US3449621A - Arrangement for correcting deflection errors in a cathode-ray tube - Google Patents

Description

June 10, 1969 E. E. HIMMELBAUER ETAL 3,449,621

ARRANGEMENT FOR CORRECTING DEFLECTION ERRORS IN A CATHODE-RAY TUBE Filed Aug. 10. 1966 Sheet of 2 F|G.2 c/ can INVENTORS ERICH E. HIMME-LBAUER BY JAN PEPER AGENT! n 1969 E. E. HIMMELBAUER ETAL 3,

ARRANGEMENT FOR CORRECTING DEFLECTION ERRORS IN A CATHODE-RAY TUBE Filed Aug. 10, 1966- Sheet Z or 2 FIG. 3c

FIG.4

INVENTORS ERICH E. HIMMELBAUER JAN PEPER assur United States Patent US. Cl. 315-25 Claims ABSTRACT OF THE DISCLOSURE A cathode ray tube that includes electrostatic deflection means for deflecting the electron beam along first and second perpendicular axes. Deflection errors are compensated by providing means for producing a quadripolar magnetic field having asymptotes that are parallel to said axes. The quadripolar field is located between the electrostatic deflection means and the screen of the tube so as to rotate the deflection axes of the electron beam.

The present invention relates to an arrangement for correcting deflection errors in a cathode-ray tube in which the electron beam is deflected by electrostatic deflection means in two directions substantially at right angles to each other.

The arrangement in accordance with the invention is characterized in that, viewed in the travelling direction of the electrons, a quadrupolar magnetic field is produced after said deflection means. The main axes of the quadrupolar field substantially coincide with the directions of deflection so that a rotation of said directions of deflection is achieved.

The invention is based on the recognition of the fact that orthogonality errors resulting from mechanical tolerances in the arrangement of the deflection plates and from any deviations in the after-acceleration field can be eliminated by means of such a quadrupolar magnetic field.

The invention will now be described more fully, by way of example, with reference to the accompanying figures, in which:

FIG. 1 shows an example of the supply, the structure and the location of coils for producing a quadrupolar magnetic field.

FIG. 2 shows a quadrupolar field produced by means of permanent magnets.

FIGS. 3a-3c illustrate a first coil configuration for use in the arrangement of FIG. 1.

FIG. 4 shows a second coil configuration.

FIG. 1 shows a cathode-ray tube 1 with having a screen 2 on which the directions of deflection are substantially at right angles to each other and are indicated by the lines AA and BB. Deflection in both directions is obtained with the aid of deflection means the operation of which is based on the electrostatic principle. A direct current source 3 supplies current to the coils 7 and 8 through control members 4 and 5 and through the lead-in and lead-out wires 6. The coils 7 and 8, supplied with direct current in a manner to be described hereinafter, produce a quadrupolar field. Such a field may also be produced, for example, by four permanent magnets or electromagnets.

In FIG. 2, reference numeral 9 designates North poles and reference numeral 10 denotes South poles of the magnets. The quadrupolar magnetic field is mainly determined by the magnetic field strength 11, the directions Patented June 10, 1969 of which extend along the axes CC and DD. At the centre point of the quadrupolar field, that is to say at the point of intersection of these main axes, the field strength is zero if the strengths of the magnets in the axis CC and in the axis DD are equal to each other. The magnetic field strength increases substantially linearly from the centre point of the quadrupolar field towards the magnets. If the direction of the electron beam is assumed to go perpendicularly into the plane of the drawing, reference numeral 12 designates the force exerted on the electrons in situ by the magnetic field strength 11. If an electron beam is deflected towards the axis CC, this deflection will be rotated under the influence of the quadrupolar magnetic field in the direction of the axis C'C. Similarly, the deflection along the axis DD will be displaced to the axis D'D'.

Consequently, it is found to be possible to displace the deflection of the electrons along the axes CC and DD to the axes C'C' and DD' by the use of the quadrupolar magnetic field. If the axes of deflection AA and BB are at an angle of (-a) to each other, the angle a can be eliminated with the aid of the quadrupolar magnetic field if the angles between the axes CC and CC and between the axes DD and DD together constitute the angle a so that the directions of deflection AA and BB on the screen 2 are put at right angles to each other. Thus, according to the invention, orthogonality errors due to mechanical tolerances in the arrangement of the electrostatic deflection means and to any deviations in the after-acceleration field can be corrected. For measuring purposes in oscillograph tubes, such orthogonality errors are often very disturbing so that, more particularly with the use of these tubes, it is desirable for said errors to be eliminated. However, if desired, it is also possible to adjust angles different from 90 with the aid of such a quadrupolar field.

