Aerial, Terrestrial and Aquatic Microbots by Wood

8/9/2019 Aerial, Terrestrial and Aquatic Microbots by Wood

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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

Documents

Aerial, Terrestrial and Aquatic Microbots by Wood