Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
  • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
  • H01J29/06—Screens for shielding; Masks interposed in the electron stream
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
  • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
  • H01J29/06—Screens for shielding; Masks interposed in the electron stream
  • H01J29/07—Shadow masks for colour television tubes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2229/00—Details of cathode ray tubes or electron beam tubes
  • H01J2229/0007—Elimination of unwanted or stray electromagnetic effects
  • H01J2229/003—Preventing or cancelling fields entering the enclosure
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2229/00—Details of cathode ray tubes or electron beam tubes
  • H01J2229/07—Shadow masks
  • H01J2229/0727—Aperture plate
  • H01J2229/0766—Details of skirt or border

Definitions

• This invention generally relates to cathode ray tubes (CRTs) and, more particularly, to a shielding arrangement for a tensioned mask/frame assembly and an internal magnetic shield (IMS).
• CTRs cathode ray tubes
• IMS internal magnetic shield
• a color cathode ray tube includes an electron gun for forming and directing three electron beams to a screen of the tube.
• the screen is located on the inner surface of the faceplate panel of the tube and is made up of an array of elements of three different color-emitting phosphors.
• a shadow mask which may be either a formed mask or a tension mask having strands or a membrane with slitted apertures with or without tie bars, is located between the electron gun and the screen. The electron beams emitted from the electron gun pass through apertures in the shadow mask and strike the screen causing the phosphors to emit light so that an image is displayed on the viewing surface of the faceplate panel.
• a tension mask comprises a set of strands that are tensioned onto a mask frame to reduce their propensity to vibrate at large amplitudes under external excitation. Such vibrations would cause gross electron beam misregister on the screen and would result in objectionable image anomalies to the viewer of the CRT.
• Another source of electron beam misregister and beam motion is residual magnetism within the CRT. To remove this residual magnetism, a degaussing process is performed.
• One of the controlling parameters for optimizing magnetic performance of a tube is degauss recovery.
• the frame In order to maintain tension in the tension mask, the frame has to have high yield stress, which is usually accompanied by poor magnetic properties, i.e., high coercive force and low permeability. This makes degaussing the frame difficult, provides poor flux coupling during the degaussing process, and leaves very high residual magnetic fields inside the CRT. These residual magnetic fields cause the CRT to have very high electron beam misregister, poor purity and poor picture quality. It is desirable to develop an improved mask frame assembly that allows tension masks to be uniformly degaussed.
• the present invention therefore provides a cathode ray tube (CRT), comprising: a tensioned mask frame for supporting a tension mask inside the CRT at a cantilevered edge thereof, a tension mask mounted on the tension mask frame at the cantilevered edge; and an internal magnetic shield mounted on the tension mask frame. At least one of the tension mask and the internal magnetic shield have an extension extending along the tensioned mask frame to a point proximate or contacting the other of the tension mask and the internal magnetic shield to provide magnetic coupling between the tension mask and the internal magnetic shield independent of the tensioned mask frame.
• CTR cathode ray tube
• Figure 1 is a sectional plan view of a typical cathode ray tube
• Figure 2 is a front view of a tension mask/frame assembly from the cathode ray tube of Figure 1 , showing a partial cut-away of the tension mask
• Figure 3 is a perspective sectional view of an existing tension mask/frame assembly and internal magnetic shield arrangement
• Figure 4 is a sectional side view of a tension mask frame assembly and internal magnetic shield arrangement according to an exemplary embodiment of the present invention
• Figure 5 is a sectional side view of a tension mask/frame assembly and internal magnetic shield arrangement according to another exemplary embodiment of the present invention
• Figure 6 is a sectional perspective side view of a tension mask frame assembly and internal magnetic shield arrangement according to yet another exemplary embodiment of the present invention
• Figure 7 is a sectional perspective side view of a tension mask/frame assembly and internal magnetic shield arrangement according to yet another exemplary embodiment of the present invention
• Figure 8 is a sectional side view of a tension mask/frame
• FIG. 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 funnel 5 has an internal conductive coating (not shown) that extends from an anode button 6 toward the panel 3 and to the neck 4.
• the panel 3 comprises a substantially cylindrical or a rectangular viewing faceplate 8 and a peripheral flange or sidewall 9, which is sealed to the funnel 5 by a glass frit 7.
• a three-color phosphor screen 12 is carried by the inner surface of the faceplate 3.
• the screen 12 is a line screen with the phosphor lines arranged in triads, each of the triads including a phosphor line of each of the three colors.
• a color selection tension mask assembly 10 is removably mounted in predetermined spaced relation to the screen 12.
• An electron gun 13, shown schematically by dashed lines in Figure 1 is centrally mounted within the neck 4 to generate and direct three inline electron beams, a center beam and two side or outer beams, along convergent paths through the tension mask assembly 10 to the screen 12.
• the tube 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 which cause the beams to scan horizontally and vertically in a rectangular raster over the screen 12.
• the tension mask assembly 10, as shown in Figure 2 has a metal frame
• the tension mask assembly 10 includes an apertured shadow mask 30 that contains a plurality of metal strips (not shown) having a multiplicity of elongated slits (not shown) therebetween that parallel the minor axis of the shadow mask 30.
• the long sides 22, 24 have a cantilever edge 25 extending toward the screen 12.
• the tension mask 30 is attached to the cantilever edge 25 of the long sides 22, 24 of the tensioned mask frame.
• the attachment may be performed, for example, by welding.
• the IMS 50 is attached to the long sides of the frame 20 at a location removed from the tension mask 30.
• the long sides 22, 24 of the frame 20 comprise L-shaped bars or angles formed by two legs at a right angle to each other with the cantilever edge 25 on the end of one leg and the IMS 50 attached to the other leg.
• the existing shielding arrangement provides magnetic flux coupling through the tensioned mask frame 20.
• the IMS 50, tension mask 30 and frame 20 are made from low carbon steel or iron-nickel alloys. Magnetic shielding and degaussing ability of the tension mask 30, tensioned mask frame 20, and IMS 50 system are improved if each of the components has high anhysteretic permeability and low coercivity.
• the tensioned mask frame 20 must have high yield stress to provide the rigidity necessary for proper function. This high yield stress is usually accompanied by poor magnetic properties, e.g., high coercivity and low permeability.
• the tensioned mask frame 20 increases the reluctance of the IMS/frame/mask assembly. Additionally, a residual magnetic field is retained after degaussing at the interface of the tension mask 30 and the tensioned mask frame 20 that is difficult to remove and leads to beam misregister. Conventional degaussing is performed using a special degaussing coil placed close to the IMS 50, and will degauss the IMS 50 adequately.
• the tension mask 30 is attached to the long sides 22, 24 of the frame 20 at the cantilever edges 25.
• the IMS 50 has extensions 55, 56 formed on the end of the IMS 50 at a right angle to one another corresponding to the surfaces of the long sides 22, 24 of the tensioned mask frame 20.
• the extension 55 extends along the tensioned mask frame 20 to a location proximate the cantilevered edge 25, where the tension mask 30 is attached to the tensioned mask frame 20.
• the extension 55 may, but does not have to contact the tension mask 30.
• the IMS 50 of this embodiment may be attached to the tensioned mask frame, only at the extension 56 for ease of access during assembly. It should be noted that the extension 55 need not touch the IMS 50 to provide magnetic coupling.
• the tension mask 30 and the IMS 50 may be magnetically coupled through a small gap with minimal magnetic flux leakage.
• the IMS 50 of this embodiment may be attached to the tensioned mask frame, only at the extension 56 for ease of access during assembly.
• one or more joining members 60 are attached to the tension mask 30 at the cantilevered edge 25 of the tensioned mask frame 20 and are attached to the IMS 50 at a location removed from the cantilevered edge 25.
• the joining members 60 may be formed of a material having a high magnetic permeability, such as steel.
• the joining members 60 may be very thin to minimize the risk of contact with the walls of the tube or other structures within the tube.
• the ends of the joining members 60 may be flat or bent on either or both sides to aid contact with the tension mask 30.
• the joining members 60 may be attached to the tensioned mask frame 20, but such attachment is not required.
• a flexible mesh 70 comprising a ferromagnetic material extends between the tension mask 30 and the IMS 50.
• the mesh 70 may extend under the tension mask 30 and the IMS 50 as shown in Fig. 6.
• the IMS 70 may extend around the corner of the angled long side 22, 24 of the tensioned mask frame, as shown in Fig. 6.
• the mesh 70 may extend around the corner of the angled long side 22, 24, allowing additional clearance.
• the mesh 70 may be attached to the tension mask 30 and IMS 50 using attachment means, such as welding, and may be welded to the tensioned mask frame 20 together with the tension mask 30 and IMS 50.
• attachment means such as welding
• one or more tabs 80 are formed on the end of the IMS 50, such that they extend toward the tension mask 30 when the IMS 50 is mounted on the tensioned mask frame 20.
• the tabs 80 may vary in size and spacing to provide adequate magnetic coupling between the IMS 50 and the tension mask 30.
• the tabs 80 may extend under the tension mask 30 at cantilevered edge 25 or may be attached to the tensioned mask frame 20 proximate cantilevered edge 25. While tabs 80 are shown extending from the IMS 50, tabs may alternatively be formed that extend from the tension mask 30 and extend toward the IMS 50.
• FIG. 1 In another alternative embodiment of the present invention, as shown in
• a coating 90 is applied to the tensioned mask frame 20 between the attachment locations for the tension mask 30 and the IMS 50.
• the coating comprises a material with a high magnetic permeability, providing magnetic coupling of the tension mask 30 to the IMS 50.
• the coating 90 may extend onto the cantilevered edge 25 of the tensioned mask frame 20 and to a location on the tensioned mask frame 20 removed from the cantilevered edge 25, such that it contacts the tension mask 30 and the IMS 50 when they are attached to the tensioned mask frame 20.
• the coating 90 may extend proximate the tension mask 30 and IMS 50 but not be in contact with either or both.
• the tension mask has extensions 35 which extend beyond the cantilevered edges 25. These extensions 35, which are formed as part of the tension mask 30 are then positioned extending along the tensioned mask frame 20 to a position proximate or in contact with the IMS 50, removed from the cantilevered edges 25, where the extensions 35 are attached to the tensioned mask frame 20.
• the IMS 50 and extensions 35 may be attached to the tensioned mask frame 20 using common attachment means, which may be, for example, spot welds.
• an extension 100 is attached to the long sides 22, 24 of the frame 20, extending from the IMS 50 along the inside surface of the frame toward the mask 30.
• the extension 100 comprises a material having high magnetic permeability, as compared to the frame 20.
• the extension 100 may be a separate part attached by press fitting, for example onto the edge opposite the cantilevered edge 25.
• the extension 100 can be inserted from the interior of the tension mask frame 20 providing enhanced shielding of the frame 20. It should be noted that the extension 100 may contact the mask 30, but physical contact is not required, as long as the extension 100 extends to a point proximate the mask 30.

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• Electrodes For Cathode-Ray Tubes (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=35463116

Family Applications (1)

Country Status (5)

Citations (3)

Family Cites Families (2)

• 2004
  • 2004-08-12 CN CNA2004800431295A patent/CN1993797A/zh active Pending
  • 2004-08-12 WO PCT/US2004/026160 patent/WO2005119726A1/en active Application Filing
  • 2004-08-12 JP JP2007515031A patent/JP2008500696A/ja not_active Withdrawn
  • 2004-08-12 EP EP04780924A patent/EP1754239A4/de not_active Withdrawn
  • 2004-08-12 MX MXPA06013702A patent/MXPA06013702A/es not_active Application Discontinuation

Patent Citations (3)

Non-Patent Citations (1)

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