U.S. patent number 3,751,899 [Application Number 05/178,229] was granted by the patent office on 1973-08-14 for tuning fork construction for electronic wrist watches.
This patent grant is currently assigned to Kabushiki Kaisha Suwa Seikosha. Invention is credited to Yuki Tsuruishi.
United States Patent |
3,751,899 |
Tsuruishi |
August 14, 1973 |
TUNING FORK CONSTRUCTION FOR ELECTRONIC WRIST WATCHES
Abstract
A tuning fork construction for electronic wrist watches
including a substantially U-shaped tuning fork oscillator and a
U-shaped magnetic circuit mounted at the end of each tine of said
tuning fork, each of said magnetic circuits including a pair of
mounting plates secured to the respective tine and carrying at
least one substantially semicircular permanent magnet. A coil is
positioned intermediate the mounting plates of both of said
magnetic circuits in the path of the flux thereof.
Inventors: |
Tsuruishi; Yuki (Suwa,
Nagano-ken, JA) |
Assignee: |
Kabushiki Kaisha Suwa Seikosha
(Tokyo, JA)
|
Family
ID: |
27551399 |
Appl.
No.: |
05/178,229 |
Filed: |
September 7, 1971 |
Foreign Application Priority Data
|
|
|
|
|
Sep 7, 1970 [JA] |
|
|
45/77732 |
Sep 30, 1970 [JA] |
|
|
45/84974 |
Oct 15, 1970 [JA] |
|
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45/01790 (UTILITY MODEL) |
Oct 19, 1970 [JA] |
|
|
45/91508 |
Oct 20, 1970 [JA] |
|
|
45/91819 |
Oct 27, 1970 [JA] |
|
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45/06113 (UTILITY MODEL) |
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Current U.S.
Class: |
368/157; 318/130;
368/167; 968/483; 968/486; 310/25; 331/156 |
Current CPC
Class: |
G04C
3/10 (20130101); G04C 3/102 (20130101); G04C
3/107 (20130101); G04C 3/069 (20130101) |
Current International
Class: |
G04C
3/06 (20060101); G04C 3/00 (20060101); G04C
3/10 (20060101); G04c 003/02 (); H02k 033/00 ();
H03b 005/36 () |
Field of
Search: |
;58/23R,23TF,23V ;84/457
;310/19,25 ;331/156,175 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wilkinson; Richard B.
Assistant Examiner: Jackmon; Edith C. Simmons
Claims
What is claimed is:
1. An electronic wrist watch comprising a substantially U-shaped
tuning fork having a pair of oscillating tines; a U-shaped magnetic
circuit mounted on an end portion of each of said tines, each of
said magnetic circuits consisting of a pair of spaced mounting
plates secured to said end portion of one of said tines and at
least two substantially semicircular permanent magnets, one being
fixed to each of the mounting plates of each of said magnetic
circuits in substantially overlapping relation in the space
therebetween, the polarity of each of said permanent magnets being
oriented so that the magnetic flux flows through each of said
magnetic circuits along a path including said mounting plates and
said end portion of the associated tine; and substantially circular
coil means positioned in the space between the mounting plates of
both of said permanent magnets in the path of the flux thereof,
said semicircular permanent magnets of each of said magnetic
circuits being aligned with their respective chords in facing
relation to the chords of the semicircular permanent magnets of the
other of said magnetic circuits, said coil means being positioned
in substantially overlapping relation to said semicircular
permanent magnets.
2. A tuning fork construction as recited in claim 1, including a
substantially circular battery mounted in said wrist watch, the
tines of said tuning fork including an arcuate region for
accomodating said substantially circular battery.
3. A tuning fork construction as recited in claim 1, including a
driving circuit having a PNP transistor and a NPN transistor, each
of said transistors having a collector, said coil means consisting
of a single coil connected between the collectors of said
transistors.
