CN102634940B - A sewing machine and a cutting method of the same - Google Patents

Abstract

The invention relates to a sewing machine and a thread cutting method of the sewing machine which can avoid increased power consumption during thread cutting. The CPU turns on the reverse solenoid at t5 after inputting the thread cutting signal. The feeding direction of the cloth is reversed. The CPU turns on the thread trimming solenoid at t8 to cut the upper thread and the lower thread. The sewing machine cuts the upper and lower threads after the needle drop point of the last stitch of the stitch is at the same position as the previous stitch. Therefore, the sewing machine can make the remaining lengths of the upper thread and the bobbin thread remaining at the end of the stitches equal to each other on the back of the cloth after thread trimming. The CPU turns on the thread cutting solenoid after turning off the reverse solenoid. The on-period of the reverse solenoid and the on-period of the thread trimming solenoid do not overlap, and the sewing machine can avoid increased power consumption during thread trimming.

Description

Thread cutting methods for sewing machines and sewing machines

technical field

The invention relates to a sewing machine and a thread cutting method of the sewing machine.

Background technique

The sewing machine automatically cuts the thread according to the operation of the operator. After the needle has turned from the lower stop position to the upward position, the sewing machine cuts the sewing thread under the sewing product in a state where the needle is at the raised position raised from the needle plate. The stitching refers to the upper thread and the lower thread. In the state where the cloth feeder is in the normal feeding direction, the sewing machine performs thread trimming of the sewing thread. The thread cutting process is carried out in the middle of the stitch formation. Since the sewing machine cuts both the upper and lower threads at the same time, no stitches are formed at the cut parts. The length of the thread end of the lower thread protruding from the back of the fabric of the sewn product is longer than the upper thread by one stitch. In order to make the remaining lengths of the upper thread and the lower thread the same, the operator needs to use scissors to remove the thread remaining on the back of the fabric. Disclosed a kind of thread trimming method of automatic thread trimming sewing machine in Japanese Patent Laid-Open No. 1989 No. 320087. The sewing machine switches the cloth feeder of the sewing machine in the forward feeding direction to the reverse feeding which feeds less than the forward feeding. After forming the stitches of the reverse feeding direction above the first needle, the sewing machine cuts the sewing thread under the sewn object in the state where the needle is in the raised position rising from the needle plate. The sewing machine switches the cloth feeder to reverse feed immediately after the operator performs the thread trimming operation, and performs thread trimming during reverse feed. For the mechanism that feeds the cloth back, solenoids are used. For the mechanism that does thread cutting, use another solenoid. In the conventional sewing machine, the timing of driving the mechanism for feeding the cloth back and the timing of driving the mechanism for cutting the thread partially overlap each other. Since the driving periods overlap, the power consumption of the sewing machine increases. Therefore, the power board needs to be enlarged.

Contents of the invention

The object of the present invention is to provide a sewing machine and a thread cutting method of the sewing machine which can avoid increased power consumption during thread cutting.

The sewing machine of technical solution 1 is a sewing machine comprising a machine needle, a needle plate, a cloth feeder, a feeding driving mechanism, a thread cutter, a thread cutting driving mechanism, and an input mechanism. The needle moves up and down. The needle plate is configured for the object to be sewn and has holes through which the machine needles pass. The cloth feeder feeds the sewing object synchronously with the vertical movement of the needle. The feeding drive mechanism drives the cloth feeder, and can change the forward feeding of the sewn object to reverse feeding. The thread cutter is located under the needle plate and cuts off the upper thread and the lower thread. The thread cutting drive mechanism drives the thread cutting knife. The input mechanism inputs an instruction to drive the thread cutter by the thread cutting drive mechanism. The sewing machine also includes a reverse feeding part, a reverse feeding stop part and a thread cutting part. When an instruction to drive the thread cutter is input from the input mechanism, the reverse feed unit drives the feed drive mechanism to perform the reverse feed of the sewing object. After the reverse feeding part performs the reverse feeding of the sewn object, the reverse feeding stop part stops the driving of the feeding driving mechanism. After the reverse feeding stopping part stops the reverse feeding of the sewn object, the thread cutting part drives the thread cutting driving mechanism. Therefore, the driving timing of the feed driving mechanism and the driving timing of the thread cutting driving mechanism do not overlap. Therefore, the sewing machine can avoid an increase in power consumption.

In the sewing machine of technical solution 2, after the cloth feeder performs the forward feeding by an amount exceeding half of the feeding amount of the sewing object within one cycle of the needle up and down movement, the reverse feeding part The feeding drive mechanism is driven to perform the reverse feeding on the sewn object.

