JPH0779894B2 - Sewing machine thread tension device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a thread tension device for a sewing machine.

(Problems to be solved by the prior art and invention) The thread tension of the sewing machine is selected by the sewing machine user according to the type of cloth, thread and sewing pattern, and individual sewing conditions such as needle amplitude and cloth feed amount. By adjusting the thread tension device, the entangled position of the upper and lower threads is set to an appropriate position in the cloth which does not hinder practical use.

However, when adjusting the upper thread tension adjuster according to the above sewing conditions, it is often necessary to adjust the lower thread tension or the lower thread extension amount in accordance with the adjustment of the upper thread tension. There is a problem that it is difficult to sufficiently cope with various sewing conditions by the adjustment of No. 2, and it sometimes occurs that good stitches cannot be obtained.

(Means for Solving Problems and Action of the Invention) In the needle thread tension device of the present invention, first, various threading mode displays are provided on the thread tension dial, and the needle thread tension is controlled by rotating the thread tension dial. In addition, since the electrical switch for generating a signal for controlling the lower thread feeding mechanism for controlling the lower thread path and the feeding amount is switched, it is possible to sufficiently cope with various sewing conditions.

Secondly, in addition to each display for manual control on the thread tension dial, the display of "auto" is provided at the end of the rotation control range, so it is easy to select "auto" which is frequently used.
It has the effect of being excellent in operability.

Thirdly, by switching the electric switch, the bobbin thread feeding mechanism is controlled according to the display of the thread tension dial and the LE for automatic display is displayed.
Since the combination of D and the switching of the display of the manual display LED is determined, the selected control mode can be recognized correctly.

Fourth, the spring receiver is brought into contact with one end of the thread tension spring,
Since the spring receiving screw in which the gear-shaped knurled portion is formed is screwed into the flange portion, and the leaf spring attached to the spring receiving member is engaged with the knurled portion to lock the rotation of the spring receiving screw. There is an effect that the initial setting of the needle thread tension can be easily performed.

Fifthly, in the tray receiver of the thread tension device, the U-shaped groove formed below the tray receiver engages with the groove portion of the pin fixed to the base plate, and the engaging portion serves as a fulcrum for the insertion hole of the tray receiver. Since a pair of conical projections formed on the left and right sides press the thread tension disc from the back side, the disc from the fulcrum to the disc by the tension spring is determined from the length from the fulcrum to the pinching part of the upper thread of the thread tension disc. The length up to the pressing portion via the receiver becomes longer, and the spring constant of the thread tension spring can be set to a relatively small value. As a result, the rotational operation force of the thread tension dial of the thread tension device can be set to a relatively small value. It has an effect.

Sixth, the separator of the thread tension device is located between the tray receiver on the thread tension shaft and the thread tension spring or is integrally provided with the tray receiver, and the separator is provided near the outer circumference of the thread tension disc from the inner surface side. Since the protrusions facing each other are formed and the separator is provided coaxially with the thread tension disc or the like, there is an effect that the initial adjustment of the machine is easy and the mechanism itself is simplified.

(Examples) The present invention will be described below with reference to examples.

In FIG. 5, holes 1a and 1b are formed in the left side plate and the right side plate of the base plate 1 of the thread tension device 55, respectively. Thread tension shaft 2
Has a slit 2a at one end and a screw hole 2b (FIG. 1) at the other end.

The thread tension shaft 2 is inserted into the hole 1a of the base plate 1, brought into contact with the right side plate 1c, and fixed to the base plate 1 with screws 3.

A protrusion 4a is formed on the inner plate 4 and is engaged with the square hole 1d of the base plate 1 to stop the rotation.

Reference numeral 5 is a thread tension disc, 6 is a tray receiver, and an insertion hole 6a into which the thread tension shaft 2 is inserted.
A pair of conical projections 6b are formed on both sides of the conical portion and face the back surface of the thread tension disc 5. A U-shaped portion 6c is formed above the dish receiver 6, and an elongated hole portion 6d and a U-shaped groove 6e are formed below the dish receiver 6.

The U-shaped groove 6e is engaged with the groove portion 7a of the pin 7 fixed to the base plate 1.

