JPH08224391A - Thread tension adjusting device of sewing machine - Google Patents

Abstract

PURPOSE: To generate a fine workmanship of sewing for different combinations of cloth and thread by operating a needle thread tension adjusting means so that the needle thread tension becomes the output value of a changeover means which changes over the output from a proper needle thread tension deciding means to a proper needle thread tension holding means and vice versa. CONSTITUTION: A needle thread tension sensor 19 has a strain gauge to sense the strain of a metal plate produced by the tension of a needle thread 11 between thread guards 13a, 13b, and if the revolving speed of sewing machine lies below a low speed reference value, stable sensing of the needle thread tension can be done, and therefore, a proper needle thread tension is computed between appropriate number of needles, and the result is stored in a memory provided in a control device 20. The control device 20 controls the needle thread tension by a thread gripping actuator 18 as a needle thread tension adjusting means so that the tension is held at the proper needle thread tension value which is stored, and when the revolving speed of the sewing machine is over the low speed reference value, changing-over is made to the proper needle thread tension value which was computed immediately before exceeding the low speed reference value, and with this value, the needle thread tension is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thread tension device for maintaining the tension of the upper thread of a sewing machine at a good value at all times.

[0002]

2. Description of the Related Art In recent sewing machines, in order to keep the upper thread tension always in a good state, the upper thread tension when the cloth is tightened by a balance, that is, the so-called cloth tightening tension is controlled to be constant. Sewing machines equipped with devices have been developed. For example, in a sewing machine with a constant upper thread tension holding device disclosed in JP-A-57-185890, when the lower thread tension is held constant, only the tension at the time of suturing the upper thread is automatically adjusted. In order to keep it at a constant level, an appropriate upper thread tension detection device is installed in the thread path between the balance of the sewing machine and the upper thread tension adjustment device, and the upper thread generated when the balance reaches the maximum position by the upper thread tension detection device. The voltage corresponding to the maximum value of the tension of the is detected, and this maximum voltage value is held by the holding device, and the held maximum voltage value and the preset upper thread and upper thread at the time of stitching the lower thread There is disclosed a configuration in which a set voltage corresponding to a desired tension is compared in a subtracter, and a servo mechanism drives the needle thread tension adjusting device so that the comparison value (deviation value) is always zero.

[0003]

However, in the above construction, the maximum value of the tension of the needle thread that occurs when the balance is at the highest position is generated only momentarily, and the rotation speed of the sewing machine causes the maximum Since the maximum value varies greatly, it is not possible to stably detect the needle thread tension at that time. Therefore, it is difficult to maintain the upper thread tension at an appropriate value regardless of the type of work cloth or thread.

According to the experimental results, when the lower thread tension is constant, when the upper thread is pulled out by the balance when the upper thread is in a free state after the sewing machine has passed over the hook and before the upper thread is tightened by the balance. Tension that occurs on the thread (thread pull-out tension)
However, the thread tightening ratio (the ratio of the position in the thickness direction of the work cloth where the knot point of the upper thread and bobbin thread is located) that is considered as good sewing is about 100% (the knot point is the thickness of the work cloth). It has been found that it is closely related to the needle thread tension (appropriate needle thread tension) in order to bring it to a position approximately at the center of the direction.

That is, the thread pull-out tension is mainly the frictional factor when pulling out the upper thread, that is, the frictional resistance between the upper thread and the lower thread, and the frictional resistance between the needle thread or the thread of the balance and the upper thread. It occurs as a result of all impacts being added. On the other hand, the upper thread tension required to pull up and stop the knot up to the center of the thickness of the work cloth, that is, the appropriate upper thread tension, is the lower thread tension and the frictional resistance between the thread and the cloth that occurs when the upper thread is pulled up. It is determined by the friction resistance between the needle thread and the hole of the balance and the needle thread.

Moreover, according to the experimental results, the bobbin thread tension is fixed at a constant value, and the relationship between the thread pull-out tension and the appropriate upper thread tension is almost linear in various combinations of cloth and thread. It was also found that when the lower thread tension is changed, the ratio of the proper upper thread tension to the standard lower thread tension is also linear. However, as described above, when the number of revolutions of the sewing machine becomes high, the upper thread tension cannot be detected stably due to the fluttering of the upper thread when crossing the shuttle.
As a result, there is a problem in that the calculated appropriate upper thread tension value varies, and a stable thread tension cannot be realized.

In view of the above experimental results, the present invention solves the above-mentioned problems of the prior art and provides a sewing machine thread tension device capable of improving the sewing of various cloth and thread combinations. It is intended.

[0008]

In order to achieve the above object, a thread tension device for a sewing machine according to a first aspect of the present invention comprises a needle that holds an upper thread and moves up and down, and a bobbin that holds a lower thread. A hook that accommodates the needle and cooperates with the needle, an upper thread tension adjusting unit that is disposed in a yarn path from the upper thread supply source to the needle and affects the upper thread tension, and the upper thread tension adjusting unit that leads to the needle. Upper thread tension detecting means arranged in the yarn path to detect the upper thread tension, and thread withdrawing for detecting the upper thread tension at the time of withdrawing the upper thread between the time when the upper thread passes over the shuttle and the lower surface of the work cloth. Tension detecting means, bobbin thread tension detecting means for measuring or inputting the bobbin thread withdrawing tension, and proper upper thread tension determining means for obtaining an appropriate upper thread tension based on the thread withdrawing tension detection value and the bobbin thread tension detecting value. A thread tension device for a sewing machine having An appropriate upper thread tension holding means for holding a value, a switching means for switching between the output of the appropriate upper thread tension determining means and the output of the appropriate upper thread tension holding means, and an upper thread tension output of the switching means. And the upper thread tension control means for operating the upper thread tension adjusting means so that the value becomes a value.

