Design of Low-Power Silicon Articulated Microrobots

Richard Yeh & Kristofer S. J. Pister

Presented by:

Shrenik Diwanji

Abstract

To design and build a class of autonomous, low power silicon articulated micro-robots fabricated on a 1 cm2 silicon die and mounted with actuators, a controller and a solar array.

Designing

Primarily based on micro-machining Pros

Feature sizes in sub micronMass production

ConsDesigning from scratch

Basic model of the micro-robot.

Actuator Design

Main backbone of the robot designShould have high W/kg3 ratioDifferent types of actuators:-

Piezoelectric Thermal and shape-memory alloy Electromagnetic Electrostatic

Piezoelectric actuators

Pros Produce large force Require low power

Cons Require high voltage ~ 100v. difficult to integrate with CMOS electronics

Thermal and Shape-memory alloy actuators

Pros Robust Easy to operate

Cons High current dissipation ( 10s of mA)

Electromagnetic actuators

Pros High Energy Density

Cons Needs external magnet and / or high

currents to generate high magnetic fields

Electrostatic actuators

Pros Low power dissipation. Can be designed to dissipate no power

while exerting a force. High power density at micro scale. Easy to fabricate.

Electrostatic actuator design

Gap Contraction Actuator

_ 1Et l v2

2 d2Fe =

Scaling EffectsActuator force

Frequency

Dissipative forceGravitational force

Squeeze-film damping

Resistance of spring support

Power density

Inch Worm Motors.

Design of Inch Worm Motors

Inch Worm Cycle

Prototype design and working

Power requirements

Main areas of power dissipation CMOS controller Actuators

Power dissipation in actuators Weight - 0.5mN Adhesion force - 100µN

C = Total capacitanceF = frequency

Designing Articulated Rigid Links

Shape of the links Flat links

Cons Less strength due to 2 thin poly crystalline layers

HTB Pros

Good weight bearing capacity

Mounting of the solar array and the chip

Designing Articulated Rigid Links

Mechanical Coupling of the legs

Power Source Solar array is used η = 10 % ( max 26%) Power density = 10mW/cm2 (100 mw/cm2, η = 26%)

Controller

Open loop control (as no sensors)CMOS controller

Simple finite state machine Clock generator Charge pump

Logic behind walking of the Robot

Gait speed

Gait speed = Δx/T In one leg cycle

Δx = 100μm

T = 15 ms.

With GCA to leg displacement factor of 1:10 GCA gap – stop size of 2μm. Operating frequency of 1kHz.

Gait Speed = 100/15 = 7mm/s

Robot assembly

Difficulty The size of the robot The strength needed for perfect

mechanical couplingSolution

Flip chip bonding Allows the micro machined devices to be

transferred from substrate to another.

Conclusion

Key design issues Actuation power density Actuators used

Key tools Micro machining