autonomous jumping microrobots micro robots for mobile sensor networks sarah bergbreiter electrical...
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Autonomous Jumping Microrobots
micro robots for mobile sensor networks
Sarah BergbreiterElectrical Engineering and Computer Sciences
UC Berkeley, Advisor: Prof. Kris Pister
Dissertation Talk, May 17, 2007
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Research at Berkeley
Walking Microrobots (Hollar, et al. Hilton Head 2002, Transducers 2003, JMEMS 2005)
Jumping Microrobots (Bergbreiter, Pister. ASME 2006, ICRA 2007)
TinyOS and CotsBots (Bergbreiter, Pister. IROS 2003)
PhotoBeacon Localization (Bergbreiter, Pister. To be published)
4mm
3/59
Sensor Networks and RobotsRemove
Legs
Add Robot Body
COTS Dust (Hill, et al. ACM OS Review 2000)
Smart Dust (Warneke, et al. Sensors 2002)
CotsBots (Bergbreiter, Pister. IROS 2003)
Microrobots (Hollar, Flynn, Pister. MEMS 2002)
Off-the-shelfOff-the-shelf
4/59
Mobile Sensor Networks
Sensor Networks for Security Sensor Networks for Science
Songhwai Oh, Luca Schenato, Phoebus Chen, and Shankar Sastry, "Tracking and coordination of multiple agents using sensor networks: system design, algorithms and experiments," Proceedings of the IEEE (to appear), 2007.M. Hamilton, E. Graham, P. Rundel, M. Allen, W. Kaiser, M. Hansen, and D. Estrin. “New Approaches in Embedded Networked Sensing for Terrestrial Ecological Observatories,”Environmental Engineering Science, Vol. 24, No. 2, pp. 192-204, March 2007.V. Kumar, D. Rus, and S. Singh, "Robot and Sensor Networks for First Responders," Pervasive computing, October, 2004, pp. 24 - 33.
Hazardous Sensor Network Deployment
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From CotsBots to Microrobots
100m
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Overview
• Challenges for Microrobots• Jumping for Locomotion• Jumping Microrobot Design
– Power and Control– Micromechanical Energy Storage – High Force, Large Displacement Actuators
• System Prototypes• Summary and Future Work
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Microrobots: Challenges
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
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Microrobots: Challenges
Locomotion
Actuators
Power
Integration
Mechanisms
• Locomotion is feasible at this scale• Interesting mechanisms can be designed
and built using simple processes
• MEMS actuators can be designed for millinewtons of force and millimeters of throw
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Locomotion
• Improve Mobility– Obstacles are large
• Improve Efficiency– What time and energy is required to move a microrobot 1
m and what size obstacles can these robots overcome?
100 m
180 J
2.8 min
80 mg
50 m
130 mJ
417 min
10 mg
1 cm
5 mJ
1 min
10 mg
**
1.5 mJ
15 sec
11.9 mg
Obstacle Size
Energy
Time
Mass
Ebefors (Walking)
Hollar (Walking)
Proposed (Jumping)
Ant (Walking)
A. Lipp, et al. Journal of Experimental Biology 208(4), 707-19.S. Hollar, PhD Dissertation, 2003. T. Ebefors, et al. Transducers 1999.
Jumping?Jumping!!
