JP2020120714A - sewing machine - Google Patents

Abstract

To provide a sewing machine capable of identifying sewing defects on the basis of needle thread tension.SOLUTION: A sewing machine executes a sewing defect determination process to determine whether or not a sewing defect that normal seams cannot be formed occurs during a sewing operation on the basis of needle thread tension that is the tension of a needle thread. The fluctuation of needle thread tension is repeated with a period by a unit of hour. The sewing defect determination process includes a thread tightening defect determination process (S111), a specific thread breakage determination process (S113), and a specific stitch skipping determination process (S115). In the process, whether or not each of sewing defects has occurred is determined by comparing the needle thread tension that fluctuates in an N-period with the needle thread tension that fluctuates in an (N-1) period by using a thread tightening defect specific threshold value, a first thread breakage specific threshold value, a second thread breakage specific threshold value, a first stitch skipping specific threshold value, and a second specific stitch skipping threshold value which are previously set corresponding to each of the defects.SELECTED DRAWING: Figure 17

Description

The present invention relates to sewing machines.

A sewing machine is known that can determine whether a sewing failure has occurred. The sewing machine disclosed in Patent Document 1 includes an incremental detector and a tension measuring device. The incremental detector outputs a pulse signal according to the rotation of the upper shaft. The tension measuring device outputs a signal indicating a temporal change of the upper thread tension, which is the tension of the upper thread. The sewing machine acquires the yarn tension function based on the detection results of the incremental detector and the tension measuring device. The thread tension function represents the needle thread tension expressed depending on the upper axis angle. The sewing machine acquires a difference (hereinafter referred to as a tension difference) between the thread tension function in each rotation cycle of the upper shaft and the thread tension function in the preceding rotation cycle. When the acquired tension difference exceeds a predetermined magnitude, the sewing machine determines that a sewing failure has occurred.

Japanese Patent No. 2821048

The poor sewing includes a poor sewing in which it is preferable to stop the sewing operation immediately after the occurrence, and a poor sewing in which it is not necessary to stop the sewing operation immediately after the occurrence. However, in the above sewing machine, the acquired tension difference does not correspond to various specific sewing defects. Therefore, the sewing machine may not be able to identify poor sewing.

An object of the present invention is to provide a sewing machine that can identify a sewing failure based on a change in needle thread tension.

The sewing machine of the present invention includes a vertically movable needle bar on which a sewing needle is mounted, a hook that catches an upper thread inserted through the sewing needle and entangles it with a lower thread, and the hook pulls up the upper thread entwined with the lower thread. A thread balance mechanism, a thread tension mechanism through which the needle thread passes upstream of the thread balance in the supply path of the needle thread leading to the sewing needle, and a tension mechanism for applying tension to the needle thread; The thread tension detection mechanism that detects the upper thread tension, which is the tension of the sewing machine, the needle bar, the hook, and the balance, and the sewing control section that executes sewing on the cloth; A sewing operation by the sewing control unit based on the tension acquisition unit that acquires the periodically changing upper thread tension based on the detection result of the thread tension detection mechanism, and the upper thread tension acquired based on the tension acquisition unit. And a judgment unit for judging whether or not a sewing failure in which a normal stitch cannot be formed occurs, and the judgment unit changes in the N-th (N is a natural number) cycle acquired based on the tension acquisition unit. A specific sewing failure determination unit that determines whether or not the sewing failure has occurred by comparing the upper thread tension with a reference upper thread tension, which is the upper thread tension that is a reference that changes in one cycle. In the sewing machine, the tension acquisition unit acquires the upper thread tension that repeats fluctuations in units of time for each cycle, and the specific sewing failure determination unit determines the upper thread tension that changes in the Nth cycle. And comparing the reference upper thread tension with a plurality of specific threshold values set in advance corresponding to each of the plurality of sewing defects, thereby determining whether the sewing defect has occurred. And

According to the above configuration, the specific sewing failure determination unit determines whether or not the sewing failure has occurred using a plurality of specific threshold values set in advance corresponding to the plurality of sewing failures. Therefore, the sewing machine can identify the specific sewing failure. Therefore, the sewing machine can identify the sewing failure based on the change in the needle thread tension.

In the sewing machine, the tension acquisition unit has a first period in which a first peak of the upper thread tension occurs and a second peak of the upper thread tension in a period of the Nth cycle. A first upper thread tension which is the upper thread tension in the first period and a upper thread tension in the second period with reference to the third upper thread tension which is the upper thread tension between two periods. The second upper thread tension may be acquired. The third upper thread tension tends to be smaller than the first thread tension and the second upper thread tension. Therefore, the first upper thread tension and the second upper thread tension based on the third upper thread tension tend to be large. Therefore, the sewing machine can acquire the first upper thread tension and the second upper thread tension with high accuracy.

In the sewing machine, the poor sewing includes a thread breakage in which the upper thread is cut during sewing, the determination unit includes a thread breakage determination unit that determines whether or not the thread breakage occurs, and the first period Is a shuttle catching period in which the shuttle catches the upper thread, the second period is a balance pull-up period in which the thread take-up pulls the upper thread, and the thread breakage judging unit is configured to detect the first upper thread. It may be determined that the yarn breakage has occurred when the tension is less than or equal to the first threshold and the second upper thread tension is less than or equal to the second threshold. When the yarn breakage occurs, the first upper thread tension becomes less than the first threshold value and the second upper thread tension becomes less than the second threshold value. Since the thread breakage determination unit can judge whether or not the thread breakage has occurred, the sewing machine can identify the thread breakage as a sewing failure.

In the sewing machine, the poor sewing includes skip stitches in which the hook catches the upper thread during sewing, and the determination unit includes a skip stitch determination unit that determines whether or not the skip stitches have occurred. The stitch skipping determination unit may determine that the stitch skipping has occurred when the first upper thread tension is equal to or lower than a third threshold and the second upper thread tension is equal to or higher than a fourth threshold. Good. When skipping occurs, the first upper thread tension becomes equal to or lower than the third threshold value, and the second upper thread tension becomes equal to or higher than the fourth threshold value. Since the stitch skipping determination unit can determine whether stitch skipping has occurred, the sewing machine can identify stitch skipping as defective sewing.

In the sewing machine, the sewing failure includes a thread tightening failure that is a poor balance between the upper thread and the lower thread that form a stitch when the balance pulls up the upper thread, and the plurality of specific threshold values are The specific sewing failure determination unit includes a first specific threshold value, and when the second peak of the needle thread tension in the N-th cycle occurs, the second peak of the reference needle thread tension occurs. A thread tightening failure determination unit that determines that the thread tightening failure has occurred when the speed is equal to or higher than the first specific threshold may be provided. When the thread tightening failure occurs, the time when the second upper thread tension is generated becomes faster. Since the thread tightening failure determination unit can determine whether or not the thread tightening failure has occurred, the sewing machine can identify the thread tightening failure as a sewing failure.

The sewing machine includes an upper shaft that moves the needle bar and the balance up and down, the thread tension mechanism includes a thread tension motor that rotates the thread tension disc, and when the sewing control unit performs sewing, When the rotation speed acquired by the speed acquisition unit and the rotation speed acquired by the speed acquisition unit is less than or equal to a first speed, the thread tension motor is driven to wind the needle thread in the winding direction. And a thread tension control unit for rotating. When the sewing speed by the sewing machine is slow, the first needle thread tension and the second needle thread tension are low. When the rotation speed of the upper shaft is equal to or lower than the first speed, the thread tension control unit rotates the thread tension disc in the winding direction, so that the looseness of the upper thread is unlikely to occur. Therefore, the sewing machine can easily generate the first upper thread tension and the second upper thread tension.

The sewing machine, when a change occurs in the rotation speed based on the speed acquired by the speed acquisition unit, at least one of the plurality of specific thresholds, the first threshold, the second threshold, and the third threshold May be provided with an acceleration correspondence changing unit that changes according to the acceleration of the rotation speed. When the rotation speed of the upper shaft changes, the upper thread tension changes according to the acceleration, and the upper thread tension when sewing failure occurs also changes. Even at this time, the acceleration correspondence changing unit changes the threshold value according to the change in the rotation speed of the upper shaft, so that the sewing machine can properly detect the sewing failure.

The sewing machine changes the speed correspondence to change at least one of the plurality of specific thresholds, the first threshold, the second threshold, and the third threshold according to the rotation speed acquired by the speed acquisition unit. You may provide a part. The needle thread tension changes according to the rotation speed of the upper shaft, and the needle thread tension also changes when a sewing failure occurs. Even at this time, the speed correspondence changing unit changes the threshold value according to the rotation speed of the upper shaft, so that the sewing machine can properly detect the sewing failure.

In the sewing machine, the determination unit may determine whether or not the sewing failure has occurred after the start of sewing, which is from the start of sewing by the sewing control unit to the sewing of a predetermined stitch. At the start of sewing, the first needle thread tension and the second needle thread tension become low. Therefore, if the determination unit determines whether or not there is a sewing failure determination at the start of sewing, the determination unit may erroneously determine that a sewing failure has occurred, even though no sewing failure has occurred. The determination unit does not determine whether or not there is a sewing failure at the beginning of sewing. Therefore, the sewing machine can prevent erroneous determination that a sewing failure has occurred.

In the sewing machine, when the rotation speed acquired by the speed acquisition unit is higher than the second speed, the determination unit may determine whether the sewing failure has occurred. When the sewing speed by the sewing machine is slow, the first upper thread tension and the second upper thread tension are low, and it is difficult for the sewing machine to detect a sewing failure based on the upper thread tension. The sewing failure determination unit does not determine whether there is a sewing failure when the rotation speed of the upper shaft is equal to or lower than the second speed. Therefore, the sewing machine can more properly judge the presence or absence of sewing failure.

