Patent Publication Number: US-10787758-B2

Title: Needle plate detachable mechanism and sewing machine having needle plate detachable mechanism

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This patent specification is based on Japanese patent application, No. 2018-96050 filed on May 18, 2018 in the Japan Patent Office, the entire contents of which are incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a needle plate detachable mechanism and a sewing machine having the needle plate detachable mechanism. 
     2. Description of the Related Art 
     Patent documents 1 and 2 below disclose a needle plate detachable mechanism of a sewing machine. In the needle plate detachable mechanism, a needle plate is fixed to a bed part of the sewing machine when a plate spring provided on the needle plate is engaged with an engaging member of a sewing machine body. In addition, the needle plate detachable mechanism has a release lever which is manually operable and a push-up bar which is arranged between the release lever and the needle plate. The engaged state between the plate spring and the engaging member is released by manually operating the release lever to push up the needle plate via the push-up bar. Consequently, the needle plate is detached from the sewing machine body. Thus, the needle plate can be replaced.
     [Patent document 1] Japanese Unexamined Patent Application Publication No. 2013-48846   [Patent document 2] Japanese Unexamined Patent Application Publication No. 2016-36570   

     BRIEF SUMMARY OF THE INVENTION 
     In the sewing machine, when a needle descends from a top dead center to a bottom dead center, the needle passes through a needle hole of the needle plate. In Patent documents 1 and 2, the release lever or the lock mechanism can be operated regardless of a vertical position of the needle. Namely, in Patent documents 1 and 2, if the release lever or the lock mechanism is operated when the needle is located at the bottom dead center, for example, a fixed state of the needle plate is released in a state that the needle passes through the needle hole. In this state, the needle plate cannot be detached from the needle since the needle passes through the needle hole although the fixed state of the needle plate is released. The above described situation is not suitable for replacing the needle plate. 
     In addition, when a sewing machine motor is driven, an operator sews sewing objects. In such situation, the operator has no intention to replace the needle plate. Thus, the above described situation is also not suitable for replacing the needle plate. 
     As explained above, it is preferable to adapt the structure of preventing the replacement of the needle plate in the situation not suitable for replacing the needle plate. 
     Considering the above described fact, the present invention provides a needle plate detachable mechanism capable of preventing the replacement of the needle plate in the situation not suitable for replacing the needle plate and a sewing machine having the needle plate detachable mechanism. 
     One or more embodiments of the present invention relate to a needle plate detachable mechanism of a sewing machine which forms a seam by vertically driving a needle by a driving force of a sewing machine motor, having: a needle plate fixing unit capable of being switched between a fixed state where a needle plate is fixed to a sewing machine body and an unfixed state where the fixed state is released; and a switching mechanism which is connected with the needle plate fixing unit for switching the needle plate fixing unit between the fixed state and the unfixed state, wherein the needle plate fixing unit is prevented from being switched when the needle is positioned below an upper surface of the needle plate or when the sewing machine motor is driven. 
     One or more embodiments of the present invention relate to the needle plate detachable mechanism characterized in that the needle plate fixing unit includes: a rotary unit provided on the lower surface of the needle plate; and a needle plate engaging unit provided to be integrally rotatable with the rotary unit, wherein when the rotary unit is rotated, the needle plate engaging unit is rotated between an engaged position where the needle plate engaging unit is engaged with the needle plate and a disengaged position where the needle plate engaging unit is disengaged from the needle plate, and the needle plate fixing unit is switched between the fixed state and the unfixed state when the needle plate engaging unit is rotated between the engaged position and the disengaged position 
     One or more embodiments of the present invention relate to the needle plate detachable mechanism characterized in that the needle plate engaging unit includes: a hook portion which is engaged with the needle plate at the engaged position; and a push-up portion which pushes up the needle plate with respect to the sewing machine body at the disengaged position. 
     One or more embodiments of the present invention relate to the needle plate detachable mechanism characterized in that the switching mechanism includes a driving unit which is connected with the rotary unit for rotatably driving the rotary unit. 
     One or more embodiments of the present invention relate to a sewing machine having the above described needle plate detachable mechanism. 
     One or more embodiments of the present invention relate to the needle plate detachable mechanism having a detector for detecting a vertical position of the needle, wherein the switching mechanism is operated interlockingly with the detector to prevent the needle plate fixing unit of the switching mechanism from being switched from the fixed state to the unfixed state when the needle is positioned below an upper surface of the needle plate. 
     By adopting the needle plate detachable mechanism and the sewing machine having the above described configuration, the replacement of the needle plate can be prevented in the situation not suitable for replacing the needle plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a needle plate detachable mechanism of the present embodiment. 
         FIG. 2  is a perspective view of an entire sewing machine to which the needle plate detachable mechanism of the present embodiment is applied, viewed obliquely from the front right. 
         FIG. 3  is a schematic diagram schematically showing a drive mechanism of the sewing machine shown in  FIG. 2 . 
         FIG. 4A  is a block diagram of the sewing machine shown in  FIG. 2 .  FIG. 4B  is a graph showing a vertical position of a needle corresponding to a rotation angle of an upper shaft. 
         FIG. 5  is an operation flow of the needle plate detachable mechanism of the present embodiment. 
         FIG. 6A  is a front view showing the state where the needle plate fixing unit shown in  FIG. 1  is arranged in the engaged position, viewed from the front.  FIG. 6B  is a front view showing a state where the needle plate fixing unit is rotated from the state shown in  FIG. 6A  to a release position.  FIG. 6C  is a front view showing a state where the needle plate fixing unit is rotated from the state shown in  FIG. 6B  to a push-up position. 
         FIG. 7  is a timing chart of the needle plate detachable mechanism of the present embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereafter, with reference to the drawings, a sewing machine  10  to which a needle plate detachable mechanism  66  of the present embodiment is applied will be explained. In the arrow marks shown in the drawings, the arrow mark UP indicates upward, the arrow mark FR indicates frontward, and the arrow mark RH indicates rightward (one of the width direction) of the sewing machine  10 . Hereafter, when front-rear, up-down and left-right directions are used in the explanation, the directions indicate the front-rear, up-down and left-right directions of the sewing machine  10  unless otherwise defined. 
     (Entire Constitution of Sewing Machine) 
     As shown in  FIG. 2 , the sewing machine  10  as a whole has an approximately U-shape opened to the left side in a front view when viewed from the front. Specifically, the sewing machine  10  includes a post part  12  which is vertically extended to form the right end of the sewing machine  10 , an arm part  14  which is extended to the left from the upper end of the post part  12 , and a bed part  16  which is extended to the left from the lower end of the post part  12  to serve as “sewing machine body.” In addition, a skeleton frame (not shown in the figure) forming a frame of the sewing machine  10  is provided inside the sewing machine  10 . 
