U.S. patent number RE40,709 [Application Number 11/591,409] was granted by the patent office on 2009-05-12 for piezoactuator and drive circuit therefor.
This patent grant is currently assigned to Seiko Epson Corporation. Invention is credited to Hidehiro Akahane, Makoto Furuhata, Akihiro Sawada.
United States Patent |
RE40,709 |
Akahane , et al. |
May 12, 2009 |
Piezoactuator and drive circuit therefor
Abstract
A piezoactuator has a diaphragm, and the diaphragm has flat
piezoelectric elements that oscillate in a longitudinal oscillation
mode and a sinusoidal oscillation mode. A first electrode for
detecting oscillation in the longitudinal oscillation mode, and a
second electrode for detecting the amplitude of oscillation in the
sinusoidal oscillation mode, are disposed on the surface of the
diaphragm. When the piezoactuator is driven with a drive signal,
the phase difference of a first detection signal output from the
first electrode and a second detection signal output from the
second electrode is detected. The frequency at which the detected
phase difference becomes the maximum phase difference is then
obtained, and a drive signal of a matching frequency is applied to
the piezoelectric elements.
Inventors: |
Akahane; Hidehiro (Suwa,
JP), Sawada; Akihiro (Suwa, JP), Furuhata;
Makoto (Suwa, JP) |
Assignee: |
Seiko Epson Corporation (Tokyo,
JP)
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Family
ID: |
18945798 |
Appl.
No.: |
11/591,409 |
Filed: |
November 1, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
10109356 |
Mar 26, 2002 |
06841919 |
Jan 11, 2005 |
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Foreign Application Priority Data
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Mar 27, 2001 [JP] |
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2001-91112 |
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Current U.S.
Class: |
310/316.01;
310/316.02; 310/323.02 |
Current CPC
Class: |
H02N
2/004 (20130101); H02N 2/103 (20130101); H02N
2/008 (20130101) |
Current International
Class: |
H01L
41/08 (20060101) |
Field of
Search: |
;310/316.01,316.02,323.02 ;318/116 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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06-014565 |
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Jan 1994 |
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JP |
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9-294384 |
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Nov 1997 |
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JP |
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09-308274 |
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Nov 1997 |
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JP |
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11-215858 |
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Aug 1999 |
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JP |
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2000-078867 |
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Mar 2000 |
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JP |
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2000-188882 |
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Jul 2000 |
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JP |
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2000-295876 |
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Oct 2000 |
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JP |
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2001-286164 |
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Oct 2001 |
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JP |
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Primary Examiner: Budd; Mark
Attorney, Agent or Firm: Gabrik; Michael T.
Claims
What is claimed is:
1. A drive circuit for a piezoactuator, comprising: at least one
piezoelectric element having a first oscillation mode and a second
oscillation mode, the at least one piezoelectric element being
adapted to oscillate when an AC signal is applied to it, the second
oscillation mode having a different oscillation direction than that
of the first oscillation mode; a driver for applying an AC drive
voltage signal to the at least one piezoelectric element; and a
frequency control unit for detecting a first electrical signal from
the at least one piezoelectric element indicative of oscillation in
the first oscillation mode, for detecting a second electrical
signal from the at least one piezoelectric element indicative of
oscillation in the second oscillation mode, and for controlling the
frequency of the AC drive voltage signal to optimize the phase
difference between the first and second electrical signals for a
particular operating condition of the at least one piezoelectric
element.Iadd., such that the phase difference is substantially
maximized, the frequency control unit further comprising: a phase
difference detection circuit for detecting the phase difference
between the first and second electrical signals; a time
differentiating circuit for determining a time differential of the
phase difference detected by the phase difference detection
circuit; and a frequency adjusting circuit for increasing the
frequency of the AC drive voltage signal when the time differential
is positive, and decreasing the frequency of the AC drive voltage
signal when the time differential is negative.Iaddend..
.[.2. A drive circuit for a piezoactuator as described in claim 1,
wherein the frequency control unit comprises a circuit for
controlling the frequency of the AC drive voltage signal so that
the phase difference between the first and second electrical
signals is substantially maximized..].
.[.3. A drive circuit for a piezoactuator as described in claim 2,
wherein the frequency control unit comprises: a phase difference
detection circuit for detecting the phase difference between the
first and second electrical signals; a time differentiating circuit
for determining a time differential of the phase difference
detected by the phase difference detection circuit; and a frequency
adjusting circuit for increasing the frequency of the AC drive
voltage signal when the time differential is positive, and
decreasing the frequency of the AC drive voltage signal when the
time differential negative..].
4. A drive circuit for a piezoactuator as described in claim
.[.2.]. .Iadd.1.Iaddend., further comprising a voltage-controlled
oscillator for supplying an output signal to the driver, wherein
the frequency control unit controls the frequency of the AC drive
voltage signal by increasing or decreasing a control voltage
applied to the voltage-controlled oscillator.
5. A drive circuit for a piezoactuator as described in claim 4,
wherein the frequency control unit comprises a memory for storing
the voltage level of the control voltage when the frequency of the
AC drive voltage signal is controlled to maximize the phase
difference, wherein the frequency control unit determines an
initial level of the control voltage based on the voltage level of
the control voltage stored in memory when frequency control of the
AC drive voltage signal is initiated and then increases or
decreases the control voltage accordingly.
6. A drive circuit for a piezoactuator .[.as described in claim
1.]. , .Iadd.comprising: at least one piezoelectric element having
a first oscillation mode and a second oscillation mode, the at
least one piezoelectric element being adapted to oscillate when an
AC signal is applied to it, the second oscillation mode having a
different oscillation direction than that of the first oscillation
mode; a driver for applying an AC drive voltage signal to the at
least one piezoelectric element; and a frequency control unit for
detecting a first electrical signal from the at least one
piezoelectric element indicative of oscillation in the first
oscillation mode, for detecting a second electrical signal from the
at least one piezoelectric element indicative of oscillation in the
second oscillation mode, and for controlling the frequency of the
AC drive voltage signal to optimize the phase difference between
the first and second electrical signals for a particular operating
condition of the at least one piezoelectric element,
.Iaddend.wherein the frequency control unit comprises a circuit for
controlling the frequency of the AC drive voltage signal so that
the phase difference substantially corresponds to a reference phase
difference.Iadd., wherein the frequency control unit further
comprises: a drive evaluator adapted to determine if drive of the
piezoactuator satisfies a particular performance characteristic;
and an initial reference phase difference adjustor adapted to
reduce the reference phase difference so that the piezoactuator
satisfies the particular performance characteristic when the drive
evaluator determines that the piezoactuator does not satisfy the
particular performance characteristic, and to increase the
reference phase difference when the drive evaluator determines that
the piezoactuator satisfies the particular performance
characteristic.Iaddend..
7. A drive circuit for a piezoactuator as described in claim 6,
wherein the frequency control unit comprises: a phase difference
detection circuit for detecting the phase difference between the
first and second electrical signals; a comparator for comparing the
phase difference detected by the phase difference detection circuit
with the reference phase difference; and a frequency adjusting
circuit for increasing or decreasing the frequency of the AC drive
voltage signal based on the comparison result obtained by the
comparator.
8. A drive circuit for a piezoactuator as described in claim 7,
wherein the frequency control unit further comprises
voltage-controlled oscillator for supplying an output signal to the
driver; and herein the frequency adjusting circuit comprises a
voltage adjusting circuit for increasing or decreasing the control
voltage applied to the voltage-controlled oscillator based on the
comparison result obtained by the comparator.
.[.9. A drive circuit for a piezoactuator as described in claim 6,
wherein the frequency control unit comprises: a drive evaluator
adapted to determine if drive of the piezoactuator satisfies a
particular performance characteristic; and an initial reference
phase difference adjustor adapted to reduce the reference phase
difference so that the piezoactuator satisfies the particular
performance characteristic when the drive evaluator determines that
the piezoactuator does not satisfy the particular performance
characteristic, and to increase the reference phase difference when
the drive evaluator determines that the piezoactuator satisfies the
particular performance characteristic..].
10. A drive circuit for a piezoactuator as described in claim
.[.9.]. .Iadd.6.Iaddend., wherein, when it is determined that the
reference phase difference at which the piezoactuator drive
satisfies the particular performance characteristic is
substantially the same for a predetermined consecutive number of
times, the initial reference phase difference adjustor is
controlled to not increase nor decrease the reference phase
difference for a pre-specified period of time.
11. A drive circuit for a piezoactuator as described in claim
.[.9.]. .Iadd.6.Iaddend., wherein the frequency control unit
comprises a frequency counter for measuring the frequency of the AC
drive voltage signal, and wherein the drive evaluator determines
whether or not the piezoactuator satisfies the particular
performance characteristic based on whether or not the frequency
measured by the frequency counter is within a predetermined
range.
12. A drive circuit for a piezoactuator.[.as described in claim
6.]. , .Iadd.comprising: at least one piezoelectric element having
a first oscillation mode and a second oscillation mode, the at
least one piezoelectric element being adapted to oscillate when an
AC signal is applied to it, the second oscillation mode having a
different oscillation direction than that of the first oscillation
mode; a driver for applying an AC drive voltage signal to the at
least one piezoelectric element; and a frequency control unit for
detecting a first electrical signal from the at least one
piezoelectric element indicative of oscillation in the first
oscillation mode, for detecting a second electrical signal from the
at least one piezoelectric element indicative of oscillation in the
second oscillation mode, and for controlling the frequency of the
AC drive voltage signal to optimize the phase difference between
the first and second electrical signals for a particular operating
condition of the at least one piezoelectric element, wherein the
frequency control unit comprises a circuit for controlling the
frequency of the AC drive voltage signal so that the phase
difference substantially corresponds to a reference phase
difference, .Iaddend.wherein the frequency control unit further
comprises: means for obtaining, each time the piezoactuator is
driven, an indication of a change in the phase difference between
the first and second electrical signals from a previous drive
operation of the piezoactuator; and means for increasing or
decreasing the reference phase difference according to the change
in the phase difference.
13. A method for controlling a drive circuit having at least one
oscillatible piezoelectric element of a piezoactuator, the method
comprising the steps of: applying an AC drive voltage signal to the
at least one piezoelectric element; outputting an output signal
having a frequency corresponding to a frequency of a control
voltage; receiving a first electrical signal from the at least one
piezoelectric element indicative of oscillation in a first
oscillation mode and receiving a second electrical signal from the
at least one piezoelectric element in indicative of oscillation in
a second oscillation mode, the second oscillation mode having an
oscillation direction different from that of the first oscillation
mode; detecting a phase different between the first and second
electrical signals; and optimizing the oscillation frequency of the
output signal based on the detected phase difference.Iadd.,
comprising increasing the oscillation frequency if a time
differential of the detected phase difference is greater than zero,
and decreasing the oscillation frequency if the time differential
is less than zero, the increasing or decreasing being performed
until the time differential of the phase difference over a
pre-specified period of time is within a specified
range.Iaddend..
.[.14. A method as described in claim 13, wherein the optimizing of
the oscillation frequency comprises increasing the oscillation
frequency if a time differential of the detected phase difference
is greater than (d/dt).sub.1, where (d/dt).sub.1 is greater than
zero, and decreasing the oscillation frequency if the time
differential is less than (d/dt).sub.2, where (d/dt).sub.2 is less
than zero, the increasing or decreasing being performed until the
time differential of the phase difference over a pre-specified
period of time is between (d/dt).sub.1 and (d/dt).sup.2..].
.[.15. A method as described in claim 13, wherein the optimizing of
the oscillation frequency comprises increasing the oscillation
frequency until the detected phase difference is greater than or
equal to a reference phase difference..].
