JPH027676B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thread processing device used in a sewing machine, and more particularly to a thread pulling mechanism for loosening bobbin thread of a lockstitch sewing machine.

When performing zigzag stitches on a sewing machine with a bobbin thread tension device located on one side of the bobbin, the needle is closer to the thread tension device when it is in one local bite position than when it is in the opposite bite position. Penetrates the workpiece at a point. Therefore, the length of the thread leg changes. Therefore, when setting a stitch at one needle position, it is necessary to make the bobbin thread less loose than at other needle positions.

In the case of lockstitch sewing machines, thread withdrawal devices are known which provide a constant bobbin thread slack for each stitch, regardless of the type of stitch being formed.
However, in the case of a zigzag pattern, this can cause one seam to be pulled too tightly and other seams to be too loose. This often results in material coding or uneven seams. The device that keeps the thread drawn constant is dated September 26, 1971.
No. 3,693,565 to Ketterer and US Pat. No. 4,091,753 to Johnson et al., May 30, 1975, which are also incorporated herein by reference.

Thread withdrawal devices for lockstitch sewing machines are also known which are adapted to provide a variable length of bobbin thread slack depending on the requirements of each stitch. See, for example, US Pat. No. 4,215,639 to Johnson, August 5, 1980. However, the Johnson mechanism is relatively complex in construction and requires a separate actuator, such as a servo motor, and associated circuitry to adjust the amount of thread withdrawal that occurs.

The present invention seeks to eliminate the above-mentioned drawbacks by a new and simple mechanism.

SUMMARY OF THE INVENTION An object of the present invention is to provide a variable thread drawer which provides an appropriate amount of slack to the bobbin thread and makes the stitches uniform.

Another object of the invention is to prevent the formation of half-hits.

Still another object of the present invention is to provide a variable thread withdrawal mechanism that is simple in construction and allows the amount of thread withdrawal to be obtained without the use of a separate actuator.

Still another object of the present invention is to provide a variable thread withdrawal mechanism such that the appropriate amount of thread withdrawal is automatically obtained as a result of the needle bite position as it penetrates the workpiece. It is.

Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention and the accompanying drawings.

According to the present invention, there is provided a thread drawing device for drawing thread from a bobbin in a lockstitch sewing machine, which provides a predetermined amount of slack to the bobbin thread according to the requirements of each stitch. The device has a movable bobbin thread withdrawal member with a thread engaging surface transverse to the thread path. A device is provided for moving the bobbin thread withdrawal member periodically in a path and synchronously with the stitch forming device of the sewing machine. The movement within said constant path has a component transverse to the thread path.

FIGS. 1, 2, 4 and 5 show a rotary hook 10, i.e. a thread remover and a workpiece feed dog 1.
A portion of a sewing machine bed 2 is shown with an upwardly open chamber 4 for accommodating a sewing machine bed 2. The thread taker 10 has an open end hollow cavity 14 and a flat top surface 1.
6. A bobbin case 20 having a thread carrying bobbin 22 therein is suspended within the cavity 14, and a bobbin thread 24 is wound on the bobbin 22. The bobbin case 20 has a lower flange surface 3
0, this surface rests lightly on the surface 16 of the thread remover 10 and partially supports the bobbin case 20. A needle bar 40 that reciprocates in the longitudinal direction is supported in a sewing machine head (not shown), and cooperates with the thread spooler 10 to impart vibrational motion to the thread carrying needle 42 when lock stitching is performed. ing. A bobbin case retention and positioning bracket 50 is rigidly mounted to the bed 2 and has a hole 52 that loosely engages the bobbin case 20. The bracket positions the bobbin case relative to the thread taker 10 and is adapted to allow the needle thread to be thrown around the bobbin case 20 without significant obstruction by the bracket 50. Said structure is well known in the art. For example, a similar structure is described in detail in Ketterer, US Pat.

