Patent Publication Number: US-11047081-B2

Title: Overlock sewing machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of International Patent Application No. PCT/JP2019/001298 filed on Jan. 17, 2019, which claims priority to Japanese Patent Application No. 2018-013311 filed on Jan. 30, 2018, the entire contents of which are incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an overlock sewing machine. 
     2. Description of the Related Art 
     A technique has been disclosed in Patent documents 1 and 2 listed below for an overlock sewing machine in which looper threading is supported by a pump driving operation, and a main shaft for sewing is driven by a single motor using clutch switching. This technique prevents abnormal switching in such an overlock sewing machine between a threading state and a sewing state. The technique is supported by providing separate respective switches, i.e., a switch used to detect an open/closed state of a looper cover or the like and a switch used to detect the switching between the looper threading state and the sewing-enabled state. 
     RELATED ART DOCUMENTS 
     Patent Documents 
     [Patent document 1] 
     Japanese Patent Application Laid Open No. 2013-063221 
     [Patent document 2] 
     Japanese Patent Application Laid Open No. 2014-018292 
     However, such an overlock sewing machine described in Patent documents 1 and 2 employs multiple switches. This involves complicated wiring, and leads to an increased cost. Furthermore, such an overlock sewing machine includes a side cover in addition to the looper cover. With such an arrangement, in a case of further providing an additional switch for detecting the open/closed state of the side cover, i.e., in a case in which the number of switches is further increased, this leads to further complicated wiring or the like. Accordingly, the overlock sewing machine is preferably configured to require only a single switch to detect the open/closed state of the looper cover and the side cover and to detect the threading switching state. 
     In view of the aforementioned fact, it is a purpose of the present invention to provide an overlock sewing machine configured to require only a single switch to detect the open/closed state of the looper cover and the side cover and to detect the threading switching state. 
     SUMMARY OF THE INVENTION 
     A first embodiment for solving the above-described issues relates to an overlock sewing machine. The overlock sewing machine comprises: a switching member configured to switch, between a threading state and a sewing-enabled state, a threading mechanism provided to a sewing machine main body so as to support threading for a looper; a looper cover coupled to a hinge shaft arranged on a front side of the threading mechanism with the left-right direction as an axial direction thereof, such that it can be operated to switch between an open state and a closed state; a side cover coupled to the sewing machine main body such that it is positioned on one side with respect to the threading mechanism defined in the left-right direction and such that it can be operated to switch between an open state and a closed state; a switch comprising an operating protrusion, and configured such that, when the operating protrusion is pressed, the switch detects the closed state of the looper cover, the closed state of the side cover, and the sewing-enabled state of the threading mechanism; a looper cover detection member configured to operate such that it is moved from a non-switching position to a switching position according to a transition of the looper cover from the open state to the closed state, and such that, after the looper cover detection member reaches the switching position, the looper cover detection member operates the switching member so as to switch the threading mechanism to the sewing-enabled state; a side cover detection member configured to operate such that it is moved from a non-detection position to a detection position according to a transition of the side cover from the open state to the closed state; and a lever coupled to the looper cover detection member and the side cover detection member, and configured to switch between a pressing state in which it presses the operating protrusion and a non-pressing state in which it does not press the operating protrusion, according to an operating state of the looper cover detection member and an operating state of the side cover detection member. When the looper cover detection member is moved to a switching position and the side cover detection member is moved to a detection position, the lever is set to the pressing state. 
     A second embodiment for solving the above-described issues also relates to the overlock sewing machine. The looper cover detection member is configured such that, when it is moved from the non-switching position toward one side in the left-right direction, it is set to the switching position. The side cover detection member is configured such that, when it is moved from the non-detection position toward the other side in the left-right direction, it is set to the detection position. The lever is rotatably coupled to the side cover detection member by a first pin. A cam groove is formed in the lever such that a second pin provided to the looper cover detection member is inserted into the cam groove so as to allow the second pin to be moved. 
     A third embodiment for solving the above-described issues also relates to the overlock sewing machine. The side cover detection member is supported by the sewing machine main body such that it can be relatively moved, and is forced toward the non-detection position side by a force-applying member. When the side cover is switched from the open state to the closed state, the side cover detection member is pressed by the side cover so as to move the side cover detection member from the non-detection position to the detection position. 
     A fourth embodiment for solving the above-described issues also relates to the overlock sewing machine. The switch is fixed by a switch fixing member. The first pin and the second pin are slidably coupled to the switch fixing member. 
     A fifth embodiment for solving the above-described issues also relates to the overlock sewing machine. The looper cover and the hinge shaft are configured such that they can be moved as a single unit in an axial direction of the hinge shaft. When the looper cover is moved to a completely closed position toward one side in the axial direction of the hinge shaft from an interim closed state after it is turned from the open state to the closed state so as to be set to the interim closed state, the looper cover is switched to the closed state. An engagement portion is formed in the looper cover detection member so as to allow the hinge shaft to be engaged with the engagement portion such that they can be moved as a single unit in the axial direction of the hinge shaft. 
     A sixth embodiment for solving the above-described issues also relates to the overlock sewing machine. The hinge shaft is rotatably supported by a support member, and is forced by a shaft force-applying member toward one side in the axial direction. A cam portion is formed in the support member such that, when the looper cover is set to the open state, it is engaged with the looper cover so as to restrict the movement of the looper cover toward one side in the axial direction of the hinge shaft. Upon turning the looper cover from the open position to the interim closed position, the engagement state between the cam portion and the looper cover is released so as to enable the movement of the looper cover toward the one side in the axial direction of the hinge shaft. 
     Advantage of the Present Invention 
     With the overlock sewing machine having the above-described configuration, this arrangement requires only a single switch to detect the open/closed state of the looper cover, the open/closed state of the side cover, and the threading switching state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing main components of the overlock sewing machine according to the present embodiment in a state in which a looper cover is opened and a front cover is detached. 
         FIG. 2  is a perspective view showing the overall configuration of the overlock sewing machine in a state in which the looper cover is opened. 
         FIG. 3  is an exploded perspective view showing the main components of the overlock sewing machine shown in  FIG. 1 . 
         FIG. 4  is an exploded perspective view showing a hinge mechanism and the looper cover shown in  FIG. 1 . 
         FIG. 5  is a perspective view showing a side cover employed in the overlock sewing machine shown in  FIG. 2 . 
         FIG. 6  is an exploded perspective view showing the side cover shown in  FIG. 5 . 
         FIG. 7A  is a perspective view showing a state before the side cover shown in  FIG. 5  is closed, and  FIG. 7B  is a perspective view showing a state after the side cover is closed. 
         FIG. 8A  is a plan view showing a position relation between a detection lever of a safety mechanism and a switch in a state in which both the looper cover and the side cover are opened,  FIG. 8B  is a plan view showing a position relation between the detection lever and the switch in a state in which the looper cover is closed and the side cover is opened,  FIG. 8C  is a plan view showing a position relation between the detection lever and the switch in a state in which the looper cover is opened and the side cover is closed, and  FIG. 8D  is a plan view showing a position relation between the detection lever and the switch in a state in which both the looper cover and the side cover are closed. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Description will be made below regarding an overclock sewing machine  10  according to the present invention. It should be noted that, in the drawings shown as appropriate, the arrow UP indicates the upper side of the overlock sewing machine  10 , the arrow FR indicates the front side thereof, and the arrow RH indicates the right side thereof. The directions used in the following description, i.e., the upper-lower direction, the front-rear direction, and the left-right direction, represent the upper and lower, front and rear, and left and right directions of the overlock sewing machine  10 , unless otherwise noted. 
     As shown in  FIGS. 1 and 2 , the overlock sewing machine  10  is configured including a looper unit  12 , a threading mechanism  20 , and a safety mechanism  100 . With such an arrangement, as shown in  FIG. 2 , most of the threading mechanism  20  and the safety mechanism  100  is covered by a front cover  134  of the overclock sewing machine  10  such that it cannot be visually confirmed from the front side. Furthermore, the overlock sewing machine  10  includes a looper cover  70  that forms a lower-right front portion of the overlock sewing machine  10  and that covers the front cover  134  from the front side, and a side cover  90  that forms a housing of the left-side portion of the overlock sewing machine  10 . Description will be made below regarding each component of the overlock sewing machine  10 . 
