JPH0328239B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a thread cutting device equipped with a movable blade for feeding out and cutting thread connected to a seam in one direction, and a thread cutting device that cuts the thread that is generated when sewing is finished. and a solenoid excited by a thread cutting command signal, and the movable blade of the thread cutting device is moved in conjunction with the unidirectional movement of the plunger of the excited solenoid to cut the thread connected to the seam. Regarding a sewing machine configured as follows.

[Prior art] Conventionally, this type of sewing machine was
As described in Japanese Patent No. 110357, a thread cutting mechanism equipped with a movable blade and a presser foot lifting mechanism for raising the presser foot against the spring are operatively connected to a single solenoid plunger. The movable blade of the thread cutting mechanism is first moved in conjunction with the unidirectional movement of the plunger to feed out and cut the thread connected to the seam, and then the plunger is moved in one direction. There is a known structure in which the presser foot is raised against the spring in conjunction with the spring.

Generally, it is well known that in a sewing machine configured as described above, a high voltage current must be applied to the solenoid in order to raise the presser foot against the tension. however,
Since the movable blade of the thread trimming mechanism is moved before the presser foot is raised, if a high voltage current is applied to the solenoid from the beginning, the movable blade will move at high speed, causing thread breakage and bobbin thread damage. Bobbin overrun, etc. will occur.

Therefore, in the past, as described in the above publication, a time constant circuit was used to gradually change the voltage applied to the solenoid from a low voltage to a high voltage, and the plunger was moved at a low speed initially. in,
In the latter stage, the movement is controlled at high speed, and the thread cutting is completed while the plunger is moving at low speed (that is, while the movable blade is moving at low speed).

[Problems to be Solved by the Invention] However, in sewing work at a sewing factory, in order to sew a large number of work-in-progress items, solenoids are repeatedly energized and the thread trimming mechanism and presser foot lifting mechanism are activated many times. I have to let it happen.

As a result, the coil of the solenoid overheats and its internal resistance changes, reducing the moving speed of its plunger, causing a high voltage current to flow through the solenoid before the movable blade can unwind the thread connected to the seam and finish cutting. As a result, the movable blade is moved at high speed, which may cause thread breakage, bobbin overrun, etc., resulting in defective products.

In the method that uses this time constant circuit, each time a defective product occurs, the sewing machine must be stopped and the current supplied to the solenoid or the time constant circuit adjusted, but this is time consuming and troublesome. It was something.

In addition, due to overheating of the solenoid, the thread trimming speed (moving speed of the movable blade) gradually decreases from the speed at which thread trimming can be performed well, and thread trimming is completed even after the time set by the time constant circuit has elapsed. As mentioned above, a high voltage current is supplied to the solenoid and the thread trimming speed increases again, causing thread breakage and bobbin overrun, as described above. exist.

That is, when the thread cutting speed (moving speed of the movable blade) decreases, there is a problem that the thicker the thread used, the more difficult it becomes to cut it, and in some cases, it becomes impossible to cut it. This change in thread cutting speed (moving speed of the movable blade) during use is not desirable from the viewpoint of thread cutting stability. Further, it is not preferable because the tension balance between the upper thread and the lower thread at the start of next sewing changes depending on the degree of overrun of the bobbin.

[Object of the Invention] The present invention has been made to solve the above-mentioned problems, and its purpose is to repeatedly energize a solenoid that interlocks the movable blade of a thread cutting device with a plunger over a long period of time. This is a sewing machine that prevents thread breakage and overrun by keeping the moving speed of the movable blade constant, and at the same time maintains the tension balance between the upper and lower threads at the start of sewing during repeated thread trimming work. The present invention provides a thread cutting speed adjusting device.

