3-AXIS BALANCED DRIVING-TYPE OPTICAL HEAD FOR HIGH-DENSITY OPTICAL DISC PLAYER

In the optical disc player, there is a necessity to correct the jitter caused by the disc eccentricity and rotation irregularity as well as focusing. For this correction, there are both the electrical correctio n method using a two-axis optical head with memory and the mechanical correction method of a three-axis optical head. If the goal is the sim plification of the electrical circuit and the lowering of cost, the la tter method is advantageous. However, in the tilting of the convention al field lens, the motion of the lens occurs in the direction of track and jitter and, for those in which the numerical aperture is 0.55 and larger, since good convergence characteristics are not obtained with respect to tilting of the lens, the three-axis method is hardly realiz ed. Therefore, the lens holder is held by parallel plate springs of ru bber material. Thus, by contriving the electrical circuit driving the lens holder for the center of gravity of the lens holder to coincide w ith the center of the drive, the rotation of the axis could be control led and an actuator realizing only translational motion effectively in the direction of the three axes (balanced drive method) was proposed and realized. An optical head based on this method was constructed and , with a high-density (Hi-Vision laser diode type) disc, a MUSE signal signal-to-noise (SN) ratio above 36 dB could be realized and an excel lent image was confirmed.