Sewing machine and bobbin thread determination method

Abstract

To provide a sewing machine and a bobbin thread determination method capable of detecting bobbin thread breakage and bobbin thread entanglement failure with better accuracy than before, irrespective of sewing conditions.SOLUTION: A sewing machine includes a needle bar, a needle bar vertical movement mechanism, a shuttle, a shuttle mechanism, a tensile force detector, a rotation detector, and a bobbin thread determination part. The needle bar mounts a sewing needle in which a needle thread is inserted. The needle bar vertical movement mechanism moves the needle bar vertically. The shuttle rotatably stores a bobbin which is provided below the needle bar, and around which a bobbin thread is wound. The shuttle mechanism rotates the shuttle synchronously with the vertical movement of the needle bar, and forms seams by capturing the annular needle thread which is inserted in the sewing needle and entangling it with the bobbin thread. The tensile force detector detects the tensile force of the needle thread or the bobbin thread. The rotation detector detects presence / absence of the rotation of the bobbin. The bobbin thread determination part determines presence / absence of the bobbin thread with respect to the seams, based on whether or not the tensile force detected by the tensile force detector is larger than a threshold value and the detection result of the rotation detector (S3-S7, S11-S19).SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a sewing machine and a bobbin thread determination method. [Background technology]

[0002] The sewing machine of Patent Document 1 is equipped with a lower thread tension sensor that detects the tension of the lower thread, and determines whether or not the lower thread has broken based on the tension of the lower thread during sewing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-33868 Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned sewing machine may not be able to accurately detect a bobbin thread breakage depending on the sewing conditions.

[0005] An object of the present invention is to provide a sewing machine and a bobbin thread detection method that can detect bobbin thread breakage and bobbin thread tangle defects more accurately than conventional methods, regardless of sewing conditions. [Means for solving the problem]

[0006] The sewing machine of claim 1 comprises a needle bar equipped with a sewing needle through which an upper thread is inserted, a needle bar up-down movement mechanism for moving the needle bar up and down, a shuttle provided below the needle bar and rotatably housing a bobbin around which a lower thread is wound, a shuttle mechanism that rotates the shuttle in synchronization with the up-and-down movement of the needle bar to capture the annular upper thread inserted into the sewing needle and entangle it with the lower thread to form a stitch, a tension detector that detects the tension of the upper thread or the lower thread, a motion detector that detects whether the bobbin is moving, and a lower thread determination unit that determines whether the tension detected by the tension detector is greater than a threshold value and the detection result of the motion detector. The sewing machine of claim 1 determines whether the lower thread is present in the stitch based on whether the tension detected by the tension detector is greater than a threshold value and the detection result of the motion detector, so that the presence or absence of the lower thread in the stitch can be determined more accurately than devices that use only a tension detector for determination.

[0007] The bobbin thread determination unit of the sewing machine of claim 2 determines that there is bobbin thread in the stitch when the operation detector detects that there is no movement of the bobbin and the tension detected by the tension detector is greater than the first threshold value, and determines that there is no bobbin thread in the stitch when the operation detector detects that there is no movement of the bobbin and the tension detected by the tension detector is equal to or less than the first threshold value. The sewing machine of claim 2 can determine that there is bobbin thread in the stitch when the tension detected by the tension detector is greater than the first threshold value even when there is no movement of the bobbin. The sewing machine can avoid determining that there is no bobbin thread in the stitch in a situation where bobbin operation has temporarily stopped but the bobbin thread is thought to be tangled with the upper thread.

[0008] The bobbin thread determination unit of the sewing machine of claim 3 determines that there is no bobbin thread in the stitch when the tension detected by the tension detector is equal to or less than the second threshold value, which is the threshold value, and the operation detector detects that the bobbin is not moving, and determines that there is bobbin thread in the stitch when the tension detected by the tension detector is equal to or less than the second threshold value and the operation detector detects that the bobbin is moving. The sewing machine of claim 3 can determine that there is bobbin thread in the stitch when there is bobbin movement, even if the tension detected by the tension detector is equal to or less than the second threshold value. The sewing machine can avoid determining that there is no bobbin thread in the stitch in a situation where the tension is relatively small but the bobbin is continuing to move and the bobbin thread is thought to be tangled with the upper thread.

[0009] The bobbin thread determination unit of the sewing machine of claim 4 makes a determination using different threshold values ​​for a first sewing period from the start of sewing until a predetermined number of stitches are sewn, and a second sewing period following the first sewing period.By changing the threshold values ​​for the first sewing period and the second sewing period, the sewing machine of claim 4 can determine the presence or absence of bobbin thread in a stitch using threshold values ​​appropriate for each of the first sewing period and the second sewing period.

[0010] The bobbin thread determination unit of the sewing machine of claim 5 determines that the bobbin thread has broken when the detection result of the tension detector is equal to or less than the threshold value for a number of consecutive times or more and the operation detector detects that the bobbin is not operating. The sewing machine of claim 5 can determine that the bobbin thread has broken based on the presence or absence of the bobbin thread in the stitches.

[0011] The bobbin thread determination unit of the sewing machine of claim 6 determines that there is no bobbin thread in the stitch when the rate at which the detection result of the tension detector is equal to or less than the threshold value relative to the number of sewn stitches is equal to or greater than a rate threshold value and the operation detector detects that there is no operation of the bobbin. The sewing machine of claim 6 can avoid erroneously determining whether there is a bobbin thread in the stitch based on a singular value of the tension detector.

[0012] The sewing machine of claim 7 further includes a memory unit that stores combinations of the number of stitches of the stitches and the threshold value, and the bobbin thread determination unit makes a determination using the threshold value corresponding to the number of stitches based on the combinations stored in the memory unit. The sewing machine of claim 7 can determine the presence or absence of bobbin thread in the stitches using a threshold value that takes the number of stitches into consideration.

[0013] The bobbin thread determination unit of the sewing machine of claim 8 makes a determination using the tension detected by the tension detector acquired at a time corresponding to the number of stitches in the stitch within one cycle of up and down movement of the needle bar. The sewing machine of claim 8 can determine the presence or absence of bobbin thread in the stitch by taking into account the influence of stitches corresponding to the number of stitches, compared to when determining the presence or absence of bobbin thread in the stitch using tension detected by a tension detector acquired at the same time regardless of the number of stitches.

[0014] The bobbin thread determination unit of the sewing machine of claim 9 changes the frequency at which the tension detector obtains the detection result per one cycle of up and down movement of the needle bar according to the number of stitches in the stitch, and makes a determination using the tension detected by the tension detector. The sewing machine of claim 9 can determine the presence or absence of bobbin thread in a stitch by taking into account the influence of stitches according to the number of stitches, compared to when the presence or absence of bobbin thread in a stitch is determined using the tension detected by a tension detector obtained at the same frequency regardless of the number of stitches.

[0015] The sewing machine of claim 10 further includes a thread take-up lever that pulls up the upper thread entangled with the lower thread by the shuttle, the tension detector detects the tension of the upper thread, and the lower thread determination unit determines the presence or absence of the lower thread in the stitch based on whether the detection result of the tension detector is greater than the threshold value during a thread take-up period when the shuttle takes up the upper thread or a hook capture period when the shuttle captures the upper thread, and based on the detection result of the operation detector. The sewing machine of claim 10 can determine the presence or absence of the lower thread in the stitch based on the tension of the upper thread detected during the thread take-up period or the hook capture period. Because the tension of the upper thread is greater during the thread take-up period or the hook capture period than during the period between the thread take-up period and the hook capture period, erroneous determination can be avoided compared to when the lower thread determination unit makes a determination during a period when the tension of the upper thread is relatively small.

[0016] The motion detector of the sewing machine of claim 11 detects whether the bobbin is rotating or not. The sewing machine of claim 11 can detect whether the bobbin is moving or not based on the detection result of whether the bobbin is rotating or not.

[0017] The operation detector of the sewing machine of claim 12 detects whether or not there is a change in the amount of bobbin thread wound on the bobbin. The sewing machine of claim 12 can detect whether or not there is bobbin operation based on the result of detecting whether or not there is a change in the amount of bobbin thread wound on the bobbin.

