A closed-loop control method for presser foot of sewing machine

Abstract

The present invention provides a closed-loop control method for the presser foot of a sewing machine, comprising the following steps: providing an electronic control module and a presser foot height sensor in the sewing machine; during the sewing process of the sewing machine, when the electronic control module determines, based on feedback from the presser foot height sensor, that the fabric thickness has changed or that overstitching has occurred, the electronic control module performs the following control: the compression amount of the pressure-adjusting spring changes, and the electronic control module obtains the change ΔF in the presser foot pressure Ff; the electronic control module adjusts the current flowing through the presser foot lifting electromagnet based on the change ΔF in the presser foot pressure Ff, thereby offsetting the change ΔF in the presser foot pressure Ff, thereby offsetting the change in the presser foot pressure Ff caused by the change in fabric thickness, and ultimately maintaining an appropriate presser foot pressure Ff. This application greatly simplifies the structure and reduces costs, and the presser foot lifting electromagnet has a fast response speed, capable of quickly offsetting the change in the presser foot pressure Ff caused by the change in fabric thickness, thereby improving the sewing quality and product competitiveness of the sewing machine.

Description

Technical Field

[0001] The invention relates to the field of sewing machines, in particular to a closed-loop control method for a presser foot of a sewing machine. Background Art

[0002] During the sewing process, a sewing machine presses the fabric with its presser foot to sew. Existing sewing machines are equipped with a compression spring that applies downward force to the presser foot. The compressed compression spring generates pressure, causing the presser foot to press the fabric downward, thereby sewing. At the same time, the sewing machine is also equipped with a presser foot lifting mechanism. The driving source of the presser foot lifting mechanism is usually an electromagnet or a motor (usually a stepping motor), which realizes automatic presser foot lifting. Compared with the traditional manual presser foot lifting method of pushing the kneerest to lift the presser foot to a certain height, this can reduce the operator's physical exertion. However, existing sewing machines have the following main defects:

[0003] 1. When the presser foot lifting mechanism uses an electromagnet as the driving source, the working mode of the electromagnet is only power on or power off, so that the height of the presser foot can only change from 0 to H. That is, after the electromagnet is energized, the lifting height of the presser foot is only H, which makes the presser foot lifting mode very single and cannot meet the needs of various sewing modes.

[0004] 2. When the presser foot lifting mechanism uses a stepper motor as the driving source, although it can achieve multiple presser foot lifting heights, the stepper motor causes the cost of the sewing machine to increase significantly, which is not conducive to the market competitiveness of the product; in addition, the response speed of the motor is slow.

[0005] 3. Compression springs with different compression amounts will exert different downward forces on the presser foot. When the fabric being sewn changes from thin to thick, or when over-stitching occurs, the presser foot is lifted by the fabric, causing the compression of the compression spring to increase, resulting in greater pressure on the presser foot, which in turn causes the force of the presser foot pressing on the fabric to increase, resulting in poor passage of the sewn fabric, jamming, and ultimately worsening of the sewing seams.

[0006] To adapt sewing machines to sewing fabrics of varying thicknesses, current sewing machines on the market are equipped with a pressure-adjusting nut. This nut is mounted on the top of the machine, with its lower end acting on the upper end of a compression spring. Manual rotation of the nut changes the compression of the spring, adjusting the presser foot pressure. This manual adjustment is not intelligent. With the continuous advancement of sewing machine control technology, some systems have emerged that use stepper motors in conjunction with a series of mechanical transmission structures to control presser foot pressure. However, these systems have a slow response speed, making it difficult to quickly adjust the pressure, and are complex and costly. Summary of the Invention

[0007] In view of the above-mentioned shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a closed-loop control method for the presser foot of a sewing machine, which can realize automatic adjustment of the presser foot pressure in a low-cost and simple manner.

[0008] To achieve the above-mentioned object, the present invention provides a closed-loop control method for the presser foot of a sewing machine, which is used for a sewing machine. The sewing machine comprises a pressure-adjusting spring, a presser foot lifting electromagnet, a presser foot lifting mechanism, and a presser foot. The presser foot lifting electromagnet is connected to the presser foot via the presser foot lifting mechanism. The presser foot lifting mechanism comprises a presser foot rod that can move up and down. The lower end of the pressure-adjusting spring acts on the presser foot rod. The presser foot is mounted on the presser foot rod. The presser foot lifting electromagnet applies a tensile force Fe to the presser foot via the presser foot lifting mechanism. The pressure-adjusting spring applies a pressure force Fs to the presser foot via the presser foot rod. The closed-loop control method for the presser foot of a sewing machine comprises the following steps:

[0009] S1, setting an electronic control module and a presser foot height sensor in the sewing machine, and connecting the presser foot lifting electromagnet and the presser foot height sensor to the electronic control module;

[0010] S2. The closed-loop control method for the presser foot of a sewing machine includes a presser foot pressure adjustment control method, and the presser foot pressure adjustment control method includes the following steps:

[0011] S21, pre-storing a critical current value in the electronic control module; when the presser foot lifting electromagnet is supplied with a current equal to the critical current value, the tension Fe applied by the presser foot lifting electromagnet to the presser foot via the presser foot lifting mechanism is equal to the pressure Fs applied by the pressure regulating spring to the presser foot via the presser foot rod;

[0012] S22. During the sewing process of the sewing machine, the presser foot height sensor detects the real-time height H of the presser foot and feeds back the height H to the electronic control module. When the electronic control module determines, based on the feedback from the presser foot height sensor, that the fabric thickness has changed or that overstitching has occurred, the electronic control module performs the following control.

