JPH0369554B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) This invention relates to an automatic thread tension switching device for a sewing machine.

(Prior Art) Conventionally, when sewing with an overlock sewing machine, an empty ring is formed by connecting the front and rear edges of the fabric. Normally, this empty ring is several times the length of the upper and lower looper threads than the needle thread, and is wide and easily frayed. Therefore, in back-tuck sewing, in which the empty loop at the beginning of sewing is sewn into the seam of the fabric, and automatic loop cutting equipment, which cuts the empty loop to a predetermined length, the following methods are used to create narrow loops that are difficult to fray. We are trying to form a

That is, when the cloth edge sensor senses the cloth edge of the work cloth fed by the feeding means, a preset number of stitches is counted from the time of sensing. After counting up the number of stitches, the tension applied to each thread is changed by a drive means such as a solenoid in the thread tension switching device, so that the needle thread is tightened at the seam of the fabric, and the needle thread is tightened at the empty loop. A good empty ring as mentioned above is formed by loosening the .

(Problem to be Solved by the Invention) However, this thread tension switching device does not operate until the solenoid actually operates after counting up the set number of stitches and when the drive signal is sent to the solenoid. As shown in FIG. 14, there are activation delay times t1 and t2 from when the solenoid is activated until the solenoid actually operates. Therefore, when the sewing machine's sewing speed is low, this operation delay time can be ignored, but when the sewing speed becomes high, the rotational speed of the sewing machine increases as shown in Figure 15.
In the case of 10,000 spm, if the operation delay time is 20 ms, the timing will be delayed by about 3 stitches. Therefore, there is a problem in that the needle thread in the stitches of the fabric becomes loose due to changes in the sewing speed, or conversely, a narrow loop that is hard to fray cannot be formed.

This invention was made in order to solve the problems of the prior art described above, and it measures the sewing speed of the sewing machine, corrects the preset number of stitches based on the sewing speed, and thereby improves the actual number of stitches. The purpose is to keep the change in thread tension constant regardless of the sewing speed.

Structure of the Invention (Means for Solving Problems) The present invention provides a sewing machine equipped with a thread tension switching device that switches thread tension based on a control signal, comprising: a stitch number detection means for detecting the number of stitches during operation of the sewing machine; A cloth edge detection means for detecting the cloth edge transferred to the sewing position; and a stitch count setting for setting the number of stitches from when the cloth edge is detected by the cloth edge detection means until the thread tension switching device is actuated. counting means for counting the number of stitches based on the detection signal of the stitch number detection means from the time the fabric edge detection means detects the fabric edge; and counting means for counting the number of stitches from the time the fabric edge detection means detects the fabric edge calculation means for calculating the sewing speed for each stitch based on the number detection signal; a correction means that calculates a speed difference, calculates the number of stitches during the operation delay time of the thread tension switching device based on the sewing speed data, and corrects the set number of stitches based on the calculation result; a comparison means for comparing the set number of stitches and the count number of the counting means; and a control means for outputting a control signal to the thread tension switching device when the comparison means determines that the set number of stitches matches the count number. The gist of this is that it is equipped with the following.

(Function) The counting means counts the number of stitches based on the detection signal of the stitch number detecting means from the time when the cloth edge detecting means detects the cloth edge. Further, the calculation means calculates the sewing speed of a predetermined needle from the time when the cloth edge detecting means detects the cloth edge, based on the stitch count detection signal, and the sewing speed of a needle one stitch or a plurality of stitches earlier than the sewing speed of the predetermined needle. Calculate the speed difference. The correction means calculates the number of stitches during the operation delay time of the thread tension switching device based on the sewing speed data calculated by the calculation means, and corrects the set number of stitches based on the calculation result. Then, the comparing means compares the corrected set number of stitches with the counted number of the counting means, and when the comparing means determines that the set number of stitches matches the counted number, the control means sends a control signal to the thread tension switching device. Output.

