Patent Publication Number: US-6981459-B2

Title: Sewing machine

Description:
TECHNICAL FIELD 
   The present invention relates to a sewing machine, which is provided at its arm with a movable controller made movable at least within a predetermined range, a thread take-up lever and a thread tension regulator and, more particularly, to a sewing machine, which can automatically engage a thread with the thread take-up lever and the thread tension regulator or can automatically pass a thread through a needle. 
   BACKGROUND ART 
   In an ordinary sewing machine, there are arranged a thread take-up lever mechanism to be driven in an arm by a spindle and a needle bar drive mechanism. A thread take-up lever is partially protruded from a vertical slit in an arm head and is reciprocally driven up and down. The arm is provided with a thread bobbin mount on its upper end side and with a thread tension regulator and a thread tension spring on its front side. A tension dial for the thread tension regulator is provided rear the thread tension regulator. A needle bar protrudes downward of the arm head, and a needle is attached to the lower end portion of the needle bar. A presser foot for pressing a cloth to be sewn and a presser bar for supporting the presser foot can be switched between a bottom position, at which the cloth is pressed by a lifting lever, and an upward retracted position. 
   In case the sewing is interrupted to exchange the thread bobbin for a needle thread, the presser foot is moved to the retracted position, and the thread tension regulator is brought in a released state. In this state, the thread bobbin is exchanged, and the needle thread fed out from the thread bobbin is guided through a plurality of thread guides to the thread tension regulator. The thread is engaged between a pair of thread tension discs in the released state, with a thread tension spring and further with a thread guard of the thread take-up lever. After this, the needle eye of a needle is threaded with the end portion of the needle thread. When the thread bobbin of the needle thread is to be thus exchanged, the thread has to be engaged with the thread tension regulator, the thread tension spring and the thread guard of the thread take-up lever and has to be passed through the needle eye. These thread engagement and passing operations are troublesome for the user because they are accompanied by the complicated operations, and the user has needed some getting used to doing those operation properly. 
   Therefore, U.S. Pat. No. 3,749,039 discloses the technique, in which the threading is simplified by mounting the needle thread cassette having the thread bobbin housed therein, removably on the arm. At a transverse center portion of the arm of the sewing machine, there is disposed a cassette mount, in which the needle thread cassette can be removably mounted. In association with the mounting action of the needle thread cassette, moreover, the needle thread fed out from the thread bobbin in said needle thread cassette is automatically engaged with the thread tension regulator, the thread tension spring and the thread guard of the thread take-up lever. 
   In JP-A-55-81693, on the other hand, there is proposed a cassette type threading device for a sewing machine. This cassette type threading device is provided with a thread take-up lever travel region of an arm, a cassette mount disposed on the right side of the region, and a cover member for opening/closing the cassette mount. The needle thread cassette having the thread bobbin housed therein is removably mounted in that cover member. A thread tension regulator and a thread take-up spring protrude into the cassette mount. The cover member is opened by turning it 90 degrees forward and is set with the needle thread cassette. By doing the action to close the cover member with the thread take-up lever being at the lowermost position, the needle thread is automatically engaged with the thread tension regulator and the thread take-up spring. When the thread take-up lever is then raised, the needle thread is automatically engaged with the thread guard of the thread take-up lever. 
   As disclosed in JP-A-5-293284, for example, there is practiced a sewing machine, which is constructed to have an automatic threading mechanism at the arm of the sewing machine so that the end of the needle thread is passed through the eye of a needle by moving the control lever of the mechanism downward by a predetermined distance. 
   DISCLOSURE OF THE INVENTION 
   By mounting the needle thread cassette which is described in U.S. Pat. No. 3,749,039 or JP-A-55-81693, in the cassette mount of the sewing machine, it is surely possible to engage the thread automatically with the thread guard of the thread take-up lever and with the paired thread tension discs and the thread tension spring of the thread tension regulator. In the sewing machine of the aforementioned publications, however, no consideration is taken into the thread engagement and the thread passing through the needle eye following the thread engagement with the aforementioned thread take-up lever and thread tension regulator. 
   After the thread guard of the thread take-up lever and the thread tension regulator were threaded as described above, therefore, it is necessary to pass the end of the needle thread manually through the needle eye. In case the needle thread pulled out from the needle thread cassette at present is not sufficiently long, however, it may not be sufficiently handled to the thread guard or the needle eye. Even if the needle thread is attempted to be pulled so that its sufficient length may be let off from the aforementioned needle thread cassette, however, it may be unable to be smoothly pulled out, after the needle thread cassette was mounted, due to the resistance received from the already engaged portion. If the needle thread is excessively forcibly pulled out unintentionally, on the contrary, the thread take-up lever or the thread tension regulator may be damaged, or the needle thread may be unintentionally loosened in the course of the pulling passage. As a result, the needle thread may be twisted, tensed or broken. Moreover, it is inefficient to pass the end of the needle thread manually through the needle eye, raising an obstruction to the improvement in the efficiency of the subsequent sewing operations. 
   In JP-A-5-293284, there is disclosed an automatic needle eye threading mechanism. However, the above described automatic threading mechanism of the prior art is premised by the facts that it is manually controlled in itself and that it is used for the threading operation after the thread was engaged with the thread tension regulator and the thread guard of the thread take-up lever. Therefore, it is difficult to pass the thread through the needle in association with the thread engagement, and to execute the thread engagement and passing in a series of continuous operations. 
   In the sewing machine with the needle thread cassette described in the aforementioned USP, moreover, with the thread guard of the thread take-up lever being retained at the lowermost position (or the thread loosening position) by turning the spindle manually, the needle thread cassette is mounted in the cassette mount. In the state where the needle thread cassette is mounted in the cassette mount, the first and second resistance applying portions are released. When the thread take-up lever moves to the uppermost position (or the thread tightening position) at the sewing starting time, therefore, the needle thread is not always fed out from the thread bobbin, and the needle thread in the needle eye may be pulled to come out of the eye. 
   In case the sewing machine is to be interrupted, it normally stops with its needle bar being at the uppermost position. At this time, the thread take-up lever is also at a position in the thread tightening course near the uppermost position. In the aforementioned USP, however, when the needle thread cassette is to be mounted, the thread take-up lever has to be switched to the lowermost position by the manual operation, but this operation is troublesome. This trouble is also likewise experienced in the sewing machine of the latter publication. 
   In the sewing machine of the prior art, moreover, a presser foot for pressing a cloth to be sewn and a presser bar for supporting the presser foot can be switched by the control of a presser foot lever between a bottom position, at which the cloth is pressed, and an upward retracted position. In order to work the cloth or thread easily after the presser foot was retracted, moreover, the sewing machine generally has a mechanical link, in which the thread tension discs of the thread tension regulator are opened/closed in association with the position of the presser foot. Specifically, the thread tension discs are opened, when the presser foot is at the retracted position, and are closed when the presser foot is at the bottom position. 
   In case the needle thread is to be engaged or passed in the sewing machine in which the position of the presser foot and the opening/closing operation of the thread tension discs are thus linked, it never fails that the needle thread is handled after the presser foot was brought into the retracted position and after the thread tension discs were brought into the open state. In case the user has accidentally brought the presser foot into the bottom position or in case the user desires to press the cloth with the presser foot, however, the user cannot or fails to engage or pass the needle thread. 
   The present invention has been conceived in view of those problems and has an object to provide a sewing machine, which can engage a needle thread fed out from a thread bobbin, from a partially engaged state where the thread is pulled out in advance to a needle along a predetermined feed passage to a needle, in a normal state with a thread take-up lever or a thread tension regulator in association with the movement of a movable controller. Moreover, the object is to provide a sewing machine, which is enabled to pass the needle thread through a needle eye by actuating an automatic threading mechanism, too. 
   In order to achieve the aforementioned object, according to the invention, there is provided a sewing machine comprising a thread take-up lever and a thread tension regulator each disposed along a predetermined needle thread passage from a thread bobbin to a needle, an arm having a front face, and a movable controller provided in the front of the arm so as to be movably at least within a predetermined range, the movable controller not protruding out of the front face of the arm when moved in the predetermined range, wherein the needle thread is engaged with at least one of the thread take-up lever and the thread tension regulator when the movable controller is moved within the predetermined range while the needle thread has been drawn from the thread bobbin near to the needle substantially along the predetermined needle thread passage. 
   In order to achieve the aforementioned object, there is also provided a sewing machine comprising: a thread take-up lever for reciprocating while being timed with the motion of a needle to take up a needle thread fed out from a thread bobbin; an automatic threading mechanism for passing the needle thread through a needle eye; an arm having a front face; and a movable controller provided in the front of the arm so as to be movable at least within a predetermined range, the movable controller not protruding out of the front face of the arm when moved in the predetermined range, wherein said movable controller is moved within said predetermined range to control and set the needle thread in a thread guard of the thread take-up lever and to actuate said automatic threading mechanism to pass the needle thread through the needle eye. 
   Here, the movable controller may be a needle thread cassette having the thread bobbin of the needle thread housed therein, a removable control member having no thread bobbin housed for engaging with the thread like the needle thread cassette, or a threading control member connected to the arm through a link mechanism or a locking lever. 
   The movable controller is so disposed in the arm of the sewing machine as to be movable at least within the predetermined range. In case the needle thread is engaged in the former construction with at least one of said thread take-up lever or said thread tension regulator, the needle thread, as fed out from the thread bobbin by the operator, is pulled out at first along a predetermined needle thread passage (or a feed passage) to the position of the needle. In this case, the needle thread may be moved and engaged in a normal state with said thread take-up lever or said thread tension regulator by the subsequent moving control of said movable controller. Therefore, said needle thread may be arranged not only at a position where it can be instantly engaged along the needle thread passage with said thread take-up lever or said thread tension regulator but also in the vicinity of said thread tension regulator or at a position corresponding to the moving locus of the thread take-up lever. Moreover, the needle thread may also be arranged either at a distance from said predetermined needle thread passage or in a mode similar to the needle thread passage (such that the portion corresponding to the horizontal portion of said needle thread passage is horizontally arranged at a more or less spacing from the normal position). By moving said movable controller in this state within said predetermined range, said needle thread can be engaged in the normal state with at least one of said thread take-up lever or said thread tension regulator. Therefore, the engagement of the thread with said thread take-up lever or said thread tension regulator can be simplified to enhance the operating efficiency. 
   In the latter construction, moreover, the needle thread can be passed through the needle eye while being engaged with the thread guard of the thread take-up lever, in association with the moving action of the movable controller. Therefore, the engagement of the thread with the thread guard of the thread take-up lever and the passing of the thread through the needle eye can be simplified to enhance the operating efficiency. 
   Another object of the invention is to provide a sewing machine, which can mount a needle thread cassette while a thread take-up lever being retained at a position on the threading tightening side and which can engage the thread with the thread take-up lever and the thread tension regulator at the time of mounting the needle thread cassette. 
   In order to achieve the aforementioned object, according to the invention, there is provided a sewing machine comprising a needle thread cassette mounted removably in a cassette mount formed in an arm, for housing a thread bobbin to feed a needle thread fed out from the thread bobbin to a thread take-up lever, wherein the thread take-up lever includes a thread guard reciprocated between a position at a thread tightening side and a position at a side opposed to the thread tightening side; said cassette mount is disposed near a region of reciprocation of the threaded guard; and with the thread guard of said thread take-up lever being retained at a position on the thread tightening side, the needle thread is engaged with the thread guard of the thread take-up lever in association with the mounting action to mount the needle thread cassette in the cassette mount. 
   When the sewing machine is to be stopped, the needle bar normally takes the uppermost position, and the thread take-up lever takes a position on the thread tightening side on the way to the top position. In this sewing machine, with the thread guard of the thread take-up lever being retained at the position on the threading tightening side, in association with the mounting action to mount the needle thread cassette in the cassette mount disposed near the region of reciprocation of the threaded guard, the needle thread can be engaged with the thread guard of the thread take-up lever. In short, with the position of the thread take-up lever being retained at the instant when the sewing machine is stopped, the needle thread cassette can be mounted, and the thread can be engaged with the thread guard of the thread take-up lever. 