[0013] S23, the compression amount of the pressure-adjusting spring changes, and the electronic control module obtains the change ΔF of the presser foot pressure Ff;

[0014] S24, the electronic control module adjusts the current of the presser foot lifting electromagnet according to the change ΔF of the presser foot pressure Ff:

[0015] When the electronic control module determines that the presser foot pressure Ff increases by ΔF, the electronic control module controls the current of the presser foot lifting electromagnet to increase within the range of zero to a critical current value, so that the tension Fe applied by the presser foot lifting electromagnet to the presser foot increases by ΔF, thereby offsetting the change in the presser foot pressure Ff by ΔF;

[0016] When the electronic control module determines that the presser foot pressure Ff decreases by ΔF, the electronic control module controls the current of the presser foot lifting electromagnet to decrease within the range of zero to the critical current value, so that the tension Fe applied by the presser foot lifting electromagnet to the presser foot is reduced by ΔF, offsetting the change ΔF in the presser foot pressure Ff.

[0017] Furthermore, in step S23, the electronic control module obtains the change ΔH of the real-time height H of the presser foot according to the feedback of the presser foot height sensor, and automatically calculates the change ΔF of the presser foot pressure Ff according to the change ΔH of the real-time height H of the presser foot.

[0018] Furthermore, the sewing machine also has a force sensor, which is used to detect the pulling force Fe applied by the presser foot lifting electromagnet to the presser foot, and the force sensor is connected to the electronic control module; in step S23, the electronic control module directly calculates the change ΔF of the presser foot pressure Ff based on the feedback of the force sensor.

[0019] Furthermore, the sewing machine presser foot closed-loop control method further includes step S3, the sewing machine presser foot closed-loop control method includes a presser foot lifting control method, and the presser foot lifting control method includes the following steps:

[0020] S31, inputting a target presser foot lift height M into the electronic control module;

[0021] S32. After the electronic control module receives the presser foot lifting instruction, the electronic control module controls the presser foot lifting electromagnet to pass a presser foot lifting current that matches the target presser foot lifting height M, and the presser foot lifting electromagnet drives the presser foot to move upward through the presser foot lifting mechanism.

[0022] Furthermore, the presser foot lifting control method further comprises the following steps:

[0023] S33, the presser foot height sensor detects the real-time presser foot height H and feeds it back to the electronic control module, the electronic control module compares the real-time presser foot height H with the target presser foot lifting height M, and performs the following control according to the comparison result;

[0024] S34, when the electronic control module determines that the real-time presser foot height H is consistent with the target presser foot lifting height M, the electronic control module controls the presser foot lifting electromagnet to maintain the current presser foot lifting current;

[0025] S35. When the electronic control module determines that the real-time height H of the presser foot is higher than the target presser foot lifting height M, the electronic control module controls the presser foot lifting current supplied to the presser foot lifting electromagnet to decrease until the real-time height H of the presser foot matches the target presser foot lifting height M;

[0026] S36. When the electronic control module determines that the real-time height H of the presser foot is lower than the target presser foot lifting height M, the electronic control module controls the presser foot lifting current passed into the presser foot lifting electromagnet to increase until the real-time height H of the presser foot matches the target presser foot lifting height M.

[0027] Furthermore, the target presser foot lifting height M is a numerical value, and the numerical value is at least one.

[0028] Furthermore, the sewing machine further comprises an electronic knee rest device, the output end of which is communicatively connected to the electronic control module; in step S31, the target presser foot lifting height M is input to the electronic control module via the electronic knee rest device.

[0029] Furthermore, the sewing machine further comprises a main control panel, which is communicatively connected to the electric control module; in the step S31, the target presser foot lifting height M is input to the electric control module via the main control panel.

[0030] Furthermore, the presser foot lifting mechanism also includes a right lever with a fixed rotating fulcrum, a presser foot lifting rod, a left lever with a fixed rotating fulcrum, a presser foot lifting plate, and a presser rod guide block fixed to the presser foot rod, the iron core of the presser foot lifting electromagnet is hinged to the right lever, the two ends of the presser foot lifting rod are respectively hinged to the right lever and the left lever, the left lever and the presser foot lifting plate are hinged, a lifting hook is provided on the presser foot lifting plate, and a connecting protrusion that engages with the lifting hook is provided on the presser rod guide block.

