WO1993005363A1

WO1993005363A1 - Stabilized antenna system

Info

Publication number: WO1993005363A1
Application number: PCT/US1992/007599
Authority: WO
Inventors: Lawrence F. Anderson; Dieter Moenig
Original assignee: Anderson Lawrence F; Dieter Moenig
Priority date: 1991-09-09
Filing date: 1992-09-08
Publication date: 1993-03-18

Abstract

A stabilized antenna tracking system provides three axis gyro stabilization of only the antenna (11) and reflector (12) employing silent torque motors (88 and 91) with unlimited azimuth angle variation and unique mounting arm (16) for maximizing the degree of antenna motion.

Description

" STABILIZED ANTENNA SYSTEM "

F I E L D OF I NV ENT I ON

Stabilized platforms for shipboard mounting of microwave antennas and the like normally employ some type of pendulum system or gyro stabilization, and these systems are widely employed for satellite tracking and navigation of vessels. In this field of endeavor, the present invention provides a marked improvement by stabilizing the antenna itself with a resultant reduction of weight of mast-mounted radomes, limitation of vibrations, reduction of noise of operation, and limitless azimuth anhle variation.

BA C K G R O UN D OF I NV ENT I ON

There have been developed many stabilization systems for shipboard tracking antennas including two axis, three axis and four axis systems. All of the foregoing stabilize a platform upon which an antenna, or radome, is mounted and it has been recognized that three axis stabilization is necessary for true tracking capabilities under conditions wherein the equipment is subject to substantial and rapid variations in azimuth, elevation and direction of the carrying facility such as a ship at sea. As a matter of information, reference is herei n made to U.S. Patent oos.

One of the requirements of shipboard antenna tracking systems is minimum weight because of the necessity of mounting same atop a mast of a ship so that the moment thereof during substantial pitch, roll or yaw with not unduly affect the vessel or the structural integrity of the mast and antenna mounting. It is also important that the system not be subject to undue vibrations that may originate from the carrier thereof or within the system itself. Another factor of importance for antennas employed for navigation or the like, is the noise of operation of the stabilization system.

Further considerations in this field are the problems of maintenance and shutdown for unwrap of cables and the rapidity of relocating the antenna direction after reaching the limit of tracking because of mechanical limitations of all systems of this type.

The present invention addresses all of the foregoing problems to provide a major advancement in this field.

S U M M A R Y OF I N V EN T I O N

There is herein provided a stabilized antenna tracking system wherein the antenna itself is continuously directed toward an object such as a satellite, rather than stabilizing a platform upon which the antenna is mounted. Although it is common practice to mount a tracking antenna upon a "stabilized platform" on a ship at sea to compensate for abrupt ship movements, the present invention proceeds alternatively to gyro-stabilize the antenna itself, while at the same time providing an unlimited azimuth angle variation and an extremely rapid reorientation of the antenna to lock into another satellite, for example, when navigational positioning requires such a change to continue uninterrupted position "fixes".

The present invention provides a three axis gyro stabilized antenna employing silent torque motors to control the gyroscope or gyroscopes together with means for "softening" gyroscope action for rapid reorientation of the antenna, or the like during intentional shifting of the antenna direction. A universal joint or igimbals of particular construction is herein mated wi th an unlimited azimuth angle bearing mount to provide a degree of angular corrections in antenna direction unknown in conventional stabilization systems. As a part of the foregoing, is the provisions herein of a "mounting arm" of unique configuration which accommodates degrees of motion beyond that available with conventional systems.

B R I E F D E S C R I P T I O N OF D R A W I N G S

The present invention is illustrated with respect to a preferred embodiment thereof in the accompanying drawings, wherein; Figure 1 is a side elevational view of a stabilization system in accordance with the present invention;

Figure 2 is a rear elevational view of the system of Figure 1; Figure 3 is a central vertical sectional view of through a pedestal bearing assembly of the present system;

Figure 4 is a side elevational view of the hub and drive mechanism for the pedestal bearing assembly of Figure 3;

Figure 5 is a rear elevational view partially in section of a universal joint and parabola drive assembly as employed in the present invention; Figure 6 is a side elevational view of the elements of Figure 5; and

Figure 7 is a schemic illustration of control means of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT

The present invention, as generally illustrated in Figures 1 and 2, includes a microwave antenna 11 having a parabolic dish 12 and a feed antenna 13 all mounted upon a base 14 that is adapted to be attached to some structure such as the mast of a ship, for example. The antenna 11 is movable about three axes intersecting adjacent the center of the dish 12 at the back thereof for aiming the antenna at a satellite, for example, and maintaining such aim during movements of the antenna. Considering an antenna mounted upon a ship at sea, it will be appreciated that as the ship proceeds, the relative bearing of a satellite will slowly change and, furthermore rapid movements of the antenna may result from roll, pitch and yaw, or turning of the ship. The present invention provides for accomplishing the aiming by stabilizing the antenna itself rather than stabilizing a platform upon which an antenna may be mounted and one or more gyroscopes are herein employed for this purpose, as described below.

The antenna mount includes an azimuth rotating arm 16 having a first horizontal section 17 and an upwardly inclined second section 18 that is shown to extend upwardly at an of angle about 40° to the first section, The arm 16 is mounted by the first section 17 thereof upon a pedestal bearing assembly 21 in the base 14. Adjacent the outer end of the second arm section 18 there is provided a tube 22 extending upward perpendicularly to such second section. This tube 22 serves as a vibration absorption element and mounts the antenna 11 by means of gimbals or a universal joint 26.

The foregoing antenna mounting system will be see to provide for movement about three axes indicated in Figure 1 as α , β and θ which intersect at the point A which is in fact the inter-section of the axes of the universal joint 26 mounting the antenna 11 on the center line thereof. The antenna may thus be pivoted over a very wide range of angles, and the dashed lines 31 and 32, in Figure 1, indicate extreme positions of rotation of the antenna in the plane of that figure. It will be appreciated that for shipboard use, for example, the degree of pitch and roll is limited, but the degree of angular variation in azimuth is not. With the particular arm mounting of the antenna as illustrated in Figure 1, and described above, there is provided more, than sufficient angular degree of freedom of antenna movement to accommodate even extreme degrees of pitch and roll. The present invention further provides for unlimited angular movement in azimuth, as further described below.

As noted above, the antenna itself is herein stabilized and the present invention employes one or more gyroscopes or gyros mounted on the antenna itself, and energized to rotate at high speed for maintaining the antenna stabilized in space. The illustrated embodiment hereof employs two gyros 33 and 34 mounted on the back of the dish 12. The axes of rotation of the gyros is the line of sight of the antenna to a satellite, for example, and inasmuch as the gyros are spinning in a plane perpendicular to the line of sight, the gyros cause the antenna to continue to point to a satellite even though a ship upon which the antenna is mounted may roll or pitch. Every attempt is made to balance the antenna perfectly in three axes, however, any imbalance is equivalent to a force or torgue applied to the antenna which causes gyro precesεing. Various other factors produce effects equivalent to the application of forces such as bearing friction and friction of air through which the antenna moves, even within a protective radome. A parabola drive assembly 36 is herein provided to apply corrective torques to the gyros 33 and 34, as further described below.

Considering first angular movement in azimuth, reference is made to Figures 3 and 4 generally illustrating the pedestal bearing assembly and drive 21. This assembly comprises a hub rotary mounted on the fixed base 14. The assembly 21 includes a vertical pedestal tube 41 adapted for connection to the bottom of base 14 interiorly thereof by mounting generally indicated at 42. A hub 43 is mounted for rotation upon the tube 41 by means of upper and lower bearings 46 and 47 respectively and carries the antenna 11. The hub 43 is connected to or forms a part of the azimuth arm 16 and is rotated about the pedestal tube 41 by an electric motor 48. A cogged pulley wheel 49 is mounted atop the pedestal tube 41 and is connected by a cogged belt or timing belt 51- to a cogged motor pulley wheel 52 affixed to the shaft 53 of the motor 48. The motor 48 is mounted on a lateral extension 56 of the hub 43 as generally indicated in Figure 4.

It will be seen that operation of the motor 48 will rotate the belt 51 so as to move the hub 43 about the pedestal tube 41,

The pedestal bearing assembly 21 includes a number of elements for mounting the hub on the pedestal tube and including bearing sleeves 61 interiorly of the bearings 46 and 47 with a cylindrical bearing separator 62 therebetween about the tube 41. Upper and lower bearing adaptors 63 and 64 fit about the bearings 46 and 47 respectively, and a top plate 66 is disposed above the upper bearing adaptor with bolts 67 extending therethrough into the lower bearing adaptor for securing the bearing to the hub 43. The bearing sleeves 61 are notched to accept the upper and lower bearings 46 and 47 agai nst the pedestal tube 41 and these sleeves are f ormed of an insulating material.