According to a second aspect of the invention, the switching means according to the first aspect includes a sewing machine rotation speed detecting means for detecting information about the sewing machine rotation speed, and the switching means is operated in accordance with the sewing machine rotation speed information. It is configured to do.
According to a third aspect of the present invention, the proper upper thread tension holding means according to the first aspect includes an accumulating means for accumulating the output of the proper upper thread tension for the number of one or more stitches, and the accumulating means. An appropriate upper thread tension learning means for calculating the upper thread tension based on the cumulative value and the number of stitches is provided, the switching means is provided with a learning mode setting means for setting a learning mode, and based on the set value of the learning mode. The switching means is operated.

[0010]

Next, an embodiment of the present invention will be described. FIG. 1 is a schematic configuration diagram of a sewing machine equipped with a needle thread tension adjusting device. The sewing machine main body 1 includes an arm portion 2 and a bed portion 3.
And one end of the main shaft 4 arranged in the arm portion 2 projects from the rear end of the sewing machine frame 1, and a belt 6 wound around a pulley 5 attached to the one end drives a sewing machine motor 7 installed under the bed. The main shaft 4 is wound around a pulley and driven by the sewing machine motor 7 to rotate the main shaft 4 in a fixed direction. The balance 8 and the needle bar 9 are reciprocally moved up and down through a balance crank, a needle bar crank rod and the like connected to the other end of the main shaft 4 in the arm section 2.

The upper thread 11 from the bobbin winding 10 as the upper thread supply source installed on the upper portion of the arm 2 is threaded by the thread hook 1
It is supplied through 2, 13a, 13b, and a thread path to a needle 15 at the tip of a needle bar 9 and a balance 8 which moves up and down in synchronization with the main shaft 4. A yarn gripping actuator 18 as upper thread tension adjusting means and an upper thread tension sensor 19 as upper thread tension detecting means for detecting the tension of the upper thread 11 are arranged in the yarn path.

Below the bed portion 3, a lower thread 1
A shuttle 17 having a conventionally known structure having a bobbin for holding the lower thread 16 for supplying 6 and a lower thread tension sensor 21 as a lower thread tension detecting means are arranged. Then, as shown in FIG. 1, in the vicinity of one end of the arm portion 2,
A photo interrupter for detecting the location of a slit formed in a disk that rotates integrally with the spindle 4.
A spindle rotation sensor 14 configured to detect a signal with a detector such as an opto-isolator is arranged. The spindle rotation sensor 14 constitutes a sewing machine rotation speed detecting means, and may be constituted by an absolute type rotary encoder. The rotation angle of the spindle 4 (the rotation phase corresponding to the vertical position of the needle 15) is detected by the phase signal pulse output from the spindle rotation sensor 14. Further, a timer (not shown) for measuring the time interval between the adjacent rising edges of the phase signal pulse is provided, and the number of revolutions of the spindle 4 per unit time (hereinafter referred to as the sewing machine revolution number) depends on the time measured by this timer. ) Can be detected simultaneously.

Further, a control device 20, which will be described later, is installed on the lower surface of the bed portion 3 and the like. As shown in FIG. 2, the thread gripping actuator 18 includes the arm portion 2 of the sewing machine.
The laminated piezoelectric element 22 is fixed between one end of the L-shaped metal fitting 23 fixed with a screw or the like and the hinge portion 24 integrally formed at the other end so that both surfaces orthogonal to the expansion and contraction direction are sandwiched. To do. The hinge portion 24 has a thread gripping arm 2
5 is attached, and the yarn gripping facing member 26 is fixed at a position facing the flat yarn gripping portion 25a at the tip of the yarn gripping arm 25 with an appropriate gap.

When a predetermined voltage is applied to the laminated piezoelectric element 22, the laminated piezoelectric element 22 expands in the laminating direction, and due to the lever principle of the hinge portion 24, the laminated piezoelectric element 22.
The extension strain amount is increased to grip the upper thread 11 between the thread gripping portion 25a on the tip end side of the thread gripping arm 25 and the thread gripping opposing body 6. In the embodiment, when the applied voltage to the laminated piezoelectric element 22 is 0V, the distance between the thread gripping portion 25a and the thread gripping opposing member 26 becomes larger than the thickness of the upper thread 11, and the upper thread 11 is completely released from the grip. In the state where a voltage of 100 V is applied to the laminated piezoelectric element 22, the needle thread 11 is set to be firmly gripped.

As shown in FIG. 3, the needle thread tension sensor 19 is a tension sensor holder 2 whose base end is fixed to the arm 2.
7, a hook-shaped upper thread hook 29 provided on the upper surface on the free end side of the metal plate 28 projecting like a cantilever, and the upper thread 11 is hung between the thread hooks 13a and 13b; and a lower surface of the metal plate 28. A strain sensor 30 such as a strain gauge stretched over the
2 and R3, and a differential amplifier circuit 32 that differentially amplifies the output of the bridge circuit 31 and outputs a positive voltage corresponding to the needle thread tension.
The strain sensor 30 detects the strain of the metal plate 29 caused by the tension of 1.
It is detected as a change in the resistance value of. As will be described later, the needle thread tension sensor 18 is used to detect the needle thread tension when the needle thread 11 is pulled out after the needle thread 11 has passed over the shuttle 17 and before reaching the lower surface of the work cloth 33. It also functions as a tension detecting means.

