Sewing machine with

Abstract

To provide a sewing machine contributing to improvement in operability of a workpiece when a user manually moves the workpiece in execution of free motion sewing.SOLUTION: A processor of the sewing machine drives a sewing machine motor in a state where an upper end of a feed dog is positioned below a throat plate, and executes free motion sewing processing for vertically moving a needle bar (S32, S35, S36). At least a part of a needle up period in which the lower end of the needle is above the throat plate is defined as a first period, and at least a part of a needle second half in which the lower end of the needle is below the throat plate is defined as a second period. The thread tension control processing includes adjusting a length of the spring in a pressure direction during a first period to a first length, and adjusting a length of the spring in the pressure direction during a second period to a second length shorter than the first length (S36).SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a sewing machine. [Background technology]

[0002] Conventional sewing machines are capable of performing free-motion sewing, in which the feed dog is in drop feed mode, meaning it does not protrude above the top surface of the sewing bed, and the sewing operation is performed while the user is moving the sewing material freely by hand. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-146481 Summary of the Invention [Problem to be solved by the invention]

[0004] In free motion sewing with conventional sewing machines, the resistance applied by the thread when the sewing object is moved can make it difficult for the user to manually move the sewing object. For example, when free motion sewing is performed with a conventional sewing machine, the thread extending from the stitches pulls the sewing object to a certain extent, which can create resistance when moving the sewing object.

[0005] An object of the present invention is to provide a sewing machine that contributes to improving the operability of the sewing object when the user manually moves the sewing object when performing free motion sewing. [Means for solving the problem]

[0006] A sewing machine according to a first aspect of the present invention comprises a needle plate, a feed dog, a needle bar to which a sewing needle can be attached, a sewing machine motor that moves the needle bar up and down, a thread tension disc, a spring that biases the thread tension disc to apply thread tension pressure to the thread tension disc, an actuator that adjusts the length of the spring, and a processor. The processor is configured to perform a free motion sewing process in which the sewing machine motor is driven to move the needle bar up and down while the upper end of the feed dog is positioned below the needle plate, and a thread tension control process in which, when at least a portion of a needle-up period in which the lower end of the sewing needle is above the needle plate is defined as a first period and at least a portion of a needle-down period in which the lower end of the sewing needle is below the needle plate is defined as a second period, during which the free motion sewing process is performed, the processor controls the actuator to adjust the length of the spring to a first length during the first period and to adjust the length of the spring to a second length that is shorter than the first length during the second period.

[0007] The thread tension control process executed by the processor of the sewing machine of the first aspect adjusts the length of the spring so that the second length is shorter than the first length. That is, because the spring is compressed, the thread tension pressure during the second period is greater than the thread tension pressure during the first period. The thread tension disc transmits the thread tension pressure to the upper thread, and the tension applied to the upper thread is adjusted. Therefore, the tension applied to the upper thread during the first period is less than the tension applied to the upper thread during the second period. The first period is a period during which a user may manually move the sewing object during the free motion sewing process. Therefore, the thread tension control process contributes to improving the operability of the sewing object when the user manually moves the sewing object compared to conventional methods.

[0008] A sewing machine according to a second aspect of the present invention comprises a needle plate, a feed dog, a needle bar to which a sewing needle can be attached, a sewing machine motor that moves the needle bar up and down, an actuator that adjusts thread tension pressure to adjust the tension applied to the upper thread, and a processor. The processor is configured to perform a free motion sewing process in which the sewing machine motor is driven to move the needle bar up and down while the upper end of the feed dog is positioned below the needle plate, and a thread tension control process in which, when at least a portion of a needle-up period in which the lower end of the sewing needle is above the needle plate is defined as a first period and at least a portion of a needle-down period in which the lower end of the sewing needle is below the needle plate is defined as a second period, during which the free motion sewing process is performed, the processor controls the actuator to adjust the thread tension pressure to a first pressure during the first period and to adjust the thread tension pressure to a second pressure greater than the first pressure during the second period.

[0009] The thread tension control process executed by the processor of the sewing machine of the second aspect adjusts the thread tension pressure so that the second pressure is greater than the first pressure. This adjusts the tension applied to the upper thread by the thread tension pressure. Therefore, the tension applied to the upper thread during the first period is less than the tension applied to the upper thread during the second period. The first period is a period during which a user may manually move the sewing object during the free motion sewing process. Therefore, the thread tension control process contributes to improving the operability of the sewing object when the user manually moves the sewing object compared to conventional methods.

[0010] A sewing machine according to a third aspect of the present invention comprises a needle plate, a feed dog, a needle bar to which a sewing needle can be attached, a sewing machine motor for moving the needle bar up and down, a first thread tension disc and a second thread tension disc, an actuator for adjusting the disc spacing between the first thread tension disc and the second thread tension disc in order to adjust the tension applied to the upper thread arranged between the first thread tension disc and the second thread tension disc, and a processor. The processor is configured to perform a free motion sewing process in which the sewing machine motor is driven to move the needle bar up and down while the upper end of the feed dog is positioned below the needle plate, and a thread tension control process in which, when at least a portion of a needle-up period in which the lower end of the sewing needle is above the needle plate is defined as a first period and at least a portion of a needle-down period in which the lower end of the sewing needle is below the needle plate is defined as a second period, during which the free motion sewing process is performed, the actuator adjusts the disc spacing to a first interval during the first period and adjusts the disc spacing to a second interval shorter than the first interval.

[0011] The thread tension control process executed by the processor of the sewing machine of the third aspect adjusts the disc spacing so that the first spacing is longer than the second spacing. The upper thread is positioned between the first thread tension disc and the second thread tension disc, and the tension applied to the upper thread is adjusted. Therefore, the tension applied to the upper thread during the first period is smaller than the tension applied to the upper thread during the second period. The first period is a period during which a user may manually move the sewing object during the free motion sewing process. Therefore, the thread tension control process contributes to improving the operability of the sewing object when the user manually moves the sewing object compared to conventional methods. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a perspective view of the sewing machine 1 to which the movement detection device 9 is attached. [Figure 2] (A) is a plan view of the thread tensioning device 20 when the length of the spring 23 in the pressure direction J1 is a first length L1, (B) is a plan view of the thread tensioning device 20 when the length of the spring 23 in the pressure direction J1 is a second length L2, and (C) is a plan view of the thread tensioning device 20 when the length of the spring 23 in the pressure direction J1 is a third length L3. [Figure 3] FIG. 2 is a front view of the thread tension device 20. [Figure 4] (A) is a left side view of the sewing machine 1 equipped with the movement detection device 9, (B) is an enlarged view of the movement detection device 9 with the presser foot 25 in contact with the workpiece C, and (C) is an enlarged view of the movement detection device 9 with the presser foot 25 positioned a predetermined distance above the workpiece C. [Figure 5] FIG. 2 is a perspective view of a movement detection device 9. [Figure 6] 2 is a perspective view of a presser foot 25, a presser foot 81, and a movement detection device 9. FIG. [Figure 7] 2 is a block diagram showing the electrical configuration of the sewing machine 1. FIG. [Figure 8] 10 is a flowchart of a main process that is executed when the movement detection device 9 is attached. [Figure 9] 10 is a flowchart of a main process that is executed when the movement detection device 9 is attached. [Figure 10] 10 is a flowchart of a single stitch sewing process executed in the main process. [Figure 11] 10 is a graph showing the relationship between the rotation angle of the main shaft 34 and the needle lower end position, thread take-up position, disc spacing, length of the spring 23 in the pressure direction J1, and pressure applied to the second thread tension disc 22. [Figure 12] Graph (A) is a graph showing the relationship between elapsed time and thread tension pressure in an example, and graph (B) is a graph showing the relationship between elapsed time and thread tension pressure in a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present disclosure will be described with reference to the drawings. In FIG. 1 , the up-down direction, the lower-left direction, the upper-right direction, the upper-left direction, and the lower-right direction correspond to the up-down direction, the left direction, the right direction, the rear direction, and the front direction of the sewing machine 1, respectively. The longitudinal direction D2 of the bed 11 and the arm 13 corresponds to the left-right direction of the sewing machine 1. The lateral direction D1 of the bed 11 and the arm 13 in a plane parallel to the horizontal direction corresponds to the front-rear direction of the sewing machine 1. In the sewing machine 1, the side on which the leg post 12 is located is the right side. The extension direction of the leg post 12 corresponds to the up-down direction of the sewing machine 1. The direction perpendicular to the up-down direction, from the needle bar 15 toward the presser bar 16, is the rearward direction and is defined as the forward direction F. The opposite direction of the forward direction F is the forward direction and is defined as the reverse direction B. The forward direction F and the reverse direction B are directions along the lateral direction D1.

[0014] As shown in Figure 1, the sewing machine 1 includes a bed 11, a leg post 12, and an arm 13. The leg post 12 extends vertically. The bed 11 has a bed surface 10 and extends leftward from the lower end of the leg post 12. The arm 13 extends leftward above the bed 11 from the upper end of the leg post 12 in parallel with the bed 11. The arm 13 has a head 14 at its left end.

[0015] Bed surface 10 extends horizontally. Bed surface 10 is provided with a needle plate 41 that also extends horizontally. Needle hole 40 is formed in needle plate 41, through which sewing needle 17 attached to needle bar 15 can be inserted. Bed 11 is provided with a feed mechanism 31 shown in FIG. 7, a shuttle mechanism (not shown), and the like below needle plate 41.

[0016] The feed mechanism 31 includes a feed dog 32. The feed mechanism 31 drives the feed dog 32 to move the workpiece by a predetermined distance in a forward direction F or a reverse direction B. The forward direction F corresponds to the direction in which the sewing machine 1 is positioned relative to the user. The shuttle mechanism includes a shuttle. The shuttle mechanism drives the shuttle to entangle the upper thread with the lower thread.

[0017] As shown in FIG. 1, a vertically long liquid crystal display (LCD) 43 and a touch screen 44 are provided on the front side of the leg column 12. The LCD 43 displays messages and the like necessary for sewing work. The touch screen 44 is provided in front of the LCD 43. When the user selects an item displayed on the LCD 43 with a pointing device such as a finger or a dedicated stylus pen, the selected position is detected by the touch screen 44. The user can input various instructions to the sewing machine 1 via the touch screen 44.

