JPH11290568A - Thread tension releasing device for sewing machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent lowering of the commodity value of sewn products by enabling the needle thread tension to be switched between releasing and non- releasing when a presser is in the raised position. SOLUTION: The input terminal of an AND circuit is switched to H by turning a switch 29 on. Thereby, a thread releasing solenoid 25 operates to release the tension on the needle thread when a thread cut signal is inputted and a presser bar is raised respectively. In a condition that the switch 29 is turned off, the pressure bar is in a lowering position and when a thread cutting signal is not inputted. Accordingly both the input terminal of the AND circuit 31 and the input terminal of the OR circuit 32 come to be L. Consequently, a thread tension releasing solenoid 25 does not operate. Sewing is executed in that condition. When sewing is completed, one of input terminals of the OR circuit 32 comes to be H and the thread tension releasing solenoid 25 is operated by a solenoid driver 33 to release applying of the needle thread tension. Thus the needle thread tension is released every thread cutting to enable to surely cut the thread.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thread loosening device for a sewing machine, and more particularly to a thread loosening device for a sewing machine having a presser vertically moving means for vertically moving a cloth presser by an operator.

[0002]

2. Description of the Related Art A thread loosening device in a sewing machine having a presser vertically moving means for vertically moving a cloth presser by operation of an operator of this kind has the following structure and operation. The configuration and operation of this conventional technique will be described with reference to FIGS. 6, 7, 8, and 9. FIG.

[0003] Reference numeral 1 denotes a holding bar, which is supported by a metal 2 provided on a frame so as to be vertically movable. A presser bar 3 is fixed to a lower end of the presser bar 1 and a holding body 4 is fixed to an upper portion thereof. Reference numeral 5 denotes a pressing spring, which applies a downward pressing force to the pressing rod 1 in a compressed state by an adjusting screw 6 whose lower end is in contact with the upper end surface of the pressing rod 1 and whose upper end is screwed into a frame. Reference numeral 7 denotes a nut screwed into the adjusting screw 6.

[0004] Reference numeral 8 denotes a lifting link as a holding up and down moving means, whose base is rotatably supported by a stepping screw 9 on a support plate fixed to a frame (not shown). Reference numeral 10 denotes a lifting plate, the upper end of which is rotatably supported by a lifting link 8 by a shaft 11, the lower end of which is bent in a U-shape. They are arranged facing each other.

Reference numeral 13 denotes a press-up link, the base of which is rotatably supported on a support plate (not shown) by a stepped screw 14. One end thereof is connected to the press-up link 13 by a connecting rod 15, and the other end is a connecting rod 16 Is connected to a holding up magnet which is operated by a switch operation of an operator, a knee raising device which is operated by an operator's operation, or the like, as holding up and down moving means.

Reference numeral 17 denotes a thread loosening plate as upper thread tension releasing means, whose base is rotatably supported by a stepping screw 18 on a support plate fixed to a frame. The thread loosening plate 17 has an engaging portion 19 protruding from the right end surface of the lifting link 8 at the upper end, a cam surface 20 at the lower end, and an arc-shaped groove centered on the step screw 18 into which the step screw 9 is loosely fitted. 17a.

The cam surface 20 presses a thread loosening pin 21 of a thread tensioner, which will be described later, by the rotation of the thread loosening plate 17, whereby the tension application to the upper thread by the thread tensioner is released. Reference numeral 23 denotes a wire tube supported on a frame of the sewing machine. One end of a wire 24 inside the wire tube is connected to the thread loosening plate 17, and the other end is connected to a magnet operated by a thread cutting signal.

The construction of the thread tensioner will be described with reference to FIG. 4
A thread tensioner 1 has a thread 43 at the base of the thread tensioner shaft 42.
Is screwed into a frame 44 of the sewing machine and fixed by a nut 45. At the right end of the thread tensioner shaft 42, a screw 4
6, and a groove 47 is formed in the axis. Reference numerals 48 and 49 denote thread tension discs whose thread holding surfaces face each other, and are loosely fitted to the thread tension device shaft 42.