The dish receiver 6 is configured so that the conical projections 6b formed on the left and right of the insertion hole 6a of the dish receiver 6 with the engaging portion as a fulcrum press the thread tension disc 5 from the back surface. As shown, the length G from the fulcrum to the vicinity of the pinching portion of the upper thread of the thread tension disc 5 is longer than the length F from the fulcrum to the pressing portion of the thread tension spring 10 via the dish receiver 6. Since the spring constant of the thread tension spring 10 can be set to be relatively small, the operating force of the thread tension device can be set to be relatively small.

The separator 8 is formed with a hook-shaped bent portion 8a,
The projecting portion 8a passes through the concave portion 6f of the dish receiver 6, and the tip thereof is opposed to the vicinity of the outer periphery of the thread tension disc 5 from the inner surface side. (FIG. 1) Since the separator 8 is provided coaxially with the thread tension disc 5 and the like, the initial adjustment of the mechanism is easy and the mechanism itself can be simplified.

The rotation stopper 9 is formed with a hole 9a into which the thread tension spring 10 is inserted and a cutout portion 9b, and a bent portion 9c is extended to engage the bent end 10a of the thread tension spring 10 with the cutout portion 9b. The bent portion 9c is engaged with the elongated hole 6d of the dish receiver 6 so that the thread tension spring 10 does not rotate. The auxiliary spring 11 is arranged on the outer circumference of the thread tension spring 10. (FIGS. 1 and 2) A female screw is formed on the right side plate 12a of the spring bearing 12 and a spring bearing screw 13 is screwed therein. The spring bearing screw 13 is brought into contact with one end of the thread tension spring 10. . A screw hole 12b is formed in the spring receiver 12, a pin 12c is implanted and a guide portion 12d is extended.

The leaf spring 14 is fitted on the pin 12c and fixed to the spring receiver 12 with a screw 15.

The leaf spring 14 includes an arm portion 14a having a spring action and a tip portion 14b thereof.
Is bent into an R shape and engages with a gear-shaped knurled portion 13a provided on the flange portion of the spring receiving screw 13
Has stopped rotating. Therefore, the initial setting of the needle thread tension can be easily performed.

The thread tension dial 16 is rotatably supported by a pin 17 of the base plate 1, thrust-stopped by an E-ring 18, and a corrugated washer 19 imparts an appropriate frictional force to the rotation.

The thread tension dial 16 is formed with a first groove cam A and a second groove cam B. The groove cam A is engaged with the pin 12c of the spring receiver 12, and the groove cam B is engaged with the pin 20a of the switching arm 20. Engaged.

The switching arm 20 is rotatably supported by a pin 21 of the base plate 1 and is thrust-stopped by an E ring 22. U groove on the switching arm 20
20b is formed and the cylindrical portion 23a of the collar 23 is fitted.
A square hole 23b is formed in the collar 23, and a knob portion 24a of a slide switch 24, which is an electric switch, is engaged with the collar hole 23b.

The slide switch 24 can be switched in three steps, and can output a signal corresponding to a combination of three levels of a bobbin thread feeding amount and an LED display described later.

On the outer circumference of the thread tension dial 16, as shown in FIG. 11, an indication of "auto", a indication of "thin" as a manual, and an indication of "0 to 9" indicating the magnitude of the upper thread tension are provided. When the respective displays are aligned with the marker 71 of the sewing machine 70, the lifts of the groove cam A and the groove cam B corresponding to the respective displays are as shown in FIG.

The groove cam A is used for controlling the auxiliary spring 11 and the thread tension spring 10, and the needle thread tension increases as the lift increases.

The groove cam B is provided with three levels of lift, whereby the slide switch 24 can be switched in three stages as shown in FIGS. 8 to 10. FIG. 8 corresponds, the part of the manual that is “thin” and the one with the larger number of figures is corresponding to FIG. 9, and the part with the smaller number of figures is corresponding to FIG. 10.

The thread loosening plate 25 and the thread loosening plate 26 are rotatably supported by a pin 27 of the base plate 1, thrust-stopped by an E ring 28, and both are connected by a screw 29. Tip of thread loosening plate 26
26a is formed in an R shape and is placed in the U-shaped portion 6c of the tray receiver 6. (Fig. 1) When the presser foot is lifted in this state, the thread loosening plate 25 moves together with the thread loosening plate 26 to the fifth position by the thread loosening lever (not shown).
The counterclockwise rotation of the drawing causes the tray receiver 6 to rotate with the groove 8a of the pin 7 as a fulcrum in FIG. 1 along with the separator 8 in the direction of the arrow in FIG. Since the upper part of the plate 5 is pulled and the protrusion 4a of the inner plate 4 is engaged with the square hole 1d, a clearance is formed in the upper parts of the inner plate 4 and the thread tension plate 5 to loosen the thread.

