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 cm 2 silicon die and mounted with actuators, a controller and a solar array.

Designing Primarily based on micro-machining  Pros  Feature sizes in sub micron  Mass production  Cons  Designing from scratch

Basic model of the micro-robot.

Actuator Design  Main backbone of the robot design  Should have high W/kg 3 ratio  Different 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 v 2 2 d 2 F e =

Scaling Effects Actuator force Frequency Dissipative force Gravitational 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- 100 µ N C = Total capacitance F = 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/cm 2 (100 mw/cm 2, 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 coupling  Solution  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