4 and 5, a lower thread tension sensor 21 as a lower thread tension detecting means for detecting the tension of the lower thread 16 is shown.
And below the needle plate 40 of the bed 3,
The metal plate 35, which is disposed above the base plate and has its base end fixed to an appropriate position such as the needle plate 40, has a sewing needle 15, an upper thread 11, and a lower thread 1.
A thread insertion hole 36 through which 6 can pass is formed, and a strain gauge 37 is stretched on the lower surface of the metal plate 35. Like the upper thread tension sensor 19, a resistance bridge circuit 38 and a differential amplifier circuit 39 that differentially amplifies the output of the bridge circuit 38 and outputs a positive voltage corresponding to the lower thread tension are provided.
When the lower thread 16 inserted through the thread insertion hole 36 contacts the metal plate 35, the strain of the metal plate 35 caused by the tension of the lower thread 16 is detected as a change in the resistance value of the strain gauge 37.

FIG. 6 is a functional block diagram of the control device 20 of this embodiment, which includes a central processing unit (CPU) such as a microcomputer, an input / output interface (not shown), and a sewing machine to be described later. A read-only memory (ROM) that stores a control program that executes control such as adjusting the tension of the upper thread, a readable / writable memory (RAM) that stores various control data, etc. are provided. The spindle rotation sensor 1
4 and an A / D converter 41 for converting an analog output value from the differential amplifier circuit 32 of the needle thread tension sensor 19 into a digital value.
And an A / D converter 42 for converting an analog output value from the differential amplifier circuit 39 of the bobbin thread tension sensor 21 into a digital value.
And the lower thread tension sensor 21 are connected to each other, and the respective detected values are input to the CPU. Further, a thread grip drive circuit 44 for driving the thread grip actuator 18 as the upper thread tension adjusting means and a motor drive circuit 45 for driving the sewing machine motor 7 are connected to the output interface connected to the CPU. To do.

Next, the needle thread tension adjustment control executed by the central processing unit (CPU) will be described with reference to the flow charts of FIGS. 7 and 8. When you start sewing,
As an initial process, the spindle rotation sensor 14 detects the spindle rotation angle θ (step S71), and stands by until the bobbin thread drawing phase (θ = 60 °) is reached (step S72:
no). When the bobbin thread withdrawal phase is reached (step S72: ye
s), the lower thread tension Tb at that time is detected by the lower thread tension sensor 21 and stored in the memory (step S73). Also,
A memory used to store the value of the detected upper thread tension Tu (hereinafter T
The information (data) in the u memory) and the memory (data) of the stitch number counter in which the stitch number N is stored are cleared (step S74). Usually, these memories are secured in a readable / writable memory (RAM) at any time.

Then, the spindle rotation angle θ is detected again (step S75), and slightly before the needle thread drawing phase (θ = 3).
It waits until it becomes (00 °) (step S76: no).
When the upper thread withdrawal phase is reached (step S7
6: yes), the initial process of steps S71 to S76 is completed, and the main process (appropriate upper thread tension determination process) (step S77) repeatedly executed next is performed, and the proper upper thread tension is maintained. Thus, the sewing is executed in the state where the upper thread tension is controlled (step S78).

As shown in the flow chart of FIG. 8, in the main processing, first, the main spindle rotation sensor 14 detects again the main spindle rotation angle θ (step S81), and the θ is the yarn drawing phase (315 ° ≦ θ ≦ 345 °). Or needle top dead center (θ =
0 °) or cloth tightening phase (30 ° ≦ θ ≦ 90 °)
It is determined (steps S82 to S84), and if the phase is other than that, the process returns to step S81.

Here, the relationship between the phase (spindle rotation angle θ) and the needle thread tension Tu is shown in the graph of FIG. 9. In the needle thread drawing phase, the needle thread tension is weak (the needle thread drawing tension Tp).
Occurs, and strong needle thread tension (cloth tightening tension Tt) is generated in the cloth tightening phase. In this processing, control is performed to optimize the cloth tightening tension Tt subsequent to the needle thread drawing tension Tp. This needle thread pull-out tension Tp is shown in FIG.
The tension generated in the state as shown by, that is, after the loop formed by the upper thread 11 passes over the shuttle 17 and before the upper thread 11 is pulled up and the lower end of the loop reaches the lower surface of the work cloth 33. The generated tension is caused by friction between the work cloth 33 and the upper thread 11, or friction between the upper thread 11 and the needle hole 40a, the balance 8, etc., because the upper thread is in a relatively free state. . It should be noted that there are peaks of the needle thread tension before the needle thread withdrawal phase and near the needle top dead center phase, but since these peaks are not related to the processing of the present invention, detailed description thereof is omitted.

In the initial processing, the main processing is started after waiting for the upper thread withdrawal phase. Therefore, immediately after finishing the initial processing, the central processing unit (CPU) judges that the upper thread withdrawal phase is set ( Step S82: yes). Then, it is determined whether or not the sewing machine rotational speed Nm at that time is equal to or lower than the low speed reference value Nrb (step S85). Here, the low speed reference value Nrb is the maximum number of revolutions of the sewing machine that is considered to be capable of detecting the upper thread withdrawing tension Tp.

