JP5142467B2 - sewing machine - Google Patents

Description

  In the present invention, the tension of the upper thread applied by the thread tension device is controlled by detecting the tension of the upper thread by the yarn tension detecting means and controlling the driving means of the thread tension device by the control means based on the detected tension. It is related to the sewing machine.

  In a conventional sewing machine, an upper thread is guided from a thread supply source to a sewing needle through a thread tension device and a balance in this order. The thread tension device is driven by a drive source such as an electromagnetic solenoid, and the tension of the upper thread is adjusted by electrically controlling the drive source (see, for example, Patent Document 1).

In addition, a tension detector that detects the tension of the upper thread is provided between the balance and the sewing needle in order to respond to changes in the cloth, thread, etc., so that the tension applied to the upper thread is peaked when the thread is pulled by the balance. The tension in the vicinity of the rising section is detected, and the thread tension device is controlled based on the detection result to control the thread tension in the lifting section of the balance (see, for example, Patent Document 2).
JP 2000-300902 A Japanese Patent Publication No. 5-75440

  However, the tension of the upper thread applied to the knot between the thread tension device and the lower thread located far away does not change immediately even if the thread tension device is controlled. The delay is greatly affected, and even if the thread tension device is controlled based on the tension detection result in the vicinity of the lift of the balance, the result is reflected only after the upper thread has been lifted by the balance. As a result, there is a problem that when the high speed operation is performed, the tension control of the upper thread cannot be followed and the knot positions of the upper thread and the lower thread are not uniform.

  Therefore, the present invention has been made to solve the above-described problems, and a sewing machine that can make the seam uniform even if it takes time until the detected tension is reflected in the tension of the upper thread. The purpose is to provide.

In order to solve the above problems, an invention according to claim 1 is directed to a sewing needle that is supported by a needle bar that moves up and down and moves up and down through a needle hole provided in a needle plate, and the sewing needle. A hook that moves to form a seam; a thread tension device that is disposed between the thread supply source and the balance in the upper thread path from the thread supply source to the sewing needle; and that can control the thread tension; and the thread tension device Drive means for changing the tension applied by the tension, tension setting means for setting a set tension, position detection means for detecting the vertical movement phase of the balance, and an upper thread path between the balance and the sewing needle. A sewing machine comprising: tension detecting means for detecting tension applied to the upper thread and control means for controlling the driving means; wherein the control means sets the set tension set by the tension setting means and the setting the first threshold value and the first threshold value lower than the tension Rimotaka rather stores a second threshold value lower than the set tension, the tension detected in when the detected phase detected by said position detecting means is a balance BDC section upper thread drawn by the loop-taker point of said hook When the detected tension detected by the means is compared with a first threshold corresponding to the set tension and a second threshold higher than the first threshold, and as a result of the comparison, the detected tension falls below the first threshold The detection phase detected by the position detecting means is a balance raising section from when the upper thread loop scooped into the hook is detached from the hook to when the sewing needle passes through the needle hole from top to bottom. The tension of the upper thread applied by the thread tension device is controlled to be lower than the set tension by controlling the driving means, and the position detection is performed when the detected tension exceeds the second threshold value. hand By controlling the drive means when the detection phase detected by the balance raising section is controlled, the tension of the upper thread applied by the thread tension device is controlled to be higher than the set tension, and the detected tension is When the detected phase detected by the position detecting means is the balance raising section when the first threshold value or more is less than or equal to the second threshold value, it is given by the thread tension device by controlling the driving means. When the detected phase detected by the position detecting means is other than the balance raising section, the tension is applied by the thread tension device by controlling the driving means. The upper thread tension is controlled to the set tension.

