US 4,481,550 AGranted

Method and apparatus for following a recorded data track with a read head

AssigneeDatacopy Corporation

InventorsArmin Miller, Lauren V. Merritt

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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.

Claims15

Dependent claims

Apparatus for following, with a reading head, a data track recorded on a recording medium comprising:

a recording medium on which information has been recorded on a data track;
a playback head;
recording medium-moving means for moving said recording medium with respect to said playback head to thereby allow said playback head to read the information recorded on said data track, said playback head having an output for carrying an electical signal representative of information recorded on said data track;
playback head-moving means for moving said playback head across said recording medium, in a direction that is substantially orthogonal to said data track;
velocity detector means for providing an electrical output which bears a direct relationship to the relative velocity of said playback head-moving means;
summing means connected to said velocity detector means, the output of said summing means being connected to said playback head-moving means to thereby drive said playback head-moving means to close a velocity loop around said playback head-moving means;
amplitude-detector means connected to said output of said playback head for providing, at an output of said amplitude detector means, a derived amplitude signal which is substantially the average amplitude of the signal output of said playback head;
dithering means for causing said playback head to vibrate at relatively high frequency in a direction that is substantially orthogonal to said data track, so that the amplitude of said signal output of said playback head varies according to the relative position of the head with respect to the center line of the data track being followed;
and,
demodulation means responsive to said dithering means for providing a steering signal which acts as a velocity request to said summing means so that the playback head is kept on the center line of the data track being followed;
whereby, if the steering signal is zero, said playback head is moved back and forth in response only to said dithering means, and if the steering signal is not zero, the playback head is moved in addition in response to said velocity request in the appropriate direction until said steering signal is zero.

8 more elements

A method for following, with a reading head, the center line of a data track recorded on a recording medium comprising the steps of:

moving said recording medium with respect to a playback head, to thereby allow said playback head to read information recorded on said data track, said playback head having an output for carrying a first electrical signal representative of said information recorded on said data track;
moving said playback head across said recording medium in a direction that is substantially orthogonal to said data track;
providing a second electrical signal which bears a direct relationship to the relative velocity of said playback head-moving means;
causing said playback head to vibrate substantially orthogonal to said data track at a relatively high frequency and low amplitude about the center line of said data track;
developing a third electrical signal which is substantially the average amplitude of said first signal output of said playback head, said third electrical signal having an amplitude modulation proportional to changes in the amplitude of said first signal caused by the vibration of said playback head about said center line;
demodulating said amplitude modulated signal to provide a demodulated signal;
and,
moving said playback head in response to said second electrical signal and said demodulated signal, such that said demodulated signal acts as a velocity request to cause said reading head to be moved an appropriate distance and in such a direction so as to maintain said playback head on the center line of said data track.

5 more elements

Dependencies are inferred from the claim text.