(1) A technique of suppressing the generation of abnormal noise related to the driving of a vibration wave motor has been known (for example, refer to Patent Document 1). In Patent Document 1, abnormal noise when stopping the vibration-wave motor is suppressed by causing the phase difference between an A-phase drive signal and a B-phase drive signal to gradually vary from 90 deg to 0 deg.
(2) An imaging device that performs processing such as auto-focus by driving an optical system by way of a vibration-wave motor has been known (Patent Document 2).
(3) A vibration actuator causes a progressive vibration wave (hereinafter abbreviated as progressive wave) to generate at the driving face of an elastic body using the expansion and contraction of a piezoelectric body, causing an elliptic motion to occur at the driving face by way of this progressive wave, thereby driving a moving element in pressurized contact with the wave crest of the elliptic motion (for example, refer to Patent Document 3). Such a vibration actuator has a characteristic in having high torque even at low revolutions, and in the case of equipping to a drive apparatus, it is possible to omit gears in the drive apparatus. For this reason, it is possible to achieve quieting by elimination gear noise, and the positioning accuracy also improves. This vibration actuator has been equipped to some electric cameras. In addition, some electric cameras can perform photography of a moving image in addition to photography of still images (refer to Patent Document 4). In the case of performing photography of a moving image, normally the capturing of sound is also performed.
(4) Conventionally, two vibration signals having different phases from each other are applied to a piezoelectric effect element in order to drive the vibration actuator. The frequency of the vibration signal inputted starts from a frequency (startup frequency) between the drive frequency used in order to drive the vibration actuator and a resonance frequency of a next higher-order vibration mode to a vibration mode (drive mode) including this drive frequency, and gradually lowers to the drive frequency (for example, refer to Patent Document 5).
(5) Conventionally, the drive apparatus of a vibration actuator has controlled the operation of the vibration actuator by causing the phase difference and frequency of alternating signals input to the vibration actuator to vary (for example, Patent Document 6).
[Patent Document 1]: Japanese Unexamined Patent Application, Publication No. 2002-199749
[Patent Document 2]: Japanese Unexamined Patent Application, Publication No. 2009-153286
[Patent Document 3]: Japanese Patent Publication No. H01-017354
[Patent Document 4]: Japanese Unexamined Patent Application, Publication No. H08-080073
[Patent Document 5]: Japanese Unexamined Patent Application, Publication No. H03-022873
[Patent Document 6]: Japanese Patent Publication No. 4765405