Optical pickup, optical disc drive employing it, and its control method

An optical disc apparatus comprising;

• disc rotational operation means for performing rotational operation of an optical disc;
• and
• an optical pick-up device for scanning, by light beams, the signal recording surface of the optical disc operated by the disc rotation operation means to perform recording or reproduction of information,
• the optical pick-up device comprising:
• a first light emitting element for emitting light beams having a first wavelength,
• a second light emitting element for emitting light beams having a second wavelength,
• a third light emitting element for emitting light beams having a third wavelength,
• a first optical system including a first object lens, and serving to converge, by the first object lens, either one of light beams which have been emitted from the first to third light emitting elements to irradiate the light beams thus converged onto the optical disc,
• a second optical system including a second object lens, and serving to converge, by the second object lens, either one of light beams which have been emitted from the first to third light emitting elements to allow the light beams thus converged to be incident on the optical disc,
• an object lens drive unit including a bobbin for holding the first and second object lenses, and serving to allow the bobbin to undergo drive displacement in three axes directions of a focusing direction which is a direction perpendicular to the recording surface of the optical disc, a tracking direction which is a substantially radial direction of the optical disc, and either one of a radial tilt direction in which movement is performed in a circular arc form on the axis in the radial direction and a tangential tilt direction in which movement is performed in a circular arc form on the axis of a tangential direction which is a direction perpendicular to the radial direction, and
• aberration correcting means for correcting comatic aberration of the second optical system relatively taking place with respect to the first optical system in which comatic aberration in the other direction of the radial tilt direction and the tangential tilt direction, which is not controlled by the object lens drive unit, is corrected.

A method of controlling an optical pick-up device,

• the optical pick-up device comprising:
• a first light emitting element for emitting light beams having a first wavelength;
• a second light emitting element for emitting light beams having a second wavelength;
• a third light emitting element for emitting light beams having a third wavelength;
• a first optical system including a first object lens, and serving to converge, by the first object lens, either one of light beams which have been emitted from the first to third light emitting elements to irradiate the light beams thus converged onto an optical disc;
• a second optical system including a second object lens, and serving to converge, by the second object lens, either one of light beams which have been emitted from the first to third light emitting elements to allow the light beams thus converged to be incident on the optical disc;
• an object lens drive unit including a bobbin for holding the first and second object lenses, and serving to allow the bobbin to undergo drive displacement in three axes directions of a focusing direction which is a direction perpendicular to the recording surface of the optical disc, a tracking direction which is a substantially radial direction of the optical disc, and either one of a radial tilt direction in which movement is performed in a circular arc form on the axis in the radial direction and a tangential tilt direction in which movement is performed in a circular arc form on the axis in a tangential direction which is a direction perpendicular to the radial direction;
• and
• aberration correcting means for correcting comatic aberration of the second optical system relatively taking place with respect to the first optical system in which comatic aberration in the other direction of the radial tilt direction and the tangential tilt direction, which is not controlled by the object lens drive unit, is corrected,
• the control method comprising:
• allowing the bobbin to undergo drive displacement on the basis of control signals in the focus direction and in the tracking direction, and a control signal in either one direction of the radial tilt direction and the tangential tilt direction to control positions and attitudes with respect to the optical disc of the first and second object lenses which have been held on the bobbin;
• and
• correcting comatic aberration of the second optical system by the aberration correcting means.