JP2009050638A - Sewing machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To give a suitable upper thread tension regardless of a cloth feed direction. <P>SOLUTION: A feed switch detection sensor 46 for detecting that the cloth feed direction is switched from a normal direction to a reverse direction by the operation of a reverse feed lever 45 is provided. When switching of the feed direction to the reverse direction is detected from a detection signal of this feed switch detection sensor 46 or a touch back switch 47, the generation of hitch stitch when switched to reverse feed is prevented by a control part 100 automatically weakly adjusting the upper thread tension by a thread tension solenoid 53 than the time of normal feed. Also, when a thread cut signal by backward operation of an operation pedal 60 is detected, the residual end length of an upper thread T remaining on the cloth side after cutting can be shortened by the control part 100 automatically strongly adjusting the upper thread tension by the thread tension solenoid 53 than the time of reverse feed. Accordingly, a beautiful thread seam is obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sewing machine, and more particularly, to a sewing machine provided with a thread tension device that makes a thread tension variable by electrical control.

2. Description of the Related Art Conventionally, there has been known a sewing machine including a thread tension device that electrically controls and changes the tension of an upper thread supplied to a sewing needle (see, for example, Patent Document 1).
The sewing machine equipped with the above thread tension device includes a first thread tension for applying tension to the upper thread supplied to the sewing needle, and the first thread tension on the upstream side of the upper thread path from the first thread tension. A pretension for preventing slack of the supplied upper thread and a touchback switch for reversing the feeding direction of the cloth by a button operation are provided. The upper thread supplied from the upper thread supply source outside the sewing machine passes through the thread guide and pretension provided on the sewing machine arm, and then passes through the first thread tension, the balance, the needle bar, and the sewing needle. It is designed to be sewn on.
Further, it is desirable that the tension of the upper thread is controlled with an appropriate tension according to, for example, the thickness of the thread, the type of the stitch pattern, and the sewing stage (for example, forward feed, reverse feed, and thread trimming). The thread tension device includes a controller that changes the tension of the upper thread at a predetermined timing and a predetermined tension set in advance according to the sewing conditions.
JP 2000-300902 A

  By the way, there are a perfect stitch (refer to FIG. 7A) and a hitch stitch (refer to FIG. 7B) in the seam in which the upper thread and the lower thread are entangled, and a predetermined tension is applied to the upper thread. When the cloth feeding direction is reversed from the normal direction to the reverse direction, the relationship between the cloth feeding direction and the rotary direction of the hook is reversed, so that the yarn may be twisted to generate a hitch stitch. This hitch stitch has a problem in that it is difficult to uniformly tighten the seam and a beautiful seam cannot be obtained because the fastening force concentrates on the immediately preceding seam when the thread is fastened by lifting the balance. In order to prevent the occurrence of hitch stitches during reversal of the feed direction, it is necessary to set the upper thread tension during reversal of the feed direction and reverse feed to be weaker than that during normal feed.

  In view of the above problem, when reversing the feed direction with the touchback switch, the needle thread tension after reversal is set to the tension for reverse feed, that is, the tension that is weaker than during normal feed. At the time of thread trimming, the upper thread was cut in a loose state. For this reason, the remaining end length of the upper thread remaining on the cloth side after cutting becomes longer, and there arises a problem that it takes time to process the remaining end of the thread. In addition, in a sewing machine that applies tension to the upper thread with a spring and manually reverses the cloth feed direction between the forward direction and the reverse direction with a reverse feed lever, it is automatically linked to the change of the feed direction during sewing. Therefore, there is a problem that the upper thread tension cannot be changed.

  An object of the present invention is to provide an appropriate upper thread tension irrespective of the cloth feeding direction.

