Browse Prior Art Database

Dual Threshold Servo Detection

IP.com Disclosure Number: IPCOM000085602D
Original Publication Date: 1976-May-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Detzi, WA: AUTHOR [+3]

Abstract

The device, as depicted schematically in the drawings, allows two levels of servo information to exist. Both pieces of servo information are used or stored in registers until the end of the servo stripes. At this time it is determined which set of information is correct, by validity checking track one information and track two information on both primary and secondary amplifier senses. If both primary and secondary information is good, primary information is sent to the system. If primary information is bad, then secondary information is sent to the system. If both secondary and primary information is bad, then a servo check is generated.

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Dual Threshold Servo Detection

The device, as depicted schematically in the drawings, allows two levels of servo information to exist. Both pieces of servo information are used or stored in registers until the end of the servo stripes. At this time it is determined which set of information is correct, by validity checking track one information and track two information on both primary and secondary amplifier senses. If both primary and secondary information is good, primary information is sent to the system. If primary information is bad, then secondary information is sent to the system. If both secondary and primary information is bad, then a servo check is generated.

The primary scheme to which this system relates is disclosed in U. S. Patent 3,845,500 issued to Gary A. Hart, assigned to International Business Machines Corporation, and entitled "Head-to-Track Alignment in a Rotating Head Magnetic Tape Unit".

As is shown in Fig. 1 and disclosed in the Hart patent, the triangular-shaped signal envelope is outputted from the servo track. The signal is rectified and only the upper half 10 is used for a track alignment. In the Hart patent, a first threshold level 12 is positioned at the 50 percent amplitude point.

As primary sense amplifier 14 senses point 16 of first amplitude level 12, primary information up-down counter 18 begins to count upward until sync bit 20, which is a double-frequency bit, is encountered. Primary information up-down counter 18 then begins to count downward to point 22. If the contents in primary information up-down counter 18 is within a predetermined range, then the read head, not shown, continues to read the data stripe. If the contents of primary information up-down counter 18 is outside the predetermined range, then a servo check is generated.

The deviating point from the Hart patent is that a secondary amplitude sense level is positioned at the 70 percent mark of the servo envelope. The information generated by secondary sense level 24 is sensed by secondary information sense amplifier 26 in a manner analogous to that described in the Hart patent. Secondary information up-down counter 30 functions in a manner similar to that of primary information up-down counter 18, to determine if the information derived from secondary amplifier sense level 24 is satisfactory.

Fig. 2 depicts a system whi...