     [Regarding the Looper Unit  12 ] 
     As shown in  FIG. 3 , the looper unit  12  is arranged on the left side of a unit base  132  that forms a part of a sewing machine main body  130  (see  FIG. 6 ). The looper unit includes an upper looper  14  and a lower looper  16  each configured as a “looper” having an approximately longitudinal, hollow structure. The upper looper  14  and the lower looper  16  have their base-end portions respectively configured as an upper looper inlet  14 A and a lower looper inlet  16 A, and have their tip-end portions respectively configured as an upper looper blade tip  14 B and a lower looper blade tip  16 B. The looper unit  12  is configured to allow the upper looper inlet  14 A and the lower looper inlet  16 A to receive an upper looper thread TH 1  and a lower looper thread TH 2  transferred via the threading mechanism  20  described later. With such an arrangement, the upper looper  14  and the lower looper  16  are configured such that they are reciprocally driven such that they intersect at an appropriate timing with a needle (not shown) driven in the upper-lower direction by the rotation of a main shaft  66  described later. 
     [Regarding the Threading Mechanism  20 ] 
     As shown in  FIGS. 1 and 3 , the threading mechanism  20  is configured including an air flow path switching mechanism  22 , a threading switching mechanism  40 , and a main shaft fixing mechanism  60 . Furthermore, the threading mechanism  20  includes an upper looper conducting tube  28  and a lower looper conducting tube  30  configured to couple the air flow path switching mechanism  22  and the looper unit  12 , and a pair of slide tubes  34 . 
     [Regarding the Air Flow Path Switching Mechanism  22 ] 
     The air flow path switching mechanism  22  includes an approximately block-shaped main body portion  24 . The main body portion  24  is fixed to the front face of the unit base  132 . An upper looper thread insertion opening  24 A and a lower looper thread insertion opening  24 B are formed in the upper face of the main body portion  24 . The upper looper thread insertion opening  24 A and the lower looper thread insertion opening  24 B are configured such that they communicate with an upper looper thread discharging tube  24 C and a lower looper thread discharging tube  24 D, respectively, provided to the lower face of the main body portion  24 . 
     A selection knob  26  is provided on the front face of the main body portion  24 . The air flow path switching mechanism  22  is configured to allow the user to operate the selection knob  26  to select the thread to be threaded from among an upper looper thread TH 1  and a lower looper thread TH 2 . An unshown tube is arranged on the rear face of the main body portion  24 . With this arrangement, the compressed air generated by a compressed air supply apparatus (not shown) is supplied to the air flow path switching mechanism  22  via the tube. Furthermore, the air flow path switching mechanism  22  is covered by the front cover  134  from the front side such that the selection knob  26  is exposed from the front cover  134  so as to allow the user to operate the selection knob  26  (see  FIG. 2 ). 
     [Regarding the Upper Looper Conducting Tube  28  and the Lower Looper Conducting Tube  30 ] 
     The upper looper conducting tube  28  and the lower looper conducting tube  30  are each configured in an approximately inverted L-shaped structure as viewed from the front and are each arranged below the air flow path switching mechanism  22 . Furthermore, the upper looper conducting tube  28  and the lower looper conducting tube  30  are arranged such that their upper-end portions are coupled to the upper looper thread discharging tube  24 C and the lower looper thread discharging tube  24 D, respectively. Moreover, the upper looper conducting tube  28  and the lower looper conducting tube  30  are arranged such that their left-side-end portions are supported by a tube support member  32  fixed to the unit base  132 . It should be noted that the tube support member  32  is configured to have an approximately U-shaped plate structure having an opening that faces the front side as viewed in a plane view. 
     [Regarding the Slide Tubes  34 ] 
     A pair of slide tubes  34  are arranged on the left side of the upper looper conducting tube  28  and the lower looper conducting tube  30  with the left-side direction as their axial direction. The slide tubes  34  are arranged side by side in the front-rear direction. Furthermore, the left-end portions of the slide tubes  34  are supported by the left-side wall of the tube support member  32  such that they can be relatively moved in the left-right direction. Moreover, the right-end portions of the slide tubes  34  are inserted into the upper looper conducting tube  28  and the lower looper conducting tube  30 , respectively, such that they can be relatively moved. This allows each slide tube  34  to be moved in the left-right direction between the threading position (position shown in  FIG. 1 ) and the sewing-enabled position (position shown in  FIG. 3 ). Specifically, when the slide tubes  34  are set to the threading position, the left ends of the slide tubes  34  are coupled to the upper looper inlet  14 A and the lower looper inlet  16 A, respectively. When the slide tubes  34  are set to the sewing-enabled position, the left ends of the slide tubes  34  are moved rightward away from the upper looper inlet  14 A and the lower looper inlet  16 A. 
     [Regarding the Threading Switching Mechanism  40 ] 
     The threading switching mechanism  40  is configured as a mechanism that switches the slide tubes  34  between the threading position and the sewing-enabled position. The threading switching mechanism  40  is configured including a support base  42 , a slide plate  44 , an operating shaft  50 , and a switching member  54 . 
     [Regarding the Support Base  42 ] 
     The support base  42  is configured to have an approximately longitudinal plate structure with the front-rear direction as the thickness direction and such that it extends in the left-right direction. The support base  42  is configured such that its right-side portion is bent so as to have an approximately U-shaped structure having an opening that faces the front side as viewed in a plan view. With such an arrangement, the right-side portion of the support base  42  is fixed to the unit base  132  by screwing on the right side of the tube support member  32 . The left-side portion of the support base  42  is arranged on the front side of the tube support member  32 . A pair of left and right pins  42 P are provided to the left-side portion such that they protrude frontward. 
     [Slide Plate  44 ] 
     The slide plate  44  is arranged on the front side of the support base  42 . The slide plate  44  is configured to have an approximately longitudinal plate structure with the front-rear direction as the thickness direction such that it extends in the left-right direction. A pair of left and right slide openings  44 A and  44 B are configured such that they pass through the slide plate  44  and such that they extend in the left-right direction. The pins  42 P of the support base  42  are respectively inserted into the slide opening  44 A and  44 B such that they can be relatively moved. With this arrangement, the slide plate  44  is supported by the support base  42  such that it can be relatively moved in the left-right direction. Furthermore, a large-diameter portion  44 B 1  is formed as a left-end portion of the right-side slide opening  44 B such that it has an approximately circular opening having a diameter that is larger than the width of the slide opening  44 B. 
     Furthermore, the slide plate  44  is arranged such that its left-end portion is positioned on the inner side of the tube support member  32  described above. Furthermore, the left-end portion of the slide plate  44  is coupled to the slide tubes  34  by a slide tube spring  46  mounted on the slide tube  34  such that they can be monolithically moved as a single unit. With this arrangement, upon sliding the slide plate  44  leftward or rightward, the slide tubes  34  are moved toward the threading position or the sewing-enabled position. 
     Furthermore, the slide plate  44  is forced leftward by a compression spring (not shown) mounted on the support shaft of the support base  42 . Moreover, a pin  44 P is monolithically provided to the right-end portion of the slide plate  44  such that it protrudes frontward. 
     [Regarding the Operating Shaft  50 ] 
     The operating shaft  50  is arranged with the left-right direction as its axial direction, and is borne by the right-side portion (U-shaped bent portion) of the support base  42 . In this state, the operating shaft  50  is rotatably supported by the support base  42 . The operating shaft  50  is arranged such that its right-end portion protrudes rightward from the right wall of the support base  42 . A switching transmission member  52  is provided to the right-end portion of the operating shaft  50 . The switching transmission member  52  is configured to have an approximately cylindrical structure with the left-right direction as its axial direction. The right-end portion of the operating shaft  50  is inserted into the switching transmission member  52  such that the switching transmission member  52  can be rotated together with the operating shaft  50  as a single unit. Furthermore, an arm portion is provided to the left-side-end portion of the switching transmission mechanism  52  such that it extends upward. Moreover, a pin  52 P is provided to the tip-end portion of the arm portion such that it protrudes leftward. The pin  52 P is slidably inserted into a long opening  42 A formed in the right wall of the support base  42  so as to have a curved arc structure. Furthermore, an engagement pin  52 A is provided to the outer circumferential portion of the switching transmission member  52  such that it protrudes outward in a radial direction of the switching transmission member  52  (specifically, frontward). 
