Stepper Motor

Abstract

The present invention provides a stepper motor that optimizes the relationship between the outer diameter of a rotor and the outer diameter of a bearing made of a magnetic material, and applies a magnetic attraction force to the bearing. The stepper motor comprises: a rotor (400) made of a permanent magnet; a stator having a plurality of pole teeth (223, 243) extending axially on the outer peripheral side of the rotor (400); a bearing (250) rotatably supporting one axial end of the rotor (400); and a bearing (260) rotatably supporting the other axial end of the rotor (400). The magnetic permeability of the bearing (260) is higher than that of the bearing (250), and the rotor (400) has a plurality of magnetic poles on the outer peripheral surface along the circumference of the rotor (400). The outer diameter D of the rotor (400) is R , the outer diameter D of the portion of the bearing (260) facing the rotor B , and the pitch P of the plurality of magnetic poles of the rotor (400) is set to the relationship of the following equation 1, (D R -P)≤D B ≤D R …(Formula 1).

Description

Technical Field

[0001] The present invention relates to a stepping motor, and more particularly to a PM (Permanent Magnet) type stepping motor including a rotor composed of permanent magnets and a stator having a plurality of pole teeth extending in the axial direction on the outer peripheral side of the rotor. Background Art

[0002] Conventionally, in the PM stepping motor as described above, a bearing is provided for rotatably supporting the rotor, and a gap is provided between the rotor and the bearing in the axial direction. For example, in a two-phase PM stepping motor, there is a phenomenon that due to the combination of the excitation of the two stators, the magnetic centers of the rotor and the stator are offset when the stepping motor is driven, and the rotor is displaced in the axial direction, and an abnormal sound is generated due to collision with the bearing.

[0003] In response to this phenomenon, there is known a stepping motor that is provided with a magnetic attraction generating member that attracts the rotor in the axial direction, attracting the rotor to one bearing side to reduce the impact sound caused by collision with the other bearing (for example, refer to Japanese Patent Publication No. 2014-3832).

[0004] The stepper motor described in the document is a two-phase PM stepper motor having a rotor magnet composed of a permanent magnet and a stator, wherein the stator has a plurality of pole teeth extending axially on the outer peripheral side of the rotor magnet, and a magnetic attraction generating component composed of a magnetic material, wherein a magnetic washer is fixed to a housing metal plate for fixing a bearing. In the stepper motor, the outer diameter D of the magnetic washer is M1 and the outer diameter D of the rotor magnet R is set to satisfy D M1 ≤D R (Technical Solution 3). Moreover, by attracting the rotor magnet to the magnetic washer side, the impact sound generated when the stepping motor is driven to rotate is reduced.

[0005] However, when a stepper motor is used in an electronic device such as a mobile phone such as a smartphone, the outer diameter of the stepper motor is less than 6 mm, and the outer diameter of the rotor of such a stepper motor is less than 3 mm, which is extremely small. In the case of such an extremely small diameter motor, it is difficult to ensure space for configuring a magnetic washer as described in the above document. Therefore, it is considered to use a magnetic body to form the bearing itself instead of the magnetic washer.

[0006] On the other hand, the above document states that a radially enlarged bearing made of a magnetic material can be used instead of a magnetic washer and a bearing as a magnetic attraction generating component (paragraph 0041). In this case, the outer diameter of the radially enlarged bearing made of a magnetic material is considered to be equal to the outer diameter D of the magnetic washer. M1 are the same, so they are set to satisfy D M1(Outer diameter of bearing)≤D R (outer diameter of the rotor magnet).

[0007] However, in the above literature, whether D M1 and D R It is not clear that satisfying the above relationship can always reduce the impact sound generated when the stepping motor is driven to rotate. In addition, the rotor magnet in the above document is magnetized not only on the side facing the excitation stator but also on the bottom facing the magnetic washer. Therefore, even if the bottom surface of the rotor magnet is not magnetized, it is not clear whether the above effect can be obtained. Summary of the invention

[0008] The present invention has been completed in view of the above situation, and its purpose is to provide a stepping motor, in which the relationship between the outer diameter of the rotor and the outer diameter of the bearing made of magnetic material is optimized when using a bearing made of magnetic material instead of a magnetic gasket and a bearing as a magnetic attraction generating component.

[0009] The stepping motor of the present invention comprises: a rotor composed of a permanent magnet; a stator having a plurality of pole teeth extending in the axial direction on the outer peripheral side of the rotor; a first bearing rotatably supporting one axial end of the rotor; and a second bearing rotatably supporting the other axial end of the rotor, wherein the magnetic permeability of the second bearing is higher than that of the first bearing, the rotor has a plurality of magnetic poles on the outer peripheral surface along the circumferential direction of the rotor, and the outer diameter D of the rotor is R , the outer diameter D of the portion of the second bearing facing the rotor B , and the pitch P of the above-mentioned multiple magnetic poles of the above-mentioned rotor is set to the relationship of the following formula 1.