[0018] A plurality of switches including a start / stop switch 45 are provided on the front surface of the arm 13. The start / stop switch 45 is a switch for instructing the start and stop of a sewing operation. An openable and closable sewing machine cover (not shown) is provided on the upper part of the arm 13. The sewing machine cover of the arm 13 is not shown in Figures 1 and 4(A).

[0019] A thread storage compartment 50 is provided on an upper surface 53 of the arm 13, which is exposed when the sewing machine cover is open. The thread storage compartment 50 is a downwardly recessed portion capable of storing a thread spool T around which an upper thread is wound. A spool pin 51 extends leftward from the inner wall surface on the right side of the thread storage compartment 50. The thread spool T is attached to the sewing machine 1 by inserting the spool pin 51 into the insertion hole for the thread spool T.

[0020] The thread tensioning device 20 is provided to the left of the thread accommodating section 50. The thread tensioning device 20 is configured to adjust the tension applied to the upper thread U. As shown in Figures 2(A) to 2(C) and 3, the thread tensioning device 20 includes a support plate 49, a first thread tensioning disc 21, a second thread tensioning disc 22, a plate member 39, a spring 23, shafts 24 and 28, a slider 26, and a cam 27, as well as an actuator 36 and a thread tension sensor 37 shown in Figure 7. The support plate 49 is an L-shaped plate member in a plan view. The support plate 49 is fixed to the sewing machine body. The left end of the shaft 24 is fixed to the support plate 49.

[0021] The shaft 24 extends in the left-right direction. The first thread tension disc 21, the second thread tension disc 22, the plate member 39, the spring 23, and the left end of the slider 26 are inserted onto the shaft 24 in this order from the left.

[0022] The first tension disc 21 and the second tension disc 22 are doughnut-shaped plates when viewed from the left side. The first tension disc 21 is disposed to the left of the second tension disc 22. The first tension disc 21 is fixed to a shaft 24.

[0023] The second tension disc 22 is movable along the shaft 24. A first surface 221 of the second tension disc 22 faces the first tension disc 21. The first surface 221 is the left surface of the second tension disc 22. A second surface 222 of the second tension disc 22 faces the plate member 39. The second surface 222 is the surface of the second tension disc 22 opposite to the first surface 221. In other words, the second surface 222 is the right surface of the second tension disc 22.

[0024] The plate member 39 supports the left end of the spring 23. The spring 23 is a compression coil spring. The plate member 39 is supported on the sewing machine body so as to be horizontally rotatable. As the spring 23 expands and contracts, the plate member 39 is displaced horizontally. The thread tension device 20 can displace the second tension disc 22 between an open state and a contact state. As shown in Figure 2(A), the open state is a state in which the second tension disc 22 is separated to the right from the first tension disc 21. As shown in Figures 2(B) and 2(C), the contact state is a state in which the second tension disc 22 abuts against the first tension disc 21.

[0025] Shaft 55 extends in the left-right direction below shaft 24. The left end of shaft 55 is fixed to support plate 49. A spring 56 is inserted through shaft 55. Spring 56 is a coil spring. The biasing force of spring 56 is smaller than the biasing force of spring 23. The end of second tension disc 22 is constantly biased leftward by spring 56. When plate member 39 is displaced horizontally, second tension disc 22 rotates with spring 56 as a fulcrum.

[0026] The slider 26 is shaped like an L-shaped plate. The slider 26 is supported in front of the support plate 49 and to the right of the spring 23 so as to be movable in the left-right direction relative to the support plate 49. The slider 26 is biased by the spring 23 in a counter pressure direction J2 opposite to the pressure direction J1. The slider 26 has a pin 29 that protrudes forward from the front surface of the slider 26. A long hole 261 is formed in the slider 26 to the right of the pin 29, penetrating in the front-rear direction and having a length longer in the left-right direction than in the up-down direction.

[0027] Cam 27 is fixed to the front end of shaft 28, which extends forward from the front surface of support plate 49, so as to be rotatable around shaft 28. Shaft 28 is inserted into elongated hole 261. As shown in FIG. 3, a gear 273 is formed on the outer periphery of cam 27. Gear 273 meshes with pinion gear 371 fixed to the rotation shaft of actuator 36, shown in FIG. 7. Actuator 36 is a pulse motor, and is attached to the back surface of support plate 49.

[0028] As shown in FIG. 3, an eccentric cam portion 271 is formed on the back surface of cam 27. Eccentric cam portion 271 is a recessed portion that is recessed forward and has a curved surface whose distance from shaft 28 is not constant. Pin 29 slides against eccentric cam portion 271. A protrusion 272 that is arc-shaped in front view and has its center on shaft 28 is formed on the front surface of cam 27. Protrusion 272 protrudes forward from the front surface of cam 27.

[0029] When the rotary shaft of the actuator 36 rotates, the cam 27 that meshes with the pinion gear 371 also rotates. The rotation of the cam 27 causes the eccentric cam portion 271 of the cam 27 to move the pin 29 in the left-right direction. Therefore, the rotation of the cam 27 causes the slider 26 to move in the left-right direction while being guided by the elongated hole 261.

[0030] The spring length, disc spacing, and thread tension pressure are all changed depending on the left-right position of the slider 26. The spring length is the length of the spring 23 in the pressure direction J1. The disc spacing is the distance between the first tension disc 21 and the second tension disc 22 in the left-right direction, and is defined, for example, by the distance between the first tension disc 21 and the second tension disc 22 on the axis Q of the shaft 24. The thread tension pressure is the pressure in the pressure direction J1 that the spring 23 applies to the second tension disc 22.

[0031] The thread tension sensor 37 is disposed in front of the cam 27 and is configured to detect the phase of the cam 27 by detecting the position of a protrusion 272 provided on the front surface of the cam 27 of the thread tensioning device 20. Since the phase of the cam 27 corresponds to the position of the slider 26, the sewing machine 1 can identify each of the spring length, disc spacing, and thread tension pressure based on the phase of the cam 27.

[0032] As shown in Fig. 1, head 14 includes therein a needle bar mechanism, a presser foot mechanism, and a thread take-up lever (not shown), as well as image sensor 8 shown in Fig. 7. As shown in Figs. 4(A) to 4(C), the needle bar mechanism has needle bar 15 that extends in the vertical direction, and moves needle bar 15 back and forth in the vertical direction.

[0033] The lower end of needle bar 15 protrudes downward from the lower end of head 14. A sewing needle 17 is removably attached to the lower end of needle bar 15. Sewing needle 17 attached to needle bar 15 moves back and forth in the vertical direction. An upper thread U inserted through sewing needle 17 is entangled with a lower thread by the shuttle to form a stitch on the sewing material.

[0034] The presser foot mechanism has a presser bar 16 that extends vertically, and moves the presser bar 16 back and forth in the vertical direction. The lower end of the presser bar 16 protrudes downward from the lower end of the head 14. The take-up lever is provided in the path of the upper thread U, between the thread tension device 20 and the sewing needle 17. The take-up lever pulls up the upper thread U that has been entangled with the bobbin thread by the shuttle.

[0035] Image sensor 8 is attached to the sewing machine body so that it can capture images of the needle drop point, which is directly below needle bar 15, and the surrounding area. The needle drop point is the point where sewing needle 17 is moved downward by the needle bar mechanism and pierces the sewing workpiece C. Image sensor 8 is equipped with a CMOS sensor and a control circuit, and captures images using the CMOS sensor.

[0036] The movement detection device 9 is used when the user sews while manually moving the sewing object C placed on the bed surface 10, without using the feed dog 32. The movement detection device 9 detects the movement of the sewing object C placed on the needle plate 41, and outputs a detection result corresponding to the amount of movement of the sewing object C. The movement detection device 9 detects the amount of movement of the sewing object C placed on the bed 11 below the presser bar 16, and outputs the result to the sewing machine 1. The sewing machine 1 controls the drive of the sewing machine motor 33 shown in FIG. 7 based on the amount of movement per unit time of the sewing object C, that is, the movement speed. In this way, the sewing machine 1 adjusts the length of the stitches to be formed on the sewing object C.

[0037] As shown in Fig. 4, the movement detection device 9 includes a housing 95, a sensor 97, a cable 99, and an attachment 98. The housing 95 is a rectangular parallelepiped that is longer in the front-to-back direction than in the left-to-right direction. The housing 95 is detachable from the presser bar 16 of the sewing machine 1. The housing 95 houses the sensor 97.

[0038] 6, a mounting portion 903 for removably mounting a presser foot (described later) is formed in a lower portion 900 of the housing 95. The mounting portion 903 is a recess recessed rearward from the front surface of the housing 95. The mounting portion 903 has a groove 905 extending in the front-to-rear direction.

[0039] The sensor 97 is located above an opening 100 formed in the lower surface 96 of the housing 95. The sensor 97 has a light-emitting element 971 and a light-receiving element 972 shown in FIG. 7. The light-emitting element 971 and the light-receiving element 972 are located above the opening 100. The light-emitting element 971 emits light toward the sewing workpiece C in order to detect the amount of movement of the sewing workpiece C. The light-emitting element 971 is, for example, an infrared light-emitting diode that emits infrared light.

[0040] When the movement detection device 9 is attached to the presser bar 16 of the sewing machine 1, the light emitting element 971 emits light downward. The emitted light passes through the opening 100, reaches the sewing workpiece C, and is reflected. The light reflected by the sewing workpiece C passes through the opening 100.

[0041] The light receiving element 972 is an element for detecting light reflected by the sewing material C located within the detection area, and detects the light reflected by the sewing material C and converts it into an electrical signal. The detection area is a circular area in a plan view located below the opening 100. The light emitting element 971 is, for example, an infrared imaging element that detects infrared rays.