4. A tuning fork construction as recited in claim 1, including
frequency adjusting means having a frequency adjuster member having
an eccentric center of gravity and means for mounting said
frequency adjuster member on at least one tuning fork tine for
selective pivotal displacement along a plane extending
substantially parallel to the plane of oscillation of said tuning
fork.
5. A tuning fork construction as recited in claim 4, wherein one of
said frequency adjuster members is mounted on each of said tuning
fork tines.
6. A tuning fork construction as recited in claim 5, wherein said
mounting means includes a screw displaceably mounted in one of the
mounting boards of each of said magnetic circuits.
7. A tuning fork construction as recited in claim 4, wherein said
frequency adjusting means includes a plurality of spaced recesses
in the path of pivotal displacement of said frequency adjuster
member, said mounting means being adapted to selectively retain
said frequency adjuster member in engagement with one of said
recesses.
8. A tuning fork construction as recited in claim 7, wherein said
mounting means retains a frequency adjuster member on a mounting
board of each of said magnetic circuits, said recesses being formed
in the surface of said mounting board.
9. A tuning fork construction as recited in claim 7, wherein said
mounting means includes spring means for biasing said frequency
adjuster member in a selected one of said recesses.
10. A tuning fork construction as recited in claim 1, including a
compensation plate member positioned in the magnetic field of the
permanent magnets of both of said magnetic circuits, said
compensating plate member being formed of a magnetic material, said
compensating plate member and said permanent magnet attracting each
other.
11. A timepiece as recited in claim 10, including a frequency
regulator member pivotably mounted on one of the mounting plates of
each of said magnetic circuits for selective pivoting in a plane
extending substantially parallel to the plane of oscillation of
said tuning fork.
12. A tuning fork construction as recited in claim 1, including a
compensating plate member positioned adjacent said oscillating
tines of said tuning fork, said compensating plate member being
formed of a permanent magnet, said permanent magnet and said
oscillating tines attracting each other.
13. A tuning fork construction as recited in claim 12, including a
frequency regulator member pivotably mounted on a mounting plate of
each of said magnetic circuits for selective pivotable displacement
in a plate extending substantially parallel to the plate of
oscillation of said tuning fork.
14. A tuning fork construction as recited in claim 1, wherein each
of said mounting plates carrying one of said permanent magnets is
formed with a rim projecting toward the other magnetic plate in its
magnetic circuit on the side thereof spaced from its associated
tine, said permanent magnet being mounted adjacent said projecting
rim and being spaced from said side of said mounting plate by said
rim.
15. A tuning fork construction as recited in claim 14, the
thickness of the region of said mounting plate including said rim
being greater than the thickness of the region of said mounting
plate against which said permanent magnet is secured, said rim
projecting beyond said last-mentioned region of said mounting plate
by about one-half of the thickness of said permanent magnets.
16. A tuning fork construction as recited in claim 15, wherein the
distance between said permanent magnet and the tine associated
therewith is greater than the width of the space in the path of the
magnetic flux in which said coil means is inserted.
17. A tuning fork construction as recited in claim 16, wherein said
distance between the tine of said tuning fork and said permanent
magnet is more than one and one-half times the width of said
space.
18. A tuning fork construction as recited in claim 17, wherein the
width of said mounting plate in the region intermediate said tine
and said permanent magnet less the width of said mounting plate in
the region in which said permanent magnet is secured thereto is
less than one-third of the thickness of said permanent magnet.
19. A tuning fork construction as recited in claim 14, wherein the
distance between the tine of the tuning fork and the permanent
magnet of each magnetic circuit is more than one and one-half times
the width of the space in the flux path of said magnetic circuit
within which said coil means is received.
20. A tuning fork construction as recited in claim 14, wherein the
thickness of said mounting plate in the region intermediate said
tine and said permanent magnet less the thickness of said mounting
plate in the region at which said permanent magnet is secured
thereto is less than one third of the thickness of said permanent
magnet.
