Patent Publication Number: US-9405244-B1

Title: Image forming apparatus with reduced load fluctuation

Description:
FIELD 
     Embodiments described herein relate generally to an image forming apparatus. 
     BACKGROUND 
     Conventionally, there is an image forming apparatus such as a Multi-functional Peripheral (hereinafter referred to as an “MFP”), a printer and the like. The image forming apparatus comprises a fixing member, a press roller and a switching mechanism. For example, it is assumed that the fixing member is a cylindrical member such as a heat roller or a fixing belt. The switching mechanism switches a position of the press roller. The switching mechanism is provided with a cam for switching the position of the press roller. For example, at the time of passing an image receiving medium (hereinafter referred to as “sheet-passing time”), the switching mechanism makes the press roller contact with the fixing member. Hereinafter, a position where the press roller is contacted with the fixing member is referred to as a “contact position”. On the other hand, at the time of not passing the image receiving medium (hereinafter referred to as a “non-sheet-passing time”), the switching mechanism separates the press roller from the fixing member. Hereinafter, a position where the press roller is separated from the fixing member is referred to as a “separation position”. There is a possibility that a motion sound generates due to a load fluctuation at the time of switching from the contact position to the separation position (hereinafter referred to as a “switch time”). 
     Especially, the pressing force of the press roller is set to be large in a color copier of which the sheet-passing speed is high (hereinafter referred to as a “high-speed color copier”) to guarantee the fixing property. The press roller presses the fixing member to form a nip. To guarantee the fixing property, it is necessary to guarantee that the nip is wide. To guarantee that the nip is wide, it is considered to increase an amount of engagement of the press roller with the fixing member (hereinafter referred to as an “amount of engagement”). Further, reducing the heat capacity of the fixing member is effective to shorten a warming-up time and a first print time. It is required to separate the press roller from the fixing member absolutely at a non-sheet-passing time to reduce the heat capacity of the fixing member. However, if the amount of engagement is increased at the sheet-passing time, the movement distance of the press roller from the contact position to the separation position becomes long. At this time, to realize miniaturization and low cost, enough space for the switching mechanism can hardly be guaranteed in the high-speed color copier. Thus, the load fluctuation at the switch time tends to become large in the high-speed color copier, and therefore there is a possibility that the motion sound becomes louder. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view illustrating an image forming apparatus according to an embodiment; 
         FIG. 2  is a perspective view illustrating a switching mechanism according to the embodiment; 
         FIG. 3  is a side view illustrating a separation position of a press roller according to the embodiment; 
         FIG. 4  is a side view illustrating a semi-contact position of the press roller according to the embodiment; 
         FIG. 5  is a side view illustrating a contact position of the press roller according to the embodiment; 
         FIG. 6  is a side view illustrating a position where the press roller is moved close to a heat roller temporarily during a period of time the press roller is separating from the heat roller according to the embodiment; 
         FIG. 7  is an illustration diagram of a first cam according to the embodiment; 
         FIG. 8  is an illustration diagram of a second cam according to the embodiment; 
         FIG. 9  is an illustration diagram of the first cam and the second cam according to the embodiment; 
         FIG. 10  is a graph illustrating a relation between a time of the first cam and the second cam and a cam position according to the embodiment; and 
         FIG. 11  is a block diagram illustrating a control system mainly controlling a switching mechanism according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In accordance with an embodiment, an image forming apparatus comprises an image forming section, a fixing section and a control section. The image forming section forms an image on an image receiving medium. The fixing section includes a first roller, a second roller and a switching mechanism. The second roller faces the first roller. The switching mechanism is provided with a cam. The cam switches positions of the first roller. The control section controls a driving of the cam. The positions of the first roller switched by the switching mechanism include a contact position and a separation position. In the contact position, the first roller contacts with the second roller. In the separation position, the first roller separates from the second roller. The cam includes a first position regulating section, a second position regulating section and a position changing section. The first position regulating section sets a contact position. The second position regulating section sets a separation position. The position changing section is positioned between the first position regulating section and the second position regulating section in a driving direction of the cam. The position changing section includes a fluctuation section. The fluctuation section moves the first roller close to the second roller temporarily during a period of time the first roller is separating from the second roller. 
     Hereinafter, an image forming apparatus  10  of the present embodiment is described with reference to the accompanying drawings. Further, the same components are applied with the same reference numerals in each figure, and therefore the detailed description thereof is not provided. 
       FIG. 1  is a side view of the image forming apparatus  10  according to the embodiment. Hereinafter, an MFP  10  is exemplified as one example of the image forming apparatus  10 . 
     As shown in  FIG. 1 , the MFP  10  comprises a scanner  12 , a control panel  13 , a sheet feed cassette section  16 , a manual sheet feed tray  17 , a printer section  18  and a sheet discharge section  20 . The MFP  10  includes a CPU  100  which controls the whole MFP  10 . The CPU  100  controls a main body control circuit  101  (refer to  FIG. 11 ). 
     The scanner  12  reads an image from an original. The control panel  13  is provided with input keys  13   a  and a display section  13   b . For example, the input keys  13   a  receive an input by a user. For example, the display section  13   b  is of a touch panel type. The display section  13   b  receives an input by the user and carries out a display to the user. 
     The sheet feed cassette section  16  includes a sheet feed cassette  16   a  and a pickup roller  16   b . The sheet feed cassette  16   a  stores a sheet P serving as an image receiving medium. The pickup roller  16   b  picks up the sheet P from the sheet feed cassette  16   a.    
     The sheet feed cassette  16   a  feeds an unused sheet P. The manual sheet feed tray  17  feeds the unused sheet P through a pickup roller  17   a.    
     The printer section  18  forms the image read by the scanner  12  from the original. The printer section  18  includes an intermediate transfer belt  21 . The printer section  18  supports the intermediate transfer belt  21  through a backup roller  40 , a driving roller  41  and a tension roller  42 . The backup roller  40  includes a driving section (not shown). The printer section  18  rotates the intermediate transfer belt  21  in a direction indicated by an arrow m. 
     The printer section  18  is provided with four image forming stations  22 Y,  22 M,  22 C and  22 K. Image forming stations  22 Y,  22 M,  22 C and  22 K are respectively used to form Y (Yellow), M (Magenta), C (Cyan) and K (Black) images. The image forming stations  22 Y,  22 M,  22 C and  22 K are arranged in parallel to each other along the rotary direction of the intermediate transfer belt  21  below the intermediate transfer belt  21 . 
     The printer section  18  includes cartridges  23 Y,  23 M,  23 C and  23 K above the image forming stations  22 Y,  22 M,  22 C and  22 K, respectively. The cartridges  23 Y,  23 M,  23 C and  23 K store Y (Yellow), M (Magenta), C (cyan) and K (black) toner for replenishing, respectively. 
     Hereinafter, the image forming station  22 Y which forms a Y (Yellow) image among the image forming stations  22 Y,  22 M,  22 C and  22 K is exemplified. Further, the constitution of the image forming stations  22 M,  22 C and  22 K is identical to that of the image forming station  22 Y, and therefore the detailed description thereof is not provided. 
     The image forming station  22 Y comprises an electrostatic charger  26 , an exposure scanning head  27 , a developing device  28  and a photoconductor cleaner  29 . The electrostatic charger  26 , the exposure scanning head  27 , the developing device  28  and the photoconductor cleaner  29  are arranged around a photoconductive drum  24  rotating in a direction indicated by an arrow n. 
     The image forming station  22 Y is provided with a primary transfer roller  30 . The primary transfer roller  30  faces the photoconductive drum  24  across the intermediate transfer belt  21 . 
     The image forming station  22 Y is exposed by the exposure scanning head  27  after the photoconductive drum  24  is charged by the electrostatic charger  26 . The image forming station  22 Y forms an electrostatic latent image on the photoconductive drum  24 . The developing device  28  develops the electrostatic latent image on the photoconductive drum  24  using a two-component developing agent consisting of toner and carrier. 
     The primary transfer roller  30  primarily transfers a toner image formed on the photoconductive drum  24  to the intermediate transfer belt  21 . The image forming stations  22 Y,  22 M,  22 C and  22 K form a color toner image on the intermediate transfer belt  21  through the primary transfer roller  30 . The color toner image is formed by sequentially overlapping a Y (Yellow) toner image, an M (Magenta) toner image, a C (Cyan) toner image and a K (Black) toner image. The photoconductor cleaner  29  removes the toner remained on the photoconductive drum  24  after the primary transfer. 