     In addition, the sewing machine  10  has a needle plate  60  which is provided on an upper part of the left side of the bed part  16 . Furthermore, the sewing machine  10  has a needle plate detachable mechanism  66  (shown in  FIG. 1 ) for detachably fixing the needle plate  60  and a needle drive mechanism  20  (shown in  FIG. 3 ) for vertically driving a needle  36 . Hereafter, configurations of the sewing machine  10  will be explained. 
     (About Needle Drive Mechanism) 
     As shown in  FIG. 3 , the needle drive mechanism  20  includes a sewing machine motor  22 , an upper shaft  26 , a connection mechanism  30 , a needle bar  34  and a lower shaft  38 . The sewing machine motor  22  is fixed to the skeleton frame so that the axial direction of the sewing machine motor  22  is aligned with the left-right direction. As shown in  FIG. 4A , the sewing machine motor  22  is electrically connected with a controller  94  which will be explained later. An operation part  24  is electrically connected with the controller  94 . As shown in  FIG. 2 , the operation part  24  is provided on the front part of the sewing machine  10  (post part  12 ) so as to be operable. The operation part  24  includes a display part and a touch panel. When an operator touches icons displayed on the operation part  24 , operation signals of the sewing machine motor  22  and the later described needle plate motor  78  are outputted from the operation part  24  to the controller  94 . 
     As shown in  FIG. 3 , the upper shaft  26  is rotatably supported by the skeleton frame in the arm part  14  (not shown in  FIG. 3 ) so that the axial direction of the upper shaft  26  is aligned with the left-right direction. In addition, a belt  28  is laid between the right end of the upper shaft  26  and an output shaft of the sewing machine motor  22 . Thus, rotative force of the sewing machine motor  22  is transferred to the upper shaft  26 . Consequently, when the sewing machine motor  22  is driven, the upper shaft  26  is rotated around its axis. In addition, a flywheel  29  (shown in  FIG. 2 ) is connected with the right end of the upper shaft  26 . The flywheel  29  is arranged on the right side of the post part  12  of the sewing machine  10  and exposed outside the sewing machine  10  to be operable. When an operator rotationally operates the flywheel  29 , the sewing machine  10  (upper shaft  26 ) can be manually driven. In addition, a crank rod  32  which forms the connection mechanism  30  is connected with the left end of the upper shaft  26 . 
     The needle bar  34  is arranged on the left side of the connection mechanism  30  so that the axial direction of the needle bar  34  is aligned with the up-down direction. The crank rod  32  of the connection mechanism  30  is connected with the needle bar  34 . When the upper shaft  26  is rotated, the needle bar  34  moves vertically. In addition, the needle  36  for sewing the sewing objects is detachably fixed to the lower end of the needle bar  34 . According to the vertical movement of the needle bar  34 , the needle  36  is moved vertically. Namely, the vertical position of the needle  36  is determined corresponding to the rotation angle of the upper shaft  26 . 
     Specifically, as shown in  FIG. 4B , the needle  36  moves vertically between the top dead center and the bottom dead center. In addition, the needle plate  60  which will be explained later is arranged between the top dead center and the bottom dead center of the needle  36 . Consequently, the sewing objects are sewn by pricking the sewing objects with the needle  36  so that the needle  36  passes through a needle hole  60 A formed in the needle plate  60 . In the explanation below, during one cycle of the vertical movement of the needle  36 , the phase of the upper shaft  26  is referred to as “release phase” when a needle tip (lower end) of the needle  36  is positioned above the upper surface of the needle plate  60 , and the phase of the upper shaft  26  is referred to as “non-release phase” when the needle tip (lower end) of the needle  36  is positioned below the upper surface of the needle plate  60 . 
     As shown in  FIG. 3 , the lower shaft  38  is rotatably supported by the skeleton frame in the bed part  16  (not shown in  FIG. 3 ) so that the axial direction of the lower shaft  38  is aligned with the left-right direction. In addition, a belt  40  is laid between the right end of the lower shaft  38  and the right end of the upper shaft  26 . Thus, the lower shaft  38  is rotated interlockingly with the upper shaft  26 . In addition, a hook  44  is connected to the left end of the lower shaft  38  via a gear mechanism  42 . When the lower shaft  38  is rotated, the hook  44  is rotated so that the axial direction of the hook  44  is aligned with the up-down direction. 
     (About Bed Part) 
     As shown in  FIG. 2 , the bed part  16  includes a cover  50  which forms an outer shell of the bed part  16 . The skeleton frame is covered with the cover  50 . In addition, a hole portion  50 A is penetratingly formed on the upper wall of the cover  50  for placing the needle plate  60  which will be explained later. The hole portion  50 A is formed in an approximately rectangular shape so that the longitudinal direction is aligned with the left-right direction when viewed from above. 
     As shown in  FIG. 1 , a fixing plate  52  is provided in the bed part  16  at the left side of the hole portion  50 A of the cover  50  (not shown in  FIG. 1 ). The fixing plate  52  is formed in an approximately rectangular plate shape so that the plate thickness direction is aligned with the up-down direction. The fixing plate  52  is connected and fixed to the skeleton frame. A first pressing member  54  having a plate shape and a second pressing member  56  having a plate shape are provided on the upper surface of the fixing plate  52  to fix the needle plate  60  which will be explained later. The first pressing member  54  and the second pressing member  56  are an element realized as “pressing member” in a broad sense. The first pressing member  54  and the second pressing member  56  are arranged in the front-rear direction so that the plate thickness direction is aligned in the up-down direction. The first pressing member  54  and the second pressing member  56  are fixed to the fixing plate  52  by screws. A pressing piece  54 A is integrally formed with the first pressing member  54 . The pressing piece  54 A is inclined upward (direction separating from the fixing plate  52 ) toward the right side. In addition, a pressing piece  56 A which is configured same as the pressing piece  54 A is integrally formed with the second pressing member  56 . The pressing piece  56 A is inclined upward (direction separating from the fixing plate  52 ) toward the right side. 
     (About Needle Plate) 
     The needle plate  60  is formed in an approximately rectangular shape and arranged in the hole portion  50 A of the cover  50  so that the plate thickness direction is aligned with the up-down direction (shown in  FIG. 2 ). A locking member  62  is provided on the lower surface of the left end (one end in the longitudinal direction) of the needle plate  60 . The locking member  62  has an approximately long plate shape extending in the front-rear direction. The locking member  62  is fixed to the needle plate  60  by screws. A pair of front and rear locking pieces  62 A is integrally formed with both ends in the longitudinal direction of the locking member  62 . The locking pieces  62 A are bent in an approximately crank shape from the left end of the locking member  62  to the left and below. The tip portions of the locking pieces  62 A are inserted into a space between the fixing plate  52  and the pressing piece  54 A of the first pressing member  54  and a space between the fixing plate  52  and the pressing piece  56 A of the second pressing member  56  from the right side. Thus, locking pieces  62 A are fixed to the pressing piece  54 A and the pressing piece  56 A. Consequently, the left end of the needle plate  60  is fixed to the fixing plate  52  via the locking member  62 . 
