US2498056A - Nutator - Google Patents

Description

Feb. 21, 1950 WERNER 2,498,056

NUTATOR Filed D80. 20, 1946 2 Sheets-Sheet INVENTOR FRANK -D. WER/V R ATTORNEY Patented Feb. 21, 1950 NUTATOR Frank D. Werner, Silver Spring, Md., assignor to the United States of America as represented by the Secretary of the Navy Application December 20, 1946, Serial No.'717,381

10 Claims. .1 1

The present invention relates to nutators, that is, to the specialized type of nutator that is used for producing nutation of a radar antenna while inservice.

Heretofore, nutators have comprised a motor connected to a wave guide in such way as to cause the dipole or other energy radiator carried at or near the end of the wave guide to describe a circle or an ellipse. There was no relation between the natural mechanical period of vibration of the dipole-support and the speed, or rate, of nutation, so that resonance effects were not utilized. Such a system required a relatively high-powered motor, and mechanically-complicated means for providing circular or elliptic motion of the dipole, as required.

.An object of the invention is to improve. and simplify the structure and effectiveness of the nutator mechanism in certain respects without in anyway limiting its effectiveness. 1

The present device depends very materially on the phenomena of mechanical resonance and consequently may utilize a very much smaller motor, and materially simpler mechanism, for

lustrated in the accompanying drawing, where- Figure 1 is aside elevation of a nutator embodying the invention; and

Figure 2 is a corresponding plan view partly in section.

Referring to the drawing, the device comprises a suitable framework having a base I. front and rear end plates 2 and 3 and top bars, or rods 4, which combine to provide a very strong and rigid support for the working parts. A bracket 5 is secured to the base I in any suitable way and serves to hold a motor 6 in position with its shaft substantially alined with a wave guide 1 extending out beyond the front plate 2, as shown.

I The wave guide is rigidly secured to an inner gimbal member 8 which is pivoted to a gimbal ring 9 at two diametrically opposite points, ball bearings l being provided at said pivots. The gimbal ring 9 is in turn mounted on pivots at two diametrically opposite points, shown as the ball bearings 12 mounted on stationary pins IS. The

thereof,

" common axis of the bearings Ill is at right angles,

plate 2.

By reason of the structure so far described, it will be seen that the wave guide I is mounted to pivot freely in all directions about the point at which the gimbal axes cross.

Rods M, shown as four in number and made rigid by metal rectangles 4| brazed or welded thereto, are secured each to the member 8 at one end and indirectly to a cross beam I6 at the other, nuts [5 being threaded on. the rods for,

adjustment and clamping on intermediate bearing housings I I aboveand belowthe beam [6. Bearings l8, only one of which shows in the plan, located respectively above and below the cross beam l6, are provided to pivotally secure the,

housings II to the cross beam l6, as shown best in Figure 2. At the ends of the beam l6 are two.

stitute in effect a universal joint.

The universal joint just mentioned differs in one important respect from most standard ones. This is the feature that the two axes represented by the parts l8 and I9 do not necessarily cross, but the vertical axis, that is, the axis of bearings 18 (Figure 2 is adjustable forward and back relative to the other axis Hi to the extent of, for ex--; ample, one-half inch. As shown, the vertical;

proper adjustment by nuts 25, the ends of the.

rods 23 being provided with threads sufficient to permit the desired range of adjustment, whereby,

the tension of springs 22 may be controlled.

The beam 24 is in turn supported by a cup-andcone device comprising a hardened cup 26 sup ported by the plate 3 and having a substantially conical depression therein, against the bottom of which rests the tip of a cone 21 secured'to'the' beam 24. Preferably theangle of the cone 2! is.

materially smaller than the angle of the cup, so. that considerable angular play is possible in or-.

der that the beam 24 may adjust itself freely. Preferably a1so, ,thetip of cone 2! is somewhat softer than the bottom of the depression in cup 25 upon which it rests, so that the point of the cone will flatten slightly and roll on its seat, without Sliding friction.

The structure so far described comprises a wave guide 1 pivoted to move freely about a point in or near the front plate 2,, with a composite structure extending backward therefrom and comprising a set of four rods M, a universal joint (Hi to 28), a pair of rods 21, a spring 22 for each rod 2|, adjusting and securing rods 23 for the springs, and an equalizing beam 24 connecting the rear ends of the last named rods. This whole structure is supported jointly on'the gimbal 8 and cup 26 and in effect floats between these parts so that it can pivot or oscillate freely and in doing so will cause the springs 22 toyield: and return, as required.