[0010] (D R -P)≤D B ≤D R …(Formula 1)

[0011] In the present invention, since the magnetic permeability of the second bearing is set higher than that of the first bearing, the magnetic force (magnetic flux) of the rotor acts on the second bearing more than the first bearing, and a magnetic attraction force against the rotor is generated in the second bearing. Here, in the magnetic poles magnetized on the outer peripheral surface of the rotor, the magnetic force spreads from the outer peripheral surface to the depth direction to a range of about 1 / 2 of the pitch P of the magnetic poles. Therefore, in the present invention, D B / 2 is (D R / 2-P / 2) or more, the magnetic force of the magnetic poles of the rotor acts on the second bearing, and the rotor is attracted by the second bearing. This can reduce the impact sound generated when the stepping motor is driven to rotate.

[0012] In the present invention, when the rotor has magnetic poles only on its outer peripheral surface, the effect based on the above formula 1 can be obtained. However, when the rotor has magnetic poles on its end surface, a greater magnetic force acts on the second bearing, so the present invention does not exclude such a mode.

[0013] In the present invention, the second bearing preferably has a small diameter portion and a large diameter portion, the small diameter portion is fixed to the cover member, and the large diameter portion faces the end surface of the rotor. Thus, the second bearing can be miniaturized to reduce material costs, and can be mounted on the cover member using the stepped portion between the small diameter portion and the large diameter portion.

[0014] In the present invention, the resin washer is provided between the rotor and the second bearing, thereby preventing metal contact between the rotor and the second bearing and preventing the generation of abnormal noise.

[0015] According to the present invention, a stepping motor can be provided in which the relationship between the outer diameter of the rotor and the outer diameter of the bearing made of magnetic material is optimized when a bearing made of magnetic material is used instead of a magnetic washer and a bearing as a magnetic attraction force generating member. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a partially cutaway exploded perspective view of a stepping motor according to an embodiment of the present invention.

[0017] Figure 2 It is a side view of the stepping motor according to the embodiment of the present invention.

[0018] Figure 3 It is a side cross-sectional view of a stepping motor according to an embodiment of the present invention.

[0019] Figure 4 is from Figure 3 The figure showing the lower end surface of the rotor in the axial direction is used to explain the relationship between the magnetic poles on the outer peripheral surface of the rotor and the bearing made of a magnetic material.

[0020] Description of Reference Numerals

[0021] 100…stepping motor; 200…A-phase stator unit; 210…front plate; 220…external yoke; 223…pole teeth; 230…bobbin; 231…coil; 233…flange; 234…flange; 235…terminal block; 236…terminal pin; 240…inner yoke; 241…circular ring; 243…pole teeth; 250…bearing (first bearing); 251…large diameter portion; 252…small diameter portion 260…bearing (second bearing); 261…large diameter portion; 262…small diameter portion; 300…B-phase stator unit; 310…end plate; 320…outer yoke; 323…pole tooth; 330…bobbin; 331…coil; 340…inner yoke; 343…pole tooth; 400…rotor; 401…shaft; 402…resin washer; 403…resin washer; 500…stator; M…magnetic pole. DETAILED DESCRIPTION

[0022] 1. The overall structure of the stepper motor

[0023] Figure 1 A stepper motor 100 according to an embodiment is shown. The stepper motor 100 is a claw-pole two-phase PM (Permanent Magnet) stepper motor. The stepper motor 100 includes a stator 500. The stator 500 has a structure that connects an A-phase stator unit 200 and a B-phase stator unit 300 in the axial direction. Here, the A-phase stator unit 200 and the B-phase stator unit 300 have the same structure, and the stator 500 is formed by flipping one of them in the axial direction relative to the other so that their back surfaces contact and connect with each other.

[0024] The front plate 210 is fixed to the A-phase stator unit 200, and the end plate 310 is fixed to the B-phase stator unit 300. The stator 500 has a substantially cylindrical shape, and the rotor 400 is rotatably accommodated inside the stator 500.

[0025] The A-phase stator unit 200 has a structure in which an outer yoke 220, a bobbin 230, and an inner yoke 240 are connected in the axial direction. The outer yoke 220 is a part that functions as a yoke that forms a magnetic circuit, and is made of a magnetic material such as electromagnetic soft iron or a rolled steel plate. The outer yoke 220 is roughly cup-shaped, with an opening in the center, and has a plurality of roughly triangular pole teeth 223 extending axially from the edge of the opening and arranged at intervals in the circumferential direction.

