©2006 university of california prepublication data september 2006 towards autonomous jumping...
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©2006 University of California Prepublication Data September 2006
Towards Autonomous Jumping Microrobots
Sarah BergbreiterProf. Kris Pister
Berkeley Sensor and Actuator CenterUniversity of California, Berkeley
©2006 University of California Prepublication Data September 2006
Motivation
• Applications– Mobile Sensor Networks– Planetary Exploration– MEMS Catapults– Bi-Modal Transportation
• Key Technologies– Energy storage– Large force, large
displacement actuators– “High output power for
short time” actuated MEMS system
Size
Input Power
Speed
Target Space
Size ~ mm
Input Power ~ 10s W
Speed ~ 10 sec / jump
©2006 University of California Prepublication Data September 2006
Why Jumping?
• 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?
Ant (Walking)
Proposed (Jumping)
Hollar (Walking)
Ebefors (Walking)
Mass 11.9 mg 10 mg 10 mg 80 mg
Time 15 sec 1 min 417 min 2.8 min
Energy 1.5 mJ 5 mJ 130 mJ 180 J
Obstacle Size ** 1 cm 50 m 100 m
©2006 University of California Prepublication Data September 2006
• Spring for energy storage– short legs imply short
acceleration times
• High force, long stroke motor– Store energy in springs
• Power for motors and control
• Controller to direct motors
• Landing and resetting for next jump are NOT discussed
Building a Jumping Microrobot
©2006 University of California Prepublication Data September 2006
How Much Energy?
• Motor work kinetic energy for jump– Drag is not large effect
at smaller energies
• Spring requirements– High energy density– Large deflection (5mm)– Large forces (10mN)– Simple process
integration
• Elastomer springs– High energy density– Large strains
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
©2006 University of California Prepublication Data September 2006
Integration Elastomer With Silicon
• Fabricate separately and assemble– Simple fabrication– Allows larger variety of
spring material
• Silicon Process– High force electrostatic
inchworm motors– Hooks to assemble
silicone
• Elastomer Process– Two methods
demonstrated
©2006 University of California Prepublication Data September 2006
Elastomer Fabrication
Laser Cut
• Simple Fabrication– Spin on Sylgard® 186
and cut with VersaLaserTM
• Poor quality– Mean 250% elongation
at break
Molded
• Complex Fabrication– DRIE silicon mold– Pour on Sylgard® 186
• High quality– Mean 350% elongation
at break
©2006 University of California Prepublication Data September 2006
Assembly
• Fine-tip tweezers under an inspection microscope
• Mobile pieces need to be tethered during assembly
• Yield > 80% and improving
©2006 University of California Prepublication Data September 2006
Spring Performance: Molded
• 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
©2006 University of California Prepublication Data September 2006
Quick Release of Energy
• Electrostatic clamps designed to hold leg in place for quick release– Normally-closed
configuration for portability
• Shot a 0.6 mg 0402-sized capacitor 1.5 cm along a glass slide
• Energy released in less than one video frame (66ms)
©2006 University of California Prepublication Data September 2006
Full System Demonstration
• Electrostatic inchworm motor translates 30m to store an estimated 4.9nJ of energy and release it quickly
• Motors will be more aggressively designed in the future to substantially increase this number
©2006 University of California Prepublication Data September 2006
Conclusions and Future Work
• Process developed for integrating elastomer springs with silicon microstructures
• Almost 20 J of energy stored in molded micro rubber bands– Equivalent jump height of 20 cm for 10 mg microrobot
• Build higher force motors to store this energy• Keep the leg in-plane
through integrated staples• Put it all together for an
autonomous jumping microrobot!
Subramaniam Venkatraman, 2006