Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-09-07
2001-12-04
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06700R
Reexamination Certificate
active
06326711
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a self-vibrating dc-operated brushless vibrator motor used for a pocketable wireless alerting or communication device such as a pager or a portable phone. The motor has a rotor having eccentric mass distribution that causes vibration.
2. Description of the Prior Art
A typical prior known dc vibrator motor has an eccentric weight made of a tungsten alloy fixedly mounted on an output shaft of the motor. The motor vibrates as the shaft rotates because of the unbalanced distribution of the mass of the rotor about the rotational axis.
However, a danger of mechanical interference pertains to this type of vibrator motor because of the existence of the externally rotating eccentric weight. In addition, the alerting device requires an extra space in which the eccentric weight rotates, and the high density material for the weight, such as tungsten alloy, is costly.
As disclosed in U.S. Pat. No. 5,036,239 (issued Jul. 30, 1991, one of the present applicants invented a flat coreless dc vibrator motor having neither output shaft nor external weight. This vibrator motor has a rotor which incorporates generally sector shaped non-overlapping flat armature coils arranged angularly partially about the shaft of the rotor, so that the center of mass of the rotor is off the rotational axis of the rotor.
As disclosed in U.S. Pat. No. 5,107,155 (issued Apr. 21, 1992), the same applicant of the present invention invented a dc vibrator motor without an output shaft. This vibrator motor has a fixed shaft on which a cylindrical magnet is fixedly mounted, and an eccentrically-weighted rotor having a cylindrical coreless winding, enclosing the fixed magnet, is mounted on the fixed shaft. The rotor has either eccentric bearings or a combination of eccentric bearings and eccentric weights, so that the center of mass of the rotor is off its rotational axis. Although the motor has been favorably accepted in the market, the rotor of this motor requires a substantial number of production process steps.
As disclosed in U.S. Pat. No. 5,341,057 (issued Aug. 23, 1994), the present applicants and another inventor jointly invented an additional dc vibrator motor without an output shaft. This vibrator motor has an eccentric armature rotor having three-pole armature iron cores and coils that are all situated within an angular range of 180° about its rotational axis.
A sector-shaped eccentric armature rotor having all of the armature poles within an angular range of 180° provides a good mass imbalance. However, the iron armature cores of the motor disclosed in U.S. Pat. No. 5,341,057 cause a cogging torque, a magnetic sticking effect, and, therefore, requires comparatively high voltage for starting.
Furthermore, all of the above vibrator motors disclosed in the U.S. patents have commutator brushes, thereby giving rise to a life span problem.
As disclosed in U.S. Pat. No. 5,373,207 (issued Dec. 13, 1994), the present applicants invented a dc brushless vibrator motor having neither an output shaft nor brushes. This vibrator motor employs a cylindrically-shaped coreless stator winding unit having at least three stator coils arranged at an even pitch angle and a rotor including an axially extended eccentrically-weighted permanent magnet having alternating north and south poles, angled partially, about the rotational axis. The rotor additionally includes a tubular yoke to provide magnetic flux paths.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a light, compact dc brushless vibrator motor having an eccentrically-weighted rotor.
It is an additional object of the present invention to provide a vibrator motor having a cored stator, but simple in construction and low in production cost.
In order to achieve the above objects, a dc brushless vibrator motor according to the present invention has a base member, a shaft connected to the base member, the shaft having a longitudinal center axis, a stator fixedly connected to the base member, the stator having plurality of magnetically conductive cores angularly evenly disposed about the center axis and respective armature coils mounted thereon, a rotor mounted on the shaft having an eccentric mass distribution with respect to the center axis. The rotor has a magnet holder, an annular permanent magnet fixedly connected to the magnet holder and disposed concentrically with the center axis and radially outside the stator. The annular magnet has alternate north and south magnetic poles arranged at an even angular pitch about the center axis. The magnet holder has a top generally flat part disposed orthogonal to the center axis.
In one embodiment, that magnet holder has a cylindrical side wall disposed concentrically with the center axis and the rotor has an arcuate weight fixed to the cylindrical side wall on the inside thereof but radially outside the annular magnet. The flat top part of the magnet holder has a plurality of through-holes so as to reduce the weight of the magnet holder. The magnet holder further has an arcuate groove between its cylindrical side wall and the annular magnet in a manner that the arcuate weight and the arcuate groove are disposed angularly 180° about the center axis in angularly non-overlapping relation with each other. The magnet holder may be made of a low-friction type synthetic resin and be rotatably mounted on the shaft in a manner that the resin-made magnet holder is in a direct sliding contact with the shaft.
In other embodiments, the magnet holder has a cutout, which may be a through-hole in a top flat part thereof, in a manner that the magnet holder per se has an eccentric mass distribution with respect to the center axis. The annular magnet is totally or partially adjoined by a part of the magnet holder on radially outside thereof. The rotor may have an arcuate weight fixedly attached to the magnet holder in a manner that the arcuate weight and the cutout in the magnetic holder are disposed diametrically opposite to each other with respect to the center axis so that the eccentric mass distribution about the center axis is enhanced. The magnet holder in these embodiments is made of a magnetically conductive material, but it may alternatively be made of a synthetic resin. The vibrator motor of these embodiments further has a cup-like stationary rotor cover fixed to the base member in a manner that rotor is protectively capped with the rotor cover.
REFERENCES:
patent: 4570093 (1986-02-01), Morii et al.
patent: 4647803 (1987-03-01), Von Der Heide et al.
patent: 5391952 (1995-02-01), Simazu et al.
patent: 5698919 (1997-12-01), Obara
patent: 5942833 (1999-08-01), Yamaguchi
patent: 4-49832 (1992-02-01), None
patent: 10-248203 (1998-09-01), None
patent: 11-098761 (1999-04-01), None
Koyanagi Naohisa
Yamaguchi Tadao
Leydig , Voit & Mayer, Ltd.
Tamai Karl
Tokyo Parts Industrial Co., Ltd.
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