Gimbal control system

• US 5,557,285 A
• Filed: 01/24/1994
• Issued: 09/17/1996
• Est. Priority Date: 01/24/1994
• Status: Expired due to Term

• Current Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Original Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Inventors: Bender, Douglas J., Eyerly, Bruce N., Bockman, Stuart F., Anagnost, John J.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US08/185,346
• Time in Patent Office: 967 Days
• Field of Search: 342/358, 342/359, 342/75, 342/77, 342/420, 342/74, 342/76, 343/757, 343/754, 343/758, 343/760, 244/164
• US Class Current: 342/359
• CPC Class Codes: B64G 1/22 Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
• CPC Class Codes: B64G 1/24 Guiding or controlling apparatus, e.g. for attitude control
• CPC Class Codes: B64G 1/36 using sensors, e.g. sun-sensors, horizon sensors
• CPC Class Codes: B64G 1/369 using gyroscopes as attitude sensors
• CPC Class Codes: H01Q 1/18 Means for stabilising antennas on an unstable platform

Abstract

A multi-loop control system for a gimballed antenna that employs devices for measuring both absolute line-of-sight (an autotrack receiver or beacon tracker) and relative angular position (a resolver). The control system uses both signals simultaneously, thereby increasing the performance and pointing accuracy capability. Two control loops operate simultaneously to provide for optimum performance. The first loop is an inner high-bandwidth control loop that uses the relative gimbal angle measurement to control pointing of the antenna along a precommanded profile. The inner loop may run alone to provide for coarse pointing. When available, the line-of sight measurement is used in a low-bandwidth outer loop to provide corrections to the command profile of the inner loop. Control logic is provided that allows switching between several control modes. By using the present invention, antenna tracking control performance is maximized, especially in the presence of attitude disturbances of a spacecraft or significant flexible interactions.

Claims

1. Apparatus comprising:

a spacecraft;

a gimbal disposed on the spacecraft;

an antenna disposed on the gimbal;

processing means coupled to the antenna for processing autotrack RF signals received by the antenna and for providing azimuth and elevation tracking error signals in response thereto that are indicative of the absolute line-of-sight of the antenna;

a control processor coupled to the processing means for processing position command signals and the azimuth and elevation tracking error signals, and for generating gimbal control signals for steering the antenna; and

a drive control and angle position measurement processing unit coupled between the control processor and the gimbal for receiving the gimbal control signals from the control processor and for generating antenna boresight angle signals that are applied to the gimbal to steer the antenna, which processing unit comprises a gimbal control system that includes an inner feedback loop that comprises angular position means for providing signals indicative of the relative angular position of the antenna and wherein the inner feedback loop is a control loop that uses the relative gimbal angle measurement to control pointing direction of the antenna along a precommanded profile.

2. The apparatus of claim 1 wherein the angular position means comprises a resolver.

3. The apparatus of claim 1 wherein the angular position means comprises an optical encoder.

4. The apparatus of claim 1 wherein the angular position means comprises an inductosyn.

5. The apparatus of claim 1 wherein the gimbal control system further comprises a second outer feedback loop that comprises an autotrack receiver for providing signals indicative of the absolute line-of-sight of the antenna, which signals provide corrections to the command profile of the inner loop.

6. The apparatus of claim 1 wherein the angular position means comprises azimuth and elevation resolvers coupled to the gimbal for producing azimuth and elevation error signals that are indicative of the error between a commanded pointing direction and the pointing direction of the antenna.

7. The apparatus of claim 1 wherein the received position command signals comprise position and slew commands.

8. The apparatus of claim 1 wherein the received position command signals comprise autotrack configuration commands.

9. The apparatus of claim 1 wherein the processing means comprises a receiver demodulator.

10. The apparatus of claim 1 wherein the processing means comprises an optical tracker.

11. A gimbal control system comprising:

a gimbal;

an antenna disposed on the gimbal;

an autotrack receiver coupled to the antenna for processing autotrack RF signals received by the antenna to provide azimuth and elevation autotracking error signals in response thereto;

a gimbal drive circuit coupled to the gimbal for producing a desired gimbal angle signal that drives the gimbal;

a resolver control loop coupled to the gimbal for processing gimbal angle signals to produce measured gimbal angle signals;

a control processor coupled to the autotrack receiver and the resolver control loop for processing position command signals received from an external source, the gimbal angle signals derived from the resolver control loop, and the azimuth and elevation autotracking error signals provided by the autotrack receiver, for generating control signals in response thereto to position the antenna, and wherein the control processor comprises;

a compensation control loop coupled between the autotrack receiver and the gimbal drive control unit that comprises;

a proportional plus integration compensation circuit coupled to the autotrack receiver for processing the autotracking error signals and to provide a commanded gimbal angle signal;

a summing device having one input coupled to the proportional plus integration compensation circuit and a second input coupled to the resolver control loop for combining the commanded gimbal angle signal and the measured gimbal angle signal to produce a gimbal angle error angle signal in response thereto; and

a compensation circuit coupled to the summing device for processing the gimbal angle error angle signal to provide a filtered gimbal angle error angle signal to stabilize gimbal dynamics; and

a step generator coupled to the compensation circuit for processing the compensated gimbal angle error angle signal to produce step commands that are coupled to the gimbal drive circuit.

12. The gimbal control system of claim 11 which further comprises:

switching circuitry coupled between the proportional plus integration compensation circuit and the summing device for providing a predetermined number of control modes for controlling the gimbal.

13. The gimbal control system of claim 11 herein the gimbal comprises a stepper drive gimbal and the compensation circuit comprises a proportional-double-integrator-derivative compensation circuit.

14. The gimbal control system of claim 13 which further comprises a notch filter coupled between the proportional-double-integrator-derivative compensation circuit and the step generator.

15. The gimbal control system of claim 13 wherein the notch filter further comprises a roll-off filter.

16. The gimbal control system of claim 11 wherein the gimbal comprises a direct drive gimbal comprising drive electronics that generates a gimbal torque signal coupled to the gimbal drive, and wherein the compensation circuit comprises a proportional-integrator-derivative compensation circuit.

17. The gimbal control system of claim 16 which further comprises a notch filter coupled between the proportional-integrator-derivative compensation circuit and the drive electronics.

18. A gimbal system comprising:

a gimbal;

an antenna disposed on the gimbal;

a control processor coupled to the gimbal for generating control signals to position the antenna;

a resolver and a derivative-type processing circuit disposed in an inner feedback loop that is coupled to the gimbal, and wherein the resolver provides resolver signals that are processed by the derivative-type processing circuit and are fed back to the gimbal to stabilize the gimbal and correct for gimbal flexibility; and

an outer feedback loop that comprises an autotrack receiver for providing signals indicative of the absolute line-of-sight of the antenna, which signals provide corrections to a command profile of the inner loop.