tongue drive system
TRANSCRIPT
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TONGUE DRIVE SYSTEM
ABSTRACT
Tongue Drive System is a new revolutionary system to help individuals
with disabilities to control wheelchairs, computers and other devices simply
by using their tongue. It is a noncontact, unobtrusive, tongueoperated
assistive technology. Tongue Drive system will be helpful to individuals with
serious disabilities, such as those with severe spinal cord injuries and will
allow them to lead more active and independent lives.
Individuals using a tonguebased system should only be able to move
their tongue, which is especially important if a person has paralyzed limbs. A
tiny magnet, only a size of a grain of rice, is attached to an individual's
tongue using implantation, piercing or adhesive. This technology allows a
disabled person to use tongue when moving a computer mouse or a powered
wheelchair. Scientists chose the tongue to control the system because unlike
the feet and the hands, which are connected by brain through spinal cord, the
tongue and the brain has a direct connection through cranial nerve. In case
when a person has a severe spinal cord injure or other damage, the tongue
will remain mobile to activate the system. Tongue movements are also fast,
accurate and do not require much thinking, concentration or effort. The
motions of the magnet attached to the tongue are spotted by a number of
magnetic field sensors installed on a headset worn outside or an orthodontic
brace inside the mouth.The signals coming from the sensors are wirelessly
sent to a portable computer that placed on a wheelchair or attached to an
individual's clothing. The Tongue Drive system is touchfree, wireless and
noninvasive technology that needs no surgery for its operation.
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INTRODUCTION
Assistive technologies are critical for people with severe disabilities to lead a
selfsupportive independent life. Persons severely disabled as a result of
causes ranging from traumatic brain and spinal cord injuries to stroke
generally find it extremely difficult to carry out everyday tasks without
continuous help. Assistive technologies that would help them communicate
their intentions and effectively control their environment, especially to
operate a computer, would greatly improve the quality of life for this group of
people and may even help them to be employed. This device could
revolutionize the field of assistive technologies by helping individuals with
severe disabilities, such as those with highlevel spinal cord injuries, return to
rich, active, independent and productive lives. The TDS provides people with
minimal or no movement ability in their upper limbs with an efficacious tool
for computer access and environmental control. Tongue Drive consists of A
small permanent magnet secured on the tongue by implantation, piercing, or
tissue adhesives is used as a tracer, the movement of which is detected by an
array of magnetic field sensors mounted on a headset outside the mouth or
on an orthodontic brace inside. The sensor outputs signals are wirelessly
transmitted to an ultraportable computer carried on the user's clothing or
wheelchair and are processed to extract the user's commands. The user can
then use these commands to access a desktop computer, control a power
wheelchair, or interact with his or her environment.
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Use of Tongue for Manipulation
TDS chose the tongue to operate the system because unlike hands and
feet, which are controlled by the brain through the spinal cord, the tongue is
directly connected to the brain by a cranial nerve that generally escapes
damage in severe spinal cord injuries or neuromuscular diseases. Tongue
movements are also fast, accurate and do not require much thinking,
concentration or effort. Movement of the magnetic tracer attached to the
tongue is detected by an array of magnetic field sensors mounted on a
headset outside the mouth or on an orthodontic brace inside the mouth. The
sensor output signals are wirelessly transmitted to a portable computer,
which can be carried on the user's clothing or wheelchair
TDS PROCESSING
In Tongue Drive system, the motion of the tongue is traced by an array
of Hall effect magnetic sensors, which measure the magnetic field generated
by a small permanent magnet that is contained within a nonmagnetic fixture
and pierced on the tongue. The magnetic sensors are mounted on a dental
retainer and attached on the outside of the teeth to measure the magnetic
field from different angles and provide continuous realtime analog outputs.
Fig. shows the Tongue Drive System block diagram with two major units: one
inside the mouth, the mouthpiece, and the other outside, a portable body
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worn controller. Small batteries such as hearing aid buttonsized cells are
intended to power the mouthpiece for extended durations up to a mouth. The
power management circuitry scans through the sensors and turns them on
one at a time to save power. The time division multiplexes (TDM) analog
outputs are then digitized, modulated, and transmitted to the external
controller unit across a wireless link. The magnetic field generated by the
tracer inside and around the mouth varies as a result of the tongue
movements. These variations are detected by an array of sensitive magnetic
sensors mounted on a headset outside the mouth, similar to a headworn
microphone, or mounted on a dental retainer inside the mouth, similar to an
orthodontic brace. The sensor outputs are wirelessly transmitted to a personal
digital assistant (PDA) also worn by the user. A sensor signal processing (SSP)
algorithm running on the PDA classifies the sensor signals and converts them
into user control commands that are then wirelessly communicated to the
targeted devices in the user's environment.The principal advantage of the
TDS is that a few magnetic sensors and a small magnetic tracer can
potentially capture a large number of tongue movements, each of which can
represent a particular user command. A set of specific tongue movements can
be tailored for each individual user and mapped onto a set of customized
functions based on his or her abilities, oral anatomy, personal preferences and
lifestyle. The user can also define a command to switch the TDS to standby
mode when he or she wants to sleep, engage in a conversation, or eat. The
signals received by the external controller unit are demodulated and
demultiplexed to extract the individual sensor outputs. By processing these
outputs, the motion of the permanent magnet and consequently the tongue
within the oral cavity is determined. Assigning a certain control function to
each particular tongue movement is done in software and can be easily
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customized control functions may then individual user. These customized
control functions may then be used to operate a variety of devices and
equipments including computers, phones, and powered wheelchairs.