The reverse feed unit drives the feed driving mechanism to perform the reverse feed on the sewn object after the forward feed is performed for an amount exceeding half of the feed amount of one pitch. The feeding amount of one pitch refers to the feeding amount of the sewing object transferred by the feeding mechanism within one cycle of the needle moving up and down.

Since half of the feed amount exceeding one pitch is forward fed and then reverse fed, the needle does not penetrate the sewing object at the same position as the sewing position of the previous stitch before the tangent, or there is a seam. Location. Therefore, the stitching of one stitch before the thread cut will not come loose after the thread is cut. The upper thread loop does not twist during thread cutting. The sewing machine can make the thread after cutting the thread and the length of the bobbin thread remaining on the back of the fabric uniform. Therefore, the sewing machine reliably prevents thread trimming errors. The amount of reverse feeding is the amount obtained by subtracting the amount of normal feeding from the amount of feeding.

The thread cutting method of the sewing machine of technical proposal 3 is a thread cutting method performed by a sewing machine including a needle, a needle plate, a cloth feeder, a feeding drive mechanism, a thread cutter, a thread cutting drive mechanism, and an input mechanism. The needle moves up and down. The needle plate is configured for the object to be sewn and has holes through which the machine needles pass. The cloth feeder feeds the sewing object synchronously with the vertical movement of the needle. The feeding drive mechanism drives the cloth feeder, and can change the forward feeding of the sewn object to reverse feeding. The thread cutter is located under the needle plate and cuts off the upper thread and the lower thread. The thread cutting drive mechanism drives the thread cutting knife. The input mechanism inputs an instruction to drive the thread cutter by the thread cutting drive mechanism. The thread cutting method includes a reverse feeding process, a reverse feeding stop process, and a thread cutting process. In the reverse feed step, when an instruction to drive the thread cutter is input from the input mechanism, the feed drive mechanism is driven to perform the reverse feed on the sewing object. In the reverse feed stop step, the drive of the feed drive mechanism is stopped after the reverse feed has been performed on the sewn object in the reverse feed step. In the thread cutting step, the thread cutting drive mechanism is driven after the reverse feeding of the sewing object is stopped in the reverse feeding stop step. Therefore, the driving timing of the feed driving mechanism and the driving timing of the thread cutting driving mechanism do not overlap. Therefore, the sewing machine can avoid an increase in power consumption.

Description of drawings

FIG. 1 is a perspective view of a sewing machine 1 .

FIG. 2 is a cross-sectional view showing the periphery of the needle 14 and the periphery of the shuttle mechanism 30. As shown in FIG.

FIG. 3 is a perspective view showing the periphery of the needle 14 and the periphery of the shuttle mechanism 30 .

FIG. 4 is a cross-sectional view showing part of the internal structure of the column portion 3 .

FIG. 5 is a block diagram showing the electrical configuration of the sewing machine 1. As shown in FIG.

FIG. 6 is a timing chart of a line end processing method.

FIG. 7 is a flowchart of thread cutting processing executed by the CPU 71 .

FIG. 8 is a timing chart of thread end processing executed by the CPU 71 .

Detailed ways

Embodiments of the present invention will be described below with reference to the drawings.

Next, the configuration of the sewing machine 1 will be described. The outer side (front side) of the drawing in FIG. 1 is the front of the sewing machine 1 . As shown in FIG. 1 , the sewing machine 1 is fitted into a concave portion (not shown) provided on the table 6 . The control device 70 is attached to the lower surface of the table 6 . The control device 70 controls the operation of the sewing machine 1 . Pedal 91 is connected to control device 70 via rod 90 . The pedal 91 is of a step-down type. When the operator depresses the pedal 91 toward the toe side or the heel side, a switch (not shown) is appropriately turned on and off. The sewing machine 1 starts and stops the sewing operation according to the on and off of the switch. When the pedal 91 is depressed toward the heel side, the thread trimming mechanism performs thread trimming and the like.

The sewing machine 1 includes a base portion 2 , a column portion 3 , and an arm portion 4 . The base part 2 is a base. The column part 3 has a column shape and is erected on the right end of the base part 2 along the vertical direction. The arm portion 4 extends leftward from the upper end portion of the column portion 3 and faces the upper surface of the base portion 2 .

