visnav full report

[seminar class]

Submitted by
Ajesh.M.L

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Introduction
Objectives
1. Find 6 DOF estimation
2. Find Robust Navigation Solution
 Consist of PSD & DSP
Limitations of GPS
1. Less Precision
2. Complex infrastructure
3. Low accuracy
Sensor Description
 Activated by energy from beacons
 Generates electrical current in 4 directions
 Current imbalances are linearly proportional to location of image centroid
Factors affecting measurement
 Short wavelength light from sun & other discharge light act as beacons
 High power beacon signal saturate output of preamplifier
Preventive Measures
 Optical filter to block visible light.
 Modulate beacon current with high frequency.
 Feed back loop to control the beacon intensity.
VISNAV Block Diagram
Signal Processing
• Sinusoidal carrier of 40kHz frequency applied to modulate each drive current from the four terminals of the PSD.
• The output of the PSD is applied to the preamplifier
• The signal is converted into digital form through an analog to digital converter.
• The digital data fed into the two DSP’s from this we get a sensor coordinates.
• Beacon control data is communicated to BCM.
• Control data is FSK modulated
• Data then transmitted via wireless page link to control amplitude of beacons.
• This closed loop system estimates 6 DOF of sensor.
DSP Implementation
 Functions of DSP TMS320C55X-act as demodulator
 Functions of DSP TMS320VC33 act as 6 DOF estimator
ADVANTAGES
 Reprogrammable
 Insensitive to temperature variation and ageing effect
 Wide field of view
 Very small and compact size
 Number can be increased upto 16 beacons
DISADVANTAGE
 The signal may be blocked by the opaque objects in their path
Applications
1. Autonomous aerial refuelling.
• Aerial Refuelling
 Requires light sources on the refuelling target frame
 optical sensor on the aircraft frame.
 Can be used even in 100% cloud cover,total darkness and adverse condition
2. Spacecraft Docking
 Beacons & beacon contoller on target spacecraft & sensor on chasing space craft
 VISNAV enables docking simple and easy
Conclusions
 100 Hz update rate 6DOF data possible with small low power sensor/beacons to 100+m.
 Beacon signal modulation and optical filtering
 Excellent ambient light rejection.
 Realtime beacon selection/intensity control
 Minimize power requirements.
 Very wide field of view, no moving parts.
 Distributed beacons
 Very large operating space