     The printer section  18  is provided with a secondary transfer roller  32 . The secondary transfer roller  32  faces the backup roller  40  across the intermediate transfer belt  21 . The secondary transfer roller  32  secondarily transfers the color toner image on the intermediate transfer belt  21  to the sheet P. The sheet P is fed by the sheet feed cassette section  16  or the manual sheet feed tray  17  along a conveyance path  33 . 
     The printer section  18  is provided with a belt cleaner  43  which faces the driving roller  41  across the intermediate transfer belt  21 . The belt cleaner  43  removes the toner remained on the intermediate transfer belt  21  after the second transfer. Further, the image forming section includes the intermediate transfer belt  21 , the four image forming stations ( 22 Y,  22 M,  22 C and  22 K) and the transfer roller  30 . 
     The printer section  18  includes a register roller  33   a , the secondary transfer roller  32 , a fixing device  34  (fixing section) and a sheet discharge roller  36  along the conveyance path  33 . The printer section  18  comprises the fixing device  34  at the downstream side of the secondary transfer roller  32 . The printer section  18  comprises a bifurcating section  37  and a reverse conveyance section  38  at the downstream side of the fixing device  34 . The bifurcating section  37  sends the sheet P subjected to a fixing processing to the sheet discharge section  20  or the reverse conveyance section  38 . In a case of duplex printing, the reverse conveyance section  38  reveres the sheet P sent from the bifurcating section  37  to the direction of the register roller  33   a  and conveys the sheet P. The MFP  10  forms a fixed toner image on the sheet P by the printer section  18 . The MFP  10  discharges the sheet P on which the fixed toner image is formed to the sheet discharge section  20 . 
     Further, the MFP  10  is not limited to an image forming apparatus of a tandem developing system. Moreover, no limitation is given to the number of the developing device  28  of the MFP  10 . In addition, the MFP  10  may transfer the toner image to the sheet P from the photoconductive drum  24  directly. 
     The fixing device  34  comprises a heat roller  50 , a press roller  51  and a switching mechanism  60  (refer to  FIG. 2 ). The press roller  51  is a first roller. The heat roller  50  is a second roller facing the press roller  51 . The fixing device  34  fixes the toner image on the sheet P through heat of the heat roller  50  and pressure of the press roller  51 . The heat roller  50  is formed into a cylindrical shape. The heat roller  50  includes a roller made of metal. For example, the heat roller  50  includes a resin layer consisting of fluororesin and the like on the outer peripheral surface of a roller made of aluminum having a thickness of about 0.8 mm. The heat roller  50  is driven by the press roller  51  to rotate in a direction indicated by an arrow U. Alternatively, the heat roller  50  may be separated from the press roller  51  to rotate in the direction indicated by the arrow U. 
     The press roller  51  is a pressurization section which presses the heat roller  50 . The press roller  51  presses the heat roller  50  through the switching mechanism  60 . The press roller  51  rotates in a direction indicated by an arrow q through a motor (not shown). For example, the press roller  51  includes an elastic layer such as a silicon rubber on the outer peripheral surface of a roller made of iron. The heat roller  50  faces the press roller  51 . A nip  54  is formed between the heat roller  50  and the press roller  51 . The sheet P passes through the nip  54  between the heat roller  50  and the press roller  51  along the conveyance path  33 . 
     The heat roller  50  includes a lamp  52  as a heating section. The lamp  52  is positioned in an area surrounded by the heat roller  50 . The lamp  52  heats the heat roller  50 . The lamp  52  faces the press roller  51  in the thickness direction thereof. The lamp  52  has a length in a width direction of the heat roller  50  (hereinafter referred to as a “roller width direction”). It is assumed that the length in the longitudinal direction of the lamp  52  is almost the same as the length in the roller width direction of the heat roller  50 . 
     The switching mechanism  60  is arranged inside the fixing device  34 . The switching mechanism  60  switches positions of the press roller  51 . The switching mechanism  60  moves the press roller  51  towards the heat roller  50 . Further, the heat roller  50  doesn&#39;t move towards the press roller  51 . That is, the position of the heat roller  50  is a fixed position. 
     Hereinafter, the switching mechanism  60  is described. 
       FIG. 2  is a perspective view illustrating the switching mechanism  60  according to the embodiment. For facilitating the description, the heat roller  50  and the press roller  51  are shown in  FIG. 2 . 
     As shown in  FIG. 2 , the heat roller  50  and the press roller  51  face each other in the radial direction. The heat roller  50  and the press roller  51  are arranged to extend in parallel to each other. 
     Supporting members  85  are arranged at both ends of a rotation axis  50   a  of the heat roller  50 . The supporting members  85  are supported by a frame (not shown) in a rotatable manner. It is assumed that the heat roller  50  can be rotated with respect to the frame (not shown) through the supporting members  85 . 
     Supporting members  86  are arranged at both ends of a rotation axis  51   a  of the press roller  51 . The supporting members  86  are supported by a second arm  82  described later in a rotatable manner. It is assumed that the press roller  51  can be rotated with respect to the second arm  82  through the supporting members  86 . 
     The switching mechanism  60  comprises cams  61  and  62 , a driving section  70  and a holding section  80 . 
     The cams  61  and  62  switch the positions of the press roller  51 . The positions of the press roller  51  switched by the switching mechanism  60  includes a separation position, a contact position and a semi-contact position which are described later. Hereinafter, the cam  61  is referred to as a “first cam  61 ”. Moreover, the cam  62  is referred to as a “second cam  62 ”. 
     Hereinafter, the positions of the press roller  51  are described. 
       FIG. 3  is a side view illustrating the separation position of the press roller  51  according to the embodiment.  FIG. 4  is a side view illustrating the semi-contact position of the press roller  51  according to the embodiment.  FIG. 5  is a side view illustrating the contact position of the press roller  51  according to the embodiment. For facilitating the description, side views of a first holding section  80 A and the first cam  61  are illustrated in  FIG. 3 ˜ FIG. 5 . Further, it is assumed that the position of the heat roller  50  is a fixed position in  FIG. 3 ˜ FIG. 5 . 
     As shown in  FIG. 3 , the press roller  51  separates from the heat roller  50 . For example, it is assumed that the switching mechanism  60  switches the position of the press roller  51  to the separation position at the non-sheet-passing time. 
     As shown in  FIG. 4  and  FIG. 5 , the press roller  51  contacts with the heat roller  50 . The nip  54  is formed between the heat roller  50  and the press roller  51 . 
     The press roller  51  shown in  FIG. 5  is contacted with the heat roller  50  at a first pressing force. At the contact position, the press roller  51  contacts with the heat roller  50  at the first pressing force. Hereinafter, the time when the press roller  51  contacts with the heat roller  50  at the first pressing force is referred to as a “contact time”. 
     The press roller  51  shown in  FIG. 4  is contacted with the heat roller  50  at a second pressing force. The second pressing force is smaller than the first pressing force. A position where the press roller  51  contacts with the heat roller  50  at the second pressing force is referred to as a “semi-contact position”. Hereinafter, the time when the press roller  51  contacts with the heat roller  50  at the second pressing force is referred to as a “semi-contact time”. 
     For example, information of normal paper, thick paper and the like serving as the information of the sheet P is set. For example, it is assumed that the normal paper is a copier paper having a thickness of about 0.09 mm. For example, it is assumed that the thick paper is a postcard having a thickness of about 0.25 mm. Alternatively, it is assumed that the thick paper is an envelope having a thickness of about 0.16 mm. The information of the sheet P is input by the user through the control panel  13  (refer to  FIG. 1 ). Further, the information of the sheet P may also be read by the scanner  12  (refer to  FIG. 1 ), a sensor (not shown) and the like. 
     The sensor is arranged enroute on the conveyance path  33 . The sensor detects a front end (downstream end) and a rear end (upstream end) of the sheet P and the thickness of the sheet P. The sensor specifies the category of the sheet P based on the detection result of the sheet P. The control panel  13 , the scanner  12  and the sensor are an input section for inputting the information of the sheet P. 
     For example, in a case of setting a normal paper as the information of the sheet P, the switching mechanism  60  switches the position of the press roller  51  to the contact position. For example, in a case of setting an envelope as the information of the sheet P, the switching mechanism  60  switches the position of the press roller  51  to the semi-contact position. 
