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Upper and Lower Extremity Exoskeletons 287

1.2.3 Rehabilitation and Motor Training
The rehabilitation field is a key application domain for the development of
exoskeletons, to help disabled people with difficulties in moving (Kiguchi
et al., 2004; Colombo, 2001).For rehabilitation applications, the exoskele-
ton permits to assist in several active and passive therapies. Thus, the device
emulates and replicates movements and exercises that a physiotherapist
executes when working with a patient. The exoskeleton should be able
to replicate with a patient the movements performed with a therapist during
the treatment.
There are a significant number of papers published concerning robotic
exoskeleton in therapy, and about their effectiveness in the functional recov-
ery after stroke (Kwakkel et al., 2008; Brokaw et al., 2013; Milot et al., 2013;
Chang and Kim, 2013). Some studies conclude that robot-aided therapy can
elicit improvements in arm function that are distinct from the conventional
therapy and supplements conventional methods to improve outcomes
(Brokaw et al., 2013).
Most of the reports in the literature using robotic exoskeletons in therapy
focus on treatment of poststroke paralysis of the upper and lower limbs
(Louie and Eng, 2016). Other works concern using exoskeletons for reha-
bilitation after cerebrospinal traumas, for multiple sclerosis, for tremor treat-
ment, and for compensation of grasping function of the hand (Maciejasz
et al., 2014).

1.2.4 Virtual Reality and Haptics
In this application, exoskeletons aim to exert a reactive force on the user
while they are using a virtual reality (VR) headset. It is the opposite of exo-
skeletons for teleoperation, which are used to extract kinematics data from
the user. It could be used for gaming, motor rehabilitation, and training.

1.3 The Role of Biomechatronics in Exoskeletons
Exoskeletons are biomechatronic devices that interact with the human
body. The human motor control system (HMCS) can be modeled as in
Fig. 2A(Lobo-Prat et al., 2014). The HMCS consists of a mechanical struc-
ture, the plant, which represents the skeleton and passive tissues; the actu-
ators, which represent the muscles; and a controller, which represents the
central nervous system and receives sensory feedback from the physiological
sensors. An artificial motor control system (AMCS) such as exoskeletons