Page 310 - Handbook of Biomechatronics

302 Andres F. Ruiz-Olaya et al.

Table 2 Sensor Technologies to Implement cHRI and pHRI
Signals to
Acquire Sensor Technology

pHRI (physical Kinematic Potentiometer, encoder,
human-robot Information electrogoniometer, accelerometer,
interaction) gyroscopes, IMU
Kinetic Strain gage, piezoresistive sensor, force/
Information torque sensor
cHRI (cognitive Muscle activity Electromyography
human-robot information
interaction) Brain activity Electroencephalography
information
Ocular Electrooculography
movement
information

A special type of pneumatic actuator, called PAMs or McKibben-type
actuators are often used in several exoskeletons (Ramos and Meggiolaro,
2014). Such actuators consist of an internal bladder surrounded by braided
mesh shell with flexible, but nonextensible, threads. The bladder is pressur-
ized, and the actuator increases its diameter and shortens according to its
volume, thus providing tension at its ends.
When selecting actuators for an exoskeleton, it is required to define an
appropriate location. Thus, the actuators could be located close to the joints
that are actuated. This configuration simplifies power transmission by using
direct drives on joint. However, it increases the weight of the distal part of
the exoskeleton and the inertia makes it more difficult to control the overall
system. On the other hand, locating the actuators in the part that remains
constrained reduces the weight and inertia of the distal part. However, a
mechanical power transmission mechanism is required. This complicates
the mechanical structure and may lead to difficulties with control due to
friction.
Energy efficiency is a major problem for robotic exoskeletons. Those
systems require considerable energy to accelerate and decelerate the limbs
and to dynamically support the body mass against gravity. Supplying power
to such devices for several hours is well beyond the capabilities of current
battery technology. Currently, there are multiple efforts to develop efficient
power sources for exoskeleton aimed to enable ambulatory applications.
Lithium polymer batteries, with a specially formed dry polymer, currently