     In the present embodiment, the press roller  51  temporarily moves close to the heat roller  50  during a period of time the press roller  51  is separating from the heat roller  50 . 
       FIG. 6  is a side view illustrating a position where the press roller  51  is moved close to a heat roller  50  temporarily during a period of time the press roller  51  is separating from the heat roller  50  according to the embodiment. For facilitating the description, side views of the first holding section  80 A and the first cam  61  are illustrated in  FIG. 6 . Further, it is assumed that the position of the heat roller  50  is a fixed position in  FIG. 6 . Hereinafter, a position where the press roller  51  is moved close to the heat roller  50  temporarily during a period of time the press roller  51  is separating from the heat roller  50  is called as a “fluctuation position”. Hereinafter, a time when the press roller  51  is moved close to a heat roller  50  temporarily during a period of time the press roller  51  is separating from the heat roller  50  is referred to as a “fluctuation time”. Herein, the “temporarily move close to” means that the press roller  51  moves close to the heat roller  50  again from the contact position to the separation position. Further, it is assumed that the fluctuation position is a fifth cam position P 5  which is described later (refer to  FIG. 9  and  FIG. 10 ). 
     As shown in  FIG. 6 , the press roller  51  separates from the heat roller  50  slightly at the fluctuation position. The press roller  51  shown in  FIG. 6  is closer than the press roller  51  at the separation position (refer to  FIG. 3 ) to the heat roller  50 . 
     Hereinafter, the first cam  61  and the second cam  62  are described. 
       FIG. 7  is an illustration diagram of a first cam  61  according to the embodiment.  FIG. 8  is an illustration diagram of a second cam  62  according to the embodiment.  FIG. 9  is an illustration diagram of the first cam  61  and the second cam  62  according to the embodiment. Hereinafter, axes Cp around which the first cam  61  and the second cam  62  rotate are referred as “rotation axes”. 
     For facilitating the description, a plurality of virtual circles a 1 ˜a 4  by taking the rotation axis Cp as a center are illustrated in  FIG. 9 . The plurality of virtual circles a 1 ˜a 4  is located concentrically when viewed from a direction along the rotation axis Cp. As the plurality of virtual circles a 1 ˜a 4 , a first virtual circle a 1 , a second virtual circle a 2 , a third virtual circle a 3  and a fourth virtual circle a 4  are exemplified. It is assumed that the first virtual circle a 1  is a base circle of the first cam  61  and the second cam  62 . The first virtual circle a 1  has a first outer diameter L 1 . The second virtual circle a 2  has a second outer diameter L 2  larger than the first outer diameter L 1 . The third virtual circle a 3  has a third outer diameter L 3  larger than the second outer diameter L 2 . The fourth virtual circle a 4  has a fourth outer diameter L 4  larger than the third outer diameter L 3 . Further, in  FIG. 9 , cam positions P 1 ˜P 5  where the positions of the press roller  51 , the fluctuation position and the like are set are illustrated. Hereinafter, a “cam position” means a position P on a cam surface displaced through the rotation of the first cam  61  and the second cam  62  taking the rotation axis Cp as the center. The cam positions include a first cam position P 1 , a second cam position P 2 , a third cam position P 3 , a fourth cam position P 4  and a fifth cam position P 5 . It is assumed that the first cam position P 1  is the contact position, the second cam position P 2  is the separation position, the third cam position P 3  is the semi-contact position, the fourth cam position P 4  is a boundary position described later, and the fifth cam position P 5  is a position functioning as the fluctuation position. 
     Hereinafter, the first cam  61  is described. 
     As shown in  FIG. 7  and  FIG. 9 , the first cam  61  includes a first cam surface S 10 . The first cam surface S 10  is smoothly continuous in a rotation direction v (driving direction) of the first cam  61 . The first cam  61  includes a first position regulating section S 11 , a second position regulating section S 12 , a third position regulating section S 13  and a position changing section S 15 . The first position regulating section S 11 , the second position regulating section S 12  and the third position regulating section S 13  are positioned at intervals in the rotation direction v of the first cam  61 . 
     The first position regulating section S 11  sets the contact position among the positions of the press roller  51  switched by the switching mechanism  60 . When viewed from the direction along the rotation axis Cp, the first position regulating section S 11  is overlapped with the first cam position P 1  in the fourth virtual circle a 4 . When viewed from the direction along the rotation axis Cp, the first position regulating section S 11  is gently curved such that a convex is formed at the outer peripheral side of the first cam  61 . 
     The second position regulating section S 12  is positioned at a side opposite to the first position regulating section S 11  in the first cam  61 . A line part (not shown) connecting the first position regulating section S 11  with the second position regulating section S 12  forms a long axis of the first cam  61 . The second position regulating section S 12  sets the separation position among the positions of the press roller  51  switched by the switching mechanism  60 . When viewed from the direction along the rotation axis Cp, the second position regulating section S 12  is overlapped with the second cam position P 2  in the first virtual circle a 1 . When viewed from the direction along the rotation axis Cp, the second position regulating section S 12  is curved such that a convex is formed at the inner peripheral side of the first cam  61 . 
     The third position regulating section S 13  sets the semi-contact position among the positions of the press roller  51  switched by the switching mechanism  60 . When viewed from the direction along the rotation axis Cp, the third position regulating section S 13  is overlapped with the third cam position P 3  between the third virtual circle a 3  and the fourth virtual circle a 4 . When viewed from the direction along the rotation axis Cp, the third position regulating section S 13  is gently curved such that a convex is formed at the outer peripheral side of the first cam  61 . 
     The position changing section S 15  is positioned between the first position regulating section S 11  and the second position regulating section S 12  in the rotation direction v of the first cam  61 . The position changing section S 15  includes a fluctuation section for setting the fluctuation position. The position changing section S 15  includes a protruding section  61   b  as a first fluctuation section (fluctuation section). When viewed from the direction along the rotation axis Cp, the protruding section  61   b  is overlapped with a fifth cam position P 5   a  in the third virtual circle a 3 . When viewed from the direction along the rotation axis Cp, the protruding section  61   b  is gently curved such that a convex is formed at the outer peripheral side of the first cam  61 . 
     The position changing section S 15  includes a boundary section S 14 . The boundary section S 14  is positioned between the first position regulating section S 11  and the protruding section  61   b  in the rotation direction v of the first cam  61 . The boundary section S 14  is positioned at the downstream side of the protruding section  61   b  in the rotation direction v of the first cam  61 . Hereinafter, the position of the boundary section S 14  is referred to as a “boundary position”. When viewed from the direction along the rotation axis Cp, the boundary section S 14  is overlapped with a fourth cam position P 4   a  in the second virtual circle a 2 . 
     The first cam  61  includes a cam main body  61   a , the protruding section  61   b  and a position regulating section forming section  61   c . For facilitating the description, a boundary part of the cam main body  61   a , the protruding section  61   b  and the position regulating section forming section  61   c  is represented by two dotted lines in  FIG. 7 . It is assumed that the first cam  61  is a plate cam having a thickness in a direction parallel to the rotation axis Cp. The first cam  61  switches the position at the first end of the press roller  51 . 
     When viewed from the direction along the rotation axis Cp, the protruding section  61   b  protrudes towards the outer peripheral side of the first cam  61 . When viewed from the direction along the rotation axis Cp, the protruding section  61   b  is curved such that a convex is formed at the outer peripheral side of the first cam  61 . When viewed from the direction along the rotation axis Cp, the protruding section  61   b  has an arc shape in which a convex is formed at the outer peripheral side of the first cam  61 . 
     When viewed from the direction along the rotation axis Cp, the position regulating section forming section  61   c  is positioned at the upstream side of the protruding section  61   b  in the rotation direction v. The second position regulating section S 12  is formed between the position regulating section forming section  61   c  and the protruding section  61   b  in the rotation direction v of the first cam  61 . The second position regulating section S 12  extends over the upstream end of the protruding section  61   b  and the downstream end of the position regulating section forming section  61   c  in the rotation direction v of the first cam  61 . The position regulating section forming section  61   c  protrudes towards the outer peripheral side of the first cam  61 . When viewed from the direction along the rotation axis Cp, the position regulating section forming section  61   c  is curved such that a convex is formed at the outer peripheral side of the first cam  61 . The position regulating section forming section  61   c  is curved more gently than the protruding section  61   b . The protruding amount of the position regulating section forming section  61   c  is smaller than that of the protruding section  61   b.    