     [Regarding the Switching Member  54 ] 
     The switching member  54  is arranged on the front side of the right-end portion of the slide plate  44 . The switching member  54  is configured to have a plate structure with the front-rear direction as the thickness direction. The switching mechanism  54  is configured to have an approximately V-shaped structure having an opening that faces diagonally downward and leftward as viewed from the front side. A support arm  54 A is formed in the right-end portion of the switching member  54  such that it is positioned at an intermediate position in the upper-lower direction and such that it is bent rearward. Furthermore, the support arm  54 A is configured such that its end portion (rear-end portion) is bent leftward. Furthermore, circular opening portions  54 B are formed as through holes in an approximately central portion of the switching member  54  and the end portion of the support arm  54 A. The opening portions  54 B are arranged coaxially ( FIG. 3  shows only one opening portion  54 B formed in an approximately central portion of the switching member  54 ). With such an arrangement, a support shaft  132 P fixed to the unit base  132  with the front-rear direction as its axial direction is inserted into the opening portions  54 B. In this state, the switching member  54  is rotatably supported by the support shaft  132 P. 
     A switching arm  54 C is formed in the upper-end portion of the switching member  54 . A contact tab  54 C 1  is formed as a left-side portion of the switching arm  54 C such that it is bent rearward. With such an arrangement, the contact tab  54 C 1  is arranged adjacent to the left side of the pin  44 P of the slide plate  44  described above. 
     Furthermore, a pair of an upper engagement arm  54 D and a lower engagement arm  54 E are formed in the upper portion of the switching member  54 . The engagement arm  54 D is configured such that it extends diagonally upward and rightward from the upper portion of the switching member  54 . On the other hand, the engagement arm  54 E is configured such that it is positioned below the engagement arm  54 D and such that it extends rightward from the upper portion of the switching member  54 . The engagement pin  52 A of the switching transmission member  52  described above is arranged between the pair of engagement arms  54 D and  54 E. 
     Furthermore, the lower-end portion of the switching member  54  is bent so as to form a step retracting rearward. A coupling pin  54 P is provided to the lower-end portion such that it protrudes frontward. 
     Furthermore, a switching knob  56  is fixed to the front face of the switching member  54  such that they can be turned together as a single unit. In the threading state of the threading mechanism  20 , upon turning the switching knob  56  in the clockwise direction around the axis of the support shaft  132 P in a front view, the contact tab  54 C 1  of the switching arm  54 C of the switching member  54  presses the pin  44 P of the slide plate  44  rightward so as to slide the slide plate  44  rightward. Furthermore, with such an arrangement in this state, the engagement arm  54 D of the switching member  54  is engaged with the engagement pin  52 A of the switching transmission member  52 . In this state, the operating shaft  50  is turned in the counterclockwise direction around the axis of the operating shaft  50  itself as viewed from the right side. 
     On the other hand, in the sewing-enabled state of the threading mechanism  20 , upon turning the switching knob  56  in the counterclockwise direction around the axis of the support shaft  132 P in a front view, the slide plate  44  is slid leftward by an unshown force-applying member. In this state, the engagement arm  54 E of the switching member  54  is engaged with the engagement pin  52 A of the switching transmission member  52 . The operating shaft  50  is rotated in a clockwise manner around the axis of the operating shaft  50  itself as viewed from the right side. 
     It should be noted that the threading mechanism  20  is covered by the front cover  134  from the front side such that the switching knob  56  is exposed from the front cover  134  frontward so as to allow the user to operate the switching knob  54  (see  FIG. 2 ). 
     [Regarding the Main Shaft Fixing Mechanism  60 ] 
     As shown in  FIG. 3 , the main shaft fixing mechanism  60  is configured including a fixing shaft  62  and a main shaft fixing plate  64 . 
     [Regarding the Fixing Shaft  62 ] 
     The fixing shaft  62  is configured to have an approximately cylindrical shape with a bottom, with the front-rear direction as the axial direction, and having an opening that faces the rear side. With such an arrangement, a rear-end portion of the fixing shaft  62  is inserted into the insertion opening  132 A formed in the unit base  132  such that it can be relatively moved in the front-rear direction. Furthermore, a front-end portion of the fixing shaft  62  is arranged within the large-diameter portion  44 B 1  formed in the slide plate  44  when it is set to the sewing-enabled position. Furthermore, the fixing shaft  62  is configured such that it is moved in the front-rear direction together with the rotation of the operating shaft  50  described above, which is not shown in the drawings. Specifically, when the operating shaft  50  is rotated in a counterclockwise manner according to the rotation of the switching knob  56  in a clockwise manner, the fixing shaft  62  is moved frontward. Conversely, when the operating shaft  50  is rotated in a clockwise manner according to the rotation of the switching knob  56  in a counterclockwise manner, the fixing shaft  62  is moved rearward. 
     Furthermore, a groove portion  62 A is formed in the outer circumferential portion of the front-end portion of the fixing shaft  62 . Specifically, the groove portion  62 A is formed over the entire circumferential portion of the fixing shaft  62 . With such an arrangement, in the state shown in  FIG. 3 , when the fixing shaft  62  is moved rearward, the positions of the groove portion  62 A and the slide plate  44  coincide with each other along the front-rear direction. In this state, this arrangement allows the slide plate  44  to be slid leftward from the sewing-enabled position. That is to say, the edge portion of the slide opening  44 B formed in the slide plate  44  is inserted into the groove portion  62 A. In this state, by sliding the slide plate  44  leftward, this arrangement allows the slide plate  44  to be slid from the sewing-enabled position to the threading position. 
     [Regarding the Main Shaft Fixing Plate  64 ] 
     The main shaft fixing plate  64  is configured in an approximately disk-shaped structure with the left-right direction as the thickness direction. The main shaft fixing plate  64  is arranged on the rear side of the fixing shaft  62 . The main shaft fixing plate  64  and the main shaft  66  are arranged coaxially with the left-right direction as the axial direction. The main shaft fixing plate  64  is fixed to the main shaft  66  such that it can be rotated as a single unit. It should be noted that, by driving an unshown motor, this arrangement allows the main shaft  66  to be rotated around the axis of the main shaft  66  itself. 
     A notch  64 A is formed in the outer circumferential portion of the main shaft fixing plate  64  such that it has an opening that faces outward in a radial direction of the main shaft fixing plate  64 . With such an arrangement, by moving the fixing shaft  62  rearward such that its rear end fits into the notch  64 A, this arrangement prevents the rotation of the main shaft fixing plate  64  (i.e., the main shaft  66 ). 
     [Regarding the Looper Cover  70 ] 
     As shown in  FIGS. 1, 2, and 4 , the looper cover  70  is arranged as a front portion of the overlock sewing machine  10 . Specifically, the looper cover  70  is coupled to a hinge mechanism  80  such that it can be opened and closed on the front side of the front cover  134 . Accordingly, first, description will be made regarding the hinge mechanism  80 . Next, description will be made regarding the looper cover  70 . 
     The hinge mechanism  80  is configured including a hinge plate  82  configured as a “support member”, a hinge shaft  84 , and a hinge spring  86  configured as a “shaft force-applying member”. 
     The hinge plate  82  is arranged in a plate shape with the upper-lower direction as the thickness direction, and is arranged below the threading mechanism  20 . Furthermore, the hinge plate  82  is fixed to the sewing machine main body  130  at an unshown position. A pair of left and right support portions  82 L and  82 R are monolithically formed in the front-end portion of the hinge plate  82  such that they are bent upward. The support portions  82 L and  82 R are arranged with the left-right direction as the thickness direction such that the front-end portions of the support portions  82 L and  82 R protrude frontward from the front cover  134 . 
     A cam tab  82 R 1  is provided to the support portion  82 R such that it is bent rightward from the lower-end portion of the support portion  82 R. The cam tab  82 R 1  is arranged with the upper-lower direction as the thickness direction. Furthermore, a cam portion  82 R 2  is formed in the right end of the cam tab  82 R 1 . The cam portion  82 R 2  is configured in an approximately arc structure such that it is inclined rightward as it extends rearward in a plan view, and such that it protrudes diagonally leftward and rearward. 
     The hinge shaft  84  is configured in an approximately longitudinal shaft structure with the left-right direction (width direction) as its axial direction. Furthermore, the hinge shaft  84  is supported by the support portions  82 L and  82 R such that it can be relatively moved in the left-right direction. 
