Design of Low-Power Silicon Articulated Microrobots

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Design of Low-Power Silicon Articulated
Microrobots
Richard Yeh Kristofer S. J. Pister
Presented by Shrenik Diwanji
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• 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.

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Designing

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

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Basic model of the micro-robot.
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Actuator Design

• Main backbone of the robot design
• Should have high W/kg3 ratio
• Different types of actuators-
• Piezoelectric
• Thermal and shape-memory alloy
• Electromagnetic
• Electrostatic

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Piezoelectric actuators

• Pros
• Produce large force
• Require low power
• Cons
• Require high voltage 100v.
• difficult to integrate with CMOS electronics

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Thermal and Shape-memory alloy actuators

• Pros
• Robust
• Easy to operate
• Cons
• High current dissipation ( 10s of mA)

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Electromagnetic actuators

• Pros
• High Energy Density
• Cons
• Needs external magnet and / or high currents to
  generate high magnetic fields

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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.

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Electrostatic actuator design

• Gap Contraction Actuator

_ 1Et l v2 2 d2
Fe
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Scaling Effects
Actuator force
Dissipative force
Gravitational force
Squeeze-film damping
Resistance of spring support
Frequency
Power density
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Inch Worm Motors.
Design of Inch Worm Motors
Inch Worm Cycle
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Prototype design and working
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Power requirements

• Main areas of power dissipation
• CMOS controller
• Actuators
• Power dissipation in actuators
• Weight - 0.5mN
• Adhesion force - 100µN

C Total capacitance F frequency
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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

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Designing Articulated Rigid Links

• Mounting of the solar array and the chip

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• Mechanical Coupling of the legs

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Power Source

• Solar array is used
• ? 10 ( max 26)
• Power density 10mW/cm2 (100 mw/cm2, ? 26)

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Controller

• Open loop control (as no sensors)
• CMOS controller
• Simple finite state machine
• Clock generator
• Charge pump

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Logic behind walking of the Robot
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Gait speed

• Gait speed ?x/T
• In one leg cycle
• ?x 100µm
• T 15 ms.
• With
• GCA to leg displacement factor of 110
• GCA gap stop size of 2µm.
• Operating frequency of 1kHz.

Gait Speed 100/15 7mm/s
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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.

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Conclusion

• Key design issues
• Actuation power density
• Actuators used
• Key tools
• Micro machining