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Description  |
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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 7b wound
around a magnetic core 7a formed of a high-permeability material, and a
stator 201 bonded to opposite ends of the magnetic core 7a 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 3a and a rotor axle 3b,
and the rotor magnet 3a is made of a ferromagnetic material and is formed
in a low-profile columnar shape. The rotor axle 3b serving as a rotation
axis is inserted into an axle hole defined at the center of the rotor
magnet 3a in the direction normal to the plane of the figure so as to be
integrally joined together, thereby magnetizing the rotor magnet 3a in
such a way as to have two poles in the diametrical direction thereof.
The rotor 3 with opposite ends of the rotor axle 3b 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 3b, 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 3a are
positioned so as to be oriented in a constant direction of an initial
phase angle .theta..sub.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 3a 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 3a, and which interconnects
the two poles thereof, is rotated by the initial phase angle .theta..sub.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 3a 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 3a, 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.degree. 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 rotational torque is caused to occur to
the rotor 3 by causing current to flow in the field coil 7, thereby
causing the rotor 3 to rotate against the resistance of the holding
torque. Consequently, the smaller the holding torque, the smaller the
rotational torque as required may be in proportion to the holding torque.
Since current which is caused to flow in the field coil 7 is proportional
to the rotational torque, current flowing in the field coil 7 can be
reduced if the holding torque can be reduced. As a result, it becomes
possible to achieve lowering of power consumption of the step motor for a
timepiece.
Now, the holding torque of the step motor for a timepiece has functions
such that even when the timepiece is subjected to an impact when the
timepiece is dropped, and so forth, the hands are securely held so as not
to be caused to jump, thereby enabling correct time to be displayed while
settling the hands at a correct stop position against the resistance of
friction torque occurring to bearings and gears inside the timepiece.
Accordingly, it is not as simple as a case where the holding torque need
only be rendered smaller in order to reduce power consumption, but it is
required that the holding torque be set so as to meet the minimum holding
torque as required to maintain the function of the timepiece.
As disclosed in International Publication No. WO 98/30939, it is described
with reference to the holding torque as required for use in timepiece that
jumping of the hands will not occur if kinetic energy occurring to the
hands by an impact is smaller than a holding potential established by the
holding torque of a rotor, that is, a magnetic potential difference.
Since kinetic energy received by the hands when subjected to the impact is
proportional to the square of moment of the hands, the holding potential,
that is, the holding torque can be rendered smaller by use of the hands
with a smaller moment.
By so doing, it becomes possible to set the minimum holding torque as
required at a very small value equivalent to a fraction of the holding
torque of a step motor for a timepiece, thereby achieving lowering of
power consumption of the timepiece.
Next, holding torque setting means, provided in a stator of the
conventional step motor for a timepiece, is now described hereinafter.
As for the holding torque setting means, provided in the stator of the
conventional step motor for a timepiece, there are primarily two types in
construction as described below.
One type has a construction such that the stator 201 of the step motor for
a timepiece , shown in FIG. 22, is formed of a high-permeability material,
and as shown in FIG. 23, there are provided holes 6, 6 defined close to
opposite ends of the stator 201 in the longitudinal direction, for bonding
the stator to opposite ends of the magnetic core 7a of the field coil 7.
A rotor hole 202 provided substantially at the center of the stator 201 is
defined in the shape of two semicircles joined together with the center of
the respective semicircles deviated from each other to permit a holding
torque and an initial phase angle .theta..sub.1 (refer to FIG. 22) to be
set.
By combining the two semicircles in such a way as to cause the center of
the respective semicircles to deviate from each other, two stepped parts
204a, 204b having a gap amount G, respectively, are formed. With the
stator 201, it is possible to set the holding torque to a desired value by
adjusting the gap amount G.
The construction wherein such stepped parts 204a, 204b described above are
formed inside the rotor hole 202 of the stator 201 is described in, for
example, Japanese Patent Laid-open No. S 49-132507.
A stator wherein such stepped parts are formed inside a rotor hole thereof
is hereinafter referred to as a gap type stator.
Next, the construction of another type of holding torque setting means is
described hereinafter with reference to FIG. 24. In the figure, some
components used in common is described where necessary by using the same
reference numerals as described with reference to FIG. 22.
