JPH10151289A - Thread breakage detection device of sewing machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the thread breakage detection device of sewing machine capable of detecting a thread breakage securely and quickly even if a sewing machine operates at a high speed. SOLUTION: A thread tension signal detected by a piezoelectric element 44 and an electric charge amplifier 54 is detected after the resonance oscillation frequency of a thread tension sensor is removed by a low pass filter 55. A CPU 51 determines the presence/absence of a thread based on a rotation angle of a main shaft rotation sensor 13 and according to a thread tension signal after filtered. A timing signal of the main shaft rotation sensor 13 is delayed according to the delay of a thread tension signal caused by the low pass filter 55. A timing of thread detection is changed according to the rotation frequency of a sewing machine motor 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting thread breakage of a sewing machine.

[0002]

2. Description of the Related Art Conventionally, there is a yarn breakage detecting device which detects the presence or absence of a yarn by measuring the contact pressure with the upper or lower thread of a sewing machine with a tension sensor. Such a yarn breakage detecting device is configured to stop the sewing machine by determining a yarn breakage based on the presence or absence of pressure or vibration generated by a force applied to a tension sensor in contact with a yarn.

[0003] For example, a thread break detecting device of a sewing machine described in Japanese Patent Application Laid-Open No. Hei 8-24460 converts an AC vibration waveform generated at the timing of thread tightening into a DC signal by a rectifier circuit, and the magnitude of the DC signal level is measured. To detect thread breakage.

On the other hand, Japanese Patent Application No. 7-3318 filed by the present applicant has been disclosed.
As shown in the lower thread breakage detecting device of the sewing machine described in No. 67, the contact pressure with the thread is directly detected, and the thread breakage is detected by the magnitude of the contact pressure level.

[0005]

However, in order to cope with high-speed rotation of the sewing machine, that is, to enable detection of a thread tension which fluctuates greatly in a short time, the self-resonance frequency of the tension sensor itself is changed by changing the thread tension. It is necessary to have high rigidity so as to be higher than the frequency corresponding to time.

On the contrary, the self-resonant vibration of the tension sensor is also slowly attenuated, and the vibration of the tension sensor vibrated by the contact with the thread continues for a long period even when the tension sensor is not in contact with the thread. Therefore, when the sewing machine rotates at high speed, the vibration is attenuated only a few stitches after the thread breakage, the thread breakage is detected, and the thread breakage cannot be detected instantaneously.

In particular, when a lower thread tension sensor is installed in a lower thread path from the needle hole of the sewing machine to the bobbin to detect breakage of the lower thread, the upper thread comes into contact with the lower thread tension sensor together with the lower thread. The vibration of the lower thread tension sensor generated by the contact of the upper thread during the high-speed rotation of the sewing machine at 2000 rpm continued until the timing of the lower thread contact. For this reason, when a lower thread break occurs, a vibration signal is output from the lower thread tension sensor even at the timing of the lower thread contact, and therefore, it is determined that there is a lower thread despite the lower thread break, and the lower thread is determined. There was a problem that the cut could not be detected.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a sewing machine thread breakage detecting device capable of reliably and instantaneously detecting a thread breakage even when the sewing machine is rotating at a high speed. With the goal.

[0009]

In order to achieve this object, a yarn breakage detecting device for a sewing machine according to the first aspect of the present invention detects a yarn contact pressure corresponding to a contact with a yarn. A thread breakage judging means for judging the presence or absence of a thread based on the magnitude of the contact pressure detected by the thread tension sensor, and particularly equivalent to a resonance vibration frequency of the thread tension sensor. And a filter means for attenuating the frequency signal component to be changed.

Therefore, the resonance vibration of the tension sensor itself excited by the contact with the yarn is attenuated or eliminated by the filter means, and only the tension component due to the contact with the yarn is detected.

Further, in the sewing machine thread detecting device according to the present invention, the thread contact timing output means for outputting a timing at which the thread should contact the thread tension sensor, and the contact pressure generated by the filter means. A yarn contact timing delay means for delaying the timing output by the yarn contact timing output means in response to a signal delay is provided.

Therefore, the influence of the delay of the signal of the contact pressure by the filter means is canceled by the delay of the thread contact timing, and the presence or absence of the thread can be always detected at the timing when the thread should contact the thread tension sensor. The thread contact timing is output when the rotation angle of the sewing machine becomes a fixed angle. However, since this timing is delayed, the thread breakage can be properly detected regardless of the rotation speed. Further, there is no need to provide a sewing machine rotation speed detecting means for detecting the rotation speed of the sewing machine, so that cost reduction can be realized.

