Page 67 - Handbook of Biomechatronics

62 Jeff Christenson

6.5 Eye Movement 89
6.6 IR Body Markers and Camera Tracking Three-Dimensional Motion Capture 90
7 Conclusion 91
References 91
Further Reading 93

1 INTRODUCTION

An important element of a biomechatronic system is the method
in which the device determines what is happening in the surrounding
environment. By monitoring the environment, systems can be built which
can enable, improve, and enhance the user’s experience. To make this
determination, sensors and transducers are used. A sensor is any “device
which detects or measures a physical property and records, indicates,
or otherwise responds to it” (https://en.oxforddictionaries.com/definition/
sensor, Accessed 21 August 2017). A transducer is a “device that converts var-
iations in a physical quantity… into an electrical signal, or vice versa” (https://
en.oxforddictionaries.com/definition/transducer, Accessed 21 August 2017).
Sensors are critical elements of any biomechatronic device, since they
allow systems to be built which respond to biological input. An electric pros-
thesis with no user input, such as control cables or sensors of muscle signals,
becomes an ill-formed tennis racket. A load cell with no sensor to measure
the load becomes a paperweight. A brain array with no brain activity sensing
capability becomes an expensive surgery with no beneficial outcome.
Biomechatronic devices need sensors to be useful devices.
The process of selecting what type of sensor to use is not a trivial matter
and requires careful consideration of form, function, and environment.
When discussing sensors, there is some general terminology often used to
define a sensor’s performance. These terms are: accuracy, precision, resolu-
tion, range, and hysteresis (Bolton, 2003a).
Accuracy refers to how close a sensor measures a defined standard
(Bolton, 2003a). For instance, the accuracy of a ruler can be determined
by measuring a block which conforms to a standard dimension and compar-
ing the results of the ruler with the standard.
Precision refers to the density of repeat measurements (Bolton, 2003a).
Tolerance gives a numeric value to the type of spread which can be expected
from the sensor. Consider the ruler and standard block example. A ruler with
high precision will give very close to the same number for each repeat
measurement, even if the numbers are not accurate.