JPH0523470A - Sewing machine capable of preventing skip stitch - Google Patents

Abstract

PURPOSE:To provide the sewing machine capable of preventing surely generation of a skip stitch with a simple control mechanism. CONSTITUTION:In a passing path of a thread loop of an outer hook 22, a leaf spring member 32 which can be deformed elastically by the thread loop, and a detection switch 36 for detecting an elastic deformation of the leaf spring member 32 are provided, and passing of the thread loop is detected. In a regular sewing period, after a passing signal of the thread loop is received from a thread loop detecting device, a needle bar oscillating mechanism and a feed dog driving mechanism are driven, based on sewind data read in from a ROM, and if the passing signal of the thread loop cannot be received, control is executed, so that the needle bar oscillating mechanism and the feed dog driving mechanism are not driven.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sewing machine capable of preventing the occurrence of stitch skipping, and in particular, when stitch skipping is detected, a sewing needle is dropped at or near a stitch position at the time of detection. The present invention relates to a sewing machine capable of preventing skipping by stopping the progress of sewing until skipping is no longer detected.

[0002]

2. Description of the Related Art Generally, in order to entangle an upper thread and a lower thread to form a stitch, a rotary hook is provided in a bed portion of a sewing machine to rotate in synchronization with the vertical movement of a needle bar. , Zigzag sewing and various pattern sewing are possible by the vertical movement and swing of the needle bar, the transfer of the work cloth by the feed dog, and the cooperation with the rotary hook.

By the way, the rotary hook comprises an inner hook having a bobbin bobbin attached thereto and an outer hook having the inner hook for accommodating the inner hook and having a sword tip. The outer hook is rotated to form the sword tip in the vicinity of the eyelet hole of the needle. The upper thread is engaged with the upper thread initial loop, and an upper thread loop is formed by enlarging the initial loop to entangle the upper thread with the lower thread. Therefore, when assembling the sewing machine, fine adjustment is performed so that the gap between the sewing needle and the tip of the sword is a predetermined distance so that the sock is not formed because the tip of the sword does not engage with the needle thread initial loop, so-called skipping does not occur. There is.

However, skipping occurs due to the type of work cloth or the upper thread, or a slight change in the timing of encounter between the upper thread initial loop and the tip of the sword during zigzag sewing or embroidery sewing. Immediately after this stitch skipping occurs, the stitch skipping occurs on the lower side of the presser foot, so it is not possible to immediately notice the occurrence of this stitch skipping, and also notice the occurrence of stitch skipping during sewing. Even in this case, stitches for several stitches or dozens of stitches are often formed from the stitch skip position. In such a case, in the conventional sewing machine, after all the stitches from the final stitch position to the stitch position where the stitch skip has occurred in order to eliminate the stitch skip, sewing is performed again from the stitch position where the stitch skip occurs. Was going on.

Further, in order to prevent the occurrence of such skipped stitches, the applicant of the present application, in Japanese Patent Application No. 2-279637, filed on Oct. 17, 1990, engaged with a sword tip near the rotary hook. When a stitch skipping signal is received from the upper thread loop detection switch that is arranged in contact with a part of the upper thread loop passage, the needle bar is temporarily stopped from moving up and down and the work cloth is fed backward. , A sewing machine having a function of restarting the sewing from the stitch position where the stitch skipping occurred was proposed.

[0006]

However, in the above-mentioned conventional sewing machine, it is necessary to loosen all the stitches formed with the stitch skipping, and the work of eliminating such stitch skipping requires a great deal of time and labor. As a result, there is a problem that the sewing efficiency is extremely reduced.

Further, Japanese Patent Application No. 2-2 filed by the applicant
The sewing machine proposed in No. 79637 is convenient because it can prevent skipping, but it is necessary to stop the vertical movement of the needle bar and reverse feed the work cloth when skipping occurs. The clutch mechanism of the needle bar is indispensable as its configuration, and as a result, the mechanism as a whole becomes complicated, and complicated control is required to return to the stitch position where the stitch skip has occurred and restart sewing. is there. As a result, there has been a problem that the cost of the sewing machine as a whole will increase in the future, and the sewing efficiency will decrease due to the elimination of skipped stitches that have occurred. Furthermore, since the work cloth is fed in the direction opposite to the sewing direction while eliminating the skipped stitches, it may cause the operator to feel uncomfortable, and in some cases may cause injury. there were.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and it is possible to prevent the occurrence of skipped stitches with a simple structure, and there is no need to eliminate skipped stitches. It is an object of the present invention to provide a sewing machine that can improve the performance and can prevent skipping at low cost.

