Browse Prior Art Database

Automatic Focus Control for Head Alignment

IP.com Disclosure Number: IPCOM000060818D
Original Publication Date: 1986-May-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Bates, KA: AUTHOR [+2]

Abstract

This article describes an automatic focus control system which will maintain an actuator lens focused on an alignment target despite small head movements. During alignment of an optical head, it is necessary to maintain focus while the optical components are being adjusted. The beam from the head is focused on a chromium target. This focus condition must be maintained within a 0.2 micron tolerance during optical component adjustment. Because the optical components are moved mechanically, some movement of the head always occurs. The head must be focused again and another attempt made to adjust the optical components. As a result, the alignment of the head is a complicated process, requiring much time.

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 60% of the total text.

Page 1 of 2

Automatic Focus Control for Head Alignment

This article describes an automatic focus control system which will maintain an actuator lens focused on an alignment target despite small head movements. During alignment of an optical head, it is necessary to maintain focus while the optical components are being adjusted. The beam from the head is focused on a chromium target. This focus condition must be maintained within a 0.2 micron tolerance during optical component adjustment. Because the optical components are moved mechanically, some movement of the head always occurs. The head must be focused again and another attempt made to adjust the optical components. As a result, the alignment of the head is a complicated process, requiring much time. If the optical head were held in focus during optical component adjustments, considerable time would be saved during head assembly. Focus during adjustment is maintained using the actuator voice coil in the head assembly to move the focusing lens to compensate for the slight head movements. A feedback control system keeps the lens focused on the target automatically. Fig. 1 is a block diagram of such a system. The focus actuator is excited by low-frequency (less than 200 Hz) sine waves from an AC source having a DC offset. A laser monitor diode circuit (not shown) in the optical head supplies a peak output voltage while the lens is focused on the target. This voltage is amplified and a peak detector stores the amplified peak...