TWM615575U - Rotary axis sensing device of sewing machine motor - Google Patents

Abstract

A rotation axis sensing device of a sewing machine motor includes a magnet turntable, a first IC board and a second IC board. The magnet turntable is magnetized with an inner ring magnetic zone, an outer ring magnetic zone and an upper positioning magnetic zone. Through the first IC board to sense the rotation of the magnet turntable, directly capture the rotation of the rotating shaft, sense the inner ring magnetic zone, output R, S, T pulse signals, and sense the outer ring magnetic zone, output A, B pulse signals, as a motor drive For control; and by sensing the rotation of the magnet turntable through the second IC board to capture the rotation of the rotating shaft, sense the upper positioning magnetic area, and output the upper positioning pulse signal to control the upper positioning needle stop position of the sewing machine.

Description

Rotary axis sensing device of sewing machine motor

This creation is related to a sensing device for the rotating shaft of a motor to accurately monitor the operating state of the rotating shaft of the motor, especially a rotating shaft sensing device for a sewing machine motor.

Current sewing machine encoders can be roughly divided into two types: contact type and non-contact type. Contact encoders have the problem of part wear. In order to avoid contact wear, related industries have developed non-contact encoders, such as optical encoders and magnetic encoders.

Please refer to my country's Certificate No. M302831 "Servo Motor Encoder" new patent case, the encoder in this case is an optical encoder. The servo motor encoder includes a shading sheet and a sensing device. The shading sheet is a circular sheet body to be combined with the rear end of the servo motor shaft center. The outer ring or the inner ring is recessed with several notches at equal intervals , Concentrically arranged multiple light holes in the inner or outer ring, the sensing device is provided with a base combined with the rear surface of the servo motor, the base is provided with a bottom plate with a perforation, and a circular arc extends vertically outward from the periphery of the bottom plate An insert body which is shaped and surrounds the light-shielding sheet, surrounds the insert body and combines three photo-interrupters for detecting the lack of grooves and a light encoder module for detecting each light-transmitting hole; accordingly, That is to say, the position and movement of the light-shielding film can be detected by the photo-interrupter and the light-encoding module, and the information can be encoded and output for detection and control of the action of the servo motor.

The aforementioned optical encoders are rotary optical encoders commonly used in sewing machines in the industry. However, the mechanism of sewing machine operation is to sew fabrics, so many thread breaks or lint will be generated during the sewing process. Broken threads or lint will adhere to the perforations of the bottom plate and the light-transmitting holes of the shading sheet, which will affect the detection accuracy of the photo-interrupter, and cause the timing error of the sewing machine to fail to operate normally.

In addition, in non-contact encoders, magnetic encoders also have the advantage of overcoming the wear problem of contact encoder components, which are used to convert the mechanical rotation angle of the shaft into digital or analog signals to realize angle, linear displacement, rotational speed and other signals. Compared with the rotary optical encoder, the output is not used in the harsh working environment such as oily or dusty (or the above-mentioned sewing machine broken thread or lint), which affects the accuracy of its sensing. Therefore, if it can be used The use of magnetic encoders on sewing machines will solve the problems encountered by the aforementioned optical encoders.

For the magnetic encoder, please refer to China's Certificate No. M473407 "Synchronization Device for Sewing Machine Direct Drive Motor and Magnetic Encoder". The output shaft of the motor is sleeved with a transmission gear, and a mounting seat is additionally arranged on the housing of the motor to install an additional shaft, and the shaft is sleeved with a driven gear, the transmission gear and the driven gear Jointly engage a transmission belt, and then place a magnetic element on the shaft. In the path through which the magnetic element passes, there is a corresponding sensor. When the motor is running, the shaft is driven by the output shaft, transmission gear, and transmission belt The transmission relationship between the moving gears rotates synchronously, and the magnetic element also rotates with the shaft. At this time, the sensor can measure the required data according to the change of the magnetic field of the rotating magnetic element. In other words, the conventional wisdom Most of the technology is to add a transmission mechanism to the output shaft to show the rotation state on another driven shaft, and then use the shaft to drive the magnetic element to rotate for monitoring, control, and code generation.

