Communications: radio wave antennas – Antennas – With means for moving directive antenna for scanning,...
Reexamination Certificate
1998-04-30
2001-01-23
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
With means for moving directive antenna for scanning,...
C073S162000, C343S765000
Reexamination Certificate
active
06177910
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus for aiming electromagnetic or optical energy, and more particularly, to a high precision gimbal drive module for allowing a large aperture through the center of an articulating gimbal and having extremely accurate pointing ability, exceptional thermal stability, and high stiffness.
DISCUSSION
In spacecraft design, spacecraft payload weight and stowage space are two critical components to designing an efficient, cost effective spacecraft. Spacecraft payload weight must be kept to a minimum so that engines and fuel tanks of reasonable size, weight and cost can be used to launch the spacecraft into orbit and to require minimal engine and fuel input to maintain the spacecraft in the desired orbit and orientation. For similar reasons, stowage space is kept at a minimum to reduce the overall size of the spacecraft, thereby reducing inertia and further minimizing launch and orbit engine requirements.
Regardless of the primary purpose of the spacecraft, almost all spacecraft communicate with either other spacecraft or ground stations, either directly or indirectly. In order to communicate with other spacecraft or ground stations, the spacecraft typically includes some form of electromagnetic or optical communication system to send and receive electromagnetic or optical energy. A typical communication system includes an antenna mounted on the outboard end of a boom or gimbal. The boom or gimbal typically moves through an azimuth and an elevation angle range so that the antenna may be pointed in the desired direction for radiating either electromagnetic or optical energy in the direction of the other spacecraft or ground station. As the spacecraft moves through an orbit, the pointing angle toward the other spacecraft or ground station varies. The change in angle requires that the antenna be redirected in order to maintain electromagnetic or optical communication with the other spacecraft or ground station. This constant redirection of the antenna requires precise movement of the antenna through the boom or gimbal in order to maintain communication with the other spacecraft or ground station.
As discussed above, two primary considerations in spacecraft design are weight and stowage space. Thus, the boom or gimbal system for positioning the antenna is preferably light weight and preferably is relatively small to minimize the required stowage space. Further, because pointing some electromagnetic or optical propagation systems requires extreme accuracy, the boom or gimbal must be extremely stiff throughout its structure in order to maintain the precise aiming required for effective electromagnetic or optical communications.
Further yet, because some communication systems, whether optical or electromagnetic, require propagation of waves though tubes or waveguides of relatively large size, a communication system must be adaptable to accommodate such requirements. In particular, the communication system typically generates and/or receives electromagnetic or optical waves which are then output or received by an antenna or other device toward or from the remote spacecraft or ground station. Propagation of these waves preferably occurs through the boom or gimbal to which the antenna or other device is mounted. For example, some applications require a boom or gimbal having an inner diameter of at least 7 inches in order to propagate waves between the antenna or other device and associated communication circuitry. Such requirements make it even more essential that the drive modules that control the boom or gimbal be configured to have a low profile to make it feasible for the spacecraft to carry such a large bore boom of support. Such large bore booms or gimbals also require extreme thermal stability and the maximum stiffness possible.
Thus, there is a need for a boom or gimbal for a spacecraft or ground station which has a relatively large interior section, but is lightweight, thermally stable, and sufficiently stiff in order to support precise electromagnetic or optical communication. Further, it is desirable that a low profile drive module be provided for the boom or gimbal which is displaceable in extremely small angle increments to provide the precise pointing required by some electromagnetic or optical energy propagation and receiving systems. Further, such a system should exhibit relatively low friction and have a controller specifically designed to generate control commands to precisely position the boom or gimbal in a manner responsive to the friction characteristics of the drive module.
SUMMARY OF THE INVENTION
This invention is directed to a large bore drive module including a first drive motor having a first fixed assembly and a first displaceable assembly for movement relative to the first fixed assembly. The first drive motor is arranged in a generally tubular configuration and has a large center bore. A generally tubular support is partially inserted into the interior of the first drive motor. The tubular support is connected to an inner diameter of the first displaceable assembly and moves in accordance with the first displaceable assembly. The generally tubular support has a large center bore in accordance with center bore of the first drive motor. The generally tubular support includes a first leg and a second leg attached at a joint to form an angle between the first and second legs, and the first and second legs of the tubular support are formed of a composite material. The first drive motor is connected to the first leg of the tubular support. A second drive motor is provided and has a second fixed assembly and a second displaceable assembly for movement relative to the second fixed assembly. The second drive motor is arranged in generally tubular configuration having a large center bore, and the fixed assembly is connected to the second leg of the tubular support. For each drive motor, an annularly shaped position encoder is connected to an outside diameter of the tubular support and moves with the respective drive motor. The position encoder has a grating formed on it. A read station emits light onto the position encoder and receives light reflected from the position encoder. The read station generates an output signal based on the reflected light.
Additional objects, features, and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings.
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patent: 5025262 (1991-06-01), Abdelrazik et al.
patent: 5049796 (1991-09-01), Seraji
patent: 5481910 (1996-01-01), Gutman
patent: 5546302 (1996-08-01), Wang et al.
patent: 5633987 (1997-05-01), Teng et al.
patent: 5850277 (1998-12-01), Dang et al.
Carroll Mark A.
Sathoff J. Blake
Stark Michael R.
Clinger James
TRW Inc.
Wong Don
Yatsko Michael S.
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