Method for detecting the movement of a light beam and optical information reproduction apparatus using the same

An optical information reproduction apparatus for reproducing information from a disc having a plurality of tracks storing the information in the form of pits, the apparatus comprising:

• radiation means for radiating a light beam toward the disc to form a light spot on the disc;
• moving means for moving the radiation means to move the light spot in a direction crossing the plurality of tracks in a radial direction of the disc;
• light detection means having a detecting plane for receiving the light beam reflected by the disc, the detecting plane being divided into two detection areas in a direction parallel to a tangent of the tracks, the two detection areas generating light intensity signals corresponding to the intensities of the light beam which is received;
• positional offset detection means for detecting a positional offset of the light spot with respect to one of the tracks based on the light intensity signals generated by the light detection means and outputting the detection result as a positional offset signal;
• signal processing means for performing processing of the light intensity signals including logic operation to obtain an operation signal;
• and
• direction detection means for detecting a direction in which the light spot moves with respect to a target track based on the positional offset signal and the operation signal during the movement of the light spot toward the target track.
• wherein the operation signal is an exclusive OR of light intensity signals generated by the two detection areas of the light detection means.

A method for moving a light spot formed by radiating a light beam toward a disc having a plurality of tracks having information in the form of pits, the light spot being moved in a direction crossing the plurality of track in a radial direction of the disc, the method comprising the steps of:

• receiving the light beam reflected by the disc by detection means having a plurality of detection areas to generate light intensity signals corresponding to the intensities of the light beam received by the respective detection areas;
• detecting a positional offset of the light spot with respect to one of the tracks based on the signals and outputting the detection result as a positional offset signal;
• performing processing of the light intensity signals including logic operation for obtaining an exclusive OR and outputting the operation result as an operation signal;
• and
• performing waveform shaping of the positional offset signal and the operation signal to detect a direction in which the light spot moves based on a phase difference between the positional offset signal with the waveform thereof shaped and the operation signal with the waveform thereof shaped, and thus generating a direction signal indicating the detected direction.