Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-12-11
2003-04-15
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
Reexamination Certificate
active
06548922
ABSTRACT:
TECHNICAL FIELD
The invention relates to a two-pole step motor for an analog electronic timepiece.
BACKGROUND TECHNOLOGY
Since an analog electronic timepiece employs a cell for its power source, the analog electronic timepiece stops its function after continuous operation for a given length of time period due to exhaustion of its capacity. Accordingly, the cell need be replaced periodically with a new one, which has been quite troublesome to users.
Further, as the users have to ask specialist shops to do such replacement, it has been impossible to have the cell replaced immediately if the cell runs down when there is a need for use of the analog electronic timepiece, and consequently, this has caused a great deal of inconvenience to the users.
Since such exhaustion of the capacity of the cell of the analog electronic timepiece poses a major problem to the users, efforts have been made lately to study on prolongation of a service life of the cell in the analog electronic timepiece or to develop a timepiece capable of eliminating a need for replacement of a cell by incorporating a generator in the timepiece, activated following the motion of the users carrying the timepiece with them, or by the agency of a power generation mechanism such as a solar cell, and so forth, incorporated in the timepiece.
However, in the case of an analog electronic timepiece with such a power generation mechanism built therein, the timepiece is designed to be driven by power stored in a capacitor or a secondary cell built therein, however, there have been cases where it has been difficult to generate sufficient power as required all the time because application conditions of the timepiece varies from one user to another.
Accordingly, even with the timepiece incorporating the power generation mechanism built therein, it has been necessary to aim at achievement of lowering power consumption in order to keep the timepiece in a stable operational condition without interruption during usage.
Meanwhile, if use can be made of a cell which is large in size, having a large capacity, it is possible to achieve prolongation of the service life thereof, however, designing constraints imposed on a timepiece does not permit the cell to be excessively large in size. Accordingly, if prolongation of the service life of the cell is called for, it has been inevitable to achieving lowering of power consumption on the part of the timepiece.
Now, a mechanism of an analog electronic timepiece is broadly described hereinafter. It has a construction such that a two-pole step motor for a timepiece is intermittently driven in accordance with a reference signal generated by a quartz oscillator, and the like, and time display is performed by transmitting motion of the step motor to the hands of the timepiece via gears.
It follows therefore that from the viewpoint of power consumption, such an analog electronic timepiece can be broadly broken down into a circuit part incorporating the quartz oscillator and the like for generating the reference signal, and a step motor part for rotating the hands of the timepiece.
However, with analog electronic timepieces in current use, a circuit part is made up of a semiconductor integrated circuit wherein power consumption is rendered small, and consequently, a greater part of power is after all consumed for driving the step motor for handling the hands. Accordingly, reduction in power consumption of the step motor has a considerable effect on lowering of power consumption of a timepiece in whole.
FIG. 22
is a plan view showing a schematic construction of a conventional two-pole step motor for a timepiece.
The two-pole step motor for a timepiece (referred to hereinafter merely as “step motor”) comprises a field coil
7
provided with a conductor
7
b
wound around a magnetic core
7
a
formed of a high-permeability material, and a stator
201
bonded to opposite ends of the magnetic core
7
a
of the field coil
7
by screws
8
,
8
, respectively, for magnetic connection.
The stator
201
is provided with a rotor hole
202
defined substantially at the center thereof, and a rotor
3
is rotatably disposed inside the rotor hole
202
.
Further, the rotor
3
is comprised of a rotor magnet
3
a
and a rotor axle
3
b
, and the rotor magnet
3
a
is made of a ferromagnetic material and is formed in a low-profile columnar shape. The rotor axle
3
b
serving as a rotation axis is inserted into an axle hole defined at the center of the rotor magnet
3
a
in the direction normal to the plane of the figure so as to be integrally joined together, thereby magnetizing the rotor magnet
3
a
in such a way as to have two poles in the diametrical direction thereof.
The rotor
3
with opposite ends of the rotor axle
3
b
rotatably supported by bearings (not shown), respectively, is positioned at the center of the rotor hole
202
. Further, the rotor
3
is constituted such that a gear is provided at one end of the rotor axle
3
b
, and rotatory motion thereof is transmitted via the gear to the hands of the timepiece.
Further, holding torque setting means is provided on the inner periphery of the rotor hole
202
, so that the magnetic poles of the rotor magnet
3
a
are positioned so as to be oriented in a constant direction of an initial phase angle &thgr;
1
by the agency of the holding torque setting means when the step motor is out of operation, thereby stopping and holding the rotor
3
in that position with a predetermined holding torque.
With the step motor, by applying a driving voltage thereto, forward and reverse current are caused to flow alternately through the field coil
7
, thereby a magnetic field oriented in a direction corresponding to the direction of the forward and reverse current, respectively, is generated inside the rotor hole
202
so as to correspond to the magnitude of the respective flowing current, and the magnetic field is caused to act on the rotor magnet
3
a
magnetized beforehand, so that the rotor
3
is rotated by 180 degrees (for one step) counterclockwise in FIG.
22
.
The motion of the step motor, made for one step, is described hereinafter.
If the direction of a magnetic field produced inside the rotor hole
202
by magnetic fluxes which are generated when current is caused to flow through the field coil
7
is designated as an excitation direction line
12
, the rotor
3
is held and stopped at a position where a line
4
, which is the direction of magnetization of the rotor magnet
3
a
, and which interconnects the two poles thereof, is rotated by the initial phase angle &thgr;
1
counterclockwise in
FIG. 22
, relative to the excitation direction line
12
, by the agency of the holding torque of the holding torque setting means, established by magnetic action between the magnetic poles of the rotor magnet
3
a
and the stator
201
in a state where no current flows through the field coil
7
.
In this state, when current is caused to flow through the field coil
7
in such a direction as to cause the rotor
3
to rotate forward, magnetic fluxes occur to the field coil
7
, and a magnetic field is generated inside the rotor hole
202
, whereupon the rotor
3
is subjected to a rotational torque caused by an interaction of the magnetic field and the permanent magnetized charge of the rotor magnet
3
a
, starting rotation against the resistance of the holding torque. Upon flowing of current through the field coil
7
for a suitable duration only, the rotor
3
stops after being rotated through 180° up to a position of the next stop.
With the step motor of the constitution as described above, power consumption for a unit of time is expressed by the product of a strength of the current caused to flow through the filed coil
7
for excitation, and a cell voltage as applied. Since the cell voltage as applied in this case remains substantially constant, lowering of the power consumption of the step motor depends on how to reduce current flowing in the field coil
7
while satisfying driving characteristics required of the step motor.
Further, with the step motor, the rotatio
Machida Takayasu
Nanya Takanori
Shimanouchi Takeaki
Suzuki Kazuo
Takahashi Shigeyuki
Armstrong Westerman & Hattori, LLP
Citizen Watch Co. Ltd.
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