EP0085238A2 - Tubes à rayons cathodiques à écran de phosphore à plusieurs couches - Google Patents

Tubes à rayons cathodiques à écran de phosphore à plusieurs couches Download PDF

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Publication number
EP0085238A2
EP0085238A2 EP82306565A EP82306565A EP0085238A2 EP 0085238 A2 EP0085238 A2 EP 0085238A2 EP 82306565 A EP82306565 A EP 82306565A EP 82306565 A EP82306565 A EP 82306565A EP 0085238 A2 EP0085238 A2 EP 0085238A2
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EP
European Patent Office
Prior art keywords
deflection
faceplate
electron beam
expansion
mesh
Prior art date
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Granted
Application number
EP82306565A
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German (de)
English (en)
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EP0085238B1 (fr
EP0085238A3 (en
Inventor
Ronald G. Reed
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HP Inc
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Hewlett Packard Co
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Publication of EP0085238A3 publication Critical patent/EP0085238A3/en
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    • 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
    • H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
    • H01J29/70—Arrangements for deflecting ray or beam
    • H01J29/72—Arrangements for deflecting ray or beam along one straight line or along two perpendicular straight lines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J31/00—Cathode ray tubes; Electron beam tubes
    • H01J31/08—Cathode ray tubes; Electron beam tubes having a screen on or from which an image or pattern is formed, picked up, converted, or stored
    • H01J31/10—Image or pattern display tubes, i.e. having electrical input and optical output; Flying-spot tubes for scanning purposes
    • H01J31/20—Image or pattern display tubes, i.e. having electrical input and optical output; Flying-spot tubes for scanning purposes for displaying images or patterns in two or more colours
    • H01J31/208—Image or pattern display tubes, i.e. having electrical input and optical output; Flying-spot tubes for scanning purposes for displaying images or patterns in two or more colours using variable penetration depth of the electron beam in the luminescent layer, e.g. penetrons

Definitions

  • This invention is concerned with improvements in or relating to cathode ray tubes (CRT).
  • CRT cathode ray tubes
  • a typical prior art cathode ray tube comprises an evacuated envelope having a principal longitudinal axis, electron gun means for producing a beam of electronics travelling along that axis; deflection means (which may be magnetic) responsive to a deflection signal and disposed about the longitudinal axis for causing the path of the electron beam to diverge therefrom by an amount corresponding to the amplitude of the deflection signal; variable acceleration means for receiving a variable acceleration potential and for accelerating and decelerating the deflected electron beam in accordance therewith; and luminescent faceplate means located in the path of the accelerated and deflected electron beam for producing luminous indications at locations excited by the impact of the electron beam upon luminescent faceplate means.
  • the color of the trace is controlled by varying the velocity at which the electrons in the electron beam strike the phosphors on the faceplate.
  • variation in velocity is produced by changing the acceleration potential that- the electron beam is subjected to.
  • this is achieved by varying a single voltage applied to both the funnel and faceplate.
  • split anode CRT it is achieved by varying a separate voltage applied to only the faceplate, while a fixed voltage is constantly applied to the funnel. In either case, presently available phosphors require a change of several thousand volts.
  • a long-standing problem with beam penetration color CRT's is that their deflection factors change by as much as forty percent as the trace color is changed. As the color is changed the resulting different electron velocities along the longitudinal ( ) axis of the CRT afford different amounts of time for radial velocities induced by the deflection mechanism to influence the location of the point of impact upon the faceplate; the slower the longitudinal velocity the greater the radial displacement, and the lower the deflection factor (v/cm). If left unaccounted for, these changes cause images written in one color to differ in size from those written in another. Ideally, images would be the same size regardless of the color they were written in.
  • any compensation for the-horizontal and vertical deflection factors must also produce appropriate composite amounts of compensation along diagonal directions, such as the major diagonals from the center of the faceplate to the corners thereof. Improper diagonal compensation will produce either barrel or pin cushion distortion of the displayed pattern.
  • tubes having an expansion mesh the degree of horizontal and vertical expansion can be controlled by variations in the strength of the electric field surrounding the mesh. Such variations in expansion can produce the required deflection factor compensation.
  • an expansion mesh does not simply affect only the horizontal and vertical radial velocities in isolation; each radial direction is expanded. Therefore, a proper amount of expansion variation must be selected and produced for each radial direction to ensure distortion free deflection factor compensation.
