US3665482A

US3665482A - Tracking antenna with anti-backlash spring in gear train

Info

Publication number: US3665482A
Application number: US122807A
Authority: US
Inventors: Richard Cresswell
Original assignee: Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1970-03-13
Filing date: 1971-03-10
Publication date: 1972-05-23
Anticipated expiration: 1989-05-23
Also published as: GB1267117A; JPS5525525B1

Abstract

A steerable aerial, driven via a differential and two reduction gearboxes, on which backlash is eliminated by a spring biassing arrangement. The spring biassing arrangement is connected between the cage member of the differential and one of the planet gears of the differential and provides a constant torque spring bias to one of the reduction gearboxes in relation to that of the other.

Description

United States Patent Cresswell [4 1 May 23, 1972 [54] TRACKING ANTENNA WITH ANTI- [56] References Cited BACKLASH SPRING IN GEAR TRAIN UNITED STATES PATENTS 72 Inventor: Richard Cremweil Essex, En and 1 81 3,396,594 8/1968 Walker ..74/409 [73] Assignee: The Marconi Company Limited, London,

England Primary Examiner-Eli Lieberman 22 Filed: Mar. 10, 1971 Attorner- Wight & Brown A steerable aerial, driven via a differential and two reduction [30] Foreign Appuufio'? Priority Data gearboxes, on which backlash is eliminated by a spring Mar. I3, 1970 Great Britain ..12,079/70 biassing arrangement. The spring biassing arrangement is connected between the cage member of the differential and one [52] US. Cl ..'....343/765, 74/409, 74/410 of the planet gears of the difi'erential and provides a constant [5 I] Int. CI. I .7 ..H01q torqug to one of the reduction gearboxes in rela.

tio n tothatofthe other; 343/762-766 5Claims,2DrawingFigures PATENTEDMMNWZ 3,665,482

SHEET 1 BF 2 ANGLE AXIS WmZni wax/m $160M BY x 5111070 This invention relates to steerable aerial installations. One of the most important examples of such an installation is that in which an aerial is required to track a target such as a satellite. A satellite tracking aerial is required to track a target such as a satellite. A satellite tracking aerial is required to track its target with great accuracy, a requirement which also applies to other steerable aerial installations. A satellite tracking aerial is, as is well known, required to move in elevation and hour angle. The driving gear for hour angle movement commonly comprises a bull gear carrying the so-called hour angle platform, i.e. a platform from which the aerial is carried and, for obvious practical reasons, there has to be a large reduction gear ratio between the driving motor and the pinion or pinions actually engaging the bull gear. For example, a quote a practical figure, the reduction gear ratio between motor and pinion may be over 3,000 to l.

Backlash or play in the gears is a source of great difficulty in installations as just described because even a very small amount of backlash or play is magnified in dependence upon the above gear ratio. Although it is well known to counter backlash or play by providing bias springing between two meshed gears, this expedient does not provide a satisfactory means of countering such backlash or play between a pinion and a bull gear if the pinion is driven through a high reduction ratio gearbox. To quote again a practical figure the amount of backlash or play to be expected in practice between a pinion and a bull gear, though small enough measured at these gears may be equivalent, measured at the drive shaft to the reduction gear box, to as much as three whole turns of that shaft and it will be apparent that spring biassing of the pinion with respect to the bull gear does not provide a satisfactory solution in a case such as this.

The present invention seeks to overcome the above mentioned difficulties by simple and relatively inexpensive means which shall be purely mechanical in nature and do not involve the cost of providing anumber of motors, specially arranged and fed to exert different ratios of torque for the mere purpose of taking up backlash or play. i

According to this invention a steerable aerial installation includes a driven gear from which the aerial is carried; a pair of driving gears engaging said driven gear to drive the same; a pair of high reduction ratio gearboxes each in the drive to one or other of said driving gears; a differential having driving means driven by a source of driving power and a pair of differentially related driven means each driving one or other of said gearboxes; and spring bias means arranged to provide substantially constant bias of the drive to one gearbox with relation to that to the other.

Preferably, the differential is of the sun and planet gear wheel type and provides the drives to the gearboxes from the shafts of its sun wheels. Preferably also the spring bias means is a spring operatively connected between the cage member of the differential and one of the planet gear wheels of the differential.

The invention is illustrated in the accompanying drawings in which FIG. I is a general schematic perspective view of one form of steerable serial installation in accordance with the present invention and FIG. 2 is a similar perspective view to a larger scale in more detail of the drive arrangement of FIG. 1.

' Referring to FIG. 1, l is an aerial reflector mounted on a platform 2. This reflector is illuminated by a primary radio source indicated conventionally at R and carried by supports S. The platform 2 is pivotally mounted about an elevation axis 3 in a U shaped bracket 4 on an hour angle platform 5. The hour angle axis is indicated by the broken line so referenced. The movement of the aerial reflector 1 about the elevation axle 3 is provided by a jack arrangement consisting of a screw 6 connected in trunnions 7 at one end to the platform 2, and a nut member 8 which is on the screw and is rotatable b means not shown. As WIII be apparent, when the nut mem r 8 is rotated the screw 6 is moved endwise and the aerial reflector is moved in elevation, i.e. about the axis 3. The hour angle platform 5 is driven about a fixed tower 9 by a motor 10 via, in the order stated, a differential gear 11, two bevel driving gears 12, two reduction gear boxes 13, two driving gears 14, a driven gear 15 and a shaft 16. This gearing is mounted in a housing 17 supported on the fixed tower 9. For simplicity, this gearing is not shown in detail in FIG. 1 only the

parts

14, 15 and 16 are indicated in FIG. 1 but is shown in some detail and to a larger scale in FIG. 2 which will now be described.

Referring to FIG. 2 the motor 10 drives via a belt 18 the cage member 19 of a differential 11 the sun or output gear wheels 20 of which drive through shafts 22 and bevel gears at 12 the two reduction gear boxes 13. The differential planet wheels driving the sun wheels 20 are referenced 21.

A substantially constant torque spring 23 operatively connected between the cage member 19 and one of the planet gear wheels 21 is arranged to provide a substantial constant torque spring bias of the drive to one of the gearboxes 13 in relation to that of the other.

The gear boxes 13 are designed to provide a high reduction gear ratio (a practical although not limiting value being of the order of 3000 l) in the drive to the driven gear wheel 15 through the pinion gear wheels 14. The directions of rotation of the shafts and gears is indicated by arrows.

I claim:

1. A steerable aerial installation including a driven gear from which the aerial is carried; a pair of driving gears engaging said driven gear to drive the same; a pair of high reduction ratio gearboxes each in the drive to one or other of said driving gears; a differential having driving means driven by a source of driving power and a pair of differentially related driven means each driving one or other of said gearboxes, and spring bias means arranged to provide substantially constant bias of the drive to one gearbox with relation to that of the other.

2. An installation as claimed in claim 1 wherein the differential is of the sun and planet gear wheel type and provides the drives to the gearboxes from the shafts of its sun wheels.

3. An installation as claimed in claim 2 wherein the spring bias means is a spring operatively connected between the cage member of the differential and one of the planet gear wheels of the differential.

4. An installation as claimed in claim 3 wherein said aerial is carried from said driven gear by means of a carrier member which is carried by and rotates with said driven gear on the axis thereof, said aerial being pivotted to said carrier member about a pivotal axis perpendicular to the axis of said driven gear and means being provided for adjusting the angular position of said aerial with respect to said carrier member about said pivotal axis.

5. A satellite tracking aerial installation in accordance with claim 4 wherein the axis of rotation of said driven gear is the hour angle axis.