     In addition, a striker  64  is provide on the lower surface of the right end of the needle plate  60 . The striker  64  is an element realized as “engaged portion” in a broad sense. The striker  64  is a bar material having a circular cross-section. The striker  64  is bent in an approximately U-shape opened to the upper side when viewed from the left-right direction. Specifically, the striker  64  includes a body portion  64 A which extends in the front-rear direction and a pair of front and rear mounting portions  64 B which extend upward from both ends in the longitudinal direction of the body portion  64 A. The upper end of the mounting portions  64 B is fixed to the lower surface of the needle plate  60 . 
     In addition, the needle hole  60 A is penetratingly formed on the needle plate  60 . When the sewing objects are sewn by the sewing machine  10 , the needle  36  penetrates through the needle hole  60 A. 
     (About Needle Plate Detachable Mechanism) 
     Next, the needle plate detachable mechanism  66 , which is an important part of the present invention, will be explained. As shown in  FIG. 1 , the needle plate detachable mechanism  66  includes a needle plate fixing unit  68  capable of being switched between a fixed state where the needle plate  60  is fixed to the bed part  16  and an unfixed state where the fixed state is released, a switching mechanism  74  for switching the state of the needle plate fixing unit  68 , an upper shaft phase sensor  92  and a controller  94  (shown in  FIG. 4A ). The upper shaft phase sensor  92  is an element realized as “detector” in a broad sense. 
     &lt;About Needle Plate Fixing Unit&gt; 
     As also shown in  FIGS. 6A-6C , the needle plate fixing unit  68  includes a rotary shaft  70  which functions as “rotary unit” and a cam hook  72  which is integrally formed with the rotary shaft  70  to function as “needle plate engaging unit.” The rotary shaft  70  is arranged below the right end of the needle plate  60  so that the axial direction of the rotary shaft  70  is aligned with the front-rear direction. Specifically, the rotary shaft  70  is separately arranged immediately below the body portion  64 A of the striker  64  of the needle plate  60 . 
     The rotary shaft  70  includes a core portion  70 A having a circular cross-section to form an axial center of the rotary shaft  70  and an outer shaft portion  70 B having an approximately cylindrical shape formed on an outer periphery of the core portion  70 A. In the present embodiment, the core portion  70 A is made of metal and the outer shaft portion  70 B is made of resin (e.g., POM: polyoxymethylene). The core portion  70 A and the outer shaft portion  70 B are integrally formed by insert molding, for example. Specifically, the outer shaft portion  70 B is integrally formed with the core portion  70 A to cover the front side (one side in the axial direction) of the core portion  70 A. Consequently, the rear end side of the core portion  70 A is projected rearward compared to the outer shaft portion  70 B. The rear end side of the core portion  70 A is rotatably supported by the skeleton frame. In addition, the rear end of the core portion  70 A is projected rearward compared to the cover  50  (shown in  FIG. 2 ). 
     In addition, an operation dial  70 D is provided on the rear end of the rotary shaft  70  (core portion  70 A) so as to be integrally rotated with the rotary shaft  70 . The operation dial  70 D is formed in an approximately disk shape so that the axial direction of the operation dial  70 D is aligned with the front-rear direction. The rear end of the rotary shaft  70  is fixed to an axial center of the operation dial  70 D. Consequently, the operation dial  70 D is arranged on the outer side (for detail, rear side) of the cover  50  so as to be operable (shown in  FIG. 2 ). When the operator rotates the operation dial  70 D, the rotary shaft  70  can be manually rotated. 
     The cam hook  72  is integrally provided on an intermediate portion in the longitudinal direction of the outer shaft portion  70 B. The cam hook  72  is formed in an approximately inverse J shape opened to the left side when viewed from the front side and connected with the upper part of the outer shaft portion  70 B. Specifically, the cam hook  72  includes a hook portion  72 A which forms the right part of the cam hook  72  and a cam portion  72 B which forms the left part of the cam hook  72  to function as “push-up portion.” 
     The hook portion  72 A is formed in an approximately U-shape having an engaging groove  72 A 1  opened to the left side when viewed from the axial direction of the rotary shaft  70 . The base end (lower end) of the hook portion  72 A is connected with the upper part of the outer shaft portion  70 B. In addition, the engaging groove  72 A 1  is curved in an approximately arc shape around the axial center of the rotary shaft  70  when viewed from the axial direction of the rotary shaft  70 . The dimension in the width direction of the engaging groove  72 A 1  is approximately same as the dimension in the diameter of the striker  64 . The body portion  64 A of the striker  64  is inserted into the engaging groove  72 A. Thus, the body portion  64 A and the hook portion  72 A are vertically engaged with each other. The above described position of the needle plate fixing unit  68  (rotary shaft  70  and cam hook  72 ) is shown in  FIG. 6A  and hereafter referred to as “engaged position.” The state of the needle plate  60  and the needle plate fixing unit  68  in the engaged position is referred to as “fixed state.” Consequently, in the fixed state of the needle plate fixing unit  68 , the vertical movement of the striker  64  is limited and the needle plate  60  is fixed by the cam hook  72 . 
     When the rotary shaft  70  is rotated from the engaged position to one of the rotation directions (direction of Arrow A in  FIG. 6A ) by the switching mechanism  74  which will be explained later, the engaged state between the body portion  64 A of the striker  64  and the hook portion  72 A is released and the fixed state of the needle plate  60  fixed by the cam hook  72  is released. The above described position of the needle plate fixing unit  68  (rotary shaft  70  and cam hook  72 ) is shown in  FIG. 6B  and hereafter referred to as “release position.” 
     The cam portion  72 B is extended to the left side from the base end (lower end) of the hook portion  72 A. Specifically, the cam portion  72 B is inclined downward and projected upward and leftward when viewed from the axial direction of the rotary shaft  70  toward the left side. In addition, the upper surface of the cam portion  72 B is formed as a cam face  72 B 1 . The distance from the axial center of the rotary shaft  70  to the cam face  72 B 1  is specified to become gradually longer from the base end to the tip end of the cam face  72 B 1 . Furthermore, the cam face  72 B 1  is smoothly connected with the inner peripheral surface of the engaging groove  72 A 1  of the hook portion  72 A. 
