infrared relative positioning with the e-pucks€¦ · possible hardware optimisations • further...
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Infrared Relative Positioning Infrared Relative Positioning with the Ewith the E--PucksPucks
Autonomous Robotics Course, June 2007
ValentinValentin LongchampLongchamp [email protected]
James F. Roberts James F. Roberts [email protected]
Michael Bonani Michael Bonani [email protected]
Summary
• Design Problem• Design Solution• Relative Positioning Using Onboard
Sensors• Advanced Relative Positioning System• Hardware Design• Recommended Future Work
Design ProblemIntroducing the E-puck :
(www.epuck.org)
Design Problem
• E-puck Onboard Sensors:• Sound – Three microphones for basic phonotaxis and tone
detection• Acceleration 3D – Tilt sensing and directional acceleration
measurement• Proximity – Eight infrared analog transceivers to detect close
obstacles• Camera – Windowed VGA CMOS camera for basic visual
processing• Bluetooth – Used to communicate with a PC• The e-puck robots currently have: • “No direct means of determining the positions of nearby
robots”
Design Problem• The Desire for E-puck Relative Positioning:• Allows coordinated movement between robots • Good for swarm & flocking experimentation• Inter-robot cooperation allows for increased task complexity• Increases environmental awareness by sharing structured sensor
information between the group• Enables relative map building
EP1
EP3
EP2
D1,3
D1,2
D2,3
EP4
D2,4
D3,4
Design Solution
• Method One:• Evaluation of onboard infrared proximity sensors• roughly determine range and bearing• robots in “Very” close proximity
• Method Two:• Designing an e-puck turret• modulated infrared signals• RSSI on multiple receivers to calculate the relative
position of other robots
Relative Positioning Using Onboard Sensors
• Initial work has been done by Marco Dorigogroup in Brussels• http://www.youtube.com/watch?v=HZu8ta6_I3o
• Proof of concept, but it has some weaknesses• Raw sensor reads• Low data throughput• No signal modulation• Very sensitive to ambient light
Relative Positioning Using Onboard Sensors: frequency modulation
• Transmissions less sensitive to noise
• Limited by e-puck hardware
• Software modulation/demodulation
Relative Positioning Using Onboard Sensors: frequency modulation
• Sampling frequency of 8 IR sensors: 12 kHz (AD converter limitation)
• Wanted bitrate: 400 bits/s• Sampling window: 30 samples
• Mark (1 encoding) frequency: 2 kHz• Space (0 encoding) frequency: 1.2 kHz
Relative Positioning Using Onboard Sensors: preprocessing and demodulation
• Robust to find best signal (bearing)
• Max(signal) –mean(signal) is related to signal distance (range)
• Demodulation must be enhanced (simple methods have phase problem)
Experimental ResultsTwo e-puck facing each other
Range Measure
0
200
400
600
800
1000
1200
1400
1600
7.5 8 8.5 9 10 11 12 14 16 18 20 22 25 28 30
Distance
Ran
ge M
easu
re
Bearing measurement correct up to 30cm
Relative Positioning Using Onboard Sensors: results
• The software modulation/demodulation is able to replace the expansion turret hardware (proof of concept on basic e-puck)
• The bearing measures are correct• The range measures are correct on short
range• Demodulation must be enhanced for real data
transfers• Code uses no more hardware resources than
standard IR sensor functions
Advanced Relative Positioning System
System Design:
IR Photodiode+ Preamp
x8
IR LED x16
HF MUX8:1 Filter + Amp Demodulator BP Filter
LED DRIVER
Dual Freq. GeneratorGlitch Filter
dsPICE-Puck Connector
A
+5V Step-up
A A
A
D
A A
D
DDD
DD
-5V Step-up
Hardware Design
• E-Puck Connector:• Allows I²C connectivity to E-Puck• Supplies 3.7V directly from onboard battery
E-Puck Connector
Hardware Design• dsPIC – Low level:
• Feeds coded data to dual frequency generator
• Selects multiplexer channel for demodulation
• Reads internal 12-bit ADC • Decodes received data stream
into bytes
• dsPIC – High level:• Calculates bearing of each
robot within range• Calculates distance to each