Further, in the sewing machine thread detecting device according to the present invention, a thread contact timing output means for outputting a timing at which a thread should contact the thread tension sensor, and a sewing machine rotational speed for detecting a rotational speed of the sewing machine. Detecting means for changing the thread contact timing according to the number of rotations of the sewing machine detected by the means for detecting the number of rotations of the sewing machine. That is, for example, at the rotation speed A, the thread contact timing is output at the sewing machine rotation angle α, and at the rotation speed B, the thread contact timing is output at the sewing machine rotation angle β.

Accordingly, there is no need to provide a thread contact timing delay means for delaying the thread contact timing, and the cost can be reduced. Further, when a plurality of yarn breakage detecting devices are installed, for example, when both an upper yarn breakage detecting device and a lower yarn breakage detecting device each having a yarn tension sensor so as to have a different resonance vibration frequency, the filter means is used. Thus, even when the contact pressure signal generated by the above has a plurality of different delays, the thread contact timing can be changed and set independently based on the number of rotations of the sewing machine.

Further, the yarn breakage detecting device of the sewing machine according to the present invention is configured to include the yarn tension sensor arranged so as to contact both the lower yarn and the upper yarn.

[0016] Therefore, as in the case of a thread tension sensor arranged in the lower thread path so as to contact both the lower thread and the upper thread, which is often used in a lower thread breakage detecting device, the above-mentioned thread is brought into contact with the upper thread. Even when the large resonance vibration generated in the tension sensor continues until the timing when the lower thread should contact, the resonance vibration is attenuated and removed by the filter means, so that the lower thread breakage can be instantaneously and reliably detected. Also,
Conversely, even when the resonance vibration caused by the contact with the lower thread continues until the timing at which the upper thread should contact, the resonance vibration is attenuated and removed by the filter means, so that the upper thread breakage can be instantaneously and reliably detected. is there.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a sewing machine according to an embodiment of the present invention;

FIG. 1 is an external view of an embroidery sewing machine in which an embodiment of the thread breakage detecting device of the present invention is applied as a lower thread breakage detecting device.

In FIG. 1, the sewing machine is roughly divided into a sewing machine arm 1 and a sewing machine bed 2.

The sewing machine arm 1 is mounted coaxially with the sewing machine spindle 10 and rotates a sewing machine spindle 10, a sewing needle 12 which moves up and down once by one rotation of the sewing machine spindle 10, and a sewing needle 12. And a spindle rotation sensor 13 for detecting the rotation angle of the sewing machine spindle 10 with the angle corresponding to the top dead center as 0 degree. Further, the upper thread 14 is supplied as a seam to the work cloth 15 from an unillustrated thread winding through the eye of the sewing needle 12.

The main shaft rotation sensor 13 is disposed inside the pulley 16 and a pulley 16 coaxially mounted on the main shaft 10 of the sewing machine as shown in a cross-sectional view showing a signal detecting section related to the main shaft of the sewing machine in FIG. The detection unit 17 includes a detection unit 17 and detectors 18 and 19 attached to the sewing machine motor 11 so as to face the detection unit 17 and configured by reflection-type optical sensors. A sheet having a high reflectivity is adhered to the detected portion 17 facing the detector 18 only at an angle corresponding to the needle top dead center position of the sewing needle 12.
A sheet having a slit-like high reflectance portion formed at every 1000-divided angle for one rotation of the sewing machine main shaft 10 is adhered to the detected portion 17 facing the surface 9. A pulse indicating the needle top dead center is output from the detector 18, and a pulse signal of 1000 pulses / rotation is output from the detector 19 for one rotation of the sewing machine main shaft 10.

On the upper surface of the sewing machine bed 2, there are provided a support frame 20 for holding the work cloth 15, and an X motor 21 and a Y motor 22 for moving the support frame 20 in the X and Y directions shown in FIG. Supported.