In order to provide power to cause the oscillatory motion, the motor 6 is connected with the cross bar thy-means of a bar or rod 28- attached tp'the; shaft of the motor and extending radiallyoutwardtherefrom, as best seen in- Figure 1. This rod may have a threaded end; to receive nuts 29' between which is-held' a spring supporting element 3!), extending forwardly therefrom. One end; ofa spring 31 is engaged in a hole of the element- 38, and the other end of this spring is attached to the mid-point of the rear surface: of the cross bar [6 so as to pull the bar, and everything attached thereto, slightly away from its normal axial position which it would otherwise be maintainedby the balanced pulls of the springs 22-. As the motor. shaft turns, the direction of this pull changes correspondingly; but the pull itself always "centri-fugal in nature.

In ord er to minimize passage of'radiantelectrical energy into the gimbal location 9 Ma, a convex spherical head is provided onthe wave guide 1, as; shown at; 32*, at least the outersurface of which is of conductingmaterial, suchas metal; A radar choke is provided by locating a companion concave member 33; having a properly dimensioned circumferential slot 34) therein, close to and concentric with the convex member 32 A flexible diaphragm 35 may be clamped in place by the member 33* to seal thejoint between the movable wave guide 1- and, the stationary plate 2, against air, dust, anc l moisture; in other words, to; provide a reasonably weatherproof closure that does not prevent the necessary motion of the mechanism. it will be understood, of course; that the open sides of the framework I, 2-, 3 and 4 will actual service be, closed weather-tight, as could be done readily by flat plates inthepresent embodiment. a

The operation of the device is as follows:

When motor 6 is started in operation, it re; volves the spring 3!; around its. point of connec; Lion to cross bar l,,the spring during this move,- ment acting continually to pull the cross bar It radially outward, as already mentioned, but, ina changing direction due to rotation of the motor. In each revolution of the motor, the spring. 31" will first pull the; cross bar, iii (and therefore the rear ends of rods HS)- upwardly, then sidethe crossbar pivots l8, l9. It'willbe evident that, asa result of this motion, the wave guide I and;

the parts connected to 'it wi ll' nutate.

The effects produced by this pull of spring 31 isradially; outward oron the cross bar l6 will depend on the closeness of the approach of the springs periods of rotation by motor 6 to the resonant rate of vibration of the mechanism in its various senses. For example, if the natural period of vibration of the entire nutating structure in the vertical mode coincides with the speed of the motor, a violent vertical vibration-will result, while at the same time the horizontal amplitude, not at resonance, will not be very great. The above principle is applied as follows:

Arod 36 (Figure 2) is secured to the gimbal ring 9 which, as already stated, is mounted to pivot about the stationary pins it so as to oscillate solely inthe vertical mode. A weight 31 slides frictionally on the rod 36 between two stops 38 and 39:. When the weight is at stop 38, the moment of inertia of the movable system is at a minimum in the vertical mode, while at the other extreme, stop 33, the said moment of inertia a maximum. i

The whole mechanism may advantageously be so designed that when at minimum, the resonant frequency of the system is about the same in both the horizontal and the vertical mode, whereas at maximum moment 0t inertia. the resonant frequency in the vertical mode is. lower than in the horizontal mode and much closer to that corresponding to the motor speed. Thus, high. amplitude response in the vertical. mode is sea cured by shifting the weight 3:7 to stop 39*, thereby giving an elliptic nutation to the wave guide i, since the horizontal mode is not altered appreciably; When the weight 3.11 is. at. stop 39, however, the oscillation will be approximately the same in both modes, thus giving nutat-ion in; a circle. t may be remarked thatv the preferred designis suchthat the natural frequency of the. floating composite structure previously described is greater than that corresponding to: the motorspeed.

While only manual shiftingof the weight has been disclosed, itis clear that mechanical or electrical devices for accomplishing this function arepossible, if preferred. If the vibration of the whole machine is objectionable, isolatingmeans, such as rubber supporting feet 40, or the use, may be provided.

The radar dish is shown at 42. It is ordinarily a paraboloid' of revolution whose axis coincides. with the center line of the Wave guide I. The radiant energyis introduced into the inner end of the wave guide 1 inany suitable way, which does not form a part of the present invention.