   Still another object of the invention is to provide a sewing machine, which can mount the needle thread cassette irrespective of the position of the presser foot and which can engage the needle thread fed out from the thread bobbin, in a normal state with the thread take-up lever and the thread tension regulator in association with the travel of the movable controller. 
   In order to achieve the aforementioned object, according to the invention, there is provided a sewing machine comprising: a control member for moving a presser foot up and down; up and down and a thread tension regulator having thread tension discs adapted to be released, when the presser foot is moved up by said control member, and closed when the presser foot is moved down; a movable controller made movable at least within a predetermined range; and an interlocking mechanism including a cam formed in the movable controller, a cam driven member having one of ends capable of abutting the cam and the other end traverting a pressing force said one end receive from the cam to an operation thereof, and an actuating plate driven by said other end of the cam driven member to open the thread tension disc, the interlocking mechanism opening the threat tension disc in association with the movement of the movable controller within the predetermined range while the presser foot is retained at a bottom position, wherein the needle thread is engaged with the thread tension disc in said open state in the course of the moving action of said movable controller within said predetermined range. 
   The construction, in which the presser foot is moved up and down and switched by the control member and in which the thread tension discs are opened/closed, is shared with the existing sewing machine. With the presser foot being retained at the bottom position through the control member, however, said interlocking mechanism acts, at the time of mounting the needle thread cassette, to open the thread tension discs in association with the mounting action of the needle thread cassette. The needle thread can be engaged with the thread tension discs in the open state. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front elevation of an electronic control sewing machine of an embodiment of the invention and its needle thread cassette. 
       FIG. 2  is a top plan view of the sewing machine in the state where the needle thread cassette is removed. 
       FIG. 3  is a longitudinal section showing the internal structure near a cassette mounting portion. 
       FIG. 4  is a top plan section showing an internal structure and so on near the cassette mounting portion. 
       FIG. 5  is a front elevation of a needle bar lifting mechanism, an automatic threading mechanism and so on. 
       FIG. 6  is a view corresponding to  FIG. 5  and shows a state immediately before the threading. 
       FIG. 7  is a view corresponding to  FIG. 5  and shows the relations between a needle bar and a stopper. 
       FIG. 8  is a view corresponding to  FIG. 5  and explains a proper height range of the needle bar. 
       FIG. 9A  is a perspective view showing the state immediately before the threading by a threading hook;  FIG. 9B  is a perspective view showing the state immediately after the threading; and  FIG. 9C  is a section of an essential portion in the state where the threading hook has risen after the threading. 
       FIG. 10  is a longitudinally sectional side elevation of a threading slider actuating mechanism, the needle thread cassette and so on. 
       FIG. 11  is a longitudinally sectional side elevation of an essential portion showing a thread take-up lever mechanism and the cassette mounting portion. 
       FIG. 12  is a longitudinally sectional side elevation of an essential portion and shows the moving range of thread guard of the thread take-up lever. 
       FIG. 13  is a view corresponding to  FIG. 12  and shows the threading range of the thread guard. 
       FIG. 14  is a front elevation of the needle thread cassette (in the state immediately before mounted) and the cassette mounting portion. 
       FIG. 15  is a front elevation of the needle thread cassette (in the state of being mounted) and the cassette mounting portion. 
       FIG. 16  is a longitudinally sectional side elevation of the needle thread cassette (in the state of being mounted) and the cassette mounting portion. 
       FIG. 17  is a front elevation of the needle thread cassette (in the state immediately before the mounting is completed) and an arm head. 
       FIG. 18  is a partially enlarged section of a second clamping portion and a cam. 
       FIG. 19  is a front elevation of the needle thread cassette (in the state after the mounting was completed) and the arm head. 
       FIG. 20  is a view corresponding to  FIG. 18  and shows the second clamping portions (in the opened state) and the cam. 
       FIG. 21  is a transverse section of the needle thread cassette mounted in the cassette mounting portion. 
       FIG. 22  is a longitudinally sectional side elevation of the needle thread cassette (in the state where the mounting is completed) and the cassette mounting portion. 
       FIG. 23  is a front elevation of the needle thread cassette (in the state where an openable cover is opened). 
       FIG. 24  is a longitudinally sectional side elevation of the needle thread cassette. 
       FIG. 25  is a top plan view of the needle thread cassette. 
       FIG. 26  is a bottom view of the needle thread cassette. 
       FIG. 27  is a partially cut-away transverse top plan view of the needle thread cassette and shows the downstream portion of a thread passage. 
       FIG. 28  is a longitudinally sectional side elevation of a cassette body and a thread bobbin (in the state before mounted). 
       FIG. 29  is a longitudinally sectional side elevation of the cassette body and the thread bobbin (in the state after mounted). 
       FIG. 30  is a front elevation of the needle thread cassette (in the state where the openable cover is opened). 
       FIG. 31  is a bottom view of the needle thread cassette (in the state where the openable cover is opened). 
       FIG. 32  is a top plan view of the cassette body and shows a first guide portion. 
       FIG. 33  is a bottom view of the needle thread cassette and shows second and third guide portions and the second clamping portion. 
       FIG. 34  is a transverse section of the cassette body and shows the second and third guide portions and the second clamping portion. 
       FIG. 35  is a front elevation of the needle thread cassette for explaining a thread holding procedure. 
       FIG. 36  is a side elevation of the needle thread cassette and shows a thread holding portion and so on. 
       FIG. 37  is a front elevation of a foot lifting lever, a thread tension regulator, an interlocking mechanism and so on. 
       FIG. 38  is a side elevation of the foot lifting lever, the thread tension regulator, the interlocking mechanism and so on. 
       FIG. 39  is a top plan view of the foot lifting lever, the thread tension regulator, the interlocking mechanism and so on. 
       FIG. 40  is a view corresponding to  FIG. 37  and shows the state where the needle thread cassette is mounted. 
       FIG. 41  is a view corresponding to  FIG. 38  and shows the state where the needle thread cassette is mounted. 
       FIG. 42  is a view corresponding to  FIG. 39  and shows the state where the needle thread cassette is being mounted. 
       FIG. 43  is a view corresponding to  FIG. 39  and shows the state after the mounting of the needle thread cassette is completed. 
       FIG. 44  is a view corresponding to  FIG. 37  and shows the state after the mounting of the needle thread cassette is completed. 
       FIG. 45  is a view corresponding to  FIG. 38  and shows the state after the mounting of the needle thread cassette is completed. 
       FIG. 46  is a front elevation of the case in which sewing is performed using the needle thread outside of the needle thread cassette. 
       FIG. 47  is a top plan view of the case in which sewing is performed using the needle thread outside of the needle thread cassette. 
       FIG. 48  is a front elevation of a sewing machine in case two needles are applied. 
       FIG. 49  is a schematic block diagram of a control system of the sewing machine. 
       FIG. 50  is a front elevation of an electronic control type sewing machine and a threading controller of another embodiment. 
       FIG. 51  is a side elevation of the sewing machine and the threading controller. 
       FIG. 52  is a top plan view of the sewing machine. 
       FIG. 53  is a partially cut-away transverse section showing an essential portion of the internal structure near a controller mount. 
       FIG. 54  is a longitudinal section of the vicinity of the controller mount and the threading controller. 
       FIG. 55  is a transverse section of an essential portion and shows the state in which the threading controller is completely mounted. 
       FIG. 56  is a transverse section of an essential portion near the lower end portion of the controller mount. 
       FIG. 57  is a transverse section showing the relations among a thread take-up lever mechanism, the thread guard and the threading controller. 
       FIG. 58  is a longitudinal section showing the relations between the interlocking mechanism and the thread tension regulator. 
       FIG. 59  is a longitudinal section showing relations between the interlocking mechanism and a resistance applicator. 
       FIG. 60  is an enlarged section of the resistance applicator (in the closed state). 
       FIG. 61  is an enlarged section of the resistance applicator (in the open state). 
       FIG. 62  corresponds to  FIG. 54  but shows the vicinity of the controller mount and the threading controller (in the completely mounted state). 
       FIG. 63  corresponds to  FIG. 57  but shows the vicinity of the controller mount and the threading controller (in the completely mounted state). 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
   An embodiment of the invention will be described with reference to the accompanying drawings. This electronic control sewing machine is constructed such that an needle thread cassette housing a thread bobbin can be mounted in a cassette mounting portion of an arm head, and such that an needle thread is engaged with the thread guard of a thread take-up lever and a thread tension regulator and is introduced into the eye of a needle in association with the mounting action to mounting an needle thread cassette  2 . 
   The description will be made at first on the basic structure of the sewing machine  1  and on a threading mechanism  10 , and then on the needle thread cassette  2 , a cassette mount  3 , a thread take-up lever  8 , a transmission mechanism  115  for the threading operation, and an interlocking mechanism  134  for a thread tension regulator  9  sequentially in the recited order. Here, the following description is made by assuming that the front/back and left/right are taken from an operator of the sewing machine. 
   As shown in  FIG. 1  to  FIG. 3 , this electronic control sewing machine  1  includes a bed  4 , a column  5  erected from the right end portion of the bed  4 , and an arm  6  extending leftward from the upper end of the column  5 . The arm  6  is provided with a needle bar lifting mechanism  7 , the cassette mount  3 , the thread take-up lever mechanism  8 , the thread tension regulator  9  and the automatic threading mechanism  10 . Here, the cassette mount  3  is provided in the head (or arm head) of the arm  6 . In this arm  6 , a spindle  11  is rotatably supported through a pair of bearings  12  and is rotationally driven by the driving force of the not-shown sewing machine motor. 
   Next, the needle bar lifting mechanism  7  will be briefly described because it has a general structure. At the arm head of the arm  6 , as shown in  FIG. 1  and  FIG. 3  to  FIG. 8 , there is upright arranged a needle bar bed frame  13 , which is provided with a rear wall portion  14  and a left wall portion  15 . A lower support portion  14   a  and an upper support portion  14   b , which extend forward, are formed integrally with the lower end and the upper end of the rear wall portion  14 , respectively. At the upper end portion of the left wall portion  15 , there is formed a hinged arm portion  15   a , which extends upward of the upper support portion  14   b . A needle bar  18  is so inserted into the upper support portion  14   b  and the lower support portion  14  as to move up and down. 
   On the upper end portion of the hinged support portion  15   a , there is fixed a transverse pin member  16   a , to which a hinged member  16  having a generally C-shape opened on the front face is fixedly connected. The hinged member  16  is so supported on the sewing machine frame through a longitudinal and horizontal support pin  17  as to rock so that the needle bar bed frame  13  can rock transversely (or in a needle deflecting direction) on the support pin  17 . Here, the mechanism for rocking/driving the needle through the needle bar bed frame  13  by the stepping motor is omitted in its description because it is a general one. 
   The needle bar  18  is vertically movably supported on the upper support portion  14   b  and the lower support portion  14   a , and carries a needle  19  removably at its lower end. 
   As shown in  FIG. 3  and  FIG. 11  to  FIG. 13 , the spindle  11  is provided on its left end side with a thread take-up lever crank  20  of the thread take-up lever mechanism  8 , to which a needle bar crank  22  is turnably connected through a crank pin  21 . On the substantially intermediate portion of the needle bar  18 , there is fixed a needle bar connecting bracket  23 , to which the needle bar crank  22  is connected. At the sewing time, the spindle  11  is rotationally driven by the sewing machine motor so that the needle bar  18  is vertically reciprocated by the needle bar crank  22 . 
   As shown in  FIG. 11  to  FIG. 15  and  FIG. 17 , the arm  6  is provided with the thread take-up lever mechanism  8 , which is equipped with a thread take-up lever  25  for taking up an needle thread  24  in synchronism with the vertical travel of the needle  19 . 
   At the leading end portion of the thread take-up lever  25 , there is formed a thread guard  26 , which can thread from above. Throughout the height of the right end side portion of the cassette mount  3 , there is formed a thread take-up lever travel region  27 , in which the thread guard  26  of the thread take-up lever  25  can reciprocate up and down. The thread tension regulator  9  for applying a passing resistance to the needle thread is provided to protrude to the lower portion of the cassette mount  3 . 
