TECHNICAL FIELD
[0001] The present invention relates to a analog electronic timepiece for indicating time
using bands, more specifically, to a technology for further reducing power consumption
of the analog electronic timepiece and for diversifying the hands.
BACKGROUND TECHNOLOGY
[0002] In a time indicating system of a timepiece (watch or clock), in addition to accuracy,
decoration is also required, and analog indication is superior due to its indication
quality and its possible variety in design. The timepiece in which a step motor is
used for an actuator is widespread.
[0003] Fig. 5 is a schematic perspective view of a conventional analog electronic timepiece
showing a state in which force is transmitted from a step motor to bands via train
wheels. In a standard three-hand timepiece, as shown in Fig. 5, a rotor 1a of a step
motor 1, a fifth wheel 2, a second wheel 3, a third wheel 4, a center wheel 5, a minute
wheel 6, and a hour wheel 7 are linked together in due order via pinions 11 to 16.
Therewith, a second hand 8 which is integrated with the second wheel 3 and the pinion
13, a minute had 9 integrated with the center wheel 5 and the pinion 15, and an hour
hand 10 integrated with the hour wheel 7 perform predetermined traveling motions.
It is noted that the second hand 8, the minute hand 9 and the hour hand 10 are actually
fitted to one another to rotate on the same axis, and are shown spread out for the
sake of clarity.
[0004] The step motor 1 comprised of the rotor 1a, a stator 1b and a coil 1c requires a
holding energy for preventing each of hands 8, 9, and 10 from being subject to a hand-skip
phenomenon on an external impact, in addition to a driving energy required for driving
each of hands 8, 9, and 10. The step motor 1 is designed in such a manner that both
energy values meet the timepiece requirements.
[0005] In designing a conventional step motor for a timepiece, a required holding energy
value according to the hands in use is determined first, and then a motor is designed
in such a manner to satisfy the above value, in order to meet the timepiece requirements.
Thereafter, suitable driving conditions are set within the above range.
[0006] The driving energy value is thus not conclusively optimized. Further, if only normal
movement of hands is necessary, it will be possible to realize the step movement of
hands with a driving energy value smaller than those required presently.
[0007] Normallly, holding energy always exists in a step motor as magnetic potential (resistance
force to moving from a still point), and only portions of energy exceeding the magnetic
potential out of an input energy is effective kinetic energy. Therefore, reduction
of the holding energy value seems to be effective to lessen the power consumption,
but from the viewpoint of holding bids as described above, the holding energy value
can not be sufficiently reduced in the conventional analog electronic timepiece.
[0008] The driving energy value in the description does not mean the so-called whole given
energy value but the effective energy value (the resultant value obtained by subtracting
the holding energy value from the whole energy value) which is required when a hand
non-steadily rotates a certain angle in a set period of time. Without the driving
force exceeding the above value, the expected rotary motion can not be obtained.
[0009] The holding energy value means the energy value which is required for holding a hand
so as to prevent a hand-skip phenomenon on an external impact, which is unconditionally
determined from the step motor requirements.
[0010] In the recent electronic timepiece, an inconvenience of replacement of batteries
once per several years is pointed out, it is desired that replacement of batteries
is made unnecessary. As a measure to that, increase in capacity of a battery and reduction
in power consumption are considered, but a large-size battery can not be used for
a wristwatch due to limitation of outer dimensions. Furthermore, the electro-mechanical
conversion efficiency of the step motor itself already comes to a limit thereof, therefore
a more drastic reduction of the power consumption can not be expected using conventional
methods.
[0011] In the conventional electronic timepiece, as described above, the value of the holding
energy is set to be larger than that of the disturbance energy that occurs at the
hand, part by an external impact, in order to prevent a hand-skip phenomenon. Which
means, conversely, that the hand can not be held when the disturbance energy value
exceeds the holding energy value.
[0012] The disturbance energy value, which means the magnitude of an external impact, relates
to the magnitude of inertial moment (inertia) with consideration of imbalance caused
by a degree of unbalanced moment of the rotary body including hands and train wheels,
with respect to the rotational axis thereof.
[0013] Concerning with bands, since the shape of the hand is restricted, the disturbance
energy value is greatly influenced by the magnitude of inertial moment. For instance,
if hands are made larger or different in shape from what should be, giving priority
to visual design, a problem would arise that the inertial moment increases according
to the amount of imbalance being larger, thereby the disturbance energy value easily
exceeds the holding energy value.