16. A method .[.as described in claim 15, further comprising a step
of.]. .Iadd.for controlling a drive circuit having at least one
oscillatible piezoelectric element of a piezoactuator, the method
comprising the steps of: applying an AC drive voltage signal to the
at least one piezoelectric element; outputting an output signal
having a frequency corresponding to a frequency of a control
voltage; receiving a first electrical signal from the at least one
piezoelectric element indicative of oscillation in a first
oscillation mode and receiving a second electrical signal from the
at least one piezoelectric element indicative of oscillation in a
second oscillation mode, the second oscillation mode having an
oscillation direction different from that of the first oscillation
mode; detecting a phase difference between the first and second
electrical signals; optimizing the oscillation frequency of the
output signal based on the detected phase difference, wherein the
optimizing of the oscillation frequency comprises increasing the
oscillation frequency until the detected phase difference is
greater than or equal to a reference phase difference; and.Iaddend.
determining if driving the piezoactuator satisfies a particular
performance characteristic, and correcting the reference phase
difference based on the determination.
17. A device-readable medium embodying a control program for
controlling a drive circuit having at least one oscillatible
piezoelectric element of a piezoactuator, the control program
comprising.Iadd.:.Iaddend. applying an AC drive voltage signal to
the at least one piezoelectric element; outputting an output signal
of a frequency corresponding to a frequency control voltage;
receiving a first electrical signal from the at least one
piezoelectric element indicative of oscillation in a first
oscillation mode and receiving a second electrical signal from the
at least one piezoelectric element indicative of oscillation in a
second oscillation mode, the second oscillation mode having an
oscillation direction different from that of the first oscillation
mode; detecting a phase difference between the first and second
electrical signals; and optimizing the oscillation frequency of the
output signal based on the detected phase difference.Iadd.,
comprising increasing the oscillation frequency if a time
differential of the detected phase difference is greater than zero,
and decreasing the oscillation frequency if the time differential
is less than zero, the increasing or decreasing being performed
until the time differential of the phase difference over a
pre-specified period of time is within a specified
range.Iaddend..
18. A device-readable medium as described in claim 17, wherein the
medium comprises a physical storage device or an electromagnetic
signal on which the program of instructions is carried.
19. A portable electronic device, comprising: a piezoactuator
comprising at least one piezoelectric element having a first
oscillation mode and a second oscillation mode, the at least one
piezoelectric element being adapted to oscillate when an AC signal
is applied to it, the second oscillation mode having a different
oscillation direction than that of the first oscillation mode; and
a drive circuit comprising: a driver for applying an AC drive
voltage signal to the at least one piezoelectric element; and a
frequency control unit for detecting a first electrical signal from
the at least one piezoelectric element indicative of oscillation in
the first oscillation mode, for detecting a second electrical
signal from the at least one piezoelectric element indicative of
oscillation in the second oscillation mode, and for controlling the
frequency of the AC drive voltage signal to optimize the phase
difference between the first and second electrical signals for a
particular operating condition.Iadd., such that the phase
difference is substantially maximized, the frequency control unit
further comprising: a phase difference detection circuit for
detecting the phase difference between the first and second
electrical signals; a time differentiating circuit for determining
a time differential of the phase difference detected by the phase
difference detection circuit; and a frequency adjusting circuit for
increasing the frequency of the AC drive voltage signal when the
time differential is positive, and decreasing the frequency of the
AC drive voltage signal when the time differential
negative.Iaddend..
20. A portable electronic device as described in claim 19, wherein
the portable electronic device is a wristwatch comprising: a rotor
adapted to be rotationally driven by the piezoactuator; and a
display mechanism linked to the rotor for displaying information
related to time.
21. A portable electronic device as described in claim 19, wherein
the portable electronic device is a contactless IC card.
.Iadd.22. A portable electronic device, comprising the drive
circuit for a piezoactuator as described in claim 6..Iaddend.
Description
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a piezoelectric actuator having a
piezoelectric device and to a drive circuit for the same.
RELATED ART
Piezoelectric devices feature outstanding response and efficiency
converting electrical energy to mechanical energy. As a result,
various types of piezoelectric actuators that use the piezoelectric
effect of piezoelectric devices have been developed in recent
years. These piezoactuators are used in such fields as
piezoelectric buzzers, inkjet heads for printers, and ultrasonic
motors. Using piezoactuators in the calendar display mechanism in
wristwatches and other such applications where there is strong
demand for size reductions has also been investigated in recent
years.
Wristwatch calendar display mechanisms to now are generally
configured to drive the date counter by indirectly transferring
rotational drive power from an electromagnetic stepping motor to
the date counter and such through the wheel train of the movement.
Wristwatches are worn held to the wrist with a band and for the
convenience of such portability are preferably thin. It is
therefore necessary to also make the calendar display mechanism
thin.
A thin calendar display mechanism is also desirable from the
perspective of improving watch production efficiency. First, there
are watches with a calendar display mechanism provided in the
watch, and there are watches that are not equipped with a calendar
display mechanism. Overall watch production efficiency can be
improved if a common mechanical system for advancing the hands (the
"movement") can be used in both watch types. This is because a
production system whereby, for example, the movements are mass
produced for both watch types and then assembled to the two types
of watches, and the calendar display mechanism is then assembled to
only the one type of watch, can be used. In order to use such a
production system, however, it is necessary to be able to place the
calendar display mechanism on top of the movement, that is, on the
face side. In order to do this, it is necessary to configure the
calendar display mechanism so that it is thin enough to fit on the
face side.
While there has thus been a strong desire for thinning the calendar
display mechanism, the stepping motors used in the calendar display
mechanism are configured such that the coil and rotor and such
parts are disposed perpendicularly to the display face, and there
is a limit to how thin these can be made. Conventional calendar
display mechanisms using a stepping motor are thus not suited to
wristwatches that must be made thin.
It is also particularly difficult when using an electromagnetic
stepping motor as the power source to make a calendar display
mechanism thin enough to be placed on the face side. It has
therefore been necessary to separately design and manufacture the
movements depending upon whether a calendar display mechanism is
included or not when watches with a calendar display mechanism and
watches without a calendar display mechanism are both
manufactured.
Considering this background an actuator other than a stepping motor
suitable for configuring a thin calendar display mechanism has been
desired. This has led to the above-noted piezoactuators being
studied for use as such an actuator.
There are, however, problems related to using a piezoactuator in
the calendar display mechanism of a watch.
First, displacement of the piezoelectric device is dependent upon
the voltage of the supplied drive signal but is very low and
normally on the submicron order. Displacement produced by the
piezoelectric device is therefore amplified by some amplifying
mechanism and transferred to the driven part. However, energy to
drive the amplifying mechanism is also consumed when an amplifying
mechanism is used, thus leading to a problem of lower efficiency. A
further problem is that when an amplifying mechanism is used the
size of the device becomes larger. A yet further problem is that
when an amplifying mechanism is interposed it is difficult to
stably transfer drive power to the driven part.
Small portable devices such as wristwatches are battery driven and
it is therefore necessary to minimize power consumption and drive
signal voltage. When assembling a piezoactuator into such portable
devices a piezoactuator with high energy efficiency and low drive
signal voltage is therefore required.
A piezoactuator having a diaphragm made from a thin rectangular
piezoelectric device to which a drive signal is applied to make the
piezoelectric device expand and contract lengthwise and excite
longitudinal oscillations, and mechanically inducing sinusoidal
oscillations by means of the longitudinal oscillations, has been
proposed as a high efficiency actuator that can be included in
compact devices.
By producing both longitudinal oscillations and sinusoidal
oscillations in the diaphragm, this type of piezoactuator moves the
part of the piezoactuator in contact with the driven part in an
elliptical path. While being small and thin, this piezoactuator can
drive with high efficiency.
While it is relatively easy to control the longitudinal
oscillations produced by the piezoelectric device with this
piezoactuator by controlling the voltage of the drive signal,
easily and accurately controlling the sinusoidal oscillations
induced according to the mechanical characteristics of the
diaphragm is difficult. It has therefore been difficult to drive
this type of piezoactuator with stability and high efficiency.
SUMMARY OF THE INVENTION
An object of this invention is to provide a drive circuit capable
of stably and highly efficiently driving a piezoactuator.
To achieve this object, the present invention provides a drive
circuit for a piezoactuator of which a major component is a
diaphragm that is a diaphragm made from piezoelectric elements and
oscillates when an ac signal is applied in a first oscillation mode
and a second oscillation mode having a different oscillation
direction, the piezoactuator drive circuit characterized by
comprising a driver for applying a drive voltage signal that is an
ac signal to the diaphragm; and a frequency control unit for
detecting an electrical signal from the diaphragm representing
oscillation in the first oscillation mode and an electrical signal
representing oscillation in the second oscillation mode, and
applying frequency control of the drive voltage signal to optimize
the phase difference between these signals. This is a first
embodiment (basic embodiment) of a piezoactuator drive circuit
provided by the present invention.
By thus optimally controlling the phase difference, driving the
piezoactuator at consistently high efficiency is enabled by the
present invention.
In a preferred embodiment the frequency control unit is a circuit
for frequency controlling the drive voltage signal so that the
phase difference is substantially maximized. This is a second
embodiment of a piezoactuator drive circuit provided by the present
invention.
The frequency control unit in this case preferably has a phase
difference detection circuit for detecting, for example, a phase
difference between an electrical signal representing oscillation in
the first oscillation mode and an electrical signal representing
oscillation in the second oscillation mode; a circuit for
determining a time derivative of the phase difference detected by
the phase difference detection circuit; and a circuit for
increasing the drive voltage signal frequency when the time
derivative is positive, and decreasing the drive voltage signal
frequency when negative. This is a third embodiment of a
piezoactuator drive circuit provided by the present invention.
In a preferred embodiment the drive circuit further has a
voltage-controlled oscillator for supplying an output signal to the
driver; and the frequency control unit controls the frequency of
the drive voltage signal by increasing or decreasing the frequency
control voltage applied to the voltage-controlled oscillator. This
is a fourth embodiment of a piezoactuator drive circuit provided by
the present invention.
In a further preferred embodiment the frequency control unit
comprises memory and means for storing to the memory the voltage
level of the frequency control voltage when the frequency of the
drive voltage signal is controlled to maximize the phase
difference; and the frequency control unit determines the initial
frequency control voltage based on the voltage level stored to
memory when starting drive voltage signal frequency control by
increasing or decreasing the frequency control voltage. This is a
fifth embodiment of a piezoactuator drive circuit provided by the
present invention.
In another preferred embodiment the frequency control unit applies
drive voltage signal frequency control so that the phase difference
goes to a reference phase difference. This is a sixth embodiment of
a piezoactuator drive circuit provided by the present
invention.
The frequency control unit in this case comprises a phase
difference detection circuit for detecting, for example, a phase
difference between an electrical signal representing oscillation in
the first oscillation mode and an electrical signal representing
oscillation in the second oscillation mode; a comparison circuit
for comparing the phase difference detected by the phase difference
detection circuit and the reference phase difference; and a
frequency adjusting circuit for increasing or decreasing the drive
voltage signal frequency according to the comparison result of the
comparison circuit. This is a seventh embodiment of a piezoactuator
drive circuit provided by the present invention.
In a preferred embodiment the frequency control unit further
comprises a voltage-controlled oscillator for supplying an output
signal to the driver; and the frequency adjusting circuit is
comprised of a voltage adjusting circuit for increasing or
decreasing the frequency control voltage applied to the
voltage-controlled oscillator based on the comparison result of the
comparison circuit. This is an eighth embodiment of a piezoactuator
drive circuit provided by the present invention.