The sewing machine rotation speed Nm is the low speed reference value N.
If rb or less (step S85: yes), the needle thread tension T
u is detected, the value is stored in the Tu memory (step S86), then the proper tension calculation flag Fo is cleared to 0 (step S87), and then the process returns to step S81 to return to the proper needle thread tension described later. The To operation will be executed.

That is, the sewing machine speed Nm is the low speed reference value N.
When it is less than or equal to rb, the upper thread tension Tu can be detected in a stable manner. Therefore, as will be described later, the appropriate upper thread tension To is calculated using the result of calculating the appropriate upper thread tension To between the appropriate number of stitches. The upper thread tension Tu is controlled so as to maintain the tension value To. When the sewing machine rotation speed Nm is equal to or higher than the low speed reference value Nrb, the value is switched to the value of the proper upper thread tension To calculated immediately before exceeding the low speed reference value Nrb, and the upper thread tension Tu is controlled with this value. .

In the embodiment of this processing, the spindle 14 is 3
° Once every rotation, it is executed by interrupt processing,
The upper thread tension Tu is measured 11 times during the upper thread drawing phase (315 ° ≦ θ ≦ 345 °), and all 11 values of the upper thread tension Tu are individually stored in the Tu memory. The step S86 functions as a yarn pull-out tension detecting means.

By the way, when the sewing machine rotational speed Nm is high (fast), the upper thread tension Tu cannot be detected stably due to the fluttering of the upper thread 11 when passing over the shuttle 17.
As a result, the appropriate upper thread tension calculation value varies or has an error, so that stable thread tension cannot be realized. Therefore, when the sewing machine rotational speed Nm exceeds the low speed reference value Nrb, the central processing unit (CPU) prevents the output of the proper upper thread tension calculation value in that state, and the latest value obtained up to that time ( Since the proper upper thread tension calculation value To (as a result of calculation just before the sewing machine rotational speed Nm exceeds the low speed reference value Nrb) is held, the value is switched (by the CPU) to this value, and the upper thread is It controls the tension Tu. Therefore, this switching means is a judgment of the central processing unit (CPU) based on the measurement result of the spindle rotation sensor 14, as described later.

The needle thread drawing phase is exceeded (step S8
2: yes) and when needle top dead center is reached (step S8)
3: Yes), it is again determined whether the sewing machine rotation speed Nm is equal to or lower than the low speed reference value (step S88), and the sewing machine rotation speed Nm is equal to or lower than the low speed reference value (step S88: yes
s), when the proper needle thread tension calculation is not completed, that is, when the proper tension calculation flag Fo is not 1 (step S8)
9: no), the appropriate needle thread tension calculation processing described below is executed.

That is, the thread pull-out tension Tp is calculated from the value of the upper thread tension Tu stored in the Tu memory in step S86 (step S90). Incidentally, the step S88
Function as switching means. In the embodiment, five of the latest 11 values of the upper thread tension Tu are extracted in ascending order, and the average value thereof is calculated to calculate the thread withdrawing tension Tp. Here, the smaller value is adopted because, for example, there are many accidental increases (increases) in the tension, such as the upper thread 11 happens to be caught by a foreign substance, but when the upper thread is broken, it is different. This is because the tension is unlikely to drop accidentally, and therefore a relatively small value is considered to be the predetermined needle thread drawing tension Tp. Further, the reason why the average value of the five values is adopted is that it is more reliable than the case where the minimum value is adopted because the tension is not always lowered due to a measurement error or the like.

Next, the reference needle thread tension Tref is calculated based on the needle thread pull-out tension Tp thus calculated (step S91). This reference upper thread tension Tref is the lower thread tension Tref.
It is an appropriate upper thread tension corresponding to the upper thread withdrawing tension Tp when b is set to 20 g, and is sampled by experimentally changing the upper thread withdrawing tension Tp variously in advance, and the upper thread withdrawing tension Tp is used as a parameter. The data is stored in the read-only memory (ROM) in advance. In this embodiment, as shown in FIG. 10A, when the horizontal axis is the upper thread withdrawing tension Tp and the vertical axis is the reference upper thread tension Tref, a graph showing a substantially linear strong correlation is obtained. is there. It has been confirmed by experiments that this correlation does not change even if the types of cloth and thread are changed and combined. Therefore, even if the type of cloth or thread is changed, if the upper thread pull-out tension Tp is determined, the reference upper thread tension Tref can be obtained.

Next, an upper thread tension correction coefficient M is calculated based on the lower thread tension Tb (step S92), and an appropriate upper thread tension To is calculated from this upper thread tension correction coefficient M and the reference upper thread tension Tref. Yes (step S93). Here, the proper needle thread tension To is the reference needle thread tension Tref shown in FIG.
It has been empirically found that there is a relationship of a straight line or a curve with respect to the graph of FIG. Therefore, if the upper thread tension correction coefficient M for converting this inclination is known, the appropriate upper thread tension To is calculated as the upper thread tension correction coefficient M and the reference upper thread tension Tref.
Can be obtained as the product of Therefore, the upper thread tension correction coefficient M is calculated based on the upper thread tension and the reference upper thread tension Tref which are obtained by experimentally changing the lower thread tension Tb in advance, and the lower thread tension Tb is used as a parameter. The data is stored in advance in a read-only memory (ROM). In the present embodiment, as shown in FIG.
The lower thread tension Tb is plotted on the horizontal axis, and the upper thread tension correction coefficient M is plotted on the vertical axis. The steps S91 to S93 function as an appropriate upper thread tension determining means.

