zigzag stitch sewing machine

Abstract

To form scheduled seams by properly adjusting thread tension.SOLUTION: A zigzag stitch sewing machine 10 which forms zigzag seams by performing needle swing alternately in the direction crossing the moving direction of sewing includes: a thread tension device 2 capable of changing and adjusting the thread tension of a needle thread U by an actuator 33; a rotating thread take-up lever 41; an upper shaft angle detection device 66; and a control device 100 for controlling the actuator. The control device controls the actuator in a no-change zone k1 or k2 of the thread tension to the needle thread by the rotating thread take-up lever, on the basis of the detection of the upper shaft angle detection device.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a zigzag stitch sewing machine. [Background technology]

[0002] 2. Description of the Related Art Sewing machines have traditionally been equipped with thread tensioning devices that apply tension to threads used in sewing in order to form proper stitches. In recent years, some thread tensioning devices are capable of arbitrarily controlling thread tension using an actuator such as a solenoid (see, for example, Patent Document 1). A sewing machine equipped with such a thread tensioning device was able to change the thread tension during one rotation of the upper shaft, making it possible to more precisely adjust the state of the stitches being formed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 09-220391 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the above-mentioned thread tensioning device is applied to a zigzag stitch sewing machine and an attempt is made to adjust the thread tension to suit each of the left and right needle swings, there are cases where the control is not properly reflected due to a delayed response, and the desired stitches cannot be obtained.

[0005] An object of the present invention is to properly adjust thread tension to form a predetermined stitch. [Means for solving the problem]

[0006] In a zigzag stitch sewing machine that forms zigzag stitches by alternately swinging the needle in a direction that intersects with the sewing direction, a thread tensioning device that can change and adjust the tension of the upper thread using an actuator; The hook extends radially outward in the direction of rotation around the upper shaft, and has a pair of thread hooks extending in both tangential directions of the rotation arc at the tip end, and a recess is formed at the edge of the base end downstream in the direction of rotation. A rotating balance and a first thread guide member and a second thread guide member provided below the rotary thread take-up on the upstream and downstream sides of an upper thread path relative to the rotary thread take-up; an upper shaft angle detection device for detecting an upper shaft angle with the top dead center of the needle bar being 0°; a control device for controlling the actuator, The control device is characterized in that, based on detection by the upper shaft angle detection device, it controls the actuator within a zone in which the thread tension of the upper thread is unchanged by the rotary take-up lever, where the magnitude and amount of change in the thread tension of the upper thread are smaller than in other zones in which the thread tension of the upper thread increases or decreases within one rotation of the upper shaft.

[0009] Furthermore, the invention described in claim 1 is A thread tension setting means is provided for individually setting thread tensions for the left needle swing and the right needle swing, The no-change section is a period from when the rotary take-up lever is turned upward and the upper thread is caught in the recessed portion to when the rotary take-up lever is turned downward and the upper thread is caught in the pair of thread catch portions. This is the section where the upper thread slides down along the edge portion on the downstream side in the rotation direction of the rotary thread take-up. It is characterized by the following. [Effects of the Invention]

