US2835892A - Antenna using single motor for rotation and nod - Google Patents

Description

May 20, 1958 o. E. szEKELY ANTENNA USING SINGLE MOTOR FOR ROTTION AND NOD Filed May 29, 1951 9 Sheets-Sheet 1 NF.. R mx m ,NAM .m

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O. E. SZEKELY ANTENNA USING SINGLE MOTOR FOR ROTATION AND NOD Filed May 29, 1951 9 Shees-Sheet 2 JNr/ENTOR. 077'@ f'. SZEKEU/ ATTORNEYS.

May 20, 1958 o. E. szEKELY 2,835,892

ANTENNA USING SINGLE MOTOR FOR ROTATION AND NOD Filed May 29, 1951 9 Sheets-ShedI 3 F/G. 2A.

INVENTOR. QTTO E. SZEKELJ/ May 20, 1958 o. E. szEKELY ANTENNA USING SINGLE MOTOR FOR ROTATION AND NOD Filed May 29, 1951 9 Sheets-Sheet 4 .v, m. ma .m NK M m r NE T IZ A s .w E. m

May 20, 1958 o. E. SZEKELY ANTENNA USING SINGLE MOTOR FOR ROTATION AND NOD Filed May 29 1951 9 Sheets-Shea?l F/G. a.

. INVENTOR. OTTO E SZEKE/ y MMM? FIG. 4.

ATTORNEYS.

May 20, 1958 o. E. szEKELY 2,835,892

ANTENNA USING SINGLE MoIoRFoR NOTATION AND Non Filed May 29, 1951 9 sheets-sheet e INVENTOR.

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May 20, 1958 o. E. szEKELY ANTENNA USING SINGLE MOTOR FOR ROTATION AND NOD 9 Sheets-.'Sheerl '7 Filed May 29, 1951 y mi. NE EK V MM 5 E. 0. T T O ATTUR EYS.

May 20, 1958 o. E. szl-:KELY 2,835,892

ANTENNA USING SINGLE MOTOR FOR ROTATION AND NOD Filed May 29, 1951 9 Sheets-Sheet 8 INVENTOR.

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ATTORNEYS.

May 20, 1958 o. E. szl-:KELY 2,835,892

ANTENNA USING SINGLE MOTOR FOR ROTATION AND NOD Filed May 29, 1951 9 Sheets-Sheet 9 F l G. IO.

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N OTTO E. SZEKELY ATTORNEYS is uniform, and

vat 130 (plus 65 and minus 65 United States PatentA ANTENNA USING SNGLE MOTOR FOR ROTATION AND NOD Otto E. Szekely, Philadelphia, Pa., assigner to 0. E.

Szekely & Associates, Inc., Philadelphia, Pa., a corporation of Pennsylvania Application May 29, 1951, Serial No. 228,951

4 Claims. (Cl. 343-7466) This invention relates to an improved radar antenna lfor use in aircraft. y.

The essential features of an aircraft radar antenna consist of a spindle which carries a wave guide on which is mounted a source of primary feed, such as a cutler type primary feed that emits electronic rays and aparabolic reilector that directs the rays out and receives the returning reflected rays. The returning rays which impinge on the reflector are carried to a screen and thus present a picture of the objects from which the rays have been reflected. Y

ln order that the maximum area may be covered, the spindle, the Wave guide, the cutler feed and the reflector are driven by a mechanism which causes them to rotate and to have azimuth Iangular deilection. Azimuth angular deilection is frequently called nod or scan.

The spindle may rotate and nod or scan at the same time. When this occurs, the wave guide, the Cutler feed and the reflector move through a spiral configuration. Thus they scan a cone of volume directly forward of the airplane. This motion is continuous and rapid since the spindle, wave guide and reflector may rotate at speeds up to 126() R. l. M.