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Jumping: Challenges
• Kinetic energy for jump derived from work done by motors– High force, large throw
motors
• Short legs require short acceleration times– Use energy storage and
quick release
vlt legacc 2=
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Robot Design
• Power for motors and control
• Controller to tell robot what to do
• Spring for energy storage
• Higher force, larger displacement motor
• Landing and resetting for next jump are NOT discussed
Power
Control
1 mm
Motors
Energy Storage
rubber
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Power and Control: Design
• Power Design– Small mass and area – Few (or no) additional
components– Simple integration to motors– Supports multiple jumps
• Control Design– Small size– Low power– Simple integration– Programmability– Off-the-shelf
EM6580, 3.5 mg
2 m
m
1.8
mm
Bellew, Hollar (Transducers 2003), 2.3 mg
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Energy Storage: Design
• Small area and mass• High efficiency• Store large amounts of energy (10s of J)
– Support large deflections (many mm) – Withstand high forces (many mN)
• Integrate easily with MEMS actuators without complex fabrication
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Energy Storage: Rubber
• High Energy Density– Capable of storing large amounts of energy with small
area and volume– 2mm x 50m x 50m rubber band can store up to 45J
• Large Strains– Stress/strain profile suitable for low-power electrostatic
actuators with large displacements
Material E (Pa) Maximum Strain (%)
Tensile Strength (Pa)
Energy Density (mJ/mm3)
Silicon 169x109 0.6 1x109 3
Silicone 750x103 350 2.6x106 4.5
Resilin 2x106 190 4x106 4
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Energy Storage: Fabrication
• Fabricate elastomer and silicon separately– Simple fabrication– Wider variety of
elastomers available
• Silicon process– Actuators– Assembly points for
elastomers
• Elastomer process– Make micro rubber
bands
100 m
+
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Silicon Fabrication
100 m
• Two Mask SOI process– Frontside and backside
DRIE etch– Commercially available
as SOIMUMPs®
• Actuators– Thick structural layer
gives higher forces
• Hooks– Assembly points for
elastomer
500m
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Elastomer Fabrication: Laser
• Simple Fabrication– Spin on Sylgard® 186 – Cut with VersaLaser™
commercial IR laser cutter– No cleanroom required
• Lower quality– Mean 250% elongation at
break– 10-20% yield
Si Wafer 500 m
Sylgard® 186 50 m
VersaLaserTM
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Elastomer Fabrication: Molding
• More Complex Fabrication– DRIE silicon mold– Pour on Sylgard® 186
• Shape flexibility• High quality
– Mean 350% elongation at break
Si Wafer 500 m
Trench 30 m + C4F8 Passivation
Sylgard® 186 30 m
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Elastomer Assembly
• Fine-tip tweezers using stereo inspection microscope
• Yield > 90% and rising
100 m
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Elastomer Characterization
• Using force gauge shown previously, pull with probe tip to load and unload spring
• Trial #1– 200% strain– 10.4 J– 92% recovered
• Trial #2– 220% strain– 19.4 J– 85% recovered
• 20 J would propel a 10mg microrobot 20 cm
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Elastomer Quick Release
• Electrostatic clamps designed to hold leg in place for quick release– Normally-closed
configuration for portability
• Shot a surface mount capacitor 1.5 cm along a glass slide
• Energy released in less than one video frame (66ms)
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
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Actuators: Design
• Small area and mass• Low input power and moderate voltage• Reasonable speed • Do large amounts of work (10s of J) to
store energy for jump– Large displacements (5 mm)– High forces (10 mN)
• Simple fabrication
1 mm
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Actuators: Electrostatic GCAs
222
1V
g
A
g
UF ⋅⋅=
∂∂
−= ε
g
AC ε=
l
+-V g
t
k
F
2
2
1CVU =
finalinitial ggx −=δ
• High forces with small gaps • Small displacements
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Actuators: Inchworm Motors
• Inchworm actuation accumulates short displacements for long throw
• May be fabricated in single mask SOI process
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Actuators: Inchworm Motors
• Inchworm actuation accumulates short displacements for long throw
• May be fabricated in single mask SOI process
26/59
Actuators: Inchworm Motors
• Inchworm actuation accumulates short displacements for long throw
• May be fabricated in single mask SOI process
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Actuators: Inchworm Motors
• Inchworm actuation accumulates short displacements for long throw
• May be fabricated in single mask SOI process
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Actuators: Inchworm Motors
• Inchworm actuation accumulates short displacements for long throw
• May be fabricated in single mask SOI process
29/59
Actuators: Inchworm Motors
• Inchworm actuation accumulates short displacements for long throw
• May be fabricated in single mask SOI process
30/59
Actuators: Inchworm Motors
• Inchworm actuation accumulates short displacements for long throw
• May be fabricated in single mask SOI process
31/59
Actuators: Inchworm Motors
• Inchworm actuation accumulates short displacements for long throw
• May be fabricated in single mask SOI process
32/59
Actuators: Inchworm Motors
• Inchworm actuation accumulates short displacements for long throw
• May be fabricated in single mask SOI process
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Actuators: Increase Force
• Increase area– Disadvantage: greater
area implies greater mass
• Increase dielectric constant– Disadvantage: processing
and small displacements
• Increase voltage– Disadvantage: power and
electronics
• Decrease gap– Disadvantage: small
