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Permanently-Embossed Band Tactile Displays

Fig 1 : A tactile band used for 6-dot braille.

This page describes a new approach to braille / tactile display design that is being investigated. The displays would use permanently-embossed bands (PEBs) of tactile effects. Please note that the PEB Tactile Displays are at an early stage of development, and that no prototypes have been produced.


Background

Many blind and deafblind people use the braille and Moon tactile codes for reading, and computer-controlled braille displays allow varying braille "dots" to be displayed, conveying text that would otherwise be displayed on a computer monitor for sighted people to read. Most existing braille displays require a controlled "actuator" (movement-causing device) for each braille dot.


Features of "PEB" Tactile Displays

PEB (Permanently-Embossed Band) Tactile Displays would present varying tactile representations of text, and of simple pixel-based tactile graphics, using a reduced number of components. Several independently-moveable bands (or discs, or rods) would each be permanently embossed with several braille dots or other tactile characters or pixels. The bands would move relative to each other in order to either present the required tactile characters, or to form simple pixel-based tactile graphics.

A PEB Tactile Display would maintain the currently-displayed tactile text and graphics when powered-down. It could display a single line of text; or several lines simultaneously, to present a page of tactile material.

The dots for braille text or tactile graphics can be arranged in special patterns which allow overlapping columns of dot patterns to be found within longer continuous columns. Figure 1 shows how 64 horizontal-dot-pairs can be arranged on a band to form all of the 6-dot braille characters (albeit overlapped).



A simple single-row display

Figure 2 shows how long PEBs (Permanently-Embossed Bands) could be used to construct a simple single-row display that presents Moon characters as well as braille. Moon is particularly suitable for persons who have lost their sight later in life or who are unable to use braille effectively.

The display works by rotating forty identical flexible marked bands (i.e. PEBs) in order to present the required characters for the user to read. The PEBs are long enough to accommodate the 39 standard Moon characters, plus 21 "Moon-character-sized" positions for the braille dots. The braille characters are larger than standard braille, in order to fit the character positions that are primarily sized for Moon characters. This may be helpful for users who wish to progress from using Moon to the more comprehensive braille coding.

Fig 2 : A single-row PEB display.

The PEBs are turned together by a single drive-bar, but are stopped individually when they are correctly positioned. 40 system-controlled solenoids each control a PEB. When a solenoid is not energised, a serrated plate is held up by a spring and presses the PEB against the reading-slot in the casing; when the solenoid is energised, it overcomes the strength of the spring and lowers the plate, allowing the PEB to engage with the drive-bar, so that the drive-bar can turn it. The drive-bar is turned by a system-controlled stepper-motor, and the whole display is controlled by a microcontroller, which contains non-volatile memory that retains the position of the bands after the display is turned off.


A two-row display

Figure 3 shows how two rows of tactile characters could be presented, by turning the PEBs via an external cylindrical sprocketed drive-bar. Having two rows of characters would allow one row of characters to be prepared by the system while the other row is being read. The design would be suitable for presenting 6-dot braille, 8-dot braille, Moon or simple tactile graphics. The example shown is for 6-dot braille i.e. with PEBs approximately 150mm long (as shown in Figure 1 above). Both rows could be updated via a single drive-bar i.e. using only one system-controlled stepper-motor.

Fig 3 : A two-row PEB display.

The display has two facing rows of cartridges which are loaded with thin PEBs that are pierced with sprocket-holes and resemble movie-film base. Due to the thinness of the band base material the small sprocket-holes are not distracting to the user.

In order to position the bands, they are drawn down onto the drive-bar by system-controlled solenoids, and engage with the sprocket-teeth on the bar. The bar is turned by the system-controlled stepper-motor, and each solenoid releases its assigned cartridge(s) when their PEBs are correctly positioned (the drive-bar stops turning when the PEBs are about to be lowered or raised).



Multi-row displays

Fig 4 : Tactile bands used for 8-dot braille.

Multi-row displays would extend the approach used for the two-row display, by using compact components that allow many rows of tactile effects to be presented. A large number of 8-dot braille characters could be displayed by splitting each 8-dot braille cell into two "4-dot" columns (i.e. using two separate bands for each cell), to produce more compact PEBs, as shown in Figure 4.

Fig 5 : Tactile bands used for Moon.

The following multi-row designs are for 15-row by 40-column 8-dot braille displays which would also be able to simultaneously display simple pixel-based tactile graphics. Figure 4 shows how the bands can have a section that contains all combinations of a column of four braille dots, and a section that contains all combinations of a column of four tactile pixels. Using different-sized dots for braille and graphics makes it clearer to the user whether braille or graphics are being presented. Braille cells are produced by presenting two bands arranged facing in opposite directions, so that the standard braille spacing is produced. The bands turn down at the top and bottom of the presented area as they pass over posts or rollers, and this produces small depressions between rows which can act as a guide for braille reading.

For displays that are primarily designed for presenting Moon characters, low-definition tactile graphics can be formed by including all possible combinations of four squarely-arranged tactile dots, with a single Moon-character-sized position presenting a set of four dots (raised or flat), as shown in Figure 5. Only eight Moon-character-sized positions are required to hold all combinations four dots, by using a similar overlap method as is used for braille dots.

Multi-row PEB displays could be configured in several possible ways :-

A) Individually-controlled cells

For certain applications it will be necessary to have a rapidly updating display and direct control of each band or pair of bands. Individual cells could be controlled via ratchet-and-pawl- or claw-type mechanisms which move the bands on by one sprocket-hole/braille dot per cycle.

Fig 6 : A PEB display with individually-controlled cells.