   This thread tension regulator  9  can be opened/closed by a foot lifting lever  29  for moving a presser foot  28  up and down, and is opened/closed, too, when the needle thread cassette  2  is mounted, as will be described hereinafter. Here, a generally upright vertical shaft is arranged in the column  5  and is interlocked with and connected to the spindle  11  through a gear mechanism so that its driving force is transmitted to a thread catching hook in the bed  4 . As in the general electronic control sewing machine, a cloth  30  is sewn by the coactions among the needle  19 , the thread catching hook and the cloth feeding mechanism, which is driven by the stepping motor. 
   Next, the automatic threading mechanism  10  for threading the eye  19   a  of the needle  19  with the needle thread  24  will be described with reference to  FIG. 5  to  FIG. 10 ,  FIG. 14 ,  FIG. 15 ,  FIG. 17  and  FIG. 19 . 
   On the upper support portion  14   b  and the lower support portion  14   a  of the needle bar bed frame  13 , there are vertically movably supported a threading pin  31  and a slider guide pin  32 , which are located on the left side of the needle bar  18 . The upper end portion of the threading pin  31  is inserted into the clearance between the bracket  16  and the pin member  16   a , and a horizontally protruding slide pin  33  is fixed on a substantially intermediate portion of the threading pin  31 . 
   A hook retaining member  34  made of a synthetic resin is fixed at the lower end portion of the threading pin  31 , and a first thread guide member  35  (as referred to  FIG. 17 ) having a general C-shape in a side view is rotatably supported at its upper support portion and at its lower support portion by the threading pin  31  corresponding to the upper side and the lower side of the hook retaining member  34 . At a vertical connecting wall  36  connecting the upper support portion and the lower support portion of the first thread guide member  35 , there is notched a thread guide  36   a  for engaging with the needle thread  24  to guide it. 
   As shown in  FIG. 9A  to  FIG. 9C , a hook mechanism  37  is fixed on the hook retaining member  34 . The hook mechanism  37  is constructed of a threading hook  37   a , two guide members  37   b  positioned on the two sides of the threading hook  37   a , and a thread retaining wire  37   c  extending horizontally through those threading hook  37   a  and guide members  37   b . At the leading end portion of the threading hook  37   a , there is formed a hook portion, which is inserted at the threading into the eye  19   a  so that the needle  19  hooks the needle thread  24  which is positioned just ahead the eye  19   a  while being guided by the aforementioned guide member  37   b.    
   On the hook retaining member  34 , there is integrally fixed a second thread guide member  38 , which is bent downward generally near its leading end portion so that the bent portion functions as a thread guide portion  38   a . This thread guide portion  38   a  is positioned substantially on the opposite side of the hook mechanism  37  with respect to the threading pin  31  and spaced at a predetermined distance. In short, the second thread guide member  38  and the hook mechanism  37  are disposed integrally with the threading pin  31  while retaining a predetermined positional relation. 
   Here will be described a turning mechanism for turning the threading pin  31  by a predetermined angle. 
   Around the upper end portions of the threading pin  31  and the slider guide pin  32  on the back side of the needle bar bed frame  13 , as shown in  FIG. 5  to  FIG. 8 ,  FIG. 14 ,  FIG. 15 ,  FIG. 17  and  FIG. 19 , there is vertically movably fitted a threading slider  40 , which is made of a synthetic resin. Specifically, this threading slider  40  is equipped with an upper hinge portion  41 , a lower hinge portion  42 , an outer circumferential wall portion  43  and a threading slider pawl  44 . 
   The upper hinge portion  41  and the lower hinge portion  42  are extended over the threading pin  31  and the slider guide pin  32 . The outer circumferential wall portion  43  is formed to connect those upper hinge portion  41  and the lower hinge portion  42  vertically and to cover about one half of the outer circumference of the aforementioned upper end portion of the threading pin  31 . A threading slider cam portion  43   a  of a helical shape is formed at the outer circumferential wall portion  43 . To the left end portions of the upper hinge portion  41  and the lower hinge portion  42 , there is connected the threading slider pawl  44 , which has a pawl portion  44   a  at a substantially intermediate portion of its left end. 
   Through the substantially intermediate portion of the threading pin  31  and at a position corresponding to the just upper side of the lower hinge portion  42 , there is fixed the slide pin  33  of a predetermined length, which engages at its deep end portion with the threading slider cam portion  43   a . A spring receiving pin  45  is fixed through the side of the threading pin  31  at a position lower than the slide pin  33  by a predetermined length. A compression coil spring  46  is mounted around the threading pin  31  and between the lower hinge portion  42  and the spring receiving pin  45 . Around the slider guide pin  32  and between the lower hinge portion  42  and the lower support portion  14   a  of the needle bar bed frame  13 , there is mounted a compression coil spring  47  for biasing the threading slider  40  upward. 
   Here will be described an offset member  48 . As shown in  FIG. 4  to  FIG. 8 , this offset member  48  is so mounted on the threading pin  31  and the slider guide pin  32  as to move vertically on the back side of the threading slider  40  and within a range of about three quarters as long as the height between the upper support portion  14   b  and the lower support portion  14   a  of the needle bar bed frame  13 . This offset member  48  is constructed to include an upper support portion  49 , a lower support portion  50  and a vertical connecting wall  51  connecting those upper support portion  49  and lower support portion  50 . The upper support portion  49  penetrates into the threading pin  31  and the slider guide pin  32 , and the lower support portion  50  penetrates only into the threading pin  31 . 
   A threading positioning member  52  is fixed as an engaging member immediately above the needle bar connecting bracket  23  of the needle bar  18 , and the right end portion of the upper support portion  49  of the offset member  48  is so constructed that it can abut against the threading positioning member  52  from above. With the right end portion of the upper support portion  49  abutting against the threading positioning member  52 , the threading hook takes the same height position as that of the eye  19   a  of the needle  19  (as referred to  FIG. 6 ). At the left end lower portion of the connecting wall  51 , there is formed an offset member cam portion  53 , which includes a slope portion  53   a  protruding more leftward as it goes more downward, and a flat portion  53   b  extending vertically downward from the lower end of the slope portion  53   a  and protruding more leftward than the pawl portion  44   a  of the threading slider pawl  44 . 
   Accordingly as the threading slider  40  is pressed downward from the upper limit position, as shown in  FIG. 5 , by a later-described needle thread cassette  2  against the biasing force of the compression coil spring  47 , the threading pin  31 , the slider guide pin  32  and the offset member  48  move down and stop when the upper support portion  49  of the offset member  48  comes into abutment against the threading positioning member  52  (as referred to  FIG. 6 ). At this time, the threading slider  40  moves down relative to the threading pin  31  and the slider guide pin  32  so that the slide pin  33  moves along the threading slider cam portion  43   a  having the helical shape. The threading is effected when the threading pin  31  is turned by a predetermined angle clockwise, as viewed in a top plan view (as referred to  FIG. 9A  to  FIG. 9C ). 
   In this threading operation, the hook mechanism  37  is turned in a direction toward the needle  19  so that the aforementioned threading hook penetrates into the needle eye  19   a . Simultaneously with this, the second guide member  38  is turned clockwise (or in the direction away from the needle  19 ) in synchronism with the hook mechanism  37 . There is further provided a link mechanism  54  for turning the first thread guide member  35 , which is turnably supported on the lower end portion of the threading pin  31 , in the threading operation in the direction away from the second thread guide member  38 . When the threading pin  31  in a standby state before turned for the threading operation, more specifically, the second thread guide member  35  takes a forward posture, and its thread guide portion  38   a  is positioned immediately inside of the thread guide  36   a  of the connecting wall  36 . 
   When the threading pin  31  turns after it went to the lower limit position, the hook mechanism  37  and the second thread guide member  38  integrally rotate clockwise, as viewed in the top plan, and the first thread guide member  35  turns counterclockwise through the link mechanism  54 . In short, the first thread guide member  35  moves apart from the second thread guide member  38  and toward the hook mechanism  37 . Here, a support plate  55  for clamping the needle thread  24  under a slight pressure and a thread guide disc  56  are also disposed near the link mechanism  54 . 
   Here will be described the needle thread cassette  2 . 
   As shown in  FIG. 1 ,  FIG. 10  and  FIG. 14  to  FIG. 36 , the needle thread cassette  2  acting as a movable operation member includes: a cassette case  57  having a shape similar to an elongated box having a small transverse width; a thread bobbin housing portion  57   a  for housing a thread bobbin  62 ; a thread bobbin retaining portion  58  for retaining the thread bobbin  62  in the thread bobbin housing portion  57   a ; the thread bobbin  62  retained in the thread bobbin retaining portion  58 ; a thread passage  59  for guiding the needle thread  24 , as supplied from the thread bobbin  62 , to a thread exit  68 ; a thread take-up lever travel region  57   b , in which the thread guard  26  of the thread take-up lever  25  of the thread take-up lever mechanism  8  reciprocates up and down; and a thread tension regulator housing portion  57   c  for penetrating the thread tension regulator  9  thereinto. Here, the thread exit  68  is formed in the bottom wall of the cassette case  57  near the right end. 
   The cassette case  57  is equipped with a cassette body  60  made of a synthetic resin and an openable cover  61 , of which the openable cover  61  is openably connected to the right end portion of the cassette body  60 . However, the openable cover  61  may also be so constructed that it may be opened/closed by sliding it up and down with respect to the cassette body  60 . As thread color discriminating means for discriminating the color of the needle thread  24  of the thread bobbin  62 , the openable cover  61  is made of a transparent material so that it may be able to discriminate the thread color of the thread bobbin  62  in the cassette case  57 . Here, another thread color discriminating means may also be exemplified either by forming an open hole in the openable cover  61  for inspecting the thread bobbin  62  or by adhering a seal in the same color as that of the needle thread  24  of the thread bobbin  62  to a portion of the surface of the cassette case  57 . 
   As shown in  FIG. 10 ,  FIG. 16  and  FIG. 28  to  FIG. 33 : the thread take-up lever travel region  57   b  is formed on the right side of the cassette case  57  to have a width of about one third of the cassette case  57 ; the thread bobbin housing portion  57   a  is at the upper two thirds of the left two thirds of the cassette case  57 ; and the thread tension regulator housing portion  57   c  is at the lower one third of the left two thirds of the cassette case  57 . The regions for the thread passage  59  are partitioned by partitions  66  and  99  on the left end portion in the cassette body  60   
   In the thread take-up lever travel region  57   b  and in the rear wall of the cassette body  60 , there is formed an elongated slit  101  for penetrating the thread guard  26  of the thread take-up lever  25  and a later-described thread guide  106 A. In the thread tension regulator housing portion  57   c  and in the rear wall and the bottom wall of the cassette body  60 , there is formed a notch  96  for introducing the thread tension regulator  9  into the thread tension regulator housing portion  57   c . Vertical partitions  67  and  100  are formed between the thread take-up lever travel region  57   b  and the thread bobbin housing portion  57   a  and the thread tension regulator housing portion  57   c , and a horizontal support wall  63  for protruding toward the openable cover  61  is formed between the thread bobbin housing portion  57   c  and the thread tension regulator housing portion  57   a.    
   The thread bobbin retaining portion  58  is constructed to retain the thread bobbin  62  vertically of its axis so that it can reduce the transverse width of the cassette case  57  and the sizes of the cassette case  57  and the cassette mount  3 . The thread bobbin retaining portion  58  is constructed of the support wall  63  (corresponding to the wall of the housing portion) and a thread bobbin retaining pin  64 . This thread bobbin retaining pin  64  is protruded upward from the support wall  63 . The thread bobbin retaining pin  64  is divided into three portions in the circumferential direction so that it can be elastically deformed in a radially widening direction thereby to retain the thread bobbin  62  having axial bores of various sizes. 
   Of the support wall  63  and at the front end portion abutting against the lower end (or one axial end) of the thread bobbin  62 , there is formed a recess  65  for pushing the thread bobbin  62  from below to take it up from the thread bobbin retaining pin  64 . This recess  65  is formed into a shape notched radially inward of the outer circumference of the thread bobbin  62  so that the needle thread  24  may not go into the clearance between the thread bobbin  62  and the support wall  63  even if it becomes slack. 
