Control method for sewing starting stage of sewing machine

Abstract

The invention relates to the technical field of sewing machines, in particular to a control method for a sewing starting stage of a sewing machine, which comprises the following steps: S1, detecting the height of a presser foot of the sewing machine through a sensing device, and sending a position signal a of the presser foot to a main control device; s2, starting a spindle motor; the sewing starting thread clamping device works and clamps the sewing thread on the thread supply side; s3, the main control device controls the driving motor to rotate by a certain angle according to the position signal a, and the presser foot is lifted; the corresponding relation between the rotation angle b of the driving motor and the position signal a is pre-stored in the main control device; s4, the rotating shuttle pulls the thread head part of the sewing thread; s5, pressing the cloth by the presser foot, and continuing the sewing operation. The main control device adjusts the rotating angle of the driving motor according to the position signal a, so that the presser foot can be slightly lifted up when sewing is started again; when the thickness of the cloth is changed, the lifting height of the presser foot is also changed; cloth drifting caused by the fact that the presser foot is lifted too high and sewing thread breaking caused by the fact that the presser foot is too tight are avoided.

Description

Technical Field

[0001] This invention relates to the field of sewing machine technology, and specifically to a method for controlling the sewing start stage of a sewing machine. Background Technology

[0002] During the initial stitching stage of a sewing operation, pulling the thread end from the top of the fabric to the bottom prevents the thread from being exposed, improving the appearance of the garment. When the worker puts the fabric in, the thread end is easily pulled under the presser foot. When the presser foot tightens the fabric, it also tightens the thread end. The rotary hook, by forcibly pulling the thread end from the top to the bottom of the fabric, is prone to breaking the thread.

[0003] CN201810130455.3 discloses a control method and a sewing machine for a sewing machine. The control method includes: step S1, controlling the thread clamp of the sewing machine to clamp the sewing thread located on the thread supply side of the sewing machine during the starting-up stage; step S2, controlling the pressure value of the presser foot of the sewing machine during the starting-up stage to be less than the pressure value of the presser foot during the normal sewing stage after the starting-up stage, so as to prevent the sewing machine's shuttle from hooking the sewing thread and breaking it. This technical solution only provides a concept of reducing the pressure value of the presser foot of the sewing machine during the starting-up stage, without further elaborating on the specific working method. The sewing machines actually sold by the applicant on the market raise the presser foot to a fixed height during the starting-up stage to solve the corresponding technical problem.

[0004] The disadvantages of existing technical solutions are as follows: 1. There are many types of presser feet for sewing machines, and the height of the presser foot can vary. The thickness of the fabric also varies. During the sewing of the same garment, changing the sewing direction may result in different thicknesses. Therefore, raising the presser foot to a fixed height at the beginning of the sewing stage cannot adapt to changes in the presser foot or the fabric. If the presser foot is too tight, thread breakage may still occur, and if the presser foot is too loose, the start-up may be slack.

[0005] 2. To avoid thread breakage, products on the market can only be configured to raise the height of the presser foot. The lifting and lowering of the presser foot is quite noticeable during the initial stitching stage, and the entire process takes a long time, which is not conducive to improving the customer experience and may pose a safety hazard. Summary of the Invention

[0006] The purpose of this invention is to provide a control method for the starting stage of a sewing machine that can automatically adjust the height of the presser foot according to the thickness of the fabric.

