JP2005058359A - Sewing machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically solve displacement of a needle bar by thermal expansion of a sewing machine frame in a simple constitution in a sewing machine having a needle swinging mechanism and the sewing machine frame formed of synthetic resin. <P>SOLUTION: This sewing machine is so formed that a transmission mechanism 40 transmitting the swinging drive of a cam lift detecting body 30 by a needle swinging cam 28 to a needle bar supporting body 32 is provided with a first transmission body 41 formed with a long hole 45 in the right end, a second transmission body 42 and a connecting screw 43. The right end of the second transmission body 42 is connected to the cam lift detecting body 30 by the connecting screw 43 slidably inserted in the long hole 45 so that, when the second transmission body 42 is expanded or contracted by the heat, the connecting screw 43 relatively moves to the first transmission body 41 along with the upper end part of the cam lift detecting body 30 to prevent the displacement of the needle bar 10 by the thermal expansion of the sewing machine frame 5. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a sewing machine, and more particularly to a sewing machine having a needle swing mechanism.

  Conventionally, various sewing machines having a needle swing mechanism capable of zigzag sewing have been proposed. For example, a sewing machine 1A shown in FIG. 6 includes a synthetic resin sewing machine frame 5 (hereinafter referred to as a frame), a needle swing mechanism 7A, and the like. The needle swing mechanism 7A includes a needle swing cam 28, a cam lift detector 30 for detecting the cam lift of the needle swing cam 28, a left end connected to the needle bar support 32 by a connecting pin 32a, and a right end to the cam lift detector 30. It has a metallic transmission body 50 connected by a connection pin 44, a needle bar support body 32 that supports the needle bar 10 so as to be slidable. The cam lift detection body 30 is rotatably supported by the frame 5 via a cam lift detection body shaft 29. The needle bar support 32 is rotatably supported by the frame 5 via a needle bar support shaft 31.

  In the needle swinging mechanism 7A, when the needle swinging cam 28 is rotated by the rotational driving force of the sewing machine motor 14, the cam lift detecting body 30 detects the cam lift of the convex portion 27 formed on the needle swinging cam 28 and the cam lift detecting body. The shaft 29 is driven to swing around the axis. This swinging drive is transmitted to the needle bar support 32 by the transmission body 50, and the needle bar support 32 is driven to swing together with the needle bar 10 around the needle bar support shaft 31.

  However, in recent years, the rigidity of the synthetic resin member has improved, and if the frame 5 is made of synthetic resin and the transmission body 50 is made of metal, like the sewing machine 1A, the thermal expansion coefficient of the synthetic resin becomes the thermal expansion coefficient of the metal. Since it is 10 times or more, a problem arises due to this difference in thermal expansion coefficient. Hereinafter, the effect of the coefficient of thermal expansion will be specifically described with reference to the case where the sewing machine 1A is used at a high temperature. 6, both the horizontal distance A ′ between the cam lift detection body 30 and the needle bar support shaft 31 and the length C ′ of the transmission body 50 are L.

  From the normal temperature state shown in FIG. 6 to the high temperature state as shown in FIG. 7, the frame 5 made of synthetic resin having a high coefficient of thermal expansion expands greatly, so the distance A ′ is (L + a ′). become. On the other hand, since the transmission body 50 made of a metal having a small coefficient of thermal expansion hardly expands, the length C ′ is maintained at L. Then, as shown in FIG. 7, the connecting pin 32 a that connects the transmission body 50 and the needle bar support 32 moves relative to the needle bar support shaft 31 by a ′ to the right. Furthermore, the tip of the sewing needle 11 provided at the lower end of the needle bar 10 moves to the right about 1.5 to 2 times to the right of a '. If zigzag sewing is performed in this state, the needle plate 13 The sewing needle 11 comes into contact with the needle.

  Therefore, it is conceivable to solve the above-mentioned problem by configuring the transmission body 50 with the same synthetic resin as that of the frame 5. However, since various components such as the needle bar 10 and the needle bar support 32 are provided in the vicinity of the left end portion of the transmission body 50, the transmission body is prevented in order to prevent interference between the configuration members and the transmission body 50. 50 must be bent. When the transmission body 50 is bent as described above, the transmission body 50 is urged by the urging spring 33 via the needle bar support 32, so that the bent portion is gradually deformed into a linear state due to creep characteristics. As a result, there arises a problem that the position of the needle bar support 32 is shifted from a predetermined position. Therefore, it is impossible to put the sewing machine 1A in which the transmission body 50 is made of synthetic resin into practical use.