robot within range• Updates relative robot
positions to E-Puck via I²C
dsPIC
Hardware Design
• Dual Frequency Generator:• Generates two frequencies at around 10.7 MHz• Data is encoded by selecting between these frequencies• Glitch filter is used to prevent a noisy switching
Dual Freq. Generator
Glitch Filter
Hardware Design• LED Driver:
• Input from the frequency generator• One MOSFET driver for each of the 16 IR LEDs• Power level has three selections for ranging optimization
LED DRIVER
IR LED x16
Hardware Design• IR Photodiode + Preamp:
• Required to convert small currents produced by the PIN diode to voltages for the ADC
• Most critical section – Difficult to adjust bias voltage
IR Photodiode+ Preamp
x8
Hardware Design
• High Frequency Multiplexer• Allows the eight IR receivers to be connected to a
single demodulator
HF MUX8:1
Hardware Design• Filter + Amplifier:
• Filters the incoming signal and amplifies for the demodulator
• Incorporates impedance matching for RF designed input
Filter + Amp
Hardware Design
• Demodulator:• Standard radio frequency narrow band receiver• Local oscillator at 10.7 MHz• Supplies direct output for RSSI• Supplies analog output for data reception
Demodulator
Hardware Design
• Band-pass Filter:• Filters and amplifies the analog output of the
demodulator• Saturated transistor for clean data recreation
BP Filter
Hardware Design• ±5V Step-up:
• Input 3.7V from E-Puck battery• Supplies both positive and negative voltages for the RF circuitry
and op-amps• Regulated outputs for noise minimisation
+5V Step-up
-5V Step-up
Hardware Design
• Omitted Electronics (compared to KIII design):
• Two multiplexers single
• Two demodulators single
• IR transmit Segmentation control removed
• Serial to USB driver removed
• Simpler band pass filter and data amplifier designed
• “Managed to reduce electronics to E-Puck size turret (70mm)”
Hardware DesignRelative Positioning Turret CAD Design :
Hardware Design
• Status:• Routing finished• 4-layer PCB • Production launched• PCB expected for 6th
July
Possible Hardware Optimisations
• Further miniaturisation:• Optimise the receiving circuitry
• Find other OPA (working at 3.3V)• Smaller band pass-filter
• Improving Efficiency:• Reduce the duty cycle from 50% to 10%
(requires emitting circuitry changes)
Firmware Design
• Random wait length between data emissions• Random length RTS• Check for other RTS in Coll. Check • Preamble used for RSSI• Data transmission with parity bit
RTS Coll. check Preamble Data Preamble
3D design for Swarmanoid
• Optimization of orientation angles according to the number of sensors• 16 receivers:
• 8 placed horizontally • 8 placed at 35°
• 26 emitters:• 8 at 0°• 8 at 14°• 8 at 46°• 2 at 80°
Conclusion and Remaining Work
• Better results on e-puck than expected
• Hardware should be compatible with KIII design
• Hardware miniaturisationproblematic
• Mounting two PCB• Firmware for new
hardware
Questions ?• Thank you for your attention
Advanced Relative Positioning System
• Technology Overview:• Relative Bearing Measurement
• Robots randomly transmit IR packet with 16 IR LEDs• The Received Signal Strength Indicator (RSSI) for each of the eight IR
receivers is read with an ADC• The strongest represents the octant of the bearing of the transmitting e-
puck (V1)• The second strongest represents the adjacent signal (V2)• The octant offset angle can then be determined:
θ = a(V1 − V2) / V1φ = Octant Angle + θ
(Limits are applied to stay within the correct octant)(a is a pre-determined constant)
(Local Range and Bearing Sensing Using Infrared Transceivers in Mobile Robotics - Jim Pugh and Alcherio Martinoli, SWIS EPFL)
Advanced Relative Positioning System
• Technology Overview:• Relative Distance Measurement
• Range (D) determined by the RSSI• The distance is calculated from the non-linear intensity curve of the
incoming signals (V1, V2) & the attained bearing (θ):
D = SQRT [ (V1² + V 2²) Cos (π/4 − θ) ]
(Local Range and Bearing Sensing Using Infrared Transceivers in Mobile Robotics - Jim Pugh and Alcherio Martinoli, SWIS EPFL)