Autonomous Jumping Microrobots micro robots for mobile sensor networks Sarah Bergbreiter Electrical Engineering and Computer Sciences UC Berkeley, Advisor:

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

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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

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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)



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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: 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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• 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


20

202

1

g

AVF ε=

gi,1 gt,f

+V

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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: Friction Clutch• Transmission requires ability to

use variable step sizes

• Remove extra drive actuator

€

δx1 = gi,0 − g final

€


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€


€


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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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Actuators: Transmission Motor

Transmission

Nitride Gap Stops

Friction Clutch

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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

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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

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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

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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

Documents

Autonomous Jumping Microrobots micro robots for mobile sensor networks Sarah Bergbreiter Electrical Engineering and Computer Sciences UC Berkeley, Advisor: