Grand Challenges for Autonomous Mobile Microrobots Sarah Bergbreiter Dr. Kris Pister Berkeley 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, 1992Yeh, 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 Move Remove Legs Add Robot Body Solar Cell Array CCRs XL CMOS 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? Sensing Small, but power hungryuW 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 toysShipping products Robust, reliable, … DRIE, composites, … Comm Cell phones taking off WiFi? Radios were >100mW <100uA low rate spread-spectrum mesh networking Power Material propertiesCOTS thin film batteries Efficient solar cell arrays Lots of power conversion ICs Motors Barely able to move themselvesInchworms, 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 height (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 min417 min2 min, 50 sec25 sec Energy 5 mJ130 mJ180 J300 mJ Obstacle Size 5 cm 50  m100  m 5 mm S. Hollar, "A Solar-Powered, Milligram Prototype Robot from a Three-Chip Process," in Mechanical Engineering: University of California, Berkeley, 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,

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, S. Hollar, "A Solar-Powered, Milligram Prototype Robot from a Three-Chip Process," in Mechanical Engineering: University of California, Berkeley, 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, Ant (Walking) Proposed (Jumping) Hollar (Walking) Ebefors (Walking) Alice (Rolling) Mass11.9 mg15 mg10 mg80 mg10 g Time15 sec1 min417 min2.8 min25 sec Energy1.5 mJ5 mJ130 mJ180 J300 mJ Obstacle Sizeclimbing1 cm 50  m100  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, 2001Lindsay, 2001 Kladitis, 2000 Lu, 2003 Wood, 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 mm 2 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 Actuators Wood, 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 90 o and assembled out of plane Thermal actuators and rotation stages have been assembled Clamp w/o Assembled PartClamp 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 mm 2 –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? Mobility Tethered walking and autonomous pushups demonstrated Autonomous Walking, jumping, hopping, crawling Actuators InchwormsHigher force, Larger displacements COTS? Mechanisms Complex fabricationMore interesting materials Microassembly Power Solar CellsCOTS solar cells Batteries + Packaging Integration WirebondingAutomated assembly Self assembly Sensing, Comm, Control All there, but in piecesIntegrated with microrobots to create bug networks

Thanks!