Patent Publication Number: US-8112022-B2

Title: Fixing device, image forming apparatus, and image fixing method capable of stably applying oil for fixing without adhering oil to sheet

Description:
PRIORITY STATEMENT 
     The present patent application claims priority from Japanese Patent Application No. 2008-120434, filed on May 2, 2008, in the Japan Patent Office, the entire contents of which are hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Example embodiments generally relate to a fixing device, an image forming apparatus, and an image fixing method, and more particularly, to a fixing device, an image forming apparatus including the fixing device, and an image fixing method for fixing a toner image on a recording medium. 
     2. Description of the Related Art 
     Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium (e.g., a sheet) according to image data using electrophotography. Thus, for example, a charger uniformly charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner particles to the electrostatic latent image formed on the image carrier to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a sheet or is indirectly transferred from the image carrier onto a sheet via an intermediate transfer member; a cleaner then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the sheet; finally, a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image on the sheet, thus forming the image on the sheet. 
     In such image forming apparatuses, oil is applied to a fixing member of the fixing device, which contacts the toner image on the sheet, to separate toner particles forming the toner image from the fixing member and to maintain fixing property, or the ability of the fixing member to fix the toner image on the sheet. Understanding the way in which the oil is applied requires a detailed discussion of the structure of a typical conventional fixing device. 
     In order to shorten a warm-up time period of the fixing device, an endless fixing belt is often used as the fixing member.  FIG. 1  is a sectional view of a fixing device  100 RA including just such an endless fixing belt. 
     As can be seen in  FIG. 1 , the fixing device  100 RA loops an endless fixing belt  92  around a fixing roller  84  and a heating roller  83  in such a manner that the fixing roller  84  and the heating roller  83  apply a reference tension to the fixing belt  92 . A pressing roller  85  rotates and presses against the fixing belt  92  and the fixing roller  84  to form a fixing nip portion AR between the fixing belt  92  and the pressing roller  85 . A heater  86  is disposed inside the heating roller  83 , and heats the fixing belt  92  via the heating roller  83 . Similarly, a second, separate heater  87  is disposed inside the pressing roller  85 , and heats the pressing roller  85 . The fixing belt  92  and the pressing roller  85  apply heat and pressure to a sheet bearing a toner image at the fixing nip portion AR to fix the toner image on the sheet. 
     An oil application roller R 1  serves as an oil applier for applying oil to the fixing belt  92 . For example, the rotating oil application roller R 1  applies oil supplied from an oil supplier to the fixing belt  92  at a contact point  95  at which the oil application roller R 1  contacts the fixing belt  92 . The rotating fixing belt  92  moves an oiled portion of the fixing belt  92  to which oil is applied to the fixing nip portion AR to separate the sheet bearing the toner image from the fixing belt  92 . At the fixing nip portion AR, a part of the oil on the fixing belt  92  moves from the fixing belt  92  onto a surface of the pressing roller  85  to separate the sheet bearing the toner image from the pressing roller  85 . Surplus oil carried on the pressing roller  85  then flows into an oil pan  96  provided under the pressing roller  85 , and is collected by the oil pan  96 . 
     However, not enough oil may adhere to the pressing roller  85 , and consequently a sheet bearing a fixed toner image may not separate cleanly from the pressing roller  85 . For example, when a plurality of sheets continuously passes through the fixing nip portion AR, oil can only move from the fixing belt  92  onto the pressing roller  85  during an interval between successive sheets, resulting in a shortage of oil. 
     To prevent or reduce such shortage of oil on the pressing roller  85 , another oil applier may be provided for the pressing roller  85  to apply oil to the pressing roller  85 . However, the oil thus applied to the pressing roller  85  may adhere to a foremost sheet fed into the fixing device  100 RA immediately after the fixing device  100 RA is driven. 
     On the other hand, gravity can easily cause a sheet passing through the fixing nip portion AR to adhere to or wrap around the pressing roller  85  at an exit side of the fixing nip portion AR. 
     To address these problems, another related-art fixing device  100 RB includes an oil applier R 3  for applying oil to the pressing roller  85  by directly contacting the pressing roller  85 , as illustrated in  FIG. 2 . However, the oil applier R 3  may not apply an amount of oil sufficient to form a toner image at high linear speed or to separate coated paper, which absorbs oil easily, from the pressing roller  85 . Moreover, it is difficult to locate an oil applier capable of applying a substantial amount of oil to the pressing roller  85  at a position above the pressing roller  85  due to limited space. 
     SUMMARY 
     At least one embodiment may provide a fixing device that includes a rotatable fixing member, a rotatable pressing member provided under the fixing member, a controller, and an oil applier. The controller switches the pressing member between a pressure application state to contact the pressing member against the fixing member and a pressure release state to separate the pressing member from the fixing member. The controller starts rotation of the pressing member before the pressing member contacts the fixing member in the pressure application state, when the pressing member switches from the pressure release state to the pressure application state. The oil applier includes an oil pan and an oil regulating member. The oil pan is provided under the pressing member to contain oil in which the pressing member is dipped. The oil regulating member is provided downstream from the oil pan in a direction of rotation of the pressing member to contact the pressing member to regulate an amount of oil adhering to the pressing member. 
     At least one embodiment may provide an image forming apparatus that includes a fixing device including a rotatable fixing member, a rotatable pressing member provided under the fixing member, a controller, and an oil applier. The controller switches the pressing member between a pressure application state to contact the pressing member against the fixing member and a pressure release state to separate the pressing member from the fixing member. The controller starts rotation of the pressing member before the pressing member contacts the fixing member in the pressure application state, when the pressing member switches from the pressure release state to the pressure application state. The oil applier includes an oil pan and an oil regulating member. The oil pan is provided under the pressing member to contain oil in which the pressing member is dipped. The oil regulating member is provided downstream from the oil pan in a direction of rotation of the pressing member to contact the pressing member to regulate an amount of oil adhering to the pressing member. 
