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AbstractThe paper investigates the use of peristaltic locomotion mainly adapted to
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inspection and rescue applications. A state of the art on peristaltic locomo-
tion is introduced and a short overview about suitable smart materials is
given. An effective solution using Shape Memory Alloys (SMA) springs is
discussed. The working principle is described and a preliminary prototype
is presented. 6278
Keywords: Peristaltic locomotion, SMA actuation, modularity.
1 Introduction
Terrestrial locomotion strategies can be pided into three main groups:
Locomotion with wheels or tracks
Leg locomotion
Crawling\waving (peristaltic, snake-like or inchworm-like)
The last two can be included in the biologically inspired ones, mimicking
natural beings. What attracts and holds attention on animal world is the ef-
ficiency of bodies structures of many insects and other lower animals, how
they accomplish tasks with minimum energy consumption, obtaining re-
sults impossible to traditional robot configurations. Many efforts have
been done in science history to mimic animal behaviour and locomotion,
but first tries were simply puppet-like devices. Today, researchers work to
replicate both animal gaits and structures in mechanisms, by using new
technologies available for actuators and materials [1]. Several crawling animals have been analysed: snakes, slugs, snails,
earthworms and inchworms. After a detailed motion analysis we focused
on the earthworm, thus the peristaltic locomotion. In fact, this kind of lo-
comotion satisfies the needs of several mini and micro robotics application
fields. Wheels offer smooth and efficient locomotion on almost plain ter-
rains; even all-wheel-drive mechanisms are limited in the type and scale of
obstacles that they can overcome. Walking mechanisms can overcome
bigger obstacles but they provide discrete, rather than continuous, contact
surfaces. This highly affects static and dynamic stability, so that control is
critical.
2 Fundamental of peristaltic locomotion
Earthworms’ body can be considered as sequence of segments, surrounded
by a hydrostatic exoskeleton. This constrains segments to have constant
volume, so that they can move by changing segments shape. Looking at a
cross section of an earthworm’s body, we can recognize two sets of mus-
cles: an inner, longitudinally oriented set, and an outer, circularly oriented
set. As earthworms crawl forward, waves of circumferential and longitudi-
nal contractions of muscles pass posteriorly along their constant-volume
body segments, forming retrograde waves. When the longitudinal muscles
of a segment contract, the segment becomes shorter (along the anterior–
posterior axis) and wider. On the contrary, when circumferential muscles
contract, the segment becomes long and thin. Peristaltic locomotion is not
only characterized by the typical behaviour of single segments, but espe-
cially by the sequence in which they work, generating waves that run in
the inverse direction than movement [2].
For all these reasons to have peristaltic locomotion, body must have at
least three segments because while a segment elongates, the other two
have to be anchored to the ground. If segments are more than three, the
wavelength of peristaltic waves is greater. The basic motion sequence,
however, is the one for a three-segmented body (see Fig. 1 c).
Peristaltic locomotion shows its best when working in somehow severe
environment where traditional machines are precluded due to size or shape
and where appendages such as wheels or legs may cause entrapment or
failure. For example in tight spaces, long narrow interior traverses, and
travelling on loose materials or dense vegetation. 3 Previous work