Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
1999-11-29
2001-10-23
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S368260, C313S402000, C313S403000
Reexamination Certificate
active
06307333
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a color display device comprising a color cathode ray tube including an in-line electron gun for generating three electron beams, a color selection electrode and a phosphor screen on an inner surface of a display window and a means for deflecting the electron beams across the color selection electrode.
Such display devices are known.
The aim is to make the outer surface of the display window flatter, so that the image represented by the color display device is perceived by the viewer as being flat. However, an increase of the radius of curvature of the outer surface will lead to an increase of a number of problems. The radius of curvature of the inner surface of the display window and of the color selection electrode should also increase, and, as the color selection electrode becomes flatter, the strength of the color selection electrode decreases and hence the sensitivity to doming, vibrations and droptest increases. An alternative solution to this problem would be to curve the inner surface of the display window more strongly than the outer surface. By virtue thereof, a shadow mask having a relatively small radius of curvature can be used. As a result, doming and vibration problems are reduced, however, other problems occur instead. The thickness of the display window is much smaller in the centre than at the edges. As a result, the weight of the display window increases and the luminosity of the image decreases substantially towards the edges.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a color cathode ray tube of the type mentioned in the opening paragraph, in which the outer surface may be flat or substantially flat, while, at the same time, the above problems are overcome or reduced.
To achieve this, a color display device in accordance with the invention comprises a color selection electrode which is flat in at least one direction, the inner surface of the display window is curved in the at least one direction and the color display device comprises means for dynamically influencing the paths of the electron beams to increase, as a function of the deflection in the at least one direction, the distance between the electron beams at the location of the deflection plane.
By virtue of the presence of the means, the distance between the electron beams (also referred to as “gun pitch”) in the plane of deflection can be changed dynamically in such a manner that this distance increases as the deflection increases. By dynamically changing this distance, as a function of the deflection, and hence as a function of the x and/or y-co-ordinate(s), i.e. the position of the electron bean(s) on the screen, the distance between the display window and the color selection electrode can decrease accordingly in the relevant deflection direction. The shape of the inner surface of the display window and the distance between the display window and the color selection electrode determine the shape, in particular the curvature, of the color selection electrode. Since the distance between the electron beams increases as a function of the deflection, the distance between the display window and the color selection electrode decreases and the shape of the color selection electrode can deviate more from the shape of the inner surface of the display window than in known cathode ray tubes, and, in particular, its curvature in the at least one direction can be zero, i.e. the color selection electrode is flat in said direction. Flat color selection electrodes are in fact insensitive, or at least much less sensitive, to doming and vibrations than color selection electrodes having a large (several meters) radius of curvature. This is due to the fact that a flat color selection electrode can be made of much thicker material and/or put under tension.
Preferably the outside surface of the display window is flat in the at least one direction.
‘Flat’ is to be understood to mean ‘having an infinite radius of curvature or at least a radius of curvature which is much (several times) larger than the radius of curvature of the inner surface’, in other words ‘flat’ is to be understood to mean ‘flat’ in the practical meaning, not of course in a mathematical meaning, since no real surface or element is ‘truly flat’ in the mathematical sense of the word. The flat outer surface offers the advantage that the appearance of the display device, especially when not in function is ‘flat’.
Preferably the means comprise a first and a second means which are at some distance from each other. Using two means enables a better control of the change in pitch, and it enables the pitch at the deflection plane to be influenced in such a manner that the convergence of the electron beams is better controllable.
Preferably the inner surface of the display window is curved in two directions, and the display device comprises further means for dynamically influencing the paths of the electron beams so as to increase the distance between the electron beams at the location of the deflection plane in a second direction. Preferably the further means comprise third and fourth means at some distance from each other. Said third and fourth means may be separate from the first and second means, but are preferably integrated in or equivalent to the first and second means.
The advantage of embodiments in which the inner surface is curved in two directions is that the thickness of the display window can be appreciably reduced compared to embodiments in which the inner surface is curved in only one direction. If the inner surface has an infinite radius of curvature in one direction (i.e. it is flat), the display window is relatively weak in that direction, which necessitates a relatively large thickness of the display window, and thus a large weight of the display window. By shaping the inner surface of the display window so that it is curved in two directions, the weight of the display window can be reduced.
Preferably the radius of curvature along the at least one and/or (preferably and) the second direction of the inner surface of the display window ranges between 8 and 16 times the diameter of the display window. For such radii of curvature the strength of the display window is sufficient, and, at normal viewing distances for TVT (television display devices), the display window conveys the impression that the image shown on the display device has an infinite, or nearly infinite, radius of curvature, i.e. it is ‘flat’. Larger radii of curvature require an increased thickness of the display window, and thus an increase in the weight and cost of the display device, and result in an image which, to the viewer, seems inwardly curved, while smaller radii of curvature result in an image which, to the viewer, seems outwardly curved.
Preferably, the first means and/or third means are integrated in the electron gun, that is, the first means and/or third means comprise one or more components of the electron gun.
In comparison with a first and/or third means which is/are separate from the electron gun, this has the advantage that fewer components are necessary and that the distance between the first and the second means is increased, thus enabling an increase of the possible variation in distance between the electron beams and hence of the variation in distance between the color selection electrode and the display screen and, consequently, a larger change in curvature of the color selection electrode.
Preferably, the first means and/or third means comprise one or more components of the prefocusing portion of the electron gun. As a result, the distance between the first and/or third means and the second and/or fourth means is increased compared to embodiments in which the first means and/or third means are situated at the location of, for example, the main lens portion, thus enabling an increase of the possible variation in distance between the electron beams and hence of the variation in distance between the color selection electrode and the display screen.
Preferably, the second means an
Den Engelsen Daniel
Sluyterman Albertus A. S.
Van Nes Johannes C. A.
Lee Wilson
U.S. Philips Corporation
Wong Don
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