Metal working – Method of mechanical manufacture – Watch or clock making
Reexamination Certificate
2000-12-29
2003-02-18
Echols, P. W. (Department: 3726)
Metal working
Method of mechanical manufacture
Watch or clock making
C072S203000, C368S238000
Reexamination Certificate
active
06519853
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of manufacturing a hand for an analog electronic timepiece, that is, a hand (especially, a second hand) for an analog electronic timepiece in which a long hand part for indicating time, a mounting part to be mounted to a hand shaft, and a short hand part extending to the opposite side to the long hand part with respect to the mounting part are integrally formed, and a weight part is provided on the short hand part.
BACKGROUND TECHNOLOGY
First, the basic structure of a three-hand analog electronic timepiece will be explained with FIG.
7
. In a typical three-hand analog electronic timepiece, torque generated by a step motor
60
composed of a rotor
60
a,
a stator
60
b,
and a coil
60
c
is transmitted from the rotor
60
a
to a fifth wheel
61
, a second wheel
62
, a third wheel
63
, a center wheel
64
until an hour wheel
66
in order through pinions
71
to
75
and a minute wheel not shown respectively with being reduced to a predetermined rotation speed.
Further, a second hand
69
, a minute hand
68
, and an hour hand
67
are mounted on the second wheel
62
, the center wheel
64
, and the hour wheel
66
respectively to fit thereon through coaxial hand shafts respectively, so that time is indicated by the hands. It should be noted that the second hand
69
, the minute hand
68
, and the hour hand
67
are collectively called the hands. Incidentally, numeral
51
denotes a main plate, and numeral
52
denotes a train wheel bridge.
While the hands are standing still, each of the hands is held by the holding energy possessed by the step motor
60
to prevent a hand-skip phenomenon from occurring on receiving an external impact.
On the other hand, while the hands are moving, the step motor
60
generates driving energy which exceeds the holding energy so as to drive the hands.
FIG. 8
is a perspective view showing an example of the shape of a conventional typical second hand. This second hand
69
is composed of a long hand part
69
a
for indicating time, a mounting part
69
b
to be mounted to a second hand shaft, and a short hand part
69
c
extending to the opposite side to the long hand part
69
a
with respect to the mounting part
69
b,
and these parts are normally made of the same material into the same thickness.
A cylindrical fitting member
50
is firmly secured to the mounting part
69
b,
and the fitting member
50
fits over the second hand shaft
62
a
which is provided integrally with the second wheel
62
, whereby the second hand
69
is mounted to the second wheel
62
. Thus, the long hand part
69
a
indicates time (second). The minute hand
68
and the hour hand
67
are the same in basic shape.
Incidentally, an inconvenience of replacement of batteries once per several years is pointed out in a recent electronic timepiece, and 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 upsizing of the battery for increasing the capacity thereof can not be expected because of limitation in size of a wristwatch. Furthermore, the reduction in power consumption already comes to a limit though improvements in electromechanical conversion efficiency of the step motor have been made mainly by reducing the size of a magnet through enhancement of the power thereof or by optimizing a driving wave form or the like, and therefore more drastic reduction in power consumption can not be expected through the use of conventional methods.
Moreover, in the analog electronic timepiece, holding energy for holding the hands is generally required in order to prevent a hand-skip phenomenon caused by rotational energy, disturbance energy, generated by an external impact received during the standing still. As the holding energy, holding energy called magnetic potential (resistance force against moving from a still point) possessed by the step motor is normally used, which needs to be set at a value larger than a value of the disturbance energy generated by the external impact.
The magnitude of the disturbance energy, to which the moment of a rotating body composed of each hand, and the gear, pinion, and shaft to which the hand is mounted is related, is generally determined by the moment of the long hand part and the short hand part of the hand in relation to the rotational axis.
However, in a typical second hand used in the conventional analog electronic timepiece, since the long hand part
69
a
and the short hand part
69
c
are the same in thickness and different in length as is clear from
FIG. 8
, the moments of both parts with respect to a rotational axis line
70
are apparently unbalanced. Therefore, the second hand has some moment, resulting in occurrence of disturbance energy by an external impact.
The longer the long hand part becomes as the hand becomes larger as especially in a wristwatch for men, the greater the moment becomes, and separately the moment becomes larger in a designed hand which is designed differently in shape from a viewpoint of decoration, resulting in increased disturbance energy.
On the other hand, during driving the hand, the step motor generates driving energy exceeding the holding energy value which is set to be larger than the disturbance energy value so as to drive the hand.
The driving energy value here is a resultant value obtained by subtracting the holding energy value from a value of the whole energy generated by the step motor. In other words, the driving energy value is a value of effective energy, which rotationally moves the hand only a fixed angle in a predetermined period of time, beyond the value of the holding energy possessed by the step motor.
Therefore, it is apparent that if the holding energy value is decreased, energy which is consumed to exceed the holding energy value decreases and the whole energy required to drive the hand also decreases. In other words, it can be said that decreasing the holding energy value is effective to reduce power consumption.
As described above, however, the holding energy value can not be made small enough from the viewpoint of holding hand. Conversely, when low power consumption is achieved by decreasing the holding value, there is a problem that the disturbance energy value is larger than the holding energy value, whereby the hand can not be held adequately though the hand can move, bringing about a hand-skip phenomenon.
Hence, it is proposed that, for example, a weight is added to the short hand part
69
c
of the second hand
69
shown in
FIG. 8
to reduce imbalance between the moments of the long hand part
69
a
and the short hand part
69
c
with respect to the rotational axis line
70
so as to decrease the disturbance energy value. This can also decrease the holding energy value, whereby the energy, which is consumed for the driving energy by the step motor to exceed the holding energy during the driving of the hand, is also decreased, making it possible to reduce the power consumption.
In order to manufacture the hand to which the weight is added as above, the whole hand has been conventionally formed by being punched out from a metal thin sheet material with a uniform thickness, and thereafter a small weight is bonded to an under face of the short hand part with an adhesive.
However, workability of the work of bonding the weight to the short hand part of a small hand such as a second hand of a wristwatch is poor, and thus it takes a great deal of time. Further, the weight is susceptible to being detached from the hand in use for a long time if the bonding is inadequate.
DISCLOSURE OF THE INVENTION
This invention is made to solve the above-described problems, and its object is to make it possible to manufacture easily and securely a hand for an analog electronic timepiece in which a weight part is provided on a short hand part and also to eliminate the danger for the weight to be detached from the hand.
To attain the above objects, the invention proposes the following first to third manufacturing methods
Machida Takayasu
Nanya Takanori
Shimanouchi Takeaki
Suzuki Kazuo
Takahashi Shigeyuki
Armstrong Westerman & Hattori, LLP
Citizen Watch Co. Ltd.
Echols P. W.
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