     When the rotary shaft  70  is rotated from the engaged position to one of the rotation directions by the switching mechanism  74  which will be explained later, after the engaged state between the engaging groove  72 A 1  of the hook portion  72 A and the body portion  64 A of the striker  64  is released, the cam face  72 B 1  of the cam portion  72 B is specified to be in contact with the outer peripheral surface of the lower part of the body portion  64 A of the striker  64 . Consequently, when the rotary shaft  70  is further rotated from the release position to one of the rotation directions, the cam portion  72 B (cam face  72 B 1 ) pushes the striker  64  upward and the right end of the needle plate  60  is pushed upward with respect to the bed part  16 . The above described position of the needle plate fixing unit  68  (rotary shaft  70  and cam hook  72 ) is shown in  FIG. 6C  and hereafter referred to as “push-up position.” In the position of the needle plate fixing unit  68  (rotary shaft  70  and cam hook  72 ), the position between the release position and the push-up position is “disengaged position” of the present invention. Namely, “disengaged position” of the present invention has a predetermined range in a circumferential direction of the rotary shaft  70 . The state of the needle plate  60  and the needle plate fixing unit  68  in the position between the release position and the push-up position is referred to as “unfixed state.” 
     &lt;About Switching Mechanism&gt; 
     The switching mechanism  74  is formed as a mechanism of switching the needle plate fixing unit  68  to the fixed state or to the unfixed state. The switching mechanism  74  includes a base plate  76 , a needle plate motor  78  which functions as “driving unit”, a transmission mechanism  80  and a link mechanism  86 . 
     [About Base Plate] 
     The base plate  76  is formed in an approximately rectangular plate shape extending in the front-rear direction so that the plate thickness direction is aligned with the up-down direction. The base plate  76  is arranged on the right side of the rotary shaft  70  to be separately from the rotary shaft  70 . The rear end of the base plate  76  is fixed to the skeleton frame. An exposure hole  76 A having a circular shape is penetratingly formed on the front part of the base plate  76  at an approximately center in the left-right direction for exposing the later described output shaft  78 A of the needle plate motor  78 . In addition, a support shaft  76 S is provided on the rear end of the base plate  76  for rotatably supporting the later described oscillating arm  84  of the transmission mechanism  80 . The support shaft  76 S is formed in an approximately cylindrical shape so that the axial direction of the support shaft  76 S is aligned with the up-down direction. The support shaft  76 S is projected upward from the base plate  76 . 
     [About Needle Plate Motor] 
     The needle plate motor  78  is arranged adjacent to the lower side of the front part of the base plate  76  so that the axial direction of the needle plate motor  78  is aligned with the up-down direction. The needle plate motor  78  is fixed to the base plate  76  at a position not shown in the figure. Specifically, the needle plate motor  78  is arranged coaxially with the exposure hole  76 A of the base plate  76 . The output shaft  78 A of the needle plate motor  78  is arranged in the exposure hole  76 A. In addition, a pinion gear  82  forming the later described transmission mechanism  80  is provided on the output shaft  78 A so as to be integrally rotated with the output shaft  78 A. The pinion gear  82  is arranged on an upper side of the base plate  76 . In the present embodiment, the needle plate motor  78  is formed as a stepping motor and electrically connected with the controller  94  which will be explained later. The needle plate motor  78  is operated by the control of the controller  94 . 
     [About Transmission Mechanism] 
     The transmission mechanism  80  includes the above described pinion gear  82  and oscillating arm  84 . 
     The oscillating arm  84  is formed in an approximately sector plate shape when viewed from above so that the plate thickness direction is aligned with the up-down direction. The oscillating arm  84  is arranged on the upper side of the base plate  76 . A support boss  84 A is formed on the base end (rear end) of the oscillating arm  84 . The support boss  84 A is formed in an approximately cylindrical shape so that the axial direction of the support boss  84 A is aligned with the up-down direction. The support shaft  76 S of the base plate  76  is inserted into the support boss  84 A so as to be relatively rotative. Consequently, the oscillating arm  84  is rotatably supported by the support shaft  76 S. Note that an E-ring ER is locked to the tip portion (upper end) of the support shaft  76 S. The oscillating arm  84  is restricted from moving upward by the E-ring ER. 
     A rack portion  84 B is formed on the tip portion (front end) of the oscillating arm  84 . The rack portion  84 B is curved in an approximately arc shape around the axial center of the support boss  84 A (support shaft  76 S) when viewed from above. The rack portion  84 B is arranged on the rear side of the pinion gear  82  of the needle plate motor  78 . In addition, a plurality of rack teeth is formed on the rack portion  84 B. The rack teeth are engaged with the pinion gear  82 . Consequently, when the needle plate motor  78  is operated, the oscillating arm  84  swings (rotates) around the axis of the support shaft  76 S. Specifically, the oscillating arm  84  reciprocally swings (rotates) between “first position” shown in a solid line and “second position” shown in a two-dot chain line in  FIG. 1 . 
     Furthermore, a connecting pin  84 P is provided on the tip end side of the oscillating arm  84 . The connecting pin  84 P is formed in an approximately cylindrical shape so that the axial direction of the connecting pin  84 P is aligned with the up-down direction. The connecting pin  84 P is projected upward from the oscillating arm  84 . 
     [About Link Mechanism] 
     The link mechanism  86  includes a first link  88  formed integrally with the front end of the rotary shaft  70  (outer shaft portion  70 B) and a second link  90 . The first link  88  is formed in a plate shape so that the plate thickness direction is aligned with the front-rear direction. The first link  88  is extended obliquely leftward and downward from the front end of the outer shaft portion  70 B when viewed from the front. 
     The second link  90  is formed in an approximately long plate shape extending in the left-right direction. Specifically, the second link  90  includes a link portion  90 L which forms the left part of the second link  90  and a link portion  90 R which forms the right part of the second link  90 . The link portion  90 L is arranged adjacent to the rear side of the first link  88  so that the plate thickness direction is aligned with the front-rear direction. The left end of the link portion  90 L (one end in the longitudinal direction of the second link  90 ) is rotatably connected with the tip portion of the first link  88  by a connecting pin P so that the axial direction of the connecting pin P is aligned with the front-rear direction. 
     The link portion  90 R is arranged on the rear side of the link portion  90 L so that the plate thickness direction is aligned with the up-down direction. The front end of the left end of the link portion  90 R is connected with the upper end of the right end of the link portion  90 L. Consequently, the link portion  90 R is arranged on the upper side of the link portion  90 L. The right end of the link portion  90 R (the other end in the longitudinal direction of the second link  90 ) is rotatably connected with the connecting pin  84 P of the oscillating arm  84 . 
