US2460609A - Beam aligning apparatus - Google Patents

Description

I Feb.

C. E. TORSCH BEAM ALIGNING' APPARATUS Filed Jan. 30, 1946,

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' COIL 58 cumfnr m COIL$( On COIL 40 28/2 iszbz? DISTANCE OF POLL-S 44 man 70. 0F GRID (Mill/METERS) (U 0v F1023) (Ii/UQMPERES) Ni 6 8 "3 CURRENT l/V CO/LS 3 Sheets- Sheet 2 xsmcma amysgu p015 PIEC$(M m Has) 01.9mm: 0F POLL-S 44 mo rap 0F GRID (Mill/METERS) COIL 40 2000 TURNS COIL 58 POLE FACES FIRST ANO0E VOLTA6E SECOND ANODE V0T46E tumsur nmouau 0011.5 40 a 58 11v SERIES (MIUMMPERFS) SECOND ANODE K/LOVOL T3 2 i 9 1b muss 300 un/vs 53 WIDE 250 rows ----6 mouozrs INVENTOR CHARLES E. TORSCH ATTORNEY Feb. 1, 1949. I c, E. T0 sc 2,460,609

BEAM ALIGNING APPARATUS Filed Jan. 50, ,1946 3 Sheets- Sheet 3 A': 98 mo 92 296 I INVENTOR I CHARLES E. TORSCH \v To DIRECT CURRENT SOURCE R ATTORNEY Patented Feb. 1,1949

EAM ALIGNING APPARATUS v I Charles Edward Torsch, Lancaster Township,

Lancaster County; Pa., assignor to Radio Corporation of America, a corporation oi. Delaware l The present invention relates to means for preventing the formation of a darkened" area or ion spot on the luminescent or fluorescent target or screen of a cathode ray tube due to bombardment of this area by the ionscontalned in the developed cathode ray beam,

A number of attempts have been made to reduce or eliminate the formation of ion spots" in a cathode ray tube employing electromagnetic deflection of the'cathode ray beam. Some.of

these attempts were based on improvements in the exhaust and de-gassing techniques used in the manufactured the cathode ray tube. Other methods involved the development of luminescent or fluorescent target or screen coating materials which would withstand the ion bombardment. To date none of the above expedients has proven completely commercially practicable for the named purpose.

It is known that an electrostatic field deflects both the ions and electrons which together make up the developed cathode ray beam. However, for practical purposes, an electromagnetic field deflects only the electrons. Hence, efforts have been made to utilize this principle in designing a so-called ion trap," and cathode ray tubes have been built in which the neck of the cathode ray tube is bent in such a way that the ions in the developed cathode ray beam follow a linear path which does not strike the useful screen area. Theelectrons in the beam are brought to the center of the screen by means of a magnetic field applied at some point between the screen and the electron gun. A disadvantage of this design is that the unsymmetrical shape of the glass bulb makes the cathode ray tube difllcult to manufacture and handle.

Other designs along the above lines mount the electron gun within the tube neck so that all or a portion of the gun-structure is positioned at an angle to the axis of the tube; This makes for complications in assembly and alignment, and in addition such a construction is not sufflciently rugged to withstand normal operating conditions. A still further method which has been tried is that of employing a set of electrostatic deflection plates mounted within the gun structure itself. However, with a relatively high voltage on the tube anode, the problem of insulation is difficult to solve.

In a copending United States patent application of Joseph Kelar, Serial No. 726,589, filed February 5, 1947, there is disclosed an ion trap electron gun structure in which all of the parts of the gun are mounted co-axially. with the axis Application January '30, 1946, Serial No. 644,202

6 Claims. (01. 250-162) of the neck or the-cathode ray tube. However, the electrostatic lens formed by the cylindrical first and second anodes is tilted by cutting the cylindrical anodes at an angle other than 90 to the axis of the tube neck. This tilted electron lens bends the beam of ions and electrons away from the axis of the tube. A magnetic field is then superimposed on the electrostatic fleld of the tilted lens in such a direction and of such a magnitude as to bend the electrons in the beam back toward the axis of the tube.