[0010] By controlling the actuator within a section where the thread tension does not change, the present invention reduces the influence of fluctuations in thread tension and enables sewing to be performed with an appropriate thread tension for each of the alternating needle swings, thereby making it possible to homogenize the stitches for each needle swing and achieve improved sewing quality. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a side view of a zigzag stitch sewing machine according to an embodiment of the present invention, viewed from the face side; [Figure 2] 2 is a cross-sectional view of a surface portion taken along line WW in FIG. 1. [Figure 3] Figures 3(A) to (G) are explanatory diagrams showing the change in the shortest path of the upper thread from the first thread guide member to the second thread guide member at each upper shaft angle of 80°, 90°, 150°, 180°, 210°, 240°, and 270°. [Figure 4] Figures 4(A) to (F) are explanatory diagrams showing the change in the shortest path of the upper thread from the first thread guide member to the second thread guide member at each upper shaft angle of 310°, 330°, 0°, 30°, 60°, and 70°. [Figure 5] FIG. [Figure 6] FIG. 2 is a block diagram showing a control system of a zigzag stitch sewing machine. [Figure 7] FIG. 10 is an explanatory diagram showing a zigzag stitch. [Figure 8] FIG. 10 is a diagram showing the change in thread tension value during one rotation of the upper shaft when performing zigzag stitching. [Figure 9] 10 is a flowchart of thread tension control executed by a CPU during sewing. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Overall configuration of the embodiment of the invention] A zigzag stitch sewing machine 10 equipped with a rotary thread take-up lever device according to an embodiment of the present invention will be described below with reference to Figures 1 to 7. Figure 1 is a side view of the zigzag stitch sewing machine 10 as seen from the face side, and Figure 2 is a cross-sectional view of the face along line WW. In the following description, the horizontal direction in which the cloth is fed will be referred to as the X-axis direction, the horizontal direction perpendicular to the cloth feed direction will be referred to as the Y-axis direction, and the vertical direction will be referred to as the Z-axis direction. The zigzag stitch sewing machine 10 includes a needle bar 12 that holds a sewing needle 11 at its lower end, a needle swing mechanism 50 that swings the needle bar 12 in a direction perpendicular to the direction, an up-and-down movement mechanism 60 that moves the needle bar up and down, a thread take-up device 40 that has a rotary thread take-up (so-called rotary thread take-up) 41, and a rotary thread tensioning device 2 that applies tension to the upper thread U.

[0013] The needle swing mechanism 50 is provided within the sewing machine arm section 14 and includes a swing table 52 connected to a support shaft 51 along the Y-axis direction, and a needle swing motor 53 (see Figure 6) that moves the support shaft 51 and the swing table 52 back and forth along the Y-axis direction. Furthermore, swing base 52 supports needle bar 12 via a slide bearing so that it can slide along the Z-axis direction.

[0014] The up-and-down movement mechanism 60 is provided within the sewing machine arm section 14, is arranged along the Y-axis direction, and comprises an upper shaft 61 that is driven to rotate by a sewing machine motor 65 (see Figure 6), a needle bar crank 62 fixedly mounted to the tip of the upper shaft 61, a needle bar crank rod 63 whose one end is connected to an eccentric position from the center of rotation of the needle bar crank 62 so as to be rotatable around the Y-axis, and a needle bar holder 64 fixedly mounted to the needle bar 12. Furthermore, the needle bar holder 64 is supported on the other end of the needle bar crank rod 63 so as to be rotatable around the Y axis and slidable along the Y axis direction. As a result, even when the needle swing mechanism 50 causes the needle bar 12 to move back and forth along the Y axis direction via the swing table 52, the needle bar holder 64 can impart up and down movement to the needle bar 12 while allowing the reciprocating movement.

[0015] The zigzag stitch sewing machine 10 also includes a shuttle mechanism that intertwines the upper thread U with the lower thread D, and a cloth feed mechanism that feeds the cloth along the X-axis direction, but these are well-known configurations and will not be described here.

[0016] [Balance device] The thread take-up device 40 includes a rotary thread take-up 41 that rotates using an upper shaft 61, a rotary disk 42 that serves as a base for the rotary thread take-up 41, a connecting shaft 43 that connects the rotary disk 42 and the upper shaft 61, a first thread guide member 44 through which the upper thread U passes from the upper thread supply source to the rotary thread take-up 41, a second thread guide member 45 through which the upper thread U passes from the rotary thread take-up 41 to the needle bar thread holder 13 of the sewing needle 11, and a protective cover 46 for the rotary thread take-up 41 (not shown in Figure 1).

[0017] 1 (the direction of arrow R in FIG. 1), like the upper shaft 61. A first thread guide member 44 is provided on the outer wall on the front side of the sewing machine arm section 14. A second thread guide member 45 is provided below a face plate 70 fixed to the face section of the sewing machine arm section 14. Both of these thread guide members 44, 45 are structured to pass the upper thread U through a hole in the thread guide member 44, 45 and guide the upper thread U so that it always passes through a fixed position.

[0018] The rotary disc 42 is loosely fitted into a circular opening 71 formed in the face plate 70 , and rotates integrally with the upper shaft 61 via the connecting shaft 43 . The rotary balance 41 has its base end fixedly supported by the rotary disc 42 and its tip end extending outward in the direction of the radius of rotation centered on the upper shaft 61 . The tip of the rotary thread take-up 41 is provided with a pair of claws 41a, 41b as thread hooking portions that extend in both tangential directions of the rotation arc, and each of the claws 41a, 41b is curved in a direction that moves away from the face plate 70 as it approaches the tip. Due to this shape, when the tip of the rotary thread take-up 41 faces downward, the upper thread U wraps around and is hooked on the back side of each of the claws 41a, 41b, preventing it from falling off the rotary thread take-up 41.