In the lower part of the sewing machine bed 2, as shown in the external configuration diagram showing the lower thread path in FIG. 3, one rotation of the sewing machine main shaft 10 below the needle plate 30 and one fixed axis line An outer hook 31 that rotates two turns around, and an outer hook 31
And a bobbin 34 rotatably supported therein, and a bobbin 34 rotatably supported in the inner hook 32 and rotatably mounted on the inner hook 32 and wound with a lower thread 33. is set up. Further, the bobbin 34 is housed in a bobbin case 35 which is fitted in the inner hook 32 and cannot be rotated in the rotation direction. The lower thread 33 is attached to the needle plate 30
The work cloth 15 is supplied as a seam through a needle hole 36 formed in the work piece.

The outer hook 31 captures the upper thread 14 supplied by the sewing needle 12 through the needle hole 36 and cooperates with the sewing needle 12 to form a sword tip 37 for forming a seam on the work cloth 15.
A fin 38 is provided for assisting the upper thread 33 to pass over the inner hook 32.

Between the lower surface of the needle plate 30 and the outer hook 31 is provided a cantilever-shaped lower thread tension sensor 40 having one end fixed to the sewing machine bed 2. The bobbin thread tension sensor 40 includes a base parallel portion 41 and a tip parallel portion 42 having a portion substantially parallel to the rotation surface of the outer shuttle 31.
And a thread contact portion 43 which is inclined with respect to the base parallel portion 41 in the direction of the path side of the lower thread 33 and is arranged to always contact the lower thread 33. A piezoelectric element 44 formed by laminating two pieces of piezoelectric ceramics is fixed to the side surface of the base end parallel portion 41 so that the polarization directions are opposite to each other. As is well known, the piezoelectric element 44 generates a charge proportional to the applied strain.
Therefore, the distortion generated in the thread contact portion 43 due to the contact of the lower thread 33 is applied to the piezoelectric element 44 through the base parallel part 41, and a charge proportional to the contact pressure of the lower thread 33 is generated in the piezoelectric element 44. In order to cope with the high-speed rotation of the sewing machine, it is desirable to increase the rigidity of the bobbin thread tension sensor 40 to increase the mechanical self-resonant frequency as much as possible. In the present embodiment, the frequency is set to about 1 kHz.

A sewing machine control device 50 shown in FIG. 4 is installed below the sewing machine bed 2. The sewing machine control device 50 includes a well-known CPU (central processing unit) 5.
1, a RAM (read / write memory) 52, and an RO
M (read only memory) 53, a charge amplifier 54 for converting the charge generated by the piezoelectric element 44 into a voltage, and an attenuator for removing the above-described component of the lower thread tension sensor 40 having a resonance vibration frequency of 1 kHz, for example. Cutoff frequency 5
A low-pass filter 55 of 00 Hz and an output voltage of the low-pass filter 55
An A / D converter 56 to be input to the sewing machine; a sewing data input device 57 to which movement amount and movement speed data of each needle in the X and Y directions of the support frame 20 during embroidery sewing and a rotation speed of the sewing machine motor 11 are input; A timer 58 for generating a clock having a period of 1 μSec.

Further, the CPU 51 can drive the sewing machine motor 11, the X motor 21, and the Y motor 22 through a drive circuit (not shown). In addition, the angle at the time of pulse output indicating the needle top dead center output from the detector 18 in the spindle rotation sensor 13 is set to 0 degree, and the detector 1
9 based on the signal of 1000 pulses / rotation,
The rotation angle of the sewing machine main shaft 10 is generated by a conversion circuit (not shown) and is input to the CPU 51.

The charge amplifier 54 includes an operational amplifier 54a
, A capacitor 54b, and a resistor 54c. The electric charge generated in the piezoelectric element 44 is moved to the capacitor 54b by the operational amplifier 54a and output as a voltage. The resistor 54c is inserted to prevent the voltage output from saturating due to the input leakage current of the operational amplifier 54a, and the time constant of the capacitor 54b and the resistor 54c determines the tension change time of the lower thread at the minimum rotation speed of the sewing machine main shaft 10. It is set to a value that is longer than a few seconds.

A tension threshold value Tth for judging the presence or absence of the lower thread 33 based on the contact pressure of the lower thread 33 is stored in the ROM 53 in advance.

The thread tension sensor of the present invention is provided by the lower thread tension sensor 40, and the thread breakage determining means is provided by the sewing machine controller 50.
The sewing machine stopping means is provided by the sewing machine motor 11 and the sewing machine control device 50; the filter means is provided by the low-pass filter 55; the thread contact timing output means and the thread contact timing changing means are provided by the main shaft rotation sensor 13 and the sewing machine control device 50; The detecting means is constituted by the sewing machine control device 50, respectively.