  • the present invention seeks to achieve this end by providing, in the cathode ray tube, deflection factor compensation means disposed about a port of the path of the electron beam subsequent to the deflection means and preceding the variable acceleration means, for receiving a variable compensation voltage whose amplitude corresponds to the amplitude of the variable acceleration potential, and for creating an electric field that alters the path of the deflected electron beam to prevent changes in the location of impact that would otherwise result from changes in the variable acceleration potential.
  • the present invention provides, in the cathode ray tube, deflection factor compensation means, disposed about a portion of the path of the electron beam preceding the magnetic deflection means, for receiving a variable compensation voltage whose amplitude corresponds to the amplitude of the variable acceleration potential, and for creating an electric field that varies the velocity of the electron beam prior to its deflection to prevent changes in the location of impact that would otherwise result from changes in the variable acceleration potential.
  • the luminescent faceplate means comprises a coating of beam penetration phosphor and the variable acceleration means comprises a conductive coating upon a surface of the luminescent faceplate means, the cathode ray tube further comprising a conductive funnel coating for receiving a fixed acceleration potential, the conductive funnel coating being located between and electrically isolated from the deflection factor compensation means and the variable acceleration means.
  • the deflection factor compensation means comprises a conductive coating upon the inside surface of the envelope and is electrically connected to the variable acceleration means, the cathode ray tube further comprising an expansion mesh located in the path of the deflected electron beam and producing amounts of expansion that vary in accordance with the electric field between the expansion mesh and the deflection factor compensation means, the variation in expansion preventing changes in deflection factor as the variable acceleration potential changes in amplitude.
  • the deflection factor compensation means comprises a generally annular shape having four lobes aligned with the major axes of deflection and four intervening concavities aligned with the major diagonals of the luminescent faceplate means.
  • variable compensation voltage increases in the positive direction as the variable acceleration voltage decreases in the positive direction.
  • the present invention further provides a method of compensating color induced deflection factor changes in an electrostatically deflected beam penetration color CRT having an expansion mesh, the method comprising the steps of generating an electron beam having a longitudinal axis and an axial velocity therealong; deflecting the electron beam by inducing radial velocities therein at right angles to the longitudinal axis; expanding the deflected electron beam by passing it through an expansion mesh to increase the radial velocities; varying an acceleration potential to vary the axial velocity of the electron beam by selected amounts, including none at all, as it approaches the CRT faceplate; the method being further characterized by carrying out the step of varying the gradient and curvature of the electric field surrounding the expansion mesh to change in each radial direction the amount of radial acceleration and compensate for changes in trace position caused by changes in axial and radial velocities near the faceplate produced by variations in the acceleration potential.
  • the present invention further provides a method of compensating for color induced deflection factor changes in a beam penetration color CRT not having an expansion mesh comprising the step of maintaining an essentially constant transit time by varying the axial velocity of the electron beam in the vicinity of the region of deflection in an opposite sense to the color producing changes in velocity of the electrons occurring prior to their striking the faceplate.
  • the present invention further provides a method of correcting pattern distortion in a CRT produced by an expansion mesh comprising the step of altering the shape of the electric field between the expansion mesh and the funnel coating by shielding the expansion mesh by selected amounts in different radial directions with a correspondingly shaped correction lens element between the expansion mesh and the funnel coating.
  • the present invention further provides a correction lens element for a CRT having an expansion mesh, the correction lens element being characterized by the provision of an annular conductive surface centered about a longitudinal axis and having an edge whose shape resembles the projection of the outline of the faceplate onto the expansion mesh through a line connecting the outline to a point on the longitudinal axis.
  • an electrostatically deflected split anode beam penetration color CRT including a correction lens centered about the axis of the tube and located in the vicinity of an expansion mesh.
  • the correction lens is a conductive region on the inside of the conical portions at the entrance to the funnel region of the CRT envelope.
  • the correction lens is electrically connected to the split anode faceplate, and both receive the same switched high voltage.
  • the shape of the correction lens is chosen to interact with the effect of the expansion mesh to produce compensatory changes in the horizontal, vertical and diagonal radial velocities (i.e., change the amount of expansion in those directions).
  • a magnetically deflected split anode beam penetration CRT has its horizontal and vertical deflection factors compensated by a correction lens centered about the axis of the tube and located'on the inside of the neck of the CRT near the entrance end of the deflection yoke.
