Page 309 - Handbook of Biomechatronics

Upper and Lower Extremity Exoskeletons 301

between human and device. This aspect could be divided into cognitive
human-robot interaction (cHRI) and physical human-robot interaction
(pHRI). cHRI relates to how the user controls the exoskeleton. pHRI
relates to the application of controlled forces between human and
exoskeleton.
Interaction of exoskeleton with the user involves three main modules:
sense, decision, and execution (Knaepen et al., 2014). Developing robotic
exoskeletons relates to including technologies to accomplish function of
each module.
The sense module acquires the information data from the human
operator as well as device sensors. The decision module interprets the
sensing information and organizes the activities in the whole system.
The execution module is responsible for the actuation, providing
mechanical power.
Acquiring information from the human operator for cHRI could be
implemented using bioelectric signals such as the electromyogram
(EMG), which evaluates and records physiologic properties of muscles; elec-
troencephalogram (EEG, which monitors brain waves), and electrooculo-
gram (EOG, which monitors eye movements). On the other hand,
pHRI involves acquiring kinematics and kinetic information. A critical
aspect while designing exoskeletons relates to measuring of the interaction
forces between the device and the user’s limbs, which can be used to assess
the performance of the user in executing a task (e.g., the level of effort spent
by a patient in completing a therapy). A common way to measure interac-
tion force/torque is to adapt a force sensor between the cuff and the exo-
skeleton link, which provide accurate measurements. Table 2 shows
several sensor technologies to implement cHRI and pHRI.
There are several actuator technologies that have been used to provide
mechanical power for exoskeletons, which include pneumatic, hydraulic,
and electric actuators (Gopura et al., 2016). Pneumatic and hydraulic actu-
ators have good power-to-weight ratio but unfortunately they don’t have
much precision, and it is difficult to implement accurate positional control
with them due to their nonlinear behavior. Electric actuators are the most
used element in the literature for powered exoskeletons, because they could
be controlled with high precision; however, the power-to-weight ratio is
not so good (Gopura et al., 2016). The series-elastic actuator (SEA) is a kind
of actuator that implements a continuously variable transmission between a
motor and a series-elastic element, used to power exoskeletons (Veneman,
2007). SEA actuators have been used in a number of exoskeletons because of
the inherent compliance.