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Robotic Mechanisms 195

More recently, new F’rubber material has been created out of silicone, which is softer, can
elongate 1050%, and is tolerant to a wider range of environmental conditions. Also, computer-
numeric-controlled (CNC) deposition of thermoplastic elastomer (TPE) into a designed matrix has
shown promising preliminary results, exhibiting elongation up to 1250%. The pores in such a
material need not be spherical; they can be shaped into complex manifolds for improved mechan-
ical and expressive behavior. They may even contain closed cells filled with liquid for still more
advanced expressive emulation of facial tissues. These processes are described further in Section
6.4.
These new material approaches may help to satisfy people’s discriminating taste for verisim-
ilitude. They may also enable to convey more relevant sociable perceptual patterns when deviating
from verisimilitude. Additionally, however, the novel materials may be used for nonrealistic
cartoon and animal faces, which will benefit from the likeness to animal soft tissues, and the
decreased weight and energy requirements.

6.4 ROBOTIC MATERIALS, STRUCTURES, AND MANUFACTURABILITY

Robots are inherently integrated systems, and will be beneficiaries of the numerous bio-inspired
technologies that can be integrated into robots. Make no mistake, robots also benefit from
technology advances that are not bio-inspired. Advancing manufacturing technologies, such as
MEMS and SDM, though not themselves bio-inspired, are being used to produce more lifelike
robots.
Multifunctional materials promise to make robots more effective. Single multifunctional ma-
terials, such as carbon nanotubes, offer mechanical strength and flexibility, provide computation,
emit light, capture sensory data, provide electrically actuated motion (Baughman et al., 1999). If
utilized in a robot’s skin, such electroactuative polymers (EAPs) may greatly streamline a robot’s
manufacturing and cost (Bar-Cohen, 2002). Likewise, multiplicity of functions in the locomotive
systems, as may be provided by biomimetic viscoelastic mechanical compliance (Full, 1999) and
reconfigurable designs, can allow a robot to transit through more diverse, complex terrain.
Advanced manufacturing is leading to faster robot design, more complex yet affordable robots,
and design control at meso, micro, and nanoscales. Rapid progress is occurring in both materials
sciences (including recent advances in EAP) and manufacturing technologies on multiple scales.
The overlaps with biomimetic engineering are increasing in number impressively.
Rapid prototyping and digital design tools are enabling complex concepts to be turned into
physical objects in very short cycles. Advanced silicon manufacturing techniques, largely innov-
ated for manufacturing microprocessors, have resulted in burgeoning techniques of MEMS in
several interesting robot projects (Dickinson et al., 2000). A comprehensive list of techniques
that may be pertinent to manufacturing and prototyping entertainment robots with EAP actuators
would be prohibitively long to include here, but are covered in more detail in Chapter 18 of Bar-
Cohen (2002/2003) and Hanson et al. (2003).
Fusing several rapid prototyping technologies with mold-making and advanced materials, SDM
has been described in Full (2000) as particularly interesting for use with biorobotics. SDM uses
various computer-aided manufacturing (CAM) technologies to layer and refine materials into
arbitrarily complex configurations, bonded without the use of mechanical fasteners. Actuators
and sensors can be imbedded directly into the ‘‘flesh’’ of a device, composed of materials of varied
elasticity and rigidity, layered and bonded in situ. This process can achieve fully functional rapid
prototypes, as well as highly efficient manufacturing procedures (Amon et al., 1996). Images of the
SDM process are shown in Figure 6.14.
SDM may be effective for MEMS microscale devices, and may be extensible to nano-devices.
The SDM process is proving decidedly useful in rubbery macroscale robots, which are simplified by
the absence of mechanical fasteners. As an example, the 15-cm (6-in.) legged robot ‘‘Sprawlita’’ at