     At least one embodiment may provide an image fixing method that includes applying oil to a pressing member, regulating an amount of oil adhering to the pressing member, contacting the pressing member against a fixing member after the pressing member rotates by at least a half turn. The image fixing method further includes contacting a separation nail against the pressing member when the pressing member contacts the fixing member, and switching the pressing member between a pressure application state, in which the pressing member is contacted against the fixing member, and a pressure release state, in which the pressing member is separated from the fixing member. 
     Additional features and advantages of example embodiments will be more fully apparent from the following detailed description, the accompanying drawings, and the associated claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of example embodiments and the many attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a sectional view of a related-art fixing device; 
         FIG. 2  is a sectional view of another related-art fixing device; 
         FIG. 3  is a sectional view of an image forming apparatus according to an example embodiment; 
         FIG. 4  is a sectional view (according to an example embodiment) of a fixing device -included in the image forming apparatus shown in  FIG. 3 ; 
         FIG. 5  is a sectional view (according to an example embodiment) of a pressure application-release device included in the fixing device shown in  FIG. 4 ; 
         FIG. 6  is a sectional view (according to an example embodiment) of an oil applier included in the fixing device shown in  FIG. 4 ; 
         FIG. 7  is a flowchart (according to an example embodiment) illustrating a procedure for applying oil from the oil applier shown in  FIG. 6  to a pressing roller included in the fixing device shown in  FIG. 4 ; 
         FIG. 8  is a top view (according to an example embodiment) of the oil applier shown in  FIG. 6 ; 
         FIG. 9  is a flowchart (according to an example embodiment) illustrating a control procedure for changing a state of a pressing roller included in the fixing device shown in  FIG. 4  from a pressure release state to a pressure application state; 
         FIG. 10  is a timing chart (according to an example embodiment) illustrating the control procedure shown in  FIG. 9 ; 
         FIG. 11A  is a top view (according to an example embodiment) of a separation nail included in the fixing device shown in  FIG.  4 ; 
         FIG. 11B  is a sectional view (according to an example embodiment) of the separation nail shown in  FIG. 11A ; and 
         FIG. 12  is a schematic view (according to an example embodiment) of an oil circulation system included in the image forming apparatus shown in  FIG. 3 . 
     
    
    
     The accompanying drawings are intended to depict example embodiments and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     It will be understood that if an element or layer is referred to as being “on”, “against”, “connected to”, or “coupled to” another element or layer, then it can be directly on, against, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, if an element is referred to as being “directly on”, “directly connected to”, or “directly coupled to” another element or layer, then there are no intervening elements or layers present. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper”, and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein are interpreted accordingly. 
     Although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, it should be understood that these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or section from another region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the present invention. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     In describing example embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, particularly to  FIG. 3 , an image forming apparatus  200  according to an example embodiment is explained. 
     As illustrated in  FIG. 3 , the image forming apparatus  200  includes an image forming device  200 A, a sheet supplier  200 B, a stacker  215 , and/or a controller  260 . 
     The image forming device  200 A includes optical writers  201 , chargers  202 Y,  202 M,  202 C, and  202 K, development devices  203 Y,  203 M,  203 C, and  203 K, first transfer devices  204 Y,  204 M,  204 C, and  204 K, photoconductors  205 Y,  205 M,  205 C, and  205 K, a transfer belt  210 , a roller  211 , a transfer roller  212 , a fixing device  100 , and/or an oil circulation mechanism  250 . The sheet supplier  200 B includes a paper tray  220 . The oil circulation mechanism  250  includes an oil tank  251  and/or an oil pump  252 . 
     The image forming apparatus  200  can be a copier, a facsimile machine, a printer, a plotter, a multifunction printer having at least one of copying, printing, scanning, plotter, and facsimile functions, or the like. According to this example embodiment of the present invention, the image forming apparatus  200  functions as a tandem type color copier for forming a color image on a recording medium at high speed by electrophotography. 
     The image forming device  200 A is provided at a center portion of the image forming apparatus  200 . The sheet supplier  200 B is provided under the image forming device  200 A. An image reader is provided above the image forming device  200 A. 
     In the image forming device  200 A, the transfer belt  210  includes a transfer surface extending in a horizontal direction. A mechanism for forming an image in a complementary color being complementary to a separation color is provided above the transfer belt  210 . For example, the photoconductors  205 Y,  205 M,  205 C, and  205 K, serving as image carriers for carrying toner images in complementary colors (e.g., yellow, magenta, cyan, and black), are arranged along the transfer surface of the transfer belt  210 . 
     The photoconductors  205 Y,  205 M,  205 C, and  205 K are formed of drums which rotate in an identical direction (e.g., counterclockwise in  FIG. 3 ), respectively. The optical writers  201 , the chargers  202 Y,  202 M,  202 C, and  202 K, the development devices  203 Y,  203 M,  203 C, and  203 K, the first transfer devices  204 Y,  204 M,  204 C, and  204 K, and cleaners surround the photoconductors  205 Y,  205 M,  205 C, and  205 K, respectively, to perform image forming processes while the photoconductors  205 Y,  205 M,  205 C, and  205 K rotate. The development devices  203 Y,  203 M,  203 C, and  203 K contain yellow, magenta, cyan, and black toners, respectively. 