Therefore, various sewing machines capable of adjusting the position of the needle bar are provided. For example, in Patent Document 1, a pattern cam having a plurality of teeth formed on the outer periphery of the needle bar, a cam follower that engages with the pattern cam, and a swing drive of the cam follower. A sewing machine including an engagement roller provided at the right end of the bar linkage and a swinging body that transmits via an engagement element and a needle bar linkage for transmitting the swing drive to the needle bar is described. Has been. In this sewing machine, when the pattern cam is driven to rotate, the cam follower engaged with the pattern cam is driven to swing by the teeth of the pattern cam. This swing drive is transmitted to the needle bar via the swing member and the needle bar linkage, whereby the needle bar is swung to form a zigzag stitch.
In this sewing machine, the user moves the engaging element provided at the right end of the needle bar linkage in the left-right direction via the switching unit, thereby adjusting the swing center of the needle bar, and the zigzag sewing center line. It is configured to be able to adjust.
Japanese Patent Publication No. 60-25147 (page 2-3, Fig. 2)

  However, in the sewing machine of Patent Document 1, since the user manually adjusts the position of the needle bar, the user must adjust the position of the needle bar every time it is used in an environment with different temperatures. Need time. Adjustment errors may occur because the user manually adjusts. In particular, it is difficult for a sewing machine capable of zigzag sewing to recognize from the outside of the sewing machine whether the position of the sewing needle is adjusted to the left or right or the center position when adjusting. Therefore, it is very difficult to adjust the position of the sewing needle only by visual recognition from the outside. In addition, since this sewing machine requires a complicated configuration to adjust the position of the switching unit, the structure of the sewing machine becomes very complicated.

  SUMMARY OF THE INVENTION An object of the present invention is a sewing machine having a needle swing mechanism and having a sewing machine frame made of a synthetic resin, and can easily eliminate a positional deviation of a needle bar due to expansion of the sewing machine frame due to heat with a simple configuration. To provide a sewing machine.

  The sewing machine according to claim 1 is a sewing machine provided with a needle swinging mechanism for swinging a needle bar, wherein the needle swinging mechanism is rotatably supported by a synthetic resin sewing machine frame via a needle bar support shaft. A needle bar support, a needle swing cam for swinging the needle bar, and a cam lift detection body that is rotatably supported by the sewing machine frame via a cam lift detection body shaft and detects the cam lift of the needle swing cam And transmission means for transmitting the swing of the cam lift detection body to the needle bar support, the transmission means being provided between the cam lift detection body and the needle bar support, and having one end A metallic first transmission body connected to the needle bar support, and extends toward the cam lift detection body along the first transmission body, and one end is located at a position closer to the needle bar support than the center of the first transmission body. Connected, the other end connected to the cam lift detector A second transmission body made of synthetic resin, a connecting member for connecting the second transmission body and the cam lift detection body, and formed at the other end of the first transmission body, in the longitudinal direction of the first transmission body A long long hole provided with a long hole through which the connecting member is slidably penetrated.

According to this sewing machine, when the cam lift of the needle swing cam is detected by the cam lift detecting body, the cam lift detecting body is driven to swing around the cam lift detecting body shaft, and the swing drive is applied to the needle bar support by the transmission means. The needle bar support shaft is swung around the needle bar support shaft.
When the synthetic resin sewing machine frame is expanded or contracted by heat, the second synthetic resin transmission body is also expanded or contracted. Since one end of the second transmission body is connected to the position closer to the needle bar support than the center of the first transmission body, the connecting member that connects the second transmission body and the cam lift detection body is a long hole in the first transmission body. The other end of the second transmission body is moved relative to the first transmission body. Accordingly, the distance between the connecting member and the connecting portion between the needle bar support at one end of the first transmission body is automatically adjusted in response to the expansion of the sewing machine frame, and the needle due to the expansion or contraction of the sewing machine frame. The displacement of the rod can be eliminated.

