Focus servo unit of optical information reader

Abstract

Abstract PURPOSE: To obtain the best photo detection output and also to carry out focus servo operation with no malfunction by adequately selecting the position relation among a cylindrical lens, photo detecting element and condenser lens. CONSTITUTION: The stop radius of condenser lens 5 and the distance between the principal point of cylindrical lens 8 and photo detecting element 9 aredenoted by R and C respectively, and the distance between conjugate point S of recording surface 7 as to condenser lens 5 when illumination light focuses on surface 7 and element 9, the distance between lens 5 and conjunction point S, and the shift from normal conjugated point S to conjugate point S' when recording surface 7 shifts in position are by D, L and Z. Lengths X and Y of the photo detection shape crossing at right angles on the photo detection surface of element 9 are expressed by equations 1 and 2. Length Y is measured in parallel to the generating line of cylindrical lens 8, and X is perpendicular to this generating line. With C greater than D, lengths X and Y are set below value (2RC/[(C+D)]) when Z is equal to C+D or below value 2RD/L when Z is equal to zero. COPYRIGHT: (C)1980,JPO&Japio

Inventors

• 👤 Hitoshi Kanamaru

Bibliographic Details