   Here will be described the thread passage  59 . As shown in  FIG. 14 ,  FIG. 15  and  FIG. 17  to  FIG. 21 , the thread passage  59  is an needle thread guide passage, which is based on a feed-out point  79  from the thread bobbin  62  retained on the thread bobbin retaining portion  58 , for guiding the needle thread  24  fed out upward from the thread bobbin  62  to the thread exit  68  of the cassette case  57 . The thread passage  59  includes a first guide portion  69 , a first clamp portion  70 , a second guide portion  71 , a third guide portion  72  and a second clamp portion  73 . With the thread bobbin  62  being retained by the thread bobbin retaining portion  58 , the needle thread  24 , as fed out upward from the thread bobbin  62 , is guided through the first guide portion  69 , the first clamp portion  70 , the second guide portion  71 , the third guide portion  72  and the second clamp portion  73  in the recited order to the thread exit  68  at the lower end portion near the right end of the cassette case  57 . 
   As shown in  FIG. 17 ,  FIG. 19  and  FIG. 22  to  FIG. 25 , the first guide portion  69  and the first clamp portion  70  are disposed in the upstream portion of the thread passage  59 . The first guide portion  69  is disposed at the top of the cassette case  57 . The first guide portion  69  is constructed to include a pin support member  74  formed in the cassette body  60 , a guide pin  75  having an L-shape, as viewed in a top plan, protruding forward from the pin support member  74  and bent rightward, and a rib  76  formed on the openable cover  61  for preventing the thread from coming out. 
   The guide pin  75  is equipped with a thread guide portion having a predetermined length in the longitudinal direction. Notched rectangular openings  77  and  78  are so formed in an opposed shape in the top walls of the cassette body  60  and the openable cover  61  as to cause the thread guide portion to face the outside, so that the needle thread fed from the thread bobbin of the outside can be introduced from the openings  77  and  78  into the first guide portion  69 . The needle thread  24  fed out from the thread bobbin  62  is so engaged with the thread guide portion of the guide pin  75  as to move freely in the longitudinal direction. Even in case the distance between the thread bobbin  62  and the first guide portion  69  is not so long, therefore, the needle thread  24  can be smoothly pulled out from the thread bobbin  62 . 
   The first clamp portion  70  will be described in the following. As shown in  FIG. 23  and  FIG. 24 , the first clamp portion  70  applies the passing resistance to the needle thread  24  in the upstream portion of the thread passage  59  and prevents the thread from being twisted and interlaced with each other. This first clamp portion  70  is disposed near the upper end of the left end portion in the cassette case  57 . The first clamp portion  70  is constructed of a thread twist preventing mechanism  82  including a presser plate  80  having a thread guide portion  80   a  and a leaf spring  81  for pressing the needle thread  24  onto the presser plate  80 . 
   The presser plate  80  and the leaf spring  81  are fixed on the partition  66  of the cassette body  60 . 
   The thread guide portion  80   a  of the presser plate  80  is a narrow notch opened upward and protruding forward of the cassette body  60 . The leaf spring  81  abuts against the left side face of the thread guide portion  80   a  to clamp the needle thread  24  between itself and the thread guide portion  80   a , and applies the passing resistance to the needle thread  24  to prevent the needle thread  24  from being twisted and interlaced. 
   Next, the second and third guide portions  71  and  72  and the second clamp portion  73  are disposed in the downstream portion of the thread passage  59 , as shown in  FIG. 14 ,  FIG. 15 ,  FIG. 17  to  FIG. 21 ,  FIG. 26  and  FIG. 27 . The second guide portion  71  is located at the lower end portion of the left end portion in the cassette case  57 ; the third guide portion  72  is located at the lower end portion of the boundary between the thread tension regulator housing portion  57   c  and the thread take-up lever travel region  57   b  in the cassette case  57 ; and the second clamp portion  73  is located near the lower end of the right end in the cassette case  57 . 
   The needle thread  24  extends obliquely from the first guide portion  69  to the first clamp portion  70 , vertically from the first clamp portion  70  to the second guide portion  71 , horizontally from the second guide portion  71  to the third guide portion  72 , and generally horizontally or at an inclination from the third guide portion  72  to the second clamp portion  73 . Thus, the needle thread  24  is guided to cross along the lower end portion of the cassette case  57 . 
   The second guide portion  71  is constructed of a pin support portion  83  disposed at the rear wall portion of the cassette body  60 , a guide pin  84  fixed on the pin support portion  83  and protruding forward, and a rib  85  formed on the openable cover  61  for preventing the thread from coming out. The pin support portion  83  and the rib  85  set the longitudinal position of the needle thread  24  properly. The third guide portion  72  is constructed of a pin support portion  86  disposed at the rear wall portion of the cassette body  60 , a guide pin  87  fixed on the pin support portion  86  and protruding forward, and a rib  88  formed on the openable cover  61  for preventing the thread from coming out. The pin support portion  86  and the rib  88  set the longitudinal position of the needle thread  24  properly. 
   The second clamp portion  73  will be described in the following. As shown in  FIG. 14 ,  FIG. 15 ,  FIG. 17  to  FIG. 21  and  FIG. 33  to  FIG. 36 , the second clamp portion  73  applies the passing resistance to the needle thread  24  in the vicinity of the thread exit  68 . No matter whether the needle thread cassette  2  might be neither mounted in the cassette mount  3  nor completely mounted, the second clamp portion  73  is constructed to apply a higher passing resistance to the needle thread  24  than the first clamp portion  70 . When the needle thread  24  is engaged with the thread guard  26  of the thread take-up lever  25  and the thread tension regulator  9  at the time of mounting the needle thread cassette  2 , therefore, the needle thread  24  is kept in the tensed state between the second guide portion  71  and the second clamp portion  73 . Therefore, the thread guard  26  of the thread take-up lever  25  and the thread tension regulator  9  can be reliably threaded, and the needle thread  24  necessary for the threading operation can be reliably fed out from the thread bobbin  62 . In other words, the third guide portion  72  and the second clamp portion  73  function as the needle thread control portion for controlling the needle thread  24  when the thread guard  26  of the thread take-up lever  25  is to be threaded. 
   The second clamp portion  73  is constructed of a movable pin member  94  having an axis directed horizontally in the transverse direction, a guide pin  89  for guiding the needle thread  24 , a thread retaining plate  90  and a leaf spring member  91 . The movable pin member  94  is composed of a radially smaller pin portion, and a radially larger control button  94   a , which is enabled to go into and out of the right side face of the lower end portion of the cassette body  60 . The movable pin member  94  is so mounted in vertical wall portions  92  and  93  near the right end and the lower end of the cassette body  60  as to move horizontally in the transverse direction, and is elastically biased rightward by the leaf spring member  91 . 
   The guide pin  89  is longitudinally inserted and fixed at its rear end portion in the left end portion of the movable pin member  94 , and the thread retaining plate  90  for retaining the needle thread  24  between itself and the guide pin  89  is fixed between the guide pin  89  and the left side face of the vertical wall portion  93 , so that the passing resistance is applied to the needle thread  24  by clamping the needle thread  24  between the guide pin  89  biased rightward together with the movable pin member  94  and the thread retaining plate  90 . 
   In the state where the needle thread cassette  2  is taken out from the cassette mount  3 , as shown in  FIG. 14  and  FIG. 18 , the leading end portion of the control button  94   a  is protruded from the right side face of the cassette body  60  by the biasing force of the leaf spring member  91 . In case the needle thread  24  is fed out from the thread bobbin  62  while the needle thread cassette  2  is not mounted in the cassette mount  3 , therefore, the movable pin member  94  and the guide pin  89  are moved leftward to open the second clamp portion  73  by pushing the control button  94   a  with the finger of the operator, so that the needle thread  24  can be fed out against the passing resistance of the first clamp portion  70 . With the needle thread cassette  62  is completely mounted in the cassette mount  3 , therefore, the second clamp portion  73  takes an open state to apply no passing resistance to the needle thread  24 , as will be described hereinafter. 
   Even in the state where the needle thread cassette  2  is completely mounted in the cassette mount  3 , as shown in  FIG. 19  and  FIG. 20 , the second clamp portion  73  is brought into the open state. For this, the cassette mount  3  is provided at its right side wall with a vertical groove  95   a  for releasing the control button  94   a , and an needle thread releasing cam  95  for bringing the control button  94   a  into a retracted state in the state where the needle thread cassette  2  is completely mounted. These components will be described together with the description of the cassette mount  3 . 
   With the needle thread cassette  2  being completely mounted in the cassette mount  3 , the second clamp portion  73  takes an open state, but the needle thread  24  is clamped by the thread tension regulator  9  being penetrated into the thread tension regulator housing portion  57   c  of the needle thread cassette  57  and is given the passing resistance, so that the needle thread  24  between the first clamp portion  70  and the thread tension regulator  9  keeps the tensed state. This prevents the needle thread  24  in the thread passage  59  upstream of the thread tension regulator  9  from being twisted or interlaced. 
   Here, the thread tension regulator  9  need not be mounted in the arm  6  but can be mounted in the needle thread cassette  2 . In this modification, too, the needle thread  24  between the first clamp portion  70  and the thread tension regulator  9  can be kept in the tensed state thereby to prevent the thread from being twisted or interlaced. 
   As described above, the needle thread  24  is clamped by the first clamp portion  70  and is clamped between later-described thread tension discs of the thread tension regulator  9  and given the passing resistance so that the needle thread is tensed between the discs. When the needle thread is clamped and resisted in this case at the entrance portion of the thread tension discs of the thread tension regulator  9 , its structurally intrinsic twist is intensified at that portion. Therefore, the twist intensified more than the structurally intrinsic one is always given to the needle thread portion between the first clamp portion  70  and the thread tension discs of the thread tension regulator  9 . 
   If the needle thread portion becomes slack, it is partially bent to cause the phenomenon that the threads are interlaced with each other at that part into a linear or entangled shape. If this interlaced part is guided to the thread tension discs of the thread tension regulator  9 , it is caught by the discs so that it is cut or frayed. 
   By clamping the needle thread  24  with the first clamp portion  70  and the thread tension discs of the thread tension regulator  9  to tense the clamped thread portion, however, it is possible to eliminate the aforementioned interlaced phenomenon. Here, the needle thread portion having passed through the thread tension discs of the thread tension regulator  9  is released from the intensified twist. 
   Here will be described the construction for penetrating the thread tension regulator  9  into the thread tension regulator housing portion  57   c  in the cassette case  57  when the needle thread cassette  2  is to be mounted in the cassette mount  3 . Below the thread tension regulator housing portion  57   c , as shown in  FIG. 1 ,  FIG. 14 ,  FIG. 15 ,  FIG. 23 ,  FIG. 26 ,  FIG. 30  and  FIG. 31 , notched rectangular openings  97  and  98  are formed in an opposed shape in the bottom walls of the cassette body  60  and the openable cover  61 , and the partially elliptic notch  96  leading to the opening  97  is formed in the rear wall portion of the cassette body  60 . When the needle thread cassette  2  is to be mounted, the thread tension regulator  9  is penetrated and housed in the thread tension regulator housing portion  57   c  through the notch  96  and the openings  97  and  98 . 
   Below the thread take-up lever travel region  57   b , as shown in  FIG. 1 ,  FIG. 3 ,  FIG. 11  to  FIG. 15 ,  FIG. 26 ,  FIG. 27 ,  FIG. 30  and  FIG. 31 , notched rectangular openings  102  and  103  are formed in an opposed shape in the bottom walls of the cassette body  60  and the openable cover  61 , and the elongated slit  101  leading to the opening  102  and extending from the lower end up to the upper end is formed in the rear wall of the cassette body  60 . When the needle thread cassette  2  is to be mounted in the cassette mount  3 , the thread guard  26  of the thread take-up lever  25  and the thread guide  106 A are penetrated and introduced into the cassette case  57  through those openings  102  and  103  and slit  101 . 
   As shown in  FIG. 21 ,  FIG. 22  and  FIG. 24 , such a rear wall of the cassette body  60  as faces the thread bobbin housing portion  57   a  bulges backward in a partially cylindrical shape for housing the thread bobbin  62 , and the portion corresponding to the lower end of the partially cylindrical portion is provided with an engaging portion  112  for engaging from above with a later-described receiving portion  109  of the cassette mount  3  to determine the height position of the needle thread cassette  2 . On the two left and right end portions of the rear wall of the cassette body  60 , there are formed ridged engaging portions  113  and  114 , which can engage with later-described guide grooves  110  and  111  of the cassette mount  3 , respectively. With the needle thread cassette  2  being mounted in the cassette mount  3 , the front face of the openable cover  61  is flush with the front face of the arm  6 , and the upper walls of the cassette body  60  and the openable cover  61  are flush with the upper face of the arm  6  (as referred to  FIG. 19  and  FIG. 22 ). 