A stator 211 in this case is provided with a pair of recesses 205a, 205b
formed at symmetrical positions against the center axis of the rotor hole
212 on the inner periphery of the rotor hole 212, as holding torque
setting means in order to provide the holding torque and the initial phase
angle of a rotor 3.
Further, a straight line 24 passing through the respective centers of the
recesses 205a, 205b is disposed so as to be tilted at an angle of
.theta..sub.11 relative to an excitation direction 21 of the rotor hole
212.
With the stator 211, an angle which the straight line 24 passing through
the respective centers of the recesses 205a, 205b forms with a straight
line 27 passing through the center axis of the rotor hole 212 and
orthogonal to the excitation direction of the stator 211, is designated as
an installation angle .theta..sub.12 of the recesses 205a, 205b expressed
in a positive value when rotated in counterclockwise direction, and the
initial phase angle .theta..sub.1 (refer to FIG. 22) of the rotor 3 is set
by adjusting the installation angle .theta..sub.12.
In the case of the step motor for a timepiece , having the stator 211 of
such a construction as described above, the holding torque of the rotor 3
is determined by the pair of the recesses 205a, 205b.
In this connection, the construction wherein the recesses 205a, 205b as
described above are formed inside of the rotor hole 212 of the stator 211
is described in, for example, Japanese Patent Laid-open No. S 51-1908.
A stator wherein recesses are formed inside a rotor hole thereof is
hereinafter referred to as a notched type stator.
As described in the foregoing, in the case of the conventional step motor
employing the gap type stator, the magnitude of the holding torque and the
initial phase angle can be adjusted by varying the gap amount of the
stepped parts formed inside the rotor hole.
With the ordinary step motor for a timepiece, since the diameter of the
rotor hole is in the order of 1700 .mu.m on average, the maximum holding
torque can be set to around 300 nNm by setting the gap amount of the
stepped parts of a stator to about 40 to 50 .mu.m.
However, if it is intended to further reduce the holding torque to a large
extent in order to achieve lowering of power consumption, the gap amount
need be rendered to be extremely small, as small as about 10 .mu.m, and
consequently, it becomes difficult in respect of precision with which to
process the stator to establish a stable holding torque.
Further, if the gap amount is rendered to be extremely small as described
above, this leads to resultant reduction in the initial phase angle (refer
to .theta..sub.1 in FIG. 22). As a result, this will result in requirement
for large power consumption when driving the rotor, so that lowering of
power consumption can not be achieved.
Further, in the case of the step motor employing the gap type stator
construction, it is possible to set the holding torque to a small value
even at the same gap amount without varying the initial phase angle by
enlarging the diameter of the rotor hole, however, such enlargement of the
diameter of the rotor hole will result in reduction of interaction between
a magnetic field occurring inside the rotor hole and the rotor magnet.
That is, in this case, as electromechanical coupling constant decreases,
the rotational torque occurring to the rotor by flow of current through
the field coil is reduced.
As a result, even if the initial phase angle is set to a proper value by
lowering the holding potential established by the holding torque, it will
become necessary to increase current flowing in the field coil to
compensate for a decrease in the rotational torque due to a decrease of
the electromechanical coupling constant, so that a power-saving effect
resulting from the holding torque being set to a small value will be
offset, thereby rendering it impossible to achieve lowering of power
consumption.
Meanwhile, in the case of the step motor employing the notched type stator
construction, the initial phase angle can be set by the installation angle
of the pair of the recesses while the holding torque is adjusted by either
increasing or decreasing the sum of areas of the recesses formed on the
inner periphery of the rotor hole, and consequently, if it is intended to
render the holding torque considerably less than the present value in
order to lower power consumption, this will require the sum of the areas
of the pair of the recesses, in other words, dimensions of the recesses to
be rendered extremely small. Accordingly, it will become difficult in
respect of precision with which to process the stator to obtain a stable
holding torque.
Further, with the notched type stator as well, it is possible to set the
holding torque to a small value without varying the sum of the areas of
the recesses by enlarging the diameter of the rotor hole, however, as with
the case of the gap type stator, such enlargement of the diameter of the
rotor hole will result in a decrease of the electromechanical coupling
constant, so that lowering of power consumption can not be achieved.
