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High-energy-density 3D-printed Composite Springs for Lightweight and Energy-efficient Compliant Robots

Amanda Sutrisno, David J. Braun

Abstract

Springs store mechanical energy similar to batteries storing electrical energy. However, conventional springs are heavy and store limited amounts of mechanical energy relative to batteries, i.e they have low mass-energy-density. Next-generation 3D printing technology could potentially enable manufacturing low cost lightweight springs with high energy storage capacity. Here we present a novel design of a high-energy-density 3D printed torsional spiral spring using structural optimization. By optimizing the internal structure of the spring we obtained a 45% increase in the mass energy density, compared to a torsional spiral spring of uniform thickness. Our result suggests that optimally designed 3D printed springs could enable robots to recycle more mechanical energy per unit mass, potentially reducing the energy required to control robots.

High-energy-density 3D-printed Composite Springs for Lightweight and Energy-efficient Compliant Robots

Abstract

Springs store mechanical energy similar to batteries storing electrical energy. However, conventional springs are heavy and store limited amounts of mechanical energy relative to batteries, i.e they have low mass-energy-density. Next-generation 3D printing technology could potentially enable manufacturing low cost lightweight springs with high energy storage capacity. Here we present a novel design of a high-energy-density 3D printed torsional spiral spring using structural optimization. By optimizing the internal structure of the spring we obtained a 45% increase in the mass energy density, compared to a torsional spiral spring of uniform thickness. Our result suggests that optimally designed 3D printed springs could enable robots to recycle more mechanical energy per unit mass, potentially reducing the energy required to control robots.
Paper Structure (12 sections, 11 equations, 6 figures, 1 table)

This paper contains 12 sections, 11 equations, 6 figures, 1 table.

Table of Contents

  1. Introduction
  2. Prediction using a Simple Model
  3. Design Modeling
  4. Optimization
  5. Theoretical Prediction
  6. Optimization
  7. Removing Material around the Neutral Axis
  8. Experimental Evaluation
  9. Setup
  10. Procedure
  11. Results
  12. Discussion and Conclusion

Figures (6)

  • Figure 1: Spiral spring optimized for high energy density.
  • Figure 2: Optimization of torsion spring designs. (a) Example of torsion spring composed of cantilevers. (b) Cantilever with spatially varying thickness. (c) Torsion spring composed of a spiral. (d) Model of a spiral with spatially varying thickness.
  • Figure 3: Optimized model of a spiral spring. (a) Energy density plot of a spring with a uniform thickness. (b) Energy density plot of a spring with spatial varying thickness. (c) Energy density plot of the spring with optimal varying thickness. (d) Total energy density over successive iterations. (e) Moment along beam length. (f) Torque-deflection relation. (g) Maximum stress along beam length.
  • Figure 4: Energy density plots of torsion springs computed using ANSYS® MechanicalTM. (a) Uniform thickness spiral spring. (b) Optimized spatially varying thickness spiral spring. (c) Optimized spatially varying thickness spiral spring with material cut near neutral axis. The gray shapes show the un-deformed springs.
  • Figure 5: Experimental setup. (a,b) The spring was mounted into a variable stiffness mechanism presented in Mathews2021, operated in fixed stiffness mode. (c) A load cell used to measure the torque generated by the spring.
  • ...and 1 more figures