JPH0218876B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sewing machine that allows automatic adjustment of sewing tension.

Currently, including household sewing machines and industrial sewing machines,
A problem that has become the subject of technological innovation is the possibility of automatic seam adjustment. Although it is possible to control the sewing tension by changing the thread tension, etc., it has been studied and researched by many people, but it is still not possible to detect the quality of sewing or detect subtle changes in sewing. It's not on. Therefore, the challenge is to develop sensors that accurately respond to these conditions.

Conventionally, the needle thread tension was adjusted by increasing or decreasing the tension of the needle thread by changing the pressure on the tension disc, but now the tension of the needle thread is adjusted by increasing or decreasing the tension of the needle thread by changing the pressure of the tension disc. Because of this, it lacked stability and required delicate adjustment of pressure changes.

According to the present invention, the length of the upper thread required for tightening the cloth is detected in advance, and the length of the upper thread is controlled so as to be supplied during each cycle of the sewing machine.

This will be explained below with reference to the drawings.

Figure 1 is an explanatory diagram showing the relationship between the upper thread and lower thread when sewing fabrics of equal thickness. There is. By the way, the amount of upper thread required for one stitch when the upper hanging stitch is performed in (a) is the feed amount P of one pitch determined by the cloth feed adjustment device, and the amount of needle thread required for the first stitch when the lower hanging stitch is performed in (b). The needle thread amount is d when the fabric thickness is
(For simplicity, let's assume that the upper and lower fabric thicknesses are equal.)
Then, P+4d is required, and the amount of needle thread required for one stitch in the case of a good stitch C is P+2d.
(In this case, in reality, the sewing thread does not bend into a rectangular shape as shown in Figure 1, but the corners are rounded, so it is necessary to correct the theoretical value by multiplying it by a coefficient. Yes). Therefore, in order to perform good sewing, it is sufficient to supply the needle thread with a length of P+2d for each stitch. However, it is very difficult to accurately measure cloth thickness during sewing work.

As a result of various studies, the present inventor has found that when a hanging stitch is formed, the upper thread is entangled with the lower thread and pulled, increasing the upper thread tension (needle thread tension is the second Therefore, if you measure the time t ₁ when the upper thread intertwines with the lower thread and the upper thread tension starts to increase, you can determine the needle thread take-up curve of the sewing machine (see Figure 3). ), it is possible to calculate the amount of thread taken up by the balance corresponding to t ₁ , that is, P + 4d, and also,
In the case of top-hung stitching, the needle thread feed amount can be set to P, so it has been realized that the needle thread supply amount P+2d for obtaining a good sewing condition can be calculated from both of these values. In a sewing machine, the thread take-up characteristic of the needle thread take-up is fixed and specific to that machine, so it is possible to detect when the needle thread becomes intertwined with the bobbin thread in a hanging stitch state and its tension increases. , the thread take-up characteristics of the thread take-up, and the fabric feed amount P are calculated by an arithmetic circuit to calculate the needle thread supply amount P + 2d that will result in good stitching, and if this amount of needle thread is fed during one stitch cycle, the needle thread will always be This means that sewing work can be performed with good seams.

To explain this in detail, Fig. 3A is a diagram showing the needle thread take-up curve of the thread take-up and the corresponding tension change due to the entanglement of the needle thread and bobbin thread. This is a fixed value specific to that sewing machine. On the other hand, the tension change due to the intertwining of the upper thread and lower thread is
The moment when the upper thread intertwines with the bobbin thread and tries to pull it into the sewing fabric, that is, the time when the amount of thread taken up by the thread take-up is at its maximum, which is greater than the time when the upper thread and bobbin thread intertwine in Figure 1 B. , that is, it reaches its maximum at the top dead center of the balance t ₀ ,
It then decreases. Therefore, if the time t ₁ at which the needle thread tension starts to increase is detected, the time when the needle thread and bobbin thread are intertwined in the hanging stitch state can be detected. The amount of thread taken up by the thread take-up after t ₁ when the needle thread tension starts to increase (the time when the needle thread and bobbin thread are intertwined) is
Since the needle thread take-up curve by the thread take-up is unique to the sewing machine, P+ is shown in FIG.
4d can be understood if you consider Figure 1 (b). When this concept is actually applied to a sewing machine, it can be easily calculated by using an electronic computer circuit as a computer for controlling the needle thread payout amount.