displacements and lithography + processing limits
l
+-V g
t
k
F
221 2V
g
Ad
UF
ε
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Actuators: Decrease Gap
• Use design to reduce initial gap beyond what is possible through processing– Transmission system
• Use processing to gain greater design flexibility and retain moderate speeds– Nitride isolation
• Use design to remove teeth from shuttle and second drive actuator– Friction clutch
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Actuators: Transmission
• Drive force depends on initial gap
• Initial gap dependent on processing limits– Lithography– Etch aspect ratio
• Design an extra component to make this initial gap smaller
gi,0 gt,0
gt,gap
20
202
1
g
AVF ε=
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Actuators: Transmission
• Drive force depends on initial gap
• Initial gap dependent on processing limits– Lithography– Etch aspect ratio
• Design an extra component to make this initial gap smaller
gi,1 gf20
202
1
g
AVF ε=
• Only needs to be actuated when more force is needed• Does not need to be changed with each step
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250 m
Actuators: Transmission
20
202
1
g
AVF ε=
gi,1 gt,f
+V
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Actuators: Decrease Gap
• Use design to reduce initial gap beyond what is possible through processing– Transmission system
• Use processing to gain greater design flexibility and retain moderate speeds– Nitride isolation
• Use design to remove teeth from shuttle and second drive actuator– Friction clutch
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Actuators: Nitride Isolation
Pattern Nitride Trenches Etch Nitride Trenches Refill Low Stress Nitride
Pattern Silicon Trenches Etch Silicon Trenches Release
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Actuators: Nitride Isolation
• Keep final gap small for larger steps– Initial gap = g2– Final gap = g2 – g1
• Use insulating stops integrated in fingers of gap closers– allow longer fingers to
minimize extra structural elements
Nitride
Silicon5 m
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Actuators: Nitride IsolationElectrically Isolated Regions
Nitride
• Electrically isolated and mechanically connected silicon– more flexibility in
motor design• Nitride bumps on
bottom of silicon structures– reduce stiction
Buried Oxide
Silic
on
Nitr
ide
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Actuators: Decrease Gap
• Use design to reduce initial gap beyond what is possible through processing– Transmission system
• Use processing to gain greater design flexibility and retain moderate speeds– Nitride isolation
• Use design to remove teeth from shuttle and second drive actuator– Friction clutch
43/59
Actuators: Friction Clutch• Transmission requires ability to
use variable step sizes
• Remove extra drive actuator
€
δx1 = gi,0 − g final
€
δx2 = gi,1 − g final
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
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Actuators: Friction Clutch• Transmission requires ability to
use variable step sizes
• Remove extra drive actuator
€
δx1 = gi,0 − g final
€
δx2 = gi,1 − g final
45/59
Actuators: Friction Clutch• Transmission requires ability to
use variable step sizes
• Remove extra drive actuator
46/59
Actuators: Friction Clutch• Transmission requires ability to
use variable step sizes
• Remove extra drive actuator
47/59
Actuators: Friction Clutch• Transmission requires ability to
use variable step sizes
• Remove extra drive actuator
48/59
Actuators: Friction Clutch• Transmission requires ability to
use variable step sizes
• Remove extra drive actuator
49/59
Actuators: Friction Clutch• Transmission requires ability to
use variable step sizes
• Remove extra drive actuator
50/59
Actuators: Friction Clutch• Transmission requires ability to
use variable step sizes
• Remove extra drive actuator
51/59
Actuators: Friction Clutch• Transmission requires ability to
use variable step sizes
• Remove extra drive actuator
52/59
Actuators: Friction Clutch
• Two sided motor– Flexural force provides symmetric clutch force
• Clutch force greater than motors with teeth– Clutch force primarily dependent on final gap
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Actuators: Friction Clutch
500 m
• Normally-closed• No teeth!
100 m
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QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Actuators: Transmission Motor
Transmission
Nitride Gap Stops
Friction Clutch
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QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Prototypes: Motor + Elastomer
• Low force electrostatic inchworm motor with micro fabricated rubber band assembled into shuttle
rubber band
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Prototypes: System level demo
• 30 V solar cells driving EM6580 microcontroller and small inchworm motor
57/59
Summary• Jumping is a feasible method
of locomotion at this size scale
• A micromechanical energy storage system can be designed and fabricated– Simple fabrication– ~20 J stored energy
• Low power actuators can be designed and fabricated to provide – Millinewtons of force– Relatively simple fabrication
• These pieces work together!
1 mm
Motors
Energy Storage
rubber
58/59
For When I Have Time…
Inchworm Motors
• Thorough characterization– Clutch interface friction– Motor dynamics
• Add elastomer to motors– Make motors more robust– Increase shuttle friction
Energy Storage
• Characterize More Materials– Latex– Other silicones
• Characterize Reliability– Elastomer reliability– Cycling endurance Top
View
• Jumping more than once– Weebles wobble but
they don’t fall down– Robustness
Microrobots
• Jump and glide– Add wings to
deploy at top of jump
59/59
Acknowledgments
• Seth Hollar and Anita Flynn• Prof. Kris Pister• Students of 471 Cory
• Prof. Ron Fearing and Aaron Hoover• Berkeley Microlab Students and Staff• Many Berkeley Undergraduates
– Leo Choi, Stratos Christianakis, Deepa Mahajan