US2904712A - Electrostatic deflection system - Google Patents

Description

Sept. 15, 1959 K.scHLl-:s1NGER 2,904,712

ELECTROSTATIC DEF'LECTION SYSTEM lFiled Feb. s, 195e INVENT OR.

tions have different wavelengths.

United States Patent Q ELECTROSTATIC DEFLECTION SYSTEM Kurt Schlesinger, La Grange, Ill., assignor to Motorola, Inc., Chicago, Ill., a corporation of Illinois Application February 3, 1958, Serial No. 712,836

8 Claims. (Cl. 313-78) This invention relates to beam deflection apparatus for cathode ray tubes, and more particularly to an electrostatic deflection structure having electrodes positioned circularly around a beam for producing bi-axial deflection thereof from a common center.

The electrostatic deflection structure of this invention is an improvement of that disclosed and claimed in the copending application of Kurt Schlesinger, Serial No. 506,203, filed May 5, 1955, now Patent No. 2,830,228, and assigned to the assignee of this invention. The structure of that Iapplication increases the uniformity of the dellection eld by compensating for certain iield distortions caused by the spacing of electrodes. In some applications, however, it has been found that undulating components of the deflection field, which primarily exist close to the electrode structure, extend into the beam vpath with sutlicient strength to impart directional as well as defocusing aberrations to the beam. This is especially likely in applications where a large sweep angle is used and the Vbeam passes quite close to the beam exit end of they structure. Consequently, the depth of penetration of these vundulating components, called fringe elds, limits the usable sweep angle.

v kIt is one object ,of this invention to provide an improved electrode structure for deflecting an electron beam from a common center through a comparatively vlarge sweep angle with a minimum of directional and defocusing distortion.

Another object of the invention is to provide an electrode structure for deecting an electron beam and for producing a more uniform deflection eld in regions where the beam passes close to the electrode structure.

Still another object of the invention is to provide a bi-axial electrostatic deflection system having electrodes positioned circularly on a tubular support form in which the depth of penetration of undulating fringe iields is controlled to-keep such elds from extending into the path of an electron beam directed through the form.

A feature of the invention is the provision of a beam deectliyon system including a circular electrode structure having interleaved zigzag electrodes with apex portions dening electrode sections. Corresponding sections` of all the electrodes have the same longitudinal extent, but the sections located at the beam exit end of the structure have smaller longitudinal extents than the adjacent sections for reducing the penetration from these shorter sections of undulating components of the deiiection ield in order to increase the usable sweep angle.

A further feature of the invention is the provision of an electrode structure having electrodes arranged in a doubly periodic sinusoidal pattern on a conical support form in which longitudinally extending cycles or sec- Cycles or sections which are located at the beam entrance and beam exit ends of the form have shorter wavelengths than the intermediate cycles and therefore confine undulating fringe fields closer to the support form in these end regions so that such fringe elds do not extend into the path of the rfice beam, thereby reducing directional and defocusing distortions.

The invention is illustrated in the accompanying drawing in which:

Fig. l is a view partly in longitudinal section showing a cathode ray tube having deflection electrodes in accordance with the invention;

Fig. 2 shows a planar development of an electrode pattern as shown in Fig. l, and having graded pitch;

Fig. 3 represents a planar development of one 1ongitudinal cycle of the electrode pattern;

Fig. 4 is a schematic diagram illustrating fringe fields lying close to electrodes positioned on a support form and extending into the path of an electron beam; and

Fig. 5 is a schematic diagram illustrating the elfect of an electrode pattern having graded pitch in withdrawing the fringe fields from the beam path.

The electrode structure of the invention comprises a plurality of conductive electrodes arranged in a pattern which provides a more uniform deflection eld. In general, that is accomplished by controlling the depth of penetration of undulating `fringe fields whose strength is greatest near the electrodes, and in particular, by making the depth of penetration slight in regions where the beam path is close to the electrodes. The basic electrode pattern has double periodicity since it has four interleaved zigzag electrodes forming peripheral cycles which extend around the circular circumference and longitudinal cycles which extend along the length of the electrode structure. In a preferred embodiment of the invention, each longitudinal cycle is characterized by having a plurality of spaced electrode sections bounded by halfwaves of a pure sinusoid to which is added a second harmonic component. The latter provides compensation for the effect of fields across the air gap between the electrodes. The complete pattern is characterized by having the complementary edges of the electrodes in different cycles of dilferent lengths, so that the longitudinal extents of these cycles are diiferent. Shorter cycles are placed at points where the beam path is nearest to the support form, and longer cycles where it is comparatively remote. When a cylindrical support form is used, it may be necessary to reduce only the cycle at the beam exit end thereof, but when a conical support form is used, it is desirable to have short cycles at both the beam entrance and beam exit ends of the form. y

