Ultrasonic motor and electronic device fitted with ultrasonic motor

An ultrasonic motor comprising:

• a piezoelectric element;
• a driver circuit having plural amplifier circuits connected in parallel for amplifying an excitation signal in accordance with excitation of the piezoelectric element;
• and
• selecting means for selecting an amplifier circuit, wherein those of said plural amplifier circuits which are made to function are selected.

An ultrasonic motor comprising:

• a piezoelectric element;
• a driver circuit having a phase-setting circuit for setting a phase of an excitation signal in accordance with excitation of the piezoelectric element;
• and
• adjusting means for adjusting the phase of the excitation signal set by the phase-setting circuit.

An ultrasonic motor comprising:

• a piezoelectric element;
• a driver circuit for generating an excitation signal in accordance with excitation of the piezoelectric element, and having a booster circuit;
• and
• adjusting means for adjusting a current supplied to the booster circuit or a current supplied to the piezoelectric element.

An ultrasonic motor comprising:

• a piezoelectric element;
• a driver circuit for generating an excitation signal for driving the piezoelectric element, the piezoelectric element and the driver circuit cooperating to form a self- excited oscillator;
• a power supply for supplying a voltage to the driver circuit;
• adjusting means for adjusting the voltage supplied to the driver circuit;
• rotational speed-detecting means for detecting a rotational speed of a moving body that is rotated based on excitation of the piezoelectric element;
• rotational speed-comparing means for comparing the rotational speed detected by the rotational speed-detecting means with a preset rotational speed;
• and
• rotational speed control means for controlling the adjusting means to bring the rotational speed of the moving body into agreement with the preset rotational speed if a result of the comparison made by the rotational speed-comparing means indicates that the detected rotational speed is not coincident with the preset rotational speed.