US2522872A - Device for controlling the path of travel of electrons in cathoderay tubes - Google Patents

Description

Sept. 19, 1950 R. HEPPNER DEVICE FOR CONTROLLING THE PATH 0F TRAVEL 0F ELECTRONS IN CATHODE RAY-TUBES Filed Jan. 10, 1949 2 Sheets-Sheet l Sept. 19, 1950 M. R. HEPPNER 2,522,372

DEVICE FOR CONTROLLING THE PATH OF TRAVEL 0F ELECTRONS IN CATHODE RAY-TUBES Filed Jan. 10. 1949 2 Sheets-Sheet 2 Patented Sept. 19, 1950 UNITED DEVICE FOR CONTROLLING THE PATH OF TRAVEL OF ELECTRONS RAY TUBES IN CATHODE- Myron R. Heppner, Chicago, Ill., assignor to Heppner Manufacturing Company,

Round Lake, Ill., a corporation of Illinois Application January 10, 1949, Serial N 0. 70,053

6 Claims. 1

This invention relates to improvements in a device for preventing the passage of ions to the fluorescent surface of a cathode-ray tube, commonly referred to as an ion trap.

It is known that a cathode-ray tube operates on the principle of projecting or discharging a stream of electrons from a discharge device into contact with a screen of fluorescent material. It is also known that the discharging of such electron stream is accompanied by the formation of ions which, if brought into contact with the fluorescent material comprising the screen, are detrimental to the screen. It is further known that a stream of electrons can be deflected by a magnetic field and that ions have the same characteristics. However, for a magnetic field of predetermined intensity, electrons and ions do not respond, in so far as deflection is concerned, to the same degree.

This has led to the development in a cathoderay tube of an electron discharge device or gun which projects the stream of electrons at an angle to the axis of the tube; passing the electron stream through a. plurality of magnetic fields of different intensities and directions and subsequently passing the stream through a relatively small aperture to the fluorescent screen. By subjecting both the electrons and ions to the same magnetic fields, deflection of the streams occurs to different degrees and, hence, the ion stream does not follow the electron stream through the aperture but is obstructed by the Wall in which the aperture is provided.

Briefly described my invention comprises a convenient and efficient means for setting up spaced magnetic fields along the length of the electron stream, the fields being of different predetermined strengths and being opposite in direction.

One of the important features of my invention resides in a device for setting up such magnetic fields wherein two spaced permanent magnets are employed, the poles of the magnets being opposite to each other and one end of each of the magnets being short-circuited by a ferro magnetic band of such material and dimensions as to be saturated at all times by the magnetomotive force employed. In this fashion constant spaced diiferential fields will exert forces upon the electron stream which assures that an adjustment once made will last substantially for the life of the tube.

Other objects and advantages of my inven tion will be apparent from the accompanying drawings and following detailed description,

In the drawing,

Fig. 1 is a side view of a cathode-ray tube, parts being broken away and parts being shown in section with my device mounted in operative position thereon.

Fig. 2 is a perspective view of my improved device.

Fig. 3 is a transverse sectional view taken on line 33 of Fig. 1.

Fig. 4 is a fragmentary view similar to Fig. 1 but with the tube rotated about its longitudinal axis through ninety degrees.

Fig. 5 is a modification of my invention, illustrating another means for removably securing the magnetic device to the neck of the tube.

Fig. 6 is an end View of the device shown in Fig. 5.

Referring in detail to the drawing, l indicates a conventional cathode-ray tube having a base 2 which carries male contact elements of prongs 3 for connecting the various elements of the tube to an external circuit. The tube is constructed of glass having a neck portion 4 and a flared portion 5, the flared portion terminating in a screen or face portion 6.