     The hinge spring  86  is configured as a compression coil spring. The hinge spring  86  is mounted on a right-side portion of the hinge shaft  84  (specifically, a portion of the hinge shaft  84  between the support portions  82 L and  82 R of the hinge plate  82 ). With such an arrangement, the right-end portion of the hinge spring  86  is engaged with the support portion  82 R. On the other hand, the left-end portion of the hinge spring  86  is engaged with an E-ring ER 1  fixed to the hinge shaft  84  via a washer W. With this, the hinge shaft  84  is forced leftward (one direction in the axial direction) by the force applied by the hinge spring  86 . 
     Next, description will be made regarding the looper cover  70 . The looper cover  70  is configured in an approximately rectangular structure, and is rotatably coupled to the hinge mechanism  80 . It should be noted that description will be made below for convenience assuming that the looper cover  70  is in the open state. 
     A hinge coupling member  72  having an approximately longitudinal plate structure is fixed to the base-end portion (rear-end portion) of the looper cover  70  such that it extends in the left-right direction with the upper-lower direction as the thickness direction. A pair of hinge portions  72 L and  72 R are respectively provided to both end portions of the hinge coupling member  72  defined in the longitudinal direction thereof such that they are bent upward. The hinge portions  72 L and  72 R are arranged with the left-right direction as the thickness direction. Furthermore, a stopper tab  72 R 1  is formed in the rear-end portion of the hinge portion  72 R such that it is bent rightward. The stopper tab  72 R 1  is arranged with the front-rear direction as the thickness direction. 
     With such an arrangement, the hinge portions  72 L and  72 R are rotatably supported by the hinge shaft  84 . Furthermore, the left-end portion of the base-end portion of the looper cover  70  is rotatably supported by the hinge shaft  84 . Specifically, the hinge portion  72 L is arranged in the vicinity of the left side of the support portion  82 L of the hinge plate  82 . Furthermore, an E-ring ER 2  is fixed to the hinge shaft  84  such that it is positioned between the hinge portion  72 L and the support portion  82 L. With this, upon moving the hinge shaft  84  leftward, the hinge portion  72 L is pressed by the E-ring ER 2 , and the left-end portion of the looper cover  70  is pressed by the hinge shaft  84 . This moves the looper cover  70  leftward together with the hinge shaft  84  as a single unit. Conversely, upon moving the looper cover  70  rightward after it is moved leftward, the hinge portion  72 L presses the E-ring ER 2  rightward, and the left-end portion of the looper cover  70  presses the hinge shaft  84 . This moves the hinge shaft  84  rightward together with the looper cover  70 . 
     On the other hand, the hinge portion  72 R is arranged on the right side of the support portion  82 R. Furthermore, in the open state of the looper cover  70 , the hinge portion  72 R is arranged on the right side of the cam tab  82 R 1  of the support portion  82 R. In this state, the stopper tab  72 R 1  is engaged with the cam portion  82 R 2  of the cam tab  82 R 1  (at a position of the looper cover  70  shown in  FIG. 1 , which will be referred to as the “open position” hereafter). Furthermore, as described above, the hinge shaft  84  is forced leftward by the hinge spring  86 . Accordingly, the looper cover  70  is held at the open position. 
     Subsequently, upon rotating the looper cover  70  rearward by approximately 90 degrees from the open position (in the direction indicated by the arrow A shown in  FIGS. 1 and 2 , which corresponds to the “closed state side” in the present invention), the engagement state between the stopper tab  72 R 1  and the cam portion  82 R 2  of the cam tab  82 R 1  is released, and the stopper tab  72 R 1  is set to a position above the cam tab  82 R 1 . In this state, the looper cover  70  and the hinge shaft  84  are moved leftward by the force applied by the hinge spring  86 . In the description that will be made below, the position at which the looper cover is rotated rearward by approximately 90 degrees from the open position will be referred to as an “interim closed position”. Furthermore, the position at which the looper cover  70  is moved leftward from the interim closed position will be referred to as a “completely closed position” hereafter. It should be noted that, when the looper cover is set to the completely closed position, the hinge portion  72 R comes in contact with the support portion  82 R, which restricts the movement of the looper cover  70  leftward. 
     [Regarding the Side Cover  90 ] 
     As shown in  FIGS. 2, 5, and 6 , the side cover  90  is arranged as a left-side portion of the overlock sewing machine  10 . The side cover  90  is configured in an approximately box structure having an opening that faces the right side. The side cover  90  is arranged on the left side (one side in the left-right direction) with respect to the looper cover  70  and the threading mechanism  20  (which are not shown in  FIGS. 5 and 6 ). With such an arrangement, the opening portion defined in the rear wall of the side cover  90  is fixed to the sewing machine main body  130  via a hinge portion  92 . Specifically, the side cover  90  is coupled to the sewing machine main body  130  such that it is switchable between the open state and the closed state with the upper-lower direction as its axial direction. 
     A housing portion  90 A is formed in the opening portion defined in the upper wall of the side cover  90  such that it has an opening that faces the right side. Such an arrangement allows the needle plate  136  of the sewing machine main body  130  to be housed in the housing portion  90 A. A pair of upper and lower fixing portions  90 B each having an approximately cylindrical structure are formed in the left-side wall of the side cover  90  such that they protrude toward the opening side of the side cover  90 . Furthermore, an engagement member  94  configured as a plate spring is provided on the opening side of the side cover  90  with respect to the fixing portions  90 B. The engagement member  94  is configured in an approximately inverted L-shaped structure as viewed in a front view. The lower portion of the engagement member  94  is fixed to the fixing portions by screwing by screws. Furthermore, a hook portion  94 A is formed in the end portion of the upper-end side of the engagement member  94  such that it protrudes upward. 
     On the other hand, a reception plate  96  that corresponds to the engagement member  94  is provided to the left side of the sewing machine main body  130 . The reception plate  96  is configured in an approximately hat-shaped structure having an opening that faces the right side as viewed in a plan view. Both ends of the reception plate  96  defined in the longitudinal direction are fixed to the sewing machine main body  130  by screwing. With such an arrangement, in the closed state of the side cover  90 , the hook portion  94 A of the engagement member  94  is engaged with the lower face of the top wall of the reception plate  96 . This allows the closed state of the side cover  90  to be maintained (see  FIG. 7B ). 
     Furthermore, a stopper  90 C having an approximately cylindrical structure is provided to the left-side wall of the side cover  90  such that it is positioned above the fixing portions  90 B. The stopper  90 C is configured such that it protrudes from the left-side wall of the side cover toward the opening side thereof. With such an arrangement, when the side cover  90  is closed, the stopper  90 C comes in contact with the reception plate  96 , thereby restricting the rotation of the side cover  90 . 
     Furthermore, a detection shaft pressing portion  90 D is provided to the left-side wall of the side cover  90  such that it is positioned below the stopper  90 C in order to press a cover detection shaft  116  described later. The detection shaft pressing portion  90 D is configured in an approximately cylindrical structure such that it protrudes from the left-side wall of the side cover  90  toward the opening side thereof. 
     [Regarding the Safety Mechanism  100 ] 
     As shown in  FIGS. 1 and 3 , the safety mechanism  100  is configured including a detection base  102  configured as a “switch fixing member”, a switch  108 , a looper cover detection member  110 , a side cover detection member  114 , and a detection lever  124  configured as a “lever”. 
     [Regarding the Detection Base  102 ] 
     The detection base  102  is configured in an approximately L-shaped structure as viewed from the left side. Specifically, the detection base  102  includes a guide plate portion  102 A configured to guide the looper cover detection member  110  and the side cover detection member  114  described later. The guide plate portion  102 A is arranged with the upper-lower direction as the thickness direction. Furthermore, the detection base  102  includes a fixing plate portion  102 B configured such that it extends upward from the rear-end portion of the guide plate portion  102 A. With such an arrangement, the fixing plate portion  102 B is fixed to the unit base  132  by screwing on the lower-right side of the threading switching mechanism  40 . 
