Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TWO HAND MOVEMENT FOR TIMEPIE OE
WITH A STEPPING MOTOR
This invention relates generally to two hand quartz
analog timepieces driven by a stepping motor. More
particularly, the invention relates to an improved arrangement
for the gear train in a timepiece having a plastic frame, and
wherein a center wheel is driven directly by a stepping motor,
which is powered by a thin large diameter energy cell.
BACKGROUND OF THE INVENTION
Electronic timepieces of the "analog" type, i.e.,
having conventional rotating hands, have been developed wherein
a stepping motor is accurately driven from a time based
electrical driving signal. The driving signal may come from a
transistor pulse-producing circuit or from an integrated
circuit having a quartz oscillator time base.
Improved movements for two hand timepieces with
plastic frames have been developed using a center wheel having
teeth of ogival shape at the periphery which are driven
directly by a stepping motor pinion. The pinion comprises two
pins which rotate 180 when the stepping motor is energized to
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advance the center wheel. Such a movement is disclosed in U.S.
Patent 4,647,218, issued March 3, 1987, to Paul Wuthrich and
assigned to the present assignee. In that patent, the center
wheel and drive pinion were located just beneath the dial of
the watch in order to allow the center wheel to overlap the
relatively thick energy cell. This arrangement reversed the
conventional positions of the hour hand and minute hand and
required a special bridge bearing to support the center
spindle. Further improvements in this movement were made in
U.S. Patent 4,725,749, issued February 16, 1988, to Paul
Wuthrich and assigned to the present assignee, wherein the
bridge bearing was eliminated and a fi~ed separate center post,
which was inserted into the plastic frame, rotatably supported
the center spindle. Axial clearance (end-shake) of the center
spindle was controlled between a bushing on the spindle and a
the center post.
The recent commercial availability of long life 3 v.
lithium energy cells, rather than the 1.5 v. silver or mercury
cells fo~ which the above movements were designed, has led to
desirability to reconfigure and rearrange of the physical
components in the available space inside a watch movement.
Specifically, lithium cells of long life are available which
are relatively thin, but of large diameter. Therefore, the
gear train, stepping motor and other components must be
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arranged in an optimum way so that the overall thickness of the
movement, including that of the energy cell, will not be too
great.
Constructions are known for two hand movements in
which a large center wheel at the back of the movement is
driven directly by teeth of the stepping motor pinion to rotate
the minute hand, with other gear reduction members arranged to
drive the hour hand. See Japanese Utility Model 55-52395 which
requires front and back frame plate members. However, such
constructions are not suitable for single piece plastic frame
construction.
Accordingly, one object of the present invention is to
provide an improved two hand movement for a quartz analog
timepiece suitable for a plastic frame incorporating a large
diameter, relatively thin, energy cell.
Another object of the invention is to provide an
improved movement for a two hand quartz analog timepiece
wherein a center wheel at the back of the movement is directly
driven by a stepping motor.
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Still another object of the invention is to provide an
improved central bearing structure for the gear train in a two
hand quartz analog timepiece.
DRAWINGS
The invention, both as to organization and method of
practice, together with further objects and advantages thereof,
will best be understood by reference to the following
specification, taken in connection with the accompanying
drawings, in which:
Fig. 1 is a top plan view of the improved movement,
looking from the dial side with dial and other portions omitted
for clarity,
Fig. 2 is a bottom plan view of the improved movement,
locking from the back side opposite the dial,
Fig. 3 is a developed, cross-sectional side
elevational view, taken along lines III-III of Fig. 1,
Fig. 4 is a partial side elevational view, showing an
alternate preferred embodiment of the invention.
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SUMMARY OF THE INVENTION
Briefly stated, the invention comprises an improved
movement for a timepiece of the type having an hour hand, a
minute hand, driving circuit adapted for connecting to an
energy cell, a stepping motor,- a plastic frame member having a
dial side and a back side, and adapted to hold said stepping
motor, and a gear train supported by said frame member and
arranged to drive the hour hand and minute hand from said
stepping motor, said gear train comprising a first assembly of
a center wheel and center pinion with said center wheel driven
directly by the stepping motor, a second assembly of a minute
wheel and minute pinion with said minute wheel driven directly
by said center pinion, and an hour wheel driven directly by
said minute pinion, wherein the improvement comprises a stub
extending from the front side of said frame, said stub defining
a center bore extending through the frame and stub, a spindle
extending through said center bore and rotatably supporting
said first assembly in the frame, said spindle including a
bushing on the f ront side of said frame adapted to hold the
minute hand and to control axial clearance for the first
assembly, said center wheel frictionally engaged with said
spindle on the back side of said frame, and a collar fixed to
said hour wheel and adapted to rotatably support said hour
wheel on the stub, said collar further adapted to hold the hour
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hand. The bushing may be separate from the spindle, but
preferably is integral therewith.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Figs. 1 and 2 of the drawing, the
movement is supported in an integral plastic frame member 1
molded as an single piece and having an intricate shape of high
precision.