[0026] The coil 231 is wound around the bobbin 230 (only in Figure 3). The bobbin 230 is made of resin and is formed by injection molding. Flanges 233 and 234 are formed at both ends of the bobbin 230 in the axial direction to prevent the coil 231 from unwinding. A terminal block 235 is formed on one flange portion 234. The terminal block 235 is a rectangular block protruding from the flange portion 234 in the axial direction and radial direction, and is integrally formed with the flange portion 234. In the terminal block 235, a plurality of (two in the present embodiment) metal terminal pins 236 are embedded by methods such as press-in and insert molding.

[0027] The bobbin 230 having the above structure is arranged to be sandwiched between the outer yoke 220 and the inner yoke 240 to constitute the A-phase stator unit 200. Similarly, the bobbin 330 of the B-phase stator unit 300 is arranged to be sandwiched between the outer yoke 320 and the inner yoke 340 to constitute the B-phase stator unit 300.

[0028] The inner yoke 240 is a part that functions as a yoke that forms a magnetic circuit, and is made of a magnetic material such as electromagnetic soft iron or rolled steel plate. The inner yoke 240 includes a plate-shaped annular portion 241, and a plurality of substantially triangular-shaped pole teeth 243 extending axially from the edge of the inner circumference of the annular portion 241 and arranged at intervals along the circumferential direction. The pole teeth 243 of the inner yoke 240 and the pole teeth 223 of the outer yoke 220 are combined in a manner that they mesh alternately in the circumferential direction.

[0029] The same component as the inner yoke 240 of the A-phase stator unit 200 is axially reversed to form the inner yoke 340 of the B-phase stator unit 300. The A-phase stator unit 200 and the B-phase stator unit 300 are connected by making the inner yoke 240 and the inner yoke 340 face and contact with each other with the same surface.

[0030] The surface of the outer yoke 220 on the opposite side to the side facing the bobbin 230 is connected to the front plate 210. The front plate 210 has a bearing (first bearing) 250 mounted thereon.

[0031] The B-phase stator unit 300 is of substantially the same structure as the A-phase stator unit 200, and is used in an axially flipped state. The B-phase stator unit 300 has a structure in which an outer yoke 320, a bobbin 330, and an inner yoke 340 are combined in the axial direction. Here, the outer yoke 320 is a component of the same structure as the outer yoke 220, and has pole teeth 323 in a substantially triangular shape. The inner yoke 340 is a component of the same structure as the inner yoke 240, and has pole teeth 343 in a substantially triangular shape. The bobbin 330 is a component of the same structure as the bobbin 230. The outer yoke 320 is connected to the end plate 310. A bearing (second bearing) 260 is mounted on the end plate 310.

[0032] 2. Details of the rotor and its supporting structure

[0033] The shaft 401 is fixed to the center of the rotor 400 in a state of being axially penetrated. Figure 3 The end portion protruding to the left is rotatably supported by the front plate 210 via a bearing 250 , and the end portion of the shaft 401 protruding to the right from the rotor 400 is rotatably supported by the end plate 310 via a bearing 260 .

[0034] The bearing 250 of the A-phase stator unit 200 is composed of, for example, a copper-based sintered oil-impregnated bearing, such as Figure 3 As shown, a two-stage structure including a large diameter portion 251 and a small diameter portion 252 is formed, and the small diameter portion 252 is fitted and fixed to the opening of the front plate 210 .

[0035] On the other hand, the bearing 260 of the B-phase stator unit 300 is formed of a magnetic body (for example, an iron-copper sintered oil-impregnated bearing or an iron sintered oil-impregnated bearing), and has a two-stage structure having a large diameter portion 261 and a small diameter portion 262, and the small diameter portion 262 is fitted and fixed to the opening of the end plate 310. In addition, the magnetic permeability of the bearing 260 is set to be higher than the magnetic permeability of the bearing 250.

[0036] A resin washer 402 is attached to the end surface of the rotor 400 facing the bearing 250. In addition, a resin washer 403 is attached to the end surface of the rotor 400 facing the bearing 260. The outer diameter D of the large diameter portion 261 of the bearing 260 is B and the outer diameter D of the rotor 400 R The relationship is set to D B ≤D R .

[0037] The rotor 400 is formed of a permanent magnet such as a ferrite magnet or a rare earth magnet having a substantially cylindrical structure, and has magnetic poles M magnetized in a state where the magnetic poles are alternately reversed to NSNS in the circumferential direction of the outer peripheral surface. Figure 4 The figure shows the state where the outer circumference of the rotor 400 is magnetized with eight poles, and the arrows in the figure indicate the magnetic flux. In the magnetic poles M magnetized on the outer circumference of the rotor 400, the magnetic force spreads from the outer circumference to a range of about 1 / 2 of the pitch P of the magnetic poles M in the depth direction, and this range is Figure 4 The area from the surface to the double-dotted line.