[0018] The bobbin thread determination method of claim 13 is a bobbin thread determination method executed by a control unit of a sewing machine that includes a needle bar to which a sewing needle through which an upper thread is inserted is attached, a needle bar up-down movement mechanism that moves the needle bar up and down, a shuttle that is located below the needle bar and rotatably houses a bobbin around which a lower thread is wound, a shuttle mechanism that rotates the shuttle in synchronization with the up-and-down movement of the needle bar, capturing the annular upper thread inserted into the sewing needle and entangling it with the lower thread to form a stitch, a tension detector that detects the tension of the upper thread or the lower thread, and a motion detector that detects whether the bobbin is moving, and includes a bobbin thread determination step that determines whether the lower thread is present in the stitch based on whether the tension detected by the tension detector is greater than a threshold value and the detection result of the motion detector. When the bobbin thread determination method of claim 13 is executed, the sewing machine determines whether or not there is bobbin thread in the stitch based on whether the tension detected by the tension detector is greater than a threshold value and the detection result of the operation detector, so that it can more accurately determine whether or not there is bobbin thread in the stitch compared to devices that make determination using only a tension detector. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a perspective view of a sewing system 10 including a sewing machine 1 and an editing device 8. FIG. [Figure 2] FIG. [Figure 3] FIG. [Figure 4] 5 is a conceptual diagram showing the process by which the hook 49 captures the upper thread 55. FIG. [Figure 5] FIG. 2 is an electrical block diagram of the sewing machine 1 and the editing device 8. [Figure 6] 10 is a flowchart of a threshold setting process. [Figure 7] 3A and 3B are conceptual diagrams of sewing data 30 and stitches formed based on the sewing data 30. [Figure 8] A diagram showing the relationship between the tension D1 of the needle thread 55, the vertical position D2 of the needle tip, and the upper shaft angle. [Figure 9] Flow chart of the sewing process. [Figure 10] 10 is a graph showing the relationship between the number of stitches N in the first sewing period and the tension of the needle thread 55 in specific examples D3 and D4. [Figure 11] (A) is a graph showing the relationship between the number of stitches N during the second sewing period and the rotation speed of the upper shaft 22 in specific example D5, (B) is a graph showing the relationship between the number of stitches N during the second sewing period and the tension of the upper thread 55 detected during the shuttle capture period in specific example D5, and (C) is a graph showing the relationship between the number of stitches N during the second sewing period and the tension of the upper thread 55 detected during the lever pull-up period in specific example D5. [Figure 12] (A) is a graph showing the relationship between the number of stitches N during the second sewing period and the rotation speed of the upper shaft 22 in specific example D6, (B) is a graph showing the relationship between the number of stitches N during the second sewing period and the tension of the upper thread 55 detected during the shuttle capture period in specific example D6, and (C) is a graph showing the relationship between the number of stitches N during the second sewing period and the tension of the upper thread 55 detected during the lever pull-up period in specific example D6. [Figure 13] 10 is a flowchart of a sewing process according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0020] An embodiment of the present invention will be described with reference to the drawings. In the following description, arrows in the drawings will be used to indicate left and right, front and back, and up and down. A sewing system 10 will be described with reference to FIG. 1. The sewing system 10 includes a sewing machine 1 and an editing device 8. The editing device 8 is a portable terminal that is connected to the sewing machine 1. The editing device 8 may also be connected to sewing machines other than the sewing machine 1, or may be connected to multiple sewing machines. The editing device 8 edits sewing data related to stitches to be formed on a sewing object (for example, cloth 69 in FIG. 4). The editing device 8 outputs the sewing data to the sewing machine 1. The sewing machine 1 performs pattern sewing to form stitches on the cloth 69 based on the sewing data output by the editing device 8.

[0021] The sewing machine 1 will be described with reference to FIGS. 1 to 4. The sewing machine 1 includes a bed 2, a pillar 3, and an arm 4. The bed 2 is placed on a table 50. The bed 2 extends in the front-to-rear direction and includes a shuttle 49 (see FIG. 4), a shuttle mechanism 48 (see FIG. 4), and a rotation detector 141 (see FIG. 5). The shuttle 49 is located below the needle bar 9 (described later) and rotatably houses a bobbin B around which a lower thread 67 is wound. The shuttle mechanism 48 rotates the shuttle 49 in synchronization with the up-and-down movement of the needle bar 9, capturing the looped upper thread 55 inserted into the sewing needle 11 and entangling it with the lower thread 67 to form a stitch. The rotation detector 141 detects whether the bobbin B is rotating, as a measure of whether the bobbin B is moving. The rotation detector 141 is, for example, a non-photoelectric proximity sensor (magnetic sensor). The bobbin B has a magnet attached to a portion of its flange, and the magnetic force around the rotation detector 141 changes in response to the rotation of the bobbin B. The rotation detector 141 can detect whether the bobbin B is rotating by reading the change in magnetic force. The pillar 3 extends vertically upward from the rear of the bed 2. The pillar 3 houses a main motor 123 (see Figure 5) and other components. The arm 4 extends forward from the upper end of the pillar 3, facing the upper surface of the bed 2, and has a front end 7. The arm 4 houses an upper shaft 22 and a needle bar up / down movement mechanism 21 and other components. The needle bar 9 extends downward from the lower end of the front end 7. A sewing needle 11, through which an upper thread 55 is inserted, is attached to the needle bar 9. The sewing needle 11 is detachably attached to the lower end of the needle bar 9 and has an eye 111 at its lower end.

[0022] The sewing machine 1 has a work table 5 and a transfer device 6 above the bed 2. The work table 5 has a needle plate 501. The needle plate 501 has a needle hole 502 directly below the sewing needle 11. The sewing needle 11 can be inserted into the needle hole 502. The transfer device 6 has an X-axis movement mechanism, a Y-axis movement mechanism, an arm 65, a support 64, a lifting / lowering unit 62, and a holder 60. The X-axis movement mechanism is provided inside the bed 2, and the Y-axis movement mechanism is provided inside the column 3. The arm 65 holds the support 64 and is connected to the Y-axis movement mechanism. The support 64 extends in the left-right direction and supports the lifting / lowering unit 62 and the holder 60. The lifting / lowering unit 62 is mounted on the support 64 so that it can be raised and lowered. The holder 60 has a transfer plate 61 and a presser plate 63. The transfer plate 61 extends horizontally and has a rectangular opening at its front end in a plan view. The transfer plate 61 is connected to the support 64. The pressure plate 63 extends horizontally and has a rectangular opening in a plan view. The pressure plate 63 is connected to the lower end of the lifting section 62. The opening of the transfer plate 61 has substantially the same shape as the opening of the pressure plate 63 and corresponds to the position of the opening of the pressure plate 63.

[0023] The X-axis movement mechanism is driven by an X-axis motor 124 (see FIG. 5) and moves the lifting / lowering unit 62 and the holder 60 left and right (in the X-axis direction). The Y-axis movement mechanism is driven by a Y-axis motor 125 (see FIG. 5) and moves the arm 65 back and forth (in the Y-axis direction). The support unit 64 moves back and forth as the arm 65 moves back and forth. The lifting / lowering unit 62 and the holder 60 move together with the support unit 64. The operator places the cloth 69 (see FIG. 4) on the transfer plate 61. When the lifting / lowering unit 62 moves downward, the presser plate 63 descends onto the transfer plate 61. The holder 60 (presser plate 63 and transfer plate 61) clamps the cloth 69 from above and below. The sewing machine 1 moves the holder 60 back and forth and left and right using the X-axis movement mechanism and the Y-axis movement mechanism, thereby moving the cloth 69 and the sewing needle 11 clamped by the holder 60 relative to each other.

[0024] As shown in Figure 2, the front end 7 is equipped with a guide mechanism 14, a needle bar 9, a presser bar 12, etc. The guide mechanism 14 is located on the right side of the front end 7 and guides the upper thread 55. The guide mechanism 14 includes a sub-thread tension controller 15, a main thread tension controller 16, a thread guide 17, a tension detector 18, a thread take-up lever 19, and a thread guide 20. The upper thread 55 passes from the thread spool through the sub-thread tension controller 15, the main thread tension controller 16, the thread guide 17, the tension detector 18, the thread take-up lever 19, and the thread guide 20, and is then inserted into the eye 111 of the sewing needle 11. The thread take-up lever 19 pulls up the upper thread 55, which has been entangled with the bobbin thread 67 by the shuttle 49 (see Figure 4). The main thread tension controller 16 has a solenoid 128 (see Figure 5). The main thread tension controller 16 adjusts the thread tension by changing the tension applied to the upper thread 55 (hereinafter referred to as the upper thread tension) in accordance with the operation of the solenoid 128. The upper thread tension is set in consideration of the tension balance between the upper thread 55 and the bobbin thread 67. The main motor 123 (see Figure 5) drives the upper shaft 22 to rotate. The needle bar up / down movement mechanism 21 moves the needle bar 9 up and down in accordance with the rotation of the upper shaft 22.

[0025] Presser bar 12 extends downward from the lower end of front end 7 to the left of needle bar 9. Presser foot 13 is attached to the lower end of presser bar 12 and has a lower end 131. Lower end 131 is cylindrical and penetrates vertically, allowing sewing needle 11 to pass through. The presser foot drive mechanism swings presser bar 12 up and down in synchronization with the vertical swing of needle bar 9 caused by the rotation of upper shaft 22. The presser foot drive mechanism has a presser motor 129 (see Figure 5). The presser foot drive mechanism can adjust the height from the top of needle plate 501 to the bottom end of presser foot 13 (hereinafter referred to as the presser foot height) by driving presser motor 129. When sewing needle 11 comes out of fabric 69, presser foot 13 presses fabric 69 against needle plate 501 from above, preventing fabric 69 from lifting up from needle plate 501. The sewing needle 11 passes through the inside of the lower end portion 131 and pierces the fabric. The sewing needle 11 passes through the needle eye 502 and moves up and down.