     In the first cam  61 , the cam main body  61   a , the protruding section  61   b  and the position regulating section forming section  61   c  are formed integrally by the same material. 
     Hereinafter, the second cam  62  is described. 
     As shown in  FIG. 8  and  FIG. 9 , the second cam  62  has a second cam surface S 20  different from the first cam surface S 10 . The second cam surface S 20  is smoothly continuous in the rotation direction v of the second cam  62 . The second cam  62  includes a first position regulating section S 21 , a second position regulating section S 22 , a third position regulating section S 23  and a position changing section S 25 . The first position regulating section S 21 , the second position regulating section S 22  and the third position regulating section S 23  are positioned at intervals in the rotation direction v of the second cam  62 . When viewed from the direction along the rotation axis Cp, the second cam  62  has a shape different from the first cam  61  between the first position regulating section S 21  and the second position regulating section S 22  in the rotation direction v. That is, when viewed from the direction along the rotation axis Cp, the position changing section S 25  of the second cam  62  has a shape different from the position changing section S 15  of the first cam  61 . In other words, when viewed from the direction along the rotation axis Cp, the part of the second cam  62  excluding the position changing section S 25  has a same shape as the part of the first cam  61  excluding the position changing section S 15 . 
     The first position regulating section S 21  sets the contact position among the positions of the press roller  51  switched by the switching mechanism  60 . When viewed from the direction along the rotation axis Cp, the first position regulating section S 21  is overlapped with the first cam position P 1  in the fourth virtual circle a 4 . When viewed from the direction along the rotation axis Cp, the first position regulating section S 21  is gently curved such that a convex is formed at the outer peripheral side of the second cam  62 . When viewed from the direction along the rotation axis Cp, the first position regulating section S 21  of the second cam  62  is consistent with the first position regulating section S 11  of the first cam  61  in the fourth virtual circle a 4 . 
     The second position regulating section S 22  is positioned at a side opposite to the first position regulating section S 21  in the second cam  62 . A line part (not shown) connecting the first position regulating section S 21  with the second position regulating section S 22  forms a long axis of the second cam  62 . The second position regulating section S 22  sets the separation position among the positions of the press roller  51  switched by the switching mechanism  60 . When viewed from the direction along the rotation axis Cp, the second position regulating section S 22  is overlapped with the second cam position P 2  in the first virtual circle a 1 . When viewed from the direction along the rotation axis Cp, the second position regulating section S 22  is curved such that a convex is formed at the inner peripheral side of the second cam  62 . When viewed from the direction along the rotation axis Cp, the second position regulating section S 22  of the second cam  62  is consistent with the second position regulating section S 12  of the first cam  61  in the first virtual circle a 1 . 
     The third position regulating section S 23  sets the semi-contact position among the positions of the press roller  51  switched by the switching mechanism  60 . When viewed from the direction along the rotation axis Cp, the third position regulating section S 23  is overlapped with the third cam position P 3  between the third virtual circle a 3  and the fourth virtual circle a 4 . When viewed from the direction along the rotation axis Cp, the third position regulating section S 23  is gently curved such that a convex is formed at the outer peripheral side of the second cam  62 . When viewed from the direction along the rotation axis Cp, the third position regulating section S 23  of the second cam  62  is consistent with the third position regulating section S 13  of the first cam  61 . 
     The position changing section S 25  is positioned between the first position regulating section S 21  and the second position regulating section S 22  in the rotation direction v of the second cam  62 . The position changing section S 25  includes a fluctuation section for setting the fluctuation position. The position changing section S 25  includes a protruding section  62   b  as a second fluctuation section (fluctuation section). When viewed from the direction along the rotation axis Cp, the protruding section  62   b  is overlapped with a fifth cam position P 5   b  in the third virtual circle a 3 . When viewed from the direction along the rotation axis Cp, the protruding section  62   b  is gently curved such that a convex is formed at the outer peripheral side of the second cam  62 . When viewed from the direction along the rotation axis Cp, the protruding section  62   b  of the second cam  62  is deviated with respect to the protruding section  61   b  of the first cam  61  at the upstream side in the rotation direction v of the second cam  62 . Further, when viewed from the direction along the rotation axis Cp, the protruding section  62   b  of the second cam  62  may be deviated from the protruding section  61   b  of the first cam  61  at the downstream side in the rotation direction v of the second cam  62 . 
     The position changing section S 25  includes a boundary section S 24 . The boundary section S 24  is positioned between the first position regulating section S 21  and the protruding section  62   b  in the rotation direction v of the second cam  62 . The boundary section S 24  is positioned at the downstream side of the protruding section  62   b  in the rotation direction v of the second cam  62 . Hereinafter, the position of the boundary section S 24  is referred to as a “boundary position”. When viewed from the direction along the rotation axis Cp, the boundary section S 24  is overlapped with the fourth cam position P 4   b  in the second virtual circle a 2 . When viewed from the direction along the rotation axis Cp, the boundary section S 24  of the second cam  62  is deviated with respect to the boundary section S 14  of the first cam  61  at the upstream side in the rotation direction v of the second cam  62 . Further, when viewed from the direction along the rotation axis Cp, the boundary section S 24  of the second cam  62  may be deviated from the boundary section S 14  of the first cam  61  at the downstream side in the rotation direction v of the second cam  62 . 
     The second cam  62  includes a cam main body  62   a , the protruding section  62   b  and a position regulating section forming section  62   c . For facilitating the description, a boundary part of the cam main body  62   a , the protruding section  62   b  and the position regulating section forming section  62   c  is represented by two dotted lines in  FIG. 8 . It is assumed that the second cam  62  is a plate cam having a thickness in a direction parallel to the rotation axis Cp. The second cam  62  switches the position at the second end of the press roller  51 . 
     When viewed from the direction along the rotation axis Cp, the protruding section  62   b  protrudes towards the outer peripheral side of the second cam  62 . When viewed from the direction along the rotation axis Cp, the protruding section  62   b  is curved such that a convex is formed at the outer peripheral side of the second cam  62 . When viewed from the direction along the rotation axis Cp, the protruding section  62   b  has an arc shape in which a convex is formed at the outer peripheral side of the second cam  62 . When viewed from the direction along the rotation axis Cp, the protruding section  62   b  of the second cam  62  has the arc shape different from that of the protruding section  61   b  of the first cam  61 . 
     When viewed from the direction along the rotation axis Cp, the position regulating section forming section  62   c  is positioned at the upstream side of the protruding section  62   b  in the rotation direction v. The second position regulating section S 22  is formed between the position regulating section forming section  62   c  and the protruding section  62   b  in the rotation direction v of the second cam  62 . The second position regulating section S 22  extends over the upstream end of the protruding section  62   b  and the downstream end of the position regulating section forming section  62   c  in the rotation direction v of the second cam  62 . The position regulating section forming section  62   c  protrudes towards the outer peripheral side of the second cam  62 . When viewed from the direction along the rotation axis Cp, the position regulating section forming section  62   c  is curved such that a convex is formed at the outer peripheral side of the second cam  62 . The position regulating section forming section  62   c  is curved more gently than the protruding section  62   b . The protruding amount of the position regulating section forming section  62   c  is smaller than that of the protruding section  62   b . When viewed from the direction along the rotation axis Cp, the position regulating section forming section  62   c  of the second cam  62  has a same shape as the position regulating section forming section  61   c  of the first cam  61 . 
     In the second cam  62 , the cam main body  62   a , the protruding section  62   b  and the position regulating section forming section  62   c  are formed integrally by the same material. 
     In the contact position, the outer diameter of the first cam  61  and the second cam  62  is the largest. The outer diameter of the first cam  61  and the second cam  62  is gradually decreased from the contact position to the boundary position. The outer diameter of the first cam  61  and the second cam  62  is gradually increased from the boundary position to the fluctuation position. That is, the outer diameter of the first cam  61  and the second cam  62  is gradually decreased from the fluctuation position to the separation position. That is, the outer diameter of the first cam  61  and the second cam  62  is temporarily increased after being decreased gradually from the contact position to the separation position. 
     In the separation position, the outer diameter of the first cam  61  and the second cam  62  is the smallest. The outer diameter of the first cam  61  and the second cam  62  is gradually increased from the separation position to the semi-contact position. The outer diameter of the first cam  61  and the second cam  62  is gradually increased from the semi-contact position to the contact position. 
     The first cam  61  and the second cam  62  rotate through the driving of the driving section  70 . Hereinafter, the driving section  70  is described. 