The sewing machine includes a thread cutting mechanism for cutting the upper thread and the lower thread, and a thread cutting control section for controlling the thread cutting mechanism to cut the upper thread and the lower thread after sewing by the sewing control section. The thread tension detection mechanism detects a movable member that comes into contact with the upper thread and moves according to the upper thread tension, a magnet provided in the movable member, and a magnetic flux density of the magnet, and detects the detected magnetic flux density. And a magnetic sensor that outputs a voltage, the tension acquisition unit acquires the upper thread tension based on the output voltage of the magnetic sensor, and the tension acquisition unit includes the upper thread and the upper thread by the thread trimming control unit. An adjustment control unit may be provided to execute a zero point adjustment for resetting an output voltage serving as a reference of the magnetic sensor when the bobbin thread is cut. When the sewing control unit repeats the sewing operation, the output voltage of the magnetic sensor may greatly change with respect to the reference output voltage. Even at that time, when the needle thread tension is reduced due to the cutting of the needle thread and the bobbin thread and the output voltage of the magnetic sensor is lowered, the adjustment control unit executes the zero point adjustment, and the sewing machine serves as a reference of the magnetic sensor. Reset the output voltage. Therefore, the sewing machine can continuously and accurately obtain the needle thread tension based on the output voltage of the magnetic sensor.

The whole perspective view of the sewing machine 1. The elements on larger scale of the head 5. Sectional drawing of the main thread tension device 60. The perspective view of the thread tension detection mechanism 130. The electric block diagram of sewing machine 1. The graph which shows the output voltage of the magnetic sensor 105 and the amplifier circuit 151. The graph which shows the variable tension at the time of performing sewing operation normally. The graph which shows the fluctuating tension when the thread tightening failure occurs. The graph which shows the fluctuating tension when a skipped stitch occurs. The graph which shows the correlation coefficient when forming a stitch normally. The graph which shows the correlation coefficient when a thread tightening defect occurs. The graph which shows the correlation coefficient when a skip is generated. The graph which shows a correlation coefficient when a thread breakage occurs. Flow chart of the sewing process. The flowchart of an upper thread winding process. The flowchart of a tension acquisition process. The flowchart of a sewing defect determination process. The flowchart of a thread tightening defect determination process. The flowchart of a specific thread breakage determination process. The flowchart of a specific skip determination process. The flowchart of a thread breakage determination process. The flow chart of the skipped stitch determination process.

A sewing machine 1, which is an embodiment of the present invention, will be described. In the following description, left and right, front and rear, and up and down indicated by arrows in the drawing will be used.

The structure of the sewing machine 1 will be described with reference to FIGS. 1 and 2. The sewing machine 1 includes a bed section 2, a pillar section 3, and an arm section 4. The bed 2 is attached to the opening of the workbench and extends in the left-right direction. The needle plate 7 is mounted on the upper surface of the bed 2. The operator places the cloth on the bed portion 2 and the needle plate 7. The needle plate 7 has a needle hole 8 and a feed dog hole 14. The needle hole 8 is circular in plan view. The feed dog hole 14 has a major axis in the front-rear direction, and is located on the left, rear, right, and front of the needle hole 8. The pedestal portion 3 extends upward from the right end of the bed portion 2. The arm portion 4 extends leftward from the upper end of the pillar portion 3 and faces the upper surface of the bed portion 2. The arm unit 4 includes an input unit 24 and a display unit 25 at a substantially central portion on the front left-right direction. The input unit 24 in this example is three input buttons. The operator operates the input unit 24 while looking at the display unit 25 to input various instructions. The arm portion 4 includes a thread spool bar 20 protruding upward on the left side of the upper surface. The thread stand bar 20 passes the needle thread 6 fed from the thread spool.

The arm portion 4 includes an upper shaft 15 and a main motor 27 (see FIG. 5) inside. The upper shaft 15 extends in the left-right direction and is connected to the output shaft of the main motor 27 via an upper shaft pulley (not shown). The upper shaft pulley is fixed to the right end of the upper shaft 15. The arm portion 4 has a head portion 5 at the left end. The head portion 5 projects downward from the arm portion 4 and faces the needle plate 7 from above. The head 5 supports the needle bar 11 so that it can move up and down. The lower end of the needle bar 11 projects downward from the head 5. The needle bar 11 is connected to the upper shaft 15 via a vertical movement mechanism (not shown). The needle bar 11 moves up and down through the up-and-down moving mechanism as the upper shaft 15 rotates. The needle bar 11 has the sewing needle 10 attached to the lower end. The sewing needle 10 holds the needle thread 6 inserted through the eyelet. The sewing needle 10 moves up and down together with the needle bar 11. The sewing needle 10 can pass through the needle hole 8, the lower end of the movable range of the sewing needle 10 is bottom dead center, and the upper end of the movable range is top dead center.

The bed portion 2 is internally provided with a shuttle, a thread cutting mechanism 17 (see FIG. 5), and a cloth feeding mechanism. The shuttle is provided below the needle plate 7 and accommodates a bobbin wound with a lower thread. The kettle has a sword tip. The hook is rotated by the power of the main motor 27, and the upper thread 6 that is inserted into the eye hole of the sewing needle 10 is caught by the sword tip and entangled with the lower thread. The thread cutting mechanism 17 (see FIG. 5) includes a fixed blade, a movable blade, and a thread cutting solenoid 17A. The movable blade is connected to the thread cutting solenoid 17A. By driving the thread cutting solenoid 17A, the movable blade moves with respect to the fixed blade, and the thread cutting mechanism 17 cuts the upper thread 6 and the lower thread by the cooperation of the movable blade and the fixed blade.

The cloth feed mechanism includes a vertical feed shaft, a feed base, feed dogs, a horizontal feed shaft, and a feed motor 123 (see FIG. 5). The vertical feed shaft extends in the horizontal direction inside the bed portion 2 and is connected to the upper shaft pulley via a belt. The feed base is swingable and is connected to the vertical feed shaft. When the vertical feed shaft is rotated by the driving force of the main motor 27, the feed base moves in the vertical direction. The feed dog is supported by the feed stand. The horizontal feed shaft extends in the left-right direction in front of the vertical feed shaft and connects the feed motor 123 and the feed base. When the horizontal feed shaft is rotated by the driving force of the feed motor 123, the feed base moves in the front-rear direction. The feed dog is swung along with the drive of the main motor 27 and the feed motor 123, so that the feed dog is projected and retracted in the feed dog hole 14.

As shown in FIG. 2, the head 5 has a sub thread tension device 26, a main thread tension device 60, a thread guide 21, and a thread tension in order from the upstream side of the supply path of the needle thread 6 which is fed from the thread spool to the sewing needle 10. The detection mechanism 130, the balance 23, and the guide hook 29 are provided.

The auxiliary thread tension device 26 is provided in the upper right portion of the front surface of the head 5. The main thread tension device 60 is provided below the auxiliary thread tension device 26 and on the front surface of the head 5. The sub thread tension device 26 and the main thread tension device 60 apply tension to the upper thread 6, respectively. The sub thread tension device 26 applies a tension required for the upper thread 6 when the upper thread 6 and the lower thread are cut by the thread cutting mechanism 17. The main thread tension device 60 optimizes the tension acting on the upper thread 6 as the sewing machine 1 is sewn. The structure of the main thread tension device 60 will be described later. The thread guide 21 is provided on the left side of the main thread tension device 60. The thread guide 21 folds back and guides the upper thread 6 that has passed through the main thread tension device 60 toward the thread tension detection mechanism 130 and the balance 23. The thread tension detecting mechanism 130 is fixed by a screw 90 to a recess 5A recessed rearward from the front surface of the head 5. The thread tension detecting mechanism 130 is located at a vertical position between the auxiliary thread tension device 26 and the main thread tension device 60. The thread tension detection mechanism 130 can detect the tension acting on the upper thread 6. The balance 23 is provided on the left side of the auxiliary thread tension device 26. The balance 23 has an insertion hole 23A through which the upper thread 6 is inserted. The balance 23 moves up and down as the main motor 27 is driven. The guide hook 29 is provided on the left side of the thread tension detecting mechanism 130. The guide hook 29 guides the needle thread 6 passing through the insertion hole 23A of the balance 23 toward the needle bar 11.

As shown in FIG. 3, the main thread tension regulator 60 includes a thread tension case 62, a thread tension stand 63, a thread take-up spring 65, a thread tension motor 16, and a thread tension disc 69.

The thread tension case 62 is an annular member. The thread tension case 62 is fixed with a fastening member inside the through hole 5C formed in the front wall portion 5B of the head portion 5. The thread tension stand 63 is an annular member fixed inside the thread tension case 62 with the screw 19. The thread take-up spring 65 is fixed to the outer surface of the thread tension stand 63 and is wound between the thread tension stand 63 and the thread tension case 62. One end of the thread take-up spring 65 is exposed forward from the front wall 5B. By rotating the thread tension base 63, the sewing machine 1 can adjust the spring pressure of the thread take-up spring 65. The thread tension motor 16 is fixed to the inside of the arm portion 4 with a bolt. The output shaft 18, which will be described later, included in the thread tension motor 16 projects forward of the front wall portion 5B through the center hole of the thread tension stand 63. The thread tension disc 69 is fixed to the front end of the output shaft 18 with a screw 28. The upper thread 6 is wound around the thread tension disc 69 about once or twice. The thread tension disc 69 is rotated by driving the thread tension motor 16. The thread tension motor 16 includes an encoder 16A (see FIG. 5). The encoder 16A detects the rotational position of the output shaft 18.

The thread tension motor 16 is a pulse motor and includes an output shaft 18 and an encoder 16A (see FIG. 5). The output shaft 18 is rotatable about the front-rear direction. The encoder 16A is provided inside the head 5. The disk included in the encoder 16A is fixed to the rear end of the output shaft 18. The encoder 16A can detect the rotational position of the output shaft 18. The front end portion of the output shaft 18 supports the pair of thread tension discs 69 on the right side of the arm portion 4. Therefore, the pair of thread tension discs 69 rotate together with the output shaft 18 by the drive of the thread tension motor 16. The sewing machine 1 can control the rotation angle phase of the output shaft 18.

The thread tension detecting mechanism 130 shown in FIG. 4 is provided between the thread tension disc 69 and the balance 23 in the supply path of the upper thread 6. The thread tension detection mechanism 130 detects the front-back position of the tension plate 50 that bends in the front-back direction according to the upper thread tension based on the output voltage of the magnetic sensor 105, thereby detecting the upper thread tension, which is the tension of the upper thread 6. To do.

The thread tension detection mechanism 130 includes a mounting base 140, a sensor holder 80, a magnetic sensor 105, a tension plate 50, a guide member 160, a magnet 58, and a substrate 135 (see FIG. 5).