In Fig. l there is shown a cathode ray tube it) having an electrostatic dellection structure il. The tube includes an electron gun 12 which directs a beam of electrons through the structure il in a predetermined path. The deflection structure 11 comprises a tubular support form 13 made of glass, ceramic, or like material having insulating properties, and four electrically conductive electrodes 14 arranged in a pattern and preferably applied as coatings of conductive material to the inside surface vof the support form. The support form 13, viewed in longitudinal section as in Fig. 1, has a conical shape which is preferable for wide angle applications, but may have a cylindrical shape. In either event, the transverse section is circular, and when reference is made herein to a circular support form, it is intended to include both shapes. The support form i3 is held in place by a framework having discs 15 and rods 16, and electrical leads 17 connect electrodes 14 to terminal pins 1S. The electron beam is directed against a viewing screen 19, a portion of which is shown broken away from the flare portion 20 of the tube. Each electrode 14 has a zigzag conguration, and the individual electrodes are spaced angularly around the periphery of the support form in interleaved relation with one another and with the overall circumferential extent of the apex portions of each electrode subtending an ang-le of 270. It has been found that with this arrangement,

each electrode produces a eld having an effective angular extent of 180 when voltages are applied to alternate electrodes. l

Fig. 2 shows the pattern of the electrodes i4 shown in Fig. l developed into a plane. The double periodicity of the pattern previously mentioned can be seen here, there being four electrodes 2l, 22, 23 and 24 providing four cycles in the arcuate direction corresponding to the periphery of the support form 13, and each having four cycles or sections in the radial direction which corresponds to the length of the form. Unless otherwise indicated, the word cycles when used herein are intended to refer only to the longitudinal cycles designated 26, 27, 28 and 29. It may be noted that these cycles are dened by the apex portions of the electrodes which are connected by dotted lines and that the cycleshave different pitch and different longitudinal extents. rl'he longitudinal extent of a cycle or section is sometimes called a wavelength herein.

Fig. 3 shows in detail a strip Bil representing any one of the cycles 26, 27, 28 and 29 shown in Fig. 2. The horizontal direction corresponds to the periphery while the vertical direction corresponds to the length along the beam. It should be understood that the pattern of the strip 30 must be projected in order to conform to the conical shape of the structure ll shown in Fig. l.

The electrode sections 3l, 32, 33 and 3d in the strip 30 are separated by gaps 36, 37, 3S and 39 which insulate the conductive areas from one another. The boundaries of the electrode sections shown as solid curves are halves of sinewaves containing a second harmonic component. For example, the centerline 35 between the boundaries adjacent thereto is described by the equation where L is the wavelength of the cycle 30, a is the angular position of the point considered, and Y is its ordinate. This curve deviates from a pure sinewave by a term containing 2a, that is, the second harmonic of the angle. If the boundaries did correspond to pure sinewaves as illustrated by the dotted lines-l, 42, 43 and 44, and if the efect of the insulating gaps were disregarded, it might be predicted mathematically that an ideal uniform rotating field should result. However, the idea performance gives Way to so-called pincushion distortion as soon as insulating gaps are introduced as explained in the aforementioned co-pending application of KIurt Schlesinger. The corrected boundaries shown by solid curves containing a second harmonic component provide the proper antidote for such distortion by increasing the area of each electrode along the centcrlines of the electrode sections, such as along line 45 which corresponds to an electrical deflection axis.

As previously indicated, several of the cycles 30 shown in Fig. 3 are placed in juxtaposition to form a complete pattern covering the inside of the structure ill. each of the cycles is corrected by itself independent of adjacent cycles, the scan geometry is not lost by juxtaposition, and the pitch of the spiral pattern of individual cycles can be made different from one cycle to the next in order to control the penetration of fringe fields. This is `done by mairing the electrode sections in different vcycles have different longitudinal dimensions.