[0014] Under the present circumstances as described above, it is a serious problem to find
bow to lessen the power consumption of the electronic timepiece and to realize a system
in which replacement of batteries is made unnecessary. In order to lessen the power
consumption, the aforesaid holding energy needs to be reduced.
[0015] In accomplishing that purpose, it is a problem to prevent a hand-skip phenomenon
from occurring even when the holding energy value of the step motor is small, while
obtaining flexibility of designs by eliminating limiting factors on design of the
hand.
[0016] An object of the present invention is to solve the above problems and to achieve
a further reduction in power consumption of the electronic timepiece by reducing the
aforementioned holding energy value, while satisfying the timepiece requirements.
[0017] Another object is to obtain further flexibility of designs by eliminating limiting
factors on bands to prevent a hand-skip phenomenon.
DISCLOSURE OF THE INVENTION
[0018] This invention is structured as follows, to achieve the aforesaid objects in an analog
electronic timepiece having: hands for indicating time; a step motor having a holding
energy for holding the hands while standing still and generating a driving energy
which exceeds the holding energy while driving the hands; and train wheels for transmitting
the movement of the step motor to the hands.
[0019] In order to lessen a moment of the whole rotary body, a weight is added at least
to apart of the rotary body including the hands and the train wheels where an external
impact causes a disturbance energy which is larger than the holding energy value possessed
by the step motor, so that the disturbance energy value which the above step motor
receives is made smaller than the above holding energy value.
[0020] Alternatively, a thin part, a through hole, or a notch may be formed, to lessen the
moment of the whole rotary body, at least in a part of the rotary body.
[0021] Furthermore, at least a part of the rotary members of the above rotary body may be
formed by a combination of members with different specific gravities from each other,
to lessen the moment of the whole rotary body.
[0022] In these analog electronic timepieces, M and I are preferably set to satisfy the
relation below:

where a moment possessed by the rotary body is M, a hand equivalent inertial moment
from the hand to the rotor of the step motor via the train wheels is I, a speed of
translational motion of the timepiece by receiving an external impact is v, and a
holding energy possessed by the step motor is Ep.
[0023] Alternatively, a reverse transmission preventing gear may be provided at a part of
the train wheels in relation to the rotary body, in order to prevent transmission
of the disturbance energy to the step motor.
[0024] The disturbance energy value in the description means the rotational energy value
that occurs at the rotary body comprised of a hand, gears, pinions, and shafts fitting
to the band when receiving an external impact. The disturbance energy value is a value
related to imbalance caused by a degree of the unbalanced moment possessed by the
rotary body and the magnitude of its inertial moment.
BRIEF DESCRIPTION OF DRAWINGS
[0025]
Fig. 1 is a schematic sectional view of a three-hand analog electronic timepiece for
explaining an embodiment of the present invention;
Fig. 2 is a graph showing relations between the values of disturbance energy occurring
at second hands when two types of hammer tests are conducted upon each of samples
shown in Table 2, and the values of holding energy possessed by the respective step
motors;
Fig. 3 is an explanatory view of normal rotational transmission motion by a reverse
transmission preventing gear which is provided at a part of train wheels for rotation
of hands in another embodiment of the present invention;
Fig. 4 is also an explanatory view of reverse transmission preventing motion of the
same as above; and
Fig. 5 is a schematic perspective view of a conventional analog electronic timepiece
showing a state in which torque is transmitted from a step motor to hands via train
wheels.
BEST MODE FOR CARRYING OUT THE INVENTION
[0026] The best mode for embodying the present invention will be described hereinafter with
reference to the accompanying drawings.
[0027] Fig. 1 is a schematic sectional view of a three-hand analog electronic timepiece
for explaining an embodiment of the present invention, and essential components are
the same as those in the conventional electronic timepiece shown in Fig. 5. Thus,
the same numerals and symbols are given to the same portions in Fig.1 as those in
Fig. 5.
[0028] More specifically, focusing attention on motion of a second hand 8, which is united
by a second wheel 3 and a second hand shaft 18, the second hand 8 performs step movement
by linking a rotor 1a of a step motor 1, a fifth wheel 2, and the second wheel 3 together
in due order via pinions 11, 12. The description of third wheels 4 and thereafter
will be omitted, and a minute hand 9 and an hour hand 10 are the same as those shown
in Fig.5.
