JPH0720518B2 - Automatic thread trimming sewing machine - Google Patents

Description

TECHNICAL FIELD The present invention relates to an automatic thread trimming sewing machine that cuts at least a needle thread after finishing sewing.

(Prior Art) As a general automatic thread trimming sewing machine, a worker operates a thread cutting mechanism by operating a manual switch or a pedal switch at the end of sewing to cut a needle thread and a bobbin thread connected to a work cloth. There is something I did. FIG. 6 shows the loci of the needle and the balance with respect to the rotation angle of the sewing machine main shaft that drives the needle of the sewing machine. The time when thread cutting operation can be performed in this sewing machine is from point A to point B in FIG. Between the points, that is, immediately after the needle comes out of the work cloth and immediately before the needle is pierced into the work cloth again, and while the needle thread is tensioned by the balance. In addition, in order to easily insert the work cloth for the next sewing operation between the work cloth support surface and the needle, it is preferable that the needle is closer to the top dead center.

In order to satisfy the above conditions, in the conventional sewing machine, thread trimming is performed about 20 degrees before the top dead center of the balance.

(Problems to be solved by the invention) However, since the above timing is set in the middle of the thread pick-up operation by the balance, the amount of thread left in the needle after cutting the needle thread becomes unstable, There is a problem that it is not possible to form seams of uniform quality at the start of the next sewing operation.

Further, when thread trimming is performed at the top dead center of the balance, the needle approaches the work cloth supporting surface after thread trimming, which makes it difficult to insert the work cloth.

(Object of the Invention) The present invention has been made to solve the above problems, and an object thereof is to be able to form stitches of uniform quality at the start of the next sewing operation and to end the thread cutting operation. It is an object of the present invention to provide an automatic thread trimming sewing machine in which the distance between the needle and the work cloth supporting surface can be widened later and the work cloth can be easily and surely set between them.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, a needle that is moved up and down, a motor that drives the needle and that is capable of shifting and forward / reverse rotation, and that motor is driven. Drive circuit, a needle position detector for detecting the position of the needle, a balance mechanism that is operated in synchronization with the vertical movement of the needle and picks up the needle thread inserted through the needle, and the balance thereof. The mechanism is set so that the needle goes over the needle top dead center and reaches the balance top dead center so that the yarn pick-up amount becomes maximum after turning to the descending step, and at least after the sewing, The thread cutting mechanism for cutting the needle thread connected to the needle, and the timing of cutting the needle thread by the thread cutting mechanism are set near the time when the balance reaches the top dead center, and the thread cutting mechanism. After the operation of
Control for reversing the motor from the balance top dead center to the needle top dead center and controlling the drive circuit to stop the rotation of the motor based on the needle top dead center signal generated by the needle position detector. And the circuit.

(Operation) According to the present invention configured as described above, the motor performs gear shifting and forward / reverse rotation to drive the needle, the drive circuit drives the motor, the needle position detector detects the position of the needle, and the balance. The mechanism operates in synchronism with the vertical movement of the needle to pick up the needle thread that has been inserted into the needle. When the thread cutting mechanism finishes sewing, at least the needle thread connected to the needle is cut, and the timing of cutting the needle thread by the thread cutting mechanism is set to the balance dead point. After the thread cutting mechanism is activated by the control circuit, the motor reverses from the balance dead center to the needle dead center and the needle position dead center signal generated by the needle position detector The drive circuit is controlled so as to stop the rotation of the motor.

(Embodiment) An embodiment embodying the present invention will be described below with reference to FIGS. 1 to 6. As shown in FIGS. 1 and 2, the sewing machine main body 1 is composed of a sewing machine arm 1a and a sewing machine bed 1b,
A sewing machine motor 2 including a pulse motor capable of forward / reverse rotation and variable speed is mounted on the right outer surface of the sewing machine arm 1a, and a sewing machine spindle (not shown) rotationally driven by the sewing machine motor 2 is installed in the sewing machine arm 1a. It is rotatably supported.

A needle bar 5 having a needle 3 and a thread guide 4 at its lower end is supported on the left side of the sewing machine arm 1a so as to be vertically movable, and is vertically moved with the rotation of the sewing machine main shaft. On the front surface of the sewing machine arm 1a, a known thread tensioner 6 located on the path of the needle thread T supplied from the needle thread supply source to the needle 3 is provided, and a plurality of thread guide bodies 7 are attached. .
Further, inside the sewing machine arm 1a, there is provided a balance 8 which is operated by a known balance mechanism which is operatively linked to the sewing machine main shaft, and its tip projects to the front surface of the sewing machine arm 1a.

