US5121371A — Optical servo system for magnetic disk

Claim 1

Independent Claim 170 words

In a disk storage system for reading data from or writing data to a disk surface having a rotational axis and a plurality of data tracks about the rotational axis including: means for rotating said disk surface about the rotational axis; a head positioned adjacent to the disk surface for read and/or writing data from said tracks; means for positioning said head with respect to said disk surface; and a servo system for controlling said means for positioning, said servo system being responsive to a servo error signal; the improvement comprising: pre-recorded optical servo tracks for indicating the radial position of said head with respect to said disk; means for producing an optical interference pattern having a fringe spacing related to the spacing of said servo tracks, said interference pattern having a length which extends over several of said servo tracks; said interference pattern being incident upon said servo tracks; and means for generating said servo error signal which is the convolution of said interference pattern and said servo tracks.

Claim 2

Dependent Claim 170 words

In a disk storage system for reading data from or writing data to a disk surface having a rotational axis and a plurality of data tracks about the rotational axis including: means for rotating said disk surface about the rotational axis; a head positioned adjacent to the disk surface for read and/or writing data from said tracks; means for positioning said head with respect to said disk surface; and a servo system for controlling said means for positioning, said servo system being responsive to a servo error signal; the improvement comprising: pre-recorded optical servo tracks for indicating the radial position of said head with respect to said disk; means for producing an optical interference pattern having a fringe spacing related to the spacing of said servo tracks, said interference pattern having a length which extends over several of said servo tracks; said interference pattern being incident upon said servo tracks; and means for generating said servo error signal which is the convolution of said interference pattern and said servo tracks.

Claim 3

Dependent Claim 17 words

The system recited in claim 1 wherein said servo tracks are pre-recorded concentrically with said data tracks.

Claim 4

Dependent Claim 19 words

The system recited in claim 1 wherein said fringe spacing is equal to the pitch of said servo tracks.

Claim 5

Dependent Claim 37 words

The system recited in claim 1 wherein said interference pattern is reflected from said servo tracks, said system further comprising: an optical detector, the reflected light being incident on said detector to produce said servo error signal.

Claim 6

Dependent Claim 22 words

The system recited in claim 1 further comprising: means for generating two optical interference patterns, one out of phase with the other.

Claim 7

Dependent Claim 71 words

The system recited in claim 5 and a binary cell photodetector, said two optical interference patterns being convolved with the servo tracks on said disk, one of the convolved optical patterns being incident on one of the binary cells of said photodetector to produce said servo error signal, the other of the convolved optical patterns being incident on the other of the binary cells to produce a quadrature servo error signal.

Claim 8

Dependent Claim 32 words

The system recited in claim 6 wherein said interference pattern is divided into two independent beams with a small angular difference therebetween to create two separate interference patterns at the focal plane.

Claim 9

Dependent Claim 51 words

The system recited in claim 7 wherein said angular difference is produced by: a wedge prism dividing the beam in a direction nearly orthogonal to that of the optical interference, the reflected image of said two interference patterns being focused onto two cells of said detector resulting in said quadrature signal.

Claim 10

Dependent Claim 52 words

The system recited in claim 7 wherein said angular difference is produced by: a holographic optical element dividing the beam in a direction nearly orthogonal to that of the optical interference, the reflected image of said two interference patterns being focused onto two cells of said detector resulting in said quadrature signal.

Claim 11

Dependent Claim 18 words

The system recited in claim 4 further comprising a collecting lens for focusing reflected light on said detector.

Claim 12

Dependent Claim 19 words

The system recited in claim 1 wherein said means for producing an interference pattern includes a coherent light source.

Claim 13

Dependent Claim 21 words

The system recited in claim 11 further comprising an aperture plate containing two slits producing two crossed beams of coherent light.

Claim 14

Dependent Claim 50 words

The system recited in claim 12 and an imaging lens, or HOE, wherein the spacing between said two slits and the imaging lens focal length or HOE focal length determines the relative angle between said two beams, the spatial frequency of said interference pattern being determined by said relative angle.

