TACTILE COMPUTER DISPLAY FOR THE BLIND

ECRAN D'ORDINATEUR TACTILE POUR LES AVEUGLES

English Abstract

This invention discloses a tactile display for computer to be used
by blind people with finger reading skills. The display is made of
a plurality of independently inflatable dots called pixel, arranged
in a dense matrix format. The matrix can display many lines of Brail
characters or graphics. The control of each pixel relies on the
expansion of a substance heated by an electric element. Each pixel is
made of a small cylinder containing the expansion substance. The
cylinders are closed up rigidly at the bottom end and by an elastic
membrane at the top end. The elastic membrane serves as the reading
surface. To raise a pixel, the corresponding electronic drivers are
turned on to activate the pixel's heater. As the substance contained
in the cylinder heats up, it expands to stretch the section of the
elastic membrane covering it. The membrane then forms a bump of
sufficient height to be sensed by the reader's finger. As soon as the
drivers deactivate the pixel's heater, the substance cools down and
shrinks. The elastic membrane is then pulled down making the surface
flat again. During normal operation, the drivers are successively
activated in order to scan the whole surface of the display activating
only the pixels that should be raised. This technology is not only
limited to be used by the blind but can also produce tactile feedback
devices for virtual reality applications or to make various massaging
devices.

French Abstract

L'invention est un écran d'ordinateur tactile pour aveugle apte à la lecture avec les doigts. L'écran est fait d'une pluralité de points gonflables indépendamment les uns des autres appelés pixels et placés dans un format matriciel dense. La matrice peut afficher plusieurs lignes de caractères braille ou des graphiques. La commande de chacun des pixels est basée sur l'expansion d'une substance chauffée par un élément électrique. Chaque pixel est constitué d'un petit cylindre contenant cette substance expansible. Les cylindres sont fermés de façon rigide à leur extrémité inférieure et par une membrane élastique à leur extrémité supérieure. Cette membrane élastique sert de membrane de lecture. Pour soulever un pixel, les dispositifs d'attaque électronique correspondants sont mis sous tension pour activer l'élément chauffant du pixel. mesure que la substance contenue dans le cylindre s'échauffe, elle se dilate et étire la section de la membrane de plastique qui la recouvre. La membrane forme alors une protubérance suffisamment élevée pour être détectée par les doigts du lecteur. Dès que les dispositifs d'attaque désactivent l'élément chauffant du pixel, la substance se refroidit et se contracte. La membrane élastique reprend sa forme initiale et sa surface redevient plane. En mode de fonctionnement normal, les dispositifs d'attaque sont activés successivement pour balayer la surface entière de l'écran en n'activant que les pixels qui doivent être soulevés. Cette technologie n'est pas limitée à l'usage des aveugles; on peut également l'utiliser pour produire des dispositifs de réaction tactiles dans les applications à réalité virtuelle ou dans divers dispositifs de messagerie.

Claims

CLAIMS:
The embodiment of the invention in which the exclusive property or
privilege is claimed are defined as follows:
1- A tactile computer display for the blind, comprising tactile
elements called pixel, in sufficient number and on a sufficiently
large area to easily display both graphics and brail text; the said
pixel driven by the thermal expansion of a substance confined into
cylinders closed rigidly at the bottom with a thermally conductive
plug and with an elastic membrane at the top; the said pixel made by
producing contiguous holes into several laminated layers of non
conductive rigid material supporting a network of conductive traces
serving as electrodes arranged in a row column fashion; the said pixel
containing a heating element and a diode connected to some electronic
drivers by the said electrodes.
2- The display of claim 1, wherein the said elastic membrane glued
to the top of the display is used as the reading surface.
3- The display of claim 1, wherein the said substance used in each
of the said pixel is either paraffin or wax both having a very high
thermal expansion coefficient.
4- The display of claim 1, wherein the said heaters increase their
electrical resistance once the maximum operating temperature is
reached making them self-regulated.