  • the voltage on the correction lens is changed in conjunction with the high voltage for the faceplate.
  • the axial velocity of the electron beam in the magnetic deflection region is varied to compensate for changes in the axial velocity in the region of the faceplate. This varies the amount of deflection in the magnetic deflection region to produce constant overall deflection factors.
  • FIG. 1 An electrostatically deflected beam penetration color C RT 1 constructed in accordance with a preferred embodiment of the invention is depicted in Figure 1.
  • an expansion mesh (not itself visible) supported upon a "mesh can” 5.
  • a four-lobed slightly conical conductive correction lens element 3 Upon the inside of the CRT's envelope, near the expansion mesh and at the entrance of the "funnel", is deposited a four-lobed slightly conical conductive correction lens element 3.
  • the correction lens 3 is electrically connected to the "split anode” faceplate by an external conductor (not shown).
  • a dielectric coated gap 4 of essentially constant width separates the conductive correction lens 3 from the conductive coating 2 inside the remaining portion of the CRT funnel.
  • the funnel coating 2 is conventional, except that it complements the shape of the correction lens 3 through the dielectric coated gap 4.
  • the funnel coating 2 is electrically isolated from the faceplate of the CRT 1.
  • the CRT 1 is intended for use in a small high quality color graphic display device. It has a viewing area approximately 12.7 cms wide (“horizontal”) by 10.2 cms high (“vertical”) and is approximately 38 cms in length. To promote clarity in depicting the various shapes, the CRT 1 has been illustrated as rotated one quarter turn about its longitudinal axis, so that the spatial relation between the horizontal and vertical axes appears interchanged. In this way the broader side of the tube is depicted, allowing a less cramped rendition of the illustrated features.
  • Figure 2 depicts a portion of a conventional split anode beam penetration color CRT 7.
  • the interior of the funnel portion of the envelope 8 is coated with a conductive coating 10 extending from ahead of the expansion mesh 11 to fairly near the faceplate.
  • a separate conductive region 9 is deposited over the phosphors upon the faceplate.
  • the conductive funnel coating 10 is connected to a source of fixed high voltage, while the conductive faceplate coating 9 is connected to a source of variable high voltage.
  • Dotted lines 12a-d represent ray traces for various amounts of deflection a-d, each with the faceplate operating at plus fifteen kilovolts (for a green trace).
  • the ray traces 12a-d form an undistorted pattern produced at some deflection factor.
  • the solid line ray traces 13a-d produced under conditions differing only in that the faceplate voltage has been lowered to plus nine kilovolts (for a red trace).
  • the ray traces 12a-d and 13a-d are essentially the same for the first two thirds of their travel after leaving the expansion mesh. Each is accelerated by substantially the same amount by the conductive coating 10, and the radial velocities, once induced by the deflection plates and expansion mesh, remain unchanged during that portion of travel.
  • the velocity of the electrons in the direction parallel to the longitudinal axis remains, once accelerated by conductive coating 10, essentially constant until the electrons strike the faceplate.
  • Their radial velocities remain constant after leaving the region of the expansion mesh.
  • the ray traces 12a-d are thus essentially straight lines.
  • Figure 3 is a top cut-away view of a CRT 14 similar to that of Figure 2, but constructed in accordance with Figure 1.
  • conductive coatings 17 (corresponding to correction lens 3 of Figure 1), 15 (corresponding to funnel coating 2) and 16 (the "split anode” at the faceplate).
  • Any conventional means may be used to make electrical contact with the correction lens coating 17, including resilient fingers, "pop throughs” and metal “anode buttons”.
  • a layer 18 of insulating "green dag” is applied over the gap 4 separating conductive coatings 17 and 15.
  • a similar insulating layer is applied over the separation between the funnel coating 15 and the faceplate coating 16. In the present example the width of the gap 4 is approximately one centimetre.
  • a conductor 19 connects the funnel coating 15 to a fixed high voltage power supply, which in the present example is plus fifteen kilovolts.
  • Another conductor 20 connects both the faceplate coating 16 and the correction lens coating 17 to a source of variable high voltage, which in the present example can range from plus nine to plus fifteen kilovolts, including various values inbetween.
  • an expansion mesh 21 located at the exit end of an electron gun assembly 22.
  • the interior portion of the envelope upon which the correction lens 17 is deposited is made up of two conical surfaces.
