Patent ID: 7307928

Claim:
An optical storage device comprising: a lens that is arranged to face a storage medium and serves to focus laser light on the storage medium; an actuator that changes a position of the lens; a first focus error signal detector that detects, within a first detection range, a difference between a focus position of the lens that focuses the laser light on the storage medium and the position of the lens; a second focus error signal detector that detects, within a second detection range that is wider than the first detection range, a difference between the focus position of the lens that focuses the laser light on the storage medium and the position of the lens; a first movement controller that causes the lens to approach the storage medium by using open-loop control by driving the actuator until the position of the lens falls within the second detection range of the second focus error signal detector from outside the second detection range of the second focus error signal detector; a target trajectory generator that generates a target trajectory signal for moving the lens; a second movement controller that causes the lens to approach the storage medium by using closed-loop control including a second focus error signal detected by the second focus error signal detector and the target trajectory signal to drive the actuator in a case where the position of the lens is within the second detection range of the second focus error signal detector; and a following controller that causes the position of the lens to follow the focus position of the lens with respect to the storage medium by using the closed-loop control by using a first focus error signal detected by the first focus error signal detector by driving the actuator in a case where the position of the lens is within the first detection range of the first focus error signal detector; wherein the second movement controller comprises a phase compensator that performs phase compensation on a difference signal between the target trajectory signal and the second focus error signal.