5- The display of claim 1, wherein the said electronic drivers can
activate simultaneously many pixel located in the same column.
6- A usage of the display of claim 1, wherein the said display is
used to provide navigational and environmental information to the
blind; the said information coming from different sensors such as; a
camera, and/or a GPS receiver, and/or diverse sensors all coupled to
a portable computer converting the said information into a suitable
graphical and textual format to be placed on the said display and read
by the blind while progressing in his environment.
7- The usage of claim 6, wherein the said display equipped with a
suitable harness is worn vertically on the hip with the said reading
surface facing away allowing the blind to freely scan it with his
fingers and control the said computer to modify the presentation of
the said information.
8- A tactile stimulation device used in virtual reality or massaging
applications, comprising tactile elements in sufficient number and on
a sufficiently large area to cover a section of the human body; the
said elements driven by the thermal expansion of a substance confined
into cylinders closed rigidly at the bottom with a thermally
conductive plug and with an elastic membrane at the top; the said
elements made by producing contiguous holes into several laminated
layers of non conductive rigid material shaped for the specific
application and supporting a network of conductive traces serving as
electrodes arranged in a row column fashion; the said elements

containing an electrical heater and a diode connected to some
electronic drivers by the said electrodes.
9- The tactile stimulation device of claim 8, wherein the said
laminated layers of the non conductive material are made flexible.

Description

- CA21 69198
FIELD OF THE INVENTION
The invention presented relates to a tactile computer display for the
blind, and more particularly to a large area of high pixel density
arranged in a two-dimensional array having a full screen capability.
The vertical movement of the pixels is the result of the thermal
expansion of a substance contained in a plurality of cylinder closed up
by an elastic membrane at the top end. This screen can display both
Brail characters and graphics.
BACKGROUND OF THE INVENTION
Much work has been devoted to produce a tactile computer display
which could represent the text and graphics available to people with
normal vision. Some Brail displays are being produced but their
mechanical complexity and their cost limit them to one or two lines of
text. Canadian Pat. No. 2,109,863 is an example of the mechanical
devices. This limitation makes them difficult to use with modern
graphics based computer programs and prevents the use of a tracking
device, such as a mouse. Some full screen tactile displays based on
mechanical or electrorheological principles have been patented refer to
US Pat. No 4,836,784 or 5,222,895. They seem to be either too slow or
too complicated to be cost effective and as far as we know were not
commercialised.

CA21 691 98
SUMMARY OF THE INVENTION
It is the main purpose of the present invention to create a full
screen tactile display using the thermal expansion of a substance
contained in a plurality of small isolated cylinders closed up rigidly
at the bottom end with a thermally conductive plug and with an elastic
membrane at the top end. The elastic membrane becomes the reading
surface of the display. Each cylinder contains an individually
controllable heating element to produce the expansion of the substance
while its cooling is done through the thermally conductive bottom.
In one of the realisations of a full screen tactile display,
thousands of pixels are placed side by side in a two dimensional 128
by 128 matrix. The substance in the pixels needs a high thermal
expansion coefficient and should be safe to use. This particular
realisation of the invention uses a fabrication process based on
printed circuit board technology to produce the dense matrix of
individually controllable pixels at a reasonable cost. The heater
resistance of approximately 300 ohms and a short power pulse in the
range of 1 Watt at 15 Volts is necessary to raise a pixel. This low
potential and the use of an inert expansion substance like paraffin
makes it safe for the operator even in case of failure of the display.
In the preferred version of the invention the tactile reading
surface is made of four identical sections placed in a two by two
matrix arrangement. This configuration simplifies both the production

~ CA21 691 98
and the testing while increasing the yield and the refreshing rate.
Each section becomes a 64 by 64 matrix easily controllable by standard
electronic drivers.
This full screen tactile display with graphics capability coupled
with a touch screen circuit permits the blind to operate almost any
standard computer program as well as a seeing person. A short program
to convert standard characters into Brail ones, and to bring the
graphics resolution to a manageable level is used but not covered in
this invention. Once the blind person can interact efficiently with
the computer, a video camera and other sensors can be added to the
system. With a certain amount of processing, the images could be
placed on the display allowing the blind to "see" the environment.
With a portable system, the blind person could walk around without a
white cane and identify the outline of the environment, read both the
civic numbers and the streets name, and possibly enjoy a visit to the
museum.