The mounting base 140 includes a mounting portion 42 and a pedestal portion 410. The mounting portion 42 and the pedestal portion 410 are integrally formed with each other. The mounting portion 42 includes a long hole 421 through which the screw 90 is inserted. The screw 90 inserted into the long hole 421 is fastened to the screw hole provided in the recess 5A (see FIG. 2). Therefore, the mounting base 140 is mounted on the head 5. The pedestal portion 410 is on the left side of the mounting base 140. The pedestal portion 410 includes a right protrusion 410A and a left protrusion 410B. The right protrusion 410A and the left protrusion 410B each have a rectangular parallelepiped shape extending in the front-rear direction.

The sensor holder 80 is formed in a rectangular parallelepiped shape, and is attached to the pedestal portion 410 between the right protrusion 410A and the left protrusion 410B. The sensor holder 80 is made of a non-magnetic material. The magnetic sensor 105 is held on the front surface of the sensor holder 80. The magnetic sensor 105 includes a Hall element. The magnetic sensor 105 is behind the front ends of the right protrusion 410A and the left protrusion 410B.

The tension plate 50 has a plate shape having a thickness in the front-rear direction and bridges the right protrusion 410A and the left protrusion 410B. The guide member 160 is attached to the right protrusion 410A and the left protrusion 410B by screws 97 and 98. The guide member 160 sandwiches the right end of the tension plate 50 between itself and the right protrusion 410A, and sandwiches the left end of the tension plate 50 between it and the left protrusion 410B. The center portion of the tension plate 50 in the left-right direction has a gap with the front surface of the sensor holder 80. Therefore, the tension plate 50 can bend in the front-rear direction with the left and right ends as fulcrums.

The magnet 58 is formed in a columnar shape whose axial direction is the front-back direction. The magnet 58 is fixed to the rear surface of the central portion of the tension plate 50 in the left-right direction with an adhesive. Therefore, when the tension plate 50 bends in the front-rear direction, the magnet 58 moves back and forth, and the distance from the magnetic sensor 105 changes. The magnetic sensor 105 detects a change in the magnetic flux density of the magnet 58. The substrate 135 (see FIG. 5) is provided inside the head 5. The substrate 135 is connected to the magnetic sensor 105 via the flat flexible cable 136. The substrate 135 acquires the detection result of the magnetic sensor 105.

The guide member 160 includes an upper thread guide groove 182 and a lower thread guide groove 172. The upper thread guide groove 182 and the lower thread guide groove 172 are arranged vertically with the tension plate 50 in between. The upper thread guide groove 182 and the lower thread guide groove 172 are opened in the vertical direction and formed in a hook shape. The upper thread guide groove 182 has an upper holding hole 181, and the lower thread guide groove 172 has a lower holding hole 171. The upper holding hole 181 and the lower holding hole 171 extend in the front-rear direction. The upper thread 6 is inserted into and held by the upper holding hole 181 and the lower holding hole 171. The upper thread 6 between the upper holding hole 181 and the lower holding hole 171 contacts the front surface of the tension plate 50 from the front. As the needle thread tension increases, the needle thread 6 biases the tension plate 50 rearward. Therefore, the sewing machine 1 can acquire the needle thread tension based on the output voltage of the magnetic sensor 105.

The electrical configuration of the sewing machine 1 will be described with reference to FIG. The control device 30 of the sewing machine 1 includes a CPU 91. The CPU 91 controls the operation of the sewing machine 1. The CPU 91 is connected to the ROM 92, the RAM 93, the storage device 94, and the I/O interface (hereinafter referred to as I/O) 45. The ROM 92 stores programs and the like for executing various kinds of processing such as sewing processing (see FIG. 14) described later. The RAM 93 temporarily stores various values. The storage device 94 is non-volatile.

The I/O 45 is connected to the drive circuits 81 to 83. The drive circuit 81 is connected to the main motor 27. The drive circuit 82 is connected to the feed motor 123. The drive circuit 83 is connected to the thread tension motor 16. The main motor 27, the feed motor 123, and the thread tension motor 16 include encoders 27A, 123A, and 16A, respectively. The encoder 27A detects the rotational position of the output shaft of the main motor 27. That is, the detection result of the encoder 27A indicates the upper shaft phase which is the rotation angle phase of the upper shaft 15. The encoder 123A detects the rotational position of the output shaft of the feed motor 123. The encoder 16A detects the rotational position of the output shaft 18 of the thread tension motor 16. The CPU 91 acquires the detection results of the encoders 27A, 123A, 16A, and sends a control signal to the drive circuits 81-83. Therefore, the CPU 91 drives and controls the main motor 27, the feed motor 123, and the thread tension motor 16. Hereinafter, the main motor 27 and the feed motor 123 are collectively referred to as a drive motor.

The I/O 45 is connected to the drive circuits 84 and 85, the input section 24, and the pedal 38. The drive circuit 84 is connected to the thread cutting solenoid 17A. The drive circuit 85 is connected to the display unit 25. The CPU 91 controls the thread cutting solenoid 17A and the display unit 25 by transmitting a control signal to the drive circuits 84 and 85. The input unit 24 outputs the result input by the worker to the input unit 24 to the CPU 91. The pedal 38 outputs the operation direction and the operation amount of the pedal 38 by the operator to the CPU 91, respectively.

The I/O 45 is connected to the CPU 135A of the board 135. The substrate 135 includes a CPU 135A, a RAM 135B, a storage device 135C, an amplification circuit 151, a subtraction circuit 152, and a timer 35. The CPU 135A is connected to the RAM 135B, the amplification circuit 151, the subtraction circuit 152, and the timer 35. The timer 35 outputs the time measurement result to the CPU 135A. The amplification circuit 151 and the subtraction circuit 152 are connected to each other, and the subtraction circuit 152 is connected to the magnetic sensor 105. In each of the two graphs shown in FIG. 6, the horizontal axis represents time and the vertical axis represents voltage. The graph shown on the left side of FIG. 6 shows a temporal change in the output voltage of the magnetic sensor 105 that detects a change in the magnetic flux density of the magnet 58. The magnetic sensor 105 outputs the output voltage to the subtraction circuit 152. The subtraction circuit 152 extracts, from the output voltage of the magnetic sensor 105, a voltage in a range of ΔV with respect to the reference voltage Vt, and outputs the extraction result to the amplification circuit 151. The reference voltage Vt is the output voltage of the magnetic sensor 105 when the needle thread tension becomes 0, and is the reference output voltage of the magnetic sensor 105. The graph shown on the right side of FIG. 6 shows a temporal change in the output voltage obtained by amplifying the extraction result of the subtraction circuit 152 by the amplification circuit 151. The amplifier circuit 151 outputs the amplified output voltage to the CPU 135A. Hereinafter, the output result of the amplifier circuit 151 will be referred to as the detection result of the magnetic sensor 105. The CPU 135A can execute zero point adjustment (also called offset adjustment) on the subtraction circuit 152. The zero point adjustment is an adjustment for resetting the reference voltage Vt of the magnetic sensor 105. The zero point adjustment is preferably performed when the needle thread tension is zero.

The storage device 135C stores a thread break flag, a skipped flag, and a thread tightening flag. The thread break flag, the skipped flag, and the thread tightening flag are switched to either 0 or 1. The thread breakage, skipping, and defective thread tightening will be described later. The storage device 135C stores a first yarn breakage threshold value, a second yarn breakage threshold value, a first stitch skipping threshold value, a second stitch skipping threshold value, a thread tightening defect identification threshold value, a first yarn breakage identification threshold value, a second yarn breakage identification threshold value, The one-eye skip identification threshold and the second-eye skip identification threshold are stored. These thresholds are values for determining whether or not a sewing failure described below has occurred. The storage device 135C stores the initial values of these threshold values. In a sewing failure determination process (see FIG. 17) described later, the CPU 135A sets these threshold values stored in the storage device 135C according to the upper shaft rotation speed that is the rotation speed of the upper shaft 15 or the rotation acceleration of the upper shaft 15. Can be changed. The details of the threshold stored in the storage device 135C will be described later.

An outline of the operation of the sewing machine 1 will be described with reference to FIGS. In the following description, the operator places the cloth on the needle plate 7. When the drive motor is driven, the upper shaft 15 moves the needle bar 11 and the balance 23 up and down, and the shuttle rotates. When the sewing needle 10 pierces the cloth and descends to the bottom dead center and then rises, the hook catches the annular upper thread 6 held by the eye hole of the sewing needle 10 with the tip of the sword and entangles it with the lower thread. The sewing needle 10 is pulled upward from the cloth. At this time, by driving the feed motor 123 and the main motor 27, the feed dog projects upward from the feed dog hole 14 and swings backward. Therefore, the cloth moves backward. The balance 23 forms a stitch on the cloth by pulling up the upper thread 6 entwined with the lower thread by the hook. The upper shaft 15, the sewing needle 10, the shuttle, the balance 23, and the cloth feed mechanism repeat the above-mentioned operations to sew cloth. The sewing for one stitch is the sewing for one cycle.

The sewing failure of the sewing machine 1 will be described. Poor sewing indicates that normal stitches could not be formed during the sewing operation. Poor sewing includes poor thread tightening, thread breakage, and stitch skipping. The thread tightening failure is a poor balance between the upper thread 6 and the lower thread that form a stitch on the cloth when the balance 23 pulls up the upper thread 6. For example, if the upper thread 6 is too tightly entangled with the lower thread, the cloth near the seam shrinks. The thread breakage is a failure in which the upper thread 6 is cut during sewing, and a seam cannot be formed on the cloth. The stitch skipping is a failure to catch the upper thread 6 by the hook during sewing, which is a defect in which normal stitches cannot be formed on the cloth.

In the sewing period for one cycle of the sewing machine 1, encounter, hook catching period, and balance lifting period occur sequentially. The encounter is when the sewing needle 10 rises from the bottom dead center and reaches the vicinity of the needle lower position, which is the height position where the hook catches the upper thread 6 with the tip of the sword. The hook catching period is a period in which the hook catches the upper thread 6 with the tip of the sword and the upper thread 6 passes through the hook. The balance pull-up period is a period in which the balance 23 pulls up the upper thread 6 from the time when the upper thread 6 is removed from the hook.