Within the tube I an electron discharge device 1 is positioned adjacent the base 2. The function of the device I is to project or discharge a. stream of electrons and is usually referred to as an electron gun. Adjacent the discharge device 1 is a member 8 which carries oppositely extending arms 9, the arms being positioned transversely with respect to the longitudinal axis of the neck 4. Intermediate the length of the neck 4 and within the tube is a partition H) which is provided with a central aperture II. The inner face of the screen portion 6 of the tube carries a fluorescent coating l2 which in the operation of the tube is acted upon by the electron stream discharged from the gun I to cause the material constituting the layer I2 to fluoresce and give 01f light. In this type of tube, the electron gun I is so oriented that the electron stream is projected at an angle to the longitudinal axis of the tube. As will be hereinafter more fully described, this stream is subsequently deflected in such a manner as to project through the aperture l2.

The tube l hereinbefore described is conventional and per se constitutes no part of the present invention. However, my invention is applicable to a tube of this type, such tubes being commonly used fOr television reception.

It is known that electrons in motion can be deflected during passagethrough a magnetic field. It is also known that in the usual cathode-ray tube, the motion of the electrons discharged from the gun I gives rise to ions. The tube 1 is evacuated but within the limits of efliciency of present day vacuum pumps, a small trace of residual gas remains in the tube. In addition, occluded gases are contained in the Walls of the tube. Consequently, during the passage of the electron stream, such gases are ionized. It is also known that the ions thus produced have a detrimental effect upon the fluorescent material 12 tending to de-activate such material or burn it.

It is further known that ions are also responsive to a magnetic field. However, for a magnetic field of predetermined intensity the electrons and ions are deflected a different degree. Consequently, the construction of tube l is such that it is to be used with a device for setting up magnetic fields in such fashion as to deflect the electron stream and ion stream at spaced points along the length of the streams. The angle of projection of the electron stream from the gun I is then so correlated with respect to the spaced magnetic field as to deflect the electron stream from its original path at an angle to the axis of the tube to a direction whereby the electron stream projects through the aperture H and impinges upon the material [2 carried upon the screen portion 6. In View of the fact that the ions'do not respond to the deflecting force of the magnetic field to the same degree that do the electrons, it can readily be seen that a force couple correlated to bring the electron stream to a position whereby it will project through the aperture H would not bring the ion stream into this coincident position. Consequently, the ions are prevented from emerging through the aperture l l and, hence, are prevented from impinging upon the layer of fluorescent material l2.

My invention is particularly directed to the setting up of magnetic fields within a conventional cathode-ray tube I and comprises a pair of bar magnets 13 and M. The magnets 13 and I4 are conveniently constructed of rectangular cross section. However, said magnets may be of any desired section. The magnets 13 and [4 are carried at corresponding ends upon opposite sides of a band 15, the magnets being so secured to the band as to not unduly increase the reluctance of the magnetic circuit established by the band 15. The band I5, of course, is constructed of a ferromagnetic material.

I have found that one eflicient and convenient form of the band l5 comprises a pair of strips [6 and I! which may be appropriately bent to outline generally a square. One bent end of the strip ll is so formed as to embrace the end of one of the magnets as shown best at [B in Fig. 3, the opposite end of the strip I1 is substantially straight and encloses the fourth side of the magnet. The strip H5 is formed identical with the strip I1 and when the strips are assembled, they are disposed together in reversed positions and joined by means of rivets Or the like IS.

The assembly comprising my invention is adapted to be mounted upon the neck 4 of the tube I and to convenientl position it upon the neck of the tube, intermediate portions of each of the strips [6 and [l are indented as shown best at in Figs. 2 and 3. In similar fashion the relatively straight ends of the strips l6 and [1 are also indented as shown best at 2| in Figs. 2 and 3. In this manner a pair of indentations which project inwardly with respect to the square so formed, are positioned diametrically opposite each other in quadrature. I have found that this arrangement comprises an efficient and convenient means for securing the assembly to the neck of the tube I.

When the assembly comprising the magnets l3 and I4 and bands [6 and I1 is mounted upon the neck of the tube, the longitudinal axes of the magnets are disposed parallel to the longitudinal axis of the tube, and said magnets are disposed diametrically opposite to each other. In addition, the poles of the magnets l3 and I4 are reversed with respect to ach other so that magnetic fields established between opposite ends of the magnets are opposite in direction. The assembly is so mounted on the neck of the tube as to bring the unsecured or free ends of the magnets l3 and [4 adjacent the projecting members or flags 9 within the neck of the tube. The secured ends of the magnets are positioned toward the screen-end of the tube.

