Ultrasonic motor

An ultrasonic motor at least comprising:

• a vibrator having a dimension ratio of a rectangle in a cross-section orthogonal to a central axis;
• and
• a rotor that is in contact with an elliptical vibration generating surface of the vibrator and that is rotated about the central axis that is orthogonal to the elliptical vibration generating surface of the vibrator, wherein
• an elliptical vibration is generated by combining a longitudinal primary resonance vibration resulting from an expansion and a contraction of the vibrator in a direction of the central axis and a torsional secondary resonance vibration or a torsional tertiary resonance vibration resulting from twisting of a rotation axis,
• the dimension ratio of the rectangle of the vibrator is chosen such that a resonance frequency of the longitudinal primary resonance vibration resulting from the expansion and the contraction of the vibrator in the direction of the central axis and a resonance frequency of the torsional secondary resonance vibration or the torsional tertiary resonance vibration resulting from twisting of the rotation axis match, and
• the vibrator includes a torsional piezoelectric body that generates a thickness shear vibration, and that is arranged at an anti-node position of the torsional secondary resonance vibration or the torsional tertiary resonance vibration.