(Embodiment) An embodiment in which the present invention is embodied in a two-needle overlock sewing machine will be described below with reference to FIGS. 1 to 12.

In the figure, 1 is a sewing machine head fixed to a cloth plate 2 of an overlock sewing machine (hereinafter referred to as a sewing machine) M, and 3 is a needle that cooperates with a looper (not shown) to form a seam forming mechanism, and is used for processing. An overlock seam is formed on cloth K. Reference numeral 4 denotes a throat plate provided with a needle hole (not shown) through which the needle 3 passes, and on which a feed dog 5 that makes four known movements moves in and out. Reference numeral 6 denotes a presser foot, which works together with the feed dog 5 to transport the workpiece cloth K in the direction of the arrow X.

Reference numeral 7 denotes a thread tension mounting plate fixed to the upper front surface of the sewing machine head 1. 8 to 11 are the thread tension mounting plates 7;
12 main thread tension devices arranged in parallel with each other on the upper front side of the
-15 are sub-thread tension devices fixed to the thread tension mounting plate 7 below the main thread tension devices 8-11, which supply the left needle thread 16 from the thread supply source through the main thread tension devices 8-11. , right needle thread 17, upper looper thread 18, and lower looper thread 19 are passed through, respectively, and these threads 16 to 1
9 is supplied to the needle 3, an upper looper (not shown), and a lower looper (not shown), respectively. and,
The main thread tension devices 8 to 11 and the sub thread tension devices 12 to 1
5, tension is applied to each thread, and the tension can be adjusted.

The main thread tension devices 8 to 11 will be described in detail. Reference numeral 21 is an adjustment rod fixed to the thread tension mounting plate 7, and an operating knob 22 is screwed to the outer end of the rod so as to be movable forward and backward. Reference numeral 23 denotes a pair of adjustment plates rotatably supported with respect to the adjustment rod 21 between a locking flange 21a provided on the outer periphery of the adjustment rod 21 and the operation knob 22. A predetermined tension is applied to the passing thread. 24 is a spring receiver interposed between the adjustment plate 23 and the operation knob 22; 25 is the spring receiver 24;
The spring is wound around the adjustment rod 21 between the operation knob 22 and the adjustment rod 2 of the operation knob 22.
The adjustment disc 23 is pressed and biased via the spring receiver 24 in response to movement in the axial direction relative to the adjustment plate 23. 26 is a locking flange 21a of the adjustment rod 21
This is a forked thread guide plate interposed between the thread tension mounting plate 7 and the thread tension mounting plate 7.

Reference numeral 27 is a solenoid fixed to the upper rear surface of the thread tension mounting plate 7, which attracts the plunger 28 along the thread tension mounting plate 7 when excited. A spring 29 is wound around the plunger 28 between the tip of the plunger 28 and the solenoid 27, and biases the plunger 28 in the projecting direction. Reference numeral 30 denotes an L-shaped stopper provided on the solenoid 27, which locks onto the set collar 28a of the plunger 28 to stop the plunger 28.
The amount of protrusion of 8 is regulated.

31 is a thread tension switching plate disposed between the upper front surface of the thread tension mounting plate 7 and the locking flange 21a of the adjusting rod 21, and has a long hole 31a through which each adjusting rod 21 is inserted; The elongated hole 31a allows movement in the left and right direction. Reference numeral 32 denotes a connecting portion protruding from the rear surface of the thread tension switching plate 31, which is a long hole 7 formed transparently in the left and right direction of the thread tension mounting plate 7.
a, and is connected to the tip of the plunger 28.

Reference numeral 33 denotes a thread adjustment shaft which is provided in a protruding manner at a distance from each other so as to be located on the left side (in FIG. 6) of the main thread tension devices 8 and 9 on the front surface of the thread tension switching plate 31. When the switching plate 31 moves to the right (in the suction direction of the plunger 28), the small disc-shaped adjusting part 33a provided at the tip of the switching plate 31 resists the biasing force of the spring 25 and adjusts the main thread tension devices 8, 9. By pushing apart the gap between the tension discs 23, both left and right needle threads 1
6 and 17 are loosened. or,
Conversely, when the thread tension switching plate 31 moves to the left, when the adjustment section 33a moves in the detachment direction from between the tension discs 23 of the main thread tension devices 8 and 9, the biasing force of the spring 25 narrows the space between the tension discs 23. Both left and right needle thread 16,1
The tension of 7 is now strengthened.

