Page 100 - Handbook of Biomechatronics

96 Naser Mehrabi and John McPhee

1.1 Mechatronic System Modeling
The first step in the design of a biomechatronic device is to understand how the
device will interact with its user and the environment. A successful device con-
siders physiology to reasonably enhance human body movements or compen-
sate forlackofmovement.Adynamic modelofabiomechatronic device can
provide in-depth insight into its dynamic behavior and can be used to design
and evaluate model-based control systems. The system model can also be used
in model-in-the-loop (MIL) simulations to improve systems design. MIL
simulationsacceleratethedesignprocessbysavingtimeindevelopingand
revising the design on the computer rather than physically creating new pro-
totypes. MIL simulations offer many other advantages such as flexibility (i.e.,
allow various scenarios) and repeatability (i.e., perform the same experiments
repeatedly). Various methods can be used to derive dynamic equations of
motion of an multidisciplinary device such as energy-based methods, linear
graph theory (McPhee, 1996), and bond graph theory (Karnoppetal.,2012).

1.2 Biomechanical Modeling
To design a device for assisting human movements, it is crucial to understand
how the human body works. By only contracting the skeletal muscles, our
body can produce very complex and meaningful movements such as walk-
ing and reaching. All these actions are initiated by thoughts in the brain and
then conveyed through the nervous system to the muscles attached to our
skeleton. Some brain activities (i.e., readiness potential) can be produced up
to 1s before the actual volitional movement, and can be captured using elec-
troencephalography (EEG) (Brinkman and Porter, 1979; Deecke and
Kornhuber, 1978). EEG is a method that captures the brain’s electrical activ-
ities by placing noninvasive electrodes along the scalp. These movement ini-
tiations are transmitted through the central nervous system (CNS) to the
motor neurons that innervate muscle fibers. Then, after a sequence of chem-
ical reactions, the muscle fiber contracts and produces a change in potential
in the muscle membrane. This electrical activity produced during muscle
contraction can be picked up through electromyography (EMG) using an
electrical sensor placed on or under the skin above the muscle of interest.
EEG and EMG are windows to our brain because they record signals orig-
inating from the brain and thus can be used to capture user intention. There
are several assistive devices available in the market [e.g., prostheses and
brain-computer interfaces (BCIs)] that take advantage of these signals to
understand user intention and control a device.