JPH07662A - Thread tension detecting device for sewing machine - Google Patents

Abstract

PURPOSE:To provide an inexpensive thread tension detecting device for sewing machine capable of precisely detecting a thread tension at sewing start or even when the rotating speed of a sewing machine is changed. CONSTITUTION:Thead tension detecting devices 17, 20 for sewing machine arranged in the thread guide from a thread supplying source 12 to a thread consuming part 19 to detect the thread tension by the contact with the thread and having a piezoelectric element at least in a part are intended, and they have an oscillation output means for voltage or current-driving the piezoelectric element by the resonance frequency or anti-resonance frequency of the piezoelectric element, and a voltage waveform detecting means for detecting the voltage waveform given to the piezoelectric element by the oscillation output means. Further, the devices have a current waveform detecting means for detecting the current waveform given to the piezoelectric element by the oscillation output means, and a tension detecting means for detecting the thread tension on the basis of the voltage waveform and the current waveform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thread tension detecting device for a sewing machine which detects a thread tension by using a piezoelectric element.

[0002]

2. Description of the Related Art Conventionally, a so-called automatic thread tension sewing machine which detects the tension of a thread by a tension detecting device and operates a thread tension adjusting device according to the detected value to automatically adjust the tension for sewing. Some sewing machines detect thread breakage by detecting whether or not the thread is in contact.

Piezoelectric elements and strain gauges capable of high-speed response are used as tension sensors in such sewing machines.

For example, in a bobbin thread breakage detecting device of a sewing machine disclosed in Japanese Patent Publication No. 59-31357, a piezoelectric element is installed at a position where the bobbin thread can come into contact with the bobbin thread. The bobbin thread breakage was detected by the presence or absence of the generated voltage.

Generally, when the tension is detected by directly using the piezoelectric effect of the piezoelectric element, the internal resistance of the piezoelectric element or the input leakage current of the amplifier connected to the output side of the piezoelectric element causes
Because the electric charge and voltage generated in the piezoelectric element fluctuates,
For the purpose of removing the influence of this fluctuation, a capacitor for cutting a direct current component was inserted between the piezoelectric element and the amplifier.

The detection of the yarn breakage is a binary value indicating whether or not the yarn breakage occurs. Therefore, the AC component of the tension value is detected by appropriately selecting the threshold value for the binarization. It was possible to judge the thread breakage only with this.

[0007]

However, in the automatic thread tension sewing machine, the steady magnitude of the thread tension, that is, the DC component value and the shape of the thread tension waveform are required as the thread tension information. In the method using the piezoelectric effect of the piezoelectric element described above, the capacitor inserted between the piezoelectric element and the amplifier acts so as to make the DC component of the yarn tension detection waveform zero, so when the shape of the tension waveform changes. , For example, when tension suddenly appears from the state of zero tension, such as at the start of sewing shown in FIG. 7,
There is a problem in that the tension detection waveform is transiently disturbed by charging / discharging the DC level to the capacitor, and the thread tension cannot be detected accurately.

For this reason, a strain gauge capable of detecting a DC tension is actually used. However, although a strain gauge can detect a steady tension, it has a low sensitivity and must be used in a bridge structure. There was a problem that the cost was high.

On the other hand, as in the thread detecting device of the sewing machine described in Japanese Patent Application Laid-Open No. 1-129881, the piezoelectric element is arranged in a self-resonant state at a position where it can come into contact with the upper thread, and the upper thread and the piezoelectric element are separated. Sewing machines that detect needle thread breakage based on a decrease in self-resonant voltage due to contact have been known, but no method for outputting a thread tension waveform applicable to an automatic thread tension sewing machine has been shown.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to make it possible to detect the thread tension including the direct current component, so that the sewing start time and the rotation speed of the sewing machine can be An object of the present invention is to provide an inexpensive thread tension detecting device for a sewing machine that can accurately detect the thread tension even when the thread tension changes.

