| 摘要 |
In a helical scan recording system, magnetic tape (31) is transported by a tape transport (98) proximate a rotating scanner (85). The scanner has a pair of read heads (82) mounted thereon, e.g., a first read head and a second read head, which travel in a helical direction on the magnetic tape in view of the transport of the tape and rotation of the scanner. A synchronization detection system (38) determines a first synchronization mark detection time at which a first synchronization mark is read by the first read head from the first track, and a second synchronization mark detection time at which a synchronization mark read by the second read head from the second track. A position error signal generator (100) develops a position error signal (PES) based upon a difference between the first synchronization mark detection time and the second synchronization mark detection time. The servo or transport controller (98) uses the position error signal to develop a servo correction signal for adjusting the position of the read heads. In accordance with one aspect of the present invention, a first distance separating the sync marks along the helical direction of head travel is sufficiently less than a second distance by which the read heads of the pair are circumferentially separated on the scanner to render the position error signal (PES) immune to any variation in the rotational speed of the scanner. In accordance with another aspect of the invention, the position error signal generator comprises a coarse position error signal generator; a fine adjustment signal generator; and a combination element. The combination element combines a course position error signal and an adjustment signal to obtain the position error signal PES which is used by the servo controller to keep the read heads traveling along a longitudinal centerline of their respective tracks.
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