US3440474A - Resilient means for supporting a directly heated planar cathode - Google Patents

Description

April 22, 5 s. L. PAWLIKOWSKI ETAL 3,440,474

RESILIENT MEANS FOR SUPPORTING A DIRECTLY HEATED PLANAR CATHODE Filed Feb. 1, 1967 Sheet 012 i I I I I w W '1 L- 142 x a X :2

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ATTORNE Y s. L. PAwLiKowsKl ETAL April 22, 1969 RESILIENT MEANS FOR SUPPORTING A DIRECTLY HEATED PLANAR CATHODE Filed Feb. 1, 1967 United States Patent US. Cl. 313--278 6 Claims ABSTRACT OF THE DISCLOSURE Plural upstanding metallic means are spacedly secured to a planar insulative positioning means to support a substantially planar directly heated rapid warm-up cathode relative to an associated electrode in a cathode ray tube electron gun. The cathode is resiliently supported at its terminal portions in a free suspension manner between two electrically conductive resilient members having definite bending moments to provide sufiicient tension to maintain constant tautness of the cathode during tube operation, the tension value being less than the hot yield strength of the cathode.

Background of the invention This invention relates to means for supporting a directly heated cathode and more particularly to resilient means for supporting a rapid warm-up directly heated cathode in a cathode ray tube electron gun structure.

In electronic equipment utilizing thermionic electron discharge devices, the time required for heater warm-up has long been recognized as an important factor in determining the interim existent between equipment turn-on and operational response. With the advent of substantially instantaneously responsive solid state ancillary components in the circuitry of cathode ray tube display equipment, the warm-up time of the cathode ray tube heatercathode combination became the main deterrent to a shortened initial Warm-up interim. In an attempt to shorten this interim, a variety of low power directly heated cathodes were devised and utilized in association with costly and intricately shaped ceramic supporting structures and tensioning means. Often the heat advantage of the cathode was radiatively dissipated through plural contact with the support means. Many of the supporting means were expensive and complicated structures, the assembly of which were time consuming operations often requiring the use of sophisticated jigs and fixtures.

Objects and summary of the invention It is an object of the invention to reduce the aforementioned disadvantages and to provide an improved means for supporting a directly heated cathode in a cathode ray tube electron gun structure.

Another object is to provide support means for a directly heated cathode to effect accurate planar positioning thereof relative to an associated electrode during tube operation.

The foregoing objects are achieved in one aspect of the invention by the provision of free suspension support means for a directly heated cathode in a cathode ray tube electron gun. The supports are two formed metallic members spaced apart in a substantially opposed manner and upstandingly secured to a substantially planar insulative positioning means oriented relative to an associated electrode. Each of the members has a cathode attachment means, and at least one of the members has one of these means formed as part of an integral resilient portion ex tending therefrom with a defined bending moment of a value to provide tensioned positioning of the cathode in a taut manner relative to the associated electrode, the applied tension being greater than the thermal expansion of the cathode but less than the hot yield strength thereof.

Brief description of the drawings FIGURE 1 is a sectional view of a cathode ray tube utilizing the invention;

FIGURE 2 is a perspective view of one embodiment of the invention showing the improved support means for the directly heated cathode;

FIGURE 3 is a plan view of a directly heated cathode of the type associated with the improved support means;

FIGURE 4 is a top plan view of the insulative positioning means and the cathode support means prior to cathode attachment; and

FIGURE 5 is a diagrammatic view showing the expansion and tensioning of the cathode.

Description of the preferred embodiment For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following specification and appended claims in connection with the aforedescribed drawings.

With reference to the drawings, there is shown in FIG- URE 1 -a cathode ray tube 11 having in the neck portion thereof an undetailed electron gun 12 which incorporates an electron generating source 13. The electron beam 19 emanating from the gun is directed to a cathodoluminescent screen, not shown, suitably disposed within the tube relative to the viewing panel 21.

In referring to FIGURE 2, there is shown an enlarged view of the G structure of the gun 12 wherein the electron generating source or directly heated cathode 13 is oriented on and between support means 27 and 27'.

