Abstract: A method and apparatus are provided in an embedded servo system for controllably moving, using a linear motor, a carriage assembly and one or more accompanying heads relative to one or more disk surfaces. Each disk surface includes sectors for reading and writing information. Each disk surface also includes servo fields spaced between the read/write sectors. The servo fields have preset servo or position information for each of the tracks on the disk. The position information is in the form of Normal and Quadrature generated signals used to determine the exact position of the head when it is located between track centers. Using the determined position of the head and knowing a target position on the disk surface, the distance remaining to the target position is found. Using the value of the distance remaining to the target position, a head velocity can be determined and the proper amount of current can be supplied to the linear motor so that the head arrives at the target position in minimal time.

Abstract: An underreamer utilizes a plurality of cutting arms each having a plurality of tungsten carbide inserts, some of which have synthetic diamond cutting surfaces. There is a synthetic diamond gage cutter at the outer end of each cutting arm, and at least one other synthetic diamond cutter located more inwardly on the arm. The gage cutter is offset a greater distance from the leading side of the arm than are such other cutters. Recessed regions in front of the synthetic diamond cutters expose their full cutting faces while leaving steel for support of the cutters. Tungsten carbide inserts on the ends of the cutting arms between the leading side and the gage cutter minimize erosion of the steel arm and help prevent the gage cutter from being dislodged. The underreamer includes a hydraulic plunger for activating the cutting arms from a fully retracted to a fully deployed position, and a nozzle which ejects fluid toward the arm cutting surfaces during deployment and operation of the cutting arms.

Abstract: An improved demodulator principally for receiving dibits from a servo track and generating a position error signal responsive to the servo head position relative to the track as indicated by the dibit signal. The invention improves the capability of the demodulator to operate when noise is encountered in the dibit signal.

Abstract: An improved demodulator principally for receiving dibits from a servo track and generating a position error signal responsive to the servo head position relative to the track as indicated by the dibit signal. The invention improves the functioning of the demodulator for movement of the servo head at both high and low speeds and when noise is encountered in the dibit signal.