Patent Publication Number: US-11036166-B2

Title: Fixing device and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2019-168447 filed on Sep. 17, 2019. 
     BACKGROUND 
     (i) Technical Field 
     The present disclosure relates to a fixing device and an image forming apparatus. 
     (ii) Related Art 
     A fixing device having a contact thermistor has been known (see, for example, Japanese Patent Number 4673638). The contact thermistor is in contact with a surface of a heating roller and measures a surface temperature of the heating roller. The contact thermistor includes a metal plate that elastically deforms to be in contact with the heating roller, and a holder that holds the metal plate. The metal plate is provided with an element that measures the temperature on an opposite side of the metal plate to a surface that is in contact with the heating roller. 
     SUMMARY 
     Aspects of non-limiting embodiments of the present disclosure relate to preventing a decrease in measurement performance of a detector as compared with a structure in which a detector that measures a temperature of a heating member provided in a fixing device is held by a leaf spring and the detector is brought into contact with a surface of a heating member by an elastic force of the leaf spring. 
     Aspects of certain non-limiting embodiments of the present disclosure address the above advantages and/or other advantages not described above. However, aspects of the non-limiting embodiments are not required to address the advantages described above, and aspects of the non-limiting embodiments of the present disclosure may not address advantages described above. 
     According to an aspect of the present disclosure, there is provided a fixing device including: a heating member configured to transport a recording medium while nipping the recording medium with a pressure member, so as to fix a toner image onto the recording medium; a detector configured to measure a temperature of the heating member; a holding member that holds the detector; and a biasing member that biases the holding member so as to bring the detector into contact with a surface of the heating member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiment(s) of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic configuration view showing an image forming apparatus according to the present exemplary embodiments; 
         FIG. 2  is a plan sectional view showing the structure of a temperature sensor that measures a surface temperature of a heating roller of a fixing device according to a first exemplary embodiment; 
         FIG. 3  is a sectional view of the structure taken along a line X-X of  FIG. 2 ; 
         FIG. 4  is a side view showing the heating roller of the fixing device according to the first exemplary embodiment and the temperature sensor that measures the surface temperature of the heating roller; 
         FIG. 5  is a side view showing a heating roller of a fixing device according to a second exemplary embodiment and a temperature sensor that measures a surface temperature of the heating roller; 
         FIG. 6  is a bottom view showing the heating roller of the fixing device according to the second exemplary embodiment and the temperature sensor that measures the surface temperature of the heating roller; 
         FIG. 7  is a bottom view showing a heating roller of a fixing device according to a third exemplary embodiment and a temperature sensor that measures a surface temperature of the heating roller; 
         FIG. 8A  is a plan view showing a temperature sensor that measures a surface temperature of a heating roller of a fixing device according to a comparative example; and 
         FIG. 8B  is a side view showing the heating roller of the fixing device according to the comparative example and the temperature sensor that measures the surface temperature of the heating roller. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Hereinafter, an upstream side in a transport direction of a recording sheet P may be simply referred to as an “upstream side” or “upstream”, and a downstream side in the transport direction may be simply referred to as a “downstream side” or “downstream”. The recording sheet P is an example of a recording medium. It is assumed that in each figure, an arrow UP indicates an upper direction of an image forming apparatus  10 . 
     Overall Configuration 
     As shown in  FIG. 1 , the image forming apparatus  10  includes a device main body  10 A that accommodates components therein. An accommodating unit  12  that accommodates the recording sheets P, a transport unit  14  that transports the recording sheet P accommodated in the accommodating unit  12 , and an image forming unit  20  that forms a toner image on the transported recording sheet P are provided inside the device main body  10 A. 
     Further, a fixing device  40  that fixes the toner image formed on the recording sheet P by the image forming unit  20  to the recording sheet P and a controller  16  that controls the operation of each unit of the image forming apparatus  10  are provided inside the device main body  10 A. A discharge unit  18  that discharges the recording sheet P on which the image is fixed by the fixing device  40  is formed on an upper part of the device main body  10 A. 
     Image Forming Unit 
     The image forming unit  20  is disposed substantially at a center in up and down directions in the device main body  10 A. The image forming unit  20  includes an image carrier  22  that carries an image on a surface (an outer peripheral surface) thereof, a charging roller  24  that charges the surface of the image carrier  22 , and an exposure device  26  that exposes the surface of the image carrier  22  charged by the charging roller  24  to form an electrostatic latent image on the surface of the image carrier  22 . 
