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A method for operating a head testing apparatus (spin stand) using a mounted hard disk that has had its servo track information pre-written in an external servo-writing apparatus rather than in the testing apparatus itself. This insures more accurate servo-track writing and renders the testing operation more efficient. The problem of repeatable runout (RRO) associated with the transfer of a disk written in one machine to another is eliminated by forming a corrected position error signal (PES) by subtracting the average offset of one or more servo sector locations previously calculated using limited bandwidth operation of the servomechanism, from the position error signal generated during full bandwidth servo operation of the apparatus.

Titel:	Magnetic head tester using magnetic disk with pre-written servo
Autor/in / Beteiligte Person:	Shrinkle, Lou ; Hu, David ; Crill, Peter ; Yee, Matthew
Link:	View record in USPTO Patent Applications (Volltext)
Veröffentlichung:	2007
Medientyp:	Patent
Sonstiges:	Nachgewiesen in: USPTO Patent Applications Sprachen: English Document Number: 20070047124 Publication Date: March 1, 2007 Appl. No: 11/217872 Application Filed: September 01, 2005 Claim: 1. A method for operating a magnetic head tester using magnetic hard disks on which servo information has been pre-written using a dedicated servo track writer, comprising: providing a magnetic head tester, said tester including a motor driven rotating spindle on which a magnetic hard disk is to be mounted, a movable head actuator assembly, a read/write head to be tested that is affixed to said head actuator assembly and is capable of being positioned at selected target locations on said disk by the movement of said actuator assembly and of reading information stored within servo sectors thereat, and an electro-mechanical servo-control system, operable at various bandwidths, for responding to a position error signal and controllably positioning said head at said disk locations; mounting on said spindle a magnetic hard disk on which has already been formed, in an external device, a plurality of concentric circular tracks containing regularly spaced servo sectors, said servo sectors including embedded information defining radial and angular positions within each track, whereby said concentric circular tracks are no longer concentric relative to said spindle; measuring and averaging offset values of the locations of selected servo sectors, said offsets being a result of said lack of concentricity; using said average offset values to correct a position error signal for each of said sectors; operating said head tester thereafter at a full servo control bandwidth, using said corrected position error signals to allow said actuator to follow a substantially circular path with minimal positional variations. Claim: 2. The method of claim 1 wherein each of said average offset values is measured by a method comprising: setting the bandwidth of the servo-control mechanism to a minimum value; locking the actuator and head to read only the location of selected servo sectors at a fixed selected radial position of the head; reading and storing an initial location of each of said servo sectors, ri, as indicated by the embedded servo information therein, during an initial rotation of said disk; reading and storing a location, r, of each of said servo sectors during each of a series of subsequent complete rotations of the disk; reading and storing a final location, rf, of each of said servo sectors during a final rotation of said disk; comparing the initial location, ri, and the final location rf of each of said sectors; and, if the initial and final locations differ by less than a programmable amount, then a minimal closure specification has been met; then computing and storing an average of all the sampled servo sectors that meet said closure specification. Claim: 3. The method of claim 2 wherein said average of said sampled servo sectors meeting said closure specification is an accurate approximation to the repeatable runout of said sectors. Claim: 4. The method of claim 1 wherein said average is the result of sampling 1000 disk rotations on average. Claim: 5. The method of claim 1 wherein only a single servo sector is selected. Claim: 6. The method of claim 1 wherein a plurality of servo sectors are selected. Claim: 7. The method of claim 1 where all of the servo sectors are selected. Claim: 8. A magnetic head testing apparatus comprising: a base; a motor driven rotating spindle attached to said base; a magnetic hard disk mounted on said spindle, said hard disk including concentric circular tracks and servo sectors formed externally to said head testing apparatus, wherein said servo sectors contain track coordinate information and wherein said circular tracks are no longer concentric relative to said spindle; a movable head actuator assembly attached to said base adjacent to said spindle, said assembly capable of positioning a magnetic head at selected target locations on said hard disk and of reading information stored within servo sectors thereat; an electro-mechanical servo-control mechanism, capable of being run at various bandwidths and responding to a position error signal, for controllably positioning said head above said disk locations; data stored in said electro-mechanical servo-control mechanism providing a means for defining an average locus of servo sector position offsets, said position error signal being derived from the difference between said locus of offsets and the current position of the head. Claim: 9. The magnetic head testing device of claim 8 wherein the data stored in said electro-mechanical servo-control mechanism is the average of the fixed positions of a plurality of servo sectors of said disk, said average being obtained over the course of repeated complete rotations of said disk while said servo-control mechanism is set at a low bandwidth condition and said average being stored only if the initial and final positions of said positions differ by no more than a programmable amount. Claim: 10. The magnetic head testing device of claim 9 wherein said average is an accurate approximation to the repeatable runout of said sectors. Current U.S. Class: 360055/000 Current International Class: 11

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Magnetic head tester using magnetic disk with pre-written servo