[0042] The sensor 97 periodically emits light toward the sewing workpiece C using a light-emitting element 971 to detect the amount of movement of the sewing workpiece C per unit time. The movement detection device 9 of this embodiment detects the amount of movement in the short-side direction D1 and the amount of movement in the long-side direction D2. The movement detection device 9 detects the amount of movement in the short-side direction D1 by regarding the amount of movement toward the rear as a positive amount of movement and the amount of movement toward the front as a negative amount of movement. The movement detection device 9 detects the amount of movement in the long-side direction D2 by regarding the amount of movement toward the right as a positive amount of movement and the amount of movement toward the left as a negative amount of movement.

[0043] The cable 99 extends upward from the rear of the upper surface of the housing 95. The cable 99 is detachably connected to a connector (not shown) provided on the back surface of the arm 13. The movement detection device 9 outputs the movement amount of the sewing workpiece C per unit time to the sewing machine 1 via the cable 99.

[0044] Mounting body 98 extends upward from the front of the upper surface of housing 95. Mounting body 98 is removably attached to presser bar 16. As a result, movement detection device 9 is removably attached to the lower end of presser bar 16.

[0045] One of a plurality of types of presser feet can be attached to and detached from the movement detection device 9. The plurality of types of presser feet in this embodiment include presser foot 25 and presser foot 81. The presser foot 25 and presser foot 81 are made of a metal such as an aluminum alloy. The presser foot attached to the movement detection device 9 is positioned a predetermined distance above the top surface of the sewing workpiece C in the normal position described below, and limits the vertical movement of the sewing workpiece C to within a predetermined distance. In this way, the presser foot attached to the movement detection device 9 prevents the sewing workpiece C placed on the bed surface 10 from floating up.

[0046] As shown in Figure 6, the presser foot 25 has an insertion plate 72, a connection plate 73, and a presser plate 75. The insertion plate 72 is perpendicular to the up-down direction and has a generally rectangular shape in a plan view. The left-right and up-down lengths of the insertion plate 72 are approximately the same as the left-right and up-down lengths of the opening provided in the front of the movement detection device 9. The front-rear length of the insertion plate 72 is approximately the same as the front-rear length of the mounting portion 903.

[0047] An opening 721 and a protrusion 722 are formed in the insertion plate 72. The opening 721 opens the insertion plate 72 in the up-down direction. The opening 721 is located between the right end of the insertion plate 72 and the center of the insertion plate 72 in the left-right direction. The opening 721 is located between the rear end of the insertion plate 72 and the center of the insertion plate 72 in the front-to-rear direction.

[0048] When presser foot 25 is attached to movement detection device 9, opening 721 fits into a fitting portion (not shown) of movement detection device 9. Protrusion 722 protrudes downward in a cylindrical shape from the underside of insertion plate 72. When presser foot 25 is attached to movement detection device 9, protrusion 722 engages with groove 905 of movement detection device 9.

[0049] The connecting plate 73 extends downward from the front end of the insertion plate 72. A hole 77 is formed in the connecting plate 73, penetrating it in the front-to-rear direction. The hole 77 allows a user positioned in front of the sewing machine 1 to easily check the condition of the workpiece C, which is placed below the presser plate 75. The condition of the workpiece C includes, for example, the spacing and sewing direction of the stitches formed on the workpiece C.

[0050] The presser plate 75 extends perpendicular to the vertical direction. The presser plate 75 is formed with an insertion portion 76 through which the sewing needle 17 is inserted in the vertical direction. The insertion portion 76 of the presser plate 75 is generally O-shaped in plan view, i.e., annular. The insertion portion 76 is an elliptical hole that is long in the left-right direction in plan view. The presser plate 75 surrounding the insertion portion 76 is cylindrical in plan view. An upper thread U can be inserted through the insertion portion 76. When the upper thread U is inserted through the insertion portion 76, the presser plate 75 restricts the horizontal movement of the upper thread U. When the presser foot 25 is attached to the movement detection device 9, the presser plate 75 comes into contact with the sewing workpiece C from above, preventing the sewing workpiece C from lifting up.

[0051] The following description focuses on the differences between presser foot 81 and presser foot 25. Presser foot 81 has an insertion plate 82 corresponding to insertion plate 72, a connecting plate 83 corresponding to connecting plate 73, and a presser plate 85 corresponding to presser plate 75. An opening 821 and a protrusion 822 are formed in insertion plate 82. A hole 87 is formed in connecting plate 83, penetrating it in the front-to-rear direction.

[0052] The presser plate 85 extends perpendicular to the vertical direction. The presser plate 85 has an insertion portion 86 through which the sewing needle 17 is inserted in the vertical direction. The insertion portion 86 is a recess extending rearward from the front end of the presser plate 85. The insertion portion 86 of the presser plate 85 is generally C-shaped with an open front in plan view, i.e., it is not annular. The left front end 851 and right front end 852 of the C-shaped presser plate 85 surrounding the insertion portion 86 are spaced apart in the horizontal direction. The distance between the left front end 851 and the right front end 852 is large enough to allow at least the upper thread U to pass through. When the upper thread U is inserted into the insertion portion 86, the presser plate 85 partially restricts horizontal movement of the upper thread U, but the upper thread U can move forward of the presser plate 85 via the gap between the left front end 851 and the right front end 852.

[0053] In the sewing machine 1 having the above configuration, a brief description will be given of the operation when the sewing material is transported by the feed dog 32. When the sewing machine 1 detects that the start / stop switch 45 is pressed, it synchronously drives the shuttle mechanism, feed mechanism 31, needle bar mechanism, and presser foot mechanism. As a result, the sewing needle 17 attached to the needle bar 15 forms a stitch on the sewing material C placed on the bed surface 10.

[0054] The electrical configuration of the sewing machine 1 will be described with reference to Figure 5. The processor 3 of the sewing machine 1 includes a CPU 61, a ROM 62, a RAM 63, a storage device 64, and an input / output interface 65. The CPU 61 is connected to the ROM 62, the RAM 63, the storage device 64, and the input / output interface 65 via a bus 66.

[0055] The CPU 61 is responsible for main control of the sewing machine 1 and executes various calculations and processes related to sewing in accordance with various programs stored in the ROM 62. The ROM 62 has a plurality of storage areas, including a program storage area (not shown). The program storage area stores various programs for operating the sewing machine 1, including a program for executing the main processing described below. The RAM 63 is provided with a storage area for storing the results of calculations performed by the CPU 61, etc.

[0056] Memory device 64 stores various parameters and the like for executing various processes by sewing machine 1. Memory device 64 stores the correspondence between the detection results of encoder 38 (described below) and the up-down position of needle bar 15, with the angle of main shaft 34 set to 0 degrees when needle bar 15 is at the top dead center.

[0057] The input / output interface 65 is connected to the drive circuits 90 to 94 of the processor 3, the touch screen 44, the start / stop switch 45, the thread tension sensor 37, the encoder 38, the image sensor 8, and the light-emitting element 971 and the light-receiving element 972 of the sensor 97 of the movement detection device 9.

[0058] Sewing machine motor 33 is connected to drive circuit 91. Drive circuit 91 drives sewing machine motor 33 in accordance with a control signal from CPU 61. As sewing machine motor 33 is driven, the needle bar mechanism is driven via main shaft 34 of sewing machine 1, and needle bar 15 moves up and down reciprocally.

[0059] Sewing machine motor 33 moves needle bar 15 up and down within a range that includes a needle up position and a needle down position. The needle up position is a position where bottom end 18 of sewing needle 17 is above needle plate 41. The needle down position is a position where bottom end 18 of sewing needle 17 is below needle plate 41. The upper end of the movable range of needle bar 15 is the top dead center, and the lower end of the movable range of needle bar 15 is the bottom dead center.

[0060] A feed amount adjustment motor 30 is connected to the drive circuit 92. The feed amount adjustment motor 30 rotates an output shaft to adjust the amount of feed of the sewing workpiece C by the feed mechanism 31 in the front-rear direction.

[0061] Drive circuit 93 drives presser motor 35 in accordance with a control signal from CPU 61. As presser motor 35 is driven, presser bar 16 moves up and down independently of the drive of main shaft 34 of sewing machine 1. Presser motor 35 moves presser bar 16 up and down within a range that includes a normal position and a lowered position where bottom end 19 of presser bar 16 is lower than the normal position. The upper end of the movable range of presser bar 16 is a raised position that is higher than the normal position, and the lower end is a contact position where presser foot 25 contacts needle plate 41.

[0062] The drive circuit 94 drives the actuator 36 in accordance with a control signal from the CPU 61. As the actuator 36 is driven, the length of the spring 23 in the pressure direction J1 is changed, and the thread tension pressure applied to the second tension disc 22 and the disc spacing are changed. The drive circuit 90 drives the LCD 43 in accordance with a control signal from the CPU 61, thereby displaying an image on the LCD 43.

[0063] The thread tension sensor 37 outputs a detection result corresponding to the phase of the cam 27 to the input / output interface 65. The encoder 38 outputs a detection result corresponding to the rotation angle of the sewing machine motor 33 to the input / output interface 65.

[0064] The process of adjusting the tension pressure applied to the upper thread U by the thread tension device 20 will be described. As shown in Figures 2(A) to 2(C), the user hooks the upper thread U pulled out from the thread spool T onto the guide pin 47. The guide pin 47 extends vertically behind the first tension disc 21 and the second tension disc 22.

[0065] The user pinches the upper thread U, which is hooked on the guide pin 47, between the first thread tension disc 21 and the second thread tension disc 22 of the thread tension device 20, then pulls it out downward and inserts it through the sewing needle 17 via the thread take-up. In the open state shown in Figure 2(A), the first thread tension disc 21 and the second thread tension disc 22 are spaced apart in the left-right direction. Therefore, in the open state, the user can easily pass the upper thread U between the first thread tension disc 21 and the second thread tension disc 22.

[0066] When sewing starts, the actuator 36 rotates a predetermined number of pulses in a predetermined direction in response to a command from the processor 3. The slider 26 moves leftward in accordance with the rotation phase of the cam 27. As the slider 26 moves leftward, the spring 23 presses the second tension disc 22 in the pressure direction J1. The disc gap, which is the distance between the first tension disc 21 and the second tension disc 22, becomes shorter than before the movement started.

