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A Wheelchair for All Seasons

It has treads that could rival Nike's. It can pass over slippery puddles, shifting sand, and bumpy terrain like a sports-utility vehicle. It can climb steps (1 mb mpeg movie) and curbs and even cross ditches. But the "all-terrain wheelchair," designed in the University's General Robotics and Active Sensory Perception Laboratory, must attract a manufacturer's interest before people with disabilities can make use of it.
   Dr. Vijay Kumar, an associate professor of mechanical engineering who has overseen the wheelchair project since 1990, says the device has recently begun to draw attention. At least one major corporation has inquired about it since a graduate research assistant, Venkat Krovi, put it on the Web.
   Kumar, whose specialty is robotic manipulation and locomotion systems, got the idea for his invention when he saw a man struggling with his wheelchair at a local park. "I was struck by the fact that people with disabilities do a wonderful job of negotiating within their own homes," he says. But as soon as they go outdoors, they encounter obstacles at every turn.
   At first Kumar experimented with a four-legged wheelchair design, which was too heavy to maneuver. Then, with a $180,000 grant from the Whitaker Foundation, he set to work on a design that combined legs and wheels. The second version, which was made into a prototype, was adapted from a real wheelchair, but its high center of gravity made it unstable. The third version, patented in 1995, appears to have addressed those earlier flaws.
   Its prototype, slightly dusty, rests in the middle of the GRASP Laboratory at 3401 Walnut Street. Its seat is a plastic classroom chair, and it is powered by the equivalent of two car batteries. To get around, it uses a combination of motor-powered legs and wheels -- two rubber tires in the back, two casters in the front, and a pair of robotic legs on the sides. The legs draw up for rides along normal surfaces, but swing down like ski poles to push the wheelchair up onto a curb or other raised surface.
   It's more stable than it looks. While showing a computer simulation of the wheelchair in motion, Kumar points to the tips of its mechanical "legs," which contain shock-absorbent springs and have rubber treads. "They're like Air Nikes," he said. "They've got some springiness built in. You would change the tread depending on what environment you would be in." The wheelchair also has computerized sensors which can calculate if one foot is slipping and get the others to compensate.
   There are some limitations, however. The wheelchair was designed to carry only 60 pounds of weight. To carry an adult, it would need higher-powered motors. The wheels are also too large to make it up a typical indoor flight of stairs, but they can negotiate wider steps (at least 20 inches apart). The all-terrain wheelchair would be expensive to produce at first, Kumar says. But potentially, the market for it is huge.

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