[0019] Further, a recess 41c is formed in the rotary thread take-up 41 at the edge portion near the base end thereof and on the leading (downstream) side in the direction of rotation. The upper thread U passing from the first thread guiding member 44 to the second thread guiding member 45 via the side edge of the rotary thread take-up 41 is caught in the recess 41c in time with the sewing needle 11 starting to penetrate the fabric near an upper shaft angle of 90° (the upper shaft angle at the top dead center of the needle bar is set to 0°), and thereby the tension of the upper thread U pulled up by the rotary thread take-up 41 is released, leaving the upper thread U slack, so that there is slack in the upper thread U when the sewing needle 11 penetrates the fabric (see FIG. 3(B)).

[0020] Figures 3(A) to (G) are state explanatory diagrams showing the change in the shortest path of the upper thread U from the first thread guide member 44 to the second thread guide member 45 at each upper shaft angle of 80°, 90°, 150°, 180°, 210°, 240°, and 270°, and Figures 4(A) to (F) are state explanatory diagrams showing the change in the shortest path of the upper thread U from the first thread guide member 44 to the second thread guide member 45 at each upper shaft angle of 310°, 330°, 0°, 30°, 60°, and 70°.

[0021] Here, the change in the shortest thread path of the upper thread U caused by the rotary thread take-up 41 will be described with reference to FIGS. 3(A) to 4(F). As shown in Figures 3(A) and 4(A), the rotary take-up lever 41 is attached to the rotary disc 42 so that the rotary take-up lever bottom dead center, where the amount of upper thread U taken up is minimum, occurs at an upper shaft angle of approximately 310°, and the rotary take-up lever top dead center, where the amount of upper thread U taken up is maximum, occurs at an upper shaft angle of approximately 80°. After the rotary thread take-up has passed the bottom dead center, the inclination of the shortest yarn path changes counterclockwise in Figures 3 and 4 around the first yarn guiding member 44, and the angle change of the shortest yarn path in the counterclockwise direction is maximum when the upper shaft angle is approximately 0°. 3 and 4, passes the rotary take-up top dead center at an upper shaft angle of approximately 80°, and then turns counterclockwise at an upper shaft angle of 150°. Furthermore, at an upper shaft angle of approximately 270°, the angle of the shortest yarn path reaches its maximum in the clockwise direction, after which the shortest yarn path changes angle counterclockwise and again reaches the rotary take-up bottom dead center.

[0022] [Thread tension device] The rotary thread tensioning device 2 includes a thread tensioner 20 and a thread tensioning solenoid 33 as an actuator for adjusting the thread tension of the thread tensioner 20 as desired.

[0023] FIG. 5 is a perspective view of the thread tensioner 20. As shown in the figure, the thread tension controller 20 comprises a thread tension disc 30 having a central hole 31, a thread tension shaft 21 that passes through the thread tension disc 30 and rotatably supports it, a pair of disc pressers 27 arranged on both sides of the thread tension disc 30 in the X-axis direction, a pair of abutment members 28 interposed between each disc presser 27 on both sides of the thread tension disc 30, a pressing shaft 22 that passes through the thread tension shaft 21 and presses one of the disc pressers 27 in a direction away from the thread tension disc 30, a thread take-up spring 23 with a torsion coil spring structure that is arranged on the outer periphery of the thread tension shaft 21, a thread tension base 24 that stores the thread take-up spring 23, a protective cover 25 that is fixed to the tip of the thread tension shaft 21, and an insertion member 26 that is inserted into the protective cover 25.

[0024] The thread tensioner base 24 is cylindrical, with its center line aligned along the X-axis direction, and its base end is embedded and fixed in the outer wall of the sewing machine arm portion 14 on the operator side (front side). The base end of the tensioner base 24 is closed, and the right end is open. A through-hole 241 is formed in the wall of the closed base end of the tensioner base 24, penetrating through the center thereof along the X-axis direction.