[Means for Solving the Problems] The present invention provides a thread cutting device equipped with a movable blade that feeds out and cuts thread connected to a seam in one direction, and a thread cutting device that is equipped with a movable blade that feeds out and cuts thread connected to a seam in one direction, and thread that is generated when sewing is completed. and a solenoid excited by a cutting command signal, and the movable blade of the thread cutting device is moved in conjunction with the unidirectional movement of the plunger of the excited solenoid to cut the thread connected to the seam. In the sewing machine configured, there is provided an end detection means for detecting the end of thread cutting by the thread cutting device and generating an end signal, and a period from the generation of the thread cutting command signal until the end signal is generated by the end detection means. A time detection means for detecting the time required for thread trimming, and a time detection means for detecting the time required for thread trimming, and based on the detected time required for thread trimming, the time required for thread trimming detected by the end detection means during the next sewing operation is for optimal operation of the thread cutting device. The thread trimming speed of the solenoid is maintained constant by adjusting the voltage of the current to be supplied to the solenoid so as to reach a preset time.

[Function] In the present invention, the time detection means detects the time required for thread trimming from the generation of the thread trimming command signal to the generation of the end signal by the end detection means, and the adjustment means adjusts the time required for thread trimming based on the detected time required for thread trimming. , the voltage of the current to be supplied to the solenoid is adjusted so that the time required for thread trimming detected during the next sewing operation matches the time preset for optimal operation of the thread trimming device.

[Example] The details of an embodiment of the present invention will be described below with reference to the drawings.

In the figure, a sewing machine 1 is a known buttonhole sewing machine as shown in Japanese Patent Publication No. 56-77. ) and a presser device (not shown) connected via the connecting rod 7 and lever 9 are installed. This thread cutting device operates at the beginning of the suction operation of the plunger 6 of the energized automatic return type solenoid 5, rotates its movable blade 10 to pay out the thread connected to the seam, and uses a fixed blade (not shown). ) is configured to cut the thread by cooperating with the thread. Further, the presser device is configured to operate in the latter half of the suction operation of the plunger 6 of the solenoid 5, and to raise the cloth presser 11 to which a springing force in the direction of pressing the work cloth is applied, against the springing force. ing.

The automatic return type termination detection switch 15 has a normally open contact 151 turned on by the lever 8 in the inactive position when the solenoid 5 is demagnetized, and a normally open contact 151 is turned on based on the attraction of the plunger 6 when the solenoid 5 is energized. At the point when the movable blade 10 has completely cut the yarn, the pusher of the switch 15 presses the lever 8.
It is fixed to the bed of the sewing machine 1 in such a position that the normally open contact 151 is turned off when it is separated from the sewing machine 1. In this off state, the normally closed contact 152 of the end detection switch 15 passes current from the DC positive power source Vc.c. to the relay R as a end signal, and the normally closed contact 153 is grounded to a connection point a, which will be described later.

Next, the electric circuit of this sewing machine will be described in detail.

A terminal between the positive power supply terminal P and the ground terminal G of the full-wave rectifier circuit 16 connected to the AC power supply is turned on by a thread trimming command signal generated when a foot pedal (not shown) is depressed. The excitation coil 51 of the solenoid 5 and the thyristor 18 are connected in series through a normally open contact 171 of the starting switch 17, and the series circuit between the coil 51 and the thyristor 18 includes a resistor 19 and an electronic volume 2 to be described later.
0 and a capacitor 21 are connected in parallel. A constant voltage element 22 is connected between the connection point f between the electronic volume 20 and the capacitor 21 and the gate terminal of the thyristor 18, and this element 22 detects when the voltage at the connection point f reaches a predetermined level. , the thyristor 18 is triggered. Further, a normally open contact R1 of the relay R and a diode 14 are connected in parallel to the series circuit of the resistor 19 and the electronic volume 20. Here, the normally open contact R1 is closed by a relay R that is energized when the end detection switch 15 is turned off, and forms a bypass circuit to the connection point f. The diode 14 is for discharging the charged capacitor 21.

When a high level signal (hereinafter referred to as "H" signal) is input to the electronic volume 20, the resistance value is changed to increase the output current stepwise, and a low level signal (hereinafter referred to as "L" signal) is input to the electronic volume 20. ” signal)
is configured to lower the output current step by step when the terminal I is input, and when the "H" signal is input to the terminal I, the above operation is performed and the "L" signal is input.
When a signal is input, the structure is such that the operation is stopped and the resistance value is maintained regardless of the state of the signal input to the terminal S. Further, the resistance value of the resistor 19 is set to be sufficiently small.

On the other hand, the one shot 23 and the integrating circuit 24,
The connection point a of the D-type flip-flop 25 with the clock terminal CP is connected via the normally open contact 151 closed by the lever 8 to the grounded normally closed contact 172 of the start switch 17 and the DC positive power supply Vc. It is connected to a normally open contact 173 connected to c.

The one shot 23 is configured to output one high level pulse to the terminal I of the electronic volume 20 in response to a fall of the voltage at the connection point a from a high level to a low level, and this pulse output time is set to the time required for the electronic volume 20 to change the output current by one step.

The integrating circuit 24 is configured to be reset when the connection point a is at a low level, and to perform a known integration operation when the connection point a is at a high level to generate an output voltage at a connection point b.

A display 28 is connected to the connection point b via the non-inverting terminal of the comparator 26 and an AD converter 27.

The comparator 26 has an inverting terminal connected to a sliding terminal of a variable resistor 29, and the variable resistor 29 is connected to a time setting voltage Vref for setting the time from generation of the thread cutting signal to generation of the end signal.
is configured to output. The data terminal D of the D-type flip-flop 25 is connected to the output terminal of the comparator 26 via a delay circuit 30.
is configured to read the value of the data terminal D and output it to the terminal S of the electronic volume 20 in response to a fall of the voltage at the connection point a from a high level to a low level.

The delay circuit 30 is configured to hold the "H" or "L" signal from the comparator 26 for a certain period of time until the D-type flip-flop 25 completes reading.

The display 28 is configured to visually display to the operator the value obtained by digitizing the output voltage from the integrating circuit 24 by the A-D converter 27.

Next, its operation will be explained with reference to the time chart of FIG.

First, before starting sewing, the worker
9 to set the time specified voltage Vref. Thereafter, the operator performs trial sewing, and upon completion of the trial sewing, when the operator depresses the foot pedal backward, a thread trimming command signal is generated and the start switch 17 is closed. At this time,
When the normally open contact 171 is closed and the voltage at the contact point f reaches a predetermined value, the constant voltage element 22 triggers the thyristor 18, the exciting coil 51 is excited, and the plunger 6 begins to be attracted. Since this trigger operation is no different from speed control using a known thyristor, further explanation will be omitted.

Based on the suction operation of the plunger 6 of the excited solenoid 5, first, the movable blade 10 of the thread cutting device begins to rotate.

Further, when the start switch 17 is closed, the normally open contact 173 is also closed at the same time, so the voltage at the connection point a rises, and accordingly, the integrating circuit 24 starts an integrating operation, and the comparator 26 is activated at the connection point a. The voltage at the node b is compared with the time specified voltage Vref, and when the voltage at the connection point b is higher than the voltage Vref, an "H" signal is output to the delay circuit 30, and otherwise, an "L" signal is output.

After that, when the movable blade 10 rotates to the position where the yarn is completely cut, the pusher of the end detection switch 15 is released from the lever 8, relay R is energized, and the voltage at connection point a changes from the high level. Fall to low level. When the relay R is energized, the normally open contact R1 is closed, and the current bypasses the resistor 19 and the electronic volume 20 and passes through the thyristor 1.
8 to full fire, which causes solenoid 5 to
The plunger 6 moves at high speed to completely raise the presser foot 11 against the springing force.

On the other hand, in response to the fall of the voltage at the connection point a, the one-shot 23 outputs one high-level pulse to enable the electronic volume 20, and the D-type flip-flop 25 activates the delay circuit 30.
The output of the comparator 26 held by the controller 26 is read and output to the terminal S of the electronic volume 20. The electronic volume 20 controls the flowing current by changing its resistance value stepwise during the period activated by the one shot 23.

That is, when the voltage at the connection point b, which represents the thread cutting time required from the start to the completion of the thread cutting operation, is smaller than the time specified voltage Vref (when the thread cutting is completed earlier than the specified time), the comparator 26 outputs "L". '' signal, the electronic volume 20 increases the resistance value and lowers the flowing current by one level. This results in
The timing at which the thyristor 18 is triggered by the thread cutting command signal generated at the end of the next sewing operation is delayed, and the speed of the plunger 6 of the solenoid 5 is slowed down.

On the other hand, the voltage at connection point b is the time specified voltage
Since the comparator 26 outputs an "H" signal when it is larger than Vref (when thread cutting is completed later than the specified time), the electronic volume 20 decreases the resistance value and increases the flowing current by one step. This results in
The speed of the plunger 6 of the solenoid 5 becomes faster.

By repeating the above operation with trial sewing, the actual thread cutting time is controlled so that the required thread cutting time is specified by the preset time specifying voltage Vref. Therefore, after starting the actual sewing work,
Even if the excitation coil 51 is repeatedly excited and generates heat, its internal resistance changes, and the suction speed of the plunger 6 changes, the thread cutting time is always controlled to be constant.

Further, if it is desired to change the thread cutting time during the process, the thread cutting time can be easily changed while looking at the thread cutting time displayed on the display 28.

It should be noted that the present invention is not limited to the above-described embodiment, but instead of generating the thread trimming command signal by pedal operation, the thread trimming command signal is automatically generated after a predetermined sewing cycle is completed. Good too.
In addition, although the time required for thread trimming from the generation of the thread trimming command signal to the generation of the end signal is detected based on the integrated voltage, it may also be detected based on data counted by a counter, as long as it does not deviate from the purpose. Various changes are possible within.

[Effects of the Invention] As described in detail above, in the present invention, the end detection means detects the end of thread trimming and generates the end signal after the thread trimming command signal that is generated in conjunction with the end of sewing is generated. The time detection means detects the time required for thread trimming until the time is reached, and the adjustment means adjusts the time required for thread trimming to be detected again by the time detection means during the next sewing operation based on the time required for thread trimming detected by the time detection means. The voltage of the current to be supplied to the solenoid that interlocks the movable blade of the thread cutting device is adjusted so that the thread cutting speed is a preset time for optimal operation of the thread cutting device, that is, the movable blade. Since the moving speed of the plunger is kept constant, even if the solenoid overheats due to repeated use over a long period of time and the moving speed of the plunger, that is, the time required for thread trimming changes, the adjusting means adjusts the current supplied to the solenoid so that the thread cutting time is always maintained at a preset time.
Therefore, unlike conventional methods, situations such as thread breakage, bobbin overrun, and thread cutting failure do not occur, and the thread cutting operation is always stable, which eliminates the need for complicated speed adjustments by the operator. has. Furthermore, since the tension balance between the upper thread and the lower thread does not change when the next sewing starts, there is also the advantage that a sewn product of stable quality can always be obtained.

[Brief explanation of the drawing]

FIG. 1 is an electrical circuit diagram of a sewing machine showing an embodiment of the present invention, FIG. 2 is a front view thereof, and FIG. 3 is a time chart thereof. 5 is a solenoid, 6 is a plunger, 10 is a movable blade, 11 is a presser foot, 15 is an end detection switch, 2
0 is an electronic volume, R is a relay, and Vc.c. is a DC positive power supply.

Claims (1)

[Scope of Claims] 1. A thread cutting device equipped with a movable blade for feeding out and cutting thread connected to a stitch in one direction, and a solenoid excited by a thread cutting command signal generated when sewing is completed. and a sewing machine configured to move the movable blade of the thread cutting device in conjunction with the unidirectional movement of the plunger of the excited solenoid to cut the thread connected to the seam. Completion detection means for detecting the completion of thread cutting by the cutting device and generating an end signal; and time for detecting the time required for thread trimming from generation of the thread cutting command signal until generation of the end signal by the end detection means. and a detection means, and based on the detected thread trimming time, the thread trimming time detected by the end detection means during the next sewing operation becomes a preset time for optimal operation of the thread cutting device. A thread cutting speed adjusting device for a sewing machine, characterized in that it is comprised of an adjusting means for adjusting the voltage of the current to be supplied to the solenoid to maintain a constant thread cutting speed due to the operation of the solenoid.