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
  • H01J29/46—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
  • H01J29/701—Systems for correcting deviation or convergence of a plurality of beams by means of magnetic fields at least
• • 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
  • H01J29/76—Deflecting by magnetic fields only

Definitions

• the present invention relates to a device for deflecting electron beams from an electron gun with three beams in line with a cathode ray tube comprising a substantially flat screen panel.
• the deflection device In cathode ray tubes using an electron gun with three coplanar beams corresponding to the three primary colors Red, Green, Blue, the deflection device, also called deflector, has the function of deflecting the beams so as to make them explore the entire surface of the tube screen to generate the images and to ensure the convergence of these beams during all the exploration.
• the volume swept by the electron beams is a pyramid whose apex coincides with the deflection center of the deflection device and whose intersection with a screen surface of large radius of curvature determines a figure with a defect in geometry called cushion. This geometrical deformation of the image is all the greater the greater the radius of curvature of the screen of the tube.
• the so-called self-converging deflectors generate magnetic fields and astigmatic lines in order to ensure the convergence of the electron beams at the height of the perforations made in the color selection mask, placed at a very short distance from the screen of the tube.
• the lines of force of the magnetic fields created must then be in cushion for the line field and in barrel for the field field.
• the deflection device for cathode ray tube with three coplanar guns comprises a pair of horizontal deflection coils and a pair of vertical deflection coils, each horizontal deflection coil being characterized in that the angular distribution of the ampere-turns density in the said coil changes by signs at at least one point in an area limited to the front part of this coil.
• FIG. 1 shows a section along a plane perpendicular to the longitudinal axis Z of the tube situated in front of the deflector, on the screen side, of the deflection pyramidal volume; There are represented the horizontal and vertical magnetic fields as well as the forces exerted on the electrons which will form the upper right corner of the image.
• FIG. 2 is a perspective view of a saddle-shaped line coil of a known deflection device.
• FIG. 3 is a perspective view of a saddle-shaped line coil according to the present invention.
• FIG. 4 is a sectional view along a plane perpendicular to the main axis Z of the tube, of the front part of a saddle coil according to the present invention.
• FIG. 6 represents the results of the amplitude measurements of magnetic fields along the Z axis created by a line coil according to the present invention.
• FIG. 7 shows the influence on harmonic 2 of the magnetic field of a coil structure according to the invention.
• FIG. 8 shows the influence on harmonic 4 of the magnetic field of a coil structure according to the present invention.
• FIGS. 9 and 10 illustrate variants of the present invention.
• the deflection system It is customary to divide the deflection system into three successive action zones along the Z axis; the rear zone, closest to the electron gun, has a particular influence on coma or difference in size of the green image compared to the blue and red images; the middle zone of the deflector acts more particularly on astigmatism or the convergence of red and blue electron beams; Finally, the front area, located closest to the screen of the tube acts on the geometry of the image that will form on the screen.
• FIG. 1 shows the action of the lines of force of the magnetic fields of horizontal deflection 1, along the direction of the X axis and vertival 2, along the disrection of the Y axis, on the geometry of the image.
• A the electron beam corresponding to the upper right corner of the image and in 3 and 4 the electron beams corresponding to the edges of the image.
• the distribution of the turns must be of the line coil is such that the decomposition in Fourier series of the angular distribution of the ampere-turns density in the coil shows a significant harmonic percentage 3 compared to the fundamental.
• This structure makes it possible to increase the part of harmonic 3 but also causes the super-convergence of the electron beams if this part is very important as it is the case when correcting the geometry of a screen with a large radius of curvature; in addition, the turns 20 decrease the L / R ratio between the value of the inductance of the coil 21 and its resistance, which has the consequence of increasing the power supplied necessary for scanning the screen.
• the line deflection coil consists of a winding in two parts: a main deflection winding extending along the length of the deflector along the Z axis and whose lateral conductors are packed as close as possible to the XZ plane
• an auxiliary deflection winding disposed in the front part of the main coil and supplied so as to generate a field of direction opposite to the direction of the field created by the main winding.
• Figure 4 is a sectional view along a plane perpendicular to the main axis Z of the tube of the front part of a saddle coil according to the invention. Given the symmetry along the Y axis, only the section of a half-coil is shown.
• This half-coil comprises a first part constituting a main coil 21, the conductors 23 of which are supplied so that the current which flows through it in a certain direction 30 and a second part 22, constituting an auxiliary coil located at the front of the diverter, supplied in such a way that the current, in the conductors 24 flows there in a direction 31, opposite to the previous one.