The base plate 1 is fixed to the thread guide cover 30 with screws 31 and 32.

33 is a thread take-up spring, 34 is a large thread hook, 35 is a divider plate,
In 35, the leading end 35a is bent toward the large thread hook so that the thread that goes from the large thread hook 34 to the balance 36 and the thread that goes from the balance 36 to the needle do not intersect. As shown in FIG. And three-dimensionally intersect.

Therefore, as shown in FIG. 4, when setting the upper thread T ₁ , if the thread is rubbed up from below, the thread enters from the clearance Y and the balance 36
The yarn is prevented from entering the inside of the weight dividing plate 35 due to the crossing amount X when the yarn is grated downward from.

In FIG. 7, the display panel 72 of the sewing machine 70 is provided with an LED for automatic display (LED1) and an LED for manual display (LED2), and is selectively turned on in each mode.

Next, the schematic structure of the sewing machine 70 provided with the thread tension device 55 of the present invention will be described with reference to FIG.

In the figure, the signal of the slide switch 24, which is switched by the operation of the thread tension device 55, is taken into the central processing unit CPU incorporated in the sewing machine, and each mode selected by the thread tension dial 16 based on the pattern data in the storage device ROM. According to the program, the bobbin thread feeding mechanism 40 is controlled by the pulse motor 50, and at the same time, one of the "auto" or "manual" LED, LED1 or LED2 corresponding to each mode is lit and displayed.

Relationship between movement of needle drop point and bobbin thread path As shown in FIGS. 13 and 14, generally in a horizontal hook, the bobbin thread feeding point J from the inner hook in the horizontal projection is the needle plate needle hole along the feed direction. In many cases, it is deviated to the left side with respect to the line segment d passing through the center of 60, and this is also the case in the present embodiment.

With a hook of such a structure, the amplitude is maximized and the feed amount P is constant.
An example in which zigzag sewing is performed will be described.

In the following description, the timing at which the lower thread for the current stitch is fed is after the previous stitch is formed and the feeding is completed. Therefore, each cycle of stitch formation has an amplitude and stitches are formed until the feeding is completed.

In FIG. 13, a route LoJ of the lower thread T on the horizontal projection plane from the lower thread feeding point J of the previous left baseline stitch Lo (feed amount P) and the current right baseline stitch R ₁ (feed amount P) in FIG. comparing R ₁ J, a LoJ <R ₁ J.

Therefore, the bobbin thread feeding amount required for forming the stitch R ₁ is larger than LoR ₁ when the cloth thickness is 0. Where L'o is the previous stitch
This is the position of Lo on the fabric after the seam formation this time.

Further, in FIG. 14, the right baseline stitch R ₁ (feed amount P) of this time
And for the next left baseline stitch L ₂ (feed amount P), route R ₁ J
And L ₂ J are compared, R ₁ J> L ₂ J. Therefore, the amount of bobbin thread feeding required to form the stitch L ₂ is R ′ ₁ L ₂ when the cloth thickness is 0.
It gets smaller. Here, R ′ ₁ is the position on the cloth after the next stitch formation of the current stitch R ₁ .

However, the bobbin thread feeding point J is not only biased to the left side with respect to the line segment d passing through the center of the needle plate needle hole 60 along the feed direction as shown in FIGS. Being located below the plate, the path of the bobbin thread T ₂ is three-dimensional and is bent at the needle plate needle hole 60.

Therefore, the actual length of the bobbin thread path with respect to the stitches of each needle drop is slightly longer than the length of the bobbin thread path shown in the horizontal projection of FIGS. 13 and 14, but the stitch formation where the needle drop point moves is formed. The above-mentioned relationship does not change qualitatively with respect to the required amount of bobbin thread feeding amount.

Therefore, if no control is applied to the bobbin thread feed amount with respect to the formation of stitches where the needle drop point moves, the cross relationship of the bobbin thread with the upper thread becomes uneven as shown in FIG. .

