Browse Prior Art Database

Method for Self Calibrating Laser Slide Assembly

IP.com Disclosure Number: IPCOM000045126D
Original Publication Date: 1983-Feb-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 5 page(s) / 72K

Publishing Venue

IBM

Related People

Grimm, CR: AUTHOR

Abstract

The laser slide assembly described in an earlier article (D. H. Brown, R. R. Grobe and P. J Schuster, "Self-Calibrating Slide Reference Position Sensor," IBM Technical Disclosure Bulletin 24, 7A 3153-3155 (December 1981) is calibrated by monitoring the voltage output of the proximity probe and calculating the slope of the voltage curve shown in Fig. 1. The point where the slope intersects the line where the voltage is unchanging is then taken as the reference point. This method is not able to maintain a 100 millionths tolerance. This is because for every slope change due to any reason, such as a change in temperature, there is a shift in the intersecting point, i.e., the reference point. The present method typically achieves a 16 millionths tolerance which is well within the 100 millionths tolerance limit.

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Method for Self Calibrating Laser Slide Assembly

The laser slide assembly described in an earlier article (D. H. Brown, R. R. Grobe and P. J Schuster, "Self-Calibrating Slide Reference Position Sensor," IBM Technical Disclosure Bulletin 24, 7A 3153-3155 (December 1981) is calibrated by monitoring the voltage output of the proximity probe and calculating the slope of the voltage curve shown in Fig. 1. The point where the slope intersects the line where the voltage is unchanging is then taken as the reference point. This method is not able to maintain a 100 millionths tolerance. This is because for every slope change due to any reason, such as a change in temperature, there is a shift in the intersecting point, i.e., the reference point. The present method typically achieves a 16 millionths tolerance which is well within the 100 millionths tolerance limit. The present method uses an analog to digital converter (ADC) to monitor the output of proximity probe 16 (Fig. 2). The calibration is performed at the point where the voltage output stops changing. Thus, irrespective of the exact position of the proximity probe or the ambient air temperature, the voltage always stops changing when the slide 22 contacts the reference surface 18 as long as this position is set for the midslope range of the probe, i.e., 20 to 30 thousandths recessed.

In order to identify the position where the voltage stops changing, two tables are used. One table is developed by storing the ADC values read from the probe output, and the other table stores the laser count associated with the probe voltage reading.

Contrary to the description in the referenced publication, the slide 22 carries the servo head (not shown) which is to write the servo tracks on a disk. The slide 22 is calibrated to the reference position 18 and is then moved from the reference position to a position where it writes the servo tracks. The calibration operation is illustrated in the flow diagram of Fig. 3 where the first step, block 100, is to check the status of all safety checks. This is done so as to eliminate any collisions prior to moving the probe. The output of the ADC is then read as indicated by block 110, and a check is made to determine if the probe voltage is at a maximum. This test is illustrated by block 115. If the voltage is not at a maximum, slide 22 is moved away from probe 16 towards the park position of the slide. This movement typically would be 1/4 inch or less. This movement operation is represented by block 120. Constants are then initialized, and the track display (not shown) is blanked, as indicated by block 125. Slide 22 is then stopped, and the laser (not shown) is zeroed, as indicated by block 130. Slide 22 is then started to move toward the calibrate position, as indicated by block 135, and a timer is started for the timer interrupt, as indicated by block 140.

A done flag, which will be described later herein, is checked by block 145, and if it is not set as the...