and power supplied to the heat-generating blocks is controlled. A conductor connected to each of the thermistors is also formed at the sliding surface layer of the heater  200 . Conductors EG 1  and EG 2  are connected to the thermistors Tp 1  to Tp 5  and Ts 1  to Ts 5  on one end side and to the ground potential of the thermistor temperature detecting unit of the control circuit. Conductors ET 1  to ET 5  are connected to the thermistors Ts 1  to Ts 5 , respectively and are formed to extend to the longitudinal ends of the heater  200 . A conductor EP 1  is connected to the ends of the thermistor Tp 1  to Tp 5  which are not connected to the conductor EG 1 . A protection glass is formed at the sliding surface layer  207  excluding the longitudinal ends of the heater  200 . A part of each of the conductors not covered by the protection glass serves as an electrode which connects to a flexible sheet  107  as a sheet member.  FIG.  4 E  shows the flexible sheet  107  bonded to electrodes at the ends of the heater. Conductor patterns EF 1  and EF 2  identical to the conductors connected to the thermistors are formed at the flexible sheet  107 , and the flexible sheet  107  is soldered to the contacts at the heater ends to overlap a part of the heater (solder joints EJ 1  and EJ 2 ). 
     Extending Direction of Flexible Sheet Bonded to Heater Now, the direction in which the flexible sheet  107  bonded to the heater  200  extends as the feature of the embodiment will be described. 
     As shown in  FIG.  3   , the flexible sheet  107  bonded to the heater  200  includes a flexible sheet  107 A as a first sheet member on the side with the driving gear (hereinafter referred to as the driving side) and a flexible sheet  107 B as a second sheet member on the opposite side (hereinafter referred to as the anti-driving side). The flexible sheet  107 A on the driving side is electrically connected to one end side of the heater  200  in the longitudinal direction. More specifically, the flexible sheet  107 A is arranged to overlap a part of one end of the heater  200  and electrically connected to one end of the heater  200  and extends from the end in a direction substantially orthogonal to the longitudinal direction of the heater. The flexible sheet  107 B on the anti-driving side is electrically connected to the other end of the heater  200  in the longitudinal direction. More specifically, the flexible sheet  107 B is arranged to overlap a part of the other end of the heater  200  and electrically connected to the other end of the heater  200  and extends from the other end in the same direction as the longitudinal direction of the heater. Since the heater  200  is in the vicinity of the pressure roller  102  through the film  103 , the flexible sheet  107 A on the driving side may contact the driving gear  108  when the sheet extends in the longitudinal direction of the heater. In order to extend the flexible sheet  107 A on the driving side in the heater longitudinal direction, if the driving gear  108  is provided apart from the heater  200  and the flexible sheet  107  to avoid contact with the sheet, the size of the apparatus can be increased. 
     Therefore, the flexible sheet  107 A on the driving side extends in a direction crossing the longitudinal direction of the heater. According to the embodiment, the flexible sheet  107 A on the driving side is extended substantially orthogonally to the longitudinal direction, but similar effects can be obtained by other kinds of arrangement. More specifically, the extending direction of the flexible sheet  107 A on the driving side may be changed for an angle different from the right angle with respect to the longitudinal direction of the heater. For example, the flexible sheet  107  may be configured to extend in a direction which crosses the heater  200  as appropriate so that the sheet does not contact the driving gear  108 . 
       FIG.  5    is a top view of the heater  200  fixed to the heater holding member  105 . When the heater  200  is misaligned with respect to the recording material P, the heating region by the heating unit  101  is misaligned with respect to the toner image on the recording material P, and a part of the toner image cannot be fixed. When the relative positions of the heating region and the recording material P are misaligned, a temperature difference occurs between the opposed ends of the pressure roller, and the recording material P cannot be stably conveyed. Therefore, the heater  200  is held in the heater holding member  105  while being abutted against abutment portions  105   a ,  105   b , and  105   c  provided at the heater holding member  105  at three locations, i.e., the downstream ends in the conveying direction at the opposed ends of the heater in the heater longitudinal direction and the heater end on the driving side in the heater longitudinal direction. Also, a silicone rubber heat resistant adhesive is applied between the backside surface of the heater and the heater holding member  105  to secure the heater  200  to the heater holding member  105 . During the manufacture of the apparatus, when the heater abutment portions  105   a ,  105   b , and  105   c  are covered with the flexible sheet  107 , the abutment portions  105   a ,  105   b , and  105   c  may not be visible and the heater  200  may not be surely abutted against the heater holding member  105 . Therefore, the heater  200  is abutted against the abutment portion  105   c  so that the abutment portion  105   a  is not covered with the flexible sheet  107 . The heater  200  is abutted against the abutment portion  105   c  to ensure at least positioning of the heating region in the longitudinal direction of the heater. 
       FIG.  6    is a schematic view for illustrating how the internal components of heater unit  111  are inserted into the film  103 . When the heating unit  101  is assembled, the internal components such as the heater  200  attached with the flexible sheet  107 , the heater holding member  105 , and the stay member  104  are inserted into the inside part (the inner tubular part) of the film  103 . At the time, when it is attempted to insert the internal components into the film  103  from the flexible sheet  107 A on the driving side extending in a direction crossing the longitudinal direction of the heater, the flexible sheet  107 A on the driving side must be bent to fit into the cross-sectional area of the inside part of the film  103 . In the case, the film  103  and the flexible sheet  107 A may be creased and damaged. Therefore, the internal components are preferably inserted into the film  103  starting from the flexible sheet  107 B on the anti-driving side extending in the longitudinal direction of the heater. Since the longitudinal direction of the film  103  and the direction in which the flexible sheet  107 B on the anti-driving side extends are the same, the flexible sheet  107 B can be inserted along the cylindrical shape of the film  103  without causing damage or the like. 
     As shown in  FIG.  7   , the heating unit  101  having the heater unit  111  inserted in the film  103  and the pressure roller  102  are mounted to a frame  100   a  of the fixing apparatus  100 . The flexible sheets  107 A and  107 B each extending toward the driving and the anti-driving sides are electrically connected to an electrical substrate  110  provided at the frame  100   a.    
     As in the foregoing, the flexible sheet  107 A on the driving side extends in a direction crossing the longitudinal direction of the heater in order to prevent contact between the sheet and the driving gear  108  and to surely fix the heater  200  to the heater holding member  105  by abutment. The flexible sheet  107 B on the anti-driving side extends in the longitudinal direction of the heater to prevent damage during insertion into the film  103 . In this way, the apparatus can be reduced in size without damaging the components during assembly of the fixing apparatus. 
     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. 2020-079239, filed on Apr. 28, 2020, which is hereby incorporated by reference herein in its entirety.