Biomedical Engineering Reference
In-Depth Information
CHAPTER
3
Actuators
Chapter Outline
3.1
Introduction ...................................................................... 91
3.2
Electromechanical Actuators ..................................................... 91
3.3
Hydraulic Actuators ............................................................. 137
3.4
Pneumatic Actuators ............................................................ 139
3.5
Shape Memory Alloy ............................................................ 142
3.6
Mechanical Amplification ....................................................... 145
3.7
Prosthetic Hand Actuation ...................................................... 154
3.8
References ..................................................................... 157
3.1
INTRODUCTION
Most biomechanical systems involve some sort of motion or an action, which can range
from the articulation of a large exoskeleton to the mechanical stimulation of the tiny
bones in the middle ear. These actions are created by a force or torque that leads to
acceleration and displacement. In most cases these actuators operate by the conversion
of electrical power; however, in biomechatronics, pneumatic and hydraulic devices offer
some advantages, discussed in this chapter.
Electrical devices that produce or trigger a physical or physiological response by
stimulating the body's musculature or nerves are also considered to be actuators. These
include pacemakers, defibrillators, transcutaneous electrical nerve stimulation (TENS)
devices, and other electrode arrays such as retinal, neural, or cochlear implants. They are
discussed in other chapters in this topic.
3.2
ELECTROMECHANICAL ACTUATORS
When a current carrying conductor is placed in a magnetic field, a force is produced in a
direction perpendicular to both the direction of the current and the magnetic field. This is
the Lorentz force law and can be stated in vector form as (Alciatore and Histand, 2003)
F
I
B
=
×
(3.1)
91