     The image forming unit  20  further includes a developing unit  28  that develops the electrostatic latent image formed on the surface of the image carrier  22  into a toner image with a developer, and a toner cartridge  30  that contains a developer to be supplied to the developing unit  28 . The toner cartridge  30  is detachably attached to the device main body  10 A. The image forming unit  20  includes a transfer roller  32  that transfers the toner image on the image carrier  22  to the transported recording sheet P. 
     Transport Unit 
     The transport unit  14  is disposed below the image forming unit  20  and includes plural transport rollers  36  that form the transport path  34  for the recording sheet P. The plural transport rollers  36  transport the recording sheet P delivered by a delivery roller  38 , which will be described later, to the discharge unit  18  along the transport path  34 . The transport unit  14  includes an inversion path  35  that reverses the recording sheet P and transports the reversed recording sheet P to the image forming unit  20  again in duplex printing. The reverse path  35  includes other transport rollers  36 . 
     Accommodating Unit 
     The accommodating unit  12  is disposed below the transport unit  14 , and accommodates the recording sheets P therein. The delivery roller  38  is provided in an upper part of the accommodating unit  12  and on a downstream side of the accommodating unit  12 . The delivery roller  38  delivers the recording sheets P accommodated in the accommodating unit  12  one by one from the top. The recording sheets P are delivered to the transport path  34  by the delivery roller  38 . 
     Fixing Device 
     The fixing device  40  is disposed downstream of the image forming unit  20 . The fixing device  40  includes a heating roller and a pressure roller  42 . The heating roller  44  is an example of a heating member. The heating roller  44  is disposed on an upper side of the transport path  34 . The heating roller  44  is driven to rotate. The pressure roller  42  is an example of a pressure member. The pressure roller  42  is disposed on a lower side of the transport path  34 . The pressure roller  42  is in contact with and pressed against a surface (outer peripheral surface) of the heating roller  44  with a predetermined pressure to form a nip portion. The pressure roller  42  rotates such that the pressure roller  42  follows the rotation of the heating roller. 
     A heater  43  is built in the heating roller  44  in an axial center part thereof (see  FIG. 4 ). The heating roller  44  heats the recording sheet P on which the toner image is transferred in the image forming unit  20  while transporting and nipping the recording sheet P with the pressure roller  42 , so that the toner image is fixed onto the recording sheet P. Other parts of the fixing device  40  will be described in detail later. 
     Effect of Overall Configuration 
     In the image forming apparatus  10  configured as described above, an image forming operation of forming an image on the recording sheet P will be briefly described by taking a case of single-sided printing as an example. 
     In the image forming unit  20 , the surface of the image carrier  22  is charged by the charging roller  24 . Then, the surface of the image carrier  22  is exposed by the exposure device  26 , so that the electrostatic latent image is formed on the surface of the image carrier  22 . The electrostatic latent image formed on the surface of the image carrier  22  is developed by the developing unit  28 , so that a toner image is formed on the surface of the image carrier  22 . 
     Meanwhile, the recording sheet P is delivered from the accommodating unit  12  by the delivery roller  38 . The recording sheet P delivered by the delivery roller  38  is transported along the transport path  34  formed by the plural transport rollers  36 , and is transported to a transfer position formed between the image carrier  22  and the transfer roller  32 . 
     Then, at the transfer position, the toner image formed on the surface of the image carrier  22  is transferred to the recording sheet P. The recording sheet P to which the toner image is transferred is transported to the fixing device  40 , and heated and pressed, so that the toner image is fixed to the recording sheet P. The recording sheet P on which the toner image is fixed is transported by the plural transport rollers  36  and is discharged to the discharge unit  18 . 
     First Exemplary Embodiment 
     Next, the other parts of the fixing device  40  will be described in detail. First, the fixing device  40  according to the first exemplary embodiment will be described. 
     As shown in  FIGS. 2 to 4 , the fixing device  40  includes a temperature sensor  60 , a holding member  50 , and a torsion spring  64 . The temperature sensor  60  may be a thermistor element. The temperature sensor  60  is an example of a detector. The temperature sensor  60  measures the surface temperature of the heating roller  44 . The holding member  50  holds the temperature sensor  60 . The torsion spring  64  is an example of a biasing member. The torsion spring  64  biases the holding member  50  so as to bring the temperature sensor  60  into contact with the surface of the heating roller  44 . 
