| 摘要 |
PURPOSE:To always ensure the correct position control even though an information track has a blank part by providing at least >=2 guide tracks at the positions near the information track. CONSTITUTION:The guide tracks 1a-1d are formed with low reflection factors and the areas adjacent to these tracks are provided with high reflection factors respectively. While the laser beams 3a and 3c are set with a distance delta secured between them so that the centers of both beams approach to the side of a high reflection factor from the end parts of the guide tracks. The distance deltacan be controlled to an optional value by attaching the light emitting matters of beams 3a-3c to an attachment part and turning this attachment part around the laser beam 3b by an angle theta or by means of an appropriate position control mechanism. Thus the beam 3b can be controlled to a correct position based on the guide signals obtained from both beams 3a and 3c.
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