Furthermore, in a preferred embodiment the frequency control unit
comprises a drive pass/fail evaluation means for determining if
piezoactuator drive succeeded or failed; and an initial reference
phase difference adjusting means for reducing the reference phase
difference until successful when piezoactuator drive fails, and
increasing the reference phase difference when successful. This is
a ninth embodiment of a piezoactuator drive circuit provided by the
present invention.
The initial reference phase difference adjusting means may omit for
a specified period the process for increasing the reference phase
difference when the reference phase difference at which
piezoactuator drive succeeds is the same for a specific consecutive
number of times. This is a tenth embodiment of a piezoactuator
drive circuit provided by the present invention.
In a preferred embodiment the frequency control unit has a
frequency counter for measuring the frequency of the drive voltage
signal; and the drive pass/fail evaluation means determines if
piezoactuator drive succeeded or failed based on whether the
frequency measurement of the frequency counter is within an
appropriate range or not. This is an eleventh embodiment of a
piezoactuator drive circuit provided by the present invention.
In a preferred embodiment the frequency control unit comprises
means for obtaining, each time the piezoactuator is driven, change
from a previous drive operation in the phase difference between an
electrical signal from the diaphragm representing oscillation in
the first oscillation mode and an electrical signal representing
oscillation in the second oscillation mode; and means for
increasing or decreasing the reference phase difference according
to change in the phase difference. This is a twelfth embodiment of
a piezoactuator drive circuit provided by the present
invention.
This invention also provides in a control method for a drive
circuit having a driver for applying a drive voltage signal that is
an ac signal to a diaphragm of a piezoactuator, a
voltage-controlled oscillator for outputting a drive voltage signal
of a frequency corresponding to a frequency control voltage to the
driver, and a phase difference detection circuit for receiving an
electrical signal from the diaphragm representing oscillation in a
first oscillation mode and an electrical signal representing
oscillation in a second oscillation mode with an oscillation
direction different from the first oscillation mode, and detecting
a phase difference of these electrical signals, a piezoactuator
drive circuit control method characterized by comprising: a
frequency control step for optimizing the oscillation frequency of
the voltage-controlled oscillator based on the phase difference
detected by the phase difference detection circuit.
In a preferred embodiment the frequency control step has a step for
increasing the oscillation frequency of the voltage-controlled
oscillator if the time derivative of the phase difference detected
by the phase difference detection circuit is positive, and
decreasing if negative, until change in the phase difference over
time is within a specific range.
In a separate preferred embodiment the frequency control step has a
step for increasing the oscillation frequency of the
voltage-controlled oscillator until the phase difference is greater
than or equal to a reference phase difference.
In this embodiment a step for determining if driving the
piezoactuator succeeded or failed, and correcting the reference
phase difference based on the result, may also be provided.
In addition to modes in which products comprising the
above-described drive circuit are manufactured or sold, the present
invention can also be achieved by modes such as distributing a
program for executing the above-described methods to users via an
electrical communication circuit, or distributing a
computer-readable storage medium storing such a program to
users.
From yet a further perspective, this invention provides a
piezoactuator characterized by comprising: a diaphragm of which
piezoelectric elements are major components for oscillating when an
ac signal is applied in a first oscillation mode and a second
oscillation mode having a different oscillation direction; a first
oscillation detection electrode disposed on a surface of the
diaphragm to detect oscillation in the first oscillation mode; and
a second oscillation detection electrode disposed on a surface of
the diaphragm to detect oscillation in the second oscillation
mode.
In a preferred embodiment the first oscillation mode is a
longitudinal oscillation mode, and the second oscillation mode is a
sinusoidal oscillation mode.
In a preferred embodiment the piezoactuator has a contact part that
is a member for contacting the rotor of a drive mechanism, moving
in an elliptical path described by oscillation in the longitudinal
oscillation mode and oscillation in the sinusoidal oscillation mode
produced in the diaphragm, and rotationally driving the rotor.
From yet another perspective, the present invention provides a
portable electronic device characterized by comprising a
piezoactuator and a drive circuit, the piezoactuator having as a
major component a diaphragm made from piezoelectric elements and
oscillating when an ac signal is applied in a first oscillation
mode and oscillating in a second oscillation mode having a
different oscillation direction; and the drive circuit having a
driver for applying a drive voltage signal that is an ac signal to
the diaphragm, and a frequency control unit for detecting an
electrical signal from the diaphragm representing oscillation in
the first oscillation mode and an electrical signal representing
oscillation in the second oscillation mode, and applying frequency
control of the drive voltage signal to optimize the phase
difference between these signals.
This portable electronic device uses any one of the above-described
twelve embodiments as the drive circuit, but can use the second to
twelfth embodiments.
In a preferred embodiment the portable electronic device is a
wristwatch comprising a rotor rotationally driven by the
piezoactuator; and a display mechanism linked to the rotor for
displaying information related to time.
In a separate preferred embodiment the portable electronic device
is a contactless IC card.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view showing the configuration of the major parts
of a wristwatch calendar display mechanism having assembled therein
a piezoactuator according to a first embodiment of this
invention.
FIG. 2 is a section view showing the basic configuration of the
same wristwatch.
FIG. 3 is a section view showing the basic configuration of the
same calendar display mechanism.
FIG. 4 is a plan view showing the detailed configuration of the
same piezoactuator.
FIG. 5 is a section view showing the configuration of the diaphragm
of the same piezoactuator.
FIG. 6 shows an example of electrodes formed on the surface of the
piezoelectric device in the same piezoactuator.
FIG. 7 and FIG. 8 show polarization states of the same
piezoelectric device.
FIG. 9 shows sinusoidal oscillation produced in the diaphragm.
FIG. 10 shows the elliptical motion produced in the end contact
part of the diaphragm.
FIG. 11 to FIG. 14 show change to the drive frequency of detection
signals obtained from the oscillation detection electrodes of the
diaphragm.
FIG. 15 and FIG. 16 show sample arrangements of the oscillation
detection electrodes of the diaphragm.
FIG. 17 is a block diagram showing the configuration of a drive
circuit for a piezoactuator according to a first embodiment of this
invention.
FIG. 18 shows examples of change in the path of the contact part in
the present embodiment due to the drive frequency.
FIG. 19 shows examples of change in the rotational speed of the
rotor and change in the phase difference of the longitudinal
oscillation and sinusoidal oscillation detection signals in the
same embodiment when the frequency of the drive voltage signal
applied to the diaphragm varies.
FIG. 20 is a block diagram showing the configuration of the .phi.-V
conversion circuit in FIG. 17.
FIG. 21 and FIG. 22 show the waveform at each part of the same
.phi.-V conversion circuit.
FIG. 23 is a flow chart showing the operation of the same drive
circuit.
FIG. 24 is a block diagram showing the configuration of the drive
circuit in a second embodiment of this invention.
FIG. 25 is a flow chart showing the operation of the same drive
circuit.
FIG. 26 and FIG. 27 show the change due to ambient temperature in
piezoactuator characteristics.
FIG. 28 is a block diagram showing the configuration of a drive
circuit in a third embodiment of this invention.
FIG. 29 shows an example of the operation of the same drive
circuit.
FIG. 30 is a block diagram showing the configuration of a drive
circuit according to a fourth embodiment of this invention.
FIG. 31 is a flow chart showing the operation of the same drive
circuit.
FIG. 32 and FIG. 33 show examples of the operation of the same
drive circuit.
FIG. 34 shows the appearance of a contactless IC card.
FIG. 35 shows the configuration of the remaining balance display
counter of the same card.
FIG. 36 is a side view showing the configuration of the high digit
display part of the same card.
FIG. 37 is a front view showing the configuration of the low digit
display part of the same card.
FIG. 38 is a side view showing the configuration of the low digit
display part of the same card.
FIG. 39 and FIG. 40 are block diagrams showing alternative drive
circuit configurations.
BEST MODE FOR ACHIEVING THE INVENTION
Preferred embodiments of the present invention are described below
with reference to the accompanying figures.
[1] Embodiment 1
[1.1] Overall Configuration
FIG. 1 is a plan view showing the configuration of a wristwatch
calendar display mechanism in which a piezoactuator A according to
a first embodiment of this invention is assembled.
As shown in FIG. 1, the main part of the calendar display mechanism
is substantially configured with a piezoactuator A according to the
present embodiment, rotor 100 rotationally driven by this
piezoactuator A, a speed-reducing wheel train for speed reducing
and transferring rotation of the rotor 100, and a date counter 50
rotated by drive force transferred through the speed-reducing wheel
train. The speed-reducing wheel train includes a date-turning
middle wheel 40 and date-turning wheel 60. The piezoactuator A has
a flat rectangular diaphragm 10; this diaphragm 10 is disposed with
the end thereof in contact with the outside surface of the rotor
100.
FIG. 2 is a section view of the watch shown in FIG. 1. The calendar
display mechanism comprising the piezoactuator A is assembled at
the hatched part in the figure. A disc-shaped dial 70 is disposed
above this calendar display mechanism. A window 71 for displaying
the date is disposed at one part at the outside of the dial 70 so
that the date on the date counter 50 can be seen through the window
71. The movement and drive circuit (not shown in the figure) for
driving the hands 72 is disposed below the dial 70.
FIG. 3 is a section view showing the detailed configuration of the
calendar display mechanism shown in FIG. 1. As shown in FIG. 3 the
watch has a base plate 103 that is a first bottom plate, and a
second bottom plate 103' on a different level than the base plate
103. A shaft 101 axially supporting the rotor 100 of the calendar
display mechanism projects from the base plate 103. The rotor 100
has a bearing (not shown in the figure) on its bottom, and the end
of the shaft 101 is held in the bearing. A gear 100c that is
coaxial to the rotor 100 and turns in conjunction with the rotor
100 is disposed at the top of the rotor 100.
A shaft 41 for axially supporting the date-turning middle wheel 40
projects from the base plate 103'. A bearing (not shown in the
figure) is disposed to the bottom of the date-turning middle wheel
40, and the end of the shaft 41 is held in the bearing. The
date-turning middle wheel 40 has a large diameter part 4b and a
small diameter part 4a. The small diameter part 4a is cylindrical
with a slightly smaller diameter than the large diameter part 4b,
and has a substantially square notch 4c formed in its outside
surface. This small diameter part 4a is affixed to the large
diameter part 4b so that they are concentric. The top gear 100c of
the rotor 100 meshes with the large diameter part 4b. Therefore,
the date-turning middle wheel 40 having large diameter part 4b and
small diameter part 4a rotates in conjunction with rotation of the
rotor 100 on shaft 41 as the axis of rotation.
The date counter 50 is ring shaped as shown in FIG. 1, and has
internal gear 5a formed on the inside circumference surface. The
date-turning wheel 60 has a five tooth gear and meshes with
internal gear 5a. As shown in FIG. 3, a shaft 61 is disposed in the
center of the date-turning wheel 60, and is fit with play in a
through-hole 62 formed in the base plate 103'. The through-hole 62
is formed oblongly in the circumferential direction of the date
counter 50.
One end of leaf spring 63 is fixed to base plate 103' and the other
end flexibly presses up and to the right as seen in FIG. 1 on shaft
61. Leaf spring 63 urges shaft 61 and date-turning wheel 60. The
urging action of this leaf spring 63 also prevents rocking of date
counter 50.
One end of leaf spring 64 is screw fixed to the second bottom plate
103', and an end part 64a bent substantially in a V-shape is formed
on the other end. Contact 65 is placed so as to contact leaf spring
64 when date-turning middle wheel 40 turns and end part 64a enters
notch 4c. A specific voltage is applied to the leaf spring 64, and
when it contacts contact 65 the voltage is also applied to the
contact 65. It is therefore possible to detect the date counting
status by detecting the voltage of contact 65. It should be noted
that a manual drive gear engaging internal gear 5a is also
preferably provided so that the date counter 50 can be driven when
a user performs a specific action with the crown (not shown in the
figure).