  In order to solve the above-mentioned problem, the invention according to claim 1 is characterized in that the feed means for switching the workpiece to be switched between the normal direction and the reverse direction, and the switching of the feed direction in the normal / reverse direction of the workpiece by the feed means. An input switching operation means, a detection means for detecting the presence or absence of a switching operation by the switching operation means, and a tension applied to an upper thread to be supplied to a sewing needle that performs sewing in cooperation with the feeding means, When the operation of switching the feed direction from the forward direction to the reverse direction is detected by the detecting means, the thread tensioner is made variable by an electromagnetically controllable actuator, and the thread tensioner is driven from the forward direction. A sewing machine comprising tension control means for applying a weak tension to the upper thread.

  According to a second aspect of the present invention, in the first aspect of the invention, the tension control unit includes a thread trimming unit that cuts the upper thread, and a thread trimming operation unit that inputs execution of thread trimming by the thread trimming unit. Is characterized in that the actuator of the thread tensioner is driven so as to change the tension of the upper thread to a predetermined value at the time of thread trimming by the thread trimming means.

  A third aspect of the invention is characterized in that, in the first or second aspect of the invention, the switching operation means manually switches a feeding direction of the sewing product by the feeding means.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, a timing in a vertical movement cycle of the sewing needle with respect to a change in tension during reverse feed executed by the tension control means. It is characterized by comprising timing setting means for setting.

  According to the first aspect of the present invention, when the switching of the feeding direction is input from the switching operation means, the switching operation is detected by the detecting means, and it is detected that the feeding direction of the sewing product has been switched by the feeding means. A signal is sent to the tension control means. Based on this, the tension control means drives the actuator of the thread tensioner so that the upper thread tension at the time of reverse feeding becomes weaker than that at the time of forward feeding. That is, according to the first aspect of the present invention, the upper thread tension at the time of reverse feeding can be automatically made weaker than the upper thread tension at the time of forward feeding based on the switching input of the feeding direction from the switching operation means. . Thereby, since an appropriate upper thread tension can be applied regardless of the cloth feeding direction, the occurrence of hitch stitches can be effectively prevented. Therefore, a beautiful seam can be obtained.

  According to the second aspect of the invention, the same effect as that of the first aspect of the invention can be obtained. Further, when the execution of the thread trimming is input from the thread trimming operation means, the tension control means controls the thread tension. The actuator is driven to change the upper thread tension to a predetermined value. That is, when thread trimming is executed by the thread trimming means, the upper thread tension can be automatically changed to a predetermined tension suitable for the thread trimming. As a result, for example, the upper thread tension at the time of thread trimming can be automatically changed to be stronger than the tension at the time of reverse feeding set to be weaker than the forward direction. The remaining end length can be shortened. Therefore, since the labor and time required for the remaining end processing of the upper thread remaining on the sewing product after cutting can be reduced, the sewing efficiency can be improved.

  According to the invention described in claim 3, in addition to obtaining the same effect as that of the invention described in claim 1 or 2, in particular, the switching operation from the switching input means performed manually is detected by the detecting means. Then, the actuator of the thread tensioner is driven by the tension control means so as to apply a weaker tension to the upper thread than during normal feeding. That is, even when the feeding direction is manually switched, it is possible to automatically apply a tension appropriate for reverse feeding and thread trimming to the upper thread. This also improves the operability of the sewing machine.

  According to the invention described in claim 4, in addition to obtaining the same effect as the invention described in any one of claims 1 to 3, in particular, at the time of reverse feed by setting from the timing setting means. The timing for changing the tension can be set to a predetermined timing in the vertical movement cycle of the sewing needle. Accordingly, for example, the upper thread tension when the workpiece is fed in the reverse direction and the upper thread tension at the time of thread trimming can be appropriately changed in accordance with the thread trimming timing in the vertical movement cycle of the sewing needle. . Therefore, the occurrence of hitch stitches can be prevented and beautiful seams can be obtained, and the productivity can be improved by shortening the remaining end length remaining on the workpiece.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to FIGS. 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. In the present embodiment, the direction of each part of the sewing machine 1 is determined based on the XYZ axes shown in the drawings. In a state where the sewing machine 1 is installed on a horizontal plane, the Z-axis direction indicates the vertical direction that is the vertical direction, the Y-axis direction indicates the left-right direction that coincides with the longitudinal direction of the sewing machine arm portion 11, the X-axis direction is horizontal and the Y-axis The front-rear direction orthogonal to the direction is shown.

