U.S. patent number 3,756,010 [Application Number 05/169,734] was granted by the patent office on 1973-09-04 for magnetic-induction clock.
This patent grant is currently assigned to Matsushita Electric Works, Ltd.. Invention is credited to Masanori Kajihara, Rokusaburo Kimura, Akihide Kotani.
United States Patent |
3,756,010 |
Kimura , et al. |
September 4, 1973 |
MAGNETIC-INDUCTION CLOCK
Abstract
In the clocks wherein the induction magnetic field of a
commercial frequency is detected, and the detected signal is
amplified, thereby driving the transistor motor, a magnetic
induction type clock of which the transistor motor is driven in
normal state by said detected signal but in abnormal state such as
in the event of any fluctuation in the external field or power
interruption, the transistor motor is driven by a signal supplied
from a separately provided standard oscillation source.
Inventors: |
Kimura; Rokusaburo (Osaka,
JA), Kajihara; Masanori (Osaka, JA),
Kotani; Akihide (Osaka, JA) |
Assignee: |
Matsushita Electric Works, Ltd.
(Osaka, JA)
|
Family
ID: |
13438262 |
Appl.
No.: |
05/169,734 |
Filed: |
August 6, 1971 |
Foreign Application Priority Data
|
|
|
|
|
Aug 11, 1970 [JA] |
|
|
45/70668 |
|
Current U.S.
Class: |
368/158; 368/204;
968/477; 968/510; 968/520 |
Current CPC
Class: |
G04C
11/084 (20130101); G04C 11/02 (20130101); G04R
40/02 (20130101); G04C 3/067 (20130101) |
Current International
Class: |
G04C
3/06 (20060101); G04C 11/00 (20060101); G04C
11/08 (20060101); G04C 3/00 (20060101); G04C
11/02 (20060101); G04b 001/00 () |
Field of
Search: |
;58/24R,152H,23R,23A
;318/16 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wilkinson; Richard B.
Assistant Examiner: Weldon; U.
Claims
What is claimed is:
1. A battery-driven cordless induction clock comprising a first
synchronizing signal source including a signal detector unit having
an induction coil for magnetically detecting the spatially leaking
induction magnetic field of commercial frequency and producing an
electrical output signal in response to the detected magnetic
field, and an amplifier for amplifying the output signal of said
detector unit, and a transistor motor unit operated by the output
signal of said detector unit for driving the clock, a second
synchronizing signal source including a standard oscillator
producing an output signal at a standard frequency equal to the
commercial frequency a synchronous coil for magnetically coupling
the rotor of said transistor motor unit to said synchronizing
signal sources, first switching means connected between said
synchronous coil and said first synchronizing signal source, second
switching means connected between said synchronous coil and said
second synchronizing signal source, and actuating means responsive
to the output signal from said first signal source for turning said
first switching means on and said second switching means off to
connect said synchronous coil only to said first signal source when
said output signal indicates a normal magnetic field, and for
turning said first switching means off and said second switching
means on to connect said synchronous coil only to said second
signal source when said output signal indicates an abnormal
magnetic field.
2. A battery-driven cordless induction clock in accordance with
claim 1, in which said actuating means comprises a circuit for
differentiating the output signal from said amplifier, a monostable
multivibrator operated by a trigger output from said
differentiation circuit, an integrating circuit for integrating the
output signal from said monostable multivibrator, and a Schmitt
circuit operated by the output signal from said integrating
circuit.
3. A battery-driven cordless induction clock in accordance with
claim 1, in which said actuating means includes means for
converting the output signal from said amplifier into direct
current and means for detecting variations in said direct current
to indicate whether said magnetic field is normal or abnormal.
4. A battery-driven cordless induction clock in accordance with
claim 1, in which said amplifier comprises a voltage amplifier
circuit, a clip circuit for clipping the output of said voltage
amplifier circuit, an RC oscillator circuit to which the output of
said voltage amplifier circuit is applied, a square wave shaper
circuit connected to the output of said RC oscillator circuit, a
differentiation circuit for differentiating the output of said
square wave shaper circuit, and a frequency divider circuit
operated by the trigger output of said differentiation circuit.
5. A battery-driven cordless induction clock in accordance with
claim 1, in which a filter circuit for passing only the signal of a
frequency component close to the commercial frequency is disposed
betweeen said induction coil and said amplifier.
6. A battery-driven cordless induction clock in accordance with
claim 1, in which said transistor motor is of free-running type,
said second synchronizing signal source is a balance wheel driver
unit comprising a drive coil, a detection coil, transistor elements
and balance wheels, and said synchronous coil magnetically coupled
with the rotor of said transistor motor is disposed in the vicinity
of said rotor.