When a drive voltage is applied from a drive circuit in the
configuration described above, the diaphragm 10 of the
piezoactuator A oscillates within the plane thereof including the
surfaces. The outside surface of the rotor 100 is struck by the
oscillations produced in this diaphragm 10, and the rotor 100 is
rotationally driven clockwise as indicated by the arrow in the
figure. This rotation of the rotor 100 is transferred through
date-turning middle wheel 40 to the date-turning wheel 60, and this
date-turning wheel 60 turns the date counter 50 clockwise.
It will be noted here that power transfer from the diaphragm 10 to
the rotor 100, from the rotor 100 to the speed-reducing wheel
train, and from the speed-reducing wheel train to the date counter
50 is in each case the transfer of power in the direction parallel
to the surfaces of the diaphragm 10. It is therefore possible to
dispose the diaphragm 10 and rotor 100 in the same plane, rather
than stacking a coil and rotor in the thickness direction as with a
stepping motor according to the related art, and the calendar
display mechanism can therefore be made thinner. Furthermore, by
making the calendar display mechanism thin it is also possible to
reduce the thickness D of the hatched part and make the overall
watch thinner.
Furthermore, because it is possible with the present invention to
house the calendar display mechanism in the hatched area in FIG. 2,
a common movement 73 can be used in watches that have a calendar
display mechanism and watches that do not have a calendar display
mechanism, and productivity can be increased.
Various wristwatches with an electrical generator function have
been proposed recently, and reducing overall watch size has been
difficult with this type of wristwatch because two large mechanical
elements must be provided, the generating mechanism and a motor
mechanism for the movement. However, by using a piezoactuator A
according to the present embodiment of the invention in place of a
motor, a thin movement can be provided and overall watch size can
be reduced.
[1.2] Details of the Piezoactuator According to the Embodiment
FIG. 4 is a plan view showing the detailed configuration of the
piezoactuator A. FIG. 5 is a section view through I-I' of the
diaphragm 10 in the piezoactuator A. As shown in FIG. 4 the
diaphragm 10 is a rectangular plate enclosed by two long sides and
two short sides. As shown in FIG. 5, the diaphragm 10 has a
lamellar structure with two rectangular flat piezoelectric elements
30 and 31 and disposed therebetween a stainless steel reinforcing
plate 32 of substantially the same shape as the piezoelectric
elements 30 and 31 and thinner than the piezoelectric elements 30
and 31.
By thus disposing a reinforcing plate 32 between piezoelectric
elements 30 and 31 damage to the diaphragm 10 caused by excessive
amplitude in the diaphragm 10 or external shock from dropping, for
example, is reduced and durability can be improved. Furthermore, by
using a part thinner than the piezoelectric elements 30 and 31 for
the reinforcing plate 32, interference with oscillation of the
piezoelectric elements 30 and 31 can be significantly avoided.
The piezoelectric elements 30 and 31 can be made from materials
such as lead zirconate titanate (PZT (TM)), quartz, lithium
niobate, barium titanate, lead titanate, lead metaniobate,
polyvinylidene fluoride, zinc lead niobate, and scandium lead
niobate. The chemical formula for zinc lead niobate is
[Pb(Zn1/3-Nb2/3)3)1--X (PbTiO3)X] (where X differs according to the
composition, and X=0.09 approximately), and the chemical formula
for scandium lead niobate is [{Pb((Sc1/2-Nb1/2)1--X TiX O3] (where
X differs according to the composition, and X=0.09
approximately).
As shown in FIG. 4, the diaphragm 10 has a contact 36 at one corner
where a long side and a short side intersect. This contact 36 is
achieved by cutting or otherwise shaping the reinforcing plate 32
shown in FIG. 5, causing an end part with a gradually rounded
surface to project from the piezoelectric elements 30 and 31. The
diaphragm 10 is positioned with the tip of this contact 36
contacting the outside surface of the rotor 100 and the long sides
thereof held at an angle of approximately 135 degrees to the radius
of the rotor 100. A support member 11 and spring 300 are disposed
to the piezoactuator A in order to hold the diaphragm 10 in this
position.
In a preferred embodiment the support member 11 is formed
integrally to the reinforcing plate 32 by cutting or otherwise
shaping the reinforcing plate 32. As shown in the figure this
support member 11 is an L-shaped member having a perpendicular part
projecting perpendicularly from substantially the center of the
long side of the diaphragm 10, and a horizontal part projecting
from the end of this perpendicular part parallel to the long side
toward the rotor 100. A pin 39 protruding from the base plate 103
as shown in FIG. 1 and FIG. 3 passes through end 38 on the opposite
end of the horizontal part from the perpendicular part. The support
member 11 and diaphragm 10 fixed thereto can turn on this pin 39 as
the axis of rotation.
End 300a of spring 300 is engaged with approximately the center
part 11a of the horizontal part of the support member 11. A pin
300b protruding from the base plate 103 (see FIG. 1 and FIG. 3)
passes through substantially the center of the spring 300. The
spring 300 can rotate on this pin 300b as the axis of rotation. The
other end part 300c of the spring 300 on the end opposite end 300a
engages the base plate 103. The pressure with which the contact 36
pushes against the outside surface of the rotor 100 can be adjusted
in this embodiment by changing the position of this end 300c.
More specifically, if end 300c is displaced clockwise as seen in
the figure around pin 300b, the force with which end 300a of spring
300 pushes up on part 11a of support member 11 increases, and this
force decreases if end 300c is displaced counterclockwise. If the
force pushing up on the support member 11 increases, the force
causing the support member 11 to rotate counterclockwise about pin
39 increases, and the force whereby the contact 36 pushes the rotor
100 increases. On the other hand, if the force pushing the support
member 11 up decreases, the force causing support member 11 to
rotate clockwise decreases, and the force of contact 36 against the
rotor 100 decreases. The drive characteristics of the piezoactuator
A can thus be adjusted by the pressure applied by contact 36
against rotor 100.
It will be noted that in this embodiment the contact 36 pushing
against the outside surface of the rotor 100 is curved. As a
result, contact between the outside surface of the rotor 100, which
is a curved surface, and the curved contact 36 will not change
appreciably even if the relative positions of the rotor 100 and
diaphragm 10 vary due to dimensional variations, for example. It is
therefore possible to maintain stable contact between the rotor 100
and contact 36. Furthermore, grinding or polishing only needs to be
applied to the contact 36 that contacts the rotor 100 in this
embodiment, and managing the contact with the rotor 100 is
therefore simple. A conductor or non-conductor can be used for the
contact 36, but shorting of the piezoelectric elements 30 and 31
can be prevented when there is contact with the rotor 100, which is
generally made of metal, if a non-conductor is used.
[1.3] Configuration of the Drive Circuit and Electrodes Disposed on
the Diaphragm
The drive electrode and oscillation detection electrodes disposed
to the diaphragm 10 are described next with reference to FIG. 6. In
the example shown in FIG. 6 rectangular oscillation detection
electrodes T1, T2, T3, and T4 are positioned at the four corners on
the surface of the rectangular piezoelectric element 30. Although
not shown in FIG. 6, oscillation detection electrodes T1, T2, T3,
and T4 identical to these are also located on the opposite side at
the corners of piezoelectric element 31. Oscillation detection
electrode T1 located on piezoelectric element 30 and oscillation
detection electrode T1 located on piezoelectric element 31 are
connected, and detection signal SD1 representing oscillation of the
diaphragm 10 is obtained from a contact therebetween. Oscillation
detection electrode T2 located on piezoelectric element 30 and
oscillation detection electrode T2 located on piezoelectric element
31 are likewise connected, and detection signal SD2 representing
oscillation of the diaphragm 10 is obtained from a contact
therebetween. The other oscillation detection electrodes T3 and T4
are the same. Drive electrode 33 is disposed on the surface of
piezoelectric element 30 in the area not covered by oscillation
detection electrodes T1 to T4. There is a gap between the drive
electrode 33 and oscillation detection electrodes T1 to T4, which
are thus electrically isolated. An identical drive electrode 33 is
also disposed to the surface of piezoelectric element 31.
Piezoelectric elements 30 and 31 are each polarized in the
thickness direction. FIG. 7 and FIG. 8 each show examples of the
polarization states of piezoelectric elements 30 and 31. In this
embodiment of the invention piezoelectric elements 30 and 31 have
the property of expanding in the longitudinal direction when a
field in the same direction as each direction of polarization is
received and contracting when a field in the direction opposite the
polarization direction is received. Therefore, when the arrangement
of the polarization directions of the two piezoelectric elements 30
and 31 is different as shown in FIG. 7 and FIG. 8, the method of
driving each piezoelectric element is also different.
In the example shown in FIG. 7 piezoelectric elements 30 and 31 are
polarized in mutually opposite directions. In this case, as shown
in FIG. 6, the reinforcing plate 32 is to ground, the drive
electrode 33 on piezoelectric element 30 and the drive electrode 33
on piezoelectric element 31 are connected, and a drive voltage
signal SDR of a specific frequency alternating between a +V voltage
and -V voltage is repeatedly applied between this contact and the
ground line. When a +V voltage is applied between the ground line
and the contact between the two drive electrodes 33, a field
opposite each polarization direction is applied to piezoelectric
elements 30 and 31, and piezoelectric elements 30 and 31 therefore
contract longitudinally. On the other hand, when a -V voltage is
applied between the ground line and the contact between the two
drive electrodes 33, a field in the same direction as each
polarization direction is applied to piezoelectric elements 30 and
31, and piezoelectric elements 30 and 31 therefore expand
longitudinally. Because of this behavior the diaphragm 10 expands
and contracts in the longitudinal direction as a result of applying
a drive voltage signal SDR of a specific frequency. This expansion
and contraction movement is called longitudinal oscillation or
oscillation in a first oscillation mode.
In the example shown in FIG. 8 the piezoelectric elements 30 and 31
are polarized in the same direction. In this case the reinforcing
plate 32 is to ground and a first phase, in which a +V voltage is
applied between the ground line and drive electrode 33 on
piezoelectric element 30 and a -V voltage is applied between the
ground line and drive electrode 33 on piezoelectric element 31, and
a second phase, in which a -V voltage is applied between the ground
line and drive electrode 33 of piezoelectric element 30 and a +V
voltage is applied between the ground line and drive electrode 33
on piezoelectric element 31, are repeated at a specific frequency.
In this first phase the piezoelectric elements 30 and 31 contract
longitudinally because a field in the direction opposite each
polarization direction is applied to piezoelectric elements 30 and
31. In the second phase, on the other hand, the piezoelectric
elements 30 and 31 expand longitudinally because a field of the
same direction as each polarization direction is applied to
piezoelectric elements 30 and 31. Longitudinal oscillation is thus
produced in the diaphragm 10 by applying such drive voltages of a
specific frequency.
It should be noted that the diaphragm 10 can be made substantially
linearly symmetrical about an axis of symmetry passing through the
center in the longitudinal direction, but is not completely
symmetrical because of such asymmetrical components contained
therein as contact 36. As a result, when longitudinal oscillation
is produced in the diaphragm 10, a moment swinging in the direction
perpendicular to the longitudinal direction of the diaphragm 10
occurs at a delay to this longitudinal oscillation. This moment
produces sinusoidal oscillation in the diaphragm 10. As shown in
FIG. 9. This sinusoidal oscillation is movement in which the
diaphragm 10 moves in the plane including the surfaces of the
diaphragm 10 perpendicularly to the longitudinal direction. When
such longitudinal oscillation and sinusoidal oscillation is
produced in the diaphragm 10, the contact 36 at the end of
diaphragm 10 moves in an elliptical pattern as shown in FIG. 10.
