Compliant Mechanisms

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Compliant Mechanisms
Presented By Ravi Agrawal, Binoy Shah, and
Eric Zimney
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Outline

• Working Principal
• Advantages and Disadvantages
• Compliance in MEMS devices
• Design and Optimization
• Analysis Static and Dynamic
• Example Devices
• Conclusion

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Working Principle
Compliant Mechanism A flexible structure that
elastically deforms without joints to
produce a desired force or displacement.

• Deflection of flexible members to store energy in
  the form of strain energy
• Strain energy is same as elastic potential energy
  in in a spring
• Since product of force and displacement is a
  constant. There is tradeoff between force and
  displacement as shown in fig on left.

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Macro-scale Examples
Non-compliant crimp
Non-compliant wiper
Compliant crimp
Compliant wiper
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Benefits of Compliant Mechanisms

• Advantages
• No Joints
• No friction or wear
• Monolithic
• No assembly
• Works with piezoelectric, shape-memory alloy,
  electro-thermal, electrostatic, fluid pressure,
  and electromagnetic actuators
• Disadvantages
• Small displacements or forces
• Limited by fatigue, hysteresis, and creep
• Difficult to design

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Compliance for MEMS
Non-Compliant Actuator - Old Design
Compliant Actuator New design
Features Impact
Monolithic and Planer -Suitable for microfabrication No assembly (a necessity for MEMS) Reduced size Reduced cost of production
Joint-less No friction or wear No lubrication needed
Small displacements or forces - Useful in achieving well controlled force or motion at the micro scale.
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Definitions

• Geometric Advantage
• Mechanical Advantage
• Localized Verses Distributed Compliance

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Design of Distributed Compliant Mechanisms

• Topology Synthesis
• Develop kinematic design to meet input/output
  constraints.
• Optimization routine incompatible with stress
  analysis.
• Size and Shape Optimization
• Enforce Performance Requirements to determine
  optimum dimensions.

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Topology Synthesis

• Energy Efficiency Formulation
• Objective function
• Optimization Problem

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Size and Shape Optimization

• Performance Criteria
• Geometric/Mechanical Advantage
• Volume/Weight
• Avoidance of buckling instabilities
• Minimization of stress concentrations
• Optimization Problem

or
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Stress Analysis

• Size and shape refinement
• Same Topology
• Optimized dimensions of the beams
• Uniformity of strain energy distribution
• Methods used
• Pseudo rigid-body model
• Beam element model
• Plane stress 2D model

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Dynamic Analysis

• Methods Used
• FEM Tools
• Example of Stroke Amplifier
• First four natural frequencies are as 3.8 kHz,
  124.0 kHz, 155.5 kHz and 182.1 kHz
• Fundamental frequency dominates
• Dynamic characteristics
• Frequency ratio vs Displacement Ratio
• Frequency ratio vs GA

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More MEMS applications
Double V-beam suspension for Linear Micro
Actuators
HexFlex Nanomanipulator
(Culpepper, 2003)
(Saggere Kota 1994)
V-beam Thermal Actuator with force amplification
The Self Retracting Fully-Compliant Bistable
Mechanism
(L. Howell, 2003)
(Hetrick Gianchandani, 2001)

• http//www.engin.umich.edu/labs/csdl/video02.html

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Contacts

• Universities

Institution Lab Faculty
1 Univ. of Michigan Compliant Systems Design Laboratory Sridhar. Kota
2 Brigham Young University Compliant Mechanism Research Larry L. Howell
3 Univ. of Illinois at Chicago Micro Systems Mechanisms and Actuators Laboratory Laxman Saggere
4 Univ. of Penn Computational Design G. Ananthasuresh
5 MIT Precision Compliant Systems Lab Martin L. Culpepper
6 Technical University of Denmark Topology optimization Ole Sigmund

• Industry
• FlexSys Inc
• Sandia National Lab

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Conclusion

• Stores potential energy and outputs displacement
  or force
• Monolithic no joints, no assembly, no friction
• Small but controlled forces or displacements
• Can tailor design to performance
  characteristics.
• Performance dependent on output
• Difficult to design
• Examples HexFlex Nanomanipulator, MicroEngine,
  Force Amplifier