INTRODUCTION *

DESIGN CONSIDERATIONS *

PRO/ENGINEER MODEL *

STEREOLITHOGRAPHY *

THERMOFORM *

CONCLUSION *

REFERENCES *

Tactile graphics are as essential to learning for a student with visual impairments as pictures are to a student who is sighted. The University of Maryland has been working with the Maryland School for the Blind in Baltimore to create learning aids in the format of tactile graphics. A main area of interest for school age children is geography. To help the teachers and children at the Maryland School for the Blind, a map of the Commonwealth of Independent States (the former Soviet Union) has been designed with Pro/ENGINEER and then created with stereolithography. Multiple copies were subsequently made using a thermoform machine.

Many things needed to be considered when developing a map for visually impaired children. A map provides a substantial amount of information and it is essential that when converting a map for sighted people into a map for blind people that the information does not become cluttered. Only necessary features should be represented. Instead of labeling all of the bordering countries and water bodies by name, a texture was assigned to generally represent the bordering land and another texture to represent the bordering water bodies. All fifteen independent states are labeled and borders are clearly defined. Latitude and longitude lines are also present as a reference to location in the world.

The first constraint that needed to be considered when creating the map was the overall size. The thermoform machine has a maximum formation area of 11 inches by 11 inches. Knowing that this size was too small to suit our needs, it was necessary to split the map into three sections.

Land, water, latitude/longitude lines, borders, and labels all needed to be added to the map. After consulting with Betsy Burnham at the Maryland School for the Blind and seeing how previous maps have been created, a texture scheme was developed based on importance. The borders are the highest features on the map, since that is the most important feature. The borders have a height of 1/8" and a width of 1/8". The land of the Commonwealth of Independent States was also raised to a height of 3/32". Most of the maps that the children are used to learning from have the land area that is being studied raised higher than the surrounding area. We wanted to maintain this convention, so that there would not be any confusion. Once these main features were defined, the less important features were determined.

The textures that had originally been developed had to be modified after the first prototype was created. Originally the water bodies were raised circles with a diameter of 1/6" and height of 1/32" and a rounded top of 1/24" with a spacing of 1/2". The bordering land remains the same as the original design of raised circles with a diameter of 1/8" and a height of 1/32" and a rounded top of 1/32" with a spacing of 1/4". The latitude/longitude lines were at a height and width of 1/16".

After the prototype was created and we consulted with Betsy Burnham, it was determined that the map was too cluttered. To ease reading of the map, the textures were changed. The land remained the same, but the water texture was too similar to the land texture, so a new idea was developed. The water texture is raised horizontal ridges with dimensions of 1/32" in height by 1/32" in width. The latitude/longitude lines were receded into the main surface of the map by 1/32" to reduce the number of raised features and to lessen the importance.

Each of the three sections of the map was created in a separate file. Base plates were created using the protrusion command. The plates are 1/8" thick. This depth was chosen to be thick enough to prevent deformation after the stereolithography was created, but thin enough to keep the cost of the stereolithography to a minimum. The borders were the first of the features that needed to be created.

After finding a map of the Commonwealth of Independent States in a world atlas, it needed to be transferred into Pro/ENGINEER. A copy of the map was made and enlarged. The features of interest were outlined in black marker and the three sections were divided. Transparencies of the three sections were created and taped onto the computer screen. The borders were created using the spline feature and outlining the lines on the transparency.

The remaining features were created via the protrusion command. Copy and pattern also were used to duplicate multiple features, such as the water bodies and the bordering land.

After the model was created, colors were assigned to the areas of interest by using the appearance command. Red was assigned to the main focus of the map, which includes all of the countries of the Commonwealth of Independent States. The latitude and longitude lines are designated with yellow. The surfaces of the water and bordering land protrusions are blue and green respectively. The colors are all bright common colors for the sighted user to understand the intent of the map.

Stereolithography is a rapid prototyping method that allows a drawing in Pro/ENGINEER to be transformed into a physical model. This physical model will serve as a template from which the thermoform images can be created.

For the stereolithography to be created, it is necessary to export the Pro/ENGINEER model in .stl format. A triangle mesh is created which is similar to the finite element meshes created in ANSYS or other finite element analysis software. This triangular mesh approximates the shape of the object, which the stereolithography machine then uses to create the object.

The fact that the stereolithography creates all objects from small triangles, certain features were limited. The rounds that were created for the Braille dots were unable to be properly represented in the rapid prototype. Therefore, to compensate for this limitation, all of the Braille was printed from a Braille printer at the Maryland School for the Blind, then properly affixed to the model.

MaestroÒ software is utilized to process the exported file for use on the stereolithography machine. The software will orient the model to the position that is most appropriate for prototyping. Supporting structures are automatically designed into the model where necessary.

The stereolithography machine is now capable of receiving the exported file. The machine used for this project was the SLA-250/40 in the Advanced Design and Manufacturing Building. The components of any SLA machine are a computer, a vat of resin, a support platform and a laser beam. The computer reads the imported file and directs the laser and the platform. The resin is a photosensitive substance, which solidifies when hit by the light from the laser. Thin layers of solidified resin are created, starting from the lowest point in the object and making its way up to the highest. The objects take several hours to form in the stereolithography machine.

The process is not complete, however, when the stereolithography machine has finished forming the object. The base structure is cut away, and the object is cleaned with alcohol. The object is still somewhat tacky, and needs to be further solidified. It is placed in a UV light chamber to finish hardening.

After the stereolithography models are fully hardened, thermoforms can be created. Since creating models with a stereolithography machine is such an expensive process, it would not be economically wise to create more than one model for each part of the object. Thermoforms act as a way to make printed copies of the models.

The BrailonÒ Thermoform Duplicator consists of a vacuum tray and a series of heating coils. The SLA model is placed on the vacuum tray, and a BrailonÒ page is secured above it. The heating coils are slid on top of the page for several seconds. The suction pump turns on after the BrailonÒ page is sufficiently hot, creating the vacuum that allows for the surface geometry of the mold to be transferred to the BrailonÒ sheet.

For the thermoform machine to properly create the images, small holes must be drilled into the stereolithography models. These holes allow for a vacuum force to be generated between all areas of the model and the BrailonÒ thermoform sheet in the thermoform duplicator.

For people whose vision is a sense that has not been compromised over time, generating a learning aide for the visually impaired can be difficult to accomplish. Since the sensitivity of touch for the blind is usually much greater than that of the sighted, the effectiveness of the textures and surfaces can be difficult to judge. Models must be created and tested on the people who they are being created for in order to be sure that they will be effective. However, since this would be too expensive, we had to take as much input as we could acquire, and use it to make educated guesses as to the correct features to produce. This method allowed the sighted designer to understand a portion of the blind student’s learning environment and teaching obstacles. Generating models through Pro/ENGINEER and the stereolithography machine is a time consuming process, but the reproduction of the model using the BrailonÒ Thermoform Duplicator is a relatively short process. This allows many learning aides to be reproduced and prepared for the teaching atmosphere with little trouble.

Atlas of the World. Oxford, New York: 1996. Page 59.

Burnham, Betsy. Tactile Media Coordinator. The Maryland School for the Blind.

Correspondence: January – May 1999.

Quick Reference World Atlas. Rand McNally, New York: 1985. Pages 10-11.

http://www.devco-cape.com/pt-mold.htm