[0025] The tension shaft 21 has an insertion hole 211 that passes through the center, and is supported by the tension shaft base 24 with its center line oriented in the X-axis direction. The tension shaft 21 has a longitudinal intermediate portion 212 that has a maximum outer diameter, and the end portion on one side that is inserted into the tension shaft base 24 has a reduced-diameter portion 213 that reduces in diameter in two stages from the intermediate portion 212. The reduced-diameter portion 213 of the tension shaft 21 is inserted into a through-hole 241 in the wall of the left end portion of the tension shaft base 24, and is fastened and fixed by a headless screw (not shown).

[0026] The opposite end of the tension shaft 21 has a split portion 214, which is entirely divided into two on the right side of the intermediate portion 212 by a slit 215 that passes through the centerline. In other words, the cross section of the split portion 214 perpendicular to the axis has two roughly semicircular shapes obtained by dividing a circle in half across the diameter. The slit 215 and the insertion hole 211 are in communication with each other. On the other hand, the pair of disc presser members 27 are disk-shaped and have circular through-holes 271 formed in their centers with central ribs 272. That is, the through-holes 271 of the disc presser members 27 are shaped like two roughly semicircular circles, with the central ribs 272 dividing a circle in half across the diameter. The cut-out portions 214 of the tension shafts 21 are inserted into the through-holes 271 of each disc presser member 27 so that the central ribs 272 are inserted inside the slits 215. On the other hand, the pair of abutment members 28 and the thread tension discs 30 each have a circular through hole 281 and a shaft hole 31 formed in the center, both of which do not have a central rib, and the cut-out portion 214 of the thread tension shaft 21 is inserted into these through hole 281 and shaft hole 31 and held between the pair of disc holders 27. Therefore, each disc presser 27 is held so as not to rotate relative to the tension shaft 21 and the tension table 24, and each abutment member 28 and tension discs 30 are held so as to be rotatable relative to the tension shaft 21 and the tension table 24. In addition, each disc presser 27, each abutment member 28 and tension discs 30 are movable along the cut-out portion 214 of the tension shaft 21.

[0027] The pressing shaft 22 is shaped like a small pin and is slidably inserted into the insertion hole 211 of the reduced diameter portion 213 of the tension shaft 21. One end of the pressing shaft 22 abuts against the central rib 272 of one of the disc presser plates 27, and the other end of the pressing shaft 22 protrudes from the reduced diameter portion 213 of the tension shaft 21 to the outside. A pressing force is input from the tension solenoid 33 to the pressing shaft 22 in the direction of being pressed into the tension shaft 21 from the end portion protruding from the reduced diameter portion 213, causing each contact member 28 to contact the tension discs 30 via the disc presser 27. By adjusting the pressing force, the sliding frictional force of each contact member 28 against the tension discs 30 can be adjusted, and the sliding frictional force against the rotation of the tension discs 30 can be adjusted.

[0028] The coil-shaped main body of the thread take-up spring 23 is inserted between the inner peripheral surface of the tension table 24 and the outer peripheral surface of the intermediate portion 212 of the tension shaft 21. At this time, one end of the wire material constituting the thread take-up spring 23 is inserted into a rotation prevention groove 216 formed on the outer peripheral surface of the intermediate portion 212 of the tension shaft 21, and is fixed so as not to rotate relative to the tension shaft 21 and the tension table 24. The other end of the wire material constituting the thread take-up spring 23 has a hook-shaped thread hook 231. This thread hook 231 extends to the outside of the tension table 24 through a slit 242 formed through the inner peripheral surface of the tension table 24 and the outer peripheral surface.

[0029] The protective cover 25 is a cylindrical body having a through hole 251 in the center, and the surface facing the dish presser 27 on one side abuts against the dish presser 27 . The protective cover 25 has a slit 252 formed along its entire length, which runs from a central through-hole 251 to the outer periphery, and can securely hold the cut-out portion 214 of the tension shaft 21 inserted into the through-hole 251. An insert member 26 is inserted into the slit 215 in the cut-out portion 214 of the tension shaft 21, and restricts the width of the slit 215 from narrowing when the cover is held down, so that the disc presser members 27, the abutment members 28, and the tension discs 30 can move smoothly along the tension shaft 21.

