Autonomous Jumping Microrobots micro robots for mobile sensor networks Sarah Bergbreiter Electrical Engineering and Computer Sciences UC Berkeley, Advisor: Prof. Kris Pister Dissertation Talk, May 17, 2007

2/59 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 Robots Remove 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-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), 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 , March V. Kumar, D. Rus, and S. Singh, "Robot and Sensor Networks for First Responders," Pervasive computing, October, 2004, pp Hazardous Sensor Network Deployment

5/59 From CotsBots to Microrobots 100  m

6/59 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

7/59 Microrobots: Challenges

8/59 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

9/59 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), S. Hollar, PhD Dissertation, T. Ebefors, et al. Transducers Jumping?Jumping!!

10/59 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

11/59 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

12/59 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 mm1.8 mm Bellew, Hollar (Transducers 2003), 2.3 mg

13/59 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

14/59 Energy Storage: Rubber High Energy Density –Capable of storing large amounts of energy with small area and volume –2mm x 50m x 50m rubber band can store up to 45J Large Strains –Stress/strain profile suitable for low-power electrostatic actuators with large displacements MaterialE (Pa)Maximum Strain (%) Tensile Strength (Pa) Energy Density (mJ/mm 3 ) Silicon169x x Silicone750x x Resilin2x x10 6 4

15/59 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 +

16/59 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 500  m

17/59 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 ®  m VersaLaser TM

18/59 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 + C 4 F 8 Passivation Sylgard ®  m

19/59 Elastomer Assembly Fine-tip tweezers using stereo inspection microscope Yield > 90% and rising 100  m

20/59 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

21/59 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)

22/59 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

23/59 Actuators: Electrostatic GCAs l + - V g t k F High forces with small gaps Small displacements

24/59 Actuators: Inchworm Motors Inchworm actuation accumulates short displacements for long throw May be fabricated in single mask SOI process

25/59 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

27/59 Actuators: Inchworm Motors Inchworm actuation accumulates short displacements for long throw May be fabricated in single mask SOI process

28/59 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

33/59 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 V g A d U F     

34/59 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

35/59 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 g i,0 g t,0 g t,gap

36/59 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 g i,1 gfgf Only needs to be actuated when more force is needed Does not need to be changed with each step

37/  m Actuators: Transmission g i,1 g t,f +V

38/59 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

39/59 Actuators: Nitride Isolation Pattern Nitride Trenches Etch Nitride TrenchesRefill Low Stress Nitride Pattern Silicon Trenches Etch Silicon Trenches Release

40/59 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 Silicon 5  m

41/59 Actuators: Nitride Isolation Electrically 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 Silicon Nitride

42/59 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

44/59 Actuators: Friction Clutch Transmission requires ability to use variable step sizes Remove extra drive actuator

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

53/59 Actuators: Friction Clutch 500  m Normally-closed No teeth! 100  m

54/59 Actuators: Transmission Motor Transmission Nitride Gap Stops Friction Clutch

55/59 Prototypes: Motor + Elastomer Low force electrostatic inchworm motor with micro fabricated rubber band assembled into shuttle rubber band

56/59 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