In greater detail and with reference to FIGURES 2, 3, and 4, the directly heated cathode 13 is a substantially planar metallic formation having substantially continuous uniform thickness and differential widths. It is formed from sheet or strip material of a cathode metal, alloy, or metallic laminated medium. Such materials are generally denoted as filament materials having high temperature strength, controlled resistance, and freedom from impurities detrimental to electron emission. An example of a suitable material is a cobalt-nickel alloy known as Cobanic, manufactured by the Wilbur B. Driver Company, Newark, New Jersey. The cathode is formed to provide a defined high temperature section substantially shaped as a circular central portion 14 having a diameter larger than that of the aperture 25 in the associated G electrode structrue. Disposed on the surface of the central high temperature portion, proximal to the G aperture, is a conventional electron emissive coating '15 comprising materials such as two or more alkaline earth salts, ineluding for example barium and strontium, which, when subsequently heated during tube processing, are chemically converted to forms capable of emitting electrons during tube operation. It is necessary that the area of emissive coating be of a size larger than the G aperture to effect proper diametrical size to the electron beam to facilitate the focusing thereof by sequential gun elements, not shown. The major part of the input power applied to the cathode is converted to thermal energy and substantially and desirably confined or concentrated in this central portion to achieve the accelerated thermal rise effecting improved cathode performance.

To achieve the improved feature of defined heat concentration there is a first heat loss deterrent section in the form of a first reduced width portion or first longitudinal leg portion 16 extending in a radial unbroken manner from the central portion to effect one electrical path and a first half of the suspension support therefor. The cross sectional area thereof being of a value to also provide limited heat conduction and defined resistance. In a similar manner, a second heat loss deterrent section in the form of a second reduced width portion or second longitudinal leg portion 16' also extends radially from the central portion in diametrical opposition to the first reduced width portion to effect a second electrical path and a second half of the suspension support therefor. The cross sectional area of the second reduced width portion is of a value equalling that of the first reduced width portion to also provide defined heat conduction and resistance. Both legs are of substantially uniform lOngitudinal widths to minimize heat loss radiation therefrom. Each of the first and second heat loss deterrent portions have like distal terminal portions or tabs 17 and 17 of increased widths to facilitate placement on and jointure with a compatible supporting structure. The larger tab areas effect heat sink characteristics at the extremeties of the cathode and make the actual positioning of the securement welds less critical.

The dimensional features of the directly heated cathode 13, as generally noted in FIGURE 3, are substantially divided i.e., the transverse axis 18 of the central portion 14 has like metallic structures dimensioned as (b) and (12) extending diametrically from either side thereof to achieve a concentration of heat in the central portion of the cathode having an overall longitudinal dimension of (11) wherein a=b+b'.

The heat loss deterrent sections or reduced width portions 16 and 16, which are longitudinally dimensioned as (d) and (d') respectively, are designed as continuous integrations extending from the central high temperature portion to provide predetermined limited heat conduction therethrough and limited radiation therefrom.

It has been found that an example of an improved directly heated planar cathode, having a warm-up period of less than two seconds at electrical conditions of .5 volt and 500 milliamperes, may have dimensions (not to be considered limiting) substantially in the order of:

Inches Material thickness .001 Overall length (a) .230 Diameter of central portion (g) .040 Leg portions 16, 16': lengths (d, d) .065 Leg portions 16, 16': width (2) .010 Terminal portions 17, 17: lengths (c, c) .030 Terminal portions 17, 17: width .040

The cathode being free of burrs, bows, ripples and twists, is tautly mounted in a plane parallel with the closed end 24 of G structure 23 at a predetermined spacing relative to the aperture 25 therein. In the improved cathode as described, the emissive covered central portion operates at approximately 800 degrees centigrade which is achieved as a rapid thermal rise. Since the cross sectional areas of the heat loss deterrent sections limits the conduction of heat therefrom, the thermal drop in the adjacent dimensionally reduced leg portions is indicated by a markedly sharp temperature gradient therein which is evidenced as being substantially below the color temperature. In addition to better warm-up the optimizing of the temperature in the central portion enhances complete conversion of the emissive materials thereon during tube processing without approaching the danger of overprocessing.

Suitably formed metallic means 27 and 27' for supporting the aforedescribed cathode relative to the associated G structure have been developed as shown in FIGURES 2 and 4. These are secured to a planar insulative positioning means 35 which is spaced from the apertured end 24 of the G electrode to provide the proper operational K-G spacing.

More specifically, as illustrated, the substantially planar insulative positioning means is dimensioned to fit within a cup-like G electrode. This is not to be construed as limiting since the to-be-described cathode positioning and supporting means is also applicable to separate mounting orientation for usage with a disc-like or shallow thimble G electrode. As shown, the insulative means is substantially formed as a wafer and may be, for example, of mica or ceramic material of a thickness such as at least .010 inch to provide rigid positioning support.