It can readily be seen that by securing one end of each magnet to the band 15, the band will constitute a low reluctance magnetic path between those two ends of the magnets. Consequently, the magnetic field established directly between the ends of the magnets will be greater between the free ends of the magnets than between the secured ends of the magnets. In addition, the construction of the conventional tube is such that the magnetic field established toward the base end of the tube will be greater than the magnetic field established toward the screen end of the tube by virtue of the presence of the flags 9 which are constructed of a ferro-magnetic material and tend to decrease the reluctance of the flux path between the free ends of the magnets. Hence,

when the stream of electrons is discharged from the gun I, it passes initially through the relatively strong magnetic field established by the free ends of the magnets. Thus, the electron stream is bent or deflected from its original projected path to a relatively great degree. As the stream proceeds further toward the screen end of the tube, it passes through the magnetic field established by the secured ends of the magnets and inasmuch as this field is weaker than the first mentioned field, deflection to a lesser degree takes place, the deflection being sufllcient to orient the stream so that it will pass through the aperture l I along the longitudinal axis of the tube.

As has been hereinbefore described, the ions formed by the electrons in motion, although deflected by the differential fields are responsive to the magnetic fields to a different degree than are the electrons and, hence, the ion stream is so oriented as not to pass through the aperture l l and is prevented from reaching the fluorescent layer l2 by the partition II).

It can readily be seen that with a tube I of predetermined construction, the differential magnetic fields must be correlated so as to insure the passage of the electron stream to the fluorescent layer while preventing the passage of the ion stream to said layer. Moreover, it is essential that the differential effect of the magnetic fields be maintained constant.

As a feature of my invention I so construct the band [5 with regard to its magnetic susceptibility and its sectional dimensions that it will be saturated under all conditions of operation with the magnets employed. Hence, there will be no variation in the magnetic field between the secured ends of the magnets which may be caused by a greater or lesser amount of flux passing through the band l5. As an example of a device which has been found suitable for one type of cathode- 5' ray tube, I e'mploymagnets which establish a field across the free ends thereof of approximately .0 gausses whereas the field across the secured ends of the magnets is approximately gausses. The band l5 isconstruoted of steel which is approximately .020" in thickness and .375 in width. I have found that employing a band of this type, the band is saturated and,consequently,-the field established directly across the secured ends of the magnets is constant.

Of course, it is to be understood that 'for tubes of different constructions, different capacities, etc, different constants of my magnetic assembly will be used and, consequently. I do not wish to be limited to the example mentioned above.

The important feature of my invention resides in a convenient assembly for mounting upon a conventional cathode-ray tube, the assembly being so constructed with respect to the strength of the magnets used that the band which secures the magnetic assembly together forms a magnetic path which is saturated.

Referring particularly to Figs. 5 and 6, a slightly modified form of my invention is shown. In this form of my invention band I5 is similar to band [5 except that the projections 20 and 21 are eliminated. Magnets i3 and M are identical with magnets I3 and M respectively and are carried by band l5 in a similar manner as are magnets 13 and 14 carried by band 15.

To removably secure the assembly comprising magnets l3, l4 and band 15' to the neck of a cathode ray tube, a pair of phosfor bronze spring plates are secured by means. of rivets 2| to the inner faces of opposite sides of the band IS. The plates 2!! are bent in the form of sides of a polygonal prism to more securely grip the cylindrical walls of the tube neck. The corners 22 of the plates 20 are flared outwardly to facilitate the mounting of the device upon the tube neck. It is to be understood that the essential function performed by the magnetic device comprising band l5 and magnets I 3 and I4 is the same as has been hereinbefore described iand the spring plates 29' being of a nonmagnetic material do not in any way influence the action of the device with respect to its function in bending the electron and ion streams.