According to the first aspect of the invention, based on the tension detected by the tension detecting means in the bottom dead center section of the balance, the tension of the upper thread is controlled by the thread tension device in the lift raising section after the bottom dead center section of the balance. Therefore, the tension detected by the tension detecting means in the bottom dead center section of the balance is reliably reflected in the tension of the upper thread in the subsequent lift section. Therefore, the followability of the tension of the upper thread is improved, and the seam can be made uniform.
The tension can be adjusted appropriately by controlling in this way for the following reason.
Even in the bottom dead center section of the scale before the scale ascending section where the lower thread and the upper thread are knotted, the upper thread between the sewing needles from the balance is drawn by the hook tip, and as a result, the tension increases. The amount of increase in tension at this time is greatly influenced by the resistance between the cloth and the upper thread. The influence of the resistance between the cloth and the upper thread is also manifested in the lifting section where the lower thread and upper thread are knotted. Therefore, if the influence of the cloth or the upper thread is detected in the bottom dead center section of the balance and the tension in the lift raising section where the knot between the lower thread and the upper thread is actually controlled based on the detection result, the cloth or the upper thread is controlled. Corresponding to the change of the upper thread, the tension at the time of knotting the upper thread and the lower thread can be controlled appropriately.
For example, when there is a step on the cloth where the tension is detected to be greater than normal in the bottom dead center section of the balance, the thread tension device increases the tension in the lift raising section by the amount affected by the step. By controlling, the tension at the time of knotting of the lower thread and the upper thread can be appropriately controlled. In particular, since this control is actually performed before the knot between the lower thread and the upper thread, it can be sufficiently followed even during high-speed operation.

  According to the first aspect of the present invention, since the tension detected by the tension detecting means in the bottom dead center section of the balance is reliably reflected in the tension of the upper thread in the subsequent lift ascent section, uniform seams can be applied. it can.

  The best mode for carrying out the present invention will be described below with reference to the drawings. However, although various technically preferable limitations for implementing the present invention are given to the embodiments described below, the scope of the invention is not limited to the following embodiments and illustrated examples.

  As shown in FIGS. 1 to 2, the sewing machine 1 includes a frame 2. The frame 2 includes a bed portion 3 and an arm portion 4 disposed above the bed portion 3. A needle bar 5 extending downward is provided at the distal end of the arm part 4 so as to be movable up and down, and a sewing needle 6 is attached to the lower end of the needle bar 5. The needle bar 5 is connected to the main shaft via a crank mechanism or the like, the main shaft is connected to the sewing machine motor 81, and the rotational movement of the main shaft is converted into the vertical movement of the needle bar 5 by the crank mechanism. And the sewing needle 6 moves up and down.

  The main shaft is provided with an encoder 83 as position detecting means for detecting the vertical movement phase of the balance 27, and the rotation angle of the main shaft is detected by the encoder 83 and converted into an electric signal. The vertical movement phase of the balance 27 is detected. For example, every time the main shaft rotates 1 °, a pulse signal is generated by the encoder 83, and the rotation angle of the main shaft and the vertical movement position of the sewing needle 6 are determined by the number of pulses.

  A needle plate 7 is attached to the upper surface of the bed portion 3, and a needle hole 8 is formed in the needle plate 7. A hook 9 is provided below the needle hole 8, and a bobbin is accommodated in the hook 9 and a bobbin thread is wound around the bobbin. The shuttle 9 also has a sword tip 10 connected to the lower shaft 11.

  On the upper surface of the arm portion 4, a yarn guide rod 21 is provided so as to stand up, and on the front upper portion of the arm portion 4, a first thread tension device 22 is provided. A second thread tension device 23 is provided below the first thread tension device 22 and in the lower front portion of the arm portion 4.

  As shown in FIG. 3, the second thread tension device 23 overlaps the mounting plate 23a attached to the front surface of the arm portion 4, the fixed plate 23b provided on the front side of the mounting plate 23a, and the fixed plate 23b. The movable plate 23c, and the movable plate 23c, the fixed plate 23b, and the mount 23a that pass through and are locked to the movable plate 23c, and a movable pin 23d that is movable in a direction perpendicular to the front surface of the arm portion 4 are provided. Prepare. The second thread tension device 23 is capable of controlling the tension applied to the thread sandwiched between the movable dish 23c and the fixed dish 23b.

