Decoding digitally sampled servo tracks

Details Decoding digitally sampled servo tracks Decoding digitally sampled servo tracks

1999-08-03

2002-07-30

Sniezek, Andrew L. (Department: 2651)

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

Controlling the head

C360S077010

Reexamination Certificate

active

06426846

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the decoding of prerecorded servo track positioning information, and, more particularly, to the decoding of servo track positioning information from adjoining servo tracks having different servo patterns as read by a servo head to allow positioning of the servo head and of read/write elements which are at an indexed position with respect to the servo head.
BACKGROUND OF THE INVENTION
In the data storage industry, advances in technology include increases in the data storage capacity of given data storage media. One means of increasing the data storage capacity of data storage media, such as magnetic tape cartridges or magnetic tape cassettes, is to increase the track density of the data storage media, and in a corresponding manner, to decrease the width of each track.
In a typical magnetic tape, data is recorded in a plurality of parallel, longitudinal data tracks. A data head may have a plurality of data heads which have fewer numbers of read/write elements than tracks. The data tracks are divided into groups, typically interleaved, and the data head is indexed laterally with respect to the tracks to access each group of data tracks. In order to properly register the data head with the data tracks, prerecorded servo tracks are provided which are parallel to the data tracks. A servo read head located at an indexed position with respect to the read/write elements reads the servo tracks. The servo tracks provide lateral positioning information which, when read by the servo read head, can be decoded to indicate whether the servo read head is correctly positioned with respect to the servo tracks. Thus, the servo head can be moved laterally to a desired position with respect to the servo tracks so as to properly register the read/write elements with respect to a desired group of data tracks. Then, the servo head can follow the servo tracks as the media and the head are moved longitudinally with respect to each other, so that the read/write elements maintain registration with the data tracks.
As an example, the prerecorded servo track positioning information comprises adjoining servo tracks having different servo patterns, one of the servo patterns comprising a constant amplitude signal of a single first frequency, and the other servo pattern alternating between a constant amplitude burst signal of a single second frequency and a zero amplitude null signal. The resultant signal read by the servo head is a maximum signal comprising the first frequency signal combined with the second frequency burst signal and a minimum signal comprising the first frequency signal combined with the null signal. If the servo head is correctly positioned at the junction of the adjoining servo tracks, the amplitude of the combined first and second frequency signals is twice the amplitude of the combined first and null signals, and is easily decoded. Coassigned U.S. Pat. No. 5,448,430 illustrates the above discussed servo track patterns and describes a track following servo positioning system employing peak detection to determine the maximum and minimum signals.
As data capacity is increased, it is also desirable to have backward compatibility to data storage media having the prior level of data capacity, to avoid the necessity of copying all of the data recorded on the prior media onto the new media.
As the result, it is desirable to increase the track density of a data storage media, while utilizing the prior media servo tracks, so that the servo system may be operated to utilize the servo track positioning information as before for the prior media, and to utilize the same servo track positioning information in a more precise manner to access tracks at a higher track density. Thus, it becomes necessary to accurately measure the maximum and the minimum signals at servo head positions not at the center directly between the adjoining servo tracks. The problem becomes especially difficult as the servo head is positioned more directly over the first single frequency track, in that the minimum signal becomes closer to the maximum signal. It becomes difficult to differentiate between the two signals, difficult to accurately measure each of the two signals, and therefore difficult to determine the ratio between the two signals. Thus, the precise positioning of the servo head and the corresponding read/write elements also becomes difficult.
SUMMARY OF THE INVENTION
An object of the present invention is to provide decoding of servo track positioning information from adjoining servo tracks having different servo patterns to provide a broad dynamic range of positioning information.
Disclosed are a servo track decoder and method for decoding asynchronous digital samples of prerecorded servo track positioning information. The prerecorded servo track positioning information comprises adjoining servo tracks having different servo patterns, one of the servo patterns comprising a maximum a constant amplitude signal of a single first frequency, and the other servo pattern alternating between a constant amplitude burst signal of a single second frequency and a zero amplitude null signal. The resultant signal read by the servo head is a maximum signal comprising the first frequency signal combined with the second frequency burst signal and a minimum signal comprising the first frequency signal combined with the null signal. A digital servo detector asynchronously samples the signals read by the servo head.
An envelope follower receives the asynchronous digital samples, detecting and providing a maximum envelope output measuring the amplitude of a burst envelope of the maximum of the asynchronous digital samples, and detecting and providing a minimum envelope output measuring the amplitude of a burst envelope of the minimum of the asynchronous digital samples.
A “DROPOUT” threshold detector receives the asynchronous digital samples and detects the received asynchronous digital samples failing to meet a “DROPOUT” threshold related to the maximum burst envelope, providing a “DROPOUT” threshold detection signal. An “ACQUIRE” detector is coupled to the “DROPOUT” threshold detector and responds to the “DROPOUT” threshold detection to detect the minimum envelope for the envelope detector, which provides the minimum envelope output. The “DROPOUT” detection distinguishes the minimum envelope from the maximum envelope and allows measurement of the minimum envelope, whereby a ratio of the measured maximum envelope amplitude output and the measured minimum envelope amplitude output represents the lateral position of the servo head.
In further embodiments of the invention, in “TRACKING” mode, the digital samples may be qualified as exceeding the “DROPOUT” threshold to provide the maximum envelope. The “DROPOUT” threshold detector detects a predetermined programmable number related to the number of sequentially received digital samples that fail to meet the “DROPOUT” threshold.
The envelope detector may additionally employ an envelope filter for filtering, with a preceding envelope amplitude, an error amplitude between a qualified digital sample and the preceding envelope amplitude, the error amplitude multiplied by a provided programmable “TRACK ATTACK” gain value upon the error amplitude indicating an increase in the envelope amplitude, and the error amplitude multiplied by a provided programmable “TRACK DECAY” gain value upon the error amplitude indicating a decrease in the envelope amplitude. The envelope amplitude is amplified by a multiplier value, also called a multiplication “factor”, in the “DROPOUT” threshold detector, by a “DROPOUT” factor to have the effect of reducing the “DROPOUT” threshold with respect to the envelope amplitude.
In a still further embodiment, upon the digital samples failing to meet the “DROPOUT” threshold, the “DROPOUT” threshold detector switches to an “ACQUIRE DECAY” mode, and an error amplitude filter filters, with the preceding envelope amplitude, an error amplitude between any digital samples, even though they are not qualified, and the preceding envel

Affiliated with

Also associated with

Rating

Decoding digitally sampled servo tracks does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Decoding digitally sampled servo tracks, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Decoding digitally sampled servo tracks will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2889089