CN111485337A - Sewing machine - Google Patents

Abstract

The invention relates to a sewing machine capable of identifying poor sewing based on the change of the surface thread tension. The sewing machine executes a sewing failure determination process in which it is determined whether a sewing failure in which a normal stitch is not formed in a sewing operation occurs based on a tension of a face thread, that is, a face thread tension. The face line tension is repeatedly varied in a cycle in which a unit is set as a time. The sewing failure judgment processing comprises the steps of taking-up failure judgment processing, specific broken thread judgment processing and specific stitch skipping judgment processing. In this processing, the thread take-up failure specific threshold, the first thread breakage specific threshold, the second thread breakage specific threshold, the first skip stitch specific threshold, and the second specific skip stitch threshold, which are preset in advance in correspondence with each sewing failure, are used to compare the thread tension varying in the nth cycle and the thread tension varying in the N-1 th cycle, and determine whether each sewing failure has occurred.

Description

Sewing machine

Technical Field

The present invention relates to a sewing machine.

Background

A sewing machine capable of determining whether a sewing failure has occurred is known. The sewing machine disclosed in japanese patent No. 2821048 has an increment detector and a tension measuring device. The incremental detector outputs a pulse signal corresponding to the rotation of the upper shaft. The tension measuring device outputs a signal indicating a change in the tension of the face line with time. The sewing machine acquires a thread tension function based on respective detection results of the increment detector and the tension measuring device. The line tension function represents the line tension depending on the upper axis angle. The sewing machine obtains a difference (referred to as a tension difference) between a thread tension function in each rotation cycle of the upper shaft and a thread tension function in a previous rotation cycle. When the obtained tension difference is larger than a predetermined value, the sewing machine judges that poor sewing occurs.

The sewing failure includes a sewing failure in which the sewing operation is preferably stopped immediately after the occurrence of the sewing failure and a sewing failure in which the sewing operation may not be stopped immediately after the occurrence of the sewing failure. In the sewing machine, the obtained tension difference does not correspond to a plurality of specific sewing defects. Therefore, the sewing machine cannot recognize a plurality of sewing failures and sometimes cannot determine whether or not the sewing operation should be stopped immediately after the sewing failure occurs.

Disclosure of Invention

The invention aims to provide a sewing machine capable of identifying poor sewing based on the change of the tension of upper thread.

The sewing machine of claim 1 comprises: a needle bar to which a needle is fitted, the needle bar being capable of moving up and down; a shuttle for catching the upper thread penetrating the needle and interlacing the upper thread with the lower thread; a thread take-up lever that takes up the upper thread interwoven with the lower thread by the shuttle; a thread take-up mechanism having a thread take-up reel through which the upper thread passes at a position upstream of the thread take-up lever on a feed path of the upper thread to the needle, the thread take-up reel applying tension to the upper thread; a thread tension detecting mechanism for detecting the tension of the upper thread, namely the tension of the upper thread; a sewing control part which controls the needle bar, the shuttle and the thread take-up lever to sew the cloth; a tension acquiring unit that acquires the upper thread tension that periodically varies with sewing by the sewing control unit based on a detection result of the thread tension detecting unit; and a determination unit that determines whether or not a sewing failure in which a normal stitch cannot be formed in a sewing operation performed by the sewing control unit has occurred by comparing the upper thread tension that varies in an nth (N is a natural number) cycle acquired by the tension acquisition unit with a reference upper thread tension that is a reference upper thread tension that varies in a cycle, the determination unit being characterized in that the tension acquisition unit acquires the upper thread tension for each cycle with respect to the upper thread tension that repeatedly varies in a cycle in which a unit is set as a time, and the determination unit determines whether or not the sewing failure has occurred by comparing the upper thread tension that varies in the nth cycle with the reference upper thread tension using a plurality of specific thresholds that are preset in advance in correspondence with a plurality of sewing failures, respectively.

The determination unit determines whether or not a sewing failure has occurred using a plurality of specific threshold values preset in correspondence with a plurality of sewing failures. Therefore, the sewing machine can identify the specific sewing failure and can identify the sewing failure based on the change of the surface thread tension.

In the sewing machine according to claim 2, the sewing failure may include a thread breakage in which the upper thread is broken during sewing, the determining unit may include a thread breakage determining unit that determines whether or not the thread breakage has occurred, the determining unit may be configured to determine that a period in which the upper thread tension first reaches a maximum value in a period of the nth cycle is a shuttle catching period in which the shuttle catches the upper thread, the period in which the upper thread tension second reaches a maximum value in a period of the nth cycle is a take-up lever lifting period in which the take-up lever lifts the upper thread, the tension acquiring unit may acquire a first surface thread tension that is the upper thread tension in the shuttle catching period in the period of the nth cycle and a second surface thread tension that is the upper thread tension in the take-up lever lifting period, and the thread breakage determining unit may be configured to acquire the first surface thread tension being equal to or less than a first threshold value and the second surface thread tension being equal to or less than a second threshold value, and judging that the wire breakage occurs. When the disconnection occurs, the first surface line tension is below a first threshold value, and the second surface line tension is below a second threshold value. The thread breakage judging section can judge whether or not thread breakage occurs, and therefore the sewing machine can recognize the thread breakage as a sewing failure.

In the sewing machine according to claim 3, the sewing failure may include a skip stitch in which the shuttle does not catch the upper thread during sewing, the determination unit may include a skip stitch determination unit configured to determine whether or not the skip stitch has occurred, and the skip stitch determination unit may determine that the skip stitch has occurred when the first surface thread tension is equal to or less than a third threshold value and the second surface thread tension is equal to or more than a fourth threshold value. When a stitch jump occurs, the first face line tension is below a third threshold value, and the second face line tension is above a fourth threshold value. The skip stitch determination unit can determine whether or not a skip stitch has occurred, and therefore the sewing machine can recognize the skip stitch as a sewing failure.

Also, in technical scheme 4's sewing machine, make up badly including the take-up lever is mentioned form the stitch during the facial suture with the equilibrium of bottom line is bad to receive the line promptly, a plurality of specific threshold values include first specific threshold value, the judgement portion has receives the line and badly judges the portion, should receive the line and badly judges the portion and be in the N cycle facial suture tension reaches very big production opportunity for the second time of benchmark facial suture tension reaches very big production opportunity early when first specific threshold value is more than, judge as having taken place receive the line badly. When poor take-up occurs, the generation time of the tension of the second surface line becomes early. The poor take-up judging part can judge whether the poor take-up occurs, so that the sewing machine can identify the poor take-up as the poor sewing.

The sewing machine according to claim 5 may further include an upper shaft that rotates the needle bar and the thread take-up lever to move up and down, wherein the thread take-up mechanism includes a thread take-up motor that rotates the thread take-up spool, and the sewing machine includes: a speed acquisition unit that acquires the rotational speed of the upper shaft when the sewing control unit performs sewing; and a thread tension control unit that drives the thread tension motor to rotate the thread tension disk in a direction opposite to a direction in which the upper thread is supplied along the supply path, when the rotation speed acquired by the speed acquisition unit is equal to or lower than a first speed. When the sewing speed of the sewing machine is slow, the tension of the first surface thread and the tension of the second surface thread are low. When the rotation speed of the upper shaft is less than or equal to the first speed, the thread tension control unit rotates the thread tension disc in a direction opposite to the direction of supplying the upper thread, so that the upper thread is less likely to be loosened. Therefore, the sewing machine can easily generate the first surface thread tension and the second surface thread tension.

The sewing machine according to claim 6 may further include an acceleration correspondence change unit that changes at least one of the plurality of specific thresholds, the first threshold, the second threshold, the third threshold, and the fourth threshold in accordance with an acceleration of the rotational speed when the rotational speed acquired by the speed acquisition unit changes. When the rotation speed of the upper shaft changes, the upper thread tension changes according to the acceleration, and the upper thread tension changes when sewing failure occurs. At this time, the acceleration-corresponding changing unit changes the threshold value according to the change in the rotational speed of the upper shaft, and therefore the sewing machine can appropriately detect a sewing failure.

The sewing machine according to claim 7 may further include a speed correspondence changing unit that changes at least one of the plurality of specific thresholds, the first threshold, the second threshold, the third threshold, and the fourth threshold in accordance with the rotational speed acquired by the speed acquiring unit. The upper thread tension changes according to the rotation speed of the upper shaft, and the upper thread tension changes when sewing failure occurs. At this time, the speed-corresponding changing unit changes the threshold value in accordance with the rotation speed of the upper shaft, and therefore the sewing machine can appropriately detect a sewing failure.

In the sewing machine according to claim 8, the determination unit may determine whether the sewing failure has occurred after an initial sewing stage from the start of the sewing by the sewing control unit to the sewing of a predetermined number of stitches. At the initial stage of sewing, the tension of the first surface thread and the tension of the second surface thread are lower. Therefore, when the judging section judges that the sewing failure has occurred in the initial stage of the sewing, the judging section may judge that the sewing failure has occurred even when the sewing failure has not occurred. The judging part does not judge whether the sewing is bad in the initial sewing stage. Therefore, the sewing machine can prevent the wrong judgment that the sewing failure occurs.

In the sewing machine according to claim 9, the determination unit may determine whether the sewing failure has occurred when the rotational speed acquired by the speed acquisition unit is higher than a second speed. When the sewing speed of the sewing machine is slow, the first surface thread tension and the second surface thread tension are low, and the sewing machine is difficult to detect poor sewing based on the surface thread tension. The sewing failure determination unit does not determine that there is a seamless failure when the rotational speed of the upper shaft is equal to or less than the second speed. Therefore, the sewing machine can more appropriately determine the presence of the seamless failure.