It was then found, with an ion trap gun structure as described above, that the beam of scanning electrons did not strike the center of the tube screen. The spot at which the beam of scanning electrons did strike the tube screen was always off-center in the same direction with respect to the tilted lens, and was further oiT- center as the physical length of the electron gun was decreased. This condition was due to the difference in the axial distances within which the electrostatic and the electromagnetic bending of the electron beam took place. The electrostatic bend occurred in a much shorter distance than that in which the beam was electromagnetically returned toward the axis. This resulted in the electron beam leaving the gun at an angle to, the axis of the cathode ray tube.

To overcome the above condition, a second magnetic field was employed so as to act upon the magnetically deviated electron beam subst'antiallyat the point where it crosses the axis 'of the cathode ray tube. This second magnetic field acts to again bend the electron beam, so

- that, as a consequence of this double magnetic deflection, the scanning beam emerges from the electron gun along a path which substantially coincides with the tube axis. A system in accordance with these principles is set forth in a further copending U. S. patent application of Joseph Kelar, Serial No. 643,095, filed January 24, 1946.

In this last-mentioned Kelar application there has been disclosed means for producing two electromagnetic fields which are substantially parallel to one another and which act substantially transversely to the axis of the cathode ray tube. Furthermore, these fields are of opposite polarity and also substantially normal to the desired direction of bending of the electron beam.

In practice, it has been found that it is fr..- quently necessary to provide means whereby the force on the electrons in the scanning beam as produced by the two magnetic fields will bear a directional relationship to one another other than exactly 180. This may be due, for examelements due to assembly line variations. It is also extremely helpful to so mount the external magnet assembly relative to the gun structure that correct compensation willbe brought about without the necessity of adjusting the amount of such compensation by experiment. Furthermore, it has been found that, by a proper inter-relationship of the elements of the external magnet assembly, as well as by'a selective positioning of these elements with respect to the electrostatic lens, the current fiow through the two coils which.- respectively produce the two magnetic fields may be made substantially equal. These two coils may then be connected in series, with a consequent saving in power in addition to reducing the required number of circuit connections to the supply source. V

One object of the present invention, therefore, is to provide an improved external magnet assembly for use with cathode ray tubes employing ion trap guns.

An additional object of the invention is to Provide an external magnet assembly of the type described which is adjustable to compensate for mechanical and electrical variations in the characteristics of the cathode .ray tube with which it is to be used.

A further object of the invention is to provide an external magnet assembly of the type described which maybe easily and quickly adjusted relative to the electron gun structure of the cathode ray tube. I

Other objects and advantages will be apparent from the following description of preferred forms electrostatic lens per se form no part of the present invention, only such elements are shown in Fig. 1 as are necessary to a full understanding thereof. However, the assembly of Fig. 1 will be understood to include a cathode ray tube l having a bulb portion l2. and a neck portion ll. An electron gun strucinire including a grid IS, a

cylindrical first anode l8, and a cylindrical second anode is mounted in the neck portion ll of tube Ill. The adjacent surfaces of the first anode I8 and the second anode 20 are so arranged that 3 the planes of ,thesurfaces are substantially parallel. Furthermore, these planes are disposed t8 form an angle other than 90 with the axis of the cylindrical anodes l8 and 20,.and hence with the axis of the neck portion ll of tube ill. Consequently, the electrostatic lens 22 formed by the adjacent surfaces of anodes l8 and '20 is, in effect.

of the invention and from the drawings, in

which:

Fig. 1 is a schematic showing of a cathode ray tube having an electron gun formed to include a tilted electrostatic lens, and also showing schematically one manner in which two magnetic fields may be employed to re-align the electron scanning beam; 7

Fig. 2 is a perspective view of amagnet assembly in accordance with the present invention for producing the two magnetic fields of Fig. 1;

Fig. 3 is a view in partial cross-section of a portion of a cathode ray tube having a tilted electrostatic lens in the manner of Fig. 1, and further showing how a magnet assembly such as illustrated in Fig. 2 may be employed in conjunction therewith;

Figs. 4 (a) and (b) are graphs showing the relationship between the currents in the coils of the magnet assembly of Fig. 2, on one hand, and the physical relationship of the magnet assembly to the electron gun of the cathode ray tube on the other;

Fig. 5 is a graph showing the manner in which the coil current varies with variations in second anode voltage when proper scanning beam realignment is effected; Figs. 6 and! are perspective and end views, respectively, of a modification of the magnet assembly of Fig. 2; and

Fig. 8 is a circuit diagram showing one method of energizing the magnet assembly of Fig, 2.