[0031] Furthermore, the presser foot lifting mechanism also includes a presser foot lifting lever with a fixed rotating fulcrum, a presser foot lifting rod, a presser foot lifting crank, and a presser foot lifting shaft rotatably installed in the sewing machine casing. The iron core of the presser foot lifting electromagnet is hinged to the presser foot lifting lever, and the two ends of the presser foot lifting rod are respectively connected to the presser foot lifting lever and the presser foot lifting crank. The presser foot lifting crank is fixed to one end of the presser foot lifting shaft, and the other end of the presser foot lifting shaft is transmission connected to the presser foot rod.

[0032] Furthermore, the sewing machine further comprises a pressure-adjusting nut threadedly connected to the sewing machine casing, and the lower end of the pressure-adjusting nut abuts against the upper end of the pressure-adjusting spring.

[0033] As described above, the closed-loop control method for the presser foot of a sewing machine according to the present invention has the following beneficial effects:

[0034] The present application controls the magnitude of the pulling force Fe applied by the presser foot lifting electromagnet to the presser foot by controlling the magnitude of the current flowing through the presser foot lifting electromagnet, so that the change in the pulling force Fe applied by the presser foot lifting electromagnet to the presser foot is offset by the change in the presser foot pressure Ff caused by the change in the compression of the pressure-adjusting spring, thereby offsetting the change in the presser foot pressure Ff caused by the change in the thickness of the fabric, and ultimately maintaining an appropriate presser foot pressure Ff. In particular, the present application adopts the existing pressure-adjusting spring, presser foot lifting electromagnet, presser foot lifting mechanism and presser foot structure in the sewing machine, and utilizes a presser foot height sensor. On the one hand, this avoids the complex structure and high cost caused by adjustment through a stepper motor, that is, greatly simplifies the structure and reduces costs. On the other hand, because the response speed of the presser foot lifting electromagnet is much faster than that of the stepper motor, it can quickly offset the change in the presser foot pressure Ff caused by the change in the thickness of the fabric, thereby improving the sewing quality and product competitiveness of the sewing machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a structural diagram of the sewing machine in this application when it is a lockstitch sewing machine.

[0036] Figure 2 for Figure 1 Schematic diagram of the structure at the presser foot lifting plate.

[0037] Figure 3 for Figure 1 Schematic diagram of the force acting on the presser foot.

[0038] Figure 4 This is a structural diagram of the sewing machine in this application when it is an overlock sewing machine.

[0039] Component number description

[0040] 10 Pressure regulating spring

[0041] 20 Presser foot lifter electromagnet

[0042] 30 Presser foot lifting mechanism

[0043] 31 Presser foot bar

[0044] 32 Pressure rod guide block

[0045] 33 Right lever

[0046] 34 Presser foot lifter

[0047] 35 Left lever

[0048] 36 Presser foot lifting plate

[0049] 37 Presser foot lifter lever

[0050] 38 Presser foot crank

[0051] 39 Presser foot lifter

[0052] 40 presser foot

[0053] 50 Pressure regulating nut

[0054] 60 force sensors

[0055] 70 Presser foot height sensor DETAILED DESCRIPTION

[0056] The following describes the implementation of the present invention through specific embodiments. People skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0057] It should be noted that the structures, proportions, sizes, etc. depicted in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions for the implementation of the present invention. Therefore, they have no substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose of the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle", etc. quoted in this specification are only for the convenience of description and are not used to limit the scope of the implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0058] The present application relates to a closed-loop control method for the presser foot of a sewing machine, which is used for sewing machines, such as flat-bed sewing machines, overlock sewing machines, interlock sewing machines, heavy-duty sewing machines, etc. These sewing machines all use an electromagnet to drive the presser foot to be raised or lowered, and use a compression spring (compression spring) to apply pressing pressure to the presser foot.

[0059] like Figure 1 or as Figure 4 The sewing machine is provided with a pressure-adjusting spring 10, a presser foot lifting electromagnet 20, a presser foot lifting mechanism 30 and a presser foot 40. The presser foot lifting electromagnet 20 is connected to the presser foot 40 through the presser foot lifting mechanism 30. The presser foot lifting mechanism 30 has a presser foot rod 31 that can move up and down. The lower end of the pressure-adjusting spring 10 acts on the presser foot rod 31. The presser foot 40 is installed on the presser foot rod 31. The pressure-adjusting spring 10, the presser foot lifting electromagnet 20, the presser foot lifting mechanism 30 and the presser foot 40 are all existing structures in the sewing machine. The structure of the presser foot lifting mechanism 30 will be different for different sewing machine models. 1. When the sewing machine is a lockstitch sewing machine, such as Figure 1 and Figure 2As shown, the presser foot lifting mechanism 30 also includes a right lever 33 with a fixed rotation fulcrum, a presser foot lifting rod 34, a left lever 35 with a fixed rotation fulcrum, a presser foot lifting plate 36, a pressure rod guide block 32, and a presser foot rod 31 installed in the sewing machine housing for vertical movement. The upper end of the iron core of the presser foot lifting electromagnet 20 is hinged to the right lever 33, the right and left ends of the presser foot lifting rod 34 are hinged to the right lever 33 and the left lever 35 respectively, the left lever 35 is hinged to the presser foot lifting plate 36, the presser foot lifting plate 36 is provided with a lifting hook, the pressure rod guide block 32 is provided with a connecting protrusion that engages with the lifting hook, the pressure rod guide block 32 is fixed to the presser foot rod 31 by screw locking, and the pressure rod guide block 32 is close to the upper end of the presser foot rod 31. The presser foot 40 is installed at the lower end of the presser foot rod 31. The lower end of the pressure regulating spring 10 directly abuts the upper end of the presser foot rod 31.