As shown in FIGS. 3 and 4, the thread pulling member 100 is arranged so that the needle
2 and the bobbin 22 and extends beyond the path of the bobbin thread 24. A thread withdrawal member 100 having a substantially rectangular shape and having a central hole 102 is connected to a pivot support member 104, which support member is formed at right angles to said thread withdrawal member 100 and is perpendicular to said withdrawal member. It has a perpendicular rotation axis. Member 104 has a slot 106 formed in bracket 50, as shown in FIGS. 4 and 5.
It is loosely engaged with the lower surface of the. The free end 103 of the thread withdrawal member 100 extends below the feed dog 12 and is biased by the force of a leaf spring 112 acting downwardly against the flap 114, into engagement with the lower surface 110 of the feed dog. The hanging piece 11
4 is the thread pulling member 1 from the rotation axis of the member 104.
It is formed outward in the direction opposite to 00. The leaf spring 112 is attached to the base member 12 which is mounted to the bracket 50 by suitable fastening members 122.
It has 0. When the feed dog 12 moves up and down, the thread drawing member 100 also moves up and down. The feed dog surface 110 drives the thread withdrawal member 100 downward when the downward movement is performed. If the feed dog rises, the spring 112
drives the hanging piece 114 downwardly, thereby pivoting the support member 104 and thread withdrawal member 10.
0 remains in engagement with surface 110 as the feed dog ascends. The central hole 102 is located at the free end 1
03 has a surface 107 which is inclined with respect to the rotation support member 104. Said surface 107
starts from point A, moves away from member 104 and bobbin 22, and reaches point 108 in FIG.

When working, the bobbin thread 24 is in the bobbin case 2.
According to the path extending from the thread tension device 26 of 0,
It passes diagonally over the top of the bobbin 22, then under the front edge of the thread withdrawal member 100, and upwardly through the hole 102 to the workpiece being sewn. 1st
The figure shows the needle in the raised position just after the stitch has been set in the left bite position of the zigzag pattern. The bobbin thread 24 is inserted into the hole 102 as shown in FIG. 4A.
It should be noted that the feed dog 12 is in its fully raised position and the thread withdrawal member 100 is pivoted upwards, with its free end 103
rises to its highest point as indicated by K in FIG. There is a small recess 150 under the leftmost leg of the feed dog 12, which allows the thread withdrawal member 100 to pivot upwardly to its maximum extent. When the needle swings to the rightmost bite position of the zigzag pattern and begins to penetrate the workpiece, the feed dog 12 is lowered by a feed dog drive mechanism (not shown), thereby causing the thread to be pulled out. Member 100 pivots about member 104 until it reaches position L shown in FIG. When the end 103 moves from position K to position L, the thread 24 is pushed downward, thereby causing a predetermined length of thread to be attached to the bobbin 22.
thread tension device 26 to create slack in the thread 24 between the thread tension device 26 and the last stitch set in the workpiece.
When needle 42 reaches the rightmost bite position as shown in FIG. 2, the workpiece leg (not shown) of the needle thread moves along ramp 107 to point 108. This allows the needle thread loop to fully expand when the thread taker begins to wrap the needle thread around the bobbin case 20. Next, the needle 42 and the feed dog 12 rise,
The thread withdrawal member 100 is allowed to rise, thereby making the bobbin thread 24 available for setting the seam. When the needle 42 moves to the leftmost bite position, the bobbin thread 24 remains substantially in the position indicated by S' as shown in FIG. When the feed dog 12 begins to descend, the thread pulling member 100 is
Move the member downward until it reaches position L shown in FIG. This downward movement of the thread withdrawal member 100 again forces the thread 24 downwardly so that a predetermined length of thread is drawn from the bobbin 22 and through the thread tension device 26 to create slack as described above. However, the loosening that occurs at this time is small. This is because the distance the thread 24 travels from S' to S in FIG. 5 is smaller than the distance it travels from the previous R' to R. Since the leftmost position of the needle 42 is closer to the thread tension device 26 from which the bobbin thread exits than the rightmost bite position, there is less slack required in the bobbin thread 24 when the stitch is set in the leftmost position. is smaller than when the seam is set in the rightmost position. This requirement is met by the variable withdrawal action of the thread withdrawal member 100, as described above. A predictable length of bobbin thread is drawn from the bobbin, and this is directly proportional to the needle penetration bite position of the workpiece. Therefore, right pattern 1 in Figure 6
A zigzag seam pattern having a uniform appearance as shown at 30 is formed. Left pattern 1 in Figure 6
40 represents a stitch that occurs when insufficient slack is provided in the bobbin thread 24 before setting the stitch at the rightmost bite position.

