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Self Calibrating Slide Reference Position Sensor

IP.com Disclosure Number: IPCOM000048049D
Original Publication Date: 1981-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 3 page(s) / 33K

Publishing Venue

IBM

Related People

Brown, DH: AUTHOR [+3]

Abstract

During the servowriting of a disk file with a dedicated servo surface, the servo head must be accurately and automatically positioned over the servo track area of the disk. A precision slide supports the servo head. A laser measuring system very accurately monitors the position of the head. By nature of its design, however, the laser system cannot determine the absolute head slide position but can only detect incremental movement (one increment is typically 0.623 micro-inch). The absolute position of the head slide must be determined by external circuitry. One technique is to have a binary location counter increment as the slide moves toward the file and decrement as the slide moves away from the file.

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Self Calibrating Slide Reference Position Sensor

During the servowriting of a disk file with a dedicated servo surface, the servo head must be accurately and automatically positioned over the servo track area of the disk. A precision slide supports the servo head. A laser measuring system very accurately monitors the position of the head. By nature of its design, however, the laser system cannot determine the absolute head slide position but can only detect incremental movement (one increment is typically 0.623 micro- inch). The absolute position of the head slide must be determined by external circuitry. One technique is to have a binary location counter increment as the slide moves toward the file and decrement as the slide moves away from the file.

The problem is in synchronizing the location counter to the slide's absolute position after any of the following conditions occur: 1. System initial power up.

2. Interruption of the laser beam.

3. Manual reset of the location counter while the

servowriter is in manual mode.

After any of these occurrences, the location counter will contain data that has no relation to the actual slide position. To synchronize the two, the slide must be moved to a reference location and then the location counter must be initialized with the number corresponding to that location.

Current methods employed are eddy current proximity sensors or linear variable differential transformers to sense when the slide is at the reference point. These devices can become uncalibrated without the servowriter electronics or computer knowing of this fact.

The subsequently written files under these circumstances appear to be good but may fail at a later test or after the product is shipped to the field. Once this condition is detected, all affected files must then be reservowritten, resulting in lost manufacturing time.

This problem is overcome by using the device illustrated in the figure. Initially, the computer moves the slide 10 in the direction of arrow A toward the file reference surface 22. The output of proximity probe 16 changes to indicate the decrease of gap 14. Eventually, the gauge block 17...