Secured to the surface of the insulative wafer facing the G aperture are first and second metallic support members 27 and 27 comprising like upstanding fixed portions 31 which are oriented in a spaced and substantially opposed manner relative to one another. One means of securement comprises a plurality of projections 28, 29, and 30 protruding from one side thereof to mate with and extend through commensurate perforations 37, 38, and 39 in the insulative wafer, whereupon the projections may be bent or twisted to effect seated securement of the member. As illustrated, both upstanding members comprising the support means are of like fabrication being vertically formed in a horizontal plane to provide securement to the positioning wafer along more than one plane perpendicular thereto as depicted by planes A, B, and C in FIGURE 4. Thus, rigid seated placement of the upright member 31 on the wafer is effected in a manner that is free of horizontal shifting and vertical rocking. Other vertical formings are also applicable including arcuate and additional angular manifestations.

In the embodiment illustrated, the support members are fabricated from nonmagnetic Type 305 stainless steel of substantially .005 inch thickness. In this instance the vertical height (v) of each member is in the order of .095 inch.

Each support member has an integral resilient arm portion 32 extending therefrom with a cathode attachment means 33 formed as an extremital part thereof to accommodate a cathode terminal portion. Thus, means for jointure are provided for the two terminal portions by a first and a second cathode attachment means respectively. Since tube processing temperatures, to which the cathode and supporting members are subsequently subjected, are in the order of 500-600 degrees centigrade, the metallic composition of the members is such that the flexure of the resilient portions is not efiected thereby.

Each cathode attachment means or shelf is formed with a surface area shaped in a manner commensurate with the shape and area of a cathode terminal portion or tab to facilitate rapid and accurate superimposing of the tab on the shelf.

After the two support members are secured to the insulative wafer, the integral resilient portion 32 of each upstanding support member is positioned or set in a manner to provide a definite bending moment thereto whereof a small predetermined angle of flexure (La) of less than 3 degrees exists between the resilient portion 32 and the adjacent fixed portion 31. This in turn defines an initial variable span (s) between the two cathode attachment means; this span being greater than the given cathode length (a). By jigging means, not shown, the two resilient portions are temporarily flexed in an equal manner toward each other to reduce the span therebetween to equal the cathode length (a); whereupon the cathode terminal portions are superimposed on the cathode attachment means and welding jointures effected thereat. Release of the jigging means permits the resilient portions to exert a bending moment and initiate potential flexure in opposed directions to provide tensioning of the cathode and maintain tautness thereof during operation. The term tension as used herein does not connote permanent extension or elongation of the cathode material. It is a force value less than the hot yield strength of the cathode material at the smallest cross-sectional region thereof. The cathode length should remain consistent in accordance with the normal thermal expansion and contraction characteristics of the material.

In referring to FIGURE 3, the cathode 13 is joined to the respective cathode attachment means of each support member as by welding the terminal portion 17 and 17 thereto, whereby one or more welds are applied substantially in relation to the two terminal transverse axes (m) and (m) respectively. Being thus joined in a tensioned manner, the cold suspension length of the cathode is substantially denoted by the dimension ((1') between axes (m) and (m The tensioning of the cathode is illustrated diagrammatically in FIGURE 5 wherein (a') represents the cold length of the cathode as defined between the regions of jointure substantially along the transverse axes (m) and (m') of the cathode terminal portions. The lines (0x) and (ox) represent the resilient portions of each support member between which the cathode is mounted in free suspension at (x) and.(x'). As the cathode is heated, it expands to the length (r,) as defined between (y) and (y). The bending moments of the resilient members 32 are equal and keep the cathode taut as it thermally expands. Since each memberassumes half of the tensioning responsibility, for purposes of clarity the tensioning characteristics of only one end will be described. As illustrated in FIGURE 4, the predetermined initial angle of fiexure 4a) of the resilient member 32 is established prior to cathode jointure thereto and is greater than the angle of movement A [3) of the resilient member consummated during cathode tensioning, i.e., La L 3. The movement of the resilient member 32 from position (0x) to (oz) exerts sufficient tension on the cathode to achieve a tensioned or taut length of (r') which is slightly in excess of the normal expansion (r), but significantly less than (t) which represents the hot yield-strength length of the cathode at the threshold of permanent elongation. Thus, the longitudinal tensioning movement of the cathode experienced during the thermal operational cycle is of a nature to keep the cathode taut in a planar position relative to the associated electrode and is represented by (w) and (w'). The relationship of (w) or (w) to cathode length can be described as The supported cathode-insulative wafer assembly is thence oriented Within the G electrode 23 against a tubular spacer 43 internally telescoped within the electrode and abutted against the closed end thereof. The spacer is of a height to provide the proper spacing between the cathode and the G aperture 25 with the cathode being in a plane parallel therewith. Being thus positioned, the axis 49 of the aperture 25 intersects the central emissive portion 14 at substantially the center point 51 thereof.