• the conductors 24 are arranged so that they occupy an opening angular ( ⁇ , • ⁇ j ) and are distributed around an average angle e ⁇ , on either side of which there is a substantially equal number of conductors 24.
• the principle of the invention will be better understood by writing the equations which govern the magnetic deflection. Because of the symmetries of the windings of the deflector, the decomposition in Fourier series of the density of ampere-turns N (e) of a coil is written:
• N ( ⁇ ) Al.COS ( ⁇ ) + A3.COS (3 ⁇ ) + A5.COS (5 ⁇ ) + ... + AK.C0S (K ⁇ ) +
• H A1 / R + (A3 / R 3 ).
• R is the radius of the ferrite magnetic circuit which covers the deflection coils in order to concentrate the fields to improve the energy efficiency of the deflection device and Al / R represents the fundamental field, (A3 / R 3 ).
• (X 2 -Y 2 ) the harmonic 2 of the field, (A5 / R 5 ).
• (X 4 -6.X 2 .Y 2 + Y 4 ) the harmonic 4 of this field etc.
• a positive A3 term corresponds to a harmonic 2 of positive field and induces lines of field strength in a cushion.
• Figure 5 represents as a function of ⁇ , the terms COS (e), COS (3 ⁇ ), COS (5 ⁇ ) ... for e between 0 "and 90".
• the conductors constituting it will preferably be arranged between 0 * and 20 * values for which C0S (3 ⁇ ) remains greater than 0.5.
• the angular position of the conductors of the main coil introduces a large percentage of harmonics 5 of the density of ampere-turns which can be compensated by the same auxiliary winding by placing the conductors 24 in an area where N ( ⁇ ) .C0S (5 ⁇ ) is negative (in order to avoid the harmonic 5 introduced by the main coil) which, for N (e) negative can be achieved by placing the majority of the conductors 24 in an angular position between 54 * and 90 *.
• the average angular position ⁇ increases as we s away from the screen.
• This coil structure also makes it possible to limit the reduction in the L / R ratio of the horizontal deflection coil to acceptable values because in this case the conductors 24 occupy a smaller area than the conductors 20 of the prior art .
• the auxiliary winding is arranged in the front third of the main winding.
• the coil 21 extends in Z over a length of approximately 90mm and has 32 turns while the coil 22 10
• the two windings are arranged in series, so that the current in the auxiliary winding flows in the opposite direction to the current in the main winding.
• the arrangement in series of the two windings is not limiting, the winding 22 being able to be obviously supplied by a second external source.
• the conductors 24 are arranged around an angular position ⁇ ⁇ between 58 * and 71 *, increasing as one moves away from the part of the winding closest to the screen of the tube, the conductors 24 being wound between 54 * and 80 *.
• the deflection device being divided into three zones, the front zone 47, closest to the screen of the tube, the central zone 46 and the rear zone 45, FIGS.
• FIG. 9.1 and 9.2 illustrate this embodiment by showing a line coil in which all of the conductors are offset towards the interior of the coil. In a section along a plane perpendicular to Z passing through zone 48, this offset is represented by the angle ⁇ .
• This offset makes it possible to locally decrease, in zone 46, the importance of harmonic 3 of the angular distribution of the density of ampere-turns in the winding, an excessive value of which could lead to a deconvergence of the electron beams, but which it is necessary to have in zone 47 in order to be able to obtain an effective correction of the cushion deformation.
• the conductors of the coil 21 of the diverter fitted to this tube are offset by an angle equal to approximately 10 "in the middle zone 46.
• the coil 22 creating a magnetic field coming to oppose that of the main coil 21 consists of conductors of the main coil, wound in such a way that they open a window 35 in the crown 36 of the main winding, window extending towards the inside of the coil 21; therefore the current flows in opposite directions 30 and 31 in the two winding parts 21 and 22.
• Another way of implementing the principle of the invention is to use an auxiliary coil 22 whose conductors are short-circuited on themselves.
• the magnetic field created by the main coil 21 induces in the auxiliary coil a current which tends to oppose the variation in flux seen from this coil 22. It therefore appears in the strands of the coil 22 a current of opposite direction to that flowing in the coil 21.
• This embodiment allows a greater correction of the NORTH / SOUTH geometry than in the case where the coils 21 and 22 are in series because the induced current reaches a value greater than that of the current flowing in the main coil.
• this type of embodiment simplifies the wiring of the coils.
• the deflection device equipped with these coils being adapted to the same ZENITH tube described above; the measurements were made at a frequency of 32KHZ, an anode voltage of 28KV, a deflection angle of 77 °:

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• Video Image Reproduction Devices For Color Tv Systems (AREA)
• Details Of Television Scanning (AREA)

Applications Claiming Priority (3)

Publications (2)

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• 1992
  • 1992-04-07 FR FR9204249A patent/FR2689679A1/fr not_active Withdrawn
• 1993
  • 1993-04-02 WO PCT/FR1993/000331 patent/WO1993020578A1/fr active IP Right Grant
  • 1993-04-02 JP JP51717193A patent/JP3502634B2/ja not_active Expired - Fee Related
  • 1993-04-02 KR KR1019940703587A patent/KR950701765A/ko not_active IP Right Cessation
  • 1993-04-02 EP EP93907920A patent/EP0635163B1/de not_active Expired - Lifetime
  • 1993-04-02 DE DE69322629T patent/DE69322629T2/de not_active Expired - Fee Related

Non-Patent Citations (1)

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