Fig. 1 is a plan view from the top (dial side) and
Fig. 2 is a plan view from the bottom (back side). Since the
elements are assembled from both sides of the frame 1, it is
convenient to refer to Figs. 1 and 2 together.
A lead frame assembly 2 shown in Figs. 1 & 2 includes
a driving circuit preferably in the form of an integrated
circuit 3. The integrated circuit 3 is encapsulated in an
insulating material along with embedded ends of projecting
electrical contact members used for attachment to the quartz
crystal, the stepping motor drive coil, and the power supply.
The integrated circuit 3, by means not material to the present
invention, provides a periodic drive pulse to a stepping motor
shown generally as 4. Stepping motor 4 best seen in Fig.
comprises a flat U-shaped stator and core piece 5, a coil 6 and
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a magnetic bridge 7. The stator member 5 defines an opening 8
surrounding a stepping motor rotor 9.
The lead frame 2 may be manufactured by processes
described in U.S. Patent 4,391,531 to Yokota, et al, issued
July 5, 1983, and assigned to the present assignee, which is
incorporated herein by reference. The stepping motor 4 may be
constructed in accordance with the stepping motor shown in U.S.
Patent 4,720,644, issued to Sedlak on January 19, 1988, and
assigned to the present assignee, and incorporated herein by
reference.
The energy cell (not shown) is preferably a relatively
thin, 3 volt lithium cell of large diameter (i.e., covering a
major portion of the back side of the movement) and fits in a
recess 10 molded into the integral plastic frame member 1 on
the back side opposite the dial. Negative and positive spring
contact members 11, 12 as integral parts of the lead frame 2,
make electrical contact with the energy cell and supply to the
integrated circuit 3. An additional holding spring 13 is fixed
to frame 1 by ultrasonic deformation of projecting plastic
frame posts la, lb. Holding spring 13 includes a flange 13a
making contact with the energy cell and a flange 13b (Fig. 2)
serving as a spring detent for a slidable and rotatable
timesetting stem member 14, with an attached setting gear
pinion 33.
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Referring now to Fig. 3 of the drawing, the gear train
arrangement and bearing support which is a main feature of the
present invention will be more clearly seen. Fig. 3 is a
cross-section elevation view developed along the zig-zag line
III-III of Fig. 1 and does not show the negative contact member
11 of the lead frame 2. Stepping motor rotor 9 comprises a
bipolar doughnut-shaped permanent magnet 15 which is overmolded
by plastic material adapted to support the magnet as well as to
form integral journals 16, 17 and diametrically disposed drive
pins 18, which serve as a pinion. Journal 16 is rotatably
supported in a bore in the center of a brass bushing 19 which
is affi~ed to stator member 5. Journal 17 is rotatably
supported in a bore in frame 1. The stepping motor assembly
comprising coil 6, stator 5, rotor 9 and bushing 19 is
preferably premounted in frame 1 as a subassembly later for
addition of the gear train components, utilizing pegs, integral
with frame 1, such as those shown in Fig. 1 as lc, ld, le,
which extend through holes in the stator 5 and magnetic bridge
7 and are deformed on the ends by ultrasonic welding. The
frame may also be deformed as shown at ld to lock the stepping
motor in place.
Driving pins 18 on the stepping motor rotor 9 are
disposed to alternately engage ogival teeth on the periphery of
a toothed center wheel 20. Wheel 20 is frictionally engaged
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with a slip fit on the end of a center spindle 21 which
includes an integral center pinion 22. The friction surface
for the slip fit may be provided either between the spindle 21
and the center wheel 20, or between the adjacent faces of the
center wheel 20 and center pinion 22.
Center spindle 21 is rotatably supported in a center
bore running through the center of a cylindrical stub 23
extending above frame 1 on the dial side of the timepiece. The
timepiece dial indicated at 24 is held (by means not material
to the present invention) on top of frame 1 when the movement
is assembled in the case. Cylindrical stub 23 extends through
an aperture 24a in the dial 24 and extends above the dial.
Center spindle 21 is rotatably supported in frame 1 by
a larger diameter journal 25 in the frame proper and a smaller
diameter journal 26 in the end of stub 23. An extension 21a on
spindle 21 projects beyond journal 26 and extends beyond the
end of stub 23. A separate center bushing 27 is press-fit on
the extension 21a of spindle 21. The bushing 27, spindle 21,
pinion 22 and center wheel 20, together make up a first
rotating assembly which is rot:atably supported in the frame on
bearing journals 25, 26. Bushing 27 serves several purposes.