[0026] As shown in Figures 2 and 3, the tension detector 18 is located on the right side of the front end 7, in a vertical position between the auxiliary thread tensioner 15 and the main thread tensioner 16, and in the path between the thread guide 17 and the thread take-up lever 19. The tension detector 18 can detect the needle thread tension. The tension detector 18 includes a mounting base 51, a holding portion 52, a magnetic sensor 53, a plate 54, a guide member 77, and a magnet 56. The mounting base 51 includes a mounting portion 57 and a base portion 59. The mounting portion 57 and the base portion 59 are formed integrally with each other. The mounting portion 57 includes an elongated hole 58 through which a screw is inserted. The screw inserted into the elongated hole 58 is fastened to a screw hole provided on the right side of the front end 7. The base portion 59 is located on the left side of the mounting base 51. The base portion 59 includes a left protrusion 71 and a right protrusion 72. The left protrusion 71 and the right protrusion 72 each have a rectangular parallelepiped shape extending in the front-rear direction.

[0027] The holding portion 52 is formed in a substantially rectangular parallelepiped shape and is attached to the base portion 59 between the left protrusion 71 and the right protrusion 72. The holding portion 52 is made of a non-magnetic material. The magnetic sensor 53 is held on the front surface of the holding portion 52. The magnetic sensor 53 is a Hall element. The magnetic sensor 53 is located rearward of the front ends of the left protrusion 71 and the right protrusion 72.

[0028] Plate 54 is a plate-like member having a thickness in the front-to-rear direction, and spans left protrusion 71 and right protrusion 72. Guide member 77 is attached to left protrusion 71 and right protrusion 72. The left end of plate 54 is sandwiched between guide member 77 and left protrusion 71, and the right end of plate 54 is sandwiched between guide member 77 and right protrusion 72. A gap is formed between the left-to-right center of plate 54 and the front surface of holding portion 52. Therefore, plate 54 bends in the front-to-rear direction, with both left-to-right ends as fulcrums.

[0029] The magnet 56 is formed in a cylindrical shape extending in the front-to-rear direction. The magnet 56 is fixed to the rear surface of the plate 54 in the center in the left-to-right direction. When the plate 54 bends in the front-to-rear direction, the magnet 56 moves forward or backward, changing the distance from the magnetic sensor 53. The magnetic sensor 53 detects the change in magnetic flux density from the magnet 56 and outputs a voltage according to the magnetic flux density.

[0030] The guide member 77 has an upper guide groove 74 and a lower guide groove 76. The upper guide groove 74 and the lower guide groove 76 are aligned vertically with the plate 54 between them. The upper guide groove 74 and the lower guide groove 76 open vertically and are formed like a hook in a plan view. The upper guide groove 74 has an upper retaining hole 73, and the lower guide groove 76 has a lower retaining hole 75. The upper retaining hole 73 and the lower retaining hole 75 are through holes that open vertically. The upper thread 55 passes through the upper retaining hole 73 and the lower retaining hole 75, respectively. The upper thread 55 between the upper retaining hole 73 and the lower retaining hole 75 contacts the plate 54 from the front. As the upper thread tension increases, the upper thread 55 urges the plate 54 backward. The magnetic sensor 53 outputs a voltage corresponding to the front-to-rear position of the plate 54, which bends forward and backward due to the upper thread tension. The sewing machine 1 can obtain the upper thread tension from the output voltage of the magnetic sensor 53.

[0031] As shown in FIG. 1, the editing device 8 is placed on a table 50 and is equipped with a display screen 86, a speaker 87 (see FIG. 5), an operation panel 88, and selection keys 89. The display screen 86 displays various screens. The speaker 87 outputs various sounds. The operation panel 88 and selection keys 89 are used to input various information and instructions to the editing device 8. The operation panel 88 is a touch panel and is provided in front of the display screen 86. The selection keys 89 are provided below the display screen 86 and include an up key 89A, a down key 89B, a left key 89C, and a right key 89D. When inputting various information and instructions to the editing device 8, the operator operates the operation panel 88 or the selection keys 89.

[0032] The electrical configuration of the sewing system 10 will be described with reference to FIG. 5. The sewing machine 1 includes a control unit 100. The control unit 100 includes a CPU 101, a ROM 102, a RAM 103, a storage device 104, an input / output interface (I / F) 106, and drive circuits 113 to 116. The input / output I / F 106 is connected to the CPU 101, the ROM 102, the RAM 103, the storage device 104, the drive circuits 113 to 116, the treadle 126, the power switch 127, the rotation detector 141, the tension detector 18, the solenoid 128, and the external connection I / F 130. The CPU 101 controls the overall operation of the sewing machine 1. The ROM 102 stores various programs, etc. The RAM 103 temporarily stores various information. The storage device 104 is non-volatile and stores various information. The storage device 104 stores a combination of the number of stitches for a stitch 35 (see FIG. 7) when sewing according to the sewing data 30 (see FIG. 7) and a threshold value used in the main processing described below. The sewing data 30 is expressed in a sewing coordinate system that drives the X-axis motor 124 and the Y-axis motor 125.

[0033] The drive circuit 113 is connected to the main motor 123. The CPU 101 controls the main motor 123 via the drive circuit 113. For example, the CPU 101 controls the rotation speed (sewing speed) of the output shaft of the main motor 123. The encoder 133 is provided on the output shaft of the main motor 123 and connected to the input / output I / F 106. The encoder 133 detects the rotation speed and rotation position of the output shaft of the main motor 123. The rotation position of the output shaft of the main motor 123 is called the upper shaft angle. The drive circuit 114 is connected to the X-axis motor 124. The CPU 101 controls the X-axis motor 124 via the drive circuit 114. The encoder 134 is provided on the output shaft of the X-axis motor 124 and connected to the input / output I / F 106. The encoder 134 detects the rotation direction, rotation speed, and rotation position of the output shaft of the X-axis motor 124. The drive circuit 115 is connected to the Y-axis motor 125. CPU 101 controls Y-axis motor 125 via drive circuit 115. Encoder 135 is provided on the output shaft of Y-axis motor 125 and connected to input / output I / F 106. Encoder 135 detects the rotation direction, rotation speed, and rotation position of the output shaft of Y-axis motor 125. Drive circuit 116 is connected to presser motor 129. CPU 101 controls presser motor 129 via drive circuit 116. Encoder 136 is provided on the output shaft of presser motor 129 and connected to input / output I / F 106. Encoder 136 detects the rotation direction, rotation speed, and rotation position of the output shaft of presser motor 129.

[0034] CPU 101 drives main motor 123 to rotate upper shaft 22, thereby controlling the up and down swing of needle bar 9 and presser bar 12 and the rotation of the vertical shuttle. Based on sewing data, CPU 101 drives main motor 123 and simultaneously drives X-axis motor 124 and Y-axis motor 125 to control the position of holder 60. Sewing machine 1 sews on fabric 69 under this control.

[0035] The treadle 126 inputs various instructions to the control unit 100. For example, an operator depresses the treadle 126 when starting a sewing operation of the sewing machine 1. The power switch 127 starts and stops the sewing machine 1. The rotation detector 141 inputs the detection result of whether or not the bobbin B attached to the shuttle 49 is rotating to the control unit 100. The tension detector 18 outputs an output voltage according to the needle thread tension to the control unit 100. The CPU 101 controls the operation of the solenoid 128. The external connection I / F 130 is connected to the external connection I / F 95 of the editing device 8 via the cable 70.

[0036] The editing device 8 includes a control unit 80. The control unit 80 includes a CPU 81, a ROM 82, a RAM 83, a storage device 84, and an input / output I / F 85. The input / output I / F 85 is connected to the CPU 81, the ROM 82, the RAM 83, the storage device 84, the display screen 86, the speaker 87, the operation panel 88, the selection keys 89, and the external connection I / F 95. The CPU 81 controls the overall operation of the editing device 8. The ROM 82 stores a program for performing the main processing described below, a plurality of types of codes, etc. The RAM 83 temporarily stores various types of information. The storage device 84 is non-volatile and stores various types of information such as sewing data. The CPU 81 controls the display on the display screen 86, controls the sound output from the speaker 87, and controls input from the operation panel 88 and the selection keys 89. The external connection I / F 95 is connected to the external connection I / F 130 of the sewing machine 1 via the cable 70.