Thus, the obtained appropriate upper thread tension To is obtained.
Is stored and held in a memory area on a readable / writable memory (RAM) at any time, and as shown in FIG. 1, a 7-segment fluorescent display panel provided on the side surface of the arm 2 of the sewing machine or a liquid crystal display panel, The proper needle thread tension To currently set by the operator is displayed on the display device 50 (step S94), and the proper needle thread tension calculation end flag Fo is set to 1 to end this computation (step S95). ), The process returns to step S81, and the cloth tightening phase (3
Standby until 0 ° ≦ θ ≦ 90 ° (step S8)
4). The step 94 functions as a proper needle thread tension holding means.

Spindle rotation angle θ detected in step S81
From this, it is determined that it is the cloth tightening phase (step S8).
4: yes), the central processing unit (CPU) controls the thread gripping actuator 18 so that the upper thread tension Tu detected by the upper thread tension sensor 19 is the calculated and held proper upper thread tension To. This is done (step S96). This step 96 functions as a needle thread tension control means.

As a result, in the upper thread drawing phase,
The cloth is tightened with the above-mentioned appropriate upper thread tension To. If it is the lower thread withdrawal phase (θ = 60 °) (step S97), the lower thread tension Tb at that time is set to the lower thread tension sensor 2
1 and stores it in the memory (step S98), then it is not the bobbin thread drawing phase (step S97: n
o) As it is, the process returns to step S81, and during the cloth tightening phase, the processes of steps S96 to S98 are repeated to adjust the needle thread tension. When the cloth fastening phase ends, the upper thread withdrawal phase is waited for again and the above processing is repeated.

As explained above, the needle thread 11 is moved to the hook 17
After reaching the upper limit of the work cloth 33, the phase section is longer than the top dead center of the needle, and the upper thread tension Tu at the time of drawing the upper thread is relatively small in absolute value. Since there is little fluttering and stability, there are few variations and detection errors in the detected value of the needle thread tension Tu. Moreover, when the rotation speed Nm of the sewing machine is equal to or lower than the predetermined low speed reference value Nrb, the upper thread tension Tu can be stably detected, so that the central processing unit (CPU) can determine the appropriate upper thread tension To in real time. Using the calculated result, the upper thread tension Tu is controlled so as to maintain the value of the appropriate upper thread tension To. Therefore, the tension of the upper thread 11 is controlled to be optimum for each stitch in real time, and the cloth can be sewn with the cloth tightening tension being optimum. When the sewing machine rotational speed Nm is equal to or higher than the low speed reference value Nrb, the needle thread tension Tu is switched to the value of the appropriate upper thread tension To calculated immediately before exceeding the low speed reference value Nrb, and the upper thread tension Tu is controlled with this value. Even when the sewing machine rotation speed is high and stable measurement of the upper thread tension cannot be performed, the tension of the upper thread 11 is controlled to be optimum, and the cloth can be sewn with the optimum cloth tightening tension To. is there.

Further, the calculated proper upper thread tension To reflects the difference in frictional resistance caused by the difference in cloth and thread, and therefore is an appropriate value even for various combinations of cloth and thread. As a result, the knitting point of the upper thread and the lower thread is formed substantially at the center in the thickness direction of the work cloth 33, as shown in FIG. .

Further, in calculating the proper upper thread tension To, since the lower thread tension is actually measured and corrected, the upper thread tension automatically changes according to the lower thread tension, and the operator adjusts the lower thread tension. Even if it is changed, it is not necessary to adjust the needle thread tension.
In addition, the display device 50 can confirm how much the upper thread tension is adjusted, which is extremely convenient. Next, a second embodiment as the needle thread tension adjustment control by the learning mode function by the computer will be described with reference to the flowchart shown in FIG. Since the initial processing is the same as that in FIG. 7, the description thereof will be omitted and only the main processing will be described.

In the main processing, first, the spindle rotation angle θ is detected again by the spindle rotation sensor 14 (step S11).
1), the θ is the thread drawing phase (315 ° ≦ θ ≦ 345
Angle), needle top dead center (θ = 0 °), or cloth tightening phase (30 ° ≦ θ ≦ 90 °) (step S81).
12 to S114), and when the phase is other than that, the process returns to step S111.

Since the relationship between the phase (spindle rotation angle θ) and the needle thread tension Tu is shown in the graph of FIG. 9 and is the same as that described in the above embodiment, detailed description thereof will be omitted. . Now, if the central processing unit (CPU) determines that it is the upper thread withdrawal phase (step S112: yes)
), It is determined whether or not the learning mode has been entered (step S115). A learning mode input switch 51 as learning mode setting means is provided on the surface of the arm portion 2 of the sewing machine, etc., and the operator turns the switch 51 on if desired.
Set to N or OFF.

The operator inputs the learning mode input switch 5
1 is turned on (step S115, yes), sewing is performed at the inching speed (slowest sewing speed), the needle thread tension Tu at that time is detected, and the value is stored in the Tu memory (step S116). After the appropriate tension calculation flag Fo is cleared to 0 (step S117), the process returns to step S111, and the appropriate needle thread tension To calculation described below is executed. The step S116 functions as a yarn pull-out tension detecting means.

