Importance

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Abstract

A playback head (155) is moved across a recording medium (151) orthogonally to a data track by playback head-moving means (157, 159, and 161), said data track being independently moved so that previously-recorded data is sequentially recovered. An electrical signal, which bears a direct relationship to the velocity of the head-moving means, is produced by a position sensor affixed to the head-moving means and a differentiator (169). Said signal is used to close a velocity loop, through a summing junction (171) and a power amplifier (173), around the head-moving means. The playback head is moved in addition, at a relatively high frequency, by dithering means which causes an amount of head motion that is small with respect to the width of the data track. The dither motion causes an amplitude modulation of the signal being recovered from the data track by the playback head. The amplitude modulation contains information on the instantaneous position of the playback head with respect to the center line of the data track. This instantaneous position information is recovered through the use of an amplitude detector (177), a bandpass filter (45), a synchronous rectifier or a pair of sample-and-holds controlled by the dither frequency, and a second filter (49), the result being a steering signal that is applied to the summing junction. The end result is that the playback head stays substantially on the center line of the data track regardless of disturbances to this alignment.

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First Claim