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Automatic Drift Correction

IP.com Disclosure Number: IPCOM000094361D
Original Publication Date: 1966-Sep-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Brown, CJ: AUTHOR

Abstract

This servo is self-correcting for long-term drift. A voice coil actuator 1 is driven by operational amplifier 2. The input signal to amplifier 2 is taken from a photodiode 3. Mask 4, moved by actuator 1, and light source 5 coact to illuminate one-half the surface of photodiode 3 when the servo system is on track. Where adjacent track positions are close together, it may be necessary to provide an optical system for enlargement of mask 4.

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Automatic Drift Correction

This servo is self-correcting for long-term drift. A voice coil actuator 1 is driven by operational amplifier 2. The input signal to amplifier 2 is taken from a photodiode 3. Mask 4, moved by actuator 1, and light source 5 coact to illuminate one-half the surface of photodiode 3 when the servo system is on track. Where adjacent track positions are close together, it may be necessary to provide an optical system for enlargement of mask 4.

In the absence of a correction signal across resistor 6, the output position. To correctly null the system, an offset signal is developed across resistor 6 by reference to home photodiode 15 and its corresponding aperture 14 in mask 4.

The offset signal is developed by signalling a home address to the servo system, causing amplifier 2 to step actuator 1 to the extreme end of its travel. Addressing the home position also resets register 7. As the home position is approached, the light from source 5 is uncovered by mask 4 and impinges on photodiode 3. Since there is no offset signal across resistor 6 due to register 7 being reset, photodiode 3 indicates home in advance of the actual position.

At this point, home detector 8, connected to the output of amplifier 2, operates to set trigger 9 to the on state. Trigger 9 functions to turn on pulse generator 10 and pulses are fed to register 7. Associated with register 7 is resistor network 11 which generates an analog voltage at the base of transistor 12 corres...