The needle plate 11 is provided on the left end side of the upper surface of the base portion 2 . As shown in FIG. 2 , the needle plate 11 has a needle accommodating hole 11A directly below the needle 14 . The needle plate 11 has a rectangular hole 12 . The feed dog 32 moves in and out of the rectangular hole 12 in the up and down direction. The feed dog 32 is a cloth feeder. The shuttle mechanism 30 is provided below the throat plate 11 in the base portion 2 . The shuttle mechanism 30 accommodates a bobbin (not shown) for the lower thread. The feed dog 32 is provided above the shuttle mechanism 30 and below the needle plate 11 . The feed dog 32 feeds the object to be sewn to the front or rear of the sewing machine 1 by a predetermined feed amount (feed amount). Cloth 10 in FIG. 2 is an example of a sewing object. The feeding dog 32 is driven by the cloth feeding mechanism.

A sewing machine motor 87 (see FIG. 5 ) is provided on the upper portion of the right side of the column portion 3 . The rotary shaft of the sewing machine motor 87 has a cylindrical pulley 5 . An operator can manually rotate an upper shaft (not shown) of the sewing machine 1 using the pulley 5 . The feeding amount adjustment pulley 21 is provided at the center of the front surface of the column portion 3 . The feeding amount adjustment pulley 21 adjusts the feeding amount of the feeding dog 32 to transfer the cloth 10 . The feed amount adjusting motor 22 is fixed to the lower right side surface of the column portion 3 by a fixing member 25 . The feed amount adjusting motor 22 is a pulse motor. The motor 22 for feed amount adjustment has 22 A of output shafts (refer FIG. 4). The drive pulley 23 is fixed to the front end portion of the output shaft 22A. 24 synchronous belts are arranged between the feeding amount adjustment pulley 21 and the driving pulley 23 . The feed amount adjusting motor 22 is connected to the control device 70 (see FIG. 5 ) via a drive circuit 83 (see FIG. 5 ). The control device 70 controls the drive of the motor 22 for adjusting the feeding amount. The driving force of the feed amount adjustment motor 22 is transmitted from the drive pulley 23 to the feed amount adjustment pulley 21 via the timing belt 24 . Therefore, the feeding amount of the cloth 10 is adjusted with the rotation of the feeding amount adjustment pulley 21 . The adjustment mechanism for adjusting the feeding amount of the cloth 10 will be described later. The feeding amount of the cloth 10 can be set using the operation panel 7 .

As shown in Fig. 1 and Fig. 2, the left end 49 of the machine arm part has a needle bar 13 at its lower part. The needle bar 13 can move up and down. The needle bar 13 is fitted with a needle 14 at its lower end. The presser foot 15 is arranged behind the needle bar 13 . The presser foot 15 presses the cloth 10 . The left end 49 of the machine arm part has a needle bar up and down movement mechanism (not shown) and a thread take-up lever mechanism (not shown) inside it. The needle bar up and down movement mechanism makes the needle bar 13 move up and down. The thread take-up mechanism moves the thread take-up lever 18 (see FIG. 1 ) up and down. The thread take-up lever 18 lifts up the upper thread 8A.

The sewing machine motor 87 is provided above the column portion 3 . The sewing machine motor 87 drives the sewing machine 1 (see FIG. 5 ). The driving force of the sewing machine motor 87 is transmitted to an upper shaft (not shown) through a joint (not shown). The upper shaft extends in the left-right direction within the arm portion 4 . The driving force of the sewing machine motor 87 is also transmitted to the lower shaft (not shown) through a transmission mechanism (not shown). The transmission mechanism is arranged on the upper shaft. The lower shaft extends in the left-right direction inside the base portion 2 . When the operator depresses the pedal 91, the sewing machine motor 87 is driven. When the sewing machine motor 87 is driven, each element including the needle bar 13, the thread take-up mechanism, the shuttle mechanism 30, and the feeding mechanism is synchronously driven. Accordingly, the sewing machine 1 forms stitches on the cloth 10 .

As shown in FIG. 1 , the arm portion 4 has an operation panel 7 at the center of its upper surface. The operation panel 7 has a horizontally long rectangular shape as seen from the front. The operation panel 7 has a liquid crystal display portion 7A on its front surface. The liquid crystal display portion 7A displays function names for executing various functions, various messages, and the like. Various functions are functions required for sewing operations such as selection and editing of sewing patterns, setting and canceling of thread cutting processing, and the like. The liquid crystal display unit 7A has a touch panel 7B on its front surface. The liquid crystal display unit 7A and the touch panel 7B are connected to the control device 70 . The operator selects a display item on the liquid crystal display unit 7A with a finger or a stylus. The touch screen 7B will sense the selected item. The operator can input various instructions to the sewing machine 1 through the liquid crystal display unit 7A and the touch panel 7B.

