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Wearable mechatronic devices for upper-limb amputees 209

3 Wearable device: Preliminary concepts
3.1 Definitions
Wearable device
In the last few decades, technology has evolved such that WD systems now
include on-body sensors for detecting physiological signals without discom-
fort, and are able to capture and continuously record data in real time
(Bonfiglio and De Rossi, 2011). In this sense, WDs have the potential to
help in both diagnosis and ongoing treatment of a vast number of individuals
with neurological, cardiovascular, and pulmonary diseases (Patel et al.,
2012). Since the development of transistors, WDs have become much smal-
ler, and with the advent of the Internet of Things (IoT) WDs are becoming
smart, portable, multi-functional, and able to connect to the Internet and
run on batteries (Hung et al., 2004). These devices have been used for many
applications, including communication, sports, optics, Virtual Reality (VR),
and Artificial Intelligence (AI). In the field of mechatronics, WDs are pro-
posed as wearable mechatronic devices or wearable robots to be worn by
humans either to augment the function of a limb or to replace it completely
(Pons, 2008). WDs are used externally to the body, either attached as an
accessory or embedded in clothes (Raskovic et al., 2004; Yang and Sahabi,
2016; Motti, 2020). To physically assist weakened and/or disabled individ-
uals with impaired upper limb function, extensive research has been carried
out in many branches of robotics, particularly wearable robots (e.g., exoskel-
etons, powered orthotic devices, etc.) and end-effector-based robotic
devices (i.e., devices that do not actively support or hold the subject’s
arm, but rather connect with the subject’s hand or forearm) (Rahman
et al., 2014).
According to Pons (2008), a wearable robot can be seen as a technology
that extends, complements, substitutes, or enhances human function and
capability or empowers or replaces (a part of ) the human limb where it is
worn. This definition is considered in this chapter. In the next section,
we present a classification of wearable robots.

Empowering robotic exoskeletons (extenders)
Extenders were defined for the first time in the 1990s as a class of robotic
manipulators that extend the strength of the human arm while maintaining
human control of the task. The defining characteristic of an extender is the
“transmission of power and information signals.” The individual wears the
extender and the physical contact between the extender and the user allows