Referring first to Fig; 1, portions of a cathode ray tube having an electron gun structure formed to include a tilted electrostatic lens of the type shown in Kelar application, Serial No. 726,589,

tilted, so that its axis does not coincide with the axis of the cylindrical anodes l8 and 20, and, consequently, with the axis of the tube neck portion H. The developed cathode ray beam, which is normally invisible, is illustrated schematically and designated by the reference character 24 in 'Fig. l, isdiverted by the lens 22 from its normal path along the axis of the cylindrical anodes l8 and 20 to take a path which may be such as indicated by the. reference character 28. Normally, this diverted cathode ray beam, including both ions and electrons, would strike the wall of anode 20 at some point such as 28.

Now, however, there is superimposed on the this upward'bending of the electrons is substantially'normal to the plane of the paper.

The ions and other heavy particles in the deviated cathode ray beam following the path 26, however, are not influenced by this magnetic field A to the same extent as are the lighter electrons, and hence the ions continue along the path 26 until they strike the wall of cylindrical second anode 20 approximately at the point 28.

The electrons which are caused to follow the path 30 after passing through the magnetic field -A are traveling at an angle to the axis 32 of tube l0. If they were allowed to continue in such a direction, they would either strike the screen of tube ill at a point. other .than in the center thereof, or else they would not pass through the aperture disk 34, depending upon the magnitude of the angle made by the electrons with the tube axis 32; To overcome this condition, asecond magnetic field B is provided, This second magnetic field B is substantially parallel to the first magnetic field A, and hence is also transverse to the axis 32 of tube l0. Field B, however, is of a polarity opposite to that of field A, and as a result the former causes the electrons following 7 path 30 to bebent or deviated back alonga path referred to above have been shown. Since the 36 which is substantially co-linear with-the axis 32 of the cathode ray tube.

v The aligned electron beam following path 36-is the one which actually strikes the screen of tube l0, and since the ions have been separated from the beam as a result of their collection by the anode 20 at or near point 28, no ion spot or other the structure shown in Fig. 1. Referring first tothe means for producing magnetic field A, there is illustrated a first electromagnet assembly 31 including a core section 38 on which is wound av coil 40. Respectively secured to the ends of core section 38, by some means such as the rivets 42, is a pair of pole pieces 44, while to the pole pieces 44 is respectively afllxed, as by the iurthe rivets 46, for instance, a pair of non-magnetic ing members 48 preferably formed of material such, for example, as Bakelite or plastic. v

The pole pieces 44 are intended to lie on oppo site sides of the neck portion l4 of tube ill of Fig. 1. Consequently, the pole pieces 44, as well as the supporting members 48 lying in partial face-to-face relation thereWith are provided with arcuate recessed portions 50. The radius of curvature of the arcuate recessed portions 50 is preferably slightly greater than the outer radius of the tube neck portion l4, so that the electromagnet assembly 31 will snugly encircle the neck of the cathode ray tube i0.

Two arcuate slots 52 are respectively formed in the non-magnetic supporting members 48. These arcuate slots 52 are concentric with the arcuate recessed portions 50 of the pole pieces 44. By a loosening of one or more bolts or screws (not shown) which are respectively receivable in the slots 52, the arcuate shape of these slots permit a rotational adjustment of the pole pieces 44 about the axis of tube Ill and relative to some fixed support (not shown), which may be of any suitable nature and which has been omitted from the drawing for the sake of simplicity of illustration.

Referring now to the means shown in Fig. 2 for producing the magnetic field B, this means includes a second electromagnetassembly 54 which is similar in many respects to the first electromagnet assembly 31 described immediately above. Included in assembly 54 is a core section 55, corresponding to the core section 38 of assembly 31, on which is wound a coil 58, corresponding to the coil 40. Secured to the core section 56, in the same manner that the pole pieces 44 are secured to the core section 38 of assembly 31, is a second pair of pole pieces 60. The coil 58, however, is either wound in a direction opposite to that of the coil 40, or else is connected in the circuit in such a manner that when direct current is caused to flow through the coils in a manner to be later described, the magnetic field B produced between the pole pieces 60 will have a direction substantially opposite to the magnetic field A produced between the pole pieces 44. This field remembers 42 may be adiustabiy secured to a fixed support (not shown) which may be the same or a different support from. that to which the nonmagnetic members 48 are adjustably secured.

