JPS60198191A - Needle thread cutting detector of sewing machine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a needle thread breakage detection device that detects needle thread breakage that occurs during sewing work.

[Prior Art] A conventional thread breakage detection device for this type of sewing machine includes a microswitch between the thread bundle and the sewing machine, and the thread tension is detected by the microswitch. Alternatively, for example, there has been a detection method using a mechanical switch described in Japanese Utility Model Application Publication No. 55-159068, which uses an electrode pin as a fixed contact and a thread take-up spring as a movable contact. Mechanical switches of this type have the disadvantage that wear of the contacts causes poor contact and fluctuations in the detection position, resulting in malfunctions. Furthermore, the technique disclosed in the above-mentioned publication has the disadvantage that sparks are generated when the thread take-up spring separates from the electrode pin, which makes the user feel uneasy and at the same time generates electrical noise. Also,
There is one that uses a semiconductor switch and uses a photocoupler to determine whether or not a thread is present at a specific position.

For example, Japanese Patent Publication No. 46-5421 and Utility Model Application Publication No. 1983-
An example of this is the technique described in Japanese Patent No. 84252. In devices that use this type of photocoupler for detection, the settings on the sewing machine are not constant, so malfunctions may occur due to ambient light, or the light emitting surface on the light source side, the light receiving surface on the light receiving element side, etc. Dust, dirt, etc. adhering to the sensor have the disadvantage that the detection operation becomes unstable and the responsiveness decreases.

[Problem of the Invention] The present invention is intended to eliminate the above-mentioned drawbacks, and by using a semiconductor switch, eliminates the drawbacks of mechanical switches and prevents malfunctions caused by dust, dirt, external light, etc.

[Structure of the Invention] According to the present invention, a piezoelectric element is disposed at a location where it comes into contact with a thread take-up spring, and the piezoelectric element is brought into elastic contact with the tension of the thread during use, so that the output of the piezoelectric element during use decreases or disappears. This feature allows for non-contact detection of thread breakage.

[Embodiments of the invention] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the usage state detection means for explaining the present invention. In the figure, 1 is a housing with a built-in mechanism, 2 is a sewing machine motor, 3 is a handwheel connected to the motor 2 by a belt, and 4 is a lower shaft that drives the lid mechanism and the feed mechanism. Reference numeral 5 denotes a timing belt that connects the timing gear 11 fixed to the lower shaft and the timing gear fixed to the upper part 6 which drives the balance mechanism and the &1 rod mechanism.

When the sewing machine motor 2 is powered on, the handwheel 3 is rotated, and the lower shaft 4 and upper shaft 6 are simultaneously rotated. At this time, the lower shaft 4 and the upper shaft 6 are synchronized by the timing belt 5, and the upper shaft 6 drives the point balance side and button frame mechanism, and the lower shaft 4 drives the feed mechanism and lid mechanism, respectively, so the lower shaft 4 or the rotation of the upper shaft 6, the usage state of the sewing machine can be detected.

The usage state detection means of the I-column sewing machine used in this embodiment is a rotating machine provided with a notch fixed to the lower shaft 4. 811a and a photocoupler 12H.

That is, the light receiving section detects whether the light beam from the light emitting section of the photocoupler 12a passes through the notch of the rotary disk 11a,
The output is used as a usage state detection signal. In this embodiment, the rotary disk 11a is provided with two 90 degree notches. The number of notches affects the detection response speed, which will be described later, but just because the number of notches is small does not necessarily mean that the detection response speed will be significantly slower in terms of probability. There is no need to increase the number of notches. Further, the ratio between the notch and the remaining portion does not need to be uniform. That is, unless a special processing circuit is used in the signal processing circuit which will be described later, since the purpose of this means is to detect the usage state of the sewing machine, it is sufficient to output a pulse output of 1η.

Further, in the present embodiment, the use state detection means of the sewing machine has the rotary disk 11a fixed to the lower shaft 4, but may be fixed to the upper shaft 6. ''The rotary plate 11 shown by the dashed line in the J1 figure
b and fo l-t? The sensor 12b is an example.