[0067] 2(B) and 2(C), when the thread tensioning device 20 is in contact with the thread tensioning device 20 due to the movement of the slider 26, the disc spacing becomes approximately 0, leaving a gap for the upper thread U to be pinched. In other words, when the thread tensioning device 20 is in contact with the thread tensioning device 20, if the upper thread U is not pinched, the disc spacing is 0.

[0068] After the thread tensioning device 20 has reached the contact state, the slider 26 moves further to the left, shortening the length of the spring 23 in the pressure direction J1 compared to before the start of movement. As the slider 26 moves leftward, the thread tensioning pressure that the spring 23 applies to the second thread tension disc 22 becomes greater compared to before the start of movement. In other words, the tension applied to the upper thread U by the thread tensioning device 20 becomes greater compared to before the start of movement. The tension applied to the upper thread U by the thread tensioning device 20 increases in the order of Figure 2(A) < Figure 2(B) < Figure 2(C).

[0069] When the thread tensioning device 20 shown in Figures 2(B) and 2(C) is switched from the contact state to the open state shown in Figure 2(A), the actuator 36 rotates a predetermined number of pulses in a predetermined direction in response to a command from the processor 3. The slider 26 moves to the right in accordance with the rotation phase of the cam 27. As the slider 26 moves to the right, the tensioning pressure applied by the spring 23 to the second tensioning disc 22 becomes smaller than before the start of movement. The disc spacing and spring length become longer than before the start of movement. In the open state shown in Figure 2(A), the tension applied to the upper thread U by the thread tensioning device 20 becomes almost zero.

[0070] The relationship between the vertical position of the lower end 18 of the sewing needle 17, the rotation angle of the main shaft 34, and the vertical position of the thread take-up lever will be described with reference to Figure 11. As shown in Figure 11, the vertical position of the lower end 18 of the sewing needle 17 changes periodically, with the sewing period being the unit cycle, according to the rotation angle of the main shaft 34. The sewing period is the time it takes to sew one stitch.

[0071] The vertical axis on the left side of Figure 11 indicates the height of the lower end 18 of the sewing needle 17 relative to the top surface of the needle plate 41. The vertical axis on the right side indicates the position of the thread take-up lever relative to the position when the thread take-up lever is at its uppermost position. The sewing period includes a thread take-up lifting period in which the thread take-up lever pulls up the needle thread U, and a hook capture period in which the needle point of the shuttle captures the circular needle thread U. Although not shown, the tension of the needle thread U fluctuates during the sewing period and generally reaches its peak during the thread take-up lifting period and the hook capture period. For example, the thread take-up lifting period is the period when the rotation angle of the main shaft 34 is from 279 degrees to 62 degrees during the next sewing period. The hook capture period is the period when the rotation angle of the main shaft 34 is from 208 degrees to 330 degrees.

[0072] The main processing of the sewing machine 1 will be described with reference to Figures 8 to 11. In the main processing, with the movement detection device 9 attached to the presser bar 16, the start / stop switch 45 is selected when sewing starts or resumes. In the main processing, in response to the detection of a sewing instruction, the needle bar 15 is moved back and forth in the vertical direction based on the detection result of the movement detection device 9, and processing is executed to sew on the sewing workpiece C. When the processor 3 detects an instruction to execute the main processing, it reads into the RAM 63 a program for executing the main processing that is stored in the program storage area of ​​the ROM 62.

[0073] The processor 3 executes the following steps in accordance with instructions contained in the program read into the RAM 63. The program contains instructions for causing the processor 3 to execute the following processes. Various parameters required to execute the main process are stored in the storage device 64. Various data obtained during the main process are stored in the RAM 63 as appropriate. In the following explanation, steps are abbreviated as S.

[0074] When the main process starts, the presser bar 16 is in the raised position, and the needle bar 15 is in the stop position or the needle down position. The stop position may be any position where the lower end 18 of the sewing needle 17 is higher than the needle plate 41. In this embodiment, the stop position is a position where the angle of the main shaft 34 is 32 degrees and the needle bar 15 is slightly below the top dead center. The needle down position is a position where the lower end 18 of the sewing needle 17 is below the needle plate 41. In this embodiment, the angle of the main shaft 34 is 125 degrees, and the lower end 18 of the sewing needle 17 is halfway from the position where it is at the same height as the needle plate 41 toward the bottom dead center.

[0075] When the main process is being performed, feed dog 32 is positioned so that the upper end of feed dog 32 is not higher than needle plate 41. When the main process is being performed, presser bar 16 does not move up and down in conjunction with the up and down movement of needle bar 15, unlike when sewing using feed dog 32.

[0076] As shown in Figure 8, in the main processing, processor 3 determines whether an instruction to select the basting mode has been detected (S1). The sewing machine 1 of this embodiment can select from a plurality of sewing modes when sewing based on the signal output from movement detection device 9. The sewing mode defines the conditions for driving needle bar 15 based on the signal output from movement detection device 9. The plurality of modes in this embodiment include an intermittent mode, a basting mode, and a continuous mode.

[0077] In the intermittent mode and the basting mode, if the amount of movement of the sewing workpiece C detected by the movement detection device 9 is zero, the processor 3 stops the up-and-down reciprocating movement of the needle bar 15. If the amount of movement is greater than zero, the processor 3 moves the needle bar 15 up and down reciprocatingly at a speed corresponding to the amount of movement. One method of moving the needle bar 15 reciprocatingly at a speed corresponding to the amount of movement may be to set a predetermined amount of movement as a threshold and start moving the needle bar 15 when the detected amount of movement reaches the threshold. The length of the stitch in the basting mode is greater than the length of the stitch in the intermittent mode. In other words, the threshold for the amount of movement in the basting mode is greater than the threshold for the amount of movement in the intermittent mode.

[0078] In the continuous mode, when the movement amount of the sewing workpiece C detected by the movement detection device 9 is 0, the processor 3 moves the needle bar 15 back and forth in the up and down direction at a predetermined speed. When the movement amount is greater than 0, the processor 3 moves the needle bar 15 back and forth in the up and down direction at a speed according to the movement amount.

[0079] The stitch length in the basting mode is greater than the stitch length in the continuous mode. That is, the movement threshold in the basting mode is greater than the movement threshold in the continuous mode. The basting mode is a mode for basting, and the intermittent mode and continuous mode are modes for lock stitching.

[0080] Basting stitches are formed, for example, to temporarily fasten two pieces of workpiece together, and are removed after the lockstitch stitches are formed. Therefore, the length of a basting stitch is usually set longer than the length of one lockstitch stitch. The length of one lockstitch stitch corresponds to the amount of workpiece fed by the feed dog 32 in one stroke, and is, for example, between 0.2 mm and 5.0 mm.

[0081] If an instruction to select the basting mode is not detected and basting is not performed (S1: NO), the processor 3 controls the actuator 36 to perform a length adjustment process (S19) to adjust the length of the spring 23 in the pressure direction J1 to a third length L3 that is shorter than the second length L2 while the free motion sewing process is being performed.

[0082] As shown in FIG. 2(C), processor 3 performs normal free motion sewing, i.e., intermittent mode or continuous mode, with the spring length adjusted to third length L3 (S20). Normal free motion sewing is a type of lock stitch. When the spring length is third length L3, the disc spacing is third spacing E3, which is approximately the same as second spacing E2. When the spring length is third length L3, the thread tension pressure is third pressure, which is greater than second pressure. Thus, if an instruction to select basting mode is not detected, that is, if basting is not to be performed (S1: NO), processor 3 does not perform the thread tension control process described below, and performs free motion sewing with the spring length, disc spacing, and thread tension pressure kept constant. The instruction to select basting mode is processed as an instruction to execute thread tension control process.

[0083] If an instruction to select the basting mode is detected (S1: YES), processor 3 controls image sensor 8 to capture an image of the presser foot attached to movement detection device 9 (S2). Processor 3 analyzes the image data captured in S2 and determines whether the presser foot attached to movement detection device 9 is a predetermined presser foot (S3). The method of analyzing the image data may be set as appropriate, and for example, learning data may be generated by using a neural network to learn the image of the predetermined presser foot. Processor 3 detects the planar shape of the presser foot attached to movement detection device 9 from the captured image data based on the learning data. The predetermined presser foot may be set as appropriate, and in this embodiment, it is a presser foot whose insertion portion has a planar shape that is O-shaped.

[0084] If presser foot 81 is attached to movement detection device 9 and it is not determined that the planar shape of the presser foot insertion portion is O-shaped (S3: NO), that is, if the planar shape of the presser foot insertion portion is C-shaped, processor 3 does not perform basting and issues a warning (S21). Processor 3 displays a warning message on LCD 43, for example, "Attach a presser foot whose planar shape of the insertion portion is O-shaped."

[0085] As described above, the processor 3 of this embodiment does not perform basting stitches when the planar shape of the presser foot insertion portion is C-shaped. When a presser foot 25 with an insertion portion having an O-shaped planar shape is attached to the movement detection device 9, the upper thread U is held by the presser foot 81. When a presser foot 81 with an insertion portion having a C-shaped planar shape is attached to the movement detection device 9, the upper thread U may come off the presser foot 25, and the upper thread U will not be held by the presser foot 25. In other words, when a presser foot 81 with an insertion portion having a C-shaped planar shape is attached to the movement detection device 9, the tension of the upper thread U stretching from the stitches already formed in the sewing workpiece C may be applied directly from the sewing needle 17 to the sewing workpiece C, and the resistance to moving the sewing workpiece C forward is relatively large, compared to when a presser foot 25 with an insertion portion having an O-shaped planar shape is attached to the movement detection device 9. The processor 3 then ends the main processing.

[0086] If the presser foot attached to movement detection device 9 is the specified presser foot (S3: YES), that is, if the planar shape of the presser foot insertion portion is O-shaped, processor 3 determines whether a start command to start free motion sewing has been detected (S4). The user operates start / stop switch 45 to input the start command. If a start command has not been detected (S4: NO), processor 3 returns the process to S4.

[0087] If a start command is detected (S4: YES), processor 3 drives presser motor 35 to start lowering presser bar 16 (S5), as shown in FIG. 2(B). Processor 3 determines whether the thickness of the sewing workpiece C has been acquired based on the position where presser foot 25 contacts the sewing workpiece C (S6). If the thickness has not been acquired (S6: NO), processor 3 returns the process to S6. If the thickness has been acquired (S6: YES), processor 3 stops the lowering of presser bar 16 at the position where presser foot 25 of movement detection device 9 contacts the sewing workpiece C (S7).