The sewing machine according to claim 10 may further include: a thread cutting mechanism for cutting the upper thread and the lower thread; and a thread cutting control unit that controls the thread cutting mechanism to cut the upper thread and the lower thread after the sewing by the sewing control unit, wherein the thread tension detection mechanism includes: a movable member which is in contact with the upper thread and moves in accordance with tension of the upper thread; a magnet provided to the movable member; and a magnetic sensor that detects a magnetic flux density of the magnet and outputs a voltage according to a detection result, wherein the tension acquiring unit acquires the upper thread tension based on the output voltage of the magnetic sensor, and the tension acquiring unit includes an adjustment control unit that performs zero point adjustment for resetting the output voltage as a reference of the magnetic sensor when the upper thread and the lower thread are cut by the thread cutting control unit. When the sewing operation is repeated by the sewing control section, the output voltage of the magnetic sensor may fluctuate to a large extent with respect to the output voltage as a reference. When the output voltage of the magnetic sensor is lowered due to the lowering of the upper thread tension accompanying the cutting of the upper thread and the lower thread, the sewing machine executes zero point adjustment by the adjustment control unit, and resets the output voltage as the reference of the magnetic sensor. Therefore, the sewing machine can continuously obtain the upper thread tension with high precision based on the output voltage of the magnetic sensor.

Drawings

Fig. 1 is an overall perspective view of the sewing machine 1.

Fig. 2 is a partially enlarged view of the head 5.

Fig. 3 is a sectional view of the main wire gripper 60.

Fig. 4 is a perspective view of the wire tension detecting mechanism 130.

Fig. 5 is an electrical block diagram of the sewing machine 1.

Fig. 6 is a graph showing the output voltages of the magnetic sensor 105 and the amplifier circuit 151.

Fig. 7 is a graph showing a variable tension when the sewing operation is normally performed.

Fig. 8 is a graph showing a varying tension when a wire rewinding failure occurs.

Fig. 9 is a graph showing a varying tension when a stitch jump occurs.

Fig. 10 is a graph showing correlation coefficients when stitches are normally formed.

Fig. 11 is a graph showing correlation coefficients when a wire rewinding failure occurs.

Fig. 12 is a graph showing correlation coefficients when a stitch skip occurs.

Fig. 13 is a graph showing correlation coefficients when a disconnection occurs.

Fig. 14 is a flowchart of the sewing process.

Fig. 15 is a flowchart of the upper thread winding process.

Fig. 16 is a flowchart of the tension acquiring process.

Fig. 17 is a flowchart of the sewing failure determination process.

Fig. 18 is a flowchart of the wire rewinding failure determination process.

Fig. 19 is a flowchart of the specific disconnection determination process.

Fig. 20 is a flowchart of the specific skip judgment processing.

Fig. 21 is a flowchart of the disconnection determination process.

Fig. 22 is a flowchart of the skip stitch determination processing.

Detailed Description

A sewing machine 1 according to an embodiment of the present invention will be described. The following description uses the left and right, front and back, and up and down shown by arrows in the drawings.

Referring to fig. 1 and 2, the structure of the sewing machine 1 will be described. The sewing machine 1 has a base 2, a column 3, and an arm 4. The base unit 2 is fitted to an opening of the table and extends in the left-right direction. The housing part 2 is equipped with a needle plate 7 on the upper surface. The operator places the cloth on the bed 2 and the needle plate 7. The needle plate 7 has a needle receiving hole 8 and a feed dog hole 14. The pin receiving hole 8 has a circular shape in plan view. The feed sprocket 14 has a long diameter in the front-rear direction, and the feed sprocket 14 is located at the left, rear, right, and front of the needle accommodating hole 8, respectively. The column part 3 extends upward from the right end of the seat part 2. The arm portion 4 extends leftward from the upper end of the column portion 3 and faces the upper surface of the base portion 2. The arm portion 4 has an input portion 24 and a display portion 25 at a substantially central portion in the left-right direction of the front surface. The input section 24 is three input buttons. The operator operates the input unit 24 while looking at the display unit 25 to input various instructions. The arm part 4 has a thread passing rod (Japanese vertical rod) 20 protruding upward on the left side of the upper surface. The thread take-up lever 20 is penetrated by the upper thread 6 drawn out from the thread spool.

The arm portion 4 includes an upper shaft 15 and a main motor 27 (see fig. 5) therein. The upper shaft 15 extends in the left-right direction and is connected to an output shaft of the main motor 27 via an upper shaft pulley. 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 a left end portion. The head 5 protrudes downward from the arm 4 and faces the needle plate 7 from above. The head 5 supports the needle bar 11 so that the needle bar 11 can move up and down. The lower end of the needle bar 11 is fitted with a needle 10 and projects downward from the head 5. The needle bar 11 is connected to the upper shaft 15 by an up-and-down movement mechanism. The needle bar 11 is moved up and down by the up-down movement mechanism in accordance with the rotation of the upper shaft 15. The needle 10 moves up and down together with the needle bar 11 while holding the needle thread 6 passing through the needle eye. The needle 10 can be passed through the needle-receiving hole 8. The lower end of the movable range of the needle 10 is a bottom dead center, and the upper end of the movable range is a top dead center.

The base unit 2 includes therein 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 houses a bobbin around which a lower thread is wound. The shuttle has a tip, and can be rotated by power of the main motor 27, and catches the upper thread 6 passing through the eye of the needle 10 with the tip, and interweaves the upper thread 6 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 tangent line electromagnetic element 17A. The movable knife is moved relative to the fixed knife by driving the thread cutting solenoid 17A, and the thread cutting mechanism 17 cuts the surface thread 6 and the ground thread by cooperation of the movable knife and the fixed knife.

The cloth feeding mechanism includes upper and lower cloth feeding shafts, a cloth feeding table, cloth feeding teeth, a horizontal cloth feeding shaft, and a cloth feeding motor 123 (see fig. 5). The upper and lower cloth feed shafts extend in the right and left direction inside the machine base 2 and are connected to the upper shaft pulleys via belts. The cloth feeding table is arranged to be capable of swinging and is connected with the upper and lower cloth feeding shafts. When the up-down feed shaft is rotated by the driving force of the main motor 27, the feed table moves in the up-down direction. The cloth feeding teeth are supported on the cloth feeding table. The horizontal feed shaft extends in the left-right direction at a position forward of the upper and lower feed shafts, and connects the feed motor 123 and the feed table. When the horizontal cloth feeding shaft is rotated by the driving force of the cloth feeding motor 123, the cloth feeding table moves in the front-rear direction. The cloth feeding table swings as the main motor 27 and the cloth feeding motor 123 are driven, and the cloth feeding teeth protrude from or retreat into the cloth feeding sprocket holes 14.

As shown in fig. 2, the head 5 includes a sub thread gripper 26, a main thread gripper 60, a thread guide 21, a thread tension detection mechanism 130, a thread take-up lever 23, and a guide hook 29 in this order from the upstream side of the upper thread 6 supply path from the thread spool to the needle 10.

The sub-chuck 26 is provided at the upper right portion of the front surface of the head 5. The main gripper 60 is provided below the sub gripper 26 and is a front surface of the head 5. The sub-gripper 26 and the main gripper 60 respectively give tension to the upper thread 6. The sub-gripper 26 applies tension to the surface thread 6, which is required when the surface thread 6 and the lower thread are cut by the thread cutting mechanism 17. The main thread tension device 60 adjusts the tension applied to the upper thread 6 in accordance with the sewing operation of the sewing machine 1. The structure of the main wire gripper 60 will be described later. The wire guide 21 is provided on the left of the main wire gripper 60. The thread guide 21 folds back the upper thread 6 passing through the main thread gripper 60 toward the thread tension detecting mechanism 130 and the thread take-up lever 23. The wire tension detecting mechanism 130 is fixed to a recess 5A recessed rearward from the front surface of the head 5 by a screw 90, and is located at a vertical position between the sub wire gripper 26 and the main wire gripper 60. The thread tension detecting mechanism 130 can detect the tension acting on the upper thread 6. The thread take-up lever 23 is provided on the left side of the sub-gripper 26 and has a through hole 23A through which the upper thread 6 passes. The thread take-up lever 23 moves up and down in accordance with the driving of the main motor 27. The guide hook 29 is provided on the left of the wire tension detecting mechanism 130. The guide hook 29 guides the upper thread 6 passing through the through hole 23A of the thread take-up lever 23 toward the needle bar 11.

As shown in fig. 3, the main gripper 60 has a thread take-up drum 62, a thread take-up holder 63, a thread take-up spring 65, a thread take-up motor 16, and a thread take-up spool 69.

The wire clamping cylinder 62 is annular and is fixed to the inside of a through hole 5C formed in the front wall 5B of the head 5 by a fastening member. The wire holder 63 is annular and is fixed to the inside of the wire holding cylinder 62 by a screw 19. The thread take-up spring 65 is fixed on the outer side surface of the thread clamping seat 63 and is wound between the thread clamping seat 63 and the thread clamping barrel 62. One end portion of the thread take-up spring 65 is exposed from the front wall portion 5B. The sewing machine 1 can adjust the spring pressure of the thread take-up spring 65 by the rotation of the thread tension holder 63. The thread take-up motor 16 is fixed to the inside of the arm portion 4 by bolts. The output shaft 18 of the thread tension motor 16 protrudes forward of the front wall portion 5B through the center hole of the thread tension holder 63. The chuck plate 69 is fixed to the front end of the output shaft 18 by a screw 28. The upper thread 6 is wound around the thread take-up reel 69 by about one to two turns. The wire clamping disk 69 is rotated by the wire clamping motor 16. The thread tension motor 16 has an encoder 16A (see fig. 5). The encoder 16A detects the rotational position of the output shaft 18.

The clamp motor 16 is a pulse motor, and has an output shaft 18 and an encoder 16A (see fig. 5). The output shaft 18 is rotatable about an axis in the front-rear direction. The encoder 16A is provided inside the head 5. The encoder 16A has a code wheel fixed to a rear end portion 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 a chuck plate 69 on the right side of the arm portion 4. The sewing machine 1 can control the rotational angle phase of the output shaft 18.

