US2837674A - Electro-magnetic deflection apparatus - Google Patents

Description

June 3,1958 W, H, BARKOW 2,837,674

ELECTRO-MAGNETIC DEFLECTION APPARATUS Filed Nov. 17. 1954 lNVENToR. I/l//LL/HM 50k/raw BY iyim VIDEO nited States ELECTRO-MAGNETIC DEFLECTIGN APPARATUS William H. Barkow, Pennsauken, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application November 17, 1954, Serial No. 469,39 iz claims. (ci. 31e- 70) atent In the three-gun shadow mask color kinescope described in the cited article, three electron beams are employed, one for each selected component color. The beams` strike a phosphor screen composed of a regular array of red, green, and blue light-emitting phosphor dots. Between the electron gun position and the phosphor screen there is placed a thin perforated metal sheet which masks the electron beams. The phosphor screen is made up of closely spaced trios of phosphor dots, each trio consisting of a red, a green and a blue dot with the centers of the dots lying at the corners of an equilateral triangle. The trios themselves lie at the corners of a still larger equilateral triangle. Associated with each of the phosphor trios is a hole or aperture in the shadow mask, such holes also being located at the corners of an equilateral triangle. The three beams, located 120 apart about the longitudinal axis of the tube, are converged to a point on the mask by a lens system. The electron beam which is to contribute the red portions of the picture is prevented by the mask from strikingthose areas on the screen containing the blue and green lightemitting phosphors. Similarly, the green and blue beams are permitted to strike only the green and blue phosphor dots, respectively.

ln order to effect proper convergence of the several beams vat the shadow mask, it has been proposed to provide in conjunction with such a tube, which includes means for producing a plurality of electron beam components which traverse predellection paths spaced relspectively about the longitudinal axis of the tube, individual electromagnetic means located respectively adjacent to the present deflection beam paths and of such a character as to be energizable directly from the beam deflection circuits.

in the setting up and operation of a shadow mask color kinescope, it is useful to employ the concept of color centers. A color center may be dened as any point in space, .determined by the geometry of the screen assembly of such a tube, from which an observer could see through the shadow mask only the phosphor dots of a particular color. ln the tri-color kinescope, the positions of the three-color centers, one for each color of phosphor, determine the plane of color centers, which plane is normal to the longitudinal axis of the tube.

It the three electron beams of a tri-color knescope are ice deflected by a common electromagnetic yoke made up of two pairs of coils disposed at right angles to each other, the three centers of deflection will determine the plane of deflection centers. lf the position of each deflection center coincides with that of a color center, then each deflected beam will excite only the phosphor dots of a particular color. In the completed tube the color centers are within the envelope and are, therefore, inaccessible. Hence the relative positions of the deflection centers and the color centers must be determined from the effects produced on the viewing screen of the tube.

From the foregoing, it will be appreciated that two basic requirements for the proper operation of a shadow y mask color kinescope are that the deflection center and the color center of each of the beams be coincident and that the beams converge at the shadow mask. These two conditions insure pure color elds in proper registry.

lt is, therefore, a primary object of the present invention to provide new and simplified apparatus for controlling electron beam deilection in such a manner as to afford control of the deflection centers in a kinescope.

Another and more specific object of the invention is to provide means for insuring the proper relationship between the color center plane and the deflection center plane of a kinescope of the shadow mask type.

As will be understood, axial movement of the deflection yoke comprising the horizontal and vertical windings will move the deflection region correspondingly. By virtue of the fact, however, that the horizontal and vertical scanning frequencies differ greatly, the eifective deflection center for the horizontal winding does not always coincide with the effective deilection center of the vertical winding. This problem is felt more acutely as the angle of deflection is increased. Moreover, in the case of shadow mask color kinescopes of the type employing individual beam convergence magnets, it has been found necessary or desirable to provide means for shielding the convergence region (i. e., the pre-deflection beam paths) from flux produced by the deflection yoke. As shown in U. S. Patent No. 2,677,779, granted May 4, 1954, to F. C. Goodrich, an effective shield of this type may be in the form of a disk-like member of magnetic material located between the deflection yoke and the location of the convergence magnets.` It has also been found desirable to place a disc of copper or other highly conductive material between the deflection yoke and the convergence magnets in order to shield the latter from the high frequency flux of the horizontal coils. The use of such shielding discs for the selective shielding of horizontal and vertical scanning frequencies has been found to cause a relative movement or shift between the horizontal and vertical deflection centers.

