ABSTRACT
A new assistive technology developed by engineers at the Georgia Institute of
Technology. It help individuals with severe disabilities lead more independent lives. The
individuals with disabilities such as to operate a computer control a powered wheelchair
and Interact with their environments simply by moving their tongues.The "Tongue
Drive" system is a tongue-operated assistive technology developed for people with severe
disability to control their environment. The tongue is considered an excellent appendage
in severely disabled people for operating an assistive device.
INTRODUCTION
Assistive technologies are critical for people with severe disabilities to lead a self-
supportive 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 high-level 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.
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 real-time analog outputs.
Fig. 1 shows the Tongue Drive System block diagram with two major units: one inside
the mouth, the mouthpiece, and the other outside, a portable body worn controller. Small
batteries such as hearing aid button-sized 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 head-worn 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 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 double-click 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, rare-earth 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 two-axis
module contained a pair of orthogonal magneto-inductive sensors, shown in Figure 2.
Hence, we had one sensor along the x-axis, one along the y-axis, and two along the z-axis
with respect to the imaginary coordinates of the face shield (Figure 3). To minimize the
effects of external magnetic field interference, including the earth magnetic field, we used
a three-axis 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 two-axis sensor
modules. All seven sensor outputs, already in digital form, were sent serially to the
ultralow-power MSP430 microcontroller (Texas Instruments; Dallas, Texas) that is the
heart of the control unit. The microcontroller took 11samples/s from each sensor while
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 coin-sized battery (CR2032), which together with the control
unit and reference compass were hidden under the face shield cap (Figure 3 inset).
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-
n-puff device that acts as a simple switch controlled by sucking or blowing through a
straw.
The Tongue Drive system is also non-invasive and does not require brain surgery
like some of the brain-computer interface technologies.
TASKS PERFORMED IN TDS
Computer mouse tasks – left, right, up and down pointer movements and
single- and double-click. For each trial, the individual began by training the system.
During the five-minute 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 brain-computer 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.
MODES IN POWERED WHEEL CHAIR
Operated the powered wheelchair using two different control strategies:
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.
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.”
ADVANTAGES OF TDS
Ø Allows disabled people to power a wheelchair
Ø Allows disabled people to use a computer
Ø Allows disabled people to not depend on others
Ø Allows disabled people to have more freedom
Ø Allows disabled people to become employable
DRAWBACKS
Ø Computer battery could die when not around charger
Ø Could take a while to learn how to use it
Ø Might not be affordable for some people
Ø Decreases job opportunities for some
Ø Computer could go down
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 self-supportive 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 position-dependent 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 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
low-power electronics that entirely fit within the mouthpiece is currently under
development.