FIG. 7 is a graph in which the horizontal axis represents time and the vertical axis represents needle thread tension, and the graph shows variable tension. The fluctuating tension is a needle thread tension that repeatedly changes in a cycle with a unit of time, and in this example, is a needle thread tension that repeatedly changes in a unit of a sewing period for one cycle. That is, the fluctuating tension is the needle thread tension that fluctuates in the Nth cycle (N is a natural number), and in FIG. 7, the fluctuating tensions for the third cycle, the fourth cycle, and the fifth cycle are shown. As will be described later, variable tension (not shown) in the first cycle and the second cycle is unlikely to occur. The faster the upper shaft rotation speed, the shorter the period of each cycle (horizontal dimension in FIG. 7). In FIG. 7, the periods of the third period, the fourth period, and the fifth period are different from each other.

The kettle capture period and the balance lifting period in the third cycle are T1 and T2, respectively. In the period of the Nth cycle, the hook catching period is a period in which the first peak of the upper thread tension occurs, and the balance lifting period is a period in which the second peak of the upper thread tension occurs. Hereinafter, the peak value of the upper thread tension during the hook catching period will be referred to as the first upper thread tension, and the peak value of the upper thread tension during the balance lifting period will be referred to as the second upper thread tension. The upper thread tension in the period between the two is called the third upper thread tension. The third upper thread tension becomes almost zero. Hereinafter, a value obtained by subtracting the first upper thread tension of the Nth cycle from the first upper thread tension of the N-1th cycle is referred to as a first upper thread tension difference, and is calculated from the second upper thread tension of the N-1th cycle. A value obtained by subtracting the second upper thread tension in the Nth cycle is referred to as a second upper thread tension difference.

In FIG. 8, the fluctuating tension when the stitch is normally formed in the (N-1)th cycle is shown by a chain double-dashed line, and the fluctuating tension when the thread tightening failure occurs at the Nth cycle is shown by a solid line. When the thread tightening failure occurs, the difference between the time when the second upper thread tension occurs and the time when the second upper thread tension occurs at the reference needle thread tension is equal to or more than the thread tightening failure identification threshold value described later. The reference needle thread tension is a variable tension that serves as a reference in one cycle. Regarding the reference needle thread tension at the time of sewing in the second cycle and thereafter and at the time of sewing in the N cycle, the variable tension in the N-1 cycle becomes the reference needle thread tension. At the time of sewing in the first cycle, the variable tension indicated by the reference data stored in the storage device 135C becomes the reference needle thread tension. The fluctuating tension indicated by the reference data indicates a fluctuating tension that occurs when the sewing of the first cycle is normally executed. As will be described later, since it is normal that the variable tension at the beginning of sewing becomes small, the variable tension indicated by the reference data is smaller than the variable tension at the time of performing the sewing in the third cycle and thereafter. The thread tightening defect identification threshold value is a threshold value for the CPU 135A to determine whether or not the thread tightening defect occurs with the execution of the thread tightening defect determination processing (S111 in FIG. 17).

Although not shown, when a thread breakage occurs, the needle thread tension is substantially zero and does not fluctuate over a sewing period of one cycle. Therefore, both the first upper thread tension and the second upper thread tension become extremely smaller than in the normal state. When thread breakage occurs, the first upper thread tension becomes less than or equal to the first thread break threshold and the second upper thread tension becomes less than or equal to the second thread break threshold. Further, when thread breakage occurs, the first upper thread tension difference becomes equal to or larger than the first thread break specific threshold value, and the second upper thread tension difference becomes equal to or larger than the second thread break specific threshold value. The first thread breakage threshold value and the second thread breakage threshold value are threshold values for the CPU 135A to determine whether or not a thread breakage has occurred with the execution of the thread breakage determination process (S117 in FIG. 17). The first yarn breakage specific threshold and the second yarn breakage specific threshold are thresholds for the CPU 135A to determine whether or not the yarn breakage occurs with the execution of the specific yarn breakage determination process (S113 in FIG. 17).

As shown in FIG. 9, when stitch skipping occurs, the first upper thread tension becomes extremely smaller than that in the normal state, and the second upper thread tension becomes a value close to that in the normal state. Therefore, when skipping occurs, the first needle thread tension becomes equal to or less than the first stitch skipping threshold and the second needle thread tension becomes equal to or more than the second stitch skipping threshold. When skipping occurs, the first needle thread tension difference becomes equal to or larger than the first stitch skip identification threshold value, and the second needle thread tension difference becomes equal to or less than the second stitch skip identification threshold value. The first-eye-skip threshold and the second-eye-skip threshold are thresholds for the CPU 135A to determine whether or not the eye-skip has occurred along with the execution of the eye-skip determination processing (S119 in FIG. 17). The first-eye-skip identification threshold value and the second-eye-skip identification threshold value are threshold values for the CPU 135A to determine whether or not the eye-eye skip has occurred along with the execution of the specific eye skip determination process (S115 of FIG. 17).

The CPU 135A needs to acquire the variable tension in cycle units in order to acquire the first upper thread tension and the second upper thread tension in cycle units. In the tension acquisition process (see FIG. 16) described later, the CPU 135A acquires the detection result of the magnetic sensor 105 to continuously acquire the variable tension and sequentially store the variable tension in the RAM 135B. The CPU 135A can obtain the variable tension in units of one cycle by performing autocorrelation analysis on the variable tension sequentially stored in the RAM 135B. The autocorrelation analysis is a well-known analysis method that finds the periodicity of data by acquiring a correlation coefficient that indicates the degree of correlation between data that is a reference for comparison and another data. The correlation coefficient fluctuates between -1 and 1, and the closer the absolute value of the correlation coefficient is to 1, the higher the degree of identity between the two data. In this example, the CPU 135A sets the reference needle thread tension to data serving as a comparison reference. The CPU 135A stores the variable tension acquired on a cycle-by-cycle basis in the RAM 135B.

10 to 13 are graphs in which the horizontal axis represents time (ms) and the vertical axis represents a correlation coefficient. The graph of FIG. 10 shows the correlation coefficient when the seams are formed normally. The correlation coefficient between the variable tension acquired by the CPU 135A and the reference needle thread tension varies with the passage of time. The correlation coefficient reaches a peak near 1 near 25 ms. Therefore, based on the correlation coefficient reaching the peak near 1, the CPU 135A can determine that the variable tension for one cycle is acquired.

FIG. 11 shows the correlation coefficient when the thread tightening failure occurs, and FIG. 12 shows the correlation coefficient when the stitch skipping occurs. Even when defective thread tightening and skipping occur, the correlation coefficient reaches a peak near 1 near 25 ms. Therefore, the CPU 135A determines that the variable tension for one cycle has been acquired based on the same determination criteria as when the stitches are normally formed.

FIG. 13 shows the correlation coefficient when yarn breakage occurs. When yarn breakage occurs, the correlation coefficient does not peak near 1 near 25 ms. That is, the correlation coefficient does not reach a peak near 1 when sewing for one cycle is completed. At this time, the CPU 135A determines that the variable tension for one cycle is acquired based on the lapse of the time for one cycle. The period corresponding to one cycle indicates a period obtained by adding a period of several ms to the period of one cycle before.

The sewing process will be described with reference to FIG. When the worker turns on the power of the sewing machine 1, the CPU 91 reads the program from the ROM 92 and starts the sewing process.

As shown in FIGS. 7 and 14 to 17, the CPU 91 determines whether to start the sewing operation of the sewing machine 1 based on the detection result of the pedal 38 (S11). Before the operator depresses the pedal 38, the CPU 91 determines that the sewing operation is not started (S11: NO) and waits. The operator places the cloth on the needle plate 7 while the CPU 91 is on standby. When the worker depresses the pedal 38 after placing the cloth (S11: YES), the CPU 91 drives the thread tension motor 16 to set the upper thread tension to a predetermined upper thread tension (S12).

The CPU 91 starts driving the drive motor (S13), and starts the sewing operation on the cloth. At this time, the CPU 91 overwrites M stored in the RAM 93 with 0. M is a counter for counting a predetermined period from when the CPU 91 determines that the sewing operation is to be ended in the later-described sewing processing until the thread cutting, which is the cutting of the upper thread 6 and the lower thread, is executed. Is. The predetermined cycle is stored in the storage device 94 in advance. The CPU 91 drives the thread tension motor 16 to maintain a predetermined upper thread tension.

The CPU 91 acquires the upper shaft rotation speed based on the detection result of the encoder 27A (S15). The CPU 91 acquires the upper shaft rotation speed by acquiring the detection result of the encoder 27A twice.

The CPU 91 executes the upper thread winding process (S16). The CPU 91 determines whether the upper shaft rotation speed acquired in S15 is less than or equal to the first speed (S81). When the rotation speed of the upper shaft rotation speed is higher than the first speed (S81: NO), the CPU 91 ends the upper thread winding process. When the upper shaft rotation speed is equal to or lower than the first speed (S81: YES), the CPU 91 controls the thread tension motor 16 to rotate the thread tension disc 69 in the winding direction to wind the upper thread 6 ( S83). The winding direction is the direction of rotation of the thread tension disc 69, which is opposite to the direction in which the upper thread 6 is supplied along the supply path. In this example, the CPU 91 rotates the thread tension disc 69 in the winding direction by a predetermined rotation amount. Therefore, the sewing machine 1 can suppress the looseness of the upper thread 6. The CPU 91 ends the upper thread winding process and returns to the sewing process.

The CPU 91 determines whether or not a sewing failure has occurred (S17). Whether or not a sewing failure has occurred is determined based on the sewing failure information transmitted by the CPU 135A in the tension acquisition process described later. When at least one of the thread breakage flag, the skip stitch flag, and the thread tightening flag is 1, the CPU 91 determines that a sewing failure has occurred (S17: YES), and moves the process to S23. When all of the thread breakage flag, stitch skipping flag, and thread tightening flag are 0, the CPU 91 determines that no sewing failure has occurred (S17: NO). The CPU 91 determines whether or not to finish sewing based on the detection result of the pedal 38 (S18). When the operator does not depress the pedal 38, the CPU 91 determines that the sewing is not completed (S18: NO), and the process proceeds to S15.

For example, when the worker depresses the pedal 38, the CPU 91 determines that the sewing operation is finished (S18: YES), and determines whether M stored in the RAM 93 has reached a predetermined cycle (S19). If M is less than the predetermined period (S19: NO), M is incremented by 1 (S71), and the process proceeds to S72. The CPU 91 acquires the upper shaft rotation speed based on the detection result of the encoder 27A (S72), and executes the upper thread winding process (S73). The processes of S72 and S73 are the same as the processes of S15 and S16. The CPU 91 determines whether or not a sewing failure has occurred (S74). When the CPU 91 determines that a sewing failure has occurred (S74: YES), the process proceeds to S75. When the CPU 91 determines that no sewing failure has occurred (S74: NO), the process proceeds to S19. The CPU 91 repeats the process until M reaches a predetermined cycle (S19: NO, S71, S72, S73, S74).

If M has reached the predetermined cycle (S19: YES), the CPU 91 controls the thread cutting solenoid 17A to execute thread cutting (S20). After cutting the upper thread 6, the upper thread tension becomes substantially zero. The CPU 91 stops driving the drive motor (S21).

The CPU 91 transmits an instruction to execute the zero point adjustment of the output voltage of the magnetic sensor 105 to the CPU 135A (S22). The CPU 91 shifts the processing to S220.

The CPU 91 determines whether or not there is an operation to turn off the power of the sewing machine 1 (S220). When the worker does not perform the operation of turning off the power of the sewing machine 1 (S220: NO), the CPU 91 shifts the processing to S11. While the CPU 91 is on standby (S11: NO), the worker places an unsewn cloth on the needle plate 7 instead of the cloth after sewing, and depresses the pedal 38 (S11: YES). When the operator turns off the power of the sewing machine 1 (S220: YES), the CPU 91 ends the sewing process.

The tension acquisition process will be described with reference to FIGS. The tension acquisition process is a process executed by the CPU 135A in parallel with the sewing process. In the tension processing, the CPU 135A determines whether or not a sewing failure has occurred based on the acquired needle thread tension. When the worker turns on the power of the sewing machine 1, the CPU 135A starts the tension acquisition process.

The CPU 135A executes an initialization process (S30). The CPU 135A sets the thread break flag, the skipped stitch flag, and the thread tightening flag stored in the storage device 135C to 0, respectively. The CPU 135A initializes the timer 35 to 0. The CPU 135A overwrites N stored in the RAM 135B with 1 (S31). The CPU 135A acquires the needle thread tension based on the detection result of the magnetic sensor 105 (S33). The detection result of the magnetic sensor 105 is, for example, the output voltage at t1 in the graph on the right side of FIG. The CPU 135A acquires the needle thread tension based on the output voltage that is the detection result of the magnetic sensor 105 and a predetermined relational expression. The CPU 135A sequentially stores the obtained needle thread tension as a variable tension in the RAM 135B.

The CPU 135A determines whether or not the sewing operation of the sewing machine 1 has started (S35). The determination is compared by an autocorrelation analysis of the needle thread tension indicated by the variable tension data at the start of sewing and the variable tension stored in the RAM 135B in S33. When the sewing operation has not started, the needle thread tension hardly changes. Therefore, even if the needle thread tension and the fluctuating tension are compared by the autocorrelation analysis, the correlation coefficient does not peak near 1. When the correlation coefficient does not peak near 1, the CPU 135A determines that the sewing operation has not started (S35: NO), and moves the process to S33. When the correlation coefficient has a peak in the vicinity of 1 (S35: YES), the CPU 135A determines that the sewing operation has started and shifts the processing to S37. The CPU 135A starts counting the time of the timer 35 (S37). The timer 35 measures the time elapsed from the start of the sewing operation (hereinafter referred to as the elapsed time).

The CPU 135A acquires the needle thread tension based on the detection result of the magnetic sensor 105 and the elapsed time based on the timing result of the timer 35 (S43). The CPU 135A acquires the elapsed time based on the time measurement result of the timer 35. The CPU 135A stores the acquired elapsed time and the needle thread tension in the RAM 135B as variable tension in association with each other. The CPU 135A determines whether or not the acquisition of the fluctuating tension in the Nth cycle has been completed (S45). The determination is compared by autocorrelation analysis of the reference needle thread tension and the fluctuating tension stored in the RAM 135B in S43. When the correlation coefficient does not peak near 1, the CPU 135A determines that the variable tension for the first cycle has not been acquired (S45: NO), and the process proceeds to S43. When the correlation coefficient peaks near 1 (S45: YES), the CPU 135A shifts the processing to S47. In S45, the CPU 135A determines that the acquisition of the fluctuating tension of the Nth cycle is completed even when the correlation coefficient does not peak near 1 for a predetermined time (S45: YES). Therefore, even when thread breakage occurs, the CPU 135A can determine whether or not the variable tension of the Nth cycle has been acquired.

Each time the CPU 135A repeats S43 and S45, the elapsed time and the needle thread tension (that is, the variable tension) are accumulated and stored in the RAM 135B (S43). When the correlation coefficient reaches the peak in the vicinity of 1 or when the correlation coefficient does not reach the peak in the vicinity of 1 for a predetermined time (S45: YES), the CPU 135A causes the variable tension in the Nth cycle, The upper thread tension and the second upper thread tension are acquired (S47). The CPU 135A extracts and acquires the variable tension of the Nth cycle from the RAM 135B. Further, the CPU 135A specifies the third upper thread tension in the variable tension of the Nth cycle, and specifies the first upper thread tension and the second upper thread tension based on the specified third upper thread tension. The upper thread tension acquired in S43 is the upper thread tension based on the detection result of the magnetic sensor 105. Therefore, the CPU 135A acquires the variable tension, the first upper thread tension, and the second upper thread tension in the Nth cycle based on the detection result of the thread tension detection mechanism 130 (S47). The upper thread 6 is easily loosened during the first cycle of sewing. Therefore, it is difficult for the first upper thread tension and the second upper thread tension (not shown) in the first cycle to have high values as shown in FIG. 7. The CPU 135A executes the sewing failure determination processing (S51).

The sewing failure determination processing is processing for determining whether or not each of thread breakage, skipped stitches, and thread tightening failure has occurred, based on the variable tension acquired in S47. The CPU 135A switches the thread break flag, the skip stitch flag, and the thread tightening flag from 0 to 1 according to the sewing failure that has occurred. The CPU 135A determines whether or not the sewing is being started (S100). The sewing start is the sewing from the sewing start (S13) to a predetermined stitch. The sewing start of this example is the sewing from the start of sewing to the second stitch, and corresponds to the sewing of the second cycle (N=2). When N is 2 or less (S100: YES), the CPU 135A ends the sewing failure determination process and returns to the tension acquisition process.

The CPU 135A transmits the sewing defect information indicating the presence or absence of the sewing defect to the CPU 91 (S53). The sewing failure information in this example includes a thread break flag, a skipped stitch flag, and a thread tightening flag. The CPU 135A determines whether or not the instruction to execute the zero-point adjustment of the output voltage of the magnetic sensor 105 is received (S55). When the CPU 91 transmits the instruction to execute the zero point adjustment in S21 of the sewing process, the CPU 135A determines that the instruction to execute the zero point adjustment has been received (S55: YES). The CPU 135A executes the zero point adjustment by inputting an instruction to reset the reference voltage Vt (see FIG. 6) to the subtraction circuit 152 (S57). After the upper thread 6 is cut, the upper thread tension becomes substantially 0, so that the reference voltage Vt can be the output voltage of the magnetic sensor 105 when the upper thread tension is 0. When the instruction to execute the zero point adjustment is received, the sewing machine 1 has finished the sewing process. CPU135A transfers a process to S30.

When the instruction to execute the zero point adjustment has not been received (S55: NO), the CPU 135A determines whether or not the driving of the drive motor is stopped (S59). The determination is based on the variable tension acquired in S47, and it is determined that the drive motor is stopped when the needle thread tension hardly changes. When the CPU 135A determines that the drive motor has stopped driving (S59: YES), the process proceeds to S30. When the CPU 135A determines that the drive motor has not stopped driving (S59: NO), the CPU 135A increments N (S61), shifts the processing to S43, and repeats S43 and S45. For example, the CPU 135A stores the variable tension of the second cycle, the first upper thread tension, and the second upper thread tension in the RAM 135B after completing the acquisition of the variable tension of the second cycle (S45: YES) (S47). In this example, the sewing in the second cycle is included at the start of sewing, and the first upper thread tension and the second upper thread tension (not shown) in the second cycle are unlikely to have high values as shown in FIG. 7. By the same process, the CPU 135A stores the variable tension, the first upper thread tension, and the second upper thread tension in the third cycle in the RAM 135B after completing the acquisition of the variable tension in the third cycle (S45: YES). S47). In FIG. 7, the variable tension in the third cycle is indicated by reference numeral 203. The CPU 135A executes the sewing failure determination processing (S51). Details of the sewing failure determination process after S101 will be described later. The CPU 135A obtains the variable tension, the first upper thread tension, and the second upper thread tension after the fourth cycle by repeating the above processing (S47). In FIG. 7, the variable tension in the fourth cycle is indicated by reference numeral 204.

The details of the sewing failure determination processing after S101 will be described with reference to FIGS. 14 and 17 to 22. When it is not the start of sewing (S100: NO), the CPU 135A acquires the upper shaft rotation speed (S101). The CPU 135A acquires the time from the start of sewing of the Nth cycle to the end of sewing based on the elapsed time of the Nth cycle stored in the RAM 135B. The angle at which the upper shaft 15 rotates in the sewing period of the Nth cycle is predetermined. Therefore, the CPU 135A can acquire the upper shaft rotation speed by using the acquired time and the predetermined relational expression. The CPU 135A determines whether the upper shaft rotation speed acquired in S101 is equal to or lower than the second speed (S103). The second speed is a preset speed and is stored in the storage device 135C. The second speed in this example is slower than the first speed. When the upper shaft rotation speed is equal to or lower than the second speed (S103: YES), the CPU 135A ends the sewing failure determination process.