     The transfer belt  210  is looped over a driving roller and a driven roller, and opposes the photoconductors  205 Y,  205 M,  205 C, and  205 K to move in a direction corresponding to the direction of rotation of the photoconductors  205 Y,  205 M,  205 C, and  205 K. The transfer roller  212  opposes the roller  211  serving as a driven roller. 
     In the sheet supplier  200 B, the paper tray  220  loads sheets P serving as a recording medium. A conveyance mechanism feeds the sheets P loaded on the paper tray  220  one by one toward the transfer roller  212 . For example, the conveyance mechanism separates an uppermost sheet P from other sheets P loaded on the paper tray  220 , and conveys the sheet P toward the transfer roller  212 . A conveyance path provided between the transfer roller  212  and the fixing device  100  conveys the sheet P in a horizontal direction. The controller  260  controls operations of the image forming apparatus  200 . 
     The following describes image forming operations performed by the image forming apparatus  200 . The charger  202 Y uniformly charges a surface of the photoconductor  205 Y. The optical writer  201  forms an electrostatic latent image on the charged surface of the photoconductor  205 Y according to image data sent by the image reader. The development device  203 Y for containing the yellow toner makes the electrostatic latent image formed on the photoconductor  205 Y visible as a yellow toner image. The first transfer device  204 Y applies a reference bias to the yellow toner image formed on the photoconductor  205 Y to transfer the yellow toner image onto the transfer belt  210 . Similarly, magenta, cyan, and black toner images are formed on the photoconductors  205 M,  205 C, and  205 K, respectively, and sequentially transferred onto the transfer belt  210  by an electrostatic force so that the yellow, magenta, cyan, and black toner images are superimposed on the transfer belt  210  to form a color toner image on the transfer belt  210 . 
     The transfer roller  212  transfers the color toner image from the transfer belt  210  onto the sheet P conveyed by the roller  211  and the transfer roller  212 . The sheet P bearing the color toner image is further conveyed to the fixing device  100 . The fixing device  100  fixes the color toner image on the sheet P. The sheet P bearing the fixed color toner image is sent to the stacker  215  via an output path. 
     The oil tank  251  collects oil used in the fixing device  100  to improve property for separating the sheet P from the fixing device  100 . The oil pump  252  resupplies oil contained in the oil tank  251  to the fixing device  100 . The oil tank  251  and the oil pump  252  serve as the oil circulation mechanism  250  (e.g., an oil circulation system) provided for the fixing device  100 . 
       FIG. 4  is a sectional view of the fixing device  100 . The fixing device  100  includes a fixing cover  100 C, a fixing roller  11 , a fixing belt  12 , a pressing roller  13 , a heater  13 H, a heating roller  14 , a heat pipe  14 A, a heater  14 H, a tension roller  15 , separation nails  16 A and  16 B, a cleaning mechanism  17 , and/or oil appliers  21  and  22 . 
     The fixing roller  11 , the fixing belt  12 , the pressing roller  13 , the heating roller  14 , the separation nails  16 A and  16 B, and the cleaning mechanism  17  are provided inside the fixing cover  100 C. The fixing belt  12 , serving as a fixing member, is looped or stretched over the fixing roller  11  and the heating roller  14  with a reference tension. The pressing roller  13 , serving as a pressing member, is provided under the fixing belt  12  and rotatably presses against the fixing belt  12  to form a fixing nip portion N between the fixing belt  12  and the pressing roller  13 . The fixing belt  12  and the pressing roller  13  apply heat and pressure to a sheet P bearing a toner image T at the fixing nip portion N to fix the toner image T on the sheet P. The separation nail  16 A is provided at an exit side of the fixing nip portion N in such a manner that a head of the separation nail  16 A contacts or is disposed close to the fixing belt  12 , so as to prevent a sheet P from wrapping around the fixing belt  12 . The separation nail  16 B is provided at the exit side of the fixing nip portion N in such a manner that a head of the separation nail  16 B contacts the pressing roller  13 , so as to prevent a sheet P from wrapping around the pressing roller  13 . The cleaning mechanism  17  cleans the fixing belt  12  by pressing a cleaning web against the fixing belt  12 . 
     The fixing belt  12  has an endless belt shape and has a double-layer structure in which an elastic layer, such as a silicon rubber layer, is formed on a base including nickel, stainless steel, and/or polyimide. The fixing roller  11  includes metal serving as a core metal and silicon rubber. In order to shorten a warm-up time period of the fixing device  100 , the fixing roller  11  may include foamed silicon rubber so that the fixing roller  11  does not absorb heat from the fixing belt  12  easily. The heating roller  14  is formed of a hollow roller including aluminum or iron. The heater  14 H, such as a halogen heater, serves as a heat source and is provided inside the heating roller  14 . Alternatively, an induction heating (IH) mechanism may serve as the heat source. A plurality of heat pipes  14 A, which is formed of hollow pipes, is provided in a thick wall of the heating roller  14 . For example, the heat pipes  14 A are embedded in the thick wall of the heating roller  14  in such a manner that the heat pipes  14 A are evenly spaced in a circumferential direction of the heating roller  14  and that a longitudinal direction of the heat pipes  14 A corresponds to a longitudinal direction (e.g., a width direction or an axial direction) of the heating roller  14 . The heat pipes  14 A improve heat transmission from the heater  14 H to a surface of the heating roller  14 , and thereby the heating roller  14  uniformly,heats the fixing belt  12  quickly. 