As described hereinbefore, with the stator of the conventional construction
as described above, if it is intended to set the holding torque to a small
value in an attempt to further reduce power consumption, it has been
necessary to render either the gap amount of the stepped parts formed in
the stator or the dimensions of the recesses formed in the stator to be
extremely small, thus posing difficulty in respect of precision with which
to process the stator. Accordingly, it has been difficult to set a stable
holding torque.
Consequently, with the step motor for a timepiece, adopting the
conventional construction, it has been difficult to achieve lowering of
power consumption.
DISCLOSURE OF THE INVENTION
The invention has been developed against the technical background described
above, and it is an object of the invention to solve the problems as
described above by devising a novel construction of a stator, and to
provide a two-pole step motor for a timepiece which is suitable for
lowering of power consumption, and which can be manufactured with ease.
To achieve the above objects, a two-pole step motor for a timepiece
according to the invention comprises: a rotor made up of a rotor magnet
and a rotor axle; a stator made of a high-permeability material, having a
rotor hole in which the rotor is installed; and a field coil for
excitation, provided with a magnetic core made of a high-permeability
material around which a conductor is wound, and opposite ends of which are
magnetically bonded to opposite ends of the stator, wherein the stator is
provided with a plurality of holding torque setting means, disposed on the
inner periphery of the rotor hole, at installation angles differing in the
direction of the inner periphery.
Herein, the installation angle of the holding torque setting means refers
to an installation angle relative to the direction orthogonal to an
excitation direction of the stator, and the installation angle that
differs by 180.degree. is deemed to be an equivalent installation angle.
It is effective for attaining lowering of power consumption to set the
initial phase angle .theta..sub.1 which is an angle formed by the magnetic
field direction line in the direction of a magnetic field produced inside
the rotor hole and the magnetizing direction line of the rotor magnet at
the standstill position of the rotor based on respective installation
angles of the plurality of the holding torque setting means, in a range of
50 degrees to 70 degrees.
With the two-pole step motor for a timepiece according to the invention,
even in the case where a single holding torque setting means can not be
installed at an installation angle required for obtaining an initial phase
angle and a holding torque as intended owing to presence of the axle hole
of gears or holes of fixed pins which are formed around the rotor hole of
the stator, the initial phase angle and the holding torque as intended can
be obtained by breaking down a holding torque established by a pair of the
holding torque setting means into vectors, and by installing two or more
holding torque setting means corresponding to the respective vectors as
broken down, at different installation angles and at locations avoiding
the axle hole and the holes of fixed pins.
Further, the stator is preferably made up by bonding a first stator part
made of a high-permeability material to a second stator part made of a
high-permeability material through the intermediary of connections made of
a low-permeability material or a nonmagnetic material.
In such a case, the stator has a construction such that it is magnetically
separated into two portions, and consequently, a magnetic field inside the
rotor hole for rotating the rotor can be efficiently produced by magnetic
fluxes excited by the field coil, so that current caused to flow in the
field coil can be reduced, thereby attaining lowering of power
consumption.
Further, since the connections are made of either a low-permeability
material or nonmagnetic material, there is no need of narrowing down the
connections to an extreme extent, thereby enabling mechanical strength as
required to be secured.
Furthermore, with the two-pole step motor for a timepiece described above,
it is preferably that the connections where the first stator part is
bonded to the second stator part serve as at least one of the plurality of
the holding torque setting means while other holding torque setting means
except the connections are disposed on the inner periphery of the rotor
hole at installation angles differing from that for the connections.
In addition, the plurality of the holding torque setting means are
preferably paired recesses or paired protuberances formed on the inner
periphery of the rotor hole, respectively. Further, the other holding
torque setting means as described above are preferably a pair of recesses
or a pair of protuberances formed on the inner periphery of the rotor
hole, including means formed in a shape asymmetrical with respect to the
center of the rotor hole.
Then, the holding torque can be adjusted by varying the dimensions of the
recesses or the protuberances, and the initial phase angle can be adjusted
by varying the installation position of the recesses or the protuberances.
Further, among the holding torque setting means, the means formed in the
shape asymmetrical with respect to the center of the rotor hole may be a
pair consisting of a recess and a protuberance facing each other, formed
on the inner periphery of the rotor hole, on opposite sides of the center
of the rotor hole, or may comprise a recess or a protuberance formed on
the inner periphery of the rotor hole only on one side of the center
thereof.