When the upper shaft rotation speed is higher than the second speed (S103: NO), the CPU 135A determines whether the rotation of the upper shaft 15 is accelerated or decelerated (S105). The CPU 135A acquires the respective upper shaft rotation speeds in the N-1th cycle sewing and the Nth cycle sewing by the same method as in S101. Acceleration/deceleration can be considered to occur when the difference between the upper shaft rotation speeds exceeds a predetermined range, and acceleration/deceleration occurs when the difference between the upper shaft rotation speeds falls below the predetermined range. It can be considered not. When the CPU 135A determines that the upper shaft rotation speed is accelerated or decelerated (S105: YES), the CPU 135A changes the thread tightening defect identification threshold according to the acceleration or deceleration of the rotation of the upper shaft 15 (S121). The CPU 135A specifies the acceleration of rotation of the upper shaft 15 based on the respective upper shaft rotation speeds in the N-1th cycle sewing and the Nth cycle sewing. The CPU 135A changes the thread tightening defect identification threshold so that the thread tightening defect identification threshold becomes smaller as the acceleration of the upper shaft 15 increases (S121). When the upper shaft 15 decelerates, the CPU 135A increases the thread tightening failure identification threshold value (S121). The thread tightening failure identification threshold value at that time is a positive value.

When acceleration/deceleration does not occur in the rotation of the upper shaft 15 (S105: NO), the CPU 135A determines the first yarn breakage threshold value and the second yarn breakage stored in the storage device 135C according to the upper shaft rotation speed acquired in S101. The threshold, the first skip threshold, and the second skip threshold are changed (S109). For example, the CPU 135A multiplies each of the first yarn breakage threshold value, the second yarn breakage threshold value, the first stitch skipping threshold value, and the second stitch skipping threshold value by a positive coefficient having a proportional relationship with the upper shaft rotation speed. That is, as the upper shaft rotation speed increases, the first yarn breakage threshold value, the second yarn breakage threshold value, the first stitch skipping threshold value, and the second stitch skipping threshold value are increased (S109).

The CPU 135A executes the thread tightening defect determination processing (S111). The CPU 135A refers to the RAM 135B to determine when the second upper thread tension of the N-1 cycle is generated (that is, when the second upper thread tension of the reference upper thread tension is generated) and the second upper thread tension of the Nth cycle. The timing of occurrence of is acquired (S124). The CPU 135A determines that the difference between the Nth cycle second upper thread tension generation timing acquired in S124 and the N-1th cycle second upper thread tension generation timing acquired in S124 is greater than or equal to the thread tightening failure identification threshold value. Or not (S125). The thread tightening defect identification threshold value at that time is the thread tightening defect identification threshold value changed in S121. When the difference between the occurrence timing of the second upper thread tension in the Nth cycle and the occurrence timing of the second upper thread tension in the N-1th cycle is less than the thread tightening failure specific threshold value (S125: NO), the CPU 135A causes the thread It is determined that the tightness failure has not occurred, and the thread tightness determination processing is ended. When the difference between the occurrence timing of the second upper thread tension in the Nth cycle and the occurrence timing of the second upper thread tension in the (N-1)th cycle is equal to or higher than the thread tightening failure specific threshold value (S125: YES), the CPU 135A When it is determined that the tightening failure has occurred, the thread tightening flag is changed to 1 (S127), the thread tightening failure determination processing ends, and the processing returns to the sewing failure determination processing.

The CPU 135A executes a specific yarn breakage determination process (S113). The CPU 135A determines whether the first upper thread tension difference is equal to or larger than the first thread breakage specific threshold value (S131). The CPU 135A acquires the first upper thread tension difference by acquiring the N-1th cycle first upper thread tension and the Nth cycle first upper thread tension stored in the RAM 135B. When the first upper thread tension difference is less than the first thread breakage specific threshold value (S131: NO), the CPU 135A determines that no thread breakage has occurred during the Nth cycle of sewing, and ends the specific thread breakage determination process. When the first upper thread tension difference is greater than or equal to the first thread break specific threshold value (S131: YES), the CPU 135A determines whether the second upper thread tension difference is greater than or equal to the second thread break specific threshold value (S133). The CPU 135A acquires the second upper thread tension difference by acquiring the N-1th cycle second upper thread tension and the Nth cycle second upper thread tension stored in the RAM 135B. When the second upper thread tension difference is less than the second thread breakage specific threshold value (S133: NO), the CPU 135A determines that no thread breakage has occurred during the Nth cycle of sewing, and ends the specific thread breakage determination process. When the second needle thread tension difference is equal to or greater than the second thread breakage specific threshold value (S133: YES), the CPU 135A determines that the thread breakage has occurred during the Nth cycle of sewing. The CPU 135A changes the thread breakage flag to 1 (S137), ends the specific thread breakage determination processing, and returns to the sewing failure determination processing.

The CPU 135A executes a specific stitch skipping determination process (S115). The CPU 135A determines whether the first needle thread tension difference is equal to or larger than the first stitch skipping specific threshold value (S141). The method for obtaining the first needle thread tension difference is the same as in S131. When the first needle thread tension difference is less than the first stitch skip identification threshold value (S141: NO), the CPU 135A determines that no stitch skip has occurred during the Nth cycle of sewing, and ends the specific stitch skip determination process. When the first needle thread tension difference is greater than or equal to the first stitch skipping specific threshold value (S141: YES), the CPU 135A determines whether the second needle thread tension difference is less than or equal to the second stitch skipping specific threshold value (S143). .. The method for acquiring the second needle thread tension difference is the same as in S133. When the second needle thread tension difference is larger than the second stitch skipping specific threshold (S143: NO), the CPU 135A determines that no stitch skipping has occurred during the Nth cycle of sewing, and ends the specific stitch skipping determination process. .. When the second needle thread tension difference is less than or equal to the second stitch skipping specific threshold (S143: YES), the CPU 135A determines that stitch skipping has occurred during the Nth cycle of sewing. The CPU 135A changes the stitch skip flag to 1 (S147), ends the specific stitch skip determination process, and returns to the sewing failure determination process.

Even when thread breakage occurs, the first needle thread tension difference may be equal to or greater than the first stitch skipping specific threshold (S141: YES). However, at that time, the second needle thread tension difference becomes larger than the second stitch skipping specific threshold value (S143: NO). Therefore, the sewing machine 1 can prevent the CPU 135A from erroneously determining that a stitch skip has occurred despite the fact that a thread break has actually occurred.

The CPU 135A executes a thread breakage determination process (S117). The CPU 135A determines whether or not the thread breakage flag is 1 (S151). When the thread breakage flag is 1 (S151: YES), the CPU 135A ends the thread breakage determination process. When the thread breakage flag is 0 (S151: NO), the CPU 135A determines whether or not the Nth cycle first upper thread tension stored in the RAM 135B is less than or equal to the first thread breakage threshold value (S153). The first yarn breakage threshold value referred to in S153 is the first yarn breakage threshold value changed in S109. When the first upper thread tension is higher than the first thread breakage threshold value (S153: NO), the CPU 135A determines that thread breakage has not occurred in the Nth cycle, and ends the thread breakage determination process. When the first upper thread tension is less than or equal to the first thread breakage threshold value (S153: YES), the CPU 135A determines whether the second upper thread tension of the Nth cycle stored in the RAM 135B is less than or equal to the second thread breakage threshold value. Yes (S155). The second yarn breakage threshold value referred to in S155 is the second yarn breakage threshold value changed in S109. When the second upper thread tension is larger than the second thread breakage threshold value (S155: NO), the CPU 135A determines that thread breakage has not occurred in the Nth cycle, and ends the thread breakage determination process. When the second upper thread tension is less than or equal to the second thread breakage threshold value (S155: YES), the CPU 135A determines that thread breakage has occurred in the Nth cycle, changes the thread breakage flag to 1 (S159), and judges the thread breakage. The process is terminated and the process returns to the sewing failure determination process.

The CPU 135A executes a skipped stitch determination process (S119). The CPU 135A determines whether the skipped flag is 1 (S161). When the stitch skip flag is 1 (S161: YES), the CPU 135A ends the stitch skip determination process. When the stitch skip flag is 0 (S161: NO), the CPU 135A determines whether the first needle thread tension at the Nth cycle stored in the RAM 135B is equal to or less than the first stitch skip threshold (S163). The first skip threshold value referred to in S163 is the first skip threshold value changed in S109. When the first needle thread tension is larger than the first stitch skip threshold value (S163: NO), the CPU 135A determines that the stitch skip has not occurred in the Nth cycle, and ends the stitch skip determination process. When the first needle thread tension is equal to or lower than the first stitch skip threshold value (S163: YES), the CPU 135A determines whether the second cycle of the second needle thread tension of the Nth cycle stored in the RAM 135B is equal to or higher than the second stitch skip threshold value. Yes (S165). The second skip threshold value referred to in S163 is the second skip threshold value changed in S109. When the second needle thread tension is smaller than the second stitch skip threshold value (S165: NO), the CPU 135A determines that the stitch skip has not occurred in the Nth cycle, and ends the stitch skip determination process. When the second needle thread tension is equal to or higher than the second stitch skip threshold (S165: YES), the CPU 135A determines that the stitch skip has occurred in the Nth cycle, and changes the stitch skip flag to 1 (S169). The stitch skipping determination processing is ended, and the processing returns to the sewing failure determination processing.

Even when thread breakage occurs, the first upper thread tension may be less than or equal to the first stitch skip threshold value (S163: YES). However, at that time, the second needle thread tension becomes smaller than the second stitch skip threshold value (S165: NO). Therefore, the sewing machine 1 can prevent the CPU 135A from erroneously determining that thread breakage has occurred, even though skipping has actually occurred.

The CPU 135A executes a threshold initialization process (S120). The CPU 135A stores the first yarn breakage threshold value, the second yarn breakage threshold value, the first stitch skipping threshold value, the second stitch skipping threshold value, the thread tightening defect identification threshold value, the first yarn breakage identification threshold value, and the second yarn breakage value stored in the storage device 135C. The specific threshold, the first skip jump specific threshold, and the second skip jump specific threshold are returned to the initial values. The CPU 135A ends the sewing failure determination process and returns to the tension acquisition process.