Next, the cloth feeding mechanism will be described. The cloth feeding mechanism is a well-known mechanism in the past. The cloth feed mechanism drives the feed dog 32 (see FIG. 2 ). The horizontal feed shaft (not shown) moves the feed dog 32 forward and backward. The base portion 2 supports both ends of the horizontal feed shaft in a rotatable manner. The upper and lower feeding shafts (not shown) make the feeding teeth 32 move up and down. The upper and lower feeding shafts are linked with the feeding platform (not shown) that is fixedly connected with the feeding teeth 32 . Therefore, the cloth feed mechanism can feed the cloth 10 in the front-rear (forward and reverse) directions. Switching of the feeding direction of the cloth 10 is determined by an inclination angle of a switcher (not shown). The switcher is arranged in the base part 2 . The cloth feeding mechanism feeds the cloth in the reverse direction according to the inclination angle of the switch. The sewing machine 1 performs reverse stitching and the like.

The well-known mechanism for adjusting the inclination angle of the switch is briefly described below. The base part 2 shown in FIG. 1 includes a reversing solenoid 58 (see FIG. 5 ), a solenoid rod (not shown), a back tacking rod shaft (not shown), and a rod (not shown) inside. , Switcher linkage group (not shown). When the reverse solenoid 58 is turned on, the reverse tack lever shaft is rotated by the solenoid rod (not shown). The rod (not shown) swings along with the rotation of the reverse tacking rod shaft. The switch linkage (not shown) swings in the up and down direction. Therefore, the inclination angle of the switch changes to a symmetrical position. Although the feeding direction of the cloth 10 is switched from the normal feeding direction to the reverse feeding direction, the feeding amount of the cloth 10 does not change. The backtacking rod shaft is connected with the backtacking rod 9 (referring to Fig. 1). The backtacking lever 9 is disposed on the lower side of the front surface of the column portion 3 . When the operator manually operated the backtacking lever 9 downward, the backtacking lever shaft rotated. When the backtacking rod shaft rotates, the inclination angle of the switcher changes to a symmetrical position. Therefore, the feeding direction of the cloth 10 becomes the reverse direction.

Next, an adjustment mechanism for adjusting the feeding amount of the cloth 10 will be described. As shown in FIG. 4 , the column portion 3 includes a feeding adjustment cam 50 inside thereof. The feed adjustment cam 50 is supported so as to be rotatable about a shaft 54 as a fulcrum. The feeding adjustment cam 50 is connected with the feeding adjustment platform 57 through a connecting rod 56 . The feeding adjustment table 57 is a well-known structure connected to the switch through a connecting rod (not shown). The feeding adjustment stand 57 is provided in the base part 2 so as to be rotatable. When the connecting rod 56 moves up and down, the feeding adjustment table 57 rotates. When the feeding adjustment table 57 rotated, the inclination angle of the switcher changed. When the inclination angle of the switcher changes, the swing amount of the horizontal feeding shaft (not shown) changes. Therefore, the amount of feeding performed by the feed dog 32 (see FIG. 2 ) fluctuates.

The feed adjustment cam 50 includes a cam surface 51 at its front end. The cam surface 51 is V-shaped in side view. The rear end of the feeding adjustment cam 50 is rotatably connected with the upper end of the connecting rod 56 . The link 56 is an element constituting the above-mentioned switch link group. The threaded hole 3A is provided on the upper front surface of the pillar portion 3 . The adjustment shaft 41 protrudes rearward from the center of the feeding amount adjustment pulley 21 . The adjustment shaft 41 is screwed into the threaded hole 3A. The front end portion 42 of the adjustment shaft 41 is engaged with the cam surface 51 of the feed adjustment cam 50 .

The cam surface 51 includes a positive feed control surface 52 and a reverse feed control surface 53 . The positive feeding control surface 52 is located on the lower side of the cam surface 51 . The anti-feed control surface 53 is located on the upper side of the cam surface 51 . The link 56 is biased downward by a spring (not shown). The connecting rod 56 urges the normal feeding control surface 52 to the front end 42 of the adjustment shaft 41 . When the operator turns the adjustment shaft 41, the adjustment shaft 41 moves in the front-rear direction (left-right direction in FIG. 4). When the adjustment shaft 41 moves, the contact position between the front end portion 42 and the normal feeding control surface 52 changes. When the contact position changes, the swing angle of the switch is changed by the link 56 . Therefore, the sewing machine 1 can adjust the feed amount of one pitch of the feed dog 32 . The structure using the feed adjustment cam 50 is the same as conventional ones.