[0030] The thread tension disc 30 has a V-shaped groove 32 formed on its outer periphery for winding the upper thread U, and the bottom of the V-shaped groove 32 has concave and convex portions formed alternately along the circumferential direction. The upper thread U is wound around the V-shaped groove 32 of the tension disc 30 one or two times before being supplied to the supply destination of the upper thread U, and as the upper thread U is consumed at the supply destination and is unwound, the tension disc 30 rotates. As described above, the tension disc 30 is provided with an adjustable sliding friction force, so that the appropriate thread tension can be applied to the unwound upper thread U.

[0031] The contact member 28 is a circular plate with a through hole 281 formed in the center. All components of the thread tension controller 20 except for the contact member 28 are made of metal such as stainless steel, but the contact member 28 is made of a resin material with excellent sliding properties such as fluororesin, polyamide resin, or polyacetal resin. By forming the contact members 28 from these materials, the tension discs 30 can be maintained at a low tension even if the pressing force that brings each contact member 28 into contact with the tension discs 30 is increased, compared to when the contact members are formed from felt material.

[0032] The thread tension solenoid 33 is supported by the sewing machine arm portion 14, and a plunger that can move forward and backward presses the pressing shaft 22 of the thread tension controller 20. The thread tension solenoid 33 can adjust the pressing force applied by the plunger to press the pressing shaft 22 according to the magnitude of the drive current. This allows the thread tension controller 20 to generate any desired thread tension.

[0033] [Control device] FIG. 6 is a block diagram showing the control system of the zigzag stitch sewing machine 10. The zigzag stitch sewing machine 10 is equipped with a control device 100 for controlling the operations of the above-mentioned components. The control device 100 includes a program memory 102 in which a thread tension control program 102a and various other programs are stored, a data memory 103 in which various setting data 103a including a thread tension setting value are stored, and a CPU 101 that executes the various programs.

[0034] A sewing machine motor drive circuit 65a that controls the sewing machine motor 65 is connected to the CPU 101 via an interface 65b, and a needle swing motor drive circuit 53a that controls the needle swing motor 53 is connected to the CPU 101 via an interface 53b. The sewing machine motor 65 is provided with an encoder 66 as an upper shaft angle detection device for detecting the upper shaft angle. A servo motor, for example, can be used as the sewing machine motor 65. Furthermore, a stepping motor, for example, can be used as the needle swing motor 53. Further, a thread tension solenoid drive circuit 33a that controls the thread tension solenoid 33 is connected to the CPU 101 via an interface 33b.

[0035] Furthermore, an operation panel 110 is connected to the CPU 101 via an interface 110b. The operation panel 110 has a display unit 111 that displays various screens and input buttons, and a touch sensor 112 that is provided on the surface of the display unit 111 and detects the contact position, and functions as an input / output means for various information. All of the input buttons and switches used on the operation panel 110 are displayed on the display unit 111, and input is detected by the touch sensor 112, so that they function in the same way as push-down buttons and switches.

[0036] [Thread tension control] The thread tension control executed by the CPU 101 during sewing based on the thread tension control program 102a will be described. As shown in Figure 7, in zigzag stitching, the needle swings alternately in one direction and the other perpendicular to the cloth feed direction in synchronization with the needle entry, forming stitches alternately in two diagonal directions that are symmetrical based on the combination of the needle swing width and the cloth feed width, thereby sewing a zigzag pattern. In FIG. 7, arrow H indicates the cloth feeding direction.

[0037] Figure 8 is a diagram showing the change in thread tension value during one rotation of the upper shaft 61 when performing the zigzag stitch. The solid line in Figure 8 shows the change in thread tension value when the needle swings to the left while facing downstream in the cloth feed direction (left needle swing state), and the dotted line shows the change in thread tension value when the needle swings to the right while facing downstream in the cloth feed direction (right needle swing state). It is assumed that the thread tension solenoid 33 is maintained at a constant output.

