2004 Conference Proceedings

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NIST REFRESHABLE TACTILE GRAPHIC DISPLAY: A NEW LOW-COST TECHNOLOGY

Presenter(s)
John Roberts
NIST
100 Bureau Dr. MS 8951
Gaithersburg MD 20899
phone 301-975-5683
Email: john.roberts@nist.gov

Background

For many blind and visually impaired users, tactile display offers an attractive option for information access. While Braille provides text-related information, tactile graphics is important for those situations where "a picture is worth a thousand words". Braille is available both in a permanent format (such as embossed printout) and on computer-controlled refreshable displays. Tactile graphics is available in permanent formats such as embossed pages and rapid prototyping. Unfortunately, refreshable tactile graphic displays have not been readily available, due to the extremely high cost using conventional technology. Fortunately, a project team at the National Institute of Standards and Technology (NIST), working in cooperation with the National Federation of the Blind (NFB), has invented a new technology that will reduce the cost of refreshable tactile graphic displays by an estimated factor of twenty compared to conventional technology, allowing them to become widely available.

NIST has constructed an operational prototype to demonstrate the technology and to get user feedback. The technology is available for use by manufacturers, and NIST has recently granted a non-exclusive research license to a university group for investigation of usability and commercialization issues.

Refreshable displays use an array of rounded pins mounted in holes in a touchable viewing surface. By raising selected pins, the desired pattern can be created. The conventional method for building such a display is to use active pins, with an individual powered linear actuator such as a piezoelectric device for every pin. This method is simple and effective, but also very costly. The main cost component of a Braille display is the hundreds of actuators and associated driving electronics needed to produce a line of Braille text. For a two-dimensional tactile graphic array, thousands of pins are needed, and the cost is much greater. A piezoelectric tactile graphic display built by KGS Corporation in Japan and bought by the NFB was reported to have cost $42000 US [1]. The goal of the NIST project is to enable a tactile graphic display that costs $2000 or less.

NIST tactile graphic technology

The NIST approach reduces cost by use of "passive pins". In contrast to the actively driven pins of conventional designs, the passive pins are simple metal pins with a large rounded head on one end and a small rounded tip on the other end. The pins are mounted in holes in a stack of flat plates that define the reading surface, and that hold the pins vertical while allowing them to move up and down to form the desired patterns. A moving mechanism positions the pins, and then all the pins are locked in place to form a rigid pattern for the user to view. After viewing, the pin array is unlocked, and the pins are returned to the default position, erasing the image and preparing the display for the next image. The prototype has over 3600 pins in a 71x51 array.

The prototype built by the NIST project team uses a single actuator to set all the pins, mounted on an X-Y positioner (a modified pen plotter was used for the prototype). A more expensive option would use a linear array of actuators, and a single dimension positioner. The pins are slightly longer than the total thickness of the stack of plates that make up the display surface, so that when the pins are in the lowered (reset) position, the rounded tips of the pins protrude slightly from the bottom plate. The actuator drives a spring loaded ball bearing (somewhat like an enlarged ballpoint pen) across the underside of the bottom plate, and wherever it moves, the pins are pushed up to the set position. The actuator can be positioned then operated to set individual pins, or it can be set and then moved using the positioner to quickly draw lines and curves. The display can be operated in "raster mode", where the positioner scans across all the pins in the display a line at a time.

It is necessary to have a "hard lock" to hold the completed image firmly in place so the pins do not move when the user touches them. The locking mechanism for the NIST display is a thin metal sheet located between the plates that make up the display surface. The thin metal sheet has thousands of holes, one for each pin in the display, and is able to move slightly in a sideways direction (parallel to the surface of the display). When the sheet is in the unlocked position, the pins can move freely through the holes in the sheet without contacting the sheet. A gentle pressure moves the sheet into the locked position, where the sides of the holes contact the shafts of the pins. The pins have tiny ridges along the shafts, which are unable to pass through the holes when the sheet is in the unlocked position. Once the sheet is locked it holds the pins with no further application of force. If desired, the user can add incremental detail to an image by unlocking the pins, adding to the existing image, and relocking the pins.

The focus of the NIST project has been on the development of the output technology for a refreshable tactile display, and the operation of the prototype has shown that this technology is highly effective. Usability issues such as the design of a user-friendly control interface are beyond the scope of the NIST project and will be addressed outside of NIST as part of the commercialization process.

Advantages of the NIST technology

The NIST technology is very simple and rugged, and requires no high-tech components or consumable material such as embossing paper. As a result, the cost to buy and operate is very low, and will become lower as manufacturing knowledge develops. Additional advantages include:

  1. "Hard" dots. Because the pins are locked mechanically, the image dots are far more resistant to finger pressure than those in a conventional piezoelectric display, enhancing viewability.

  2. Pin density options. The number of dots per unit area in a conventional display is limited by the space requirements of the powered actuators. The passive pins of the NIST design can be made smaller without much increase in cost. The NIST prototype uses ten pins per linear inch (2.54 mm spacing), and at least double that linear density should be feasible.

  3. Portability. Very little force is needed to set the pins, and no power is required to retain the image after it is locked. Low power requirements make the technology ideal for a portable device.

Applications

The NIST technology complements embosser technology, providing the greatest benefits in situations where a permanent printout is not needed, where cost is an issue, where users want to select and view a large number of images, and where users want to modify images and view the changes. The project team developed the technology in response to requests from blind scientists and engineers who need to view scientific images, and to view incremental images of their work. Mathematics (plotting curves) and artistic design are other important applications. General uses include employment, education, libraries, public information kiosks, and home and portable use.

User participation in the technology development:

The National Federation of the Blind's Committee for Research and Development has been providing input on technical issues and accessibility needs from the start of the project. On October 24, 2002, the Department of Commerce / NIST and the NFB publicly announced the technology and the NFB's plans to pursue user control and usability issues for the technology: http://www.nfb.org/coming/nfbrelease.htm

NIST has also worked to keep technical experts within the American Council of the Blind and the American Foundation for the Blind informed of progress in the project, and has received feedback from many users of accessibility technology.

References:

[1] Discussion with Curtis Chong, National Federation of the Blind

Additional information:

A captioned video showing the prototype NIST tactile graphic display in operation is available online in RealPlayer format at http://realex.nist.gov:8080/ramgen/tactile_display.smi

NIST's patent application on the technology is available on the US Patent and Trademark office (http://www.uspto.gov ), application number 20030151597, "Extended refreshable tactile graphic array for scanned tactile display".

Thanks are due to the many accessibility technology users who have provided input into the project, and to NIST/DOC management and the NIST Advanced Technology Program for their support of the work.


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