[0037] An overview of the operation of the sewing machine 1 will be described with reference to Figures 1 to 5. The operator holds the fabric 69 on the holder 60 on the needle plate 501. When the operator inputs sewing instructions, the sewing machine 1 drives the main motor 123, X-axis motor 124, and Y-axis motor 125 in accordance with the sewing data. Driven by the main motor 123, the upper shaft 22 rotates, moving the needle bar 9 and thread take-up lever 19 up and down. The shuttle 49 rotates in synchronization with the rotation of the upper shaft 22.

[0038] The sewing needle 11, which descends together with the needle bar 9, penetrates the fabric 69 and passes through a needle eye 502 (see Figure 2) formed in the needle plate 501. As shown in Figure 4(a), the needle thread 55 near the eye 111, which has descended to below the needle eye 502, becomes circular. As shown in Figure 4(b), the shuttle 49 rotates clockwise as viewed from the front, causing the point 46 to capture the circular needle thread 55. Hereinafter, the period during which the point 46 captures the circular needle thread 55 will be referred to as the shuttle capturing period. The sewing needle 11 rises above the fabric 69, and the shuttle 49 rotates further clockwise as viewed from the front. The point 46 pulls in the circular needle thread 55 in the rotational direction, causing the circular needle thread 55 to expand in diameter.

[0039] As shown in FIG. 4(c), when the looped upper thread 55 passes through the shuttle 49, the upper thread 55 becomes entangled with the bobbin thread 67. The rotation direction of the shuttle 49 is switched to counterclockwise as viewed from the front. As shown in FIG. 4(d), the thread take-up lever 19 pulls up the upper thread 55 that has become entangled with the bobbin thread 67. Hereinafter, the period during which the thread take-up lever 19 pulls up the upper thread 55 will be referred to as the thread take-up lift-up period. The looped upper thread 55 contracts in diameter, and the sewing machine 1 completes sewing one stitch. In this embodiment, the sewing machine 1 sews one stitch each time the upper shaft 22 rotates once. The sewing machine 1 repeats the above operations to form multiple stitches 68 on the fabric 69.

[0040] 6 to 8, the threshold setting process of the sewing machine 1 will be described using the specific example of Fig. 7. When the operator turns on the power of the sewing machine 1 and then inputs a start command, the CPU 101 reads out a program and sewing data from the ROM 102 and starts the threshold setting process.

[0041] As shown in FIG. 6, the CPU 101 acquires sewing data 30 (S51). As shown in FIG. 7, the sewing data 30 in this specific example is data for forming a rectangular stitch 35, including needle locations P1 to P70 according to a predetermined sewing sequence. The needle locations are the positions where the sewing needle 11 attached to the needle bar 9 is intended to insert into the fabric 69. Needle location P1 is the first start point in the sewing sequence, and needle location P70 is the last end point in the sewing sequence. Stitches based on needle locations P1 to P3 are formed in the direction indicated by arrow J1, and stitches based on needle locations P4 to P70 are formed counterclockwise from needle location P3 in the directions indicated by arrows J2 to J6. The editing device 8 can output the sewing data 30 to the sewing machine 1. In the sewing machine 1, the CPU 101 receives the sewing data 30 output by the editing device 8. The CPU 101 sets a variable N to 1, which is used to read out the needle locations P1 to P70 of the received sewing data 30 in the order from the start point P1 to the end point P70, and starts sewing based on the sewing data 30 acquired in S51 (S52). The sewing machine 1 drives the main motor 123, X-axis motor 124, and Y-axis motor 125 in accordance with the sewing data 30. The main motor 123 rotates the upper shaft 22, moving the needle bar 9 and thread take-up lever 19 up and down. The shuttle 49 rotates in synchronization with the rotation of the upper shaft 22.

[0042] The CPU 101 determines whether it is time (phase) to detect the needle thread tension based on the head shaft angle detected by the encoder 133 (S53). As shown in FIG. 8, during sewing, the needle thread tension and the height of the lower end (needle tip) of the sewing needle 11 fluctuate periodically, with the sewing period being the unit cycle, depending on the head shaft angle. A sewing period is the period during which one stitch is sewn. The vertical axis on the right side of FIG. 8 indicates the height of the lower end of the sewing needle 11 relative to the top surface of the needle plate 501. When the head shaft angle is H1 or H2, the lower end of the sewing needle 11 is at the same height as the top surface of the fabric 69 placed on the top surface of the needle plate 501. In other words, the period when the head shaft angle is from H1 to H2 is the penetration period during which the sewing needle 11 penetrates the fabric 69. The period when the head shaft angle is less than H1 or greater than H2 is the non-penetration period during which the sewing needle 11 is above the fabric 69. The sewing period includes the thread take-up period and the shuttle capture period. The needle thread tension peaks during the sewing period, during the thread take-up lever lifting period and the hook capture period. The CPU 101 of this embodiment determines the timing for determining the needle thread tension (detection timing) from the upper shaft angle based on the detection results of the encoder 133. The CPU 101 of this embodiment changes the timing for determining the needle thread tension between the first sewing period, which is the period from the start of sewing until a predetermined number of stitches are sewn, and the second sewing period following the first sewing period. The length of the first sewing period may be set as appropriate, and in this embodiment, it is the period from the start of sewing until the number of stitches is less than 10. The CPU 101 determines the presence or absence of the bobbin thread 67 in the stitches of the first sewing period using the needle thread tension detected by the tension detector 18 during the hook capture period. The CPU 101 determines the presence or absence of the bobbin thread 67 in the stitches of the second sewing period using the needle thread tension detected by the tension detector 18 during the thread take-up lever lifting period. The CPU 101 determines whether the sewing period is the first sewing period or the second sewing period based on the variable N, and specifies the detection timing. If it is not time for detection (S53: NO), the CPU 101 waits until it is time for detection.

[0043] If it is time to detect the tension (S53: YES), the CPU 101 stores the detection result output by the tension detector 18 as the tension corresponding to the variable N (S54). The CPU 101 determines whether the variable N is the final number of stitches in the sewing data 30 acquired in S51 (S55). If it is not the final number of stitches (S55: NO), the CPU 101 adds 1 to the variable N (S56) and returns the process to S53. If it is the final number of stitches (S55: YES), the CPU 101 stops sewing based on the sewing data 30 (S57). The CPU 101 determines whether to continue the process (S58). In this embodiment, the CPU 101 executes the processes of S52 to S57 multiple times to acquire multiple pairs of correspondence between the number of stitches and the tension, and acquires the average tension value and the standard deviation for each number of stitches. The number of pairs may be set as appropriate, for example, between 5 and 20. The operator of the sewing machine 1 changes the position of the cloth 69 relative to the holder 60 and inputs a continuation instruction to execute the processes of S52 to S57. When the continuation instruction is detected (S58: YES), the CPU 101 returns the process to S52.

[0044] When the CPU 101 does not detect a continue instruction (S58: NO), the CPU 101 sets a threshold value for each stitch number based on the correspondence between multiple pairs of stitch numbers and tensions (S59). The CPU 101 sets a first threshold value H1(N), which is the threshold value for the stitch number N in the first sewing period, according to equation (1), and sets a second threshold value H2(N), which is the threshold value for the stitch number N in the second sewing period, according to equation (2). First threshold H1 (N) = average tension (N) - C1 × standard deviation (N) Equation (1) Second threshold H2 (N) = average tension (N) - C2 × standard deviation (N) Equation (2) Here, the average tension (N) is the average tension corresponding to the number of stitches N, and the standard deviation (N) is the standard deviation of the tension corresponding to the number of stitches N. C1 and C2 are constants, and may be the same as or different from each other. C1 and C2 may be set by the operator of the sewing machine 1, or may be set automatically by the CPU 101 according to the sewing conditions. In this embodiment, as an example, C1 is 2, and C2 is 2 or 3. In other words, C1 is a value equal to or smaller than C2. The CPU 101 stores the set threshold value in the storage device 104 in association with the number of stitches N. The CPU 101 then ends the threshold value setting process.

[0045] The sewing process of the sewing machine 1 will be described with reference to FIGS. 9 to 12. After the operator specifies the sewing data, when the operator inputs a command to start sewing, the CPU 101 reads a program from the ROM 102 and starts the sewing process of FIG. 9. Specific examples D3 to D6 of FIGS. 10 to 12 are used as specific examples for determining whether or not there is bobbin thread 67 for a stitch when sewing according to the sewing data 30. Specific example D3 shows an example of the relationship between the needle thread tension and the number of stitches N when there is bobbin thread 67 for the stitch throughout the first sewing period. Specific example D4 shows an example of the relationship between the needle thread tension and the number of stitches N when there is no bobbin thread 67 for the stitch at the start of sewing. Specific example D5 shows an example of the relationship between the needle thread tension and the number of stitches N when the second threshold value H2 is set under the condition that C2 is 3 and the bobbin thread 67 for the stitch runs out (bobbin thread breakage) partway through the second sewing period. Specific example D6 shows an example of the relationship between the needle thread tension and the number of stitches N in the case of multi-needle pseudo-sewing during the second sewing period when the second threshold value H2 is set under the condition that C2 is 2. Note that pseudo-sewing refers to defective sewing in which a stitch-like object is formed only with the needle thread 55, and a stitch appears to have been made, but the bobbin thread 67 is not entangled with the needle thread 55. Multi-needle pseudo-sewing refers to a sewing example in which such pseudo-sewing has occurred multiple times. In the case of pseudo-sewing, the bobbin thread 67 is not supplied sequentially.

