Horology: time measuring systems or devices – Power supply details
Reexamination Certificate
1999-10-20
2001-10-16
Roskoski, Bernard (Department: 2859)
Horology: time measuring systems or devices
Power supply details
C368S203000
Reexamination Certificate
active
06304520
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a wrist watch having a thermoelectric generator provided with thermoelectric elements comprising a plurality of thermocouples which are mounted in a watch case together with a movement for driving hands and serve as a power source for the movement.
2. Description of the Related Art
Each thermoelectric element is a generating element comprising a plurality of thermocouples for converting thermal energy into electric energy, which generates a voltage when there is a difference in temperature supplied to both end faces thereof. A wrist watch which comprises the thermoelectric elements is a wrist watch having a thermoelectric generator. The thermoelectric elements are mounted in a watch case together with a movement for driving the hands and this serves as a power source for the movement. The thermoelectric elements convert heat energy, caused by the difference in temperatures supplied to case back and the metal case body constituting the watch case to electric energy. And the movement is driven by this generated power (thermoelectromotive force).
The internal construction of the conventional wrist watch having a thermoelectric generator is described with reference to
FIG. 10
which shows a sectional view thereof and
FIG. 11
which shows a rear view thereof with the removal of the case back.
FIG. 10
is a sectional view taken along the line C—C of FIG.
11
.
A wrist watch having a thermoelectric generator
100
constitutes a watch case comprising an insulating body
120
fixedly attached to the lower side (underside) of the metal case body
110
with a glass plate
111
circular in a plane shape, fixedly attached thereto, a case back
130
made of metal securely fixed to the underside of the insulating body
120
. The watch case houses therein a dial
40
, hands (hour hand, minute hand)
51
and a movement
50
including a step motor, a gear train, a crystal oscillation circuit for driving the movement and thermoelectric elements
160
.
As shown in
FIGS. 10 and 11
, the thermoelectric elements
160
are mounted inside the insulating body
120
but outside the dial
40
and movement
50
. The thermoelectric elements
160
are housed in the watch case in a manner that they are brought into contact with the metal case body
110
at one end face and with the case back
130
at the other end face. The insulating body
120
is provided for insulating between the metal case body
110
and the case back
130
so as to easily bring about the difference in temperatures therebetween.
If a user wears the wrist watch having a thermoelectric generator
100
having such a construction on user's wrist, the case back
130
contacting the wrist is heated by the user's body temperature while the metal case body
110
opposite to the case back
130
is cooled by outside air temperature. Accordingly, the difference in temperatures between the body temperature and the air temperature is supplied to both end faces of the thermoelectric elements
160
, and this difference in temperatures generates thermoelectromotive force. The movement
50
is driven by this thermoelectromotive force.
FIG. 12
is a schematic perspective view of the thermoelectric elements
160
to be mounted in this wrist watch.
Each of the thermoelectric elements
160
is of such a size to be mounted in this wrist watch having a thermoelectric generator
100
and comprise a plurality of columnar p-type thermoelectric semiconductor devices
180
, a plurality of columnar n-type thermoelectric semiconductor devices
181
which are arranged regularly respecticely, and insulating resins
182
which fill between the p-type thermoelectric semiconductor devices
180
and the n-type thermoelectric semiconductor devices
181
, so as to fix them integrally with one another as a whole.
In
FIG. 12
, respective one faces of the p-type thermoelectric semiconductor devices
180
and n-type thermoelectric semiconductor devices
181
are visible. The p-type thermoelectric semiconductor devices
180
and n-type thermoelectric semiconductor devices
181
are made of a bismuthtelluride (BiTe) alloy semiconductor.
Although not shown, electrode films are provided at both end faces of the respective p-type thermoelectric semiconductor devices
180
and the n-type thermoelectric semiconductor devices
181
for connecting mutually adjoined semiconductors with one another so as to connect these semiconductors in a series as a whole. A pair of thermocouples are constituted by the adjoined p-type thermoelectric semiconductor devices
180
and n-type thermoelectric semiconductor devices
181
which generate thermoelectromotive force respectively in accordance with the difference in temperatures. Since respective thermocouples are connected in a series with each other by the electrode films, the entire thermoelectric elements
160
generate thermoelectromotive force in accordance with the number of thermocouples contained therein.
The thermoelectric elements
160
are mounted in the wrist watch having a thermoelectric generator
100
in a manner that one of the upper and lower end faces thermally contact the metal case body
110
while the other of the upper and lower end faces thermally contact the case back
130
so as to supply a difference in temperature to each pair of thermocouples.
Meanwhile, it is known that the magnitude (power) of the thermoelectric elements
160
is determined by a gross sectional area of the p-type thermoelectric semiconductor devices
180
and n-type thermoelectric semiconductor devices
181
each constituting the thermoelectric elements
160
and the magnitude of the difference in temperatures supplied to both end faces thereof.
Suppose that each length of the p-type thermoelectric semiconductor devices
180
and n-type thermoelectric semiconductor devices
181
are about 2 mm, the difference between both temperatures produced in the wrist watch having a thermoelectric generator
100
is about 1° C. in average.
Considering the material characteristics of the BiTe thermoelectric semiconductor, and since the thermoelectromotive voltage is 200 &mgr;V/K, and the specific resistance is about 1.2×10
−5
&OHgr;m including a wiring resistance, the maximum output per unit sectional area is 40 &mgr;W/cm
2
.
However, this value of the output is applied to the case when all the thermoelectric elements are made up by thermoelectric semiconductors. It must be considered that the p-type semiconductor devices
180
and the n-type semiconductor devices
181
are actually filled with the insulating resins
182
which do not contribute to the generation of power. Suppose that the ratio of the areas occupied by the end faces of the p-type semiconductor devices
180
, and n-type semiconductor devices
181
to the insulating resins
182
are 1:1, the areas of the p-type semiconductor devices
180
and n-type semiconductor devices
181
become merely a quarter of the entire area of the thermoelectric elements
160
. Accordingly, the maximum output set forth above becomes a quarter of 40 &mgr;W/cm
2
, namely, 10 &mgr;W/cm
2
.
On the other hand, although the power to be consumed by the present wrist watch is about 1 &mgr;W, the power needed by the wrist watch including power for charging the wrist watch so as to drive the wrist watch even if it is not worn by a user is ten times as much as 1 &mgr;W, namely, about 10 &mgr;W.
Accordingly, the power of about 10 &mgr;W needed by the thermoelectric elements used by the wrist watch having a thermoelectric generator
100
requires about 1 cm
2
as the areas of end faces of the thermoelectric elements. If the thermoelectric elements having the area of end faces of 1 cm
2
are mounted inside the wrist watch, the following problem occurs.
In the case of a wrist watch as shown in
FIGS. 10 and 11
, suppose that the thermoelectric elements have areas of about 1 cm
2
, for example, if the thermoelectric elements each having 1 cm×1 cm in length to width are to be housed in the wrist watch, it would be very diffic
Armstrong Westerman Hattori McLeland & Naughton LLP
Citizen Watch Co. Ltd.
Roskoski Bernard
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