[0060] 2. When the sewing machine is an overlock machine, Figure 4 As shown, the presser foot lifting mechanism 30 also includes a presser foot lifting lever 37 with a fixed rotation fulcrum, a presser foot lifting rod 34, a presser foot lifting crank 38, and a presser foot lifting shaft 39 rotatably installed in the sewing machine housing. The lower end of the iron core of the presser foot lifting electromagnet 20 is hinged to the presser foot lifting lever 37, the lower and upper ends of the presser foot lifting rod 34 are connected to the presser foot lifting lever 37 and the presser foot lifting crank 38 respectively, the presser foot lifting crank 38 is fixed to the right end of the presser foot lifting shaft 39, and the left end of the presser foot lifting shaft 39 is transmission-connected to the front end of the presser foot rod 31. The presser foot 40 is installed at the rear end of the presser foot rod 31. The lower end of the pressure regulating spring 10 indirectly abuts the upper end of the rear section of the presser foot rod 31.

[0061] When sewing fabrics, the sewing machine (i.e. the above-mentioned flat sewing machine or overlock sewing machine) Figure 3 As shown, the pressure-adjusting spring 10 applies a vertical downward pressure Fs to the presser foot 40 via the presser foot rod 31, and the presser foot lifting electromagnet 20 applies a vertical upward pulling force Fe to the presser foot 40 via the presser foot lifting mechanism 30. The magnitude of this pulling force Fe is related to the magnitude of the current flowing through the presser foot lifting electromagnet 20: the greater the current flowing through the presser foot lifting electromagnet 20, the greater the vertical upward pulling force Fe applied by the presser foot lifting electromagnet 20 via the presser foot lifting mechanism 30 to the presser foot 40; the smaller the current flowing through the presser foot lifting electromagnet 20, the smaller the vertical upward pulling force Fe applied by the presser foot lifting electromagnet 20 via the presser foot lifting mechanism 30 to the presser foot 40. When the sewing machine is sewing fabric, when the presser foot 40 is not lifted upward, the presser foot pressure Ff (i.e., the material pressing pressure) exerted by the presser foot 40 on the fabric is: Ff = Fs - Fe.

[0062] When the sewing machine needs to lift the presser foot, the current flowing into the presser foot lifting electromagnet 20 must satisfy the following conditions: the tension Fe applied by the presser foot lifting electromagnet 20 to the presser foot 40 via the presser foot lifting mechanism 30 is greater than the pressure Fs applied by the pressure-adjusting spring 10 via the presser foot rod 31. The presser foot lifting mechanism 30 then overcomes the pressure Fs of the pressure spring and drives the presser foot 40 upward, achieving automatic presser foot lifting. The presser foot 40 is separated from the fabric, and there is no presser foot pressure Ff exerted by the presser foot 40 on the fabric. Specifically, the closed-loop control method for the presser foot of a sewing machine disclosed in this application includes the following steps:

[0063] S1, the sewing machine is provided with the above-mentioned compression spring, presser foot lifting electromagnet 20, presser foot lifting mechanism 30 and presser foot 40, as Figure 1 and Figure 2 ,or Figure 4 As shown, an electronic control module and a presser foot height sensor 70 are set in the sewing machine, and the presser foot lifting electromagnet 20 and the presser foot height sensor 70 are both communicatively connected to the electronic control module; the presser foot height sensor 70 is used to detect the real-time height H of the presser foot 40, and feed back the real-time height H of the presser foot 40 to the electronic control module.

[0064] S2. The closed-loop control method for the presser foot of a sewing machine includes a pressure regulation control method for the presser foot 40, and the pressure regulation control method for the presser foot 40 includes the following steps:

[0065] S21. A critical current value is pre-stored in the electronic control module. When the presser foot lifting electromagnet 20 is energized by a current equal to the critical current value, the tension Fe exerted by the presser foot lifting electromagnet 20 on the presser foot 40 via the presser foot lifting mechanism 30 is exactly equal to the pressure Fs exerted by the pressure-adjusting spring 10 on the presser foot 40 via the presser foot rod 31. Therefore, when the current flowing through the presser foot lifting electromagnet 20 is less than the critical current value, the tension Fe exerted on the presser foot 40 is less than the pressure Fs, and the presser foot 40 is not lifted; the presser foot 40 remains pressed against the fabric. The pressure Ff exerted by the presser foot 40 on the fabric is: Ff = Fs - Fe. When the current flowing through the presser foot lifting electromagnet 20 is greater than the critical current value, the tension Fe exerted on the presser foot 40 is greater than the pressure Fs, and the presser foot 40 is lifted upward.