  Further, an electromagnetic solenoid 82 is provided in the arm portion 4, and a plunger 82a of the electromagnetic solenoid 82 is connected to the movable plate 23c. The electromagnetic solenoid 82 is a drive unit that drives the plunger 82a and the movable pin 23d in the axial direction to vary the tension applied to the yarn sandwiched between the fixed plate 23b and the movable plate 23c. As described in Japanese Patent Application Laid-Open No. 2000-202183, the electromagnetic solenoid 82 has a characteristic that the thrust applied by the plunger 82a is constant even if the stroke of the plunger 82a changes within a specific stroke section. . The electromagnetic solenoid 82 has a characteristic that, when the stroke of the plunger 82a is constant, the thrust generated by the plunger 82a increases as the current flowing through the electromagnetic solenoid 82 increases. The electromagnetic solenoid 82 is set so that the plunger 82a advances and retreats in a specific stroke section, and the thrust is varied by controlling the current, so that the thread sandwiched between the fixed plate 23b and the movable plate 23c. The tension to be applied is variable.

  As shown in FIG. 1, a thread take-up spring 24 is provided in the second thread tension device 23, and a thread hook 25 is provided on the left side of the second thread tension device 23.

  A first thread guide 26 is provided between the first thread tension device 22 and the second thread tension device 23 on the front surface of the arm portion 4. A second thread guide 28 is provided on the left side of the first thread guide 26. A balance 27 is provided between the first thread guide 26 and the second thread guide 28 so as to extend forward from the front surface of the arm portion 4, and the balance 27 extends along the front surface of the arm portion 4. It is provided to reciprocate up and down. The balance 27 is connected to the main shaft via a balance transmission mechanism or the like, and the balance 27 is moved up and down by a sewing machine motor 81.

  A yarn tension detector 29 is provided on the front surface of the arm portion 4 and below the second yarn guide 28. This thread tension detector 29 has threading 29a, 29b, and 29c arranged in order from the top, and a strain gauge 29d is provided on the threading 29b. The yarn tension detector 29 detects the yarn tension with a strain gauge 29d and converts it into an electrical signal.

  The upper thread path is as follows. The upper thread 51 from the upper thread supply source is passed through the hole of the thread guide rod 21, and then guided and sandwiched by the first thread tension device 22, and then guided by the second thread tension device 23. Between the fixed plate 23b and the movable plate 23c, then hooked on the thread take-up spring 24, then on the thread hook 25, and then passed through the first thread guide 26, Next, it is passed through the balance 27, then through the second thread guide 28, then guided to the thread tension detector 29, and finally through the hole of the sewing needle 6.

  The needle bar 5, the sewing needle 6, and the balance 27 are driven up and down by a sewing machine motor 81, and the lower shaft 11 and the sword tip 10 are also rotated by the sewing machine motor 81. When the sewing needle 6 descends, it penetrates the needle hole 8 downward, and the upper thread passed through the sewing needle 6 is captured by the sword tip 10, and when the sewing needle 6 moves up, the captured upper thread is below the bobbin. Intertwined with yarn. The seam is formed on the cloth by the cooperation of the sewing needle 6 and the shuttle 9.

  4 shows a needle bar curve C representing the movement of the needle bar 5, a balance curve D representing the movement of the balance 27, and a hook thread take-up curve E representing the thread take-up amount by the hook 9. The horizontal axis in FIG. 4 represents the rotation angle of the main axis. The vertical axis in FIG. 4 represents the position of the needle bar 5 in the vertical direction on the needle bar curve C, the position of the balance 27 in the vertical direction on the balance curve D, and the thread take-up amount on the shuttle thread take-up curve E.