A reduction in the power required to drive this imechanism results in a reduction in the weight and cost of the driving mechanism. The power is required to drive electric generators to provide current for electric motors. These motors, in turn, drive mechanical mechanisms such as gears, shafts, racks and pinions to carry out the functions as described above. Therefore, it is evident that any reduction in the power required will result in .substantial savings in cost, weight and size ci the mechanism since all items such as generators, motors and mechanical mechanisms are reduced in proportion to the reduced pon-'er requirement, Reduction in weight and size is or' utmost irri-partance in all airborne equipment.

ilerctol'ore, it has been considered necessary to drive spindle in rotation by one motor and drive the nod by another motor. ln addition to the weight, cost and complications of two motors, this dual motor arrangement has the even more serious disadvantage that, due to line voltage iiuctuations, these drive motors vary in speed. Thus, the drive motor for rotation may speed up while the drive motor for nod `may slow down or vice verf' Hence, the spiral conguration due to rotation :u and is unpredictable. With a single motor producing both rotation and nod, the coniguration of the spira., through which the spindle and reflector proceed, the overlap between the successive sweeps of scanning i'nechanisrn is always the same. Thisoverlap insures that all the volume contained in the eld of view is investigated during a cycle of operation.

On wide scan, that is when the unit is noding as much from the .straight ahead center line of the unit) and rotating for example at i200 il. ifi., the motion of the spindle, the wus/c guide, the cutler feed and the reflector is extremely rap id near the point of extreme angular deflection. This motion is so rapid that even with electronic pulses at the rate of 5704000 per second, so few returning pulses may be received that the electronic signal may decay before the following signal is received. When this occurs, no image appears on the screen and the target will not be seen at all.

it is, therefore, an object of this invention to provide an improved radar antenna in which the spindle, wave guide, cutler feed and reflector are driven in both rotation and nod by a single drive motor.

it is a further object of this invention to provide an improved radar antenna, having a single drive motor for both rotation and nod, which can be shifted from wide to narrow scan by reversing the direction of rotation ,of the drive motor.

it is a further object of this invention to provide `an improved radar antenna,` having a single drive motor for both rotation and nod, in which a novel shifting mechanism is employed for shifting from Wide to narrow scan.

It is a further object of this invention to provide an improved radar antenna, having a single drive motor for both rotation and nod, in which a Speed control device is employed which reduces the speed of the drive motor in proportion to the cosecant of the nod angle. This reduces the speed of the motion of the unit at the point of extreme angular deflection in wide scan to such an extent that a minimum of three successive hits are obtained on a target. This insures the production of an image of the target on the screen when the target is viewed near the point of extreme angular deflection of the unit. y

The accompanying drawings are illustrative of one embodiment of this invention, in which:

Figure 1A is a side view of the left-hand. portion of the improved radar antenna showing the parts broken away.

Figure 1B is a side view of the right-hand portion of the improved radar antenna showing the parts broken away.

Figure 2A is a top view `of the left-hand portion of the improved radar antenna showing the parts broken away.

Figure 2B is a top View of the right-hand portion of the improved radar antenna showing the parts broken away.

Figure 3 is a sectional view taken on line 3-3 of Fgure 1B.

Figure 4 is a sectional view taken on `line 4-4 of Figure 3.

Figure 5 is an end View of the Vshifting mechanism taken on line 5-5 of Figure 2B.

Figure 6 is a sectional view taken on line 6-6 of Figure 5.

Figure 7 is an end view of the speed control unit taken on line 7-7 of Figure 6.

Figure 8 is a sectional view taken on line 8--8 of Figure 1B.

Figure 9 is a schematic perspective view of the complete improved radar antenna.

Figure l() is a wiring diagram showing electrical connections between elements of the speed control apparatus.

Referring specically to Figure lA, Cutler feed 2 is mounted on the end of wave guide 4. Wave guide 4 has dipole 6 mounted thereon and is joined at its right-hand end to azimuth pinion 8, as shown at 7. Azimuth pinion 8 is journalled in supporting bracket 1t) on bearings 13 and 14. Secured to the top of azimuth pinion 8 as by press fitting, welding or other convenient means, is weight frame l2. Weight frame 12 is rotatably mount ed on supporting bracket 1i) `at the bottom thereof, as

3 viewed in Figure lA, by pin which engages bearings 16.

As best seenin Figure 2A, weight frame 12 has two ears 18 and 20 projecting from the front thereof, having two holes therein for the reception of bearing sleeves 22 and 24, respectively. Journallcd in bearing sleeves 22 and 24 are headed machine bolts 26 and 28 respectively', each of said bolts being threaded into reflector supporting bracket 30. Mounted on reilector supporting bracket are bearings 32 which support reector backing piate 34. Reflector backing plate 34 is secured to bearings 82 by cap member 36 and bolts 38. Secured to redactor backing plate 34 is perforated parabolic reflector 48 which may be secured to the backing plate as by rivets 42 or other convenient means.