7. A battery-driven cordless induction clock in accordance with
claim 6, in which the axial direction of said induction coil, the
axial direction of the balance wheel of said standard oscillation
source, and the axial direction of the rotor of said transistor
motor unit are disposed in parallel with each other on the same
plane.
Description
BACKGROUND OF THE INVENTION
This invention relates to induction type clocks.
The commercial service power is generally used to drive electric
equipment, appliances and devices everywhere in buildings,
factories, offices and homes and, thus, there are produced
therearound certain induction fields (induction magnetic field and
induction electric field) of the commercial frequency. Since the
frequency of commercial power is very low (for example, 60Hz and
50Hz in Japan), however, there exists no radiation field
(electromagnetic waves) and only an induction field exists in the
vicinity of the power line. The longer the distance from the power
line, the weaker becomes the induction field and, thus, unless the
sensitivity of pickup means is high, it is impossible to detect the
induction field.
Such induction field is produced from the electric current and
electric charge, but it is known that the induction electric field
is present even where no load current flows, while the induction
magnetic field is produced upon occurrence of a flow of a load
current.
With recent developments in power plant services, power
interruption has become minimized or eliminated and, as well as the
fact that the frequency accuracy has been increased, it is possible
to obtain highly accurate clocks synchronizing with the commercial
frequency. The clock according to this invention is to be operated
in such induction magnetic field.
There have been already suggested clocks utilizing commercial power
frequency, typical of which is an AC clock using a synchronous
motor such as Waren motor. This type of clock has such drawbacks
that for example, the use of power cord is indispensable, and the
clock must be placed within the reach of power cord or near the
power socket. To solve this problem the induction type clock has
been proposed.
Reviewing the magnetic field intensity measured in general homes,
it is known that mean field intensity is 5 .times. 10.sup..sup.-4
oersted, and minimum field intensity is 2.5 .times. 10.sup..sup.-7
oersted. The clock utilizing the induction magnetic field is
required to be sufficiently operable in such field intensity. To
this end, the detected signal must be amplified by suitable means,
such as by a highly sensitive pickup. A known clock of this type,
as disclosed, for example, in U.S. Pat. No. 2,786,972, is such that
the induction magnetic field is detected by the magnetic pickup and
then amplified by an amplifier to drive the synchronous motor,
whereby the clock is operated. In the conventional induction type
clock, the accuracy is high as the clock synchronizes with the
commercial frequency as long as the induction magnetic field is
comparatively stable.
However, the induction field is not always stable at any place or
any time. Practically, various electric devices or equipments are
used in the buildings, factories, offices and general homes, where
the magnetic fields produced from electric devices and power lines
interfere with each other, to often result in an extremely low
field intensity, or in some cases, the induction field is disturbed
or fluctuated by an action or movement of strong magnetic material.
For example, in large type air conditioners, a large steel blower
drum is rotated, thereby the magnetic field is disturbed at a
frequency around 10Hz. The external magnetic disturbance takes
place also at on-off occurrence of a large current in electric
welding works. Further, any movement of a magnetic member in the
vicinity of the magnetic pickup is also a cause of magnetic field
disturbance. Nevertheless, in the prior art, no provision is made
for compensating the influence due to external field disturbance,
weakened field or power interruption and, as a result, the accuracy
of the clock is often deteriorated.
According to the present invention, all the foregoing problems are
solved by providing a induction type clock in which a highly
accurate standard oscillator is separately disposed and, in the
event of the external magnetic disturbance, the detected signal
voltage is automatically interrupted by an electrical circuit, and
the clock is driven synchronously with the frequency provided from
said standard oscillator, whereby the accuracy of the clock is
maintained so as to be free of any external magnetic
disturbance.
A principal object of the present invention is, therefore, to
provide a magnetic induction type clock operable with a high
accuracy at all times free of the external magnetic
disturbance.
The present invention will be disclosed in detail in the following
with reference to accompanying drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a magnetic induction type clock
embodying this invention,
FIG. 2 is a detailed circuitry diagram illustrating the clock in
FIG. 1,
FIGS. 3, 4a and 4b are a block diagram and a circuit diagram,
respectively showing another embodiment of this invention,
FIGS. 5(I) and 5(II) are circuitry and characteristic diagrams
showing the operation of the clock of this invention,
FIG. 6 shows in detailed circuitry diagram transistor motor and
standard oscillator sections in the clock,
FIGS. 7(I), 7(II) and 7(III) are diagrams showing operations of
switching circuit in the clock,
FIG. 8(I) shows another embodiment of this invention and FIG. 8(II)
is a characteristic diagram thereof, and
FIG. 9 is a perspective view showing schematically internal
arrangement of the clock with the back cover removed.