--, Since the electromagnet assemblies 31 and 54 the tube i8. This is of importance in securing a correct re-alignment of the electron scanning beam, since, as shown schematically in Fig. 1, the second bend of the electron beam should occur substantially at the point wherethe beam, following its diversion by the first magnetic field, crosses the axis of the tube. The obtaining of such correct're-alignment may require a redetermination of the spacing between the pole pieces which produce the electromagnetic fields A and B, as will be further discussed in connection with Fig. 4. Furthermore, a rotational adjustment of one field with respect to the other permits compensation for a rotational or polar misalignment of the various parts of the electron gun structure, such as may be caused, for example, by assembly line variations.

Fig. 3 illustrates one manner in which the electromagnet assembly of Fig. 2 may be employed in conjunction with the cathode ray tube structure of Fig. 1. In the showing of Fig. 3, the cathode ray tube of Fig. 1 has been rotated about its axis 32 through an angle of substantially 90. The pole pieces 44 of Fig. 2 are so disposed relative to the tube neck that the direction of the magnetic field A produced therebetween lies substantially in the plane of the paper. The center plane 58 of the pole pieces 44 is separated by a distance L from a plane 10 which includes the top surface of grid i6 as shown. The center plane 12 of the pole pieces 60 lies at a distance M from the center plane 68 of the pole pieces 44.

A pair of oppositely-disposed angle-shaped pole pieces 14 are soldered or otherwise afiixed to the outer surface of the first anode l8, and are so positioned within tube l0 as to be intersected by the plane 58. These internal pole pieces (4 lie respectively adjacent the faces of the external pole pieces 44, and tend to sharpen the field pattern produced by the external pole pieces 44 within the cylindrical first anode I 8.

fields A and B should be reversed in direction when lens 22 is revolved 180 about axis 32 of the tube from the indicated position.

A second pair of non-magnetic supporting members 62 is respectively secured to the pole pieces 60 in the same manner that the members Fig. 4 (a) illustrates the relationship between the strength of the current in coils 40 and 58 of the electromagnet assembly of Fig. 2, and the spacing of the poles 44 from the top of grid iii of the gun structure of Fig. 1. The latter spacing is that indicated by the letter L in Fig. 3. In obtaining the curves of Fig. 4 (a), the pole pieces 44 are spaced away from the pole pieces 60 (center to center) or, in other words, the distance M in Fig. 3 is It is assumed that the coils 40 and 58 of Fig. 2 are separately energized bysuitable sources of direct current, the strength of which may be varied in any conventional manner. It is also assumed, for the purpose of explaining the curves of Fig. 4 (a), that coil 40' is wound with 2,000 turns, that coil 58 is wound with 300 turns, that the voltage on the first anode I8 is 250 volts, and that the voltage on the second anode 20 is 6 kilovolts. The faces of pole pieces 44 and 60 are taken as being approximately wide.

'ielectron scanning beam) decreases as the pole pieces 44 are moved away from the top of grid i8 until a certain point is reached." The current then begins to rise. It will be noted that the two current curves intersect at a. point which is approximately millimeters from the top-oi! grid i6, and that the current in each of coils 48 and 58 at that point is approximately 150 milliamperes.

The conditions for the graph of Fig. 4 (b) are similar in all respects to the conditions under which the graph of Fig. 4 (a) is obtained, except that the distance M (Fig. 3) between the pole pieces 88 and 12 is increased to one inch. The currents in the two'coils, for a satisfactory realignment of the cathode ray beam, are now equal at approximately 75 milliamperes, and the spacing of the pole pieces 44 from grid l8 for" these equal currents (distance L, Fig. 3) has been increased. Thus the equal currents required in coils 48 and 58 for series operation thereof have been decreased in value from approximately 150 milliamperes to about '75 milliamperes, or 50%, by increasing the spacing between the pole pieces 44 and 88 (or distance M) from to 1".