Claim 15

Dependent Claim 43 words

The system recited in claim 13 wherein said slit spacing and the focal length of said imaging lens are selected to produce a beam angle of approximately 2.2° at a wavelength of about 780 nm to achieve fringe spacing of approximately 20 μm.

Claim 16

Dependent Claim 20 words

The system recited in claim 1 wherein said means for producing an optical interference pattern is a holographic optical element.

Claim 17

Dependent Claim 65 words

The system recited in claim 1 wherein said servo tracks are pre-recorded on said disk further comprising: a fixed grating; means for generating another optical interference pattern, said other optical interference pattern being incident upon said fixed grating; and a multiple cell detector producing a signal responsive to light incident upon said servo tracks and another signal responsive to light incident upon said fixed grating.

Claim 18

Dependent Claim 54 words

The system recited in claim 15 further comprising: means for generating two further optical interference patterns, each being out of phase with the first recited two interference patterns; and a quadrant photodetector producing quadrature signals for each pair of interference patterns, said signals being differenced to provide two quadrature signals without a dc component.

Claim 19

Dependent Claim 131 words

An optical tracking servo system for a disk storage system in which information is read form or written to a plurality of data tracks about the rotational axis of the disk by a head comprising: optical servo tracks pre-recorded in relation to said data tracks for indicating the radial position of said head with respect to said disk; means for producing an optical interference pattern having a fringe spacing related to the spacing of said servo tracks, said interference pattern having a length which extends over several of said servo tracks; said optical interference pattern being incident upon said servo tracks; means for imaging said interference pattern on said servo tracks; and means for generating a servo error signal which is the convolution of said interference pattern and said servo tracks.

Claim 20

Dependent Claim 131 words

An optical tracking servo system for a disk storage system in which information is read form or written to a plurality of data tracks about the rotational axis of the disk by a head comprising: optical servo tracks pre-recorded in relation to said data tracks for indicating the radial position of said head with respect to said disk; means for producing an optical interference pattern having a fringe spacing related to the spacing of said servo tracks, said interference pattern having a length which extends over several of said servo tracks; said optical interference pattern being incident upon said servo tracks; means for imaging said interference pattern on said servo tracks; and means for generating a servo error signal which is the convolution of said interference pattern and said servo tracks.

Claim 21

Dependent Claim 43 words

The system recited in claim 18 further comprising: means for generating a second optical interference pattern, said second optical interference pattern being out of phase with the first recited optical interference pattern, both of said interference patterns being imaged on said disk surface.

Claim 22

Dependent Claim 52 words

The system recited in claim 19 and a binary cell detector, said first and second optical interference patterns being convolved with the servo tracks on said disk, the convolved optical patterns being incident on the binary cells of said photodetector to produce said servo error signal and a quadrature servo error signal.

Claim 23

Dependent Claim 34 words

The system recited in claim 18 further comprising: means for dividing said interference pattern into two independent beams with a small angular difference therebetween to create two separate interference patterns at the focal plane.

Claim 24

Dependent Claim 60 words

The system recited in claim 21 wherein said means for dividing said interference pattern comprises: a wedge prism dividing the beam in a direction nearly orthogonal to that of the optical interference, the convolved image of said two interference patterns being focused onto two cells of said detector resulting in said servo error signal and a quadrature servo error signal.

Claim 25

Dependent Claim 32 words

The system recited in claim 18 wherein said means for producing an interference pattern includes a coherent light source and an aperture plate containing two slits producing two crossed beams of light.

Claim 26

Dependent Claim 43 words

The system recited in claim 23 and an imaging lens wherein the spacing between said two slits and the lens focal length determines the relative angle between said two beams, the spatial frequency of said interference pattern being determined by said relative angle.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1995-06-09	1995-12-09	1996-06-09	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1999-06-09	1999-12-09	2000-06-09	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2003-06-09	2003-12-09	2004-06-09	$7700.00	Window Closed / Lapsed

Optical servo system for magnetic disk

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