Automatic navigation systems have been developed previously to aid the visually impaired, but these devices have not been as reliable and easy to use as a cane — the type of metal-tipped cane that visually impaired people frequently use to identify clear walking paths. These canes, however, have drawbacks. First, the obstacles they come in contact with are sometimes other people. Second, they can't identify certain types of objects, such as tables or chairs, or determine whether a chair is already occupied.
Researchers have developed a new system that uses a 3D camera, a belt with separately controllable vibrational motors distributed around it, and an electronically reconfigurable Braille interface to give visually impaired users more information about their environments. The system could be used in conjunction with, or as an alternative to, a cane.
Tests were conducted with blind users who sought a device that did not infringe on their other senses, so the researchers chose not to use audio. They found that the one area of the body that is the least used for other senses is around the abdomen.
The system consists of a 3D camera worn in a pouch hung around the neck, a processing unit that runs proprietary algorithms, the sensor belt that has five vibrating motors evenly spaced around its forward half, and the reconfigurable Braille interface worn at the user's side.
The key to the system is an algorithm for quickly identifying surfaces and their orientations from the 3D camera data. The researchers experimented with three different types of 3D cameras that used three different techniques to gauge depth, but all produced relatively low-resolution images — 640 pixels by 480 pixels — with both color and depth measurements for each pixel.
The algorithm first groups the pixels into clusters of three. Because the pixels have associated location data, each cluster determines a plane. If the orientations of the planes defined by five nearby clusters are within 10 degrees of each other, the system concludes that it has found a surface. It doesn't need to determine the extent of the surface or what type of object it's the surface of; it simply registers an obstacle at that location and begins to buzz the associated motor if the wearer gets within 2 meters of it.
Chair identification is similar, but a little more stringent. The system needs to complete three distinct surface identifications in the same general area, rather than just one; this ensures that the chair is unoccupied. The surfaces need to be roughly parallel to the ground, and they have to fall within a prescribed range of heights.
The belt motors can vary the frequency, intensity, and duration of their vibrations, as well as the intervals between them, to send different types of tactile signals to the user. For instance, an increase in frequency and intensity generally indicates that the wearer is approaching an obstacle in the direction indicated by that particular motor. But when the system is in chair-finding mode, a double pulse indicates the direction in which a chair with a vacant seat can be found.
The Braille interface consists of two rows of five reconfigurable Braille pads. Symbols displayed on the pads describe objects in the user's environment; for instance, a “t” for table or a “c” for chair. The symbol's position in the row indicates the direction in which it can be found; the column it appears in indicates its distance. A user adept at Braille should find that the signals from the Braille interface and the belt-mounted motors coincide.
In tests, the chair-finding system reduced subjects' contacts with objects other than the chairs they sought by 80 percent, and the navigation system reduced the number of cane collisions with people loitering around a hallway by 86 percent.