     Consequently, interlocked with the reciprocating swing of the oscillating arm  84 , the second link  90  reciprocally moves in the front-rear direction and the first link  88  (i.e., rotary shaft  70 ) reciprocally rotates around the axis of the rotary shaft  70 . Specifically, the rotary shaft  70  is arranged at the non-release position when the oscillating arm  84  is in the first position, and the rotary shaft  70  is shifted to the push-up position via the release position when the oscillating arm  84  swings from the first position to the second position. 
     &lt;About Upper Shaft Phase Sensor&gt; 
     As shown in  FIG. 3 , the upper shaft phase sensor  92  is provided on an intermediate portion in the longitudinal direction of the upper shaft  26 . The upper shaft phase sensor  92  is formed as a sensor for detecting a rotation phase of the upper shaft  26 . In the present embodiment, the upper shaft phase sensor  92  is formed as a rotary encoder as an example. Specifically, the upper shaft phase sensor  92  includes a rotary plate  92 A and a phase detector  92 B. 
     The rotary plate  92 A has a circular disk shape. The rotary plate  92 A is arranged coaxially with the upper shaft  26  and fixed to the upper shaft  26  so as to be integrally rotated with the upper shaft  26 . A plurality of slits extending in the radial direction of the rotary plate  92 A is penetratingly formed on the rotary plate  92 A. The slits are arranged at predetermined intervals in the circumferential direction of the rotary plate  92 A. 
     The phase detector  92 B has a light emitting element and a light receiving element although they are not illustrated. The light emitting element and the light receiving element are arranged on the rotary plate  92 A opposing to each other in the plate thickness direction. The rotary plate  92 A is arranged between the light emitting element and the light receiving element. In addition, the phase detector  92 B is electrically connected with the controller  94  which will be explained later (shown in  FIG. 4A ). The light emitting element emits light toward the rotary plate  92 A, and the light receiving element receives the light passing through the slits of the rotary plate  92 A. Thus, the upper shaft phase sensor  92  detects the rotation angle (phase) of the upper shaft  26  and outputs the detection signals to the controller  94 . 
     &lt;About Controller&gt; 
     As shown in  FIG. 4A , the above described sewing machine motor  22 , operation part  24 , needle plate motor  78  and upper shaft phase sensor  92  are electrically connected with the controller  94 . The controller  94  controls operations of the sewing machine motor  22  and the needle plate motor  78  (switching mechanism  74 ) based on the operation signals outputted from the operation part  24 . 
     Furthermore, the controller  94  has a determination unit  96 . The determination unit  96  determines to allow or prohibit the operations of the needle plate motor  78  and the controller  94  controls the operations of the needle plate motor  78  based on the judgement of the determination unit  96 . Specifically, the determination unit  96  determines to allow and prohibit the operations of the needle plate motor  78  based on the phase state of the upper shaft  26  (i.e., vertical positon of the needle  36 ) and the driving state of the sewing machine  10 . 
     For more detail, when the sewing machine  10  is driven by the sewing machine motor  22  (i.e., in a motor driving state), the determination unit  96  determines to prohibit the operations of the needle plate motor  78 . Namely, in the motor driving state of the sewing machine  10 , the switching mechanism  74  is prevented from switching the needle plate fixing unit  68  from the fixed state to the unfixed state. 
     In addition, the determination unit  96  judges whether the rotation phase of the upper shaft  26  is the release phase or the non-release phase based on the detection signals detected by the upper shaft phase sensor  92 . In other words, the determination unit  96  judges whether or not the needle tip of the needle  36  is positioned below the upper surface of the needle plate  60 . When the sewing machine  10  is not driven by the motor (i.e., in a non-driving state of the sewing machine motor  22 ) and the phase of the upper shaft  26  is the non-release phase, the determination unit  96  determines to prohibit the operations of the needle plate motor  78 . Namely, the needle plate motor  78  is operated interlockingly with the upper shaft phase sensor  92 . When the sewing machine  10  is not in the motor driving state and the phase of the upper shaft  26  is in the non-release phase, the switching mechanism  74  is prevented from switching the needle plate fixing unit  68  from the fixed state to the unfixed state. 
     On the other hand, when the sewing machine  10  is not in the motor driving state and the phase of the upper shaft  26  is in the release phase, the determination unit  96  determines to allow the operations of the needle plate motor  78 . When the determination unit  96  determines to allow the operations of the needle plate motor  78 , the controller  94  operates the needle plate motor  78  based on the operation signals (operation signals for operating the needle plate motor  78 ) transmitted from the operation part  24 . 
     (Operations and Effects) 
     Next, operations of the needle plate detachable mechanism  66  will be explained with reference to a flowchart shown in  FIG. 5 . 
     In the fixed state of the needle plate fixing unit  68  of the needle plate detachable mechanism  66 , the rotary shaft  70  of the needle plate detachable mechanism  66  is arranged on the engaged position (shown in  FIG. 6A ) and the striker  64  of the needle plate  60  is engaged with the hook portion  72 A of the cam hook  72 . Consequently, the needle plate  60  is fixed to the bed part  16 . In the above described state, in order to start driving the sewing machine  10 , the operator performs touch operation on the icons displayed on the operation part  24  (Step S 1 ). Consequently, the operation signals are outputted from the operation part  24  to the controller  94  and the sewing machine  10  is shifted to the motor driving state (driven by the sewing machine motor  22 ). Therefore, the determination unit  96  of the controller  94  determines to prohibit the operations of the needle plate motor  78  (Step S 2 ). As a result, the switching mechanism  74  is prevented from switching the needle plate fixing unit  68  from the fixed state to the unfixed state. Thus, the fixed state of the needle plate fixing unit  68  is kept. 
     After the process of Step S 2 , the process shifts to Step S 3  and the controller  94  starts driving the sewing machine motor  22 . Consequently, the needle  36  is vertically moved between the top dead center and the bottom dead center to sew the sewing objects. 
     After the process of Step S 3 , in order to stop driving the sewing machine  10 , the operator performs touch operation on the icons displayed on the operation part  24  (Step S 4 ). As a result, the operation signals are outputted from the operation part  24  to the controller  94 . The operation of the sewing machine motor  22  is stopped by the controller  94 , which receives the operation signals from the operation part  24 , and the sewing machine  10  is shifted from the motor driving state to the stop state (Step S 5 ). 
     After the process of Step S 5 , the process shifts to Step S 6  and the determination unit  96  of the controller  94  judges the phase state of the upper shaft  26  based on the detection signals of the upper shaft phase sensor  92 . Specifically, the determination unit  96  judges whether or not the phase of the upper shaft  26  is the release phase. When the phase of the upper shaft  26  is the release phase (Yes in Step S 6 ), the process shifts to Step S 7 . In Step S 7 , the determination unit  96  determines to allow the operations of the needle plate motor  78 . Namely, the switching mechanism  74  is allowed to switch the needle plate fixing unit  68  from the fixed state to the unfixed state. 
