Patent ID: 8304962

Claim:
An ultrasonic motor at least comprising: a vibrator having a dimension ratio of a rectangle in a cross-section orthogonal to a central axis; a rotor that is in contact with an elliptical vibration generating surface of the vibrator and that is rotated around the central axis, which is orthogonal to the elliptical vibration generating surface, 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 resonance vibration resulting from twisting of the vibrator around the central axis as a torsional axis, and 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 resonance vibration resulting from twisting of the vibrator around the central axis as the torsional axis match, and the ultrasonic motor includes a vibration detecting electrode layer, and the torsional resonance vibration is a torsional secondary resonance vibration, and the vibrator is formed by stacking a plurality of piezoelectric sheets, the vibration detecting electrode layer includes a piezoelectric sheet having internal electrodes formed thereon at positions on either side of a center in a width direction thereof, and a piezoelectric sheet having internal electrodes formed thereon at positions on either side of a center in a width direction thereof that are short circuited, and polarity directions of the internal electrodes at the positions on either side of the center in the width direction of the piezoelectric sheet are the same.