FIG. 4 shows a state where the reverse solenoid 58 is off. The front end portion 42 of the adjustment shaft 41 is in contact with the normal feed control surface 52 . After the reverse solenoid 58 is turned on, the link 56 rises against the spring force. When the connecting rod 56 rises, the front end 42 of the adjustment shaft 41 is in contact with the anti-feed control surface 53 . The swing angle of the switcher is switched from the positive feeding angle to the reverse feeding angle. Therefore, the feeding direction of the feed dog 32 is reversed.

Next, the thread trimming mechanism will be described. The thread cutting mechanism is the same as the previous mechanism. As shown in FIG. 3 , the thread cutting mechanism includes a moving knife 61 and a fixed knife 62 . The movable knife 61 and the fixed knife 62 are provided so as to be close to the needle accommodating hole 11A of the needle plate 11 and sandwich the needle accommodating hole 11A therebetween. The movable knife 61 and the fixed knife 62 are driven by a thread cutting solenoid 65 (see FIG. 5 ). The thread cutting solenoid 65 is accommodated in the base portion 2 . After the thread cutting solenoid 65 is turned on, the moving knife 61 is moved by a thread cutting cam (not shown). The loop of the upper thread 8A is formed when the needle 14 rises from the bottom dead center. The shuttle mechanism 30 catches the wire loop. The shuttle mechanism 30 expands the loop. The wire loop becomes a triangular wire loop R. The tip of the moving knife 61 enters the triangular thread loop R to separate the upper thread 8A and the lower thread 8B. A thread wiper (not shown) gradually spreads the upper thread 8A and the lower thread 8B caught by the movable knife 61 . The wire puller has the fanned shape of a moving knife. The front ends of the movable knife 61 and the fixed knife 62 cut the upper thread 8A and the lower thread 8B.

Next, the electrical configuration of the sewing machine 1 will be described. As shown in FIG. 5 , the sewing machine 1 includes a control device 70 . The control device 70 includes a CPU 71 . ROM 72 , RAM 73 , EEPROM 74 (registered trademark), and I/O interface (hereinafter referred to as I/O) 76 are connected to CPU 71 via bus 77 . Pedal 91 , touch panel 7B, drive circuits 81 to 85 , and the like are connected to I/O 76 . The drive circuit 81 drives the liquid crystal display unit 7A. The drive circuit 82 drives the sewing machine motor 87 . The drive circuit 83 drives the feed amount adjusting motor 22 . The drive circuit 84 drives the reversing solenoid 58 . The drive circuit 85 drives the thread cutting solenoid 65 .

The thread end processing method of the sewing machine 1 will be described with reference to the timing chart of FIG. 6 . This description is a description of the outward appearance and operation of the sewing machine 1 that performs thread end processing. In FIG. 6 , the needle tip position of the machine needle 14 is indicated by a solid line, and the phase of vertical feeding of the feed dog 32 is indicated by a dotted line. The horizontal axis represents the rotation angle of the upper axis. The operator uses the operation panel 7 to set and cancel the thread end processing.

During the sewing operation, the operator depresses the pedal 91 toward the heel side at t1. By depressing the pedal 91 (depressing the pedal 91 toward the heel side), a thread cutting signal is input to the control device 70 . The needle tip of the machine needle 14 is located below the needle plate 11 . The feed dog 32 is also located below the needle plate 11 . The needles 14 move toward the needle plate 11 at t2. The feed dog 32 moves above the needle plate 11 at t3. The feed dog 32 feeds the cloth 10 in the normal rotation direction while being located above the needle plate 11 .

The needle 14 reaches the top dead center at t4. The upper shaft rotates by a predetermined angle (for example, 35°) from the upper dead center at t5. At t5, the control device 70 turns on the reverse solenoid 58 (see FIG. 5 ). The t5 at which the reverse solenoid 58 is turned on is adjusted to be the moment when more than half of the feeding amount of the cloth 10 in one cycle of the needle 14 is being fed. By turning on the reverse solenoid 58, the inclination of the switch changes to a symmetrical position. Therefore, the feeding direction is reversed. From t5 to t6, the feed dog 32 transports the cloth 10 in the reverse direction (Q section shown in FIG. 6). The feed dog 32 arrives at the needle plate 11 at t6 and moves below the needle plate 11 . Therefore, the needle drop point of the last needle of the stitch falls in the position near the previous needle. In the present embodiment, the feed dog 32 also moves below the needle plate 11 almost simultaneously with the tip of the needle 14 passing through the needle plate 11 from the top dead center.