  According to a second aspect of the present invention, the second transmission body is made of a synthetic resin having a higher thermal expansion coefficient than that of the synthetic resin constituting the sewing machine frame. According to this sewing machine, the second transmission body, which is shorter than the distance between the needle bar support body shaft and the cam lift detection body shaft, is made of a synthetic resin having a higher coefficient of thermal expansion than the synthetic resin constituting the sewing machine frame. The expansion amount of the distance between the needle bar support body shaft and the cam lift detection body shaft is substantially equal to the expansion amount of the second transmission body.

  According to the first aspect of the present invention, the other end of the second transmission body moves relative to the first transmission body as the synthetic resin sewing machine frame expands or contracts due to heat, and one end of the first transmission body Since the distance from the cam lift detecting body to which the other end of the second transmission body is connected changes in accordance with the expansion and contraction of the sewing machine frame, the needle bar support body shaft and the cam lift detecting body axis due to the expansion and contraction of the sewing machine frame This change in distance can be automatically eliminated by the above-mentioned relative movement without the user performing complicated adjustments, and the needle bar can always be held at a predetermined position. Also, a simple configuration is provided in which a second transmission body is provided, a long hole is formed in the first transmission body, and a long hole is provided to slidably support a connecting member that connects the second transmission body and the cam lift detection body. As a result, the above-described effects can be achieved, so that the configuration of the sewing machine can be simplified.

  According to the invention of claim 2, the expansion amount of the second transmission body and the expansion amount of the distance of the sewing machine frame between the cam lift detection body shaft and the needle bar support body shaft can be made substantially equal, and more precisely zigzag. Sewing such as sewing can be performed. In addition, the same effects as those of the first aspect can be obtained.

  A book that provides a sewing machine that has a needle swinging mechanism and that has a simple structure and can automatically eliminate misalignment of the needle bar due to expansion of the sewing machine frame due to heat in a sewing machine that is made of synthetic resin. It is an object of the present invention to provide a needle bar support that is rotatably supported by a synthetic resin sewing machine frame via a needle bar support shaft, and a needle swing for swinging the needle bar. A cam, a cam lift detecting body that is rotatably supported by the sewing machine frame via a cam lift detecting body shaft, and detects the cam lift of the needle swing cam; and the swing of the cam lift detecting body is transmitted to the needle bar support. A first transmission body made of metal provided between the cam lift detection body and the needle bar support, and having one end connected to the needle bar support; The first transmission body A second transmission body made of a synthetic resin having one end connected to a position closer to the needle bar support body than the center of the first transmission body and the other end connected to the cam lift detection body. A connection member for connecting the second transmission body and the cam lift detection body; and a long hole formed in the other end of the first transmission body and extending in the longitudinal direction of the first transmission body, the connection member This is realized by providing a long hole that is slidably penetrated.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, the top, bottom, left, and right in FIG. In this embodiment, the present invention is applied to a zigzag sewing machine in which a sewing machine frame is integrally formed of a synthetic resin (for example, ABS).

  As shown in FIG. 1, a zigzag sewing machine 1 includes a bed portion 2, a leg column portion 3 erected on the right end portion of the bed portion 2, and the bed portion 2 facing the upper end portion of the leg column portion 3. And an arm portion 4 extending leftward. The bed portion 2, the pedestal column portion 3, and the arm portion 4 are integrally configured by a synthetic resin-made sewing machine frame 5 (hereinafter referred to as a frame 5). Further, the frame 5 is provided with a sewing mechanism 6 and a needle swinging mechanism 7 for swinging the needle bar 10 in the left-right direction. Although not shown, the frame 5 is integrally formed with a reinforcing plate for reinforcement, a rib for connecting the reinforcing plate and the outer periphery of the frame 5, and the like.

The sewing mechanism 6 includes a needle bar 10, a sewing needle 11 that is connected to the lower end of the needle bar 10 and passes through an upper thread supply source such as a thread spool through a thread tensioner, and the needle bar 10. Needle bar up / down drive mechanism 12 to be driven up and down, a balance mechanism (not shown), and a thread loop catcher (not shown) provided below the needle plate 13 provided on the upper surface of the bed 2 below the sewing needle 11. And a lower thread bobbin (not shown) accommodated in the thread catcher.
The needle bar up / down drive mechanism 12 includes a sewing machine motor 14, a belt 15, an output shaft 14a of the sewing machine motor 14 and a belt pulley 16 connected by the belt 15, a main shaft 17 fixed to the belt pulley 16, and a main shaft 17 The crank drive 18 is transmitted to the needle bar 10 by changing the rotational drive transmitted to the needle bar 10 to the vertical drive.

