Infrared Relative Positioning Infrared Relative Positioning with the Ewith the E--PucksPucks

Autonomous Robotics Course, June 2007

ValentinValentin LongchampLongchamp valentin.longchamp@epfl.ch

James F. Roberts James F. Roberts james.roberts@epfl.ch

Michael Bonani Michael Bonani michael.bonani@epfl.ch

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)