(overall structure)
FIG. 1 is a schematic perspective view showing an external structure of a sewing machine 1 according to this embodiment.
As shown in FIG. 1, the sewing machine 1 includes a sewing machine frame 10 disposed on the upper surface of a sewing machine table (not shown), and a sewing machine 21 that is provided in the sewing machine frame 10 and moves the sewing needle 21 up and down in conjunction with driving of the sewing machine motor 5. A needle driving mechanism 20 for driving, a hook mechanism (not shown) that forms a seam in cooperation with the needle driving mechanism 20, and a seam formed by the hook mechanism and the sewing needle 21 are synchronized with the sewing needle 21. A balance mechanism 30 that is fastened by pulling up the thread T, a feed mechanism 40 that is a feed means that feeds the cloth to be sewn in the forward direction and the reverse direction, and switching between the forward and reverse feed directions of the cloth by the feed mechanism 40 A reverse feed lever 45 and a touchback switch 47 as switching operation means for inputting the input, and a feed switching detection sensor as a detection means for detecting the presence or absence of the switching operation by the reverse feed lever 45 6 and a thread that makes the tension applied to the upper thread T supplied to the sewing needle 21 that performs sewing in cooperation with the feed mechanism 40 variable by a thread tension solenoid 53 that is an actuator that can be electrically or electromagnetically controlled. A thread tension device 50 serving as a tension device, a thread trimming mechanism (not shown) serving as a thread trimming means for cutting the upper thread T, and an operation pedal 60 (not illustrated) serving as a thread trimming operation means for inputting execution of thread trimming by the thread trimming mechanism. And an operation panel 70 (not shown) for inputting setting values of each part of the sewing machine 1 and a control part 100 for controlling driving of the above-described components. Hereinafter, each part will be described in detail.

(Sewing frame)
As shown in FIG. 1, the sewing machine frame 10 includes an upper part of the sewing machine frame 10 and a sewing machine arm part 11 extending along the longitudinal direction (Y-axis direction) of the sewing machine table and a lower part of the sewing machine frame 10. The sewing machine bed part 12 facing the table 2, the sewing machine arm part 11 and the sewing machine bed part 12 are connected to each other, and is erected in the vertical direction (Z-axis direction) perpendicular to the longitudinal direction of the sewing machine arm part 11 and the sewing machine bed part 12. The outer body 13 is formed in a substantially U-shape when viewed from the front. Further, below the sewing machine table on which the sewing machine frame 10 is placed, an operation pedal 60 is provided for inputting start and stop of driving of the sewing machine motor 5 and the thread trimming mechanism by a user's stepping operation.

(Needle drive mechanism)
As shown in FIGS. 1 to 3, the needle drive mechanism 20 includes an upper shaft (principal shaft) (not shown) that extends rotatably in the longitudinal direction (Y-axis direction) in the sewing machine arm portion 11, and the upper shaft. A rotating weight 23 fixed to the tip of the rotating weight 23, a crank rod 24 whose upper end is rotatably connected to an eccentric part of the rotating weight 23, a needle bar 22 rotatably connected to the lower end of the crank rod 24, A sewing needle 21 supported on the lower end of the needle bar 22 is provided. The upper shaft is provided with an encoder 80 (see FIG. 5) that detects a predetermined rotation angle around the upper shaft. When the upper shaft connected to the sewing machine motor 5 is rotated by driving the sewing machine motor 5 (see FIG. 5), the rotation is converted into vertical movement via the rotary weight 23 and the crank rod 24, and the needle bar 22 is moved. The needle bar 22 and the sewing needle 21 reciprocate up and down.

