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Upper and Lower Extremity Exoskeletons 297

the wearer, and for the efficiency of the exoskeleton, since it must rely on
correct kinematics and kinetics information. On the other hand, the physical
interaction is mostly related to the low-level controller of the robotic
system—for example, bandwidth of the system, motor own dynamics,
performances, and characteristics of the power supply and of the actuation
elements (leverages, springs, pneumatic chambers) (Pons, 2010).

3 DESIGN AND IMPLEMENTATION OF EXOSKELETONS
3.1 Kinematics and Dynamics of Exoskeletons
Kinematics can be defined as the branch of mechanics dealing with the
description of the motion of bodies or fluids without reference to the forces
producing the motion (Pons, 2008). When referring to multi-body, jointed
mechanisms as in the case of robots, and more specifically exoskeletons,
kinematics deals with analysis of the motion of each robot link with respect
to a reference frame (Pons, 2008). Dynamics is the part of classical mechanics
that studies objects in motion and the causes of this motion, for example,
forces (Pons, 2008). When considering multibody, jointed mechanisms like
wearable robots, dynamics deals with the analysis of movement in specific in
a configuration and working space as a function of internal forces
(e.g., torque at each joint actuator) and external forces (e.g., interaction force
with the environment) (Pons, 2008).
The kinematics involves an analytical description of motion as a function
of time and the nonlinear relationship between robot end effector position as
well as the orientation and robot configuration (Pons, 2008). The mobility,
M, of a robot composed of a number of links is defined as the number of
!
independent parameters, q , required to fully specify the position of every
link (Pons, 2008). A particular robot configuration is a vector of realizable
values, q i , i¼1, …, n, for the independent parameters at time t. The redun-
dancy of a robot is an indicator of the number of available robot configura-
tions for a particular position of the end effector position. High redundancy
makes control complex but improves dexterity (Pons, 2008).
From the explanation above, there may be a forward and an inverse
relationship between a robot position and orientation and its configuration.
The forward kinematics problem deals with the specification of robot posi-
tion and orientation, as a function of robot configuration. The inverse kine-
matics involves the determination of robot configuration as a function of
robot position and orientation (Pons, 2008). Any type of coordinates