Piezoelectric actuator having separate frictional portions

A piezoelectric actuator comprising:

• a piezoelectric element that is composed of a stack of a plurality of piezoelectric material layers and generates a vibration mode in which a longitudinal vibration mode and a bending vibration mode are combined in response to an applied voltage, the piezoelectric element including:
• a pair of principal surfaces having rectangular shapes and facing each other, the pair of principal surfaces being located in a direction orthogonal to a stacking direction of the plurality of piezoelectric material layers;
• a pair of end surfaces facing each other in a long-side direction of the pair of principal surfaces;
• a pair of lateral surfaces facing each other in a short-side direction of the pair of principal surfaces and in the stacking direction;
• and
• antinodes having maximum amplitude in the bending vibration mode at positions which are asymmetric with respect to a straight line passing through a center in a longitudinal direction of the piezoelectric element and parallel to a facing direction of the pair of principal surfaces when viewed in a facing direction of the pair of lateral surfaces;
• a first frictional portion disposed on one of the pair of principal surfaces and configured to contact a driven object to generate frictional force with the driven object, the first frictional portion being disposed at a position other than the antinodes of the piezoelectric element at which a distance from one of the end surfaces is less than ⅓ L, where L represents a length in the longitudinal direction of the piezoelectric element;
• and
• a second frictional portion disposed on the one of the pair of principal surfaces and configured to contact the driven object to generate frictional force with the driven object, the second frictional portion being disposed at a position other than the antinodes of the piezoelectric element at which a distance from the other of the end surfaces is less than ⅓ L,
• wherein the first frictional portion and the second frictional portion are not part of a same structure.