Details of the rotatable mounting of the parabolic reflector are disclosed and claimed in my copending application, Serial No. 223,216, led April 27, i951, now

issued as Patent No. 2,653,240, dated September 22, 1953.

Referring again to Figure 1A, wave guide 4 has a pas- Asage 44 therein which connects with passage 46 through dle 56 connects with passage 58 in stationary housing end plate 60. End plate 60 has a tube 62 received in an aperture therein having passageway 64 therethrough.

Referring specifically to Figure 1B, azimuth pinion supporting bracket 10 is fixedly secured to hollow spindle 56 as by pin 66. Hollow spindle 56 is journalled in housing 68 on bearings 70 and 72. Bearings 7d are supported by housing end plate 74 having sealing gasket 76 mounted therein. Housing end plate 74 is supported by bracket 75. Bracket 75 may be affixed to an aircraft by any desired means. Housing 68 may be secured to end plate 74 as by machine bolts 77. Mounted adjacent end plate 74 is breather 78.

Mounted on the upper right-hand end of housing 68, as viewed in Figure 1B, is tilt motor 80. Tilt motor 88 has a pinion 82 mounted thereon which engages rack 84, the purpose of which is toA shift collar 86 on hollow spindle 56. Shifting collar 86 is rotatably mounted on spindle 56 and has arod 88 attached thereto which engages `a tilting fork, not shown, which is mounted in azimuth pinion 8. The purpose of tilt motor is to tilt the reflector in a vertical plane when the mechanism is nodding only.

Fixedly secured to spindle 56 is spindle drive gear 90 which meshes with worm gear 92, said worm gear being rotatably mounted on cross-shaft 94. Mounted below i spindle drive'gear 90 is indexing solenoid 96, the purpose of which is to index spindle 56 so that dipole 6 is in the Vertical position when the spindle is stationary.

Referring specifically to Figure 3, worm gear 92 is rotatably mounted on shaft 94, said shaft being journalled in housing 68 on bearings 96 and 98. Splined to shaft 94 is clutch 100, which is actuated by a solenoid, not shown. The purpose of clutch is to engage worm gear 92 for rotation with shaft 94. Shaft 94 has gear 102 mounted at the right-hand end thereof as viewed in Figure 3, said gear meshing with gear 184- Gear 104 is supported by bearings 106 and 198. Gear 104 is slotted at its left-hand end and is engaged by a tongue on the drive shaft of main drive motor 11i), as shown at 112. Main drive motor is a direct current compound wound reversible motor. Mounted at the top left-hand end of the main drive motor 118, as shown in Figure 3, is conduit fitting 114 which carries wires which may be joined to a source of current.

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4 Aftixed to housing 68 at its lower right-hand side thereof, as viewed in Figure 3, is azimuth potentiometer 116, the purpose of which is to' determine the magnitude of the sweep on the oscilloscope. The gearing arrangement for driving potentiometer 116 is not shown.

Referring specifically to Figure 2B, tilt potentiometer 118 is mounted adjacent the top right-hand end of housing 68. Potentiometer 118 is actuated by shaft 120, having gear 122 thereon. Gear 122 meshes with gear 124, which is journalled in bearings 126 and 128. Gear 124 has a gear 132 aixed thereto which is rotated by a rack mounted on shifting fork 134.

Referring specically to Figure 2A, azimuth pinion 8 has a collar 136 mounted thereon, said collar being secured to pinion 8 by machine bolt 138. Collar 136 has teeth 140 cut therein, said teeth engaging with corresponding teeth 142 on rack 144. Rack 144 has rod 146 threadedly received in the end thereof, the other end of rod 146 being threaded into shifting collar 148. Shifting collar 148 is rotatably mounted on hollow spindle 56.

As best seen in Figure 8, shifting collar 148 is engaged by two bearing members 150 and 152, respectively, which are supported by shifting fork 154. Shifting fork 154 is rotatably secured to housing 68 by headed machine bolt 156. Shifting fork 154 is provided with a slot 158 in the left arm thereof, as viewed in Figure 8. The left arm of the fork is provided with a pair of apertures on either side of the slot 158, for the reception of stem 160 of bearing member 150. Mounted on stem'16i) by means of bearings is one end of a connecting rod 162. On the top left-hand side of the slotted rleft fork arm are provided rack teeth -164 which mesh with corresponding teeth on gear 166. Gear 166 is mounted on the shaft of generator potentiometer 168, the purpose of which is to maintain the generator output constant, irrespective of changes in the speed of the drive motor,

As Will be seen from Figure 2B, connecting rod 162 is made in three parts and a sleeve is provided intermediate the ends thereof so that the length of the connecting rod may be varied by threading one end into the sleeve.

