Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2002-11-27
2004-08-03
Lee, Wilson (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S399000, C313S440000
Reexamination Certificate
active
06771030
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a color cathode ray tube apparatus used for a high-quality color television set or high-resolution display, and more particularly, to a color cathode ray tube apparatus improved in focusing properties that arose a problem related to flattening of a screen and reduction of the depth thereof.
2. Description of the Related Art
In general, a color cathode ray tube apparatus of an in-line self-convergence type comprises an in-line electron gun structure and a deflection yoke. The electron gun structure emits three electron beams, which are arranged in a line and include a center beam and a pair of side beams that pass on the same horizontal plane. The deflection yoke generates a non-uniform deflecting magnetic field that is formed of a horizontally deflecting magnetic field of the pincushion type and a vertically deflecting magnetic field of the barrel type.
However, the in-line self-convergence color cathode ray tube apparatus has the following two problems. The problems include (1) a problem that involves distortion of beam spots that causes lowering of the resolution at the horizontal axis end portions of the phosphor screen, in particular, and (2) a problem that the focusing properties worsen if a bendless coil is used as a horizontal deflecting coil in view of reduction in power consumption.
The first problem will be described first.
The angle of incidence of the three electron beams is a cause of this problem. The three electron beams that are directed toward the central portion of the phosphor screen land on the phosphor screen substantially at right angles thereto (angle of incidence ≈0°). Therefore, beam spots that are formed on the central portion of the phosphor screen are free from distortion. On the other hand, the angle of incidence of the three electron beams that land on the peripheral portion of the phosphor screen increases as the deflection angle increases. Therefore, beam spots that are formed on the peripheral portion of the phosphor screen are distorted into a shape that extends in the radial direction. This distortion is further promoted as the screen flattens or the deflection angle widens.
However, the electron beams that are directed to the vertical axis end portions of the phosphor screen are subjected to reciprocal influences, that is, the influence of the barrel-type vertically deflecting magnetic field and the influence of the angle of incidence upon the phosphor screen. Thus, the distortion of the beam spots is eased. On the other hand, the electron beams that are directed to the horizontal axis end portions of the phosphor screen are subjected to synergetic influences, that is, the influence of the pincushion-type horizontally deflecting magnetic field and the influence of the angle of incidence upon the phosphor screen. Thus, the distortion of the beam spots is promoted.
In the color cathode ray tube apparatus with the aforesaid construction, therefore, beam spots are distorted in the manner shown in
FIG. 10. A
special problem here is that the beam spots are distorted to be oblong at the end portions in the direction of a horizontal axis H that contains the directions of diagonal axes D of the phosphor screen. The importance of this problem has recently increased as the reduction of the depth of the color cathode ray tube apparatus and the flatness of the screen have started to be considered seriously. If a face panel is simply flattened, the angle of incidence of the electron beams at the H-axis end portions of the phosphor screen increases, so that the beam spots are distorted to be oblong.
In a color cathode ray tube apparatus of which the effective diagonal length of the phosphor screen is 46 cm, the deflection angle is 90°, the curvature radius of the outer surface of the face panel is 1,330 mm, and the curvature radius of the inner surface of the face panel is 1,240 mm, the aspect ratio of the beam spots at the H-axis end portions of the phosphor screen is 0.50 (vertical diameter/horizontal diameter). In a color cathode ray tube apparatus in which the inner and outer surfaces of the face panel are perfectly flattened (curvature radius is infinite), on the other hand, the aspect ratio of the beam spots at the H-axis end portions of the phosphor screen is lowered to 0.45.
The following is a description of the second problem.
In the color cathode ray tube apparatus, the deflection yoke is a substantial source of power consumption. In order to reduce this power consumption, it is essential to reduce power consumption by the horizontal deflecting coil of the deflection yoke, in particular. In order to solve this problem, a horizontal deflecting coil 75H having a bendless coil structure is used as shown in FIG.
11
. This bendless coil structure, compared with a bend-up coil structure, can make the deflection efficiency of electron beams on the neck side higher and the power consumption lower.
It is believed that the outside diameter of the bendless horizontal deflecting coil 75H on the neck side should be lessened to minimize the inside diameter of a magnetic core in order to reduce the power consumption. To attain this, the thickness of a neck-side flange portion
79
is reduced so that the tube-axis-direction length of the flange portion
79
is 20 mm or more, that is, the tube-axis-direction width of the flange portion
79
is made generous.
The flange portion
79
has a sectional area Sf shown in
FIG. 12A
along line A-A′ of
FIG. 11
, a sectional area Sm shown in
FIG. 12B
along line B-B′, and a sectional shape shown in
FIG. 12C
along line C-C′. Naturally, moreover, a maximum coil thickness Tf-max of the neck-side flange portion
79
shown in
FIG. 12C
is the same as a maximum coil thickness Tm-max of a main coil portion
80
shown in
FIG. 12B
near the neck side thereof. Likewise, a sectional area Sf on a plane that contains a tube axis Z of the neck-side flange portion
79
and a vertical axis V is the same as a sectional area Sm on a plane perpendicular to a tube axis Z of the main coil portion
80
, since the number of turns of the coil of the flange portion
79
is fixed.
FIG. 13
shows properties obtained as a result of analysis of pincushion-barrel magnetic field distributions on the respective tube axes of horizontally deflecting magnetic fields for the case where the horizontal deflecting coil 75H is formed of a bendless coil and the case where it is formed of a bend-up coil. In the diagram, continuous line a represents a property of the bendless coil, and broken line b represents a property of the bend-up coil. A pincushion-barrel magnetic field distribution on the tube axis of an ideal horizontally deflecting magnetic field is a property indicated by broken line b in the diagram, like that of the bend-up coil. Thus, a magnetic field distribution is preferred such that a barrel magnetic field c and a pincushion magnetic field d are formed on the neck side and the phosphor-screen side, respectively.
More specifically, the barrel magnetic field c on the neck side corrects a dislocation (HCR) between the center beam and the pair of side beams, having reached the horizontal axis end portions of the phosphor screen, in a positive direction (such that the center beam is situated nearer to the peripheral side of the phosphor screen than the center between the pair of side beams is). Further, the pincushion magnetic field d on the phosphor-screen side corrects a dislocation (XH) between the pair of side beams, having reached the horizontal axis end portions of the phosphor screen, in a negative direction (or under-convergence direction). Thus, the three electron beams on the phosphor screen can be converged.
In the neck-side portion of the bendless coil, however, coil elements
81
on the side of the horizontal axis H are formed so that their magnetic path length (length in the direction of the tube axis Z) has its maximum (Lm) on the neck side, as shown in FIG.
11
. On the other hand, coil elements
82
on the side of the vertical
Lee Wilson
Pillsbury & Winthrop LLP
Tran Chuc
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