[0007] The purpose of this invention is achieved as follows: A method for controlling the start-up phase of a sewing machine, used to pull the thread end of the sewing thread from above the fabric to below the fabric during the start-up phase. The sewing machine includes: The presser foot lifting device includes a presser foot assembly, a drive motor, and a transmission assembly; the drive motor drives the transmission assembly, which is used to lift or lower the presser foot rod of the presser foot assembly, on which a presser foot is mounted; the transmission assembly and the presser foot rod are separable. The sensing device detects the height of the presser foot of the sewing machine and sends the presser foot position signal a to the main control device. The main control device is used to control the rotation angle b of the drive motor according to the position signal a; A thread clamp for clamping the sewing thread located on the thread feed side of the sewing machine during the starting stage; The control method includes: Step S1. Detect the height of the sewing machine presser foot using a sensing device and send the presser foot position signal a to the main control device; when the value of position signal a is 0, the program terminates; when the value of position signal a is greater than 0, execute step S2. Step S2. The main spindle motor starts; the thread clamp works and clamps the sewing thread on the supply side; Step S3. The main control device controls the drive motor to rotate at a certain angle according to the position signal a, and lifts the pressure foot; the main control device has a pre-stored correspondence between the drive motor rotation angle b and the position signal a; Step S4. The main shaft motor drives the rotary hook, which pulls the sewing thread head from the top of the fabric to the bottom of the fabric; Step S5. The drive motor resets, and the presser foot presses the fabric tightly; the spindle motor continues the sewing operation.

[0008] Preferably, a reset step A1 is also provided to reset the pre-stored correspondence between the drive motor rotation angle b and the presser foot position signal a in the main control device: when there is no fabric, the main control device controls the drive motor to perform a presser foot lifting action once. During the process of the presser foot rising from the bottom to the top, the sensing device collects the presser foot position signal a in real time and sends it to the main control device. The main control device records the correspondence between the drive motor rotation angle b and the presser foot position signal a, and establishes a mapping table between the rotation angle b and the position signal a.

[0009] Preferably, the feed dog protrudes from the needle plate when starting to sew; In step S2, the value of the position signal a is the sum of the value of the fabric thickness corresponding signal c1 and the value of the height of the feed dog exposed above the needle plate corresponding signal d. The formula is: a = c1 + d.

[0010] Preferably, in step S3, the main control device first controls the drive motor to rotate, and the first rotation angle corresponds to the value of signal c1; When the main control device detects that the sewing machine's spindle motor has rotated to the hook position, it controls the drive motor to continue rotating. The second rotation angle corresponds to signal c2, and the value of signal c2 is slightly greater than the value of signal c1.

[0011] Preferably, the spindle motor of the sewing machine rotates at a speed of less than 1500 rpm during the initial sewing stage, and the speed of the spindle motor increases to the set speed after the thread head is pulled out.

[0012] Preferably, the sensing device is a Hall element and a sensing magnet; the sensing magnet is mounted on the presser foot bar and moves up and down with the presser foot bar; the Hall element is fixed on the frame of the sewing machine.

[0013] The outstanding and beneficial technical effects of this invention compared to the prior art are: 1. The height of the presser foot is detected by a sensor, and the position signal 'a' of the presser foot height is sent to the main control device. The main control device adjusts the rotation angle of the drive motor according to the position signal 'a', so that the presser foot can be slightly raised when sewing. When the fabric thickness changes, the height at which the presser foot is raised also changes. This prevents the presser foot from being raised too high, causing the fabric to drift, and prevents the presser foot from being too tight, causing the sewing thread to break.

[0014] 2. After the presser foot is replaced, the pre-stored correspondence between the drive motor rotation angle b and the presser foot position signal a in the main control device can be reset through the program to ensure that the presser foot is raised to a suitable height during the seam-starting stage.

[0015] 3. During the starting process, the presser foot is raised in two stages, one before the other. In the first stage, the presser foot is raised to the height corresponding to the fabric. When the main spindle motor is about to hook the thread, the presser foot is raised to the height corresponding to the feed dog. This ensures that the height at which the presser foot is raised is sufficient to release the sewing thread without creating a large gap between the presser foot and the fabric, which would cause the fabric to drift. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the sewing machine of the present invention.

[0017] Figure 2 This is a schematic diagram of the presser foot lifting device of the sewing machine of the present invention.

[0018] Figure 3 This is a schematic diagram of the presser foot height before the drive motor of the present invention rotates for the first time.

