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Data Reduction System - Scan Positioning

IP.com Disclosure Number: IPCOM000097776D
Original Publication Date: 1961-Jun-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 3 page(s) / 66K

Publishing Venue

IBM

Related People

Kamentsky, LA: AUTHOR

Abstract

A scanning beam of light, such as is provided by a flying spot scanner, is accurately directed toward a target by a closed loop control system which uses a group of reference gratings, through which portions of the light beam are directed. The control circuit makes use of signals which are generated by photomultipliers receiving light passing through coarse and vernier gratings. The light beam is controlled in two dimensions. The circuit handles one-dimensional control. The second dimension is controlled by an identical circuit.

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Data Reduction System - Scan Positioning

A scanning beam of light, such as is provided by a flying spot scanner, is accurately directed toward a target by a closed loop control system which uses a group of reference gratings, through which portions of the light beam are directed. The control circuit makes use of signals which are generated by photomultipliers receiving light passing through coarse and vernier gratings. The light beam is controlled in two dimensions. The circuit handles one-dimensional control. The second dimension is controlled by an identical circuit.

Entry register 1 stores the difference between the present position of the light beam and the desired position. The sign of the difference indicates the desired direction of a beam movement. The amplitude of the difference comprises coarse and vernier bits which make a bi-level number system having a radix corresponding to the relative grating spacings on the coarse and vernier gratings.

The sign and coarse bit data stored in 1 are applied to coarse updown counter 2 upon the application of a readin signal to the register. Each coarse grating signal applied to 2 causes it to approach zero (count up or down, depending upon the sign of the stored difference) by one unit. Comparator 3 generates a voltage whose polarity depends upon the sign stored in 2 when it provides a non-zero output. This voltage is applied through AND 4 and OR 5 to integrator 6 during the coarse positioning phase of the scan positioning cycle. The output of 6 is applied to the deflection coil 7 to control the light beam position provided by the flying spot scanner 8. A signal is provided by OR 9 to set flip-flop 10 which in turn applies an inhibit signal to AND 4 when the coarse positioning phase is terminated. This signal is provided to OR 9 through AND 11 when counter 2 contains a count of 1 and a deceleration signal is supplied from the coarse grating at a time immediately before the application of the next coarse grating signal.

If the difference stored in register 1 is such that the coarse bit output is zero (indicating a desired scan motion that is less than the spacing between two coarse gratings), the resulting zero count output of counter 2 is applied through OR 9 to set flip-flop 10. Thus, the comparator 3 output voltage is passed by AND 4 to integrator 6 only during the coarse positioning phase which includes the time before the presence of the deceleration signal that immediately precedes the coarse grating signal which causes the coarse counter to provide a zero count.

The sign and vernier bit data are applied to a vernier up-down counter 12 which operates in a similar manner to counter 2. The vernier grating signals are applied through AND 13 when the reference signal (indicative of the beam intensity) is adequate to condition the gate. An entrained oscillator 14 supplies the missing vernier grating signals when the reference signal is inadequate. The vernier grating signals are then...