(Hook mechanism)
A shuttle mechanism (not shown) is provided on the front end side in the sewing machine bed portion 12. The hook mechanism is supported by a hook shaft, a hook shaft (not shown) rotatably supported along the Z-axis direction (vertical direction) inside the hook shaft base, and the hook shaft. And a hook provided rotatably in a horizontal plane. Then, when the lower shaft extending rotatably along the Y-axis direction in the sewing machine bed portion 12 is rotationally driven together with the upper shaft, the shuttle shaft is rotated via a shuttle shaft gear (not shown) and the shuttle (outside The hook) rotates and the upper thread loop formed in the sewing machine bed 12 when the sewing needle 21 starts to rise is captured by the sword tip of the hook (outer hook) and the lower thread is passed through the upper thread loop to form a seam. It has come to be.

(Balance mechanism)
As shown in FIGS. 1 to 3, the balance mechanism 30 includes a balance 31 that swings up and down to pull up the upper thread T, and converts the rotational drive of the upper shaft into a reciprocating swing operation to the balance 31. A balance crank (not shown) for transmission is provided. The balance 31 moves with the rotation of the upper shaft (not shown) connected to the sewing machine motor 5 and moves up and down along the groove 11a formed in the sewing machine arm portion 11, so that the balance 31 is passed through the cloth. Tighten the thread T. In this balance mechanism 30, the balance 31 is synchronized with the vertical movement of the sewing needle 21 by obtaining power for swinging up and down from the upper shaft to the balance 31. Further, the top dead center of the balance 31 is adjusted so that the phase is slightly delayed from the top dead center of the sewing needle 21 (for example, 60 to 70 °). Then, the balance mechanism 90 fastens the seam by pulling the upper thread T upward when the sewing needle 21 penetrating to the lower side of the cloth comes out of the cloth and rises.

(Feeding mechanism)
The feed mechanism 40 has a feed dog 41 that performs a feed operation while drawing a substantially elliptical movement trajectory in the sewing machine bed portion 12, and the feed dog 41 is configured to transport the cloth in the horizontal direction. Further, the feed mechanism 40 can change the cloth feed amount (feed pitch) per stitch to obtain a desired stitch length by adjusting the cloth feed amount by a feed amount adjusting mechanism (not shown). It has become. The feed mechanism 40 can switch the feed direction between the forward direction and the reverse direction by an input of a switching operation from a later-described reverse feed lever 45 or a touchback switch 47.

(Reverse feed lever)
The reverse feed lever 45 is for switching the cloth feed direction by the feed mechanism 40 to a forward direction or a reverse direction by a user's manual operation. As shown in FIGS. 1 and 6, the reverse feed lever 45 extends from the inner side to the outer side at the right end of the vertical body portion 13, and one end extended to the outer side of the sewing machine frame 10 is the front of the sewing machine 1. It is arranged in parallel and horizontally with the side, that is, the side surface on the user operation position side. The reverse feed lever 45 has a base end portion fixed to a shaft extending from the vertical body portion 13, and an end portion on the front side about the shaft is supported so as to swing up and down. In the present embodiment, the cloth is conveyed in the forward direction (in the direction of arrow A shown in FIG. 1) in a state where the reverse feed lever 45 is disposed at the upper position indicated by a two-dot chain line in FIG. The cloth is fed in the reverse direction (in the direction of arrow B shown in FIG. 6) with 45 being disposed at the lower position shown by the solid line in FIG.

(Feed switching detection sensor)
As shown in FIGS. 1 and 6, the feed switching detection sensor 46 is attached to the lower part of the side surface of the vertical body 13 that is the base end side of the reverse feed lever 45. The feed switching detection sensor 46 detects that the cloth feed direction has been switched from the normal direction to the reverse direction or vice versa by the operation of the reverse feed lever 45 by the user. As the feed switching detection sensor 46, for example, an optical sensor having a light receiving part and a light emitting part is adopted, but the reverse feed lever 45 is at a predetermined position (lower position on the reverse feed side in this embodiment). Various sensors can be employed as long as they can be detected.
When the feed switching detection sensor 46 detects that the cloth feed direction has been switched from the normal direction to the reverse direction by the operation of the reverse feed lever 45 by the user, a detection signal to that effect is sent to the control unit 100 described later. To be sent to.