Hence it is a further object of the present invention to provide novel means for effecting the desired relative positioning of horizontal and vertical deflection centers of a deflection yoke, despite the presence of frequency selective shielding means in the region of the deflection yoke.

In general, the present invention provides an otherwise conventional electromagnetic dellection yoke having two pairs of perpendicularly disposed coils, each pair of coils having its end conductors turned up, with a disc-like member of metallic material between the turned up ends of the two coil pairs nearer the electron gun location of the tube. Such member affords a relative shift of the centers of horizontal and vertical deflection in a frequency-selective manner and is capable of rendering those centers substantially coincident. Moreover, as will be understood, the fact that the metallic member which is disposed between the end conductors of the two sets of coils serves to displace one pair of coils longitudi- `nally with respect to the other pair, further shifting of the center of deflection of the displaced coil pair is afforded in the direction of the displacement.

Additional objects and advantages of the present invention will become apparent to persons skilled in the art from a study of the following detailed description of the accompanying drawing in which:

Fig. 1 is a side-elevational view partially in section, of a tri-color kinescope having associated therewith a deflection yoke apparatus embodying the principles of the present invention; and

Fig. 2 is a fragmentary View illustrative of the operation of a kinescope of the type shown in Fig. l.

Referring to the drawing, the system of Fig. 1 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, except that its phosphor screen and mask are curved. The kinescopes spherical luminescent screen 12 is provided with a multiplicity of small phosphor areas arranged in groups and capable respectively of producing light of the different primary colors in which the image is to be reproduced when excited by an electron beam. In back of and spaced from the screen 12, but concentric therewith, is an apertured masking electrode 13 having an aperture for and in alignment with each group of phosphor areas of the screen 12.

In 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, an accelerating grid and a focusing electrode. Since the three guns are identical, the dilerent parts thereof will be referred to collectively as the cathodes 14', the control grids 14, accelerating grids 1S, and the focusing electrodes 16. The three electron guns produce schematically represented beams 1'7, 18 and 19 by which to energize, respectively, the blue, red and green phosphor areas of the screen 12, as shown in Fig. 2. When these electron beams are properly converged at the masking electrode 13, they pass through the apertures thereof from dilferent directions and impinge upon different phosphor areas of the various groups so as to reduce blue, red and green light. It is to be noted that in Fig. 2, the size of the phosphor areas, the angles between the beams and the spacing of the mask 13 from the screen 12 as compared with the length of the tube are exaggerated for better illustration of the operation of the kinescope.

The electron-optical apparatus of the kinescope 11 also includes a beam-accelerating electrode consisting, in the present instance, of a conductive wall coating 2h formed on the inner surface of the tubular glass neck 21 of the kinescope extending from the region adjacent toV the outer end of the electrodes 16 to the conical section 22 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. A cylinder 20 electrically connected to the wall coating 20 also serves in the focusing of the several beams. Preferably, the target electrode structure, including the masking electrode 13 and the luminescent screen 12 which for this purpose may be metallized, is electrically connected to the metal cone 22. by suitable means (not shown). Metallization of a luminescent screen of the character described may be effected in the manner disclosed in a paper by D. W. Epstein and L. Pensak titled Improved Cathode Ray Tubes With Metal-Backed Luminescent Screens, published in the RCA Review, vol. VII, March 1946, at pages 5-10. t

The described electrode structure of the kinescope may be energized in a conventional manner such ,as that illustrated. The source of energy is represented bya battery 23 across the terminals of which there is connected a voltage divider Z4. The cathodes 141V are connected to the grounded point of the voltage divider and the control grids 14 are connected to a point which is somewhat negative relative to ground. The accelerating grids 15 are supplied with a potential of, for example, 200 volts. Similarly, the focusing electrodes 16 are connected to a point on the voltage divider which may conventionally be at a potential of approximately 8000 volts positive relative to the grounded cathodes. Also, the beamaccelerating anode, including the wall coating 20 and metal cone 22, is connected to the voltage divider 24 at a point which may conventionally be at a high positive potential (e. g., 27,000 volts) relative to the grounded cathodes.

