Abstract: An optical pickup is provided below an optical disk. A laser beam is emitted from a semiconductor laser onto a track, through an objective lens. The objective lens is capable of shifting, and is shifted in the direction of the track width by a magnetic force from a tracking actuator, thereby performing lens tracking. The optical pickup is mounted on a carriage. The carriage is shifted along the radial direction of the optical disk by a voice coil motor. This shifts the laser beam along the radial direction of the optical disk, thereby performing track access. Upon reception of an access command, a velocity control mode commences, and the shift velocity of the carriage is controlled in accordance with a velocity control signal corresponding to the distance between a target track and a current track. When the pickup arrives near the target track, the generation of velocity control signal ceases and the location control mode commences.

Abstract: An input signal containing a base line which fluctuates to a great extent is detected or restored by comparing the input signal with reference levels which are shifted in accordance with the fluctuation of base line. The input signal is sampled at a variable sampling rate and an average of sampled values for a predetermined period is derived to produce a profile signal which resembles accurately the fluctuation of the base line. The profile signal thus obtained is added to upper and lower threshold voltages to produce the reference levels which have been corrected in accordance with the fluctuation of the base line of input signal.

Abstract: In order to read out information recorded on a disc rotating at a constant angular velocity by means of a pick-up head movably arranged in a disc radius direction, a head position on the disc is detected to obtain a position signal representing a distance from a disc center to the pick-up head, and then a pulse signal having a frequency corresponding to the position signal thus obtained is generated. A detection signal supplied from the pick-up head and the pulse signal are supplied to an AND gate and pulses of the gated out pulse signal are counted by a counter. The number of the counted pulses represents correctly a length of the information recorded on the disc irrespective of position of the information on the disc.

Abstract: An apparatus for detecting optically defects in object such as original glass disc for use in manufacturing video and audio discs by projecting a laser light flux onto the object includes an objective lens for focussing the incident laser light flux onto the object as a small light spot, the laser light flux passing through the objective lens at only its central portion. When the object has no defect in the light spot area, the laser light flux is regularly reflected by the object surface, but when the object includes a defect in the light spot area, the light flux is scattered by the defect. The directly reflected and scattered light fluxes are collected by the objective lens and are then separated from each other by means of a small mirror arranged in an optical axis of the directly reflected light flux. The directly reflected and scattered light fluxes thus separated are received by first and second light detectors.