Then, the needle thread T supplied from the needle thread supply source is supplied to the needle 3 via each thread guide body 7, thread tension device 6, thread balance 8 and thread guide 4, and the thread balance 8 is fed by the thread balance 8 at the time of stitch formation. The needle thread T is picked up by being moved up and down in synchronization with the rotation of the sewing machine main shaft in synchronization with the needle 3. Further, when the needle 3 and the balance 8 are moved up and down so as to draw the locus shown in FIG. It is set to maximize the thread pick-up amount.

As shown in FIGS. 3 and 4, a lower shaft 9 is rotatably supported in the sewing machine head 1b, and a thread catcher 10 is attached to the left end of the lower shaft 9. When the needle 3 descends, the thread catcher 10
After the needle thread T is captured by the needle thread loop and the needle thread loop is formed, the lower thread is paid out from the bobbin in the thread loop catcher 10 by the needle thread loop, and then the thread take-up by the balance 8 is performed. Allows the work cloth W on the work cloth supporting surface of the sewing machine bed 1b to be
The seams are formed on the.

A fixed blade 11 is mounted at its base end in the sewing machine bed 1b so as to be located above the thread catcher 10. A movable blade holder 12 is rotatably arranged within a predetermined angle range on the back side of the thread catcher 10 so as to be rotatable on the axis of the lower shaft 9, and is movable on its outer peripheral edge. The blade 13 is attached. And the movable blade 13 is the fourth together with the movable blade holder 12.
When the needle blade T and the bobbin thread are captured by the movable blade 13 when the needle blade T is rotated forward from the rest position shown in the figure in the clockwise direction, the both threads are cut by cooperation with the fixed blade 11. It is like this.

As shown in FIG. 3, a thread cutting cam 14 having a cam surface on the outer periphery is fixed to the middle portion of the lower shaft 9. On the other hand, a driven shaft 15 is rotatably supported in the sewing machine bed 1b so as to extend in parallel with the lower shaft 9 and is movable in the axial direction within a predetermined range. Cutting cam
The cam follower 16 facing 14 is fixed. An engagement roller 17 that can be engaged with and disengaged from the thread cutting cam 14 is attached to one end of the cam follower 16. Further, on the right side of the driven shaft 15, a thread cutting solenoid 18 is arranged in the sewing machine bed 1b, and an armature 19 thereof is arranged opposite to the right end of the driven shaft 15.

When the thread cutting solenoid 18 is demagnetized, the armature 19 is placed at the closing position as shown in FIG.
While being separated from the right end of 15, the cam follower 16 and the driven shaft 15 are arranged at the right end of the moving range by the biasing force of the spring 20, and the engagement roller 17 is disengaged from the thread cutting cam 14. on the other hand,
When the thread cutting solenoid 18 is energized, the armature
19 is projected, and by its engagement with the armature 19, the spring 20
The driven shaft 15 and the cam follower 16 are moved leftward to the left end of the movement range against the urging force of. As a result, the engagement roller 17 is engaged with the thread cutting cam 14.

A swing shaft 21 extending parallel to the driven shaft 15 is rotatably supported in the sewing machine bed 1b, a disc 22 is fixed to the right end thereof, and a swing arm 23 is fixed to the left end thereof. .
Then, one end of the cam follower 16 is linked to the disk 22 via a top 24, and an end of a swing arm 23 is rotatably connected to the movable blade holder 12 via a connecting lever 25. Has been done. A winding spring 26 is attached to the outer periphery of the mounting portion of the swing arm 23, and the swing spring 26 biases the swing arm 23 to rotate counterclockwise in FIG. Therefore, the movable blade holder 12 is urged to rotate counterclockwise in the figure via the connecting lever 25, and is always arranged and held in the rest position shown in the figure.

Then, the engagement roller 17 on the cam follower 16 is
When the thread trimming cam 14 is rotated while being engaged with the cam 14, the cam follower 16 is reciprocally rocked via the engagement roller 17 according to the cam shape, and the rocking motion is caused by the top 24, the disk. 22, swing axis 2
1, the movable blade 13 is reciprocally swung together with the movable blade holder 12 via the swing arm 23 and the connecting lever 25.

The fixed blade 11, the movable blade holder 12, the movable blade 13 and other members constitute a thread cutting device C.