As shown in FIG. 16, the CPU 135A transmits the sewing defect information (S53). As shown in FIG. 14, when the CPU 91 determines that a sewing failure has occurred (S17: YES), the CPU 91 identifies the sewing failure that has occurred (S23). For example, the CPU 91 specifies the flag that is 1 out of the thread breakage flag, the stitch skipping flag, and the thread tightening flag to specify the sewing failure that has occurred. The CPU 91 notifies the specified sewing failure (S24). For example, the CPU 91 displays the identified defective sewing on the display unit 25. The CPU 91 determines whether to stop driving the drive motor (S25). The CPU 91 determines to stop driving the drive motor when the specified sewing failure is thread breakage or stitch skipping. When it is determined to stop driving the drive motor (S25: YES), the CPU 91 stops driving the drive motor (S26), and the process proceeds to S220. When it is determined that the drive motor will not be stopped (S25: NO), the CPU 91 shifts the processing to S18. In the present embodiment, the drive motor does not stop even if the thread tightening failure occurs (S17: YES) (S25: NO). The operator may depress the pedal 38 (S18: NO) or depress the pedal 38 (S18: YES) after confirming the occurrence of the thread tightening failure on the display unit 25.

When the CPU 91 determines that a sewing failure has occurred at the end of sewing and before M reaches the predetermined period (S74: YES), the sewing failure that has occurred is identified (S75), and the identified sewing failure is notified ( S76). The CPU 91 determines whether to stop driving the drive motor (S77). When the CPU 91 determines to stop driving the drive motor (S77: YES), it stops driving the drive motor (S78) and shifts the processing to S220. When the CPU 91 determines not to stop driving the drive motor (S77: NO), the process proceeds to S19. The processing of S75 to S78 is the same as the processing of S23 to S26. Similarly to the above, even if the thread tightening failure occurs (S74: YES), the drive motor does not stop (S77: NO). At this time, the CPU 91 may continue the process until M reaches a predetermined cycle.

As described above, the CPU 135A acquires the variable tension based on the detection result of the magnetic sensor 105 of the yarn tension detecting mechanism 130 (S47). The CPU 135A executes a thread tightening defect determination processing (S111), a specific thread breakage determination processing (S113), and a specific stitch skipping determination processing (S115). In this process, the presence or absence of a sewing failure is determined by comparing the Nth cycle upper thread tension with the N-1th cycle upper thread tension, which is the reference upper thread tension. More specifically, the CPU 135A sets the variable tension of the Nth cycle and the variable tension of the N−1th cycle, which is the reference upper thread tension, acquired in S47, to the thread tightening failure identification threshold value, the first thread breakage identification threshold value, By using the second yarn breakage identification threshold value, the first stitch skip identification threshold value, and the second stitch skip identification threshold value, it is determined whether or not a sewing failure has occurred. The thread tightening failure specific threshold is a threshold value set in advance corresponding to thread tightening failure, the first thread tightening failure specific threshold value and the second thread breakage specific threshold value are preset threshold values corresponding to thread breakage, and The stitch skipping specific threshold value and the second stitch skipping specific threshold value are preset threshold values corresponding to the stitch skipping. The CPU 135A determines whether or not there is a sewing failure by using these specific threshold values. Therefore, the sewing machine 1 can identify a specific sewing failure. Therefore, the sewing machine 1 can identify the sewing failure based on the change in the needle thread tension.

The CPU 135A acquires the first upper thread tension and the second upper thread tension based on the third upper thread tension (S47). The third upper thread tension is smaller than the first upper thread tension and the second upper thread tension, and tends to be zero. The first and second upper thread tensions based on the third upper thread tension tend to be large. Therefore, the sewing machine 1 can acquire the first upper thread tension and the second upper thread tension with high accuracy.

When thread breakage occurs, the first upper thread tension becomes less than or equal to the first thread break threshold and the second upper thread tension becomes less than or equal to the second thread break threshold. In the thread breakage determination process (S117), the first upper thread tension in the Nth cycle is less than or equal to the first thread breakage threshold (S153: YES), and the second upper thread tension in the Nth cycle is less than or equal to the second thread breakage threshold. If (YES in S155), the CPU 135A determines that a thread break has occurred and changes the thread break flag to 1 (S159). Since the CPU 135A can determine whether thread breakage has occurred, the sewing machine 1 can identify thread breakage as a sewing failure.

When the skipping occurs, the first needle thread tension becomes equal to or lower than the first stitch skipping threshold, and the second needle thread tension becomes equal to or higher than the second stitch skipping threshold. In the stitch skipping determination process (S119), the first upper thread tension in the Nth cycle is less than or equal to the first stitch skipping threshold (S163: YES), and the second upper thread tension in the Nth cycle is less than or equal to the second stitch skipping threshold. If YES (S165: YES), the CPU 135A determines that the stitch skip has occurred and changes the stitch skip flag to 1 (S169). Since the CPU 135A can determine the presence or absence of skipped stitches, the sewing machine 1 can identify skipped stitches as defective sewing.

When the thread tightening failure occurs, the amount of consumption of the upper thread 6 increases, so that the timing of generation of the second upper thread tension becomes earlier. In the thread tightening defect determination processing (S111), when the second upper thread tension occurrence time of the Nth cycle is earlier than the thread tightening failure specific threshold value with respect to the N-1th cycle second needle thread tension occurrence time. (S125: YES), the CPU 135A determines that the thread tightening defect has occurred, and changes the thread tightening flag to 1 (S127). Since the CPU 135A can determine whether or not the thread tightening failure has occurred, the sewing machine 1 can identify the thread tightening failure as the sewing failure.

When the sewing speed by the sewing machine 1 is low, the consumption amount of the upper thread 6 is low, so that the first upper thread tension and the second upper thread tension are low. When the upper shaft rotation speed acquired in S15 is equal to or lower than the first speed (S81: YES), the CPU 91 controls the thread tension motor 16 to rotate the thread tension disc 69 in the winding direction to wind the upper thread 6. (S83). Therefore, the looseness of the upper thread 6 is unlikely to occur. Therefore, the sewing machine 1 can easily generate the first upper thread tension and the second upper thread tension.

When the rotating speed of the upper shaft changes due to the acceleration and deceleration of the rotating upper shaft 15 (S105: YES), the CPU 135A changes the thread tightening failure identification threshold value according to the acceleration of the upper shaft 15 (S121). The changed thread tightening defect identification threshold is used in S125. When the upper shaft rotation speed changes, the upper thread tension changes according to the acceleration, and the upper thread tension changes when sewing failure occurs. More specifically, if the upper shaft 15 is accelerated when the thread tightening failure occurs, the second upper thread tension is generated when the second upper thread tension is generated when the upper shaft 15 is rotated at a lower speed. Will also be late. Even at this time, the CPU 135A changes the thread tightening defect identification threshold according to the change in the upper shaft rotation speed, so that the sewing machine 1 can properly detect the thread tightening defect.

When the upper shaft rotation speed changes, the needle thread tension changes, and the needle thread tension also changes when a sewing failure occurs. Specifically, when the upper shaft 15 rotates at a relatively low speed, the fluctuating tension becomes small, and when the sewing failure occurs, the needle thread tension also becomes small, and when the upper shaft 15 rotates at a relatively high speed, it fluctuates. The tension increases, and the needle thread tension also increases when a sewing failure occurs. Even when the needle thread tension changes when a sewing failure occurs, the CPU 135A changes the threshold value according to the upper shaft rotation speed acquired in S100 (S109), so that the CPU 135A can properly detect the sewing failure.

In the sewing failure determination process, the CPU 135A executes S111 to S120 after the start of sewing (S100: NO). At the start of sewing, the upper thread 6 is easily loosened. That is, it is difficult for the first upper thread tension and the second upper thread tension to be proper values. Therefore, if the CPU 135A determines whether or not there is a sewing failure at the start of sewing, there is a possibility that it may be determined that a sewing failure has occurred even though no sewing failure has occurred. The CPU 135A does not determine whether there is a sewing failure at the start of sewing (S100: YES). Therefore, the sewing machine 1 can suppress erroneously determining that a sewing failure has occurred.

When the upper shaft rotation speed acquired in S101 is higher than the second speed (S103: NO), the CPU 135A executes S111 to S119 to determine whether there is a sewing failure. When the sewing speed by the sewing machine 1 is low, the first upper thread tension and the second upper thread tension are low, and it is difficult to properly generate the first upper thread tension and the second upper thread tension. Therefore, it is difficult for the sewing machine 1 to detect a sewing failure based on the needle thread tension. In the present embodiment, when the upper shaft rotation speed is equal to or lower than the second speed (S103: YES), the CPU 135A does not determine whether there is a sewing failure. Therefore, the sewing machine 1 can more properly determine the presence or absence of sewing failure.

Upon execution of thread trimming (S20), the CPU 135A which has received the zero point adjustment instruction (S22) from the CPU 91 executes zero point adjustment (S57). When the sewing operation is repeated, the temperature of the magnetic sensor 105 rises due to the repeated sliding of the needle thread 6 and the tension plate 50. The output voltage of the magnetic sensor 105 may change significantly with respect to the reference voltage Vt. Even at that time, when the needle thread tension is reduced with the execution of thread trimming and the output voltage of the magnetic sensor 105 is reduced, the CPU 135A executes the zero point adjustment (S57), and the sewing machine 1 causes the reference voltage of the magnetic sensor 105 to be adjusted. Reset Vt. Therefore, the sewing machine 1 can continuously and accurately obtain the needle thread tension based on the output voltage of the magnetic sensor 105. At the time of executing the zero point adjustment, the CPU 135A does not judge whether there is a sewing failure. Therefore, the sewing machine 1 can suppress erroneously determining that a sewing failure has occurred.

In the above description, the main thread tension device 60 is an example of the thread tension mechanism of the present invention. The tension plate 50 is an example of the movable member of the present invention. CPU91 which performs S13 and S21 is an example of a sewing control part of the present invention. CPU135A which performs S47 is an example of the tension acquisition part of the present invention. The CPU 135A that executes S51 is an example of the determination unit of the present invention. CPU135A which performs S117 is an example of the thread breakage judgment part of this invention. The CPU 135A that executes S119 is an example of the skipped stitch determination unit of the present invention. CPU135A which performs S111 is an example of the thread tightness judging part of the present invention. CPU91,135A which performs S15, S72, and S101 is an example of the speed acquisition part of this invention. CPU91 which performs S83 is an example of the thread tension control part of the present invention. The CPU 135A that executes S121 is an example of the acceleration correspondence changing unit of the present invention. The CPU 135A that executes S109 is an example of the speed correspondence changing unit of the present invention. CPU91 which performs S20 is an example of the thread trimming control part of the present invention. CPU135A which performs S57 is an example of the adjustment control part of this invention. The thread tightening failure identification threshold value, the first thread breakage identification threshold value, the second thread breakage identification threshold value, the first stitch skip identification threshold value, and the second stitch skip identification threshold value are examples of the particular threshold value of the present invention. The thread tightening failure identification threshold is an example of a first identification threshold. The first yarn breakage threshold value is an example of the first threshold value of the present invention. The second yarn breakage threshold value is an example of the second threshold value of the present invention. The first skip threshold is an example of the third threshold of the present invention. The second skip threshold is an example of the fourth threshold of the present invention.