   Next, a thread holder  104  of the needle thread cassette  2  will be described in the following. As shown in  FIG. 25 ,  FIG. 30 ,  FIG. 35  and  FIG. 36 , the thread holder  104  is constructed such that the end side portion of the needle thread  24  extending to the outside of the needle thread cassette  2  is temporarily held between a chamfered portion  105  of the hinged portion of the openable cover  61  of the outer face portion of the cassette case  57  and the cassette body  60  to contact with the chamfered portion  105  when the openable cover  61  is closed. The chamfered portion  105  and a portion of the cassette body  60  construct the thread holder  104 . However, a thread holder  104 A may also be constructed by providing the outer face portion of the cassette case  57  with a leaf spring member biased to the case and by holding the end portion of the needle thread  24  temporarily on the leaf spring member. 
   Here will be described the cassette mount  3  for mounting the needle thread cassette  2  removably from above. As shown in  FIG. 1 ,  FIG. 2 ,  FIG. 4  and  FIG. 21 , the cassette mount  3  as the controller mount is so formed at the front face of the leading end portion (or the arm head) of the arm  6  of the sewing machine as to have a longitudinally long rectangular shape, as viewed in a front elevation, and a transversely short grooved section. The cassette mount  3  is provided on the right end side with the vertically long thread take-up lever travel region  27 , in which the thread guard  26  of the thread take-up lever  25  reciprocates, and its substantial portion excepting the thread take-up lever travel region  27  is located on the left side of the thread take-up lever travel region  27 . 
   The cassette mount  3  is shaped to have its upper end and lower end opened so that the needle thread cassette  2  may be able to be mounted from above in the vertical direction and removed to above in the vertical direction with the axis of the thread bobbin  62  retained in the thread bobbin retaining portion  58  being generally in parallel with the reciprocating direction of the thread guard  26  of the thread take-up lever  25 . Near the lower end of the portion, as located rather on the left than the center, of the cassette mount  3 , the thread tension regulator  9  is disposed to protrude forward with its axis being directed in the longitudinal direction. In the lower portion of the rear wall of the cassette mount  3 , there is formed the stepped receiving portion  109  for receiving the engaging portion  112  of the needle thread cassette  2  to position the needle thread cassette  57  at a predetermined height. Near the rear ends of the left side wall and the right side wall of the cassette mount  3 , respectively, there are formed the guide grooves  110  and  111  for introducing and guiding the engaging portions  113  and  114  of the needle thread cassette  2  slidably. 
   Here will be described the needle thread releasing cam  95 , which is disposed at the cassette mount  3  for switching the second clamp portion  73  into the open state. At the rear portion of the right side wall of the cassette mount  3 , as shown in  FIG. 18  and  FIG. 20 , there are formed the aforementioned vertical groove  95   a  and the needle thread releasing cam  95  positioned on the terminal end side of the former. The vertical groove portion  95   a  continues from the upper end to the vicinity of the lower end of the cassette mount  3 , and the needle thread releasing cam  95  continues to the lower end of the vertical groove portion  95   a  through a taper portion  95   b , and protrudes to the left side of the vertical groove portion  95   a.    
   As shown in  FIG. 17  and  FIG. 18 , therefore, the control button  94  protruding from the right side face of the cassette body  60  moves along the groove portion  95   a  till immediately before the needle thread cassette  2  is completely mounted in the cassette mount  3 . At this time, the second clamp portion  73  applies the passing resistance to the needle thread  24 . When the needle thread cassette  2  is completely mounted in the cassette mount  3  so that the mounting is completed, the control button  94  comes into abutment against the needle thread releasing cam  95  and is pushed leftward. At this time, the second clamp portion  73  is released so that no passing resistance is applied to the needle thread  24 . 
   Next, the thread take-up lever mechanism  8  will be described in detail. 
   As shown in  FIG. 11  to  FIG. 14 , this thread take-up lever mechanism  8  is given such a specially devised structure as can thread the thread guard  26  with the needle thread  24  in association with the action to mount the needle thread cassette  2  in the cassette mount  3 . This thread take-up lever mechanism  8  is exemplified by a cam type, but the following construction can likewise be applied to a link type thread take-up lever mechanism. 
   This thread take-up lever mechanism  8  is provided with the thread take-up lever  25  which is driven through the thread take-up lever crank  20  by the driving force of the spindle, and the thread guide  106 A for forming a thread guide clearance  108  extending in a curved shape along the whole length of the moving locus of the thread guard  26  of the thread take-up lever  25 . The thread take-up lever mechanism  8  can introduce the needle thread  24  from above into the thread guide clearance  108  thereby to thread the thread guard  26  with the needle thread  24 . 
   The thread guide  106 A is provided with a pair of thread guide members  106 , which extend in a curved shape along the whole length of the moving locus of the leading end portion (or the thread guard  26 ) of the thread take-up lever  25  and which are longitudinally spaced from each other through the thread guide clearance  108 . The paired thread guide members  106  are made of a single wire material (of a metal or a synthetic resin) continued at the lower end portion. The upper end portion of the thread guide member  106  on the rear side extends horizontally backward and is so supported on the top frame of the sewing machine frame as to turn through a hinge member  107  so that the lower end portion of the thread guide  106 A is left as a free end. The upper end portion of the thread guide member  106  on the front side is bent forward to form an inlet port  108   a  for introducing the needle thread  24  from above into the thread guide clearance  108 . Here, the thread guide  106 A and the thread guard  26  of the thread take-up lever  25  protrude from the opening of the rear wall of the cassette mount  3  into the cassette mount  3 . 
   The thread take-up lever  25  is equipped at its leading end side with a guide portion  25   a  having a U-shaped, as viewed in a top plan, which is formed by folding back the leading end portion of a predetermined length. The paired thread guide members  106  insert the U-shaped guide portion  25   a  slidably relative to each other. When the U-shaped guide portion  25   a  vertically reciprocates, the paired thread guide members  106  are guided, while being turned at their upper portions, by the U-shaped guide portion  25   a  so that their sliding resistance to the U-shaped guide portion  25   a  is so low as to generate no substantial noise. In the portion, as corresponds to the clearance (i.e., the thread guide clearance  108 ) between the paired thread guide members  106 , of the U-shaped guide portion  25   a , there is formed the thread guard  26 , which has a threading U-shaped recess formed in its upper face for threading the needle thread  24  from above. 
   When the needle thread cassette  2  is mounted vertically from above with the axis of the thread bobbin  62  being generally in parallel with the reciprocating direction of the thread guard  26  of the thread take-up lever  25 , therefore, the needle thread  24  between the third guide portion  72  and the second clamp portion  73  of the needle thread cassette  57  can be introduced from the inlet port  108   a  into the thread guide clearance  108  and can be easily engaged with the thread guard  26  of the thread take-up lever  25 . Here, the thread guide  106 A need not be made of the wire material but may be constructed of a sheet material made of a metal or a synthetic resin. 
   Here will be described the transmission mechanism  115  for transmitting the actions of the needle thread cassette  2  to the automatic threading mechanism  10 . As shown in  FIG. 5  to  FIG. 8 , this transmission mechanism  115  transmits the actions of the needle thread cassette  2  to the automatic threading mechanism  10  through a threading slider actuating mechanism  116 , and is provided with an engaging mechanism  117  for releasing when engaged with the threading positioning member  52 . This threading slider actuating mechanism  116  is constructed to include: a threading slider actuating shaft  118  (as will be called the “shaft”); a threading slider actuating member  119 ; a threading slider actuating lever  120  (as will be called the “lever  120 ”); a threading slider actuating pawl  121  (as will be called the “actuating pawl  121 ”); a threading slider actuating pawl spring  122  (as will be called the “torsion spring  122 ”); and a threading slider actuating stopper  123  (as will be called the “stopper  123 ”). 
   In the arm  6  near the cassette mount  3 , as shown in  FIG. 4 ,  FIG. 5  and  FIG. 10 , there is vertically supported the shaft  118 , on which the slider actuating member  119  having a general C-shape, as viewed in a side elevation, is vertically movably supported. On the threading slider actuating member  119 , there is fixed the lever  120  having a C-shape, as viewed in a top plan. A plate-shaped lever portion  120   a  is so disposed at a substantially intermediate portion of the right end of the front plate portion of the lever  120  as to protrude forward. The leading end portion of the lever portion  120   a  is formed to protrude by a predetermined length from the inside of the arm  6  through the receiving portion  109  of the cassette mount  3 . From the substantially intermediate portion to the lower end of the receiving portion  109 , there is formed a slit  124 , along which the lever portion  120   a  can move up and down. 
   A bracket  125  is fixed on the top plate near the upper end of the shaft  118 , and a tension coil spring  126  is interposed on the back side of the shaft  118  over between the stopper  123  and the lever  120  thereby to bias the lever  120  (i.e., the lever portion  120   a ) upward. In order to retain the completely mounted state (or the sewing position) of the needle thread cassette  2 , the frictional resistance to act between the control button  94  and the cam  95  is made higher than the biasing force of the tension coil spring  126 . 
   Here will be described the engaging mechanism  117 . At the right end upper portion of the lever  120 , as shown in  FIG. 4  to  FIG. 8 , there is hinged the actuating pawl  121 . This actuating pawl  121  is constructed to rock over a lock position, in which its lower end portion can engage with the pawl portion  44   a  of the threading slider pawl  44 , and a release position, in which the actuating pawl  121  is released from the engagement with the pawl portion  44   a . Around a hinge pin  127 , however, there is mounted the torsion spring  122  to act between the threading slider actuating member  119  and the actuating pawl  121 , thereby to bias the actuating pawl  121  to the lock position side. 
   The lower end portion of the actuating pawl  121  is constructed to come into and out of abutment against the offset member cam portion  53 . When the threading slider actuating member  119  is pushed down in the lock position, the lower end portion of the actuating pawl  121  abuts against the slope portion  53   a  of the offset member cam portion  53  and moves leftward along the slope portion  53   a . In the state where the right end portion of the upper support portion  49  of the offset member  48  is abutting against the threading positioning member  52  from above, as shown in  FIG. 6 , the actuating pawl  121  is switched to the release position so that the engaging mechanism  117  is released. When the actuating pawl  121  is switched to the release position, the threading slider  40  and the offset member  48  are turned upward from the lower limit position, as shown in  FIG. 6 , by the biasing forces of the compression coil springs  46  and  47 . 
   Here will be described the stopper  123 . On the left end portion of the bracket  125 , as shown in  FIG. 4  to  FIG. 8 , there is longitudinally supported a stopper pin  128 , to which the stopper  123  having a general L-shape, as viewed in a side elevation, is hinged. This stopper  123  is provided with: a vertical portion  129  extending generally vertically downward from the stopper pin  128 ; a horizontal portion  130  extending generally horizontally rightward from the stopper pin  128  to the top position of the needle bar  18 ; and the aforementioned coil spring  126  (as referred to  FIG. 10 ) for biasing those vertical portion  129  and horizontal portion  130  clockwise in  FIG. 8 . At the lower end of the vertical portion  129 , there is formed a slope portion  131 , which is sloped the more leftward as it goes the more downward. 
   At the left end portion in which the slope portion  131  and the vertical portion  129  intersect, there is formed a stopper portion  132  (corresponding to a step portion). This stopper portion  132  can be engaged from above with a stopper engaging portion  119   a , which is formed at the lower end portion of the threading slider actuating member  119 . In case the upper end of the needle bar  18 , i.e., the stopper  123  is within a proper range from  500 A to  500 B (as referred to  FIG. 8 ), the stopper engaging portion  119   a  comes into contact with the slope portion  131  of the stopper  123  when the threading slider actuating member  119  is moved downward from the upper limit position, as shown in  FIG. 5 , by the needle thread cassette  2 . After this, a guide wall  119   b  of the threading slider actuating member  119  slides with respect to the left end of the slope portion  131 . 
