Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-08-03
2001-11-20
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S316010, C310S316020
Reexamination Certificate
active
06320298
ABSTRACT:
This application is based on patent application Ser. No. 10-219221 filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
This invention relates to an actuator driving circuit capable of preventing howling sounds when an actuator is driven, and an actuator driving device provided with such an actuator driving circuit, and an actuator driving method.
Conventionally, there has been known an actuator in which a driving member is fixedly attached to an electromechanical transducing element such as a piezoelectric element, and is reciprocatingly displaced by applying a drive voltage comprising a pulse having a serrated waveform to this electromechanical transducing element to expand and contract it, thereby moving a movable member coupled with the driving member by friction along expanding and contracting directions. Such an actuator is hereinafter referred to as “piezoelectric actuator”).
FIG. 14
is a block diagram showing a driving circuit for the piezoelectric actuator. A voltage of about 30V is used to operate the piezoelectric actuator. Accordingly, in the case that a voltage in a power supply unit
100
is 5V as shown in
FIG. 14
, an output voltage from a dc-to-dc converter
102
having a switching regulator circuit
101
is boosted to 30V.
A pulse signal generated in a pulse signal generating circuit
104
of a CPU
103
has its frequency divided into a specified frequency by a pulse frequency dividing circuit
105
, and a drive pulse signal having a serrated waveform is generated from this pulse and the output voltage of 30V in a drive pulse signal generating circuit
106
and applied to a piezoelectric actuator
107
.
FIG. 15
is a diagram showing a circuit construction of the switching regulator circuit
101
of
FIG. 14
, and
FIG. 16
is a timing chart showing waveforms of voltages from the respective outputs in FIG.
15
.
A field-effect transistor Q is turned on and off by a PWM drive voltage DRIVE from a drive circuit
110
. By turning the transistor Q on and off, storage of energy in a coil L and discharge thereof from the coil L are continuously performed, and a capacitor C is charged with this energy to increase an output voltage VOUT as shown in FIG.
16
.
On the other hand, a feedback signal FB is obtained by amplifying a difference between the output voltage VOUT and a reference voltage VREF by an error amplifier
111
, and a serrated wave signal SAW is outputted from a serrated wave signal generating circuit
112
in accordance with a synchronization pulse SYNC of a specified frequency. A PWM signal is outputted after the feedback signal FB and the serrated wave signal SAW are compared by a PWM comparator
113
, and the PWM drive voltage DRIVE from the drive circuit
110
is controlled, thereby controlling an on-off duty ratio of the transistor Q. As a result, the output voltage VOUT is held at a specified level.
In the switching regulator circuit of
FIG. 15
, power noise is generated when the energy stored in the coil L is discharged by turning the transistor Q off as shown in the waveform of the output voltage VOUT in FIG.
16
. This power noise affects the output voltage via wiring, with the result that the output voltage may be rippled and/or spike voltages SP may be added thereto as shown in FIG.
16
. If the drive pulse signal having a serrated waveform comprising a driving voltage experiencing this spike voltage SP is applied to the piezoelectric actuator
107
, the piezoelectric actuator
107
slightly expands and contracts in synchronism with the spike voltage SP. These expansion and contraction generate sounds.
If a switching frequency obtained by turning the transistor Q on and off and the frequency of the drive pulse signal fed to the piezoelectric actuator
107
are both ultrasonic frequency, the sounds generated by the expansion and the contraction of the piezoelectric actuator
107
by the drive pulse signal and by the spike voltage lie outside an audible range by humans. However, if the expansion and the contraction by the drive pulse signal and those by the spike voltage interfere each other, the so-called “howling” occurs. At this stage, if “howling” of an audible frequency is produced, this becomes a noise, thereby giving an unpleasant feeling to humans.
Japanese Unexamined Patent Publication No. 8-80075 discloses an apparatus provided with a plurality of ultrasonic actuators whose drive frequencies are ultrasonic frequencies, in which the respective drive frequencies are so set as not to cause mechanical howling between the actuators.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an actuator driving circuit, an actuator driving device, and an actuator driving method which have overcome the problems residing in the prior art.
It is another object of the present invention to provide an actuator driving circuit, an actuator driving device, and an actuator driving method which can make howling quieter by shifting the frequency of howling produced from an actuator itself resulting from imposition of a power noise onto a drive pulse signal for driving an actuator.
According to an aspect of the present invention, an actuator driving circuit comprises a drive pulse signal generator for generating a drive pulse signal having a specified ultrasonic frequency, and a drive voltage generator for generating a drive voltage for drive pulse signal generation upon receipt of a power supplied from a power source. The relationship between the frequency of power noise cyclically produced from the drive voltage generator and imposed on the drive voltage and the frequency of the drive pulse signal is so set as to satisfy the following equation:
4000<|
m·f
1
−
n·f
2
|
wherein
m: positive integer below a specified value;
n: positive integer below a specified value;
f
1
:frequency of power noise; and
f
2
:frequency of the drive pulse signal.
The actuator may be a ultrasonic motor, and have an electromechanical transducing element expandable and contractible in accordance with the drive pulse signal.
According to another aspect of the present invention, an actuator driving device comprises the above-mentioned actuator driving circuit, a drive member secured to one end of an electromechanical transducing element arranged in the actuator its expanding and contracting directions, and a friction member frictionally coupled with the driving member.
According to still another aspect of the present invention, an actuator driving method comprises generating a drive voltage upon receipt of a power supplied from a power source, generating a drive pulse signal upon receipt of the generated drive voltage, the drive pulse signal being generated at a frequency (f
2
) satisfying the following equation:
4000<|
m·f
1
−
n·f
2
|
wherein
m: positive integer below a specified value;
n: positive integer below a specified value; and
f
1
:frequency of power noise cyclically produced in the drive voltage generation and imposed on the drive voltage; and
supplying the generated drive pulse signal to an actuator.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a block diagram showing a construction of an actuator driving circuit according to an embodiment of the invention;
FIG. 2
is a circuit diagram showing a circuitry of the actuator driving circuit;
FIG. 3
is a timing chart showing voltage waveforms of output signals of the respective terminals and a drive pulse signal;
FIGS. 4A
to
4
C are diagrams showing one motion of a movable member by a piezoelectric actuator;
FIGS. 5A
to
5
C are diagrams showing another motion of the movable member by the piezoelectric actuator;
FIG. 6
is an exploded perspective view showing a construction of an actuator driving device provided with the actuator driving circuit;
FIG. 7
is a perspective view showing the actuator driving device in its assembled
Budd Mark O.
McDermott & Will & Emery
Minolta Co. , Ltd.
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