First, it holds the first assembly in the frame while
controlling axial clearances (end-shake). Secondly, it is
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adapted on its outer surface to hold a minute hand 28. Hand 28
is pressed over the outside of bushing 27, which may be splined
or simply a friction fit. Thirdly, the bushing 27 has a flange
27a that holds the hour wheel in place and controls hour wheel
"end-shake", as will be explained.
A second rotating assembly comprises a minute wheel 29
pressed on the end of a spindle 30. The spindle 30 is
fabricated as an integral member with a minute pinion 31.
Spindle 30 is journaled in a bore passing through frame 1.
Minute wheel 29 has ordinary spur gear teeth engaging those of
center pinion 22 and also includes an a~ially extending set of
beveled "crown" teeth 32 used for time setting. The crown
teeth may be selectively engaged by the setting gear pinion 33
when the stem 14 is axially withdrawn.
Lastly, an hour wheel 34 is rotatably journalled in
the frame by means of a collar 35 which forms close rotating
clearances with the exterior of the stub 23. Hour wheel 33
engages with and is driven by teeth on the minute pinion 31.
The exterior of the collar 35 is adapted to hold an hour hand
36, using splines or friction fit.
Flange 27a of bushing 27 engages the end of stub 23
and also projects radially beyond it so as to engage also the
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end of collar 35 on the hour whee:L. Therefore, the bushing
flange serves to limit axial movement of the first rotating
assembly and also to limit axial movement of the hour wheel.
Axial movement of these two rotating members in the opposite
direction is, in both cases, limited by the frame l.
MODIFICATION
An alternate arrangement is shown in Fig. 4 which is
the preferred embodiment, because of its simplicity. Only the
portions of the movement are shown which are necessary for an
understanding, the rest of the parts being identical to those
in Figs. 1-3.
Frame member 37 includes an integral cylindrical stub
38 defining a center bore 39 coaxial therewith and rotatably
journaling a first assembly 40. Assembly 40 includes a spindle
41 with asially spaced first journal 42 in the frame and second
journal 43 in the stub. Bushing means 44 is a member similar
to bushing 27 shown in Fig. 3, but made integral with spindle
41. Bushing means 44 includes a flange 45 abutting the end of
stub 38 and also extending radially beyond the diameter of stub
38. An hour wheel 46 with collar 47 is rotatably journaled on
the stub and held in place by flange 45.
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A center pinion 48 is pressfit onto spindle 41 after
it has been inserted in bore 39, and center wheel 49 is then
fitted onto spindle 41. Frictional slip fit of the center
wheel on the first assembly may be provided either between
spindle and center wheel or between center pinion and center
wheel faces.
OPERATION OF THE INVENTION
The movement shown in Figs. 1-3 is assembled by first
assembling and attaching the stepping motor 4 to plastic frame
1. Then the hour wheel 34 and minute pinion 30 are placed on
the dial side; minute wheel 29 and center wheel assembly added
from the back side; and lastly the center bushing is fixed to
the center spindle extension 21a on the dial side. After the
gear train is assembled, the dial 24 and hands 28, 36 are added
in the usual manner during assembly into the case. In the Fig.
4 embodiment, the integral bushing and spindle are inserted
from the dial side once the hour wheel is in place. The center
pinion and center wheel are added from the back side.
When the integrated circuit 3 is powered by the energy
cell, drive pulses rotate the driving pins 18 one-half
revolution once each minute to advance center wheel 20,
advancing first rotating assembly including the center spindle
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21 and the minute hand Z8. Speed reduction to drive the hour
hand is accomplished by the second rotating assembly,
comprising minute pinion 31, spindle 30 and minute wheel 29.
Advancement of ~inute wheel 29, when driven by pinion 22,
rotates hour wheel 34 and the attached hour hand 35.
When it is desired to reset the timepiece, stem 14 is
a~ially withdrawn so that setting pinion gear 33 engages crown
teeth 32. When time setting takes place, center wheel 20 is
locked in place by the reactive torque of the stepping motor
and slips on spindle 21 by virtue of the friction fit to allow
the spindle to turn.
The foregoing improvement allows a very simple and
thin physical arrangement of the gear train suitable for a
large diameter energy cell which covers the major portion of
the back side of the plastic frame. The use of a frame stub 23
with central bore serving as a bearing for two rotating members
and using the bushing to control end shake of both rotating
members provides a simple movement construction.
While there has been described what is considered to
be the preferred embodiment of the invention, other
modifications will become apparent to those skilled in the
art. For e~ample, while the stub 23 in its preferred mode is
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an integral part of the frame, it could also be a separate
fixed post staked or otherwise fit into the frame in the manner
shown in aforementioned United States Patent No. 4,720,644.
Other modifications will become apparent to those ski led in
the art and it is desired to secure in the appended claims all
such modifications as fall witllin the true spirit and scope of
the invention.