Furthermore, the plurality of the holding torque setting means are
preferably combination of those of different types with the installation
angles thereof in the direction of the inner periphery of the rotor hole
differing from each other.
In this connection, the combination of those of different types among the
holding torque setting means is preferably combination of the gap type and
the notched type, described in the foregoing, or combination of an oval
type as described hereinafter and the notched type described above.
Still further, with the two-pole step motor for a timepiece having the
plurality of the holding torque setting means including the means formed
in a shape asymmetrical with respect to the center of the rotor hole, the
first stator part is preferably bonded to the second stator part through
the intermediary of the connections made of a low-permeability material or
nonmagnetic material, the connections serving as at least one of the
plurality of the holding torque setting means.
Similarly, with the two-pole step motor for a timepiece having the
plurality of the holding torque setting means of different types, the
first stator part is preferably bonded to the second stator part through
the intermediary of the connections made of a low-permeability material or
nonmagnetic material, the connections serving as at least one of the
plurality of the holding torque setting means.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view showing a schematic construction of a two-pole step
motor for a timepiece according to a first embodiment of the invention.
FIG. 2 is a plan view showing the construction of a stator of the two-pole
step motor for a timepiece in FIG. 1.
FIG. 3 is a graph showing the relation between a holding torque of the
two-pole step motor for a timepiece in FIG. 1 and a power consumption of
the same.
FIG. 4 is a graph showing the relation between an initial phase angle of
the two-pole step motor for a timepiece in FIG. 1 and a power consumption
of the same.
FIG. 5 is a plan view showing a schematic construction of a two-pole step
motor for a timepiece according to a second embodiment of the invention
like FIG. 1.
FIG. 6 is a plan view showing the construction of a stator of the two-pole
step motor for a timepiece in FIG. 5.
FIG. 7 is a plan view enlarging a recess provided in the stator serving as
holding torque setting means in FIG. 5.
FIG. 8 is a graph showing the relation between installation angles of a
pair of recesses 15e, 15f of the two-pole step motor for a timepiece in
FIG. 5, a maximum holding torque and initial phase angle of the same.
FIG. 9 is a graph showing the relation between each depth of the recess and
the maximum holding torque of the two-pole step motor for a timepiece in
FIG. 5.
FIG. 10 is a graph showing the relation between each width of the recess
and the maximum holding torque of the step motor for a timepiece in FIG.
5.
FIG. 11 is a plan view showing a schematic construction of a step motor for
a timepiece according to a third embodiment of the invention like FIG. 1.
FIG. 12 is a plan view showing the construction of a stator of the step
motor for a timepiece in FIG. 11.
FIG. 13 is a plan view showing a schematic construction of a step motor for
a timepiece according to a fourth embodiment of the invention like FIG. 6.
FIG. 14 is a plan view showing the construction of a stator of the step
motor for a timepiece according to a fifth embodiment of the invention
like FIG. 12.
FIG. 15 is a plan view showing the construction of a stator of the step
motor for a timepiece according to a sixth embodiment of the invention
like FIG. 13.
FIG. 16 is a plan view showing the construction of a stator of the step
motor for a timepiece according to a seventh embodiment of the invention
like FIG. 15.
FIG. 17 is a plan view showing the construction of a stator of the step
motor for a timepiece according to an eighth embodiment of the invention
like FIG. 14.
FIG. 18 is a plan view showing the construction of a stator of the step
motor for a timepiece according to a ninth embodiment of the invention
like FIG. 15.
FIG. 19 is a plan view showing the construction of a stator of the step
motor for a timepiece according to a tenth embodiment of the invention
like FIG. 17.
FIG. 20 is a plan view showing the construction of a stator of the step
motor for a timepiece according to an eleventh embodiment of the invention
like FIG. 18.
FIG. 21 is a plan view showing the construction of a stator of the step
motor for a timepiece according to a twelfth embodiment of the invention
like FIG. 20.
FIG. 22 is a plan view showing a schematic construction of a conventional
two-pole step motor for a timepiece.
FIG. 23 is a plan view showing the construction of a stator of the step
motor for a timepiece like FIG. 2.
