Three‐axis balanced driving‐type optical head for high‐density optical disc player

Abstract

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 correction 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 simplification of the electrical circuit and the lowering of cost, the latter method is advantageous. However, in the tilting of the conventional 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 realized. Therefore, the lens holder is held by parallel plate springs of rubber material. Thus, by contriving the electrical circuit driving the lens holder for the center of gravity of the lens holder to coincide with the center of the drive, the rotation of the axis could be controlled 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 excellent image was confirmed.