[0009]

To achieve this object, a sewing machine according to the present invention comprises a needle bar drive mechanism for vertically moving a needle bar having a sewing needle attached to its lower end, and a feed mechanism for vertically and forwardly and backwardly moving a feed dog. A sewing machine having a tooth drive mechanism, an inner hook having a bobbin bobbin attached thereto, and a rotary hook having an outer hook provided with a sword tip, and forming a stitch on cloth by cooperation of these, a sword tip of the rotary hook Is arranged in the passage path of the needle thread loop engaged with
A stitch switch having a detection switch for detecting passage of the upper thread loop, detecting stitch skipping based on an output signal from the detection switch, and the stitch skipping detecting means detecting stitch skipping, The control means controls the needle bar drive mechanism and the feed dog drive mechanism so as to drop the sewing needle at or near the stitch position at the time of detecting the jump.

Further, according to the present invention, a counter means for counting the number of times of stitch skip detection detected by the stitch skip detection means, and a sewing needle of the sewing needle when the number of stitch skip detection by the counter means reaches a predetermined number And a drop position changing means for changing the drop position. Further, when the number of times of skip detection by the counter means reaches a predetermined number,
And a warning means for issuing a warning to the outside.

[0011]

In the sewing machine of the present invention having the above-mentioned structure, which is capable of preventing stitch skipping, when stitch skipping is detected by stitch skipping detecting means, stitching is performed at or near the stitch position at the time when the stitch skipping is detected. Drop the needle. Furthermore,
When the count value of the number of skipped stitches detected by the counter means reaches a predetermined number, the dropping position of the sewing needle is changed and the alarm means issues an alarm to the outside. Also,
When no skipping is detected by the skipping detecting means, sewing is performed by cooperation of the needle bar driving mechanism, the feed dog driving mechanism and the rotary hook.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the drawings based on an embodiment embodying an electronically controlled zigzag sewing machine. FIG. 1 is a perspective view showing an outer appearance of a zigzag sewing machine according to this embodiment. A needle bar vertical drive mechanism and a needle bar swing drive mechanism are incorporated in an arm portion 2 of a sewing machine M, and these mechanisms are usually It is similar to the sewing machine. The outline of these mechanisms will be described. The needle bar 9 provided on the head 4 is mounted on the needle bar support 11 so as to be movable up and down.
An upper end of the needle 1 is pivotally attached to a machine frame 18 by a pivot pin 12, and a needle bar 9 has a lower end to which a sewing needle 10 is attached.

The needle bar 9 is connected to the sewing machine motor 75 (see FIG. 6) via the needle bar holder 13, the crank 5, the sewing machine main shaft 3, etc., and the rotation of the sewing machine motor causes the balance 7 to move up and down and the needle. The rod 9 and the sewing needle 10 are adapted to reciprocate up and down. A stepping motor 7 for swinging the needle bar is connected to the lower end of the needle bar support 11 via a connecting rod 14.
6 (see FIG. 6), the sewing needle 10 swings via the needle bar support 11 and the needle bar 9 by driving the stepping motor 76 for rocking the needle bar.

The presser bar 15 disposed immediately behind the needle bar 9 is supported by the machine frame 18 so as to be switchable between an ascending position and a descending position for pressing the work cloth onto the needle plate 17 by an operating member (not shown). A presser foot 16 is detachably attached to the lower end of the presser bar 15. Further, the pedestal portion 1 is provided with an operation unit 6 including a known operation switch 6a for selecting a sewing pattern and a display unit 6b such as a liquid crystal for confirming and displaying the pattern.