[0019] Figure 4This is a schematic diagram of the presser foot height before the drive motor of the present invention rotates for the second time. Detailed Implementation

[0020] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0021] A method for controlling the start-up phase of a sewing machine, used to pull the thread end of the sewing thread from above the fabric to below the fabric during the start-up phase. The sewing machine includes: Rack 1; The presser foot lifting device includes a presser foot assembly, a drive motor 7, and a transmission assembly 6. The drive motor drives the transmission assembly, which is used to lift or lower the presser foot rod 2 of the presser foot assembly. A presser foot 3 is mounted on the presser foot rod. The transmission assembly and the presser foot rod are separable. The drive motor 7 is a stepper motor or a servo motor, preferably a stepper motor with a lower cost. The specific structure of the presser foot lifting device is the same as that of the prior art. A sensing device detects the height of the presser foot of the sewing machine and sends the presser foot position signal a to the main control device; the sensing device consists of a Hall element 5 and a sensing magnet 9; the sensing magnet 9 is mounted on a fixed sleeve 10 on the presser foot bar 9 and moves up and down with the presser foot bar; the Hall element is fixed on the frame of the sewing machine.

[0022] The main control device (not shown in the figure, its main structure is a control circuit board) is used to control the rotation angle b of the drive motor according to the position signal a; A thread clamp 13 is used to clamp the sewing thread located on the thread supply side of the sewing machine during the starting stage; the thread clamp is prior art. The control method includes: Step S1. When the existing sewing machine is working, the operator applies force through the foot pedal, which sends a start signal to the main control device. After receiving this start signal, the main control device recognizes that sewing operations need to begin and enters the sewing start state. The main control device detects the height of the sewing machine presser foot through a sensor, specifically, it detects the position of the presser foot bar. The sensor sends the presser foot position signal a to the main control device. When the value of position signal a is 0, the sewing start procedure terminates, but sewing operations still begin. When the value of position signal a is greater than 0, step S2 is executed. Step S2. The main spindle motor starts; the thread clamp works and clamps the sewing thread on the supply side; the main spindle motor rotates in subsequent steps, and the first rotation of the main spindle motor completes the starting action of this scheme; the main spindle motor is a servo motor; Step S3. After the spindle motor rotates, the main control device controls the drive motor to rotate a certain angle according to the position signal a, and lifts the pressure foot; the manufacturer will pre-store the correspondence between the drive motor rotation angle b and the position signal a in the main control device; the pre-stored relationship between the rotation angle b and the position signal a is generally based on the original installed pressure foot or a universal pressure foot.

[0023] Step S4. The main shaft motor drives the rotary hook. During the rotation of the rotary hook, it will hook the sewing thread and pull the end of the sewing thread from the top of the fabric to the bottom of the fabric. Step S5. The drive motor resets, and the presser foot presses the fabric 11 tightly; the main spindle motor continues the sewing operation.

[0024] Preferably, a reset step A1 is also provided to reset the pre-stored correspondence between the drive motor rotation angle b and the presser foot lever position signal a in the main control device: When there is no fabric, the main control device controls the drive motor to perform a presser foot lifting action. During the process of the presser foot rising from the bottom to the top, the sensing device collects the presser foot lever position signal a in real time and sends it to the main control device. The main control device records the correspondence between the drive motor rotation angle b and the presser foot lever position signal a, and establishes a mapping table between the rotation angle b and the position signal a. During the reset step A1, the feed dog is located below the needle plate 4, so the presser foot is attached to the needle plate when it is at the bottom. If the presser foot is replaced, executing the reset step A1 can recalibrate it, avoiding the impact of changes in presser foot height on the mapping relationship between the rotation angle b and the position signal a.

[0025] The process of the drive motor rotating and the change in the height of the pressure foot are as follows: 1. Idle travel phase (no change in altitude) When the drive motor 7 starts up and the rotation angle is small (e.g., 0°~10°), the "base circle part" of the cam 8 on the drive motor shaft contacts the connecting rod. At this time, the cam does not generate effective thrust, the connecting rod assembly and the presser foot rod are stationary, and the presser foot remains in the initial position of being close to the needle plate.