When the machine needle 14 is near the bottom dead center at t7, the needle down signal is turned on. When the needle down signal is turned on, the control device 70 turns off the reverse solenoid 58 . Therefore, the inclination angle of the switch is restored, and the cloth feeding direction is changed back to the forward rotation direction. t8 is the timing when the upper shaft rotates by a predetermined angle (for example, 25°). The thread cutting solenoid 65 is energized for a predetermined time from t8. When t7 passes, the shuttle mechanism 30 catches the upper thread loop. The upper thread loop is formed when the needle 14 rises from the bottom dead center.

The shuttle mechanism 30 expands the upper thread loop on the lower side of the needle plate 11, and the upper thread loop becomes a thread loop R. The wire loop R has a substantially triangular shape. In the present embodiment, after the thread cutting signal is input to the control device 70, the cloth 10 is forwardly fed by half or more of the cloth feeding amount, and then reverse feeding is performed. The needle does not pierce the sewing object at the same position as the sewing position of the previous stitch before cutting the thread and the position where the stitches exist. Therefore, after the thread is cut, the stitching of the stitch one stitch before the thread cut will not come loose. In addition, the upper thread loop will not be distorted during thread trimming. The shuttle mechanism 30 can catch the untwisted upper thread loop to form the thread loop R (see FIG. 3 ). Since the upper thread loop is not twisted, the thread loop R does not become smaller. Therefore, the tip of the movable knife 61 can reliably enter the triangular thread loop R, and the sewing machine 1 can also reliably prevent thread cutting errors. The thread take-up lever 18 (refer to FIG. 1 ) is located at a position slightly raised from the lowest position. The upper thread 8A and the lower thread 8B caught by the movable knife 61 are gradually spread by a thread wiper (not shown). Since the thread looseners (not shown) operate at the same time, no excessive force is applied to the upper thread 8A. The front ends of the movable knife 61 and the fixed knife 62 cut the upper thread 8A and the lower thread 8B.

Next, the thread cutting process executed by the CPU 71 will be described with reference to FIGS. 7 and 8 . The operator depresses the pedal 91 toward the heel side during the sewing operation. The pedal 91 inputs a thread trimming signal to the control device 70 at t11. The CPU 71 calls the thread cutting processing program to execute this processing. The thread cutting processing program is stored in ROM 72 (see FIG. 5 ).

The CPU 71 judges whether or not the thread end processing has been set through the operation panel 7 (S10). When the thread end processing is set, the CPU 71 stores "1" in the thread cut flag in the RAM 73 (see FIG. 5 ). When the thread end processing is not set, the CPU 71 stores the thread cut flag as "0". The CPU 71 judges whether or not the thread end processing is set based on whether the thread cutting flag is "0" or "1".

When it is determined that the thread end processing is set (S10: YES), the CPU 71 determines whether or not the needle down signal is on (S11). When the CPU 71 determines that the needle down signal is OFF (S11: NO), it returns to S11 and enters the standby state. When the CPU 71 determines that the needle down signal is ON at t12 (S11: YES), the needle tip position of the needle 14 is located below the needle plate 11. The feed dog 32 is also located below the needle plate 11 .

The CPU 71 judges whether or not the phase of the upper shaft is at the reverse solenoid ON position (S12). The reverse solenoid ON position is a position where the upper shaft rotates by a predetermined angle from the position where the needle tip position reaches the top dead center. The predetermined angle of the upper shaft for turning on the reverse solenoid 58 is set to an angle capable of forward feeding more than half of the feeding amount of the cloth 10 in one cycle of the needle 14 . In the present embodiment, it is set to a position rotated by 35° from the position at which the needle tip position reaches the top dead center. The predetermined angle can be changed according to the operating conditions of the sewing machine (for example, the rotation speed of the sewing machine motor 87, etc.). The predetermined angle is preferably adjusted within a range of, for example, -55° to +75°.

When the CPU 71 determines that the phase of the upper shaft is not the reverse solenoid ON position (S12: NO), it returns to S12 and enters the standby state. When the CPU 71 determines that the phase of the shaft is at the reverse solenoid ON position at t13 (S12: YES), it turns on the reverse solenoid 58 (see FIG. 5) (S13). Therefore, since the inclination angle of the switch changes to a symmetrical position, the feeding direction is reversed. The cloth 10 is transferred in the reverse direction until the feed dog 32 moves below the needle plate 11 . Therefore, in the sewing machine 1, the needle drop point of the final needle of the stitch can be located near the previous needle.

