US2820174A - Tri-color kinescope beam convergence system - Google Patents

Description

Jan. 14, 1958 H. c. GooDRlcH 2,820,174

TRI-COLOR KINEscoPE BEAM coNvERGENcE SYSTEMl Filed May 28, 1953 United States Patent TRI-COLOR KINESCOPE BEAM CONVERGENCE SYSTEM Hunter C. Goodrich, Collingswood, N. I., assigner to Radio Corporation of America, a corporation of Delaware Application May 28, 1953, Serial No. 357,956

4 Claims. (Cl. S15- 13) This invention relates to systems for controlling the electron beams of cathode ray tubes and particularly to systems in which a plurality of beams is deflected by a common deilection apparatus.

One type of cathode ray tube with which the present invention may be successfully employed is a color kinescope of the general type described in `an article titled "A three-gun shadow-mask color kinescope, by H. B. Law, published in the Proceedings of the I. R. E., vol. 39, No. 10, October 1951, at page `1186. Such a tube forms the subject matter of Patent No. 2,595,548, issued May 6, 1952, to Alfred C. Schroeder, and titled Picture Reproducing Apparatus. Such a tube has a luminescent screen as part of a target electrode in which different phosphor areas produce diierently colored light when excited by electrorn beam components impinging upon it from different angles, the angle of impingement determining the particular color of the light produced by the phosphor areas. The invention also pertains to a kinescope of the type described in another article titled A one-gun shadow-mask color kinescope, by R. R. Law, published in the Proceedings of the I. R. E., vol. 39, No. 10, October 1951, at page 1194. Such a tube is the subject matter of a copending U. S. patent application of Russell R. Law, Serial No. 165,553, filed June 1, 1950, and titled Color Television.

It lis necessary for the satisfactory operation of such kinescopes to eifect substantial convergence of the different electron beam components at all points of the raster scanned thereby at the target electrode. In general, this convergence may be eiected by means of apparatus such as that disclosed in an article titled Deilection and convergence in color kinescopes, by A. W. Friend, published in the Proceedings of the l. R. E., vol., 39, No. 10, October 1951, at page 1249. One such system in accordance with the disclosure of this article forms the subject matter of a copending application of Albert W. Friend, Serial No. 164,444, iiled May 26, 1950, now Patent No. 2,751,519, granted June 19, 1956, and titled Electron Beam Controlling System. Such beam convergence apparatus includes an electrnoptical system by which to control the beam convergence angles. The electronoptical system is variably energized as a function of the radial angle of beam deflection.

Another type of apparatus for controlling the convergence of a plurality of electron beam components in a predeterminedplane and with which the present invention is more particularly concerned comprises, in general, a means for producing a plurality of electron beam components which traverse pre-deection paths that are spaced respectively about the longitudinal axis of the tube, and individual electromagnetic means located respective- 1y adjacent to the pre-deflection beam paths and of such a charcter to be energizable directly from the beam deflection circuits ina manner to elect the desired beam convergence. In this .mannen the beam convergence angle may be varied in a manner suitable to maintain the ice desired beam convergence in the predetermined plane at all points in the raster scanned at the target electrode.

More particularly, it will be understood that the term beam components as used in this specication and in the appended claims denotes either a plurality of individual electron beams emanating, respectively, from a plurality of electron guns or from a single electron gun provided with suitable electron-optical, or other apparatus, for forming three individual beams and, in addition, those components of a single electron beam to which is imparted a spinning motion so as to trace a substantially conic locus at different positions thereof. Accordingly, the apparatus by which a plurality of such electron beam components lis produced may include on the one hand, three electron guns or, on the other hand, a single electron gun, together with. the auxiliary apparatus by which the spinning motion is imparted to the beam.

The particular beam convergence electromagnetic apparatus to which this invention pertains includes for each beam component a pair of pole pieces located internally of the kinescope envelope. lt has been found that magnetic flux leaking from the deflection yoke traverses the various pairs of pole pieces ditferfently, thereby tending to cause a misconvergence of the beam components.

it, therefore, is an object of the present invention to prevent leakage ilux from a raster-scanning deflection yoke from affecting individual beam-convergence electromagnets in a manner to cause misconvergence of a plurality of beam components.