As shown in FIG. 4, when the rotation angle of the main shaft is zero ° (= 360 °), the needle bar 5 is at the top dead center, and when the rotation angle of the main shaft is 180 °, the needle bar 5 is At bottom dead center. When the rotation angle of the main shaft is 90 °, the sewing needle 6 starts to be inserted into the needle hole 8, and when the rotation angle of the main shaft is 270 °, the sewing needle 6 comes out of the needle hole 8 from the bottom to the top . When the rotation angle of the main shaft is about 75 °, the balance 27 is at the top dead center, and when the rotation angle of the main shaft is about 300 °, the balance 27 is at the bottom dead center. When the rotation angle of the main shaft is about 115 °, the upper thread is captured by the blade tip 10 of the hook 9 and when the rotation angle of the main shaft is 115 to 380 ° (= 20 °), the upper thread is transferred to the blade tip 10 of the hook 9. The upper thread loop is formed by scooping, and the upper thread loop is detached from the sword tip 10 of the hook 9 when the rotation angle of the main shaft is 20 °. Further, in a section where the rotation angle of the main shaft is between 270 and 350 °, the balance 27 is at or near the bottom dead center. Hereinafter, this section is referred to as a balance bottom dead center section A. In the section where the rotation angle of the main shaft is 20 to 100 °, after the upper thread loop scooped by the sword tip 10 of the hook 9 comes off from the hook 9, the tip of the sewing needle 6 moves the needle hole 8 of the needle plate 7 downward from above. It is a section until it comes off. Hereinafter, this section is referred to as a balance raising section B.

  In FIG. 5, the tension of the upper thread between the balance 27 and the sewing needle 6 detected by the thread tension detector 29 described above, the horizontal axis represents the rotation angle of the main shaft, and the vertical axis represents the tension. As shown by a curve F in FIG. 5, since the upper thread is drawn by the sword tip 10 of the hook 9 in the bottom dead center section A of the balance 9, the upper thread tension peak appears in the bottom dead center section A of the balance. The tension in the bottom dead center section A of the balance acts so that the intersection of the upper thread and the lower thread approaches the back side of the cloth (closer to the needle plate 7).

  Further, in the balance raising section B, the balance 27 is raised and the upper thread is pulled and entangled with the lower thread, and the lowering of the loop of the upper thread is limited by the lower thread, so another peak appears in the balance raising section B. The tension in the balance raising section B acts to bring the intersection of the upper thread and the lower thread closer to the surface of the cloth (close to the cloth presser).

  As shown in FIG. 2, the sewing machine 1 includes a control device 91, an operation panel 92, and a start / stop switch 93. The operation panel 92 includes a display that performs display in accordance with a display signal input from the control device 91, and a touch panel that is superimposed on the display surface of the display. When an operator's finger or the like comes in contact with the surface of the touch panel, an operation signal corresponding to the contact position is output from the touch panel to the control device 91. The operation panel 92 is tension setting means for setting the tension of the second thread tension device 23. When the user touches the touch panel of the operation panel 92, the set tension corresponding to the operation is input to the control device 91. The The start / stop switch 93 is a switch for starting / stopping sewing.

  The control device 91 stores an interface for inputting an operation signal from the operation panel 92 and outputting a display signal to the operation panel 92, an interface for inputting a tension detected by the yarn tension detector 29, and a program. ROM, microcomputer for executing program stored in ROM, drive circuit for driving sewing machine motor 81 by being controlled by microcomputer, drive circuit for driving electromagnetic solenoid 82 by being controlled by microcomputer With.

  The control device 91 functions as follows by the processing of the microcomputer in accordance with the ROM program. The control device 91 has a function of temporarily storing the set tension γ (see FIG. 5) set by the operation panel 92 in the RAM. In addition, the control device 91 sets a set tension i (where set tension i <set tension γ) and set tension j (where set tension j> set tension γ) corresponding to the set tension γ set by the operation panel 92. It has a function of reading from the ROM and temporarily storing it in the RAM. The control device 91 also includes a first threshold value α (where the first threshold value α <set tension γ) and a second threshold value β (where the first threshold value α <the first threshold value) corresponding to the set tension γ set by the operation panel 92. 2 threshold value β <setting tension γ) is read from the ROM and temporarily stored in the RAM. The control device 91 has a function of driving the sewing machine motor 81 to control the rotational speed of the sewing machine motor 81. Further, the control device 91 has a function of recognizing the rotation angle of the main shaft based on a signal input from the encoder 83 during the operation of the sewing machine motor 81. The control device 91 has a function of recognizing the tension applied to the upper thread from the second thread tension device 23 by a signal input from the thread tension detector 29 during the operation of the sewing machine motor 81.

