Electricity: single generator systems – Generator control – Magnetic structure
Reexamination Certificate
2004-01-08
2004-12-14
Lam, Thanh (Department: 2834)
Electricity: single generator systems
Generator control
Magnetic structure
C310S049030, C368S157000, C029S596000
Reexamination Certificate
active
06831446
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power generator, a timepiece and electronic device having the power generator and a cogging torque adjustment method for the power generator, the power generator being adapted for supplying power in an electronic clock etc. More specifically, it relates to a technique for optimizing a cogging torque (non-excitation torque/detent torque of a step motor) of a power generator.
2. Description of the Related Art
As shown in
FIG. 1
, an electronic clock with a crystal oscillator as a time standard has a power supply
10
having a small-size power generator
20
and a secondary power supply
30
. The power supply
10
actuates a step motor etc. of a processor
14
. As shown in
FIG. 2
, the small-size power generator
20
is provided with a rotor
21
to be rotated by a transmitted rotary drive force, a stator
22
sandwiching the rotor
21
and a power-generating coil
23
wound around a magnetic core constituting a magnetic circuit together with the stator
22
and the rotor
21
. The rotor
21
has a power-generating gear train
60
for speeding up and transmitting a rotation of an oscillating weight
25
.
In order for the rotor
21
to remain at a desired position when no load is applied, outer notches
221
and
222
for the magnetic saturation portion on a periphery of the rotor
21
are formed on the stator
22
as shown in FIG.
14
. The rotor
21
is a permanent magnet having N and S magnetic poles. When the rotor
21
remains at a certain angular position and the rotation of the oscillating weight
25
is transmitted through the power-generating gear train
60
, the magnetic poles N and S are rotated to generate electromotive force to the power-generating coil
23
. Since a cogging torque is applied to the rotor
21
, the rotor
21
is biased to remain at a predetermined angular position (rotor stop position without applying load—referred to “no-load rotor stop position” hereinafter.).
Accordingly, in order to rotate rotor
21
the oscillating weight
25
has to be capable of transmitting greater torque to the rotor
21
than the cogging torque.
However, the size and thickness of respective components of an electronic clock have been reduced to minimize its overall thickness. Thus, the size and weight of the oscillating weight
25
of the small-size power generator
20
are necessarily reduced. Accordingly, with the conventional small-size power generator
20
, when the size and weight of the oscillating weight
25
are reduced while the magnitude of the cogging torque applied to the rotor
21
does not change, rotation of the oscillating weight
25
can be hampered, thus rendering it incapable of charging the secondary power supply
30
.
In another type of power generator, the rotor of the power generator is rotated by a mechanical energy source such as a power spring. However, when the size of the power spring etc. is reduced, the rotation of the rotor can be hampered, thus causing the same problem in charging the secondary power supply.
Accordingly, it has been desired that the magnitude of cogging torque is made as small as possible so as to facilitate rotation of the rotor even when the size of the oscillating weight
25
and the power spring etc. is reduced.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a power generator capable of efficiently reducing the cogging torque applied to the rotor and thus capable of efficiently generating electric power by improving rotation startability of the rotor, a timepiece and electronics having the power generator and a cogging torque adjustment method of power generator.
A power generator according to the present invention includes: a rotor having a permanent magnet rotated by a transmitted rotary drive force; a stator having a rotor accommodation hole for the rotor to be disposed; and a power-generating coil wound around a magnetic core constituting a magnetic circuit along with the stator and the rotor, where magnetic reluctances of a first magnetic circuit extending from the rotor through the stator and the magnetic core back to the rotor and a second magnetic circuit with magnetic flux thereof closing around a stator adjacent the rotor are compared without forming an inner notch on an inner periphery of the rotor accommodation hole, where, when the magnetic reluctance of the first magnetic circuit is smaller, the inner notch is formed on the inner periphery of the rotor accommodation hole of the stator within angular range of ±45° around a magnetic flux direction of the first magnetic circuit at a rotation center of the rotor, and where, when the magnetic reluctance of the second magnetic circuit is smaller, the inner notch is formed on the inner periphery of the rotor accommodation hole of the stator within angular range of ±45° around a magnetic flux direction of the second magnetic circuit at a rotation center of the rotor.
In the present invention, the inner notch is not restricted to a cut portion formed on the inner periphery of the rotor accommodation hole, but may be a dent (reduced thickness of a part of the stator) on the inner periphery of the rotor accommodation hole or alternatively may be a hole (a through-hole penetrating the stator in thickness direction) formed adjacent to the inner periphery of the rotor accommodation hole. In other words, any arrangement is possible for the inner notch as long as the inner notch can enlarge a part of the gap between the rotor and the inner periphery of the rotor accommodation hole or the through-hole is provided to the magnetic circuit to adjust the magnetic reluctance of the magnetic circuit.
When the stator is, for instance, divided at the rotor accommodation hole section, the first magnetic circuit starts from the rotor (magnet), passes through one of the stators and the magnetic core to the other stator and returns back to the rotor. Similarly, when the stator is integrally formed without being divided, the first magnetic circuit starts from the rotor, passes through the stator on one side of the rotor and the magnetic core to the other side of the stator and returns back to the rotor.
The magnetic flux direction of the second magnetic circuit at the rotation center of the rotor (referred to the second magnetic circuit direction hereinafter) is a direction for the second magnetic circuit with magnetic flux thereof closing at the stator around the rotor, which is ordinarily a direction orthogonal to the magnetic flux direction of the first magnetic circuit at the rotation center of the rotor (referred to the first magnetic circuit direction hereinafter).
The cogging torques by the main first magnetic circuit and the second magnetic circuit with its magnetic flux closing around the rotor are applied to the rotor. Since the respective magnet circuits ordinarily cross perpendicularly at the rotor section, the magnetic circuit that applies a strong magnetic attraction force due to high magnetic flux density, i.e. the magnetic circuit with smaller magnetic reluctance, exerts a large influence. Accordingly, by forming the inner notch in the magnetic circuit having the smaller magnetic reluctance to enlarge the gap between the rotor and the stator to increase magnetic reluctance, the magnetic attraction force applied to the rotor, i.e. the cogging torque can be reduced. Therefore, even when the size and weight of the oscillating weight or the power spring are reduced by reducing the thickness of devices, power can be efficiently generated and the secondary power supply can be efficiently charged. Further, since the actuation torque of the rotor can be reduced when a power spring is used, duration of the power spring can be lengthened with the power spring of the same size, so that the power generator can be worked for a longer time.
Incidentally, when the inner notch is arranged beyond ±45° disposition relative to either the first or the second magnetic circuit direction having the smaller magnetic reluctance, the magnetic reluctance of eith
Lam Thanh
Seiko Epson Corporation
Watson Mark P.
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