     When the fixing device  100  is driven, a driving force input from an outside of the fixing device  100  drives and rotates the pressing roller  13  counterclockwise in  FIG. 4 , for example. Accordingly, the rotating pressing roller  13  rotates the fixing roller  11  clockwise in  FIG. 4  in a direction of rotation D 1  via the fixing belt  12 . For example, in a state in which the tension roller  15  presses against the fixing belt  12  to apply proper tension to the fixing belt  12 , the fixing belt  12  rotates clockwise in  FIG. 4  in a direction of rotation D 2  in which the fixing belt  12  feeds a sheet P out of the fixing nip portion N. In order to fix a toner image T on a sheet P, the heater  14 H provided inside the heating roller  14  generates heat to heat the fixing belt  12  until a thermistor detects that the fixing belt  12  is heated up to a reference temperature (e.g., a proper fixing temperature). According to this example embodiment, the fixing belt  12 , that is, an endless belt, serves as a fixing member. Alternatively, a fixing roller, for example, a hollow cylindrical roller may serve as a fixing member. 
     The pressing roller  13  is formed of a cylindrical roller in which an elastic layer including silicon rubber is provided on a core metal including aluminum or iron. The heater  13 H is provided inside the pressing roller  13 , and generates heat to heat the pressing roller  13  up to a reference temperature as needed, for example, to fix a toner image T on a sheet P. 
     In the fixing device  100 , the oil appliers  21  and  22  apply a proper amount of oil to the fixing belt  12  and the pressing roller  13 , respectively, and the separation nails  16 A and  16 B, which are provided at the exit side of the fixing nip portion N, function as needed. Thus, a sheet P can be discharged to the exit side of the fixing nip portion N without adhering to or wrapping around the fixing belt  12  or the pressing roller  13 . 
       FIG. 5  is a partially sectional view of the fixing device  100 . The fixing device  100  further includes a pressure application-release device  30 . The pressure application-release device  30  includes a pressing cam  31 , a first pressing arm  32 , a second pressing arm  33 , an elastic member  34 , and/or a support shaft  35 . The second pressing arm  33  includes a pressing portion  33 A. The pressing roller  13  includes a shaft  13 J. 
     The pressure application-release device  30  switches a state of the pressing roller  13  between a pressure application state in which the pressing roller  13 , contacts the fixing belt  12  to apply pressure to the fixing belt  12  and a pressure release state in which the pressing roller  13  separates from the fixing belt  12  to release pressure applied to the fixing belt  12 . 
     A driving force input from an outside of the pressure application-release device  30  rotates the pressing cam  31 . The elastic member  34  is fixed to an end of each of the first pressing arm  32  and the second pressing arm  33 . In  FIG. 5 , the second pressing arm  33  is shaded. The support shaft  35  is fixed to a frame of the fixing device  100 , and supports the first pressing arm  32  and the second pressing arm  33 . 
     Referring to  FIG. 5 , the following describes pressure application operations of the pressure application-release device  30  for applying pressure to the fixing belt  12  by moving the pressing roller  13  toward the fixing belt  12 , and pressure release operations of the pressure application-release device  30  for releasing pressure applied to the fixing belt  12  by moving the pressing roller  13  away from the fixing belt  12 . 
     The following describes the pressure application operations of the pressure application-release device  30 . When a driving force transmitted-from the outside of the fixing device  100  rotates the pressing cam  31  by a reference angle of rotation in a direction of rotation D 3 , the pressing cam  31  pushes up a spinning top of the first pressing arm  32  in a direction D 4 . 
     When the spinning top of the first pressing arm  32  is pushed up, the first pressing arm  32  rotates about the support shaft  35  counterclockwise in  FIG. 5 . Simultaneously, the elastic member  34  fixed to an end of the first pressing arm  32  opposite another end of the first pressing arm  32 , to which the support shaft  35  is attached, also rotates to push up a contact end of the second pressing arm  33 , which contacts the elastic member  34 , with reference pressure in a direction D 5 . 
     When the contact end of the second pressing arm  33  for contacting the elastic member  34  is pushed up, the second pressing arm  33  rotates about the support shaft  35  counterclockwise in  FIG. 5 . 
     Accordingly, the pressing portion  33 A, which is provided between the contact end of the second pressing arm  33  for contacting the elastic member  34  and the support shaft  35 , contacts the shaft  13 J of the pressing roller  13  to push the pressing roller  13  toward the fixing roller  11  in a direction D 6 . 
     The pressing roller  13  presses against the fixing roller  11  via the fixing belt  12 , and applies reference pressure based on an elastic force of the elastic member  34  to the fixing roller  11  in a direction D 7  to form the fixing nip portion N between the fixing belt  12  and the pressing roller  13 . 
     Thus, when the fixing device  100  is driven, the pressure application-release device  30  presses the pressing roller  13  against the fixing belt  12  by pushing the pressing roller  13  toward the fixing belt  12  with the reference pressure. 
     The following describes the pressure release operations of the pressure application-release device  30 . When a driving force transmitted from the outside of the fixing device  100  rotates the pressing cam  31  further by a reference angle of rotation in the direction of rotation D 3  from a position of the angle at which the pressing cam  31  causes the pressing roller  13  to press against the fixing roller  11  in the pressure application state, the pressing cam  31  releases pushing up the spinning top of the first pressing arm  32  in a direction opposite the direction D 4 . 
     When pushing up the first pressing arm  32  is released, the first pressing arm  32  rotates about the support shaft  35  in a direction of rotation opposite the direction of rotation during the pressure application operations, that is, clockwise in  FIG. 5 , with a repulsive force transmitted through the fixing nip portion N, the pressing portion  33 A, and the elastic member  34 . Accordingly, the contact end of the second pressing arm  33  corresponding to the elastic member  34  fixed to the end of the first pressing arm  32  opposite another end of the first pressing arm  32 , to which the support shaft  35  is attached, is pulled together with the elastic member  34  in a direction opposite the direction during the pressure application operations, that is, in a direction opposite the direction D 5 . 