   As the threading slider actuating member  119  moves downward, the stopper  123  rocks counterclockwise against the biasing force of the tension coil spring  126  so that the threading sliding actuating member  119  can move from the upper limit position to the lower limit position, as shown in  FIG. 6 . In case the upper end of the needle bar  18  is outside of the proper range, the stopper  123  rocks further clockwise from the position  500 B (as referred to  FIG. 8 ). Even if the threading slider actuating member  119  in this state is moved downward, the stopper engaging portion  119   a  engages with the stopper portion  132 . Therefore, the threading slider actuating member  119  cannot move to inhibit the threading. 
   As shown in  FIG. 7 , the guide wall  119   b  of the threading slider actuating member  119  slides on the slope portion  131  of the stopper  123 . As a result, the height position of the horizontal portion  130  of the stopper  123  is regulated to form a small clearance S between the upper end of the needle bar  18  at the highest position and the horizontal portion  130  thereby to prevent the knocking sound between the needle bar  18  and the stopper  123 . 
   Here will be described the thread tension regulator  9  and the interlocking mechanism  134  for the thread tension regulator  9 . 
   The interlocking mechanism  134  is a mechanism for opening a pair of thread tension discs  133  by the needle thread cassette  2  in the course of the action to mount the needle thread cassette  2  in the cassette mount  3  and for closing the thread tension discs  133  at the time of completing the mounting operation. 
   In the state where the needle thread cassette  2  is mounted in the cassette mount  3 , as shown in  FIG. 4 ,  FIG. 10 ,  FIG. 16  and  FIG. 37  to  FIG. 45 , the thread tension regulator  9  penetrates into the thread tension regulator housing portion  57   c  in the cassette case  57 . The thread tension regulator  9  has a general structure including: the paired thread tension discs  133 ; pin members for supporting those thread tension discs  133 ; an actuating plate  139  located on the back side of the rear thread tension disc  133 ; a spring member for elastically biasing the rear thread tension disc  133  and the actuating plate  139  forward; a thread tension spring  135  for supporting the needle thread  24  elastically near the thread tension discs  133 ; and a thread tension dial  136  for adjusting the spring force. 
   As shown in  FIG. 37  to  FIG. 45 , the interlocking mechanism  134  is provided with a cam portion  137  formed on the rear side face of the needle thread cassette  57 , a cam follower member  138  having a vertical lever shape, and a turning arm  151 . The cam portion  137  like a ridge slightly protruding backward is formed on the upper half of the left end side of the cassette body  60 . At the upper portion of the frame  140  for supporting the thread tension regulator  9 , there is formed a bracket  141 , on which the longitudinal intermediate portion of the cam follower member  138  is turnably supported by a transverse horizontal pin. This cam follower member  138  is biased clockwise in  FIG. 41  by a torsion spring  144 . 
   A roller  142  is freely rotatably hinged to the upper end portion of the cam follower member  138 . 
   At the left side portion of the rear wall of the cassette mount  3 , there is formed a slit  143  (as referred to  FIG. 14 ) for protruding the cam portion  137  of the needle thread cassette  57  backward. The roller  142  can abut against the cam portion  137  which is protruded backward from that slit  143 . The right end portion of the turning arm  151  is so connected to the lower portion of a base plate  155  through a vertical pin as to turn horizontally, and the lower end portion of the cam follower member  138  abuts against the rear face of the left end portion of the turning arm  151 , so that the turning arm  151  can abut at its protrusion  151   a  against the actuating plate  139 . 
   By setting the shape of the cam portion  137  and the position of the roller  142  properly, the thread tension discs  133  are opened in the mounting course of the needle thread cassette  57  thereby to thread the paired thread tension discs  133  and the thread tension spring  135 . After this, the thread tension discs  133  are closed when the needle thread cassette  57  is completely mounted. When the needle thread cassette  57  is mounted in the cassette mount  3  so that the needle thread cassette  2  reaches a predetermined distance above the thread tension regulator  9 , more specifically, the roller  142  rides over the cam portion  137  so that the cam follower member  138  turns counterclockwise in  FIG. 41  thereby to open the thread tension discs  133  with the turning arm  151  and the actuating plate  139 . 
   When the needle thread cassette  57  moves down in this state, the needle thread  24  between the second and third guide portions  71  and  72  is engaged between the paired thread tension discs  133 . After this, the cam portion  137  becomes lower and does not push the roller  142  backward, when the needle thread cassette  57  comes into the completely mounted state. Therefore, the turning arm  151  rotationally returns backward, and the actuating plate  139  returns backward, so that the paired thread tension discs  133  are closed. Here, the aforementioned actions of the interlocking mechanism  134  at the time of mounting the needle thread cassette  57  occur irrespective of the position (e.g., the lower turned position or the upper turned position) of the foot lifting lever  29 . 
   Next, the mechanism for opening the paired thread tension discs  133  by the action of the foot lifting lever  29  as in the ordinary sewing machine is well known in the art so that it will be briefly described. As shown in  FIG. 37  to  FIG. 45 , the upper end portion of the foot lifting lever  29  is turnably hinged to the machine frame, and the upper end portion of an engaging arm  152  engaging with a cam portion  29   a  of that foot lifting lever  29  is also turnably hinged to the machine frame. The engaging arm  152  is connected to the rear end portion of a triangular plate  154  by a connecting rod  153 . The triangular plate  154  is arranged on the lower side of the lower plate portion of the base plate  155  on the machine frame side. The left end portion of the front end portion of the triangular plate  154  is turnably hinged to the lower plate portion of the base plate  155  through a vertical pin, and the right end portion of the front end portion of the triangular plate  154  abuts against the actuating plate  139 . 
   When the foot lifting lever  129  takes its lower turning position, therefore, the connecting rod  153  is not pulled rightward, so that the triangular plate  154  does not turn to keep the thread tension discs  133  in their closed state. When the foot lifting lever  29  is switched to the upper turning position, the connecting rod  153  is pulled rightward, so that the triangular plate  154  turns to bring the thread tension discs  133  into the open state. 
   Here will be described the actions of the aforementioned sewing machine  1  and the actions of the needle thread cassette  2 . 
   In the state where the needle thread cassette  2  is not mounted in the cassette mount  3 , as shown in  FIG. 14  and  FIG. 23  to  FIG. 27 , the openable cover  61  of the needle thread cassette  2  is opened, and the thread bobbin  62  is mounted in the thread bobbin retaining portion  58 . Next, the needle thread  24 , as pulled out from the thread bobbin  62 , is engaged with the first guide portion  69  and with the thread guide portion  80   a  of the first clamp portion  70 , and is pressed by the leaf spring  81 . Next, the needle thread  24  is engaged sequentially with the second and third guide portions  71  and  72  and is clamped between the guide pin  89  of the second clamp portion  73  and the thread retaining plate  90 . 
   Next, the control button  94   a  is pressed with the finger of the operator against the biasing force of the leaf spring member  91  to bring the guide pin  89  apart from the thread retaining plate  90 . After this, the needle thread  24  is pulled out by a predetermined length to the outside, and the control button  94   a  is then released. The needle thread  24  is clamped by the second clamp portion  73 , and the openable cover  61  is closed. In order to make the threading procedures of the needle thread cassette  2  understandable, marks of threading orders may be adhered to the individual vicinities of the first guide portion  69 , the first clamp portion  70 , the second and third guide portions  71  and  72  and the second clamp portion  73  so that the threading may be done according to the mark orders. 
   When the sewing machine  1  is in the sewing interrupted state, on the other hand, the needle bar  18  is normally stopped at its top stop position and the thread guard  26  of the thread take-up lever  25  is stopped at the substantially intermediate position on the thread-tightening side as shown in  FIG. 13 . In this state, the needle thread cassette  2  is mounted from above in the cassette mount  3 . The cassette mount  3  is opened both upward and downward so that the needle thread  24 , as pulled out by about 20 cm from the thread exit  68  of the needle thread cassette  2 , sags vertically downward of the cassette mount  3 . At the time of starting the sewing operation, the thread guard  26  of the thread take-up lever  25  moves up from the substantially intermediate position on the aforementioned thread-tightening side and then moves down. 
   In the course of mounting the needle thread cassette  2 , as shown in  FIG. 15  and.  FIG. 16 , the needle thread cassette  2  is once stopped with its engaging portion  112  abutting against the lever portion  120   a . At this time, the needle thread  24  between the third guide portion  72  and the second clamp portion  73  is introduced into the thread guide clearance  108  and engaged with the thread guard  26  of the thread take-up lever  25 , as shown in  FIG. 15 . In this case, the second clamp portion  73  applies a higher passing resistance than that of the first clamp portion  70  so that the needle thread  24  is fed out by a necessary amount from the thread bobbin  62  without being pulled back into the cassette  2 . Here, a pair of notch marks  146  for confirming the travel stop position are formed on the needle thread cassette  2  and the sewing machine  1 . 
   Next, the needle thread  24  sagging downward from the thread exit  68  of the needle thread cassette  2  is engaged with the needle bar thread hook  147  and the thread guide  36   a  in the recited order and is clamped under a low pressure between the support plate  55  and the thread guide disc  56 . After this, the thread end is cut with the not-shown thread trimming blade. Next, the needle thread cassette  2  is pressed downward against the biasing force of the tension coil spring  126 , as shown in  FIG. 17 . Then, the action of the needle thread cassette  2  is transmitted through the transmission mechanism  115  to the automatic threading mechanism  10  so that the needle thread  24  is threaded into the needle eye  19   a . The engaging portion  112  as the threading action portion of the needle thread cassette  2  moves the lever portion  120   a  at the leading end of the lever  120  downward so that the movement of the needle thread cassette  2  is transmitted to the transmission mechanism  115 . In parallel with this, the needle thread cassette  57  moves downward relative to the thread take-up lever  25  so that the thread passage between the third thread guide portion  72  and the second clamp portion  73  is elongated to feed out the needle thread  24  from the thread bobbin  62 . 
   At this time, the thread tension discs  133  of the thread tension regulator  9  are opened by the interlocking mechanism  134 , as has been described hereinbefore, so that the needle thread  24  between the second and third guide portions  71  and  72  is engaged with the clearance between the thread tension discs  133  and with the thread tension spring  135 . By the first clamp portion  70  and the second clamp portion  73 , the needle thread  24  inbetween is subjected to a constant tension so that it is engaged with the thread take-up lever  25 , the thread tension discs  133  and the thread tension spring  135  without fail. The second clamp portion  73  applies a higher passing resistance than that of the first clamp portion  70  to the needle thread  24  so that the needle thread  24  in an amount necessary for the threading is reliably fed out from the thread bobbin  62 , as described above, without being fed back through the second clamp portion  73  and returned into the cassette  2 . Moreover, the needle thread  24  from the first clamp portion  70  to the second clamp portion  73  does not become slack so that it is neither twisted nor interlaced. 
   In the state where the needle thread cassette  2  is completely mounted in the cassette mount  3  (that is, where the engaging portion  112  engages from above with the receiving portion  109 ), as shown in  FIG. 19  and  FIG. 20 , the thread tension discs  133  are closed by the interlocking mechanism  134 , and the threading slider actuating member  119  is retained at the lowermost position by the needle thread cassette  2 . In this state, the threading pin  31  and the slider guide pin  32  are returned upward to thread the needle eye  19   a  with the needle thread  24 . As shown in  FIG. 20 , moreover, the control button  94   a  is pushed leftward by the thread releasing cam  95 , and the guide pin  89  leaves the thread retaining plate  90  to release the second clamp portion  73 , so that the needle thread  24  is released to be in a sewing state. 
   In the state where the needle thread cassette  57  is completely mounted, moreover, the paired thread tension discs  133  may be closed, and the second clamp portion  73  may be released. Even in this case, the needle thread  24  is clamped by the first clamp portion  70  to apply the passing resistance to the needle thread  24 , so that the needle thread  24  in the needle thread cassette  57  is neither twisted nor interlaced. As a result, the thread is hardly cut during the sewing operation by the interlace. With the needle thread cassette  2  being mounted in the cassette mount  3 , the thread guide  106 A and the thread guard  26  of the thread take-up lever  25  protrude into the needle thread cassette  57  so that the thread guard  26  of the thread take-up lever  25  can reciprocate generally vertically in the needle thread cassette  2 . 