     A first guide opening  102 C (which is regarded in a broad sense as a “guide portion”) is formed as a through hole in the left-side portion of the front-end portion of the guide plate portion  102 A such that it extends in a linear fashion in the left-right direction. Furthermore, a second guide opening  102 D (which is regarded in a broad sense as a “guide portion”) is formed as a through hole in the right-side portion of the rear-end portion of the guide plate portion  102 A such that it extends in a linear fashion in the left-right direction. The second guide opening  102 D is designed to have a length in the longitudinal direction that is shorter than that of the first guide opening  102 C. 
     Furthermore, a switch fixing portion  102  is formed in the right-end portion of the fixing plate portion  102 B such that it is bent rearward. The switch fixing portion  102 E is arranged with the left-right direction as the thickness direction. Moreover, a switch fixing base  106  is arranged adjacent to the right side of the switch fixing portion  102 E, which is configured to fix the switch  108  described later. The switch fixing base  106  is formed of an insulating material, and is fixed to the switch fixing portion  102 E by screwing. 
     [Regarding the Switch  108 ] 
     The switch  108  is configured to have an approximately rectangular block-shaped structure. The switch  108  is arranged on the lower side of the front-end portion of the switch fixing plate  106 , and is fixed to the switch fixing base  106  by screwing. With this, the switch  108  is fixed to the detection base  102  via the switch fixing base  106 . The switch  108  includes an operating protrusion  108 A. The operating protrusion  108 A is configured such that it protrudes frontward from the front face of the switch  108 . With such an arrangement, when the operating protrusion  108 A is pressed rearward, the switch  108  is operated. Specifically, when the operating protrusion  108 A is pressed, the switch  108  is set to an ON state. In this state, this enables a motor (not shown) for driving the main shaft  66  to be driven (the motor power supply is set to an on state). In contrast, when the operating protrusion  108 A is not pressed such that it protrudes, the switch  108  is set to an OFF state. In this state, the motor is set to the driving-disabled state (the motor power supply is set to a disconnection state). 
     [Regarding the Looper Cover Detection Member  110 ] 
     The looper cover detection member  110  is arranged between the detection base  102  and the hinge shaft  84 . Furthermore, the looper cover detection member  110  is configured in an approximately L-shaped plate structure as viewed from the left side. Specifically, the looper cover detection member  110  is configured including a base plate portion  110 A configured with the upper-lower direction as the thickness direction, and a switching plate portion  110 B configured such that it extends upward from the rear-end portion of the base plate portion  110 A. 
     A hinge shaft linkage portion  110 C configured as an “engagement portion” is monolithically formed in the front-end portion of the left-end portion of the base plate portion  110 A. The hinge shaft linkage portion  110 C is configured such that it is bent in an approximately inverted U-shaped structure having an opening that faces the lower side as viewed in the left-right direction. With such an arrangement, the hinge shaft  84  is arranged within the hinge shaft linkage portion  110 C so as to couple the hinge shaft linkage portion  110 C and the hinge shaft  84  such that they can be moved as a single unit in the left-right direction. Specifically, the E-ring ER 1  described above is arranged adjacent to the right side of the hinge shaft linkage portion  110 C. On the other hand, an E-ring ER 3  fixed to the hinge shaft  84  is arranged adjacent to the left side of the hinge shaft linkage portion  110 C. With this, when the hinge shaft  84  and the looper cover  70  are to be moved in the left-right direction, the hinge shaft linkage portion  110 C is engaged with the hinge shaft  84  via the E-rings ER 1  and ER 3 . This arrangement allows the hinge shaft linkage portion  110 C (that is, the looper cover detection member  110 ) to be moved together with the hinge shaft  84  and the looper cover  70  in the left-right direction. 
     With such an arrangement, the position of the looper cover detection member  110  when the looper cover  70  is at the open position is designed as a non-switching position. When the looper cover  70  is set to the completely closed position, the looper cover detection member  110  is moved leftward from the non-switching position, and is set to the switching position. 
     The switching plate portion  110 B is configured in an approximately U-shaped structure having an opening that faces the upper side as viewed in a front view. The upper-end portion of the right-end portion of the switching plate portion  110 B is configured such that it is bent rearward by approximately 90 degrees, and is arranged adjacent to the lower side of the guide plate portion  102 A of the detection base  102 . Furthermore, a guide pin  112  is provided to the upper-end portion as a “second pin” having a cylindrical structure. The guide pin  112  is configured such that it protrudes upward from the upper-end portion, and is inserted into the first guide opening  102 C of the detection base  102  such that it can be relatively moved. With this arrangement, the movement of the looper cover detection member  110  in the left-right direction is guided by the first guide opening  102 C of the detection base  102 . 
     Furthermore, the upper-end portion of the left-end portion of the switching plate portion  110 B is configured as a pressing portion  110 D. The pressing portion  110 D is arranged on the right side of the coupling pin  54 P of the switching member  54 . With such an arrangement, when the looper cover detection member  110  is moved from the non-switching position to the switching position in the threading state of the threading mechanism  20 , the pressing portion  110 D presses the coupling pin  54 P of the switching member  54  leftward, thereby rotating the switching member  54  in a clockwise manner as viewed in the front view. With this, the slide plate  44  is moved from the threading position to the sewing-enabled position, thereby switching the threading mechanism  20  from the threading state to the sewing-enabled state. 
     [Regarding the Side Cover Detection Member  114 ] 
     The side cover detection member  114  is configured including a cover detection shaft  116 , a detection spring  118  configured as a “force-applying member”, and a cover detection rod  120 . 
     [Regarding the Cover Detection Shaft  116 ] 
     As shown in  FIG. 6 , the cover detection shaft  116  is inserted into a through hole  130 A formed in the sewing machine main body  130  such that it can be relatively moved with the left-right direction as its axial direction. Furthermore, the cover detection shaft  116  is arranged coaxially with the detection shaft pressing portion  90 D when the side cover  90  is in the closed state (see  FIG. 7B ). Furthermore, in a state in which the cover detection shaft  116  is inserted into the sewing machine main body  130 , the left-side portion of the cover detection shaft  116  is arranged such that it protrudes leftward with respect to the sewing machine main body  130 . Furthermore, the right-end portion of the cover detection shaft  116  is arranged such that it protrudes rightward with respect to the sewing machine main body  130 . 
     [Regarding the Detection Spring  118 ] 
     The detection spring  118  is configured as a compression coil spring. The detection spring  118  is mounted on the left-side portion of the cover detection shaft  116  (specifically, a portion of the cover detection shaft  116  that protrudes leftward with respect to the sewing machine main body  130 ). The left-end portion of the detection spring  118  is engaged by an E-ring ER 4  fixed to the left-end portion of the cover detection shaft  116 . The right-end portion of the detection spring  118  is engaged with the sewing machine main body  130 . Furthermore, in a state in which the detection spring  118  is mounted on the cover detection shaft  116 , the detection spring  118  is compressed such that its shape is changed. With this, the cover detection shaft  116  is forced leftward by the detection spring  118 . 
     [Regarding the Cover Detection Rod  120 ] 
     As shown in  FIGS. 1 and 3 , the cover detection rod  120  is configured in an approximately longitudinal plate structure that extends in the left-right direction with the upper-lower direction as the thickness direction. The cover detection rod  120  is arranged on the right side of the cover detection shaft  116 . A coupling tab  120 A is formed as a left-end portion of the cover detection rod  120  such that it is bent upward. A circular coupling opening  120 B is formed as a through hole in the coupling tab  120 A. With such an arrangement, the right-end portion of the cover detection shaft  116  is inserted into the coupling opening  120 B. In this state, the coupling tab  120 A is arranged such that it is interposed between a pair of E-rings ER 5  fixed to the cover detection shaft  116  along the left-right direction. With this, the cover detection shaft  116  and the cover detection rod  120  are coupled such that they can be moved as a single unit in the left-right direction. 
     With such an arrangement, as shown in  FIG. 7A , in a state in which the side cover  90  is opened, the detection shaft pressing portion  90 D of the cover  90  is moved away leftward with respect to the cover detection shaft  116 , and the E-ring ER 5  comes in contact with the right-side face of the sewing machine main body  130  by the force applied by the detection spring  118 . This maintains the position of the cover detection shaft  116  (i.e., the position of the side cover detection member  114 ) (the position of the side cover detection member  114  will be referred to as a “non-detection position”). In contrast, in a state in which the side cover  90  is closed as shown in  FIG. 7B , the detection shaft pressing portion  90 D presses the left end of the cover detection shaft  116  rightward against the force applied by the detection spring  118 , thereby moving the cover detection shaft  116  (i.e., the side cover detection member  114 ) rightward from the non-detection position (the position of the side cover detection member  114  will be referred to as a “detection position” hereafter). 