[0066] S22. During the sewing process of the sewing machine, the presser foot height sensor 70 detects the real-time height H of the presser foot 40 and feeds it back to the electronic control module. When the electronic control module determines that the fabric thickness has changed or the sewing has been over-sewn based on the feedback from the presser foot height sensor 70, the electronic control module performs the following control;

[0067] S23. The compression of the pressure-adjusting spring 10 changes, and the electronic control module obtains the change ΔF of the presser foot pressure Ff. Specifically, during the sewing process, the presser foot lifting electromagnet 20 is not energized, and the pressure generated by the pressure-adjusting spring 10 acts completely on the presser foot 40 through the presser foot rod 31, causing the presser foot 40 to press the fabric with a rated presser foot pressure Ff for sewing. When the fabric changes from thin material to thick material, or when sewing over-stem, the bottom of the presser foot 40 is lifted upward by the fabric, and the compression of the pressure-adjusting spring 10 increases, then the pressure Fs applied by the pressure-adjusting spring 10 on the presser foot 40 increases, causing the presser foot pressure Ff to increase by ΔF. When the fabric changes from thick material to thin material, the compression of the pressure-adjusting spring 10 decreases, then the pressure Fs applied by the pressure-adjusting spring 10 on the presser foot 40 decreases, causing the presser foot pressure Ff to decrease by ΔF.

[0068] S24, the electronic control module adjusts the current of the presser foot lifting electromagnet 20 according to the change ΔF of the presser foot pressure Ff:

[0069] When the fabric changes from thin material to thick material, or when the fabric is sewn over the stem, the electronic control module determines that the presser foot pressure Ff increases by ΔF. At this time, the electronic control module controls the current of the presser foot lifting electromagnet 20 to increase within the range of zero to the critical current value, and the presser foot lifting electromagnet 20 starts to be energized. The presser foot lifting electromagnet 20 also starts to apply a pulling force Fe to the presser foot 40, so that the pulling force Fe applied by the presser foot lifting electromagnet 20 to the presser foot 40 increases by ΔF, offsetting the change in the presser foot pressure Ff ΔF, and then making the presser foot pressure Ff maintain the size before the fabric thickness changes, and the presser foot pressure Ff remains constant.

[0070] When the fabric changes from thick to thin, the electronic control module determines that the presser foot pressure Ff decreases by ΔF. At this time, the electronic control module controls the current of the presser foot lifting electromagnet 20 to decrease within the range of zero to the critical current value, so that the tension Fe applied by the presser foot lifting electromagnet 20 to the presser foot 40 is reduced by ΔF, offsetting the change ΔF in the presser foot pressure Ff, and then making the presser foot pressure Ff maintain the size before the fabric thickness changes, and the presser foot pressure Ff remains constant.

[0071] Therefore, the present application controls the magnitude of the pulling force Fe applied by the presser foot lifting electromagnet 20 to the presser foot 40 by controlling the magnitude of the current flowing through the presser foot lifting electromagnet 20, so that the change in the pulling force Fe applied by the presser foot lifting electromagnet 20 to the presser foot 40 and the change in the presser foot pressure Ff caused by the change in the compression amount of the pressure-adjusting spring 10 are offset, thereby offsetting the change in the presser foot pressure Ff caused by the change in the thickness of the fabric, and ultimately maintaining a suitable and constant presser foot pressure Ff. In particular, the present application adopts the existing pressure-adjusting spring 10, presser foot lifting electromagnet 20, presser foot lifting mechanism 30 and presser foot 40 structure in the sewing machine. The present application utilizes the presser foot height sensor 70 on the basis of the original structure of the sewing machine. On the one hand, it avoids the complex structure and expensive cost brought about by adjustment through a stepper motor, that is, it greatly simplifies the structure and reduces the cost. On the other hand, since the response speed of the presser foot lifting electromagnet 20 is much faster than that of the stepper motor, it can quickly offset the change in presser foot pressure Ff caused by changes in fabric thickness, which is simple to implement and provides a new way to better control the presser foot pressure Ff, thereby improving the sewing quality and product competitiveness of the sewing machine.