Next, the electrical construction of the sewing machine in this embodiment will be described with reference to FIG. A central processing unit (CPU) 30 which constitutes a control circuit is connected to a read only memory (ROM) 31 and a random access memory (RAM) 32 which have a program for controlling the operation of the entire sewing machine.
Further, a start switch 33 and an end switch 34 are connected to the CPU 30, respectively, and the start switch 33 is turned on by the front stepping operation of the foot pedal 35 and outputs a start signal to the CPU 30. The end switch 34 is turned on by the backward stepping operation of the foot pedal 35, and outputs an end signal to the CPU 30.

On the other hand, the sewing machine motor 2 detects the top dead center and the bottom dead center of the needle 3 based on the rotation of the main shaft of the sewing machine, outputs a needle top dead center signal and a needle bottom dead center signal, and sets a predetermined angular interval. Is equipped with a needle position detector 36 that outputs a synchronization signal,
The signal from the detector 36 is input to the CPU 30.

A motor drive circuit 37 for driving the sewing machine motor 2 and a solenoid drive circuit 38 for driving the thread cutting solenoid 18 are connected to the CPU 30. Then, in response to the activation signal from the activation switch 33, the CPU 30 rotates the sewing machine motor 2 at high speed via the motor drive circuit 38. Further, in response to the end signal from the end switch 34, the CPU 30 causes the sewing machine motor 2 to normally rotate at a low speed via the motor drive circuit 38, and based on the needle top dead center signal and the synchronization signal input during the normal rotation. Then, the CPU 30 calculates the time when the balance 8 reaches the top dead center (point B in FIG. 6). Then, the CP is set so that the thread cutting operation is performed at the time when the thread take-up amount by the balance 8 becomes maximum, that is, at the time when the balance 8 reaches the top dead center.
U30 outputs a control signal to the thread cutting solenoid 18 via the solenoid drive circuit 38.

Further, after the thread trimming operation in response to the end signal is completed, the CPU 30 causes the sewing machine motor 2 to operate via the motor drive circuit 37.
When the needle top dead center signal is output from the needle position detector 36 during the reverse rotation, the sewing machine motor 2 is stopped at the point C shown in FIG.

Next, the operation of the sewing machine configured as described above will be described with reference to FIGS. 5 and 6.

In step S1 shown in FIG. 5, when the start switch 33 is turned on based on the front depression operation of the foot pedal 35, the CP
The U30 rotationally drives the sewing machine motor 2 at high speed via the motor drive circuit 37. As a result, the sewing machine main shaft and the lower shaft 9 are rotated, the needle 3 and the thread catcher 10 are actuated, the stitches are formed on the work cloth W on the sewing machine bed 1b, and the balance 8 is actuated, and the needle thread Taking up of T is carried out.

Next, after the front stepping operation of the foot pedal 35 is released and the start switch 33 is turned off, when the foot pedal 35 is stepped backward from step S3, the end signal is output from the end switch 34. CPU30 in response to this end signal
Rotates the sewing machine motor 2 at a low speed via the motor drive circuit 37 in step S4. Then, in step S5, the balance 8
When is raised to a predetermined position near the top dead center, the CPU 30 energizes the thread cutting solenoid 18 for a predetermined time via the solenoid drive circuit 38. Based on the excitation of the solenoid 18, the cam follower 16 is moved together with the driven shaft 15 via the armature 19, and the engagement roller 17 is engaged with the thread cutting cam 14.

With the rotation of the thread trimming cam 14, the cam follower 16, the disk 22,
When the movable blade holder 12 and the movable blade 13 are reciprocally rotated through the swing shaft 21, the swing arm 23, and the connecting lever 25, and the thread take-up 8 reaches the top dead center to maximize the yarn pick-up amount. Its movable blade 13
And the fixed blade 11 cooperate to cut the needle thread T and the bobbin thread (step S6). Then, after this thread trimming operation is completed,
The CPU 30 demagnetizes the thread cutting solenoid 18. Therefore, the cam follower 16 and the driven shaft 15 are moved back by the urging force of the spring 20, and the engagement roller 17 is separated from the thread cutting cam 14.

Further, in step S7, the sewing machine motor 2 is stopped at a position corresponding to the vicinity of the needle top dead center. Next, the CPU 30 reverses the sewing machine motor 2 in step S8, and stops the sewing machine motor 2 in response to the needle top dead center signal being input in the next step S9.