DESCRIPTION OF THE INVENTION
Referring to FIG. 1, there is shown in a block diagram an example
of the clock according to the present invention. This clock
comprises a signal detector A for detecting signals from an
external induction magnetic field, a transistor motor B, a standard
oscillation source C, and a switching circuit D. Further, as shown
in FIG. 2, the above mentioned signal detector circuit A comprises
an induction coil 1 with a ferrite core for detecting the space
magnetic field of a commercial frequency, an amplifier 2 for
amplifying the detected signal, an RC differential circuit 3 for
converting square wave amplified output of the amplifier into a
trigger voltage, and a frequency divider circuit 4 comprising a
astable multivibrator for dividing the trigger voltage into a
frequency being 1/4 (for example, 15Hz) of the commercial
frequency. The transistor motor B is of free-running type
consisting of a transistor Tr.sub.5 a motor coil 5, and a four-pole
rotor 6. The standard oscillation source C consists of a
balance-wheel 7 acting as a standard oscillator, a driving coil 8,
a detection coil 8', a synchronous coil 9, a transistor Tr.sub.2,
and transistor switching elements S.sub.1 S.sub.2 and S.sub.3. The
synchronous coil 9 is magnetically coupled with the rotor of the
transistor motor and electrically connected to the frequency
divider 4 in the signal detector circuit through a transistor
switching element S.sub.1 and a transistor Tr.sub.1. The switching
circuit D consists of a monostable multivibrator 10 operated by the
trigger voltage from the amplifier 2 and thereby generating a
square wave voltage with a constant pulse width, a resistor 11 and
a capacitor 12 for converting the output square wave of the
monostable multivibrator 10 into a DC voltage, and a Schmitt
circuit 13 having transistors Tr.sub.3 and Tr.sub.4. The collector
of the transistor Tr.sub.3 is connected to the bases of the
switching elements S.sub.1 S.sub.2 and S.sub.3 of the standard
oscillation source. The switching element S.sub.1 is of NPN type,
S.sub.2 is of PNP type, and S.sub.3 is of NPN type, so that when
the induction field is normal, S.sub.1 will be ON, S.sub.2 will be
OFF, and S.sub.3 will be ON, while in the occurrence of power
interruption or external field disturbance S.sub.1 and S.sub.3 will
be OFF, and S.sub.2 will be ON.
FIG. 3 shows in a block diagram an improved induction type clock of
the one in FIG. 1. The clock shown in FIG. 3 has additionally an RC
oscillator circuit and a battery voltage and magnetic field level
indicating circuit. The RC oscillator circuit, which has a
free-running frequency of about 50 or 60Hz receives an input signal
from the voltage amplifying circuit and locks its frequency at the
commercial power frequency of 50 or 60Hz. The purpose of the
battery voltage and magnetic field level indicator is to monitor
magnitudes of the induction magnetic field at the place the clock
is placed.
The circuitry arrangement and the operating principle of the clock
as in FIG. 3 will be described below with reference to FIGS. 4a and
4b, which shows a more detailed circuit of FIG. 3.
The commercial frequency induction magnetic field pickup device
used in the embodiment comprises an induction coil having a
ferromagnetic core. A capacitor C3 6 is connected in parallel with
the induction coil, and the capacity of this capacitor is
determined so that this LC circuit is tuned to the commercial
frequency.
When the magnetic force lines of the induction field pass through
the induction coil, a sine wave voltage of commercial frequency is
produced across the induction coil. This signal voltage which being
very weak is applied between the base and emitter of the transistor
T.sub.1, to obtain an amplified voltage from its collector. R.sub.2
is a bias resistor, R.sub.3 is a collector resistor, R.sub.4 is an
emitter resistor, and D12 is a bias compensation diode for
temperature. C.sub.1 and C.sub.7 represent bypass capacitors. Said
amplified voltage appearing at the collector of the transistor
T.sub.1 is further amplified by transistors T.sub.3 and T.sub.4 at
an amplifying stage. R.sub.5, R.sub.9, R.sub.6 and R.sub.10 denote
bias resistors, R.sub.7 and R.sub.11 are collector resistors,
R.sub.8 and R.sub.12 are emitter resistors, C.sub.8, C.sub.10 and
C.sub.12 are coupling capacitors, and C.sub.9 and C.sub.11 are
bypass capacitors.