Bobbin thread feeding mechanism In order to correct the left-right unevenness of the cross relationship with the needle thread of the bobbin thread in this zigzag sewing, theoretically, the bobbin thread needs to correspond to different bobbin thread required amounts at the left and right needle entry points. It suffices to control the bobbin feed amount, but as a result of the experiment, only the control of the bobbin thread feed amount causes other inconveniences in sewing, and as a result, it is possible to control the bobbin thread path for sewing at the left and right needle entry points It has been found that the combined use of controlling the thread feeding amount can correct the left-right non-uniformity of the intersecting relationship with the upper thread of the bobbin thread in zigzag sewing without causing other problems in sewing.

The bobbin thread feeding mechanism controlled by the thread tension device of the present invention will be described below. The bobbin thread feeding mechanism 40 is a mechanism that deforms the feeding path of the bobbin thread T ₂ by controlling the swing amount of the feeding lever 41 to control the feeding path of the bobbin thread T ₂ and also controls the bobbin thread feeding amount.

In FIG. 16, an eccentric cam 43 is attached to the lower shaft 42,
The eccentric cam 43 engages with the forked rod 44, the forked rod 44 engages with the feeding arm 46 via the pin 45, and the feeding arm 46 has a pair of bearings 47.
It is screwed to a feeding shaft 48 which is rotatably supported by. A feeding lever 41 is attached to the feeding shaft 48.

The vicinity of the middle of the bifurcated rod 44 is engaged with the adjuster 49 via a square sesame (not shown), and the adjuster 49 is controlled in posture by the pulse motor 50 via the link mechanism 51.
With this, the swing amount of the feeding lever is controlled.

Reference numeral 52 is a thread guide plate, the details of which are the rising portions as shown in FIG.
52a is formed. 52b is an upper surface portion. Thread guide plate 52
The position of the rising portion 52a of the needle plate 60
Is displaced to the left with respect to the line segment d passing through the center of the.

Movement of needle drop point and control of bobbin thread feeding mechanism When the current stitch changes from the previous left baseline stitch to the right baseline stitch as shown in Fig. 13, as shown in Fig. 18 By controlling the lower surface of the lever 41 at the uppermost position 41a (balance thread tightening phase) to be above the upper surface portion 52b of the lower thread guide plate 52, the lower thread T ₂ can be moved as shown by the solid line in FIG. The lower thread guide plate 52 and the rising portion 52a are not locked and pulled out independently. Hereinafter, this condition is referred to as a rightward condition. In this case, the bobbin thread feeding amount is controlled by controlling the swing amount l ₁ between the lower surfaces of the uppermost position 41a and the lowermost position 41b of the yarn feeding lever 41 within the range satisfying the rightward condition as shown in FIG. It is done by

Next, when the stitch is changed from the right baseline stitch to the left baseline stitch as shown in FIG. 14, as shown in FIG.
The lower thread at the uppermost position 41c (balance thread tightening phase) is controlled to be lower than the upper surface portion 52b of the upper surface plate 52 of the thread guide plate 52, so that the lower thread T ₂ is shown by the dotted line in FIG. Thus, the lower thread guide plate 52 is pulled out in a state of being locked to the rising portion 52a. Hereinafter, this condition is referred to as a leftward condition. In this case, the control of the bobbin thread feeding amount is performed as shown in FIG.
It is performed by controlling the swing amount l ₂ between the lower surfaces of 1d.

In these cases, as shown in FIG. 20, the position of the rising portion 52a of the thread guide plate 52 is displaced to the left with respect to the line segment d passing through the center of the needle plate needle hole 60. As for the bobbin thread path after the formation of the left baseline seam, the path after the formation of the right baseline seam is longer than the path after the formation of the left baseline seam, as indicated by the solid line and the dotted line, respectively.

Therefore, the relationship between the swing amount l ₁ when forming the right baseline stitch and the swing amount l ₂ when forming the left baseline stitch is l ₁ > l ₂ .

The swing amounts l ₁ and l ₂ as variables in the rightward condition and the leftward condition are controlled to appropriate values according to the amplitude amount and the feed amount of the stitch, respectively, even when the maximum amplitude is not set. .

These controls are control programs stored in the storage device (ROM) of the sewing machine, and are performed based on the pattern data by a control program that is different for each mode selected by the thread tension device 55.

(Operation) The operation of the embodiment of the present invention will be described below. By rotating the thread tension dial 16 of the thread tension device and aligning each display with the instruction line of the sewing machine, the following three control modes are selected.

This will be described below with reference to FIG.