  In addition, as shown in FIG. 5, the control device 91 controls the electromagnetic solenoid 82 while the rotation angle of the main shaft detected by the encoder 83 is 100 to 360 (zero) to 20 ° (that is, other than the balance raising section B). By controlling the tension applied to the upper thread by the second thread tension device 23 to the set tension γ. Further, the control device 91 determines that the tension input from the yarn tension detector 29 is the first threshold value α while the rotation angle of the main shaft detected by the encoder 83 is 270 to 350 ° (that is, the bottom dead center section A of the balance). Has a function of determining whether or not the threshold is exceeded. Further, the control device 91 has a function of determining whether or not the tension input from the yarn tension detector 29 exceeds the second threshold value β while the rotation angle of the main shaft detected by the encoder 83 is 270 to 350 °. Have. When the tension input from the thread tension detector in the balance bottom dead center section A does not exceed the first threshold value α as shown by the curve G, the control device 91 turns off the electromagnetic solenoid 82 in the next lift section B. By controlling, it has a function of adjusting the tension applied to the upper thread from the second thread tension device 23 to the set tension i lower than the set tension γ as shown by the curve I. Further, when the tension input from the yarn tension detector in the balance bottom dead center section A exceeds the second threshold value β as shown by the curve H, the control device 91 turns off the electromagnetic solenoid 82 in the next lift section B. By controlling, it has a function of adjusting the tension applied to the upper thread from the second thread tension device 23 to the set tension j higher than the set tension γ as shown by the curve J. Further, the control device 91 controls the electromagnetic solenoid 82 in the next balance raising section B when the tension input from the yarn tension detector in the bottom dead center section A of the balance is not less than the first threshold value α and not more than the second threshold value β. By doing so, it has a function of maintaining the tension applied to the upper thread from the second thread tension device 23 at the set tension γ.

Next, the operation of the sewing machine 1 will be described with reference to FIG.
The user sets the cloth on the needle plate 7, and the thread guide bar 21, the first thread tension device 22, the second thread tension device 23, the thread take-up spring 24, the thread hook 25, and the first thread guide 26. The upper thread is passed through the balance 27, the second thread guide 28, the thread tension detector 29, and the sewing needle 6 in this order. Further, the user sets the bobbin around which the lower thread is wound in the hook 9.

  When the user operates the operation panel 92, the set tension γ corresponding to the operation content is input from the operation panel 92 to the control device 91. The control device 91 sets the set tension γ, the set tension i, the set tension j, the first The threshold value α and the second threshold value β are stored. Then, the control device 91 reads and temporarily stores the set tension i, the set tension j, the first threshold value α, and the second threshold value β corresponding to the set tension γ (step S1). Then, the controller 91 controls the electromagnetic solenoid 82 so that the tension applied to the upper thread from the second thread tension device 23 becomes the set tension γ (step S2).

  When the user operates the start / stop switch 93 (step S3: Yes), the control device 91 rotates the sewing machine motor 81 (step S4). As a result, the needle bar 5, the sewing needle 6 and the balance 27 move up and down, the shuttle 9 and the lower shaft 11 rotate, and the stitches are formed on the cloth by the cooperation of the sewing needle 6 and the shuttle 9.

  During such sewing, the control device 91 performs the following feedback control. During sewing, the rotation angle of the main shaft is detected by the encoder 83, a signal indicating the rotation angle of the main shaft is input to the control device 91, and the tension of the upper thread is detected by the thread tension detector 29. Is input to the control device 91. Then, while the rotation angle of the main shaft detected by the encoder 83 is 270 to 350 °, the control device 91 compares the tension input from the yarn tension detector 29 with the first threshold value α and the second threshold value β.

Specifically, it is detected by the yarn tension detector 29 from when the rotation angle of the main shaft detected by the encoder 83 reaches 270 ° (step S5: Yes) until it reaches 350 ° (step S7: No). When the tension exceeds the variable P (however, the initial value of the variable P is zero), the control device 91 rewrites the variable P with the detected tension (step S6), thereby detecting the peak of the detected tension when the rotation angle is 270 to 350 °. (Value of variable P at 350 °) is detected. When the rotation angle of the main shaft reaches 20 ° (step S8: Yes), the control device 91 sets the variable P (peak of detected tension when the rotation angle is 270 to 350 °) as the first threshold value α and the second threshold value β. Compare (step S9).

