Research from the Institute for Collaborative Biotechnologies (ICB) at the University of California at Santa Barbara
(UCSB) has identified swarming algorithms used by flocks of birds and schools of fish that enable these animals to move
in tight formation and cooperatively track prey with minimal estimation errors, while relying solely on local communication
between the animals. This paper describes ongoing work by UCSB, the University of Florida (UF), and the Toyon
Research Corporation on the utilization of these algorithms to dramatically improve the capabilities of small unmanned
aircraft systems (UAS) to cooperatively locate and track ground targets.
Our goal is to construct an electronic system, called GeoTrack, through which a network of hand-launched UAS
use dedicated on-board processors to perform multi-sensor data fusion. The nominal sensors employed by the system
will EO/IR video cameras on the UAS. When GMTI or other wide-area sensors are available, as in a layered sensing
architecture, data from the standoff sensors will also be fused into the GeoTrack system. The output of the system will be
position and orientation information on stationary or mobile targets in a global geo-stationary coordinate system.
The design of the GeoTrack system requires significant advances beyond the current state-of-the-art in distributed
control for a swarm of UAS to accomplish autonomous coordinated tracking; target geo-location using distributed sensor
fusion by a network of UAS, communicating over an unreliable channel; and unsupervised real-time image-plane video
tracking in low-powered computing platforms.
Shape Memory Alloys have been used in a wide variety of actuation applications. A bundled shape memory alloy cable actuator, capable of providing large force and displacement has been developed by United Technologies Corporation (patents pending) for actuating a Variable Area fan Nozzle (VAN). The ability to control fan nozzle exit area is an enabling technology for the next generation turbofan engines. Performance benefits for VAN engines are estimated to be up to 9% in Thrust Specific Fuel Consumption (TSFC) compared to traditional fixed geometry designs. The advantage of SMA actuated VAN design is light weight and low complexity compared to conventionally actuated designs. To achieve the maximum efficiency from a VAN engine, the nozzle exit area has to be continuously varied for a certain period of time during climb, since the optimum nozzle exit area is a function of several flight variables (flight Mach number, altitude etc). Hence, the actuator had to be controlled to provide the time varying desired nozzle area. A new control algorithm was developed for this purpose, which produced the desired flap area by metering the resistive heating of the SMA actuator. Since no active cooling was used, reducing overshoot was a significant challenge of the controller. A full scale, 2 flap model of the VAN system was built, which was capable of simulating a 20% nozzle area variation, and tested under full scale aerodynamic load in NASA Langley Jet Exit Test facility. The controller met all the requirements of the actuation system and was able to drive the flap position to the desired position with less than 2% overshoot in step input tests. The controller is based on a adaptive algorithm formulation with logical switches that reduces its overshoot error. Although the effectiveness of the controller was demonstrated in full scale model tests, no theoretical results as to its stability and robustness has been derived. Stability of the controller will have to be investigated for the next stage of technology readiness.
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