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Extending the Reach of Exoskeletons

Extending the Reach of Exoskeletons

The rest of us may think mechatronics is the ultimate in multidisciplinary work, but to Jacob Rosen, associate professor of computer engineering at the University of California of Santa Cruz, "the human body is the most multidisciplinary thing I know of."

That's why Rosen has been working since 1993 on building a robot that someone can wear, a concept best known as an exoskeleton. (See some of Rosen's previous research from the University of Washington's BioRobotics Laboratory.) He received a National Science Foundation grant to develop a fully articulated arm, and worked with the design of a University of Washington mechanical engineering PhD student named Joel Perry.

The result is now ready for commercialization, Rosen believes. People with muscular dystrophy and other neuromuscular disabilities could use the exoskeleton to amplify their muscle strength, and it could also be used for rehabilitation and physical therapy, according to Rosen.

He adds that one of the major challenges in this field is to establish an effective human-machine interface, such that the robot becomes a natural extension of the human body. Rosen has dubbed this the "bio-port," and he cites it as one of the differentiations of his design. "I decided to use a different level of the neural system. My approach is to use surface electronics on the skin on top of the muscles."

Rosen, who has degrees in mechanical engineering, biomedical engineering, and computer engineering, says that his exoskeleton provides seven degrees of freedom, covering 95% of the traditional range of motion. Other systems only offer five degrees of freedom, he notes.

To support seven degrees of freedom requires seven actuators, but in his design, four of the actuators are on the 40-pound base of his device. "Because you only move three of the seven actuators, it's lightweight, and the inertia is less."

While the primary applications of this kind of medical robotics focus on augmenting human capabilities, especially among the disabled, it also brings capabilities to the field of haptics, the science of applying touch to interaction with software. His design uses cables and pulleys because gears generate friction. "The principal idea in haptics is to minimize the effect of the device. You don't want to feel anything. All the gearing system is done with cables so you get almost no friction at all."

As a result, the weight of the exoskeleton to users is about the same weight as their own arm. "We developed a gravity compensation algorithm so that when you wear it, you don't feel the weight as well. To the user, it's weightless."

Rosen is excited by the challenge and the potential of medical mechatronics. "Medical robotics is by definition a multidisciplinary field, and that's one reason I was so attracted to it," Rosen says. "One of the most challenging issues in research and development of medical technology is to create a multidisciplinary group of clinicians and engineers that can effectively communicate and collaborate. We speak different languages, and we have to overcome these barriers in order to work together. But the opportunities to benefit people's lives are tremendous."

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