The thread tension detecting mechanism 130 shown in fig. 4 is provided between the thread take-up reel 69 and the thread take-up lever 23 on the feed path of the upper thread 6. The thread tension detecting means 130 detects the front and rear positions of the plate 50 which is deflected in the front and rear direction in accordance with the upper thread tension based on the output voltage of the magnetic sensor 105, and detects the tension of the upper thread 6, that is, the upper thread tension.

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

The mount 140 has a mounting portion 42 and a pedestal portion 410. The mounting portion 42 and the pedestal portion 410 are integrally formed. The mounting portion 42 has an elongated hole 421 through which the screw 90 passes. The screw 90 inserted through the long hole 421 is fastened to a screw hole provided in the recess 5A (see fig. 2). Thus, the mount 140 is mounted to the head 5. The mount 410 is located to the left of the mount 140. The pedestal portion 410 has a right protrusion 410A and a left protrusion 410B. The right protrusion 410A and the left protrusion 410B are each rectangular parallelepiped-shaped extending in the front-rear direction.

The sensor holder 80 is a rectangular parallelepiped non-magnetic body, and is attached to the pedestal portion 410 between the right protrusion 410A and the left protrusion 410B. 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 located more to the rear side than the front ends of the right protrusion 410A and the left protrusion 410B.

The plate 50 has a thickness in the front-rear direction, and is bridged between 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 the screws 97 and 98. The guide member 160 sandwiches the right end portion of the plate 50 with the right protrusion 410A, and sandwiches the left end portion of the plate 50 with the left protrusion 410B. The left-right direction center portion of the plate 50 has a gap with the front surface of the sensor holder 80. Therefore, the plate 50 can be flexed in the front-rear direction with both ends in the left-right direction as fulcrums.

The magnet 58 is cylindrical with the front-rear direction as the axial direction, and is fixed to the rear surface of the left-right direction center portion of the plate 50 with an adhesive. Therefore, when the plate 50 is flexed in the front-rear direction, the magnet 58 moves forward and backward, 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 an FPC 136. The substrate 135 acquires the detection result of the magnetic sensor 105.

The guide member 160 has an upper guide groove 182 and a lower guide groove 172. The upper guide groove 182 and the lower guide groove 172 are vertically aligned with the plate 50 interposed therebetween, and are formed in a hook shape that opens in the vertical direction. The upper guide groove 182 has an upper holding hole 181, and the lower 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 penetrates the upper and lower holding holes 181 and 171. The upper thread 6 positioned between the upper holding hole 181 and the lower holding hole 171 is in contact with the front surface of the plate 50 from the front. The more the tension of the needle thread increases, the more the needle thread 6 applies a force to the plate 50 in the rearward direction. Therefore, the sewing machine 1 can acquire the upper thread tension based on the output voltage of the magnetic sensor 105.

An electrical structure of the sewing machine 1 is explained with reference to fig. 5. The control device 30 of the sewing machine 1 has a CPU 91. The CPU91 controls the operation of the sewing machine 1. The CPU91 is connected to a ROM92, a RAM93, a storage device 94, and an I/O interface (hereinafter referred to as I/O) 45. The ROM92 stores programs and the like for executing various processes such as a sewing process (see fig. 14) described later. The RAM93 temporarily stores various values. The storage device 94 is a non-volatile storage device.

The I/O45 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 cloth feed motor 123. The drive circuit 83 is connected to the clamp motor 16. The main motor 27, the cloth feeding motor 123, and the thread take-up motor 16 include an encoder 27A, an encoder 123A, and an encoder 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 rotation angle phase of the upper shaft 15, that is, the upper shaft phase. The encoder 123A detects the rotational position of the output shaft of the cloth feeding motor 123. The encoder 16A detects the rotational position of the output shaft 18 of the clamp motor 16. The CPU91 acquires the detection results of the encoders 27A, 123A, and 16A, and sends control signals to the drive circuits 81 to 83. Therefore, the CPU91 controls the driving of the main motor 27, the cloth feeding motor 123, and the thread take-up motor 16. Hereinafter, the main motor 27 and the cloth feeding motor 123 will be collectively referred to as a drive motor.

The I/O45 is connected to the drive circuit 84, drive circuit 85, input 24, and pedal 38. The drive circuit 84 is connected to the tangent electromagnetic element 17A. The driving circuit 85 is connected to the display unit 25. The CPU91 controls the tangent line solenoid 17A and the display unit 25 by sending control signals to the drive circuit 84 and the drive circuit 85. The input unit 24 outputs the input result input to the input unit 24 by the operator to the CPU 91. The pedal 38 outputs an operation direction and an operation amount of the pedal 38 operated by the operator to the CPU 91.

The I/O45 is connected to the CPU135A of the substrate 135. The substrate 135 has a CPU135A, a RAM135B, a storage device 135C, an amplifier circuit 151, a subtractor circuit 152, and a timer 35. The CPU135A is connected to the RAM135B, the amplifying circuit 151, the subtracting circuit 152, and the timer 35. The timer 35 outputs the count 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 the two graphs of fig. 6, the horizontal axis represents time, and the vertical axis represents voltage. The magnetic sensor 105 detects a change in the magnetic flux density of the magnet 58. The graph on the left side of fig. 6 shows the change in the output voltage of the magnetic sensor 105 with time. The magnetic sensor 105 outputs the output voltage to the subtraction circuit 152. The subtraction circuit 152 extracts a voltage in a range of Δ V with respect to the reference voltage Vt from the output voltage of the magnetic sensor 105, and outputs the extraction result to the amplification circuit 151. The reference voltage Vt is an output voltage of the magnetic sensor 105 when the face line tension is 0, and is an output voltage which is a reference of the magnetic sensor 105. The right graph of fig. 6 shows the change with time of the output voltage amplified by the amplification circuit 151 as a result of the extraction by the subtraction circuit 152. The amplifier circuit 151 outputs the amplified output voltage to the CPU 135A. The output result of the amplifier circuit 151 is referred to as a detection result of the magnetic sensor 105. The CPU135A can perform zero point adjustment (also referred to as offset adjustment) on the subtracting circuit 152. The zero point adjustment resets the reference voltage Vt of the magnetic sensor 105. The timing of execution of the zero point adjustment is preferably 0.

The storage device 135C stores the wire breakage flag, the needle skipping flag, and the wire collection failure flag. The broken wire mark, the jumping pin mark and the poor take-up mark are respectively switched to be 0 or 1. The defects of broken wire, jumping pin and winding wire are described later. The storage device 135C stores the first disconnection threshold value, the second disconnection threshold value, the first skip stitch threshold value, the second skip stitch threshold value, the poor wire take-up specific threshold value, the first disconnection specific threshold value, the second disconnection specific threshold value, the first skip stitch specific threshold value, and the second skip stitch specific threshold value. Each threshold value is a value for determining whether or not sewing failure described later has occurred. The storage device 135C stores initial values of the respective thresholds. In the sewing failure determination process (see fig. 17) described later, the CPU135A can change the threshold value stored in the storage device 135C according to the upper shaft rotation speed, which is the rotation speed of the upper shaft 15, or the rotation acceleration of the upper shaft 15. The threshold value stored in the storage device 135C will be described in detail later.

With reference to fig. 1 to 3, an outline of the operation of the sewing machine 1 will be described. The operator places the cloth on the needle plate 7. The upper shaft 15 moves the needle bar 11 and the thread take-up lever 23 up and down by driving of the driving motor, and the shuttle rotates. When the needle 10 is inserted into the fabric and then ascends after descending to the bottom dead center, the shuttle catches the endless upper thread 6 held by the eye of the needle 10 with the tip of the shuttle and weaves the upper thread 6 with the lower thread. The needle 10 is withdrawn upward from the fabric. At this time, the feed dog is driven by the feed motor 123 and the main motor 27 to project upward from the feed dog hole 14 and swing rearward. Therefore, the cloth moves rearward. The thread take-up lever 23 lifts the upper thread 6 interlaced with the lower thread by the shuttle, thereby forming a stitch on the fabric. The cloth is sewn by repeating the above operations by the upper shaft 15, the needle 10, the shuttle, the thread take-up lever 23, and the cloth feeding mechanism. One stitch is sewed into a cycle.

The sewing failure of the sewing machine 1 will be described. The sewing failure indicates that a normal stitch is not formed in the sewing operation. The sewing failure comprises poor winding, broken thread and stitch skipping. The poor take-up is poor balance between the upper thread 6 and the lower thread which form a stitch on the cloth when the upper thread 6 is lifted by the take-up lever 23. For example, when the face thread 6 is too strongly interwoven with the ground thread, the cloth near the stitch shrinks. The thread breakage is a defect that the upper thread 6 is broken during sewing and a stitch is not formed on the fabric. The skip stitch is a failure in catching the needle thread 6 by the shuttle in sewing and is a failure in forming a normal stitch on the cloth.

In a one-cycle sewing period of the sewing machine 1, there are a convergence period, a shuttle catching period, and a thread take-up lever lifting period in this order. The convergence is a timing at which the needle 10 rises from the bottom dead center and reaches the vicinity of the needle-lower position. The under-needle position is a height position where the shuttle captures the upper thread 6 with the shuttle tip. The shuttle catching period is a period in which the shuttle catches the upper thread 6 with the shuttle tip and the upper thread 6 passes through the shuttle. The thread take-up lever lifting period is a period from when the upper thread 6 is ejected from the shuttle to when the thread take-up lever 23 lifts the upper thread 6.