As described above, in this embodiment, since the thread trimming operation is performed when the thread take-up amount of the thread take-up is maximized, the thread remaining amount on the needle 3 can be made constant and the quality of the next sewing can be improved. Uniform seams can be formed. Further, after the thread trimming operation, the sewing machine motor 2 is reversely rotated and the needle 3
When the machine reaches top dead center, the sewing machine's operation is stopped,
At the start of the next sewing, the work cloth W can be easily inserted and set between the work cloth support surface and the needle 3 without being disturbed by the needle 3.

Next, another embodiment embodying the present invention will be described with reference to FIG. 7, focusing on the differences from the above embodiment. In this embodiment, the sewing machine arm 1a is provided at the bottom of the sewing machine bed.
1b is rotatably supported, and at the lower end of the sewing machine arm 1a, the sewing machine arm 1a is rotated between a first position shown by a solid line in FIG. 7 and a second position shown by a two-dot chain line in FIG. The piston 41 of the air cylinder 40 for connecting the air cylinder 40 is connected. In addition, the sewing machine spindle in the sewing machine arm 1a and the sewing machine bed 1b
The inner lower shaft 9 is rotationally driven separately in synchronization with the sewing machine motor 2 and a motor (not shown).

Then, similarly to the above-described embodiment, when the sewing machine spindle is rotationally driven at a low speed based on the end signal from the end switch 34, and the balance 8 is raised to a predetermined position due to the rotation, the thread cutting operation is performed. The operation of each member 18, 15 and the like is started, and when the balance 8 reaches the top dead center, the thread cutting operation by the movable blade 13 and the fixed blade 11 is executed. Therefore, similarly to the above-described embodiment, the thread remaining amount on the needle 3 after thread cutting can be made constant and the quality of the stitches at the time of the next sewing can be kept uniform.

After the thread cutting operation is completed, the CPU 30 operates the air cylinder 40 via the electromagnetic valve 42 to rotate the sewing machine arm 1a from the first position shown by the solid line in FIG. 7 to the second position shown by the chain line in FIG. To move. Thereby, the distance between the needle 3 and the work cloth supporting surface is widened, and the work cloth W can be easily set on the work cloth supporting surface.

The present invention is not limited to the above-mentioned embodiments, and the configuration of each part can be arbitrarily changed without departing from the spirit of the present invention.

(Effects of the Invention) As described in detail above, in the present invention, the thread is cut at the thread balance dead point where the thread take-up amount by the thread balance mechanism is maximized, and then the motor is rotated in the reverse direction at the needle dead center point. Since it is stopped, it is possible to form a seam of uniform quality at the start of the next sewing operation, and after the end of the thread trimming operation, set a wide distance between the needle and the work cloth support surface, and The work cloth can be easily and surely set between them.

[Brief description of drawings]

1 to 6 show an embodiment embodying the present invention. FIG. 1 is an explanatory view showing the structure of a sewing machine, FIG. 2 is a partial front view of the sewing machine, and FIG. FIG. 4 is an enlarged bottom view of the essential parts of the sewing machine bed, FIG. 4 is an enlarged side sectional view of the essential parts of the sewing machine bed, FIG. 5 is a flowchart, and FIG. 6 is a graph showing the loci of the needle and the balance. FIG. 7 is an explanatory view showing another embodiment embodying the present invention. In the figure, 2 is a sewing machine motor, 3 is a needle, 8 is a balance, and 30
Is a CPU constituting a control circuit, 36 is a needle position detector, 37 is a motor drive circuit, T is a needle thread, and C is a thread cutting mechanism.

Claims (1)

[Claims] 1. A vertically movable needle (3), a motor (2) for driving the needle (3) capable of shifting and forward / reverse rotation, and a drive circuit (37) for driving the motor (2). , A needle position detector (3 for detecting the position of the needle (3)
6), and a balance mechanism that is operated in synchronization with the vertical movement of the needle (3) and picks up the needle thread (T) inserted through the needle (3), and the balance mechanism is the needle (3). Is set so that the thread take-up amount is maximized after the needle goes over the needle top dead center and goes to the descending process, and at least after the sewing is completed, at least the needle (3) is The thread cutting mechanism (C) for cutting the continuous needle thread (T) and the timing of cutting the needle thread (T) by the thread cutting mechanism (C) are set near the time when the dead center of the balance is reached. And that after the thread cutting mechanism (C) is operated, the motor (2) is reversed from the balance top dead center to the needle top dead center, and is generated by the needle position detector (36). The drive circuit (37) is controlled so as to stop the rotation of the motor (2) based on the needle top dead center signal. An automatic thread trimming sewing machine characterized by being provided with a control circuit (30).