JP2022176000A - brushless motor - Google Patents

Abstract

To provide a brushless motor capable of reducing a thickness with a simplified structure.SOLUTION: A brushless motor includes: a stator 20 in which a coil 24 is wound around a plurality of teeth 23; a rotor 30 that includes a rotor core 32, a back yoke 33, and a driving magnet 34, which are rotatably supported by a rotational shaft 31 supported by a first bearing 40 and a second bearing 41 having a diameter larger than that of the first bearing 40 in an inner side of the stator 20; an encoder 60 that includes an encoder magnet 61 provided at the rotor core 32 and an encoder IC62 containing a magnetic field detection element; and a cylindrical housing 50 that supports the first bearing 40 and the second bearing 41. The rotor core 32 includes a spigot part 324 which is fitted with the second bearing 41 on an outer peripheral side. One part of the cylindrical housing 50 enters the spigot part 324, and a height H of the cylindrical housing 50 is set so as to be smaller than a sum of a width Ba of the first bearing 40 and a width Bb of the second bearing 41.SELECTED DRAWING: Figure 6

Description

The present invention relates to a brushless motor incorporating a magnetic encoder.

2. Description of the Related Art Inner-rotor type brushless motors having a structure in which a rotor is arranged inside a stator are used in information equipment, industrial equipment, and the like. Since the inner rotor type brushless motor has a small inertial force, it has the advantage of being excellent in controllability. In particular, brushless motors with built-in magnetic encoders are used in fields where high stopping accuracy is required (for example, tape feeders).

In order to mount electronic components on a substrate, the tape feeder feeds the carrier tape holding the electronic components at a predetermined pitch, for example, by a sprocket driven by a brushless motor with a built-in absolute encoder capable of detecting absolute position. An encoder controls the sprocket to stop at the correct rotation stop position. Brushless motors with magnetic encoders are described, for example, in US Pat.

In Patent Document 1, a stator 60, a rotor 70 rotating inside the rotor 70, and an encoder 80 having a magnetic sensor 12 for detecting the rotation angle of the rotor 70 are provided. In addition, it is described that by fitting the magnet holder 10 to the inner peripheral surface of the upper bearing 8 that supports the rotor 70, the thickness can be reduced.

Patent Document 2 discloses an encoder-side rotating shaft 53 to which the rotation of a motor-side rotating shaft 31 provided in a motor 2 is transmitted, a magnet holder 60 fixed to the encoder-side rotating shaft 53, and a In order to reduce the size of the magnet holder 60 in the axial direction, the magnet holder 60 and the encoder-side rotating shaft 53 are fixed by press-fitting. is stated.

Further, Patent Document 3 discloses a rotor 5 having a shaft 4 fixed to its center, a small-diameter ball bearing 1 having the shaft 4 fixed to an inner ring 1a, and an outer ring 1b of the small-diameter ball bearing 1. It consists of a bearing case 3 fixed to the peripheral surface and a large-diameter ball bearing 2 having an inner ring 2a fixed to the outer peripheral surface of the bearing case 3 and an outer ring 2b fixed to the outer peripheral portion 5a of the rotor 5. describes that the motor can be made thinner by arranging a small-diameter ball bearing 1 and a large-diameter ball bearing 2 on a substantially single plane.

JP 2020-162399 A JP 2017-167014 A Japanese Patent No. 4732601

With the structures described in Patent Documents 1 and 2, it is possible to reduce the thickness of a brushless motor incorporating a magnetic encoder. However, there is a demand for further thinning of the motor with a simpler structure.

As described in Patent Document 3, it is possible to reduce the thickness of the motor by arranging two ball bearings in the radial direction. However, in the structure described in Patent Document 3, the length of the fitting portion between the rotor and the shaft crimped and fixed (so-called press-fit) to the center of the rotor is short, and the press-fit strength of the shaft is insufficient. There is a risk that the shaft press-fit position may change due to impact, vibration, long-term driving, etc. (problem that the shaft may come off the rotor), which may pose a problem in terms of reliability.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a brushless motor which has a simple and highly reliable structure and which can be made thinner.