   Here in the thread tension regulator housing portion  57   c  of the cassette body  60 , as shown in  FIG. 19 , an needle thread pressing member  180  (as indicated by a dotted line) including a thread guide portion notched downward may be disposed downstream of the thread tension regulator thereby to press and arrange the needle thread  24  extending downstream of the thread tension regulator  9 , downward by the action of mounting the needle thread cassette  2  in the cassette mount  3 . In this case, the portion of the needle thread  24  to contact with the pin member of the thread tension regulator  9  is increased to prevent the needle thread  24  from being suddenly disengaged and to increase the take-up amount of the needle thread  24  by the thread tension spring  135 . When the needle thread cassette  2  is to be removed, the needle thread  24  can be easily released from the needle thread pressing member  180 . 
   With the needle thread cassette  57  being mounted in the cassette mount  3 , as has been described hereinbefore, the sewing operation can be performed while feeding the needle thread  24  to the thread bobbin  62 . When the needle thread cassette  2  is demounted from the cassette mount  3  so as to change the color of the needle thread  24  or to supply the needle thread  24 , the needle thread cassette  2  can be simply removed by pushing its lower end upward with the finger of the operator. 
   After this removal, the slack thread disengaged from the thread take-up lever  25  and the thread tension regulator  9  is left in the needle thread cassette  2 . Therefore, the control button  94   a  is pressed with the finger to switch the second clamp portion  73  into the release state, and the slack thread in the needle thread cassette  2  is pulled out in that state and is wound on the outer circumference of the cassette. The end portion of the needle thread  24  is temporarily held on the thread holder  104  or the thread holder  104 A. After this, the control button  94  is returned to bring the second clamp portion  73  into the closed state. 
   As shown in  FIG. 46  and  FIG. 47 , the aforementioned openings  77  and  78  also act as the introducing openings  77  and  78  for introducing the needle thread extending from the thread bobbin  62 A outside of the needle thread cassette  2 , into the first guide portion  69 . In the case of sewing using the needle thread  24  outside of the needle thread cassette  2  with the thread bobbin  62  in the needle thread cassette  2  being removed, the needle thread  24  extending from the thread bobbin  62 A can be guided from the introducing openings  77  and  78  into the first guide portion  69  and further through the thread passage  59  into the thread exit  68 . In case two needles  19 A are applied as the needle, as shown in  FIG. 48 , the needle thread  24  of the thread bobbin  62  inside the needle thread cassette  2  and the needle thread  24  of the thread bobbin  62 A outside are introduced along the thread passage  59  into the thread exit  68  so that the two needle threads  24  can be fed to the two needles  19 A. 
   The sewing machine  1  and the needle thread cassette  2  according to the embodiment have the following effects. 
   1) The thread bobbin  62  is housed in the needle thread cassette  2 , and the thread bobbin  62  can be exchanged by exchanging the needle thread cassette  2  so that the needle thread  24  can be easily exchanged. Especially in association with the mounting action of the needle thread cassette  2 , the thread guard  26  of the thread take-up lever  25 , the thread tension discs  133  of the thread tension regulator  9  and the thread tension spring  135  are automatically threaded so that the threading operation is remarkably simplified and can be efficiently performed. In association with the action of mounting the needle thread cassette  2 , the automatic threading mechanism  10  is actuated to thread the needle eye  29   a  automatically so that the threading itself can be remarkably simplified to be able to exchange the needle thread  24  quickly and efficiently. 
   Especially in the state where the sewing operation is interrupted to stop the needle bar  18  at the needle top position and the thread guard  26  of the thread take-up lever  25  at the position of the thread tightening side, without changing the position of the thread take-up lever  25 , the needle thread cassette  2  can be mounted, and the thread guard  26  of the thread take-up lever  25  and the thread tension regulator  9  can be threaded to make the mounting of the needle thread cassette  2  and the threading operation remarkably simple and efficient. Moreover, the needle thread cassette  2  can be mounted in the cassette mount  3  by moving it linearly from above and can be removed by moving the mounted needle thread cassette  2  linearly upward. Therefore, the mounting/demounting operations of the needle thread cassette  2  are so simple that the needle thread cassette  2  can be quickly exchanged. 
   Moreover, the cassette case  57  of the needle thread cassette  2  is transparent so that the thread color of the internal thread bobbin  62  can be easily discriminated. It is, therefore, convenient to exchange the needle thread  24  or the needle thread cassette  2 . The recess  65  is formed in the support wall  63  for supporting the thread bobbin  62  in the needle thread cassette  2  so that the thread bobbin  62  can be simply removed from the thread bobbin retaining portion  58  by catching the recess  65  and pushing the lower end of the thread bobbin  62  with the finger of the operator in the recess  65 . 
   2) The thread bobbin  62  is retained in the needle thread cassette  2  with its axis being vertical, and the needle thread  24  is fed out upward from the thread bobbin  62  and is guided through the thread passage  59  into the thread exit  68 , so that the needle thread cassette  2  can be reduced in the transverse width. Alternatively, the axis of the thread bobbin  62  and the feed-out direction of the needle thread  24  from the thread bobbin  62  are generally parallel to the reciprocating direction of the thread guard  26  of the thread take-up lever  25  thereby to mount the needle thread cassette  2  in the cassette mount  3 . Therefore, it is possible to reduce the transverse width of the needle thread cassette  2  and the transverse width of the cassette mount  3 . 
   Thus, the needle thread cassette  2  is small-sized elongated box shape having a small transverse width so that the cassette mount  3  can be arranged in the reciprocal travel region and its left side portion of the thread guard  26  of the thread take-up lever  25 , that is, in the arm head. As a result, the cassette mount  3  can be formed in a region overlapping the reciprocal travel region of the thread guard  26  of the thread take-up lever  25  so that it is advantageous in space. Moreover, the cassette mount  3  can be arranged as backward as possible without any interference with the internal mechanism of the arm  6 . As a result, the needle thread cassette  2  does not protrude, when mounted, from the front face of the arm  6 , and the appearance of the arm  6  is not deteriorated while retaining the degree of freedom for the design of the front face of the arm  6 . 
   3) The first clamp portion  70  for applying the passing resistance always to the needle thread  24  is disposed upstream of the thread passage  59  in the needle thread cassette  2 , and the needle thread  24  between the first clamp portion  70  and the thread tension regulator  9  is kept tense with the needle thread cassette  24  being mounted. Therefore, it is possible to prevent the thread from being twisted or interlaced and to prevent the thread from being broken or frayed due to the interlace during the sewing operation. 
   Moreover, the second clamp portion  73  is disposed near the thread exit  68  to apply the passing resistance to the needle thread  24  before the needle thread cassette  2  is mounted or completely mounted. The second clamp portion  73  applies a higher passing resistance than that of the first clamp portion  70  so that the needle thread  24  is not accidentally fed out while the needle thread cassette  2  being handled. When the thread guard  26  of the thread take-up lever  25  and the thread tension regulator  9  are threaded at the time of mounting the needle thread cassette  2 , moreover, the needle thread can be fed out without fail from the thread bobbin  62 . 
   With the needle thread cassette  2  being not mounted, moreover, the control button  94   a  is operated with the finger of the operator so that the second clamp portion  73  can be released to feed out the needle thread  24  freely. 
   After the needle thread cassette  2  was completely mounted, the control button  94   a  is pressed by the needle thread releasing cam  95  to switch the second clamp portion  73  into the released state. During the sewing operation, therefore, the passing resistance of the second clamp portion  73  does not act on the needle thread  24  to smoothen the feed-out of the needle thread  24 . 
   When the needle thread cassette  2  is demounted from the cassette mount  3 , the needle thread  24  extending to the outside of the cassette case  57  can be wound on the outer face of the cassette case  57  and can be remarkably conveniently held on the thread holder  104  or  104 A. Therefore, it is very convenient. 
   4) On the top of the needle thread cassette  2 , there are disposed the first guide portion  69 , the longitudinally long openings  77  and  78  and the thread guide portion of the guide pin  75  confronting them in parallel. Therefore, the needle thread  24  can be freely moved along the guide pin  75  and can be smoothly fed out from the thread bobbin  62  without any resistance in a manner to draw an arc. In addition, the needle thread from the thread bobbin arranged outside of the needle thread cassette  2  can be introduced from the openings  77  and  78  into the needle thread cassette  2  and can be guided for the sewing operation from the inside thread passage  59  to the thread exit  68 . When the needle  19  is replaced by two needles for the sewing operation with two needle threads, therefore, the needle threads can be fed for the sewing operations from the thread bobbin  62  in the needle thread cassette  2  and from the thread bobbin retained in the thread bobbin retaining portion at the top of the arm  6  outside of the needle thread cassette  2 . 
   5) There is provided the interlocking mechanism  134  for releasing the thread tension regulator  9  in association with the mounting action of the needle thread cassette  2  and for closing the thread tension discs  133  after the needle thread cassette  2  was mounted. Therefore, the thread tension regulator  9  can be threaded in association with the action of mounting the needle thread cassette  2 , as described hereinbefore. Here, the thread tension regulator  9  is arranged on the lower end side of the cassette mount  3 . Therefore, it is especially advantageous to thread the thread tension regulator  9  in association with the mounting action to mount the needle thread cassette  2  from above in the cassette mount  3 . 
   6) The thread take-up lever mechanism  8  has such an especial structure as to thread the thread guard  26  in association with the action of mounting the needle thread cassette  2 . Specifically, the thread guide  106 A is provided for forming the curved thread guide clearance  108  extending throughout the length of the moving locus of the thread guard  26  of the thread take-up lever  25 , so that the needle thread  24  can be introduced from the inlet port  108   a  at the upper end of the thread guide clearance  108  and can be engaged with the thread guard  26 . Therefore, the thread inlet  108   a  is so positioned as not to retract from the moving locus of the thread guard  26 . With the thread guard  26  of the thread take-up lever  25  being stopped in the position (corresponding to the needle top stop position of the needle bar  18 ) on the aforementioned thread tightening side, therefore, the thread guard  26  can be threaded in association with the action to mount the needle thread cassette  2  in the cassette mount  3 . 
   Moreover, the thread guide clearance  108  extends throughout the length of the moving locus of the thread guard  26 , and the paired thread guide members  106  composing the thread guide  106 A are made so slidable relative to the U-shaped guide portion  25   a  of the thread take-up lever  25 . Even if the thread take-up lever  25  is vertically reciprocated at the time of sewing, therefore, the needle thread  24  is so guided by the thread guide members  106  that it does not come out of the thread guard  26 . 
   Moreover, the thread guide member  106  on the back side is turnably hinged at its upper end portion so that the U-shaped guide portion  25   a  of the thread take-up lever  25  can be guided by the paired thread guide members  106 . Therefore, the paired thread guide members  106  can be made of such a material of a wire member at a low cost as can be easily worked, and little sliding resistance acts on between the U-shaped guide portion  25   a  and the paired thread guide members  106  thereby to cause little sliding sound. 
   7) In the aforementioned automatic threading mechanism  10 , the automatic passing of a thread through the needle eye  19   a  in association with the operation to mount the needle thread cassette  2  can be effected only in case the needle bar  18  is within a predetermined height range at the needle top position, that is, only in case the stopper  123  is within the proper range from  500 A to  500 B of  FIG. 8 . This makes no fear of causing a passing error of the thread into the needle eye  19   a , as might otherwise be caused by mounting the needle thread cassette  2  with the needle bar  18  being at an improper position, so that the operations are excellent in reliability and controllability. Considering that the needle bar  18  may be stopped at an erroneous top position, moreover, the threading slider  40  and the threading positioning member  52  disposed in the needle bar  18  are engaged to adjust the height position of the automatic threading mechanism  10  to the needle bar  18 . Therefore, the thread can be reliably passed through needle eye  19   a.    
   Here will be described a modified mode, in which the foregoing embodiment is partially modified. 