[0011]

To achieve this object, the present invention is arranged in a yarn path from a yarn supply source to a yarn consuming portion and detects a yarn tension by contacting the yarn, and at least one of them is detected. In a thread tension detecting device for a sewing machine having a piezoelectric element in its portion, an oscillation output means for driving the piezoelectric element by voltage or current at a resonance frequency or an anti-resonance frequency of the piezoelectric element, and the oscillation output means provides the piezoelectric element with the oscillation output means. Voltage waveform detecting means for detecting a voltage waveform, current waveform detecting means for detecting a current waveform applied to the piezoelectric element by the oscillation output means, and tension for detecting a yarn tension based on the voltage waveform and the current waveform. It is equipped with detection means.

The tension detecting means may detect the thread tension based on the phase difference between the voltage waveform and the current waveform.

Further, the tension detecting means may detect the yarn tension based on an amplitude ratio between the voltage waveform and the current waveform.

[0014]

In the thread tension detecting device for a sewing machine of the present invention having the above structure, the oscillation output means drives the piezoelectric element by voltage or current at its resonance frequency or anti-resonance frequency, and the voltage waveform detecting means causes the oscillation. The output means detects the voltage waveform applied to the piezoelectric element, the current waveform detection means detects the current waveform applied to the piezoelectric element by the oscillation output means, and the tension value detection means detects the voltage waveform and the current. The thread tension is detected based on the waveform.

Further, the thread tension can be detected based on the phase difference between the voltage waveform and the current waveform.

Further, the yarn tension can be detected based on the amplitude ratio between the voltage waveform and the current waveform.

[0017]

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

First, a schematic configuration of a first embodiment of a thread tension detecting device for a sewing machine according to the present invention will be described with reference to FIG.

That is, the sewing machine arm 10 has an upper thread supply source 12 as a bobbin-shaped thread supply source for feeding the upper thread 11.
An upper thread tension adjusting device 13, thread hooks 14, 15, and 16, an upper thread tension detector 17, a balance 18 that moves up and down in synchronization with a sewing machine spindle (not shown), and a sewing needle 19 as a thread consuming portion are installed. On the other hand, the needle thread tension adjusting device 13, the needle thread tension detector 17, and the sewing machine control device 2 for controlling the sewing machine spindle.
0 is installed near the sewing machine arm 10. Here, the thread tension detecting device is constituted by the needle thread tension detector 17 and the sewing machine controller 20.

Upper thread 11 fed from upper thread supply source 12
Passes through the needle thread tension adjusting device 13, the thread hooks 14, 15, the needle thread tension detector 17, the thread hook 16, and the balance 18, and then the sewing needle 1
9 is supplied.

The needle thread tension adjusting device 13 is constructed so as to sandwich the needle thread between two tension discs, and the clamping pressure applied to the needle thread by the tone disc is adjusted by an electromagnetic actuator (not shown). .

The needle thread tension detector 17 is, as shown in FIG. 2, a rectangular plate-shaped piezoelectric element 17a having electrodes on the upper and lower surfaces.
And the upper thread 11 fixed to the longitudinal end of the piezoelectric element 17a.
And the sewing machine arm 1 which holds the central portion of the piezoelectric element 17a in the longitudinal direction by contacting with the sensor thread hook 17b for transmitting the needle thread tension.
It is configured by a holding body 17c for attaching to 0.

The sewing machine control device 20 has an oscillator 21 as an oscillation output means for generating a sine wave having a resonance frequency with respect to the longitudinal direction of the piezoelectric element 17a, and a voltage of the oscillator 21 is power-amplified and given to one electrode of the piezoelectric element 17a. The buffer amplifier 22 (also serving as voltage waveform detection means) and the piezoelectric element 1
7a connected to the other electrode of the piezoelectric element 17a
The current-voltage converter 23 as a current waveform detecting means for inverting the polarity of the current flowing in the current and converting it into a voltage, and the needle thread tension is calculated from the phase difference between the output signal of the buffer amplifier 22 and the output signal of the current-voltage converter 23. Phase comparison circuit 24 as a tension detecting means for outputting a voltage, an actuator drive circuit 25 for driving an electromagnetic actuator in the needle thread tension adjusting device 13, and an actuator drive based on the needle thread tension value output from the phase comparison circuit 24. The sewing machine control circuit 26 has a function of operating the circuit 25 and controls the rotation of the sewing machine main shaft.