     As shown in  FIGS. 1 and 3 , the cover detection rod  120  is configured such that its intermediate portion in the longitudinal direction is bent in an approximately crank shape. The right-end portion of the cover detection rod  120  is arranged above the guide plate portion  102 A of the detection base  102  with a gap between them. A guide pin  122  configured as a “first pin” is provided to the right-end portion of the cover detection rod  120 . The guide pin  122  is configured in an approximately cylindrical structure such that it protrudes downward from the right-end portion of the cover detection rod  120 . With such an arrangement, the guide pin  122  is inserted into the second guide opening  102 D of the detection base  102  such that it can be relatively moved. This allows the second guide opening  102 D to guide the movement of the cover detection rod  120  between the non-detection position and the detection position. It should be noted that the tip portion (lower-end portion) of the guide pin  122  is arranged such that it protrudes downward from the guide plate portion  102 A. An E-ring ER 6  is fixed to the tip portion of the guide pin  122 . This prevents the guide pin  122  from detaching from the second guide opening  102 D. 
     [Regarding the Detection Lever  124 ] 
     The detection lever  124  is configured in an approximately longitudinal plate structure that extends in the left-right direction with the upper-lower direction as the thickness direction. The detection lever  124  is arranged between the guide plate portion  102 A of the detection base  102  and the right-end portion of the cover detection rod  120 . A circular coupling opening  124 A is formed as a through hole in an intermediate portion in the rear-end portion of the detection lever  124  in the longitudinal direction. With such an arrangement, the guide pin  122  of the cover detection rod  120  is inserted into the coupling opening  124 A such that it can be relatively rotated. With this arrangement, the detection lever  124  is configured such that it can be moved together with the cover detection rod  120  as a single unit in the left-right direction. 
     Furthermore, a cam opening  124 B configured as a “cam groove” is formed as a through hole in the left-side portion of the detection lever  124  (specifically, a left-side portion with respect to the coupling opening  124 A). The cam opening  124 B is configured such that it is positioned on the left side and on the front side with respect to the coupling opening  124 A and such that it extends in the left-right direction. Furthermore, the cam opening  124 B is configured such that its left-side portion is bent rearward in an approximately crank shape. Specifically, the cam opening  124 B is configured including a first cam opening portion  124 B 1  configured as the left-end portion of the cam opening  124 B such that it extends in the left-right direction, an inclined cam opening portion  124 B 2  configured such that it is inclined frontward as it approaches the right side from the right-end portion of the first cam opening portion  124 B 1 , and a second cam opening portion  124 B 3  configured such that it extends rightward from the right-end portion of the inclined cam opening portion  124 B 2 . 
     With such an arrangement, the guide pin  112  of the looper cover detection member  110  is inserted into the cam opening  124 B such that it can be relatively moved. With this, the position of the guide pin  112  of the detection lever  124  is changed in a range in the left-right direction defined by the cam opening  124 B according to the relative position between the looper cover detection member  110  and the side cover detection member  114  in the left-right direction. This changes the orientation of the detection lever  124 . It should be noted that the guide pin  112  is arranged such that its tip portion (upper-end portion) protrudes upward from the detection lever  124 . An E-ring ER 7  is fixed to the upper-end portion of the guide pin  112 . This arrangement prevents the guide pin  112  from detaching from the cam opening  124 B. 
     Furthermore, a switch pressing portion  124 C is monolithically formed as a right-end portion of the detection lever  124  such that it protrudes downward. The switch pressing portion  124 C is configured to press the operating protrusion  108 A of the switch  108 . 
     With such an arrangement, when both the looper cover  70  and the side cover  90  are in an open state, the detection lever  124  is arranged on the left side of the switch  108 . Furthermore, the switch pressing portion  124 C is arranged such that it is positioned on the left side and the front side with respect to the operating protrusion  108 A of the switch  108  with a gap between them. That is to say, the switch  108  is set to the OFF state. 
     Furthermore, with such an arrangement, when both the looper cover  70  and the side cover  90  are in a closed state, the switch pressing portion  124 C presses the operating protrusion  108 A so as to set the switch  108  to the ON state, which will be described later in detail. Moreover, with such an arrangement, when either the looper cover  70  or the side cover  90  is in an open state, the switch pressing portion  124 C does not press the operating protrusion  108 A. In this state, the switch  108  is set to the OFF state. 
     [Operations and Effects] 
     Next, description will be made below regarding the operations and effects with reference to the operations of the safety mechanism  100  in four kinds of states, i.e., states  1  through  4 . 
     [Regarding the State  1 ] 
     In the state  1 , both the looper cover  70  and the side cover  90  are in an open state. In this state, the looper cover  70  is in an open state. Accordingly, the hinge portion  72 R of the looper cover  70  is arranged on the right side of the cam tab  82 R 1  of the support portion  82 R of the hinge plate  82 . Furthermore, the stopper tab  72 R 1  is engaged with the cam portion  82 R 2  of the cam tab  82 R 1 . Accordingly, the looper cover  70  is maintained at the open position. 
     With such an arrangement, when the looper cover  70  is set to the open position, the looper cover detection member  110  is set to the non-switching position. Specifically, as shown in  FIG. 8A , the guide pin  112  of the looper cover detection member  110  is arranged at the right-end portion of the cam opening  124 B (second cam opening portion  124 B 3 ) of the detection lever  124 . 
     Furthermore, in the state  1 , the side cover  90  is also in the open state. Accordingly, as shown in  FIG. 7A , the detection shaft pressing portion  90 D of the side cover  90  is arranged on the left side of the cover detection shaft  116  of the side cover detection member  114  with a gap between them. With this, the side cover detection member  114  is arranged at the non-detection position by the force applied by the detection spring  118 . 
     With such an arrangement, as shown in  FIG. 8A , when the looper cover detection member  110  is set to the non-switching position, and when the side cover detection member  114  is set to the non-detection position, the detection lever  124  is arranged such that it is positioned on the left side of the operating protrusion  108 A of the switch  108  and such that it is inclined somewhat frontward toward the right side. In this state, the second cam opening portion  124 B 3  extends along the left-right direction. More specifically, the switch pressing portion  124 C of the detection lever  124  is arranged such that it is positioned on the left side and the front side of the operating protrusion  108 A of the switch  108  with a gap between them. Accordingly, the switch  108  is set to the OFF state, and the motor power supply is set to the disconnection state. 
     [Regarding the State  2 ] 
     In the state  2 , the looper cover  70  is set to the closed state, and the side cover  90  is set to the open state. That is to say, the state  2  is the same as the state  1  except that the looper cover  70  is switched from the open state to the closed state. With such an arrangement, when the looper cover  70  is to be switched from the open state to the closed state, the looper cover  70  is turned rearward from the open position thereof so as to set the looper cover  70  to the interim closed position. Subsequently, the looper cover  70  is moved leftward from the interim closed position, thereby setting the looper cover  70  to the completely closed position. 
     Specifically, upon turning the looper cover  70  from the open position to the interim closed position, the engagement state between the stopper tab  72 R 1  of the looper cover  70  and the cam portion  82 R 2  of the cam tab  82 R 1  of the hinge plate  82  is released. With this, the looper cover  70  and the hinge shaft  84  are moved leftward by the force applied by the hinge spring  86 , thereby setting the looper cover  70  to the completely closed position. 
     Furthermore, when the looper cover  70  and the hinge shaft  84  are moved leftward, the hinge shaft linkage portion  110 C of the looper cover detection member  110  is moved leftward in conjunction with the hinge shaft  84  and the looper cover  70 , thereby moving the looper cover detection member  110  to the switching position. 
