JPS6018223Y2 - Automatic upper thread tension device for sewing machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic upper thread tension device for a sewing machine, which automatically adjusts the upper thread tension to the optimum level at all times, thereby achieving good sewing performance.

The most preferable stitch cannot be obtained unless the needle thread tension in the sewing machine is adjusted according to various conditions related to sewing.

However, in the past, nothing has been proposed that automatically adjusts the needle thread tension in response to changes in conditions, and therefore, it is difficult to sew properly without manual adjustment and trial sewing each time. However, the operation was cumbersome and inefficient.

The present invention was developed in consideration of the above-mentioned circumstances, and was developed by specifying the amount of needle thread payout based on sewing-related conditions such as weight, thread thickness and type, fabric feed amount, and needle swing width. In addition, by measuring the actual amount of let-out and comparing this measured value with the designated value to adjust the thread tension, an appropriate thread tension can always be obtained.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a control block diagram, in which 1 is a signal related to the weight, and 2 is a signal related to the feed amount of the fabric and the swing width of the needle.

3 is a signal relating to the thickness and type of thread (for example, silk, katan, etc.), which is inputted together with the signals 1 and 2 to a computing unit 4, and the computing unit 4 specifies an appropriate amount of needle thread payout.

Since the output signal of the calculator 4 is input to the D/A converter 5, the specified needle thread payout amount is converted into an analog value and input to the comparator 6, and the comparison reference input signal of the comparator 6 is become.

Reference numeral 7 denotes a signal relating to the actual needle thread payout amount, which is input to the comparator 6, and the comparator 6 compares the comparison reference input signal input from the D/A converter 5 with the signal related to the actual needle thread payout amount. The output of the comparator 6 controls the thread tension pressure adjusting device 8 to adjust the thread tension pressure so that the specified needle thread payout amount matches the actual needle thread payout amount. There is.

FIG. 2 shows an example of a thickness measuring mechanism for obtaining the thickness signal 1, in which a sliding variable resistor 9 is linked with a presser bar 10, and the vertical movement of the presser bar 10 is controlled by a change in resistance value. As shown in the second diagram, the presser foot rod 1
0 presses and feeds a plurality of cloths 11 to be sewn together.
The total thickness of the plurality of cloths 11 can be measured from the resistance value of the variable resistor 9 when the cloth 2 is in the lower position.

Figure 3 shows a mechanism for obtaining signals regarding the thickness and type of thread and a mechanism for measuring the actual amount of needle thread being let out.
Information about the thickness and type of thread is written as a bar code 16 on the lower end of the hollow shaft 15 of the thread spool 14 around which the thread spool 14 is wound. An optical sensor such as a phototransistor for reading the barcode 16 is disposed in the hole 18 surrounding the lower part of the hollow shaft 15. By inserting the thread into the hole 18, the bar code 16 is read to obtain confidence as to the thickness and type of thread.

Reference numeral 19 denotes a roller that is rotatably supported on the outside of the machine frame of the sewing machine and measures the amount of needle thread being fed out.Since the needle thread 13 is wound several times around the thread spool 14, when the needle thread 13 is fed out, As the roller 19 rotates, the rotational speed of the roller 19 changes in proportion to the amount of the needle thread 13 fed out.When the rotation amount of the roller 19 is measured with a rotation detection sensor such as a rotary generator or a rotary encoder, the rotation speed of the roller 19 changes in proportion to the amount of the needle thread 13 fed out. The amount of feed can be measured.

FIG. 4 shows an example of a thread tension pressure adjustment mechanism, in which a threaded portion 22 is formed on a rotating shaft 21 of a reversible motor 20 such as a pulse motor, and a stopper 2 is formed on the threaded portion 22.
A shaft 24 of No. 3 is screwed together, and the stopper 23 moves in the left-right direction in the figure depending on the rotation direction of the reversible motor 20.

Reference numeral 25 denotes two thread tension discs that sandwich the upper thread, and a thread tension spring 26 is interposed between the stopper 23 and the thread tension disc 25 on the stopper side. Since the tension pressure changes, when the reversible motor 20 is controlled by the comparator 6, the stopper 23 is moved and an appropriate thread tension pressure can be obtained.

In addition, the amount of cloth feed and the width of the needle can be obtained directly from a cam or link inside the sewing machine that determines the amount of feed and amplitude, or it can be obtained directly from a cam or link inside the sewing machine that determines the feed amount and amplitude. If the sewing machine is equipped with a selection button, the information can also be obtained from the selection button.

Further, in a sewing machine that has a built-in storage device such as an IC memory inside the sewing machine and stores the pattern, feed amount, and stitch width in the storage device, the information can be obtained from the storage device.

Similarly, regarding the thickness and type of thread, multiple selection buttons corresponding to the thickness and type of thread are arranged outside the machine frame of the sewing machine.
Signals regarding the thickness and type of thread can be obtained from the button.