The electron beams 17, 18 and 19 are modulated suitably in intensity under the control of color-representative video signals derived from a source 25. It will be understood that the video signal source is represented herein entirely diagrammatically since it does not form an essential part of the present invention. The signal source 25 usually will be part of a signal receiver and may be understood to include a signal detector, or equivalent device, together with one or more stages of video signal amplification. Also, it will be understood that the illustrated connection of the video signal source 25 to the electron guns ofthe kinescope 11 is merely diagrammatic and accordingly these connections may or may not be made directly to the cathodes 14.

Also associated with the color kinescope 11 is a deflection yoke 26 in accordance with the invention and which will be described more fully below. The yoke, briefly, includes 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 as to scan the usual rectangular raster. Energization of the deflection coils comprising the yoke 26 may be effected by conventional vertical and horizontal .dellection Wave generators 62 and 64, respectively. Such apparatus will be understood to function suitably to produce substantially sawtooth energy at both horizontal and vertical deflection frequencies so that the fields produced by the yoke 26 are varied in a substantially sawtooth manner.

The beam convergence system also includes a plurality (e. g., three) of electromagnetic eld producing elements such as the magnets 29 and 30 mounted around the neck 21 of the color kinescope adjacent to the predeflection paths of the electron beam components. It is to be understood that the precise location of these magnets is not necessarily indicated in this figure. Instead, as will be understood, 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 are transverse to the associated beam paths.

Each of these convergence electromagnets may include a pair of spaced pole pieces and an energizing winding. The convergence magnets are energized by substantially unidirectional energy so as to effect an initial convergence of the electron beam components sub-' stantially in the plane of the apertured masking electrode 13. The convergence magnets such as 29 and 30 also are dynamically energized by the control Wave energy derived from a suitable generator (not shown) so as to effect a variation in the magnitude of the transverse fields produced respectively thereby These held strength variations are in accordance with a predetermined function of the beam deflection. Variations in the strength of the fields produced by the convergence magnets 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.

2E While not shown, it will be understood that, for each of the magnets, there may be provided on the inside of the tube neck 21 extended pole pieces so as to increase the effectiveness of these magnets. .By such means, the reluctance of the magnetic circuit is considerably decreased, and also the linx distribution of the eld produced between the internal pole pieces is considerably improved.

With beam convergence apparatus of this general character, it may be seen that such apparatus is adversely effected by both horizontal and vertical deflection flux from the deflection yoke. Hence, in accordance with the above-cited Goodrich patent, there is provided means for preventing the leakage ux from the deflection yoke from adversely affecting the individual beam convergence electromagnets in the manner described, which means comprises a magnetic shield located between the deflection yoke 26 and the convergence electromagnets, such as 29 and 3l). The magnetic shield includes a disk-like shielding member 45 of magnetic material located externally of the tube and having a centrally located aperture of proper diameter to enable it to be suitably mounted in close proximity to the outside of the tube neck 2 1. The outside diameter of the magnetic shielding member 45 is made suliicient to elect the desired shielding.

It has also become the practice to provide means for shielding selectively against the high frequency, horizontal deflection field. Since conventional horizontal and vertical deliection rates are of the order of 15.75 kilocycles and 60 cycles, respectively, an-efective shielding which is frequency-selective as to the higher frequency has taken the simple form of a disk 48 of copper or other non-magnet material having high electrical conductivity placed between the deflection yoke and the apparatus to be shielded (i. e., the beam-convergence magnets). The disk 4S has, as shown, a central aperture of such size as to accommodate the neck 21 of the kinescope and is ordinarily located `between the deflection yoke 26 and the magnetic disk d'. As in the case of the magnetic disk, copper disk i8 should be of suiicient thickness to possess the necessary mechanical strength and may be arranged to enable a sliding adjustment thereof. While the spacing of disk 48 from yoke 26 is not critical, it is located between the yoke and the magnetic disk 45.