FIG. 24 is a plan view showing the construction of a stator having a pair
of recesses serving as conventional holding torque setting means like FIG.
23.
FIG. 25 is a plan view showing another construction of a stator of a
conventional step motor for a timepiece like FIG. 24.
BEST MODE FOR CARRYING THE INVENTION
The embodiments of the inventions are now described in detail with
reference to the accompanied drawings.
First Embodiment: FIGS. 1 to 4
FIG. 1 is a plan view showing a schematic construction of a two-pole step
motor for a timepiece according to a first embodiment of the invention,
FIG. 2 is a plan view showing the construction of a stator of the two-pole
step motor for a timepiece in FIG. 1, FIG. 3 is a graph showing the
relation between a holding torque of the two-pole step motor for a
timepiece in FIG. 1 and a power consumption of the same, and FIG. 4 is a
graph showing the relation between an initial phase angle of the two-pole
step motor for a timepiece in FIG. 1 and a power consumption of the same.
The two-pole step motor for a timepiece (hereinafter referred to simply as
a step motor) comprises: a rotor 3 made up of a rotor magnet 3a and a
rotor axle 3b; a stator 1 having a rotor hole 2 in which the rotor is
installed; and a field coil 7 for excitation, provided with a magnetic
core 7a made of a high-permeability material around which a conductor 7b
is wound, and opposite ends of which are magnetically bonded to opposite
ends of the stator 1.
Inasmuch as the construction of the step motor is the same as that of the
conventional two-pole step motor for a timepiece as explained with
reference to FIG. 22, components which are the same as those shown in FIG.
22 are depicted by the same reference numerals, and the explanation
thereof is omitted.
The stator 1 of this step motor comprises a first stator part 1a and a
second stator part 1b formed of a high-permeability material respectively
(hereinafter simply referred to as stator part 1a and stator part 1b)
which are bonded to each other through the intermediary of connections 1c,
1d formed of a low-permeability material or nonmagnetic material
respectively.
A plurality of holding torque setting means are provided at the inner
periphery of the rotor hole 2 defined substantially at the center of the
stator 1 for holding the rotor 3 at a given position of the rotating
direction of the rotor 3 as shown in FIG. 1, namely, the position where a
line 4 for connecting two magnetic poles which are magnetized in the
diametrical direction of the rotor magnet 3a is positioned at an angle of
initial phase angle .theta..sub.1 when the step motor is not driven so
that the rotor 3 is not rotated, with a given holding torque owing to a
magnetic action between the magnetic poles of the rotor magnet 3a and the
stator 1.
The plurality of holding torque setting means comprise a pair of recesses
5a, 5b formed in the inner periphery of the rotor hole 2 and a pair of
connections 1c, 1d wherein both pairs are positioned at the symmetrical
positions with respect to the center of the rotor hole 2, as shown in FIG.
2.
The pair of recesses 5a, 5b and the pair of connections 1c, 1d are
different from each other in installation angles as shown in the drawing.
The installation angle is an arrangement angle relative to a line
orthogonal to a magnetic field direction line 12 in an excitation
direction of the stator 1, however, the detail thereof is explained with
reference to a second embodiment and subsequent embodiments of the
invention (FIG. 6 and subsequent figures).
Holes 6, 6 are formed on both end portions of the stator 1 in the
longitudinal direction so as to connect magnetically to both terminals of
the magnetic core 7a of the field coil 7.
In order to manufacture this stator 1, a pilot hole being the positioning
hole for the later press working, a prepared hole for the rotor hole 2,
and fixing holes 6, 6 are formed by pressing a high permeability band
permalloy of 500 .mu.m thickness, and the external shape partially
remaining a joint part (not illustrated) to couple the band material is
punched.
Next, slits of 200 .mu.m width are punched on the connections 1c, 1d, wires
of predetermined length made of a low permeability or non-permeability
material are inserted in the slits, and the stator part 1a and the stator
part 1b separated by the slits are joined to be matched by the laser
welding.
Then, the rotor hole 2 and the recesses 5a, 5b are punched by press
working, and finally the joint part to couple the band material is punched
to complete the external shape working. And, the magnetic annealing is
applied to the above band material that completed the external shape
working to make up the stator 1 of the step motor.