A transistor T.sub.5, bias resistors R.sub.13 and R.sub.14, a bias
compensation diode D13 for temperature, collector resistors
R.sub.15 and R.sub.16, an emitter resistor R.sub.17, and a bypass
capacitor C.sub.13 constitute a nonlinear amplitude limiter circuit
for clipping the input signal voltage and thus limiting an excess
input voltage applied to the RC oscillator in the next stage.
A transistor T.sub.7, bias resistors R.sub.20, R.sub.21 and
VR.sub.2, a bias temperature-voltage compensation diode D14, a
collector resistor R.sub.22, an emitter resistor R.sub.23, a bypass
capacitor C.sub.15, an RC feedback circuit, capacitors C.sub.16,
C.sub.17 and C.sub.18, resistors R.sub.18, VR.sub.1 and R.sub.19
are forming an RC phase shifting type sine wave oscillator circuit,
in which the oscillation frequency is set to be substantially
nearly the commercial frequency (60 or 50Hz) by the resistor
VR.sub.1 which is variable. The bias resistor VR.sub.2 is a
variable resistor for setting the voltage characteristic of the
oscillation frequency to be at the best point. The output signal
voltage from the nonlinear amplitude limiter is applied to the base
of the above RC oscillator via said coupling capacitor C.sub.14.
The oscillation frequency of the RC oscillator is synchronized with
the input signal voltage so as to operate as an external signal
synchronous oscillator.
This oscillator serves as a sort of filter circuit so that, even
when the induction field is somewhat distorted by any irregular
external magnetic force or other reason, the interference signal is
absorbed by this filter, and the detected signal will be
shaped.
If, however, an excessive input voltage is applied to the base of
this oscillator and if the waveform of this input voltage is
disturbed, the effect of the filter in the oscillator is reduced
and the output voltage waveform becomes distorted. To increase the
filter effect, therefore, it is necessary to limit the input
voltage to the base to be as small as possible. On the other hand,
this input voltage must be large enough to so that the oscillation
frequency of the oscillator will be synchronized in its input
signal frequency, even when there exist certain variations in the
oscillation frequency including variations in the power supply
voltage, ambient temperature and aging.
The above nonlinear amplitude limiter will be described more in
detail with reference to FIGS. 5(I) and 5(II). In the drawing, FIG.
5(I) is a nonlinear amplifier circuit, and FIG. 5(II) shows its
output characteristics. As indicated by the characteristic curve A,
the collector output starts to be saturated from an input voltage
of 140 mVp-p. The saturated output voltage is about 1.3 Vp-p. Since
this output voltage is large enough to be the input to the RC
oscillator, the voltage is divided through the collector resistors
R.sub.15 and R.sub.16 so as to be a clipped output voltage of 140
mVp-p in the clip output characteristic as indicated by the curve
B.
Referring again to FIGS. 4a and 4b, the output voltage of the
oscillator is applied through a resistor R.sub.24 to the base of an
emitter follower circuit comprising a transistor T.sub.9, a
collector resistor R.sub.25 and an emitter resistor R.sub.26.
Output sine wave voltage of the emitter of the follower is applied
to a two-stage nonlinear amplifier circuit comprising transistors
T.sub.10 and T.sub.11 at the next stage, whereby the applied sine
wave is converted into a square wave.
The output voltage from the emitter of transistor T.sub.9 is
applied to the base of the transistor T.sub.10 through a coupling
capacitor C.sub.19. This output voltage causes the transistor
T.sub.10 to operate with a large amplitude and, as a result, the
collector output voltage of the transistor T.sub.10 is saturated,
whereby wave the output of the transistor T10 is formed into a
square wave. The output voltage also causes the transistor T.sub.11
to operate in the same manner.
The square wave output voltage as divided through collector
resistors R.sub.33 and R.sub.34 is applied to a differential
circuit comprising a capacitor C.sub.23 and a resistor R.sub.36 so
that a trigger voltage is produced. Then, a negative trigger
voltage is applied to astable multivibrator frequency divider
circuit via a diode D.sub.4 at the next stage. This frequency
divider consists of transistors T.sub.12, T.sub.13 diodes D.sub.5
and D.sub.6, timing resistors R.sub.38 and R.sub.39, timing
capacitors C.sub.24 and C.sub.25, and collector resistors R.sub.37
and R.sub.40. Transistor T14 amplifies the output of the frequency
divider.