Fig. 5 is a graph illustrating the rise in coil current required as the second anode voltage on the cathode ray tube is raised, and is based on the optimum current values given by the graphs of Fig. 4 (a) and Fig. 4 (b).

Figs. 6 and 7 show a modification of the electromagnet assembly of Fig. 2. A pair of ring-shaped disks composed of magnetic material are shaped to form a pair of substantially U-shaped or horseshoe core sections 16 and 18, respectively. A coil 88 is wound mid-way on the U-shaped core section 16, and a coil 82 is similarly wound'mid-way on the U-shaped core section 18. Coils 88 and 82 correspond tothe coils 48 and 58, respectively, in Fig. 2.

The U-shaped core sections I8 and 18 are held in spaced-apart parallel relation by means of two pairs of internally threaded tubular spacers, one

only of these pairs being visible in Fig. 7 due to the manner of taking the end view. The two spacers comprising the pair which is visible in Fig. 7 are designated by the reference numerals 84 and 86, respectively. Since each pair of spacers is identical in design and function to the remaining pair, only the pair designated by the reference numerals 84 and 86 in Fig. 7 will hereinafter be mentioned.

A relatively short screw 81a is receivable in the threaded spacer 84, and passes through an opening in the U-shaped core section '18. A relatively longer screw 81b is receivable in the threaded spacer 86, and passes through an opening in the U-shaped core section 16.

Th screw 81b is sufficiently long to extend into the open end of the threaded spacer 84, and when in such position it acts to hold in place between the two spacers 84 and 86 a pair of disk-shaped spring metal positioning members 88 and 90. The two spring members 88 and 98 are held flat in face-to-face relation between the spacers 84 and 86, but normally flare outwardly away from each other at their upper or free ends, as shown in the drawing. The circular central openings in the- spring members 88 and 98 adapt these members to he slipped over the neck portion I4 of the cathode ray tube l8 of Fig. 1 when the free ends of these spring members are manually pressed together. However, when the manual pressure is released. the free ends of the members 88 and y as a ll spring away from one anothersecurely to rip the neck portion or the cathode ray tube.

Thus, the device of Figagd and 7 provides a simple and effective way g 'quiekly and easily adjusting the position of the'core sections 18 and I8 relative to the'internal elements or the cathode ray tube shown'in Figs. 1' and 3.

Fig. 8 shows one manner in which, the coils 48 and 58 of the electromagnet assembly oi Fig. 2 (or the coils 88 and 82 0! Fig. 6) may be enersized so that the ratio of the currents through the two coils may be selectively controlled. A potentiometer 92 is shunted across a'suitable source or direct current connected to the terminals 94. By varying the position of the movable contact 88, the amount of direct current flowin through the two coils 48 and 58 in series may be adjusted, except that. two additional potentiometers 98 and I88 respectively shunt the two coils 48 and 58. While both potentiometers 88 and I88 may be employed in the manner shown, it will be obvious that one of them may be omitted while still retaining a variable control over the current ratio in the two coils.

The potentiometer 82 provides an overall current control to allow for changes in the voltage on the second anode 28 of cathode ray tube l8.

and also permits compensation for variations in tube constants beyond the limits of physical adjustment of the electromagnet assemblies of Figs. 2 and 6. It should be noted that'when the total power supply current available is limited and either or both of the potentiometers 88 and I88 of Fig. 8 are employed, additional turns should be added to either or both of the coils 48 and 58 so as to maintain their original flux density, and hence the strength or the electromagnetic fields A and B.

Having-thus described my invention, I claim:

1. Apparatus for re-aligning the electron scanning beam in a cathode ray tube of the typ in which the ions in the developed cathode ray beam are separated therefrom through the medium of an electrostatic field which acts to bend cathode ray beam away from the axis of the oathode ray tube, said apparatuscomprising means for producing a first electromagnetic field, acting substantially transversely to the axis of the cathode ray tube, whereby the electrons which have been bent away from the axis of the cathode ray tube by the action of said electrostatic field are caused to follow a path which intersects the axis of said tube, while the ions are substantially unafiected by said first electromagnetic field, means for producing a second electromagnetic field also acting substantially transversely to the axis of said cathode ray tube and in a direction normally opposite to that of said first electromagnetic field, whereby the electrons following said path are caused to be deviated by said second electromagnetic field in such a manner as to follow a new path which is substantially coincident withthe axis of said cathode ray tube, and further means for permitting a limited rotational'adjustment of said second-mentioned means about said axis and relative to said firstmentioned means, whereby the normally opposite direction of said second electromagnetic field relative to said first electromagnetic field may be altered.