     In contrast, in the state  2 , the side cover  90  is in the open state. The left-right position of the side cover detection member  114  matches that in the state  1 . Furthermore, the guide pin  122  of the cover detection rod  120  included in the side cover detection member  114  is coupled to the coupling opening  124 A of the detection lever  124  such that it can be relatively rotated. Accordingly, the left-right position of the detection lever  124  also matches that in the state  1 . That is to say, the point of difference between the state  2  and the state  1  is that, in the state  2 , the looper cover detection member  110  is relatively displaced leftward with respect to the detection lever  124  while maintaining the position of the detection lever  124  in the left-right direction. Specifically, as shown in  FIG. 8B , the guide pin  112  of the looper cover detection member  110  is moved leftward along the longitudinal direction (left-right direction) of the second cam opening portion  124 B 3  from the right-end portion of the cam opening  124 B (second cam opening portion  124 B 3 ) included in the detection lever  124 . With such an arrangement, when the looper cover detection member  110  is in the switching position, the guide pin  112  is arranged at the right-end portion of the inclined cam opening portion  124 B 2  of the cam opening  124 B included in the detection lever  124 . 
     Accordingly, in the state  2 , the same position and the same orientation are maintained with respect to the detection lever  124  as in the state  1 . Accordingly, the switch pressing portion  124 C of the detection lever  124  is maintained on the left side and the front side of the operating protrusion  108 A of the switch  108  with a gap between them. Accordingly, as in the state  1 , the switch  108  is set to the OFF state, and the motor power supply is set to the disconnection state. 
     [Regarding the State  3 ] 
     In the state  3 , the looper cover  70  is set to the open state, and the side cover  90  is set to the closed state. That is to say, the state  3  is the same as the state  1  except that the side cover  90  is switched from the open state to the closed state. Upon switching the side cover  90  from the open state to the closed state, as shown in  FIG. 7B , the detection shaft pressing portion  90 D of the side cover  90  presses the left end of the cover detection shaft  116  included in the side cover detection member  114  rightward against the force applied by the detection spring  118 . With this, the cover detection shaft  116  (side cover detection member  114 ) is moved from the non-detection position rightward, thereby setting the cover detection shaft  116  to the detection position. 
     As shown in  FIG. 8C , when the side cover detection member  114  is moved rightward, the guide pin  122  of the cover detection rod  120  is moved rightward along the second guide opening  102 D (not shown in  FIG. 8C ) formed in the detection base  102 . With such an arrangement, the guide pin  122  is coupled to the coupling opening  124 A of the detection lever  124  such that it can be relatively rotated. Accordingly, the detection lever  124  is moved rightward together with the guide pin  122 . 
     In contrast, in the state  3 , the looper cover  70  is set to the open state. Accordingly, the left-right position of the looper cover detection member  110  matches that in the state  1 . That is to say, the looper cover detection member  110  is set such that it is positioned at the non-switching position. Accordingly, the difference between the state  3  and the state  1  is that the detection lever  124  is relatively displaced rightward with respect to the looper cover detection member  110  while maintaining the position of the looper cover detection member  110 . That is to say, the detection lever  124  is moved rightward together with the cover detection rod  120  while relatively displacing the cam opening  124 B of the detection lever  124  rightward with respect to the guide pin  112  of the looper cover detection member  110 . Specifically, the guide pin  112  of the looper cover detection member  110  is relatively displaced from the right-end portion of the second cam opening portion  124 B 3  to an intermediate portion of the second cam opening portion  124 B 3  defined in the longitudinal direction. With this, the detection lever  124  is moved rightward in parallel with respect to the first state  1 . That is to say, in the state  3 , the detection lever  124  is moved rightward while maintaining the switch pressing portion  124 C of the detection lever  124  such that it is positioned on the front side of the operating protrusion  108 A of the switch  108  with a gap between them. 
     Accordingly, in the state  3 , the switch pressing portion  124 C of the detection lever  124  is positioned on the front side of the operating protrusion  108 A of the switch  108 . However, the switch pressing portion  124 C is arranged on the front side of the operating protrusion  108 A with a gap between them. Accordingly, in the state  3 , as in the state  1 , the switch  108  is set to the OFF state, and the motor power supply is set to the disconnection state. 
     [Regarding the State  4 ] 
     In the state  4 , the looper cover  70  and the side cover  90  are set to the closed state. In this state, the looper cover detection member  110  is set to the switching position as in the state  2 . Furthermore, the side cover detection member  114  is set to the detection position as in the state  3 . That is to say, the looper cover detection member  110  is relatively displaced leftward with respect to the detection lever  124  while displacing the detection lever  124  rightward together with the side cover detection member  114 . 
     Subsequently, as shown in  FIG. 8D , when the looper cover detection member  110  is set to the switching position, and when the side cover detection member  114  is set to the detection position, the guide pin  112  of the looper cover detection member  110  is moved in a range defined by the cam opening  124 B of the detection lever  124  from the second cam opening portion  124 B 3  to the first cam opening portion  124 B 1  (not shown in  FIG. 8D ) via the inclined cam opening portion  124 B 2 . With this, when the guide pin  112  is moved in a range defined by the cam opening  124 B, the guide pin  112  presses the inner circumferential face of the inclined cam opening portion  124 B 2 . Accordingly, as viewed in a plan view, the detection lever  124  is swung (turned) toward the side indicated by the arrow B shown in  FIG. 8D  with the guide pin  122  as the center of rotation. Specifically, the switch pressing portion  124 C of the detection lever  124  is displaced rearward (in a direction in which it approaches the operating protrusion  108 A of the switch  108 ) in a state in which it is arranged on the front side of the operating protrusion  108 A of the switch  108 . 
     As a result, in the state  4 , the switch pressing portion  124 C of the detection lever  124  presses the operating protrusion  108 A of the switch  108  rearward. This sets the switch  108  to the ON state, and sets the motor power supply to the on state. 
     Furthermore, when the looper cover detection member  110  is moved to the switching position, the pressing portion  110 D of the looper cover detection member  110  comes in contact with the coupling pin  54 P of the switching member  54  included in the threading mechanism  20  in the threading state. In this state, the pressing portion  110 D presses the coupling pin  54 P leftward. Accordingly, the switching member  54  is rotated in a clockwise manner as viewed in a front view. In this state, the slide plate  44  is slid from the threading position to the sewing-enabled position. With this, the threading mechanism  20  is switched from the threading state to the sewing-enabled state. 
     As described above, with the overlock sewing machine  10  according to the present embodiment, when the looper cover  70  is switched from the open state to the closed state, the looper cover detection member  110  is operated by the looper cover  70  such that it is moved from the non-switching position to the switching position. With such an arrangement, after the looper cover detection member  110  is set to the switching position, the switching member  54  is operated by the looper cover detection member  110 , thereby switching the threading mechanism  20  from the threading state to the sewing-enabled state. With this, after the looper cover  70  is set to the closed state, such an arrangement allows the threading mechanism  20  to be set to the sewing-enabled state. 
     When the side cover  90  is switched from the open state to the closes state, the side cover detection member  114  is operated by the side cover  90  such that it is moved from the non-detection position to the detection position. Furthermore, when the looper cover detection member  110  is moved to the switching position and when the side cover detection member  114  is moved to the detection position, the detection lever  124  is switched from the non-pressing state to the pressing state. In this state, the detection lever  124  presses the operating protrusion  108 A. This arrangement allows the switch  108  to detect both the closed state of the looper cover  70  and the closed state of the side cover  90 . That is to say, when the closed state of the looper cover  70  and the closed state of the side cover  90  are detected by the switch  108 , the threading mechanism  20  is always set to the sewing-enabled state. Accordingly, this arrangement allows the switch  108  to further detect the sewing-enabled state of the threading mechanism  20 . 
     As described above, such an arrangement requires only the single switch  108  to detect the sewing-enabled state of the threading mechanism  20 , the closed state of the looper cover  70 , and the closed state of the side cover  90 . That is to say, such an arrangement requires only the single switch  108  to detect the open/closed state of the looper cover  70 , the open/closed state of the side cover  90 , and the threading switching state. 
     Furthermore, the detection lever  124  is coupled to the side cover detection member  114  by the guide pin  122  such that it can be relatively rotated. When the side cover detection member  114  is moved from the non-detection position toward the other side (right side) in the axial direction of the hinge shaft  84 , the detection lever  124  is displaced to the detection position. This arrangement allows the detection lever  124  to be displaced in the left-right direction according to the movement of the side cover detection member  114  in the left-right direction. This allows the detection lever  124  to be pressed in contact with and to be moved away from the switch  108  arranged on the right side of the detection lever  124 . 