     As shown in  FIG. 2 , the driving section  70  comprises, a direct-current motor  71  (DC motor), a gear box  72  and a cam shaft  73 . 
     It is set that the DC motor  71  can rotate in one direction. In this way, the electrical element for controlling the rotation direction is not required, thus reducing the cost. Further, it may be set that the DC motor  71  rotates in both the forward direction and the reverse direction. 
     The DC motor  71  has no function of controlling the motor speed. The DC motor  71  has a T-I (torque versus current) characteristic in which torque is linearly proportional to the input current. The DC motor  71  has a T-N (torque versus number of rotation) characteristic in which number of rotation is linearly inversely proportional to the torque. For example, the DC motor  71  is set to a brush motor. 
     The gear box  72  has a plurality of gears including a gear  72   a . The plurality of gears are meshed with each other. As a result, the gear box  72  decelerates the rotation speed of the DC motor  71 . 
     The cam shaft  73  extends in parallel to the roller width direction. The cam shaft  73  includes a first end  73   t  and a second end  73   e . The first cam  61  is fixed at the first end  73   t  of the cam shaft  73 . The second cam  62  is fixed at the second end  73   e  of the cam shaft  73 . The first cam  61  and the second cam  62  rotate integrally together with the cam shaft  73 . The protruding section  61   b  (refer to  FIG. 7 ) of the first cam  61  and the protruding section  62   b  (refer to  FIG. 8 ) of the second cam  62  differ from each other in the phase. 
     Hereinafter, a phase difference of the first cam  61  and the second cam  62  is described. As shown in  FIG. 9 , the first cam  61  and the second cam  62  rotate integrally taking the cam shaft  73  as a shaft. When viewed from the direction along the rotation axis Cp, it is assumed that the positions of the first position regulating section S 11  of the first cam  61  and the second position regulating section S 21  of the second cam  62  is a phase reference in which there is no phase difference. 
     At the time of the phase reference, there is no phase difference between the second position regulating section S 12  of the first cam  61  and the second position regulating section S 22  of the second cam  62 . At the time of the phase reference, there is no phase difference between the third position regulating section S 13  of the first cam  61  and the second position regulating section S 23  of the second cam  62 . At the time of the phase reference, there is no phase difference between the position regulating section forming section  61   c  of the first cam  61  and the position regulating section forming section  62   c  of the second cam  62 . 
     On the other hand, at the time of the phase reference, there is a phase difference between the position changing section S 15  of the first cam  61  and the position changing section S 25  of the second cam  62 . Specifically, at the time of the phase reference, there is a phase difference between the protruding section  61   b  of the first cam  61  and the protruding section  62   b  of the second cam  62 . At the time of the phase reference, there is a phase difference between the boundary section S 14  of the first cam  61  and the boundary section S 24  of the second cam  62 . 
     As shown in  FIG. 2 , a gear  73   a  is installed on the second end  73   e  of the cam shaft  73 . The gear  73   a  is positioned at the further outer side than the second cam  62  in the longitudinal direction of the cam shaft  73 . 
     A rotation position detection section  106  is installed on the second end  73   e  of the cam shaft  73 . The rotation position detection section  106  is provided with a light shielding plate  108  and an optical sensor  107  (refer to  FIG. 11 ). The light shielding plate  108  is positioned between the second cam  62  and the gear  73   a  in the longitudinal direction of the cam shaft  73 . The optical sensor  107  emits light to the light shielding plate  108  to detect the position of the light shielding plate  108 . 
     The gear  73   a  of the cam shaft  73  is meshed with a gear  72   a  of the gear box  72 . The gear  73   a  is rotated through the rotation of the DC motor  71 . The gear  73   a , the cam shaft  73 , the light shielding plate  108 , the first cam  61  and the second cam  62  rotate integrally. Through the rotation of the DC motor  71 , the gear  73   a , the cam shaft  73 , the light shielding plate  108 , the first cam  61  and the second cam  62  rotate in both the forward direction and the reverse direction. 
     Through the rotation of the DC motor  71 , the light shielding plate  108  shields the light from the optical sensor  107 . Alternatively, through the rotation of the DC motor  71 , the light shielding plate  108  doesn&#39;t shield the light from the optical sensor  107 . Specifically, the light from the optical sensor  107  passes through a cutout section  108   a  of the light shielding plate  108  through the rotation of the DC motor  71 . 
     For example, the optical sensor  107  detects a signal when the light passes through the cutout section  108   a  as a bright signal. The optical sensor  107  detects a signal when the light shielding plate  108  shields the light as a dark signal. The optical sensor  107  detects the rotation positions of the first cam  61  and the second cam  62  according to the bright signal and the dark signal. 
     The first cam  61  and the second cam  62  are held by the holding section  80 . Hereinafter, the holding section  80  is described. 
     As shown in  FIG. 2 , the holding section  80  is positioned at both ends of the rotation axis of the press roller  51 . The holding section  80  comprises the first holding section  80 A and a second holding section  80 B. The first holding section  80 A is positioned at the first end of the rotation axis of the press roller  51 . The second holding section  80 B is positioned at the second end of the rotation shaft of the press roller  51 . Hereinafter, the first holding section  80 A is described. The second holding section  80 B has the same constitutions as the first holding section  80 A, and therefore the description is not provided. 
     The first holding section  80 A has a swing shaft  80   a  extending in parallel to the roller width direction. The first holding section  80 A comprises a first arm  81  and the second arm  82 . It is assumed that the first arm  81  and the second arm  82  can swing through the rotation of the swing shaft  80   a . The switching mechanism  60  maintains the separation position (refer to  FIG. 3 ) through the gravity of the first holding section  80 A. 
     The first arm  81  is formed into an L shape when viewed from the roller width direction. The first arm  81  has a bend section  81   c . The bend section  81   c  is supported by the swing shaft  80   a  in a swingable manner. When viewed from the roller width direction, the first arm  81  is gently inclined such that it is positioned below the cam shaft  73  starting from the bend section  81   c . The first arm  81  extends linearly starting from the bend section  81   c.    
     The first cam  81  includes a first end  81   a  and a second end  81   b . It is assumed that the first end  81   a  is an end at the side of the cam shaft  73  of the first cam  61 . A cam follower  83  is arranged in a rotatable manner in the first end  81   a . The first arm  81  supports the cam follower  83  in a rotatable manner. For example, it is assumed that the cam follower  83  is a roller. 
     It is assumed that the second end  81   b  is an end opposite to the first end  81   a  in the first arm  81 . The second end  81   b  is arranged above the press roller  51 . An elastic member  84  is installed in the second end  81   b . For example, the elastic member  84  is a spring. For example, when viewed from the roller width direction, the stretching direction of the spring is set to a direction intersecting with a line (not shown) passing through the center of the rotation axis  51   a  of the press roller  51  and the center of the swing shaft  80   a.    
     The second arm  82  supports the press roller  51  in a rotatable manner through the supporting members  86 . The second arm  82  is supported by the first arm  81  in a rotatable manner through the swing shaft  80   a  and the elastic member  84 . 
     The second arm  82  covers an upper portion including the bend section  81   c  of the first arm  81 . The second arm  82  includes a first end  82   a  and a second end  82   b . When viewed from the roller width direction, the first end  82   a  overlaps with the bend section  81   c . The first end  82   a  is supported by the swing shaft  80   a  in a rotatable manner. 
     It is assumed that the second end  82   b  is an end opposite to the first end  82   a  in the second arm  82 . The second end  82   b  is positioned above the press roller  51 . The second end  82   b  includes an inner wall surface facing the second end  81   b  of the first arm  81 . The elastic member  84  is installed on the inner wall surface of the second end  82   b . The elastic member  84  extends in one direction. The elastic member  84  includes a first end  84   a  and a second end  84   b . The first end  84   a  of the elastic member  84  is installed in the second end  81   b  of the first arm  81 . The second end  84   b  of the elastic member  84  is installed in the inner wall surface of the second end  82   b  of the second arm  82 . 
     Hereinafter, the cam follower  83  of the first holding section  80 A is described. 