Next, the full-rotation horizontal hook 21 and the stitch skipping detection device provided in the bed portion 8 will be described with reference to FIGS. 2 to 4. The outer hook 22 is supported by the machine frame 18 so as to be rotatable about a vertical axis, and is driven in a predetermined rotation direction by the lower shaft 20 in synchronization with the vertical movement of the needle bar 9, and a part of the outer circumference thereof. A sword tip 23 for catching the upper thread 40 and forming an upper thread loop 41 is formed on.

An inner pot 24 made of synthetic resin is provided inside the outer pot 22.
Is rotatably fitted in the inner hook 24, and an accommodating portion 26 for accommodating the lower thread bobbin 25 is formed in the inner hook 24, and the sewing needle 10 having a predetermined width is dropped on the outer peripheral edge of the inner hook 24. An opening 27 for use is formed. This drop opening 27
A concave portion 28 is formed on the upper surface of the inner pot 24 opposed to the inner pot 24, and a protrusion 29 protruding upward is formed on the outer periphery of the inner pot 24 facing the drop opening 27.

Further, the reverse rotation stop member 30 fixed to the machine frame 18 is engaged with the recess 28, and the inner hook 24 is moved to the lower thread bobbin 25.
It is prevented from rotating clockwise with the rotation of.
Further, a thread locking notch 31 is formed in a substantially central portion of the peripheral edge of the drop opening 27, and the needle thread loop 4 engaged with the sword tip 23 is formed.
The thread portion of the upper thread loop portion 41a that passes below the inner hook 24 of the first hook engages with the thread locking notch 31, and the upper thread loop portion 41a is attached to the outer hook at the peripheral edge of the drop opening 27. Two
It is designed to prevent movement in the direction opposite to the rotation direction of 2.

On the other hand, the inner pot 2 is brought into contact with the protrusion 29 from the right side.
A thin leaf spring member 32 is provided to prevent the counterclockwise rotation of 4. As shown in FIGS. 2 to 4, the leaf spring member 32 is disposed in contact with a part of the passage path of the upper thread loop portion 41b of the upper thread loop 41 that passes above the inner hook 24 and is in front view. Machine frame 1 with substantially crank-shaped support 33
It is attached to 8.

The leaf spring member 32 has a mounting portion 32a which is mounted on the supporting member 33 with a screw 34, and the mounting portion 32.
At the left end of a, the protrusion 29 is bent backward at a right angle in plan view.
And an actuating portion 32c that is bent rightward at a right angle when viewed from the front at the upper end of the abutting portion 32b that abuts against the. The actuating portion 32c is bent in a substantially crank shape when viewed from the front. 3 and always has the reference shape shown by the solid line in FIG.

By the way, the needle thread loop 41 engaged with the sword tip 23 by the counterclockwise rotation of the sword tip 23 moves from the left end portion to the right end portion in the passage route between the upper side and the lower side of the inner hook 24. . While the upper thread loop 41 is moving, the upper thread loop portion 41b on the upper side abuts on the abutting portion 32b to hinder the movement thereof. As shown by the chain double-dashed line in FIG. 3 and FIG. 4, the upper thread loop portion 41b does not move because it is elastically deformed at the substantially central portion in the left-right direction of the mounting portion 32a and the bent portion between the mounting portion 32a and the contact portion 32b. It becomes possible and moves along the passage along with the movement of the sword tip 23.

Next, an upper thread loop 41 formed by engaging the upper thread 40 passing through the eye of the sewing needle 10 with the sword tip 23.
A skipped stitch detection device that detects the presence or absence of a skipped stitch based on the detection result of is described. A photo interrupter (detection switch) 36 having a substantially U-shape in a front view is attached to the machine frame 18 via a mounting plate 37 at the position of the tip of the operating portion 32c of the leaf spring member 32, and the leaf spring member 32 serves as a reference. The actuating portion 32c is located immediately behind the detection section in the middle stage of the photo interrupter 36 when it is in the shape, but when the leaf spring member 32 is in the deformed shape that is elastically deformed by the passage of the needle thread loop 41, the actuating portion 32c is located. Move into the detector.