The leakage flux from the deflection yoke 26, in the absence of the shielding means, is indicated in Figure l, as following generally the path 46. lt is seen that this path links the electromagnetic convergence apparatus and produces the deleterious elfects previously described. By virtue of the copper shield, however, the horizontal frequency leakage linx is effectively shielded and confined to the region bounded by disk 48. Specifically, the horizontal flux traveling along path shown by dotted line 49 induces eddy currents in disk 48, which currents produce a reverse magnetic field to cancel the leakage field. Moreover, while the horizontal field is thus prvented from reaching the convergence apparatus, it is not distorted.

By means of the magnetic shunt 45, the lower frequency leakage liux from the vertical deflection field is confined substantially to the path indicated by the broken line 47. In this case, it is seen that the vertical lield linx, which is not appreciably affected by the copper shield 48, is shunted into a path which is harmless, so far as the beam convergence apparatus is concerned.

In performing their respective functions of shunting and shielding the convergence magnet region from leakage flux of the deflection yoke, the members 45 and 4S also deline the rearward (toward the electron guns) limits of the vertical and horizontal leakage linx. Thus since the members 45 and 4S are, as a matter of physical necessity, spaced along the axes of the tube 1l, the rear limits of the vertical and horizontal leakage iiux are also spaced. More specilically, it Will be understood from the foregoing that, since the vertical frequency leakage liux travels farther back than does the horizontal leakage linx, the effective center of the vertical deflection lield isfarther back than is the center of the horizontal deflection field. In order to illustrate the foregoing, the dotted lines 50 and 52 in Fig. l show, in an exaggerated manner, the respective planes in which the vertical and horizontal deflection centers lie as a result of the action of the members 45 and 48 as well as by reason of certain selective shielding which occurs in the kinescope neck.

'The present invention, therefore, provides the novel yoke 26 which includes means for compensating for selective shielding effects upon the location of a deiiection center of the yoke. Specifically, the yoke 26 comprises a pair of horizontal deflection coils 56 and a pair of vertical deflection coils 58, each pair of coils having longitudinal and end conductors. In accordance with conventional practice, the front and rear end turns of each of the coils are bent upwardly so that, for example, the rear end turns of the horizontal coils 56 are shaped as at 56', while the rear end turns of the verticalA coils 58 are shaped as at 58. As may also be noted from the drawing, the vertical coils 5S are conventionally disposed around the horizontal coils, so that the end turns 56 of the horizontal coils overlie the end turns 58 of the vertical coils. Surrounding both pairs of coils is a magnetic core or sleeve 60 which may be of generally cylindrical formation. The core 60 serves in a Well-known manner as a low-reluctance return path for the flux produced by the two pairs of coils.

As thus far described, the yoke 26 is in general ccnformity with conventional practice. Hence it will be understood that, when suitably energized by sawtooth currents of field and line frequencies, respectively, from sources 62 and 64, the coils 58 and 56 will produce generally uniform transverse fields which are at right angles to each other.

in accordance with the present invention a disk or washer 66 of a material having high magnetic permeability (e. g., ferrite, Mu-Metal and the like), is provided between the turned-up end turns 56' and 58 of the horizontal and vertical deflection coils. The function of the disk 66 is, as will be explained, that of effecting coincidence of the centers of deflection of the vertical and horizontal coils. The manner in which such action occurs is as follows: By virtue of the high permeability of the ferrite or Mu-Metal disk 66, the leakage linx rearwardly of the vertical deection coil and turns 58' is appreciably reduced. Such reduction in the rearwardly extending leakage liux effectively shortcns the vertical deection field in the axial direction of the tube, so that the deflection [center of the vertical lield is effectively shifted forwardly to lie in the plane indicated by the dot-dash line 70. This forward shift of the vertical deliection center is also aided somewhat by the fact that the vertical deflection coils 58 are, in accordance with the invention, made slightly shorter axially than is usual, in order that the disk 66 may be accommodated between the end turns of the coil pairs.