If the sewing is performed at the inching speed (slowest sewing speed), the upper thread tension Tu can be detected stably as in the case of the low speed reference value Nrb in the first embodiment. Then, the appropriate upper thread tension To for each stitch is calculated, and the average value of the several stitches is calculated as the upper thread tension learning value Ts. Then, the operator returns (switches) the learning mode to the OFF state to set the normal sewing mode, and the sewing is executed at a speed higher than the inching speed. In this normal sewing mode, the result calculated in the learning mode is calculated. Is used to hold the upper thread tension learning value Ts as the target upper thread tension Tu.
Is to control.

In the embodiment of this processing, the spindle 4 is 3 °.
It is executed once by every interruption by the interrupt processing, and the upper thread tension Tu is measured 11 times during the upper thread withdrawal phase (315 ° ≦ θ ≦ 345 °).
All u values are stored individually in Tu memory. In order to calculate the appropriate upper thread tension To and calculate the upper thread tension learning value Ts from the average value of the plurality of needles, first, the needle thread drawing phase is exceeded (step S112: yes), and the needle top dead center is reached. If it is (step S113: yes), it is again determined whether or not the learning mode is set (step S118). If the learning mode is set (step S118: yes) and the proper needle thread tension calculation is not completed, That is, when the proper tension calculation flag Fo is not 1 (step S119: no),
The thread pull-out tension Tp is calculated for each stitch from the value of the needle thread tension Tu stored in the Tu memory in step S116 (step S120). Incidentally, the step S118
Function as switching means.

Next, the reference needle thread tension Tref is calculated based on the needle thread pull-out tension Tp calculated as described above (step S121), and then the needle thread tension correction coefficient M is calculated based on the bobbin thread tension Tb. Is calculated (step S122),
An appropriate upper thread tension To is calculated from the upper thread tension correction coefficient M and the reference upper thread tension Tref (step S123).
The relationship between the reference needle thread tension Tref and the needle thread tension correction coefficient M in this case is shown in FIGS. 10 (a) and 10 (b).
Since it is the same as that described in the first embodiment, the description thereof will be omitted. The steps 121 to 123 function as a proper needle thread tension determining means.

If the thus determined proper upper thread tension To for each stitch is adopted as it is, there is a possibility that the variation may become large due to a measurement error or the like. Therefore, an average value when sewing a plurality of stitches is adopted as the proper upper thread tension. In order to do so, the number N of needles appropriately set by a needle thread tension accumulation counter (not shown) provided in the central processing unit (CPU) or the like, and the cumulative appropriate upper thread tension Toa (= (Toa + To) is calculated (step S124). Then, the arithmetic mean value is obtained by calculating the needle thread tension learning value Ts (= Toa / N) (step S125). In addition, in step S12
4 functions as an accumulating means, and step 125 functions as an appropriate upper thread tension learning means.

The needle thread tension learning value Ts is stored and held in a memory area on a readable / writable memory (RAM) at any time, and as shown in FIG. 1, it is provided on the side surface of the arm 2 of the sewing machine or the like for 7 segments. The proper needle thread tension To currently set by the operator is displayed on the display device 50 such as a fluorescent display panel or a liquid crystal display panel (step S1).
26) together with setting the appropriate upper thread tension calculation end flag Fo to 1 to end this calculation (step S127),
Returning to step S111, the cloth tightening phase (30 ° ≦ θ ≦ 9
It waits until it becomes 0 ° (step S114). The step S126 functions as a proper needle thread tension holding means.

When the learning mode is ON, and when the OF
In any case of F, when it is determined from the spindle rotation angle θ detected in step S111 that the cloth tightening phase is reached (step S114: yes), the calculated needle thread tension learning value Ts is set as the target needle thread tension. Thus, the central processing unit (CPU) controls the thread gripping actuator 18 as the upper thread tension adjusting means (step S12).
8). This step 128 functions as a needle thread tension control means.

As a result, in the upper thread drawing phase,
The cloth is fastened so that the above-mentioned needle thread tension learning value Ts becomes the target needle thread tension. The bobbin thread withdrawal phase (θ = 60
°) (step S129), the bobbin thread tension Tb at that time is detected by the bobbin thread tension sensor 21 and stored in the memory (step S130), and then it is not the bobbin thread drawing phase (step S129: no). As it is, step S1
Returning to step 11, during the cloth tightening phase, steps S128 to S1.
By repeating the process of 30, the upper thread tension is adjusted.

As described above, in this embodiment, the operator sets the learning mode and executes low-speed sewing, and at the same time, measures the appropriate upper thread tension To for a plurality of stitches,
Based on this, the needle thread tension learning value Ts is calculated and stored,
Next, when switching to the normal sewing mode and performing high-speed sewing, if the sewing operation is performed so that the needle thread tension learning value Ts becomes the target needle thread tension value, a stable needle thread withdrawal tension can be obtained. It is possible to obtain a stable thread tension even in the high-speed sewing state.

When the learning mode switch 51 as the mode setting means is switched from the learning mode to the normal sewing mode (or the mode setting switch is set so that the learning mode side is OFF), the appropriate upper thread tension To is set to the proper upper thread tension To. It may be configured not to output. As a modification of the first and second embodiments, the bobbin thread tension T
b is not detected by the bobbin thread tension sensor 21, but the bobbin thread tension input switch 52 which can be arbitrarily set by the operator or the key for numerical value input and function display is used to set the bobbin thread tension Tb to an arbitrary value. May be input. In this case, it is known that the optimum bobbin thread tension value experimentally found in ordinary sewing is 20 g. Therefore, the operator inputs such a value using the bobbin thread tension input switch 52 with a display device.