21. A tuning fork construction as recited in claim 1, wherein each
of said magnetic plates and the associated tines of said tuning
fork are formed with apertures therethrough in registration, said
tuning fork construction including pins extending through said
apertures for securing said mounting plates and tines together.
22. A tuning fork construction as recited in claim 1, wherein each
of said pairs of mounting plates are formed with further apertures
therethrough in registration with each other but out of
registration with said tines, and including a further pin receives
in said further apertures, said further pin being formed with a
central region of increased thickness dimensioned to maintain said
mounting plates in spaced substantially parallel relation.
23. A tuning fork construction as recited in claim 22, wherein said
mounting plates are formed with a region projecting beyond said
tines on a side thereof opposed from said permanent magnets, said
further apertures being located in said projecting region.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to wrist watches having tuning
forks, wherein the tuning fork is utilized as a time standard and
the oscillation of the tuning fork is converted into the rotary
motion of a ratchet wheel and transmitted to the index mechanism of
the watch.
The conventional tuning fork construction for electronic wrist
watches incorporates a magnetic circuit formed with a cylindrical
permanent magnet disposed in a cup and a hollow cylindrical coil
inserted in the space between said cup and magnet. The magnetic
circuits of the two lines of the tuning fork are each closed in
order that they may not affect each other, and cause fluctuation in
frequency. However, the shape of such cups is substantially
cylindrical, and such having fork constructions cannot be utilized
for thin-type wrist watches. Further, such prior art constructions
proved expensive to maintain and assemble. By providing the
U-shaped magnetic circuits according to the invention, and by
providing means for adjusting the frequency of the tuning fork, the
foregoing deficiencies in the prior art have been avoided.
SUMMARY OF THE INVENTION
Generally speaking, in accordance with the invention, a tuning fork
construction for electronic wrist watches is provided including a
substantially U-shaped tuning fork type oscillator, a U-shaped
magnetic circuit associated with each tine of said tuning fork,
each including a pair of spaced overlapping mounting plates mounted
on the end of each tine, and carrying at least one substantially
semicircular permanent magnet, and a coil positioned in the space
between said mounting plates in the path of the flux of said
magnetic circuit, said permanent magnets being oriented to produce
a flux which follows a path including the mounting plates and the
end of the tine associated therewith.
A pair of semicircular permanent magnets may be mounted
respectively on each mounting plate of each of said magnetic
circuits in spaced relation, and said coil may consist of a single
circular coil positioned in the space between both pairs of
permanent magnets in overlapping relation therewith. The end
portions of the tines of said tuning fork may be substantially
arcuate to permit accommodation of a substantially circular battery
within said watch.
Said wrist watch may include a driving circuit including a pair of
transistors of different polarities, one of the two terminals of
said coil being connected to the collector of each of said
transistors.
A frequency adjusting device may be provided consisting of an
adjustor member having an eccentric center of gravity and pivotably
mounted on at least one of said mounting plates of said magnetic
circuits for selective pivotable positioning in the plane of
vibration of said tuning fork. The surface of said mounting board
may be provided with a plurality of recesses, said adjustor member
being provided with means for registration with said recesses for
the selective positioning of said adjustor member. Further
frequency regulation may be provided by including a member formed
of magnetic material positioned in the magnetic field of the
permanent magnets of each of said magnetic circuits for attraction
by said permanent magnets, or providing a permanent magnet near the
oscillating tines of said tuning fork for attracting said
oscillating tines. Further improvements in the operation of the
tuning fork according to the invention may be achieved by
controlling the dimensions and positioning of the components of the
magnetic circuit according to the invention.
A pair of mounting plates of the magnetic circuits according to the
invention may be secured to the respective tines by means of one or
more posts extending through said mounting plates and the end of
said tine. A further post may be provided in a region of said
mounting plates out of overlapping relation with said tine, said
further post being providd with a region of increased diameter for
defining a spacer for supporting said mounting plates in the
desired spaced relation.