The photo interrupter 36 is composed of a light emitting diode and a phototransistor, and the emitted light emitted from the light emitting diode is blocked by the moving operation part 32c. Therefore, the output signal (thread passing signal) of the photo interrupter 36 is "L". "Level" to "H" level. Therefore, during the detection period (see FIG. 9) where the needle thread loop 41 passes through the leaf spring member 32 and has a phase angle of about 300 °, it is possible to detect the passage of the needle thread loop 41 based on the yarn passing signal of the photo interrupter 36. You can

On the other hand, when the passage of the upper thread loop 41 is not detected, the emitted light emitted from the light emitting diode is not blocked by the actuating portion 32c, so that the output signal from the photo interrupter 36 is at "L" level. There is. In this way, the detection device determines that skipping has not occurred when the passage of the upper thread loop 41 is detected by the photo interrupter 36, and on the other hand, when the passage of the upper thread loop 41 is not detected. It is determined that a jump has occurred.

Next, the feed dog drive mechanism provided in the bed portion 8 will be described with reference to FIG. The feed dog drive mechanism includes a feed table 50 that supports the feed dog 19 and the feed dog 1.
It has a mechanism for horizontally moving the feed dog 9 and a mechanism for vertically moving the feed dog 19. The feed table 50 is formed in an inverted U shape, and the feed dog 19 is fixed to the upper surface of the upper horizontal portion 50a.

Further, in the lower horizontal portion 50b of the feed table 50,
An overhanging portion 50c extending horizontally is formed on the front surface side (the side facing the worker), and the elongated hole 53 is formed in this overhanging portion 50c.
Has been drilled. In the elongated hole 53, the guide pin 5 vertically protruding from the board 63 provided on the machine frame 18 of the sewing machine M is provided.
2 is slidably faced, and the feed base 50 is linearly movable back and forth under the guiding action of the guide pin 52 facing the long hole 53.

A pivot pin 56 is erected on the board 63 at a position close to the feed table 50, and a horizontal arm 54 is pivotally supported on the pin 56 so as to be rotatable in the horizontal direction. The horizontal arm 54 includes a first arm portion 54a and a second arm portion 5 that extend in opposite directions with respect to the pivot point.
4b is provided. The first arm portion 54a extends toward the feed table 50, and the tip thereof is at the feed table 5
It faces 0 between the upper horizontal part 50a and the lower horizontal part 50b.

A shaft 51 protruding vertically is vertically fixed to the tip of the first arm portion 54a, and the upper and lower end portions of the shaft 51 have upper and lower horizontal portions corresponding to the upper and lower horizontal portions of the feed table 50. It is slidably inserted in the insertion holes formed in 50a and 50b. In addition, the upper end of the shaft 51 has a feed table 50.
It is also commonly inserted in an insertion hole formed in the feed dog 19 fixed to.

A compression spring 55 wound around the shaft 51 is elastically interposed between the lower horizontal portion 50b of the feed table 50 and the first arm portion 54a. Therefore, the feed stand 5
0 is always urged downward by the elastic action of the compression spring 55, and the lower surface of the overhanging portion 50c is brought into contact with a contact member 62 provided on a vertical arm 61 described later.

The second arm portion 54b extends in a direction away from the feed table 50, and a sector gear 54c is integrally formed at the tip thereof. This sector gear 5
4c is meshed with a pinion 57 of a stepping motor 58 for longitudinal movement which is vertically arranged on the substrate 63. Therefore, by driving the stepping motor 58 for forward and backward movement, the horizontal arm 54 rotates about the pivot pin 56 as a fulcrum, and the feed base 50 and the feed dog 19 supported by the first arm portion 54a via the shaft 55 are moved. It is horizontally driven forward and backward, and as described above, the feed table 50 is under the guiding action of the guide pin 52 facing the elongated hole 53, and as a result, the feed table 50 and the feed dog 19 are linearly moved back and forth. To do.