A pressing plate 50 is loosely fitted to the thread tensioner shaft 42, and a central pressing portion 50 a is loosely fitted to the groove 47.
Reference numeral 51 denotes an adjusting knob which is screwed into the screw 46 of the thread tensioner shaft 42, compresses the conical spring 52 provided between the thread tensioner shaft 42 and the presser plate 50, and presses the thread tension discs 48, 49 through the presser plate 50. ing. Reference numeral 21 denotes the above-described thread loosening pin, which is loosely fitted to the axis of the thread tensioner shaft 42, the right end of which faces the pressing portion 50a of the holding plate 50, and the left end of which is the aforementioned thread loosening plate 17
Of the cam surface 20.

Next, the operation of the conventional yarn loosening device will be described with reference to FIG.
This will be described with reference to FIGS. 7, 8, and 9. FIG. 9A shows a standby state, in which the pressing rod 1 is pressed downward by the pressing force of the pressing spring 5 in FIG. 6, and the cloth is pressed against the upper surface of the needle plate (not shown) by the lower surface of the presser 3.

From this state, when the sewing of the cloth is completed and the magnet or the knee raising device is operated in order to take out the cloth from the lower surface of the presser foot 3, the connecting rod 16 is pushed upward, and the press-up link 13 is raised. The lifting link 8 is rotated counterclockwise about the screw 14, whereby the lifting link 8 is rotated clockwise about the stepped screw 9 via the connecting rod 15 as shown in FIG.

By the rotation of the lifting link 8, the lifting plate 10 is pulled upward, the engaging portion 12 is engaged with the holding member 4, and the holding bar 1 is in the raised position, and the holding metal 3 is also raised. The right end face of the lifting link 8 pushes the engaging portion 19 of the thread loosening plate 17 rightward as shown in FIG. 9B, and the thread loosening plate 17 is rotated clockwise about the stepped screw 18.

By the rotation of the thread loosening plate 17, the thread loosening pin 21 is pushed rightward by the cam surface 20 from the state shown in FIG. 7 to the pressing portion 5 of the pressing plate 50 as shown in FIG.
0a is pushed rightward, and the thread tension plate 48 by the conical spring 52 is pressed.
Is released, and the tension application to the upper thread by the thread tensioner is released. For this reason, when pulling out the cloth from the lower surface of the presser foot 3, since the tension application of the upper thread is released, the cloth can be easily pulled out from the lower surface of the presser foot 3.

When the magnet or the knee raising device is deactivated from this state, the lifting link 13 is rotated clockwise, and the lifting link 8 is rotated counterclockwise to lower the presser bar 1 and the presser foot 3. Together with the thread loosening plate 17
Also rotates in the counterclockwise direction, whereby the thread tension plates 48 and 49 of the thread tension device change from the state of FIG. 8 to the state of FIG. 7, and the tension by the thread tension device is applied to the upper thread, and Is a in FIG.
Return to the position.

When a thread cutting signal is generated in the standby state shown in FIG. 9A, the wire 24 is pulled to the right by a magnet or the like, and only the thread loosening plate 17 is turned around the stepped screw 18 as shown at c in FIG. In this state, the tension applied to the upper thread by the thread tensioner is released as described above, and thread trimming is performed in this state. When the thread trimming is completed, the magnet becomes inactive, and the thread loosening plate 17 rotates counterclockwise to apply tension to the upper thread by the thread tensioner.
Return to the position.

As described above, in the conventional thread loosening device, the tension applied to the upper thread by the thread tensioner is always released each time the pressing up / down moving means such as the knee raising device or the magnet is operated.

[0017]

However, in this conventional thread loosening device, the tension applied to the upper thread by the thread tensioner is always released each time the presser vertical movement means such as a knee raising device or a magnet is operated. Therefore, the following problem occurs. For example, during the sewing process of the sewing machine, the sewing process of continuously forming a seam on a cornered cloth, or changing the cloth feeding direction of the sewing machine in the middle of sewing, slightly turning the cloth around the needle, There is a sewing process for forming a continuous seam.

At the corners or the changing points of the cloth feeding direction in these sewing steps, the sewing machine is stopped with the needle piercing the cloth, and the presser vertical movement means is operated to set the cloth presser foot 3 to the raised position. It is necessary to turn the cloth around the needle. In the conventional thread loosening device, the tension of the upper thread by the thread tensioner is released by the operation of the presser up / down moving means, so that when the cloth is turned, the tension of the thread becomes unstable. For this reason, when the next stitch is formed with the presser foot 3 at the lowered position, the stitch at the start of sewing may have a poor thread tightening or a thread loop may occur on the lower surface of the cloth.