Another object of the invention is to counteract the misconverging eifect of leakage ilux from the beam deliection apparatus by suitable energization of the beam convergence electromagnets.

ln accordance with the invention, multi-beam cathode ray tube apparatus, having a plurality of beam convergence electromagnets located in a predeection region of the beams, is provided with an energizing system for the electromagnets by which all of the electromagnets are similarly energized as a function of the raster-scanning beam deiiection angle, and by which predetermined ones of the electromagnets are dissimilarly energized as a function of the raster-scanning beam deflection angle in such a manner as to counteract the misconverging eiect of linx leakage from the beam deflection apparatus into the beam convergence region including the electromagnets.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof; will best be understood from the following description when read in conjunction with the accompanying drawings.

ln the drawings:

Figure l is a View showing the general arrangement of image-reproducing apparatus embodying one form of an electron beam convergence system in accordance with this invention;

Figure 2 is a transverse cross-sectional view taken generally on the line 2 2 of Figure l and showing the arrangement of the beam convergence electromagnets; and,

Figure 3 is a schematic circuit diagram of an arrangement in accordance with the invention for energizing the electromagnetic beam convergence apparatus.

Reference first will be made to Figure l for a general description of an illustrative embodiment of electron beam convergence system in accordance with the present invention. The system includes a tri-color kinescope 11 which may be of the same general type as that disclosed in the H. B. Law paper previously referred to. It will be understood, however, that the kinescope, alternatively, may be of other types such as that shown in the R. R. Law paper.

in either case, however, the kinescope preferably has a substantially flat luminescent screen 12 provided with a multiplicity of small phosphor areas arranged in groups and capable respectively of vproducing light of the different primary colors in Which'the image is'to be reproduced when excited by anelectron beam. 'En back of and spaced from the screen 12 there is-an aperturedfmasking electrode f3 having an aperture-for and in alignment with cach group of phosphor areas of thescreen 12.

ln the particular tube illustrated, the kinescope also has a plurality of electron guns, equal in number to the number of primary colors in which the image is to be reproduced. Each of these guns may be conventional, consisting of a cathode,'a control grid and a focussing electrode4 Since the three guns are identical,5the different parts there-- of will be referred to collectively as the cathodes tft, the control grids 15, and the 'focussing electrodes lo. `The three electronguns produced schematically represented beams 17, '118 and 19 by which'to energize, respectively, the blue, red and green phosphor areas of the 'screen12- Vthen these electron beams are properly converged in the plane of the masking electrode 13 they pass through the apertures thereof from ditferentVdircctions land impinge upon different phosphor'areas'of thev various groups so as to produce blue, red andgreen light. ltis to be noted that the size of the lphosphor areas, the angles between the beams and the spacing of the mask 1'3 from the screen l2 as compared with the length of the tube are exaggerated for better illustrati-n of the operation of the kinescope.

The electron-optical apparatus 4of the kinescope ll also includes a beam-accelerating electrode consisting, 'in the present instance, of a conductive wall coating 2t) formed on the inner surface of the Itubular 'glass neck 2l of the lrinescope extending from the region adjacentV to the outer end of he focusing electrodes'16 tothe conical section Z2 of the tube which in this case is'metallic. Suitable electrical connection (not shown) is 'made at the junction of the wall coating with the metal cone 22. Preferably, the target electrode structure, including the masking'electrode i3 and the luminescent screen'l'2`which for this purpose may be metallized, iselectrically connected to the metal cone`22 byV suitable means (not/shown). Metallization of a luminescent'screen of the'character described may be effected vin the manner disclosed in'a D. W. Epstein and and L. Pensak titled Improved cathode ray tubes with metal-backed"luminescent screens, publ5isttd in the RCA review, vol. VIIgMar'ch" 1946, at'pages The described electrode" structure`f 'the' kinescot'iev may grounded point'of the voltage divider and the control grids i l5 are connected to a point Vwhich is somewhat negative relative to ground. Similarly, the focussing electrodes 16 are connected toa point on the voltage divider which may conventionally be at a potential of approximately 3G00 volts positive relative-to the grounded cathodes. Also the beam-accelerating anode, including the'wall coating 2i and metal cone22., is c'nnected to the voltage divider 24 at a point Whi'chmay conventionallynbe approximately 18,000 volts positive relative Vtothe grounded cathodes.

