Development of Finite Active Control Elements for Large Flexible Space Structures.
Annual rept. 15 Mar 83-14 May 84,
MASSACHUSETTS INST OF TECH CAMBRIDGE MA SPACE SYSTEMS LAB
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A quasi free-free beam, simulating a flexible space structure, was equipped with inertial proof-mass actuators and sensors capable, in principle, of functioning in the space environment. Then tuning rules were derived which determine the optimal actuator passive stiffness and damping which minimizes the control effort required while increasing the modal damping in the structure. Active control using two local and one component level processor was demonstrated next. Lastly, multi-input, single output collocated feedback tests were performed. Optimal passive vibration absorber designs were derived to provide maximum structural damping. Theoretically, addition of an absorber mass equaling 0.5 of structural mass can result in a single mode structural damping ratio of 5. Analysis of multimode damping using a single absorber indicated that the absorber stiffness should be tuned to the lowest mode in order to maximize the achievable damping in all the modes. Passive actuator components and active feedback gains were derived simultaneously and sequentially yielding identical results whose passive components equal those of the passive vibration absorber. Passive absorber and active feedback damping tests were performed. A single mode damping ratio of 4.2 was achieved by adding 2.3 of structural mass 77 of which corresponds to dead absorber mass. Multi-input, single-output control provided damping ratios ranging from 2 to 3. This functioning collocated control element, composed of actuators, sensors and local and component level processors, constitutes the first stage of research and experimentation into distributed, hierarchic active control of elastic structural behavior.
- Unmanned Spacecraft