[0029] Numeral 21 shows a main plate, numeral 22 shows a train wheel bridge, and numeral
23 shows a dial in Fig. 1. The rotor 1a of the step motor 1, the fifth wheel 2, the
second wheel 3, third wheel 4, a center wheel 5, and a minute wheel 6 (see Fig. 5)
are respectively pivotally supported between the main plate 21 and the train wheel
bridge 22.
[0030] An hour wheel 7 is supported between the main plate 21 and the dial 23 which is provided
above the main plate 21, and is rotatably fitted outside a minute hand shalt 24 in
which the second hand shaft 18 is rotatably inserted.
[0031] When this electronic timepiece receives an external impact, the second hand 8 causes
disturbance energy and tends to rotate. The magnitude of the disturbance energy relates
both to imbalance caused by a degree of the unbalanced moment possessed by the second
band 8 to the second hand shaft 18, and to the magnitude of inertial moment (inertia)
possessed by a rotary body which is comprised of the second hand 8 and train wheels
from the rotor 1a of the step motor 1 to the second wheel 3 via the fifth wheel 2.
[0032] Henceforth, in this embodiment, by adding a weight 20 having a certain mass to a
short hand part 8b that is on the opposite side of a indicating part 8a with respect
to the second hand shaft 18 of the second hand 8, the amount of unbalanced moment
of the second had 8 against the second hand shaft 18 is decreased by a counterbalance
system, resulting in a reduction of the moment as of the whole rotary body, consequently,
the value of a disturbance energy that occurs at the rotary body can be decreased.
Therefore, if the holding energy value of the step motor 1 is set to be small, it
becomes possible that the value of the disturbance energy, which the step motor 1
receives, is made smaller than that of the above holding energy.
[0033] For that purpose, first, in a conventional electronic timepiece as shown in Fig.
5, the respective moving conditions of components of the driving mechanism with mechanical
movements are checked to estimate the generated energy values.
[0034] In the driving mechanism of the analog electronic timepiece which is comprised of
a step motor 1, train wheels from a fifth wheel 2 to an hour wheel 7, and hands 8,
9, 10, each rotational movement information of the respective components is obtained
as time information of its rotation angle. The angular acceleration derived from the
above time information is multiplied by the respective inertial moments of the components
to measure the produced torque value at a certain time while each of components is
moving.
[0035] Of the above, the third wheel 4 and after have large reduction gear ratios, which
is supposed to have minimal contributions to the driving energy. Hereinafter, attention
is thus focused on motions of each component of a rotor 1a of the step motor 1 to
the second hand 8 via the fifth wheel 2 and the second wheel 3 which are linked together.
[0036] The amount of driving energy used when each component moves is respectively calculated
from a relation between the produced torque value while each component is moving measured
by the aforementioned method and its rotation angle.
[0037] Next, the correlation is examined between the amounts of respective driving energies
in the rotor 1a, the fifth wheel 2, the second wheel 3, and the second hand 8 and
the respective inertial moments thereof. As a result, it is found that a idea of "rotor
equivalent inertial moment" can be employed to explain the amounts of energies that
are distributed to the respective components.
[0038] "Equivalent inertial moment" in this description means the idea that the inertial
moments (inertia) with consideration of differences of the respective rotation speeds
are added on one point to estimate a motion as of the whole rotary mechanism, since
the step motor, the train wheels and the hands are all linked together to rotate as
described above in a standard analog electronic timepiece. The idea is referred to
as "rotor equivalent inertia" from the rotor side, and "had equivalent inertia" from
the hand side.
[0039] In other words, the relation between the whole rotary mechanism and the rotor equivalent
inertial moments of the respective components is expressed by the following mathematical
expression.

[0040] In this expression, J represents a rotor equivalent inertial moment of the whole
rotary mechanism, ad Jr, J5, J4, and Js respectively represent inertial moments of
the rotor, the fifth wheel, the second wheel, and the second hand. Each of numerical
values of denominators in each term in this expression of "36" is the squared reduction
gear ratio of the fifth wheel to the rotor, ad of "900" is the squared reduction gear
ratio of the second wheel to the rotor.
[0041] Since the values of the squared reduction gear ratios of the third wheel ad thereafter
jump further, it is clear that contributions of the third wheel and thereafter to
the rotor equivalent inertial moment are negligible.