Fig. 7 is a graph in which the horizontal axis represents time and the vertical axis represents varying tension. The variable tension is the upper thread tension which repeatedly varies in a period in which the unit is set as time. In this example, the variable tension is a thread tension which is repeatedly varied with a sewing period of one cycle set as a unit cycle. That is, the variable tension is the upper thread tension which varies in the nth period (N is a natural number) from the start of sewing. Fig. 7 shows the variation tension of the third, fourth, and fifth cycles. As will be described later, the variable tension is less likely to be generated in the first and second cycles. The period of each cycle (the lateral dimension in fig. 7) is shorter as the upper shaft rotation speed is higher. In fig. 7, the periods of the third period, the fourth period, and the fifth period are different from each other.

The shuttle catching period and the thread take-up lever lifting period in the third cycle are T1 and T2, respectively. In the period of the Nth period, the catching period of the shuttle is the period when the tension of the upper thread reaches the maximum for the first time, and the lifting period of the thread take-up lever is the period when the tension of the upper thread reaches the maximum for the second time. Hereinafter, the maximum value of the upper thread tension during the catching period of the shuttle is referred to as a first surface thread tension, and the maximum value of the upper thread tension during the lifting period of the thread take-up lever is referred to as a second surface thread tension. The value obtained by subtracting the first surface line tension of the nth period from the first surface line tension of the nth-1 th period is referred to as a first surface line tension difference, and the value obtained by subtracting the second surface line tension of the nth period from the second surface line tension of the nth-1 th period is referred to as a second surface line tension difference.

Fig. 8 shows a variable tension in the case where the stitches are normally formed in the N-1 th cycle by a two-dot chain line, and shows a variable tension in the case where the take-up failure occurs in the N-1 th cycle by a solid line. When the thread take-up failure occurs, the difference between the timing of generating the second surface thread tension and the timing of generating the second surface thread tension under the reference surface thread tension is equal to or greater than a thread take-up failure specific threshold value described later. The reference face line tension is a variable tension as a reference in one cycle. When sewing is performed after the second cycle, the variable tension of the N-1 cycle is the reference surface thread tension with respect to the reference surface thread tension during the sewing of the N cycle. When the sewing of the first cycle is performed, the variable tension indicated by the reference data stored in the storage device 135C is the reference needle thread tension. The variable tension indicated by the reference data indicates a variable tension generated when the sewing of the first cycle is normally performed. As described later, since the fluctuating tension at the initial stage of sewing is normally small, the fluctuating tension indicated by the reference data is smaller than the fluctuating tension at the time of executing sewing after the third cycle. The wire rewinding failure specific threshold is a threshold for the CPU135A to determine whether or not a wire rewinding failure has occurred in the wire rewinding failure determination process (S111 in fig. 17).

When the thread breakage occurs, the upper thread tension is substantially 0 in one sewing cycle and does not fluctuate, but the above is not shown. Therefore, both the first face line tension and the second face line tension become extremely small as compared with the normal time. When a wire break occurs, the first surface wire tension is below a first wire break threshold value, and the second surface wire tension is below a second wire break threshold value. When the yarn breakage occurs, the first surface yarn tension difference is greater than or equal to a first yarn breakage specific threshold value, and the second surface yarn tension difference is greater than or equal to a second yarn breakage specific threshold value. The first disconnection threshold and the second disconnection threshold are thresholds for the CPU135A to determine whether or not a disconnection has occurred in the disconnection determination processing (S117 in fig. 17). The first disconnection specifying threshold and the second disconnection specifying threshold are thresholds for the CPU135A to determine whether or not a disconnection has occurred in the specific disconnection determination processing (S113 in fig. 17).

As shown in fig. 9, when the stitch skipping occurs, the first face line tension becomes extremely small as compared with the normal state, and the second face line tension is a value close to the normal state. Therefore, when the stitch skipping occurs, the first surface thread tension is equal to or less than the first stitch skipping threshold value, and the second surface thread tension is equal to or more than the second stitch skipping threshold value. When the stitch skipping occurs, the first face line tension difference is greater than or equal to a first stitch skipping specific threshold, and the second face line tension difference is less than or equal to a second stitch skipping specific threshold. The first stitch threshold and the second stitch threshold are thresholds for the CPU135A to determine whether or not a stitch has occurred in the stitch determination processing (S119 in fig. 17). The first skip stitch specific threshold value and the second skip stitch specific threshold value are threshold values for the CPU135A to determine whether or not a skip stitch has occurred in the specific skip stitch determination process (S115 in fig. 17).

The CPU135A acquires the variation tension in the cycle unit so as to acquire the first and second surface line tensions in the cycle unit. The CPU135A acquires the detection result of the magnetic sensor 105 in a tension acquisition process (see fig. 16) described later, continuously acquires the varying tension, and sequentially stores the varying tension in the RAM 135B. The CPU135A can acquire the fluctuating tension in units of one cycle by performing autocorrelation analysis on the fluctuating tensions sequentially stored in the RAM 135B. The autocorrelation analysis is a known analysis technique for finding the periodicity of data by obtaining a correlation coefficient indicating the degree of correlation between the data serving as a reference for comparison and other data. The correlation coefficient varies from-1 to 1, and the closer the absolute value of the correlation coefficient is to 1, the higher the degree of identity between the two data is. The CPU135A sets the reference face line tension as data as a comparison reference. The CPU135A stores the varying tension acquired in the cycle unit in the RAM 135B.

Fig. 10 to 13 show graphs in which the horizontal axis represents time (ms) and the vertical axis represents a correlation coefficient. Fig. 10 shows the correlation coefficient when the stitches are normally formed. The correlation coefficient between the fluctuation tension acquired by the CPU135A and the reference face line tension fluctuates with the lapse of time. In the vicinity of 25ms, the correlation coefficient is approximately 1, and reaches a maximum. Therefore, the CPU135A can determine that the fluctuating tension of one cycle has been acquired based on the fact that the correlation coefficient is substantially 1 and extremely large.

Fig. 11 shows the correlation coefficient when a take-up failure occurs, and fig. 12 shows the correlation coefficient when a stitch skipping occurs. In any case of a wire rewinding failure or a skip stitch, the correlation coefficient is substantially 1 and has a maximum value in the vicinity of 25 ms. Therefore, the CPU135A can determine that the varying tension of one cycle is obtained based on the same determination criteria as when the stitches are normally formed.

Fig. 13 shows correlation coefficients when a disconnection occurs. When a disconnection occurs, the correlation coefficient is not substantially 1 in the vicinity of 25ms, and the maximum value is not obtained. That is, at the timing when sewing is completed in one cycle, the correlation coefficient is not substantially 1, and does not become the maximum value. At this time, the CPU135A determines that the fluctuating tension of one cycle has been acquired based on the elapse of time corresponding to one cycle. The term "one cycle" means a period after adding a period of several ms to a one cycle period before the one cycle.

The sewing process will be described with reference to fig. 14 and 15. When the operator turns on the power of the sewing machine 1, the CPU91 reads out the program from the ROM92 and starts the sewing process.

The CPU91 determines whether the sewing machine 1 starts a sewing operation based on the detection result of the pedal 38 (S11). Before the operator depresses the pedal 38, the CPU91 determines that the sewing operation is not started (S11: no), and stands by. The operator places the cloth on the needle plate 7 while the CPU91 is on standby. When the operator depresses the pedal 38 (yes in S11), the CPU91 drives the needle thread tension motor 16 to set the needle thread tension to a predetermined needle thread tension (S12).

The CPU91 starts driving of the drive motor (S13) and starts a sewing operation for the cloth. At this time, the CPU91 overwrites the variable M stored in the RAM93 with 0. M is a count value for counting a predetermined period from when the CPU91 determines that the sewing operation is finished to when the upper thread 6 and the lower thread are cut, that is, the thread is cut. The predetermined period is stored in the storage device 94 in advance. The CPU91 drives the thread tension motor 16 to maintain a predetermined thread tension.

The CPU91 acquires the upper axis rotation speed based on the detection result of the encoder 27A (S15). The CPU91 calculates the difference by acquiring the detection results of the encoder 27A twice, and acquires the upper axis rotation speed.

The CPU91 performs the upper thread winding process (S16). The CPU91 determines whether the upper shaft rotation speed acquired in S15 is the first speed or less (S81). When the CPU91 judges that the upper shaft rotation speed is higher than the first speed (S81: NO), the upper thread winding process is ended, and the process returns to the sewing process. When the CPU91 determines that the upper shaft rotation speed is equal to or less than the first speed (yes in S81), the CPU 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 a direction opposite to the direction in which the upper thread 6 is fed along the feeding path by the thread take-up reel 69. The CPU91 rotates the wire chuck 69 by a predetermined rotation amount in the winding direction. Therefore, the sewing machine 1 can suppress the slackening of the upper thread 6. The CPU91 ends the needle thread winding process and returns to the sewing process.

The CPU91 determines whether a sewing failure has occurred (S17). The CPU91 determines whether a sewing failure has occurred based on the sewing failure information transmitted from the CPU135A in the tension acquisition process described later. When at least one of the thread breakage flag, the stitch skipping flag, and the thread take-up failure flag is 1, the CPU91 determines that a sewing failure has occurred (yes in S17), and shifts the process to S23. When all of the thread breakage flag, the stitch skipping flag, and the thread take-up failure flag are 0, the CPU91 determines that no sewing failure has occurred (S17: no). The CPU91 determines whether sewing is finished based on the detection result of the pedal 38 (S18). If the operator does not step back on the pedal 38, the CPU91 determines that sewing is not to be ended (S18: no), and the process proceeds to S15.