At the-same time, the horizontal frequency lield is extended in length and, in particular, rearwardly by the action of the disk 66. That is to say the disk 66 serves, in addition to its function of reducing the leakage llux of the vertical coils, as an additional core means for the horizontal deflection coils. Stated otherwise, the main deflection field of a deflection yoke is determined by the axial length of the core (e. g., the core 60), since flux produced by that portion of the coils which is not surrounded by corc material must travel through the relatively higher reluctance patn afforded by the air and is thereby appreciably reduced in strength. The high permeability disk 66, however, serves as a core for that portion of the horizontal coils which it overlies or surrounds, thereby increasing the activity of the llux linking that portion of the coils, Such an effective increase iuV the axial length of the horizontal deflection eld produces the result of moving the horizontal center of deliection rearwardly from the plane 52. By selecting the proper thickness of the washer 66, it is practicable to shift the horizontal lields center of deflection from the plane 52 to the plane lli so that it substantially coincides with the center of dellection or" the vertical deection lield.

From the foregoing, it will be appreciated that the relatively simple structure of the deection yoke of the present invention aiords an eliective arrangement for bringing about the desired coincidence of horizontal and vertical deflection iield centers. An additional advantage realized with the invention is that the disk 6d provided thereby serves the additional function of aiding the usual ferrite shunt 45' in protecting the convergence magnets from the vertical deliection flux.

Having thus described my invention, what l claim as new and desire to secure by Letters Patent is:

l. An electromagnetic deflection yoke comprising a lirst pair of electromagnetic `coils adapted to surround the neck of a cathode ray tube, said lirst pair of coils having upwardly-turned end conductors; a second pair of electromagnetic coils surrounding said lirst pair of coils and oriented substantially normally with respect thereto, said second pair of coils also having upwardlyturned end conductors adjacent to said end conductors of said iirst coils; and a member of magnetic permeability disposed between the turned-up end conductors of said first and second coil pairs.

2. An electromagnetic deflection yoke comprising a first pair of electromagnetic coils adapted to surround the neck of a cathode ray tube; said first pair of coils having upwardly turned end conductors; a second pair of electromagnetic coils surrounding said first pair of coils and oriented substantially normally with respect thereto; said second pair of coils also having upwardly turned end conductors adjacent to said end conductors of said rst coils; and a disk-like member of/magnetic permeability disposed between the turned-up end conductors of said first and second coil pairs.

3. An electromagnetic deflection yoke comprising a first pair of electromagnetic coils adapted to surround the neck of a cathode ray tube; said first pair of coils having upwardly turned end conductors; a second pair of electromagnetic coils surrounding said iirst pair of coils and oriented substantially normally with respect thereto; said second pair of coils also having upwardly turned end conductors adjacent to said end conductors of said first coils; and a member of magnetic permeability disposed continuously between the turned-up end conductors of said rst and second coil pairs.

4. An electromagnc'ic deiiection yoke comprising a first pair or electromagnetic coils having longitudinal conductors and outwardly-turned end conductors; a second pair of electromagnetic coils surrounding said iirst pair of coils, said second pair of coils having longitudinal conductors parallel to those of said 'first coils and outwardlyturned end conductors and said second pair of coils being oriented normally with respect to said iirst pair of coils, the end conductors of said second pair being adjacent to those of said first pair; and a sheet of magnetic material disposed between the outwardly-turned end conductors of said first and second coil pairs for shifting the center of detiection of the magnetic field produced by at least one of said coil pairs.

5. The invention as defined by claim 4 wherein said lirst pair of coils comprises line dellection coils adapted to be energized by television line frequency current and wherein said second pair of coils comprises 'Field deflection coils adapted to be energized-by lield frequency current, whereby said sheet of high magnetic permeabilityY serves to reduce the region of activity of linx produced by said second pair of coils.

6. An electromagnetic deflection yoke for a cathode .ray tube having a gun and a target, said yoke comprising -a first pair of electromagnetic coils having longitudinal lllV conductors and outwardly-turned end conductors at their ends adapted to be nearer the gun end of such tube; a second pair of electromagnetic coils surrounding said lirS-t pair of coils and having longitudinal conductors parallel to those of said lirst coils and outwardly-turned end conductors adjacent to those of said lirst coils, said second pair of coils being oriented substantially normally to said first pair of coils; a magnetic core surrounding the longitudinal conductors of said first and second pairs of coils; and a f .r permeable by magnetic flux disposed be- .n said cnn conductors of said lirst coil pair and the end conductors of said second coil pair.