     A support shaft  46  having the same axial direction as the heating roller  44  is provided above the heating roller  44 . Both axial end portions of the support shaft  46  are rotatably supported by bearing portions  47 ,  48 , respectively. The holding member  50  includes a housing  52  and a pair of arms  54 . The housing  52  is integrally provided on the outer peripheral surface of the support shaft  46 . The housing  52  has a substantially “T” shape in a plan view. The arms  54  are integrally provided at a tip end portion of the housing  52 . 
     That is, the housing  52  and the arms  54  are configured to rotate about the support shaft  46  together with the rotation of the support shaft  46 . The housing  52  and the arms  54  are made of heat-resistant resin having excellent insulation properties. Examples of the heat-resistant resin include polyphenylene sulfide (PPS) and glass fiber reinforced polyethylene terephthalate (GF-PET). 
     A pair of electrode members  56  is provided inside a pair of the arms  54 . Each electrode member  56  is made of metal such as stainless steel. A wiring harness  58  is attached to a base portion of each electrode member  56 . 
     In order to control the heat generation of the heater  43  built in the heating roller  44 , a temperature sensor  60  is provided at a tip end portion of the pair of electrode members  56 . The temperature sensor  60  is brought into contact with the surface of the heating roller  44  to measure the surface temperature of the heating roller  44 . In other words, the temperature sensor  60  for temperature control of the heating roller  44  is sandwiched between the tip end portions of the electrode members  56 . 
     The arms  54  and the electrode members  56  have the following configuration to facilitate sandwiching the temperature sensor  60  (see  FIG. 6 ). That is, each of the arms  54  and the electrode members  56  is formed in a rectangular cross-sectional shape. A longitudinal direction of the rectangular shape is identical with a contact direction along which the temperature sensor  60  is brought into contact with the surface of the heating roller  44 . A widthwise direction of the rectangular shape is identical with a sandwiching direction in which the electrode members  56  sandwich the temperature sensor  60 . 
     Further, the pair of arms  54 , the pair of electrode members  56 , and the temperature sensor  60  are covered together by one protective sheet  62 . That is, the pair of arms  54 , the pair of electrode members  56 , and the temperature sensor  60  are protected from dust and the like by the protective sheet  62 . 
     A coil portion  64 A of the torsion spring  64  is fitted to the support shaft  46 . Then, one end portion  64 B of the torsion spring  64  is hooked to one of the bearing portions  47 ,  48  (that is, the bearing portion  48 ). The other end portion  64 C of the torsion spring  64  is hooked to the housing  52 . 
     With this configuration, the temperature sensor  60  is biased via the housing  52  and the arms  54  so as to be brought into contact with the surface of the heating roller  44 . The temperature sensor  60  is brought into contact with the surface of the heating roller  44  by the torsion spring  64  with a contact pressure that is a predetermined light pressure (for example, 0.01 kgf/cm 2 ≈980 Pa or less). 
     Next, an operation of the fixing device  40  according to the first exemplary embodiment configured as described above will be described. 
     First, a fixing device  70  according to a comparative example shown in  FIGS. 8A and 8B  will be described. As shown in  FIGS. 8A and 8B , in the fixing device  70  according to the comparative example, a temperature sensor  60  that measures the temperature of a heating roller  44  is held at tip end portions of a pair of right and left leaf springs  72 . The leaf springs  72  are, for example, thin leaf springs having a thickness of about 0.10 mm to about 0.15 mm. 
     The leaf springs  72  and the temperature sensor  60  are protected by a protective sheet  62 . Base portions of the leaf springs  72  are fixed to a housing  74  provided at a predetermined position. The tip end portions of the leaf springs  72  are elastically deformed to be in contact with the surface of the heating roller  44 . That is, the temperature sensor  60  is brought into contact with the surface of the heating roller  44  by elastic force (elastic restoring force) of the leaf spring  72 . 
     During assemble of the fixing device  70  according to the comparative example, for example, the operator may touch the leaf spring  72  to thereby deform the leaf spring  72 . When the leaf spring  72  is deformed, the elastic force of the leaf spring  72  would change, and the temperature sensor  60  may not be in contact the surface of the heating roller  44  properly. That is, measurement performance of the temperature sensor  60  that measures the surface temperature of the heating roller  44  may be reduced. 
