Page 316 - Handbook of Biomechatronics

308 Andres F. Ruiz-Olaya et al.

4.2.3 Mechanical Domain
An exoskeleton must be able to interact with the human body, a very com-
plex kinematic structure that includes multiple DOF. Exoskeletons must
have a large number of active joints, each with a wide range of motion
to be able to follow as well as to assist movements within a large workspace.
For rehabilitation applications, the majority of existing exoskeletons cannot
be widely used by patients with limited functions of the upper and lower
limbs because they are heavy, dependent on external power supply, and
expensive (Ruiz et al., 2006).
Smaller, lighter actuators with gearboxes could generate sufficient forces;
however, gearboxes add friction to the system, reducing overall dynamic
performance. The power transmission technologies with high transmission
efficiency and minimum friction are required so the exoskeleton systems can
be more efficient. Moreover, the back-drivability of the transmission is also
essential for these systems to eliminate possible discomfort to the user.
According to appearance, most of existing robotic exoskeletons often
cause discomfort to the user, especially when they wear it for daily activities.
Thus, a challenge for new exoskeletons is to improve esthetics.

4.3 Exoskeleton Design
In the field of healthcare, field exploration, and cooperative human assis-
tance, robots and machines must become increasingly less rigid and special-
ized and instead approach the mechanical compliance and versatility of
materials and organisms found in nature. As with their natural counterparts,
this next generation of robots must be elastically soft and capable of safely
interacting with humans or navigating through tightly constrained environ-
ments (Majidi, 2014). This is the choice of Soft robots, which are primarily
composed of easily deformable matter such as fluids, gels, and elastomers that
match the elastic and rheological properties of biological tissue and organs.
A soft robot must adapt its shape and locomotion strategy for a broad range of
tasks, obstacles, and environmental conditions (Majidi, 2014). This emerg-
ing class of elastically soft, versatile, and biologically inspired machines rep-
resents an exciting and highly interdisciplinary paradigm in engineering that
could revolutionize the role of robotics in health care, field exploration, and
cooperative human assistance. The most immediate application of emerging
soft robot technologies will be in the domain of human motor assistance and
co-robotics. For example, a soft active ankle-foot orthotic (AFO) could help
prevent foot dragging for patients that suffer gait abnormalities such as drop
foot (Majidi, 2014).