The CPU 71 judges whether or not the needle down signal is on (S14). When the CPU 71 determines that the needle down signal is off (S14: No), it returns to S14 and enters the standby state. When the CPU 71 determines that the needle down signal is ON at t14 (S14: YES), since the needle 14 is located near the bottom dead center, the reverse solenoid 58 is turned off (S15). Therefore, the inclination angle of the switch is restored, and the cloth feeding direction is changed back to the normal feeding direction.

The CPU 71 judges whether or not the phase of the upper shaft is at the ON position of the thread cutting solenoid (S16). The ON position of the thread trimmer solenoid is the position where the upper shaft has rotated by a predetermined angle (for example, 25°) since the needle down signal was ON. In the present embodiment, the predetermined angle is set to a position where the upper shaft has rotated by 25° from when the needle down signal was turned ON. The predetermined angle can be changed according to the operating conditions of the sewing machine (for example, the rotation speed of the sewing machine motor 87, etc.). When the CPU 71 determines that the phase of the upper shaft is not the thread cutting solenoid ON position (S16: NO), it returns to S16 and repeats the process.

When the CPU 71 determines that the phase of the upper shaft is the thread cutting solenoid ON position (S16: YES), the thread cutting solenoid 65 is turned on at t15 (S17). The thread trimming mechanism starts the thread trimming action. As shown in FIG. 6 , the shuttle mechanism 30 forms a triangular thread loop R on the upper thread 8A on the lower side of the needle plate 11 . In this embodiment, after the thread cutting signal is input, an amount exceeding half of the feeding amount of the cloth 10 in one cycle of the needle 14 is forwardly fed, and then the reverse feed is performed. Therefore, the needle 14 does not pierce the same position in the sewing object as the sewing position of the previous stitch before cutting the thread or the position where the seam exists. Then, the thread cutting mechanism cuts the upper thread 8A and the lower thread 8B.

The CPU 71 judges whether the needle up signal is ON (S18). When the CPU 71 judges that the needle up signal is not ON (S18: NO), it returns to S18 and repeats the process. When the CPU 71 determines that the needle up signal is ON at t16 (S18: YES), it determines whether or not the phase of the upper shaft is at the needle up stop position (S19). The needle up stop position is, for example, a position where the upper shaft rotates by a predetermined angle (for example, 10°) after the needle up signal is turned on. The predetermined angle can be changed according to the operating conditions of the sewing machine (for example, the rotation speed of the sewing machine motor 87, etc.).

When the CPU 71 determines that the phase of the upper shaft is not the needle up stop position (S19: No), it returns to S19 and enters the standby state. When the CPU 71 determines that the phase of the upper shaft is at the needle up stop position (S19: YES, t17), the thread cutting solenoid 65 is turned off, and the driving of the sewing machine motor 87 is stopped (S20). The CPU 71 ends this processing.

The reverse solenoid 58 shown in FIG. 5 is an example of the feed driving mechanism of the present invention. The thread cutting solenoid 65 is an example of the thread cutting driving mechanism of the present invention. The pedal 91 is an example of the input mechanism of the present invention. The CPU 71 that executes the processes of S12 and S13 shown in FIG. 6 is an example of the reverse feed unit of the present invention. The CPU 71 that executes the processes of S14 and S15 is an example of the reverse feed stop unit of the present invention. The CPU 71 executing the processes of S16 and S17 is an example of the thread cutting unit of the present invention.

As described above, the sewing machine 1 of this embodiment feeds the cloth 10 in the reverse feed direction within a predetermined period of time after the thread cutting signal is input via the pedal 91, and then cuts the upper thread 8A and the lower thread 8B. The sewing machine 1 cuts the upper thread 8A and the lower thread 8B after the needle drop point of the last needle falls near the position of the preceding needle. The sewing machine 1 can make the remaining lengths of the upper thread 8A and the bobbin thread 8B remaining at the ends of the stitches uniform on the back of the cloth 10 after thread cutting. Therefore, it is possible to save the operator's work of cutting the thread on the back side of the cloth with scissors or the like.

In this embodiment, in particular, the thread cutting solenoid 65 is energized after the reversing solenoid 58 is energized and then turned off. After the sewing machine 1 has fed the cloth 10 in the reverse feed direction, the upper thread 8A and the lower thread 8B are cut. Therefore, the ON period (conduction period) of the reversing solenoid 58 and the ON period (conduction period) of the thread cutting solenoid 65 do not overlap, and power consumption does not increase during thread cutting.