7. The invention as deined by claim 6 wherein said first pair of coils comprises line dellection coils and of coils comprises iield dellection coils linx-permeable member shifts the center .said pair of coils toward end Y 8. The invention "t pair of coils -nedby claim 6 line deflection pair of coils comprises ticld dei?.

(Y il -1 ermeable member si.v

center oi deflection of said second of coils i said end conductors.

9. in a cathode ray tube system ray tube hay' including a cathode neck housing an electron gun one end and a ta'get at the opposite end and frequcncv live lluXV shi means associated with such the region ot such gun end; electromagnetic deli yoke disposed around such neck between such frequency'- selective shielding means and such get, said yoke coinprisi a lirst p l" electromagnetic coils having lon i tudinal conductors and outwardly-turned end conductors at their ends adapted to be nearer the gun end of such tube; a second pair electromagnetic coils surrounding said First pair of coils and having longitudinal conductors parallel to those of said first coils and outwardly turned end conductors adjacent to those of said lirst coils; sa second pair of coils being oriented substantially i .N to said irst pair of coils; a magnetic core surrouno the longitudinal conductors of said first and seconc of coils; and a member permeable by magnetic ilu?i 1sposed between said end conductors or said first coil pair and the end conductors of said second coil pair.

l0. A cathode ray tube system including a cathode ray tube having an electron gun at one end and a at 'the opposite end; an electromagnetic deflection surrounding said tube in a region between said gun aid target, and frequency-selective shie.ding means loated. between said yoke and said gun for shielding a region between said yoke and gun from high and low frequency leakage llux from said yoke, said yoke com prising: a tirst pair of electromagnetic coils having longitu inal conductors and outwardly-turned end conductors at their ends adapted to be nearer the gun end ol Such tube; a second pair of electromagnetic coils surrounding said lirst pair of coils and having longitudinal conductors parallel to those o' said lirst coils and outwardly turned end conductors adjacent to those of said first coils; said second pair of coils being oriented substantially normally to said first pair of coils; a magnetic core surrounding the longitudinal conductors of said rst and second pairs of coils; and a member permeable by magnetic linx disposed between said end conductors of said first coil pair and the end conductors or" said second coil pair.

ll. in combination with a color kinescope of the type having gun means for producing a plurality of electron beams, a mosaic target up of a plurality ot` ciernental areas of respectively dillerent color character tics and means including convergence apparatus for causing tion yoke disposed between said target and said convergence apparatus, said yoke comprising: a rst pair of electromagnetic coils having longitudinal conductors and outwardly-turned end conductors at their ends adapted to be nearer the gun end of such tube; a second pair of electromagnetic coils surrounding said irst pair of coils and having longitudinal conductors parallel to those of said first coils and outwardly turned end conductors adjacent to those of said rst coils; said second pair of coils being oriented substantially normally to said rst pair of coils; a magnetic core surrounding the longitudinal conductors of said rst and second pairs of coils; and a member permeable by magnetic flux disposed between said end conductors of said first coil pair and the end conductors of said second coil pair.

12. An electromagnetic deflection yoke comprising a first pair of electromagnetic coils having longitudinal conductors and outwardly-turned end conductors and adapted to be energized with deflection current of a certain frequency; a second pair of electromagnetic coils surrounding said rst pair of coils, said second pair of coils having longitudinal conductors parallel to those of said rst coils and outwardly-turned end conductors adjacent to the end conductors of said first coils, said second pair of coils being oriented normally with respect to said rst pair or' coiis and being adapted for energization with deflection current of a frequency a plurality of times different from said certain frequency; and a metallic member interposed between said end conductors of said rst coil pair and the end conductors of said second coil pair for frequency-selectively shielding the ux from one of said pairs of coils.

References Cited in the file of this patent UNITED STATES PATENTS 2,074,764 Tolson Mar. 23, 1937 2,207,777 Blain July 16, 1940 2,463,720 Schade Mar. 8, 1949 2,562,394 Schlesinger July 31, 1951 2,605,433 Friend July 29, 1952 2,677,779 Goodrich May 4, 1954 2,692,355 Sickles Oct. 19, 1954

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