However, this kind of technical means of adding a transmission mechanism and additionally driving a shaft is prone to unnecessary loss of output and transmission loss, belt wear and dust, belt transmission slippage, belt wear and transmission gap, and unilateral force on the contact position of the belt is easy to cause. Rotation resonance... and many other problems, which will lead to the problem of detection distortion. Furthermore, it will take up too much motor configuration space, affect heat dissipation, etc., and the magnetic components cannot directly perform physical level adjustment operations. The positioning deviation correction adjustment is carried out through the method of electronic parameter setting. It is also difficult for those who are not familiar with the control function, and the setting error is easy to occur, which affects the product yield. In view of this, the rotation axis sensing device of the sewing machine motor is carried out. Optimization and improvement are the focus of improvement for this creation.

The main purpose of this creation is to provide a dual-sensing IC board to directly sense the rotation axis of the sewing machine motor, so as to make the operation of the sewing machine more accurate and improve production efficiency and yield.

To achieve the above-mentioned purpose, the technical means adopted in this creation include: a magnet turntable with a central circular hole sleeved in a ring groove fixed on the rotating shaft, so that the magnet turntable rotates synchronously with the rotating shaft, and the magnet turntable is charged The magnet has an inner ring magnetic area and an outer ring magnetic area; a first IC board is fixed on the back cover to sense the inner ring magnetic area and the outer ring magnetic area to output R, S, T respectively Pulse signal and output pulse signals of A and B; since the magnet turntable is directly fixed on the rotating shaft and rotates synchronously with the rotating shaft, the absolute position of the rotating shaft can be sensed, so that the generated signal is not distorted .

The sensing device further includes a second IC board fixed on the back cover, and the magnet turntable is provided with an upper positioning magnetic area between the inner ring magnetic area and the outer ring magnetic area for the second IC board. The two IC boards are correspondingly sensed, output positioning pulse signals, and cooperate with the pulse signals output by the first IC board to control the operation of the motor.

The sensing device is provided with a positioning mechanism on the back cover, the positioning mechanism is fixedly provided with a second IC board, and the magnet turntable is provided with an upper positioning magnetic zone between the inner ring magnetic zone and the outer ring magnetic zone , For corresponding sensing of the second IC board, outputting a positioning pulse signal, and cooperating with the pulse signal output by the first IC board to control the operation of the motor.

The back cover is provided with at least one first stud for fixing the first IC board, and the positioning mechanism is provided with a first opening corresponding to the first stud for the first stud to pass through; the positioning The peripheral edge of the mechanism has a plurality of lugs, and each lug penetrates an adjustment hole for locking. When the lug is released, the positioning mechanism can be rotated to adjust the relative position of the second IC board and the upper positioning magnetic zone, and The first opening rotates relative to the first stud; the positioning mechanism has a boss, and a groove is formed between the boss and each of the lugs for a turntable cover to be embedded in the groove.

The peripheral edge of the positioning mechanism has a plurality of lugs, and each of the lugs penetrates an adjustment hole for locking, and the positioning mechanism can be rotated when loosened to adjust the second IC board and the upper positioning magnetic zone The relative position of the positioning mechanism; the positioning mechanism has a boss, and a groove is formed between the boss and each of the lugs for a turntable cover to be embedded in the groove.

The sensing device further includes a turntable cover, which is sleeved inside the ring groove of the rotating shaft and fixed on the back cover to cover the outer side of the magnet turntable and the first IC board.

The sensing device further includes a turntable cover, which is arranged on the outer side of the magnet turntable and the first and second IC boards and fixed on the back cover.

The inner ring magnetic area of the magnet turntable is magnetized with at least 4 poles arranged in polarity for the first IC board to sense.

The outer ring magnetic area of the magnet turntable is magnetized with a number of poles that is twice as many as the first IC board according to the polarity arrangement; the number of poles of the outer ring magnetic area is 60 poles.

The upper positioning magnetic area of the magnet turntable is magnetized with 3 poles, arranged according to one of NSN polarity or SNS polarity, for sensing by the second IC board.

The magnet turntable is provided with a lower positioning magnetic area at a position 180 degrees opposite to the upper positioning magnetic area, so that the second IC board can correspondingly sense the lower positioning magnetic area to output a lower positioning pulse signal to control the sewing machine. The lower positioning needle stop position; the magnet turntable further includes a non-magnetic pole area, the height of the non-magnetic pole area is less than the height of the lower positioning magnetic area; the height of the non-magnetic pole area is reduced between 0.2~0.6mm; the non-magnetic pole area is reduced The height is 0.4mm.