Buffer amplifier 22 and current-voltage converter 2
3 is configured by using a well-known operational amplifier, and in particular, the current-voltage converter 23 can detect a current while keeping the input terminal at 0 volt by the well-known virtual ground operation of the operation amplifier input. is there.

In the phase comparison circuit 24, the buffer amplifier 2
2 and the output signal of the current-voltage converter 23 are compared with 0 volt by the well-known analog comparators 25 and 26, respectively, and further applied to the well-known exclusive OR circuit 27.
Logically inverted by the NOT circuit 28, smoothed by the integration circuit 29 composed of a resistor and a capacitor, and the tension value output 3
It is output to 0.

The first embodiment is constructed as described above.

The thread tension detecting action of the sewing machine based on the above construction will be described below.

First, the piezoelectric element 17a is driven through a buffer amplifier 22 by an oscillator 21 which oscillates at a resonance frequency in the longitudinal direction with respect to the holder 17c. Piezoelectric element 1
7a has the characteristics that the impedance is minimal at the resonance frequency and the phase difference between the voltage and the current is zero.
FIG. 3A shows the output of the buffer amplifier 22 applied to the piezoelectric element 17a, so-called voltage waveform V, and the output of the current-voltage converter 23 that converts the current flowing through the piezoelectric element 17a into a voltage value, so-called current waveform I. The output waveform is shown.

2 and 3A, since the current-voltage converter 23 is an inverting amplifier, the piezoelectric element 17a
When the thread tension is not applied to V, the phase difference between V and I is 180 degrees, as shown by I (zero tension), and the phases are inverted. Here, when the upper thread 11 is pulled upward and a tension is applied to the piezoelectric element 17a through the sensor thread hook 17b, an advance phase is obtained with respect to the waveform of I (zero tension) as indicated by I (large tension), The greater the tension, the greater the amount of phase advance. Needle thread tension is applied I
The operation of the phase comparison circuit 24 in the case of (high tension) will be described. As shown in FIG.
Is +5 volts for the positive half-wave of the voltage waveform V and 0 for the negative half-wave.
Output as volt. Further, as shown in FIG. 3C, the analog comparator 26 also outputs a positive half wave of the current waveform I by +5.
Outputs 0 Volts and negative half-wave.

The exclusive OR circuit 27 has 0 volt when the two inputs have the same logic, and +5 when the two inputs have different logics.
Since the voltage is output, the waveform becomes as shown in FIG.
The output of the exclusive OR circuit 27 is applied to the NOT circuit 28, logically inverted, and has a waveform indicated by 280 in FIG. Further, it is smoothed by the integrating circuit 29, and the result of 3 in FIG.
The voltage of the pulse width output from the NOT circuit 28 as shown by the waveform 00 is an averaged voltage. For example, when the phase difference between I (large tension) and I (zero tension) is 45 degrees, +
5 volts × 45 degrees / 180 degrees = 1.25 volts.
Here, since the phase difference between I (zero tension) and V is constant at 180 degrees, if the inverted waveform of V is V1, the pulse width of the output pulse of the NOT circuit 28 becomes the phase difference between V1 and I. Therefore, the tension value output 30 outputs a voltage proportional to the phase difference between V1 and I.

Next, the general operation of the sewing machine using the thread tension detecting device for the sewing machine of the first embodiment will be described.

First, when the sewing machine is activated and sewing is started, the needle thread 11 is pulled upward, so that the piezoelectric element 17a is inserted between the thread hooks 16 and 15 via the sensor thread hook 17b. Tension is applied. As described above, due to the tension applied to the piezoelectric element 17a, the current waveform I detected by the current-voltage converter 23 and the piezoelectric element 17 are detected.
A phase shift occurs with the voltage waveform V applied to a. Therefore, the phase difference between the state in which the tension is not applied and the state in which the tension is applied is detected as the upper thread tension value by the phase comparison circuit 24 and is output to the tension value output 30.
Here, the needle thread tension output to the tension value output 30 is as shown in FIG.
As shown in, the DC component is completely detected. The sewing machine control circuit 26 operates the actuator drive circuit 25 and controls the rotation of the sewing machine spindle based on the needle thread tension value output to the tension value output 30. Sewing is performed based on this control. The actuator drive circuit 25 drives the electromagnetic actuator of the needle thread tension adjusting device 13 to adjust the clamping pressure on the needle thread 11.

