US2400332A - Self-adjusting electrode support - Google Patents

Description

M y 4 I v c. H. BACHMAN SELF-ADJUSTING ELECTRODE SUPPORT Filed Sept. 27, 1944 v Inventor: v Charles H. Bachman,

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His Attorney.

Patented May 14, 1946 SELF-ADJUSTING ELECTRODE SUPPORT Charles H. Bachman, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application September 27, 1944, Serial No. 556,023 Claime (01. 250-452) The present invention relates to cathode ray tubes and it has for its object to provide an improved electron lens system for such a tube.

In a cathode my device, such as an electron microscope in which a visible image is formed by the action of an electron stream, it is customary to use an electrostatic lens system in the form of a plurality of metallic disks axially aligned and spaced the center disk operating at a different potential from that of. the outer ones. One of the problems in the construction of an electron lens of thisltype is that of maintainingvery accu% rate alignment of the elements and, atrthe same time, insulating one or more elements from the rest.- 1

It is an object of the present invention to pr vide an improved insulator -meansfo r such electrostatic lens systein.

It is .a further object of mylnvention to provide a new and'improvedinsulator for supporting-a removable .electrodein an electronic tube which permits easy insertion of the electrode in ;the insulator and which prevents vibration ofthe electrode in its insulator support. I a

The foregoing objects are accomplished in accordance with one embodiment of the invention by providing 'an insulator. in the form of a rod which extends around substantially the entire periphery of the electrode member operating at a high potential with respect to an enclosing envelope and which is grooved at a plurality of points to support the electrode, Iniaddition, the insulator is slotted in at least onepoint to form a spring-like section which may be deflected. to insert the electrode in the grooves in the :in-

sulator. I a

The features which I desire to protect herein are pointed out with particularity in the appende ed claims. The invention itself may best be understood by reference tothe following description taken in connection with the accompanyin drawing, in which Fig. 1 shows schematically an electron microscope which includes an electrostatic lens system of the type considered in the present invention, and Fig. 2 is an enlarged end view of the insulator used in my improved lens system.-

Referring to Fig. 1, there is shown an electron microscope comprising an elongated vacuumtight container I of a tubular metal construction.

At one end of the container there is rovided a glass insulator 2 which serves to support an electron source in the form of a filamentary cathode 3. Thecathode is surrounded by a tubular metal member 4 which confines the emitted electrons to a narrow beam and is cooperatively positioned with respect to an apertured electrode 5 which is in contact with the metal envelope 1. The opposite end of the envelope I is sealed by a glass window 6. A fluorescent coating forming a viewing screen I is placed on the inner surface of the window 6. In the normal use of the apparatus, the envelope I and the apertured electrode 5 are maintained at ground potential and the cathode is maintained at a high negative potential, for example, being connected to a potential source represented by the battery 8 so thatelectrons emitted from the cathode are projected axially of the container with the object of producing a visible image on the fluorescent screen-I. Between the cathode, 3 and the image-reproducing screen I there is placed an object 9 supported by any suitable supporting means (not shown) and to be trans-radiated by an electron beam, the beam being passed through the object and its passage assuming the characteristics of the object. r r In order that the electron beam, after modification in accordance with the structural character of the object under investigation as the beam trans-radiates that object, may be caused to provide an enlarged visible image of the. object in accordance with the intended use of the micro scope, the beam Ill, after passing through the object, is caused to pass throughan electron lens system of known character. In the drawing, the lens system is illustrated as of the electrostatic type and comprises a series of three apertured metallic diaphragms numbered II-I3 axially aligned and spaced. The diaphragms or disks arev provided, respectively, with central apertures I4, I 5, I6 through which is projected the cathode ray beam to be deflected by theelectron. lens system. To this end, the outer disks I land I3 are connected to the positive terminal of the battery. 8 by conductive connection with the inner surface of the tube I, While the central disk I2 is connected to the negative terminal of this battery through a conductor H which is brought into the microscope enclosure I through an insulating bushing IS. Because of the resultant difference in potential between the diaphragm I2 and the diaphragms .I I, I3, lens fields. are established be tween these diaphragms which have the effect of refracting the electron beam in a manner analogous to the refraction of a light beam in an optical lens. Additional lens fields may be employed in an electron microscope where so desired.