2. Apparatus in accordance with claim 1, further comprising means for permitting an axial adjustment of said second electromagnetic fieldproducing means with respectto said first elec- 9 tromagnetic field-producing means, whereby the action of said second electromagnetic field on said electrons may be caused to occur substantially at the point where the path followed by said electrons intersects the axis of said cathode ray tube.

3. An electromagnet assembly designed to substantially encircle the neck of a cathode ray tube, said assembly including a first core section, a first coil wound on said first core section, a pair of pole pieces respectively secured to the two ends of said first core section and extending in a direction substantially parallel to one another, each of said pair of pole pieces having an arcuate recessed portion designed to contact the neck of said cathode ray tube, a pair of non-magnetic supporting members respectively secured to said pair of pole pieces, each of said pair of nonmagnetic supporting members having an arcuate slot formed therein concentric with the arcuate recessed portions of said pole pieces, a second core section, a second coil wound on said second core section, a second pair of pole pieces respectively secured to the two ends of said second core section and extending in a direction substantially parallel to one another, each of said second pair of pole pieces having an arcuate recessed portion designed to contact the neck of said cathode ray tube, and a second pair of nonmagnetic supporting members respectively secured to said second pair of pole pieces, each of said second pair of non-magnetic supporting members having an arcuate slot formed therein concentric with the arcuate recessed portions of said second pair of pole pieces.

4. An electromagnet assembly in accordance with claim 3, in which the recessed portions of said first and second pairs of pole pieces are mutually concentric, and further means for permitting an adjustment of said first core section relative to said second core section and along the axis of the neck of said cathode ray tube.

5. Apparatus for re-aligning the electron scanning beam in a cathode ray tube of the type in which the ions in the developed cathode ray beam are segregated therefrom through the medium of an electrostatic field which acts to bend both the ions and the electrons in the developed cathode ray beam away from the axis of the cathode ray tube, said apparatus comprising an electromagnet assembly designed to substantially encircle the neck of said cathode ray tube, said assembly including a first U-shaped core section, the ends of said U-shaped core section being adapted to lie adjacent the neck of said cathode ray tube in such a nianner that said ends are diametrically opposite the axis of said cathode ray tube, and a coil wound centrally on said first U-shaped core section, said assembly also including a second U-shaped core section, means for positioning said second U-shaped core section in substantially parallel spaced-apart relation to said first U-shapcd core section, a coil wound centrally on said second U-shaped core section, and a pair of ring-shaped resilient members carried by said positioning means, said pair of ringshaped resilient members being adapted to encircle the neck of said cathode ray tube.

6. Apparatus in accordance with claim 5, in which said ring-shaped resilient members are designed so as to lie substantially surface-to-surface along the portions thereof which are in contact with said positioning means. and are further designed to be normally increasingly spaced apart toward a point diametrically opposed to such contacting portions, whereby said resilient members will normally be in frictional engagement with the neck of said cathode ray tube, and whereby those portions of said resilient members which are normally spaced apart may be manually compressed toward one another so as to free said resilient members from frictional engagement with the neck of said cathode ray tube and thus permit a movement of said electromagnet assembly axially along said cathode ray tube.

CHARLES EDWARD TORSCH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 860,816 Marcum July 23, 1907 2,102,421 Kuehni Dec. 14, 1937 2,148,588 Snow Feb. 28, 1939 2,211,613 Bowie Aug. 13, 1940 2,264,567 Gunther Dec, 2, 1041 2,274,586 Branson Feb. 24, 1942 FOREIGN PATENTS Number Country Date 498,491 Great Britain Jan. 9, 1939 518,221 Great Britain Feb. 21, 1940

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