     After the process of Step S 7 , the process shifts to Step S 8 . In Step S 8 , icons for urging the operation instruction to the needle plate motor  78  (switching mechanism  74 ) are displayed on the display part of the operation part  24  and the controller  94  judges whether or not the touch operation is performed on the icons of the operation part  24 . 
     When the operation instruction to the needle plate motor  78  is performed in Step S 8  (Yes in Step S 8 ), the process shifts to Step S 9 . In Step S 9 , the controller  94  receives the operation signals from the operation part  24  and operates the needle plate motor  78  to rotate the output shaft  78 A of the needle plate motor  78  in a normal direction. Consequently, the switching mechanism  74  switches the needle plate fixing unit  68  from the fixed state to the unfixed state. After the process of Step S 9 , the processes to the needle plate detachable mechanism  66  are finished. 
     In the process of Step S 9 , the output shaft  78 A of the needle plate motor  78  is rotated together with the pinion gear  82  in a normal direction. Consequently, the oscillating arm  84  engaged with the pinion gear  82  swings from the first position to the second position. When the oscillating arm  84  swings from the first position to the second position, the second link  90  of the link mechanism  86  connected with the oscillating arm  84  is displaced leftward. Consequently, the first link  88  which is connected with the second link  90  so as to be relatively rotative is rotated in one of the rotation directions together with the rotary shaft  70 . Namely, the rotary shaft  70  is rotated in one of the rotation directions (direction of Arrow A in  FIG. 6A ) from the engaged position. 
     As shown in  FIG. 6B , when the rotary shaft  70  is rotated in one of the rotation directions from the engaged position, the body portion  64 A of the striker  64  comes out from the engaging groove  72 A 1  of the hook portion  72 A. Thus, the engaged state between the hook portion  72 A and the striker  64  is released. 
     When the rotary shaft  70  is further rotated in one of the rotation directions from the above described state, the cam face  72 B 1  of the cam portion  72 B abuts with the outer periphery of the lower part of the body portion  64 A of the striker  64 . Specifically, the cam face  72 B 1  slides on the outer peripheral surface of the body portion  64 A while the contact part between the cam face  72 B 1  and the striker  64  is changed from the base end to the tip end of the cam face  72 B 1 . Here, the distance from the axial center of the rotary shaft  70  to the cam face  72 B 1  is specified to become gradually longer from the base end to the tip end of the cam face  72 B 1 . Therefore, when the rotary shaft  70  is rotated, together with the needle plate  60 , the striker  64  is pushed upward by the cam face  72 B 1 . As shown in  FIG. 6C , when the rotary shaft  70  reaches the push-up position, the striker  64  is in contact with the tip end of the cam face  72 B 1 . Thus, the needle plate  60  is pushed upward with respect to the bed part  16 . Consequently, the needle plate  60  can be detached from the bed part  16 . 
     On the other hand, when the operation instruction to the needle plate motor  78  is not performed in Step S 8  (No in Step S 8 ), the process returns to Step S 6  and the determination unit  96  judges the phase state of the upper shaft  26  based on the detection signal transmitted from the upper shaft phase sensor  92 . Namely, after the sewing machine motor  22  is stopped, the operator may sew the sewing objects with manual operation by operating the flywheel  29  without detaching (replacing) the needle plate  60 . Therefore, when the operation instruction to the needle plate motor  78  is not performed in Step S 8 , the process returns to Step S 6  and the determination unit  96  makes judgement based on the rotation phase of the upper shaft  26 . 
     In Step S 6 , when the phase of the upper shaft  26  is the non-release phase (No in Step S 6 ), the process shifts to Step S 10 . In Step S 10 , the determination unit  96  determines to prohibit the operation of the needle plate motor  78 . As a result, the icons for urging the operation instruction to the needle plate motor  78  (switching mechanism  74 ) are not displayed on the operation part  24  (or the icons are displayed in an inoperable state). Thus, the operation instruction to the needle plate motor  78  is disabled. Namely, the switching mechanism  74  is prevented from switching the needle plate fixing unit  68  from the fixed state to the unfixed state. Thus, the fixed state of the needle plate fixing unit  68  is kept. After the process of Step S 10 , the process returns to Step S 6  and the determination unit  96  repeats the judgement based on the rotation phase of the upper shaft  26 . 
     In order to attach (fix) the needle plate  60  to the bed part  16  again, the needle plate  60  is placed on the cam face  72 B 1  in the unfixed state as shown in  FIG. 6C . When the operator performs the operation instruction to the needle plate motor  78  by the operation part  24 , the needle plate  60  is attached (fixed) to the bed part  16 . 
     Namely, in the state shown in  FIG. 6C , the needle plate motor  78  is operated by the controller  94  so that the output shaft  78 A of the needle plate motor  78  is rotated in a reverse direction. Consequently, the rotary shaft  70  is rotated in the other of the rotation directions (direction of Arrow B in  FIG. 6C ) from the push-up position and shifted to the engaged position via the release position. When the rotary shaft  70  is rotated to the engaged position, the striker  64  is inserted into the engaging groove  72 A 1  of the hook portion  72 A. Thus, the striker  64  and the cam hook  72  are vertically engaged with each other. As a result, the needle plate fixing unit  68  is switched from the unfixed state to the fixed state by the switching mechanism  74  and the needle plate  60  is fixed to the bed part  16  again. 
     Hereafter, the operation of the needle plate detachable mechanism  66  explained with reference to the above described flowchart will be further explained with reference to the timing chart shown in  FIG. 7 . In the timing chart of  FIG. 7 , (1) indicates the driving state of the sewing machine  10  and (2) indicates the operation state of the sewing machine motor  22 . In addition, in the timing chart of  FIG. 7 , (3) indicates the phase state of the upper shaft  26  and (4) indicates the judgement state of the determination unit  96  with respect to the needle plate motor  78 . 
     In the stop state (shown as stage “a” in  FIG. 7 ) of the sewing machine  10 , the sewing machine motor  22  is in the non-operation state (OFF state). At that time, the phase of the upper shaft  26  is the release phase, and the needle  36  is positioned above the needle plate  60 . Therefore, the determination unit  96  determines to allow the operation of the needle plate motor  78 . Namely, the switching mechanism  74  is allowed to switch the needle plate fixing unit  68  from the fixed state to the unfixed state. 