[0042] When reduction in power consumption of a gents' watch with a second band is considered
as an example, the two following facts are observed, since the driving energies of
the respective components are expressed as the expression (1).
[0043] One is that the smaller the rotor equivalent inertial moment J as of the whole rotary
mechanism is, the more the whole driving energy decreases. The other is that contributions
of the respective components to the rotor equivalent inertial moment J are different
from one another, and a variation in inertial moment Js of the hand has little influence
on a variation of J.
[0044] In other words, focusing on driving of the second hand, the facts show that when
the driving energy value is more than a designed value, the smaller the rotor equivalent
inertial moment J possessed by the components is, the more the whole driving energy
can lessen.
[0045] Next, the holding energy values possessed by various step motors are estimated. Conventionally,
a balance weight is hung from the second hand part and then a holding torque is measured
from the weight with which the second hand can start to move, on the basis of which
the holding energy value is estimated. This method, however, can not accurately estimate
owing to the influence of friction and a fitting state.
[0046] Hence, using a method similar to the aforementioned method for measuring the produced
energy value, rotational information of the rotor of the step motor during free rotation
(during rotation under no loading) is obtained as time information of the rotation
angle. On the basis of the above information, rotational information of the holding
energy value is obtained by calculating the moving energy value of the rotor at a
rotational position, on the basis of which the holding energy value is then estimated.
[0047] On the basis of the above results, a rotor, a fifth wheel, and a second wheel (a
third wheel and thereafter are omitted) which are the next smaller size compared to
the components of the hand rotational mechanism designed for a conventional gents'
watch, are fabricated to confirm the effects thereof. The values of the inertial moments,
the driving energy and the holding energy are shown in Table 1 with those of the conventional
watch.
[0048] E―11, E―12, and E―13 in this table respectively mean ×10
-11, × 10
-12, and × 10
-13. Note "←" means being the same as in the box in the left-hand side. These expressions
are also applied to Table 2 and Table 3, which are shown later.
[0049] It is apparent from Table 1 that both values of the inertial moments Js of the second
hands are the same, since the second hand of the newly made electronic watch is the
same as that of the conventional watch, and that the value of the rotor equivalent
inertial moment J considerably decreases in the newly made electronic watch and therewith
the driving energy indicates 136 nJ (nanojoule) which is less than 1/3 of 435 nJ which
is the value of the conventional watch.
[0050] As described above, the second hand is driven by a combination of components which
are the next smaller size than those of the conventional watch and the same second
hand as that of the conventional watch, resulting in the hand moving as well as the
conventional one as expected.
[0051] Furthermore, when a minute hand and an hour hand are also attached to move, the moving
states are not different from the conventional ones.
[0052] The holding energy value of the newly made step motor is 154 nJ (nanojoule), which
is less than 1 / 2 as compared with 334 nJ of the conventional one, and in addition
to the reduction of the rotor equivalent inertial moment J, the input energy which
is required to drive the second hand for 1 step substantially decreases from 1450
nJ of the conventional one to 630 nJ.
[0053] It is consequently clear that the use of the hand rotary mechanism as described above
enables substantial reduction in power consumption, while realizing the same moving
function as the conventional one.
[0054] However, since the holding energy value becomes 154 nJ which is less than 1/2 as
compared with 334 nJ of the conventional one, the hand in this state can not stand
a disturbance energy occurring on receiving an external impact, which causes a had-skip
phenomenon. As measures against the above, in this embodiment, the weight 20 is added
to the short hand part 8b of the second hand 8 as shown in Fig. 1, to lessen the moment
of the second hand 8 as of the rotary body by a counterbalance system.
[0055] The second hand of a gents' watch normally has an inertial moment of the order of
2.1 × 10
-11 kg · m
2 and a moment of the order of 2.7 × 10
-9 kg · m.
[0056] In the embodiment shown in Fig. 1, the weight 20 having a certain inertial moment
is provided as a counterbalance on the short hand part 8b of the second hand 8, to
correct imbalance of the moment with respect to the second hand shaft 18, and to reduce
a disturbance energy occurring at the second hand part, in order to check whether
a hand-skip phenomenon can be prevented.
[0057] To this end, hammer tests in conformity to ISO 1413 are carried out to check the
presence or absence of a hand-skip phenomenon by actually giving an external impact
to each sample of electronic watches.