In this modification, it is not necessary to detect the lower thread tension as an initial process in the first and second embodiments. Instead, the reference needle thread tension T during the main processing
Input the value of the bobbin thread tension Tb between the step of calculating ref and the step of calculating the needle thread tension correction coefficient M, store this value in a predetermined memory, and read it from the memory when necessary. It should be configured to. Further, in this modification, it is not necessary to detect the bobbin thread tension between the cloth fastening phases (30 ° ≦ θ ≦ 90 °). Other processes are the same as those in the first and second embodiments, and detailed description thereof will be omitted.

As described above, also in this modified example, the stable proper upper thread tension To can be calculated in the state where the sewing speed is low, and based on this value, the upper thread 11 is real-time for each stitch at the time of high-speed sewing. The tension of can be optimally controlled, and optimal cloth fastening can be performed. Further, the calculated appropriate upper thread tension becomes an appropriate value for various kinds of cloths and combinations of threads, and as a result, good sewing is achieved with a so-called thread tightening rate of almost 100%.

Further, in this modification, since the lower thread tension sensor is not required, the cost can be reduced by that amount, and the lower thread arbitrarily input through the process of calculating the upper thread tension correction coefficient M and the like. Since the needle thread tension is automatically changed according to the tension value, the effect that the manual adjustment of the needle thread tension is not required is the same as in the first and second embodiments.

Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various modes can be adopted without departing from the scope of the present invention. For example, the thread gripping actuator 18 as the needle thread tension adjusting means may use an electromagnetic force such as an inexpensive electromagnetic solenoid having a low response speed instead of the laminated piezoelectric element having an excellent response speed.

Further, the appropriate upper thread tension holding means, instead of holding the value itself of the calculated appropriate upper thread tension To in the memory, replaces the upper thread tension Tu and the lower thread tension which are the basis of the calculation. The value of Tb may be held in the memory as a value related to the proper needle thread tension. Further, as the control means of this embodiment, instead of the software configuration of the microcomputer or the like, the output from the appropriate upper thread tension determining means, the appropriate upper thread tension holding means, and the appropriate upper thread tension determining means The switching means for switching the output from the thread tension holding means and the upper thread tension control means for operating the upper thread tension adjusting means so that the upper thread tension becomes the output value of the switching means are constituted by a hardware electric circuit. You may choose to do so.

[0054]

As described above, claim 1
A thread tension device for a sewing machine according to the invention described in (1), a needle that holds an upper thread and moves up and down, a shuttle that accommodates a bobbin that holds a lower thread and cooperates with the needle, and an upper thread supply source An upper thread tension adjusting means which is arranged in the yarn path to reach and which affects the upper thread tension,
When the upper thread tension detecting means is arranged in the yarn path from the upper thread tension adjusting means to the needle to detect the upper thread tension, and when the upper thread is pulled out after the upper thread passes over the shuttle and reaches the lower surface of the work cloth. The thread withdrawing tension detecting means for detecting the upper thread tension, the lower thread tension detecting means for measuring or inputting the lower thread withdrawing tension, and an appropriate upper limit based on the thread withdrawing tension detection value and the lower thread tension detection value. In a thread tension device of a sewing machine having an appropriate upper thread tension determining means for determining a thread tension, an appropriate upper thread tension holding means for holding a value relating to the appropriate upper thread tension, an output of the appropriate upper thread tension determining means and the appropriate value. And a switching means for switching and outputting the output of the upper thread tension holding means, and an upper thread tension control means for operating the upper thread tension adjusting means so that the upper thread tension becomes the output value of the switching means. Is.

As described above, after the needle thread has passed the shuttle and before reaching the lower surface of the work cloth, there is a longer phase section compared to the top dead center of the needle, and the upper section at the time of needle thread withdrawal in that section is longer. Although the thread tension has a relatively small absolute value, it has little fluttering and is stable, so there are few variations and detection errors in the detected value of the needle thread tension. Moreover, when the rotation speed of the sewing machine is low, the stability thereof is further improved.

Therefore, since there is no variation in the value of the proper upper thread tension calculated based on the detected value of the upper thread tension in this stable state, the proper state of that state can be obtained as in the case of low-speed sewing. By outputting the value of the upper thread tension by the appropriate upper thread tension determination means and controlling the upper thread tension adjusting means based on this, the upper thread tension can be controlled to the optimum value in real time.

When the stable detection of the upper thread tension is inappropriate, such as when sewing at a high speed, the value calculated in advance by the appropriate upper thread tension determining means is set to the appropriate upper thread tension as described above. The thread tension holding means may hold the thread tension, and the switching means may switch to output the value, and the needle thread tension adjusting means may be controlled based on this. With this configuration, the needle thread tension can always be kept stable irrespective of fluctuations in the sewing machine rotational speed, and the sewing finish can be well maintained.