Accordingly, it is an object of this invention to provide a wrist
watch having a tuning fork designed for ease of assembly and mass
production, while being thin, thereby providing a relatively
inexpensive thin wrist watch.
Another object of the invention is to provide a tuning fork
construction for wrist watches provided with an easily regulated
frequency adjusting arrangement, and wherein the frequency is
stable even though the amplitude of the tuning fork is changed by
reduction of battery voltage or fluctuation of load.
Still other objects and advantages of the invention will in part be
obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction,
combination of elements, and arrangement of parts which will be
exemplified in the construction hereinafter set forth, and the
scope of the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the invention, reference is had to
the following description taken in connection with the accompanying
drawings, in which:
FIG. 1 is a top plan view of a wrist watch having the tuning fork
construction according to the invention;
FIG. 2 is an enlarged top plan view of the end portion of one tine
of the tuning fork of FIG. 1;
FIG. 3 is a sectional view taken along line A--A' of FIG. 2;
FIG. 4 is a top plan view of the frame of the coil of the
embodiment of FIG. 1;
FIG. 5 is a circuit diagram of a driving circuit for use with the
wrist watch having the tuning fork according to the invention;
FIG. 6 is a circuit diagram of another embodiment of the driving
circuit for use with the tuning fork construction according to the
invention;
FIG. 7 is a top plan view of a second embodiment of the tuning fork
construction according to the invention;
FIG. 8 is a sectional view taken along line A.sub.1 -A.sub.2
-A.sub.3 of FIG. 7;
FIG. 9 is a partial enlarged side elevational view of the tuning
fork of FIG. 7;
FIG. 10 is an enlarged partial perspective view of the mounting
board of the magnetic circuit of the tuning fork embodiment of FIG.
7;
FIG. 11 is a side elevational view of another embodiment of the
frequency adjusting mechanism according to the invention;
FIG. 12 is a top elevational view of a third embodiment of the
tuning fork construction according to the invention;
FIG. 13 is a graph showing the amplitude and frequency
characteristics of the tuning fork construction of FIG. 12;
FIG. 14 is a sectional view taken across the magnetic circuit of
the tuning fork construction according to the invention showing the
dimensional relationship between the portions thereof;
FIG. 15 is a partial top plan view showing still a further
embodiment of the tuning fork construction according to the
invention; and
FIG. 16 is a partial perspective view of the embodiment of FIG.
15.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to FIGS. 1 - 3, the wrist watch according to the
invention depicted includes a voltage source of direct current 1, a
tuning fork 2, a coil 3, mounting plates 4, a frame 5 for
supporting coil 3, a ratchet wheel 6, and a block 7 incorporating
the driving circuit for said coil connected by a terminal 8 to the
negative pole of battery 1 and by terminal 9 to the coil 3. The
diameter of the battery 1 is generally somewhat smaller than the
radius of the movement of the wrist watch, and the tuning fork 2 is
provided with arcuate tines in order to accommodate the
substantially circular battery 1. The ends of each tine of said
tuning fork is connected to a pair of mounting plates 4a and 4b by
means of pins 10 as shown in FIG. 2. Said mounting plates are
maintained in spaced overlapping relation. A permanent magnet 11a
and 11b is mounted respectively on the inner surface of said
mounting plates 4a and 4b. The polarities of permanent magnets 11a
and 11b are disposed to form a closed magnetic circuit wherein the
magnetic flux passes through the space between the magnets, through
mounting plate 4b, through the intermediate portion of the tine of
tuning fork 2, through mounting plate 4a, and back to said
permanent magnet. If desired, only one permanent magnet may be
provided in the magnetic circuit associated with each tine, mounted
either on the upper or lower mounting plate.