[0046] As shown in FIG. 9, the CPU 101 executes a variable initialization process (S1). The CPU 101 sets counters E and F, which count the number of consecutive times an abnormality stored in the RAM 103 has been detected, to 0, and sets counter N, which counts the number of stitches, to 1. The CPU 101 determines whether the first sewing period is in progress based on variable N (S2). If the first sewing period is in progress (S2: YES), the CPU 101 determines whether rotation of the bobbin B has been detected based on the detection result of the rotation detector 141 (S3). In specific example D3, rotation of the bobbin B is detected (S3: YES), and the CPU 101 determines that there is bobbin thread 67 for the stitch, sets counter E for the first sewing period to 0 (S18), and then performs the process of S21, which will be described later. In specific example D4, it is detected that the bobbin B is not rotating (S3: NO), and it is determined whether the upper thread tension detected by the tension detector 18 at a predetermined time within the first sewing period is greater than the first threshold value H1(N) set in S59 (S4). The CPU 101 uses the first threshold value H1(N) corresponding to the number of stitches N, based on a combination of the number of stitches N and the first threshold value H1 stored in the memory device 104. As shown in Figure 10, when the number of stitches N is 1, the upper thread tension in specific example D4, indicated by a white square, is greater than the first threshold value H1(1), indicated by a white circle (S4: YES). Therefore, the CPU 101 determines that there is a lower thread 67 for the stitch, sets counter E to 0 (S18), and then performs the processing of S21, which will be described later. In this way, when the rotation detector 141 detects that the bobbin B is not rotating (S3: NO) and the tension detected by the tension detector 18 is greater than the first threshold value H1(N) (S4: YES), the CPU 101 determines that there is a lower thread 67 for the stitch. On the other hand, when the number of stitches N is any one of 3 to 6, the upper thread tension in specific example D4 is equal to or less than the first threshold value H1(N) (S4: NO), so the CPU 101 increments the counter E that detects an abnormality in the lower thread 67 by 1 (S5).

[0047] The CPU 101 determines whether the counter E is greater than the count threshold (S6). The count threshold may be preset to a value smaller than 9, which is the maximum number of stitches included in the first sewing period. The rotation threshold in this embodiment is 3. When the variable N is 6, the counter E in specific example D4 is 4, which is greater than the count threshold (S6: YES), so the CPU 101 determines that there is no bobbin thread 67 for the stitch (S17). The CPU 101 may output an instruction to the editing device 8 to display the determination result on the display screen 86. If the sewing machine 1 is equipped with an alarm unit such as an LED lamp, the CPU 101 may notify the alarm unit of the determination result that there is no bobbin thread 67 for the stitch. In this way, when the rotation detector 141 detects that there is no rotation of the bobbin B (S3: NO) and the tension detected by the tension detector 18 is equal to or less than the first threshold H1(N) (S4: YES), the CPU 101 determines that there is no bobbin thread 67 for the stitch (S17). In this embodiment, if the amount of tension detected by tension detector 18 is equal to or less than first threshold value H1(N) for a number of consecutive times equal to or greater than the threshold value (S4: NO, S6: YES), and if rotation detector 141 detects that bobbin B is not rotating (S3: NO), CPU 101 determines that there is no bobbin thread 67 for the stitch (S17). CPU 101 ends sewing based on sewing data 30 midway through the sewing (S23), thereby ending the sewing process. Note that in this embodiment, there is no bobbin thread 67 (for the stitch) means that the bobbin thread 67 has run out and broken, or that the bobbin thread 67 has come off when the fabric is fed during sewing, and is therefore not entangled with the upper thread 55.

[0048] In specific example D4, when variable N is 5 or less, counter E is equal to or less than the number threshold value (S6: NO), so CPU 101 determines that there is bobbin thread 67 for the stitch (S7) and determines whether stitch count N is the final stitch count (S21). If stitch count N is not the final stitch count (S21: NO), CPU 101 adds 1 to stitch count N (S22) and returns the process to S2. If stitch count N is the final stitch count (S21: YES), CPU 101 ends sewing (S23), thereby completing the sewing process.

[0049] If it is not the first sewing period (S2: NO), the CPU 101 determines whether the needle thread tension detected by the tension detector 18 at a predetermined time within the second sewing period is greater than the second threshold value H2(N) set in S59 (S11). The CPU 101 uses the second threshold value H2(N) corresponding to the number of stitches N, based on a combination of the number of stitches N and the second threshold value H2(N) stored in the storage device 104. As shown in FIG. 11(C), in specific example D5, when the number of stitches N is 10, the needle thread tension indicated by the black circle is greater than the second threshold value H2(10) indicated by the white square (S11: YES). Therefore, the CPU 101 determines that there is a bobbin thread 67 for the stitch, sets the counter F for the second sewing period to 0 (S18), and then performs the processing of S21 described above. As shown in FIG. 12(C), in specific example D6, when the number of stitches N is 10, the needle thread tension indicated by a black circle is equal to or less than the second threshold value H2(N) indicated by a white square (S11: NO), so the CPU 101 outputs an instruction to the editing device 8 to display on the display screen 86 that an abnormality has been detected (S12). If the sewing machine 1 is equipped with an alarm unit such as an LED lamp, the CPU 101 may notify the alarm unit that an abnormality has been detected. The CPU 101 increments the counter F for the second sewing period by 1 (S13). The CPU 101 determines whether the counter F is greater than the count threshold value (S14). The count threshold value in S14 may be the same as or different from the count threshold value in S6. In this embodiment, the count threshold value is, for example, 5.

[0050] In specific example D6, when the number of stitches N is 10, counter F is 1, which is less than the number threshold (S14: NO), so CPU 101 determines whether the upper thread tension detected by tension detector 18 at a predetermined time within the second sewing period is greater than a third threshold (S15). The third threshold is smaller than the second threshold. The third threshold is a threshold for detecting when the lower thread 67 is not tangled in the stitch. In specific example D6, when variable N is 10, if the upper thread tension is greater than the third threshold (S15: YES), CPU 101 performs the process of S21. In specific example D3, when the number of stitches N is 11, the upper thread tension is greater than the second threshold H2(N) (S11: YES), so CPU 101 determines that the lower thread 67 is present, sets counter F to 0 (S18), and then performs the process of S21 described above. Thus, in specific example D6, there are cases where the upper thread tension falls below the second threshold H2(N), but there is no period during which the upper thread tension is continuously equal to or greater than the number of times threshold or less than the second threshold H2(N), so it is determined that there is bobbin thread 67 throughout the second sewing period. When the upper thread tension is equal to or less than the third threshold (S15: NO), CPU 101 determines that there is no bobbin thread 67 for the stitch (S17), ends sewing based on sewing data 30 (S23), and ends the sewing process. In other words, if the upper thread tension falls below the third threshold even once, CPU 101 detects that there is no bobbin thread 67 for the stitch.

[0051] On the other hand, in specific example D5, when the number of stitches N is 36, counter F is 6, which is greater than the number threshold value (S14: YES), so CPU 101 determines whether rotation detector 141 has detected rotation of bobbin B (S16). When the detection result of rotation detector 141 indicates that rotation is present (S16: YES), CPU 101 determines that there is bobbin thread 67 for the stitch (S19) and performs processing of S21. In this way, when the tension detected by tension detector 18 is equal to or less than second threshold value H2(N) and rotation detector 141 detects that there is rotation of bobbin B (S16: YES), CPU 101 determines that there is bobbin thread 67 for the stitch.

[0052] When the detection result of the rotation detector 141 indicates no rotation (S16: NO), the CPU 101 determines that there is no bobbin thread 67 for the stitch (S17). As described above, when the tension detected by the tension detector 18 is equal to or less than the second threshold value H2(N) (S11: NO) and the rotation detector 141 detects that the bobbin B is not rotating (S16: NO), the CPU 101 determines that there is no bobbin thread 67 for the stitch. In this embodiment, when the tension detected by the tension detector 18 is equal to or less than the second threshold value H2(N) for a number of consecutive occurrences equal to or greater than the number of times threshold value (S11: NO, S14: YES) and the rotation detector 141 detects that the bobbin B is not rotating (S16: NO), the CPU 101 determines that the bobbin thread 67 has run out (bobbin thread breakage) (S17). The CPU 101 ends sewing based on the sewing data 30 midway through sewing (S23), and the sewing process ends.

