Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2000-11-27
2001-11-13
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S402000
Reexamination Certificate
active
06316870
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a color display tube comprising a display window with a circumferential upright edge and corner areas, a color selection electrode having a frame comprising corner sections having a rigid portion, which color selection electrode is suspended from supporting elements secured to the corner areas, with suspension means coupled to the corner sections.
The invention also relates to a corner section for use in a color selection electrode of a color display tube, having a rigid portion and suspension means, and to a color selection electrode provided with such a corner section.
SUMMARY OF THE INVENTION
A color display tube as described in the opening paragraph is disclosed in U.S. Pat. No. 5,003,218. The color display tube according to this specification is provided with a color selection electrode having a frame consisting of four diaphragm parts and four corner sections, suspended in the corners of the display window.
The color display tube described in U.S. Pat. No. 5,003,218 is provided with a color selection electrode to ensure that electron beams coming from three electron guns, mounted in a neck portion of the tube, only excite one color of electroluminescent material on the inner side of the display window. This color selection is achieved by applying, for instance, a shadow mask in the tube. This mask has a large number of apertures, generally arranged in either a slotted or a dotted pattern. If the color selection electrode is not positioned in the color display tube in a stable manner, small deviations of its position will lead to a deterioration of the picture quality. When the color selection electrode is shifted slightly, the shadowing effect of the color selection electrode changes and, consequently, the electron beams do not hit the appropriate electroluminescent material on the display window. This misregistration causes a lack of the corresponding color, or even worse, the wrong color of electroluminescent material is excited. These misregistrations cause discoloration of the display tube, leading to a deterioration of the quality of the picture on the color display tube. In practice, color display tubes provided with the suspension system as described in U.S. Pat. No. 5,003,218 show discolorations that are too large to fulfil the ever-increasing demand for picture quality. Especially wide-screen tubes and tubes with a real flat or almost flat outer surface of the display window suffer from these problems. It is a disadvantage of the known color display tube that it shows too large misregistrations.
It is an object of the invention to provide a color display tube having a color selection electrode with an improved suspension system as compared with the type described in the opening paragraph, which minimizes the registration errors on the display window.
According to the present invention, this object is realized with a color display tube which is characterized in that each rigid portion is provided with a part, fixed onto the rigid portion, increasing the stiffness of the corner section.
The invention is based on the recognition that the registration errors are minimized when the position accuracy of the color selection electrode with respect to the display window is improved. This is realized when the stiffness of the suspension system of the color selection electrode is increased. In that case, fewer deformations of the color selection electrode occur during the manufacturing process. Also in the final product, the color selection electrode is positioned much more accurately.
A second source of misregistrations is shifts of the color selection electrode that may occur in the color display tube after it has been manufactured. These shifts are caused by heavy shocks to which the color display tube is exposed, for instance, during transportation. For this situation as well, a larger stiffness of the suspension system leads to a larger positional stability of the color selection electrode.
This larger stiffness can be realized by adding a part to the rigid portion and fixing it thereon. Here, fixing is understood to cover all kinds of firm, not necessarily permanent connections by means of, for example, welding, gluing, screwing.
A preferred embodiment of the color display tube according to the present invention is characterized in that the rigid portion comprises a main plate and an oblique surface, and the part for increasing the stiffness comprises an additional support plate interconnecting the main plate and the oblique surface.
This additional support plate decreases the amount of bend in the suspension element. This leads to a more rigid connection between the color selection electrode and the support element in the corner area of the glass panel. In this construction, the mask position accuracy is improved and so is the picture quality.
A second preferred embodiment is characterized in that the stiffness is further increased by having free end portions of the supporting elements substantially located in a plane which coincides with the main plates of the rigid portions of the corner sections.
This measure increases the position accuracy of the color selection electrode with respect to the display window, because a possible shift of the color selection electrode can now only occur in the plane of the main plate of the corner sections which practically coincides with the plane of the supporting elements. Due to this construction, there is no, or practically no, momentum between the free ends of the supporting elements and the main plate of the rigid portion. This makes the color selection system very robust against, for instance, shocks, because it can hardly rotate around the supporting element.
A further embodiment is characterized in that the rigid portions of the corner sections are provided with an upright edge. The stiffness of the corner section can be further increased by this measure. For example, an upright edge can be realized by folding the edges of the main plate.
A still further embodiment is characterized in that the stiffness is further increased by having free end portions of the supporting elements substantially located in a plane which coincides with an upright edge of the rigid portions of the corner sections. In this situation, the torsion between the suspension element is diminished and the positional accuracy is improved.
The invention also relates to the corner sections of a color selection electrode and to a color selection electrode provided with such corner sections.
These and other aspects of the invention are apparent from and will be elucidated by way of non-limitative examples with reference to the drawings and the embodiments described hereinafter.
REFERENCES:
patent: 5003218 (1991-03-01), Gijrath et al.
patent: 5982085 (1999-11-01), Lakshmanan et al.
patent: 8800424 (1988-04-01), None
Hendriks Arnoldus Antonius Maria
Van De Steen Wilhelmus Marinus Maria
Van Rens Piet Christiaan Jozef
Winters Jean
Patel Vip
U.S. Philips Corporation
Waxler Aaron
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