     FIG. 49  shows the control system of the aforementioned sewing machine  1  schematically. To a control unit, there are inputted signals from a needle top/bottom detecting sensor, a spindle phase angle detecting sensor, and other not-shown sensors and switches. The control unit includes a computer for controlling on the basis of various control programs for controlling the sewing machine, and a plurality of drive circuits for a plurality of devices to be driver. This control unit controls the drives of a sewing machine motor, a needle up/down stepping motor, a cloth feeding stepping motor and so on. In order to allow the mounting of the needle thread cassette  2  on the cassette mount  3  only in case the aforementioned needle bar  18  is at the top position but to inhibit the mounting in case the needle bar  18  is at a position other than the top position, a stopper capable of going into and out of the cassette mount  3  is disposed near the upper end of the cassette mount  3 , and an electric actuator such as a solenoid actuator is provided for driving the stopper to go. On the basis of the signal detected by the needle top/bottom detecting sensor, the electric actuator is driven and controlled by the control unit. Only in case the needle bar  18  is at its top position, the mounting of the needle thread cassette  2  is allowed by retaining the stopper at a retracted position. In case the needle bar  18  is at a position other than the top position, the stopper is switched to an advanced position to inhibit the mounting of the needle thread cassette  2 . 
   Next, another embodiment of the invention will be described with reference to the accompanying drawings. 
   However, the same members as those of the foregoing embodiment will be suitably omitted in description by designating them by the common reference numerals. 
   In an electronic control type sewing machine  1 A according to another embodiment, as shown in  FIG. 50  to  FIG. 52 , a controller mount  200  is formed in the thread take-up lever travel region, in which the thread guard  26  of the thread take-up lever  25  reciprocally travels up and down, and in the front face near the region. There are provided a thread engaging controller  201  as the movable controller to be removably mounted in that controller mount  200 , a thread tension regulator  9 , a resistance applicator  205 , and an interlocking mechanism  202  (as referred to  FIG. 58 ) for opening/closing the thread tension discs  133  of the thread tension regulator  9  and the resistance applicator  205  in association with the mounting action of the thread engaging controller  201 . 
   The thread passage will be described at first. As shown in  FIG. 50  to  FIG. 52 , the needle thread  24  extending from a thread bobbin  62 A retained horizontally at the top of the root end side of the arm  6  is guided sequentially through a transverse thread guide groove  203  formed in the upper face side of the arm  6 , the controller mount  200  and a vertical thread guide groove  204  formed in the front face on the leading end of the arm  6  and is engaged with the needle bar thread hook  147 , the thread guide  36   a  and the thread guide disc  56 . The resistance applicator  205  and the thread tension regulator  9  are arranged sequentially from the upstream of the thread guide groove  203 . The thread guard  26  of the thread take-up lever  25  is so arranged at the central portion of the controller mount  200  as to reciprocate up and down. Here is also provided a thread tension dial  206  for adjusting the spring force of the thread tension regulator  9 . 
   Here will be described the thread engaging controller  201 . 
   As shown in  FIG. 50 ,  FIG. 51 ,  FIG. 54 ,  FIG. 55  and  FIG. 57  to  FIG. 59 , the thread engaging controller  201  is formed into a general box shape elongated in the vertical direction and can travel at least within a predetermined range with respect to the controller mount  200 . The thread engaging controller  201  is provided with a front wall  201   c  leading from the upper end to above the lower end, a left side wall  201   a  and a right side wall  201   b . At the rear end of the left side wall  201   a , there is formed a guided portion  208 , which is folded leftward. This guided portion  208  is vertically movably guided by a slit  200   a  of the controller mount  200 . At the rear end of a right side wall  201   b , there is formed a guided portion  208   b , which is folded rightward. This guided portion  208   b  is vertically movably guided by the guide groove  200   b  of the controller mount  200 . The front wall  201   c  of the thread engaging controller  201  is vertically movably guided by a guide wall  200   c  on the front side of the controller mount  200 . 
   The lower end faces of the left side wall  201   a  and the right side wall  201   b  are formed horizontal, and the lower end portion of the right side wall  201   b  provides a needle thread control portion for controlling the needle thread  24  extending from the thread tension regulator  9  to the thread take-up lever  25  to engage with the thread guard  26  when the thread engaging controller  201  is to be inserted and mounted in the controller mount  200 . 
   A small forward protrusion  209  is formed at the upper end portion of the thread engaging controller  201  which is disengagiable from the controller mount  200  by catching the protrusion by a finger so as to move the thread engaging controller  201  upward. 
   At the lower end portion of the guided portion  208 , as shown in  FIG. 50 ,  FIG. 53  to  FIG. 55  and  FIG. 62 , there is formed an actuation portion  208   a , which acts as a threading actuation portion to actuate the automatic threading mechanism  10  when the needle thread  24  is passed into the needle eye  19   a . In the threading slider actuating mechanism  116 , there is formed in the lever  120  a lever portion  120   b , which protrudes forward in an L-shape from the upper step portion of the right end. The automatic threading mechanism  10  like that of the foregoing embodiment is actuated by pushing the lever portion  120   b  from above in the course of the mounting operation of the thread engaging controller  201 . 
   On the wall face of the controller mount  200 , there is fastened with screws a leaf spring  210  for retaining the thread engaging controller  201  removed from the controller mount  200  at the upper most position shown in  FIG. 54 . Here, the thread engaging controller  201  can also be made removable from the controller mount  200 . In this modification, the thread can be easily engaged with the thread guard  26  of the thread take-up lever  25 . The controller mount  200  is so formed in the vicinity of the front face of the arm  6  and in the vicinity of the thread take-up lever travel region as to mount the thread engaging controller  201  by the vertical and linear travel so that it can insert and mount the thread engaging controller  201  smoothly. 
   Here will be described the interlocking mechanism  202  for associating the mounting actions of the thread engaging controller  201  with the thread tension regulator  9 . As shown in  FIG. 53  to  FIG. 62 , the interlocking mechanism  202  includes a cam portion  211 , a cam follower member  212  and an actuation plate  213 . In the course of mounting action to mount the thread engaging controller  201  in the controller mount  200 , the thread tension discs  133  of the thread tension regulator  9  and the resistance applicator  205  are opened by the thread engaging controller  201 . At the completion of the mounting action, the thread tension discs  133  and the resistance applicator  205  are closed. As shown in  FIG. 54 , more specifically, the cam portion  211  is vertically formed in the right lower half of the thread engaging controller  201  and is provided with a slope portion  211   a , a flat portion  211   b , a slope portion  211   c  and a flat portion  211   d  sequentially from below. 
   On a support pin  214  hinged to the sewing machine frame, there is turnably supported the lower end portion of the cam follower member  212 . This cam follower member  212  includes two lever portions  215  and  216 , a connection portion  217  connecting those lever portions  215  and  216  integrally at their lower end portions, and a cam follower pin  218 . The two lever portions  215  and  216  are so arranged in parallel at a suitable spacing as to take a phase angle of about 15 degrees, as viewed in a side elevation. The lever portion  215  is provided at its end, i.e., at its upper end portion with the cam follower pin  218 , which protrudes leftward to abut against the cam portion  211 . 
   As shown in  FIG. 54  and  FIG. 58 , the thread tension regulator  9  is provided with the actuation plate  213 , which is pushed and driven by the upper end portion of the lever portion  216  (i.e., the other end portion of the cam follower member) so that the thread tension discs  133  are opened by the pushing drive of the actuation plate  213 . Around the support pin  214 , there is mounted a torsion spring  219 , which biases the cam follower member  212  counterclockwise in  FIG. 58 . 
   The resistance applicator  205  applies a proper passing resistance to the needle thread  24  on the upstream side of the thread tension regulator  9  thereby to prevent the needle thread  24  from being twisted or interlaced. The upper end portion of the aforementioned lever portion  216  is folded rightward at a right angle to form a horizontal plate portion  220 . This horizontal plate portion  220  pushes and drives a holding plate  205   a  of the resistance applicator  205  to open the holding plate  205   a  synchronously as the actuation plate  213  opens the thread tension discs  133  (as referred to  FIG. 60  and  FIG. 61 ). While the horizontal plate portion  220  is inactive, the holding plate  205   a  is retained in the closed state by the biasing force of a resistance applying spring  205   b.    
   The actions of the sewing machine  1 A thus far described will be explained in the following. 
   As shown in  FIG. 50  to  FIG. 52 , the needle thread  24 , as fed out from the thread bobbin  62 A, is passed into the thread guide groove  203  by the operator. In the state where the thread engaging controller  201  is moved to the upper most position, the needle thread  24  is engaged with the thread guard  26  of the thread take-up lever  25  and is pulled out through the thread guide groove  204  to the vicinity of the needle  19  and engaged with the needle bar thread hook  147 , the thread guide  36   a  and the thread guide disc  56  (as referred to  FIG. 5 ). Next, the tread end is cut to a predetermined length, and the thread engaging controller  201  is linearly pushed into the controller mount  200  so that it is inserted and mounted in the controller mount  200 . 
   In accordance with this mounting action, the cam follower pin  218  abuts at first against the slope portion  211   a  of the cam portion  211  so that the thread tension discs  133  and the holding plate  205   a  are opened to catch the needle thread  24 . Concurrently with this, the needle thread  24  is further engaged with the thread tension spring  135  so that its portion between the thread tension regulator  9  and the thread guard  26  of the thread take-up lever  25  is pushed downward to elongate the thread passages on the two sides of the thread take-up lever  25  by the needle thread control portion at the lower end portion of the right side wall  201   b  of the thread engaging controller, thereby to retain the thread take-up amount of the thread take-up lever  25 . 
   After this, the flat portion  211   b  and the slope portion  211   c  come to abut to the pin  218  and then the flat portion  211   d  comes into abutment against the pin  218  substantially in the completely mounted state, as shown in  FIG. 62  and  FIG. 63 , so that the thread tension regulator  9  and the holding plate  205   a  are closed. In the course of the inserting and mounting the thread engaging controller  201  in the controller mount  200 , on the other hand, the action of the thread engaging controller  201  is transmitted through the transmission mechanism  115  to the automatic threading mechanism  10  substantially like the foregoing embodiment, by which the thread passing into the needle eye  10   a  is executed to make the state ready for the sewing operation. At this time, the actuation portion  208   a  pushes the lever portion  120   b  downward so that the mounting action of the thread engaging controller  201  is transmitted to the transmission mechanism  115 . 
   The sewing machine  1 A and the thread engaging controller  201  thus far described have the following effects. 
   1) The thread engaging controller  201  elongated in the vertical direction is adopted in place of the aforementioned needle thread cassette  2  so that the thread engaging controller  201  and the controller mount  200  can be small-sized to reduce the affection on the appearance of the front face portion of the arm  6 . 
   2) The interlocking mechanism  202  enables the thread engaging controller  201 , in the course of the mounting action to mount the thread engaging controller  201  in the controller mount  200 , to open the thread tension discs  133  of the thread tension regulator  9  and the holding plate  205   a  of the resistance applicator  205  in association with the mounting action so that the needle thread  24  can be engaged with the thread tension regulator  9  and the resistance applicator  205  in the open state. When the thread engaging controller  201  is completely mounted, moreover, the thread tension regulator  9  and the resistance applicator  205  can be closed. Concurrent with this threading action, the threading can also be automated in association with the mounting action to mount the thread engaging controller  201  in the controller mount  200 . 
   Thus, in association with the operation for mounting the thread engaging controller  201 , the needle thread  24  can be engaged with the thread tension regulator  9  and the resistance applicator  205  and can be automatically threaded. Therefore, the thread engaging operation and the thread passing operation at the time of supplying and exchanging the needle thread  24  can be simplified to enhance the operating efficiency. 
   3) The interlocking mechanism  202  includes: the cam portion  211  formed on the thread engaging controller  201 ; the cam follower member  212  supported to abut at its one end against the cam portion  211  and to freely turn at its longitudinal intermediate portion; and the actuation plate  213  pushed and driven by the other end portion of the cam follower member  212  to open the thread tension regulator  9 . Therefore, an inexpensive thread tension regulator  9  having a general construction can be adopted as the thread tension regulator  9 . 
   Here, the aforementioned thread engaging controller  201  is not directly connected to the arm  6  of the sewing machine  1 A but can be removed from the arm  6 . However, the thread engaging controller  201  can be connected to the arm  6  through a parallel link, another link mechanism or a rocking link member. 
   INDUSTRIAL APPLICABILITY 
   According to the present invention, the handling of the needle thread such as the engagement of the thread with the thread take-up lever or the thread tension regulator can be simplified to enhance the operating efficiency.