Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the record
Reexamination Certificate
2000-02-01
2001-11-13
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the record
C360S073110
Reexamination Certificate
active
06317283
ABSTRACT:
TECHNICAL FIELD
The present invention relates to tape drives, and more particularly, to methods and apparatus for calibrating a rotating scanner within the tape drive to a plurality of digital data tracks recorded on a tape.
BACKGROUND ART
Tape drives, such as, for example, digital data storage (DDS) tape drives are commonly used to back up and record information in the form of digital data from a computer system. A DDS tape drive, for example, is a helical scanning tape drive that writes and reads information in the form of digital data to and from a magnetic tape. DDS tape drives provide a low cost storage mechanism that is light weight, compact and typically very reliable. DDS tape drives have continued to evolve over time, such that each new generation of DDS drives and DDS formatted tapes provides additional storage capacity over the earlier generations.
One advantage of DDS tape drives over linear tape drives is the use of a helical scanning method that allows very high recording densities. Basically, a helical scanning method, such as, for example, in a DDS tape drive, uses a rapidly rotating scanner that has two read heads and two write heads (i.e., for a total of four transducers). The rotating scanner is tilted at an angle in relation to the horizontal movement of the tape, which is being transported at a given speed, and the tape is wrapped about at least a portion of the scanner. Thus, the horizontal tape movement against the tilted and rotating scanner causes diagonally positioned tracks to be written to the tape (and subsequently read from the tape). The speed and tension of the tape are typically kept constant by a tape drive servoing system that includes controlling circuitry and mechanical mechanisms, such as, for example, a capstan and series of rollers and guides.
The format of the recorded data tracks (e.g., containing raw, compressed, timing, control and/or error correction data) on a DDS formatted tape, for example, is mandated by a specific DDS standard.
During a read operation of a DDS formatted tape, it is essential to match the tracks as laid down during the previous write operation with the read heads located on the scanner so as to read the data within each track. This is typically done by calibrating the speed at which the tape is transported to properly align the read heads of the scanner to the previously recorded tracks.
Earlier DDS standards, such as, for example, the DDS1 and DDS2 formats, use an automatic track finding (ATF) technique to calibrate the scanner to the tracks. In an ATF formatted tape there are a plurality of sub code areas recorded within each track that can be detected and used to determine if a read head is properly aligned over the track. Thus, for example, in a DDS2 formatted tape, the resulting signals from the read head scanning different sub code areas are used to determine if the tracking is proper (i.e., that the read head is centered over the track). Thus, based on the sub codes recorded in the tracks of the DDS2 tape, the speed of the tape within the DDS tape drive is adjusted such that the read head is properly aligned with the recorded tracks. As such, several sub codes are typically required in the earlier DDS formatted tapes. For example, a DDS2 formatted tape includes eight sub codes at the top of each track and eight sub codes at the bottom of each track.
One drawback to an ATF formatted tape, such as DDS2 formatted tape, is the number and size of the sub codes and the amount of space on the recording tape that is required to record these sub codes.
Moreover, because there is a continuing effort to increase the amount of data storage capacity in the DDS tape drive family, the next generation standard format, namely a DDS3 format, does not include ATF. As a result, timing and tracking has to be accomplished through different techniques.
The DDS3 format does not specify how the timing and tracking of a read operation is to be accomplished within the tape drive. Instead this decision has been left to the DDS tape drive design community. Thus, there is a need for efficient methods and apparatus for calibrating and controlling the timing and tracking in a DDS tape drive capable of supporting a DDS formatted tape that does not include ATF information.
SUMMARY OF THE INVENTION
The present invention provides methods and apparatus that provide efficient, reliable and effective calibration of a tape drive's scanner to the tracks recorded on the tape. These methods and apparatus can be included, for example, in a tape drive as part of a servoing system that synchronizes a rotating scanner with the tape during and/or prior to a read operation. The various embodiments of the present invention can be, for example, embodied within a dedicated circuit and/or general purpose circuit, and/or in computer implement instructions stored in a computer readable medium and for use with a computer processor or like circuit.
Thus, in accordance with an embodiment of the present invention there is provided a calibration method for controlling a speed at which a tape is transported past a rotating scanner. The calibration method includes setting the speed of the tape to a first speed and scanning the tape with the scanner to produce a set of scanned signals wherein each of the scanned signals includes sub code data, and measuring an envelope measurement and a delay time for each of the scanned signals. The envelope measurement is based on a sample of an envelope of the scanned signal and the delay time is based on an indexing signal corresponding to a rotational position of the scanner and detection of the sub code data.
The calibration method further includes determining an optimal delay time based on an interpolation of the envelope measurements and delay times associated with the set of scanned signals. The optimal delay time occurs when the envelope measurement is substantially at a maximum value based on an interpolation and/or approximating function relating to the envelope measurements. The calibration further includes setting the speed of the tape to a second speed based on the calculated optimal delay time. Thus, when the tape is transported at this second speed, the scanner and tracks will be significantly aligned during subsequent scans.
In accordance with certain embodiments, the first speed is either greater than or less than an expected speed associated with the tape. For example, in one embodiment the first speed is approximately 10% greater or less than the expected speed.
The earlier stated needs are also satisfied by a method for calibrating a tape drive to the tracks recorded on a tape. The tape drive has a rotating scanner, and the tape has a timing mechanism that includes discretely located sub code data that is recorded within a plurality of tracks recorded on a tape. The method includes transporting the tape past the rotating scanner at a first speed, while the tape is wrapped about a portion of the rotating scanner. The method includes generating a plurality of scanned signals with at least one transducer located on the rotating scanner, wherein each of the scanned signals is proportional to a portion of the recorded data in at least one of the tracks on the tape as sensed by the transducer. The method continues by detecting a corresponding envelope for each of the scanned signals, detecting sub code data within each of the scanned signals, and measuring a delay time, for each of the scanned signals. The delay time is measured between a corresponding indexing signal and the detection of the sub code data, wherein the indexing signal is associated with a rotational position of the rotating scanner.
The method flier includes discretely sampling each of the envelopes to produce a corresponding envelope measurement for each envelope, determining a substantially maximum value for an approximating function corresponding to a combined plot of the envelope measurements versus the measured delay times associated with at least a subset of the scanned signals. Next, a substantially optimal delay time is determined based
McDermott & Will & Emery
Seagate Removable Storage Solutions LLC
Sniezek Andrew L.
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