[0053] As with the above embodiment, the sewing process of the first modified example will be described with reference to FIG. 9 . After the operator specifies the sewing data 30 and inputs a command to start sewing, the CPU 101 reads a program from the ROM 102 and starts the sewing process of the first modified example shown in FIG. 9 . In the first modified example, the CPU 101 changes the frequency of judgment between a first sewing period, which is from the start of sewing until a predetermined number of stitches are sewn, and a second sewing period, which follows the first sewing period. The CPU 101 judges the presence or absence of the bobbin thread 67 in the stitches during the first sewing period using the detection results detected by the tension detector 18 during the thread take-up lever pull-up period and the hook capture period. The CPU 101 judges the presence or absence of the bobbin thread 67 in the stitches during the second sewing period using the detection results detected by the tension detector 18 during the thread take-up lever pull-up period. That is, during the first sewing period, the CPU 101 detects the needle thread tension twice per cycle of the up-and-down movement of the needle bar 9 and makes the judgment in S4. The CPU 101 makes the judgment in S4 using a first threshold value H1(N) corresponding to the timing of detecting the needle thread tension. During the second sewing period, the CPU 101 detects the needle thread tension once for each cycle of the up and down movement of the needle bar 9, and makes the determination in S11. The other processing is the same as in the above embodiment, so a description thereof will be omitted.

[0054] The sewing process of the second modified example will be described with reference to FIG. 13. In the sewing process of the second modified example, the CPU 101 determines whether or not the proportion of abnormalities detected relative to the number of stitches N is greater than a proportion threshold. When the operator specifies the sewing data 30 and then inputs a command to start sewing, the CPU 101 reads a program from the ROM 102 and starts the sewing process of FIG. 13. In FIG. 13, the same processes as those in the sewing process of FIG. 9 are denoted by the same reference numerals. As shown in FIG. 13, the sewing process of the second modified example differs from the sewing process of FIG. 9 in that S31 is performed instead of S6, S32 is performed instead of S14, and S33 is performed instead of S18. Below, S31 to S33 that differ from the sewing process of FIG. 9 will be described, and a description of the other processes will be omitted.

[0055] In S31, the CPU 101 determines whether the ratio obtained by dividing the counter E by the number of stitches N is greater than a ratio threshold (S31). The ratio threshold may be set in advance to a value smaller than 1. The ratio threshold is, for example, any value between 20% and 60%. If the ratio is greater than the ratio threshold (S31: YES), the CPU 101 determines that there is no lower thread 67 for the stitch (S17). If the ratio is equal to or less than the ratio threshold (S31: NO), the CPU 101 determines that there is lower thread 67 for the stitch (S7).

[0056] In S32, the CPU 101 determines whether the ratio obtained by dividing the counter F by the value obtained by subtracting 9, which is the maximum number of stitches in the first sewing period, from the number of stitches N (i.e., the number of stitches in the second sewing period) is greater than a ratio threshold (S32). The ratio threshold may be set in advance to a value smaller than 1. The ratio threshold of S32 may be the same as or different from the ratio threshold of S31. The ratio threshold is, for example, anywhere from 5 to 10%. If the ratio is greater than the ratio threshold (S32: YES), the CPU 101 determines whether rotation of the bobbin B has been detected based on the detection result of the rotation detector 141 (S16). If the ratio is equal to or less than the ratio threshold (S31: NO), the CPU 101 determines whether the upper thread tension detected by the tension detector 18 at a predetermined time within the second sewing period is greater than a third threshold (S15). In S33, the CPU 101 determines that there is bobbin thread 67 (S33) without initializing counters E and F. In a modified example, when the ratio threshold is set to 0.1, in the case of specific example D6 in Fig. 12, if the ratio is greater than the ratio threshold (S32: YES) and the rotation detector 141 detects that there is no rotation of bobbin B (S16: NO), the CPU 101 can determine that there is no bobbin thread 67 in the stitch, and in particular that there is a multi-needle pseudo stitching.

[0057] In the above embodiment, first modified example, and second modified example, the sewing machine 1, needle bar 9, sewing needle 11, tension detector 18, needle bar up-down movement mechanism 21, shuttle mechanism 48, shuttle 49, upper thread 55, lower thread 67, memory device 104, and rotation detector 141 are examples of the sewing machine, needle bar, sewing needle, tension detector, needle bar up-down movement mechanism, shuttle mechanism, shuttle, upper thread, lower thread, memory device, and motion detector of the present invention, respectively. The CPU 101 that executes the processes of S3 to S7 and S11 to S19 in FIG. 9 is an example of a lower thread determination unit of the present invention. The processes of S3 to S7 and S11 to S19 in FIG. 9 are an example of a lower thread determination step of the present invention. The CPU 101 that executes the processes of S3 to S5, S7, S11 to S13, S15 to S17, S19, and S31 to S33 in FIG. 13 is an example of a lower thread determination unit of the present invention. The processes of S3 to S5, S7, S11 to S13, S15 to S17, S19, and S31 to S33 in FIG. 13 are an example of the lower thread determination step of the present invention.

[0058] The sewing machine 1 of the above embodiment, first modified example, and second modified example includes a needle bar 9, a needle bar up-and-down movement mechanism 21, a shuttle 49, a shuttle mechanism 48, a tension detector 18, a rotation detector 141, and a CPU 101. The needle bar 9 is fitted with a sewing needle 11 through which an upper thread 55 is passed. The needle bar up-and-down movement mechanism 21 moves the needle bar 9 up and down. The shuttle 49 is provided below the needle bar 9 and rotatably houses a bobbin B around which a lower thread 67 is wound. The shuttle mechanism 48 rotates the shuttle 49 in synchronization with the up-and-down movement of the needle bar 9, capturing the loop-shaped upper thread 55 passed through the sewing needle 11 and entangling it with the lower thread 67 to form a stitch. The tension detector 18 detects the tension of the upper thread 55 or the lower thread 67. The rotation detector 141 detects whether the bobbin B is rotating. The CPU 101 determines whether or not the lower thread 67 is present in the stitch (S3 to S7, S11 to S19) based on whether or not the tension detected by the tension detector 18 is greater than a threshold value and on the detection result of the rotation detector 141. The sewing machine 1 determines whether or not the lower thread 67 is present in the stitch based on whether or not the tension detected by the tension detector 18 is greater than a threshold value and on the detection result of the rotation detector 141, and therefore can more accurately determine whether or not the lower thread 67 is present in the stitch compared to devices that make a determination using only the tension detector 18.

[0059] The CPU 101 of the sewing machine 1 determines that there is a bobbin thread 67 in the stitch (S18, S33) when the rotation detector 141 detects that there is no rotation of the bobbin B (S3: NO) and the tension detected by the tension detector 18 is greater than the first threshold value H1(N) (S4: YES). The CPU 101 determines that there is no bobbin thread 67 in the stitch (S17) when the rotation detector 141 detects that there is no rotation of the bobbin B (S3: NO) and the tension detected by the tension detector 18 is equal to or less than the first threshold value H1(N) (S4: NO). Even if there is no rotation of the bobbin B, the sewing machine 1 can determine that there is a bobbin thread 67 in the stitch if the tension detected by the tension detector 18 is greater than the first threshold value H1(N). The sewing machine 1 can avoid determining that there is no lower thread 67 for the stitch in a situation where the rotation of the bobbin B has temporarily stopped but the lower thread 67 is thought to be entangled with the upper thread 55.

[0060] When the tension detected by the tension detector 18 is equal to or less than the second threshold value H2(N) (S11: NO) and the rotation detector 141 detects that the bobbin B is not rotating (S16: NO), the CPU 101 of the sewing machine 1 determines that there is no bobbin thread 67 in the stitch (S17). When the tension detected by the tension detector 18 is equal to or less than the second threshold value H2(N) (S11: NO) and the rotation detector 141 detects that the bobbin B is rotating (S16: YES), the CPU 101 determines that there is bobbin thread 67 in the stitch (S19). Even if the tension detected by the tension detector 18 is equal to or less than the second threshold value H2(N), the sewing machine 1 can determine that there is bobbin thread 67 in the stitch when the bobbin B is rotating. The sewing machine 1 can avoid determining that there is no lower thread 67 for the stitch in a situation where the tension is relatively small but the bobbin B continues to rotate and the lower thread 67 for the stitch is thought to be entangled with the upper thread 55.

[0061] The CPU 101 of the sewing machine 1 uses different threshold values ​​to determine whether a first sewing period, which is from the start of sewing until a predetermined number of stitches are sewn, and a second sewing period following the first sewing period (S4, S11). By changing the threshold values ​​between the first sewing period and the second sewing period, the sewing machine 1 can determine whether the bobbin thread 67 is present in the stitches using threshold values ​​appropriate for each of the first sewing period and the second sewing period.