[0088] Processor 3 determines whether needle bar 15 is in the needle down position based on the detection result of encoder 38 (S8). If needle bar 15 is not in the needle down position (S8: NO), processor 3 executes the process of S11, which will be described later. If needle bar 15 is in the needle down position (S8: YES), processor 3 controls sewing machine motor 33 to start raising needle bar 15 at an raising speed (S9). The raising speed may be a preset speed, for example, 70 rpm.

[0089] The processor 3 determines whether the rotation angle of the main shaft 34 has reached a predetermined angle based on the detection result of the encoder 38 (S10). The predetermined angle is an angle at which the lower end 18 of the sewing needle 17 is at the needle up position above the needle plate 41. In this embodiment, the needle up position is a position at which the lower end 18 of the sewing needle 17 is at the needle up position above the needle plate 41 and above the top surface of the sewing workpiece C. The needle up position may be set based on the thickness of the sewing workpiece C acquired in S2, or may be a value set based on the maximum thickness of the sewing workpiece C that is normally sewn. In this embodiment, the predetermined angle is, for example, 273 degrees.

[0090] If the rotation angle of the main shaft 34 has not reached the predetermined angle (S10: NO), the processor 3 returns the process to S10. If the rotation angle of the main shaft 34 has reached the predetermined angle (S10: YES), the processor 3 controls the presser motor 35 to start raising the presser bar 16 (S11).

[0091] Processor 3 determines whether presser bar 16 has reached the normal position (S12). Processor 3 may make the determination in S12 based on the drive amount of presser motor 35 from S11. Processor 3 may also make the determination in S12 based on the detection result of an encoder that detects the rotation angle of presser motor 35. As shown in FIG. 2(C), after obtaining the thickness of the sewing workpiece C, processor 3 drives presser motor 35 to set the normal position to a predetermined distance above the position where presser foot 25 contacts the sewing workpiece C. The predetermined distance is set to a value between 1 mm and 4 mm, for example.

[0092] If presser bar 16 has not reached the normal position (S12: NO), processor 3 returns the process to S12. If presser bar 16 has reached the normal position (S12: YES), processor 3 controls presser motor 35 to stop raising presser bar 16 (S13). Based on the detection result of encoder 38, processor 3 determines whether the rotation angle of main shaft 34 has reached the stop angle corresponding to the stop position (S14). The stop position is a position where lower end 18 of sewing needle 17 is above throat plate 41.

[0093] If the rotation angle of the main shaft 34 has not reached the stop angle (S14: NO), the processor 3 returns the process to S14. If the rotation angle of the main shaft 34 has reached the stop angle (S14: YES), the processor 3 stops driving the sewing machine motor 33 (S15).

[0094] As shown in FIG. 9, the processor 3 controls the actuator 36 to start a process of adjusting the length of the spring 23 in the pressure direction J1 during the first period T1 to the first length L1 shown in FIG. 2A (S28). At this time, from the viewpoint of improving operability when moving the sewing workpiece C during the free motion sewing process, it is preferable that the first interval E1 be a distance sufficiently larger than the thickness of the upper thread U, for example, a distance at least twice the thickness of the upper thread U. In other words, it is preferable that the first pressure be a value that is approximately zero. The processor 3 initializes a cumulative value of the movement amount of the sewing workpiece C based on the detection result of the movement detection device 9 (S29). The processor 3 starts updating the cumulative value based on the detection result of the movement detection device 9 (S30). A separately executed process adds the movement amount of the sewing workpiece C to the cumulative value based on the detection result of the movement detection device 9.

[0095] The processor 3 determines whether a stop command has been detected (S31). When free motion sewing is to be ended, the user operates the start / stop switch 45 to input a stop command.

[0096] If a stop command is not detected (S31: NO), the processor 3 determines whether the absolute value of the cumulative value is greater than a predetermined amount (S32). In the free motion sewing process, the processor 3 of this embodiment determines whether the movement amount detected by the movement detection device 9 has reached the predetermined amount during the needle up period TU, but not during the needle down period TD. The predetermined amount may be set in advance taking into account the length of the basting stitch, and may be set automatically or by the user from a range of 10 mm to 40 mm, for example. The processor 3 of this embodiment sets the predetermined amount to a value selected automatically or by the user from among 10 mm, 20 mm, and 30 mm.

[0097] If the absolute value of the cumulative value is greater than the predetermined amount (S32: YES), processor 3 initializes the cumulative value, setting it to 0 (S35), and then executes the one-stitch sewing process (S36). Processor 3 controls sewing machine motor 33 to start the one-stitch sewing process while the length of spring 23 in pressure direction J1 is at first length L1. In the one-stitch sewing process, processor 3 executes free motion sewing process and thread tension adjustment process. In the free motion sewing process, processor 3 drives sewing machine motor 33 to move needle bar 15 up and down while the upper end of feed dog 32 is positioned below needle plate 41. In the free motion sewing process, if the movement amount detected by movement detection device 9 reaches the predetermined amount (S32: YES), processor 3 controls sewing machine motor 33 to sew one stitch (S36).

[0098] In the thread tension adjustment process, the processor 3 controls the actuator 36 during the free motion sewing process to adjust the length of the spring 23 in the pressure direction J1 to a first length L1 during the first period T1. The processor 3 controls the actuator 36 during the free motion sewing process to adjust the length of the spring 23 in the pressure direction J1 to a second length L2 that is shorter than the first length L1 during the second period T2. In other words, the thread tension adjustment process is a process in which the actuator 36 is controlled during the free motion sewing process to adjust the thread tension pressure to a first pressure during the first period T1 and to a second pressure that is greater than the first pressure during the second period T2. In the thread tension adjustment process, the processor 3 controls the actuator 36 during the free motion sewing process to adjust the disc spacing to a first spacing E1 during the first period T1. In the thread tension adjustment process, the processor 3 is controlled during the free motion sewing process to adjust the disc spacing to a second spacing E2 that is shorter than the first spacing E1 during the second period T2.

[0099] The first period T1 is at least a part of the needle up period TU during one stitch sewing cycle in which the lower end 18 of the sewing needle 17 is above the needle plate 41. In this embodiment, the first period T1 includes the period during which the needle bar 15 is positioned at the stop position. In this embodiment, the first period T1 is the period from the time when the needle bar 15 is positioned at the stop position to the time when the vertical position of the lower end 18 of the sewing needle 17 is the same as the vertical position of the upper surface of the needle plate 41.

[0100] The second period T2 is a period of one stitch sewing cycle that does not overlap with the first period T1, and is at least a part of the needle down period TD during which the lower end 18 of the sewing needle 17 is below the needle plate 41. In this embodiment, the second period T2 is the period from when the spring length is adjusted to the second length L2 to when the needle bar 15 is positioned at the stop position. The time at which the spring length is adjusted to the second length L2 is between when the vertical position of the lower end 18 of the sewing needle 17 is aligned with the vertical position of the upper surface of the needle plate 41 and when the needle bar 15 is positioned at the bottom dead center. The second period T2 includes the shuttle capture period. The second period T2 includes a part of the thread take-up lever lift period.

[0101] In this embodiment, the processor 3 performs thread tension adjustment processing when an instruction is detected in S1, that is, when basting is to be performed (S1: YES). In this embodiment, the processor 3 performs basting when the planar shape of the presser foot attached to the movement detection device 9 is O-shaped (S3: YES).

[0102] As shown in Figure 10, in the one-stitch sewing process, processor 3 starts driving sewing machine motor 33 at a first speed (S39). The first speed is set taking into consideration the time required for actuator 36 to change the spring length from first length L1 to second length L2 during the processes from S41 to S44. Specifically, if the movement amount detected by movement detection device 9 during free motion sewing process reaches a predetermined amount in S41 (S32: YES), processor 3 sets the first speed to a speed at which the spring length during second period T2 can be adjusted to second length L2, and drives sewing machine motor 33 at the first speed. The first speed is, for example, 300 rpm.

[0103] The processor 3 determines whether the rotation angle of the main shaft 34 has reached 100 degrees based on the detection result of the encoder 38 (S40). As shown in FIG. 11, when the rotation angle of the main shaft 34 is 100 degrees, the vertical position of the lower end 18 of the sewing needle 17 is the same as the vertical position of the upper surface of the needle plate 41. If the rotation angle of the main shaft 34 has not reached 100 degrees (S40: NO), the processor 3 returns the process to S40. If the rotation angle of the main shaft 34 has reached 100 degrees (S40: YES), the processor 3 controls the actuator 36 to start a process of adjusting the spring length for the second period T2 to a second length L2 that is longer than the first length L1 (S41).

[0104] Processor 3 determines whether the rotation speed of sewing machine motor 33 has reached the first speed based on the detection result of encoder 38 (S42). If the rotation speed of sewing machine motor 33 has not reached the first speed (S42: NO), processor 3 returns the process to S42.

[0105] If the rotation speed of the sewing machine motor 33 has reached the first speed (S42: YES), the processor 3 determines, based on the detection result of the encoder 38, whether the rotation angle of the main shaft 34 has reached 240 degrees (S44). As shown in FIG. 11, when the rotation angle of the main shaft 34 is 240 degrees, the lower end 18 of the sewing needle 17 is positioned below the needle plate 41. If the rotation angle of the main shaft 34 has not reached 240 degrees (S44: NO), the processor 3 returns the process to S44. If the rotation angle of the main shaft 34 has reached 240 degrees (S44: YES), the processor 3 decelerates the sewing machine motor 33 to a second speed that is slower than the first speed (S45). The second speed may be any speed slower than the first speed, for example, 70 rpm.

[0106] The processor 3 determines whether the spring length has reached the second length L2 based on the detection result of the thread tension sensor 37 (S46). As shown in Fig. 11, in the sewing machine 1 of this embodiment, the spring length has reached the second length L2 when the rotation angle of the main shaft 34 has reached 240 degrees. In other words, the disc spacing is adjusted to the second spacing E2, and the thread tension pressure is adjusted to the second pressure.

