Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1984-12-10
1986-12-16
Britton, Howard W.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358242, 315370, H04N 1700
Patent
active
046301151
DESCRIPTION:
BRIEF SUMMARY
This invention relates to cathode ray tube display devices, more especially cathode ray tube display devices suitable for operation under vibration, for example in an aircraft or tank.
A cathode ray tube (CRT) comprises at least one electron gun for producing a beam of electrons, a luminescent screen and means for deflecting the beam of electrons across the screen. When such a tube is exposed to vibration, relative movement of the component parts of the tube leads to image distortion. The remedy used at present takes one of two forms. The tube can be especially strengthened to resist vibration, e.g. so that the gun position always remains fixed with respect to the screen, or the tube can be mounted in a vibration-proof mount. Both solutions are expensive and they are not cures for all conditions.
An alternative solution to this problem is to provide a cathode ray tube display device comprising: a cathode ray tube including electron gun means; means for periodically operating the tube to direct a beam of electrons produced by the electron gun means onto a target; sensor means for producing an output signal representing the deviation of the position of impact of the beam on the target from a desired position; and means for utilising said output signal to reduce said deviation.
It is an object of the present invention to provide. a practical form of such a cathode ray tube display device.
Accordingly, the present invention provides a cathode ray tube (CRT) display device comprising a cathode ray tube including electron gun means, control means for periodically operating the CRT to direct a beam of electrons produced by the electron gun means onto a target, sensor means for producing an output signal dependent on the deviation of the position of impact of the beam on the target from a desired position on the target and correction means for utilising said output signal to reduce said deviation, characterised in that said sensor means comprises: sensing means responsive to the position of impact of the electron beam on the target; first circuit means responsive to the output of said sensing means to produce an output indicative of the direction of the deviation of said position of impact from said desired position; storage means for storing said output of said first means; and second circuit means for integrating said stored output to produce said output signal.
In a preferred arrangement in accordance with the invention said output of said first circuit means comprises two components each representative of said deviation from said desired position in a different one of two orthogonal directions.
In one such preferred arrangement the sensing means comprises four sensing areas extending in different directions from a position defining said desired position, each said area subtending an angle of substantially 90.degree. at said desired position, and said first circuit means comprises comparator means responsive to signals V.sub.a, V.sub.b, V.sub.c V.sub.d respectively produced by said four sensing areas on impact of the electron beam to produce output signals V.sub.a -V.sub.b, V.sub.c -V.sub.d, V.sub.a -V.sub.c and V.sub.b -V.sub.d and adder means for adding said comparator means output signals to produce outputs (V.sub.a -V.sub.b)+(V.sub.c -V.sub.a) and (V.sub.a -V.sub.c)+(V.sub.b -V.sub.d).
One cathode ray tube display device in accordance with the invention will now be described by way of example with reference to one accompanying drawings in which:
FIG. 1 is a schematic diagram of the device;
FIGS. 2(a) and 2(b) show diagrammatically two possible forms of a sensing means used in the device;
FIGS. 3(a) and 3(b) illustrate two possible forms of an optical system associated with the sensing means; and
FIG. 4 is a block schematic diagram of a sensor and correction circuit used in the device.
FIG. 1 shows a cathode ray tube 1 comprising an electron gun 2, deflection plates 3 and a luminescent screen 4. The synchronising part of a video signal 7 of raster-scan format coming from, for example, a television broadcast
REFERENCES:
patent: 3743883 (1973-07-01), Burns
patent: 4142132 (1979-02-01), Harte
patent: 4159484 (1979-07-01), Strathman
patent: 4234893 (1980-11-01), Peters
patent: 4441120 (1984-04-01), Gerritsen
patent: 4456853 (1984-06-01), Robinder et al.
Britton Howard W.
Kostak Victor R.
The General Electric Company p.l.c.
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