The brushless motor of the present invention includes a stator having windings wound around a plurality of teeth housed in a space surrounded by a motor case and a base plate, and a first bearing supported on the inner diameter side of the stator. a rotor having a rotor core rotatably supported by a rotating shaft and a second bearing having a diameter larger than that of the first bearing; a back yoke fixed to the outer peripheral side of the rotor core; and a rotor having a driving magnet; An encoder having an encoder magnet and a magnetic field detecting element fixed to the inner peripheral surface of the motor case, and a step portion fixed to the base plate and supporting the first bearing and a step portion supporting the second bearing. The rotor core is formed between an outer flange portion that supports the back yoke, an inner flange portion into which the rotating shaft is press-fitted, the outer flange portion, and the inner flange portion. A second bearing has a spigot portion that fits on the outer peripheral side thereof, a portion of the cylindrical housing enters the spigot portion, and the height of the cylindrical housing is equal to the width of the first bearing. It is characterized by being smaller than the sum of the widths of the second bearings.

In the present invention, it is preferable that the rotating shaft and the rotor core are non-magnetic.

In the present invention, it is preferable that the drive magnet and the encoder magnet are made of rare earth magnets.

The present invention provides a stator having a plurality of coils, a rotor having an encoder magnet and a drive magnet, a rotor having a rotor core into which a rotating shaft is press-fitted, an encoder having the encoder magnet and a magnetic field detecting element, and supporting the rotating shaft. a first bearing for supporting the rotor core; a second bearing for supporting the rotor core; a cylindrical housing for supporting the first bearing and the second bearing; The first bearing is fitted on the inner peripheral surface of the cylindrical housing, and the second bearing is fitted on the outer peripheral surface of the cylindrical housing so as to partially overlap the first bearing when viewed in the radial direction. The rotor core may be configured such that a portion into which the rotating shaft is press-fit extends toward the first bearing.

According to the present invention, the rotor is supported by bearings having different diameters, and when viewed from the radial direction, the small diameter bearing and the larger diameter bearing are arranged so that they partially overlap in the axial direction. Also, a thinner brushless motor can be obtained with a simplified structure. Moreover, since the rotor has a portion into which the rotating shaft is press-fitted with a sufficient length, sufficient press-fitting strength can be obtained against high-temperature environments, shocks, and vibrations, and reliability can be ensured.

1 is a perspective view showing a brushless motor according to a first embodiment of the invention; FIG. 1 is a plan view of a brushless motor according to a first embodiment of the invention; FIG. 1 is a bottom view of a brushless motor according to a first embodiment of the invention; FIG. 1 is a side view of a brushless motor according to a first embodiment of the invention; FIG. FIG. 3 is a cross-sectional view taken along the line XX of FIG. 2; FIG. 6 is an enlarged cross-sectional view of the main part of FIG. 5; 5 is a cross-sectional view taken along line YY of FIG. 4; FIG.

The details of the invention are illustrated by the accompanying drawings.

The brushless motor 10 shown in FIGS. 1 to 7 is, for example, a three-phase motor with 16 poles and 12 slots. A rotatably supported rotor 30, a first bearing 40 and a larger diameter second bearing 41 for supporting the rotor 30, and a cylinder holding the first bearing 40 and the second bearing 41. , an encoder 60 having an encoder magnet 61 fixed to the rotor core 32 and an encoder IC 62 installed on a substrate 63 provided on the inner surface of the motor case 1 . A pinion gear 70 as an output member is fixed to one end of the rotor 30 . In the brushless motor of the present invention, the number of magnetic poles is set to 4n (n: an integer of 1 or more) and the number of slots is set to 3m (m: an integer of 1 or more) in order to obtain a high starting torque. A pole 12-slot type (n=4, m=4) motor is used.

Referring particularly to FIGS. 5 to 7, the configuration of each part of this brushless motor 10 is as follows. a

The stator 20 has a core 22 supported by a core holder 21 fixed to the base plate 2, and a coil 24 (air-core coil) wound around a plurality of teeth 23 via an insulator 25. The coil 24 is a U-phase coil. It is composed of a winding, a V-phase winding and a W-phase winding, and is connected to the circuit board 80 . The base plate 2 is formed with a pedestal portion 3 for fixing the brushless motor 10 to a mating member. The circuit board 80 is provided with wiring (FPC, etc.) for energizing the coils 24 from a drive circuit (not shown) and wiring patterns for supplying currents to the coils of the stator 20, as well as the encoder IC 62. A mounted substrate 63 is connected. The coil 24 generates a rotating magnetic field by being supplied with current from a drive circuit (not shown), thereby rotating the rotor 30 .