Further, since the calculated appropriate upper thread tension reflects the difference in frictional resistance caused by the difference in cloth and thread, it becomes an appropriate value for various combinations of cloth and thread.
As a result, the knot point of the upper thread and the lower thread is formed substantially in the center in the thickness direction of the work cloth, which is a so-called thread tightening rate of about 100.
%, The sewing will be finished well. According to a second aspect of the present invention, the switching means according to the first aspect includes a sewing machine rotation speed detection means for detecting information about the sewing machine rotation speed,
The switching means is operated in accordance with the sewing machine rotation speed information.

As described above, the sewing machine rotation speed detecting means detects whether the rotation speed is high or low. When the rotation speed of the sewing machine is equal to or lower than a predetermined value, the needle thread tension can be stably detected. If the upper thread tension is controlled so as to maintain the value of the appropriate upper thread tension by using the result of calculating the appropriate upper thread tension by the upper thread tension determination means in real time, the tension of the upper thread in real time for each stitch. Is controlled to be optimal,
It can be sewn with the cloth tightened at the optimum cloth tension. And
When the number of revolutions of the sewing machine is equal to or higher than a predetermined value, the value is switched to the appropriate upper thread tension value calculated immediately before exceeding that value, and the needle thread tension is controlled with this value, so that the sewing machine rotation speed is high and stable. Even when the upper thread tension cannot be measured, the upper thread tension is controlled to be optimum, and the cloth can be sewn with the cloth tightened at the optimum cloth tightening tension.

According to a third aspect of the present invention, the proper upper thread tension holding means according to the first aspect is an accumulation means for accumulating the output of the proper upper thread tension with respect to the number of one or more stitches, and An appropriate upper thread tension learning means for calculating the upper thread tension based on the cumulative value by the accumulating means and the number of stitches; and the switching means, a learning mode setting means for setting a learning mode,
The switching means is operated based on the set value of the learning mode.

With this structure, low-speed sewing capable of detecting stable upper thread tension is executed in the learning mode, and a plurality of proper upper thread tensions for each stitch obtained as a result of the learning mode are output. Since the accumulated values are accumulated by the accumulating means, an appropriate upper thread tension without variation can be obtained by setting the average value as the upper thread tension learning value. When the normal high speed correction is executed, the learning mode is set to OFF or the like so that the calculated needle thread tension learning value becomes the target value of the needle thread tension. Just activate it. Further, unless the needle thread tension learning value once obtained is cleared (erased), this value can be used any number of times in the normal sewing mode, which can contribute to the efficiency of the sewing work.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a sewing machine including an automatic upper thread feeder.

FIG. 2 is a perspective view of a thread gripping actuator.

FIG. 3 is a perspective view of a needle thread tension sensor.

FIG. 4 is an explanatory diagram showing the behavior of the lower thread during the thread drawing phase.

FIG. 5 is a perspective view of a lower thread tension sensor.

FIG. 6 is a functional block diagram of control means.

FIG. 7 is a flow chart of a first embodiment of thread tension control.

FIG. 8 is a flowchart of a main process of the first embodiment of thread tension control.

FIG. 9 is a diagram showing a needle thread tension waveform.

FIG. 10 (a) is a graph showing the relationship between the thread pull-out tension and the reference needle thread tension when the lower thread tension is 20 g, and FIG.
Is a graph showing the relationship between the lower thread tension and the upper thread tension correction coefficient.

FIG. 11 is a flowchart of a main process of a second embodiment of thread tension control.

[Explanation of symbols]

 4 spindle 7 sewing machine motor 8 balance 11 needle thread 14 spindle rotation sensor 15 needle 16 bobbin thread 17 hook 18 thread gripping actuator 19 needle thread tension sensor 20 controller 21 bobbin thread tension sensor 20 controller 33 work cloth 51 learning mode input switch

Claims (3)

[Claims] 1. A needle that holds an upper thread and moves up and down, a shuttle that accommodates a bobbin that holds a lower thread and cooperates with the needle, and a needle disposed in a yarn path from an upper thread supply source to the needle. An upper thread tension adjusting means for affecting the upper thread tension, an upper thread tension detecting means arranged in the yarn path from the upper thread tension adjusting means to the needle for detecting the upper thread tension, and the upper thread passing over the shuttle. A thread withdrawing tension detecting means for detecting the upper thread tension when the upper thread is withdrawn from the back to the lower surface of the work cloth; a bobbin thread tension detecting means for measuring or inputting the bobbin thread withdrawing tension; and the thread withdrawing tension. In a thread tension device of a sewing machine having an appropriate upper thread tension determining means for obtaining an appropriate upper thread tension based on a detected value and the lower thread tension detected value, an appropriate upper thread tension holding means for holding a value related to the appropriate upper thread tension. And the output of the appropriate upper thread tension determining means and the appropriate Switching means for switching between the output of the thread tension holding means and outputting; and upper thread tension control means for operating the upper thread tension adjusting means so that the upper thread tension becomes the output value of the switching means. Characteristic sewing machine thread tension device. 2. The switching means includes a sewing machine rotation speed detecting means for detecting information on the sewing machine rotation speed, and the switching means is operated according to the sewing machine rotation speed information. A thread tension device for a sewing machine according to item 1. 3. The proper needle thread tension holding means is based on an accumulating means for accumulating the output of the proper needle thread tension for the number of one or more stitches, and a cumulative value by the accumulating means and the number of stitches. An appropriate upper thread tension learning means for calculating the upper thread tension, the switching means includes a learning mode setting means for setting a learning mode, and the switching means is operated based on the set value of the learning mode. The thread tension device for a sewing machine according to claim 1, wherein the thread tension device is configured.