The electron beams`17, `18'and-19-are modulated suitably in intensity under the control of color-representative video signals derived from asourceZS. lt will be understood that the video signal source isrepresented herein entirely diagrammatically since it-doesnot form an essential part of the present invention. yThe. signal source 25 usually Will'be part of a signal receiver andmay be understood to include a signal detector, 'or'` equivalent device, together with yone or more stages'of video'signal amplitication. Alternatively, the'videoi-signalsource maybea paper by l Cil color television camera in the event that the kinescope 1i is employed as a monitor, for example. Also, it will be understood that the illustrated connection of the video signal source 25' to the electron guns of the kinescope ll is merely diagrammatic and accordingly these connections may or may not be made .directly to the cathodes lf3. instead, it will be understood that they.may be vmade to the grids 15 or, in accordance with some modes of operation of color image-reproducing apparatus, the video signal source may be connected .both to the cathodes'and to the control grids of the 'electron guns.

Also associated with the color knescope 11 is a deflection yoke 2.6 which may be entirely conventional including two pairs of suitably placed coils electrically connected together in such a manner that, when properly energized, electromagnetic fields are produced, whereby to effect both horizontal and vertical angular deflections of the electron beams so asto `scanthe usual rectangular raster. Energization of the deflection coils comprising the yoke 26 may be effected by conventional vertical and'horizontal deflection Wave generators 27 and' 2S, respectively (see Figure 3). Such apparatus will be .understood to function 4suitably tlc-produce substantially sawtooth energy at both horizontal and vertical deflection frequenciestso that the fields produced by the yoke 26 iare varied in a substantially sav/tooth manner.

The beam convergence system, in accordance with the present invention, also includes a plurality :of electromagnetic field producing elements-such as the magnets 29 and 30 mounted around rthe neck 21 of the color kinescopeadjacent to the pre-deflection paths of theelectron beam components. lt is to beA understood that the precise location of these magnets is not necessarily indicated in this gure. Instead, as will appear in greater detail from a subsequent portion of the specification, it is to be understood that each of these magnets is located relative to one of the electron beam components so as to influence its associated beam component to the substantial exclusion of the others. Furthermore, it is to be understood that these magnets are of a character which, when .suitably energized, produce respective fields which aretransverse to the associated beam paths.

Each of these convergence electromagnets includes a pair of spaced pole pieces and vat leastcne energizing Winding. Preferably two windings are provided for each of the electromagnets for separate energization. lIn addition, predetermined lones of the electromagnets are provided, respectivcly,'with third windingsin accordance with this invention. These features 'will be"described subsequently in greater detail.

Before describing the details of 'theconvergence system Ywith which the present invention is related,'a brief description will be given of the generalmanner in Which the apparatus functions to produce the desired results. The convergence magnets such as 29 and 30 are. energized by substantially unidirectional energy so as to effect an initial convergence of the electronv beam components substantially in theplane of the apertured masking electrode In order to do this, the unidirectional'encrgization of these magnets is effected in suchcaA way 4that the magnets may be individually energized in different magnitudes. In effecting this initial beam convergence, it is to be understood thatl thebeams may be Vinany desiredv one of theirdifferent deectedpositions. For example, they may be initially converged at the center of the raster -to be scanned. Alternatively, they vmayfbe initiallyconverged atone corner-of the raster.

The convergence magnets-such as 29 and v30 also are dynamically energized by the control-wave energy derived from a suitable generator (not shown in 1 Figure l) so as to effect a variation'in' the fmagnitude'ofthe VAtrans- -verse fields produced respectively thereby. `rhesefield strength` variations are in t accordancel 'withra `predeterlmined function of-thebeam deflection. "Variationsin the strength of the fields produced bye the convergence magnets such as`29 and 30 effect corresponding variations in the paths of the electron beam components relative to the longitudinal axis of the tube. Hence, suitable variations are made in the convergence angles between the various beam components so as to produce the desired convergence of the beam components substantially in the plane of the masking electrode 13. a

