Patent ID: 7808154

Claim:
An actuator unit, comprising: a friction drive actuator which is powered by an electromechanical conversion element; a drive section which applies an electric signal to the electromechanical conversion element to drive the friction drive actuator by a resonant drive mode and an expansion and contraction drive mode as drive modes for driving the friction drive actuator, wherein in the resonant drive mode, the friction drive actuator is vibrated in resonance, and in the expansion and contraction drive mode, the friction drive actuator is expanded and contracted, and when the resonant drive mode is terminated, the vibration of the friction drive actuator caused by the drive section continues as a residual vibration after the termination of the resonance drive, and the residual vibration decays with time; and a control section which switches the drive mode from the resonant drive mode to the expansion and contraction drive mode, wherein when the control section switches the drive mode from the resonant drive mode to the expansion and contraction drive mode, the control section terminates the resonant drive mode and then starts the friction drive mode after an amplitude of the residual vibration of the friction drive actuator has decayed to a predetermined value and a predetermined period of time has passed since the control section terminated the resonant drive mode.