Design and Fabrication of Multi-material Structures for Bio-inspired Robots

Working copy of paper materials on Yoda SVN at svn+ssh://cutkosky@yoda.stanford.edu/svn/papers/CutkoskyKim_BioDesign

Mark R. Cutkosky
Dept. of Mechanical Engineering, Stanford University
Stanford, CA 94305; email: cutkosky@stanford.edu
and
Sangbae Kim
School of Engineering and Applied Sciences, Harvard University 
Cambridge, MA 02138; email: sangbae.kim@gmail.com

Outline

Introduction

• Observation that heterogeneous and anisotropic materials and structures are the norm in nature and rare in man-made artifacts.
• Motivation and examples of the role of multi-material structures, with spatially varying physical properties, in making animal locomotion and manipulation more versatile and more robust. Examples from [Full, Vogel, others].
• “Preflexes” [e.g., per Brown and Loeb] and the role of tuned mechanical compliance and damping in simplifying control and conferring robust open-loop dynamic stability.
• Integration of sensing with actuation and with the dynamic behavior of mechanisms. In nature, these functions are invariably coupled.
  • Here or later, in Design section (?) maybe point out that while complexity in nature is daunting, it also appears that nature uses simplifying templates conrolling very complex, high DOF systems as though they had fewer DOF and behaved like abstracted models. [Example from Koditschek and Full Templates & Anchors. SLIP.]
  • Side note that this can also relate to Kinematic Similarity [R McNeill Alexander, Cha 2, Body Support, Scaling, and Allometry]. This is why measures like Froude number work across wide range of species and sizes to, for example, predict onset of gait change. Requires not only superficially common morphology (legs that swing) but also common ratios of elasticity to inertia.
• Preview of fundamental design and manufacturing challenges associated with synthesizing, optimizing and fabricating multi-material structures and mechanisms.

Maybe move next section to be after the Design section?

Multi-material fabrication methods, challenges and opportunities

• Methods, challenges and solutions. Comparison of shaping followed by assembly with concurrent shaping and material addition.
• Characteristics of material addition versus removal processes (e.g., achievable tolerances and finish in comparison to feature dimensions) and discussion of hybrid addition/removal processes.
• Discussion of SDM and related methods.
• Advantages and disadvantages of serial versus parallel processes.
• Growth direction implications and multi-axis methods, etc.
• Fabrication examples from iSprawl, Stickybot, etc.
• Specialized techniques for higher specific strength, in-situ sensor fabrication, embedded fibers, etc. Current challenges.

Analysis and synthesis of multi-material structures

• Representations for heterogeneous structures [e.g., Dutta et al.].
• Design tuning (iSprawl example)
  • Hogan [1985] advantages of low impedance when interacting with an unkown environment.
  • Preflexes [Brown and Loeb 1999], [Full et al. 1998] templates and anchors [Koditschek and Full]
• Managing complexity – Tradeoffs: the role of design rules (e.g., as used in VLSI and MEMS design and fabrication) versus freeform fabrication.
• Special challenges concerning complexity over a range of length scales. Hieararchy: motivating examples from gecko.
• Challenges and opportunities for synthesis, analysis

Conclusions

• Looking ahead at future possibilities: Argument that top-down bulk fabrication processes must ultimately be supplanted with self-organizing or self-assembling technologies.
• Future synthesis methods for multi-material bio-inspired components.

-- MarkCutkosky - 06 Aug 2008