[0072] Preferably, the presser foot lifting electromagnet 20 is fixed on the sewing machine housing. The presser foot height sensor 70 is preferably a linear Hall sensor. In a lockstitch sewing machine, the method for detecting the real-time height H of the presser foot 40 is as follows: Figure 1 As shown, a magnet is fixed in the pressure rod guide block 32, and a linear Hall sensor is fixed on the housing of the sewing machine and cooperates with the magnet. The linear Hall sensor detects the real-time height H of the presser foot 40 by sensing the high and low positions of the magnet. In the overlock sewing machine, the method for detecting the real-time height H of the presser foot 40 is as follows: Figure 4 As shown, a magnet is fixed in the presser foot rod 31, and a linear Hall sensor is fixed on the housing of the sewing machine and cooperates with the magnet. The linear Hall sensor detects the real-time height H of the presser foot 40 by sensing the high and low positions of the magnet. Figure 1 or Figure 4 As shown, the sewing machine further comprises a pressure-adjusting nut 50 threadedly connected to the sewing machine housing, the lower end of the pressure-adjusting nut 50 abuts against the upper end of the pressure-adjusting spring 10 for adjusting the desired presser foot pressure Ff.

[0073] Furthermore, in the above step S23, the electronic control module obtains the change ΔF of the presser foot pressure Ff in the following two ways.

[0074] Method 1: The electronic control module obtains the change ΔH of the real-time height H of the presser foot 40 based on the feedback of the presser foot height sensor 70. The electronic control module also pre-stores known parameters such as the elastic modulus of the pressure-adjusting spring 10. The electronic control module automatically calculates the change ΔF of the presser foot pressure Ff based on the change ΔH of the real-time height H of the presser foot 40.

[0075] Method 2: The sewing machine further includes a force sensor 60, which is used to detect the tension Fe applied by the presser foot lifting electromagnet 20 to the presser foot 40. The force sensor 60 is connected to the electronic control module for communication; thus, the electronic control module directly calculates the change ΔF of the presser foot pressure Ff based on the feedback of the force sensor 60. Preferably, in a lockstitch sewing machine, Figure 2 As shown, the force sensor 60 is fixed on the lower end surface of the presser foot lifting plate 36.

[0076] In addition, after the force sensor 60 is configured in the sewing machine, during the adjustment process of the above-mentioned presser foot pressure Ff, the electronic control module determines whether the real-time change in the tension Fe is equal to the target change ΔF based on the real-time tension Fe fed back by the force sensor 60, thereby assisting in offsetting the change in the presser foot pressure Ff caused by the change in the compression of the pressure-adjusting spring 10, and accurately maintaining the presser foot pressure Ff of the presser foot 40 on the fabric within a stable range, so that the sewing machine can maintain appropriate presser foot pressure Ff regardless of whether the fabric is being changed or sewn, thereby increasing the applicability of the machine and making the sewing seams more beautiful.

[0077] Furthermore, the closed-loop control method for the presser foot of a sewing machine further includes step S3. The closed-loop control method for the presser foot of a sewing machine includes a presser foot lifting control method, and the presser foot lifting control method includes the following steps:

[0078] S31 , inputting a target presser foot lifting height M into the electronic control module, where the target presser foot lifting height M is a numerical value, which is at least one.

[0079] S32. After receiving the presser foot lifting instruction, the electronic control module controls the presser foot lifting electromagnet 20 to pass a presser foot lifting current that matches the target presser foot lifting height M. The presser foot lifting electromagnet 20 drives the presser foot 40 to move upward through the presser foot lifting mechanism 30.

[0080] Therefore, by controlling the magnitude of the presser foot lifting current fed into the presser foot lifting electromagnet 20, the presser foot 40 can be lifted to different heights instead of only being able to move from zero to a certain height, thereby improving the adaptability of the machine.

[0081] Furthermore, the presser foot lifting control method further comprises the following steps:

[0082] S33: The presser foot height sensor 70 detects the real-time height H of the presser foot 40 and feeds it back to the electronic control module. The electronic control module compares the real-time height H of the presser foot 40 with the target presser foot lifting height M and performs the following control according to the comparison result.

[0083] S34, when the electronic control module determines that the real-time height H of the presser foot 40 is consistent with the target presser foot lifting height M, the electronic control module controls the presser foot lifting electromagnet 20 to maintain the current presser foot lifting current;

[0084] S35. When the electronic control module determines that the real-time height H of the presser foot 40 is higher than the target presser foot lifting height M, the electronic control module controls the presser foot lifting current supplied to the presser foot lifting electromagnet 20 to decrease until the real-time height H of the presser foot 40 matches the target presser foot lifting height M.

[0085] S36. When the electronic control module determines that the real-time height H of the presser foot 40 is lower than the target presser foot lifting height M, the electronic control module controls the presser foot lifting current passed into the presser foot lifting electromagnet 20 to increase until the real-time height H of the presser foot 40 matches the target presser foot lifting height M.

[0086] In this way, closed-loop control is performed through the feedback of the presser foot height sensor 70, and the electronic control module accurately controls the presser foot lifting current of the presser foot lifting electromagnet 20, so that the presser foot 40 is accurately lifted to the desired target presser foot lifting height M, which can improve the accuracy of the presser foot lifting control.

