Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-02-04
2002-05-14
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06388362
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in an ultrasonic motor having an oscillation drive circuit for forming an excitation signal based on excitation of a piezoelectric element and an electronic apparatus having an ultrasonic motor.
In recent times, ultrasonic motors producing driving force by making use of the piezoelectric effect of a piezoelectric element have attracted attention in the field of micromotors. The ultrasonic motor is a motor making use of a mechanical resonance phenomenon, a drive frequency thereof is varied by environmental temperature or outside load and accordingly, there is needed a complicated drive circuit such that a frequency tracking function is added to an outside oscillator or the like. However, an oscillator bonded with a piezoelectric element can simply be driven by making use of oscillation drive system for driving the oscillator by self-excited oscillation.
As an example of an oscillation drive circuit making use of such self-excited oscillation, as shown by
FIG. 23
, there has been known a type having a piezoelectric element
102
to be excited, a 3-state inverter
502
as well as 3-state buffers
501
a
and
501
b
for amplifying an initial signal based on the excitation to an excitation signal and condensers
505
and
506
for setting the excitation signal to a predetermined frequency (refer to JP-A-8-251952).
Further, a flection standing wave is caused in an oscillator
101
bonded to the piezoelectric element
102
and frictional force is exerted to a moving body (not illustrated) pressed to the oscillator
101
to thereby rotate the moving body in a predetermined direction.
However, according to an oscillation drive circuit
405
making use of self-excited oscillation as mentioned above, when the circuit is restarted after the oscillation drive has been stopped, there poses a problem of remaining electric charge of the condensers
505
and
506
or a problem in which even when the 3-state inverter
502
as well as the 3-state buffers
501
a
and
501
b
are brought into an active state, both of a Pch transistor and an Nch transistor are brought into an OFF state, that is, an output is brought into a high impedance state which is caused by a dispersion in the semiconductor process, and there poses a problem in which an initial signal constituting a basis of self-excited oscillation becomes difficult to produce in the oscillation drive circuit
405
, much time is required to rise of oscillation, further, failure of starting oscillation is resulted and so on to thereby deteriorate reliability or high response which is a feature of an ultrasonic motor.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an ultrasonic motor and an electronic apparatus having an ultrasonic motor which is excellent in response or stability in restarting operation and highly reliable.
In order to resolve the above-described problem, according to claim
1
, the oscillation drive circuit comprises a power amplifier for amplifying an excitation signal, a capacitive circuit for adjusting a frequency of the oscillation signal, and a switching circuit connected in parallel with a capacitive element constituting the capacitive circuit for shortcircuiting terminals of the capacitive element based on an output signal from the start/stop signal generating means, wherein when the oscillation drive circuit is brought into the stop state based on the output signal from the start/stop signal generating means, the switching circuit is made ON and the terminals of the capacitive element is brought into a shortcircuited state.
According to the invention, electric charge remaining in the capacitive element is discharged in the stop state and in restarting operation, there is provided excellent oscillation rise characteristic by facilitating to form an initial signal constituting the basis of oscillation and the ultrasonic motor and an electronic apparatus having the ultrasonic motor excellent in response and which is highly reliable are realized.
According to the invention described in claim
2
, the oscillation drive circuit comprises a power amplifier for amplifying an excitation signal, a capacitive circuit for adjusting a frequency of the excitation signal, and an oscillation starting circuit for generating an oscillation start trigger based on the output signal from the start/stop signal generating means, and wherein the oscillation starting circuit is operated during a rise time period in which the oscillation drive circuit is brought into an active state and starts oscillation based on the output signal from the start/stop signal generating means.
According to the invention, in respect of a high impedance state of an output from the power amplifier which is caused in rise of oscillation which is brought about by a dispersion in semiconductor process regardless of the fact that the power amplifier is brought into an active state, failure in starting to oscillate is avoided by generating the oscillation start trigger during the rise time period of starting the oscillation and there can be realized the ultrasonic motor and an electronic apparatus having the ultrasonic motor with high response and high reliability providing excellent oscillation rise characteristic.
According to the invention described in claim
3
, the oscillation drive circuit comprises a power amplifier for amplifying an excitation signal, a capacitive circuit for adjusting a frequency of the excitation signal, a switching circuit connected in parallel with a capacitive element constituting the capacitive circuit for shortcircuiting terminals of the capacitive element based on an output signal from the start/stop signal generating means, and an oscillation starting circuit for generating an oscillation start trigger based on the output signal from the start/stop signal generating means, wherein when the oscillation drive circuit is brought into the stop state based on the output signal from the start/stop signal generating means, the switching circuit is made ON and the terminals of the capacitive element are brought into a shortcircuited state, and wherein when the oscillation drive circuit is brought into an active state based on the output signal from the start/stop signal generating means, the switching circuit is made OFF and the oscillation starting circuit for generating the oscillation start trigger is operated during a rise time period of starting oscillation.
According to the invention, electric charge remaining in the capacitive element is discharged in the stop state and an initial signal constituting a basis of oscillation is facilitated to form in restarting operation and in respect of a high impedance state of an output from the power amplifier caused in rise of oscillation which is brought about by a dispersion in semiconductor process, failure of starting oscillation is avoided by generating the oscillation start trigger during a rise time period of starting oscillation by which there is realized the ultrasonic motor with excellent response and high reliability providing further excellent oscillation rise characteristic and an electronic apparatus having the ultrasonic motor.
According to the invention described in claim
4
, the oscillation drive circuit comprises a capacitive circuit for adjusting a frequency of the oscillation signal and the power amplifier constituted by using an inverter at an input unit.
According to the invention, there is realized the ultrasonic motor with excellent response and high reliability avoiding failure of starting oscillation caused by dispersion in semiconductor process and providing excellent oscillation rise characteristic.
According to the invention described in claim
5
, the oscillation drive circuit comprises a capacitive circuit for adjusting a frequency of the excitation signal, a switching circuit connected in parallel with a capacitive element constituting the capacitive circuit for shortcircuiting terminals of the capacitive element based on an output signal from the start/stop si
Iino Akihiro
Katou Kazuo
Suzuki Kenji
Suzuki Makoto
Yamanaka Takashi
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