[0107] If the spring length has not reached the second length L2 (S46: NO), the processor 3 returns the process to S46. If the spring length has reached the second length L2 (S46: YES), the processor 3 stops driving the actuator 36 to maintain the spring length at the second length L2. The processor 3 determines, based on the detection result of the encoder 38, whether the rotation angle of the spindle 34 has reached the stop angle corresponding to the stop position (S47).

[0108] If the rotation angle of the main shaft 34 has not reached the stop angle (S47: NO), processor 3 returns the process to S47. If the rotation angle of the main shaft 34 has reached the stop angle (S48: YES), processor 3 executes one-stitch stop processing (S48). The one-stitch stop processing is processing that controls the sewing machine motor 33 to stop the needle bar 15 after each stitch at a stop position where the lower end 18 of the sewing needle 17 is above the needle plate 41. In the basting mode, the length of one stitch is longer than the length of a lock stitch, so processor 3 executes the processing of S48 to ensure sufficient time to move the sewing workpiece C.

[0109] Processor 3 controls actuator 36 to start processing to adjust the spring length for first period T1 to first length L1 (S49). Processor 3 determines whether the spring length has reached first length L1 based on the detection result of thread tension sensor 37 (S50). If the spring length has not reached first length L1 (S50: NO), processor 3 returns the processing to S50.

[0110] If the spring length reaches the first length L1 (S50: YES), the processor 3 stops driving the actuator 36 to maintain the spring length at the first length L1. The processor 3 then ends the one-stitch sewing process and returns the process to the main process. That is, when the one-stitch sewing process is to be executed again, the processor 3 can control the sewing machine motor 33 to start the one-stitch sewing process when the length of the spring 23 in the pressure direction J1 is the first length L1.

[0111] 9, after the process of S36, processor 3 returns the process to S31. If the absolute value of the accumulated value is not greater than the predetermined amount (S32: NO), processor 3 stops driving sewing machine motor 33 at the stop position (S33).

[0112] The processor 3 determines whether the sewing workpiece C has been stopped for a predetermined period of time based on the detection result of the movement detection device 9 (S34). The predetermined period of time may be a period set in advance or may be a period set by the user. The predetermined period of time is, for example, 7 seconds. If the sewing workpiece C has not been stopped for a predetermined period of time (S34: NO), the processor 3 returns the process to S31. If the sewing workpiece C has been stopped for a predetermined period of time (S34: YES), the processor 3 ends the main process.

[0113] If a stop command is detected (S31: YES), processor 3 stops driving sewing machine motor 33 when the rotation angle of main shaft 34 reaches the stop angle (S37). Processor 3 then ends the main processing.

[0114] 12(A) and 12(B), an evaluation test will be described, which was conducted under the following conditions: the spring length of the sewing machine 1 was set to the second length L2 based on the detection result of the movement detection device 9; and a presser foot 25 having an O-shaped insertion portion in plan view was attached. In the evaluation test, a comparative example was used in which the sewing machine 1 performed free motion sewing without executing the thread tension adjustment process. In the evaluation test, an example was used in which the sewing machine 1 performed the main process. FIGS. 12(A) and 12(B) show the change in tension of the upper thread U over time when two stitches worth of free motion sewing were performed in basting mode. The movement speed of the workpiece C was approximately the same in the comparative example and the example. The tension of the upper thread U was measured using a standard digital tension meter, the DT series, a hand-use digital tension meter manufactured by SCHMIDT, a well-known tension meter. In Figures 12(A) and 12(B), for reference, the rotation angle of the main shaft 34 corresponding to the elapsed time is plotted on the upper axis. However, since the sewing machine motor 33 stops when the rotation angle of the main shaft 34 is 32 degrees and the target value of the rotation speed of the sewing machine motor 33 is changed to the first speed and the second speed, the amount of change in the rotation angle of the main shaft 34 on the graph is not constant.

[0115] As shown in Fig. 12(B), in the comparative example, tension peaks K1 and K4 are peaks during the shuttle capture period. Tension peaks K2 and K5 are peaks during the take-up lever pull-up period before the machine stops at the stop position. Tension peaks K3 and K6 are peaks during the take-up lever pull-up period after the machine stops at the stop position and then resumes sewing.

[0116] Between peak K2 and peak K3, the tension decreases from peak K2 by a change amount K7. The tension at peak K3 is greater than the tension at peak K2. Between peak K5 and peak K6, the tension decreases from peak K5 by a change amount K8. The tension at peak K6 is greater than the tension at peak K5.

[0117] On the other hand, as shown in Figure 12(A), in this embodiment, tension peaks H1 and H4 are peaks during the shuttle capture period. Tension peaks H2 and H5 are peaks during the take-up lever pull-up period before the machine stops at the stop position. Tension peaks H3 and H6 are peaks during the take-up lever pull-up period after the machine stops at the stop position and then resumes sewing.

[0118] Between peaks H2 and H3, the tension decreased from peak H2 by a change amount H7. Between peaks H5 and H6, the tension decreased from peak H5 by a change amount H8. The changes H7 and H8 in the example are greater than the changes K7 and K8 in the comparative example. This is because, in the sewing machine 1 of the example, the spring length is set to the first length L1, the disc spacing is set to the first spacing E1, and the thread tension pressure is set to the first pressure during the first period T1, so the pressure applied to the upper thread U while the sewing machine 1 is stopped at the stop position is reduced compared to the second period T2. Therefore, the operability of the sewing machine 1 of the example when moving the upper thread U to operate the sewing machine C was better than the operability of the sewing machine 1 of the comparative example when moving the upper thread U to operate the sewing machine C.

[0119] The tension at peak H3 is lower than the tension at peak H2. The tension at peak H6 is lower than the tension at peak H5. Peaks H3 and H6 occur during the period when the spring length is set to the first length L1. At the time of peaks H3 and H6, the second tension disc 22 does not transmit the tension pressure of the spring 23 to the upper thread U, but it was confirmed that sufficient tension was being applied to form a stitch. There was no significant difference in the finish between the stitches formed in the example and the comparative example. From the above, it was confirmed that performing the thread tension adjustment process during free motion sewing improves operability when the user manually moves the sewing object C compared to conventional methods.

[0120] In the above embodiment, the sewing machine 1 is an example of a sewing machine of the present invention. The processor 3 is an example of a processor of the present invention. The movement detection device 9 is an example of a movement detection device of the present invention. The needle bar 15 is an example of a needle bar of the present invention. The presser bar 16 is an example of a presser bar of the present invention. The sewing needle 17 is an example of a sewing needle of the present invention. The sewing machine motor 33 is an example of a sewing machine motor of the present invention. The needle plate 41 is an example of a needle plate of the present invention. The first thread tension disc 21 is an example of a first thread tension disc of the present invention. The second thread tension disc 22 is an example of a thread tension disc and a second thread tension disc of the present invention. The actuator 36 is an example of an actuator of the present invention. The presser feet 25 and 81 are examples of presser feet of the present invention. The insertion portions 76 and 86 are examples of insertion portions of the present invention. The spring 23 is an example of a spring of the present invention. The processing of S32, S35, S39, S42, S43, S45, S47, and S48 is an example of free motion sewing processing of the present invention. The processes of S41, S46, S49, and S50 are an example of the thread tension adjustment process of the present invention. The processes of S47 and S48 are an example of the one-stitch stop process of the present invention. The process of S19 is an example of the length adjustment process of the present invention.

[0121] The sewing machine 1 of the above embodiment includes a needle plate 41, a feed dog 32, a needle bar 15, a sewing machine motor 33, a second thread tension disc 22, a spring 23, an actuator 36, and a processor 3. A sewing needle 17 can be attached to the needle bar 15. The sewing machine motor 33 moves the needle bar 15 up and down. The spring 23 biases the second thread tension disc 22 to apply thread tension pressure to the thread tension disc 22. The actuator 36 adjusts the length of the spring 23. With the upper end of the feed dog 32 positioned below the needle plate 41, the processor 3 drives the sewing machine motor 33 to perform a free motion sewing process that moves the needle bar 15 up and down (S32, S35, S39, S42, S43, S45, S47, S48). At least a portion of the needle-up period TU, during which the lower end 18 of the sewing needle 17 is above the needle plate 41, is defined as a first period T1. At least a portion of the needle down period TD, during which the lower end 18 of the sewing needle 17 is below the needle plate 41, is defined as the second period T2. During the free motion sewing process, the processor 3 controls the actuator 36 to adjust the length of the spring 23 in the pressure direction J1 during the first period T1 to a first length L1. The processor 3 then executes a thread tension control process (S41, S46, S49, S50) to adjust the length of the spring 23 in the pressure direction J1 during the second period T2 to a second length L2 that is shorter than the first length L1. The thread tension control process executed by the processor 3 of the sewing machine 1 adjusts the length of the spring 23 in the pressure direction J1 so that the second length L2 is shorter than the first length L1. Therefore, the tension applied to the upper thread U during the first period T1 is smaller than the tension applied to the upper thread U during the second period T2. The first period T1 is a period during which the user may manually move the sewing object C during the free motion sewing process. Therefore, the thread tension control process contributes to improving the operability of the sewing material C when the user manually moves the sewing material C compared to the conventional case.

[0122] The processor 3 performs the thread tension control process when an instruction to perform the thread tension control process is detected (S1: YES), and does not perform the thread tension control process when an instruction to perform the thread tension control process is not detected (S1: NO). The processor 3 of the sewing machine 1 contributes to switching whether or not to perform the thread tension control process during the execution of the free motion sewing process, depending on whether or not an instruction to perform the thread tension control process is detected.

[0123] Processor 3 performs thread tension control processing when basting is performed (S1: YES), and does not perform thread tension control processing when basting is not performed (S1: NO). Basting creates a longer stitch length than lock stitching, resulting in a greater amount of movement of the workpiece C. Therefore, the amount of tension that the thread extending from the stitches formed in the workpiece C exerts on the workpiece C is greater when basting is performed than when lock stitching is performed. The resistance caused by the movement of the workpiece C is greater when basting is performed than when lock stitching is performed. Processor 3 of sewing machine 1 contributes to switching whether or not to perform thread tension control processing during free motion sewing processing, depending on whether basting is performed or not.