One prototype for human trials, shown in Figure 2, was built on a face shield
to facilitate positioning of the sensors for different subjects. The main function
of this prototype was to directly emulate the mouse pointing and selection
functions with the tongue movements. Six commands were defined: left,
right, up, and down pointer movements Q3 and single and doubleclick
movements. As long as the SSP algorithm was running in the background, no
additional software or learning was needed if the user was familiar with the
mouse operation and any piece of software that was operable by a mouse.
Small, cylindrical, rareearth permanent magnets were used as magnetic
tracers. A pair of two axis magnetic field sensor modules (PNI; Santa Rosa,
California) was mounted symmetrically at right angles on the face shield
close to the user's cheeks. Each twoaxis module contained a pair of
orthogonal magnetoinductive sensors, Hence, we had one sensor along the
xaxis, one along the yaxis, and two along the zaxis with respect to the
imaginary coordinates of the face shield. To minimize the effects of external
magnetic field interference, including the earth magnetic field, we used a
threeaxis module as a reference electronic compass. The reference compass
was placed on top of the face shield so as to be far from the tongue magnet
and to only measure the ambient magnetic field. The reference compass
output was then used to predict and cancel out the interfering magnetic fields
at the location of the main twoaxis sensor modules. All seven sensor outputs,
already in digital form, were sent serially to the ultralowpower MSP430
microcontroller (Texas Instruments; Dallas, Texas) that is the heart of the
control unit. The microcontroller took 11samples/s from each sensor while
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activating only one module at a time to reduce power consumption. After
reading all sensors, we arranged the samples in a data frame and wirelessly
transmitted them to a personal computer (PC) across a 2.4 GHz wireless link
established between two identical nRF2401 transceivers (Nordic
Semiconductor; Trondheim, Norway). The entire system was powered by a 3.3
V coinsized battery (CR2032), which together with the control unit and
reference compass were hidden under the face shield cap.
PROTOTYPE TONGUE DRIVE SYSTEM
The system can potentially capture a large number of tongue
movements, each of which can represent a different user command. A unique
set of specific tongue movements can be tailored for each individual based on
the user's abilities, oral anatomy, personal preferences and lifestyle. An
individual could potentially train our system to recognize touching each
tooth as a different command. The ability to train our system with as many
commands as an individual can comfortably remember is a significant
advantage over the common sip npuff device that acts as a simple switch
controlled by sucking or blowing through a straw. The Tongue Drive system
is also noninvasive and does not require brain surgery like some of the brain
computer interface technologies.
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TASKS PERFORMED IN TDS
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Computer mouse tasks ± left, right, up and down pointer movements and
single and doubleclick. For each trial, the individual began by training the
system. During the fiveminute training session, the individual repeated each
of the six designated tongue movements 10 times. During the testing session,
the user moved his or her tongue to one of the predefined command
positions and the mouse pointer started moving in the selected direction. To
move the cursor faster, users could hold their tongue in the position of the
issued command to gradually accelerate the pointer until it reached a
maximum velocity. Results of the computer access test by novice users with
the current Tongue Drive prototype showed a response time of less than one
second with almost 100 percent accuracy for the six individual commands.
This is equivalent to an information transfer rate of approximately 150 bits per
minute, which is much faster than the bandwidth of most braincomputer
interfaces. The research team has also begun to develop software to connect
the Tongue Drive system to a wide variety of readily available
communication tools such as text generators, speech synthesizers and
readers. In addition, the researchers plan to add control commands, such as
switching the system into standby mode to permit the user to eat, sleep or
engage in a conversation while extending battery life.
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MODES IN POWERED WHEEL CHAIR
Operated the powered wheelchair using two different control strategies:
1. DISCRETE MODE
Discrete mode, designed for novice users, and continuous mode for
more experienced users. In discrete mode, if the user issued the command to
move forward and then wanted to turn right, the user would have to stop the
wheelchair before issuing the command to turn right. The default stop
command was when the tongue returned to its resting position, bringing the
wheelchair to a standstill.Discrete mode is a safety feature particularly for
novice users, but it reduces the agility of the wheel chair movement.
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2. CONTINUOUS MODE
In continuous mode, however, the user is allowed to steer the powered
wheelchair to the left or right as it is moving forward and backward, thus
making it possible to follow a curve.
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ADVANTAGES OF TDS
• Allows disabled people to power a wheelchair
• Allows disabled people to use a computer
• Allows disabled people to not depend on others
• Allows disabled people to have more freedom
• Allows disabled people to become employable
DRAWBACKS
• Computer battery could die when not around charger
• Could take a while to learn how to use it
• Might not be affordable for some people
• Decreases job opportunities for some
• Computer could go down
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CONCLUSION
Tongue drive system technology is a gift for the physically challenged and
disabled persons to lead their life equal to the normal persons in the society.
A tongue operated magnetic sensor based wireless assistive technology has
been developed for people with severe disabilities to lead a selfsupportive
independent life enabling them to control their environment using their
tongue. This technology works by tracking movements of permanent magnet,
secured on the tongue, utilizing an array of linear Hall effect sensors. The
sensor outputs are a function of the positiondependent magnetic field
generated by the permanent magnet. This allows a small array of sensors to
capture a large number of tongue movements. Thus, providing quicker,
smoother, and more convenient proportional control compared to many
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existing assistive technologies. Other advantages of the Tongue Drive system
are being unobtrusive, low cost, minimally invasive, flexible, and easy to
operate. A more advanced version with custom designed lowpower
electronics that entirely fit within the mouthpiece is currently under
development.