(Touchback switch)
As shown in FIG. 1, the touchback switch 47 is disposed on the jaw portion of the so-called sewing machine 1 that is the lower end of the tip of the sewing machine arm portion 11. The touchback switch 47 includes a push-type button unit and a touchback solenoid (not shown) that is provided in the sewing machine frame 10 and operates when the button unit is pressed. When the touch back solenoid is actuated as the button is pressed, the touch back solenoid acts on a feed switching mechanism (not shown) provided in the sewing machine frame 10 to switch the feed direction to the forward direction or the reverse direction. Can be done. The touchback switch 47 is electrically connected to the control unit 100 described later, and a detection signal indicating that the button unit has been pressed is transmitted to the control unit 100 when the button unit is pressed. It has become.

(Thread tension device)
Next, the thread tension device 50 according to the present embodiment will be described in detail with reference to FIGS.
As shown in FIGS. 2 to 4, the thread tension device 50 is provided in the vicinity of the jaw portion of the sewing machine arm portion 11 so as to penetrate from the front side to the back side. Appropriate tension is applied to the upper thread T drawn from the source, and the upper thread T is clamped and guided to the balance 31.
This thread tension device 50 is a so-called active tension in which the tension applied to the upper thread T can be changed during sewing by the thread tension solenoid 53 as an electromagnetic solenoid.
As shown in FIGS. 2 to 4, the thread tension device 50 includes a thread tensioner unit 52 that applies tension to the upper thread T by a pair of thread tension plates 55 and 56 disposed so as to sandwich the upper thread path. As a connecting shaft 54 as a driving mechanism for driving the plate presser 57 so that one thread tension plate 56 approaches the other thread tension plate 55, and as a drive unit 51 for applying a driving force to the thread tension unit 52 The thread tension solenoid 53 is provided.

The thread tension device 52 is provided to protrude from the sewing machine arm 11 on the front side of the sewing machine arm 11 (side on which the user faces during sewing). The thread tension solenoid 53 is provided inside the sewing machine arm 11 together with the main shaft and the like. The thread tension solenoid 53 is electrically connected to a control unit 100 to be described later via an electromagnetic valve 53b, and is driven based on a signal from the control unit 100.
The thread tension plates 55 and 56 are formed in a disk shape, and are arranged side by side along the moving direction of one thread tension plate 56 on the front side of the sewing machine arm portion 11. On the opposite side of the thread tension tray 56 from the side facing the thread tension tray 55, a dish presser 57 that presses the thread tension tray 56 so as to move the thread tension tray 56 toward the thread tension tray 55 is provided. .
The dish presser 57 functions as a drive mechanism together with the connecting shaft 54 and is configured to be movable so that one thread tension tray 56 is brought into contact with and separated from the other thread tension tray 55, and has, for example, three claw portions. It is a plate material and is held by a dish presser holder that prevents the dish presser 57 from rotating about its axis.
The connecting shaft 54 connects the thread tension unit 52 and the thread tension solenoid 53, transmits the drive of the thread tension solenoid 53 to the thread tension unit 52, and drives the thread tension plate 56.

(Thread trimming mechanism)
A thread trimming mechanism (not shown) includes a yarn catching portion that catches the upper yarn T and the lower yarn, and a blade portion that cuts the upper yarn T and the lower yarn caught by the yarn catching portion. Then, the upper thread T and the lower thread are cut at a timing when the user performs a later stepping operation on the operation pedal described later.

(Operating pedal)
The operation pedal 60 is an operation unit of the sewing machine 1 provided below the sewing machine table. The operation pedal 60 outputs a signal for driving the sewing machine motor 5 from the neutral position by the user's front stepping operation to the control unit 100 and also by the user. A thread trimming signal for operating the thread trimming mechanism by a rear stepping operation is output to the control unit 100.

