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 indi-

viduals 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 move-

ment 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 wire-

lessly transmitted to an ultraportable computer carried on the user’s clothing or wheel-

chair and are processed to extract the user’s commands. The user can then use these com-

mands 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-ef-

fect 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 ana-

log 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 con-

troller 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 de-

tected 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 per-

sonal 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 demulti-

plexed 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 deter-

mined. 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 move-

ments. 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 symmet-

rically 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 re-

spect 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 can-

cel out the interfering magnetic fields at the location of the main two-axis sensor mod-

ules. 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 ar-

ranged the samples in a data frame and wirelessly transmitted them to a personal com-

puter (PC) across a 2.4 GHz wireless link established between two identical nRF2401

transceivers (Nordic Semiconductor; Trondheim, Norway). The entire system was pow-

ered 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 dis-

abled persons to lead their life equal to the normal persons in the society. A tongue oper-

ated 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 propor-

tional 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.