For example, when the operator steps back on the pedal 38, the CPU91 judges that the sewing operation is ended (S18: YES), and judges whether or not a predetermined cycle has been reached based on M stored in the RAM93 (S19). When the CPU91 determines that it is less than the predetermined period (S19: no), 1 is added to M (S71), and the process proceeds to S72. The CPU91 acquires the upper axis rotation speed based on the detection result of the encoder 27A (S72), and executes the upper thread winding process (S73). The processing of S72, S73 is the same as the processing of S15, S16. The CPU91 determines whether a sewing failure has occurred (S74). When the CPU91 determines that a sewing failure has occurred (S74: yes), the process proceeds to S75. If the CPU91 determines that a sewing failure has not occurred (S74: no), the process proceeds to S19. The CPU91, upon determining that the predetermined cycle has not been reached, repeats the processing (S19: no, S71, S72, S73, S74).

When the CPU91 judges that the predetermined cycle is reached (S19: YES), it controls the thread cutting solenoid 17A to cut thread (S20). After cutting the face line 6, the face line tension is substantially 0. The CPU91 stops driving of the drive motor (S21).

The CPU91 transmits an instruction to execute zero point adjustment of the output voltage of the magnetic sensor 105 to the CPU135A (S22). The CPU91 shifts the process to S220.

The CPU91 judges whether or not there is an operation to cut off the power supply of the sewing machine 1 (S220). When the CPU91 determines that the operation for turning off the power of the sewing machine 1 has not been performed (S220: no), the process proceeds to S11. When the operator places an unsewn cloth on the needle plate 7 instead of the sewn cloth and depresses the pedal 38 (S11: yes), the CPU91 performs the processing after S12. When the CPU91 judges that the operation for cutting off the power supply of the sewing machine 1 is available (S220: Yes), the sewing process is ended.

The tension acquisition process will be described with reference to fig. 16 to 22. The tension acquiring process is executed by the CPU135A in parallel with the sewing process. The CPU135A determines the presence or absence of a sewing failure based on the acquired needle thread tension by the tension acquisition processing. When the operator turns on the power of the sewing machine 1, the CPU135A starts the tension acquisition process.

The CPU135A executes initialization processing (S30). The CPU135A sets the disconnection flag, the skip stitch flag, and the wire rewinding failure flag stored in the storage device 135C to 0, respectively. The CPU135A initializes the timer 35 to 0. The CPU135A overwrites the variable N stored in the RAM135B with 1 (S31). The CPU135A 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, an output voltage at t1 in the right graph of fig. 6. The CPU135A acquires the face line tension based on the output voltage of the magnetic sensor 105 and a predetermined relational expression. The CPU135A sequentially stores the acquired upper thread tension in the RAM135B as a varying tension.

The CPU135A determines whether the sewing operation of the sewing machine 1 has been started (S35). This determination is made by autocorrelation analysis in which the upper thread tension indicated by the fluctuating tension at the start of sewing is compared with the fluctuating tension stored in the RAM135B in S33. When the sewing operation is not started, the tension of the upper thread is not changed. Therefore, when the face line tension and the fluctuating tension are compared in the autocorrelation analysis, the correlation coefficient is not near 1 and does not reach a maximum. When the correlation coefficient does not reach the maximum value in the vicinity of 1, the CPU135A determines that the sewing operation is not started (S35: no), and the process proceeds to S33. When the correlation coefficient becomes maximum in the vicinity of 1, the CPU135A determines that the sewing operation is started (S35: yes), and the process proceeds to S37. The CPU135A starts the counting of the timer 35 (S37). The timer 35 counts the elapsed time from the start of the sewing operation.

The CPU135A acquires the needle thread tension based on the detection result of the magnetic sensor 105 and the elapsed time based on the count result of the timer 35 (S43). The CPU135A associates the acquired elapsed time with the surface tension and stores the resultant in the RAM135B as a varying tension. The CPU135A determines whether the fluctuating tension of the nth cycle is acquired (S45). This determination is made by autocorrelation analysis by comparing the reference needle thread tension with the fluctuating tension stored in the RAM135B in S43. When the correlation coefficient does not reach the maximum value in the vicinity of 1, the CPU135A determines that the fluctuation tension of the nth cycle is not acquired (S45: no), and shifts the process to S43. The CPU135A shifts the process to S47 when the correlation coefficient reaches the maximum in the vicinity of 1 (S45: yes). In S45, the CPU135A determines that the fluctuating tension in the nth cycle is acquired when the predetermined time correlation coefficient is not in the vicinity of 1 and does not reach the maximum value (S45: yes). Therefore, the CPU135A can determine whether or not the fluctuating tension of the nth cycle is acquired even when the disconnection occurs.

The CPU135A stores the elapsed time and the upper thread tension (i.e., the variation tension) in the RAM135B every time S43 and S45 are repeated (S43). When the correlation coefficient reaches the maximum in the vicinity of 1 or when the correlation coefficient does not reach the maximum in the vicinity of 1 for a predetermined time (yes in S45), the CPU135A acquires the variation tension, the first surface line tension, and the second surface line tension in the nth cycle (S47). The CPU135A acquires the varying tension of the nth cycle from the RAM 135B. The upper thread tension acquired in S43 is the upper thread tension based on the detection result of the magnetic sensor 105. Therefore, the CPU135A acquires the fluctuating tension, the first surface line tension, and the second surface line tension in the nth cycle based on the detection result of the line tension detecting mechanism 130 (S47). In addition, the upper thread 6 is easily loosened when the sewing of the first cycle is performed. Therefore, the first surface line tension and the second surface line tension in the first period are difficult to be high values of the degree shown in fig. 7. The CPU135A executes a sewing failure determination process (S51).

The sewing failure determination process determines whether or not a thread breakage, a stitch skipping, or a thread take-up failure has occurred based on the fluctuating tension acquired in S47. The CPU135A switches the thread breakage flag, the skip stitch flag, and the thread take-up failure flag from 0 to 1 in accordance with the sewing failure. The CPU135A determines whether or not the sewing is in the initial stage (S100). The initial stage of sewing is sewing from the beginning of sewing (S13) to a predetermined number of stitches. For example, the initial stage of sewing is sewing from the start of sewing to the second needle, which corresponds to sewing until the second cycle (N ═ 2). When N is 2 or less (S100: yes), the CPU135A ends the sewing failure determination process and returns to the tension acquisition process.

The CPU135A transmits sewing defect information indicating the presence or absence of a sewing defect to the CPU91 (S53). The sewing failure information is a broken thread mark, a skip stitch mark and a winding failure mark. The CPU135A determines whether or not an instruction to perform zero point adjustment of the output voltage of the magnetic sensor 105 has been received (S55). When the CPU91 issues an instruction to execute the zero point adjustment in S21 of the sewing process, the CPU135A determines that the instruction to execute the zero point adjustment has been received (S55: yes). The CPU135A inputs an instruction to reset the reference voltage Vt (see fig. 6) to the subtraction circuit 152, and executes zero point adjustment (S57). Since the face line tension is substantially 0 after the face line 6 is cut, the reference voltage Vt can be set to the output voltage of the magnetic sensor 105 when the face line tension is 0. When receiving the instruction to execute the zero point adjustment, the sewing machine 1 is in a state of ending the sewing process. The CPU135A shifts the process to S30.

When determining that the instruction to execute the zero point adjustment has not been received (no in S55), the CPU135A determines whether or not the drive motor is in a state of stopping the drive (S59). The CPU135A determines that the drive motor is in the state of stopping the drive when the upper thread tension is not varied based on the varied tension acquired in S47. When the CPU135A determines that the drive motor is in the state of being stopped (S59: yes), the process proceeds to S30. When determining that the drive motor is not in the stopped state (no in S59), the CPU135A adds 1 to N (S61), shifts the process to S43, and repeats S43 and S45. For example, after acquiring the second cycle of the varying tension (S45: yes), the CPU135A stores the second cycle of the varying tension, the first surface line tension, and the second surface line tension in the RAM135B (S47). The sewing in the second cycle is in the initial stage of sewing, and the first surface thread tension and the second surface thread tension in the second cycle hardly have high values of the degree shown in fig. 7. By the same process, the CPU135A, after acquiring the varied tension of the third cycle (S45: yes), stores the varied tension of the third cycle, the first face line tension, and the second face line tension in the RAM135B (S47). In fig. 7, the varying tension of the third cycle is shown by reference numeral 203. The CPU135A executes a sewing failure determination process (S51). The sewing failure determination processing after S101 will be described in detail later. The CPU135A obtains the varied tension, the first face line tension, and the second face line tension in the fourth and subsequent periods by repeating the above-described processing (S47). In fig. 7, the varying tension of the fourth cycle is shown by reference numeral 204.

The details of the sewing failure determination processing after S101 will be described. When the sewing is not in the initial stage (S100: NO), the CPU135A obtains the upper shaft rotation speed (S101). The CPU135A acquires the time from the start of sewing to the end of sewing in the nth cycle as the sewing period based on the elapsed time in the nth cycle stored in the RAM 135B. The angle of rotation of the upper shaft 15 during the nth cycle of sewing is known. Therefore, the CPU135A can acquire the upper shaft rotation speed using the acquired sewing time and a predetermined relational expression. The CPU135A determines whether the upper axis rotation speed acquired in S101 is equal to or less than the second speed (S103). The second speed is a preset speed and is stored in the storage device 135C. The second speed is slower than the first speed. When the CPU135A determines that the upper shaft rotation speed is equal to or less than the second speed (yes in S103), it ends the sewing failure determination process.

When the CPU135A determines that the upper shaft rotation speed is greater than the second speed (no in S103), it determines whether acceleration or deceleration has occurred in the rotation of the upper shaft 15 (S105). The CPU135A obtains the upper axis rotation speed of each of the sewing in the N-1 th cycle and the sewing in the N-th cycle in the same manner as in S101. The CPU135A determines that acceleration/deceleration has occurred when the difference between the upper axis rotational speeds is equal to or larger than a predetermined range. The CPU135A determines that acceleration/deceleration has not occurred when the difference between the upper axis rotational speeds is smaller than a predetermined range. When the CPU135A determines that acceleration/deceleration has occurred (yes in S105), the CPU changes the wire-rewinding failure specifying threshold value according to the degree of acceleration/deceleration (S121). The CPU135A determines the acceleration of the rotation of the upper shaft 15 based on the upper shaft rotation speed in the sewing of the N-1 th cycle and the sewing of the N-th cycle. The CPU135A changes the wire-receiving failure specific threshold value so that the wire-receiving failure specific threshold value becomes smaller as the acceleration of the upper shaft 15 becomes larger. The CPU135A increases the wire-rewinding failure specific threshold when the upper shaft 15 decelerates. The poor take-up specific threshold value at this time is a positive value.