When the commercial power frequency is assumed to be f.sub.HZ, this
frequency can be divided into 1/4 by so selecting the OFF time t of
the transistor T.sub.13 determined by the capacitor C.sub.24 and
resistor R.sub.38 as to be a suitable value between (1/f) /3 < t
< 1/4/4 .
D.sub.5 and D.sub.6 represent diodes for compensating the
free-running oscillation cycle of the frequency divider circuit for
temperature and voltage.
The voltage of the above quarter-frequency (for example, of 15Hz in
the case of 60Hz) is amplified by the amplifier transistor
T.sub.14, and the amplified current flows through synchronous coil
L.sub.c, transistor T.sub.15, resistor 41 and transistor T.sub.14
to the ground.
FIG. 6 shows the transitor motor driving section. In FIG. 6, the
part encircled by the chain-line indicates a frequency divider
circuit 4, and the other region C encircled by chain-line shows a
standard oscillation source. L.sub.1 is a drive coil, L.sub.2 is a
detection coil, C.sub.36 is a capacitor for preventing abnormal
oscillation, L.sub.c is a sychronous coil, 14 is a rotor, 15 is a
worm, 16 is a worm wheel, 17 is a second-hand wheel, 18 is a
second-hand, 19 is a shaft, 20 is a bearing for the shaft, 21 is a
hair spring fixed to the shaft 19, 22 and 23 are forming a pair of
rotating disks mounted to the shaft 19, 24 and 25 are magnets
respectively mounted to each said disk so as to oppose to each
other inside the rotating disks, 26 are balancers, 27 is a drive
coil, and 28 is a detection coil.
The transistor motor is adjusted for a rotation at the rate of
about 450rpm. A square wave current of 15Hz which is a quarter
division of the commercial frequency flows in the synchronous coil
L.sub.c to synchronize the free-running transistor motor rotated at
about 450rpm for the accurate rotation of the 450rpm rate. The
speed of this rotation is reduced by the worm 15, worm wheel 16 and
second-hand wheel 17, thereby moving the second-hand 18. This
operation is performed when the induction magnetic field of the
commercial frequency is stable. In the event of external field
disturbance or power interruption, the detection signal current
flowing in the synchronous coil is disturbed, resulting in an
irregular rotation of the transistor motor and an inaccurate time
keeping.
To avoid this, the switching circuit is actuated so that, in the
event of external field disturbance, the switching transistor
T.sub.15 is turned off to interrupt the 15Hz square wave current
therefrom. At the same time, the synchronous signal current of 15Hz
provided from the separately provided standard oscillator unit C is
supplied to the synchronous coil L.sub.c through the switching
transistor T.sub.30, so that the transistor motor will rotate as
synchronized with the frequency of the standard oscillator unit C.
FIG. 6 is illustrating an example where a balance wheel is used for
the standard oscillator unit. This unit consists of a transistor
T.sub.32, a capacitor C.sub.37 for preventing abnormal oscillation,
a drive coil 27, a detection coil 28 and a balance wheel block
which comprises a wheel, a balancer 26, magnets 24 and 25, a hair
spring 21, etc. This balance wheel oscillating unit is operated at
all times.
The switching circuit comprises a voltage amplifier circuit, a
differential circuit, a monostable multivibrator, an integrator
circuit, a Schmitt circuit, and a two-stage inverter circuit to
convert the control voltage from the Schmitt circuit to a higher
level. The series arrangement of the voltage amplifying circuit,
the differentiation circuit, the monostable multivibrator and the
integration circuit produce a d-c. voltage to control the Schmitt
circuit and the inverter circuit. The output voltage of the Schmitt
circuit and inverter circuit, in turn, operate the switching
transistors T15, T29 and T30 in accordance with the state of the
external induction magnetic field. The collector of the switching
transistor T15 is connected to the positive d-c. power line A
through the synchronous coil L.sub.c, the emitter of T15 is
connected to ground through the transistor T14 and the resistor
R41, and the base of T15 is connected to the collector of
transistor T26 of the Schmitt circuit. The collector of the
switching transistor T29 is connected to the positive d-c. power
line A, the emitter of T29 is connected to one end of the drive
coil of the balance wheel oscillator, and the base of T29 is
connected to the collector of transistor T28 of the inverter
circuit. The emitter of the switching transistor T30 is connected
to the positive d-c. power line A, the emitter of T29 is connected
to one end of the drive coil of the balance wheel oscillator, and
the base of T29 is connected to the collector of transistor T28 of
the inverter circuit. The emitter of the switching transistor T30
is connected to the positive d-c. power line A through the
synchronous coil L.sub.c, and the collector of T30 is connected to
the emitter of transistor T29, and the base of T30 is connected to
the collector of transistor T28 of the inverter circuit through
resistor R75. This switching circuit is operated in the following
manner. Referring to waveforms illustrated in FIGS. 7(I), 7(II) and
7(III), respective in which A shows a collector waveform, B shows a
trigger voltage waveform at the point a in the circuit of FIG. 4, C
shows an output waveform of the monostable multivibrator, and D
shows a DC voltage waveform at the point b in FIG. 4. FIG. 7(I)
shows the operation in normal magnetic field, wherein the amplified
signal voltage waveform is stable as indicated by A. In this
switching circuit, a voltage amplifier circuit having transistors
T.sub.17, T.sub.18, T.sub.19 and T.sub.20 is additionally provided.
