Patent Publication Number: US-4151441-A

Title: Cathode support means in electron gun structure of a cathode ray tube

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to cathode ray tube electron gun structures and more particularly to improved means for supporting the cathodes utilized therein. 
     In present day television equipment utilizing thermionic electron emission devices, the time required for cathode warm-up has long been recognized as an important factor in determining the span of time between equipment turn-on and operational response. The substantially instantaneous activation of solid state circuitry has made the warm-up time required of the cathode ray tube (CRT) thermionic cathode means a major deterrent to the achieving of a rapid operational state. Such CRT cathodes are conventionally cylindrical sleeves having closed ends whereupon electron emissive material is terminally disposed. Heating elements encompassed within the sleeves provide the thermal energy necessary to achieve electron emission. 
     These cathode elements have been supported within the electron gun structure in several ways, i.e., by crimping or otherwise affixing the sleeve within an apertured supporting ceramic, or by several adaptations of metallic cylindrical members or eyelets wherein the cathode sleeve is substantially encompassed and positionally affixed. Such supportive means have all evidenced appreciable conductive contact with the cathode sleeve thereby producing undesirable heat sink characteristics, which relate directly to the length of the pre-operational time span. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the invention to reduce and obviate the aforementioned disadvantages evidenced in the prior art. 
     It is another object of this invention to provide support means for a cathode in a CRT electron gun structure that evidences minimal heat sink characteristics. 
     A further object of the invention is the provision of cathode support means that, while having minimal mass, has features promoting facile positional alignment in the gun structure. 
     These and other objects and advantages are achieved in one aspect of the invention wherein a thermionic cathode is supported in a CRT electron gun structure by a clip-like means. Substantially, this cathode supportive means is formed of a folded length of wire to provide a dual leg component having a closed end, an open end and a pair of intermediate sections wherebetween the rearward portion of the cathode is affixed in a manner substantially normal thereto. This cathode support clip has the respective end portions thereof configurated to seat on and be attached to spaced apart parallel walls of a formed cathode positioning member which is part of the gun structure. The cathode, being spatially oriented between the parallel walls of the positioning member, is supported in a manner whereby the forward end thereof projects through an accommodating opening in the member to the proximity of the control electrode element of the gun structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view illustrating a section of the closure region of the neck portion of a CRT wherein a prior art embodiment of a cathode support means is shown in cross-section as part of the partially detailed electron gun structure positioned within the neck; 
     FIG. 2 is another elevation further detailing the prior art as taken along the line 2--2 of FIG. 1; 
     Fig. 3 is a prior art plan view taken along the line 3--3 of FIG. 2; 
     FIG. 4 is an elevational view wherein the cathode supportive means of the invention are illustrated; 
     FIGS. 5A and 5B are enlarged elevational and plan views respectively detailing the structural aspects of the invention; and 
     FIG. 6 is a plan view further illustrating the invention as taken along the line 6--6 of FIG. 4. 
    
