| 摘要 |
PURPOSE:To miniaturize the tracking actuator while preventing an optical axis from being shifted by driving the actuator by using first and second spring members, and deciding the length and spring constant of the member when energizing the central part of a galvano mirror so that a distance ratio and the inverse ratio between a virtual axial line and each member can be respectively equal. CONSTITUTION:When an actuator 43 is driven, force F is exerted vertically to the face of a galvano mirror 42, and the 1/2 force is exerted, respectively to first and second spring members 46 and 47. Therefore, when the lengths of the respective members are defined as L1 and L2, the spring constants are defined as K1 and K2, and the distances are defined as X1 and X2, the member 46 is extended for L1a=F/(2K1) and the member 47 is extended for L2a=F/(2K2). Accordingly, the ratio between a full length L1+L1a of the member 46 and a full length L2+L2a of the member 47 is made equal to the ratio between the distances X1 and X2. Thus, the extended face of the mirror 42 is turned to pass through a virtual curve 50 at all times, the optical axis of reflected light 60 is not shifted to that of incident light 61, and a tracking control signal having no offset can be obtained. |