As a result of comparison, when the tension peak (variable P) input from the yarn tension detector 29 in the bottom dead center section A of the balance (between the main shaft rotation angle 270 ° and 350 ° ) exceeds the second threshold value β ( In step S9: No, step S10: No, the control device 91 immediately controls the electromagnetic solenoid 82, thereby adjusting the applied tension by the second thread tension device 23 to a set tension j higher than the set tension γ (step S12). ). As a result, the tension detected by the thread tension detector 29 in the balance raising section B is represented by the curve K.

On the other hand, if the tension input from the thread tension detector 29 does not exceed the first threshold value α in the bottom dead center section A of the balance (step S9: No, step S10: Yes), the control device 91 immediately turns off the electromagnetic solenoid 82. By controlling, the tension applied by the second thread tension device 23 is adjusted to a set tension i lower than the set tension γ (step S11). As a result, the tension detected by the thread tension detector 29 in the balance raising section B is represented by the curve L.
After the applied tension by the second thread tension device 23 reaches the set tension i or the set tension j, when the rotation angle of the main shaft reaches 100 ° (step S13: Yes), the control device 91 controls the electromagnetic solenoid 82. Thus, the tension applied by the second thread tension device 23 is adjusted to the set tension γ (step S14), and the processing of the control device 91 proceeds to step S15.

When the tension input from the thread tension detector 29 in the bottom dead center section A of the balance is not less than the first threshold value α and not more than the second threshold value β (step S9: Yes), the control device 91 operates in the balance raising section B. By controlling the electromagnetic solenoid 82, the tension applied by the second thread tension device 23 is maintained at the set tension γ, and the processing of the control device 91 proceeds to step S15.
In addition to the balance raising section B, the control device 91 controls the electromagnetic solenoid 82 to set the applied tension by the second thread tension device 23 to the set tension γ.

  In step S15, the control device 91 determines the input of the start / stop switch 93, and when the switch-off of the start / stop switch 93 is detected by the user (step S15: Yes), the control device 91 stops the sewing machine motor 81. When the switch-off of the start / stop switch 93 by the user is not detected (step S15: No), the process of the control device 91 returns to step S4. When the process of the control device 91 returns to step S4, the control device 91 resets the variable P to the initial value.

  As described above, according to this embodiment, based on the tension detected by the thread tension detector 29 in the bottom dead center section A of the balance, the upper thread of the upper thread is adjusted by the second thread tension device 23 in the next lift section B. Since the tension is controlled, the tension detected by the thread tension detector 29 in the bottom dead center section A of the balance is reliably reflected in the tension of the upper thread in the subsequent lift ascent section B. In particular, as shown by the curve H in FIG. 5, when the upper thread tension is large and exceeds the second threshold value β in the bottom dead center section A, the tension applied by the second thread tension device 23 is higher than the set tension γ. Then, the tension that acts to bring the intersection of the upper thread and the lower thread closer to the back side of the cloth in the bottom dead center section A of the balance is closer to the cloth surface in the balance raising section B. It balances with the tension that acts to bring it closer. On the other hand, when the upper thread tension is small and does not exceed the first threshold value α in the bottom dead center section A of the balance G as shown in FIG. 5, the tension applied by the second thread tension device 23 is lower than the set tension γ. Then, the tension acting so that the crossing portion of the upper thread and the lower thread is brought closer to the surface of the cloth in the bottom dead center section A of the balance, the crossing portion of the upper thread and the lower thread is moved closer to the back surface of the cloth in the lift ascent section B. It balances with the tension that acts to bring it closer. Therefore, during sewing, the upper thread and lower thread can be balanced, and the knot position of the upper thread and lower thread can be made constant. Therefore, in the finished seam, the upper thread and the lower thread intersect at the middle part in the thickness direction of the cloth, and a beautiful seam can be uniformly applied.