[0026] 2. Effective travel phase (linear association) When the drive motor rotates beyond its idle travel angle (e.g., 10°~120°), the cam's "lift section" begins to push the connecting rod: as the cam rotates, the distance (radial direction) from a point on its profile to the center of rotation gradually increases. This "radial increment" is converted into the presser foot's "vertical lifting height" through the connecting rod assembly. Since the cam's lift section profile is typically designed as a constant velocity lift curve (ensuring smooth presser foot lifting without impact), within this range: presser foot lifting height (H) = motor rotation angle (θ) × transmission ratio (K) Transmission ratio K (unit: mm / °): a fixed coefficient determined by mechanical structure parameters, reflecting "the number of millimeters the presser foot is lifted for every 1° of motor rotation".

[0027] 3. Full travel phase (constant altitude) When the drive motor rotates to its maximum effective angle (e.g., 120°, slightly different for different models), the cam's "lift end point" (maximum radial distance) contacts the connecting rod. At this point, the presser foot rises to its highest height (typically 3-10mm for household models and 5-15mm for industrial models, depending on the design). If the motor continues to rotate (exceeding 120°), the cam enters the "fall section" or "far-end section," and the presser foot begins to descend or maintains its highest height. At this point, further increases in rotation angle no longer correspond to a corresponding increase in height.

[0028] During the process of lifting the pressure foot, the rotation angle b of the drive motor and the position signal a collected by the sensing device are recorded one by one to form a mapping table.

[0029] Preferably, the feed dog is exposed on the needle plate when starting to sew; placing the fabric 11 on the feed dog can prevent the fabric from drifting.

[0030] In step S2, as Figure 3 As shown, since the feed dog 12 is exposed above the needle plate and at its highest point; after the fabric is placed, when the presser foot moves down and presses the fabric, the actual height the presser foot moves is the sum of the fabric thickness h2 and the feed dog height h1; the value of the position signal a is the sum of the value of the signal c1 corresponding to the fabric thickness h2 and the value of the signal d corresponding to the height h1 of the feed dog exposed above the needle plate; the value of the feed dog corresponding to the signal d is a constant set by the manufacturer. Assuming that the drive motor rotates by an angle b1 and raises the presser foot from the height of the needle plate to the height h1, the value of the feed dog corresponding to the signal d is the position signal a at that moment; The formula is: a = c1 + d.

[0031] Preferably, in step S3, the main control device first controls the drive motor to rotate, and the first rotation angle corresponds to the value of signal c1; c1=ad. During the first run in this step, the main control program controls the drive motor to execute a rotation angle b corresponding to the value of signal c1. Due to unavoidable tolerances, the actual constant of signal d set in the program will deviate to a certain extent from the theoretical value of signal d calculated by the feed dog height h1. During the process of the main spindle motor rotating to the hook position, the height of the feed dog gradually moves down to below the needle plate; therefore, at the very beginning, when the drive motor rotates for the first time, the value of the feed dog corresponding to signal d needs to be subtracted. If the value of the corresponding signal d is not subtracted, the presser foot will be lifted when the drive motor rotates for the first time. The purpose of the first rotation is to prepare for lifting the presser foot in advance to improve the efficiency of lifting the presser foot and the stability of the engagement. Ideally, after the drive motor rotates for the first time, the transmission component 6 just contacts the fixed sleeve on the presser foot rod, but no force is applied to the fixed sleeve 10, so that when the drive motor rotates for the second time, the transmission component can directly lift the fixed sleeve. The spindle motor is a servo motor, and the main control device can provide precise feedback on the spindle motor's rotation angle in real time. When the main control device detects that the sewing machine's spindle motor has rotated to the thread-hooking position (for example, the spindle motor rotates another 20 degrees from this position to hook the sewing thread), the main control device then controls the drive motor to continue rotating. The second rotation angle corresponds to signal c2, and the value of signal c2 is slightly greater than the value of signal c1. Because the fabric has a certain degree of elasticity, if the value of signal c1 is equal to the value of signal c1, the presser foot will not actually detach from the fabric. In this implementation, the value of the execution signal c2 is 1mm higher than the value of the execution signal c1 in terms of increasing the presser foot lifting height.