[0058] A gents' electronic watch using a normal second hand is designated as Sample 1, and
then Sample 2 to 8 of electronic watches, in which the moment correction ratios are
gradually increased by elongating the length of the short hand part of the second
hand by degrees. The moments of the second hands, the inertial moments (inertia) thereof,
the values of the hand equivalent inertial moments, the corrective ratios to Sample
1, which the respective samples have, and the presence or absence of a hand-skip phenomenon
as results of the hammer tests are shown in Table 2.
[0059] It is noted that the shown' values are results of giving a normal external impact
energy in the hammer test I (dropping a hammer onto the sample from the height of
30 cm), and of giving an external impact energy twice as much as that in ,the hammer
test I in the hammer test II (dropping the hammer onto the sample from the height
of 63 cm). The hammer tests are carried out ten tunes for each condition, and then
as results of the tests, X for when a hand-skip occurs at every time, Δ for when it
sometimes occurs , and ○ for when it never occurs, are filled in boxes corresponding
to respective tests in Table 2.
[0060] As is obvious from Table 2, a hand-skip phenomenon can not be completely prevented
in Sample 1 having no counterbalance even in the hammer test I. In contrast to that,
it is shown that when the moment correction ratio is made more than 7 % by adding
a weight having a certain inertial moment to the short hand part of the second hand
(by increasing in length of the short hand part in this case), a hand-skip phenomenon
can be surely prevented against an external impact
[0061] The weight 20 which is added to the short hand part of the second hand to counterbalance
to the degree as above is just ,a minute item, which can be realized without spoiling
the appearance of the conventional watch. It is noted that the value of the inertial
moment Js of the second hand slightly increases by adding the weight 20, but the moving
condition stays unchanged, since the influence by the weight 20 to the rotor equivalent
inertial moment J is negligible as is obvious from the expression (1).
[0062] Next, the magnitudes of disturbance energies occurring at the second hand parts of
samples 1 to 8 listed in Table 2 on receiving external impacts are estimated, and
then it is attempted to compare these with the holding energy 154 nJ which is possessed
by the step motor in the newly made electronic watch shown in Table 1.
[0063] The occurring mechanism of the disturbance energy, which occurs on receiving an external
impact due to the degree of unbalanced moment possessed by the second hand, is considered
to derive the following mathematical expression.

[0064] In the above expression, E represents the value of a disturbance energy which occurs
at the second hand part, v represents a speed of the watch when it performs translational
motion by receiving an external impact, M represents a moment possessed by the second
hand, and I represents a band equivalent inertial moment.
[0065] The hand equivalent inertial moment I is the equivalent inertial moment, from the
hand side, of the whole rotary body including train wheels for transmission of torque
between the band and the rotor of the step motor, which is obtained from the following
mathematical expression.

[0066] In this expression, Js, J4, J5, and Jr respectively represent inertial moments of
the second hand, the second wheel, the fifth wheel, and the rotor, and each numerical
value of "25" is the squared speed increasing ratio of the fifth wheel from the second
hand side, and of "900" is the squared speed increasing ratio of the rotor from the
second hand side.
[0067] Next, the correlation between the holding energy Ep which the step motor retains
and the disturbance energy E which is derived from the expression (2) is shown in
Fig. 2, in addition to the results of a hand-skip phenomenon by the hammer tests I,
II shown in Table 2.
[0068] In Fig. 2, round black dots and square black dots respectively represent values of
disturbance energies in the hammer tests I, II shown in Table 2, and numerals marked
near the respective dots are sample numbers in Table 2. A broken line shows a level
where the holding energy Ep possessed by the step motor is 154 nJ shown in a case
of the newly made electronic watch in Table 1.
[0069] From the results of Table 2 and Fig. 2, it turns out that a hand-skip phenomenon
can be prevented in a range where the following mathematical expression is satisfied.

As is clear from the results of the hammer tests in Table 2, the holding range is
difficult to explicitly define due to the existence of a region where the results
thereof are △ depending on conditions, however, the above expression (4) is probably
a guide from these results of the tests.
[0070] Actually, a holding energy operates including friction losses in the train wheels.
When the above energy is Eq,

, as shown by a two-dotted chain line in Fig. 2, in the structure of the step motor
and the train wheels used in these hammer tests. Accordingly, no hand-skip phenomenon
actually occurs on Samples 2 to 8, since E < Eq in each case of Samples 2 to 8 in
the impact test I as shown in the test results shown in Table 2.
