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Finally, exoskeletons work close to human body, thus the following aspects
must be considered:
(a) the external framework should replicate the structure of the upper
or lower limb;
(b) the device should be lightweight, strong, and safe;
(c) there must be a possibility of changing the elements to permit the
exoskeleton structure be length adaptable; and
(d) exoskeletons should perform a range of movements required to accom-
plish the activity or function.
One of the biggest challenges for robotic exoskeletons that interface with
persons closely is to assure the safety of the user. It is important to establish
a safety guideline appropriate for elderly and disabled human users and to
develop and integrate both mechanical and electrical safety systems in exo-
skeletons. To meet stringent standards, redundant safety mechanisms must
be in place.

2 A BRIEF HISTORY OF EXOSKELETON RESEARCH

The first mention of a device resembling an exoskeleton was Yang’s
running aid (Yagn, 1890) patented in 1890. It was a simple bow/leaf-spring
operating parallel to the legs, whose function is to augment running and
jumping. Each leg spring was engaged during the foot contact to effectively
transfer the body’s weight to the ground and to reduce the forces borne by
the stance leg. During the aerial phase, the parallel leg spring was designed to
disengage in order to allow the biological leg to freely flex and to enable the
foot to clear the ground.
The studies on wearable equipment have been going on for more than
50 years by military institutions, private companies, and research groups in
several countries. The main components for the development of exoskele-
ton robots (XoRs) include mechanism design technology, human intent
measurement technology, and human-robot control technology. For the
successful development of robotic exoskeleton systems, designers should
take into consideration the field of application, the purpose of power sup-
port, and to which part of the body the robot would give support. In the late
1960s, the General Electric company, funded by military institutions of the
United States of America (USA), developed and tested what the researchers
called a body amplifier prototype based on a master-slave system named