  The rotational driving force of the sewing machine motor 14 is transmitted to the main shaft 17 via the belt pulley 16, and the rotational driving transmitted to the main shaft 17 is converted into the vertical drive by the crank mechanism 18 and transmitted to the needle bar 10. The sewing needle 11 is driven up and down together with the needle bar 10. The upper thread passed through the eye hole of the sewing needle 11 that is driven up and down is entangled with the lower thread by the thread catcher provided in the bed portion 2 to form a seam.

  As shown in FIG. 1, the needle swing mechanism 7 includes a first bevel gear 21 fixed to the main shaft 17, a second bevel gear 22 that meshes with the first bevel gear 21, and a second bevel gear 22. Is formed with a rotating shaft 23 fixed to the upper end portion, a worm gear 24 fixed to the rotating shaft 23, a rotating gear 25 meshing with the worm gear 24, and a convex portion 27 for swinging the needle bar 10 on the outer peripheral portion. The cam lift detecting body 30 is always needled by urging the needle swing cam 28, the cam lift detecting body 30 for detecting the cam lift of the convex portion 27, the needle bar supporting body 32, and the needle bar supporting body 32 to the left. An urging spring 33 to be brought into contact with the swing cam 28 and a transmission mechanism 40 for transmitting the swing of the cam lift detection body 30 to the needle bar support 32 are provided.

  The rotation gear 25 and the needle swing cam 28 are rotatably mounted on the frame 5 of the leg post 3 via the shaft 26, and when the rotational drive is transmitted to the rotation gear 25 by the worm gear 24, the needle swing is performed together with the rotation gear 25. The cam 28 is rotated. Although only one needle swing cam 28 is shown for convenience, a plurality of needle swing cams 28 are actually provided so that various stitches can be formed. The cam lift detection body 30 is rotatably supported by the frame 5 of the pedestal column 3 by a cam lift detection body shaft 29. The cam lift is a numerical value obtained by subtracting the radius of the base circle from the radius of the cam. The needle bar support 32 has bearing portions 34a and 34b formed at the lower end portion and the intermediate portion, and supports the needle bar 10 by the bearing portions 34a and 34b so as to be slidable in the vertical direction. The needle bar support 32 is rotatably supported via a needle bar support shaft 31 fixed to the frame 5 of the arm portion 4.

As shown in FIGS. 1 to 3, the transmission mechanism 40 includes a first transmission body 41 made of metal, a second transmission body 42 made of synthetic resin (for example, polyacetal), a connection screw 43, and a connection pin 44 ( Equivalent to a connecting member).
As shown in FIG. 1, the first transmission body 41 is shaped like a “heavy” in a side view, and is provided between the cam lift detection body 30 and the needle bar support body 32. The left end of the first transmission body 41 is connected to the lower end of the needle bar support 32 via a connection pin 32a. As shown in FIGS. 2 and 3, a long hole 45 that is long in the longitudinal direction of the first transmission body 41 is formed in the right end portion of the first transmission body 41. A screw hole 43 a into which the connecting screw 43 is screwed is formed at a position from the needle bar 10 at the center of the first transmission body 41.

  As shown in FIG. 1, the second transmission body 42 is formed in a plate shape slightly longer than ½ of the length of the first transmission body 41, and moves toward the cam lift detection body 30 along the first transmission body 41. It is provided to extend. As shown in FIG. 3, a screw hole 43 b into which the connection screw 43 is inserted is formed at the left end portion of the second transmission body 42. As shown in FIG. 2, at the position corresponding to the long hole 45 of the first transmission body 41 at the right end of the second transmission body 42, a boss 46 fitted into the long hole 45 and the boss 46 are formed coaxially. A pin hole 47 into which the connecting pin 44 is inserted is formed. The left end of the second transmission body 42 is fixed at a position on the needle bar 10 side from the center of the first transmission body 41 by a connection screw 43, and the right end is a cam lift detection body by a connection pin 44 and a nut 44a fitted in the pin hole 47. 30.