FIG. 5 is a flowchart showing the operation of the lower thread breakage detecting device of the sewing machine according to the embodiment constructed as described above, FIG. 4 is a block diagram of the sewing machine control device 50, and FIG. This will be described with reference to the drawings. The following operation is performed by the CPU 51 reading out and executing a program stored in the ROM 53 in advance.

First, in S1 (S indicates a step; the same applies hereinafter), embroidery sewing data, that is, movement amount data of the support frame 20 for each needle in the X and Y directions and the sewing machine motor 11 are input in advance from the sewing data input device 57. Is read and stored in the RAM 52. Next, in S2, by driving a drive circuit (not shown), the sewing machine motor 11 is started and sewing is started.

In S3, the rotation speed of the sewing machine motor 11 is adjusted according to the rotation speed of the sewing machine motor 11 stored in the RAM 52.

Next, in step S4, the time interval of the pulse output from the detector 19 in the spindle rotation sensor 13 is measured based on a clock having a period of 1 μS generated by the timer 58, so that the actual sewing machine motor 11 The rotation speed is detected. That is, if the rotation speed of the sewing machine main shaft 10 mounted coaxially with the sewing machine motor 11 is R [rpm],
If the number of clocks output by the timer 58 during the time corresponding to one pulse output from the detector 19 is n, the sewing machine rotation speed R is detected as an equation of R = 60 * 1000 / n.

Now, the waveform detected by the lower thread tension sensor 40 and the timing of detecting the presence or absence of the lower thread 33 will be described with reference to the tension waveform diagram with respect to the rotation angle of the sewing machine spindle 10 shown in FIG. A description will be given based on an external configuration diagram showing a yarn path.

FIGS. 6A to 6C show sewing machine rotation speeds of 300.
6 (d) to 6 (g) show tension voltage waveforms at a rotation speed of the sewing machine of 2000 rpm, and FIGS. 6 (a), (d) and (b), (e) show lower thread respectively. 33 (c), (f) and (g) show the voltage of the output 60 of the charge amplifier 54 and the voltage of the output 61 of the low-pass filter 55 when there is the lower thread 33, respectively. 2 shows the voltage of the output 60 and the voltage of the output 61 of the low-pass filter 55.

As shown in the waveform after the filtering at the rotation speed of the sewing machine of 300 rpm in FIG. 6B, the tension of the lower thread 33 shown in FIG. 3 is between about 30 degrees and about 120 degrees of the rotation angle of the main shaft 10 of the sewing machine. Out of which about 30-
The tension having a peak at 90 degrees is the pulling tension of the lower thread 33 due to the movement of the work cloth 15, and the tension having a peak at about 90 to 120 degrees is the tension generated when the lower thread 33 is pulled out by the fin 38 of the outer hook 31. It is.

Here, as shown in the waveform diagram of FIG.
The lower thread 33 at a rotation angle of 30 to 120 degrees of the above-described sewing machine spindle 10 comes into contact with the lower thread tension sensor 40,
In the vicinity of 270 degrees, the upper thread 14 which is captured by the sword 37 and drawn into the lower portion of the inner hook 32 at high speed also comes into contact. As described above, the lower thread tension sensor 40 is about 1 kHz.
6 (a) and 6 (c), compared with the tension waveforms in the case of the sewing machine rotation speed 300 rpm in FIG.
(D), sewing machine rotation speed 2000 rpm shown in (f)
In the tension waveform in the case of, the attenuation of the resonance vibration is relatively delayed.

Therefore, when the sewing machine is rotating at a low speed such as 300 rpm, the vibration generated in the lower thread tension sensor 40 due to the contact of the upper thread 14 at the sewing machine main shaft rotation angle of 270 degrees as shown in FIG. Sewing machine spindle 10
Is attenuated before the rotation angle of 30 degrees, and the absence of the lower thread can be detected.

However, as shown in FIGS. 6 (d) and 6 (f), at the time of high-speed rotation of the sewing machine rotation speed of 2000 rpm,
The large vibration generated in the lower thread tension sensor 40 due to the contact of the upper thread 14 at the sewing machine main shaft rotation angle 270 degrees with or without the lower thread 33 reaches the contact timing of the lower thread 33 at the sewing machine main shaft rotation angle 30 to 120 degrees. 6 (f). Therefore, even when the lower thread is not provided in FIG.
At 0 degrees, an output is generated due to the resonance vibration of the lower thread tension sensor 40. However, as shown in the voltage waveform of the output 61 in FIG. 6G, the resonance vibration component is removed by the low-pass filter 55.