[0038] As shown in Figure 8, there is a difference in the change in thread tension between left and right needle swings. This is because the timing and position at which the shuttle catches the upper thread differs between left and right needle swings, and the direction of the thread path from the rotary take-up lever 41 to the sewing needle 11 differs between left and right needle swings. As shown in Fig. 8, if the upper shaft angle at which the sewing needle 11 reaches its top dead center is set to 0°, the upper shaft angle section k0 of approximately 310° to 50° corresponds to the period during which the shuttle that has caught the loop of the upper thread U pulls the loop of the upper thread U below the workpiece and passes it through the shuttle. Within this upper shaft angle section k0, it can be seen that the change in the thread tension is significantly different between the left needle swing and the right needle swing.

[0039] In general, in zigzag stitching, it is desirable that uniform stitches be formed whether the needle is swung to the left or to the right. If the integral value of the thread tension in one rotation of the upper shaft 61 becomes equal when the needle swings to the left and when the needle swings to the right, the uniformity of the stitches can be improved. Therefore, in this zigzag stitch sewing machine 10, the thread tension can be set individually for the left needle swing and the right needle swing from the operation panel 110. In other words, the operation panel 110 functions as a thread tension setting means. The set data 103a of the data memory 103 includes table data that defines the drive current value of the thread tension solenoid 33 corresponding to the set value of the thread tension.

[0040] When the needle swing is switched from left to right or from right to left, the CPU 101 changes the output of the thread tension solenoid 33 at a specified upper shaft angle and controls the rotary thread tension device 2 to achieve the set thread tension. In this case, it is desirable that the change in output of the thread tension solenoid 33 be made at a timing that does not affect the formation of stitches.

[0041] Referring again to Figure 8, in angle section k1 where the upper shaft angle is 120° to 300°, and further in angle section k2 where the upper shaft angle is 150° to 300°, the tension is low for both the left needle swing and the right needle swing, and tension fluctuations therebetween are small. In this way, the section where the tension is below a specified value and fluctuations are small is called the no-change section. The upper shaft angle of 120° is the upper shaft angle at which the sewing needle 11 begins to pierce the sewing material, and the upper shaft angle of 300° is the upper shaft angle at which the rotary thread take-up lever 41 is at its bottom dead center. This angle section of the upper shaft angle of 120° to 300° is called the first no-change section k1 of thread tension. Furthermore, upper shaft angle 150° is the position where rotary thread take-up 41 starts to rotate downward from a vertically upward facing state (see FIG. 3(C)), and from this point onwards, up to an upper shaft angle of around 300°, this is the angle section where the upper thread U slides down along the edge portion on the downstream side in the rotation direction of rotary thread take-up 41 (see FIGS. 3(D) to 4(A)). Therefore, the angle section from upper shaft angle 150° to 300° is the section where the upper thread U is released from the tension of rotary thread take-up 41, and where almost no tension is applied to the upper thread U by the rotary thread tension device 2 downstream of rotary thread take-up 41. This angle section from upper shaft angle 150° to 300° is referred to as second no-change section k2 of thread tension.

[0042] In thread tension control, the CPU 101 reads the set thread tension value for each needle point, detects the upper shaft angle based on the output of the encoder 66 of the sewing machine motor 65, and controls the output of the thread tension solenoid 33 so that the thread tension becomes the set value within the first or second no-change section k1, k2 of the thread tension.

[0043] FIG. 9 is a flowchart of the thread tension control executed by the CPU 101 during sewing. As shown in the figure, when the sewing machine motor 65 is driven, the CPU 101 reads the set value of the thread tension for the next needle drop from the data memory 103 at a specified upper shaft angle (step S1). Then, the CPU 101 monitors the output of the encoder 66 (step S3) and continues monitoring as long as the angle of 150°, which is the start angle of the no-change section k2 of the thread tension, has not been reached, and when it detects that 150° has been reached, it controls the drive current of the thread tension solenoid 33 to the set value of the thread tension (step S5). The thread tension control is performed for each stitch, and when the thread tension is set individually for the left needle swing and the right needle swing, the thread tension solenoid 33 is controlled so that the thread tension reflects the setting. Although this flowchart illustrates an example in which the output of the thread tension solenoid 33 is controlled within the unchanged section k2 of the second thread tension, the output of the thread tension solenoid 33 may be controlled within the unchanged section k1 of the first thread tension.