The magnet turntable further includes a pole-free area, the height of the pole-free area is smaller than the height of the inner ring magnetic area, the outer ring magnetic area, and the upper positioning magnetic area; the height of the non-magnetic area is reduced by 0.2~0.6mm The lowered height of the non-magnetic pole area is 0.4mm.

The material of the magnet turntable is plastic material and iron oxide magnet.

The sensing device further includes a hand wheel fixed on the rotating shaft.

Please refer to Figures 1-3, which are schematic diagrams showing the preferred embodiment of this creation. The sensing device of this creation is correspondingly arranged at the position of the rotating shaft 11 of the motor 10, and includes a magnet turntable 20 and a first IC The board 30, a second IC board 40, a positioning mechanism 50 and a turntable cover 60.

As shown in Figure 3, the motor 10 is provided with a first stud 121 on the rear cover 12. The positioning mechanism 50 has a boss 51 with a smaller area than the main body on the side of the body, and a central hole 52 penetrates therethrough, corresponding to each first The position of the stud 121 is preset with a first opening 53 for the first stud 121 to pass through. On the premise that it is sufficient for the first IC board 30 to be locked, the number of the first studs 121 can also be increased or decreased.

The positioning mechanism 50 also has a plurality of lugs 54 extending outward from the periphery of the body, so that a groove 55 is formed between the lug 51 and the lug 54, as shown in Figure 5, and each lug 54 penetrates a long Arc-shaped adjustment hole 541. In this embodiment, the positioning mechanism 50 has three lugs 54 which can be increased or decreased according to requirements.

When assembling, the positioning mechanism 50 is inserted into the rotating shaft 11 with the central hole 52, and the first stud 121 is inserted through the first opening 53, and finally the adjusting hole 541 is passed through the screw 56 to fix the positioning mechanism 50 on the rear cover 12. .

The first IC board 30 is fixed on the first stud 121 passing through the first opening 53 with screws 31, and the second IC board 40 is locked on the second stud 57 of the positioning mechanism 50 with screws 41.

The positioning mechanism 50 in this embodiment has a pair of second studs 57 for locking the second IC board 40. When necessary, the position of the second studs 57 is also changed, or as shown in Figure 3 , There are second studs 57 at different angles in advance for optional use. On the premise that it is sufficient for the second IC board 40 to be locked, the number of the second studs 57 can also be increased or decreased.

The magnet turntable 20 has a disc-shaped body and a flange 21 is formed on the body to surround the central circular hole 211. The magnet turntable 20 in this embodiment is made of plastic materials with iron oxide magnets, but the material is not limited to these.

When assembling, the side of the magnet turntable 20 and the gap adjustment piece 22 are inserted into the rotating shaft 11 together, and then the C-shaped buckle 23 is correspondingly buckled in the ring groove 111 of the rotating shaft 11 to be fixed on the rotating shaft as shown in Figure 5. 11, and a flange 21 is provided on the other side for the turntable cover 60 to be inserted, so that the magnet turntable 20 is clamped between the ring groove 111 of the rotating shaft 11 and the turntable cover 60.

After the turntable cover 60 is inserted into the rotating shaft 11, the magnet turntable 20, the positioning mechanism 50, the second IC board 40 on the second stud 57, and the first IC on the first stud 121 passing through the positioning mechanism 50 The plates 30 are all covered in the accommodating space formed together with the positioning mechanism 50 as shown in Figure 5, and the turntable cover 60 can be inserted into the groove 55 between the boss 51 and the lug 54, and then screw 61 is locked on the back cover 12.

As shown in Figure 4, the magnet turntable 20 is magnetized with an inner ring magnetic area 201, an outer ring magnetic area 202 and an upper positioning magnetic area 203. The outer ring magnetic area 202 is located at the outer ring around the body of the magnet turntable 20. The inner ring magnetic area 201 is located at the outer ring around the central circular hole 211 of the magnet turntable 20, and the upper positioning magnetic area 203 is relatively located between the inner ring magnetic area 201 and the outer ring magnetic area 202.

The inner ring magnetic area 201 is equally divided as shown and magnetized with at least 4 poles arranged according to the NSNS polarity. In fact, it can be increased by a multiple of 2 poles (NS) according to requirements, such as 6 poles, 8 poles, 10 poles, 12 poles, etc. The number of poles; the outer ring magnetic zone 202 is equally divided as shown and magnetized according to the NSNS polarity. There are 30 pole pairs (60 poles), which can be increased by a multiple of 2 poles (NS) according to actual needs; the upper positioning magnetic zone 203 is such as As shown in the figure, there are 3 poles magnetized according to the NSN polarity arrangement. Actually, it depends on the sensing device. The polarity arrangement of SNS can be selected.