[0124] The sewing machine 1 is equipped with a movement detection device 9 and a presser bar 16. The movement detection device 9 detects the amount of movement of the sewing workpiece C placed on the needle plate 41. The movement detection device 9 can be attached to the presser bar 16. In the free motion sewing process, the processor 3 drives the sewing machine motor 33 based on the amount of movement detected by the movement detection device 9 (S62: YES) (S32, S35, S39). The processor 3 of the sewing machine 1 controls the sewing machine motor 33 in accordance with the detection result output by the movement detection device 9, thereby contributing to forming free motion stitches.

[0125] Processor 3 of sewing machine 1 controls sewing machine motor 33 to execute a one-stitch stop process that stops needle bar 15 after each stitch at a stop position where lower end 18 of sewing needle 17 is above needle plate 41 (S47, S48). When the amount of movement detected by movement detection device 9 during free motion sewing process reaches a predetermined amount (S32: YES), processor 3 controls sewing machine motor 33 to sew one stitch. The one-stitch stop process executed by processor 3 of sewing machine 1 stops needle bar 15 at a stop position after each stitch, thereby contributing to ensuring sufficient time for movement of the sewing object C. Compared to when needle bar 15 is not stopped at a stop position after each stitch, the one-stitch stop process contributes to improving operability of sewing object C when manually moving the sewing object C during needle up period TU.

[0126] The first period T1 includes a period during which the needle bar 15 is positioned at the stop position. In the thread tension control process executed by the processor 3 of the sewing machine 1, the tension applied to the upper thread U during the first period T1, which includes a period during which the needle bar 15 is positioned at the stop position, is smaller than that during the second period T2. Therefore, the thread tension control process contributes to improving the operability of the sewing object C when manually moving the sewing object C while the needle bar 15 is stopped at the stop position.

[0127] The sewing machine 1 is equipped with a presser foot having an insertion portion formed therein through which the sewing needle 17 is inserted. The processor 3 does not perform basting stitches if the planar shape of the presser foot insertion portion is C-shaped, but performs basting stitches if the planar shape of the presser foot insertion portion is O-shaped. When the planar shape of the presser foot insertion portion is O-shaped, the upper thread U is inserted through the sewing needle 17 and the presser foot. On the other hand, when the planar shape of the presser foot insertion portion is C-shaped, the upper thread U is not inserted through the presser foot insertion portion depending on the movement distance and movement direction of the sewing object C, making it difficult to stabilize the tension applied to the upper thread U, and making it easy for resistance to be applied when the user moves the sewing object C. The thread tension control process contributes to preventing unstable operability of the sewing object C when manually moving the sewing object C, which is caused by the use of a presser foot that is prone to resistance from the upper thread U stretching from the stitches when the sewing object C is moved.

[0128] When basting is not being performed, processor 3 performs a length adjustment process during free motion sewing to adjust the length of spring 23 to a third length L3 that is shorter than second length L2 (S19). The thread tension adjustment process of processor 3 of sewing machine 1 forms stitches with a tension greater than the tension imparted to the upper thread U during basting when basting is not being performed, for example, in the case of lock stitching. In other words, the length adjustment process of processor 3 of sewing machine 1 contributes to stabilizing free motion sewing stitches when basting is not being performed.

[0129] When the movement amount detected by the movement detection device 9 reaches a predetermined amount during the free motion sewing process, the processor 3 drives the sewing machine motor 33 at a speed that allows the length of the spring 23 during the second period to be adjusted to the second length L2. If the movement speed of the sewing workpiece C is relatively fast, driving the sewing machine motor 33 to match the movement speed of the sewing workpiece C may result in the process of adjusting the spring length from the first length L1 to the second length L2 being delayed. In this case, a stitch may be formed without the upper thread U being properly tensioned. In contrast, the free motion sewing process of the processor 3 of the sewing machine 1 prioritizes thread tension control over forming stitches at a speed that matches the movement amount of the sewing workpiece C. Therefore, the free motion sewing process of the sewing machine 1 contributes to preventing a stitch from being formed without the upper thread U being properly tensioned.

[0130] In the free motion sewing process, the processor 3 drives the sewing machine motor 33 when the length of the spring 23 is the first length L1, thereby starting the one-stitch sewing control process. If the movement speed of the workpiece C is relatively fast, driving the sewing machine motor 33 to match the movement speed of the workpiece C may result in the process of adjusting the spring length from the second length L2 to the first length L1 being delayed. In this case, the sewing machine 1 may not be able to fully achieve the effect of improving operability compared to conventional methods during the first period T1, during which the user may manually move the workpiece C. In contrast, the free motion sewing process of the processor 3 of the sewing machine 1 prioritizes thread tension control over forming stitches at a speed that matches the movement of the workpiece C. Therefore, the free motion sewing process of the sewing machine 1 contributes to fully achieving the effect of improving operability compared to conventional methods during the first period T1, during which the user may manually move the workpiece C.

[0131] In the sewing machine 1, the actuator 36 adjusts the thread tension pressure applied to the second tension disc 22. While the free motion sewing process is being performed, the processor 3 executes a thread tension control process that controls the actuator 36 to adjust the thread tension pressure during the first period T1 to a first pressure and to adjust the thread tension pressure during the second period T2 to a second pressure greater than the first pressure. The thread tension control process executed by the processor 3 of the sewing machine 1 adjusts the thread tension pressure so that the second pressure is greater than the first pressure. Therefore, the tension applied to the upper thread U during the first period T1 by the thread tension pressure is less than the tension applied to the upper thread U during the second period T2. Therefore, the thread tension control process contributes to improving the operability of the sewing object C when the user manually moves the sewing object C compared to conventional methods.

[0132] The actuator 36 of the sewing machine 1 adjusts the spacing between the first and second tension discs 21 and 22 to adjust the tension applied to the needle thread U disposed between the first and second tension discs 21 and 22. While the free motion sewing process is being performed, the processor 3 controls the actuator 36 to execute a thread tension control process that adjusts the spacing between the discs to a first spacing E1 during the first period T1 and to a second spacing E2 during the second period T2, the second spacing E2 being shorter than the first spacing E1. The thread tension control process executed by the processor 3 of the sewing machine 1 adjusts the spacing between the discs so that the second spacing E2 is shorter than the first spacing E1. Therefore, the tension applied to the needle thread U during the first period T1 is smaller than the tension applied to the needle thread U during the second period T2. Therefore, the thread tension control process contributes to improving the operability of the sewing object C when the user manually moves the sewing object C.

[0133] The present invention is not limited to the above-described embodiment and various modifications are possible. The present invention may be realized in the form of a sewing machine control method, a sewing machine program, and a non-transitory medium storing the sewing machine program. The sewing machine 1 may be a dedicated sewing machine using the movement detection device 9, in which case the feed amount adjustment motor 30, the feed mechanism 31, and the feed dog 32 may be omitted.

[0134] The sewing machine 1 may include the movement detection device 9, or the movement detection device 9 may be omitted. The movement detection device 9 is attached to the presser bar 16 and may detect the movement of the workpiece C placed on the needle plate 41, and the configuration, shape, etc. may be changed as appropriate. The movement detection device 9 may be built into the sewing machine 1. In that case, for example, a configuration equivalent to the movement detection device 9 may be built into the bed 11 or the head 14.

[0135] The movement detection device 9 is only required to be able to detect the movement of the sewing workpiece C, and does not have to be able to detect the amount of movement of the sewing workpiece C. The movement detection device 9 may be able to detect only one of the amount of movement of the sewing workpiece C in the short direction D1 and the amount of movement in the long direction D2. The movement detection device 9 may be able to detect the amount of movement in the horizontal direction. The detection result of the movement detection device 9 may represent only the amount of movement of the sewing workpiece C, and not necessarily the direction of movement. The image sensor 8 may be omitted as appropriate.

[0136] The spring length may be expressed as the length of the spring 23 in the pressure direction J1, or as the distance between the left end of the slider 26 and the right end of the plate member 39. The disc spacing may be measured when the upper thread U is positioned between the first tension disc 21 and the second tension disc 22. The disc spacing may be measured when the upper thread U is not positioned between the first tension disc 21 and the second tension disc 22. The change in thread tension pressure can be measured, for example, by determining whether or not the force pulling out the upper thread U changes when the upper thread U is positioned between the first tension disc 21 and the second tension disc 22.

[0137] The thread tension device 20 may omit the first tension disc 21. The arrangement of the thread tension device 20 may be changed as appropriate; for example, the shaft 24 may be arranged in a position facing the front-to-rear direction. The actuator 36 may be a pulse motor or other actuators such as a servo motor, a linear motor, or a solenoid. The type of spring 23 may be changed as appropriate. The spring 23 may directly contact the second tension disc 22. The mechanism for transmitting the driving force of the actuator 36 to the spring 23 may be changed as appropriate depending on the type of actuator 36 and the arrangement of the thread tension device 20. The first tension disc 21 and the second tension disc 22 may be a first roller and a second roller. In this case, the upper thread U is clamped between the first roller and the second roller, and the upper thread U is reeled out by the rotation of the first roller and the second roller. The first tension disc 21 and the second tension disc 22 may be omitted as appropriate. In this case, the thread tension pressure may be transmitted to the upper thread U via a member other than the tension discs.

[0138] Various types of information may be input to the sewing machine 1 by any device and method that can input information to the processor 3. The input interface that can input information to the processor 3 may be a pointing device such as a keyboard, a mouse, a trackball, a touchpad, or a graphics tablet, a scanner, a touch screen incorporated into a display, an audio input device such as a voice recognition system, or another type of input device such as a microphone.

[0139] The program including the instructions for executing the main processing of Fig. 8 may be stored in the storage device of each device before the processor 3 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 processor 3 may be received from another device via a cable or wireless communication and stored in a storage device. The other device may include, for example, a PC and a server connected via a network.

[0140] The steps of the main processing are not limited to being executed by the processor 3, but may be executed in part or in whole by other electronic devices, for example, an ASIC. The steps of the main processing may be distributed among multiple electronic devices, for example, multiple CPUs. The order of the steps of the main processing may be changed, and steps may be omitted or added as necessary. The following modifications may be made to the main processing as appropriate.