34 is located on the right side of the main thread tension devices 10 and 11 on the front side of the thread tension switching plate 31 (in FIG. 1).
When the thread tension switching plate 31 moves to the left, a small disc-shaped adjusting part 34a provided at the tip of the thread tension switching plate 31 is activated by a spring. By pushing apart the tension discs 23 of the main thread tension devices 10 and 11 against the urging force of the thread tensioners 25, the tension of the upper and lower looper threads 18 and 19 is relaxed. Also, conversely, the thread tension switching plate 31
When the adjustment section 34a moves in the direction of separation from between the tension discs 23 of the main thread tension devices 10 and 11 when the tension discs 23 of the main thread tension devices 10 and 11 move in the right direction, the space between the tension discs 23 narrows due to the biasing force of the spring 25, and both the upper and lower looper threads 18, 19 tension is being increased.

Reference numeral 36 denotes a cloth edge detection device as a cloth edge detection means for detecting the transferred workpiece cloth K, which is composed of a photosensor 37 and is arranged at a distance from the needle 3 drop point in the opposite direction of feed. The photosensor 37 is composed of a light emitting element 37a such as a light emitting diode and a light receiving element 37b such as a phototransistor.
A is attached to the sewing machine head 1 via a bracket 38. Further, the light receiving element 37b is embedded in the cloth board 2 opposite to the light emitting element 37a,
The light emitted from the light emitting element 37a is sensed, and the workpiece cloth K blocks the light to perform cloth detection.

Note that a reflecting plate is placed in place of the light receiving element 37b at the buried position of the light receiving element 37b, and the light from the light emitting element 37a is reflected by the reflecting plate.
Light receiving element 3 provided on the same bracket 38 side as 7a
Cloth detection may be performed at step 7b.

Reference numeral 39 is a pulley provided on the main shaft (not shown) of the sewing machine, and a belt (not shown) is hung between it and the drive source. Numeral 40 is a magnet provided on the pulley 39, and 41 is a needle position detector as a needle number detection means, which is composed of a magnetic sensor, and is fixed to the housing of the sewing machine or the like via a mounting plate 42, and is attached to the pulley 39. The magnet 40, which rotates as the needle 39 rotates, is detected and a stitch number signal is output.

Next, the electrical configuration of this thread tension switching device will be explained with reference to FIG.

A control box (not shown) is equipped with a microcomputer MC, and the microcomputer MC is equipped with a central processing unit (hereinafter referred to as CPU) as calculation means, correction means, comparison means, and control means.
) 44, read-only memory (hereinafter referred to as ROM)
) 45, a readable and writable memory (hereinafter referred to as RAM) 46, and an I/O interface 48. Said ROM45
A control program for controlling this switching device is stored in the .

47 is a clock circuit connected to the CPU 44, which generates a reference time generation pulse every 0.5 ms.
Output to CPU44. I/O interface 4
A cloth edge sensing circuit 52 is connected to the input terminal 8.
The cloth edge detection signal from the photosensor 37 is converted into a predetermined signal by the cloth edge detection circuit 52 and inputted.

Reference numerals 49 and 50 designate a sewing start stitch number setting switch and a sewing end stitch number setting switch as stitch number setting means, which are digital switches and are connected to other input terminals of the I/O interface 48. The switch 49 for setting the number of stitches at the beginning of sewing and the switch 50 for setting the number of stitches at the end of sewing are provided on the panel of the control box, and operate the thread tension switching device after the front cloth edge or the rear cloth edge is detected by the cloth edge detection device 36. It is now possible to set the number of stitches until it is finished. This number of stitches is set in accordance with the distance between the cloth edge detection position of the cloth edge detection device 36 and the needle 3 drop point.

