JPH07178275A - Device for detecting thread tension of sewing machine - Google Patents

Abstract

PURPOSE:To limit the influence of the detected output fluctuation within the sewing time by one needle and to detect the thread tension by storing the thread tension value where the thread tension is always zero as a reference value at the time of zero tension and detecting the thread tension value by one needle as the relative value from the reference value. CONSTITUTION:A main axis driving circuit 54 is controlled to rotate a sewing machine main axis 16 and the sewing is started. In this case, the tension of an upper thread 11 to be produced by the sewing is detected by a tension detecting device 15 between a thread guide 14 and a balance 17. With the rotation of the main axis 16, a pulse is generated from a main axis rotating sensor 19. Then it is inputted from an input port 52 through an A/D converter 51 to a CPU 57. Further, the signal of a zero tension detecting sensor 20 is inputted to an input port 53. The output reference value of the upper thread tension, that is the reference tension value, stored in a reference tension storage area 561b is subtracted from the upper thread tension value stored in a present tension storage area 56a of a RAM56.

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 of a sewing machine for detecting thread tension.

[0002]

2. Description of the Related Art Conventionally, the tension of a thread is detected by a tension detector, and a thread tension adjusting device is operated according to the detected tension value.
There was a sewing machine that sewed while automatically adjusting the tension.

The thread tension detector in this type of sewing machine is
It is known to detect a yarn tension value by a change in voltage or charge amount caused by the piezoelectric effect of a piezoelectric element or a change in resistance value of a strain gauge.

For example, a conventional needle thread tension detector using a piezoelectric element detects the needle thread tension by the charge and voltage generated in the piezoelectric element, but the leak current of the piezoelectric element and the generation of charge in response to temperature changes are generated. In order to prevent the influence of temperature drift of the amplifier, a high pass filter circuit composed of a capacitor and a resistor for cutting a direct current component has been used. The time constants of the condenser and the resistance are generally set to a value of about several seconds, which is longer than the thread tension change time at the lowest rotation speed of the sewing machine spindle.

On the other hand, a conventional needle thread tension detector using a strain gauge has the effect of temperature drift of resistance of the strain gauge, as in the needle thread tension detector disclosed in Japanese Patent Publication No. 55-22115. In order to remove it, multiple strain gauges were constructed in a bridge shape. Further, in order to reduce the cost, there is a method in which a single strain gauge is used, and a direct current component is cut by a high-pass filter of a capacitor and a resistor as in the case of a piezoelectric element to remove the influence of temperature drift.

[0006]

However, while the temperature drift component can be removed by cutting the direct current component in the high pass filter, it acts so as to make the direct current component of the needle thread tension waveform zero, so that it is particularly effective at the start of sewing. As shown in FIG. 6, when the sewing speed of the sewing machine changes transiently, the level of the needle thread tension waveform gradually decreases as shown in FIG. 6, and the tension level is reduced even when the tension should originally be zero. Became a negative value, making it impossible to properly adjust the needle thread tension based on the absolute tension level.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a sewing machine capable of stably detecting the thread tension even when the temperature and the sewing speed change. An object is to provide a yarn tension detecting device.

[0008]

To achieve this object, a thread tension detecting device for a sewing machine according to the present invention is arranged in a thread path from a thread supply source of a sewing machine to a thread consuming section, and detects thread tension. Yarn tension detecting means, and zero tension phase detecting means for detecting a predetermined spindle rotation phase at which the yarn tension becomes zero,
The reference tension storage means for storing the thread tension output by the thread tension detection means in the phase detected by the zero tension phase detection means, the thread tension value detected by the thread tension detection means, and the reference tension storage means. Compensation thread tension calculation means for calculating a difference from the stored thread tension value is provided.

[0009]

According to the thread tension detecting device for a sewing machine of the present invention having the above structure, the thread tension detecting means arranged in the thread path from the thread supply source of the sewing machine to the thread consuming section detects the thread tension, The zero tension phase detection means detects a predetermined spindle rotation phase at which the thread tension becomes zero, and the reference tension storage means
The thread tension output by the thread tension detecting means in the phase detected by the zero tension phase detecting means is stored. Then, the corrected thread tension calculation means calculates the difference between the thread tension value detected by the thread tension detection means and the thread tension value stored in the reference tension storage means.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to the drawings.

