Browse Prior Art Database

Data Sampling in an Optical Storage Device Having Focus Dither

IP.com Disclosure Number: IPCOM000040425D
Original Publication Date: 1987-Nov-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Arter, NK: AUTHOR [+2]

Abstract

A low cost optical storage device, using removable optical storage media, such as a multitrack disk or card, is constructed and arranged to provide nominal focus of a detector head on the media. The head is moved back and forth, i.e., dithered, at a known high frequency in the direction of its optical axis, so as to bring the head into true media focus a number of times for each media track data cell. A detector responds to the magnitude of the energy reflected from the media in order to determine when the head is in focus on the media. The binary (Image Omitted) data content of each data cell is sampled only when the head is in focus. A tracking servo (not shown) is provided to insure that the head follows the media track being read. However, a focusing servo is not necessary. In Fig.

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Data Sampling in an Optical Storage Device Having Focus Dither

A low cost optical storage device, using removable optical storage media, such as a multitrack disk or card, is constructed and arranged to provide nominal focus of a detector head on the media. The head is moved back and forth, i.e., dithered, at a known high frequency in the direction of its optical axis, so as to bring the head into true media focus a number of times for each media track data cell. A detector responds to the magnitude of the energy reflected from the media in order to determine when the head is in focus on the media. The binary

(Image Omitted)

data content of each data cell is sampled only when the head is in focus. A tracking servo (not shown) is provided to insure that the head follows the media track being read. However, a focusing servo is not necessary. In Fig. 1, a motor 10, for example a piezoelectric element, is used to move lens 11 back and forth at a high frequency, and along the optical axis of the lens, as indicated by arrow
12. An optical disk data storage card 13 contains a number of parallel binary data tracks, one of which is shown at 14. Laser 15 provides a beam of energy which impinges upon card 13. A portion of this laser energy is reflected back from the card onto tracking detector 16. A servo network (not shown) is provided to maintain the laser's beam centered on track 14, as card 13 moves in the linear direction indicated by arrow 17. Fig. 2 shows a portion of card 13, and depicts a "1011" binary data portion of track 14. The binary "1" data bits are formed by pits 20 in the card, whereas a binary "0" is the absence of a pit in a ca...