The modified office chair uses software algorithms, or computer instructions, that interpret information collected by an array of pressure sensors in the backrest and seat. When tested on 30 people, the chair demonstrated an overall accuracy of 96 percent in determining whether people were slouching, leaning in various positions, crossing their legs or sitting upright.

"The chair senses how the pressure is distributed in the seat and the backrest," said Hong Tan, an assistant professor at Purdue's School of Electrical and Computer Engineering. "We train the computer to recognize pressure patterns associated with different seating postures by showing the computer examples of such patterns."

Lynne A. Slivovsky, a doctoral student working with Tan, will present a research paper about the work Nov. 9 during the 2000 International Mechanical Engineering Congress & Exposition, sponsored by the American Society of Mechanical Engineers in Orlando, Fla.

Special software enables a computer to interpret a person's posture by analyzing pressure patterns, which are represented by thousands of numbers fed to the computer by numerous sensing elements, or "sensels," in the chair. Each time a person sits in the chair, the computer creates precise "pressure maps" that can distinguish between different people, even if they are sitting in the same position.

The system is limited in that it is capable only of sensing "static posture," or how a person is sitting at any one given time.

"Currently, we are working on a dynamic system so that we can see how people are moving, throughout an eight-hour day, for example," Tan said.

Such an advanced "real-time sitting posture tracking system" would lead to many applications. Because the system would be able to recognize the pressure patterns peculiar to specific people, a potential application might be to verify authorized personnel for computer-security purposes.

A sensing chair also might be used in cars to automatically adjust the driver's seat according to who is behind the wheel, or to control an airbag's deployment by adjusting for a person's seating position and weight.

Another potential application could be to improve the ergonomics of furniture.

"People come into the showroom, they sit down, they think, 'Oh, this chair feels great,'" Tan said. "They buy it, and then they return it because after several hours of sitting in it, it doesn't feel great any more.

"So, chair manufacturers are interested in how to evaluate a chair over an extended period of time. They want to understand the long-term dynamics of seating."

The chair is most adept at sensing when someone is slouching, correctly interpreting that posture with an accuracy of 99.8 percent.

"For anybody who wants to do anything related to ergonomics, slouching is the one posture you probably really want to discourage," said Tan, who specializes in research focusing on the haptic human-machine interface, or how machines and people interact through the sense of touch.

Perhaps such a sensing chair might sound a warning beep every time its user assumed a slouching posture, she said.

Researchers said they were surprised the chair was able to accurately distinguish between the subtle posture differences of leaning left, crossing the right leg while leaning left or crossing the right leg without leaning at all.

"We were expecting to see a lot of confusion among those three because they are so similar," Tan said.

Tan and Slivovsky will present the findings during the engineering conference's Symposium on Haptic Interfaces for Virtual Environments and Teleoperation, sponsored by the mechanical engineering society's Dynamic Systems and Control Division.

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