`-- CA216ql98
DESCRIPTION OF THE DRAWINGS
The following paragraphs relate to the figures included in this
document. Figure 1 shows the tactile display with its finger reading
area while figure 2 shows its cross-section. The operation of the
reading surface is demonstrated in figure 3 where the two activated
pixel contrast with the two at rest. This figure shows the reader's
finger approximately to scale. Finally figure 4 is a simplified
electrical schematic of an array where an example of the row drivers
activating two pixel from the same column is given. This mode of
activation improve the speed of response of the display.
Figure 1 shows the tactile display with its finger reading area
(10), the enclosure (12), and various function keys (13). The
function keys are laid out around the perimeter to make them easy to
access. Their function is written on them in brail. The blank area
(11) around the reading area (10) is left to help the reader to reach
the limits of the text.
Figure 2 shows a simplified cross-section of the display. It is
made of a reading board (10) holding an array of up to sixteen
thousand pixel. The electronic drivers for the pixel are mounted on
the printed circuit board below (31). Connectors (32) are used to
link the two boards electrically. Air is forced by one or more fan(s)
(33) to cool the base of the reading board (10). An enclosure (12)
protects the electronic components.

CA~169198
Figure 3 shows a cross-section of the reading surface. The
operation of each pixel relies on the expansion of a heated substance
(21) . In the illustration the two left pixel are at rest while the
two others are activated, stretching the elastic membrane into a small
bump. The finger of a reader (25) has been drawn to illustrate the
dimension of the pixel. Each pixel is in fact a cylinder (23) which
is rigidly closed at one end (26) and covered by an elastic membrane
(22) at the other. The membrane (22) is glued to the body (29) of the
reading surface. The wall of the cylinder is covered by a resistive
material (28) which serves as the electric heater.
One of the fabrication processes used relies on printed circuit
board technology. The body (29) of the reading surface is produced
by laminating three layers of printed circuit containing a plurality
of holes which form the pixel's cylinders (23) . The two external
layers hold the conducting traces and electrodes (27) used by the
drivers to activate the pixel. The thermally conductive plugs (26)
of the bottom layer are produced by soldering the plurality of plated
through holes it contains before laminating it to the other layers.
The heaters (28) are made by depositing and curing a controlled amount
of resistive material in each cylinder (23) . The diodes (40) are then
mounted to the bottom board. The next production steps consist in
filling the cylinders (23) with the expansion substance (21) and
sealing the top of the reading surface with the elastic membrane (22) .
Thorough testing is performed at each production step to insure a high
yield.

- CA2169198
To raise a pixel, power is applied to its electrodes (27). The
substance (21) heats up and expands while melting. Since the cylinder
is rigid, the increase in volume stretches the elastic membrane (22)
up. This forms a bump which can be sensed by the reader's finger.
To retract the pixel, the power is removed. The heat is evacuated
through the bottom of the board by the thermally conductive base (26).
The volume of the substance decreases and the elastic membrane returns
to its flat position.
The speed at which the pixel can raise or lower depends on how fast
the temperature of the substance can be changed, and which substance
is used. Paraffin and wax are some of the substances known to give
satisfactory results. To create a temperature regulating effect for
each pixel, the heater's material contains thermistor ceramics. This
material has an electrical resistance which increases sharply once a
certain temperature has been reached. This releases the electronic
control from having to limit the power to the pixel when approaching
the maximum temperature.
Figure 4 is the simplified electrical schematic of an array. The
resistors (41) represent the pixel's heater. Each pixel must be
driven through a small diode (40). The diode prevents conduction when
the pixel is not selected by the drivers. In the example given, the
rows driver (42) supplies a positive potential to the rows 1 and 4
containing the pixel to be raised. The columns driver (43) pulls its

~ C`A~ r~ !98
output number 2 to zero volts to bias only this one column. After a
few thousandths of a second, the next column is selected with new row
drivers activated. The whole board is scanned a few times per second
so it appears continuous. The reaction time of the pixel being longer
than the scan time, its expansion is smooth and continuous.
While many aspects of the principles of operation, the production
techniques, and the material used have been shown and described,
further implementation or combinations of those described herein will
be apparent to those with knowledge in the field without departing
from the spirit of the invention.

Representative Drawing