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Double Stripe Beam Position Servo System

IP.com Disclosure Number: IPCOM000075533D
Original Publication Date: 1971-Oct-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Rowe, SH: AUTHOR

Abstract

A beam-positioning servo system is necessary in CRT addressed data systems. Such a system is divided into two sequences. The first entails gross positioning (i.e., correct to within one spot diameter) and is termed "slewing," whereas the second sequence is the procedure of linear servoing to obtain fine positioning to within a fraction of a spot diameter. In one scheme, linear servo action is affected by allowing the light spot to ride at the dividing edge between bright and opaque areas of a photographic plate, termed "edge" servoing. The amount of light passing through the photographic plate is collected by a detector and the relative misregistration of the spot is described by a cumulative error distribution.

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Double Stripe Beam Position Servo System

A beam-positioning servo system is necessary in CRT addressed data systems. Such a system is divided into two sequences. The first entails gross positioning (i.e., correct to within one spot diameter) and is termed "slewing," whereas the second sequence is the procedure of linear servoing to obtain fine positioning to within a fraction of a spot diameter. In one scheme, linear servo action is affected by allowing the light spot to ride at the dividing edge between bright and opaque areas of a photographic plate, termed "edge" servoing. The amount of light passing through the photographic plate is collected by a detector and the relative misregistration of the spot is described by a cumulative error distribution.

For an improved signal/noise ratio, instead of allowing the spot image to ride at a photographic edge, it is made to ride between two sets of photodetective stripes, as shown in Fig. 1, such as Schottky barrier detectors. Incident light spot 2 is shown upon both stripes. The error signal is the difference in currents derived from neighboring stripes. Consider the case of a spot, whose irradiance is described by the gaussian exp (-x2 over 2rho/2/), and where the width of the stripes is 2rho. For an error x, the error signal is given by, apart from a constant of proportionality, E = S(3 rho-x) - S(rho-x) + S(rho+x) - S(3rho+x). where S refers to the cumulative probability distribution.

Fig. 2 shows the error signal E pl...