Browse Prior Art Database

Tracking Light Pen

IP.com Disclosure Number: IPCOM000092403D
Original Publication Date: 1967-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Thorpe, RA: AUTHOR

Abstract

A light pen tracking system for controlling the generation of a display on cathode ray tube 21 includes light pen 23 having a plurality of photosensors 24 arranged orthogonally in relation to each other. Each photosensor is associated with an optical fiber 25, 27, 29 or 31 of glass, quartz, plastic or the like. Fibers 25, 27, 29, 31 transmit light detected by one or more of photosensors 24 to photodetectors 33 which convert the light signals to electrical signals. The latter are applied through difference amplifiers 43 and 45 and threshold detectors 47 and 49 to tracking and control logic. Such signals designate the particular zone or zones in the field of view of light pen 23 at which light is detected on CRT 21.

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Tracking Light Pen

A light pen tracking system for controlling the generation of a display on cathode ray tube 21 includes light pen 23 having a plurality of photosensors 24 arranged orthogonally in relation to each other. Each photosensor is associated with an optical fiber 25, 27, 29 or 31 of glass, quartz, plastic or the like. Fibers 25, 27, 29, 31 transmit light detected by one or more of photosensors 24 to photodetectors 33 which convert the light signals to electrical signals. The latter are applied through difference amplifiers 43 and 45 and threshold detectors 47 and 49 to tracking and control logic. Such signals designate the particular zone or zones in the field of view of light pen 23 at which light is detected on CRT 21.

A light spot on CRT 21 is positionally controlled by registers 95 and 97 which have inputs from an external control for initial positioning and are subsequently controlled from counters 75 and 81. The latter are controlled in turn by the tracking logic which actuates the counters to increment or decrement. Such is in accordance with whether or not light is detected by the respective light pen zones so that the light spot is controlled to follow the motion of light pen 23.

By eliminating the requirement for continuous regeneration of the tracking symbol, the system is not time dependent, permitting the use of long persistence phosphor to reduce flicker in the display.

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