US 2001/0019230 A1Published application

Motor having rotational-speed detector

OwnerShigeru Furukiinventor

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Abstract

A motor provided with a rotational-speed detector has a driving coil for driving the motor, a driving magnetized portion, a rotational-speed detecting magnetized portion, and a frequency generator (FG) pattern. When the number of magnetic poles of the driving magnetized portion is indicated by n, and the number of magnetic poles of the rotational-speed detecting magnetized portion is represented by m, m and n are selected to satisfy a condition expressed by m/a:n/a=an even number:an even number, where a indicates a given integer, and the number of detecting lines of the FG pattern is set to be m/a. Upon rotating the motor, magnetic flux produced from the driving magnetized portion passes through the detecting lines to generate power in the detecting lines. However, since a total number of detecting lines facing the N poles of the driving magnetized portion is equal to that facing the S poles, the current induced in the detecting lines due to the magnetic flux from the driving magnetized portion is canceled. As a consequence, the level of a rotational-speed detection output of the motor is stabilized, thereby achieving highly precise rotational-speed control.

Claims2

Dependent claims

A motor provided with rotational-speed detection means comprising:

a stator;
a rotor rotatably provided on said stator;
a driving coil provided adjacent to said stator;
a driving magnetized portion provided adjacent to said rotor and having N poles and S poles that are alternately magnetized in the circumferential direction at a regular pitch;
a rotational-speed detecting magnetized portion provided adjacent to said rotor and having N poles and S poles that are alternately magnetized in the circumferential direction at a regular pitch;
and
a detecting pattern provided adjacent to said stator in such a manner that it faces said rotational-speed detecting magnetized portion, said detecting pattern, which is formed in a zigzag shape, having radially extending detecting lines, in accordance with a pitch between each of the N poles and each of the S poles of said rotational-speed detecting magnetized portion,
wherein a number of said detecting lines of said detecting pattern and a number of poles of said driving magnetized portion are determined so that a total number of said detecting lines facing the N poles of said driving magnetized portion is constantly equal to a total number of said detecting lines facing the S poles of said driving magnetized portion.

5 more elements

Dependencies are inferred from the claim text.