EP0650180A1 - Tube d'affichage en couleur muni d'un blindage magnétique - Google Patents

Tube d'affichage en couleur muni d'un blindage magnétique Download PDF

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Publication number
EP0650180A1
EP0650180A1 EP94202987A EP94202987A EP0650180A1 EP 0650180 A1 EP0650180 A1 EP 0650180A1 EP 94202987 A EP94202987 A EP 94202987A EP 94202987 A EP94202987 A EP 94202987A EP 0650180 A1 EP0650180 A1 EP 0650180A1
Authority
EP
European Patent Office
Prior art keywords
shield
display tube
display screen
color display
long
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP94202987A
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German (de)
English (en)
Other versions
EP0650180B1 (fr
Inventor
Adrianus Johannes Van Mensvoort
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Koninklijke Philips NV
Original Assignee
Koninklijke Philips Electronics NV
Philips Electronics NV
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Filing date
Publication date
Priority claimed from BE9301127A external-priority patent/BE1007665A3/nl
Application filed by Koninklijke Philips Electronics NV, Philips Electronics NV filed Critical Koninklijke Philips Electronics NV
Priority to EP94202987A priority Critical patent/EP0650180B1/fr
Publication of EP0650180A1 publication Critical patent/EP0650180A1/fr
Application granted granted Critical
Publication of EP0650180B1 publication Critical patent/EP0650180B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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

Definitions

  • the invention relates to a color display tube comprising an envelope with a longitudinal axis, having a neck portion, a funnel portion and a window portion; an electron gun arranged in the neck portion, a display screen having a short central axis and a long central axis and a pattern of phosphor elements (for example in the form of rows) on the inner surface of the window portion; a color selection means arranged proximate to the display screen; a funnel-shaped shield of a magnetically permeable material having two long wall portions parallel to the long axis of the display screen and two short wall portions parallel to the short axis of the display screen, and an aperture at the gun-sided end, which aperture extends transversely to the longitudinal axis and constitutes an aperture for passing electron beams produced by the gun and scanning the display screen.
  • a color selection means is herein understood to mean, for example an apertured shadow mask sheet or a wire mask.
  • the ratio between the dimension of the long central axis and the dimension of the short central axis of the display screen characterizes the picture format.
  • Modern display tubes are provided with an internal magnetic shield to limit the deviation of the electron path due to the earth's magnetic field. A complete shielding is not possible due to an aperture which is required for the passage of the electron beam. A horizontally directed spot displacement caused by the lateral earth's magnetic field produces a risk of discoloration in the corners only (N effect).
  • the internal residual field can be influenced by means of an additional measure in such a way that the electron beam still passes the mask at the desired angle. This measure involves the use of a shield with "vertically" directed slits (situated in a plane through the longitudinal axis parallel to the short axis of the display screen). The internal residual field is then influenced in such a way that there is less spot displacement in the horizontal direction. The slits enhance the magnetic resistance in the shield in the horizontal direction so that there is more spot displacement in the vertical direction. However, for display tubes having phosphor rows extending in this direction this is not important because it does not lead to discoloration.
  • a problem of "vertically" directed slits is that the slit length is to be limited to ensure the mechanical stability of the shield so that an unacceptable spot displacement remains in the corners, particularly in large tubes.
  • extremely large tubes having, for example a picture diagonal of 41 cm or more, such as 80 cm FS ("Flat Square") and 36 inch WS ("Wide Screen”), i.e. the ratio between the short central axis of the display screen and the long central axis of the display screen is 9:16, it has been attempted to lengthen the slits to a maximum extent and to restore the resultant loss of mechanical strength by welding on strips of a non-ferromagnetic material which bridge the slits.
  • the following problems then occur.
  • a display tube of the type described in the opening paragraph is therefore characterized in that in the material of each of the long wall portions of the shield at least one area having a reduced magnetic permeability and extending in the longitudinal direction of the tube is present between the edge of the wall portion and the aperture.
  • a reduced magnetic permeability is understood to mean a lower permeability as compared with the magnetic permeability of conventional shielding materials for display tubes.
  • the reduced permeability is obtained by locally giving the material of the wall a treatment decreasing the permeability, as will be described hereafter.
  • the provision of slits in the material can therefore e dispensed with. This leads to a mechanically more stable display tube shield.
  • the process of making (stamping) a shield from one metal sheet benefits from the fact that slits are not necessary.
  • the cutting of slits in the formed (borol-shaped) shield is cumbersome.
  • An embodiment of the invention is characterized in that the area having a reduced magnetic permeability in each of the long wall portions has a magnetic permeability which is lower than the permeability in the rest of the relevant wall portion.
  • the invention may also be advantageously used in display tube shields which consist of a plurality of parts.
  • An embodiment of this type is characterized in that the magnetic shield comprises two separate short wall portions and two separate long wall portions whose ends are secured to each other so as to form a funnel-shaped shield, and in that the material of the long wall portions has a lower magnetic permeability than the material of the short wall portions. Since in this construction the long walls (the 6 o'clock and 12 o'clock walls, or the lower and upper walls) can entirely be made from a material having a lower magnetic permeability than the material of the short walls, a treatment for locally decreasing the magnetic permeability is not necessary.
  • multi-part shields comprise, for example assemblies of two U-shaped or L-shaped bent sheets (so-called folding type shield).
  • the magnetic permeability for lateral field of the walls can be reduced in different ways, for example, by
  • the above-mentioned treatments may be performed on the formed display tube shield. However, in some cases it is advantageous to manufacture the shields from sheet material which has previously undergone a local treatment decreasing the magnetic permeability.
  • the sheet material may be, for example magnetically permeable sheet material having an intermediate portion with a decreased magnetic permeability.
  • the areas of reduced permeability each include a plurality of sub-areas each extending in the longitudinal direction of the tube, said sub-areas being spaced by areas of unreduced permeability.
  • Fig. 1 shows a color display tube 1 having a glass envelope which comprises a neck portion 2 accommodating an electron gun system 3, a funnel-shaped portion 4 within which a magnetic shield 5 is arranged, and a window portion 6 whose inner surface is provided with a display screen 7, in this case having a pattern of phosphors arranged in rows parallel to a central axis of the display screen.
  • a shadow mask 8 is arranged opposite the display screen 7.
  • the shape of the magnetic shield 5 in display tube 1 roughly follows the contours of the funnel-shaped portion.
  • Modern display tubes are provided with an internal magnetic shield so as to limit the deviation of the electron path due to the earth's magnetic field. A complete shielding is not possible due to the (gun-sided) aperture required for passing the electron beam. In a lateral field only the horizontally directed spot displacement in the corners causes a risk of discoloration (N effect).
  • the internal residual field is influenced by means of an additional measure in such a way that the electron beam still passes the mask at the desired angle.
  • Fig. 2A shows an example of a shield 9 in a rear view, in which no residual field correction is realised.
  • Fig. 2B shows the associated spot displacement in the corners, as occurs in a lateral earth's magnetic field.
  • Fig. 2C shows a shield 5 with "vertically" directed slits 10a, 10b.
  • the internal residual field is influenced thereby in such a way that the spot displacement in the horizontal direction is reduced.
  • the slits increase the magnetic resistance in the shield in the horizontal direction so that there is more spot displacement in the vertical direction (Fig. 2D).
  • this is not important for display tubes having their electron guns arranged in one plane, because it does not cause discoloration.
  • Fig. 2E shows the shield 25 split completely magnetically. Overcompensation of the N effect may even occur in this case (see Fig. 2F).
  • a problem of the "vertically" directed slits is that the slit length is to be limited to ensure the mechanical stability of the shield. The consequence is that an unacceptable spot displacement remains in the corners, particularly in large tubes.
  • the magnetic permeability for the lateral component of the earth magnetic field in the area of the aforementioned vertically directed slits is reduced, for example by local mechanical deformation and/or by local diffusion of non-magnetic material.
  • values of the permeability for transverse field in the areas of reduced permeability which are smaller than turned out to produce practical effects.
  • Fig. 3 is a rear view of a sheet of iron 13 provided with a central aperture 12 from which a shield 5 (Fig. 1) is formed.
  • This treatment may be a mechanical deformation (for example, by means of a centre punch) or a deformation by means of a laser beam, or, very effectively, diffusion of non-magnetic material (for example Al, CrNi, Mn, C or N).
  • Fig. 4 is a perspective elevational view of a shield formed from sheet material having a long wall portion 18, a transversal area 14 of which has a decreased magnetic permeability so as to render the magnetic resistance in the lateral direction sufficiently large.
  • the width of the area 14 may range from some mm to some cm and even to a considerable part of the length L of the original sheet. In the latter case, widths of 5% or 10% or more of the length L of the original sheet may be concerned, dependent on the extent to which the permeability in the area 14 has been decreased.
  • ⁇ r represents the (reduced) relative permeability of area 14, t the thickness of the shield material, a the width of area 14, and L the (mean) length of the shield portion which includes area 14, measured in the direction of the applied (lateral) field.
  • the saturation magnetization should be high so as to remove much flux with little material.
  • the magnetic permeability must be high. This relates specifically to a permeability at demagnetization, referred to as the anhysteresis magnetization curve.
  • the anhysteresis ⁇ is much higher for low-carbon steel than the initial ⁇ of, for example ⁇ metal.
  • the coercive field should be low so as to dissipate minimal energy during demagnetisation. Yet, some coercive field should remain so as to maintain the pole distributions fixed during demagnetization.
  • the effect of diffusing Al on the permeability is shown in Fig. 5.
  • curve I shows the anhysteresis permeability ⁇ anh of a sheet of iron (VK steel thickness, for example between 0.05 and 0.8 mm) (after annealing ⁇ anh at a temperature of 750°C)
  • curve II shows the anhysteresis permeability ⁇ anh of the same sheet of iron (after annealing at a temperature of 720°C) in which Al is diffused at a temperature of 600°C in an area having a width of 4 cm.
  • the diffusion of Al may be combined, for example with a deformation step (for example, sandblasting).
  • Fig. 6 shows a shield 20 composed of two long portions 22, 24 and two short portions 21, 23 which are secured to each other, in this case by causing the ends 25, 25a; 26, 26a; 27, 27a and 28, 28a to overlap and to be welded to each other.
  • the long portions 22, 24 are made of a material having a decreased magnetic permeability as compared with the magnetic permeability of conventional display tube shield material, whereas the short portions 21, 23 are made of a conventional display tube shield material.
  • Fig. 7 shows a shield 30 which is composed of two U-shaped bent portions 31, 32 which are secured to each other, in this case by causing the ends 33, 33a and 34, 34a to overlap and to be welded to each other.
  • Portion 31 is treated for obtaining areas 37, 38 having a decreased magnetic permeability in the long walls and portion 32 is treated for obtaining areas 35, 36 having a decreased magnetic permeability in the long walls.
  • Fig. 8 shows a shield 40 which is composed of two L-shaped bent portions 41 and 42 which are secured to each other, in this case by causing the ends 43, 43a and 44, 44a to overlap.
  • the portions 41 and 42 are treated for obtaining areas 45, 46 having a decreased magnetic permeability in the long walls.
  • Fig. 9 is a plan view of a portion of a metal strip 47 of magnetically permeable material whose intermediate portion 48 is treated for obtaining a decreased magnetic permeability.
  • a plurality of display tube shields 49, 50 of the type according to the invention may be made from this sheet material.
  • the material which is conventionally used for display tube shields may be used for the strip 47, such as (cold-rolled) AK steel or low-carbon (cold-rolled) steel.
  • An internal shield has been referred to in the foregoing.
  • the invention is not limited thereto and may alternatively be used to advantage for an external magnetic shield.

Landscapes

  • Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
EP94202987A 1993-10-22 1994-10-14 Tube d'affichage en couleur muni d'un blindage magnétique Expired - Lifetime EP0650180B1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP94202987A EP0650180B1 (fr) 1993-10-22 1994-10-14 Tube d'affichage en couleur muni d'un blindage magnétique

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
BE9301127A BE1007665A3 (nl) 1993-10-22 1993-10-22 Kleurenbeeldbuis met magnetische afscherming.
BE9301127 1993-10-22
EP94200504 1994-02-28
EP94200504 1994-02-28
EP94202987A EP0650180B1 (fr) 1993-10-22 1994-10-14 Tube d'affichage en couleur muni d'un blindage magnétique

Publications (2)

Publication Number Publication Date
EP0650180A1 true EP0650180A1 (fr) 1995-04-26
EP0650180B1 EP0650180B1 (fr) 1997-09-17

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP94202987A Expired - Lifetime EP0650180B1 (fr) 1993-10-22 1994-10-14 Tube d'affichage en couleur muni d'un blindage magnétique

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EP (1) EP0650180B1 (fr)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2159386A1 (de) * 1970-12-07 1972-06-15 Rca Corp Magnetische Abschirmung für eine Kathodenstrahlröhre
EP0217473A2 (fr) * 1985-10-03 1987-04-08 North American Philips Corporation Tube image couleur muni d'un écran magnétique interne
EP0518431A1 (fr) * 1991-06-14 1992-12-16 Koninklijke Philips Electronics N.V. Procédé de fabrication d'un capot de blindage magnétique magnétiquement fendu pour un tube-image

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0570065B1 (fr) * 1992-05-15 1996-04-10 Koninklijke Philips Electronics N.V. Tube image en couleur muni d'un blindage magnétique interne

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2159386A1 (de) * 1970-12-07 1972-06-15 Rca Corp Magnetische Abschirmung für eine Kathodenstrahlröhre
EP0217473A2 (fr) * 1985-10-03 1987-04-08 North American Philips Corporation Tube image couleur muni d'un écran magnétique interne
EP0518431A1 (fr) * 1991-06-14 1992-12-16 Koninklijke Philips Electronics N.V. Procédé de fabrication d'un capot de blindage magnétique magnétiquement fendu pour un tube-image

Also Published As

Publication number Publication date
EP0650180B1 (fr) 1997-09-17

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