In this embodiment, in particular, reverse feeding is performed by energizing the reverse solenoid 58 after inputting the thread trimming signal and feeding more than half of the feeding amount of the cloth 10 in one cycle of the needle 14 . In conventional sewing machines, immediately after a thread trimming signal is input, the cloth feeding direction is reversed to cut the thread. Therefore, the needle 14 penetrates into the sewing object at the same position as the sewing position of the previous stitch before cutting the thread or the position where the seam exists. After the thread is cut, the seam of the stitch one stitch before the thread cut will be loosened. Since the upper thread loop is twisted when the thread is trimmed by the thread trimming mechanism, the triangular thread loop R is small. In the present embodiment, the needle 14 does not pierce the same position as the sewing position of the previous stitch before cutting the thread or a position where stitches exist in the to-be-sewn object. Therefore, the stitching of one stitch before the thread cut will not come loose. Since the upper thread loop does not twist when the thread is trimmed by the thread trimming mechanism, the triangular thread loop R does not become smaller. Therefore, the front end of the movable knife 61 can enter into the triangular wire loop R reliably. The sewing machine 1 can make the lengths of the thread 8A and the bobbin thread 8B remaining on the back of the cloth equal after the cut thread.

The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, in the above-described embodiment, the operator inputs the thread trimming signal to the control device 70 by depressing the pedal 91, but other methods may also be employed. The operator can also input the thread cutting signal to the control device 70 by pressing the hand switch P (see FIG. 1 ). It is also applicable to the following situation: as in the automatic reverse stitching program, a thread trimming signal is automatically generated after several stitches of reverse stitching are automatically performed at the end of sewing. An auxiliary device for feeding the cloth can also be installed on the sewing machine, and the thread trimming signal can be input to the sewing machine from the auxiliary device side.

Claims (3)

1. A sewing machine, comprising: Machine needle (14), this machine needle moves up and down; a needle plate (11), which is configured for the object to be sewn (10) and has holes for the machine needles to pass through; a cloth feeder (32), which synchronously moves the sewing object with the up and down movement of the needle; A feeding driving mechanism (58), which drives the cloth feeder and can change the forward feeding of the sewn object to reverse feeding; A thread cutter (61, 62), which is located under the needle plate, cuts off the upper thread and the lower thread; a thread cutting drive mechanism (65), which drives the thread cutting knife; and an input mechanism (91), which inputs an instruction to drive the thread cutter by the thread cutting drive mechanism, It is characterized in that it also includes: The reverse feeding part (71), when an instruction to drive the thread cutter is input from the input mechanism, the reverse feeding part drives the feeding driving mechanism to perform the reverse feeding on the sewn object; The anti-feed stop part (71), after the anti-feed part performs the reverse feed on the sewn object, the anti-feed stop part stops the drive of the feeding drive mechanism; and A thread cutting part (71), which drives the thread cutting driving mechanism after the reverse feeding stop part stops the reverse feeding of the sewn object. 2. The sewing machine according to claim 1, wherein: After the cloth feeder performs the forward feeding by an amount exceeding half of the feeding amount of the sewing object within one cycle of the needle moving up and down, the reverse feeding part drives the feeding driving mechanism to The object to be sewn is subjected to the reverse feeding. 3. A thread cutting method for a sewing machine, the sewing machine comprising: The needle, which moves up and down; a needle plate configured for the object to be sewn and having a hole through which the machine needle passes; a cloth feeder for transferring the object to be sewn synchronously with the up and down movement of the needle; A feeding driving mechanism, which drives the cloth feeder and can change the forward feeding of the sewn object to reverse feeding; A thread cutter, which is located under the needle plate, cuts off the upper thread and the lower thread; a thread cutting driving mechanism, which drives the thread cutting knife; and an input mechanism for inputting an instruction to drive the thread cutter by the thread cutting drive mechanism, The thread cutting method of the sewing machine is characterized in that it includes: The reverse feeding process, when an instruction to drive the thread cutter is input from the input mechanism, drive the feeding driving mechanism to perform the reverse feeding on the sewn object; In the reverse feeding stop process, after the reverse feeding is performed on the sewn object in the reverse feeding process, the driving of the feeding driving mechanism is stopped; and In the thread cutting step, the thread cutting drive mechanism is driven after the reverse feeding of the sewing object is stopped in the reverse feeding stopping step.

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