Biomimetics Laboratory

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Contact Modeling and Testing of Directional
Adhesives

• Daniel Santos

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Contact What and Why
Transmission of Forces through Mechanical
Interaction

• Contact Defines
• Slip Limits Pulloff Limits
• Guide Design
• Enable Control

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Contact Models
Coulomb Friction
Hertz Contact
FNormal
FTangential

• Rigid-Body vs. Deformable Contact
• Point Contact vs. Area Contact

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Analysis

• Stability Analysis
• Force Distribution
• Foot Orientation

Stability vs. Inclination Angle
Stability vs. Foot Orientation
Stable
Unstable
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Adhesive Models
What is the Right Adhesive Model for Climbing?

• JKR Isotropic
• FA Anisotropic

What do StickyBot Pads Do?
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Experimental Contact Testing

• Goals
• Analyze Behavior of StickyBot Pads
• Develop 3D Model of Directional Adhesion
• Method
• Apply Controlled Motions to Sample Pads
• Measure Forces
• Obtain Limits Associated with Slip and Pulloff

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Mechanical Test Setup

• 3 Motor-Driven Lead Screws
• X/Y 0.2 per Revolution 1.7um per Tick
• Z 0.05 per Revolution 0.4um per Tick
• 6-axis Force/Torque Sensor
• Wall-mounted -gt /-25mN Noise
• 2-axis Alignment Stage

Sample
Wall
Force Plate
Alignment
Bench
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Electronic Test Setup
Forces/Torques
1kHz
Voltage Encoder
Position
500Hz
Trajectory
1kHz
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Experimental Procedure

• Preload
• Along 45
• Different Depths 01000um
• Pulloff
• In Y-Z Plane between 0-180
• In X-Z Plane between 0-180

Z
Y
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Raw Data
Preload
Pulloff
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Determining Pulloff
165,90
150,45
150,90
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Determining Pulloff

• Buckling?
• Pulloff vs. Sliding
• Finding Pulloff
• Maximum Normal Adhesion
• Maximum Force in Velocity Direction
• Maximum Force Magnitude

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Data YZ Plane
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Data YZ Plane
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Data XZ Plane
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Data 3D
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Data 3D
Show Demo
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Summary of Results

• Experimental Procedure Challenges
• Absolute Positioning
• Alignment
• Data Interpretation Challenges
• Buckling
• Pulloff vs. Sliding
• Preload INCREASES Adhesion (up to limit)
• Adhesion CONTROLLABLE via Tangential Angle
• Lateral Loads DECREASE Adhesion

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Future Work

• Continue Testing
• Fill in Sparse Areas of 3D Contact
• Test Different Samples
• Understand/Explain Anomalies
• Model Experimental Data
• Linear?
• Incorporate Findings into Previous Work
• Posture, Foot-Orientation Analysis
• Control of Internal Forces

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Questions?

• Tidbits of Info
• 5,577 Trials
• 15 Hours of Continuous Operation
• 4GB of Data!