Electricity: motive power systems – Open-loop stepping motor control systems
Reexamination Certificate
2000-06-27
2002-01-15
Ip, Paul (Department: 2837)
Electricity: motive power systems
Open-loop stepping motor control systems
C318S685000, C368S076000, C368S157000
Reexamination Certificate
active
06339306
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates to a control device for an electronic timepiece, and in particular to a control device for controlling a stepping motor used in an electronic timepiece which uses kinetic energy to drive a electricity generating device to provide electronic power for driving the stepping motor.
In recent years, timing devices, such as wrist-watches, have been sold with built-in electricity generators in which the energy generated by the movement of the user's arm is converted into electricity which is used to drive the stepping motor which moves the hands of the device. These timing devices operate without batteries and can continuously run off the energy generated by the user's movement. Also, these timing devices eliminate the often cumbersome process of changing batteries as well as help reduce the environmental hazard associated with battery disposal. As a result, built-in electricity generators are being closely evaluated for future widespread use in wristwatches and similar devices.
Generally, electronic timepieces that incorporate electricity generators include a stepping motor for driving the hands of the timepiece. These stepping motors, also referred to as a pulse motors or digital motors, are driven by pulse signals and are also extensively used as actuators for digital control devices. In recent years, compact electronic devices and information equipment have been developed in which portability is desirable, and compact and lightweight stepping motors are in widespread use as actuators for this equipment. Representative of such electronic devices are timing devices including electronic timepieces, time switches and chronographs.
Referring now to
FIG. 12
, there is shown a prior art timing device
9
, for example a wristwatch, which includes a stepping motor
10
, a driving circuit
30
for driving stepping motor
10
, a gear train
50
for transferring the force of stepping motor
10
, a second hand
61
, a minute hand
62
, and an hour hand
63
which are moved by gear train
50
. Stepping motor
10
generates magnetic force in response to driving pulses supplied from a control device
20
. Stepping motor
10
includes a driving coil
11
, a stator
12
which is excited by driving coil
11
, and a rotor
13
which rotates within stator
12
as a result of the excited magnetic field. By selecting a disk-shaped bipolar permanent magnet for rotor
13
, a PM-type (Permanent Magnet rotational) stepping motor is formed. Stator
12
is provided with a magnetism saturating unit
17
so that the different magnetic poles that result from the magnetic force generated by driving coil
11
are generated at the phases (poles)
15
and
16
, respectively surrounding rotor
13
. Also, an internal notching
18
is provided at the appropriate location on the inner periphery of stator
12
so that cogging torque is generated and rotor
13
is stopped at the appropriate position.
The rotation of rotor
13
of stepping motor
10
is transferred to each of the timepiece hands by gear train
50
which includes a fifth gear
51
meshing with a fourth gear
52
, which also meshes with a third gear
53
, which meshes with a center wheel
54
. Center wheel
54
meshes with a minute wheel
55
, which meshes with an hour wheel
56
. Second hand
61
is connected to the axis of fourth gear
52
, minute hand
62
is connected to the axis of center wheel
54
, and hour hand
63
is connected to the axis of hour wheel
56
. Time is displayed by each of the timepiece hands operating synchronously with the rotation of rotor
13
. Of course, a transfer system for displaying the year, month, and day (not shown) may also be connected to gear train
50
. In order for timing device
9
to display the time as a result of the rotation of stepping motor
10
, stepping motor
10
is supplied with driving pulses which are based on counting (timing) of signals generated by a reference frequency.
Control device
20
, which controls stepping motor
10
, includes a pulse synthesizing circuit
22
for generating reference pulses of a standard frequency using a reference oscillator
21
such as a crystal oscillator, or pulse signals of a different pulse width or timing. The reference pulses are input to a control circuit
23
for controlling stepping motor
10
based on the various pulse signals supplied from pulse synthesizing circuit
22
. Control circuit
23
has a driving control circuit
24
which receives the reference pulses for controlling driving circuit
30
, and a detecting circuit
25
for detecting whether driving rotor
13
rotated. Driving control circuit
24
includes: a driving pulse supplying unit
24
a
for supplying driving pulses to driving circuit
30
which in turn drives driving rotor
13
of stepping motor
10
; a rotation detection pulse supplying unit
24
b
for outputting rotation detecting pulses to detection circuit
25
for inducing induction voltage to determine whether driving rotor
13
rotated in response to the driving pulse; a magnetic detection pulse supplying unit
24
c
for outputting magnetic field detecting pulses to detection circuit
25
prior to the output of the driving pulse, for inducing induction voltage to detect the presence of a magnetic field external to stepping motor
10
; an auxiliary pulse supplying unit
24
d
for generating an auxiliary pulse that has an effective electric power that is greater than that of the driving pulse, the auxiliary pulse being output if the driving pulse does not cause driving rotor
13
to rotate or if an external magnetic field has been detected; and a demagnetizing pulse supplying unit
24
e
for producing a demagnetizing pulse having a polarity that is opposite that of the auxiliary pulse and which is used to demagnetize driving coil
11
after the auxiliary pulse is output.
Detecting circuit
25
includes a rotating detecting unit
26
for comparing the rotation detecting induction voltage, obtained by outputting the rotation detecting pulse, with a set value, and detecting whether driving rotor
13
rotated. Detecting circuit
25
also includes a magnetic field detecting unit
27
for comparing the magnetic field detecting induction voltage, obtained by outputting the magnetic field detecting pulse, with a set value for detecting the presence of a magnetic field.
Referring now to
FIG. 13
, there is shown rotation detecting unit
26
which employs a pair of comparators,
29
a
and
29
b
, to compare the value of the bi-directional excitation voltage generated in driving coil
11
with a set value SV
1
, to determine whether driving rotor
13
has rotated. Comparator
29
a
receives one input from the standard signal SV
1
and a second input &phgr;
1
from one side of driving coil
11
and produces a first comparison signal. Similarly, comparator
29
b
receives a first input SV
1
and a second input &phgr;
2
from the other side of driving coil
11
and produces a second comparison signal. An OR gate
29
c
receives the first and second comparison signals and produces an output to driving control circuit
24
. Similarly, magnetic field detecting unit
27
uses a pair of inverters,
28
a
and
28
b
, each having a threshold value of SV
2
, which receive the inputs of &phgr;
1
and &phgr;
2
, respectively. These inverted signals are input to an OR gate
28
c
for detecting the presence of a magnetic field. The results of each comparison are fed back to driving control circuit
24
, and are used for controlling stepping motor
10
.
Driving circuit
30
, which supplies various driving pulses to stepping motor
10
under the control of driving control circuit
24
, coupled between driving control circuit
24
and a battery
41
, has a bridge circuit which includes a serially connected p-channel MOSFET
33
a
and n-channel MOSFET
32
b
, and serially connected p-channel MOSFET
33
b
and n-channel MOSFET
32
a
, configured for controlling the voltage supplied to stepping motor
10
from battery
41
. Also included are a pair of rotation detecting resistors
35
a
and
35
b
connected
Ip Paul
Seiko Epson Corporation
Stroock & Stroock & Lavan LLP
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