FIG. 2 is an exploded perspective view of the assembled parts of a sensor mounting portion according to an embodiment of the present invention, and FIG. 3 is a side view showing the relationship between the needle thread and the thread take-up spring. ! FIG. 4 is a front view showing how the thread take-up spring holder is installed.

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It is screwed onto the thread guide plate 21 with +-+-+- screws 27. The guide plate 21 is provided with a mounting hole 21a through which a thread is passed and fixed to the first guide missing part 21b and the main body housing. The thread take-up spring holder 24 is attached to the tip 23a of the coil spring.
The thread take-up spring 23, which has an inverted U-shape, is inserted into the fitting hole 24d and is screwed into the hole 21c of the thread guide plate 21 with a mounting screw 27. At this time, 1 of the thread take-up spring boulder 24
(2) Since the end 23b of the thread take-up spring 23 is fitted into the matching hole 24d, the tip 23a of the thread take-up spring 23 moves within the range of the four moving parts 24G against the tension of (. The thread take-up spring holder 24 is formed with a flange 24b, which is further provided with a mounting hole 24a, into which the sensor support 25 is screwed with a mounting screw 29 via a flat washer 30. .The lead 11A3 of the piezoelectric element 26 is inserted into the hole 24a bored in the other flange 24b.
A cord clamp 28 that supports 4 is screwed with a mounting screw 29. The piezoelectric element 26 has a flat end 25a at the tip of the sensor support 25.
The position is such that the piezoelectric element 26 will not be touched even if it comes into contact with the tip of the piezoelectric element 26. Therefore, due to the tension of the upper thread 31, the piezoelectric element 26 detects that the thread take-up spring 23 comes into contact with the sensor support 25, and outputs a pulse signal accordingly.

In the thread take-up spring 23 configured as described above, an upper thread path is formed in the following tsubo. The upper thread 31 is adjusted to be suppressed by the tension of the thread tensioner 22, is hung on the inverted U-shaped tip 23a of the thread take-up spring 23, and then passed through the hole of the thread take-up 32 and guided to the sewing needle.

Therefore, when sewing is performed in a known manner with the needle thread 31 hooked once as described above, the thread tension of the needle thread 31 hooked on the thread take-up spring 23 is increased for each stitch due to the vertical movement of the thread take-up lever 32. In addition to the thread take-up spring 23, the tip 23a of the thread take-up spring 23 comes into elastic contact with the sensor support 25 at each thread tension, thereby causing the piezoelectric element 26 to generate a pulse. However, if thread breakage occurs, the thread tension J due to the vertical movement of the thread take-up lever 32 will not occur, and the sensor support 25 and the tip 23a of the thread take-up spring 23 will not come into elastic contact, so a pulse will be generated in the piezoelectric element 26. do not. In this embodiment, it is detected that the thread take-up spring 23 comes into elastic contact with the senna support 25 due to the tension of the needle thread 31, but conversely, when the tension of the needle thread 31 disappears, the thread take-up spring 23 detects the tension of the needle thread 31. In order to make elastic contact with the support 25, the sensor support 25 to which the piezoelectric element 26 is bonded may be placed at the bottom.

The output of the piezoelectric element 26 is impedance-converted by the output circuit of the piezoelectric sensor shown in FIG. The output of the piezoelectric element 26 is input to the gate of the FET, and a pulse signal is obtained from both ends of the resistor 2, which is used as a piezoelectric sensor detection signal.

J3 and R1 are resistors, and +VCC is a power supply voltage.

FIG. 6 shows the signal processing circuit after the usage state detection signal a shown in FIG. 1 and the piezoelectric sensor detection signal S shown in FIG. 5 are input. Moreover, FIG. 7 shows the timing chart 1. It should be noted that as the usage state detection signal a and the piezoelectric detection signal a, known amplified and waveform-shaped signals are used as necessary. The signal processing circuit is connected so that the power is turned on at the same time as the sewing machine motor 2 is turned on.