The upper and lower bearings 46 and 47 of the pedestal bearing assembly 21 are employed to form an electrically conducting path from the stationery portion of the assembly to the rotary or hub portion in order to provide electrical power to the rotary mounted elements of the present invention. Electrical connections, are schematically illustrated in Figure 3, wherein a pair of electrical conductors 71 and 72 are shown to be separately connected to inner portions, or radially inner parts of the bearings 46 and 47 through appropriate openings provided in elements of the bearing assembly. There are also schematically illustrated a pair of electrical conductors 73 and 74 connected to the outer portions of the bearings 46 and 47 which will be noted to rotate with hub 43. Electrical power is applied externally across the conductors 71 and 72, and such electrical power is then available between the conductors 73 and 74 connected to the rotary portion of the bearings 46 and 47. It be will appreciated that electrical current then passes through the bearings and this may be facilitated by employing particular materials in the bearings and including silver alloy metal.

Internally of the pedestal tube 41, there is mounted a conventional RF rotary joint 76 which serves to transmit RF energy into the system and out of the system. Thus, it will be seen that the pedestal bearing assembly 21 not only provides for controlled azimuth positioning of the azimuth arm 16 and consequently the antenna mounted thereon, but also provides for electrical connections to the interior or rotary portion of the invention. While the connection of RF energy may be conventional, the present invention also provides for the connection of AC power without the use of cables that necessarily wrap about the vertical axis or azimuth axis of the antenna. It is known from conventional stabilization systems that powering of same to the rotary portion of the system necessarily incorporates provisions for cable wrap and unwrap as the azimuth angle changes radically. The conventional use. of cables impart a limitation upon the capability of an antenna to track a satellite, for example, inasmuch as the cable can only be wrapped about the ver t i cal axis to the extent of available cable length. When this length is exhausted, it is necessary to discontinue tracking and rotate the unit to unwrap the cable. The present invention, on the other hand provides unlimited azimuth angle variation without interruption to thereby materially improve the overall performance of the stabilization system horeof. The parabolic drive assembly 36 hereof is herein provided to controllably precess the gyros 33 and 34, and referring to

Figures 5 and 6 of the drawings, it will be seen that such assembly is connected to the universal joint 26, Referring more particularly to these figures, there is shown an L-shaped bracket 81 secured to the inner or upper end of the tube 22, and mounting a first shaft 82 of the joint 26. A housing 83 is mounted by bearings for rotation about the shaft 82, and carries a pulley wheel 84 at one end thereof. A timing belt 86 extends about the pulley wheel 84 and about a pulley wheel

87 on the shaft of a motor 88 mounted on the bracket 81. The pulley wheels are preferably to mesh with the cogs on the timing belt.

In addition to the foregoing, the drive assembly 36 also includes a second motor 91 mounted on an arm 92 mounted on a shaft 93 extending from the housing 83. The shaft 93 is mounted within a cylinder 94 secured to the housing 83 and is carried by bearings 96. The arm 92 is secured as by bolts or the like to the back of the parabola or dish 12. A timing belt 101 extends about a pulley wheel 102 on the shaft of the motor 91, and also about a pulley wheel 103 secured to the housing 83. It will be appreciated that energization of the motor 91 will cause the. arm 92 to rotate about the shaft 93, and thus to swing the parabola 12 about the axis of the shaft 93. There is also provide a motion sensor 106 having a first part mounted for rotation on bearings 107 about an extension of the shaft 93, and another part secured to the back of parabola.