Fig. 4 is a schematic diagram in which element 5l represents the support form of a dedection structure, elements 52 represent the electrodes positioned thereon, and the shaded area 53 represents the undulating fringe field which extends from the electrodes toward the beam. The strength of the fringe iield 53 actually decreases according to an inverse exponential relation with the ratio between the distance D from the supporting wall and the wavelength L of the corresponding cycle. Thus, the

`ield penetration to the inside varies approximately as exp. -21rD/L. In this View, each of the cycles 26, 27, 28

Since and 29 has the same Wavelength, and when comparatively great sweep angles are used, the deflected beam represented by the solid line 54 passes so close to the supporting wall at the entrance and exit portions of the structure that it traverses regions of non-uniform field.

Fig. 5 is similar to Fig. 4 except that the wavelengths L1, L2, L3 and L4 in the 'corresponding cycles 26, 27, 28 and 29 are different. Since -the fringe field ,strength is governed bythe above-mentioned relationship, the'penetration of the field cany be controlled b'yfplacingK4 cycles having shorter wavelengths at the entranc'eand'exit portions of the support form. The eifect'ofthis isf,to prevent the fringe field 53 from extending into thevbealm path, and to create a substantially uniform field beyond a radial distance from the electrode structure which is shorter in regions where the beam passes closest. It has been found that satisfactory results are obtained when the wavelengths Lil, L2, rL3 and L4- vary accordingy t'othe ratioof7:ll:l2:l0. gr

When electrical voltages areyappliedto alternate electrodes, a field is produced which has a substantially sinusoidal distribution over the periphery of the support form, and these voltages can be adjusted in a well-known Vmanner to provide rectangular scan or circular scan; Thus, the invention lmay be used effectively' in television Ireceivers, radar equipment, and other like applications. The electrode structure described herein provides improved performance in several respects, such as better scan geometry, greater usable sweep angle, and reduced tendency for deflection defocusing.

That which is claimed is: y A

l. In an electrostatic deflection system fora-cathode ray tube having a gun for directing an 'electron beam along a predetermined path, an electrode structure'in'- cluding four conductive electrodes positioned'angularly and symmetrically around the predetermined beam path, each of said electrodes extending longitudinally in spaced relation to the beam path and Ybeing 'of zigzag'shape with apex portions extending in opposite'directions circumferentially around the beam path, said electrodes being `interleaved and adjacent ones having spaced ycomplen'rentary edges of substantially sinusoidalconiguration, said apex portions defining longitudinal electrode sections with the end electrode sections at one end of said structurev having a shorter longitudinal dimension than-thefadjacent longitudinal electrode sections. l 'f 2. An electrode structure l'for providing' electrostatic deflection of Ya cathodey rayvbeam including a'fplurality of interleaved .zigzag electrodes extending longitudinally, said electrodes having apex'portionsextendingv circumferentially in a circular'form and defining vlongitudinal electrode sections, with corresponding sections of'all o fsaid electrodes having thesame longitudinal' extents, andwith the electrode sections located atione endV of said structure having a smaller longitudinal extent vthan thelongitudinally adjacent sections for reducing the penetration from such smaller sections of undulating components of a'jde- Flection eld producedl by theapplicati'onfo'f Avoltage :to alternate ones of saidv electrodes. l v rf" 3. An electrode structure'for providing electrstaticldeflection of a cathode ray beam includingin combination, a tubular support form of insulating material havinga longitudinal opening" therein through'which the'beam passes from a beam entrance end to a Ibeam `exit'e'nd thereof, four conductive electrodes symmetrically v'positioned With respect to the longitudinalaxis of the cathode ray beam on a surface of lsaid supportmembenin .said opening, each of said electrodes extending longitudinally of said tubular member and being ofhzi'gzagshapevand having apex portions extending in .opposite `directions around said tubular member, lsaid .electrodes/being l.interleaved and adjacent ones having spaced opposedledgeslof substantially vsinusoidal configuration; said apex 'portions of each electrode defining longitudinal electrode-sections having different longitudinal extents such that an electrical field produced by application of a voltage between alternate electrodes has a substantially sinusoidal distribution over the periphery of said support form and has a uniform strength without substantial undulating components beyond a radial distance from said support form which is shorter at said beam exit end thereof than at a point intermediate said beam entrance and beam exit ends.

