Northwestern University Compliant Mechanisms ME 381 – Fall 2004
Compliant MechanismsCompliant Mechanisms
Presented By:
Ravi Agrawal, Binoy Shah,Ravi Agrawal, Binoy Shah, and and Eric ZimneyEric Zimney
Northwestern University Compliant Mechanisms ME 381 – Fall 2004
OutlineOutline
• Working Principal
• Advantages and Disadvantages
• Compliance in MEMS devices
• Design and Optimization
• Analysis: Static and Dynamic
• Example Devices
• Conclusion
Northwestern University Compliant Mechanisms ME 381 – Fall 2004
Working PrincipleWorking Principle
• 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.
Compliant Mechanism: A flexible structure that elastically deforms without joints to produce a desired force or displacement.
Northwestern University Compliant Mechanisms ME 381 – Fall 2004
Macro-scale ExamplesMacro-scale Examples
Non-compliant crimp Non-compliant wiper
Compliant crimp Compliant wiper
Northwestern University Compliant Mechanisms ME 381 – Fall 2004
Benefits of Compliant MechanismsBenefits of Compliant Mechanisms
Advantages1. No Joints2. No friction or wear3. Monolithic4. No assembly5. Works with piezoelectric, shape-memory
alloy, electro-thermal, electrostatic, fluid pressure, and electromagnetic actuators
Disadvantages1. Small displacements or forces2. Limited by fatigue, hysteresis, and creep3. Difficult to design
Northwestern University Compliant Mechanisms ME 381 – Fall 2004
Compliance for MEMSCompliance for MEMS
Features ImpactMonolithic 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.
Compliant Actuator – New design
Non-Compliant Actuator - Old Design
Northwestern University Compliant Mechanisms ME 381 – Fall 2004
DefinitionsDefinitions• Geometric Advantage:
• Mechanical Advantage:
• Localized Verses Distributed Compliance
in
out
u
uGA
in
out
F
FMA
Northwestern University Compliant Mechanisms ME 381 – Fall 2004
Design of Distributed Compliant Design of Distributed Compliant MechanismsMechanisms
• 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.
Northwestern University Compliant Mechanisms ME 381 – Fall 2004
Topology SynthesisTopology Synthesis
max
• Energy Efficiency Formulation– Objective function:
– Optimization Problem:
dttutF
dttutF
work
work
inin
outout
in
out
1Re sourceMaxVolumeV
max,min, iii aaa
Northwestern University Compliant Mechanisms ME 381 – Fall 2004
Size and Shape OptimizationSize and Shape Optimization• Performance Criteria:
– Geometric/Mechanical Advantage– Volume/Weight– Avoidance of buckling instabilities– Minimization of stress
concentrations
• Optimization Problem: max
max,min, iii aaa
1Re sourceMaxVolumeV
11
1
MAF
Fh
in
out 11
1
GAu
uh
in
out
1max
iFS
oror
Northwestern University Compliant Mechanisms ME 381 – Fall 2004
Stress AnalysisStress 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
Northwestern University Compliant Mechanisms ME 381 – Fall 2004
Dynamic AnalysisDynamic 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
Northwestern University Compliant Mechanisms ME 381 – Fall 2004
More MEMS applicationsMore MEMS applications
Double V-beam suspension for Linear Micro Actuators
(Saggere & Kota 1994)
HexFlex Nanomanipulator
(Culpepper, 2003)
The Self Retracting Fully-Compliant Bistable Mechanism
(L. Howell, 2003)
V-beam Thermal Actuatorwith force amplification
(Hetrick & Gianchandani, 2001)
http://www.engin.umich.edu/labs/csdl/video02.html
Northwestern University Compliant Mechanisms ME 381 – Fall 2004
ContactsContacts• Universities
• Industry– FlexSys Inc
– Sandia National Lab
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
Northwestern University Compliant Mechanisms ME 381 – Fall 2004
ConclusionConclusion• 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