Therefore, there is a problem that the commercial value of the sewn product is reduced. When sewing a thick cloth and a stepped cloth by a sewing machine having a thread releasing device of this kind, when the step is sent below the presser foot 3, the operator operates the presser vertical movement means. Then, the presser foot 3 is raised so that the stepped portion can easily pass below the presser foot 3.

Also in this case, the tension of the upper thread by the thread tensioner is released by the operation of the presser vertical movement means.
For this reason, there is a problem that the tension of the upper thread is lost at the step portion of the cloth, and the thread tightening at the step portion of the cloth becomes poor, and the commercial value of the sewn product is reduced.

[0021]

Means for Solving the Problems To solve the above-mentioned problems, the invention according to claim 1 is a press-up / down moving means for moving a cloth press up and down by an operation of an operator, and applying tension to the upper thread at the time of thread trimming. A sewing machine provided with a needle thread tension releasing means for releasing the needle thread tension, when the presser foot is lifted by the presser vertical movement means, it is possible to switch between releasing and not releasing the needle thread tension. .

According to a second aspect of the present invention, there is provided a sewing machine having a presser vertically moving means for vertically moving a cloth presser by an operator's operation, and an upper thread tension releasing means for releasing the tension applied to the upper thread at the time of thread trimming. In the above-mentioned structure, a switching means is provided which can switch between a transmitting state in which the lifting movement of the cloth presser by the presser vertical moving means is transmitted to the upper thread tension releasing means and a non-transmitting state in which the lifting movement is not transmitted.

According to the present invention, the tension is always released from the upper thread every time the thread is trimmed by the presser vertical movement means, so that the thread can be reliably trimmed. When the cloth holding rod is moved to the raised position by the moving means, the upper thread tension is released, and normal sewing of the cloth can be performed. Further, by switching the switching means, every time the thread is trimmed, the tension applied to the upper thread is always released, and the thread can be reliably trimmed. Thread tension is not released.

For this reason, in the present invention, the sewing process for forming stitches continuously on a cornered cloth, or changing the cloth feeding direction of the sewing machine during sewing, and slightly turning the cloth around the needle to continuously In the sewing process for forming the seam to be formed, the seam at the corner or the conversion point of the cloth feeding direction is reliably formed,
Effects such as improvement in the commercial value of the sewn product can be obtained. Further, in the present invention, by switching the switching means, even when the presser vertical movement means is operated, the upper thread tension is not released, so that the thread is securely tightened at the step of the cloth and the commercial value of the sewn product Are obtained.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. In the embodiment shown in FIGS. 1 and 2, the switching means is performed by electrical means. Parts having the same configuration and operation as those of the conventional mechanism are denoted by the same part numbers as those of the conventional mechanism, and the description of the configuration of the same part number will be omitted, and different configurations will be mainly described.

Reference numeral 25 denotes a thread loosening solenoid as upper thread tension releasing means. The plunger 26 and the thread loosening plate 17 are connected by a link 27. Reference numeral 28 denotes a press-up switch, which is fixed to the frame of the sewing machine and generates a press-up signal by the holding member 4 accompanying the lifting of the presser bar 1. FIG. 2 is a circuit diagram for controlling the thread loosening solenoid 25 of FIG. 1, 29 is a changeover switch as a changeover means for arbitrarily changing the operation by an operator, 28 is a press-up signal from the press-up switch described above, and 30 is a press-up signal from the press-up switch described above. It is generated when a plunger of an automatic thread trimming solenoid (not shown) operates in response to a thread trimming signal.

31 is an AND circuit, 32 is an OR circuit, 3
3 is a solenoid driver, 25 is the above-mentioned thread loosening solenoid as upper thread tension releasing means, and Vsol is a solenoid drive power supply. In this circuit, the output of the OR circuit 32 is H
When, the thread loosening signal is output to the thread loosening solenoid 25 through the solenoid driver 33, and the thread loosening solenoid 25 is driven.

Next, the operation of the embodiment shown in FIGS. 1 and 2 will be described. First, when sewing a general thin cloth, or when there is no step of turning the cloth in the middle of a seam such as corner stitching of the cloth, the changeover switch 29 in FIG. The terminal is set to H. This allows
As described below, when the thread trimming signal is input and when the presser bar 1 is raised to the raised position, the thread loosening solenoid 25 is operated to release the tension application to the upper thread by the thread tensioner. Is done.