The coil 3 is positioned in the space defined by permanent magnets
11a and 11b. Both the tines and the magnetic circuits associated
therewith are formed symetrically for balanced oscillation. Coil 3
is fixed to frame 5, shown more particularly in FIG. 4, and the
frame and coil assembly is inserted in the space at the end of the
tuning fork between the mounting plate 4, leaving a proper spacing
so as to avoid contact between said coil and the tuning fork and
the components of the magnetic circuit. Frame 5 is then fixed to
the plate of the watch. Conductive portions 12 and 13 are formed in
the surface of frame 5 in order to receive the lead wires of coil
3, and to provide a conductive path between the driving circuit 7
and the battery 1. Frame 5 is preferably formed from a printed
circuit board having a thin copper plate deposited thereon, the
pattern of the desired conductive surface being defined in the thin
copper plate by removing portions of said plate utilizing an
etching reagent.
Referring now to FIG. 5, one embodiment of a driving circuit
utilized to drive coil 3 is depicted, the electronic components of
said driving circuit being being preferably mounted in block 7 of
the watch according to the invention.
Said circuit consists of a battery 14 which could correspond to
battery 1, a coil 15, which could correspond to coil 3, NPN type
transistor 16, a PNP transistor 17 having its emitter connected to
the emitter of transistor 16, a base resistor 18 connected between
the base and collector of transistor 16, a trigger condensor
connected between the base of transistor 16 and one end of coil 15,
a variable resistor 20 connected between said end of coil 15 and
the collector of transistor 17 for controlling the amplitude of
oscillation, and a base resistor 21 connected between the base of
transistor 17 and the other end of coil 15. Battery 14 is connected
between said other end of coil 15 and the collector of transistor
16. This circuit is known as an astable locking oscillator. Other
driving circuits utilizing a single coil may be utilized, and the
tuning fork arrangement according to the invention is not limited
to a particular driving circuit. A second embodiment of a circuit
suitable for driving the tuning fork according to the invention is
depicted in FIG. 6. Said circuit consists of a battery 22, a PNP
type transistor 23, a NPN type transistor 24, a coil 25 which would
correspond to coil 4 connected in series with variable resistor 30
between the collectors of transistors 23 and 24, a trigger
condenser 26 connected between the base of transistor 24 and the
collector of transistor 23, a base bias resistor 27 connected in
parallel with trigger condenser 26, a base bias resistor 28
connected between the base of transistor 23 and the collector of
transistor 24, and a decoupling condenser 29 connected between the
base and collector of transistor 23. Decoupling condensor 29 serves
to prevent the oscillation of harmonic waves, while variable
resistor 30 is utilized for regulating the amplitude of
oscillation. The circuit of FIG. 6 is particularly adapted for
driving the tuning fork according to the invention through the use
of a single coil. Variable resistor 30 may be dispensed with if not
required.
It is frequently required to provide a frequency adjuster device
for a time keeping vibrator such as the mechanical,
electro-magnetically driven tuning fork according to the invention.
Three approaches may be followed to regulate the frequency of a
tuning fork. First, the equivalent length of the vibrating tines
may be controlled. The second and third methods involve the
regulation of the elasticity of the tuning fork, either by a
mechanical or a magnetic method. The regulation of the equivalent
length of the vibrating tines may be performed by turning a
rotatable mass which has an eccentric center of gravity and is
placed on the free end of the respective times. In the art, such
frequency adjusters have taken the form of an adjusting member
pivoted along an axis parallel to the vibrating plane of the tuning
fork. Such an adjusting member is rotated in the vertical direction
relative to the watch crystal, so that a large adjusting member
cannot be utilized.
Referring now to FIG. 7, a tuning fork construction according to
the invention is depicted having a frequency adjusting member
provided with a pivot extending vertically relative to the vibrator
plane. As such, it is particularly useful in thin wrist watches,
since the mass and the eccentricity of the adjuster may be
increased without affecting the thickness of the watch. The
provision of the frequency adjusting mechanism depicted permits the
manufacture of the tuning fork with lower tolerances. In the
embodiment of FIGS. 7 and 8, the tuning fork assembly includes a
tuning fork 31, a coil support 32, a screw 33 for fixing coil
support 32 to the plate of the watch (not shown), a pair of
mounting boards 35 secured to each tine of tuning fork 31 in spaced
relation, a permanent magnet 36 mounted on the inner surface of
each of said mounting boards formed of substantially semicircular
shape, pins 37 for fixing each of said pairs of mounting boards 35
on tuning fork 31, and a frequency adjuster member 38 mounted on
the upper surface of each of the upper mounting boards 35 by means
of a screw 39.