     When the contact end of the second pressing arm  33  for contacting the elastic member  34  is pulled down, the second pressing arm  33  rotates about the support shaft  35  in a direction of rotation opposite the direction of rotation during the pressure application operations, that is, clockwise in  FIG. 5 . 
     Accordingly, the pressing portion  33 A, which is provided between the contact end of the second pressing arm  33  for contacting the elastic member  34  and the support shaft  35 , moves in a direction in which the pressing portion  33 A separates from the shaft  13 J of the pressing roller  13  in a direction opposite the direction D 6 . 
     Thus, pressure applied by the pressing portion  33 A to the pressing roller  13  is released, and the pressing roller  13  moves in a direction in which the pressing roller  13  separates from the fixing roller  11 , that is, a direction opposite the direction D 7 . Accordingly, the fixing nip portion N is not formed between the fixing belt  12  and the pressing roller  13  in the pressure release state. 
     Thus, when driving of the fixing device  100  stops, the pressure application-release device  30  does not press the pressing roller  13  against the fixing belt  12 , and the pressing roller  13  separates from the fixing belt  12  in the pressure release state. 
     As illustrated in  FIG. 4 , when the pressing roller  13  contacts the fixing belt  12  in the pressure application state, the separation nail  16 B contacts the pressing roller  13 . By contrast, when the pressing roller  13  separates from the fixing belt  12  in the pressure release state, the separation nail  16 B separates from the pressing roller  13 . 
     According to this example embodiment, the pressing roller  13  having a roller shape serves as a pressing member. Alternatively, an endless belt looped over at least two rollers may serve as a pressing member. 
     In the fixing device  100 , a surface of the fixing belt  12  is heated up to a reference temperature in a state in which the fixing belt  12  and the pressing roller  13  are driven and rotated. When a sheet P bearing an unfixed toner image T passes through the fixing nip portion N, that is, when the sheet P moves leftward in  FIG. 4 , the fixing belt  12  and the pressing roller  13  apply heat and pressure to the sheet P at the fixing nip portion N to melt and fix the unfixed toner image T on the sheet P. 
     When the sheet P bearing the fixed toner image T is discharged from the fixing nip portion N, the sheet P may adhere to or wrap around the fixing belt  12  or the pressing roller  13 . To address this, the oil appliers  21  and  22  apply oil to the fixing belt  12  and the pressing roller  13  to improve property for separating the sheet P from the fixing belt  12  and the pressing roller  13 , respectively. The applied oil may be heat-resistant fixed oil, such as silicon oil. When the head of the separation nail  16 A or  16 B contacts a leading edge of the sheet P, the separation nail  16 A or  16 B separates the sheet P from the fixing belt  12  or the pressing roller  13 , respectively. The sheet P discharged from the fixing nip portion N passes through a discharge path and is sent out of the fixing device  100 . 
       FIG. 6  is a partially sectional view of the fixing device  100 . The oil applier  22  includes an oil pan  22 A, a blade  22 B, and/or a cleaning felt  22 C. The oil pan  22 A includes a sub oil pan  22 A 1  and/or a main oil pan  22 A 2 . 
     In the fixing device  100 , the rotatable fixing belt  12 , serving as a fixing member, contacts the rotatable pressing roller  13 , serving as a pressing member, provided under the fixing belt  12  to form the fixing nip portion N between the fixing belt  12  and the pressing roller  13 . The sub oil pan  22 A 1  is provided under the pressing roller  13  and contains oil O in which a part of the pressing roller  13  is dipped. The blade  22 B is provided downstream from the sub oil pan  22 A 1  and upstream from the fixing nip portion N in the direction of rotation of the pressing roller  13 , and serves as an oil regulating member for regulating an amount of oil O adhering to the pressing roller  13 . 
     The oil pan  22 A is fixed inside the fixing cover  100 C (depicted in  FIG. 4 ) of the fixing device  100 , and includes two pans, which are the sub oil pan  22 A 1  serving as an oil pan for containing oil O in which a part of the pressing roller  13  is dipped and the main oil pan  22 A 2  serving as an oil receiver for holding the whole sub oil pan  22 A 1 . Oil O to be applied to the pressing roller  13  is supplied from an outside of the oil applier  22  into the sub oil pan  22 A 1  and stored in the sub oil pan  22 A 1 . The sub oil pan  22 A 1  has a rectangular shape. A long length of the sub oil pan  22 A 1  is equal to or longer than at least a long length (e.g., a width) of the pressing roller  13 , that is, a length in a longitudinal direction (e.g., a width direction or an axial direction) of the pressing roller  13 . 
     The pressing roller  13  is constantly dipped in oil O in the sub oil pan  22 A 1  wholly in the width direction (e.g., the axial direction) and partially in a diametrical direction (e.g., a direction perpendicular to the width direction) of the pressing roller  13 . For example, an oil level of the sub oil pan  22 A 1  is higher than a lower end of the pressing roller  13  even when the pressure application-release device  30  (depicted in  FIG. 5 ) presses the pressing roller  13  against the fixing belt  12 . The lower end of the pressing roller  13  does not touch an inner bottom of the sub oil pan  22 A 1  even when pressure applied by the pressure application-release device  30  to the pressing roller  13  is released. 
     The main oil pan.  22 A 2  serves as an oil receiver for receiving oil O overflowing the sub oil pan  22 A 1 . An outlet through which oil O is collected into the oil tank  251  depicted in  FIG. 3  is provided under the main oil pan  22 A 2 . 