In this state, since the presser bar 1 is at the lowered position and no thread cutting signal has been input, the input terminals of the AND circuit 31 are H and L, and the output terminals thereof are L. The input terminals of the OR circuit 32 are L, L
Therefore, the output signal from the OR circuit 32 is L, and the thread loosening solenoid 25 does not operate. From this state, the sewing machine is driven to sew the cloth. When the sewing is completed and a thread trimming signal is generated, one of the input terminals of the OR circuit 32 becomes H, and an output signal is generated from the OR circuit 32. The thread loosening solenoid 25 shown in FIG. 1 is operated by the solenoid driver 33.

By the operation of the thread loosening solenoid 25,
The plunger 26 of FIG. 1 is pulled to the right, the thread loosening plate 17 is rotated clockwise around the step screw 18 via the link 27, and the thread loosening pin 21 is pushed by the cam surface 20. As shown in 8, the application of the upper thread tension by the thread tensioner is released. When the thread trimming is completed, the thread trimming signal is cut off, one of the input terminals of the OR circuit 32 becomes L, the output signal from the OR circuit 32 becomes L, and the thread loosening solenoid 25 becomes inoperable. As shown in 7, the upper thread tension is again applied by the thread tensioner.

When the presser bar 1 is in the lowered position and the thread trimming signal is not input, the sewing machine is driven to sew the cloth, and the sewing is completed. When the connecting rod 16 as a means is pushed upward by an operation of an operator or an electric means, the press-up link 13 rotates counterclockwise around the step screw 14. In this rotation, the lifting link 8 is rotated clockwise through the connecting rod 15 to raise the lifting plate 10, and the engaging portion 12 is engaged with the lower end surface of the holding member 4, and the holding rod 1 is moved.
To rise. When the presser bar 1 rises, the upper end surface of the holding body 4 presses the press-up switch 28 to generate a press-up signal.

When this hold-up signal is generated, the input terminals of the AND circuit 31 in FIG. 2 go to H and H, and one of the input terminals of the OR circuit 32 goes to H. When an output signal is generated, the thread release solenoid 25 of FIG. 1 is operated by the solenoid driver 33. By the operation of the thread loosening solenoid 25, the plunger 26 of FIG. 1 is pulled rightward, and the thread loosening plate 17 is rotated clockwise around the stepped screw 18 via the link 27, and the cam surface 20 of the thread loosening plate 17 is rotated. By pushing the thread loosening pin 21, the application of the upper thread tension by the thread tensioner is released.

In the above state, when the lifting of the connecting rod 16 by the pressing up / down moving means is released, the pressing rod 1 is pressed downward by the elastic force of the pressing spring 5 and descends.
When the holding rod 1 is lowered, first, the holding-up switch 28 is pressed.
2, the input terminal of the AND circuit 31 in FIG. 2 becomes H and L, one of the input terminals of the OR circuit 32 becomes L, and the output signal from the OR circuit 32 disappears. In operation, the upper thread tension is again applied by the thread tensioner.

When the holding rod 1 is lowered, the lifting plate 10 is pushed downward by the lower end surface of the holding member 4 to rotate the lifting link 8 counterclockwise around the stepped screw 9. Hold-up link 13, connecting rod 16
Etc. are moved and rotated in the opposite directions to the above. Next, in a sewing process in which the cloth feed direction of the sewing machine is changed and the cloth is turned to form a stitch, or when a cloth having a step portion or the like is sewn, the changeover switch 29 in FIG. Let L be the input terminal to 31.

Thus, as described below, when the thread trimming signal is input, the thread loosening solenoid 34 is operated. However, the press-up switch 28 generates the press-up signal from the press-up switch 28 with the presser bar 1 in the raised position. Also, the thread loosening solenoid 25 does not operate. Changeover switch 2 in FIG.
In a state in which 9 is turned off, the presser bar 1 is at the lowered position, and no thread cutting signal is inputted, so that the input terminals of the AND circuit 31 are L and L, and the output terminal thereof is L. The input terminals of the OR circuit 32 are L, L
Therefore, the output signal from the OR circuit 32 becomes L, and the thread loosening solenoid 25 does not operate.

