Multiple UAV Collision Avoidance with Realistic UAV Models

Joel George and Debasish GhoseGuidance, Control, and Decision Systems Laboratory

(GCDSL)Department of Aerospace Engineering,Indian Institute of Science, Bangalore

India 560012.

Problem Description

Multiple UAVs fly to their destinations in a ‘free flight’ zone

Need to detect and avoid mid-air collisions

Each UAV has a safety zone UAVs have limited sensor ranges

Objective

Obtain high efficiency with lower number of near misses

Efficiency =

Near Miss

Devi

Idea

ated

l path l

path le

ength

ngth

A breach into each other’s safety zones

Assumptions

Positions and velocities of other UAVs within the sensor range are known

6 Degree of Freedom UAV model

Solution approach

Multiple UAV collision avoidance by handling pair wise conflict

When a UAV encounters multiple conflicts, it does a maneuver to avoid a near miss with the ‘most threatful’ neighbor. Every UAV doing so, in a multiple UAV conflict scenario, will result in a high efficiency with lower number of near misses.

The Thesis

Solution approach (continued)

Most threatful neighbor (of a UAV U): A UAV in the sensor range of U with which U has a projected near miss and the least time-to-go for that near miss to occur.

Collision avoidance maneuver: Turn in a direction that will increase the Line-of-Sight (LOS) rate between the UAVs.

Deciding the ‘most threatful’ neighbor and the desired collision avoidance maneuver

Pair wise collision avoidance maneuver

In this example, where ,

the UAVs U1 and U2 turning in the directions of lateral accelerations a1 and a2 (green arrows) will result in an increase of LOS rate between them.

2 1

Realistic UAV Model

UAV of span 1.4224 m, weighing 1.56 kg Stability and control derivatives from Aviones

A UAV flight simulator developed by the Brigham Young University

(an open source software)

Available: http://aviones.sourceforge.net/

Controller design

Controllers designed through successive loop closure

Separate controllers for holding altitude, attitude, and velocity

PI controllers with parameters tuned manually

Controller design

Altitude hold controller

Similar controllers for attitude and velocity holds are designed

Controller response

Response of UAV model (with controller) to a 3-2-1-1 bank angle command

The plots of system state response: bank angle ( ), height (h), and velocity (V), and the control demands: aileron deflection ( ), elevator deflection ( ), and throttle ( ). Demanded bank angle is shown in dotted lines.

e Ta

Test of collision avoidance

A example of collision avoidance of 5 UAVs. The test case is tailored such that the avoidance of one conflict will lead into another

Random flights test case

UAVs appear at random points in outer circle (radius 500 m) and fly to randomly assigned points in inner circle (radius 400 m) with a velocity of 12 m/s and a maximum turn rate capability of 10 deg/sec.

The scenario is simulated for 1 hour and at any instant during the simulation, the number of UAVs in the airspace is kept constant by replacing the UAVs that reached target points by new ones. Any approach of two UAVs within 10 m is considered a near miss. An approach within 2 m is a collision.

• Test case of random flights for dense traffic

Results

No. of UAVswithout collision avoidance with collision avoidance

Near Misses Efficiency Near Misses Efficiency

204060

218.1899.1

2027.9

100100100

0.11.61.4

96.1589.1789.11

Results of the random flight test case

Summary

Gave a collision avoidance algorithm, for multiple UAV scenarios, that gives a good performance – low near misses and high efficiency

Designed PI controllers for a realistic UAV model using successive loop closure

Tested the collision avoidance algorithm on this realistic UAV model augmented with the designed controller

Results showed a good performance of the algorithm