The purpose of this amplifier is to ensure operation of the
monostable multivibrator in the next stage since even three-stage
amplifiers may not produce the trigger voltage needed to drive the
monostable multivibrator in the minimum magnetic field intensity of
2.5 .times. 10.sup..sup.-7 oersted at general homes. With the
provision of this amplifier, the gain is increased to obtain a
sufficient square amplified output, which is then converted into a
voltage for triggering the monostable multivibrator. This voltage
amplifier circuit is a four-stage amplifier. The amplified signal
voltage of square wave is converted into a trigger voltage as in B
of FIG. 7(I) by the RC differential circuit comprising a capacitor
C.sub.33 and a resistor R.sub.60.
The monostable multivibrator is triggered by this trigger voltage,
whereby a square wave signal of the same frequency as the
commercial frequency is obtained, as indicated by C of FIG. 7(I)
(pulse width at a constant duty). This square wave output is
converted into a DC voltage by the RC integrator circuit, as
indicated by D in FIG. 7(I). When the RC time constant of this
integrator is determined to be large, the square wave output is
given in a DC voltage waveform.
This DC voltage is applied to the base of the Schmitt circuit
comprising transistors T.sub.25 and T.sub.26, resistors R.sub.66,
R.sub.67, R.sub.68, R.sub.69 and R.sub.70 at the next stage. When
the induction magnetic field is stable, the square wave output of
the monostable multivibrator is not disturbed, so the d-c. voltage
integrated by the integration circuit is higher than the threshhold
voltage of the Schmitt circuit. In this state, transistor T25 is
ON, transistor T26 is OFF, and the inverter transistor T28 is OFF,
so that the control voltage to the base of the switching transistor
T15 is +1.5 volts, the control voltage at the bases of transistors
T30 and T29 is +3 volts. Consequently, the switching transistors
T15 and T29 are ON, and the switching transistor T30 is OFF.
While, if an external magnetic disturbance occurs, the amplified
waveform becomes such as A in FIG. 7 (II), where the waveforms are
linked together or intermittent at certain intermediate points. If
this waveform signal is converted into a trigger voltage, the
waveform becomes FIG. 7 (II) b, where the trigger disappears
partly. If this trigger voltage is used, the output of the
monostable multivibrator becomes FIG. 7 (II) C, where the waveform
is partly lacking. The DC voltage obtained from such partly lacking
waveform output of the monostable multivibrator as above when
converted by the integrator circuit becomes lowered as indicated by
FIG. 7 (II) D. When this DC voltage comes down below a certain
threshold voltage, the state of the Schmitt circuit is inverted. At
this moment, the transistor T.sub.25 turns OFF, and transistor
T.sub.26 turns ON. The collector potential of the transistor
T.sub.26 is decreased nearly to zero potential from the collector
supply voltage. This zero potential is applied to the base of the
switching transistor T.sub.15 to turn this transistor OFF. As a
result, the synchronous current which is a divided quarter of the
detected commercial frequency is interrupted.
The collector of the Schmitt circuit receives its supply voltage
from a constant voltage source through line B. Therefore, the
collector output control voltage is zero when the transistor
T.sub.26 is ON, or it is about 1.5V when the transistor T.sub.26 is
OFF. This voltage is too low to control the switching transistors
T.sub.30 and T.sub.29 which are to control the synchronous current
supplied from the balance wheel circuit. To obtain sufficient
collector output control votage of 3V, a circuit comprising
transistors T.sub.27 and T.sub.28 is used, whereby a control
voltage of 0 to 3V is obtained from the collector of the transistor
T.sub.28 and thus the switching transistors T.sub.29 and T.sub.30
are controlled.
