WO2006091267A2

WO2006091267A2 - Cathode ray tube having shadow mask with instant geometric thermal transition compensation

Info

Publication number: WO2006091267A2
Application number: PCT/US2005/046672
Authority: WO
Inventors: Louis Emmanuel Matalon
Original assignee: Thomson Licensing
Priority date: 2005-02-24
Filing date: 2005-12-22
Publication date: 2006-08-31
Also published as: WO2006091267A3

Abstract

Disclosed is a cathode ray tube having a shadow mask with doming reduction features. The shadow mask has a limited mask border and skirt region and has instant geometric compensation feature. The limited mask border and skirt region permits the border to quickly heat and expand and cool and contract as freely as the mask. The instant geometric compensation feature translates any movement due to thermal expansion of the mask to the mask border and skirt in such a manner to maintain electron beam register. The instant geometric compensation feature requires certain portions of the skirt be in contact with the mask frame and angle away from the longitudinal axis of the shadow mask. As the mask expands, the angled portions of the skirt in contact with the mask frame flex to diminish the angle with the longitudinal axis and cause the mask to move towards a luminescent screen to such an extent that electron beam register is effectively maintained.

Description

CATHODE RAY TUBE HAVING SHADOW MASK WITH INSTANT GEOMETRIC THERMAL TRANSITION COMPENSATION

Cross-Reference to Related Application

This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application Serial No. 60/656,447, entitled "Instant Geometric Thermal Transition Compensation of the Shadow Mask within a Color CRT," filed February 24, 2005, which is incorporated by reference herein in its entirety.

Field of the Invention

The invention relates to cathode ray tubes and, more particularly, to a shadow mask in a cathode ray tube having doming reduction features.

Background of the Invention

It is well recognized that shadow masks for cathode ray tubes (CRTs) heat up during CRT operation because approximately 82 % of the electron beams that would otherwise bombard the screen are intercepted by the shadow mask. This is pointed out in U.S. Pat. No. 5,045007, issued to Edwards et al. It is further pointed out therein that shadow masks without special heat dissipative coatings such those in U.S. Pat. No. 4,884,004, issued to Deal et al., will have the kinetic energy of the intercepted electrons transferred to it in the form of thermal energy, thereby increasing shadow mask temperatures and causing thermal expansion of the shadow mask. The coating materials described in U.S. Pat. No. 4,884,004 are effective in reducing doming and blister warpage when the coating is applied to the electron gun-facing surface of the shadow mask. The problem with the application of such coatings is that it increases CRT manufacturing costs and requires additional processing.

Also, because the shadow mask is usually supported by a frame of substantial mass, the temperature of the mask during initial warm-up will rise more rapidly in the center than at the edge. This causes the mask to dome, so that the center portion of the PU050033

mask moves toward the screen, while the edge of the mask maintains its spacing with the screen. Furthermore, when a large number of electrons impinge upon a local area of the mask, to create high picture brightness, localized doming or blister warpage occurs unless temperature equilibrium in the plane of the mask is reestablished with sufficient speed. Both blister warpage and overall doming of the mask result in color errors due to electron beam misregister with the phosphor elements of the screen.

Another approach to minimize doming and blister warpage has been to simply use materials which have low coefficients of the thermal expansion. When used, these materials (INVAR, for example), dramatically reduce the propensity for the mask to dome or otherwise warp. The problem with low expansion materials is that such materials are significantly more expensive than the typical high expansion materials (such as AK steel) normally used for masks.

The thermal problems of doming and warping are of particular significance for flat screen CRTs, which have become a preferred product in the color display market. Flat screen CRTs contain shadow masks that are flatter than the curved screen CRTs. Thermal gradients applied to a flatter shadow mask cause more out-of-plane motion (i.e., doming) than in the curved screen CRTs. However, flatter CRTs are already significantly more expensive than curved screen CRTs, thereby making the above-mentioned approaches to addressing thermal effects even more cost prohibitive for flat screen CRTs.

In light of the increased costs associated with using coatings or low expansion materials, a practical, cost effective solution is needed to produce CRTs having masks with a decreased propensity for doming or warping.

Summary of the Invention

Disclosed is a cathode ray tube having a shadow mask with doming reduction features. The shadow mask has a limited mask border and skirt region and has instant geometric compensation feature. The limited mask border and skirt region permits the border to quickly heat and expand and cool and contract as freely as the mask. The instant geometric compensation feature translates any movement due to thermal expansion of the mask to the mask border and skirt in such a manner to maintain electron PU050033

beam register. The instant geometric compensation feature requires certain portions of the skirt be in contact with the mask frame and angle away from the longitudinal axis of the shadow mask. As the mask expands, the angled portions of the skirt in contact with the mask frame flex to diminish the angle with the longitudinal axis and cause the mask to move towards a luminescent screen to such an extent that electron beam register is effectively maintained.