As shown in FIG. 8, mounting boards 35a and 35b are mounted at the
free end of one tine of tuning fork 31, while mounting boards 35c
and 35d are mounted on the free end of the other tine of said
tuning fork. Permanent magnets 36a, 36b, 36c, and 36d are mounted
respectively on the mounting boards 35a, 35b, 35c, and 35d. The
construction of the embodiment of FIG. 7 is substantially similar
to the embodiment of FIG. 1, except with regard to the frequency
adjustment arrangement. A plurality of spaced grooves 40 are formed
in the upper surface of mounting plates 35a and 35c, said grooves
extending radially relative to an axis defined by screw 39. As more
particularly shown in FIG. 9, said grooves cooperate with the end
41 of the adjuster member 39 which project into said groove for the
purpose of fixing the adjuster member 38 in any one of a plurality
of preselected positions. The provision of the cooperative
engagement between the adjuster member and the mounting plates
prevents the accidental displacement of the adjuster member due to
the motion of the wearer's arm, and further permits accurate and
discrete adjustment of the frequency of the tuning fork.
Tuning fork 1 is preferably formed of an invariable elastic
material, and formed with tines having an arcuate end portion for
the purpose of accomodating a battery. The flux path and operation
of the embodiment of FIG. 7 is substantially identical to that of
the embodiment of FIG. 1.
The narrower the spacing between two neighbouring grooves 10, the
more accurate the regulation which may be performed. It is possible
to determine the precise variation in frequency with each
incremental step of displacement of the adjuster member 38 relative
to the grooves 40, for the purposes of calibrating frequency
adjustment, and for the purposes of permitting such frequency
adjustment without resorting to special measuring instruments. In
the embodiment of FIG. 10, the mounting boards 42 are formed with a
fan-shaped array of grooves 43, wherein said grooves are defined by
a sawtooth wave. Apertures 44 are provided in mounting board 42 for
the purposes of pinning the mounting board to the tine of the
tuning fork, while aperture 45 is provided for fixing the adjusting
member to the mounting boards. The embodiment of FIG. 10 offers the
minimum spacing between grooves.
Referring now to FIG. 11, another embodiment of the frequency
adjustment mechanism is depicted, wherein mounting board 46 has an
elastic plate 48 secured thereto by means of fixing screw 47. A
frequency adjuster mass 49 is fixed, as by welding, to the end of
elastic plate 48, said elastic plate serving to bias said mass
firmly within a recess 50 in the surface of mounting board 46, to
further contribute to the resistance of the mechanism to shocks. In
both this embodiment and the embodiment of FIGS. 8 and 9,
adjustment is effected by opening the screw 39 or 47 and pivoting
the adjusting member.
Referring now to FIG. 12, still another embodiment of the tuning
fork construction according to the invention is depicted, wherein
tuning fork 51 has a pair of mounting plates 55 secured to each
tine thereof by means of pins 57, said pins being inserted in
apertures extending through said mounting plates and tuning fork
tines and being caulked at both ends for retention therein. A
permanent magnet 56 is secured to the inner surface of each of the
mounting plates 55 while a regulator member 58 is pivotally mounted
on each of the upper mounting plates by means of a screw 59. A coil
54 is disposed in the space between the permanent magnets 56 and is
carried by a coil frame 52 fixing the plate of the watch by screws
53. The structure, flux path and operation of the embodiment of
FIG. 12 is substantially identical to the embodiments of FIGS. 1
and 7, and FIG. 8 represents a cross section taken along line
A.sub.1 -A.sub.2 -A.sub.3 of FIG. 12. Referring to FIG. 8, the
permanent magnets 36a and 36c have poles which repel each other and
in the embodiment of FIG. 12, a magnetic plate 60 is inserted
between these two permanent magnets for the purposes of
compensation, said plates being fixed to the plate of the watch by
means of screws 61. Since the polarities of the permanent magnets
on the two lines of the tuning fork 51 repel each other, the rate
of isochronism is increased when the amplitude of oscillation is
increased.