[0087] Furthermore, in the above step S31, there are three ways to input the target presser foot lifting height M.

[0088] Method 1: The sewing machine also includes an electronic knee-rest device, the output of which is in communication with the electronic control module. Thus, when sewing is completed or the fabric needs to change direction during sewing, the presser foot 40 needs to be raised to a certain height. The user inputs a target presser foot lift height M to the electronic control module via the electronic knee-rest device, providing an analog signal. The electronic control module then controls the current input to the presser foot lift electromagnet 20 based on the magnitude of the received analog signal, raising the presser foot 40 to the desired height.

[0089] Method 2: The sewing machine also includes a foot pedal, the output of which is in communication with the electronic control module. This allows the presser foot 40 to be raised to a certain height when sewing is finished or when the fabric needs to change direction during sewing. The user uses the foot pedal to input a target presser foot lift height M into the electronic control module, sending an analog signal. The electronic control module then controls the current input to the presser foot lift electromagnet 20 based on the magnitude of the received analog signal, raising the presser foot 40 to the desired height.

[0090] Method 3: The sewing machine further comprises a main control panel, which is in communication with the electronic control module; thus, the target presser foot lifting height M is input to the electronic control module via the main control panel.

[0091] In summary, the present invention effectively overcomes various shortcomings of the prior art and has high industrial utilization value.

[0092] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A closed-loop control method for the presser foot of a sewing machine, used for a sewing machine, wherein the sewing machine comprises a pressure-adjusting spring (10), a presser foot lifting electromagnet (20), a presser foot lifting mechanism (30) and a presser foot (40), wherein the presser foot lifting electromagnet (20) is connected to the presser foot (40) via the presser foot lifting mechanism (30), wherein the presser foot lifting mechanism (30) comprises a presser foot rod (31) movable up and down, wherein the lower end of the pressure-adjusting spring (10) acts on the presser foot rod (31), and the presser foot (40) is mounted on the presser foot rod (31), wherein the presser foot lifting electromagnet (20) applies a tensile force Fe to the presser foot (40) via the presser foot lifting mechanism (30), and wherein the pressure-adjusting spring (10) applies a pressure Fs to the presser foot (40) via the presser foot rod (31), and wherein: The sewing machine presser foot closed-loop control method comprises the following steps: S1, arranging an electric control module and a presser foot height sensor (70) in the sewing machine, and connecting the presser foot lifting electromagnet (20) and the presser foot height sensor (70) to the electric control module for communication; S2. The closed-loop control method for the presser foot of a sewing machine includes a presser foot pressure adjustment control method, and the presser foot pressure adjustment control method includes the following steps: S21, a critical current value is pre-stored in the electronic control module; when the presser foot lifting electromagnet (20) is supplied with a current of the critical current value, the tension Fe applied by the presser foot lifting electromagnet (20) to the presser foot (40) through the presser foot lifting mechanism (30) is equal to the pressure Fs applied by the pressure regulating spring (10) to the presser foot (40) through the presser foot rod (31); S22, during the sewing process of the sewing machine, the presser foot (40) is not lifted upward, and the presser foot pressure Ff exerted by the presser foot (40) on the fabric is: Ff=Fs-Fe; the presser foot height sensor (70) detects the real-time height H of the presser foot (40) and feeds it back to the electronic control module, and when the electronic control module determines that the fabric thickness changes or the sewing is over-sewn based on the feedback of the presser foot height sensor (70), the electronic control module performs the following control; S23, the compression amount of the pressure regulating spring (10) changes, and the electronic control module obtains the change amount ΔF of the presser foot pressure Ff; S24, the electronic control module adjusts the current of the presser foot lifting electromagnet (20) according to the change ΔF of the presser foot pressure Ff: When the electronic control module determines that the presser foot pressure Ff increases by ΔF, the electronic control module controls the current of the presser foot lifting electromagnet (20) to increase within the range of zero to a critical current value, so that the tension Fe applied by the presser foot lifting electromagnet (20) to the presser foot (40) increases by ΔF, thereby offsetting the change ΔF of the presser foot pressure Ff; When the electronic control module determines that the presser foot pressure Ff decreases by ΔF, the electronic control module controls the current of the presser foot lifting electromagnet (20) to decrease within the range of zero to a critical current value, so that the tension Fe applied by the presser foot lifting electromagnet (20) to the presser foot (40) decreases by ΔF, thereby offsetting the change ΔF of the presser foot pressure Ff; S3. The closed-loop control method for the presser foot of a sewing machine includes a presser foot lifting control method, and the presser foot lifting control method includes the following steps: S31, inputting a target presser foot lift height M into the electronic control module; S32, after the electronic control module receives the presser foot lifting instruction, the electronic control module controls the presser foot lifting electromagnet (20) to pass a presser foot lifting current that matches the target presser foot lifting height M, and the presser foot lifting current satisfies: the tension Fe applied by the presser foot lifting electromagnet (20) to the presser foot (40) through the presser foot lifting mechanism (30) is greater than the pressure Fs applied by the pressure regulating spring (10) to the presser foot (40) through the presser foot rod (31), and the presser foot lifting mechanism (30) drives the presser foot (40) to move upward after overcoming the pressure Fs of the pressure spring, thereby realizing automatic presser foot lifting; the presser foot (40) is separated from the fabric, and there is no presser foot pressure Ff exerted by the presser foot (40) on the fabric.

