uc santa cruz, autonomous systems lab, an improved line-of- sight guidance law for uavs r. curry, m....
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UC SANTA CRUZ, AUTONOMOUS SYSTEMS LAB
, An Improved Line-of-Sight Guidance Law for
UAVs
R. Curry, M. Lizarraga, B. Mairs, and G.H. Elkaim
University of California, Santa Cruz
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UC SANTA CRUZ, AUTONOMOUS SYSTEMS LAB
Accelerating UAV Demand
Military Civilian
Forestry Marine Fisheries Photography Border surveilance
New Missions New Autopilot Designs
UC SANTA CRUZ, AUTONOMOUS SYSTEMS LAB
Line-of-Sight Guidance
Originally proposed by Amidi (1991) for robots
Park, Deyst, How (2007) made significant contributions Theory
Linear Analysis Asymptotic stability
Flight demonstrations A form of pursuit guidance originally
used in air-to-air missiles
UC SANTA CRUZ, AUTONOMOUS SYSTEMS LAB
Acceleration
Geometry
Kinematics
Combined L1 constant
UAV Bank angle
UC SANTA CRUZ, AUTONOMOUS SYSTEMS LAB
Linear Model (cont)
System Response
where
Note: wn increases with Vg
Let
UC SANTA CRUZ, AUTONOMOUS SYSTEMS LAB
Summary of Guidance
Asymptotically stable assuming instantaneous acceleration response
Reduced stability with increasing ground speed
not specified in operational situations Errors larger than (track acquisition) If desired track does not exist (go direct)
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UC SANTA CRUZ, AUTONOMOUS SYSTEMS LAB
Guidance
Look ahead distance depends on ground speed
T* is constant Poles independent of ground speed
ALWAYS define an aim point Limit intercept angle (reduce overshoot) Limit down track aim point distance
Large errors and track acquisition
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UC SANTA CRUZ, AUTONOMOUS SYSTEMS LAB
Simulations
6 DOF nonlinear rigid body model of Rascal UAV Hobby aircraft, wing span of 1.2m Inputs: throttle, elevator, aileron, rudder Outputs: 12 state variables
Dryden model wins Constant wind Gust levels depend on height above ground
and mean wind
UC SANTA CRUZ, AUTONOMOUS SYSTEMS LAB
Homing Mode
What if there is a destination but no path?
Point ground track from current position to objective Aircraft use “direct to” everyday
uses one guidance law in all conditions
Automatic “Return To Base” if comm failure
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UC SANTA CRUZ, AUTONOMOUS SYSTEMS LAB
Moving “Base”
The homing mode only requires a line of sight to the objective
There is no requirement that the objective be stationary
Useful for tracking moving objectives We used the L2+ homing mode on
moving base without any modification