IEEE Circuits and Systems Magazine - Q3 2021 - 80

to give the control instructions while obtaining environmental
information. Behavioral studies conclude that
nearly 83.0% of the factors that affect communication
come from vision. Thereupon, we envision whether the
control can be achieved through eyes. Eye tracking, as
a method to detect the presence, attention and focus,
is a current hotspot in visual research [2], [3]. Through
analyzing the visual behaviors, we can obtain the implied
mental activities for further applications.
The eye tracker, a powerful input device in a host of
visually-mediated applications, records the characteristics
of human eye movements when processing visual
information. Generally, there are four methods for estimation,
i.e., electro-oculography, iris contact lens/
search coil method, photo/video-oculography, and pupil
center and cornea reflection (PCCR) technique [4]. Although
the contact methods developed since the 1950s
can achieve very high measurement accuracy, external
objects are required to touch the susceptible parts of
the human body and partly limit the human movements.
Currently, the non-contact eye tracker designed by the
PCCR technique is widely used, which mainly depends
on the reflection of the pupil, the iris-sclera boundary,
or the cornea to the proximal light source. Moreover,
real-time eye movements could be easily tracked and
analyzed bolstered by the increasing computing power.
Hence, thanks to the pioneering technology, a fully automatic
wheelchair for the handicapped is formed. Our
main contributions can be listed as follow:
■ A monocular algorithm to improve recognition accuracy
is proposed.
■ The whole wheelchair system, from sampling to
the signal processing, and from the power supply
to the mechanical structure, is implemented.
■ The control logic on iterative versions through
multiple clinical trials is optimized.
The remainder of this article is organized as follows.
Section II illustrates the system overview. Section
III introduces the background on the core technology
PCCR and relative applicability in multi-senor control
system. Control logic and details of each module are
reviewed in Sections IV-V. Section VI proposes clinical
trials and cost valuation. Finally, conclusion is drawn
in Section VII.
II. System Overview
As shown in Fig. 1, the PCCR based wheelchair consists
of the sampling system, signal processing system, and
interaction system.
In the sampling system, two eye trackers and one
gyroscope are deployed to collect eye movements and
wheelchair posture. The motion signals will be transformed
into electrical signals and transferred to the
microcomputer via the TTL-USB transformer. In the
signal processing part, two microcomputers calculate
received data in real-time. Next,
the electrical signals
generated by the microcomputer are converted
to wheelchair control signals. In the interaction part,
emergency call guarantees the user's safety in emergencies.
Electrical motors provide the power supply
and drive the whole system.
III. Sampling Module
A. Eye Structure & Imaging Principle
The eye serves as a special organ for light perception.
The typical structure of the human eye1 is shown in Fig. 2,
based on which the gaze-tracking system is illustrated.
As a sampling camera of the human body, retinal imaging
is similar to convex lens imaging, i.e., the lens and
retina are equivalent to a convex lens with a variable
focal length and a light screen, respectively.
Visual perception starts at the
Intel NCU5i5RYB
Microphone
Tobii Eye
Tracker 5
GY-521
MPU-6050
GY-521
MPU-6050
Tobii Eye
Tracker 5
Sampling
Coaxial_in
RAM
Unity SDK
USB_in
Intel NCU5i5MYBE
RAM
i5 CPU
USB_in
Core SDK
Signal Processing
Figure 1. System overview of the PCCR based wheelchair.
80
IEEE CIRCUITS AND SYSTEMS MAGAZINE
Multi-Relay
Interaction
Convertor
Electrical
Motors
i5 CPU
Wi-Fi CPE
Wi-Fi CPE
Skype
Phone
User Interface
HDMI_in
light, which is emitted or reflected
from an object and then enters
our eyes. The cornea and lens
focus and project light onto the
photoreceptor layer of the cells located
on the retina. The lens makes
necessary adjustments to the focus
of objects at different distances [5].
Meanwhile, the size of the pupil
changes the amount of light reaching
the retina which converts the
1Source: Schematic diagram of the human
eye en.svg - Wikimedia Commons. by Rhcastilhos
and Jmarchn https://commons
.wikimedia.org/w/index.php?curid=1597930
(accessed on Oct. 17, 2020 and licensed under
CC BY-SA 3.0)
THIRD QUARTER 2021
https://commons.wikimedia.org/w/index.php?curid=1597930 https://commons.wikimedia.org/w/index.php?curid=1597930
IEEE Circuits and Systems Magazine - Q3 2021

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