Design, Manufacturing, and Control of Soft Foam Robots.
Kastor, Nikolas.
2018
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Soft robots are
constructed of materials which absorb energy and therefore do not harm people or their
environments. Indeed, it is possible that soft elastomer foams may be the best choice
for constructing such a robot because the thin walled lattice that makes up the foam
endows the elastomer with a far greater softness than that of a bulk polymer. Robots
whose main structural components are ... read moremade from elastomeric foams are under-explored.
Several key concepts for design, manufacturing and control of foam robots are examined
in this work and demonstrated by two motor-tendon actuated polyurethane foam terrestrial
robots. A method of design is introduced in order to create a robust robot platform that
can change shape, by compressing and folding in multiple dimensions, allowing for
complex behaviors (e.g. locomotion) with a minimal number of actuators. Motor-tendon
actuators are integrated into the foam body of the robot in a manner inspired by
vertebrate tendons and ligaments. By matching of like materials, implementing material
gradients between hard and soft materials, and proper lubrication of moving parts, wear
of the foam body is virtually eliminated. The robot produced with this method operated
for more than 425 cycles without noticeable wear or failure. Two robot examples are cast
from inexpensive, light, and easily compressible polyurethane foam, offering
deformations greater than 70%. 'Hard' components, such as motors, are sutured into
cavities to facilitate the construction process and reduce interaction with the soft
body. The manufacturing method produces a highly deformable robotic platform that is
used to evaluate factors that affect locomotion including interaction with the
environment, material selection, structural design, and control methodologies. One of
the example robots is constructed from a rectangular foam slab and driven by two
motor-tendon actuators. Using open loop control, this robot was capable of complex
behaviors such as forward crawling at 2.6 body lengths per minute, turning at
approximately 9 degrees per second, and end over end flipping. The second foam robot
example demonstrates a method for control of crawling soft terrestrial robots undergoing
1D, quasi-static locomotion. Using dynamic weight redistribution at two ground
interaction points to control friction, 1D locomotion is achieved even in the presence
of an uncertain friction coefficient at the ground/robot interface. This robot crawls in
one dimension at about 10 body lengths per minute. The locomotion control scheme is
demonstrated by capturing quantitative dynamics of a motor-tendon driven, terrestrial,
foam-bodied robotic platform using a 5-camera Vicon system. To achieve robust
locomotion, detailed knowledge of the foam mechanical properties and precise knowledge
of the surface properties are not required. This is because friction at the ground/body
interface dominates the locomotion and is controlled by modulating the normal force at
these contact points in phase with the extension and compression of the robot's soft
foam body. The Vicon data shows that if the ratio of normal forces at the two contact
points switches between 0.5 and 1.7 during the locomotion gait cycle the robot crawls
forward. If the ratio switches between 0.5 and 0.8, total distance traveled drops by 80%
and variability of locomotion increases by about 50% because the robot tends to slip and
not make forward progress. Therefore, it is determined that a ratio of normal forces
that significantly crosses 1 during the gait cycle is required for robust terrestrial
locomotion.
Thesis (Ph.D.)--Tufts University, 2018.
Submitted to the Dept. of Mechanical Engineering.
Advisor: Robert White.
Committee: Chris Rogers, Anette Hosoi, and Barry Trimmer.
Keyword: Mechanical engineering.read less - ID:
- vq280169r
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