# US 2018/0020923 A1 · Electric motor capable of reducing cogging torque

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- Number: US 2018/0020923 A1
- Document ID: US20180020923A1
- Status: Published application
- Kind: A1
- Application number: 15/699,005
- Filed: 2017-09-08
- Published: 2018-01-25
- Earliest claimed: 2014-10-08
- Assignees: Fanuc Corporation
- Applicants: Fanuc Corporation
- Inventors: Takuya Maeda
- Web page: https://patentgrep.com/patent/US20180020923A1

## CPC

- A61B 5/0066: {Optical coherence imaging}
- A61B 3/0025: {characterised by electronic signal processing, e.g. eye models}
- A61B 3/102: {for optical coherence tomography [OCT]}
- G01B 9/02044: {Imaging in the frequency domain, e.g. by using a spectrometer}
- G01B 9/02084: {Processing in the Fourier or frequency domain when not imaged in the frequency domain}
- G01B 9/02091: Tomographic interferometers, e.g. based on optical coherence
- H02K 1/16: Stator cores with slots for windings
- H02K 1/24: Rotor cores with salient poles {; Variable reluctance rotors}
- H02K 1/2773: {consisting of tangentially magnetized radial magnets}
- A61B 2562/0233: Special features of optical sensors or probes classified in A61B5/00
- A61B 2576/00: Medical imaging apparatus involving image processing or analysis (A61B1/00009, A61B6/52 and A61B8/52 take precedence)
- H02K 1/2706: Inner rotors
- H02K 29/03: with a magnetic circuit specially adapted for avoiding torque ripples or self-starting problems
- H02K 2213/03: Machines characterised by numerical values, ranges, mathematical expressions or similar information
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- H02K: DYNAMO-ELECTRIC MACHINES (dynamo-electric relays H01H53/00; conversion of DC or AC input power into surge output power {H03K3/53})

## Abstract

An electric motor including a rotor including magnetic pole units and a stator including slots facing an outer peripheral surface of the rotor. Each of the magnetic pole units is bulged to an outside in a radial direction so that a waveform of a magnetic flux density generated from the rotor is a sine wave shape, and a concave part or convex part which is small enough to prevent changing of a waveform cycle of cogging torque determined by a least common multiple of the number of slots and the number of magnetic poles of the rotor, is formed at a central part in a circumferential direction of an outer peripheral surface in each of the magnetic pole units.

## Claims

### Claim 1

A method of reducing cogging torque in a synchronous electric motor comprising:
providing a rotor including a plurality of magnetic pole units, each magnetic pole unit having the same shape wherein each magnetic pole unit has an outer peripheral surface and each of the magnetic pole units has a magnetic pole center P1; and
providing a stator including slots facing the outer peripheral surface of the rotor, wherein,
correcting the outer peripheral surface of each of the magnetic poles by adding a correction amount based on a sine function to a reference surface to create a corrected outer peripheral surface, wherein the corrected outer peripheral surface of each of the magnetic pole units is bulged to an outside in a radial direction so that a waveform of a magnetic flux density generated from the rotor is a sine wave shape, and
a concave part or convex part is formed at a central part in a circumferential direction of an outer peripheral surface in each of the magnetic pole units, the concave part or convex part being small enough to prevent changing of a waveform cycle of cogging torque determined by a least common multiple of the number of slots and the number of magnetic poles of the rotor, wherein the corrected outer peripheral surface differs from the reference surface everywhere except at the magnetic pole center P1.

### Claim 2 (depends on 1)

The method according to claim 1, wherein a depth of the concave part or a height of the convex part is equal to or less than 0.1 mm.

### Claim 3 (depends on 1)

The method according to claim 1, wherein the outer peripheral surface of each of the magnetic pole units is set by adding a correction amount in the radial direction to a reference surface bulged to the outside in the radial direction so that the waveform of the magnetic flux density generated from the rotor is the sine wave shape.

### Claim 4 (depends on 3)

The method according to claim 3, wherein the correction amount is set so that the concave part or the convex part is formed with a smooth curve.

### Claim 5 (depends on 3)

The method according to claim 3, wherein the correction amount is set based on a function using, as a parameter, a phase in which a center in the circumferential direction of each of the magnetic pole units is 0°.

### Claim 6 (depends on 5)

The method according to claim 5, wherein the function is any one of a sine function, a cosine function, and a hyperbolic cosine function.

### Claim 7 (depends on 1)

The method according to claim 1, wherein the least common multiple of the number of magnetic poles of the rotor and the number of slots is equal to or less than 100.