A support piece 59 is provided on the base plate 63 at a position close to the overhanging portion 50c of the feed table 50, and the vertical arm 61 is moved in the direction of the arrow by a pivot pin 60 laterally inserted in the support piece 59. It is pivotally supported to. The vertical arm 61 has a first arm portion 61a and a second arm portion 61b that extend on opposite sides of each other on both sides of the pivotal support portion. This first arm portion 61a
Extends from the pivotal support portion toward the feed table 50, and its tip faces below the overhanging portion 50c of the feed table 50. The projecting portion 50c is urged downward by the elastic action of the compression spring 55, and is in contact with a cylindrical contact member 62 provided at the tip of the first arm portion 61a.

The second arm portion 61b of the vertical arm 61
Is a vertical movement mechanism (not shown) of the second arm portion 61b (for example, a cam member for transmitting the rotation of the main shaft via a vertical shaft, a dedicated pulse motor similar to the horizontal arm 54, etc.).
The vertical arm 61 rotates in the direction of the arrow with the pivot pin 60 as a fulcrum by this vertical movement mechanism, and as a result, the feed table 50 that abuts the abutting member 62 of the first arm portion 61a moves up and down. Driven to.

At this time, the feed table 50 and the feed dog 19 are guided by the vertical shaft 51 provided on the first arm portion 54a of the horizontal arm 54 to move up and down while maintaining the parallel posture. That is, the feed dog 19 is driven forward and backward by the forward-backward moving mechanism at the raised position and the lowered position, respectively, when the vertical movement is applied by the upward-downward moving mechanism so that the forward-backward movement is performed. The work cloth placed on 8 is moved in a predetermined direction.

Next, the control system of the sewing machine M will be described with reference to FIG. FIG. 6 shows a block diagram of the control system of the sewing machine M. A start / stop key 42 provided on the head 4 for instructing start / stop of sewing operation, and a pattern provided on the pedestal 1 for selecting a desired sewing pattern Selection key 6a,
Photo interrupter 36 and timing signal generator 70
Are connected to the control device 71.

The timing generator 70 is the same as the ordinary one, and the reference signal (the needle bar uppermost position) is synchronized with the rotation of the main shaft 3 when the needle bar 9 is at the uppermost position, that is, when the phase angle of the main shaft 3 is 0 °. Signal) and a timing signal every minute rotation of the spindle 3 (for example, every rotation of about 10 °) (see FIG. 9). Further, to the control device 71, a sewing machine motor 75 is connected via a drive circuit 72, a needle bar swing stepping motor 76 is connected via a drive circuit 73, and a feed dog longitudinal movement stepping motor 58 is connected via a drive circuit 74. Has been done.

Further, the control device 71 has a counter 78 for counting the number of times the skipped stitch is detected based on the signal from the photo interrupter 36 of the skipped stitch detecting device, and
An alarm device 80 including a lamp, a buzzer, and the like that issues an alarm to the outside when the count value of the counter 78 reaches a predetermined number is connected.

The control unit 71 basically comprises an input / output interface, a ROM, a RAM provided with various counters and memories, etc., and controls all of the sewing machine M. The program memory of the ROM stores a sewing control program for controlling each motor based on the stitch data of the selected pattern and the timing signal from the timing signal generator 70.

Further, in the sewing pattern data memory of the ROM, a plurality of stitch data for each of a large number of sewing patterns are stored in association with the pattern numbers. When the number of skipped stitches detected by the counter 78 reaches a predetermined number as described later, the control device 71 configured as above drives and controls the stepping motor 58 for forward / backward movement of the feed dog to move the sewing needle 10 to the cloth. The drop position of is changed by a small amount.

Next, a skip skip prevention control routine executed by the controller 71 of the sewing machine M will be described based on the flowcharts of FIGS. 7 and 8 with reference to FIG. In the figure, Si (i = 1, 2, 3, ...) Is each step. When the power is turned on, this control is started, and the initial setting is first executed (S1). After execution of this initial setting, while the sewing machine motor 75 is being driven, a timing signal output from the timing signal generator 70 is read by a routine (not shown) every minute rotation of the spindle 3.
The contents of the timing counter are incremented when the level becomes "H", and the counter value is reset by the input of the reference signal.