In operation, the motorspeed" isenough lower than the resonant frec m.en ;y"'oi the vibrating system that the vibratingsystem responds; with, for example, /10 or /20 its maximum amplitude at resonance. the-resonant frequencies-for both horizontal" and vertical modes are practically identicaljthe vibration or nutatory sys-- tem will respond in a circular nutatory motion', which is transmitted to thewave guide i 'Ioshift to elliptical nutatory motion, weight is added or shiited 'insuch a m-a-imer as to lower" the resonant frequency in the vertical mode of" the composite vibrating ornutati-n'gstructure without affecting its resonant frequency in the horizontal mode. elf-course, when the vertical resonant frequencyis lowered (making itnearer the motor speed)-,'it will respond with much larger amplitude, and an elliptical nutatory mo,- tion, of wave guide 1" will result." By sliding the H mass along bar '36: away from the girnballcenter,'the mutating system iss'et'for' the elliptical" motion, it being understood that the resonant conditions correct for circular motion are-present when the mass 31 is at its position nearest the gimbal center. For this arrangement, the gimbal ring 9 must be so arranged that it moves with thevertical mode but does not move with the horizontal mode. There are a number of other ways of accomplishing this result, which is only a lowering of the resonant frequency of the vertical made without changing the resonant frequency of the horizontal mode. Springs can be added which affect the vertical mode only. Another way is to arrange the cup and cone bearing 26, 21 in two parts, so that in circular motion the horizontal mode swings about a bearing point which is perhaps an inch behind the bearing point about which the vertical mode swings; For elliptical motion, the forward bearing point is released, permitting the motion for both modes to take place about the rear cup and cone bearing.

Mention has been made of the necessity of adjusting the resonant frequency of the horizontal mode with respect to the vertical mode, or vice versa. Adjustment of the universal joint I8, l9 makes this possible. To raise the resonant frequency of the horizontal mode, the rear axis [9 of this universal joint is moved nearer the motor, making the distance between the horizontal and vertical axes of the universal joint greater.

To increase the amplitude, the tension of spring 3| is increased or the main springs 22 may be adjusted so as to bring the resonant frequency of the system nearer the motor speed. For optimum setting in elliptical motion, the resonant frequency of the vertical mode should be so far above the motor speed that it responds with perhaps to A; maximum amplitude at resonance. This done, the tension of 3| is set so that the desired amplitude is obtained.

The new nutator is of simple construction and requires relatively low power input. It is capable of changing readily from elliptical motion to circular motion.

It should be borne in mind that while circular and elliptic motions are discussed in the present disclosure, essentially all the motions actually to be encountered are elliptic, although some of the ellipses may approach so nearly to equality of major and minor axes that for all practical purposes they may be treated as circles. However, except by the rarest of chances, a mathematically true circle would never be produced, and even then it would not remain stably so, since an infinitesimally small change in the operating conditions would suffice to destroy the equality of the axes. The term elliptic, as used in the claims, therefore is to be understood as covering all closed conics, from those which are approximately true circles to those whose major axes are decidedly greater than their minor axes.

I claim: 1. A nutator for a device, comprising a gimbal member for supporting one end of said device,

a gimbal ring surrounding and pivotally supporting said member for motion about an axis, means for supporting the ring for pivotal motion about an axis at right angles to the first-named axis, a rigid extension projecting from the side of said member opposite the device, resilient means 00- acting with said movable elements, means for adjusting the tension of said resilient means, to provide a desired natural mechanical period for the entire movable assembly on said gimbal member, a motor, and means operatively connecting said motor to the assembly, for nutating" the assembly on the gimbal member.

2. A nutator which comprises a member for supporting a device that is to be nutated, a gimbal ring in which said member is pivoted for movement about an axis, a frame on which said ring is pivoted for movement about an axis at right angles to said first axis, a mass supported on said member and projecting therefrom in a direction opposite to that of the said device, re silient means ooacting with said mass to provide a natural mechanical period for said mass, supporting member and ring, a motor, means opera:

tively connecting said motor to said mass, for nutating said mass, and means, comprisinga weight adjustable toward and from one of said axes, for adjusting said natural mechanical period in one mode to vary the motion incident to nutation of said mass.