As described in the foregoing, the transistor T.sub.26 is OFF when
the magnetic field is stable. In this state, the transistor
T.sub.27 is ON, and T.sub.28 is OFF. The switching transistors
T.sub.29 and T.sub.30 are controlled by the collector voltage (3V)
of the transistor T.sub.28. The switching transistor T.sub.29 is of
NPN type, and T.sub.30 is of PNP type. Under this condition, the
switching transistor T.sub.30 turns OFF, and T.sub.29 turns ON.
Thus the balance wheel drive current flows from the voltage source
(+3V) to the ground through the switching transistor T.sub.29,
drive coil and transistor T.sub.32, but does not flow into the
synchronous coil.
On the other hand, if an external magnetic disturbance occurs, the
transistors T.sub.25 and T.sub.26 of the Schmitt circuit are
inverted so as to turn the transistors T.sub.26 and T.sub.28 ON and
T.sub.25 and T.sub.27 OFF. As a result, the collector control
voltage of the transistor T.sub.28 becomes zero. At this moment,
the switching transistor T.sub.29 turns off, and T.sub.30 turns ON.
Thus, the balance wheel drive current flows from the voltage source
(+3V) to the ground through the synchronous coil, switching
transistor T.sub.30, drive coil and transistor T.sub.32. Under this
condition, the transistor motor is rotated synchronously with the
oscillation frequency of the balance wheel, the latter of which
must be of course regulated to oscillate at the rate of 15
vibrations/sec. The transistor motor is thus synchronized with the
frequency of the balance wheel and rotated accurately, even if the
induction magnetic field is affected by the external field
disturbance.
In the event of very weak induction magnetic field or power
interruption, referring next to FIG. 7 (III), the amplified output
takes the waveform as indicated by A, which is a sine wave without
being a square wave. When power service is interrupted, this
amplified output may be ignored.
In such event, as shown by FIG. 7 (III) B, no trigger voltage is
presented through the differentiation circuit, and the monostable
multivibrator delivers no output. That is, the DC output voltage of
the integrator circuit becomes substantially zero. The operation at
this time is similar to the case of FIG. 7 (II), where the clock is
synchronized with the oscillation of the balance wheel.
The purpose of resistor R.sub.75 is to block the flow of an excess
current from power source (+3V) to the ground through the
synchronous coil, the base and emitter of switching transistor
T.sub.30, and transistor T.sub.28 when the collector potential of
transistor T.sub.28 becomes zero (transistor T.sub.28 is ON).
The purpose of diodes D14 and D15 is to make the square wave output
voltage of the monostable multivibrator stable against variations
in the power source voltage. At the same time, these diodes serve
to slightly lower the square wave output voltage when the ambient
temperature is raised. As a result, due to lowering of the rise
voltage of the diode, the DC voltage of the integrator circuit is
lowered. This serves to compensate for any variation in the
threshold voltage due to decrease of the base-emitter voltage
V.sub.BE of the transistor T.sub.25.
When the ambient temperature is lowered, the square wave output
voltage is increased, and the DC voltage is also increased. At this
time, the base-emitter voltage V.sub.BE of the transistor T.sub.25
is increased, and, therefore, the variation in the threshold
voltage is compensated for as in the case of the ambient
temperature rise.
As has been described above, the switching circuit of the clock of
this invention is operated in such manner that the amplified
waveform of the detected signal is converted into a DC voltage, the
variation in the DC potential due to irregular waveform is detected
by the Schmitt circuit. Sequential inversion of the Schmitt circuit
is utilized for forming a control voltage, with which the switching
transistor is actuated so as to switch the synchronous current.
In the present instance, incidentally, the monostable multivibrator
employed is not always necessary. However, with the provision of
this monostable multivibrator, the probability of vanishing the
pulse becomes higher and the DC potential tends to be readily
varied (as apparently seen in FIG. 7 (II) A, B and C) when the
monostable multivibrator is actuated through a trigger voltage in
the event of disturbance in the amplified waveform due to external
magnetic disturbance, and even if the disturbance of the amplified
waveform is small. The use of the monostable multivibrator makes it
possible, at the same time, to produce a square wave of constant
duty. Thus, whereas the square wave duty is variable due to bias
change and variation in the input magnetic field intensity if the
amplifier circuit alone is relied on, the use of monostable
multivibrator enables it possible to provide a switching system
which is operable at a high stability, regardless of any DC
potential variation due to any other reason than the external
magnetic disturbance.