When the CPU135A determines that acceleration/deceleration has not occurred (no in S105), the first disconnection threshold, the second disconnection threshold, the first skip stitch threshold, and the second skip stitch threshold stored in the storage device 135C are changed in accordance with the upper axis rotation speed acquired in S101 (S109). For example, the CPU135A multiplies the first disconnection threshold, the second disconnection threshold, the first skip point threshold, and the second skip point threshold by positive coefficients having a proportional relationship with the upper axis rotation speed, respectively. That is, the CPU135A changes the first disconnection threshold, the second disconnection threshold, the first skip stitch threshold, and the second skip stitch threshold to be larger as the upper shaft rotation speed is larger.

The CPU135A executes the wire rewinding failure determination process (S111). The CPU135A refers to the RAM135B and acquires the generation timing of the second face line tension in the N-1 th cycle (i.e., the generation timing of the second face line tension of the reference face line tension) and the generation timing of the second face line tension in the N-th cycle (S124). The CPU135A determines whether or not the difference between the timing of generating the second surface line tension in the nth cycle and the timing of generating the second surface line tension in the N-1 th cycle acquired in S124 is equal to or greater than the take-up failure specific threshold (S125). In this case, the wire rewinding failure specific threshold is the wire rewinding failure specific threshold changed in S121. When the CPU135A determines that the difference between the timing of generating the second surface line tension in the nth period and the timing of generating the second surface line tension in the N-1 th period is smaller than the specific threshold value for the defective take-up (S125: no), it determines that the defective take-up has not occurred, ends the defective take-up determination process, and returns to the defective sewing determination process. When the CPU135A determines that the difference between the timing of generating the second surface line tension in the nth period and the timing of generating the second surface line tension in the N-1 th period is equal to or greater than the take-up failure specific threshold (S125: yes), it determines that a take-up failure has occurred, and changes the take-up failure flag to 1 (S127). The CPU135A ends the take-up failure determination processing and returns to the sewing failure determination processing.

The CPU135A executes the specific disconnection determination process (S113). The CPU135A determines whether or not the first face line tension difference is equal to or greater than a first disconnection specific threshold value (S131). The CPU135A acquires the first face line tension of the N-1 th cycle and the first face line tension of the N-th cycle stored in the RAM135B, and acquires the first face line tension difference. When the CPU135A determines that the first surface thread tension difference is smaller than the first thread breakage specific threshold value (no in S131), it determines that thread breakage has not occurred at the time of the nth cycle sewing, ends the specific thread breakage determination processing, and returns to the sewing failure determination processing. When the CPU135A determines that the first surface-line tension difference is equal to or greater than the first disconnection specific threshold value (yes in S131), it determines whether or not the second surface-line tension difference is equal to or greater than the second disconnection specific threshold value (S133). The CPU135A acquires the second surface line tension of the N-1 th cycle and the second surface line tension of the N-th cycle stored in the RAM135B, and acquires the second surface line tension difference. When the CPU135A determines that the second surface thread tension difference is smaller than the second thread breakage specific threshold value (no in S133), it determines that thread breakage has not occurred during the nth cycle of sewing, ends the specific thread breakage determination processing, and returns to the sewing failure determination processing. When the CPU135A judges that the second surface thread tension difference is equal to or greater than the second thread breakage specific threshold value (S133: YES), it judges that thread breakage has occurred at the time of sewing in the Nth cycle. The CPU135A changes the thread breakage flag to 1(S137), ends the specific thread breakage determination process, and returns to the sewing failure determination process.

The CPU135A executes the specific skip judgment process (S115). The CPU135A determines whether or not the first face line tension difference is equal to or greater than the first stitch-skipping specific threshold value (S141). The first surface tension difference is obtained in the same manner as in S131. When the CPU135A determines that the first surface thread tension difference is smaller than the first stitch skipping specific threshold value (S141: no), it determines that no stitch skipping has occurred during the nth cycle of sewing, ends the specific stitch skipping determination process, and returns to the sewing failure determination process. When the CPU135A determines that the first surface-line tension difference is equal to or greater than the first stitch-skipping specific threshold value (yes in S141), it determines whether or not the second surface-line tension difference is equal to or less than the second stitch-skipping specific threshold value (S143). The second areal line tension difference is obtained in the same manner as in S133. When the CPU135A determines that the second surface thread tension difference is greater than the second stitch skipping specific threshold value (S143: no), it determines that no stitch skipping has occurred during the nth cycle of sewing, ends the specific stitch skipping determination process, and returns to the sewing failure determination process. When the CPU135A determines that the second surface thread tension difference is equal to or less than the second stitch skipping specific threshold value (S143: yes), it determines that a stitch skipping has occurred during the nth cycle of sewing. The CPU135A changes the skip stitch flag to 1(S147), ends the specific skip stitch determination process, and returns to the sewing failure determination process.

When the yarn breakage occurs, the first yarn tension difference may be equal to or greater than the first stitch skipping specific threshold (S141: YES). At this time, the second face line tension difference is larger than the second stitch-skipping specific threshold value (S143: No). Therefore, the sewing machine 1 can suppress the occurrence of a stitch skipping even when a thread breakage actually occurs.

The CPU135A executes the disconnection determination process (S117). The CPU135A determines whether the disconnection flag is 1 (S151). When the CPU135A determines that the thread breakage flag is 1 (S151: yes), the thread breakage determination process is terminated, and the process returns to the sewing failure determination process. When the CPU135A determines that the disconnection flag is 0 (S151: no), it determines whether or not the first surface tension of the nth cycle stored in the RAM135B is equal to or less than the first disconnection threshold (S153). The first disconnection threshold referred to in S153 is the first disconnection threshold changed in S109. When the CPU135A determines that the first surface thread tension is greater than the first thread breakage threshold value (S153: no), it determines that thread breakage has not occurred in the nth cycle, ends the thread breakage determination process, and returns to the sewing failure determination process. When the CPU135A determines that the first surface line tension is equal to or less than the first disconnection threshold value (S153: yes), it determines whether or not the second surface line tension of the nth cycle stored in the RAM135B is equal to or less than the second disconnection threshold value (S155). The second disconnection threshold referred to in S155 is the second disconnection threshold changed in S109. When the CPU135A determines that the second face thread tension is greater than the second thread breakage threshold value (S155: no), it determines that thread breakage has not occurred in the nth cycle, ends the thread breakage determination process, and returns to the sewing failure determination process. When the CPU135A determines that the second surface wire tension is equal to or less than the second disconnection threshold value (S155: yes), it determines that a disconnection has occurred in the nth cycle and changes the disconnection flag to 1 (S159). The CPU135A ends the thread breakage determination processing and returns to the sewing failure determination processing.

The CPU135A executes the skip stitch determination processing (S119). The CPU135A determines whether the skip stitch flag is 1 (S161). When the CPU135A determines that the skip stitch flag is 1 (S161: yes), the skip stitch determination process is ended, and the process returns to the sewing failure determination process. When determining that the stitch jumper flag is 0 (S161: no), the CPU135A determines whether or not the first surface line tension of the nth cycle stored in the RAM135B is equal to or less than the first stitch jumper threshold value (S163). The first skip stitch threshold referred to in S163 is the first skip stitch threshold changed in S109. When the CPU135A determines that the first face line tension is greater than the first stitch skipping threshold (S163: no), it determines that no stitch skipping has occurred in the nth cycle, ends the stitch skipping determination process, and returns to the sewing failure determination process. When the CPU135A determines that the first surface line tension is equal to or less than the first stitch skipping threshold (S163: yes), it determines whether or not the second surface line tension of the nth cycle stored in the RAM135B is equal to or more than the second stitch skipping threshold (S165). The second skip stitch threshold referred to in S163 is the second skip stitch threshold changed in S109. When the CPU135A determines that the second face line tension is smaller than the second stitch skipping threshold value (S165: no), it determines that no stitch skipping has occurred in the nth cycle, ends the stitch skipping determination process, and returns to the sewing failure determination process. When determining that the second surface line tension is equal to or greater than the second stitch skipping threshold (yes in S165), the CPU135A determines that a stitch skipping has occurred in the nth cycle and changes the stitch skipping flag to 1 (S169). The CPU135A ends the stitch skipping determination processing and returns to the sewing failure determination processing.

When a thread break occurs, the first face thread tension may be equal to or less than the first stitch skipping threshold (S163: YES). At this time, the second face line tension is smaller than the second stitch skipping threshold (S165: NO). Therefore, the sewing machine 1 can suppress erroneous judgment that thread breakage has occurred despite actually occurring stitch skipping.

The CPU135A executes the threshold initialization process (S120). The CPU135A restores the first disconnection threshold, the second disconnection threshold, the first skip point threshold, the second skip point threshold, the poor wire take-up specific threshold, the first disconnection specific threshold, the second disconnection specific threshold, the first skip point specific threshold, and the second skip point specific threshold stored in the storage device 135C to the initial values. The CPU135A ends the sewing failure determination processing and returns to the tension acquisition processing.