    
     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 above-described drawings. 
     With reference to the drawings, there is shown in prior art FIGS. 1, 2 and 3 a section of the envelope neck portion 11 of a cathode ray tube 13 wherein the electron gun assembly 15 is accommodated, such being structurally supported from the integral neck closure portion 17. While the invention, to be subsequently described, is applicable to either single or multi-gun structures, in this instance a multi-gun assembly is delineated, such being the type conventionally employed in color television applications. To promote clarity, certain irrelevant supportive and connective elements have been eliminated in the drawings. Each individual gun of the plural-gun inline assembly 15 is composed of a plurality of aligned electrodes integrated into the gun structure by embedment of supportive straps into at least two longitudinal rod-like insulative members 19a and 19b. The several elements of the partially illustrated exemplary gun structure 15 include similar cathode assemblies 21a, 21b and 21c, a common first or control electrode member 23, a common second or accelaration electrode member 25 and a third or focusing electrode member 27. 
     Referring in greater detail to the prior art, the thermionic cathode assembly 21a, for example, is comprised of a cathode sleeve 29a having a closed forward end 31 and an open rearward end 33. The forward end 31, being proximal to a respective aperture 35a in the control electrode 23, has heat responsive electron emissive material 37 terminally disposed thereon. A heater element 39a is positioned within the cathode sleeve 29a to provide the temperature necessary for achieving electron emission. As shown, the cathode sleeve is surrounded and supported by a shielding eyelet 41a, attachment being made to the rearward area of the cathode. 
     The eyelet is supported in a cathode positioning member 43a having a substantially planar base section 44a wherein a substantially central opening 45a is formed. This opening, which is of a size larger than the cross-sectional dimension of the eyelet, accommodates placement of the eyelet therein with the annular flange 47a of the eyelet being seated upon and affixed to the planar section 44a of the positioning member 43a. 
     Each of the cathode positioning members 43a, 43b and 43c is formed in a related manner in keeping with its position in the multigun structure. For example, in member 43a, the material forming the planar section 44a is continued therefrom to have two spaced apart parallel transverse bends 49 and 50, on either side of the planar section 44, wherefrom side members 51 and 52 project in a manner substantially perpendicular to the planar section. These shaped side members 51 and 52 form two parallel substantially similar skirt-like walls, each having a terminative edge, 53 and 54 respectively wherefrom a span relationship &#34;S&#34; is evidenced therebetween. Each of the side members or walls 51 and 52 has extending extremital portions 55, 56, and 57, 58 shaped for embedment in the respective insulative support members 19a and 19b. 
     In the aforedescribed cathode support means, the shielding eyelet and cathode attachment relationship evidences a considerable mass of material which constitutes a significant heat sink and thereby contributes to slower cathode warm-up. 
     The invention pertains to a cathode support member that employs a much reduced mass of material, which in turn lessens the heat sink characteristic and thereby promotes more rapid cathode warm-up. In describing the invention, attention is directed to FIGS. 4, 5A, 5B and 6 wherein the cathode support means of the invention utilizes the previously described cathode positioning members 43a, 43b and 43c. The parallel sides or skirt-like walls 51 and 52 provide shielding, for example, for cathode sleeve 59a, therefore the cathode shielding eyelet has been eliminated. 
     The unique cathode support means 61 of the invention is formed of a folded length of wire to provide a clip-like component having dual legs 62a and 62b and evidencing a closed end 63, an opposed open end 65 and a pair of intermediate portions 67a and 67b therebetween. Proximal to the respective closed and open ends 63 and 65, the support means has two parallel transverse perpendicular bends 69 and 70 formed in a common direction normal to the legs. This provides upstanding or outstanding closed and open end portions 71 and 72 which define equal lengths &#34;L&#34; of the intermediate leg portions 67a, 67b therebetween. This intermediate length &#34;L&#34; is substantially equal to the length of the span &#34;S&#34; separating the two spatially related parallel sidewalls 51 and 52 of the positioning member 43a, plus the respective wall thickness thereof. Thus, the configurated dual-leg cathode support member is dimensioned to seat on the terminative edges 53 and 54 of the parallel walls of the positioning member 43a and be suitably affixed thereto as by welding. Accordingly, the outstanding end portions 71 and 72 of the support member are positioned substantially contiguous with the outer surfaces of the sidewalls 51 and 52. 
     To adequately accommodate encompassement of the cylindrical cathode sleeve 59a, the intermediate sections 67a, 67b of the respective dual legs 62a, 62b of the support member 61 have concavely facing arcuate shapings 73 and 74 formed substantially centrally therein defining a circumferential arc approximating the outer circumference of the cathode sleeve at the region of affixation. As shown, swaging or partially flattening the wire material in the arcuate regions 73 and 74, to provide substantially flat surfaces for cathode affixation, also promotes improved means for cathode alignment. 
     The material from which the configurated cathode support member 61 is formed is preferably a round wire stock exhibiting a rigid strength sufficient to maintain positive support of the sleeve. The material should exhibit a low coefficient of linear thermal expansion and evidence a degree of stiffness or resilience. The resilience of the material is advantageous in maintaining a slight inward cant to the legs to provide a moderate inwardly directed pressure on the encompassed cathode sleeve positioned therebetween. Such pressure facilitates accurate positioning and affixation of the sleeve. With the sleeve being oriented in this manner, the forward end 77 therof is spatially accommodated within the central opening 45a of the cathode positioning member 43a in a manner to protrude therethrough to the proximity of the control electrode 23. 
     In each of the respective positioning members 43a, 43b, and 43c it has been found advantageous to form a pair of shallow recesses 79 and 81 in the parallel walls 51 and 52, inward from  pg,8 the terminative edges 53 and 54 thereof, to provide alignment notches for facilitating accurate and facile placement of the cathode support means 61 on the respective positioning member. 
     As is evident, the improved cathode support means of the invention provides minimal heat sink characteristics and therefore promotes rapid cathode warm-up. The low-mass structure of the invention enables the usage of shorter cathode sleeves along with shorter and more compact heating elements. 
     While there has been shown and described what are at present considered the preferred embodiments of the invention, 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.