Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Track Step on an Optical Disk

IP.com Disclosure Number: IPCOM000061250D
Original Publication Date: 1986-Jul-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Arter, NK: AUTHOR [+2]

Abstract

In an optical disk drive there is a track-following servo which keeps the transducer (laser scanning head) positioned over a single disk track. This servo must also be able to step the transducer to an adjacent track quickly and reliably. It is not feasible to do this under closed-loop control due to instability in the tracking error signal between tracks, and because of imperfections in the disk or in the optics, such as varying track widths, disk defects, and lens off-axis performance, which make the tracking error signal quite variable. Typical open-loop stepping is very unreliable because of the relatively large run out of the disk, compared to the track pitch.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 61% of the total text.

Page 1 of 2

Track Step on an Optical Disk

In an optical disk drive there is a track-following servo which keeps the transducer (laser scanning head) positioned over a single disk track. This servo must also be able to step the transducer to an adjacent track quickly and reliably. It is not feasible to do this under closed-loop control due to instability in the tracking error signal between tracks, and because of imperfections in the disk or in the optics, such as varying track widths, disk defects, and lens off-axis performance, which make the tracking error signal quite variable. Typical open- loop stepping is very unreliable because of the relatively large run out of the disk, compared to the track pitch. In an optical disk drive, the lens has to follow disk run out of up to 200 tracks, so there are large variations in acceleration, velocity, and position conditions over which a single-track-step must work. If the step is not completed properly, the loop may close in an unstable region, causing the lens to be driven across many tracks, and even causing loss of focus. This article describes a method of stepping which decreases the amount of settling time required, and also produces steps properly, even with large tracking offsets. Fig. 1 shows the tracking error signal versus position on a disk. Also indicated is the tracking error signal seen during a single track step. Figs. 2A and 2B show the tracking error signal for 0 and .4 microns of tracking offset. Note that there...