  • the left-hand portion of the funnel in the vicinity of the gap 4 forms a portion of an eight degree cone, while the adjoining portion just to the left (the so-called "reducer") forms a portion of a thirty-eight degree cone.
  • a convenient point of reference in this Figure, for things to be depicted in subsequent Figures, is the circle (in three dimensions) formed by the intersection of the two frusto-conical surfaces.
  • the tip of the expansion mesh 21 extends beyond the plane of that circular line of intersection, and along the longitudinal axis of the tube, by approximately 0.5 cms.
  • the shape of the narrowest opening in the thirty-eight degree portion of the correction coating 17 is of little concern, if any, since it is so far removed from the electrons emanating from the expansion mesh 21. That shape may conveniently be circular.
  • the shape of the intersection of the two conical surfaces has already been described as circular.
  • the shape of the remaining right-hand edge (as viewed in Figure 3) of the eight degree conical surface of the correction lens 17 and the corresponding shape of the left hand edge of the conductive funnel coating 14, are not so easily described.
  • a four-lobed shape is involved. This four-lobed shape will be described in terms of the shape of the gap 4 between the correction lens 17 and the funnel coating 15. This is because the three dimensional shape of the gap 4 is much more readily depicted than the shape of either of the things it separates. It is clear, however, that each of the remaining shapes can be clearly and unambiguously understood and appreciated from an understanding of the shape of the gap 4.
  • Figures 4A and 4B show, for the particular CRT of Figures 1 and 3, the exact shape of the gap 4. What is shown is a planar shape, that if constructed upon a suitable medium, such as a sheet of paper or mylar, then cut out, joined at its ends and bent along the dotted lines, forms the actual three dimensional shape of the gap 4. That is, Figures 4A and 4B are essentially a recipe for creating a shape, most of which lies on the surface of an eight degree cone.
  • dotted line 23 is a circle of radius 27.18 cms, and corresponds to the circular line of intersection between the two cones.
  • the angle 6 is approximately fifty-one degrees, and was chosen to produce an eight degree cone.
  • To construct the shape of Figure 4B proceed as follows: Construct adjacent segments of concentric large circles of the following radii: 26.67cms; 27.18cms; 27.69cms; 28.83cms; 29.85cms. Each segment must subtend the same 51° central angle. Divide the central angle into four equal portions corresponding to the horizontal and vertical axes. Sub-divide each of the four equal portions to correspond to the location of its major diagonal (determined by the aspect ratio).
  • the angle a is less than ⁇ owing to the differing symmetries about the different major diagonals.
  • a tube with a square faceplate a would equal ⁇ .
  • the nine radial lines defining the eight portions. Locate along these radial lines the indicated centers of the various small circle segments of the specified radii, and draw the small circles. Each of these small circles is tangential to an associated large circle, at a point along the associated radial line. Draw the tangent lines connecting the successive small circles along the inner and outer edges of the shape. Mark the shape H, V and D as shown. Cut out the resulting shape and join the corresponding edges along the first and ninth radial. Bend inwards those portions of the shape of radius 0.635cans that line within the circle of radius 27.18 cms.
  • Figures 5A and 5B show the orientation of the gap 4 in the CRT of Figures 1 and 3. This is important, since it will be observed that the lobes marked V are one 6.35 millimeters longer than those marked H.
  • Both the conductive correction lens and the conductive funnel coating are formed by vapor deposition of aluminium.
  • a masking fixture having the shape of the gap is created from thin stainless steel. It is held in place by gravity against the interior of the reducer. It is thin enough to sufficiently conform to any slight eccentricity in the conical surfaces.
  • the bottle, less faceplate and electron gun, is placed in the aluminization fixture and the conductive coatings (3 and 2, or 17 and 15) are deposited. Afterwards, the coating 18 of insulating green dag may be applied by any convenient means, including hand painting with a brush.
  • Figure 6 illustrates the compensatory influence the correction lens 17 has upon the electron beam as it leaves the expansion mesh 21.
  • dotted lines 28a-d represent ray traces for various amounts of deflection while the split anode faceplate 16 is at the same high voltage (+l5kv) as the conductive funnel coating 15.
  • Solid line ray traces 29a-d represent the same amounts of deflection when the voltage at the split anode faceplate is lowered to +9kv. Note that for each of the various amounts of initial deflection a-d the final point of impact upon the faceplate remains unchanged, despite the change in faceplate voltage.