When the sewing machine motor 2 is powered on, the lower shaft 4 rotates.
)A1-A pulse signal, that is, a usage state detection signal a is output from the cover 12a. Furthermore, as the lower shaft 4 rotates, the upper shaft 6 also rotates, and the thread take-up 32 starts to move up and down, so the tension of the thread causes the piezoelectric element 26 to generate a pulse signal, that is,
Piezoelectric sensor detection signal is generated. Usage state detection signal a
is guided to the retrigger type monostable multivibrator 41, and the retrigger type monostable multivibrator 41 is placed in a metastable state at the rising edge of the detection signal a. The quasi-stable period is set to be longer than the pulse period of the usage state detection signal a when the sewing machine motor 2 is rotated at a speed slightly slower than the reference speed. Therefore, under normal sewing machine usage conditions, the output C of the retrigger type monostable multivibrator 41 is H
What's the level status?

Similarly, the piezoelectric sensor detection signal is also guided to the retrigger type monostable multivibrator 42. The re-trigger type ■宕1? centre
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I use something similar to the L2 retrigger type monostable multi-vibration break 41 of my home C-city In+11+. Therefore, the output e of the 1-Riga type monostable multivibrator 42 also changes from 1 to 100 degrees under normal sewing machine usage conditions.

The output 0 and output e are led to a NAND circuit, and when both outputs C and e are at H level, that is, both detection signals a and b
is arriving normally, the output f of the NAND circuit is set to L.
level.

Then, the output C of the retrigger type monostable multivibrator 41 is differentiated by the leading edge differentiator 43, and the monostable multivibrator 44 is triggered by the differential signal, and an ND gate is applied to only the metastable period of the monostable multivibrator 44. This is the signal d that closes the . That is, during signal d, the thread breakage is not determined during the delay in the generation of the piezoelectric sensor detection signal due to loosening of the thread at the time of starting use of the sewing machine. You may also make settings.

Therefore, after the output d of the monostable multi-bi break 44 is inverted to the L level, detection of thread breakage is started. That is, when thread breakage occurs, the piezoelectric sensor detection signal does not generate a pulse output, and the piezoelectric element generates a final pulse.The output of the retriggered monostable multivibrator 42 becomes stable. Invert state. The NAND output f becomes 1 (level), the output q becomes H level, and the light emitting diode LED emits light.

In the signal processing circuit shown in FIG. 6 of this embodiment, the usage state detection signal a is simply used for triggering the re-1~trigger type monostable multivibrator. Avoid generating.

The notch of the rotary disk 11a may generate a trigger timing pulse. Furthermore, if the pulse width of the foil is large, its differential output may be used.

Note that R3 is a bias current setting resistor.

As described above, in this embodiment, the light emitting diode LED
Thread breakage can be visually notified by emitting light, but if the output is 0 and a buzzer or the like is sounded, thread breakage can be detected audibly. However, at this time,
In the processing circuit shown in Figure 6, the light emitting diode is configured to instantaneously emit light to clearly indicate that the circuit is operating normally when the power is turned on, but if a buzzing sound is emitted at the same time, it may cause discomfort. Therefore, it is recommended to close the AND gate by triggering a spreading circuit or a monostable multivibrator when the power is turned on.In this case, the leading edge differentiator circuit 43 and monostable multivibrator of the processing circuit shown in The vibrator 44 becomes unnecessary.

[Effects of the Invention] As described above, the present invention has an upper thread tension and thread take-up lever, and a piezoelectric element fixed to the thread take-up spring each time the thread thread take-up is operated. The piezoelectric element is brought into elastic contact with the sensor support, thereby transmitting pulses from the piezoelectric element to 19
Since the switching operation is performed by a piezoelectric element, it is possible to eliminate defects such as poor contact of mechanical switches, and even if the sensor becomes dirty with dust, dirt, etc., the thread take-up spring can be Since the output is obtained by bringing the sensor into elastic contact with the sensor support, it is not affected in any way.