"Auto" mode Rotate the thread tension dial 16 to display "Auto" on the instruction line 71.
, The needle thread tension is set to a certain value within the control range by the groove cam A, and the slide switch 24 is switched to the first step shown in FIG. 8 by the groove cam B.
The LED for "auto" (LED1) lights up in the LED display section, and the bobbin thread delivering control mode by the bobbin thread delivering mechanism 40 is the mode I in FIG.

As described above, the mode I is a mode in which the upper and lower threads are entangled in the left and right stitches so that the entangled relationship between the left and right stitches is even.

"Thin" mode Rotate the thread tension dial 16 to move the indication line 71 to "Thin"
When the indication of is adjusted, the groove thread A sets the needle thread tension to the minimum value within the control range, and the groove cam B switches the slide switch 24 to the second stage shown in FIG. The "Manual" LED (LED2) lights up, and the bobbin thread delivery control mode by the bobbin thread delivery mechanism 40 is the 21st
It becomes the mode of II in the figure. This II mode has the same control method as that of I mode, but the amount of delivery is largely extended by a value obtained by multiplying the amount of extension by a certain expansion rate α with respect to I mode. This is a mode in which the upper and lower threads are entangled in the seam evenly in the left and right.

"0-9" mode Rotate the thread tension dial 16 to move the indication line 71 to "0-9".
When the indication of the range is matched, the groove cam A sets the needle thread tension in the range from the minimum value to the maximum value within the control range corresponding to the indication of "0-9", and the groove cam B causes the slide switch 24 to move. Since it can be switched to the third stage shown in FIG. 10, LE
The LED (LED2) for "manual" lights up on the D display, and the bobbin thread feeding control mode by the bobbin thread feeding mechanism 40 is the mode of I in Fig. 21 in the range of small numbers, and the same in the range of large numbers. It becomes the mode of II. The modes of I and II are the same as those explained in the modes of "auto" and "thin", respectively. As described above, the left and right seams of the upper and lower threads are over the display range of the numbers "0 to 9". The confounding relationship is controlled evenly on the left and right.

(Effect) As described above, according to the present invention, firstly, the thread tension dial is provided with indications of various sewing modes, and rotation of the thread tension dial controls not only the upper thread tension but also the lower thread path and the feeding amount. Since the electric switch for generating a signal for controlling the thread feeding mechanism is switched, it is possible to sufficiently cope with various sewing conditions.

Secondly, in addition to each display for manual control on the thread tension dial, the display of "auto" is provided at the end of the rotation control range, so it is easy to select "auto" which is frequently used.
It has the effect of being excellent in operability.

Thirdly, the LE switch for controlling the bobbin thread feeding mechanism according to the display of the thread tension dial by switching the electric switch and the LE for automatic display.
Since the combination of D and the display switching of the manual display LED is determined, there is an effect that the selected control mode can be correctly recognized.

Fourthly, the spring receiver of the thread tension device is brought into contact with one end of the thread tension spring, and the spring receiving screw having the gear-shaped knurled portion formed on the flange portion is screwed into the leaf spring attached to the spring bearing. Since it is configured to engage with the knurled portion and lock the rotation of the spring receiving screw, there is an effect that the initial setting of the needle thread tension can be easily performed.

Fifthly, in the tray receiver of the thread tension device, the U-shaped groove formed below the tray receiver engages with the groove portion of the pin fixed to the base plate, and the engaging portion serves as a fulcrum for the insertion hole of the tray receiver. Since a pair of conical projections formed on the left and right sides press the thread tension disc from the back side, the length from the fulcrum to the pinching part of the upper thread of the thread tension disc is larger than the fulcrum by the tension spring. The effect of being able to set the rotation operating force of the thread tension dial of the thread tension device to a relatively small value as a result of the length of the thread tension spring being set to be relatively small and the spring constant of the thread tension spring being set to a relatively small value. There is.

Sixthly, the separator of the thread tension device is located between the dish receiver on the thread tension shaft and the thread tension spring, or is provided integrally with the dish receiver, and the separator has an inner surface side near the outer circumference of the thread tension disc. Since the protrusions facing each other are formed and the separator is provided coaxially with the thread tension tray or the like, there is an effect that initial adjustment of the mechanism is easy and the mechanism itself is simplified.