4. An electrode structure for providing electrostatic deilection of a cathode ray beam including a tubular suport form of insulating material having a longitudinal conical opening therein through which the beam passes from a beam entrance end to a beam exit end having a larger diameter, four conducting electrodes symmetrically positioned with respect to the cathode ray beam on a surface of said suport member in said opening, each of said electrodes extending longitudinally of said tubular member and being of zigzag shape and having apex portions extending in opposite directions around said tubular member, said electrodes being interleaved and adjacent ones having spaced opposed edges of substantially sinusoidal configuration, said apex portions of each electrode dening longitudinally extending electrode sections with corresponding sections of said electrodes having the same length, and with the electrode sections nearest said entrance and exit ends having shorter longitudinal lengths than the intermediate sections adjacent to the same.

5. An electrode structure as dened in claim 4 with each of said electrodes having four longitudinal sections, and with the lengths thereof varying from said beam entrance end of said suport form to said beam exit end thereof in the ratio of 7: 11:12: 10.

6. In an electrostatic deiiection system for a cathode ray tube having a gun for directing an electron beam along a predetermined path, an electrode structure including four conducting electrodes positioned angularly and symmetrically around the predetermined beam path, each of said electrodes extending longitudinally in spaced relation with the beam path and being of zigzag shape and having apex portions extending in opposite directions circumferentially around the beam path to an angular extent of 270, said electrodes being interleaved and adjacent ones having spaced complementary edges of substantially sinusoidal configuration, said apex portions of each electrode dening longitudinal electrode sections with an end section having a shorter longitudinal dimension than the adjacent section whereby an electric potential produced by application of a voltage between alternate electrodes has an effective angular extent of 180 and a substantially sinusoidal distribution, and said end electrode sections of shorter longitudinal dimension conne undulating iields to a region extending a comparatively short radial distance therefrom.

7. In an electrostatic deflection system for a cathode ray tube having a gun for directing an electron beam along a predetermined path, an electrode structure including four conductive electrodes positioned angularly and Asymmetrically around the predetermined beam path, each of said electrodes extending longitudinally in spaced relation with the beam path and being of zigzag shape and having apex portions extending in opposite direction circumferentially around the beam path to an angular extent of 270, said electrodes being interleaved and adjacent ones having spaced opposed edges of substantially sinusoidal configuration, said apex portions dening electrode sections with end sections having shorter longitudinal dimensions than the longitudinally adjacent sections, and said electrode sections each having portions of increased area Within 45 on both sides of a longitudinally extending centerline thereof, so that an electric potential produced by application of a voltage between alternate electrodes has an effective angular extent of 180 and a sinusoidal distribution, with said portions of increased area providing compensation for eld irregularity due to the spaces between said electrodes, and with said electrode sections of shorter longitudinal dimensions confining undulating elds to a region extending a comparatively short radial distance therefrom. 8. In an electrostatic deection system for a cathode ray tube having a vgun for directing an electron beam along a predetermined path, an electrode structure including four conductive electrodes positioned angularly and symmetrically around the predetermined beam path, each of said electrodes extending longitudinally in spaced relation with the beam path and being of zigzag shape and having apex portions extending in opposite direction circumferentially around the beam path to an angular extent of 270, said electrodes being interleaved and adjacent ones having spaced opposed edges of the configuration of half wave of a sinusoidal Wave form including a second harmonic component, said apex portions deiining electrode sections with end sections having shorter longitudinal dimensions than the longitudinally adjacent sections, so that an electric potential produced by application of a voltage between alternate electrodes has an eiective angular extent of 180 and a sinusoidal distribution, with the second harmonic sinusoidal configuration of said edges providing compensation for eld irregularity due to the spaces between said electrodes, and with said electrode sections of shorter longitudinal dimensions conning undulating fields to a region extending a comparatively short distance therefrom.

References Cited in the le of this patent UNITED STATES PATENTS 2,770,748 Schlesinger et al. Nov. 13, 1956

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