[0071] This means that a moment M possessed by a second hand, a hand equivalent inertial
moment I, a speed v when a the timepiece receives an external impact to perform translations,
and a holding energy Ep possessed by a step motor, which conventionally seemed to
be completely different parameters, correlate with one another, and at least in a
range (M
2/I < 2 × Ep/v
2) where the expression (4) is satisfied the hand is surely held.
[0072] Conventionally, restrictions are imposed on conditions of use for hands only by a
range where a moment is established from the results of the hammer test actually carried
out on the set step motor. The range where the hand needs to satisfy the conditions
is determined in advance by substituting each value of the parameters in the expression
(4), which achieves holding of the hand within this range.
[0073] In the aforementioned embodiment of the present invention, it is found that the second
hand can be held if more than 7 % of moment is corrected to imbalance of the moment
possessed by the second hand.
[0074] However, since decoration is added to the hand in practice, the inertial moment and
the moment are not unconditionally determined and so are distributed in a certain
range. As a measure to that, once the above hand is counterbalanced on the assumption
that the moment correction ratio is the largest in a range where the expression (4)
is satisfied, the same components as those of the original one can be used for various
hands.
[0075] In the aforementioned embodiment, the weight 20 having a certain inertial moment
is added to the short had part 8b of the second band 8 as a counterbalance (including
the short had part that is lengthened or thickened). However, as measures same as
above, a weight may be added at least to a part of the second wheel 3 and the pinion
13 which constitute the train wheels between the second hand 8 ad the rotor 1a shown
in Fig. 1, at positions corresponding to the short hand part 8b of the second hand
8 with respect to each rotation axis.
[0076] Consequently, the moment of the whole rotary body including the second hand 8 is
reduced, which enables the value of the disturbance energy that the step motor receives
to be less than the holding energy value.
[0077] The second hand 8, the second wheel 3, the pinion 13, and the second hand shaft 18
are linked together to move, in which the unbalanced amount can be thus controlled
by each of them separately or by a combination of two or more out of them As a means
for controlling the moment, instead of adding a weight, formation of a thin part,
a through hole, or a notch at least in a part of the rotary body comprised of the
second hand 8, the second wheel 3, the pinion 13, and the second hand shaft 18, to
lessen the moment as of the whole rotary body, can be employed.
[0078] Alternatively, at least a part of rotary members (wheels and the like) of the rotary
body can be formed with a combination of members with different specific gravities
from each other in order to lessen the moment as of the whole rotary body.
[0079] In these cases, the resultant disturbance energy value, that is, the value of the
disturbance energy which the step motor receives, can be also made smaller than the
holding energy value.
[0080] Furthermore, although the aforementioned embodiment is described in a case of the
second hand as an example, the same idea can be also employed to the minute hand and
the hour hand.
[0081] More specifically, when a hand to be driven is known, the driving energy value which
is derived from driving conditions of the hand is first estimated, and components
of a rotary body including train wheels are then designed in such a manner to have
a rotor equivalent inertial moment J as small as possible while satisfying the estimated
value.
[0082] Consequently, the above had is counterbalanced in such a manner as to make the disturbance
energy value smaller than the holding energy value possessed by the step motor, thereby
a reduction in size and a substantial decrease in power consumption are possible while
satisfying the watch requirements of driving and holding of the hand at the same level
as of the conventional one. Application of the present invention to a lady's watch
can realize a watch which has a smaller size and a less power consumption than the
conventional one, and can also cope with various designs.
[0083] Next, another embodiment of the present invention will be described with reference
to Fig. 3 and Fig. 4.
[0084] In this embodiment, a surface of a dial is regarded as a world map, not specifically
shown, and a second hand, on which a member modeled on a shape of an aircraft is attached
in the vicinity of the tip thereof is fabricated to express an image where the aircraft
flies around above the map. The values of the inertial moments and the holding energies,
which are possessed by the above second band and each component of the rotary body
composed of train wheels for rotating the second band, are shown in Table 3, in addition
to those of the conventional gents' watch.
[0085] The inertial moment Js of the above second had increases up to be ,about eight times
as large as the conventional gents' watch due to the design added to the second hand,
resulting in a fear of influence on a moving behavior. However, as is estimated from
the expression (1), the increment of the rotor equivalent inertial moment J is about
10 % at the maximum, and little variation is found in the actual motion, and also
there is little variation in input energy as shown in Table 3.