     The sub oil pan  22 A 1  and the main oil pan  22 A 2  may include heat-resistant metal or plastic not reacting to oil O. 
     The blade  22 B includes an elastic member having a paddle-like shape and has a width equal to or longer than at least the width of the pressing roller  13 . A long edge of the blade  22 B constantly contacts a surface of the pressing roller  13 . In other words, a longitudinal direction of the blade  22 B corresponds to the longitudinal direction (e.g., the width direction or the axial direction) of the pressing roller  13 . Thus, the blade  22 B regulates an amount of oil O adhering to the pressing roller  13  so that a reference amount of oil O is adhered to the pressing roller  13  uniformly in the width direction of the pressing roller  13 . The blade  22 B includes a material not damaging the surface of the pressing roller  13 , such as fluorocarbon rubber. 
     The surface of the pressing roller  13  includes a material corresponding to oil O. For example, when silicon oil is used as oil O, the surface of the pressing roller  13  includes silicon rubber. Therefore, when the pressing roller  13  is dipped in oil o in the sub oil pan  22 A 1 , the silicon rubber of the pressing roller  13  swells and holds oil O. The blade  22 B contacts a lower surface of the pressing roller  13  to scrape oil O off the surface of the pressing roller  13 . For example, an angle θ formed by a head of the blade  22 B and a tangent line of the head of the blade  22 B tangent to a curve of the pressing roller  13  is an acute angle smaller than about 90 degrees. The head of the blade  22 B opposes the direction of rotation of the pressing roller  13  to scrape surplus oil O off the surface of the pressing roller  13  into the oil pan  22 A. Accordingly, the surface of the pressing roller  13  carries a sufficient amount of oil O uniformly applied on the surface of the pressing roller  13  in the width direction of the pressing roller  13 , which can provide proper property for separating a sheet P bearing a fixed toner image T from the pressing roller  13 . Surplus oil O on the pressing roller  13  is collected into the oil pan  22 A and reused. Namely, surplus oil O is circulated and applied to the pressing roller  13  again. 
     The cleaning felt  22 C may be provided between the oil pan  22 A and the blade  22 B. The cleaning felt  22 C serves as a cleaner for cleaning the surface of the pressing roller  13  by contacting the pressing roller  13 . The cleaning felt  22 C may be a compressed sheet including heat-resistant fiber not reacting to oil O, such as meta-aramid fiber. While oil O permeates the fiber of the cleaning felt  22 C, the cleaning felt  22 C captures fine solid impurities inside. Thus, fine solid impurities (e.g., dust and calcium carbonate originating from a sheet P) contained in oil O can be removed from the surface of the pressing roller  13 , while the oil O remains on the surface of the pressing roller  13 . 
     A support supports the cleaning felt  22 C in such a manner that the cleaning felt  22 C contacts the pressing roller  13 . When the support is formed of a metal material by sheet metal processing to have proper spring property, the support causes the cleaning felt  22 C to contact the pressing roller  13  while applying constant pressure to the pressing roller  13 , so as to adjust an amount of oil O adhering to the pressing roller  13 . 
     Referring to  FIGS. 5 to 7 , the following describes a procedure for applying oil O from the oil applier  22  to the pressing roller  13  with the above-described structure.  FIG. 7  is a flowchart illustrating the procedure for applying oil O from the oil applier  22  to the pressing roller  13 . 
     In step S 11 , the controller  260  depicted in  FIG. 3  starts driving the fixing device  100 . Accordingly, the pressure application-release device  30  causes the pressing roller  13  to contact the fixing belt  12  by applying constant pressure to the fixing belt  12  to form the fixing nip portion N between the fixing belt  12  and the pressing roller  13 . Simultaneously, the pressing roller  13  starts rotating, and the rotating pressing roller  13  rotates the fixing belt  12 . Alternatively, the fixing roller  11  interlocked with the pressing roller  13  may rotate the fixing belt  12 . 
     In step S 12 , when the pressing roller  13  starts rotating, the surface of the pressing roller  13  dipped in oil O in the sub oil pan  22 A 1  is lifted toward the fixing nip portion N in a state in which the oil O is adhered to the surface of the pressing roller  13 . 
     In step S 13 , the oil O adhered to the surface of the pressing roller  13  permeates the cleaning felt  22 C, and the cleaning felt  22 C removes solid impurities from the oil O. 
     In step S 14 , the blade  22 B regulates the oil O adhered to the surface of the pressing roller  13  uniformly in the width direction of the pressing roller  13 . Thereafter, the regulated oil O on the surface of the pressing roller  13  moves to the fixing nip portion N. 
     As described above, according to this example embodiment, the oil applier  22  applies oil O to the pressing roller  13  provided under the fixing nip portion N in a dip method by utilizing a space under the pressing roller  13 . Thus, the oil applier  22  can supply a sufficient amount of oil O to the pressing roller  13  stably. 
       FIG. 8  is a top view of the oil applier  22 .  FIG. 8  does not illustrate the blade  22 B. The oil applier  22  further includes an oil spatter prevention member  22 D. 
     In  FIG. 8 , the oil spatter prevention member  22 D covers an oil surface of oil O contained in the oil pan  22 A. For example, the oil spatter prevention member  22 D covers a region of the oil surface of oil O contained in the sub oil pan  22 A 1  and the main oil pan  22 A 2  of the oil pan  22 A other than a region of the oil surface of oil O in which the pressing roller  13  is dipped. The oil spatter prevention member  22 D may not cover a region of the oil surface of oil O provided under the cleaning felt  22 C. Thus, the oil spatter prevention member  22 D can reduce or prevent oil O spattering from the oil surface of oil O contained in the oil pan  22 A due to rotation of the pressing roller  13  or other vibration and thereby adhering to and staining a sheet P or a peripheral device. 
