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
  • H01J29/07—Shadow masks for colour television tubes

Definitions

• the present invention relates to a color cathode ray tube having a substantially planar screen, and more specifically to the color selection mask fitted to such a tube.
• the invention finds its application in any type of tube comprising a mask for selecting colors and is more particularly suitable for tubes whose mask is produced by stamping held by a rigid frame on which it is secured.
• a conventional color cathode ray tube is composed of a vacuum glass envelope.
• the tube has, inside the envelope, a color selection mask located at a precise distance from the glass front face of the tube, front face on which are deposited arrays of red, green and blue phosphors to form a screen.
• An electron gun placed inside the tube, in its rear part, generates three electron beams in the direction of the front face.
• An electromagnetic deflection device generally placed outside the tube and close to the electron gun, has the function of deflecting the electron beams in order to make them scan the surface of the panel on which the phosphor networks are arranged. Under the influence of three electron beams each corresponding to a given primary color, the phosphor networks allow the reproduction of colored images on the screen, the mask allowing each determined beam to illuminate only the phosphor of the corresponding color. .
• the color selection mask must be placed and maintained during the operation of the tube in a precise position inside the tube.
• the mask holding functions are performed by means of a generally very rigid rectangular metal frame on which the mask is conventionally welded.
• the frame / mask assembly is mounted in the front face of the tube by means of suspension means welded to the frame and cooperating with pins inserted in the glass constituting the front face of the tube.
• the color selection mask is produced from a very thin metal sheet and has a surface called an active surface pierced with openings, produced by chemical etching and generally arranged in vertical columns; the active surface is surrounded by a non-perforated peripheral border; a skirt generally produced by stamping, borders the assembly, extending in a direction substantially perpendicular to the active surface.
• the mask is secured to the frame by welding at the level of the skirt.
• the tubes whose front face is more and more flat correspond to the current trend, until evolving towards completely flat front faces.
• the visibility for the spectator of an image formed on the screen of the tube is influenced by the shape of the glass front face of the tube, and in particular by the internal and external surfaces of said front face.
• the internal surface may have curvatures in particular to ensure the mechanical resistance of the glass envelope, curvatures resulting in excess thickness of glass visible to the viewer .
• New generations of tubes have made it possible to remedy this problem by having internal and external surfaces defined by very large radius of curvature.
• the surface of the mask must follow the shape of the internal part of the front face of the tube, so that their curvature is substantially identical.
• the color selection mask of a conventional tube has a surface defined by horizontal and vertical profiles with small radii of curvature, of the order of one or two meters in the central area; this curved surface can be represented by a complex polynomial expression and the low value of the radii of curvature ensures the mechanical rigidity of the mask surface.
• the radii of curvature defining the surface of the mask are large values.
• the surface of the mask facing the screen of the tube is found to be substantially flat and no longer makes it possible to have sufficient mechanical rigidity to maintain all of this surface at a predetermined distance from said screen.
• the mask becomes very sensitive to external vibrations; under the influence of shock or external mechanical vibrations, for example acoustic vibrations due to the loudspeakers of the television set in which the tube is inserted, the mask can then enter into vibration according to its natural frequency of resonance.
• the vibrations of the mask have the effect of modifying the landing zone of the electron beams on the screen of the tube, the points of impact of each beam then being offset with respect to the associated phosphor network, thus creating a discoloration of the image reproduced on the screen.
• the present invention relates to a cathode ray tube in colors whose mask, formed for example by stamping, has sufficient mechanical rigidity to avoid the drawbacks associated with a substantially flat surface.
• the color cathode ray tube according to the invention comprises:
• - a substantially planar rectangular front face
• - a rectangular color selection mask defined by two axes of symmetry, the horizontal major axis and the vertical minor axis intersecting at the center of an active surface pierced with orifices, said active surface being surrounded by a peripheral border, and by a skirt extending in a direction substantially perpendicular to the active surface, - a rectangular frame secured to the skirt of the mask by welding, characterized in that in a direction parallel to the major axis, the mean radius of curvature Rse of the active surface of the mask is greater than the mean radius of curvature Rbp of the peripheral border.
• FIG. 1 shows in section a cathode ray tube according to the invention with its various operating members
• FIG. 2 shows in perspective a color selection mask for a cathode ray tube according to the state of the art
• FIG. 3 illustrates in a sectional view the problems encountered by a mask whose surface is defined by a large radius of curvature along the major axis X
• FIG. 5 is a section along the major axis of a mask according to the invention.
• Figure 1 depicts a color cathode ray tube according to the invention.
• the tube comprises a glass envelope in which there is a high vacuum, the envelope being composed of a front face 2 and a rear part in the form of a funnel 4.
• a side skirt 1 surrounds the front face 2 which has an external face 10 substantially flat and rectangular.
• the major axis of the front face is a horizontal X axis
• the minor axis is a vertical Y axis
• the two axes X and Y intersect the main axis Z of the tube at right angles.
• the rear part 4 in the form of a funnel ends in a cylindrical part 3 inside which is arranged an electron gun 12.
• a luminescent screen 5, constituted by a network of bands of luminescent materials green, red and blue is deposited on the internal surface of the front face.
• FIG. 2 illustrates a mode production of a mask according to the state of the art in which the mask comprises an active surface 19 pierced with a multitude of openings arranged at regular intervals, the active surface being surrounded by a solid peripheral border 18; during the forming of the mask generally carried out by stamping a flat metal sheet, a skirt 17 is produced, extending in the direction of the main axis Z, substantially perpendicular to the border 18.
• the electron gun 12 emits three electron beams 11 towards the screen 5.
• the three beams are deflected by a magnetic deflection device 13 also called deflector.
• the colored images are displayed on the screen 5 by the horizontal and vertical scans of said screen by the electronic beams 11 passing through the openings 6 of the mask.
• the tube according to the invention has an outer surface 10 of the substantially planar front face.
• the current trend is to make the internal surface of said front face as flat as possible so as to minimize variations in glass thickness.
• the designer of the tube is then faced with the choice of using a mask with a large radius of curvature, or of using a mask whose curvature follows the curvature of the internal surface of the front face.
• the first solution has the advantage of offering significant mechanical rigidity and also the advantage that during the mask forming step, usually carried out by stamping, the mechanical stresses generated by the shape of the mask guarantee that this shape is maintained.
• the variations in distances between the active surface of the mask and the screen for different zones of this active surface induce deteriorations in the quality of the image formed on the screen, in particular on the peripheral zones, the impacts of the electron beams on the screen then being enlarged and deformed, relative to the center.
• the second solution makes it possible to minimize the variations in distance between the active surface of the mask and the screen; however, the mask will then have a substantially flat surface with little mechanical stress induced by this shape. As a result, once secured to the frame, the mask has areas of weakness as illustrated in FIG. 3.
• the profile 20 of a mask according to the state of the art for 4/3 format tube and screen diagonal equal to 68cm; the section is taken along the major axis X, FIG. 3 showing more particularly the area located near the vertical border, at a distance of between 155 mm and 250 mm relative to the center O of the mask; the mask surface has along the major axis X an average radius of curvature Rse greater than 3000 mm between the points A and A 'extremes of said active surface.
• Rse average radius of curvature
• This hollow has a width of more than 30mm in the horizontal direction X and extends in the vertical direction Y over practically the entire height of the active surface of the mask.
• This zone in addition to the fact that it will be able to expand more easily than other parts of the mask, introduces problems of sensitivity of the mask to vibrations due to the environment of the tube.
• the folds at the level of the mask skirt being areas of stiffening
• the large area masks for example for a tube diagonal greater than 63 cm, have large portions distant from these folding areas and are more likely to to be confronted with this problem.
• the invention intends to keep the advantages of keeping the active area of the mask substantially parallel to an internal surface of the front face defined by large radii of curvature, which results in keeping this active surface substantially flat, without having to suffer the drawbacks of mechanical strength of said surface.
• the invention uses the solid peripheral border parallel to the minor axis Y.
• this zone 18 was, in the state of the art, in continuity with the surface active 19 to the skirt 17, said new peripheral border 28 present in the direction parallel to the major axis a radius of curvature much larger than the radius of curvature of the active surface.
• the mean radius of curvature Rbp of the peripheral border at the level of the major axis, between the end points A and B of said border was of the same order of magnitude.
• the mean radius of curvature Rbp of the peripheral edge 28 is chosen to be equal to 62mm at the level of the major axis, between the end points A and C of said border.
• the radius of curvature of the peripheral edge 28, at the level of the major axis must be at least ten times smaller than the radius curvature of the active surface of the mask.
• the peripheral border has an even greater radius of curvature.
• the ratio between Rbp / Rse can, in the context of the invention, then be advantageously chosen between 0.01 and 0.05.
• the radius of curvature of the peripheral border 28 varies from point A representing the middle of the vertical side to the corner of the mask so that this radius decreases as we moves away from point A.
• FIG. 3 illustrates the improvements made by the invention.
• the profile of the active surface of the mask, 68 cm diagonal, in the area where it had a pronounced recess 21, has been modified in such a way that the new profile 30 obtained by implementing the invention only has a hollow 31 less than a tenth of a millimeter, complies with the tolerances allowed in the manufacture and operation of cathode ray tubes.
• the passage, in a direction parallel to the major axis X, of the active zone of the mask to the peripheral border 28 is carried out continuously so that the slopes of the tangents to the surface of the mask on the active surface and peripheral border are equal.
• the surface of the mask being defined by a polynomial expression of the type:
• Z (X A , Y) Z '(X A , Y) and ⁇ x Z (X A , Y) ⁇ ⁇ Z' (X A , Y) where A is a point of the border between the active area of the mask and the peripheral border 28.
• the invention is not limited to tubes having a flat front face.
• the invention has the advantage of reinforcing the mechanical strength of the mask, which minimizes the local expansions of the mask in the case of an image having very different light intensity zones. Indeed, in this case the active surface of the mask in the brightest areas heats up and tends to expand, which locally decreases the distance between the mask and the screen; this local expansion leads to variations in colors detrimental to the good rendering of the image.

