JPH0221830B2 - - Google Patents

Description

[Detailed Description of the Invention] When sewing cloth with a sewing machine, the pressure applied to the thread tension disk is changed between normal feeding and reverse feeding, so that the pressure that occurs during normal feeding and reverse feeding is improved. This invention relates to a thread tension mechanism that prevents changes in stitch tension.

In a sewing machine, the presser foot is provided with a groove in front of the hole through which the sewing machine needle passes, and the operator passes through this groove and performs the work while checking the part to be sewn and the part through which the needle will pass. Because the presser foot has this structure, as shown in Figure 6, when sewing in normal feed, the upper thread is held between the fabric and the presser foot and is pulled up with a thread take-up. However, under these conditions, the pressure applied to the thread tension plate is adjusted so that the upper thread and lower thread intertwine in the middle of the fabric. However, in the case of reverse feeding, as shown in Figure 7, the upper thread is not held down by the presser foot because there is a groove in front of the needle hole of the presser foot, and it immediately moves upwards from the point where it intertwines with the bobbin thread. Since the upper thread is pulled up by the thread take-up, the frictional force between the cloth and the presser foot as shown in Figure 6 is not applied to the needle thread, so the same pressure is applied to the thread tension disc as in the case of normal feeding. If the upper thread remains tied, the tensile force exerted on the bobbin thread by the upper thread becomes large, causing the bobbin thread to be pulled out to the upper surface of the fabric, causing problems such as uneven thread tension and crinkling of the fabric. The present invention improves this point.

FIG. 1 shows a part of the head of a sewing machine embodying the present invention, and the sewing machine head 1 is provided with a presser foot mechanism 2, a thread take-up 3, and a thread tension mechanism 4. In the embodiment shown in FIG. 1, the forked wedge 5 is inserted into and retracted from the thread tension disc portion by an electromagnetic mechanism 6 to change the pressing force applied between the thread tension discs. The case is shown. The details of the thread tension mechanism 4 are shown in FIG.
9 is inserted, and a spring 10 for pressing the spring 10 is adjustable and held down by an adjustment nut 12 screwed into a screw 11 cut into the thread tension shaft. Furthermore, the wedge 5 is adapted to be inserted into and removed from the back surface of the thread tension disc 9, and a slope corresponding to the slope of the wedge 5 is formed on the back surface of the thread tension disc 9.
As the wedge 5 moves up and down, the thread tension plate 9 moves left and right while maintaining a right angle to the thread tension shaft 7. Therefore, in FIG. 2, when the wedge 5 is raised, the thread tension disc 9 moves to the left and compresses the spring 10 via the thread tension disc 8, so that the thread passing between the thread tension discs is strongly pressed down. Therefore, the stitch thread is tightened strongly by the thread take-up lever 3, and conversely, when the wedge 5 is moved downward, the thread tightening is performed weakly. Therefore, when the cloth is fed in the forward direction, the wedge 5
By raising the wedge and lowering the wedge when the cloth feed is in the opposite direction, the pressing force between the thread tension disks can be changed in conjunction with switching between the forward and reverse directions of the cloth feed.

In FIGS. 1 and 2, the pressing force between the thread tension discs was changed by inserting a wedge, but as shown in FIG. 14, and when one spring 14 is pushed up by the tubular spring push-up member 15 that moves left and right in conjunction with switching the feed order and reverse, the spring 13
The thread tension mechanism may be configured such that only the thread tension disc acts on the thread tension disc. Alternatively, as shown in FIG. 4, a linear motor 16 may be provided in the thread tension disc, and switching may be performed by changing the current value of the linear motor. In FIG. 1, the wedge 5 is moved using an electromagnetic mechanism 6 to correspond to switching between forward and reverse cloth feed, but the wedge 5 is moved mechanically via a lever mechanism. Good too. Note that FIG. 5 is a diagram showing an example of a wedge drive circuit using an electromagnetic mechanism.

As explained above, according to the present invention, since the pressing force generated between the thread tension discs is changed in conjunction with switching between the forward and reverse directions of the cloth feeding mechanism, the phenomenon that the sewing tension becomes incorrect due to forward and reverse feeding occurs. This prevents the sewing machine from scratching, resulting in cleaner sewing.

[Brief explanation of drawings]

Fig. 1 is a partially omitted perspective view of a sewing machine head showing an embodiment of the present invention, Fig. 2 is an enlarged side view of the thread tension mechanism shown in Fig. 1, and Fig. 3 is a case where a double spring is used. FIG. 4 is a sectional view showing an embodiment of the thread tension mechanism; FIG. 4 is a perspective view showing an embodiment using a linear motor;
FIG. 5 is a diagram showing an example of an electromagnetic control circuit, FIG. 6 is a diagram showing the state of the upper thread in the case of forward feeding of the cloth, and FIG. 7 is a diagram showing the state of the upper thread in the case of reverse feeding. 1...Sewing machine head, 4...Thread tension mechanism, 5...
Wedge, 8, 9...thread tension plate.

Claims (1)

[Claims] 1 In conjunction with the forward/reverse switching operation of the forward/reverse cloth feed mechanism,
The pressing force applied between the tension discs so that the pressure applied to the tension discs when the fabric is fed in reverse is smaller than the pressure that is applied between the tension discs when the fabric is forward fed. A thread tension mechanism for a sewing machine, characterized in that it is equipped with a device for switching and controlling.