Comparison of ANSYS? to Pseudo-Rigid Body Model in the Analysis of an Ortho-Flapper Compliant Mechanism

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Comparison of ANSYS? to Pseudo-Rigid Body Model
in the Analysis of an Ortho-Flapper Compliant
Mechanism

• ME 501
• 20 June, 2001
• Kris Downey Jeremiah Johnstun

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Presentation Outline

• Introduction of mechanism
• Setup of ANSYS model
• Analysis results
• Comparisons between analyses
• Conclusions What we learned

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Ornithopter Mechanism

• Current design
• Nine separate parts
• Plastic and aluminum rods connected by pin joints

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Ornithopter Mechanism

• Proposed changes
• Compliant mechanism
• Single part design
• Polypropylene material

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Ornithopter Mechanism

• Actual machined mechanism

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Analysis Setup

• Area with thickness (PLANE82)
• Composed of lines and fillets
• Simple Boolean operations
• Mesh
• Multiple mesh areas tried
• Mesh edge size .05 in
• Refined mesh at high stress points
• Nonlinear analysis
• Large deflections

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Analysis Setup

• Symmetrical model
• Constraints at hole and on right side
• Displacement at center node (node 198)

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Analysis Results

• Maximum stresses
• Fillets contribute to stress concentration factor
• Thin members experience high stress in tension
  and compression

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Analysis Results

• Range of displacements tested
• Successful results from input displacements

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Analysis Results

• Range of motion
• 80º of motion with given inputs
• High stresses no failure

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Analysis Results

• Comparisons Pseudo-rigid vs. Ansys

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Analysis Results

• Comparisons Pseudo-rigid vs. Ansys

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Hardware Results

• 80º range of motion
• No yielding or plastic deformation
• Too heavy to fly

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ConclusionsWhat We Learned

• Linear vs. Nonlinear model
• Large deflection necessitates nonlinear model
• Linear results far from accurate

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ConclusionsWhat We Learned

• Symmetrical model
• Easy to model with directional constraints
• Cut number of elements in half
• Same results with decreased computation time

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ConclusionsWhat We Learned

• Pseudo-rigid model comparison
• Stress concentration factor must be included

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Conclusions

• Nonlinear analysis for large deflections
• Symmetric models when possible
• Pseudo-rigid body models
• Reasonable results for forces
• Stresses very inaccurate
• Stress concentration factor needed

Questions?