Grand Challenges for Autonomous Mobile Microrobots

Sarah Bergbreiter

Dr. Kris PisterBerkeley Sensor and Actuator Center, UC Berkeley

What is an Autonomous Mobile Microrobot?

• Size– Total size on order of millimeters

• Mobility– Should be able to move around a given

environment– Speeds of mm/sec

• Autonomous– Power and control on-board– Communication between robots (?)

Applications for Autonomous Mobile Microrobots

• Mobile Sensor Networks– Monitoring/surveillance– Search and rescue

• Cooperative Construction– Assisted assembly– Sacrificial assembly

Previous Microrobots

Seiko, 1992

Yeh, 1995-2001 Hollar, et al, 2002

Ebefors, et al, 1999

Sandia, 2001

Donald, et al, 2006

COTS Dust (Hill, et al. ACM OS Review 2000)

Making Silicon MoveRemove

Legs

Add Robot Body

Solar Cell Array

CCRs

XLCMOS

IC

Smart Dust (Warneke, et al. Sensors 2002)

1mm

Microrobots (Hollar, Flynn, Pister. MEMS 2002)

1mm

CotsBots (Bergbreiter, Pister. IROS 2003)

How Close Are We?

1995 2005

Sensing Small, but power hungry uW interface electronics

Low power sensors

Computation Clear trends

No COTS uPower

Talk of 1MIP/mW

10 MIP/mW COTS

100 MIP/mW demoed

Mechanisms Lab demos of toys Shipping products

Robust, reliable, …

DRIE, composites, …

Comm Cell phones taking off

WiFi?

Radios were >100mW

<100uA low rate spread-spectrum mesh networking

Power Material properties COTS thin film batteries

Efficient solar cell arrays

Lots of power conversion ICs

Motors Barely able to move themselves Inchworms, polymers

Solar Powered 10mg Silicon Robot

Why Is This So Hard?

1mm

Locomotion

Actuators

Power

Integration

Mechanisms

Challenge 1: Locomotion

1mm

Locomotion

Challenge 1: Locomotion

• Interaction with Environment– Obstacles are large

• Reduce Complexity– Difficult to actuate out of plane– Difficult to fabricate bearings

• Efficiency– Internal v. external work

Locomotion: Jumping

0 10 20 30 40 50-10

-5

0

5

10

15

20

25

30

35

Hopping Trajectory, Mass = 15 mg, Angle = 60 deg

distance (cm)

heig

ht (

cm)

5 uJ10 uJ25 uJ50 uJ

heig

ht (

cm)

distance (cm)

Hopping Trajectory, Mass = 15mg, Angle = 60deg

Locomotion: Comparison

• What time and energy is required to move a microrobot 1 m and what size obstacles can these robots overcome?

Proposed

(Jumping)

Hollar

(Walking)

Ebefors

(Walking)

Alice

(Rolling)

Time 1 min 417 min 2 min, 50 sec 25 sec

Energy 5 mJ 130 mJ 180 J 300 mJ

Obstacle Size 5 cm 50 m 100 m 5 mm

S. Hollar, "A Solar-Powered, Milligram Prototype Robot from a Three-Chip Process," in Mechanical Engineering: University of California, Berkeley, 2003. T. Ebefors, J. U. Mattsson, E. Kalvesten, and G. Stemme, "A walking silicon microrobot," presented at International Conference on Sensors and Actuators (Transducers '99), Sendai, Japan, 1999. http://asl.epfl.ch/index.html?content=research/systems/Alice/alice.php

Locomotion: Comparison

• What time and energy is required to move a microrobot 1 m and what size obstacles can these robots overcome?

A. Lipp, H. Wolf, and F.O. Lehmann., “Walking on inclines: energetics of locomotion in the ant Camponotus," Journal of Experimental Biology 208(4) Feb 2005, 707-19.S. Hollar, "A Solar-Powered, Milligram Prototype Robot from a Three-Chip Process," in Mechanical Engineering: University of California, Berkeley, 2003. T. Ebefors, J. U. Mattsson, E. Kalvesten, and G. Stemme, "A walking silicon microrobot," presented at International Conference on Sensors and Actuators (Transducers '99), Sendai, Japan, 1999. http://asl.epfl.ch/index.html?content=research/systems/Alice/alice.php

Ant (Walking)

Proposed (Jumping)

Hollar (Walking)

Ebefors (Walking)

Alice (Rolling)

Mass 11.9 mg 15 mg 10 mg 80 mg 10 g

Time 15 sec 1 min 417 min 2.8 min 25 sec

Energy 1.5 mJ 5 mJ 130 mJ 180 J 300 mJ

Obstacle Size climbing 1 cm 50 m 100 m 5 mm

Challenge 2: Actuators

1mm

Actuators

Challenge 2: Actuators

• Low Power• Small Size• Force/Displacement• Efficient• Simple Fabrication

and Integration• Power Supply

Compatibility• Robust

Pelrine, 2002

Yeh, 2001 Lindsay, 2001

Kladitis, 2000

Lu, 2003Wood, 2005

Actuators: Electrostatic Inchworm Motors

• High force at low power and moderate voltage

• Accumulate short displacements for long throw

• Fabricated in single mask process

• Hollar inchworm designed for 500 N of force and 256 m of travel in ~ 2.8 mm2

l

+-V d

t

k

F

Electrostatic Inchworm Motor

Challenge 3: Mechanisms

1mm

Mechanisms

Challenge 3: Mechanisms

• Simple Fabrication– Process Complexity– Batch v. Serial

• Efficient– Friction

• Robust

• Matching to ActuatorsWood, et al, 2003

Hollar, et al, 2002

Mechanisms: Silicon

• 2 months in the microlab, but very pretty!

Mechanisms: Assembly• Orthogrippers fabricated in

same process• Parts rotated 90o and

assembled out of plane• Thermal actuators and

rotation stages have been assembledClamp w/o Assembled Part

Clamp w/ Assembled Part

Challenge 4: Power

1mm

Power

Challenge 4: Power

• Small Mass and Volume

• Compatible with Actuators– Any converter

circuitry should be included

• Simple Integration

Nielsen, 2003

Cymbet

Roundy, 2003

Bellew, 2003

Power: Solar Cells

• Use isolation trenches to stack solar cells for higher voltages

• 0.5 – 100V demonstrated

• 10-14% efficiency• Small Size

– Chip area: 3.6 x 1.8 mm2

– Chip mass: 2.3 mg

• Complex Process

Challenge 5: Integration

1mm

Integration

Challenge 5: Integration

• Need to connect all of the pieces– Actuators, control,

power supply, sensors, radio…

• Robust• Compatibility• Serial v. Batch

Last, 2006

Srinivasan, 2001

What Next?

2005 2015

Mobility Tethered walking and autonomous pushups demonstrated

Autonomous

Walking, jumping, hopping, crawling

Actuators Inchworms Higher force, Larger displacements

COTS?

Mechanisms Complex fabrication More interesting materials

Microassembly

Power Solar Cells COTS solar cells

Batteries + Packaging

Integration Wirebonding Automated assembly

Self assembly

Sensing, Comm, Control

All there, but in pieces Integrated with microrobots to create bug networks

Thanks!