A drive circuit 51 drives and controls the solenoid 27, and its input terminal is connected to the output terminal of the I/O interface 48. or,
Connected to other input terminals of the I/O interface 48 are a needle position detector 41 and a counting circuit C serving as a counting means for counting the number of stitches based on a detection signal from the detector 41.

Next, the operation of the sewing machine constructed as described above will be explained with reference to the flowcharts shown in FIGS. 9 to 11.

When a power supply switch (not shown) is turned on to start sewing, the main routine initializes the contents of various registers and memory, energizes the solenoid 27, and sets the thread tension for forming an empty ring as described later. (Step 1, hereinafter the step will be expressed as S). In the main routine, interrupt routine A and interrupt routine B are executed from time to time. That is, in interrupt readin A, the clock circuit 47
When the reference time generation pulse that occurs every 0.5ms changes from L to H, the CPU 44 outputs V1 of the RAM 46.
Stack up the reference time generation pulses (0.5ms) in the register.

Also, when the main shaft of the sewing machine M rotates and the magnet 40 of the pulley 39 approaches the needle position detector 41,
The stitch number signal changes from H to L, and the needle position is detected. For example, if the rotational speed of the sewing machine M is 10,000 spm, a stitch count signal will be generated every 6 ms.
When the magnet 40 leaves the needle position detector 41, the stitch number signal changes from L to H, and at this time, interrupt routine B is executed.

In this interrupt routine B, RAM is
Save the value of the V2 register in S52 to the V3 register and clear the V2 register.
Save the value of the V1 register to the V2 register and clear the V1 register. Then, in S53, the reference time generated pulses are accumulated in the V1 register again by the interrupt routine A. Then, while the photosensor 37 does not detect the edge of the work cloth K, the loop of S51, S52, and S53 is repeated in the interrupt routine B. In this way,
The reference time currently in progress is accumulated in the V1 register, and the pulley 3 of the previous stitch is stored in the V2 register.
The time required for the pulley 39 to rotate once is stored in the V3 register, and the time required for the pulley 39 two stitches before to rotate once is stored in the V3 register.

The feed dog 5 and the presser foot 6 cooperate to feed the workpiece cloth K in the direction of the arrow X, and the photo sensor 37 detects the workpiece cloth K.
When the front fabric edge is detected, the determination in S2 is made YES based on the detection signal from the photosensor 37, the counting circuit C is reset, and counting of the stitch number signal output from the needle position detector 41 is started (S
3). Next, at S4, switch 35 for setting the number of stitches at the beginning of sewing.
Read out the setting value N1 of the number of stitches at the beginning of sewing set in .

Also, the speed V2,
V3 is read, and based on this value, the sewing speed V0 of the sewing machine at that time for correcting the set value of the number of stitches is calculated using the following formula in S5.

V0 = 2V2 - V3 This calculation formula is calculated from the relationship between the change in speed V and the number of stitches n shown in Fig. It is determined based on the time required for V3. n ₃ is 2 stitches ahead,
n ₂ indicates the number of previous stitches, and n ₀ indicates the number of next stitches.

Then, in S6, the number of stitches n (=t/V0,
In this embodiment, the set value N1 (=N) of the number of stitches at the beginning of sewing is corrected at t=20ms. That is, the following calculation is performed.

N=N1-t/V0 Then, the CPU 44 sets the corrected number of stitches as a new N and counts the number of stitches until N matches the number of stitches C counted by the number of stitches signal input by the counting circuit C from time to time. . That is, each time the stitch count signal is input, the stitch count setting value N1 is corrected, and when the corrected stitch count setting value N and the counted stitch count C do not match, S
7 is NO, returns to S5, calculates based on the new time V2 required for one rotation of the pulley 1 stitch before, and time V3 required for 1 rotation of the pulley 2 stitches ago, and repeats the loop of S5 to S7. Repeat.

When the CPU 44 determines that N=C in S7,
In S8, the CPU 44 outputs a control signal to the drive circuit 51, and the drive circuit 51 demagnetizes the solenoid 27 based on the control signal.

As a result, the plunger 28 is driven by the spring 29 in the anti-suction direction, so that the thread adjustment shaft 33 is moved in the direction away from the tension discs 23 of the main thread tension devices 8 and 9 via the thread tension switching plate 31. Left and right needle thread 1
Tighten the thread tension in steps 6 and 17. Meanwhile, at the same time, the thread adjustment shaft 34 is moved to the tension plate 2 of the main thread tension device 10, 11.
3, use both upper and lower looper threads 18 and 19.
thread tension becomes weak. In this way, the thread tension for sewing the fabric is set. As a result, both the left and right needle threads 16 and 17 are tightened, and the upper and lower looper threads 1 are tightened at the seam of the fabric compared to when an empty loop is formed with the front fabric edge as the border.
The thread tension of numbers 8 and 19 is loose. Next, to explain the case at the end of sewing, when the work cloth K is fed and the photosensor 37 detects the trailing edge of the work cloth K, the determination in S9 is set to NO based on the detection signal from the photosensor 37, and the count circuit C is reset, and counting of the stitch number signal output from the needle position detector 41 is started (S10).

Next, in S11, the setting value N2 of the number of stitches at the end of sewing set by the number of stitches at the end of sewing setting switch 50 is read out.

Also, the speed V2,
Read each V3, and based on this value, S12
In order to correct the set value of the number of stitches, the sewing speed V0 of the sewing machine at that time is calculated using the same calculation formula as at the beginning of sewing.

V0 = 2V2 - V3 Then, in S13, the number of stitches within the operation delay time t of the thread tension switching device is calculated based on the calculation result V0 and the setting value N2 of the number of stitches at the end of sewing read earlier. In the embodiment, the set value N2 (=N) of the number of stitches at the end of sewing is corrected at t=20ms). That is, the following calculation is performed.

N=N2-t/V0 Then, the CPU 44 sets the corrected number of stitches as a new N and counts the number of stitches until N matches the number of stitches C counted by the number of stitches signal input by the counting circuit C from time to time. . That is, each time the stitch count signal is input, the stitch count setting value N2 is corrected, and when the corrected stitch count setting value N and the counted stitch count C do not match, S
Return to S12 with the determination of 14 as NO, and create a new 1
Calculations are made based on the time V2 required for one rotation of the pulley before the needle and the time V3 required for one rotation of the pulley two stitches before, and the loop of S12 to S14 is repeated.

When the CPU 44 determines that N=C in S14, the CPU 44 outputs a control signal to the drive circuit 51 in S15, and the drive circuit 51 outputs and excites the solenoid 27 with a drive signal based on the control signal.

As a result, the plunger 28 is suctioned and held, so that the tension plates 23 of the main thread tension devices 8 and 9
The thread adjustment shaft 33 that was separated from the thread tension switching plate 3
1, push out the tension plate 23 and tighten both left and right needle threads 1.
Loosen the thread tension in steps 6 and 17. Meanwhile, at the same time, the thread adjustment shaft 34, which had been inserted between the tension discs 23 of the main thread tension devices 10 and 11, moves in the direction away from the tension discs 23, so that both the upper and lower looper threads 18, 19
The thread tension becomes stronger. In this way, the thread tension for forming an empty ring is set.

In this example, the setting value for the number of stitches at the beginning of sewing is N1,
The setting value for the number of stitches at the end of sewing is N2, the operation delay time of solenoid 27 is t = 20ms, and the sewing machine rotation speed is
If the stitch count signal is generated every 6ms at 10,000 spm, the timing chart in Figure 13 will be obtained. Therefore, unlike the conventional example in which the set value N1 for the number of stitches at the beginning of sewing, the set value N2 for the number of stitches at the end of sewing, the operation delay time t of the solenoid 27, and the number of rotations of the sewing machine are the same, in this example, the front and rear fabric edges are accurately separated. The thread tension can be changed as follows.

In this embodiment, the number of stitches for the operation delay time t of the solenoid 27 is calculated based on the sewing speed when the fabric edge detection device 36 detects the fabric edge.
Even after detecting the edge of the material, the sewing speed is detected and the solenoid 27
Depending on the sewing speed just before operating solenoid 2,
It is also possible to make arbitrary changes without departing from the spirit of the invention, such as by calculating the number of stitches for the operation delay time t in No. 7.

Effects of the Invention As detailed above, this invention corrects the set number of stitches by calculating the speed difference between the sewing speed of a predetermined needle and the sewing speed of a needle one or more stitches before it. As a result, even if the sewing speed changes with acceleration, data creation processing can be easily and reliably performed in a short time with a single operation procedure and calculation processing, improving operability and processing capacity. be able to.

[Brief explanation of drawings]

Fig. 1 is an electrical block circuit diagram of a thread tension switching device according to an embodiment of the present invention, Fig. 2 is a perspective view of the sewing machine, Fig. 3 is a side sectional view of the main parts, and Fig. 4 is needle position detection. Fig. 5 is a front view of the main part of the needle thread tension switching device, Fig. 6 is a plan view, and Fig.
The figures are also side views, Figure 8 is a perspective view of the work cloth, Figure 9 is a flowchart of the main routine, and Figure 1 is a flowchart of the main routine.
0 is a flowchart of interrupt routine A, FIG. 11 is a flowchart of interrupt routine B,
Fig. 12 is an explanatory diagram showing the relationship between the sewing machine's sewing speed and the number of stitches, Fig. 13 is a timing chart for comparison with a conventional example, Fig. 14 is an explanatory diagram showing the operation of the solenoid, and Fig. 15. is an explanatory diagram showing the relationship between the delay time of a solenoid and the number of stitches. 3 is a needle, 8 to 11 are main thread tension devices, 27 is a solenoid constituting a thread tension switching device, 28 is a plunger, 31 is a thread tension switching plate, 33, 3
4 is also a thread adjustment shaft, 33a and 34a are adjustment parts,
36 is a cloth edge detection device as a cloth edge detection means; 41
44 is a CPU as calculation means, correction means, comparison means and control means; 45 is ROM; 46 is RAM; 49 is stitch number setting at the beginning of sewing as stitch number setting means. Switch,
Reference numeral 50 indicates a switch for setting the number of stitches at the end of sewing as a stitch number setting means, M a sewing machine, K a work cloth, MC a microcomputer, and C a counting circuit as a counting means.

Claims (1)

[Scope of Claims] 1. A sewing machine equipped with a thread tension switching device that switches thread tension based on a control signal, comprising: needle detection means for detecting the number of stitches during sewing machine operation; and detecting the edge of cloth transferred to a sewing position. a cloth edge detecting means for detecting a cloth edge; a stitch number setting means for setting the number of stitches from when the cloth edge is detected by the cloth edge detecting means until the thread tension switching device is actuated; From the moment the edge is detected,
a counting means for counting the number of stitches based on the detection signal of the stitch number setting means; and a calculating means for calculating the sewing speed for each stitch based on the stitch number detection signal from the time when the cloth edge detection means detects a cloth edge. The speed difference between the sewing speed of a predetermined needle calculated by the calculating means and the sewing speed of a needle one stitch or several stitches before it is calculated, and the thread tension is adjusted based on the sewing speed data. a correction means for calculating the number of stitches during the operation delay time of the switching device and correcting the set number of stitches based on the calculation result; and a comparison means for comparing the corrected set number of stitches with the count number of the counting means. A thread tension switching device for a sewing machine, comprising: control means for outputting a control signal to the thread tension switching device when the comparing means determines that the set number of stitches and the counted number match.