©2006 University of California Prepublication Data September 2006 Towards Autonomous Jumping Microrobots Sarah Bergbreiter Prof. Kris Pister Berkeley Sensor.

©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