JP2000175417A - Brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a brushless motor with a rotor shaft made of a nonmagnetic body for achieving high torque and high-speed rotation, without inducing the reduction of the outside diameter dimension of the rotor shaft for causing the reduction in natural frequency. SOLUTION: A brushless motor is provided with a rotor where a plurality of permanent magnets are arranged in the peripheral direction, so that S and N poles are aligned alternately in a peripheral direction while being magnetized in a diameter direction and a stator where a coil for generating a rotary magnetic field for giving a rotary torque to the rotor, while being arranged so that the rotor surrounded is wound. In this case, a rotor shaft 11 is made of an electrical insulator, where a fitting part 11a of a permanent magnet 13 is formed at nearly the central position in the axial direction. A plurality of permanent magnets 13 are fitted to the fitting part 11a via a cylindrical auxiliary yoke 12. The auxiliary yoke 12 is made of a cylindrical body, that is formed by winding a plate-shaped magnetic body around the fitting part 11a of the rotor shaft 11 in the peripheral direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor using an electric insulator for a rotor shaft.

[0002]

2. Description of the Related Art As shown in FIG. 6, a brushless motor comprises a rotor 1 magnetized or excited in a radial direction, and a stator 2 for generating a rotating magnetic field for applying a rotating torque to the rotor 1. Is configured as The rotor 1 is
The permanent magnet 4 includes a rotor shaft 3 and a plurality of permanent magnets 4 mounted on an outer peripheral surface of the rotor shaft 3.
Are arranged such that S poles and N poles are alternately arranged in the circumferential direction, as shown in FIG. The stator 2 includes a yoke 5 surrounding the rotor 1 and a multi-phase coil 6 wound around the yoke 5, and the multi-phase coil 6 generally includes a three-phase coil.

The rotor 1 is connected to a case 9 via bearings 7 and 8.
It is supported rotatably. If the phase angle (torque angle) between the magnetic pole position (rotation angle) of the rotor 1 and the rotating magnetic field generated by the polyphase coil 6 exceeds 90 °, a step-out phenomenon occurs. For this reason, the magnetic pole position of the rotor 1 is constantly monitored by a magnetic pole position sensor (not shown). And the torque angle is 0-9
The voltage and frequency supplied to the multi-phase coil 6 are controlled so as to maintain the optimum angle in the range of 0 °.

When a brushless motor of this kind is used, for example, as a spindle motor of an electric discharge machine, the spindle causes an electric discharge between the rotating tool and the stationary work, so that the rotating tool and the rotor shaft are separated from each other. Must be insulated. If the rotor shaft is made of a good electrical conductor such as a ferrous metal, the entire spindle must be insulated from the mechanical structure. In this case, since the volume and surface area of the spindle itself are several times larger than the rotor shaft alone, the stray capacitance also increases accordingly,
Deteriorates discharge characteristics.

Therefore, when the rotor shaft is formed of an insulator such as ceramics, the volume and surface area of the metal portion (conductive portion) are limited to the rotary tool and its chuck mechanism. Since the capacity can be reduced accordingly, the discharge characteristics are improved.

[0006]

However, when the rotor shaft is formed of an electrical insulator, the torque is extremely reduced since the electrical insulator is also a non-magnetic material. That is, as shown in FIG.
Is a magnetic material, the magnetic resistance inside the rotor shaft 3 is small, so a strong magnetic loop is formed by lines of magnetic force generated from the permanent magnets 4, the magnetic flux density appearing outside the permanent magnets 4 is increased, and the torque is increased. can do.
However, when the rotor shaft 3 is a non-magnetic material, the magnetic resistance (permeance) in the rotor shaft increases, the magnetic flux density appearing outside the permanent magnet decreases, and the torque also decreases.

In the case of a non-magnetic rotor shaft, it is desirable to interpose an auxiliary yoke made of a high magnetic permeability material between the rotor shaft and the permanent magnet, instead of directly attaching a permanent magnet. . As a result, the magnetic field lines do not pass through the insulating material having high magnetic resistance but pass through the auxiliary yoke having high magnetic permeability. Further, mechanically, it is easy to tightly couple the rotor shaft, the auxiliary yoke, and the permanent magnet so that transmission of torque is not hindered at all.