  • the correction lens 17 When the faceplate 16 is operated at the same potential as the funnel coating 15, the correction lens 17 exhibits the same potential, also. The net effect is as if the entire tube had one unified interior conductive coating, with neither a separate split anode nor a separate correction lens.
  • the expansion mesh 21 operates as it normally does. That is, there is a high gradient electric field between the region just outside the expansion mesh (at say +lOOv) and the adjacent portion of the bottle (+15kv). This high gradient field produces maximum "magnification" by the expansion mesh 21.
  • the concomitant.reduction of potential at the correction lens 17 reduces the gradient of the electric field surrounding the expansion mesh 21.
  • the reduction is chosen to be an amount that is restored by the progressive axial deceleration and slight radial acceleration experienced by the electron beam as it approaches the faceplate.
  • the amount of reduction automatically varies correctly as the voltage applied to the faceplate is changed, even if by arbitrary amounts.
  • Figure 6 shows a portion of a top view of the tube, so what is seen is horizontal deflection.
  • the above remarks concerning the operation of the correction lens 17 tacitly assume that there is no accompanying vertical deflection. That is, pattern correction along a diagonal is not considered. Such consideration is, however, necessary to prevent substantial pattern distortion in off-axes directions.
  • the potential on the surface of the expansion mesh is approximately +lOOv.
  • the principal potential outside the expansion mesh is that possessed by the funnel coating 2 or 15.
  • the purpose of the correction lens is first, to act at high voltages like the funnel coating in a conventional split anode beam penetration CRT, and second, to act at low voltages to diminish the effective value of V 2 in Eq. (1), by partially shielding the expansion mesh 21 from the influence of the high voltage on the funnel coating through an intervening region at the lower voltage.
  • the degrees of demagnification in the horizontal and vertical axes produced upon leaving the expansion mesh in any given radial location are functions of at least two things: (1) the width of the correction lens in that radial direction; and (2), how far from the center of expansion mesh along that radial direction the beam leaves the mesh.
  • the second condition is important for the same reason as the first: it influences the degree of separation of that portion of the mesh from the high voltage funnel coating 2 or 15, and therefore the effective value of V 2 - Note that condition (2) (how far from the center on the mesh the beam exits) is essentially a function of the extent the deflection plates have influenced the beam before it passes through the expansion mesh.
  • the correction lens described herein can be shaped so that for any given tube exact correction occurs, that shape depends in part upon the size and shape of the CRT envelope. If little or no attention is paid to tolerances for the envelope, a given shape may not correct exactly each tube wherein it is used, even though those tubes are each of the same type and are each directly replaceable by the other. If adequate tolerances for the size and shape of the envelope are not to be maintained, it may be desirable to equip the deflection amplifier circuitry with an adjustable amount of electrically variable gain, anyway. However, such variability need only amount to a change in gain of a few percent, and would still be easier than providing a forty percent change. The exact amount of the gain variation would be adjusted in a calibration process once the CRT was installed, as its amount would be a function of that particular CRT.
  • Figure 7 shows a cut-away view of a conventional electrostatically deflected CRT 30 having an expansion mesh 31.
  • the expansion mesh 31 is at about +100v, while the funnel coating 32 and faceplate 33 are each at 15kv.
  • the various isopotential lines for the electric field between the expansion mesh 31 and the rest of the tube are found closest to the expansion mesh 31.
  • the majority of the expansion performed for ray traces 34a-d occurs by the time an electron in the ray reaches the 11.9v isopotential line. All but a very small amount of expansion is complete by the time the 13.9kv isopotential line is reached. From that point on the electronics..are essentially in a drift space and their trajectories are almost perfect straight lines.
  • Figure 8 shows a cut-away view of a CRT 35 similar to the CRT 30 of Figure 7, save for the introduction of a split anode faceplate 38 isolated from the funnel coating 37.
  • the expansion mesh 36 of Figure 8 is the same as the expansion mesh 31 of Figure 7, and is surrounded by (perhaps not exactly, but virtually) the same electric field. Therefore the same amounts of expansion for given amounts of deflection occur, up until the end of the drift space, for both the CRT 35 of Figure 8 and CRT 30 of Figure 7.
  • the drift space of the CRT 35 of Figure 8 ends well before the faceplate 38, upon encountering the curved isopotential lines of the electric field in the vicinity of the reduced voltage faceplate 38. It is in this region that the electrons in the various rays 39a-d are slightly accelerated radially and greatly decelerated axially.