The first IC board 30 is fixed on the first stud 121 that passes through the positioning mechanism 50, and is located oppositely between the magnet turntable 20 and the positioning mechanism 50, and is used to correspondingly sense the inner ring magnetic area 201 and the outer magnetic area of the magnet turntable 20.环磁区202。 Ring magnetic area 202.

The first IC board 30 cooperates with the inner ring magnetic area 201 of the magnet turntable 20 to detect by the principle of magnetism to output pulse signals of R, S, T, and the outer ring magnetic area 202 cooperates with the magnet turntable 20 to detect by the principle of magnetism. Perform detection to output pulse signals of A and B.

The sensing device uses the first IC board 30 to output R, S, T pulse signals and output A, B pulse signals, and transmit the signals to the controller for processing (not shown in the figure) through electrical connections, as a motor drive control, for example Detect the rotation direction, speed, etc. of the rotating shaft 11 to obtain the best control effect.

The second IC board 40 is fixed on the second stud 57 with screws 41 and is located opposite to the magnet turntable 20 and the positioning mechanism 50 for correspondingly sensing the upper positioning magnetic area 203 of the magnet turntable 20.

The second IC board 40 cooperates with the upper positioning magnetic zone 203 of the magnet turntable 20 to detect by the principle of magnetism to output the upper positioning pulse signal, and then transmit the upper positioning pulse signal to the controller for processing through an electrical connection (not shown in the figure) , As the stop position of the upper positioning needle to control the sewing machine.

According to operational requirements, a set of 3-pole lower positioning magnetic regions 204 can be arranged at a position 180 degrees opposite to the upper positioning magnetic region 203, as shown in Figure 4A, similar to the upper positioning magnetic region 203, arranged in NSN polarity, It can also be arranged according to SNS polarity, corresponding to the positioning position under the motor. The second IC board 40 cooperates with the lower positioning magnetic zone 204 to detect by using the principle of magnetism to output the lower positioning pulse signal as the stop position of the lower positioning needle for controlling the sewing machine.

In order to avoid the phenomenon of magnetic interference during magnetization, the height of the inner ring magnetic area 201, outer ring magnetic area 202 and the upper positioning magnetic area 203 or the lower positioning magnetic area 204 outside the magnetic pole-free area 205 is set to be greater than The ring magnetic region 201, the outer ring magnetic region 202, and the upper positioning magnetic region 203 or the lower positioning magnetic region 204 are low. The height reduction range of the non-magnetic pole region 205 is between 0.2 and 0.6 mm, preferably 0.4 mm.

The second IC board 40 can also be adjusted according to actual operation requirements by loosening the screw 56 originally locked in the adjustment hole 541 as shown in Fig. 6, and then directly rotating and moving the positioning mechanism 50 as shown in Fig. 6A to adjust the second The position of the second IC board 40 on the stud 57 is used to adjust the relative position of the second IC board 40 and the upper positioning magnetic area 203, and to fine-tune the upper positioning point, which is convenient for unfamiliar operators to make adjustments. According to actual needs, the second stud 57 can also be directly arranged at an appropriate position on the back cover 12 to cooperate with the magnet turntable 20 for detection, and the adjustment function is omitted.

During adjustment, the diameter and shape of the first opening 53 through which the first stud 121 passes through the positioning mechanism 50 and the adjustment hole 541 can be matched with each other as shown in Figure 6A. When the positioning mechanism 50 rotates, the first opening 53 is used. The structure of allowing the first stud 121 to pass through is maintained, so that the positioning mechanism 50 can rotate relative to the first stud 121 through the first opening 53 without affecting the rotation of the positioning mechanism 50. Under the premise of not affecting the rotation of the positioning mechanism 50, the position where the first stud 121 is set, the structure of the first IC board 30 and the shape of the positioning mechanism 50 body can also be selectively changed accordingly.

The first IC board 30 in this embodiment can also be used alone with the magnet turntable 20. When the first IC board 30 is used alone, as shown in Figure 7, the first IC board 30 can be directly locked to the first stud 121 on the back cover 12, and the corresponding magnetic zone of the magnet turntable 20 can output pulse signals. In addition, another external positioning signal device is added to control the operation of the motor 10.

