Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1999-10-04
2001-03-20
Sniezek, Andrew L. (Department: 2753)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S077020
Reexamination Certificate
active
06204990
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a precision servo-demodulator for providing the actuator which positions a read head of a rigid magnetic disc with the data necessary to maintain the correct alignment of the read/write head over the center of a track.
BACKGROUND OF THE INVENTION
It is known that magnetic discs are recorded with concentric circular tracks each divided into sectors, with each sector being provided with a read/write field called a header containing information defining which of the various tracks the sector belongs to and which sector among the various track sectors, and other information. In order to be able to obtain a high track density, and therefore a high disc capacity, and to ensure that data is correctly written to and read from a track, it is necessary to control the position of the head on the track and correcting it if the head is not exactly aligned on the track center.
To this end, in the header field of each sector two short successions of sinusoidal signals, called “servo bursts” of equal amplitude are recorded, one on either side of the track center, over separate arcs of the header field. If, during the course of a subsequent reading, the read head is correctly positioned over the track center, the previously effected recording induces two identical signals in the read head when the two separate arcs of the header field are read. Otherwise, the two signals differ in amplitude and provide an indication of the displacement of the head from the center of the track. This indication is utilized by a control system to correct the position of the head, aligning it on the center of the track.
The known techniques for measuring the displacement of the head from the track center to compare between the two signals read from the servo recording are essentially of two types:
1) Peak detection: the peak, that is, the maximum value of the signals provided by the head upon reading each of the two servo bursts, is memorized and compared with the other. This recognition method has the advantage of requiring relatively simple sampling and memory circuits and of being independent of the timing signals which activate the sampling operation (which must be activated only for reading the two servo bursts, and not when the other data is read). A serious disadvantage of this method is the low immunity to noise and therefore low precision. In fact, a disturbance which causes an increase, even of a single signal peak, contributes its amplitude integrally to the detection of an erroneous amplitude value of the peak. It is to be noted that in the case of signals provided by a read head (generally through a preamplifier) with asymmetrical characteristics, as is the case when the read head is of magnetoresistive type, two identical sampling circuits are necessary, respectively, for the recognition of the maximum positive peak and the maximum negative peak, which is converted into a positive peak with a simple inversion of the connection of the input terminals. The sum of the two measurements provides the peak-to-peak amplitude of the signal.
2) Area detection: This technique is based on the measurement of the area of the rectified signal. Although conceptually very simple, this technique, which involves an integration of the signal over a predetermined time interval, requires complex and expensive circuits. Moreover, the measurement precision depends on the precision with which the integration time interval is defined. The advantage of this technique, which has a high immunity to noise, is that it does not require circuit duplication in the case of asymmetric signals, but this only partly compensates for the above-mentioned disadvantages.
What is desired is a technique which is constructionally simple with a high immunity to noise without being influenced by imprecisions in the timing signal.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a servo-demodulator which, while being constructionally simple, has a high immunity to noise without being influenced by imprecisions in the timing signal.
The present invention provides a servo-demodulator for a pair of successive alternating variable signals, generated by a magnetic disc read head and indicative of the position of the read head on a recorded track on the disc, the signals of the pair having a plurality of positive peaks and a plurality of negative peaks. The servo-demodulator comprises a pair of input terminals for receiving the alternating variable signals and a detector for detecting the positive peaks of the signals of the pair. The detector is connected to the pair of input terminals and includes a first sample and hold capacitor and a first normally open reset switch closed by a reset pulse. The servo-demodulator also includes a means connected to the pair of input terminals for generating a first signal, the assertion of which defines a periodic time window for sampling each of the positive peaks and a second signal, the assertion of which defines a second periodic time window separate from the sampling window, containing one of the negative peaks. The servo-demodulator further comprises a second sample and hold capacitor and a second normally open switch for connecting the second capacitor in parallel with the first capacitor when closed by an averaging command signal. The servo-demodulator further comprises logic control means connected to the means for generating the first and second signal for receiving the first signal, the logic control means being activated by an asserted external signal indicative of the generation by the head of one of the pair of alternate variable signals, to produce the reset pulse at its output upon assertion of the first signal and the averaging command signal coasserted with a first assertion of the first signal and with the assertions of the second signal subsequent to two preceding assertions of the first signal.
The present invention also provides a servo-demodulator for a pair of asymmetrical successive alternating variable signals generated by a read head of a magnetic disc and indicative of the position of the read head on a magnetic record track, the signals of the pair having a plurality of positive peaks and a plurality of negative peaks. The servo-demodulator comprises a first servo-demodulator, a second servo-demodulator wherein the variable signals are applied through the pair of input terminals with a signal inversion relative to the application of the signals to the input terminals of the first servo-demodulator, and a third, normally open, switch closed by a control pulse for averaging the averages, for connecting the second capacitor of the first and second servo-demodulators respectively in parallel with one another. The servo-demodulator further comprises a means for generating the command pulse when the external signal is deasserted.
The servo-demodulator comprises a signal peak detector and other circuits which together detect the amplitude of each of the different signal peaks and takes a weighted average.
REFERENCES:
patent: 4380034 (1983-04-01), Krake
patent: 4833551 (1989-05-01), Song
patent: 5400201 (1995-03-01), Pederson
patent: 5483393 (1996-01-01), Mento et al.
patent: 5483394 (1996-01-01), Harman
patent: 5583706 (1996-12-01), Dudley et al.
patent: 5801895 (1998-09-01), Abramovich
patent: 5825318 (1998-10-01), Patapoutian et al.
Bruccoleri Melchiorre
Demicheli Davide
Demicheli Marco
Patti Giuseppe
Galanthay Theodore E.
Jenkens & Gilchrist P.C.
SGS-Thompson Microelectronics S.r.l.
Sniezek Andrew L.
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