The rotor 100 is thus struck on the outside surface by contact 36
moving in this elliptical path, and is thus rotationally
driven.
The amplitude of the longitudinal oscillation and the amplitude of
the sinusoidal oscillation differs according to the position on the
surface of the diaphragm 10. That is, a phenomenon occurs in which
longitudinal oscillation is conspicuous at certain positions on the
surface and sinusoidal oscillation is conspicuous at other
positions. The diaphragm 10 also has a resonance characteristic to
the longitudinal oscillation and a resonance characteristic to the
sinusoidal oscillation. Resonance with respect to longitudinal
oscillation of the diaphragm 10 and resonance with respect to
sinusoidal oscillation is determined by the shape and material of
the diaphragm 10, but the latter resonance frequency is slightly
higher than the former resonance frequency.
In this preferred embodiment oscillation detection electrode pairs
are disposed at plural locations on the piezoelectric elements 30
and 31 of diaphragm 10, and longitudinal oscillation and sinusoidal
oscillation are thereby detected. FIG. 11 to FIG. 14 show the
voltage amplitude of the detection signals from each of the
oscillation detection electrodes T1 to T4 when the frequency of the
drive voltage signal SDR applied to drive electrode 33 is changed
when a load is not connected to the diaphragm 10.
Referring to FIG. 6, oscillation detection electrodes T1 and T3 are
disposed to positions where longitudinal oscillation of the
diaphragm 10 is conspicuous. As a result, as shown in FIG. 11 and
FIG. 13, the amplitude voltage of the detection signals obtained
from these electrodes is greatest near the resonance frequency band
fr (approximately 283.5 [kHz]) related to longitudinal oscillation
of the diaphragm 10. On the other hand, oscillation detection
electrodes T2 and T4 are disposed to positions where sinusoidal
oscillation of the diaphragm 10 is conspicuous. As a result, as
shown in FIG. 12 and FIG. 14, the amplitude voltage of the
detection signals obtained from these electrodes is greatest near
the resonance frequency band fr2 (approximately 287.5 [kHz])
related to sinusoidal oscillation of the diaphragm 10. This
tendency is the same when a load is connected to the diaphragm
10.
Various methods of arranging the oscillation detection electrodes
other than as shown in FIG. 6 are also possible. FIG. 15 and FIG.
16 show examples of these. Only oscillation detection electrodes T1
and T2 shown in FIG. 6 are provided in the example shown in FIG.
15. In the example shown in FIG. 16, only oscillation detection
electrodes T1 and T4 shown in FIG. 6 are provided.
FIG. 17 is a block diagram showing the configuration of the drive
circuit 200 supplying drive voltage signal SDR to the drive
electrodes 33 of the diaphragm 10 in the present embodiment. This
drive circuit 200 has a function for controlling the frequency of
drive voltage signal SDR to maintain substantially the greatest
phase difference between longitudinal oscillation and sinusoidal
oscillation produced in the diaphragm 10. This method of frequency
control is used in order to efficiently transfer the kinetic energy
of diaphragm 10 to the rotor 100. This is described in detail
below.
FIG. 18 shows an example of the path described by contact 36 of
diaphragm 10. Describing the x axis and z axis in the figure, the z
axis is the axis for the longitudinal direction of diaphragm 10 as
shown in FIG. 10, and the x axis is the axis perpendicular to the z
axis in the plane containing the surfaces of the diaphragm 10. In
FIG. 18 Ra is the path of contact 36 when the frequency of drive
voltage signal SDR matches the resonance frequency fr of
longitudinal oscillation, and Rd is the path of contact 36 when the
frequency of drive voltage signal SDR matches the resonance
frequency fr2 of sinusoidal oscillation. In addition, Rb and Rc
denote the path of contact 36 when the frequency of the drive
voltage signal SDR is a frequency fb, fc (fb<fc) between fr and
fr2.
Because sinusoidal oscillations produced in diaphragm 10 are
induced by the longitudinal oscillation, the phase of sinusoidal
oscillation is delayed relative to the phase of longitudinal
oscillation. The path of contact 36 is an elliptical path with a
bulge as shown in FIG. 18 instead of a linear path because there is
a phase difference between the longitudinal oscillation and
sinusoidal oscillation. This phase difference of the longitudinal
oscillation and sinusoidal oscillation depends on the frequency of
the drive voltage signal SDR. When the phase difference changes
according to frequency, the shape of the elliptical path described
by the contact 36 changes, and a change is also thought to occur in
the rotational drive force applied to the rotor 100.
As also shown in FIG. 18, the orientation of the long diameter of
the elliptical path gradually moves away from the z axis and slopes
to an orientation parallel to the x axis as the frequency of the
drive voltage signal moves from the resonance frequency fr of
longitudinal oscillation to the resonance frequency fr2 of
sinusoidal oscillation. When the slope of the elliptical path of
contact 36 thus changes due to change in the frequency of the drive
voltage signal SDR, the magnitude of the rotational drive force
applied to the rotor 100 is also thought to change.
Following the above lines of thought, the inventors investigated
the relationship between the frequency of the drive voltage signal
SDR and rotation of the rotor 100 in detail. FIG. 19 shows the
frequency characteristic of diaphragm 10 obtained as a result of
these investigations: the horizontal axis denotes the frequency of
the drive signal applied to the drive electrodes of the diaphragm
10, the first vertical axis on the left denotes the phase
difference, and the second vertical axis on the right denotes the
rotational speed of the rotor 100 driven by contact 36. Graph
.theta.1 denotes the phase difference between the phase of the
drive voltage signal SDR applied to drive electrodes 33 and the
phase of detection signal SD1 obtained from oscillation detection
electrodes T1. Graph .theta.2 denotes the phase difference between
the phase of the drive voltage signal SDR applied to drive elect
codes 33 and the phase of detection signal SD2 obtained from
oscillation detection electrodes T2. Graph .theta. denotes
.phi.2-.theta.1, that is, the phase difference between the phase of
detection signal SD1 obtained from oscillation detection electrodes
T1 and the phase of detection signal SD2 obtained from oscillation
detection electrodes T2. This phase difference is equivalent to the
phase difference between the phase of longitudinal oscillation and
the phase of sinusoidal oscillation. Graph V denotes the rotational
speed of the rotor 100.
As will be known from FIG. 19, when the frequency of the drive
voltage signal SDR applied to diaphragm 10 is near 287 kHz, the
phase difference of detection signal SD1 and detection signal SD2,
that is, phase difference .phi. of longitudinal oscillation and
sinusoidal oscillation, is greatest, and the rotational speed V of
rotor 100 is also highest at this time.
The drive circuit 200 shown in FIG. 17 was designed with
consideration for the characteristics of such a diaphragm 10, and
controls the frequency of drive voltage signal SDR in order to
maintain the substantially greatest phase difference between
detection signals SD1 and SD2.
This drive circuit 200 has a driver 201, .phi.-V conversion circuit
202, delay circuit 203, comparator circuit 204, voltage adjusting
circuit 205, and VCO (voltage-controlled oscillator) 206.
The driver 201 is a circuit for amplifying output signal Sdr of VCO
206 and applying drive voltage signal SDR to drive electrodes 33 of
diaphragm 10. It should be noted that in the initialized state the
driver 201 outputs a drive voltage signal SDR of a specific default
frequency. Output of this drive voltage signal SDR at the default
frequency is to set the initial oscillations of the diaphragm 10,
that is, to make the diaphragm 10 oscillate at the default
frequency in the initialization state. This initialization can be
achieved by such methods as inputting a signal with a default
frequency to the driver 201, or applying a frequency control
voltage for oscillating at the default frequency to the VCO
206.
When the diaphragm 10 oscillates due to application of the drive
voltage signal SDR, detection signal SD1 and detection signal SD2
are output from oscillation detection electrodes T1 and T2 of
diaphragm 10. The .phi.-V conversion circuit 202 is a circuit for
outputting a signal according to the phase difference of detection
signal SD1 and detection signal SD2, and as shown in FIG. 20 has a
phase difference detector 202A and an average voltage converter
202B. FIG. 21 and FIG. 22 show the waveforms at parts of the
.phi.-V conversion circuit 202. The phase difference detector 202A
generates a phase difference signal SDD of a pulse width equivalent
to the phase difference of detection signals SD1 and SD2. The
average voltage converter 202B averages the phase difference
signals SDD, and outputs a phase difference signal SPD at a level
proportional to the phase difference of detection signals SD1 and
SD2. In the example shown in FIG. 21 the phase difference of
detection signals SD1 and SD2 is small. As a result, a phase
difference signal SDD with a small pulse width .theta.1 is output,
and a phase difference signal SPD with a low voltage level Vav1 is
output. In the example shown in FIG. 22, the phase difference of
detection signals SD1 and SD2 is large. As a result, a phase
difference signal SDD with a large pulse width .theta.2 is output,
and a phase difference signal SPD with a high voltage level Vav2 is
output.
Phase difference signal SPD is supplied to comparator circuit 201.
SPD is also delayed a specific time by the delay circuit 203, and
then supplied to the comparator circuit 204 as signal DSPD.
The comparator circuit 204 determines the difference of signal SPD
and signal DSPD, determines if the time derivative of the phase
difference of signals SD1 and SD2 is positive or negative, and
based on the result of this determination applies voltage
adjustment control signal SCT to voltage adjusting circuit 205.
The voltage adjusting circuit 205 increases or decreases the
frequency control voltage SVC applied to VCO 206 according to the
voltage adjustment control signal SCT applied from comparator
circuit 204. The VCO 206 oscillates at a frequency determined by
this frequency control voltage SVC, and outputs signal Sdr to the
driver 201.
In the drive circuit 200 thus described, control increasing the
oscillation frequency of the VCO 206 is applied by the comparator
circuit 204 when the phase difference of detection signals SD1 and
SD2 increases due to an increase of the oscillation frequency of
VCO 206. In addition, when the phase difference of detection
signals SD1 and SD2 decreases due to an increase in the oscillation
frequency of VCO 206, control lowering the oscillation frequency of
VCO 206 is applied by the comparator circuit 204. As a result of
applying such control, VCO 206 oscillates at a frequency
maintaining the substantially greatest phase difference between
detection signals SD1 and SD2.
[1.4] Operation of this Embodiment
FIG. 23 is a flow chart showing the operation of the drive circuit
200 in the present embodiment. Operation of the present embodiment
is described below according to this flow chart. When a time at
which the date changes and date counter 50 must be turned the
amount for one day comes, a start operation command is applied to
the drive circuit 200 from a control circuit not shown in the
figures, and the initialization drive signal is applied to the
driver 201 for a specific period of time. While this initialization
drive signal is applied to the driver 201, the frequency of the
initialization drive signal gradually rises with time. The range of
change in the frequency of the initialization drive signal is set
to a frequency range sufficiently lower than the frequency at which
the phase difference of longitudinal oscillation and sinusoidal
oscillation in the diaphragm 10 is maximized. The driver 201
amplifies the default drive signal thus supplied to apply it as
drive voltage signal SDR to the diaphragm 10. As a result, the
diaphragm 10 beings to oscillate, and the frequency gradually
rises.