In this state, the sewing machine is driven to sew the cloth. When the sewing is completed and a thread cut signal is generated, one of the input terminals of the OR circuit 32 becomes H, and the output of H from the OR circuit 32 becomes H. Signal is generated and solenoid driver 3
3, the thread loosening solenoid 25 of FIG. 1 is operated. Thus, the application of the upper thread tension by the thread tensioner is released as described above.

When the thread trimming is completed, the thread trimming signal is cut off, and one of the input terminals of the OR circuit 32 becomes L,
The output signal from the OR circuit 32 becomes L, the thread loosening solenoid 25 is deactivated, and the upper thread tension is again applied by the thread tensioner. At this time, the changeover switch 2 in FIG.
Since 9 is OFF, the input terminal from the changeover switch 29 to the AND circuit 31 is always L. For this reason, even if the step portion of the thick cloth is sent below the presser foot 3 and the presser bar 1 rises, a press-up signal is generated from the press-up switch 28, and even if one input terminal of the AND circuit 31 becomes H. Since the output terminal of the AND circuit 31 is maintained at L and the output signal does not become H, the thread loosening solenoid 25 does not operate, the tension application to the upper thread by the thread tensioner is not released, and the corners of the cloth and Thread tightening at the step portion is ensured.

FIGS. 3, 4 and 5 show a second embodiment in which the switching means is performed by mechanical means. Also in this embodiment, the same configuration as the conventional mechanism,
The parts having an action are given the same part numbers as those of the conventional mechanism, and the description of the configuration of the same part numbers is omitted.
The different configuration will be mainly described.

Reference numeral 35 denotes a switching arm, which is rotatably supported by a shaft 36 on the rear surface of the pull-up link 8 and has a screw 37 formed at the tip. Reference numeral 38 denotes a box screw serving as a switching means.
Arc-shaped groove 3 formed in the lifting link 8 with the center at 6
9, is screwed into the screw 37 of the switching arm 35,
By loosening the box screw 38, the box screw 38 can be moved to an arbitrary position in the groove 39, and can be fixed to the lifting link 8 by screwing the box screw 38 at the moved position. Reference numeral 40 denotes an engagement end face formed on the thread loosening plate 17, and this engagement end face engages with the box screw 38 only when the box screw 38 is fixed below the groove 39 as shown in FIG. Is configured.

This embodiment has the above configuration, and the operation will be described next. First, when sewing a general cloth having a small cloth thickness or when there is no sewing step of changing the cloth feeding direction of the sewing machine and turning the cloth to form a seam, as shown in FIG. Fix below. Thereby, as described below, when the thread trimming signal is input and when the presser bar 1 is raised to the raised position by the presser vertical movement means, the thread loosening plate 17 is turned around the stepped screw 18 respectively. Then, the tension application to the upper thread by the thread tensioner is released.

In the state shown in FIG. 3A, since the presser bar 1 is at the lowered position and no thread cutting signal has been inputted, the box screw 38 and the engaging end face 40 are in the engaged state. From this state, the sewing machine is driven to sew the cloth. When the sewing is completed and a thread trimming signal is generated, the wire 24 is cut.
Is pulled to the right, and as shown in FIG. 3C, the thread loosening plate 17 rotates around the stepped screw 18, and the tension application to the upper thread by the thread tensioner is released.

When the thread trimming is completed, the wire 2
4 is released to the right, the thread loosening plate 17 rotates around the stepped screw 18 in the opposite direction to the above, and the upper thread tension is again applied by the thread tensioner. The sewing machine is driven to sew the cloth from the state shown in FIG. 3A where the presser bar 1 is at the lowered position and the thread trimming signal is not input.
When the suturing is completed, the connecting rod 15 is
, The lifting link 8 is rotated clockwise, the lifting plate 10 is raised, and the holding bar 1 is raised.

By turning the link 8 clockwise,
The box screw 38 engages with the engagement end face 40 of the thread loosening plate 17, and the thread loosening plate 17 rotates around the step screw 18 in conjunction with the rotation of the link 8, as shown in FIG. The tension application to the upper thread by the thread tensioner is released. Further, when the pulling of the connecting rod 15 by the pressing up / down moving means is released, each part rotates and moves in the opposite direction to the above, and the pressing rod 1 is moved.
At the lower position, and the tension is again applied to the upper thread.

