Servo system of storage apparatus for controllably projecting an optical beam to an optical disk

摘要

An optical storage apparatus having an improved focus servo means is disclosed. A focus error signal is obtained by an optical system comprising a pair of photo-sensors (3, 4) adjacently disposed sharing a boundary (5) therebetween. The system contains a small number of optical elements. A laser beam (1) reflected on a disk surface (100) is projected simply on the photo-sensors (3, 4), naturally having a circular spot thereon. The center of the spot is fixed being displaced from the boundary (5) by a predetermined distance (D), resulting in different photoelectric currents outputted from both photosensors (3, 4). Each photoelectric current is amplified by each amplifier (6, 31; 7, 32) having a variable amplification factor which is adjusted such that both amplified currents become equal when the laser beam is just focused to the disk surface (100). As the laser beam (1) is defocused on the disk (100), then the circular spot expands or shrinks, generating a differential current varying in polarity and amplitude, as a focus error signal (F) for the focus servo means. Thus, the dimensional setting of the photosensors (3, 4) is allowed to be rather relaxed, because the final setting is accomplished by adjusting the amplification factors of two amplifiers (6, 31; 7, 32) which can be performed very easily. , This system is featured by its simple optical system and an easy setting adjustment. Further modification of the optical spots on the photosensor is introduced. Furthermore, external disturbance caused by a tracking signal is avoidable, ! ensuring a reliable operation.