When the specified time passes, supplying the default drive signal
stops and drive circuit 200 operates according to the flow shown in
FIG. 21. First, when detection signals SD1 and SD2 are output from
oscillation detection electrodes T1 and T2 due to oscillation of
the diaphragm 10, they are input to .PHI.-V conversion circuit 202
(step S1). The .PHI.-V conversion circuit 202 detects the phase
difference .PHI. of detection signals SD1 and SD2, and outputs
average phase difference voltage signal SPD having a voltage V.PHI.
equivalent to the average phase difference (step S2). The delay
circuit 203 receives this average phase difference voltage signal
SPD from the .PHI.-V conversion circuit 202 (step S3): then, time
tp after receiving SPD from the conversion circuit 202, the delay
circuit 203 outputs the average phase difference voltage signal SPD
as signal DSPD (step S4). When comparator circuit 204 receives
signal SPD and signal DSPD (step S5), it determines if voltage
V.PHI. of signal SPD is greater than V.PHI.tp of signal DSPI).
It is assumed here, for example, that the phase difference .phi. of
detection signals SD1 and SD2 is .phi.k shown in FIG. 19, and a
signal SPD with voltage V.phi. corresponding to this .phi.k is
applied to the comparator circuit 204. Furthermore, at the time
earlier by time tp the phase difference .phi. of detection signals
SD1 and SD2 is .phi.j, which is less than .phi.k, and a signal DSPD
of voltage V.phi.tp corresponding thereto is applied to the
comparator circuit 204. The result of step S6 in this case is YES
because V.phi.>V.phi.tp. In this case the comparator circuit 204
sends a high level voltage adjustment control signal SCT to the
voltage adjusting circuit 205 (step S7), and voltage adjusting
circuit 205 increases the frequency control voltage SVC applied to
the VCO 206 (steps S8, S11). When frequency control voltage SVC
thus rises, the oscillation frequency of VCO 206 rises (steps S12,
S13).
The same operation described above repeats for as long as phase
difference .phi. increases due to an increase in the frequency of
drive voltage signal SDR. As a result, drive voltage signal SDR
gradually increases, and the phase difference .phi. of detection
signals SD1 and SD2 gradually rises accordingly (see arrow P in
FIG. 19).
As shown by way of example in FIG. 19, phase difference .phi. is
greatest at a particular frequency (a frequency near 287 kHz in
FIG. 19), but there are cases with the above operation in which the
drive voltage signal SDR exceeds this frequency. The following
operation is applied in such cases.
First, if the phase difference .phi. of detection signals SD1 and
SD2 at a particular time is .phi.n shown in FIG. 19, for example, a
signal SPD of a voltage V.phi. corresponding to .phi.n is applied
to the comparator circuit 204. At the time earlier by time tp the
phase difference .phi. of detection signals SD1 and SD2 is .phi.m,
which is greater than .phi.n, and signal DSPD of voltage V.phi.tp
corresponding thereto is applied to the comparator circuit 204. The
result returned by step S6 in this case is NO because
V.phi.<V.phi.tp. In this case the comparator circuit 204 sends a
low level voltage adjustment control signal SCT to the voltage
adjusting circuit 205 (step S9), and the voltage adjusting circuit
205 lowers the frequency control voltage SVC applied to VCO 206
(steps S10, S11). When the frequency control voltage SVC thus
drops, the oscillation frequency of VCO 206 drops (steps S12, S13).
As a result, phase difference .phi., which had dropped, rises again
as indicated by arrow Q in FIG. 19.
As a result of repeating such control the frequency of drive
voltage signal SDR is held to a frequency at which the phase
difference .phi. of detection signals SD1 and SD2, that is, the
phase difference of longitudinal oscillation and sinusoidal
oscillation of diaphragm 10, is substantially maximized, and rotor
100 rotates at the highest rotational speed. Rotational drive of
the rotor 100 is also transferred by the calendar display mechanism
shown in FIG. 1 and the date counter 50 turns only an angle
equivalent to one day. The control circuit sends a drive stop
command to the drive circuit 200 when it detects from a change in
the voltage of contact 65 that the date counter 50 has turned an
angle equivalent to one day. As a result, the drive circuit 200
stops outputting drive voltage signal SDR.
[2] Embodiment 2
This embodiment and the first embodiment described above differ
only in the configuration of the drive circuit, and the other parts
are therefore described with reference to the same figures as the
first embodiment.
FIG. 24 is a block diagram showing the configuration of the drive
circuit 200A according to the present embodiment of the invention.
This drive circuit 200A does not have a delay circuit 203 such as
used in the drive circuit 200 of the first embodiment. The drive
circuit 200A instead has a voltage regulator circuit 210. This
voltage regulator circuit 210 outputs reference voltage SREF to
comparator circuit 204A. This reference voltage SREF is a voltage
of the same level as the voltage output from .phi.-V conversion
circuit 202 when the phase difference .phi. of detection signals
SD1 and SD2 obtained from diaphragm 10 is reference phase
difference .phi.d. This reference phase difference .phi.d is a
phase difference slightly lower than the maximum phase difference
.phi. of detection signals SD1 and SD2 from diaphragm 10. When
voltage SPD output from .phi.-V conversion circuit 202 is lower
than reference voltage SREF, the comparator circuit 204A outputs a
voltage adjustment command signal instructing an increase in
frequency control voltage SVC causing the oscillation frequency of
VCO 206 to rise. When voltage SPD is lower than reference voltage
SREF, comparator circuit 204A outputs a voltage adjustment command
signal instructing a decrease in frequency control voltage SVC, and
the oscillation frequency of the VCO 206 decreases.
FIG. 25 is a flow chart showing the operation of drive circuit 200A
in the present embodiment. Operation of the present embodiment is
described below according to this flow chart. When detection
signals SD1 and SD2 from diaphragm 10 are input to .phi.-V
conversion circuit 202 (step S21), .phi.-V conversion circuit 202
detects phase difference .phi. of these detection signals SD1 and
SD2, and outputs average phase difference voltage signal SPD having
a voltage V.phi. equivalent to this average phase difference (step
S22). On the other hand, constant voltage circuit 210 constantly
outputs reference voltage V.phi.d (step S23). When the comparator
circuit 204 receives average phase difference voltage signal SPD
and reference voltage V.phi.d (step S24), it determines if voltage
V.phi. of signal SPD is lower than reference voltage V.phi.d (step
S25).
When diaphragm 10 first starts to oscillate, the frequency of drive
voltage signal SDR and the phase difference of detection signals
SD1 and SD2 is small. As a result, step S25 returns YES. In this
case comparator circuit 204 outputs a high level voltage adjustment
control signal SCT to voltage adjusting circuit 205 (step S26) and
voltage adjusting circuit 205 increases the frequency control
voltage SVC applied to the VCO 206 (steps S27, S30). When the
frequency control voltage SVC thus rises, the oscillation frequency
of VCO 206 rises (steps S31, S32).
The operation described above repeats when the phase difference
.phi. of detection signals SD1 and SD2 is less than reference phase
difference .phi.d and voltage V.phi. of signal SPD is less than
reference voltage V.phi.d. As a result, the oscillation frequency
of VCO 206 gradually rises, and the phase difference .phi. of
detection signals SD1 and SD2 increases. When phase difference
.phi. exceeds reference phase difference .phi.d and voltage V.phi.
of signal SPD exceeds reference voltage V.phi.d, step S25 returns
NO.
In this case comparator circuit 204 sends a low level voltage
adjustment control signal SCT to voltage adjusting circuit 205
(step S28), and voltage adjusting circuit 205 reduces the frequency
control voltage SVC applied to VCO 206 (steps S29, S30). As a
result, the oscillation frequency of VCO 206 drops when frequency
control voltage SVC drops (step S31, S33).
As a result of repeating this control, the frequency of drive
voltage signal SDR is held at a frequency at which the phase
difference .phi. of detection signals SD1 and SD2, that is, the
phase difference of longitudinal oscillation and sinusoidal
oscillation of diaphragm 10, goes to the reference phase difference
.phi.d, and rotor 100 rotates at an appropriate rotational speed.
Rotational drive of the rotor 100 is also transferred by the
calendar display mechanism shown in FIG. 1 and the date counter 50
turns only an angle equivalent to one day. The control circuit
sends a drive stop command to the drive circuit 200 when it detects
from a change in the voltage of contact 65 that the date counter 50
has turned an angle equivalent to one day. As a result, the drive
circuit 200 stops outputting drive voltage signal SDR.
[3] Embodiment 3
In the second embodiment described above the frequency of drive
voltage signal SDR is controlled so that the phase difference of
detection signals SD1 and SD2 obtained from diaphragm 10 goes to
reference phase difference .phi.d. In order to efficiently drive
the rotor 100 with such frequency control, reference phase
difference .phi.d must be set as high as possible within a range
not exceeding the maximum phase difference of detection signals SD1
and SD2 obtained from diaphragm 10. However, the maximum phase
difference of detection signals SD1 and SD2 differs with individual
piezoactuators and even with load and temperature. FIG. 26 shows
the frequency characteristic of drive efficiency and the phase
difference of detection signals SD1 and SD2 at a temperature of
25.degree. C., and FIG. 27 shows the same frequency characteristic
at a temperature of 60.degree. C. If the reference phase difference
.phi.d is set to 60.degree., the frequency of drive voltage signal
SDR achieving this phase difference when the temperature is
60.degree. C. can be determined. However, the frequency of the
drive voltage signal SDR at which the phase difference of detection
signals SD1 and SD2 goes to reference phase difference .phi.d
cannot be determined when the temperature is 25.degree. C.
This third embodiment of the invention solves this problem. FIG. 28
is a block diagram showing the configuration of a drive circuit
200B in the present embodiment. This drive circuit 200B comprises a
frequency counter 211, control unit 212, and non-volatile memory
213 such as RAM backed up by battery added to the configuration of
the drive circuit 200A in the second embodiment (FIG. 24).
The frequency counter 211 is a circuit for measuring the frequency
of the drive voltage signal SDR. The non-volatile memory 213 has
the job of storing the reference phase difference .phi.d. When a
piezoactuator according to the present embodiment is used in a
wristwatch, a sufficiently large reference phase difference is
stored to non-volatile memory 213. For example, the maximum
possible phase difference of detection signals SD1 and SD2 or a
greater value is first stored to the non-volatile memory 213. The
reference phase difference in this non-volatile memory 213 is then
updated by control unit 212 each time rotor 100 is driven. The
control unit 212 determines the reference phase difference .phi.d
when rotor 100 is driven, and instructs the constant voltage
circuit 210 to output reference voltage SREF corresponding to this
reference phase difference .phi.d. The reference phase difference
stored to non-volatile memory 213 is referenced to determine
reference phase difference .phi.d. The control unit 212 also
controls optimizing the reference phase difference in non-volatile
memory 213.
Operation of drive circuit 200B when rotor 100 is driven three
times is shown in FIG. 29.
When the rotor 100 is driven the first time, .phi.d7 is stored as
the reference phase difference in non-volatile memory 213. The
control unit 212 therefore defines .phi.d8, which is a specific
amount greater than .phi.d7, as reference phase difference .phi.d,
and commands the constant voltage circuit 210 to output a
corresponding reference voltage SREF. When a reference voltage SREF
corresponding to phase difference .phi.d8 is output by constant
voltage circuit 210, the frequency of drive voltage signal SDR
begins to rise. At first the phase difference .phi. of detection
signals SD1 and SD2 also rises in conjunction with the increase in
the frequency of drive voltage signal SDR. However, after this
phase difference reaches a maximum level, the phase difference
.phi. of detection signals SD1 and SD2 decreases in conjunction
with increase in the frequency of drive voltage signal SDR. The
frequency of drive voltage signal SDR then reaches an upper
frequency limit without phase difference .phi. reaching reference
phase difference .phi.d8.