3. In combination, in a nutator, a member for supporting the device that is to .be nutated, a gimbal ring in which said memberis pivoted for movement about a substantially vertical axis, a frame on which the ring is pivoted for movement about a substantially horizontal axis, a'rigid ex-. tension projecting from said member, a cross beam adjustably mounted on said extension and pivotable thereon about a substantially vertical axis, rods pivotally connected to the ends of the cross beam, said beam being pivotable relative to the rods about a substantially horizontal axis offset from said last vertical axis, an equalizing beam pivotally mounted on said frame, tension springs adjustably connected between the ends of said last beam and said rods, a motor on the frame and having a drive shaft disposed with its axis substantially aligned with said device to be nutated, an arm on said shaft extending at right angles thereto, a tension spring connected at one end to said arm and at the other end to said cross beam intermediate its ends, whereby rotation of said shaft operates through said last spring to nutate said extension, supporting member, gimbal ring and device, and adjustable means carried by the nutatable structure for varying the resonant frequency of said extension, supporting member and device about one of said first axes to vary the motion of said device incident to said nutation.

4. In combination, in a nutator, a member for supporting the device that is to be nutated, a gimbal ring in which said member is pivoted for movement about a substantially vertical axis, a frame on which the ring is pivoted for movement about a substantially horizontal axis, a rigid extension projecting from said member, a cross beam adjustably mounted on said extension and pivotable thereon about a substantially vertical axis, rods pivotally connected to the ends of the cross beam, said beam being pivotable relative to the rods about a substantially horizontal axis offset from said last vertical axis,

an equalizing beam pivotally mounted on said' frame, tension springs adjustably connected between the ends of said last beam and said rods, a motor on the frame and having a drive shaft disposed with its axis substantially aligned with said Wave guide, an arm on said shaft extending at right angles thereto, a tension spring connected at one end to said arm and at the other end to said cross beam intermediate its ends, whereby rotation of said shaft operates through said last spring to nutate said extension, supporting member, gimbal ring and device, and a weight mounted on the gimbal ring and adjustcause ihle. between, two positions thereon to vary the resonant frequency or said extension, supporting member. and device about the imbal ring axis and thereby vary the motion of said device incident. to said nutation.

ii. A mechanical oscillator including av device to be oscillated, said oscillator being mounted to pivot in any direction abouta fixed point and having .a longitudinal axis extending throu h said point, said oscillator normally having substantially the same moment of inertia with respect to any .linepassing through said point'and perpendicular to. said axis, means, including amass shiftab'le toward and from the axis, for changing saidmoment in one modeof oscillation and thus altering the natural period said mode, and means comprising a single element in conrotation about said axis; and exerting a substantially constant radial force on said oscilla-tor, ioruexciting elliptic mechanicaloscillation of I said Y oscillator.

6. A nutator comprising a mechanical system including a device to be, nutated, said mechane ical system vhaving two pivotal axes at right angles "to each other, whereby it may oscillate mechanically substantially as a whole. about. their intersection point, said system, however, having apart which is pivotally movable about: only one of said axes, adjustable. means carried by said part for varying. the corresponding moment of inertia of the system, and a source. of mechanical-power for excitingoscill'ation oi the system, said source comprising a member rotating uniformly abouta tl'lird' axis through the intersecrtion of the first-two axes and perpendicular to both, said member exerting a. substantially constant radial force on said system.

- i". Anutator as definedinclaimfi wherein the source of power has a rotating shaft, and whence in aspring provides the connection between the mechanical system and said shaft.

8.. A nutator as defined in claim 6, whereinthe source of power has .a rotating shaft and a spring provides. the connection between, the mechanical system and the shaft, there being means for ad-, justing the tension of. the spring to. vary. the amount of power supplied to the system 9 A nutator as defined in claim 6, wherein the mechanical system includes resilient; means for exerting tension in a direction substantially parallel to the length of the device being nutated, and means for adjusting said tension to vary the natural period of oscillation of the system.

10; Anutator as defined in :claim 6,. wherein the. mechanical system includes a universal joint hav- 'ing two normally non-intersecting axes, and means for varying the distance between said'axesi to adjust the natural period of mechanical 050119 lation of one mode of the system withrespectto that of the other mode.

REFERENCES CITED The following references are of record ln the file of this patent:

UNITED STATES PATENTS Number Name Date I,208,l00 Cornwall Dec.- 12-, 1916- 2,407,3 05 Langstroth Sept. I6; 1946 2,408,825 Varian et al. Oct. 8;, 1946 2310,666 Leck Nov. 5-, 1946 2,412,867 Briggs et a1 Dec. 17'; 1946

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