For a further description of this type of beam convergence apparatus, reference now will be made to Figure 2 ofthe drawings. This ligure shows more clearly `the relativ-e positions of the convergence magnets, such as 29 and 30 and, additionally, 31, relative toA one another and to -the electron beams with which they are respectively associated. Inasmuch as all of these magnets are substantially the same, only one of them will be described in detail. The convergence magnet 29, which is associated with the blue electron beam 17, is provided with a core having a body portion 32 and -two external pole pieces 33 and 34. These pole pieces are mounted so as to be in close association with the tube neck 21. Also, as indicated in Figure 1, the pole pieces extend for some distance longitudinally of the tube substantially as indicated. The magnet also is provided with an energizing coil structure 35 mounted upon the body portion 32. The energizing coil 35 preferably is provided with two windings, one for static energization and the other for dynamic energization in a manner to Ibe described subsequently. Also, in accordance with this invention, the coils of magnets 30 and 31 have third windings. The convergence magnet 29 produces a field which, in the vicinity of the electron beam 17, is substantially transverse to the axis of the kinescope. By means of such a lield, the electron beam 17 may be moved toward or away from the longitudinal tube axis. The direction and magnitude of such a beam movement is controlled by the energization of the magnet by means including the coil 35.

In Figure 2, it also is illustrated that for each lof the magnets there are provided on the inside of the tube neck 21 extended pole pieces so as to increase -the electiveness of these magnets. The magnet 29, for example, is provided with a pair of inwardly extending pole pieces 36 and 37, lassociated respectively with the external pole pieces 33 and 34. By such means, it is seen that the reluc-tance of the magnetic circuit is considerably decreased, and also the flux distribution of the lield produced between the internal pole pieces 45 and 46 is con siderably improved.

With beam convergence apparatus of this gen-eral character, it may be seen from a further consideration f Figure 2 that such apparatus is adversely elected by leakage flux from ythe dellection yoke. Leakage deflec- -tion flux of a character to deflect the electron ybeam components 17, 18 and 19 to the left as viewed in the drawing is indicated by the broken lines 38. With respect to the internal pole pieces 36 and 37 associated with the electromagnet 29, no adverse elects of the leakage deflection flux are produced. However, it is seen that the leakage deflection flux 38 passes between the internal pole pieces 39 and 4l) of the electromagnet 30 substantially at right angles to these pole pieces since this is the path of lowest reluctance. Similarly, the leakage deflection liux 38 passes between the in-ternal pole pieces 41 and 42 of the electromagnet 31 at right angles to these pole pieces. As a result, it may be seen that when the beams are being deliected to the left, the red beam 18 will be moved to a higher' position than it would have in the asbence of the leakage llux from the deliection yoke, Ias indicated by the arrow. Similarly, -the green beam 19 will have a lower than normal position when 'beam deflection is toward Ithe left. Conversely, when beam deection by the yoke is toward the right, as viewed in Figure 2, the leakage flux 38 will be in the opposite f 6 direction, thereby tending to move the red beam downwardly and the green beam upwardly. Consequently, there is elected a misconvergence of the electron beam components as a result of the leakage liux from the deflection yoke traversing the internal pole pieces of cer- `tain of the convergence electromagnets.

Reference now will be made to Figure 3 of the drawings for a general description of an illustrative manner in which the beam convergence apparatus may be energized. The energizing coils of the convergence magnets 29, 30 and 31 include dynamic windings 43, 44 and 45 respectively. These convergence magnets also include static windings 46, 47 and 48, respectively. The energizing circuit for the static convergence windings 43, 44 and 45 includes a series circuit of resistors 49, 50 and 51 connected between the positive terminal of a power supply and its load. Preferably, these resistors are adjustable so as to enable the individual control of the energizing current for the associated static windings of ythe convergence magnets 29, 30 and 31, respectively.

The dynamic windings 43, 44 and 45 of the convergence magnets 29, 30 and 31, respectively, are connected in series with one another and to vertical and horizontal convergence wave generators 52 and 53, respectively. These convergence wave generators may be of the general type disclosed in the I. R. E. Friend paper or any other suitable forms. ln general, the substantially sawtooth wave energy 54 of field frequency which is derived from a conventional vertical deection wave generator 27 for energization of the vertical deliection coils 5S is converted by means of the vertical convergence wave generat-or 52 into a substantially parabolic wave 56. This parabolic wave energy is coupled by a capacitor 57 to the series connection of the dynamic windings of the convergence electromagnets. In a substantially similar manner, the line frequency sawtooth wave energy 58 derived from the horizontal deflection wave generator 28 for the energization of the horizontal delieotion yoke windings 59 is converted by the horizontal convergence wave generator 53 to substantially parabolic wave 60 for impression Iby means including a coupling capacitor 61 upon the dynamic windings of the beam lconvergence electromagnets 29, 30 and 31. By such means, it is seen that all of the convergence magnets are similarly energized dynamically as functions of both vertical and horizontal beam deliection angles so as to eiect substantial convergence of the electron beam components in the plane of the target electrode structure at all points in the scanned raster.