The rotor 30 has a rotor core 32 fixed to the rotating shaft 31 , and the rotor core 32 consists of a plate portion (bottom portion) 321 , an outer flange portion 322 and an inner flange portion 323 . The rotor 30 has a back yoke 33 fixed to a groove 325 on the outer peripheral side of the rotor core 32 (outer flange 322 ) and a drive magnet 34 fixed to the outer peripheral surface of the back yoke 33 . The outer peripheral surface of the drive magnet 34 is magnetized with, for example, 16 poles so that N poles and S poles are arranged at equal intervals in the circumferential direction (the polarities of the magnetic poles are omitted in FIG. 7). A first bearing 40 and a second bearing 41 for supporting the rotor 30 are supported in a cylindrical housing 50 fixed to the base plate 2 . The cylindrical housing 50 has a holding groove 51 that holds the first bearing 40 and a holding groove 52 that holds the second bearing 41 . The rotor core 32 is configured to fit with the outer peripheral side of the second bearing 41 .

The core 22 is formed of a ferromagnetic material (steel material), and for example, the core 22 can be configured by laminating a plurality of ring-shaped electromagnetic steel plates having teeth 23 in the motor shaft direction. Ball bearings, for example, are used as the first bearing 40 and the second bearing 41 .

The encoder 60 includes a disk-shaped encoder magnet 61 (axially magnetized) fixed to a housing portion 326 formed on the end surface of the plate portion 321 of the rotor core 32 and a substrate 63 provided on the inner peripheral surface of the motor case 1 . It has an encoder IC 62 mounted thereon. As the encoder IC 62, one incorporating a magnetic field detection element (for example, a Hall element for detecting a horizontal magnetic field), an AD converter, and an arithmetic circuit is used. By using an encoder magnet that is magnetized in the axial direction (or radial direction), the centers of the rotating shaft, the encoder magnet, and the Hall element are aligned, and the angular error due to axial misalignment can be reduced.

The rotating shaft 31 and the rotor core 32 are made of a non-magnetic material (for example, austenitic stainless steel such as SUS304) in order to allow the magnetic field of the encoder magnet 61 to effectively act on the encoder IC 62 (hall element inside). If the magnet 61 is magnetized in the axial direction, it may be a ferromagnetic material (for example, martensitic stainless steel such as SUS420J2). The back yoke 33 is made of a ferromagnetic material (for example, steel material such as carbon steel).

The drive magnet 34 and the encoder magnet 61 are made of, for example, rare earth magnets. The drive magnet 34 is preferably made of a rare earth sintered magnet (such as an R--Fe--B system sintered magnet (R: one or more rare earth elements)) in order to reduce size and increase thrust. More preferably, it has a maximum energy product of 435 kJ/m3 [45-55 MGOe] and a residual magnetic flux density of 1.3 T or more. The encoder magnet 61 is preferably made of an isotropic rare earth bonded magnet in which rare earth magnet powder is bonded with a polymer material such as resin or rubber in order to reduce the weight of the rotor. 12 MGOe] and a residual magnetic flux density of 1.3 T or more. As isotropic rare earth bonded magnets, isotropic rare earth magnet powder (for example, Nd--Fe--B system magnet powder or Sm--Fe--N system magnet powder) is bound with resin (thermoplastic resin or thermosetting resin). A permanent magnet can be used.

The brushless motor 10 can generate a rotating magnetic field when the coil 24 is supplied with current from a drive circuit (not shown), thereby rotating the rotor 30 . For example, the magnetic pole position of the rotor is detected by three magnetic field detection elements (e.g. Hall elements (not shown)), a sine wave voltage corresponding to the magnetic pole position is output, the sine wave voltages are compared in a comparison circuit, and the control circuit By outputting a PWM signal and then outputting drive voltages with a phase difference of 120° from an inverter circuit to excite a three-phase coil at an appropriate timing, sine wave driving is performed. In the case of a sensorless sensor without three magnetic field detection elements (for example, Hall elements (not shown)), the rotor magnetic field position is detected using the back electromotive force from the coil 24, and the sine wave voltage at the magnetic pole position is detected. , the comparison circuit compares the sine wave voltages, the control circuit outputs a PWM signal, and then the inverter circuit outputs drive voltages 120° out of phase to excite the three-phase coils at appropriate timing. and is sinusoidally driven. In this way, by selectively energizing the coils of each phase and changing the direction of the energizing current, when energizing between two phases (for example, U phase and V phase), depending on the strength of the generated magnetic flux, one An N pole is formed at the tip portion of the tooth 23 of one phase, and an S pole is formed at the tip portion of the tooth 23 of the other phase. Therefore, the two-phase coils present in the adjacent slots are sequentially excited, and the magnetic flux passes between the two adjacent phases. attracts and repels, and rotational torque is generated in the motor.