The control unit 212 detects that the frequency of drive voltage
signal SDR reached the maximum frequency from the measurement
results from frequency counter 211. The control unit 212 at this
time assumes that driving rotor 100 failed, and tells the constant
voltage circuit 210 to stop reference voltage SREF. Next, control
unit 212 decreases reference phase difference .phi.d8 a specific
amount to .phi.d7, and tells the constant voltage circuit 210 to
output a corresponding reference voltage SREF and operate the drive
circuit 200B. In the example shown in the figure this drive attempt
also ends in failure. Driving rotor 100 by drive circuit 200B with
the reference phase difference set to .phi.d6 is also attempted,
but this attempt also ends in failure. When the control unit 212
then reduces the reference phase difference a specified amount from
.phi.d6 to .phi.d5 and operates the drive circuit 200B, and the
frequency of drive voltage signal SDR reaches frequency f1, the
rotor 100 is driven with optimum efficiency. When the control unit
212 detects that driving rotor 100 ended normally, it stores
reference phase difference .phi.d5 to non-volatile memory 213.
Operation when driving the rotor a second time after this is
described next.
In this case control unit 212 attempts to drive the rotor 100 by
means of drive circuit 200B using .phi.d6, which is a specific
amount greater than .phi.d5 stored in non-volatile memory 213, as
reference phase difference .phi.d, but this ends in failure. The
control unit 212 therefore lowers the reference phase difference
from .phi.d6 to .phi.d5, and operates the drive circuit 200B. This
.phi.d5 is the reference phase difference at which rotor drive was
successful the first time. When the rotor is driven the second
time, however, phase difference .phi.d of detection signals SD1 and
SD2 obtained from diaphragm 10 is lower overall, and driving rotor
100 using reference phase difference .phi.d5 also fails. As a
result, the control unit 212 operates the drive circuit 200B using
.phi.d4, which is a specific amount less than .phi.d5, as the
reference phase difference. In this case phase difference .phi. of
detection signals SD1 and SD2 goes to reference phase difference
.phi.d4 when the frequency of drive voltage signal SDR reaches
frequency f2. As a result, the rotor 100 is driven with optimum
efficiency. When the control unit 212 detects that driving rotor
100 ended normally, it stores reference phase difference .phi.d4 to
non-volatile memory 213.
Operation when driving the rotor a third time after this is
described next.
In this case control unit 212 attempts to drive the rotor 100 by
means of drive circuit 200B using .phi.d5, which is a specific
amount greater than .phi.d4 stored in non-volatile memory 213, as
reference phase difference .phi.d. Rotor drive failed the last time
the reference phase difference was .phi.d5. In this third rotor
drive attempt, however, the phase difference .phi.d of detection
signals SD1 and SD2 obtained from diaphragm 10 is higher overall,
and driving rotor 100 using reference phase difference .phi.d5 is
successful. When the control unit 212 detects that driving rotor
100 ended normally, it stores reference phase difference .phi.d5 to
non-volatile memory 213.
It will be noted that driving rotor 100 will be successful even if
the reference phase difference .phi.d is set to .phi.d6, which is a
specific amount greater. However, the rotor 100 is not driven using
this reference phase difference .phi.d6 during the third rotor
drive operation. This is because the date counter already turned
using reference phase difference .phi.d5 and the drive object has
been achieved. If there is no change in the characteristics of the
diaphragm 10 the fourth time the rotor is driven, the rotor will be
driven using reference phase difference .phi.d6 at that time and
reference phase difference .phi.d6 will likely be stored to
non-volatile memory 213.
As described above the present embodiment tracks changes in the
characteristics of the piezoactuator, and is able to drive the
rotor 100 with extremely high efficiency.
[4] Embodiment 4
FIG. 30 is a block diagram showing the configuration of a drive
circuit 200C for a piezoactuator in a fourth embodiment of this
invention. In FIG. 30 VCO 206, driver 201, and .phi.-V conversion
circuit 202 are the same as in the drive circuit 200 (FIG. 17) in
the first embodiment, and description thereof is omitted.
A/D converter 214 is a circuit for converting the phase difference
signal SPD output from .phi.-V conversion circuit 202 to a digital
value according to a command from control unit 212A. Operating unit
215 is a circuit for determining the digital value DF of the
frequency control voltage SVC supplied to VCO 206 according to a
command from control unit 212A. Non-volatile memory 213A is memory
for storing the digital value DF for frequency control and the
digital value of the phase difference signal SPD when driving the
rotor 100. The control unit 212A is a device for controlling each
of the above-described parts. This control unit 212A has a function
for calculating by means of the operating unit 215 an optimized
digital value DF for frequency control considered to improve
piezoactuator drive efficiency over the present when drive circuit
200C is driven to drive rotor 100, and update digital value DF.
FIG. 31 is a flow chart of this digital value DF update operation.
Control unit 212A performs this routine for rotor drive. First,
control unit 212A sends the digital value DF stored to non-volatile
memory 213A directly to D/A converter 216 through operating unit
215, causing it to output a corresponding frequency control voltage
SVC (step S31). When this frequency control voltage SVC is output
from D/A converter 216, VCO 206 oscillates at a corresponding
frequency, and a drive voltage signal SDR with the same frequency
is applied to diaphragm 10. The diaphragm 10 thus oscillates and
motor 100 is driven. During this time the phase difference .phi. of
detection signals SD1 and SD2 obtained from diaphragm 10 is
detected by .phi.-V conversion circuit 202, and phase difference
signal SPD is output.
Using this time while the rotor is driven, control unit 212A
advances a process for updating DF and SPD in preparation for the
next drive. First, the control unit 212A commands the A/D converter
214 to A/D convert this phase difference signal SPD (step S32).
Next, control unit 212A updates digital value DF in the
non-volatile memory 213 according to the following process. First,
it subtracts the digital value (here assumed to be SPDO) in
non-volatile memory 213 from the digital value (here assumed to be
SPDN) of the phase difference signal SPD obtained this time to
determine difference P. Next, it obtains a new digital value DFN
from the following equation using operating unit 215, and stores
this as the new DF in non-volatile memory 213 (step S33).
DFN=DFO+.alpha..times..DELTA.P where .alpha. is a constant
optimized through tests and simulations.
Next, control unit 212A stores the digital value of phase
difference signal SPD obtained this time to non-volatile memory 213
(step S34).
The above operation is performed each time the piezoactuator is
driven to optimize the drive frequency of diaphragm 10.
FIG. 32 and FIG. 33 show exemplary operations for optimizing the
digital value DF of each frequency control voltage.
First, in the example shown in FIG. 32, phase difference signal SPD
obtained from diaphragm 10 during piezoactuator drive is |.DELTA.P|
greater than the previous time, the drive time. If this situation
continues there is a chance that phase difference .phi. will
increase by further increasing the frequency of drive voltage
signal SDR. Therefore, in preparation for the next drive the
digital value DF of the frequency control voltage is increased just
|.alpha..times..DELTA.P|.
On the other hand, in the example shown in FIG. 33, phase
difference signal SPD obtained from diaphragm 10 during
piezoactuator drive is |.DELTA.P| lower than the previous time, the
drive time. If the frequency of the drive voltage signal SDR is
left as is in this case, there is the chance that phase difference
.phi. will drop suddenly. Therefore, in preparation for the next
drive the digital value DF of the frequency control voltage is
reduced just |.alpha..times..DELTA.P|.
This embodiment also achieves the effect of tracking change in
piezoactuator characteristics to drive the rotor 100 with extremely
high efficiency.
[5] Other Applications for a Piezoactuator According to the Present
Invention
The calendar display mechanism of a wristwatch described above is
not the only application for a piezoactuator according to the
present invention. This piezoactuator can also be applied in a
variety of other applications. Examples of these are described
below.
[5.1] Other Applications (1)
FIG. 34 is an oblique view showing the appearance of a contactless
type IC card. A remaining balance display counter 401 for
displaying the remaining balance is provided on the front side of
the contactless type IC card 400. The remaining balance display
counter 401 displays a four-digit remaining balance, and as shown
in FIG. 35 has a display part 402 for displaying the two high
digits and a display part 403 for displaying the two low
digits.
FIG. 36 is a side view showing the configuration of the high digit
display part. 402. The high digit display part 402 is linked to
piezoactuator A1 through intervening rotor 100A, and is driven by
the drive force of the rotor 100A. The main parts of the high digit
display part 402 include drive gear 402A having a driving part 402A
and rotating one revolution when rotor 100A turns 1/n revolution, a
first high digit display wheel 402B that turns one graduation for
each revolution of the drive gear 402A, a second high digit display
wheel 402C that rotates one graduation for each revolution of the
first high digit display wheel 402B, and a holding pawl 402D for
stopping the first high digit display wheel 402B when the first
high digit display wheel 402B does not turn. It should be noted
that a holding pawl not shown in the figures for stopping the
second high digit display wheel 402C is also provided for the
second high digit display wheel 402C.
The drive gear 402A rotates one revolution when the rotor 100A
turns 1/n revolution. The driving pawl 402A meshes with the feed
gear part 402B3 of the first high digit display wheel 402B, and the
first high digit display wheel 402B turns one graduation.
It should be noted that turning rotor 100A 1/n revolution is only
one operating example and the invention shall not be so limited.
Furthermore, turning the first high digit display wheel 402B one
graduation when the drive gear 402A turns one revolution is also
just one example of operation, and the invention shall not be so
limited.
In addition, when the first high digit display wheel 402B turns and
rotates one revolution, feed pin 402B disposed on the first high
digit display wheel 402B causes feed gear 402B2 to turn, turning
feed gear 402C of second high digit display wheel 402C meshed with
feed gear 402B, and thereby turning the second high digit display
wheel 402C one graduation.
The low digit display part 403 is linked to piezoactuator A2
through intervening rotor 100B and is driven by the drive power of
the rotor 10B. The main parts of the low digit display part 403
include drive gear 403A having a driving pawl 403A1 and rotating
one revolution when rotor 100B turns 1/n revolution, a first low
digit display wheel 403B that turns one graduation for each
revolution of the drive gear 403A, and a second low digit display
wheel 403C that rotates one graduation for each revolution of the
first low digit display wheel 403B.
A front view of the low digit display part 403 is shown in FIG. 37
and a side view in FIG. 38.
The first low digit display wheel 403B has a feed gear part 403B1
meshed with driving pawl 403A1 of drive gear 403A, and turns one
graduation for each one revolution of the drive gear 403A.
A feed pin 403B2 is also provided on the first low digit display
wheel 403B to turn feed gear 403B3 each time the first low digit
display wheel 403B turns one revolution, and thereby turn second
low digit display wheel 403C one graduation.
A holding pawl 403D of the first low digit display wheel 403B
engages the feed gear part 403B1 when not turning to stop the first
low digit display wheel 403B. Holding pawl 403E of the second low
digit display wheel 403C engages feed gear part 403F when the
second low digit display wheel 403C is not turning to stop the
second low digit display wheel 403C.
In this configuration actuator A1 and actuator A2 are set to be
synchronously driven by drive circuit 200B, and drive circuit 200B
is driven when a drive control signal equivalent to the transaction
amount is input by an IC card chip not shown in the figures.
A remaining balance display can thus be achieved even in a thin
contactless IC card, and because the display can be presented even
when not driven without requiring a power source, the balance can
be displayed with low power consumption and the balance to that
point can be displayed even when the power supply is depleted.