Sectional views of the coils 7 and 8 in a plane at right angles to the axis of the cathode-ray tube 1 are shown in FIG. 3.

The directions of the currents in the coils are designated by a dot for the current coming out of the plane of the drawing and by a cross for the current going into the plane of the drawing. Currents of equal strengths in the coils 7 and 8 having the directions indicated in FIG. 3a produce the quadrupolar magnetic field already described hereinbefore. Currents of equal strengths in the coils 7 and 8 having the directions indicated in FIG. 3b produce a normal bipolar magnetic field which may be used as a deflection field. If the strengths of the currents in the coils 7 and 8 of FIG. 3a are different, for example, in the coil 7 one unit current and in the coil 8 three units current, the current in the coil 7 may have the course shown in FIG. Be. It can now be readily understood that a quadrupolar field is produced by two units current (shown together in FIG. 30) while a bipolar deflection field is produced by one unit current (shown separately in FIG. 3c). The quadrupolar field provides the desired orthogonality correction, while the bipolar deflection field may be used for centering the image on the screen 2 in one direction. Consequently, the average field strength of the resulting field is greater in the direction of the bipolar field than in the direction at right angles thereto.

If two units current are applied to the coil 8 while the coil 7 does not receive current, this results in that in the manner described above one unit current produces a quadrupolar magnetic field while the other unit produces a bipolar magnetic field. Consequently, if desired, the coil 7 could be omitted so that the coil 8 alone provides both an orthogonality correction and a centering of the image in one direction of deflection. The correction of an orthogonality error of 1 to 2 then results in a negligible displacement of the image.

If, beside the desired angular rotation, a centering of the image on the screen 2 in both directions of deflection brought about by the electrostatic deflection means should be required, use may be made of the coil configuration shown in FIG. 4. The coils 7 and 8 in which the currents have the directions shown in FIG. 4 and different strengths may be used for the angular rotation of both directions of deflection and for the centering of the image in one direction of deflection of the electrostatic deflection means, While the coils 13 and 14 in which the currents have the indicated directions and equal strengths may bring about the centering of the image in the direction of deflection at right angles to the above direction of deflection.

It should be appreciated that an increase of the average field strength in one of the directions with respect to this average field strength in the other direction may also be achieved, for example, by the use of two diflerent permanent magnets located diametrically opposite one another in an arrangement shown in FIG. 2.

Moreover, it should be appreciated that an orientation of the bipolar field with respect to the quadrupolar field different from that described hereinbefore may give rise to a displacement of the image which does not coincide with one of the directions of deflection.

What is claimed is:

1. An arrangement for correcting deflection errors in a cathode ray tube having an electron beam source and a screen for receiving the electron beam comprising, electrostatic deflection means positioned along the beam path for deflecting said beam in two directions substantially at right angles to each other, and means positioned along the beam path between said electrostatic deflection means and said screen for producing a quadrupolar magnetic field in said tube having asymptotes that are substantially parallel to said directions of deflection to produce a rotation of said directions of deflection of the electron beam.

2. An arrangement as claimed in claim 1 wherein said magnetic field producing means includes means for superimposing a bipolar magnetic field on said quadrupolar field thereby to displace the image formed on said screen.

3. An arrangement as claimed in claim 1 wherein said magnetic field producing means comprises first and second coils mounted on said tube and means for applying thereto DC currents that are adjustable in amplitude and direction.

4. A cathode ray tube comprising, an electron gun, a screen for receiving the electron beam produced by said gun, electrostatic deflection means positioned between said gun and screen for deflecting the electron beam along first and second substantially perpendicular axes, and means for producing a quadrupolar magnetic field in said tube having a pair of asymptotes that are perpendicular to the electron beam and coincide with said first and second axes, said field producing means being positioned between said electrostatic deflection means and said screen thereby to produce a rotation of the electron beam.

5. A cathode ray tube as claimed in claim 4 wherein said magnetic field producing means comprises, first and second coils mounted on said tube, a source of DC current coupled to said coils, and means for individually adjusting the amplitudes of the currents supplied to said coils.

References Cited UNITED STATES PATENTS 2,102,421 12/1937 Kuehni 313-79 2,188,579 1/ 1940 Schlesinger 3l379 2,212,640 8/1940 Hogan 31379 X 2,454,345 11/1948 Riidenberg 5 313--79 2,795,717 6/1957 Finkelstein et al. 315--27 X 2,889,547 6/1959 Wesley 3l527 X RODNEY D. BENNETT, JR., Primary Examiner.

CHARLES L. WHITHAM, Assistant Examiner.

US. Cl. X.R. 313-79; 315-27

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