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Browse Prior Art Database

Interactive Display Storage Cathode Ray Tube

IP.com Disclosure Number: IPCOM000073805D
Original Publication Date: 1971-Feb-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 3 page(s) / 63K

Publishing Venue

IBM

Related People

Kazan, B: AUTHOR

Abstract

Information may be added to or subtracted from information electrically stored on the screen of a bistable-phosphor storage tube by a light pen. The resultant image may then be observed visually or read out electrically. The external memory and continuous recirculation of information, associated with other cathode-ray tube interactive systems are thus not required and problems of flicker are avoided.

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Interactive Display Storage Cathode Ray Tube

Information may be added to or subtracted from information electrically stored on the screen of a bistable-phosphor storage tube by a light pen. The resultant image may then be observed visually or read out electrically. The external memory and continuous recirculation of information, associated with other cathode-ray tube interactive systems are thus not required and problems of flicker are avoided.

Illustratively, present bistable-phosphor tubes, as shown in Drawing A, depend on local areas of the phosphor screen (which may be porous or in the form of a mosaic of small elements) being maintained at either zero or +150 volts by the secondary-emission action of the flood beam. Since flood-beam electrons can land only at the positive areas, only these portions of the screen emit light. The conventional technique of writing involves charging zero-potential, i.e., "off" or "erased", phosphor areas to a positive potential by means of the secondary emission action of the writing beam. These areas are then held at +150 volts by the flood beam and appear visible.

It has been determined that local "off" areas which are at zero potential can also be charged positive by exposure to a transient light beam. As indicated above, a potential difference of 150 volts exists across "off" elements since the phosphor backplate is maintained at +150 volts. Assuming the phosphor to be photoconductive, if it is locally illuminated and its conductivity is sufficiently increased, it will shift positive toward the backplate potential against the action of the flood beam. The phosphor elements which had been illuminated will then be held at +150 volts by the flood beam and remain "on" as in the case of electrical writing.

In the case of a conventional bistable-phosphor storage tube, a Zn(2)SiO(4) phosphor screen is generally used. This has a very small photoconductivity and ordinary room light has no effect on the tube operation. However, it has been demonstrated that if the erased screen of such a tube is exposed to a single flash from a small photographic flash lamp at a distance of about 6 inches, the entire illuminated screen area is caused to shift to the "on" or bright state. By placing a mask consisting of an opaque sheet with a pattern cut in it, between the tube face and the flash lamp, a stored visible image of the open areas is produced on the phosphor screen by the light flash. Alternatively, if a light pen which produces a sufficiently bright spot is moved across the screen, a written trace can be stored on the tube screen which is superimposed on any information which had been written electrically. In a similar manner, the tube may be used to record the position or trace of a laser beam.

As illustrated in Drawing B, a light pen may be employed for erasing as well as writing, if a suitable tube structure is used. In this case, a transparent collector mesh which is maintained at +150 volts is placed n...