Horology: time measuring systems or devices – Power supply details – Electrical
Reexamination Certificate
2001-04-20
2003-11-11
Martin, David (Department: 2841)
Horology: time measuring systems or devices
Power supply details
Electrical
C368S066000, C320S101000
Reexamination Certificate
active
06646960
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electronic timepiece (watch and clock) incorporating power generation means (generator) for generating electricity by utilizing external available energy, and particularly, to an electronic timepiece having a function of storing the electric energy generated by the power generation means, and driving time-indicating means for executing a time display operation by the agency of the electric energy stored.
BACKGROUND TECHNOLOGY
There has lately become commercially practical an electronic timepiece provided with built-in power generation means for converting external energy such as optical energy, thermal energy, mechanical energy, and so forth into electric energy, and utilizing the electric energy as driving energy for executing a time display operation.
Among such electronic timepieces provided with the built-in power generation means, there are included a solar cell timepiece using a solar cell, a mechanical electric power generation timepiece converting mechanical energy generated by a rotary weight into electric energy and utilizing the same, and a thermoelectric power generation timepiece generating electricity by utilizing the difference in temperature between the opposite ends of each of thermocouples connected in series.
It is essential for these electronic timepieces provided with the built-in power generation means to have built-in means for storing generated electric energy therein while the external energy is available so that the timepieces are driven continuously and stably all the time even when the external energy is no longer available. Such an electronic timepiece has been disclosed in, for example, JP, 4-81754, B.
FIG. 7
shows an example of a conventional electronic timepiece provided with a built-in power generation means, including electric energy storage means.
With the timepiece, power generation means
10
is a solar cell, and the positive terminal thereof is grounded, forming a closed circuit with a first diode
43
and time-indicating means
21
. The time-indicating means
21
is comprised of a time-indicating block
22
for executing time display by the agency of electric energy, and a capacitor
23
having capacitance of 22 &mgr;F, which are connected in parallel.
Further, the power generation means
10
forms another closed circuit with a second diode
44
, a first switching device
41
, and storage means
30
.
A second switching device
42
interconnects the negative terminal of the capacitor
23
and the negative terminal of the storage means
30
such that the capacitor
23
and the storage means
30
can be coupled in parallel.
A switch circuit
40
for performing transfer or interruption of electric energy among the power generation means
10
, the storage means
30
, and the time-indicating means
21
is comprised of the first switching device
41
, the second switching device
42
, the first diode
43
, and the second diode
44
.
Further, a first voltage comparator
16
compares a terminal voltage of the capacitor
23
with a first threshold value, and a second voltage comparator
17
compares the terminal voltage of the capacitor
23
with a second threshold value. The comparison result of the first voltage comparator
16
and that of the second voltage comparator
17
are caused to be inputted to a time-indicating block
22
, thereby controlling the first switching device
41
by a first switching signal S
21
outputted by a control circuit within the time-indicating block
22
.
In this case, the first threshold value is −2.0 V, and the second threshold value is −1.5 V.
Further, a third voltage comparator
18
compares a terminal voltage of the storage means
30
with a third threshold value, and the comparison result thereof is caused to be inputted to the time-indicating block
22
, thereby controlling the second switching device
42
by a second switching signal S
22
outputted by the control circuit within the time-indicating block
22
. In this case, the third threshold value is −2.0 V as well.
The first, second, and third voltage comparators
16
,
17
,
18
perform a comparison operation intermittently in a cycle of one second, respectively.
In a circuit diagram shown in
FIG. 7
, upon the start of generation of electric energy by the power generation means
10
, the capacitor
23
of small capacitance is first charged with the electric energy, and the time-indicating means
21
starts a time-indicating operation by the agency of the electric energy stored in the capacitor
23
. At this point in time, the second switching device
42
is open.
Upon a voltage between the terminals of the capacitor
23
reaching 2.0 V or higher, and an input voltage to the first voltage comparator
16
becoming −2.0 V or lower since the positive terminal thereof is grounded, the first voltage comparator
16
detects such a condition, and depending on the result of detection, the time-indicating block
22
closes the first switching device
41
, thereby causing the storage means
30
to be charged.
Conversely, upon a voltage between the terminals of the capacitor
23
becoming lower than 1.5 V, and an input voltage to the second voltage comparator
17
becoming higher than −1.5 V, the second voltage comparator
17
detects such a condition, and depending on the result of detection, the time-indicating block
22
opens the first switching device
41
, thereby causing the capacitor
23
side of the time-indicating means
21
to be charged.
Further, upon a voltage between the terminals of the storage means
30
exceeding 2.0 V as the charging of the storage means
30
proceeds, and an input voltage to the third voltage comparator
18
becoming −2.0 V or lower, the third voltage comparator
18
detects such a condition, and depending on the result of detection, the time-indicating block
22
closes the second switching device
42
, thereby causing both the storage means
30
and the capacitor
23
to be charged.
However, the electric energy generated by the power generation means
10
undergoes variation depending on the external environment. For example, in the case of the solar cell, variation occurs mainly in quantity of electric current that can be outputted, and in the case of a thermoelectric power generation device, a generated voltage undergoes variation depending on the difference in temperature impressed from outside.
That is, depending on the external environment, the electric energy generated by the power generation means
10
undergoes an abrupt increase at times, thereby causing a voltage between the terminals of the capacitor
23
inside the time-indicating means
21
to undergo an abrupt rise.
As a result, there have occurred cases where an under-load driving operation of the time-indicating block
22
connected with the capacitor
23
in parallel becomes unstable, so that time display can not be executed properly.
It is possible to solve this problem by various means such as by increasing capacitance of the capacitor
23
, by causing the respective voltage comparators to perform a comparison operation in a shorter cycle, and so forth, however, a large capacitance capacitor results in an increase of the size thereof, so that such a capacitor can not be incorporated in a small-sized electronic timepiece such as a wrist watch.
Further, since an amplifier such as the first, second, and third voltage comparators
16
,
17
,
18
has relatively large energy consumption, there has also arisen a problem that frequent activation of the voltage comparators deteriorates energy efficiency.
The invention has been developed to solve the above-described problems encountered by the conventional electronic timepiece provided with the built-in power generation means, and it is therefore an object of the invention to enable control of the under-load driving operation for time display and the charging of the storage means to be efficiently executed even if variation occurs to a terminal voltage of the power generation means or to that of the storage means.
DISCLOSURE OF TH
Armstrong Westerman & Hattori, LLP
Citizen Watch Co. Ltd.
Goodwin Jeanne-Marguerite
Martin David
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