Considering now the operation of the parabola drive assembly 36, it is first noted that the motors 88 and 91 are provided as torque motors, i.e., conventional motors that upon energization may operate at zero RPM, and in either direction. Energization of the motor 91 will cause the shaft thereof to attempt to turn and inasmuch as the shaft is connect to the housing 83 by the timing belt 101, the result is that a torque will be applied to the arm 92 in an effort to rotate the parabola about the axis of the shaft 93. Alternatively energization of the motor 88 will cause the belt 86 to attempt to turn the pulley wheel 84 on the housing 83, so as to transmit to the parabola a torque about the axis of the shaft

82. These torques are applied to the parabola to precess the gyroscopes 33 mounted on the parabola disk. It will be appreciated that a force or torque applied to a spinning gyro causes same to move in a direction 90° with respect to the applied force. Consequently in the present invention, a force or torque applied by the motor 88 will produce a motion about the cross axes or axis of the shaft 93. A torque applied by the motor 91, on the other hand, will cause the gyros to precess to move the parabola about the elevation axis of the shaft 82. It will be appreciated that the antenna 11 of the present invention is mounted to move about the vertical axis α , the horizontal axis β, and the cross axis ft. Azimuth movement about the vertical axis α is accomplished by the motor 48 through the pedestal bearing assembly 21, and is controlled by the heading of a ship or the like mounting the antenna with respect to a target such as a satellite.

Movement of the antenna about the the two mutually perpendicularly horizontal axes β and θ is accomplished by the torque motors 88 and 91 which apply appropriate precessing forces to the gyro scopes 33 and 34 . Control of the torque motors 88 and 91 is derived from motion sensor 106 and 108 associated with the universal joint 26. Control of the antenna is schematically illustrated in Figure 7 wherein the above described elements of the present invention are schematically illustrated as being connected to a computer 111. Outputs from the motion sensors 106 and 108 are applied to the computer as are signals from a turn indicator 112 associated with the pedestal bearing assembly and signals from a ship's gyro indicating ship heading at a terminal 116. The computer 111 applies control signals to the azimuth bearing motor 48 and torque motors 88 and 91. As noted above, the antenna 11 hereof is directed toward a target such as a satellite and is then stabilized in such direction despite motions of the means, such as a the ship, mounting the antenna. The system corrects for imbalances, vibrations, and the like which tend to cause the antenna to stray from the line of sight thereof. The torgue motors 88 and 91 precess the gyros 33 and 34 by the application of appropriate forces to the antenna parabola 12.

With the present system, there are employed no stepping motors as are normally required in stabilizing a platform for an antenna, and consequently the noise level of the present invention is very much less than that encountered with conventional stabilization systems.

There is further provided herein means for rapidly moving the antenna from one sector to another in the sky, and also for stopping the gyroscopes when maintenance may be required. It is noted in this respect that the gyroscopes 33 and 34 are driven by conventional single phase capacitor motor and the present invention operates the computer 111 to reverse the drive of these motors in order rapidly slow down the gyroscopes in order "soften" the gyroscopes so that rapid processing of the gyros may be accomplished. Referring again to Figure 7, it is noted that the gyroscope on the left is shown to include a rotating disk 116 driven by a capacitor motor 117 energized from a terminal 118 through a switch 119. Control means 121 is provided to switch the drive of motor 17 from one direction to the nother and such means 121 are controlled by the computer 111. In practice, the switch 119 and control means 121 may comprise a Triad, and same is operated to rapidly slow down rotation of the gyro disk 116 so that the antenna dish may be rapidly moved from one direction to another either for switching the aim thereof from one target to another or for stopping the gyros so that maintenance may be carried out on the system.

The present invention may incorporate a substantial amount of sophisticated control equipment, however, the basic elements of the present invention are described about with respect to the stabilized mounting of an antenna aboard means such as a ship that may be subject to wide variations in position and direction. It will be appreciated that mounting of the present invention atop a tall mast on a ship moving through rough sea results in the antenna itself making many varied and sometimes radical motions. The gyroscopes, as corrected by the torque motors, hereof will maintain their line of sight to a target such as a satellite, and by means of the azimuth control hereof variations in ship's heading is compensated. The stabilization system of the present invention is of relatively low weight and in fact a system built in accordance with this invention weighs only about 80% of the lightest ship board antenna stabilization presently known. This saving of weight at the top of the mast upon a ship is extremely important inasmuch as the lever arm of the mast materially increases the effect of the weight, not only with regard to the strain on the mast, itself, but also with regard to the stability of the ship carrying the present invention.

With regard to vibrations which are extremely detrimental to antenna stabilization, it is noted that mounting the antenna by means of the tube 22 decreases vibrations transmitted to the parabola 12 and from same. Additionally, the exclusion of step motors in the present invention materially reduces the mount of vibration introduced into the system internally thereof. As a further point of interest, it is noted that vibrations of the parabola or disk 12 produce sound waves with are amplified and broadcast therefrom as from a horn and thus on pleasure craft, for example, the amount of noise generated and broadcast by a conventional antenna stabilization system may be very objectional, whereas the present invention produces an almost silent operation.