[0062] The CPU 101 of the sewing machine 1 in the above embodiment and the first modified example determines that there is no bobbin thread 67 in the stitch (S17) when the tension detected by the tension detector 18 is equal to or less than the threshold value for a number of consecutive times or more (S4: NO, S6: YES) and the rotation detector 141 detects that the bobbin B is not rotating (S3: NO). The CPU 101 of the sewing machine 1 determines that there is no bobbin thread 67 in the stitch (S17) when the tension detected by the tension detector 18 is equal to or less than the threshold value for a number of consecutive times or more (S11: NO, S14: YES) and the rotation detector 141 detects that the bobbin B is not rotating (S16: NO). The sewing machine 1 can determine that there is a bobbin thread breakage based on the presence or absence of the bobbin thread 67 in the stitch. 11(A), when the bobbin thread 67 for the stitches runs out during sewing, no abnormality is observed in the number of rotations indicated by the black circle during sewing, but as shown in Figures 11(B) and (C), the loss of the bobbin thread 67 for the stitches causes the needle thread tension to continuously drop below the second threshold value H2 (N), so by using the sewing process of the above embodiment, it is possible to detect early that the bobbin thread 67 for the stitches has run out. Furthermore, the sewing machine 1 can more accurately detect early that the bobbin thread 67 for the stitches has run out by determining the presence or absence of the bobbin thread 67 for the stitches using the tension detected by tension detector 18 obtained during the thread take-up pull-up period as shown in Figure 11(C), rather than determining the presence or absence of the bobbin thread 67 for the stitches using the tension detected by tension detector 18 obtained during the hook capture period as shown in Figure 11(B).

[0063] The CPU 101 of the sewing machine 1 of the second modified example determines that there is no bobbin thread 67 in the stitch (S17) when the ratio of the tension detected by the tension detector 18 that is equal to or less than the threshold to the number of sewn stitches is equal to or greater than the ratio threshold (S4: NO, S31: YES) and the rotation detector 141 detects that the bobbin B is not rotating (S3: NO). The CPU 101 determines that there is no bobbin thread 67 in the stitch (S17) when the ratio of the tension detected by the tension detector 18 that is equal to or less than the threshold to the number of sewn stitches is equal to or greater than the ratio threshold (S11: NO, S32: YES) and the rotation detector 141 detects that the bobbin B is not rotating (S16: NO). The sewing machine 1 can avoid erroneously determining whether there is a sewing defect due to tangled bobbin thread 67 based on the singular value of the tension detector 18. As shown in Figure 12(A), in the case of multi-needle pseudo-sewing, no abnormality is observed in the rotation speed indicated by the black circle, and as shown in Figures 12(B) and (C), there is no period during which the upper thread tension is continuously below the second threshold value H2 (N), so it is difficult to detect pseudo-sewing in the sewing process of the above embodiment. However, by performing the sewing process of the second modified example, pseudo-sewing can be properly detected based on the upper thread tension of multiple stitches and whether or not the bobbin B is rotating.

[0064] The sewing machine 1 of the above embodiment, first modified example, and second modified example further includes a storage device 104 that stores combinations of the number of stitches in a seam and threshold values, and the CPU 101 makes a determination using a threshold value that corresponds to the number of stitches based on the combinations stored in the storage device 104. The sewing machine 1 can determine whether or not the bobbin thread 67 is present in a seam using a threshold value that takes the number of stitches into consideration. Because the sewing machine 1 can form similar stitches on similar fabrics 69 based on the sewing data 30, stitches corresponding to the number of stitches in the sewing data will be similar to each other. Therefore, when forming stitches on similar fabrics 69 in accordance with the sewing data, the sewing machine 1 can appropriately determine whether or not the bobbin thread 67 is present in a seam using a threshold value that is set in consideration of the influence of the thickness of the fabric 69, whether or not the fabric is curved, the feed amount, etc.

[0065] The CPU 101 makes the determination using the tension detected by the tension detector 18 acquired at a timing corresponding to the number of stitches in the stitches during one cycle of the up-and-down movement of the needle bar 9. The sewing machine 1 can determine the presence or absence of the bobbin thread 67 in the stitches by taking into account the influence of the stitches depending on the number of stitches, compared to when determining the presence or absence of the bobbin thread 67 in the stitches using the tension detected by the tension detector 18 acquired at the same time regardless of the number of stitches. In this embodiment, the CPU 101 determines the presence or absence of the bobbin thread 67 in the stitches during the first sewing period using the detection result detected by the tension detector 18 during the hook capture period. By setting the detection timing of the tension detector 18 in this manner, the sewing machine 1 can appropriately detect when the bobbin thread 67 is absent during the first sewing period. Meanwhile, as shown in FIG. 11 , when the bobbin thread 67 in the stitches runs out midway, the deviation between the needle thread tension and the second threshold value H2 is more significant in the detection result acquired during the hook take-up lift period shown in FIG. 11(C) than in the detection result acquired during the hook capture period shown in FIG. 11(B). Therefore, the sewing machine 1 determines whether or not there is a bobbin thread 67 for the stitches during the second sewing period by using the detection results detected by the tension detector 18 during the balance pull-up period, and can therefore preferably detect when there is no bobbin thread 67 for the stitches during the second sewing period.

[0066] The CPU 101 of the first modified example changes the frequency at which tension detector 18 acquires detection results for one cycle of up and down movement of needle bar 9 depending on the number of stitches in the stitch, and makes a determination using the tension detected by tension detector 18. Compared to determining the presence or absence of bobbin thread 67 in a stitch using the tension detected by tension detector 18 acquired at the same frequency regardless of the number of stitches, the sewing machine 1 can determine the presence or absence of bobbin thread 67 in a stitch by taking into account the influence of stitches depending on the number of stitches.

[0067] The sewing machine 1 further includes a thread take-up lever 19 that pulls up the upper thread 55 entangled with the lower thread 67 by the shuttle 49, a tension detector 18 that detects the tension of the upper thread, and the CPU 101 determines whether or not the tension detected by the tension detector 18 is greater than a threshold value during a thread take-up period when the shuttle 19 pulls up the upper thread 55, or during a shuttle capture period when the shuttle 49 captures the upper thread 55, and based on the detection result of the rotation detector 141. The sewing machine 1 can determine whether or not the lower thread 67 is present in the stitch based on the upper thread tension detected during the thread take-up period or the shuttle capture period. Because the upper thread tension is greater during the thread take-up period or the shuttle capture period than during the period between the thread take-up period and the shuttle capture period, erroneous determination can be avoided compared to when the CPU 101 makes a determination during a period when the upper thread tension is relatively small.

[0068] The present invention can be modified in various ways in addition to the above-described embodiment. The configuration of the sewing machine 1 may be modified as needed. For example, the sewing machine may not clamp the fabric 69 with the holder 60. The configuration, arrangement, detection method, etc. of the tension detector 18 and the rotation detector 141 may be modified as needed. The sewing machine 1 may also have the functions of the editing device 8. Specifically, the tension detector 18 may be disposed between the auxiliary thread tensioner 15 and the main thread tensioner 16 in the path of the upper thread 55, or may be disposed downstream of the thread take-up lever 19 in the path of the upper thread 55. Furthermore, the sewing machine 1 in the above-described embodiment is a single-needle sewing machine in which one sewing needle 11 is attached to the needle bar 9. However, in the case of a twin-needle sewing machine in which two sewing needles are attached to the needle bar 9 or a sewing machine with three or more sewing needles, the sewing machine may be provided with multiple thread tension detectors to detect the tension of each of the upper threads 55. Furthermore, in these cases, the sewing machine 1 may be provided with a plurality of rotation detectors 141 to detect the rotation of each of the bobbins B in the plurality of shuttles 49. The tension detector 18 has a configuration using a magnetic sensor 53, but it may also be configured to receive the force of the thread with an electrostrictive element and detect the tension based on the output of the element.

[0069] The program for processing by the sewing machine 1 may be stored in the storage device 104 of the sewing machine 1 before the CPU 101 executes the program. Therefore, the program acquisition method, acquisition path, and device storing the program may each be changed as appropriate. The program executed by the CPU 101 may be received from another device via a cable or wireless communication and stored in a storage device such as a flash memory. The other device may include, for example, a PC and a server connected via a network.

[0070] Some or all of the processing performed by sewing machine 1 may be performed by an electronic device (e.g., an ASIC) separate from CPU 101. The processing performed by sewing machine 1 may be distributed among multiple electronic devices (e.g., multiple CPUs). The order of each step of the processing performed by sewing machine 1 may be changed, steps may be omitted, or steps may be added as necessary. The scope of the present invention also includes an embodiment in which an operating system (OS) running on sewing machine 1 performs some or all of each process in response to commands from CPU 101. For example, the following modifications may be made to the above embodiment as appropriate.

