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Bistable Spring Design for Endoscopic Stabilization
Soft Robotics | Mechanical Engineering
As part of a soft robotic stabilization system for endoscopic tools, I led the design and integration of elastomeric bistable springs that enable rapid, passive anchoring against anatomical walls. These springs were embedded in a 4-bar linkage sleeve and served to mechanically stabilize the endoscope tip during procedures like colonoscopy. Their bistable behavior allowed for snap-through transitions between deployed and retracted states, without requiring continuous energy input or active control.
Technical Implementation
To achieve bistability, I developed a dynamic simulation pipeline in MATLAB using Lagrangian mechanics. The model incorporated:
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Realistic geometry and material properties of Ecoflex 30-based springs.
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Torque-angle analysis using nonlinear spring models
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Equilibrium condition solving with fzero under varied external torques.
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Full parameter sweeps to identify spring geometries achieving equilibrium at both 0° and 90°, critical for stability and deployment.
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A bistability evaluation script that plotted final rest positions across initial angle conditions to confirm multi-stability.
The final design used silicone-cast springs formed in custom 3D-printed molds. Material tearing was resolved by incorporating fiber reinforcement, which enhanced durability without compromising compliance. These refinements led to reliable mechanical behavior across multiple actuation cycles.
Key Challenges
Geometric Folding: Oversized springs folded during retraction. This was mitigated by repositioning attachment points based on simulation outputs.
Material Fatigue: Spring tear-out under load was eliminated using fiber-reinforced casting, informed by stress concentration analysis.
Design Selection: A full sweep of over 10,000 parameter combinations was simulated to isolate configurations with desired bistable equilibria, optimizing both energy landscape and manufacturability.
More Resources
Design Paper for reference (groupwork)
[description] Spring in open position, Spring in closed position (diagram + video), simulation videos, spring mehcanism video, mold making iteration, spring iterations, bistability analysis, final fibre-reinforced mold
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