  • the various legends Aa - Ad indicate the amounts of error in the resulting trace positions.
  • Figure 9 shows how an instance of the invention operates to modify and combine aspects of Figures 7 and 8.
  • An electrostatically deflected beam penetration color CRT 40 includes a conductive correction lens element 41 electrically connected to a split anode faceplate 43. Between the two, and electrically isolated from each, is a conductive funnel coating 42.
  • the left-hand portion of Figure 9 shows the isopotential lines of the electric field surrounding the expansion mesh 44. In contrast with the corresponding fields of Figures 7 and 8, the field around the expansion mesh 44 of Figure 9 exhibits a lesser field gradient and a lesser degree of curvature.
  • rays 45a-d are each expanded by a lesser amount than their counterparts 39a-d of Figure 8.
  • the axial deceleration and slight radial acceleration encountered by rays 45a-d as they pass through the isopotential lines surrounding the faceplate 43 counteract the reduced amounts of expansion to produce points of impact that are the same as for rays 34a-d of Figure 7 (assuming a-d represent the same amounts of initial deflection).
  • the curved isopotential lines of the electric field surrounding the expansion mesh 44 and those in the vicinity of the faceplate 43 can each be considered a lens.
  • the "power" of each lens is determined by the difference in voltage of the elements that form the lens, and by the geometries of those elements. Since the voltages for elements 41 and 43 are equal, vary together, and are always greater than the mesh voltage and less than or equal to the funnel voltage, decreasing the voltage difference (between elements 41 and 44) for the "expansion mesh lens” lowers the power of that lens, while that same change in potential (but now between elements 42 and 43) increases the power of the "faceplate lens". The change in the powers of these lenses are complicated functions of the voltage differences. Very roughly speaking, the power is the ability of the field to accelerate or decelerate electrons.
  • the function describing the decrease in radial acceleration by the mesh lens produced by a drop in correction element voltage is similar in nature to the functions describing the deceleration in axial velocity and increase in radial velocity by the faceplate lens.
  • the mesh lens function can be "scaled" to match combined effects of the faceplate lens functions, not just at the extreme lowest voltage, but at intervening values as well. Thereafter, variations in one lens are automatically offset by a complementary variation in the other lens, for any given change in voltage.
  • the electric field between the funnel coating 42 and the faceplate 43 has its greatest curvature at the corners of the faceplate. That is, the lines of electric force (not the isopotential lines) emanating from the funnel coating to the faceplate are crowded together as the envelope bends in the region where the surfaces that are the "vertical side” and'horizontal side” meet to form an edge.
  • the faceplate lens therefore has its greatest "power" in the corners. Nevertheless, it appears fairly certain that for the particular tube of the present example this did not contribute significantly to pattern distortion experienced with certain early correction element shapes.
  • the described shape for the corrector lens element 41,17,3 does indeed produce a nominal amount of demagnification for maximally deflected diagonal rays, commensurate with that for other directions of deflection.
  • the shape of the edge of the correction lens element either is or resembles a projection of the rectangular shape of the faceplate onto the conical surface adjoining the funnel portion of the CRT envelope.
  • a right section of a right eight degree cone of dimensions corresponding to the CRT envelope in the vicinity of the expansion mesh. Select a first point lying along the axis of the conical section, probably one closer to the narrower end of the section than to the wider end.
  • the principles of the present invention have been employed in-modifying the behavior of an expansion mesh in another electrostatically deflected CRT having an expansion mesh.
  • That CRT was a monochrome CRT operating at a fixed acceleration potential, and was of a design that did not originally include an expansion mesh. It was desired to put a standard and readily available expansion mesh into the tube to increase its deflection sensitivity. The desired increase was achieved, but at the expense of a perceptible amount of pattern distortion caused by an improper amount of expansion along diagonal directions.
  • the distortion was removed by the use of a correction lens element essentially similar to that which has been described, but operated at a fixed potential.
  • correction lens element described herein need not necessarily be a conductive coating upon the inside of the CRT envelope, although that will often be the most convenient method.
  • Other means influencing the trajectory of the electron beam could be used, including shapes formed from sheet metal and suitably disposed about the path of the beam.
  • metal tabs were attached to the mesh can by insulating standoffs.