The cute-r disks I I, l 3 are machined to fit snu ly within the envelope I. The center electrode I2 is supported by an insulator I9 to be described Where it is desired to operate the electrode 7 l2 at very high potential with respect to the remaining part of the electron system, the surface and volume leakage of the insulating means employed must be considered. One manner in which the insulating path may be increased, while the insulating area is reduced, is illustrated in the enlarged view of insulator l9 shown in Fig. 2, in which the rod-like insulator I9 is formed of a suitable insulating material, such as porcelain, Micalex, or of a vitreous material, such as Pyrex. The member E 9 extends about substantially the entire periphery of the len member I2 and is bent into a shape such that it contacts the envelope l and lens member 2 at aplurality of spaced points 24 on lens l2 and points 25 on envelope I. The portions of the insulator member l9 adjacent the points 24 are grooved to engage the outer edge of the lens member or electrode [2, while the insulator I9 is machined at the points 25 to conform to the inner diameter of the invelope I.

In manufacturing the insulator, the rod-like member [9 is formed of aslightly larger outside diameter and a slightly smaller inside diameter than is normally desired. The insulator may then be held to a face plate using three holes 26 drilled through the insulator adjacent the points 24 a means to support the insulator on such a face plate. The grooves 24 are then ground in the insulator and the surfaces 25 are similarly prepared as by grinding. After the insulator is thu shaped as to inner and outer diameters and as to thickness, it is removed from the face plate and anarrow blade saw is used to cut slots 21 through the holes 25 and parallel to the sides of the insulator. Likewise, a narrow slot 28 is cut through one of the contact points 25. Alternatively, the slotsmay be molded inthe original insulator blank.

In the use of the insulator, the slots 21 provide means for permitting easy insertion of the lens l2 in the grooves at points 24. The slot 28 permits decreasing the outer diameter of the insulator to permit easy insertion within the envelope I9. During such insertion of the lens structure in the envelope, arms 29 formed by the slots 27 act as springs which facilitate insertion of the lens in the envelope.

One of the advantages of my improved insulator is that the spring arms .29 of the insulator take up any wear which would ordinarily cause looseness of the lens electrode. Suchlooseness is obviously undesirable, since it allows vibration of the center electrode of the lens and also permit the electrode to locate in off center positions causing aberrations of the lens system. Another advantage is the long length of the insulator between the electrode [2 and the envelope I which permits operation of the electrode l2 at increased potentials over those which are normally permitted.

The inventionadescribecl herein a may be used to advantage in cathode ray device orin other types of electronic tubes for supporting an electrode. Numerous additional modifications may obviously be made to my invention and I aim in the appended claims to cover all such modifications at come within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electronic tube having a metallic envelope and a metallic electrode maintained at a substantial voltage with respect to said en- 'velope,,an insulator for supporting said electrode within said envelope comprising a rod forming a substantially closed loop engaging said electrode and said envelope at a plurality of spaced points said rod being grooved at its points of engagement with said electrode and having a longitudinal slot at one of said point to permit insertion of said electrode in said grooves.

2. In an electronic tube have a metallic envelope and a metallic electrode maintained at a substantial voltage with respect to said envelope, an insulator for supporting said electrode within said envelope having a central aperture for receiving said electrode, said insulator having a plurality of flexible arms adjacent said aperture adapted to engage the outer edge of said electrode to prevent vibration of said electrode.

3. In an electronic tube having a metallic envelope and a metallic electrode maintained at a substantial voltage with respect to said envelope, an insulator interposed between said electrode and said envelope, said insulator being grooved at its point of engagement with said electrode and being provided with a resilient arm near said point of engagement to facilitate insertion of said electrode in said grooves.

4. In a cathode ray tube having a metallic envelope and a centrally apertured metallic disklike lens member maintained at a substantial voltage with respect to said envelope, an insulator' for supporting said lens member within said envelope comprising a rod member extending around substantially the entire periphery of said lens member and contacting said envelope and said lens member at a plurality of spaced points, said memberbeing grooved at said points and said member having a longitudinal slot to permit flexing of said member and insertion of said electrode in'said grooves.

5. A self-adjusting support for an electrode comprising a member having a central aperture provided with a groove for receiving said electrode, said member being provided with a slot parallel with said grooved portion for increasing the diameter of said aperture to permit insertion of said electrode in said grooves.

CHARLES H. BACI-IMAN.

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