  Further, according to the present embodiment, the tension value in the balance raising section B is determined by the tension detected in the balance bottom dead center section A before the balance raising section B. Since the second thread tension device 23 is controlled based on the determined tension, it can be controlled to give a desired tension to the upper thread in advance before the knot between the lower thread and the upper thread. . Therefore, even if it takes time from when the second thread tension device 23 is controlled to change the tension until the result is reflected in the actual tension, the changed tension is applied to the actually required section. Compared to the conventional case where the tension in the rising section of the balance can be detected and the tension is controlled based on the result, a thread tension device with better responsiveness can be provided. can do.

  In the embodiment described above, the thread tension detected in the section A is determined by two threshold values α and β, and the tension output value by the thread tension device is also controlled as three tension values γ, i, and j. However, the threshold value or the output value may be further multi-staged, or the tension of the thread tension device may be controlled steplessly based on the detected value of the thread tension.

  In the above-described embodiment, the thread tension device 23 capable of changing the tension by controlling the drive current is used. However, if the thread tension device 23 is a thread tension device capable of controlling the tension, for example, two sheets of motors are used by the motor. The present invention can also be applied to a thread tension device that moves its position to change the tension.

It is the front view which showed the front of the arm part of the sewing machine in the embodiment of the present invention, and the fracture surface of the bed part under it. It is the block diagram which showed the structure of the sewing machine. It is the side view which showed the thread tension device provided in the arm part, and its drive source. 3 is a timing chart showing the operation timing of the sewing machine. 5 is a timing chart showing tension detected by a thread tension detector and tension applied by a thread tension device. It is the flowchart which showed the flow of the process by a control apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sewing machine 5 Needle bar 6 Sewing needle 7 Needle plate 8 Needle hole 9 Hook 23 Second thread tension device 27 Balance 29 Thread tension detector (tension detection means)
82 Electromagnetic solenoid (drive means)
83 Encoder (Position detection means)
91 Control device (control means)
92 Operation panel (tension setting means)

Claims (1)

A sewing needle that is supported by a needle bar that moves up and down and moves up and down through a needle hole provided in a needle plate;
A hook that cooperates with the sewing needle to form a seam;
A thread tension device arranged between the thread supply source and the balance in the upper thread path from the thread supply source to the sewing needle and capable of controlling the thread tension;
Drive means for varying the tension applied by the thread tension device;
Tension setting means for setting the set tension;
Position detecting means for detecting the vertical movement phase of the balance;
Tension detecting means that is disposed in an upper thread path between the balance and the sewing needle and detects a tension applied to the upper thread;
A sewing machine comprising: control means for controlling the driving means;
The control means includes
Said storing said a set tension set by the tension setting means and the setting second threshold value lower than the high rather the set tension than lower first threshold value and the first threshold value than the tension,
The detected tension detected by the tension detecting means when the detection phase detected by the position detecting means is a bottom dead center section in which the upper thread is drawn by the sword tip of the shuttle, the detected tension detected by the first threshold and the second Compared to the threshold,
If the detected tension falls below the first threshold as a result of the comparison, the sewing needle is removed after the upper thread loop in which the detection phase detected by the position detecting means is scooped by the hook is removed from the hook. The tension of the upper thread applied by the thread tension device is controlled to be lower than the set tension by controlling the driving means in the balance raising section until the needle hole passes from the top to the bottom.
When the detected tension exceeds the second threshold value, the detected tension is applied by the thread tension device by controlling the driving means when the detection phase detected by the position detecting means is the balance raising section. The upper thread tension is controlled to be higher than the set tension,
When the detected tension is not less than the first threshold and not more than the second threshold, the yarn is controlled by controlling the driving means when the detection phase detected by the position detecting means is the balance raising section. The tension of the upper thread applied by the tension device is controlled to the set tension,
When the detection phase detected by the position detection means is other than the balance raising section, the tension of the upper thread applied by the thread tension device is controlled to the set tension by controlling the drive means. A sewing machine characterized by

Images