On the other hand, the maximum number of revolutions of the rotor is determined by the bearing performance, and the diameter of the rotor shaft is increased to the allowable limit of the bearing. Further, the length of the rotor shaft is made as long as possible within a range permitted by the bending mode natural frequency. When a permanent magnet for generating rotational torque is attached to the rotor shaft determined in this way, it is necessary to increase the maximum torque to make the outermost diameter of the permanent magnet larger than the rotor shaft because of centrifugal fracture, Windage,
It is not preferable because of problems such as wind noise. That is, it is preferable that the outermost diameter of the permanent magnet be the same as that of the rotor shaft. Accordingly, the radius of the rotor shaft on which the permanent magnet is mounted must be reduced by the sum of the thickness of the magnet and the thickness of the auxiliary yoke. It is desirable that these thicknesses are as small as possible because the magnet mounting portion of the rotor shaft does not have to be so thin. This is because the thinner the rotor shaft, the lower the bending resonance frequency and the lower the maximum number of revolutions. On the other hand, since the magnet is liable to be demagnetized, a certain thickness (5 mm or more) is required. The auxiliary yoke only needs to guide the lines of magnetic force, so if a material having high magnetic permeability is used, it can be thinned to about 0.2 mm. In addition, it is desirable that the relative position of the magnet mounting portion with respect to the entire length of the rotor shaft be as close as possible to the bearing and near the center in order to bring the node of the bending mode resonance closer to the bearing.

According to the present invention, the outermost periphery of the permanent magnet is made equal to the diameter of the rotor shaft, the maximum torque is secured, and the bending mode resonance frequency is reduced with respect to the restrictions due to the bearing performance, the bending mode resonance frequency, and the position of the bending mode node. It is an object of the present invention to provide a brushless motor having a non-magnetic rotor shaft capable of realizing high-speed rotation by not performing the rotation.

[0010]

SUMMARY OF THE INVENTION A brushless motor according to the present invention has a plurality of permanent magnets arranged in the circumferential direction such that the magnets are magnetized in the radial direction and the S pole and the N pole are alternately arranged in the circumferential direction. A brushless motor comprising a rotor and a stator, the coil being wound around the rotor and generating a rotating magnetic field for applying a rotating torque to the rotor. A rotor shaft made of an electrical insulator formed with a portion,
An auxiliary yoke mounted on the mounting portion formed of a cylindrical body formed by winding a plate-shaped magnetic body around the mounting portion of the rotor shaft in the circumferential direction; and a mounting portion of the rotor shaft via the auxiliary yoke. And a plurality of permanent magnets mounted on the main body.

According to the present invention, the permanent magnet mounting portion is provided substantially at the center of the rotor shaft, and the permanent magnet is mounted on the mounting portion via the auxiliary yoke. And
The auxiliary yoke is formed in a tubular shape by winding a plate-shaped magnetic body around a mounting portion of the rotor shaft so that the thickness in the radial direction is reduced. As a result, the natural bending mode resonance frequency of the rotor shaft does not need to be significantly reduced from the (original) resonance frequency before the magnet mounting portion is provided. Further, since the auxiliary yoke forms a magnetic circuit with low magnetic resistance between the magnetic poles of the plurality of permanent magnets, the magnetic flux density appearing outside can be increased, thereby realizing a high torque. When the mounting portion of the permanent magnet is disposed substantially at the center of the rotor shaft in the axial direction, the position of the node in the bending resonance mode and the position of the bearing are close to each other, and the stability is improved.

If the auxiliary yoke is divided into a plurality of parts along the axial direction of the rotor shaft so that each auxiliary yoke has a congruent shape, the auxiliary yoke is divided into recesses forming a mounting portion of the rotor shaft. Since the yoke can be mounted from the side, the auxiliary yoke can be easily mounted on the rotor shaft.

In this case, if the auxiliary yoke is divided so that the mounting surface of the permanent magnet on the auxiliary yoke is divided into two along the axial direction of the rotor shaft at the center thereof, the magnetic poles of the permanent magnet are separated therefrom. Since the lines of magnetic force reaching the magnetic poles of the permanent magnets adjacent on both sides do not cross the divided portion, it is possible to suppress a decrease in magnetic resistance while the auxiliary yoke has the divided structure.