[Brief description of drawings]

1 is a front view of the main part of the thread tension device, FIG. 2 is a view taken in the direction of arrow C in FIG. 1, FIG. 3 is a view taken in the direction of arrow D in FIG. FIG. 4 is a sectional view taken along the line EE in FIG.
FIG. 6 is an exploded perspective view of the thread tension device, FIG. 6 is a view showing the relationship between the thread tension tray and the tray receiver, FIG. 7 is a perspective view of a sewing machine according to the present invention, and FIGS. FIG. 11 is a diagram showing each step of switching the slide switch by the dial, FIG. 11 is a diagram showing a relation between each display of the thread tension dial and the lifts of the groove cam A and the groove cam B, and FIG. 12 is a sewing machine control according to the present invention. Block diagrams of the relationship, Figs. 13 and 14 are diagrams showing the relationship between the movement of the needle drop point and the bobbin thread path, Fig. 15 is a perspective view showing an example of zigzag stitches, and Fig. 16 is a bobbin thread feeding. FIG. 17 is a perspective view showing the mechanism, FIG. 17 is a perspective view showing the bobbin thread guide plate, FIG. 18 is a diagram for explaining rightward conditions in the bobbin thread feeding mechanism, and FIG. 19 is a left side condition in the bobbin thread feeding mechanism. Fig. 20 is a diagram for explaining the lower thread path in the left and right needle drops, and Fig. 21 is for turning the thread tension dial of the thread tension device to the display position. It is a diagram showing a relationship between each controlled object. 1 is a base plate, 2 is a thread tension shaft, 4 is a medium plate, 5 is a thread plate, 6
Is a dish receiver, 6a is an insertion hole, 6b is a conical protrusion, 6e is a U-shaped groove, 7 is a pin, 7a is a groove, 8 is a separator, 8a is a protrusion, 10 is a tension spring, and 11 is an auxiliary spring. , 12 are spring bearings, 13
Is a spring receiving screw, 13a is a knurled portion, 14 is a leaf spring, 16
Is a thread tension dial, 24 is a slide switch as an electric switch, 55 is a thread tension device, 70 is a sewing machine, A is a first groove cam, B is a second groove cam, LED1 is an LED for auto, LED
2 is a manual LED, T ₁ is an upper thread, and T ₂ is a lower thread.

Claims (6)

[Claims] 1. A thread tension tray for holding an upper thread between a thread tension shaft fixed to a bed plate and an inner tray, and a thread for urging the thread tension tray against the inner tray via a tray receiver. A thread which is rotatably supported on a bed plate, in which a tension spring, an auxiliary spring concentrically arranged with the spring, and a spring receiver for controlling the biasing force of these springs at a position on the thread tension axis are fitted. The tension dial is provided with a first groove cam for controlling the position of the spring bearing on the thread tension shaft and a second groove cam for switching an electric switch via a switching arm arranged on the bed plate. A thread tension device for a sewing machine, characterized in that a display corresponding to the control by the first and second groove cams is provided on the outer circumference. 2. A thread tension dial according to claim 1, wherein in addition to each display for manual control, a display of "auto" is provided at an end of the rotation control range. Sewing machine thread tension device. 3. A combination of control of the bobbin thread feeding mechanism according to the display of the thread tension dial and switching of the display of the automatic display LED and the manual display LED is determined by switching the electric switch. The thread tension device for a sewing machine according to claim 1 or 2. 4. A spring bearing screw, which is brought into contact with one end of a thread tension spring and has a gear-shaped knurled portion formed on a flange portion, is screwed into the spring bearing, and a leaf spring attached to the spring bearing is the knurled leaf spring. The thread tension device for a sewing machine according to claim 1, 2 or 3, wherein the rotation of the spring receiving screw is locked by engaging with the portion. 5. The dish receiver is a U formed below the dish receiver.
The groove is engaged with the groove of the pin fixed to the base plate, and a pair of conical projections formed on the left and right of the insertion hole of the dish receiver with the engaging portion as a fulcrum press the thread tension disc from the back surface. A thread tension device for a sewing machine according to any one of claims 1, 2, 3, or 4 characterized in that. 6. A separator is provided between the tray receiver on the thread tension shaft and the thread spring, or integrally with the tray receiver, and the separator faces the outer periphery of the thread tray from the inner surface side. A thread tension device for a sewing machine according to any one of claims 1, 2, 3, 4, or 5, wherein a protrusion is formed.