     The cam follower  83  of the first holding section  80 A is contacted with the first cam  61 . Specifically, at the contact time, the cam follower  83  of the first holding section  80 A is contacted with the first position regulating section S 11  (refer to  FIG. 5 ) of the first cam  61 . At the separation time, the cam follower  83  of the first holding section  80 A is contacted with the second position regulating section S 12  (refer to  FIG. 3 ) of the first cam  61 . At the semi-contact time, the cam follower  83  of the first holding section  80 A is contacted with the third position regulating section S 13  (refer to  FIG. 4 ) of the first cam  61 . At the fluctuation time, the cam follower  83  of the first holding section  80 A is contacted with the protruding section  61   b  of the first cam  61  (the fluctuation section of the position changing section S 15 ) (refer to  FIG. 6 ). 
     The cam follower  83  of the first holding section  80 A is driven by the rotation of the first cam  61  to rotate. The elastic member  84  of the first holding section  80 A energizes in a direction in which the cam follower  83  is pressed against the first cam  61 . Further, the elastic member  84  of the first holding section  80 A energizes in a direction in which the press roller  51  is pressed against the heat roller  50 . 
     Hereinafter, the cam follower  83  of the second holding section  80 B is described. 
     The cam follower  83  of the second holding section  80 B is contacted with the second cam  62 . Specifically, at the contact time, the cam follower  83  of the second holding section  80 B is contacted with the first position regulating section S 21  of the second cam  62 . At the separation time, the cam follower  83  of the second holding section  80 B is contacted with the second position regulating section S 22  of the second cam  62 . At the semi-contact time, the cam follower  83  of the second holding section  80 B is contacted with the third position regulating section S 23  of the second cam  62 . At the fluctuation time, the cam follower  83  of the second holding section  80 B is contacted with the protruding section  62   b  of the second cam  62  (the fluctuation section of the position changing section S 25 ). 
     The cam follower  83  of the second holding section  80 B is driven by the rotation of the second cam  62  to rotate. The elastic member  84  of the second holding section  80 B energizes in a direction in which the cam follower  83  is pressed against the second cam  62 . Further, the elastic member  84  of the second holding section  80 B energizes in a direction in which the press roller  51  is pressed against the heat roller  50 . 
     Hereinafter, the switching of the positions of the press roller  51  by the switching mechanism  60  is described. 
     The switching mechanism  60  switches the positions of the press roller  51  through the rotation of the DC motor  71 . In other words, the switching mechanism  60  switches the contact position, the separation position and the semi-contact position of the press roller  51  through the rotation of the DC motor  71 . 
     The elastic member  84  energizes in a direction in which the press roller  51  is pressed against the heat roller  50 . The elastic member  84  is compressed according to an amount of swing displacement of the first arm  81  against the second arm  82  when the press roller  51  is pressed against the heat roller  50 . At the contact position, the elastic member  84  is compressed according to a first amount of swing displacement. At the semi-contact position, the elastic member  84  is compressed according to a second amount of swing displacement. The second amount of swing displacement is smaller than the first amount of swing displacement. 
     The press roller  51  presses the heat roller  50  resiliently through a restoring force of the elastic member  84 . The pressing force of the elastic member  84  generates when the press roller  51  is contacted with the heat roller  50 . 
       FIG. 10  is a graph illustrating a relation between a cam position P and a time T of the first cam  61  and the second cam  62  according to the embodiment. 
     Herein, the “time T” means a time the first cam  61  and the second cam  62  rotate when the first cam  61  and the second cam  62  rotate around the rotation axis Cp in the direction indicated by the arrow v at constant speeds. Hereinafter, a distance from the rotation axis Cp to the cam surface S 10 , S 20  displaced through the rotation of the first cam  61  and the second cam  62  around the rotation axis Cp in the direction indicated by the arrow v is referred to as “an amount of cam displacement”. That is, the amount of cam displacement means a change of cam ridge when the first cam  61  and the second cam  62  rotate at a constant speed. 
     Hereinafter, the relation between the time T of the first cam  61  and the second cam  62  and the cam position P is described with reference to  FIG. 9  and  FIG. 10 . 
     In  FIG. 10 , a graph C 1  indicated by a solid line indicates a relation between the time T of the first cam  61  and the cam position P. A graph C 2  indicated by a dotted line illustrates a relation between the time T of the second cam  62  and the cam position P. It is assumed that a time T 0  is a time when the first cam  61  and the second cam  62  start to rotate (hereinafter referred to as a “rotation start time”). It is assumed that the first cam position P 1  (contact position) when the time T 0  is set to a rotation start time is a reference position before the first cam  61  and the second cam  62  rotate. 
     Hereinafter, as to the time T 0  and times T 1 ˜T 10 , the changes of the cam position P of the first cam  61  are mainly described. 
     As shown in  FIG. 9  and  FIG. 10 , the first cam  61  is maintained at the first cam position P 1  from the time T 0  to the time T 1 . From the time T 1  to a time T 2 , the cam position P of the first cam  61  changes. Specifically, from the time T 1  to the time T 2 , the amount of cam displacement is gradually reduced from the first cam position P 1  in the fourth virtual circle a 4  to a fourth cam position P 4   a  in the second virtual circle a 2 . 
     The first cam  61  is maintained at the fourth cam position P 4   a  from the time T 2  to a time T 3 . From the time T 3  to a time T 4 , the cam position P of the first cam  61  changes. Specifically, from the time T 3  to the time T 4 , the amount of cam displacement is gradually increased from the fourth cam position P 4   a  in the second virtual circle a 2  to a fifth cam position P 5   a  in the third virtual circle a 3 . 
     The first cam  61  is maintained at the fifth cam position P 5   a  from the time T 4  to a time T 5 . From the time T 5  to a time T 6 , the cam position P of the first cam  61  changes. Specifically, from the time T 5  to the time T 6 , the amount of cam displacement is gradually reduced from the fifth cam position P 5   a  in the third virtual circle a 3  to a second cam position P 2  in the first virtual circle a 1 . 
     The first cam  61  is maintained at the second cam position P 2  from the time T 6  to a time T 7 . From the time T 7  to a time T 8 , the cam position P of the first cam  61  changes. Specifically, from the time T 7  to the time T 8 , the amount of cam displacement is gradually increased from the second cam position P 2  in the first virtual circle a 1  to a third cam position P 3 . 
     The first cam  61  is maintained at the third cam position P 3  from the time T 8  to a time T 9 . From the time T 9  to a time T 10 , the cam position P of the first cam  61  changes. Specifically, from the time T 9  to the time T 10 , the amount of cam displacement is gradually increased from the third cam position P 3  to the first cam position P 1  in the fourth virtual circle a 4 . 
     The first cam  61  repeats the changes of the cam position P described above after the time T 10 . In other words, the time T 10  is equivalent to the time T 0 . 
     Hereinafter, as to the time T 0  and times T 11 ˜T 20 , the changes of the cam position P of the second cam  62  are mainly described. 
     As shown in  FIG. 9  and  FIG. 10 , the second cam  62  is maintained at the first cam position P 1  from the time T 0  to the time T 11 . By setting an interval from the time T 0  to the time T 11  to be longer than an interval from the time T 0  to the time T 1 , the second cam  62  is maintained at the first cam position P 1  for a period of time longer than that of the first cam  61 . 
     From the time T 11  to a time T 12 , the cam position P of the second cam  62  changes. Specifically, from the time T 11  to the time T 12 , the amount of cam displacement is gradually reduced from the first cam position P 1  in the fourth virtual circle a 4  to a fourth cam position P 4   b  in the second virtual circle a 2 . 
     The second cam  62  is maintained at the fourth cam position P 4   b  from the time T 12  to a time T 13 . By setting the time T 12  to be longer than the time T 3 , a maintained time of the fourth cam position P 4   b  of the second cam  62  is deviated with respect to a maintained time of the fourth cam position P 4   a  of the first cam  61 . That is, the maintained time of the fourth cam position P 4   b  of the second cam  62  is delayed in time with respect to the maintained time of the fourth cam position P 4   a  of the first cam  61 . 
     From the time T 13  to a time T 14 , the cam position P of the second cam  62  changes. Specifically, from the time T 13  to the time T 14 , the amount of cam displacement is gradually increased from the fourth cam position P 4   b  in the second virtual circle a 2  to a fifth cam position P 5   b  in the third virtual circle a 3 . 
     The second cam  62  is maintained at the fifth cam position P 5   b  from the time T 14  to a time T 15 . By setting the time T 14  to be longer than the time T 5 , a maintained time of the fifth cam position P 5   b  of the second cam  62  is deviated with respect to a maintained time of the fifth cam position P 5   a  of the first cam  61 . That is, the maintained time of the fifth cam position P 5   b  of the second cam  62  is delayed in time with respect to the maintained time of the fifth cam position P 5   a  of the first cam  61 . 