As shown in fig. 16, the CPU135A transmits the sewing failure information (S53). As shown in FIG. 14, when the CPU91 judges that a sewing failure has occurred (S17: YES), it judges the sewing failure (S23). The CPU91 determines the sewing failure by specifying a 1 flag among the thread breakage flag, the stitch skipping flag, and the thread take-up failure flag. The CPU91 notifies the determined sewing failure (S24). For example, the CPU91 displays the determined sewing failure on the display unit 25. The CPU91 determines whether to stop driving the drive motor (S25). The CPU91 determines to stop driving the driving motor when the sewing failure is determined to be a broken thread or a stitch skipping. When determining that the drive motor is to be stopped (yes in S25), the CPU91 stops the drive of the drive motor (S26) and proceeds to S220. When determining that the drive motor is not to be stopped (S25: no), the CPU91 advances the process to S18. At this time, if the CPU91 determines that a wire rewinding failure has occurred (S17: yes), the CPU does not stop the drive motor (S25: no). The operator may continue to depress the pedal 38 after the display unit 25 confirms that the wire rewinding failure has occurred (S18: no) or may depress the pedal 38 (S18: yes).

When the CPU91 judges that a sewing failure has occurred before M reaches a predetermined cycle at the end of sewing (S74: YES), it judges the sewing failure (S75) and notifies the judged sewing failure (S76). The CPU91 determines whether to stop driving the drive motor (S77). When determining that the drive motor is to be stopped (yes in S77), the CPU91 stops the drive of the drive motor (S78) and proceeds to S220. When determining that the drive motor is not to be stopped (S77: no), the CPU91 advances the process to S19. The processing of S75 to S78 is the same as the processing of S23 to S26. Therefore, if the CPU91 determines that a wire rewinding failure has occurred (S74: yes), the CPU does not stop the drive motor (S77: no). At this time, the CPU91 continues processing until M reaches a predetermined period.

As described above, the CPU135A acquires the varying tension based on the detection result of the magnetic sensor 105 of the line tension detecting mechanism 130 (S47). The CPU135A executes a wire-rewinding failure determination process (S111), a specific wire breakage determination process (S113), and a specific stitch skipping determination process (S115). The CPU135A determines that there is a no seam defect by comparing the needle thread tension of the nth cycle with the needle thread tension of the reference needle thread tension, that is, the needle thread tension of the nth-1 cycle. That is, the CPU135A compares the variable tension of the nth cycle acquired in S47 with the variable tension of the reference needle thread tension, that is, the variable tension of the N-1 th cycle using the take-up failure specifying threshold, the first thread breakage specifying threshold, the second thread breakage specifying threshold, the first skip stitch specifying threshold, and the second skip stitch specifying threshold, and determines whether or not a sewing failure has occurred. The poor take-up specific threshold is a preset threshold corresponding to the poor take-up. The first disconnection specifying threshold and the second disconnection specifying threshold are thresholds that are preset in association with disconnection. The first skip point specific threshold value and the second skip point specific threshold value are threshold values set in advance in correspondence with skip points. The CPU135A determines whether or not there is a seamless failure using each specific threshold. Therefore, the sewing machine 1 can recognize a specific sewing failure and can recognize the sewing failure based on the change in the upper thread tension.

When a wire break occurs, the first face wire tension is below a first wire break threshold, and the second face wire tension is below a second wire break threshold. In the disconnection determination process (S117), the CPU135A determines that a disconnection has occurred and changes the disconnection flag to 1(S159) when the first surface line tension in the nth cycle is equal to or less than the first disconnection threshold value (S153: yes) and the second surface line tension in the nth cycle is equal to or less than the second disconnection threshold value (S155: yes). Since the sewing machine 1 can determine whether or not a thread break occurs, the thread break can be recognized as a sewing failure.

When a stitch jump occurs, the first face line tension is below a first stitch jump threshold, and the second face line tension is above a second stitch jump threshold. In the stitch skipping determination process (S119), the CPU135A determines that a stitch has occurred and changes the stitch skipping flag to 1(S169) when the first surface line tension in the nth cycle is equal to or less than the first stitch skipping threshold (S163: yes) and the second surface line tension in the nth cycle is equal to or more than the second stitch skipping threshold (S165: yes). Since the sewing machine 1 can determine whether or not there is a skip stitch, the skip stitch can be recognized as a sewing failure.

When the take-up failure occurs, the consumption amount of the upper thread 6 increases, and therefore, the timing of generation of the second face thread tension becomes early. In the wire rewinding failure determination process (S111), when the timing of generation of the second surface line tension in the nth cycle is earlier than or equal to the specific threshold value of the wire rewinding failure with respect to the timing of generation of the second surface line tension in the N-1 th cycle (S125: yes), the CPU135A determines that the wire rewinding failure has occurred, and changes the wire rewinding failure flag to 1 (S127). Since the sewing machine 1 can determine whether or not a defective thread take-up occurs, the defective thread take-up can be recognized as a defective sewing.

When the sewing speed is slow, the consumption amount of the upper thread 6 is low, and therefore, the first and second face thread tensions are low. When the CPU91 determines that the upper shaft rotation speed acquired in S15 is equal to or less than the first speed (yes in S81), it 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 upper thread 6 is less likely to be slackened, and the sewing machine 1 can easily generate the first surface thread tension and the second surface thread tension.

When the upper shaft rotation speed changes due to acceleration/deceleration of the upper shaft 15 (yes in S105), the CPU135A changes the wire-rewinding failure specific threshold according to the acceleration of the upper shaft 15 (S121), and uses the changed wire-rewinding failure specific threshold in S125. When the rotation speed of the upper shaft changes, the tension of the upper thread changes according to the acceleration, and the tension of the upper thread changes when sewing failure occurs. Specifically, when the upper shaft 15 is accelerated when the wire rewinding failure occurs, the second surface line tension is generated at a timing later than the second surface line tension when the upper shaft 15 rotates at a low speed. At this time, the sewing machine 1 changes the thread take-up failure specific threshold value according to the change in the upper shaft rotation speed, and therefore, the thread take-up failure can be appropriately detected.

When the rotation speed of the upper shaft changes, the tension of the upper thread changes, and the tension of the upper thread changes when sewing failure occurs. Specifically, when the upper shaft 15 rotates at a low speed, the fluctuation tension is small, and the upper thread tension when sewing failure occurs is also small. When the upper shaft 15 is rotated at a high speed, the fluctuation tension is large, and the upper thread tension is also large when a sewing failure occurs. When the needle thread tension changes when a sewing failure occurs, the CPU135A changes the threshold value according to the upper axis rotation speed acquired in S100 (S109). Therefore, the CPU135A can appropriately detect a sewing failure.

The CPU135A executes S111-S120 after the initial sewing stage (S100: NO) in the sewing failure judgment processing. The upper thread 6 is easily loosened at the initial stage of sewing. That is, it is difficult to set the first surface line tension and the second surface line tension to appropriate values. Therefore, if the CPU135A determines that there is a no sewing failure in the initial stage of sewing, it may be determined that there is a sewing failure even if there is no sewing failure. The CPU135A does not determine whether or not sewing failure occurs in the initial stage of sewing (S100: yes). Therefore, the sewing machine 1 can suppress erroneous determination that a sewing failure has occurred.

When determining that the upper axis rotation speed acquired in S101 is greater than the second speed (no in S103), the CPU135A executes S111 to S119 and determines that there is no defective seam. When the sewing speed is low, the first and second face thread tensions are low, and it is difficult to appropriately generate the first and second face thread tensions. Therefore, the sewing machine 1 is difficult to detect a sewing failure based on the upper thread tension. When the CPU135A determines that the upper axis rotation speed is equal to or less than the second speed (yes in S103), it does not determine that there is a seamless failure. Therefore, the sewing machine 1 can more appropriately determine the presence of the seamless failure.

When the tangent is executed (S20), the CPU135A receives an instruction of zero point adjustment from the CPU91 (S22), and executes the zero point adjustment (S57). When the sewing operation is repeated, the temperature of the magnetic sensor 105 may rise due to repetition of the sliding of the upper thread 6 and the plate 50, and the output voltage of the magnetic sensor 105 may fluctuate to a large extent from the reference voltage Vt. At this time, when the upper thread tension decreases with the execution of the tangent and the output voltage of the magnetic sensor 105 decreases, the CPU135A executes zero point adjustment (S57). The sewing machine 1 resets the reference voltage Vt of the magnetic sensor 105. Therefore, the sewing machine 1 can continuously obtain the upper thread tension with high accuracy based on the output voltage of the magnetic sensor 105. The CPU135A does not determine that there is a seamless failure when performing zero point adjustment. Therefore, the sewing machine 1 can suppress erroneous determination that a sewing failure has occurred.

The main wire gripper 60 is an example of the wire gripping mechanism of the present invention. The plate 50 is an example of the movable member of the present invention. The CPU91 when executing S13 and S21 is an example of the sewing control unit of the present invention. The CPU135A when executing S47 is an example of the tension acquiring section of the present invention. The CPU135A executing S51 is an example of the determination unit of the present invention. The CPU135A when executing S117 is an example of the disconnection determining section of the present invention. The CPU135A when executing S119 is an example of the skip stitch determination section of the present invention. The CPU135A executing S111 is an example of the wire rewinding failure determination unit according to the present invention. The CPUs 91 and 135A executing S15, S72, and S101 are examples of the speed acquisition section of the present invention. The CPU91 executing S83 is an example of the thread tension control unit of the present invention. The CPU135A executing S121 is an example of the acceleration response changing unit according to the present invention. The CPU135A executing S109 is an example of the speed response changing unit according to the present invention. The CPU91 executing S20 is an example of the tangent line control unit of the present invention. The CPU135A executing S57 is an example of the adjustment control unit of the present invention. The specific threshold for poor take-up, the specific threshold for first broken wire, the specific threshold for second broken wire, the specific threshold for first skip pin and the specific threshold for second skip pin are examples of the specific threshold of the present invention. The poor take-up specific threshold is an example of the first specific threshold. The first disconnection threshold is an example of the first threshold of the present invention. The second disconnection threshold is an example of the second threshold of the present invention. The first skip point threshold is an example of the third threshold of the present invention. The second skip point threshold is an example of the fourth threshold of the present invention.