     The oil spatter prevention member  22 D may be a compressed sheet (e.g., a felt sheet) including heat-resistant fiber not reacting to oil O, such as meta-aramid fiber. The oil spatter prevention member  22 D may float on the oil surface of oil O or may separate from the oil surface of oil O. Alternatively, the oil spatter prevention member  22 D may include a plurality of spherical members floating on the oil surface of oil O to cover the oil surface of oil O. 
     As illustrated in  FIG. 4 , when driving of the fixing device  100  is interrupted after the fixing device  100  is driven, the pressure application-release device  30  (depicted in  FIG. 5 ) separates the pressing roller  13  from the fixing belt  12  in the pressure release state, and the pressing roller  13  stops rotating. Thereafter, when driving of the fixing device  100  is resumed and an image forming job starts, oil O may adhere to and stain a sheet P passing through the fixing device  100 . 
     In other words, when driving of the fixing device  100  is resumed, oil O may adhere to the separation nail  16 B, and the oil  0  may adhere from the separation nail  16 B to the sheet P. For example, when the fixing device  100  is driven, the oil applier  22  applies oil O to the pressing roller  13 . When driving of the fixing device  100  is interrupted and the pressure application-release device  30  releases pressure applied to the pressing roller  13 , oil O carried on the pressing roller  13  near the fixing nip portion N falls down along the surface of the pressing roller  13 , and the oil O accumulates on a contact portion of the pressing roller  13 , which contacts the blade  22 B depicted in  FIG. 6 . When driving of the fixing device  100  is resumed, the pressing roller  13  presses against the fixing belt  12  again, and the separation nail  16 B contacts the pressing roller  13 . The rotating pressing roller  13  moves the accumulation portion of the pressing roller  13 , on which the oil O is accumulated, toward the separation nail  16 B, and the oil O is adhered to the separation nail  16 B at a position at which the pressing roller  13  contacts the separation nail  16 B. When the separation nail  16 B contacts a sheet P passing through the fixing nip portion N during an image forming operation, the oil O is adhered from the separation nail  16 B to the sheet P. 
     To address this, the fixing device  100  is controlled as described below, when driving of the fixing device  100  is resumed. 
     In the fixing device  100  illustrated in  FIG. 4 , in order to change the state of the pressing roller  13  from the pressure release state in which the pressing roller  13  separates from the fixing belt  12  to the pressure application state in which the pressing roller  13  presses against the fixing belt  12 , the pressing roller  13  starts rotating while the pressing roller  13  separates from the fixing belt  12 , and then the pressing roller  13  contacts the fixing belt  12  to press against the fixing belt  12 . 
       FIG. 9  is a flowchart illustrating a control procedure for changing the state of the pressing roller  13  from the pressure release state to the pressure application state.  FIG. 10  is a timing chart illustrating the control procedure for changing the state of the pressing roller  13  from the pressure release state to the pressure application state. The state of the pressing roller  13  changes from the pressure release state to the pressure application state when driving of the fixing device  100  is resumed and when an image forming operation is performed. 
     As illustrated in  FIG. 9 , in step S 21 , in order to resume driving of the fixing device  100  (depicted in  FIG. 5 ) when driving of the fixing device  100  is interrupted after the fixing device  100  is driven, the controller  260  (depicted in  FIG. 3 ) drives a motor for driving the pressing roller  13  (depicted in  FIG. 5 ) at point A illustrated in  FIG. 10  to rotate the pressing roller  13  by at least a half turn, preferably a turn, for at least 1 second. 
     In step S 22 , the controller  260  drives the pressure application-release device  30  (depicted in  FIG. 5 ) to cause the pressing roller  13  to contact the fixing belt  12  (depicted in  FIG. 5 ) in the pressure application state in which the pressing roller  13  presses against the fixing belt  12  at point B illustrated in  FIG. 10 . 
     In step S 23 , when rotation of the fixing belt  12  and the pressing roller  13  is stabilized in the pressure application state in which the pressing roller  13  presses against the fixing belt  12 , the controller  260  allows reload to start heating the fixing belt  12  by the heater  14 H of the heating roller  14  (depicted in  FIG. 4 ) at point C illustrated in  FIG. 10 . 
     In step S 24 , when temperature of the fixing belt  12  reaches a reference temperature (e.g., a reload temperature), operations for resuming driving of the fixing device  100  are finished. For example, the controller  260  stops driving the motor for driving the pressing roller  13  to stop rotating the pressing roller  13 , and causes the pressure application-release device  30  to release pressure applied by the pressing roller  13  to the fixing belt  12  at point D illustrated in  FIG. 10 . 
     In step S 25 , in order to start an image forming job, the controller  260  drives the motor for driving the pressing roller  13  again at point E to rotate the pressing roller  13  by at least a half turn, preferably a turn. 
     In step S 26 , the controller  260  drives the pressure application-release device  30  to cause the pressing roller  13  to contact the fixing belt  12  in the pressure application state in which the pressing roller  13  presses against the fixing belt  12  at point F illustrated in  FIG. 10 . 
     In step S 27 , when the image forming job is finished, that is, when a fixing process for fixing a toner image T on a sheet P passing through the fixing nip portion N is finished, the controller  260  stops driving the motor for driving the pressing roller  13 , and causes the pressure application-release device  30  to release pressure applied by the pressing roller  13  to the fixing belt  12  at point G illustrated in  FIG. 10  in a standby mode. 