(control panel)
An operation panel 70 (not shown) includes a display unit and various operation key groups, and serves as an input operation unit for setting the operation amount and operation timing of the drive source of each unit of the sewing machine 1. Various setting values set by an input operation from the operation panel 70 are stored in a RAM 103 or an EEPROM 104 of the control unit 100 described later. The operation panel 70 functions as a timing setting unit in the present embodiment that sets the timing in the vertical movement cycle of the sewing needle 21 with respect to the change in the upper thread tension during reverse feed executed by the control unit 100 described later.

(Sewing machine control system)
Next, the configuration of the control unit 100 in the present embodiment will be described based on FIG.
FIG. 5 is a control block diagram of the sewing machine in the present embodiment. As shown in FIG. 5, a drive source such as a sewing machine motor 5 and a thread tension solenoid 53, detection means such as an encoder 80, an operation pedal 60 and an operation panel 70 are connected to the control unit 100. FIG. 5 shows a configuration necessary for the present embodiment, and the control unit 100 also includes other drive sources, sensors, and the like.
The control unit 100 includes an MPU (Micro Processor Unit) 101 which is a microcomputer, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and an EEPROM (Electrically Erasable and Programmable ROM) 104. Yes.
The ROM 102 stores a control program for the sewing machine 1. The RAM 103 is a memory that provides a work area to the MPU 101. Various data related to sewing are backed up in the EEPROM 104. Then, the MPU 101 performs processing according to the control program stored in the ROM 102.
Further, the control unit 100 according to the present embodiment drives the thread tension solenoid 53 to apply a weaker tension than the forward direction when the feed switching detection sensor 46 detects a feed direction switching operation from the forward direction to the reverse direction. It functions as a tension control means in this embodiment that is applied to the upper thread T. In addition, the control unit 100 executes control for driving the thread tension solenoid 53 of the thread tension device 50 so that the tension of the upper thread T is changed to a predetermined value at the time of thread trimming by the thread trimming mechanism.

(Description of operation of embodiment)
Next, the operation of the sewing machine 1 having the above configuration will be described.
The thread tension device 50 pulls the connecting shaft 54 via the output shaft 53a by the thrust of the thread tension solenoid 53, and applies tension to the upper thread T passing between the two thread tension plates 55 and 56. This tension is adjusted by changing the value of the current flowing through the thread tension solenoid 53 and changing the thrust of the thread tension solenoid 53.
First, when the touchback switch 47 is pressed, the control unit 100 operates a touchback solenoid (not shown) to reverse the feed direction, and changes the tension of the thread tension solenoid 53 to a set value at the time of reverse feed. The set value at the time of reverse feed can be changed as appropriate by setting from the operation panel 70.
It is preferable that the timing of switching the thrust of the thread tension solenoid 53 is performed between the end of pulling up the forward feed balance and the time when the sewing needle 21 of the first stitch at the time of reverse feed is stuck in the cloth. That is, when the timing of tension switching is too early, it affects the pulling of the seam at the time of forward feeding, so that the pulling of the seam at the time of forward feeding becomes loose. Further, if the timing of tension switching is too late, a hitch stitch may occur at the reverse feed stitch.
Timing for switching the tension of the thread tension solenoid 53 is performed by operating a group of operation keys on the operation panel 70 or the like.
Next, when the reverse feed lever 45 is pushed down by the user's operation and the feed switching detection sensor 46 detects that the reverse feed lever 45 is operated to the reverse feed side, the control unit 100 outputs a detection signal. Based on this, by driving the thread tension solenoid 53 via the electromagnetic valve 53b, the tension is changed to a tension for backward feeding that is weaker than that during forward feeding.