     In contrast, in the fixing device  40  according to the first exemplary embodiment, as described above, the temperature sensor  60  is brought into contact with the surface of the heating roller  44  by a biasing force of the torsion spring  64  provided on the support shaft  46 . Therefore, even if the operator touches the torsion spring  64  during assemble of the fixing device  40 , the biasing force of the torsion spring  64  does not change. 
     That is, according to the fixing device  40  of the first exemplary embodiment, the temperature sensor  60  is appropriately in contact with the surface of the heating roller  44 , and decrease in the measurement performance of the temperature sensor  60  that measures the surface temperature of the heating roller  44  is prevented as compared with the configuration according to the comparative example. Thus, deterioration of image quality caused by the decrease in the measurement performance of the temperature sensor  60  is prevented. 
     As described above, the biasing member for bringing the temperature sensor  60  into contact with the surface of the heating roller  44  includes the torsion spring  64 . Thus, the fixing device  40  is easily assembled as compared with a case where the biasing member includes the leaf spring  72  or a coil spring (not shown). Since the coil portion  64 A of the torsion spring  64  is fitted to the support shaft  46 , the torsion spring  64  is unlikely to fall off from the support shaft  46 . 
     The holding member  50  includes the pair of arms  54  that respectively support the electrode members  56  sandwiching the temperature sensor  60  at the tip end portions thereof. Therefore, insulating property between the electrode members  56  is good as compared with a case where the holding member  50  includes a single (common) arm (not shown) that supports the pair of electrode members  56 . 
     Second Exemplary Embodiment 
     Next, a fixing device  40  according to a second exemplary embodiment will be described. The same components as those in the first exemplary embodiment are denoted by the same reference numerals, and detailed descriptions thereon (including the common operation) will be omitted as appropriate. 
     As shown in  FIGS. 5 and 6 , the fixing device  40  according to the second exemplary embodiment differs from the first exemplary embodiment only in length and shape of the arms  54 . That is, the arms  54  are longer than those of the first exemplary embodiment. The arms  54  are disposed along an outer shape (surface) of the heating roller  44 . 
     Specifically, the pair of arms  54  includes a pair of first arms  54 A, a pair of second arms  54 B, and a pair of third arms  54 C (see  FIG. 5 ). When viewed from the axial direction of the support shaft  46 , the first arms  54 A project from the tip end portion of the housing  52 , the second arms  54 B are rotatably connected to tip end portions of the first arms  54 A in a frictional manner, and the third arms  54 C are rotatably connected to tip end portions of the pair of second arms  54 B in a frictional manner. 
     Therefore, when viewed from the axial direction of the support shaft  46 , each second arm  54 B may be disposed at a rotation angle such that a substantial center part of the each second arm  54 B in the longitudinal direction is close to the surface of the heating roller  44  (see  FIG. 5 ). When viewed from the axial direction of the support shaft  46 , each third arm  54 C may be disposed at a rotation angle such that the tip end portion of each third arm  54 C is close to the surface of the heating roller  44  (see  FIG. 5 ). That is, each of the second and third arms  54 B,  54 C may be disposed at any position with respect to the surface of the heating roller  44  using the rotational resistance force due to the described friction, and may maintain a posture with which (a state in which) each of the second and third arms  54 B,  54 C is disposed at the position. 
     Further, a pair of electrode members  56  (see  FIG. 2 ) is provided inside the pair of third arms  54 C. The temperature sensor  60  is sandwiched between the tip end portions of the electrode members  56 . Therefore, the protective sheet  62  in this case may be disposed so as to protect (cover) at least the pair of third arms  54 C, the pair of electrode members  56 , and the temperature sensor  60 . 
     In the second exemplary embodiment, a temperature sensor  66  (see  FIG. 6 ) different from the temperature sensor  60  is provided at the same position in a circumferential direction of the heating roller  44 . That is, the temperature sensor  66  is provided as close as possible to an upstream side of the nip portion through which the recording sheet P passes. Two heaters  43 A and  43 B are built in a shaft center part of the heating roller  44  of the second exemplary embodiment. Heat generation of the respective heaters  43 A,  43 B are individually controlled using temperature measurement by the temperature sensors  60 ,  66  which are provided separately. 
     Next, an operation of the fixing device  40  according to the second exemplary embodiment configured as described above will be described. 