Incidentally, while the above-described low-pass filter 55 can remove the resonance vibration component of the lower thread tension sensor 40, the cut-off frequency of the low-pass filter 55 is 500H.
By z, the tension voltage waveform at the output 61 is delayed from the actual tension waveform detected by the lower thread tension sensor 40 by 2 ms, that is, by the cycle indicated by the reciprocal of the cutoff frequency. Therefore, it is necessary to change the lower thread tension detection angle by delaying the lower thread tension detection angle by the angle Δθ [degree] shown in the following equation in accordance with the delay time. Here, R is the number of revolutions of the sewing machine [rpm] detected in step S4.

Δθ = 0.002 * (R / 60) * 360 In S5 in the flowchart of FIG. 5, the above-mentioned Δθ is calculated.

Next, in S6, the X stored in the RAM 52 is
The X motor 21 and the Y motor 22 are driven through a drive circuit (not shown) in synchronization with the rotation of the sewing machine main shaft 10 based on the movement amount data in the Y direction and the support frame 20 and the work cloth 15 supported by the support frame 20. Is moved. At the same time, the contact pressure of the lower thread 33 with respect to the thread contact section 43 is detected by the piezoelectric element 44 and read via the charge amplifier 54, the low-pass filter 55, and the A / D converter 55, and the rotation angle (30 + Δθ) of the main shaft 10 of the sewing machine. ) To (1)
The maximum tension voltage Vm at (20 + Δθ) degrees is detected. For example, the rotation speed of the sewing machine is 300 rpm, 2000 rpm.
In the case of 300 m, Δθ is calculated to be 3.6 degrees and 24 degrees, respectively.
FIG. 6 at 2000 rpm between 6 and 123.6 degrees
(E) shows the maximum tension voltage V between 54 and 144 degrees.
m is detected.

Then, in the following S7, the tension threshold value Tt for judging the presence or absence of the bobbin thread 33 stored in the ROM 53
h is compared with the maximum tension voltage Vm. If Vm> Tth, it is determined that there is a lower thread, and the process returns to S3 to sew the next stitch. On the other hand, if Vm ≦ Tth, it is determined that there is no lower thread, and the flow shifts to S8, where the sewing machine motor 11 is stopped.

The present invention is not limited to the above-described embodiment, but can be variously modified and used without departing from the scope of the invention.

For example, in the present embodiment, the low-pass filter 55 is configured not only to cut the resonance frequency of the lower thread tension sensor 40 but also to attenuate and remove noise components higher than the resonance frequency. However, if the high-frequency noise component is at a low level, a band-elimination filter that can attenuate and remove the resonance frequency of the lower thread tension sensor 40 may be used. The delay time for calculating the lower thread tension detection angle is set as the cutoff frequency of the low-pass filter or the reciprocal of the band rejection frequency of the band rejection filter, or the delay time between the input and output waveforms of the actual filter is measured. Alternatively, the filter may be realized by a digital circuit.

The attenuation level of the resonance frequency by the filter is determined by the fact that the signal level of the resonance vibration of the lower thread tension sensor 40 at the maximum number of rotations of the sewing machine used corresponds to the tension threshold value Tth at the detection angle of the presence or absence of the lower thread tension. Any attenuation level may be used as long as the configuration is smaller than that.

In this embodiment, the main spindle 10 for detecting the presence or absence of the lower thread 33 according to the rotation speed of the sewing machine is used.
It is configured to change the rotation angle of
The timing signal from the spindle rotation sensor 13 is configured to be temporally delayed by a time substantially equal to the delay time of the filter. For example, a pulse signal indicating the needle top dead center output from the detector 18 is converted into a similar analog signal. It is also possible to use a filter or a delay circuit or a digital filter or a digital delay circuit so as to delay the signal, and to configure the yarn contact timing delay means.

Further, in this embodiment, Δθ is configured to change continuously with respect to the rotation speed of the sewing machine. However, it may be configured to change stepwise, or may be configured to change stepwise. As described above, Δθ for the detection start and the detection end of the lower thread 33 does not necessarily have to be equal, and may be configured slightly differently.

