Design Of Visual Sensor For All Weather High Speed Navigation

Unmanned Aerial Vehicle(UAV)has gained great advance in performance due to the development of technology.Though it was developed for the purpose of military target drone,UAV could accomplish various tasks both in military and civil field because of its versatility,becoming more and more important in modern world.However most UAVs could only achieve a flight time of four to five hours which is far less than enough to complete some quests.Considering the fact that technologies for manned aerial vehicle aerial refueling are pretty mature,it would greatly boost UAV's endurance,making UAV more capable and universal for complex tasks.Through analysis of modern aerial refueling technologies for manned vehicle,an aerial refueling procedure could be divided into four steps: gathering,docking,refueling and separation,among which docking is the most difficult step.The tanker releases a flexible hose which ends with a drogue and the receiver should plug its retractable probe into the drogue.After being released the hose would move erratically with turbulence thus it requires high precision maneuvering of the receiver.With the lack of precision and unreliability of GPS navigation system when tanker and receiver are close,new high performance visual navigation need to be developed.In this paper a design of visual sensor based on TMS320C6748 embedded processor for unmanned aerial vehicle autonomous aerial refueling navigation with all-weather capability and high performance is proposed.This design includes the following features:(1)This design adopts infrared active light sources as marks on the tanker side and uses PSD(Position Sensitive Detector)as infrared light sensor on the receiver side.(2)An algorithm for the receiver to gather and process light signal and separate light sources based on modulation and demodulation is proposed.(3)A method to calibration visual sensor on the receiver side is proposed,which could get intrinsic parameters and distortion coefficient.(4)An algorithm for estimating relative pose between the target drogue and the receiver is proposed.(5)Experiments are carried out to test the performance of proposed visual sensor design.Firstly,experiments to separately test modules function and performance are conducted.Then the whole visual sensor is tested.Last,experiments of sensor's performance under conditions with different kind of interferences are carried out.The results indicate the visual sensor design proposed in this paper could achieve high precision,high working frequency and possesses the ability to work properly under certain interferences.