     Furthermore, the guide pin  112  of the looper cover detection member  110  is inserted into the cam opening  124 B of the detection lever  124  such that it can be relatively moved. When the looper cover  70  is moved from the non-switching position toward one side (left side) in the axial direction of the hinge shaft  84 , the detection lever  124  is moved to the switching position. Accordingly, this arrangement allows the detection lever  124  to be swung (turned) with respect to the switch  108  (operating protrusion  108 A) according to the relative position relation between the side cover detection member  114  and the looper cover detection member  110 . With this, as described above, by arranging the detection lever  124  in the vicinity of the switch  108 , and by allowing the detection lever  124  to be swung with respect to the switch  108 , this arrangement allows the detection lever  124  to be switched between the pressing state and the non-pressing state. As described above, this arrangement requires only a simple configuration to switch the detection lever  124  between the pressing state and the non-pressing state. 
     Furthermore, the cover detection shaft  116  of the side cover detection member  114  is forced leftward by the force applied by the detection spring  118 . With such an arrangement, when the side cover  90  is switched from the open state to the closed state, the cover detection shaft  116  is pressed by the detection shaft pressing portion  90 D of the side cover  90 , thereby moving the side cover detection member  114  from the non-detection position to the detection position. Accordingly, when the side cover  90  is opened from the closed state, this arrangement allows the side cover detection member  114  to be automatically moved from the detection position to the non-detection position by the force applied by the detection spring  118 . This allows the side cover detection member  114  to be switched between the non-detection position and the detection position according to the open/closed state of the side cover  90 . 
     Furthermore, the switch  108  is fixed to the detection base  102  via the switch fixing base  106 . Furthermore, the first guide opening  102 C is formed in the guide plate portion  102 A of the detection base  102 . The guide pin  112  of the looper cover detection member  110  is slidably coupled to the first guide opening  102 C. Furthermore, the second guide opening  102 D is formed in the guide plate portion  102 A. The guide pin  122  of the side cover detection member  114  is slidably coupled to the second guide opening  102 D. Accordingly, by using the detection base  102  configured to fix the switch  108 , this arrangement is capable of guiding the movement of the looper cover detection member  110  and the side cover detection member  114  in the left-right direction. 
     Furthermore, the guide pin  112  of the looper cover detection member  110  and the guide pin  122  of the side cover detection member  114  are coupled to the detection base  102 . Accordingly, this arrangement allows the detection lever  124  to be coupled to the detection base  102  via the guide pins  112  and  122 . With this, using the detection base  102  configured to fix the switch  108 , this arrangement is capable of stabilizing the orientation (state) of the detection lever  124  to be switched between the pressing state and the non-pressing state. 
     Furthermore, the hinge shaft linkage portion  110 C is monolithically formed in the looper cover detection member  110 . The hinge shaft  84  is arranged within an inner space defined by the hinge shaft linkage portion  110 C. With such an arrangement, when the hinge shaft  84  and the looper cover are moved in the left-right direction, the hinge shaft linkage portion  110 C engaged with the hinge shaft  84  via the E-rings ER 1  and ER 3  is moved in the left-right direction. This arrangement allows the hinge shaft linkage portion  110 C (i.e., the looper cover detection member  110 ) to be moved in the left-right direction in conjunction with the hinge shaft  84  and the looper cover  70 . 
     Furthermore, the cam tab  82 R 1  is provided to the support portion  82 R of the hinge mechanism  80 , and the cam portion  82 R 2  is formed in the right end of the cam tab  82 R 1 . With such an arrangement, when the looper cover  70  is set to the open state, the hinge portion  72 R of the looper cover  70  is arranged on the right side of the cam tab  82 R 1  of the support portion  82 R. In this state, the stopper tab  72 R 1  is engaged with the cam portion  82 R 2  of the cam tab  82 R 1 . Accordingly, this arrangement allows the looper cover  70  to be held at the open position. 
     Furthermore, upon rotating the looper cover  70  from the open position to the interim closed position, the engagement state between the stopper tab  72 R and the cam portion  82 R 2  of the cam tab  82 R 1  is released, thereby enabling the looper cover  70  to be moved leftward. Accordingly, after the looper cover  70  reaches the interim closed position, the looper cover  70  is automatically slid (moved) from the interim closed position to the completely closed position by the force applied by the hinge spring  86 . Accordingly, this arrangement provides improved convenience for the user. 
     It should be noted that, with the present embodiment, after the looper cover  70  reaches the interim closed position from the open position, the looper cover  70  is moved from the interim closed position to the completely closed position by the force applied by the hinge spring  86 . Also, the looper cover  70  may be moved from the interim closed position to the completely closed position by a combination of the force applied by the hinge spring  86  and the operating force applied by the operator. 
     Description has been made in the present embodiment regarding an arrangement in which the switch  108  is fixed to the detection base  102  via the switch fixing base  106 . Also, the switch  108  may be directly fixed to the detection base  102  formed of an insulating material. 
     Description has been made in the present embodiment regarding an arrangement in which the guide pin  122  is provided to the cover detection rod  120  included in the side cover detection member  114 , and the coupling opening  124 A is formed in the detection lever  124 . Also, an arrangement may be made in which a coupling opening is formed in the cover detection rod  120 , and a guide pin is provided to the detection lever  124 . 
     DESCRIPTION OF THE REFERENCE NUMERALS 
       10  overlock sewing machine,  12  looper unit,  14  upper looper (looper),  14 A upper looper inlet,  14 B upper looper blade tip,  16  lower looper (looper),  16 A lower looper inlet,  16 B lower looper blade tip,  20  threading mechanism,  22  air flow path switching mechanism,  24  main body portion,  24 A upper looper thread insertion opening,  24 B lower looper thread insertion opening,  24 C upper looper thread discharging tube,  24 D lower looper thread discharging tube,  26  selection knob,  28  upper looper conducting tube,  30  lower looper conducting tube,  32  tube support member,  34  slide tube,  40  threading switching mechanism,  42  support base,  42 A long opening,  42 P pin,  44  slide plate,  44 A slide opening,  44 B slide opening,  44 B 1  large-diameter portion,  44 P pin,  46  slide tube spring,  48  support shaft,  50  operating shaft,  52  switching transmission member,  52 P pin,  52 A engagement pin, switching member,  54 A support arm,  54 B opening portion,  54 C switching arm,  54 C 1  contact tab,  54 D engagement arm,  54 E engagement arm,  54 P coupling pin,  56  switching knob,  60  main shaft fixing mechanism,  62  fixing shaft,  62 A groove portion,  64  main shaft fixing plate,  64 A notch,  66  main shaft,  70  looper cover,  72  hinge coupling member,  72 L hinge portion,  72 R hinge portion,  72 R 1  stopper tab,  80  hinge mechanism,  82  hinge plate (support member),  82 L support portion,  82 R support portion,  82 R 1  cam tab,  82 R 2  cam portion,  84  hinge shaft,  86  hinge spring (shaft force-applying member),  90  side cover,  90 A housing portion,  90 B fixing portion,  90 C stopper,  90 D detection shaft pressing portion,  92  hinge member,  94  engagement member,  94 A hook portion,  96  reception plate,  100  safety mechanism,  102  detection base (switch fixing member),  102 A guide plate portion,  102 B fixing plate portion,  102 C first guide opening,  102 D second guide opening,  102 E switch fixing portion,  106  switch fixing base,  108  switch,  108 A operating protrusion,  110  looper cover detection member,  110 A base plate portion,  110 B switching plate portion,  110 C hinge shaft linkage portion (engagement portion),  110 D pressing portion,  112  guide pin (second pin),  114  side cover detection member,  116  cover detection shaft,  118  detection spring (force-applying member),  120  cover detection rod,  120 A coupling tab,  120 B coupling opening,  122  guide pin (first pin),  124  detection lever (lever),  124 A coupling opening,  124 B cam opening (cam groove),  124 B 1  first cam opening portion,  124 B 2  inclined cam opening portion,  124 B 3  second cam opening portion,  124 C switch pressing portion,  130  sewing machine main body,  130 A through hole,  132  unit base,  132 A insertion opening,  132 P support shaft,  134  front cover,  136  needle plate, ER 1  E-ring, ER 2  E-ring, ER 3  E-ring, ER 4  E-ring, ER 5  E-ring, ER 6  E-ring, ER 7  E-ring, TH 1  upper looper thread, TH 2  lower looper thread, W washer.