By the way, since the piezoelectric element 17a has a minimum impedance at its resonance frequency,
As shown in (a), the amplitude of the current waveform becomes maximum when the tension is zero, and decreases as the applied tension increases. As a tension detecting means of the thread tension detecting device for a sewing machine of the present invention using this phenomenon, a schematic configuration of a second embodiment for detecting the upper thread tension value by the current waveform I will be described with reference to FIG.

That is, in the second embodiment, the phase comparison circuit 24 of the first embodiment is replaced with the amplitude detection circuit 50 shown in FIG. 5, and the current waveform I output from the current-voltage converter 23 is
The only difference is that the voltage waveform V input to the amplitude detection circuit 50 is not used. The amplitude detection circuit 50 is connected to the integration circuit 52 after the output of the current-voltage converter 23 is input to the diode 51, and is output to the tension value output 53. Further, the tension value output 53 is input to the sewing machine control circuit 26. Has been done.

Next, the operation will be described with reference to FIG.
When the yarn tension is not applied to the piezoelectric element 17a in FIG. 5, the current waveform indicated by I (tension zero) is rectified by the diode 51 into a positive half-wave and detected by the integrating circuit 52 to obtain the tension value as I _0. It is output to the output 53. On the other hand, when the thread tension is applied, it is detected similarly and I
Output as _T. In this case, when the thread tension is zero, I
₀ is output, and an output whose magnitude decreases like I _T as the thread tension increases is obtained. Also in the case of the second embodiment, as in the case of the first embodiment, the sewing machine control circuit 2
6 is based on the needle thread tension value output to the tension value output 53,
Sewing is performed by operating the actuator drive circuit 25 and controlling the rotation of the sewing machine main shaft. The actuator drive circuit 25 drives the electromagnetic actuator of the needle thread tension adjusting device 13 to adjust the clamping pressure on the needle thread 11.

In the above-described embodiments, the sine wave voltage is applied to the piezoelectric element 17a, the current at that time is detected, and the tension is detected by the tension detecting means. However, a sine wave current is supplied to the piezoelectric element 17a in advance. It is also possible to detect the voltage at that time and detect the tension by the tension detecting means. A configuration example of the oscillation output, current detection and voltage detection means in this case is shown in FIG. 6 as a third embodiment.

That is, in FIG. 6, the oscillation output means is composed of an oscillator 60 (which also serves as a current waveform detection means) oscillating at the resonance frequency of the piezoelectric element 17a and a constant current amplifier 61 using an operational amplifier, and the voltage detection means is It is composed of a differential amplifier 62 using an operational amplifier. Piezoelectric element 17a
Is connected to a constant current amplifier 61 and is current-driven by a sine wave current. At that time, the voltage applied between the electrodes of the piezoelectric element 17a is detected by the differential amplifier 62. In this configuration, the output of the oscillator 60 as the current waveform I,
The output of the differential amplifier 62 as the voltage waveform V is input to the tension detecting means.

The present invention is not limited to the above-mentioned embodiments, but can be variously modified and used without departing from the scope of the invention. For example, although the output voltage of the buffer amplifier 22 is used as the voltage detection means in the first embodiment, the output voltage of the oscillator 21 may be used. Alternatively, the oscillator 21 may directly drive the piezoelectric element 17a without using the buffer amplifier 22. Further, in order to prevent the inertia of the sensor thread hook 17b from interfering with the high-speed response of tension detection in the needle thread tension detector 17, the piezoelectric element 17a directly contacts the needle thread without using the sensor thread hook 17b. It may be configured as follows.