In view of the nature of the cordless magnetic induction clocks, it
is desirable that the clock is synchronized with the commercial
frequency at all times. Therefore, the level for the switching is
to be set so that the Schmitt circuit is switched immediately after
the waveform disturbance occurs due to external irregular magnetic
field. This is because, if the operation of the frequency divider
of the astable multivibrator is disturbed, the synchronous current
to the transistor motor is immediately disturbed.
The magnetic induction clock in FIG. 4 showing an embodiment of
this invention is provided with an induction magnetic field and
battery voltage indicator mechanism, which comprises a transistor
T.sub.16, a bias resistor R.sub.42, a collector resistor R.sub.43,
an emitter resistor R.sub.44, diodes D.sub.9 and D.sub.10, a
coupling capacitor C.sub.26, switches SW-1 and SW-2 and a high
sensitivity ammeter.
The amplified output voltage from the transistor T.sub.4 is applied
to the base of the transistor T.sub.16, to further amplify the
output voltage. This signal is supplied to the loads D.sub.9 and
D.sub.10 and to the meter through the coupling capacitor C.sub.26.
When the field intensity is strong, a large output voltage is
obtained at the collector of the transistor T.sub.16, whereby a
large half cycle current of the signal frequency flows in the
meter, whereas when the induction field intensity is weak, the
collector output voltage is small, and a small current flows in the
meter to actuate the indicator in a small extent. Since a capacity
is not connected in parallel with the meter, the meter maintains
good damping (but the meter indication does not follow the input at
a degree of a half cycle of the signal frequency). When the
detected signal waveform is disturbed due to entrance of an
irregular external magnetic field of low frequency, the meter
pointer fluctuates unstably in response to the disturbance.
By operatively associating the switch SW-1 and SW-2, it is possible
to use the meter for both battery voltage indication and induction
field intensity indication.
Further in the embodiment of FIG. 4, a resistor R.sub.1, diodes
D.sub.1, D.sub.2 and D.sub.3, and a capacitor C.sub.1 constitute a
constant voltage circuit, which is capable of maintaining a
constant voltage of 1.5V even if the battery voltage is varied to
near 2V from 3V. C.sub.1 is a smoothing capacitor for removing
ripple voltage.
FIG. 8 (I) shows another embodiment of the invention, wherein a
filter F for absorbing the disturbed signal caused by rotation of
the rotor and vibration of the balance wheel is inserted between
the induction magnetic field detector and the voltage amplifier
circuit. In this circuit, only the voltage of the desired frequency
can be voltage-amplified to drive the transistor motor. The
response characteristic thereof is as shown in FIG. 8 (II).
According to this embodiment, the circuitry block diagram can be
simplified.
FIG. 9 schematically shows the internal arrangement of the
induction type clock of this invention, with the rear side lid
removed. In the drawing, 29 is a case, 1 is an induction coil, 30
is a base plate to which the clock mechanism is installed, 19 is a
shaft, 20 is a pair of bearings, 21 is a hair spring, 22 and 23 are
balance wheels, 24 and 25 are magnets, 26 are balancers, 14 is a
rotor, 15 is a worm, 16 is a worm wheel, 17 is a second-hand wheel,
and 18 is a second-hand. X, Y and Z denote, respectively, the axial
direction of the magnetic core of the induction coil, the axial
direction of the shaft 21, and the axial direction of the rotor
14.
Because the rotor and balance wheel using magnets are used for the
clock driver unit and the standard oscillator unit, a magnetic
disturbance is produced by the rotation and vibration of these
units, and such magnetic field (at a frequency of 15Hz) is detected
by the induction coil. To minimize the influence of this magnetic
field, the induction coil 1, the rotor of the transistor motor, and
the balance wheel are arranged, as shown in FIG. 9, so that their
shafts (X, Y, and Z axes) are parallel with each other and these
elements are located at the mid point so as to be on the same
perpendicular line Z', Y' and X' with respect to the axes X, Y and
Z. With this arrangement, the magnetic interference from the driver
unit and standard vibration unit which are to cross the induction
coil can be minimized.
According to this invention, as has been described above, the
transistor motor is rotated as synchronized with the commercial
frequency when the induction magnetic field is normal. In the event
of power interruption or irregular external field or weak magnetic
field, the synchronous signal from the commercial frequency is
automatically blocked and the transistor motor is synchronized with
the frequency of the standard vibration unit which is vibrated at
all times. Thus, the clock operation is perfectly free of the
influences of power interruption, field disturbance or weak
magnetic field, and a highly accurate induction clock can be
realized.
While a few embodiments of the invention and particular
modifications thereof have been described above, it is to be
clearly understood that this description is made only by way of
example and not as a limitation on the scope of the invention.
* * * * *