Connecting rod 162 is driven by stud 170, as best shown in Figures 5 and 6, Connecting rod 162 is supported on stud 170 by bearings, and is secured thereto by castellated nut 172. Threaded stud 170 is formed integral with a slidable plate 174, which is interposed between plates 176 and 178. Plates 176 and 178 may be joined together as by screws 189. Plate 178 has a U-shaped opening 182 formed therein and it will be seen from Figure 5 that stud 170, made integral with slidable member 174, is driven from one end of slot 182 to the other as the direction of rotation of plate 178 is reversed. Secured to plate 176 is plate 184, having threaded stud 186 formed integral therewith, said plate 184 being secured to gear 188 by a castellated nut 190. Gear 188 is secured to member 192 as by pins 194, said member 192 being formed integral with shaft 196. Shaft 196 has a pilot 198 at the end thereof which projects through gear 188, plate 184 and into plate 176, thus helping to secure these members together.

Thus, it will be seen from the foregoing description that plates 176 and 178, having slidable member 174 interposed therebetween, are mounted eccentrically with respect to shaft 196. Thus it will be seen that as the direction of rotation of member 176 and 178 is reversed, stud 170 will be caused to shift to the opposite end of slot 182. For example, if the device is turned clockwise, as viewed in Figure 5, the length of the crank arm driving the connecting rod 162 will be from the center of shaft 196 to the center of threaded stud 170. If the direction of rotation is reversed so that the plate 178 rotates in a counter-clockwise direction, as viewed in Figure 5, threaded stud 170 will shift to the opposite end of slot 182, as viewed in Figure 5, and the length of the crank arm from the center of shaft196 to the center of stud 170 will be reduced as a result of the eccentric mounting of plates 116 and 178 with respect to shaft 196. Due to the fact that connecting rod 162 actuates shifting collar 148, rod 146 and rack 144, which turns azimuth pinion 8 about its vertical axis as viewed in Figure 1A, it will be appreciated that the azimuth angular deection of the wave guide and reiiector will be reduced.

Shaft 196 is journalled in bearings 200. Meshing with gear 188 is worm gear 202, cut on shaft 204, as best shown in Figure 4. Shaft 204 is journalled at its upper and lower ends in bearings 206 and 208, respectively. Mounted on the top of shaft 204 is gear 210 which meshes with worm gear teeth 211 cut on shaft 94.

Thus it will be seen that the rotation of shaft 94 serves to rotate spindle 56, when clutch 100 is engaged, and also drives wave guide 4 and reflector 40 through azimuth angular dellection or nod due to the drive through shaft 204, gear 188, stud 170, connecting rod 162, shifting collar 148, rack 144 and collar 136, mounted on azimuth pinion 8.

Shaft 196, at the lower end thereof, as viewed in Fig ure 6, has a gear 212 secured thereto by key 214. Shaft 196 is threaded at its lower end and has castellated nut with shoulder 2.14 formed on shaft 226. Shaft 226 has a collar 236 mounted thereon which supports insulating ring 238 and spacer member 240. Collar is st ported at its upper end, as viewed in Figure 6, by b ing sleeve 242, and is secured at its upper end by bea plate 244 and spring collar 246.

A rotating switch indicated generally at 237 in ures 7 and l0 includes, as best shown in Figures 7, a contact arm 248 secured to an insulating riff The contact arm 248 mounts a member 249 eng slip ring 250 mounted on insulating ring 262, 252 'also supporting a plurality of contact bu c which are engaged by the other end of arm l' tact buttons 254 and slip ring are` connected means of wires to a resistor box 25S shown in Figure 10 having a plurality of resistors therein for a purpose to be hereinafter described. insulating ring 252 is secured to supporting member 256 by bolts 258. Member 256 is secured to plate 260 by a plurality of threaded studs 262, said threaded studs being secured to plate 264 by nuts 266. Secured to shaft 226 by screw 263 is cam 270. As shaft 226 rotates, cam 270 trips two microswitches 272 and 274, as best shown in Figure 2B. Micro-switches 272 and 274 are supported by threaded studs 276. The purpose of these micro-switches will be hereinafter described.