However it may be simpler to mount the PEBs in "cassettes" which are moved up and down, so that they engage and disengage with a common drive-mechanism when they need to be changed (each cassette contains facing pairs of PEBs that form one braille cell or two columns of tactile dots). The drive-mechanism could be several continuous toothed drive-bands that are driven via a cogged bar, powered by a single system-controlled stepper-motor, as shown in Figure 6.

B) Row-by-row or column-by-column update

Fig 7 : A PEB display that is updated "row-by-row".

Configuring the display to update on a serial row-by-row or column-by-column basis allows the actuators to be arranged around the edge of the display, so reducing the need for compact actuators, and reducing the height of the display. Fewer actuators are needed.

The display shown in Figure 7 would perform row-by-row processing. An entire "row-tray" of cassettes is lowered a small distance when it needs to be updated (each cassette containing a facing pairs of PEBs). The cassettes are drawn down onto the drive-bars, so that their PEBs can be turned (several PEBs can be turned simultaneously). When the PEBs are correctly positioned, the rods raise the cassettes back to their partially-lowered position.

C) "Solid" columns or rows

Fig 8 : A "column-rod" PEB display.

Column-by-column processing could be performed by using whole-column banks of pairs of PEBs, which are rapidly set by simultaneously-acting pairs of drive-bars, as shown in Figure 8. The 15 pairs of PEBs in a column are contained within single units known as "column-rods", which are selected and lowered onto drive-bars.

Figure 8 shows a design which uses a single stepper-motor, but it is also practical to use 30 system-controlled stepper-motors, each of which directly turns a drive-bar, so allowing fast simultaneous update of the PEBs.



Using a moving "setting-head"

Low-height displays can be produced by keeping the actuators to the edge of the display. However if the height is not important, and slower serial updating is acceptable, then the stepper-motors that update groups of cells could be moved directly to the required group by mounting them on a platform (referred to as a "setting-head") in a Cartesian arrangement. For whole-row or whole-column update (i.e. the "setting-head" covers a whole row or whole column) then the setting-head need only be moved back and forth along a line. The setting-head would be moved up to the PEBs, which would then be lowered and turned by the setting head.


Intermediate screens

Using an "intermediate screen" (located between the user's fingers and the tactile bands) allows the tactile effects to be felt indirectly.

Fig 9 : Cross-section of an "intermediate screen".

An intermediate screen could consist of two horizontally-aligned sheets pierced with holes, through which small rods pass. As a rod's flat circular head produces a braille "dot" effect, the rods are referred to as "dot-rods". The dot-rods can move freely up and down.

If an intermediate screen is used then the tactile bands can be produced by forming holes or indentations in the bands, rather than raised areas. This is because the tactile effects are felt indirectly, and so can be produced in "reverse" so that dots are raised by the flat surface of the band, and dots are lowered by letting the dot-rods fall into the holes in the bands. The bands could be produced by cutting additional perforations in the bands when the sprocket-holes are cut. Such bands would be of consistent overall thickness, making the band handling easier.

Using an intermediate screen would remove the tactile effects that are present at the top and bottom of a PEB's reading area, and no finger-guard would be required. The upper surface could be shaped (non-flat), which might be more comfortable to read than a completely flat surface.


Locked dot-rods

An intermediate screen could be made "lockable", so that the dot-rods are held in the "up" or "down" positions to which they have been moved by a sequentially-acting setting-head. Only one set of PEBs would be needed to produce the impressions formed by the dot-rods, which would then be locked in place, being released when they need to be updated.

Fig 9A : Top view of sprung "locking-bars" that hold and release dot-rods.

Fig 9A shows how the dot-rods could be held in place by sprung "locking-bars" (small 8 row by 4 column locking-bars are shown, but they would normally be larger). The locking-bars would be located between the upper and lower sheets of an intermediate screen, and would be perforated with holes, the layout of which would match that of the dot-rods.

Two sets of locking-bars, at right-angles to each other, could be used to control and release smaller areas of the display : two system-controlled solenoids could be moved along with the setting-head, and act on the locking-bars for whichever section of the display is being updated.


Manually-set displays

Manually-set displays could be used to set up braille messages, or to communicate with deafblind people.

Fig 10 : A manually-set display.

Figure 10 shows an example of a manually-set display : a rectangular slab contains several long rectangular channels, each of which holds a pair of moveable rods that are embossed with braille dots for ten dot positions. Each column of ten dots contains all of the combinations of three dot states (raised or un-raised). The dots follow the pattern "0011101000".


Fig 11 : A cylindrical manually-set display.

Alternatively a cylindrical configuration could be used in which circular "hoops", embossed with braille dots, are mounted on a rod, and are positioned manually.

The resultant message is displayed along the length of the rod. Each hoop contains 16 dot-positions, allowing 8-dot braille characters to be presented. A guide-bar signifies the top or bottom of the cells, allowing both 6-dot and 8-dot braille to be used.

Flexible continuous bands embossed with braille dots (i.e. "PEBs") could also be used, as shown in Figure 12.

Fig 12 : A flat thumb-wheel-set PEB display.

If whole-braille-cell PEBs are used (rather than single-column half-cell bands) then a compact manual version could be produced by using PEBs which pass over two sets of rollers, the PEBs being moved by thumb-wheels. In order to save space, thin tactile spacers could be used between cells, the spacers either filling the gap between PEBs, or rising up to signify a word break. Lettering could be printed on the PEBs to allow sighted users to easily read the message.


This page is maintained by David Dewhurst. Any enquiries or feedback should be sent to info@stve.org.
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Copyright © 2001 by David C. Dewhurst.  All rights reserved.    V5.00.    Updated 24-DEC-2001.