Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
1999-03-01
2001-11-27
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Envelope
C313S634000
Reexamination Certificate
active
06323591
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a picture display device comprising a display tube having an evacuated envelope, which envelope comprises, around a longitudinal axis, a display window with a display screen on its inner side, a conical portion and a neck portion, the conical portion being connected to an upstanding wall of the display window.
The invention also relates to a conical portion for use in a picture display device.
Picture display devices of the type described in the opening paragraph are used, inter alia, in television apparatuses and computer monitors and are referred to as cathode ray tubes (CRTs).
A picture display device of the type described in the opening paragraph is known.
The known picture display device has some drawbacks, notably a large weight and high cost price of its conical portion.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a picture display device in which said problem is alleviated.
To this end, the picture display device according to the invention is characterized in that the conical portion has a wall thickness, wherein the wall thickness d
sa
along a short axis of the conical portion as a function of a distance z in a first area of the conical portion adjacent to the upstanding wall of the display window is defined by the relation:
&dgr;d
sa
/&dgr;z=C
1
,
and, in a second area adjacent to the first area, is defined by the relation:
&dgr;d
sa
/&dgr;z=C
2
,
in which |C
1
|>|C
2
|, and in which the first area comprises a part of the conical portion for which 0≦z≦a, and the second area comprises a part of the conical portion for which a≦z≦80%, in which z represents a relative distance measured with respect to the projection on the longitudinal axis between the connection with the upstanding wall of the display window and the transition to at least substantially axial symmetry in the conical portion, and in which a is in the range of 10%≦a≦60%.
The conical portion is provided as a kind of linking element between the upstanding wall of the display window of the known picture display device, which upstanding wall usually has a relatively large wall thickness, and the neck portion which usually has a relatively small wall thickness, the wall thickness of the conical portion, measured from the upstanding wall towards the neck portion, generally decreasing linearly. In other words, in the known display device, the variation (direction coefficient) &dgr;d
sa
/&dgr;z of the wall thickness d
sa
along the short axis of the conical portion as a function of the relative distance z is constant across the conical portion. Hitherto, it has been assumed that such a linear variation of the wall thickness of the conical portion was necessary, both from a design point of view and for reasons of moldability. The inventors have recognized that such a linear variation is not necessary. Due to the measure according to the invention, the wall thickness of the conical portion in the first area undergoes a larger variation (decrease) than that in the second area. Consequently, a conical portion is obtained which comprises less material (glass) than the conical portion of the known picture display device. Due to the reduction of the quantity of material, the picture display device as a whole will be less heavy. A reduction in weight of picture display devices is notably important for those devices having a relatively large picture diameter because such apparatuses can otherwise be hardly lifted. The measure according to the invention may be used to advantage, notably for picture display devices having a large deflection angle (>100%). For picture display devices having such a large deflection angle, the tensions in the glass of the conical portion are relatively high. To compensate for such high tensions, thicker glass is generally used. Due to the measure according to the invention, such an increase of the quantity of material is not necessary in picture display devices having a large deflection angle (>100%). The weight reduction of the conical portion has the additional advantage that the picture display device as a whole thus has a lower cost price.
In this application, three main directions (see
FIG. 2
) are distinguished, namely the thickness variation of the conical portion along a cross-section of the conical portion parallel to the diagonal (to one of the corners of the display window), the thickness variation along a cross-section of the conical portion parallel to the short axis (to the upper and lower side of the display window), and the thickness variation along a cross-section of the conical portion parallel to the long axis (to the sides of the display window). The short axis is also referred to as “short cross-section” and the long axis is also referred to as the “long cross-section”.
It is to be noted that C
1
and C
2
do not need to be constants but may be dependent on the relative distance z. Notably in the first area adjacent to the upstanding wall of the display window, a strong decrease of the wall thickness is preferably realized, so that in the second area, adjacent to the first area, the wall thickness in a direction remote from the display window does not decrease or hardly decreases. An embodiment of the picture display device according to the invention is characterized in that |C
2
|≦0.02. In the second area, the wall thickness d
sa
along the short axis as a function of the relative distance z is at least substantially constant, as measured with respect to the wall thickness in the first area. An alternative embodiment of the picture display device according to the invention is characterized in that the ratio between the variation of the wall thickness d
sa
in the second area, divided by the length of the second area, and the variation of the wall thickness d
sa
in the first area, divided by the length of the first area, is larger than 5. In this way, a considerable saving in weight of the conical portion is realized.
According to the invention, the value of the parameter a is in a range of 10%≦a≦60%. If a≈10%, the first area is 0%≦z≦10%, in which the wall thickness d varies (decreases) to a relatively large extent, and relatively small with respect to the second area of 10%≦z≦80% in which the wall thickness d varies (decreases) to a relatively small extent. If a≈60%, the first area is 0%≦z≦60%, which is relatively large with respect to the second area of 60%≦z≦80%. Values for a<10% or a>60% are unfavorable for realizing material savings. The value for the parameter a is preferably in a range of 25%≦a≦50%. Notably in this range of the parameter a, the conical portion can be satisfactorily molded (at a relatively low molding force) and so-called folds are prevented when molding the conical portion. A particularly suitable value of the parameter is a≈40%, at which a minimal molding force of the conical portion is realized.
An embodiment of the picture display device according to the invention is characterized in that the wall thickness d
sa
in the second area is defined by the relation
0.9
xd
pa
≦d
sa
≦1.25
xd
pa
,
in which d
pa
is a wall thickness of the conical portion at the area of the transition to at least substantially axial symmetry.
The upstanding wall of the display window generally has a non-axially symmetrical shape with respect to the longitudinal axis, whereas the neck portion of the picture display device usually has an axially symmetrical shape. Viewed from the display window, the conical portion has a shape in the first and the second area which is adapted to the symmetry of the display window (for example, an at least substantially fourfold symmetry) and has a transition to axial symmetry at an end portion of the second area remote from the display window.
By choosing the ratio of the wall thicknesses d
sa
/d
pa
to be between 0.9 and 1.25 in the second area, a considerable saving of material for the conical portion is realized and a s
Bruisten Peter M.
Kleine Jan W.
Oosterhout Gerardus M.
Schoone Petrus R. M.
Sterken Paul F. A.
Patel Vip
Spain Norman N.
U.S. Philips Corporation
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