[0044] [Technical Effects of the Embodiments of the Invention] In the zigzag stitch sewing machine 10, the control device 100 controls the thread tension solenoid 33 based on the detection of the encoder 66 to keep the first or second thread tension applied to the upper thread U by the rotary thread take-up 41 within the unchanged section k1, k2. In the first thread tension unchanged section k1 and the second thread tension unchanged section k2, the thread tension generated in the upper thread U is sufficiently reduced and the fluctuations in the thread tension are sufficiently small. Therefore, by controlling the thread tension solenoid 33 to change the thread tension during these sections, the influence of the fluctuations in the thread tension is reduced, and it becomes possible to apply a thread tension to the upper thread U that corresponds to the set value with greater accuracy. Therefore, even if different thread tensions are set for the left and right needle swings of the zigzag stitch, stitches can be formed with thread tensions appropriate for each, making it possible to achieve uniform stitches and improve sewing quality.

[0045] In particular, by controlling the thread tension solenoid 33 in the first unchanged section k1, which is the range from when the sewing needle starts to pierce the sewing material to the bottom dead point of the thread take-up lever, it is possible to form stitches with appropriate thread tension for each left and right needle swing of the zigzag stitch, thereby making it possible to uniformize the stitches and improve sewing quality. Furthermore, by controlling the thread tension solenoid 33 in the second unchanged section k2, which is the upper shaft angle range of 150 to 310 degrees, stitches can be formed with more appropriate thread tension for each left and right needle swing of the zigzag stitch, making it possible to further uniformize the stitches and improve sewing quality.

[0046] In addition, the zigzag stitch sewing machine 10 is equipped with an operation panel 110 for setting thread tensions separately for left and right needle swings, so that it is possible to separately set thread tensions suitable for left and right needle swings based on the results of actual sewing, etc.

[0047] [others] The details shown in the above embodiment can be modified as appropriate without departing from the spirit of the invention. For example, in the rotary thread tensioning device 2, a solenoid is exemplified as an actuator for adjusting the thread tension, but any actuator that can control the amount of pressing of the pressing shaft 22 can be used.

[0048] Furthermore, the set value of the thread tension is not limited to being settable in two patterns for left needle swing and right needle swing, but may be settable individually in order for one stitch or a range of multiple stitches. Furthermore, as an example of zigzag stitching, a basic zigzag stitch in which the needle swings left and right for each stitch has been given, but the invention is not limited to this and the thread tension control can also be applied to zigzag stitching in which the needle swing direction is changed in units of multiple stitches or scallop stitching. [Explanation of symbols]

[0049] 2 Rotary thread tension device 10. Zigzag stitch sewing machine 11 Sewing Needles 12 Needle bar 14 Sewing machine arm 20 Thread tension controller 33 Thread tension solenoid (actuator) 40 Balance device 41 Rotating balance 65 Sewing machine motor 66 Encoder (upper shaft angle detection device) 100 control device 110 Operation panel (thread tension setting means) k1 First unchanged section k2 Second unchanged section U Upper thread

Claims

[Claim 1] In a zigzag stitch sewing machine that forms zigzag stitches by alternately swinging the needle in a direction that intersects with the sewing direction, a thread tensioning device that can change and adjust the tension of the upper thread using an actuator; a rotary thread take-up extending radially outward from the upper shaft and having a pair of thread hooking portions extending in both tangential directions of the rotation arc at its tip end, and a recess formed in an edge portion of the base end portion downstream in the rotation direction; a first thread guide member and a second thread guide member provided below the rotary thread take-up on the upstream and downstream sides of an upper thread path relative to the rotary thread take-up; an upper shaft angle detection device for detecting an upper shaft angle with the top dead center of the needle bar being 0°; a control device for controlling the actuator, the control device controls the actuator within a range of no change in the thread tension of the upper thread caused by the rotary take-up, based on the detection by the upper shaft angle detection device, in which the magnitude and amount of change in the thread tension of the upper thread are smaller than in other ranges in which the thread tension of the upper thread increases or decreases during one rotation of the upper shaft; A thread tension setting means is provided for individually setting thread tensions for the left needle swing and the right needle swing, The zigzag stitch sewing machine is characterized in that the no-change section is the section from when the rotary take-up is turned upward and the upper thread is hooked on the recessed section until when the rotary take-up is turned downward and the upper thread is hooked on the pair of thread hooking sections, during which the upper thread slides down along the edge section on the downstream side in the rotation direction of the rotary take-up.

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