| 摘要 |
PURPOSE:To position an optical disc with a high precision by forming a part of a supporting body to a round shape and providing a reflecting object on it to condense the light and detecting the position of the supporting body by the quantity of return light from the reflecting object and fixing an objective lens provided on the supporting body in a prescribed position at the access time. CONSTITUTION:With respect to an optical head, the outside of a radial unit 12 is made round, and the reflecting object is provided on its outside wall, and a sensor part consisting of a light emitting part 28 and light detecting pats 29a and 29b is provided on a focus unit 11 on the outside of the unit 12. When the radial unit 12 is oscillated as shown by A, B, and C in the figure, quantities of light reflected to light detecting parts 29a and 29b provided on both sides of the light emitting part 28 are changed in accordance with the position of the radial unit 12. That is, the quantity of light to the light detector 29b is increased by the curvature of an outer cylinder if the unit 12 is placed in the position B, and that of the light detecting part 29a is increased if the unit 12 is placed in the position C. The difference signal between quantities of light of light detecting parts 29a and 29b is obtained to detect the position of the unit 12.
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