A retainer 45, fitted within the electrode in seated peripheral engagement with the bottom of the insulative. wafer, fixes placement of the cathode support assembly.

Electrical connections 53 and 53' for the directly heated cathode are made to respective projections on each of the support members.

Since the cathode is confined in the restricted space between the positioning wafer and the end of the electrode, the inclusion of an aperture 41 in the wafer has een found expeditious to facilitate subsequent exhausting of the outgassed products resultants from cathode activation and tube processing.

While the described embodiment of cathode support utilizes a resilient portion on each of the support members, it is Within the scope of the invention to use resilient cathode attachment on one support member and nonresilient attachment on the opposing member.

Thus there is provided an improved directly heated cathode and supporting means for use in a cathode ray tube. The cathode has optimum temperature at its emissive portion and the structure is such that heat losses are reduced on either side thereof. Both the cathode and its associated support means are facilely fabricated and assembled. The rapid warm-up of the cathode achieves marked improvement in accelearting initial tube operation.

While there has been shown and described what is at present considered the preferred embodiment of the in vention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

We claim:

1. In a cathode ray tube, means for effecting tensioned support of a substantially planar directly heated cathode Within the electron gun thereof in spaced relationship with an associated grid aperture, said cathode being defined by tWo diametrically opposed terminal portions with a centralized high temperature electron emissive portion intermediate thereto in relative orientation with an associated electrode, said cathode having a cold suspension length (a'), a heated expansion length (r), a tensioned expansion length (r'), a longitudinal tensioned movement (w), and a hot yield-strength length (t) determining the threshold of permanent elongation, said cathode support means comprising:

an insulative positioning means oriented relative to said grid aperture;

a first upstanding metallic support member having an upright fixed portion with provisions thereon for securement to the surface of said insulative positioning means facing said grid aperture, said first support member also having an integral resilient arm portion formed adjacent to and extending from said upright fixed portion in a flexual manner and having a bending moment of predetermined value, said resilient arm portion having a first cathode attachment means formed as an extremital part thereof to accommodate a first of said cathode terminal portions;

a second upstanding metallic support member having provisions for securement to the surface of said positioning means facing said grid aperture and being oriented in a spaced and substantially laterally opposed manner relative to said first support memher, said second support member having a second cathode attachment means thereon formed to accom modate a second of said cathode terminal portions, said resiliently oriented first cathode attachment means and said second cathode attachment means defining a predetermined variable span therebetween, said terminal portions of said cathode being placed on and jonied to said first and said second cathode attachment means in a manner that said bending moment of said resilient portion eflects constant tautness and tensioned positioning of said cathode relative to said electrode, the tensioned movement (w) of said heated cathode effecting a heated cathode expansion length (1') less than said yield-strength length (r) thereof.

2. Means for supporting a directly heated planar cathode in the electron gun of a cathode ray tube according to claim 1 wherein each of said upstanding support members is vertically formed in a horizontal plane to effect rigid seated placement on said surface of said positioning means along more than one plane perpendicular thereto in a manner free of horizontal shifting and vertical rocking.

3. Means for supporting a directly heated planar cathode in the electron gun of a cathode ray tube according to claim 1 wherein both upstanding support members are of the first support member type having an integral resilient arm portion with a cathode attachment means formed as an extremital part thereof, said resilient arm portions being adjusted in a susbstantially equal manner to effect definite bending movements for defining a predetermined span between said cathode attachment means.

4. Means for supporting a directly heated planar cathode according to claim 1 wherein both upstanding support members are formed of like nonmagnetic metallic material.

'5. Means for supporting a directly heated planar cathode according to claim 1 wherein said insulative positioning means has at least one perforation therein to accommodate at least one of said securement provisions.

6. Means for supporting a directly heated planar cathode according to claim 3 wherein said span defined between said cathode attachment means provides to the planar cathode subsequently attached thereto a resultant tension of a value less than the hot yield strength of said cathode, and wherein the longitudinal tensioned movement at each end of said cathode is expressed in a relationship of length as:

l l 'LU=2- whereof I r 2a and I t 2a References Cited UNITED STATES PATENTS 2,491,995 12/1949 McIntosh et al. 313--37 2,879,431 3/1959 Longacre 313-37 X JAMES W. LAWRENCE, Primary Examiner.

V. LAFRANCHI, Assistant Examiner.

US. Cl. X.R. 313-292

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