The operation of the device is as follows:

Assuming that it is desired to drive the radar antenna in rotation and nod at wide scan, impulses are transmitted through passageway 64 and member 62, passageway 54 in hollow spindle 56, through hollow elbow zii through passageway 46 in azimuth pinion 8 and through passageway 44 in wave guide 4 and through cutler feed 2 against reflector 40, from which they are directed forward of the antenna. skilled in the art that received as well as transmitted impulses pass through this same channel. Drive motor 110 is energized and due to the driving connection between gear 104 and gear 102, shaft 94 will be rotated. rClutch 100 will be engaged and worm gear 92 will drive lt will be appreciated by those f assassin main Spindle drive gear which will rotate spindle 56, azimuth pinion 8, wave guide 4 and cutler feed 2. The rotation of shaft 94 will also rotate gear 210 axed to shaft 204, and worm gear 202 on shaft 204 will rotate gear 188. Gear 188 will rotate plates 176 and 178 having slidable member 174 interposed therebetween and ysince stud 170 is formed integral with slidable plate 174,

it will also rotate and will reciprocate connecting rod 162. It will be appreciated that in order to drive the mechanism in wide scan, stud 170 must be positioned in slot 182 as it is shown in Figure 5, since this arrangement provides a long crank arm from the center of rotation of shaft 196 to the center of stud 170.

As connecting rod 162 reciprocates, it in turn, recip rocates shifting collar 148 rotatably mounted on spindle rThis results from the fact that connecting rod 162 is secured to shifting fork 154, which has bearings engaging shifting collar 14S. Attached to shifting collar 148 is rod 146 having rack 144 secured thereto at its left-hand end, as viewed in Figure 2A. Rack 144 has teeth 142 thereon which engage with teeth 140 on collar 136 and since collar 136 is xedly secured to azimuth pinion 8, it will be appreciated that the reciprocation of shifting collar 148, rod 146 and rack 144 will cause azimuth pinion 8 to rotate about its vertical axis, :is viewed in Figure 1A. The reciprocating motion of ruck 144 will cause the wave guide, cutler feed and reflector to move through an azimuth angular deflection or nod. Since spindle 56, having azimuth pinion 3 and wave guide 4 affixed thereto, is rotated, it will be appreciated that the wave guide 4, cutler feed 2 and reflector 40 will move through a spiral configuration. As gear 188 rotutes, it, in turn, will rotate Shaft 226 of the speed control unit, due to the driving connection between gears 212 and 218. As shaft 226 rotates, arm 248, mounted on insulating ring 238, is caused to travel around button contacts 254 of switch 237. Button contacts 254 are connected to a plurality of resistors and the resistor box 2535 as shown in Figure l() in such a manner that when the spindle, wave guide, cutler feed and reilector are near the point of extreme angular deflection, resistance is put in series with the drive motor, which serves to decrease the speed of the drive motor at the point of extreme angular deflection, thus insuring a sumcient decrease in speed of the drive motor so that a minimum of three successive hits are obtained on the target by the transmiied pulses. Also at the point of extreme angular dede tion, micro-switch 272 is actuated by cam 270 to rer the current to the motor for a short period in order to rapidly decrease the motor Speed. The function of micro-switch 274 is to prevent the speed control unit from becoming operative until the device is rotating at the desired speed. These functions of the switches 272 and 274 are made evident by the wiring diagram of Figure 10.

Resistance is added in series with the drive motor by the rotation of shaft 226 having arm 248 afixed thereto so that the speed of the drive motor is reduced in proportion to the cosecant of the nod angle of the spindle,

wave guide and reflector.

When it is desired to operate the antenna on narrow scan, drive motor is reversed and it will be appreciated that this reversal causes a similar reversal in the direction of rotation of shaft 94 and spindle 56. Also,

gear 188 will be driven in the opposite direction, which will cause stud to travel to the opposite end of slot- 182, from the position shown in Figure 5. This will shorten the crank arm from the center of rotation of shaft 196 to the center of stud 170, which will, in turn, decrease the travel of shifting collar 148 and rack 144. Hence, rack 144 will drive azimuth pinion 8l through a smaller angular deilection than is the case when stud 170 is positioned in slot 182, as shown in Figure 5.