Furthermore, since no optical detection means is used as a sensor outside the housing of the sewing machine, it is not affected by external light.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a usage state detection means for carrying out the present invention, Fig. 2 is a perspective view of an assembled part of a sensor mounting portion according to an embodiment of the present invention, and Fig. 3 is a needle thread Fig. 4 is a front view showing the installation state of the thread take-up spring holder, Fig. 5 is an output circuit of the piezoelectric sensor of the present invention, and Fig. 6 is a usage state detection signal. FIG. 7 is a timing chart of the signal processing circuit shown in FIG. 6. In the figure, 21... thread guide plate, 22... upper thread tension, 23... thread take-up spring, 25... sensor support, 26... piezoelectric element, 32... thread take-up. In addition, in the figures, the same reference numerals and the same symbols indicate the same or equivalent parts. Patent Applicant: Aisin Seiki Co., Ltd. Agent, Patent Attorney: Takehisa Higuchi (Figure 5 Procedure Amendment Writing Method) July 19, 1980 Patent Application No. 54981 2, Title of Invention Upper thread breakage detection device for sewing machine 3, Relationship with the case of the person making the amendment Patent applicant name (ooi) Aisin Seiki Co., Ltd. Representative Reitai Nakai 4, Agent 500 ffi 0582-62-4722 Name (name) (8973) Patent attorney Higuchi Written by Naozen Take, revised by Akira wI Book 1, Name of the invention, Needle thread breakage detection device for sewing machine 2, Claims (1) Needle thread tension and thread take-up lever, and a stage between them. An upper thread breakage detection device for a sewing machine, characterized in that the thread take-up spring is configured to come into elastic contact with a sensor support to which a piezoelectric element is fixed each time the thread take-up is operated. (2) The upper thread of a sewing machine according to claim 1, characterized in that the sensor support to which the upper thread tension, thread take-up spring and piezoelectric element are fixed is mounted on a thread guide plate and attached to the sewing machine main body. Cut detection device. 3. Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to an upper thread breakage detection device for detecting upper thread breakage that occurs during sewing work. [Prior Art] A conventional thread breakage detection device for this type of sewing machine includes a microswitch provided between the thread bundle and the sewing machine, and the tension of the thread is detected by the microswitch. Or, for example,
There has been a detection method using a mechanical switch which uses an electrode pin as a fixed contact and a thread take-up spring as a movable contact, as described in Japanese Utility Model Application Publication No. 55-159068. Mechanical switches of this type have the disadvantage that wear of the contacts causes poor contact and fluctuations in the detection position, resulting in malfunctions. Furthermore, in the technique disclosed in the above-mentioned publication, sparks are generated when the thread take-up spring separates from the electrode pin, which makes the user feel uneasy and at the same time generates electrical noise. Furthermore, there is a device using a semiconductor switch that uses a photocoupler to determine whether or not a thread is present at a specific position. For example, Japanese Patent Publication No. 46-5421 and Utility Model Application Publication No. 1983-
An example of this is the technique described in Japanese Patent No. 84252. In devices that use this type of photocoupler for detection, the settings on the sewing machine are not constant, so malfunctions may occur due to ambient light, or the light emitting surface on the light source side, the light receiving surface on the light receiving element side, etc. Dust, dirt, etc. adhering to the sensor have the disadvantage that the detection operation becomes unstable and the scent emitting property decreases. [Problem of the Invention] The present invention is intended to eliminate the above-mentioned drawbacks, and by using a semiconductor switch, eliminates the drawbacks of mechanical switches and prevents malfunctions caused by dust, dirt, external light, etc. [Structure of the Invention] According to the present invention, a piezoelectric element is disposed at a location where it comes into contact with a thread take-up spring, and the piezoelectric element is brought into elastic contact with the tension of the thread during use, so that the output of the piezoelectric element