I claim as my invention:

1. A device of the class described for positioning upon the neck of a cathode-ray tube which comprises, a pair of bar magnets, a square band of ferro-magnetic material secured to one end of each magnet at an intermediate portion of 0pposite sides of the square band, said bar magnets being held in spaced parallel relationship to each other, said square band being adapted for positioning upon the neck of a cathode-ray tube with intermediate portions of each side of the square in contact with the neck of said tube and with the bar magnets disposed substantially parallel to the axis of said neck, a pair of projections carried on each side of said square comprising said band for COl'lfillillg said band in desired position upon said tube neck, said. ferrmmagnetic band being of restricted cross-sectional area as to be saturated by the magnets so carried.

2. A device for selectivel deflecting a composite beam of electrons and ions in a cathode ray tube which comprises, a pair of bar magnets each having unlike poles at opposite ends, a band of ferro-magnetic material secured to one end of each magnet to hold the magnets in spaced longitudinally parallel relationship to each other and upon the neck of a cathode ray tube in longitudinal parallel relationship'to said neck, said bar magnets being disposed with unlike poles opposite each other to provide spaced parallel magnetic fields of opposite direction transverse to said neck, said ferro-magnetic band being of restricted cross-sectional area as to be saturated by the magnets so carried.

I 3. .A device for selectively deflecting a composite beam of electrons and ions in a cathode ray tube which comprises, a pair of bar magnets of substantially equal magnetic strength each havin unlike poles at opposite ends, a band of ferro-magnetic material secured to one end of each magnet to hold the magnets in spaced longitudinally parallel relationship to each other and upon the neck of a cathode ray tube in longitudinal parallel relationship to said neck, said bar magnets being disposed with unlike poles opposite each other to provide spaced parallel magnetic fields of opposite direction transverse to said neck, said ferro-magnetic band being of restricted cross-sectional area as to be saturated by the magnets so carried.

4. A device for positioning upon the neck of a cathode ray tube for selectively deflecting a composite beam of electrons and ions in said cathode ray tube which comprises a pair of bar magnets each having unlike poles at opposite ends, a square band of ferro-magnetic material secured to one end of each magnet at an intermediate portion of opposite sides of the square band, said bar magnets being held in spaced parallel relationship to each other, with unlike poles opposite each other, said square band being adapted for positioning upon the neck of a cathode ray tube with the bar magnets disposed substantially parallel to the axis of said neck to provide spaced magnetic fields of opposite direction across the neck of said tube, said ferro-magnetic band bein saturated by the magnets so carried.

5. A device for positioning upon the neck of a cathode ray tube for selectively deflecting a composite beam of electrons and ions in said cathode ray tube which comprises a pair of bar magnets each having unlike poles at opposite ends, a square band of ferro-magnetic material secured to one end of each magnet at an intermediate portion of opposite sides of the square band, said bar magnets being held in spaced parallel relationship to each other with unlike poles opposite each other, said square band being adapted for positioning upon the neck of a cathode ray tube with intermediate portions of each side of the square in substantial contact with the neck of said tube and with the bar magnets disposed parallel to the axis of said neck to provide spaced magnetic fields of opposite direction across the neck of said tube, said ferro-magnetic band being saturated by the magnets so carried.

6. A device for positionin upon the neck of a cathode ray tube for selectively deflecting a composite beam of electrons and ions in said cathode ray tube which comprises a pair of bar magnets each having unlike poles at opposite ends, a band of ferro-magnetic material secured to one end of each magnet upon opposite sides of said band, said bar magnets being held in spaced parallel relationship to each other by said band and with unlike poles opposite each other, a pair of spring plates carried by said band upon its inner side for removably positioning said band and magnets upon the neck of a cathode ray tube whereby to dispose said bar magnets substantially parallel to the longitudinal axis of said tube to provide spaced magnetic fields of opposite direc- MYRON R. HEPPNER.

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

Number 8 UNITED STATES PATENTS Name Date Nicoll Nov. 28, 1939 Schlesinger Jan. 30, 1940 Bowie Aug. 13, 1940 Holst et a1 Aug. 20, 1940 Branson Feb, 24, 1942 Bocciarelli Dec. 14, 1948 Wainwright Dec. 14, 1948 Torsch Feb. 1, 1949 Woodbridge June 7, 1949

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