     As described above, in the second exemplary embodiment, the arms  54  are longer than those of the first exemplary embodiment. The arms  54  are disposed along the surface (outer shape) of the heating roller  44 . Therefore, for example, even when (i) an installation position of the support shaft  46  is limited and (ii) the other temperature sensor  66  that measures the surface temperature of the heating roller  44  is provided at a position away from the support shaft  46 , the temperature sensor  60  may be disposed in accordance with the position of the other temperature sensor  66 . 
     Specifically, from a viewpoint of improving the accuracy of the temperature control of the heating roller  44 , the temperature sensor  60  and the temperature sensor  66  may be disposed as close as possible to the upstream side of the nip portion through which the recording sheet P passes. Therefore, when the temperature sensor  66  (one of the temperature sensors  60 ,  66 ) is disposed at a position close to the upstream side of the nip portion through which the recording sheet P passes, the temperature sensor  60  (the other of the temperature sensors  60 ,  66 ) may be disposed at the same position as the temperature sensor  66 . 
     Third Exemplary Embodiment 
     Finally, a fixing device  40  according to a third exemplary embodiment will be described. The same components as those in the first exemplary embodiment are denoted by the same reference numerals, and detailed descriptions thereon (including the common operation) will be omitted as appropriate. 
     As shown in  FIG. 7 , the fixing device  40  according to the third exemplary embodiment is different from the first exemplary embodiment only in that plural temperature sensors  60  and plural holding members  50  (each including the housing  52  and the pair of arms  54 ) are provided along the axial direction of the heating roller  44 . That is, the plural holding members  50  are provided integrally with the outer peripheral surface of one support shaft  46  and face the same direction. The holding members  50  are rotatably supported by the support shaft  46  (the holding members  50  are configured to rotate together with the rotation of the support shaft  46 ). 
     Each holding member  50  is biased by one common torsion spring  64 . Specifically, the coil portion  64 A of the torsion spring  64  is fitted only to one end portion in the axial direction of the support shaft  46 . One end portion  64 B of the torsion spring  64  is hooked only to one of the bearing portions  47 ,  48  (that is, the bearing portion  48 ; see  FIG. 2 ). The other end portion  64 C of the torsion spring  64  is hooked only to one of the housings  52  on the one end portion side in the axial direction of the support shaft  46 . 
     As shown by a phantom line in  FIG. 7 , the torsion springs  64  may be attached not only to one end portion in the axial direction of the support shaft  46  but also to the other end portion in the axial direction of the support shaft  46 . That is, the plural holding members  50  may be biased by the two common torsion springs  64  provided at both end portions in the axial direction of the support shaft  46 . 
     Next, an operation of the fixing device  40  according to a third exemplary embodiment configured as described above will be described. 
     As described above, in the third exemplary embodiment, the plural temperature sensors  60  and the plural holding members  50  (each including the housing  52  and the pair of arms  54 ) are provided along the axial direction of the heating roller  44 . Therefore, the temperature of the heating roller  44  is measured more appropriately, and the accuracy of the temperature control of the heating roller  44  is improved as compared with a configuration in which a single temperature sensor  60  and a single holding member  50  are provided along the axial direction of the heating roller  44 . 
     Further, in the third exemplary embodiment, the plural holding members  50  are biased by the one (or two) common torsion springs  64 . Therefore, as compared with a case where the plural holding members  50  are biased by the torsion springs  64  provided separately, the number of components and manufacturing cost are reduced, and the fixing device  40  is assembled easily. 
     The fixing device  40  and the image forming apparatus  10  according to the exemplary embodiments have been described with reference to the accompanying drawings. It should be noted that the fixing device  40  and the image forming apparatus  10  according to the exemplary embodiments are not limited to those shown in the drawings, but may be appropriately changed or modified without departing from the scope of the present disclosure. 
     For example, a size of the protective sheet  62  is not limited to the illustrated size. The protective sheet  62  may have a size such that the protective sheet  62  covers at least the temperature sensor  60  and the tip end portions of the electrode members  56  sandwiching the temperature sensor  60 . Further, the biasing member is not limited to the torsion spring  64 . The biasing member may be implemented by, for example, a coil spring or the like (not shown). 
     Further, in the second exemplary embodiment, the pair of arms  54  is not limited to the arms each including the three sub-arms that are rotatably connected to each other. Although not shown, each of the arms  54  may include, for example, two sub-arms or four or more sub-arms that are rotatably connected to each other. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.