[0086] It is checked in another test that a hand can move with little variation in motion
in the step motor used in this test, within the increment of the rotor equivalent
inertial moment J up to about 100%.
[0087] The moment possessed by the second had in this embodiment is about 1.8 × 10
-8 kg · m, which is about seven times as large as 2.7 × 10
-9 kg · m possessed by a conventional gents' watch. On the second hand in this state,
as described in the aforementioned embodiment, a hand-skip phenomenon occurs on an
external impact at the same level as of the conventional one.
[0088] To prevent that, in this embodiment, a reverse transmission preventing gear is provided
at a part of wheels which constitute train wheels between the second hand and the
rotor of the step motor in order to prevent transmission of a disturbance energy to
the step motor.
[0089] Fig. 3 and Fig. 4 are drawings for explaining a motion when the reverse transmission
preventing gear is used at least with any one of a pinion 31 (corresponding to any
one of the pinions 11, 12 in Fig. 5) and a gear 32 (corresponding to the fifth wheel
2 or the second wheel 3 in Fig. 5) which constitute train wheels between the second
bad and the rotor of the step motor in the train wheels structure of an analog three-hand
electronic timepiece.
[0090] A force is normally transmitted by rotation of the pinion 31 in the A direction indicated
by an arrow as shown in Fig. 3 to rotate the gear 32 in the B direction indicated
by an arrow. The above relation continues from the rotor to the fifth wheel, the second
wheel, the third wheel, and so on in due order to thereby transmit the force efficiently.
[0091] On the other hand, when the watch main body receives an external impact, a torque
caused by the disturbance energy occurring at the second hand part acts on the gear
32 in order to transmit the torque to the pinion 31. The pinion 31 and the gear 32,
however, mesh and push against each other at the point a and the point b as shown
in Fig. 4, so that both of them can not rotate. Therefore, the torque of the gear
32 in the C direction indicated by a arrow, which is opposite to the direction of
a normal transmission of force, is not transmitted to the pinion 31.
[0092] In order to hold the second hand, a reverse transmission preventing gear may be used
at least at any one place of the pinion of the rotor and the fifth wheel, and the
pinion of the fifth wheel and the second wheel. It is noted that a case where the
gear 32 rotates to the left when receiving a external impact is explained in Fig.
4, and transmission of the force is prevented similarly to the above in a case of
rotating to the right.
[0093] Employment of this mechanism enables a hand-skip phenomenon to be prevented even
when the holding energy value possessed by the step motor is smaller than the disturbance
energy value. Consequently, even when a hand which has a inertial moment ad a moment
larger than those of the conventional one is used, the timepiece requirements of driving
and holding of the bad can he satisfied at the same level as of the conventional one,
in a similar manner to the aforementioned embodiment. This effect is checked by actually
carrying out a hammer test in conformity to ISO 1413 upon a finished timepiece equipped
with an hour hand, a minute hand and a second hand.
[0094] Furthermore, it is likely that a rotational energy is also added to a timepiece with
the translational energy as described above by a external impact, to which a shock
test is performed to check that there occurs no inconvenience.
[0095] The above shock test refers to a method of testing in consideration of a rotational
impact, which is caused by placing a timepiece in a arbitrary orientation in an empty
box and allowing it to fall freely from a predetermined height. It is required that
there is no displacement of hands before and after the test.
[0096] Under normal use conditions, a big rotational impact is not given to a timepiece
body, therefore there seems to be no problem if it passes the hammer tests.
[0097] In the two aforementioned embodiments, while effects of a counterbalance provided
by adding a weight and the like ad of a reverse transmission preventing gear are described,
using both mechanisms together produces other effects.
[0098] More specifically, the value of the disturbance energy occurring at the hand is quite
small and does not produce a force which achieves a great change in train wheels due
to the counterbalance mechanism in a region where the external impact is small, therefore
the hand is held. Moreover, with a large external impact against which the hand can
not be held only by the counterbalance, the reverse transmission preventing gear mechanism
prevents a force from reverse transmission.
[0099] At this time, since the disturbance energy value substantially decreases due to the
counterbalance, the force acting on the pushing-out part (the point b) between the
gear 32 and the pinion 31 shown in Fig. 4 decreases, resulting in no danger of shape-deterioration
of the pushing-out part.