Landscapes

• Electrodes For Cathode-Ray Tubes (AREA)
• Vessels, Lead-In Wires, Accessory Apparatuses For Cathode-Ray Tubes (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=31726546

Family Applications (1)

Country Status (10)

Family Cites Families (11)

• 2002
  • 2002-08-13 IT IT001824A patent/ITMI20021824A1/it unknown
• 2003
  • 2003-08-07 PL PL03373236A patent/PL373236A1/xx not_active Application Discontinuation
  • 2003-08-07 KR KR1020057001850A patent/KR20050030224A/ko not_active Withdrawn
  • 2003-08-07 CN CNB038180464A patent/CN1303636C/zh not_active Expired - Fee Related
  • 2003-08-07 MX MXPA05001685A patent/MXPA05001685A/es unknown
  • 2003-08-07 AU AU2003274234A patent/AU2003274234A1/en not_active Abandoned
  • 2003-08-07 EP EP03758217A patent/EP1529304A2/de not_active Withdrawn
  • 2003-08-07 JP JP2004528588A patent/JP2005536022A/ja active Pending
  • 2003-08-07 WO PCT/FR2003/002482 patent/WO2004017354A2/fr not_active Ceased
  • 2003-08-07 US US10/524,125 patent/US20060097618A1/en not_active Abandoned

Non-Patent Citations (1)

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