(Effect of embodiment)
As described above, according to the sewing machine 1 according to the present embodiment, even when the feed direction is reversed and the forward feed is changed to the reverse feed, the occurrence of hitch stitches is prevented by appropriately controlling the tension. Because it can, beautiful seams can be obtained.
Further, by attaching a feed switching detection sensor 46 for detecting a reverse feed input operation by the user and a touch back switch 47, it is automatically detected that the cloth feed direction is reversed from the forward direction to the reverse direction. In addition, it is possible to apply an appropriate tension for reverse feed to the upper thread T during reverse feed.
Further, at the time of thread trimming, the tension can be automatically changed at a desired timing so as to obtain an appropriate tension for thread trimming.

(Other)
The feed switching detection sensor 46 only needs to detect that the feed direction has been switched by operating the reverse feed lever 45. For example, the feed switch detection sensor 46 may detect that the reverse feed lever 45 has moved from the position on the forward feed side. Good.
Further, since the movable range (stroke) of the reverse feed lever 45 changes depending on the feed amount set by a feed amount adjusting mechanism (not shown), even if the feed amount is changed by the feed amount adjusting mechanism, the reverse feed lever 45 It is preferable to arrange the feed switching detection sensor 46 so that the state arranged on the reverse feed side can be detected.

It is a schematic perspective view which shows the external appearance structure of the sewing machine which mounts the thread tension device which is this embodiment. It is a schematic perspective view which shows the structure around a sewing machine head. It is the figure seen from the arrow C direction in FIG. 1, and is explanatory drawing which shows the thread tension device which is this embodiment. It is a perspective view which shows schematic structure of the thread tension device of the sewing machine which is this embodiment. It is a block diagram which shows the structure of the control system in this embodiment. It is the schematic which shows the feed switching detection sensor in this embodiment. (A) is the schematic which shows a perfect stitch, (b) is the schematic which shows a hitch stitch.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sewing machine 10 Sewing machine frame 11 Sewing machine arm part 11a Groove 12 Sewing machine bed part 13 Vertical body part 20 Needle drive mechanism 21 Sewing needle 22 Needle bar 23 Rotating weight 24 Crank rod 30 Balance mechanism 31 Balance 40 Cloth feed mechanism 41 Feed tooth 45 Reverse feed Lever 46 Feed switching detection sensor (detection means)
47 Touchback switch 50 Thread tension device (Thread tension device)
51 Driving part 52 Thread tensioner part 53 Thread tension solenoid 53a Output shaft 53b Solenoid valve 54 Connection shaft 55, 56 Thread tension plate 57 Dish presser 60 Operation pedal 70 Operation panel 100 Control unit (tension control means)
101 CPU
102 ROM
103 RAM
104 EEPROM
T Upper thread

Claims (4)

Feeding means for switching the workpiece to be switched between the forward direction and the reverse direction;
Switching operation means for inputting switching of the forward and reverse feed directions of the sewing product by the feed means;
Detecting means for detecting the presence or absence of a switching operation by the switching operation means;
A thread tensioner that varies the tension applied to the upper thread to be supplied to the sewing needle that performs sewing in cooperation with the feeding means by an actuator that can be controlled electrically or electromagnetically;
A tension control unit that drives the thread tensioner to apply a weaker tension to the upper thread than the normal direction when a switching operation of the feed direction from the forward direction to the reverse direction is detected by the detection unit. Characteristic sewing machine. Thread trimming means for cutting the upper thread;
Thread trimming operation means for inputting execution of thread trimming by the thread trimming means,
2. The sewing machine according to claim 1, wherein the tension control means drives the actuator of the thread tensioner so that the tension of the upper thread is changed to a predetermined value when the thread trimming means performs the thread trimming.   The sewing machine according to claim 1 or 2, wherein the switching operation means manually switches a feeding direction of the sewing product by the feeding means.   4. The apparatus according to claim 1, further comprising a timing setting unit configured to set a timing in a vertical movement cycle of the sewing needle with respect to a change in tension during reverse feed performed by the tension control unit. 5. The described sewing machine.

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