1. Technical Field
The present invention relates in general to servo controls for a tape drive, and in particular to a technique for stabilizing a servo system for a cartridge tape drive that employs a tape on which servo and data tracks are arranged longitudinally.
2. Description of the Related Art
Around half a century has passed since the first open reel tape drives appeared, and today, tape drives continue to be widely used as mass backup storage for computers. Currently, small tape cartridge drives play a leading role and widely used for a variety of computers from low to high end. Generally, multiple data tracks are longitudinally arranged on a backup tape (normally, a magnetic tape) to record a large amount of data, and a tape head is precisely positioned on a target data track by servo control.
The timing based servo (TBS) system is a well known servo control system for a tape drive. According to this system, at least one specially patterned servo track is provided in parallel with data tracks, i.e., in the longitudinal direction of the tape, such that the timing of the servo position signal obtained by reading the servo pattern varies continuously as the tape head is moved across the width of the tape. To this end, the servo pattern is composed of magnetic transitions recorded in non-parallel directions, like a pattern composed of slash and backslash pairs, or a pattern composed of first and second chevron pairs with the first and second chevrons having different orientations. An exemplary TBS system is disclosed in U.S. Pat. Nos. 5,689,384 and 5,930,065 and U.S. patent application Ser. No. 09/370256 filed on Aug. 9, 1999.
In addition, several types of tape cartridge drives which implement the timing based servo, such as IBM 3570, are commercially available.
At present, a servo circuit for a tape cartridge drive (hereinafter referred to as xe2x80x9ctape drivexe2x80x9d or xe2x80x9cdrivexe2x80x9d) has filter coefficients which are determined based on a certain ideal model by taking mechanical and electrical margins into account. The mechanical margin relates, for example, to the tape feeding system and head system of the drive, tape distortion and servo pattern shifting, and the electrical margin relates, for example, to electrical disturbance, offset and computational error.
However, even if the filter coefficients are determined by taking these margins into account, there are some drive and cartridge combinations which lack servo stability. For example, some drive and cartridge combinations may have an impulse-like spectrum with an abnormal magnitude at a certain frequency. Current servo systems may have a setup which amplifies this frequency component so that the servo can not follow the tape, which eventually results in a failure of tape writing. Although it is desirable to obtain an optimum set of filter coefficients for all drive and cartridge combinations, it is practically impossible to obtain such optimum filter coefficients since the frequency component which causes instability is not fixed and varies depending on the drive and cartridge combination.
It is, therefore, an object of the present invention to stabilize a servo system by eliminating the cause of instability due to a particular tape drive and cartridge combination.
It is another object of the present invention to provide a method and system for stabilizing a servo system by re-setting filter coefficients each time a tape cartridge is inserted into a tape drive.
According to a first aspect of the present invention; in a tape drive system performing read/write operations for a tape by inserting a tape cartridge into a tape drive, where the tape cartridge has a tape on which servo and data tracks are arranged longitudinally and a predetermined servo pattern is recorded on each of said servo tracks, a method for stabilizing a servo system for the tape drive is provided which comprises the steps of re-setting coefficients of a low-pass filter for servo control of the tape drive, each time the tape cartridge is inserted into the tape drive, in response to the inserted tape cartridge.
More specifically, the method according to the first aspect comprises the steps of reading a servo pattern recorded on the tape in said tape cartridge inserted into the tape drive, performing a frequency analysis of the servo pattern, detecting, from frequency components obtained by the frequency analysis, a singularity that exceeds a predetermined spectrum range, and setting said coefficients of the low-pass filter so as to cancel a power spectrum of the singularity.
According to a second aspect of the invention, a tape drive is provided into which a tape cartridge is inserted, the tape cartridge having a tape on which servo and data tracks are arranged longitudinally and a predetermined servo pattern is recorded on each of the servo tracks, and which comprises a servo control circuit including a low-pass filter for servo signals, and a circuit for re-setting coefficients of the low-pass filter each time a tape cartridge is inserted, in response to the inserted tape cartridge.
Preferably, the circuit for re-setting the coefficients of the low-pass filter comprises a circuit for reading a servo pattern recorded on the tape in the tape cartridge inserted into the tape drive, a circuit for performing a frequency analysis of the servo pattern, a circuit for detecting, from frequency components obtained by the frequency analysis, a singularity that exceeds a predetermined spectrum range, and a circuit for setting the coefficients of the low-pass filter so as to cancel a power spectrum of the singularity.