This brushless motor 10 is made thinner by devising the structure of the bearings, and the details will be described with reference to FIG. FIG. 6 is an enlarged cross-sectional view of the main part of FIG. 5, with the stator 20 omitted for easy understanding.

As shown in FIG. 6, the rotor core 32 is a bottomed cylindrical member comprising a plate portion (bottom portion) 321, an outer flange portion 322 (length L3) and an inner flange portion 323 (length L1). Further, the rotor core 32 supports the second bearing 41 over substantially the entire width of the inner peripheral surface (length L4) of the outer flange portion 322, and the stepped portion 52 formed on the outer peripheral side of the cylindrical housing 50 However, in order to support the second bearing 41 over its entire width, a portion of the cylindrical housing 50 is configured to enter the spigot portion 324 (length L2 on the inner flange portion side). The first bearing 40 is supported by a stepped portion 51 (length Ha) formed on the inner peripheral side of the cylindrical housing 50 . A portion of the cylindrical housing 50 is inserted into the spigot portion 324 of the rotor core 32 so that the rotor core 32 is fitted to the outer peripheral side of the second bearing 41 . One end side of the rotating shaft 31 is press-fitted into the central portion (inner flange portion 323 ) of the rotor core 32 , and the pinion 70 is fixed to the other end side of the rotating shaft 31 . The cylindrical housing 50 accommodates the first bearing 40

In particular, the height H of the cylindrical housing 50 is set to be smaller than the sum of the width Ba of the first bearing 40 and the width Bb of the second bearing 41 . As a result, the total width of the two bearings in the axial direction is smaller than the sum of the widths of the bearings (Ba+Bb) by ((Ba+Bb)-H), and the thickness of the motor can be reduced. Specifically, according to the present invention, it is possible to obtain a thin brushless motor whose thickness dimension is one-third or less of the outer diameter dimension.

Moreover, the inner flange portion 323 of the rotor core 32 into which the rotating shaft 31 is press-fitted can have a sufficient length (for example, a length greater than the outer diameter of the rotating shaft) to ensure a high press-fitting strength of the rotating shaft 31 . Therefore, the rotating shaft does not slip out even in a high-temperature environment, in an environment where vibration or impact is applied, and even in long-term use, and sufficient reliability can be ensured.

The brushless motor 10 can be assembled by preparing each member and performing the following steps, for example.

(a) Each member including the base plate 2, the stator 20, the rotor 30, the first bearing 40, the second bearing 41, the cylindrical housing 50, the pinion gear 70, the motor case 1, the substrate 63 and the circuit substrate 80 is prepared.

(b) In the stator 20, after attaching an insulator 25 (the insulator may be a resin molded product or an insulating coating instead of the insulator) to the core 22, the core holder 21 is fixed to the core 22, and then the teeth 23 are attached to the coil. It is assembled by winding 24.

(c) The rotor 30 has the rotating shaft 31 fixed (for example, press-fitted) to the rotor core 32 , the back yoke 33 fixed to the groove 325 on the outer peripheral side, the driving magnet 34 fixed to the outer peripheral surface thereof, and the encoder It is assembled by fixing the magnet 61 . As means for fixing the back yoke 33 and the drive magnet 34, for example, an adhesive can be used.

(d) After attaching the circuit board 80 to the base plate 2 , the cylindrical housing 50 is fixed to the base plate 2 .
(e) The stator 20 prepared in advance is fixed to the base plate 2, the first bearing 40 is fitted in the retaining groove 51 of the cylindrical housing 50, and the second bearing 41 is fitted in the retaining groove 52 of the cylindrical housing 50. mating.
(f) fitting the rotor 30 prepared in advance to the first bearing 40 and the second bearing 41; Thereby, the rotating shaft 31 is supported by the first bearing 40 and the rotor core 32 is supported by the second bearing 41 .
(g) The pinion gear 70 is fixed to the end of the rotary shaft 31 by, for example, press-fitting.
(h) The brushless motor 10 is assembled by attaching the substrate 63 to the inner surface of the motor case 1 and then fixing the motor case 1 to the base plate 2 .

As described above, according to the present invention, a brushless motor with a built-in encoder can be assembled with the minimum required number of man-hours. In addition, since the cylindrical housing having the bearings mounted on the inner and outer peripheral surfaces is inserted into the rotor core having the spigot portion, the rotor is supported by the two bearings, and the assembly accuracy can be improved.

