Patent ID: 7480218

Claim:
An optical disk control device comprising: a converging projecting means that converges and projects a light beam via an objective lens to an information carrier having a plurality of information surfaces; a spherical aberration regulating means that sets the amount of spherical aberration of the focal point of the light beam that is converged by the converging projecting means, according to a target surface; a focus-moving means that, by moving the objective lens, moves the focal point of the light beam converged by the converging projecting means in a direction normal to the surface of the information carrier; a focus error detecting means that generates a focus error signal in response to the positional displacement of the focal point of the light beam with respect to the surfaces of the information carrier; a reflected light quantity detecting means that detects a signal corresponding to the amount of light reflected from the information carrier; a phase relationship detecting means that detects the phase relationship between the focus error signal and the reflected light quantity signal based upon the level of the reflected light quantity signal from the reflected light quantity detecting means when the focus error signal takes a maximum value and a minimum value and the maximum value of the reflected light quantity signal from the reflected light quantity detecting means; an information surface discriminating means that detects the target surface from the plurality of information surfaces of the information carrier based upon the phase relationship output from the phase relationship detecting means; a reversal instruction means that outputs a reversal instruction using the output signal from the information surface detecting means; a driving signal generating means, that, along with outputting a signal to the focus moving means to move the objective lens toward the information carrier, switches the signal so as to move the objective lens away from the information carrier in response to the reversal instruction, and outputs that signal; a controlling means that, using the focus error signal, controls the focus moving means such that the focal point follows each of the information surfaces of the information carrier; and a focus pulling-in means that switches an object of the operation from the driving signal generating means to the controlling means, and lets the focus moving means perform a focus pulling-in action.