[5.2] Other Applications (2)
A piezoactuator and drive circuit therefor according to the present
invention are also suited to applications such as rotating a driven
part only a specific angle according to some sort of trigger. In a
preceding embodiment the present invention was applied to a
calendar display mechanism as an example of a display mechanism for
time-related information. Essentially, in each of the above
embodiments the drive circuit drives a piezoactuator when the time
at which the date should be advanced is reached, and this
piezoactuator drives the calendar display mechanism of the
wristwatch and turns the date counter an amount equivalent to one
day. In addition, wristwatches also have a display mechanism for
information relating to time, and application of the piezoactuator
to such display mechanisms is also possible. A drive mechanism for
a second hand for displaying seconds is one such example. The
present invention can be applied to the second hand drive mechanism
by configuring the second hand drive system so that it is linked to
a rotor rotationally driven by the piezoactuator in the above
embodiments. When thus configured the piezoactuator is also driven
by the drive circuit each time passage of one second is indicated
by the clock circuit. Piezoactuator drive in this case lasts until
piezoactuator drive force is transferred through the rotor to the
second hand drive mechanism and the second hand advances one
second.
[6] Variations of the Embodiments
[6.1] First Variation
In order to converge the frequency of the drive voltage signal SDR
to the frequency at which the phase difference of the detection
signals SD1 and SD2 obtained from diaphragm 10 is greatest, the
first embodiment described above determines the time derivative of
this phase difference, increases the frequency of the drive voltage
signal SDR when the time derivative is positive, and decreases the
frequency when negative. In order to quickly maximize the phase
difference of detection signals SD1 and SD2, it is effective here
to increase the gain of the closed loop (see FIG. 17) consisting of
diaphragm 10, .phi.-V conversion circuit 202, delay circuit 203,
comparator circuit 204, voltage adjusting circuit 205, VCO 206, and
driver 201. However, if the gain of this closed loop is too high,
the closed loop responds excessively to slight changes in the phase
difference, and a frequency at which the phase difference is an
extreme high value that is not the maximum may be captured so that
sweeping the frequency of drive voltage signal SDR stops. To
address this problem, this variation inserts a loop filter with an
adjustable filter coefficient to a suitable place in the closed
loop. By adjusting the filter coefficient of the loop filter, this
variation can adjust the closed loop gain so that the phase
difference of detection signals SD1 and SD2 can be quickly driven
to the true maximum.
[6.2] Second Variation
When the initial frequency of the drive voltage signal SDR is low
in the above first embodiment, the time required to bring the
frequency of the drive voltage signal SDR to the frequency at which
the phase difference of detection signals SD1 and SD2 is maximized
becomes longer. In the present variation, therefore, when the
frequency of the drive voltage signal SDR converges to the
frequency at which the phase difference of detection signals SD1
and SD2 is maximized during rotor 100 drive, the frequency control
voltage SVC at that time is converted to a digital value and stored
in memory. Then, the next time the rotor 100 is driven the digital
value stored in memory is converted to an analog voltage, and a
frequency control voltage SVC that is lower by a specific amount is
applied to the VCO 206 to start drive voltage signal SDR frequency
control. When thus comprised the time required for the frequency of
the drive voltage signal SDR to reach the frequency at which the
phase difference of detection signals SD1 and SD2 is maximized can
be shortened.
[6.3] Third Variation
Longitudinal oscillation and sinusoidal oscillation can be
separately detected with a piezoactuator in each of the above
embodiments because electrodes for detecting longitudinal
oscillation and electrodes for detecting sinusoidal oscillation are
separately provided. A variation using this characteristic is shown
in FIG. 39.
This drive circuit 200D shown in FIG. 39 adds a gain control
circuit 251 to the drive circuit (see FIG. 17) in the first
embodiment.
In order to appropriately drive the rotor 100, the amplitude of
both longitudinal oscillation and sinusoidal oscillation must be
high enough to overcome the surface roughness of the rotor 100.
Therefore, the gain control circuit 251 of the present variation
increases the gain of the driver 201 to raise the drive voltage
signal SDR when the magnitude of either longitudinal oscillation
detection signal SD1 or sinusoidal oscillation detection signal SD2
obtained from diaphragm 10 is less than or equal to a threshold
value. Automatic gain control using both detection signals SD1 and
SD2 in this way is able to stabilize driving the rotor 100 by means
of contact 36.
It should be noted that this variation can also be applied to the
drive circuits of the second to fourth embodiments, and not just in
the first embodiment.
[6.4] Fourth Variation
As does the first embodiment above, the variation shown in FIG. 40
also uses the ability to separately detect longitudinal oscillation
and sinusoidal oscillation. This drive circuit 200E shown in FIG.
40 adds a failure detection circuit 252 to the drive circuit (see
FIG. 17) in the first embodiment.
The amplitude of detection signal SD1 or SD2 decreases when the
diaphragm 10 fails due, for example, to a crack developing in the
piezoelectric elements of the diaphragm 10. When a phenomenon such
as this is confirmed by the failure detection circuit 252, a signal
indicative thereof is sent to the wristwatch control unit to
display a failure.
This variation has the effect of being able to quickly inform the
user when it becomes necessary to repair the piezoactuator.
It should be noted that this variation can also be applied to the
drive circuits of the second to fourth embodiments, and not just in
the first embodiment.
[6.5] Fifth Variation
When the above-described third embodiment sets a reference phase
difference to operate the drive circuit and successfully drives the
piezoactuator, it increases the reference phase difference a
specific amount the next time the drive circuit is driven and
attempts to drive the piezoactuator. Therefore, if there is no
change over time in the characteristics of the piezoactuator, drive
fails at the first drive circuit operation and drive succeeds the
second time the drive circuit operates, and this sequence repeats
each time the piezoactuator is driven. Conditions such as this are
not desirable when this embodiment is applied to an apparatus
driving the piezoactuator at relatively short time intervals. The
present variation improves on this.
In the present variation control unit 212 of drive circuit 200B
stores the reference phase difference at which drive succeeded to
non-volatile memory 213 each time the piezoactuator is driven. When
the piezoactuator is to be driven, the control unit 212 reads a
specific number of past reference phase differences stored to
non-volatile memory 213 and determines if the reference phase
differences are the same. If the determination is YES, control unit
212 determines that the piezoactuator characteristics are stable
over time, and for a specific period thereafter omits the process
increasing the initial reference phase difference from the
reference phase difference used the previous drive time. After this
specific period passes, it resumes the process increasing the
initial reference phase difference from the phase difference used
the previous drive time.
[6.6] Sixth Variation
In the second to fourth embodiments the frequency of drive voltage
signal SDR is controlled in order to achieve the greatest possible
phase difference .phi. within the range in which the phase
difference .phi. of detection signals SD1 and SD2 increases with an
increase in the frequency of the drive voltage signal SDR (range in
which the slope is positive). The embodiments of the invention
shall not, however, be so limited. That is, it is also possible to
control the frequency of drive voltage signal SDR to achieve the
greatest possible phase difference .phi. within the range in which
the phase difference .phi. of detection signals SD1 and SD2
decreases with an increase in the frequency of the drive voltage
signal SDR (range in which the slope is negative).
[6.7] Seventh Variation
A variation in which a part of the drive circuit is controlled by
software in the first to third embodiments above is also
conceivable. Examples of software control in this case are
described below.
<Variation of Embodiment 1 (FIG. 17)>
In this variation components other than the .phi.-V conversion
circuit 202, VCO 206, and driver 201 are replaced by a CPU and
memory. The memory is used for data storage and program storage. An
A/D converter is also disposed after the .phi.-V conversion circuit
202, and a D/A converter is disposed before the VCO 206.
In this variation the CPU executes the following process according
to routines stored in memory when a piezoactuator drive command is
asserted.
S31: The digital value applied to the D/A converter is increased
for a specific time to raise the oscillation frequency of VCO 206
to the initial value.
S32: Phase difference .phi. is received from the A/D converter, and
the time derivative thereof is obtained.
S33: The digital value applied to the D/A converter is increased if
the time derivative is positive, and decreased if negative.
S34: Processing ends if the change in phase difference .phi. is
within a specific tolerance range, and processing otherwise returns
to step S32.
<Variation of Embodiment 2 (FIG. 24)>
In this variation components other than the .phi.-V conversion
circuit 202, VCO 206, and driver 201 are replaced by a CPU and
memory. The memory is used for data storage and program storage. An
A/D converter is also disposed after the .phi.-V conversion circuit
202, and a D/A converter is disposed before the VCO 206.
In this variation the CPU executes the following process according
to routines stored in memory when a piezoactuator drive command is
asserted.
S41: A digital value corresponding to the initial value of
frequency control voltage SVC is applied to the D/A converter.
S42: Phase difference .phi. is received from the A/D converter, and
the digital value applied to the D/A converter is increased if the
phase difference is less than the reference phase difference, and
is decreased if greater than.
S43: The process ends if the phase difference .phi. is within a
specific tolerance range of the reference phase difference, and the
process otherwise returns to step S42.
<Variation of Embodiment 3 (FIG. 28)>
In this variation components other than the frequency counter 211,
.phi.-V conversion circuit 202, VCO 206, and driver 201 are
replaced by a CPU and memory. The memory is used for data storage
and program storage. The reference phase difference is stored as
data in memory. An A/D converter is also disposed after the .phi.-V
conversion circuit 202, and a D/A converter is disposed before the
VCO 206.
In this variation the CPU executes the following process according
to routines stored in memory when a piezoactuator drive command is
asserted.
S51: The failure count is initialized to 0, and the reference phase
difference is read from memory and increased a specific amount.
S52: The digital value applied to the D/A converter is
initialized.
S53: Whether phase difference .phi. exceeds the reference phase
difference is determined, and the process skips to step S56 if the
result is YES.
S54: The digital value applied to the D/A converter is increased a
specific amount.
S55: Whether the frequency of the drive voltage signal SDR output
from frequency counter 211 is less than or equal to a specific
value is determined; if the result is YES, the digital value
applied to the D/A converter is increased a specific amount (S55A),
and the routine returns to step S53; if the result is NO, the
failure count is incremented 1, the reference phase difference is
decreased a specific amount (S55B), and the routine returns to step
S52. S56: If the failure count is 0, the reference phase difference
is increased a specific amount (step S56A) and the routine returns
to step S52, otherwise the reference phase difference is stored to
memory (step S56B) and the process ends.
The present invention can also be achieved by such modes as
distributing the routines described above via an electrical
communication circuit to users, or storing such routines to a
computer-readable storage medium distributed to users. The users
can write the desired routines thus obtained to the drive circuit
memory.
[6.7] Seventh Variation
Wristwatches and contactless IC cards are described above as the
portable devices, but it will be noted that the present invention
can be applied to any type of portable device insofar as it is a
portable electronic device requiring a drive system, and
particularly a rotational drive system.
[6.8] Eighth Variation
A longitudinal oscillation mode oscillating in the longitudinal
direction of the piezoactuator is used as the first oscillation
mode, and a sinusoidal oscillation mode corresponding to the first
oscillation mode is used as the second oscillation mode in the
embodiments described above, but the invention shall not be so
limited.
Specifically, a first longitudinal oscillation mode that is a
longitudinal oscillation mode oscillating lengthwise to the
piezoactuator can be used as a first oscillation mode, and a second
longitudinal oscillation mode oscillating in a direction orthogonal
to the first oscillation mode can be used as the second oscillation
mode.
Furthermore, it is also possible to use the above-noted second
longitudinal oscillation mode as the first oscillation mode, and
use a sinusoidal oscillation mode corresponding to the second
longitudinal oscillation mode.
The locations of the oscillation detection electrodes in these
cases can be determined from tests.
[6.9] Ninth Variation
In addition to using a battery (primary cell or secondary cell) as
the power source of the actuator, configurations using a power
supply with an internal generator mechanism having a solar cell,
thermoelectric generator, mechanical generator, or storage device
(capacitor or secondary battery) can also be used.
* * * * *