JPH0241357B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic needle thread tension adjustment device that automatically adjusts the pressure applied to the needle thread tension disc so that good stitching can always be achieved.

Conventionally, when sewing with a sewing machine, in order to obtain good stitches, the spring pressure on the upper thread tension disc is adjusted to adjust the upper thread tension so that the intersecting point of the upper thread and lower thread is in the middle of the sewn fabric. I was trying to get a good stitch by adjusting it. However, it is difficult to obtain good results with this process, so it is necessary to repeat trial sewing, which is difficult for experienced people.

The present invention automatically adjusts the pressure applied to the upper thread tension disc so that anyone can easily perform a good sewing job.

Figure 1 is an explanatory diagram of the conditions for good stitching.
This shows a state in which two pieces of cloth 1 and 2 are sewn together using upper thread 3 and lower thread 4, resulting in a good stitch, that is, a state in which the intertwining point of upper thread 3 and lower thread 4 is in the middle of cloth 1 and 2. . Assuming that the fabric thickness is d and the stitch pitch is P, it is understood that the needle thread length required for one stitch is P+2d. Thinking in the opposite direction, when sewing, it is sufficient to let out the upper thread from the upper thread bobbin by a length of P+2d for each stitch.

Figure 2 shows the thread take-up curve of the thread take-up, which has characteristics unique to that sewing machine. Figure 2B is a partially enlarged view of Figure A, but in the explanation for Figure 1, it is stated that in order to obtain good stitches, it is sufficient to supply needle thread by P+2d for each stitch. In order to pick up the upper thread of length P + 2d with the balance in Figure 2 (B), the top dead center t ₀ must be reached from the time t _1.
It is only necessary to perform the needle thread take-up action by the thread take-up only during the period leading up to . The thread take-up characteristics by the thread take-up are as follows:
Since this is unique to each sewing machine, if the amount of needle thread to be picked up by the thread take-up is known, the time to start picking up the needle thread by the thread take-up can be calculated.

Taking the above points into consideration, it is clear that if the timing at which the thread take-up starts to pay out the needle thread by the thread take-up and the timing to start picking up the needle thread calculated from the needle thread take-up curve coincides with each other, a good stitch is obtained. In this case, if the pressure applied to the upper thread tension disk is adjusted to adjust the upper thread tension and automatic adjustment is made so that the above-mentioned timings coincide, good stitching can always be achieved.

FIG. 3 is an explanatory view showing an embodiment of the present invention, in which an upper thread movement start timing detector 6 is provided in the sewing machine head 5 between an upper thread tension disc device 7 and an upper thread bobbin 8. . In the figure, reference numeral 9 is a base tension device for applying a weak tension to the needle thread so as not to disturb the thread, 10 is a thread take-up, and 11 is a needle. The upper thread movement start timing detector 6 may be configured to detect the movement of the upper thread or the timing of sudden increase in tension using a potentiometer or a strain gauge.

FIG. 4 is an explanatory view showing one example of the upper thread tension disc device 7. In order to adjust the pressure applied to the upper thread 3 sandwiched between the tension discs 12 and 13, the gear 15 is operated by the reversible rotation of the motor 14. , 16, and is configured to press down a spring 18 via a screw shaft 17.

Next, to explain the operation of the embodiment according to the present invention, the thickness 2d of the cloth to be sewn is appropriately detected by changes in the vertical movement of the cloth pressing device, and the thickness 2d of the cloth to be sewn is detected as appropriate by changes in the vertical movement of the cloth pressing device, and the thickness 2d of the cloth to be sewn is detected as appropriate by changing the vertical movement of the cloth pressing device. The required length of thread is calculated by the built-in arithmetic circuit, and the timing t for starting needle thread supply by the thread take-up is determined based on the calculated value and the needle thread take-up curve by the thread take-up stored in the thread take-up characteristic storage means (ROM). ₁ is calculated by the calculating means (CPU), this time t ₁ is compared with the time t' ₁ when the upper thread actually starts moving, and the motor 14 is rotated in forward and reverse directions based on the result. The pressure applied to the thread tension disc is automatically adjusted so that the two timings coincide with each other. When these match, it means that good sewing is being performed.

Incidentally, FIG. 5 is an operational block diagram of an embodiment according to the present invention.

As explained above, according to the present invention, the needle thread take-up characteristic by the thread take-up is used to detect the timing at which the thread take-up starts to be supplied by the thread take-up, and the needle thread supply starts at a required correct needle thread supply amount. Since the pressure applied to the upper thread tension plate is adjusted to match the timing, there is no need to consider thread thickness, friction coefficient, etc. even on sewing machines that use a tension plate. Therefore, it is possible to always perform good sewing automatically with a relatively simple device.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the conditions for good stitching, Fig. 2 A is a diagram showing the needle thread take-up curve by the thread take-up, B is a partially enlarged explanatory diagram of A, and Fig. 3 is a diagram according to the present invention. Without explaining the embodiment, FIG. 4 is an explanatory diagram of the upper thread tension disc device, and FIG. 5 is an operational block diagram of the embodiment according to the present invention. 1, 2... Suture cloth, 3... Upper thread, 4... Lower thread,
6... Needle thread movement start timing detector, 7... Upper thread tension disc device, 12, 13... Tension disc, 14... Reversible motor, P... Stitch pitch, d... Thickness of each fabric,
2d...cloth thickness.

Claims (1)

[Claims] 1. A detector for detecting the start time of needle thread movement from the needle thread bobbin due to the needle thread take-up action of the thread take-up, a storage means that stores the needle thread take-up characteristics of the thread take-up, and the thickness of the fabric to be sewn and the sewing pitch. a calculation means for calculating the upper thread supply start time required for good sewing from the storage means in consideration of the above, a comparison circuit for comparing the upper thread supply start time with a signal from the detector, and the comparison circuit This automatic upper thread tension adjustment device is comprised of a reversible rotary motor that automatically adjusts the pressure to the upper thread tension disc based on the output of the thread.