     In the stop state of the sewing machine  10 , when the operator operates the operation part  24  to start driving the sewing machine  10 , the sewing machine  10  is shifted from the stop state to the motor driving state (shown as stage “b” in  FIG. 7 ). Therefore, the sewing machine motor  22  is operated by the controller  94  and shifted from the non-operation state (OFF state) to the operation state (ON state). Consequently, the upper shaft  26  is rotated and the needle  36  is vertically moved. Thus, the phase of the upper shaft  26  is repeatedly changed between the release phase and the non-release phase. In the above described state, the determination unit  96  determines to prohibit the operation of the needle plate motor  78 . Thus, the switching mechanism  74  is prevented from switching the needle plate fixing unit  68  from the fixed state to the unfixed state. 
     From the above described state, when the operator operates the operation part  24  to shift the sewing machine  10  from the motor driving state to the stop state (shown as stage “c” in  FIG. 7 ), the operation of the sewing machine motor  22  is stopped by the controller  94 . Thus, the sewing machine motor  22  is shifted from the operation state (ON state) to the non-operation state (OFF state). In the example shown in  FIG. 7 , when the driving of the sewing machine  10  is stopped, the phase of the upper shaft  26  is the non-release phase. Therefore, the determination unit  96  determines to prohibit the operation of the needle plate motor  78 . Thus, the switching mechanism  74  is prevented from switching the needle plate fixing unit  68  from the fixed state to the unfixed state. 
     From the above described state, when the operator manually operates the sewing machine  10  by using the flywheel  29  of the sewing machine  10 , the sewing machine  10  is shifted from the stop state to the manual driving state (shown as stage “d” in  FIG. 7 ). In the above described state, the non-operation state of the sewing machine motor  22  is kept. In addition, since the upper shaft  26  is rotated in the manual operation, the phase of the upper shaft  26  is changed between the non-release phase (shown as stage “d 1 ” in  FIG. 7 ) and the release phase (shown as stage “d 2 ” in  FIG. 7 ) alternately and repeatedly. Consequently, when the phase of the upper shaft  26  is the release phase, the determination unit  96  determines to allow the operation of the needle plate motor  78 . Therefore, when the operator operates the operation part  24  to drive the needle plate motor  78 , the controller  94  receives the operation signals from the operation part  24  and the needle plate motor  78  is operated. Consequently, the fixed state of the needle plate  60  is released. 
     On the other hand, when the phase of the upper shaft  26  is the non-release phase, the determination unit  96  determines to prohibit the operation of the needle plate motor  78 . Therefore, the non-operation state of the needle plate motor  78  is kept and the fixed state of the needle plate  60  is kept. 
     As explained above, in the needle plate detachable mechanism  66  of the present embodiment, when the sewing machine motor  22  is not driven and (the needle tip of) the needle  36  is positioned below the upper surface of the needle plate  60 , the switching mechanism  74  is prevented from switching the needle plate fixing unit  68  from the fixed state to the unfixed state. When the needle  36  is positioned below the upper surface of the needle plate  60 , the needle  36  is inserted into the needle hole  60 A of the needle plate  60 . Therefore, if the switching mechanism  74  is operated in this state, the fixed state of the needle plate  60  is released while the needle  36  is inserted into the needle hole  60 A of the needle plate  60 . Thus, the above described situation is not suitable for replacing the needle plate  60 . Consequently, the replacement of the needle plate  60  can be prevented in the situation not suitable for replacing the needle plate  60  by prohibiting the detachment of the needle plate  60  from the bed part  16 . 
     In addition, when the sewing machine motor  22  is driven, the switching mechanism  74  is prevented from switching the needle plate fixing unit  68  from the fixed state to the unfixed state. When the sewing machine motor  22  is driven, the operator sews sewing objects. Therefore, the operator has no intention to replace the needle plate  60  in the above described situation. Consequently, the above described situation is also not suitable for replacing the needle plate  60 . Thus, in the above described situation not suitable for replacing the needle plate  60 , the needle plate  60  is prevented from being detached from the bed part  16 . Thus, the replacement of the needle plate  60  can be prevented. As explained above, in the situation not suitable for replacing the needle plate  60 , the replacement of the needle plate  60  can be prevented. 
     In addition, the needle plate fixing unit  68  of the needle plate detachable mechanism  66  includes the rotary shaft  70  and the cam hook  72  which is integrally rotatable with the rotary shaft  70 . Since the cam hook  72  is arranged on the engaged position, the hook portion  72 A of the cam hook  72  is engaged with the striker  64  of the needle plate  60 . Thus, the needle plate fixing unit  68  is shifted to the fixed state. On the other hand, when the cam hook  72  is rotated from the engaged position to the push-up position (release position), the engaged state between the hook portion  72 A of the cam hook  72  and the striker  64  of the needle plate  60  is released. Thus, the needle plate fixing unit  68  is shifted to the unfixed state. Namely, the needle plate  60  can be switched to the fixed state or the unfixed state by rotating the needle plate fixing unit  68  around the axis of the rotary shaft  70  to engage/disengage the hook portion  72 A of the cam hook  72  with/from the needle plate  60  (striker  64 ). Therefore, the needle plate  60  can be switched to the fixed state or the unfixed state by a simpler structure compared to the needle plate detachable mechanism described in the prior art (i.e., the structure formed by separate members: an engaging member provided on the sewing machine body side for fixing the needle plate; and an operation lever/push-up bar for releasing the fixed state of the needle plate). 
     In addition, the cam hook  72  has the cam portion  72 B. When the cam hook  72  is rotated from the engaged position to the push-up position together with the rotary shaft  70 , the hook portion  72 A of the cam hook  72  is disengaged from the striker  64  of the needle plate  60  and then the striker  64  (needle plate  60 ) is pushed upward by the cam portion  72 B. Consequently, the needle plate  60  of the unfixed state can be easily detached from the bed part  16 . Accordingly, convenience for replacing the needle plate  60  can be improved. 
     In addition, as explained above, when the needle plate  60  is fixed to the bed part  16 , the needle plate  60  is placed on the cam portion  72 B which is arranged on the push-up position and the switching mechanism  74  is switched from the unfixed state to the fixed state. Thus, the needle plate  60  can be automatically fixed to the bed part  16 . Consequently, convenience of the operator can be improved when attaching (fixing) the needle plate  60  to the bed part  16 . 
     In addition, as explained above, in the cam hook  72  of the needle plate fixing unit  68 , the hook portion  72 A for engaging with the striker  64  and the cam portion  72 B for pushing up the striker  64  are arranged on the same (corresponding) position in the axial direction of the rotary shaft  70 . Therefore, a space of the cam hook  72  can be saved compared to the structure where the hook portion  72 A and the cam portion  72 B are displaced in the axial direction of the rotary shaft  70 . 