It has been previously noted that the stabilized antenna of the present invention is preferably enclosed in an envelope, and there is indicated in Figure 1 of the drawings, a radome 126 which may be formed of fiberglass or the like which is pervious to microwave radiation for enclosing the antenna. In actual practice, the overall system may have a height of slightly more than four feet and a diameter of less than four feet.

The present invention, as described above, will be seen to provide numerous and significant advantages over prior art antenna stabilization systems. The present system provides a substantially silent operation with unlimited azimuth variations to preclude the problem of cable wrap with a materially reduced weight of overall system and capability of rapidly realigning the line of sight of the antenna despite the use of gyroscopes thereon. Although the present invention has been described above with respect to a particular preferred embodiment thereof, it will be appreciated by those skilled in the art that numerous modifications and variations are possible within the scope of the present invention, and thus it is not intended to limit the invention to the precise details of illustration or terms of description.

Claims

W H A T IS C L A I M E D IS:

1. A stabilized antenna systems comprising an azimuth mounting arm mounted upon a bearing assembly with an azimuth motor connected to controllably rotate said arm about an axis of said assembly, an elongated element extending from said arm and carrying a universal joint at an outer end thereof adapted to mount a directional antenna thereon, said universal joint having a pair of orthagonal shafts, a pair of torque motors connected one to each of said shafts for controllably applying torque thereto, and at least one gyroscope adapted for mounting upon an antenna mounted on said universal joint with an axis of rotation thereof in line with the direction of said antenna,

whereby controlled operation of said azimuth motor and controlled torques applied to said gyroscope to precess said gyroscope maintain the directional orientation of said antenna despite movements of said antenna in space.

2. The system of claim 1 further defined said azimuth arm having a first portion extending substantially perpendicularly to the axis of rotation of said bearing assembly and a second portion extending outwardly and upwardly from the end of said first portion for mounting said elongated element that extends to an extension of said axis of said bearing assembly to provide space for very large angle movement of an antenna mounted by the system.

3. The system of claim 2 further defined by said azimuth arm having the first and second portions thereof disposed at an angle of substantially forty-five degrees to each other and said elongated element being disposed substantially perpendicular to the second portion of said arm.

4. The antenna of claim 2 further defined by said elongated element comprising a vibration absorbing tube and mounting said universal joint substantially upon an extension of the axis of said bearing assembly.

5. The system of claim 1 further defined by said bearing assembly having a central axial tube having a hub rotatably mounted thereon by upper and lower bearings with inner .and outer races and spaced apart by an insulating sleeve, and a first pair of exterior electrical connections extending from the inner races of said bearings and a second pair of electrical connections extending from the outer rotating races of said bearings whereby electrical power may be transmitted through said bearing assembly from the stationary inner sleeve to the rotatable outer hub.

6. The system of claim 5 further defined by said sleeve enclosing a rotary RF joint for transmission of RF energy through said bearing assembly.

7. The system of claim 1 further defined by said bearing assembly having a hub rotatably mounted on an axial sleeve with a motor mounted on said hub and connected by a drive belt to said sleeve for controllably moving said hub about said sleeve to rotate said azimuth arm in azimuth about said bearing assembly.

8. The system of claim 1 further defined by a first bracket extending from said elongated element and rotatably mounting a first shaft of said joint, a first torgue motor mounted on said first bracket and being connected to said first shaft for controllably applying a torgue thereto, a second bracket connected to a second shaft of said joint and adapted for connection to an antenna to be stabilized, a second torque motor mounted on said second bracket and being connected to a second shaft of said joint for controllably applying a torque thereto, whereby energization of said torque motors apply torques to precess said gyroscope and move the antenna mounting the gyroscope.

9. The system of claim 8 further defined by a motion sensor having parts mounted on said joint and on an antenna carried thereby for supplying signals to control said torque motors.

10. The system of claim 1 further defined by said gyroscope having a rotatable disc and a capacitor motor connected to rotate same, and switching means for reversing the direction of rotation of said motor for rapidly slowing down the rate of disc rotation to facilitate rapid large angle changes of direction of an antenna mounted by the system.