Next, when the sewing is started, the sewing data of the desired pattern is read from the ROM and the sewing data is updated (S2), and the work cloth feed amount and the needle bar swing width are determined based on the data. (S3). Then, after the number of skipped stitches of the counter 78 is reset (S4), the work cloth is fed forward or backward to the worker, or
Stepping motor 5 for forward / backward movement of the feed dog according to the feed amount
8 is driven to set the front and rear positions of the feed dog 19 at appropriate positions (S5).

At this time, as shown in FIG. 9, the vertical position of the feed dog 19 is at least the needle plate 17 with the lowering motion completed.
Is a position that does not protrude from the upper surface of. Then, the thread passing signal is reset to the "L" level (S6), and based on the counter value of the timing counter, the phase angle becomes about 290 ° as shown in FIG. Sometimes (S7: YES), the yarn passing signal is read from the photo interrupter 36 (S8). If the detection start timing is not determined in S7, the process waits until the detection timing arrives.

When the determination in S8 is "H" level, that is, when the needle thread loop 41 is engaged with the sword tip and skipping does not occur (S9: YES), S14 to S17 are executed to start sewing. It The process waits until the needle bar swing timing is detected in S14, and when detected, the needle bar 9 is swung through the needle bar swing stepping motor 76 (S15). Then, wait until the cloth feed timing is detected in S16,
When detected, the work cloth is fed through the stepping motor 58 for forward / backward movement of the feed dog (S17), the process returns to S2, the sewing data is updated, and the same loop is executed again to continue sewing.

Here, the start timing of the needle bar swing and the work cloth feed is after the yarn passage detection period (see FIG. 9).
It is not necessary to specify the start order of both, and either order may be performed first (by the way, in the flowchart of FIG. 7, the needle bar swing is controlled to be performed first).

On the other hand, the thread passing signal read from the photo interrupter 36 at the timing of detecting the passing signal of the upper thread loop 41 (S7: YES) remains at the "L" level by the end of the detection period. In a state in which the needle thread loop 41 is not engaged with the sword tip and skipping occurs as it is (S10: YES), the needle bar 9 is not swung and the work cloth is not fed, and the value of the counter 78 is determined in S11. Is incremented by 1.

Next, in S12, it is judged whether or not the count value of the counter 78 is 5 or more. In this case, the count value is 5 or more.
Since it is the following (S12: NO), after the needle drop position correction control is executed (S13), the process returns to S5. If the determination in S12 is YES, that is, if the number of skipped stitches detected by the counter 78 exceeds 5, the alarm device 80 issues an alarm (S25) and then the sewing machine is stopped.

Next, the correction control of the needle drop position will be described with reference to FIG. FIG. 8 is a flowchart showing a subroutine for correcting the needle drop position. First,
If the count value of the counter 78 is determined to be 1 in S18, and if the count value is 1, cloth feeding is not performed by the stepping motor 58 for forward and backward movement of the feed dog (S19), and the sewing needle 10 is dropped to the stitch position where skipped stitches are detected. . On the other hand, if the count value of the counter 78 is not 1, it is determined in S20 whether the count value is 2, and if the count value is 2, the stepping motor 5 for the feed dog front and back movement is performed during the cloth feed timing period.
8 to drive the cloth 0.3 mm backward (S21, S
23, S24).

If the count value of the counter 78 is not 2 (S20: NO), the cloth feed amount is set to 0.3 mm and the stepping motor 58 is set during the cloth feed timing period.
The fabric is fed and driven in the forward direction via (S22, S23,
S24).

As described in detail above, in the sewing machine of this embodiment, when skipped stitches are detected, the needle bar 9
Since the driving and the cloth feeding are not performed, there is no possibility that stitches are formed with stitch skipping. Therefore, the work of eliminating the stitches accompanied by such skipping is not necessary at all, and as a result, the sewing efficiency can be remarkably improved.

Further, since the cloth is not fed in the direction opposite to the sewing direction in order to eliminate stitches that cause skipped stitches, a complicated mechanism or control such as a clutch mechanism which is necessary for such control is unnecessary. The cost of the sewing machine can be kept lower than this.

