Northwestern University Compliant MechanismsME 381 – Fall 2004 Compliant Mechanisms Presented By: Ravi Agrawal, Binoy Shah, and Eric Zimney

Northwestern University Compliant MechanismsME 381 – Fall 2004Outline Working Principal Advantages and Disadvantages Compliance in MEMS devices Design and Optimization Analysis: Static and Dynamic Example Devices Conclusion

Northwestern University Compliant MechanismsME 381 – Fall 2004 Working 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 MechanismsME 381 – Fall 2004 Macro-scale Examples Non-compliant crimpNon-compliant wiper Compliant crimp Compliant wiper

Northwestern University Compliant MechanismsME 381 – Fall 2004 Benefits of Compliant Mechanisms Advantages 1.No Joints 2.No friction or wear 3.Monolithic 4.No assembly 5.Works with piezoelectric, shape-memory alloy, electro-thermal, electrostatic, fluid pressure, and electromagnetic actuators Disadvantages 1.Small displacements or forces 2.Limited by fatigue, hysteresis, and creep 3.Difficult to design

Northwestern University Compliant MechanismsME 381 – Fall 2004 Compliance for MEMS FeaturesImpact 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. Compliant Actuator – New design Non-Compliant Actuator - Old Design

Northwestern University Compliant MechanismsME 381 – Fall 2004Definitions Geometric Advantage: Mechanical Advantage: Localized Verses Distributed Compliance

Northwestern University Compliant MechanismsME 381 – Fall 2004 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.

Northwestern University Compliant MechanismsME 381 – Fall 2004 Topology Synthesis Energy Efficiency Formulation –Objective function: –Optimization Problem:

Northwestern University Compliant MechanismsME 381 – Fall 2004 Size and Shape Optimization Performance Criteria: –Geometric/Mechanical Advantage –Volume/Weight –Avoidance of buckling instabilities –Minimization of stress concentrations Optimization Problem: or

Northwestern University Compliant MechanismsME 381 – Fall 2004 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

Northwestern University Compliant MechanismsME 381 – Fall 2004 Dynamic Analysis Methods Used – –FEM Tools Example of Stroke Amplifier – –First four natural frequencies are as 3.8 kHz, kHz, kHz and kHz – –Fundamental frequency dominates Dynamic characteristics – –Frequency ratio vs Displacement Ratio – –Frequency ratio vs GA

Northwestern University Compliant MechanismsME 381 – Fall 2004 More 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 Actuator with force amplification (Hetrick & Gianchandani, 2001)

Northwestern University Compliant MechanismsME 381 – Fall 2004 Contacts Universities Industry –FlexSys Inc –Sandia National Lab InstitutionLabFaculty 1Univ. of MichiganCompliant Systems Design Laboratory Sridhar. Kota 2Brigham Young UniversityCompliant Mechanism ResearchLarry L. Howell 3Univ. of Illinois at ChicagoMicro Systems Mechanisms and Actuators Laboratory Laxman Saggere 4Univ. of PennComputational DesignG. Ananthasuresh 5MITPrecision Compliant Systems LabMartin L. Culpepper 6Technical University of DenmarkTopology optimizationOle Sigmund

Northwestern University Compliant MechanismsME 381 – Fall 2004 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