1. Towards Autonomous Jumping Microrobots
Sarah Bergbreiter
Prof. Kris Pister
Berkeley Sensor and Actuator Center
University of California, Berkeley

2. Motivation Applications Key Technologies Mobile Sensor Networks
Size
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
Target Space
Input Power
Size ~ mm
Input Power ~ 10s mW
Speed ~ 10 sec / jump
Speed

3. Why Jumping? Improve Mobility Improve Efficiency Obstacles are large!
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
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

4. Building a Jumping Microrobot
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
From what we’ve already shown, the robot is going to require.
Emphasize that landing and resetting for next jump are not discussed.

5. Energy Density (mJ/mm3)
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
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

6. 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

7. 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

8. Assembly Fine-tip tweezers under an inspection microscope
Mobile pieces need to be tethered during assembly
Yield > 80% and improving

9. Spring Performance: Molded
Using force gauge shown previously, pull with probe tip to load and unload spring
Trial #1
200% strain
10.4 mJ
92% recovered
Trial #2
220% strain
19.4 mJ
85% recovered
20 mJ would propel a 10mg microrobot 20 cm

10. 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)

11. Full System Demonstration
Electrostatic inchworm motor translates 30mm 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

12. Conclusions and Future Work
Process developed for integrating elastomer springs with silicon microstructures
Almost 20 mJ 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