In this embodiment, the detection of the presence or absence of the bobbin thread 33 is started based on the rotation angle of the sewing machine main shaft 10 of 30 degrees as a reference when the rotation speed of the sewing machine is zero. In the rotation angle before the degree, the upper thread 14 which has passed over the inner hook 32 is an angle at which the upper thread 14 is quickly pulled upward. At this time, the upper thread 14 comes into contact with the lower thread tension sensor 40, and a transitional tension may be generated. Because there is a nature. However,
If the transient tension level at the rotation angle before 30 degrees is small, the lower thread tension detection start angle does not need to be moved by the sewing machine rotation speed, and only the detection end angle may be moved.

Further, in this embodiment, the detection of the presence or absence of the bobbin thread 33 is performed at 30 to 120 degrees as a reference when the rotation speed of the sewing machine is zero. In particular, the sewing machine main shaft from which the bobbin thread 33 is pulled out by the fin 38. Since a large bobbin thread tension is generated around the rotation angle of 100 degrees, the detection angle of the presence or absence of the bobbin thread 33 may be configured to include around 100 degrees when the sewing machine rotation speed is zero.

Further, the lower thread tension sensor 40 of the present embodiment
Is arranged at a position where the lower thread 33 always contacts the lower thread 33 between the needle plate 30 and the outer shuttle 31. However, this is not necessary. Thread 3
3 can be arranged at a position where it makes intermittent contact, or can be provided at any part that can come into contact with the lower thread 33, for example, at the needle hole 36 or hook stop.

Further, in this embodiment, the lower thread breakage detecting device is constituted, but the upper thread 14 determines the rotation angle of the sewing machine main shaft 10 when the rotation speed of the sewing machine is zero.
It is also possible to configure as an upper thread breakage detecting device that detects the presence or absence of the upper thread 14 by making the angle of contact with 0, for example, 240 to 300 degrees.

Also, instead of the lower thread tension sensor 40 in the present embodiment, an upper thread tension sensor installed in the path of the upper thread 14 of the sewing machine arm 1 and detecting the contact pressure of the upper thread is used in the present embodiment. It is configured as the lower thread tension sensor 40, and is configured as an upper thread breakage detection device by configuring the detection angle of the presence or absence of the upper thread 14 when the sewing machine rotation speed is zero as 30 to 90 degrees at which the upper thread tension is generated. It is also possible.

Further, in this embodiment, the lower thread tension sensor 4
Although the distortion of 0 is detected using the piezoelectric effect of the piezoelectric element 44, the distortion of the lower thread tension sensor 40 is converted into an electric signal by detecting the distortion using a resistance change of a strain gauge instead. Any configuration that can be detected by the switch is possible.

Furthermore, the work cloth 15 can be moved in the X and Y directions as in the present embodiment,
The sewing machine motor 11 may be configured to move in the radius and rotation directions, may be configured to move only in one-dimensional direction,
It is also possible to adopt a configuration in which the movement is performed using the power of.

[0057]

As is apparent from the above description, according to the thread break detecting device for a sewing machine according to the first aspect of the present invention, the yarn tension for detecting the contact pressure corresponding to the contact with the yarn. A thread breakage judging means for judging the presence or absence of a thread based on the magnitude of the contact pressure detected by the thread tension sensor, and particularly equivalent to a resonance vibration frequency of the thread tension sensor. And a filter means for attenuating the frequency signal component to be changed.

Therefore, even if the attenuation of the resonance vibration of the tension sensor itself caused by the contact with the yarn is very slow and continues for several stitches after the yarn breaks, the contact pressure signal component due to the resonance vibration is Since it is attenuated or removed by the filter means and only the tension component due to the contact with the yarn is detected, the yarn breakage can be instantaneously and reliably detected.

According to a second aspect of the present invention, there is provided a thread breakage detecting device for a sewing machine, wherein a thread contact timing output means for outputting a timing at which a thread should contact the thread tension sensor, and the contact generated by the filter means. A yarn contact timing delay means for delaying the timing output by the yarn contact timing output means in accordance with the delay of the pressure signal is provided.

Therefore, even when the effect of the delay of the signal of the contact pressure by the filter means becomes large, especially at the time of high-speed rotation of the sewing machine, the effect of the delay is canceled by similarly delaying the thread contact timing, Since the presence or absence of a thread can always be detected at the timing when the thread should come into contact with the thread tension sensor irrespective of the number of rotations of the sewing machine, it is possible to reliably detect a thread break regardless of the number of rotations of the sewing machine. Further, a sewing machine rotation speed detecting means for detecting the rotation speed of the sewing machine is not required, which has an effect of cost reduction.