2. The closed-loop control method for the presser foot of a sewing machine according to claim 1, characterized in that: In step S23, the electronic control module obtains the change ΔH of the real-time height H of the presser foot (40) based on the feedback of the presser foot height sensor (70), and the electronic control module automatically calculates the change ΔF of the presser foot pressure Ff based on the change ΔH of the real-time height H of the presser foot (40).

3. The closed-loop control method for the presser foot of a sewing machine according to claim 1, wherein: The sewing machine further comprises a force sensor (60) for detecting a pulling force Fe applied by the presser foot lifting electromagnet (20) to the presser foot (40), and the force sensor (60) is connected to an electronic control module; in step S23, the electronic control module directly calculates a change ΔF of the presser foot pressure Ff based on feedback from the force sensor (60).

4. The closed-loop control method for the presser foot of a sewing machine according to claim 1, wherein: The presser foot lifting control method further comprises the following steps: S33, the presser foot height sensor (70) detects the real-time height H of the presser foot (40) and feeds it back to the electronic control module, the electronic control module compares the real-time height H of the presser foot (40) with the target presser foot lifting height M, and performs the following control according to the comparison result; S34, when the electronic control module determines that the real-time height H of the presser foot (40) is consistent with the target presser foot lifting height M, the electronic control module controls the presser foot lifting electromagnet (20) to maintain the current presser foot lifting current; S35, when the electronic control module determines that the real-time height H of the presser foot (40) is higher than the target presser foot lifting height M, the electronic control module controls the presser foot lifting current passed into the presser foot lifting electromagnet (20) to decrease until the real-time height H of the presser foot (40) matches the target presser foot lifting height M; S36. When the electronic control module determines that the real-time height H of the presser foot (40) is lower than the target presser foot lifting height M, the electronic control module controls the presser foot lifting current passed into the presser foot lifting electromagnet (20) to increase until the real-time height H of the presser foot (40) matches the target presser foot lifting height M.

5. The closed-loop control method for the presser foot of a sewing machine according to claim 1, wherein: The target presser foot lifting height M is a numerical value, and the numerical value is at least one.

6. The closed-loop control method for the presser foot of a sewing machine according to claim 1, wherein: The sewing machine further comprises an electronic knee rest device, the output end of which is in communication connection with the electronic control module; in step S31, the target presser foot lifting height M is input to the electronic control module via the electronic knee rest device.

7. The closed-loop control method for the presser foot of a sewing machine according to claim 4, wherein: The sewing machine further comprises a main control panel, which is in communication with the electric control module. In step S31 , the target presser foot lifting height M is input to the electric control module via the main control panel.

8. The closed-loop control method for the presser foot of a sewing machine according to claim 1, wherein: The presser foot lifting mechanism (30) further comprises a right lever (33) having a fixed rotation fulcrum, a presser foot lifting rod (34), a left lever (35) having a fixed rotation fulcrum, a presser foot lifting plate (36), and a presser foot guide block (32) fixed to the presser foot rod (31); the iron core of the presser foot lifting electromagnet (20) is hinged to the right lever (33); the two ends of the presser foot lifting rod (34) are hinged to the right lever (33) and the left lever (35) respectively; the left lever (35) is hinged to the presser foot lifting plate (36); a lifting hook is provided on the presser foot lifting plate (36); and a connecting protrusion engaged with the lifting hook is provided on the presser foot guide block (32).

9. The closed-loop control method for the presser foot of a sewing machine according to claim 1, wherein: The presser foot lifting mechanism (30) further comprises a presser foot lifting lever (37) having a fixed rotation fulcrum, a presser foot lifting rod (34), a presser foot lifting crank (38), and a presser foot lifting shaft (39) rotatably mounted in a sewing machine housing, the iron core of the presser foot lifting electromagnet (20) being hinged to the presser foot lifting lever (37), the two ends of the presser foot lifting rod (34) being respectively connected to the presser foot lifting lever (37) and the presser foot lifting crank (38), the presser foot lifting crank (38) being fixed to one end of the presser foot lifting shaft (39), and the other end of the presser foot lifting shaft (39) being transmission-connected to the presser foot rod (31).

10. The closed-loop control method for the presser foot of a sewing machine according to claim 1, wherein: The sewing machine further comprises a pressure-adjusting nut (50) threadedly connected to the sewing machine housing, wherein the lower end of the pressure-adjusting nut (50) abuts against the upper end of the pressure-adjusting spring (10).

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