This creation can also choose to add a handwheel 70 as shown in Figure 5. The handwheel 70 is directly fixed on the rotating shaft 11 so that the handwheel 70 can directly drive the rotating shaft 11 and the magnet turntable 20 can also be synchronized. The rotation status of the handwheel 70 is sensed; a heat shield (not shown in the figure) can also be added to cover the motor 10 for heat insulation.

In this creation, because the magnet turntable 20 is directly set on the rotating shaft 11 and rotates synchronously with the rotating shaft 11, the generated induction signal is obtained from the absolute position, the signal will not be distorted, and because all the values are directly captured on the rotating shaft 11. Therefore, compared with general indirect acquisition methods, it can generate more accurate and undistorted signals, more absolute monitoring and control values, and thus obtain the best control effect for the operation of the sewing machine motor.

Because this creation uses magnetic induction to control the motor drive and positioning, it is not afraid of oil and gas or water pollution, and the cover of cotton dust, so that the operation of the sewing machine motor can obtain the best control effect.

The above-listed embodiments are examples to illustrate the best and possible implementation of this creation, and are not intended to limit the scope of the creation of the patent. For example, simple replacements or constituent elements and methods based on the technical means of creation Equal replacements shall fall within the scope of the patent application for this creation.

10: Motor 11: Rotation axis 111: Ring groove 12: back cover 121: The first stud 20: Magnet turntable 201: Inner ring magnetic area 202: Outer Ring Magnetic Zone 203: Upper positioning sector 204: Lower positioning sector 205: No magnetic pole area 21: flange 211: Center hole 22: Gap adjuster 23: C-shaped clasp 30: The first IC board 31: Screw 40: The second IC board 41: Screw 50: positioning mechanism 51: boss 52: Center hole 53: first opening 54: lug 541: adjustment hole 55: Groove 56: Screw 57: second stud 60: Turntable cover 61: Screw 70: Handwheel

Figure 1 is a combined three-dimensional schematic diagram of a preferred embodiment of the creation; Figure 2 is an exploded schematic diagram of a preferred embodiment of creation; Figure 3 is a detailed partial schematic diagram of the preferred embodiment of the creation; Figure 4 is a schematic diagram of the magnetic area of the magnet turntable in the preferred embodiment of creation; Figure 4A is another schematic diagram of the magnetic area of the magnet turntable in the preferred embodiment of creation; Figure 5 is a schematic cross-sectional view of a preferred embodiment of the creation; Figure 6 is a schematic diagram of the positioning mechanism before rotation in the preferred embodiment of the creation; Figure 6A is a schematic diagram of the positioning mechanism after rotation in the preferred embodiment of the creation; Figure 7 is a schematic diagram of using the first IC board in the preferred embodiment of this creation alone.

10: Motor

12: Motor back cover

60: Turntable cover

70: Handwheel

Claims (22)