[0141] The method of obtaining the thickness of the sewing workpiece C may be changed as appropriate, and the processor 3 may place the presser bar 16 in the lowered position without obtaining the thickness of the sewing workpiece C. The lowered position and the normal position may be changed as appropriate. The lowered position may be the position where the presser foot 25 contacts the sewing workpiece C, or may be a position several mm above the position where the presser foot 25 contacts the sewing workpiece C. The first period T1, the second period T2, and the stop position may each be changed as appropriate.

[0142] The instruction to perform the thread tension control process may be changed as appropriate. The instruction used to determine whether to perform the thread tension control process may be detected, for example, when the stitch length is equal to or greater than a predetermined value, or when the upper thread tension detected by the tension sensor is equal to or greater than a predetermined value. The thread tension control process may be performed in a mode other than the basting mode.

[0143] The thread tension control process may be executed when the movement detection device 9 is not attached to the presser bar 16. In this case, the free motion sewing process may involve, for example, controlling the sewing machine motor 33 at a speed instructed by a foot controller or the like to sew one stitch. The processor 3 of the sewing machine 1 contributes to forming a stitch by controlling the sewing machine motor 33 in accordance with the detection result output by the movement detection device 9. The processor 3 may omit the one-stitch stop process and continuously move the needle bar 15 back and forth in the up and down direction at a predetermined speed. In this case, since the needle bar 15 is not stopped at the stop position, the first period T1 may not include the period during which the needle bar 15 is positioned at the stop position.

[0144] Processor 3 may perform basting stitches if the planar shape of the presser foot insertion portion is C-shaped. Processor 3 may not perform basting stitches if the planar shape of the presser foot insertion portion is a specific shape other than O-shaped or C-shaped, such as V-shaped. If the planar shape of the presser foot insertion portion is O-shaped, processor 3 may perform normal basting stitches or lockstitches while keeping the spring length, disc spacing, and thread tension pressure constant. The stitch length of a normal basting stitch is longer than the stitch length of a normal lockstitch.

[0145] The processor 3 may detect the planar shape of the presser foot without using a neural network. For example, the processor 3 may attach a unique marker to each presser foot and detect the shape by reading the marker with the image sensor 8. The marker may be, for example, a two-dimensional code or a specific graphic such as a star. The processor 3 may identify the planar shape of the presser foot based on image data generated by the image sensor 8, or may identify the planar shape based on information input by the user via an input interface. The processor 3 may identify the planar shape based on information read by a reader from an RFID tag attached to the presser foot. If the movement detection device 9 is equipped with a sensor that mechanically identifies the type of presser foot, the processor 3 may identify the planar shape of the presser foot based on information output from the movement detection device 9.

[0146] The sewing machine 1 may be capable of mounting one type of presser foot. The sewing machine 1 may execute the thread tension control process regardless of the type of presser foot.

[0147] The method of determining the spring length, disc spacing, and thread tension pressure may be changed as appropriate. The sewing machine 1 may omit the thread tension sensor 37. The processor 3 may determine the spring length, disc spacing, and thread tension pressure based on the output value to the actuator 36. The processor 3 may determine the spring length, disc spacing, and thread tension pressure based on the output value of an encoder that detects the drive amount of the actuator 36.

[0148] The spring length, disc spacing, and tensioning pressure during sewing each fluctuate slightly due to vibrations caused by sewing. Therefore, the spring length, disc spacing, and tensioning pressure during each of the first and second periods do not need to be strictly constant and may fluctuate. The difference between the first length L1 and the second length L2 needs to be sufficiently larger than the slight fluctuations in spring length due to vibrations, etc. The difference between the first spacing E1 and the second spacing E2 needs to be sufficiently larger than the slight fluctuations in spring length due to vibrations, etc. The difference between the first pressure and the second pressure needs to be sufficiently larger than the slight fluctuations in thread tension pressure due to vibrations, etc. Similarly, the difference between the second length L2 and the third length L3 needs to be sufficiently larger than the slight fluctuations in spring length due to vibrations, etc. The first spacing E1 does not need to be sufficiently larger than the thickness of the upper thread U; for example, it may be greater than 1.0 times the thickness of the upper thread U and less than 1.2 times the thickness of the upper thread U.

[0149] When basting stitches are not being performed, processor 3 may adjust the length of spring 23 in the pressure direction J1 to a length equal to or greater than second length L2 during free motion sewing processing. When the amount of movement detected by movement detection device 9 during free motion sewing processing reaches a predetermined amount, processor 3 may control sewing machine motor 33 at a speed greater than the speed at which the length of spring 23 in the pressure direction J1 during second period T2 can be adjusted to second length L2, thereby sewing one stitch. Processor 3 may drive sewing machine motor 33 when the spring length is not the first length to start sewing one stitch. Processor 3 may determine during needle down period TD during free motion sewing processing whether the amount of movement detected by movement detection device 9 has reached the predetermined amount.

[0150] The above-mentioned modifications may be combined as appropriate within the scope of the claims. The applicant intends to obtain patent rights for not only the combinations exemplified in the claims, but also for other combinations that do not deviate from the gist of the present invention and do not cause any contradictions. [Explanation of symbols]

[0151] 1: sewing machine, 3: processor, 9: movement detection device, 15: needle bar, 16: presser bar, 17: sewing needle, 21: first thread tension disc, 22: second thread tension disc, 25, 81: presser foot, 33: sewing machine motor, 36: actuator, 41: needle plate, 45: start / stop switch, 76, 86: insertion part, C: sewing material, J1: pressure direction

Claims

1. The needle plate and Feed teeth and A needle bar to which a sewing needle can be attached; a sewing machine motor that moves the needle bar up and down; Thread tension disc and a spring that biases the tension disc to apply tension pressure to the tension disc; an actuator for adjusting the length of the spring; a processor; The processor: a free motion sewing process in which the sewing machine motor is driven to move the needle bar up and down while the upper end of the feed dog is positioned below the needle plate; at least a part of a needle-up period during which the lower end of the sewing needle is above the needle plate is defined as a first period; When at least a part of a needle-down period in which the lower end of the sewing needle is below the needle plate is defined as a second period, The sewing machine is configured to execute a thread tension control process that controls the actuator while the free motion sewing process is being executed to adjust the length of the spring to a first length during the first period and to adjust the length of the spring to a second length that is shorter than the first length during the second period.

2. The processor: When an instruction to perform the thread tension control process is detected, the thread tension control process is performed; If the instruction is not detected, the thread tension control process is not performed.

2. The sewing machine according to claim 1,

3. The processor: When basting is performed, the thread tension control process is performed. When the basting stitch is not performed, the thread tension control process is not performed.

2. The sewing machine according to claim 1,

4. a movement detection device that detects the amount of movement of a sewing workpiece placed on the needle plate; a presser bar to which the movement detection device can be attached, The processor:

4. The sewing machine according to claim 3, wherein the sewing machine motor is driven based on the amount of movement detected by the movement detection device during the free motion sewing process.

5. The processor: The sewing machine is further configured to execute a stitch stop process for controlling the sewing machine motor to stop the needle bar at a stop position where the lower end of the sewing needle is above the needle plate, for each stitch, 5. The sewing machine according to claim 4, wherein, when the movement amount detected by the movement detection device reaches a predetermined amount during the free motion sewing process, the sewing machine motor is driven to start sewing one stitch.

6. The sewing machine according to claim 5 , wherein the first period includes a period during which the needle bar is positioned at the stop position.

7. The sewing machine further includes a presser foot having an insertion portion formed therein through which the sewing needle is inserted, The processor: When the plane shape of the insertion portion is C-shaped, the basting is not performed, When the plane shape of the insertion portion is O-shaped, the basting is performed.

4. The sewing machine according to claim 3,

8. The processor: The sewing machine according to claim 3, further comprising a thread tension adjustment process for adjusting the length of the spring to a third length shorter than the second length during the free motion sewing process when the basting stitch is not performed.

9. The processor: The sewing machine according to claim 5, characterized in that, when the movement amount detected by the movement detection device reaches the predetermined amount during the free motion sewing process, the sewing machine motor is driven at a speed that allows the length of the spring during the second period to be adjusted to the second length.

10. The processor:

6. The sewing machine according to claim 5, wherein, in the free motion sewing process, the sewing machine motor is driven to start sewing one stitch while the length of the spring is at the first length.

11. The needle plate and Feed teeth and A needle bar to which a sewing needle can be attached; a sewing machine motor that moves the needle bar up and down; an actuator for adjusting thread tension pressure to adjust tension applied to the upper thread; a processor; The processor: a free motion sewing process in which the sewing machine motor is driven to move the needle bar up and down while the upper end of the feed dog is positioned below the needle plate; at least a part of a needle-up period during which the lower end of the sewing needle is above the needle plate is defined as a first period; When at least a part of a needle-down period in which the lower end of the sewing needle is below the needle plate is defined as a second period, The sewing machine is configured to execute a thread tension control process that controls the actuator to adjust the thread tension pressure to a first pressure during the first period and to adjust the thread tension pressure to a second pressure greater than the first pressure during the second period while the free motion sewing process is being executed.

12. The needle plate and Feed teeth and A needle bar to which a sewing needle can be attached; a sewing machine motor that moves the needle bar up and down; a first thread tension disc and a second thread tension disc; an actuator that adjusts the distance between the first thread tension disc and the second thread tension disc in order to adjust the tension applied to the needle thread disposed between the first thread tension disc and the second thread tension disc; a processor; The processor: a free motion sewing process in which the sewing machine motor is driven to move the needle bar up and down while the upper end of the feed dog is positioned below the needle plate; at least a part of a needle-up period during which the lower end of the sewing needle is above the needle plate is defined as a first period; When at least a part of a needle-down period in which the lower end of the sewing needle is below the needle plate is defined as a second period, The sewing machine is configured to execute a thread tension control process that controls the actuator while the free motion sewing process is being executed to adjust the disc spacing to a first spacing during the first period and to adjust the disc spacing to a second spacing shorter than the first spacing during the second period.

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