Next, when sewing a cloth having steps or the like on the cloth,
In the case of sewing a cloth having a sewing process of changing the cloth feeding direction of the sewing machine and turning the cloth to form a seam, the box screw 38 at the position a in FIG. 3 is loosened, and as shown in FIG. The switching arm 35 is rotated upward to be moved, and the box screw 38 is tightened and fixed. Thereby, as described below, when the thread trimming signal is input, the thread loosening solenoid 34 operates, but the presser vertical movement means
Even if the presser bar 1 is set to the raised position, the tension application to the upper thread by the thread tensioner is not released.

That is, when a thread cutting signal is generated from the state shown in FIG. 4A, the wire 24 is pulled rightward, and the thread loosening plate 17 is pulled.
4 rotates clockwise about the stepped screw 18 as shown in FIG. 4C, whereby the tension application to the upper thread by the thread tensioner is released. When thread trimming is completed and the thread trimming signal disappears from the state of the thread loosening plate 17 in FIG. 4C, the pulling of the wire 24 to the right is released, and the thread loosening plate 17 rotates counterclockwise. Thus, tension is again applied to the upper thread.

In the state shown in FIG. 4A, the connecting rod 15 is pulled to the right by the holding up / down moving means, and the lifting link 8 rotates clockwise about the stepped screw 18, but as shown in FIG. Since the box screw 38 does not engage with the engagement end face 40 of the thread loosening plate 17 as shown in FIG. 7, the thread loosening plate 17 does not rotate, so that the tension application to the upper thread by the thread tensioner is not released.

[0047]

As described above, according to the present invention, the presser vertical movement means for vertically moving the cloth presser by the operation of the operator, and the upper thread tension releasing means for releasing the tension applied to the upper thread at the time of thread trimming. When the presser foot is raised by the presser vertical movement means, the needle thread tension is released,
By providing a switching means that can switch whether or not to release the tension, the tension applied to the upper thread is always released every time the thread is trimmed, and the thread trimming can be reliably performed. When the rod is in the raised position, the upper thread tension is released, and normal sewing of the cloth can be performed.

Further, by switching the switching means, every time the thread is trimmed, the tension application to the upper thread is always released, and the thread trimming can be surely performed. Even if the holding bar rises,
Since the needle thread tension is not released, change the cloth feed direction of the sewing machine and turn the cloth to form a seam.
The seam at the conversion point of the cloth feeding direction and the thread tightening at the step of the cloth are reliably performed, and effects such as an increase in the commercial value of the sewn product can be obtained.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a first embodiment.

FIG. 2 is a circuit diagram of the first embodiment.

FIG. 3 is a partial front view of the second embodiment, illustrating the operation of each unit.

FIG. 4 is a partial front view of the second embodiment, illustrating the operation of each unit.

FIG. 5 is an exploded perspective view of a portion of the second embodiment.

FIG. 6 is an exploded perspective view of a conventional technology.

FIG. 7 is a cross-sectional view of the thread tensioner in a state where tension is applied to the thread.

FIG. 8 is a sectional view of the thread tensioner in a state where tension on the thread is released.

FIG. 9 is a partial front view of a conventional technique, illustrating the operation of each part.

[Explanation of symbols]

 DESCRIPTION OF REFERENCE NUMERALS 1 holding rod 4 holding 8 lifting link 10 lifting plate 13 holding lifting link 16 connecting rod 17 thread loosening plate 21 thread loosening pin 24 wire 25 thread loosening solenoid (upper thread tension releasing means) 28 holding up switch 29 switching switch (switching means) 31 AND circuit 32 OR circuit 35 Switching arm 38 Box screw (switching means) 41 Thread tensioner 48 Thread tension plate 49 Thread tension plate

Claims (2)

[Claims] 1. A sewing machine comprising: a presser vertically moving means for vertically moving a cloth presser by an operation of an operator; and an upper thread tension releasing means for releasing tension application to an upper thread at the time of thread trimming. A thread releasing device for a sewing machine, comprising: a switching means for switching between releasing and not releasing the upper thread tension when the cloth presser is lifted. 2. A sewing machine comprising a presser vertically moving means for vertically moving a cloth presser by an operation of an operator, and an upper thread tension releasing means for releasing tension application to an upper thread at the time of thread trimming. And a non-transmitting state in which the lifting motion of the cloth presser is transmitted to the upper thread tension releasing means, and a non-transmitting state in which the transmitting pressure is not transmitted.