The present invention is not limited to the above embodiment. The CPU 135A determines the first yarn breakage threshold value, the second yarn breakage threshold value, the first stitch skipping threshold value, the second stitch skipping threshold value, the first yarn breakage specific threshold value, and the second yarn breakage specific threshold value according to the acceleration of the upper shaft rotation speed. , The first skipping specific threshold and the second skipping specific threshold may be changed (S121). For example, when the upper shaft 15 is decelerating (S105: YES), the fluctuating tension tends to be small, so the CPU 135A sets the first yarn breakage threshold value, the second yarn breakage threshold value, the first stitch skipping threshold value, and the second stitch skipping threshold value. Even if it is changed so as to be smaller (S121) and the first yarn breakage specific threshold value, the second yarn breakage specific threshold value, the first stitch skipping specific threshold value, and the second stitch skipping specific threshold value are respectively increased. Good (S121).

In addition to the first threshold value, the second threshold value, and the third threshold value, the CPU 135A rotates the first yarn breakage specific threshold value, the second yarn breakage specific threshold value, the first stitch skipping specific threshold value, and the second stitch skipping specific threshold value with the upper axis rotation. The speed may be changed according to the speed (S109). In addition to the first specific threshold, the CPU 135A may change the first threshold, the second threshold, and the third threshold according to the rotational acceleration of the upper shaft 15 (S121).

When acceleration/deceleration of the upper shaft rotation speed is occurring (S105: YES), the CPU 135A replaces the thread tightening failure identification threshold value with the first thread breakage threshold value, the second thread breakage threshold value, the first stitch skipping threshold value, and the second skipping threshold value. The stitch skipping threshold, the first yarn breakage specifying threshold, the second yarn breakage specifying threshold, the first stitch skipping specifying threshold, and the second stitch skipping specifying threshold may be changed (S121). For example, when the upper shaft 15 is decelerating (S105: YES), the CPU 135A may lower the first yarn breakage threshold value. The start of sewing may be from the start of sewing to the first cycle of sewing or up to the third cycle of sewing. The predetermined number of stitches that defines the start of sewing may differ depending on poor sewing. For example, when determining the presence or absence of skipped stitches, the presence of skipped stitches is determined at the time of sewing from the third cycle onward, starting from the second cycle (S115, S119), and when determining the presence or absence of thread tightening, The sewing may be started up to the first cycle and the presence or absence of thread tightening may be determined at the time of sewing after the second cycle.

The CPU 135A may determine whether or not the fluctuating tension in the first cycle has been acquired based on the timing result of the timer 35 (S45). For example, the RAM 135B stores the time required to complete the acquisition of the fluctuating tension in the first cycle, and the CPU 135A determines from the time measurement result of the timer 35 whether or not the time has elapsed, thereby determining the first cycle. It may be determined whether or not the variable tension has been finished. The CPU 91 may output a signal of the needle up position or the needle down position to the CPU 135A based on the detection result of the encoder 27A as the needle bar 11 moves up and down. The needle up position is a position near the top dead center of the sewing needle 10. At this time, the CPU 135A may determine whether or not the sewing operation has started in the process of S35 based on the signal of the needle up position or the needle down position, or obtain the variable tension of the Nth cycle in the process of S45. It may be determined whether or not it has been finished, or the upper shaft rotation speed may be acquired in the process of S101.

In the above embodiment, when the worker depresses the pedal 38, the CPU 91 determines that the sewing operation is finished (S18: YES). The sewing machine may store the sewing data for N cycles in the storage device 94, finish the sewing operation after sewing the sewing data for N cycles. At this time, the processing of S19 and S71 to S78 may be omitted.

Instead of the predetermined rotation amount, the CPU 91 may rotate the thread tension disc 69 in the winding direction by a rotation amount according to the upper shaft rotation speed (S83). The magnetic sensor 105 may include a magnetic impedance element, a magnetoresistive effect element, or the like instead of the Hall element. Even at that time, the magnetic sensor 105 can detect a change in the magnetic flux density of the magnet 58.

1 Sewing machine 10 Sewing needle 11 Needle bar 15 Upper shaft 16 Thread tension motor 17 Thread trimming mechanism 23 Balance 50 Tension plate 58 Magnet 60 Main thread tension device 69 Thread tension disc 91, 135A CPU
105 magnetic sensor 130 thread tension detection mechanism

Claims (11)

A needle bar that can move up and down to attach a sewing needle,
A hook that catches the upper thread that is inserted through the sewing needle and entangles it with the lower thread,
A balance for pulling up the upper thread in which the hook is entangled with the lower thread,
A thread tension mechanism having a thread tension tray through which the upper thread passes on the upstream side of the balance in the supply path of the upper thread leading to the sewing needle, and applying tension to the upper thread;
A thread tension detecting mechanism for detecting the upper thread tension which is the tension of the upper thread,
A sewing control unit that controls the needle bar, the shuttle, and the balance to perform sewing on cloth,
A tension acquisition unit that acquires the upper thread tension that periodically changes with sewing by the sewing control unit based on the detection result of the thread tension detection mechanism,
A determination unit that determines whether or not a sewing failure that cannot form a normal stitch occurs during the sewing operation by the sewing control unit based on the needle thread tension acquired based on the tension acquisition unit,
The determination unit determines the upper thread tension that changes in the Nth cycle (N is a natural number) acquired based on the tension acquisition section and the reference upper thread tension that is the reference upper thread tension that changes in one cycle. By comparing, in a sewing machine including a specific sewing failure determination unit that determines whether or not the sewing failure has occurred,
The tension acquisition unit acquires the upper thread tension that repeats fluctuations in units of time for each cycle,
The specific sewing failure determination unit uses the plurality of specific threshold values that preset the needle thread tension that varies in the Nth cycle and the reference needle thread tension in correspondence with each of the plurality of sewing failures. A sewing machine characterized by determining whether or not the sewing failure has occurred by comparing. The tension acquisition unit includes a first period in which the first peak of the upper thread tension occurs and a second period in which the second peak of the upper thread tension occurs in the Nth cycle. Based on the third upper thread tension which is the upper thread tension between the two, the first upper thread tension which is the upper thread tension in the first period and the second upper thread which is the upper thread tension in the second period The sewing machine according to claim 1, wherein the tension is acquired. The poor sewing includes thread breakage in which the upper thread is cut during sewing,
The determination unit includes a yarn breakage determination unit that determines whether or not the yarn breakage has occurred,
The first period is a hook catching period in which the hook catches the upper thread,
The second period is a balance pull-up period in which the balance pulls up the upper thread,
The yarn breakage determination unit determines that the yarn breakage has occurred when the first upper thread tension is less than or equal to a first threshold value and the second upper thread tension is less than or equal to a second threshold value. The sewing machine according to claim 2, wherein The poor sewing includes stitch skipping that the hook catches the upper thread and fails during sewing.
The determination unit includes a stitch skipping determination unit that determines whether the stitch skipping has occurred,
The stitch skip determination unit determines that the stitch skip has occurred when the first upper thread tension is equal to or lower than a third threshold value and the second upper thread tension is equal to or higher than a fourth threshold value. The sewing machine according to claim 3, wherein The sewing failure includes thread tightening failure, which is a poor balance between the upper thread and the lower thread that form a stitch when the balance pulls up the upper thread,
The plurality of specific thresholds includes a first specific threshold,
The specific sewing failure determination unit determines that the timing of the second peak of the needle thread tension in the Nth cycle is equal to or greater than the first specific threshold with respect to the timing of the second peak of the reference needle thread tension. The sewing machine according to claim 4, further comprising a thread tightening failure determination unit that determines that the thread tightening failure has occurred at an early stage. An upper shaft for vertically moving the needle bar and the balance is provided,
The thread tension mechanism includes a thread tension motor that rotates the thread tension tray,
When sewing by the sewing control unit, a speed acquisition unit that acquires the rotation speed of the upper shaft,
A thread tension control section that drives the thread tension motor to rotate the thread tension tray in a winding direction for winding the upper thread when the rotation speed acquired by the speed acquisition section is equal to or lower than a first speed. The sewing machine according to claim 5, wherein: When a change occurs in the rotation speed based on the speed acquired by the speed acquisition unit, at least one of the plurality of specific thresholds, the first threshold, the second threshold, the third threshold, and the fourth threshold The sewing machine according to claim 6, further comprising an acceleration correspondence changing unit that changes a threshold value according to the acceleration of the rotation speed. Speed correspondence that changes at least one threshold value of the plurality of specific threshold values, the first threshold value, the second threshold value, the third threshold value, and the fourth threshold value according to the rotation speed acquired by the speed acquisition unit. The sewing machine according to claim 6, further comprising a changing unit. 9. The determination unit determines whether or not the sewing failure has occurred after the start of sewing, which is from the start of sewing to the sewing of a predetermined stitch by the sewing control unit. Sewing machine described in one. 10. When the rotational speed acquired by the speed acquisition unit is higher than a second speed, the determination unit determines whether or not the sewing failure has occurred, according to any one of claims 6 to 9. The listed sewing machine. A thread cutting mechanism for cutting the upper thread and the lower thread,
After sewing by the sewing control section, a thread cutting control section for controlling the thread cutting mechanism to cut the upper thread and the lower thread is provided.
The thread tension detection mechanism,
A movable member that comes into contact with the upper thread and moves according to the upper thread tension;
A magnet provided on the movable member,
A magnetic sensor that detects the magnetic flux density of the magnet and outputs a voltage according to the detection,
The tension acquisition unit acquires the needle thread tension based on the output voltage of the magnetic sensor,
The tension acquisition unit includes an adjustment control unit that executes zero point adjustment for resetting an output voltage that is a reference of the magnetic sensor when the thread cutting control unit cuts the upper thread and the lower thread. The sewing machine according to any one of claims 1 to 10.

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