First, a schematic structure of a thread tension detecting device for a sewing machine according to the present invention will be described with reference to FIG. That is, on the sewing machine arm 10, a bobbin 12 serving as a thread supply source for delivering the upper thread 11, an upper thread tension adjusting device 13, a thread hook 14,
An upper thread tension detector 15, a balance 17 that moves up and down once in synchronization with one rotation of the sewing machine main shaft 16, and a sewing needle as a thread consuming portion that similarly moves up and down once to sew one stitch. 18,
Spindle rotation sensor 1 for detecting the rotation angle of the sewing machine spindle 16.
9 and a zero tension phase detection sensor 20 for detecting the main shaft rotation phase at which the needle thread tension becomes zero.

The upper thread 11 supplied from the bobbin winding 12 includes an upper thread tension adjusting device 13, a thread hook 14 and an upper thread tension detector 1.
5, it is supplied to the sewing needle 18 via the balance 17.

The needle thread tension adjusting device 13 is composed of an electromagnetic actuator (not shown) and two tone discs driven by the electromagnetic actuators, whereby the clamping pressure applied to the needle thread by the tone disc can be adjusted. Is configured.

As shown in FIG. 2, the needle thread tension detector 15 is composed of a detector in which a single piezoelectric element 30 and a metal plate 31 are bonded together, and a charge amplifier 35. Thread hooks 32 that come into contact with each other and transmit the thread tension are fixed to the piezoelectric element 30, and one ends of the piezoelectric element 30 and the metal plate 31 are held by a holder 33 fixed to the sewing machine arm 10. Further, the electrode 34 and the metal plate 31 formed on the upper surface of the piezoelectric element 30 are connected to the charge amplifier 35. The charge amplifier 35 includes a well-known operational amplifier 35a, a capacitor 35b for storing charges generated in the piezoelectric element 30, and a resistor 35c for preventing the output from being saturated due to the temperature drift of the piezoelectric element 30 and the operational amplifier 35a. Composed, capacitor 35b
The time constants of the resistance 35c and the resistance 35c are set to a value of about 2 seconds, which is longer than the thread tension change time at the lowest rotation speed of the sewing machine main shaft 16. Therefore, the charge amplifier 35 amplifies a signal having a frequency higher than the time constant, that is, a component of the change in the needle thread tension that appears during sewing, and a temperature drift that is a frequency component lower than the time constant is generated. On the other hand, it acts as a so-called high-pass filter that cuts off.

The spindle rotation sensor 19 is used for the sewing machine arm 10.
It is installed inside the machine, and 3 times for one rotation of the sewing machine spindle 16.
It is configured to output a pulse for each predetermined angle with respect to 60 degrees, and the output is guided to the sewing machine control circuit 21.

Inside the zero tension phase detection sensor 20, as shown in FIG. 3, a black disk 40 is mounted coaxially with the sewing machine main shaft 16 and has a notch in a part thereof.
And a U-shaped light-shielding sensor 41 attached to the sewing machine arm 10 so as to sandwich the disk 40. A light emitting diode (not shown) is provided on one arm of the light shielding sensor 41 so as to face the light shielding sensor 41 with the disc 40 interposed therebetween.
A light receiving sensor (not shown) is installed on each of the other arms. The light shielding sensor 41 is the sewing machine control device 21.
It is connected to the. When the rotational phase angle of the sewing machine main shaft 16 at the uppermost point of the sewing needle 18 (so-called needle top dead center) is 0 degree, the notch of the disk 40 is 240 degrees to 25 degrees.
The light-shielding sensor 41 is configured to transmit light between the light-emitting diode and the light-receiving sensor at an angle of 15 degrees up to 5 degrees, and to shield light at other angles.
The light-shielding sensor 41 is configured to output an H level signal at an angle of 240 degrees to 255 degrees and an L level signal at other angles.

The angle between 240 degrees and 255 degrees is from the lowest point of the sewing needle 18 (so-called needle bottom dead center) to the lowest point of the balance 17 (so-called balance bottom dead center) during sewing. This is the region where the needle thread 11 reaches its maximum, and the amount of slack of the needle thread 11 is maximum, and therefore the needle thread tension is zero.

As shown in FIG. 1, the sewing machine control device 21 is connected to an electromagnetic actuator inside the needle thread tension adjusting device 13, and an actuator drive circuit 50 for driving the electromagnetic actuator, and inside the needle thread tension detector 15. An A / D converter 51 connected to the output of the operational amplifier 35a for inputting a needle thread tension signal for A / D conversion, and a main shaft rotation sensor input port 52 for inputting a signal from the main shaft rotation sensor 19. A zero tension phase detection sensor input port 53 for inputting a signal from the light shielding sensor 41 inside the zero tension phase detection sensor 20, a main shaft drive circuit 54 for rotationally driving the sewing machine main shaft 16 by a mechanism not shown, and a well-known ROM 55.
And a RAM 56 and a CPU 57.