[0100] Thereby, the step motor retaining a small holding energy is reliable in use and can
surely hold the hand against a wide range of impacts.
[0101] It is already assured in the description in Table 1 that there is a possibility of
a sufficient reduction in power consumption in the present invention as compared with
the conventional one. A further reduction in power consumption is made possible by
improving efficiency by optimizing conditions of components of a step motor, reduction
in moment by further reduction in size of components or by employing plastic materials,
relaxing drive conditions, and so on.
[0102] A mechanism omitting the counterbalance can be employed, if it can ultimately reduce
an external impact to have a disturbance energy value smaller than a holding energy
value. For example, a shock absorber disposed around a module may absorb an external
impact at some midpoint, or the shape and material of a hand may reduce the disturbance
energy value itself. Alternatively, components may be mechanically fixed against an
external impact, or a structure in which a rock system works only on detecting an
external impact, may be employed.
[0103] The embodiments of the present invention can be also applied to a clock, though only
a wristwatch using a step motor as an actuator is described. If anything, in the ease
of a clock, an external impact is not as significant as in the case of a wristwatch,
so that a holding torque value thereof may be small. A rage of the driving energy
required for driving hands is estimated, in which the rotor equivalent inertial moment
J is reduced, thereby the power consumption can be substantially reduced.
Table 1
|
Conventional Gent's Watch |
Newly Made Electronic Watch |
Driving Energy (nJ) |
435 |
136 |
Holding Energy (nJ) |
334 |
154 |
J (kg · m2) |
1.3E-12 |
2.3E-13 |
Jr (kg · m2) |
1.1E-12 |
1.6E-13 |
J5 (kg · m2) |
6.4E-12 |
1.9E-12 |
J4 (kg · m2) |
8.0E-12 |
3.5E-12 |
Js (kg · m2) |
2.1E-11 |
← |
Input Energy (nJ) |
1450 |
630 |
Table 2
Sample No. |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
Moment (kg · m) |
2.7E-9 |
2.5E-9 |
2.3E-9 |
1.9E-9 |
1.6E-9 |
1.1E-9 |
5.9E-10 |
1.6E-11 |
Inertial Moment of the Second Hand (kg · m2) |
2.1E-11 |
← |
2.2E-11 |
2.3E-11 |
2.4E-11 |
2.6E-11 |
2.8E-11 |
3.0E-11 |
Hand Equivalent Inertial Moment (kg · m2) |
2.0E-10 |
← |
← |
← |
2.1E-10 |
← |
← |
← |
Moment Correction Rate compared to Sample 1 (%) |
0 |
7 |
17 |
29 |
43 |
60 |
78 |
99.4 |
Hand-Skip |
Hammer Test I |
△ |
○ |
← |
← |
← |
← |
← |
← |
Hammer Test II |
X |
← |
← |
△ |
○ |
← |
← |
← |
Table 3
|
Conventional Gent's Watch |
Electronic Watch In The Embodiment Of The Present Invention |
Holding Energy (nJ) |
334 |
← |
J (kg · m2) |
1.3E-12 |
1.4E-12 |
Jr (kg · m2) |
1.1E-12 |
← |
J5 (kg · m2) |
6.4E-12 |
← |
J4 (kg · m2) |
8.0E-12 |
← |
Js (kg · m2) |
2.1E-11 |
1.6E-10 |
Input Energy (nJ) |
1450 |
← |
INDUSTRIAL APPICABILITY
[0104] According to the present invention, in a range where the value of the driving energy
required for driving hands in a timepiece is satisfied, the equivalent inertial moment
of the whole rotary body including the hands and train wheels for rotating the hands
is reduced. Then the value of the disturbance energy occurring at the hands, caused
by an external impact, is reduced to be smaller than the reduced holding energy value.
[0105] Thereby, a substantially lower power consumption can be achieved, and a system not
requiring frequent replacement of batteries can he realized, while keeping the driving
and holding performances at the same level as of the conventional one.
[0106] Conversely, when the same power is used as in the conventional one, even a had having
an inertial moment which is ten times or more as compared with the conventional one
is used, the same driving and holding performances at the same level as of the conventional
one can be secured. Therefore, decorations and functional elements can be applied
to a hand part, which can not be achieved under the conventional conditions, resulting
in substantial increase of flexibility.