during use decreases or disappears. This feature allows thread breakage to be detected without contact. [Embodiments of the Invention] Examples of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the usage state detection means for carrying out the present invention. In the figure, 1 is a housing with a built-in mechanism, 2 is a sewing machine motor, 3 is a handwheel connected to the motor 2 by a belt, and 4 is a lower shaft that drives the lid mechanism and feed Ia mechanism. Reference numeral 5 denotes a timing belt that connects a timing gear fixed to the lower shaft and a timing gear fixed to the upper shaft 6 that drives the balance Ia structure and needle bar mechanism. When the sewing machine motor 2 is powered on, the handwheel 3 is rotated V1, and the lower shaft 4 and upper shaft 6 are simultaneously rotated. At this time, the lower shaft 4 and upper shaft 6 are synchronized by the timing belt 5, and the upper shaft 6 drives the point bar mechanism and needle bar mechanism, and the lower shaft 4 drives the feed mechanism and the lid mechanism, respectively. By detecting the rotation of the shaft 4 or the upper shaft 6, the usage state of the sewing machine can be detected. The usage state detection means of the sewing machine used in this embodiment is implemented by a rotary disk 11a provided with a notch fixed to the lower shaft 4 and a photocoupler 12a. That is, the light receiving section detects whether the light beam from the light emitting section of the photocoupler 12a passes through the notch of the rotary disk 11a,
The output is used as a usage state detection signal. In this embodiment, the rotary disk 11a is provided with two 90 degree notches. The number of notches affects the detection response speed, which will be described later, but just because the number of notches is small does not necessarily mean that the detection response speed will be significantly slower in terms of probability. There is no need to increase the number of notches. Further, the ratio between the notch and the remaining portion does not need to be uniform. That is, unless a special processing circuit is used in the signal processing circuit which will be described later, since the purpose of this means is to detect the usage status of the sewing machine, it is sufficient to obtain a pulse output as its output. Further, in the present embodiment, the usage state detection means of the sewing machine has the rotary disk 11a fixed to the lower shaft 4, but may be fixed to the upper shaft 6. The rotary plate 11'b indicated by the dashed line in FIG.
and photosensor 12b are examples thereof. Fig. 2 is an exploded perspective view of the assembled parts of a sensor mounting section according to an embodiment of the present invention, Fig. 3 is a side view showing the relationship between the needle thread and the thread take-up spring, and Fig. 4 shows how the thread take-up spring holder is attached. It is a front view showing a state. Install the upper thread tension 22 and thread take-up spring holder 24 with the screw 2.
It is screwed onto the thread guide plate 21 at 7. On the guide plate 21,
A mounting hole 21a is provided through which the thread passes and is fixed to the guide portion 21b and the main body housing. Thread take-up spring holder 2
4 is a mounting screw 27 with the thread take-up spring 23 having an inverted U-shaped tip 23a inserted into the fitting hole 24d.
It is screwed into the hole 21c of the thread guide plate 21. At this time, since the end 23b of the thread take-up spring 23 is fitted into the fitting hole 24d of the thread take-up spring boulder 24, the tip 23a of the thread take-up spring 23 moves within the range of the recess 24c against the tension. The thread take-up spring holder 24 is formed with a flange 24b, in which a mounting hole 24a is drilled, into which the sensor support 25 is inserted via a flat washer 30. It is screwed in with a mounting screw 29. A cord clamp 2 that supports the lead wire 34 of the piezoelectric element 26 is inserted into the mounting hole 24a drilled in the other flange 24b.
8 is screwed on with a mounting screw 29. The piezoelectric element 26 is bonded to the flat end 25a of the sensor support 25. The bonding position is such that even if the tip 23a of the thread take-up spring 23 comes into contact with the tip of the sensor support 25, it does not touch the piezoelectric element 26. Therefore, the tension of the needle thread 31 causes the piezoelectric element 26 to move the thread take-up spring 23 to the sensor support 25.