  The connection pin 44 is for connecting the second transmission body 42 and the cam lift detection body 30. The connecting pin 44 passes through the pin hole 47 of the second transmission body 42, the long hole 45 of the first transmission body 41, and the pin hole 47 formed in the upper end portion of the cam lift detection body 30, and is screwed into the nut 44a. Yes. The connecting pin 44 is supported so as to be slidable with respect to the long hole 45, and is configured to be relatively movable to the left and right with respect to the long hole 45 as the second transmission body 42 is thermally expanded and contracted. .

Next, the operation of the needle swing mechanism 7 when zigzag sewing is performed will be described.
When the rotational driving force of the sewing machine motor 14 is transmitted to the main shaft 17 via the belt 15 and the belt pulley 16, the first bevel gear 21 is rotated together with the main shaft 17. The rotational driving force transmitted to the first bevel gear 21 is transmitted to the rotary gear 25 via the second bevel gear 22, the rotary shaft 23, and the worm gear 24, and the needle swing cam 28 is rotated together with the rotary gear 25. . When the needle swing cam 28 is rotated, the cam lift detecting body 30 abutted on the needle swing cam 28 is swung by detecting the cam lift of the convex portion 27 and is connected to the upper end portion of the cam lift detecting body 30. The swing drive of the cam lift detecting body 30 is transmitted to the needle bar 10 through the second transmission body 42, the first transmission body 41, and the needle bar support body 32, and the needle bar 10 swings in the left-right direction together with the sewing needle 11. Driven to form a zigzag stitch.

Next, the operation of the transmission mechanism 40 when the frame 5 is expanded and contracted by heat will be described with reference to FIGS.
First, as shown in FIGS. 1, 4-1, and 5-1, when the second transmission body 42 is not expanded and contracted by heat, the connecting pin 44 is the middle point of the elongated hole 45 in the left-right direction. Located at M. In this state, the horizontal distance A from the needle bar support body shaft 31 to the cam lift detection body shaft 29 and the horizontal distance B from the connection pin 32a to the connection pin 44 are both L, and the connection screw 43 and the connection pin 44 Let the distance C be Lo. For simplification of explanation, the expansion of the first metal transmission body 41 is set to “0” because of the small expansion.

  Next, it is assumed that the frame 5 is expanded by heat and the distance A is expanded to (L + a). As shown in FIGS. 4B and 5B, when the second transmission body 42 is also expanded by the length b in the horizontal direction due to heat, the left end of the second transmission body 42 is fixed to the first transmission body 41. Therefore, the right end portion of the second transmission body 42 is moved relative to the first transmission body 41 to the right by the distance b, and the cam lift connected to the right end portion of the second transmission body 42 by this relative movement. Since the upper end portion of the detection body 30 is also moved relative to the first transmission body 41 by the distance b to the right, the length C becomes (Lo + b), and the distance B also becomes (L + b). .

  The length C of the second transmission body 42 is slightly longer than half of the distance A, but the polyacetal constituting the second transmission body 42 has a larger coefficient of thermal expansion than the ABS resin constituting the frame 5. Therefore, a≈b. Accordingly, since the deviation (ab) between the distance A and the distance B is substantially “0”, there is almost no deviation between the distance A and the distance B, and the needle bar 10 is held at a predetermined position without being displaced. The

  Next, it is assumed that the frame 5 contracts at a low temperature and the distance A contracts to (La). As shown in FIGS. 4-3 and 5-3, if the second transmission body 42 is also contracted by the length b, the right end portion of the second transmission body 42 together with the upper end portion of the cam lift detection body 30 is the first. It moves to the left with respect to the transmission body 41. Accordingly, the length C is contracted to (Lo−b), and accordingly, the distance B is also contracted to (L−b). Therefore, as described above, since the deviation (ab) between the distance A and the distance B is almost absorbed, the needle bar 10 is held at a predetermined position without being displaced.

Next, the effect of the sewing machine 1 will be described.
According to the sewing machine 1, since the second transmission body 42 is made of a synthetic resin, even if the frame 5 is expanded or contracted by heat, the second transmission body 42 is also expanded or contracted. A connecting pin 44 that connects the cam lift detecting body 30 and the second transmission body 42 at the right end of the body 42 is slid in a long hole 45 formed at the right end of the first transmitting body 41, and the connecting pin Since the horizontal distance B between the pin 32a and the connecting pin 44 changes corresponding to the expansion or contraction of the frame 5, the distance A between the needle bar support body shaft 31 and the cam lift detection body shaft 29 increases as the frame 5 expands or contracts. The shift of the needle bar support 32 due to the above can be automatically eliminated without complicated adjustment by the user.