Brief Description of the Drawings

The invention will now be described by way of example with reference to the accompanying drawings.

Figure 1 is a profile of a CRT according to the invention.

Figure 2 is a perspective view of a long side of the mask according to the invention.

Figure 3 is a perspective view of a short side of the mask according to the invention.

Figure 4 is plan view of the front of the mask according to the invention.

Figure 5 is a sectional view of the mask and mask frame according to the invention during CRT operation.

Figure 6 is a sectional view of a prior art mask and mask frame during CRT operation.

Detailed Description of the Invention

Figure 1 shows a cathode ray tube (CRT) 1 having a glass envelope 2 comprising a rectangular faceplate panel 3 and a tubular neck 4 connected by a funnel 5. The faceplate panel 3 consists of a viewing faceplate 8 and a peripheral flange or sidewall 10 with a panel seal edge 15. The panel seal edge 15 is sealed to a funnel seal edge 17 by a glass frit 7. The funnel 5 has an internal conductive coating (not shown) that extends from an anode button 6 toward the faceplate panel 3 and to the neck 4. A three-color phosphor screen 20 can be carried by an inner surface of the faceplate panel 3. The screen 20 may be, for example, a line screen of phosphor lines arranged in triads. A PU050033

mask support frame assembly 21 is removably mounted in predetermined spaced relation to the screen 20. A glass mount 16 containing an the electron gun assembly 13, shown schematically by dashed lines in Figure 1, is centrally mounted within the neck 4 and generates and directs three inline electron beams, a center beam and two side or outer ^~ beams, along convergent paths through the mask frame assembly 21 to the screen 20. The mask frame assembly 21 includes the mask 31 and a mask frame 25 shown in Figure 5.

The CRT 1 is designed to be used with an external magnetic deflection yoke 14 shown in the neighborhood of the funnel-to-neck junction. When activated, the yoke 14 subjects the three beams to magnetic fields that cause the beams to scan horizontally and vertically in a rectangular raster over the screen 20. The CRT further can include an implosion protection band 12 applied to the sidewall 10 of the panel 3.

Now with reference to Figures 2 and 3, the mask will be described in greater detail. The mask 31 is general maintained in a frame 25 (not shown in Figures 2 and 3) which surrounds the periphery of the mask 31. The mask 31 has two long sides 34 and two short sides 35. The long sides 34 include long side skirts 32L and the short sides 35 include short side skirts 32S as shown in Figures 2 and 3. hi the figures, the mask 31 is shown having a face portion which includes an aperture portion 28 and a mask border 30. The long side skirt 32L has a predominant long side skirt height 37, wherein the majority of the long side skirt 32L has the predominant long side skirt height 37 and a minority of the long side skirt 32L has a height that exceeds the long side skirt height 37. The minority portions of the long side skirt 32L are referred to as long side elongated regions 33.

The short side skirt 32S has a predominant short side skirt height 38, wherein the majority of the short side skirt 32S has a predominant short side skirt height 38 and a minority of the short side skirt 32S has a height that exceeds the short side skirt height 38_* The mask 31 can also have corner tabs 39 which may be welded to a mask frame 25. The minority portions of the short side skirt 32S are referred to as short side elongated regions 41.

Figure 4 shows the mask in plan view, showing the mask border 30 and the aperture portion 28. The border can have a border width 42 that either varies or remains PU050033

constant around the periphery of the aperture portion. The mask border 30 is characterized as being the front surface portion of the mask 31 that is outside of the active array region of the luminescent screen 20.

In a preferred embodiment of the invention the border width 42, the predominant long side skirt height 37, and a predominant short side skirt height 38 are to be kept as small as possible. Keeping these dimensions as small as possible is a first fold means of preventing electron beam misregister due to thermal conditions of the mask. Having the mask border width being kept low allows the border 30 to quickly heat and cool as fast as the mask, thereby giving the border the opportunity to move laterally within a plane parallel to the X-Y plane of the CRT 1. Essentially it has been observed that when the border 30 contains less material the border 30 heats and cools as rapidly as the aperture portion 28 of the mask 31. As such, as the aperture portion 28 expands because of the temperature changes, the border 30 expands, which tends to reduce doming and warpage of the mask 31. When the mask border 30 is too massive, the border 30 acts as a cold ring and remains rigid and in its original position, resulting in the aperture portion 28 being forced up and toward the screen 20, while the border 30 remains stationary, hi a preferred embodiment, the mask border 42 should be no larger than 5 % of the diagonal dimension of the aperture portion 28 of the mask 31. Additionally, the invention includes minimizing the mask border 30 and skirt 32 together so that the entire border is directly heated with over-scan of the electron beam.

With respect to the predominant skirt heights 37, 38, when these are sufficiently low, conductive and radiation heat loss of the mask border 30 is reduced. If the skirt 32 is massive and/or long, it will act as a heat sink and draw thermal energy from the mask border, thereby making the mask border 30 behave differently than the aperture portion 28 from the expansion and contraction perspective. The predominant skirt heights 37, 38 should be less than 2.0 cm. However, in a preferred embodiment, the predominant skirt heights 37, 38 are 1.0-1.5 cm.

Another feature of the invention is an instant geometric compensation of the mask position to offset quick peripheral expansion. The instant geometric compensation feature is associated with the mask skirt having a flare that is angled away from the longitudinal PU050033

axis of the CRT 1. Figure 5 A shows angle 51. This creates an immediate geometric compensation of the shadow mask position during thermal transitions. This is achieved by contacting the fonned shadow mask 31 to the frame 25 with mask skirt 32. Figure 5 shows the advantages of the invention during tube operation. Figure 5 A shows the configuration of the mask skirt 32 in contact with the mask frame 25 when the CRT is just turned on and no temperature change in the mask has occurred. This feature of the invention has the skirt 32 being in contact with the interior portion of the mask frame 25. Figure 5B, however, shows the dynamics of the novel instant geometric compensation when the CRT is in operation and the mask 31 has experience expansion because of increased temperatures. What happens is that as the electron beams 50 heats the mask and causes the aperture portion 28 and the border portion 30 to expand in the direction of element 52 in Figure 5B, wherein the direction of element 52 is away from the longitudinal axis Z of the CRT 1. Element 52 is essentially a lateral force due to the expansion. Now with the skirt portions being angled away from the longitudinal axis and extending from the border portion, the skirt 32 moves in the direction of element 52, providing the spring force of the skirt portion toward the longitudinal axis is less than a lateral force of element 52. As the skirt flexes, the mask aperture portion 28 and the border 30 rise toward the screen 20. However, because the aperture portion 28 and th& border 30 both move toward the screen and away from the longitudinal axis, the amount of electron misregister is acceptable. In Figure 5B, elements 28', 30' and 32' represents the original positions of the mask aperture portion 28, border portions 30, and the skirt 32, respectively, before expansion occurred. Figure 5B shows that the landing of the green electron beams 50 on the green phosphor (G) on the screen 20 is essentially maintained. Also, with the instant geometric compensation feature, compensation is also ■ provided during a cooling transition. When power is reduced, the aperture portion 28 and border 30 shrink, in a reversible fashion, maintaining electron beam register in the process. ,

However, in sharp contrast, as shown in Figure 6, a prior art system does have electron beam misregister. In the prior art system the skirt 32' is not angled and is in contact with the mask frame 25. Here, in the prior art, the mask border is more rigid PU050033

because of it configuration (i.e., flat contact against the frame 25). As such, when expansion of the aperture portion 28 occurs the aperture portion will buckle up, causing the aperture portion to dome towards the screen with relatively little expansion away from the longitudinal axis Z. As a result the electron beams 50 from the electron gun propagate through the mask aperture such that misregister can occur as shown by element 60 in Figure 6B. hi Figure 6B, elements 28' and 30' represents the original positions of the mask aperture portion 28 and border portions 30, respectively, before expansion occurred.

In one embodiment, the skirt portions each extends from the border portion, wherein the skirt portion at the opposing short sides has an angle that decreases from a midpoint portion to end portions. This configuration is particularly useful for standard CRTs with the conventional vertical lines screens. In this case, the angle on the short side should be above 2 degrees. However, it is preferred to have the angle range from 8 degrees to 12 degrees, where the angle is 12 degrees near the major axis X and the angle decreases to 8 degrees at the end.

For CRTs with transposed scanning (i.e., the phosphor line structure is horizontal and the electron beams are vertically oriented), the preference is to make the skirt portion at the opposing long sides have an angle that increase from a midpoint portion to end portions. It is also effective to have the angle on the long side be at 12 degrees near the minor axis Y and decrease to 8 degrees near the corners.

In another embodiment, the skirt portions on the long and short sides each extend from the border portion and faces the interior surfaces of the opposing sides of the mask frame, wherein skirt portion at the opposing long sides have an angle that increases from a long side midpoint portion to long side end portions and the skirt portion 32 at said short sides 35 having an angle that decreases from a short side midpoint portion to short side end portions. It is preferred to have the angle range from 8 degrees to 12 degrees, where the angle is 12 degrees near the major axis X and the angle decreases to 8 degrees at the end. It is also effective to have the angle on the long side be at 2 degrees near the minor axis Y and increase to 8 degrees near the corners. PU050033

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The scope of the invention is intended to include configurations wherein only portions of the skirt are angled or instances where only two sides have angles. In each of the embodiments, the mask can be attached to the mask frame by welding the corner tabs 39 to the frame. Further, the mask can be attached to the frame by welding elongated portions 33 to the mask frame. However, it is preferred to only weld centrally located elongated portions 41 to the frame as shown in Figure 2 (noted by weld marks "xxx").

Claims

PU0500339 What is claimed is:

Claim 1. A cathode ray tube including a panel having a luminescent screen on an interior surface of the panel, a mask frame assembly suspended in the panel, and a longitudinal axis being positioned at the center of the panel and being perpendicular to the luminescent screen at the center, the mask frame assembly comprising the frame having four sides, wherein at least one pair of opposing sides have interior surfaces facing the longitudinal axis, and a formed shadow mask including a face portion and skirt portions, wherein: the face portion faces the luminescent screen and has a central region with electron transmitting apertures and a border portion surrounding the central region, and the skirt portions each extends from the border portion and faces the interior surfaces of the opposing sides, parts of the skirt portions are angled away from the longitudinal axis and have regions away from the border portions contacting the interior surfaces, wherein the spring force of the skirt portion toward the longitudinal axis is less than a lateral force of the face portion, perpendicular to the longitudinal axis and directed away from the longitudinal axis at operational temperatures.

Claim 2. A cathode ray tube including a panel having a luminescent screen on an interior surface of the panel, a mask frame assembly suspended in the panel, and a longitudinal axis being positioned at the center of the panel and being perpendicular to the luminescent screen at the center, the mask frame assembly comprising a frame having two opposing short sides and two opposing long sides, wherein the opposing short sides have interior surfaces facing the longitudinal axis, and a formed shadow mask including a face portion and skirt portions, wherein: the face portion faces the luminescent screen and has a central region with electron transmitting apertures and a border portion surrounding the central region, and the skirt portions each extends from the border portion and faces the interior surfaces of the opposing sides, parts of the skirt portion of one pair of opposing sides are angled away from the longitudinal axis. PU050033

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Claim 3. The cathode ray tube of claim 2, wherein the one pair of opposing sides having angled skirt portions is the short sides.

Claim 4. The cathode ray tube of claim 3, wherein the angle of the skirt, with respect to the longitudinal axis, decreases from near the major axis to end portions.

Claim 5. The cathode ray tube of claim 3, wherein the angles of the skirt, with respect to the longitudinal axis, are at least 2 degrees.

Claim 6. The cathode ray tube of claim 4, wherein the angle of the skirt, with respect to the longitudinal axis, decreases from 12 degrees to 8 degrees.

Claim 7. The cathode ray tube of claim 2, wherein the one pair of opposing sides having angled skirt portions is the long sides.

Claim 8. The cathode ray tube of claim 7, wherein the angle of the skirt, with respect to the longitudinal axis, decreases from near the minor axis to end portions.

Claim 9. The cathode ray tube of claim 7, wherein the angles of the skirt, with respect to the longitudinal axis, are at least 2 degrees.

Claim 10. The cathode ray tube of claim 8, wherein the angle of the skirt, with respect to the longitudinal axis, decreases from 12 degrees to 8 degrees.

Claim 11. The cathode ray tube of claim 2, wherein the border portion has a width that does not exceed 5% of the longitudinal dimension of the aperture portion of the mask,.

Claim 12. The cathode ray tube of claim 3, wherein the border portion has a width that does not exceed 5% of the longitudinal dimension of the aperture portion of the mask. PU050033

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Claim 13. The cathode ray tube of claim 7, wherein the border portion has a width that does not exceed 5% of the longitudinal dimension of the aperture portion of the mask.

Claim 14. The cathode ray tube of claim 3, wherein the skirt on the short side has a predominant height that does not exceed 2 cm.

Claim 15. The cathode ray tube of claim 7, wherein the skirt on the long side has a predominant height that does not exceed 2 cm.

Claim 16. The cathode ray tube of claim 12, wherein the skirt on the short side has a predominant height that does not exceed 2 cm.

Claim 17. The cathode ray tube of claim.13, wherein the skirt on the long side has a predominant height that does not exceed 2 cm.

Claim 18. The cathode ray tube of claim 3, wherein the luminescent screen has vertical phosphor line structure and electrons beams have a slow vertical scan and a rapid horizontal scan.

Claim 19. The cathode ray tube of claim 7, wherein the luminescent screen has horizontal phosphor line structure and electrons beams have a rapid vertical scan and a slow horizontal scan.