Abstract: The object of this invention is, in magnetic disk surface texture processing by abrasive tape, to achieve uniformity of roughness of the processed surface by automatically adjusting the feed speed of the abrasive tape, and to increase productivity. It consists of a sensor unit that measures the processing state of the surface of a magnetic disk on which texture processing has been completed, a holding unit for rotating the magnetic disk during measurement, and a processing equipment that compares the measured values with predetermined processing conditions and again corrects the processing conditions when they depart from the set conditions, and it maintains stable processing accuracy.

Abstract: A servo tracking system enables a beam spot formed on a photodisc through an objective lens to trace a track on the disc. After opening the tracking servo loop, a drive signal is supplied to a lens actuator so as to move the objective lens across the tracks thereby generating a tracking error signal. The tracking error signal is sampled for detection of the central value of the same. An offset control is conducted so as to make the central value of the tracking error signal fall within an allowable standard range.

Abstract: A gain control device for controlling the loop gain of a servo tracking system which enables a beam spot formed on a photodisc through an objective lens to trace a track on the disc. The gain control device opens the tracking servo loop and applied a drive signal to a lens actuator so as to move the objective lens across the tracks thereby generating tracking error signals. The device samples the tracking error signals and detects the amplitudes of these signals, and controls the loop gain such that the detected amplitudes fall within a predetermined allowable range.