FIG. 4 is an explanatory diagram showing an embodiment in which the present invention is applied to a sewing machine.The sewing machine head 1 is provided with a thread take-up lever 2, needle thread guides 3, 4, as in a general sewing machine, and an upper A strain gauge (needer thread tension detection device) 5 is provided in the guide portion between the thread guide 3 and the thread take-up that guides the needle thread in reverse, and this strain gauge 5 is used to detect changes in the tension of the needle thread. It is configured.
Further, instead of the normally used thread tension disc, a pulse motor 7 equipped with an upper thread pay-out roller 6 is provided between the upper thread guide 3 and the strain gauge 5, and the upper thread pay-out roller 6 The needle thread is supplied to the sewing fabric by a bobbin winder 8 via a needle thread guide 3, a needle thread pay-out roller 6, a strain meter 5, a thread take-up 6, and a needle thread guide 4. It is designed to perform only a cloth tightening action.

Furthermore, the sewing machine is equipped with a computer device that stores the thread take-up characteristics of the needle thread take-up, and as described above, when the time t ₁ at which the needle thread tension starts to increase due to the entanglement of the needle thread and bobbin thread is input, The corresponding needle thread take-up amount, that is, P+4d, is calculated by the thread take-up, P+2d is calculated from the cloth feed amount P in the sewing operation, and the pulse motor 7 is driven by the corresponding pulse output, and the needle thread pay-out roller 6 This allows the sewing machine to supply the optimum amount of needle thread required for one stitch cycle. The required amount of needle thread may be fed continuously during the entire period. This is convenient when driving at high speeds.

In this way, the necessary amount of upper thread required for good sewing is always supplied accurately by the upper thread supply control device consisting of the upper thread feed roller 6 and the pulse motor 7, so that the thread take-up is It is not necessary to carry out a thread letting-out action, and it is sufficient to simply perform a cloth tightening action. Therefore, there is no need to adjust the needle thread tension or use a thread take-up spring to deal with the increased resistance to thread pulling when the needle thread passes through the hook during high-speed rotation, and it is also necessary to apply strong tension to tighten the stitches. The texture of the sutures also improves because there are no scratches.

The present invention has been described using an example in which the thickness of the fabric to be sewn is the same, but even if the thickness of the upper fabric and lower fabric are different, there is a point where the upper thread and lower thread intertwine between the upper fabric and the lower fabric. Therefore, good stitching can be obtained in any case.

FIG. 5 is a diagram illustrating the outline of the calculation circuit used in the present invention, in which the strain meter 5 detects the timing t ₁ at which the needle thread tension starts to increase due to the entanglement of the needle thread and bobbin thread during sewing work, and the timing pulse and timing and content
Output to ROM, hold the result in register,
The arithmetic circuit calculates the held value, outputs P+2d, and supplies this to the step motor 7.

In addition, in the explanation so far, the purpose was to obtain a case of good stitching, but in order to make it possible to easily remove the sewing thread, as in the case of basting, for example,
It is also possible to intentionally sew in a top hanging stitch or a bottom hanging stitch. That is, if the upper thread supply amount is P, it will be a top hanging stitch, and if it is P+4d, it will be a bottom hanging stitch, so this can be easily done by switching the calculation circuit.

As explained above, according to the present invention, the sewing tension can be automatically adjusted, which was conventionally considered to be very difficult, and it is possible to always perform the best sewing work without the need for the operator to make any adjustments. Summer.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the sewing state by the sewing machine.
A shows upper hanging stitching, B shows lower hanging stitching, C shows good sewing condition, Figure 2 is a diagram showing changes in needle thread tension, and Figure 3 shows
Figure A is a diagram showing the relationship between the needle thread take-up characteristic curve by the thread take-up lever and the needle thread tension change, Figure 3B is an enlarged partial view of the same part, Figure 4 is a diagram showing an embodiment of the present invention, 5
The figure is an explanatory diagram showing one example of a computer circuit used in the present invention. 1... Sewing machine, 2... Balance, 5... Strain meter (needle thread tension detection device), 6... Needle thread pay-out roller, 7...
Step motor, P... Fabric feed amount of the sewing machine (1 sewing stitch), d... Fabric thickness.

Claims (1)

[Claims] 1. In a needle thread supply device for a sewing machine that includes an upper thread unwinding device, an upper thread tension detection device, a balance, and a calculator for controlling an upper thread reeling amount, the computer for controlling an upper thread reeling out amount is connected to a thread take-up thread take-up. a storage means storing the top characteristic, and in response to the detection of the tension increase start time by the needle thread tension detection device, the top is taken up from the top thread take-up characteristic between the tension increase start time and the top dead center of the balance; It consists of a counting means that outputs the yarn amount, and a calculation means that calculates the necessary thread payout amount from the cloth feed amount input from the cloth feed adjustment device and the above-mentioned calculated needle thread amount, and the yarn output from the calculation means This is an automatic stitch tension adjustment sewing machine that controls the needle thread payout device according to the feed amount to supply the necessary needle thread.