Referring to FIG. 13, which shows a plot of frequency f vs.
amplitude A, curve 62 shows the synchronous curve where the
compensation plate 60 is not provided. If the end portion of the
tuning fork is made small in size, and powerful permanent magnets
are used, the slope of the synchronous curve increases, and a high
precision watch utilizing a tuning fork cannot be achieved.
The synchronous curve 63 shows the effect of compensation plate 10.
Since the permanent magnets attract one another and the
compensation plate 60, the synchronous curve 63 depicted in FIG. 13
is such that the amplitude increases as frequency decreases. Curve
64 shows the compensated synchronous curve, which has only a slight
upward curve. The compensation plate 60 furthers the leakage flux
of the permanent magnets so non-compensation is desirable over
overcompensation. The compensation plate 60 can also be formed of a
permanent magnet. When so formed, said plate may not be provided
between the permanent magnets 36a and 36c, because usually, the
tuning fork is made of a material having a constant temperature
coefficient of elasticity. Such material is generally magnetic, so
that the permanent magnet compensation plate may be disposed near
the tines of fork 51 and can attract said tine. In such an
embodiment, the same compensating effect can be expected.
Where the embodiment of FIG. 12 is utilized, fluctuations in
amplitude of oscillation due to reduction in battery voltage,
temperature change or load fluctuation have only a slight effect on
frequency, thereby insuring the reliability of the time piece over
a long period.
One problem with the tuning fork construction according to the
invention is that the magnetic leakage of the permanent magnets of
the magnetic circuit is large as compared with the prior art cup
constructions. This increased magnetic leakage results in the
deterioration of the isochronism. Thus, if the amplitude of the
tuning fork is increased, the frequency becomes high. Such magnetic
leakage can be minimized if the components of the magnetic circuit
are dimensioned as illustrated in FIG. 14, which shows a cross
section through the magnetic circuit of one tine of the tuning fork
construction according to the invention. Said embodiment consists
of a pair of mounting plates 65c and 65d secured to a tine of
tuning fork 67, and respectively carrying permanent magnets 66c and
66d. Each of the permanent magnets is mounted in a recess in the
inner surface of the mounting plates, each of said mounting plates
being formed with a rim projecting toward the facing mounting
plates on the side thereof adjacent the other tine of said
permanent magnet. Thus, said projecting rims serve to partially
block the permanent magnets associated with each tine from the
permanent magnets associated with the other tine. Said projecting
rim extends about one-half of the thickness of the permanent
magnet, the width of said rim, and therefore the spacing between
the permanent magnet and the inner edge of the mounting plate is
defined by the dimension f.
The thickness of the mounting plate in the region intermediate the
permanent magnet and the region engaging the tine of tuning fork 67
is of a thickness a, while the region of said mounting plates
adjacent the recess receiving permanent magnets 66 is of a
thickness b. It is preferred that the thickness a be not much
larger than the thickness b, in order to reduce the magnetic flux
paths in the magnetic circuit. Accordingly, it is preferred that
the value of dimension a less the dimension b be less than
one-third of the thickness of the permanent magnet. For the same
reason, it is preferred that the distance d between the tuning fork
tine and the permanent magnet is larger than the distance e between
the permanent magnets. At the least, the distance d should be more
than one and one-half times the value of the distance e.