     From the time T 15  to a time T 16 , the cam position P of the second cam  62  changes. Specifically, from the time T 15  to the time T 16 , the amount of cam displacement is gradually reduced from the fifth cam position P 5   b  in the third virtual circle a 3  to the second cam position P 2  in the first virtual circle a 1 . 
     The time T 16  is set to be identical with the time T 6 . That is, an interval from the time T 0  to the time T 16  is set to be identical with an interval from the time T 0  to the time T 6 . 
     The second cam  62  is maintained at the second cam position P 2  from the time T 16  to a time T 17 . By setting the time T 17  to be identical with the time T 7 , the maintained time of the second cam position P 2  is set to be identical with each other in both the first cam  61  and the second cam  62 . 
     From the time T 17  to a time T 18 , the cam position P of the second cam  62  changes. Specifically, from the time T 17  to the time T 18 , the amount of cam displacement is gradually increased from the second cam position P 2  in the first virtual circle a 1  to the third cam position P 3 . By setting the time T 18  to be identical with the time T 8 , the amounts of cam displacement are set to be identical with each other in both the first cam  61  and the second cam  62 . 
     The second cam  62  is maintained at the third cam position P 3  from the time T 18  to a time T 19 . By setting the time T 19  to be identical with the time T 9 , the maintained time of the third cam position P 3  is set to be identical with each other in both the first cam  61  and the second cam  62 . 
     From the time T 19  to a time T 20 , the cam position P of the second cam  62  changes. Specifically, from the time T 19  to the time T 20 , the amount of cam displacement is gradually increased from the third cam position P 3  to the first cam position P 1  in the fourth virtual circle a 4 . By setting the time T 20  to be identical with the time T 10 , the amounts of cam displacement are set to be identical with each other in both the first cam  61  and the second cam  62 . 
     The second cam  62  repeats the changes of the cam position P described above after the time T 20 . In other words, the time T 20  is equivalent to the time T 0 . 
     Hereinafter, the operations of the first cam  61  and the second cam  62  from the first cam position P 1  (reference position) to the second cam position P 2  are described with respect to  FIG. 7 ˜ FIG. 9 . 
     Hereinafter, the actions of the first cam  61  are mainly described. As to the parts having same action as the first cam  61  in the second cam  62 , the description thereof is not provided. 
     As shown in  FIG. 7  and  FIG. 9 , the protruding section  61   b  is positioned between the first cam position P 1  and the second cam position P 2  in the rotation direction v of the first cam  61 . By arranging the protruding section  61   b  at such a position, the following action is provided. When the first cam  61  moves from the first cam position P 1  to the second cam position P 2  in the rotation direction v of the first cam  61 , the protruding section  61   b  moves the press roller  51  close to the heat roller  50  temporarily during a period of time the press roller  51  is separating from the heat roller  50 . When the first cam  61  moves from the first cam position P 1  to the second cam position P 2  in the rotation direction v of the first cam  61 , the press roller  51  moves close to the heat roller  50  temporarily. Compared to a case in which the protruding section  61   b  is not arranged, a speed of separating the press roller  51  from the heat roller  50  (hereinafter referred to as a “separation speed”) decelerates between the first cam position P 1  and the second cam position P 2 . By decelerating the separation speed of the press roller  51 , the load fluctuation at the switch time is reduced. 
     When viewed from the direction along the rotation axis Cp, the protruding section  61   b  is curved such that a convex is formed at the outer peripheral side of the first cam  61 . By arranging the protruding section  61   b  in such a manner, the separation speed of the press roller  51  decelerates gradually. Consequently, the load fluctuation at the switch time is reduced gradually. 
     Hereinafter, the actions of the second cam  62  different from those of the first cam  61  are described. 
     As shown in  FIG. 8  and  FIG. 9 , when viewed from the direction along the rotation axis Cp, the protruding section  62   b  of the second cam  62  is slightly deviated to the upstream side of the protruding section  61   b  of the first cam  61  in the rotation direction v. By making the protruding section  62   b  of the second cam  62  deviate from the protruding section  61   b  of the first cam  61  in the rotation direction v, deceleration timings of the first cam  61  and the second cam  62  are deviated from each other. As a result, the load fluctuation at the switch time is distributed. Further, when viewed from the direction along the rotation axis Cp, the protruding section  62   b  of the second cam  62  may be slightly deviated to the downstream side of the protruding section  61   b  of the first cam  61  in the rotation direction v. 
     Hereinafter, a control system  110  which controls the switching mechanism  60  is described. 
       FIG. 11  is a block diagram illustrating the control system  110  mainly controlling the switching mechanism  60  according to the embodiment. 
     As shown in  FIG. 11 , the control system  110  comprises a main body control circuit  101 . In the main body control circuit  101 , a temperature sensor  104 , a timer  105 , a power supply circuit  102 , a motor driving circuit  103 , the DC motor  71  and the optical sensor  107  are electrically connected. 
     The temperature sensor  104  detects the temperature of the heat roller  50 . The timer  105  manages the time. The power supply circuit  102  supplies power to the lamp  52 . The motor driving circuit  103  rotates the heat roller  50  and the press roller  51  in a conveyance direction of the sheet P. By enabling the DC motor  71  to rotate in one direction, the first cam  61  and the second cam  62  can also be set to rotate in one direction (the direction indicated by the arrow v). Further, by enabling the DC motor  71  to rotate in both the forward direction and the reverse direction, the first cam  61  and the second cam  62  may also be set to rotate in both the forward direction and the reverse direction. The optical sensor  107  detects the rotation positions of the first cam  61  and the second cam  62 . 
     The main body control circuit  101  controls ON/OFF of power supply to the power supply circuit  102  based on the detection result of the temperature sensor  104 . In this way, the heat generation of the lamp  52  is controlled. As a result, the heat generation of the heat roller  50  is controlled. Thus, the fixing temperature is maintained. 
     The main body control circuit  101  switches the positions of the press roller  51  by rotating the DC motor  71 . For example, at the non-sheet-passing time, the main body control circuit  101  sets the press roller  51  at the separation position, which prevents the heat roller  50  and the press roller  51  from roller creep. 
     On the other hand, at the sheet-passing time, the main body control circuit  101  sets the press roller  51  to be at the contact position. For example, the main body control circuit  101  switches the positions of the press roller  51  based on the information of the sheet P. For example, in a case of setting the normal paper as the information of the sheet P, the press roller  51  is set to be at the contact position. For example, in a case of setting the thick paper as the information of the sheet P, the press roller  51  is set to be at the semi-contact position. 
     The main body control circuit  101  stops at each position of the positions of the press roller  51  switched by the switching mechanism  60  based on the detection result of the optical sensor  107 . 
     Incidentally, there is a possibility that a motion sound generates due to the load fluctuation at the switch time. Especially, the pressing force of the press roller  51  is set to be large in the high-speed color copier to guarantee the fixing property. The press roller  51  presses the heat roller  50  to form the nip  54 . To guarantee the fixing property, it is necessary to guarantee that the nip  54  is wide. To guarantee that the nip  54  is wide, it is considered to increase an amount of engagement. Further, reducing the heat capacity of the heat roller  50  is effective to shorten a warming-up time and a first print time. It is required to separate the press roller  51  from the heat roller  50  absolutely at a non-sheet-passing time to reduce the heat capacity of the heat roller  50 . However, if the amount of engagement is increased at the sheet-passing time, the movement distance of the press roller  51  from the contact position to the separation position becomes long. At this time, to realize miniaturization and low cost, enough space for the switching mechanism can hardly be guaranteed in the high-speed color copier. Thus, in the high-speed color copier, the load fluctuation at the switch time tends to become large, and therefore there is a possibility that the motion sound becomes louder. 