Further, the thread breakage detecting device for a sewing machine according to claim 3, wherein a thread contact timing output means for outputting a timing at which the thread should contact the thread tension sensor, and a sewing machine rotational speed for detecting the rotational speed of the sewing machine. Detecting means for changing the thread contact timing according to the number of rotations of the sewing machine detected by the means for detecting the number of rotations of the sewing machine.

Therefore, there is no need for a yarn contact timing delay means for delaying the yarn contact timing, which has the effect of reducing costs. Further, when a plurality of thread breakage detecting devices are installed, for example, when both an upper thread breakage detecting device and a lower thread breakage detecting device each having a yarn tension sensor having a different resonance vibration frequency are provided, the filter means generates the same. Even when the contact pressure signal has a plurality of different delays, the thread contact timing can be changed and set independently based on the number of rotations of the sewing machine, so that the configuration is simplified and the cost is reduced.

Further, a thread breakage detecting device for a sewing machine according to a fourth aspect of the present invention includes the thread tension sensor arranged so as to contact both the lower thread and the upper thread.

Therefore, as in the case of a thread tension sensor arranged in the lower thread path so as to contact both the lower thread and the upper thread, which is often used in a lower thread breakage detecting device, the above-described thread is brought into contact with the upper thread. Even when the large resonance vibration generated in the tension sensor continues until the timing when the lower thread should contact, the resonance vibration is attenuated and removed by the filter means, so that the lower thread breakage can be instantaneously and reliably detected. Also,
Conversely, even when the resonance vibration due to the contact with the lower thread continues until the timing at which the upper thread should come into contact, the resonance vibration is attenuated and removed by the filter means, so that the upper thread breakage can be instantly and reliably detected.

[Brief description of the drawings]

FIG. 1 is an external view of an embroidery sewing machine according to an embodiment.

FIG. 2 is a cross-sectional view illustrating a signal detection unit related to a sewing machine main shaft.

FIG. 3 is an external configuration diagram of a sewing mechanism showing a lower thread path.

FIG. 4 is a block diagram showing an electrical control configuration of the embroidery sewing machine according to the embodiment.

FIG. 5 is a flowchart showing a lower thread breakage detecting operation according to the embodiment;

FIGS. 6A to 6C are tension voltage waveform diagrams with respect to the rotation angle of the sewing machine main shaft 10, in which FIGS.
(d) to (g) are tension voltage waveforms at 2,000 rpm of the sewing machine, and (a), (d), (b), and (e) respectively show the lower thread 33.
(C), the voltage of the output 60 of the charge amplifier 54 and the voltage of the output 61 of the low-pass filter 55
(F) and (g) are the voltage of the output 60 of the charge amplifier 54 and the voltage of the output 61 of the low-pass filter 55 when the lower thread 33 is not present, respectively.

[Explanation of symbols]

 11 sewing machine motor 13 main shaft rotation sensor 14 upper thread 33 lower thread 40 lower thread tension sensor 50 sewing machine controller

Claims (4)

[Claims] 1. A yarn tension sensor for detecting a contact pressure corresponding to contact with a yarn, and a yarn breakage determining means for determining the presence or absence of a yarn based on the magnitude of the contact pressure detected by the yarn tension sensor. And a filter means for attenuating a frequency signal component corresponding to a resonance vibration frequency of the thread tension sensor. 2. A yarn contact timing output means for outputting a timing at which a yarn is to be brought into contact with the yarn tension sensor; and a yarn contact timing output means corresponding to a delay of a signal of the contact pressure generated by the filter means. 2. A thread breakage detecting device for a sewing machine according to claim 1, further comprising a thread contact timing delay means for delaying a timing outputted by the thread contact timing. 3. A thread contact timing output means for outputting a timing at which the thread should come into contact with the thread tension sensor; a sewing machine speed detecting means for detecting a speed of the sewing machine; The thread breakage detecting device for a sewing machine according to claim 1 or 2, further comprising a thread contact timing changing unit configured to change the thread contact timing in accordance with the number of rotations of the sewing machine. 4. The thread breakage detecting device for a sewing machine according to claim 1, wherein the thread tension sensor is arranged so as to contact both the lower thread and the upper thread.