A rotating shaft sensing device of a sewing machine motor is used to cooperate with a motor for installation. The motor has a rotating shaft on its back cover. The sensing device includes: a magnet turntable with a central circular hole sleeved and fixed on the rotating shaft. A ring groove on the shaft makes the magnet turntable rotate synchronously with the rotating shaft. The magnet turntable is magnetized with an inner ring magnetic zone and an outer ring magnetic zone; a first IC board is fixed on the back cover for sensing Measure the inner ring magnetic area and outer ring magnetic area to output R, S, T pulse signals and output A, B pulse signals respectively; since the magnet turntable is directly fixed on the rotating shaft, it is synchronized with the rotating shaft Rotation, the absolute position of the rotating shaft can be sensed, so that the generated signal is not distorted. For example, the rotation axis sensing device of a sewing machine motor of claim 1, wherein the sensing device further includes a second IC board fixed on the back cover, and the magnet turntable is located between the inner ring magnetic area and the outer ring magnet An upper positioning magnetic area is provided between the areas for corresponding sensing by the second IC board, outputting an upper positioning pulse signal, and cooperating with the pulse signal output by the first IC board to control the operation of the motor. For example, the rotation axis sensing device of a sewing machine motor of claim 1, wherein the sensing device is provided with a positioning mechanism on the back cover, the positioning mechanism is fixedly provided with a second IC board, and the magnet turntable is in the inner ring magnetic zone An upper positioning magnetic area is provided between the outer ring magnetic area for corresponding sensing by the second IC board, outputting an upper positioning pulse signal, and cooperating with the pulse signal output by the first IC board to control the operation of the motor. For example, the rotation axis sensing device of a sewing machine motor of claim 3, wherein the back cover is provided with at least one first stud for fixing the first IC board, and the positioning mechanism is provided with a first stud corresponding to the first stud. An opening for the first stud to pass through. For example, the rotation axis sensing device of a sewing machine motor of claim 4, wherein the positioning mechanism has a plurality of lugs on the periphery, and each of the lugs penetrates an adjustment hole for locking, and the positioning mechanism can be rotated when the lug is released , Adjust the relative position of the second IC board and the upper positioning magnetic area, and rotate relative to the first stud through the first opening. For example, the rotation axis sensing device of a sewing machine motor of claim 3, wherein the positioning mechanism has a plurality of lugs on the periphery, and each of the lugs penetrates an adjustment hole for locking, and the positioning mechanism can be rotated when the lug is released , To adjust the relative position of the second IC board and the upper positioning magnetic area. For example, the rotation axis sensing device of a sewing machine motor of claim 5 or 6, wherein the positioning mechanism has a boss, and a concave groove is formed between the boss and each of the lugs for a turntable cover to be embedded in the Groove. For example, the rotating shaft sensing device of a sewing machine motor of claim 1, wherein the sensing device further includes a turntable cover, the turntable cover is sleeved inside the ring groove of the rotating shaft and fixed on the back cover so as to cover it The magnet turntable and the outer side of the first IC board. For example, the rotation axis sensing device of a sewing machine motor of claim 2 or 3, wherein the sensing device further includes a turntable cover, the turntable cover is arranged on the outside of the magnet turntable and the first and second IC boards and is fixed on The back cover. For example, the rotation axis sensing device of a sewing machine motor of claim 1, wherein the inner ring magnetic area of the magnet turntable is magnetized with at least 4 poles arranged in polarity for the first IC board to sense. For example, the rotation axis sensing device of a sewing machine motor of claim 1, wherein the outer ring magnetic area of the magnet turntable is magnetized with a number of poles that are twice as many according to the polarity arrangement for the first IC board to sense. For example, the rotation axis sensing device of the sewing machine motor of claim 11, wherein the number of poles of the outer ring magnetic zone is 60 poles. For example, the rotation axis sensing device of a sewing machine motor of claim 2, wherein the upper positioning magnetic area of the magnet turntable is magnetized with 3 poles, arranged according to one of NSN polarity or SNS polarity, for the second IC board to sense . For example, the rotation axis sensing device of a sewing machine motor of claim 2, wherein the magnet turntable is provided with a lower positioning magnetic area at a position 180 degrees opposite to the upper positioning magnetic area for the second IC board to correspondingly sense the lower Position the magnetic area to output the lower positioning pulse signal to control the stop position of the lower positioning needle of the sewing machine. For example, the rotation axis sensing device of a sewing machine motor of claim 14, wherein the magnet turntable further includes a non-magnetic pole area, and the height of the non-magnetic pole area is smaller than the height of the lower positioning magnetic area. For example, the rotation axis sensing device of the sewing machine motor of claim 15, wherein the height of the non-magnetic pole area is reduced by 0.2 to 0.6 mm. For example, the rotation axis sensing device of the sewing machine motor of claim 16, wherein the reduced height of the non-magnetic pole area is 0.4 mm. For example, the rotation axis sensing device of a sewing machine motor of claim 2 or 3, wherein the magnet turntable further includes a pole-free area, the height of the pole-free area is smaller than the inner ring magnetic area, the outer ring magnetic area and the upper positioning The height of the magnetic zone. For example, the rotation axis sensing device of the sewing machine motor of claim 18, wherein the height of the non-magnetic pole area is reduced by 0.2 to 0.6 mm. For example, the rotation axis sensing device of a sewing machine motor of claim 19, wherein the reduced height of the magnetic pole-free area is 0.4 mm. For example, the rotation axis sensing device of sewing machine motor of claim 1 or 2 or 3, wherein the material of the magnet turntable is plastic material and iron oxide magnet. According to claim 1, the rotating shaft sensing device of a sewing machine motor, wherein the sensing device further includes a hand wheel fixed on the rotating shaft.

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