Isochronism is substantially improved if the distance f between the
rim of the mounting plate and the permanent magnet is large.
However, it is structurally difficult to make this dimension
extremely large, so the value of the dimension f is selected by
taking into account the distance e between the magnets or the
isochronous characteristics. If the width of the projecting rim, as
indicated by the difference between the value of the dimension c
and the value of the dimension b, is about one-half of the
thickness of the permanent magnet, then the repulsion of the
respective permanent magnets associated with each tine caused by
the leakage flux is reduced, and the isochronism of the tuning fork
is improved. Similar dimensional relations would apply where only
one permanent magnet is mounted on each of the magnetic circuits
associated with each tine.
As noted above, the mounting plates are secured to the respective
tines by means of pins which are retained in position by caulking
on the opposed ends thereof. This approach offers a substantial
advantage over the prior art wherein the magnetic circuit cups were
secured to the tuning fork by welding as by silver solder, a
process which proved difficult and, due to the high-heat treatment
involved, was found to adversely affect the characteristics of the
tuning fork as a vibrator. Referring now to FIGS. 15 and 16, a
further embodiment of the mounting plates according to the
invention is depicted, wherein said mounting plates are provided
with projecting portions which extend beyond the outside of the
tines of the tuning fork. The mounting plates 70 are secured by
pins 71 and 72 to said tines. A further pin 73 extends through the
projecting portions of the mounting plates 70, said further pin
being provided with a central region 74 of increased diameter which
serves to maintain the mounting plates 70 in spaced parallel
relation. The provision of the additional pin 73 with the thicker
region 74 adds substantial stabilaJy to the mounting of the
mounting plates 70 to the relatively thin tines.
A wrist watch having the tuning fork construction according to the
invention offers substantial advantages over the prior art tuning
fork wrist watches. Firstly, since the coil and coil frame are
inserted in the space between the mounting plates from the end of
the tuning fork, the coil can be mounted and removed without
displacing the tuning fork for the purposes of assembly and
disassembly, thereby permitting rapid and automatic assembly.
Secondly, the magnetic field generated by the permanent magnets
covers substantially the whole coil, so that the strength of the
magnetic field on the surface of the coil is substantially uniform,
and such strength can be increased, so that sufficient flux density
can be obtained by a relatively thin magnet. The turns of the coil
can be reduced by about one-third as compared with a conventional
coil, thereby further contributing to the production of a thin
wrist watch.
Thirdly, a single coil having only two terminals is utilized for
both detecting and driving, so that the winding of the coil can be
quickly performed, an advantage where mass production techniques
are utilized. The prior art arrangements utilize two coils, only
one being required in the arrangement according to the
invention.
Fourthly, a portion of the tine of the tuning fork forms a part of
the magnetic path in the respective magnetic circuits according to
the invention. For this reason, it is not necessary to weld the
tuning fork and the end portion of the tine by means of silver
solder, as in the prior art arrangements, said end portion being
readily secured by means of a pin or a screw in the arrangement
according to the invention. As noted above, the tuning fork is
preferably formed of a material having constant elasticity in the
face of temperature changes, in order to maintain the frequency of
the tuning fork at a constant level. It is not desirable to heat
treat such material, so that the pinning arrangement according to
the invention, as described above, avoids an otherwise undesirable
potential damage to the tuning fork present in the prior art
arrangement.
Accordingly, a wrist watch having the tuning fork construction
according to the invention is particularly adapted for mass
production, and a low-priced thin-type wrist watch utilizing a
tuning fork as a time standard may be produced.
It will thus be seen that the objects set forth above, among those
made apparent from the preceding description, are efficiently
attained and, since certain changes may be made in the above
construction without departing from the spirit and scope of the
invention, it is intended that all matter contained in the above
description or shown in the accompanying drawings shall be
interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended
to cover all of the generic and specific features of the invention
herein described, and all statements of the scope of the invention
which, as a matter of language, might be said to fall
therebetween.
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