A part of the RAM 56 is a current tension storage area 56a for storing the tension value detected by the needle thread tension detector 15, and a reference tension storage area for storing the tension value in the zero tension phase. Area 56b is prepared.

This embodiment is constructed as described above.

Next, the operation of the thread tension detecting device of the sewing machine having the above construction will be described.

The control operation is performed by the CPU 57 shown in FIG. 1 by reading and executing the program in the ROM 55. In the flowchart of FIG. 4, first, when the sewing machine spindle 16 is rotationally driven by controlling the spindle drive circuit 54 and sewing is started (S1 and S indicate steps. The same applies hereinafter). Between the thread hook 14 and the balance 17, an upward pressure is applied to the thread hook 32 of the needle thread tension detector 15 by the tension of the needle thread 11 generated by sewing, and further, in FIG. Electric charges are generated in the piezoelectric element 30 by the piezoelectric effect. This generated charge is the charge amplifier 3
5 is converted into a voltage by the capacitor 35b,
Output as needle thread tension value.

As described above, with the rotation of the sewing machine main shaft 16, a pulse is generated from the main shaft rotation sensor 19 (see FIG. 5 (a)). The CPU 57 reads the main shaft rotation sensor input port 52 and waits until a pulse is input (S2).

When a pulse is input from the main shaft rotation sensor input port 52, the upper thread tension output from the upper thread tension detector 15 is detected by the A / D converter 51 in synchronism with this, and the RAM 56 of the RAM 56 is detected. It is currently stored in the tension storage area 56a (S3, see FIG. 5B).

Next, the signal of the zero tension detecting sensor 20 is inputted through the zero tension phase detecting sensor input port 53 (S4). Here, when the rotation angle of the sewing machine main shaft 16 enters between 240 degrees and 225 degrees with respect to the needle top dead center, the gap of the light blocking sensor 41 blocked by the disk 40 is released, and the needle thread tension becomes zero. The zero tension phase signal 60 considered is
It is output as an H level signal (see FIG. 5C).
Next, if the input from the zero tension detection sensor 20 is H level in S5, the process proceeds to S6. If the input is at the L level, the process proceeds to S7 described later.

At S6, the needle thread tension value currently stored in the tension storage area 56a is copied to the reference tension storage area 56b. Therefore, as shown in FIG. 5D, when the zero tension phase signal 60 is at the H level, the needle thread tension detected by the A / D converter 51 in synchronization with the pulse from the spindle rotation sensor 19 is It is stored as the output reference value of the needle thread tension detector 15 at zero tension.

Then, in S7, the output reference value of the upper thread tension stored in the reference tension storage area 56b, that is, the reference tension value is subtracted from the upper thread tension value currently stored in the tension storage area 56a. That is, the output reference value at the time of zero tension phase shown in FIG. 5D is subtracted from the actual needle thread tension value shown in FIG. 5B to obtain the needle thread tension value after the reference level correction. (See FIG. 5 (e)). Figure 5
As is clear from (e), the fluctuation of the reference level when the tension due to the capacitor 35b and the resistance 35c in the needle thread tension detector 15 is zero, is one rotation time unit of the sewing machine main shaft 16,
That is, it is removed in units of sewing time for one stitch.

On the other hand, in S5, the zero tension detection sensor 20
When the input level from is, that is, in the area where the needle thread tension is not considered to be zero, the needle thread tension value is not stored in the reference tension storage area 56b, and the reference tension value is simply subtracted from the current needle thread tension value. Then, the needle thread tension value after the reference level correction is obtained (S7).

Then, returning to S2, the pulse from the spindle rotation sensor 19 is again waited for, and the above routine is repeated.

The CPU 57 controls the actuator drive circuit 50 at an appropriate timing based on the needle thread tension value after the above-mentioned reference level correction, and adjusts the holding pressure of the tension disc of the needle thread tension adjusting device 13. .

In the above embodiment, the yarn tension detector 15 constitutes a yarn tension detecting means, the zero tension phase detecting sensor 20 constitutes a zero tension detecting means, and the RAM 56. Standard tension storage area 5
Reference numeral 6b constitutes a reference tension storing means, and in the processing step of S7 based on the CPU 57, the correction thread tension calculating means functions as S7.