It detects that it is in contact with the object, and outputs a pulse signal 1- in response to the detection. In the thread take-up spring 23 configured as described above, an upper thread path is formed as follows. The upper thread 31 is adjusted to be suppressed by the tension of the thread tensioner 22, and after being hung on the inverted U-shaped tip 23a of the thread take-up spring 23, it passes through the hole of the thread take-up 32 and is guided to the sewing needle. Therefore, when sewing is performed in a known manner with the needle thread 31 hooked as described above, the thread tension of the needle thread 31 hooked on the thread take-up spring 23 is increased by the vertical movement of the thread take-up spring 23 for each stitch. 23, the tip 23a of the thread take-up spring 23 makes elastic contact with the sensor support 25 for each thread tension,
This causes the piezoelectric element 26 to generate a pulse. However, when thread breakage occurs, no thread tension is generated due to the vertical movement of the thread take-up lever 32, and the sensor support 25 and the tip 23a of the thread take-up spring 23 do not come into elastic contact, so that no pulse is generated in the piezoelectric element 26. In this embodiment, it is detected that the thread take-up spring 23 comes into elastic contact with the sensor support 25 due to the tension of the needle thread 31, but conversely, when the tension of the needle thread 31 disappears, the thread take-up spring 23 contacts the sensor support 25 due to the tension of the needle thread 31. In order to make elastic contact with the support 25, the sensor support 25 to which the piezoelectric element 26 is bonded may be placed at the bottom. The output of the piezoelectric element 26 is impedance-converted by the output circuit of the piezoelectric sensor shown in FIG. The output of the piezoelectric element 26 is input to the gate of the FET, and a pulse signal is obtained from both ends of the resistor R2, which is used as a piezoelectric sensor detection signal. Note that R1 is a resistor, +vcc1. Lightning 8! It is voltage. FIG. 6 shows the signal processing circuit after receiving the usage state detection signal a shown in FIG. 1 and the piezoelectric sensor detection signal S shown in FIG. 5. Moreover, FIG. 7 is a timing chart thereof. It should be noted that as the usage state detection signal a and the piezoelectric sensor detection signal a, known amplified and waveform-shaped signals are used as necessary. The signal processing circuit is connected so that the power is turned on at the same time as the sewing machine motor 2 is turned on. When the sewing machine motor 2 is powered on, the lower shaft 4 rotates.
A pulse signal, that is, a usage state detection signal a is output from the photocoupler 12a. Further, as the lower shaft 4 rotates, the upper shaft 6 also rotates, and the thread take-up 32 starts to move up and down, so that the piezoelectric element 26 generates a pulse signal, that is, a piezoelectric sensor detection signal, due to the tension of the thread. The usage state detection signal a is guided to a retrigger type monostable multi-bi break 41,
At the rising edge of the detection signal a, the retrigger type monostable multi-bi break 41 is brought into a metastable state. The metastable period is
The pulse period is set to be equal to or longer than the pulse period of the usage state detection signal a when the sewing machine motor 2 is rotated at a speed considerably slower than the reference speed. Therefore, when the sewing machine is normally used, the output C of the retrigger type monostable multivibrator 41 is in the truvel state. Similarly, the piezoelectric sensor detection signal is also guided to the retrigger type monostable multivibrator 42. The metastable period of the retrigger type monostable multivibrator 42 is approximately 6, which is the same as that of the above two retrigger type monostable multivibrator 41. Therefore, the output e of the retrigger type monostable multivibrator 42 is also at the H level when the sewing machine is normally used. The outputs C and e are led to a NAND circuit, and when the outputs C and e are at H level, that is, the rain detection signals a and b are
is arriving normally, the output f of the NAND circuit is set to L.
level. Then, the output C of the retrigger type monostable multivibrator 41 is differentiated by a leading edge differentiating circuit 43, and the differentiated signal triggers the monostable multivibrator 44, which is a signal that closes the AND gate only during the metastable period of the monostable multivibrator 44. d. That is, during signal d, thread breakage is not determined during the delay in the generation of piezoelectric sensor detection signal s due to loosening of thread at the time of starting use of the sewing machine.