[0071] In the above embodiment, the sewing machine 1 updates the abnormality detection counter (S13) when the detected needle thread tension is equal to or less than the second threshold (S11: NO), but it may also be possible to detect whether the bobbin B is rotating before updating the counter, and update the counter only when it is not possible to detect the rotation of the bobbin B. In that case, the sewing machine 1 may not detect the rotation of the bobbin B in S16, and may instead determine that there is no bobbin thread 67 for the stitch (S17) when the counter exceeds the rotation threshold (S14: YES) or when the ratio exceeds the ratio threshold (S32: YES).

[0072] The processes of S11 to S16 may be executed during the first sewing period, and the processes of S3 to S7 may be executed during the second sewing period. Similar processes may be executed during the first sewing period and the second sewing period. The threshold value may be the same for the first sewing period and the second sewing period. The CPU 101 may acquire the tension detected by the tension detector 18 at the same time during the first sewing period and the second sewing period. The CPU 101 does not need to determine the presence or absence of the bobbin thread 67 in the stitch for each stitch. For example, the CPU 101 may determine the presence or absence of the bobbin thread 67 in the stitch after every predetermined number of stitches. The CPU 101 may acquire the tension detected by the tension detector 18 at the same frequency during the first sewing period and the second sewing period. The number threshold and the percentage threshold may be 0, and the CPU 101 may determine that the bobbin thread 67 is not present in the stitch when the tension detected by the tension detector 18 is equal to or less than the threshold value only once and the rotation detector 141 detects that the bobbin B is not rotating. The first threshold value H1 and the second threshold value H2 do not have to be values ​​corresponding to the number of stitches N, and for example, a common value may be set for some or all of a plurality of stitch numbers. The tension detector 18 may detect the tension of the bobbin thread 67. When the sewing machine 1 forms stitches not based on sewing data, the threshold values ​​may be changed depending on conditions such as the material of the fabric 69 or thread, the thickness of the fabric 69, the type of stitch, the feed amount (stitch length), and the sewing speed. The above-mentioned modified examples may be combined as appropriate within a range that does not contradict each other.

[0073] In the sewing machine 1 of the above embodiment, the rotation detector 141 detects whether the bobbin B is rotating, and the movement of the bobbin B is detected based on the result of the detection. However, instead of the rotation detector 141, a bobbin thread remaining amount detector that detects whether there is a change in the amount of bobbin thread 67 wound around the bobbin B may be used as a movement detector, and the movement of the bobbin B may be detected based on the change in the amount of bobbin thread remaining. Specifically, the sewing machine 1 may include a light-transmitting portion on the side of the bobbin case that houses the bobbin B and on a portion of one of the flanges of the bobbin B, forming a reflective surface on the inner wall of each flange, and an optical sensor as a movement detector, which includes an irradiating portion that irradiates light from the light-transmitting portion and a light-receiving portion that receives the reflected light. The change in the amount of bobbin thread remaining may be detected based on the change in the reflected light output by the optical sensor. Alternatively, the sewing machine 1 may include a weight sensor that measures the weight of the bobbin B as a movement detector in the shuttle 49, and detect the change in the amount of bobbin thread remaining based on the change in the output of the weight sensor. When the bobbin B is operating normally during sewing, the amount of bobbin thread 67 wound on the bobbin B decreases according to the amount of sewing, so the sewing machine 1 of this modified example can accurately detect whether the bobbin B is operating by detecting whether there is a change in the amount of bobbin thread 67 wound on the bobbin B. [Explanation of symbols]

[0074] 1: Sewing machine 9: Needle bar 11:Sewing needle 18: Tension detector 21: Needle bar vertical movement mechanism 48: Hook mechanism 49: Kettle 55: Upper thread 67: Lower thread 101: CPU 104: Storage device 141: Rotation detector B: Bobbin H1: First threshold H2: Second threshold

Claims

1. a needle bar to which a sewing needle for threading an upper thread is attached; a needle bar up-down movement mechanism that moves the needle bar up and down; a hook provided below the needle bar and rotatably housing a bobbin around which a lower thread is wound; a shuttle mechanism that rotates the shuttle in synchronization with the up-and-down movement of the needle bar, and captures the annular upper thread that is passed through the sewing needle and entangles it with the bobbin thread to form a stitch; a tension detector for detecting the tension of the upper thread or the lower thread; a motion detector for detecting whether the bobbin is moving; a lower thread determination unit that determines whether or not the lower thread is present in the stitch based on whether or not the tension detected by the tension detector is greater than a threshold value and on the detection result of the operation detector; A sewing machine comprising:

2. The lower thread determination unit When the motion detector detects that the bobbin is not moving and the tension detected by the tension detector is greater than the first threshold value, it is determined that the bobbin thread is present in the stitch, 2. The sewing machine according to claim 1, wherein when the motion detector detects that the bobbin is not moving and the tension detected by the tension detector is equal to or less than the first threshold value, it is determined that there is no bobbin thread for the stitch.

3. The lower thread determination unit When the tension detected by the tension detector is equal to or less than the second threshold value, which is the threshold value, and when the operation detector detects that the bobbin is not operating, it is determined that there is no lower thread for the stitch, The sewing machine according to claim 1 or 2, characterized in that when the tension detected by the tension detector is equal to or less than the second threshold value and the operation detector detects that the bobbin is moving, it is determined that there is a bobbin thread for the stitch.

4. The sewing machine according to any one of claims 1 to 3, characterized in that the bobbin thread determination unit uses different threshold values ​​to make a determination during a first sewing period from the start of sewing until a predetermined number of stitches are sewn, and a second sewing period following the first sewing period.

5. The sewing machine according to any one of claims 1 to 4, characterized in that the bobbin thread determination unit determines that the bobbin thread has broken when the detection result of the tension detector is below the threshold value for a number of consecutive times or more, and when the operation detector detects that there is no operation of the bobbin.

6. The sewing machine according to any one of claims 1 to 4, characterized in that the bobbin thread determination unit determines that there is no bobbin thread for the stitch when the proportion of the detection result of the tension detector that is below the threshold value relative to the number of sewn stitches is equal to or greater than a proportion threshold value, and when the operation detector detects that there is no operation of the bobbin.

7. The sewing machine further includes a storage unit that stores a combination of the number of stitches of the stitches and the threshold value, 7. The sewing machine according to claim 1, wherein the lower thread determination unit makes a determination using the threshold value corresponding to the number of stitches based on the combination stored in the memory unit.

8. The sewing machine according to any one of claims 1 to 7, characterized in that the bobbin thread determination unit makes a determination using the tension detected by the tension detector, which is acquired at a time corresponding to the number of stitches in the stitch within one cycle of up and down movement of the needle bar.

9. The sewing machine according to any one of claims 1 to 7, wherein the bobbin thread determination unit changes the frequency at which the tension detector obtains the detection result for one cycle of up and down movement of the needle bar in accordance with the number of stitches in the stitch, and makes a determination using the tension detected by the tension detector.

10. The hook further includes a take-up lever that pulls up the upper thread entangled with the lower thread, the tension detector detects the tension of the upper thread; The sewing machine according to claim 8 or 9, wherein the bobbin thread determination unit determines whether or not the bobbin thread is present in the stitch based on whether or not the detection result of the tension detector is greater than the threshold value during a lever pull-up period in which the lever pulls up the upper thread and a hook capture period in which the hook captures the upper thread, and based on the detection result of the operation detector.

11. 11. The sewing machine according to claim 1, wherein the motion detector detects whether or not the bobbin is rotating.

12. 11. The sewing machine according to claim 1, wherein the operation detector detects whether or not there is a change in the amount of the lower thread wound on the bobbin.

13. a needle bar to which a sewing needle for threading an upper thread is attached; a needle bar up-down movement mechanism that moves the needle bar up and down; a hook provided below the needle bar and rotatably housing a bobbin around which a lower thread is wound; a shuttle mechanism that rotates the shuttle in synchronization with the up-and-down movement of the needle bar, and captures the annular upper thread that is passed through the sewing needle and entangles it with the bobbin thread to form a stitch; a tension detector for detecting the tension of the upper thread or the lower thread; A bobbin thread determination method executed by a control unit of a sewing machine having an operation detector that detects whether the bobbin is in operation, a bobbin thread determination step of determining whether or not the bobbin thread is present in the stitch based on whether the tension detected by the tension detector is greater than a threshold value and the detection result of the operation detector.

14. The bobbin thread determination unit determines whether the bobbin thread has broken or whether a bobbin thread tangle has occurred based on whether the tension detected by the tension detector is greater than the threshold value and the detection result of the operation detector, 2. The sewing machine according to claim 1, further comprising an informing unit that distinguishes between the result of the determination by the bobbin thread determining unit that the bobbin thread has broken and the result of the determination by the bobbin thread tangling failure and notifies the result.

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