The operation of the present invention has been described above with respect to the case where the needle occupies the leftmost position and the rightmost position, but the device can provide appropriate slack to any position of the cutting tool within the operating range of the sewing machine. . An important feature of the present invention is that the thread withdrawal member 100 withdraws various lengths of bobbin thread 24, depending on the slack required for each particular bite position of the seam being set. This result is achieved by the combination of pivoting movement and a substantially straight thread engagement surface. Similar results can be achieved with other combinations of thread engagement surface shape and relative motion imparted to the surface. For example, a straight thread engaging surface that is inclined relative to the sewing machine bed and is subjected to vertical linear movement will provide the desired results. Importantly, the shape of the thread-engaging surface must be combined with its predetermined movement so that a predetermined length of thread is withdrawn for each needle penetration position.

Another important feature of the present invention is to minimize half-hits that occur when the sewing machine performs straight stitches with needle 42 in the leftmost position. Immediately before each needle penetration takes place, the bobbin thread 24 is moved by the thread withdrawal member 100 to the position indicated by A in FIG. 4. This causes the needle to always move to the right of the bobbin thread, thus preventing half-hits.

A review of the above description will show that various modified structures are possible. Such a structure may use various forms of thread withdrawal members with or without holes and with pivoting, arcuate or linear movement.

[Brief explanation of drawings]

1 and 2 are perspective views of a portion of the sewing machine in the area of the thread taker, illustrating a preferred embodiment of the invention. 3 is a perspective view of the thread withdrawal member and spring; FIG. 4 is a plan view of the area of the sewing machine shown in FIG. 1; and FIG. 5 is a section taken along line 5--5 in FIG. Figure 6 is a schematic diagram of the workpiece.
Two zigzag stitch patterns are shown. In the figure, 10 is a thread remover, 12 is a feed dog, 2
0 is a bobbin case, 26 is a thread tension device, 50 is a bracket, 100 is a thread pulling member, 102 is a central hole, 107 is an inclined surface, and 112 is a leaf spring.

Claims (1)

[Scope of Claims] 1. A sewn product feed device that is provided with a feed dog that moves up and down and establishes the feed direction of the sewn product, and that swings within a predetermined range in the lateral direction of the feed direction and penetrates the sewn product. a needle that reciprocates to define a zigzag sewing pattern in cooperation with the sewing product feeding device; a thread taker that cooperates with the needle when forming a lock stitch; and a cavity that accommodates a bobbin. a bobbin contained within the cavity; and a thread tension device associated with the thread taker and establishing passage of the bobbin thread to a location through which the needle passes. In a bobbin thread pulling device for a zigzag sewing machine, the bobbin thread drawing device has a portion extending substantially parallel to the swinging direction of the needle and disposed between the swinging position of the needle and the bobbin. a rod member extending beyond the passage of the bobbin thread and below the feed dog; a rotational support device held on a sewing machine; and an angular movement device for angularly moving the bar member around the axis, thereby pulling out a bobbin thread of a length corresponding to the needle penetration position from the bobbin. and an angular motion device having an elastic device that urges the rod member upward to engage the feed dog.