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aerial, terrestrial, and aquatic microrobots
Robert J WoodSchool of Engineering and Applied Sciences
Harvard [email protected]
http://www.eecs.harvard.edu/~rjwood
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Primary argument
For untethered and autonomous applications,the performance of a robotic system (P),
whether defined by capability or robustness, canbe related to an agents intelligence (I), mobility(M), and multiplicity (N):
( ),NfMIP
( ) ( ) { } + RnNfNMI :,,...2,1,0,1,0,1,0
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Secondary argument
No biological subsystem should be viewed asglobally optimal. Evolution produces systems
that are good enough for a given task. Thereare typically multiple functions for any givenorgan/structure.
Instead, biological systems should be examinedto extract the guiding principles. These can beused in conjunction with the best engineering
techniques to produce biologically inspired, notbiomimicry
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Third argument
To achieve high performance with power andprocessor limited systems, rigorous mechanical
design is imperative! Control of nonlinear, non-holonomic, underactuated
dynamical systems is hard for systems with low MIPS
or MIPS/mW To minimize any control challenges, we should focus
on minimizing the complexity and loss of mechanicalsystems.
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Outline
Example Micro Air Vehicles Example ambulatory microrobots Example bioinspiration: Insect Aerodynamics
Microrobot Overview The Berkeley MFI The Harvard Microrobotic Fly RoBlatt
Mechanical challenges A mechanical solution: new fabrication paradigm Mechanical building blocks:
exoskeleton, transmission, actuation, and airfoils
Results 0.1g MFI 0.06g Harvard Microrobotic Fly
2g fixed wing MAV 3g crawling microrobot
Next steps Power Sensors Future challenges
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Flapping wing micro air vehicles
Caltech Microbat
11.5g, 8in
Vanderbilt Piezoelectric actuators
Dynamically tuned
University of Delaware ornithopterhttp://touch.caltech.edu/research/bat/bat.html
http://fourier.vuse.vanderbilt.edu/cim/faculty/goldfarb.htmhttp://mechsys4.me.udel.edu/research/birdproject/
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Ambulatory microrobots
MEMS
Ebefors
Berkeley
Macro-robotics
Case Western Whegs
Vanderbilt
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Dipteran parameters: 3DOF wings
Large stroke plane flapping
pronation/supination Stroke plane deviation
Wing beat frequency: 50-1000Hz Weight: 1mg-1g
Unsteady aerodynamics and thebasis of insect flight1
1Dickinson, et al, Science, 1999
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Biological insights Use of mechanical amplification Stroke plane deviation not essential
Tuned resonance for efficiency Power actuators and tuning actuators
Open questions Aeroelastic wing compliance?
Passive or active rotation? Recreate wing hinge? Power?
Sensing/electronics/control?
Some things we can do better thannature, other things we cannot
Unsteady aerodynamics and thebasis of insect flight
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Overview: The BerkeleyMicromechanical Flying Insect
2 wings, 4 total actuated DOFs 100mg, >200Hz
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Overview: The Harvard Microrobotic Fly
2 wings, 1 actuated DOF 2 passive 60mg, 120Hz
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Mechanical challenges
Challenges: As size decreases, surface forces dominate
Cannot use gears, rotary joints, sliding joints
MEMS materials brittle and cost-prohibitive, macro-roboticsystems too massive
The wing hinge will need to rotate through >100at highfrequencies
Solutions: Frictionless flexure hinges
Control surface manipulation
Power transmission
Rigid robotic links Tensegrity exoskeletons/airframes
Electroactive motors & control surface manipulation
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Fabrication capabilities
We seek a fabrication method that will give us basicbuilding blocks for these meso-scale devices
Feature sizes from micron to centimeter Not only build these subsystems, but they must be comparable
larger-scale devices
The solution is called Smart Composite Microstructures
Coupled with MEMS/NEMS (Harvard CNS) andtraditional machining, we can cover almost 10 orders ofmagnitude in fabrication
CNS SCM macro
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Microrobotics using composite materials(smart composite microstructures)
Rigid links and compliant flexures2:
2Wood et al, ICRA, 20033Wood et al, Sensors and Actuators A, 2004
Actuation/control surface manipulation Process with electroactive materials3:
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Laser micromachining
Versatility: composites, polymers, ceramics, metals
Spot (feature) size < 5m
LMS-600, TeoSys4
4www.teosys.com
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Building blocks: exoskeletons
Rigid microstructures based upon tensegrity
Created using unidirectional composite prepreg
Cured flat, released and folded, joints frozen
Extremely rigid, lightweight airframes
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Building blocks: actuation and controlsurface manipulation
Ultra-High Energy Density
Piezoelectric Bending Actuators
Integrating into SCM
1mg-1g (very scalable) ~2Jkg-1
50 times greater energydensity than best
commercially available
counterpart!
>400Wkg-1
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For one wing: thorax consists of 2 actuators,2 slider-cranks, 2 parallel fourbars, aspherical fivebar differential, and a wing
15 joints per wing, 30 total
SCM is enabling!
MFI thorax
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For two wings, 10 joints total
Very simple transmission
SCM is enabling!
Harvard Microrobotic Fly thorax
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Building blocks: airfoils
Current wings:
13-16mm long, AR 3-4
UHM carbon veins, 1.5m polyester membrane
We can create wings with any level of compliance or rigidity (andisotropy), but what is ideal?
passive rotation w/ joint stops
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Total of 3DOF, >+/-50flapping,+/-50rotation, 120Hz, 60mg,FL(mg)
-1 >1!
SCM is enabling!
Initial results from the HarvardMicrorobotic Fly
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Initial results from the HarvardMicrorobotic Fly
Guide wires restrict the fly to purely vertical motion
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2g autonomous glider
Two control surfaces, onboard power,control, sensing
Molded composite airfoil, control surfaces
SCM is enabling!
A Fixed Wing MAV: MicroGlider5
5Wood et al, Robotics & Automation Magazine, 2007
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Ambulatory microrobots
Initial versions:
3g crawler with tripod gait 50mg 2DOF leg
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Microrobotic fish
Actuation and morphology
Controlling angles between adjacent links or controlling
individual link curvatures
(a) SCM-based (b) IPMC-based
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Power
Current COTS Li-Poly batteries
Power electronics: Electrically resonant systems are difficult at this frequency and size
Charge pump?
Energy harvesting?
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Simple sensors: ocelli
Four photodiodes in an inverted pyramid configuration Work so long as:
Light intensity independentof longitude
Light intensity monotonically decreasingfunction of latitude
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Simple sensors: halteres
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Haltere morphology
Anti-phase to the wings at the wingbeat frequency
Sweep through an angle of 180
Two non-coplanar halteres will detect rotations about all three axes
Several hundred sensillae at the haltere base sense the Coriolis force
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Fabrication & results
Haltere connected to output of four bar mechanism
Beam in the plane of haltere beating provides compliance to lateralforces
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75106025
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Future challenges
1. Low Re thrust optimization (flying and swimming)
2. Further sensor development and packaging
3. Power source/energy harvesting4. Control:
Stabilization (low level)
Swarm intelligence (decentralized control)
5. Further mechanism miniaturization and optimization
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applications
Surveillance
Search & rescue
Reconnaissance Planetary exploration
Environmental monitoring
Agents for swarm experimentation
In vivo diagnosis/minor procedures
Hazardous environment exploration
Humanitarian demining/IED detection
Controlled biomechanics experiments Structural maintenance, inspection, repair
Sensor placement, mobile sensor networks