     As illustrated in  FIG. 4 , with the above-described control procedure, the accumulation portion of the pressing roller  13  bearing oil O accumulated at a position at which the pressing roller  13  contacts the blade  22 B (depicted in  FIG. 6 ) passes through a position at which the pressing roller  13  is to contact the separation nail  16 B before the separation nail  16 B contacts the pressing roller  13 . Further, the surface of the pressing roller  13  bearing oil O reaches the position at which the separation nail  16 B contacts the pressing roller  13  after the blade  22 B adjusts an amount of oil O on the pressing roller  13 . Therefore, surplus oil O may not adhere to the separation nail  16 B, reducing or preventing oil O adhering to a sheet P. 
       FIG. 11A  is a top view of the separation nail  16 B.  FIG. 11B  is a sectional view of the separation nail  16 B. The separation nail  16 B includes a nail member  16 B 1  and/or a through-hole  16 B 2 . 
     The nail member  16 B 1  contacts the pressing roller  13  depicted in  FIG. 4 . Oil O passes through the through-hole  16 B 2  from a surface S 1  of the nail member  16 B 1 , that is, a non-contact surface not contacting the pressing roller  13  to face the discharge path for discharging a sheet P out of the fixing device  100 , to an opposite surface S 2  of the nail member  16 B 1 , that is, a contact surface provided opposite the non-contact surface to contact the pressing roller  13 . A plurality of the separation nails  16 B is distributed in the width direction of the pressing roller,  13 . Thus, even when surplus oil O adhering to the pressing roller  13  moves to the separation nail  16 B, the surplus oil O is discharged from the surface S 1  of the nail member  16 B 1  through the through-hole  16 B 2 , reducing or preventing the surplus oil O adhering to the sheet P. 
     Referring to  FIG. 12 , the following describes the oil circulation mechanism  250 , serving as an oil circulation system, included in the image forming apparatus  200 .  FIG. 12  is a schematic view of the oil circulation mechanism  250 . The oil circulation mechanism  250  further includes a conveyance path  253 , an oil receiver  254 , a tube  255 , and/or a conveyance path  256 . The oil tank  251  includes an oil sensor  251 A. 
     The oil tank  251  contains oil to be used in the fixing device  100 . The oil pump  252  uses a piezoelectric element. The conveyance path  253  connects the oil pump  252  to the oil applier  21  of the fixing device  100 . The oil receiver  254  receives surplus oil sent from the oil applier  21 . The tube  255  conveys the oil sent from the oil receiver  254  to the oil applier  22 . The conveyance path  256  connects the oil applier  22  to the oil tank  251 . The oil tank  251 , the oil pump  252 , and the conveyance paths  253  and  256  are disposed outside the fixing device  100 . The oil receiver  254  and the tube  255  are disposed inside the fixing device  100 . The oil sensor  251 A detects an amount of oil remaining in the oil tank  251 . 
     In the image forming apparatus  200 , the oil circulation mechanism  250  circulates oil as described below so that the oil appliers  21  and  22  sequentially apply oil to the fixing belt  12  and the pressing roller  13  depicted in  FIG. 4 , respectively. 
     For example, when an image forming operation starts, the oil pump  252  pumps silicon oil from the oil tank  251 , which stores a total volume of about  4  liters of silicon oil, and conveys the oil to the oil applier  21  through the conveyance path  253 . For example, the oil is put into the oil applier  21  at a supply speed of about 3 grams per minute. 
     The oil receiver  254  collects surplus oil from the oil applier  21 . The surplus oil is conveyed to the sub oil pan  22 A 1  of the oil applier  22  provided for the pressing roller  13  (depicted in  FIG. 6 ) through the tube  255 . 
     Oil used in the oil applier  22  is filtered by a filter to remove impurities, and is collected into the oil tank  251  through the conveyance path  256 . 
     As illustrated in  FIG. 6 , in a fixing device (e.g., the fixing device  100 ) according to the above-described example embodiments, a pressing member (e.g., the pressing roller  13 ) is dipped in oil (e.g., oil O) contained in an oil pan (e.g., the sub oil pan  22 A 1 ) to adhere oil to the pressing member. Thus, a sufficient amount of oil can be stably applied to the pressing member provided under a fixing nip portion (e.g., the fixing nip portion N), maintaining improved property for separating a recording medium (e.g., a sheet P) from the pressing member. 
     When driving of the fixing device stops, the pressing member separates from a fixing member (e.g., the fixing belt  12 ), and thereby does not apply pressure to the fixing member. Accordingly, oil accumulates on a contact portion on the pressing member, which contacts an oil regulating member (e.g., the blade  22 B). However, the control procedure according to the above-described example embodiments, which is performed when the fixing device is driven, can reduce or prevent accumulation of oil on the pressing member and resultant adhesion of the oil to a recording medium. 
     According to the above-described example embodiments, an image forming apparatus (e.g., the image forming apparatus  200  depicted in  FIG. 3 ) including the fixing device can provide improved fixing and separation functions, and therefore can handle various types of paper, such as thin paper and thick paper, and various types of image formation, such as a narrower top margin on a sheet. Further, the image forming apparatus can reduce or prevent adhesion of oil to a recording medium, when driving of the fixing device is resumed or when an image forming operation starts. 
     The present invention has been described above with reference to specific example embodiments. Nonetheless, the present invention is not limited to the details of example embodiments described above, but various modifications and improvements are possible without departing from the spirit and scope of the present invention. It is therefore to be understood that within the scope of the associated claims, the present invention may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative example embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.