[0032] Preferably, the spindle motor of the sewing machine rotates at a speed of less than 1500 rpm during the initial sewing stage, and increases its speed to the set speed after the thread head is pulled out. If the speed is too high, the initial rotation time of the drive motor will be insufficient.

[0033] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for controlling the starting stage of a sewing machine, used to pull the thread end of the sewing thread from above the fabric to below the fabric during the starting stage, characterized in that, The sewing machine includes: The presser foot lifting device includes a presser foot assembly, a drive motor, and a transmission assembly; the drive motor drives the transmission assembly, which is used to lift or lower the presser foot rod of the presser foot assembly, on which a presser foot is mounted; the transmission assembly and the presser foot rod are separable. The sensing device detects the height of the presser foot of the sewing machine and sends the presser foot position signal a to the main control device. The main control device is used to control the rotation angle b of the drive motor according to the position signal a; A thread clamp for clamping the sewing thread located on the thread feed side of the sewing machine during the starting stage; The control method includes: Step S1. Detect the height of the sewing machine presser foot using a sensing device and send the presser foot position signal a to the main control device; when the value of position signal a is 0, the program terminates; when the value of position signal a is greater than 0, execute step S2. Step S2. The main spindle motor starts; the thread clamp works and clamps the sewing thread on the supply side; Step S3. The main control device controls the drive motor to rotate at a certain angle according to the position signal a, and lifts the pressure foot; the main control device has a pre-stored correspondence between the drive motor rotation angle b and the position signal a; Step S4. The main shaft motor drives the rotary hook, which pulls the sewing thread head from the top of the fabric to the bottom of the fabric; Step S5. The drive motor resets, and the presser foot presses the fabric tightly; the spindle motor continues the sewing operation.

2. The method for controlling the starting stage of a sewing machine according to claim 1, characterized in that, Before step S1, a reset step A1 is set to reset the pre-stored correspondence between the drive motor rotation angle b and the presser foot position signal a in the main control device: when there is no fabric, the main control device controls the drive motor to perform a presser foot lifting action. During the process of the presser foot rising from the bottom to the top, the sensing device collects the presser foot position signal a in real time and sends it to the main control device. The main control device records the correspondence between the drive motor rotation angle b and the presser foot position signal a, and establishes a mapping table between the rotation angle b and the position signal a.

3. The method for controlling the starting stage of a sewing machine according to claim 2, characterized in that, When starting to sew, the feed dog protrudes from the needle plate; In step S2, the value of the position signal a is the sum of the value of the fabric thickness corresponding signal c1 and the value of the height of the feed dog exposed above the needle plate corresponding signal d. The formula is: a = c1 + d.

4. The method for controlling the starting stage of a sewing machine according to claim 3, characterized in that, In step S3, the main control device first controls the drive motor to rotate, and the first rotation angle corresponds to the value of signal c1. When the main control device detects that the sewing machine's spindle motor has rotated to the hook position, it controls the drive motor to continue rotating. The second rotation angle corresponds to signal c2, and the value of signal c2 is slightly greater than the value of signal c1.

5. The method for controlling the starting stage of a sewing machine according to claim 4, characterized in that, The main spindle motor of the sewing machine rotates at a speed of less than 1500 rpm during the initial sewing stage. After the thread head is pulled out, the main spindle motor speed increases to the set speed.

6. The method for controlling the starting stage of a sewing machine according to claim 1, characterized in that, The sensing device consists of a Hall element and a sensing magnet; the sensing magnet is mounted on the presser foot bar and moves up and down with the presser foot bar; the Hall element is fixed on the frame of the sewing machine.

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