JPH0575440B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an automatic tension adjustment device for a sewing machine.

(Prior art) Automatic thread tension sewing machines have been put into practical use that can obtain the appropriate thread tension according to the sewing pattern, but it is difficult to control the thread tension according to the type of fabric or thread. I haven't gotten anything satisfactory.

(Objects and Solution) The present invention focuses on the fact that by changing the needle thread tension, the peak position of the needle thread tension waveform corresponding to the movement of the thread take-up changes during sewing, and calculates the waveform. By setting and controlling the sewing machine rotation phase at which the peak value appears while changing the needle thread tension, an appropriate needle thread tension can be obtained.

(Example) Examples of the present invention will be described below based on the drawings. In FIG. 1, the sewing machine main body 1 includes a bobbin 2
An automatic thread tension device 5 is provided in the path of the upper thread 3 that is fed out from the thread take-up lever 4. Similarly, a needle thread tension detector 7 is provided in the path from the thread take-up 4 to the needle 6. As shown in FIG. 2, the detector 7 has a cantilevered measuring lever 8 attached to the sewing machine body 1, and the upper thread 3 moves while pressing the lever 8. A strain gauge 9 is attached to the lever 8 to detect the strain of the lever 8 and output an electric signal related to the tension of the needle thread 3.

In the present invention, if the output signal of the strain gauge 9 is the sewing machine rotation phase on the horizontal axis as shown in FIG. 3, and the vertical axis is the electric signal of the strain gauge 9, in this case the detection voltage V, then A peak value appears at a phase θ ₁ where We focus on the fact that there is a causal relationship between the method and the form of seam formation. Note that in FIG. 3, minute waveforms may appear at phases other than phase θ ₁ , but since this has no direct relation to the present invention, the explanation will be omitted.

FIG. 4 shows that the waveform of the detected voltage V, which is similar to that in FIG. 3, changes depending on the needle thread tension adjustment value of the thread tension regulator 5, and waveform A shows that the needle thread tension is adjusted to a large value. , and waveforms B, C,
Cases in which the values are adjusted to D, E, and F in order are shown.

FIGS. 5a to 5f correspond to the waveforms A to F in FIG. 4 and show the formation of each seam. For example, in FIG. In the process of sequentially sewing the cloth 10, the tension of the upper thread 3 is excessive compared to the tension of the lower thread 11, so that the stitch intersection 12 is on the upper surface of the cloth 10. It shows. Similarly, FIG.
This indicates that it is located on the bottom surface of the . Generally, the seam is such that the seam intersection 12 is located at the cloth 10 as shown in Fig. 5c.
It is desirable that it be near the center of .

Figures 6 and 7 are for explaining the causes of the waveform in Figure 4, and as shown in Figure 6,
When the tension of the needle thread 3 is too small compared to the tension of the bobbin thread 11, the thread take-up 4 moves up while tightening the thread relatively weakly, and the tension of the needle thread gradually increases.
At the position shown by the solid line before reaching the top dead center, the stitch intersection 12 is formed on the lower surface of the cloth 10, and reaches its peak value at this time, for example, at phase θ _E in FIG. 4E. In this phase θ _E , the upper thread 3 has already been unwound from the thread take-up 4, and from now on, the thread take-up 4 reaches the top dead center position shown by the chain line.
That is, in the process of reaching phase θ ₁ in FIG. 4, the needle thread tension decreases, and continues to decrease as the thread take-up 4 continues to descend. As shown in FIG. 7, when the tension of the upper thread 3 is excessive compared to the tension of the lower thread 11, the thread take-up
goes up while strongly tightening the thread, and at this time, the needle thread 3 pulls the bobbin thread 11 up to the upper surface of the cloth 10 without being supplied with the needle thread 3 from the thread take-up 4, and the needle thread tension gradually increases. , when the top dead center shown by the solid line is reached, the stitch intersection 12 is formed on the upper surface of the cloth 10, and at this time, for example, at a phase θ A that coincides with the top dead center phase θ ₁ as shown in FIG _{. 4A.} It reaches a peak value, and the needle thread tension decreases thereafter. This is because the thread tension device 5 increases the resistance to letting out the upper thread 3, so the upper thread 3 is not let out excessively near the top dead center. Figure 4 B, C, and D are the fourth
The peak phase θ _B , θ _C , θ _D of the previous stage that occurs in accordance with the peak phase θ E _etc. in FIG. It has a common peak phase θ ₁ in the subsequent stage that occurs in accordance with the phase θ _A in FIG. These differ depending on where each stitch intersection 12 occurs on the cloth 10 in FIG.
This is due to the fact that the resistance to and the phase of its occurrence are different, and when the tension of the upper thread 3 is somewhat strong as shown in FIG. The peak value at θ _B is smaller than the peak value at phase θ ₁ , and when the tension of the needle thread 3 is slightly weak as shown in FIG. In waveform D, the peak value at phase θ _D is larger than the peak value at phase θ ₁ .
Similarly, when the stitch intersection 12 is near the center of the cloth 10, in the waveform C, the peak value at phase θ _C and the peak value at phase θ ₁ are equal.

