Optical disc system having servo motor and servo error detection

Abstract

An optical drive system includes an optical assembly, a light source capable of transmitting light through the optical assembly, an objective lens positioned to direct light between the optical assembly and a respective information storage medium, and an actuator suspending the objective lens for relative motion thereof with respect to the actuator. A photodetector is disposed in a path of returning light to measure return light received from the respective medium. A monitoring circuit is provided to monitor a Quad Sum signal associated with the return light. A first servomotor is employed to move the objective lens in a tracking direction relative to the actuator and to move the objective lens during focus capture relative to the respective medium being read while system circuitry searches for a maximum Quad Sum signal. A second servo motor is employed to move the objective lens in a focusing direction relative to the actuator assembly. A first electronic circuit is provided to control the first and second servomotors. A servo error circuit is coupled to the first electronic circuit and the photodetector to determine when the return light exceeds a predetermined value, to search for a first zero crossing determining when the Quad Sum signal exceeds a predetermined amplitude, and to indicate to the first electronic circuit to direct close of focus by the second servomotor when the Quad Sum signal exceeds the predetermined amplitude.