     In addition, the engaging groove  72 A 1  of the hook portion  72 A is curved in an arc shape around the axial center of the rotary shaft  70  when viewed from the axial direction of the rotary shaft  70 . Therefore, even if the rotary shaft  70  is displaced in the circumferential direction in the engaged position of the rotary shaft  70 , the engaged state between the hook portion  72 A (engaging groove  72 A 1 ) and the striker  64  (body portion  64 A) can be kept. Consequently, the displacement of the rotary shaft  70  in the circumferential direction can be absorbed by the engaging groove  72 A 1  and the engaged state between the hook portion  72 A (engaging groove  72 A 1 ) and the striker  64  (body portion  64 A) can be kept. In addition, since the displacement of the rotary shaft  70  in the circumferential direction is absorbed by the engaging groove  72 A 1 , it is not required to constantly keep the rotary shaft  70  in the engaged position by supplying electrical power to the needle plate motor  78 , for example. Consequently, power consumption of the sewing machine  10  can be reduced. 
     In addition, the needle plate detachable mechanism  66  has the upper shaft phase sensor  92 . The upper shaft phase sensor  92  detects the rotation phase of the upper shaft  26  which vertically moves the needle  36 . Therefore, since the rotation phase (angle) of the upper shaft  26  is detected by the upper shaft phase sensor  92 , the vertical position of the needle  36  can be easily detected. Thus, the vertical position of the needle  36  can be detected by a simple configuration in the needle plate detachable mechanism  66 . 
     In addition, the rotary shaft  70  includes the core portion  70 A made of metal to form an axial center of the rotary shaft  70  and the outer shaft portion  70 B made of resin to form an outer periphery of the rotary shaft  70 . The cam hook  72  is integrally formed with the outer shaft portion  70 B. Therefore, the rotary shaft  70  having the cam hook  72  can be manufactured at low cost while the strength of the rotary shaft  70  is kept. 
     In addition, if the outer shaft portion  70 B is formed by a material (POM) having a relatively good sliding property, for example, the cam face  72 B 1  is slid well on the needle plate  60  when the rotary shaft  70  is rotated. Thus, the needle plate  60  can be pushed up to the upper side by the cam portion  72 B. 
     Furthermore, since the outer shaft portion  70 B is made of resin, generation of abnormal noise can be suppressed when the cam face  72 B 1  slides on the lower surface of the needle plate  60 . 
     In addition, the operation dial  70 D is provided on the rear end of the rotary shaft  70  so as to be integrally rotated with the rotary shaft  70 . The operation dial  70 D is exposed outside the cover  50  so as to be operable. Therefore, when the operation dial  70 D is rotationally operated, the fixed state of the needle plate  60  can be released by manually rotating the rotary shaft  70 . Consequently, the needle plate  60  can be removed from the bed part  16  in an emergency, for example, when the needle plate motor  78  is broken. 
     In addition, the switching mechanism  74  includes the link mechanism  86  which is connected with the rotary shaft  70  and the transmission mechanism  80  which transmits a driving force of the needle plate motor  78  to the link mechanism  86 . Consequently, the driving force of the needle plate motor  78  is transmitted to the link mechanism  86  and the rotary shaft  70  can be rotated between the engaged position and the push-up position. In addition, by using the link mechanism  86 , the needle plate motor  78  can be installed in an arbitrary position in the bed part  16  which is separated from the rotary shaft  70 . 
     In addition, the transmission mechanism  80  of the switching mechanism  74  includes the pinion gear  82  which is provided on the output shaft  78 A of the needle plate motor  78  so as to be integrally rotated and the oscillating arm  84  having the rack portion  84 B engaged with the pinion gear  82 . The second link  90  of the link mechanism  86  is connected with the oscillating arm  84  so as to be relatively rotative. Consequently, the rotative force of the needle plate motor  78  is converted into linear motion and the rotary shaft  70  can be reciprocally rotated by the link mechanism  86  by a simple configuration. 
     Although the cam portion  72 B (cam face  72 B 1 ) of the cam hook  72  slides on the striker  64  to push up the needle plate  60  in the present embodiment, the configuration for pushing up the needle plate  60  is not limited to the above described configuration. For example, a push-up pin having a bar shape projecting outward in the radial direction of the rotary shaft  70  can be formed on the rotary shaft  70  instead of the cam portion  72 B. In the above described case, a tip end of the push-up pin abuts with the lower surface of the needle plate  60  when rotating the rotary shaft  70  to push up the needle plate  60  by the tip end. 
     Although the rotary shaft  70  is formed by the core portion  70 A made of metal and the outer shaft portion  70 B made of resin in the present embodiment, the configuration of the rotary shaft  70  is not limited to the above described configuration. For example, entire the rotary shaft  70  can be made of metal or resin. 
     Although the operation dial  70 D is formed on the rear end of the rotary shaft  70  so as to be integrally rotated in the present embodiment, the operation dial  70 D can be omitted in the rotary shaft  70 . In the above described case, the rotary shaft  70  can be formed in a long cylindrical shape to rotatably support the rotary shaft  70  by the support shaft fixed to the skeleton frame, for example. 
     Although the switching mechanism  74  includes the transmission mechanism  80  and the link mechanism  86  in the present embodiment, the transmission mechanism  80  and the link mechanism  86  can be omitted in the switching mechanism  74 . In the above described case, the needle plate motor  78  can be arranged so that the axial direction of the needle plate motor  78  is aligned with the front-rear direction to fix the rotary shaft  70  to the output shaft  78 A of the needle plate motor  78  so as to be integrally rotated, for example. 
     In addition, the operation part  24  of the sewing machine  10  is formed as the operation part including the display part and the touch panel in the present embodiment. Instead of the above described configuration, the operation part  24  can be formed by a plurality of operation buttons exposed outside the sewing machine  10  so as to be operable. In the above described case, the controller  94  can be configured not to receive the operation signals from the operation part  24  when the sewing machine motor  22  is not driven and (the needle tip of) the needle  36  is positioned below the upper surface of the needle plate  60  or when the sewing machine motor  22  is driven even if the operation buttons are operated. 
     Note that, this invention is not limited to the above-mentioned embodiments. Although it is to those skilled in the art, the following are disclosed as the one embodiment of this invention.
         Mutually substitutable members, configurations, etc. disclosed in the embodiment can be used with their combination altered appropriately.   Although not disclosed in the embodiment, members, configurations, etc. that belong to the known technology and can be substituted with the members, the configurations, etc. disclosed in the embodiment can be appropriately substituted or are used by altering their combination.   Although not disclosed in the embodiment, members, configurations, etc. that those skilled in the art can consider as substitutions of the members, the configurations, etc. disclosed in the embodiment are substituted with the above mentioned appropriately or are used by altering its combination.       

     While the invention has been particularly shown and described with respect to preferred embodiments thereof, it should be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the sprit and scope of the invention as defined in the appended claims.