Described next is a result of an experiment which is performed for
determining a proper condition necessary for achieving lowering of power
consumption when forming the step motor into which the stator 1 having the
foregoing construction is integrated.
With the experiment, the relation between a holding torque of the step
motor and the power consumption, the relation between an initial phase
angle and a power consumption, and the relation between a power
consumption and the construction of the connections of the step motor were
checked.
The experiment was performed by the known two-pole step motor for a
timepiece into which the stator 1 according to the first embodiment of the
invention was integrated so as to perform measurement. A chopper driving
waveform is used as a driving waveform and an ON/OFF ratio of each pulse
of the driving waveform is adjusted, and determined the minimum
consumption power capable of performing a normal driving.
Particularly, regarding the stator 1 that was used for measurement, the
portion of the recesses 5a, 5b are not formed by press working but they
are formed by an electric discharge machining in accordance with varieties
of measurement conditions before a magnetic annealing is applied thereto.
First of all, the relation between the holding torque and the power
consumption is described.
The power consumption in the step motor for a timepiece can be probably
achieved by reducing the holding torque because a current necessary for
excitation caused to flow in the field coil 7 can be reduced by reducing
the holding torque.
Accordingly, the change of the power consumption when the holding torque
was changed actually was checked with experiments.
With regard to the stator 1 used for the measurements, several kinds having
different cuts of depths of the semicircular recesses 5a, 5b provided on
the inner periphery of the rotor 2 were prepared to adjust the holding
torque. The self-made measuring instrument of the rotor rotational angle
measured the angular velocity against the displacement angle of the rotor
3, and from the measured results and the inertia of the rotor 3, the
equation of motion was solved, thereby calculating the holding torques as
to the stator 1.
And, the power consumption was calculated through integrating the products
of a current caused to flow through the coil 7 and a drive voltage applied
across it when the motor was driven for one step. Further, since the
magnitude of the holding torque depends upon the displacement angle, the
comparison of the measurement was made using the maximum holding torque.
And, for the maximum holding torque of the stator 1 used for the
measurements, the torques of 50 nNm through 250 nNm were prepared in
increments of about 50 nNm.
The measurement result by this experiment is shown in FIG. 3. According to
the measurement result, when the maximum holding torque is 250 nNm, the
power consumption is about 800 nJ, while when the maximum holding torque
is lowered to 100 nNm, the power consumption becomes about 350 nJ, from
which it has been found that the relation between the set maximum holding
torque and the power consumption necessary for driving for one step is
substantially proportional.
In such a manner, since when the holding torque is reduced to half, the
power consumption is also reduced to half, so that it has been found that
the reduction of the holding torque has a great effect on the reduction of
the power consumption.
Meanwhile, as mentioned above, in the step motor for a timepiece , the
minimum holding torque is required to prevent the hands from jumping by an
impact when the timepiece is dropped, or to indicate an exact time, and to
enable hands to be stably stopped at the standstill position against the
resistance of frictional torque produced at the bearing and gears.
If a motion energy which hands of a timepiece receive due to the impact is
smaller than the holding potential formed by the holding torque of the
rotor, the jumping of the hands do not occur. That is, when the moment of
hands is adjusted to be small, the holding potential can be made small,
the holding torque can be made small.
In such a manner, when the moment of hands is adjusted to be small, the
minimum holding torque as required can be reduced to an extremely small
holding torque, namely, to a fraction of the holding torque of the
ordinary step motor for a timepiece.
As mentioned above, it has been found, from the measurement result shown in
FIG. 3, that the reduction of the holding torque is effective for the
reduction of the power consumption, and this holding torque can be reduced
to an extremely small value, namely, at a fraction of a holding toque of
an ordinary step motor for a timepiece .
Then, the relation between the initial phase angle and the power
consumption is described.
The initial phase angle .theta..sub.1 shown in FIG. 1 shows a phase
difference between the rotary torque and the holding torque, and it is an
angle formed by the magnetic field direction line 12 in the direction of a
magnetic field produced inside the rotor hole 2 and the magnetizing
direction line 4 of the rotor magnet 3a at the standstill position of the
rotor 3, which is a very important parameter for driving the step motor.
With the experiment, several kinds of stators 1 are used, which are set the
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