In accordance with the present invention, predetermined ones of the convergence electromagnets are provided with additional windings as part of the energizing means by which the misconverging etlect of the leakage llux from the deection yoke is counteracted. In the particular illustrative example of the invention disclosed in the drawings, the electromagnets 30 and 31 are provided with these additional windings since these are the electromagnets, the operation of which is adversely affected byl the leakage linx. In Figure 3, the electromagnets 30 and 31 are provided respectively with additional leakage flux counteracting windings 62 and 63, respectively. These windings are connected in. series with one another and also in series with the horizontal yoke windings 59. Accordingly, the leakage ilux counteracting windings 62 and 63 are traversed by the substantially sawtooth current wave 58 at horizontal deflection frequency.

It is to be noted, however, that the windings 62 and 63 are wound on their respective electromagnets 30 and 31, or are connected in the energizing circuit, in such a way as to produce in the respective pole piece gaps field components of opposite polarity. The reason for this may be seen by again referring to Figure 2. In order to counteract the adverse eiect of the leakage flux between the pole pieces 39 and 40 of the electromagnet 30, it is 7 necessary tofproduce a'i'eld component .ofsucha character as to move the red beam'lSfradially otward'ifrom the longitudinal axis of the tube. "In order to counteract the eiect ofthe same flux in thegapbetween the pole pieces di and 42 ofthe electromagnet 31, 'it' isl necessary that the additional iield component'be of such a character as to move "the green electron beam 19 radially inward toward the longitudinalV axis of the'kinescope. lt, thus, is seen that` the leakage :deflection duxis counteracted by dissimilarly energizing predetermined ones of the convergence 'electromagnets' as a function of the beam derlection angle.

The particular illustrative embodiment ofthe' invention. discloses the provision of acounteracting `iieldcomponent as a function ofthe horizontalbeam deectionan'gle. 'lt is to be understood that, 'shouldthe' vertical. dede-ation flux leakage into the beam convergence region cause objectionable misconvergence ofthe'bearns, the convergence'electromagnets may'beadditionally energized as a'function of the vertical beam deflection.

lt may be seen, therefore, from the' foregoing description of an illustrativeernbodiment of thepresent invention that there is provided a means for counteracting the leakage iiux from a raster scanning deflection yoke which Vtends to influence the beam convergence apparatus adversely to produce objectionable misconvergence ofthe beams. The system for accomplishing this'is'r'elatively simple `and effective in accordance with'thepresent invention, consisting essentially in the dynamic energization oi predetermined ones of-a plurality of=convergence electromagnets as a function of the beam deiiection angle.

The invention, having been illustratively"disclosed, lis dened in the appended claims.

What is claimed is:

l. In a cathode ray tube image-reproducing system wherein a plurality of electron beam componentsnvhich traverse predetiection paths that are spaced respectively about the longitudinal axis of the'tube, are angularly deflected both horizontally and-vertically by electromagnetic beam deiiection apparatus to fscan a raster at a target electrode, electron beam convergence apparatus comprising: a plurality of electromagnets =respectively-mounted adjacent to said predelectionbeam paths and energizable to produce respective elds transverse'to saidl beam paths, each of said electromagnets having apair of pole ieccs located internally of said tube and respectivelyr extending into v.the region of said-associated beam `cornponent; .means developing lcorrection '-wave fenergy' varying in magnitude continuously during theentirerasterscanning period asa function osaid raster-scanning -beam deilection angle; and means venergizing-predetermined ones of said electromagnets by said. correction-wave energy in such a manner as to produce transverse-field components of opposite polarity in respective ones of said predetermined electromagnets, whereby to counteract` the misconverging eect oi` flux leakage from-said beam deiection apparatus to said predetermined electromagnets.