The present invention is not limited to the above-described embodiments. The CPU135A may change the first disconnection threshold value, the second disconnection threshold value, the first stitch skipping threshold value, the second stitch skipping threshold value, the first disconnection specific threshold value, the second stitch skipping specific threshold value, the first stitch skipping specific threshold value, and the second stitch skipping specific threshold value according to the acceleration of the upper axis rotation speed (S121). For example, since the fluctuating tension is likely to decrease when the upper shaft 15 decelerates (S105: yes), the CPU135A may change the first disconnection threshold, the second disconnection threshold, the first skip stitch threshold, and the second skip stitch threshold so as to decrease, respectively, and may change the first disconnection specific threshold, the second disconnection specific threshold, the first skip stitch specific threshold, and the second skip stitch specific threshold so as to increase, respectively (S121).

The CPU135A may change the first threshold value, the second threshold value, and the third threshold value in accordance with the speed of the upper shaft rotation speed, and may change the first disconnection specific threshold value, the second disconnection specific threshold value, the first skip stitch specific threshold value, and the second skip stitch specific threshold value in accordance with the speed of the upper shaft rotation speed (S109). The CPU135A may change the first specific threshold value in accordance with the rotational acceleration of the upper shaft 15, and may change the first threshold value, the second threshold value, and the third threshold value in accordance with the rotational acceleration of the upper shaft 15 (S121).

When determining that acceleration/deceleration has occurred in the upper axis rotation speed (yes in S105), the CPU135A may change the first disconnection threshold, the second disconnection threshold, the first skip point threshold, the second skip point threshold, the first disconnection specific threshold, the second disconnection specific threshold, the first skip point specific threshold, and the second skip point specific threshold instead of the wire collection failure specific threshold (S121). For example, when the upper shaft 15 decelerates (yes in S105), the CPU135A may decrease the first disconnection threshold value. The initial stage of sewing may be from the start of sewing to the first cycle of sewing or to the third cycle of sewing. The predetermined number of stitches defining the initial stage of sewing may be different depending on the sewing failure. For example, the CPU135A may determine whether or not there is a skip stitch by taking a period until the second cycle as an initial sewing stage when determining whether or not there is a skip stitch, determine whether or not there is a skip stitch when performing sewing after the third cycle, determine whether or not there is a defective take-up stitch by taking a period until the first cycle as an initial sewing stage when determining whether or not there is a defective take-up stitch, and determine whether or not there is a defective take-up stitch when performing sewing after the second cycle.

The CPU135A may determine whether the fluctuating tension of the first cycle is acquired based on the count result of the timer 35 (S45). For example, the RAM135B may store the time required to complete acquisition of the variable tension in the first cycle, and the CPU135A may determine whether or not the variable tension in the first cycle has been completed by determining whether or not the required time has elapsed as a result of counting by the timer 35. The CPU91 may output a signal of the needle up position or the needle down position to the CPU135A 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 needle 10. At this time, the CPU135A may determine whether the sewing operation has started in the process of S35 based on the signal of the needle up position or the needle down position, determine whether the fluctuating tension of the nth cycle has been acquired in the process of S45 based on the signal of the needle up position or the needle down position, or acquire the upper shaft rotation speed in the process of S101 based on the signal of the needle up position or the needle down position.

When the operator steps back on the pedal 38, the CPU91 judges that the sewing operation is finished (S18: YES). The sewing machine 1 may store the sewing data of N cycles in the storage device 94, and may finish the sewing operation after sewing the sewing data of N cycles. In this case, the processing of S19, S71 to S78 may be omitted.

The CPU91 may rotate the wire chuck 69 in the winding direction by a rotation amount corresponding to the upper shaft rotation speed (S83). The magnetic sensor 105 may also include a magnetic impedance element, a magnetoresistance effect element, or the like instead of the hall element. At this time, the magnetic sensor 105 can detect a change in the magnetic flux density of the magnet 58.

Claims (10)

1. A sewing machine, wherein,

the sewing machine has:

a needle bar (11) to which a needle (10) is fitted, the needle bar being capable of moving up and down;

a shuttle for catching the upper thread penetrating the needle and interlacing the upper thread with the lower thread;

a thread take-up lever (23) for taking up the upper thread interwoven with the lower thread by the shuttle;

a thread take-up mechanism (60) having a thread take-up reel (69) for applying tension to the upper thread, the upper thread passing through the thread take-up reel at a position upstream of the thread take-up lever on a feed path of the upper thread to the needle;

a thread tension detection mechanism (130) for detecting the tension of the upper thread, namely the tension of the upper thread;

a sewing control part (91) for controlling the needle bar, the shuttle and the thread take-up lever to sew the cloth;

a tension acquiring unit that acquires the upper thread tension that periodically varies with sewing by the sewing control unit based on a detection result of the thread tension detecting unit; and

a determination unit which determines whether a sewing failure in which a normal stitch is not formed in the sewing operation by the sewing control unit has occurred by comparing the upper thread tension varying in the Nth cycle acquired by the tension acquisition unit with a reference upper thread tension which is the upper thread tension varying in one cycle,

wherein, N is a natural number,

the sewing machine is characterized in that the sewing machine is provided with a sewing machine,

the tension acquiring unit acquires the upper thread tension for each cycle of the upper thread tension which repeatedly varies in a cycle with a unit as a time,

the judging section judges whether or not the sewing failure has occurred by comparing the face thread tension varying in the Nth cycle with the reference face thread tension using a plurality of specific thresholds preset in advance corresponding to a plurality of kinds of the sewing failures, respectively.

2. The sewing machine of claim 1,

the sewing failure includes a broken thread in which the upper thread is broken during the sewing process,

the judging section has a disconnection judging section for judging whether or not the disconnection has occurred,

the period in which the upper thread tension is maximized for the first time in the period of the Nth cycle is a shuttle catching period in which the shuttle catches the upper thread,

the period during which the upper thread tension reaches maximum for the second time in the period of the Nth period is a take-up lever lifting period during which the take-up lever lifts the upper thread,

the tension acquiring unit acquires a first surface thread tension that is the surface thread tension during capturing of the shuttle in the Nth cycle and a second surface thread tension that is the surface thread tension during lifting of the thread take-up lever,

the wire breakage determination unit determines that the wire breakage has occurred when the first surface line tension is equal to or less than a first threshold value and the second surface line tension is equal to or less than a second threshold value.

3. The sewing machine of claim 2,

the sewing failure includes a skip stitch in which the upper thread is not caught by the shuttle in the sewing process,

the judging unit has a skip stitch judging unit for judging whether the skip stitch occurs,

the skip stitch determination unit determines that the skip stitch has occurred when the first surface line tension is equal to or less than a third threshold value and the second surface line tension is equal to or more than a fourth threshold value.

4. The sewing machine of claim 3,

the poor sewing comprises poor balance of the upper thread and the bottom thread which form a stitch when the upper thread is lifted by the take-up lever, namely poor take-up,

the plurality of specific thresholds includes a first specific threshold,

the judging part is provided with a poor take-up judging part, and the poor take-up judging part judges that poor take-up occurs when the second maximum generation time of the facial line tension in the Nth period is earlier than or equal to the first specific threshold value relative to the second maximum generation time of the reference facial line tension.

5. The sewing machine of claim 4,

the sewing machine has an upper shaft (15) for moving the needle bar and the thread take-up bar up and down by rotation,

the wire clamping mechanism is provided with a wire clamping motor (16) for rotating the wire clamping disc,

the sewing machine has:

a speed acquisition unit that acquires the rotational speed of the upper shaft when the sewing control unit performs sewing; and

and a thread tension control unit that drives the thread tension motor to rotate the thread tension disk in a direction opposite to a direction in which the upper thread is supplied along the supply path, when the rotation speed acquired by the speed acquisition unit is equal to or lower than a first speed.

6. Sewing machine as in claim 5,

the sewing machine includes an acceleration correspondence changing unit that changes at least one of the plurality of specific thresholds, the first threshold, the second threshold, the third threshold, and the fourth threshold in accordance with an acceleration of the rotational speed when the rotational speed acquired by the speed acquiring unit changes.

7. Sewing machine as in claim 5,

the sewing machine includes a speed correspondence changing unit that changes at least one of the plurality of specific thresholds, the first threshold, the second threshold, the third threshold, and the fourth threshold in accordance with the rotational speed acquired by the speed acquiring unit.

8. Sewing machine as in any of claims 5 to 7,

the judging section judges whether the sewing failure occurs after an initial sewing stage, which is a stage from the start of the sewing by the sewing control section to the sewing of a predetermined number of stitches.

9. Sewing machine as in any of claims 5 to 8,

the determination unit determines whether the sewing failure has occurred when the rotational speed acquired by the speed acquisition unit is greater than a second speed.

10. The sewing machine according to any one of claims 1 to 9,

the sewing machine has:

a thread cutting mechanism (17) for cutting the upper thread and the lower thread; and

a thread cutting control part for controlling the thread cutting mechanism to cut the upper thread and the bottom thread after the sewing by the sewing control part,

the wire tension detection mechanism includes:

a movable member (50) which is in contact with the upper thread and moves in accordance with the tension of the upper thread;

a magnet (58) provided to the movable member; and

a magnetic sensor (105) for detecting the magnetic flux density of the magnet and outputting a voltage corresponding to the detection result,

the tension acquiring unit acquires the upper thread tension based on the output voltage of the magnetic sensor,

the tension acquisition unit includes an adjustment control unit that performs zero point adjustment for resetting an output voltage that is a reference of the magnetic sensor when the upper thread and the lower thread are cut by the thread cutting control unit.

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