  • Figure 10 shows a magnetically deflected beam penetration color CRT 46 having a split anode faceplate 47 separated from a funnel coating 48.
  • a conductor 49 connects the split anode faceplate 47 to a first variable high voltage source (not shown), while another conductor 50 connects the funnel coating 48 to a fixed source of high voltage (also not shown).
  • An electron gun assembly (not shown) in the neck of the CRT 46 supplies a focused electron beam 51.
  • a magnetic deflection yoke assembly 52 contains both horizontal and vertical deflection coils, to be driven by suitable deflection amplifiers (not shown).
  • trace color changes are achieved by altering the positive high voltage applied to the split anode faceplate.
  • the funnel coating operates at a fixed high voltage of plus twenty kilovolts, and that the split anode faceplate operates over the range of from plus ten kilovolts to plus twenty kilovolts.
  • a broken line 53 denotes a ray trace for an initial given amount of deflection of the electron beam 51, assuming that the faceplate is raised to its full potential of plus twenty thousand volts.
  • a dotted line 54 denotes the resulting ray trace, for the same given amount of initial deflection as for the ray trace 53 when the split anode faceplate 47 is lowered to plus ten thousand volts.
  • the deflection process induces a radial velocity into the electron beam.
  • the reduced faceplate voltage reduces the axial velocity of the beam as it nears the faceplate.
  • the resulting increase in transit time allows the radial velocity to produce a greater displacement prior to impact, resulting in greater deflection.
  • a correction lens 55 in the form of an annular conductive surface located inside the neck of the CRT 46, centered on the path of the electron beam 51 and axially positioned prior to where the electron beam 51 enters- the region of magnetic deflection produced by the yoke 52.
  • a conductor 56 connects the correction lens 55 to a second variable high voltage source (not shown).
  • the first and second high voltage sources vary simultaneously in the following manner.
  • a positive high voltage applied to the correction lens 55 increases.
  • the increase in voltage to the correction lens axially accelerates the electron beam 51 by the amount required to maintain a constant transit time.
  • the illustrated embodiments of the present invention each provide a beam penetration color CRT whose horizontal and vertical deflection factors automatically and continuously adjust themselves to remain constant despite arbitrary changes in the applied high voltage that are within the range corresponding to maximum color change. Furthermore the CRT having an expansion mesh has a constant deflection factor that is also free of color induced barrel or pin cushion distortion.

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  • Vessels, Lead-In Wires, Accessory Apparatuses For Cathode-Ray Tubes (AREA)
EP19820306565 1982-01-19 1982-12-09 Tubes à rayons cathodiques à écran de phosphore à plusieurs couches Expired EP0085238B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US34068382A 1982-01-19 1982-01-19
US340683 1982-01-19

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EP0085238A2 true EP0085238A2 (fr) 1983-08-10
EP0085238A3 EP0085238A3 (en) 1985-07-17
EP0085238B1 EP0085238B1 (fr) 1990-07-11

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JP (1) JPS58126653A (fr)
DE (1) DE3280208D1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2255441A (en) * 1991-04-18 1992-11-04 Mitsubishi Electric Corp Cathode -ray tube screening arrangement

Citations (8)

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US2681426A (en) * 1952-03-06 1954-06-15 Motorola Inc Deflection system
US2803781A (en) * 1952-08-13 1957-08-20 Philips Corp Device comprising a cathode-ray tube
FR1550161A (fr) * 1966-08-11 1968-12-20
GB1162149A (en) * 1965-12-27 1969-08-20 Polaroid Corp Improvements relating to Electronic Display Systems
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FR2091547A5 (fr) * 1970-05-14 1972-01-14 Siemens Ag
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GB2255441A (en) * 1991-04-18 1992-11-04 Mitsubishi Electric Corp Cathode -ray tube screening arrangement
US5357166A (en) * 1991-04-18 1994-10-18 Mitsubishi Denki Kabushiki Kaisha Cathode-ray tube having alternating electric field reduction device
GB2255441B (en) * 1991-04-18 1995-06-21 Mitsubishi Electric Corp Cathode-ray tube having alternating electric field reduction device

Also Published As

Publication number Publication date
JPH0360148B2 (fr) 1991-09-12
JPS58126653A (ja) 1983-07-28
EP0085238B1 (fr) 1990-07-11
DE3280208D1 (de) 1990-08-16
EP0085238A3 (en) 1985-07-17

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