Settings between them may be made using a counter. Therefore, after the output d of the monostable multivibrator 44 is inverted to the L level, detection of thread breakage is started. That is, when thread breakage occurs, a pulse output is not generated immediately after the piezoelectric sensor detection signal, and the output of the retrigger type monostable multivibrator 42 triggered by the final pulse generated by the piezoelectric element is reversed to a stable state. . NAND output f
The output becomes -bell, the output q becomes H level, and the light emitting diode LED emits light. In the signal processing circuit shown in FIG. 6 of this embodiment, since the usage state detection signal a is only used to trigger the retrigger type monostable multivibrator, the usage state detection signal a is generated as described above. let The notch of the rotary disk 11a may generate a trigger timing pulse. Furthermore, if the pulse width of the foil is large, its differential output may be used. Note that R3 is a bias current setting resistor. As described above, in this embodiment, the light emitting diode LED
Thread breakage can be visually notified by emitting light from the thread, but furthermore, by making a beep or the like sound using the output q, thread breakage can be detected audibly. However, at this time,
In the processing circuit shown in Figure 6, the light emitting diode is configured to instantaneously emit light to clearly indicate that the circuit is operating normally when the power is turned on, but if the buzzer sounds at the same time, it will cause discomfort. Therefore, it is preferable to trigger a delay circuit, a monostable multivibrator, etc. from 1 to 1 when the power is turned on, and close the AND gate during that time. In this case, the leading edge differentiator circuit 43 and monostable multivibrator 44 of the processing circuit shown in FIG. 6 become unnecessary. [Effects of the Invention] As described above, the present invention has an upper thread tension and thread take-up lever, and a piezoelectric element fixed to the thread take-up spring each time the thread thread take-up is operated. Since the piezoelectric element is configured to make elastic contact with the sensor support and thereby obtain pulses from the piezoelectric element, the switching operation is performed by the piezoelectric element, eliminating defects such as contact failure of mechanical switches. Moreover, even if the sensor becomes dirty with dust, dirt, etc., there is no negative impact because the output is obtained by bringing the thread take-up spring into elastic contact with the sensor support. Furthermore, since no optical detection means is used as a sensor outside the housing of the sewing machine, it is not affected by external light. 4. Brief description of the drawings FIG. 1 is a perspective view of a usage state detection means for carrying out the present invention, FIG. Fig. 3 is a side view showing the relationship between the needle thread and the thread take-up spring, Fig. 4 is a front view showing the installation state of the thread take-up spring holder, Fig. 5 is the output circuit of the piezoelectric sensor of the present invention, and Fig. 6 is a side view showing the relationship between the needle thread and the thread take-up spring. is a signal processing circuit diagram after inputting a usage state detection signal and a piezoelectric sensor detection signal, and FIG. 7 is a timing pulse of the signal processing circuit shown in FIG. 6. In the figure, 21... Thread guide plate, 22... Upper thread tension, 23... Thread take-up spring, 25... Sensor support, 26... Piezoelectric element, 31... Needle thread, 32... ...It's a balance. In addition, in the figures, the same reference numerals and the same symbols indicate the same or equivalent parts. Patent applicant: Aisin Seiki Co., Ltd. Representative: Takehisa Higuchi

Claims (2)

[Claims] (1) The upper thread tension and the thread take-up lever and the thread take-up spring provided between them cause the thread take-up spring to come into elastic contact with the sensor support to which the piezoelectric element is fixed each time the thread take-up is operated. This is a needle thread breakage detection device for sewing machines. (2) The upper thread of a sewing machine according to claim 1, characterized in that the sensor support to which the upper thread tension, thread take-up spring and piezoelectric element are fixed is mounted on a thread guide plate and attached to the sewing machine main body. Cut detection device.