FIG. 8 is a block diagram showing a first embodiment of control, in which the needle thread tension detector 7 continuously detects the tension of the needle thread 3, and the detected value is transmitted to the automatic thread tension controller. This is shown by the chain line. The signal from the detector 7 is converted into a digital value by the A/D converter 13 and is provided to the arithmetic unit 14 . The computing device 14 is
Upon receiving the sewing machine rotation phase signal from the sewing machine rotation phase detector 15 and the needle thread tension signal from the needle thread tension detector 7,
The waveform for the sewing machine rotation phase θ in FIG. 4 is calculated. In this case, the rotational phase θ changes from 0° to approximately θ ₁
Find the slope ΔV/Δθ of the waveform from the tension change ΔV for each minute rotational phase Δθ over the interval leading to Δθ. For example, as in waveform F, when the phase θ _F at which this becomes 0 is considerably before the phase θ ₁ , When there is one position, the arithmetic unit 14 controls the thread tension controller 5 for the thread tension command means 16.
For example, waveform A
If the phase θ _A is near the phase θ ₁ at one point, the output will be decreased in the same way, and if there are two phases where ΔV/Δθ is 0, the output will be output as shown in waveform D. , when the peak value at the peak phase θ _D of the previous stage is larger than the peak value at the peak phase θ ₁ of the latter stage, the output is similarly output to increase the adjustment value of the thread tension regulator 5, and as shown in waveform B, the peak phase of the previous stage is When the peak value at θ _B is smaller than the peak value at the subsequent peak phase θ ₁ , it is output to be similarly decreased, and therefore, as shown in waveform C, the peak values at phases θ _C and θ ₁ are almost equal. Then, the output for the increase or decrease becomes 0. The thread tension command means 16 controls the drive of the thread tension device 5 to increase or decrease the adjustment value based on the output for increasing or decreasing.

In the above configuration, the needle thread tension detector 7 continuously detects the needle thread tension during the sewing operation of the sewing machine, and the calculation device 14 calculates the waveform related to the needle thread tension based on the detected value. By controlling the thread tension device 5 in a feedback manner according to the peak value or peak phase, an appropriate upper thread tension can be obtained, and the stitch intersection 12 can be located approximately at the center of the cloth 10 as shown in FIG. 5c. You can get a nice seam.

FIG. 9 is a control block diagram showing another embodiment. In FIG. 8, the arithmetic unit 14 calculates the waveform related to the needle thread tension during sewing to perform feedback control, while the operation The trial sewing command means 17 is activated by the operator's operation, and at this time, the thread tension command means 16' specifies that the adjustment of the thread tension device 5 should be relatively weak, and as the sewing machine rotates, the arithmetic unit 1 is activated.
4' detects a peak value, for example at phase θ _F in FIG. Peak phase θ _A in Figure 4 A
When a thread tension having one peak phase and matching the phase θ ₁ is obtained as shown in FIG.
In order to shift from waveform A to waveform C in the figure, a signal for decreasing the thread tension is output. Then, when the trial sewing command is canceled, the thread tension set at that time becomes the same.

(Effects) As described above, according to the present invention, since the thread tension is automatically set according to the stitch form, the ideal thread tension can be obtained even when the fabric or thread changes. Furthermore, when detecting needle thread tension, it is only necessary to find its peak value and peak value phase, so there is no need to find the absolute value of needle thread tension, which simplifies the configuration including the control circuit. .

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a sewing machine showing an embodiment of the present invention, FIG. 2 is a detailed diagram of its needle thread tension detector, and FIG.
The figure is an output waveform diagram of the needle thread tension detector, Figure 4 is an output waveform diagram when changing the adjustment value of the thread tension regulator, and Figure 5 is an output waveform diagram when the adjustment value of the thread tension regulator is changed.
Figures a to f are examples of seam formation corresponding to Figures 4 A to F, Figures 6 and 7 are diagrams explaining the causes of waveform generation in Figure 4, and Figures 8 and 9 are control circuits, respectively. FIG. 2 is a block diagram showing an example. In the figure, 4 is a thread take-up lever, automatic thread tension device 5 is a needle thread tension applying device, 7 is a needle thread tension detector, and calculation devices 14, 1
4' is the main element of the control device.

Claims (1)

[Claims] 1. A needle thread tension applying device that is located between the bobbin winder and the thread take-up and adjusts the needle thread tension, and a needle thread tension detector that is located between the thread take-up and the needle that continuously detects the needle thread tension;
Receiving the output of the needle thread tension detector, calculating the needle thread tension waveform with respect to the rotational phase of the sewing machine, and operating the needle thread tension applying device in accordance with the peak value thereof or the rotational phase of the sewing machine that produces the peak value. An automatic thread tension sewing machine equipped with a control device for controlling thread tension.