2. in a cathode ray tube .image-reproducing system wherein a plurality of .electron beam-components, which traverse predeliection paths that are spaced respectively about the longitudinal axisof thetube, `are angularly deiiccted both horizontally and vertically by electromagnetic beam deiiection-apparatus toscan a raster at :a target electrode, electron beam convergence f apparatus comprising: a plurality of electromagnets respectively mounted adjacent to said predei'lection beam pathsand .energizable to produce respective fields transverse to said beam paths, each of said electromagnets having a pair of polepieces located internally of said tube and respectively extending into the region ot' said associated beam component; means developing convergence wave energy varying in magnitudeV as a function of. said raster-scanning beam detlection angle; means energizing said electromagnets by said'convergence wave'energy'in such va manner as`to effect dy- 'namicconvergence of saidbeam 'components;means `de- "velopingcorrection wave"energy"varying in magnitude continuously' during the* entire raster-scanning period as a function 'ofV said .raster-scanning beam deilection angle, "and means 'energizing'predetermined ones of said electromagnets by said-'correction Wave energy in such a manner asto produce transverse field components of opposite polarity in respective ones of said predetermined electromagnets, whereby to counteract the misconverging effectofflux leakage from said beam deflection apparatus to said'predetermined electroma'gnets.

3. in a cathode ray tube image-reproducing system wherein Aa plurality of electron beam components, which traverse predeiiection paths that are spaced respectively aboutthelongitudinal axis ofthe tube, are angularly deiiccted'hoth horizontally andl verticallyby electromagnetic beam deection 'apparatus to'scan -a raster at va target electrode, `electron beam convergence apparatus comprising: a plurality ofelectromagnets respectively mounted adjacent to said predefiection beam paths and energizable `to produce respective fields transverse to said beam paths, cachot said electromagnets having a pair of pole pieces located internally of said tube and respectively extending into the region of-said associated beam component; means developing substantiallyparabolic convergence wave `energy varying in magnitude `as a function of said rasterv-scanning'beam deflection angle; means energizing said electromognets by'said convergence Wave energy in such `a manner as to effect dynamic convergence of said beam components; lmeans developing substantially sawtooth correction wavefenergy varying in magnitude continu- -ously during the entire raster-scanning period as a func- .tion ofsaid raster-scanning beam deection angle; and lmeans energizing; predetermined ones of said electromagnets by said correction wave energy in such a manner as to'prcduce transverse field components of opposite polarity in respective ones of said predetermined electro- Amagnets, vwhereby to counteract the misconverging effect of ux leakage from said beam deflection apparatus to said predetermined electromagnets.

4. In a cathode ray tube image-reproducing system kwherein three electron' beam components, which traverse ypredeflection paths that are symmetrically spaced respectively about the longitudinal axis of the tube, and angularly deflected both horizontally and vertically by electromagnetic beam deection apparatus to scan a raster ata target electrode, electron beam convergence apparatus comprising: three electromagnets respectively mounted adjacent to said predeflection beam paths and energizable to produce respective fields transverse to said beam paths, eachv of -said electromagnets having a core including a body-portion located externally of said tube and a pair 'of pole pieces located internally of said tube and respectively extending from points adjacent to opposite ends of said body portion into the region of said associated beam-component, the pole pieces of a iirst one of said electromagnets extending substantially parallel to leakage fiux fromlsaid beam deection apparatus; means developing convergence Wave energy varying in magnitude as a function of said raster-scanning beam deflection angle; means energizing all of lsaid electromagnets substantially 'similarly by said convergence wave energy in such 'a manner as 'to etiect dynamic convergence of said beam components; means developing correction wave energy'varyingr-in magnitude*continuously during the entirerasterscanningperiodas a function'of said raster-scanning beam .deflection angle; and meanslenergizing second andthird ones of said electromagnets by said correction wave energy in such a manner as to produce transverse field components of opposite polarity in respective ones of said second and third electromagnets, wherebyto counteract the misconverging effect-of ux leakagefrom said beam deilectionapparatus to .said secondland third electromagnets "'(Rferences @following page) References Cited in the file of ths patent UNITED STATES PATENTS Parker Dec. 28, 1948 Hutter Oct. 30, 1951 5 Jenny Sept. 16, 1952 1G Friend Apr. 7, 1953 Evans Mar. 15, 1954 Goodrich May 4, 1954 Goodrich Apr. 26, 1955 Goodrich Apr. 17, 1956

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