     In accordance with the present embodiment, the first cam  61  includes the first position regulating section S 11 , the second position regulating section S 12 , and the position changing section S 15 . The first position regulating section S 11  sets the contact position. The second position regulating section S 12  sets the separation position. The position changing section S 15  is positioned between the first position regulating section S 11  and the second position regulating section S 12  in the rotation direction v of the first cam  61 . The position changing section S 15  includes the fluctuation section for setting the fluctuation position. The position changing section S 15  includes the protruding section  61   b  as the first fluctuation section (fluctuation section). The protruding section  61   b  moves the press roller  51  close to the heat roller  50  temporarily during a period of time the press roller  51  is separating from the heat roller  50 . The protruding section  61   b  is positioned between the first position regulating section S 11  and the second position regulating section S 12  in the rotation direction v of the first cam  61 , in this way, the following action is provided. When the first cam  61  moves from the first cam position P 1  to the second cam position P 2  in the rotation direction v of the first cam  61 , the protruding section  61   b  moves the press roller  51  close to the heat roller  50  temporarily during a period of time the press roller  51  is separating from the heat roller  50 . When the first cam  61  moves from the first cam position P 1  to the second cam position P 2  in the rotation direction v of the first cam  61 , the press roller  51  moves close to the heat roller  50  temporarily. Compared to a case in which the protruding section  61   b  is not arranged, the separation speed of the press roller  51  decelerates between the first cam position P 1  and the second cam position P 2 . By decelerating the separation speed of the press roller  51 , the load fluctuation at the switch time is reduced. Thus, it is possible to lower the motion sound at the switch time. 
     The first cam  61  and the second cam  62  different from the first cam  61  are arranged as the cam. A first fluctuation section arranged in the first cam  61  and a second fluctuation section arranged in the second cam  62  are arranged as the fluctuation section. The first cam  61  is provided with the protruding section  61   b  as the first fluctuation section. The second cam  62  is provided with the protruding section  62   b  as the second fluctuation section. The first cam  61  switches the position at a first end of the press roller  51 . The second cam  62  switches the position at a second end of the press roller  51 . By arranging the first cam  61  and the second cam  62 , the deceleration timings at the two ends of the press roller  51  can be deviated from each other. As a result, the load fluctuation at the switch time can be distributed. Thus, the motion sound at the switch time can be effectively lowered when compared with a case in which cams having same fluctuation sections are arranged. 
     The first cam  61  and the second cam  62  rotate integrally together with the cam shaft  73 . The protruding section  61   b  (first fluctuation section) and the protruding section  62   b  (second fluctuation section) differs from each other in phases. For example, by making the protruding section  62   b  of the second cam  62  deviate from the protruding section  61   b  of the first cam  61  in the rotation direction v, the deceleration timings of the first cam  61  and the second cam  62  are deviated from each other. As a result, the load fluctuation at the switch time can be distributed. Thus, the motion sound at the switch time can be effectively lowered when compared with a case in which cams having same phases are arranged. 
     When viewed from the direction along the rotation axis Cp, the protruding section  61   b  is curved such that a convex is formed at the outer peripheral side of the first cam  61 . By arranging the protruding section  61   b  in such a manner, the separation speed of the press roller  51  can decelerate gradually. Consequently, the load fluctuation at the switch time can be reduced gradually. Thus, the motion sound at the switch time can be effectively lowered. 
     When viewed from the direction along the rotation axis Cp, the second position regulating section S 12  is curved such that a convex is formed at the inner peripheral side of the first cam  61 . The separation position is easier to be maintained when compared with a case in which the second position regulating section S 12  is curved such that a convex is formed at the outer peripheral side of the first cam  61 . 
     The DC motor  71  is provided as a motor for driving the first cam  61 . The DC motor  71  has no function of controlling the motor speed. For example, the DC motor  71  is set to a brush motor. When compared with a case of comprising a stepping motor as the motor for driving the first cam  61 , simplicity and low cost can be realized while motion sound at the switch time occurs easily in a case of comprising the brush motor. Thus, by comprising the DC motor  71 , simplicity and low cost can be realized and the practical benefit in lowering the motion sound at the switch time is large. 
     The cam main body  61   a  and the protruding section  61   b  are formed integrally with the same material. When compared with a case in which the cam main body  61   a  and the protruding section  61   b  are formed separately from each other with different materials, the simplicity and low cost of the first cam  61  can be realized. 
     The first cam  61  further comprises the third position regulating section S 13  for setting the semi-contact position. Thus, the motion sound at the switch time can be lowered in the constitution having the separation position, the contact position and the semi-contact position as the positions of the press roller  51 . 
     Hereinafter, modifications are described. 
     For example, a fixing belt may be arranged as the fixing member. The fixing belt has a conductive layer. By heating the conductive layer of the fixing belt through an electromagnetic induction heating system (hereinafter referred to as an “IH system”), the conductive layer generates heat through induction current. Thus, the motion sound at the switch time can be lowered in the IH system. 
     The cam is not limited to the plate cam. For example, the cam may be a translating cam, a plane groove cam, a conjugate cam, an end face cam, a cylindrical cam, a spherical cam, and the like. The switching mechanism may be changed according to the design specification. 
     The driving of the cam is not limited to rotating the cam. For example, in a case in which the cam is a translating cam, the driving of the cam may be straight advancing driving. The driving of the cam may be changed according to the shape of the cam and the like. 
     Cams having same fluctuation sections with each other may be arranged as the cams. When compared with a case of comprising cams having fluctuation sections different from each other, the simplicity and low cost can be realized. 
     The first cam  61  and the second cam  62  may rotate separately from the cam shaft  73 . The first cam  61  and the second cam  62  may be driven independently from each other. For example, the first cam  61  may switch the position at the first end of the press roller  51  separately from the switching by the second cam  62 . The second cam  62  may switch the position at the second end of the press roller  51  separately from the switching by the first cam  61 . 
     When viewed from the direction along the rotation axis Cp, the fluctuation section is not limited to include a protruding section which protrudes towards the outer peripheral side of the cam. For example, when viewed from the direction along the rotation axis Cp, a recess part (recess) recessed towards the inner peripheral side of the cam may be formed as the fluctuation section. 
     The holding section  80  may not comprise the first arm  81  and the second arm  82 . For example, the holding section may comprise one arm but not a plurality of arms. The holding section may support the press roller  51  and the cam follower  83  in a rotatable manner through the one arm. 
     It is not limited to arrange a brush motor as the motor for driving the first cam  61 . For example, a stepping motor may be arranged as the motor for driving the first cam  61 . 
     The cam main body  61   a  and the protruding section  61   b  are not limited to be formed integrally with same material. For example, the cam main body  61   a  and the protruding section  61   b  may be formed separately from each other with different material. 
     The first cam  61  may not comprise the third position regulating section S 13  for setting the semi-contact position. In a case of not comprising the third position regulating section S 13 , the motion sound at the switch time can be lowered in the constitution having the separation position and the contact position as the positions of the press roller  51 . 
     Further, it is not limited to that the press roller  51  (the first roller) moves towards the heat roller  50  (the second roller). For example, the heat roller  50  (the second roller) may move towards the press roller  51  (the first roller). In a case in which the heat roller  50  moves towards the press roller  51 , the press roller  51  doesn&#39;t move towards the heat roller  50 . That is, the position of the press roller  51  is set to a fixed position. 
     In accordance with at least one embodiment described above, the first cam  61  includes the first position regulating section S 11 , the second position regulating section S 12 , and the position changing section S 15 . The first position regulating section S 11  sets the contact position. The second position regulating section S 12  sets the separation position. The position changing section S 15  is positioned between the first position regulating section S 11  and the second position regulating section S 12  in the rotation direction v of the first cam  61 . The position changing section S 15  includes the fluctuation section for setting the fluctuation position. The position changing section S 15  includes the protruding section  61   b  as the first fluctuation section (fluctuation section). The protruding section  61   b  moves the press roller  51  close to the heat roller  50  temporarily during a period of time the press roller  51  is separating from the heat roller  50 . The protruding section  61   b  is positioned between the first position regulating section S 11  and the second position regulating section S 12  in the rotation direction v of the first cam  61 , in this way, the following action is provided. When the first cam  61  moves from the first cam position P 1  to the second cam position P 2  in the rotation direction v of the first cam  61 , the protruding section  61   b  moves the press roller  51  close to the heat roller  50  temporarily during a period of time the press roller  51  is separating from the heat roller  50 . When the first cam  61  moves from the first cam position P 1  to the second cam position P 2  in the rotation direction v of the first cam  61 , the press roller  51  moves close to the heat roller  50  temporarily. Compared to a case in which the protruding section  61   b  is not arranged, the separation speed of the press roller  51  decelerates between the first cam position P 1  and the second cam position P 2 . By decelerating the separation speed of the press roller  51 , the load fluctuation at the switch time is reduced. Thus, it is possible to lower the motion sound at the switch time. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.