[0038] Here, in order to make the bearing 260 function as a magnetic attraction generating member, the magnetic force (magnetic flux) of the rotor 400 needs to act on the bearing 260. Therefore, the outer diameter D of the large diameter portion 261 of the bearing 260 facing the end surface of the rotor 400 needs to be BThe diameter is set to be greater than the diameter of the arc (arc indicated by the double-dashed line) at a depth of about 1 / 2 of the magnetic pole pitch P from the outer peripheral surface of the rotor 400, preferably closer to the outer peripheral surface. Specifically, (D R -P)≤D B ≤D R relationship.

[0039] The outer diameter D of the large diameter portion 261 of the bearing 260 B is set to (D R -P)≤D B ≤D R Therefore, the magnetic force (magnetic flux) leaking from the end face of the rotor 400 affects the large diameter portion 261 of the bearing 260, thereby acting as a magnetic attraction generating component. Therefore, the rotor 400 is attracted to the bearing 260 side, and the end face of the rotor 400 abuts against the resin washer 403.

[0040] When an excitation current is applied to the coils 231 and 331 wound on the bobbins 230 and 330, the magnetic flux excited by the stator 500 and the magnetic flux of the rotor 400 as a permanent magnet interact with each other, thereby rotating the rotor 400. Due to the combination of the excitation method of the stator 500, when only the A-phase stator unit 200 is excited (single-phase excitation), the magnetic centers of the rotor 400 and the stator 500 are offset, and a force is generated that causes the rotor 400 to move toward the bearing 250 side, but the axial movement of the rotor 400 is suppressed by the magnetic attraction force generated by the bearing 260 formed of a magnetic body. Therefore, the impact sound generated when the stepping motor 100 is driven to rotate can be reduced.

[0041] Furthermore, the magnetic attraction force acting between the bearing 260 formed of a magnetic body and the rotor 400 is set to be larger than the magnetic force acting in the axial direction of the rotor 400 (in the direction of the bearing 250), so that the axial movement of the rotor 400 can be prevented. Such a setting can be obtained by adjusting the thickness dimension (axial dimension) of the resin washer 403 disposed between the bearing 260 and the rotor 400, or adjusting the magnetic permeability of the bearing 260, for example.

[0042] In particular, in the above-mentioned embodiment, the bearing 260 includes a small diameter portion 262 and a large diameter portion 261, the small diameter portion 262 is fixed to the end plate 310, and the large diameter portion 261 faces the end surface of the rotor 400, so that the bearing 260 can be miniaturized and the material cost can be reduced, and can be installed on the end plate 310 using the stepped portions of the small diameter portion 262 and the large diameter portion 261.

[0043] In the above embodiment, since the resin washer 403 is provided between the rotor 400 and the bearing 260 , it is possible to prevent metal contact between the rotor 400 and the bearing 260 and prevent the generation of abnormal noise.

[0044] 3. Change Examples

[0045] The present invention is not limited to the claw-pole type two-phase stepping motor as in the above-described embodiment, but can also be applied to other multi-phase PM type stepping motors.

[0046] The present invention can be used in the technical field of stepper motors.

Claims

1. A stepper motor, wherein: have: The rotor, which is composed of permanent magnets; A stator having a plurality of pole teeth extending in the axial direction on the outer peripheral side of the rotor; a first bearing rotatably supporting one axial end portion of the rotor; as well as A second bearing rotatably supports the other axial end portion of the rotor, The magnetic permeability of the second bearing is higher than the magnetic permeability of the first bearing, The rotor has a plurality of magnetic poles on its outer peripheral surface along the circumferential direction of the rotor. The outer diameter D of the rotor R , the outer diameter D of the portion of the second bearing facing the rotor B , and the pitch P of the plurality of magnetic poles of the rotor is set to the relationship of the following formula 1, (D R -P)≤D B <D R …(Formula 1).

2. The stepper motor according to claim 1, wherein: The rotor has magnetic poles only on its outer peripheral surface.

3. The stepper motor according to claim 1, wherein: The second bearing includes a small diameter portion and a large diameter portion, the small diameter portion being fixed to the cover member, and the large diameter portion facing an end surface of the rotor.

4. The stepper motor according to claim 2, wherein: The second bearing includes a small diameter portion and a large diameter portion, the small diameter portion being fixed to the cover member, and the large diameter portion facing an end surface of the rotor.

5. The stepping motor according to any one of claims 1 to 4, wherein: A resin washer is provided between the rotor and the second bearing.

Images