The mounting section of the rotor shaft and the auxiliary yoke may have a regular n-gonal cross section (n is an even number of 4 or more) or a circular cross section orthogonal to the axial direction.

[0015]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a diagram showing a main part of a brushless motor for a spindle of an electric discharge machine according to an embodiment of the present invention. FIG. 1A is a sectional view, and FIG. This motor is
N wound on the stator 100 (N is a natural number of 3 or more)
The rotor 11 has m (m is an even number of 2 or more) magnetic poles formed in the rotation direction so as to rotate in synchronization with the rotating magnetic field generated by the phase coil 101. FIG. 2 is an exploded perspective view showing only a rotor portion of the motor. FIG. 2 (a) shows a rotor shaft 11, FIG. 2 (b) shows an auxiliary yoke 12, and FIG. 2 (c) shows a permanent magnet 13. Is shown.

As shown in FIG. 1A, the rotor shaft 11 is entirely formed of a non-magnetic material such as ceramics.
The mounting portion 11a of the permanent magnet 13 is formed substantially at the center, and a tapered portion 11b for tool chuck is formed at one end. The mounting portion 11a forms a regular hexagonal column that is thinner than the end portions 11c and 11d on both sides in the axial direction and has a regular hexagonal cross section perpendicular to the axial direction. A permanent magnet 13 is mounted on the mounting portion 11 a of the regular hexagonal column via an auxiliary yoke 12. For example, for example, end 1
The diameter of 1d is 22 mmφ, the height of a regular hexagonal prism forming the mounting portion 11a is 15 mm, and the distance between side surfaces is 14 mm.

The auxiliary yoke 12 is a regular hexagonal cylinder as shown in FIG. 1B, and is divided into six parts so that each side is bisected along the axial direction. It is constituted by six congruent divided bodies 12a.
Each of the divided bodies 12a is made of a magnetic material (low magnetic resistance material) such as a carbon steel such as S25C (JIS standard), a crystalline alloy such as Sendust, Permalloy, and silicon steel, and an Fe-based or Co-based amorphous alloy. For example, it is formed by pressing a plate-like magnetic material having a thickness of about 1 mm.

The six divided bodies 12a are attached to the mounting portion 11a such that the gap between them is as small as possible.
When the auxiliary yoke 12 is attached to the mounting portion 11a, six permanent magnets 13 are attached to each side surface of the auxiliary yoke 12 from the outside. In consideration of the rotational balance, all the permanent magnets 13 have a congruent shape. These six permanent magnets 13
Is attached to the auxiliary yoke 12 so that S poles and N poles are alternately arranged in the circumferential direction, as shown in FIG.

As described above, the permanent magnet 13 is
When mounted on the mounting portion 11a through the, the magnetic field lines generated from the permanent magnet 13 pass through the inside of the auxiliary yoke 12 having a small magnetic resistance, so that the magnetic flux density on the outer peripheral portion of the permanent magnet 13 increases, and the torque increases. I do. Although a gap is generated between the divided bodies 12a constituting the magnetic circuit, the lines of magnetic force generated from the magnetic poles of the respective permanent magnets 13 reach the poles of the adjacent permanent magnets 13. Do not pass. For this reason, even if the auxiliary yoke 12 is divided, the magnetic resistance of the magnetic circuit is almost the same as the state without division.

FIG. 4 is an exploded perspective view showing only a rotor portion of a brushless motor according to another embodiment of the present invention. FIG. 4 (a) shows a rotor shaft 21, FIG. 4 (b) shows an auxiliary yoke 22, FIG. 3C shows the permanent magnets 23, respectively. As shown in FIG. 2A, the rotor shaft 21 has both a tapered portion 21b and end portions 21c and 21d except that the mounting portion 21a is formed in a columnar shape.
Part 11b and end part 11 of rotor shaft 11
Same as c and 11d. The auxiliary yoke 22 has a cylindrical shape as a whole, is divided into two in the axial direction, and is configured by two congruent half-pipe-shaped divided bodies 22a. Then, six arc-shaped permanent magnets 23 are mounted on the mounting portion 21a via the auxiliary yoke 22. Also in this case, as shown in FIG.
The permanent magnet 23 is attached to the auxiliary yoke 22 so that the position where the adhesive surface of the auxiliary yoke is divided into two along the axial direction coincides with each other. An increase in resistance can be suppressed.

