Wangtek

Persci, Inc.

Pertec Computer Corporation

Jefferson H Harman

Hamid Baheri

G Randall Stevens

Daniel L Griffith

Peter Campbell

A track following positioning system including filtered average servo demodulators for maintaining the position of a magnetic tape head in alignment with tracks of data stored in magnetic medium. A servo head tracks a centerline in a servo written region of the magnetic medium and generates servo head signals corresponding to the displacement of the servo head from the centerline. A filtered average servo demodulator detects the servo head signals and generates servo error signals for realigning the tape head with respect to the magnetic medium in response thereto. To generate servo error signals, the filtered average servo demodulator peak detects and averages the rectified and filtered output signals and then subtracts a proportion of the peak detected signals from the average detected signals.

Filtered average servo demodulator

A magnetic recording head positioning system includes a Terfenol-D magnetostrictive rod prestressed by a lever arm to operate in a linear range to microposition the magnetic recording head in accordance with an electromagnetic field. The mechanical advantage of the lever arm amplifies changes in the magnetostrictive rod to position the head. The varying electromagnetic field is applied to the rod by a coil in response to a position error signal produced from servo data tracks on the magnetic tape. A permanent magnet system biases the magnetostrictive element with a DC field so that varying the field provides bi-directional motion of the magnetic recording head. The DC field also reduces coil current and size requirements. The position signal is filtered so that changes in length of the magnetostrictive rod provide fast, fine positioning of the head while a stepper motor and lead screw subassembly system provide slow, coarse positioning of the magnetic recording head by moving the magnetostrictive element assembly in an open loop and/or closed or servo loop mode.

Servo controlled magnetic head positioner

An oscillating erase current circuit for erasing information recorded on magnetic media. The inductance of an erase head is coupled with capacitors to form a tank circuit having a natural resonant frequency. The self-oscillating erase current circuit generates an oscillating signal having a frequency of oscillation determined by and therefore equal to the natural resonant frequency of the tank circuit. Once enabled, the self-oscillating erase current circuit continuously oscillates without any external drive circuit.

Oscillating erase current circuit

A closed loop resolution enhancement technique for reducing density effects to permit increased digital data storage density on magnetic media and improve data reliability for at a given density, uses a predetermined test pattern written on the medium to determine the ratio of amplitudes of high and low frequency components of the test pattern and adjust a resolution value. After a test pattern read operation is used to adjust the resolution value, the same value is used during normal data recovery operations.

Automatic closed loop adjustment of analog read signals under

A stepper motor in a magnetic tape cartridge head positioning system applies vernier control to achieve a final target after a preliminary target has been achieved by stepping. The vernier control is provided by a closed loop servo system in which current is applied to stator coils selected so that the target is at a torque maximum rather than at a torque null. Current proportional to a servo error signal is applied to selected stator coils so that the torque is sufficiently linearly related to position to permit classical linear servo analysis for the design of a stable, non-oscillating system. An example of stator coil selection for advancing and retarding a permanent magnet stepper motor operated in eight half steps is provided below in Table 1.

Stepper motor with vernier control mode

The signal read-back from a magnetic disk is processed in dependance upon the track diameter in order to cut higher frequencies for outer tracks and to boost high frequencies for inner tracks for, respectively, correcting flat signal portions and eliminating or reducing peak displacement. The circuit develops a signal-amplitude-modifying factor in form of a cosine function of the frequencies of the read-back signal as applied. Two thus modified read-back signals are developed, varying oppositely in strength in dependance upon the track diameter. These two signals are combined to obtain the selective cutting or boosting as required.

Processing read-back signals in magnetic disk systems

The tunnel-erase-type guard band 'writing' along the tracks of a disk in a disk file is controlled by the same microcomputer which controls transducer repositioning in the seek mode. The micro-computer meters different delays for onset and cessation of erasing in relation to a signal (write gate) accompanying the data to be recorded; and these delays are longer for tracks having smaller diameters. The leading and trailing edges of the write gate signal trigger interrupts for the microcomputer, the interrupt channel is released only after the particular delay has been metered.

Guard band control for magnetic disks

A voice coil type linear motor controls the movement and positioning of a transducer which cooperates with a spinning disk. The motor is feedback controlled for separate speed (seek) and positioning modes in which respectively the transducer is moved across the disk towards a different track and is held centered above that track. In order to offset the effect of a tilted axis of carriage movement, the control condition in the positioning mode representing a correct transducer position in which it is held by the motor, is continuously sampled and held during a period when the transducer is moved to another track to be applied as correction for the control moving the transducer towards another track. This correction signal is also used in the initial phases of holding the transducer above the newly selected track, until sampling and positioning control proper takes over.

Position control in disk drive system

The spindle motor for a flexible recording disk is connected to a disk with an annular track of optical markings which are scanned to derive therefrom a train of reset pulses for a counter counting higher frequency clock pulses. Reaching of a particular count state is ascertained for each reset cycle to obtain a train of pulses of constant duration with pauses inbetween, varying with motor speed. A steady signal linearly varying with motor speed is derived from that train, compared with a reference and used to controlthe motor.

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Thousand Oaks, CA, United States of America

Jefferson H Harman