Mirror driving device and driving method thereof

A mirror driving device comprising:

• a mirror having a reflecting surface;
• a mirror support which is connected to the mirror and supports the mirror so as to be rotatable about a rotation axis, the mirror having a first side and a second side which are disposed opposite to each other across a center of the mirror and along an axial direction of the rotation axis, the mirror support including a first torsion bar and a second torsion bar which are parallel to the axial direction, separated from each other across the mirror and along the axial direction, and connected respectively to the first side and the second side of the mirror;
• a piezoelectric actuator which is connected to the mirror support and generates a driving force to rotate the mirror about the rotation axis;
• and
• a fixing frame which supports the piezoelectric actuator, wherein:
• the piezoelectric actuator has a laminated structure in which a vibration plate, a lower electrode, a piezoelectric body, and an upper electrode are laminated in this order, and includes a first actuator and a second actuator which are piezoelectric unimorph actuators that are deformed by an inverse piezoelectric effect of the piezoelectric body caused by application of a drive voltage,
• the first actuator and the second actuator are disposed opposite to each other across the rotation axis and along an orthogonal direction which is orthogonal to both a film thickness direction of the piezoelectric body and the axial direction of the rotation axis,
• the first actuator is connected to the first torsion bar and the second torsion bar respectively through a first connector and a second connector which are connected to the first actuator respectively at a first connection point and a second connection point,
• the second actuator is connected to the first torsion bar and the second torsion bar respectively through a third connector and a fourth connector which are connected to the second actuator respectively at a third connection point and a fourth connection point,
• each of the first actuator and the second actuator is supported by the fixing frame in a both-end supported beam structure,
• the first actuator has a first base end and a second base end which are disposed opposite to each other along the axial direction and are fixed to the fixing frame, the first base end is further than the first connection point from the center of the mirror, and the second base end is further than the second connection point from the center of the mirror,
• the first actuator includes a first movable base that extends between the first base end and the second base end and overlaps the mirror,
• the second actuator has a third base end and a fourth base end which are disposed opposite to each other along the axial direction and are fixed to the fixing frame, the third base end is further than the third connection point from the center of the mirror, and the fourth base end is further than the fourth connection point from the center of the mirror,
• the second actuator includes a second movable base that extends between the third base end and the fourth base end and overlaps the mirror,
• the first base end and the third base end are disposed separately from and opposite to each other along the orthogonal direction, and the second base end and the fourth base end are disposed separately from and opposite to each other along the orthogonal direction,
• the mirror support is driven to be tilted by causing the first actuator and the second actuator to bend in opposite directions,
• the first actuator has a first upper electrode and a second upper electrode as the upper electrode, and has a first lower electrode and a second lower electrode as the lower electrode, which respectively oppose the first upper electrode and the second upper electrode with the piezoelectric body interposed therebetween, and each of a first piezoelectric converter having the first upper electrode and the first lower electrode as an electrode pair and a second piezoelectric converter having the second upper electrode and the second lower electrode as an electrode pair is constituted by a single or a plurality of electrode pairs,
• the second actuator has a third upper electrode and a fourth upper electrode as the upper electrode, and has a third lower electrode and a fourth lower electrode as the lower electrode, which respectively oppose the third upper electrode and the fourth upper electrode with the piezoelectric body interposed therebetween, and each of a third piezoelectric converter having the third upper electrode and the third lower electrode as an electrode pair and a fourth piezoelectric converter having the fourth upper electrode and the fourth lower electrode as an electrode pair is constituted by a single or a plurality of electrode pairs,
• an arrangement of the first piezoelectric converter, the second piezoelectric converter, the third piezoelectric converter, and the fourth piezoelectric converter corresponds to a stress distribution of principal stresses in an in-plane direction orthogonal to the film thickness direction of the piezoelectric body during resonance mode vibration accompanied with tilt displacement of the mirror due to rotation about the rotation axis, and
• a piezoelectric portion corresponding to positions of the first piezoelectric converter and the third piezoelectric converter and a piezoelectric portion corresponding to positions of the second piezoelectric converter and the fourth piezoelectric converter are configured to generate stresses in opposite directions during the resonance mode vibration.