  Since the above effect is realized by a simple configuration in which a long hole 45 is formed at the right end portion of the first transmission body 41 and a second transmission body 42 and a connecting pin 44 are provided, the structure of the sewing machine can be simplified. Can do. Since the second transmission body 42 is made of polyacetal having a larger expansion coefficient than the ABS resin constituting the frame 5, the expansion amount of the second transmission body 42 and the expansion amount of the distance A can be made substantially equal, and the needle bar The positional deviation from the origin of 10 can be further reduced.

Next, a modified embodiment in which the above-described embodiment is partially changed will be described.
1) In the above-described embodiment, the frame 5 is made of ABS resin, and the second transmission body 42 is made of polyacetal. However, the materials constituting the frame 5 and the second transmission body 42 are limited to the above-described materials. It is not a thing. However, the distance A between the cam lift detecting body shaft 29 and the needle bar support body shaft 31, the distance B between the connecting screw 43 and the connecting pin 44, the thermal expansion coefficient X of the synthetic resin constituting the frame 5, and the second transmission. The relationship of the thermal expansion coefficient Y of the synthetic resin constituting the body 42 is
A × X ≒ C × Y
It is desirable to use a synthetic resin having an expansion coefficient such that

  It should be noted that the present invention is not limited to the examples described above, and those skilled in the art can implement various modifications to the above embodiments without departing from the spirit of the present invention. And the invention encompasses those variations.

It is an internal block diagram of the sewing machine concerning the Example of this invention. It is a fragmentary perspective view of the right end part of a 1st transmission body and a 2nd transmission body. It is a side view of a 1st transmission body and a 2nd transmission body. It is a top view explaining the effect | action of the transmission mechanism in the normal time. It is a top view explaining the effect | action of the transmission mechanism at the time of expansion | swelling. It is a top view explaining the effect | action of the transmission mechanism at the time of contraction. FIG. 4 is a view corresponding to FIG. 4A at the right end of the transmission mechanism. FIG. 4 is a diagram corresponding to FIG. 4B at the right end of the transmission mechanism. FIG. 4 is a diagram corresponding to FIG. 4C at the right end of the transmission mechanism. It is an internal block diagram of the sewing machine provided with the conventional needle swing mechanism. FIG. 7 is a view corresponding to FIG. 6 during expansion.

Explanation of symbols

1 sewing machine 5 sewing machine frame 7 needle swing mechanism 10 needle bar 28 needle swing cam 29 cam lift detection body shaft 30 cam lift detection body 31 needle bar support body shaft 32 needle bar support body 40 transmission mechanism 41 first transmission body 42 second transmission body 44 Connecting pin 45 Long hole 47 Pin hole

Claims (2)

In a sewing machine equipped with a needle swing mechanism that swings the needle bar,
The needle swing mechanism includes a needle bar support body rotatably supported by a synthetic resin sewing machine frame via a needle bar support body shaft, a needle swing cam for swinging the needle bar, and the sewing machine. A cam lift detecting body which is rotatably supported by a frame via a cam lift detecting body shaft and detects the cam lift of the needle swing cam; and a transmission means for transmitting the swing of the cam lift detecting body to the needle bar support. Prepared,
The transmission means includes
A metal first transmission body provided between the cam lift detection body and the needle bar support body, one end of which is connected to the needle bar support body;
It is made of synthetic resin and extends toward the cam lift detection body along the first transmission body, one end is connected to a position closer to the needle bar support body than the center of the first transmission body, and the other end is connected to the cam lift detection body. A second transmitter,
A connecting member for connecting the second transmission body and the cam lift detecting body;
A long hole formed in the other end portion of the first transmission body and long in the longitudinal direction of the first transmission body, and having a long hole through which the connecting member is slidably passed. sewing machine.   The sewing machine according to claim 1, wherein the second transmission body is made of a synthetic resin having a larger coefficient of thermal expansion than that of the synthetic resin constituting the sewing machine frame.

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