In the second embodiment, the piezoelectric element 1
Since the amplitude of the sine wave voltage applied to 7a is constant,
Although the tension is detected using only the current waveform I, when the voltage applied to the piezoelectric element 17a changes, the peak value V of the voltage waveform V is further calculated using the voltage waveform V by a circuit similar to the amplitude detection circuit 50. It is also possible to detect _M and normalize it with a voltage such as I ₀ / V _M and I _T / V _M by an operational amplifier to eliminate the influence of voltage fluctuation.

The piezoelectric element has a so-called anti-resonance frequency in which the impedance is maximum and the phase difference between the current and the voltage is zero, in addition to the resonance frequency described in the above embodiment.
For this reason, in the present embodiment, the piezoelectric element is driven at the resonance frequency, but it is driven at the anti-resonance frequency, the voltage and current waveform detecting means detect the voltage and current, and the tension detecting means detects tension. May be

The tension detecting means in this embodiment is
Although it is configured by using an electronic circuit such as an operational amplifier, an analog comparator, and a logical operation element, it is also possible to use a well-known central processing unit (CPU) and perform the operation by software.

Further, in the present embodiment, the tension of the thread guided to the sewing needle 19 as the thread consuming section is detected, but it can also be used for detecting the thread tension at another thread consuming section such as a looper. It is possible.

[0043]

As is apparent from the above description, the thread tension detecting device for a sewing machine of the present invention applies a voltage or current of the resonance frequency or anti-resonance frequency to the piezoelectric element, and the voltage and current at that time are applied. By measuring and detecting the thread tension applied to the piezoelectric element based on the phase difference between the voltage and the current or the ratio of the magnitude of the current and the voltage, it is possible to detect the DC component of the thread tension as well. Even when the tension suddenly changes from the state where the tension is zero, or when the rotation speed of the sewing machine changes, the thread tension can be accurately detected. Further, since a piezoelectric element having a simple structure is used, it has an excellent effect that it can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a sewing machine embodying the present invention.

FIG. 2 is a schematic configuration diagram of a needle thread tension detecting device according to a first embodiment of the present invention.

FIG. 3 is a graph showing a tension detecting operation of first and second embodiments embodying the present invention.

FIG. 4 is a graph showing a needle thread tension waveform detected by the needle thread tension detecting device according to the first embodiment of the present invention.

FIG. 5 is a circuit diagram showing a configuration of tension detecting means in a needle thread tension detecting device according to a second embodiment of the present invention.

FIG. 6 is a circuit diagram showing a configuration of an oscillation output means, a current waveform detection means, and a voltage waveform detection means in a needle thread tension detecting device according to a third embodiment of the invention.

FIG. 7 is a graph showing a needle thread tension waveform detected by a conventional needle thread tension detecting device.

[Explanation of symbols]

 11 needle thread 12 needle thread supply source 17 needle thread tension detector 17a piezoelectric element 19 sewing needle 20 sewing machine controller 21, 60 oscillator 22 buffer amplifier 23 current voltage converter 24 phase comparison circuit 50 amplitude detection circuit 61 constant current amplifier 62 difference Dynamic amplifier

Claims (3)

[Claims] 1. A thread tension detecting device for a sewing machine, which is arranged in a thread path from a thread supply source to a thread consuming section, detects thread tension by contacting the thread, and has a piezoelectric element in at least a part thereof. Oscillation output means for driving the piezoelectric element by voltage or current at the resonance frequency or anti-resonance frequency of the piezoelectric element, voltage waveform detection means for detecting the voltage waveform applied to the piezoelectric element by the oscillation output means, and the oscillation output means A sewing machine comprising: a current waveform detecting means for detecting a current waveform applied to the piezoelectric element by means of; and a tension detecting means for calculating and detecting a yarn tension based on the voltage waveform and the current waveform. Yarn tension detection device. 2. The thread tension detecting device for a sewing machine according to claim 1, wherein the tension detecting means detects the thread tension based on a phase difference between the voltage waveform and the current waveform. 3. The thread tension detecting device for a sewing machine according to claim 1, wherein the tension detecting means detects the thread tension based on an amplitude ratio of the voltage waveform and the current waveform.