The present invention is not limited to the above-described embodiments, but can be variously modified and used without departing from the scope of the invention. For example, in this embodiment, with respect to the needle thread tension detector 15 having a high-pass filter function of a capacitor and a resistor, the output of the needle thread tension detector 15 in the sewing machine spindle rotation phase where the needle thread tension is always zero is used as a reference. It was configured to correct and remove the output fluctuation component due to the high pass filter, but if the output of the needle thread tension detector is within the range where it is not saturated due to temperature drift etc., the configuration without using the high pass filter, that is, the charge It is also possible to apply the output fluctuation removing function of the present embodiment to the needle thread tension detector which does not use the resistor 35c in the amplifier 35.

In the present embodiment, the tension detector has a structure in which the charge generated in the piezoelectric element 30 is converted into a voltage by the charge amplifier 35 and output. However, the output of the piezoelectric element 30 is directly or through a high input impedance amplifier. It may be configured to output as a voltage. Furthermore, as a high pass filter, any passive element, active element, or A
It is also possible to use a digital filter after the / D conversion.

On the other hand, although the piezoelectric element is used as the needle thread tension detector in this embodiment, the needle thread tension is always zero even in the case of using an element having a pressure detecting mechanism such as a strain gauge. It is possible to make a correction by using the output of the needle thread tension detector in the sewing machine spindle rotation phase as a reference.
With such a configuration, the temperature drift of the strain gauge, the resistor used together, the operational amplifier, and the like can be removed in a unit of sewing time for one stitch.

The zero tension phase detection sensor 20 of this embodiment is mounted independently of the spindle rotation sensor 19, but instead of the zero tension phase detection sensor 20, for example, a sensor for detecting needle top dead center is added. The rotation angle from the needle top dead center may be detected by counting the pulses of the spindle rotation sensor 19 to obtain the zero tension phase. In such a configuration, if the phase at which the needle thread tension becomes zero fluctuates greatly due to, for example, the rotation speed of the sewing machine spindle, the rotation speed of the sewing machine spindle is detected using a timer such as a crystal oscillator, and the detected rotation is detected. It is also possible to adopt a configuration in which the zero tension phase is changed according to the speed value.

In the present embodiment, the reference tension value digitized by the A / D converter 51 is stored in the digital memory and digitally subtracted. However, the analog value is sample-held and calculated. An analog subtraction may be performed by an amplifier or the like.

Furthermore, in the present embodiment, the tension of the thread guided to the sewing needle 18 as the thread consuming section is applied to the detection, but the thread tension is detected at other thread consuming sections such as the looper,
It can also be used as a tension fluctuation removing function in detecting the lower thread tension.

[0038]

As is apparent from the above description, the thread tension detecting device for a sewing machine according to the present invention detects the thread tension in the sewing machine spindle phase in which the thread tension is always zero during the sewing of one stitch of the sewing machine. The thread tension value output by the machine is stored as a reference value at zero tension, and the thread tension value for one stitch is detected as a relative value from this reference value. 1) and the influence of the output fluctuation of the thread tension detector due to the DC component cut by the high pass filter.
There is an excellent effect that the thread tension can be detected stably even when the stitching time is limited to the sewing time and the temperature and the sewing speed change.

[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 detector to which a high pass filter is added.

FIG. 3 is a perspective view showing a configuration of a zero tension phase detection sensor.

FIG. 4 is a flowchart showing a needle thread tension detecting process by the needle thread tension detecting device of the present invention.

FIG. 5 is a graph showing a waveform of each operation part by the needle thread tension detecting device of the present invention.

FIG. 6 is a graph showing a tension detection waveform by a conventional needle thread tension detector.

[Explanation of symbols]

 11 Upper thread 12 Thread winding 15 Upper thread tension detector 16 Sewing machine spindle 18 Sewing needle 20 Zero tension phase detection sensor 51 A / D converter 53 Zero tension phase detection sensor input port 55 ROM 56 RAM 57 CPU

Claims (1)

[Claims] 1. A thread tension detecting means arranged in a thread path from a thread supply source of a sewing machine to a thread consuming section for detecting thread tension, and detecting a predetermined spindle rotation phase at which the thread tension becomes zero. Zero tension phase detection means, reference tension storage means for storing the thread tension output by the thread tension detection means in the phase detected by the zero tension phase detection means, and thread tension value detected by the thread tension detection means And a correction thread tension calculation means for calculating a difference between the thread tension value stored in the reference tension storage means and a thread tension detection device for a sewing machine.