When this embodiment is compared with the previous embodiment, when the thickness of the center of the permanent magnets 13 and 23 is made the same and the outer diameters of the portions where the permanent magnets 13 and 23 are mounted are equal, this embodiment is used. Since the outer diameter of the mounting portion 21a in the example is equal to the distance between the side surfaces of the mounting portion 11a of the previous embodiment, the cross-sectional area of the mounting portion 21a is smaller than the cross-sectional area of the mounting portion 11a. The bending rigidity at 21a becomes weak. However, in this embodiment, the two half-pipe-shaped divided bodies 22a may be mounted on the side surface of the mounting portion 21a, so that the assembly is facilitated.

The present invention is not limited to the embodiment described above. In the above embodiment, the cross section of the mounting portion 11a and the auxiliary yoke is a regular hexagon, but may be a regular n-gon other than a regular hexagon (n is an even number of 4 or more). However, a regular square (four poles) to a regular hexagon (six poles) are desirable for increasing bending rigidity.

[0023]

As described above, according to the present invention, the mounting portion for the permanent magnet is provided substantially at the center of the rotor shaft, and the mounting portion is provided with the thin cylindrical auxiliary yoke in the radial direction. Since the permanent magnet is mounted on the rotor shaft, the thickness of the rotor shaft does not need to be extremely thin, and the natural bending mode resonance frequency of the rotor shaft can be slightly reduced. Further, a magnetic circuit having low magnetic resistance is formed between the magnetic poles of the plurality of permanent magnets by the auxiliary yoke, so that the magnetic flux density appearing outside can be increased, thereby providing an effect that a high torque is realized.

[Brief description of the drawings]

FIG. 1 is a sectional view and an exploded perspective view showing a main part of a brushless motor according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view of a rotor in the motor.

FIG. 3 is a sectional view of the rotor.

FIG. 4 is an exploded perspective view of a rotor of a brushless motor according to another embodiment of the present invention.

FIG. 5 is a sectional view of the rotor.

FIG. 6 is a schematic longitudinal sectional view of a conventional brushless motor.

FIG. 7 is a sectional view of a rotor portion of the motor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... rotor, 2 ... stator, 3, 11, 21 ... rotor shaft, 4, 13, 23 ... permanent magnet, 12, 22 ... auxiliary yoke.

Claims (6)

[Claims] 1. A rotor in which a plurality of permanent magnets are arranged in a circumferential direction such that S poles and N poles are alternately arranged in a circumferential direction by being magnetized in a radial direction, and are arranged so as to surround the rotor. A brushless motor comprising: a stator on which a coil for generating a rotating magnetic field for applying a rotating torque to the rotor is wound, wherein the rotor is formed of an electrical insulator formed with a mounting portion for the permanent magnet. A rotor shaft, an auxiliary yoke that is formed of a cylindrical body formed by winding a plate-shaped magnetic body around a mounting portion of the rotor shaft in a circumferential direction, and an auxiliary yoke mounted on the mounting portion; A brushless motor comprising: a plurality of permanent magnets mounted on a mounting portion of a shaft. 2. The brushless motor according to claim 1, wherein the mounting portion of the rotor shaft is formed substantially at the center of the rotor shaft in the axial direction. 3. The mounting portion of the rotor shaft is formed to have a smaller diameter than both ends in the axial direction, and the auxiliary yoke is divided into a plurality along the axial direction of the rotor shaft so as to have a congruent shape. The brushless motor according to claim 1, wherein the brushless motor is provided. 4. The auxiliary yoke is divided so that a mounting surface of the permanent magnet on the auxiliary yoke is bisected at the center thereof along the axial direction of the rotor shaft. The brushless motor according to any one of claims 1 to 3. 5. A cross section orthogonal to the axial direction of the mounting portion of the rotor shaft and the auxiliary yoke has a regular n-gon shape (n is 4
The brushless motor according to any one of claims 1 to 4, wherein: 6. The brushless motor according to claim 1, wherein the mounting portion of the rotor shaft and the auxiliary yoke have a circular cross section orthogonal to the axial direction.