Further, in the sewing machine of this embodiment, the counter 7
When the number of skipped stitches detected by 8 exceeds a predetermined value, the sewing needle 10 is controlled so as to change the drop position. Therefore, the change of the drop position causes the engagement of the needle thread loop 41 by the sword tip 23. It is possible to create a state in which it is easy to carry out, and therefore, even if stitch skipping occurs, a few stitch needles 1
Skipping can be eliminated after the vertical movement of 0.

In the sewing machine of this embodiment, the counter 7
When the number of skipped stitches detected by 8 exceeds a predetermined value, an alarm is issued to the outside via the alarm device 80. Therefore, when the skipped stitches cannot be eliminated by the above operation, the skipped stitches are skipped. The worker can be notified that the problem has not been resolved, and the worker can immediately perform the process for eliminating the skipped stitch.

In this embodiment, the fall position of the sewing needle 10 due to the stitch skipping is corrected and changed by the cloth feeding operation, but the needle bar 9 may be swung. Of course. Further, in the present embodiment, the number of skipped stitches detected by the counter 78 is set to 5 and each control is performed at the boundary of 5 times, but the number of times is not limited to 5 and there is an obstacle in sewing. It goes without saying that the number of detections can be freely set within the range of no detection.

[0052]

As described above, according to the present invention, it is possible to reliably prevent the occurrence of skipped stitches with a simple structure, and it is not necessary to eliminate the skipped stitches, so that the sewing efficiency can be improved, and
It is possible to provide a sewing machine that is low in cost and can prevent skipping, and its industrial effect is great.

[Brief description of drawings]

FIG. 1 is a perspective view showing an appearance of a zigzag sewing machine.

FIG. 2 is a perspective view of a full-rotation horizontal hook and a skipping mechanism.

FIG. 3 is a plan view of a full-rotation horizontal hook and a skipping mechanism.

FIG. 4 is an enlarged perspective view of a leaf spring member.

FIG. 5 is a perspective view of a feed dog drive mechanism.

FIG. 6 is a block diagram of a control system of the sewing machine.

FIG. 7 is a flow chart diagram for explaining skip prevention control.

FIG. 8 is a flowchart showing a subroutine for correcting a needle drop position.

FIG. 9 is a time chart diagram of each operation of the sewing machine.

[Explanation of symbols]

M Sewing machine 9 Needle bar 10 Sewing needle 19 Feed dog 21 Full rotation hook 22 Outer hook 23 Sword tip 24 Inner hook 25 Lower thread bobbin 32 Leaf spring member 35 Upper thread loop detector 36 Photo interrupter 41 Upper thread loop 58 Stepping motor for forward and backward feed teeth movement 71 control device 76 needle bar swing stepping motor 78 counter 80 alarm device

Claims (3)

[Claims] 1. A needle bar drive mechanism for vertically moving a needle bar having a sewing needle attached to a lower end thereof, a feed dog drive mechanism for vertically moving and back and forth movement of a feed dog, an inner hook equipped with a bobbin bobbin and a sword tip. A sewing machine having an outer hook and a rotary hook, and forming a seam on the cloth by cooperation of the outer hook and the outer hook, the upper hook being disposed in a passage path of an upper thread loop engaged with a sword tip of the rotary hook. A stitch switch having a detection switch for detecting passage of a loop, and a stitch skipping detection unit that detects a stitch skipping based on an output signal from the detection switch, and when the stitch skipping detection unit detects a stitch skipping, the stitch skipping is detected. A sewing machine capable of preventing stitch skipping, comprising: a control unit that controls the needle bar drive mechanism and the feed dog drive mechanism so as to drop the sewing needle at or near the stitch position at the time of detection. 2. A counter means for counting the number of times of stitch skip detection detected by the stitch skip detection means, and a drop position of the sewing needle when the number of stitch skip detection by the counter means reaches a predetermined number. 2. A sewing machine capable of preventing skipped stitches according to claim 1, further comprising drop position changing means. 3. A counter means for counting the number of times of skipped stitches detected by the skipped stitches detecting means, and an alarm means for issuing an alarm to the outside when the number of times of skipped stitches detected by the counter means reaches a predetermined number. The sewing machine capable of preventing skipped stitches according to claim 1, further comprising: