EP0650180B1 - Farbbildröhre mit einer magnetischen Abschirmung - Google Patents

Farbbildröhre mit einer magnetischen Abschirmung Download PDF

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Publication number
EP0650180B1
EP0650180B1 EP94202987A EP94202987A EP0650180B1 EP 0650180 B1 EP0650180 B1 EP 0650180B1 EP 94202987 A EP94202987 A EP 94202987A EP 94202987 A EP94202987 A EP 94202987A EP 0650180 B1 EP0650180 B1 EP 0650180B1
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EP
European Patent Office
Prior art keywords
display screen
long
shield
wall portions
funnel
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.)
Expired - Lifetime
Application number
EP94202987A
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English (en)
French (fr)
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EP0650180A1 (de
Inventor
Adrianus Johannes Van Mensvoort
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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/de
Publication of EP0650180A1 publication Critical patent/EP0650180A1/de
Application granted granted Critical
Publication of EP0650180B1 publication Critical patent/EP0650180B1/de
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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
  • 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.
  • the reduced permeability is obtained by locally giving the material of the wall a treatment decreasing the permeability, as will be described hereinafter.
  • 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.
  • the application EP-A-0 518 431 discloses a shield comprising an insert of non-magnetic material. But is does not speak about a shield of one material in which certain areas have been treated.
  • Colour display tubes having magnetic shields comprising 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, are known from DE-A-2 159 386.
  • 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 afore-mentioned 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.
  • ⁇ 2 a ⁇ t ln ( L a ) in which ⁇ 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 demagnetization. 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)

Claims (9)

  1. Farbbildröhre mit:
    - einer Hülle mit einer Längsachse, die einen Halsteil, einen Trichterteil und einen Fensterteil aufweist,
    - einem in dem Halsteil vorgesehenen Elektronenstrahlerzeugungssystem,
    - einem Bildschirm mit einer kurzen Zentralachse und einer langen Zentralachse und mit einem Muster aus Phosphorelementen (beispielsweise in Form von Zeilen) auf der Innenfläche des Fensterteils,
    - einem in der Nähe des Bildschirms vorgesehenen Farbselektionsmittel,
    einer trichterförmigen Abschirmung aus magnetisch durchlässigem Material mit zwei zu der langen Bildschirmachse parallelen langen Wandteilen und zwei zu der kurzen Bildschirmachse parallelen kurzen Wandteilen und mit einer am erzeugungssystemseitigen Ende vorgesehenen Öffnung, die sich quer zu der Längsachse erstreckt und eine Durchlaßöffnung für von dem Elektronenstrahlerzeugungssystem erzeugte, den Bildschirm abtastende Elektronenstrahlen bildet, dadurch gekennzeichnet, daß die langen Wandteile keine sich in der Längsrichtung erstreckenden Schlitze aufweisen und daß in dem Material jedes der langen Wandteile der Abschirmung mindestens ein sich in der Längsrichtung der Röhre zwischen dem Rand des Wandteils und der Öffnung erstreckendes Gebiet mit einer gegenüber dem restlichen Teil des langen Wandteils verringerten magnetischen Permeabilität befindet.
  2. Farbbildröhre nach Anspruch 1, dadurch gekennzeichnet, daß jedes Gebiet mit herabgesetzter Permeabilität eine Anzahl Hilfsgebiete hat, die sich in der Längsrichtung der Röhre erstrecken, wobei diese Hilfsgebiete durch Gebiete mit nicht verringerter Permeabilität voneinander gestrennt sind.
  3. Farbbildröhre mit:
    - einer Hülle mit einer Längsachse, die einen Halsteil, einen Trichterteil und einen Fensterteil aufweist,
    - einem in dem Halsteil vorgesehenen Elektronenstrahlerzeugungssystem,
    - einem Bildschirm mit einer kurzen Zentralachse und einer langen Zentralachse und mit einem Muster aus Phosphorelementen (beispielsweise in Form von Zeilen) auf der Innenfläche des Fensterteils,
    - einem in der Nähe des Bildschirms vorgesehenen Farbselektionsmittel,
    - einer trichterförmigen Abschirmung aus magnetisch durchlässigem Material mit zwei zu der langen Bildschirmachse parallelen separaten langen Wandteilen und zwei zu der kurzen Bildschirmachse parallelen separaten kurzen Wandteilen und mit einer am erzeugungssystemseitigen Ende vorgesehenen Öffnung, die sich quer zu der Längsachse erstreckt und eine Durchlaßöffnung für von dem Elektronenstrahlerzeugungssystem erzeugte, den Bildschirm abtastende Elektronenstrahlen bildet, wobei die Enden der zwei separaten kurzen Wandteile und der zwei separaten langen Wandteile aneinander befestigt sind, damit die trichterförmige Abschirmung erhalten wird, dadurch gekennzeichnet, daß das Material der langen Wandteile eine niedrigere magnetische Permeabilität aufweist als das Material der kurzen Wandteile.
  4. Farbbildröhre nach Anspruch 1, dadurch gekennzeichnet, daß die magnetische Abschirmung zwei U-förmig abgewinkelte Metallplatten aufweist, deren Enden aneinander befestigt sind zum Bilden einer trischterförmigen Abschirmung, wobei jede U-förmig abgewinkelte Metallplatte zwei Teile aufweist, die sich parallel zu der langen Bildschirmachse erstrecken und wobei das Gebiet mit herabgesetzter magnetischer Permeabilität sich in den genannten Teilen erstreckt.
  5. Farbbildröhre nach Anspruch 1, dadurch gekennzeichnet, daß die magnetische Abschirmung zwei L-förmig abgewinkelte Metallplatten aufweist, deren Enden aneinander befestigt sind zum Bilden einer trichterförmigen Abschirmung, wobei jede L-förmig abgewinkelte Platte einen Teil hat, der sich parallel zu der langen Bildschirmachse erstreckt und wobei das Gebiet mit herabgesetzter magnetischer Permeabilität sich in dem genannten Teil erstreckt.
  6. Farbbildröhre nach Anspruch 1, dadurch gekennzeichnet, daß die Gebiete mit herabgesetzter magnetischer Permeabilität nach der Bildung der Trichterform verwirklicht worden sind.
  7. Farbbildröhre nach Anspruch 1, dadurch gekennzeichnet, daß die Gebiete mit herabgesetzter magnetischer Permeabilität vor der Bildung der Trichterform verwirklicht worden sind.
  8. Farbbildröhre nach Anspruch 1, dadurch gekennzeichnet, daß der Fensterteil eine Bilddiagonale von wenigstens 41 cm hat.
  9. Farbbildröhre nach Anspruch 1, dadurch gekennzeichnet, daß das Verhältnis zwischen der kurzen zentralen Achse des Bildschirms und der langen zentralen Achse des Bildschirms 9 : 16 beträgt.
EP94202987A 1993-10-22 1994-10-14 Farbbildröhre mit einer magnetischen Abschirmung Expired - Lifetime EP0650180B1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP94202987A EP0650180B1 (de) 1993-10-22 1994-10-14 Farbbildröhre mit einer magnetischen Abschirmung

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
BE9301127 1993-10-22
BE9301127A BE1007665A3 (nl) 1993-10-22 1993-10-22 Kleurenbeeldbuis met magnetische afscherming.
EP94200504 1994-02-28
EP94200504 1994-02-28
EP94202987A EP0650180B1 (de) 1993-10-22 1994-10-14 Farbbildröhre mit einer magnetischen Abschirmung

Publications (2)

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

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0570065A1 (de) * 1992-05-15 1993-11-18 Koninklijke Philips Electronics N.V. Farbbildröhre mit innerer magnetischer Abschirmung

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA942370A (en) * 1970-12-07 1974-02-19 Terry M. Shrader Cathode ray tube with four-piece internal magnetic shield and method of making same
DE3677310D1 (de) * 1985-10-03 1991-03-07 Philips Corp Farbbildroehre mit innerer magnetischer abschirmung.
EP0518431B1 (de) * 1991-06-14 1995-08-30 Koninklijke Philips Electronics N.V. Verfahren zum Herstellen einer magnetisch gespalteten innenmagnetischen Abschirmkappe für Bildwiedergaberöhre

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0570065A1 (de) * 1992-05-15 1993-11-18 Koninklijke Philips Electronics N.V. Farbbildröhre mit innerer magnetischer Abschirmung

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