It will be appreciated that when operating on narrow scan, the nod angle may be reduced as much as desired by the proper positioning of slot 182, relative torshaft 196. If the nod angle is suiciently reduced, the speed of the spindle, wave guide, cutler feed and reflector may lbe reduced suiciently so that it is not necessary to add resistance in series to the drive motor at the point of extreme angular detiection. Thus, when operating on narrow scan, the speed control unit may not be used if the nod angle is suciently reduced.

From the foregoing description it will `be appreciated that the improved radar antenna provides for the elimination of one of the motors commonly used in radar antennae which perform a similar function. By the device of the present invention, a radar antenna may be driven in both rotation and nod by a single drive motor, thus eliminating the Weight of the additional motor and, at the same time, insuring that the conliguration of the spiral through *which the spindle and the reiiector proceed is uniform and that the overlap between the successive sweeps of the, scanning mechanism is always the same. speed differences between the two motors formerly used, due to line voltage fluctuations, have ybeen completely eliminated due to the fact that only a single motor is employed.

Further, the device of the present invention provides L for driving a radar antenna in both rotation and nod, and also for shifting from wide to narrow scan, using only a single drive motor. The device is shifted from wide to narrow scan by the simple expedient of reversing the drive motor, which decreases the nod angle as a result of the shortening of the crank arm, which actuates the rack in engagement with the azimuth pinion.

The radar antenna of the present invention also provides for a better picture due to the action of the speed control unit, which serves to decrease the speed of the drive motor when a target is viewed near the point of extreme angular dellection ofthe unit.

It will be appreciated by those skilled in the art that various modifications may be made within the scope of this invention without departing from the spirit thereof and the scope ot' the invention is to be restricted only in accordance with the appended claims,

What is claimed is:

l. A radar antenna comprising a rotatable spindle,

means mounting a wave guide and reflector on said rotatable spindle, said mounting means `being pivotable on an axis substantially perpendicular to the axis of said spindle, a reversible motor, drive means connecting said motor to' said spindle to rotate said spindle, means connecting said motor to said mounting means to oscillate This results from the fact that the said mounting means and nod the wave guide and reflector and including means actuated by reversing the drive motor for varying the angle of said oscillation.

2. A radar antenna comprising a rotatable spindle, means mounting a wave guide and rellector on said rotatable spindle, said mounting means being pivotable on an axis substantially perpendicular to the axis of said spindle, a reversible motor, drive means connecting said motor to said spindle to rotate said spindle, means including a crank connecting said motor to said mounting means to oscillate said mounting means and nod the wave guide and reflector and including means actuated by reversing the drive motor for varying the angle of said oscillation.

3. A radar antenna comprising a rotatable spindle,

means mounting a wave guide and reilector on said rotatable spindle, said mounting means being pivotable on an axis substantially perpendicular to the axis of said spindle, a reversible motor, drive means connecting said motor to said spindle to rotate said spindle, means connecting said motor to said mounting means to oscillate said mounting means and nod the wave guide and reilec'tor and means to reverse the current to said motor to rapidly decrease the speed of the motor in the range of maximum nod.

4. A radar antenna comprising a rotatable spindle, means mounting a wave guide and reflector on said rotatable spindle, said mounting means being pivotable on an axis substantially perpendicular to the axis of said spindle, a reversible motor, drive means connecting said motor to said spindle to rotate said spindle, means connecting said motor to said mounting means to oscillate said mounting means and nod the wave guide and reflector and speed control means for decreasing the speed of said motor in proportion to the cosecant of the nod angle by adding successive resistances in series with the motor as the nod angle increases.

References Cited in the le of this patent UNITED STATES PATENTS 312,709 De Valin Feb. 24, 1885 1,779,981 Nickerson Oct. 28, 1930 2,407,305 Langstroth Sept. 10, 1946 2,452,916 Fleischmann Nov. 2, 1948 2,518,511 White Aug. 15, 1950 2,543,188 Moseley Feb. 27,-1951 2,552,566 Levine May 15, 1951 2,566,843 Lappin et al. Sept. 4, 1951 2,576,836 Hlsinger Nov. 27, 19,51 2,590,540 Jackson Mar. 25, 1952

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