In particular, the brushless motor of the present invention comprises a stator 20 having a core 22 in which a plurality of electromagnetic steel plates are laminated in the axial direction, an encoder magnet 61 comprising a rare earth bonded magnet magnetized in the axial direction, and a rare earth sintered magnet. A rotor 30 having a rotor core 32 made of austenitic stainless steel into which a rotating shaft 31 made of austenitic stainless steel (or martensitic stainless steel) is press-fitted, and a first rotor supporting the rotating shaft 31. The second bearing 41 that supports the bearing 40 and the rotor core 32 is a ball bearing, and the austenitic stainless steel (or It has a cylindrical housing 50 made of free-cutting steel such as brass), the first bearing 40 is fitted to the inner peripheral surface of the cylindrical housing 50, and the second bearing 41 is the first The rotor core 32 is fitted to the outer peripheral surface of the cylindrical housing 50 so as to overlap the bearing 40 of the rotor core 32, and the rotor core 32 has a length larger than the outer diameter of the rotating shaft 31 at the portion where the rotating shaft 31 is press-fitted. It is extremely preferable from the viewpoint of thinning the motor, motor performance, and reliability.

The present invention is not limited to the embodiments described above, and various modifications can be made without departing from the gist of the present invention. For example, in the present invention, the Hall element is not used (sensorless), but can be driven by feedback control using the output of the encoder IC. Alternatively, it can be driven by using a sensorless dedicated drive IC or the like, or intermittent or continuous step driving is possible by inputting a step signal. Furthermore, a driving method using a Hall element may be used.

10: brushless motor,
1: motor case, 2: base plate, 3: pedestal,
20: Stator, 21: Core holder, 22: Core, 23: Teeth, 24: Coil, 25: Insulator,
30: rotor, 31: rotating shaft, 32: rotor core, 321: plate portion, 322: outer flange portion, 323: inner flange portion, 324: spigot portion, 325: groove portion, 326: housing portion, 33: back yoke, 34 : drive magnet,
40: first bearing, 41: second bearing,
50: cylindrical housing, 51, 52: stepped portion,
60: encoder, 61: encoder magnet, 62: encoder IC, 63: substrate,
70: pinion gear,
80: circuit board,
H: height of cylindrical housing, Ha: length of stepped portion 51,
Ba: width of the first bearing, Bb: width of the second bearing,
L1: length of the inner flange portion 323, L2: length of the inner flange portion 323 on the spigot portion 324 side, L3: length of the outer flange portion 322, L4: length of the spigot portion 324 side of the outer flange portion 322,

Claims (4)

a stator that is housed in a space surrounded by the motor case and the base plate and has windings wound around a plurality of teeth;
A rotating shaft supported by a first bearing on the inner diameter side of the stator, a rotor core rotatably supported by a second bearing having a larger diameter than the first bearing, and a back fixed to the outer circumference side of the rotor core. a rotor having a yoke and drive magnets;
an encoder having an encoder magnet provided on the rotor core and a magnetic field detection element fixed to the inner peripheral surface of the motor case;
a cylindrical housing fixed to the base plate and having a stepped portion for supporting the first bearing and a stepped portion for supporting the second bearing;
The rotor core is formed between an outer flange portion that supports the back yoke, an inner flange portion into which the rotating shaft is press-fitted, the outer flange portion, and the inner flange portion. has a spigot that fits in the
A brushless bearing characterized in that a part of the cylindrical housing enters the spigot portion, and the height of the cylindrical housing is smaller than the sum of the width of the first bearing and the width of the second bearing. motor. 2. The brushless motor according to claim 1, wherein said rotating shaft and said rotor core are made of non-magnetic material. 3. The brushless motor according to claim 1, wherein said drive magnet and said encoder magnet are made of rare earth magnets. a stator having a plurality of coils;
a rotor having an encoder magnet and a drive magnet and having a rotor core into which a rotating shaft is press-fitted;
an encoder having the encoder magnet and the magnetic field detection element;
a first bearing that supports the rotating shaft and a second bearing that supports the rotor core;
a cylindrical housing that supports the first bearing and the second bearing;
The first bearing is fitted to the inner peripheral surface of the cylindrical housing, and the second bearing is fitted to the outer peripheral surface of the cylindrical housing so as to partially overlap the first bearing when viewed in the radial direction. A brushless motor according to claim 1, wherein said rotor core is configured such that a portion into which said rotating shaft is press-fitted extends toward said first bearing.

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