Next, to explain the outline of the calculations performed by the calculator 4 using straight stitching and zigzag stitching as examples, changes in the amount of needle thread let out due to differences in needle thread thickness and type can be explained using a simple proportional relationship. It is known through experiment that the proportionality constant changes depending on the thickness and type of upper thread.
shall be.

FIG. 5 is a cross-sectional view along the feeding direction when straight stitching is ideally performed, 11 indicates a plurality of fabrics to be sewn together, and t indicates the total thickness of the plurality of fabrics 11.

[- indicates the feed amount by which the cloth 11 is fed by the feed dog 12 for each stitch.

13 is the upper thread, and 27 is the lower thread. When straight stitching is ideally performed, the upper thread 13 and the lower thread 27 intersect at the center of the cloth as shown in the figure. The amount of needle thread let out is determined by C(1+2X-;).

FIG. 6 is a top view when zigzag stitching is ideally performed, and FIG. 7 is a sectional view viewed from the feeding direction.

W indicates the swing width of the needle, P indicates the length of the needle thread exposed at the top of the fabric for each - stitch, and a indicates the length of the portion of the needle thread exposed at the bottom of the fabric.

When zigzag stitching is ideally performed, the upper thread is exposed at the bottom of the fabric and intersects with the bobbin thread as shown in the figure. In this case, the amount of needle thread let out for each -stitch is obtained by C (P + 2t + 21). It will be done.

Furthermore, the length P of the part of the needle thread exposed at the top of the cloth is p=AX
4. Length a of the needle thread obtained in step 1 and exposed at the bottom of the fabric
It has been experimentally confirmed that good zigzag stitching can be performed by making the stitch width proportional to the stitch width W. Therefore, if this proportionality constant is K, then a=KW, which is the ideal value for each stitch in zigzag stitching. The needle thread payout amount is C(, /F+
W2+Δ+2KW), and the ideal needle thread payout amount can be calculated from the thickness of the fabric, the thickness and type of thread, the feed amount of the fabric, and the swing width of the needle, as in the case of straight stitching.

If it becomes necessary to slightly change the calculation formula of the calculator 4 when sewing various complicated patterns, use the pattern selection button provided on the outside of the sewing machine frame or the pattern stored in the IC memory built into the sewing machine. This is possible by controlling the arithmetic unit 4 using a storage device or the like that stores .

As described above, according to the present invention, the amount of needle thread to be let out is specified based on various sewing conditions such as weight, thickness and type of thread, feed amount of cloth, and needle swing width, and the actual amount to be let out is controlled. The thread tension can be automatically adjusted by comparing the measured value with the specified value.Furthermore, as shown in the above embodiment, various conditions related to sewing are constantly measured by each measuring mechanism, so that each condition can be adjusted. It can automatically deal with changes, and compared to conventional manual adjustment, there is no need to change the thread tension pressure every time the pattern or thread changes, and good sewing is always achieved. This is a highly effective idea in practical terms.

[Brief explanation of the drawing]

Figure 1 is the control block diagram, Figure 2 is the weight measurement mechanism, and Figure 3 is the control block diagram.
The figure shows a mechanism that obtains signals about the thickness and type of needle thread and a mechanism that measures the amount of needle thread payout. FIGS. 6 and 7 are a top view and a sectional view taken from the feeding direction when zigzag stitching is ideally carried out. In the figure, 1 is a heavy weight signal, 2 is a fabric feed amount and needle swing width signal, 3 is a signal related to the thickness and type of thread, 6 is a comparator, 7 is a signal related to the actual needle thread payout amount, 8 1 is a thread tension pressure adjusting device, 9 is a sliding variable resistor, 10 is a presser bar, 11 is a cloth, 12 is a feed dog, and 13 is an upper thread.

Claims (1)

[Scope of utility model registration request] It is equipped with a plurality of thread tension discs for clamping the upper thread to be paid out, a thread tension pressure adjustment mechanism for adjusting the clamping pressure of the thread tension discs, and a thread tension adjustment mechanism for adjusting the clamping pressure of the thread tension discs, as well as thread thickness, thread thickness, type, feed amount, and needle swing. In a sewing machine equipped with a needle thread payout amount specifying device that specifies an appropriate needle thread payout amount based on various conditions such as width and converts it into an appropriate electrical signal, the device is attached to the sewing machine frame and is connected to the needle thread drawn out from the supply source. A feeder that measures the amount of needle thread payout by measuring the amount of rotation of the locked rotating roller via a rotation detection sensor, and measures the feed-out speed of the needle thread and converts the feed-out speed into an appropriate electrical signal. An automatic upper thread tension device for a sewing machine, which is provided with an amount measuring mechanism and a comparator that compares an electrical signal of the measuring mechanism with an electrical signal of the upper thread payout amount designating device and automatically adjusts the thread tension pressure adjusting mechanism. .